Close
About
FAQ
Home
Collections
Login
USC Login
Register
0
Selected
Invert selection
Deselect all
Deselect all
Click here to refresh results
Click here to refresh results
USC
/
Digital Library
/
University of Southern California Dissertations and Theses
/
Benthic and pelagic marine ecology following the Triassic/Jurassic mass extinction
(USC Thesis Other)
Benthic and pelagic marine ecology following the Triassic/Jurassic mass extinction
PDF
Download
Share
Open document
Flip pages
Contact Us
Contact Us
Copy asset link
Request this asset
Transcript (if available)
Content
Benthic and Pelagic Marine Ecology Following the Triassic/Jurassic
Mass Extinction
by
Kathleen Anita Ritterbush
A Dissertation Presented to the
Faculty of the USC Graduate School
University of Southern California
In Partial Fulfillment of the
Requirements for the Degree
Doctor of Philosophy
(Geological Sciences)
December, 2013
Acknowledgements
Collaboration with many professors and students contributed richly to the design
of analyses, execution of field observations, and development of interpretations included
here. For overarching direction and advice in these investigations I thank Dave Bottjer,
Frank Corsetti, Silvia Rosas, Will Berelson, and Josh West. For assistance in the field I
am indebted to Julio Zarate, Carlos Astorga, Scott Mata, Lydia Tackett, Carlie Pietsch,
Marlo Gawey, Liz Petzios, Ben Haravitch, and Rowan Martindale, Sarah Greene, Mike
Lewis, Amir Allam, and many staff geologists at Pan American Silver in Morococha,
Peru. For contribution of crucial ideas and co-authorship of manuscripts related to the
specific chapters herein I thank Silvia Rosas, Carlie Pietsch, Sarah Greene, Rowan
Martindale, William Berelson, Frank Corsetti, Dave Bottjer, Kenneth DeBaets, Rene
Hoffman, Alex Lukenender, Christian Klug, and Sean Loyd.
I thank Jean Guex, Gerd Westermann, David Raup, Michael Foote, and Dave
Jacobs, Neil Landmann, Peg Yacobucci, and William Gilly for valuable conversations
and correspondence about cephalopods and stratigraphy. For support and encouragement
among Canadian ammonoids I would also like to thank J.P. Zonneveld, Mike Orchard,
Peter Krausse, Steve Grasby, and Benoit Beauchamp. I am indebted to all the instructors
and students of Camp Alroy 2010 for broadening my research capabilities and objectives:
Dr.s Hunt, Lawing, Wagner, Alroy and Olszewsky, as well as Monica Carvalho, Frank
Fortino and Max Christy.
The entire Earth Sciences faculty has been very supportive during my research,
and I’d especially like to thank Yahuda BenZion, Julien Emile-Geay, Doug Hammond,
Sarah Feakins, John Platt and Dave Okaya for instruction and encouragement. I also
thank department lifeblood John Yu, John McRaney, Cindy Waite, Karen Young, and
Vardui Tersmionian for logistical support over the years. Addition heroes include the
incomparable Priya Hanson, Ann Close, Ronald Popper, Jean Crampon and the staff of
interlibrary loan and of the campus pharmacy. For moral support I also am gratefully
indebted to my graduate student cohort and leaders, as well as Alex Winqvist, Jen
Goldberg, Paul Jay, Amanda Haddad, Brandon Kayser, Laura Loyola, Carie Franz, Scott
Blanco Palmer, Joyce Yeager and Jeff Thompson.
For funding I must thank the wonderfully warm, wise, and generous Sonosky
family and the USC Wrigely Institute for summer support in the field and at the island.
Additionally I am very grateful for field and research support from the American
Museum of Natural History, American Philosophical Society, Geological Society of
America, Society for Sedimentary Geology (SEPM), American Association of Petroleum
Geologists as well as donors to their various award programs.
Support over the years from families has been unfailing and monumental. I wish
to warmly thank Silvia Rosas, as well as Cesar and Lio, for their generous roles as hosts,
and for bringing excellent new challenges into my research life. I thank George Morales
and honor Gary Gotcher for years of encouragement. I am grateful for years of support
from Mo, Hal, Hannah, Bev, and Ahmed Allam. From my father, Bob Ritterbush, and
sister Kristine Rodriguez I’ve enjoyed constant cheerleading.
I would like to dedicate this dissertation to my mother, Linda Anita Ritterbush, in
gratitude for her years of support on a tack between scientific discernment and
unwavering encouragement.
Finally, support from my husband Amir Allam significantly broadened the scope
of my work, largely from his assurance that I could accomplish more than I thought. I
thank him for long evenings deriving equations, long days escaping flash floods and bear
traps, and a long future pursuing love and science.
Table
of
Contents
1
ABSTRACT
4
CHAPTER
1:
INTRODUCTION
AND
OVERVIEW
OF
THE
TRIASSIC
/
JURASSIC
MASS
EXTINCTION
4
The Triassic/Jurassic Extinction and Concomitant Volcanism
5
The Triassic/Jurassic Mass Extinction among Marine Faunas
11
Modern Experimental Progress on Understanding Marine Biotic Responses
to Ocean Acidification
18
Terrestrial Matters: Dinosaur Proliferation and the End-Triassic Mass
Extinction
21
New Research on the Paleoecological Consequences of the
Triassic/Jurassic mass extinction
26
CHAPTER 2: CONSEQUENCES OF THE TRIASSIC 552 JURASSIC
MASS EXTINCTION IN BENTHIC HABITATS: SEDIMENTOLOGY
AND PALEOECOLOGY IN THE GABBS VALLEY RANGE OF
NEVADA, USA
26
Introduction
28
Methods: Sedimentology, Paleontology, and Detailed Locality
Descriptions
31
Results
34
Discussion
36
CHAPTER 3: A DIAGENETIC HETTANGIAN CARBONATE SINK:
CONCRETION FACIES OF THE HETTANGIAN SUNRISE
FORMATION
36
Introduction
37
Methods
38
Results: Sedimentology of the Lower Hettangian
43
Discussion
47
CHAPTER 4. SILICEOUS SPONGE FACIES OF THE HETTANGIAN IN
THE GABBS VALLEY RANGE OF NEVADA AND THE CENTRAL
ANDES OF PERU
47
Introduction
50
Methods
52
Environments and Ecology in the Nevada Record
54
Peru
58
Discussion
61
CHAPTER 5: SILICA CYCLING AND THE TRIASSIC/1339
JURASSIC EXTINCTION
61
Overview
of
Sensitivity
Analysis
62
Reasonably
Estimating
Mesozoic
Marine
Silica
Concentration
65
Doubling
Time
66
Silica
Demand
by
Sponges
68
CHAPTER 6: PELAGIC ECOLOGY: RECENT UPDATES TO THE
STUDY OF AMMONOID PALEOBIOLOGY
68
Introduction
68
The
Ammonoid
Animal
69
Ammonoid
Shell
Shape
through
Time
and
Space
73
CHAPTER 7: WESTERMANN MORPHOSPACE D 1584 ISPLAYS
AMMONOID SHELL SHAPE AND HYPOTHETICAL
PALEOECOLOGY
73
Introduction
75
Previous
Research
77
Three
End-‐Member
Morphotypes
79
Methods
88
Drafting
the
Morphospace
89
Example
Applications
98
Discussion
103
CHAPTER 8: CONTRASTING ECOLOGICAL AFTERMATH OF THE
PERMIAN/TRIASSIC AND TRIASSIC/JURASSIC MASS
EXTINCTIONS
103
Introduction
109
Methods
112
Results
115
Discussion
123
CHAPTER
9:
CONCLUSIONS
127
CITATIONS
151
TABLES
161
FIGURES
161
Chapter
1
Figures
164
Chapter
2
Figures
186
Chapter
3
Figures
220
Chapter
4
Figures
247
Chapter
5
Figures
250
Chapter
6
Figures
254
Chapter
7
Figures
262
Chapter
8
Figures
ABSTRACT 1
The Triassic/Jurassic mass extinction (201.3 Mya) is the most severe biotic crisis in the 2
history of the Modern Fauna, the marine invertebrates that dominate modern oceans (e.g., 3
gastropods, bivalves). The ecological consequence in marine habitats is an outstanding question 4
of particular interest because similar mechanisms of environmental change are revolutionizing 5
marine ecosystems today. This dissertation investigates these consequences by examining 6
evidence of ecological complexity within benthic (sea floor-dwelling) and pelagic (water 7
column-dwelling) fossil faunas. First, analysis is presented of sedimentology and benthic fossils 8
within post-extinction strata (~ 2 Ma record) in North and South America, with comparison to 9
other records from across the globe. Second, a framework is established for evaluating the 10
ecology of pelagic faunas, specifically ammonoids, in general and with respect to extinction 11
aftermath, contrasted between the Triassic/Jurassic and Permian/Triassic events. 12
Benthic ecology is examined in the Gabbs Valley Range of Nevada, USA and in the 13
Central Andes of Peru, by determining the environments of deposition and the contribution of 14
biology to sedimentation. First order investigations of the sedimentology and fossil abundance in 15
Nevada, presented in Chapter 2, show that the reappearance of abundant rock-forming metazoan 16
biocalcifiers occurs about two million years after the extinction, despite continual and increasing 17
intensity of carbonate facies accumulation. This demonstrates decoupling of carbonate saturation 18
and biocalcifier production associated with previously unrecognized long-term ecological 19
collapse of marine shelf carbonate ramp systems. The post-extinction interval of non-metazoan- 20
mediated carbonates is examined in Chapter 3. This analysis shows that widespread concretions 21
formed early near the sediment/water interface, completely replacing otherwise dominantly 22
biosiliceous clasts, and formed a profound carbonate sink. Microfacies techniques are used in 23
1
conjunction with body fossil observations to determine the nature of metazoan ecology during 24
the extinction aftermath in Chapter 4. In both Nevada and Peru, Upper Triassic carbonate 25
systems are replaced by siliceous fossil sponge-dominated ecosystems in the Lower Jurassic. The 26
“sponge takeover” was likely facilitated by a unique confluence of circumstances: extinction- 27
driven changes in benthic ecology coupled with increased global silica flux (a limiting nutrient 28
for sponges) from weathering of the massive Central Atlantic Magmatic Province (CAMP). The 29
sensitivity of global silica cycling to changes in weathering flux is calculated to learn more about 30
this sponge interval in Chapter 5. Specifically, it is shown that the Central Atlantic Magmatic 31
Province could have provided enough silica for sponges to have expanded across tropical 32
carbonate shelves in less than one million years. 33
Pelagic ecology is evaluated using fossil ammonoids. Chapter 6 presents a review of 34
recent developments in ammonoid paleobiology. Relatively direct ecological evidence springs 35
from body fossils: hard and soft part preservation; development; isotopes; and hydrodynamics. 36
Indirect evidence on ammonoid ecology stems from analyses of shell shape distributions through 37
time and space: in long-term “stable” conditions; during extinction events; and during radiations. 38
The Westermann Morphospace method, presented in Chapter 7, displays fundamental 39
morphotypes and hypothesized life modes of measured ammonoid fossils in a ternary diagram. 40
By linking measured shells to hypothesized life modes, this method can address hypothetical 41
ecospace occupation in collections with tight stratigraphic, lithologic, and abundance control, 42
even when taxonomy is in dispute. Chapter 8 uses Westermann Morphospace to compare and 43
contrast the ammonoid faunas that flourished directly after the Permian/Triassic (251 Mya) and 44
the Triassic/Jurassic (201.3 Mya) mass extinctions. Abundant, cosmopolitan, and large 45
ammonoids which flourished globally after the Triassic/Jurassic mass extinction produced simple 46
2
coiled, “serpenticonic” shells, to which current hydrodynamic assessments ascribe a lack of 47
dynamic directed swimming capabilities. In contrast, the small abundant ammonoids which 48
flourished following the Permian/Triassic mass extinction produced significantly more species 49
with different shell morphotypes, implying different ecological roles. It is further shown that the 50
Early Triassic ammonoids maintained dynamic shell shapes despite repeated extinctions, which 51
were triggered by high temperature and sudden low-oxygen events. The Early Triassic 52
ammonoids also had significantly more species of streamlined “oxyconic” shells in the tropics 53
than in temperate settings within two million years of the extinction. These ecology dynamics are 54
much more complex than those demonstrated for the Early Jurassic, which can only be 55
interpreted to have complex ecology if more studies can show support for more dynamic motion 56
within the limited shell shapes. 57
Overall, though the Permian/Triassic event had a higher death toll and longer-lasting (5 58
Ma) duration before recovery, the Triassic/Jurassic extinction had extensive global ecological 59
consequences in both benthic and pelagic habitats. Though it may have lasted only 2 Ma, the 60
switch from carbonate to siliceous sponge dominated habitats on the sea floors, and the switch to 61
ubiquitous drifting ammonoids in the seas, presents a very different picture from pre-extinction 62
conditions. 63
64
3
CHAPTER 1: INTRODUCTION AND OVERVIEW OF THE TRIASSIC / JURASSIC 65
MASS EXTINCTION 66
67
The Triassic/Jurassic Extinction and Concomitant Volcanism 68
The Mesozoic Era is a time of profound reorganization of life on Earth. The Mesozoic 69
began when the Paleozoic’s dominant sea life were largely eradicated at the end of the Permian 70
Period, which allowed the gradual diversification of marine clades during the Triassic which 71
dominate seas to this day (Sepkoski, 1981; Alroy et al., 2008). The Mesozoic era also ended in a 72
mass extinction, which removed all non-avian dinosaurs and marine ammonites at the end of the 73
Cretaceous Period. Compared to these two well-known intervals of biotic turnover, the transition 74
from the Triassic to the Jurassic Periods has received far less attention until recent years. There 75
are two chief reasons for this. First, previous compilations of global biodiversity estimated from 76
fossils failed to recognize the intensity and selectivity of the mass extinction (Alroy et al., 2008). 77
Second, advanced chronometric methods finally allowed recognition that basalts distributed 78
across four continents are pieces of one gigantic igneous province which erupted across Pangea 79
during the extinction (e.g., (Marzoli et al., 2004; Blackburn et al., 2013). 80
The Triassic/Jurassic mass extinction is the most severe biotic crisis in the history of the 81
Modern Fauna, the marine invertebrates most common in modern oceans (e.g., gastropods, 82
bivalves) (Sepkoski, 1981; Alroy, 2010a; Alroy, 2010b). It was very selective, and rivaled the 83
end-Permian crisis in overall severity (Alroy, 2010a; Kiessling and Aberhan, 2007a; Kiessling et 84
al., 2007). The extinction occurred during ongoing emplacement of the Central Atlantic 85
Magmatic Province flood basalts as Pangea split apart in the last 300 kyr of the Triassic period 86
(Schoene et al., 2010). Figure 1.1 shows a timeline of these events. Environmental 87
4
consequences of the volcanism interpreted to account for the selective extinctions include rapid 88
global warming and ocean acidification associated with volatile release. A thorough review of 89
the available data (Greene et al., 2012b) concludes that ocean acidification was possible if 90
highest end-member proxies for pace and volume of volatile release gain support in future 91
research. The most recent data show that the main volcanic activity occurred in phases of tens of 92
thousands of years occurring over approximately 600 kyr (Blackburn et al., 2013). The most 93
outstanding question of the Triassic/Jurassic transition is the ecological consequence in marine 94
habitats, which is of particular interest as similar mechanisms of environmental change are 95
revolutionizing marine ecosystems today (Jackson, 2008). The following passages address the 96
apparent extinction selectivity during the T/J transition, and compare these to results of recent 97
biological experiments of ocean acidification. The extinction’s consequences for terrestrial 98
faunas are also briefly described. 99
100
The Triassic/Jurassic Mass Extinction among Marine Faunas 101
The severity and rapidity of the end-Triassic extinction event have only recently come 102
into sharper focus with the advent of the Paleobiology Database (PBDB). Kiessling et al. 103
(Kiessling et al., 2007) showed that 41% of benthic Rhaetian genera that survived the Norian 104
died out before the beginning of the Jurassic (Hettangian) resulting in a 33% decline in standing 105
diversity between the Rhaetian and Hettangian (Kiessling et al., 2007). Planktonic macrofauna 106
also experienced severe extinctions at the end of the Triassic, with complete extinction of the 107
conodonts (Clark, 1987) and near-extinction of the ammonoids (Page, 1996). Microfossil 108
records show severe and sudden extinctions in calcareous groups (Crne et al., 2011; van de 109
5
Schootbrugge et al., 2007), including foraminiferans (Clémence et al., 2010), and in the siliceous 110
radiolarians (Kiessling and Danelian, 2011). 111
The extinction interval has an estimated duration of 50 to 300 kyr (Ward et al., 2001; 112
Schoene et al., 2010; Hillebrandt and Krystyn, 2009), but the biotic consequences lasted far 113
longer. Biodiversity recovered on the million-year scale for some groups (e.g., radiolarians 114
(Carter and Hori, 2005) and ammonoids (Schaltegger et al., 2008)), but far slower for marine 115
invertebrate diversity as a whole (Alroy, 2010b). Apparent disaster or opportunistic taxa include 116
non-calcareous microfaunas (organic-walled nannoplankton (van de Schootbrugge et al., 2007), 117
agglutinated forams (Clémence et al., 2010) and certain bivalves (Agerchlamys scallops and 118
Modiolus mussels (McRoberts et al., 2012; Mander and Twitchett, 2008; Ward et al., 2007). 119
Global biodiversity compilations now have adequate resolution to test for associations between 120
extinction rate and environmental setting, but statistical approaches have less power in crisis 121
aftermath, when quantifiable factors (like genera) are fewer. Paleontological studies do show 122
long-term ecological transitions from reef to level-bottom habitats; reefs did not fully reestablish 123
global distributions and intensity for tens of millions of years (Flugel, 2002; Flugel and 124
Kiessling, 2002; Thorne et al., 2011). Studies of benthic faunas across the boundary often seek to 125
identify groups that are the most sensitive to extinction or are apparently flourishing 126
opportunistically (McRoberts et al., 2012; Mander and Twitchett, 2008; Delecat et al., 2011), but 127
often studies are hampered by facies changes across the boundary, and/or by condensed sections. 128
129
End-Triassic extinction selectivity vs. background extinction patterns 130
The suspicion that ocean acidification contributed to the extinction rates of some 131
organisms and within some ecosystems is fueled by differences between the Triassic/Jurassic 132
6
event and background intervals, although other factors, such as warming (Kiessling and 133
Simpson, 2011), may have also contributed. The end-Triassic mass extinction was one of the 134
most severe events to have affected sensitive carbonate biomineralizers through the entire 135
Phanerozoic (Kiessling and Simpson, 2011). Based on previous categorizations (Knoll et al., 136
2007; Bambach, 2002; Pörtner et al., 2004; Portner et al.; Knoll et al., 1996), which assume that 137
organisms with a massive calcium carbonate skeleton and little physiological buffering are 138
sensitive to acidification (corals, hyper-calcifying sponges, calcareous algae, calcareous 139
foraminifers, calcifying bryozoans, calcareous brachiopods, pelmatozoans), Kiessling and 140
Simpson (2011) find that in addition to the T-J reef crises, acid-sensitive groups experienced 141
higher extinction rates between the Rhaetian and Hettangian. The authors concede, however, that 142
little or no experimental data exists to support many of these classifications, particularly for 143
groups with a rich fossil record (hyper-calcified sponges, calcareous brachiopods, calcifying 144
bryozoans, pelmatozoans) (Kiessling and Simpson, 2011). Extinction rates of corals and 145
calcareous sponges were higher than other benthic invertebrates (Kiessling et al., 2007) and the 146
T-J event was the most severe extinction for scleractinian corals in their entire history, with a 147
>50% extinction rate at the genus level (Kiessling et al., 2009). Benthic genera with an affinity 148
for inshore, for carbonate, or for reef habitats experienced increased extinction rates between the 149
Rhaetian and Hettangian (Kiessling et al., 2007). In a departure from background extinction 150
patterns, wide geographic range and high abundance are not significant predictors of success 151
during the Triassic-Jurassic event (Kiessling and Aberhan, 2007b). 152
153
154
155
7
Extinction selectivity and carbonate mineralogy 156
The same numbers of calcium and carbonate ions can be arranged into different mineral 157
structures, creating subtly differing mineral polymorphs: calcite, aragonite, and ikiite. Molluscs, 158
cnidarians, arthropods, and even annelids can generate calcitic or aragonitic skeletal components 159
and coatings, with varied degrees of biological control. Aragonite is more soluble than calcite in 160
modern marine conditions. Calcite solubility increases with increasing Mg content, and high-Mg 161
calcite (when more Mg is incorporated into the calcite crystal lattice) has solubility close to 162
aragonite (Tucker and Wright, 1990). Stanley (Stanley, 2006) interpreted that changes in marine 163
Mg concentrations during the Phanerozoic have driven trends in molluscan abundance due to 164
their mineralogy, and Hautmann (2004) asserted that solubility differences between mineral 165
polymorphs should impart different metabolic costs on organisms to explain extinction rates 166
during the T/J extinction. In contrast, Carter et al.’s (1996) detailed mineralogical studies of the 167
development of polymorph regions within Mesozoic bivalves are inconsistent with the timing 168
and mechanism of external forcing; there is not evidence that bivalves have any metabolic cost 169
associated with producing different carbonate polymorph, and the timing of their evolutionary 170
transitions does not match the interpreted shifts in marine chemistry. Within clades that utilize 171
multiple carbonate polymorphs, genera that utilized the less-stable polymorphs experienced 172
higher extinction rates across the end-Triassic extinction, but this result is within statistical error 173
and is not significant (Hautmann et al., 2008). Extinction rates calculated from sub-sampled 174
occurrence data show no significant correlation with carbonate polymorph (Kiessling et al., 175
2007), except for within the bivalves. Background extinction of bivalves does not correlate to 176
mineralogy, so a strong mineralogical effect at the T/J boundary is intriguing. The aragonitic 177
8
bivalves were also infaunal, however, so the selective mechanism is more parsimoniously life 178
mode (McRoberts and Newton; Kiessling et al., 2007). 179
Caution must be used in interpreting an association between an organism’s carbonate 180
polymorph production and extinction. Physiological control over shell mineralization within an 181
organic matrix in bivalves is complex and occurs in internal fluids with chemistry different from 182
surrounding seawater (Lorens and Bender, 1977; Falini et al., 1996; Carter et al., 1998; Mount et 183
al., 2004; Dalbeck et al., 2006; Cusack et al., 2008; Tunnicliffe et al., 2009), so producing 184
different carbonate polymorphs does not have a direct metabolic cost that corresponds to the 185
saturation state of ambient seawater. The assumption that producing mineral phases with lower 186
thermodynamic stability in abiotic conditions will be metabolically disadvantageous enough to 187
drive extinction selectivity in biomineralizers during an acidification event (e.g., Hautmann, 188
2004; 2008) is not supported by experimental evidence, particularly, when this expectation is 189
applied broadly to all calcifying organisms (Ries et al., 2009). Minute larval forms may face the 190
greatest risk of dissolution, and larval polymorphs often differ from adult mineralogy (Beniash et 191
al., 1997; Weiss et al., 2002). 192
193
Acidification and the fidelity of the fossil record 194
Solubility differences between carbonate polymorphs has been invoked to explain 195
preservational biases favoring calcite over aragonite (Tucker and Wright, 1990). Fraiser et al. 196
(Fraiser et al., 2011) suggest that acidification resulting from high pCO
2
can enhance this bias, 197
helping to explain the prevalence of Lazarus taxa (taxa that briefly disappear from the fossil 198
record in the aftermath of an extinction only to reappear later (Flessa and Jablonski, 1983)) in the 199
Early Triassic (following the end-Permian mass extinction). Kiessling and Simpson (2011) point 200
9
out that acidification-induced preservation gaps are geologically short-lived phenomena; 201
decreased preservation would be immediately succeeded by an episode of enhanced carbonate 202
preservation (Kump et al., 2009). Thus acidification is not a mechanism that would produce a 203
sustained (i.e. million year timescale) preservational bias against more soluble polymorphs 204
beyond background biases. 205
The “naked coral hypothesis” is another acidification-induced preservational effect 206
(Stanley, 2003; Medina et al., 2006). Some modern scleractinian corals can exist for a year in 207
under-saturated water as polyps without a skeleton, maintaining their symbionts and their ability 208
to reproduce (Fine and Tchernov, 2007). When returned to supersaturated waters these corals 209
resume biomineralization. There is a lag between the origination of scleractinians (based on 210
molecular clock dating) and the first scleractinian fossil (Medina et al., 2006), suggesting that 211
corals may have lived as polyps without a carbonate skeleton for the first 60 Ma of their 212
evolutionary history. Therefore Stanley (2003) suggests scleractinian corals may have the ability 213
to survive ocean acidification events, or other intervals of biocalcification stress by living as 214
polyps without a skeleton, as “naked corals”. Since several coral species survived the end– 215
Triassic mass extinction but are absent from the fossil record for the first ammonite zone 216
(Kiessling et al., 2009; Martindale et al., 2012a), ~370,000 kyr (Ruhl et al., 2010), it is possible 217
that earliest Jurassic corals did not leave a fossil record because they were living as naked corals 218
and thus, without a skeleton, could not build reefs. 219
220
221
222
10
Modern Experimental Progress on Understanding Marine Biotic Responses to Ocean 223
Acidification 224
The potential mechanisms that caused the Triassic/Jurassic mass extinction are not 225
mutually exclusive, and share many similarities to the suites of environmental change facing 226
modern marine faunas. As described above, the extinction was particularly severe for carbonate 227
producing faunas. In the modern some of the most intense pressures on these habitats are 228
overfishing and eutrophication, which intensify sensitivity to warming and acidification (e.g., 229
(Jackson, 2008; Norström et al., 2009). Overfishing is an important process to note, as changed 230
predation pressures from higher trophic levels in the water column can have strong influences on 231
state shifts in benthic carbonate habitats (Norström et al., 2009). Local and regional state shifts 232
differ in the exact faunas that take over, and in the timing of these changes. Though the end- 233
Triassic mass extinction is effectively global and synchronous, it occurred over a time period of 234
50 to 300 kyr (Ward et al., 2001; Schoene et al., 2010). Thus the rate and specifics of changes 235
within each region and locality, from reef platforms to level bottom assemblages to inactive 236
ramps, most likely progressed at very different rates and with different key faunas. Heterogeneity 237
of Late Triassic carbonate habitats must be noted, which is not necessarily related to the mass 238
extinction interval. The Steinplatte reef complex in the Tethyan record of Austria (Delecat et al., 239
2011), for example, appears to have been active or at least un-degraded through the Rhaetian, 240
whereas in the boundary sites in the Gabbs Valley Range Panthalassan record of Nevada, 241
brachiopod and bivalve level bottom habitats (Laws, 1982) were more widespread than the coral 242
and calcareous sponge reefs that flourished in the Norian (Martindale et al., 2012b). Ocean 243
acidification is only one of the potential kill mechanisms of the mass extinction interval, but it 244
has been given substantial consideration in the paleontological literature (see Greene et al., 245
11
2012b for a review). Below, some modern perspectives on ocean acidification are organized to 246
comment on potential signals that might be found in the rock record. New biological experiments 247
typically concern short timescales, and are producing surprisingly heterogenous results for some 248
groups and processes. 249
Ocean acidification in the modern is a predicted and measured response to anthropogenic 250
carbon dioxide emissions (Wootton et al., 2008) about which there has been rising concern over 251
the past several years (Kerr, 2010). Despite the “acidification” moniker, ocean acidification does 252
not imply that the ocean will actually become acidic (pH <7), simply that ocean pH will fall 253
below steady state or normal levels. As CO
2
levels increase in the atmosphere (Keeling et al., 254
1995), CO
2
dissolves into the surface ocean and reacts with water, producing H
2
CO
3
(carbonic 255
acid). At modern ocean pH of 8.2, H
2
CO
3
dissociates into HCO
3
-
(bicarbonate) and H
+
, lowering 256
the pH of the ocean. Perhaps more importantly, CO
3
2-
(carbonate ion) can complex with H
+
, 257
lowering the concentration of one of the building blocks of calcium carbonate. The overall 258
reaction reads CO
2
+ H
2
O + CO
3
2-
à 2HCO
3
-
. Over long timescales, (ca. 10
6
years) this reaction 259
is counterbalanced by silicate weathering, which delivers alkalinity to the ocean. On short 260
timescales, where CO
2
is released faster than the buffering capacity of carbonate mineral 261
dissolution and silicate weathering, ocean acidification may occur (Stuecker and Zeebe, 2010). 262
Biologists predict ocean acidification will have deleterious effects on corals and coral reefs 263
(Kleypas et al., 1999; Fine and Tchernov, 2007; Hoegh-Guldberg et al., 2007; Anthony et al., 264
2008; Veron et al., 2009; Pelejero et al., 2010; de Putron et al., 2011) and calcification in general 265
within many groups (Orr et al., 2005; Fabry et al., 2008; Ries et al., 2009). 266
Studies of modern marine organisms reveal that acidic conditions impact physiology in 267
complex ways, often with drastic—but sometimes unpredictable— consequences for 268
12
biomineralization, growth, reproduction, and survival, particularly in integrated communities 269
(Fabry et al., 2008; Doney et al., 2009; Hendriks et al., 2010). It is difficult to generalize the 270
biotic response from modern experiments across, or even within, clades because 1) experimental 271
conditions vary from one study to the next and are thus difficult to compare with one another; 2) 272
it is uncertain which carbonate parameter (low Ω, pH, or [CO
3
2-
]) is most important for each 273
organism; 3) most studies limit the upper range of the carbonate parameters to values appropriate 274
for the projected short-term anthropogenically-induced changes versus values more appropriate 275
for deep time (Doney et al., 2009; Hendriks et al., 2010; Kroeker et al., 2010). Regardless, it is 276
useful to survey the effects noted in the modern acidification experiments in order to appreciate 277
the range of effects—some preserve-able in the rock record, and some not—that organisms can 278
display when faced with acidification of their environment. 279
The following sections address consequences for biomineralization, metabolism, 280
reproduction, and complications of ecology and adaptation. Many if not most of the effects 281
noted in the various experiments would be difficult to directly observe in the rock record. For 282
example, some clades display drastic effects to acidification at the larval stage versus the adult 283
stage—such a result would be difficult to directly observe in the rock record, although it is likely 284
that such a clade would reveal extinction or drastic reduction in diversity. Furthermore, 285
biological experiments likely miss the evolutionary capacity for adaption only apparent on 286
(multi-generational) geological timescales (Honisch et al., 2012); this is one of the main 287
drawbacks of ocean acidification predictions from biological experimentation. 288
289
290
291
13
Biomineralization 292
A recent review of acidification experiments involving organisms including 293
coccolithophores, corals, and bivalves reports that calcification rates decreased among all 294
functional groups tested as carbon dioxide concentrations increased or saturation states decreased 295
(Hendriks et al., 2010). In addition to suppressed biocalcification, undersaturated conditions can 296
also cause exterior shell dissolution (Nienhuis et al., 2010). Two types of invertebrates fair well 297
in acidification experiments; crustaceans (Ries et al., 2009) and cuttlefish (Gutowska et al., 298
2010) actually increase calcification at very low carbonate saturation states. In light of these 299
complexities, paleontological investigations that differentiate between different groups of 300
calcifiers (e.g., Kiessling and Simpson, 2011) may be more informative than those that treat all 301
calcifiers equally (e.g., Hautman 2008). 302
It is important to distinguish the use of carbonate and bicarbonate ions in marine 303
biomineralization. Many experiments focus on the saturation state of calcium carbonate with 304
respect to carbonate ion concentration, but many organisms are actually taking in bicarbonate 305
ion, which increases in concentration continually as “acidification” progresses. Putron et al., 306
(Putron et al., 2010), showed non-linear significant decreases in coral polyp recruit calcification 307
in decreased carbonate ion concentration, and a lack of response to bicarbonate. Though 308
mineralogy-minded researchers attribute changes in calcification to an abiotic principal – 309
decreased aragonite saturation – Jury et al., (2010) point out that it is likely far subtler effects on 310
ion transport. Corals use bicarbonate ion at the cite of calcification, of which 75% is sourced 311
from respiratory CO2, and 25% from seawater (Furla et al., 2000). In a set of six experiments to 312
test the effects of pH, carbonate, and bicarbonate ion, Jury et al. (Jury et al., 2010) demonstrated 313
that corals decrease calcification in response to low bicarbonate ion concentration, even in 314
14
normal pH. Corals also actively pump calcium ions (Tambutte et al., 2011) influencing passive 315
transport of carbon dioxide (Furla et al., 2000). Corals are also sensitive to warming and in both 316
present and past acidification events, it may be challenging to distinguish the impacts of 317
combined environmental shifts. 318
319
Metabolism 320
Ocean acidification also affects invertebrate metabolism and growth, indicating that the 321
survival of an organism is determined by more than just its biomineralization response to 322
acidification. Photosynthetic organisms generally increase metabolism and growth in 323
acidification experiments due to the increased availability of CO
2
(Hendriks et al., 2010), and in 324
calcifying organisms that photosynthesize or contain photosynthesizing symbionts (e.g., 325
zooxanthellae in corals), increased metabolism may potentially offset deleterious effects of 326
calcification rates (Doney et al., 2009; Hendriks et al., 2010). Conversely, growth rates are 327
significantly reduced in echinoids, nematodes, bivalves, and gastropods during acidification 328
experiments (Hendriks et al., 2010). With respect to cephalopods, experiments show that 329
decreased pH levels significantly alter oxygen consumption and are interpreted to increase 330
extinction risk for predatory jumbo squids (Dosidicus gigas) (Rosa and Seibel, 2008), while 331
cuttlefish (Sepia officinalis) can maintain metabolism and growth rates in atmospheric carbon 332
dioxide concentrations as high as 6000 ppm (Gutowska et al., 2008). To be applied to the fossil 333
record, such physiological responses need to be expressed by organisms with common 334
phylogeny, life mode, or habitats. For example, echinoderms, bivalves, and gastropods leave 335
excellent fossil records, and growth decreases as a response to acidification in each of these taxa 336
(Hendriks et al., 2010). 337
15
Reproduction 338
Reproduction decreases and larvae success is compromised in most ocean acidification 339
experiments. Experiments revealed a decrease in reproductive rates in copepods, echinoids 340
(Hendriks et al., 2010) coral larvae (Nakamura et al., 2011), abalone (Crim et al., 2011) scallops 341
(Argopecten irradians), clams (Mercenaria mercenaria) and oysters (Talmage and Gobler, 2009; 342
Watson et al., 2009; Beniash et al., 2010). Some experiments show alteration in surviving 343
juvenile forms, such as reduced size for developing mussel (Mytilus edulis) larvae and delayed 344
development time for shrimps (Pandalus borealis) (Bechmann et al., 2011). Cuttlefish embryos 345
and juveniles tolerate acidification without deleterious effect (Gutowska et al., 2008; 2010), 346
following the trends for cuttlefish in biomineralization and metabolism. Non-feeding 347
lecithotrophic sea star (Crossaster papposus) larvae even show increased growth in acidified 348
conditions (Dupont and Lundve, 2010). These experiments may have the most significant 349
impact on paleontological studies of extinction selectivity, by uncovering selective pressures 350
hidden from direct view in fossil evidence. Ascribing different sensitivity to classes of mollusks 351
with excellent fossil records (e.g., scallops and cephalopods) is very informative. 352
353
Ecosystem effects and evolutionary adaptation 354
In addition to acidification responses at the level of the individual or species, acidification 355
may induce compounding implications for integrated communities. Anthropogenic acidification 356
is projected to significantly affect biogeochemical cycling, particularly with respect to nitrogen 357
cycling (Hutchins et al., 2009; Beman et al., 2011). In reefs, lowered pH is interpreted to cause 358
decreased diversity and structure complexity, and low enough pH can cease coral growth and 359
reef development altogether (Fabricius et al., 2011). Where tolerant and intolerant species are in 360
16
direct competition, intolerant species are at an even further disadvantage. For instance, coral 361
mortality increases significantly in the presence of both elevated CO
2
and CO
2
-tolerant seaweed, 362
with which they compete for habitat space (Diaz-Pulido et al., 2010). Thus, even if corals 363
survive an acidification event, they may be outcompeted for niche space by CO
2
-tolerant 364
organisms. When such state shifts occur, the newly incumbent fauna (e.g., algae) is typically 365
supported by positive feedback mechanisms, and removal of the initial disturbance will not bring 366
the original ecosystem back (Norström et al., 2009). Ecosystems are complex and the 367
interdependence of organisms highlights the need for a nuanced experimental approach that 368
considers whole ecosystems and ecosystem thresholds. 369
When organisms with common phylogeny, life mode, or habitats show common 370
responses to acidification, these may be found in the fossil record. In terms of net shell material 371
left behind as a fossil, calcification seems to decrease for corals and bivalves, stay the same for 372
some gastropods, and may increase in crustaceans and cephalopods. Bivalves, along with 373
echinoderms and gastropods, should decrease through an acidification event. Based on 374
decreased reproductive success, benthic mollusks might have higher extinction rates than the 375
apparently resilient cephalopods. Though the data are complex regarding adaptation and species 376
interactions, extinction rates should actually depend on ecology as much as physiology. For this 377
reason, analyses of the fossil record that assess success within specific habitats (e.g., Kiessling et 378
al., 2007) will continue to be important as more is learned from modern biological experiments. 379
The new field work presented in this dissertation will focus on detecting biofacies regimes and 380
their sedimentological context. 381
382
383
17
Terrestrial Matters: Dinosaur Proliferation and the End-Triassic Mass Extinction 384
The end-Triassic global mass extinction likely facilitated the proliferation of dinosaurs. 385
This section presents recent perspectives on the context, cause, and consequences of this pivotal 386
event in life history. Dinosaurs evolved gradually during the Triassic, and shared ecosystems 387
with non-dinosaurs for tens of millions of years. Unequivocal ecological dominance by 388
dinosaurs occurred in the Early Jurassic, after the end-Triassic mass extinction. On land, the 389
extinction removed most archosaurs, leaving dinosaurs to diversify and attain ecological 390
dominance. Previous explanations of dinosaurian success, such as ecological competition, or 391
rapid proliferation in the wake of the Carnian/Norian or Manicoagan events, are rejected. 392
New absolute dates have shifted the geologic timescale so much that Upper Triassic 393
rocks actually record most of Triassic history; the Carnian, Norian, and Rhaetian stages span 35 394
million years (the whole Triassic lasted approximately 50 Ma) (Brusatte et al., 2010). Therefore 395
the appearance of dinosaur forms throughout the “Late Triassic” actually represents tens of 396
millions of years of gradual evolution, rather than a sudden opportunistic expansion. The Early 397
Triassic, which featured low-diversity, cosmopolitan archosaur forms e.g., (Fraser and Sues, 398
2011) lasted a mere 5 million years (Lehrmann et al., 2006). The Middle Triassic increases in 399
archosauromorph diversity and abundance, actually occurred rather early in the Triassic Period 400
as well (e.g., Fraser et al., 2011). It is now clear that dinosaurs co-existed with basal 401
dinosauromorphs and non-dinosaurian tetrapods for tens of millions of years e.g., (Irmis et al., 402
2007; Fraser et al., 2002). Whether dinosaurs did achieve ecological dominance during the 403
Triassic is debatable and possibly regionally heterogeneous (see Irmis et al., 2007 and Olsen et 404
al., 2002). Dinosaurian anatomical superiority as an ecologically competitive trait is not 405
supported by morphometric studies (Brusatte et al., 2008). Brusatte et al., (2008) suggest that 406
18
dinosaurs, like other archosaurs, demonstrated rapid morphological changes early in the Triassic 407
but significantly decreased rates of shape change during the rest of the Period. 408
The shifted timescale removes support for interpretations of a “two-pulse” environmental 409
crisis causing extinction at the end of the Triassic Period. Evidence for significant biodiversity 410
change across the Carnian/Norian boundary is removed because new specimens have been 411
discovered and ages re-assigned for previous finds (e.g., Fraser et al., 2011). No ecological 412
change is apparent in North American vertebrate ichnofaunas across the stage boundary (Olsen, 413
2002). Moreover, the Carnian/Norian transition occurred 27 million years before the close of the 414
Triassic (Brusatte et al., 2010). Similarly, the Manicouagan impact event occurred 415
approximately 14 million years before the close of the Triassic, and with currently low temporal 416
resolution of the Norian stage, there is no recognized shift in biodiversity or ecology yet 417
attributable to the impact (e.g., Fraser et al., 2011). Shifts between arid and humid climates 418
throughout the 35 Ma Late Triassic may be due to gradual continent rearrangement, and 419
demonstrate neither sudden nor synchronous global changes (Brusatte et al., 2010). 420
In light of increasing temporal overlap of Central Atlantic Magmatic Province eruptions 421
and marine extinctions, reports of shocked quartz or iridium at some end-Triassic sites (e.g., 422
Fraser et al., 2011) require explanation but are not sufficiently compelling to support an end- 423
Triassic impact as a causal extinction mechanism. Intensive searches found no iridium or any 424
other impact indicators at either of North America’s two best-constrained marine sections 425
(Queen Charolotte Islands, British Columbia and New York Canyon, Nevada; D. Kring, personal 426
communication March 2011). 427
Biotic turnover was rapid in terrestrial habitats across the Triassic/Jurassic transition. 428
Spore and leaf records point to high extinction rates and ecological collapse among plants 429
19
(McElwain et al., 1999; McElwain et al., 2009). Most crurotarsan archosaurs (“rauisuchids”, 430
aetosaurs, and phytosaurs) went extinct, leaving only the croccodylamorphs (e.g., Brusatte et al., 431
2008). Pterosaurs and dinosaurs survived the extinction, and proliferated in the Early Jurassic 432
(e.g., Brusatte et al., 2008). Ecological changes are evident in terrestrial ichnological records 433
across the boundary from eastern North America (Olsen et al., 2002). Within a ~ 50ky window, 434
diversity of forms attributed to primitive archosaurs decreases, and the diversity of dinosaurian 435
track forms increases (Olsen et al., 2002). 436
Dinosaur diversity, disparity, and ecological dominance increased dramatically in the 437
Early Jurassic. Though earliest Jurassic vertebrate trace fossil assemblages have low diversity, 438
Olsen et al., (2002) also report a 20% increase in therapod track size, which may be an 439
evolutionary response to reduced competition from other (extinct) competitors. Therapod 440
diversification included increased size and disparity, as Ceratosaurs and Tetanurae both evolved 441
in the Early Jurassic (Brusatte et al., 2010). Early Jurassic diversification among 442
sauropodomorphs is characteristic of adaptive radiation; homoplasy is ubiquitous as differences 443
in feeding and locomotory structures developed (Yates et al., 2010). After sauropodomorphs 444
achieved cosmopolitan distributions, apparently only true sauropods survived after the Early 445
Jurassic radiation to dominate later Mesozoic herbivore ecology (Brusatte et al., 2010). After the 446
end-Triassic extinction, diversification and ecological prominence changed most notably for 447
ornithiscians. Only three true ornithiscians are known from Triassic body fossils, though 448
phylogenetic reconstructions infer more may be found in the future (Brusatte et al., 2010). By 449
contrast, deposits of diverse heterdontid and thyreophorans are very abundant Early Jurassic 450
strata (Brusatte et al., 2010). 451
20
Eruption of the Central Atlantic Magmatic Province is the best-supported causal 452
mechanism for extinctions across the Triassic/Jurassic boundary. Though some authors interpret 453
that dinosaurs gradually achieved ecological dominance during the Late Triassic through 454
morphological superiority and direct completion, more evidence supports the interpretation that 455
dinosaurs proliferated opportunistically after the end-Triassic mass extinction. 456
457
New Research on the Paleoecological Consequences of the Triassic/Jurassic mass extinction 458
Investigations presented in the following chapters differ greatly from the primary way 459
mass extinctions are currently analyzed. Increasingly, statistical assessment of extinction rate, 460
severity, selectivity, etc., are performed on fossil occurrence data compiled into the Paleobiology 461
Database (pbdb.org) from thousands of individual field studies. For this reason it is useful when 462
new field studies quantify the species, genus, and abundance of fossil faunas. Additionally, fossil 463
size and measurement data are increasingly valuable for interpretations of physiology and 464
searches for selectivity effects. Low diversity post-extinction faunas can lack the statistical 465
robustness for diversity studies, though if low-diversity faunas are at least abundant, ample data 466
can allow statistics on abundance, dominance, evenness, and size analysis. Paleoecology can be 467
assessed from diversity, abundance, and physiology studies, even more so when the fossil 468
occurrence data are paired with decent lithological observations. The current difficulty of 469
tracking quantitative fossil data and detailed, often qualitative lithological observations is one of 470
the chief targets of current government funding initiatives under the National Science 471
Foundation’s EarthCube program, and new organization tools might revolutionize 472
paleontological studies in the next ten years. The studies presented in the following chapters aim 473
to bring different perspectives to interpretation of the paleoecological consequences of the T/J 474
21
mass extinction, to add to what is already known from statistical analysis of fossil occurrences. 475
Here benthic ecology is assessed as the biological control of sedimentary systems, and pelagic 476
ecology is assessed as the potential functional consequences of shell shape among ammonoids. 477
The premise and background of each study is described below. 478
479
New Field Studies in Benthic Paleoecology 480
Substantial challenges arise because few geologic sections in the world record continuous 481
fossiliferous marine deposition across the Triassic/Jurassic (Hallam and wignall, 1999). Most 482
carbonate records show a facies change across the boundary (see Greene et al., 2012a for a 483
thorough review), which supported long-held interpretations that the extinction was caused by or 484
co-occurred with a synchronous global transgression (Hallam and wignall, 1999; Wiedmann, 485
1973; Greene et al., 2012b). While many sites throughout Europe have sedimentological 486
evidence of regressions and transgressions such as karst in carbonate sections and coarse 487
sandstones in silicilcastic sections (Hallam and wignall, 1999), increasing observations from 488
non-European sites have undermined the interpretation that this was a globally synchronous 489
phenomenon. There is not convincing sedimentological evidences for a eustatic change in 490
siliciclastics of Tibet (Hallam et al., 2000) or in the mixed carbonate and shales of Northern Peru 491
(Hallam and wignall, 1999; Hillebrandt, 1994). Evidence for widespread benthic anoxia, once 492
cited as a primary mechanism for eustatic changes to drive mass extinction, is admittedly not 493
common or temporally relevant (Hallam and wignall, 1999). With the new understanding of 494
widespread volcanism, volatile release, climate change and potential ocean acidification, T/J 495
boundary sites that show profound facies changes must be re-evaluated to determine the relative 496
impact of biotic and abiotic factors on sedimentation. 497
22
The International Subcommission on Jurassic Stratigraphy’s (ISJS) search for a Global 498
Statotype Section and Point (GSSP) for the basal Hettangian stage at the Triassic/Jurassic 499
boundary produced substantially more higher-resolution data on the key sites of interest. These 500
are shown in Table 1.1, below. See Greene et al., (2012b) for a thorough review of the 501
lithologies and isotopic trends at each of these and other important sites, illustrated in Figure 1.2 502
(Golonka, 2007; Dore, 1992). 503
Debate over the record’s potential evidence for ocean acidification requires new focus on 504
the contribution of biology and diagenesis to carbonate sedimentation. Particularly, Hautmann 505
(2004) reinterpreted the primary geology and stratigraphy in T/J boundary sections in the Gabbs 506
Valley Range in Nevada, the Pucara Group in Peru, and the Austrian Alps to show evidence of 507
direct dissolution and non-deposition of carbonate sediment at the boundary. There are several 508
logistical challenges to this specific interpretation, which highlight the need for more information 509
from direct field observations. In Nevada, Hautmann’s (2004) placement of the system boundary 510
is too low by several meters; he places it at the base, rather than in the center of, a fissile siltstone 511
interval. In Northern Peru the facies changes are not as prominent as in the Central Andes, and 512
Hautmann (2004) reinterprets a bed as marine dissolution facies. This is inconsistent with 513
Hillebrandt’s (1994) original observations; co-occurrence of Late Triassic ammonoid 514
Choristoceras and Early Jurassic ammonoid Psiloceras in a coarse grained erosive-bottomed bed 515
is explained by reworking in a storm deposit but would not be caused by mere time-averaging in 516
a condensed section. And, as Hallam and Wignall (Hallam and wignall, 1999) point out, these 517
two genera are now known to co-occur in the earliest Hettangian (Guex et al., 2012). Larger 518
problems are quantitative; an ocean acidification event would not last 500 kyr (Greene et al., 519
2012b), the duration of the fissile siltstones in Nevada (Bartolini et al., 2012). It is possible that 520
23
an ocean acidification event occurred and was part of the cause of extinction of carbonate ramp 521
producing faunas worldwide. Constraining the duration of this disturbance must be done in detail 522
in the field, rather than using measured sections to assess that the re-establishment of massive 523
limestone facies equates to ecological recovery. 524
Detailed field studies are presented in Chapters 2 – 4 to determine the ecological 525
consequence of the extinction in marine benthic habitats, and to distinguish the relative 526
contributions of diagenetic and metazoan carbonate sedimentation. Chapter 2 examines the 527
sedimentology and benthic paleoecology of metazoan biocalcifiers throughout the earliest 528
Jurassic (Hettangian and early Sinemurian stages, ~ 2Ma duration after the extinction) in the 529
Gabbs Valley Range in Nevada. Following this, Chapter 3 presents detailed analysis of 530
diagenetic carbonate sinks, and Chapter 4 presents high resolution microfacies analysis revealing 531
the ecological system that dominated this Hettangian-early Sinemurian shelf in northern 532
Panthalassa. This is matched in Chapter 4 with observations from the Pucará Group in the 533
Central Andes of Peru. Chapter 5, finally, estimates changes that occurred in global silica cycling 534
as a response to the massive volcanism and its consequences for the post-mass extinction faunas. 535
536
New Studies of Pelagic Paleoecology 537
Chapters 6-7 investigate the ecology of Mesozoic systems using ammonoids as a target 538
organism. These shelled cephalopods ruled the seas for hundreds of millions of years, and their 539
Mesozoic record is incredibly detailed due to the widespread and abundant fossils that formed 540
the basis of chronostratigraphy for the last century. For context, Chapter 6 presents preliminary 541
results from a new literature review on ammonoid paleoecology in general. Next, Chapter 7 542
presents a new method in paleobiology, which is a quantitative method to sort ammonoid shells 543
24
into different hydrodynamic categories. The method was developed in part to test for statistical 544
differences in ammonoid shell collections that would be relevant to ammonoid life mode, 545
physiology, metabolism, and hence ecology. The other purpose for developing the method is to 546
frame targets for new hydrodynamic investigations through physical experiments and computer 547
models. In Chapter 8, the method is used in its current form to examine differences between the 548
post-extinction faunas that radiated immediately after the Permian/Triassic and Triassic/Jurassic 549
mass extinctions. 550
551
25
CHAPTER 2: CONSEQUENCES OF THE TRIASSIC JURASSIC MASS EXTINCTION 552
IN BENTHIC HABITATS: SEDIMENTOLOGY AND PALEOECOLOGY IN THE 553
GABBS VALLEY RANGE OF NEVADA, USA 554
555
Introduction 556
A prominent facies change from carbonates to siltstones or marls appears at most marine 557
records of the Triassic/Jurassic mass extinction boundary (Greene et al., 2012b), and this 558
phenomenon has been interpreted as evidence of global changes in eustacy (Hallam and Wignall; 559
Schoene et al., 2010), chemistry (e.g., Hautmann, 2004), and/or biology (Greene et al., 2012b). 560
Resolving the roles of these factors requires determining the depositional environment and 561
biological control on sedimentation at each site in detail. Here analysis is presented of the 562
Triassic/Jurassic boundary and earliest Jurassic rocks (Hettangian and early Sinemurian stages, a 563
duration of ~ 2 Ma; (Schoene et al., 2010; Bartolini et al., 2012) in the Gabbs Valley Range of 564
Nevada, USA. Specifically, sedimentary structure (macro and microfacies) is analyzed and 565
surveys of marcroscopic fossil life are reported. The results show that calcium carbonate formed 566
readily in shallow marine sediments, despite the paucity of macroscopic metazoan biocalcifiers 567
through most of the studied interval. This demonstrates the decoupling of carbonate saturation 568
and biocalcifier production associated with a previously unrecognized long-term ecological 569
collapse of marine shelf carbonate ramp systems. 570
571
Stratigraphy of the Upper Triassic and Lower Jurassic in the Gabbs Valley Range 572
The paleogeography, tectonics, and chronology of the Gabbs Valley Range is well 573
studied. Triassic marine strata in the Gabbs Valley Range accumulated in an expanding basin 574
26
between the sierran island arc and northern Panthalassa, which gradually closed in the Early 575
Jurassic (Fig. 2.1). Various models and reconstructions share this basic geometry, though the 576
specific tectonic processes are debated e.g.,(Wyld, 2000). The Luning, Gabbs, and Sunrise 577
Formations record fully marine conditions from the Norian through Pliensbachian stages, and are 578
overlain by non-marine Toarcian conglomerates (Muller and Ferguson, 1939; Taylor et al., 579
1983). The thrust belt offers many repeating exposures of the same Triassic/Jurassic (T/J) 580
transitional strata (Muller and Ferguson, 1939) (Fig. 2.2). The Gabbs Formation (Fig. 2.3) 581
contains Norian and Rhaetian strata differentiated by sparse ammonoids (Laws, 1982), abundant 582
but unevenly distributed conodonts and radiolarians (Orchard et al., 2007), and newly revealed 583
strontium isotope ratio changes (Tackett et al., in review, Chemical Geology). The first 584
occurrence of the ammonite Psiloceras spelea (Guex et al., 2004) in the uppermost Muller 585
Canyon Member of the Gabbs Formation indicates the Triassic/Jurassic boundary. Pb/U dating 586
on adjacent and correlated ash beds gives a date of 201.31 +/- 0.18 Mya. In the conformably 587
overlying Ferguson Hill Member of the Sunrise Formation, the boundary between the Hettangian 588
and Sinemurian stages is indicated by ammonites (Geux, 1995; Guex et al., 2004; Bartolini et al., 589
2012; Taylor, 1998), and dated by ammonite-correlative ash beds in Peru as 199.53 +/- 0.19 Mya 590
(Schaltegger et al., 2008). 591
Sedimentology and some paleoecological sampling is known for most of the Gabbs and 592
Sunrise Formations, but there is substantial disagreement about the depositional setting of the 593
Triassic/Jurassic boundary strata. Laws (1982) sampled macrofossil abundance throughout the 594
robust mid-shelf carbonates of the Gabbs Formation, which ends in the 17 m-thick Muller 595
Canyon Member of fissile siltstones. Laws (1982) interpreted this interval as lagoonal due to the 596
bivalve fauna and gypsum, but Hallam and Wignall (2000) rejected this due to the commonality 597
27
of that particular fauna throughout global Hettangian strata, and the recent diagenetic nature of 598
the gypsum. Taylor (Taylor, 1982) developed a Jurassic biofacies model to indicate different 599
depth zones, but when this was applied to the New York Canyon area in a consensus paper with 600
Taylor, Guex, Laws, and Smith (Taylor et al., 1983) there was apparently no consensus on the 601
depth represented by the Muller Canyon Member strata. Schoene et al. (2010) invoke a profound 602
deep-shallow-deep change within the Muller Canyon Member to fit an interpretation of post- 603
volcanic glaciation, though no sedimentological evidence is presented to support this. Lucas et 604
al., (2007) document the section’s carbonate clasts as amorphous and interpret re-working along 605
the mid-to-outer-shelf expanse of an inactive carbonate factory. Overlying this, Taylor et al. 606
(1983) defined the Ferguson Hill Member as beginning with the first carbonate beds to occur in 607
close succession, though the bedding thickness varies by outcrop (see Guex, 1995: Fig. 3). 608
Taylor et al. (1983) characterize the Ferguson Hill Member as 5 m of silty limestone and 35 m of 609
cherty limestone (unit 5 of Muller and Ferguson, 1939) overlain by 15 m of oolitic limestone 610
(unit 6 of Muller and Ferguson, 1939). 611
612
Methods: Sedimentology, Paleontology, and Detailed Locality Descriptions 613
Without regard to the causal mechanism, the interpretation that the Muller Canyon 614
Member records a hiatus in carbonate deposition implies that the robust overlying limestones 615
record a return of metazoan carbonate sedimentation comparable to pre-extinction facies. It is a 616
testable prediction, then, that the Ferguson Hill Member of the Sunrise Formation should be rich 617
in macroscopic metazoan biocalcifier fossils. Laws’ (1982) surveys of fossil abundance 618
terminated in the Muller Canyon Member, and surveys in the Ferguson Hill Member are chiefly 619
faunal lists (Muller and Ferguson, 1939; Taylor et al., 1983) and biostratigraphic range charts 620
28
(Geux, 1995; Lucas et al., 2007) that do not allow comparison of Late Triassic and Early Jurassic 621
benthic biocalcifier paleoecology or contribution to sedimentation. This expectation is tested 622
here with sedimentology and fossil surveys. The fossil surveys include bulk sampling and 623
counting shells on weathered cliff face outcrops. The six stratigraphic sections considered here 624
(Fig. 2.4) are outcrops along continuous sedimentary sequences, which are easily walked in each 625
of two major canyons adjacent to New York Canyon, which is the main mining road from 626
Luning, Nevada into the Gabbs Valley Range (Fig. 2.5). 627
Muller Canyon (Fig. 2.6) is accessible by hiking SE up a wash from a prominent curve 628
along the New York Canyon road. The Ferguson Hill Member of the Sunrise Formation is best 629
exposed along its namesake hill that forms the NW wall of Muller Canyon (Fig. 2.7). 630
Fossiliferous bedding planes and cross-cut cliff faces of the upper Sunrise are best exposed along 631
a gulch (Herein: Guex Gulch) parallel to Muller Canyon, which meets the canyon floor at the 632
south-west extent of the target facies. Standing up-canyon on the SE canyon wall provides an 633
excellent view of the strata along Ferguson Hill, though on closer examination the washing of 634
tallus debris challenges sampling of the Muller Canyon Member beds. The lower Sunrise, and 635
contact with the Muller Canyon Member of the Gabbs Formation, are best exposed in the 636
periodically storm-washed minor fault contact midway up Ferguson Hill (Fig. 2.8). Guex (1995) 637
labeled the main cliff-face exposures along the NW wall of Muller Canyon site 6 (Fig. 2.9), and 638
the main Ferguson Hill exposures site 7. These are separated by a fault (illustrated on the Muller 639
and Ferguson (1939) map; Fig. 2.2) best viewed from an overlook on the SE canyon wall. 640
Though the beds can be recognized and walked along strike and across the fault, the different 641
weathering features of the different exposures offered distinct observations and sampling 642
29
opportunities. The applicable stratigraphic columns are here presented as Muller Canyon and 643
Ferguson Hill, respectively. 644
Reno Draw (Fig. 2.10) passes between two thrust packages of Triassic-Jurassic boundary 645
strata. It is best accessed by hiking due south over the saddle from a small mining excavation at 646
the end of the road north of New York Canyon road, though a robust four wheel drive vehicle 647
can also reach Reno Draw by departing the main north/south foothill frontage road and driving 648
east up the Reno Draw wash. The low hill that forms the western side of Reno Draw (Herein: 649
Vlad’s Hill) contains the uppermost Ferguson Hill Member. The eastern edge of Reno Draw is a 650
slope containing discontinuous outcrops of Muller Canyon Member at the base and expansive, 651
thoroughly traceable exposures of the entire Ferguson Hill Member that extend relatively 652
continuously about 600 meters to the NE, as shown on the map (Fig. 2.11). Guex (1995) labeled 653
these sites 3, 2, and 1, with 1 being the Northeasternmost exposure. Laws (1982), meanwhile, 654
labeled these NE sites 1 and 2, opposite the order of Guex (1995). The Northeasternmost site 655
(Guex’s 1 and Laws’ 2) forms another talus-covered sharp-peaked hill like a twin of Ferguson 656
Hill (Fig. 2.12). Herein the dipslope on the eastern face of this hill, which overlooks Luning 657
Draw, is named Sponge Jackpot. The southern exposures on the eastern wall of Reno Draw are 658
herein given 3’s following Guex (1995). When the eastern wall is viewed from the saddle at the 659
northern overlook above the mine, there are three prominent towers of strata with cliff-faces and 660
clear views of listric faulting and its impact on the apparent bedding dip severity. The outcrops 661
are named with respect to their orientation, with the nickname Aplite referring to the ubiquitous 662
Cenozoic intrusives: Aplite 3 North (A3N), Aplite 3 Middle, and 3 South Primary (3SP) (Fig. 663
2.13). Guex’s (1995) original site 3 may be the secondary exposures to the furthest SE of 3SP; 664
30
due to faulting and talus cover it is difficult to walk out beds connecting these two outcrops. The 665
three 3-series outcrops offer slightly different weathering surfaces and cliff faces. 666
667
Results 668
Sedimentology 669
Triassic / Jurassic boundary strata in the Muller Canyon Member are fine siltstones to 670
coarse sandstones. These are typically fissile and slope-forming in covered outcrops (Fig. 2.7), 671
and there is no site that provides a complete and un-faulted sequences through this member (J. 672
Guex, personal communication 2010). Bedding is best viewed in narrow, steep exposures 673
cleared by intense weathering, as occurred during the flash flood of May 31, 2009 (Fig. 2.14). 674
This cleared most of the upper eight meters of the Muller Canyon Member, from the base of the 675
Jurassic as bed N9 of Guex et al. (2004), for examination in the present study. Guex et al. (2004) 676
handle the stratigraphy by numbering the few distinctive and more-resistant marker beds that 677
stand out from the shales (see also Lucas et al., 2007; Bartolini et al., 2012). Caution must be 678
used when measuring the section at Ferguson Hill because a fault causes minor off-sets within 679
the hill at the formation transition that can be obscured by talus. 680
In outcrop these packages are thin-bedded and sulfurous when broken. Ripples are not 681
apparent in outcrop but some units bear low-angle cross stratification, and others fairly coarse 682
potentially planar laminated bedding (Fig. 2.15). None appear as convincing Bouma sequences 683
or turbidites because most beds lack apparent sedimentary structures. Results of section point 684
counting and grain size analysis (Figs. 2.16 and 2.18) at a resolution of approximately every 685
three meters through the section (from a collection by R. Martindale at approximately every two 686
meters) are very heterogeneous. Some beds contain very large (300+) micron coarse clasts (Fig. 687
31
2.16). Others are almost entirely composed of secondary carbonate (Fig. 2.17). Most are in 688
between, with few terrigenous clasts, which are silt to medium sand and very angular ( Fig. 689
2.18). These beds are readily broken and conducive to bulk sampling for fossils, and the results 690
are presented below. 691
Bedding in the Ferguson Hill Member forms first approximately ten meters of blocky, 692
resistant cliff-forming medium carbonate beds, then another ten meters of readily-weathered-out 693
concretions in matrix of varying resistance, overlain by 20-30 m of intensely cherty carbonate, 694
which interfinger with and are finally overlain by medium to thick bedded wackestones of 695
varying resistance. In the resistant cliff forming beds of the lower Ferguson Hill Member, 696
sporadic thin erosive-bottomed beds of course grains are visible, but in general the thin-to 697
medium bedded limestones lack distinctive sedimentary structures, contain only very rare visible 698
macroscopic fossils, and show no convincing signs of bioturbation. Guex’s (1995) detailed 699
“lithostratigraphy” illustrates the challenging mixture of chert and carbonate rock that at first 700
appears to vary as much laterally as vertically, making definition of sedimentary packages and 701
units difficult (Fig. 2.19). It is now clear that all distinctive recognizable beds are found in all six 702
sites, effectively described as two sites in Muller Canyon and four in Reno Draw. 703
704
Biofacies 705
Some beds of the Muller Canyon Member contained bioturbation; pervasive fine 706
Helmenthoides worm-sized burrows or isolated disturbances to fine laminations. This is 707
consistent with trace-fossil investigations by Hallam and Wignall, (2000), and Twitchett and 708
Barras, (2004), as well as thin sections in the site guide-book by Lucas et al., (2007). Bulk 709
sampling detected macroinvertebrate body fossils limited to sparse accumulations on bedding 710
32
planes at few horizons. The sampled specimens are almost all bivalves, most either Agerchlamys 711
or Modiolus (see also Ward et al., 2007). Additional specimens include mostly very small 712
unidentified bivalves and Choristoceras ammonoids. Additionally, Lucas et al., (2007) report 713
rare sponge spicules, and other microfossils from dissolution. 714
The Ferguson Hill Member is conducive to bulk sampling. Wide bedding planes and 715
cliffs of the concretion facies of the Ferguson Hill Member offered ample views of bioturbation 716
and benthic body fossils, but the latter were very few. The cherty carbonates are resistant 717
enough to prevent bulk sampling, and initially the lack of detectable body fossils in studied cliff 718
faces was attributed to possible obfuscation in the irregular weathering surfaces. Regular 719
sampling for benthic body fossils, then, was not possible until higher in the section, in cliffs and 720
bedding planes of the overlying wackestones. 721
The most fruitful sampling technique for the Ferguson Hill Member wackestones is grid- 722
normalized surveying of shelly fossils on weathered cliff and bedding plane outcrops. Results of 723
an initial project to bulk-sample the gastropod-rich wackestones (at SF 22 in Guex Gulch and in 724
the wash opposing on the southern canyon wall) were uninterpretable due largely to diagenesis 725
and breaking character of the rock. The shells are largely recrystallized into sparry calcite and 726
fragmented bulk samples rarely revealed facets of fossils that would allow identification. In 727
contrast, shells and ornament details stand out clearly in weathered rock faces (Fig. 2.20), so a 728
sampling technique to assess fossil abundance in cliff faces was developed using a 20cm x 20cm 729
wire frame divided into sixteen equal grids with clear fishing line. Initially a potential sequence 730
stratigraphic driver for the cherty intervals was suspected, and for sake of consistency eight 731
carbonate dominated intervals were chosen to target with grid sampling. At each interval, two to 732
four lateral meters were marked out with chalk, then the grid was laid along the meter stick. 733
33
Apparent taxonomy, guild, morphotype, size, and biostratinomic position of every fossil larger 734
than 5 mm and its position within the bed, meter, and grid were recorded. Results summarized in 735
Figure 2.21. 736
737
Discussion 738
The Muller Canyon Member is rich in carbonate but poor in fossil biocalcifiers. 739
Observations presented here are consistent with the interpretation by Lucas et al., (2007) of a an 740
inactivated carbonate ramp at the mid- to outer-shelf. Though distinctive from the over-and- 741
underlying medium to thick bedded resistant carbonates, the Muller Canyon Member siltstones 742
contain substantial carbonate content see (Guex et al., 2004; Ward et al., 2007). In thin section 743
this is overwhelmingly secondary cements and distinguishable bioclasts are not encountered. 744
This suggests adequate marine chemistry for carbonate formation but inadequate metazoan 745
activity for ramp production. Coarse-grained beds suggest proximity to storm deposition, and 746
the medium-sized sand grains suggest the site is not extremely deep. A lagoonal setting is 747
possible but does not seem to fit the presumably fully marine ammonoids, and would be better 748
supported if there were any thicker prominent storm or channel deposits. 749
The return of massive carbonate accumulation in the sequence is not due to rejuvenation 750
of benthic biocalcifiers ecosystems. Macrofossils are very sparse in the initial 20 m of the 751
Ferguson Hill Member, and include limited to rare isolated Agerchlamys in unit 1, some 752
unidentified clams in unit 8, and numerous microgastropods on concretion tops in unit 4 (as 753
measured in Muller Canyon). Abundant fossils first appear with scallops, then infaunal bivalves, 754
then gastropods, then corals (Fig. 2.21). A diverse fauna does not occur until well into the 755
Sinemurian stage, ~ 2Ma after the mass extinction. 756
34
This analysis establishes two important previously unrecognized consequences of the T/J 757
mass extinction. First, the ecosystems did not return to even simple ramp-producing metazoan 758
biocalcifier level bottom habitats for millions of years. Second, carbonate ramp production was 759
thoroughly decoupled from apparent carbonate saturation in the seawater. 760
These phenomena require further investigation, which is presented in the next two 761
chapters. Chapter 3 presents thorough macro and micro facies analysis of the diagenetic 762
carbonate in the concretion facies of the Ferguson Hill Member of the Sunrise Formation. 763
Chapter 4 presents thorough analysis of the biological contribution to sedimentation, and reveals 764
evidence of a massive interval of dominance by siliceous sponges. 765
766
35
CHAPTER 3: 767
A DIAGENETIC HETTANGIAN CARBONATE SINK: CONCRETION FACIES OF 768
THE HETTANGIAN SUNRISE FORMATION 769
770
Introduction 771
Concretions are interesting sedimentary features that can form in very late diagenesis or as syn- 772
sedimentary features near the sediment water interface (e.g., Loyd et al., 2012a; Loyd et al., 773
2012b; Hall and Savrda, 2008; Savrda and Bottjer, 1988; Landman and KLOFAK, 2012). As a 774
time of reduced reef and carbonate ramp production and a global “gap” in primary carbonate 775
records, the potentially substantial diagenetic carbonate sink is of special interest during the 776
Triassic/Jurassic transition (Greene et al., 2012a). Outstanding questions surround potential 777
carbonate chemistry changes associated with the most severe extinction of the Modern Fauna 778
(Alroy, 2010a; Alroy, 2010b) and of scleractinian corals (Kiessling and Simpson, 2011). Here 779
analysis is presented of indications of depositional environment and diagenetic history within the 780
lowest Jurassic rocks of the Gabbs Valley Range, one of the world’s most important and best- 781
dated Triassic/Jurassic boundaries (Guex et al., 2004; Bartolini et al., 2012). The concretions 782
formed early near the sediment water interface, completely replacing otherwise dominantly 783
biosiliceous clasts, and formed a profound carbonate sink that was not metazoan-mediated. This 784
reveals important changes in the paleoecology of the extinction aftermath. Comparisons to other 785
localities invite interpretations of carbonate chemistry worldwide. 786
787
788
789
36
Methods 790
The main purpose of this investigation was to constrain the extent, timing, and proximity 791
to the sediment water interface of the diagenetic carbonates recorded in the Hettangian rocks of 792
the Gabbs Valley Range, Nevada. From the Triassic/Jurassic (T/J) boundary upwards, 8 m in the 793
fissile Muller Canyon Member of the Gabbs Formation, and then 20 m of the conformably 794
overlying resistant Ferguson Hill Member of the Sunrise Formation, were analyzed for 795
macroscopic sedimentary structures and microscopic signs of diagenetic history, with particular 796
focus on carbonate cements and replacement. Maps, location images, descriptions of the 797
sedimentary facies, and basic fossil counts are provided in the Chapters 1 and 2, above. Thin 798
section analysis was performed at every 4 m in the upper Muller Canyon Member and at least 799
every 2 m in the first 12 m of the Ferguson Hill Member, which forms resistant cliff facies. 800
Once the Ferguson Hill Member transitions into beds with discrete concretions and non- 801
concretion matrix, special observations were made bed-by-bed of the matrix. Each bed (every 802
20-30 cm thick horizon) was searched for matrix compaction, trace fossil characteristics, and 803
body fossil presence. 804
The distribution and size of concretions, associated fossils, and chemical and physical 805
properties were also examined in detail. Almost all fossils found associated with the concretions 806
are already visible on the top surface, so no systematic concretion breaking survey was 807
performed. Instead, one concretion was examined by x-radiograph to check for bioturbation, and 808
two were microdrilled to measure oxygen and carbon isotopic composition of both bulk 809
carbonate and sparry calcite. Several small field surveys included the measuring and spacing of 810
concretions within an x-y plot, and the frequency of fossil preservation apparent on concretion 811
tops. 812
37
813
Results: Sedimentology of the Lower Hettangian 814
Stratigraphic columns presented in Figure 3.1 and a composite figure in 3.2 show new 815
sedimentological observation of the Jurassic strata in the Gabbs Valley Range. Refer to 816
generalized stratigraphic columns of the same outcrops in Figure 2.4. Most of the sedimentology 817
of the Muller Canyon Member siltstones is discussed in Chapter 2, and the results of point 818
counting for clasts vs carbonate cements are shown in Figures 2.16 and 2.28. The siltstones 819
contain only 8-38% terrigenous clasts, with most of the remaining material as carbonate cements 820
and amorphous carbonate clasts. Increasing frequency of resistant carbonate beds defines the 821
gradual transition to the Sunrise Formation. 822
The first ten meters of the Ferguson Hill Member of the Sunrise Formation are resistant 823
cliff-forming carbonate beds (Fig. 3.3), and the overlying ten meters contain oblong to spherical 824
concretions surrounded by less-resistant matrix. Carbonate is present in the beds as cements, 825
echinoderm ossicles, and most abundantly as replacement in siliceous sponge spicules (Fig. 3.4). 826
Sponge spicules have been dissolved out of Upper Triassic rocks of the Gabbs Formation in the 827
Mt Hyatt Member (Tackett et al., in prep) and across the Triassic/Jurassic transition in the Muller 828
Canyon Member (e.g., Lucas et al., 2007), but are not abundant enough to view in thin section 829
until the Sunrise Formation, as shown in Lucas et al., (2007). Thin sections prepared from 830
carbonate sampling every two meters in the first unit of the Ferguson Hill Member contained 831
compacted and transported straight style spicules, and one out of the eight samples contained silt 832
and very fine sand in lieu of spicules (Fig. 3.5). The spicules contain axial filaments indicative 833
of siliceous sponge origin, clearly visible despite complete carbonate replacement (Fig. 3.6). 834
Besides the few originally carbonate grains (echinoderm ossicles) and any amorphous carbonate 835
38
clasts, the carbonate in these beds is diagenetic. Additionally, the site contains horizons of 836
distinctively layered dark-and-clear carbonate cement layers known colloquially in England as 837
“beef calcite”, the microfacies of which have been described in detail by Greene et al., (2012a). 838
These layers are found at the base of the Ferguson Hill Member in both Muller Canyon (on 839
Ferguson Hill) and in Reno Draw. 840
The next 8 meters of section are rounded carbonate concretions in typically less-resistant 841
sediment. Within each lateral bed the concretions are very evenly distributed, and usually fall 842
within a narrow size distribution. The transition from fully carbonate beds to concretions is best 843
exposed along Ferguson Hill (Fig. 2.7) and the cliffs on the northern wall of Muller Canyon (Fig. 844
2.9). The floor of Muller Canyon offers the most expansive and varied views of the beds in 845
coherent succession (Fig. 3.7). Here it is possible to track the transition from fully carbonate 846
beds to broad expanses of very large (~ 50 cm) concretions set in slightly-less resistant matrix 847
(Fig. 3.8). Unit 2 is still cliff-forming pervasive carbonates (Fig. 3.9), but thin sections reveal 848
these to be secondary replacement of siliceous sponge spicules, as in the lower units. Unit 3 has 849
lenticular, lumpy bedding and some less-resistant matrix, transitioning to bedding distinctively 850
dominated by concretions. Unit 4 is an interval of small 15-cm diameter nearly spherical 851
concretions (Fig. 3.10) overlain by large >50 cm diameter concretions. Unit five is a 0.5 m thick 852
unit of fissile matrix punctuated by very large (~ 30-40 cm) concretions that are nearly spherical 853
(Fig. 3.11). The contacts with under and overlying units contain very large (~ 50 cm) concretions 854
(Fig. 3.12), and the measurements and illustrations support this as Guex’s (1995) level Z69. 855
Concretion size decreases above the base of unit 6, and remains small (~ 15 cm) through unit 7. 856
In units 8 and 9, the concretions are small (~15 cm), and surrounded by pervasive chert (Fig. 857
3.13). The final round concretions occur in unit 10, and are small ~10 cm surfaces that protrude 858
39
above the surrounding matrix, with an appearance almost like saddle pommels (Fig. 3.14). The 859
overlying units are pervasively cherty, and remaining occurrences of carbonate in isolated 860
patches are more like non-resistant lenses than distinctive rounded and resistantly-weathering 861
shapes (Fig. 3.15). The same succession of sizes and features is also clear in outcrops throughout 862
the New York Canyon area, and is well exposed in Reno Draw. 863
Material in the matrix is more compacted than in the concretions, and the matrix can be 864
seen draping and compacted around the concretions. Compaction around the concretions by 865
matrix sediment is best visible in units 5 and 7 (Fig. 3.16). Thin sections show the greater 866
compaction in the matrix (Fig. 3.17) compared to the concretions (Fig 3.18). 867
The abundance and size of trace fossils changes markedly through the concretion 868
interval. Trace fossils are not detected in the cliff-forming carbonate beds for the first ten meters 869
of the Ferguson Hill Member. In unit 3 of the concretion facies, trace fossils occur in isolated 870
patches as small (1 cm wide) burrows with y-shaped lateral branches (Fig. 3.19). Most beds, 871
such as in unit 7 that show the matrix around the concretions, do not record much bioturbation. 872
The transition to unit 8 and 9 is very striking, as bioturbation abruptly appears pervasively 873
surrounding the concretions. 874
The thick ropey fossil burrows which surround the concretions are well exposed on very 875
expansive bedding planes (Fig. 3.7) and cliff features (Fig. 3.13). This bedding is very 876
distinctive, as the concretions form bright light grey weathering oblong shapes within the very 877
resistant dark cherty burrowed matrix. The distinctive appearance makes this a prominent marker 878
bed allowing correlation between all outcrops, and appearing in Muller Canyon, Reno Draw, 879
parts of New York Canyon near Reno Draw, and adjacent to Luning Draw (on the upwash 880
approach from New York Canyon). The thick (2-3 cm wide) burrows are pervasive throughout 881
40
the ~20 cm thick beds, and can be seen overlapping and branching on bedding planes (Fig. 3.19). 882
In cliff sections, the burrows and matrix appear black and brown, respectively, and form a sharp 883
mottled surface (Fig. 3.20) and in rare cases weather to show more detailed branching structure 884
(Fig. 3.21). Thin sections show that the burrows are completely filled with sponge spicules (Fig 885
3.22), which are chiefly still siliceous and surrounded by chert chalcedony cements, which 886
accounts for the cherty resistant outcropping. The matrix contains abundant spicules but is more 887
full of amorphous material. In the matrix some of the spicules are replaced with carbonate and 888
some are still siliceous, and the cements are of either minerology (Fig. 3.23). In the concretions, 889
the spicules are completely replaced with carbonate, all cements are carbonate, and the clasts are 890
less compacted overall (Fig. 3.18). These burrows are diagnosed as Thalassinoides because they 891
show prominent branches in a complex three dimentional structure and lack any burrow lining at 892
the microscopic or macroscopic scale. 893
X-rays on slices of concretions were used to search for burrows passing through these 894
carbonate cemented areas. In the field, none of the Thalassinoides burrows can be seen entering 895
in or passing out of a concretion, or crossing through one. On some concretions within unit 8, 896
there are possible borings (Fig. 3.24). The x-rays of one concretion have so far detected only one 897
burrow, and it is very small (3 mm) and u-shaped (Fig. 3.25). 898
Ammonite fossils are very common at the tops of concretions throughout the interval. In 899
an area of 3.4 square meters, ammonites were counted on 7 of 73 concretions in unit 4 (Fig. 3.10, 900
3.26), which are about 10 to 15 cm in width. They are well exposed on a bedding plane on the 901
floor of Muller Canyon, where they have weathered out of the matrix well enough to see that the 902
uniform size is consistent in height and width. Very large ammonites are also very common, 903
particularly on the large concretions below and above unit 5. Walking this unit along strike up 904
41
the side of Ferguson Hill leads to the discovery of common ammonite concretions weathering 905
out of the section (Fig. 3.27). These ammonite fossils range up to 35 cm in diameter (Fig. 3.28), 906
within concretions up to 50 cm (Fig. 3.12). Some of the most ornate fossils were destroyed in the 907
flash flood on May 30, 2009. Some cases contain full fossilization of the ammonite shell (Fig. 908
3.28) but more commonly only the upper surface of the shell is retained, and the lower part of the 909
shell is completely formed into the concretion. In these beds, concretions with and without 910
ammonoids typically have flat tops and rounded bottoms. The concretions are typically uniform 911
in size and evenly distributed in the sediment, and in beds with abundant ammonites the size of 912
the ammonite corresponds to the size of the concretions. The ammonites typically occur at the 913
tops of the concretions or within the top centimeters; only one large one has been found not at 914
the top of the concretion, and very small ammonoids sometimes occur within the concretion 915
mass, sometimes in association with larger ones. In Units 8 and 9 where burrows surround 916
concretions, small ammonoids are still common on the concretion surfaces (Fig. 3.29), and one 917
has been found deeper within a concretion. Ammonoids on tops of concretions are best viewed 918
on extensive bedding planes in the Muller Canyon floor along unit 4, 6, and 8. 919
Measured ratios of carbon isotopes within the concretions have values near modern day 920
seawater. Figure 3.30 shows the values increasing very slightly within each concretion, and all 921
but one measurement of bulk carbonate falls between about negative one and zero per mil, 922
compared to modern Standard Marine Ocean Water (SMOW). 923
Net rock accumulation rates can be estimated from chronometric dating, sub-zone 924
biostratigraphy, and cyclostratigraphic divisions of correlate-able strata. This is presented in 925
Figure 3.31. The apparent accumulation rate of the boundary strata in the Muller Canyon 926
Member is highest, several cm per thousand years. This decreases in overlying units, to a low of 927
42
mere mm per thousand years. Net rock accumulation is, of course, a consequence of both 928
sedimentation and erosion, including that by storm deposition, which is discussed below. 929
930
Discussion 931
The carbonate in the Hettangian strata at the New York Canyon area outcrops is almost 932
entirely diagenetic. The first 30 m record extensive secondary carbonates, and primary carbonate 933
bioclasts are not the dominant grains. At the Triassic/Jurassic transition, silty Muller Canyon 934
Member beds are pervasively cemented with carbonate. Increasing frequency of heavily 935
cemented resistant beds initiates the transition to the Ferguson Hill Member of the Jurassic 936
Sunrise Formation, consisting of 10 m of solidly cemented carbonate beds, and 10 m of beds 937
with rounded concretions. The concretions show complete replacement in the most abundant 938
bioclasts, spicules of siliceous sponges. 939
The diagenetic carbonate formed near the sediment water interface during active 940
sedimentation of non-carbonate grains. Several conditions support this interpretation. 941
942
1. The concretions surrounded by Thalassinoides burrows formed near the sediment water 943
interface. The Thalassinoides burrows bioturbated the matrix in units 8 and 9, but do not 944
penetrate the rounded concretions. The most parsimonious interpretation of this is that the 945
concretion areas were cemented first, then the surrounding material was thoroughly 946
burrowed. The very small burrow found within one of the x-rayed concretions shows 947
activity of some organisms before cementation. Thalassinoides typically form within the 948
first meter of the sediment water interface (Bromley and Frey, 1974; MacGinitie, 1934), 949
so the concretions likely formed within a meter of marine waters. It’s possible that the 950
43
mixed zone sediments are winnowed away. The burrows in units 8 and 9 are completely 951
filled with siliceous sponge spicules and cemented with silica. The steps of concretion 952
formation are illustrated in Fig 3.32. 953
2. Another example of early carbonate growth is exemplified by the “beef” calcite horizons 954
(Fig. 3.33), which were originally aragonitic fans that grew just below the sediment/water 955
interface (Greene et al., 2012a). Grains in the concretions are not as compacted as grains 956
in surrounding matrix or burrows. The carbonate cements in the concretions represent 957
greater original porosity, and formed before the sediment was deeply buried. 958
3. Many of the concretions formed around and underneath ammonite shells. Within an 959
individual concretion, an ammonite shell provided both a nucleation site for carbonate 960
cementation, and a pressure-inducing environment that might drive precipitation. The 961
fairly uniform size and distribution of concretions within each lateral bed, as well as the 962
fully-cemented beds below, indicates diffusion-regulated cementation of pore spaces on a 963
large scale. 964
4. The values of carbon and oxygen isotopes in the concretions indicate involvement of 965
marine bottom waters, rather than isolated pore waters. 966
967
The facies changes indicate ecological changes that cannot be completely reduced to 968
changes in marine chemistry. The Triassic/Jurassic transition and Hettangian rocks contain 969
abiotic (or microbial) secondary carbonate production in shallow sediments instead of metazoan 970
bioclast production. As a change from the robust carbonate biocalcifier ramp of the Mount Hyatt 971
Member, the carbonate cemented siltstones of the Muller Canyon Member fits an ecological 972
collapse associated with the mass extinction, during a 300 kyr interval at the end of the Triassic. 973
44
An ocean acidification event is a possible trigger for the end-Triassic ecological collapse, 974
though the resolution on volatile volumes and release rate is still insufficient (Greene et al., 975
2012b). Relatively low carbonate accumulation within the Muller Canyon Member has been 976
interpreted as a sign of ocean acidification, but does not directly show this. Though it is 977
debatable if the volume of diagenetic carbonate in the siltstones was sufficient to have sustained 978
the previously incumbent benthic level-bottom assemblages of brachiopods and bivalves, models 979
do not support the occurrence of an ocean acidification event for hundreds of thousands of years. 980
Bivalves were sporadically abundant during the very earliest Hettangian stage, but were not 981
building shell beds in the region. Very little recrystallized shell material remains of the flat 982
Agerchlamys scallops, and the Modiolus mussels are dissolved, leaving only a trace of the 983
proteinaceous periostracum. The Muller Canyon Member records < 500 kyr, an interval here 984
interpreted as ecological collapse, despite recovered (if ever lowered) carbonate saturation states 985
and ample oxygenation at least sporadically (supported by the trace fossils). Persistent or 986
transient decreases in carbonate saturation state or availability of dissolved inorganic carbon 987
would be consistent with the earliest Hettangian fauna, but are not supported by marine 988
chemistry modeling during the interval as a whole (Greene et al., 2012b). 989
In the wake of the ecological collapse, the volume of the diagenetic carbonate factory is 990
profound, and consistent with many other contemporary locations. This process was so pervasive 991
that it replaced dominant siliceous sponge spicules, which might otherwise have functioned more 992
like siliciclastic systems. Unlike carbonate bioclast accumulations that are readily cemented by 993
dissolution and reprecipitation in pore fluids, the spicules, before reaching critical mass to 994
facilitate chalcedony cements, might have simply been redistributed into deeper water or 995
compacted like terrigenous silt. Instead, carbonate filled pore space in shallow sediment, and 996
45
grew aragonitic fans (now the “beef calcite”). Though the concretions are most striking when 997
isolated as spheroids, the entire Hettangian record is effectively secondary carbonate. In the 998
lower units of the Ferguson Hill Member, the carbonate replacement of siliceous spicules 999
occurred near enough to the sediment water interface that the silica did not form cements or 1000
nodules and must have fluxed out of the sediments. Biogenic silica and chalcedony are absent 1001
throughout the first 30 meters of the Jurassic strata, until the spicule-filled burrows. Most other 1002
fossiliferous marine Triassic/Jurassic boundary sites also record a transition to beef, concretions 1003
and/or marls in an apparently wide-spread phenomenon of diagenetic carbonate production in 1004
collapsed biocalcifier habitats (Greene et al., 2012a, 2012b). 1005
The intensity of bioturbation might reflect sporadic benthic oxygenation. These 1006
observations agree with surveys of bioturbation by Hallam and Wignall (2000) and Twitchett 1007
and Barras (2004). The robust branching burrows of the Ferguson Hill Member are here 1008
interpreted as Thalassinoides rather than Rhizocoralium (as in Twitchett and Barras, 2004) 1009
because branching was observed (Fig. 3.20, 3.21) but not backfilling. 1010
After the collapse of the carbonate ramp biocalficier ecosystems, the regional ecology 1011
was dominated by siliceous sponges and non-fossilized producers of burrows. Chert does not 1012
accumulate in the record until the siliceous sponge spicules filled Thalassinoides burrows in 1013
upper Hettangian strata, despite the density of spicules in underlying Hettangian concretionary 1014
horizons. The ecology of the sponge cherts that dominate the rest of the Hettangian strata is 1015
explored in the next chapter. 1016
46
CHAPTER 4. SILICEOUS SPONGE FACIES OF THE HETTANGIAN IN THE GABBS 1017
VALLEY RANGE OF NEVADA AND THE CENTRAL ANDES OF PERU 1018
1019
Introduction 1020
The end-Triassic mass extinction (c. 200 Mya) was the most severe biotic crisis 1021
experienced by modern marine invertebrate faunas. Although diversity patterns are increasingly 1022
well known, the ecological response after the mass extinction in marine habitats is less clear. 1023
New paleoecological data from two widely separated and stratigraphically expanded Lower 1024
Jurassic successions (Nevada, USA and Central Andes, Peru) demonstrate complete ecological 1025
restructuring of benthic marine habitats that lasted approximately two million years after the 1026
mass extinction. At both sites, Late Triassic carbonate systems are replaced by siliceous sponge- 1027
dominated ecosystems in the Early Jurassic. The “sponge takeover” was likely facilitated by a 1028
unique confluence of circumstances: extinction-driven changes in benthic ecology coupled with 1029
increased global silica flux (a limiting nutrient for sponges) from weathering of the massive 1030
Central Atlantic Magmatic Province (CAMP). 1031
The end-Triassic mass extinction is characterized by simultaneous reef collapse, global 1032
paucity of carbonate deposition, and extinction selectivity against biocalcifiers in carbonate and 1033
reef habitats (Greene et al., 2012b; Kiessling et al., 2007; Kiessling and Simpson, 2011). Of the 1034
major mass extinctions of the Phanerozoic, the Triassic/Jurassic (T/J) event is particularly 1035
pertinent to the modern Earth system, as it involved organisms closely related to extant groups 1036
(including scleractinian reefs) and their response to a massive release of CO
2
during 1037
emplacement of CAMP, the largest terrestrial igneous province of the Phanerozoic (Fig. 4.1) 1038
(Whiteside et al., 2010; Alroy, 2010a; Alroy, 2010b; Kiessling and Simpson, 2011; Honisch et 1039
47
al., 2012; Greene et al., 2012b). Changes in climate and ocean chemistry associated with volatile 1040
release from CAMP have been postulated as a primary cause of the extinction (Greene et al., 1041
2012b; Schoene et al., 2010; Whiteside et al., 2010). Globally, carbonate systems flourished in 1042
the latest Triassic, collapsed in the earliest Jurassic (Hettangian and Early Sinemurian stages), 1043
and returned approximately 2 Ma into the Jurassic (later Sinemurian stage) (Greene et al., 2012b; 1044
Delecat et al., 2011; Taylor et al., 1983). 1045
Diversity and actualism (the present gives clues to the past), two tools traditionally 1046
applied to determine paleoecological change, are problematic in cases of mass extinction (Bottjer 1047
et al., 1995; Clapham et al., 2006). Taxonomic diversity trends miss crucial ecological changes 1048
(Clapham et al., 2006) (abundance, dominance and habitat engineering) and often ignore soft- 1049
bodied and morphologically plastic faunas that cannot be identified to genus level. Actualistic 1050
sedimentological paleoenvironmental analysis asserts that biologically mediated facies are 1051
consistently restricted to depth-bounded habitats (Bottjer et al., 1995). Because biofacies 1052
production is also sensitive to changes in marine chemistry and extinction driven changes in 1053
diversity and ecology, actualistic paleoenvironmental assumptions are problematic during mass 1054
extinction times (Bottjer et al., 1995; Greene et al., 2012b; Racki and Cordey, 2000; Maldonado 1055
et al., 1999). 1056
Biofacies analysis is presented for two widely separated earliest Jurassic successions 1057
from eastern Panthalassa: western Nevada and Peru (Fig. 4.1). These are the only two sequences 1058
with adequate stratigraphic resolution to record uninterrupted T-J transition in shallow 1059
fossiliferous settings in Panthalassa (Guex et al., 2004; Guex et al., 2012; Bartolini et al., 2012) 1060
(see Table 1.1). In each locality, the Late Triassic – Early Jurassic paleoecological conditions 1061
are known in detail for carbonate biofacies, but the first ~ 2 Ma of the Jurassic, deposited during 1062
48
the collapse and subsequent recovery of the carbonate system, remain neglected (Taylor et al., 1063
1983; Taylor, 1998; Szekely and Grose, 1972; Senowbari-Daryan and Stanley, 1994; Rosas, 1064
1994). To interpret consequences of the mass extinction, paleoenvironmental information was 1065
collected (grain size, energy to deposit bedforms, etc.) and distinguished from the ecological 1066
biofacies (biologically mediated sedimentary structures, macrofossils and microfacies) in order 1067
to account for potential non-actualistic processes during the extinction interval (Bottjer et al., 1068
1995). 1069
1070
Geologic Background 1071
In west-central Nevada, the Gabbs Formation represents an extensively studied, Upper 1072
Triassic carbonate ramp system within a back-arc basin (Wyld, 2000; Taylor et al., 1983; Laws, 1073
1982). The uppermost Muller Canyon Member records the T/J transition and abrupt termination 1074
of ramp facies (Bartolini et al., 2012; Lucas et al., 2007; Laws, 1982). In the overlying Jurassic 1075
Sunrise Formation, absolute dates, subzone ammonoid biostratigraphy and 30 meters of 1076
Hettangian record make the succession an excellent target for paleoecological investigation of 1077
the carbonate-poor interval (Bartolini et al., 2012; Delecat et al., 2011; Schoene et al., 2010). 1078
Paleoecology is well known in the upper Sunrise Formation, once carbonate ramp facies 1079
reappear (Taylor, 1982; Taylor et al., 1983; Taylor and Guex, 2002). The succession is of global 1080
significance and was considered for the recently determined basal Jurassic GSSP (Lucas et al., 1081
2007). 1082
In the Central Andes of Peru, the Pucará Group parallels the record in Nevada but the 1083
geology, structure, and sedimentology are more widely studied across a much broader 1084
depositional and geographic extent (Loughman and Hallam, 1982b; Rosas, 1994; Szekely and 1085
49
Grose, 1972). The Chambará Formation records a robust fossiliferous Late Triassic carbonate 1086
platform (Rosas, 1994; Senowbari-Daryan and Stanley, 1994). The overlying Jurassic 1087
(Hettangian and early Sinemurian) Aramachay Formation records the carbonate platform 1088
collapse and crops out as non-resistant mudstones (road cuts near Levanto in the North (Guex et 1089
al., 2012), and the Tarma section near La Oroya in Central Peru (Rosas et al., 2007; Rosas, 1994; 1090
Sempere et al., 2002) and very resistant cherty limestone (in total, 73 to 125 meters thick; near 1091
La Oroya in the Central Andes (Rosas, 1994; Szekely and Grose, 1972). Finally, the 1092
Condorsinga Formation records the re-establishment of a fossiliferous carbonate platform 1093
(Rosas, 1994; Senowbari-Daryan and Stanley, 1994). Guex et al., (2012) and Schaltegger et al 1094
(2008) provide high-resolution ammonoid biostratigraphy and chronometric dates (U/Pb from 1095
ash beds) for the Triassic/Jurassic and Hettangian/ Sinemurian boundaries. The Pucará’s 1096
carbonate biofacies (Chambará and Condorsinga Formations) have been studied extensively, but 1097
the biofacies of the Aramachay Formation is relatively unstudied (Rosas, 1994; Rosas et al., 1098
2007; Loughman and Hallam, 1982a; Senowbari-Daryan and Stanley, 1994; Szekely and Grose, 1099
1972; Prinz, 1985). 1100
1101
Methods 1102
In each region, the basic geology, geochronology, and sedimentology has already been 1103
established, so the current investigation focused on detailed sedimentologic and fossil 1104
observations. The sedimentology in Nevada, including microfacies and diagenetic analysis, is 1105
presented in Chapters 2 and 3. Further investigation presented here focused chiefly on 1106
determining the biological contribution to sedimentation via microfacies analysis on lithologic 1107
thin sections. Thin sections were taken from rock sample surveys collected for two different 1108
50
purposes in at least three field expeditions. First, collections were made and the section was 1109
measured, to establish the basic sedimentology of the main units. Second, samples were taken 1110
from each style of potential sponge fossil identified in the field. Finally, rock samples were taken 1111
for microfacies analysis at intervals of every 2 m in the lower Ferguson Hill Member (see 1112
Chapter 2) and at least every meter in the cherts. Cliff faces and bedding planes were searched 1113
for potential sponge body fossils, particularly in connection with carbonate deposits with 1114
tempestite features. Once large-scale exposures of sponge body fossil beds were found, these 1115
were searched systematically in 10 cm x 30 cm grids for biocalcifying or reef-forming faunas 1116
(corals, bryozoans, brachiopods, infaunal bivalves, epifaunal bivalves, gastropods, and crinoids). 1117
In Peru, a previous collection of ~300 thin sections allowed for the search and targeting 1118
of sponge spicule rich facies. Only one siliceous spiculite comparable to the Nevadan strata was 1119
found, from the Malpaso field site. Field work then focused on Malpaso and that interval in 1120
particular. A field team of local exploration geologists split up to search for potential sponge 1121
body fossils, fossil burrows, and to distinguish potentially biological facies signals from 1122
diagenetic and depositional features. In addition, sites near Morococha and Tingocancha were 1123
examined. At each site, the goal was to identify sedimentary structures indicative of depositional 1124
environment, to diagnose the apparent centers of chert nodule growth, to search for potential 1125
sponge body fossils and bulk spiculites, and to assess the presence and abundance of 1126
biocalcifying benthic faunas. Thin sections were made to examine the spectrum of facies at 1127
Malpaso, and to search for spicules and sponge body fossils in materials from all three sites. 1128
1129
1130
1131
51
Environments and Ecology in the Nevada Record 1132
The studied interval in Nevada is here interpreted to record increasingly shallow 1133
depositional environments through time, during the initiation and growth of a carbonate ramp, 1134
which is consistent with previous interpretations (Lucas et al., 2007; Hallam and wignall, 2000). 1135
Figure 4.2 shows a composite stratigraphic column. Siltstones of the Muller Canyon Member 1136
represent distal shelf deposition without an active carbonate ramp; in outcrop they lack distinct 1137
storm beds and in thin section they bear indistinct carbonate grains and cements, but lack 1138
substantial carbonate mud. Resistant carbonate beds that mark the base of the Sunrise 1139
Formation are concretionary for the first 20 meters (Figs. 3.3, 3.8), and record early diagenetic 1140
carbonate rather than an active metazoan carbonate factory (Greene et al., 2012a). The section is 1141
not, however, devoid of bioclasts, and is in fact dominated by sponge spicules. Laterally 1142
continuous beds of pervasive thick branching burrows (Thalassinoides: Figs. 3.7, 3.19) are filled 1143
completely by siliceous sponge spicules and chert cements (meters 20-25). Next, the strata are 1144
completely dominated by cherty deposits of collapsed and well-preserved sponge body fossils. 1145
Abundant storm beds in the chert interval support a location on the middle shelf. This indicates 1146
that the sponges are not simply deep dwellers, but present in great abundance on the shelf. The 1147
development of a carbonate ramp up-section is first recorded as mollusk-rich storm beds and 1148
finally by massive wackestones deposited between storm and fairweather wave base. 1149
Biofacies analysis on the micro, meso, and macroscopic scale shows that siliceous 1150
sponges dominated midshelf settings during the Hettangian and early Sinemurian, both in terms 1151
of sedimentology and ecology. Analysis of 77 thin sections (Fig. 4.2) reveals that spicules are 1152
the first abundant bioclasts, and dominate 45 meters of strata in the Sunrise Formation 1153
(“spiculite”). Consistent with the shallowing-up sedimentary facies, the sponges are first 1154
52
recorded as distal sedimentation from disarticulated spicules, then in-situ body fossils. First, 1155
abundant styles (long needles) broken in transport dominate beds with reworked carbonate grains 1156
and echinoderm fragments (10-20 m). Axial filaments indicate siliceous sponge origin, even 1157
though the first ten meters of spiculite are typically replaced by carbonate (Uriz et al., 2000). 1158
Next, spicules exclusively fill the thick Thalassinoides burrows (25-30 m). In meters 30-55, the 1159
bedded cherts are in-situ spiculites, almost completely devoid of terrigenous grains or other 1160
bioclasts. In thin section, collapsed sponges are distinguished as large and complex spicules 1161
(Figs. 4.3 and 4.4) suspended among autochthonous mineral growths (dolomite rhombs are 1162
common, Fig. 4.5) and chalcedony cements. Complex dichotraenes (branching spicules, Fig. 4.6) 1163
indicate astrophorid demosponges (Uriz et al., 2003; Boury-Esnault and Rützler, 1997). Desmas 1164
(large complex spicules, Fig. 4.5) are very common within the upper 20 m of bedded chert and 1165
typically indicate sponge growth in the presence of high silica concentrations (Maldonado et al., 1166
1999). 1167
The ecological dominance of the sponges is clear when viewed on the meso and macro 1168
scale. Bedded cherts form resistant cliffs, 25 m thick, clear even in satellite imagery (Fig. 2.5). 1169
Individual sponge-dominated beds are easily traced over a kilometer in Reno Draw and in nearby 1170
Muller Canyon (Fig. 2.5). Rapid burial with carbonate clasts and micrite from shallower settings 1171
preserves sponge body shapes and distribution in great detail (Fig. 4.7, Fig. 4.8). A dip slope in 1172
Luning Draw exposes the upper 10 m of cherts as sponge bedding planes each ~ 20 meters long 1173
(Fig. 4.9). Here, sponges exclusively dominate every non-storm bed (Fig. 4.10). Grid surveys on 1174
the best-exposed bed, at 8 intervals (100 x 30 cm panels), revealed abundant large individual in- 1175
situ scallops (Weyla) (76) and rare gastropods and crinoid stalks (2 each), but no corals, infaunal 1176
bivalves, or bryozoans. The entire sequence represents a level-bottom environment; despite very 1177
53
detailed preservation of sponge and scallop positions, there are no indications of reef or bioherm 1178
build-ups. Bulk sampling of the fissile T/J boundary siltstone recovered mussels (Modiolus) and 1179
small pectinids (Agerchlamys), consistent with previous reports, but bivalve bioclasts are not 1180
abundant enough to be represented in the thin section analysis (Lucas et al., 2007; Ward et al., 1181
2009). Grid surveys performed on cliffs in Muller Canyon (Fig. 2) show that biocalcifiers are not 1182
abundant or ecologically diverse until wackestones appear overlying the sponges. 1183
Sponges dominated these midshelf habitats in northern Panthalassa during the Hettangian 1184
and early Sinemurian (Taylor et al., 1983; Guex et al., 2004). Absolute dates from this site in 1185
Nevada and in northern Peru, as well as biostratigraphic correlation between the two (Fig. 3.30), 1186
assign 1.55 Ma to the first 25 meters of Hettangian spiculites (Guex et al., 2012; Schaltegger et 1187
al., 2008; Bartolini et al., 2012; Schoene et al., 2010). The additional 20 m of Sinemurian 1188
sponge cherts likely accumulated at a slower rate because they are made of amalgamated in situ 1189
sponge body fossils rather than silty spiculitic concretions (Brachert, 1991). This is consistent 1190
with decreasing net rock accumulation rates throughout the Hettangian (Bartolini et al., 2012). 1191
The sponge phenomenon conservatively lasted at least 2 Ma. Moreover these dates allow 1192
correlation to CAMP; the spiculites appear about 480 kyr after the initiation of the North 1193
Mountain flood basalts (Schoene et al., 2010; Bartolini et al., 2012). 1194
1195
Peru 1196
The tools developed to assess sponge biofacies in Nevada were next applied to the Pucará 1197
Group in Peru. First, we searched thin sections (n >300) through the 700 m T/J interval for signs 1198
of spicules and in-situ sponge preservation (Rosas, 1994). We focused field work on three sites 1199
that represent a transect from the midshelf to the inner shelf: (Fig. 4.11) Morococha, Malpaso, 1200
54
and Tingocancha (Rosas, 1994; Rosas et al., 2007). Each location offers an extensive canyon or 1201
valley scale outcrop where the lowermost Jurassic beds can be traced on the kilometer scale 1202
laterally and are in contact with over and underlying formations. 1203
The Pucará Basin formed as a successor basin above a dissected and deformed platform 1204
of Permo-Carboniferous to Middle Triassic rocks. The pre-Pucará rocks, clastic molasses and 1205
alkaline volcanics (Middle Triassic), were deposited in a suite of rift depocenters (Sempere et al., 1206
2002). As fault-controlled subsidence gradually ceased, the various depocenters yoked together 1207
to form the broad epeiric Pucará Basin, expressed by widespread transgression of marine 1208
sediments, persisting without regard to the previous structural framework. In this way the Pucará 1209
Basin was a regional sag in which local depocenters formed by intermittent transtensional 1210
subsidence (Rosas et al., 2007). As a consequence the Pucará Group presents major facies and 1211
thickness changes over short distances. 1212
Morococha (Fig. 4.12) represents midshelf deposition on a distally steepened ramp along 1213
the basin border (Fig. 4.11). The lower Aramachay Formation contains thick silicified branching 1214
Thalassinoides burrows (Fig. 4.13). Between burrow horizons, lenticular cross bedding of chert 1215
and carbonate indicates either amalgamated storm deposits or a setting closer to fairweather 1216
wave base (Fig. 4.14). The upper Aramachay consists of mottled alternating beds of carbonate 1217
and black chert (Fig. 4.15). These are completely filled with compacted siliceous spicules, 1218
visible in polished hand sample and thin section (Fig. 4.16). Cores from Moracocha also contain 1219
exquisitely preserved in-situ sponge fossils (Fig. 4.17). The best outcrop terminates with thick 1220
mollusk-rich storm deposits and silicified beds bearing hundreds of ammonoids, including the 1221
late Hettangian Paracaloceras cf. P. coregonense (Fig. 4.18). The cores show a transition from 1222
these storm beds to finer grained massive bioclastic limestones of the Condorsinga Formation. 1223
55
Malpaso (Fig. 4.19) represents a shallower setting. Massive dolomites of the Upper 1224
Triassic Chambará Formation contain well-studied carbonate platform biofacies (Rosas, 1994), 1225
with bioclasts most visible on broad bedding planes. The lower Aramachay Formation is 1226
ammonoid-rich massive mudstone bounded by horizons of pervasive, well-exposed 1227
Thalassinoides burrows (Fig. 4.20). The upper Aramachay Formation is highly resistant due 1228
primarily to massive sandstones of immature volcanic grains overlying thick tuffs. Successive 1229
beds contain increasingly mature grains of the same provenance surrounded by pervasive 1230
chalcedony cements and very cryptic sponge spicules. Chert is present in the resistant beds as 1231
cements and increasingly dense nodules, which dominate the remaining Aramachay Formation 1232
until it gradually transitions into massive Sinemurian Condorsinga limestones. The sedimentary 1233
facies of the Condorsinga limestones appear very similar to the Upper Triassic Chambará 1234
Formation, but thin sections reveal more sponge remains. 1235
Though most chert nodules at Malpaso form within burrows (Fig. 4.21), some chert 1236
nodules are actually large sponge body fossils preserved in place. Matrix surrounding 1237
elaborately branching burrows contains ubiquitous spicules, visible to the naked eye (Fig. 4.22). 1238
Similarly to Nevada, at Malpaso sponges are recognizable on the meso scale as flat-bottomed 1239
chert layers with undulose upper contacts overlain by massive carbonate deposits (Fig. 4.23). In 1240
polished slabs and thin sections, the microfacies of unbroken complex spicules suspended in 1241
chert cement matrix clearly show sponge body fossils (Fig. 4.4) (Brachert, 1991). There are no 1242
indications of reefs or bioherms, and sponges show approximately 15 cm of apparent synoptic 1243
relief. Like Nevada, scallops are common as individuals and rare clusters. Also like Nevada, the 1244
sponges contain abundant dichotraenes, indicating Astrophorid demosponges (Fig. 4.4) (Uriz et 1245
al., 2003; Boury-Esnault and Rützler, 1997). Though not detected in these samples, desma 1246
56
sponges have been reported from the Pucará (Prinz, 1985). Our detection of abundant sponge 1247
fossils and spicules in Malpaso suggests the Aramachay’s characteristic chert was sourced from 1248
dissolved sponge spicules. Previously, chert nodules in the Aramachay, clearly secondary in thin 1249
section, were ascribed to a volcanic source, but with unsatisfactory support (Rosas, 1994). 1250
Tingocancha (Fig. 4.24) represents the shallowest deposition (Rosas et al., 2007; Rosas, 1251
1994). Thin to thick bedded dolostones contain abundant high-angle cross stratification, 1252
indicating deposition above fair-weather wave base (Fig. 4.25). Across the T/J transition, white 1253
dolomites are mixed with thin chertified horizons and sedimentary structures indicate persistent 1254
wave activity. We interpret the whole sequence of members to represent deposition above 1255
fairweather wave base. Examined Aramachay chert contains small spicules and shell debris, and 1256
occurs subjacent to crinoid grainstone. 1257
Sponges were the first dominant clast producer on these south Panthalassa shelves and 1258
maintained dominance at least throughout the early Sinemurian, a phenomenon that lasted 1259
approximately 2 Ma. Newest ammonoid biostratigraphy and absolute dates from northern Peru 1260
show the Aramachay Formation spans the Triassic/Jurassic boundary at 201.35 +/- 0.10 Mya, 1261
and the Hettangian/Sinemurian stage boundary at 199.43 +/- 0.10 Mya (Guex et al., 2012; 1262
Schaltegger et al., 2008). Abundant Lower Sienmurain ammonoids overlying Morococha 1263
spiculite cliffs show that sponges dominated the midshelf during the Hettangian, until the 1264
sponge-rich Aramachay was overwhelmed with biocalcified clasts to form the Condorsinga 1265
Formation during the Early Sinemurian. 1266
1267
1268
1269
57
Discussion 1270
The detected biofacies show that siliceous sponges dominated widespread areas of the 1271
shelf, not simply deep basin environments, in two distant Panthalassic successions for 1272
approximately two million years following the collapse of the carbonate system during the end 1273
Triassic extinction. Diverse biocalcifiers (e.g., mollusks, echinoderms, and brachiopods) were 1274
replaced with level-bottom sponge meadows, dominantly crustacean soft-bodied burrowers 1275
(Bromley and Frey, 1974), and scallops, which are still commonly associated with sponge 1276
habitats today (Bell, 2008). This ecological signal has been overlooked in the past because of 1277
very cryptic sponge preservation, and represents how macrofossil diversity studies can miss key 1278
ecological reorganization. At both field sites, the lack of a carbonate ramp biofacies was 1279
previously interpreted as eustatic sea level change, but this sedimentological analysis supports 1280
consistently mid-shelf settings (Taylor et al., 1983; Schoene et al., 2010; Bartolini et al., 2012; 1281
Rosas et al., 2007; Delecat, 2005; Rosas, 1994). 1282
Changes in ecology and geochemical cycling during the T/J transition can explain the 1283
sponge expansion. Whether or not ocean acidification was a direct kill mechanism (Greene et al., 1284
2012b), carbonate bioclast production was interrupted by the mass extinction, which severely 1285
selected against biocalcifiers (Greene et al., 2012b; Kiessling et al., 2007; Kiessling and 1286
Simpson, 2011). As in the global ocean Panthalassa, in the Tethys Sea the Hettangian/early 1287
Sinemurian strata also reveal dramatic expansion of siliceous sponges from intraplatform settings 1288
to shallow platform-wide dominance (Delecat et al., 2011; Delecat and Reitner, 2005; Delecat, 1289
2005; Zimmerle, 1991). At Austria’s Late Triassic Steinplatte reef complex, the entire 1290
Hettangian stage is represented by a condensed layer of siliceous sponge material (Fig. 4.26) 1291
(Delecat et al., 2011). Open shelves, with a stressed carbonate fauna, likely posed ecological 1292
58
opportunity for sponges to colonize. Modern carbonate habitats exhibit shifts to alternative stable 1293
states (Norström et al., 2009), where positive feedback loops prevent re-establishment of the 1294
disturbed groups. After even a very brief disturbance to benthic biocalcifiers (e.g., coral 1295
bleaching), modern sponges can rapidly take-over widespread habitats, where they drastically 1296
outcompete other benthic fauna for substrate space, and can even overtake living corals 1297
(Johnston and Clark, 2007; Norström et al., 2009). The rapid competitive settling of sponges 1298
exerts bottom-up control on modern carbonate habitats while immune even to intense predation, 1299
so these systems may have much more longevity than algal take-overs that might be reversed if 1300
intensive top-down predation pressures are reestablished (Norström et al., 2009). Because 1301
modern examples span only decades, the function of these processes over hundreds of thousands 1302
to millions of years is more difficult to infer. A model of the biological control on marine facies 1303
across the Triassic/Jurassic boundary is presented in Figure 4.26. 1304
Even an auspicious entrance into open ecological space may not explain their ~2-million 1305
year dominance of siliceous sponges in such widespread habitats and regions, and geochemical 1306
cycling was probably a contributing factor. During the T/J transition, intensified weathering 1307
(Michalik et al., 2010) and the presence of 10
6
km
2
of fresh basalt (CAMP (Nomade et al., 2007); 1308
roughly the size of modern Europe) boosted annual silica supply to the oceans. Increased marine 1309
silica concentrations are evident in the complex desmid spicules (Maldonado et al., 1999) (which 1310
are only produced at high Si concentrations) throughout the midshelf Nevada record, whereas 1311
desma were rare globally during the Triassic (Pisera, 2006). The relatively shallow setting of 1312
these sponges is a crucial observation. Today’s major siliceous sponges are only dominant in 1313
deep and Antarctic habitats, because the entire surface ocean is under-saturated in SiO
2
1314
(Maldonado et al., 1999)
.
Widespread proliferation of siliceous sponges in shallow waters would 1315
59
have required significantly higher concentrations of Si in the global oceans
.
Deep export of silica 1316
from surface waters by marine plankton may not have created a concentration gradient as intense 1317
as modern diatom-dominated oceans (Racki and Cordey, 2000), and may have been briefly 1318
interrupted by radiolarian extinctions (Carter and Hori, 2005). Even lacking a direct record of 1319
Mesozoic silica concentrations, we can estimate the Si flux from CAMP and the doubling time of 1320
marine silica concentrations in response across a range of reasonable starting variables (see 1321
Chapter 3). Conservatively, the increased flux would have supplied enough silica annually for 1322
sponges to dominate previously carbonate tropical shelves, and could even have increased global 1323
concentrations by an order of magnitude within a million years (Chapter 3). This would be a 1324
large global supply increase in addition to regional volcanic (Schaltegger et al., 2008; Rosas, 1325
1994) silica sources. 1326
Revealing the profound ecological shifts improves our understanding of the historic crisis 1327
perhaps most relevant to modern climate change (Honisch et al., 2012; Greene et al., 2012b). It is 1328
consistent with, but a substantially more insightful finding than, the general taxonomic 1329
diversification of sponges and gradual appearance of abundant sponges throughout the Jurassic 1330
(Zimmerle, 1991). Dominance of siliceous sponges over previously carbonate habitats is 1331
demonstrated in three distant regions of the globe during the earliest Jurassic, and in the global 1332
ocean Panthalassa (Nevada, Peru) it was not a mere consequence of sea level change. With 1333
modern reefs and carbonate habitats in jeopardy due to anthropogenic climate change, it is a 1334
significant finding that past volatile release resulted not only in global mass extinction, but 1335
profound ecological restructuring lasting millions of years (Honisch et al., 2012; Greene et al., 1336
2012a; Veron, 2011). 1337
1338
60
CHAPTER 5: SILICA CYCLING AND THE TRIASSIC/JURASSIC EXTINCTION 1339
1340
Overview of Silica Sensitivity Analyses 1341
The earliest Jurassic record of intensely-siliceous sponges dominating shallow shelves at 1342
distant locations around the world demonstrates a change in silica cycling from the Late Triassic. 1343
Silica cycle fluxes and concentrations are not well constrained during the Mesozoic. The 1344
sensitivity of global silica cycling to changes in weathering flux is explored to learn more about 1345
this sponge interval. Specifically, calculations estimate if weathering of the Central Atlantic 1346
Magmatic Province could have provided enough silica for sponges to expand across tropical 1347
carbonate shelves in less than one million years. 1348
These analysis shows that CAMP basalts could have weathered rapidly, doubling 1349
Pangea’s silica flux. This would provide enough excess silica to cover 40 to 100% of the earliest 1350
Jurassic shelves in sponges, and could have increased marine concentrations by an order of 1351
magnitude within one million years. 1352
1353
Three simple analyses were executed. 1354
1) Constraints on potential Mesozoic marine silica residence time from overall weathering 1355
intensity and whole ocean concentration 1356
2) Constraints on the doubling time of marine silica concentration from starting 1357
concentrations and basalt weathering intensity 1358
3) Comparison of basalt weathering intensity, potential excess supply, and the silica demand 1359
of siliceous sponges 1360
1361
61
Reasonably estimating Mesozoic marine silica concentration 1362
Phanerozoic silica concentrations are not known directly, but are constrained within two 1363
orders of magnitude. Though common before the Cambrian, shallow a-biogenic silica 1364
sedimentation is not known from Phanerozoic time, when the surface oceans were evidently 1365
under-saturated in amorphous hydrated silica (biogenic opal) (Maliva et al., 1989; Racki and 1366
Cordey, 2000). Modern shallow oceans are under-saturated with respect to opal by two orders of 1367
magnitude (DeMaster, 2002) due to extremely efficient uptake by competitively evolved diatoms 1368
and radiolarians (Racki and Cordey, 2000). 1369
Mesozoic silica concentrations are not well constrained. The flux of marine silica sinks 1370
and sources both change over time. Ignoring silica sources (volcanism, seafloor spreading, 1371
weathering) that change on fairly short geologic timescales, Siever (1991) and Racki and Cordey 1372
(2000) interpret the evolution of increasingly efficient biological uptake to cause a 100 Ma scale 1373
uni-directional decrease in marine silica concentration. They maintain high (50-60 mg/L) 1374
concentrations through the Phanerozoic due to Siever’s conclusion (1991) that this is evidenced 1375
by diagenetic chert nodule formation. This claim deserves further scrutiny, briefly included here. 1376
Siever noted in a meeting presentation abstract (1986) that the silica within chert nodules 1377
is difficult to explain by precipitation of interstitial biosiliceous clasts alone, so an additional 1378
silica source seemed necessary. Later, Siever (1991) concludes that chert nodules formed from 1379
amorphous opal in supersaturated pore waters fed by local remineralized biosiliceous clasts and 1380
by direct diffusion of supersaturated marine bottom waters. “This diffusion from an infinite 1381
reservoir”, he reasoned, “would solve the mass balance problem” (p. 293, (Siever, 1991). There 1382
are three fundamental problems with this, according to the actual microfacies analyses by Maliva 1383
and Siever (1988; 1989). 1384
62
First, their detailed microfacies study of nodule-adjacent carbonates (Maliva and Siever 1385
1989, pg 431) points out that it is not possible to know how many siliceous bioclasts (i.e., sponge 1386
spicules) disappeared from neighboring limestones, preventing a mass balance demonstrating 1387
inadequate interstitial biosilica, and they further concede that the abundance of sponge spicules 1388
could be the regulating factor on nodule formation. 1389
Second, they do not provide sufficient evidence that chert nodules formed regularly or 1390
entirely from opal. Microcrystaline quartz or chalcedony gives no evidence of original opal 1391
precursor ((Maliva and Siever, 1988) p.805). Nodules now with microcrystalline quartz or 1392
chalcedony may have formed from quartz directly, may have also included some opal precursors, 1393
or may have included pervasive opal precursors (Maliva and Siever, 1988). Even nodules with 1394
opal precursors could simultaneously grow quartz cements and replacements (Maliva and Siever, 1395
1988). The only direct evidence of opal precursors are remnant lepispheres (Maliva and Siever, 1396
1988). Quartz does not replace opal with large crystals, so macrocrystaline nodules formed 1397
without an opal precursor. This is not evidence that microcrystalline nodules formed with an 1398
opal precursor. Nevertheless, Maliva and Siever (1988) assert opal precursors for nodules of 1399
mixed crystal size, and later Siever (1991) generalizes that chert nodules formed as opal and 1400
required marine silica. 1401
Finally, pore water diffusion of silica from supersaturated marine bottom waters would 1402
not be involved with nodule formation at 30-1000 meters depth, which Maliva and Seiver (1989) 1403
conclude for two of the three studied sites in Maliva and Siever (1988), and three of the six sites 1404
in Maliva and Siever (1989). 1405
Diagenetic chert formation, then, does not constrain contemporaneous marine silica 1406
concentrations. The parsimonious interpretation of evidence presented in Maliva and Siever 1407
63
(1988, 1989) is that Cambrian – Cretaceous shelf chert nodules likely formed as silica from 1408
interstitial bioclasts dissolved in pore water and precipitated as either opal or quartz without 1409
additional silica flux from supersaturated marine bottom waters. For deep sea cherts, Moore 1410
(2008) provides compelling evidence from ODP core measurements that cherts form as warm 1411
hydrothermal fluids mobilize dissolved biogenic silica in deep sediments. 1412
Without a minimum concentration required by nodule formation, further examination of 1413
the interpretation of silica concentrations stable on the 100 Ma scale are offered. Here steady 1414
state residence time was calculated, considering four orders of magnitude in moles of total 1415
marine silica (1017, 1018, 1019, 1020), and two orders of magnitude in weathering flux of silica 1416
from the continent to the oceans. Starting values are shown in Table 5.1, and results are shown in 1417
Figure 5.1. 1418
Figure 5.1 is a contour plot showing the residence times (diagonal contour lines) of 1419
marine silica at different concentrations (y axis), given different intensities of weathering (silica 1420
influx; x axis). This is a one-box model of the ocean at steady state (sources matching sinks). 1421
These geologically short timescales suggest that silica concentrations were subject to rapid 1422
change. 1423
This analysis suggests that silica concentrations could change on the sub-million year 1424
scale throughout the Phanerozoic. Earliest Jurassic concentrations arguably reached 100 µM 1425
even in shallow marine settings, to accommodate desmid expression (Maldonado 1999; see text). 1426
Shallow to deep export was driven primarily by radiolarians (Racki and Cordey, 2000). The 1427
Late Triassic may have had much lower silica concentrations. Desmids are very rare in the 1428
Triassic generally (Pisera, 2006), though are reported (Prinz, 1985) from the latest Triassic 1429
Chambará Formation in Peru (see text). The abundance of siliceous sponges in the northern and 1430
64
southern Panthalassic back arc basins (see text) could be a response to silica sourced from 1431
regional volcanism. First, though, it makes sense to analyze the largest contemporaneous 1432
volcanic province on the planet, to see if it would have affected silica concentrations in all 1433
regions on a reasonable timescale, potentially dwarfing the impacts of smaller regional supplies. 1434
1435
Doubling Time 1436
Weathering of the Central Atlantic Magmatic Province might have boosted marine silica 1437
concentration. But would it do so on a timescale relevant to the sponge expansion? Fresh basalts 1438
weather quickly and can supply 2 to 10x more dissolved silica than other lithologies on a unit 1439
area basis (Taylor, 2000; Meybeck, 1987) (Hartmann et al., 2010). In addition to the greater 1440
susceptibility of basalt to weathering, there is evidence that Hettangian weathering would have 1441
been more intense due to a wetter and warmer climate (e.g., (McElwain et al., 1999; Zajzon et 1442
al., 2012; Michalik et al., 2010). We considered the impact of possible weathering factors by 1443
asserting that the area covered by CAMP (10
7
km
2
, from Nomade et al., 2007) might supply 2 to 1444
20 times as much silica as equal area of averaged modern continental material. Figure 5.2 shows 1445
the results across the spectrum of values bracketing possible Phanerozoic silica concentrations. 1446
If marine silica was this concentrated already during the Late Triassic, and if the Basalt 1447
Weathering Factor were very low, then the silica boost from CAMP would still double marine 1448
silica concentrations on the million-year scale. If Rhaetian silica concentrations were lower, they 1449
could have reached elevated levels very rapidly, by doubling over hundreds of thousands of 1450
years, high enough to support desmid expression in shallow waters during the Hettangian. 1451
Increase from Triassic to Jurassic time is broadly supported by records of both silicified fossil 1452
faunas and bedded cherts (Kidder and Erwin, 2001). These records, normalized for area and 1453
65
time, show that Triassic silica accumulation was among the lowest of Phanerozic values, and the 1454
Jurassic values among the highest (Kidder and Erwin, 2001). 1455
1456
Silica Demand by Sponges 1457
Finally, it is possible to evaluate if the amount of silica from CAMP was relevant to the 1458
sponge demand for silica. This is possible given new data on sponges as a silica sink. These data 1459
are used to estimate how much demand sponges might have if they expanded across the shelves. 1460
On the right y axis, the potential excess silica released by weathering of the fresh CAMP basalt is 1461
bracketed depending on the intensity of weathering relative to background continental material. 1462
Results in Figure 5.3 juxtapose the potential demand for silica by sponges with the supply 1463
of silica from basalt weathering. CAMP basalts could have supplied enough excess silica to 1464
cover the tropical carbonate shelves in siliceous demosponges. Silica (Si) demand by modern 1465
siliceous sponge assemblages is increasingly well known, and ranges from 0.3 to 2.5 moles of Si 1466
m
-2
yr
-1
for demosponges (dots) and hexactinellids (circles), respectively ((Chu et al., 2011; 1467
Maldonado et al., 2011). Hexactinellid (glass sponge) spicules are found in the Hettangian 1468
Alpine spiculites discussed in the text. Demosponges are found in the Hettangian Nevada, Peru, 1469
and Austrian spiculites (Delecat et al., 2011). If sponge meadows covered increasing portions of 1470
tropical carbonate shelf area (bottom axis, from (Walker et al., 2002), the demand of Si would 1471
increase (left axis). The yield of Si from CAMP basalts (right axis), compared to weathering over 1472
a comparable area of typical continental material, would determine the total increase in global 1473
silica flux. Here weathering factors are shaded between 2 and 10 as likely values, though a 1474
weathering up to a factor of 20 was calculated to add consideration of increased Early Jurassic 1475
weathering from elevated CO2, and warmer wetter conditions (Michalik et al., 2010). 1476
66
Weathering of CAMP basalts may have produced enough excess marine silica to cover 1477
40-100% of the tropical carbonate shelves in sponges annually. Based on these analyses, the 1478
silica flux from the weathering of CAMP was a relevant supply that supported the ecological 1479
dominance of siliceous sponges during the Hettangian stage. The silica flux from CAMP should 1480
have increased global marine silica concentrations during the Triassic/Jurassic transition. The 1481
speed of this change is sensitive to original starting silica concentration. If Late Triassic silica 1482
concentration was close to modern values (which prohibit desmid spicule expression in shallow 1483
settings), influx from CAMP could have increased it by an order of magnitude (to values 1484
allowing widespread desmid expression) in less than one Ma. This scenario is consistent with 1485
available data. 1486
67
CHAPTER 6: PELAGIC ECOLOGY: RECENT UPDATES TO THE STUDY OF 1487
AMMONOID PALEOBIOLOGY 1488
1489
Introduction 1490
To non-specialists ammonoids are best known from their wide variety of coiled shells. 1491
Ammonoids apparently diverged from nautiloids approximately 400 million years ago, and are 1492
stem-group representatives of the coleoids, which include modern squid, octopus, and cuttlefish 1493
(Kröger et al., 2011). Typical shells were planispiral with chambers for buoyancy control and a 1494
body chamber for a soft-bodied squid-like animal at the accreting growing end. Extensive 1495
reviews of ammonoid paleobiology have helped target areas of new or revitalized research (Korn 1496
and Klug, 2012; Westermann, 1996). The information presented here is intended as a sampled 1497
update covering some of the growing fields of inquiry into the lives of these widespread fossil 1498
organisms that ruled the seas for hundreds of millions of years. 1499
1500
The Ammonoid Animal 1501
Fairly direct constraint on ammonoid ecology comes from hard and soft parts excellently 1502
preserved in rare body fossils. The soft parts of ammonoids are still known in detail from very 1503
few studies (see Klug et al., 2012) for a review), but include eye capsules, digestive tracts, 1504
putitive oviducts, and feeding anatomy. Synchrotron technology has substantially increased the 1505
level of detail known about the ammonoid buccal mass. Most ammonoids had non-mineralized 1506
jaws similar to modern coleoid beaks, and a set of homodont radular teeth (e.g.,(Tanabe and 1507
Mapes, 1995). By the Cretaceous, the most abundant ammonoids had a mineralized lower jaw 1508
(aptychus) and an array of more complex radular teeth (Kruta et al., 2012; Kruta et al., 2011). 1509
68
This buccal architecture is more similar to rare pelagic coleoids than most other modern 1510
cephalopods (Kruta et al., 2011).The size and shape of both teeth and jaws vary substantially, 1511
and this may prove to co-vary with phylogeny, shell shape, or both (Kruta et al., 2012; Kruta et 1512
al., 2011; Klug et al., 2012). Diet, which is explored further below, is generally limited to small 1513
pelagic animals in the aptychus-bearing Cretaceous groups. As in modern nautiloids, the mantle 1514
secreted the calcium carbonate (aragonite) shell and proteinaceous coating (periostracum), 1515
repaired shell damage at the aperture when possible (e.g., (Kröger, 2002), and apparently 1516
secreted metabolic biproducts under stress (Klug et al., 2007a) Ammonoid buoyancy was 1517
controlled by fluid transport through the siphuncle, a tube that passed through the shell chambers 1518
via a series of “connecting rings”. Soft tissue properties of these have been detailed by Tanabe, 1519
et al., (2000). Connecting rings have also been asserted to show pores (Mutvei and Dunca, 2007) 1520
that would allow rapid buoyancy changes, and may share affinity to the architecture of the 1521
modern cuttlefish internal shell (Doguzhaeva and Mutvei, 2012). The pores have been dismissed 1522
as artifacts of preservation (Kulicki, 2007), on a non-porous siphuncle like that of the modern 1523
chambered nautilus. Efficient fluid removal may also have been aided by membranes lining the 1524
chamber walls, which vary substantially by clade, but are unfortunately thus far rarely preserved 1525
and detected (Landman et al., 2006). 1526
1527
Ammonoid Shell Shape through Time and Space 1528
Ammonoid ecology can also be constrained by linking shell shapes to hydrodynamic 1529
properties, facies associations, or biogeographic patterns (eg., Jacobs et al., 1994; Tsujita and EG 1530
Westermann, 1998; Barskov et al., 2008). Shell shape is a particularly interesting factor in recent 1531
studies of dispersal and endemism (e.g., (Brayard and Escarguel, 2012). Tolerance of changing 1532
69
marine conditions apparently varied substantially among different ammonoid clades and 1533
morphotypes. These interpretations are based on isotopic studies (see more below) and by 1534
tracking the shifts of ammonoid groups within regions that experienced changes in marine 1535
salinity, oxygenation, temperature, and sea level (Fernández-López and Meléndez, 1996; Tsujita 1536
and EG Westermann, 1998). For example, Tsujitsa and Westermann (1998) interpret the 1537
positions of ammonites in the water column from oxygen isotope values (for salinity), suture 1538
structure (for habitat depth) and strength of the shell and jaws, producing an overall 1539
interpretation that regional benthic oxygenation events controlled the spread of straight and 1540
planispiral ammonoids through the northern Western Interior Seaway during the Late 1541
Cretaceous. Some immigrants diversify within seaways and show gradual morphologic and 1542
possibly ecological changes (Yacobucci, 2004; Klug et al., 2005) while some fail to establish 1543
endemic lineages (Fernandez-Lopez and Melendez, 1996). 1544
Mass extinction events offer particularly broad temporal and spatial intervals for 1545
ecological studies. The ecological radiations following the two largest mass extinctions in Earth 1546
history, the Permian/Triassic and Triassic/Jurassic mass extinctions, have gained considerable 1547
attention. Analyses of taxonomic extinction and biodiversification (Brayard et al., 2009; 1548
Barskov et al., 2008) are matched with characterizations of decreasing or increasing 1549
morphological disparity (McGowan, 2004b; Dommergues et al., 1996; Dera et al., 2010) and 1550
detection of biogeographic trends in distribution of both taxa and morphotypes (Brayard et al., 1551
2007; Brayard and Escarguel, 2012; Brosse et al., 2013; Dommergues et al., 2001; Dera et al., 1552
2011; Barskov et al., 2008). Notably, Brayard et al., (2007) detected a latitudinal gradient in the 1553
distribution of recovering ammonoids following the Permian/Triassic extinction; assemblages of 1554
ammonoid genera were more similar on opposing coasts of Pangea than at neighboring sites 1555
70
along the coasts at higher latitude. Through Early Jurassic extinctions associated with locally 1556
varying anoxia, Dera et al., (2011) demonstrate very complex migration patterns between small 1557
basins expanding as the Atlantic ocean opened. 1558
Methods to detect changes in shell shape through space and time include direct 1559
comparison of shell shape parameters (Whiteside and Ward, 2011; Raup, 1967; Smith,1986; 1560
Yacobucci, 2004; Barskov et a., 2008), more commonly the combination of many parameters in 1561
ordinated spaces (Brosse et al., 2013; Klug et al., 2005; Korn and Klug, 2012), and recently the 1562
use of ternary diagrams comparing three features judged to indicate different hydrodynamic 1563
properties (Monnet et al., 2011; Ritterbush and Bottjer, 2012). Ordinations are excellent for 1564
detecting shape change within a specific collection of shells (Klug et al., 2005) or the extent of 1565
variation within a collection (Brosse et al., 2013), but direct comparison of results from these 1566
studies is not possible without combining all of the data and generating new customized shape 1567
spaces. Ternary diagrams allow direct comparison because the results are shown in a fixed 1568
frame, which is like peering down the corner of a 3-dimensional data cube. Westermann 1569
Morphospace is a ternary diagram that projects planispiral ammonoid shells as gradations 1570
between three end-member morphologies which have been shown to feature different 1571
hydrodynamic properties (Ritterbush and Bottjer, 2012; Westermann, 1996). Assignment of life 1572
modes based on basic outer shell shape alone may prove inadequate for certain intervals and 1573
clades. Profound intra-taxon shape variation is sometimes associated with gradual directional 1574
evolution (Yacobucci, 2006; Korn et al., 2005; Monnet et al., 2010), but in some cases occurs in 1575
a single time interval and may imply a lack of selection on shell shape (Dagys and Weitschat, 1576
1993). Body chamber length and ornamentation are two features not directly addressed in the 1577
ternary diagram, though they can co-vary with shell shape (e.g., Westermann 1996). Recent 1578
71
ordination studies produce distributions very similar to Westermann Morphospace (Korn and 1579
Klug: 2012, Fig. 10; Dera et al., 2010: Fig.7; Brosse et al., 2013: Fig. 5), from which it appears 1580
that ammonoid shells of the Paleozoic varied more in overall inflation than those of the 1581
Mesozoic. In figures 1-3, results from four recent ammonoid ecological studies are compared 1582
using Westermann Morphospace. 1583
72
CHAPTER 7: WESTERMANN MORPHOSPACE DISPLAYS AMMONOID SHELL 1584
SHAPE AND HYPOTHETICAL PALEOECOLOGY 1585
1586
Introduction 1587
The Westermann Morphospace method displays fundamental morphotypes and 1588
hypothesized life modes of measured ammonoid fossils in a ternary diagram. It quantitatively 1589
describes shell shape, without assumption of theoretical coiling laws, in a single, easy-to-read 1590
diagram. This allows direct comparison between data sets presented in Westermann 1591
Morphospace, making it an ideal tool to communicate morphology. By linking measured shells 1592
to hypothesized life modes, the diagram estimates ecospace occupation of the water column. 1593
Application of this new method is demonstrated with Mesozoic data sets from monographs. 1594
Temporal variation, intraspecies variation, and ontogenetic variation are considered. This method 1595
can address hypothetical ecospace occupation in collections with tight stratigraphic, lithologic, 1596
and abundance control, even when taxonomy is in dispute. 1597
Westermann Morphospace is a new method to compare shell shapes included in ammonoid 1598
fossil collections. Ammonoids are extinct fossil cephalopods with external shells that may or may 1599
not have facilitated swimming. The new method displays empirical data in a ternary frame fixed 1600
around recognized morphotypes. Hypothetical mobility constraints determined for morphotypes can 1601
then be extended to quantitatively similar specimens. Like other paleoecological tools, this sorts 1602
fossil animals into hypothetical guilds. It is a quantitative space in which to further test and refine 1603
ecological interpretations. The first half of this paper details calibration of the method, then the 1604
second half of this paper demonstrates example applications of the method. 1605
73
Westermann Morphospace quantifies visible external shell shape, without regard to 1606
theoretical growth. A specimen may have arrived at a given shape via a variety of developmental 1607
paths. Development can be addressed through theoretical growth models (Raup, 1967; Urdy et al., 1608
2010a; Urdy et al., 2010b), and ontogenetic trajectory analyses (e.g., 1609
(Smith, 1986; Gerber et al., 2008; Gerber et al., 2007; Monnet and Bucher, 2005). 1610
Ammonoid morphometric studies support investigation of growth through theoretical 1611
modeling and comparison of shell shapes included in ammonoid fossil collections. Raup presented a 1612
thorough theoretical framework of shell coiling geometry (Raup, 1966) and a practical method to 1613
express ammonoid shell shape (Raup, 1967). Ever since, much of the ammonoid morphometric 1614
literature has included this theory (recently in (Korn and Klug, 2007; Saunders et al., 2008; Dera et 1615
al., 2010) and method (McGowan, 2004a; Gerber, 2011). Also since the 1960s, understanding of 1616
ammonoid paleobiology has broadened immensely (see extensive reviews in Landman et al., 1996) 1617
Landman et al. 1996 and recent advances in (Landman et al., 2007). Drawing on advances in 1618
paleontology and biology, Urdy et al. (2010a,b) addressed developmental complexity in a thorough 1619
new theoretical approach to shell coiling geometry. In light of all these changes, our paper presents 1620
a new method to express shell shapes included in ammonoid fossil collections that is independent of 1621
theoretical growth models. 1622
Three variables account for much variation within planispiral ammonoid shells. Exposure of 1623
the umbilicus, degree of inflation, and expansion of the whorl fundamentally define the overall shape 1624
of the shell (Raup and Michelson, 1965). A simple way to express shell shapes included in a 1625
collection is to display these three variables in a single plot. Below is a brief review of studies that 1626
establish the description of ammonoid shape through these three variables, but for a more extensive 1627
review of advances in theoretical morphology of coiled shells, see Urdy et al. (2010a). Next is a 1628
74
description of the construction of the morphospace, presentation of example applications of the 1629
method, with some interpretations of results, and discussion the usefulness of and potential 1630
improvements to Westermann Morphospace. 1631
1632
Previous Research 1633
Theoretical geometry of shell formation (Raup 1966) led to mathematical characterization of 1634
planispiral ammonoid shell shapes based on the logarithmic spiral (Raup 1967), and a method with 1635
broadly applicable measurements and a new morphospace. One plot compares whorl expansion with 1636
umbilical exposure (W × D space), and often an accompanying plot compares umbilical exposure 1637
with aperture shape (D × S space) (Raup 1967). W × D space displays data at theoretical values for 1638
whorl expansion, derived with a formula that assumes logarithmic expansion (Raup 1967: Fig. 1). 1639
More complex theoretical models have shown that the logarithmic model does not accurately 1640
describe fossil ammonoid shells (e.g., (Burnaby, 1966; Okamoto, 1996; Urdy et al., 2010a; Urdy et 1641
al., 2010b), but have not presented an equally applicable method for describing shell shapes included 1642
in a large collection. Because accreted shell obscures previous geometry in many ammonoids, 1643
methods that more accurately address change in shape with growth require several specimens per 1644
species or specimens cut to reveal multiple stages of shell growth (Burnaby, 1966; Gerber et al., 1645
2011). Some alternative displays that explore change in geometry through ontogeny (e.g., Smith 1646
1986) retain a logarithmic formula for whorl expansion. The logarithmic assumption is in continual 1647
use because logarithmic equations are embedded in the growing variety of methods used to assess 1648
shape within large shell collections. 1649
Ammonoid shells vary in more than basic shape, and statistical evaluation of many shell 1650
characters is often handled with principal components analysis (PCA). Additional conch 1651
75
measurements address keels, flares, complex aperture cross-sections, body chamber lappets, 1652
ornamentation, and sutures (recently Korn and Klug 2007; Saunders et al. 2008). PCA allows 1653
measurement of the variation within a collection of shells, and comparison of trends within the 1654
sample (see innovative application by Dera et al. 2010). Because every PCA is unique (see 1655
discussion in McGowan 2004), one cannot visually compare plots formed by different data sets. The 1656
weighting of characters in each principal component, and the overall appearance and orientation of 1657
data within the morphospace, will be different for each PCA. Saunders et al. (2008: p. 135) used 1658
PCA to compare 21 characters on ~95% of all named Paleozoic genera, spanning three mass 1659
extinctions, and found that “The importance of shell geometry in determining whole shell 1660
morphology is further emphasized by the results of the current analysis; the coiling parameters are 1661
the main contributors to variance loaded on the first principal axis, and thus determine much of the 1662
morphospace structure.” 1663
Empirically, these parameters—exposure of the umbilicus, inflation, and whorl expansion— 1664
account for many of the differences between ammonoid shell shapes. As presented later, 1665
Westermann Morphospace uses these three variables to characterize shell shapes. 1666
Interest in ammonoid shape occupation spurred investigations into the functional 1667
consequences of shell shape. Raup (1967) demonstrated that only part of the theoretical shape space 1668
was occupied by normal ammonoids. Hydrodynamic experiments and buoyancy analysis suggested 1669
mobility constraints associated with certain shapes (e.g., (Saunders and Shapiro, 1986; Hewitt, 1996; 1670
Jacobs, 1996). Empirical studies of ammonoid distribution among depositional environments and 1671
through sea level cycles supported interpretations of shell function (e.g., (Batt, 1989; Courville, 1672
1992). In the review “Ammonoid Life and Habit,” Westermann (1996) summarized his conclusions 1673
on ammonoid mobility in two diagrams, one for planispirals (Fig. 7.1A), and a separate diagram for 1674
76
heteromorphs. The diagram for planispirals organizes ammonoid shell shapes as variations between 1675
three end-member morphotypes and indicates broad, overlapping ecological niches, which he argued 1676
were strongly supported by the above sorts of empirical and circumstantial evidence (Westermann 1677
1996: p. 613-677). 1678
The distribution of shapes in Westermann’s diagram can be generated quantitatively, because 1679
each end-member morphotype maximizes one major variable of ammonoid shell shape, while 1680
minimizing the other two. The resulting graph is a ternary diagram, in which measured specimens 1681
are arranged according to their overall shape. This will link measured specimens to extensively 1682
studied morphotypes and to hypothesized life modes. For this reason, the new quantitative method 1683
is called the Westermann Morphospace. It is not a theoretical morphospace, but rather a quantitative 1684
space in which to form and scrutinize hypotheses that link shell shapes to life modes. This paper 1685
will deal exclusively with planispiral ammonoids. 1686
1687
Three End-Member Morphotypes 1688
In Westermann’s diagram (Fig. 7.1A), shell shapes grade between three extreme, end- 1689
member morphotypes: serpenticones, sphaerocones, and oxycones. A discussion is presented of 1690
evidence that links of shell shapes of each morphotype to a particular life mode, but for a more 1691
extensive consideration, see Westermann (1996). 1692
Serpenticonic shells are evolute, with much of the umbilicus exposed. This has been shown 1693
to generate excessive drag against propulsion (Jacobs, 1992). The shell form is overall fairly 1694
compressed, even if the aperture itself is not compressed. The venter does not produce as much 1695
drag, and at larger sizes, less energy would be required for propulsion because turbulent flow would 1696
de-emphasize friction drag along the umbilicus (Jacobs 1992). Strong propulsion has not been 1697
77
demonstrated to be possible in serpenticones; many serpenticones featured long body chambers, 1698
which are linked to very low shell stability (Saunders and Shapiro 1986). In Westermann’s 1699
illustration (Fig. 7.1A), note that height of the body chamber barely expanded during accretion of the 1700
last half whorl. Westermann (1996) interprets ammonoids with serpenticonic shells to be incapable 1701
of directed swimming, and thus classifies them as plankton. 1702
Sphaerocone shells are overall inflated, and may be wider than the planispiral diameter. 1703
Sphaerocones have most or all of the umbilicus covered. Locomotion would be optimized at low 1704
speeds (Jacobs 1992). At very small sizes, such as hatching size, viscosity ensures laminar flow, and 1705
a lower friction drag makes the sphaerocone more efficient than compressed forms (Jacobs 1992). 1706
Note that in Westermann’s illustration (Fig. 7.1 A), as with serpenticones the height of the body 1707
chamber barely expands during accretion of the last half whorl. Like serpenticones, sphaerocones 1708
often featured long body chambers, which would impart low stability (Saunders and Shapiro 1986). 1709
Westermann (1996) interprets sphaerocones as vertical migrants. Increased volume-to-surface area 1710
might aid vertical migration, for which buoyancy control by fluid exchange is a continually debated 1711
hypothesis (e.g., Kulicki et al. 2007; Mutvei and Dunca 2007). 1712
In oxycones, the umbilicus is not exposed, and the overall shell form is compressed. In 1713
Westermann’s illustration (Fig. 7.1 A), the whorl height shows pronounced expansion during 1714
accretion of the recent 180° of shell whorl. Oxycones would have offered higher stability and 1715
maneuverability than other forms, and generally a short body chamber (Westermann 1996). The 1716
aperture shape is compressed with flanks that cover the umbilical region. In oxycones, turbulent 1717
flow decreases friction drag with increasing size and speed; in addition to reduced energetic cost for 1718
swimming, the oxycones could hypothetically allow faster acceleration than other shell shapes 1719
78
(Jacobs 1992). The form of the oxycone is interpreted as having allowed efficient swimming 1720
(Westermann 1996). 1721
These mobility restrictions remain interpretations. Until soft body parts are better 1722
understood, evidence concerning the shell is the best indication of how each animal may have 1723
moved. In the Discussion we suggest approaches for gaining more information that can be 1724
incorporated into the space. Each of the above morphotypes maximizes one aspect of shell shape 1725
while minimizing the other two. Note that the intermediate morphotypes in Westermann’s 1726
illustration (Fig. 1A) grade between these end-members by increasing one of the traits. 1727
Planorbicones resemble serpenticones, but with an increased overall inflation of shape. Discocones 1728
resemble sphaerocones, but with an increased expansion visible in the final whorl. Platycones 1729
resemble oxycones, but more of the umbilicus is exposed. 1730
1731
Methods 1732
The goal of the new morphospace is to quantify Westermann’s (1996) arrangement by 1733
displaying serpenticones, sphaerocones, and oxycones at opposing positions of a ternary 1734
diagram. Specimens can be sorted into morphotypes by the way each shape parameter is 1735
expressed in the overall outer visible fossil shell. 1736
Quantification of Parameters 1737
The first step is to quantify each parameter. Each parameter is assessed in a way that can 1738
be measured on the outer shell, without regard to what shell shapes may have been present in 1739
earlier development. For this method to describe shape, independent of specimen size, 1740
dimensionless ratios must be calculated from raw measurements. Below, calculations to assess 1741
each parameter are compared to determine which measurements are necessary. It is important to 1742
79
select measurements that are practical for a wide variety of fossil specimens, to allow broad 1743
application of the method. 1744
An exploratory data set (see Ritterbush and Bottjer, 2012 Supplement) of measurements from 1745
55 Triassic and Jurassic specimens was compiled for comparison of calculations. The specific 1746
monographs that are sources of these specimens 1747
(Poulton, 1991; Westermann, 1992; Tozer, 1994; Geux, 1995; Jenks et al., 2007) were of interest to 1748
the authors, and are not suggested to represent all ammonoids. The purpose of the exploratory data 1749
set is to find sources of deviation in calculated values, not to assess the limits of ammonoid shape 1750
variation. Triassic and Jurassic ammonoids were selected from five monographs (Poulton 1991; 1751
Westermann 1992; Tozer 1994; Guex 1995; Jenks et al. 2007) with the following restrictions. Only 1752
planispiral, non-heteromorph ammonoids were selected. Selected ammonoids include a range of 1753
morphotypes, including serpenticones, sphaerocones, and oxycones. Specimens were chosen in 1754
which the heights of both the final whorl and previous whorl are measureable (see measurements 1755
marked in Fig. 7.2A). Such specimens are unusual because body chambers are often broken, 1756
obscuring the height of the previous whorl. Measurements (Fig. 7.2) were taken from each specimen 1757
to allow comparison between calculations, including those presented by Raup (1967) and Smith 1758
(1986). 1759
Umbilicus. The exposure of the umbilicus is commonly represented as a fraction of the 1760
radius or diameter of the whole shell. In the logarithmic model (Raup 1966) (measurements shown 1761
in Fig. 2B) the relative distance of the generating curve from the coiling axis accounts for exposure 1762
of the umbilicus. The calculation simply describes the ratio of umbilical radius to shell radius. 1763
=
!!!
!
(1) 1764
1765
80
To examine change in shape through ontogeny, Smith (1986) (measurements shown in Fig. 7.2C) 1766
used the umbilical ratio calculation, which quantifies the exposure of the umbilicus across the 1767
diameter: 1768
=
!"
!
(2) 1769
These calculations were compared in the exploratory data set (n = 55). If the value for D does not 1770
change, then either radius will yield an identical value. 1771
=
!!!
!
!
(3) 1772
For the specimens in the exploratory data set (n = 55), each of the three equations listed above was 1773
used to calculate exposure of the umbilicus. Yields were compared in paired Wilcoxon Rank Sum 1774
tests in R (R). The three calculations yielded significantly different values. Equation (3) yielded 1775
significantly smaller values than equation (2), which yielded significantly smaller values than 1776
equation (1) (p < 1 × 10
-7
). Equation (2) is the best calculation to represent the exposure of the 1777
umbilicus on a shell for two reasons. First, characterization of umbilical presence along the diameter 1778
describes the effect of exposure of the umbilicus to the whole shell. Because the parameter in 1779
consideration is overall exposure of the umbilicus, rather than distance from the coiling axis (which 1780
implies measurement over the radius), the variable used in this paper is U. Second, the umbilical 1781
diameter is more often accurately measureable, because on some specimens the coiling axis is 1782
obscured, as pointed out by Korn (2000). Nonetheless, the center of the shell should still be 1783
measured whenever possible, to allow further investigation of trends in the data. 1784
Shell Inflation. Shell inflation has been quantified through ratios of the aperture shape (Raup 1785
and Michelson 1965), 1786
=
!
!
(4) 1787
or of the entire shell, called the thickness ratio (e.g., Jacobs and Chamberlain 1996): 1788
81
ℎ =
!
!"#$%&%'
(5) 1789
Sphaerocones yield a relatively large value for each of these calculations. Serpenticones and 1790
oxycones each yield low thickness ratios (eq. 5), but they yield very different aperture shape ratios 1791
(eq. 4). Oxycones yield an aperture shape ratio much smaller than serpenticones, because the 1792
measurement of a includes the involute whorl flank. Thickness ratio (eq. 5) is appropriate for the 1793
new method because it expresses the overall shape of the shell, and is optimized in sphaerocones 1794
while minimized in both opposing forms. Different aperture shapes (compressed, rounded, 1795
depressed) will be represented throughout Westermann Morphospace, as they are present in various 1796
morphotypes (see cross-section drawings in Fig. 7.1A). Aperture shell shape can be very complex, 1797
and is not necessarily characterized by a single variable. 1798
Expansion Rate. Expansion rate of the most recent whorl can be calculated directly, thanks 1799
to the unusual quality of specimens selected for the exploratory data set (see measurements in Fig. 1800
7.2A). 1801
Actual Whorl Expansion =
!
!
!!
(6) 1802
Insofar as a logarithmic spiral approximates the growth of an ammonoid shell, the whorl expansion 1803
calculation (Raup 1967), 1804
=
!
!
!
, (7) 1805
should express whorl expansion rate. If the logarithmic spiral describes the mode of growth at any 1806
life stage (Raup 1967), then measurements of the final half whorl should still yield the actual whorl 1807
expansion rate: 1808
=
!
!
!
!
(8) 1809
82
Theoretical expansion values (yields of eqs. 7 and 8) and actual whorl expansion rate (eq. 6) 1810
were compared by using paired Wilcoxon rank sum tests 1811
(Glover and Mitchell, 2002; R). In both cases, the logarithmic equation yielded a value significantly 1812
different from observed actual whorl expansion. The theoretical whorl expansion value (eq.7) 1813
significantly overestimates both the actual whorl expansion (eq. 6; p = 7 × 10
-4
) and the whorl 1814
expansion estimated by measurements of the final whorl (eq. 8; p = 3 × 10
-4
). Theoretical expansion 1815
based on measurements of the recent whorl (eq. 8) underestimates the measured actual whorl 1816
expansion rate (eq. 6; p = 0.03), but may be considered a closer approximation than the value 1817
derived from the radius measurements (eq. 7). It is not necessary for the present method to assert a 1818
value for expansion applicable to portions of the shell that are covered. Only outer visible shell 1819
shape needs to be represented. For the new method, whorl expansion is represented by the ratio of 1820
measurements of the most recent whorl, 1821
=
!
!
!
(9) 1822
and a lowercase w is used to denote this difference. The recent whorl measurements can be made 1823
with the most accuracy, because, as discussed above, the center of the coiling axis can be obscured. 1824
As described above and illustrated by Westermann (Fig. 7.1A), expansion of the recent whorl of the 1825
shell is maximized in oxycones and minimized in opposing forms. 1826
Recommended Shell Measurements.—Measurement of shell diameter, height of the most 1827
recent whorl (a and aʹ′) and overall shell width (b) are required to place data in Westermann 1828
Morphospace. Additionally, it would be a practical choice to also measure the large radius (d) 1829
(insofar as it is visible) when compiling an ammonoid measurement data set. This is recommended 1830
because then the data could be organized to fit into various theoretical and analytical spaces (e.g., 1831
Raup 1967; Smith 1986; Monnet and Bucher 2005; Gerber et al. 2007). 1832
83
Table 7.1. In Westermann Morphospace, outer shell shape is characterized by three parameters. 1833
Each parameter is maximized in one of the end-member morphotypes, and minimized in the 1834
opposing two. 1835
1836
Scaling the Parameters 1837
Each parameter describes a portion of total shell shape characterization. By normalizing 1838
these portions into percentages, data can be fixed in a ternary diagram. First, the parameters each 1839
need to be scaled, because they have naturally different ranges. The following section describes the 1840
calibration of reasonable scaling values. Umbilical exposure (U) is always less than one, and whorl 1841
expansion (w) is generally greater than one; without scaling, all normalized data would crowd into 1842
the w corner of the ternary diagram because w accounts for an unnecessarily large portion of the total 1843
shell shape characterization. A simple approach is to scale all parameter values so that they fall on a 1844
spectrum between zero and one, making them directly comparable: 1845
!
=
!!!"#
!"#!!"#
(10) 1846
This equation will scale all values in a data set on a spectrum from zero to one, if the actual 1847
minimum and maximum values of that data set are used. To prepare data for Westermann 1848
Morphospace, however, a researcher should not use the actual minimum and maximum values of a 1849
particular ammonoid data set, because this would prevent comparisons with ammonoid data from 1850
other data sets. To enable all data collections displayed in Westermann Morphospace to be directly 1851
comparable, a set of minimum and maximum values were sought that could represent common 1852
ammonoids. Two data sets were used to determine the scaling values: (1) a cluster of specimens 1853
from the Treatise 1854
84
(Arkell et al., 1957; Selden, 2009) that represents each end-member morphotype (serpenticone, 1855
sphaerocone, oxycone), and (2) Raup’s data set (1967), which represents shapes of common 1856
ammonoids. 1857
To obtain the cluster from the Treatise, first, measured genera listed as examples in 1858
morphotype definitions were measured (Arkell et al. 1957; Westermann 1996). Next, all specimens 1859
were measured that corresponded to taxonomic descriptions that included mention of the 1860
morphotype term, and were consistent with the Treatise (Arkell et al. 1957) definition. This resulted 1861
in a cluster of specimens representative of each morphotype. Because only six sphaerocones could 1862
be found in the original Treatise (Arkell et al. 1957), Volume L4, Revised, Vol. 2 of the Treatise 1863
(Selden 2009) was also included, using the term “globular” to search for sphaerocones. Specimens 1864
measured frrom these two sources included 12 serpenticones, 16 sphaerocones, and 17 oxycones to 1865
measure (see Ritterbush and Bottjer, 2012 Supplement). 1866
To assess the shape of common ammonoids, Raup’s data from 1967 was approximated. 1867
Raup (1967) demonstrated that normal ammonoids do not tend to occupy all of his theoretical 1868
morphospace. Westermann Morphospace, by contrast, is an arrangement of common shapes formed 1869
by ammonoids. Raup (1967) measured Treatise (Arkell et al. et al. 1957) specimens from 405 1870
genera, and used this data set to represent the portion of theoretical space that is occupied. From a 1871
digital list of D, W, and S values (M. Foote and D. Raup personal communication 2010), the relative 1872
value of each shell measurement (shown in Fig. 7.2B) was solved by setting e equal to one. Because 1873
aʹ′ was not measured by Raup, umbilical exposure is still represented along the radius (eq. 1), and 1874
whorl expansion is represented with radii (eq. 11) in this data set. 1875
w
radius
=
!
!
(11) 1876
Thickness ratio (eq. 5) was calculated with relative values of b and diameter. 1877
85
In Figure 7.3A, unscaled parameter data from the Treatise (Arkell et al. et al. 1957) 1878
morphotype clusters are shown in a ternary diagram. The effect of using unscaled data is visible in 1879
the crowding of points into the w corner of the diagram, which occurs because the large calculated 1880
values represent an unnecessarily large portion of the shape characterization. For the quantitative 1881
display to approximate Westermann’s diagram, parameter scaling should make the mean data point 1882
of each morphotype cluster fall in a separate corner of ternary space. Then the center of the 1883
morphospace is open to fit specimens that grade between the three end-member morphotypes, just as 1884
Westermann’s original diagram does. Empirical physical evidence suggests that a serpenticone shell 1885
would not facilitate strong swimming, whereas an oxycone shell would (Jacobs 1992). If 1886
experimentation continues and new data are gathered, the range of shapes that do and do not support 1887
strong directed swimming would arguably be something between a serpenticone and an oxycone. 1888
Therefore it is practical for this area of the figure to have some resolution. To balance the display of 1889
morphotypes within Westermann Morphospace, we sought scaling values that would place the mean 1890
of each morphotype at 60% of its corner. After such scaling, umbilical exposure, thickness ratio, 1891
and whorl expansion should each account for about 60% of the shape characterization of an average 1892
serpenticone, sphaerocone, and oxycone, respectively. 1893
To determine appropriate scaling values, first each morphotype was represented by the mean 1894
of parameter values from the cluster of specimens identified by the Treatise (Arkell et al. et al. 1957; 1895
Selden 2009) (shown in bold in Fig. 7.3). Next, each mean parameter value was scaled by equation 1896
(10), wherein the minimum and maximum values relate to Raup’s data set. These values are shown 1897
in Table 7.2. The maximum value for equation (10) was given by the mean of each parameter found 1898
in Raup’s data set, and the minimum value by the mean less two standard deviations. This scaling 1899
results in placement of the morphotype means close to 60% of the appropriate corner of Westermann 1900
86
Morphospace, but not perfectly. When the values from Raup’s data set are used, there is about 21% 1901
total residual between the target of 60% and the actual placement of each morphotype mean. 1902
Similarly, if we apply minimum and maximum values derived from data from the Treatise cluster, 1903
the total residual is about 25%. 1904
1905
Next, a simple computer program permuted the initial scaling values, within practical 1906
limitations, until new scaling was found that would reduce the residual to ~1%. The Microsoft Excel 1907
program Solver was used in a spreadsheet of the data, which is provided in (see Ritterbush and 1908
Bottjer, 2012 Supplement). The minimum values were not permitted to shift below the low values 1909
found for the morphotype clusters (found by examining the opposing shapes; mean less two standard 1910
deviations; shown in row 1 of Table 7.2). This process found scaling values that place each 1911
morphotype mean at 60% in its respective corner of the diagram, as shown in Figure 7.3B (values 1912
shown in the last rows of Table 7.2; for more details see (see Ritterbush and Bottjer, 2012 1913
Supplement). The entire Westermann Morphospace method, from measurements to plotting, is 1914
shown in Figure 7.4. 1915
Two important consequences result from scaling the data depicted in Westermann 1916
Morphospace. First, two exceptional ammonoid shell shapes will plot just outside of Westermann 1917
Morphospace. Data for an ammonoid specimen in which whorl height decreases during accretion of 1918
the last half whorl will plot just above the upper leg of the diagram. Data for an ammonoid shell 1919
with a width less than 14% of its diameter will plot just outside the left leg of the diagram. Inclusion 1920
of all possible planispiral ammonoid shapes within Westermann Morphospace is not necessary for 1921
the diagram to associate empirical data with recognized morphotypes, but the scaling used in 1922
Westermann Morphospace is necessary to deliver resolution of the space between morphotypes. 1923
87
Second, it is important to note that three dimensions of data are being represented in two dimensions 1924
of space. The life mode hypotheses presented by Westermann (1996) are too general to plot 1925
throughout three-dimensional space. By mimicking his arrangement of recognized morphotypes and 1926
including intermediate shapes, Westermann Morphospace offers a framework to extend life mode 1927
hypotheses to quantitatively similar specimens. These concepts will be revisited in the Discussion. 1928
1929
Drafting the Morphospace 1930
Measurement data for each ammonoid shell yield shape parameter values, which are then 1931
scaled and normalized into percentages for the ternary diagram. These steps are shown in Figure 7.4 1932
for both a general and a specific case. Ternary diagrams are traditionally drawn with a flat base and 1933
a corner pointing upward. To visually match the diagram created by Westermann, the morphospace 1934
is presented as a ternary diagram with a flat leg across the top, and the w corner pointing downward. 1935
This is a stylistic choice and has no bearing on mathematics. Ternary diagrams for this publication 1936
were prepared in Trinity, Version 1.5 (Appel 2008), a free program for Macintosh. 1937
Westermann (1996) concluded that certain shell shapes facilitated certain life modes, and 1938
indicated these in the lower left of his diagram (Fig. 7.1A). Those life mode interpretations are 1939
simply drawn over the quantitative morphospace (Fig. 7.1B). Westermann’s small (inset) life mode 1940
diagram was superimposed within the ternary diagram, at 40% the area of the ternary diagram, so 1941
that the qualitative life mode corners reach the 60% mark of each ternary axis. Dashed lines for 1942
hypothetical life modes were traced in Adobe Illustrator. Nekton are active swimmers and plankton 1943
are not. The other two terms in Figure 1 imply occupation within the water column: vertical 1944
migrants move up and down in the water column, and demersal animals spend time near the 1945
seafloor. The hypothetical demersal field, which includes planorbicones, platycones, and shapes in 1946
88
between, is shown as a blue shaded zone. At the three corners of the morphospace, traces of the 1947
Treatise (Arkell et al. et al. 1957) specimens of Dactylioceras, Eurycephalites, and Oxynoticeras are 1948
shown (Fig. 7.1B). These three genera were given as examples of each morphotype by Westermann 1949
(1996). This illustrated data frame is available by e-mail from the first author, or can be re-created 1950
in any ternary space. 1951
The hypothetical life mode fields are added to the diagram, because they are judged to be 1952
matched appropriately to quantifications of the shapes Westermann discussed (1996). This invites 1953
specific scrutiny and continued experimentation. Placement of the dashed lines should shift with 1954
further investigation. For example, if data suggest a line or zone of shape space that separates shells 1955
that facilitate swimming from those that do not, it should be noted on the diagram. 1956
1957
Example Applications 1958
Westermann Morphospace is designed to communicate the basic shape and hypothetical life 1959
modes of shells within a collection. Data are viewed in the context of recognized ammonoid shell 1960
shapes. Small collections of ammonoid shells are shown below in Westermann Morphospace, as 1961
examples of potential applications. Additionally, values calculated from Raup’s (1967) data set are 1962
shown in Westermann Morphospace. Below, data selection, observations, and interpretations are 1963
considered for each application (Figs. 7.5-8). 1964
1965
Middle Triassic (Anisian) Ammonoids. 1966
The Triassic Period began and ended with history’s most severe global mass extinctions, in 1967
terms of invertebrate diversity loss (Alroy, 2010a). Both of these events caused severe genetic 1968
bottlenecks and near-complete extinction of ammonoids (McGowan, 2004a; Dommergues et al., 1969
89
2001). The next example will consider the radiation of ammonoids following the end-Triassic mass 1970
extinction. First, a view of shell shapes typical of Middle Triassic (Anisian stage: ca. 247-241 Mya 1971
(Lehrmann et al., 2006)) ammonoids is presented. A guidebook (Jenks et al. 2007) and related 1972
monograph (Monnet and Bucher 2005) present well-preserved specimens collected in Nevada by 1973
various specialists. The data offer a snapshot of shells present after ammonoids had recovered from 1974
the end-Permian mass extinction, and before effects of the end-Triassic mass extinction. By this 1975
time in the Triassic, ammonoids had regained the full range of Paleozoic morphotypes, but did not 1976
yet include the heteromorphs of the Late Triassic (McGowan, 2004a; Whiteside and Ward, 2011). 1977
The following steps for measurement and calculations for plotting data in Westermann Morphospace 1978
are shown in Figure 7.4. Each specimen was measured for a, aʹ′, b, umbilical diameter, and 1979
diameter. Measurement comparisons quantified the shell shape parameters, which were then scaled, 1980
and finally normalized into percentages that fix data in a ternary diagram. Data corresponding to the 1981
largest specimen of each species (n = 85) are displayed in Westermann Morphospace in Figure 1982
7.5A. 1983
The Middle Triassic collection occupies much of the shape space, and many different 1984
morphotypes are represented. Each life mode interpretation field is also occupied. The highest 1985
concentration in shape space is near the oxycone corner, and in the hypothetically nektonic field. 1986
One specimen (Isculites tozeri) plots above the top leg of the diagram, because the whorl height 1987
decreases during accretion of the final whorl. Hypothetically, ammonoids in eastern Panthalassa 1988
during the Anisian may have taken advantage of the mobility styles facilitated by their shells. 1989
Westermann Morphospace suggests that the ammonoids could swim, drift, and vertically migrate, 1990
and that the whole water column could have been occupied by ammonoids. 1991
1992
90
Early Jurassic (Hettangian) Ammonoids. 1993
After the end-Triassic mass extinction, ammonoids quickly recovered taxonomic diversity during the 1994
Hettangian Stage of the Early Jurassic, which lasted about 2 Myr (ca. 201-199 Ma) (Schaltegger et 1995
al., 2008; Schoene et al., 2010; Bartolini et al., 2012; Guex et al., 2012). Biogeographic patterns 1996
suggest that repeated migrations from Panthalassa established new endemic lineages throughout the 1997
Tethys (Hillebrandt and Krystyn, 2009), but shell shapes were fairly limited (Guex, 2006; 1998
Dommergues et al., 1996; Dommergues et al., 2001). Proposed mechanisms of this limitation will 1999
be discussed below. Guex’s (1995) monograph figures many different specimens of species 2000
occurring within the Gabbs Valley Range of Nevada, which has the most complete ammonite record 2001
of the Hettangian in North America (Guex et al., 2004). After each adequate specimen was 2002
measured, shape parameters were calculated, scaled, and normalized for plotting in a ternary 2003
diagram. Data representing the largest specimen for each of 35 species are framed in Westermann 2004
Morphospace in Figure 7.5B. 2005
The Hettangian collection occupies less shape space overall than the Anisian collection. Of 2006
hypothetical life mode fields, the vertical migrant field is unoccupied and the nektonic field is the 2007
most lightly occupied. The highest concentration in shape space is in the serpenticone corner, and in 2008
the hypothetically planktonic field, where 69% of the data plot. Statistically, the ammonoids in the 2009
Early Jurassic collection have higher values of umbilical exposure than the ammonoids of the 2010
Middle Triassic collection (p < 1 x 10
-4
). This is true when only the largest specimen of each 2011
species (as shown in Fig. 5) represents the collection, and it is true when each total measured 2012
collection (Middle Triassic n = 136 specimens, earliest Jurassic n = 163 specimens) is compared. 2013
This was determined with a Wilcoxon Rank Sum test in R (R Development Core Team 2010). 2014
91
Various explanations have been proposed for the limitations on ammonoid shell shapes 2015
during the Early Jurassic radiation. Guex (2001; Guex, 2006) concluded that serpenticonic shell 2016
shapes exhibited by the new Jurassic lineages are an intrinsic evolutionary response to stress. The 2017
moderately shaped Triassic Phylloceratoidea, in contrast, display enduring morphological 2018
conservatism during the early Jurassic (Ward and Signor, 1983; Page, 1996). Other explanations 2019
cite extrinsic factors implicitly or explicitly related to life modes. Wiedmann (1973) concluded that 2020
the Early Jurassic ammonoids adaptively radiated into new or vacated niches, which implies that 2021
new shapes indicate new life modes. Dommergues et al. (2001) showed distinct associations 2022
between morphotypes and paleogeographic patterns that may relate to environments and dispersion, 2023
but need to be investigated individually. More recently, Whiteside and Ward (2011) and Dera et al. 2024
(2010) explicitly connected potential life modes to patterns of taxa exhibiting particular shapes. 2025
Whiteside and Ward (2011) concluded that Early Jurassic trends in taxonomic richness of 2026
morphotypes reflect ecological instability. “Morphoselective” events in the Early Jurassic suggest 2027
ecological stresses consistent with independently proposed environmental crises (Dera et al., 2010). 2028
Dera et al. (2010) also show rapid (< 2 Myr) taxonomic recovery among ammonoids influenced by 2029
new habitats, following the Early Toarcian biotic collapse. 2030
Distribution in Westermann Morphospace suggests that despite taxonomic diversification, 2031
Hettangian ammonoids did not fill the same ecological roles as Anisian ammonoids. Ammonoids 2032
originating in the earliest Jurassic of Nevada descended either from the morphologically 2033
conservative Triassic clade Phylloceratoidea (6 species; 5 are represented in Fig. 7.5B), or from the 2034
new Jurassic descendants of Psiloceras, which spawned four families (37 species; 30 are represented 2035
in Fig. 5B) (Guex 1995). Only one of the species within Phylloceratoidea plots in the planktonic 2036
field in Westermann Morphospace, whereas 74% of the remaining species do. Guex (2001, 2006) 2037
92
proposed that these serpenticonic shapes originated through stress, and hypothesizes that 2038
morphologically simple Psilocerataceae succeeded in occupying available niche space during a time 2039
of prolonged environmental stress. Whiteside and Ward (2011), citing poor hydrodynamic stability 2040
of serpenticones, suggested that the Hettangian species were planktonic opportunists. 2041
Hypotheses suggested by the quantitative Westermann Morphospace can be examined for 2042
compatibility with independent observations of abundance and occurrence data, paleogeography, 2043
environmental and ecological conditions, and physiology. Display in Westermann Morphospace 2044
suggests that, hypothetically, a planktonic life mode would have suited most (74%) species 2045
descending from the superfamily Psilocerataceae, including all species in the latest arising family, 2046
the Arietinae. A planktonic life mode is consistent with reports that Hettangian ammonites were 2047
most abundant in open ocean habitats (Hillebrandt, 1990) and traversed the global ocean Panthalassa 2048
(Hillebrandt and Krystyn, 2009). Evidence from diverse habitats of benthic invertebrates shows that 2049
extinction rates peaked in the latest Triassic (Kiessling et al. 2007) and selected against nearshore 2050
faunas (Kiessling and Aberhan, 2007a). Distributions of bryozoans suggest prolonged 2051
environmental stress in both offshore and nearshore benthic environments throughout the Early 2052
Jurassic (Powers and Bottjer, 2007). It is possible that planktonic Hettangian ammonites flourished 2053
by operating above inhospitable bottom-water conditions. The relatively low-metabolism life mode 2054
of a drifting cephalopod e.g., (Seibel and Drazen, 2007) might provide resilience in times of stress, 2055
for example, with limited food supply. Success by Hettangian serpenticonic specimens is 2056
demonstrated by substantial sizes (specimens >100 cm (Longridge et al., 2008: p. 246-248). 2057
2058
2059
2060
93
Intraspecies Variation 2061
When shell shapes made by a given species are projected in Westermann Morphospace, the 2062
frame relates them to morphotypes that potentially facilitated certain levels of mobility. Guex’s 1995 2063
monograph figures multiple specimens of some species, revealing intraspecies variation among some 2064
Hettangian ammonites. Only the largest specimen of each species is shown in Figure 7.5B. In 2065
Figure 7.6A, data are shown for all pictured specimens of Psiloceras polymorphum (n = 25) and 2066
Angulaticeras dumetricai (n = 7), species of the superfamily Psilocerataceae that appear early and 2067
late in the Hettangian, respectively (Guex 1995). We could find no direct pattern or correlation 2068
between shell shape parameters and specimen size in either of these species. An independent 2069
investigation with ordinations suggested that up to 10% of the shape variation in A. dumetricai could 2070
be attributable to changes in shape with size. Ontogenetic variation in shell shape will be discussed 2071
in the following example, and is not considered a major factor in the intraspecies variation reflected 2072
in Figure 7.6A. 2073
Shell shapes of these two species (Fig. 7.6A) occupy much the same shape space as all 35 2074
Hettangian species (Fig. 7.5B). This supports the overall impression that shell shape space was 2075
distinctly limited during Hettangian time among these eastern Panthalassa ammonites. More 2076
specifically, Westermann Morphospace suggests life mode interpretations appropriate for each 2077
species. All of the represented P. polymorphum shells are relatively serpenticonic, and all of the 2078
corresponding data plot within the planktonic life mode field. The broad variety of shell shapes 2079
made by P. polymorphum does not support an interpretation that the shell shape was tightly 2080
controlled by intrinsic patterns or natural selection. Hypothetically, each P. polymorphum shell 2081
would have been adequately suited to a drifting life mode, and that life mode may have been a target 2082
of natural selection. The shapes of A. dumetricai offer a more complex case. Data for one specimen 2083
94
plots near the oxyconic corner, and well within the nektonic life mode field; this shell is associated 2084
with shapes that could facilitate directed swimming. Data for other specimens plot near the 2085
serpenticonic corner, within the planktonic field; these shells are associated with shapes that would 2086
not have facilitated directed swimming. The rest of the data plot on a spectrum between these, in the 2087
shape space for which the demersal life mode is one hypothesis. These patterns suggest that strong 2088
directed swimming was not essential for A. dumetricai. A species that produced different shell 2089
shapes could maintain common buoyancy by varying septal spacing (Hammer and Bucher, 2006). 2090
Even though some specimens formed shells that hypothetically would have facilitated swimming, 2091
the animal inside may have lacked the anatomic and behavioral adaptations to take full advantage of 2092
this shape. If A. dumetricai needed directed swimming to function, such adaptations should have 2093
been in place, but then the survival of serpenticonic-shelled individuals would be difficult to explain. 2094
For the serpenticones, the impediments to swimming are stability and turbidity (Saunders and 2095
Shapiro 1986; Jacobs 1992). If the situation were simpler – if most specimens of a species plotted in 2096
the demersal field, and some in the nektonic field – then it would be fair to hypothesize that some 2097
individuals were just better suited to swimming than others. This case highlights the need to 2098
understand shape factors that would support a demersal life style, and this will be considered again 2099
in the Discussion. 2100
2101
Ontogenetic Variation 2102
In Westermann Morphospace, ontogenetic trajectories can be linked to hypothetical 2103
transitions in life mode. In paleoecological and evolution studies, ontogenetic trajectories should be 2104
considered, because natural selection may act on juvenile shapes as well as adults (Gerber 2011). 2105
We searched for an example of an ammonoid species that changes shell shape through growth 2106
95
stages, and for which abundant background data and geological context was available. Such an 2107
example is Anagaudryceras seymouriense, a cosmopolitan taxon from the latest Cretaceous 2108
(Maastrichtian) (Macellari, 1986) from Seymour Island, Antarctica. From Macellari (1986), three 2109
specimens are available: a juvenile shell, 37 mm; a subadult shell, 79 mm; and an adult shell, 197 2110
mm (traced and resized in Fig. 7.7C). On each shell, we made two measurements. The first 2111
represents the shape of the final shell at its largest size (37, 79, and 197 mm, respectively). The 2112
second measurement represents the shape of the shell before the final half whorl was accreted, at 2113
sizes 31, 55, and 132 mm, respectively. Thus six shell shapes are represented by the data shown in 2114
Westermann Morphospace (Fig. 7.6B). The juvenile shell is serpenticonic, and the adult shell is 2115
closest in shape to a discocone. In Westermann Morphospace, the shells are matched to hypothetical 2116
life modes of planktonic and nektonic, respectively. The intermediate shell shape occupies the field 2117
for which demersal is one of the hypothetical life modes. 2118
Hypothetically, a juvenile shell that supported dispersal in a planktonic life mode was 2119
followed by an adult shell that supported active swimming in a nektonic life mode. These 2120
hypotheses concerning Anagaudryceras seymouriense are consistent with paleobiogeography of the 2121
species, and facies changes in the environment of deposition 2122
(Macellari, 1984; Macellari, 1986). A. seymouriense was a cosmopolitan taxon, appearing in the 2123
Seymour Island depositional system as it recorded deepening facies of the middle shelf (Macellari 2124
1984). This change coincided with increased abundance of cosmopolitan ammonite taxa, more 2125
streamlined forms of endemic ammonite taxa, and abundant deposition of juvenile specimens 2126
(Macellari 1986). While they are more abundant offshore, in deep facies, genera in the 2127
Lytocerataceae superfamily also occur in shallow-water deposits; they were not restricted to deep 2128
water. The planktonic life mode suggested by the shape of the juvenile shell may also apply to 2129
96
juvenile forms of contemporary cosmopolitan taxa. Two other species (A. mikobokense and 2130
Vertebraites kayei) produced juvenile shells of the exact same shape, which can be distinguished 2131
only by suture pattern (Macellari 1984, 1986). Natural selection imposes different pressures on 2132
planktonic juvenile forms than on adult metamorphosed forms (Vance, 1973). As modern coleoid 2133
cephalopods transition to adulthood, physiological consequences of ecology show intense change 2134
(Seibel, 2007). A shell gradually transitioning from a serpenticone to a discocone will necessarily 2135
cross over the morphospace that includes planorbicones and platycones. Life modes hypothesized 2136
for shells of this shape include demersal, but in this example there is no specific evidence to support 2137
a benthic habitat for these subadult specimens. 2138
2139
Raup’s 1967 Data Set 2140
Westermann Morphospace is framed to show differences between common ammonoids, and to sort 2141
ammonoids into morphotypes. Data derived from Raup’s (1967) data set (discussed above), which 2142
represents many different ammonoid shapes through Phanerozoic time, is shown in Westermann 2143
Morphospace in Figure 7.8. Raup (1967) measured specimens from the Treatise (Arkell et al. 1957) 2144
that he judged to exhibit “normal” coiling, and compiled a data set representing 405 different genera. 2145
The data plot throughout Westermann Morphospace. Specimens include each recognized 2146
morphotype and many shapes between morphotypes. Each hypothetical life mode is represented. 2147
Highest concentration is in the field between planorbicones and platycones, in the shape space for 2148
which the demersal life mode is one hypothesis. Morphospace nearest the top leg of the triangle is 2149
the least occupied. This area corresponds to very low whorl expansion values. Because we 2150
calculated whorl expansion with shell radii instead of whorl heights, the very low whorl expansion 2151
values seen in, e.g., Figure 7.5A, are not common in Raup’s data set. Three data points plot outside 2152
97
of the left leg of the diagram. Overall shell thickness of these specimens is less than 14% of shell 2153
height. As discussed in Scaling the Parameters, Raup’s (1967) data set was used to frame 2154
Westermann Morphospace around recognized morphotypes while acknowledging the shapes of 2155
common ammonoids. The central part of Westermann Morphospace retains resolution on shell 2156
shapes that are not distinctly categorized as one morphotype or another. Further investigations of 2157
shells that do and do not support efficient mobility can adjust the placement of life mode hypothesis 2158
fields within this central portion of the diagram. 2159
2160
Discussion 2161
Westermann Morphospace sorts ammonoid shells as morphotypes and suggests hypothetical 2162
life modes. In the future, the life mode interpretation fields can be shifted to reflect new data. 2163
Physical experiments and advanced hydrodynamic modeling (e.g., Hammer and Bucher 2006) can 2164
continue to support or reject hypothesized links between certain shapes and life modes. Advances 2165
with hydrodynamic experiments have lagged in recent years, but by directly juxtaposing 2166
hypothesized mobility with quantified shape space, this tool suggests specific hypotheses to be tested 2167
in the laboratory. For example, Westermann (1996) pointed out the large overlap between the nekton 2168
and demersal fields; he interpreted some ammonoids with platycone to planorbicone shapes as 2169
swimmers, and some as fitting a demersal habitat. It is an important region of shape space to 2170
understand; specimens that the Treatise (Arkell et al. et al. 1957) described as either serpenticones or 2171
oxycones plot in this overlapping space (Fig. 3B), and the highest concentration of shells within 2172
Raup’s data set falls in this space as well (Fig. 8). Study of specimens that show demersal affinities 2173
(e.g., (Moriya et al., 2003); (but see also Cusack et al., 2008) could focus the demersal field more 2174
precisely. In a sense, the demersal life mode is an end-member ecological niche, but it is not yet 2175
98
associated with an end-member shell shape. Display in Westermann Morphospace is determined by 2176
external shell characteristics, but the life mode hypotheses draw on more varied and complex 2177
analyses. 2178
For some faunas, for some environments, and for some size classes, the hypothetical 2179
ecospace may be very different from Westermann’s (1996) interpretations. Tank experiments show 2180
that the size of ammonoid shells makes a significant difference to the hydrodynamics of shell shape 2181
(Jacobs 1992). It should be possible to designate life mode fields that better fit the data for certain 2182
size classes of ammonoids, for example, those <1 cm in diameter. Moreover, major shifts in 2183
ammonoid anatomy through time—for example, with regard to the hyponomic sinus, sutural 2184
complexity, and ornament—might also affect the space. Ammonoid collections with excellent 2185
stratigraphic and facies control are ideal for study within the Westermann Morphospace, because life 2186
mode hypotheses can be rejected or supported with lithologic evidence and paleobiogeographic 2187
perspective 2188
(Macellari, 1986; Batt, 1989; Yacobucci, 2003; Bardhan et al., 2007). Specimens with jaws or gut 2189
contents, which Westermann (1996) considered in his interpretations, can be plotted in the 2190
morphospace as well. Technological advances, such as the detection of a buccal mass in a Baculites 2191
sp. (Kruta et al., 2011; Kruta et al., 2012), may vastly increase what is known of fossil cephalopod 2192
functional anatomy beyond the shell, and even diet. Such finds may support or reject specific life 2193
mode interpretations for specific taxa. Further examination of Late Cretaceous taxa that express 2194
pronounced shifts between morphotypes at different growth stages (e.g., Macellari 1986) would 2195
supply interesting paleobiological context to ontogenetic investigations. When the recommended 2196
measurements are collected, a data set can be shown in Westermann Morphospace and scrutinized 2197
using allometric space (e.g., Gerber 2011). Similarly, hypotheses for ammonoid life modes can be 2198
99
tested in high-resolution data sets spanning extinctions (e.g., (Brayard et al., 2009; Dera et al., 2010) 2199
and radiations (Yacobucci 2004). In this way, the ecological consequences of evolution, and the 2200
impact of ecology on evolution, can be further explored. 2201
Westermann Morphospace is framed to enhance visibility of differences between commonly 2202
occurring ammonoid shells, when they are sorted into morphotypes. Because including every 2203
existing ammonoid would decrease the resolution on the shape space of interest, data for two shell 2204
shapes will not plot within the diagram. If an ammonoid exhibits a whorl that decreases in height 2205
during accretion of the final visible whorl, the data point for that ammonoid will fall just above the 2206
upper leg of the diagram (Fig. 7.5A). Whorl height is a special parameter; it cannot continually 2207
decrease, and sometimes the decrease occurs in sphaerocones at the final life stage (Arkell et al. 2208
1957). If whorl height did decrease, the shell shape plots somewhere on the spectrum between 2209
serpenticone to planorbicone to cadicone to sphaerocone (see Fig. 7.1A). The plotted location of the 2210
data point will communicate both morphotype and hypothetical life mode, even if it sits outside of 2211
the diagram (Fig. 7.5A). Similarly, shells that have a width less than 14% of their height will not fit 2212
within the diagram. These are also rare; this dimension is found in fewer than 1% of Raup’s (1967) 2213
chosen specimens. These shell shapes will be on a spectrum between serpenticone to platycone to 2214
oxycone. 2215
A theoretical morphospace in three dimensions corresponding to the three shell shape 2216
parameters has the advantage of including all specimen data, but Westermann’s (1996) life mode 2217
conclusions were not articulated in such a complex space. Westermann Morphospace is similar to a 2218
projection of three-dimensional space, and is inherently not linear. After projection into 2219
Westermann Morphospace has illuminated areas of further inquiry for an ammonoid collection, 2220
examining the distribution of the same specimens within a three-dimensional space would be 2221
100
interesting. Perhaps eventually mobility limitation fields for shells could be projected into a three- 2222
dimensional space. 2223
Westermann Morphospace can characterize the shapes included in collections, even when the 2224
taxonomy is in doubt due to poor preservation. Field specimens with indistinct morphological 2225
details—aperture shape, body chamber length, suture, coiling center—can still be used in 2226
Westermann Morphospace. Field collections can be displayed in Westermann Morphospace to 2227
reflect the abundance of different shell shapes in a fossil deposit. This will create hypothetical life 2228
mode assignments for the most common shells, and allow exploration of adaptive peaks with 2229
abundance data. Measurement of the long radius (and thereby the center or coiling axis) is not 2230
required to plot a specimen within the Westermann Morphospace, but it is recommended whenever 2231
possible to allow data set versatility. 2232
Taxonomic or abundance data placed in ecospace reveal the hypothetical complexity of 2233
niches represented in a fossil collection. Presentation of data in ecospace has been common, 2234
including the documentation of tiering trends through the Phanerozoic (Ausich and Bottjer, 1982) 2235
and investigations using the ichnofabric index method (Droser and Bottjer, 1986). Tiering and 2236
trophic mode combined reveal ecological guilds (Bambach, 1993). With the additional 2237
consideration of mobility, the guild concept was refined to create 216 components within one large 2238
cube representing ecospace occupation (Bambach et al., 2007). In this ecospace, ammonoids 2239
throughout the Phanerozoic can contribute to perhaps two of the 216 spaces. The ecospace cube 2240
(Bambach et al. 2007) is a tool that assesses benthic ecology but does not maximize the ecological 2241
information presented in the rich fossil history of ammonoids. Cephalopod fossils present a rich data 2242
set for stratigraphy and paleobiology, and they can present a rich data set for paleoecology. 2243
Conclusion 2244
101
Westermann Morphospace is a useful tool in which to display information gathered from 2245
fossil ammonoid shells. It incorporates all three of the major parameters that affect the overall shape 2246
of the outer shell. Plots in Westermann morphospace show at a glance what planispiral ammonoid 2247
shell shapes are included in any collection. Data plot independently; specimens can be added to or 2248
removed from an investigation without changing the position of remaining data points. Any 2249
planispiral ammonoid collections depicted in the diagram are directly comparable, and the 2250
measurements required are common in other methods. For these reasons, the diagram is a useful 2251
accompaniment to other ammonoid morphometric displays, such as principal components analysis. 2252
The life mode fields in Westermann Morphospace are simple hypotheses. Potential mobility 2253
restrictions of certain shell shapes, based on sound data, can be extended to quantitatively similar 2254
specimens by using the diagram. The required measurements allow consideration of various 2255
preservation types, and a wide variety of projects can use Westermann Morphospace. Further 2256
mobility assessment experiments can focus on the regions of the space that are the least understood. 2257
Ammonoid specimens for which life mode hypotheses are supported through a variety of means— 2258
modeling, experiments, geology, paleontology—can be projected into the space to critique 2259
placement of life mode fields. Data from investigations of evolutionary events can be projected into 2260
the morphospace to suggest potential ecological patterns for further inquiry. Ultimately, 2261
Westermann Morphospace can be a tool to reveal the ecological complexity represented by a 2262
collection of fossils from the water column. 2263
2264
2265
2266
102
CHAPTER 8: CONTRASTING ECOLOGICAL AFTERMATH OF THE 2267
PERMIAN/TRIASSIC AND TRIASSIC/JURASSIC MASS EXTINCTIONS 2268
2269
Introduction 2270
A challenge to assessing ecological recovery among ammonoid faunas radiating after the 2271
Triassic/Jurassic mass extinction is finding a basis of comparison. Late Triassic faunas were very 2272
different from Norian or Hettangian ammonoids. For much of the Rhaetian stage, the final ~ 2 2273
Ma of the Triassic, ammonoids were fairly rare in some localities (Laws, 1982) which still 2274
challenges biostratigraphic correlations that much rely on ammonoid-to-conodont-to-ammonoid 2275
interpretations (Orchard et al., 2008) to bridge between European and American strata. 2276
Moreover, the Rhaetian ammonoid faunas include many heteromorphs, such as the slightly 2277
uncoiled Choristoceras and Rhabdoceras and helically spiraled Cochloceras (e.g., Laws, 1982; 2278
Whiteside and Ward, 2011). This is such a contrast to the ubiquitously planispiral, abundant, 2279
large, cosmopolitan ammonoid fauna of the earliest Jurassic, that it is understandable when the 2280
system is declared recovered within two million years on the basis of taxonomic diversity alone. 2281
But the striking homogeneity of form of earliest Jurassic ammonoids is perplexing, and deserves 2282
still further comparison. Perhaps the narrow expression of form was a necessary consequence of 2283
genetic bottleneck, or a common response to mass extinctions, or an ecologically favored form 2284
for the environmental conditions of the earliest Jurassic specifically. The approach presented 2285
here is a comparison of recovery faunas that radiated after Earth history’s two greatest mass 2286
extinction events, the Permian/Triassic and Triassic/Jurassic extinctions. Specifically, a case 2287
study of species from the Canadian arctic is presented in high temporal and taxonomic 2288
resolution, following the work of Tozer (1994), adding a search for differences in the 2289
103
representation of different shell morphotypes across time and space in the Early Triassic. 2290
Particular attention is given to the first three stages of the Triassic, the Griesbachian, Dienerian, 2291
and Smithian, with a total duration of about 2 Ma which is comparable to the Hettangian stage of 2292
the earliest Jurassic. Comparing the speciosity within each morphotype allows statistical tests of 2293
similarities and differences between the two recovery intervals. Some of the differences may be 2294
explained by the very different environmental stresses acting at these times. 2295
Since its discovery as the most severe taxonomic and ecological crisis recorded in life 2296
history, the biological response to the end-Permian mass extinction (252 Mya) event has received 2297
intense scrutiny. Approximately 95% of marine invertebrate species disappeared amid global 2298
environmental change as the Siberian Traps volcanic province erupted in northern Pangea (near 2299
modern-day Siberia) (Saunders and Reichow, 2009; Sobolev et al., 2011). Global warming, 2300
euxinia, and ocean acidification are interpreted to have devastated marine communities around 2301
the world at the extinction boundary (Wignall and Twitchett, 2002; Clapham and Payne, 2011; 2302
Song et al., 2012). Following the initial extinction event, persistent expanded oxygen minimum 2303
zones, intense temperature increases, and sudden incursions of shallow shelf anoxia are 2304
interpreted to have lasted during the ensuing recovery interval which is divided into the four 2305
stages of the Early Triassic epoch (Algeo et al., 2011; Sun et al., 2012; Grasby et al., 2012) 2306
The ecological consequences of the event were severe; coral reefs disappeared ((Knoll et 2307
al., 2007)but see (Brayard et al., 2011); minute and opportunistic fauna dominated level-bottom 2308
communities (Schubert and Bottjer, 1995), see discussion in(Twitchett, 2006); and a new 2309
mollusk-dominated fauna arose (Fraiser and Bottjer, 2007; Alroy et al., 2008) but see (Greene et 2310
al., 2011). The pace of recovery from the extinctions is constantly debated. Global biodiversity 2311
may not have returned to pre-extinction levels for hundreds of millions of years (Alroy 2010). 2312
104
However, recent work has highlighted rapid re-diversification within a one million year interval 2313
for specific clades, sedimentary environments, and paleogeographic regions in contrast with 2314
previous interpretations of gradual improvement over 5 million years (Twitchett et al., 2004; 2315
Kershaw et al., 2007; Beatty et al., 2008; Brayard et al., 2009; Brayard et al., 2011; Payne et al., 2316
2011; Schubert and Bottjer, 1995). 2317
This study focuses on the ecological response to mass extinction in the pelagic 2318
environment of the Boreal Ocean. General ecological recovery from mass extinctions has been 2319
modeled by Sole et al (2002), framing the expectation that diversity should increase in order of 2320
increasing trophic level. The Boreal Ocean is an interesting location to test for this pattern. 2321
Despite its geographic proximity to the source of environmental change, the Boreal Ocean’s 2322
benthic habitats show evidence of both higher diversity and greater ecological complexity 2323
directly following the extinction event than records of lower latitudes (Beatty et al., 2008). In 2324
contrast, pelagic groups (ammonoids and conodonts) expressed repeated diversity crashes and 2325
morphometric patterns interpreted as depressed ecological complexity (Payne et al. 2004; 2326
(Stanley, 2009; Whiteside and Ward, 2011; Sun et al., 2012). We scrutinized the ammonoid 2327
record of the Boreal Ocean through the Early Triassic for support or rejection of the expected 2328
recovery model. 2329
Fossil evidence shows that ammonoids were typically part of a complex pelagic ecology. 2330
Ammonoids were predators at least to small ammonoids, isopods, and other small invertebrates, 2331
and were prey to large vertebrates and powerful shell-damaging invertebrates (Kröger, 2002; 2332
Kruta et al., 2011). Ammonoid shells exhibit complex life histories and associations to habitats 2333
with differing temperatures (Lukeneder et al., 2010), oxygenation (Tsujita and EG Westermann, 2334
1998) and hydrodynamic regimes (Jacobs, 1992; Jacobs et al., 1994; Wilmsen and Mosavinia, 2335
105
2011). Their jaws and soft-parts, including musculature, digestive tracts, and putitive eyes (see 2336
(Klug et al., 2012) for a review) were similar to various modern coleoid cephalopods (the 2337
octopus, squid, and cuttlefish), their closest extant relatives (Kröger et al., 2011). In modern 2338
coleoid cephalopods, metabolic demand corresponds closely to locomotion specialization. 2339
Considering animals of equal size, oxygen consumption and metabolic enzyme synthesis varies 2340
over three orders of magnitude between the fastest (continuously jet-propelling) and the slowest 2341
(fin-swimming) squids (Seibel, 2007; Seibel and Drazen, 2007). First-order constraint on 2342
locomotion in ammonoids may have been limited or improved by hydrodynamic properties of 2343
their wide-ranging shell shapes. Fossil and model analyses support that ammonoids jet propelled 2344
from a secure position within their shells (see muscle attachment scars, e.g., (Klug et al., 2345
2007b)neutrally buoyant shells (Hammer and Bucher, 2006), and laboratory experiments show 2346
that inflated and evolute shells create more drag against forward propulsion, compared to 2347
streamlined forms (see(Jacobs, 1996), for a review). Even small differences in drag should have 2348
been very important limitations on ammonoid mobility because jet propulsion is so inefficient. A 2349
squid must exert twice as much energy to swim half as fast as a fish (O'Dor and Webber, 1991; 2350
Seibel and Drazen, 2007). Analyses also treat stability (Hammer and Bucher 2006), orientation 2351
(Saunders and Shapiro, 1986), ornamentation consequences (Ward, 1980), and potential viable 2352
habitat depth (see a review in(Hewitt, 1996). Though the outer shell shape does not constrain 2353
everything about the animals’ life mode, it should indicate first order controls on locomotory 2354
potential and therefore metabolic demand. 2355
To study ecology of Early Triassic Boreal Ocean ammonoids, we used a new quantitative 2356
method specifically calibrated to distinguish shell shapes linked to different hydrodynamic 2357
properties (Ritterbush and Bottjer 2012). The most broadly-accepted tools to assess ammonoid 2358
106
shell shape are comparisons of bivariate (e.g., Yacobucci 2004; Klug and Korn 2004; Whiteside 2359
and Ward, 2011; (Monnet et al., 2008) or ordinated shape parameters (e.g., (Dommergues et al., 2360
2001; McGowan, 2004b; Yacobucci, 2004; Klug et al., 2005; Saunders et al., 2008; Dera et al., 2361
2010; Korn and Klug, 2012; Brosse et al., 2013). Results of ordinations project unique spaces 2362
that vary with the exact specimens and parameters analyzed. In contrast, Westermann 2363
Morphospace is a new method that projects data into a fixed frame differentiating shape 2364
categories with distinct hydrodynamic properties (Ritterbush and Bottjer 2012). The fixed frame 2365
allows direct visual and statistical comparison between datasets of different ammonoid 2366
collections, which is not possible with typical ordinations. Westermann Morphospace is a ternary 2367
diagram, a projection through an orthogonal space of the three parameters determined to be best 2368
reproducible in measurement and most relevant to hydrodynamic limitations. Pending additional 2369
hydrodynamic experimental results, the projection is currently delineated into four 2370
conservatively broad shape categories (based on Westermann 1996). Because these categories 2371
are mutually exclusive, their unequivocal assignment is an advantage over some studies that 2372
distinguish shape using Raup’s (1967) bivariate plots (see Whiteside and Ward 2011 supplement 2373
figure DR2, points A, B, and E). 2374
Here we use Westermann Morphospace to test for ecological consequences of changes in 2375
ammonoid diversity and Boreal Ocean environment through the Early Triassic Epoch at the 2376
highest resolution available. In a work of remarkable scope and detail, Tozer (1994) described 2377
all Canadian Triassic ammonoid species at high stratigraphic resolution. Recent chronometric 2378
dates resolve many of Tozer’s (1994) fourteen Early Triassic stratigraphic subzones to 2379
approximately the hundred thousand year timescale, allowing high precision correlation to 2380
emerging environmental proxies. We used Westermann Morphospace to categorize the shell 2381
107
shapes produced by Boreal Ocean ammonoid species in each of the fourteen stratigraphic 2382
subzones into morphotypes with distinct hydrodynamic and metabolic implications. This allowed 2383
us to statistically test for morphometric patterns supporting the ecological development model by 2384
where taxonomic diversity should return within increasingly complex trophic tiers. 2385
In addition, we compared the Boreal Ocean data to other regions. Early Triassic 2386
ammonoid biostratigraphy and diversity is currently receiving much scrutiny (e.g., (Ware et al., 2387
2011; Bruhwiler et al., 2008; Brayard et al., 2013; Zakharov and Mousavi Abnavi, 2011). 2388
Globally ammonoids apparently diversified quickly (Brayard et al., 2009; Zakharov and Mousavi 2389
Abnavi, 2011), increased in endemism (Brayard et al., 2006), and occupied cross-Panthalassic 2390
coasts with increasingly latitudinal stratification (Brayard et al., 2007). Comparison of Tozer’s 2391
(1994) Boreal Ocean ammonoids with records from other regions can test for an ecological 2392
consequence to these taxonomic spatial trends. 2393
If application of Westermann Morphospace can support or reject specific hypotheses 2394
about the ecological conditions among Early Triassic ammonoids. the results should then direct 2395
further investigations into thresholds and subtleties between shell shape categories. The Methods 2396
section will next detail how the following hypotheses were tested: 2397
1) If the ecological recovery of ammonoids in the Boreal Ocean followed the model by 2398
Sole et al. (2002) which predicts increasing diversity in order of increased trophic levels, then 2399
shell shapes produced by Boreal Ocean ammonoid species should include increasing numbers of 2400
streamlined oxycones over time. 2401
2) Early Triassic environmental events such as decreased oxygen saturation and high 2402
temperature should show selectivity against some or all shape categories of Boreal Ocean 2403
108
ammonoids in a way that mirrors environmental selection against modern cephalopods with 2404
similar metabolic demands. 2405
3) If the global latitudinal gradient observed in ammonoid taxonomic assemblage 2406
similarity had an ecological consequence, then the relative distribution of shell shape categories 2407
that allowed ammonoid success should have differed by region along the same latitudinal 2408
gradient. 2409
2410
Methods 2411
The Westermann Morphospace method was scrutinized in three ways. First, available 2412
hydrodynamic experimental data on the efficiency of different ammonoid shell shapes were 2413
examined for any significant trends within Westermann Morphospace that might support, or 2414
conversely reject, its interpretive scheme. The cost of locomotion in power (ergs/s/cm
3
) for each 2415
of seven shells, as tested and calculated by Jacobs (1992) was tested for correlation (F statistic 2416
using linear model fit in R; R Core Development Team, 2010) with the scaled and normalized 2417
Westermann Morphospace parameters (umbilical exposure, overall inflation, and whorl 2418
expansion) for those same shells. This tested whether the apparent cost of locomotion 2419
significantly trended with the characteristics that distinguish the shells’ placement within the 2420
diagram, beyond already expected correlation with raw individual shape parameters. 2421
Second, intraspecies variation was examined to determine if multiple individual shells of 2422
each species needed to be included in analysis, as opposed to the more common practice of using 2423
a single type specimen to represent each species. To achieve this, the authors visited Tozer’s 2424
extensive Early Triassic ammonoid collections at the Canadian Geological Survey facility in 2425
Vancouver, British Columbia, where remain his prepared specimens sorted by species and 2426
109
locality. Each species represented by at least three specimens was included in a photographic 2427
analysis (N=190 specimens) to allow shape characterization in Westermann Morphospace 2428
(measurement of diameter, umbilical diameter, aperture height, and width, all in one plane). Of 2429
these, 70 specimens representing five species were chosen for analysis because they had more 2430
than five specimens per species. First, the type specimens (Tozer, 1994) were plotted in 2431
Westermann Morphospace to create a prediction of where the 70 additional specimens should 2432
also plot. Each of the additional Canadian Geological Survey specimens was measured digitally 2433
with ImageJ, plotted in Westermann Morphospace, and the results were tallied and tested against 2434
the expectation with a chi-squared test in R (R Core Development Team, 2010). 2435
Finally, the analysis of Early Triassic Boreal Ocean ammonoids executed in Westermann 2436
Morphospace (described below) was repeated with a principle components analysis (hereafter 2437
PCA), the ordination more commonly used by ammonoid paleobiologists. Statistical analysis 2438
(Wilcoxon Rank Sum test) were applied to determine if the PCA distinguished differences 2439
between ammonoid groups in a way that is consistent with designations made in Westermann 2440
Morphospace. 2441
We investigated pelagic ecology in the Boreal Ocean by comparing changes in shell 2442
shape expression of Early Triassic ammonoid species to changes in their taxonomic diversity and 2443
environment. First, we examined shell shape expression by plotting the data measured for each 2444
type specimen of each ammonoid species (Tozer 1994) in Westermann Morphospace (using the 2445
R functions published in supplement for Ritterbush and Bottjer 2012) and tallying the number of 2446
species within each category for each time bin (manually in Adobe Illustrator). We used chi- 2447
squared to test for significant change in shape expression between stratigraphic stages. Next, we 2448
examined the number of species expressing shells within each shape category at the highest 2449
110
temporal resolution available: Tozer’s fourteen Early Triassic stratigraphic subzones. We used 2450
Spearman Rank Coefficient to test for significant correlations in speciosity between each shape 2451
category and overall regional species diversity. The high temporal resolution allows comparison 2452
to proxies for environmental conditions and interpretation of any apparent selectivity in the 2453
success or elimination of specific shell shape categories during the “boom and bust” diversity 2454
dynamics. Changes in diversity within taxonomic suborders were also tested for significant 2455
change between stratigraphic stages and correlation to diversity within shape categories. 2456
We also compared Boreal Ocean ammonoids to ammonoids of distant regions to test for 2457
ecological consequences of the previously established latitudinal gradient in taxonomic 2458
assemblage similarity. This analysis was isolated from time series investigations by selecting 2459
only the Smithian stage for examination. The Smithian stage was chosen because it had the most 2460
accessible species-level ammonoid collections in each region, and because the latitudinal 2461
gradients in question were amply expressed by that time in the Early Triassic (Brayard et al. 2462
2007). First, we examined if the regions demonstrated significantly different trends in Early 2463
Triassic taxonomic diversity that might discourage their direct comparison. Diversity of 2464
cosmopolitan and endemic species in the Boreal Ocean, Temperate Tethys, and Tropical Tethys 2465
(data from Brayard et al. 2006) were compared to overall global diversity using chi-squared. 2466
Next, we compiled a dataset of measurements from type specimens of Smithian species from 2467
each region following references in Brayard et al. (2006). We plotted measurement data for the 2468
type specimens of each species in Westermann Morphospace and tallied the number of species 2469
within each shape category. We used chi-squared to test if the speciocity of each shape category 2470
differed between regions during the Smithian Stage. This was designed to test for ecological 2471
consequences to the apparent latitudinal stratification of taxonomic assemblages. Lately these 2472
111
faunas are undergoing reevaluation for the whole Early Triassic epoch, so we also examined 2473
whether potential over-splitting of taxa by older references could create trends that would 2474
accentuate or diminish any significance in our findings. 2475
Finally, we compared the Early Triassic data to an earlier investigation of Early Jurassic 2476
ammonoids, to check for a common response by ammonoids to mass extinction events. The end- 2477
Triassic mass extinction 201.3 Mya eliminated all but two ammonoid genera, and the following 2478
Hettangian Stage of the Jurassic lasted about 1.6 million years, about the same duration as the 2479
Griesbachian – Smithian Stages of the Early Triassic (Schoene et al. 2010; Schaltegger et al. 2480
2008). For ammonoids the extinction severity, taxonomic diversification and initial recovery 2481
interval for both global biological crises are similar. Hettangian ammonoids from Nevada 2482
published by Guex (1995) were examined in Westermann Morphospace by Ritterbush and 2483
Bottjer (2012). Here we use chi-squared to test for significant differences between the speciocity 2484
within shape categories during the Hettangian and during the Early Triassic in each of the above- 2485
described analyses. 2486
2487
Results 2488
Vetting the Method 2489
Placement within Westermann Morphospace significantly correlates with Jacobs’ (1992) 2490
experimental and analytical assessments of hydrodynamic efficiency of ammonoid shells (Fig. 2491
8.1; Table 8.1). At low and high Reynolds numbers (small size and low speed vs. large size and 2492
high speed) the power required to propel ammonoid shells of different shapes correlates 2493
significantly with overall inflation. At high Reynolds numbers (large size and fast speed) power 2494
required to overcome drag also correlates significantly with the percent of shape that is 2495
112
accounted for by whorl expansion (Fig. 8.1b). The power values do not correlate with raw whorl 2496
expansion measures alone; it is the calibrated Westermann Morphospace placement that 2497
correlates to shell efficiency (Table 8.1). 2498
Intraspecies variation did not produce Westermann Morphospace distributions 2499
significantly different than those expected from the ammonoid species type specimens alone. 2500
The 22 specimens of Kashmirites warreni were expected to plot as serpenticones, seven 2501
Wasachites macconnelli were expected to plot as oxycones, and the remaining 41 specimens (of 2502
three different species) were expected to plot in the intermediate zone. The results for each 2503
species are shown in Figure 8.2. The final count of 23 serpenticones, 32 intermediate and 15 2504
oxycones shapes was not significantly different (X
2
= 2.38; degrees of freedom =2; p=0.1331; 2505
chi squared test in R) than the original expectation based on the type specimens. 2506
2507
Shell Shape through Time and Space 2508
Repeated “booms and busts” in ammonoid diversity across the Early Triassic did not 2509
result in significant differences in the distribution of expressed shell shapes until the final 2510
Spathian stage of the Early Triassic, which featured significantly more species with oxyconic 2511
shells (X
2
= 5.78; degrees of freedom = 1; p=0.016; Fig. 8.3, Table 8.2). The Spathian 2512
ammonoids are also significantly different when considered in PCA (p=0.016; Fig. 8.4). 2513
Throughout the epoch, species richness within each shape category increases with (and correlates 2514
significantly to) overall Boreal Ocean species diversity (Fig. 8.5, Table 8.2). Figure 8.5 shows 2515
bar graphs of ammonoid species shell shape (Fig. 8.5A) and taxonomic suborder (Fig. 8.5B) in 2516
each subzone of the Early Triassic. Species diversity within each shape category correlates 2517
significantly to the diversity of multiple suborders, though the diversification of Spathian 2518
113
Ceratina represent the only significant change in higher taxonomic makeup throughout the 2519
interval. Finally, species shell shape categorizations are compared to proxies for regional 2520
environmental conditions from recent studies in Figure 8.6. 2521
During the Smithian stage, the shapes of ammonoid shells differed significantly by 2522
latitude. There is no significant difference in cosmopolitan genus diversity through time at the 2523
sites compared (Fig. 8.7, Table 8.3), but endemism increased throughout the Early Triassic. 2524
Figure 8.8 compares Smithian species from the Boreal Ocean to Smithian species from the 2525
western US (tropical Panthalassic Ocean), South China (tropical Tethys Ocean), and Pakistan 2526
(high-latitude Tethys Ocean) (following the literature cited by Brayard et al. 2006). Streamlined 2527
oxycones are significantly more speciose at both low latitude sites compared to the Boreal Ocean 2528
(Table 8.4). The Pakistan, high latitude Tethys Ocean, site is an intermediate to the two 2529
latitudinal end-members; the ratio of oxycones is statistically indistinguishable from either 2530
tropical region or the Boreal realm. 2531
Early Jurassic Hettangian species shape distributions (Fig. 8.9) are compared to the above 2532
listed analyses of Early Triassic shape distributions in Table 8.5. The Hettangian collection 2533
contains significantly (p=1.15*10
-5
) more serpenticones than those ammonoids occurring in the 2534
Boreal Ocean during the Griesbachian through Smithian Stages. The Hettangian data are from a 2535
lower latitude setting than Early Triassic Boreal ammonoids, but their difference in shell shape 2536
representation is the opposite of the trend between tropical and high latitude regions in the Early 2537
Triassic. 2538
2539
2540
2541
114
Discussion 2542
The statistical tests of Westermann Morphospace method support its use to examine 2543
pelagic ecology. The results are statistically consistent with a principal components analysis. 2544
The specific projection is also significantly correlated to hydrodynamic efficiency data that 2545
provides compelling quantitative evidence for a link between shell shape, life mode, and 2546
metabolic demand. Though ammonoids are extinct, their basic physiology should be constrained 2547
to the first order by their extant sister clade (coleoids) and outgroup (Nautilus). In ammonoids 2548
closest living relatives, the coleoids (octopus, squid, cuttlefish), locomotion style is orders of 2549
magnitude more indicative of metabolic demand than is size. Ammonoid locomotion within a 2550
streamlined shell (oxycone) is significantly more efficient at higher speeds. Locomotion within 2551
non-streamlined shells (serpenticones, spherocones) is more efficient at low speeds. If moving 2552
very slowly, ammonoids within an oxyconic shell would have higher metabolic demand than 2553
similarly paced ammonoids in shells of other shapes. Once moving quickly, an ammonoid in an 2554
oxyconic shell would be more metabolically efficient. It is our parsimonious interpretation that 2555
ammonoids with streamlined oxyconic shells employed active locomotion with an elevated 2556
metabolic demand, while less-streamlined forms employed less active locomotion with lower 2557
metabolic demand. Although this reasoning is simplified, it is consistent with previous 2558
interpretations (Dera et al. 2010; Whiteside and Ward 2011). It is also statistically significant and 2559
therefore provides a starting point to query links between ammonoid shell shape dynamics, 2560
diversity, and environmental change. Shell ornamentation exists in some of the species 2561
considered in the this study but has yet to be quantified as a primary influence on shell 2562
hydrodynamics, and is here assumed to be secondary to overall shape. 2563
115
We expected that intraspecies shell shape variation in the Boreal Ocean ammonoids 2564
examined might produce statistically significant differences in Westermann Morphospace 2565
categorization, however we did not observe any evidence for this trend. Therefore, type 2566
specimens of species are considered to be sufficient to examine trends in occupation of the four 2567
simple categories of Westermann Morphospace. Modern studies typically use a single specimen 2568
to represent a species or even entire genus (Dera et al., 2010; McGowan, 2004a) in ordinations 2569
that explore trends in shell shape across time and space. The use of different numbers of 2570
specimens for each species prevents statistical analysis of results. Intraspecies variation should 2571
continuously be considered. There are noted cases that would preclude categorization of a 2572
species as a single shell shape category (Dagys and Weitschat, 1993). Intraspecies variation may 2573
become increasingly important as more specific hydrodynamic thresholds or gradients between 2574
ammonoid shell shapes are integrated into Westermann Morphospace. These concerns, however, 2575
could not be shown to significantly affect the current investigation. 2576
Taxonomic diversity after extinctions is modeled to increase in tiers of increasing trophic 2577
complexity (Sole et al., 2002). Thus, we expected to see a change in the distribution of shell 2578
shapes produced by Boreal Ocean species throughout the Early Triassic. Specifically, we 2579
expected to see significant increase in the diversity of ammonoids producing oxyconic shells, 2580
because these significantly correlate with hydrodynamics that imply higher metabolic demand. 2581
Directly following the extinction event, earliest Triassic Boreal ammonoids occupied a wide 2582
range of potential ammonoid morphotypes. This result suggests that ecological opportunity 2583
existed at high latitudes for both non-streamlined, low metabolism ammonoids as well as 2584
streamlined, actively mobile ammonoids with potentially high metabolic demand. This pattern of 2585
diverse ammonoid shape occupation continued throughout the rest of the Griesbachian through 2586
116
the Smithian and the species richness of each morphotype correlated significantly with overall 2587
diversity trends in Boreal Ammonoids. Though oxycones did not dominate any diverse Triassic 2588
ammonoid assemblage until the Spathian stage, they were persistently produced by ammonoid 2589
species from a mosaic of higher taxa. At the end of the Early Triassic, during the 3.25 million 2590
year interval represented by the Spathian Stage, Boreal ammonoids produced significantly more 2591
oxyconic shapes than they had in the preceding 1.75 million years represented by the 2592
Griesbachian-Smithian Stages. This rise in oxycones during the last few million years of the 2593
recovery is a realization of the ecological predictions of Sole et al (2002). This is partially the 2594
result of taxonomic turnover as the suborder Pinacocertina declined at the Smithian-Spathian 2595
boundary and Ceratitina arose producing oxycones. Ecologically it implies that ammonoids 2596
diversified to fill higher trophic tiers following the extinction. 2597
The significant correlation of hydrodynamic demand and shell shape affects the 2598
discussion of ammonoid shells shape distributions and Early Triassic environmental events. The 2599
impact of Early Triassic changes in temperature, anoxic bottom water, euxinia, and persistent 2600
oxygen minimum zones (OMZ) on Mesozoic ammonoids can be informed by their sister clade 2601
(coleoids) and outgroup (Nautilus). Repeated crashes in Early Triassic Boreal Ocean ammonoid 2602
diversity did not show evidence for selection against different implied metabolic rates. This 2603
suggests ecological or environmental opportunity for each mobility grade existed in the Boreal 2604
Ocean, and is consistent with shell shape trends at the genus level (Brosse et al., 2013). Abrupt 2605
loses of taxonomic diversity are correlated with global and local carbon isotope excursions 2606
(Payne et al. 2004, Grasby et al. 2013) (Fig. 8.6). These fluctuations, associated with 2607
sedimentary indicators, are interpreted as low oxygen water mass incursion events. These sudden 2608
events are the likely cause for the more minor drops in Boreal ammonoid diversity. Studies of 2609
117
ammonoids’ extant relatives show temperature as a single factor that severely limits cephalopods 2610
with both high and low metabolic demands, within ammonoids’ sister clade and outgroup 2611
(coleoids (Rosa and Seibel, 2008) and nautiloids (Dunstan et al., 2011)). Recent data (Sun et al., 2612
2012; Romano et al., 2012) reveal evidence for extreme sea surface temperature spikes at the 2613
Smithian/Spathian stage boundary. This coincides with the most profound drop in Boreal Ocean 2614
ammonoid diversity (Fig. 8.6) and may explain the lack of apparent ecological selectivity. These 2615
drops in diversity of Boreal Ocean ammonoids are consistent with extinctions in marine reptiles, 2616
fish, and terrestrial tetrapods, as well as ecological limitations such as decreased body size in 2617
gastropods and other benthic invertebrates {Fraiser et al. 2004, Sun:2012jx}. These findings 2618
support Stanley’s (2009) conclusion that the ammonoids’ high origination and extinction rates 2619
illuminated the recurring, but otherwise difficult to detect taxonomically, Early Triassic 2620
extinction events which had consequences across the benthic and pelagic realms. 2621
The shell shapes of ammonoids of the Boreal Ocean differed significantly, during the 2622
Smithian Stage, from the shell shapes of ammonoid species at lower latitudes. Brayard et al. 2623
(2007) demonstrated that ammonoid endemism increased and taxonomic assemblages became 2624
increasingly latitudinally stratified throughout the Early Triassic. We found that a consequence 2625
of the latitudinal faunal gradient was significantly more species with oxyconic shells at low 2626
latitudes (Fig. 9). This is supported by recent findings by Brayard and Escarguel (2012) which 2627
showed on average narrower and more involute shells in the Western USA than the Canadian 2628
Arctic. Early Triassic ammonoids are currently undergoing species-level systematic revisions so 2629
we must examine potential bias in our results from taxonomic over-splitting by original 2630
investigators. Brayard and Escarguel (Brayard and Escarguel, 2012) predict that previous 2631
taxonomic practices would have over-split heavily ornamented evolute forms and lumped 2632
118
relatively unornamented oxycones. The significant trend we identify, more oxycones in the 2633
tropics, is the opposite of what one would expect by taxonomic bias as a result of over-splitting 2634
by previous investigators and indeed may persist despite such bias. 2635
The ecological phenomenon of significantly more species of oxycones at low latitudes 2636
corresponds to the presence of persistent, vertically limited (400-800m) oxygen minimum zones 2637
(OMZ) in tropical seas during the Smithian stage (Wignall and Twitchett, 2002; Algeo et al., 2638
2011; Winguth and Winguth, 2012) (Fig. 9). Even ammonoids’ extant outgroup relatives (Kröger 2639
et al., 2011), the Nautilus, have adaptations to survive in low oxygen environments (Staples et 2640
al., 2003). More specifically, very high metabolism coleoids are flourishing opportunistically in 2641
modern expanded OMZ that exclude vertebrate predators (Bazzino et al., 2010). We suggest that 2642
persistent shallow ocean OMZ in the Early Triassic created an ecological opportunity for ably 2643
swimming, high metabolism oxycone ammonoids. Moreover, modern cephalopod adaptation to 2644
low oxygen environments heightens sensitivity to hypercapnia and temperature spikes(Rosa and 2645
Seibel, 2008), again supporting elevated sea surface temperatures as a limiting factor for 2646
diversity at the Smithian/Spathian transition. 2647
The observation that earliest Triassic and Jurassic ammonoids produced significantly 2648
different shell shapes should be explained either by taxonomic limitation or by different 2649
environmental/ ecological factors following the different mass extinction events. One hundred 2650
five of the 106 ammonoid species in the Boreal Ocean time series were considered part of the 2651
suborder Ceratitina (Treatise 1957). Page (1996) divided the superfamilies into several distinct 2652
suborders, and a cladistics analysis by McGowan and Smith (2004) supported the monophyletic 2653
Ceratina as a clade, maintained some of its superfamilies, and split others. McGowan and Smith 2654
(McGowan and Smith, 2007) conclude that the Ceratina contain polytomies that remain 2655
119
ambiguous, and suggest that several Early Triassic superfamilies have un-recoded Late Permian 2656
ghost lineages. The only recorded survivors of the end-Permian mass extinctions belong to three 2657
mutually derived superfamilies (each given distinct suborders by Page 1996): Medlicottidae, 2658
Xenodiscidae, and Otoceratidae. Of these, the latter two produced the earliest Triassic species 2659
found in the Boreal Ocean record, including serpenticones and oxycones, respectively. The 2660
cascade of superfamilies and suborders derived from Xenodiscidae are the “rootstock” for most 2661
Triassic and all post-Triassic ammonoids. Though Otoceratidae was a “dead clade walking”, new 2662
suborders that arose, even before Otoceratids went extinct, promptly produced new species with 2663
oxyconic shells. The suborder Phylloceratina finally appeared at the very end of Early Triassic, 2664
and itself gave rise to all of the Jurassic lineages, as it produced the only two genera to survive 2665
the end-Triassic mass extinction well into the first Jurassic Hettangian stage. As in the Early 2666
Triassic, the earliest surviving Jurassic lineage gave rise to three competing superfamilies (each 2667
with their own suborder according to Page 1996) within a million and a half years of the 2668
extinction. Also like the Early Triassic, the one surviving and three new Early Jurassic lineages 2669
demonstrated the genetic capability to produce ammonoid species with oxyconic shells. The key 2670
difference is that significantly more serpenticonic species proliferated during the Early Jurassic 2671
than the Early Triassic. 2672
Because of the striking similarity in the pace and potential shell shape expression of 2673
suborder diversification during both post-extinction intervals, we interpret that the significant 2674
differences between earliest Triassic and earliest Jurassic ammonoid shell shapes would be better 2675
explained by different environmental or ecological conditions of the post-extinction intervals. 2676
The broad interpretation of serpenticones as drifters implies that the pelagic realm still did not 2677
recover substantial ecological complexity until later in the Early Jurassic. Earliest Jurassic 2678
120
faunas of cosmopolitan and large serpenticonic ammonoids may have been a prolonged interval 2679
of opportunism not seen in the Early Triassic Boreal Ocean (see also: Guex 2012; Hillebrandt 2680
and Krystyn 2010; Whiteside and Ward 2011). Perhaps the repeated extinction and 2681
diversification events and repeated environmental disturbances in the Early Triassic actually 2682
stimulated ecological expansion as whole tiers of niches were repopulated. 2683
2684
Conclusions 2685
After about 1.7 million years of producing varied and consistent shell shapes, 2686
significantly more ammonoid species with oxyconic shells inhabited the Boreal Ocean during the 2687
Spathian Stage. We interpret that this supports the extinction recovery model of Sole et al. 2688
(2002) by increasing diversity among higher trophic levels through time. We also interpret that 2689
the Griesbachian through Smithian ammonoid assemblages are surprisingly varied, compared to 2690
the significantly serpenticone-dominated early Jurassic, and surprisingly persistent, in light of 2691
continual extinction and taxonomic turnover. Smithian Stage endemism and latitudinal 2692
taxonomic gradient resulted in significantly more ammonoid species with oxyconic shells at low 2693
latitudes. Physiological constraint by extant relatives and significant correlation between 2694
ammonoid locomotion efficiency and shell shape supports interpretations of these shell shape 2695
patterns as ecological phenomena. We interpret that the Boreal Ocean ammonoids produced 2696
rapid and resilient ecological complexity in the water column, despite repeated non-selective 2697
elimination by high-temperature events. We interpret that tropical settings featured more high 2698
metabolism ammonoid species by the Smithian Stage, and that these may have benefited 2699
opportunistically from widespread low-latitude oxygen minimum zones. 2700
121
These investigations show that there are significant differences between the ammonoid 2701
shell shapes produced by different faunas around the world following different mass extinctions, 2702
and their ecological consequences should be explored more rigorously. Revitalized experimental 2703
investigations of the thresholds or gradients in hydrodynamic efficiency that could more 2704
specifically distinguish oxycone shells would be very useful to shell shape analyses in the future. 2705
122
CHAPTER 9: CONCLUSIONS 2706
The complexity of both benthic and pelagic ecosystems was surprisingly limited for 2707
about two million years following the end-Triassic mass extinction. Studied benthic sites 2708
recorded siliceous sponge terrains striking in their homogeneity, distribution, and lack of small 2709
scale topography that might have fostered complex habitats and biodiversity. Indeed, when 2710
sampled for associated fauna, these sponge meadows featured only scallops (Weyla) in 2711
abundance, even after a suite of bivalves and gastropods had already established themselves 2712
along the apparently narrow inner shelf. The tenure of the sponges represents an interval of 2713
inactive carbonate ramp production by biocalcifiers. The long term suppression of shelly 2714
biocalcifiers fits expectations from modern studies that show disturbances to carbonate systems 2715
such as reefs can have positive feed back enforcement so strong that the ousted faunas do not 2716
return even if the offending environmental force is lowered far beyond problematic levels. 2717
Insofar as inadequate carbonate saturation contributed to biocalcifier elimination, these groups 2718
do not rapidly return, despite apparently over-whelming carbonate saturation in the Early 2719
Jurassic. Spikes in temperature may also have contributed to biocalcifier removal, and may have 2720
posed a continued threat to their return. The great abundance and size of gastropods by the early 2721
Sinemurian is an interesting feature, whereas these are not known from the underlying Upper 2722
Triassic Gabbs Formation (Newton, 1986). 2723
Further constraint on the duration and distribution of the siliceous sponge take-over in 2724
the Early Jurassic is an important goal for future work. This will have substantial bearing on 2725
estimates of global marine silica concentrations, which are virtually unconstrained throughout 2726
the Paleozoic and Mesozoic. At present, it appears the phenomenon was wide spread, occurring 2727
across narrow shelf systems in north and south coasts of eastern Panthalassa, and within the 2728
123
Tethys seaway. It will also be of interest to distinguish or connect these sponges with the better 2729
known and widely distributed masses of siliceous sponge terrains and spiculites throughout the 2730
Jurassic rocks of Europe. Sponges are generally overlooked in quantitative paleoecology, and 2731
are difficult to track in studies of taxonomic occurrence because their taxonomy is so dubious in 2732
ancient fossils. For now, the observation and conceptualization of biologically mediated 2733
sedimentary systems is necessary to continue developing so that the vast history of this clade’s 2734
impact on benthic ecology may be better documented. Ongoing efforts by the National Science 2735
Foundation to support dynamic cyber infrastructure development offer exciting opportunities to 2736
learn, as a community of sedimentologists, how such observations can be curated, quantified, 2737
and used in further analyses. 2738
In the pelagic realm, too, apparent ecology was very limited compared to before the 2739
extinction and compared to the aftermath of other global extinction intervals in Earth history. 2740
Apparently only two ammonoid genera survived into the mid Hettangian, and these gave rise 2741
rapidly to many species. Curiously, most of these species bore very simply coiled serpetinconic 2742
shells. A phylogenetic explanation would be expected, but leaves unanswered questions. It is 2743
unclear why the Phylocerid lineage produced so few species, and by comparison the Psilocerids 2744
are not only speciose but terrifically abundant and cosmopolitan. Also, the simply coiled 2745
serpentiones reached very great sizes, up to 50 cm. (For context, fewer than 1% of ammonoid 2746
species reached sizes of 25 cm throughout the entire Phanerozoic (Jacobs, 1992; Raup, 1967)). 2747
The size, abundance, and cosmopolitan distribution of Hettangian ammonoid species implies the 2748
incredibly simple geometry of the outer shell was either selected for or was simply not hindering 2749
survival and long individual life spans. This might be attributed to a number of ecological 2750
conditions. For one, the expectedly low metabolic demands of a shell that would best facilitate 2751
124
very slow drifting might have suited ammonoids that grew slowly and may have endured 2752
inconsistent access to prey in the extinction aftermath. Also, since ammonoids are one of the 2753
main known prey items of other ammonoids, the ubiquitous cephalopods might have fueled their 2754
own taxonomic recovery, if not an ecosystem of apparent complex differences in life mode. The 2755
extinction also had an effect on vertebrates including conodonts, and though data are sparse, may 2756
have majorly effected the marine reptiles and fishes at the top of the ammonoid food web. 2757
There is an alternate possibility, which is that the communities of ammonoids were more 2758
complex than currently recognized. This will take more investigation to determine. Ammonoids 2759
may have mitigated the hydrodynamic limitations of serpenticonic shells with advances in shell 2760
ornamentation and soft bodied behaviors. In the ammonoid research community, ornament is 2761
generally discussed in association with increased drag, in a trade off necessary for increased 2762
protection from shell-crushing predators. In contrast, engineering studies support that correctly 2763
placed ornamentations might reduce drag, increase lift and propulsion, and control vortices 2764
around the shell margins. The behavior of the animal in manipulation of the soft body and jet 2765
propulsion system may have greatly improved propulsion efficiency. For example, if 2766
acceleration was very slow, but steady flow at very low speeds was optimal, then an ammonoid 2767
would benefit from a steady and continual jet propulsion. Ornament varied on Hettangian 2768
ammonoids and increased in intensity on Sinemurian ammonoids. While the basic anatomy of 2769
the ammonoid body is well-known, there may never be fossil evidence for jet behavior. New 2770
experiments in flume tanks can further test the impact of ornament and jet rhythm on shell 2771
locomotion efficiency. If neither feature significantly improves the efficiency of serpenticonic 2772
shells compared to more streamlined forms, then very limited ecological complexity could still 2773
be interpreted for the earliest Jurassic pelagic realm. If ornament and behavior might have 2774
125
generated locomotion efficiencies significantly more varied than the outer shell shape alone 2775
implies, then the ecological complexity of earliest Jurassic ammonoids may have been far more 2776
complex than previously acknowledged. 2777
2778
126
CITATIONS 2779
2780
Algeo, T.J., Chen, Z.Q., Fraiser, M.L., and Twitchett, R.J., 2011, Terrestrial--marine 2781
teleconnections in the collapse and rebuilding of Early Triassic marine ecosystems: 2782
Palaeogeography, Palaeoclimatology, Palaeoecology, v. 308, no. 1-2, p. 1–11, doi: 2783
10.1016/j.palaeo.2011.01.011. 2784
Alroy, J., 2010a, Fair sampling of taxonomic richness and unbiased estimation of origination and 2785
extinction rates: Paleontological Society Special Papers, v. 16, no. 16, p. 1–26. 2786
Alroy, J., 2010b, The Shifting Balance of Diversity Among Major Marine Animal Groups: 2787
Science, v. 329, no. 5996, p. 1191–1194, doi: 10.1126/science.1189910. 2788
Alroy, J., Aberhan, M., Bottjer, D.J., Foote, M., Fürsich, F.T., Harrie, P.J., Hendy, A.J., Holland, 2789
S.M., Ivany, L.C., and Kiessling, W., 2008, Phanerozoic trends in the global diversity of 2790
marine invertebrates: Science, v. 321, no. 5885, p. 97–100. 2791
Anthony, K., Kline, D.I., Diaz-Pulido, G., Dove, S., and Hoegh-Guldberg, O., 2008, Ocean 2792
acidification causes bleaching and productivity loss in coral reef builders: Proceedings of the 2793
National Academy of Sciences, v. 105, no. 45, p. 17442–17446. 2794
Arkell, W.J., Frunish, W.M., Kummel, B., MIller, A.K., Moore, R.C., Shindewolf, O.H., 2795
Sylvester-Bradley, P.C., and Wright, W.C., 1957, Mollusca 4, Cephalopoda, Ammonoidea: 2796
Geological Society of America, New York. 2797
Ausich, W.I., and Bottjer, D.J., 1982, Tiering in suspension-feeding communities on soft 2798
substrata throughout the Phanerozoic.: Science, v. 216, no. 4542, p. 173–174. 2799
Bambach, R.K., 2002, Anatomical and ecological constraints on Phanerozoic animal diversity in 2800
the marine realm: Proceedings of the National Academy of Sciences, v. 99, no. 10, p. 6854– 2801
6859, doi: 10.1073/pnas.092150999. 2802
Bambach, R.K., 1993, Seafood through time: changes in biomass, energetics, and productivity in 2803
the marine ecosystem: Paleobiology,, p. 372–397. 2804
Bambach, R.K., Bush, A.M., and Erwin, D.H., 2007, Autecology and the filling of ecospace: key 2805
metazoan radiations: Palaeontology, v. 50, no. 1, p. 1–22. 2806
Bardhan, S., Shome, S., and Roy, P., 2007, Biogeography of Kutch Ammonites During the 2807
Latest Jurassic (Tithonian) and a Global Paleobiogeographic Overview, in Landman, N.H., 2808
Davis, R.A., and Mapes, R.H. eds., Cephalopods Present and Past: New Insights and Fresh 2809
Perspectives, Springer, Dordrecht, Netherlands, p. 375–395. 2810
Barskov, I.S., Boiko, M.S., Konovalova, V.A., Leonova, T.B., and Nikolaeva, S.V., 2008, 2811
Cephalopods in the marine ecosystems of the Paleozoic: Paleontological Journal, v. 42, no. 2812
11, p. 1167–1284, doi: 10.1134/S0031030108110014. 2813
127
Bartolini, A., Guex, J., Spangenberg, J., Schoene, B., Taylor, D., Schaltegger, U., and Atudorei, 2814
V., 2012, Disentangling the Hettangian carbon isotope record: Implications for the aftermath 2815
of the end-Triassic mass extinction: Geochemistry Geophysics Geosystems, v. 13, no. 1, p. 2816
Q01007, doi: 10.1029/2011GC003807. 2817
Batt, R.J., 1989, Ammonite shell morphotype distributions in the Western Interior Greenhorn 2818
Sea and some paleoecological implications: PALAIOS,, p. 32–42. 2819
Bazzino, G., Gilly, W.F., Markaida, U., Salinas-Zavala, C.A., and Ramos-Castillejos, J., 2010, 2820
Horizontal movements, vertical-habitat utilization and diet of the jumbo squid (Dosidicus 2821
gigas) in the Pacific Ocean off Baja California Sur, Mexico: Progress in Oceanography, v. 2822
86, no. 1-2, p. 59–71, doi: 10.1016/j.pocean.2010.04.017. 2823
Beatty, T.W., Zonneveld, J.P., and Henderson, C.M., 2008, Anomalously diverse Early Triassic 2824
ichnofossil assemblages in northwest Pangea: A case for a shallow-marine habitable zone: 2825
Geology, v. 36, no. 10, p. 771, doi: 10.1130/G24952A.1. 2826
Bechmann, R.K., Taban, I.C., Westerlund, S., Godal, B.F., Arnberg, M., Vingen, S., 2827
Ingvarsdottir, A., and Baussant, T., 2011, Effects of Ocean acidification on early life stages 2828
of shrimp (Pandalus borealis) and mussel (Mytilus edulis): Journal of Toxicology and 2829
Environmental Health, Part A, v. 74, no. 7-9, p. 424–438. 2830
Bell, J.J., 2008, The functional roles of marine sponges: Estuarine, Coastal and Shelf Science, v. 2831
79, no. 3, p. 341–353, doi: 10.1016/j.ecss.2008.05.002. 2832
Beman, J.M., Chow, C.E., King, A.L., Feng, Y., Fuhrman, J.A., Andersson, A., Bates, N.R., 2833
Popp, B.N., and Hutchins, D.A., 2011, Global declines in oceanic nitrification rates as a 2834
consequence of ocean acidification: Proceedings of the National Academy of Sciences, v. 2835
108, no. 1, p. 208–213. 2836
Beniash, E., Aizenberg, J., Addadi, L., and Weiner, S., 1997, Amorphous calcium carbonate 2837
transforms into calcite during sea urchin larval spicule growth: Proceedings of the Royal 2838
Society B: Biological Sciences, v. 264, no. 1380, p. 461–465. 2839
Beniash, E., Ivanina, A., Lieb, N.S., Kurochkin, I., and Sokolova, I.M., 2010, Elevated level of 2840
carbon dioxide affects metabolism and shell formation in oysters Crassostrea virginica 2841
(Gmelin): Marine Ecology Progress Series, v. 419, p. 95–108, doi: 10.3354/meps08841. 2842
Blackburn, T.J., Olsen, P.E., Bowring, S.A., McLean, N.M., Kent, D.V., Puffer, J., McHone, G., 2843
Rasbury, E.T., and Et-Touhami, M., 2013, Zircon U-Pb Geochronology Links the End- 2844
Triassic Extinction with the Central Atlantic Magmatic Province: Science,, doi: 2845
10.1126/science.1234204. 2846
Bottjer, D.J., Campbell, K.A., Schubert, J.K., and Droser, M.L., 1995, Palaeoecological models, 2847
non-uniformitariansim, and tracking the changing ecology of the past, in Bosence, D.W.J. 2848
and Allison, P.A. eds., Marine Palaeoenvironmental Analysis from Fossils, Geological 2849
Society Special Publication, p. 7–26. 2850
128
Boury-Esnault, N., and Rützler, K. (Eds.), 1997, Thesaurus of sponge morphology: Smithsonian 2851
Contributions to Zoology. 2852
Brachert, T.C., 1991, Environmental control on fossilization of siliceous sponge assemblages: a 2853
proposal, in Reitner, J. and Keupp, H. eds., Fossil and Recent Sponges, Springer-Verlag, 2854
Berlin Heidelberg. 2855
Brayard, A., and Escarguel, G., 2012, Untangling phylogenetic, geometric and ornamental 2856
imprints on Early Triassic ammonoid biogeography: a similarity-distance decay study: 2857
Lethaia,, p. no–no, doi: 10.1111/j.1502-3931.2012.00317.x. 2858
Brayard, A., Bucher, H., Escarguel, G., Fluteau, F., Bourquin, S., and Galfetti, T., 2006, The 2859
Early Triassic ammonoid recovery: Paleoclimatic significance of diversity gradients: 2860
Palaeogeography, Palaeoclimatology, Palaeoecology, v. 239, no. 3-4, p. 374–395, doi: 2861
10.1016/j.palaeo.2006.02.003. 2862
Brayard, A., Bylund, K.G., Jenks, J.F., Stephen, D.A., Olivier, N., Escarguel, G., Fara, E., and 2863
Vennin, E., 2013, Smithian ammonoid faunas from Utah: implications for Early Triassic 2864
biostratigraphy, correlation and basinal paleogeography: Swiss Journal of Palaeontology,, 2865
doi: 10.1007/s13358-013-0058-y. 2866
Brayard, A., Escarguel, G., and Bucher, H., 2007, The biogeography of Early Triassic ammonoid 2867
faunas: clusters, gradients, and networks: Geobios, v. 40, p. 749–765. 2868
Brayard, A., Escarguel, G., Bucher, H., Monnet, C., Bruhwiler, T., Goudemand, N., Galfetti, T., 2869
and Guex, J., 2009, Good Genes and Good Luck: Ammonoid Diversity and the End-Permian 2870
Mass Extinction: Science, v. 325, no. 5944, p. 1118–1121, doi: 10.1126/science.1174638. 2871
Brayard, A., Vennin, E., Olivier, N., Bylund, K.G., Jenks, J., Stephen, D.A., Bucher, H., 2872
Hofmann, R., Goudemand, N., and Escarguel, G., 2011, Transient metazoan reefs in the 2873
aftermath of the end-Permian mass extinction: Nature Geoscience, v. 4, no. 10, p. 693–697, 2874
doi: 10.1038/ngeo1264. 2875
Bromley, R.G., and Frey, R.W., 1974, Redescription of the trace fossil Gyrolithes and taxonomic 2876
evaluation of Thalassinoides, Ophiomorpha and Spongeliomorpha: Bulletin of the 2877
Geological Society of Denmark, v. 23, no. 3-4, p. 311–335. 2878
Brosse, M., Brayard, A., Fara, E., and Neige, P., 2013, Ammonoid recovery after the Permian- 2879
Triassic mass extinction: a re-exploration of morphological and phylogenetic diversity 2880
patterns: Journal of the Geological Society, v. 170, no. 2, p. 225–236, doi: 10.1144/jgs2012- 2881
084. 2882
Bruhwiler, T., Brayard, A., Bucher, H., and Guodun, K., 2008, Griesbachian and Dienerian 2883
(Early Triassic) ammonoid faunas from northwestern Guangxi and southern Guizhou (south 2884
China): Palaeontology, v. 51, no. 5, p. 1151–1180, doi: 10.1111/j.1475-4983.2008.00796.x. 2885
Brusatte, S.L., Benton, M.J., Ruta, M., and Lloyd, G.T., 2008, Superiority, Competition, and 2886
Opportunism in the Evolutionary Radiation of Dinosaurs: Science, v. 321, no. 5895, p. 2887
129
1485–1488, doi: 10.1126/science.1161833. 2888
Brusatte, S.L., Nesbitt, S.J., Irmis, R.B., Butler, R.J., Benton, M.J., and Norell, M.A., 2010, The 2889
origin and early radiation of dinosaurs: Earth-Science Reviews, v. 101, no. 1-2, p. 68–100, 2890
doi: 10.1016/j.earscirev.2010.04.001. 2891
Burnaby, T.P., 1966, Allometric growth of ammonoid shells: a generalization of the logarithmic 2892
spiral:. 2893
Carter, E., and Hori, R., 2005, Global correlation of the radiolarian faunal change across the 2894
Triassic–Jurassic boundary: Canadian Journal of Earth Sciences, v. 42, no. 5, p. 777–790. 2895
Chu, J., Maldonado, M., Yahel, G., and Leys, S., 2011, Glass sponge reefs as a silicon sink: 2896
Marine Ecology Progress Series, v. 441, p. 1–14, doi: 10.3354/meps09381. 2897
Clapham, M.E., and Payne, J.L., 2011, Acidification, anoxia, and extinction: A multiple logistic 2898
regression analysis of extinction selectivity during the Middle and Late Permian: Geology, v. 2899
39, no. 11, p. 1059–1062, doi: 10.1130/G32230.1. 2900
Clapham, M.E., Bottjer, D.J., Powers, C.M., Bonuso, N., Fraiser, M.L., Marenco, P.J., Dornbos, 2901
S.Q., and Pruss, S.B., 2006, ASSESSING THE ECOLOGICAL DOMINANCE OF 2902
PHANEROZOIC MARINE INVERTEBRATES: PALAIOS, v. 21, no. 5, p. 431–441, doi: 2903
10.2110/palo.2005.P05-017R. 2904
Clark, D.L., 1987, Conodonts: the final fifty million years, in Aldridge, R.J. ed., Paleobiology of 2905
the Conodonts, Ellis Horwood, Chichester, p. 165–174. 2906
Clémence, M.E., Gardin, S., Bartolini, A., Paris, G., Beaumont, V., and Guex, J., 2010, Bentho- 2907
planktonic evidence from the Austrian Alps for a decline in sea-surface carbonate production 2908
at the end of the Triassic: Swiss Journal of Geosciences, v. 103, no. 2, p. 293–315. 2909
Courville, P., 1992, Les Vascoceratinae et les Pseudotissotiinae (Ammonitina) d’Ashaka (NE 2910
Nigeria): Relations avec leur environnement biosédimentaire: Bulletin des Centres de 2911
Recherches Exploration-Production, Elf Aquitaine, v. 16, p. 235–457. 2912
Crim, R.N., Sunday, J.M., and Harley, C.D.G., 2011, Elevated seawater CO2 concentrations 2913
impair larval development and reduce larval survival in endangered northern abalone 2914
(Haliotis kamtschatkana): Journal of experimental marine biology and ecology, v. 400, no. 1- 2915
2, p. 272–277, doi: 10.1016/j.jembe.2011.02.002. 2916
Crne, A., Weissert, H., and Gorican, S., 2011, A biocalcification crisis at the Triassic-Jurassic 2917
boundary recorded in the Budva Basin (Dinarides, Montenegro): Bulletin of the …. 2918
Cusack, M., Parkinson, D., Freer, A., Perez-Huerta, A., Fallick, A., and Curry, G., 2008, Oxygen 2919
isotope composition in Modiolus modiolus aragonite in the context of biological and 2920
crystallographic control: Mineralogical Magazine, v. 72, no. 2, p. 569–577. 2921
Dagys, A.S., and Weitschat, W., 1993, Extensive intraspecific variation in a Triassic ammonoid 2922
130
from Siberia: Lethaia, v. 26, no. 2, p. 113–121. 2923
de Putron, S.J., McCorkle, D.C., Cohen, A.L., Dillon, AB, 2011, The impact of seawater 2924
saturation state and bicarbonate ion concentration on calcification by new recruits of two 2925
Atlantic corals: Coral Reefs, v. 30, no. 2, p. 321–328. 2926
Delecat, S., 2005, Porifera-microbialites of the Lower Liassic (Northern Calcareous Alps)-Re- 2927
settlement strategies on submarine mounds of dead Rhaetian reefs by ancestral benthic 2928
communities:. 2929
Delecat, S., and Reitner, J., 2005, Sponge communities from the Lower Liassic of Adnet 2930
(Northern Calcareous Alps, Austria): Facies, v. 51, no. 1-4, p. 385–404, doi: 2931
10.1007/s10347-005-0045-x. 2932
Delecat, S., Arp, G., and Reitner, J., 2011, Aftermath of the Triassic–Jurassic Boundary Crisis: 2933
Spiculite Formation on Drowned Triassic Steinplatte Reef-Slope by Communities of 2934
Hexactinellid Sponges (Northern Calcareous Alps, Austria): Advances in Stromatolite 2935
Geobiology,, p. 355–390. 2936
DeMaster, D., 2002, The accumulation and cycling of biogenic silica in the Southern Ocean: 2937
revisiting the marine silica budget: Deep Sea Research Part II: Topical Studies in 2938
Oceanography, v. 49, no. 16, p. 3155–3167. 2939
Dera, G., Neige, P., Dommergues, J.-L., and Brayard, A., 2011, Ammonite paleobiogeography 2940
during the Pliensbachian–Toarcian crisis (Early Jurassic) reflecting paleoclimate, eustasy, 2941
and extinctions: Global and Planetary Change, v. 78, no. 3-4, p. 92–105, doi: 2942
10.1016/j.gloplacha.2011.05.009. 2943
Dera, G., Neige, P., Dommergues, J.-L., Fara, E., Laffont, R., and Pellenard, P., 2010, High- 2944
resolution dynamics of Early Jurassic marine extinctions: the case of Pliensbachian-Toarcian 2945
ammonites (Cephalopoda): Journal of the Geological Society, v. 167, no. 1, p. 21–33, doi: 2946
10.1144/0016-76492009-068. 2947
Diaz-Pulido, G., Gouezo, M., Tilbrook, B., Dove, S., and Anthony, K.R.N., 2010, High CO2 2948
enhances the competitive strength of seaweeds over corals: Ecology Letters, v. 14, no. 2, p. 2949
156–162, doi: 10.1111/j.1461-0248.2010.01565.x. 2950
Doguzhaeva, L.A., and Mutvei, H., 2012, Connecting stripes: An organic skeletal structure in 2951
Sepia from Red Sea: Geobios, v. 45, no. 1, p. 13–17, doi: 10.1016/j.geobios.2011.11.008. 2952
Dommergues, J.-L., Laurin, B., and Meister, C., 2001, The recovery and radiation of Early 2953
Jurassic ammonoids: morphologic versus palaeobiogeographical patterns: Palaeogeography, 2954
Palaeoclimatology, Palaeoecology, v. 165, no. 3, p. 195–213. 2955
Dommergues, J.-L., Montuire, S., and Neige, P., 1996, Evolution of ammonoid morphospace 2956
during the Early Jurassic radiation: Paleobiology, v. 22, no. 2, p. 219–240, doi: 2957
10.1666/0094-8373(2002)028<0423:SPTTTC>2.0.CO;2. 2958
131
Doney, S.C., Fabry, V.J., Feely, R.A., and Kleypas, J.A., 2009, Ocean Acidification: The Other 2959
CO 2Problem: Annual Review of Marine Science, v. 1, no. 1, p. 169–192, doi: 2960
10.1146/annurev.marine.010908.163834. 2961
Dore, A.G., 1992, Synoptic palaeogeography of the Northeast Atlantic Seaway: late Permian to 2962
Cretaceous: Geological Society, London, Special Publications, v. 62, no. 1, p. 421–446, doi: 2963
10.1144/GSL.SP.1992.062.01.31. 2964
Droser, M.L., and Bottjer, D.J., 1986, A semiquantitative field classification of ichnofabric: 2965
Journal of Sedimentary Research, v. 56, no. 4, p. 558–559. 2966
Dunstan, A.J., Ward, P.D., and Marshall, N.J., 2011, Vertical distribution and migration patterns 2967
of Nautilus pompilius: PloS one, v. 6, no. 2, p. e16311, doi: 2968
10.1371/journal.pone.0016311.g001. 2969
Dupont, S., and Lundve, B., 2010, Near future ocean acidification increases growth rate of the 2970
lecithotrophic larvae and juveniles of the sea star Crossaster papposus: Journal of 2971
Experimental Zoology, Part B. 2972
Fabricius, K.E., Langdon, C., Uthicke, S., Humphrey, C., Noonan, S., De'ath, G., Okazaki, R., 2973
Muehllehner, N., Glas, M.S., and Lough, J.M., 2011, Losers and winners in coral reefs 2974
acclimatized to elevated carbon dioxide concentrations: Nature Climate Change, v. 1, no. 6, 2975
p. 165–169, doi: 10.1038/nclimate1122. 2976
Fabry, V.J., Seibel, B.A., Feely, R.A., and Orr, J.C., 2008, Impacts of ocean acidification on 2977
marine fauna and ecosystem processes: ICES Journal of Marine Science: Journal du Conseil, 2978
v. 65, no. 3, p. 414–432. 2979
Fernández-López, S., and Meléndez, G., 1996, Phylloceratina ammonoids in the Iberian Basin 2980
during the Middle Jurassic: a model of biogeographical and taphonomic dispersal related to 2981
relative sea-level changes: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 120, no. 2982
3, p. 291–302. 2983
Fine, M., and Tchernov, D., 2007, Scleractinian Coral Species Survive and Recover from 2984
Decalcification: Science, v. 315, no. 5820, p. 1811–1811, doi: 10.1126/science.1137094. 2985
Flessa, K.W., and Jablonski, D., 1983, Extinction is here to stay: Paleobiology, v. 9, no. 4, p. 2986
315–321. 2987
Flugel, E., 2002, Triassic Reef Patterns, in Kiessling, W., Flugel, E., and Golonka, J. eds., 2988
Phanerozoic Reef Patterns, Society for Sedimentary Geology (SEPM), Tulsa, p. 391–463. 2989
Flugel, E., and Kiessling, W., 2002, Patterns in Phanerozoic Reef Crises, in Kiessling, W., 2990
Flugel, E., and Golonka, J. eds., Phanerozic Reef Patterns, Society for Sedimentary Geology 2991
(SEPM), Tulsa, p. 691–733. 2992
Fraiser, M.L., and Bottjer, D.J., 2007, When bivalves took over the world: Paleobiology, v. 33, 2993
no. 3, p. 397–413, doi: 10.1666/pbio05072.s1. 2994
132
Fraiser, M.L., Clapham, M.E., and Bottjer, D.J., 2011, Taphonomic Processes: Fidelity of the 2995
Guadelupian, Lopingian, and Early Triassic Fossil Records 2996
, in Alison, P.A. and Bottjer, D.J. eds., Taphonomy: Process and Bias through Time, Springer, 2997
Netherlands, p. 569–590. 2998
Fraser, N.C., and Sues, H.-D., 2011, The beginning of the “Age of Dinosaurs”: a brief overview 2999
of terrestrial biotic changes during the Triassic: Earth and Environmental Science 3000
Transactions of the Royal Society of Edinburgh, v. 101, no. 3-4, p. 189–200, doi: 3001
10.1017/S1755691011020019. 3002
Fraser, N.C., Padian, K., Walkden, G.M., and Davis, A.L.M., 2002, Basal Dinosauriform 3003
Remains from Britain and the Diagnosis of the Dinosauria: Palaeontology, v. 45, no. 1, p. 3004
79–95, doi: 10.1111/1475-4983.00228. 3005
Furla, P., Galgani, I., Durand, I., and Allemand, D., 2000, Sources and mechanisms of inorganic 3006
carbon transport for coral calcification and photosynthesis: Journal of Experimental Biology, 3007
v. 203, no. 22, p. 3445–3457. 3008
Gerber, S., 2011, Comparing the differential filling of morphospace and allometric space through 3009
time: the morphological and developmental dynamics of Early Jurassic ammonoids: 3010
Paleobiology, v. 37, no. 3, p. 369. 3011
Gerber, S., Eble, G.J., and Neige, P., 2008, Allometric space and allometric disparity: a 3012
developmental perspective in the macroevolutionary analysis of morphological disparity: 3013
Evolution, v. 62, no. 6, p. 1450–1457. 3014
Gerber, S., Eble, G.J., and Neige, P., 2011, Developmental aspects of morphological disparity 3015
dynamics: a simple analytical exploration: Paleobiology, v. 37, no. 2, p. 237–251. 3016
Gerber, S., Neige, P., and Eble, G.J., 2007, Combining ontogenetic and evolutionary scales of 3017
morphological disparity: a study of early Jurassic ammonites: Evolution & Development, v. 3018
9, no. 5, p. 472–482, doi: 10.1111/j.1525-142X.2007.00185.x. 3019
Geux, J., 1995, Ammonites hettangiennes de la Gabbs Valley Range (Nevada, USA):. 3020
Glover, T., and Mitchell, K., 2002, An Introduction to Biostatistics: McGraw-Hill, New York. 3021
Golonka, J., 2007, Late Triassic and Early Jurassic palaeogeography of the world: 3022
Palaeogeography, Palaeoclimatology, Palaeoecology, v. 244, no. 1-4, p. 297–307, doi: 3023
10.1016/j.palaeo.2006.06.041. 3024
Grasby, S.E., Beauchamp, B., Embry, A., and Sanei, H., 2012, Recurrent Early Triassic ocean 3025
anoxia: Geology,, doi: 10.1130/G33599.1. 3026
Greene, S.E., Bottjer, D.J., Corsetti, F.A., Berelson, W.M., and Zonneveld, J.P., 2012a, A 3027
subseafloor carbonate factory across the Triassic-Jurassic transition: Geology, v. 40, no. 11, 3028
p. 1043–1046, doi: 10.1130/G33205.1. 3029
133
Greene, S.E., Bottjer, D.J., Hagdorn, H., and Zonneveld, J.-P., 2011, Palaeogeography, 3030
Palaeoclimatology, Palaeoecology: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 3031
308, no. 1-2, p. 224–232, doi: 10.1016/j.palaeo.2010.08.019. 3032
Greene, S.E., Martindale, R.C., Ritterbush, K.A., Bottjer, D.J., Corsetti, F.A., and Berelson, 3033
W.M., 2012b, Recognising ocean acidification in deep time: An evaluation of the evidence 3034
for acidification across the Triassic-Jurassic boundary: Earth-Science Reviews, v. 113, no. 1- 3035
2, p. 72–93, doi: 10.1016/j.earscirev.2012.03.009. 3036
Guex, J., 2001, Environmental stress and atavism in ammonoid evolution: Eclogae Geologicae 3037
Helvetiae, v. 94, p. 321–328. 3038
Guex, J., 2006, Reinitialization of evolutionary clocks during sublethal environmental stress in 3039
some invertebrates: Earth and Planetary Science Letters, v. 242, no. 3-4, p. 240–253, doi: 3040
10.1016/j.epsl.2005.12.007. 3041
Guex, J., Bartolini, A., Atudorei, V., and Taylor, D., 2004, High-resolution ammonite and carbon 3042
isotope stratigraphy across the Triassic–Jurassic boundary at New York Canyon (Nevada): 3043
Earth and Planetary Science Letters, v. 225, no. 1-2, p. 29–41. 3044
Guex, J., Schoene, B., Bartolini, A., Spangenberg, J., Schaltegger, U., O'Dogherty, L., Taylor, 3045
D., Bucher, H., and Atudorei, V., 2012, Geochronological constraints on post-extinction 3046
recovery of the ammonoids and carbon cycle perturbations during the Early Jurassic: 3047
Palaeogeography, Palaeoclimatology, Palaeoecology, v. 346-347, p. 1–11, doi: 3048
10.1016/j.palaeo.2012.04.030. 3049
Gutowska, M., Portner, H.O., and Melzner, F., 2008, Growth and calcification in the cephalopod 3050
Sepia officinalis under elevated seawater pCO2: Marine Ecology Progress Series, v. 373, no. 3051
2007, p. 303–309. 3052
Gutowska, M.A., Melzner, F., Pörtner, H.O., and Meier, S., 2010, Cuttlebone calcification 3053
increases during exposure to elevated seawater pCO2 in the cephalopod Sepia officinalis: 3054
Marine Biology, v. 157, no. 7, p. 1653–1663, doi: 10.1007/s00227-010-1438-0. 3055
Hall, J.T., and Savrda, C.E., 2008, Ichnofossils and Ichnofabrics in Syngenetic Phosphatic 3056
Concretions in Siliciclastic Shelf Deposits, Ripley Formation, Cretaceous, Alabama: 3057
PALAIOS, v. 23, no. 4, p. 233–245, doi: 10.2110/palo.2006.p06-094r. 3058
Hallam, A., and Wignall, P.B. Mass extinctions and their aftermath: Oxford University Press,, p. 3059
320. 3060
Hallam, A., and Wignall, P.B., 2000, Facies changes across the Triassic–Jurassic boundary in 3061
Nevada, USA: Journal of the Geological Society, v. 157, no. 1, p. 49–54. 3062
Hallam, A., and Wignall, P.B., 1999, Mass extinctions and sea-level changes: Earth-Science 3063
Reviews, v. 48, no. 4, p. 217–250. 3064
Hallam, A., Wignall, P.B., Yin, J., and Riding, J.B., 2000, An investigation into possible facies 3065
134
changes across the Triassic–Jurassic boundary in southern Tibet: v. 137, no. 3-4, p. 101–106, 3066
doi: 10.1016/S0037-0738(00)00155-X. 3067
Hammer, O., and Bucher, H., 2006, Generalized ammonoid hydrostatics modelling, with 3068
application to Intornites and intraspecific variation in Amaltheus: Paleontological Research, 3069
v. 10, no. 1, p. 91–96, doi: 10.2517/prpsj.10.91. 3070
Hartmann, J., Jansen, N., Dürr, H.H., Harashima, A., Okubo, K., and Kempe, S., 2010, 3071
Predicting riverine dissolved silica fluxes to coastal zones from a hyperactive region and 3072
analysis of their first-order controls: International Journal of Earth Sciences, v. 99, no. 1, p. 3073
207–230. 3074
Hautmann, M., Benton, M.J., and Tomašových, A., 2008, Catastrophic ocean acidification at the 3075
Triassic-Jurassic boundary: Neues Jahrbuch für Geologie und Paläontologie - 3076
Abhandlungen, v. 249, no. 1, p. 119–127, doi: 10.1127/0077-7749/2008/0249-0119. 3077
Hendriks, I.E., Duarte, C.M., and Alvarez, M., 2010, Vulnerability of marine biodiversity to 3078
ocean acidification: A meta-analysis: Estuarine, Coastal and Shelf Science, v. 86, no. 2, p. 3079
157–164, doi: 10.1016/j.ecss.2009.11.022. 3080
Hewitt, R.A., 1996, Architecture and Strength of the Ammonoid Shell, in Landman, N.H., 3081
Tanabe, K., and Davis, R.A. eds., Ammonoid Paleobiology, Plenum Press, p. 297–343. 3082
Hillebrandt, von, A., 1994, The Triassic/Jurassic boundary and Hettangian biostratigraphy in the 3083
area of the Utcubamba valley (Northern Peru): Geobios, v. 27, no. Supplement 2, p. 297– 3084
307. 3085
Hillebrandt, von, A., 1990, The Triassic/Jurassic boundary in northern Chile: Université 3086
Catholiquede Lyon, Cahiers, Série Sciences, v. 3, p. 27–53. 3087
Hillebrandt, von, A., and Krystyn, L., 2009, On the oldest Jurassic ammonites of Europe 3088
(Northern Calcareous Alps, Austria) and their global significance: Neues Jahrbuch für 3089
Geologie und Paläontologie - Abhandlungen, v. 253, no. 2, p. 163–195, doi: 10.1127/0077- 3090
7749/2009/0253-0163. 3091
Hoegh-Guldberg, O., Mumby, P.J., Hooten, A.J., Steneck, R.S., Greenfield, P., Gomez, E., 3092
Harvell, C.D., Sale, P.F., Edwards, A.J., Caldeira, K., Knowlton, N., Eakin, C.M., Iglesias- 3093
Prieto, R., Muthiga, N., et al., 2007, Coral Reefs Under Rapid Climate Change and Ocean 3094
Acidification: Science, v. 318, no. 5857, p. 1737–1742, doi: 10.1126/science.1152509. 3095
Honisch, B., Ridgwell, A., Schmidt, D.N., Thomas, E., Gibbs, S.J., Sluijs, A., Zeebe, R., Kump, 3096
L., Martindale, R.C., Greene, S.E., Kiessling, W., Ries, J., Zachos, J.C., Royer, D.L., et al., 3097
2012, The Geological Record of Ocean Acidification: Science, v. 335, no. 6072, p. 1058– 3098
1063, doi: 10.1126/science.1208277. 3099
Hutchins, D., Mulholland, M., and Fu, F., 2009, Nutrient Cycles and Marine Microbes in a CO2- 3100
Enriched Ocean: Oceanography, v. 22, no. 4, p. 128–145, doi: 10.5670/oceanog.2009.103. 3101
135
Irmis, R.B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D., and Downs, A., 3102
2007, A Late Triassic Dinosauromorph Assemblage from New Mexico and the Rise of 3103
Dinosaurs: Science, v. 317, no. 5836, p. 358–361, doi: 10.1126/science.1143325. 3104
Jackson, J.B., 2008, Ecological extinction and evolution in the brave new ocean: Proceedings of 3105
the National Academy of Sciences, v. 105, no. Supplement 1, p. 11458–11465. 3106
Jacobs, D., 1992, Shape, drag, and power in ammonoid swimming: Paleobiology, v. 18, no. 2, p. 3107
203–220. 3108
Jacobs, D.K., 1996, Chambered cephalopod shells, buoyancy, structure and decoupling: history 3109
and red herrings: PALAIOS,, p. 610–614. 3110
Jacobs, D.K., Landman, N.H., and Chamberlain, J.A., 1994, Ammonite shell shape covaries with 3111
facies and hydrodynamics: iterative evolution as a response to changes in basinal 3112
environment: Geology, v. 22, no. 10, p. 905–908. 3113
Jenks, J.F., Spielman, J.A., and Lucas, S.G., 2007, Triassic Ammonoids: A Photographic 3114
Journey: Triassic of the American West, New Mexico Museum of Natural History and 3115
Science Bulletin 40,, p. 33–80. 3116
Johnston, E.L., and Clark, G.F., 2007, Recipient environment more important than community 3117
composition in determining the success of an experimental sponge transplant: Restoration 3118
Ecology, v. 15, no. 4, p. 638–651. 3119
Jury, C.P., Whitehead, R.F., and Szmant, A.M., 2010, Effects of variations in carbonate 3120
chemistry on the calcification rates of Madracis auretenra (= Madracis mirabilis sensuWells, 3121
1973): bicarbonate concentrations best predict calcification rates: Global Change Biology, v. 3122
16, no. 5, p. 1632–1644, doi: 10.1111/j.1365-2486.2009.02057.x. 3123
Kerr, R.A., 2010, Ocean Acidification Unprecedented, Unsettling: Science, v. 328, no. 5985, p. 3124
1500–1501, doi: 10.1126/science.328.5985.1500. 3125
Kershaw, S., Li, Y., Crasquin-Soleau, S., Feng, Q., Mu, X., Collin, P.-Y., Reynolds, A., and 3126
Guo, L., 2007, Earliest Triassic microbialites in the South China block and other areas: 3127
controls on their growth and distribution: Facies, v. 53, no. 3, p. 409–425, doi: 3128
10.1007/s10347-007-0105-5. 3129
Kidder, D.L., and Erwin, D.H., 2001, Secular Distribution of Biogenic Silica through the 3130
Phanerozoic: Comparison of Silica‐Replaced Fossils and Bedded Cherts at the Series Level: 3131
The Journal of geology, v. 109, no. 4, p. 509–522, doi: 10.1086/320794. 3132
Kiessling, W., and Aberhan, M., 2007a, Environmental determinants of marine benthic 3133
biodiversity dynamics through Triassic–Jurassic time: Paleobiology, v. 33, no. 3, p. 414– 3134
434, doi: 10.1666/06069.1. 3135
Kiessling, W., and Aberhan, M., 2007b, Geographical distribution and extinction risk: lessons 3136
from Triassic?Jurassic marine benthic organisms: Journal of Biogeography, v. 34, no. 9, p. 3137
136
1473–1489, doi: 10.1111/j.1365-2699.2007.01709.x. 3138
Kiessling, W., and Danelian, T., 2011, Trajectories of Late Permian - Jurassic radiolarian 3139
extinction rates: no evidence for an end-Triassic mass extinction: Fossil Record, v. 14, no. 1, 3140
p. 95–101, doi: 10.1002/mmng.201000017. 3141
Kiessling, W., and Simpson, C., 2011, On the potential for ocean acidification to be a general 3142
cause of ancient reef crises: Global Change Biology, v. 17, no. 1, p. 56–67. 3143
Kiessling, W., Aberhan, M., Brenneis, B., and Wagner, P.J., 2007, Extinction trajectories of 3144
benthic organisms across the Triassic–Jurassic boundary: Palaeogeography, 3145
Palaeoclimatology, Palaeoecology, v. 244, no. 1-4, p. 201–222, doi: 3146
10.1016/j.palaeo.2006.06.029. 3147
Kiessling, W., Roniewicz, E., Villier, L., Léonide, P., and Struck, U., 2009, An early Hettangian 3148
coral reef in southern France: Implications for the end-Triassic reef crisis: PALAIOS, v. 24, 3149
no. 10, p. 657–671. 3150
Kleypas, J.A., Buddemeier, R.W., Archer, D., Gattuso, J.-P., Langdon, C., and Opdyke, B.N., 3151
1999, Geochemical consequences of increased atmospheric carbon dioxide on coral reefs: 3152
SCIENCE, v. 284, no. 5411, p. 118–120, doi: 10.1126/science.322.5899.189b. 3153
Klug, C., BRÜHWILER, T., Korn, D., SCHWEIGERT, G., Brayard, A., and TILSLEY, J., 3154
2007a, AMMONOID SHELL STRUCTURES OF PRIMARY ORGANIC COMPOSITION: 3155
Palaeontology, v. 50, no. 6, p. 1463–1478, doi: 10.1111/j.1475-4983.2007.00722.x. 3156
Klug, C., Montenari, M., Schulz, H., and Urlichs, M., 2007b, Soft-tissue Attachment of Middle 3157
Triassic Ceratitida from Germany 3158
, in Landman, N.H., Davis, R.A., and Mapes, R.H. eds., Cephalopods Present and Past: New 3159
Insights and Fresh Perspectives, Springer, p. 205–220. 3160
Klug, C., RIEGRAF, W., and LEHMANN, J., 2012, Soft-part preservation in heteromorph 3161
ammonites from the Cenomanian-Turonian Boundary Event (OAE 2) in north-west 3162
Germany: Palaeontology,, p. no–no, doi: 10.1111/j.1475-4983.2012.01196.x. 3163
Klug, C., Schatz, W., Korn, D., and Reisdorf, A.G., 2005, Morphological fluctuations of 3164
ammonoid assemblages from the Muschelkalk (Middle Triassic) of the Germanic Basin— 3165
indicators of their ecology, extinctions, and immigrations: Palaeogeography, 3166
Palaeoclimatology, Palaeoecology, v. 221, no. 1-2, p. 7–34, doi: 3167
10.1016/j.palaeo.2005.02.002. 3168
Knoll, A.H., Bambach, R.K., Canfield, D.E., and Grotzinger, J.P., 1996, Comparative Earth 3169
history and Late Permian mass extinction: SCIENCE, p. 452–457. 3170
Knoll, A.H., Bambach, R.K., Payne, J.L., Pruss, S., and Fischer, W.W., 2007, Paleophysiology 3171
and end-Permian mass extinction: Earth and Planetary Science Letters, v. 256, no. 3, p. 295– 3172
313. 3173
137
Korn, D., 2000, Morphospace occupation of ammonoids over the Devonian-Carboniferous 3174
boundary: Paläontologische Zeitschrift, v. 74, no. 3, p. 247–257. 3175
Korn, D., and Klug, C., 2007, Conch form analysis, variability, morphological disparity, and 3176
mode of life of the Frasnian (Late Devonian) ammonoid Manticoceras from Coumiac 3177
(Montagne Noire, France), in Landman, N.H., Davis, R.A., and Mapes, R.H. eds., 3178
Cephalopods Present and Past New Insights and Fresh Perspectives, p. 57–85. 3179
Korn, D., and Klug, C., 2012, Palaeozoic Ammonoids – Diversity and Development of Conch 3180
Morphology, in Springer Netherlands, Dordrecht, p. 491–534. 3181
Kroeker, K.J., Kordas, R.L., Crim, R.N., and Singh, G.G., 2010, Meta-analysis reveals negative 3182
yet variable effects of ocean acidification on marine organisms: Ecology Letters, v. 13, no. 3183
11, p. 1419–1434, doi: 10.1111/j.1461-0248.2010.01518.x. 3184
Kröger, B., 2002, Antipredatory traits of the ammonoid shell—indications from Jurassic 3185
ammonoids with sublethal injuries: Paläontologische Zeitschrift, v. 76, no. 2, p. 223–234. 3186
Kröger, B., Vinther, J., and Fuchs, D., 2011, Cephalopod origin and evolution: A congruent 3187
picture emerging from fossils, development and molecules: BioEssays, v. 33, no. 8, p. 602– 3188
613, doi: 10.1002/bies.201100001. 3189
Kruta, I., Landman, N., Rouget, I., Cecca, F., and Tafforeau, P., 2011, The Role of Ammonites in 3190
the Mesozoic Marine Food Web Revealed by Jaw Preservation: Science, v. 331, no. 6013, p. 3191
70–72, doi: 10.1126/science.1198793. 3192
Kruta, I., Landman, N.H., Rouget, I., Cecca, F., and Tafforeau, P., 2012, The radula of the Late 3193
Cretaceous scaphitid ammonite Rhaeboceras halli(Meek and Hayden, 1856): Palaeontology, 3194
v. 56, no. 1, p. 9–14, doi: 10.1111/j.1475-4983.2012.01188.x. 3195
Kulicki, C., Tanabe, .K., Landmann N.H., 2007, Brief report: Primary structure of the connecting 3196
ring of ammonoids and its preservation:, p. 1–5. 3197
Kump, L., Bralower, T., and Ridgwell, A., 2009, Ocean Acidification in Deep Time: 3198
Oceanography, v. 22, no. 4, p. 94–107, doi: 10.5670/oceanog.2009.100. 3199
Landman, N., Tanabe, K., and Davis, R.A. (Eds.), 1996, Ammonoid Paleobiology: Plenum 3200
Press, New York. 3201
Landman, N.H., and Klofack, S.M., 2012, Anatomy of a concretion: Life, death, and burial in the 3202
Western Interior Seaway: PALAIOS, v. 27, no. 10, p. 671–692, doi: 10.2110/palo.2011.p11- 3203
105r. 3204
Landman, N.H., Davis, R.A., and Mapes, R.H. (Eds.), 2007, Cephalopods Present and Past: New 3205
Insights and Fresh Perspectives: Springer, Dordrecht, Netherlands. 3206
Landman, N.H., Polizzotto, K., Mapes, R., and Tanabe, K., 2006, Cameral membranes in 3207
prolecanitid and goniatitid ammonoids from the Permian Arcturus Formation, Nevada, USA: 3208
138
Lethaia, v. 39, no. 4, p. 365–379, doi: 10.1080/00241160601008395. 3209
Laws, R.A., 1982, Late Triassic depositional environments and molluscan associations from 3210
west-central Nevada: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 37, p. 131– 3211
148. 3212
Lehrmann, D.J., Ramezani, J., Bowring, S.A., Martin, M.W., Montgomery, P., Enos, P., Payne, 3213
J.L., Orchard, M.J., Hongmei, W., and Jiayong, W., 2006, Timing of recovery from the end- 3214
Permian extinction: Geochronologic and biostratigraphic constraints from south China: 3215
Geology, v. 34, no. 12, p. 1053, doi: 10.1130/G22827A.1. 3216
Longridge, L.M., Pálfy, J., Smith, P.L., and Tipper, H.W., 2008, Middle and late Hettangian 3217
(Early Jurassic) ammonites from the Queen Charlotte Islands, British Columbia, Canada: 3218
Revue de Paléobiologie, v. 27, p. 191–248. 3219
Loughman, D., and Hallam, A., 1982a, A facies analysis of the Pucará Group (Norian to 3220
Toarcian carbonates, organic-rich shale and phosphate) of central and northern Peru: v. 32, 3221
no. 3, p. 161–194. 3222
Loughman, D.L., and Hallam, A., 1982b, A Facies Analysis of the Pucara Group (Norian to 3223
Toarcian Carbonates, Organic-Rich Shale and Phosphate) of Central and Northern Peru: 3224
Sedimentary Geology, v. 32, p. 161–194. 3225
Loyd, S.J., Berelson, W.M., Lyons, T.W., Hammond, D.E., and Corsetti, F.A., 2012a, 3226
Constraining pathways of microbial mediation for carbonate concretions of the Miocene 3227
Monterey Formation using carbonate-associated sulfate: Geochimica et Cosmochimica Acta, 3228
v. 78, p. 77–98. 3229
Loyd, S.J., Corsetti, F.A., Eiler, J.M., and Tripati, A.K., 2012b, Determining the Diagenetic 3230
Conditions of Concretion Formation: Assessing Temperatures and Pore Waters Using 3231
Clumped Isotopes: Journal of Sedimentary Research, v. 82, no. 12, p. 1006–1016, doi: 3232
10.2110/jsr.2012.85. 3233
Lucas, S.G., Taylor, D.G., Guex, J., Tanner, L.H., and Krainer, K., 2007, The Proposed Global 3234
Stratotype Section and Point for the base of the Jurassic system in the New York Canyon 3235
Area, Nevada, USA (S. G. Lucas & J. A. Spielman, Eds.): Triassic of the American West, 3236
New Mexico Museum of Natural History and Science Bulletin 40,, p. 139–161. 3237
Lukeneder, A., Harzhauser, M., Müllegger, S., and Piller, W.E., 2010, Ontogeny and habitat 3238
change in Mesozoic cephalopods revealed by stable isotopes (δ18O, δ13C): Earth and 3239
Planetary Science Letters, v. 296, no. 1-2, p. 103–114, doi: 10.1016/j.epsl.2010.04.053. 3240
Macellari, C.E., 1986, Late Campanian-Maastrichtian ammonite fauna from Seymour Island 3241
(Antarctic Peninsula): Memoir (The Paleontological Society),, p. 1–55. 3242
Macellari, C.E., 1984, Late Cretaceous stratigraphy, sedimentol- ogy, and macropaleontology of 3243
Seymour Island, Antarctic Peninsula, Vols. I and II.: Ohio State University. 3244
139
MacGinitie, G.E., 1934, The natural history of Callianassa californiensis Dana: American 3245
Midland Naturalist,, p. 166–177. 3246
Maldonado, M., Carmona, M.C., Uriz, M.J., and Cruzando, A., 1999, Decline in Mesozoic reef- 3247
building sponges explained by silicon limitation: Nature, v. 401, p. 785–788. 3248
Maldonado, M., Navarro, L., Grasa, A., Gonzalez, A., and Vaquerizo, I., 2011, Silicon uptake by 3249
sponges: a twist to understanding nutrient cycling on continental margins: Scientific reports, 3250
v. 1. 3251
Maliva, R.G., and Siever, R., 1988, Pre-Cenozoic nodular cherts; evidence for opal-CT 3252
precursors and direct quartz replacement: American Journal of Science, v. 288, no. 8, p. 3253
798–809, doi: 10.2475/ajs.288.8.798. 3254
Maliva, R.G., KNOLL, A.H., and Siever, R., 1989, Secular change in chert distribution: a 3255
reflection of evolving biological participation in the silica cycle: PALAIOS,, p. 519–532. 3256
Mander, L., and Twitchett, R.J., 2008, Quality of the Triassic Jurassic Bivalve Fossil Record in 3257
Northwest Europe: Palaeontology, v. 51, no. 6, p. 1213–1223, doi: 10.1111/j.1475- 3258
4983.2008.00821.x. 3259
Martindale, R.C., Berelson, W.M., Corsetti, F.A., Bottjer, D.J., and West, A.J., 2012a, 3260
Constraining carbonate chemistry at a potential ocean acidification event (the Triassic 3261
Jurassic boundary) using the presence of corals and coral reefs in the fossil record: 3262
Palaeogeography, Palaeoclimatology, Palaeoecology. 3263
Martindale, R.C., Bottjer, D.J., and Corsetti, F.A., 2012b, Platy coral patch reefs from eastern 3264
Panthalassa (Nevada, USA): Unique reef construction in the Late Triassic: Palaeogeography, 3265
Palaeoclimatology, Palaeoecology, v. 313, p. 41–58. 3266
Marzoli, A., Bertrand, H., Knight, K.B., Cirilli, S., Buratti, N., Vérati, C., Nomade, S., Renne, 3267
P.R., Youbi, N., and Martini, R., 2004, Synchrony of the Central Atlantic magmatic province 3268
and the Triassic-Jurassic boundary climatic and biotic crisis: Geology, v. 32, no. 11, p. 973– 3269
976, doi: 10.1130/G20652.1. 3270
McElwain, J., Beerling, D., and Woodward, F., 1999, Fossil plants and global warming at the 3271
Triassic-Jurassic boundary: Science, v. 285, no. 5432, p. 1386. 3272
McElwain, J., Wagner, P., and Hesselbo, S., 2009, Fossil plant relative abundances indicate 3273
sudden loss of Late Triassic biodiversity in East Greenland: Science, v. 324, no. 5934, p. 3274
1554. 3275
McGowan, A.J., 2004a, Ammonoid taxonomic and morphologic recovery patterns after the 3276
Permian–Triassic: Geology, v. 32, no. 8, p. 665–668. 3277
McGowan, A.J., 2004b, The effect of the Permo-Triassic bottleneck on Triassic ammonoid 3278
morphological evolution: Paleobiology, v. 30, no. 3, p. 369. 3279
140
McGowan, A.J., and Smith, A.B., 2007, Ammonoids across the Permian/Triassic boundary: a 3280
cladistic perspective: Palaeontology, v. 50, no. 3, p. 573–590. 3281
McRoberts, C.A., and Newton, C.R. Selective extinction among end-Triassic European bivalves: 3282
Geology, v. 23, n. 2, p. 102-104. 3283
McRoberts, C.A., Krystyn, L., and Hautmann, M., 2012, Macrofaunal response to the end- 3284
Triassic mass extinction in the West-Tethyan Kossen Basin, Austria: PALAIOS, v. 27, no. 9, 3285
p. 607–616, doi: 10.2110/palo.2012.p12-043r. 3286
Medina, M., Collins, A.G., Takaoka, T.L., Kuehl, J.V., and Boore, J.L., 2006, Naked corals: 3287
skeleton loss in Scleractinia: Proceedings of the National Academy of Sciences, v. 103, no. 3288
24, p. 9096–9100. 3289
Meybeck, M., 1987, Global chemical weathering of surficial rocks estimated from river 3290
dissolved loads: American Journal of Science, v. 287, no. 5, p. 401–428. 3291
Michalik, J., Biron, A., Lintenerova, O., Gotz, A., and Ruckwied, K., 2010, Climate change at 3292
the Triassic/Jurassic boundary in the northwestern Tethyan realm, inferred from sections in 3293
the Tatra Mountains (Slovakia): Acta Geologica Polonica, v. 60, p. 535–548. 3294
Monnet, C., and Bucher, H., 2005, New Middle and Late Anisian (Middle Triassic) ammonoid 3295
faunas from northwestern Nevada (USA): taxonomy and biochronology: Fossils and Strata, 3296
v. 52, p. 1–120. 3297
Monnet, C., Brack, P., Bucher, H., and Rieber, H., 2008, Ammonoids of the middle/late Anisian 3298
boundary (Middle Triassic) and the transgression of the Prezzo Limestone in eastern 3299
Lombardy-Giudicarie (Italy): Swiss Journal of Geosciences, v. 101, no. 1, p. 61–84, doi: 3300
10.1007/s00015-008-1251-7. 3301
Monnet, C., Bucher, H., Guex, J., and Wasmer, M., 2011, Large-scale evolutionary trends of 3302
Acrochordiceratidae Arthaber, 1911 (Ammonoidea, Middle Triassic) and Cope’s rule: 3303
Palaeontology, v. 55, no. 1, p. 87–107, doi: 10.1111/j.1475-4983.2011.01112.x. 3304
Moriya, K., Nishi, H., Kawahata, H., Tanabe, K., and Takayanagi, Y., 2003, Demersal habitat of 3305
Late Cretaceous ammonoids: Evidence from oxygen isotopes for the Campanian (Late 3306
Cretaceous) northwestern Pacific thermal structure: Geology, v. 31, no. 2, p. 167–170. 3307
Muller, S.W., and Ferguson, H.G., 1939, Mesozoic stratgraphy of the Hawthorne and Tonopah 3308
quadrangles, Nevada: GSA Bulletin, v. 50, no. 10, p. 1573. 3309
Mutvei, H., and Dunca, E., 2007, Connecting ring ultrastructure in the Jurassic ammonoid 3310
Quenstedtoceras with discussion on mode of life of ammonoids, in Landman, N.H., Davis, 3311
R.A., and Mapes, R.H. eds., Cephalopods Present and Past New Insights and Fresh 3312
Perspectives, Springer, Dordrecht, Netherlands, p. 239–256. 3313
Nakamura, M., Ohki, S., Suzuki, A., and Sakai, K., 2011, Coral Larvae under Ocean 3314
Acidification: Survival, Metabolism, and Metamorphosis (S. A. Sandin, Ed.): PloS one, v. 6, 3315
141
no. 1, p. e14521, doi: 10.1371/journal.pone.0014521.t004. 3316
Nienhuis, S., Palmer, A.R., and Harley, C.D., 2010, Elevated CO2 affects shell dissolution rate 3317
but not calcification rate in a marine snail: Proceedings of the Royal Society of London. 3318
Series B: Biological Sciences, v. 277, no. 1693, p. 2553–2558. 3319
Nomade, S., Knight, K., Beutel, E., Renne, P., Vérati, C., Féraud, G., Marzoli, A., Youbi, N., and 3320
Bertrand, H., 2007, Chronology of the Central Atlantic Magmatic Province: Implications for 3321
the Central Atlantic rifting processes and the Triassic–Jurassic biotic crisis: 3322
Palaeogeography, Palaeoclimatology, Palaeoecology, v. 244, no. 1, p. 326–344. 3323
Norström, A.V., Nyström, M., Lokrantz, J., and Folke, C., 2009, Alternative states on coral reefs: 3324
beyond coral–macroalgal phase shifts: Marine Ecology Progress Series, v. 376, p. 295–306, 3325
doi: 10.3354/meps07815. 3326
O'Dor, R.K., and Webber, D., 1991, Invertebrate Athletes: trade offs between transport 3327
efficiency and power density in cephalopod evolution: Journal of Experimental Biology, v. 3328
160, p. 93–112. 3329
Okamoto, T., 1996, Theoretical Modeling of Ammonoid Morphology, in Landman, N.H., 3330
Tanabe, K., and Davis, R.A. eds., Ammonoid Paleobiology, Plenum Press, p. 225–252. 3331
Olsen, P.E., 2002, Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic 3332
Boundary: Science, v. 296, no. 5571, p. 1305–1307, doi: 10.1126/science.1065522. 3333
Orchard, M.J., Carter, E.S., Lucas, S.G., and Taylor, D.G., 2007, Rhaetian (Upper Triassic) 3334
conodonts and radiolarians: ALBERIANA, v. 35, p. 59–65. 3335
Orr, J.C., Fabry, V.J., Aumont, O., Bopp, L., Doney, S.C., Feely, R.A., Gnanadesikan, A., 3336
Gruber, N., Ishida, A., and Joos, F., 2005, Anthropogenic ocean acidification over the 3337
twenty-first century and its impact on calcifying organisms: Nature, v. 437, no. 7059, p. 3338
681–686. 3339
Page, K.N., 1996, Mesozoic Ammonoids in Space and Time, in Landman, N., Tanabe, K., and 3340
Davis, R.A. eds., Ammonoid Paleobiology, Plenum Press, New York, p. 755–794. 3341
Payne, J.L., Summers, M., Rego, B.L., Altiner, D., Wei, J., Yu, M., and Lehrmann, D.J., 2011, 3342
Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a 3343
carbonate platform in south China: implications for tempo and mode of biotic recovery from 3344
the end-Permian mass extinction: Paleobiology, v. 37, no. 3, p. 409–425. 3345
Pelejero, C., Calvo, E., and Hoegh-Guldberg, O., 2010, Paleo-perspectives on ocean 3346
acidification: Trends in Ecology & Evolution, v. 25, no. 6, p. 332–344. 3347
Pisera, A., 2006, Palaeontology of sponges — a review: Canadian Journal of Zoology, v. 84, no. 3348
2, p. 242–261, doi: 10.1139/z05-169. 3349
Portner, H.O., Langenbuch, M., and Basile, M. Synergistic effects of temperature extremes, 3350
142
hypoxia, and increases in CO2 n marine animals: From Earth History to global change: 3351
Journal of Geophysical Research - Oceans, v. 110, no. C9, p. C09S10. 3352
Poulton, P.T., 1991, Hettangian through Aalenian (Jurassic) guide fossils and biostratigraphy, 3353
northern Yukon and adjacent Northwest Territories 3354
: Geological Survey of Canada Bulletin. 3355
Powers, C.M., and Bottjer, D.J., 2007, Bryozoan paleoecology indicates mid-Phanerozoic 3356
extinctions were the product of long-term environmental stress: Geology, v. 35, p. 995–998. 3357
Pörtner, H.O., Langenbuch, M., and Reipschläger, A., 2004, Biological impact of elevated ocean 3358
CO2 concentrations: lessons from animal physiology and earth history: Journal of 3359
Oceanography, v. 60, no. 4, p. 705–718. 3360
Prinz, P., 1985, Stratigraphie und ammonoitenfauna der Pucara-Gruppe (obertrias-uniterjura) 3361
von nord-Peru: Palaeontographica Abteilung A, Palaozoologie, Stratigraphie, v. 188, p. 153– 3362
197. 3363
Putron, S.J., McCorkle, D.C., Cohen, A.L., and Dillon, A.B., 2010, The impact of seawater 3364
saturation state and bicarbonate ion concentration on calcification by new recruits of two 3365
Atlantic corals: Coral Reefs, v. 30, no. 2, p. 321–328, doi: 10.1007/s00338-010-0697-z. 3366
R Core Development Team, 2010. R: a language and environment for statistical computing:, no. 3367
ISBN 3-900051-07-0. 3368
Racki, G., and Cordey, F., 2000, Radiolarian palaeoecology and radiolarites: is the present the 3369
key to the past?: Earth-Science Reviews, v. 52, p. 83–120. 3370
Raup, D., and Michelson, A., 1965, Theoretical morphology of the coiled shell.: Science (New 3371
York. 3372
Raup, D.M., 1967, Geometric analysis of shell coiling: coiling in ammonoids: Journal of 3373
Paleontology,, p. 43–65. 3374
Raup, D.M., 1966, Geometric analysis of shell coiling: general problems: Journal of 3375
Paleontology,, p. 1178–1190. 3376
Ries, J.B., Cohen, A.L., and McCorkle, D.C., 2009, Marine calcifiers exhibit mixed responses to 3377
CO2-induced ocean acidification: Geology, v. 37, no. 12, p. 1131, doi: 10.1130/G30210A.1. 3378
Ritterbush, K.A., and Bottjer, D.J., 2012, Westermann Morphospace displays ammonoid shell 3379
shape and hypothetical paleoecology: Paleobiology, v. 38, no. 3, p. 424–446, doi: 3380
10.1666/10027.1. 3381
Romano, C., Goudemand, N., Vennemann, T.W., Ware, D., Schneebeli-Hermann, E., Hochuli, 3382
P.A., Bruhwiler, T., Brinkmann, W., and Bucher, H., 2012, Climatic and biotic upheavals 3383
following the end-Permian mass extinction: Nature Geoscience, v. 6, no. 1, p. 57–60, doi: 3384
143
10.1038/ngeo1667. 3385
Rosa, R., and Seibel, B.A., 2008, Synergistic effects of climate-related variables suggest future 3386
physiological impairment in a top oceanic predator: Proceedings of the National Academy of 3387
Sciences, v. 105, no. 52, p. 20776–20780. 3388
Rosas, S., 1994, Facies, diagenetic evolution, and sequence analysis along a SW-NE profile in 3389
the southern Pucará basin (Upper Triassic-Lower Jurassic), Central Peru: Heidelberger 3390
Geowissenschaftliche Abhandlungen. 3391
Rosas, S., Fontbote, L., and Tankard, A., 2007, Tectonic evolution and paleogeography of the 3392
Mesozoic Pucará Basin, central Peru: Journal of South American Earth Sciences, v. 24, no. 3393
1, p. 1–24, doi: 10.1016/j.jsames.2007.03.002. 3394
Ruhl, M., Deenen, M.H.L., Abels, H.A., Bonis, N.R., Krijgsman, W., and Kürschner, W.M., 3395
2010, Astronomical constraints on the duration of the early Jurassic Hettangian stage and 3396
recovery rates following the end-Triassic mass extinction (St Audrie's Bay/East 3397
Quantoxhead, UK): Earth and Planetary Science Letters, v. 295, no. 1-2, p. 262–276, doi: 3398
10.1016/j.epsl.2010.04.008. 3399
Saunders, A., and Reichow, M., 2009, The Siberian Traps and the End-Permian mass extinction: 3400
a critical review: Chinese Science Bulletin, v. 54, no. 1, p. 20–37, doi: 10.1007/s11434-008- 3401
0543-7. 3402
Saunders, W., Greenfest-Allen, E., and Work, D., 2008, Morphologic and taxonomic history of 3403
Paleozoic ammonoids in time and morphospace: Paleobilogy, v. 34, no. 1, p. 128-154. 3404
Saunders, W.B., and Shapiro, E.A., 1986, Calculation and simulation of ammonoid hydrostatics: 3405
Paleobiology, v. 12, no. 1, p. 64–79. 3406
Savrda, C.E., and Bottjer, D.J., 1988, Limestone concretion growth documented by trace-fossil 3407
relations: Geology, v. 16, no. 10, p. 908–911. 3408
Schaltegger, U., Guex, J., Bartolini, A., Schoene, B., and Ovtcharova, M., 2008, Precise U–Pb 3409
age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian 3410
post-extinction recovery: Earth and Planetary Science Letters, v. 267, no. 1, p. 266–275. 3411
Schoene, B., Guex, J., Bartolini, A., Schaltegger, U., and Blackburn, T.J., 2010, Correlating the 3412
end-Triassic mass extinction and flood basalt volcanism at the 100 ka level: 3413
libproxy.usc.edu, v. 38, no. 12, p. 387–390, doi: 10.1130/G24017A.1. 3414
Schubert, J.K., and Bottjer, D.J., 1995, Aftermath of the Permian-Triassic mass extinction event: 3415
Paleoecology of Lower Triassic carbonates in the western USA: Palaeogeography, 3416
Palaeoclimatology, Palaeoecology, v. 116, no. 1, p. 1–39. 3417
Seibel, B.A., 2007, On the depth and scale of metabolic rate variation: scaling of oxygen 3418
consumption rates and enzymatic activity in the Class Cephalopoda (Mollusca): Journal of 3419
Experimental Biology, v. 210, no. 1, p. 1–11, doi: 10.1242/jeb.02588. 3420
144
Seibel, B.A., and Drazen, J.C., 2007, The rate of metabolism in marine animals: environmental 3421
constraints, ecological demands and energetic opportunities: Philosophical Transactions of 3422
the Royal Society B: Biological Sciences, v. 362, no. 1487, p. 2061–2078, doi: 3423
10.1098/rstb.2007.2101. 3424
Selden, P.A. (Ed.), 2009, Mollusca 4, Vol. 2. Carboniferous and Permian Ammonoidea. Part L 3425
(Revised) of R. C. Moore, ed. Treatise on Invertebrate Paleontology: Geological Society of 3426
America, Boulder, Colorado and University of Kansas, Lawrence. 3427
Sempere, T., Carlier, G., Soler, P., Fornari, M., Carlotto, V., Jacay, J., Arispe, O., Néraudeau, D., 3428
Cárdenas, J., and Rosas, S., 2002, Late Permian–Middle Jurassic lithospheric thinning in 3429
Peru and Bolivia, and its bearing on Andean-age tectonics: Tectonophysics, v. 345, no. 1, p. 3430
153–181. 3431
Senowbari-Daryan, B., and Stanley, G.D., 1994, Mesozoic sponge assemblage in Peru: Zbl. 3432
Geol. Paläont. Teil I,, p. 403–412. 3433
Sepkoski, J.J., Jr, 1981, A factor analytic description of the Phanerozoic marine fossil record: 3434
Paleobiology, v. 7, n. 1, p. 36–53. 3435
Siever, R., 1991, Silica in the oceans: biological-geochemical interplay: Scientists on Gaia, MIT 3436
Press, p. 287–295. ISBN: 9780262691604 3437
Smith, P.L., 1986, The implications of data base management systems to paleontology: a 3438
discussion of Jurassic ammonoid data: Journal of Paleontology,, p. 327–340. 3439
Sobolev, S.V., Sobolev, A.V., Kuzmin, D.V., Krivolutskaya, N.A., Petrunin, A.G., Arndt, N.T., 3440
Radko, V.A., and Vasiliev, Y.R., 2011, Linking mantle plumes, large igneous provinces and 3441
environmental catastrophes: Nature, v. 477, no. 7364, p. 312–316. 3442
Sole, R.V., Montoya, J.M., and Erwin, D.H., 2002, Recovery after mass extinction: evolutionary 3443
assembly in large-scale biosphere dynamics: Philosophical Transactions of the Royal Society 3444
B: Biological Sciences, v. 357, no. 1421, p. 697–707, doi: 10.1098/rstb.2001.0987. 3445
Song, H., Wignall, P.B., Tong, J., Bond, D.P.G., Song, H., Lai, X., Zhang, K., Wang, H., and 3446
Chen, Y., 2012, Earth and Planetary Science Letters: Earth and Planetary Science Letters, v. 3447
353-354, no. c, p. 12–21, doi: 10.1016/j.epsl.2012.07.005. 3448
Stanley, G.D., Jr, 2003, The evolution of modern corals and their early history: Earth-Science 3449
Reviews, v. 60, no. 3, p. 195–225. 3450
Stanley, S.M., 2006, Influence of seawater chemistry on biomineralization throughout 3451
phanerozoic time: Paleontological and experimental evidence: Palaeogeography, 3452
Palaeoclimatology, Palaeoecology, v. 232, no. 2-4, p. 214–236, doi: 3453
10.1016/j.palaeo.2005.12.010. 3454
Stanley, S.M., 2009, Evidence from ammonoids and conodonts for multiple Early Triassic mass 3455
extinctions: Proceedings of the National Academy of Sciences, v. 106, no. 36, p. 15264– 3456
145
15267, doi: 10.1073/pnas.0907992106. 3457
Staples, J.F., Webber, D.M., and Boutilier, R.G., 2003, Environmental Hypoxia Does Not 3458
Constrain the Diurnal Depth Distribution of Free-Swimming Nautilus pompilius: 3459
Physiological and Biochemical Zoology, v. 76, no. 5, p. 644–651, doi: 10.1086/376428. 3460
Stuecker, M.F., and Zeebe, R.E., 2010, Ocean chemistry and atmospheric CO2 sensitivity to 3461
carbon perturbations throughout the Cenozoic: Geophysical Research Letters, v. 37, no. 3, 3462
doi: 10.1002/grl.50792. 3463
Sun, Y., Joachimski, M.M., wignall, P.B., Yan, C., Chen, Y., Jiang, H., Wang, L., and Lai, X., 3464
2012, Lethally Hot Temperatures During the Early Triassic Greenhouse: Science, v. 338, no. 3465
6105, p. 366–370, doi: 10.1126/science.1224126. 3466
Szekely, T.S., and Grose, L.T., 1972, Stratigraphy of the Carbonate, Black Shale, and Phosphate 3467
of the Pucara Group (Upper Triassic--Lower Jurassic), Central Andes, Peru: Bulletin of the 3468
Geological Society of America, v. 83, no. 2, p. 407–428. 3469
Talmage, S.C., and Gobler, C.J., 2009, The effects of elevated carbon dioxide concentrations on 3470
the metamorphosis, size, and survival of larval hard clams (Mercenaria mercenaria), bay 3471
scallops (Argopecten irradians), and Eastern oysters (Crassostrea virginica): Limnology and 3472
oceanography, v. 54, no. 6, p. 2072. 3473
Tambutte, E., Tambutte, S., Segonds, N., Zoccola, D., Venn, A., Erez, J., and Allemand, D., 3474
2011, Calcein labelling and electrophysiology: insights on coral tissue permeability and 3475
calcification: Proceedings of the Royal Society B: Biological Sciences, v. 279, no. 1726, p. 3476
19–27, doi: 10.1146/annurev.nutr.010308.161202. 3477
Tanabe, K., and Mapes, R.H., 1995, Jaws and radula of the Carboniferous ammonoid 3478
Cravenoceras: Journal of Paleontology,, p. 703–707. 3479
Tanabe, K., Mapes, R.H., SASAKI, T., and Landman, N.H., 2000, Soft‐part anatomy of the 3480
siphuncle in Permian prolecanitid ammonoids: Lethaia, v. 33, no. 2, p. 83–91. 3481
Taylor, A.S., 2000, Chemical weathering rates and Sr isotopes: Yale University, 256 p. 3482
Taylor, D., 1982, Jurassic shallow marine invertebrate depth zones, with exemplification from 3483
the Snowshoe Formation, Oregon: Oregon Geology, v. 44, p. 51–56. 3484
Taylor, D., and Guex, J., 2002, The Triassic/Jurassic system boundary in the John Day inlier, 3485
east-central Oregon: Oregon Geology, v. 64, p. 3–28. 3486
Taylor, D.G., 1998, Late Hettangian-Early Sinemurian (Jurassic) ammonite biochronology of the 3487
Western Cordillera, United States: Geobios, v. 31, no. 4, p. 467–497. 3488
Taylor, D.G., Smith, P.L., Laws, R.A., and Guex, J., 1983, The stratigraphy and biofacies trends 3489
of the Lower Mesozoic Gabbs and Sunrise formations, west-central Nevada: Canadian 3490
Journal of Earth Sciences, v. 20, p. 1598–1608. 3491
146
Thorne, P.M., Ruta, M., and Benton, M.J., 2011, Resetting the evolution of marine reptiles at the 3492
Triassic-Jurassic boundary: Proceedings of the National Academy of Sciences, v. 108, no. 3493
20, p. 8339–8344. 3494
Tozer, E.T., 1994, Canadian Triassic Ammonoid Faunas: Geological Survey of Canada. 3495
Tsujita, C.J., and EG Westermann, G., 1998, Ammonoid habitats and habits in the Western 3496
Interior Seaway: a case study from the Upper Cretaceous Bearpaw Formation of southern 3497
Alberta, Canada: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 144, no. 1, p. 135– 3498
160. 3499
Tucker, M.E., and Wright, V.P., 1990, Carbonate Sedimentology: Blackwell Scientific, Boston. 3500
Twitchett, R.J., 2006, The palaeoclimatology, palaeoecology and palaeoenvironmental analysis 3501
of mass extinction events: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 232, no. 3502
2-4, p. 190–213, doi: 10.1016/j.palaeo.2005.05.019. 3503
Twitchett, R.J., Krystyn, L., Baud, A., Wheeley, J.R., and Richoz, S., 2004, Rapid marine 3504
recovery after the end-Permian mass-extinction event in the absence of marine anoxia: 3505
Geology, v. 32, no. 9, p. 805, doi: 10.1130/G20585.1. 3506
Urdy, S., Goudemand, N., Bucher, H., and Chirat, R., 2010a, Allometries and the morphogenesis 3507
of the molluscan shell: a quantitative and theoretical model: Journal of Experimental 3508
Zoology Part B: Molecular and Developmental Evolution, v. 314, no. 4, p. 280–302. 3509
Urdy, S., Goudemand, N., Bucher, H., and Chirat, R., 2010b, Growth‐dependent phenotypic 3510
variation of molluscan shells: implications for allometric data interpretation: Journal of 3511
Experimental Zoology Part B: Molecular and Developmental Evolution, v. 314, no. 4, p. 3512
303–326. 3513
Uriz, M.J., Turon, X., and Becerro, M., 2000, Silica deposition in Demosponges: spiculogenesis 3514
in Crambe crambe: Cell and Tissue Research. 3515
Uriz, M.J., Turon, X., Becerro, M.A., and Agell, G., 2003, Siliceous Spicules and Skeleton 3516
Frameworks in Sponges: Origin, Diversity, Ultrastructural Patterns, and Biological 3517
Functions: Microscopy Research and Technique, v. 62, p. 279–299, doi: 3518
10.1002/jemt.10395. 3519
van de Schootbrugge, B., Tremolada, F., Rosenthal, Y., Bailey, T.R., Feist-Burkhardt, S., 3520
Brinkhuis, H., Pross, J., Kent, D.V., and Falkowski, P.G., 2007, End-Triassic calcification 3521
crisis and blooms of organic-walled “disaster species”: Palaeogeography, Palaeoclimatology, 3522
Palaeoecology, v. 244, no. 1-4, p. 126–141, doi: 10.1016/j.palaeo.2006.06.026. 3523
Vance, R.R., 1973, On reproductive strategies in marine benthic invertebrates: American 3524
Naturalist,, p. 339–352. 3525
Veron, J., Hoegh-Guldberg, O., Lenton, T.M., Lough, J.M., Obura, D.O., Pearce-Kelly, P., 3526
Sheppard, C., Spalding, M., Stafford-Smith, M.G., and Rogers, A.D., 2009, The coral reef 3527
147
crisis: The critical importance of <350 ppm CO2: Marine Pollution Bulletin, v. 58, no. 10, p. 3528
1428–1436. 3529
Veron, J.E.N., 2011, Ocean Acidification and Coral Reefs: An Emerging Big Picture: Diversity, 3530
v. 3, no. 2, p. 262–274, doi: 10.3390/d3020262. 3531
Walker, L.J., Wilkinson, B.H., and Ivany, L.C., 2002, Continental drift and Phanerozoic 3532
carbonate accumulation in shallow‐shelf and deep‐marine settings: The Journal of geology, 3533
v. 110, no. 1, p. 75–87, doi: 10.1086/324318. 3534
Ward, P., 1980, Comparative shell shell shape distributions in Jurassic-Cretaceous ammonites 3535
and Jurassic-Tertiary Nautilids: Paleobiology, n. 6, n. 1, p. 32-43. 3536
Ward, P., McRoberts, C., and Williford, K., 2009, Reply to comment on: "The organic carbon 3537
isotopic and paleontological record across the Triassic–Jurassic boundary at the candidate 3538
GSSP section at Ferguson Hill, Muller Canyon, Nevada, USA" by Ward et al., (2007): 3539
Palaeogeography, Palaeoclimatology, Plaeoecology, v. 273, p. 205-206. 3540
Ward, P.D., and Signor, P.W., III, 1983, Evolutionary tempo in Jurassic and Cretaceous 3541
ammonites: Paleobiology,, p. 183–198. 3542
Ward, P.D., Garrison, G.H., Williford, K.H., Kring, D.A., Goodwin, D., Beattie, M.J., and 3543
McRoberts, C.A., 2007, The organic carbon isotopic and paleontological record across the 3544
Triassic–Jurassic boundary at the candidate GSSP section at Ferguson Hill, Muller Canyon, 3545
Nevada, USA: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 244, no. 1-4, p. 281– 3546
289, doi: 10.1016/j.palaeo.2006.06.042. 3547
Ward, P.D., Haggart, J.W., Carter, E.S., Wilbur, D., Tipper, H.W., and Evans, T., 2001, Sudden 3548
productivity collapse associated with the Triassic-Jurassic boundary mass extinction: 3549
Science, v. 292, no. 5519, p. 1148–1151. 3550
Ware, D., Jenks, J.F., Hautmann, M., and Bucher, H., 2011, Dienerian (Early Triassic) 3551
ammonoids from the Candelaria Hills (Nevada, USA) and their significance for 3552
palaeobiogeography and palaeoceanography: Swiss Journal of Geosciences, v. 104, no. 1, p. 3553
161–181, doi: 10.1007/s00015-011-0055-3. 3554
Watson, S.-A., Southgate, P.C., Tyler, P.A., and Peck, L.S., 2009, Early larval development of 3555
the Sydney rock oyster Saccostrea glomerata under near-future predictions of CO2-driven 3556
ocean acidification: Journal of Shellfish Research, v. 28, no. 3, p. 431–437. 3557
Weiss, I.M., Tuross, N., Addadi, L., and Weiner, S., 2002, Mollusc larval shell formation: 3558
amorphous calcium carbonate is a precursor phase for aragonite: Journal of Experimental 3559
Zoology, v. 293, no. 5, p. 478–491, doi: 10.1002/jez.90004. 3560
Westermann, G.E.G., 1996, Ammonoid Life and Habitat, in Landman, N., Tanabe, K., and 3561
Davis, R.A. eds., Ammonoid Paleobiology, Plenum Press, New York, p. 607–707. 3562
Westermann, G.E.G., 1992, The Jurassic of the Circum-Pacific: Cambridge Univ Press, New 3563
148
York. 3564
Whiteside, J., and Ward, P.D., 2011, Ammonoid diversity and disparity track episodes of chaotic 3565
carbon cycling during the early Mesozoic: Geology, v. 39, p. 99–102. 3566
Whiteside, J.H., Olsen, P.E., Eglinton, T., Brookfield, M.E., and Sambrotto, R.N., 2010, From 3567
the Cover: Compound-specific carbon isotopes from Earth's largest flood basalt eruptions 3568
directly linked to the end-Triassic mass extinction: Proceedings of the National Academy of 3569
Sciences, v. 107, no. 15, p. 6721–6725, doi: 10.1073/pnas.1001706107. 3570
Wiedmann, J., 1973, Evolution or revolution of ammonoids at Mesozoic system boundaries: 3571
Biological Reviews, v. 48, p. 159–194. 3572
Wignall, P.B., and Twitchett, R.J., 2002, Extent, duration, and nature of the Permian-Triassic 3573
superanoxic event: SPECIAL PAPERS-GEOLOGICAL SOCIETY OF AMERICA,, p. 395– 3574
414. 3575
Wilmsen, M., and Mosavinia, A., 2011, Phenotypic plasticity and taxonomy of Schloenbachia 3576
varians (J. Sowerby, 1817)(Cretaceous Ammonoidea): Paläontologische Zeitschrift, v. 85, 3577
no. 2, p. 169–184. 3578
Winguth, C., and Winguth, A.M.E., 2012, Simulating Permian-Triassic oceanic anoxia 3579
distribution: Implications for species extinction and recovery: Geology, v. 40, no. 2, p. 127– 3580
130, doi: 10.1130/G32453.1. 3581
Wootton, J.T., Pfister, C.A., and Forester, J.D., 2008, Dynamic patterns and ecological impacts 3582
of declining ocean pH in a high-resolution multi-year dataset: Proceedings of the National 3583
Academy of Sciences, v. 105, no. 48, p. 18848–18853. 3584
Wyld, S.J., 2000, Triassic evolution of the arc and backarc of northwestern Nevada and evidence 3585
for extenstional tectonism, in Soreghan, M.J. and Gehrels, G.E. eds., Paleozoic and Triassic 3586
Paleogeography and Tectonics of Western Nevada and Northern California, Geological 3587
Society of America Special Paper, p. 185–207. 3588
Yacobucci, M.M., 2003, Controls on shell shape in acanthoceratid ammonites from the 3589
Cenomanian-Turonian Western Interior Seaway 3590
, in Harrie, P.J. and Geary, D.H. eds., High-resolution approaches in stratigraphic paleontology, 3591
Plenum Press, New York, p. 195–223. 3592
Yacobucci, M.M., 2004, Neogastroplites meets Metengonoceras: morphological response of an 3593
endemic hoplitid ammonite to a new invader in the mid-Cretaceous Mowry Sea of North 3594
America: Cretaceous Research, v. 25, p. 927–944, doi: 10.1016/j.cretres.2004.09.001. 3595
Yates, A.M., Bonnan, M.F., Neveling, J., Chinsamy, A., and Blackbeard, M.G., 2010, A new 3596
transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the 3597
evolution of sauropod feeding and quadrupedalism: Proceedings of the Royal Society B: 3598
Biological Sciences, v. 277, no. 1682, p. 787. 3599
149
Zajzon, N., Kristály, F., Pálfy, J., and Németh, T., 2012, Detailed clay mineralogy of the 3600
TriassicJurassic boundary section at Kendlbachgraben (Northern Calcareous Alps, Austria): 3601
Clay Minerals, v. 47, no. 2, p. 177–189, doi: 10.1180/claymin.2012.047.2.03. 3602
Zakharov, Y., and Mousavi Abnavi, N., 2011, The ammonoid recovery after the end-Permian 3603
mass extinction: evidence from the Iran-Transcaucasia area, Siberia, Primorye, and 3604
Kazakhstan: Acta Palaeontologica Polonica,, doi: 10.4202/app.2011.0054. 3605
Zimmerle, W., 1991, Stratigraphic distribution, lithological paragenesis, depositional 3606
environments and diagenesis of fossil siliceous sponges in Europe, in Reitner, J. and Keupp, 3607
H. eds., Fossil and Recent Sponges, Springer-Verlag, Berlin Heidelberg. 3608
150
Table
1.1.
Candidate
Global
Stratotype
Section
and
Point
(GSSP)
locations
considered
by
the
International
Subcommission
on
Jurassic
Stratigraphy
(ISJS)
Location
Reference
Depositional
setting
Paleo-‐geography
Kujoch
Section,
Karwendal
Mountains,
Tyrol,
Austria
von
Hillenbrandt
et
al.,
2007,
p.
1-‐20.
ISJS
Newsletter
34
Inter-‐platform
trough
Tethys
Kunga
Island,
Queen
Charlotte
Islands,
Brittish
Columbia,
Canada
Longridge,
et
al.,
2007,
p.
21-‐33.
ISJS
Newsletter
34
Outer
shelf
to
upper
slope
setting
NE
Panthalassa;
connected
to
open
ocean
New
York
Canyon,
Nevada,
USA
Lucas
et
al.,
2007,
p.
34-‐
42.
ISJS
Newsletter
34
Between
storm
and
fairweather
wave
base
on
a
narrow
shelf
Back-‐arc
basin
along
NE
Panthalassa
Waterloo
Bay,
Larne,
Northern
Ireland
Simms
and
Jeram,
2007,
p.
50-‐68.
ISJS
Newsletter
34
Triassic
strata:
above
wave
base
to
emersive;
Jurassic
strata:
hemipelagic
marine
mudstone
Tethys;
Northwestern
European
Seaway
Chilingote
site
in
the
Utcubamba
Valley,
Northern
Peru
von
Hillenbrandt,
1994,
Geobios
27,
Special
Issue
2,
p
297-‐307.
Outer
carbonate
ramp
Back-‐arc
basin
along
SE
Panthalassa
St.
Audrie’s
Bay
–
Doniford
Bay,
Somerset,
England
Warrington
et
al.,
2008;
ISJS
Newsletter
35
Debated;
includes
foreshore
and
erosion
surfaces
Tethys
151
Table
5.1
Values
for
Estimation
of
Marine
Silica
Doubling
and
Residence
Times
Variable
Value
Units
Source
Weathering
factors
A
range
from
0.1:20
none
weathering
intensity
factors,
x
axis
for
the
residence
and
doubling
time
contour
plots
Modern
silica
inventory
in
oceans
(baseline
for
the
silica
inventory
variable)
10
17
moles
Treguer,
1995
Modern
silica
concentration
8
x
10
-‐5
mM
{Sarmiento:2006vs}
Amorphous
silica
solubility
1.25
*
10
-‐2
mM
{Sarmiento:2006vs}
Modern
silica
input
from
rivers
5.6*10
12
mol
yr
-‐1
DeMaster,
2002
Modern
silica
input
from
eolian
transport
0.5*10
12
mol
yr
-‐1
DeMaster,
2002
Modern
silica
input
from
hydrothermal
0.6*10
12
mol
yr
-‐1
DeMaster,
2002
Modern
land
area
subject
to
weathering
1.21*10
8
km
2
Hartmann
et
al.,
2009
Pangean
land
area
2.0*10
8
km
2
{Bradley:2011fd}
152
Table
5.2
Values
for
Mass
Balance
of
Sponge
Silica
Demand
Variable
Value
Unit
Source
Hexactinellid
silica
demand
2.5836
mol
m-‐2
yr-‐1
Maldonado
et
al.,
2011
Demosponge
silica
demand
0.3285
mol
m-‐2
yr-‐1
{Maldonado:2011ud}
Earliest
Jurassic
shelf
area
55
*
10
6
km
2
{Walker:2002kz},
fig.
6
Earliest
Jurassic
tropical
carbonate
shelf
area
10*
10
6
km
2
Walker
et
al.,
2002,
fig.
6
Earliest
Jurassic
tropical
total
shelf
area
23.4*
10
6
km
2
Walker
et
al.,
2002,
fig.
6
Earliest
Jurassic
tropical
total
shelf
area
22.5*
10
6
km
2
Walker
et
al.,
2002,
fig.
3
habitat
10
13
m
2
Estimated
tropical
carbonate
shelf
area
from
Walker
et
al.,
2002.
153
Table
7.1
Parameters
of
Westermann
Morphospace
Parameter
Maximized
in
Calculation
Exposure
of
umbilicus
serpenticone
=
Overall
inflation
sphaerocone
ℎ=
Whorl
expansion
oxycone
=
!
In
Westermann
Morphospace,
outer
shell
shape
is
characterized
by
three
parameters.
Each
parameter
is
maximized
in
one
of
the
end-‐member
morphotypes,
and
minimized
in
the
opposing
two.
154
Table
7.2
Scaling
Parameters
for
Westermann
Morphospace
Variable
Morphotype
clusters
(Arkell
et
al.
1957;
Selden
2009)
Normal
ammonoids
(Raup
1967)
Westermann
Morphospace
Scaling
values
(eq.
10)
Min
(mean
–
2σ)
Opposing
clusters
Max
(mean)
Representativ
e
cluster
Min
(mean
–
2σ)
Max
(mean)
Min
Max
U
0
0.47
0
0.60
0
0.52
Th
0.15
0.74
0.068
0.59
0.14
0.68
w
0.99
1.50
1.1
1.78
1.0
1.77
Total
residual
25%
21%
1.1%
Scaling
values
associated
with
three
morphotypes
(Arkell
et
al.1957;
Selden
2009),
with
normal
ammonoids
(Raup
1967),
and
the
values
used
to
scale
Westermann
Morphospace.
When
each
set
of
minimum
and
maximum
values
is
applied
to
the
morphotype
means
in
equation
(10),
each
morphotype
mean
plots
close
to
60%
of
the
appropriate
corner,
but
there
is
some
residual,
shown
in
the
bottom
row.
The
Westermann
Morphospace
scaling
values
were
generated
by
an
iterative
process
that
started
with
values
shown
for
normal
ammonoids
(Raup
1967)
and
altered
them
to
minimize
the
residuals.
Note
that
the
scaling
values
of
Westermann
Morphospace
differ
from
the
values
of
normal
ammonoids
by
being
closer
to
values
given
by
the
morphotype
clusters.
155
Table
8.1
Correlation
of
Hydrodynamic
Efficiency
of
Ammonoid
Specimens
from
Jacobs
(1992)
to
their
Percent
Characterization
by
each
Parameter
of
Westermann
Morphospace.
Genus
Diameter
a
Umbilical
Diameter
b
Power
required
2.5
cm
length,
2.5
cm/s
speed
(ergs/s/cm3)
Power
required
10
cm
length,
25
cm/s
speed
(ergs/s/cm3)
Sphenodiscus
5.13
3.22
0.32
1
5.71
450
Cardioceras
4.84
2.04
1.35
1
5.82
449
Oppelia
4.32
2.22
0.78
1.1
4.52
391
Cadoceras
5.02
2.16
1.31
3.1
3.32
831
Lytoceras
5.77
2.13
2.02
1.91
3.29
783
Gastroplites
5.32
2.70
1.29
2.25
2.59
589
Scaphites
3.5
1.93
0.48
1.6
2.15
567
U%
p
=
0.9402
p
=
0.478
w%
p
=
0.5658
p
=
0.0259
Th%
p
=
0.028
p
=
0.0347
156
Table
8.2
Morphologic
Categorization
of
Boreal
Ammonoid
Species
by
Subzone.
Subzone
Concavum
Boreal
Commune
Strigatus
Candidus
Sverdrupi_I
Sverdrupi_II
Sverdrupi_II_III
Sverdrupi_III
Hedenstroemi
Romunderi
Tardus
Pilaticus
Subrobustus
p
value;
correlation
to
total
Grisbachian
-‐
Smithian
Spathian
oxycones
1
1
0
2
2
1
1
2
2
1
4
4
4
7
0.0035
18
3
serpenticones
0
0
3
1
3
0
1
1
0
0
7
3
0
3
8.39E-‐06
38
3
intermediate
1
2
3
2
7
0
1
2
1
0
5
14
1
2
0.0035
20
11
sphaerocones
0
0
0
1
1
0
0
0
0
0
6
1
0
5
0.00013
8
5
n
2
3
6
6
13
1
3
5
3
1
22
22
5
17
84
22
Stage
Griesbachian
Dienerian
Smithian
Spath.
157
Table
8.3.
Genus
Diversity
and
Endemism
Cosmopolitan
Global
Total
Global
Endemic
Global
British
Columbia
South
China
Pakistan
Griesbachian
11
1
10
8
8
5
Dienerian
23
8
15
14
14
12
Smithian
61
19
42
21
30
19
Spathian
93
44
42
17
25
10
158
Table
8.4.
Morphologic
Categorization
of
Smithian
Species
by
Region
Boreal
US
West
S
China
Pakistan
Serpenticones
10
14
24
30
Intermediates
19
24
29
48
Oxycones
8
27
36
32
Sphaerocones
6
4
10
4
p
value
0.02265
0.03549
0.2248
The
p
values
are
for
chi
square
tests
of
the
number
of
oxycones
vs
all
other
species,
compared
to
the
Boreal
ammonoids.
159
Table
8.5
Morphologic
Categorization
of
Ammonoid
Species
Hettangian
G-‐Sm
Boreal
Smithian
US
West
Smithian
S
China
Smithian
Pakistan
Serpenticones
28
16
14
24
30
Other
morphs
19
66
55
75
84
p
value
when
compared
to
Hettangian
1.15E-‐05
3.70E-‐05
6.88E-‐05
0.000136
160
-31 -30 -29 -28 -27 -26 -25
δ
13
C
org
Rhaetian (Tr) Hettangian (J)
Rhaetian Hettangian (J)
1 m
<<290,000 years
Pucara basin (N. Peru)
New York Canyon (Nevada, USA)
AC5
N3
N6b
N6c
N9
N11
N13
M2
1 m
TJB
extinction interval
extinction interval
200.5
201.0
201.5
202.0
MESOZOIC
Cretaceous Jurassic Triassic
L
M
E
L
M
E
L
E
199.5 Ma ± 0.29
203.6 Ma ± 1.5
Rhaetian (Late Triassic)
Hettangian (Early Jurassic)
201.29
+/- 0.16
201.36
+/- 0.13
201.40
+/- 0.18
201.33
=/- 0.13
Siltstone Black shale
Ash bed
Thick bed limestone
Thin bed limestone
Carb. siltstone
Pulses of
CAMP Volcanism
Marine
Biostratigraphy
Figure 1.1
161
Figure
1.1
Timeline
of
events
during
the
transition
from
the
Triassic
to
the
Jurassic
Period,
including
the
end-‐Triassic
extinction
at
205.5
Mya
and
the
Triassic/Jurassic
boundary
at
201.3
Mya.
The
lowest
tested
occurrences
of
Central
Atlantic
Magmatic
Province
(CAMP)
basalts
show
a
series
of
eruption
events
spanning
600
kyr
(after
Blackburn
et
al.,
2013).
The
oldest
events
coincide
with
turnover
of
pollen
and
other
biostratigraphic
markers
of
the
end-‐Triassic
Mass
Extinction
at
about
201.56
Mya
(U/Pb
on
zircons),
and
the
last
occurrence
of
Choristoceras
crickmayi
in
marine
strata
(after
Schoene
et
al.,
2010).
U/Pb
dating
on
ash
beds
adjacent
to
the
first
occurrence
of
Psiloceras
spelae
place
the
Triassic/Jurassic
boundary
at
201.33
+/-‐
0.43
Mya.
Combining
these
new
dates
puts
about
250
kyr
between
the
extinction
and
first
Jurassic
ammonite
that
marks
the
system
boundary.
Rhaetian
(estimated)
and
Hettangian
dates
and
timeline
after
Greene
et
al.
(2012b).
162
Shallow
Deep
2
3
8
5
7
10
4
16
6 12
Pangaea
Tethys
Panthalassa
14
1
9
11
12
15
13
2
3
8
5
7
10
4
16
6 12
14
1
9
11
12
15
13
5
16
14
1
17
6
9
11
2
3
8
7
10
4
12 12
15
13
Shallow Shelf
Deep Basin
Carbonate Gap
Continuous Carbonate
Siliclastic
FIgure 1.2 Reconstruction of Pangea at the Triassic/Jurassic transition, showing the paleogeographic settings of sites with recognized fossilif-
erous marine records of the system boundary, after Greene et al., (2012). Squares indicate shelf settings and circles indicate basin settings.
Siliciclastic settings are marked in blue, apparent continously carbonate settings are shown in white, and settings with an apparent carbonate
gap are shown in red. See Greene et al., (2012) for a description of each site. Inadequate sedimentologic and paleontologic resolution to
distinguish the pressence and nature of carbonate gaps from present literature partly motivated the eld investigations documented in Part I,
chapters 1 and 2. All sites taken from the review by Greene et al., (2012); 1: Queen Charlotte Islands, British Columbia, Canada (Ward et al.,
2001, 2004; Carter and Orchard, 2007); 2: Williston Lake, British Columbia, Canada (Wignall et al., 2007); 3:New York Canyon, Nevada, USA
(Guex et al., 2004); 4: Chilingcote, Utcubamba Valley, Peru (von Hillebrandt, 1994; Hautmann, 2004; Schaltegger et al., 2008); 5: St. Audrie's Bay,
England (Hesselbo et al., 2002, 2004; Warrington et al., 2008); 6: Asturias, Northern Spain (Barrón et al., 2006); 7: Mingolsheim core, Germany
(Quan et al., 2008; van de Schootbrugge et al., 2008); 8: Northern Calcareous Alps, Austria (Hallam and Goodfellow, 1990; von Hillebrandt et al.,
2007; Ruhl et al., 2009); 9: Csővár section, northern Hungary (Pálfy et al., 2001, 2007; Zajzon, 2003); 10: Tatra Mountains (Carpathians) Slovakia
(Michalík et al., 2007, 2010); 11: Tolmin Basin (Southern Alps), Slovenia (Rožič, 2008; Rožič et al., 2009); 12: Lombardian Basin (Southern Alps),
Italy (Galli et al., 2005, 2007); 13: Budva Basin (Dinarides), Montenegro (Črne et al., 2011); 14: Southern Apennines, Italy (Reggiani et al., 2005);
15: Northern and Central Apennines, Italy (Ciarapica, 2007); 16: Germig, Tibet (Hallam et al., 2000); 17: Southwest Japan (Hori et al., 2007).
163
Fig. 2.1: Paleogeographic maps (top) and tectonic reconstructions (bottom) modied from Ron Blakey
for the Late Triassic (ca. 215 Mya), left, and the Early Jurassic (ca. 180 Mya), right. The yellow star
approximates the depositional setting for the Triassic/ Jurassic boundary strata now exposed in the
Gabbs Vallye Range of West Central Nevada, USA.
164
6,000’
5,750’
5,500’
5,250’
5,000’
4,750’
6,500’
6,250’
6,000’
5,750’
5,500’
5,250’
Reno Draw
Muller Canyon
A
A’
A”
B
B’
B’ B
A A’ A”
Figure 2.2 Geologic map and cross sections of the Gabbs Valley Range around New York Canyon, Nevada, USA, after
Muller and Ferguson (1939) and Guex (1995). Members of the Gabbs Formation are the Nun Mine (2), Mount Hyatt (3),
and Muller Canyon Member (4). The Norian/Rhaetian boundary occurs within the Mt. Hyatt Member, and the Triassic
Jurassic bounary occurs midway through the Muller Canyon Member (see text). Members of the Sunrise Formation are
the Ferguson Hill (5,6), Five Card Draw (7), New York Canyon (8), Joker Peak (9) and Mina Peak (9) (Taylor et al., 1983).
Disconformity
9
8
7
6
5
4
3
2
1
10
11
Upper Triassic Lower Jurassic
Gabbs Formation Dunlop Fm Sunrise Formation Luning Fm
165
San
Francisco
Los
Angeles
Las
Vegas
Gabbs Valley
Range
Reno
Muller Canyon
Ferguson
Hill
Five Card
Draw
New York
Canyon
Joker
Peak
Mina
Peak
Nun
Mine
Sunrise Formation
Gabbs Formation
Pleinsbachian
Sinemurian
Hett. Rheatian
Upper Triassic
Lower Jurassic
Figure 2.3 Stratigraphy of the Upper Triassic and Lower Jurassic sedimentary rocks in the Gabbs Valley Range of
West Central Nevada, after Taylor et al., (1983). Inset map top right shows location of the Gabbs Vallye Range. Refer
to Figure 2.2 for the geologic map.
166
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Jackpot Hill
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Jackpot Hill
Muller Canyon
Reno Draw
10 meters
Aplite 3 South Primary
Ferguson Hill
NB
MCA
MCB
N9
Sinemurian
Hettangian
Sunrise
Formation
Gabbs
Formation
Triassic Period Jurassic Period
Hettangian Stage Rhaetian Stage
Marshi Zone Planorbis Zone Liasicum Angulata
8m/800kyr
100ky/m
.100 cm/kyr
8 m/750 kyr
93.75ky/m
.107 cm/kyr
17 m/250 kyr
14.7 kyr/m
6.80 cm/kyr
8m/120kyr
15 kyr/m
6.7 cm/kyr
10m/530
53ky/m
1.89 cm/ky
4m/520kyr
130kyr/m
.769 cm/kyr
8m/ 130 kyr
16.3 kyr/m
6.15 cm/kyr
20m/1030kyr
51.5 kyr/m
1.94 cm/kyr
Duration
Estimates
from Ruhl
et al., 2010
Duration
Estimates
from Bartolini
et al., 2012
Muller Canyon
Figure 3.31 Stratigraphic columns of the
Ferguson Hill Member of the Sunrise
Formation, showing the approximate net
rock accumulation rates calculated by
comparing the meters of stratigraphy to
the estimated geologic duration of each
ammonoid biozone.
Reno Draw Fault Gully
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SP-5ii
NB
MCA
MCB
3SPMCAiii
3SPMCAi
3SPMABi
3SPAx
3SPCiii
3SPCii
3SPDi
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
Aplite3Eyehole
Arch
BestSEM
3SP-4Popcorn
YadisBioherm
Aplite 3 middle
(book 1, 6/8/11)
StromoA3Middle
PM
N9
SF1A
SF1B
StromoGSSP
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
JigsawC
Cutie6
popcorn
A3N SEM2
A3N SEM
3SP-5viii
Lithologic Samples (stars)
Collection Year
2008
2009
2010
2011
3SP-5ix
3SP-5iix
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF13
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
SF7Concretion
SF7Matrix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
Wackestone
Grainstone
Particular
sponge taphonomy
Condensed
and insitu sponge
Spiculite
Siltstone
Thin section content
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic
Aplite 3 North
Muller Canyon
Reno Draw
Luning Draw
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
Jackpot Hill
Hettangian
Sinemurian
0.5 cm = 1 m
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SPMCAiii
3SPMCAi
3SPMABi
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
PM
N9
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF7
Concretion
SF7Matrix
SF1A
SF1B
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
SFNA
SFNC
Node Large
3SPAx
3SPCiii
3SPCii
3SPDi
SF1: 2m
N9
10
20
25
40
30
50
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
BestSEM
3SP-4Popcorn
3SP-5viii
3SP-5ix
3SP-5iix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
YadisBioherm
Cutie6
SF13B
SF13A
JigsawC
Aplite3Eyehole
Arch
A3N Gum
A3N SEM2
A3N SEM
StromoGSSP
StromoA3Middle
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
3SP-5ii
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Wackestone
Condensed
and in-situ sponge
Spiculite
Siltstone
Other
Thin section content
Figure 3.2 Composite Stratigraphic Column
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic Hettangian
Rhaetian
Thin sections
from Reno Draw
Thin Sections
from Muller Canyon
Thin sections
from Reno Draw
Thin Sections
from Muller Canyon
Hettangian
Sinemurian
0.5 cm = 1 m
N9
10
20
25
40
30
50
Silty cacarenite
CaCO3 concretions
Chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Figure 2.21 Fossil Survey Results
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic Hettangian
Rhaetian
36
338
57
52
5
6
7
36
Key to Fossil Survey Pie Charts
Solitary Scleractinian
Corals
Infaunal
Bivalves
Epifaunal Bivalves
Gastropods
Specimens
Infaunal and Epifuanal
Bivalves Recovered in
Bulk Sampling
Very Rare Epifaunal
Bivalves Spotted
167
Figure
2.4
Statigraphic
columns
measured
in
the
Gabbs
Valley
Range
of
west
central
Nevada,
USA.
Figure
2.5
Satellite
image
from
Google
Maps
(taken
10/20/2011)
showing
target
field
sites
and
chert
beds.
Dashed
lines
indicate
paths
to
walk
to
each
field
site.
Reno
Draw
is
best
reached
from
a
mine
at
the
end
of
the
road
north
of
New
York
Canyon.
Luning
Draw
and
Muller
Canyon
are
both
reached
from
New
York
Canyon.
Site
numbers
after
Guex
(1995).
Site
3
corresponds
roughly
to
Reno
Draw
stratigraphic
columns
for
3
South
Primary,
Aplite
3
North,
and
Aplite
3
Middle.
The
very
white
regions
of
the
satellite
image
are
outcrops
of
the
igneous
unit
mapped
as
aplite,
which
aids
matching
the
geologic
map
and
satellite
images.
Note
the
prominent
dark
stripes
that
can
be
traced
across
sites
3,
2,
and
1,
in
Reno
Draw,
and
the
stripes
spreading
between
sites
6
and
7
in
Muller
Canyon.
These
are
resistant
chert
cliffs
of
the
upper
Ferguson
Hill
Member
of
the
Lower
Jurassic
Sunrise
Formation.
168
Luning
Draw
Reno
Draw
Muller
Canyon
Ferguson
Hill
1
2
3
6
7
Figure 2.5
N
100 m
169
Figure 2.6 Photomosaic of the north wall of Muller Canyon, with the ridge to the right (NE) ending as Ferguson Hill. The prominent beds of chert
form resistant clis very visible on the satelite imagery (Fig. 2.5). The Ferguson Hill section was the proposed Global Stratotype Section and Point for
the Triassic/Jurassic boundary (Lucas et al., 2007), and contains some of the best exposed contact between the Muller Canyon Member (MCM) of
the Gabbs Formation and the Ferguson Hill Member (FHM) of the Sunrise Formation. The Triassic/Jurassic boundary occurs within the MCM (e.g.,
Guex et al., 2004). Guex’s (1995) sites 6 and 7 are marked (see map Figs. 2.2 and 2.5), and in the present work are represented as stratigraphic
sections for Muller Canyon and Ferguson Hill, respectively. Note the prominent faults near 6 and 7, which do not have much displacement.
6
7
MCM
FHM
170
Fig. 2.7 A closer view of the Triassic/Jurassic boundary strata on Ferguson Hill, showing the ssile talus
slopes of shales covering the light colored Muller Canyon Member strata, and the conformable transi-
tion to increasingly resistant limestones and cherts of the Ferguson Hill Member of the Sunrise Forma-
tion. Outcrops to the lower right of the image include the Mt Hyatt Member of the Gabbs Formation,
but this is oset from the Muller Canyon Member by a fault (Guex et al., 2007). The vertical fault in the
left portion of the image does not present much displacement, and can form a channel for water to
erode fresh outcrops during storms (Fig. i.6.8). IMG_157 taken May 14, 2009.
Fault
Muller Canyon Member
Ferguson Hill Member
171
Figure 2.8 Fresh outcrops of Muller Canyon Member strata exposed by the ash ood of May 31, 2009.
The sta is one meter. This photo was taken near the fault on Ferguson Hill shown in the left of Figure
2.7. IMG_254 taken June 3, 2009.
172
concretions
chert clis
173
Figure 2.10 View to the south west into Reno Draw from the saddle by the mine (shown in Figure 2.5 at the head of the dashed white line). The
three labeled outcrops at the left are oset by normal faults and correspond roughly to site 3 of Guex (1995), and are here refered to as Aplite 3
North (A3N), Aplite 3 Middle (A3M) and 3 South Primary (3SP). Each contains most of the cherty interval of the Ferguson Hill Member. Vlad’s Hill has
chert beds at the base and gastropod-rich wackestones at the top. See Figure 2.2 for a cross section from Muller and Ferguson (1939).
Vlad’s Hill
A3N
A3M
3SP
174
Figure 2.11 Photomosaic of outcrops spanning to the north east from Reno Draw, numbered as 1, 2, and 3 (A3N and A3M, see Fig. 2.10) following
Guex (1995). The photomosaic introduces distortion; photos centered at outcrop 1 are viewing roughly north east, and photos centered at outcrop
A3M are viewing roughly south west. Photos taken from the sadle above the mine in the road north of New York Canyon. The prominent dark cli
ridges are cherts of the upper Ferguson Hill Member of the Sunrise Formation.
A3M
A3N
2
1
175
Figure 2.12 Jackpot Hill, view approximately facing northeast, detail from site 1 in Figure 2.11. This hill is
very similar to Ferguson Hill, with ssile talus-covered beds of the Muller Canyon Member of the Gabbs
Formation along the slope (in pink), and conformable Ferguson Hill Member of the Sunrise Formation
above. This site was sampled by both Guex (1995) and Laws (1982). Like most outcrops, the hill ends
within the cherty beds, which form excellent broad bedding planes on the rear side of the hill, which
overlooks Luning Draw (see Fig. 2.5).
176
Figure 2.13: Photomosaic of Hettangian outcrops in Reno Draw. In the text these are referenced as, from left to right: Aplite 3 North (A3N), Aplite 3
Middle (A3M) and 3 South Primary (3SP). The outcrops are oset by normal faults and contain the same strata, but each exposure features slightly
dierent weathering. The resistant beds are cherts of the Ferguson Hill Member of the Sunrise Formation. The contact at the base of 3SP is eec-
tively continuous to the Muller Canyon Member of the Gabbs Formation, which is isolated to a few very small disconnected outcrops.
177
Figure 2.14: A major ash ood struck on May 31, 2009, which destroyed the gravel road built in New
York Canyon, dispersing the gravel and small bulders, and forming meter-deep ravines. The ood
burried and destroyed some prominent ammonoid fossils, but also exposed new outcrops of
Triassic/Jurassic boundary strata on Ferguson Hill.
178
Figure 2.15 Low and high angle cross bedding in a small outcrop of the Muller Canyon Member in Reno
Draw, near the base of outcrop 3 South Primary. Most of the member is ssile and slope-forming, and
only small resistant outcrops are found along the eastern slopes of Reno Draw, between outcrops of
igneous rock. Scale in cm. Note the coarse sand in the top (pink) 2 cm, and the muddier matrix below.
IMG_0134, taken May 20, 2010
179
Figure 2.16 Top left, silt and very ne sand clasts of quartz and feldspar in a photomicrograph of the
Muller Canyon Member of the Gabbs Formation. Top right, a large imature volcanic glass clast. Center,
plot of size of counted grains in each of seven thin sections from the Muller Canyon Member, spanning
roughly 18 m of stratigraphy. There is no apparent trend in grain size to indicate a profound change in
depositional setting.
10
100
1000
5 10 15 20
Grain Size (micrometers)
Stratigraphic Order
180
Figure 2.17 Photomicrographs show carbonate cements and amorphous carbonate grains that make
up 75 - 90% of counted points in the Muller Canyon Member thin sections. Lower image in cross polar-
ization.
181
Figure 2.18 Top, photomicrograph of a typical thin section of the Muller Canyon Member of the Gabbs
Formation, showing few terrigenous grains (silt and very ne sand of quartz or feldspar) surrounded by
amorphous carbonate grains and carbonate cements. Center, results of point counts for the seven
Muller Canyon Member thin sections analyzed.
0
5
10
15
20
25
30
35
40
1 2 3 4 5 6 7
Percent of counted points
that were terrigenous grains
Stratigraphic Order
182
Fig. 2.19 Mixed carbonate and chert dominates the upper half of the Ferguson Hill Member of the
Sunrise Formation. The unusual and amorphous bedding structures at rst appear to vary as much
laterally as vertically, which can challenge measuring the sections and designating units. Guex’s (1995)
lithostratigraphic columns (example at right, from section 3) illustrations are evocative but are, like the
rocks, dicult to distinguish and interpret without a facies model in mind to interpret the bedding.
IMG_0102, May 19, 2010.
183
Figure 2.20 Shelly fossils, such as these solitary scleractinian corals, are clearly visible on well-
weathered cli-face outcrops of the wackestone units in the upper Ferguson Hill Member of the Sun-
rise Formation. these weathered surfaces were most useful for fossil surveys, performed with a grid of
wire (20 x 20 cm) divided into 16 squares with shing line. Photo DSC_0398, taken June 8, 2011, in
Reno Draw.
184
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Jackpot Hill
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Jackpot Hill
Muller Canyon
Reno Draw
10 meters
Aplite 3 South Primary
Ferguson Hill
NB
MCA
MCB
N9
Sinemurian
Hettangian
Figure 3.31
Sunrise
Formation
Gabbs
Formation
Triassic
Jurassic
Hettangian
Rhaetian
Marshi Planorbis Liasicum Angulata
8m/800kyr
100ky/m
.100 cm/kyr
8 m/750 kyr
93.75ky/m
.107 cm/kyr
17 m/250 kyr
14.7 kyr/m
6.80 cm/kyr
8m/120kyr
15 kyr/m
6.7 cm/kyr
10m/530
53ky/m
1.89 cm/ky
4m/520kyr
130kyr/m
.769 cm/kyr
8m/ 130 kyr
16.3 kyr/m
6.15 cm/kyr
20m/1030kyr
51.5 kyr/m
1.94 cm/kyr
Duration
Estimates
from Ruhl
et al., 2010
Duration
Estimates
from Bartolini
et al., 2012
Muller Canyon
Reno Draw Fault Gully
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SP-5ii
NB
MCA
MCB
3SPMCAiii
3SPMCAi
3SPMABi
3SPAx
3SPCiii
3SPCii
3SPDi
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
Aplite3Eyehole
Arch
BestSEM
3SP-4Popcorn
YadisBioherm
Aplite 3 middle
(book 1, 6/8/11)
StromoA3Middle
PM
N9
SF1A
SF1B
StromoGSSP
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
JigsawC
Cutie6
popcorn
A3N SEM2
A3N SEM
3SP-5viii
Lithologic Samples (stars)
Collection Year
2008
2009
2010
2011
3SP-5ix
3SP-5iix
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF13
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
SF7Concretion
SF7Matrix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
Wackestone
Grainstone
Particular
sponge taphonomy
Condensed
and insitu sponge
Spiculite
Siltstone
Thin section content
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic
Aplite 3 North
Muller Canyon
Reno Draw
Luning Draw
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
Jackpot Hill
Hettangian
Sinemurian
0.5 cm = 1 m
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SPMCAiii
3SPMCAi
3SPMABi
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
PM
N9
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF7
Concretion
SF7Matrix
SF1A
SF1B
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
SFNA
SFNC
Node Large
3SPAx
3SPCiii
3SPCii
3SPDi
SF1: 2m
N9
10
20
25
40
30
50
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
BestSEM
3SP-4Popcorn
3SP-5viii
3SP-5ix
3SP-5iix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
YadisBioherm
Cutie6
SF13B
SF13A
JigsawC
Aplite3Eyehole
Arch
A3N Gum
A3N SEM2
A3N SEM
StromoGSSP
StromoA3Middle
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
3SP-5ii
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Wackestone
Condensed
and in-situ sponge
Spiculite
Siltstone
Other
Thin section content
Figure 3.2 Composite Stratigraphic Column
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic Hettangian
Rhaetian
Thin sections
from Reno Draw
Thin Sections
from Muller Canyon
Thin sections
from Reno Draw
Thin Sections
from Muller Canyon
Hettangian
Sinemurian
0.5 cm = 1 m
N9
10
20
25
40
30
50
Silty cacarenite
CaCO3 concretions
Chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Figure 2.21 Fossil Survey Results
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic Hettangian
Rhaetian
36
338
57
52
5
6
7
36
Key to Fossil Survey Pie Charts
Solitary Scleractinian
Corals
Infaunal
Bivalves
Epifaunal Bivalves
Gastropods
Specimens
Infaunal and Epifuanal
Bivalves Recovered in
Bulk Sampling
Very Rare Epifaunal
Bivalves Spotted
185
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Jackpot Hill
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Jackpot Hill
Muller Canyon
Reno Draw
10 meters
Aplite 3 South Primary
Ferguson Hill
NB
MCA
MCB
N9
Sinemurian
Hettangian
Figure 3.31
Sunrise
Formation
Gabbs
Formation
Triassic
Jurassic
Hettangian
Rhaetian
Marshi Planorbis Liasicum Angulata
8m/800kyr
100ky/m
.100 cm/kyr
8 m/750 kyr
93.75ky/m
.107 cm/kyr
17 m/250 kyr
14.7 kyr/m
6.80 cm/kyr
8m/120kyr
15 kyr/m
6.7 cm/kyr
10m/530
53ky/m
1.89 cm/ky
4m/520kyr
130kyr/m
.769 cm/kyr
8m/ 130 kyr
16.3 kyr/m
6.15 cm/kyr
20m/1030kyr
51.5 kyr/m
1.94 cm/kyr
Duration
Estimates
from Ruhl
et al., 2010
Duration
Estimates
from Bartolini
et al., 2012
Muller Canyon
Reno Draw Fault Gully
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SP-5ii
NB
MCA
MCB
3SPMCAiii
3SPMCAi
3SPMABi
3SPAx
3SPCiii
3SPCii
3SPDi
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
Aplite3Eyehole
Arch
BestSEM
3SP-4Popcorn
YadisBioherm
Aplite 3 middle
(book 1, 6/8/11)
StromoA3Middle
PM
N9
SF1A
SF1B
StromoGSSP
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
JigsawC
Cutie6
popcorn
A3N SEM2
A3N SEM
3SP-5viii
Lithologic Samples (stars)
Collection Year
2008
2009
2010
2011
3SP-5ix
3SP-5iix
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF13
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
SF7Concretion
SF7Matrix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
Wackestone
Grainstone
Particular
sponge taphonomy
Condensed
and insitu sponge
Spiculite
Siltstone
Thin section content
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic
Aplite 3 North
Muller Canyon
Reno Draw
Luning Draw
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
Jackpot Hill
186
Figure
3.1
Stratigraphic
columns
of
sections
measured
at
each
site
indicated.
Lithologic
samples
are
indicated
with
stars
colored
by
collection
date,
and
corresponding
thin
sections
names
are
colored
by
microfacies
content.
Figure
3.2
Composite
stratigraphic
column,
split
at
the
Hettangian/Sinemurian
stage
boundary,
which
is
defined
by
Guex
(1995)
based
on
ammonoids.
Here
thin
sections
are
shown
categorized
by
their
canyon
of
provenance,
and
the
color-‐
labeling
is
simplified.
187
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Jackpot Hill
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Jackpot Hill
Muller Canyon
Reno Draw
10 meters
Aplite 3 South Primary
Ferguson Hill
NB
MCA
MCB
N9
Sinemurian
Hettangian
Figure 3.31
Sunrise
Formation
Gabbs
Formation
Triassic
Jurassic
Hettangian
Rhaetian
Marshi Planorbis Liasicum Angulata
8m/800kyr
100ky/m
.100 cm/kyr
8 m/750 kyr
93.75ky/m
.107 cm/kyr
17 m/250 kyr
14.7 kyr/m
6.80 cm/kyr
8m/120kyr
15 kyr/m
6.7 cm/kyr
10m/530
53ky/m
1.89 cm/ky
4m/520kyr
130kyr/m
.769 cm/kyr
8m/ 130 kyr
16.3 kyr/m
6.15 cm/kyr
20m/1030kyr
51.5 kyr/m
1.94 cm/kyr
Duration
Estimates
from Ruhl
et al., 2010
Duration
Estimates
from Bartolini
et al., 2012
Muller Canyon
Reno Draw Fault Gully
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SP-5ii
NB
MCA
MCB
3SPMCAiii
3SPMCAi
3SPMABi
3SPAx
3SPCiii
3SPCii
3SPDi
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
Aplite3Eyehole
Arch
BestSEM
3SP-4Popcorn
YadisBioherm
Aplite 3 middle
(book 1, 6/8/11)
StromoA3Middle
PM
N9
SF1A
SF1B
StromoGSSP
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
JigsawC
Cutie6
popcorn
A3N SEM2
A3N SEM
3SP-5viii
Lithologic Samples (stars)
Collection Year
2008
2009
2010
2011
3SP-5ix
3SP-5iix
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF13
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
SF7Concretion
SF7Matrix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
Wackestone
Grainstone
Particular
sponge taphonomy
Condensed
and insitu sponge
Spiculite
Siltstone
Thin section content
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic
Aplite 3 North
Muller Canyon
Reno Draw
Luning Draw
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
Jackpot Hill
Hettangian
Sinemurian
0.5 cm = 1 m
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SPMCAiii
3SPMCAi
3SPMABi
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
PM
N9
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF7
Concretion
SF7Matrix
SF1A
SF1B
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
SFNA
SFNC
Node Large
3SPAx
3SPCiii
3SPCii
3SPDi
SF1: 2m
N9
10
20
25
40
30
50
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
BestSEM
3SP-4Popcorn
3SP-5viii
3SP-5ix
3SP-5iix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
YadisBioherm
Cutie6
SF13B
SF13A
JigsawC
Aplite3Eyehole
Arch
A3N Gum
A3N SEM2
A3N SEM
StromoGSSP
StromoA3Middle
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
3SP-5ii
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Wackestone
Condensed
and in-situ sponge
Spiculite
Siltstone
Other
Thin section content
Figure 3.2 Composite Stratigraphic Column
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic Hettangian
Rhaetian
Thin sections
from Reno Draw
Thin Sections
from Muller Canyon
Thin sections
from Reno Draw
Thin Sections
from Muller Canyon
188
Figure 3.3 Resistant clis of the lower carbonate beds of the Ferguson Hill Member of the Sunrise
Formation outcropping at site 7 along Ferguson Hill (Fig. i.6.6). The rst ~ 10 of the Ferguson Hill
Member are fully cemented resistant carbonate clis, which gradually transition to concretion beds.
IMG_0446, taken November 13, 2010.
189
Figure 3.4 Photomicrographs showing carbonate clasts in the lower Ferguson Hill Member of the
Sunrise Formation, which include replaces siliceous spicules and echinoderm ossicles. Top image, note
the radial center clast, an echinoid spine. Bottom images with cross polarized light. Notice the speckled
regions in the left image, which dissapear into a center of like-colored cements in the image at right.
These are syntaxial overgrowths over echinoderm fragments.
500 μm
100 μm 100 μm
190
Figure 3.5 Photomicrograph of a thin section through a sample 14 above the base of the Ferguson Hill
Member of the Sunrise Formation, in cli-forming carbonate unit 1. Carbonate-replaced siliceous
sponge spicules are the most common clast, and are very broken and transported. Most appear as
rectangular or circlular cross sections, though some show branching.
191
Figure 3. 6 Photomicrographs of a siliceous sponge spicule in the Ferguson Hill Member of the Sunrise
Formation (unit 2). Although the spicule is replaced with calcium carbonate (top image, in cross polar-
ized light) the axial lament running along it shows that it was originally a siliceous sponge (Uriz et al.,
2000).
100 μm
192
Figure 3.7 Photomosaic of an expansive bedding plane of unit 8 concretions exposed on the oor of Muller Canyon (see Fig. i.6.9). Sta is one
meter. The blue-ish portion of the bed was exposed during the ood on May 31, 2009. Note the regular size and distribution of the concretions
(grey to beige weathering), which are completely surrounded by cm-scale ropey branching Thalassinoides burrows that weather black due to chert
content.
193
Figure 3.8 The concretion beds of the Ferguson Hill Member are well exposed as bedding planes
standing on the lower half meter of unit 6 and is touching the top of unit 7. Above, the cherts surround
isolated concretions in units 8 and 9. The light grey bedding plane in shadow is unit 4, and unit 5 is
mostly weathered away below Yadi’s feet. Similar beds exposed along the south wall of the canyon (in
background) are too covered in caliche for close inspection. DSC_0938, taken May 21, 2011.
194
Figure 3.9 Unit 2 includes the highest cli-forming fully cemented beds in the lower Ferguson Hill
Member, here shown outcropping in the middle of Muller Canyon (to the left of the frame in Fig. I.1.8).
Three pound sledgehammer for scale is about 30 cm. IMG_0030, taken October 8, 2010.
195
Figure 3.10 Small round concretions form a bed outcropping along Muller Canyon oor, in unit 4 of
the Ferguson Hill Member of the Sunrise Formation. Sta is marked in 10 cm intervals. Note the ammo-
nite fossil on the top of the concretion marked with the arrow. IMG_0015, taken May 13, 2009.
196
Figure 3.11 Unit 5, a distinctive concretion horizon found throughout the New York Canyon area, including at Muller Canyon (top image) and Reno
Draw (bottom). The bed is ~ 50 cm thick, mostly ssile matrix with occassional ~30 cm round concretions. Concretion beds directly above and
below unit 5 (units 4 and 6, labeled) feature particularly large (>45 cm) concretions. Scale is marked with 10 cm intervals. The top image is the same
cli as Figure I.1.8, and Yadi was standing approximately at the level where the scale rests in this image.
5
4
6
6
197
Figure 3.12 A serpenticonic ammonite measuring at least 45 cm in diameter, outcropping in unit 4 of
the Ferguson Hill Member on the broad bedding plane of concretions at the base of the cli in Figs.
3.11 and 3.8. Estwing hammer for scale. This specimen was lost, destroyed, or burried in the ash
ood on May 31, 2009. IMG_0093, taken May 14, 2009.
198
Figure 3.13 The top of unit 9 of the Ferguson Hill Member, outcropping in Reno Draw, at 3 South
Primary. Scale bar marked in 10 cm intervals. Note the oblong light grey concretions and mottled
black and brown-weathering cherty matrix. DSC_0020, taken June 12, 2011.
199
Figure 3.14 Unit 10 of the Ferguson Hill Member, which is the uppermost unit of distinctive resistant
carbonate concretions below the increasingly-pervasive cherty beds. Sharpie marker for scale. Small ~
10 cm concretions occur approximately every 30-40 cm laterally at the top of the bed (see two indi-
cated by arrows). Note that the concretions are not distinct from the bed itself, but are very distinct
from overlying material. This may be due to early formation followed by winnowing of shallow mixed
layer debris. IMG_0076, taken in Muller Canyon May 13, 2009.
200
Figure 3.15 In the cherty units overlying the concretion beds in the Ferguson Hill Member, carbonate
intervals are in odd shapes but are less-resistant than cherty matrix, contrasting to the very resistant
concretions below. Marks on sta are 10 cm. IMG_0108, taken in Reno Draw May
19, 2010.
201
Figure I.1.16 Matrix sediment compacted around concretions in the Ferguson Hill Member. Both images from the cli face in Figure I.1.8. Left:
sediment matrix compacted around the bottoms of large wide concretions near the base of unit 6. Scale marked in 10 cm intervals. Right: sediment
matrix compacted around the top of small concretions near the top of unit 7.
202
Figure 3.17 Photomicrographs in plane (top) and cross (bottom) polarized light, showing the compac-
tion of bioclasts in sediments surrounding carbonate concretions in the Ferguson Hill Member of the
Sunrise Formation. The concentric rings are siliceous sponge spicules. Note that some have carbonate
replacment (lower image) represented by beige color, but most of the spicules and martix are siliceous.
This is a slide through a burrow in unit 9.
203
Figure 3.18 Photomicrograph of a concretion from unit 8 of the Ferguson Hill Member of the Sunrise
Formation. Taken with plane polarized light and a white piece of paper between the stage and slide to
clarify carbonate crystal boundaries. Several cross sections through siliceous sponge spicules are
visible as concentric rings. All of the spicules within the concretions are replaced, and clasts within the
concretions are less compacted than surrounding matrix.
204
Figure 3.19 Burrows surrounding concretions in unit 8 viewed on a bedding plane in Muller Canyon
(see Fig. 3.7). The concretions weather grey with beige cover, and the burrows are most resistant,
weathering in cherty black. The pervasive bioturbation challenges distinction of burrow structure, but
note the branching and curving portions in the center of the frame. Scale is 30 cm. DSC_0234, taken
May 16, 2011.
205
Figure 3.20 Mottled brown matrix and black cherty burrows surrounding a concretion in unit 9 of the
Ferguson Hill Member. Scale in cm. DSC_232, taken in Muller Canyon May 16, 2011.
206
Figure 3.21 Detail of a branching Thalassinoides burrow from unit 8, taken in the weathering cli face
(Fig. 3.8) of Muller Canyon. The main burrow goes from the lower arrow to the scale bar (with cm
marks). Note two side branches indicated by arrows. Both matrix and burrows are quite resistant to
weathering, so detailed exposures like this are rare. DSC_0923, taken May 21, 2011.
207
Figure 3.22 Photomicrograph of a thin section cross cutting a Thalassinoides burrow and surrounding
matrix, from unit 8 of the Ferguson Hill Member of the Sunrise Formation, wherein burrows completely
surround carbonate concretions. Plane polarized light. The siliceous sponge spicules are preserved and
cemented with chalcedony, which gives the burrows their distinctive cherty weathering resistance in
outcrop.
Burrow Matrix
208
Figure 3.23 Photomicrographs of non-burrowed matrix surrounding the carbonate concretions in unit
9 of the Ferguson Hill Member of the Sunrise Formation. The central clast is a broken dichotraene
siliceous sponge spicule. Bottom, cross polarized light. Notice the mix of carbonate and chert cements
between the clasts. Also note the presence of many small dolomite rhombs in both images.
209
Figure 3.24 Possible boring (arrow) on a concretion of unit 8. These are rare and have not been matched
up to any Thalassinoides burrows penetrating into a concretion from the side (see Fig. 3.20 and 3.7).
Scale marked in cm. DSC_0091, taken May 16, 2011.
210
Figure 3.25 Scans of x-rays of the two halves of one 1.5 cm thick slice of a concretion in unit 8 (see
Figs. 3.7 and 3.19). Note the very small u-shaped burrow (arrow) in the left side of the concretion.
UP
211
Figure 3.26 Ammonites fosslized on the very tops of small concretions in unit 4 of the Ferguson Hill Member of the Sunrise Formation. Some are
very clear (top, right) but most are obscure. This bed is heavily weathered and exposed across the oor of Muller Canyon (Figs. 2.10, 2.9). It is not
possible to assess how many of the small, evenly distributed concretions may have had ammonites that are destroyed by weathering. These
concretions are typically about 10 cm in diameter (see cm ruler) but are cylindrical and about 15-20 cm tall, surrounded by less resistant matrix.
None of the concretions has been found to have an ammonoid in the center or base. Most contain coarse sediment including sparse small < cm
gastropods. All images taken November 13, 2010.
212
Figure 3.27 Large serpenticonic ammonites fossilized in concretions in unit 4 of the Ferguson Hill Formation, exposed on the weathering hillside
on the north slope of Muller Canyon. Top left: the bed can be traced through the talus by following the large resistant concretions; arrows indicate
the specimen shown second to the left on the top row, and bottom right. Scale bar is marked in 10 cm intervals. Some of the ammonites are very
clear, but most are obscure and, as on other beds (see Fig. 3.26) it is not clear how many concretions originally had ammonite fossils. All images
taken June 4, 2009.
213
Figure 3.28 Serpenticonic ammonite with prominent ornament fossilized on top of a concretion in
unit 4 of the Ferguson Hill Member of the Sunrise Formation, exposed on a bedding plane in Muller
Canyon. Note the very small ammonite with a white drusy-calcite-lled phragmacone near the right-
most outer whorl on the larger specimen. Three pound sledge hammer is ~30 cm. IMG_264, taken
June 4, 2009.
214
Figure 3.29 Small ammonite fossils on the tops of concretions in unit 8, as exposed on the oor of Muller Canyon (see Figs. 3.7, 3.19). Some are
very detailed, with drusy-calcite spar lled phragmacones (left top and detail of it in left bottom), but others are obsure (top right). In this bed the
concretion size is not matched closely to the ammonite size. Images all taken November 13, 2010.
215
Figure 3.30 Isotope measurments on calcite within two concretions from the Ferguson Hill Member of
the Sunrise Formation. Top: Concretion sampled from the bedding plan in unit 8 (see bedding plane in
Fig. 3.7 and 3.19, and x-ray in Fig. 3.25). Note the oset between the values of bulk calcite (diagenetic
cements and silica replacement) and the drusy calcite ll within the phragmacone of an ammonite at
the base of the concretion (K1-Sp). Bottom: Concretion from unit 4 with an ammonite fossil on top (see
Figs. 3.10 and 3.26).
216
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Jackpot Hill
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Aplite 3 North
Muller Canyon
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Reno Draw
10 meters
Luning Draw
Aplite 3 Middle
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
NB
MCA
MCB
N9
Jurassic
Triassic
Sinemurian
Hettangian
Figure 2.4
Fault Gully
Sunrise
Formation
Gabbs
Formation
Jackpot Hill
Muller Canyon
Reno Draw
10 meters
Aplite 3 South Primary
Ferguson Hill
NB
MCA
MCB
N9
Sinemurian
Hettangian
Sunrise
Formation
Gabbs
Formation
Triassic Period Jurassic Period
Hettangian Stage Rhaetian Stage
Marshi Zone Planorbis Zone Liasicum Angulata
8m/800kyr
100ky/m
.100 cm/kyr
8 m/750 kyr
93.75ky/m
.107 cm/kyr
17 m/250 kyr
14.7 kyr/m
6.80 cm/kyr
8m/120kyr
15 kyr/m
6.7 cm/kyr
10m/530
53ky/m
1.89 cm/ky
4m/520kyr
130kyr/m
.769 cm/kyr
8m/ 130 kyr
16.3 kyr/m
6.15 cm/kyr
20m/1030kyr
51.5 kyr/m
1.94 cm/kyr
Duration
Estimates
from Ruhl
et al., 2010
Duration
Estimates
from Bartolini
et al., 2012
Muller Canyon
Figure 3.31 Stratigraphic columns of the
Ferguson Hill Member of the Sunrise
Formation, showing the approximate net
rock accumulation rates calculated by
comparing the meters of stratigraphy to
the estimated geologic duration of each
ammonoid biozone.
Reno Draw Fault Gully
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SP-5ii
NB
MCA
MCB
3SPMCAiii
3SPMCAi
3SPMABi
3SPAx
3SPCiii
3SPCii
3SPDi
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
Aplite3Eyehole
Arch
BestSEM
3SP-4Popcorn
YadisBioherm
Aplite 3 middle
(book 1, 6/8/11)
StromoA3Middle
PM
N9
SF1A
SF1B
StromoGSSP
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
JigsawC
Cutie6
popcorn
A3N SEM2
A3N SEM
3SP-5viii
Lithologic Samples (stars)
Collection Year
2008
2009
2010
2011
3SP-5ix
3SP-5iix
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF13
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
SF7Concretion
SF7Matrix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
Wackestone
Grainstone
Particular
sponge taphonomy
Condensed
and insitu sponge
Spiculite
Siltstone
Thin section content
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic
Aplite 3 North
Muller Canyon
Reno Draw
Luning Draw
Aplite 3 South Primary
Ferguson Hill
Muller Canyon
Jackpot Hill
Hettangian
Sinemurian
0.5 cm = 1 m
3SPNi
3SPNiii
3SPNii
3AP-8i
matrix
3SP-7i
3SPMCAiii
3SPMCAi
3SPMABi
3SP-5vii
3SP-5v
3SP-5vdn
3SP-5iv
3SP-5iii
3SP-6
3SP-7c
PM
N9
SF2
SF4
SF5A
SF8A
SF9A
SF11A
SF12
SF7
Concretion
SF7Matrix
SF1A
SF1B
SF1: 4m
SF1: 6m
SF1: 8m
SF1:10m
SF1: 12m
SFNA
SFNC
Node Large
3SPAx
3SPCiii
3SPCii
3SPDi
SF1: 2m
N9
10
20
25
40
30
50
3SP0i
3SP1iiB
3SP2ii
3SP2i
3SP3ii
3SP3i
3SP4
BestSEM
3SP-4Popcorn
3SP-5viii
3SP-5ix
3SP-5iix
3SP-4i
3SP-4ii
3SP-4iii
3SP-4iv
3SP-1i
3SP0ii
3SP1i
3SP1iii
3SP1iv
YadisBioherm
Cutie6
SF13B
SF13A
JigsawC
Aplite3Eyehole
Arch
A3N Gum
A3N SEM2
A3N SEM
StromoGSSP
StromoA3Middle
SF17
sandstone
SF18
SF22
SF29;
coral/at pebble
conglomerate bed
SF19
sandstone
SF14Storm
SF14StormMatrix
SF14Bleb
SF14Matrix
3SP-5ii
Silty cacarenite
CaCO3 concretions
Spicule-rich chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Wackestone
Condensed
and in-situ sponge
Spiculite
Siltstone
Other
Thin section content
Figure 3.2 Composite Stratigraphic Column
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic Hettangian
Rhaetian
Thin sections
from Reno Draw
Thin Sections
from Muller Canyon
Thin sections
from Reno Draw
Thin Sections
from Muller Canyon
Hettangian
Sinemurian
0.5 cm = 1 m
N9
10
20
25
40
30
50
Silty cacarenite
CaCO3 concretions
Chert
Wackestone
Siltstone
Sandstone
Carbonate concretion
Irregular concretion
Key to Lithologic Symbols
Figure 2.21 Fossil Survey Results
Hettangian
Sinemurian
Gabbs Formation
Sunrise Formation
Triassic
Jurassic Hettangian
Rhaetian
36
338
57
52
5
6
7
36
Key to Fossil Survey Pie Charts
Solitary Scleractinian
Corals
Infaunal
Bivalves
Epifaunal Bivalves
Gastropods
Specimens
Infaunal and Epifuanal
Bivalves Recovered in
Bulk Sampling
Very Rare Epifaunal
Bivalves Spotted
217
Figure 3.32 Diagram illustrating diagenesis near the sediment water interface in the beds of units 8
and 9 in the Ferguson Hill Member of the Sunrise Formation. a. Formation of very small Arenicolites
burrow in unconsolidated sediment. b. Calcium carbonate replaced silica within siliceous sponge
spicules, allowing silica to ux out of the sediment. Calcium carbonate also cemented pore spaces
within quasi-spherical areas, forming concretions. c. Some amount of additional sediment may have
settled on the seaoor during and after concretion formation. d. Thalassinoides burrows formed in the
sediment, without penetrating the rounded concretions. Later, the open burrows were completely
lled with straight style spicules of siliceous sponges, either due to abandonment by the burrow
makers, a sedimentation event, or both. Silica cemented the porespaces between the spicules within
the burrows. In the unburrowed sediment, carbonate replaced some spicules and formed some
cements, and silica cemented the remaining pore spaces. This last stage of cementation may have
occurred over more time, as clasts in the matrix and burrows are more compacted than within the
concretions.
Arenicolites
burrow
Concretion
formation
Additional
sedimentation
Thalassionoides
burrows
Time
SiO
2
out
spicules
a
b c d
218
Figure 3.33 Beef calcite horizons near the base of the Ferguson Hill Member of the Sunrise Formation in Muller Canyon. Though they appear
similar to late diagenetic vein lls, the microfacies reveal unidirectional upward growth of acicular aragonite fans. See Greene et al., (2012a) for
more details.
219
Figure 4.1 Map indicating Triassic/Jurassic orientation of Pangea, the global ocean Panthalassa, and
the Tethys Seaway, after Schoene et al. (2010). Shaded region indicates extent of CAMP ,
after Whiteside et al (2010). Stars indicate paleolatitudes of eld sites in USA and Peru
(this study) and Austria (Delecat et al., 2011).
220
Figure 4.2: Stratigraphic, fossil and thin section analysis for the Gabbs and Sunrise Formations of
Nevada. A. Fossils counted on cli faces in Muller Canyon, within two grids 100 x 20 cm, at each inter-
val. B. Composite stratigraphic column. C. Comparison of thin sections from sites in Reno Draw (site 3
of Guex(1995)). D. Composition of thin sections from Muller Canyon (sites 6 and 7 of Guex(1995).
The Triassic/Jurassic boundary date by 206Pb/238U from an ash bed in the Muller Canyon area,
and the Hettangian/Sinemurian boundary date is by correlation to 206Pb/238U ash date the Aram-
achay Formation in northern Peru (Bartolini et al., 2012; Schoene et al., 2010; Schaltegger et al., 2008).
n = 36
338
57
52
5
6
7
Jurassic
Triassic
201.33 Mya
Sinemurian
Hettangian
199.35 Mya
Concretions
Chert
Wackestone
Siltstone
Lithologic Symbols
Burrows
Thin Section Key
wackestone
in situ sponge
spiculite
siltstone
other
Shell Count
Key
Pectinid
Other Bivalve
Gastropod
Coral
a b c d
Sunrise Fm.
Gabbs Fm.
20 10 0 m 30 40 50 60
221
Figure 4.3 Mosaic photomicrograph of a large thin sections through a collapsed fossil sponge accumu-
lation. Note that in addition to a matrix of densly packed spicules, there are numerous very long spic-
ules packed together in a curved swath through the center of the image. In hand samples from this
unit, polished slabs show mottled regions of light and dark spicule arrays, but no evidence of sedimen-
tary structures or bioturbation. From sample 3SP -5ix from Reno Draw, 24 m above the base of the
Ferguson Hill Member of the Sunrise Formation.
2 mm
222
Figure 4.4 Mosaic photomicrograph of a large thin section through a fossil sponge. Field of view is
approximately one centimeter wide. Note the large branching (dichotraene) spicules aranged in a
circle. From unit M4 of the Aramachay Formation at Malpaso.
223
Figure 4.5 Mosaic photomicrograph of a large desmid spicule. Note also the large straight style spicule
in the background, and numerous dolomite rhombs in the foreground. The desmid and rhombs are
traced for emphasis. Unit 3Sp-3 in Reno Draw; 29 m above the base of the Ferguson Hill Member of the
Gabbs Formation.
224
Figure 4.6 Composite photomicrograph of a complex branching dichotraene siliceous spicule. The
image is a stack of three photomicrographs taken at dierent depths within the thin section combined
in Adobe Photoshop, with an outline added to show the boundaries of the spicule. The top left point is
most likely broken. From unit 14 in Muller Canyon, 29 m above the base of the Ferguson Hill Member
of the Sunrise Formation.
225
Figure 4.7 Sponge body fossils preserved as a bed of chert underneath a layer of light grey allochtho-
nous carbonate debris storm bed. DSC_195, taken June 5, 2011 in Reno Draw.
226
Figure 4.8 Sponge body fossils on a bedding plane at the top of outcrop Aplite3 North, with scale
marked in cm. DSC_0050, taken June 4, 2011.
227
Figure 4.9 Photomosaic image of bedding planes of resistant siliceous sponge body fossils extend >20 m on a dipslope on the southeast slope of
Jackpot Hill (see Fig. i.6.12) that is also the north side of Luning Draw (see Fig. 2.5). All of the people are standing along one dark brown bedding
plane. More bedding planes are exposed parallel behind them.
228
Figure 4.10 Sponge body fossils covering a bedding plane on the dipslope of Jackpot Hill (see Fig. 4.9). This bedding plane is exposed > 20 m,
allowing surface surveys for benthic body fossils. Meter stick marked in 10 cm intervals. DSC_156, taken June 14, 2011.
229
Figure 4.11 Geologic map and stratigraphic columns of Pucará Group Triassic/Jurassic boundary rocks
outcropping in the La Oroya area of the central Peruvian Andes. a. Geology. Pucará Group outcrops:
Triassic/Jurassic (blue); Cretaceous-Tertiary (grey); Quaternary (white). Major faults, folds, and roads are
marked. (La Oroya is to the east at the junction between highways 3N and 22.) b. Uppermost Triassic
(Chambará) and lowermost Jurassic (Aramachay, Condorsinga) formations are shown for three eld
sites. In the Aramachay at Morococha, burrowed and cross-bedded siltstones are overlain by approxi-
mately two hundred meters of cherts. Examined chert microfacies were composed entirely of sponge
spicules, and examined core contains exquisite sponge body preservation. The clearest sponge body
fossils were found in Malpaso, among ubiquitous cherty nodules that also form in burrows. Mollusc-
rich storm beds at both sites indicate mid-shelf settings. Beds of very abundant ammonites occur at
both sites, and indicate Hettangian age for the upper Aramachay at Morococha. Extensive ammonite
biostratigraphy and absolute dates establish the Aramachay Formation spanning the entire Hettangian
(~1.8 Ma) in the Utcubamba region to the north(Schaltegger et al., 2008). Tingocancha represents
much shallower deposition, where the Aramachay contains consistent cross bedding of shoreface
grains and evaporate pseudomorph horizons. Columns after Rosas et al.(Rosas, 1994) and Szekely and
Grose(1972), with new ndings added.
Mal
Mor
Tin
Chambara
Aramachay
Condorsinga
Limestone
Dolostone
Chert
Siltstone
Clastic
Igneous
100 m
Burrows
Ammonites
Crossbeds
Spicules
Triassic Jurassic
Malpaso
Tingocancha
22
2 km
Morococha
3N
La Oroya
230
Figure 4.12 The site near the town and mine of Morococha is an anticline, with the bedding near
vertical at the top of the stratigraphic section shown in Figure I.2.11. DSC_0878, taken August 14, 2012.
231
Figure 4.13 Thick, branching Thalassinoides burrows exposed in the lower strata of the Aramachay
Formation at Morococha. Scale is marked in 10 cm intervals.
232
Figure 4.14 Wavy lenticular cross bedded mixed chert and carbonate occurs between distinctive
Thalassinoides beds in the lower strata of the Aramachay Formation at Morococha, Peru. DSC_0932,
taken August 13, 2012.
233
Figure 4.15 At Morococha, Peru (left) the upper Aramachay Formation consists of massive black cherts with thin beds or lenses of carbonate,
representing midshelf deposition of transported carbonate tempestites over autochthonous sponge material. The same facies is present in much
of the upper Ferguson Hill Member of the Sunrise Formation in the Gabbs Valley Range of Nevada, USA (right). Scales marked with 10 cm intervals.
Left: DSC_0916, taken Agust 14, 2012. (The white patches are lichen.) Right: DSC_0712, taken in Reno Draw, May 19, 2011.
234
Figure 4.16 Mosaic photomicrograph of broken and transported siliceous sponge spicules. Note the
axial laments in some, and otherwise the circular or rectangular cross sections. From lithic sample 4 of
the Aramachay Formation at Morococha.
1 mm
235
Figure 4.17 Core from Morococha, on loan from Pan American Silver Company. a. Core showing the
transition from the sponge-rich Hettangian/Early Sinemurian Aramachay Formation to the overlying
fossiliferous limestone Sinemurian Condorsinga Formation. b. Small piece of core on loan from Pan
American Silver, showing a well-preserved fossil sponge, 3 x 3 cm. c. The center region of the fossil
sponge contains well preserved in situ spicules radiating outward toward the concentric rings.
a
b
c
Aramachay Formation
Condorsinga Formation
Aramachay / Condorsinga
Transition
236
Figure 4.18 Three ammonite specimens from Moroco-
cha, Peru (See text Figure 4 for map and stratigraphic column). The outcrop terminates in vertically
oriented silicied shell packstone beds with very abundant ammonites. Though the sutures are not
visible, the conch shape, ribbing, and ventral ornamentation of these three silicied specimens t
Frebold’s denition of Paracaloceras cf. P . coregonense (Frebold, 1967). a-c: Specimen 1, 23.9 mm. At an
approximate size of 17.6 mm, the venter has a keel and at sides (b). At the full size, distinct but shallow
furrows are developed. The same is true for specimen 2 (d-f) with the keel developed at approximately
17.4 mm and minor furrows at the full size of 25.5 mm. The third specimen (g) is 15.0 mm in diameter,
lacks a keel, and has a whorl approximately as wide as high. The latest list of Hettangian Pacic ammo-
noid taxa does not include P . coregonense, but the other six species of Paracaloceras (including one
indeterminate) all occur in the nal Unitary Association of the Hettangain stage. This constrains the
approximately 200 m of spiculite in the Aramachay Formation at Morococha to the Hettangian stage,
evidence of widespread siliceous sponge presence dominating the shelf for 1.8 Ma.
a b c
d e f
g
237
Figure 4.19 Beds of the Aramachay Formation are accessible alongside the river at near Malpaso, and
outcrops in the foreground can be tracked continously for hundreds of meters to the hill in the back-
ground. Here the Chambara, Aramachay, and Condorsinga Formations contact conformably in acces-
sible outcrops.
Chambara
Aramachay
238
Fiigure I.2.20 The lower 20 m of the Aramachay Formation at Malpaso consists of massively bedded
siltstone beds separated by intervals of intense bioturbation and distinctive large branching Thalassinoi-
des burrows. This is best viewed along the road by the river, looking up at the undersides of the beds
along the cli (see Fig. 4.19). This image shows a fallen block, on which weathering and ambient light
highlight the curves of the wide burrows on the block’s underside. Scale marked in 10 cm intervals.
239
Figure 4.21 Complex branching fossil burrows in massive sandstone (Unit M4) in the middle strata of
the Aramachay Formation at Malpaso. Chert cements ll the burrows, and can result in nodule growth.
Arrows indicate branches of the burrow complex. Note the bottom arrow, pointing to where the
burrow splits into many dierent directions. Photomosaic of DSC_515 and DSC_519, taken August 13,
2012.
240
Figure 4.22 Simple style spicules visible weathering out of matrix surrounding burrows in the cli
faces of the Aramachay Formation at Malpaso. Scale is ~ 1cm. DSC_0153, taken August 11, 2012.
241
Figure 4.23 Siliceous sponge horizon in the middle Aramachay Formation at Malpaso, Peru. The
sponge horizon has a relatively at bottom and lumpy top, and is overlain by course sandstone. It
occurs on top of a bed with complex branching Thalassinoides burrows. Both the burrows and sponges
appear as resistant cherty forms and can grow into larger diagenetic nodules. DSC_614, taken August
13, 2012.
Burrows
Sponge
242
Figure 4.14 The Pucara Group outcrops at Tingocancha with the upper Chambara, entire Aramchay,
and lower Condorsinga Formations visible from the Carretera Central. DSC_0182, taken August 11,
2012.
Condorsinga
Aramachay
Chambara
243
Figure 4.25 Cross bedding in inner shelf to shoreface sediments in the Aramachay Formation at
Tingocancha, Peru.
244
Figure 4.26 Sponge-dominated facies in Nevada, USA, the Central Andes, Peru, and Plattenkogel,
Austria, after Taylor et al. (1983), Rosas et al. (2007), and Delecat et al. (2011), respectively. At each site,
Upper Triassic carbonate ramp or platform facies cease across the system boundary, and siliceous
sponges dominate the overlying Hettangian strata. The spiculites in Nevada and the Central Andes
(this study) are orders of magnitude thicker than the extensively studied but very condensed Austrian
site on Plattenkogel hill (Delecat et al., 2011).
0 cm
200 cm
Gabbs Sunrise
Chambara Cond. Aramachay
Adnet
CL
Sponge
Nevada, USA Central Andes, Peru Plattenkogel, Austria
100 cm
0 cm
200 cm
Hett. Rheatian
Triassic
Gabbs Sunrise
Chambara Cond. Aramachay
Adnet
CL
Sponge
200 m
200 m
400 m
100 m
Sinemurian
Jurassic
245
Figure 4.27 Conceptual model for biologically controled facies development from the Norian through
Sinemurian stages across the Triassic/Jurassic boundary. Norian carbonate platforms near the Pilot
Mountains ajacent to the Gabbs Valley Range feature common platy and nger coral reefs. Rhaetian
strata in the Gabbs are dominated by bivalves and brachiopods, with some occurance of carbonate
sponges. The top two frames illustrate accumulation of sponge cherts on the dormant ramp, and
ultimtate return of biocalciers in the Sinemurian stage.
Norian
Rhaetian
Hettangian
Sinemurian
Triassic
Jurassic
246
Figure 5.1 is a contour plot showing the residence times (diagonal contour lines) of marine silica at
dierent concentrations (y axis), given dierent intensities of weathering (silica inux; x axis). This is a
one-box model of the ocean at steady state (sources matching sinks). These geologically short times-
cales suggest that silica concentrations were subject to rapid change.
Mean Ocean [Si] μM
0.1 0.2 0.5 1.0 2.0 5.0 10.0 20.0
ave Cenozoic Mesozoic solubility
0.1 0.2 0.5 1.0 2.0 5.0 10.0 20.0
Si Residence Time
Overall weathering flux
(relative to present)
100 200 500 1,000 2,000 5,000 10,000
Ten Thousands
Hundred Thousands
Millions
Thousands
247
Figure 5.2. The “Mesozoic” label on the right side of the graph marks the 60 mg/L concentration inter-
preted by Racki and Cordey (2000) and Siever (1991) for the Mesozoic. If marine silica was this concen-
trated already during the Late Triassic, and if the Basalt Weathering Factor were very low, then the silica
boost from CAMP would still double marine silica concentrations on the million-year scale. If Rhaetian
silica concentrations were lower, they could have reached elevated levels very rapidly, by doubling over
hundreds of thousands of years, high enough to support desmid expression in shallow waters during
the Hettangian. Increase from Triassic to Jurassic time is broadly supported by records of both silicied
fossil faunas and bedded cherts {Kidder:2001dx}. These records, normalized for area and time, show
that Triassic silica accumulation was among the lowest of Phanerozic values, and the Jurassic values
among the highest {Kidder:2001dx}.
2 5 10 20
100 200 500 1,000 2,000 5,000 10,000
Doubling Time of Silica
Basalt Weathering Factor
Mean Ocean [Si] μM
Ten Thousands
Hundred Thousands
Millions
248
Figure 5.3 CAMP basalts could have supplied enough excess silica to cover the tropical carbonate
shelves in siliceous demosponges sponges. Silica (Si) demand by modern siliceous sponge assem-
blages is increasingly well known, and ranges from 0.3 to 2.5 moles of Si m-2 yr-1 for demosponges
(dots) and hexactinellids (circles), respectively (Chu et al., 2011; Maldonado et al., 2011). Hexactinellid
(glass sponge) spicules are found in the Hettangian Alpine spiculites discussed in the text. Demo-
sponges are found in the Hettangian Nevada, Peru, and Austria spiculites (Delecat et al., 2011). If
sponge meadows covered increasing portions of tropical carbonate shelf area (bottom axis, from
(Walker et al., 2002), the demand of Si would increase (left axis). The yield of Si from CAMP basalts (right
axis), compared to weathering over a comparable are of typical continental material, would determine
the total increase in global silica ux. Here we shade weathering factors between 2 and 10 as likely
values, though we calculated weathering up to a factor of 20 to add consideration of increased Early
Jurassic weathering from elevated CO2, and warmer wetter conditions (Michalik et al., 2010).
Silica Flux (10 moles /yr)
20
5
10
2
1
0.5
0.1
0.2
0 20 40 60 80 100
% tropical carbonate shelf
area covered by sponge meadows
2
5
10
20
Basalt Weathering Factor
249
Oxycone
Spherocone
Serpenticone
Platycone
Discocone
Cadicone Planorbicone
N. haasi
N. muelleri
N. americanus
Neogastroplites
mclearni
N. cornutus
Metengonoceras
in blue
Time
250
Figure
6.1
Yacobucci
(2004)
examined
morphological
change
in
ammonoid
shells
of
genus
Neogastroplites
within
the
mid
Cretaceous
Mowry
Sea,
shown
here
in
Westermann
Morphospace
with
samples
from
biozones
with
approximate
stratigraphic
durations
of
300-‐350
kyr
(each
data
point
=
one
specimen).
It
is
unclear
whether
each
temporal
grouping
is
actually
an
independent
species,
or
represents
a
population
of
one
variable
species.
Yacobucci
(2004)
hypothesized
that
interspecific
competition
from
the
immigration
of
Metengonoceras
to
the
epiritic
sea
during
the
N
Muelleri
zone
would
cause
a
decrease
in
variation
within
Neogastroplites
populations.
Instead,
Neogastroplites
populations
expressed
a
morphological
shift
away
from
the
shape
of
Metengonoceras
without
decreasing
overall
variation.
Projecting
the
data
in
Westermann
Morphospace
reveals
some
tight
constraints
on
the
renowned
variation
in
this
group.
The
major
trade-‐off
is
whorl
expansion
rate
vs.
overall
inflation.
These
changes
from
originally
oxyconic
and
discoconic
shells
to
finally
cadicone
shapes
can
be
directly
compared
to
the
trajectories
of
other
case
studies
(Fig.
6.2).
Figure
6.2
Klug
et
al.
(2005)
investigated
morphological
change
in
ammonoid
shells
of
the
genera
Ceratites,
Paraceratites,
and
Discoceratites
within
the
Middle
Triassic
Germanic
Basin,
shown
here
in
Westermann
Morphospace
with
specimens
(n=275)
from
16
stratigraphic
horizons
spanning
a
total
of
<
3
Ma.
The
photographs
(top
right)
from
Klug
et
al.
(2005)
show
representative
specimens
from
key
intervals.
Each
stratigraphic
interval
is
represented
by
all
the
available
measured
specimens
(contours),
and
the
largest
specimens
are
plotted
individually
(with
numbers
corresponding
to
their
stratigraphic
horizon).
In
each
plot,
the
colors
correspond
to
increasing
stratigraphic
level;
red,
orange,
green,
blue,
purple,
black.
The
lowest
plot
illustrates
the
ammonoids’
gradual
shift
from
discocone
to
planorbicone
shells.
The
next
two
plots
show
gradual
shifts
from
serpenticonic
to
more
oxyconic
shells
that
followed
each
of
two
immigration
events.
Finally,
from
intervals
14
to
16,
the
ammonoids
gradually
acquired
distinctly
platyconic
shells.
Each
interval
represents
an
average
of
3.5
species.
The
top
three
plots
show
changes
that
likely
increased
the
overall
hydrodynamic
efficiency
of
the
outer
shell
shape,
but
note
the
potential
influence
of
ornament
is
ignored
here.
251
Stratigraphic
Intervals 1 through 5
Stratigraphic
Intervals 7 through 9
Stratigraphic
Intervals 10 through 13
Stratigraphic
Intervals 14 through 16
Immigration Event
Immigration Event
Figure 6.2
Time
2
2
3
3
3
3
4
4
4
5
5
5
6
6
6
6
6
6
7
7
7
7
7 8
8
8
8
8 8
8
9
9
9
Oxycone
Spherocone Serpenticone
Platycone
Discocone
Cadicone Planorbicone
0
0
1
1
2
2
2
3
3
3
3
4
5
5
5
5
6
6
252
Smithian Ammonoids of
Equitorial Panthalassa (red)
and Southern Tethys (blue)
Oxycone
Spherocone Serpenticone
Vertical Migrant Nekton
Plankton Demersal
Figure 6.3. Dierences between ammonoid shell shape expression between regions may represent an
important ecological phenomenon of the Early Triassic. Brayard et al. (2007) demonstrated that Early
Triassic ammonoid taxonomic assemblages were increasingly latitudinally stratied, and later Brosse et al.
(2013) explored regional shell shape disparity increases. Here data from Brosse et al. (2013) are displayed in
Westermann Morphospace to contrast the shells produced by low and high latitude faunas. Initial projec-
tion in the morphospace specied the removal of specimens with incompatible measurements. The largest
specimen of each genus is represented by an open circle, and the contour lines represent the density of
remaining specimens. Signicantly more of the largest specimens of low latitude ammonoids are
oxyconic, compared to the higher latitude specimens (X2 = 5.58, degrees of freedom = 1, p = 0.018).
red oxy:11
inter: 6
serp:4
blue oxy:17
int:21
sph:2
serp:17ce
red
serp:4
int:6
oxy: 14
blue
serp:17
int: 22
oxy:18
sph:2
253
Figure 7.1. In Westermann Morphospace, ammonoids of dierent shapes are associated with dierent
hypothetical life modes. A, Summary of ammonoid mobility, from Westermann (1996). Common
planispiral shell shapes grade between three forms: serpenticone, sphaerocone, and oxycone. Hypo-
thetical life modes are indicated by the inset triangle. Each illustration includes a side view of the outer
shell and a cross-section through the whorls, superimposed. B, Westermann Morphospace. Three
components of shell shape (exposure of the umbilicus, overall ination, and whorl expansion) dictate
data placement within this ternary diagram. Serpenticones (high umbilical exposure, low overall
ination, low whorl expansion) plot in the plankton eld. Sphaerocones (low umbilical exposure, high
ination, and low whorl expansion) plot in the vertical migrant eld. Oxycones (low umbilical expo-
sure, low ination, and high whorl expansion) plot in the nekton eld. Platycones and planorbicones
plot in the demersal eld. Each drawing is a trace of a genus gured in the Treatise (Arkell et al. 1957),
Dactyloceras, Eurycephalites, and Oxynoticeras (respectively).
A From Westermann (1996)
B Westermann Morphospace
Oxycone
Spherocone
Serpenticone
Vertical Migrant Nekton
Plankton Demersal
254
Figure 7.2 Illustration of measurements on an ammonoid fossil, shown in cross-section. A, Measure-
ments of the whorl. The height of the nal whorl is a. A measurement of the whorl 180 degrees from
this measurement is a’ . A measurement of the height of the whorl before the nal rotation accreted is
a’’ . In fossil shells, a’’ is usually obscured by a broken body chamber or intricate aperture. B, Measure-
ment of the larger radius of the shell, d, and the smaller radius of the shell, e, height of the nal whorl, a,
and whorl width, b (Raup 1967). C, Measurement of the diameter, D, the umbilical diameter, UD, and
the whorl height, WH, which are three of 14 quantitative descriptors recommended by Smith (1986).
d
a
e
D
UD
WH
b
a
a”
a’
B C
A
255
Figure 7.3 Data measured from Treatise (Arkell 1957) specimens of three morphotypes plotted in
ternary diagrams with the parameters of Westermann Morphospace. A, Unscaled data cluster in the
lower (w) corner. B, Data distribution is balanced once the data are scaled. Each morphotype is repre-
sented by a cluster of specimens with a mean (enlarged symbol). Serpenticones (circles) have high
umbilical exposure (U), which represents 60% of shape characterization in the mean (bold circle).
Sphaerocones (diamonds) have high overall shell ination (Th), which represents 60% of shape charac-
terization in the mean (bold diamond). Oxycones (dots) have high whorl expansion (w), which repre-
sents 60% of shape characterization in the mean (bold dot). Data are in Appendix 7.B.
A Unscaled Morphotype Data
B Scaled Morphotype Data
w
U Th
w
U Th
256
Figure 7.4 The Westermann Morphospace method. The top panel shows the steps and calculations to
be applied to any planispiral ammonoid. The bottom panel shows a specic example, with a specimen
of Psiloceras polymorphum (Guex 1995: Plate 11, Fig. 7). Measurements taken on each shell are used to
calculate three shape parameters. Umbilical diameter and diameter yield umbilical ratio (U). Overall
shell thickness and diameter yield thickness ratio (Th). Two measurements of the nal whorl yield the
whorl expansion rate (w). Next, each shape parameter is scaled, so that the values will be comparable.
Finally, the scaled values are normalized to percentages of total shape characterization. This allows
display in a ternary diagram. For this specimen of P . polymorphum, umbilical exposure is the most
prominent characteristic, and the data point plots near the U corner of the ternary diagram.
umbilical
diameter
diameter
= U
a
a’
= w
b
diameter
= Th
(U - 0)
(.52 - 0)
(Th - .14)
(.68 - .14)
(w - 1.0)
(1.77-1.0)
.40
.52
(.33 - .14)
.54
(1.25 - 1.0)
.77
12
30
= .40
10
8
= 1.25
10
30
= .33
Normalize
Scale
Parameter
Calculate
Parameter
= .77
= .36
= .32
= U’
= Th’
= w’
U’
(U’ + Th’ + w’)
Th’
(U’ + Th’ + w’)
w’
(U’ + Th’ + w’)
.77
(1.45)
= 53%
.36
(1.45)
= 25%
.32
(1.45)
= 22%
U
Th
w
Plot
U
Th
w
Measure
Normalize
Scale
Parameter
Calculate
Parameter Plot Measure
Example
Standard
257
Figure 7.5 Comparison of shell shapes and hypothetical life modes in Westermann Morphospace. A,
Middle Triassic ammonoids of Nevada include each major morphotype. Each point represents the
largest measurable specimen of each species (n = 85) in the collections (Monnet and Bucher 2005;
Jenks et al. 2007). B, Earliest Jurassic ammonoids of Nevada include a comparatively limited variety of
shell shapes. Each point represents the largest measurable specimen of each species (n = 35) from the
collection (Guex 1995). All specimens were measured from monographs with calipers. Measurement
error is about 1.7 mm. When repeat measurements of a specimen are plotted together in Westermann
Morphospace, the plotted points partially overlap; the error is not great enough to cause noticeable
change in the position of points. Data of the above collections are included in Appendix 7.D. Speci-
mens corresponding to circled data points are illustrated in Figure 7.
A Middle Triassic
(Anisian)
Oxycone
Spherocone Serpenticone
Vertical Migrant Nekton
Plankton Demersal
B Early Jurassic
(Hettangian)
Oxycone
Spherocone
Serpenticone
Vertical Migrant Nekton
Plankton Demersal
258
Figure 7.6 Shell shapes and hypothetical life modes for a collection showing intraspecies variation and
a collection showing ontogenetic trajectory. A, Specimens of earliest Jurassic species Psiloceras poly-
morphum (closed circles; n = 25) and the descendant Angulaticeras dumetricai (open circles; n = 7).
Compare intraspecies variation with contemporary interspecies variation (Fig. 5B). Neither species
shows a signicant correlation between shape and specimen size in these data, from Guex (1995). B,
Changes in shell shape through juvenile, intermediate, and adult specimens of Anagaudryceras
seymouriense (latest Cretaceous [Maastrichtian]; from Macellari 1986). Each of three specimens (Fig.
II.2.7G–I) was measured twice (see text) to give six total snapshots of shell shapes produced. Shells
from size 31 mm to 197 mm plot in order from left to right. Hypothetically, the juvenile ammonite
would have been planktonic, and grown into an adult with a shell that facilitated swimming.
A Intraspecies Variation
B Ontogenetic Trajectory
Oxycone
Sphaerocone Serpenticone
Vertical Migrant Nekton
Plankton Demersal
Oxycone
Sphaerocone Serpenticone
Vertical Migrant Nekton
Plankton Demersal
259
Figure 7.7 Specimens featured in Figures II.2.5 and II.2.6 are illustrated with a trace of the monograph
image, resized for direct comparison. A–C, Triassic specimens shown in Figure II.2.5A, from monograph
by Jenks et al. (2007). A, The serpenticone Constrigymnites robertsi. B, The sphaerocone Nevadadiscu-
lites taylori. C, The oxycone Sageceras walteri. D–F, Jurassic specimens shown in Figure II.2.5B, from
monograph by Guex (1995). D, The serpenticone Alsatites proaries. E, Psiloceras tilmani. F, Phylloceras
psilomorphum. G–I. Three specimens of Anagaudryceras seymouriense (Fig. II.2.4B) from monograph by
Macellari (1986). G, Juvenile. H, Intermediate form. I, Adult A. seymouriense.
A
B
C
D
E
F
G
H
I
260
Figure 7.8 Shell shapes and hypothetical life modes are shown for Raup’s 1967 data set, in Westermann
Morphospace. Raup (1967) selected specimens from the Treatise (Arkell 1957), from 405 genera across
the Phanerozoic, to show what portion of theoretical morphospace was occupied by normally coiled
ammonoids. Those ammonoids include each recognized planispiral morphotype, and hypothetically
could have lled each ecological niche. To plot the data, the original value of D was combined with
derived values of Th and w(radius. Theoretically, in these specimens, D and wradius should equal the
corresponding Westermann Morphospace parameters U and w. The data are sparse in the low-w area
of the plot (along the top leg). Three specimens plot outside of the left leg of Westermann Morpho-
space, because they exhibit very low thickness ratios (<0.014; see text).
Normally Coiled Ammonoids
(Raup 1967)
Oxycone
Spherocone
Serpenticone
Vertical Migrant Nekton
Plankton Demersal
261
Figure 8.1 The hydrodynamic eciency of ammonoid shells signicantly correlates to their placement
within Westermann Morphospace (see Chapter 7 for calibration details). Jacobs (1991) calculated the
power required (ergs/s/cm) to propel dierent ammonoid shells shapes based on ume tank experi-
mental results. (a) The power required to propel small shells slowly (low Reynolds numbers) signi-
cantly correlates with the percent of shell shape characterized by the thickness ratio in Westermann
Morphospace (p = 0.028). (b) The power required to propel larger shells quickly (high Reynolds num-
bers) signicantly correlates with the percent of shell shape characterized by thickness ratio (p = 0.035)
and whorl expansion ratio (p = 0.023).
Oxycone
Spherocone
Serpenticone
5.71
5.82
4.52
3.32
3.29
2.59
2.15
Oxycone
Spherocone
Serpenticone
450
449
391
831
783
589
567
Shell: 2.5 cm
Speed: 2.5 cm/s
Shell: 10 cm
Speed: 25 cm/s
a
b
Sphenodiscus
Cardioceras
Anahoplites
Oppelia
Stephanoceras
Cadoceras
Microceras
Lytoceras
Otohoplites
Gastroplites
Scaphites
Sphenodiscus
Cardioceras
Oppelia
Cadoceras
Lytoceras
Gastroplites
Scaphites
Sphenodiscus
Cardioceras
Oppelia
Cadoceras
Lytoceras
Gastroplites
Scaphites
262
Figure 8.2 Intraspecies variation. For each species, the type specimen from Tozer (1994) is plotted as a
solid circle, and the specimens in Tozer’s stratigraphic collections at the Canadian Geological Survey in
Vancouver, British Columbia are plotted as open circles. Shell shape variation did not produce a catego-
rization in Westermann Morphospace signicantly dierent than that predicted by type specimens
alone (X = 2.26, degrees of freedom = 1, p = 0.13). Meekoceras gracilitatis (red, with hypotype), Anawa-
sachites tardus (green, with topotype), Kashmirites warreni (black, with holotype), Wasachites deleeni
(orange, with holotype), Wasachites macconnelli (blue, with holotype).
Intraspecies Variation
Oxycone
Spherocone
Serpenticone
263
Figure 8.3 a,b. Westermann Morphospace sorts ammonoids into shape categories based on param-
eters that constrain potential mobility. The morphotypes (serpenticone, oxycone, spherocone, inter-
mediate) are interpreted to facilitate drifting, swimming, vertical migration, and weak swimming,
respectively. Each datapoint represents the type specimen for a Boreal Ocean species during the (a)
Griesbachian and Dienerian and (b) Smithian and Spathian stages. Symbols indicate subzones. Griesba-
chian (black): Concavum (squares), Boreal (dots), Commune (triangles), Strigatus (diamonds). Dienerian
(green): Candidus (squares), Sverdrupi 1 (inverted triangle), Sverdrupi 2 (dots), Sverdrupi 2/3 (triangles),
Sverdrupi 3 (diamonds). Smithian (blue): Hedenstroemi (inverted triangle), Romunderi (squares), Tardus
(dots). Spathian (red): Pilaticus (triangles), Subrobustus (diamonds). c. Histograms show the number of
Boreal Ocean species in each shape category through the Early Triassic (black = oxycone, white =
spherocone, dark grey = serpenticone, grey = intermediate). Bar width indicates the duration of each
subzone. Categorization of shell shapes is very consistent during Griesbachian through Smithian time.
There is not signicant change until the Spathian Stage, which features signicantly more species of
oxycones (X = 5.78, degrees of freedom = 1, p = 0.016).
c
247.
Griesbach.
Die-
Smithian Spathian
249 251.2 252.2 250.5
0 5 0 5 10 15 0 5 10 0 5
Oxycone
Spherocone
Serpenticone
Intermediate
Smithian
& Spathian
b
Oxycone
Spherocone
Serpenticone
Intermediate
Griesbachian
& Dienerian
a
c
wardiei
blomstrandi
spathi
wardiei
blomstrandi
spathi
pilaticus
subtilis
monoceros
czekanowskii
pulchrum
modestus canadensis
bombus
triton
freboldi
chowadei
subrobustus
264
Figure 8.4 Ammonoid shell shapes are represented in both Westermann Morphospace (top) and
Principal Components Analysis (PCA; bottom plot). Black dots represent Griesbachian, Dienerian and
Smithian ammonoids species. Open circles represent Spathian ammonoid species. The PCA is consis-
tent in recognizing the increase in oxycones and sphearocones among the Spathian ammonoid
species: Spathian ammonoid species have signicantly higher values of Principal Component Two
(Wilcoxon Rank Sum Test in R: p = 0.016).
Oxycone
Spherocone Serpenticone
Vertical Migrant Nekton
Plankton Demersal
-0.2 0.0 0.2 0.4
0.8 0.6 0.4 0.2 0.0 -0.2 -0.4
U
Th
w
Early Triassic Boreal Ammonoid Species
Principal Component 1 (59.4% of total variace)
Principal Component 2 (28.4% of total variance)
265
Figure 8.5 The relative distribution of Boreal Ocean ammonoid species within each shape category (top
bar plot) is fairly stable and does not change signicantly until the increase of oxycones during the
Spathian Stage (Table 8.2). The lower barplot of species within each suborder demonstrates that there
is not a simple relationship between higher taxonomy and ammonoid shell shape in this case. For
example, the Spathian increase in oxycones coincides with the appearance of the suborder Ceratina,
but oxycones were produced by multiple suborders throughout the Early Triassic interval.
247.2
Griesbach. Dienerian Smithian Spathian
252 250 248 249 251.22 252.28 250.55
247.2
Griesbach. Dienerian Smithian Spathian
252 250 248 249 251.22 252.28 250.55
0 5 10 15 20
Species
0 5 10 15 20
Orange
Grey
Green
Red
Blue
Pink
Otoceras
Paraceltina
Pinacoceratina
Sageceratina
Ceratina
Phylloceratina
Red
Lt Grey
Black
Dk Grey
Oxycone
Serpenticone
Intermediate
Spherocone
Species
266
Figure 8.6 Early Triassic Boreal ammonoid diversity is compared to oxygen and carbon isotope data
and their interpreted environmental implications. A. Trends in Boreal ammonoid shape space occupa-
tion at the subzone scale (this study): key as in Figure 6. B. Oxygen isotopes derived from sea surface
and shallow water dwelling conodonts and inferred uctuations in Early Triassic temperature (Sun et
al., 2012). The Smithian/Spathian boundary shows a sharp decline in δO suggesting an abrupt rise in
temperatures. C. Composite carbon isotope trend from South China (Payne et al. 2004), which repre-
sents a global signal. D. Carbon isotopes from the Boreal Sea (Grasby et al., 2012) which echo Payne et
al. 2004 and E. Interpretations of these carbon isotopes and other chemical and sedimentological data
as shallow water oxygenated, dysoxic, anoxic, and euxinic intervals (Grasby et al., 2012).
Δ
Estimated Temperature (°C, ice free world)
40 28 30 32 34 36 38
Gries. Dienerian Smithian Spathian
252.28
247.2
17.5 18.5 18.0 19.0 20.0 19.5 20.5
δ18Oapatite (‰ VSMOW) ← warming
Δ Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Permian
B.
251.22
250.55
252
251
250
249
248
A.
Euxinic
Anoxic
Dysoxic
Oxic
C. D. E.
δ13C carb (‰)
-2 0 2 4 6 8
Boreal Ammonoid Speices Diversity
0 5 10 15 20
-32 -26 -28 -30
δ13C org (‰)
267
Figure 8.7 Barplots of genus diversity, all data from genus counts in Brayard et al., (2006). The top row
of histograms show global genus diversity counts. Each vertical bar represents genus diversity during
an Early Triassic stage (G=Griesbachian, D=Dienerian, Sm=Smithian, Sp=Spathian). Global diversity
consists of genera found within more than one region added to genera uniquely occurring within a
single region. Endemism increases throughout the Early Triassic.
The middle row of histograms shows the diversity of ammonoids within three regions through
the Early Triassic, including the unique genera. The bottom row of histograms shows that when unique
endemic genera are removed, there is no statistically signicant dierence (X = 6.85, degrees of free-
dom = 6, p = 0.34) in diversity pattern through time between any of the three sites or the global diver-
sity pattern.
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100
Genus Diversity Genus Diversity Genus Diversity
G D Sm Sp
G D Sm Sp G D Sm Sp
G D Sm Sp G D Sm Sp G D Sm Sp G D Sm Sp
Total Global Diversity
Total Global Diversity
Genera occuring in
more than one region
Genera occuring in
more than one region
Genera unique
to a single region
Boreal Ocean
(Canada)
Tropical Tethys
(South China)
Temperate Tethys
(Pakistan)
Boreal Ocean
(Canada)
Tropical Tethys
(South China)
Temperate Tethys
(Pakistan)
G D Sm Sp G D Sm Sp G D Sm Sp G D Sm Sp
268
Figure 8.8 The Early Triassic globe contained three major ocean basins, the Panthalassic, Tethys, and
Boreal Oceans. Enduring shallow oxygen minimum zones existed throughout equatorial Panthalassa
and much of the Tethys (Algeo et al. 2010, 2011; Winguth and Winguth 2012). Westermann Morpho-
space diagrams represent ammonoid shape occupation during the Smithian Stage at four relative
paleogeographic locations indicated. Low latitude (South China, American Southwest) settings
featured signicantly more species of oxycones than the Boreal Ocean (Table 8.4). The second high
latitude site, in the Tethys (Pakistan), represents a midpoint in the latitudinal gradient of relative
oxycone speciosity, and does not dier signicantly from the other three regions.
Low oxygen
zones Panthalassic
Ocean
Boreal Ocean
Tethys
Ocean
Panthalassa
Tropical
Boreal
Oxycone
Spherocone Serpenticone
Plankton Demersal
Nekton Vertical Migrant
Oxycone
Spherocone Serpenticone
Plankton Demersal
Nekton Vertical Migrant
Tethys
Temperate
Oxycone
Spherocone Serpenticone
Plankton Demersal
Nekton Vertical Migrant
Tethys
Tropical
Oxycone
Spherocone Serpenticone
Plankton Demersal
Nekton Vertical Migrant
269
Figure 8.9 Earliest Triassic and Jurassic ammonoids compared in Westermann Morphospace. A. Triassic
(Griesbachian – Smithian stages, ~1.7 Ma) from the Boreal Ocean based on Tozer’s (1994) type speci-
mens (n=84). B. The complete Jurassic Hettangian Stage (~1.8 Ma) record of ammonoids from Nevada,
based on type and largest available specimens (n=47) from Guex (1995). There are signicantly more
serpenticone species in the earliest Jurassic (X = 19.2, degrees of freedom = 1, p= 1.15*10-5). If shell
shapes expressed by earliest Triassic and Jurassic species were the same, the dierence in latitude
would predict the opposite trend (see Figure 8.8).
A. Griesbachian-Smithian (Tozer 1994)
B. Hettangian (Guex 1995)
Intermediate
Intermediate
Oxycone
Spherocone Serpenticone
Oxycone
Spherocone Serpenticone
Serpenticones: 18
Intermediates: 66
Serpenticones: 28
Intermediates: 19
270
Abstract (if available)
Abstract
The Triassic/Jurassic mass extinction (201.3 Mya) is the most severe biotic crisis in the history of the Modern Fauna, the marine invertebrates that dominate modern oceans (e.g., gastropods, bivalves). The ecological consequence in marine habitats is an outstanding question of particular interest because similar mechanisms of environmental change are revolutionizing marine ecosystems today. This dissertation investigates these consequences by examining evidence of ecological complexity within benthic (sea floor-dwelling) and pelagic (water column-dwelling) fossil faunas. First, analysis is presented of sedimentology and benthic fossils within post-extinction strata (~ 2 Ma record) in North and South America, with comparison to other records from across the globe. Second, a framework is established for evaluating the ecology of pelagic faunas, specifically ammonoids, in general and with respect to extinction aftermath, contrasted between the Triassic/Jurassic and Permian/Triassic events. ❧ Benthic ecology is examined in the Gabbs Valley Range of Nevada, USA and in the Central Andes of Peru, by determining the environments of deposition and the contribution of biology to sedimentation. First order investigations of the sedimentology and fossil abundance in Nevada, presented in Chapter 2, show that the reappearance of abundant rock-forming metazoan biocalcifiers occurs about two million years after the extinction, despite continual and increasing intensity of carbonate facies accumulation. This demonstrates decoupling of carbonate saturation and biocalcifier production associated with previously unrecognized long-term ecological collapse of marine shelf carbonate ramp systems. The post-extinction interval of non-metazoan-mediated carbonates is examined in Chapter 3. This analysis shows that widespread concretions formed early near the sediment/water interface, completely replacing otherwise dominantly biosiliceous clasts, and formed a profound carbonate sink. Microfacies techniques are used in conjunction with body fossil observations to determine the nature of metazoan ecology during the extinction aftermath in Chapter 4. In both Nevada and Peru, Upper Triassic carbonate systems are replaced by siliceous fossil sponge-dominated ecosystems in the Lower Jurassic. The "sponge takeover" was likely facilitated by a unique confluence of circumstances: extinction-driven changes in benthic ecology coupled with increased global silica flux (a limiting nutrient for sponges) from weathering of the massive Central Atlantic Magmatic Province (CAMP). The sensitivity of global silica cycling to changes in weathering flux is calculated to learn more about this sponge interval in Chapter 5. Specifically, it is shown that the Central Atlantic Magmatic Province could have provided enough silica for sponges to have expanded across tropical carbonate shelves in less than one million years. ❧ Pelagic ecology is evaluated using fossil ammonoids. Chapter 6 presents a review of recent developments in ammonoid paleobiology. Relatively direct ecological evidence springs from body fossils: hard and soft part preservation
Linked assets
University of Southern California Dissertations and Theses
Conceptually similar
PDF
The early Triassic recovery period: exploring ecology and evolution in marine benthic communities following the Permian-Triassic mass extinction
PDF
Ecological recovery dynamics of the benthic and pelagic fauna in response to extreme temperature events and low oxygen environments developed during the early Triassic
PDF
Paleoecology of Upper Triassic reef ecosystems and their demise at the Triassic-Jurassic extinction, a potential ocean acidification event
PDF
Paleoenvironmental and paleoecological trends leading up to the end-Triassic mass extinction event
PDF
The geobiology of fluvial, lacustrine, and marginal marine carbonate microbialites (Pleistocene, Miocene, and Late Triassic) and their environmental significance
PDF
Benthic paleoecology and macroevolution during the Norian Stage of the Late Triassic
PDF
Community paleoecology and global diversity patterns during the end-Guadalupian extinction (middle-late Permian) and the transition from the Paleozoic to modern evolutionary faunas
PDF
Unraveling mass extinctions: Permian to Early Jurassic onshore-offshore trends of marine stenolaemate bryozoans
PDF
Paleoenvironments and the Precambrian-Cambrian transition in the southern Great Basin: Implications for microbial mat development and the Cambrian radiation
PDF
Evolution & ecology of Mesozoic birds: a case study of the derived Hesperornithiformes and the use of morphometric data in quantifying avian paleoecology
PDF
Integrated approaches to understanding diversification through time using sea urchins as a model system
PDF
Sedimentary geochemistry associated with the end-Triassic mass extinction: changes to the marine environment from an age constrained sedimentary section
PDF
Sulfur isotope geochemistry and the end Permian mass extinction
PDF
Assessing the quality of the fossil record using a phylogenetic approach
PDF
Stromatolites in the ancient and modern: new methods for solving old problems
PDF
Evolution of the Indian Monsoon and rise of C₄ photosynthesis in the Miocene and Pliocene
PDF
A systematic review of Enantiornithes (Aves: Ornithothoraces)
PDF
The geobiological role of bioturbating ecosystem engineers during key evolutionary intervals in Earth history
PDF
How open ocean calcifiers broke the link between large igneous provinces and mass extinctions
PDF
Bioturbation in Cambrian siliciclastic shelf strata: paleoecological, paleoenvironmental, and temporal patterns
Asset Metadata
Creator
Ritterbush, Kathleen Anita
(author)
Core Title
Benthic and pelagic marine ecology following the Triassic/Jurassic mass extinction
School
College of Letters, Arts and Sciences
Degree
Doctor of Philosophy
Degree Program
Geological Sciences
Publication Date
10/23/2015
Defense Date
09/27/2013
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
abundance,diversity,Ecology,Liassic,Mesozoic,morphometrics,OAI-PMH Harvest
Format
application/pdf
(imt)
Language
English
Contributor
Electronically uploaded by the author
(provenance)
Advisor
Bottjer, David J. (
committee chair
), Caron, David A. (
committee member
), Corsetti, Frank A. (
committee member
)
Creator Email
ritterbu@dornsife.usc.edu,ritterbu@usc.edu
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c3-339972
Unique identifier
UC11296445
Identifier
etd-Ritterbush-2114.pdf (filename),usctheses-c3-339972 (legacy record id)
Legacy Identifier
etd-Ritterbush-2114.pdf
Dmrecord
339972
Document Type
Dissertation
Format
application/pdf (imt)
Rights
Ritterbush, Kathleen Anita
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...
Repository Name
University of Southern California Digital Library
Repository Location
USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA
Tags
abundance
Liassic
Mesozoic
morphometrics