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Benthic paleoecology and macroevolution during the Norian Stage of the Late Triassic
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Benthic paleoecology and macroevolution during the Norian Stage of the Late Triassic
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Content
Benthic Paleoecology and Macroevolution
During the Norian Stage of the Late Triassic
by
Lydia S. Tackett
April 2014
2
Table of Contents
Pg. 3 Acknowledgements
Pg. 4 List of Figures
Pg. 17 List of Appendices
Pg. 18 Chapter 1.
Pg. 66 Chapter 2. Chronostratigraphy of the Norian Stage
Pg. 104 Chapter 3. Benthic Paleoecology in Tethys
(Lombardian Basin) During the Norian Stage
Pg. 124 Chapter 4. Benthic Paleoecology in Panthalassa
(Nevada and Oregon) During the Norian Stage
Pg. 148 Chapter 5. Global Trends During the Norian Stage
Pg. 197 List of References
Pg. 216 Figures
Pg. 288 Appendices
3
Acknowledgements
Thank you, Dave, my advisor – I will always be grateful for the opportunity you
gave me to come and study evolution. It has been even more fun than I dreamt it
would be.
To the people that made the process of going to graduate school and completing
this dissertation a pleasure: thank you. To Josh–I thank you for your unwavering
support these last five six years. You have been an exceptional partner, field
assistant, and friend. To my wonderful family–you’ve been a source of inspiration
for me: Mom, Dad, Julia, Doris, Moe, Don, June, and Kim.
I have been fortunate to have a strong scientific community within several yards
of my desk for this half-decade–thank you, Frank Corsetti, for your help with so
many projects and questions. My qualifying committee members challenged me
in wonderful ways that greatly improved the quality of my research: John Platt,
Steve Lund, and Dave Caron. I have also benefitted from scientific prodding from
Will Berelson and Josh West. I would also like to thank the faculty that helped me
become a better teacher, including Ken Nealson and Greg Davis.
I would also like to thank my lab mates for being both creative collaborators and
insufferable distractions, both of which I have appreciated very much. Thank you,
Rowan, Scott, Kathleen, Yadi, Liz, Carlie, Sarah, Kirk, and Yadi. I would also like
to thank my dear friends who have been so supportive (Andy, Praz, John, Jim,
Emily, Sylvia, Allison, and even Amir). I would specifically like to thank the
members of the various excellent clubs in which I am a member–the QLMC,
DDT, and the LAAC, and other squash partners (Thorsten, Meghan, Pete).
Fieldwork had been a major part of my research, and I have only been able to
successfully do this work with the help from my many tired and dusty field
assistants (Josh, Liz, Scott, Brandon) and the generous field guidance and
paleoecological discussions from Andrea Tintori. Alan Jay Kaufman, Paul Olsen,
David Kring, and Neil Landman have contributed enormously to my
understanding of complex scientific concepts. My research has been advanced
with help in analytical methods from Miguel Rincon, Jason Visser, and Huan Cui.
The administrative staff at USC has played a crucial role in my success at USC
and beyond, and I would like to thank Cindy, John McRaney, John Yu, Vardui,
and the lovely people from SCEC for their tireless efforts.
I have received funding from several generous sources: USC Department of
Earth Sciences, William M. Keck Foundation, USC Dana and David Dornsife
College funds, Evolving Earth Foundation, SEPM, the American Museum of
Natural History, the Geological Society of America, and the AAPG Paul Danheim
Nelson Grant.
4
Figure Captions
Chapter 1 Figures
Figure 1.1. The Phanerozoic timescale, showing the relation of the Norian Stage
and substages to other intervals of time (Walker et al., 2012). *Rhaetian base is
uncertain - see discussion in text.
Figure 1.2. Changing timescale of the Triassic Period. The Norian-Rhaetian
boundary is still undefined and highly uncertain. Dotted line indicates the relative
placement of the Manicouagan impact event to the Late Triassic stages. Modified
from Mundil et al. (2010). *Duration is based on estimate of the Norian-Rhaetian
boundary at 207Ma, but this date is uncertain. Black diamonds represent
analytical uncertainty.
Figure 1.3. The Evolutionary Faunas through the Phanerozoic. Range data from
Sepkoski (1981)(top, modified) and generic occurrences from Alroy (2010)
(bottom). Factors I, II, and III correspond to the Cambrian, Paleozoic, and
Modern Faunas, respectively.
Figure. 1.4. Comparison of Carnian sedimentary accumulations from regions
around the world. Modified from Greene et al. (2011).
Figure 1.5. Transition from Middle Triassic dominance of epifauna to the Late
Triassic dominance by infauna. Modified from Bonuso and Bottjer (2008).
5
Figure 1.6. Extinction rates for invertebrate marine genera from the Phanerozoic.
The end-Cretaceous extinction is marked by the arrow. (modified from Alroy,
2008)
Figure 1.7. Paleogeography and diversity gradients for (a) the Chicxulub impact
and (b) the Manicouagan impact. From Walkden and Parker (2006).
Figure 1.8. (left) Gravity anomaly map of the Chicxulub crater (Sharpton et al.,
1993) and (right) an aerial view of the Manicouagan crater (NASA).
Figure 1.9. Impact crater cross-sections of Manicouagan and Chicxulub. Modified
from Walkden and Parker (2008).
Figure 1.10. Impact signatures at a terrestrial Cretaceous-Paleogene boundary
and mass extinction horizon (modified from Orth et al., 1982).
Figure 1.11. Atmospheric blow-out produced by large impact events. From
Winslow (unpublished), modified from Melosh (1996).
Figure 1.12. Summary of changes for the timing of evolutionary and geologic
events of the Mesozoic, based on Triassic timescale changes and results from
this research. MMR = Mesozoic Marine Revolution, PF-MF = Paleozoic Fauna-
Modern Fauna Transition.
Figure 1.13. Modes of tiering in marine level-bottom ecosystems.
Figure 1.14. Ecological niches based on life mode characteristics of marine
animals. From Bush et al. (2007).
6
Chapter 2 Figures
Figure 2.1. (top)
87
Sr/
86
Sr curve for the Phanerozoic from Veizer et al. (1999) with
the Late Permian and the Triassic Period highlighted, (bottom) for the Triassic,
modified from Korte et al. (2003).
Figure 2.2. Fossil shells from the Riva di Solto Formation, with growth bands and
coloration, possibly original.
Figure 2.3. Field locality maps. (top left) Nevada, grey box shown below. (bottom
left) Landmarks and the area of the Gabbs Valley Range (white star indicates the
location of New York Canyon) and the Shoshone Mountains (black star indicates
the location of the Berlin-Ichthyosaur State Park). (center) New York Canyon and
Muller Canyon, with locations of samples and important sequences discussed in
the text. (right) New York Canyon samples. Geologic map modified from Hallam
and Wignall (2000). Referenced sections: A-Muller Canyon. B-Reno Draw. C-
Luning Draw.
Figure 2.4. Generalized stratigraphic column for Late Triassic formations and
members sampled in this analysis.
Figure 2.5. Stratigraphy, sampling horizons,
87
Sr/
86
Sr, and strontium/manganese
concentrations from the carbonate member of the Luning Formation in the
Shoshone Mountains at Berlin-Ichthyosaur State Park. Strontium values
indicated by an open circle come from brachiopod shell material, black circles
7
represent bivalve shell material. Published ranges of
87
Sr/
86
Sr from Korte et al.
(2003). C=Covered, S=Shale, M=Mudstone, W=Wackestone, P=Packstone.
Figure 2.6. Approximate ranges of biostratigraphically significant conodont
species discussed in the text, and correlation with other biostratigraphic zonation
schemes. Modified from Orchard (2010), including all conodont ranges and
biozone divisions, except North American conodont biozones, which are from
Orchard and Tozer (1997) and McRoberts et al. (2008). The division between E.
mosheri and M. posthernsteini in the North American division is approximate.
Figure 2.7. Stratigraphic columns and
87
Sr/
86
Sr values from the Nun Mine
Member of the Gabbs Formation in New York Canyon, NV. Published strontium
isotope values from Tethyan succession in Korte et al. (2003). All measurements
are derived from bivalve shell material.
Figure 2.8. Different luminescence (Lm) in carbonates from the Nun Mine
Member. (a) Lowest observed Lm in sample 6, with non-luminescent matrix and
shells; (b,c) slightly luminescent matrix with non-luminescent shells; (d) dull
luminescence in matrix and slightly more in bivalve shell; (e) moderately
luminescent calcite vein; (f) brightly luminescent void-fill. Exposure time is 4s
unless otherwise indicated. Scale bar = 0.2mm.
Figure 2.9. Stratigraphic correlation and age determinations of the Gabbs
Formation. (A) Previous ages attributed to the upper Luning Formation and
Gabbs Formation, and updated ages based on chemostratigraphy in (B). (B)
87
Sr/
86
Sr from Tethyan conodonts (colored circles) from Korte et al. (2003), and
8
87
Sr/
86
Sr from the Nun Mine Member (NMM) of the Gabbs Formation (black
closed circles), correlated to the conodont ranges in (C), and an upper Muller
Canyon Member sample (open black circle). Tethyan measurements correlated
to New York Canyon values based on range similarity. (C) Approximate conodont
ranges from the Gabbs Formation of New York Canyon and North American
biozones from Orchard et al. (2007). Luning Formation ranges were not reported.
NA = North America.
Figure 2.10. Approximate correlation of sedimentary sequences dated and
analyzed herein. Not drawn to scale. MCM = Muller Canyon Member.
Chapter 3 Figures
Figure 3.1. (a) (left) Map of northern Italy, and (right) the Southern Alps (dashed
line), and the Bergamasc Alps (black box) which are shown below; (b) map of
sampling localities in the Imagna Valley (left) and Lake Iseo (right), with detailed
insets (c, d). DP refers to the Dolomia Principale Formation.
Figure 3.2. Generalized cross-section of the Lombardian Basin. Circles represent
approximate level of bulk samples. Modified from Jadoul et al. (Jadoul et al.,
1994; Jadoul et al., 2004).
Figure 3.3. Idealized stratigraphic column of the Lombardian basin, with sampling
horizons. For relative thickness of formations, see Fig. 3.2.
9
Figure 3.4. Field, stratigraphic, and hand sample examples of facies from the
Riva di Solto Formation.
Figure. 3.5. Different types of carbonate beds associated with the Riva di Solto
Formation. (A) Field view of carbonate bed types. (B) Type 2 carbonate bed with
Pinna in life position. (C) Type 1 carbonate bed with winnowed, concentrated
bivalve deposits.
Figure 3.6. Paleoecological niche data in Norian bulk samples from the Dolomia
Principale and Riva di Solto formations (top) and evolutionary change-points
(bottom) suggested by probability analysis. AIC=Akaike information criterion;
BIC=Bayesian information criterion.
Figure 3.7. Relative abundance of stationary epifauna and mobile infauna from
the Tethyan bulk samples.
Figure 3.8. Paleoecological succession within Norian bulk samples. (top) Relative
abundances of categories relating to an organism’s life position relative to the
sediment-water interface. (center) Relative abundances of niche categories
relating to mobility and life position. (bottom) Plotted relative abundances of
major ecological guilds.
Figure 3.9. Schematic depiction of the faunal assemblages grouped by
evolutionary change-points identified with AIC/BIC rankings of the
paleoecological data.
10
Chapter 4 Figures
Figure 4.1. Common facies and fossils from the Carbonate Member of the Luning
Formation in Berlin-Ichthyosaur State Park. (a) brachiopod wackestone, (b) large
gastropods, (c) shell hash wackestone, (d) medium-bedded limestone.
Figure 4.2. Previously published ages for the members of the Gabbs and Sunrise
formations. *Pre-Rhaetian ages are based on biostratigraphic ranges reported.
(Ages from Ferguson and Muller, 1949; Dagys and Dagys, 1994; Hallam and
Wignall, 2000; Orchard et al., 2007; Taylor et al., 1983; Ward et al., 2004).
Figure 4.3. Late Triassic field localities and stratigraphy. (left) Nevada, with the
field area denoted the by grey box, inset below. Stars mark the field localities
sampled in this study, black is the Berlin-Ichthyosaur State Park and white is
New York Canyon. (center) Generalized stratigraphic column of the Late Triassic
formations, with black bars indicating the sampled successions. Formational
thicknesses are approximate and not drawn to scale. (right) Stratigraphic
columns of the sampled successions in this study, with sample numbers to the
right. A is the carbonate member of the Luning Formation in the Berlin-
Ichthyosaur State Park and B is the lower Nun Mine Member of the Gabbs
Formation in New York Canyon. Covered sections may represent more height
than what is represented in stratigraphic column.
Figure 4.4. Field photos from the Carbonate Member of the Luning Formation in
West Union Canyon near the Berlin-Ichthyosaur State Park (left) and the lower
Nun Mine Member of the Gabbs Formation in New York Canyon, Nevada (right).
11
Figure 4.5. Relation of number of taxa to number of specimens. Number of
specimens does not include specimens which were not identified. (top) all bulk
samples from Nevada, (bottom) samples 3-12.
Figure 4.6. Relative abundances of paleoecological niche categories in bulk
samples from Berlin-Ichthyosaur State Park (the Carbonate Member of the
Luning Formation) and New York Canyon, Nevada (the Nun Mine Member of the
Gabbs Formation).
Figure 4.7. Abundance of taxa observed in bulk samples from the Luning
Formation and the Gabbs Formation. Singletons can be found in Appendix 5.
(Each dash on the axis is 10 specimens, unless otherwise indicated)
Figure 4.8. (A) Correlation of percentages of total specimens for stationary
epifauna (x-axis) and mobile infauna (y-axis). (B) Relative abundances of major
ecological groups. (C) Stacked percentages of the total fauna for the
“intermediate” ecological niches: mobile epifauna, stationary semi-infauna,
cementing stationary epifauna.
Figure 4.9. Schematic depiction of the Panthalassan faunal assemblages
grouped by evolutionary change-points identified with AIC/BIC rankings of the
paleoecological data.
Figure 4.10. Oregon field locality (modified from Yancey and Stanley (1999). (A)
Wallowa terrane in reference to the Luning and Gabbs formations and the North
American craton, (B) terranes in Oregon, (C) Black Marble Quarry in relation to
12
geographic landmarks and the main succession of the Martin Bridge and Hurwal
formations. U and D refer to hanging and footwalls of fault lines, respectively.
Figure 4.11. Fauna and facies from the Black Marble Quarry, Oregon. (a)
Wallowaconchidae, (b) ammonoid, (c) coral-dominated wackestone, (d) bioclastic
packstone. Scale bar in each image = 4cm.
Figure 4.12. Bulk sample horizons from Black Marble Quarry.
Figure 4.13. Relative abundance of taxa (top) aand paleoecological niches
(bottom) from Black Marble Quarry bulk samples.
Figure 4.14. Plotted relative abundance of particular ecological niches utilized in
bulk samples from Black Marble Quarry. SE = stationary epifauna, MI = Mobile
Infauna, ME = Mobile epifauna.
Figure 4.15. Correlation between mobile infauna (MI) and mobile epifauna (ME)
from Nevada (top), all samples except sample 5, and Italy (bottom), Middle and
Late Norian samples.
Figure 4.16. Correlation of Black Marble Quarry (Oregon) paleoecological
structure with the assemblages from Nevada and Italy.
Chapter 5 Figures
Figure 5.1. Relative abundances of feeding modes among shelly benthic fauna
from Italy and Nevada.
13
Figure 5.2. Relative abundances of different animal clades from Nevada (a,b)
and Italy (c,d); (left) total specimens by clade, (right) relative abundance in time-
series.
Figure 5.3. Relative abundances of taxa in Norian bulk samples from
Panthalassa (Nevada) and Tethys (Italy). Each color represents a taxon, data in
Appendices 4 and 5.
Figure 5.4. Relative abundances of paleoecological niche categories in bulk
samples from Berlin-Ichthyosaur State Park and New York Canyon, Nevada
(top), and the Dolomia Principale and Riva Di Solto formations in Italy (bottom).
Figure 5.5. Relative abundances of mobility styles in Nevada and Tethys.
Figure 5.6. Relative abundances of tiering animals from Nevada and Tethys.
Figure 5.7. Stacked abundances of ecological “intermediates” from Nevada (top)
and Italy (bottom). (A) relative abundances of ecological niches of interest and
(B) specific relative abundances of ecological “intermediates”.
Figure 5.8. Taxonomic occurrences of major durophagous predators from the
Ladinian to the Sinemurian.
Figure 5.9. (top) Occurrences of predators specizalized for durophagy; Groups
are listed in supplemental material. (top-middle) Occurrences of crinoid clades, *
= non-stationary epifauna. (bottom-middle) Originations of cementing bivalve
clades. (bottom) Paleoecological changes in this study for prey adapted against
durophagy.
14
Figure 5.10. Occurrences of durophagous-specialized or drilling-specialized
predators, and prey with anti-predators strategies. Thick lines represent common
occurences and diverse fauna, thin thinks represent present but not common,
dotted lines indicate inferred presence. Data in Appendix 1.
Figure 5.11. Brachiopod dynamics through the Mesozoic. (top) brachiopod
genera and (bottom) ornamentation index. Rh = Rhynchonellid, Te = terebratulid.
Data from Vörös (2010). *Mean Ornamentation Index is determined by taking the
average of the ornamentation index for the standing genera per stage;
ornamentation index is a qualitative descriptor to characterize the height of the
ribs of the shell surface; larger numbers indication greater spinosity.
Figure 5.12. Size changes for non-cementing stationary epifauna from Nevada
(top) and Italy (bottom).
Figure 5.13. For the measured stationary epifauna per bulk sample, the average
size of those stationary epifauna plotted against the proportion of stationary
epifaunal specimens out of all specimens (Italy).
Figure 5.14. Comparison of drill hole morphologies. (top) Gastropod drill holes
(from Chojnacki and Leighton, 2013 [left] and Sohl, 1969 [right]); (bottom)
octopod drill holes—note small size and x-shape (Bromley, 1993).
Figure 5.15. Area of stationary epifaunal (non-cementing) fossil specimens from
the Lombardian Basin (Italy, Tethyan Sea) through the Norian Stage, by genus.
15
Figure 5.16. Size changes which occur within a genus, Avicula, during the Norian
Stage, based on Tethyan specimens. Images are representative specimens
close to the average area for the genus in the bulk sample indicated by the
number by the image. Scale bar = 1cm.
Figure 5.17. Size characteristics of Tethyan stationary epifauna during the Norian
Stage. (a) Relative proportion of size categories for measured stationary
epifaunal specimens, (b) overlapping size distributions, and (c) stacked size
categories for measured stationary epifauna from Italian specimens.
Figure 5.18. Chlamys (top) and Plicatula (bottom) measured specimens from
Nevada, height vs. width.
Figure 5.19. Locality information for the K-Pg Boundary section at Brazos River,
TX. Data from Hansen et al. (1993).
Figure 5.20. Paleoecological succession across the K-Pg boundary section in
Brazos River, TX (right), Norian successions in Panthalassa (left, top) and Tethys
(left, bottom). K-Pg data from Hansen (1988).
Fig. 5.21. Methods for identifying horizons of rapid faunal turnover. (A) Relative
abundances of each paleoecological category represented in each bulk sample
from Tethys (above) and Panthalassa (below), with rapid transitions indicated for
each, and results of high-resolution inter-bulk sampling for Panthalassa. (B)
Schematic depiction of the process of identifying the effects of an impact event.
16
Figure 5.22. Higher-resolution bulk sampling from the upper Luning Formation
and the lower Gabbs Formation in intervals of high faunal/paleoecological
change. (top) All bulk samples, (bottom) high-resolution bulk sample data. Grey
boxes represent intervals of relatively rapid paleoecological change. Black box
represents the interval of rapid change within a high-resolution bulk sample
range.
Figure 5.23. Preliminary sampling methods in the intervals of non-gradual
paleoecological change within the Nun Mine Member of the Gabbs Formation
(top), field image (bottom left) and schematic stratigraphy (bottom right). White
boxes represent shale samples collected, black boxes represent limestone
column samples.
17
List of Appendices
Appendix 1. Appearances and major radiations of durophagous predators and
prey with anti-durophagy adaptations
Appendix 2. Elemental and isotopic data (Strontium, Carbon, Oxygen,
Manganese, Magnesium) for samples from the Carbonate Member of the Luning
Formation, the Gabbs Formation, and the Sunrise Formation (Nevada)
Appendix 3. Identification sources for Tethyan fossils of the Norian Stage
Appendix 4. Tethyan (Italian Alps) fossil occurrences and paleoecological
categories for Norian bulk samples
Appendix 5. Panthalassa (Nevada) fossil occurrences and paleoecological
assignments for Norian bulk samples
Appendix 6. Panthalassa fossil occurrences for bulk samples from Black Marble
Quarry, OR
Appendix 7. Size data for non-oyster stationary epifauna from Nevada and Italy
Appendix 8. Faunal occurrences (excluding singletons) from Tethys and
Panthalassa with ranges ending in the Norian (orange) or beginning in the Norian
(blue)
18
Chapter 1. Introduction
The use of databases and meta-analytic methods in paleoecology has
illustrated several intervals in the history of life that uniquely influenced biotic
communities and shaped the way modern ecosystems function. Fossil data is
now continuously pooled from different localities and time periods, and two
important outcomes of this approach have become apparent: the identification of
large-scale evolutionary and paleoecological transitions and the identification of
intervals that are relatively understudied. One particular interval, the Norian
Stage of the Late Triassic, appears to represent both a stage which can be
characterized as understudied, but which is also likely to have been an interval in
which several of the most important evolutionary and geologic events in the
Phanerozoic occurred, such as the Manicouagan bolide impact (Walkden and
Parker, 2008), and the origin of the Mesozoic Marine Revolution (Ch. 4). The
ambiguity of this particular stage is compounded by several major
chronostratigraphic problems, including a dearth of absolute dates and the
reliance on regional biostratigraphic schemes. This stage represents a key to
many important questions in paleobiology, and I posit answers by resolving some
of the temporal issues and the lack of faunal data within this stage.
The fauna of the Triassic Period experienced some of the most
catastrophic geologic events known to occur on Earth (large asteroid impacts
and igneous provinces) and recovered from the most severe biotic crisis of the
entire Phanerozoic, the end-Permian mass extinction (McGhee et al., 2004). Two
major evolutionary transitions are believed to have begun during this period (the
19
Mesozoic Marine Revolution [Vermeij, 1987] and the Paleozoic Fauna–Modern
Fauna transition [Sepkoski et al., 1981]), the mass extinction which ended the
Triassic Period is recognized as being an important analogue to modern ocean
systems because this mass extinction is closely correlated with rapid global
warming and possible ocean acidification (Greene et al., 2012b). Dinosaurs
evolved during the Triassic (Irmis et al., 2011) and experienced their first major
taxonomic radiation in the Norian Stage (Brusatte et al., 2010). Modern coral reef
ecosystems developed (Flugel, 2002) and calcareous nannoplankton evolved.
Despite all of these fascinating geologic and evolutionary events occurring within
a single period, we know surprisingly little about the paleoecological progression
of shallow marine fauna through the majority of the Triassic.
The Late Triassic timescale
This uncertainty surrounding the biological and geological events of the
Late Triassic is due to several compounded problems related to Late Triassic
chronostratigraphy, including recent timescale revisions (Furin et al., 2006;
Muttoni et al., 2010), lack of successional faunal data for the Norian Stage, new
range-extending faunal discoveries, new absolute dates for several geologic
events (Hodych and Dunning, 1992), and the relatively recent ratification of the
Rhaetian Stage as the last stage of the Triassic.
The Norian is the penultimate stage of the Triassic, the first period of the
Mesozoic (Fig. 1.1). It is one of three stages of the Late Triassic: the Carnian,
Norian, and Rhaetian. Three substages are recognized for the Norian Stage: the
20
Lacian, Alaunian, and Sevatian. Some debate has recently arisen over this final
substage, and some consider the Sevatian to be divided into two parts (Sevatian
1 and 2)(Fig. 1.1), the second part belonging to the Rhaetian Stage (Lucas et al.,
2005; Hüsing et al., 2011). This is primarily due to disagreement over the use of
different chronostratigraphic schemes (Lucas, 2013), namely whether to use the
first occurrence of Misikella hernsteini or M. posthernsteini as the base of the
Rhaetian, although the issue is complex and involves several chronostratigraphic
methods with separate caveats (Hüsing et al., 2011). The second part of the
Sevatian (Sevatian 2) most likely represented a relatively short interval of time
(Lucas et al., 2012), and the issue is not currently resolved . Most stages of the
Phanerozoic have been established for many decades, but the Rhaetian Stage of
the Late Triassic has proven to be an enigmatic issue.
Stage durations of the Late Triassic have gone through several revisions,
as new absolute dates have become available for some stage boundaries and as
new chronostratigraphic methods have been applied (Fig. 1.2). In the absence of
absolute dates, the durations of the Carnian, Norian, and Rhaetian stages were
estimated based on number of biozones and magnetostratigraphy (Krystyn,
1990). These estimates tended to make the Carnian and Norian stages of similar
duration (~8-12my), while the duration of the Rhaetian Stage has fluctuated
wildly (1-10my) depending on the method of correlation employed (Hüsing et al.,
2011; Muttoni et al., 2010). Due to this high degree of uncertainty, correlating the
biotic response to geologic events - even those with absolute dates such as the
Manicouagan impact – has been fraught with problems.
21
Recently, the Triassic timescale received its most dramatic revision in
decades with the discovery of an ash bed in uppermost Carnian sediments from
Italy (Pignolo 2)(Furin et al., 2006). This locality is correlated to a
biostratigraphically-resolved succession from another Italian succession, Pizzo
Mondello. The U-Pb values from zircons in the ashes provided a crystallization
date of ~230Ma, suggesting a Carnian–Norian boundary age of ~228mya. This
date was over ten million years older than most estimates for this boundary (Fig.
1.2).
Unfortunately, there is still very little age control for the Norian–Rhaetian
boundary. Magnetostratigraphic correlations between terrestrial and marine
realms are still debated (Olsen et al., 2011). Rhaetian biostratigraphy suggests a
short stage due to the small number of biozones, but the longest estimates for
the Rhaetian Stage which are based on magnetostratigraphy and
cyclostratigraphy suggest a duration of ~10my (~209-199mya)(Muttoni et al.,
2004). This duration still renders the Norian Stage as the longest single stage of
the entire Phanerozoic if the Carnian–Norian boundary is ~228Ma. The long
duration of this stage has important implications for several important geologic
and evolutionary events, including those that occurred in other stages.
Because there is still wide disagreement about how the Norian–Rhaetian
boundary (NRB) is to be defined, it is possible that some results based on
boundary delineations will need to be re-interpreted in the future. Here, we use
the first appearance datum (FAD) of Misikella posthernsteini as the base of the
Rhaetian Stage, which coincides with a conodont faunal turnover (Krystyn, 2008)
22
and a strontium isotope excursion (Korte et al., 2003). In this definition, M.
hernsteini is a rare occurrence in Epigondolella-dominated assemblages, and
represents the latest Norian/NRB transition (Krystyn et al., 2007). This boundary
definition is optimal because it has field recognition ability (using the FAD of
ammonoid species Paracochloceras suessi), and global correlative ability (using
strontium isotope chronostratigraphy, Ch. 2). In paleomagnetic stratigraphy, M.
posthernsteini appears immediately above a reversal event, which allows for
terrestrial correlation (Krystyn et al., 2007).
The Manicouagan impact event is very likely to have occurred during the
Norian Stage, and most likely during the Middle Norian (Fig. 1.2). In order to
identify the biotic effects of this event, successional data is required for the Early,
Middle, and Late Norian. This long stage duration also presents a problem for
analyses related to the end-Triassic mass extinction. Most estimates for percent
genus or familial extinction at this period boundary are based on diversity
calculations which group the Norian and the Rhaetian stages together (Foote,
2000; Alroy et al., 2008). Clearly, if these two stages represent nearly 30 million
years of accumulated faunal change, it cannot be reconciled that the total
reported faunal turnovers occurred at the Triassic–Jurassic boundary. For
evolutionary events that are not dependant on timescale boundaries (such as the
Mesozoic Marine Revolution and the Paleozoic Fauna–Modern Fauna transition)
the timescale change does not provide any immediate problems for
interpretations. However, the long duration of the Norian Stage, which now
encompasses nearly half of the Triassic Period, means that binning the faunal
23
data for the entire stage will result in a lack of temporal resolution if either of
these events developed during the Norian Stage. Grouping the faunal data for a
20-26 million year interval removes the possibility of examining these
evolutionary events in a geologic context or for determining the rate of change on
a global and regional scale. Therefore, successional faunal sampling through the
Norian Stage has the potential to resolve several questions.
Recent research has revised the known rates and characteristics of the
MMR and PF/MF transition. For the MMR, the timing of its origin was unclear,
and this was due to the lack of faunal data for predators and shelly prey in the
Late Triassic. Vermeij (1987) noted the appearances of several predator clades
that did not seem to radiate until the Early Jurassic, such as predatory asteroids
and heterodontid sharks. New studies have shown that many of the groups
actually radiated in the Late Triassic and a revised list of predator clades
appearing in this interval including as belemnites (Iba et al., 2012), sharks
(Underwood, 2006), and possibly crabs (Rinehart et al., 2003). A lack of faunal
data also contributed to problems in estimating the timing for the PF–MF
transition. Originally thought to have occurred after the end-Permian mass
extinction, due to the lack of brachiopods and crinoids in the extinction recovery
interval (Gould and Calloway, 1980), recent studies have shown that bivalves
were not persistently dominant after the short Early Triassic (Greene et al.,
2011). Common Paleozoic constituents such as crinoids (Baumiller et al., 2010)
and brachiopods (Vörös, 2010) diversified and became abundant in the Middle
and early Late Triassic. Thus, new research suggests that the Late Triassic was
24
an important time for these two evolutionary events, and the successional faunal
data for the Late Triassic may address how and why these transitions occurred.
Finally, one of the largest problems in evaluating the role of geological
events and the nature of evolutionary events in the Late Triassic is the lack of
data for the Norian Stage itself and the way that data is typically treated. The
fauna of the Norian have been studied for several centuries, and many seminal
monographs by historically-renowned paleontologists have documented the great
diversity of shelly fauna. However, the majority of paleontological research has
focused on the Tethyan deposits of Europe, and very little work addressed the
changing fauna through the stage, even at the regional level. Also, the
abundances of different taxa were not described in most analyses except for
perhaps the most abundant group, although this was common practice before the
field of paleoecology was developed in the 20
th
century. This type of research
resulted in a paleontological data pool that excellently described the diversity of
Tethyan fauna, but did very little to illustrate the temporal changes in diversity or
ecological dominance.
Implications of the unstable and changing timescale
The expansion of the Norian Stage served to highlight how little is known
about this interval. Some first-order implications of these findings are that the
Norian biozones cannot each represent 1 million years. Furthermore, events in
the geologic record with absolute dates must be reevaluated based on the new
Late Triassic timescale. For example, the Manicouagan impact crater in eastern
25
Canada is one of the largest confirmed impact craters of the Phanerozoic, and
has been dated to 215±1 Ma (Van Soest et al., 2009). Older timescales would
have put this impact event near the Carnian-Norian boundary (Fig. 1.2), but the
revised timescale places the impact closer to the middle of the stage.
Determining the effects of this impact event require a better understanding of
what particular animals were living on the planet at the time of the impact.
Finally, certain methods of dating sedimentary successions must be re-
callibrated to the new timescale. The use of cyclostratigraphy is a very common
method for dating Late Triassic successions, and the existing estimates do not
predict a stage of this duration unless the Rhaetian Stage is also much longer
than previously estimated. Alternatively, the disagreement could be due to
unconformities or some other error in the primary cyclostratigraphic section, the
Newark basin (Hüsing et al., 2011). Unfortunately, correlating marine and
terrestrial sections of Late Triassic age is still difficult to do with certainty (Lucas,
2010), and in Chapter 2, I outline the use of strontium isotope chemostratigraphy
to correlate the biozones between ocean basins as an attempt to resolve this
long-standing issue.
Macroevolution in the Norian
Several important evolutionary events occur within the Triassic Period for
which the fauna of the Norian Stage may be of critical importance, including: the
Mesozoic Marine Revolution, the transition from Paleozoic Fauna to Modern
Fauna, and the Manicouagan impact, a non-biotic event which may have
26
profoundly affected the planet’s biota. Furthermore, the timescale change
involving the Norian requires that these events be reconsidered in light of the
longer duration of the stage and new findings involving the Late Triassic and the
end-Triassic mass extinction.
The Mesozoic Marine Revolution
First postulated by Vermeij (1977; 1987), the Mesozoic Marine Revolution
(MMR) was put forward to explain the apparent amplification of evolutionary co-
adaptation among marine predators and prey throughout the Mesozoic Era.
While nearly all phyla and ecological life-modes appeared in the Early Paleozoic
(Harper, 2006; Servais et al., 2009), many of the predatory strategies and anti-
predator adaptations observed in modern oceans first appeared in the Mesozoic,
along with taxonomic radiations of the clades utilizing these adaptations
(Appendix 1; Ch. 5). Some of these characteristics have become common
features of research due to their quantifiable nature, such as the increased
frequency of drill holes and the appearance of modern drilling snails, the naticids
and the muricids during the Cretaceous (e.g.: Kelley and Hansen, 1993).
The Late Triassic was an important interval in the development of an
evolutionary arms race, which resulted in a suite of adaptations among marine
groups, termed the Mesozoic Marine Revolution (MMR) (Vermeij, 1977; Vermeij,
1987). The MMR describes a phenomenon observed among marine taxa of
Jurassic and Cretaceous deposits, which increasingly exhibited a set of
adaptations and taxonomic radiations that may reflect intensifying predatory
27
pressure. This amplification of predatory stress is hypothesized to have induced
adaptive responses among prey taxa, including thicker shells, increased
infaunalization, increased mobility, and defensive shell ornamentation (1987).
These trends have been observed in Mesozoic taxa, and several additional lines
of evidence support a predation-based arms race explanation, including
increased drill hole and repair scar frequency in the Early Cretaceous
(Kowalewski et al., 1998), and the appearance and diversification of important
shell-crushing predator taxa, such as homaridean and palinuran lobsters (Harper,
2003) and shell-crushing fish (Tintori, 1998) in the Late Triassic and Jurassic.
Researchers have also suggested a post-Paleozoic increase in bioturbation
depth and degree, and increasing bed-thickness in the Mesozoic may be related
to increased infaunal activities by burrowers (Sepkoski Jr, et al., 1991). Several
of these trends occurred early in the Mesozoic—in order to determine the
origination time, rate, and faunal characteristics of this ecological shift, the prey
dynamics of the Carnian, Norian, and Rhaetian stages must be examined in
detail.
Various metrics have been used to determine if predatory pressure
increased through the Mesozoic, including taxonomic diversity of predators, drill
hole frequency, breakage scars, shell thickness, and many others (Kowalewski et
al., 1998; Harper and Wharton, 2000; Fürsich and Jablonski, 1984; Vermeij et al.,
1982; Vermeij, 1982). These metrics are appropriate in different sedimentary
settings and faunal assemblages, and reflect different predator strategies (e.g.:
drilling versus crushing). Individual usage of these metrics has led to disparate
28
dates for the onset of the MMR. In the St. Cassian Formation, Carnian
invertebrates lack evidence of shell-breaking by fish and arthropods (Vermeij et
al., 1982), presenting levels that are indistinguishable from the Paleozoic, but are
followed by a post-Triassic increase in these features. Interestingly, the St.
Cassian Formation was also noted to have several of the only Tethyan drill hole
occurrences from the Triassic Period (Fürsich and Jablonski, 1984). By the
Rhaetian Stage, however, the shallow marine level-bottom communities were
comprised of a higher proportion of mobile infauna than previously in the Triassic
(McRoberts et al., 1995). This study also suggested that the end-Triasssic mass
extinction may have selectively affected bivalves in these newly expanded
niches—epifaunal bivalves were ecologically dominant in the earliest Jurassic.
This resurgence was not permanent, however, and the biota in the remainder of
the Jurassic exhibited a gradual increase in taxa that were mobile and/or infaunal
(Aberhan et al., 2006). Direct evidence of drilling predation (drill holes) does not
increase in frequency until the Early Cretaceous, or possibly Late Jurassic
(Bardhan et al., 2012)—although taphonomy may factor into the recognition of
these trace fossils (Harper et al., 1998). Despite the dearth of drill holes,
communities of shallow marine level-bottom benthos were clearly undergoing
significant changes in the Late Triassic-Early Jurassic. The expansion of the
Norian Stage provides a long interval in which the MMR may have developed,
resulting in the more-infaunal assemblages of the Rhaetian.
29
Timing of the MMR.
Vermeij (1987) noted that many of the morphological features and
adapted clades of the MMR were present by the Early Jurassic, including several
groups of shell-crushing fish, sharks, and rays. Bulldozing echinoids and
predatory asteroids also appeared by the Early Jurassic. Among predator clades,
several groups believed to have radiated in the Early Jurassic have now been
shown to have Late Triassic origins such as belemnites (Iba et al., 2012),
durophagous sharks (Underwood, 2006), and even turtles (Li et al., 2008),
although it is clear that radiations continued to occur in the Jurassic, especially
for the durophagous arthropods (Schweitzer and Feldmann, 2010). Some
important first occurrences in the Late Triassic include several durophagous
arthropod groups and turtles, and fish, sharks, and placodonts experienced major
Late Triassic radiation events.
Among prey, this paleoecological phenomenon has been more difficult to
quantify. Some features among prey that notably increased during the Mesozoic
include spinosity, mobility, burrowing depth, shell thickness, and ribosity
(Vermeij, 1987; Vermeij, 2008). Among prey groups, several trends have been
identified specifically in the Late Triassic, which suggests that this interval was
important for the earliest stages of the MMR. These include diversifications of
burrowing bivalves, fused-siphon heterodont bivalves, cementating bivalves
(Harper, 1991), and shelly animals with spines (Vörös, 2010). The predicted
(Fürsich and Jablonski, 1984) discoveries of gradually increasing drill hole
frequencies in the latest Triassic and Early–Middle Jurassic have not been
30
observed, however, and while some rare examples exist in the Late Triassic and
Early Jurassic (Harper and Wharton, 2000), they remain in very low frequencies
until the Early Cretaceous (Kowalewski et al., 1998).
These revisions are critical to understanding the MMR, one of the most
significant biotic events in Earth’s history, which defined the ecological structure
of modern oceans.
The Paleozoic Fauna–Modern Fauna Transition
Another paradigm in modern paleontology was the establishment of three
“Evolutionary Faunas” by Sepkoski (1981), later confirmed by Alroy (2010)(Fig.
1.3). After compiling the occurrences and temporal ranges of all known marine
taxa, Sepkoski (1981) found that three groups of animals experienced similar
timing for initial radiations, and were affected during mass extinction events with
similar drops in diversity. The first of these faunas was termed the “Cambrian
Fauna”, which was characterized by animals appearing in the Cambrian
explosion, and included many “progenitor” groups and “experiments” that did not
persist beyond the Ordovician Period. The “Paleozoic Fauna” (PF) included
animals that played a dominant role in the oceans throughout the Paleozoic, and
include groups such as the stenolaemate bryozoans and articulate brachiopods.
Several higher taxa originated early in the Paleozoic, including the articulate
brachiopods. Many of these groups are not extinct in modern seas but live in
cryptic environments and have lower diversity than in the Paleozoic.
31
After the end-Permian mass extinction, the diversity of many PF groups
declined, or became completely extinct. This mass extinction is considered to be
the most extensive biotic crisis of the Phanerozoic, with 95% of marine species
becoming extinct, perhaps in two phases (Clapham et al., 2009). The recovery
from this event took place over several million years (Bottjer et al., 2008), and
these faunal assemblages were long considered to be the incipient
representatives of the “Modern Fauna” (MF). The MF are comprised of animals
that more common in modern oceans, and include the bivalves, many worms,
and mammals. These groups first appeared long before the Mesozoic, but
existed in smaller proportions than the PF.
Much discussion in the past fifty years has addressed the transition
between the Paleozoic Fauna and Modern Fauna (PF–MF), specifically when it
occurred and under what circumstances. Some researchers have observed that
articulate brachiopods (a PF group) were replaced by mollusks (bivalves and
gastropods, members of the MF) following the mass extinction event, which was
highlighted in the Sepkoski Compendium of marine fauna (Sepkoski, 1981).
Initially it was thought that the Modern Fauna out-competed the Paleozoic Fauna
due to their higher overall rate of metabolism among bivalves than brachiopods,
presumably being evolutionarily advantageous in competition for resources
(Steele-Petrovic, 1979). Others have disputed this, however, and hypothesized
that the decline of brachiopods resulted in emptied paleoecological niche space
that allowed bivalves to move in and become dominant in marine ecosystems
(Gould and Calloway, 1980). This line of reasoning can be compared to the end-
32
Cretaceous mass extinction (K–Pg) that ended the Mesozoic period and
heralded both the extinction of non-avian dinosaurs and other large reptilian
predators and the subsequent diversification of mammals (Novacek, 1999).
Mammals did not out-compete the dinosaurs per se, but they took advantage of
the vacant ecosystems emptied by the mass extinction, expanding into several
new niches and growing in body size (Novacek 1999). Prior to the extinction
event, they existed in low numbers and in limited ecological niches, and
expanded to fill many new ecological niches in the Paleogene.
The impact of the end-Permian mass extinction on global diversity was
enormous, however, recent findings have called into question the role of PF and
MF in the recovery and post-recovery from the extinction event. Bivalves
experienced lower levels of extinction during the end-Permian mass extinction
than brachiopods (Gould and Calloway, 1980), and this has been hypothesized
to have resulted in Triassic ecosystems dominated by MF. However, some
typical PF groups, such as the rhynchonellid brachiopods, did become abundant
and ecologically important by the Middle Triassic (Bottjer et al., 2008). Greene et
al. (2011) noted that in shallow marine successions from Tethys and Panthalassa
(oceans of the Triassic Period), encrinites and brachiopod-dominated beds were
more common than bivalve-dominated beds during the Middle Triassic, a time
thought to be fully recovered from the end-Permian mass extinction (Fig. 1.4).
Encrinites are rare following the end-Triassic mass extinction (Greene et al.,
2011). Brachiopod dynamics following the end-Triassic mass extinction are not
straight-forward; some research indicates they were even more abundant after
33
the mass extinction, especially in the Early Jurassic (Clapham and Bottjer, 2007),
others report that brachiopod diversity declines throughout the Jurassic (Gould
and Calloway, 1980). Vörös (2010) found that Triassic brachiopod diversity grew
quickly during the Early and Middle Triassic and declining after the Norian Stage,
and continuing to fall until the Early Jurassic. Rhynchonellid and terebratulid
brachiopods rebound again after the end-Triassic mass extinction, and began a
more permanent decline in the Middle Jurassic, after the Bajocian (Vörös, 2010).
Based on these findings, bivalves were more successful during the end-Permian
mass extinction recovery interval, but PF seemed poised to make a comeback in
the Middle Triassic. By the latest Triassic, however, benthic assemblages are
considerably more mobile and infaunal (McRoberts et al., 1995)(Fig. 1.5),
suggesting that the Late Triassic was an important interval in the shift in
dominant taxa—a trend which continues in modern oceans.
iii. The Differential Effects of Large Asteroid Impact Events: Case Studies
of Chicxulub and Manicouagan
I. Introduction
The Manicouagan impact event, one of the largest impacts of the
Phanerozoic, occurred during the Norian Stage, but almost nothing is known of
the effects it had on environmental, biological, or ecological systems. Here I
compare physical and biological characteristics of the Norian Manicouagan
impact event, with the end-Cretaceous Chicxulub impact, which caused the end-
Cretaceous mass extinction. The purpose of this comparison is to identify how
34
likely a significant faunal turnover due to the Manicouagan impact would have
been and to predict the nature of such a faunal turnover in the fossil record using
the faunal response to the Chicxulub impact as a metric. Five mass extinctions
have punctuated the history of fossilized life on Earth (Fig. 1.6) (Raup and
Sepkoski, 1982; Alroy, 2008). The most recent of these mass extinctions–the
end-Cretaceous mass extinction–occurred 65.5 million years ago (Ma), and the
event profoundly changed the faunal composition of life on Earth (Lockwood,
2004; Novacek, 1999). This extinction included the non-avian dinosaurs and the
ammonites–major predators of the land and sea, respectively. This extinction is
also notable for what caused the crisis: a bolide impact (Schulte et al., 2010).
The 180km-diameter crater, named Chicxulub, is located on the Yucatan
peninsula in Mexico, buried beneath hundreds of meters of sediment (Hildebrand
et al., 1991). The ejecta from the impact is found in virtually every sedimentary
succession containing a preserved Cretaceous–Paleogene (K–Pg) boundary,
either in the form of spherules or the iridium-enriched clay layer (Schulte et al.,
2010). Across this horizon, dinosaurs, ammonoids, and ~65% of the other known
late Cretaceous genera disappear in a geologic instant, to be replaced by many
of the major groups that dominate modern ecosystems .
The Chicxulub crater is the largest confirmed impact crater from the last
545 million years (the Phanerozoic–the time of macroscopic fossilized life), and it
is the only impact event correlated with significantly increased extinction levels
(Walkden and Parker, 2008). The second largest confirmed impact crater of the
Phanerozoic is the Manicouagan crater (or third, depending on estimates of
35
original diameter)(Walkden and Parker, 2008), located in eastern Canada (Fig.
1.7). This impact occurred 215.56 ± 0.05, with a younger age for the melt sheet
(Van Soest et al., 2009), and very little is known about the effects of this event on
marine fauna, the uncertainty of which is particularly evident in light of the most
recent Late Triassic timescale changes (Fig. 1.2). There are mid-Norian tetrapod
turnovers which may be correlated to the impact (Irmis et al., 2011). Here I
evaluate the similarities and differences of the physical and biological parameters
surrounding the impact events to make informed predictions regarding the biotic
effects of the Manicouagan impact.
II. Features
A. Age.
The Chicxulub impact crater was identified several years after an impact
was hypothesized to have caused the end-Cretaceous mass extinction, based on
the iridium-enriched clay layer found at several K–Pg boundaries (Alvarez et al.,
1980). The crater was identified by well-logs in the Yucatan peninsula, Mexico
(Hildebrand et al., 1991), and later was dated to 65Ma (Swisher et al., 1992).
The Manicouagan crater melt rocks provided a range of potential ages in
early studies and was long thought to have been a potential cause for the
Triassic-Jurassic mass extinction (~200Ma)(Olsen et al., 1987). Several reports
of impact sediments such as shocked quartz (Bice et al., 1992) and spherules
(Walkden et al., 2002) in Rhaetian (or poorly dated Norian) sedimentary
successions seemed to provide some support for this hypothesis. However, this
36
was determined to be unlikely once the crater was isotopically dated to
215.56±0.05Ma (Van Soest et al., 2009), nearly 15 million years earlier than the
end-Triassic mass extinction. The impact ejecta may have been sourced from
other small impact events which are dated to the latest Triassic, such as the
25km-diameter Rochechuart crater in France (Schmieder et al., 2010), which is
in relatively close proximity to the impact sediment localities in Britain and Italy.
B. Physical
i. Crater morphology
The Chicxulub and Manicouagan impact craters have several important
similarities that distinguish them from most other impact craters on Earth. Both
are very large and multi-ringed, as opposed to the vast majority of known craters,
which are typically small and simple (without multiple rings)(Melosh, 1996).
These features suggest that particular physical events took place following both
of the impact events that may have induced a similar set of environmental
perturbations.
a. Size and Preservation
The Chicxulub impact crater is exquisitely preserved because it is buried
under hundreds of meters of sediment soon after the impact (Urrutia-Fucugauchi
et al., 2011)(Fig. 1.8). Current estimates of the diameter of the crater are ~180km
(Hildebrand et al., 1991)(Fig. 1.9). Several rings are associated with Chicxulub
(Sharpton et al., 1993), which lie outside of the crater, but these are not included
in the calculations because they are formed through a different process after the
37
impact, discussed below. Conversely, the Manicouagan crater is imperfectly
preserved, as it is located on the Canadian craton shield and the upper portion of
the crater has eroded away (Walkden and Parker, 2008). The remaining crater is
~70km in diameter, but the original crater was much larger – closer to 100km
(Grieve, 1987). However, Manicouagan is unique among most cratonal impact
structures in that it not deformed (O'Connell-Cooper and Spray, 2010), and the
original structure below the erosional level is essentially pristine (Fig. 1.8, Fig.
1.9).
b. Multi-rings
The largest impact structures on rocky planets have a distinctive complex
morphology and character set, while smaller impacts are typically “simple” –
characterized by bowl-shaped craters and no additional rings surrounding the
structure (Melosh, 1996). Larger impacts are characterized by at least two
special features: (1) annular uplift, and (2) multiple rings surrounding the crater.
Annular uplifts are formed by lithologic rebound immediately following the initial
impact and the intense pressure placed on the host material by the impactor
(Taylor, 1982). The complete uplift structure protrudes from the center of the
crater and is immediately subjected to erosive processes (Melosh, 1996). Thus,
the final crater morphology of large impacts may resemble a large, deep ring, as
opposed to the bowl-shape of smaller simple craters. Multiple rings not formed
immediately by the impact – rather, the impact creates or amplifies weaknesses
in the host material over a wide area, and the surrounding rings are formed by
normal faults that form after the impact due to gravity-driven collapse (Melosh,
38
1996). These large pieces of rock slide downward, and create a ringed
appearance.
Chicxulub has a large, and well-preserved annular uplift because the
entire structure is buried, and has several rings that are known to reach at least
300 km diameter (Sharpton et al., 1992). The rings which formed around the
Manicouagan impact have been deeply eroded, but depressions 140km in
diameter around the crater support their original presence (Melosh, 1996;
O'Connell-Cooper and Spray, 2010). Others have questioned whether multiple
rings did in fact form around Manicouagan (Walkden and Parker, 2008), but
craters of this size and depth typically do form multiple rings (Taylor, 1982).
ii. Host Material
The impactors that formed Chicxulub and Manicouagan encountered very
different host materials (i.e.: rocks that were impacted)(Walkden and Parker,
2008). The Chicxulub crater is in a thick carbonate rock sequence several
kilometers thick, and overlying metamorphic and cratonal material (Hildebrand et
al., 1991; Sharpton et al., 1993). Manicouagan’s host material is currently only
comprised of crystalline metamorphic and igneous cratonal material, primarily
amphibolites and granulites (O'Connell-Cooper and Spray, 2010), but proximal
ejecta blocks suggest that the surficial host material was a carbonate platform at
least 30m thick. The true thickness of the overlying material is unknown due to
erosion.
39
The carbonate platform impacted during the formation of the Chicxulub
crater contained material that is predicted to have been extremely volatile when
shock-heated, and would have formed several atmospherically actives gases,
such as CO
2
, SO
2
, and CO (Kring, 2007). Manicouagan’s host material most
likely contained much less of this volatile material (Walkden and Parker, 2008). In
both cases, however, the vast majority of ejected material was relatively inert
cratonal material (Tanner et al., 2004), which would have produced little volatile
gas, but is predicted to have interacted with the atmosphere, creating climatically
volatile materials. We explore these interactions in a later section.
iii. Paleolatitude
Currently the two impact craters occupy very different latitudes –
Chicxulub is found in the sub-tropics (21˚N degrees) and Manicouagan is in the
cool-temperate region (51˚N). However, the paleolatitudes of the impacts were
much more similar, within ~5 degrees (Fig. 1.7). Since the Late Triassic, North
America has rotated counter-clockwise, and while the Chicxulub crater is
relatively close to it’s original paleolatitude, Manicouagan would have been much
closer to the equator, at ~20˚N (Walkden and Parker, 2006). This similarity is
important in considering the pattern of ejecta distribution predicted for the two
events, and their similar placement supports a similar ejecta pattern.
iv. Impact Ejecta
One of the most characteristic features of K–Pg boundary deposits found
in so many localities around the world is the spherule layer which underlies the
40
globally distributed iridium-enriched clay layer (Schulte et al., 2010)(Fig. 1.10).
These deposits represent two different depositional regimes for the impact
ejecta: the high-energy proximal deposits and low-energy distal deposits,
respectively (Schulte et al., 2010). The spherule layer thickness decreases with
distance from the crater, indicating that these larger grains were deposited in
trajectories from the impact crater (Kring and Durda, 2002). Spherules are
composed primarily of silica, and most likely derived from non-carbonate airborne
craton particles that condensed and cooled before deposition (Ebel and
Grossman, 2005). The clay layer, however, was deposited over days to months
following the impact, because the particles were small enough to be controlled by
atmospheric turbulence to keep them suspended (Kring and Durda, 2002). These
atmospheric injection of sediments spread around the world in a west-ward
direction (Kring and Durda, 2002), and the global envelopment by dust is
supported by the near-uniform thickness of this layer at distal K–Pg sites
independent of crater distance (with variations between depositional
environments) (Schulte et al., 2010).
No impact ejecta layer has yet been confirmed to be derived from the
Manicouagan impact, but an ejecta layers in mid-Norian sediments was recently
discovered which is a reasonable candidate for an impact sediment horizon
(Onoue et al., 2012). Based on the composition of the host material and the
ejecta content from the Chicxulub impact (spherules formed from condensed
silica), it is likely that Manicouagan would have produced spherules and a clay
layer.
41
C. Biological
i. Global
The standing biodiversities immediately prior to the Chicxulub and
Manicouagan impact events may have been significantly different, a
characteristic that would be primarily attributed to paleogeography. The level of
faunal endemism and standing diversity are important features in predicting
extinction and survival selectivity—cosmopolitan taxa are less likely to become
extinct in most scenarios (Jablonski, 1998). At the time of the Chicxulub impact,
all the major continents were dispersed; that is, they were not clustered into a
supercontinent. The planet was in a greenhouse climate, although prior to the
impact the climate may have been cooling (Bralower et al., 2002). Sea levels
were also high, resulting in wide swaths of large shallow marine zones and a
wider tropical and subtropical belt. These characteristics resulted in large regions
of high diversity shallow marine ecosystems. The paleogeographic dispersement
of continents increased the geographic barriers between the diverse populations,
increasing levels of endemism (i.e.: limited taxonomic ranges). These factors
contributed to the particularly high standing levels of biodiversity at the time of
the Chicxulub impact event.
During the Late Triassic, however, the continents were sutured together
into a supercontinent, Pangaea (Stampfli and Hochard, 2009). This continental
configuration limited both the total area of shallow marine habitat and the
geographical barriers between the habitats, thereby reducing the level of
42
endemism (Walkden and Parker, 2008). This is interpreted to have resulted in
Late Triassic taxa that were more cosmopolitan than during intervals when the
continents were widely separated like the Late Cretaceous (Walkden and Parker,
2008). This aspect is important for estimating extinction risk during an impact
event, because the geographic area of a genus is considered to be one of the
most significant predictors of extinction and survival during the end-Cretaceous
mass extinction for marine mollusks (Jablonski, 1998). However, what is not
typically considered in this Late Triassic supercontinent scenario is the great
number of island arcs that existed in the Late Triassic (Smith et al., 1990; Hallam,
1986), which were associated with unique faunas that were separated by great
swaths of deep ocean (Newton, 1987). The two major oceanic realms of the Late
Triassic were Tethys (formed a great shallow sea in the southern Europe region)
and Panthalassa (the proto-Pacific ocean. At this time, the Tethyan basin was
experiencing extensional tectonics (Berra et al., 2010), which produced many
basins divided by topographic highs bounded by normal faults. This region was
very diverse. Eastern Panthalassa contained many volcanic island arcs that
accreted onto the western coast of the Americas in the later Mesozoic. There
arcs had distinctive faunas from the Tethys region and from each other (Newton,
1987), and the faunal diversity of the Late Triassic has not been widely explored.
Thus, the Late Triassic had several sources of diversity: two widely separated
ocean basins that were each hotbeds of diversity and endemism.
43
ii. Local
The local regions of the impact craters in the two impact events were most
likely very different, although this has less of an effect for the global nature of an
extinction and more to do with the region impact deposits.
The Chicxulub impact punctured a large shallow marine platform, which
was a highly diverse region (Walkden and Parker, 2008). During the impact,
everything in the immediate vicinity was vaporised, and hyper-velocity winds
flattened vegetation for hundreds of kilometers (Kring and Durda, 2002). On a
marine platform this explosive event created enormous tsunamis that traveled to
nearby shallow marine areas (Schulte et al., 2010) and potentially had a
devastating effect on the shallow marine fauna (Walkden and Parker, 2008).
The Manicouagan impact occurred in what was likely to have been the
terrestrial interior of Pangaea, although the eroded cratonal surface of the region
increases the uncertainty of the environment at the time. However, the
sedimentary rocks in large blocks of ejected material surrounding the
Manicouagan crater are primarily Paleozoic (O'Connell-Cooper and Spray,
2010), indicating that it was most likely most an aqueous depositional
environment. Tsunamis are not likely to have formed (Walkden and Parker,
2008), and the windblast would have primarily affected terrestrial ecosystems
(Kring and Durda, 2002) that increased in diversity toward the coasts. Therefore,
the regional effect on shallow marine faunas caused by Manicouagan was much
less than Chicxulub. The terrestrial ecosystem near the Manicouagan impact site
44
was not necessarily barren and arid, as suggested by some researchers
(Walkden and Parker, 2008), and may have hosted a rich forest region (Kring,
2003) – a crucial element to predicting the atmospheric effects of the impact.
III. Predictions
A. Environmental
While both impacts would have caused massive levels of local devastation
(primarily shallow marine for Chicxulub and terrestrial for Manicouagan), the
global effects may have been similar in kind. The global effects of the Chicxulub
impact are considered to have been the main cause for the subsequent biotic
extinctions, although the precise relationship between the environmental effects
and biotic extinction is not always clear. Environmental effects of the impact
include darkness, widespread wildfires, gravity flows, and acid rain (Kring, 2007).
The way these and other effects perturbed marine ecosystems is discussed
below, but there is still considerable uncertainty, in the extent and degree of
perturbation makes direct correlations between impact events difficult.
After the impacts, the excavated material became airborne. Larger
particles traveled on a ballistic trajectory away from the crater, while smaller
particles and vaporized materials rose in a super-heated ejecta plume (Kring and
Durda, 2002). This expanding plume was large enough to extend above the
lower atmospheric layers, sending massive amounts of material into orbit
(Melosh, 1996)(Fig. 1.11). The vaporized particles in some cases condensed into
new material, such as spherules, and re-entered the lower atmosphere for
45
deposition (Ebel and Grossman, 2005). Many of the smaller particles remained in
atmospheric suspension for at least several days before settling out (Kring and
Durda, 2002). During re-entry, the particles increased their speed and became
extremely hot. This barrage of heated particles had two primary effects: (1)
shock-heating the atmosphere, creating large amounts of nitric acid, and (2)
widespread particle re-entry, which had an overall heating effect on the
atmosphere (Kring and Durda, 2002).
Superheated particles are hypothesized to have made contact with
terrestrial flora, causing global wildfires (Kring and Durda, 2002). These fires
injected large amounts of carbon dioxide into the atmosphere, and the
subsequent lack of floral cover resulted in massive sediment flows during the
rains.
Recent research has questioned the wildfire hypothesis after the
Chicxulub impact, citing the decline in charcoal levels across the boundary
(Belcher et al., 2003). These studies observed an increase in polycyclic aromatic
hydrocarbons (PAHs) across the K–Pg boundary in several localities, interpreted
to be the re-deposited sediments from the hydrocarbon-rich Yucatan platform
that was impacted, rather than carbon-rich deposits from widespread fires. This
finding is difficult to accept in light of the well known “fern spike” which occurs
across the K–Pg boundaries in terrestrial successions in North America (Schulte
et al., 2010). This spike in fern spores is interpreted to represent the adaptive
response of many plants to release spores in response to burning–a regular
event in plant life history. Interestingly, many of these plants became extinct
46
across the boundary. Belcher et al. (2003) interprets the absence of charcoal
particles in the immediate impact layer to mean that no burning took place, citing
experiments that required temperatures which were unrealistically high to destroy
charcoal particles, rendering them undetectable. These experiments were
performed using fragments of charcoal in ovens, and they did not combust until
545˚C (Belcher et al., 2003). However, plant material was blasted by high-speed
winds following the impact, flattened over huge areas, and thus was probably
fairly easy to ignite either by lightning (Melosh et al., 1990), or re-entering ejecta
(Kring and Durda, 2002). Furthermore, these fires would have been concentrated
at large swaths of the Earth’s surface, not heated in isolated conditions (Melosh,
1996). Therefore, while it is possible that wildfires did not occur after the
Chicxulub impact, sedimentological evidence in the form of spores suggests
otherwise (Nichols and Johnson, 2008), and the conspicuous lack of charcoal
and spike of PAHs suggests that unknown factors were operating. This issue is
still unresolved, but the dose of thermal radiation caused by re-entering ejecta
during the Chicxulub impact most likely still caused widespread faunal
destruction by a heat pulse (Schulte et al., 2010), and a similar effect could be
expected with large amounts of terrestrial ejecta following the Manicouagan
impact.
Long periods of darkness and possibly freezing temperatures are
hypothesized to have occurred following the Chicxulub impact due to the
suspended clay particles causing a temporary albedo effect (Kring, 2003). More
recent models, however, suggest that a long atmospheric residence time for clay-
47
sized particles is unlikely, but great uncertainties do exist in this issue (Kring,
2003). The darkness is likely to have lasted for at the very least a single day,
based on the global distribution of the clay layer, which was deposited uniformly
due to the planetary rotation under the upper atmospheric ejecta plume – a
process termed “atmospheric blow-out” (Melosh, 1996). The collapse of the
primary producers across the K–Pg is a well-known phenomenon (D'Hondt,
2005), but it is not clear if darkness or cooling were the primary causes (Jiang et
al., 2010).
Acid rain was most certainly formed following both impact events – nitric
acid was created by super-heated reentry ejecta, but only during the Chicxulub
impact was sulfuric acid formed (Kring, 2007), due to the sulfur-rich target rock of
this impact. The two main types of acid rain would have compounded their
atmospheric effects in shallow marine systems, but the estimates of released
sulfur gases and liquids are very uncertain (Kring, 2007). Furthermore, it is not
clear how large amounts of acid rain would have directly affected marine
systems, and models have indicated that the ocean was sufficiently buffered in
the Late Cretaceous to not dramatically change pH conditions (Kring, 2003). Very
shallow systems, such as lagoons and peritidal areas, were not likely to have
been so well-buffered, however, and these systems are dominated by
phototrophs that may have been sensitive to rapid influxes of acid.
48
B. Biological
Due to the different conditions at the times of the Chicxulub and
Manicouagan impacts, the effects on global biota are predicted to have been
different as well. The high numbers of endemic taxa in the latest Cretaceous
were particularly susceptible to extinction, as populations that are limited in range
may not repopulate as easily as those which have widespread constituents that
may repopulate a decimated region. In fact, the occupied range of a taxon an
important survival predictor for the K–Pg extinction (Jablonski, 1998). Lower
levels of endemism during the Late Triassic may have limited the extent of the
biotic extinctions following the Manicouagan impact (Walkden and Parker, 2008),
if endemism was in fact very low. Yet marine environments on these separated
island arcs were very common in the Late Triassic, especially in Panthalassa
(Newton, 1987), and more research on the Panthalassan faunas is needed to
determine now diverse this ocean realm was, and to compare it to the fauna
present in Tethys.
C. Paleoecological
The bottom-up collapse of the end-Cretaceous food webs caused higher-
level extinctions among taxa with similar ecological characteristics. In shallow
marine ecosystems, mollusks that fed on suspended microbiota were more likely
to have become extinct following the impact, whereas mollusks that fed on
deposited material on the seafloor, or were more versatile in their feeding
strategies, were more likely to have survived the impact event (Hansen, 1988).
49
Mobility also appears to have been favored following the mass extinction, with
burrowing bivalves surviving and proliferating in greater numbers than stationary
bivalves (Lockwood, 2004). While different taxa lived in the Late Triassic and
latest Cretaceous, many taxa utilized the same set of ecological niches in both
intervals (e.g.: Fig. 5.21), and presumably the same types of environmental
perturbations would have affected them. One significant difference between the
Late Triassic and latest Cretaceous is the type of microfaunal phototrophs
present – calcareous nannoplankton were only just evolving in the Late Triassic
and had not experienced major taxonomic radiations yet (Bown, 2005). These
groups experienced major extinctions across the K–Pg boundary, but these
extinctions often seem to be tied to photosynthesis (Jiang et al., 2010). The
record of noncalcareous nannoplankton extinction would be more nebulous in the
Late Triassic, but if phototrophic microbiota was negatively affected by acid rain
or greater turbidity due to increased terrestrial weathering and sediment input,
suspension feeders depending on this base of the food chain would be predicted
to have experienced higher levels of extinction than deposit-feeders following the
Manicouagan impact.
Thus, if the ejecta from the Manicouagan impact event induced wildfires,
acid rain, increased weathering, and/or darkness, it is reasonable to predict
increased levels of biotic extinction among the same groups that became extinct
at high rates following the Chicxulub impact. If these environmental effects are
caused by super-heated reentry ejecta and atmospheric particulates,
Manicouagan is likely to have caused those environmental effects based on the
50
shear size of the impact alone. These perturbations would have certainly been
smaller than those following the Chicxulub impact, but they are likely to have
been similar in kind.
IV. State of Knowledge
The Chicxulub impact is closely correlated to one of the largest biotic
extinctions in Earth history, the end-Cretaceous mass extinction (Schulte et al.,
2010). Impact sediments divide distinctly different faunas in marine realms (e.g.:
extinction of the entire ammonoid family, 65% marine family extinction) and
terrestrial realms (e.g.: total extinction of non-avian dinosaurs, several other
reptilian groups, and many plants).
The Manicouagan impact is not yet associated with any faunal extinctions
in the marine realm (Walkden and Parker, 2008), but this is primarily due to the
compounding effects of a lack of Late Triassic paleontological research and a
relatively recent change to the Late Triassic timescale. The Late Triassic is
defined by three stages: the Carnian, the Norian, and the Rhaetian. Each stage
is defined by fossil assemblages that are considered to be distinct, as are all
stages of the Phanerozoic (540 million years to present). The Triassic Period
(250-200 million years ago) ends with a mass extinction, termed the end-Triassic
mass extinction, that is closely correlated with a large volcanic eruption
associated with the break-up of the supercontinent Pangaea (Schoene et al.,
2010). Prior to the recent timescale change, the age of the Carnian–Norian stage
51
boundary was believed to be ~216-212 Ma (Fig. 1.2), roughly coincident with the
age of the Manicouagan impact. The lack of a significant extinction across or
around this stage boundary led researchers to conclude that Manicouagan had
no appreciable effect on the biota. In 2006, an ash-bed was discovered in Italy
only 3m below the Carnian–Norian boundary (CNB), which contained minerals
that could be isotopically dated (Furin et al., 2006). The resulting age was 230
Ma, indicating that the CNB was ~228 Ma. The Rhaetian Stage is thought to be
quite short, 2-7 million years in duration, which means that the updated Norian
Stage lasted from ~228-204 Ma, although this is poorly constrained (Hüsing et
al., 2011). This adjusted age nearly doubled the previous duration for the Norian
Stage, but it also meant a different relative age for the Manicouagan impact;
once thought to have occurred around the CNB, the Manicouagan impact is now
known to have occurred mid-way through the Norian Stage (Fig. 1.2). Therefore,
to evaluate the effects of the impact, one must examine the faunal succession
within the Norian Stage.
Unfortunately, very little is known about the succession of shallow marine
faunas during the Norian. Much research in the 19
th
and early 20
th
century by
paleontologists focused on the taxonomy of Norian-age deposits (Stoppani,
1860; Dittmar, 1864), but no research has attempted to describe the faunal
assemblages sequentially. Many species are described from Norian-age
deposits, but their distribution throughout the stage is virtually unknown. To
compare this with Chicxulub, the K–Pg boundary is defined by a faunal turnover
(rapid or protracted) across the boundary around the world (Jablonski, 1998). In
52
order to examine the faunal turnover during the Norian Stage, the fauna must be
sequentially sampled. Despite this dearth of sequential faunal data from the
Norian Stage, researchers assert that no significant faunal turnover occurred
(Walkden and Parker, 2008; Walkden and Parker, 2006). This hypothesis is, of
course, impossible to evaluate using the data currently available.
For these reasons, the two impact events are presently regarded to have
caused very different environmental perturbations and biotic responses (Walkden
and Parker, 2008), and this reasoning is then applied to other important
geological events. The main physical difference between the cratering events is
the presence of the carbonate platform in Chicxulub’s case, and this difference
has been used to explain the apparently different effects of the two impacts
(Tanner et al., 2004). The proposed influence of carbonate-derived atmospheric
volatiles is also used to model the effects of contact metamorphism during the
end-Permian mass extinction–the largest biotic crisis in the Phanerozoic (Ganino
and Arndt, 2009). Immediately prior to the main extinction phase, large intrusive
bodies contacted a thick carbonate and shale section, which was ultimately
punctured and resulted in the massive igneous province known as the Siberian
Traps (Sobolev et al., 2011). These intrusions are hypothesized to have
volatilised the carbonate and shale material, releasing noxious gases that
poisoned the global biota (Sobolev et al., 2011). This hypothesis for the end-
Permian mass extinction is directly related to prior research on the Chicxulub
impact, and is based on the hypothesis that a shock-heated carbonate platform
has such widespread environmental effects. Paleontological research on Norian
53
faunas during the Manicouagan impact event is required to test this hypothesis
by evaluating a similar impact event which lacks the extensive carbonate
platform.
V. Conclusion
The environmental, biological, and paleoecological effects of the
Manicouagan impact event were likely to have been considerably less severe to
those caused by the Chicxulub impact. However, the size of the Manicouagan
impact suggests that considerable environmental perturbation would have
occurred following the impact. Although no biotic extinctions are currently
associated with the Manicouagan impact, this is primarily due to a lack of
sequential sampling efforts from shallow marine successions of Norian age.
iv. Other
The end-Triassic mass extinction
While the end-Triassic mass extinction occurred several million years after
the end of the Norian Stage, these analyses will have some implications for this
area of study by constraining the faunal occurrences prior to the Rhaetian Stage
and better characterizing the paleoecological structure common to Late Triassic
shallow marine communities prior to the extinction events.
The end-Triassic mass extinction is a poorly understood event, and this
may be due to the nature of the extinction itself (Greene et al., 2012b). This biotic
crisis is closely correlated to the main eruptive phase of the Central Atlantic
54
Magmatic Province (CAMP), of which the extrusive lava deposits cover much of
the northeastern coast of the U.S. and other areas where the supercontinent
Pangaea rifted apart (Schoene et al., 2010). The effects of the emplacement of
this large igneous province are hypothesized to include massive release of
carbon dioxide into the atmosphere in addition to other volatile gases (Ganino
and Arndt, 2009). These gases may have caused global warming and the
subsequent extinctions for plants (primarily seed ferns (Tanner et al., 2004)) and
terrestrial vertebrates (Olsen et al., 1987). The rapidly ejected carbon dioxide is
also thought to have dissolved into the oceans, increasing ocean acidity, possibly
causing the extinction of many carbonate-shelled organisms and the collapse of
carbonate ramps worldwide. This acidification may be the reason for the lack of
carbonate boundary deposits (Greene et al., 2012b), which has led to a
complicated sedimentary record across the extinction horizons and in the
recovery interval (Greene et al., 2012a).
Thus, there is often an attempt to characterize the pre-extinction fauna by
combining all the faunal occurrences from the Rhaetian – as opposed to only the
Late Rhaetian – or sometimes by combining the faunal data from both Norian
and Rhaetian stages. This is obviously problematic not only because of the long
duration of the Norian Stage, but also because stage boundaries are defined by
faunal turnover, therefore extinction estimates are by definition inflated by
including the faunal turnover at the Norian–Rhaetian boundary.
55
Summary
The combination of the large timescale change for the Late Triassic, new
absolute dates for other events, and new paleontological findings in the last two
decades has major implications for how these major transitions in evolutionary
history occurred (Fig.1.12).
With regard to the origin of the Mesozoic Marine Revolution, new
paleontological discoveries shift the main phase of evolutionary innovation to the
Triassic, and the new Triassic timescale highlights the need for more research in
this important interval. The diversification of major predators of shelly prey
diversified earlier than previously thought, but very little is known about how the
shelly prey changed in the Norian Stage. To determine the effects of these
predators on ecological structure and how quickly it occurred, I developed a
baseline dataset of shelly benthic invertebrates faunal succession through the
stage.
The timing of the Paleozoic Fauna–Modern Fauna Transition has also
changed in light of new paleontological discoveries. The actual decline in
ecological dominance of the PF seems to have occurred much later than the
taxonomic decline, sometime after the Middle Triassic. Again, recent findings
have highlighted the importance of the Late Triassic and determining the
succession of faunas through the Norian Stage are likely to be of upmost
importance.
56
For determining the effects of the Manicouagan impact, new dates for the
stage boundary and the impact itself have a drastic change on the expected
fauna affected by the impact. Previous timescales would have Carnian faunas
affected, while new timescales have mid-Norian faunas affected. Here, most of
all, understanding of faunal and paleoecological changes through the Norian is
critical for understanding the effects of this major geological event.
Finally, for the end-Triassic mass extinction, knowing the standing
diversity and paleoecological structure of communities prior to the extinction is
one of the most important paleoecological features in determining the extent of
the extinction as well as the forcing mechanisms during this extinction. In order to
make hypotheses regarding the selectivity of the extinction, accurate calculations
of diversity are crucial and many studies which combine the Norian and Rhaetian
stages inflate the diversity. Furthermore, the paleoecological changes in marine
ecosystems may appear very different depending on how data is binned,
conflating the effects of pre-mass extinction changes and those which drastically
affect animals across the mass extinction horizon. If major ecological changes
took place during the Norian Stage, several paleoecological changes attributed to
the end-Triassic mass extinction may be misplaced, and this can affect the types
of environmental perturbations experienced by pre-extinction faunas.
57
Plan of Research
Based on the previous discussion, the Late Triassic represents a critical
interval in Earth’s history, about which we know very little. The Norian Stage is
particularly mysterious – the dramatic revision of the Norian Stage duration was
only determined very recently, and almost nothing beyond biostratigraphic
groups is known about the succession of marine animals within the stage. In the
course of this research, I have attempted to characterize the succession of
shallow marine benthic macroinvertebrates through the Norian Stage to evaluate
the faunal changes which may have taken place at this time and to better
understand the role of these animals in the larger evolutionary events.
Several questions I will address are:
-‐ What were the dominant evolutionary faunas in the Norian Stage, and how
did they change through time?
-‐ Are the evolutionary faunas consistent with regard to their paleoecological
roles in this interval?
-‐ Did the MMR affect shelly benthic animals during the Norian Stage? If so,
how quickly did the changes occur, and what groups were affected? Can
the early MMR be characterized by specific ecological features? Are
taxonomic radiations and ecological strategies of predators correlated to
prey radiations and anti-predation strategies?
58
-‐ Can the Manicouagan impact horizon be determined in Norian shallow
marine sedimentary successions? Did the impact have an effect on
diversity or paleoecological structure? If so, how does it compare to the
Chicxulub impact event? If Manicouagan did not have a significant effect
on global fauna, what were the controlling physical, biological, or
ecological parameters that differed between the events?
-‐ How does a high-resolution faunal succession database through the
Norian Stage affect the existing knowledge about faunal change across
the Triassic–Jurassic boundary?
To answer these questions, I have chosen to study the faunal changes in
shallow marine level-bottom carbonate systems, primarily because this type of
depositional environment represents one of the most common types of
fossiliferous deposits in global successions throughout the Phanerozoic, and
therefore meaningful comparisons may be made for deposits of this type
throughout space and time.
I have chosen to analyze bulk samples and the relative abundances of shelly
invertebrates at a generic level because of their high preservation potential and
simplicity for quantitative analyses. Some invertebrates included in this analysis
have many fossilizable body components (crinoids, echinoids), but overall these
animals were not common.
59
Parameters to follow the discussions of macroevolutionary trends
The goals of these studies are to identify macroevolutionary and
paleoecological trends throughout the Norian Stage of the Late Triassic, and to
place these findings in a larger temporal context. This analysis was designed to
compare the resulting datasets to studies from other intervals of time and in
different regions. The studied faunal assemblages represent paleoecological
communities which have been present throughout the entire Phanerozoic. The
characteristics of the samples which I have collected for this analysis have been
normalized in the following ways:
Types of animals studied
The majority of animal phyla for which we have fossil records originated in
the Cambrian Period, but the diversity and abundance of different clades has
fluctuated through time (Servais et al., 2009). The vast majority of marine fossils
are those which belonged to animals that secreted some type of calcareous
skeleton (Schopf, 1978). Furthermore, many invertebrates with high fossilization
potential secrete skeletons or shells with only one or two components (Schopf,
1978). For shelly invertebrates from shallow marine depositional environments,
quantities and qualities of shells from the Late Triassic may be compared for the
entire Phanerozoic.
Only level-bottom assemblages were studied, instead of reefs. For
biological reasons, quantitative studies of reefs are difficult to compare through
time. The fauna which have constructed reefs throughout the Phanerozoic have
60
changed considerably (James, 1983), and are not necessarily comparable from
an ecological perspective. For sedimentary reasons, developing a successional
dataset of reef assemblages is difficult. Reefs often have different assemblages
in different zones of the reef, regardless of depth (Walker and James, 1992),
making it very difficult to study a particular faunal assemblage in a sedimentary
succession. Reef studies tend to compare reef complexes as a whole for this
particular reason. Level-bottom assemblages are more discrete, with
sedimentary deposits are occupied as distinct layers, thus facilitating a
succession of faunal samples with confidence that time is being represented in a
linear way through the sedimentary deposit. These faunal successions may be
compared between regions and between different intervals of time.
Types of depositional environments studied
Different environments contain different assemblages of animals, and
some environments have not been occupied by animals consistently through the
Phanerozoic (Jablonski et al., 1983; Bottjer and Ausich, 1986). However, shallow
marine environments have hosted shelly invertebrates since the Cambrian
Period (Ausich and Bottjer, 1991). It is crucial to specify which shallow marine
environments are being studied, due to great differences in faunal components
and diagenetic differences which may exist along a depth gradient on the sea
floor. Water energy levels are not consistent along an ocean shelf, and groups of
animals with different activities and biological requirements will occupy a
particular range that is ideal for their activities. Furthermore, the potential for
deposition and preservation of the shelly inhabitants are different along a depth
61
gradient, and some depths are more likely to transport dead individuals away
from their original living space.
This research focused on the depositional environment between storm
wave-base and fair weather wave base (SWB–FWWB). This depositional
environment can be confidently identified using sedimentary structures,
lithologies, and quality of fossil preservation (Walker and James, 1992). The
seafloor surface is typically oxygenated but not usually subaerially exposed, so
animals may reside there continuously. Carbonates can form in these
environments, which allows some autocyclic control of the ocean shelf that
enables a single succession to contain many sedimentary layers of similar depth
(Walker and James, 1992). Many carbonate successions are superbly
homogenous (Ch. 2 and Ch. 3), and represent excellent sources for sampling a
consistent paleoenvironment.
Preservation is expected to be fairly consistent in the SWB-FWWB region,
as compared to deposits from deeper and shallower depths. Below SWB,
oxygenation is more periodic, and many deposits are more likely to consist of
transported assemblages. Many of the fossils observed in this analysis appeared
to have been found in life position, indicating that there is a fair expectation that
the assemblages are representative of the time-averaged living shelly
community.
62
Methods of faunal analysis
To develop samples which might be compared in a succession, as well as
in different regions and times, the same sampling methods were applied at all
field localities.
Sampling
Samples for this study are large (~18,000cm
3
), and in some cases, I re-
collected bulk samples to confirm that the assemblages were consistent (Chapter
4).
The intervals of my samples have varied, depending on the availability
and amount of strata appropriate for this analysis. In most areas, sample
selection was made after measuring the sedimentary succession and identifying
how common a particular type of deposit was. In cases where the level-bottom
deposits were consistent and common, samples were collected every ~10m. In
other areas where a complete stratigraphic column was not possible, samples
were collected from carbonate beds that spanned the full succession. For
example, the Riva di Solto shales of the Lombardian basin are highly fragmented
and the complete succession does not exist in a single locality. Because the
interval of time represented by this formation is limited to the Late Norian, and I
was able to determine stratigraphic position based on particular lithological
characteristics, I collected samples from the lower, middle, and upper part of the
formation.
63
Diversity and Abundance
Fossil specimens were identified to a genus-level as often as possible.
Species assignments were sometimes possible, and sometimes necessary as
several groups of bivalves have been reassigned to different genera in particular
species, but in many cases identifying the species was not possible due to lack
of preservation of fine features or a lack of access to interior morphological
characteristics, or the identification of species was not possible due to a lack of
taxonomic information for a genus from a particular region, especially in
Panthalassic successions. The paleoecological assignments were made based
on a genus-level identification, because ecology is mostly conserved within a
genus (Bush et al., 2007). In some cases, in particular for gastropods,
identification at a genus level is very difficult because the identifying
characteristics were simply not preserved. These fossils were almost always
simply noted as gastropod, although further fossil preparation may reveal more
taxonomic information.
Brachiopods were nearly always observed as articulated specimens, and
counted as one specimen each. Echinoderm fossils were rare, and each element
was counted as one specimen. If these fossils were very common, a different
quantitative analysis would have been utilized, but their rare occurrence suggests
that they do not require special treatment. Gastropods were often identified in
cross-section, and were each identified as one specimen.
64
Bivalves were not typically articulated, but when found articulated were
counted once. Isolated shells were disaggregated with the cast and mould, and
the pair was counted as one specimen. I have included analyses indicating the
“halved” approach, in which the total number of shells is reduced by ½, to
represent the lowest possible number of individuals, and other methods where it
is reduced by 25% to achieve a more realistic number. However, these reduction
methods for bivalves are difficult to apply to studies with brachiopods (which
were nearly always articulated) and gastropods (which were only counted singly),
which are not reduced. Furthermore, these depositional environments are highly
energetic and oxygenated, and most likely would not preserve both shells of a
single animal, as compared to deeper environments where single layers are
more often preserved by a storm deposit, and in which both bivalve shells have a
similar preservation potential as does a single valve. Therefore, the primary
analyses do not reduce the number of individuals.
Paleoecology
While most shelly phyla appeared in the fossil record in the Cambrian
Period, different groups of animals dominated shallow marine ecosystems at
different times. To examine the secular paleoecological trends through time, the
paleoecological roles of animals were analyzed in addition to changes in
taxonomic diversity, turnover, and dominance. To perform these analyses,
genera were categorized by three life-mode characteristics: mobility, feeding
style, and tier (where the animal lived relative to the sediment-water
interface)(Bottjer and Ausich, 1986)(Fig. 1.13, Fig. 1.14). This method of
65
paleoecological niche analysis was developed by Bambach (1983), and later
refined by Bush et al. (2007). This way, faunal assemblages may be compared
through space and time regardless of the actual genera present, and the
ecological structure and paleoecological succession may also be considered.
This approach solves some of the problems inherent in studying faunal change
through an interval for which the component taxonomic groups have only been
regionally described, such it is for the Norian Stage.
Conclusion to the Introduction
By developing a faunal dataset from shallow marine level-bottom
assemblages that is temporally resolved between geographically distant basins,
it was possible to evaluate ecologically comparable and synchronous faunal
associations during this critical interval in Earth’s evolutionary history. A
successional dataset of taxonomic and paleoecological abundance is appropriate
for several types of quantitative analyses and for comparison and integration with
existing data of other groups of animals. Datasets of this type will be useful to
future analyses that may include high-resolution faunal sampling or geochemical
measurements in particular intervals of interest, especially as more absolute
dates are incorporated into the existing timescale.
66
Chapter 2: Chronostratigraphy of the Norian Stage
I. Introduction
The Norian Stage of the Late Triassic has recently been nearly doubled in
duration in light of new absolute dates that were correlated to the
biostratigraphically resolved Carnian-Norian boundaries from Pizzo Mondello,
Italy, and Silická Brezová, Western Carpathians (Furin, et al., 2006)(Fig.1.2). The
stage is now considered to have ranged from ~228–204Ma (Mundil, et al., 2010),
although the stage boundary has not yet been officially defined (Lucas, et al.,
2012). This revision has transformed our understanding of Late Triassic stages
and has major implications for the Phanerozoic timescale, because this single
stage is now the longest of the Phanerozoic and nearly half of the entire Triassic.
Unfortunately, the Norian is also one of the least-studied stages with regard to
shallow marine level-bottom faunas, and the faunal dynamics of these groups
within the stage are poorly understood.
No absolute dates from within the stage have yet been correlated with
shallow marine sections; thus, there is a major problem in determining rates of
faunal and paleoecologicalchange throughout the stage.
Determining the precise age of Norian marine sedimentary rocks is an
exercise with many problems and caveats. No absolute dates have been found
for biostratigraphically-resolved marine successions, so researchers have relied
on combinations of several chronostratigraphic methods to correlate sedimentary
67
successions around the world, including biostratigraphy, magnetostratigraphy,
and to a lesser extent, chemostratigraphy.
Biostratigraphy is the most commonly used method for dating Norian
sedimentary rocks, and the taxonomic successions of several taxa have been
resolved and correlated for this purpose. In the marine realm, paper clams
(McRoberts, 2010), conodonts (Orchard, 2010), radiolaria (Carter, 1993),
ammonoids (Balini et al., 2010), and palynomorphs (Lucas, 2010) are used. Due
to the separation of major marine realms by the supercontinent Pangaea, most of
these groups have different successions of biozones for the two major oceans,
Tethys and Panthalassa. Some species are shared in the biozone schemes,
although it is difficult to determine synchroneity of their regional appearances.
Magnetostratigraphy is often used in conjunction with biostratigraphy to
achieve higher resolution age correlation. While biostratigraphic groups can be
difficult to correlate due to migration times, endemism, and different biozone
durations, magnetostratigraphy is recorded globally, although the correlation of
sections can be uncertain. For the Late Triassic, the main section for global
correlations is that which is found in the Newark basin (Olsen et al., 2011). This
thick, primarily lacustrine, deposit spans the Carnian to the latest Rhaetian, and
includes basalts from the Central Atlantic Magmatic Province (CAMP) toward the
top of the succession. The Newark Basin deposits have been analyzed using
magnetostratigraphy and astrochronology (Milankovich cycles) to determine the
duration of stages and sub-stages of the Late Triassic. There is considerable
debate over the methods of correlation for the Newark Basin to other global
68
sections, and whether the Newark succession contains recognizable
unconformities (Lucas et al., 2012). Because the biostratigraphic units utilized for
this terrestrial succession are different from those used in marine successions,
correlation between units without independent corroboration is difficult and
creates considerable uncertainty.
Absolute dates are rare for the Late Triassic (except for the latest Triassic,
for which there are abundant ages for CAMP basalts (Schoene et al., 2010)), and
recent dates for the uppermost Carnian Stage determined that the Carnian-
Norian boundary was far older than previously thought (Furin et al., 2006). There
are still no dates available for the Norian-Rhaetian boundary currently, and
estimates for the duration of this stage range from 2-10 million years (Muttoni et
al., 2004). Even if the Rhaetian Stage is ten million years in duration, the Norian
Stage would be 18 million years long, making it one of the longest stages of the
Phanerozoic, if not the longest. The dates for the CNB are still debated, and
there is some concern that the dates are incorrectly correlated with the Newark
magnetozones (Lucas et al., 2012). These arguments are problematic, however,
because the dated section is not only correlated to global sections by
magnetostratigraphy – conodonts indicate that the dates are indeed late Carnian
in age (Furin et al., 2006).
The dramatic differences between the stage durations estimated using
biostratigraphy, astrochronology, and absolute dates highlight the uncertainty of
many accepted chronostratigraphic methods. Here, I accept the absolute dates
for the latest Carnian in estimating the age of the CNB, and contribute a
69
chemostratigraphic method to correlate biostratigraphic zones between the main
oceanic regions.
Chemostratigraphy has been used to a limited degree in Late Triassic
successions. However, many commonly-used elements in chemostratigraphy are
subject to diagenesis and/or regional effects, and in long temporal expanses
such as the Norian Stage, correlating short-term variations can lead to
inconclusive results. A promising chemostratigraphic method in correlating global
marine successions is the use of strontium isotopes, which avoid many of the
main problems inherent in many chronostratigraphic methods.
Strontium as a Chemostratigraphic Tool in Norian Successions
Strontium has been used to interpret weathering profiles in modern
environments and in the geologic past for several decades. Strontium has two
common isotopes that exist in aqueous environments, and each of these has a
unique source (Hodell et al., 1990). The heavier isotope, strontium-87 (
87
Sr)
comes from mantle-derived materials: hydrothermal vents and weathered
basalts. The lighter isotope, strontium-86 (
86
Sr) is formed by radioactive decay of
rubidium-86, a common replacement for potassium in granites.
86
Sr is delivered
to the oceans through continental weathering, and thus, the ratio of
87
Sr/
86
Sr has
been used to interpret the relative importance of continental weathering and
oceanic spreading, respectively (Korte et al., 2003).
Strontium is found in trace quantities in limestones and carbonate shells
as a replacement for calcium, and is apparently taken up with no significant vital
70
effects (Reinhardt et al., 1998). This ratio is representative of the ocean water
ratio globally, as strontium has a long residence time, ~1my (McArthur et al.,
2012), allowing the ocean signal to be well-mixed.
87
Sr/
86
Sr is relatively resistant to meteoric diagenesis and low-temperature
metamorphism. During meteoric diagenesis of carbonates, dissolved calcium is
often replaced by manganese, which is abundant in rainwater while strontium is
not common. Thus, the recrystallized carbonates will not replace the original
strontium in a significant way, allowing the original signal to be diluted but not re-
set. Even in dolomites, which contain very low amounts of the strontium
regardless of whether they are primary or secondary dolomites, the strontium
ratios will follow the same directional trends as non-dolomite limestones (e.g.: the
Dolomia Principale in Italy (Faure et al., 1978)). After burial, most aragonite and
high-mg calcite quickly becomes unstable and undergoes neomineralization to
low-mg calcite. This tends to happen quickly and the strontium is typically
removed to some degree without replacement (Reinhardt et al., 2000).
One important caveat to using strontium isotopes is that the signals are
typically long-term (~1my), as opposed to the short-term trends that may be
observed in other isotope systems, such as carbon or oxygen. This is due to the
long-residence time of strontium in the oceans, ~10
6
million years(McArthur et
al., 2012), which allows it to be interpreted as a well-mixed, global signal, but
renders it somewhat immune to short term changes that are likely to occur at a
local scale.
71
Therefore, strontium isotopes have the capacity to correlate:
-‐ global successions
-‐ biostratigraphic groups
-‐ deep time
-‐ altered sediments
Strontium isotopes in the Triassic-Early Jurassic
Strontium isotopes are considered here to be a useful correlative tool in
the Late Triassic due to the multiple excursions that occur in this interval and
distinct values for the Carnian, Early Norian, Late Norian, the Rhaetian, and even
into the Early Jurassic (Fig. 2.1). Korte et al. (2003) measured
87
Sr/
86
Sr from
conodont elements and brachiopod shells for the Triassic Period, thereby
allowing for biostratigraphic correlation to this chemostratigraphic time-series.
Carnian
87
Sr/
86
Sr isotopic measurements are very low and represent the nadir of
values following the early Triassic excursion, and these values transition to
slightly heavier values in the Early Norian. The Middle Norian
87
Sr/
86
Sr values
from Silická Brezová are somewhat problematic, as there is some uncertainty
due to faulting in the sedimentary succession measured (Korte et al., 2003). By
the Late Norian, strontium isotopes were much lighter, although it is unclear if
this excursion happened gradually, rapidly, or if there were several excursions in
a relatively short period of time. Late Norian isotopic values appear to show
several small shifts toward heavier values. The Norian-Rhaetian boundary (as
recognized by the first appearance [FA] of Misikella posthernsteini) is
72
characterized by a rapid excursion into consistently negative values. This
trajectory continues to the Triassic-Jurassic boundary, where there is a brief
plateau in the earliest Jurassic before the isotope trajectory continues into
heavier values (Jones et al., 1994). Because of these excursions and distinct
ranges, strontium isotopes may be used to determine relative age in a broad
sense, and to identify important stage boundaries.
Strontium and Diagenesis: Reliability of the Strontium Record
Strontium isotope stratigraphy must be undertaken with important caveats
in mind, most importantly the susceptibility of carbonates to diagenesis and
metamorphism. Strontium is precipitated in the carbonate matrix of shells as a
substitute for Ca with no discernable vital effects (Reinhardt et al., 1998).
Dolomitization and recrystallization, however, often results in flushing of
strontium from carbonate minerals or addition of radiogenic strontium from the
decay of
87
Rb in clay minerals, both of which can alter depositional isotope
compositions (Atwood and Fry, 1967). Samples originally composed of aragonite
typically contain the highest concentrations of strontium, followed by high-Mg
calcite, then by low-Mg calcite; only minute quantities of strontium are typically
preserved in dolomite. The highest quality record for this time period comes from
the analysis of the low magnesium calcite secondary layer in brachiopod shells
with strontium concentrations higher than 400 ppm, and in conodonts, which
typically preserve several thousand ppm of Sr in their phosphatic matrices (Korte
73
et al., 2003). Regardless, an empirically-derived screening system would
suggest Mn/Sr values less than 1 coupled with δ
18
O values greater than -10 per
mil (VPDB) are more likely to preserve original
87
Sr/
86
Sr, regardless of the origin
of the carbonate (e.g., (Kaufman et al., 1993), and interaction with meteoric or
metamorphic fluids most typically results in more radiogenic
87
Sr/
86
Sr ratios.
Furthermore, detailed studies reveal that non-luminescent phases as determined
by cathodoluminescence more faithfully record marine
87
Sr/
86
Sr versus
luminescent phases. Thus, inversion of aragonite to calcite, a common
occurrence in ancient carbonates, can indeed preserve marine
87
Sr/
86
Sr values
when water-rock interactions are low, given the abundance of strontium in the
aragonite versus potential diagenetic fluids, even though the original shell
structure is lost.
Conclusion to the Introduction
The Late Triassic timescale has historically been primarily defined using
relative dating methods, including biostratigraphy and magnetostratigraphy. The
recently discovered absolute dates for the Carnian-Norian boundary produced
dramatically different estimates for the duration of the Late Triassic stages and
suggest that the correlations between chronozones must be confirmed using
independent methods. Chemostratigraphic methods correlated to biostratigraphy,
such as strontium isotope time-series based on conodonts and brachiopods, may
represent an important method of independent confirmation for determining the
synchroneity of biostratigraphic turnovers.
74
The ability to accurately determine the age (at least to a stage level) is
crucial for analyzing faunal patterns and the biotic response to major geologic
events. Incorrect intra-basinal correlations and ages result in inaccurate
estimates for the timing and rate of change for several important geological,
paleoecological, and evolutionary events that were taking place in the Late
Triassic, including the Manicouagan impact, the early Mesozoic Marine
Revolution, and the Paleozoic Fauna-Modern Fauna Transition. Finally, due to
the different boundary-delineating biostratigraphic groups in Tethys and
Panthalassa, it is easily possible to place the occurrences of taxa in the wrong
stage, especially for the Norian and Rhaetian stages, which contributes to
inaccurate estimates of extinction and survival selectivity during the End-Triassic
mass extinction.
75
II. Field Studies
The purpose of this analysis is to evaluate the ages for Norian
successions used in this study. Three main questions must be answered by
chronostratigraphy:
-‐ Where in each of the studied formations are the Carnian-Norian
boundaries?
-‐ Can the Middle Norian be delineated, or only estimated?
-‐ Where in each of the studied formations are the Norian-Rhaetian
boundaries?
Answering these questions is important for defining the age of the fauna
are observed in a particular sedimentary succession, in order to successfully
compare results between different field localities.
Two Norian collections were analyzed for this study, one from Tethys and
one from Panthalassa, and in both cases, two formations together comprised a
full Norian succession (i.e., containing the Carnian–Norian and Norian–Rhaetian
boundaries). In most cases, the boundaries were found within a formation and
within a formational member, which emphasizes the importance of multiple
proxies for defining boundaries in marine successions. I have also included a
discussion about the poorly constrained shallow marine succession from a
different Panthalassan allochthon in southeast Oregon at a locality called the
Black Marble Quarry.
76
Chronostratigraphy in the Tethyan Succession
Shallow marine sedimentary successions of Late Triassic age can be
found throughout Europe, and the fauna and stratigraphy of many of these
formations has been studied for over a century (ex.: Stoppani, 1860). This long
history of research has resulted in highly resolved correlations of deposits
representing the different depositional regimes, such as the shallow Dolomia
Principale and the deeper Haupdolomit.
In the Lombardian Alps, the fauna from two Norian formations were
examined: the Dolomia Principale and the Riva di Solto formations. The entire
Dolomia Principale is ~3000m thick (Jadoul et al., 1994), and may be considered
in three packages of similar thickness. This mainly dolomitic formation contains
many different facies, including oolites, microbialites, and deeper deposits in
addition to carbonate platform shallow marine facies. Continuous deposition
occurred during this long interval due to normal subsidence and to
synsedimentary extensional tectonics (Jadoul et al., 1994). The Dolomia
Principale represents tectonic highs with small basinal deposits found nearby
(Dolomia Zonate). At some point during the Norian Stage, the carbonate factory
of the Tethys ceased to function (Berra et al., 2010), and a thick siliciclastic
deposit draped over coeval successions of various depths. This formation, the
Riva di Solto, is dominated by shales, but carbonate beds increase in thickness
and frequency toward the top of the formation.
77
The Carnian–Norian boundary lies within the Dolomia Principale, between
the lower and middle members, although this is not well-defined paleontologically
(Jadoul et al., 1992). Sampling for Norian marine faunas commenced well-into
the Middle member of the DP, so Carnian sampling is unlikely. The middle
member of the DP is considered to represent the Early Norian, while the upper
member of the DP can be estimated to represent the middle Norian, based on
palynology (Jadoul et al., 1994).
The Riva di Solto Formation is Late Norian in age, as defined by
conodonts (Rigo et al., 2009a), and the Norian–Rhaetian boundary is estimated
to lie in the boundary between the RSS and the Zu Formation, or within the
lowest Zu, as recognized by the appearance of the earliest Rhaetian conodont,
Misikella posthernsteini.
The ages suggested by previous workers and by biostratigraphic groups
for the Dolomia Principale and the Riva di Solto are supported by strontium
isotope chronostratigraphy (Faure et al., 1978). Faure et al. (1978) confirmed that
strontium concentrations were very low in samples from the Dolomia Principale
(~40ppm), which is expected for this mineral type, and much higher values
(7000ppm) for limestones from the Riva di Solto. This high degree of
preservation for the RSS is further supported by the excellent quality of shells
from this area, which have visible growth bands and coloration (Fig. 2.2).
87
Sr/
86
Sr values for the Dolomia Principale are isotopically heavy (0.70747), and
slightly heavier than those values reported from the conodont shells from Silická
Brezová (Korte et al., 2003). This is not unexpected, however, because the
78
signal from a dolomite is very diluted from the original concentration of strontium,
and these values are very similar to values reported from the Early Norian
elsewhere. Values from the better-preserved RSS (0.70815) are in very good
agreement with Late Norian values reported from Silicka Brezova. The values for
the overlying Rhaetian and Hettangian formations (the Zu and Sedrina limestone)
show decreasing values within Rhaetian and Hettangian ranges (Korte et al.,
2003).
In this Tethyan example, several lines of evidence (biostratigraphy,
sedimentology, and chemostratigraphy) can be integrated to identify and confirm
the relative ages of the Late Triassic formations of interest.
79
Chronostratigraphy in Panthalassa
Faunal analyses were undertaken from two localities representing
Panthalassan deposition in a shallow marine level-bottom system. The
chronostratigraphy of these sections is made more complicated by the use of
different biostratigraphic index groups than those utilized in Tethyan realms.
Nevada
The Luning and Gabbs formations, located in west-central Nevada (Fig.
2.3) were deposited in a back-arc basin during the Late Triassic and earliest
Jurassic (Taylor and Guex, 2002). Part of the Luning Allochthon, the formations
were accreted to North America during the late Mesozoic along with many other
terranes (Oldow, 1981). The Gabbs Formation is comprised of three members
(Taylor et al., 1983), including the Nun Mine Member (~90m), the Mount Hyatt
Member (~30m), and the Müller Canyon Member (~15m). In New York Canyon
the Gabbs Formation conformably overlies the Luning Formation – a shallow
marine carbonate succession that lithologically resembles the Gabbs Formation
(the uppermost member, however, is dolomitized). The Luning and Gabbs
formations include medium to thick-bedded (10cm to 70cm) limestone and
interbedded shale, with intercalated mudstones, wackestones, and packstones.
Faunas from both the Luning and Gabbs formations are characterized by shelly
shallow marine groups – bivalves are most common, and brachiopods,
ammonoids, gastropods, and echinoderms are also present. The beds are not
typically mottled from bioturbation, but individual burrows are common.
80
Microfossil assemblages include ostracods, sponge spicules, micro-gastropods,
and conodonts.
Berlin–Ichthyosaur State Park: Carnian-Norian Boundary
The Luning Formation is found in the New York Canyon area, where it is
heavily dolomitized. It is also found nearby in the West Union Canyon of the
Berlin–Ichthyosaur State Park (BISP) (Fig. 2.3), where dolomitization is
significantly less pervasive. There, the formation is comprised of the 1) clastic, 2)
shaley limestone, 3) calcareous shale, and 4) carbonate members (Silberling,
1959)(Fig. 2.4). The calcareous shale member contains the Carnian-Norian
boundary, as recognized by ammonoids, and the formation is unconformably
overlain by Tertiary volcanics. The exact duration of time represented by the
carbonate member within the Norian Stage is uncertain, but its equivalent in the
Shoshone Mountains is not considered to be younger than middle Norian in age
(Sandy and Stanley, 1993). Typical faunas of the carbonate member include
brachiopods, oysters, and gastropods, with rare ammonoids and nautili.
Shell material from the upper Luning Formation was sampled at consistent
intervals (~8m) within the Carbonate Member (Fig. 2.5), which is exclusively
Norian in age. A total of five samples of carbonate shell material were analyzed,
with the oldest sample composed of brachiopod shell material and the remaining
samples composed of bivalve shell material.
New York Canyon: Norian–Rhaetian Boundary
81
The sedimentary succession in New York Canyon, Nevada, a former
Triassic–Jurassic GSSP candidate (Lucas et al., 2007), preserves one of the
clearest examples of this lithological transition, with a rapid shift from carbonate
to shale across the Triassic–Jurassic (T–J) boundary (Guex et al., 2004; Greene
et al., 2012b). This section is also important for faunal studies insofar as it
represents a rare example of the Late Triassic–Early Jurassic shallow marine
successions from the Panthalassa Ocean – one of the two major marine realms
during the Early Mesozoic. Here, the T–J boundary is found within the
fossiliferous Gabbs Formation, whose faunal composition and diversity have
been studied as a prelude to the succeeding carbonate crisis (Laws, 1982; Taylor
et al., 1983; Guex et al., 2004).
Correlation of Late Triassic Panthalassic biotas with those of the other
major marine realm, the Tethys, however, remains problematic because different
biostratigraphic schemes are used in the two ocean realms. For example, the
base of the ultimate stage of the Triassic, the Rhaetian, is difficult to recognize in
the Gabbs Formation of west-central Nevada and its Panthalassic equivalents,
because the Tethyan index ammonoids for this boundary are not known to occur,
while index conodonts are rare and appear above the boundary in the
Panthalassic successions (Orchard, 2010). The penultimate stage of the Late
Triassic, the Norian, is much longer in duration than the Rhaetian Stage (~24my)
(Furin et al., 2006) and suffers from similarly problematic biostratigraphic
correlations between the Tethyan and Panthalassic realms; only the Juvavites
magnus ammonite biozone is known from both regions for the entire stage.
82
Several of the same ammonoid species occur in both oceans, but their ranges
are not short enough to recognize stage boundaries – a critical component in
evaluating faunal turnover events and mass extinctions.
In order to address the problematic correlations between regions, we
constructed time-series of strontium isotope trends from geochemically well-
preserved bivalve and brachiopod fossils in the Gabbs and Luning formations for
comparison with those of brachiopods and conodonts from Tethyan successions.
While strontium isotope compositions of marine carbonates have often been
used as a proxy for the balance between global weathering and hydrothermal
inputs (Kaufman et al., 1993), they are also valuable as chronostratigraphic
markers. Because of the long residence time of strontium in seawater, oceanic
values are homogenous on short time scales (Korte et al., 2003) and excursions
recorded in well-preserved carbonate minerals, often of biogenic origin, should
be synchronous on million year timescales.
Chronostratigraphic methods
Biostratigraphy
The relative ages of Late Triassic marine successions are typically
determined using one or more biostratigraphic index groups, such as conodonts,
halobiids, ammonoids, radiolarians, or palynomorphs. Each group has well-
known intra-basinal distributions, and they are often used to correlate
sedimentary successions from different depositional environments (Balini et al.,
2010; McRoberts, 2010; Orchard, 2010; Lucas et al., 2012). However, inter-
83
basinal correlation between the two main Triassic oceanic realms – separated by
the Pangaean supercontinent until the Early Jurassic – remains problematic.
The systems of each ocean are sometimes tethered by a particular clade (e.g.,
Juvavites magnus in Lower Norian), which is assumed to appear synchronously
but is difficult to confirm.
A major confounding problem in correlating Panthalassic and Tethyan
biostratigraphic zones from the Late Triassic is the presence of time-
transgressive species, particularly at the Norian-Rhaetian boundary (NRB). The
GSSP for this boundary has not yet been ratified, but the groups used to
recognize the boundary and biozones within have been consistently used for
decades. However, different index taxa are used to identify the boundary in
Tethys and Panthalassa, introducing a confusing aspect to the intercontinental
correlation of the stage boundary. For example, in Panthalassa, the NRB is
currently recognized by the appearance of the A morphotype of Epigondelella
mosheri. E. mosheri morphotype B occurs below the NRB, and E. mosheri
morphotype C occurs above the boundary (Fig. 2.6) (Orchard et al., 2007). In
Tethys, E. mosheri morphotype A and B also occur, but in the reverse order: E.
mosheri morphotype A appears well before the NRB, and morphotype B appears
slightly after the NRB. Similarly, in the Tethyan realm, the lowest occurrence of
Misikella posthernsteini is widely used to recognize the NRB (Balini et al., 2010),
and while the species also occurs in Panthalassa, it is described to have its
lowest occurrence at a higher stratigraphic horizon of Rhaetian age. Similar
problems exist for ammonoid biostratigraphy of the Late Triassic; the NRB is
84
recognized by the appearance of two different ammonoids in the two oceanic
realms: Sagenites reticulatus in Tethys and Paracochloceras amoenum in
Panthalassa (Balini et al., 2010).
This dual succession of boundary-marking species and variants raises
important questions regarding the temporal significance of the two different
biostratigraphic schemes. While many of the same species occur in both
oceans, confirming the synchroneity of their appearances in two regions
separated by vast distances is difficult to test. Lacking independent means of
correlation, it is difficult to determine if an apparently time-transgressive but
biostratigraphically important species like M. posthernsteini does post-date the
NRB in Panthalassa. The implications of this include the increased uncertainty
for evaluating the severity of the End-Triassic mass extinction in Panthalassa,
due to the rarity of shallow marine successions and the temporal blurring of
Norian-Rhaetian taxonomic ranges. Using the global chemostratigraphic signal
provided by strontium isotopes, we hope to address these correlation issues.
Chemostratigraphy
Late Triassic strontium isotope values from bioapatite of Tethyan
conodonts and biocarbonate from brachiopods define two significant excursions
in the Late Triassic interval. Early Norian
87
Sr/
86
Sr values of ~0.7077 rise to as
high as ~0.7082 by the Late Norian and then precipitously fall back to pre-
excursion values in the Rhaetian (Korte et al., 2003). The return to less
radiogenic values occurs between Norian-Rhaetian stage boundary conodont
85
species, Misikella hernsteini and M. posthernsteini, and thus should represent a
global chemostratigraphic marker linked to the Tethyan biostratigraphic scheme.
Sample collection
Gabbs Formation carbonate samples (n = 11) were collected from New
York Canyon (Fig. 2.7) where the unit conformably overlies the Dolomite Member
of the Luning Formation. Sampling in the lower Nun Mine Member commenced
at the first cohesive non-dolomite limestone bed. Fossil shell samples were
collected at consistent intervals (~5m) (Fig. 2.7) to the point where the
succession is terminated by an applite intrusion and a road-cut. Sampling ended
several meters below the intrusive rocks; specimens near the intrusion, however,
showed no signs of enhanced alteration (discussed below). Sampling continued
across the road-cut until the succession is terminated by a thrust fault; the
hanging wall contained large Early Jurassic bivalves. Here, it appears that most
of the Mount Hyatt Member and the entirety of the Müller Canyon Member of the
Gabbs Formation are missing, while ~65m of the Nun Mine Member is
represented.
Four additional samples from the upper member of the Gabbs Formation
and from the overlying Early Jurassic formations were included for strontium
isotope analysis: one sample from uppermost Rhaetian strata in Müller Canyon
(Müller Canyon Member, Gabbs Formation), and three samples from the Early
Jurassic Ferguson Hill Member of the Sunrise Formation. These four additional
samples were collected from other successions in the nearby area: Müller
86
Canyon (which contains the Triassic-Jurassic boundary) and from Reno Draw
(Fig. 2.3).
Elemental and Isotopic Measurements
The collected samples were slabbed, polished, and shell material of
bivalves and one brachiopod were micro-drilled to extract powder for elemental
and isotopic analysis. Concentrations of Sr and Mn in the drilled samples were
measured at USC using an Ultima-C ICP-AES. Calibration curves for Sr and Mn
were based on serial dilution of a solution standard (Inorganic Ventures' ICP-MS
Complete Standard), and uncertainties of sample measurements are estimated
at 5% for Sr and 10% for Mn (Appendix 2).
Micro-drilled powders of shell material (ca. 5 mg) were sequentially
leached (three times) with 0.2 M ammonium acetate (pH~8.2) and rinsed after
each leach with Milli-Q
®
ultrapure water. Leached samples were then acidified
with distilled 0.5 M acetic acid and allowed to react for 12 h. The supernatant
was separated from insoluble residues by centrifugation and then decanted,
dried, and dissolved with 200 µl of 3M HNO
3
. Strontium was separated by cation
exchange using polyethylene columns with ~1 cm of Eichrom
®
Sr specific resin
above a filter composed of quartz wool. The samples were leached with
sequential treatments of 3M and 7M HNO
3
to remove Rb, Ca, and REEs, and the
Sr subsequently eluted with 0.05M HNO
3
and collected into a V-shaped
polyethylene beaker. Dried Sr was transferred onto degassed (~4.2 A) high
purity Re filaments with 0.7 µl of Ta
2
O
5
activator. Strontium samples were
87
ionized under high vacuum at temperatures between 1350 and 1550
o
C a using a
VG Sector 54 thermal ionization mass spectrometer in the University of Maryland
Geology Department. Analysis of the NBS 987 strontium standard (n = 11)
during the analytical sessions when samples were measured yielded a value of
0.710247 ± 0.000014.
At the University of Maryland Paleoclimate CoLaboratory a refined method
for the analysis and correction of carbon (δ
13
C) and oxygen (δ
18
O) isotopic
composition of 10-100µg carbonate samples by continuous flow mass
spectrometry has been recently developed (Spötl, 2011). Up to 180 samples
loaded into 3.7mL Labco Exetainer vials and sealed with Labco septa are flushed
with 99.999% helium and manually acidified at 60
o
C. The carbon dioxide analyte
gas is isolated via gas chromatography and water is removed using a Nafion trap
prior to admission into an Elementar Isoprime stable isotope mass spectrometer
fitted with a continuous flow interface. Data are corrected via automated Matlab
scripting on the VPDB-LSVEC scale (Coplen et al., 2006) using periodic in-run
measurement of international reference carbonate materials and/or in-house
standard carbonates, from which empirical corrections for signal amplitude,
sequential drift, and one or two-point mean corrections are applied. Precision for
both isotopes is routinely better than 0.1‰. Including acidification, flush fill,
reaction and analysis, true throughput exclusive of correcting standards is 2-3
samples/hour, or up to 144 samples over a 40 hour analytical session.
88
Results
Petrography and Cathodoluminescence
Thin sections were prepared and evaluated from shell-bearing samples,
examined by cathodoluminescence and micro-drilled for isotopic analysis (Fig.
2.8). The carbonate samples are identified as either mudstones or wackestones,
containing up to 20% of shelly material, including bivalves, brachiopods, and
echinoderms, in a micrite matrix. Of the thin sections examined, none of the
bivalve or brachiopod shells were brightly luminescent, while the carbonate
matrix was occasionally moderately luminescent (Fig. 2.8). The stratigraphically
lowest sample from New York Canyon (NYC 1) contained bivalve shell material
with dull luminescence, notable only because it was the only sample in which the
shell material was more luminescent than the micrite matrix.
Elemental abundances
Elemental analyses of samples from this study (Appendix 2 and Figs. 2.4
and 2.6) show that the Luning Formation is enriched in Sr (up to 2000 ppm) and
depleted in Mn (less than 200 ppm) relative to both the Gabbs and Sunrise
formations. The Gabbs samples contain approximately equal amounts of Sr
(ranging between 361 and 1069 ppm) and Mn (284 to 1049 ppm) similar to the
ranges seen in the Surprise Formation samples. Given the generally high Sr
contents of all of these samples the Mn/Sr is uniformly low in all three units, but
especially so in the Luning Formation.
89
Carbon and oxygen isotopes
Results of carbon and oxygen isotope measurements of micro-drilled
shells from the Gabbs, Sunrise, and Luning formations are reported in Appendix
2 and for the Gabbs samples illustrated in Fig. 2.6. With the exception of the
lowest sample from a predominantly shaley interval, most of the Gabbs samples
lie near 0‰ for C and -9‰ for O. The three Sunrise Formation samples range
from -5.3 to 0.6‰ for C and -9.2 to -7.9‰ for O, while the single analyzed Luning
sample has δ
13
C = 2.1‰ and δ
18
O = -12.4‰.
Strontium isotopes
The range of Sr isotope compositions of micro-drilled samples from this
study is relatively small, although those from the Gabbs Formation are more
radiogenic (ranging from 0.70768 to 0.70801) than those from either the Luning
(0.70753 to 0.70764) or Sunrise (0.70764 to 0.70781) formations. Most notably,
there is an apparent up-section decline in the
87
Sr/
86
Sr of Gabbs Formation
samples from within the Nun Mine Member.
Discussion
Sample quality and preservation
The shelly material sampled from fine-grained carbonate mudstone and
wackestone samples collected for this study was well preserved and found to be
largely non-luminescent relative to surrounding micrite. Bivalve shells were
largely neomorphosed from aragonite to calcite during burial, but most of these
90
samples (as well as those of brachiopods) retained high and consistent
concentrations of strontium as well as low Mn/Sr suggesting insignificant
interaction with meteoric fluids (Banner, 1995). Furthermore, the range Sr
isotope compositions of samples from this study was narrow, although two
closely-spaced samples from the lower Gabbs Formation (Fig. 2.9) have
87
Sr/
86
Sr
compositions slightly lower than the average of other Norian samples from the
same succession. Furthermore, a comparison of bivalve and brachiopod data
from the Luning Formation (Fig. 2.5) reveals little difference in
87
Sr/
86
Sr
compositions supporting the view that vital effects were also negligible.
Carbon and oxygen isotope results from samples of the Gabbs Formation
are similarly constant with the exception of the sample (NYC 1) from a shaley
interval near the base of the unit, which is depleted in both
13
C and
18
O (and has
the lowest Sr abundance) relative to all other samples from the unit. It is likely
that this sample has been diagenetically altered and is not considered further
here.
Chemostratigraphic correlations
Chemostratigraphic correlation of widely-separated Triassic successions
is possible if samples are well-preserved and established isotope trends reveal
significant secular variations that are global in scope. The oxygen isotope
system in carbonates is prone to meteoric and metamorphic alteration due to the
solubility of these minerals and the preponderance of oxygen in solutions. On
the other hand, the carbon isotope system is more resistant to alteration due to
91
the lack of carbon in diagenetic fluids. Nonetheless, it may be difficult to
constrain whether carbon isotope variations between successions are temporal,
facies dependent, or related to environmental gradients along ocean margins.
Our comparison of carbon and oxygen isotope compositions of shell carbonate
from the Gabbs Formation with Late Norian and earliest Rhaetian Panthalassa
(British Columbia, Canada; Ward et al., 2004) and Tethys (Korte et al., 2003)
equivalents reveals strong contrasts in d
18
O values between sections, but d
13
C
values are near zero or moderately positive in all. Small variations in carbon
isotope composition between sections in the Tethyan and Panthalassic realms
likely reflect depositional differences between the different water masses rather
than diagenetic grades, especially considering the consistency of strontium
isotope compositions.
Due to the isotopic homogeneity and long residence time (ca. 1-2 Ma) of
strontium in the world oceans,
87
Sr/
86
Sr of well-preserved biogenic carbonates
have been used in concert with biostratigraphy to tell relative Phanerozoic time
(e.g., Depaolo and Ingram, 1985). Our petrographic, elemental, isotopic, and
stratigraphic tests suggest that our samples are well preserved and hence useful
for Sr isotope correlations. Notably, samples of brachiopods and bivalves from
the Luning Formation at the Berlin–Ichthyosaur State Park yielded values that
were less radiogenic than values reported from Early and Late Norian conodonts
in Tethys (Fig. 2.4; Korte et al., 2003). The
87
Sr/
86
Sr of most of the lower Nun
Mine Member (Lower Gabbs Formation) samples are within the published range
of Late Norian samples (ca. 0.7079 to 0.7081) from the Tethyan realm (Korte et
92
al., 2003), while two others near the base of the interval fell in the lower range of
published Rhaetian values (Appendix 2 and Fig. 2.6). NYC samples 2 and 3 are
indistinct both petrographically and geochemically from samples above and
below. Insofar as alteration of strontium isotopes typically results in more
radiogenic compositions (Banner, 1995), it seems possible that these abnormally
low values record a short-term oceanic signal that has not been recorded
elsewhere. By comparison, strontium isotopic values of all samples from the
upper Nun Mine Member had consistently lower values (ranging from 0.7077 to
0.7078) – all within the Rhaetian range reported from the Tethys equivalent.
Finally, all samples from above the New York Canyon sequence (samples 12-15)
had
87
Sr/
86
Sr values consistent with their reported ages from the Rhaetian or
Early Jurassic intervals (Korte et al., 2003).
For correlation of the Norian-Rhaetian boundary, we are particularly
focused on the noted drop in
87
Sr/
86
Sr compositions of samples within the Nun
Mine Member, which appears between NYC sample 8 and 9 (Fig. 2.7).
However, NYC sample 8 contains significantly higher concentrations of Mn,
suggesting that its
87
Sr/
86
Sr composition may have been altered to higher values
(although luminescent properties and carbon and oxygen isotope compositions of
this sample are consistent with others from the Nun Mine Member). In this case,
the Norian-Rhaetian isotope excursion might occur slightly lower in the Gabbs
Formation.
93
Age of the Luning Formation
87
Sr/
86
Sr from the lower and middle Carbonate Member of the Luning
Formation indicated a range typical of Early to Middle Norian ranges, in
agreement with the ages previously attributed by biostratigraphy (Silberling,
1959).
Age of the Gabbs Formation
The contrast in
87
Sr/
86
Sr within the Nun Mine Member suggests a Late
Norian age for the lower part of the succession and a Rhaetian age for the upper
part, as well as the overlying Mount Hyatt Member. This chemostratigraphic age
assignment is in contrast to previous determinations based on the occurrence of
earliest Rhaetian biostratigraphic index fossils, such as E. mosheri morphotype A
(Orchard et al., 2007)(Fig. 2.9), which place the entirety of the Gabbs Formation
in the Rhaetian Stage.
Assuming that all samples are well preserved, the pattern of
87
Sr/
86
Sr
variations in Berlin–Ichthyosaur State Park and New York Canyon indicates that
the
87
Sr/
86
Sr composition of seawater throughout the exceptionally long Norian
Stage may be more complicated than previously estimated (Korte et al., 2003).
A broader range of
87
Sr/
86
Sr values during the Norian is not unexpected. Despite
representing only two conodont biozones, this stage is estimated to have lasted
for ~24 million years (Furin et al., 2006). Specifically, the non-radiogenic values
from carbonate shells in the Luning Formation have not been previously recorded
in Norian-aged successions elsewhere (although they are consistent with those
94
from the Carnian and very similar to Early Norian values). Furthermore, our
results suggest that there may be a significant excursion to less radiogenic
values in the Late Norian lower Nun Mine Member of the Gabbs Formation. It is
possible that short-term climatic, tectonic, or even extraterrestrial events could
have impacted the strontium isotope composition of seawater during this interval.
On the other hand, the upper part of the Nun Mine Member and lower Mount
Hyatt Member exhibit values entirely consistent with Rhaetian compilations (Fig.
2.9). In Korte et al. (2003) no Rhaetian fossils produced
87
Sr/
86
Sr values in the
late Norian range.
Discrepancies with other studies
Orchard et al. (2007) documented a succession of conodonts from the
Nun Mine Member where it conformably overlies the Luning Formation at the
Luning Draw locality (Taylor et al., 1983), only 1km from the section described
here. Identical lithologies and lower formational contacts with the Luning
Formation allow for a reasonable comparison between the two successions. In
Panthalassa, the Norian-Rhaetian boundary succession is biostratigraphically
characterized by the uppermost Norian conodont bidentata biozone, and the
stage boundary recognized by the first occurrence of Epigondolella mosheri
morphotype A. In New York Canyon, Orchard et al. (2007)reported E. mosheri
morphotypes A and B, and Late Norian-Rhaetian conodont Epigondolella
bidentata in the Nun Mine Member of the Gabbs Formation (Fig. 2.6), supporting
a Rhaetian age for the Gabbs Formation. E. mosheri morphotype C, which
95
appears in the early Rhaetian, does not appear in the Nun Mine Member, but
does first occur in the Mount Hyatt Member. These authors also reported
Parvigondolella spp. A and B in the lower 15m of the Nun Mine - also known from
Late Norian formations in British Columbia (Orchard et al., 2007).
Here, we report strontium isotope values from the lower Gabbs Formation
that are consistent with those reported from Late Norian conodonts Epigondolella
(=Mockina) bidentata and Misikella hernsteini in Tethys, and are overlain by
samples with values consistent with those from the earliest Rhaetian conodont
Misikella posthernsteini (Fig. 2.9). This result conflicts with an entirely Rhaetian
age of the Nun Mine Member of the Gabbs Formation, and suggests a Late
Norian age for the lower portion of the unit.
The temporal discrepancy may be attributed to two potential sources of
error. First, the strontium isotope composition of the Tethys ocean might be
distinct from contemporaneous Panthalassa ocean mass. While possible, this is
an unlikely scenario given that Sr isotopic ratios are considered well mixed in
marine systems and the long residence time of this element. The factors that
control the strontium isotope composition of non-restricted oceans are likely to be
non-regional in scope, and produce differential values only in the immediate area
of weathering material (Reinhardt et al., 1998) or in extremely restricted
depositional environments. The homogeneity of the strontium isotope record in
our sections from Nevada is supported by the consistently similar Rhaetian
values in the upper Nun Mine Member and in higher samples of Early Jurassic
age. Second, the conodonts Epigondella mosheri morphotypes A and B have a
96
longer Panthalassic range than previously thought, with an earlier FAD.
Therefore, it is possible that both E. mosheri morphotypes A and B occur below
the Norian-Rhaetian boundary in this region, just as morphotype A does in the
Tethyan region. This hypothesis may be tested by measuring the strontium
isotopes of these species in other sedimentary successions of the same
presumed age.
The most parsimonious explanation is a Late Norian age for the lower half
of the Nun Mine Member of the Gabbs Formation, which requires a shift in age
determinations for several Panthalassic biostratigraphic groups. The
biostratigraphic support for this includes the presence of Parvigondolella spp. B
in the Nun Mine Member and other Norian successions (Orchard et al., 2007),
and the Late Norian occurrence of E. mosheri morphotype A in Tethys (Orchard,
2010). If confirmed, this modification of the Panthalassic biostratigraphic scheme
is important for Norian and Rhaetian faunal studies throughout eastern
Panthalassa, and biostratigraphic successions of ammonoids, halobiids, and
radiolarians across the Norian-Rhaetian boundary.
Interpretation of strontium isotope values
While a comprehensive interpretation for the causes of the strontium
isotope excursions is outside the scope of this investigation, we note that the
earliest Rhaetian negative excursion occurs several million years before the End-
Triassic mass extinction. This event is closely correlated to the main eruptive
phase of the Central Atlantic Magmatic Province (CAMP). The basalt flows of this
97
large igneous province cover an enormous area of terrestrial deposits, and it
follows that an oceanic spreading phase may have initiated earlier (Korte et al.,
2003; Callegaro et al., 2012). The strontium isotope excursion is interrupted by a
positive jump that is likely related to continental rifting and weathering before
continuing a negative trajectory as is most likely related to the continuing
weathering of terrestrial CAMP basalt deposits. Since nonradiogenic strontium
may be sourced from basalt or hydrothermal vent fluids, oceanic crust rifting prior
to continental rifting would provide a parsimonious explanation for the timing,
magnitude, and direction of this excursion.
Conclusions
Previous biostratigraphic research has produced several highly resolved
index fossil successions for Late Triassic faunas in both Tethyan and
Panthalassan sedimentary sequences, but correlating the faunal successions
has proven difficult. Strontium isotope chemostratigraphy is a useful tool for
testing the synchroneity of biozones during isotopic excursions. In this study,
87
Sr/
86
Sr analyses of bivalve and brachiopod shells suggest two key revisions to
Panthalassian biostratigraphy: (1) the Gabbs Formation is not entirely Rhaetian
in age, with the lower half of the Nun Mine Member related to Late Norian events,
and (2) the Norian-Rhaetian boundary is not defined by the first occurrence of E.
mosheri morphotype A in Panthalassa; it likely precedes the Norian-Rhaetian
boundary, as the morphotype does in Tethys. More research is needed to
determine appropriate boundary-delineating species based on these revised
98
temporal schemes. This revision should be reflected in future biostratigraphically-
dated sedimentary successions from Panthalassan terranes.
Furthermore, our strontium isotope results of Norian bivalve and
brachiopod carbonates in Panthalassa reveal significant differences with those
defined by conodont analyses from Tethyan sections used in time-series
compilations. In particular, Luning Formation
87
Sr/
86
Sr values are less radiogenic
than previously reported Early Norian values, and the lowest Nun Mine Member
appears to preserve a previously undocumented strontium isotope negative
excursion of unknown origin.
The strontium isotope excursion at the Norian-Rhaetian boundary is a
useful global correlation tool for concurrent biostratigraphic schemes. Further
work on middle Norian marine sections is needed to characterize the excursion
documented by Korte et al. (2003) between the Early and Late Norian. Age
corrections should be made for faunal collections from this important fossiliferous
Panthalassic locality to clarify the temporal ranges of the macrofossils that occur
within these formations.
99
Oregon
The Late Triassic sedimentary successions of Oregon represent tectonic
allochthons that are part of the Wallowa terrane, and are distinct allochtons from
those in Nevada (Whalen, 1988). Two formations represent marine deposits
during the Norian Stage: the Martin Bridge Formation and the Hurwal Formation,
which may be found in Hells Canyon (southeastern Oregon). Both formations are
characterized by interbedded carbonate mudstones, wackestones, and
packstones, and include some volcaniclastic deposits, and are interpreted to
represent a deepening carbonate platform (Follo, 1994). The fossils are fairly
metamorphosed and in poor condition, except in places where they have been
silicified in some horizons (Newton et al., 1987). A third sedimentary succession
can be identified nearby (Black Marble Quarry), which is more homogenous in
depositional environment, but is less constrained biostratigraphically.
The Black Marble Quarry is a relatively short sedimentary succession
(~70m) on the eastern slopes of the Northern Wallowa Mountains in northeast
Oregon (Fig. 4.10). The succession is tectonically uplifted and capped by
Columbia River basalts. BMQ sediments are a distinctive black limestone, whose
color is not caused by high organic content (0.86-1.19% organic carbon)(Stanley
et al., 2008). Rather, the color is likely due to increased thermal maturation due
to granitic intrusive activity from nearby plutons. The organic content was heated
without oxidation, causing the organics to become black (Yancey and Stanley,
1999). Nearby sedimentary formations include the Carnian to Norian age Martin
Bridge Limestone Formation (MBL) and the Norian to Rhaetian age Hurwal
100
Formation. The Martin Bridge Formation is a thick limestone succession
deposited in a shallow marine setting. The MBL is overlain by the Hurwal
Formation - a siliciclastic-rich succession which appears gradationally in the
region, and is intercalated with the upper MBL. This sedimentological change is
attributed to drowning carbonate platform due to sea level changes, although the
timing of this sedimentological change is similar to the same transition in the
Tethyan region. In Tethys, however, the sedimentological regime change is
attributed to the development of a monsoonal belt, which increased siliciclastic
weathering and choked the existing carbonate factory (Berra et al., 2010). Due to
the lack of age controls, it is not currently possible to compare the timing of these
events.
The age of BMQ sediments is uncertain for several reasons. The lithology
of the BMQ somewhat resembles the sediments from the upper MBL; however,
the upper MBL does not have a black color and thus may differ in the thermal
history from the BMQ sediments. Furthermore, the fauna of the BMQ differ
considerably from those of the MBL (Yancey and Stanley, 1999). The BMQ is at
a higher stratigraphic level than the MBL, indicating that it may be held within the
Hurwal Formation. Giant olistoliths are known from the Hurwal, and are
considered to be composed of MBL. BMQ does not resemble the more
siliciclastic Hurwal, and thus has been hypothesized to be an olistolith of the MBL
(Stanley et al., 2008). Clearly, there are problems with this interpretation, but by
using paleoecological structure of the faunas, we will attempt to date the BMQ
using a global paleoecological development scheme (Ch. 4). This date must be
101
confirmed with biostratigraphic age dates, but can be used to confirm the global
extent of the previously described paleoecological transitions in the Norian
Stage.
102
Summary
The Tethys sedimentary successions represent the samples with the
highest age control in this study, due to the correlation of the studied formations
with coeval deposits and high-resolution biostratigraphy at boundary intervals for
the Norian–Rhaetian boundary. Strontium isotopes in previous studies were
collected from dolomitic rocks, which do not contain sufficient strontium to draw
accurate measurements of the original isotopic values, but the succession of
isotopic measurements follows the trends observed in successions which have
been analyzed previously.
Panthalassan successions are more poorly constrained, but the use of
87
Sr/
86
Sr excursions to correlate the successions allows for confirmation of the
synchroneity of the biostratigraphic schemes in the Luning and Gabbs
formations, which represent some of the best-known shallow marine deposits of
Panthalassa. My analysis indicated that the boundary species for the Norian-
Rhaetian boundary in New York Canyon lies within the Nun Mine Member of the
Gabbs Formation, as opposed to previous reports that placed it between the
Luning and Gabbs Formation.
The temporal constraints on the limestones of the Black Marble Quarry in
Oregon remain problematic. Here, I adopt a tentative estimate of a Middle Norian
age for this succession, although more work is required to better define these
deposits.
103
Determining the absolute ages for these deposits is not currently possible.
No absolute dates from sedimentary deposits within the Norian Stage have been
correlated to marine biostratigraphy, so age estimates continue to be relative.
Therefore, precisely correlating faunal trends to geologic events such as the
Manicouagan impact event, is not currently possible, although the faunal and
paleoecological analyses provide some insights into sedimentary intervals that
may be useful in the future.
Overall, the sedimentary successions used in this analysis represent three
separate depositional regions (Fig. 2.10). Two successions are from the
Panthalassa Ocean, one from Tethys. Two successions are constrained by
Carnian-Norian and Norian-Rhaetian boundaries and represent the faunal
succession through the entire Norian Stage. Thus, the faunal and
paleoecological trends observed within these successions are considered to
represent a reasonable survey of global, regional, and local changes in shallow
marine benthic faunas.
104
Chapter 3: Benthic Paleoecology in Tethys During the Norian Stage
1. Introduction
Triassic fossils from the Italian Alps have been studied for well over a
century, but this work has primarily focused on regional taxonomic assemblages.
Very little is known about how the faunal assemblages and paleoecological
structure of the shallow marine shelly fauna changed during the Triassic,
especially in the long Late Triassic interval.
The paleoecological structure and succession of Norian faunas may be
characterized by sequential samples through the entire stage. This type of study
is possible in the Southern Alps of Northern Italy (Fig. 3.1), where the entire
stage is represented by formations deposited in the Lombardian basin of the
Tethys Sea (Fig. 3.2). This research has three main goals: (1) characterize the
faunal succession of Norian shallow marine level-bottom benthos in the
Lombardian basin, (2) characterize the paleoecological succession of those
Norian faunas, and (3) place this dataset into the larger context of
macroevolutionary trends and evolutionary paleoecology.
A. Localities and their geological and paleoecological context
The entire shallow marine sequence of Norian age is represented in the
Lombardian Alps (Fig. 3.1) by three successive formations: (1) the Dolomia
Principale, which contains the Carnian-Norian boundary; (2) the Riva di Solto
Shale; and (3) the Zu Limestone, which likely contains the Norian-Rhaetian
boundary (Fig. 3.3). The precise location of the Norian-Rhaetian boundary in
105
these formations is not entirely certain, but the first occurrence of the lowermost
Rhaetian conodont Misikella posthernsteini occurs in the lowermost Zu
Limestone (Rigo et al., 2009b), indicating that the uppermost Norian is either
within or immediately underlying the Zu, and that the Riva di Solto Shale is
entirely Norian in age. These formations were deposited in the Lombardian basin
(Fig. 3.2) of the Tethys sea, and were accreted and uplifted during late
Mesozoic–early Cenozoic alpine tectonics (Stampfli and Hochard, 2009).
i. Dolomia Principale
The Dolomia Principale (DP) is a thick (~3km), dolomite succession
deposited in a shallow marine setting of the Tethyan sea (Jadoul et al., 1994). As
the formation was being deposited, the entire region was experiencing
extensional tectonics, which created a series of topographic highs separated by
deeper basinal facies (Cozzi, 1999). These coeval deeper deposits are known as
the Dolomia Zonate (a fossil depauperate dolomite succession with bands of light
and dark laminae) and the overlying Zorzino Limestone (also fossil depauperate,
without obvious lamination and not dolomitized)(Berra et al., 2010).
Depositional Environment
The Dolomia Principale represents many different depositional
environments (Jadoul et al., 1992). Slumps and collapse breccias characterize
the lower DP and indicate a deeper environment, and subaerial exposure is
indicated by microbial fabrics and teepee structures scattered throughout the
106
middle and upper DP. Oolites are observed as well as serpulid “reefs” (Berra and
Jadoul, 1996). The most common lithology is thick-bedded dolomites without
obvious sedimentary structures, including mudstones, wackestones, and rare
packstones. The lower DP is characterized by sedimentary structures such as
breccias and dark laminated dolomites, indicating a restricted lagoon
environment developing into a carbonate platform (Jadoul, et al., 2004; Jadoul, et
al., 1994). The middle and upper DP is characterized by a homogeneous
carbonate wackestones and packstones, with rare void-fills and fenestrate fabrics
indicating periodic subaerial exposure (Jadoul, et al., 2004). Sedimentary dykes
increase toward the top of the DP, related to synsedimentary extension of the
region. The middle and upper DP primarily consists of shallowing-upward
sequences deposited in subtidal to platform margin depths, respectively.
Sampling was restricted to carbonate beds with similar lithologies and
sedimentary structures, further discussed below.
Age of the DP
The lower DP is upper Carnian in age, and the middle DP, characterized
by the end of slumps and collapse breccias, is considered to represent the
beginning of the Norian Stage (Jadoul et al., 1992). The upper DP represents the
middle Norian and the early Late Norian (Jadoul et al., 1992).
The overlying Riva di Solto Formation is present in this area, but is not
fully accessible, as small towns were developed in the topographically lower
areas, which are typically the shales of the Riva di Solto.
107
ii. Riva di Solto
The Riva di Solto Formation (RSS) contains interbedded shale and
limestone units and is deposited throughout the region (Berra et al., 2010). The
RSS is overlain by the Rhaetian Zu Formation, a carbonate sequence with a
diverse reef fauna (Jadoul et al., 2004). The shales of the RSS are well-known
for their diverse and well-preserved fish fossils (Tintori, 1991), while the
carbonate units contain a diverse shelly fauna.
An accurate estimate of the thickness of this formation is difficult due to
the tectonic history of the region and the fissile nature of the rocks, although
Jadoul et al. (1994) estimate <250m for the lower, early Late Norian portion, and
500-1500m for the upper RSS. Unlike the Dolomia Principale, which is
completely lithified and can be found in thicker, cohesive units, the shale content
of the Riva di Solto allowed for the deposits to be separated, shifted, and
commonly duplexed. In the Imagna Valley, where the RSS is found over an
enormous area, the relative placement of any particular sedimentary sequence
within the entire RSS can be estimated based on the thickness and frequency of
the carbonate beds compared to that of the shales. The lower RSS is dominated
by shales (Fig. 3.4), with rare and thin (<20cm thickness) carbonate beds. Most
carbonate “beds” are extremely thin (<5cm) shelly packstones, which are
interpreted to represent winnowed deposits (“Type 1” carbonate beds [Fig. 3.5]).
Wackestone or mudstones from carbonate beds of medium thickness (~20cm)
were present but not common (“Type 2” carbonate beds [Fig. 3.5]). The middle
RSS contains thicker carbonate units (10-30cm) in higher overall frequency. The
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upper RSS is dominated by limestone beds up to 150cm thickness, and with
several beds in a sequence.
The shales of the RSS have been interpreted to represent an dysoxic
sedimentary environment, based on the preservational quality of the fish fossils
(Tintori, 1991), while the carbonate units represent an oxygenated state, based
on the diverse assemblage of shelly taxa, often observed in life-position (Fig.
3.5B). The fossil packstones have been interpreted to represent normal shelly
deposits which have been winnowed by currents that concentrated the shells
while removing smaller sedimentary particles (Tintori, 1991). These packstones
do not contain evidence for transport by storms, because the shells are in
excellent condition, and do not show evidence for abrasion. Many of the shells
are articulated (Fig. 3.5B).
Sampling the entire RSS at a single locality is not possible for the reasons
described above. Instead, the intra-formational differences (Fig. 3.4) were used
to distinguish the level within the formation at different localities in the Imagna
Valley (Fig. 3.1). The lowest RSS sample was collected from a site within 50m of
the upper DP, from a non-packestone carbonate bed. One sample was collected
from a Middle RSS section. The Upper RSS was sampled at a thick succession
which was overlain by the Zu Formation, with a sample from within 20m of the
RSS/Zu boundary.
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iii. DP/RSS Sedimentary Transition
The transition from the clearly shallow Dolomia Principale and the shaley
Riva di Solto formations is rapid, and much research has addressed whether the
transition represents a rapid change in sea-level, drowning the DP carbonate
platform (Berra et al., 2011; Berra et al., 2010; Cozzi, 1999). This hypothesis has
not been supported based on several lines of evidence. The DP is only one of
several formations capped by the RSS, some of which represent deeper
depositional environments which contain no shales (Zorzino Limestone, Dolomia
Zonate) (Jadoul et al., 2004). An alternative hypothesis for this sedimentological
transition is the development of a climatic belt in the region, increasing the
weathering of siliciclastic rocks, and stifling the carbonate factory (Jadoul et al.,
1992). This is supported by the presence of shallow marine fauna in both
formations (in carbonate horizons) as well as the strontium isotope record for this
period, which indicates a mid-Norian increase in continental weathering (Fig.
2.0).
2. Methods
Due to the prolonged duration of this stage, successional data is required
to analyze how benthic communities may have changed during the Norian,
possibly in response to increasing predatory pressure. Taxonomic, abundance,
and ecological successions were considered in generating this data because
together they allow the analysis of long-term trends in dominance, disruptive
events, and ecological structure as separate entities and as correlative factors.
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Abundance is used in assessing dominance in this study of benthic invertebrates
because relative abundance is considered to be a reliable index of shelly
biomass in time-averaged deposits (Kidwell, 2002) and allows for comparison
between numerically disparate collections. Determining the direct influence of
predators in these samples is difficult because Triassic drill holes are rare, and
most of the important diversifying predators in these shallow systems (fish,
lobsters) are not typically preserved in carbonate deposits, although fish scales
are very common in the RSS. Due to the lack of predator fossils, ecological niche
utilization and expansion were tracked through the stage to determine if prey
taxa exhibited adaptive responses to changing stresses.
i. Bulk Sampling
All samples were collected from medium to thick carbonate beds in the DP
and RSS formations, and from the upper 10cm of a bed. The total amount of
material collected per sample is roughly equivalent to 18,000cm
3
. Each rock
fragment was disaggregated manually to a maximum size of 125 cm
3
, and any
identifiable specimens larger than 5mm were included in the analysis.
To avoid sampling Carnian faunas, sampling commenced at the beginning
of the middle DP (Fig. 3.1). Three bulk samples were taken from the middle DP,
and three were collected from the upper DP at eastern Lake Iseo. Several facies
exist within the DP, as indicated by various sedimentary features. To control for
these differences, sampling horizons were chosen based on accessibility and
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exclusion of beds that had characteristics of subaerial exposure, ooids, slumping,
or breccias.
Three bulk samples were collected from the RSS, from the lower, middle,
and upper RSS, respectively. Type 2 carbonate beds were sampled, with any
overlying Type 1 deposits removed from the sample by hand. This selection was
done not to avoid transported fossils (no evidence for transport was observed)
but to avoid concentrated deposits. The lower RSS sample was collected from a
section in very close proximity to the uppermost DP, and the upper RSS sample
was collected from a site underlying the Zu Limestone, both in the Imagna Valley.
Placement of the Norian-Rhaetian boundary in the Zu Limestone is not certain in
the field, so sampling concluded with the uppermost RSS to avoid sampling the
Rhaetian.
ii. Faunal and Paleoecological Analysis
Specimens were identified with illustrations from monographs (Appendix
3), the Treatise of Invertebrate Paleontology, and other available literature.
Genera, rather than species, are used in this study for several reasons. While
preservation of the body fossils is typically very good—fossils were not
significantly degraded and fragments in the sampled beds were relatively rare—
the shells often lacked the fine-scale features in the umbo or internal scars that
would be required for species identification. Species were identified in some
cases of taxonomic updating, when certain species had been reassigned to
another genus, but these incidences were uncommon, so species were removed
from analysis. Overall, bivalve genera were possible to identify and allowed for
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identification of ecological life-modes, which typically do not vary within a genus.
Since the focus of this study was abundance and paleoecological dominance, a
more inclusive dataset was the better option. Paleoecological categorization of
taxa was based on three life-mode characteristics that define several niches: life
position relative to the sediment-water interface (i.e. tiering), mode of feeding,
and degree of mobility (Fig. 1.14). This method was developed by Bambach
(1983) and subsequently updated by Bush et al. (2007), and produces
paleoecological categories that may easily be compared between samples. Most
of the taxa involved in this analysis have known life modes, but some are
ambiguous in one or more categories. To resolve this, some categories were
simplified to reduce uncertainty—for example, the fast-motile and slow-motile
categories were merged, and shallow-infauna and deep-infauna categories were
considered as a single category.
To test the null hypothesis that Norian communities were essentially static
and that sedimentological differences between the DP and RSS were the
controlling factors, I utilized a probabilistic model-rank method outlined by
Handley et al. (2009). This method assesses the probability that differences
between the bulk samples are due to chance (no change in the single underlying
population being sampled), or real differences in the underlying populations
being sampled. For a given set of samples, the analysis considers all
combinations of turnover horizons (change points) between samples, assigns
likelihood probabilities, and then ranks the models according to either AIC
(Akaike Information Criterion) or BIC (Bayesian Information Criterion) weights.
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Although the approaches of AIC and BIC weights are identical, the weights are
ranked with somewhat different criteria (Ivany et al., 2009), and the latter tends to
be more conservative in assigning likely change points. This analysis identifies
the most important transitional points in the sequence, and has the benefit of
being appropriate for abundance data (taxonomic and paleoecologic) from a
succession of samples.
3. Results
The succession of bulk samples from the Lombardian basin provided a
large dataset composed of diverse and dynamic assemblages of fossils
(Appendix 4). Both taxonomic composition and relative abundances of the
samples were nonstatic within and between the two formations studied and
several trends were identified.
Using Handley et al.’s (2009) method, significant change points were
identified within the succession of bulk sample taxa (Fig. 3.6). AIC weights
supported a model of four change points in the faunal succession, including one
within the DP, one between the DP and RSS, and two within the RSS. The model
had a high AIC weight of 0.898121, indicating that the model was ~90% likely
over all other models. Model ranking with BIC determined that the most
significant change point occurred between the DP and RSS. This indicates that,
according to the BIC criteria, the most significant change in taxa (and taxonomic
dominance) exists between the two formations, supporting the hypothesis that
sedimentological affinity or environmental factors were important determinants of
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the Norian assemblages. One might also consider the second-best fit model to
determine if the favored models tend to support more change points or not. The
Bayes factor for the more simplistic BIC model highly supported the top model
over the slightly more complex second-best model (8433). For paleoecological
niche abundances, both AIC and BIC found that the model with the highest
probability to explain differences between samples had four change points –
identical to the models identified by AIC using taxonomic abundance data. AIC
weights were lower than for taxonomic data (73% likely) and the Bayes factor
was less conclusive (2.87). In all cases (taxonomic and paleoecologic data, AIC
and BIC), the second-favored model increased the number of change points, and
the two probabilistic methods converging on one model is strong support for
multiple turnovers, particularly when they also agree with the AIC model for
faunal succession that was highly supported. This analysis supports the
hypotheses that (1) paleoecological change was occurring before the
sedimentological transition to the RSS occurred, and (2) paleoecological change
was occurring throughout the formations in several intervals.
These intervals show several phases of change in taxonomic and
paleoecological composition. The middle DP—deposited mainly during the early
Norian—is taxonomically and numerically dominated by the relatively large
bivalves Bakevellia, Isognomon, and Avicula. In the first two bulk samples,
together these three genera comprise 70% and 71% of their samples,
respectively, while the following four samples from the DP contain 2-37% of
these taxa, and are < 4% of the individuals observed in the RSS bulk samples.
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These groups inhabited a similar ecological niche in the Norian, where they
functioned as stationary low-level epifaunal suspension-feeders (StES), with the
exception of Bakevellia, a semi-infaunal suspension feeder.
In the upper middle DP to the lower upper DP, gastropods increase in
abundance, and there is an overall increase in diversity and niche utilization (Fig.
3.6). Avicula is the only StES taxon consistently present in the upper DP. The
proportion of mobile infauna began to increase in the older samples, and jumped
initially in the upper DP, but maintained a modest proportion until the final part of
the DP, increasing in overall proportion from 7% to ~30% in the DP (Fig. 3.6).
Diversity levels are lower in the upper DP than in some older samples, but many
of the genera not observed in the intervening bulk samples do appear in younger
samples, usually in much smaller numbers. In the final sample of the DP ~20% of
the taxa appear for the final time in the Norian bulk samples. Many of the other
taxa with low proportions in the uppermost DP increase in abundance throughout
the RSS samples, such as Gresslya and Thracia. The final sample of the DP
exhibits the decline of gastropods to levels consistent with those in the RSS.
Ecologically, the mobile infauna consistently increase throughout the entire DP—
the group is nearly absent in the earliest samples, and comprises a large
proportion of the higher samples, while exhibiting greater diversity and niche
utilization in the these samples.
The RSS begins with the highest number of first occurrences among all
the bulk samples—which is expected, based on the results of the probability
analysis (Fig. 3.6) —but of all the new taxa only Myophoriopis is a dominant
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group in the lower RSS. In fact, diversity remained comparatively high for the rest
of the Norian, with the first two RSS samples exceeding the DP bulk sample
diversity high of 22 taxa. A number of ecological trends that began in the DP
continue into the RSS. Mobile infauna increased in abundance and expanded the
types of feeding strategies within this niche from two to four, culminating with a
diverse mobile infauna dominating the assemblage. Stationary semi-infauna that
appeared in the upper DP following the decline of the mobile epifauna in the
uppermost DP continued to play an important role in the RSS (Fig. 3.6).
Overall, familial categories do not appear to confer any predictable
increase in survivorship through the Norian. No group was consistently dominant
in either formation, and no particular group shows a consistent increase or
decrease through the stage, except possibly the Nuculanoida.
4. Discussion
A. Mesozoic Marine Revolution
The succession of bulk samples from the Lombardian basin documents
the timing of the onset of the MMR in the region, the rate of its development, and
particular aspects of the phenomenon that are parsimonious with the known
predator fossil record for this interval.
The main trends observed in the succession of Norian bulk samples are:
(1) gradual decrease in dominance among stationary suspension-feeding
epifauna; (2) gradual increase in abundance and niche diversification of the
mobile infauna (Fig. 3.7); and (3) an intermediate stage of mobile epifauna that
117
persists only until infauna and semi-infauna become dominant in later samples
(Fig. 3.6). These stage-long trends can be interpreted as responses to increasing
predatory pressure on benthic prey and are predicted by the hypothesized effects
of the MMR, including increased mobility and infaunalization. In the early Norian,
demersal and epifaunal predation appears to have been relatively minimal, as
reflected by a benthic community composed almost entirely of stationary
epifauna. This is consistent with other Middle Triassic and early Late Triassic
assemblages which suggest that predation levels were low (Vermeij et al., 1982).
By the end of the middle Norian, the infaunal taxa have a comparable proportion
of the benthic fauna as stationary epifauna, and this upward trajectory is
maintained to the very end of the Norian (Fig. 3.8).
Interestingly, the Norian succession is not a clear covariance between
stationary epifauna and mobile infauna. Rather, alternatives to stationary
epifaunal suspension feeding (SES) such as the mobile epifauna (mainly
gastropods) and the stationary semi-infauna (primarily Pinna and Modiolus) are
observed to have booms before they are outnumbered by mobile infauna. The
latter taxa continued to play important roles in the benthic ecosystem along with
the mobile infauna, suggesting that infaunalization was ultimately the life-mode
that imparted the greatest protection from types of predators exacting stress on
these organisms.
Certain aspects of the Norian fauna are stable—or at least persistent—
throughout the stage. Bivalves are dominant throughout the entire stage, ceding
some abundance to gastropods in the middle Norian. Suspension feeding is the
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dominant feeding mode for the entire stage, experiencing a decline only in the
second faunal stage, when grazers increase in dominance. After the decline of
the mobile epifauna, however, suspension feeding returns to dominance,
suggesting that many of the other trends are not determined by changes in
primary consumers’ food base. Motility, as a single characteristic, has a major
shift favoring mobility early in the Norian samples, but stationary and mobile
organisms vary in dominance throughout the stage until the final sample, where
mobile organisms become dominant with 80% of the fauna at the end of the
Norian (Fig. 3.8). This stage-long persistence of nonmobile taxa is mainly due to
the interplay of not only stationary epifauna and mobile infauna, but also the
mobile epifauna and stationary semi-infauna (Fig. 3.6). The persistence of the
stationary fauna suggests that under increased pressure to evade predation,
some taxa were favored for utilizing an infaunal tier rather than remaining on the
surface and utilizing functional mobility. By using mobility or infaunalization,
avoidance was the strategy utilized by increasing proportions of animals toward
the end of the Norian (Fig. 3.9).
These findings are generally in agreement with previous Norian studies,
but the intra-stage sampling method employed in this study resulted in different
conclusions about the timing and rate of some major paleoecological transitions
that were not apparent in studies that considered the entire Norian Stage as a
single data set. McRoberts (2001) found that stationary epifaunal bivalves had
higher rates of extinction throughout the Triassic until the Norian, but infaunal
species increased overall. This result might indicate some decoupling between
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taxonomic diversity and ecological dominance, and is not entirely at odds with
results presented here. Many SES taxa in the Norian samples persisted until very
late in the stage, although their community roles were greatly diminished, while
infaunal groups appeared early, but did not play significant ecological roles until
much later in the stage. Ros et al. (2011), using an updated database and single-
stage data bins for the Triassic, found that unattached stationary epifauna
declined in the Rhaetian. The results of the present study indicate that this
transition most likely preceded the Rhaetian by ~20 Ma, beginning in the early
Norian. Ros et al. (2011) also found that semi-infaunal taxa diversified throughout
the Late Triassic, but semi-infauna in this sampled succession were variably low
in diversity and highly abundant, and exhibited more complex associations. The
semi-infauna were abundant in assemblages dominated by SES taxa in the early
Norian, as well as in mobile infauna-dominated assemblages from the late
Norian, indicating that predatory pressures possibly affecting other groups may
have differently influenced the semi-infauna.
Evidence for increased predation by various shell crushers and breakers
in the Late Triassic is apparent in other studies (Ch. 5). Harper (1991) found that
cementation of bivalves may be an adaptive response to shell breakage by
arthropods that must manipulate their prey to access them. This adaptation is not
useful against drilling predators or external ingesters; rather, it imparts a distinct
advantage against breaking, crushing, and prying predators (Harper, 1991). At
least 20 groups of bivalves developed cementing ability during the Mesozoic
(Yonge, 1979), and six of these groups experienced major radiations in the Late
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Triassic (Appendix 1). In the Lombardian samples of this study, two of these
groups were present: Gryphaeidae and Plicatulidae (Appendix 4), which
appeared in small proportions in the upper middle DP and lower upper DP, and
are coincident with the initial decline of SES taxa and preceding the proliferation
of infauna (Fig. 3.8). No cementers were observed in the RSS, where the mobile
infauna and large semi-infauna may have engineered (through bioturbation) a
less stable substrate to which the cementers would have had difficulty attaching.
Comparing the results of this study to a synthesis of other studies (Ch. 5)
supports the hypothesis that the earliest form of the MMR involved the
mobilization and infaunalization of shallow marine level-bottom benthos observed
in the Lombardian basin, and this gradual change coincides with the
diversification of many shell-crushing and surficially grazing predator groups,
increased levels of bioturbation, and diversification of cementing bivalves. These
evolutionary events appear to be temporally separate from the later Mesozoic
trends of increasing drill hole frequencies and radiation of carnivorous gastropod
groups.
B. Paleozoic Fauna (PF) to Modern Fauna (MF) Transition
Taxonomically, the Modern Fauna dominated the entire Norian Stage in
the Lombardian basin—assemblages consisted almost entirely of bivalves and
gastropods, indicating that the taxonomic transition from PF to MF preceded the
Norian in this region. Many of the paleoecological traits usually associated with
the MF are not prominent for a considerable portion of the Norian Stage,
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however, with infaunalization and mobility gradually increasing from very low
proportions throughout the stage. This decoupling of taxonomic and ecological
dominance during the Late Triassic is intriguing and requires further research.
C. Sedimentological changes at the DP-RSS boundary
The depositional change from the Dolomia Principale to the Riva di Solto
Shale has been discussed by Berra et al. (2010), who attribute the
sedimentological change to an overall cooling trend that first incapacitated the
carbonate factory, increased precipitation and subsequently increased siliciclastic
input, ultimately leading to a basin-wide shale cover. While this climatic change is
sufficient to cause the sedimentological change from a carbonate system to a
siliciclastic system, it is unlikely to be the primary cause for the observed faunal
changes for several reasons: (1) The timing of the observed trends is not coupled
to the formations in which they occur, as evidenced by the decline of StES taxa
that begins in the middle DP, much earlier than the sedimentological change.
(2a) The gradual nature of the biotic changes within the formations is dissimilar to
the abrupt sedimentological change across the DP-RSS. If sedimentological
affinity were a primary factor in the observed faunal change, the transition would
have been rapid, or gradual beginning with the introduction of siliciclastics in the
RSS. (2b) Samples were collected from similar sediment types (medium-
thickness carbonate wackestone) between the two formations. Affinities of
infaunal bivalves to siliciclastic systems and epifaunal bivalves to carbonate
systems has been previously documented (Aberhan et al., 2006; Clapham et al.,
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2006) and may have contributed to the faunal composition of the RSS at the end
of the Norian, but mobile infauna were increasing in dominance long before the
siliciclastic-input increased in the basin. The role of the siliciclastics may have
served as an amplifier of an existing trajectory. (3) The consistent preservation
style of taxa that are present in both formations suggests autochthonous
deposition. In the RSS, taxa that had also been observed in the DP (~75% of the
total taxa) did not exhibit characteristics of transported fossils. If transported, this
would be expected particularly for the most dominant DP taxa, which were
typically larger and flatter bivalve groups, rather than the easily transported,
small, round bivalves common in the upper DP and RSS. Many RSS fossils were
found in life position (especially Pinna) or associated with possible burrows
(Nucula). The lack of fragmented or abraded specimens in either formation’s
samples supports the conclusion that the changes in abundance and dominance
were due primarily to biological factors over factors such as climate and/or sea
level changes.
5. Conclusion
The shallow marine benthic faunas of the Norian Stage in the Lombardian
Basin were not static, and these assemblages underwent dramatic changes
during this interval. Animals capable of facultative movement and/or inhabiting an
infaunal life mode became increasingly dominant through the stage over the
startionary surface-dwellers. These changes do not coincide with basin-scale
sedimentological changes, but may have been synchronous with the
123
appearances of predators that were specialized for shell-crushing in shallow
marine environments.
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Chapter 4: Benthic Paleoecology in Panthalassa (Nevada and Oregon)
During the Norian Stage
I. Introduction
I. a. Tectonics of the Western U.S.
The Mesozoic sedimentary rocks of the western United States are a
patchwork of mostly allochthonous terranes that were originally deposited in
volcanic island arcs scattered throughout the Proto-Pacific ocean, Panthalassa
(Dorsey and LaMaskin, 2008). These arcs accreted onto North America later in
the Mesozoic (Oldow, 1981), and represent several latitudes of deposition.
Because the faunas on these arcs are often endemic to their allochthon, some
work has focused on quantifying the faunal differences in order to reconstruct
distance between the arcs and their relation to Tethyan deposits (Newton, 1987;
Hallam, 1986). Here, I consider the faunal and paleoecological succession for
two Norian allochthons, representing high and low latitudes of deposition.
I. b. Existing Data
Marine faunal data for the Norian Stage in Panthalassa is very sparse,
and is dominated by reef collections and deep-sea faunal successions that are
typically monospecific (e.g.: Halobia). Shallow, non-reefal faunal assemblages
can be assigned to an incorrect stage (see discussion in Chapter 2) or to non-
specific time intervals (“Late Triassic”). However, previous research by Hogler
(1993) and Newton et al. (1987) have provided important taxonomic information
for Panthalassic faunas. The excellent faunal succession data from the Nun Mine
125
Member (as well as the Mount Hyatt and Muller Canyon Members) collected by
Laws (Laws, 1982), represent only the very uppermost Nun Mine Member, and
are therefore entirely Rhaetian in age.
I. b. Nevada Paleogeography
Several formations of Norian age can be found throughout Nevada and
Eastern California. Two formations, the Luning and Gabbs Formations, were
deposited in shallow marine settings throughout the Norian Stage and were
sampled for faunal successions.
Both formations are part of the Luning Allochthon (Oldow, 1981), and
represent similar paleogeographic regions, even though the formations are
sampled from different localities. The dark grey carbonate mudstones of the
Luning Formation near the Berlin Ichthyosaur State Park can be seen below the
lowermost wackestones of the Gabbs Formation in New York Canyon. Overlap
between the successions sampled is unlikely because the lithologies are
discernable, and strontium isotope values differ strongly between the
successions as well (Ch. 2).
I. b. i. A. Berlin–Ichthyosaur State Park
Berlin–Ichthyosaur State Park is located in the Shoshone Mountain range
of west-central Nevada. In this region, the Luning Formation is comprised of four
informal members (from lowest to highest in stratigraphic sequence): the Clastic
Member, Shaley Limestone Member, Calcareous Shale Member, and Carbonate
Member (Silberling, 1959)(Fig. 2.3). The Calcareous Shale Member contains the
126
Carnian–Norian boundary, and so the Carbonate Member was sampled for Early
Norian fauna until the sedimentary succession is truncated by Tertiary volcanics.
The uppermost Luning Formation is represented by the Dolomite Member, which
can be found in New York Canyon, Nevada, ~55km from Berlin–Ichthyosaur
State Park. This member conformably underlies the Gabbs Formation, an
interbedded carbonate and shale succession.
Elsewhere, the Luning Formation is comprised of different types of rocks
(Silberling, 1959), but the thick Carbonate Member found in BISP is a relatively
homogenous, thick-bedded limestone succession.
I. b. i. B. New York Canyon
New York Canyon is ~55km distant from BISP, but contains the
uppermost Luning Formation. In this area, the upper Luning Formation is
completely dolomitized, and conformably overlain by the Gabbs Formation. The
Gabbs is comprised of interbedded limestones and shales, and has three
members: the Nun Mine Member, the Mount Hyatt Member, and the Muller
Canyon Member. The Muller Canyon member also contains the Triassic–
Jurassic boundary, and is overlain by the Early Jurassic Sunrise Formation.
Depositional environment
Some disagreement exists over the depositional environments
represented by the Luning (Hogler, 1993; Silberling, 1959) and Gabbs
Formations (Taylor et al., 1983; Hallam and Wignall, 2000), but both formations
contain sedimentological indicators of a range of depositional depths (Fig. 4.1).
127
For the sampled successions in this study, a relatively narrow range of
depositional environments were included and were limited to limestone beds
interpreted to represent deposition above storm-weather wave base and below
fair weather wave base. This was determined based on field observations, fossil
preservation and diversity, and thin-section microscopy. Sampled sedimentary
beds represented normal shallow marine carbonate environments under aerobic
conditions.
I. b. i. C. Dating the Luning and Gabbs Formations
Absolute dates for the Norian Stage are sparse, and correlating global
localities is difficult due to the segregation of the two major ocean realms, Tethys
and Panthalassa, by the supercontinent Pangaea. Based on strontium isotope
chemostratigraphy (Chapter 2, Tackett et al., 2014), I have dated the lower half
of the Nun Mine Member of the Gabbs Formation as Late Norian in age (Fig.
4.2), and the Carbonate Member of the Luning Formation as Early and Middle
Norian. Isotopes suggest that there is some amount of time missing between
these successions, as the values are fairly consistent with particular value ranges
for the Norian in the Tethyan sections to which they are compared (Korte et al.,
2003).
II. Methods - Nevada
Both sedimentary successions at Berlin–Ichthyosaur State Park (BISP)
and New York Canyon (NYC), Nevada, were measured and described prior to
faunal sampling. Each bulk sample was collected from medium- to thick-bedded
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limestones (20-70cm)(Fig. 4.3), and only from the upper 10cm of the beds. Only
mudstones and wackestones were sampled, although BISP sample 2 contained
a high fossil concentration that was observed to be patchily packstone, but
primarily wackestone. In BISP, sampling commenced ~100m above the base of
the carbonate member at the first coherent carbonate beds, below the
brachiopod-rich cliff-forming bluffs (Fig. 4.4). Sampling terminated near the top of
the carbonate outcrops, above which is a nonconformity overlain by Tertiary
volcanic rocks. In NYC, sampling began above the dolomite sedimentary layers
at the first cohesive carbonate layer of the Nun Mine Member. About 20m above
this layer, the sedimentary succession is interrupted by igneous intrusions and a
road-cut. The Nun Mine Member continues in the succession across from this
road-cut and is overlain by the remaining members of the Gabbs Formation (Fig.
2.2). Strontium isotope chemostratigraphy has indicated that the Norian-Rhaetian
stage boundary is slightly below where the succession is terminated by the road-
cut (Tackett et al, in review)(Ch. 2), and so sampling terminated at the end of this
succession.
Each bulk sample was disaggregated using a rock hammer and chisel,
until hand samples were no larger than ~125cm
3
. Each fossil specimen was
identified to the most specific taxonomic level possible. In some cases, assigning
a specimen to a particular species was possible, but due to shell recrystallization
and lack of species systematics for many Panthalassic taxa, the majority of the
fossil identifications were limited to the genus-level. However, the scope of this
paper is to evaluate paleoecological changes through the Norian Stage, and
129
because ecology is generally conserved within a genus (Bush et al., 2007), this
level of identification is considered here to be sufficient. Fossil specimens larger
than 5mm were included in the analysis, as well as moulds if the corresponding
casting specimen was destroyed during disaggregation.
Fossil genera were then assigned to a paleoecological category using the
three characteristics used by Bush et al. (2007): tiering, feeding, and motility.
These categories are appropriate for shallow marine, benthic, non-reefal
invertebrates, thus allowing for paleoecological comparisons from different
localities and from different time periods. The categories were largely assigned
based on affinities with living relatives and/or morphological characters. In some
cases, the paleoecological function of a taxon is debated; for example, the paper-
clam Halobia (and other paper clams, which are commonly found in concentrated
monospecific horizons) may have been benthic stationary, suspension-feeding
epifauna (McRoberts et al., 2008), but others have suggested a life-mode in
which the clams were attached to flotsam. Other taxa have changing life-modes
based on the maturity of the organism; for example, Gryphaea, which cement to
some surface during juvenile periods and are reclining epifauna as adults
(Hallam, 1968). In general, the paleoecological category was assigned based on
the adult mode of life, as we only included adult-sized fossils in the study
(>5mm), and used the PaleoBiology Database (pbdb.org) assignment for
disputed life-mode taxa. None of these disputed taxa comprised a significant
proportion of the faunal assemblages, so discrepancies would result in negligible
changes to the dataset.
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Sample exclusion
Bulk samples were collected in consistent intervals but several samples
were removed from the study after collection for not meeting sampling criteria.
First, two samples from BISP and one sample from NYC were removed because
they contained <25 specimens. Second, one sample from NYC was removed
because petrographic analysis of this sample indicated a different depositional
environment than other samples, which was not recognized in the field. This
excluded sample is the lowest sample of the Nun Mine Member, and seems to
represent a deeper depositional environment. This interpretation is supported by
the atypical faunal assemblage - a nearly monogeneric collection of flat clams –
and the darker color of the limestones than in younger samples. In petrographic
thin-section, sediments of the included samples include small fragments of shells
that are observed in more complete forms in the bulk samples, as well as
microfossils (foraminifera, spicules), and juvenile tests of macrofaunal
components. In thin-section, the excluded sample from NYC was a bivalve
macrofossil (>5mm) packstone in a silty matrix – suggesting a deeper, storm-
winnowed assemblage. The four excluded samples were interspersed among the
sampled succession, and no excluded samples were adjacent to another
excluded sample. The faunal and/or sedimentological features of these excluded
samples suggest different depositional environments than the consistently
diverse assemblages included in the analysis.
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Results - Nevada
Bulk sample diversity and abundance
There was no significant correlation between number of specimens and
the number of taxa (r
2
=0.308)(Fig. 4.5). The correlation between specimen
counts and taxa counts improved slightly when the relationship was considered
as a logarithmic correlation (r
2
=0.359). The two oldest samples showed the least
agreement to the number of taxa present, and when these samples were
removed, the agreement improved considerably (r
2
=0.757). However, in both of
these samples, over 40% of the specimens were brachiopods without a genus-
level identification. Therefore, the real diversity of these two samples is likely to
be higher, reducing the agreement between taxa and specimens.
Bulk Sample Compositions
Early Norian faunal samples are dominated by brachiopods (Appendix 5,
Fig. 5.2), although they are gradually replaced by mollusks before the Late
Norian. Ammonoids are present in low numbers (1-3 specimens in most
samples) throughout the Norian samples, and several other mollusks
(aulacocerids and scaphopods) appear inconsistently and in low numbers.
Bivalves comprise the greatest proportion of fauna in Middle and Late Norian
samples, although the youngest sample from BISP has gastropods in nearly
equal numbers. Many different abundance patterns were observed for the most
common taxa, with high frequencies of occurrence of limited duration (Fig. 4.6).
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No single taxa was dominant in all samples, and very few were dominant in more
than 4 samples.
Bulk Sample Paleoecology
Three, or possible four, paleoecological assemblages characterize the
Norian shallow marine benthic communities in west-Central Nevada. Samples of
Early Norian age from the mid-Carbonate Member of the Luning Formation are
composed of stationary epifauna (non-cementing), and very low numbers of
burrowing or mobile taxa (Fig. 4.7). The stationary non-cementing epifauna are
not dominant in younger Norian samples.
The early Middle Norian (upper Carbonate Member of the Luning
Formation) and the late Middle Norian (lower samples from the Nun Mine
Member of the Gabbs Formation) are both characterized by smaller numbers of
stationary non-cementing epifauna, larger numbers of mobile infauna
(burrowers), and increase in shelly animals which are either mobile epifauna or
cementing bivalves (Fig. 4.6). In the upper Luning Formation, mobile epifauna
are primarily grazers (gastropods) and the cementing bivalves are ostreids such
as Lopha. In the late Middle Norian of the Gabbs, cementing bivalves are still
very common, but the most common genus is the less-robust Plicatula. Mobile
epifauna in the late Middle Norian are more likely to be bivalve suspension-
feeders that are facultatively mobile, and may live attached using byssi normally,
and become a diverse group.
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Late Norian faunal samples from the middle Nun Mine Member of the
Gabbs Formation are paleoecologically diverse, but with assemblages
predominantly composed of mobile infauna, which make up an average of 46%
of the total niches represented in the bulk samples. Stationary epifauna are still
present in low numbers and are now composed primarily of bivalves, instead of
brachiopods. Cementing bivalves and mobile epifauna continue to be present in
numbers comparable to stationary epifauna, although they show more variation
between samples.
Repeated samplings successfully reproduced the intervals of greatest
faunal turnover and paleoecological structure within each bulk sample. This
result was interesting because the first round of collections were made and
analyzed with much greater uncertainty in taxonomic identifications. The second
phase of collecting produced more fossils which were identified to a higher
taxonomic level, but the proportion of paleoecological groups were relatively
similar between the samples, and similar transitional intervals were identified.
Discussion – Nevada
Some paleoecological trends stand out in the succession of Norian
benthic faunas: the Early Norian dominance of non-cementing stationary
epifauna, the ecologically diverse Middle Norian dominated by cementers and
mobile epifauna, and the Late Norian dominated by mobile infauna (Fig. 4.6).
This gradual expansion of utilized ecospace during the Norian is significant when
compared to paleoecological successions in Tethys and in the context of
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predator taxa that were experiencing major taxonomic radiations at this time.
Many of these predators were epifaunal or demersal shell-crushers, which
corresponds to several of the paleoecological transitions observed in
Panthalassic and Tethyan successions.
The co-variance of non-cementing stationary epifauna and mobile infauna
show some agreement (Fig. 4.8), although the non-cementing stationary
epifauna are not replaced by an entirely mobile infauna set of taxa; several
different paleoecological groups increase in abundance before the MI become
consistently dominant. These groups are mobile, reclining, or cementing, and are
referred to as ecological intermediates (Fig. 4.8). In Tethys, ecological
intermediates are also common beginning in the Middle Norian, but in different
proportions than what is observed in Panthalassa.
Comparison with Tethyan successions
The trends observed in these Panthalassic successions are consistent
with those observed in Tethyan shallow marine successions of benthic fauna. In
the Dolomia Principale and Riva di Solto formations of the Southern Alps, Norian
shelly benthic assemblages were dominated by stationary epifauna in the Early
Norian, and were replaced by mobile infauna toward the end of the Norian
(Tackett and Bottjer, 2012)(Fig. 4.8). Unlike the Panthalassic faunas,
brachiopods were not common in any of the Norian samples, and the stationary
epifauna were composed of bivalve genera.
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Furthermore, the presence of ecological intermediates differed between
Tethys and Panthalassa in the sedimentary sequences examined in this study.
Middle Norian paleoecological communities were dominated by diverse taxa that
can be categorized as ecological intermediates of stationary epifauna and mobile
infauna, such as stationary semi-infauna and mobile epifauna. These taxa are
often found in greater abundance than stationary epifauna or mobile infauna (Fig.
4.8b). Unlike in Panthalassa, cementing bivalves were not common while
relatively large stationary semi-infauna such as Pinna and Modiolus were
common. The Early Norian was dominated by stationary epifauna, but semi-
infauna were present in low numbers. Both successions from Tethys and
Panthalassa exhibited bursts of mobile epifauna in the Middle Norian (Fig. 4.8c),
and a Late Norian fauna dominated by mobile infauna. In Panthalassa, the non-
cementing stationary epifauna persist in low numbers until the end of the stage,
but Tethyan successions had very few. The reasons for these particular
differences requires further study, but it is clear that mobile infauna are the
dominant ecological components of level-bottom benthic communities toward the
Late Norian in both oceanic realms (Fig. 4.9).
Several taxa are common between these ocean realms, but the dominant
taxa are different. In Tethys, Isognomon, Bakevellia, and Pinna, and myophorids
are very common, while in Panthalassa, Plectoconcha, Lopha, Plicatula, and
Nucula are the most common groups.
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The Mesozoic Marine Revolution
The paleoecological trends of shelly benthic fauna in both Tethys and
Panthalassa correspond well to the taxonomic radiations of predators during the
Late Triassic (Ch. 5). These diversifying groups include durophagous groups of
lobsters, crabs, sharks, and fish (Fig. 5.10). These predators lived benthic or
demersal life modes, and fed upon surface-dwelling prey, of which the non-
cementing stationary epifauna would have been particular susceptible (Vermeij,
1987).
The correlation between predation modes and prey behaviors strongly
suggests a relationship based on the proliferation of durophagy, a key feature of
the Mesozoic Marine Revolution (MMR) described by Vermeij (Vermeij, 1987).
Several of the characteristics associated with the MMR are in progress among
prey during the Norian Stage: increasing mobility, infaunality, and cementation.
However, drill holes were not observed (except a small number of questionable
examples which require further examination) in either faunal realm, suggesting
that the increase in drilling occurs later in the Mesozoic and is not a feature of the
early MMR.
These results suggest that the early MMR can be characterized by
adaptations in both predators and prey which are specifically related to benthic
durophagy, and that this escalation occurred relatively early in the Late Triassic,
more than 20 million years before the End–Triassic mass extinction. Despite the
137
different taxa found in the oceanic realms, similar paleoecological trends occur in
both.
These paleoecological findings are consistent with the appearances of
durophagous taxa during the Late Triassic. Durophagous fish experience major
radiations in Tethys (Tintori, 1998; Lombardo and Tintori, 2005), and
durophagous sharks increasingly occur in both ocean realms throughout the Late
Triassic (Ch. 5). Shell-crushing arthropods are more difficult to analyze because
of their complex body types and the lower preservation potential (Schweitzer and
Feldmann, 2010), but several groups make early appearances in the Late
Triassic, including the Brachyura (Rinehart et al., 2003), Macrura (Garassino and
Teruzzi, 1993), and Palinura (Glaessner, 1960). These predators swam or
crawled close to the seafloor, and the non-cementing stationary epifauna would
have been vulnerable to these types of predation. Mobility appears to have been
adaptive for escape, while many animals used a strategy of avoidance by living
in the sediment.
Cementing epifaunal bivalves also experienced taxonomic radiations
throughout the Late Triassic, although they are not present in large numbers in
Tethyan successions. Cementing bivalves have been shown to experience lower
levels of predation by shell-crushing arthropods in laboratory experiments than
byssally-attached bivalves (Harper, 1991), and thus is consistent with the
hypothesis of increased pressure by durophagous predators throughout the
Norian Stage. This is supported by the synchronous radiations of cementing
bivalves and shell-crushing arthropods in the Late Triassic.
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Another striking change in the paleoecological structure of Norian benthic
communities is the increased niche-use of the infauna. Chemosymbiotic,
deposit/suspension-feeding, and deep infauna all increase in frequency through
the Norian (Fig. 4.6). This diversification within the infaunal niche suggests that
this region provided an adaptive habitat.
While not found in large numbers, gryphaeid bivalves are present and are
common to shallow marine successions of Panthalassa. These bivalves lived in
an unattached stationary reclining life-habit, and apparently experienced major
radiations at this time (Hallam, 1968). This is antithetical to the hypothesis that
reclining bivalves were driven to extinction by increased durophagy by
arthropods toward the end of the Cretaceous (LaBarbera, 1981), if that is the
time when this type of predation increased to critical levels for this type of
bivalve. Durophagous arthropods experienced radiations in the Late Triassic, and
this continued into Tethys during the Early Jurassic, suggesting that immediate
predation by these groups did not affect the gryphaeids to such a great degree.
However, it may be that the sediment was more stable in Panthalassa than in
Tethys, which is thought to be a key feature in gryphaeid survival (LaBarbera,
1981).
Many different adaptations against shell-crushing are utilized by shelly
prey today, and this is due to the wide variety of ways in which predators have
evolved to perform this task. However, when this type of predation increased
quickly in the Late Triassic, it was primarily utilized by durophagous predators
operating on or close to the sediment surface, inducing a particular set of
139
paleoecological changes among their shelly prey. This suite of characteristics
among predators and prey is characteristic of the MMR and appears to have
occurred globally and synchronously during the Norian Stage.
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II. OREGON
I. b. ii. A. Black Marble Quarry
The Black Marble Quarry limestone (BMQ) is a geographically isolated
succession in eastern Oregon (Fig. 4.10), found as part of the northern Wallowa
Mountains. BMQ is relatively close to the shallow marine successions of the
Martin Bridge Limestone and the Hurwal Formations, but it has significant
sedimentological dissimilarities that cause problems with stratigraphic and
temporal correlations.
BMQ is a dark limestone, although the color is derived from thermal
maturation of the limestone during later igneous intrusive activity, rather than
larger proportions of organic material, of which there is very little (~1%).
The age and lithologic affinity of the Black Marble Quarry in northeast Oregon
is problematic. The unit is a distinctive black limestone succession of Late
Triassic age, deposited in a lagoonal setting on one of many disparate
Panthalassic terranes of Triassic age, now assembled along the western coast of
North and Central America. BMQ does not have biostratigraphic age controls and
it is dissimilar to the two adjacent formations in several key ways. In the absence
of stratigraphic and biostratigraphic constraints, we propose a tentative age of
the BMQ based on paleoecological structure as compared to successions in
other global shallow marine successions.
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Lithology of BMQ
Several different facies can be found in the BMQ (Fig. 4.11), including
reefal limestones, shell hash-dominated packstones, and homogenous
wackestones with body fossils in relatively good condition. This combination of
deposits suggests a relatively shallow marine depositional environment.
Methods – Oregon
To analyze the paleoecological structure of the BMQ faunas, the entire BMQ
succession was measured and four bulk samples were collected (Fig. 4.12).
Each bulk sample comprised ~.018m
3
and samples were only collected from the
upper 10cm of a sedimentary bed. Only limestone beds were sampled that were
not reefal, not comprised of visible shell hash. The samples were disaggregated
by hand to a maximum size of 125 cm
3
. Each fossil specimen observed was
identified to a genus-level if possible, and the abundance of each taxon was
determined for each bulk sample.
Taxa were assigned to paleoecological categories, or guilds, using the
paleoecological approach developed for shallow marine faunas (Bambach, 2002;
Bush et al., 2007). This scheme is based on three important life-mode
characteristics: life-position relative to the sediment-water interface (tiering),
degree of motility, and mode of feeding. For example, an early Mesozoic
gastropod would be categorized as a mobile, epifaunal grazer.
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Results – Oregon
Four bulk samples were collected from the Black Marble Quarry, Oregon.
The lower three samples yielded diverse assemblages with over 25 identified
specimens per sample. The stratigraphically-highest sample (Fig. 4.12) yielded
only three identifiable specimens, and was thus excluded from the analysis. The
remaining samples contained similar levels of raw diversity, total specimens, and
total ecological niches present (Appendix 6).
The fauna of the BMQ are characterized by taxa which are generally
cosmopolitan in the Late Triassic (Nuculana, Modiolus) or regionally abundant
(Tutcheria, Septocardia). The most common four taxa appear in all three
samples and there is no apparent turnover between samples (Fig. 4.13).
Paleoecological analysis of the bulk samples indicates a high degree of
paleoecological structural similarity between the samples (Fig. 4.13). The low
proportion of stationary epifauna appears to be a consistent feature, and there is
a moderate decrease in the amount in mobile herbivores, primarily snails. The
greatest change through the short section is the increased abundance of mobile
infauna, which increase from 35% to 60%. These paleoecological transitions are
consistent with those observed globally in Norian age shallow marine
successions. The BMQ samples contained low numbers of stationary epifauna
(11.9–15.7%), low to moderate numbers of mobile epifauna (21.4–51.6%) and
two of the three samples were dominated by mobile infauna.
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As was observed in bulk samples from Nevada and Italy, the correlation
between mobile infauna and stationary epifauna is not straightforward, and this
appears to be due to the importance of animals such as the mobile epifauna.
There is a very low correlation between MI and SE (Fig. 4.14), although the
succession only contains three data points for comparison. There is excellent
negative correlation between the occurrence of mobile infauna and mobile
epifauna in the BMQ, however (r
2
=0.98). Interestingly, these groups show a
positive correlation in Norian samples from Nevada, but Middle and Late Norian
mobile infauna and mobile epifauna show a similar negative correlation in Tethys
(Fig. 4.15). These correlations are not significant when proportions of these
groups are plotted, only raw counts produce a correlation.
Discussion – Oregon
The faunal assemblages of the BMQ are typical of many Norian-age
shallow marine successions. However, the paleoecological structure of the BMQ
faunal assemblage is telling of the particular age of the sedimentary sequence.
The three bulk samples indicate an increasing proportion of mobile infauna,
which is already the dominant ecological niche of the assemblage. Both in
Tethyan sections of Northern Italy (Tackett and Bottjer, 2012) and in
Panthalassic assemblages from the Luning and Gabbs Formations in Nevada
(Tackett & Bottjer, in review), this feature is a paleoecological signature of the
late Middle Norian or the early Late Norian. This is also supported by the low
occurrence of stationary epifauna and the moderate proportion of mobile
epifauna. In Northern Italy and Nevada, the paleoecological succession of the
144
benthic fauna can be characterized in very similar ways (Fig. 4.16). The early
Norian is dominated by stationary epifaunal taxa, the middle Norian exhibits a
decline of these groups and increases in mobile epifauna, stationary semi-
infauna, and/or cementing stationary epifauna, and the late Norian is dominated
by mobile infauna. The proportions of these ecological guilds in the BMQ
correspond well to the Middle Norian–Late Norian paleoecological transition (Fig.
4.16).
Not included in this analysis is the presence of the large winged bivalve
family, Wallowaconchidae, found in the lowest stratigraphic levels of the BMQ,
and is known from several Panthalassic terranes (Yancey and Stanley, 1999).
These bivalves would have existed in a stationary epifaunal life mode, but they
appear to be additionally adapted to durophagous predation by their large size,
thick shell, alatoform shape (the round, football-shaped morphology would be
difficult to grasp and crack open, presumably), and was possibly adapted to
chemosymbiosis. Additional adaptations within stationary epifaunal bivalves are
a feature of Panthalassic faunas that is not as widespread in Tethys. For
example, in the Luning and Gabbs formations of west-central Nevada, cementing
bivalves become important components of the Middle Norian and early Late
Norian paleoecological communities. Ultimately, these groups are displaced by
mobile infauna to a smaller total proportion of the shelly assemblage, but the
cementing strategy is in agreement with the hypothesized increase in demersal
and benthic durophagy. Crabs and lobsters that crush or crack shells have
greater success when they are able to pick up and maneuver the shell, and have
145
much lower successes when the shell is cemented to some surface (Harper,
1991). Large size may be adaptive if coupled with a thicker shell, but a flat shape
is clearly disadvantageous at this time. The unique shape of the
Wallowaconchidae and other megalodonts may have allowed these groups to
persist with their uncemented stationary epifaunal life-mode during the Norian.
Fauna in the Late Triassic became increasingly adapted for predation by
demersal and benthic durophagous predators. This is supported in the Black
Marble Quarry, where fauna were increasingly comprised of mobile infauna. The
large (and increasing in succession) proportion of mobile infauna, low proportion
of stationary epifauna, and the moderate but decreasing proportion of mobile
epifauna suggest a late Middle-early Late Norian age for the BMQ faunas, based
on comparison with global paleoecological trends. The main stationary epifauna
(not analyzed here) are the Wallowaconchidae, observed in the lowest
sedimentary layers of the BMQ. Large stationary epifauna became increasingly
rare toward the end of the Triassic, and the wings associated with this family
were also adapted for a soupier substrate engineered by burrowing bivalves,
while the alatoform shape possibly resisted durophagous predators.
The interesting correlation between mobile epifauna and mobile infauna in
BMQ that is absent from Nevadan and poorly correlated in Italian successions is
intriguing. One explanation for the correlation might be that increased burrowing
activity disrupted the sediment surface enough to create mobility or byssal
attachment problems for mobile epifauna. In the Nevadan successions,
146
cementing bivalves are common in the Middle Norian, suggesting that some level
of stability was achieved.
Conclusion: Oregon
The paleoecological structure and succession of shallow marine
limestones from the Black Marble Quarry are similar to those of the early Late
Norian samples from both New York Canyon and the Lombardian Alps (Fig.
4.16). Similarities included high proportions of mobile infauna and relatively low
numbers of stationary epifauna. Like in the Nevadan successions, stationary
epifauna and pelagic carnivores were not common, but there were no instances
of cementing bivalves, except for one questionable Atreta. This lack of cementing
bivalves may be due to colder water, due to the lower paleolatitude of this
succession. Martindale et al. (2014) found key differences in reef communities
based on paleolatitude in Carnian and Norian reefs, and this may reflect a similar
disparity, as colder temperature can inhibit carbonate precipitation, all other
things being equal (Martindale et al., 2014). Based on these paleoecological
characteristics, and in the absence of other dating methods, I would estimate an
early Late Norian age for the BMQ sedimentary rocks – which would place the
formation as synchronous deposition with the Hurwal Formation (Stanley et al.,
2008).
Due to this imprecise dating method and the small number of samples
(n=3), I will not include this data with other global comparisons in Chapter 5
(Global Trends). The paleoecology of the level-bottom fauna do indicate that the
147
trends observed in the BMQ are consistent with those observed in Nevada and
elsewhere.
Summary of Panthalassa Faunas
Faunas from Nevada and Oregon shared several characteristics, but there
were too few samples from the Oregon succession to perform a meaningful
analysis of paleoecological succession. Based on shared paleoecological
characteristics, the sedimentary rocks from Black Marble Quarry are most similar
to late Middle or early Late Norian sedimentary rocks from New York Canyon.
The only notable difference between these successions are the lack of
cementing bivalves in from Black Marble Quarry which are very common in the
Middle Norian and early Late Norian of the Luning and lowest Gabbs Formations
in Nevada. This may be due to different water temperatures between these
allochthons. Unlike in Tethys, where cementing bivalves are also uncommon
compared to other types of animals, the temperature was at a similar
paleolatitude to the depositional environment for Nevadan sedimentary
successions, but circulation patterns at this time may control temperature and
carbonate saturation differences between these regions, affecting
paleoecological components of these environments.
The paleoecological structure and succession in Panthalassa and Tethys are
remarkably similar in many ways, including an Early Norian decline in stationary
epifauna and the rise to dominance by the mobile infauna in the Late Norian.
148
Chapter 5: Global Trends During the Norian Stage
A. Summary of new Norian data
The faunal successions of benthic fauna from Tethys (Southern Italian Alps)
and Panthalassa (west-Central Nevada) share several paleoecological trends,
but also differ in key ways that may highlight biological and ecological differences
between the regions. These trends within a single stage (the Norian) may be
placed into a larger context for other large-scale evolutionary transitions, such as
the Mesozoic Marine Revolution and the Paleozoic Fauna⎯Modern Fauna
transition to elucidate the nature of these events in new ways.
1. Shared Features
In both Tethyan and Panthalassan successions, the majority of animals
are suspension-feeders (Fig. 5.1), and the vast majority of total observed taxa
are bivalves (Fig. 5.2). In both Nevadan (Panthalassan) and Italian (Tethyan)
successions, the faunal assemblages are not static or taxonomically consistent
through the stage – there is considerable faunal turnover throughout the
successions (Fig. 5.3). Both successions can be characterized by intervals where
the fauna is relatively stable paleoecologically, i.e., the faunal turnovers do not
occur between every sample collected (Fig. 5.4). The assemblages do not repeat
after a turnover has occurred – once the stationary epifaunal groups of the Early
Norian lose their dominance to a variety of organisms utilizing several non-SE
niches, those groups do not regain dominance.
149
Both Tethyan and Panthalassa successions share paleoecological
characteristics in time and in sequence. Early Norian faunal assemblages in both
regions were dominated by stationary epifauna. These assemblages are
relatively low in diversity but high in number of observed specimens. The Middle
Norian and early Late Norian assemblages are much more ecologically complex,
and differ between the regions in what niches are being utilized (Fig. 5.4, Fig.
4.8), but in both successions, the stationary epifauna are increasingly replaced
by animals that are more mobile or that live infaunally or semi-infaunally. Late
Norian faunal assemblages contain very few stationary epifauna, and are
dominated by burrowing animals. Late Norian samples tended to have one
ecological “intermediate” as an important component in addition to the mobile
infauna, although the particular group differed between the regions. Overall, the
trends that characterize the faunal successions in both regions are increasing
mobility (Fig. 5.5) and infaunality (Fig. 5.6).
2. Different Features
While the major paleoecological trends are the same in both ocean
realms, the differences between the regional datasets provide more context and
allow for specific biological or physical differences to be tested between the
regions.
One important feature is the taxonomic composition of the two localities
and how they differ. In Tethys, the Early Norian stationary epifauna are
exclusively bivalves (Avicula, Isognomon), but in Panthalassa they are almost
150
entirely brachiopods (Plectoconcha). Brachiopods are present in low quantities in
Tethys but they are observed consistently in Panthalassan assemblages, at least
in the Early Norian.
As might be expected by two oceans separated by a supercontinent, the
fauna between the two realms are somewhat dissimilar. The two faunal
successions share none of the same dominant taxa; the five most dominant taxa
in any collection in one region are not the most dominant taxa at any time in the
other oceanic realm. However, many of the same genera are present in both
(Fig. 5.3).
While the Early Norian paleoecology of Tethys and Panthalassa are
similar (dominated by stationary epifauna)(Fig. 5.4), the Middle Norian and early
Late Norian paleoecological structure is quite different (Fig. 5.7). In Tethys, the
Middle Norian is primarily composed of mobile epifauna (gastropods and several
bivalve taxa) and moderate proportions of stationary epifauna and mobile
infauna. The Middle Norian and early Late Norian paleoecology in the
Panthalassan succession is often dominated by cementing bivalve groups, such
as Lopha and Plicatula. These assemblages also contain moderate proportions
of stationary epifauna, mobile infauna, and mobile epifauna, but the abundance
of cementers is striking. Finally, the Late Norian fauna of Tethys is primarily
burrowing bivalves and large semi-infauna (Pinna, Modiolus), the latter of which
is not very common in Panthalassa. Late Norian fauna in Panthalassa remain
ecologically complex, while dominated by burrowers. Burrowers comprise the
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most abundant niche, but not to the same degree as that which is observed in
Tethys.
The faunal transitions here are mostly in agreement with other studies that
use databases such as the Treatise on Invertebrate Paleontology (Ros et al.,
2011) or the PaleoBiology Database (Kiessling et al., 2007), in that
infaunalization is shown to increase before the Jurassic. However, the intra-stage
approach employed here highlights specific intervals of paleoecological transition
that were not previously recognized, in particular the complex Middle Norian.
Furthermore, the timing of the transition was not recognized to be within the
Norian when the entire stage was binned together – rather, it previously
appeared as if the transition occurred in the Rhaetian or between the Norian and
Rhaetian.
3. Data Summary
This study recognized several new aspects of Late Triassic faunal
evolution. First, the decline of the stationary epifauna began long before the start
of the Jurassic, perhaps 25 million years before this period boundary. Second,
the transition from sessile epifauna-dominated faunal assemblages to a more
mobile, burrowing assemblage was not a simple replacement. Rather, a complex
intermediate interval occurred in which stationary epifauna were replaced by
animals representing several different ecological guilds, all of which utilized
increased mobility, cementation, infaunalization, or smaller size. Ultimately,
mobile and infaunal animals became the most abundant, and were the most
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common animals in the Late Norian and Rhaetian stages. Third, the transition
from stationary epifaunal assemblages to burrowing assemblages was not rapid,
although it occurred in two distinct transitional phases. Most importantly, this
transition did not occur at the Norian−Rhaetian boundary, as has been
suggested.
The faunal transitions of the Norian Stage identified herein are crucial to
evaluating the biotic effect of the Manicouagan impact, the taxonomic and
paleoecological aspects of the Paleozoic Fauna−Modern Fauna transition, and
the timing, rate, and nature of the Mesozoic Marine Revolution. Finally, the high-
resolution dataset describing the diversity and paleoecology of the Norian Stage
provides critical information for evaluating selectivity of the End-Triassic mass
extinction and subsequent recovery interval.
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II. MMR – updating a classic idea
Since the Mesozoic Marine Revolution (MMR) was introduced (Vermeij,
1987), several new studies have highlighted particular interactions between
predators and prey, and many new discoveries have illuminated the timing of
important evolutionary events among both predators and prey. Here, I
summarize the existing literature on diversity and morphological trends in the
predator and prey taxa which may have played a significant role in the MMR,
highlighting new discoveries in timing of taxonomic radiations or other
characteristics that have improved our understanding of the MMR.
A. Predators
While shelly prey groups were experiencing major ecological changes in
the Norian Stage (Chapters 3 and 4), so were many groups of predators. By
examining behavioral, morphological, and paleoecological commonalities among
these groups, it is possible to find adaptive strategies which may have played a
larger role in the “arms-race” associated with the MMR, and serve to highlight the
particular features in it’s early stages.
1. Fish
Several important groups of fish first appeared or rapidly diversified in the
Late Triassic. Of these groups, many exhibited adaptations specialized for
durophagy, in particular the neopterygians (Tintori, 1998). The neopterygians
underwent their massive taxonomic radiation in the Middle Norian, as has been
shown in the extensively-studied fish deposits of the Zorzino Limestone of the
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Southern Italian Alps. Several important orders appeared, including the
Semionotiformes, Macrosemiiformes, Pycnodontiformes, and Pholidoformes
(Tintori, 1998). These orders exploited the durophagous trophic niche for the first
time within this class, and exhibited a range of traits associated with
specializations for durophagy. This trophic change represented a significant
departure from the semi-durophagous adaptations observed in Middle Triassic
neopterygians that were somewhat specialized for arthropod predation. Of these
durophagous neopterygians, several groups, such as the pycnodonts and deep-
bellied fishes, appear to be demersal durophagous “grazers” that sluggishly
swam along the seafloor for shelly prey (Tintori, 1998). This may be compared to
the Late Cretaceous fish radiations that included the derived, faster Teleostei
(Lombardo and Tintori, 2005), in which durophagous predators had a second
taxonomic radiation event.
Norian neopterygians had major skull/jaw changes that allowed them to
become excellent shell-crushers, but were slow-movers (Tintori, 1998). Earlier
(Middle Triassic) paleopterygians were more stream-lined and faster, but only a
few developed stout dentition for generalized predation (Tintori, 1998). Tooth
specializations varied among the different groups, but included stout chisel-like
dentition and anterior-posterior specializations for grasping and crushing sessile
or slow shelly prey (Lombardo and Tintori, 2005). Other groups such as the
macrosemiids developed teeth that were more specialized for shelly crustaceous,
which were also diversifying at this time. Thus, durophagy was proliferating in the
Norian and creating new complex relationships within existing food chains.
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One important aspect of this radiation of derived actinopterygians is that
they did not displace the trophic niches of other fishes. Basal actinopterygians
continued to exist, and in some places thrive, in higher trophic levels (predating
on other fish) (Lombardo and Tintori, 2005), while demersal durophagous fish
proliferated. The benthic environment was not widely utilized by durophagous
fish previously, and it was increasingly exploited during the Norian. These higher
predators were eventually replaced in the Early Jurassic by neopterygians, while
the demersal trophic niche was slowly populated by newer teleosts (Lombardo
and Tintori, 2005). Perhaps this replacement reflected the lack of shelly prey in
the earliest Jurassic and the repopulation of the demersal durophagous niche
during the Early Jurassic benthic recovery.
2. Sharks and Rays
Prior to the Late Triassic, specialized durophagous predators were not
common. Hybodontid sharks represented the only durophagous vertebrates of
the Early Triassic (Tintori, 1998), and, along with the placodonts, hybodonts were
apparently the only durophagous predators of the Middle Triassic and Carnian
Stage (Tintori, 1998). In the Late Triassic, hybodonts continued to be common in
shallow marine ecosystems (Tintori, 1998), and they represent one of the few
predators consistently reported from Panthalassan deposits (Fig. 5.8). They
utilized a wide variety of feeding habits (Maisey et al., 2004), but several groups
were specialized for durophagy. Not enough is known about the abundance or
diversity of this group to determine if they underwent major taxonomic radiations
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in the Norian Stage, but they appear to have been thriving in this changing
ecosystem as the dominant shark group (Maisey et al., 2004).
Neoselachians comprise another important shark clade, although this
group experienced dramatic radiations throughout the Jurassic and Cretaceous
(Underwood, 2006). However, at least four genera appeared in the Norian and
Rhaetian stages (Fig. 5.9), and pre-Jurassic shark diversity is still understudied
(Underwood, 2006). The current understanding of assemblage diversity in the
Early Jurassic suggests that some groups did experience major radiations in the
earliest Jurassic and Late Triassic, such as the Hexanchiformes and
Synechodontiformes, which share many dental similarities for specialized
crushing techniques (Underwood, 2006). In most cases for this order, the Early
Jurassic occurrences are used to infer Late Triassic radiations events.
Rays (Batoids) are also neoselachians, and are important durophages of
modern oceans. While there are no known Triassic occurrences of this clade,
they first appear in the Early Jurassic (Underwood, 2006). Phylogenetic anayses
suggest that they must have evolved in the Late Triassic, before diversifications
of other neoselachian clades (Underwood, 2006).
In general, the Late Triassic appears to have represented an important interval
for shark and ray stem groups, while important cladogenesis events so far
appear relegated to the Early Jurassic and onwards.
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3. Marine Reptiles
Seven groups of marine reptiles evolved in the Mesozoic, of which six
originated in the Triassic. Four major groups of marine reptiles lived during the
Late Triassic: Nothosaurids, Plesiosaurs, Ichthyosaurs, and Placodonts (Lucas,
1995), the latter two of which had durophagous members. Furthermore, the
stem-groups of these secondarily marine reptiles appear to have begun trophic
niche partitioning in the late Middle to Late Triassic as they were radiating
(Rieppel, 2002). Along with the increasing occurrence of adaptations related to
durophagy, this expanding niche-use is strong evidence for the importance of
shelly prey at this time.
3a. Placodonts
Placodonts were apparently always rare (Tintori, 1998) and were
restricted to Europe (Lucas, 1995), but they are important components to the
MMR because of their adaptations in dentition and in the jaw that facilitated
sucking in water for prey (specialized for non-attached prey), and their grinding
posterior teeth (Rieppel, 2002). Placodonts did not survive beyond the Triassic,
and this may be correlated to the decline in reclining stationary epifauna.
3b. Ichthyosaurs
Ichthyosaurs participated in several ecological roles, including pelagic and
demersal carnivores beginning in the Triassic, and increasingly so throughout the
Mesozoic (Kelley et al., 2012). The Omphalosauridae were specialized for
durophagy (Vermeij, 1987; Kelley et al., 2012), but this group did not survive
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beyond the Triassic. Ichthyosaurs may have been more important to the complex
pelagic interactions that developed later in the Mesozoic, while the demersal and
benthic predators increased on the seafloor.
3c. Others
Among the sauropterygians, several stem groups and their descendants
were specialized for durophagy, including Simosaurus and cyamodontoids
(Rieppel, 2002). This included predators with both benthic and pelagic lifestyles.
In general, it appears that the sauropterygians were diversifying
throughout the Mesozoic, and that the Middle Triassic saw trophic differentiation
within the stem-group and generic-level taxonomic radiation. Several
durophagous groups appeared and radiated throughout the Late Triassic as well,
although others have associated the Late Triassic with a decline in marine reptile
diversity (Kelley et al., 2012). However, the Late Triassic stands out as the
largest source of generic diversity for placodonts (7 of 13 total genera [pbdb.org,
8/27/13]).
Finally, early turtles appear to have originated in the Norian Stage (Li et
al., 2008), and were possibly durophagous in their early stages (Vermeij, 1987),
although these fossils are putative and require further analysis. Regardless, this
is an important discovery of a group evolving in the Late Triassic.
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4. Arthropods
Evaluating adaptive and taxonomic radiations among Mesozoic and
Paleozoic arthropods has many caveats. One of the most difficult issues to
resolve is the low preservation potential of this group in normal marine
environments, i.e., deposits where shelly fossils are also found. For this reason,
arthropod fossils are rarely found in the same depositional environments as their
prey. A second problem for interpreting functional morphology is the limited
number of components of the complex arthropod body that have fossilization
potential and inform the researcher about the feeding mechanisms. Therefore,
diversity and paleoecological analyses of arthropods are difficult to perform in
similar ways as with other predator groups which produce calcareous fossils or
teeth. For this same reason, they also must be treated differently from shelly
animal analyses, that may use abundance or genus-level taxonomy. A first
occurrence of a taxon is not assumed to represent an accurate estimate of
origination time; rather, phylogenetic studies of stem groups and last common
ancestors are often utilized to estimate divergence times due to their known
scarcity in the fossil record (Schweitzer and Feldmann, 2010). First occurrences
are therefore interpreted as commonality in this analysis - ranges are not used,
nor are abundances.
My analysis here is focused on groups for which we have a fossil record
and are known to act as predators on shelly animals in marine settings, namely,
certain decapods and stomatopods. Arthropod adaptations that are known to
relate to specialized methods for durophagy have been summarized elsewhere
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(Schweitzer and Feldmann, 2010). Hard parts that suggest shell-crushing or
peeling include heterochelous first pereiopods, molariform teeth and/or a curved
proximal tooth on the chelae, and calcified mandibles (Schweitzer and Feldmann,
2010). However, these features are not always observed in the arthropod fossils
found, so interpreting the existing fossil record for the Late Triassic has many
uncertainties.
However, the current state of knowledge has increasingly shown that the
Late Triassic is an important time for the radiation of specialized durophagous
arthropods in addition to the Early Jurassic. Durophagous decapods which
appeared in the Late Triassic include the Erymidae (Clytiella), Eryonidae,
Coeiidae, and Tetrachelidae (Schweitzer and Feldmann, 2010). More groups
appeared in the Early Jurassic, currently no specialized durophagous decapods
are known to have originated in the Early or Middle Triassic. Paleozoic decapods
specialized for durophagy are of questionable interpretation
(Paleopalaemon)(Schweitzer and Feldmann, 2010), and were probably
opportunistic scavengers, and durophagy by arthropods is not likely to have been
a significant paleoecological factor before the Triassic (Schweitzer and
Feldmann, 2010).
Arthropods are also often prey of durophagous predators, such as
neopterygians (Lombardo and Tintori, 2005), and may also be useful as
indicators of areas experiencing increased predation. For example, arthropods
from the middle Norian in the Zorzino Limestone dominantly utilize a netantian
(swimming) lifemode, but by the Late Norian in the Riva di Solto shale, most
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arthropods are reptant (crawling)(Garassino and Teruzzi, 1993). The cause of
this change has been suggested to be environmental (the spread of anoxia in the
Lombardian basin), but both the RSS and the Zorzino are considered to be
periodically anoxic, so an ecological hypothesis is also appropriate. This would
conflict with the hypothesis that demersal durophages were affecting the seafloor
assemblages, unless these arthropods were able to avoid or repel the fish in
some way. Due to the lack of data on pre-Jurassic arthropods, these issues are
not currently resolvable.
Another important group of durophagous arthropods may have also arisen
in the Norian Stage, the Brachyura. A specimen was found in a lacustrine deposit
of the Chinle Petrified Forest Formation in New Mexico (Rinehart et al., 2003),
which would indicate a great expansion of the range of this group. This
phylogenetic relationship has been challenged by others (Schweitzer and
Feldmann, 2010), and may not represent a diversification event.
An additional consideration in this discussion of arthropod durophagy is
the complexity of feeding modes observed among modern marine arthropods.
Many groups are not sololy durophagous, but will resort to durophagy as needed
(Schweitzer and Feldmann, 2010). Most of the Late Triassic-Early Jurassic
decapods were specialized for prying or peeling shells open (Schweitzer and
Feldmann, 2010), although the Early Jurassic lobsters first exhibited shell-
crushing adaptations.
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The Late Triassic-Early Jurassic therefore seems to be a significant
interval for the arthropod radiation of durophagous predators, in which maybe
chelate forms and molariform appendages possibly appear (Schweitzer and
Feldmann, 2010)(Fig. 5.9). However, the fossil record for the Late Triassic is still
developing, and the potential to extend ranges is quite high (Schweitzer and
Feldmann, 2010). Various families and morphological adaptations appeared
throughout the Jurassic and Cretaceous (Schweitzer and Feldmann, 2010), but a
second radiation seems to have occurred in the Late Cretaceous, and continued
in the early Cenozoic (Vermeij, 1987). Many studies have examined the effects of
these predators on gastropods and other shelly marine animals (Leighton, 2002;
Huntley and Kowalewski, 2007), and many gastropod drilling clades were rapidly
diversifying in the Cretaceous and early Paleogene (Sohl, 1969; Taylor et al.,
1980). It seems possible that the dramatic increase in slow-moving epifaunal
predators may be connected with this second radiation of shell-crushing
arthropods.
5. Asteroids
Vermeij (1987) proposed that an important predatory asteroid, the
Asteriidae, appeared for the first time in the Early Jurassic, and were critical to
the MMR due to their ability to pry apart bivalved animals. Recent studies from
the Middle Triassic (Blake and Hagdorn, 2003) suggest that the Asteriidae crown
group is present by that time which has morphological similarities to modern
predatory asteriids and may have fed in a similar manner, although it is not yet
confirmed. Other Tethyan studies have found more fragmentary evidence for the
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presence of asteriids in Norian deposits (Blake et al., 2000). Asteriids did not
develop a shell-crushing ability, but they were seemingly capable of shell-prying,
which would have been focused at the sediment-water interface.
6. Durophagy Trace fossils
6a. Late Triassic/Early Jurassic Drill holes
Drill holes, usually by gastropods, are a widely used proxy for estimating
the degree of predation in shallow oceans (Kowalewski et al., 1998; Kelley and
Hansen, 1993). Rare occurrences of drill holes have been reported from Late
Triassic bivalves (Fürsich and Jablonski, 1984), and early Jurassic brachiopods
(Harper and Wharton, 2000), but these instances seem to be rare and do not
show a gradual increase from the Triassic to the Cretaceous. Gastropods of the
Late Triassic appear to primarily have been grazers, as opposed to carnivores,
but the isolated occurrences of Late Triassic and Early Jurassic drill holes are
thought to represent early, diffuse drilling attempts by gastropods (Aronowsky
and Leighton, 2003). However, this is a much-debated topic and Triassic
gastropod taxonomy is a poorly understood area (Erwin, 1990). Of the families
present at this time, none include drilling carnivores present today (Sohl, 1969).
Of what is currently known, no gastropod radiations of suspected predator taxa
were underway in the Late Triassic or early Jurassic (Sohl, 1969).
5b. Bromalites/Regurgitalites
Evidence for durophagy by vertebrate predators is evidenced by the
Norian/Late Triassic proliferation of coproliths containing shell fragments in fish-
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dense deposits (Lombardo and Tintori, 2005). Other deposits of the late Middle
Triassic include bromalites containing dense pockets of shell debris (Salamon et
al., 2012), indicating that durophagy was certainly occurring by the Late Triassic.
6. Summary of Predators
Trace fossils and body fossils of predator taxa indicate that many new
groups of benthic or demersal durophagous predators appeared and diversified
in the Late Triassic, and several in the Norian Stage. The fossil record for many
of these groups is scant for the Norian Stage, however, so it is possible that more
groups will be shown to appear. There is very little evidence for significant drilling
predation in the Late Triassic, which, based on the use of this metric as a proxy
for overall predation intensity, would suggest that there is no significant increase
in predation at this time. This does not agree with the trends in diversity observed
among specialized Late Triassic durophages at this time. Based on the changes
in shelly fauna through the Norian Stage, I would predict that more specialized
durophagous arthropods and fish will be found in Panthalassa. Among the well-
studied groups, such as the fishes, the Norian was clearly a time of great
innovation and diversification, with an emphasis on durophagy specialization.
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B. Prey
The Late Triassic appears to represent an important interval for the
diversifications of several taxonomic clades. Among predators, these
diversifications were often among those genera which utilized novel methods of
demersal or benthic durophagy. In an arms-race scenario, the increasing
expression of adaptations related to this feeding specialization would be
complimented by corresponding adaptations that specifically address these
predatory behaviors. Prey groups appear to have reflected this change in
predation in the form of morphological and behavioral adaptation in a variety of
ways, many of which may be directly related to benthic/demersal durophagy.
These changes also occurred within several different phyla, including Mollusca,
Echinodermata, Annelida, and Brachiopoda. One commonality these groups
have is a consistent presence in shallow marine ecosystems, suggesting that the
predatory pressure increased within a particular environment. In making these
correlations, it is important to make testable predictions, as well as considering
that the established set of bauplans and life-modes in marine animals is diverse
and different groups have different biological limitations. An evolutionary
response to a directed type of predation may manifest in several different ways.
Listed below are several biological trends in prey groups that have important
implications for our understanding of the MMR.
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1. Cementers
Cementing animals attach themselves to a surface using a strong mineral
binding material, and this is ideally a permanent position. This life-mode has
several disadvantages – the animal cannot escape or move to a more ideal
location for feeding, and competition for space becomes more difficult. The use
of a cementing life mode in relatively marine environments characterized by
relative low water energy was explored in empirical studies (Harper, 1991), which
found that cemented bivalves were less-susceptible to durophagous predation by
arthropods. Arthropods must manipulate the shell in order to access the relatively
soft ligaments in the umbo, which, once disrupted by spearing one claw into the
umbonal area, can more easily crush the shell with the other appendage.
Yonge (1979) examined the diversifications of cementing bivalve clades in
the fossil record, and found that many groups appeared to develop the ability to
cement throughout the Mesozoic. Using the Paleobiology Database and new
literature, I was able to update the first occurrences of several cementing clades
(Appendix 1), and found that at least four groups first appear in the Norian Stage,
and two more are currently reported to appear in the Rhaetian Stage. This burst
of cementing bivalve groups is greater than at any point in the Mesozoic (Fig.
5.10), and suggests that this life mode offered some adaptive benefits. Based on
the study undertaken by Harper (1991), this radiation would suggest and
increased role of arthropod durophagous predation. While the Triassic arthropod
record is very sparse (Schweitzer and Feldmann, 2010), some groups may have
first developed specializations for durophagy in the Norian Stage.
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2. Ligament changes for cementation and swimming
Adaptations related to cementation among previously non-cementing
sessile benthic bivalve clades primarily affected the ligament area of the shell,
and other related sessile benthic animals also underwent considerable
morphological adaptation in the umbonal area, resulting in two significant
adaptive events in the Late Triassic that are likely to reflect an anti-predator
response to increased durophagy. First, for some of the most important
cementers of the Late Triassic (Ostrea, Lopha), the ability to cement was derived
from a change in the ligament type (Hautmann, 2004). In several groups, which
apparently developed this modification independently, the ligament attachment
area was greatly expanded to reduce shear (Hautmann, 2004). All of the groups
that developed this modification also developed the ability to cement to hard
surfaces, and in non-rocky shore environments, there is no known purpose for
bivalve cementation other than as an anti-predator strategy. The independent
appearance of the cementing ability and the anti-shear ligament attachment
modification and the proliferation of these taxa in the Norian Stage support the
idea that increased benthic durophagy had a major impact on this group.
Also in the Late Triassic, a second group of the Pteriomorpha that
represented an important clade of epifaunal bivalves in shallow marine systems
developed a distinct, but revolutionary, ligament attachment morphology from the
primitive type. This group, the pectinids, altered their ligament attachments such
that they were provided with a unique adaptation that was likely adapted against
benthic durophagy by predators at that time. This modification to the ligament
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attachment area facilitated rapid mobility by clapping the valves enabling rapid,
facultative mobility (Hautmann, 2004). There is no other known purpose to
swimming except primarily as an escape strategy (Hautmann, 2004). Pectinids
experienced major taxonomic radiations during the Late Triassic, and continue to
be one of the most common non-attached epifauna in modern seas (Waller,
2006).
These two changes resulted in dramatically different behavioral strategies
for these bivalve groups, but involved the modification of the similar
morphological element. One group took an approach of resisting the
durophagous attempts of predators which were likely to be diversifying at this
time, although they are common targets of drilling predators in modern oceans
(Sawyer and Zuschin, 2010), while the second group adopted an avoidance
strategy using the ability to rapidly transport their body. The predators from the
Late Triassic appear to have been specialized for shell-crushing, but they were
also quite slow, especially for fish and placodonts. The ability to quickly swim
away from the area would most likely have represented a successful escape
strategy from many predators operating at this time.
3. Mobilization – mobile epifauna
Pectinids were not the only group of animals that adopted mobile life
habits in the Late Triassic. The increase in burrowing animals is a well-known
Mesozoic phenomenon, but mobility among shelly benthic animals occurred in
several different clades and this occurred in a significant way in the Late Triassic.
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Mobility is more difficult to interpret as a specifically anti-predation strategy, and
most of the bivalve groups discussed here were already adapted to a mobile
(facultatively or functionally). What is notable is the transition from previously
sessile epibenthic animals to a mobile lifestyle, like the pectinids in the previous
section, who continue to exploit the same feeding niche. This change suggests
that mobility imparted a distinct advantage, and the increasing presence of
mobility among several phyla in the Late Triassic suggests a similar pressure,
like epibenthic predation, may correspond to these changes among shelly prey.
Among the crinoids, the Late Triassic represented a major evolutionary
interval towards increased mobility, arguably their last major evolutionary
transition (Baumiller et al., 2010). Crinoid clades radiated in the Middle Triassic
and continued to do so in the Late Triassic, with the appearance of three new
clades (Baumiller et al., 2010), of which only one group was strictly stationary
epifaunal. Crinoids appear to have stopped radiating after the Triassic. Of the six
groups of crinoids extant during the Norian Stage, only two were stationary and
epifauna, two were capable of benthic locomotion, and two were nektonic or
planktonic (Baumiller et al., 2010). Post-Triassic crinoid diversity dynamics
appear to have been evolutionarily uneventful (Baumiller et al., 2010). This
change in crinoid life strategy is also correlated to increased occurrence of bite
marks in the Triassic (Gorzelak et al., 2012), suggesting that the increase in
mobility is related to an increase in durophagy by benthic predators.
Mobile bivalves, according to some estimates, only slightly increased
during the Norian Stage (Franch, 2009). In this compilation, however, several
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facultatively mobile groups are considered to be stationary, instead of
facultatively mobile, such as Limea and Parallelodon. For this reason, the
number of mobile epifaunal bivalves is likely to be considerably higher than what
is depicted in the database compiled by Franch (2009).
Gastropods represent the quintessential mobile epifaunal animal in these
ecosystems, and the Late Triassic is known for several morphological
adaptations that may relate to increased durophagy, such as the independent
appearance of thickened shell lips in at least three archaeogastropod groups in
the Triassic (Vermeij, 1987), and a second radiation of this adaptation occurs in
the Cretaceous. Gastropod taxonomy is also notoriously difficult, and particularly
understudied for Late Triassic taxa. It is difficult to analyze diversity dynamics for
this group during the Norian Stage, so occurrence estimates are often
problematic fot the Triassic. Despite this lack of occurrence data, gastropods
exhibit several major morphological changes through the Late Triassic that
indicate an adaptive response to durophagy. It is, however, unlikely that
gastropods were highly affected by escalatory trends in the Late Triassic as they
were in the Cretaceous: the appearance of the anti-durophagy adaptations
appeared in the Triassic, but were not common until the Cretaceous (Vermeij,
1987), and a comparison of breakage scars between the Paleozoic, Late
Triassic, and Cretaceous indicated that the Late Triassic scarring frequency
(likely due to peeling by arthropods) was not elevated (Vermeij et al., 1982).
Perhaps the mobility of this group compared to the relatively slow moving
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predators in the Triassic provided some resistance that was not sufficient later in
the Mesozoic.
4. Infaunalization
Due to the increased number of durophagous, usually slow-moving,
predators on the sedimentary surface, the infaunal life-habit would have
represented a successful avoidance strategy (as opposed to the escape strategy
among mobile epifauna). Those animals exploiting the infaunal habitat would
have had an advantage, as opposed to the vulnerable surface-dwellers. In many
analyses, infaunality is included with mobility. To live under the sediment,
animals must have the ability to transport themselves there. I analyzed non-
infaunal but mobile animals in the preceding section, and while mobile epifauna
do experience important evolutionary and morphological changes during the Late
Triassic, the burrowers experience the greatest successes.
Infaunal animals included mostly bivalves, as well as some worms.
Infaunal bivalves increased throughout the Middle Triassic (Ros et al., 2011),
which may have been related to the full recovery from the Permo-Triassic mass
extinction. But their most dramatic increase in diversity occurred in the Carnian
and Norian stages, when many boundary-crossing genera appeared (Ros et al.,
2011). Stationary epifauna also increased their generic diversity in the Middle
Triassic, but this diversity remained stagnant through the rest of the Triassic, until
infaunal bivalves became more diverse for the first time in the Triassic in the
Norian Stage. This trend of increased infaunalization of bivalves increased
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throughout the Mesozoic, with a brief set-back after the End-Triassic mass
extinction (McRoberts et al., 1995).
Most brachiopods are limited in life-mode to the epibenthic realm and are
not capable of expanding their ability to take on this strategy. Crinoids are not
known to burrow either. This limitation may have led to the migration of these
groups to deeper, more cryptic environments that they now inhabit (Steele-
Petrovic, 1979; Gorzelak et al., 2012).
5. Ribbing/Spinosity
Ribbing of shells, or surface ornamentation, may have several functions,
including the increased ability to burrow (Stanley, 1975). An alternative function
is to strengthen the shell from crushing or abrasion. Due to the increasing
numbers of crushing predators in the Late Triassic, it is worth considering this
characteristic as one which may reflect increasing pressure of durophagous
predation.
During the Late Triassic, several clades of shelly benthic animals exhibit
increased ornamentation, including brachiopods (Vörös, 2010)(Fig. 5.11).
Brachiopods increased their levels of ornamentation throughout the Late Triassic,
and greatly increased their diversity, before experiencing high extinction rates
across the TJB, after which exhibited greater ornamentation persisted in greater
numbers into the Mesozoic. In addition to the size changes exhibited in the
limited Early Norian specimens from Berlin–Ichthyosaur State Park, this suggests
an increase in benthic durophagous predation was coupled with these changes.
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6. Worms
Worms encompass several animal clades, but some groups experienced
adaptive radiation in the Late Triassic. Of these, large burrowing polychaetes
(such as arenicolids) appear in the Late Triassic and were capable of rapidly
burrowing deeply into the sediment (Vermeij, 1987), and developed a life-mode
that injected large amounts of surface water into anoxic sediments (Grossmann
and Reichardt, 1991), as opposed to the lined burrows that were previously
common and mainly interacted with water above the sediment. This group is not
necessarily correlated to the same types of specializations among shelly prey
and shell-crushing predators, but the increase in burrowing depth and speed is
ancillary evidence that living on the sediment-surface was a dangerous area in
the Late Triassic. The Late Triassic is also known for the proliferation of worms
with calcareous tubes, which formed large reefs in Tethys and elsewhere (Berra
and Jadoul, 1996). This lifemode may have allowed these animals to continue an
epifaunal life-mode with a more protected habitat.
7. Summary of Prey
As with the durophagous predators, many marine prey groups of the Late
Triassic diversified and exhibited adaptations related to predation by shell
crushing (Fig. 5.10). In particular, infauna and mobile animals and those with
shell-strengthening adaptations increased over free-living epifauna and immobile
forms.
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C. Relating the trends in my data
The previously-described adaptive radiations among prey and predator
taxa have shown that the Late Triassic, and often the Norian Stage in particular,
represent critical intervals in the development of the MMR. However, the Norian
is a long stage, and the trends described previously do not offer the resolution
needed to determine many critical aspects of the early MMR. In order to
determine the timing and rate of paleoecological change in benthic communities,
here I place my successional faunal datasets from major ocean basins in the
context of this larger trend to describe the rate and nature of the early stages of
the MMR.
1. INFAUNALIZATION
One of the most striking trends in the shallow marine sedimentary
successions sampled from Panthalassa and Tethys is the proliferation of mobile
infauna, and is in agreement with previous studies (Ros and Echevarría, 2011).
Infaunal animals in Norian sedimentary successions increased in occurrence
through the stage, and exhibited wider ranges of feeding diversity (Fig. 5.4). This
expansion of the infaunal niche suggests that this life mode provided protection
from the surface-dwelling predators that were increasingly present. There is also
some negative correlation between infauna and mobile epifauna toward the end
of the Norian Stage, suggesting increased seafloor instability.
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2. MOBILIZATION
Mobility (active and facultative) among Tethyan and Panthalassan faunas
increased throughout the Norian Stage (Fig. 5.4), and increased for epifaunal
bivalves as well. Many shelly groups that were normally stationary but
facultatively mobile increased in abundance during the Norian Stage in both
Tethys and Panthalassan sections. This may represent escape strategies and/or
the ability to respond to a loosened substrate from increased infaunal burrowing.
This is a topic that has not been closely examined beyond this analysis for the
Late Triassic, but with the increased abundance of mobile groups beginning in
the middle Norian along with diversity data for other animal groups that became
increasingly mobile at this time, mobility was clearly and adaptive strategy in
these changing environments.
3. Evolutionary events among the stationary epifauna
The paleoecological features described so far can be characterized as
ecological replacements (infauna replacing epifauna, mobile replacing
stationary), and could possibly be interpreted as responses to shifting
environmental parameters that are unrelated to predation. However, various
morphological changes and population shifts also took place during the Norian
Stage among animals which would be hypothesized to be particularly vulnerable
during a scenario of increased benthic durophagy. The stationary epifauna from
the Norian successions in Tethys and Panthalassa exhibited trends that are in
agreement with many predictions related to the MMR, and the successional
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samples illustrate the different rates of change among this vulnerable
paleoecological niche.
3a. CEMENTERS
In Panthalassa, cementing bivalves became far more common than non-
cementing stationary epifauna after the Early Norian. Several cementing groups
appeared and became abundant, although no group was persistently dominant
for the majority of the stage. In the Carbonate Member of the Luning Formation,
younger samples were often dominated by Lopha and Ostrea, very large
(>10cm) oysters with very thick shells (>5mm). The oldest samples from the
Gabbs Formation, however, are dominated by another, less-robust cementing
bivalve, Plicatula. These were observed to be smaller (1-5cm) and the shells
observed were no thicker than 3mm. Tethyan cementing bivalves were not
common in the successions studied.
3b. SIZE CHANGES
Populations of non-cementing stationary epifauna from both Tethyan and
Panthalassan succession changed in the observed size ranges throughout the
Norian Stage (and possibly continued into the Rhaetian Stage as well). This size
change has not been previously suggested and may represent a new faunal
response to the MMR. If there is a benefit to benthic or demersal predators to
consume more calories per predation attempt, large epifaunal animals without
thick cemented shells would impart more calories than smaller shelly prey.
Stationary epifauna decline in abundance through the Norian Stage, but it is
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possible that increased durophagous predation would have a gradual impact on
populations that may be apparent in their fossil record. Here, I measured the
sizes of all non-cementing stationary epifauna from my collections to determine if
there is a change in size distributions throughout the Norian Stage.
Width and height measurements were taken from all non-cementing
stationary epifaunal specimens that were complete or visible enough to
determine these features accurately. “Area” is H*W, but because the specimens
are often oblong, the term is loosely used in this context. A total of 89 specimens
from Tethyan successions and 153 specimens from Panthalassan successions in
Nevada were identified and measured (Appendix 7). No cementing bivalves were
included in this analysis because these are often found as large fragments.
Among the non-cementing stationary epifauna, there were very few
specimens observed in the Tethyan faunal assemblages but a decreasing size
trend is apparent (Fig. 5.12). The Early Norian SE had a wide variety of sizes and
there was a rapid decrease in size range between the Early and Middle Norian in
Tethys, that was also correlated with a decline of SE specimens (5.13). In
Nevada, the pattern appears to show no directional trend, unless brachiopods
and bivalves are separated. Brachiopods dominate Early Norian successions,
and they appear to exhibit a decline in size range, although later Norian
brachiopod specimens are rare. Panthalassa bivalves begin the Middle Norian
with a larger average size for the stationary epifauna and with a wide range of
sizes observed, and these features decline, along with the occurrences of non-
cementing stationary epifauna overall, duringthe Norian Stage (Fig. 5.12). It
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appears that a decreasing size trend occurs twice in Nevada, once for each
dominant group of animals. The decreasing size trend can also be seen within a
genus – there are not many SE that are found throughout the Norian (5.15), but
some do occur at least in small numbers, such as Avicula (Fig. 16). The change
occurs overall, although not necessarily in a gradual way, especially in the Italian
specimens (Fig. 5.17). Among common SE, there is typically a good relationship
between height and width, indicating that while the area metric is rough, it should
approximate the area well (Fig. 5.18).
I hypothesize that this change is related to feeding preference by
demersal predators, selectively picking up non-cemented stationary epifauna
(SE). Large SE may have been easier to identify and provide more calories for
the predator, and smaller SE may have had some advantage in this environment.
Because this trend occurs in both oceans and among different types of dominant
SE, I interpret this to mean that the predatory pressure is increasing in a similar
way for both environments.
3c. Disappearance of Eocrinus columnals
In Panthalassa, crinoid columnals disappear toward the top of the
sampled succession, and none were found in bulk samples from New York
Canyon. Because of the multi-part nature of the bodies of this crinoid group, it is
not possible to treat this in a similar quantitative way as with the univalve and
bivalved groups. However, it stands simply as an observation that this stationary
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epifaunal group declined in occurrences in Panthalassan deposits during the
Norian Stage.
4. Is there a spatial component to the early MMR?
The overall similarities of faunal changes among the shelly prey and the
taxonomically widespread development of adaptations related to benthic or
demersal durophagy suggest that the Norian was host to a global reorganization
of shallow marine ecosystems which has persisted until today. Some differences
in the fauna between Tethys and Panthalassa indicate that the predation types
may have had some subtle differences that resulted in different mid-Norian
paleoecological compositions – in particular for the ecological “intermediates”
(Fig. 5.7). The high frequency of cementing bivalves in Panthalassa would
suggest that arthropods may have played a large role in the life-habits of the
shelly prey, although this strategy would have been effective against attempts by
fish and sharks as well.
D. The Second Pulse
The MMR has often been described as a gradual evolutionary event, one
that became amplified throughout the Mesozoic. Drilling frequencies have been
widely examined in marine shelly animals to represent a general proxy for
predation pressure in marine animals (Kowalewski et al., 1998; Harper et al.,
1999). However, since the MMR was introduced, this proxy has been shown to
represent a limited range of predation behaviors that are rarely observed prior to
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the Early Cretaceous. The previous discussion has highlighted the evidence for
an arms-race which begins and amplifies in the Late Triassic, and this indicates
that the drill hole proxy may be of limited use in the early phase of the MMR.
Here I briefly describe the record of drilling predation in the Phanerozoic,
including several caveats, to illustrate the usefulness of this trace fossil as a
predation proxy, especially for the MMR.
1. Drilling Predator Evolution
Several different animal groups are capable of drilling into calcareous
shells, and considerable research has addressed whether physical
characteristics of drill holes allow for the identification of the driller as well as the
timing of the development of this skill for each group. (Fig. 5.14.)
1a. Gastropods
Gastropod drill holes are very common in modern ecosystems, and they
are primarily made by naticids and muricids (Kelley and Hansen, 1993). The
holes have a variety of sizes, and they do vary in their placement on the shell.
However, drill holes tend to be concentrated on the thinner part of the bivalve
shell. Gastropod drill holes have a relatively consistent shape: they are circular,
smooth-walled, usually perpendicular to the shell surface, and they taper toward
the internal part of the shell (Wodinsky, 1969).
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1b. Octopods
Octopods leave behind a very poor body fossil record, but they are
capable of making an extraordinarily diverse ichnofossil record for drilling
predation. As a mollusk, the holes left by octopods are formed by radular
abrasion (Bromley, 1993), and they may be quite similar in appearance to those
formed by gastropods (Bromley, 1993). Octopod drill holes have a wide variety of
shapes, and this is most likely because they often physically rotate the shell in
stages as they drill, which can produce circular, square, or even x-shaped holes
(Fig. 5.14). They tend to be smaller, and while like gastropods there is variety in
their placement on the shell, they tend to cluster above the muscle scars
(Wodinsky, 1969). They also commonly make more than one drill hole per animal
(Bromley, 1993) and they tend to be smaller in size and can taper at a more
extreme angle than gastropod drill holes (Wodinsky, 1969).
2. Drillhole Occurrences
2a. Paleozoic
Rare boreholes are known from brachiopod shells of the Paleozoic
(Cameron 1969), but the diverse size and shape of those drill holes suggests a
lack of specialization for drillers of brachiopods (Kowalewski, 2005). These were
not likely to be made by gastropods; rather, polychaetes (Cameron, 1969) or
octopods are the more likely trace-makers.
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2b. Mesozoic
2bi. Early Mesozoic – a gap in the drilling record
Triassic drill holes were discovered in Late Triassic bivalve shells (Fürsich
and Jablonski, 1984), but further research has not revealed a continuous
presence or gradual increase in frequency for the remainder of the Triassic or the
early-middle Jurassic (Kowalewski et al., 1998). One study reported a relatively
high frequency of drill holes in brachiopods from the Early Jurassic (Harper and
Wharton, 2000), but the next occurrence of increased drilling frequencies are
from the Late Jurassic at a single locality (Bardhan et al., 2012). The increase in
drilling frequencies in the Cretaceous was rapid and continued to increase into
the Paleogene (Kowalewski et al., 1998; Kelley and Hansen, 1993). Thus it
seems more likely that the Early Mesozoic drilling occurrences did not represent
a significant feature of the predatory activity at this time, and would indicate that
drilling became a major factor in the later Cretaceous (Kowalewski et al., 1998).
2bii. Late Mesozoic/Early Cenozoic – correlated drilling frequencies and drilling
predators
Drilling frequencies dramatically increased in the Cretaceous and
continued to do so in the early Cenozoic (Kowalewski et al., 1998; Kelley and
Hansen, 1993). Recent studies have shown that Late Jurassic drilling
frequencies were still quite low and patchily distributed (Bardhan et al., 2012) but
seem to exhibit the gradual increase into the Early Cretaceous, followed by a
dramatic increase in the Late Cretaceous (Kowalewski et al., 1998). Furthermore,
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increased drilling frequency seems to be closely correlated with the appearance
and diversification of naticid and muricid gastropods (Harper et al., 1999;
Bardhan et al., 2012)(Fig. 5.10), who are the primary drillers in modern marine
ecosystems.
The rapid increase in drilling predators may have had a significant effect
on Mesozoic marine ecosystems. Naticid and muricid gastropods can target
infauna and cementing bivalves, but their predation attempts in modern systems
are more successful with non-cemented stationary epifauna (Sawyer and
Zuschin, 2010). Increases in infauna and cemented stationary epifauna are
observed in the Late Triassic, but drill hole frequency is still very low. It is
possible that the rare Late Triassic drillers were gastropods, but the predators
which were radiating at this time were also benthic or demersal durophages,
which perhaps influenced the population densities of the typically epifaunal
gastropods. This does little to explain why drilling increases occurred in the Late
Mesozoic, along with great radiations of fish and arthropods.
The drillers of the Late Triassic remain a mystery, although there has been
some speculation as to their identity (Aronowsky and Leighton, 2003). This
represents an important departure from the original iteration of the MMR
hypothesis and highlights that drilling frequency may not be tied to predation
intensity for the majority of the Mesozoic and particularly not in the earliest
phases. The lack of reported drill holes in the Jurassic did not represent a lack of
research, but a lack of drillers. The Late Triassic drill holes have been described
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subsequently as a failed evolutionary experiment, and that seems to be
supported by newer studies.
Therefore, the drilling revolution appears to represent a punctuated
evolutionary event that developed long after the onset of the MMR in the Late
Triassic. Here, I ascribe this event to a second pulse of the MMR, with the first
pulse occurring in the Late Triassic and being characterized by increased benthic
durophagy by predators and the proliferation of avoidance and resistance
strategies among prey. The second pulse of increased predation pressure
affected different groups than the first, and was accompanied by the
synchronous diversifications of drilling animals and their trace fossils.
2c. Drilling Frequencies in Norian Successions
No drill holes were observed in Panthalassan specimens, and ~6 possible
drill holes were observed in total from Tethyan successions. These potential drill
holes only occurred in the Late Norian deposits from the Riva di Solto Formation.
It is possible that the drill holes were only preserved due to the excellent
preservation of this assemblage, and it is notable that they only occurred in
infaunal bivalve shells.
2d. Modern Drilling – Evidence for the role of drillers in benthic assemblages
In modern shallow marine ecosystems, drill holes are very common in
bivalves and gastropod shells. In a transect study of the Adriatic Sea, drilling
frequencies of bivalve and gastropod shells are very high, with bivalves being
drilled at a higher frequency than gastropods (Sawyer and Zuschin, 2010).
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Epifaunal bivalves are drilled at a higher frequency than infaunal bivalves, and
cemented bivalves are drilled at a very high rate but with much lower success
than non-cemented attached epifauna (Sawyer and Zuschin, 2010). In the
Adriatic, size differences are not correlated with different rates of drilling
predation (Sawyer and Zuschin, 2010). In general, there is a poor relationship
between life-mode and prey resistance (calculated as the number of incomplete
drill holes and observed drill holes), but infaunal bivalves have both the lowest
drilling frequencies and the highest prey effectiveness over epifauna, commensal
bivalves, and nestling (reclining) bivalves (Sawyer and Zuschin, 2010). The
highest prey effectiveness is found in cementing bivalves, possibly due to the
spininess of their shells. Modern brachiopods are often found in deeper, more
cryptic environments (Gould and Calloway, 1980), and have relatively lower rates
of drilling predation than mollusks (Kowalewski, 2005).
4. Drilling Summary
Drilling predation occurs patchily throughout the Phanerozoic (Kowalewski
et al., 1998), although potential gastropod drill holes are not observed until the
Late Triassic. Drilling frequencies remain low until the Cretaceous, with the
radiation of modern drilling gastropod groups. It is possible that modern groups of
drilling gastropods operated at low levels throughout the Mesozoic, but it is clear
that the increase in frequency was not gradual throughout the Mesozoic, and is
better characterized as a pulse in the late Mesozoic. This is not the pattern
observed for durophagous predators and shelly prey with anti-durophagy
adaptations, both of which undergo major changes in the Early Mesozoic.
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E. Summary of MMR Features
Sequential faunal samples from Tethyan and Panthalassa shallow marine
benthic fauna and data from Late Triassic marine predators suggests that Norian
paleocommunities were increasingly influenced by predation throughout the
stage, specifically by demersal and benthic durophages. Prior to this
paleoecological transition, shelly assemblages resembled those of the Paleozoic
– dominated by sessile epifauna. This Late Triassic co-evolutionary transition
was distinct from that which occurred in the Cretaceous period, which was
dominated by the influence of drilling predators. Thus, the MMR appears to have
occurred in two main phases, the first in the Late Triassic with adaptations
related to epibenthic durophagy and the second in the Cretaceous with changes
related to drilling.
The idea of a two-pulse MMR is not an entirely new concept, but here I
have shown that the onset of the early stage occurred in the Norian Stage within
shallow marine benthic communities, and that it developed globally perhaps in
two main phases within the Norian Stage.
Previous work has suggested that predation did not significantly increase
until the Cretaceous or that co-evolution between predators and prey was not a
significant interaction throughout the Mesozoic. These conclusions may be based
on datasets that are not sufficiently resolved to recognize this transition or may
be utilizing a set of proxies that are limited in application through time (e.g.:
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gastropod drill holes). Here I have evaluated several animal clades and
morphological features to identify important paleoecological correlation between
predators and prey.
Differences in Norian paleoecological structure between Tethys and
Panthalassa might highlight different types of predation in these regions (Fig.
5.10). For example, the large proportion of cementing bivalves in Panthalassa
and their relative rarity in comparable depositional environments in Tethys
suggest a greater influence of arthropod durophages in the former. Alternatively
the prevalence of cementing bivalves may also be related to regional
temperature differences or carbonate geochemistry. More data for Triassic
predators is needed to confirm this correlation.
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III. PF–MF Transition
The Paleozoic Fauna–Modern Fauna (PF–MF) transition has undergone
several important changes since it was introduced. Originally presented as a
taxonomic phenomenon, the concept outlined how several related clades of
animals radiated at a similar time in the Paleozoic and became less diverse
through extinction at a similar time, while other clades of animals radiated during
the downturn of the PF. The brachiopods represent a well-known PF group, and
much debate has focused on whether their decline in diversity was related to
ecological replacement by Modern Faunal groups such as the bivalves, or if they
began declining for unrelated reasons simultaneously to the rise of the bivalves
(Gould and Calloway, 1980) .
The concept has also been related to paleoecology – many of the most
common PF groups tend to be stationary epifauna (brachiopods, crinoids,
stenolaemate bryozoans), while many common Modern Fauna are associated
with mobility and infaunal or nektonic lifemodes (bivalves, annelids, vertebrates).
However, the timing of both the taxonomic and paleoecological trends have
become more complicated with continued research. The mass extinction at the
end of the Permian certainly affected the brachiopods severely, and the disaster
taxa of the earliest Triassic were mostly bivalves (Bottjer et al., 2008), but
whether this defined the PF-MF transition is not straight-forward. Brachiopods do
have an ecological resurgence and a moderate taxonomic radiation in the Middle
189
Triassic that continues into the Norian (Vörös, 2010)(Fig. 5.11). By the Early
Norian, brachiopods are almost completely absent from Tethyan shallow marine
successions (Fig. 5.2), but they continue to be dominant in Panthalassan
successions from Nevada. Interestingly, brachiopods experience continued
diversifications in the Early Jurassic (Clapham and Bottjer, 2007; Vörös, 2010),
but this radiation occurs as ornamentation is increasing in the rhynchonellids and
because the brachiopods are increasingly living in offshore environments in the
Jurassic and onward (Vermeij, 1987).
Crinoids have a Middle and Late Triassic taxonomic radiation as well
(Baumiller et al., 2010), and enjoy considerable abundance which also appears
to end before the start of the Jurassic (Greene et al., 2011). Encrinites are rare
after the Triassic and the crinoids do not experience other major taxonomic
radiations after the Early Jurassic (Baumiller et al., 2010).
If the paleoecology of diversifying groups is considered, the PF–MF transition
becomes even more complicated. Most of the bivalve disaster taxa of the early
Triassic are stationary epifauna (Bottjer et al., 2008), a similar paleoecological
niche as that which is utilized by the majority of brachiopods (Vermeij, 1987), and
this paleoecological lifemode persists as the most common niche utilized by
bivalves in the Middle Triassic and into the Early Norian (Bonuso and Bottjer,
2008).
Therefore, the taxonomic transition appears to have a spatial component –
the transition was complete in Tethys by the Norian Stage, but the ecological
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aspect still favored the methods utilized by the Paleozoic Fauna. This does
suggest some non-paleoecological explanation for the bivalve-brachiopod
transition in Tethys, possibly metabolism. However, the Early Norian appears to
represent one of the last times when brachiopod-dominated assemblages were
common in shallow marine level-bottom communities, before they began to
invade other depositional environments such as offshore systems (Vermeij,
1987) or reefs (Clapham and Bottjer, 2007), and it is not clear if this transition
was due to the increasing pressure of benthic durophages, a change in the
sedimentary environment (increased soupiness of the sediment-water interface
due to increased burrowing activity), or some combination of both. What is clear
is that the non-cemented stationary epifaunal life-mode was not advantageous in
Tethys or Panthalassa as the Norian Stage progressed, and this life-mode was
utilized less in shallow marine level-bottom environments throughout the early
Mesozoic.
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IV. Identifying the biotic effects of the Manicouagan impact
The Manicouagan impact event is often cited as an event with little or no
biotic effects. Some attribute this lack of extinction to the host material (Hodych
and Dunning, 1992), others to the insufficient size of the impactor (Melosh,
2012). However, the assertion that the impact did not induce biotic extinction is
based on outdated timescales and a lack of successional data for the Norian
Stage.
The only impact known to have caused significant extinction is the Chicxulub
impact which caused the End-Cretaceous mass extinction. By sampling the
Norian fauna in sequences that should have contained sedimentary rocks of the
same age as the Manicouagan impact, it is possible to evaluate the potential
biotic effects of Manicouagan and to identify similarities between the two impacts
before and after the actual event.
A. Extinction – diversity
Identifying extinction in the fossil record remains difficult for most marine
fauna due to the lack of successional studies for the Norian Stage. Using the
data presented herein, the successions are only loosely correlated with other
regional sedimentary successions that lack sequential sampling, so it is difficult
to ascribe the disappearance of certain taxa in one locality to total extinction of
the group. Furthermore, the lack of species-level taxonomy for many Late
Triassic groups makes determining the timing of extinction even more uncertain.
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However, I have provided a very rough estimate of generic extinction
based on the appearance of the genera I observed in sequential bulk samples
(Appendix 8). If a genus has not been reported from the Rhaetian Stage, the
extinction horizon was attributed to the interval above the bulk sample where the
genus was last observed. This method is problematic for several reasons,
because it does not account for species extinction, and several genera from the
Late Triassic are thought to represent polyphyletic groups (McRoberts, pers.
comm.). Furthermore, the intervals between bulk samples is often >10m, so
sampling for impact sediments at the resolution required (millimeter-scale) was
not possible for this project, but is underway. Very few genus-level extinctions
appear to have occurred in the Norian Stage based on the collections made
herein. However, major paleoecological changes occurred through the Norian
and the dominant fauna dramatically changed at least twice within the stage. It is
possible that Manicouagan did not affect environments enough to cause generic
extinctions, but dominant taxa were affected enough to be overtaken by more
adapted organisms.
B. Paleoecology
Clearly, major evolutionary changes were underway in the Norian Stage
among shallow marine faunas. Stationary epifauna decline while mobile and
infaunal animals proliferate. This is reminiscent of the paleoecological changes
which apparently took places across the K–Pg boundary in localities such as
Brazos River, TX (Hansen, 1988)(Figs. 5.19 and 5.20). What is unclear in this
analysis is whether the paleoecological changes of the Triassic were caused by
193
or exacerbated by the impact event, or if the changes were underway well before
the impact thereby buffering these ecosystems from the effects of the impact. It is
also possible that Manicouagan had very limited impact on global biotic systems,
although this seems unlikely (see discussion in the Introduction).
C. Impact Ejecta Horizon Correlations
Based on correlation with the radiolarian-correlated impact horizon, an impact
layer lies somewhere between the latest Middle and earliest Late Norian
biozones (Onoue et al., 2012). Onoue et al. (2012) found that this layer was not
associated with any radiolarian turnover, but there is considerable turnover
slightly above this interval. It is possible that this turnover in deep marine fauna is
not associated with the impact, or it is possible that the specimens took a long
time to settle out of the water. Post-impact layer sediments at K–Pg boundary
sections often have high numbers of re-worked Maastrichthian fossils of pelagic
animals (ammonites)(Fig. 5.20), so this would not be unexpected.
D. Bulk subsampling in Nevada
Recent high-resolution subsampling work focused on intervals of significant
faunal and/of paleoecological change (Fig. 5.21) as identified using the
probabilistic models from Handley et al. (2009), and outlined in Ch. 3. Smaller
bulk samples (~7,000cm
3
) were collected from these intervals to confirm if the
relatively rapid faunal/paleoecological changes observed were gradual or rapid,
and if they were the latter, if anomalous sediments were found in relation with the
faunal turnover.
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Results of this study were ambiguous. Both intervals of rapid change in the
Carbonate Member of the Luning Formation showed relatively gradual changes
in the intervals between larger samples (Fig. 5.22). Only the transition in the Late
Norian of the Gabbs Formation contained a rapid faunal turnover event (Fig.
5.23). This interval is also characterized by several shaley units, which may
indicate a cessation of carbonate production, which also is characteristic of the
K–Pg boundary. However, if the Nun Mine Member is latest Norian in age, this is
very late in the stage to observe the effects of Manicouagan, although if the
Rhaetian Stage is longer than most estimates, and begins ~210 Ma, it is possible
that the turnover might occur in the lower Nun Mine Member. The latest impact
ejecta layer attributed to Manicouagan lies in the latest Middle Norian radiolarian
biozone (Onoue et al., 2012), which suggests that this placement may be
parsimonious. This is an ongoing area of research.
V. Conclusions
The data collected for this study provides important context for describing the
reorganization of marine paleoecological communities in the Late Triassic, and
how these changes elucidate unknown aspects of several major evolutionary
events that occurred within this interval.
I found that the faunal and paleoecological succession in the Norian Stage
indicated that the faunal assemblages were not static, and several significant
195
transitional events occurred throughout the stage. Fauna of the Early, Middle,
and Late Norian are distinct.
The paleoecological changes observed throughout the Norian Stage seem to
be consistent with the MMR, if the predators operating within these systems are
benthic or demersal durophages. Using an updated predator database, these
predators appear to have been experiencing taxonomic radiations in this same
interval. There is little evidence for drilling predation via trace fossils, and I
suggest that the MMR was not a gradual event, but rather a two-pulse feature, in
which the earliest stage occurred in the Late Triassic and was related to
durophagy, while the second phase occurred in the Early Cretaceous and related
to drilling and expansion of other durophagous groups, possibly in response to
the new pulse of accessible epifaunal and shallow infaunal gastropod predators.
The Paleozoic-Modern Faunal transition appears to have been underway by
the Norian Stage, but is perhaps only in effect taxonomically in Tethys.
Brachiopods were all but absent in these successions, but they continued to
persist as dominant ecological elements in Early Norian successions in
Panthalassa (Nevada). The ecological characteristics of Early Norian
brachiopods are shared with the “Modern Fauna” of the stationary epifaunal
bivalves in Tethys. I suggest that the PF-MF transition is taxonomically and
ecologically decoupled, and the timing of the ecological event coincides with the
onset of the MMR.
196
The biotic effects of Manicouagan are still unclear based on this analysis, but
at least one interval in the lowest Nun Mine Members of the Gabbs Formation
shows a rapid paleoecological transition and anomalous sedimentary features
that must be examined in further detail (Fig. 5.23). Based on the faunal changes
that occurred within this stage it is clear that previous claims that the
Manicouagan impact is not associated with faunal change because the Norian
fauna is stable are unfounded. The recent timescale changes clearly indicate that
very little is known about how the impact fits into the faunal succession of the
Norian and must be further studied.
197
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& Holkema, Utrecht, p. 83–106.
Mesozoic
Phanerozoic “visible life”
Paleozoic
Triassic Jurassic Cretaceous
Early Middle Late
65
250
545
200
140
245
235
present
Rhaetian
Norian Carnian
228
209*
Cenozoic
Alaunian Lacian Sevatian
substages
1 2
Figure 1.1. The Phanerozoic timescale, showing the relation of the Norian Stage and
substages to other intervals of time. (Walker et al. 2012) *Rhaetian base is uncertain
- see discussion in text.
stages
periods
eras
216
224-210 Ma
14 million
years
220-205 Ma
15 million
years
220-210 Ma
10 million
years
216-204 Ma
12 million
years
228-207 Ma
21 million
years*
Mundil et al 2010
Norian
Rhaetian
Carnian
Ladinian
Anisian
Olenkian
Induan
Changsingian
Figure 1.2. Changing timescale of the Triassic Period. The Norian-Rhaetian boundary is still
undefined and highly uncertain. Dotted line indicates the relative placement of the Manicouagan
impact event to the Late Triassic stages. Modified from Mundil et al (2010). *Duration is based on
estimate of the Norian-Rhaetian boundary at 207 Ma, but this date is uncertain. Black diamonds
represent analytical uncertainty.
Hettangian
Harland
et al. 1990
Odin 1994
Gradstein
et al. 1995
Ogg 2004
in Gradstein
et al. 2004
stages
217
Figure 1.3. The Evolutionary Faunas through the Phanerozoic. Range data from Sep-
koski (1981)(top, modified) and generic occurrences from Alroy et al.(2010)(bottom).
Factors I, II, and III correspond to the Cambrian, Paleozoic, and Modern Faunas,
respectively.
number of genera
Time
218
24
34
31
3.9
7
19.8
Figure. 1.4. Comparison of Carnian sedimentary accumulations from regions around the world.
Modied from Greene et al. (2011).
219
78%
99%
88%
38%
62%
35%
65%
Figure 1.5. Transition from Middle Triassic dominance of epifauna to the Late Triassic
dominance by infauna. Modified from Bonuso and Bottjer (2008).
220
Figure 1.6. Extinction rates for invertebrate marine genera from the Phanerozoic.
The end-Cretaceous extinction is marked by the arrow. (modified from Alroy, 2008)
500 400 300 200 100 0
Cm O S D C P Tr J K Pg Ng
0.0 0.5 1.0 1.5 2.0 2.5
Extinction Rate
Time (Ma)
221
Figure 1.7. Paleogeography and diversity gradients for (a) the Chicxulub impact and (b)
the Manicouagan impact. From Walkden and Parker (2008).
Ocean Shelf Reefs
High Biodiversity
Low Biodiversity
>155 mph Winds
Impact Site
(a) 65 million
years ago
(b) 214 million
years ago
222
Figure 1.8. (left) Gravity anomaly map of the Chicxulub crater (Sharpton et al. 1993) and
(right) an aerial view of the Manicouagan crater (NASA)
223
Figure 1.9. Impact crater cross-sections of Manicouagan and Chicxulub. From Walkden
and Parker (2008).
Manicouagan
Chicxulub
Breccia (allochthon) Melt sheet Uplift (parautochthon) Key:
224
Figure 1.10. Impact signatures at a terrestrial Cretaceous-Paleogene boundary and mass
extinction horizon (modified from Orth et al., 1982).
225
Figure 1.11. Atmospheric blow-out produced by large impact events. From Winslow
(unpublished), modified from Melosh (1996).
226
Old timescale and ranges
MMR
PF/MF
Manicouagan impact
New timescale and ranges
MMR
PF/MF
Manicouagan impact
PF MF
MF
Norian Jurassic Cretaceous
Carnian
Middle
Tri
Norian Jurassic Cretaceous
Ca
Middle
Tri
Figure 1.12. Summary of changes for the timing of evolutionary and geologic events of the
Mesozoic, based on Triassic timescale changes and results from this research. MMR =
Mesozoic Marine Revolution, PF-MF = Paleozoic Fauna-Modern Fauna Transition.
Chicxulub impact
Chicxulub impact
227
Stationary
epifauna
Mobile
epifauna
Stationary
semi-infauna
Mobile
infauna
Mobile
nekton
Figure 1.13. Modes of tiering in marine level-bottom ecosystems.
228
Figure 1.14. Ecological niches based on life mode characteristics of marine animals. From
Bush et al. (2007).
Pelagic
Erect
Surcial
Semi-Infaunal
Shallow Infaunal
Deep Infaunal
Suspension
Surface Deposit
Mining
Grazing
Predatory
Other
Non-mobile, attached
Nonmobile, unattached
Facultatively mobile, attached
Facultatively mobile, unattached
Fully mobile, slow
Fully mobile, fast
Tiering
Feeding
Motility
229
Figure 2.1. (top)
87
Sr/
86
Sr curve for the Phanerozoic from Veizer et al. (1999) with the Late
Permian and the Triassic Period highlighted, (bottom) for the Triassic, modied from Korte et al.
(2003).
Time (millions of years ago)
Triassic
Olen Anis Ladi Carnian Norian
Rh
Permian
Ind
230
Figure 2.2. Fossil shells from the Riva di Solto Formation, with growth bands and
coloration, possibly original.
231
Luning Formation:
Dolomite
Early Jurassic
Rhaetian: Gabbs Fm.
Norian - Rhaetian:
Gabbs Fm.
Norian: Luning Fm.
Time:
#
California
Nevada
Oregon Idaho
Utah
Arizona
20 km
CA
NV
50
Hawthorne
Luning
95
Walker
Lake
Gabbs
Valley
Range
23
Nun Mine: Shaly
Limestone
Nun Mine: Limestone
and Shale
Mount Hyatt:
Limestone and Shale
Fan- or conglomerate
Sunrise: Limestone
and Shale
Sunrise: Shale
Intrusive
Igenous/Applite
Strontium Isotope
Samples
1
2
3
4
5
6
9
10 7
8
11
A
12
500 m
5000
5200
5000
13
14
15
C
Shoshone
Range
B
5400
5600
6400
6200
6000
5800
5600
5400
5200
4800
4700
New York Canyon
Muller Canyon
Figure 2.3. Field locality maps. (top left) Nevada, grey box shown below. (bottom left) Landmarks and the
area of the Gabbs Valley Range (white star indicates the location of New York Canyon) and the Shoshone
Mountains (black star indicates the location of the Berlin-Ichthyosaur State Park). (center) New York
Canyon and Muller Canyon, with locations of samples and important sequences discussed in the text.
(right) New York Canyon samples. Geologic map modified from Hallam and Wignall (2000). Referenced
sections: A-Muller Canyon. B-Reno Draw. C-Luning Draw.
232
Luning
Gabbs
Clastic
Shaly LS
Calc. Shale
Carbonate
Dolomite
Nun Mine
Mount Hyatt
Muller Canyon
Carnian Norian
Rhaetian
Berlin-Ichthyosaur State Park
New York Canyon
Fm. Member
Figure 2.4. Generalized stratigraphic column for Late Triassic formations and
members sampled in this analysis.
233
Tertiary volcanics
Early
Norian
range
Late
Norian
range
P W M S C
Norian (early)
Strontium
(ppm)
Mn/Sr
Mn (ppm)
0.7078
0.7080
0.7076
0.00
0.08
0.16
1000
1250
1500
1750
125
150
175
200
⁸⁷Sr/⁸⁶Sr
5m
Triassic
Luning Formation (Carbonate Member)
Figure 2.5. Stratigraphy, sampling horizons,
87
Sr/
86
Sr, and strontium/manganese
concentrations from the carbonate member of the Luning Formation in the Shoshone
Mountains at Berlin-Ichthyosaur State Park. Strontium values indicated by an open circle
come from brachiopod shell material, black circles represent bivalve shell material.
Published ranges of
87
Sr/
86
Sr from Korte et al. (2003). C=Covered, S=Shale, M=Mudstone,
W=Wackestone, P=Packstone.
234
E. mosheri B
E. mosheri A
E. mosheri C
M. posthernsteini
M. hernsteini
E. bidentata
E. mosheri A
E. mosheri B
E. bidentata
M. hernsteini
M. posthernsteini
Upper Triassic
Upper Norian Rhaetian
Sagenites
quinquepunctatus
Paracochloceras
suessi
Vandaites
stuerzenbaumi
Choristoceras
marshi
E. bidentata
E.bid.-
M.hern.
E. bidentata-
M. posthernsteini
M. posthern-
steini
M.
rhaetica
M.
ultima
Austria
deweveri monoliformis tozeri
Gnomohalorites
cordilleranus
Paracochloceras
amoenum
Choristoceras
crickmayi
Amm Rad North America
E. bidentata E. mosheri
Cono
(M. posterhernsteini)
Cono Amm
Tethys Panthalassa
Figure 2.6. Approximate ranges of biostratigraphically significant conodont species
discussed in the text, and correlation with other biostratigraphic zonation schemes.
Modified from Orchard (2010), including all conodont ranges and biozone divisions,
except North American conodont biozones, which are from Orchard and Tozer
(1997) and McRoberts et al. (2008). The division between E. mosheri and M.
posthernsteini in the North American division is approximate.
235
1m
1
3
5
7
9
10
11
4
6
8
P W M
Limestone
Shale
Late Norian Range Rhaetian Range Assigned Age
Triassic
Norian (mid- to Late) ? Rhaetian
δ¹³Ccarb (‰) δ¹ O
Strontium
Manganese
(ppm)
2
Mn/Sr
-4.0
-2.0
0.0
0.70765
0.70775
0.70785
0.70795
0.70805
-12.0
-10.0
-8.0
-6.0
0.4
0.8
1.2
1.6
2.0
400
600
800
1000
S
Gabbs Formation (Nun Mine Member)
Figure 2.7. Stratigraphic columns and
87
Sr/
86
Sr values from the Nun Mine Member of the
Gabbs Formation in New York Canyon, NV. Published strontium isotope values from Tethyan
succession in Korte et al. (2003). All measurements are derived from bivalve shell material.
previous
new
236
NYC 8 NYC 9
NYC 4
3 sec exposure
8 sec exposure
A B C
D E F
NYC 1 NYC 3 NYC 1
5 sec exposure
Figure 2.7. Different luminescence (Lm) in carbonates from the Nun Mine Member. (a)
Lowest observed Lm in sample 6, with non-luminescent matrix and shells; (b,c) slightly
luminescent matrix with non-luminescent shells; (d) dull luminescence in matrix and slightly
more in bivalve shell; (e) moderately luminescent calcite vein; (f ) brightly luminescent
void-fill. Exposure time is 4s unless otherwise indicated. Scale bar = 0.2mm.
237
Ep. mosheri B
Ep. mosheri A
Ep. mosheri C
Mis. posthernsteini
Ep. bidentata
Paracochloceras amoenum rhaeticum or
Ch. crickmayi
NA amm
zones
New York Canyon
Conodont Ranges
E. mosheri NA cono zones (Mis. posterhernsteini)
Dolomite Mbr. Nun Mine Member Mt. Hyatt Mbr.
Muller
Canyon Mbr.
striata minaensis
newyor-
kensis
Ch.
crickmayi
spelae
minutum
E. bidentata M. hernsteini M. posterhernseini M. ultima
Upper Triassic
Upper Norian Rhaetian This Paper
conodonts
Z. rhaeticum
Jurassic
Sagenites quinquepunctatus
Paracochloceras
suessi
Vandaites stuerzenbaumi Choristoceras marshi
E. bidentata E. bid.- M.hern.
E. bid.-
M. posthern.
M. posthernsteini Mis. rhaetica Mis. ultima
Approx. Tethyan
biozone
(A)
(B)
Upper Norian Rhaetian Previous
Luning Fm.
Gabbs Formation
(C)
0.70805
0.70795
0.70785
0.70775
0.70765
Figure 2.9. Stratigraphic correlation and age determinations of the Gabbs Formation. (A)
Previous ages attributed to the upper Luning Formation and Gabbs Formation, and updated
ages based on chemostratigraphy in (B). (B)
87
Sr/
86
Sr from Tethyan conodonts (colored circles)
from Korte et al. (2003), and
87
Sr/
86
Sr from the Nun Mine Member (NMM) of the Gabbs Forma-
tion (black closed circles), correlated to the conodont ranges in (C), and an upper Muller
Canyon Member sample (open black circle). Tethyan measurements correlated to New York
Canyon values based on range similarity. (C) Approximate conodont ranges from the Gabbs
Formation of New York Canyon and North American biozones from Orchard et al. (2007).
Luning Formation ranges were not reported. NA = North America.
238
Late Triassic
Panthalassa
Rhaetian
Carnian
Luning Formation BISP
Carbonate Member
Gabbs Formation NYC
Nun Mine Member
Hurwal Formation (OR)
Martin Bridge Formation
Black Marble Quarry
Dolomia Principale Riva di Solto
Zu Tethys
Figure 2.10. Approximate correlation of sedimentary sequences dated and analyzed herein. Not drawn to
scale. MCM = Muller Canyon Member.
Early Norian Middle Norian
Late Norian
Mt. Hyatt Mbr. MCM Clastic Shaly LS Calc. Sh.
Lower Middle Upper
(NV) (OR)
239
Via Bergamo
Brembilla
3km
Berbenno
Zogno
Via Nazionale
L. Endine
Zorzino
Riva di
Solto
Zu
Via Vittorio Veneto
Lovere
Bergamo
Lake
Iseo
Corna
Trentapassi
Middle DP
Upper DP
Marone
Lower DP
500m
1
2
3
4
5
6
Dolomia Principale
7
8
9
Via Pagliaro
Via Damiano
Chiesa
Via Antonio
Stoppani
Riva di Solto Fm.
500m
Figure 3.1. (a) (left) Map of northern Italy, and (right) the Southern Alps (dashed line), and
the Bergamasc Alps (black box) which are shown below; (b) map of sampling localities in
the Imagna Valley (left) and Lake Iseo (right), with detailed insets (c, d). DP refers to the
Dolomia Principale Formation.
N. Italy
Switz.
Aus.
Rome
N
a
b
c
d
240
Figure 3.2. Generalized cross-section of the Lombardian Basin. Circles represent
approximate level of bulk samples. Modified from Jadoul et al. (2004, 1994).
1
2
3
4
5
6
7
8
9
241
Formation Lithology Sample Age
Rhaetian
Late Middle Early
Carnian
Norian
Shale
Dolomite
Limestone
Bulk
Sample
Zu
Riva di
Solto
Zorzino
Dolomia Principale
Upper Middle Lower
1
2
3
4
5
6
7
8
9
Figure 3.3. Idealized stratigraphic column of the Lombardian basin, with sampling
horizons. For relative thickness of formations, see Fig. 3.2.
242
Field picture Schematic
Fossil Picture
LOWER RSS
MIDDLE RSS UPPER RSS
shale
Figure 3.4. Field, stratigraphic, and hand sample examples of facies from the Riva di Solto
Formation.
MS WS PS
243
Type 1 Type 2
A
2cm
B
C
Figure. 3.5. Different types of carbonate beds associated with the Riva di Solto
Formation. (A) Field view of carbonate bed types. (B) Type 2 carbonate bed with
Pinna in life position. (C) Type 1 carbonate bed with winnowed, concentrated bivalve
deposits.
244
Paleoecologic Data
Taxonomic Data
BIC
AIC
BIC & AIC
Paleoecologic Change-points
Figure 3.6 — Paleoecological niche data in Norian bulk samples from the Dolomia Principale and Riva di
Solto formations (top) and evolutionary change-points (bottom) suggested by probability analysis.
AIC=Akaike information criterion; BIC=Bayesian information criterion.
Stationary Suspension-feeding Epifauna
Stationary
Suspension-feeding
Semi-infauna
Mobile
Suspension-
feeding Infauna
Mobile
Deposit/Suspension-
feeding Infauna
Mobile Deposit-
Feeding Epifauna
Relative abundances of ecological guilds
Mobile Chemosymbiotic
Infauna
Mobile Deposit-feeding
Infauna
Mobile
Suspension/Deposit-
feeding Infauna
Mobile Suspension-feeding
Infauna
Mobile Suspension-feeding
Epifauna
Mobile Deposit-feeding
Epifauna
Stationary Suspension-
feeding Semi-infauna
Stationary Suspension-
Feeding Epifauna
Dolomia Principale Riva di Solto Formations
1 2 3 4 5 6 7 8 9 Bulk Samples
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
245
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
R = 0.77218
2
1 2 3 4 5 6 7 8 9
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
1 2 3 4 5 6 7 8 9
R = 0.75958
2
Stationary Epifauna Mobile Infauna
Bulk Samples Bulk Samples
Figure 3.7. Relative abundance of stationary epifauna and mobile infauna from the Tethyan
bulk samples.
246
100%
80%
60%
40%
20%
100%
80%
60%
40%
20%
Figure 3.8. Paleoecological succession within Norian bulk samples. (top) Relative
abundances of categories relating to an organism’s life position relative to the
sediment-water interface. (center) Relative abundances of niche categories relating to
mobility and life position. (bottom) Plotted relative abundances of major ecological guilds.
Mobile Infauna
Mobile Epifauna
Stationary Semi-
Infauna
Stationary Epifauna
Infauna
Semi-Infauna
Epifauna
1 2 3 4 5 6 7 8 9
Bulk Samples
Stationary Epifauna Mobile Infauna
R = 0.72551
2
R = 0.82283
2
100
80
60
40
20
0
247
1. Avicula
2. Bakevellia
3. Isognomon
4. Aguilerella
5. Palaeoneilo
6. Costatoria
7. Nucula
8. Gastropod
9. Hoferia
10. Modiolus
11. Unionites
12. Myophoricardium
13. Myophoriopis
14. Pinna
15. Nuculana
16. Schafhauetlia
Figure 3.9. Schematic depiction of the faunal assemblages grouped by evolutionary
change-points identified with AIC/BIC rankings of the paleoecological data.
Early Norian
(Middle DP)
1
2
3
4
Middle Norian
(Upper DP)
7 8
6
9
5
13
12
11
late-Middle
Norian
(Lower RSS)
10
14
Latest Norian
(Upper RSS)
16
Late Norian
(Middle RSS)
14
15
248
Figure 4.1. Common facies and fossils from the Carbonate Member of the Luning Formation in
Berlin-Ichthyosaur State Park. (a) brachiopod wackestone, (b) large gastropods, (c) shell hash
wackestone, (d) medium-bedded limestone.
a b
c
d
249
Gabbs
Luning
Early Jurassic
Rhaetian
Norian
Not Discussed
* Pre-Rhaetian,
reconstructed
Sunrise
Based on:
Nun Mine
Muller Canyon
Mount Hyatt
Ferguson Hill
Carbonate
This Data
(Fig. 7)
isotope
Ward et al.
(2007)
isotope
Orchard
et al.
(2007)
conodonts,
radiolaria
Formation Member
Hallam and
Wignall
(2000)
ammonoids,
isotopes (T-J)
Ferguson
and Muller
(1949)
?
sedimentol-
ogy
Dagys and
Dagys
(1994)
ammonoids,
paper clams
Taylor et al.
(1983)*
ammonoids
Figure 4.2. Previously published ages for the members of the Gabbs and Sunrise
formations. *Pre-Rhaetian ages are based on biostratigraphic ranges reported.
250
Luning
Gabbs
Clastic
Shaly Limestone
Calcareous Shale
Carbonate
Dolomite
Nun Mine
Mount Hyatt
Muller Canyon
Carnian Norian Rhaetian
Berlin Ichthyosaur State Park New York Canyon
Fm. Member
P W M S C
5m
6
8
10
12
9
11
P W M
Limestone
Shale
7
S
California
Nevada
Oregon Idaho
Utah
Arizona
20 km
CA
NV
50
Hawthorne
Luning
95
Walker
Lake
Gabbs
Valley
Range
23
Shoshone
Range
Early Middle Late
A
A
B
B
1
3
5
4
2
Figure 4.3. Late Triassic field localities and stratigraphy. (left) Nevada, with the field area denoted the by grey box, inset
below. Stars mark the field localities sampled in this study, black is the Berlin-Ichthyosaur State Park and white is New York
Canyon. (center) Generalized stratigraphic column of the Late Triassic formations, with black bars indicating the sampled
successions. Formational thicknesses are approximate and not drawn to scale. (right) Stratigraphic columns of the
sampled successions in this study, with sample numbers to the right. A is the carbonate member of the Luning Formation in
the Berlin-Ichthyosaur State Park and B is the lower Nun Mine Member of the Gabbs Formation in New York Canyon.
Covered sections may represent more height than what is represented in stratigraphic column.
251
Figure 4.4. Field photos from the Carbonate Member of the Luning Formation in West Union
Canyon near the Berlin-Ichthyosaur State Park (left) and the lower Nun Mine Member of the
Gabbs Formation in New York Canyon, Nevada (right).
252
Figure 4.5. Relation of number of taxa to number of specimens. Number of specimens does
not include specimens which were not identified. (top) all bulk samples from Nevada,
(bottom) samples 3-12.
10
20
30
40
50
60
0 50 100 150 200 250
0 50 100 150 200 250
10
20
30
40
50
60
Number of taxa
Number of Specimens
All bulk samples (Nevada)
Bulk samples 3-12 (Nevada)
R
2
= 0.30812
R
2
= 0.75744
Number of taxa
253
Stationary epifauna
Cementing stationary epifauna
Stationary semi-infauna
Mobile epifauna
Mobile infauna
Early Norian Late Norian
Berlin Ichthyosaur State Park New York Canyon
1 2 3 9 8 7 6 5 4 10 11 12
Nektonic carnivore
90%
70%
50%
30%
10%
Figure 4.6. Relative abundances of paleoecological niche categories in bulk samples from Berlin-Ichthyosaur State Park
(the Carbonate Member of the Luning Formation) and New York Canyon, Nevada (the Nun Mine Member of the Gabbs
Formation).
bulk samples
254
Mobile Infauna
Stationary semi-infauna
Mobile Epifauna
Cementing stationary epifauna
Stationary epifauna
Nektonic carnivores
Figure 4.7 Abundance of taxa observed in bulk samples from the Luning Formation and the Gabbs
Formation. Singletons can be found in Appendix 5. (Each dash on the axis is 10 specimens, unless
otherwise indicated)
5
Ammonoid
Aulacoceras
NEC Singles
0
SE Singles
Harpax
Meleagrinella
Avicula
Pteria
cf. Halobia
Antiquillima
Hoernesia
Rhaetavicula
Pseudolimea
Arca
Gryphaea
Arcavicula
Zeilleria
Gervillaria
Cassianella
Mytilus
Crinoid
Isognomon
Mysidioptera
Chlamys
Plectoconcha
Brachiopod
cf. Atreta
Gonodon
Liostrea
Oyster indet.
Lopha
Plicatula
Gervillia
Bakevellia
Modiolus
Pinna
cf. Megalodon
MI Singles
Anisocardia
cf. Isopristes
Cardinia
Protocardia
Cucullaea
Cardium
Cardita
Septocardia
Paleocardita
Gresslya
Cardinoides
Astarte
Myophorium
Gruenewaldia
Myophoria
Unionites
Frenguelliella
Tutcheria
Palaeonucula
Nuculana
Nucula
Paleoneilo
Scaphopod
Lucina
Schafhaeutlia
Limopsis
Pichleria
Catella
Limatula
Cingentolium
Hoferia
Parallelodon
Pecten
Camptonectes
Eolima
Lima
Entolium
Echinoid spine
Gastropod
1 2 3 9 8 7 6 5 4 10 11 12
bulk samples
255
Lombardian Alps
(Tethys)
Nevada
(Panthalassa)
Figure 4.8. (A) Correlation of percentages of total specimens for stationary epifauna (x-axis)
and mobile infauna (y-axis). (B) Relative abundances of major ecological groups. (C) Stacked
percentages of the total fauna for the “intermediate” ecological niches: mobile epifauna,
stationary semi-infauna, cementing stationary epifauna.
A.
C.
0
20%
40%
60%
80%
10% 30% 50% 70%
0
20%
40%
60%
80%
10% 30% 50%
B.
100%
80%
60%
40%
20%
1 2 3 4 5 6 7 8 9
100%
80%
60%
40%
20%
1 2 3 4 5 6 7 8 9 10 11 12
bulk samples
10%
20%
30%
40%
50%
60%
70%
1 2 3 4 5 6 7 8 9
bulk samples
10%
20%
30%
40%
50%
60%
70%
80%
90%
1 2 3 4 5 6 7 8 9 10 11 12
stationary epifauna stationary epifauna
mobile infauna
mobile infauna
R
2
=0.66346
R
2
=0.41477
mobile
infauna
intermediates
stationary
epifauna
cementing
stationary epifauna
mobile epifauna
deposit-feeders
stationary
semi-infauna
mobile epifauna
suspension-feeders
256
Early Norian
upper Luning Fm.
1 2
3
early Middle Norian
(upper Luning Fm.)
8
6
9
5
13
12
11
14
Late Norian
(Middle Nun Mine
Mbr.)
16
late Middle Norian
(Lower Nun Mine
Mbr.)
15
1. Plectoconcha
2. Zeilleria
3. Nucula
4. Gastropod
5. Lopha
6. Crinoid fragments
7. Plicatula
8. Unionites
9. Tutcheria
10. Mysidioptera
11. Chlamys
12. Entolium
13. Mytilus
14. Schafhaeutlia
15. Modiolus
16. Eolimea
17. Frenguelliella
18. Pinna
19. Lima
20. Isognomon
21. Myophoria
4
17
18
19
20
21
Figure 4.9. Schematic depiction of the Panthalassan faunal assemblages grouped by
evolutionary change-points identified with AIC/BIC rankings of the paleoecological data.
257
Figure 4.10. Oregon field locality (modified from Yancey [1999]). (A) Wallowa terrane in
reference to the Luning and Gabbs Formations and the North American craton, (B)
terranes in Oregon, (C) Black Marble Quarry in relation to geographic landmarks and the
main succession of the Martin Bridge and Hurwal Fms. U and D refer to hanging and
footwalls of fault lines, respectively.
Luning
Allochthon
A
B
C
258
a
b
c
d
Figure 4.11. Fauna and facies from the Black Marble Quarry, Oregon. (a)
Wallowaconchidae, (b) ammonoid, (c) coral-dominated wackestone, (d) bioclastic
packstone. Scale bar in each image = 4cm.
259
1
2
3
4
Figure 4.12. Bulk sample horizons from Black Marble Quarry.
260
100%
80%
60%
40%
20%
100%
80%
60%
40%
20%
Stationary Epifauna
Stationary
Semi-Infauna
Mobile Epifauna
Mobile Infauna
Bulk Samples
1 2 3
Figure 4.13. Relative abundance of taxa (top) aand paleoecological niches (bottom) from
Black Marble Quarry bulk samples.
cf. bone
cf. Botulopis
cf. Tutcheria
cf. Modiolus
Mytilus
Gresslya
cf. Atreta
cf. Pachycardia
Crinoid
Brachiopod indet.
Myophoricardium
Paralellodon
Costatoria
Septocardia
cf. Pteria
Schafhaeutlia
cf. Lima
cf. Scaphopod
Echinoid fragment
Nucula
Nuculana
Unionites
Gastropod
261
Figure 4.14. Plotted relative abundance of particular ecological niches utilized in bulk
samples from Black Marble Quarry. SE = stationary epifauna, MI = Mobile Infauna, ME =
Mobile epifauna.
16
12
8
4
0 10 20 30 40 50 60 70
Percent of total fauna: Mobile Infauna
Percent of total fauna:
Stationary Epifauna
60
50
40
30
20
10
0 10 20 30 40 50 60 70
Percent of total fauna:
Mobile Epifauna
r
2
=0.98772
Percent of total fauna: Mobile Infauna
262
Figure 4.15. Correlation between mobile infauna (MI) and mobile epifauna (ME)
from Nevada (top), all samples except sample 5, and Italy (bottom), Middle and
Late Norian samples.
r
2
=0.92214
30
25
20
15
10
5
0
0 20 40 60 80 100
Mobile Infauna
Nevada
r
2
=0.73172
10
8
6
4
2
0
0 20 40 60 80 100 120 140 160
Italy
Mobile Epifauna Mobile Epifauna
263
Italy
(Tethys)
100%
80%
60%
40%
20%
Nevada
(Panthalassa)
Stationary Epifauna
Stationary Cementing
Epifauna
Stationary Semi-
Infauna
Mobile Epifauna
Mobile Infauna
100%
80%
60%
40%
20%
Black Marble
Quarry
(Panthalassa)
Early Norian Late Norian Middle Norian
Figure 4.16. Correlation of Black Marble Quarry (Oregon) paleoecological structure
with the assemblages from Nevada and Italy.
100%
80%
60%
40%
20%
1 2 3 4 5 6 7 8 9 10 11
1 2 3 4 5 6 7 8 9
1 2 3
264
Figure 5.1. Relative abundances of feeding modes among shelly benthic fauna from
Italy and Nevada.
100%
80%
60%
40%
20%
0%
100%
80%
60%
40%
20%
0%
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10 11 12
Suspension
Deposit
Deposit-Suspension
Chemosymbiotic
Carnivore
Nevada
Italy
bulk samples
265
Figure 5.2.. Relative abundances of different animal clades from Nevada (a,b) and
Italy (c,d); (left) total specimens by clade, (right) relative abundance in time-series.
a
b
c
d
Bivalve
Ammonoid
Aulacocerid
Brachiopod
Echinoderm
Gastropod
Scaphopod
100%
80%
60%
40%
20%
0%
100%
80%
60%
40%
20%
0%
Nevada Italy
bulk samples
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10 11 12
266
Italy
1 2 3 4 5 6 7 8 9 10 11 12
bulk samples
bulk samples
Nevada
1 2 3 4 5 6 7 8 9
Figure 5.3. Relative abundances of taxa in Norian bulk samples from Panthalassa (Nevada) and
Tethys (Italy). Each color represents a taxon, data in Appendices 4 and 5.
267
Early Norian Late Norian
1 2 3 9 8 7 6 5 4 10 11 12
90%
70%
50%
30%
10%
Figure 5.4. Relative abundances of paleoecological niche categories in bulk samples from
Berlin-Ichthyosaur State Park and New York Canyon, Nevada (top), and the Dolomia Principale
and Riva Di Solto formations in Italy (bottom).
bulk samples
Italy
Nevada
90%
70%
50%
30%
10%
1 2 3 9 8 7 6 5 4
Early Norian Late Norian
bulk samples
Stationary epifauna
Cementing stationary
epifauna
Stationary Semi-infauna
Mobile Epifauna
Mobile infauna
Nektonic carnivore
268
Figure 5.5. Relative abundances of mobility styles in Nevada and Tethys.
100%
80%
60%
40%
20%
0%
100%
80%
60%
40%
20%
0%
Stationary
Mobile
Nevada
Italy
bulk samples
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9
269
Figure 5.6. Relative abundances of tiering animals from Nevada and Tethys.
90%
70%
50%
30%
10%
90%
70%
50%
30%
10%
Infauna
Semi-infauna
Epifauna
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9
Nevada
Italy
bulk samples
270
Figure 5.7. Stacked abundances of ecological “intermediates” from Nevada (top) and Italy
(bottom). (A) relative abundances of ecological niches of interest and (B) specific relative
abundances of ecological “intermediates”.
B. A.
100%
80%
60%
40%
20%
1 2 3 4 5 6 7 8 9
100%
80%
60%
40%
20%
1 2 3 4 5 6 7 8 9 10 11 12
bulk samples
10%
20%
30%
40%
50%
60%
70%
1 2 3 4 5 6 7 8 9
bulk samples
10%
20%
30%
40%
50%
60%
70%
80%
90%
1 2 3 4 5 6 7 8 9 10 11 12
mobile
infauna
intermediates
stationary
epifauna
cementing
stationary
epifauna
mobile
epifauna
deposit-fdr.s
Stationary
semi-
infauna
mobile
epifauna
suspension-fdr.s
Nevada Italy
271
Carnian
Norian
early late
Rhaetian Early Jurassic
TRIASSIC
LATE
Ladinian
Continued presence of
sharks, placodonts, and sh.
Appearance of specialized
arthropod predators.
Occurances of
durophagous predators
expands to eastern Tethys.
Durophagous sharks
and marine reptiles
Diverse occurances
of sh, placodonts,
and sharks. Some
potentially
durophagous
arthropods
Fish
Sharks Placodonts
Specialized Functional
Marine
Reptiles
Arthropods:
No durophagous
predators
reported
Earliest occurance of
specialized
durophagous crabs
Single
durophagous
shark
occurance
No
durophagous
predators
reported
Specialized
arthropods
occur in
greater
numbers
Fish are the dominant
durophagous
predators.
Fish and placodonts
continue to be
dominant predators.
Fish, placodonts, and
sharks continue to
diversify..
Following the
Triassic-Jurassic mass
extinction, specialized
arthropods reach
larger numbers in
addition to sh and
sharks, while
placodonts disappear.
middle
Figure 5.8. Taxonomic occurrences of major durophagous predators from the Ladinian to the
Sinemurian.
272
Carnian
Norian
Rhaetian
Italy (Infauna)
NV (Infauna)
Italy (Mobile)
Nevada (Mobile)
8
0
New appearances
of cementing taxa
0
100
Lacian Alaunian Sevatian
Figure 5.9. (top) Occurrences of predators specizalized for durophagy; Groups are
listed in supplemental material. (top-middle) Occurrences of crinoid clades, * =
non-stationary epifauna. (bottom-middle) Originations of cementing bivalve clades.
(bottom) Paleoecological changes in this study for prey adapted against durophagy.
Crinoids
Tuvalian
Roveacrinida
Millericrinida
Paracomitulida
Isocrinidae
Pentacrinidae
Holocrinidae
Arthropods
Reptiles
Placodonts
Sharks
Fish
Durophagous Predators
Prey
Data from this study
0
100
0
100
0
100
Percentage of total ecological niches
5
0
10
140
120
100
80
60
40
20
273
repaired crushes
Ammonoids
placodonts
muricid gastropods
octopods
palinuran lobsters
spiny brachiopods
spiny bivalves
spiny gastropods
spiny echinoids
spiny crinoids
cementing brachiopods
Teleosts Fish
Cymatiidae gastropods
Drilling
Predators Anti-predator Prey
Late Triassic
Gryphaeidae
Ostreidae
Plicatulidae
Terquemiidae
Dimyidae
Atreta
New appearances
of cementing
bivalve clades
Pseudomonotidae
Lithiotidae
Spondylidae Eopecten
‘Rudists’
Prohinnites
Chondrodontidae
Chamidae
12
10
8
6
4
2
cementing annelids
boring annelids
burrowing bivalves
burrowing spatangoids
boring clionids
cementing barnacles
Demersal and epifaunal shell-crushing/breaking
Predators Anti-predator Prey
drilling naticid gastropods
Stomatopoda
Neoselachian sharks
Hybodontid sharks
homaridian lobsters
Semionotiform Fish
Brachyuran crabs
obliquely-ribbed bivalves
Belemnites
Pycnodontiform Fish
Macrosemiid Fish
Holostean Fish
Macrura
nautiloids
250
200
Triassic Jurassic Cretaceous
Norian Rh Carn
110
Lower Upper Lower Middle Upper Upper Middle Low
Het Sinemur Pliens Toarc Aal Bajo Bat Call Oxfo Kimm Tith Be Val H Ba Aptian Albian Cenoman Turonian Con San Campanian Maastrich
Ladi Anisi Ol In
150
Permian
65
drillholes
Figure 5.10. Occurrences of durophagous-specialized or drilling-specialized predators, and prey with anti-predators strategies.
Thick lines represent common occurences and diverse fauna, thin thinks represent present but not common, dotted lines indicate
inferred presence. Data in Appendix 1.
274
Figure 5.11. Brachiopod dynamics through the Mesozoic. (top) brachiopod genera and
(bottom) ornamentation index. Rh = Rhynchonellid, Te = terebratulid. Data from Voros
(2010). *Mean Ornamentation Index is determined by taking the average of the ornamenta-
tion index for the standing genera per stage; ornamentation index is a qualitative descriptor
to characterize the height of the ribs of the shell surface; larger numbers indication greater
spinosity.
E Triassic
Anisian
Ladinian
Carnian
Norian
Rhaetian
Hettanian
Sinemurian
Pliensbachian
Toarcian
Aalenian
Bajocian
Bathonian
Callovian
Oxfordian
Kimmeridgian
Tithonian
Berriasian
Valangian
Hauterverian
Barremian
Aptian
Albian
Cenomanian
Turonian
Coaniacian
Santonian
Campanian
Maastrichthian
3
2.5
2
1.5
1
0.5
0
70
60
50
40
30
20
10
0
Number of Genera Ornamentation Index*
Rhynchonellid
Terebratulid
Triassic Jurassic Cretaceous
275
0
200
400
600
800
1000
1200
1400
1600
1800
0 2 4 6 8 10 12 14
Bivalves
Brachiopods
Area of Shells: Nevada
Sample Number
Time
Height x Width
Outliers Outliers
Area of Shells: Italy
-During the early Norian, brachiopods
were the dominant stationary epifaunal
animals.
size distribution but decrease in size in a
short amount of time.
-Bivalves become dominant in the middle
Norian with a big size distribution.
-The bivalves have a pattern that shows
the decrease in size if the outliers are
taken out of consideration.
N= 153
Height x Width
0
500
1000
1500
2000
2500
2
4
-The stationary epifaunal bivalves in
size. There are also fewer outliers
that disrupt the pace of the
decrease in size.
-In this bulk sample bivalves are the
dominant animals.
N= 89
6 8 9
Early Norian Middle Norian Late Norian
Early Norian Middle Norian Late Norian
Change for all stationary epifaunal fossil specimens through the Norian stage
Key
Figure 5.12. Size changes for non-cementing stationary epifauna from Nevada (top) and
Italy (bottom).
276
Figure 5.13. For the measured stationary epifauna per bulk sample, the average size of
those stationary epifauna plotted against the proportion of stationary epifaunal
specimens out of all specimens (Italy).
200
400
600
10% 30% 50% 70%
R
2
= 0.70419
Proportion of the total fauna
Average SE size within a sample
277
~2x
Figure 5.14. Comparison of drill hole morphologies. (top) Gastropod drill holes (from
Chojnacki 2012 [left] and Sohl 1969 [right]); (bottom) octopod drill holes - note small size and
x-shape (Bromley 1993).
Octopod
gastropod octopod
278
Figure 5.15. Area of stationary epifaunal (non-cementing) fossil specimens from the Lom-
bardian Basin (Italy, Tethyan Sea) through the Norian Stage, by genus.
Area (height x width)
Avicula
Cassianella
Dreissena
Edentula
Hoernesia
Isognomon
Liostrea
cf. Mytilus
Mysidiella
Mysidioptera
Mytilus
Pteria
Septifer
Tirolidia
bulk samples
Early Norian Late Norian
279
1
2
4 6 8
9
7
Avicula : A Common Stationary Bivalve
Avicula is the most common genus in the early Norian Italian samples and one of the only stationary epifaunal
genera that appears in the later Norian samples. They illustrate the distinct decrease in average size. Scale bar =
1cm.
Early Norian Middle Norian Late Norian
Change within a genus through the Norian stage
Figure 5.16. Size changes which occur within a genus, Avicula, during the Norian Stage, based on Tethyan specimens.
Images are representative specimens close to the average area for the genus in the bulk sample indicated by the number
by the image. Scale bar = 1cm.
280
Figure 5.17. Size characteristics of Tethyan stationary epifauna during the Norian Stage.
(a) Relative proportion of size categories for measured stationary epifaunal specimens, (b)
overlapping size distributions, and (c) stacked size categories for measured stationary
epifauna from Italian specimens.
a.
b.
c.
mm
3
size range
number of specimens
per size category
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9
bulk samples
Early Norian Late Norian
901-1000
801-900
701-800
601-700
501-600
401-500
301-400
201-300
101-200
0-100
1
2
3
4
5
6
7
8
9
0-
100
101-
200
201-
300
301-
400
401-
500
501-
600
601-
700
701-
800
801-
900
901-
1000
16
12
8
4
0
number of specimens
per size category
bulk samples
1 2 3 4 5 6 7 8 9
bulk samples
mm
3
size range
901-1000
801-900
701-800
601-700
501-600
401-500
301-400
201-300
101-200
0-100
relative abundance of size
category per bulk sample
90%
80%
70%
60%
50%
40%
30%
20%
10%
Early Norian Late Norian
281
Figure 5.18. Chlamys (top) and Plicatula (bottom) measured specimens from
Nevada, height vs. width.
height
height
r
2
= 0.86252
18
16
14
12
10
8
6
4
2
0
0 5 10 15 20 25
30
25
20
15
10
5
0
0 5 10 15 20 25 30 35 40
r
2
= 0.73223
width
282
Figure 5.19. Locality information for the K-Pg Boundary section at Brazos River, TX.
Data from Hansen (1993).
283
Figure 5.20.. Paleoecological succession accross the K-Pg boundary section in Brazos River, TX (right),
Norian successions in Panthalassa (left, top) and Tethys (left, bottom). K-Pg data from Hansen (1993).
100%
80%
60%
40%
20%
100%
80%
60%
40%
20%
100%
80%
60%
40%
20%
1 2 3 4 5 6 7 8 9
bulk samples
1 2 3 4 5 6 7 8 9 10 11 12
Paleogene Maastrichthian
Early Norian Late Norian
Early Norian Late Norian
284
9 8 7 6 10 11 12
100%
80%
60%
40%
20%
1 2 3 4 5 6 7 8 9 Bulk Samples
Stable
assemblages
Rapid
transitions
Early Norian Late Norian
Italy (Tethys)
Transitions
Stationary
Epifauna
Stationary
Cementing Epifauna
Stationary
Semi-Infauna
Mobile
Epifauna
Fig. 5.21. Methods for identifying horizons of rapid faunal turnover. (A) Relative abundances of each paleoecological
category represented in each bulk sample from Tethys (above) and Panthalassa (below), with rapid transitions
indicated for each, and results of high-resolution inter-bulk sampling for Panthalassa. (B) Schematic depiction of the
process of identifying the effects of an impact event.
Bulk
Samples
1 7 6 5 4 3 2 8
Early Norian Late Norian
Species’ Ranges
Scenario 1 Scenario 2
3 2 a f e d c b
Higher Resolution
Sampling
Higher Resolution
Sampling
2 3
a f e d c b
Species’ Ranges
High Resolution sediment
sampling for Ir, REEs, and
other impact signatures
Bulk
Samples
Present?
YES NO
Goal completed.
Dene
biostratigraphy
and correlate
other sections.
Dene horizon with
biostratigraphy and
examine correlative
sections for impact
indicators and/or
coincident biotic
turnover.
Two resulting hypotheses:
1. Manicouagan’s impact horizon is
not at this level.
--> investigate other horizons of
signicant turnover
2. The impact horizon is within this
range, but the event had very little
biotic impact.
--> dene the unaected range with
biostratigraphy to systematically rule
out stratigraphic sections, and follow
the protocol with samples 5 & 6
Species’ Ranges
No rapid
turnover
No rapid
turnover
Mobile
Infauna
100%
80%
60%
40%
20%
1 2 3 5 4
Nevada
(Panthalassa)
Nevada
(Panthalassa)
Early Norian Late Norian
???
Inter-bulk
sample results
A. B.
285
Stationary epifauna
Cementing stationary epifauna
Stationary Semi-infauna
Mobile Epifauna
Mobile infauna
Early Norian Late Norian
Berlin Ichthyosaur State Park New York Canyon
1 2 3 9 8 7 6 5 4 10 11 12
Nektonic carnivore
90%
70%
50%
30%
10%
bulk samples
7 8
A B C D
4 5
A B C D
3 4
A B D
Figure 5.22. Higher-resolution bulk sampling from the upper Luning Formation and the lower
Gabbs Formation in intervals of high faunal/paleoecological change. (top) All bulk samples,
(bottom) high-resolution bulk sample data. Grey boxes represent intervals of relatively rapid
paleoecological change. Black box represents the interval of rapid change within a
high-resolution bulk sample range.
286
7 8
A B C D
7A
7B
shale 1
shale 2
shale 3
7A
7B
Figure 5.23. Preliminary sampling methods in the intervals of non-gradual paleoecological
change within the Nun Mine Member of the Gabbs Formation (top), field image (bottom left)
and schematic stratigraphy (bottom right). White boxes represent shale samples collected,
black boxes represent limestone column samples.
samples
s1a
s1b
s2a
s3a
s3b
s3c
s3d
s3e
s3f
s3g
287
Appendix 1. Appearances and major radiations of durophagous predators and prey with anti-durophagy
adaptations
Group Pred/Prey Ecology
Range or
appearances Source(s)
Range
(pbdb)
Notes
(diversity)
Notes
(Ecology)
SHELL-
CRUSHING
PREDATORS
Belemnites Pred Shell-Crusher
Paleozoic -
present
Walker and
Brett (2002)
Paleozoic -
present
First Occur in
the Late
Triassic,
Become
diverse and
abundant in
Jurassic
Stomatopods Pred Shell-Breaker
Devonian -
present
Walker and
Brett (2002)
Carboniferous -
present
Very few pbdb
references,
diversity is
unclear
Use raptorial
thoracopods to
smash or spear
prey, known
from
Carboniferous.
Listed as
omnivore on
PBDB, but they
are obligate
carnivores if
they have
folding
thoracopods
288
Brachyuran
Crabs Pred Shell-Breaker
Triassic -
present
Paleobiology II
(p94), Harper
(2006), Walker
& Brett (2002),
Forster (1985)
Norian -
present
Single Triassic
occurrence is
non-marine,
appear to
diversify in the
Cretaceous. No
Early Jurassic
occurences on
PBDB, but the
Triassic
occurrence is
with many
specimens
Pycnodontiform
Fish Pred Shell-Crusher
Late Triassic -
Eocene
Lombardo &
Tintori (2005),
Vermeij
(1987),
Paleobiology II,
Harper (1991),
Tintori (1991)
Norian -
Pleistocene
Appear
consistently in
Late Triassic
and Norian,
also radiate in
the Norian,
further
diversify in
Cretaceous
Shell-crushing
dentition
Palinuran
Lobsters Pred Shell-Breaker
Mid-Triassic -
recent
Vermeij
(1987),
Garassino et al
(1996), Walker
& Brett (2002),
Forster (1985)
Jurassic -
Eocene
One occurence
in Carnian
(pbdb),
Teleosts Fish Pred Shell-crusher
Early Triassic
(primitive) -
present
Harper (2006),
Vermeij (2008) Nor - present
Single Carnian
and Norian
occurences
(pbdb), several
Early Triassic
occurences of
primitives
Variety of
feeding
strategies
289
Macrosemiid
Fish Pred Shell-Crusher
Late Triassic -
Cretaceous
Tintori (1991),
Lombardo &
Tintori (2005)
Norian -
Cretaceous
Few
occurences on
PBDB, and
none in the
Jurassic,
radiated in the
Norian
Possibly a
small
crustacean-
eater, and shell-
crushing
dentition
Holostean Fish Pred Shell-Crusher Late Triassic
(Tintori 1998),
Walker & Brett
(2002)
Early Triassic -
present
Appear in Early
Triassic but
radiate in the
Norian
"Sub-
holostean"
Possibly an
Ammonoid-
eater
Homaridian
Lobsters Pred Shell-Breaker
Earliest Jurassic
- present
Paleobiology II
(p94), Harper
(1991)
Cretaceous-
present
No pre-
Cretaceous
pbdb
occurences,
but there are
in the literature
Macrura Pred Shell-Breaker Norian Garassino
Ladinian -
Callovian
Single
Smithian
occurrence
Nautiloids Pred Shell-Crusher
Paleozoic -
present
Walker and
Brett (2002)
Permian -
present
Diversify in the
Jurassic
Semionotiform
Fish Pred Shell-Crusher
Induan -
Campanian
Tintori (1991),
Lombardo &
Tintori (2005),
Vermeij (1987)
Triassic to
Cretaceous
Become
abundant and
diverse in the
Late Triassic
Many strictly
durophaous;
Shell-crushing
dentition
Placodonts Pred Shell-Crusher Triassic only
Tintori (1998),
Harper (2006)
Anisian -
Rhaetian
Always Rare
(Tintori);
Abundant
(Harper)
Sluggish, shell-
eaters
290
Neoselachian
Sharks Pred Shell-Crusher
Permian -
present
Maisey et al
(2004), Walker
and Brett
(2002),
Underwood
(2006)
Carboniferous -
Pleistocene
Present in low
abundance and
diversity until
the Norian
(pbdb) where
they increased
in abundance
(Underwood),
further
diversifications
in Cretaceous
Hybodontid
Sharks Pred Shell-Crusher
Permian -
Cretaceous
Paleobiology II
(p94), Tintori
(1998), Brett
(2002)
Permian -
Danian
Family
Lonchidiidae,
Very low
diversity and
abundance
until the Mid to
Late Triassic
Shell-crushing
dentition
Ammonoids Pred Shell-Crusher
Paleozoic - End-
Cretaceous
Harper (2006),
Walker & Brett
(2002),
Paleobiology II
(p94)
Paleozoic to
End-
Cretaceous
Very diverse
and abundance
in Permian,
great
extinction at
P/T, new
diversity in
Triassic
Shell-crushing
groups
# Families
Crushing
Crustaceans Pred Harper (2003)
291
PREY WITH
ANTI-
PREDATOR
STRATEGIES
FOR SHELL-
CRUSHING
Cementing
Barnacles Prey Protected
Late Jurassic -
Tertiary
Walker & Brett
(2002)
Possible
presence in
Carboniferous -
Late Jurassic
Boring Clionids Prey Hidden
Early Jurassic -
Tertiary
Walker & Brett
(2002) Eocene
Very few pbdb
records;
Possible
presence in
Carboniferous -
Early Jurassic
Burrowing
Spatangoids Prey Escape
Late Triassic -
Tertiary
Walker & Brett
(2002)
Diversify in
mid-Jurassic
Cementing
Annelids Prey Protected
Early Ordovician
- Tertiary
Walker & Brett
(2002)
Diversify in
Late Triassic
Boring Annelids Prey Hidden
Early Ordovician
- Tertiary
Walker & Brett
(2002)
Diversify in
Late Triassic
Burrowing
Bivalves Prey Escape
Cambrian -
Tertiary
Walker & Brett
(2002)
Diversify in
Late Triassic
Obliquely-
ribbed bivalves Prey
Protected/Esca
ped
Paleocoic to
present Checa (2003)
Appear in
Paleozoic,
diversify in
Late Triassic,
and decline in
Late
Cretaceous
Ribs reinforce
shells and may
facilitate
burrowing
292
Cementing
Brachiopods Prey Protected
Ordovician - Mid
Triassic
Walker & Brett
(2002)
Diversfy in mid-
Ordovician,
possible
presence Late
Permian to
Early Jurassic
Clades of
Cementing
Bivalves List appearance
appearance
(pbdb)
Pseudomonotid
ae Prey
Cementer/Prot
ected Permian Harper (1991) Permian
Three isolated
occurences in
Carboniferous
(pbdb)
Gryphaeidae Prey
Cementer/Prot
ected Norian Harper (1991) Carnian
Two
occurences in
Ladinian. Low
Diversity until
Norian
Juvenile
cementer, adult
unattached
recliner
Ostreidae Prey
Cementer/Prot
ected Norian Harper (1991) Latest Permian
Lopha in
Permian - a
problemmatic
taxa. Low
diversity until
late Triassic
Plicatulidae Prey
Cementer/Prot
ected Norian Harper (1991) Anisian
Appears
monospecific in
Anisian,
diversifies in
Norian
293
Terquemiidae Prey
Cementer/Prot
ected Norian Harper (1991) Anisian
Only diverse in
Anisian
China,very rare
in Ladinian, but
present
consistently
Late Triassic,
though not
especially
diverse
Dimyidae Prey
Cementer/Prot
ected Rhaetian Harper (1991) Carnian
No Rhaetian
occurences
Atreya Prey
Cementer/Prot
ected Rhaetian Harper (1991) Rhaetian
Minor Norian
occurences
Lithiotidae Prey
Cementer/Prot
ected Sinemurian Harper (1991) Bajonian
Only one
occurrence on
PBDB
Spondylidae Prey
Cementer/Prot
ected Aalenian Harper (1991) Bajonian
Single
occurrence in
Hettangian
Eopecten Prey
Cementer/Prot
ected Bajonian Harper (1991) Late Triassic
Low diversity
in general, but
becomes
common in mid-
Jurassic
Rudists Prey
Cementer/Prot
ected Kimmeridgian Harper (1991) Cenomanian
Lots of Ceno
occurences, no
Jurassic
occurences in
pbdb
Prohinnites Prey
Cementer/Prot
ected Aptian Harper (1991) Hauterivian
Not common at
any time
Chondrodontid
ae Prey
Cementer/Prot
ected Cenomanian Harper (1991) Aptian
Single non-
species
occurrence in
Hauterivian
294
Chamiidae Prey
Cementer/Prot
ected Campanian Harper (1991) Barremian
More
occurrences in
latest
Cretaceous,
but diversifies
post-
Cretaceous
SHELL-
CRUSHING
TRACE
FOSSILS
Repair
Crushes Prey
Unsuccessful
breakage Late Cretaceous
Walker & Brett
(2002),
Vermeij et al
(1982) N/A
more common
in Paleozoic,
then a
disappearance
in Triassic and
Jurassic
Ineffectual
predation
(Tintori 1998)
DRILLING
PREDATORS
Cymatiidae
Gastropods Pred Driller
Cretaceous -
present
Walker & Brett
(2002), Sohl
(1969)
Paleocene -
Pleistocene
Don't radiate
until post-
Cretaceous
Cassidae Pred Driller
Late Cretaceous
- present
Walker & Brett
(2002)
Late
Cretaceous -
present
Not common
until post-
Cretaceous
Muricid
Gastropods Pred Driller
Early
Cretaceous -
present
Harper (2006),
Walker & Brett
(2002), Sohl
(1969)
Cretaceous -
present
First appears in
Cretaceous
295
Naticid
Gastropods Pred Driller
Early
Cretaceous -
present
Vermeij
(1987), Harper
(2006), Walker
& Brett (2002),
Sohl (1969)
Triassic (moon
snails) -
present
Relatively
common
elements in
Jurassic
Triassic
Naticidae were
bulldozers
(Moon Snails),
possibly not
drillers (Sohl);
Drilling range
begins in
Cretaceous
Octopods Pred Driller
Carboniferous -
Tertiary Harper (2006)
Jurassic -
Miocene
Scanty fossils
from the
Carboniferous,
first fossils in
Jurassic
(pbdb),
possible
presence in
Triassic
Rapid drillers,
only drill larger
prey
PREY WITH
ANTI-
PREDATOR
STRATEGIES
FOR DRILLING
Spiny
Echinoids Prey Protected
Silurian - Early
Triassic
Walker & Brett
(2002)
Diverse in mid-
Cretaceous
Spiny
Gastropods Prey Protected
Devonian -
Tertiary
Walker & Brett
(2002)
Diversify in Mid-
Cretaceous,
possible
presence in
Silurian
Spiny Bivalves Prey Protected
Carboniferous -
Tertiary
Walker & Brett
(2002)
Never very
diverse
296
Spiny Crinoids Prey Protected
Silurian - Early
Triassic
Walker & Brett
(2002)
Diverse in
Silurian to
Pennsylvanian,
possible
presence in
Permian
Spiny
Brachiopods Prey Protected
Devonian - Late
Permian
Walker & Brett
(2002)
Diverse in
Carboniferous
to Permian,
possible
presence in
Silurian,
Triassic, and
Early Jurassic
DRILLING
TRACE
FOSSILS
Drillholes Prey
Paleozoic, Late
Triassic, Early
Juassic,
Cretaceous
Harper (2003)
summary,
References
Harper, E. (2003). The Mesozoic Marine Revolution. Predator-Prey Interactions in the Fossil Record (book): 1-25.
Brett, C. (2002). Predators and predation in Paleozoic marine environments. Paleontological Society Papers.
Checa, A. G. and A. P. Jiménez-Jiménez (2003). Evolutionary morphology of oblique ribs of bivalves. Palaeontology. 46: 709-724.
Forster, R. (1985). Evolutionary trends and ecology of Mesozoic decapod crustaceans. Transactions of the Royal
Garassino, A., G. Teruzzi, et al. (1996). The macruran decapod crustaceans of the Dolomia di Forni (Norian, Upper
Harper, E. (1991). The role of predation in the evolution of cementation in bivalves. Palaeontology. 34: 455-460.
Harper, E. (2006). Dissecting post-Palaeozoic arms races. Palaeogeography, Palaeoclimatology, Palaeoecology. 232: 322-343. Lombardo, C. and A. Tintori (2005). Feeding specializations in Late Triassic fishes. Annali dell’Università di Ferrara, Museologia
Scientifica e Naturalistica volume speciale: 25-32. Maisey, J. G., G. J. P. Naylor, et al. (2004). Mesozoic elasmobranchs, neoselachian phylogeny and the rise of modern
elasmobranch diversity. Mesozoic fishes. 3: 17-56.
297
Bardhan, et al (2012). Record of intense predatory drilling from Upper Jurassic bivalves of Kutch, India: Implications for the history of
biotic interaction. Palaeogeography, Palaeoclimatology, Palaeoecology. 317-318: 153-161.
Vermeij, G. (1987). Evolution and Escalation: An Ecological History of Life. Princeton, Princeton University Press. Vermeij, G., E. Zipser, et al. (1982). Breakage-induced shell repair in some gastropods from the Upper Triassic of Italy. Journal of
Paleontology: 233-235. Walker, S. and C. Brett (2002). Post-Paleozoic patterns in marine predation: was there a Mesozoic and Cenozoic marine predatory
revolution? Paleontological Society Papers. 8: 119-194.
Sohl, N. F. (1969). The fossil record of shell boring by snails. American Zoologist, Soc Integ Comp Biol. 9: 725-734. Tintori, A. (1998). Fish biodiversity in the marine Norian (Late Triassic) of northern Italy: the first Neopterygian radiation. Italian
J. of Zoology. 65: 193-198. Underwood, C. (2006). Diversification of the Neoselachii (Chondrichthyes) during the Jurassic and Cretaceous. Paleobiology. 32:
215-235.
298
Appendix 2. Elemental and isotopic data (Strontium, Carbon, Oxygen, Manganese, Magnesium) for samples from the Carbonate
Member of the Luning Formation, the Gabbs Formation, and the Sunrise Formation (Nevada)
1
Sample
Name Locality Formation Member
87
Sr/
86
Sr Prev. Age New Age
BISP 1 Berlin Ichthyosaur State Park Luning Carbonate 0.7076461 Early Norian Early Norian
BISP 2 Berlin Ichthyosaur State Park Luning Carbonate 0.7075309 Early Norian Early Norian
BISP 3 Berlin Ichthyosaur State Park Luning Carbonate 0.7075599 Early Norian Early Norian
BISP 4 Berlin Ichthyosaur State Park Luning Carbonate 0.7075390 Early Norian Early Norian
BISP 5 Berlin Ichthyosaur State Park Luning Carbonate 0.7075757 Early Norian Early Norian
NYC 1 New York Canyon Gabbs Nun Mine 0.7079695 Rhaetian Late Norian
NYC 2 New York Canyon Gabbs Nun Mine 0.7078258 Rhaetian Late Norian
NYC 3 New York Canyon Gabbs Nun Mine 0.7077460 Rhaetian Late Norian
NYC 4 New York Canyon Gabbs Nun Mine 0.7080025 Rhaetian Late Norian
NYC 5 New York Canyon Gabbs Nun Mine 0.7078868 Rhaetian Late Norian
NYC 6 New York Canyon Gabbs Nun Mine 0.7080138 Rhaetian Late Norian
NYC 7 New York Canyon Gabbs Nun Mine 0.7078550 Rhaetian Late Norian
NYC 8 New York Canyon Gabbs Nun Mine 0.7079305 Rhaetian Rhaetian
NYC 9 New York Canyon Gabbs Nun Mine 0.7077691 Rhaetian Rhaetian
NYC 10 New York Canyon Gabbs Nun Mine 0.7077787 Rhaetian Rhaetian
NYC 11 New York Canyon Gabbs Nun Mine 0.7076792 Rhaetian Rhaetian
NYC 12 Muller Canyon Gabbs Muller Canyon 0.7077150 Rhaetian Rhaetian
NYC 13 Muller Canyon Sunrise Ferguson Hill 0.7077246 Early Jurassic Early Jurassic
NYC 14 Muller Canyon Sunrise Ferguson Hill 0.7078143 Early Jurassic Early Jurassic
NYC 15 Reno Draw Sunrise Ferguson Hill 0.7076357 Early Jurassic Early Jurassic
299
Appendix 2. Elemental and isotopic data (Strontium, Carbon, Oxygen, Manganese, Magnesium) for samples from the Carbonate
Member of the Luning Formation, the Gabbs Formation, and the Sunrise Formation (Nevada)
2
Sample
Name
87
Sr/
86
Sr
Ratios
87
Sr/
86
Sr
SdError
87
Sr/
86
Sr SdDev
Sr
Concentration
(ppt)
Mn
Concentration
(ppt) Mn/Sr Ratio
BISP 1 100 0.0032 0.0000226 1.975 0.174 0.08810127
BISP 2 87 0.0019 0.0000134 1.435875734 0.140946195 0.09816044
BISP 3 47 0.0024 0.000017 1.35720347 0.121542989 0.08955399
BISP 4 57 0.0018 0.0000127 1.109524695 0.193516534 0.1744139
BISP 5 92 0.0011 0.0000078 2.052783757 0.13070606 0.06367259
NYC 1 103 0.0025 0.0000177 0.3186 0.25355 0.79582549
NYC 2 96 0.0026 0.0000184
NYC 3 111 0.0031 0.0000219 0.4876 0.63 1.29204266
NYC 4 96 0.00360 0.00003 0.48055 0.40325 0.83914265
NYC 5 104 0.01100 0.00008 0.36135 0.25835 0.7149578
NYC 6 96 0.0038 0.0000269 0.4485 0.31175 0.69509476
NYC 7 112 0.00220 0.00002 0.44395 0.34165 0.76956865
NYC 8 84 0.0015 0.0000106 0.422 1.04975 2.48755924
NYC 9 102 0.0021 0.0000149 1.06935 0.9682 0.90540983
NYC 10 96 0.0023 0.0000163 0.67915 0.9179 1.35154237
NYC 11 95 0.0027 0.0000191 0.40475 0.8223 2.03162446
NYC 12 107 0.00250 0.00002 0.595758498 0.521615213 0.87554809
NYC 13 106 0.00310 0.00002 0.321888999 0.207501514 0.64463686
NYC 14 103 0.00230 0.00002 0.528809516 0.40587455 0.76752505
NYC 15 104 0.00340 0.00002 0.512351102 0.351734074 0.68650984
300
Appendix 2. Elemental and isotopic data (Strontium, Carbon, Oxygen, Manganese, Magnesium) for samples from the Carbonate
Member of the Luning Formation, the Gabbs Formation, and the Sunrise Formation (Nevada)
3
Sample
Name
Height
(nA)
Weight
(mg) 13C 18O
delta18O
w.r.t.
SMOW 13C corr 13C stdev 18O corr d
18
O stdev
BISP 1 7.51 0.09 -3.09 0.69 31.57 2.14 0.11 -12.41 0.09
BISP 2
BISP 3
BISP 4
BISP 5
NYC 1 7.53 0.11 -8.71 0.80 31.68 -3.48 0.11 -12.29 0.09
NYC 2 7.65 0.10 -5.83 5.58 36.61 -0.60 0.11 -7.52 0.09
NYC 3 8.53 0.10 -5.43 5.09 36.11 -0.20 0.11 -8.00 0.09
NYC 4 6.07 0.10 -5.19 3.81 34.78 0.04 0.11 -9.29 0.09
NYC 5 8.37 0.11 -4.73 4.31 35.30 0.50 0.11 -8.78 0.09
NYC 6 7.70 0.11 -5.22 4.31 35.31 0.02 0.11 -8.78 0.09
NYC 7 9.46 0.11 -4.49 4.50 35.50 0.74 0.11 -8.59 0.09
NYC 8 4.30 0.10 -5.03 3.09 34.05 0.20 0.11 -10.00 0.09
NYC 9 11.42 0.11 -4.20 4.96 35.97 1.03 0.11 -8.13 0.09
NYC 10 4.43 0.09 -5.07 3.39 34.36 0.17 0.11 -9.71 0.09
NYC 11 6.84 0.09 -4.96 3.23 34.19 0.27 0.11 -9.87 0.09
NYC 12 6.28 0.10 -4.05 4.03 35.02 1.18 0.11 -9.06 0.09
NYC 13 7.87 0.10 -6.11 5.16 36.18 -0.88 0.11 -7.93 0.09
NYC 14 6.23 0.10 -10.49 3.91 34.89 -5.26 0.11 -9.18 0.09
NYC 15 7.46 0.10 -4.62 5.17 36.19 0.61 0.11 -7.92 0.09
301
Appendix 4. Tethyan (Italian Alps) fossil occurrences and paleoecological categories for Norian bulk samples
Bulk Samples
Paleoeco Taxa 1 2 3 4 5 6 7 8 9
SSIS Bakevellia (King 1848) 5 23 1 1 3
SSIS Modiolus (Lamarck 1799) 1 4 1 1 1 30 2 1
SSIS Pinna (Linnaeus 1758) 6 1 14 74 12
SSIS Megalodon (Agassiz 1843) 1 2
SES Avicula 9 19 3 8 2 4 7 2 3
SES Promysidiella (Waller and Stanley 2005) 7 9
SES Isognomon (Lightfoot 1786) 2 16 5
SES Aguilerella (Chavan 1951) 1 8 2
SES Edentula=Waagenoperna 1
SES Retroceramus (Koschelkina 1958) 3 1 1
SES Mysidioptera (Salomon 1895) 2 1
SES Mytilus (Linnaeus 1758) 1 1 2 10 1
SES Cassianella (Beyrich 1862) 1 1 1 2
SES Pteria (Scopoli 1777)
SES Septifer (Récluz 1848) 2 1
SES Hoernesia 1
SES Gryphaea (Lamarck 1801) 1 1
ScES Plicatula (Lamarck 1801) 1
ScES Liostrea (DouvillŽ 1904) 1
MIS Thracia (Blainville 1824) 2 2 7 1 5
MIS Gresslya (Agassiz 1843) 1 1 6 1 4
MIS Myoconcha (Sowerby 1824) 1 3
MIS Pholadomya (Sowerby 1823) 1
MIS Unionites (Wissman 1841) 1 17 1 13
MIS Anatina (Schumacher 1817) 0 2
MIS Costatoria 4 2 1
MIS Cucullaea (Lamarck 1801) 1
MIS Myophoria (Bronn 1834) 1
MIS Myophoricardium (Wöhrmann 1889) 13
MIS Myophoriopis (Wöhrmann 1889) 29 1
MIS Neoschizodus (Giebel 1855)
MIS Pachycardia 1
MIS Rhaetidia 1
MIS Trigonodus 2
MIS Unicardium (d'Orbigny 1850) 4 1 2
MIS Unio (Philipsson 1788) 1 1
MIDS Nucula (Lamarck 1799) 2 2 3 4 27 11 14
MIDS Nuculana (Link 1807) 1 1 11 14 8
MID palaeoneilo 1 1 14 3 1
MID Tancredia 1
MICh Schafhaeutlia 4 5 15
MES Macrodon = Parallelodon (Meek and Worthen 1866) 1 2
MES Hoferia (Bittner 1894) 3
302
Appendix 4. Tethyan (Italian Alps) fossil occurrences and paleoecological categories for Norian bulk samples
303
Appendix 4. Tethyan (Italian Alps) fossil occurrences and paleoecological categories
for Norian bulk samples
Bulk Samples
Paleoeco Taxa 1 2 3 4 5 6 7 8 9
SSIS Bakevellia (King 1848) 5 23 1 1 3
SSIS Modiolus (Lamarck 1799) 1 4 1 1 1 30 2 1
SSIS Pinna (Linnaeus 1758) 6 1 14 74 12
SSIS Megalodon (Agassiz 1843) 1 2
SES Avicula 9 19 3 8 2 4 7 2 3
SES Promysidiella (Waller and Stanley 2005) 7 9
SES Isognomon (Lightfoot 1786) 2 16 5
SES Aguilerella (Chavan 1951) 1 8 2
SES Edentula=Waagenoperna 1
SES Retroceramus (Koschelkina 1958) 3 1 1
SES Mysidioptera (Salomon 1895) 2 1
SES Mytilus (Linnaeus 1758) 1 1 2 10 1
SES Cassianella (Beyrich 1862) 1 1 1 2
SES Pteria (Scopoli 1777)
SES Septifer (Récluz 1848) 2 1
SES Hoernesia 1
SES Gryphaea (Lamarck 1801) 1 1
ScES Plicatula (Lamarck 1801) 1
ScES Liostrea (DouvillŽ 1904) 1
MIS Thracia (Blainville 1824) 2 2 7 1 5
MIS Gresslya (Agassiz 1843) 1 1 6 1 4
MIS Myoconcha (Sowerby 1824) 1 3
MIS Pholadomya (Sowerby 1823) 1
MIS Unionites (Wissman 1841) 1 17 1 13
MIS Anatina (Schumacher 1817) 0 2
MIS Costatoria 4 2 1
MIS Cucullaea (Lamarck 1801) 1
MIS Myophoria (Bronn 1834) 1
MIS Myophoricardium (Wöhrmann 1889) 13
MIS Myophoriopis (Wöhrmann 1889) 29 1
MIS Neoschizodus (Giebel 1855)
MIS Pachycardia 1
MIS Rhaetidia 1
MIS Trigonodus 2
MIS Unicardium (d'Orbigny 1850) 4 1 2
MIS Unio (Philipsson 1788) 1 1
MIDS Nucula (Lamarck 1799) 2 2 3 4 27 11 14
MIDS Nuculana (Link 1807) 1 1 11 14 8
MID palaeoneilo 1 1 14 3 1
MID Tancredia 1
MICh Schafhaeutlia 4 5 15
MES Macrodon = Parallelodon (Meek and Worthen 1866) 1 2
MES Hoferia (Bittner 1894) 3
304
Appendix 5. Panthalassa (Nevada) fossil occurrences and paleoecological
assignments for Norian bulk samples
Bulk Samples
Paleo Taxa 1 2 3 4 5 6 7 8 9 10 11
MIS Tutcheria 2 2 19 11 12 20 28 10
ScES Plicatula 1 3 2 76 22 16 1 3 9
MIDS Nucula 4 1 5 3 1 32 8 8
MIS Frenguelliella 2 1 2 13 6 4 8
SES Chlamys 1 1 1 2 5 3 13 4 3 3
SSIS Pinna 1 1 1 1 18 4
MES Entolium 1 6 2 11 6 3
SES Mysidioptera 1 16 4 1 6
MES Lima 1 4 4 6
SES Isognomon 1 2 1 5 1 1
MIS Unionites 2 1 2 1 7 1
MIS Myophoria 1 2 1 3 1 5
MED Gastropod 2 6 3 31 3 2 2 2
SES Gervillaria 1 5 1 1
MIC Schafhaeutlia 1 1 1 3 2 3 1 2 1
MES Camptonectes 4 1
SSIS Modiolus 2 1 3 3 1 3 1 1
SES Cassianella 1 1 1 1 1 3 1
SES Brachiopod 22 78 32 2 1 3 1 1
NEC Aulacoceras 1 3 1
MIS Gruenewaldia 4
MIDS Nuculana 2 1 1 5
SES Pseudolimea 2 2
MIS Astarte 2 1
MES Eolimea 1 3 1 1
SES Mytilus 1 1 2 5
SES Arcavicula 1 1 2 1
SES Arca 1 3
SES Antiquillima 1 1 1
ScES Liostrea 1 1 1
MIS Gresslya 1 1 1 1
MIS Septocardia 1 1 2
MIS Cardinioides 1 2
MIS Cardita 2
MIS Cardium 1 1
MIS Cucullaea 2 1
MES Pecten 1 1 1 1
MES Paralellodon 2 1
SSIS cf. Megalodon 2
SES Zeilleria 4 1 1 1 1
MIS Myophoricardium 2 1 1 1
MIS Palaeocardita 1 1 1 1
MIS Protocardia
MIS Cardinia 1
305
MIS Anisocardia 1 1
MID Scaphopod 2
MES Cingentolium 1 1
MES Limatula 2
MED Echinoid spine 1 1 1 1 1 1
SSIS Bakevellia 1 1 1
SES Rhaetavicula 2 1 1
SES Gryphaea 2 2 1
SES Pteria 2 1
SES Hoernesia 1 1
SES Meleagrinella 1 1
SES Harpax 1 1
SES cf. Halobia 1 1 1
SES Bakevelloides
SES Mysidiella
SES Pleuromysidia
SES Rhaetina 1
SESCrenamussium 1
SES cf. Cultriopsis 1
SES Oxytoma 1
SES Placunopsis 1
NEC Ammonoid 2 1 3 1 3 1
NEC Belemnite
NEC Dictyoconites 1
MIS cf. Isopristes 1
MIS Pachycardia
MIS Homomya 1
MIS cf. Pleuromya 1
MID Palaeoneilo 1 1
MES Hoferia 1 1 1
MES Limopsis 1
SSIS Gervillia 1 1
SESWaagenoperna 1
SES Crinoid 1 10 2
SES Plectoconcha 4 85 6
SES Avicula 1 1 1
SES cf. Septihoernesia 1
SES cf. Plagiostoma 1
ScES Gonodon 3 1
ScES cf. Atreta 1
ScES Lopha 1 4 21
ScES Oyster indet. 2 13
NEC cf. Arcestes 1
MIS Myophoriopis 1
MIS cf. Cyprina 1
MIS cf. Myoconcha 1
MIDS Palaeonucula 1
MIC Lucina 1
MES Catella 2
306
MES Pichleria 1 1
307
Appendix 6. Panthalassa fossil occurrences for bulk samples from
Black Marble Quarry, OR
1 2 3 Total
Gastropod 18 9 7 34
Unionites 5 8 6 19
Nuculana 2 6 9 17
Nucula 1 5 5 11
Echinoid 5 4 9
cf. Scaphopod 7 1 8
cf. Lima 2 3 5
Schafhautlia 3 2 5
cf. Pteria 2 2 4
Septocardia 3 3
Costatoria 1 1 2
Paralellodon 2 2
Myophoricardium 2 2
Brachiopod indet. 1 1
Crinoid 1 1
cf. Pachycardia 1 1
cf. Atreta 1 1
Gresslya 1 1
Mytilus 1 1
cf. Modiolus 1 1
cf. Tutcheria 1 1
cf. Botulopis 1 1
cf. bone 1 1
Total 38 51 42
Diversity 12 13 12
308
Appendix 7. Size data for non-oyster stationary epifauna from Nevada and Italy
1
Appendix 7. Size data for non-oyster stationary epifauna from
Nevada and Italy
Nevada
Locality Bulk Sample # Seq # Genus Height Width
Height x Width
(Area) Specimen
NYC 2 7 Arcavicula 13 19 247 48
BISP 2 2 Brachiopod 15 12 180 2-j
BISP 2 2 Brachiopod 6 5 30 36
BISP 2 2 Brachiopod 21 18 378 72
BISP 2 2 Brachiopod 10 10 100 84
BISP 4 3 Brachiopod 13 10 130 11
BISP 4 3 Brachiopod 15 14 210 44
NYC 1.5 6 Cassianella 17 15 255 119
NYC 2 7 Cassianella 7 6 42 35b
BISP 4 3 Chlamys 6 6 36 13a
BISP 6 4 Chlamys 11 11 121 6-n-i(B)
NYC 3 8 Chlamys 8 9 72 45a
NYC 3 8 Chlamys 10 7 70 61
NYC 3 8 Chlamys 15 13 195 67
NYC 3 8 Chlamys 12 10 120 71
NYC 3 8 Chlamys 14 11 154 79
NYC 3 8 Chlamys 20 16 320 108
NYC 3 8 Chlamys 12 9 108 149
NYC 3 8 Chlamys 15 0 150B
NYC 3 8 Chlamys 12 10 120 D11
NYC 3.5 9 Chlamys 10 9 90 60b
NYC 3.5 9 Chlamys 12 11 132 81
NYC 4 10 Chlamys 12 10 120 s1
NYC 4.5 11 Chlamys 7 5 35 s2
NYC 3 8 Crenamussium 7 7 49 D18c
BISP 2 2 Entolium 8 5 40 34
NYC 1.5 6 Eolimea 19 17 323 188
NYC 1.5 6 Gryphaea 18 12 216 86Bb
NYC 2 7 Harpax 21 12 252 39
BISP 7 5 Hoernesia 35 30 1050 41
NYC 1.5 6 Isognomon 18 16 288 187
NYC 2 7 Isognomon 9 0 5a
NYC 2 7 Isognomon 16 15 240 43
NYC 3 8 Isognomon 23 28 644 28
NYC 3.5 9 Isognomon 27 23 621 9
NYC 3.5 9 Isognomon 31 31 961 D-7
NYC 4 10 Isognomon 24 20 480 11a
NYC 5 12 Isognomon 23 20 460 46
NYC 2 7 Liostrea 19 21 399 D-28
NYC 3.5 9 Liostrea 44 38 1672 26
309
Appendix 7. Size data for non-oyster stationary epifauna from Nevada and Italy
2
NYC 3.5 9 Meleagrinella 8 6 48 17
NYC 1.5 6 Mysidioptera 20 18 360 30
NYC 1.5 6 Mysidioptera 22 19 418 34a
NYC 1.5 6 Mysidioptera 12 10 120 76
NYC 1.5 6 Mysidioptera 23 20 460 105
NYC 1.5 6 Mysidioptera 21 18 378 166
NYC 1.5 6 Mysidioptera 35 29 1015 205
NYC 3 8 Mysidioptera 12 14 168 35c
NYC 3 8 Mysidioptera 18 15 270 73b
NYC 4 10 Mysidioptera 35 32 1120 1
NYC 4 10 Mysidioptera 18 16 288 D-20
NYC 5 12 Mysidioptera 17 15 255 13
NYC 5 12 Mysidioptera 15 12 180 110
NYC 1.5 6 Mytilus 29 27 783 134
NYC 2 7 Mytilus 20 15 300 16
NYC 2 7 Mytilus 18 22 396 19
NYC 2 7 Mytilus 17 20 340 D-7
NYC 2 7 Mytilus 17 23 391 D-8
NYC 5 12 Mytilus 12 11 132 114
NYC 3 8 Oxytoma 7 6 42 98B
BISP 2 2 P. aequiplicata 23 20 460 a-1
BISP 2 2 P. aequiplicata 19 18 342 a-2
BISP 2 2 P. aequiplicata 17 15 255 a-3
BISP 2 2 P. aequiplicata 19 17 323 a-4
BISP 2 2 P. aequiplicata 15 13 195 a-05
BISP 2 2 P. aequiplicata 18 13 234 a-06
BISP 2 2 P. aequiplicata 17 13 221 a-07
BISP 2 2 P. aequiplicata 23 17 391 a-08
BISP 2 2 P. aequiplicata 16 14 224 a-09
BISP 2 2 P. aequiplicata 18 15 270 a-10
BISP 2 2 P. aequiplicata 17 14 238 a-11
BISP 2 2 P. aequiplicata 18 15 270 a-12
BISP 2 2 P. newbyii 18 16 288 n-1
BISP 2 2 P. newbyii 15 13 195 n-2
BISP 2 2 P. newbyii 16 14 224 n-03
BISP 2 2 P. newbyii 15 12 180 n-04
BISP 2 2 P. newbyii 17 15 255 n-05
BISP 2 2 P. newbyii 18 16 288 n-06
BISP 2 2 P. newbyii 15 13 195 n-07
BISP 2 2 P. newbyii 6 6 36 n-08
BISP 2 2 P. newbyii 15 14 210 n-09
BISP 2 2 P. newbyii 18 16 288 n-10
BISP 2 2 P. newbyii 15 13 195 n-11
BISP 2 2 P. newbyii 14 12 168 n-12
NYC 3 8 Placunopis 8 7 56 11
BISP 2 2 Plectoconcha 17 15 255 2-l
310
Appendix 7. Size data for non-oyster stationary epifauna from Nevada and Italy
3
BISP 2 2 Plectoconcha 17 15 255 3a
BISP 2 2 Plectoconcha 15 15 225 6
BISP 2 2 Plectoconcha 22 20 440 19
BISP 2 2 Plectoconcha 17 15 255 27
BISP 2 2 Plectoconcha 13 11 143 49
BISP 2 2 Plectoconcha 12 10 120 67
BISP 2 2 Plectoconcha 16 14 224 p-1
BISP 4 3 Plectoconcha 17 14 238 4-j
BISP 4 3 Plectoconcha 12 10 120 73
NYC 1.5 6 Plicatula 19 16 304 10
NYC 1.5 6 Plicatula 25 22 550 16
NYC 1.5 6 Plicatula 17 14 238 20
NYC 1.5 6 Plicatula 14 12 168 21
NYC 1.5 6 Plicatula 18 16 288 27
NYC 1.5 6 Plicatula 30 25 750 29
NYC 1.5 6 Plicatula 16 14 224 37
NYC 1.5 6 Plicatula 12 10 120 47
NYC 1.5 6 Plicatula 16 14 224 52
NYC 1.5 6 Plicatula 12 12 144 53
NYC 1.5 6 Plicatula 14 12 168 71a
NYC 1.5 6 Plicatula 14 12 168 81
NYC 1.5 6 Plicatula 9 7 63 86Ba
NYC 1.5 6 Plicatula 12 10 120 103
NYC 1.5 6 Plicatula 13 11 143 107
NYC 1.5 6 Plicatula 16 14 224 125a
NYC 1.5 6 Plicatula 15 12 180 140
NYC 1.5 6 Plicatula 16 14 224 143b
NYC 1.5 6 Plicatula 18 16 288 185
NYC 2 7 Plicatula 13 7 91 4
NYC 2 7 Plicatula 14 0 23a
NYC 2 7 Plicatula 15 0 58
NYC 2 7 Plicatula 5 4 20 76
NYC 2 7 Plicatula 8 0 D-1
NYC 2 7 Plicatula 14 18 252 D-2
NYC 2 7 Plicatula 15 17 255 D-5
NYC 2 7 Plicatula 19 0 D-14
NYC 2 7 Plicatula 16 0 D-15
NYC 2 7 Plicatula 23 0 D-24
NYC 2 7 Plicatula 26 25 650 D-30a
NYC 3 8 Plicatula 17 14 238 14
NYC 3 8 Plicatula 13 0 43
NYC 3 8 Plicatula 5 5 25 59b
NYC 3 8 Plicatula 8 9 72 60
NYC 3 8 Plicatula 34 23 782 94b
NYC 3 8 Plicatula 7 6 42 153a
NYC 3 8 Plicatula 11 22 242 D4-B
311
Appendix 7. Size data for non-oyster stationary epifauna from Nevada and Italy
4
NYC 3 8 Plicatula 18 14 252 D8e
NYC 3 8 Plicatula 31 21 651 D19
NYC 4.5 11 Plicatula 24 0 1
NYC 4.5 11 Plicatula 8 7 56 D-4a
NYC 5 12 Plicatula 20 20 400 D5
NYC 5 12 Plicatula 14 12 168 D16b
NYC 3 8 Pseudolimea 6 4 24 17c
NYC 3 8 Pseudolimea 9 8 72 51
NYC 2 7 Pteria 7 16 112 D-30b
NYC 2 7 Pteria 12 12 144 D-34c
NYC 2 7 Rhaetavicula 12 20 240 D-17
BISP 2 2 Zeilleria 15 13 195 2-b-b
BISP 2 2 Zeilleria 22 18 396 2-i
BISP 2 2 Zeilleria 14 12 168 2-k
BISP 2 2 Zeilleria 11 10 110 8
Italy
Bulk
Sample
# Sequence #
Specim
en Genus Height Width
Height x Width
(Area)
DP 56 1 4832 Avicula 6 5 30
DP 56 1 4778 Avicula 10 7 70
DP 56 1 4796 Avicula 18 18 324
DP 56 1 4848 Hoernesia 21 18 378
DP 56 1 4818 Edentula 28 24 672
DP 56 1 4780 Avicula 32 27 864
DP 56 1 4770 Avicula 32 28 896
DP 56 1 4782 Isognomon 45 43 1935
DP 31.5 2 4240 Isognomon 6 5 30
DP 31.5 2 4542 Isognomon 8 5 40
DP 31.5 2 4314 Hoernesia 7 7 49
DP 31.5 2 4182 Avicula 8 7 56
DP 31.5 2 4457 Isognomon 9 6 54
DP 31.5 2 4133 Avicula 10 6 60
DP 31.5 2 4348 Avicula 10 7 70
DP 31.5 2 4403 Avicula 9 8 72
DP 31.5 2 4473 Avicula 12 6 72
312
Appendix 7. Size data for non-oyster stationary epifauna from Nevada and Italy
5
DP 31.5 2 4443 Isognomon 12 10 120
DP 31.5 2 4423 isognomon 13 10 130
DP 31.5 2 4520 Isognomon 12 11 132
DP 31.5 2 4360 Isognomon 14 12 168
DP 31.5 2 4453 Isognomon 14 12 168
DP 31.5 2 4461 Isognomon 14 12 168
DP 31.5 2 4286 Avicula 15 12 180
DP 31.5 2 4403 Avicula 14 13 182
DP 31.5 2 4194 Avicula 15 13 195
DP 31.5 2 4258 Avicula 17 11 187
DP 31.5 2 4401 Isognomon 15 13 195
DP 31.5 2 4437 Plicatula 18 10 180
DP 31.5 2 4477 Avicula 18 12 216
DP 31.5 2 4485 Hoernesia 17 13 221
DP 31.5 2 4149 Pteria 20 10 200
DP 31.5 2 4234 Hoernesia 20 15 300
DP 31.5 2 4228 Isognomon 20 15 300
DP 31.5 2 4397 Avicula 19 17 323
DP 31.5 2 4292 Isognomon 20 17 340
DP 31.5 2 4514 Isognomon 20 18 360
DP 31.5 2 4200 Isognomon 20 20 400
DP 31.5 2 4536 Plicatula 23 18 414
DP 31.5 2 4364 Avicula 22 20 440
DP 31.5 2 4178 Cassianella 18 24 432
DP 31.5 2 4260 Isognomon 30 15 450
DP 31.5 2 4314 Isognomon 25 23 575
313
Appendix 7. Size data for non-oyster stationary epifauna from Nevada and Italy
6
DP 31.5 2 4350 Isognomon 28 25 700
DP 31.5 2 4139 Isognomon 54 0
DP 31.5 2 4310 Isognomon 30 25 750
DP 31.5 2 4360 Isognomon 30 27 810
DP 31.5 2 4358 Avicula 35 30 1050
DP 31.5 2 4228 Isognomon 40 30 1200
DP 31.5 2 4238 Isognomon 40 30 1200
DP 31.5 2 4153 Avicula 50 40 2000
DP 55 3 4719 Mysidiella 8 6 48
DP 55 3 4701 Liostrea 14 13 182
DP 43 4 4642 Gryphaea 7 6 42
DP 43 4 4554 Mysidioptera 11 5 55
DP 43 4 4678 Isognomon 10 9 90
DP 43 4 4652 Septifer 11 9 99
DP 43 4 4640 Avicula 12 9 108
DP 43 4 4606 Hoernesia 12 9 108
DP 43 4 4650 Mytilus 18 15 270
DP 43 4 4548 Isognomon 17 17 289
DP 53 5 5161 Isognomon 8 7 56
DP 54 6 4044 Dreissena 6 6 36
DP 54 6 4054 Isognomon 8 6 48
DP 54 6 3988 Dreissena 9 8 72
DP 54 6 4060 avicula 12 6 72
DP 54 6 3986 Isognomon 10 8 80
DP 54 6 4010 Avicula 10 9 90
DP 54 6 4030 Dreissena 15 12 180
DP 54 6 4092 Tirolidia 15 13 195
DP 54 6 4062 Mysidioptera 24 22 528
RSS-A 7 5042 Cassianella 5 3 15
RSS-A 7 4970 Mytilus 7 6 42
RSS-A 7 4932 Avicula 13 8 104
RSS-A 7 5032 Avicula 16 8 128
RSS-A 7 4946 Mytilus 14 12 168
RSS-A 7 4984 Mytilus 14 12 168
RSS-A 7 4946 Mytilus 18 11 198
RSS-A 7 4946 Mytilus 16 14 224
RSS-A 7 5095 Mod/Myt 19 16 304
RSS-A 7 4946 Mytilus 22 18 396
RSS-A 7 4954 Hoernesia 25 19 475
RSS-B 8 3794 Avicula 9 8 72
314
Appendix 7. Size data for non-oyster stationary epifauna from Nevada and Italy
7
RSS-B 8 3762 Cassianella 12 11 132
RSS-B 8 3728 Cassianella 14 12 168
RSS-B 8 3573 Cassianella 15 14 210
RSS-D 9 5171 Avicula 7 5 35
RSS-D 9 3845 Avicula 7 6 42
RSS-D 9 3840 Hoernesia 9 8 72
315
Appendix 8. Faunal occurrences (excluding singletons) from Tethys and Panthalassa with ranges ending in the Norian (orange)
or beginning in the Norian (blue)
Appendix 8. Faunal Occurrences (excluding singletons) with ranges ending in the Norian (orange)
or beginning in the Norian (blue).
Italy
1 2 3 4 5 6 7 8 9
Rhaetian
Occurrence
Bakevellia (King 1848) 5 23 1 1 3 yes
Modiolus (Lamarck 1799) 1 4 1 1 1 30 2 1
Pinna (Linnaeus 1758) 6 1 14 74 12
Megalodon (Agassiz 1843) 1 2
Avicula 9 19 3 8 2 4 7 2 3
Promysidiella (Waller and Stanley 2005) 7 9 no
Isognomon (Lightfoot 1786) 2 16 5 yes
Aguilerella (Chavan 1951) 1 8 2 yes?
Edentula=Waagenoperna 1 no
Retroceramus (Koschelkina 1958) 3 1 1 yes
Mysidioptera (Salomon 1895) 2 1 yes
Mytilus (Linnaeus 1758) 1 1 2 10 1 yes
Cassianella (Beyrich 1862) 1 1 1 2 yes
Pteria (Scopoli 1777)
Septifer (Récluz 1848) 2 1 yes?
Brachiopod 2 3
Hoernesia 1 yes
Gryphaea (Lamarck 1801) 1 1 yes
Plicatula (Lamarck 1801) 1 yes
Liostrea (DouvillŽ 1904) 1 yes
Thracia (Blainville 1824) 2 2 7 1 5
Gresslya (Agassiz 1843) 1 1 6 1 4
Myoconcha (Sowerby 1824) 1 3 yes
Pholadomya (Sowerby 1823) 1 yes
Unionites (Wissman 1841) 1 17 1 13
Anatina (Schumacher 1817) 0 2 yes
Costatoria = Myophoria 4 2 1 yes
Cucullaea (Lamarck 1801) 1 yes?
Myophoria (Bronn 1834) 1 yes
Myophoricardium (Wöhrmann 1889) 13 yes
316
Appendix 8. Faunal occurrences (excluding singletons) from Tethys and Panthalassa with ranges ending in the Norian (orange)
or beginning in the Norian (blue)
Myophoriopis (Wöhrmann 1889) 29 1
Neoschizodus (Giebel 1855)
Pachycardia 1 no
Rhaetidia 1 ?
Trigonodus 2 no
Unicardium (d'Orbigny 1850) 4 1 2
Unio (Philipsson 1788) 1 1 yes
Nucula (Lamarck 1799) 2 2 3 4 27 11 14
Nuculana (Link 1807) 1 1 11 14 8
palaeoneilo 1 1 14 3 1
Tancredia 1 yes
Schafhaeutlia 4 5 15
Macrodon = Parallelodon (Meek and Worthen 1866) 1 2
Hoferia (Bittner 1894) 3 no
Gastropod 1 8 8 5 2 2
26 101 19 33 15 34 203 127 84
Last Occ.s 1 2 3 3 0 7 5 6 0
Norian last occurrences with no Rhaetian occurrences (Italy)
1 2 3 4 5 6 7 8 9
Rhaetian
Occurrences?
Promysidiella (Waller and Stanley 2005) 7 9 no
Edentula=Waagenoperna 1 no
Pachycardia 1 no
Trigonodus 2 no
Hoferia (Bittner 1894) 3 no
317
Appendix 8. Faunal occurrences (excluding singletons) from Tethys and Panthalassa with ranges ending in the Norian (orange)
or beginning in the Norian (blue)
Nevada
1 2 3 4 5 6 7 8 9 10 11
Plicatula 2 75 21 16 1 3 8
Brachiopod 22 78 32 2 1 3 1 1
Tutcheria 2 1 19 11 12 19 26 10 7
Plectoconcha 4 85 4 no
Nucula 3 1 5 3 32 7 6 4
Gastropod 2 6 3 31 3 2 2 2
Chlamys 1 1 2 5 3 12 4 3 2 5
Frenguelliella 2 2 13 6 3 7
Mysidioptera 16 4 1 4 7
Pinna 1 1 1 1 17 4 4
Entolium 1 6 1 11 5 3 1
Lopha 4 20 yes
Modiolus 2 1 3 3 1 3 1 1 1
Oyster indet. 2 13
schafhaeutlia 1 1 3 2 3 1 2 1
Crinoid 1 10 2
Unionites 2 1 2 1 5 1 1
Isognomon 1 2 1 3 1 1 3
Ammonoid 2 1 3 1 3 1
Lima 1 3 2 4 1
Myophoria 1 1 3 4 1
Mytilus 1 2 5 2
Cassianella 1 1 1 1 1 3 1 yes
Gervillaria 1 5 1 1 yes
Nuculana 1 1 1 5 yes
cf. Plicatula 1 3 1 1 1
Eolimea 1 3 1 1 1
Camptonectes 4 2
Echinoid spine 1 1 1 1 1 1
Zeilleria 3 1 1 1 yes
cf. Lima 1 2 2
cf. Nucula 1 1 1 2
cf. Tutcheria 1 1 2 1
318
Appendix 8. Faunal occurrences (excluding singletons) from Tethys and Panthalassa with ranges ending in the Norian (orange)
or beginning in the Norian (blue)
Gruenewaldia 4 1
Gryphaea 2 2 1 yes
Myophoricardium 2 1 1 1 yes
Arcavicula 1 1 2 yes
Liostrea 1 1 1 1
Pseudolimea 2 2 yes
Rhaetavicula 2 1 1 yes
Septocardia 1 1 2 yes
Antiquillima 1 1 1 yes
Astarte 2 1 yes
Cardinioides 2 1
cf. Aulacoceras 2 1
cf. Chlamys 1 1 1
cf. Frenguelliella 1 1 1 yes
cf. Halobia 1 1 1 no?
cf. Isognomon 2 1
cf. Myophoria 1 1 1
cf. Mysidioptera 1 2
cf. Unionites 2 1
Gonodon 2 1 no
Hoernesia 1 1 1
Paralellodon 2 1 yes
Pecten 1 1 1 yes
Pteria 2 1 yes
Arca 2 yes
Arcoptera=Hoferia 1 1 no
Aulacoceras 1 1 no
Avicula 1 1 yes
Bakevellia 1 1 yes?
Cardinia 1 1
Cardita 2 yes
Cardium 1 1 yes
Catella 2 yes
cf. Arca 1 1 yes
cf. Entolium 1 1
cf. Gresslya 1 1 Italy
319
Appendix 8. Faunal occurrences (excluding singletons) from Tethys and Panthalassa with ranges ending in the Norian (orange)
or beginning in the Norian (blue)
cf. Isopristes 1 1
cf. Lopha 1 1 yes
cf. Megalodon 2 Italy
cf. Mytilus 1 1
cf. Pecten 1 1 yes
cf. Plectochoncha 2 no
cf. Zeilleria 1 1 yes
Cingentolium 1 1 yes
Cucullaea 2 yes
Gresslya 1 1 Italy
Limatula 2 yes
Meleagrinella 1 1 yes
Palaeocardita 1 1 1 1 yes
Protocardia 2 yes
Last Occ.s 0 0 5 2 2 1 1 7 6 17 11
Nevada Last Occurences
Plectoconcha 4 85 4 no
cf. Halobia 1 1 1 no?
Gonodon 2 1 no
Arcoptera=Hoferia 1 1 no
Aulacoceras 1 1 no
(minus singletons)
320
Abstract (if available)
Abstract
Shallow marine benthic animals underwent major paleoecological changes during the Norian Stage of the Late Triassic. This research identified these biological transitions by collecting several thousand macroinvertebrate fossils from sedimentary sequences representing two major oceanic realms in the Triassic: the Tethys Sea and Panthalassa. The faunal turnovers were correlated with a combination of chronostratigraphic methods, including strontium isotope chemostratigraphy. Among shelly invertebrates, stationary surface-dwellers that were ecologically dominant in the Early Norian were replaced in multiple phases by animals that were facultatively mobile, or capable of burrowing into the sediment, or cemented to the seafloor. These transitions coincided with taxonomic radiations of predators that were specialized for durophagy in shallow marine environments. The synchronous appearance of morphological features and behaviors related to benthic durophagy among multiple clades of predators and prey suggest the Norian Stage was a non‐static interval in which evolutionary and geological forcers operated at a global scale to reorganize shallow marine ecosystems.
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Asset Metadata
Creator
Tackett, Lydia S.
(author)
Core Title
Benthic paleoecology and macroevolution during the Norian Stage of the Late Triassic
School
College of Letters, Arts and Sciences
Degree
Doctor of Philosophy
Degree Program
Geological Sciences
Publication Date
04/30/2014
Defense Date
04/30/2014
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
chemostratigraphy,escalation,Evolution,invertebrates,macroevolution,Manicouagan,mass extinction,Mesozoic,Mesozoic marine revolution,Norian,OAI-PMH Harvest,paleoecology,paleontology,Panthalassa,predation,predator‐prey interactions,strontium,Tethys,Triassic
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
Lydia.Tackett@gmail.com,tackett@usc.edu
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c3-409452
Unique identifier
UC11296417
Identifier
etd-TackettLyd-2479.pdf (filename),usctheses-c3-409452 (legacy record id)
Legacy Identifier
etd-TackettLyd-2479.pdf
Dmrecord
409452
Document Type
Dissertation
Format
application/pdf (imt)
Rights
Tackett, Lydia S.
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
chemostratigraphy
escalation
invertebrates
macroevolution
Manicouagan
mass extinction
Mesozoic
Mesozoic marine revolution
Norian
paleoecology
paleontology
Panthalassa
predation
predator‐prey interactions
strontium
Tethys
Triassic