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Large epifaunal bivalves from Mesozoic buildups of western North America

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Large epifaunal bivalves from Mesozoic buildups of western North America

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Content s INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter free, while others may be from any type o f computer printer. The quality of this reproduction is dependent apon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, pri nt bleedthrough, substandard margins, a n d improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript a n d there are missing pages, these will be noted. Also, if unauthorized copyright material h a d to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the up pe r left-hand comer and continuing from left to right in equal sections with small overlaps. 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LARGE EPIFAUNAL BIVALVES FROM MESOZOIC BUILDUPS OF WESTERN NORTH AMERICA Nicole M arie Fraser f. jj __________________ A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA f In Partial Fulfillment of the y Requirements for the Degree MASTER OF SCIENCE (Earth Sciences) August, 1997 Copyright 1997 Nicole Fraser Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1387819 r UMI Microform 1387819 Copyright 1998, by UMI Company. All rights reserved. j This microform edition is protected against unauthorized v copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UNIVERSITY O F S O U T H E R N C A L IF O R N IA THC SRAOUATC SCHOOL. UNIVERSITY PARK LOS ANCCLCS. CALIFORNIA S 0 0 0 7 This thesis, written by Nicole Marie Fraser_________________ under the direction of hSS. Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of Tint* July 15, 1997 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. u ACKNOWLEDGEMENTS This project thus far has gone through three phases: inspiration, field work, and writing. And will continue with the aid of many people. Foremost is Dr. David J. Bottjer, who not only took me in to his lab but took the time to help me find a project that would interest both him and me. Dr. Alfred G. Fischer has offered a tremendous am ount of information and inspiration. Three years ago, Dr. Donn S. Gorsline gave me the opportunity to come to USC and much more. More than a committee, they have also w ritten many letters to send me far away. This project could not have been completed w ithout the patience of my field assistants: Ross Hartleb, Deanna Major, Stephen Schellenberg and Carol Tang. Dr. George Stanley, Jr., of the University of Montana was kind enough ‘ to take me on a personalized tour of his Eastern Oregon Upper Triassic sites, f Access to field sites on private land was granted by Don Jung of New 1 Pass Mine, John and Mary Magoffin of Mexican Saddleback Ranch, and the r operators of Paul Spur Quarry. Other assistance for field site location and I collection permits came from the staff of the Wallowa-Whitman National | Forest headquarters in Baker, Oregon, specifically Dr. John T. McDonald, | forest archaeologist. * Assistance w ith the statistics was graciously donated by Dr. Loren | Smith (Department of Biology, U.S.C.) and Dr. Ann Pufall (Departments of Psychology and Mathematics, Smith College). Drs. Adolf Seilacher, Tom f Yancey, Alan Kohn discussed w ith me the wonders of abberant bivalves. Assistance during writing was given by Pat and Jack Fraser and Stephen * ! Schellenberg (drafting/graphics, reassurance, and references). Computer f facilities were loaned by the Southeast Asian Studies Institute of Arizona T State University, Tempe. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This project was supported by the Graduate Student Research Fund of the Department of Earth Sciences and the Trojan League of the Hancock Institute for Marine Sciences, both at the University of Southern California. Continuation of this research has been prom ised by the Libby Hyman Research Fund, Henry Luce Foundation and the Paleontological Society. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. f iv TABLE OF CONTENTS Acknowledgements................................................................................................. ii List of Figures........................................................................................................... vi List of Tables-----------------------------------------------------------------------------------ix Abstract............................................ x Chapter 1 - Introduction...........................................................................................1 General Statem ent------------------------------------------ 1 Reef and Bioherm Terminology.........................................................................2 Role of N utrients in M odem Carbonate Buildups...........................................7 Modem Carbonate Buildups and Nutrient-Level C hanges..........................10 Overview o f Mesozoic Climate and Ocean Systems...................................... 12 Mesozoic Clim ates......................................................................................... 12 1. Triassic .................................................................... 13 2. Jurassic.................................................................................................... 15 3. Cretaceous...............................................................................................15 Mesozoic Paleoceanography.........................................................................17 [ Mesozoic Tectonics and Paleogeography.................................................... 19 : Mesozoic Carbonate Buildups...................................................................... 25 I 1. Triassic.................................................................................................... 25 1 2. Jurassic.................................................................................................... 27 | 3. Cretaceous.............................................................................................. 28 I Bivalves in Modem Carbonate Buildups...................................................29 Photosymbiosis in M odem Bivalves.......................................................... 31 Focus of This Study........................................................................................32 Chapter 2 - Stratigraphy and Sedimentology of Studied Buildups...................34 Site #1 - N ew Pass Mine, N ew Pass Range, N evada......................................34 Site #2 - Mina, N evada...................................................................................... 38 Site #3 - Summit Point, Wallowa M ountains, Oregon................................. 42 1 Site #4 - Black Marble Q uarry, Wallowa Mountains, Oregon....................... 46 ? Site #5 - A nt M il Bioherm, Suplee-Izee, Oregon............................................ 49 I Site #6 - N orth and South Paul Spur Reefs, Bisbee, Arizona....................... 52 I Site #7 - Mexican Saddleback, Huachuca Mountains, Douglas, A rizona... 55 | Chapter 3 - Functional Morphology...................................................................... 59 | Introduction to Bivalvia..................................................................................... 59 { Recognition of Life and Trophic Mode in Fossil Bivalves............................ 61 ! History of Bivalvia in Carbonate Buildups..................................................... 65 • Methods............................................................................................................... 68 ! Results................................................................................................................. 69 Upper Triassic - Megalodonts.......................................................................71 Lower Jurassic -Lithiotids............................................................................. 78 Lower Cretaceous -R udists......................................................................... 82 Lower Cretaceous - Chondrodontids.......................................................... 92 Discussion............................................................................................................94 Guild Assignment..........................................................................................94 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Trophic Mode - Filter Feeders o r Photosymbiosis.................................... 96 Probable N utrient Regime...........................................................................98 Chapter 4 - Cluster Analysis--------------------------------------------------- 100 General Statement---------------------------------------------------------------------100 Taphonomy and Community- Preservation.................................................102 Methods.............................................................................................................105 1 -Data Transformations................................... 107 2 -D istances................................................................................................. 110 3 -Cluster Methods...................................................................................... 112 4 -Two-way Cluster Analysis..................................................................... 116 Discussion.........................................................................................................124 Upper Triassic Bioherms............................................................................124 Lower Cretaceous Reefs..............................................................................125 Conclusions--------------------------------------------------------------------- 126 Chapter 5 - Conclusions........................................................................................ 128 Sum m ary-------------------------------------------------------- 128 > Future research.................................................................................................130 | References............................................................................................................... 133 Appendix I - Raw line-intercept data converted to abundance data................149 Appendix U - O uster dendograms generated using methods other than the UPGMA method disscussed in Chapter 4............................................... 152 y f I i Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V I LIST OF FIGURES Figure 1. Schematic diagram of Fagerstrom's (1987) reef guilds assignm ents and relative roles......................................................................................................4 Figure 2. Summary diagram of Triassic global climates, hypothesized paleoceanography and reef/biostrom e occurrence.............................................. 14 Figure 3. Summary diagram of Jurassic global climates, hypothesized paleoceanography and reef/biostrom e occurrence.............................................. 16 Figure 4. Summary diagram of Early Cretaceous global climates, hypothesized paleoceanography and reef/biostrom e occurrence.............................................. 18 Figure 5. Hypothetical reconstruction of Triassic W estern North America and off-shore elements w ith the current state boundaries of Nevada given as a reference from paleomagnetic data....................................................................... 21 ; Figure 6. Hypothetical reconstruction of Early Jurassic Western N orth America and off-shore elements with the current state boundaries of N evada | given as a reference for the paleogeographic position......................................... 23 | Figure 7. Hypothetical reconstruction of Early Cretaceous Western N orth America and off-shore elements with the current state boundaries of A rizona given as a reference from paleomagnetic data.....................................................24 Figure 8. Diagrams of the nine large Mesozoic buildup epifaunal bivalves....30 Figure 9. Locality map of studied sites..................................................................36 Figure 10. A - Locality map for New Pass Mine, NV. B - Photograph of New Pass Mine looking North across South Canyon.................................................. 37 Figure 11. Stratigraphic section of Augusta Formation (Ladinian), South Canyon, New Pass Mine, NV................................................................................ 39 Figure 12. A - Locality map for Mina, NV. B - Photograph of Cinnabar Canyon looking west, the biostrome is below the tree (-4 feet tall)................. 40 Figure 13. Stratigraphic section of Luning Formation (Norian), Dunlop Canyon, Mina, NV................................................................................................. 41 Figure 14. A - Locality map for Summit Point Reef, OR. B - Photograph of Summit Point from a logging road at the southern section of the reef 43 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vu Figure 15. Stratigraphic section of Summit Point Reef, M artin Bridge Formation (Upper Triassic), OR............................................................................ .45 Figure 16. A - Locality map for Black Marble Quarry, OR. B - Photograph of Black Marble Quarry................................................................................................47 Figure 17. Stratigraphic section of M artin Bridge Formation (?) (Upper Triassic, Black Marble Quarry, OR..........................................................................48 Figure 18. A- Locality m ap for Ant H ill Bioherm, OR. B - Photograph of A nt Hill Bioherm.............................................................................................................50 Figure 19. Stratigraphic section of A nt Hill Bioherm, Robertson Form ation (Lower Jurassic), Suplee-Izee, OR...........................................................................51 Figure 20. A - Locality m ap for Paul Spur Reef, AZ. B - Photograph of N orth Paul Spur Reef from US 80 looking north............................................................53 Figure 21. Stratigraphic section of N orth and South Paul Spur Reef, Upper Mural Limestone (Lower Cretaceous), A Z ...........................................................54 Figure 22. A - Locality m ap for Mexican Saddleback Reef, AZ. B - Photograph of Mexican Saddleback Reef looking to the east, the ridge in the center of the photo is approximately 17 m tall........................................................................... 56 Figure 23. Stratigraphic section of Mexican Saddleback Reef, Upper M ural | Limestone (Lower Cretaceous), A Z........................................................................58 J . Figure 24. Cerastoma edule........................................................................................62 | Figure 25. Megalodon.................................................................................................72 I Figure 26. Neomegalodon.......................................................................................... 74 Figure 27. Wallowaconchid.................................................................................... 76 Figure 28. Lithiotis problematica..............................................................................79 Figure 29. Lithiotis problematica in the field......................................................... 81 Figure 30. Monopleura cf. M. Marcida....................................................................84 Figure 31. Petalodontia felixi....................................................................................86 Figure 32. Coalocomana ramosa............................................................................... 89 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. t \ vm Figure 33. Caprinuloidea gracilis..............................................................................91 Figure 34. Chondrodonta chondrodonta..................................................................93 Figure 35. Modem coral reef (coastal Yucatan) R-mode dendogram from Warme et al (1976), taxa are not included in the diagram but the com m unities cluster at relatively low distances when compared to oyster reefs..................101 Figure 36. UPGMA Q-mode dendogram of Bahr's (1976) data set for a m odern oyster reef near Sapelo Island, Georgia............................................................... 103 Figure 37. UPGMA Q-mode dendogram of Ant Hill Bioherm.......................106 Figure 38. Distance calculation for hypothetical ecosystem consisting of taxa A, B, and C.................................................................................................................. I l l Fiugre 39. UPGMA (Unweighted Pairgroup Method) dendogram of Upper Triassic buildups.................................................................................................... 117 Figure 40. UPGMA (Unweighted Pairgroup Method) dendogram of Lower Cretaceous buildups.............................................................................................. 118 Figure 41. UPGMA Q-mode cluster dendogram of Upper Triassic (Camian- Norian) buildups from New Pass Mine, Augusta Form ation (NPM cases) and Dunlop Canyon, Luning Formation (DC cases)................................................. 120 Figure 42. UPGMA Q-mode cluster dendogram of Aptian-Albian buildups from Mexican Saddleback (MS cases) and Paul Spur (PS) of the M ural Limestone................................................................................................................121 Figure 43. Two-way UPGMA cluster dendogram of Upper Triassic (Camian- Norian) buildups from New Pass Mine, Augusta Form ation (NPM cases) and Dunlop Canyon, Luning Formation (DC cases)................................................ 122 Figure 44. Two-way UPGMA cluster cluster dendogram of Aptian-Albian buildups from Mexican Saddleback (MS cases) and Paul Spur (PS) of the Mural Limestone....................................................................................................123 Figure 45. Summary figure of the relative guilds and nutrient levels of large epifaunal buildup bivalves from the Mesozoic and m odern environments..........................................................................................................129 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IX LIST OF TABLES Table 1. Criteria for guild assignment of reef-building organisms (excluding destroyer and dweller guilds) from both modem and ancient communities....6 Table 2. Various biological, physical and chemical factors associated with nutrient conditions...................................................................................................8 Table 3. Summary description of field sites......................................................... 35 Table 4. Summary chart of bivalve features........................................................ 70 Table 5. Summary chart of studied epifaunal reef bivalve ecology...................95 Table 6. Descriptive statistics on the various transform s of the Upper Triassic bioherm data..........................................................................................................108 Table 7. Descriptive statistics on the various transforms of the Lower Cretaceous bioherm data...................................................................................... 109 1 Table 8. A - Tables of distances converted to sim ilarities for the original | arcsine transform ed Upper Triassic bioherms and the similarities generated [ by the Euclidean distance measurement. B - Com parison of various distance * m easurem ents to the original data set via Pearson coefficient for Upper Triassic bioherm data............................................................................................113 Table 9. A - Tables of distances converted to sim ilarities for the original arcsine transform ed Lower Cretaceous bioherms and the sim ilarities generated by the Euclidean distance measurem ent. B - Comparison of various distance measurements to the original data set via Pearson coefficient for Lower Cretaceous bioherm data.....................................................................114 i I Table 10. Tables of distances converted to sim ilarities for the original arcsine transform ed U pper Triassic bioherm data set and the similarities generated by the various cluster methods discussed in the text............................................. 119 Table 11. Tables of distances converted to sim ilarities for the original arcsine transform ed Lower Cretaceous bioherm data set and the sim ilarities generated by the various cluster methods discussed in the text...................... 119 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT x Seven Mesozoic carbonate buildups of Western N orth America were investigated to determine the potential role of large epifaunal bivalves as indicators of nutrient levels in various buildup paleocommunities. These Mesozoic buildups differ from modem buildups in having a relatively increased number of large epifaunal bivalves but a decreased biovolume of sderactinian corals. These differences may be potentially attributed to one of two hypotheses: (1) these buildups all occurred in oligotrophic environments and the bivalves had adapted to such an environment via the acquisition of photosymbionts; or (2) the Mesozoic was a time of unique paleoceanographic and tectonic conditions allowing the expansion of large epifaunal filter- feeding bivalves into environments that lack modem analogs. Nine large Mesozoic epifaunal bivalves were studied: Megalodon, Neomegalodon, w allow aconchids, Lithiotis, Monopleura, Petalodontia, Coalocomana, Caprinuloidea and Chodrodonta. Six morphological features (hinge, ligament, valve shape, shell mineralogy, prim ary porosity and ornamentation) and three autecologic features (attachment to substrate, packing and pseudocoloniality) were examined. Of the above bivalves only wallowaconchids. Monopleura and Caprinuloidea showed possible adaptations for photosymbionts in an oligotrophic/m esotrophic setting. Only Lithiotis was conclusively characterized as an organism living in a strongly eutrophic environment. All the others w ere most likely filter-feeding bivalves in areas of mixed to low levels of nutrients. Cluster analysis of transect data delineated paleocommunities that had been qualitatively defined by previous workers [Stanley (1977) and Cornwall Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (1979) for Upper Triassic buildups; Hartshorn (1989) and Scott (1979) for the Lower Cretaceous]. The differences between the well-defined paleocommunities of the Lower Cretaceous and the relatively less well- defined U pper Triassic paleocommunities were attributed to differences in paleocommunity organization possibly in response to varying nutrient regimes. The Upper Triassic buildups may exhibit reduced paleocommunity delineation because without a constant oligotrophic setting they lacked the constant background selection pressure for niche specialization, when compared to studied Lower Cretaceous paleocommunities. However, the degree of boring and algal growth in both buildup regimes suggest nutrient levels greater than those found in modem oligotrophic settings. i I \ i I \ I i r Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. f 1 INTRODUCTION General. Statement Modem and fossil reefs, as "sensitive" ecosystems, are used to monitor the effects of global warming , anthropogenic influences in the marine realm and the severity of mass extincitons (Smith and Buddmeier, 1992; Copper, 1994; Droser et al. 1997). Because in modem reefs filter-feeding bivalves are used as a barometer of ecosystem health and nutrient regime, they are of particular importance (Widdows and Donkin, 1992; Tripp and Farrington, 1985). The fossil record of reef bivalves may be used as a tool to define changes in paleoceanographic and paleoclimatic conditions affecting reef developm ent through geologic time. The Mesozoic is a particularly apt choice for such a study because much is known of its climate, and several end-member buildups, from those found in oligotrophic to eutrophic conditions, may be observed. Mesozoic reefs differ from m odem reefs in two fundamental respects: (1) the suppressed role/biovolum e of sderactinian corals; and (2) increased presence of large epifaunal bivalves (Fagerstrom, 1987; Scott, 1995). In order to understand the evolution of reefs it is necessary to understand the relative roles of these large epifaunal Mesozoic bivalves and whether their presence is a result of: (1) evolutionary innovations leading to photosymbiosis w hile in an oligotrophic regime sim ilar to m odem reefs (Johnson et al. 1996); or (2) the maintenance of the filter-feeding life mode while in a eutrophic regime, which presumably would have excluded, sderactinian corals, unique to Mesozoic carbonate platform s. To initiate a test of these competing hypotheses (photosymbiosis or eutrophication) for the presence of these large epifaunal reef bivalves, a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. survey of Mesozoic reefs and bioherms in the W estern North American Cordillera was undertaken. The survey involved of three steps. First, the recognition of various types of bioherms and possible indicators of paleonutrient level. Second, an analysis of the large epifaunal bivalves to determine which if any were likely candidates for photosymbiosis. Last, community level associations were determined by cluster analysis to compare Late Triassic reefs to those of the Early Cretaceous. The purpose of this chapter is to introduce modem and Mesozoic buildups and the factors that controlled their distribution and the relative role of bivalves in carbonate buildups. The terminology and the role that nutrients play in m odem reefs is examined. The setting of Mesozoic 1 carbonate platforms is complicated by the differences in climate, oceanography, tectonics and fauna from that of m odem carbonate platforms. i | Reef and Bioherm Terminology ! M odem "reef" definitions are self-evident as most authors are familar 1 | with the classic m odem reef localities (e.g. The Great Barrier Reef of i Australia). Holocene reefs are typically comprised of a rigid framework j (usually sderactinian corals), whose skeletons are large, colonial, or | gregarious, intergrown with rapid calcification rates (James and Borque, 1992). | M odem reefs have positive topographic relief and high spedes diversity | (Longman, 1981). The definitions of ancient reefs are more murky. Kauffman and Johnson (1993) use the term "reef framework" for assemblages of 50% or more biogenic grains w ith other sediment; and reefs, for them, consist of elevator organisms in direct contact w ith each other and having about 2% sediment. Gili et al. (1995a) emphasize that true reefs have Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I 3 superstratal fabrics in which the organisms grow above the substrate in a framework that has relief above the sediment surface. For the purpose of this paper, a reef is a "biologically influenced buildup of carbonate sediment which affected deposition in adjacent areas..., and stood topographically higher than surrounding sediments during deposition..." (Longman, 1981). Most recent reef workers avoid the problem of reef definitions altogether. Two terms, bioherms and biostromes, are commonly used to designate biogenically-constructed stratigraphic structures. A bioherm is a lens-shaped reef or mound-shaped carbonate buildup enclosed by sediments of different lithology and composed mostly of the skeletal remains of in situ organisms and syndepositional cements (Cumings, 1932). A biostrome is a laterally extensive, bedded blanket-like carbonate body composed mostly of the skeletal remains of organisms and syndepositional cements (Kershaw, 1994). Biostromes may have constratal fabrics w ith the organisms embedded in and supported by the sediment, but traditionally they do not normally have significant topographic relief to influence sedimentation (Scott, 1995). Another commonly used generic term with no compositional, size or shape connotation is carbonate buildup (Ross and Skelton, 1993). | Fagerstrom (1987) delineated five guilds (major functional units) of Cenozoic reefs: constructors, binders, bafflers, dwellers and destroyers (Fig. 1). t f I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Constructor Baffler O® (encruster) Cementation, compaction Fossil Reef O ia g e n e s js l Community U ^ ? en e s i s Baffler Cementation, etc Death Dweller (grazers; nestlers) Destroyer (borers; raspers) i \ i ] Figure 1. Schematic diagram of Fagerstrom’ s (1987) reef guild assignments and relative roles. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. O Guild membership is partly based on functional morphology, skeletal arrangement and life habit: The upw ard grow th of the constructors provides most of the skeletal volum e and rigidity of the reef. The bafflers slow down the velocities of currents crossing the reef surface, and the lateral growth of the binders unifies and consolidates the framework and the internal sediment. The members of the destroyer guild break dow n the framework, and the dwellers are passive (neither build nor destroy the framework). - Fagerstrom (1987, p. 197) This definition of m odem reef guilds has several teleological aspects (i.e., the organisms are desirous of filling their roles as reef constituents and adapt accordingly; see Sheehan, 1988 for caveats). However, the reef guild concept is ^ generally valid for ancient carbonate buildups with few modifications: j compensation for ancient reef organism s without m odem analogs and guild overlap. Table 1 displays modifications of Fagerstrom's (1991) guild revision . to include organism s that construct, bind, baffle etc., in ancient buildups w ithout the stereotypic modem archetype (i.e. colonial, sderactinian, photosymbiodc). One speties m ay inhabit multiple guilds ("guild overlap"). For example, the herm atypic coral Montastraea annularis in very shallow t | w ater has a dom inant upward grow th habit making it a "constructor." 1 However, in deeper w aters near it's physiological lim its, the organism has a | dom inant lateral grow th habit across sands, making it a "binder" (Fagerstrom, f 1991). * When com paring ancient reefs to one another, criteria extend beyond simple faunal lists. Scott (1995) outlines six properties of carbonate buildups for comparison: (1) framework fabric consisting of attachm ent mode, morphotypes and proxim ity of skeletons; (2) taxonomic composition; (3) abundance patterns of the biota; (4) diversity of speries; (5) guild Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Criteria Pafftec Binder 1 Habit growth habit; growth direction Upwards, erect Upwards, erect Lateral, reptant (i.e. recumbent) 2 Life-form; growth form; form massive; domes; branches; cups; columns Cylinders; cones, blades Sheets; lenses; runners; webs; plates; umbrellas 3 Skeletonization; skeletal strength and rigidity Well-skeletonized; strong; rigid Poorly skeletonized mostly as skeletal fragments Well-skeletonized 4 Skeletal volume; coloniality 5 Biostratinonomy; taphonmy; transportability 6 Skeletal packing density Large; colonial or gregarious In growth position or in situ (toppled; broken) As in life or less dense Smaller; solitary or colonial In situ (toppled; broken); commonly transported Highly variable from dispered to concentrated Medium size; colonial or gregarious In growth position; encrust; roof-over or trap sediment As in life Table 1. Criteria for guild asignment of reef-building organisms (excluding destroyer and dweller guilds) from both m odem and ancient communities. Fagerstrom (1991) arranged the criteria from most important (1) to least (6). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. representation; and (6) feeding habit-substrate relations. All of these properties are susceptible to environmental influence. Climate exerts an im portant role on m odem buildups, influencing a variety of factors: (1) am ount and composition of fresh water runoff and terriginous input; (2) storm frequency and resultant biological and sedimentological stresses; (3) upwelling and associated nutrient and therm al fluxes; and (4) salinity fluctuations. As climate has changed throughout the Phanerozoic, so has the biota. For example, modem sderactinian corals acquired photosymbionts in the Late Triassic, forever changing the complexion of reef construction (Stanley and Swart, 1995). Therefore, the history of reefs is the commingling of these two factors: evolutionary innovation or demise and climatic change. 0 i Role of N utrients in Modem Carbonate Buildups [ M odem coral reefs and their associated fauna have puzzled both biologists and geologists as they are anomalous in the history of carbonate buildups, a by-product of the current vigorous ocean mixing. Reefs are regarded as one of the most highly productive types of ecosystems. Yet their high productivity, constructional and calcium carbonate deposition rates, by definition, are largely independent of the productivity and nutrient supply in the surrounding oceanic waters (Hallock and Schlager, 1986). Increasingly it is recognized that nutrient-levels and related turbidity, not temperature, determ ine the distribution and complexion of modem reefs (Wood, 1993). Therefore, m odem buildups may be classified according to nutrient regime: oligotrophic (<1jiM dissolved inorganic nitrate), mesotrophic (>1 - < 10 gM) and eutrophic (>10 nM)(Wood 1993). Table 2 summarizes the characteristics of these buildups in these various regimes. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. with permission o f th e copyright owner. Further reproduction prohibited without permission. CD ■ o - 5 O Q. Q. Nutrient Condition Water clarity/color/sediments Ecosystem characteristics Dominant biota characteristics Associated sediments Modern settings Oligotrophic • high clarity • long, complex food chains • K-strategy • oolitic limestones • reefs of tire Ked Sea • blue color • high biodiversity • large body size, slow growth • shelly-bcnthic limestone • atolls of the southwest Pacific • low turbidity and sediment input • low bioerosion • stable populations • often colonial • auto/mixotrophs>helerutrophs • framework limestones Mesotrophic • mixed clarity • long complex food chains • mixed strategies • mud mounds • Adriatic Sea • mixed color • medium to low biodiversity • curylopic • heterotrophic bafflestones • Coastal communities of Vietnam • sporadic/seasonal sediment input or constant low levels of turbidity • medium bioerosion levels • unstable populations • hclerolorphsK mixo/autotrophs • Kanehoehoe Bay Eutrophic • low clarity • short, simple food chains • r-stratcgy • dolostones • Upwelling areas of the west coasts of Suuth America and Africa • green color • low diversity • small body sizes, rapid growth • black shales • red tides common • intense bioerosion • solitary unstable populations • diatomiles, etc. • high turbidity and sediment input • heterotrophs»auto/mixotrophs ' Table 2. Various biological, physical and chemical factors associated with nutrient conditions. Compiled from Wood (1993), Braiser (1995); and Hallock and Schlager (1986). 00 t I 9 Oligotrophic environments are recognized by high diversity, high w ater clarity, high carbonate production and low net productivity (Hallock and Schlager, 1986; Hallock, 1988). Ecosystems adapted to these "blue water" conditions are characterized by the m odem large colonial sderactinian coral reefs found in the Caribbean, Indian and Central Pacific Oceans. Organisms from "blue water" ecosystems are well adapted to low levels of nutrients; m any are phototrophs or mixotrophs (Coates and Jackson, 1987). For example, sderactinian corals and the large epifaunal bivalve Tridacna harbor dinoflagellates in their soft tissues that act as photosymbionts (Yonge, 1936). In such environments, after mixotrophic sderactinian corals, filter feeders are second in benthic biovolume (Dubinsky, 1990). Oligotrophic environments \ tend to be phosphate-limited, because the nitrogen budget is subsidized by C nitrogen-fixing bacteria and cyanobacteria on the reef (Braiser, 1995). Rates of nitrogen fixation in coral reefs are 250 times greater than those in other phosphate-limited ecosystems such as lakes (Capone and Carpenter, 1982). I The high diversity of coral reefs in oligotrophic waters (e.g. central Pacific atolls) is often used as the paradigm for all reefs (e.g. James and Bourque, 1992). However, reefs situated in mesotrophic and even in ’ eutrophic waters, such as those off the coasts of Australia, the Bay of Siam t (Nam su Islands) or of central Vietnam, have prim ary phytoplankton I production one to two orders of m agnitude greater than those in oligotrophic [ w aters (Kreypas, 1996; Sorokin, 1990). The reefs in these diverse conditions : have high levels of primary production (up to 10-15 g C m ^ d a y 1 ; Dubinsky, 1990) and the necessary relief for "reef ’ dassification. However, biota between oligotrophic and eutrophic reefs varies w ith increasing nutrient input. In particular, filter feeding organisms (sponges, polychaetes, bivalves, corals) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i i 10 predominate among the bottom fauna of eutrophic and mesotrophic reefs (Wood, 1993). These "green w ater," nitrate-limited, environments are found today in areas of upwelling on the west coasts of Africa and South America (Braiser, 1995). Most "reef" workers focus on Holocene sderactinian framework, high- diversity reefs whereas low diversity "green water" bivalve reefs are frequently overlooked. Low diversity oyster reefs made by accumulations of Crassostrea virginica are common in the brackish water tidal channels and bays of the Texas-Florida coasts (Norris, 1953; Shier, 1981; Stenzel, 1971). The largest of these oyster-shell frameworks are elongate parallel to the channels and have linear dimensions of 8-10 km, widths up to 150 m and are as much h * | as 4 m thick w ith well-defined steep margins (Stenzel, 1971). Therefore, these s . reefs contain the requisite superstratal topographic relief for reef definition. M ost of these structures occur at depths from the low tide line to 2 m. Bioherms of Ostrea edulis have been described in the N orth Sea at depths of * i - 23-28 m in alm ost normal marine salinity (Caspers, 1950). i t M odem Carbonate Buildups and Nutrient-Level Changes Increased nutrient levels or eutrophication afreets the physical environment by decreasing w ater clarity, increasing the sedimentation rate and destabilizing oxygen levels and pH (Braiser, 1995). M odem coral reef workers have noted that nutrients appear to be the controlling factor of reef | faunal development by changing phytoplankton and macrofauna distributions, predation, and herbivory, which all influence the reef community structure (Margalef, 1968). Small increases in the nutrient flux in an oligotrophic environment result in very small changes in sderactinian Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 coral populations- Scleractinian corals are effectively nutrient-independent and will respond modestly to slight increases in nutrients (Hallock, 1988). To test the effects of large increases in nutrient flux, modem reef workers have documented eutrophication and resulting community shifts from "natural experiments" of the effects of sewage pollution on reefs (e.g. Kaneohe Bay, northeast coast of Oahu; Grigg, 1992). To date, m ost of the sewage-related effects on coral reefs have been the result of stim ulatory (nutrient subsidy), rather than the inhibitory (toxic), nature of sewage effluent (Dunn, 1995). hi general, detrimental effects of phosphate subsidy appear to be caused by shifts in competitive advantage toward species that out-compete scleractinian corals. Using a variety of treated effluents, Marsalak (1981) found that the most pronounced effects on coral morbidity and m ortality were not directly related to effluent toxicity, but were the result of competition with algae for space and light. At Kaneohe Bay during the peak sewage discharge, no corals were observed in the south bay, possibly the result of anaerobic conditions in the sediments leading to release of hydrogen sulfide (Grigg, 1992). Sewage nutrients supported extremely dense growth of the "green bubble algae," Dictyosphaeria cavemose, which sm othered much of the reef corals and associated oligotrophic fauna. A t another site on Oahu, Grigg (1992) implicated sewage as the cause of a community shift from zooxanthellate corals to the arenaceous polychaete, Chaetopterus. Highsmith (1980) documented an increase in boring activity and herbivory of gastropods on and in corals of Panamanian reefs w ith increasing nutrient input. The result of these dramatic shifts in the physical environment via nutrient input is that "blue water" mixotroph scleractinian corals are often out-competed by "green water" heterotroph worms and molluscs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 i 1 ) 12 Overview of Mesozoic Climate and Ocean Systems As mentioned above, the properties of carbonate buildups are controlled by environmental factors: climate, oceanography and tectonics. These systems are summarized for the Late Triassic, Early Jurassic and Early Cretaceous in Figures 2-7. Mesozoic Climates Hallam’ s (1985) review of Mesozoic climates describes the Mesozoic as more equable than today w ith reduced polar-equator temperature gradients, higher sea-levels and few or no ice caps. An abundance of evidence testifies i * * to warm conditions and the general absence of indicators of cold climates \ gam ers further support for climates to be warmer than present. Geochemical |r evidence suggests that at least in the m iddle latitudes conditions were warm er than present climatic conditions (as outlined below), while in latitudes from 50° to 70° rainfall appears to have been very abundant (Frakes et al., 1992). The extensive formation of low latitude evaporite deposits implies strong poleward transport of heat in the atmosphere via the mechanism of latent heat of evaporation. This in turn suggests that Mesozoic I atmospheric and oceanic circulation patterns differed markedly from those of i the present. The reduction of temperature gradients probably reduced stability of the water column (Hallock and Schlager, 1988). Salinity differences may have compensated for the lack of a temperature-driven gradient. * Temperature differences dominate ocean circulations except in closed and semi-closed basins (Berger, 1982). For example, the M editerranean today has haline-driven circulation and is more prone to overturn (Berger, 1982). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i 13 If the Mesozoic had thermo-haline driven circulation as proposed by Hallock and Schlager (1988) the resulting warm , saline bottom waters and cool, fresh surface waters were less stable and more prone to overturn than temperature-dominated stratification in m odem oceans (Berger, 1982). Low levels of Mesozoic continental glaciation anywhere on the globe are inferred from the lack of glacially-deposited rocks (the exception is some recently interpreted mid-Cretaceous ice-rafted deposits; Frakes et al., 1992). Mesozoic thermal shifts may be summarized by strong warming in the Middle Triassic from the cooler Permian climates, increased warming in the Late Jurassic and finally cooling in the Late Cretaceous (Frakes, 1986). 1. Triassic - Global Triassic climates are dom inated by the effects of low sea level and the formation of the greatest volum e of m arine evaporites recorded for any geologic period (Stanley, 1988). The Dominion Coal Measures accumulated at about 65° paleolatitude in Antarctica, signifying high latitude humidity, and, therefore, seasonal climates persisted in the high latitudes (Frakes, et al. 1992). The tem perate and tropical zones of the Late Triassic were characterized by dry-climates reaching 50° latitude and regional monsoonal settings in the eastern Tethys (Fig. 2). The Triassic climate of Western N orth America falls into this arid zone w ith relatively low hum idity exemplified in this study by the shallow Star Peak/Luning Basin and the associated formations of the New Pass Mountains in Nevada (see following sections). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. eh Seasonally Wet Figure 2. Summary diagram of Triassic global climates, hypothesized paleoceanography and reef/biostrome occurrence. Distribution of Late Triassic reefs are represented by closed circles and without regard for possible suspect terrance displacement. Adapted from Fliigel and Fliigel-Kahler (1994), paleogeographic reconstruction from Smith et al, 1994, reconstruction of Late Triassic continental humid and arid belts from Hallam (1985), and paleoceanographic reconstruction from Stanley (1988). 15 2. Jurassic -A wealth of oxygen isotope determinations is available for the Jurassic period that is just now coining under scrutiny for as a basis the possibility of diagenetic alteration in the molluscs used (e.g. Gryphaea). On global data summarized by Frakes et aL, (1992; Fig. 3), Jurassic and Early Cretaceous paleotemperatures range from about 10°-25°C, but should however be taken as maximum temperatures since diagenetic alteration often lowers 51 8 0 values. The data also show great variability of temperature relative to geographic location and stratigraphic position, but other climatic indicators suggest that climatic fluctuations were subdued throughout the period (Hallam, 1985). One interpretation from the paleobotanical data is that the climate warmed slightly from the Late Triassic into the late Early Jurassic i (Toartian), cooled to a minimum in the Middle Jurassic, and warmed again to i » a plateau in the Late Jurassic (Vakhrameev, 1982). The most striking aspect of I | Jurassic climate is that subtropical conditions possibly reached to 60°N and i I global temperatures in the Late Jurassic may have averaged as much as 7° C warmer than those of the present (Fig. 3). Another important feature is the continued presence of evaporitic basins of Middle and Late Jurassic age (Hallam, 1985). ; Crowley and North (1991) suggest that the depiction of an "equable" f t Jurassic climate is not entirely accurate. Based on their models, the large Pangaean supercontinent was coherent for much of the period and was likely to have experienced a strong seasonality. 3. Cretaceous -Paleotemperatures have been deduced from the oxygen isotope signal of carbonates and fossils for this period and are relatively well- constrained. The climate is considered to be genuinely equable with some Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Dry SeasonalyWet I I I 11 Wet , < > ■ Figure 3. Summary diagram of Jurassic global climates, hypothesized mleoceanography and reef/biostrome occurrence. Distribution of Early Jurassic reefs is represented by closed circles and without regard for possible suspect terrane displacement. Adapted from Fliigel and Fliigel- Kahler (1994), paleogeographic reconstruction from Smith et al. 1994, reconstruction of Early Jurassic continental humid and arid belts from Hallam (1985), hypothetical global ocean circulation for the early Jurassic adapted from Haq (1984) and Frakes et al. (1992). Small arrows represent surface ocean currents. Some recent models by Barron and Peterson (1989) suggest that Tethyan circulation was more likely to have been clockwise. 17 seasonal monsoon seasons (Fig. 4). A general warming trend is noted during the Albian-Cenomanian interval by the 8l80 values (Kennett and Barker, 1990). Temperatures based on analyses of rudists substantiate the isotope curve from the Aptian-Turonian, but the Conianacian-Campanian rudists record higher temperatures than the pelagic fossils (Steuber, 1996). Steuber (1996) calculated a similar range of isotope values from Santonian- Campanian hippuritids in Greece at 30°N paleolatitude, which display a 12°C seasonal variation. Seasonality increased throughout the Cretaceous with the reconfiguration of the continents and the continued opening of the Atlantic (Johnson et al., 1996). Traditionally, Cretaceous paleodimates have been i assumed to have lacked the effects of continental glaciers. New evidence ? • from a Valanginian-Albian shale with erratic boulders found in central and northern Australia does suggest ice-rafting processes at play (Frakes and Krassay, 1992). These authors summarize similar sedimentary deposits . between 65°-78° N paleolatitude and indicate that ice-rafting and hence i seasonal polar ice was present during the Early Cretaceous. Plants from 5 Upper Albian deposits at 85°N paleolatitude in Alaska suggest a strong | seasonality in a cool, humid climate, with a mean annual temperature estimated at 10°C ± 3 (Spicer and Parrish, 1986; Fig. 4). i 1 i j Mesozoic Paleoceanography The Mesozoic is recognized as a time of relatively sluggish oceanic circulation, largely because of continental configuration due to the breakup of Pangea and Tethyan equatorial circulation (Hallam, 1985). The Pacific Ocean exhibits a unique tectonic history differing from that of the Atlantic and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4. Summary diagram of Early Cretaceous global climates, hypothesized paleoceanography and reef/biostrome occurrence. Distribution of Early Cretaceous reefs are represented by closed circles and without regard for possible suspect terrance displacement. Adapted from Fliigel and Fliigel-Kahler (1994), paleogeographic reconstruction from Smith et al 1994, reconstruction of Early Cretaceous continental humid and arid belts from Hallam (1985) and Barron and Moore (1994), hypothetical global ocean circulation for the Early Cretaceous adapted from Roth (1986), brakes et al (1992) and Barron and Moore (1994). 00 I 19 Indian oceans. The early Mesozoic marks the largest size of the Pacific Ocean, represented by the super or global ocean, Panthalassa (Kennett, 1988). Therefore, terrestrial influences and inputs decrease as one goes back further in time for Mesozoic Panthalassa. The large size, climatic homogeneity and large heat capacity of Panthallassa suggest that a broad westward-flowing equatorial current could have extended into the region bordering modem Africa (with India still "undocked" from Asia) while Australia and Antarctica were still joined (Kennett, 1988). The long equatorial transit would have transported very warm and low oxygen waters to the western Panthalassa and to the continental margin abutting modem Asia (Fig. 3 for Jurassic reconstruction). Low surface-water temperature gradients are surmised due to the dearth of early Mesozoic glaciation evidence (Wood, 1993). Mesozoic Tectonics and Paleogeography The Western Cordillera is now considered to be a composite of accreted terranes, igneous rocks associated with the docking of the terranes and the craton itself (Davis et al., 1978). Jones et al. (1983) classified terranes in three groups: terranes that originated in the east Panthalassa (allocthonous), North America (autocthonous), or "in-between" (suspect). Oceanic terranes are characterized as "oceanic" (pillow basalts, hemipelagic carbonates and atoll like carbonate sequences) or "arc-bearing" (volcanic and volcaniclastic sediments combined with occasional thick carbonate platforms and silidclastic sediments) (Jones et al., 1983). Faunal evidence and paleomagnetic evidence place paleolatitude of many of these terranes as originating from a southemly position relative to the craton with subsquent movement Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 northward before collision with other terranes and the craton (Gabrielse and Yorath, 1992). For example, many terranes have low-latitude tropical faunas but now abut cratonic boreal faunal assemblages. Paleolongitudinal assignments of terranes lack rigorous control and are still hotly contested (see review in Belasky and Runnegar, 1993). The Western North American tectonic setting for the early Mesozoic is marked by two tectonic events: the Sonoman and the Nevadan orogens. The Sonoman is marked by truncation of the Paleozoic continental margin, eastward directed thrusting of shallow back-arc and intra-arc basins, and deposition of late Paleozoic-early Mesozoic island arc sequences (Dickinson et al., 1989). In the Late Triassic, the northeast-southwest axis abruptly shifted to the new Nevadan mountain belts that trended northwest-southeast. This dramatic shift in the collision of the North American and oceanic plates is attributed to the reorganization of plates due to the global break-up of Pangaea (Burchfiel et al., 1992). The Andean-style Nevadan orogeny is the mechanism attributed for the "docking" of several oceanic and arc-like terranes of the Cordillera: Wrangellia, Alexander and Cache Creek (Saleeby, 1992; fig. 5). Late Triassic depositional settings of the submerged continental margin were those of a volcanic archipelago with both shallow and deep marine platforms, some characterized by carbonate deposition (e.g. Hosselkus Limestone of the Klamath Mountains) and deeper marine basins with | turbidite and hemipelagic sedimentation (Hacker et al., 1993). By the Late t Triassic, farther east of the now docked "Sonomia” Arc, lay a moderately deep, epicontinental basin in what is now modern-day Nevada, (see Figure 5 for paleoshoreline reconstruction) (Marzolf, 1993). The mid- late Triassic Star Peak/Luning Basin was bordered on the east and south by shallow-marine Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21 Farralon Plate ■ 2 0 North America X Plate Figure 5. Hypothetical reconstruction of Triassic Western North America and off-shore elements with the current state boundaries of Nevada given as a reference from paleomagnetic data. Base map from Smith et al. (1994), paleoshoreline of Nevada and California from Busby-Spera et al. (1990), Wallowa terrane configuration and paleolatitude from Vallier (1995), Saleeby (1992) and Ross and Ross (1983) reconstructions were used for the relative placements of other terranes. The placement of most of the elements in the Northern Hemisphere is only one possible orientation. The paleolongitudinal placements are unconstrained and are only gross estimates. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 (shelf) environments, deltaic systems, and the terrestrial continental realm (e.g. Chinle Formation; Marzolf, 1993). The Star Peak/Luning Basin has since been thrust eastward onto the craton for distances estimated to be greater than 50 km of displacement, and now rests on other Triassic formations in Central Nevada (Silberling, 1972). The Upper Triassic and Lower Jurassic limestones of the northeastern Oregon Wallowa terrane are poorly understood in their relation to the larger superterranes of the Western North American Cordillera (e.g. Wrangellia and Stikinia). The Wallowa terrane represents an island-arc active from the Early Permian and ending in the Late Jurassic (Fig. 6; Vallier, 1995). Paleomagnetic evidence places the terrane near the equator in the Late Permian with a slow migration northeastward until its final collision with : the North American craton near 93 Ma (Harbert et al., 1995). The paleo- i ; longitudinal position of the Wallowa terrane is still in dispute (see Newton, [ 1988; Smith et al., 1990). Upper Triassic Wallowan limestones have two faunal modes, one similar to that of the Tethys (Stanley and Senowbari- ! Daryan, 1986) and one distinctly Cordilleran (or eastern Panthalassan), r i > deposited on the leeward side of the volcanic arc. Lower Jurassic sedimentary deposits of the Izee microterrane in the Wallowa deposits are thought to represent an intra-arc basin setting of the Baker/Wallowa terrane and the Olds Ferry Terrane (Silberling et al., 1984; Fig. 6). ■ After the Early Cretaceous, the area of tectonic activity increased in the southwest region of eastern California and Arizona (Fig. 7). Sediments of Early Cretaceous southwestern North America were deposited in a northwest-trending extensional feature (the Chihuahua Trough) associated with Late Jurassic-Late Cretaceous opening of the Gulf of Mexico (Bilodeau & Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40 Baker/Wallowa Suplee/lzee inter ire basin 30 North I America ' Plate Olds Ferry 20 Farallon Plate Figure 6. Hypothetical reconstruction of Early Jurassic Western North America and off-shore elements with the current state boundaries of Nevada given as a reference for the paleogeographic position. Base map from Smith et al. (1994), paleoshoreline data of Nevada and Utah from Marzolf (1993), Baker, Suplee-Izee and Olds Ferry terranes represent the fragments of die older Wallowa arc, reconstruction from Vallier (1995), configuration of off-shore elements and subduction zone placement from Saleeby (1992). The paleolongitudinal placements are unconstrained and are only gross estimates and one hypothesis of the many plausible configurations. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40- Kula Plate 30 2 0 - Farallon Plate Pacific Plate 1 0 - i i • Figure 7. Hypothetical reconstruction of Early Cretaceous Western North America with current state boundaries of Arizona as a reference for paleogeographic position. Base map from Smith et al. (1994), paleoshoreline data of Arizona and extent of thrusting from Bilodeau and Lindberg (1983), subduction zone placement horn Gabrielese and Yorath (1992), relative arrangement of oceanic plates (Kula, Farallon and Pacific) from Engebretson etal. (1984). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 25 Lindberg, 1983). Later back-arc spreading extended the depression northwestward through Arizona and New Mexico to penetrate the back side of a magmatic arc on the western continental margin resulting in the Bisbee trough (Dickinson et al., 1989). The Bisbee Trough remained open in the Valangian-Turonian with organic bioherms and platform development peaking during the Aptian-Albian (Warzeski, 1986). Mesozoic Carbonate Buildups Concurrent with these warmer climates and sluggish oceanic circulation and dynamic tectonic history, reef and bioherm construction in [ the Mesozoic Western North American Cordillera was also appreciably | different from both the modem and the Paleozoic. Two qualities of Mesozoic ■ » I reefs and bioherms separate them from the modem style of reef construction: 1) despite the acquisition of photosymbionts, scleractinian corals never gained their dominance characteristic of modem reef environments; and 2) volumetrically, more large epifaunal bivalves are relatively more common in Mesozoic reefs. 1. Triassic- The Middle Triassic marks the acquisition of photosymbiosis by certain species of scleractinian corals (Stanley and Swart, 1995). In Figure 2, the distribution of buildups is concentrated in modem Europe, however, buildups do occur in other areas (e.g. Thailand, Peru, Western North America, etc.). "Oyster" reefs are relatively uncommon, but similar bivalve- dominated domal structures up to 4.5 m thick and 10 m in diameter have been described from Middle and Upper Triassic rocks in the Muschelkalk of southern Germany (Bachmann, 1979; Geister, 1984). These frameworks were Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26 formed by the encrusting right valve of the bivalve Placunopsis ostracina. The dense packing of these relatively small (1.5 cm diameter) valves virtually excluded all other organisms except for a few foraminifera, brachiopods, other bivalves, gastropods, serpulids and an unknown borer. Bachmann (1979) estimated the overall composition as 75% P. ostracina valves, 5% other sessile benthic organisms, and 20% micritic interstitial mud. It is unclear at this time whether or not these bioherms have the necessary superstratal relief to be classified as reefs. In the latest Triassic, sderactinians, stromatoporoids and chaetetids predominate as framework builders in reefs. These reefs are noted for a large Solenopora and Mitchelldeania (algae) component and abundant, thick- t | shelled megalodontid bivalves. Detailed studies of European Upper Triassic r i j carbonate platform sequences (Fliigel, 1981; Stanton and Flugel, 1987) describe | sequences of reef and reef-flank facies over 1000 m thick. The most important I framework builders of the Norian-Rhaetian Dachstein Reef of Austria and | Bavaria are corals and caldsponges, followed by hydrozoans and i solenoporacean algae (Flugel, 1981). Large reclining megalodont bivalves ; were common in the Tetyan Upper Triassic reefs. An aberrant megalodont, 1 to be defined in a future publication by Yancey and Stanley (pers. comm, 1996) I ' as a wallowaconchid, is assocated with the same Dachstein coral/sponge biota but this bivalve appears to be restricted to the Cordillera. Corals and i caldsponges were restricted to different parts of Tethyan reefs and strong fades control of other accessory biota resulted in twelve distinct "facies units" unique to the Upper Triassic (Stanton and Flugel, 1987). Reefs and bioherms of Western North America lack the scale of European reefs, the largest Upper Triassic reef in the United States reaching only 20 m in thickness. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 i 27 2. Jurassic - During the recovery interval of the Triassic-Jurassic mass extinction, scleractinian or sponge reef construction ceased; however, bioherms constructed by the bivalve Lithiotis problematica, were cosmopolitan. The paucity of Early Jurassic reef distribution, relative to the Late Triassic and Early Cretaceous, may be seen by the sporadic bioherm occurences in Figure 4. One Sinemurian reef in the Telkwa Range of British Columbia is a coral bioherm reaching 40 m in height with bivalves and brachiopod interstitial fauna (Poulton, 1988). Stanley and Beauvais (1994) interpreted this reef to be a refugium from the mass extinction as the dominant coral in the fauna was a species presumed to be extinct by the end- Triassic event. Early Jurassic (Pliensbachian-Toarcian) bioherms in Western North America and Europe are limited to lithiotid-style accumulations. These two deposits indicate continued low paleolatitude for these terranes. In contrast, autocthonous assemblages of Gryphaea in the Yukon and ahermatypic coral deposits in Idaho (Stanley and Beauvais, 1990) suggest a higher latitude, boreal paleogeography for these assemblages. Contemporaneous reefs are found in the Assemsouk section of the central High Atlas Mountains of Morocco constructed by Cochelarites sp. (a bivalve highly convergent on the form of Lithiotis), other thick-shelled bivalves (Opiosoma mechikofft) and megalodonts, as well as to a lesser extent stromatoporoid mounds and domed or branching scleractinian corals (Lee, 1983). The high diversity of the Lower Jurassic Assemsouk reef is a rarity for this time interval and is a striking example of the rapidity of community reorganization after the Triassic-Jurassic mass extinction. Middle and Late Jurassic reefs are of a somewhat deeper-water origin built by siliceous sponges or by algae where these framework builders Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 \ i 28 exceeded corals in both volume and diversity (Scott, 1988). Late Jurassic reefs are well developed and preserved in Germany's Southern Franconian Alb. Bioherms and reefs from this area attained heights of 60 m on a shallow carbonate shelf (Leinfelder et al., 1994). Late Jurassic and early Early Cretaceous reef-builders were taxonomically heterogeneous; skeletal and non- skeletal algae, diverse calcareous and siliceous sponges, scleractinians and the rapidly emerging hippuritacean (rudist) bivalves (Fagerstrom, 1987). Middle and Late Jurassic reefs are virtually unknown in Western North America 3. Cretaceous- Scleractinians regained volumetric importance in earliest Cretaceous reefs. However, an important transition occurred in the late Early Cretaceous (Aptian-Albian) as scleractinian-algal reefs were replaced by rudistid bivalve banks (Scott, 1979). Whether this transition from coral-reefs to rudist-banks is a result of competitive displacement (Kauffman and Johnson, 1988) or as environmentally induced successions (Gili et al., 1995a and 1995b), has resulted in debate. Late Cretaceous Tethyan assemblages from the Pyrenees are marked by a three-stage succession: 1) plate-like to low domal scleractinian coral colonies; 2) massive-tabular and high-relief low domal scleractinians and smaller accessory rudists; and 3) clustered hippuritid bivalves (Gili et al., 1995b). The overwhelming success of the rudists in the Middle and Late Cretaceous represented a culmination of an increased presence of large epifaunal bivalves in reefs through the Mesozoic. In particular a variety of large epifaunal bivalves were abundant: megalodonts (Upper Triassic), wallowaconchids (Upper Triassic), lithiotids (Lower Jurassic), chondrodontids (Cretaceous), and rudists (Cretaceous; Fig. 8). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. * - n h*i trV ~ * i * n iir i airf nfTMi u t t i m - * ' • - r 29 Bivalves in Modem Carbonate Buildups Filter-feeding bivalves in modem bioherms and reefs are used as "sentinel" organisms because of their sedentary habits and their ability to bioconcentrate pollutants as well as the fact that their presence as filter-feeders signals a change in the nutrient regime (Tripp and Farrington, 1985). After mixotrophic scleractinian corals, filter feeders (usually bivalves) are second in benthic biovolume in modem coral reefs (Dubinsky, 1990). Some volumetrically important bivalves in modem oligotrophic settings include Tridacna and Hippopus. These bivalves differ from their smaller counterparts in that they are mixotrophs adapted to the low-nutrient setting and appear to have increased calcification rates due to the energetic subsidy of photosymbiosis (discussed below). Large mixotrophic bivalves (Tridacna and Hippopus) are common in modem Indo-Pacific reefs while absent from modem Atlantic reefs (Stoddart, 1969). As discussed above, as nutrient levels increase the number of filter feeding bivalves increases. Experiments with radiocarbon labeling have shown that the fine filterers of the reef consume bacteria at concentrations less than 1 mg m-3 , which is one-third to one-half that in oligotrophic waters and 1 to 2 orders of magnitude less than that in neritic mesotrophic waters (Sorokin, 1990). Thus, the efficiency of filtering reef fauna in oligotrophic systems is extremely high: for every 1 g of filter-feeder biomass, the bacteria of i size 0.2 to 0.5 nm are removed from 400 to 600 1 of sea water everyday (Sorokin, 1990). As particulate food matter increases with nutrient levels, the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I 30 f i s a i . iw If Figure 8. Diagrams of the nine large Mesozoic buildup epifaunal bivalves. A - Megalodon. (x 0.25) B - wallowaconchid (x 0.10) C - Neomegalodon. (x 0.25). D - Lithiotis (x0.12). E - Monopleura (x0.33). F - Petalodontia (x0.25). G - Coalcomana (x0.25). H - Caprinuloidea (x0.20). I - Chondrodonta (x0.33). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. j i 31 efficiency of filter-feeding organisms decreases while their populations increase. In contrast the eutrophic end-member bioherm is typified by oyster reefs, constructed by Crassostrea virginica common off the coasts of Georgia and Texas and Ostrea ednlis in the North Sea (Bahr, 1976; Caspers, 1950). Photosymbiosis in Modem Bivalves The tropical giant clam family, Tridacnidae (including Tridacna gigas, T. maxima, T. derasa, T. squamosa, T. corocea, Hippopus hippopus and H. porcellanus) as well as the heart cockle, Corculum cardissa, have symbiotic I relationships with the zooxanthellae Symbiodinium microadriaticum, a t dinoflagellate. The large size associated due to increased calcification rates as a result of photosymbiosis is evident in T. gigas; one specimen was reported to exceed 1.2 m in length and 250 kg in weight (Yonge, 1936; only superseded in size by Mesozoic rudists). Unlike scleractinian corals, where the zooxanthellae are housed within the cells of the corals, these algae are found intercellularly in bivalves. It has been postulated that only organisms with "thin-tissues" (e.g. diploblastic - two layers of tissues such as corals and ctenophores) can effectively use the photosynthate produced by the zooxanthellae (Cowen, 1988). The success of the triploblastic bivalves in photosymbiosis is a result of this key difference of where the symbionts are housed in the host. However, since bivalves are not clonal, like scleractinian corals, zooxanthellae are passed from adult to the veliger stage. The passage of zooxanthellae to the tridacnid larvae occurs in the veliger stage of development (Fitt and Trench, 1981). When submerged, adult tridacnid clams gape and extrude their mantle folds during the day only, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32 at night they are inactive (Yonge, 1936). This exposes the zooxanthellae located in the mantle tissue to light and permits photosynthesis to take place. Corculum cardissa, by contrast, keeps its valves shut and light is transmitted through the shell to the photosymbionts housed in the gills and anterior mantle (Carter and Schneider, 1997). The metabolic gain for the bivalves from the photosymbionts is the released photosynthate products (Muscatine, 1967). Tridacnid clams are referred to as "nutritional opportunists" in a nutrient poor environment as they are not dependent on the photosymbionts but are true mixotrophs (Dame, 1996). They filter feed on suspended particles including diatoms, crustaceans and zooxanthellae released from heat-stressed corals (35% of the diet, as compared to 65% of heterotrophic bivalves); take up dissolved organic matter; and incorporate photosynthates released by the zooxanthellae (percentage varies with light intensity; Klumpp et al., 1992; Hawkins and Klumpp, 1995). Focus of This Study Some workers have suggested that some Mesozoic reef bivalves were mixotrophs based on large size (enhanced calcification due to increased energy supply from photosymbiotic algae) and their association with modem "blue water” fauna, similar to the modem Tridacna (rudists - Kauffman and Johnson, 1988 or Vogel, 1975; megalodonts - Cowen, 1983). However, not all of these bivalves display compelling evidence for adaptations to a photosymbiotic life-mode. These authors have assumed a strict uniformitarianist view of reef environments through time (i.e. modem reefs occur only in oligotrophic waters, therefore all ancient reefs are also oligotrophic). However, it is known that "blue water" fauna do exist in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i i 33 mesotrophic conditions and nutrient levels in all environments have fluctuated through time with changes in global oceanic circulation (Wood, 1993). An alternative hypothesis from the blue-water hypothesis, is that these bioherms represent settings with increased nutrients and not photosymbiotic innovations. Hallam’ s (1985) description of an equable Mesozoic climate and sluggish oceanic circulation has been corroborated by the distribution of high paleolatitude carbonate platforms, coals and evaporites, and oxygen isotope data (e.g. Insalaco, 1996; Johnson et al. 1996). These combined factors may have resulted in repeated periods of anoxia or oxygen-defidency in deeper waters when compared to the vigorous oceanic-drculation of the Cenozoic, j where the oceans do not tend to stagnate and become oxygen-deficient | (Hallock, 1987). Because there was less oxygen available in the Mesozoic for i metazoan inhabitation, oxygen-defirient waters were higher in organic content and hence nutrients (Fischer and Bottjer, 1995). One difficulty with the eutrophication hypothesis is that the usual cadre of oligotrophic organisms (corals, sponges, etc.) are found near the large epifaunal bivalves. | Another difficulty is that some of the bivalves in question do appear to have j | structural changes that are indicative of a photosymbiotic relationship, in | particularly some of the rudists (Seilacher, 1996). i ! Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. t i 34 STRATIGRAPHY AND SEDIMENTOLOGY OF STUDIED CARBONATE BUILDUPS On the western-most margin of the proto-Pacific, Mesozoic reefs of Western North America display a different biota from their Tethyan (European) contemporaries. The exception is one Upper Triassic reef from Summit Point, Oregon which virtually matches species lists from Upper Triassic Dachstein-style reefs of Austria (Stanley and Senowbari-Daryan, 1986). Seven Mesozoic reef sites from Arizona, Nevada and Oregon were used in this study: Upper Triassic - Mina, New Pass Mine, Summit Point, Black Marble Quarry; Lower Jurassic - Ant Hill Bioherm; Early Cretaceous - Paul Spur Reef and Mexican Saddleback Reef (Fig. 9; Table 3). Triassic and Jurassic reefs of the North American Cordillera were thrust on to the craton (Nevada) or accreted in allocthonous terranes (Oregon) during the Nevadan Orogeny. Cretaceous reefs and bioherms of Arizona were deposited directly on the craton. The studied buildups are arranged in chronological order and presented by (1) setting and stratigraphy, (2) lithofades, (3) fossils, (4) description and possible significance to other contemporaneous Tethyan buildups. Site # 1 - New Pass Mine. New Pass Range. Nevada The Augusta Formation (Ladinian-Camian) is exposed near the New Pass Mine in the western wall South of Bull Canyon and across the canyon as two limestone knobs to the east (fig. 10). The area is relatively free from faulting and other structural deformation; all beds dip steeply (-45° to the southwest). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Site Name Location Formation Ass: Peppsilional Buildup form Ritf-buildmg Large epifaunal setting fauna bivalves 1 New Pass Mine Austin, Augusta Central Nevada Late Triassic Shallow biostrome coral, algae, Neonii'gnlnlon (Ladinian) cratonic basin sponges 2 Dunlop & Cinnabar Mina, SW Luning Late Triassic (Norian) Shallow bioherm sponges, coral Mrgolodon Canyons Nevada cratonic basin (spongiomorphs absent) 3 Summit point Halfway, NE Martin Bridge Late Triassic Volcanic island reef corals, sponge, Megalodon Oregon (Camian-Norian) arc algae 4 Black Marble Enterprise, Martin Bridge? Late Triassic Volcanic island biostrome bivalves, corals, Wallowaconchid Quarry NE Oregon (Camian-Norian) arc sponges 5 Ant Hill Bioherm Suplee-lzee, Robertson EarlyJurassic(Upper Volcanic intra- biostrome bivalves Lithiotis NE Oregon Pleinsbachian) arc basin probhmticu 6 Paul Spur Bisbee, SE Upper Mural Early Cretaceous Shallow biostrome corals, algae, Mompelurtt, Arizona (Aptian-Albian) cratonic trough bivalves Caprinuloiilea, Coalocomam 7 Mexican Saddleback Douglas, SE Upper Mural Early Cretaceous Shallow reef corals, algae, Pttotodontia, Arizona (Aptian-Albian) cratonic trough bivalves Monopltura, Caprimiloidca, Coalocomam Kck'rciwcii Macmillan (1972), Stanley (1977) Stanley (1979), Cornwall (1979) Stanley and Senowbari-Daryan (1986) Stanley and Yancey (1996), Stanley (1977) Nauss and Smith (1988) Scott (1979) Hartshorn (198V) Table 3. Summary description of field sites. I Figure 9. Locality map of studied sites. Triangles refer to Triassic sites: 1 - New Pass Mine, 2 - Dunlop and Cinnabar Canyons, 3 - Summit Point, 4 - Black Marble Quarry. The circle designates a Jurassic site: 5 - Ant Hill Bioherm. Squares designate Cretaceous sites: 6 - Paul Spur, 7 - Mexican Saddleback Reef. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 7 . A . Wfnnemucca Map Area Battle Mountain .Austin Falllcn Scale in kilometers Figure 10. A - Locality map for New Pass Mine, NV (Mt. Airy 7.5" Quadrangle, T20N, R40E, Section 9, N l/2, SW1/4). B - Photograph of New Pass Mine looking North across South Canyon. The biostrome comprises the highly resistant beds. Field of view is approximately one km wide. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 The regional setting of the New Pass Mine area during the Late Triassic was a broad shallow embayment in an arid region (Busby-Spera et al., 1990. The buildup was assigned to a mollusk-echinoderm grainstone facies and a coral-bivalve bindstone-packstone facies by Macmillan (1972; Fig. 11 for stratigraphic column). An oolite-algal grainstone is found in direct contact with both the biofacies. The corals and bivalves occur in an interval nearly 19 m thick. The corals at New Pass Mine form a strikingly different assemblage than those of the later Camian-Norian buildups of Mina and reefs of Summit Point. Actinastrea sp. and Astraeomorpha sp. dominate the buildups. Also, megalodonts are far more abundant at the site. Other bivalves at New Pass Mine are preserved as internal molds of a Lima-like species. When compared ? to Tethyan counterparts, the biostromes of New Pass Mine are remarkable in that they lack spongiomorphs completely. Site #2 - Mina. Nevada . Rocks of the Upper Triassic (Norian) Luning Formation crop out in two canyons near the town of Mina in the Pilot Mountains: Dunlop Canyon and Cinnabar Canyon (Stanley, 1979; Fig. 12). The canyons may be reached by a dirt road off of Route 95,1.2 km north of Mina, heading west into the Pilot Mountains. The Luning Formation at its type locality is over 2 km thick and I | contains a mixture of limestone, dolomite and conglomeratic sandstone (Fig. it 3 13). Reefoid limestone bodies in the formation range from 0.5-5.3 m thick. I The area is structurally deformed with numerous thrust faults running i through the outcrops, possibly associated with allocthonous thrusting during the Nevadan orogeny. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. t 39 Thin to medium bedded limestone, ooids, ribbon-like colonies of corals, megalodont bivalves common - 22.0 m Red silty limestone - 9.1 m Covered interval - 9.2 m Limestone, thin to medium bedded, light gray calcarenite. Gastropod, bivalve, and crinoid fragments/molds common - 22.3 m Interbedded limestone and thin shales -15.3 m Very coarse-grained calcarenite, highly fossiliferous, crinoid columnals and large megalodont bivalves, small encrusting Thamnastrea common, ooids in som e areas • 2.4 m Coarse-grained calcarenite, thin bedded, numerous thin shale partings, abundant platy encrusting corals, impressions of pectinids - 4.6 m Thin bedded light-gray limestone with platy colonies of Actinastrea - 5.2 m Alternating limestone and thin shale beds, abundant algal bodies, some large megalodont bivalves, corals rare - 6.7 m Argillaceous mottled tan limestone, fossils rare - 1 0 m Coarse-grained, dark brown, fossiliferous limestone with crinoid columnals common -1 .5 m Argillaceous interval with ammonoid and bivalve impressions, limestone beds fine to coarse grained and fossiliferous - 50 m Total thickness = 153.5 m 1 cm = 10 m Figure 11. Stratigraphic section of Augusta Formation (Ladinian), South Canyon, New Pass Mine, NV. Lithofacies terms from MacMillan (1972). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Map Area Cinnabar Canyon )& Hawfiome Dunlop Canyon Mo u n t a i n s Mo unt a i ns Scale in kilometers Figure 12. A-Locality map for Mina, NV (Mina 7.5" Quadrangle, T6N, R36E, Section26; Dunlop Canyon: SW1/4, SE1/4; Cinnabar Canyon: NW1/4, SW1/4). B - Photograph of Cinnabar Canyon looking west, the biostrome is below the tree (~ 4 feet tall). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 Gray shale, no fossils observed -1 .5 m Coralliferous limestone, thin bedded, corals and abundant Ostrea hash in between thickets -1 .5 m Covered interval - 3.0 m Argillaceous limestone, fine to coarse grained, bivalve shells abundant with Ostrea: brachiopods common, corals rare; more argillaceous toward the top • 23.3 m Limestone, reefal, medium bedded, massive platy ribbon corals of Actinastrea, branching and encrusting spongiomorphs common; Reb'ophyllia present near the top forming large thickets • 25.3 m Shale, light gray, draping over coral plates of underlying unit with small pyrite; unfossiliferous - 2.4 m Reefal limestone with abundant encrusting and upright sponge colonies at the base grading upwards into encrusting coral communities of Thamnasteria rectilamellosa -23.3 m Light gray, fissile shale; rare bivalves and impressions of ammonoids; few Ascosymplegma sponge colonies encrusting on large ichthyosaur vertebrae - 20.6 m Total thickness * 109.9 m 1 cm = 10 m Figure 13. Stratigraphic section of Luning Formation (Norian), Dunlop Canyon, Mina, NV. Lithofades terms from Cornwall (1979). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42 Stanley (1979) delineated four distinct biofades within the reef fades: 1) sponge framestone-bindstone, 2) corai-spongiomorph framestone-bindstone, 3) mollusk-echinoderm-coral grainstone, 4) pelletoidal oolitic grainstone. The sponge framestone-bindstone occurs at the base and is easily recognized by massive upright, cylindrical sponges (Polytholosia sp.; Seilacher, 1962) and encrusting or sediment-binding sponges (Asocsymplegma expansum; Seilacher, 1962). The coral-spongiomorph fades created the buildup's framework assemblages consisting of massive and branching corals (Retiophyllia, sp. Cuif, 1988), and ribbon-like spongiomorphs. Bivalves (megalodonts and Trichites sp.) are abundant in the coral-spongiomorph fades. The mollusk-echinoderm packstone fades is characterized by [ numerous banks of Ostrea sp. The pelloidal-oolitic fades caps the succession. | The Cinnabar and Dunlop Canyon mounds did not have the topographic expression usually assodated with reefs. In the Tethys at this time, the large Dachstein reef complex was deposited. Of interest in the contemporaneous Mina reefs, is the lack of bryozoans and algae seen in other European reefs. In the Dachstein complex, bryozoans and algae belonged to the binder guild. In contrast, the diversity of sponges in the Cordilleran reefs surpasses the Upper Triassic reefs of the Northern Calcareous Alps (Stanton and Fliigel, 1987). Site # 3 - Summit Point. Wallowa Mountains. Oregon [ The Upper Triassic (Camian-Norian) Martin Bridge Formation crops out as four large spurs south-west of Summit Point Lookout Station (Fig. 14). The formation is part of the Wallowa Terrane of Oregon. Paleomagnetic and lithologic evidence suggest that the Wallowa terrane originated about 18° Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Map Area Summit !\Point I Reef Wallowa- Whitman McBride Campground Halfway Scale in kilometers Richland Figure 14. A - Locality map for Summit Point Reef, OR (Juntown 7.5" Quadrangle, T7S, R45E, Section 5, NE1/4). B - Photograph of Summit Point Reef from a logging road at the southern section of the reef. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 from the Triassic equator as a volcanic island arc and docked with the North American craton during the Cretaceous at -93 my, after several pulses of initial metamorphism (Malmquist, 1991). Some authors have tried to correlate the Wallowa terrane with the larger Wrangellia terrane, however faunal and paleomagnetic correlations are currently in dispute (see Harbert et al., 1995, for review). The Upper Triassic Martin Bridge unconformably overlies the volcanidastic and sandstone/siltstone breccias of the middle Triassic Clover Creek Formation (Fig. 15). The Lower Jurassic Hurwall Formation, of laminated argillite, mudstones, greywackes and cherts overlies the Martin Bridge. The Martin Bridge Formation near the edges of the spurs has been recrystallized by the Cretaceous Idaho Batholith. Lower on the spurs details of coral septae and other fine-scale features are preserved. The Martin Bridge at the Summit Point site is up to 50 m thick and is located near McBride Camp and the Summit Point Lookout Station, 10 miles west of Halfway Oregon on USFS #7715. At the base of the section 33 m of massive reef limestone with a coral-sponge-algal framework are preserved (see Fig. 15 for stratigraphic column). Above this member, a facies of bedded limestone is found, comparable to the back reef facies of the Dachstein locality in the Northern Alps (Stanley and Senowbari-Daryan, 1986). The corals at the site include Retiophyllia, sp., a colonial phaceloid branching coral and Distichophylia norica, a solitary cup-like coral, both found at Mina. Numerous megalodonts have been reported in direct contact with the corals within the reef-core facies (G. D. Stanley, Jr. pers. comm., 1995). Because the reef is zoned in a fashion akin to that of the classical Alpine reef facies, no biofades delineation have been published. Due to the nature of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45 Alternating bioclastic limestone with oncolites and cavity infillings, corals and sponges present and cavities up to 4 cm in diameter are infilled by pale yellow, laminated sediment- 15 m Oncolite bed, contains oncolites up to 10 cm in diameter, with crinoid columnals or broken fragments of other fossils as nuclei, other fossil material is fragmental • mostly abraded echinoderm fragments -2 m Medium-bedded, bioclastic limestone similar to lower units, grades upward into coarse, skeletal and oncolitic facies - 7.8 m Bioclastic thin-bedded limestone with broken fragments of corals, tabulozoans and gastropods • 4.8 m Light gray, massive reef limestone of a coral-sponge-algal framework with numerous fragments of thin-shelled megalodonts. The coral Distichophyllia norica increases in abundance upward and dominates the uppermost sector of the framework - 33 m Total thickness = 66.2 m 1 cm = 5 m Figure 15. Stratigraphic section of Summit Point Reef, Martin Bridge Formation (UpperTriassic), OR. Section lithology and measurements from Stanley and Senowbari-Daryan (1986). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 accreted terrane preservation, vital parts of a true paleoecological reconstruction are missing (i.e. no Iagoonal or reef front/slope facies have been identified). Site #4 - Black Marble Quarry. Wallowa Mountains. Oregon Currently the deposits at Black Marble Quarry have been assigned to the Martin Bridge Formation (Camian-Norian). West of Enterprise, Oregon, the Black Marble Quarry is located within the Waliowa-Whitman National Forest on Lime Quarry Road (Fig. 16). The formation is also part of the Wallowa terrane. The lithology of this quarry is a very black limestone with a high carbon content. The quarry walls are nearly 20 m high with a well- exposed vertical face where two high-angle, normal faults and some gentle folding were observed (Fig. 16B). The fauna of this formation consists of shailow-water spongiomorphs, corals and bivalves. Abundant spongiomorphs, corals, caldsponges and corals formed patchy biostromes. Wallowaconchids, or Black Marble Quarry Bivalves (G. D. Stanley, Jr. and T. Yancey, pers. comm., 1995; see following section), an alatoform bivalve, formed extensive horizons, commonly overlying the branching coral Retiophyllia and overlain in turn by spongiomorphs similar to those found at the New Pass Mine, NV (Fig. 17; Yancey and Stanley, 1996). The site also contains coral and spongiomorph genera not found in the other Southern Wallowas or other Upper Triassic sites of Western North America, but which are found in the St. Cassiano Formation (Late Camian) of Italy (Stanley, 1979). Most of the corals are flat and encrusting species and appear as small domes; framework construction was dominated by a diverse spongiomorph population. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I I A. Wallowa Lostne Black Marble Quany Joseph Wallowa- Whitman National Forest Scale in kilometers 47 B. Figure 16. A - Locality map for Black Marble Quarry, OR (Enterprise75" Quadrangle, T2S, R44E, Section 19, W l/4). B - Photograph of Black Marble Quarry. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 Unfossiliferous black recrystallized limestone - 3.1 m Layer of tumbled fragments of corals and stromatoporoids, upside down wallowaconchids - 0.3 m Unfossiliferous black recrystallized limestone - 6.0 m Horizon of overlapping wallowaconchids - 0.5 m Unfossiliferous black recrystallized limestone - 2.4 m Thin bed of the spongiomorph Heptastytis and the branching coral Retiophyttia, minor amounts of the encrusting coral Byastrea - 0.7 m Unfossiliferous black recrystallized limestone - 7.5 m Massive black limestone of a coral-spongiomorph-wallowaconchid packstone; horizon of branching corals, Retiophyllia (" T . dawsonnf and T suttenesis0 ) and large spongiomorphs, Heptastytis form dormal and encrusting structures, these occur above and below the wallowaconchid overlapping horizon • 1.2m Unfossiliferous black recrystallized limestone - 3.2 m Total thickness = 24.9 m 1 cm = 2.5 m Figure 17. Stratigraphic section of Martin Bridge Formation (?) (Upper Triassic), Black Marble Quarry, OR. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i 49 Site #5 - Ant Hill Bioherm. Suplee-Izee. Oregon The Robertson Formation of the Early Jurassic (Upper Pleinsbachian) has several exposures of lithiotid bioherms. Dickinson and Thayer (1978) suggested that the Roberston formation and other sedimentary rocks of the Suplee-Izee terrane were deposited in an intra-arc basin of the older volcanic arc Olds Ferry terrane, which was active in the Permian and was accreted onto the craton during the Early Cretaceous. The Olds Ferry terrane has been correlated with the Quesnellia terrane based on paleomagnetic data, deformational history and igneous rock trends (Vallier, 1995). The Robertson Formation is part of a largely volcaniclastic sequence called the Mowich Group located on the Suplee-Izee Terrane. It rests on an angular uncomformity over folded chert-pebble conglomerates of the Triassic Begg and Bribois Formations and is overlain by the Suplee and Snowshoe Formations of volcanic sandstones (Nauss and Smith, 1988; Fig. 18). The Robertson Formation is comprised of a sandy pebble conglomerate, volcanic sandstone and minor grey limestone units and reaches thicknesses of 60 m. Lithiotis bioherms create a baffiestone biofacies and death assemblages of lithiotids form a rudstone facies. Outcrops of the bioherms are up to 10 m thick. The Ant Hill bioherm study locality is located just north of the fork of Cow Creek and Pine Creek (Fig. 18). The "reef-flank” facies is the most diverse assemblage with Nerinea gastropods, terebratulid brachiopods and j Lithiotis in a calcarenite or caldlutite matrix (Fig. 19; Nauss and Smith, 1988). The inter-bioherm facies areas are characterized by a bivalve wackestone with a diverse pelecypod fauna, lesser numbers of gastropods and brachiopods and sometimes mudcracks (Nauss and Smith, 1988). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Suplee Scale in kilometers Bums Figure 18. A-Localitymap for AntHillBioherm,OR(1.2km westof Cow Creek on Suplee-Ise Road; Izee 75” Quadrangle, T17S, R27E, Section 9, NE1/4). B - Photograph of Ant Hill Bioherm. The two bioherms are visible outcropingas light colored rocks on the left and middle rightof the horizon. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. m 51 Argillaceous mudstone with small amounts of gastropod and minor brachiopod shell hash -4.1m Reef flank - som e in situ Lithiotis, mostly rubble, brachiopod and gastropod hash in interstices -2 m Rubble of Lithiotis fragments, no other fossils noted, mud matrix, high energy - 4.4 m M M Lithiotis bioherm, most specimens all in life position, one gastropod found in the bioherm- 11.2 m Rubble of lithiotid fragments, no other fossils noted, mud matrix, high energy, shells ailigned - 6.9m Light colored mudstone, unfossiliferous -10.3 m Limestone lenses in mudstone matrix, shell debris (unidentified gastropods and brachiopods in the lowermost meter) - 20.2 m Argillaceous mudstone with small amounts of gastropod and minor brachiopod shell hash - 3.8 m Volcanic sandstone with clasts from the Upper Triassic Begg formation, unfossiliferous -16.8 m Argillaceous limestone with ammonoid impressions • 5.3 m Rubble of lithiotid fragments, no other fossils, mud matrix, medium energy, shells non-alligned - 4.2 m Total thickness = 89.2 m 1 cm = 5 m Figure 19. Stratigraphic section, of Ant Hill Bioherm, Robertson Formation (Lower Jurassic), Suplee-Izee, AZ. Lithofades terms from Nauss and Smith (1988). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52 As discussed earlier, the Early Jurassic was a period of recovery after the end-Triassic mass extinction. Reef-building was experiencing a hiatus during the Pliensbachian-Toarcian in the Tethys with the exception of other similar lithiotid bioherms and the unusual Assemmouk Sequence, High Atlas Mountains, Morocco (Lee, 1983). The dominant reef builders in that system were bivalves as well and to a lesser extent stromatoporoids and scleractinian corals. Site #6 - North and South Paul Spur Reefc, Bisbee. Arizona The Lower Cretaceous (Aptian-Albian) Mural Limestone records the maximum marine transgression across southeast Arizona, in the Bisbee Trough. The Mural Limestone is found above the transgressive Morita Formation and below the regressive Cintura Formation. The Mural Limestone was deposited upon a carbonate and siliddastic shelf to shelf margin complex, thickening eastward. Paul Spur Reef is located approximately 3.2 km southeast of Bisbee, Arizona on U.S. highway 80 (Fig. 20). North Paul Spur Reef is approximately 50 m north of the highway, while South Paul Spur Reef is about 700 m south of the highway and forms a much taller scarp. The upper unit (90 to 150 m) of the Mural contains numerous coral- algal-rudist buildups (Fig. 21). Scott (1979) delineates five fades: 1) coral- stromatolite-rudist boundstone (reef core), 2) coral-rudist fragment packstone (reef flank), 3) peloid-ooid grainstone (shoal), 4) mollusk-milliolid-orbitolinid wackestone (shallow shelf to open lagoon); 5) ostracod-mollusk-skeletal algae wackestone (restricted lagoon or shelf). The uppermost reef core is characterized by the branching coral Calamophyllia sandbergeri, with Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lowell South Paul Spur Reef Oouglas Figure 20. A - Locality map for Paul Spur Reef, AZ (Paul Spur 7.5" Quadrangle, T32S, R25E, Section 36, NW1/4, SE1/4, NE1/4). B - Photograph of North Paid Spur Reef from US 80 looking north. The limestone ridge cropping out at the center of the photo is approximately 10 m tall. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 Coral dominated boundstone of erect branching forms, light gray, micritic matrix with geopetai structures, climax community of reef core, no molluscs visible, rare stromatolites, some specimens with red rinds - 1.7 m Coral boundstone dominated by massive domal and tabular corals, Microsolena, associated with the most diverse reef succession enrusting stromatolite forms, boring bivalve and sponges occur with the stromatolite facies and penetrate into corals; upper reef core - 9.3 m Coral boundstone dominated by pioneer community of encrusting Actinastrea corals, also enrusting stromatolite forms, rarely rudist fragments of Caprinuloidea gracilis, basal reef core • 5.6 m Light gray coral-rudist packstone with abundant micritized grains of corals and rudists, associated with the reef flank environment - 4.4 m Light gray laminated to mottled wackestone/packstone. micritic matrix with some microspar, abundant miliolids and orbitoiinids. Monopleura fragments and intact specimens, horizons of Chondrodonta chondrodonta; some Toucasia hancockensis, associated with the back reef environment > 6.1 m Total thickness = 27.1 m 1 cm = 2.5 m Figure 21. Stratigraphic section of North and South Paul Spur Reef, Upper Mural Limestone (LowerCretaceous), AZ. Lithofaries terms from Scott (1979) and Hartshorn (1989). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I O D branches 1 cm in diameter and 25-30 cm high. The reef-core facies is dominated by the colonial corals Actinastrea whitneyi and Microsolena texans; the latter coral is commonly encrusted by stromatolites. Caprinids (Caprinuloidea gracilis and Coalocomana ramosa) and monopleurid rudistid bivalves are secondary in abundance. The shallow shelf is characterized by the rudists Monopleura cf. M. Marcida and Toucasia hancockensis as well as Chondrodonta chondrodonta and nerineid gastropods. The restricted lagoon facies contain Exogyra and Crassostrea communities and abundant Arenicolites trace fossils. Boring and bioerosion is common in all facies. Absent at Paul Spur, but present in other outcrops of the Mural Formation (Lee Siding Quarry, Grassy Hill, Mexican Saddleback Reef) is a well-developed Petalodontia felixi reef core. Similar coral-algal patch reefs are known from the Barremian-Aptian of Southern France and Yugoslavia (Masse and Phillip, 1981; Simo et al., 1993). In these examples, stromatoporoids are common contributors to the reef-frame wo r k. However, in the Mural Limestone stromatoporoids are virtually absent. I Site #7 - Mexican Saddleback Reef. Huachuca Mountains. Douglas. Arizona ; Mexican Saddleback Reef, also of the Mural Limestone (Aptian- K. | Albian), forms a knoll near the Mexican Border, southeast of Douglas AZ, ‘ with beds dipping 17° to the northwest. The reef is located in the southeastemmost comer of Arizona, just west of the Pelondllo Mountains in Guadalupe Canyon (Fig. 22). Hartshorn (1989) completed a study of this reef and constructed a facies arrangement of 11 biofacies. All of these biofacies, may be simplified using Scott’ s (1979) system. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. New Mexico Map Area Douglas Agua Prieta Scale in kilometers B . Figure 22. A - Locality map for Mexican Saddleback Reef, AZ (Guadalupe Canyon 75" Quadrangle, T24S, R32E, Sectionl7, N l/2, SE1/4). B - Photograph of Mexican Saddleback Reef lookingto the east, the ridge in the centerof the photo is approximately 17 m tall. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A slightly different assemblage of rudists from Paul Spur Reef is observed at Mexican Saddleback Reef. Actinastraea and Microsolena still build the inner reef-core, however the monopleurid rudist Petalodontia is also found within the inner reef-core and builds an outer reef-core framework as well (Fig. 23). Caprinids are found creating mounds in the outer reef to back reef areas. A shallow shelf area is found at this site comparable to at found at Paul Spur. Of note, is the absence of stromatolites at Mexican Saddleback in contrast to their prevalence at Paul Spur in the upper reef core facies. ! f i i i I > r Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 Miliolid-monopleurid lime mudstone, micritic matrbc with abundant miiiolids and lesser amounts of orbitolinids, varying amounts of the rudist Monopleura, some found as individuals others as thickets, upright elevators, silicified burrows of Thalassinoides - 3.1m Chondrodontid-caprinid floatstone/boundstone, biostromal arrangement of Chondrodonta with lesser numbers of Caprinuloidea - 2.3 m Toucasid wackestone/floatstone facies, micrite and sparry caicite matrix, abundant miiiolids, mollusc fragments and peloidal grains., Toucasia hancockensis, abundant but random arrangement - 4.0 m Caprinid floatstone/rudstone facies, lenticular bed. matrix foraminiferal wackestone (Hartshome, 1989); Caprinuloidea gracilis and Coaicomana ramosa, lesser amounts of miliolid and orbitolinid foraminifera not as closely packed as the petalodontid framestone, more recumbent forms, outer reef core/back reef areas - 8.2 m Petalodontid boundstone facies associated with the outer reef core, lenticular bed, micrite in-between erect, elevated petalodontids and fills cavities, fragments of petalodontids common at the base - 21.8 m Coral boundstone dominated by massive domal and tabular corals associated with the inner reef core of the pioneer community of encrusting Actinastrea corals • 9.1 m Fossiliferous coated-grain packstone/grainstone with variable amounts of micrite and sparry caicite in matrix, dominated by coated bivalve and echinoderm fragments - 2.0 m Total thickness = 50.5 m 1 cm = 5m Figure 23. Stratigraphic section of Mexican Saddleback Reef, Upper Mural Limestone (Lower Cretaceous), AZ. Lithofades terms from Scott (1979) and Hartshorn (1989). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i t 59 FUNCTIONAL MORPHOLOGY Introduction to Bivalvia Bivalves have typically been the most abundant and diverse fossils in shallow-water benthic environments since the beginning of the Mesozoic (Raup and Boyajian, 1988). More importantly, however, is the wide variety of bivalve life modes (cementing, reclining, burrowing, or byssally attached) and trophic habits (filter vs. deposit feeders, photosymbiotic or chemosymbiotic; Dame, 1996). The ecological versatility of this class has allowed its into virtually all marine and fresh-water environments, and development of a wide diversity of forms. The various ecological roles of bivalves may be described as trophic constituents, influence {e.g. nutrient cycling and construction), or recorders (monitors or "sentinels"; Tripp and Farrington, 1985). Bivalves may be categorized into several feeding or trophic groups. Suspension or filter feeding bivalves are common in shallow coastal marine habitats with firm to rocky substrates (Jorgensen, 1990). These organisms commonly graze on phytoplankton in the water column, resuspended I benthic microalgae, protozoans, organic detritus with attached microflora and f I often their own larvae (Small and Prins, 1993). Deposit-feeding bivalves are [ typically found on or in soft or muddy sediments where they consume sediments and remove organically rich particles (Jorgensen, 1990). hi this deposit feeding mode, bivalves are in competition with the sediment microbial community for food (Levinton, 1995). It has been suggested that deposit-feeders alter the benthic environment so as to hinder the presence of filter feeders resulting in competitive exclusion (Rhoads and Young, 1970; Thayer, 1979). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 Symbiotic feeding relationships are found in a number of different bivalves. Photosymbiosis is prevalent in the modem Tridacnidae in oligotrophic coral reef systems (Hawkins and Klumpp, 1995). As described earlier, feeding of these organisms is partitioned between the uptake of photosynthates generated by the symbiont, dissolved organic matter and digestion of zooxanthellae cells (Klumpp et al., 1992). The symbiotic relationship results in a nutritional subsidy expressed as rapid growth rates and increased calcification (Muscatine, 1967). Chemosymbiotic relationships are found in a number of bivalves in deep sea hydrothermal vents, methane seeps and anaerobic sediments (Fisher, 1990). In these symbioses, bacteria living in the bivalve's tissues convert inorganic chemicals, usually reduced sulfur, into compounds that can be utilized by the organism (Fisher, 1990). Bivalves process materials by consuming particulate or dissolved organic matter and excreting inorganic nutrients. In performing this process, they may couple the water column to the benthos, bioturbate the sediments and change the biogeochemical environment of adjacent substrates (Dame, 1993; Levinton, 1995). As a result, in bivalve-dominated ecosystems they are integral for the cycling of nutrients. Bivalves process materials at high rates and thus speed up nutrient cycling (Levinton, 1995). Nutrient processing by bivalves increases the concentrations of limiting nutrients within their environments and in doing so may regulate primary production (Dame, 1996). Bivalves are excellent indicators of stress in marine ecosystems (Tripp and Farrington, 1985). Because they are sessile as adults and pump water through their bodies, their shells are records of ecosystem change (e.g. temperature shifts via stable isotopes or nutrient flux via elemental ratios) through time (Klein et al., 1996). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 Bivalves may influence their immediate environment by being a major component of the biological structure whether in a coral reef, oyster bank or biostrome. Several styles of construction and aggregations of bivalves are recognized. Seilacher (1984) divided these epifaunal aggregational styles into two basic strategies: mudstickers (cone-shaped, spoon-shaped and stick shaped) and edgewise rediners. Recognition of Life and Trophic Mode in Fossil Bivalves A variety of morphological characters represent variables used to identify and infer life habit. Skeletal features include hinge dentition (or lack of), pattern of shell ornamentation, morphology of the ligament, shell microstructure, and gross shell form (Stanley, 1977; Fig. 24). Non-skeletal features include degree of mantle fusion, presence or absence of an adult byssus (array of threads for attachment), and anatomy of the ctenidia (respiratory/feeding structures) and stomach. Non-skeletal features are commonly expressed in preserved hard parts. For example, muscle "scars" found on the valve interior are expressions of the soft part morphology of the muscles that keep the valves closed (see Fig. 24). Similarly, the pallial line is a similar demarcation of the size and placement of the mantle (Fig. 24). The presence of a byssus (threads that a bivalve uses to attach to the substrate) may be inferred from the presence of a byssal gape or other shell modifications (Stanley, 1972). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62 Umbo Hinge Plate Ligamental groovi Tooth area (posterior lateral socket) Posterior adductor muscle scar n Tooth area (cardinal teeth and sockets) Tooth area anterior lateral socket) Anterior adductor muscle scar Pallial Line Figure 24. Cerastoma edule. Interior left valve of a Recent heterodont bivalve. Morphological terms listed are illustrated for those used in the text. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Characteristics used to determine the constructional role of bivalves in bioherms and biostromes include the attachment of the organism to the substrate (cemented, free-lying, etc.)/ associations with other fauna (boring or elevators above the substrate) and co-cementation between individual shells (pseudocoloniality; Kauffman and Johnson, 1988). Packing potential may be estimated by the shell form of the attached valve (Kauffman and Johnson, 1988) or by measuring the distances between organisms (Coates and Jackson, 1985). Two of these characteristics, packing and degree of pseudocoloniality, are vital in placing the organisms in their respective guilds. Packing is used as a quantitative estimate for pseudocoloniality, a feature associated with aggregative behavior due to larval selection, nutrient availability or evolutionary innovation (i.e. photosymbiosis; Cowen, 1988). For example, a large bivalve with low packing potential value and low pseudocoloniality was most likely a dweller in the bioherm. In contrast, an erect organism elevated above the substrate that is tightly packed with other similar organisms associated with a large degree of cocementation is most likely a "constructor." The criteria for recognizing trophic level in ancient bivalves rely heavily on modem analogs and p aleoenvironmental reconstruction. Because the organisms studied in this research are all epifaunal in shallow marine environments, the assignment of trophic mode is restricted to filter feeder or photosymbiotic. Particularly contentious is the recognition of photosymbiosis in the fossil record. Because algal symbionts occur in the soft tissues of extant bivalves and reef dwellers, evidence for symbiosis in the hard-part-dominated fossil record is typically equivocal (Seilacher, 1990). Cowen (1983, 1988) recommended several criteria: 1) oligotrophic permission of the copyright owner. Further reproduction prohibited without permission. 64 paleoenvironmental setting; 2) light isotopic signature; 3) large shell size; 4) aberrant shell morphologies that may in some cases, promote exposure of soft tissue to light, and 5) epifaunal habit, particularly where preserved with other infaunal clams. Assignment of bivalves to a trophic level is more complicated because of the variety of forms and adaptations in modem bivalves not all of which reflect their life mode. For example, Jones and Jacobs (1992), in a study on the modem photosymbiotic Clinocardium cardissa, concluded that it has a "typical" shell structure and isotopic signature, suggesting that the number of potential fossil bivalve photosymbionts may be currently underestimated. In the specimens used in this study, none were amenable to stable \ isotopic analysis as most had been recrystallized. Therefore, hard part I morphological characteristics were used to analyze trophic mode. For example, an increase in shell primary porosity (via accesory cavities or pallial canals) may be interpreted in two ways: 1) filter feeder - a mechanism to increase shell height in response to increased sedimentation as in the extant Saccostrea; or 2) photosymbiotic - a mechanisms to increase exposure of soft I parts housing zooxanthellae to light as in Corculum (Carter and Schneider, I 1997). Therefore, it is critical that paleoenvironmental analysis I (sedimentology and life mode of co-occurring organisms) is incorporated in any study. Other variables that aid in trophic mode or guild assignment include: valve form, hinge, ligament, shell mineralogy and ornamentation (Kauffman and Johnson, 1988; Fagerstrom, 1991). Aberrant shell morphologies may be assessed by deviations in valve form. Most bivalves are roughly equivalved (e.g. the common surf clam, Mercenaria mercenaria). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. "rwc i 65 However, bivalves in the constructor realm exhibit strongly inequivalved forms. For example, the modem oyster Saccostrea has a large cone-shaped attached valve and small cap-shaped free valve and constructs bioherms off of the West Africa Coast (Seilacher, 1984). Modifications of the valve form are often accommodated by alteration in the means of valve attachment, the hinge and ligament. Shell mineralogy (aragonite or calcite) and structure (prismatic, fibrous, nacreous, etc.) are indicators of adaptations to environment or life mode (Stanley, 1968). The "fiber-optic" prisms of Corculum allow light transmission to zooxanthellae in the soft tissue, without direct exposure to sunlight (Carter and Schneider, 1997). Kauffman and Johnson (1988) suggested that increased ornamentation is a feature correlated with advanced specialization in response to the variety of niches seen in modem coral reef environments. History of Bivalvia in Carbonate Buildups The Class Bivalvia of the Early Cambrian is documented by two genera Pojetaia and Fordilla (Pojeta, 1987). The diversity of marine bivalves has been evidenced by an overall expansion since the Ordovician (Raup and Boyajian, 1988). Many bivalves were reef dwellers by Middle Ordovician time, but their abundance remained low throughout the Paleozoic and Early Mesozoic (Fagerstrom, 1987). The oldest epibyssate epifaunal bivalves are known from the Middle Ordovician (Stanley, 1977). A rapid Ordovician radiation ended during the Silurian, followed by a period of relative evolutionary stability (Stanley, 1977). The most important attribute that differentiated bivalves from other contemporary invertebrate groups was the hydraulically operated, muscular foot, which permitted mobility on or within the substratum and, in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 some cases, provided a byssal apparatus for temporary or permanent attachment (Stanley, 1968). Other special adaptations were the ligament- bearing, hinged shell, the ciliated gill and labial palp structures for feeding (Dames, 1996). Watkins (1996) documented the minor role of a group of suspension-feeding bivalves in a Silurian reef complex. These bivalves lacked the high diversity and the extent of adaptations to various niches seen in modem or Mesozoic reefs. In fact, these bivalves differed little from neighboring clastic facies (Watkins, 1996). The first unattached epifaunal bivalve, Pemopecten, occurs in the early M ississippi^ followed by the first appearance in epifauna of the eulamellibranch gill type (Cox et al., 1969). The first bivalve to exhibit attachment by cementation, Pseudomonotidae, appeared in the Permian. Cementation is an important innovation as it is the means of attachment for many modem and ancient reef bivalves (Seilacher, 1984). The majority of modem cemented bivalves are shelf- dwellers and are concentrated in the inner sublittoral benthic zone (Stenzel, 1971). Cemented bivalves prefer exposed or semi-exposed substrates subject to periodic wave and current action, good lighting, agitation, periods of turbidity and an abundant food supply (Seilacher, 1984). Bivalvia exhibited a second radiation in the Mesozoic when the number of superfamilies increased from 9 (Permian) to 16,23 and 27 in the Triassic, Jurassic, and Cretaceous, respectively (Cox et al, 1969). Stanley (1968) attributes the post-Paleozoic adaptive radiation of infaunal bivalves to mantle fusion and siphon formation. The appearance and evolutionary success of epifaunal bivalve groups (e.g. oysters, inoceramids, rudists) in the Mesozoic has commonly been attributed to the open ecospace after the Permian-Triassic mass extinction (see Raup and Boyajian, 1988 for review of literature). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ! 67 Oysters did not appear until the Late Triassic and they are commonly associated with reefs of this time. Early Mesozoic reefs have large portions of megalodonts. Common in the Upper Triassic Dachstein facies of the Alps, these bivalves are essentially dwellers (Fagerstrom, 1987). The Triassic-Jurassic mass extinction disproportionately selected against bivalves and reef organisms (McRoberts et al., 1995). Many of the elaborate reef-associated megalodont forms went extinct at this boundary (Hallam, 1981). The Early Jurassic is notable for its cosmopolitan Lithiotis and Cochelarites bioherms (Fagerstrom, 1987). Middle Jurassic bioherms and reefs are characterized by deeper-water sponge-algal buildups with lesser amounts of bivalves (Wood, 1993). In shallow marine settings at low latitudes, from the Late Jurassic (mid- Oxfordian) to the Late Cretaceous (Maastrichtian), the superfamily | Hippuritacea arose from the order Hippuritoidea (the same order as that of | the megalodonts). Middle and Late Cretaceous bioherms had large I | biovolumes of rudistid bivalves. Some species of rudists constructed I bioherms and biostromes (in particular the large barrel-shaped radiolitids) ! while others were dwellers living on the reef flanks or in the lagoons (Scott, | 1995). Kauffman and Johnson (1988) have suggested that for over 40 m.y. ? rudists out-competed other reef fauna by evolving "new morphological and I ecological features convergent on the bauplan of successful Phanerozoic reef- I ! building taxa." Bivalves in Mesozoic reefs display a number of different life- modes (from solitary to closely packed) and different guilds (dweller, destroyer, constructor). Rudists and other reef-associated bivalves suffered extinction at the end-Maastrichtian event (Pojeta, 1987). During, the Miocene, the oyster Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. r,n.T**vfv . 'j m gifi ~ I i 68 Crassostrea gryphoides (or C. gigantissima) grew to lengths of 60 cm with shells as thick as 15 cm and formed reefs in warm shallow brackish waters (Stenzel, 1971). Today, oyster reefs are formed by brackish water species such as Crassostrea and Mytilus, with these reefs restricted to the temperate zone (compare to tropical water restriction of modem coral reefs; Hughes, 1991). As described earlier, bivalves in modem carbonate buildups exhibit a variety of roles that are dependent on life-mode concomitant with the ambient nutrient regime. For example, the oligotrophic-adapted Tridacnidae dwellers are found in modem coral reefs in contrast to the eutrophic-adapted constructors, Ostrea or Saccostrea (Seilacher, 1985). Increases in populations of lithophagid bivalves (destroyers) and filter-feeding bivalves (dwellers) are associated with increases in nutrient flux in carbonate buildups (Highsmith, 1980). Methods Data were collected from studied sites using a modified line-intercept transect method, which is commonly used on both modem and ancient reefs (Perrin et al., 1995). On two-dimensional outcrops parallel or slightly oblique to the reef-front, one meter horizontally offset sampling lines were taken when possible on previously logged geological sections or biofades. The intersecting length of the different components along transect lines was measured to the nearest half centimeter. Measured components induded organism, matrix or unknown. This method produced data that was used for organism counts and size, hides diversity and biovolume (Appendix 1). Thus, the data were applicable to a variety of statistical approaches (functional morphology and autecology of bivalves; paleoecology) and minimized Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I t i 69 problems arising from outcrop conditions and comparisons between different reef-building taxa. Six morphological characters and three autecologic characters were examined for nine bivalves: Megalodon, Neomegalodon, wallowaconchids, Lithiotis, Monopleura, Petalodontia, Coalocomana, and Caprinuloidea and Chondrodonta. The morphologic features - hinge, ligament, valve shape, shell mineralogy, primary porosity and ornamentation - were collected from field observations as well as the literature. Autecologic characters - attachment to substrate, packing and pseudocoloniality - were observed and measured in the field using the line-intercept method. Packing values were obtained by calculating the mode of all the distances (including matrix or another organism) between the bivalve and another bivalve (Coates and Jackson, 1985). Small packing values are typical of bivalves that are gregariousm or constructors (e.g. oyster banks have values less than 1 cm; Bahr, 1976). Whereas, larger packing values are associated with bivalves that are dwellers or less likely to form dense aggregates (e.g. Tridacna has a packing value of 30 cm or greater; Dame, 1996). Results The studied bivalves are described in chronological order with the stratigraphic and geographic range. Morphological descriptions are summarized in Table 4. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Llmua Valve form Megtihklaii cquivalved, thin subtrigonal/ovate S ize 14 cm lull; 12 cm wide H inte/T m illisltuclun! Ugilltlvnl Shell m ineralogy Shell porosity heterodont; massive hinge plate external calcilc imne Om aincntalhiii weak concentric mgae and costae NnmKgalodon equivalved, thick, subtrigonal/ovate; 8 cm tall; well-developed lunules heterodont; left valve two subequal external 1 0 cm wide cardinal teeth; right valve one triangular cardinal tooth calcite unknown unknown wallowaconchids equivalved, thick, ovate with alatoform 32 cm high; massive hinge plate; unknown unknown extensions 80 cm wide dentition unknown, presumed concentric cavities weak concentric lobecalcilic within wings growth rugae strongly inequivalved; right valve I • 3 cm high; edentulous; hinge plate on central "moved" 1.5 cm thick; left valve 1-2 mm thick 5-6 cm wide right valve interior; not articulated upward with arranged at maturity shell growth aragonilic, radially longitudinal canals exterior well-dehncd growth rugae; interior of right valve complex ligamental grooves Munupfrura strongly inequivalved: AV • conical 4.3 cm high; pachydont; AV single tooth; FV two external- gently aragonilic; two slender, twisted; FV - opcrculate 1 cm wide unequal teeth '"LT-shaped layers: outer prismatic layer and inner spar layer concentric growth lines; longitudinal striae (Vla/cx/onlia strongly inequivalved: AV - conical, 9 cm high; 4.5 pachydont; AV- one tooth; FV • two external- gently aragonilic; two straight; FV - opcrculate 6 cm wide unequal teeth '"U"-shaped layers: outer prismatic layer and inner spar layer randomly arranged longitudinal striae; well-developed growth rugae Cmlnctimiu inequivalved: AV • long slender loosely 20 cm high; pachydont; AV • large central tooth; external- gently aragonilic; two coiled; FV • shorter, strongly curved; 8 cm wide FV-two subequal teeth '"LT-shaped layers: outer- main cavity partitioned into smaller prismatic; inner-spar pyriform body and accessory cavities one row ol canals; faint "growth" rugae outer • small, Caprinuloidra inequivalved: AV straight; FV shorter, 12 cm high; 3-pachydont; AV • three massive external- gently aragonilic; two two rows of strongly curved; main cavity 4 cm wide teeth; FV-two teeth ”U"-shaped layers: outer- canals; Inner • partitioned into smaller body and prismatic; inner-spar large polygonal; accessory cavities outer-small, pyriform unknown Cluinifnxfunla equivalved, subtrigonal 15 cm high; edentulous, valves articulated via ligamental "sub-nacreous" 6 cm wide complex double-hook structure groove with resilifers deep plicated valves Table 4. Summary chart of bivalve features. Attached valve ("AV") and free valve ("FV") are rudists terms. I k k i c t K c a Vegh- Neuhrandt, Vegh- Neubrandt, 1982 Yancey and Stanley, 19% Chineei, 1982, Sava/id, 1996 Whitney, 1952 Scott, 1981, Hartshorn, 1989 Whitney, 1952; I’almer, 1928 Coogan, 1977, I’ erkins, 1969 Cox el al, 1969 I 71 Upper Triassic - Megalodonts Order HlPPURITOIDEA Newell, 1965 Superfamily MEGALODONTOACEA Morris and Lyett, 1853 Family MEGALODONTIDAE Morris and Lyett, 1853 The stratigraphic range of megalodonts is from the Upper Silurian to the Lower Cretaceous, but they were most common in the tropical Tethys of the Late Triassic (Vegh-Neubrandt, 1982). Of specimens collected from Summit Point Reef and Dunlop Canyon, most were large with thin valves (~14 cm tall; Fig. 25). Specimens collected from New Pass Mine were of a thicker shelled species and smaller size (~ 8 cm tall; Fig. 26). A third type of megalodont was collected from Black Marble Quarry, the recendy described ? ■ wallowaconchids (Fig. 27). Genus MEGALODON Sowerby, 1827 Only two-thin shelled megalodonts are known, Megalodon, Sowerby, 1827 and Pomarangina Diener, 1908. Pomarangina is only known from the Himalayas (Cox and Newell, 1969). Therefore, these specimens are assigned to the more cosmopolitan genus Megalodon. The stratigraphic range of this genus is from Devonian to Upper Triassic (Cox et al., 1969). These Camian- Norian specimens have thin valves that are large, gibbose, subtrigonal or ovate with prosogyrous beaks (Fig. 25). The largest specimen from Summit Point has a height at the beak of 14 cm and is 12 cm across the shell. The hinge plate is massive with the cardinal teeth varying in number from one or two in the left valve and one to three in the right valve (Cox et al., 1969). The ligament is external. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 25. Megalodon. A - Cross-sectional view from Summit Point, Upper Triassic (Camian-Norian), Martin Bridge Formation, near Halfway, Oregon. B. Reconstruction of a Megalodon, adapted from Vegh-Neubrandt (1982). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I t 73 The shell mineralogy is predominantly calcite w ith little w all porosity. Because most specimens are found in limestone reef deposits, m ost are recrystallized resulting in a lack of knowledge about the initial shell crystal arrangem ent (e.g. fibrous, or prismatic, etc.). Ornamentation consists of weak concentric folds or radial ribs with rare alatoform structure (A. G. Fischer, 1995, pers. comm.). Most Megalodon specimens were found reclining on the substrate with the comissure pointing up. Modal packing value is very high, 25 cm, therefore habit of the organism is mostly solitary. Genus NEOMEGALODON Guembel, 1862 The thicker-shelled specimens from Ladinian New Pass Mine are assigned to the genus Neomegalodon. The genus is cosmopolitan in Upper Triassic low latitudes (Cox and Newell, 1969). Valves are thick, ovate equivalved, so strongly prosogyrous that the umboes have the appearance of slight coiling, and the lunule is well-developed (Fig 26; Vegh-Neubrandt, 1982). The hinge plate is-massive and tapers towards the posterior. The dentition of the left valve consists of a distinct posterior cardinal tooth with one or two anterior teeth usually subequal and radially elongated; right valve dentition is variable but usually has a triangular posterior cardinal tooth (Cox et al., 1969). Like Megalodon, Neomegalodon has an external ligament, predom inantly calcific shell, and is presumed (but unknown) to have no porosity in the valves (i.e. features that could harbor photosymbionts). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. w e : - r w i f f l w v . *■:v f w ~ & f j n a F T W * y r r - > rr * * w »^ r » r v .■ , I Figure 26. Neomegalodon. A - Cross-sectional view from New Pass Mine, Upper Triassic (Ladinian), Augusta Formation, near Austin, Nevada. B - Reconstruction of a Neomegalodon adapted from Vegh-Neubrandt (1982). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75 Neomegalodon also reclined on the substrate. However, it was found in closer association w ith other organisms w ith relatively lower packing values than Megalodon, (16 cm) between organisms. Therefore, Neomegalodon had a solitary habit but was commonly found w ith encrusting algae or lam ellar, encrusting corals. Genus WALLOW ACONCHA? These organisms are currently being described, however they have been assigned to the family Megalodontoidea (Yancey and Stanley, 1996). Informally nam ed wallowaconchids, they are found only in Upper Triassic (Cam ian-Norian) deposits w ithin three accreted terranes of W estern North ! America: W allowa and Stikinia in the Pacific Northwest and the Antimonio in Mexico. W allowaconchids lived in the same environmental niche as that occupied by the large m egalodontid bivalves of Upper Triassic Tethys. The valve form consists of two portions: 1) an ovate equivalved form sim ilar to that of other megalodont;, and 2) large wing-like extensions , containing chambers generating horn the umbonal region (Fig. 27). Large valve sizes are common, w ith some wingspans reaching 80 cm, and the tallest S - | measured specimen was 32 cm high. The hinge plate is massive and expands f into the body cavity, dividing the space and leaving it inoperational in | m ature forms (G. D. Stanley Jr., 1995, pers. comm.). The nature of the ligament is unknown and shell mineralogy is presumed to be caldtic. O rnam entation consists of fine to weak, concentric growth bands. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I Figure 27. Wallowaconchid. A - Cross-sectional view from Black Marble Q uarry Upper Triassic (Camian-Norian), Martin Bridge Formation, near Enterprise, Oregon. B. Hypothetical reconstruction of a wallowaconchid. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 Wallowaconchids reclined on the substrate in such a manner that the "wings" overlap with one another (see Fig. 27A). The organisms were very gregarious w ith a the measured modal packing value is 6 cm, with the acknowledgment that most specimens were found in continuous gregarious horizons. Although not cemented to one another, pseudocolonialty appears to have been very high. Shells of wallowaconchids possess some unique characteristics unseen in other bivalves: internal partitioning of alate wings, dividing that portion of the shell into elongate, open-ended chambers, and development of non articulating thin vanes on an expanded hinge plate (Yancey and Stanley, 1987). It is proposed that these bivalves evolved from the smaller i | m egalodontid lineages (Triadomegalodon and Neomegalodon), based on I f hinge plate morphologies, and not the larger megalodont Diceracartidae I lineage, which superficially has alatoform projections similar to that of I Wallowaconchids (Yancey and Stanley, 1996). I , X Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I ! 78 Loiver Jurassic -Lithiotids O rder PTERIOIDA Newell, 1965 Suborder PTERHNA Newell, 1965 ? Superfamily PTERIACEA Gray, 1847 (1820) ? Family ISOGNOMONIDAE Woodring, 1925 Genus LlTHIOTIS Gumbel, 1874 LlTHIOTIS PROBLEMATIC^ Gumbel, 1874 Lithiotis problematica was originally described as a calcareous alga (Gumbel, 1871). It flourished throughout the Tethyan Ocean with occurrences also known Panthallassa (occurrences in Peru and Northern Chile), but w ith a very short stratigraphic range, Pliensbachian-Toarcian (Loriga and Neri, 1976). Lithiotids and a convergent bivalve of the same time, Cochelarites, were both thought to be oysters despite their aragonite shell mineralogy (Nauss and Smith, 1988). Lithiotids are now thought to be taxonomically closest to the Pteriacea, particularly to the Isognomonidae, based on shell (radially arranged aragonite) and ligament structure (Chinzei, 1982). Lithiotis specimens from Suplee-Izee reached 30 cm or more in maximum height and 5 to 6 cm in w idth with an average thickness of 1 to 1.5 cm in the thick right valve (Fig 28). The thin (1-2 mm) left valves, collected by Loriga and Neri (1976), covered m ost of the cardinal area, therefore both valves were roughly the same height. A small cavity for the soft-parts of the organism was located at the ventral-m ost end with a deep conical notch at the umbonal end of the body space. Savazzi (1996) described an exceptionally well-preserved specimen w ith the ligam ent intact. The ligament is long and thin, joined both valves and was housed in ligamental grooves. Savazzi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i : Figure 28. Lithiotis problematica. A - Specimen from Ant Hill Bioherm, Lower Jurassic (Pleinsbachian-Toarcian), Robertson Formation, near Suplee-Izee, Oregon. B - Reconstruction of right valve interior, from Chinzei (1982). C - Reconstruction of longitudinal cross section through both valves, from Chinzei (1982). D - Cross section through right valve at x-x’ , from Cox et al. (1969). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I 80 (1996) concluded that the free valve was closed by flexing, not by articulation (the m ore common mode for modem bivalves), and the ligamental area did not "m igrate" as observed in other cementing bivalves (i.e. oysters). Wall porosity in the thick valve consisted of small internal tubes arranged along the cardinal axis of the shell, about 0.5 mm in diameter, and also one major tube in the shell interior, with varying diameters between specimens (Chinzei, 1982). Exterior ornamentation consists of heavy concentric growth lines. The central interior area (the portion covered by the thin valve, interpreted as the hinge plate) has an elaborate feathered chevron texture, and on either side are delicate ridge and groove features (Savazzi, I 1996). Lithiotids appear to have lived in a sub-vertical position in muddy i ( sediments and continuously extended the shell length to overcome sedim entation and sinking into the substrate (Chinzei et al., 1982). Packing of y lithiotids, computed as a 0.83 modal distance between thick valves, was extremely close, hi life position, lithiotids constructed upright bouquet-like aggregates and bioherms, in monospecific aggregations (Fig. 29). Lithiotid life habit has been compared to and assumed to be convergent with the extant oysters Konbostrea, Crassostrea, and Saccostrea (Chinzei et al., 1982). j ! Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 29. Lithiotis problematica. A - Cross-sectional view from Ant Hill Bioherm, Lower Jurassic (Pleinsbachian-Toardan), Robertson Formation, near Suplee-Izee, Oregon. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 Lozver Cretaceous - Rudists Order HIPPURITOIDA Newell, 1965 Superfamily HIPPURITACEA Gray, 1848 In the tropical Cretaceous (from m odem latitudes o f 9°-32° N), rudists are widely distributed from the West Indies, Baja California, Middle East and Southern Europe (Kauffman and Johnson, 1988). Rudist-bearing sequences hundreds to thousands of feet thick are present in the subsurface Cretaceous of the southeastern United States and eastern Mexico (Scott, 1979). Rudists differ from most other bivalves in being strongly inequivalve. In an individual, thetwo valves usually differ in both size and shape and therefore in function. The two families of rudists in this study are the Monopleuridae and the Caprinidae. Family MONOPLEURIDAE M unier-Chalmas, 1873 The attached valves of monopleurids are straight, curved or twisted cones (Donovan, 1992). The smaller free valves are usually operculiform or very low, spiral coils (Perkins, 1969). Some monopleurids reached heights of 20 cm, but most measured specimens at Paul Spur and Mexican Saddleback were generally sm all with heights of 2-6 cm. The two-layered shell w all of monopleurids is thin and compact. The inner layer is 0.1 to 1 mm thick and is always altered in the Arizona specimens to a caldte mosaic in which no original microstructure is preserved. The laminated outer layer is 1-4 mm thick. Because the teeth and sockets are sm all, the hinge structures are not prom inent and the mantle shell cavity is the most conspicuous feature of the shell. Myophore plates are inward projections of the inner wall into the body cavity, sometimes associated w ith the teeth, b u t specifically the adductor muscle scars on the plates indicate their utility as sites of muscle attachment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 This feature is unique to rudists and is used in identification (Perkins, 1969). Externally m onopleurid shells are generally smooth, but the attached conical valve may be marked by strongly developed growth laminae and fine to coarse longitudinal ribbing. Monopleurids are easily differentiated in outcrop from the other rudistid family (Caprinidae) common in the M ural Limestone, by the lack of the pallial canals within the attached valve's microstructure and the absence of partitioned body-chambers. Two genera of monopleurids are noted from the Arizona bioherms: Petalodontia and Monopleura. Genus MONOPLEURA M atherton, 1843 M o n o p l e u r a cf. M. m a r c id a White, 1884 Monopleura marcida W hite, 1884, p. 8, PI. 3, 4. Monopleura is common in the fore-reef and lagoonal facies of Paul Spur Reef. The valve morphology of Monopleura consists of a conical, slender, slightly twisted attached valve w ith a single tooth (Fig. 30). The free valve is operculate, flat or gently convex, w ith two unequal teeth; myophore plates are weakly developed. The shallow, gently spirally curved ligament groove is observed on the exterior of the attached valve. These fossils at the study sites are commonly observed upright w ith respect to the substrate w ith the "tops" planed off to reveal a subelliptical-ovate cross section. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Valve 84 Tooth #1 from Inner sp layer Outer prismatic layer Ligamental groove Attached Valve Tooth #2 om FV Body Cavity Figure 30. Monopleura cf. M. marcida. A - Reconstruction from field specimens collected at Paul Spur Reef (Aptian-Albian, M ural Formation). B - Transverse view through the attached valve. Free valve is denoted by "FV." Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 When removed from the matrix, the attached valve's ornamentation consists of concentric growth lines and longitudinal striae. Two shell layers are present, an outer prismatic layer and a thinner inner spar layer. Specimens from the Mural Limestone tend to be small (mean diameter .95 x 1.5 cm, mean length 4.3 cm) and more "twisted" when compared to W hite's Albian specimens from the Edwards Limestone of Texas (Whitney, 1952) . This genus was found usually in solitary associations w ith a median packing value of 6.2 cm and cemented to the substrate (large dome-shaped corals) but rarely to one another. Genus PETALODONTIA P o cta, 1889 PETALODONTIA FELIXI (Douville, 1900) Monopleura (Petalodontia) felixi Douville, 1900, p. 211-213, figs. 8-10. The attached valve of Petalodontia is large and conical, reaching heights of 9 cm and diameters of 4.5 to 6 cm (Fig. 31). In cross section the attached valve is a symmetrical oval-shape. Ornamentation on the attached valve consists of irregular and random arrangements of longitudinal costae and well-developed and concentric rugae. The free valve is rectangular in shape, operculate and flattened with an elongated myophore plate and a sm all posterior tooth. The shell wall is two-layered like that of Monopleura, w ith the outer layer prismatic and the inner sparry. The outer layer is dark gray in outcrop and consists of growth lamellae (0.1-0.2 mm thick) inclined 50-70° to the commissure; these are expressed on the surface as the growth rugae (Scott, 1981). Presumably, the original layers were originally composed of aragonite. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Growth Rugae Valve Ligamental groove Tooth #1 from FV Inner sp layer Outer q prismatic layer Attached Valve Tooth #2 from FV Body Cavity Figure 31. Petalodontia felixi. A - Cross-sectional view from Mexican Saddleback, Lower Cretaceous (Aptian- Albian), Mural Formation, near Douglas, Arizona. B - Reconstruction adapted from Scott (1981). C- Transverse view through the attached valve. Note the similarity in shell structure to Monopleura. Free valve is denoted by "FV." Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 Petalodontia constructed the reef-core at Mexican Saddleback reef, commonly cemented to one another, with a low packing value of 2.1 cm (similar to values of modem oyster banks; Bahr, 1976). Petalodontids were more gregarious and formed dense, monospecific banks w ithin a normally diverse coral-algal-rudist reef (Hartshorn, 1989). Family CAPRINIDAE d'Orbigny, 1850 Subfamily COALCOMANINAE Coogan, 1973 The family Caprinidae is recognized by shells w ith slightly curved to strongly coiled cone-shaped attached valves. The valves may be nearly equal in size, but usually the attached valve is much larger and more heavily < calcified than the free valve (Perkins, 1969). Most caprinids of Arizona are | assigned to the genus Caprinuloidea Palmer, 1928. I The most distinct feature of caprinids is the developm ent of abundant, thin-walled longitudinal canals (Palmer, 1928). The canals are bounded by vertical, radial plates which may be simple or polyfurcate or transected by vertical, tangential plates to polygonal canals in transverse section. These canals give a finely to coarsely honeycombed texture to caprinid shells. Seilacher (1996) describes sim ilar canals in other families of rudists (e.g. radiolitids) as possible adaptations for photosymbiotic associations. External ^ features of well-preserved caprinid shells are smooth or corrugated by coarse, | rounded, transverse wrinkles; poorly preserved specimens commonly have remnants of longitudinal ribs which are edges of vertical radial plates in the inner shell wall exposed by the removal of the outer calcific shell layer (Perkins, 1969). Caprinid teeth are large and massive in both valves and the accompanying sockets are large cavities. The teeth and hinge area make up to I : Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 one-third or one-half of the cross-sectional area of the valve (Donovan, 1992). Muscle insertions are on elevated, vertical plates separated from the shell wall by deep cavities. Genus COALOCOMANA Harris and Hodson, 1922 COALOCOMANA RAMOSA (Boehm, 1898) Caprina ramosa Boehm, 1898, p.327-328, fig. 4. The attached valve is long, slender, loosely coiled and ovate to rectangular in cross section (Fig. 32). Vertical radial plates of the attached valve branch two to three times, forming pyriform canals ventrally and posteriorly. The myophores are thin and elongate (Palmer, 1928). The free j 1 valve is short and strongly curved w ith two teeth: one large anterior and an I ovate, small posterior tooth (Whitney, 1952). Extremely subtle "growth" | rugae were seen, b u t no longitudinal costae belying the complexity of the wall | interior were noted. | Arizona specimens are 10-25 cm high and 2-8 cm in cross-sectional f diameter, but some Jamaican species attain large sizes of over 100 cm high I and 35 cm in cross-section (Kauffman and Sohl, 1974). This species was 1 common in the reef and the reef flank facies. l i Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 Pyriform Canals 89 Body Cavity Attached Valve Accessory Cavity Tooth Socket #3 Figure 32. Coalocomana ramosa. A - Cross-sectional view from Paul Spur Reef, Lower Cretaceous (Aptian- Albian), Mural Formation, near Bisbee, Arizona. B. Reconstruction adapted from Deschaux (1969). C - Cross section through x-x', note the presence only of the pyriform canals; polygonal canals common to Caprinuloidea are absent. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I I 90 Genus CAPRINULOIDEA Palmer, 1928 CAPRINULOIDEA g r a c il is Palmer, 1928 The attached valve of Caprinuloidea is long, slender, and sinuous with heights around 10-12 cm and diameters about 3-4 cm (Fig. 33). In cross section, the attached valve is ovate with vertical radial plates dividing the valve into two or three oval-shaped accessory cavities and a single kidney shaped body cavity, depending on maturity (Scott, 1981). Three cardinal teeth extend from the attached valve into spaces within the free valve (Perkins, 1969). W ithin the outer prismatic layer one or two rows of inner polygonal canals are present; the innermost row on the ventral side is larger than the outer row (Palmer, 1928). The free valve continues the body cavity space * ; from the attached valve and this area is larger, and more ovoid in f 6 : comparison (Coogan, 1977). An accessory cavity is also found in the free i | valve. Two teeth are on the free valve; an ovate anterior and a long, curved g | posterior. Myophore plates on both valves are expansions of the inner body b | wall. A U-shaped ligamental groove is located on both valves. 5 I Caprinuloidea are commonly found cemented to the substrate or to | one another. These specimens were typically more gregarious than ij % Monopleura found at Paul Spur Reef, and found in close association w ith the i coral-stromatolite reef core facies or as smaller banks on either side of the reef i core. Packing modal value is 2.3 cm and strongly pseudocolonial. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 Free Valve Polygonal Canals Pyriform Canals Body Cavity Accessory Cavity #2, Accessory Cavity #1 attached Valve Figure 33. Caprinuloidea gracilis. A - Cross-sectional view from Paul Spur Reef, Lower Cretaceous (Aptian- Albian), Mural Formation, near Bisbee, Arizona, specimens are recrystallized so the diagnostic shell microstructure is not preserved but valve form is characteristic. B. Reconstruction adapted from Perkins (1969). C - Cross section through x- x', note the presence of both the pyriform canals and polygonal canals. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I Lower Cretaceous - Chondrodontids ? Superfamily OSTREACEA Rafinesque, 1815 ? Family CHONDRODONTIDAE Freneix, 1959 Genus CHONDRODONTA Stanton, 1901 C h o n d r o d o n t a CHONDRODONTA Stanton, 1901 Found in Albian-Campanian tropical environm ents, chondrodontids were commonly associated w ith back-reef and lagoonal environments and commonly associated with rudists. Chondrodonta are thick-shelled, strongly inequivalved dimaryian bivalves (Fig. 34). The triangular and deeply plicated ' valves reach lengths of 15 cm at Mexican Saddleback Reef in Arizona. Shell I ; mineralogy is sub-nacreous in well-preserved specimens from Texas (Palmer, I 1928). No primary shell porosity was observed. The valves are thin, | elongated and triangular with radially plicated ornamentation. The ligament [ attachm ent site area is similar to that of oysters. The hinge of chondrodontids f consists of a unique and complex double hook and is edentulous. Chondrodontids attached to the substrate (or to each other) by the | cementation of the left valve. Packing modal value is 2.1 cm between t organisms. This low value suggests that these organisms were very gregarious forming monospecific, dense aggregate banks. Chondrodontids formed book-like aggregates, similar to that of Seilacher's (1984) suggested life mode for spoon-shaped mudstickers. Despite the superficial similarities to ! oysters, chondrodontids are not easily placed taxonomically in modem bivalve orders due to the double-hook hinge structure. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i B. Figure 34. Chondrodonta chondrodonta. A - Cross-sectional view from Mexican Saddleback, Lower Cretaceous (Aptian- Albian), Mural Formation, near Douglas, Arizona. B - Exterior view of right valve from Edwards Limestone, Texas (AMNH Specimen #103420). C - Reconstruction of the left valve interior adapted from Cox et al. (1969). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 D iscussion Key to understanding the role of the studied bivalves is an understanding of their guild assignment, plausible trophic mode (filter- feeding or photosymbiotic) and the ambient nutrient regime. These data are summarized in Table 5. Guild Assignment The studied bivalves may be classified in three of Fagerstrom's (1987) guilds: dw eller (Megalodon, Neomegalodon, Monopleura; Table 5), binder (W allowaconchid, Chondrodonta), and constructor (Lithiotis, Petalodontia, Caprinuloidea). In modem coral reefs, epifaunal bivalves are commonly dwellers (Fagerstrom, 1987). Chondrodontids and Wallowaconchids effectively stabilized soft substrates as binders do in m odem coral reefs. Chondrodontids binded the substrate by creating book-like aggregates and beds. Wallowaconchids stabilized the substrate by overlying the sponge-coral- strom atoporoid banks they dwelled in, forming dense horizons. The constructional role of bivalves is common in m odem eutrophic oyster reefs and rare in oligotrophic coral reef environments. Lithiotis constructed bioherms and biostromes globally during the Triassic-Jurassic mass extinction aftermath (Nauss and Smith, 1988). These buildups may be likened to m odem oyster reefs - monospecific aggregations in a eutrophic environment. The rapid rates of calcification and accessory cavities appear to have been a response to rapid sedimentation rate. The overall environment was most likely turbid and organic rich. The rudist constructors, Petalodontia and Caprinuloidea, lack direct modem analogs. These organisms constructed monospecific banks within the reef core or w ithin the flanks of the reef in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Attachment to Seilacbs- Guild Candidate for 95 Prvbabls. Miitnent Genus substrate Packing Pseudocolonialitv Classtfication ■Assignment Photovsmbiosis regime M egalodon reclined 25 cm solitary edgewise rediner dweller 7 oligotrophic to meso trophic Ncam egaladon reclined 16 cm solitary; but found edgewise in association with rediner encrusting algae and corals dweller 7 oligotrophic to meso trophic Wallowaconchid reclined 6cm gregarious. forming overlapping horizons edgewise rediner binder/dweller yes oligotrophic to meso trophic L ith io tis u p rig h t dotsai section of valve buried in substrate 0.83 cm gregarious, forming bouquet- like aggregations stick-shaped mudsticker constructor no eutrophic M onopleura cemented to the 6.2cm substrate usually solitary, sometimes in association with corals cup-shaped mudsticker dweller no meso trophic P etalodontia cemented to substrate or one another 2 .1cm gregarious; form dense monopsedfic banks within the reef core cup-shaped mudsticker constructor yes meso trophic Coalocomana cemented to substrate 5.1cm solitary, in association with organisms in the reef-core cup-shaped mudsticker (slightly recumbent) dweller 7 meso trophic C aprinuloidea cemented to subtrate or to one another 2 3 a n strongly pseudocolonial; cemented to each other in reef-core or reef banks cup-shaped mudsticker (slightly recumbent) constructor yes meso trophic C hondrodonta cementation by left valve 2 .1cm gregarious; formed spoon-shaped book-like mudsticker binder no meso trophic to eutrophic aggregates Table 5. Summary chart of studied epifaunal reef bivalve ecology. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96 association with other probable light-dependent organisms (Scott, 1979). High calcification rates, extensive cocementation and lack of interstitial sediments suggest responses to two possible scenarios: 1) high sedimentation with much winnowing; or 2) reduced sedimentation and superstratal growth within the photic zone. Trophic Mode - Filter Feeders or Photosymbiosis For this study, it was assumed that all bivalves were filter-feeders unless morphological and ecological evidence suggested a possible photosymbiosis. Most morphological features used to determine the presence of photosymbionts are equivocal. Some of the studied bivalves have compelling characteristics that suggest the possible presence of photosymbiosis and thus require further analysis w ith appropriate specimens. The most appropriate analyses to date are 5C1 3 and SO1 8 isotopes on appropriate (i.e. un-recrystallized) specimens. These candidates are W allowaconchids, Petalodontia, and Caprinuloidea. The diagnostic criteria for the presence of photosymbiosis come from Kauffman and Johnson (1988) and Co wen (1983,1988). Admittedly, Gili et al. (1995a) and Ross and Skelton (1993) question the validity of these criteria; however, the gregarious behavior, rapid calcification rates, modification of shell interior and association with other presumed light-dependent organisms (e.g. strom atolites and scleractinian corals) gamer some support for questioning the ubiquitous filter-feeding mode. Wallowaconchids are the strongest candidate for photosymbiosis. The shell form is similar to the modem Corculum and the extinct megalodont Dicerocardium. The former is photosymbiotic and the latter has been Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 proposed to have had a photosymbiotic lifestyle (Seilacher, 1985). Yancey and Stanley (1996) suggested that the elaborate vanes and chambers may have been utilized as surfaces to farm microalgal symbionts, providing an energy subsidy for their large sizes. Their extremely gregarious behavior (overlapping "wings") and their association with Retiophyllia daiosoni (a scleractinian coral, possibly photosymbiotic; Stanley, pers. comm.) is reminiscent of Tridacna beds in the Coral Sea (Frey, 1996). The two rudists, Petalodontia and Caprinuloidea, both created monospecific bioherms and occurred in coral-algal-rudist reefs of the M ural Limestone. Petalodontia felixi lacks the pallial canals of Caprinuloidea gracilis, which may have been effective for light transmission to photosymbionts in the mantle w ithout opening the valves. Caprinuloidea's large free valve with its strong coiling may have been cumbersome to open in the dense aggregations it formed (note the packing value for Caprinuloidea is slightly less than that of Petalodontia). Few extant photosymbiotic bivalves have such shell modifications for light transmission. Therefore, it is possible that Petalodontia had such photosymbiotic associations and that the small, operculate free valve was an adaptation to having the mantle exposed for long periods of time despite close packing with other organisms. Petalodontia is an excellent candidate for stable isotope studies; the large shell and the growth rugae provide the opportunity to retrieve several samples w ith some tem poral control. O ther studied bivalves (Megalodon, Neomegalodon and Coalocomana) lacked the gregarious habit common to the photosymbiotic candidates but have some morphological characteristics (large size and faunal associations) that are compatible w ith photosymbiotic criteria. De Freitas et al. (1993) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. J r 98 suggested that some Silurian megalodonts (similar in form to the Upper Triassic megalodonts of this study) were photosymbiotic but did not pursue lines of evidence other than morphological and uniformitarianist associations. The above mentioned bivalves may be candidates for photosymbiotic investigations but it is unlikely that appropriate megalodont specimens could be collected for stable isotopes. Also, it is unlikely that Coalocomana had photosymbionts if the more "successful" Caprinuloidea did not, since the two are morphologically sim ilar and virtually occupied the same niche. Probable Nutrient Regime Bivalve-constructed bioherms are common in eutrophic and mesotrophic environments. Lithiotids and chondrodontids (in a lagoonal facies of the Mural Limestone) are unquestionably filter-feeders forming aggregations in response to high sedim entation/nutrient flux. The other assignments of nutrient regime are more problematic. It is of interest that none of these Mesozoic carbonate buildups are easily identified as sim ilar to the oligotrophic regimes that dominate Recent systems. Contemporaneous buildups in Tethys were undoubtedly oligotrophic. But as mentioned in Chapter 2, the studied buildups lack certain faunal characteristics that differentiate them from their Tethyan counterparts. For example, bryozoans are not found in the Camian-Norian Mina reefs (see Stanton and Fliigel, 1987 for Tethyan faunal lists) and bryozoans were important "binders" and "bafflers" in Tethyan buildups. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Upper Triassic and Lower Cretaceous buildups all exhibit high amounts of bioerosion activity as w ell as large biovolumes of presum ed light- dependent organisms (Cornwall, 1979; Scott, 1979). Therefore, it is proposed that these Mesozoic buildups inhabited shallow carbonate environments w ith episodic nutrient fluxes and am bient nutrient levels higher than that of modem oligotrophic systems (i.e. mesotrophic). Quantitative criteria for analyzing the paleonutrient levels in ancient reefs are currently being explored (v. Braiser, 1995 for review). Some of the most promising include biological (ratio of P- to G-cysts of organic walled phytoplankton) and geochemical data (8N1 5 , C d/C a or B a/C a ratios, Ce anomalies). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 CLUSTER ANALYSIS General Statement Paleoecological studies often, use duster analysis to determine the structure of paleocommunities. The term "community" is almost as contentious as the word "reef" (Ginsburg and James, 1974). For the purposes of this paper a community is a naturally occurring group of organisms that inhabit the same ecospace or ecozone, and that can be statistically defined (Petersen, 1924). A paleocommunity is defined as a community that existed in geologic history and is represented only by fossils or other evidence of past organism s (Thorson, 1957). Cluster analysis is an appropriate method for determining paleocommunities because the m ethod links variables (e.g. organisms) on the basis of similarity or co-occurrence in multiple cases (e.g. sites, transects or localities). Modem reefs are ecosystems that are strongly ecologically zoned (Odum, 1971). The terms back reef, reef core and reef front represent different morphologies and communities of organisms (Kauffman and Scott, 1976). M odem reef cores are typified by erect, branching corals such as the staghom coral Acropora palmata and a host of other organisms, (e.g. sponges, herbivorous fish, lithophagid bivalves, crinoids, etc.)(Ginsburg and James, 1974). The strong zonation and concomitant diversity of m odem reefs is attributed to the constant selection pressure provided by a stable, oligotrophic environm ent (Hallock, 1988). Therefore, cluster analyses of modem and Pleistocene reefs are able to delineate several distinct communities and paleocommunities (Fig. 35). Figure 35 is a cluster analysis generated from data from a modem reef ecosystem in Quintana Roo, Yucatan, Mexico Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Restricted Lagoon Open Lagoon Back Reef Fore Reef Reef Core Open — -i ~ 1 L — -------------------------------- Figure 35. Modem coral reef (coastal Yucatan) R-mode dendogram from Warme et al. (1976), taxa are not included in the diagram but the communities cluster at relativerly low distances when compared to oyster reefs. Data from Ekdale (1972). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • 5 - I T * " - 102 (Ekdale, 1972). Note the strong community associations designated by short "branches" connecting taxa and the longer "trunks" connecting ail the data. The lengths of the lines represent the similarity (or conversely distances) between taxa. If oligotrophic environments are typified by multiple communities with distinct similarity linkages, mesotrophic and eutrophic communities are typified by fewer communities with lower similarities (or higher distances) linking them together (Warme et al, 1976). Mesotrophic systems are ecosystems inhabiting areas characterized by fluctuating levels of nutrients salinity and light (Wood, 1993). Therefore, diversity decreases and the ecosystem is inhabited by more eurytopic ecological generalists as nutrient flux increases in the environment (Braiser, 1995). Eutrophic bioherms represent an end-member system. As they are usually monospecific aggregations of organisms, a cluster analysis will often delineate a single community. Smaller accessory organisms will join the main "trunk" at distances comparable to that of their abundance. Figure 36 represents the data from a modem oyster reef. Note the dominant community of Ostrea edulis with other organisms joining the main "trunk" with increasing distances (or decreasing similarity). Taphonomy and Community Preservation The preservational opportunities for intact communities decrease as one moves back in the geological record. Soft-bodied organisms are abundant on modem reefs, however, they are rarely preserved. Community reconstruction, is also more tenuous for periods when the dominant organisms do not have morphologically similar extant taxa. It is unlikely that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I I I 103 Variable = (Distance of Link/Maximum distance) * 100 Variable 1 10 20 30 40 50 60 70 80 90 100 I Crassostrea -------------------------------------------- I Modiolus L . Brachidontes----------------------------------------------- Eurypanopeus ■ ■ ■ — 1 Neanthes --------------------------------------------------- -------------- ► \ t i Figure 36. UPGMAQ-mode dendogram of Bahr’ s (1976) data set for a modem oyster reef near Sapelo Island, Georgia. Taxa in this study include all hard and soft bodied fauna with biomass greater than 1% of the total biomass. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 a duster analysis on an Upper Triassic or Lower Cretaceous reef would precisely reproduce the original community structure. Therefore, whatever analysis is performed to determine paleocommunities, it must be tempered with the knowledge and appreciation of taphonomic effects (Fraser and Greenstein, 1993). However, some Upper Triassic European reefs show much ecological zonation, high diversity and strong paleocommunity delineation (Stanton and Fliigel, 1987; Flugel, 1981). These paleocommunities are easily recognized both in the field and statistically. Slight alterations of duster analysis permit stronger recognition of paleocommunities to countermand the loss of community information. For example, a duster analysis may focus on the dominant taxa limiting the analysis, to 13 or 15 taxa, if the dominant taxa appear to be differentiated ■ between fades (i.e. strong ecological zonation). Or if the differences are more A j subtle so that rarer taxa define the paleocommunities and the dominant | organisms are not fades controlled, a data transformation may be applied to | the data set to increase the "relative" abundance of the rarer taxa. The i | number of cases may be altered to increase the fidelity of the duster analysis a j by decreasing or increasing the number of sites, particularly over a large range - of ecozones (e.g. sampling not only the reef core and reef flank fades, but also > lagoon or back reef fades). By adding multiple ecozones into the analysis, the s j j relative bioherm community assodations will not necessarily appear to be more discrete if the system is dominated by organisms that occur across all environments. If the accessory environments duster separately and join the other branches at high distances, then the addition of such environments may be inappropriate. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 Applications of cluster analysis, like other multivariate methods, are influenced strongly by the addition or omission of cases; nonetheless, the resultant dendogram is often a powerful visual tool to reconstruct p aleoen vironments. The purpose of this chapter is to characterize the paleocommunities of the Upper Triassic and Lower Cretaceous buildups of Western North America using cluster analysis. The cluster method is reviewed and the results discussed. The Lower Jurassic bioherms were omitted from discussion because of the monospecific nature of the buildups (i.e. Lithiotis and one nereneid gastropod occurrence in over 40 transects). The cluster tree for the lithiotid bioherm is presented in Figure 37. The resemblance to the modem oyster bioherm is not inconsequential. Results from the other systems (the Upper Triassic and Lower Cretaceous) circumvent the problem of identifying paleocommunities by decreasing the number of taxa to the dominant fauna and increasing the sampling beyond the bioherm proper and into adjacent environments. Methods Ouster analysis groups data together on the basis of similarity or distance. The first step in clustering is to transform the original similarity matrix into a distance matrix. In this study, taxa are variables and transects are cases. The mutually highest correlations (the shortest distances) in the matrix are found to join taxa, in an R-mode cluster (while a Q-mode clusters the data set in terms of transects). Next, the similarity or distance matrix is recomputed with the previously grouped or clustered elements from the prior step as single elements. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V a ria b le = (D is ta n c e o f lin k / M a x im u m d is ta n c e ) * 1 0 0 V a ria b le 1 1 0 20 3 0 4 0 5 0 60 7 0 8 0 90 100 \ Lithiotid » , \ Neieneid Figure 37. UPGMA Q-mode dendogram of Ant Hill Bioherm. See text discussion. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 The clustering procedure is repeated until all mutually high pairs are found and linked. Choice of (1) data transformation, (2) correlation coefficients; and (3) distance measurements and linkage methods may alter the generated tree style. I - Data Transformations Ecological data typically do not have normal distributions; however, normal distributions are an assumption of most multivariate statistics (Reyment, 1971). Data transformations may be applied to data matrices that do not have normal distributions. Three transformations are commonly applied to the original data sets: log, square root and arc sine. Descriptive statistics (minimum, maximum, standard error and deviation, skewness and ; kurtosis) for Upper Triassic and Lower Cretaceous bioherms are reported in - Tables 6 and 7. The arcsine transformation was selected for this study because | it decreased the skewness and kurtosis from the original data but also | accentuated the differences of rarer taxa in both Upper Triassic and Lower I | Cretaceous bioherms (Sokal and Rohlf, 1969). Since data were already 1 collected as a percentage of a one-meter transect (see chapter three - methods I ; section for a description of the transect collection procedure), the data were • not scaled again, and the arcsine was performed on the raw data matrix. i | Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 108 OnamatOata N U n Max Mean Std.B r. StdO ev. Skewness Kurtosis A ctm astrea St 0 95.000 9.049 2.721 21.250 2.818 8.102 Algae 61 0 37.000 2.984 1.070 8.360 3.083 8.915 Bivalve 61 0 90.000 3.982 2.268 17.714 4.325 17.435 Brachiopod 61 0 15.000 2.082 0.485 3.792 1.998 3.058 Gastropod 61 0 29.000 0.582 0.476 3.716 7.703 59.838 Crmoid 61 0 62.000 9 .H 5 1.904 14.870 1.691 2.170 Uma 61 0 8.000 0.164 0.133 1.036 7.477 57.220 Pecten 61 0 5.000 0.107 0.085 0.665 7.011 51.111 Mytiilid 61 0 4.000 0.115 0.081 0.635 5.556 30.502 Megalodont 61 0 27.000 4.754 0.934 7.293 1.673 1.918 RetiophytSa 61 0 28.000 0.787 0.560 4.371 5.617 31.403 Sponge 61 0 66.000 2.410 1.497 11.695 5.090 25.435 Ostrea 61 0 4.000 0.066 0.066 0.512 7.810 61.000 Coral 61 0 59.200 1.790 1.260 9.840 5.443 28.806 Ascosymptagma 61 0 60.000 3.721 1.344 10.498 3.726 15.384 Loo N Mm Max Mean Std-Err. StdO av. Skewness Kurtosis Actinastraa 61 0 1.982 0.342 0.084 0.655 1.523 0.556 Algae 61 0 1.580 0.193 0.059 0.459 2.161 3.170 Bivalve 61 0 1.959 0.094 0.053 0.417 4.278 16.858 Brachiopod 61 0 1.204 0.269 0.051 0.397 1.114 -0.239 Gastropod 61 0 1.477 0.055 0.027 0.209 5.675 36.828 Crmoid 61 0 1.799 0.515 0.084 0.654 0.693 -1.261 Lima 61 0 0.954 0.026 0.017 0.132 6.248 42.104 Pecten 61 0 0.778 0.019 0.014 0.111 6.161 39.357 MytiUid 61 0 0.699 0.021 0.015 0.117 5.430 28.602 Megalodortt 61 0 1.447 0.445 0.066 0.517 0.588 -1223 RetiophytSa 61 0 1.462 0.046 0.032 0.250 5.403 28.203 Sponge 61 0 1.826 0.081 0.046 0.362 4.420 18.511 Ostrea 61 0 0.699 0.011 0.011 0.089 7.810 61.000 Coral 61 0 1.780 0.057 0.040 0.313 5.384 27.920 Ascosymptagma 61 0 1.785 0.234 0.063 0.488 1.917 2.377 SauarB Root N Mm Max Mean Sid. Err. Std-Oev. Skewness Kurtosis Actinastraa 61 0 9.747 1.351 0.347 2.710 1.836 2.173 Algae 61 0 6.083 0.656 0.206 1.611 2.385 4.508 Bivalve 61 0 9.487 0.442 0.251 1.962 4.287 16.976 Brachiopod 61 0 3.873 0.808 0.154 1.205 1.191 0.060 Gastropod 61 0 5.385 0.189 0.095 0.745 5.997 40.621 Crinoid 61 0 7.874 1.814 0.312 2.434 0.950 •0.584 Uma 61 0 2.828 0.079 0.051 0.400 5.991 38.832 Pecten 61 0 2.236 0.057 0.042 0.324 6.039 37.596 MytiBid 61 0 2.000 0.061 0.043 0.336 5.426 28.550 Megalodont 61 0 5.196 1.396 0.216 1.689 0.802 •0.697 RetiophytSa 61 0 5.292 0.160 0.113 0.880 5.443 28.798 Sponge 61 0 8.124 0.334 0.196 1.529 4.653 21.061 Ostrea 61 0 2.000 0.033 0.033 0.256 7.810 61.000 Coral 61 0 7.694 0.242 0.170 1.327 5.396 28.102 Ascosymptegma 61 0 7.746 0.800 0.227 1.770 2.340 4.918 Arcsine N men Max Mean Sid. Err. Std.0av. Skewness Kurtosis Actinastraa 61 0 1.253 0.102 0.033 0.259 3.338 11.915 Algae 61 0 0.379 0.030 0.011 0.085 3.108 9.102 Bivalve 61 0 1.120 0.047 0.027 0.210 4.394 18.307 Brachiopod 61 0 0.151 0.021 0.005 0.038 2.002 3.075 Gastropod 61 0 0.294 0.006 0.005 0.038 7.706 59.870 Crinoid 61 0 0.669 0.093 0.020 0.154 1.786 2.735 Lima 61 0 0.080 0.002 0.001 0.010 7.478 57.227 Pecten 61 0 0.050 0.001 0.001 0.007 7.011 51.117 Mytiilid 61 0 0.040 0.001 0.001 0.006 5.556 30.504 Megalodont 61 0 0.273 0.048 0.009 0.074 1.687 1.984 RetiophytSa 61 0 0.284 0.008 0.006 0.044 5.625 31.534 Sponge 61 0 0.721 0.026 0.016 0.127 5.130 25.821 Ostrea 61 0 0.040 0.001 0.001 0.005 7.810 61.000 Coral 61 0 0.634 0.019 0.013 0.104 5.460 29.057 Ascosympiegma 61 0 0.644 0.038 0.014 0.110 3.877 16.886 Table 6. Descriptive statistics on the various transforms of the Upper Triassic bioherm data. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. O riainal Data N Min M ax M ean Std-Err. Std-O ev. Skew ness K u n o sis C hondrodonta 36 0 55.000 2.250 1.566 9.394 5.396 3 0 .5 1 2 O ysters 36 0 29.000 1.500 0.893 5.359 4.471 21.280 Gastropod 36 0 1.000 0.026 0.028 0.167 6.000 3 6 .0 0 0 Caprinuloidea 36 0 35.000 5.917 1.599 9 .594 1.740 2 .480 C oalcom ana 36 0 38.000 1.056 1.056 6.333 6.000 36 .0 0 0 P etalodontia 3 6 0 85.000 7.333 3.662 21.970 2-921 7 .3 7 4 Calamophytlia 36 0 63.000 4.667 1.947 11.679 4.021 18.416 A ctm a strea 36 0 70.000 5.000 2.513 15.079 3.322 11.102 M icrosoiena 36 0 50.000 10.361 2.327 13.959 1.207 0.579 Algae 36 0 38.000 10.361 2.158 12.949 0.973 -0.481 Miliolid 36 0 4.000 0.111 0.111 0 .6 6 7 6.000 36.000 M onopteura 36 0 60.000 18.083 3.228 19.371 0.876 -0.351 Sponge 36 0 10.000 0.528 0.327 1.964 4.091 17 .2 2 2 L o o N Min M ax Mean Std-Err. Std.D ev. Skew ness K u rto sis C hondrodonta 36 0 1.748 0.137 0.064 0.385 3.077 9 .492 O ysters 36 0 1.477 0.127 0.058 0 .350 2.872 7.736 Gastropod 36 0 0.301 0.008 0.008 0.050 6.000 36.000 Caprinuloidea 36 0 1.556 0.439 0.098 0 .5 8 6 0.731 *1.272 Coalcom ana 3 6 0 1.591 0.044 0.044 0 .2 6 5 6.000 36.000 P etalodontia 36 0 1.934 0.201 0.096 0 .5 7 7 2.617 5.199 CalamophyiBa 36 0 1.806 0.343 0.086 0.518 1.288 0.605 A ctin a stra a 36 0 1.851 0.202 0.088 0.528 2.431 4 .448 M icrosoiena 36 0 1.708 0.608 0.113 0.679 0.327 -1.784 Algae 36 0 1.591 0.651 0.110 0.660 0.159 -1.823 Miliolid 36 0 0.699 0.019 0.019 0 .116 6.000 36.000 M onopleura 36 0 1.785 0.899 0.116 0 .697 -0.326 -1.597 Sponge 36 0 1.041 0.069 0.040 0.238 3.409 10.771 S a u a re P oot N Min Max Mean Std.Err. Std.D ev. Skew ness K urtosis C hondrodonta 36 0 7.416 0.472 0.241 1.444 3.801 15.897 O ysters 36 0 5.385 0.409 0.195 1.171 3.203 10.422 Gastropod 36 0 1.000 0.028 0.028 0 .1 6 7 6.000 36.000 Caprinuloidea 36 0 5.916 1.441 0.331 1.987 0.930 -0.639 Coalcom ana 36 0 6.164 0.171 0.171 1.027 6.000 36.000 P etalodontia 36 0 9.220 0.892 0.432 2.593 2.702 5.822 Calamophytlia 36 0 7.937 1.128 0.311 1.868 1.960 4.128 A ctin a stra a 36 0 8.367 0.783 0.354 2.124 2.669 6.079 M icrosoiena 36 0 7.071 2.118 0.410 2.458 0.532 -1.365 Algae 36 0 6.164 2.227 0.393 2 .357 0.376 -1.505 Miliolid 36 0 2.000 0.056 0.056 0.333 6.000 36.000 M onopleura 36 0 7.746 3.275 0.459 2.751 0.061 -1.399 Sponge 36 0 3.162 0.204 0.118 0 .707 3.465 11.309 A rcsin e data N Min M ax Mean Std-Err. S td.D ev. Skew ness K urtosis C hondrodonta 36 0 0.130 0.009 0.004 0 .026 3.638 13.919 O y sters 36 0 0.294 0.015 0.009 0 .054 4.493 21 .4 9 6 Gastropod 36 0 0.010 0.000 0.000 0 .0 0 2 6.000 36 .0 0 0 Caprinuloidea 36 0 0.358 0.060 0.016 0 .097 1.770 2 .625 C oalcom ana 36 0 0.390 0.011 0.011 0.065 6.000 36 .0 0 0 P etalodontia 36 0 1.016 0.083 0.042 0 .252 3.019 8.1 1 4 CalamophylSa 36 0 0.682 0.048 0.021 0.124 4.193 19.928 A ctin a stra a 36 0 0.775 0.053 0.027 0 .162 3.464 12.357 M icrosoiena 36 0 0.524 0.105 0.024 0.143 1.263 0 .8 1 7 Algae 36 0 0.390 0.105 0.022 0 .132 0.993 -0.432 Miliolid 36 0 0.040 0.001 0.001 0 .007 6.000 36.000 M onopleura 36 0 0.644 0.187 0.034 0.204 0.959 -0.142 Sponge 36 0 0.100 0.005 0.003 0.020 4.093 17.243 Table 7. Descriptive statistics on the various transforms of the Lower Cretaceous bioherm data. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 110 2 - Distances Distances are assigned to the taxa on the basis of their occurrence with all of the other taxa. For the hypothetical case of three taxa, A, B and C, the distances are reported in a schedule in terms of similarities (Fig. 38). The similarity of A~A will always be 1 as that taxon is perfectly "similar" to itself (i.e. it always "co-occurs"). Organisms with decreasing co-occurrences have correspondingly lower similarity coefficients. It two taxa are completely dissimilar (e.g. competitive exclusion, see taxon A-C), the similarity coefficient is -1. The calculation of distances can be accomplished in a variety of ways. Three distances were tested as to which would be the most appropriate method for fidelity to the data set: Euclidean, dty-block and squared Euclidean. The following distance equations are from Manly (1994). The Euclidean distance may be expressed by the equation: Where x and y represent two different taxa. The city block, or mean character distance may be expressed by the equation D = AA B = £ |x u - y 2i| eq.2 i=l The mean Euclidean distance may be expressed by the equation: D = a A B = X (X .,-y .,): eq.3 ? i=l The distances were generated for each method and then converted to a similarity coefficient: r n . . \ eq.4 ? [ i ( D**\ = 1 - — where D unk = the distance between two variables and D m ax is the maximum distances of the entire matrix. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I l l z i i * A B C A 1 - - B 0.2 1 - C -1 0.7 1 i i > Figure 38. Distance calculation for hypothetical ecosystem consiting of taxa A, B, and C. A - The arrangement of taxa within the ecospace, the three boxes, represent three sets of transect measurements. B - The distance chart for the above community generated using the Squared Euclidean distance equation, then converted to a similarity coefficient for comparison. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 To test the fidelity of the distance measurements a correlation coefficient (Pearson) was calculated for the three distances for comparison with the original data set. The Pearson coefficient may be represented by the equation: For Upper Triassic bioherms, the values were 0.440, 0.468, and 0.340 for city- block. Euclidean and squared Euclidean, respectively (Table 8). For Lower Cretaceous bioherms the values were 0.564,0.646, and 0.516 for city-block, Euclidean and squared Euclidean, respectively (Table 9). Euclidean distances were determined to be the most appropriate for both data sets when applied to the arcsine data matrix. 3 - Cluster method The above collected distances for each organism are then "linked" to other organisms. Several clustering methods may be used and then tested for algorithms were performed on the arcsine data matrix using Euclidean distances: single linkage, complete linkage, UPGMA (unweighted pair-group method with arithmetic averages), WPGMA (weighted), UPGMC (centroid averages) and WPGMC (Manly, 1994). Dendograms were created by the program Statistica (a software program by MS Software Enterprises, 1992; Appendix 2). For each of the cluster methods the clustering algorithm is defined. The following cluster equations are from Sokal and Rohlf (1969). /i(Z X T )-(Z X )(IT ) eq. 5 (Sokal & Rohlf, 1969) fidelity to the original data set (i.e. cophenetic correlation). Six cluster Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. A O rio i/iA l latcsine) Acilnew e* A lo a e 4 sc o s v m £ > J0 a m a B iv a lv e B r a c h lo o o d C o ra ) G a s t r o o o d C iin o ld Lime M e o a l o d o n l Mvuina O s i r e a P e c t e n R eh P P fty Jf* # S p o n n u AcUnesltee 1 .0 0 0 A lg a e • 0 . 1 4 3 1 . 0 0 0 Ascosympiegrm • 0 . 0 9 0 • 0 .0 8 1 1 . 0 0 0 B iv a lv e • 0 . 1 5 3 0 . 3 6 8 • 0 . 1 2 6 1 . 0 0 0 B r a c h l o p o d • 0 . 0 6 3 • 0 . 0 5 6 0 . 6 1 9 • 0 . 0 6 9 1 . 0 0 0 C o ra l • 0 . 2 1 6 0 . 1 6 4 • 0 . 1 3 8 0 . 1 6 5 • 0 . 0 6 9 1 . 0 0 0 G a s t r o p o d • 0 . 0 4 1 0 . 0 8 4 • 0 . 0 3 6 • 0 . 0 3 3 • 0 . 0 2 6 • 0 .0 6 1 1 . 0 0 0 C r tm tid • 0 . 0 6 4 • 0 . 0 5 6 0 . 1 2 4 • 0 . 0 2 3 0 . 3 0 1 • 0 . 0 6 0 • 0 . 0 2 6 1 . 0 0 0 t i m e 0 . 0 3 6 • 0 . 0 6 6 • 0 . 0 4 1 0 . 0 3 7 • 0 . 0 2 9 • 0 .1 1 1 • 0 . 0 2 9 • 0 . 0 2 9 1 . 0 0 0 Megelodonl • 0 . 1 1 6 0 . 2 1 3 • 0 . 1 1 2 • 0 . 0 7 6 • 0 . 0 9 6 0 . 1 6 4 0 . 1 1 9 • 0 . 1 0 6 • 0 . 1 1 9 1 . 0 0 0 MylilllU • 0 . 0 6 4 • 0 . 0 6 5 • 0 . 0 4 1 • 0 . 0 6 0 • 0 . 0 0 8 • 0 . 0 6 7 • 0 . 0 2 9 0 . 6 4 1 • 0 . 0 3 3 • 0 . 1 1 9 1 . 0 0 0 OStfM • 0 . 0 8 2 • 0 . 0 7 4 • 0 . 0 4 7 • 0 . 0 9 4 • 0 . 0 0 9 • 0 . 1 2 3 • 0 . 0 3 3 • 0 . 0 3 3 • 0 . 0 3 8 • 0 . 1 3 6 • 0 . 0 3 7 1 . 0 0 0 P e c t e n • 0 .0 5 1 • 0 . 0 4 6 • 0 . 0 2 9 0 . 3 4 1 • 0 . 0 2 0 • 0 . 0 7 9 • 0 .0 2 1 • 0 .0 2 1 • 0 . 0 2 4 • 0 . 0 8 6 • 0 . 0 2 3 • 0 . 0 2 7 1 . 0 0 0 Reltophyllla • 0 . 0 0 6 • 0 . 0 6 6 • 0 . 0 4 1 • 0 . 1 0 1 • 0 . 0 1 5 • 0 . 1 1 2 • 0 . 0 2 9 • 0 . 0 3 0 • 0 . 0 3 3 • 0 . 1 2 0 • 0 . 0 3 3 • 0 . 0 3 8 • 0 . 0 2 4 1 . 0 0 0 Sponge • 0 . 1 3 3 • 0 . 1 2 6 0 . 0 7 6 • 0 .0 2 1 • 0 . 0 1 4 • 0 , 1 6 4 • 0 . 0 5 6 0 . 6 7 7 • 0 . 0 6 4 • 0 . 2 0 7 0 . 3 8 1 • 0 . 0 1 0 • 0 . 0 4 6 0 . 0 5 5 1 . 0 0 0 BucMeen AcHnMite* A lo a e ■ Xscosvrnohom* B iv a lv e B r a c h lo o o d C o ra l G a s t r o p o d C r ln o id Lime i Meaelodonl Mvlillid Qftre* P e c i e n RetmphylUe S p o n g e Aciinatite* 1 . 0 0 0 A l o a e 0 . 1 0 8 1 . 0 0 0 B iv a lv e • 0 . 0 7 0 0 . 2 8 2 1 . 0 0 0 B r a c h l o p o d 0 . 1 4 8 0 . 7 6 7 0 . 3 3 4 1 . 0 0 0 G a s t r o p o d 0 . 1 4 4 0 . 7 0 2 0 . 4 0 1 0 . 8 2 7 1 . 0 0 0 C h n o td 0 . 0 0 0 0 . 4 6 5 0 . 1 4 7 0 . 4 8 6 0 . 4 4 1 1 . 0 0 0 Urn* 0 . 1 6 2 0 . 7 2 6 0 . 3 4 7 0 . 8 6 6 0 . 8 8 0 0 . 4 6 1 1 . 0 0 0 Peclen 0 . 1 5 2 0 . 7 2 6 0 . 3 6 0 0 . 8 6 8 0 . 8 8 9 0 . 4 6 1 0 . 9 6 2 1 , 0 0 0 Mytma 0 . 1 5 4 0 . 7 2 6 0 . 3 4 7 0 . 8 6 9 0 . 6 8 2 0 . 4 6 0 0 . 9 6 3 0 . 9 7 2 1 . 0 0 0 M e g e l o d o n l 0 . 1 4 0 0 . 6 8 2 0 . 3 0 2 0 . 7 2 8 0 . 7 1 0 0 . 4 9 5 0 . 7 3 7 0 . 7 3 2 0 . 7 3 2 1 . 0 0 0 Reliophytti* 0 . 1 4 2 0 . 6 8 3 0 . 3 3 3 0 . 6 1 4 0 . 6 2 3 0 . 4 3 9 0 . 8 6 0 0 . 8 7 4 0 . 8 6 2 0 . 7 0 0 1 . 0 0 0 Sponge 0 . 0 6 5 0 . 5 2 1 0 . 2 3 8 0 . 5 8 8 0 . 6 9 3 0 . 3 2 6 0 . 6 0 6 0 . 6 0 7 0 . 6 0 7 0 . 6 2 5 0 . 6 8 4 1 . 0 0 0 Osttoe 0 . 1 6 2 0 . 7 2 6 0 . 3 4 7 0 . 8 7 3 0 . 8 8 3 0 . 4 5 0 0 . 9 6 4 0 . 9 7 4 0 . 9 7 6 0 . 7 3 3 0 . 8 6 3 0 . 6 0 7 1 . 0 0 0 C o r a l 0 . 1 1 1 0 . 5 7 7 0 . 2 7 2 0 . 6 5 2 0 . 6 6 9 0 . 3 6 3 0 . 6 7 6 0 . 6 7 7 0 . 6 7 7 0 . 6 8 1 0 . 6 6 0 0 . 4 9 2 0 . 6 7 7 1 . 0 0 0 Ascosymplegm* 0 . 0 8 3 0 . 6 6 2 0 . 3 0 4 0 . 6 4 1 0 . 6 3 2 0 . 3 5 9 0 . 6 4 5 0 , 6 6 0 0 . 6 4 6 0 . 6 6 1 0 . 6 7 6 0 . 4 8 7 0 . 6 4 6 0 . 6 4 9 1 . 0 0 0 jr__________________ Datum* M w w » P<mon C l t y - M o d i 0 . 4 4 0 E u d M e a n 0 . 4 0 0 S q u a t e d E u d k t o M 0 . 3 4 0 Table 8. A - Tables of distances converted to similarities for the original arcsine transformed Upper Triassic bioherms and the similarities generated by the Euclidean distance measurement. B - Comparison of various distance measurements to the original data set via Pearson coefficient for Upper Triassic bioherm data. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. A Otiotnsl /mtatMl Ctiondrodonta O v s t e r s G a s t r o o o d 1 Coaleomana Patalodontla CatamophvUta Actinaslraa Microsotona A lo a e M ilio d d Motiooleura S p o n n u Chotidrodoata 1 . 0 0 0 O y s t e r s • 0 . 0 3 4 1 . 0 0 0 G a s t r o p o d 0 . 2 6 0 0 . 1 4 2 1 . 0 0 0 CaptinuMdsa 0 . 3 2 1 • 0 . 1 7 6 • 0 . 1 0 5 1 . 0 0 0 Coaloomana • 0 . 0 5 6 0 . 3 6 6 • 0 . 0 2 6 • 0 . 1 0 6 1 . 0 0 0 Patatodoatta • 0 , 1 ( 0 • 0 , 0 6 4 • 0 , 0 5 6 • 0 . 1 4 3 • 0 . 0 6 6 1 .0 Q Q Caiantoptiyttia • 0 . 1 3 0 0 . 2 2 8 • 0 . 0 6 6 • 0 . 0 6 8 • 0 . 0 6 6 • 0 .1 3 1 1 . 0 0 0 AcUnastraa • o . t o g • 0 . 0 8 4 • 0 . 0 5 6 • 0 . 0 2 3 • 0 . 0 5 6 • 0 . 1 1 0 • 0 . 0 0 3 1 . 0 0 0 Mfctosobna • 0 . 1 6 3 • 0 . 1 7 7 • 0 . 1 2 6 0 . 0 3 2 • 0 . 1 2 6 • 0 . 2 4 0 • 0 . 0 0 6 • 0 . 2 4 7 1 . 0 0 0 A lg a e • 0 . 1 3 3 • 0 . 1 6 6 • 0 . 1 3 6 • 0 . 2 0 0 • 0 . 1 3 6 • 0 . 2 7 0 • 0 . 1 4 7 • 0 . 2 1 0 0 . 4 8 3 1 .0 0 0 M ill o d d 0 . 7 6 6 • 0 . 0 4 6 • 0 . 0 2 6 0 . 6 2 6 • 0 . 0 2 6 • 0 . 0 6 6 • 0 . 0 6 6 • 0 . 0 5 6 • 0 . 1 2 6 • 0 . ( 3 6 1 . 0 0 0 Monoptoura 0 . 0 0 6 • 0 .2 3 1 • 0 . 1 6 7 • 0 . 1 1 6 • 0 . 1 3 2 • 0 . 3 1 0 • 0 . 1 3 6 • 0 . 2 7 0 • 0 . 1 6 2 0 . 0 1 1 • 0 . 1 6 7 1 . 0 0 0 S p o n g e • 0 . 0 6 0 • 0 , 0 7 7 • 0 . 0 4 6 0 . 1 0 6 • 0 . 0 4 6 • 0 .0 6 1 • 0 . 0 6 3 • 0 . 0 6 0 0 . 4 5 7 0 . 1 1 6 • 0 . 0 4 6 * 0 .1 1 1 1 . 0 0 0 EuckUan Ctiondrodonta O v s t e r s G a s t r o p o d Caixinotoidaa Coakxxnana PaiaiodofWa i s Actinastraa Microsotona A lo a e M iU oIkI Monooteuta S o o n o e Ctiondrodonta 1 . 0 0 0 O y s t e r s 0 . 6 4 0 1 , 0 0 0 G a s t r o p o d 0 . 0 2 6 0 . 0 6 4 1 . 0 0 0 Capdnutokhta 0 . 7 2 6 0 . 6 6 6 0 . 7 0 2 1 . 0 0 0 Coakxmana 0 . 6 1 4 0 . 8 2 0 0 . 6 2 8 0 . 6 6 7 1 . 0 0 0 Pelatodontla 0 . 3 0 6 0 . 2 6 6 0 . 3 1 0 0 . 2 6 3 0 . 2 8 8 1 . 0 0 0 CalamoptiyHia 0 . 6 4 6 0 . 6 6 7 0 . 6 6 3 0 . 5 7 6 0 . 6 1 3 0 . 2 2 8 1 . 0 0 0 Actlnattraa 0 . 6 6 0 0 . 6 3 3 0 . 6 6 6 0 . 6 0 3 0 . 6 2 4 0 . 1 6 0 0 . 4 6 8 1 . 0 0 0 Mtoototona 0 . 6 3 6 0 . 6 1 7 0 . 6 3 6 0 . 6 4 1 0 . 6 0 6 0 . 1 6 8 0 . 4 6 2 0 . 3 6 8 1 . 0 0 0 A l g a e 0 . 6 6 1 0 . 6 4 2 0 . 6 6 9 0 . 6 2 0 0 . 6 2 7 0 . 1 8 1 0 . 4 7 4 0 . 3 0 8 0 . 6 3 9 1 . 0 0 0 M U iottd 0 . 6 4 0 0 . 6 5 3 0 . 8 6 2 0 . 7 1 1 0 . 8 2 0 0 . 3 1 0 0 . 6 6 2 0 . 6 6 6 0 . 6 3 6 0 . 6 6 9 1 . 0 0 0 Monoptoura 0 . 2 6 8 0 . 2 6 6 0 . 2 7 6 0 . 3 0 1 0 . 2 6 0 0 . 0 0 0 0 . 2 4 6 0 . 1 6 1 0 . 2 7 4 0 . 3 3 6 0 . 2 7 6 1 . 0 0 0 S p o n g e 0 . 6 1 0 0 . 6 4 4 0 . 8 4 7 0 . 7 1 0 0 . 8 2 1 0 . 3 0 6 0 . 6 6 0 0 . 5 6 3 0 . 5 6 0 0 . 6 7 0 0 . 9 4 4 0 . 2 0 0 1 0 0 0 u.________________________ B m s a M a s m f l w w o n C lly -M o c k 0 . 5 8 4 E u c l i d e a n 0 . 6 4 6 S q u a r e d E u c M a a n 0 . 6 1 6 Table 9. A - Tables of distances converted to similarities for the original arcsine transformed data set and the similarities generated by the Euclidean distance measurement. B - Comparison of various distance measurements to the original data set via Pearson coefficient for Lower Cretaceous bioherms. 114 I 115 The single linkage cluster method, or nearest neighbor analysis, recomputes the similarity matrix by fusing taxa via the equation: S(A.B,.c = max(SA C ,SB C ) eq. 6 where S is the similarity (or distance), A and B are the newly fused taxa and C is the next taxon with the highest similarity (or shortest distance). The complete linkage cluster method, farthest neighbor, has a similar equation: S ( a.bkc ~ m infS ^cS B c) ecl* 7 The algorithm for recomputation of the matrix when using the WPGMA method is c Sac + Ssc S f A.BK C ~ 2 eC l ‘ The algorithm for recomputation of the matrix when using the UPGMA ^ method is [ n tu /ic S tc + n a icS tc _ e» 9 ► where n.and nc are the number of occurrences of taxon A and taxon C. Both centroid methods transform the correlation matrix (S) back into a distance matrix (D), the WPGMC method may be represented by the equation: d = 2sin^arccos(s) j eq. 10 c q u The UPGMC method recomputes the distance matrix by the equation: d — I n An C ^ A C + n Bn C ^B C r l An B(^AB ^2 . y n.A nc — nB nc (nA+ nB ) The process of averaging together members of a cluster and treating them as a new object causes distortion of the original similarity matrix. The degree of distortion may be calculated by plotting the cophenetic value matrix (matrix of apparent correlations contained within the dendogram) against elements in the original similarity matrix. In this study the cophenetic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 116 correlation was approximated by using the distances calculated by the amalgamation schedules from Statistica for each method. These cluster distance values were then converted to similarity values as described from above (eq. 2) and then compared to the original data matrix using the Pearson coefficient (eq. 3). The Pearson values are reported for each method in Tables 10 and 11, and the UPGMA cluster method has the highest correlation to the original data matrix with a value of 0.703 for the Cretaceous localities and 0.502 for the Triassic localities. A correlation of the cluster to the original data matrix is considered appropriate if greater than 0.75. The low correlation of all of these methods, even the method with the highest correlation, UPGMA, | may possibly be attributed to the nature of ecological data (Krebs, 1989). | Figures 38 and 39 display the generated UPGMA dendograms for the Upper j . Triassic and Lower Cretaceous buildups, respectively. 4 - Two-way Cluster Analysis The above description has focused on the clustering of taxa. The clustering of transects is equally informative, as local or regional 4 phenomenon may be explored. Q-mode clusters for both data sets are * presented in Figures 41 and 42. Q-mode and R-mode clusters may be combined to cluster taxa and transects simultaneously (Fig. 43 and 44). The L clustering values are now represented by circles. Circles with the largest | diameters represent high correlations. For both the Q-mode and the two-way i cluster analysis the protocol of the R-mode clusters (i.e. arcsine transformation, Euclidean distances and UPGMA clustering) was observed for consistency and comparison. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 117 V a ria b le = (D is ta n c e o f lin k / M a x im u m d is ta n c e ) * 100 V a ria b le 1 10 2 0 30 4 0 5 0 6 0 70 8 0 9 0 100 Actinastrea Algae Bivalve Brachiopod Gastropod Crinoid Lima Pecten Mytillid Megalodont Retiophyllia Sponge Ostrea Coral Ascosymplegma i ! Figure 39. UPGMA (Unweighted Pairgroup Method) dendogram of Upper Triassic buildups. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 118 V a ria b le = (D is ta n c e o f L in k /M a x im u m d is ta n c e ) * 1 00 V a ria b le 1 10 2 0 3 0 4 0 50 6 0 7 0 80 9 0 100 Chondrodonta Gastropod — Miliolid - Sponge - Oysters - Coalcomana - Caprinuloidea - Calamopkyllia - Microsolena - Algae - Actinastrea Monopleura Petalodontia Figure 40. UPGMA (Unweighted Pairgroup Method) cluster dendogram of Aptian-Albian buildups from the Mural limestone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 119 Cluster Method Dmax Pearson Single 2.158 0.544 Complete 2.729 0.534 UPGMA 2.280 0.548 WPGMA 2.586 0.535 UFGMC 1.837 0.549 WFGMC 2.586 0.544 Table 10. Tables of distances converted to similarities for the original ■ arcsine transformed Upper Triassic bioherm data set and the j similarities generated by the various cluster methods discussed in the text. i I f it ,t • f Cluster Method Dmax Pearson Single 2.050 0.701 Cluster 1.310 0.674 UPGMA 1.740 0.703 WPGMA 2.050 0.691 UFGMC 1.310 0.652 WFGMC 1.510 0.663 1 Table 11. Tables of distances converted to similarities for the original arcsine transformed Lower Cretaceous bioherm data set and the similarities generated by the various cluster methods discussed in the text. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 1 a . V a ria b le = (D is ta n c e o f lin k /M a x im u m d is ta n c e ) * 100 V a ria b le 1 10 20 3 0 4 0 50 6 0 7 0 80 9 0 100 NPM -t NPM-U NPM-7 NPM-6 NPM-17 NTPM -5 NPM-23 NPM-2 NPM-16 NPM-3 NPM-4 NPM-8 NPM-10 NPM-15 NPM-9 NPM-41 NPM-18 DC-6 DC-7 DC-9 NMP-19 DC-8 NPM-26 NPM-35 NPM-37 DC-12 NPM-42 NPM-31 NPM-30 NPM-38 NPM-40 DC-1X NPM-25 NPM-28 NPM-29 DC-15 DC-13 DC-5 NPM-12 NPM-13 NPM-14 NPM-20 NPM-21 NPM-34 NPM-27 NPM-32 NPM-22 DC-2 DC-19 DC-14 DC-3 DC-4 NPM-33 NPM-36 DC-17 DC-18 DC-1 DC-16 DC-20 120 Figure 41. UPGMA Q-mode cluster dendogram of Upper Triassic (Camian- Norian) buildups from New Pass Mine, Augusta Formation (NPM cases) and Dunlop Canyon, Luning Formation (DC cases). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V a ria b le = (D is ta n c e o f L ink/ M a x im u m d is ta n c e ) * 100 V a ria b le 1 10 20 3 0 4 0 50 6 0 7 0 80 9 0 1 0 0 121 MS-1 MS-7 M S-2 PS-1 PS-5 MS-5 MS-10 MS-11 M S-12 P S -15 PS-2 PS-8 PS-3 MS-15 P S -16 PS-18 P S -13 P S -19 PS-4 PS-9 P S -10 P S -12 P S -17 MS-8 PS-7 MS-9 PS-20 PS-6 PS-11 MS-3 M S-14 MS-13 P S -14 MS-4 MS-6 MS-16 E l a n _ ZL Figure 42. UPGMA Q-mode cluster dendogram of Aptian-Albian buildups from Mexican Saddleback (MS cases) and Paul Spur (PS cases) of the Mural Limestone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 2 2 I I r— r— i— T 1 l . I l , 3 s I f l l ttti 5 S .. i s S 1 & ! ? S3 § • l u a l s it £ 5- go •« o o o o o o o o O o o Distance Legend o 0.375 - 0.751 0 0.752-1.127 • 1.128-1.502 N PM -l N P M -ll N PM -7 NPM -4 NPM -17 N PM -5 NIPM-23 N PM -2 NPM -16 NPM -3 NPM -4 NPM -8 NPM -IO N PM -I5 NPM -9 NPM -41 NFM -18 DC-6 D C D C n m p -: DC-8 NPM -26 NPM -35 NPM -37 DC-12 NPM -42 NPM -31 NPM -30 NPM -38 NPM -40 D C -ll NPM -2S MPM-28 NPM -29 DC-15 DC-13 ) DC-5 NPM -12 NPM -13 NPM -14 NPM -20 NPM -21 NPM -34 NPM -27 NPM -32 NPM -22 D C-2 DC-19 DC-14 DC-3 DC-4 NFM -33 O NPM -36 DC-17 _ DC-18 O DC-1 Oa DC-16 O D C - 2 0 Figure 43. Two-way UPGMA cluster dendogram of Upper Triassic (Camian- Norian) buildups from New Pass Mine, Augusta Formation (NPM cases) and Dunlop Canyon, Luning Formation (DC cases). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ChomirodonUi— r i 123 E. 5 .si j» ••= I s a a 5 < < 5 £ o o o o o o o o o o o o o Distance Legend o 0.335 - 0.672 O 0.673-1.007 • 1.008-1.343 M S-1 M S -7 M S -2 P S-1 O P S -5 M S-5 M S-10 MS-11 M S-12 P S-15 P S -2 P S -8 P S -3 M S-15 PS-16 PS-18 O PS-13 P S -19 PS -4 P S -9 PS-10 P S -12 P S-17 M S-8 P S -7 M S-9 PS-20 P S -6 P S - ll M S-3 M S-14 M S -13 O P S-14 M S-4 # M S - 6 O M S-16 E = l Figure 44. Two-way UPGMA Cluster dendogram of Aptian-Albian buildups from Mexican Saddleback (MS cases) and Paul Spur (PS cases) of the Mural Limestone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Upper Triassic Bioherms Fauna of Upper Triassic bioherms correspond roughly to Stanley's (1979) biofacies: 1) sponge framestone-bindstone, 2) coral-spongiomorph framestone-bindstone, 3) mollusk-echinoderm-coral grainstone; and 4) pelletoidal ooilitic grainstone. The cluster analysis divided the coral- spongiomorph facies of Stanley (1979) into two groups, a mixed coral-sponge zone composed of encrusting and low relief branching species (e.g. Retiophyllia) and a second climax community of Actinastrea sp. The sponge framestone-bindstone formed a paucispecific base with a low similarity \ coefficient (0.210 similarity for UPGMA, Table 10). The next community is § j the encrusting coral-spongiomorph facies with a similarity of 0.180. A climax i [ community consisting solely of Actinastrea was the last to cluster with the other taxa, indicating a high dissimilarity coefficient. Tightly linked in these reefs was a community of bivalves, brachiopods, gastropods, crinoids, Lima and pectinid bivalves (0.586 similarity or UPGMA, Table 10). Also associated with this community are large megalodonts and mytillids, now identified as Trichites (Cornwall, 1979). These Upper Triassic bioherms lack distinct biozones found in modem reefs and contemporaneous Dachstein reefs (Stanley and Senowbari-Daryan, 1986). The very low cophenetic correlation i. estimates also represent this break. j The Q-mode and R-mode comparison, as a two-way comparison, did i not delineate between the Ladinian (New Pass Mine) and the Camian-Norian (Dunlop and Cinnabar Canyon) buildups (see Figures 41 and 43). Therefore, the low biofacies organization of these reefs appears to be representative for Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 125 the Upper Triassic of Western North America with little change between other reefs linked to the craton or through time. Lower Cretaceous Reefs Fauna of the Mural Limestone is dominated by coral-algal-rudist reef associations which grade into a lagoon facies represented by a Chondrodonta- gastropod-millioiid-sponge community. The coral-stromatolite-rudist community represents the reef core (Fig. 40). This community consists of a massive lenticular, convex-upward limestone buildup which interfingers with and grades laterally into thinner beds of the lagoonal facies. The reef core was formed by the growth of three faunal associations. The pioneer encrusting and sometimes branching coral Actinastrea occupied the base of the reef, commonly binding sediments together. This is equivalent to the colonization stage and is not tightly linked with other taxa (0.345 similarity for UPGMA, Table 11). The climax stage is represented by the dominantly encrusting coral Microsolena and stromatolites comprising the major part of the inner reef core. These organisms are clustered consistently after the lagoonal facies, therefore suggesting a high level of species interaction or at least co-occurrence (0.528 linkage UPGMA). Also, this facies is marked by intense boring by both lithophagid bivalves and sponges. The outer reef core consists of the monopleurids and petalodontid rudist communities. Locally, at Mexican Saddleback Reef, Petalodontia forms a monospecific outer reef core and the caprinid Caprinloidea interfingers with the Microsolena- stromatolite community. The two-way cluster analysis groups transects MS-4, MS-5, MS-6, MS-16 as the Mexican Saddleback reef core. Paul Spur reef transects PS-20, PS-7, PS-9 and PS-11 display the more diverse coral- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 126 stromatolite-rudist associations (Fig. 42). Monopleura (0.046 UPGMA similarity) and Petalodontia (0.00 UPGMA similarity) are the last taxa to be clustered, indicative of low similarity coefficients of these species. The lagoonal facies, consisting of the Chondrodonta-gasttopod- milliolid-sponge community, is the first cluster generated by all of the cluster methods (linked by a similarity of 0.904-0.779 for UPGMA). This tightly linked association of the oyster-like Chondrodonta, various gastropods and large benthic foraminifera is attributed to a shallow-shelf to open lagoon environment. In outcrop, the rocks of this facies are associated with thin, even bedding, alternating with mottled, bioturbated layers with very fine 1 grained laminae alternating with coarser grained laminae. Also in this I lagoonal environment, the rudist Toucasia, is found; but because of the relatively low similarity coefficient (0.770 for UPGMA), it is thought that the | presence of this rudist is random and is not as interdependent as the i | C/towdrodonfa-gastropod-miliolid-sponge community. Caprinid rudists had i an elevated morphotype and are closer to the reef-core than to the lagoon, § with a distance usually median between the two (0.601 for UPGMA). The 1 branching coral Calamophyllia does not cluster with the Microsolena- | stromatolite association, and most likely represent a "supra-dimax" | community. • ? K i Conclusions Previous paleoecologic models of Mesozoic bioherms have successfully delineated paleocommunities [Cornwall (1979) and Stanley (1977) for Upper Triassic bioherms; Hartshorn (1989) and Scott (1979) for Lower Cretaceous bioherms]. The Upper Triassic bioherms lack fire strong paleocommunity Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 127 assignment of the Lower Cretaceous reefs. As mentioned before, in comparison to their complimentary Tethyan counterparts, these Western North American Triassic buildups are not as strongly zoned ecologically. This could have been a result of presumed low-oxygen waters reaching Western North America because of a Panthallassan equatorial transect longer than that in the Pacific today (Hallock and Schlager, 1986; Kennett, 1988). The lack of strongly defined Late Triassic paleocommunities could also be a result of the stressed environment of a tectonically active zone that sporadically inundated the system with turbid, high-nutrient water and therefore the diversity associated with oiigotrophic regimes would have been replaced by the ecological generalists of mesotrophic and eutrophic systems. The same scenario could be argued for the restricted waters of the Bisbee Trough, where the Lower Cretaceous bioherms occur (Bilodeau and Lindberg, 1983). The appearance of borers, algae and other mesotrophic-associated fauna in the both Upper Triassic and Lower Cretaceous bioherm cores are biological evidence of nutrient conditions differing from those of today. Alternatively, the lack of tightly knit paleocommunities might represent a lack of I evolutionary innovation key to modem reefs. This, however, is doubtful, 9 I because scleractinian corals did have photosymbionts by the Upper Triassic i | (Stanley and Swart, 1995), and all the buildups studied with the exception of » the Lower Jurassic reefs did have corals from photosymbiotic lineages. r An effort to relate these paleocommunites to the broad evolutionary succession of Mesozoic reefs demands the addition of Tethyan examples and additional geochemical information to test (via factor analysis) if environmental factors controlled distribution of taxa within facies. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 128 CONCLUSIONS Sum m ary 1) Seven Mesozoic carbonate buildups of Western North America were investigated for the potential role of large epifaunal bivalves in various paleocommunities as indicators of nutrient levels. The majority of these buildups did have a bivalve biovolume, considerably larger than modem reefs, and a relatively decreased biovolume of scleractinian corals, another difference with modem reefs. These differences may be potentially attributed either to modifications for photosymbiosis, or to a unique environment for carbonate buildups in the Mesozoic lacking extensive modem analogs. 2) Nine large Mesozoic epifaunal bivalves were studied: Megalodon, Neomegalodon, wallowaconchids, Lithiotis, Monopleura, Petalodontia, Coalocomana and Caprinuloidea. Six morphological features (hinge, ligament, valve shape, shell mineralogy, primary porosity and ornamentation) and three autecologic features (attachment to substrate, packing and pseudocoloniality) were used. Of the above bivalves only Wallowaconchids, Monopleura and Caprinuloidea showed possible adaptations for photosymbionts in an oligotrophic/mesotrophic setting (see Fig. 45 for summary diagram). Only Lithiotis was conclusively characterized as an organism living in a strongly eutrophic environment. All the others were most likely filter-feeding bivalves in areas of mixed to low levels of nutrients. 3) Cluster analysis delineated paleocommunities that had been qualitatively defined by previous workers [Stanley (1979) and Cornwall (1979) for Upper Triassic buildups; Hartshorn (1989) and Scott (1979) for the Lower Cretaceous]. The differences between the well-defined paleocommunities of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 129 U M 0 N 0 c n w Z & w 0 0 2 dwellers/binders photosymbiotic wallowaconchids • dwellers photosymbiotic bivalves (e.g. Tridacna) • minor dwellers suspension feeders (e.g. Spongdylus, pectinids) Oligotrophic • constructors ?photosymbiotic (e.g. Petalodontia and Caprinuloidea) • dwellers (e.g. Coalocomana, Monopelura, Megalodon and Neomegalodon) • constructors filter-feeding (e.g. Lithiotis and Chondrodonta) constructors filter feeding (e.g. oysters and mussels) Mesotrophic Eutrophic Figure 45. Summary figure of the relative guilds and nutrient levels of large epifunal buildup bivalves from the Mesozoic and modem environments. «r Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 130 the Lower Cretaceous and the ill-defined Upper Triassic are attributed to a paleocommunity organization that developed possibly in response to varying nutrient regimes. The Upper Triassic buildups lacked strong paleocommunity delineation because without the constant oligotrophic setting they lacked a constant background selection pressure for niche specialization when compared to the Lower Cretaceous communities. However, the levels of boring and algal growth in both buildup regimes suggest nutrient levels greater than those found in modem oligotrophic settings. 4) The line-intercept transect method used in all aspects of data collection proved to be extremely flexible for the generation of multi-use data: ; organism, community and facies analysis. This method has many x proponents in modem coral reef research but its use by paleontologists is still t limited (Perrin et al., 1995). Sample sizes greater than thirty transects offered | the most "normal" data distributions for faunal counts, f [ Future research | To resolve the more troubling questions that this research initially a | attacked must be expanded in three areas: stable isotope sderochronology, I inclusion of Tethyan examples, analysis of modem mesotrophic systems | (biological and geochemical signatures). \ The use of stable isotopes from bivalve shells has been used to explain |o a variety of environmental parameters (Jones, 1983). Specifically 5 O isotopes have been used to constrain temperature variations. The 5lsO variation in photosymbiotic bivalves is sometimes unequivocal (Jones and Jacobs, 1992). Therefore, it is necessary not only to collect diagenetically unaltered bivalve Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 131 specimens but also enough information about the am bient environment to discern the likely trophic habit. The use of 8I 5 N isotopes has potential to illuminate this problem, although, w ith some caveats [see Dunn (1995), Sweeney et al. (1980) and Caplan et al. (1995) for reviews of the applications of stable isotopes in m odem and ancient environments]. H. Weissert (pers. comm., 1997) is currently working on the problem of matching carbonate platform sequences to the 81 5 N curved generated in basinal environments in the Cretaceous of France and Italy. The use of 81 5 N in modem oligotrophic environments is complicated by the biological fractionation by non- phototrophic organisms. Organisms w ith photosymbionts lack a significant i fractionation effect. Dunn's (1995) study demonstrated this dilemma in coral \ specimens collected from both oligotrophic and mesotrophic environments - ( both had a value of -5 % o although organic matter from both regimes ' recorded a 10 % o shift. The similarity in the values came from the stress response of most corals to release their photosymbionts and therefore increase the fractionation potential from the 1 5 N reservoir, in an equal and * | opposite direction from the environment shift. Therefore, if this method | were to be potentially used in any other study it would behoove the | investigator to use non-photosymbiotic organisms for comparison, f The uniqueness of the Mesozoic buildups of Western North America f | was discussed in detail in chapter 2, and in particular many of these buildups lack some of the im portant "constructors" found in other contemporaneous buildups (e.g. algae, bryozoans, stromatoporoids, etc.). If one were to propose to document the entirety of Mesozoic buildup phenomena for comparison with the modem, it would be necessary to expand the study to other reefs to understand if these changes were regional or global in scope. Much Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 132 information is available for the European Tethyan buildups but most was not collected w ith the line-intercept transect method (Flugel, 1981). A limited analysis, w ithout additional field work, could be done adapting the Cordillera data to the measured data on European reefs. Modem mesotrophic systems have not been carefully analyzed as a unique ecosystem with diagnostic taxa and geochemical signatures. Are they merely a m iddle-point in the continuum between oligotrophic and eutrophic environm ents, or potentially an environm ent w ith many paleoanalogs? Wood (1993) and Hallock and Schlager (1988) suggest that these environments should be found frequently in Mesozoic buildups due to ; unique paleoceanographic and tectonic regimes but examples thus far have s only come from the Paleozoic and Cenozoic (Caplan et al. 1995). It is proposed I | that the difficulty with assigning a paleobuildup as occurring in a | mesotrophic system is that there is insufficient information about modem «' | mesotrophic systems. Filter-feeding bivalves (non-obligate photosymbiotic bivalves) are an ideal organism with which to begin such a study because of the amount of data currently available about bivalves in various nutrient regimes and their ubiquity in all environments. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REFERENCES Bachmann, G. H., 1979. Bioherme der Muschel Placiinopsis ostracina v. Schlotheim und ihre Diagenese: Nenes farhbuch fuer Geologie und Palaeontologie, Abhandlungeti 158:381-407. Bahr, L. M., 1976. Energetic aspects of the intertidal oyster reef community at Sapelo Island, Georgia (USA): Ecology 57:121-131. Barron, E. J. and Peterson, W. H., 1989. Model simulation of the Cretaceous ocean circulation: Science 244:684-686. Barron, E. 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Further reproduction prohibited without permission. 149 S O O O O O Q O O O O O O O O O O O O O O O O O O C ^ O O O O O O O Q O O O O ( V '^ ^ T o o n 0 « ( w o * o o o o * o e o e o o v o o v < :o*»QO'0«<a > a* goooooooe«eooooeooo( >000000000000000000000 o o o o o ^ o © 3oooooooooooooeooooooooooooooooooooooooo'< >-~ _o«*ooooo< 5 • • 3 » £ ? . « 3 e» o 2 jc R 5 T 3 c u u s R 5 T3 c 3 -Q <o T3 2 Ll 0) > c o u «5 4a# C 3 T3 a O ) a 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ^ 0 0 0 0 0 0 ^ 0 0 0 0 0 ^ - 0 0 1 9 2 >«»090aooo 2 1 0 o' ® n 0 0 0 0 0 — 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 — 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 £*>0000000 s ~ o |OOOOM«0*>M^OO( oooooooexooooooooooooooewoooMn 50*0— 00000 o - > 00—0 0 0 — 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 | O O Q O * e H O M I 0 1 c 3 c/2 s. T < u t > — £ <« Ol a. C l < C A u •*4 CA c/i • p 4 M t « O ) CL 0 > N n T f l < 8 N 9 9 ) O * N t 1 t d O S < e A Q ^ < N Q f 4 4 ^ $ 0 M N M » » - » - » - - - - N N N « N N « N N N n n o n n r t n B n t » f 2 5* *§S§S»SSS U3ZZZZZZZZZZZZZZZZZZ2ZZZZZZZ2Z22ZZZZZZZZZ2Z y j Q a a o c a a a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150 sonmnonooooo ooooooooooO< a. o o o o 0 1 m e o 5 5 o o ® o o o o o o o o o KiOQNiOlOflNN 5----------- ♦ s 'OOOQOOOOOOO 0009000C9C4000 s ° : s 3 I o o o o o < ^© © © © « © © o o ^ S 1 0 0 0 0 * 0 0 0 0 0 0 0 '3090^000' 8 ' ? >0 *00*0000000 [000*00^00 5 « o o OOOO0*~OOOOOO m -^00000^-00 s ¥ ocvno**NMOOooo 0000000 © 000 © »q o 0 « oooc I 4 I • oo<o<ocu«ioo ^ 5 ® ° 4 * e ft * I •— 8 Sg«oooooo $ . ? S (5 o i u 5 i i 3,= S T 0 ) 0 fl O 6 6 6 6 6 6 0 6 0 6 6 6 * s ! o o o o c o o o o o o o © to c h* < U ^ £ o - N n v i a o K s a o 1 S £ x x x x x x x x x x x x x x x x x x x O T < < < < < < < < < < < < < < < < < < < < O ) C A 5 3 I O I 4 J I U * C Q o « o m 9 o 2 r u 1 §3 O £ . Q I t"1 ? -J S222 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151 o o ooooooooooooooo oo ooooooooooooooo rt o oooooooooaooooo >«ooooooooooooo< oo ooooooooooooooo oooooooooooooooo I ** a» ooooooooooooooo 3 0 0 0 0 0 0 ^ 0 0 0 0 0 0 ^ 0 0 r 00 oo«*soor>r^op»oor»-«00 _ _ _ _ — __ ~ -.Qt*c*nnae*fi 3 n o 0 0 0 0 ( 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ooooooooooooooo [OOOOOOOOOOOOOOOO lOOOOOOOOOOOOQO 0 0 OOOOOOOOOOOOOOO ^OOOOOOOOOOOOOOO 3 0 10*000*00^*000000 00 nooooAA«ottAOr»fto s « O - N A * ifl I * t t £ £ ± i ± ± ± t i i t i ± & Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 152 APPENDIX H -Ouster dendograms generated using methods other than the UPGMA method discussed in chapter 4. A. O uster dendograms of Upper Triassic sites. A l. Single linkage cluster dendogram. STAT1STZCA T re e CLUSTER STATS Dendrogram V a r ia b le V a ria b le O rd e r o f Am algamation (d is ta n c e s a r e non-m onotonlc) LIMA - l LIMA PECTEN -A— | PECID* CRINOID ■ ■ 1 1 CRIMOID ___ 1 GASTROPO ------------------------l - i _______________J BRACHIOP BIVALVE ~ ■ 1 BIVALVE MTTILUD —— — - MTTZLLID ALGAE M EG A LO O O ------------ M EGALOOO RETXOPfflf SPONGE OSTREA COPAL ASCOSTMP ACTINAST A2. Complete linkage duster dendogram. STATISTICA CLUSTER STATS Dendrogram v a r ia b le O rd er o f Am algamation (d is ta n c e s a r e n o n m o n o to n ic) T re e V a r ia b le LIMA PECTEH CRINOID GASTRCPO BRACHIOP BIVALVE MTTIIXZD M E G A L O O O ALGAE RETIOPHT SPONGE OSTREA CORAL ASCOSYM P ACTINAST LIMA PECTIN CRINOID GASTROPO BRACHIOP B IV A L V E MTTZLLID M EGALOOO ALGAE RETIOPHT SPONGE OSTREA CORAL ASCOSYMP ACTINAST Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 153 A 3 . W e ig h te d p a ir - g r o u p a v e r a g e d d u s t e r d e n d o g r a m . STATISTICA CLUSTER STATS (D llnk/O nax) *100 v a r ia b le 1— 10— 20— 30- —40 SO 60-----70-----80-----90-----100 T ree v a r ia b l e ACTINAST A LG A E BIVALVE BRACHIOP GASTROPO H crinoid — LIMA PECTEH IttTXZLXD frC G A LC O O RETIOPHT SPONGE OSTREA C O RA L ASCQSTM P ACTINAST ALGAE BIVALVE BRACHIOP GASTROPO CRINOID LIMA PECTEH MCTIXI.XD M EG A LO O O RETIOPHT SPONGE OSTREA CORAL ASCOSTMP A4. Unweighted pair-group centroid duster dendogram. STATISTICA CLUSTER STATS (Dlink/Dmax) *100 v a r ia b le I — 10- -20---- 30-----40-----50-----60-----70-----80----- 90- T re e V a r ia b le -100 ACTINAST A LG A E BIVALVE BRACHIOP LIM A PECTEH tflrriLLZD M E G A L O O O RETIOPfflf SPONGE OSTREA CORAL ASCOSYMP ACTINAST ALGAE BIVALVE BRACHIOP GASTROPO CRINOID LIMA PECTEH MVTIUID M EGALOOO RETICPHY SPONGE OSTREA CORAL ASCOSTM? Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 154 A 5 . W e ig h te d p a ir - g r o u p c e n tr o id c lu s te r d e n d o g r a m . STATISTIC* T ree CLUSTER STATS (DLirJc/Dmax) *100 Variable Variable 1— 10— 20— 30— 40— S O — 60—-70— 80— 90— 100 ACTINAST A LG AE BIVALVE BRACHIOP gastropo CRINOID LIMA PECTEN MOTLLID M E G A L O O O SPONGE R E T T O P H T OSTREA C O R A L ASCOSTM P ACTINAST ALGAE BIVALVE BRACHIOP GASTROPO CRINOID LIMA PECTQt MXTHXID M EG A LO D O SPONGE RETIOPHT OSTREA CORAL ASCOSTM P B. Cluster dendograms of Lower Cretaceous sites B l. Single linkage cluster dendogram. STATISTICA CLUSTER STATS (DLlnk/Dnax) *100 V a ria b le I 10----- 20— 30----- 40----SO — 60- -70— 80---- 90— 100 T ree V a ria b le C H O N D B O O GASTROPO MILIOLID SPONGE BIVALVE TOUCASIA CAPRXNUL BRANCHIN MICROSOL ALGAE ACTINAST M CNPLSUR PETAIODO CH O N D B O O GASTROPO MILIOLID SPONGE BIVALVE TOUCASIA CAPRXNUL BRANCHIN MICROSOL ALGAE ACTINAST M ONPLEUR PETALODO Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 155 B 2. C o m p le te lin k a g e d u s t e r d e n d o g r a m . STATISTICA CLUSTER STATS (D lln k /D n ax )*100 v a r ia b l e 1-----10— 20— 30— 40— 50— 60— 70— 80— 90— 100 T re e V a r ia b le C H O N D R O D — -I GASTROPO - i MILIOLID - h SPONGE — BIVALVE —:---- TOUCASIA —— CAPRINUL -------- BRANCHIN -------- CHONDROD GASTROPO MILIOLID SPONGE BIVALVE TOUCASIA CAPRINUL BRANCHIN ACTINAST MICROSOL ALGAE PETALODO MONPLEUR MICSOSOL - - - ~ -1 PETALOOO - - ■ - ~ - - ■ 1 ----------------- 1 M0NPLEUR --------- ------------------ ■ -------------------- ■ 1 f I j i t i t i t I i j Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. B3. Weighted pair-group averaged cluster dendogram. STATISTICA. CLUSTER STATS (D link/D nax) *100 v a r ia b le 1— 10-----20— 30— 40- -50— €0----- 70— 80---- 90-----100 T r e e V a ria b le C H O N D R O D GASTROPO MILIOLID SPONGE B IV A L V E TOUCASIA CAPRINUL BRANCHIN M IC R O S O L ALGAE ACTINAST MONPLSUR PETALOOO CHONDROD GASTROPO MILICLID SPONGE BIVALVE TOUCASIA CAPRINUL ERANCHIN MICROSOL ALGAE ACTINAST [JONPLEUR FETALCDC 156 B4. U n w e ig h te d p a ir-g ro u p c e n tr o id c lu s te r d e n d o g r a m . S T A T IS T IC S CLUSTER STATS D endrogram Variable Order of Amalgamation' (distances are non-oonotonlc) G A S T R O P O M I L I O L I D SPONGE C H O N D R O D BIVALVE TOUCASIA CAPRINUL BRANCHIN MICS0SOL ALGAE ACTINAST M ONPLEUR PETALOOO T ree V a r ia b le GASTROPO MILIOLID SPONGE C H O N D R O D BIVALVE TOUCASIA CAPRXNUL BRANCHIN MICROSOL A LGAE ACTINAST M ONPLEUR PETALOOO B5. Weighted pair-group centroid cluster dendogram. STATISTICA CLUSTER STATS Dendrogram variable Order of Amalgamation (distances are non-oonotonlc) GASTROPO MTLIOLXD SPO N G E CHONDROD BIVALVE TOUCASIA CAPRINUL BRANCHIN ML CKOSOL ALGAE ACTINAST MONPLEUR PETALOOO T ree V a r ia b le GASTROPO MILIOLID SPONGE CHO N D RO D BIVALVE TOUCASIA CAPRINUL BRANCHIN MICROSCL ALGAE ACTINAST MONPLEUR PETALODO Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

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Creator Fraser, Nicole Marie (author)

Core Title Large epifaunal bivalves from Mesozoic buildups of western North America

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