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Dynamic Development Of Jurassic-Pliocene Cold-Seeps, Convergent Margin Of Western North America
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Dynamic Development Of Jurassic-Pliocene Cold-Seeps, Convergent Margin Of Western North America
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IN FO R M A TIO N TO U SER S 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 face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed through, substandard margin^ and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had 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 upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. A Bell & Howell Information C om pany 300 North Z eeb Road. Ann Arbor. M l 48106-1346 USA 313/761-4700 800/521-0600 DYNAMIC DEVELOPMENT OF JURASSIC-PLIOCENE COLD-SEEPS, CONVERGENT MARGIN OF WESTERN NORTH AMERICA by Kathleen A. Campbell A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (Earth Sciences) May, 1995 Copyright 1995 Kathleen A. Campbell UMI N um ber: 9616939 UMI Microform 9616939 Copyright 1996, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 UNIVERSITY O F S O U T H E R N CALIFORNIA TH E GRADUATE SC H O O L UNIVERSITY PARK LO S A NGELES. C A L IF O R N IA 9 0 0 0 7 This thesis, written by under the direction of h.SX...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 Doctor o f Philosophy Kathleen Ann Campbell Dean Date L. THESIS COMMITTEE ACKNOWLEDGMENTS My graduate advisor, David J. Bottjer contributed to this project in myriad ways, but two of his contributions had a particularly far-ranging influence on my development as a scientist. The first was his early insight that ancient cold-seeps ought to be relatively common in convergent margin geologic settings based on one example I had studied in Washington. From that point forward and before I had even arrived at USC, I was off and running with a dissertation topic. The second gift was giving me the freedom to study and do research however I best saw fit, with plenty of shared discussions and field adventures along the way. Many thanks, David, for fueling my scientific inquisitiveness. I had a great time. My thesis committee— Alfred Fischer, Donn Gorsline, Richard Ku, and Margaret McFall-Ngai— pushed me to think hard and succeed in the difficult but rewarding realm of multi-disciplinary studies, and I thank them for insights, encouragement, advice, and shared expertise in their respective fields. In addition, several scientists that I have encountered during my graduate career have inspired aspects of my professional development, including: Benoit Beauchamp, Joanne Bourgeois, Christine Carlson, Robert Garrison, Carole Hickman, Susan Kidwell, Alan Kohn, Mike LaBarbera, Ldo Laporte, Ken MacLeod, Isabel Montanez, Cathy Newton, Dan Orange, Charles Pauli, and Dolf Seilacher. The Donors of the Petroleum Research Fund, administered by the American Chemical Society, are acknowledged for financial support of this research through a grant to D. J. Bottjer. Funding also was provided by the National Geographic Society, the Department of Earth Sciences at the University of Southern California, the Theodore Roosevelt Memorial Fund of the American Museum of Natural History, the Paleontological Society, the Society of Sigma Xi, the American Association of Petroleum Geologists, and the Geological Society of America. The American Association of University Women and the ARCS (Achievement Rewards for College Scientists) Foundation, Inc. are gratefully acknowledged for timely support during preparation of several manuscripts and the thesis. The research staffs at several museums and institutions assisted me in early seep site data searches, and include personnel from the County Museum of Natural History (Los Angeles), the U.S. Geological Survey (Menlo Park), the California Academy of Sciences (San Francisco), the Museum of Paleontology (University of California, Berkeley), and the Burke Museum (University of Washington, Seattle). Miriam Campbell, Logan Campbell, Jim Goedert, Gail Goedert, Mary Reinhart, Cheryl Salvati, Kate Whidden, and Hoss Ahmed provided assistance in the field. The Goederts, David Jones, and Ellen Moore were especially instrumental in pin-pointing localities. Carole Hickman allowed inspection of personal Keasey collections. LouElla Saul and Will Elder supplied important Mesozoic faunal information. Suzanne Harris of the Hancock Library of Biology and Oceanography, University of Southern California, was of most valuable assistance in locating obscure references. Moreover, the entire library staff at Hancock was ready and willing to assist me at any time in my research. Alicia Thompson of the Center for Electron Microscopy and Microanalysis, University of Southern California, assisted with SEM photography. Sandy Carlson and Michael Sandy provided insights and references during the brachiopod phase of research. Sarah Meigs loaned a personal computer at a crucial thesis writing interval. Michelle Robertson supplied printing access and encouragement. The office staff in the Department of Earth Sciences assisted me by navigating bureaucratic waters with ease and grace. My peers in graduate school were exceptionally supportive, full of ideas to get me through each day, and also reminded me to have some fun. These special people include Reese Barrick, Susan Chaffee, Jim Rocks, David Foley, Ken Fowler, Julio Friedmann, James Whitey Hagadom, Hong-Chun Li, Heather Moffat, Andrew Meigs, Mary Parke, Anne Petrenko, Jennifer Schubert, Stephen Schellenberg, Carol Tang, Malcolm Webster, Katherine Whidden, and Jerry Wiggert. Andrew Meigs in particular has walked the extra kilometer alongside me. Other friends who were supportive in innumerable ways include Paul Bierman, Kathy Browne, Caroline Brumlevc, Carolee Caffrey, Elizabeth Eschenbach, Antonella Fabri, Rick Gutierrez, Stephanie Hensey, Paula Lackie, Michfele Lussier, Sarah Meigs, Nicole O'Bryan, Jill Schneiderman, Ellin Sherman, Jacqueline Smith, and Lara Weber. Members of my family have been continuous supporters throughout the years in school: Miriam, Logan, Paul, Tamara and Mason Campbell, and Richard, Bob, Dianna, and Jenna Snelgrove. My mother, Miriam, understands my love for my work and instilled in me at an early age a deep appreciation for the natural world. Daniela Ahmed helped me launch my Ph.D. and has long championed my finishing this thesis. And finally, the significant person in my life is Andrea Alfaro, whose steadfast support, encouragement, incredible technical wizardry, field assistance, scientific curiosity, and love for me have made every moment of the work put into this Ph.D. worth the effort to make her proud of me. Thank you all for helping me reach my goals and being in my life. iv TABLE OF CONTENTS ACKNOWLEDGMENTS .................................................................................................... ii TABLE OF CONTENTS ...................................................................................................... v LIST OF FIGURES ................................................................................................................. viii LIST OF TABLES .................................................................................................................. xii ABSTRACT ...............................................................................................................................xiii CHAPTER 1. RECOGNITION OF ANCIENT COLD-SEEP DEPOSITS ALONG THE CONVERGENT MARGIN OF WESTERN NORTH AMERICA .......................................................................................................................... 1 Introduction ................................................................................................................. 1 Evaluating the potential for identification of ancient chemosynthetic settings and chemosymbiotic fossils in the stratigraphic record .................. 5 Methods: A paleoecological approach to recognize ancient cold- scep deposits in Western North America ......................................................... 7 Introduction and tectonic context .............................................................. 7 Recurring seep-type fossil taxa .................................................................. 13 Unusual carbonates in siliciclastic depositional environments ............ 17 Results: Geologic description of ancient cold-seep sites (Jurassic- Pliocene) of Western North America ................................................................ 19 Site descriptions of ancient cold-seeps identified in this study ........... 25 Site #1, the Quinault locality, Washington ............................ 25 Site #2, the Vemonia-Timber locality, Oregon ...................... 26 Site #3, the Holcomb locality, Washington ............................... 36 Site #4, the West Fork Satsop locality, Washington ............. 38 Site #5, the Paskenta locality, California .................................... 40 Site #6, the Cold Fork of Cottonwood Creek locality, California .................................................................................... 46 Site #7, the Wilbur Springs locality, California ......................... 50 Site #8 , the Rice Valley locality, California .............................. 56 Other reported or suspect-seep localities from the Northeast Pacific convergent margin .................................................. 59 Site #9, the Humptulips locality, Washington ........................... 59 Site #10, the Bear River locality, Washington ........................... 59 Site #11, the Menlo locality, Washington ................................... 59 Site #12, the Shipwreck Point locality, Washington ................. 60 Site #13, fossil whale fall localities, Washington ..................... 61 Site #14, the Twin River locality, Washington .......................... 61 Site #15, the Canyon River locality, Washington ..................... 62 Site #16, the San Luis Dam locality, California ........................ 62 Site #17, Humboldt area, California ............................................ 62 Site #18, Santa Cruz mountains locality, California ................. 63 Site #19, Irishman's Hat locality, California .............................. 63 Site #20, Potter Valley locality, California ................................ 63 Site #21, Lowrey's locality, California ........................................ 63 Site #22, Devil's Kitchen locality, California ............................ 63 Discussion and summary ......................................................................................... 64 v CHAPTER 2. MICROFACIES ANALYSIS AND FAUNAL- SEDIMENTOLOGICAL PATTERNS OF SELECTED MESOZOIC SEEPS OF NORTHERN CALIFORNIA ..................................................................... 72 Introduction ................................................................................................................. 72 Methods ....................................................................................................................... 73 Microfacies analysis ..................................................................................... 73 Definition ......................................................................................... 73 Field framework and sampling .................................................... 74 Thin section maps ........................................................................................ 77 Petrographic analysis .................................................................................. 77 Stable carbon and oxygen isotopes ........................................................... 79 Results ........... 79 Petrographic observations of carbonate cement components and other fabric types ...................................................... 80 Fossiliferous micrite ....................................................................... 80 Irregular yellow calcite cement .................................................... 82 Fibrous cement ................................................................................ 82 Peloidal deposits ............................................................................. 86 Blocky calcite spar ......................................................................... 86 Pyrite-coated corrosion surfaces .................................................. 88 Internal sediment ............................................................................. 88 Microbial fabrics ............................................................................. 90 Cathodoluminescent observations ............................................................. 96 Paragenetic sequence .................................................................................. 96 Stable isotopic analysis of cement components ...................................... 98 Fossil faunal-carbonate microfacies associations ....................................107 Discussion ...................................................................................................................113 CHAPTER 3. INHERENT VARIABILITY OF ANCIENT COLD-SEEP DEPOSITS ...........................................................................................................................118 Introduction .................................................................................................................118 Background: Modes and levels of variability in modem hydrothermal vent and cold-seep environments ............................................ 119 Fine-scale levels of variability at individual modem vent- secp sites ................................................................................................... 121 Meso-scale levels of variability among modem vent-seep fields ...........................................................................................................123 Large-scale levels of variability across modem oceanic regions ........................................................................................................124 Variability preserved in the geologic record of seep paleoenvironments ................................................................................................127 Fine-scale levels of variability at individual ancient seep sites ............ 127 Meso-scale (outcrop-scale) levels of variability among ancient vent-seep fields ..... 129 Large-scale variability in ancient cold-seep systems of Western North America ..........................................................................133 Summary ...................................................................................................................... 137 CHAPTER 4. BRACHIOPODS AND CHEMOSYMBIOTIC BIVALVES IN PH A NEROZOIC HYDROTHERMAL VENT AND COLD-SEEP ENVIRONMENTS ............................................................................................................ 140 Introduction ..................................................................................................................140 Peregrinella: an Early Cretaceous cold-seep restricted brachiopod .................143 vi Early Cretaceous paleoenvironments of Peregrinella ............................ 148 The Wilbur Springs and Rice Valley localities, Northern California .................................................................... 148 The Rottier, Chatillon-en-Diois, Ddvoluy, and Cumier localities, southeastern France ...................................151 Other localities of Eurasia ...............................................................152 Implications for brachiopod paleobiology ................................................ 153 Phylogenetic affinities of Peregrinella .........................................153 Adaptations of brachiopods to chemosynthetic settings ..........................................................................................154 Environmental origins of brachiopods in chemosynthetic settings .............................................................155 Paleogeography and mode of larval development ..................... 155 Brachiopods and chemosymbiotic bivalves in Phanerozoic vent- seep settings ........................................................................................................... 157 Data and results ..............................................................................................157 Discussion and implications of contrasting history of brachiopods and chemosymbiotic bivalves in vent-seep paleoenvironments ...................................................................................162 CHAPTER 5. CONCLUSIONS .......................................................................................... 166 REFERENCES CITED ........................................................................................................... 171 APPENDIX I: GEOGRAPHIC LOCALITY INFORMATION ..................................... 193 APPENDIX II: RELATIVE MICRITE:CEMENT RATIOS AND FOSSIL ABUNDANCES FOR BULK SAMPLES COLLECTED IN TRANSECTS AT PASKENTA SEEP-CARBONATE LOCALITY, NORTHERN CALIFORNIA ............................................................................................195 vii LIST OF FIGURES Figure 1. Locality map of 22 identified or inferred ancient cold-seep deposits (Jurassic- Pliocene) from convergent margin siliciclastic strata of western North America. Figure 2. Cross-section of modem northeast Pacific convergent margin showing structure of the accretionary prism and location of fluid seepage sites. Boxed inset depicts modem methane-seep community. Figure 3. Hickman's (1984) recurring Solemya-Thyasira-Uicinoma paleoecological association from Ccnozoic, deep-water, terrigenous strata of the Pacific Northwest. Figure 4. Hand sample of Mesozoic seep-carbonate from California, illustrating complex fabrics and cements. Figures. Modiola major {Gabb, 1869) from isolated "white limestones" in Mesozoic Great Valley Group forearc strata, California. Figure 6. Geographic locality map for Vemonia-Timber site (#2), northwestern Oregon and for Holcomb site (#3), southwestern Washington. Figure 7. Outcrop sketch (to scale) of Vemonia-Timber carbonate morphotypes and their strati graphic positions with respect to surrounding siltstone strata of the Keasey Formation (late Eocene). Figure 8. Field photograph of carbonate mound at Vemonia-Timber site (#2), northwestern Oregon. Figure 9. Polished carbonate slab from mound in Figure 8, illustrating glauconite-rich micritic lithology and large specimens of the bivalve Thyasira. Figure 10. Distinctive anomuran decapod-crustacean fecal pellets (Favreina) (longitudinal and cross-sectional views) from Vemonia-Timber site; crabs that form such pellets are common at hydrothermal vents today. Figure 11. Eocene carbonate chimney (18 cm high) collected adjacent to carbonate mound of Figure 8 at Vernonia-Timber locality. Figure 12. Entire thin-section view of cross-section through carbonate chimney of Figure 11, depicting concentric layers of cement around central fluid-flow conduit, Vemonia-Timber site. Figure 13. Field photograph illustrating occurrence of white carbonate nodules at Holcomb locality, which are embedded in glauconitic siltstone of "Keasey Beds" (=Lincoln Creek Formation). Figure 14. Geographic and geologic locality map for West Fork of the Satsop River site (#4), southwestern Washington. Figure 15. Field photograph of small limestone block at West Fork of Satsop River site, southern Olympic Mountains. Figure 16. Oligocene limestone doughnut-shaped fluid-conduit structure from West Fork of Satsop River locality; such features are common at modem methanc-seep sites offshore Oregon today. Figure 17. Geologic, structural and stratigraphic locality map for Paskenta site (#5), northern California. Figure 18. Field photograph of two low relief carbonate mounds at Paskenta site, surrounded by slope turbidites of Great Valley Group (Stony Creek Formation, Tithonian). Figure 19. Concentric double fluid-conduit feature lined with isopachous, fibrous cement. Paskenta locality. Figure 20. Geographic, structural and geologic locality map for Cold Fork of Cottonwood Creek site (#6), northern California. Figure 21. Field photograph of 260 m long limestone lens at Cold Fork of Cottonwood Creek locality, surrounded by turbidites of Great Valley Group (Lodoga Formation, Albian). Figure 22. Mass of tube worm remains, longitudinal and cross-sectional views, Cold Fork of Cottonwood Creek site. Figure 23. Thin section photomicrograph of thin rim of yellow calcite cement coating organic tube-wall lining, Cold Fork of Cottonwood Creek locality. Figure 24. Geographic, structural, and geologic locality map for Wilbur Springs site (#7), northern California. Figure 25. Field photograph of quarried white limestone at Wilbur Springs locality. Figure 26. Geographic, structural, and geologic locality map for Rice Valley site (#8), northern California. Figure 27. Map of Pacific Northwest showing outcrop extent of deep-water Cenozoic strata that contain "gradational," reduced-sediment deposits with the Thyasira-Lxtcinoma- Solemya fossil bivalve association. Figure 28. Carbonate slab illustrating diversity and abundance of Bear River (Eocene) cold-seep megafossils. Figure 29. Great Valley Group fossil cold-seep localities and simplified geologic map of late Mesozoic arc-trench belts exposed in north-central California. Figure 30. Summary of stratigraphic context of Great Valley Group fossil cold-seep localities (Tithonian-Cenomanian) with respect to current nomenclature. Figure 31. Bulk sample transects for Paskenta cold-seep deposit. Figure 32. Gastropod fossils, their burrows, and overall bioturbate (mottled) texture of fossiliferous micrite microfacies from Paskenta locality. Figure 33. Vug (5 mm across) lined with irregular yellow calcite cement, followed by fibrous cement growth into cavity. Remaining pore space filled with clear, blocky calcite spar. Figure 34. Transition from irregular yellow calcite cement to radiating bundles of fibrous cement sub-crystals. Fibrous cements contain organic-rich, hydrocarbon inclusions (seen in [a] plain light and [b] UV light) which occur as black streaks along sub-crystal boundaries or as brown globules along concentric growth lines within cement bundles. Figure 35. Peloidal fabric type, illustrating a region of aggrading irregular yellow calcite cement which "consumed1 ' micrite. Larger peloids may have resisted in situ replacement (owing to ?mucus linings), and subsequently served as growth substrates for radial fibrous cements. Figure 36. Pyrite-coated corrosion surfaces separating dark micrite from lighter-colored cements. Figure 37. Internal sediment infill of preserved tube worm structures, entire thin-section view, Cold Fork of Cottonwood Creek limestone. Dark detrital material partially fill or line tubes; pore space was subsequently cemented with blocky clear spar. Figure 38. Microbial fabrics associated with outer or inner tube worm surfaces: (a) thinly coating outside of tube, longitudinal section; (b) forming clumps inside tube pore space, following or contemporaneous with decay of worm organic material. Figure 39. Microbial fabrics preserved as finely laminated, mat-like layers (a); or (b) intercalated at a fine-scale with pyrite horizons and layers of irregular yellow and fibrous calcite cements. Figure 40. Plot of 6 anc] 5 1 8 q values for Paskenta carbonate components. Figure 41. Paragenetic sequence of Paskenta fabrics adjacent to range in stable carbon and oxygen values for irregular yellow calcite, fibrous calcite, clear blocky spar cements. Figure 42. Entire thin-section view of preserved tube worms in peloidal or wavy laminated cements, from Cold Fork of Cottonwood Creek locality. Figure 43. Gastropod nestled between two tube worms; tubes preserved in longitudinal section, and coated with microbial mat. Figure 44. Schematic diagram illustrating distribution of fossils with microfacies components for Californian Mesozoic seep-carbonates. Figure 45. Spatial association of fossiliferous micrite microfacies and wavy-laminated cements at outcrop-scale for California Mesozoic seep carbonates. Figure 46. Part of Beauchamp and Savard's (1992) model of paragenetic events leading to chemosynthetic mound development. Beauchamp and Savard (1992) recognized two phases of mound development: a) an early phase (not shown), characterized by anaerobic micrite development, followed by aerobic biogenic activity within micritic deposits; and, x b) a later phase, shown here, that depicts yellow cement formation beneath bacterial mats in anaerobic microenvironmental conditions. Figure 47. Three-tiered hierarchical context for observations of spatial heterogeneity in modem hydrothermal vent ecosystems: ( 1) individual vent in vent field, (2) clusters of vent fields along spreading axis, and (3) regional ridge segments. From Van Dover and Hesslcr (1990). Figure 48. Range in carbonate volume from western North American ancient cold-seep sites: (a) small "blebs" from storm-shelf siltstone of Mio-Pliocene Quinault Formation, Washington; and (b) large limestone mound from Bear River Quarry in Eocene siltstone of Cliff Point, Washington. Figure 49. Paleogeographic map for the Early Cretaceous (Hauterivian) (from Smith and Briden, 1978) depicting 13 worldwide localities of the fossil seep-restricted, cosmopolitan brachiopod genus Peregrinella along the margin of the Tethys Ocean. Figure 50. Hauterivian rhynchonellid brachiopod Peregrinella whitneyi and core mytilid Modiola major from Wilbur Springs, California ancient cold-seep. Figure 51. Occurrence of brachiopods as well as bivalves with extant chemosymbiotic descendants in Phanerozoic hydrothermal vents and cold-seep paleoenvironments. LIST OF TABLES Table 1. Marine invertebrates with chemoautotrophic bacterial symbionts that have taphonomic potential for preservation in the fossil record. Table 2. Geologic description of primary ancient cold-seep sites recognized in this study using a paleoecological approach. Compare age, carbonate form and dimensions, associated seep-taxa, and broad depositional settings. Table 3. Summary of stable carbon and oxygen isotope data on carbonate phases (shells, fibrous calcite cement, irregular yellow calcite cement, clear blocky calcite spar) for Paskenta, Cold Fork of Cottonwood Creek and Wilbur Springs localities (Tithonian- Albian), northern California. Table 4. Summary of heretofore unrecognized seep-suspect aspects of the stratigraphy, sedimentology, structure and biotic associations for 13 ?Late Berriasian-Hauterivian age Peregrinella occurrences worldwide. ABSTRACT A paleoecologic approach was used to identify cold-seep deposits preserved in siliciclastic, marine forearc strata (Jurassic-Pliocene age) of western Washington, Oregon and California. Ancient cold-seep sites are recognized along the convergent margin of western North America based on co-occurrence of: 1) mega-invertebrate fossils with modern chemosymbiotic representatives (e.g., tube worm remains, certain bivalves), and 2) anomalous sedimentologic associations (e.g., isolated methane-derived carbonates). These similar features recur in seep deposits across ~150 m.y. and 1600 km of forearc history for this region. Variability also was observed in geo-tectonic setting, seep- carbonate volume, and diversity and abundance of associated fossil taxa. Petrographic and isotopic analyses of Mesozoic seep-carbonates in California revealed: 1) a consistent paragenetic sequence of recurring carbonate phases; 2) evidence for presence of sulfide (pyrite-coated corrosion surfaces) and methane (cements isotopically depleted in carbon) during carbonate formation; and 3) restriction of fossil taxa to particular carbonate types. Laminated and clotted microbial fabrics are preserved in some deposits. Most biogenic activity was restricted to the early-formed micrite microfacies; however, tube worm fabrics are associated with cement-rich phases. The cement stratigraphy of Californian seep-carbonates is similar to that reported for Cretaceous age methane seeps of the Canadian Arctic. Cenozoic and late Mesozoic age seeps in western North America contain chemosymbiotic bivalve-dominated fossil assemblages; whereas, some early Mesozoic seeps (Tithonian-Hauterivian age) are characterized by abundant articulate brachiopods (Peregrinella, Cooperrhynchia). Peregrinella, the largest of all Mesozoic rhynchonellids, is seep-suspect worldwide during the Neocomian based on anomalous tectono-stratigraphic and other associations. A global compilation of 42 fossiliferous Phanerozoic marine deposits interpreted herein to represent ancient hydrothermal vent or cold-seep habitats indicates that brachiopods were common constituents of such xiii chemosynthetic settings from the Late Devonian through the Early Cretaceous, but were rare in younger vent-seep paleoenvironments. Some Paleozoic and Mesozoic vent-seep rhynchonellids appear to be phylogenetically related (Dzieduszyckia, TEoperegrinella, Peregrinella). Bivalve genera with extant chemosymbiotic descendants first appeared in vent-seep deposits during the Jurassic and have been prevalent-therein since the Early Cretaceous. xiv CHAPTER 1. RECOGNITION OF ANCIENT COLD-SEEP DEPOSITS ALONG THE CONVERGENT MARGIN OF WESTERN NORTH AMERICA INTRODUCTION Until dense aggregations of molluscs and giant tube worms were discovered at hydrothermal vents along oceanic spreading centers in the deep-sea (Lonsdale, 1977), the impact of chemosynthesis on the composition, geographic extent and evolution of entire benthic marine communities had not been considered or even imagined. Continuing investigation of modem chemosynthetic ecosystems not only has revealed extraordinary invertebrate adaptations to extreme environmental conditions (e.g., Somero et aL, 1989), but also has opened up geological inquiry into the nature and distribution of these unusual physical-chemical-biological constructs of the past. Potential insights to be gained by study of ancient hydrothermal vent and cold-seep deposits include: 1) possible links between vent-type habitats and the origin of life (e.g., Miller and Bada, 1988); 2) geochemical evolution of vent-seep fluids in tectonically active sedimentary basins (e.g., Beauchamp and Savard, 1992; von Bitter etal., 1992); 3) role of the chemosynthetic life strategy in the evolution and paleoenvironmental associations of various taxonomic lineages (e.g., Reid and Brand, 1986; Seilacher, 1990; Campbell and Bottjer, in press; in review); 4) paleobiogeography and dispersal of vent-type organisms (e.g., Campbell etal., 1993; Campbell and Bottjer, in review); 5) role of vent-seep habitats as refugia during periods of global crisis (e.g., Kauffman and Howe, 1990); and, 6) the extent to which uniformitarian models can be applied to geochemically based paleocommunities throughout the Phanerozoic (e.g., Bottjer et aL, 1995; Campbell and Bottjer, in press; in review). 1 Before any of these second-order problems can be analyzed in the context of ancient chemosynthetic settings, it is important to first recognize and predict the occurrence of fossil hydrothermal vent and cold-seep deposits in the geologic record. Such identification requires understanding of the interconnected biological, chemical and physical processes that coalesce to produce modem hydrothermal vent or cold-seep settings. Chemosynthesis is defined as primary production of organic matter by means of chemical energy rather than sunlight. Chemosynthetic manufacture of organic matter is performed by only a few groups of specialized bacteria that are present in modem vent-seep habitats. These prokaryotes oxidize reduced inorganic substrates (i.e., the dissolved hydrogen sulfide or methane concentrated in the shimmering vent-fluid effluent), and use the released energy to synthesize organic compounds from carbon dioxide in seawater, a process known as chemoautotrophy (Cavanaugh, 1985; Lutz and Kennish, 1993). For modem hydrothermal vent settings, the geological source of these reduced inorganic compounds is the high- temperature reaction of seawater with newly formed crustal rocks along oceanic spreading ridges (Rona etal., 1983). For hydrocarbon- or brine-rich modem cold-seeps, reduced fluids are generated in porewaters during deposition of sediments and burial of organic matter in marine basins adjacent to continental margins. Sulfate-reducing and methane- producing bacteria break down organic matter in sediments to produce hydrogen sulfide and methane, respectively (e.g., Barnes and Goldberg, 1976; Berner, 1980; Jprgensen, 1982a,b; Claypool and Kvenvolden, 1983; Ritger etal., 1987; Masuzawa etal., 1992). Methane also may originate by thermogenic (inorganic) decomposition of buried organic carbon at depth (Claypool and Kvenvolden, 1983; Kvenvolden etal., 1989). The reduced connate waters produced by these processes subsequently migrate up to the sediment- seawater interface along faults, diapirs, unconformities, or coarse sedimentary layers, which serve as fluid conduits activated by rifting, subduction, or by passive circulation through sedimentary basins (e.g., Langseth and Moore, 1990; Lewis and Cochrane, 1990; Pauli etal., 1991). 2 Fluids exiting to the seafloor at hydrothermal vent and cold-seep sites affect organism populations and produce anomalous sedimentary precipitates in the local marine environment. Chemoautotrophic bacteria serve as the base of the chemosynthetic food chain in these settings at several trophic levels: 1) filter-feeding invertebrates strain free- living bacteria from vent waters; 2) grazing benthos exploit surface microbial mats; and, 3) chemosymbiotic molluscs and tube worms are sustained directly by bacterial symbionts housed in host-invertebrate tissues (Jannasch, 1983; 1985; Jannasch and Mottl, 1985; Lutz and Kennish, 1993). The oxidation of vent-seep fluids upon contact with seawater forms localized sedimentary deposits such as sulfides, sulfates, and isotopically distinctive authigenic carbonates (e.g., Koski etal., 1985; Han and Suess, 1989). Two important generalizations have arisen from studies of modem hydrothermal vents and cold-sceps that contribute to our overall ability to distinguish ancient vent-seep deposits in the stratigraphic record. First, present-day hydrothermal vent taxa "constitute a coherent faunal unit around the globe" (p. 346, Tunnicliffe, 1992) with major species representation from just a few dominant invertebrate groups {i.e., polychaetes, crustaceans, molluscs, vestimentiferan tube worms) (Van Dover, 1990; Tunnicliffe, 1992). Second, modem chemosynthetic settings are now known to be relatively common worldwide, with frequent discoveries of new vent or seep habitats reported as submersibles continue to explore the deep sea. Therefore, characteristics of recurring, distinctive, vent-seep- restricted biotas and their associated, anomalous sedimentary precipitates can be used to predict occurrences of ancient hydrothermal vent and cold-seep deposits in the geologic record (Campbell, 1992; Campbell and Bottjer, 1993a). Furthermore, these paleoenvironments should be better represented than previously recognized in the stratigraphic record. The purposes of this chapter are two-fold: 1) to detail a paleoecological approach used in the present study to systematically identify cold-seep paleoenvironments, particularly for the field region of westernmost North America; and, 2) to describe the 3 overall characteristics of eight fossil seep sites discovered and analyzed during the course of this investigation. Also summarized briefly are features of 14 other similar deposits from the same tectono-sedimentary system that represent either seep-suspect fossil localities (identified during field or museum reconnaissance but which are as yet unstudied or located), or that have been interpreted as fossil cold-seeps in recent years by other investigators. Together, these 22 probable fossil cold-seep deposits record ~-150 m.y. of convergence history in stratigraphic sequences exposed in western Washington, Oregon and California. Petrographic observations and microfacies associations for several of the seep-carbonate deposits of this chapter are discussed in detail in Chapter 2. Chapter 3 addresses the variability observed within and among Mesozoic and Cenozoic sites with respect to seep faunal-sedimentological composition and distribution. Finally, Chapter 4 places the westernmost North American sites in global context through exploration of the evolutionary paleoecoiogy of brachiopods versus core bivalves in Phanerozoic hydrothermal vent and cold-seep deposits worldwide. Few geologists or paleontologists have studied the effects of chemosynthesis on the development and evolution of Phanerozoic mega-invertebrate pal eocom muni ties, since the significance of the phenomenon in modem marine ecosystems has been appreciated only very recently. Virtually all paleobiological and geological data collected on fossilized benthos throughout the history oflife in the marine realm have come from analyses of photosynthetic paleoenvironments (e.g., intertidal, reef, level-bottom, pelagic). Yet it is now clear that a chemosynthetic life strategy, once thought to be biologically meaningful only in the domain of free-living microbes, is relatively common among larger invertebrates, and that the acquisition of this novel metabolic pathway, via symbiosis, has led to evolutionary innovation from cellular to ecosystem levels (Somero et aL, 1989; Vetter, 1991). Prior to the present study, many reported ancient hydrothermal vent and cold-seep deposits worldwide appear to have been found by chance discovery, and they typically represent single site examples or single time slices (e.g., Banks, 1985; Gaillard et 4 al., 1985; Howe, 1987; Clari etal., 1988; Campbell, 1989; Niitsumae/o/., 1989; von Bitter etal., 1990; Kelly etal., in press). This investigation, however, is unique in that a systematic search was conducted to identify new cold-seep deposits that record a part of the 150 m.y. history of convergence, sedimentation, and biotic evolution across one quasi- continuous, active tectono-sedimentary system (Campbell, 1992; Campbell and Bottjer, 1993; Campbell etal., 1993). EVALUATING THE POTENTIAL FOR IDENTIFICATION OF ANCIENT CHEMOSYNTHETIC SETTINGS AND CHEMOSYMBIOTIC FOSSILS IN THE STRATIGRAPHIC RECORD This investigation of chemosynthetic paleoenvironments and associated ancient chemosymbiotic taxa relies in part on uniformitarian principles. Two intrinsic limitations to such an approach are acknowledged. First, chemosynthetic activity in modem marine environments is not limited to hydrothermal vents nor to cold-seeps but exists in a spectrum of reduced sedimentary habitats. Since reduced fluids are produced in deeply buried sediments, any place where such fluids issue in the marine realm provides a potential site for a chemosynthetic community to be established, although certain tectonic settings favor such seepage. Therefore, multiple lines of evidence should be used to distinguish ancient vent-seep deposits in the stratigraphic record. Second, chemosymbiotic relationships between living bacteria and their mega-invertebrate hosts are typically confirmed in modern studies by biochemical and ultrastructural investigations (review in Fisher, 1990). By contrast, in the stratigraphic record, the taphonomic and diagenetic processes of fossilization typically destroy organic tissues and therefore preclude direct verification of chemosymbiosis as a life strategy for fossil invertebrates, especially for extinct taxa with no modem analogous relatives in modem chemosynthetic habitats. The first problem of accurately identifying different types of chemosynthetic marine paleoenvironments in the stratigraphic record can be mitigated in large part by a detailed and comprehensive analysis of the geologic setting of a given suspect deposit. Presently, a variety of modem chemosynthetic habitats are known to exist which contain chemosymbiotic mega-invertebrates, including hydrothermal vents, marine grass banks, mud flats, sewage outfalls, pulp mill effluent areas, fjords, and other anoxic basins, sunken whale carcasses, and methane, oil and brine seeps (Cavanaugh, 1985; Hovland and Judd, 1988; Smith etal., 1989). These relatively restricted habitats tend to be conducive to chemosynthetic activity because they are characterized by limited oxygen supply or by spatial-temporal partitioning of oxygen and reduced fluids that allow chemosymbiotic bacteria to biochemically control the oxidation of hydrogen sulfide and methane locally for use in the manufacture of organic matter, while the larger invertebrate hosts simultaneously obtain oxygen from seawater for respiration (J0rgensen, 1982a; Cavanaugh, 1985). Hence, conditions that favor chemosynthesis usually occur along oxic-anoxic interfaces in sedimentary basins, or they occur in tectonically active regions where reduced chemical compounds are injected by fluid seepage into the local marine environment (J0rgensen, 1982a; Cavanaugh, 1985). The typically vigorous, advective fluid-flow at vent-seep sites produces volumetrically significant and distinctive sedimentary precipitates and fluid-flow structures (e.g., Koski etal., 1985; Kulm and Suess, 1990) that also aid in recognition of these deposits. The second problem of inferring a chemosymbiotic life strategy for a given fossil invertebrate taxon in the geologic record cannot be resolved directly although two possible methods are in use currently, of which the paleoecologic approach outlined herein appears to yield the most geological versatility and applicability. CoBabe (1991) described a method for "direct" detection of chemosymbiosis in molluscs from the stable isotopic composition of organic matrix that is enclosed in bivalve shell-carbonate. However, the lipids and polysaccharides that comprise the organic matrix of the shell do not appear to maintain their integrity through the fossilization process beyond about 1 m.y.b.p., even in the best preserved examples (CoBabe, 1991). Alternatively, Seilacher (1990) explored 6 potential bivalve symbioses in the fossil record by examining shell form and function. He concluded that "chemosymbiosis requires primarily physiological adaptations (such as protection of the host against the toxic sulfide) and may leave shell morphology largely unaffected, [so that] one must rely largely on indirect evidence, including facies criteria, to pinpoint chemosymbiotic species among fossil bivalves" (p. 297, Seilacher, 1990). The present study relies on a variety of geological criteria to independently characterize the paleoenvironmcntal context of fossil taxa that likely were chemosymbiotic, including tectono-stratigraphic associations, sedimentary facies relationships, petrographic characteristics, and stable isotopic analysis. For this study, the only fossil invertebrates inferred to have been chemosymbiotic in the past are those fossil groups with extant chemosymbiotic descendants, which commonly are comparable at the genus level and are termed "core" taxa herein. METHODS: A PALEOECOLOGICAL APPROACH TO RECOGNIZE ANCIENT COLD-SEEP DEPOSITS IN WESTERN NORTH AMERICA Introduction and Tectonic Context A paleoecological approach is used in the present study to recognize ancient cold- seep paleoenvironments and chemosymbiotic fossil taxa in western North America. This method comprises evaluation of a broad range of geologic criteria within a seep-suspect setting, from global to microscopic scales of observation. It also can be modified and applied to locate ancient, suspect hydrothermal vent and cold-seep deposits worldwide throughout the duration of the Phanerozoic. Fossil hydrothermal vent deposits are described elsewhere from single-site studies (e.g., Oudin and Constantinou, 1984; Papke, 1984; Banks, 1985; Oudin etal., 1985; Haymon and Koski, 1985; Moore etal., 1986; Kuznetzov eta!., 1988; 1990; Poole etal., 1991), and are not evaluated further herein. Cold-seep deposits discovered during the course of this investigation are exposed in strata of Jurassic-PIiocene age from outcrops in western California, Oregon, and Washington 7 (Figure 1) (to date, regional published studies on reported sites and associated fossils include Campbell, 1989; 1992; 1994; Campbell and Bottjer, 1990, 1991, 1992a,b, 1993a,b; 1994; in press; in review; Goedert and Squires, 1990; 1993; Squires and Goedert, 1991; Campbell etal., 1993; Elder and Miller, 1993; Nesbitt etal., 1994; Sandy and Campbell, 1994; Goedert and Campbell, 1995; Squires, 1995). In this section, I describe the tectonic context of the stratigraphic sequences that contain seep-suspect sites , and then outline the paleontologic and sedimentologic criteria used to identify cold-seep deposits in western North America. In general, the choice of an active convergent continental margin is an ideal tectonic setting within which to search for modem or ancient cold-seeps because the geological processes typical of plate subduction (i.e., rapid sedimentation and burial, structural deformation owing to compression, volume of over-pressured connate waters escaping to the seafloor) can generate both the sources and conduits for the chemically reduced fluid- flow that sustains chemosynthetic marine communities (Suess etal., 1985; Ritger etal., 1987; Langseth and Moore, 1990; Moore and Vrolijk, 1992). Along the northeast Pacific convergent margin today, methane-rich fluids exude offshore of Oregon and Washington, where compressional forces associated with subduction facilitate fluid migration into overlying marine forearc basins and accretionary prism sediments (Figure 2). The Juan de Fuca oceanic plate has been subducting beneath the North American continental plate since the mid-Late Eocene (~ 42 m.y. ago), when the still-active Cascades volcanic arc was first established (Wells etal., 1984; Duncan and Kulm, 1989). The oceanic trench that marks the present-day subduction zone offshore is filled with marine sediment that has been accumulating upon and scraped off of the down-going oceanic plate to form the Cascadia accretionary prism, a highly deformed, wedge-shaped pile of marine terrigenous sediments rich in pore fluids (Figures 1, 2). These sediments are generally composed of fine-grained sands and muds derived from deeper-water sedimentary deposits that currently are being tectonically plastered onto the continental margin in today's outer British Columbia I g / V Seattle i?< 3 \ W ashing’o n JUAN 1 1 DE FUCA PLATE -J Oregon NORTH AM ER IC A I /PLATE PACIFIC PLATE Nevada San Francisco California P AC I F I C O C E A N Los Angeles Figure 1. Locality map of 22 reported or inferred ancient cold-seep deposits (Jurassic-Pliocene) from convergent margin terrigenous strata of western North America. Modem analogous tectonic setting shown for Juan de Fuca oceanic plate offshore of Oregon and Washington, which is presently subducting beneath the North American continental plate. Modem trench is filled with terrigenous sediments that form an accretionary wedge that is dewatering owing to the compressive stresses of subduction. Fluids exit at seafloor around which modem methane-seep communities (stars) congregate. Site numbers refer to localities described in the text. 9 Figure 2. Cross-section of modern northeast Pacific convergent margin showing structure of the accretionary prism, fluid- flow pathways (small arrows), and location of several fluid seepage sites (stars). Example locations where fluids can escape to the seafloor include: a) at the outer toe of the wedge, where large-scale dewatering and sediment deformation occur today; b) above compressional faults formed within the accretionary complex; and, c) in marine forearc basins where sediment is accumulating behind the deforming wedge. Boxed inset illustrates modem methane-seep community and anomalous limestone precipitates from offshore of Oregon. Figure modified after Langseth and Moore (1990), and Suess et al. (1985). shelf to lower slope environments (Kulm and Fowler, 1974; Kulm and Suess, 1990). Over time, tectonic compression and compaction reduce sediment porosities and displace pore fluids within the accretionary prism. The elevated pore pressure and presence of fluids between sedimentary grains decreases the shear strength of the buried deposits and eventually causes large-scale dcwatering of the sedimentary wedge; these displaced fluids eventually migrate up to the seafloor along zones of focused flow (Moore and Vrolijk, 1992). For example, dewatering occurs along tectonically induced faults, diapirs, mud volcanoes and/or through coarse-grained turbidite deposits (brought into the basin by turbidity currents that break loose down the continental slope within deep-sea submarine fan systems) (Langseth and Moore, 1990; Lewis and Cochrane, 1990). Several example locations [a,b,c] where fluids can escape to the seafloor are depicted in Figure 2 above the Cascadia accretionary complex of the Pacific Northwest, including: a) at the outer toe of the wedge, where large-scale dewatering and sediment deformation occur today; b) above comprcssional faults formed within the accretionary complex; and, c) in marine forearc basins where sediment is accumulating behind the deforming wedge (Langseth and Moore, 1990). Other fluid migration paths (Figure 2, arrows) and subduction-related mechanisms of sediment deformation also exist in accretionary prisms, and these are described in detail elsewhere (e.g., Langseth and Moore, 1990; Moore and Vrolijk, 1992). Associated with these tectonically induced, fluid- generating processes offshore of Oregon today are flourishing marine invertebrate communities which contain chemosymbiotic taxa such as the pogonophoran tube worm Lamellibractua Ixiriia/ni and the bivalves Calyplogena sp. and Solemya sp. (Suess etal., 1985) (Figure 2, boxed inset). The modem Oregon cold-seeps (Figure 1, stars) also discharge methane-rich fluids which, upon contact with seawater, precipitate distinctive authigenic carbonates around the effluent areas (Kulm et at., 1986; Ritger et at., 1987; Han and Suess, 1989; Suess and Whiticar, 1989; Kulm and Suess, 1990). Hence, the present- day active tectonic setting along the continental margin of western North America supports 11 chemosynthetically based biotas and contains sedimentary deposits representative of anomalous fluid seepage (Figure 2, boxed inset). Therefore, tectono-sedimentary processes occurring in this setting today comprise an excellent modem analog for comparison with fossil seep-suspect deposits that are preserved in older, subduction-related strata of the Pacific Northwest region. Ancient marine sedimentary sequences that conceivably could preserve fossil cold- seep deposits have been accumulating in comparable tectonic regimes along this same continental margin since the Late Jurassic (~ 150 m.y. ago). In the Pacific Northwest throughout the Cenozoic (<65 m.y. ago), an offshore oceanic plate was always being consumed beneath the North American continent, although specific plate configurations differed somewhat from those of present-day geometries (Figure 1) (Duncan and Kulm, 1989; Snavely and Kvenvolden, 1989). Nonetheless, deep-water marine sediments probably have been deposited relatively continuously in subduction-related tectono- sedimentary settings offshore of Washington, Oregon and northern California for at least the past 45 million years. Further south into California along the continental margin during the late Mesozoic, convergence was also the dominant plate tectonic process that affected the sedimentary history of marine basins along this portion of western North America. Before the transform plate motion of the Cenozoic San Andreas fault system was established in western California, a now-mostly-consumed oceanic plate (= Farallon Plate) was being subducted beneath the North American continent (Atwater, 1989). Within this older volcanic arc-trench convergence system accumulated a sequence of deep-water, marine forearc sediments and a mdlange of accretionary prism deposits, both of Late Jurassic to Late Cretaceous age (~150 - 70 m.y. old), which have since been lithified, accreted to the continent, and are now exposed in northwestern California (e.g., Hamilton, 1969; Ernst, 1970; Dickinson, 1971; Dickinson and Seeley, 1979; Ingersoll and Dickinson, 1981). To date, ancient seep sites have been predicted and identified in both Mesozoic- and Cenozoic-age, subduction-related deposits along the entire western margin 12 of the United States of America (Figure 1), and these sedimentary strata provide the appropriate tectono-sedimentary context within which to evaluate fossil cold-seep evolution in this region. Recurring Seep-Type Fossil Taxa One type of paleontologic evidence used to identify ancient seep localities within stratigraphic sequences of the western U.S. is the presence of unusual concentrations of fossil invertebrate taxa with extant chemosymbiotic relatives common today in hydrothermal vent and cold-seep habitats. These inferred chemosymbiotic fossil taxa are termed "core" taxa in this study. In particular for the study area, a first clue that ancient cold-seep deposits might be relatively common came with a re-evaluation of Hickman's (1974; 1984) studies of recurring moiluscan assemblages from different deep-water, Cenozoic sedimentary sequences in the Pacific Northwest. Hickman (1974; 1984) developed the taxonomic structure method of paleobathymetric interpretation while attempting to regionally characterize the environmental controls upon and stratigraphic distribution of poorly studied invertebrate paleocommunities in the region. Specifically, entire fossil assemblages were evaluated based on feeding mode patterns that change with depth for different invertebrate communities in modem analogous settings, and thereby six major recurring paleoecological associations were recognized in Oregon and Washington (Hickman, 1984). One of these recurring fossil faunal associations is the generalized Thyasira-Lucinoma-Soiemya paleocommunity (Figure 3), "dominated by low diversity assemblages of large infaunal bivalves adapted for suspension feeding in low productivity settings" (p. 1215, Hickman, 1984). The modem biotic counterparts of these bivalves are known to possess chemosymbiotic bacteria, and these genera have been reported from both modem and ancient seep sites, and from other organic-rich, low-oxygen settings. Reid and Brand (1986) first postulated that the driving force behind at least some of these Thyasira- Lucinoma-Solemya occurrences could have been ancient hydrocarbon and/or sulfide fluid- seepage to the seafloor which, in turn, could have supported chemosynthetically based 13 Thyasira - Lucinoma - Solemya Association 3 1 from Hickman, 1984 Figure 3. Hickman’ s (1984) recurring Solemya-Thyasira-Lucinoma paleoecological association from Cenozoic, deep-water, terrigenous strata of the Pacific Northwest. Modem representatives of these bivalves are chemosymbiotic. Modified after Hickman (1984). 14 faunas. Using field and laboratory analysis, the results of this study are a direct test of the Reid and Brand (1986) hypothesis. For this study, I recognize several additional groups of living, chemosymbiotic mega-invertebrates in addition to the bivalve genera Solemya, Thyasira and Lxicinoma that also occur in modem hydrothermal vent and cold-seep habitats (e.g., Fisher, 1990; Tunnicliffe, 1992). Those taxa with preservation potential in the fossil record— i.e., those with calcified shells or hard, proteinaceous-chitonous tubes— are summarized in Table 1 as being useful core taxa that may aid in identification of an ancient vent-seep suspect deposit. Excluded from the list are soft-bodied chemosymbiotic taxa (e.g., Desbruy&res et al., 1985; Giere, 1989; Gaill and Hunt, 1991) that have less likelihood of preservation or identification in the geologic record. Some of the bivalves, gastropods, and vestimentiferan and pogonoferan tube worms listed are presently known from both modem and ancient vent-seep settings, and these groups arc demarcated with an asterisk (Table 1). Furthermore, many non-chemosymbiotic mega-invertebrates commonly recur in modem vent-seep habitats, but are not necessarily restricted to chemosynthetic settings in the marine realm overall (e.g., Van Dover, 1990; Tunnicliffe, 1992). Certain of these non- obligate, "associate" taxa also recur at both modem and ancient vent-seep sites. Associate fossil components that are affiliated with both past and present vent-seep deposits include the gastropods Provatim, Margarites (Dalhymargarites at modem hydrothermal vents), hyalogyrinids, and various limpets, as well as serpulid worm tubes, and fecal pellets of anomuran decapod crustaceans (Stanton, 1895; Squires and Goedert, 1991; Tunnicliffe, 1992; Campbell and Bottjer, 1993a,b; Campbell etal., 1993; Goedert and Campbell, 1995; Squires, 1995). Hence, distinctive, recurring core and associate fossil faunal components with strong representation in both modem and ancient vent-seep habitats can be used to aid in identification of additional seep-suspect deposits in western North America (however, see Chapter 4 for caveats to this approach, especially for older deposits). 15 TABLE 1. Chemosymbiotic Marine Invertebrates with Taphonomic Potential for Fossil Preservation. (*) indicates genera with established record in both modem and ancient hydrothermal vent or cold-seep habitats. Inferred chemosymbiotic fossil taxa are termed "core" taxa. (t) indicates fossil core genus collected only from ancient cold-seep deposit, but with very close phylogenetic relations to similar chemosymbiotic taxa from present day vent-seep settings. Each chemosymbiotic taxon in the list has strong potential for preservation in the geologic record because of possession of either skeletal hard parts or hard proteinaceous-chitonous tubes that become coated with sedimentary precipitates or sulfide metals during life (as reported in Jannasch and Wirsen, 1979; Banks, 1985; Tunnicliffe and Fontaine, 1987; Beauchamp and Savard, 1992). Modem and fossil generic data from Lemoine etal. , 1982; Howe, 1987; Clari et al., 1988; Fisher, 1990; Bouchetand Waren, 1991; Squires and Goedert, 1991; Campbell, 1992; Tunnicliffe, 1992;Campbell etal., 1993; Campbell and Bottjer, in press. Phylum Vestimentifera* — at least 6 genera in 5 families (little potential at present for identification below phylum level in fossil record) Phylum Pogonophora* — 5 genera, taxonomy in dispute (little potential at present for identification below phylum level in fossil record) Phylum Mollusca Class Bivalvia — 19 genera in 5 families; Family Lucinidae Anodontia Codakia Linga Loripes Lucina* Lucinella Lucinoma* Myrtea Nymphalucina t Parvilucitia Pseudomiltha * Family Thyasiridae Thyasira * Family Solemyidae Solemya * Acharaxf Family Vesicomyidae Calyptogena* Vesicomya * Family Mytilidae Bathymodiolus Modiolust Modiola t Class Gastropoda — 2 genera in one family: Family aff. Trichotropidae Alviniconcha Ifremeria 16 Unusual Carbonates in Siliciclastic Depositional Environments A second type of evidence used to identify ancient seep localities in the present study is the stratigraphically restricted association of core and associate taxa with anomalous, authigenic, sedimentary precipitates indicative of fluid venting at the seafloor. For example, both modem and ancient cold-seeps are typically characterized by the presence of unusual, in situ, methane-derived sedimentary carbonates (Figure 4) (e.g., Arthur etal., 1982; Gaillard etal., 1985; Howe, 1987; Ritger etal., 1987; Clari etal., 1988; Beauchamp etal., 1989; Campbell, 1989; 1992; von Bitter et al., 1990; Campbell and Bottjer, 1992b; 1993a,b; Aharon etal., 1993; Campbell etal., 1993; Elder and Miller, 1993; Orange etal., 1993b; Kelly etal., in press). These carbonate sediments typically form today at a fluid-seep site when methane (carried in diffusing or advecting porewaters) is oxidized upon contact with seawater to bicarbonate ion or carbonate ion; these carbon compounds then combine with the calcium in seawater to produce an authigenic carbonate precipitate (for a more detailed treatment of the geochemical reactions see Ritger et al., 1987; Han and Suess, 1989; Suess and Whiticar, 1989). The thermogenic and/or biogenic methane-source reservoirs tapped from buried porewaters ideally can be distinguished from one another based on stable carbon isotopic differences in the carbonate end-products; however in practice, mixing from several carbon reservoirs can affect the final isotopic signature (e.g., Schoell, 1980; Coleman etal., 1981; Anderson and Arthur, 1983; Ritger el al., 1987; Campbell, 1992). Until the relatively recent discovery of isolated, authigenic carbonates precipitated in association with modem deep-sea fluid seepage, the only other facies models routinely applied in the geologic record to explain deep-water carbonate bodies surrounded by siliciclastic strata were for occurrences of pelagic sedimentation, slump/debris deposits from shallower water settings, or slope/basinal turbidites derived from a carbonate source on the shelf (e.g., Wilson, 1975; Cook and Enos, 1977, Fliigel, 1982; Sliter, 1984). Specifically for the terrigenous-based, marine continental margin of westernmost North Figure 4. Hand sample slab of Mesozoic seep-carbonate from Paskenta locality, California, illustrating complex, irregular fabrics. Note spar-filled (white) vug (top of photo) with internal sedimentary infill layer as geopetal feature. Central portion of slab characterized by wavy, hemispheric (convex-up) layers of cements: alternating irregular yellow calcite cement (dark) and fibrous calcite cement (light). Lower basal portion of slab comprised predominantly of peloidal and laminated micrite. 18 America, limestones are considered to be volumetrically insignificant compared to the thick sequences of sandstone and mudstone that represent ancient forearc basins and their adjacent accretionary prisms (e.g., Bailey etal., 1964; Ingersoll and Dickinson, 1981). Where ancient carbonates are found in strata of the Northeast Pacific region, they usually have originated from one of several sources: 1) deep-water oozes accumulated on seamounts (Sliter, 1984); 2) shallow-water deposits formed atop structurally controlled topographic highs (Dickinson and Seeley, 1979; Whidden, 1994); 3) localized, concentrated shell beds (e.g., Bottjer and Douglas, 1984); 4) "normal" marine concretions formed during sediment porewater-diagenetic reactions (Berner, 1980); or, 5) seep- carbonates precipitated during methane oxidation (e.g., Campbell, 1992). All of these limestone-forming processes are now known to exist in this ancient convergent margin tectonic setting, and can be distinguished from one another based on sedimentary composition, sedimentary fabric and geochemical criteria. When examined closely, both modem and ancient authigenic seep-carbonates tend to be morphologically distinctive, and their range in form can be attributed, at least in part, to variations in fluid-flow strength during precipitation. In present-day examples (Ritger et al., 1987; Han and Suess, 1989; Kulm and Suess, 1990; Haggerty, 1991), nodular, patchy carbonate masses appear to form where fluid flow is diffuse through the sediment (e.g., via coarse sand layers); whereas, carbonate slabs and mounds with some positive relief are more common where fluid flow is concentrated into areas of discrete fluid venting (e.g., above faults). Carbonate chimneys and doughnuts form in cases of even greater fluid advection. RESULTS: GEOLOGIC DESCRIPTION OF ANCIENT COLD-SEEP SITES (JURASSIC-PLIOCENE) OF WESTERN NORTH AMERICA Eight hitherto unknown ancient cold-seep deposits were discovered during the course of this study using paleontologic and sedimentologic evidence for their identification 19 gleaned from literature and museum searches, field reconnaissance, and laboratory analysis. Fourteen additional sites in the same tectono-stratigraphic region are considered seep-suspect or have been confirmed as fossil seeps by other investigators. These 22 probable fossil cold-seep deposits include the oldest yet reported example (Tithonian age) in a convergent margin tectonic setting. Collectively, these deposits also span the greatest interval of geologic time yet examined (~150 m.y., Jurassic-Pliocene) for one quasi- continuous tectono-stratigraphic regime that provides a larger framework within which to examine the evolutionary history of ancient constituent seep-type biotas. Results are presented in two parts: 1) a geologic description of the eight sites predicted from application of the paleoecologic approach; and, 2) an outline of the 14 other reported or suspect-scep sites from the same region that were deposited in tectonic settings similar to the one active offshore Oregon and Washington today. Geographic locality coordinates for the 22 sites are listed in Appendix I. At the beginning of this study, one fossil cold-seep site had been discovered in southwestern Washington within the tectono-sedimentary context described above (Site #1, Figure 1) (Campbell, 1989; 1992). An extensive search was conducted to generate additional ancient seep-suspect localities in the Pacific Northwest, beginning with Hickman's (1984) list of Cenozoic deep-water marine sequences that contain the Thyasira- Lucinoma-Solemya fossil association. Development of such a strategy for identifying Tossil seeps included recognition that modem chemosymbiotic taxa also occur in environments other than seeps. Hence, faunal checklists from the literature and invertebrate fossil collections from museums were also examined for any clues of an anomalous association with carbonates in these sandstone- and mudstone-dominated depositional settings. For example, sedimentological descriptions in Talmadge (1974) and Danner (1966) provided important clues that aided in identification of previously unknown seep-suspect limestones in northern California and western Washington, respectively. All seep-suspect localities thus identified were subsequently evaluated during field 20 reconnaissance and, if appropriate, were then subjected to detailed laboratory analysis. At the same time these field surveys were being implemented, three new fossil cold-seeps of Eocene age were independently reported upon by Goedert and Squires (1990) from isolated, deep-water limestones of southwestern Washington (see other reported localities, below). The search for ancient cold-seep paleocommunities was gradually extended back further into the past to include Mesozoic strata in north-central California (Figure 1). In these older Californian deposits, it is noteworthy that the unusually large fossil mussel, Modiola major has been reported (Figure 5), as well as lucinids and solemyids (Gabb, 1869; Stanton, 1895), all of which have closely affiliated chemosymbiotic relatives in vent- seep habitats today (Fisher, 1990). These Mesozoic bivalves were described by Stanton (1895) to be restricted to "white limestones" surrounded by shale and sandstone deposits, the latter of which are now interpreted as deep-water forearc turbidites (Great Valley Group), that were deposited adjacent to accretionary prism sediments (Franciscan Group) during Jurassic and Cretaceous times (Hamilton, 1969; Ernst, 1970; Dickinson, 1971; Dickinson and Seeley, 1979; Ingersoll and Dickinson, 1981; Ingersoll, 1983; Suchecki, 1984). According to field surveys conducted during the late 19th century, this unique faunal-carbonate association occurs in localized patches along the entire extent of Great Valley outcrops (Gabb, 1869; Stanton, 1895), not all of which have been re-located at present (see additional seep-suspect deposits, below). These northern Californian Mesozoic white limestones preserve the earliest yet discovered examples of convergence- related, cold-seep paleoenvironments known from the geologic record. Paleontologic and sedimentologic data from eight sites that were identified during the course of this investigation are summarized in Table 2. Each of these localities contains a suite of core fossil taxa and is associated with localized carbonates that are stratigraphically restricted, as well as morphologically and texturally distinctive. Cenozoic sites ranging in age from Eocene to Pliocene (~ 40-5 m.y. old) have been identified in Modiola major Qabb P t L l C Y "°°* : from Stanton, 1895 Figure 5. Modiola major Gabb, 1869 from isolated "white limestones" in Mesozoic Great Valley Group forearc strata, California. Modiolid bivalves are common chemosymbiotic constituents of modem hydrocarbon seeps, and have been reported from ancient cold-seep deposits. Length of original specimen = 20 cm. Figure from Stanton (1895). 22 Table 2. Geologic description of primary ancient cold-seep sites identified from paleoecotogic evidence. Compare age, carbonate form and dimensions, associated seep-taxa, and broad depositional settings. 23 Site Location * Quinault Tribal 1 Lands, SW Washington » Vemonia-Ttmber L Road, NW Oregon * Holcolmb, Willapa ■ * River, SW Washington a W.FoifcSauop * River, SW Washington ^ Paskerla, California Formatlan Aee Keasey "Keajey Beds" (=Linco In Creek Fonnalion) Late Eocene Late Eocene Lincoln Geek Late Eocene Stony Creek, Great Valley Group Carbonate Form and Seeu-Assoclate* Fauna Environm ent References Pimeaslgfls Quinault Mio-Plioccne localized nodules, burrow- and shell-Iill Solemya sp., Modiolus sp., Lucinoma sp. conical mounds (2-3 m high, to 4 m wide); lenses; chimney; nodules nodules, bunch-of-grapc concretions throughout Thyasira aff. T. disjuxcta, Acharaxdaili, lucinids Thyasira aff. T. disjuxcta, Acharaxdaili, lucinids limestone ridge (30 m high, Modiolus (Modiolus) 400 m long) JwiUapaensis Late Jurassic (Tithonian) two low relief mounds (1 m thick, 20 m long, 3-7 m wide) mid-shelf bathyal bathyal bathyal Modiola major, Lucixa slope to bathyal ovalis, Lucina colusaensis, Solemya ocddenlalis Campbell, 1989:1992 Campbell and BoUjcr, 1993a Beikman et at., 1967; herein Rau, 1966; Campbell and Botljer, 1993a Stanton, 1393; Campbell and Bottjer, 1993a; Campbell e ra /, 1993 Cold Fork of Cottonwood Creek, California Wilbur Springs, California Rice Valley, California Lodoga, Great Valley Group Story Creek Formation, Great Valley Group structural outlier; Great Vslley Group equivalent Early Cretaceous (Albian) lens (1-2 m thick, 260 m long, 2-3 m wide) Modiola major, limpet, lucinid, tube worm remains slope to bathyal Jones and Bailey, 1973; Ingersoll and Dickinson, 1981; Campbell and Bottjer, 1993a; et al., 1993 Hauterivian several lenses originally 1-10 Solemya occidextalis, slope; flank of Carlson, 1984; m long; since quarried Modiola major, tube worm submarine Campbell el al., remains serpentine diapir 1993 7Hauterivian several white limestone pods Solemya sp., Modiola major, 7slope to bathyal Berkland, 1973; and lenses, to 3 m diameter tube worm remains Campbell era/.. 1993; herein * fossil taxa that have modem counterparts that are either chemosymbiotic or are vent/secp-related today Washington and Oregon, whereas older sites of late Mesozoic age ranging from late Jurassic to early-mid Cretaceous (~150-110 m.y. old) have been found in northern California. A brief geologic description of each site follows, with site numbers corresponding to the specific numbered geographic locations depicted in Figure 1. Fourteen additional seep-suspect or confirmed fossil cold-seep deposits reported on by other workers for the same tectono-stratigraphic region are also briefly described in a subsequent sub-section below. Site Descriptions of Ancient Cold-Seeps Identified in this Study Site #1, the Quinault Locality, Washington. As described in detail by Campbell (1989; 1992), and summarized here for comparative purposes, a 10-meter thick stratigraphic interval of storm-shelf deposits preserves a fossil cold-seep site in the Quinault Formation (Mio-Pliocene), north of the town of Taholah in southwestern Washington (see Campbell, 1992, her Figure 1, p. 423) (Table 2). The Quinault seep is different from most other sites described herein in that the presence of carbonates is volumetrically limited: buff-colored carbonate mudstone occurs as scattered nodules, and as burrow- and shell-fill, surrounded by volumetrically extensive, thin-bedded sandstone and siltstone (see Campbell, 1992, her Figure 5, p. 426). Core fossil bivalves (Solemya, Lucinoma, Modiolus) are strati graphically restricted to the locality, which contains no geologic evidence for any other environmental factors that may have sustained such faunas (e.g., low oxygen conditions, or elevated organic content in the sediment) (Campbell, 1992). The authigenic Quinault carbonates yield stable carbon isotopic signatures depleted in their 13c/12c ratios to ~ -35%e PDB (see Campbell, 1992, her Table 1, p. 427), suggesting a methane influence during precipitation. In general, stable isotopes of carbon can be used in this and other examples to trace the carbonate carbon to its original source reservoir because the isotopic ratio is set in carbon-rich substances by known chemical and physical processes that formed the carbonate (e.g., evaporation-precipitation, biological uptake of carbon from the environment, etc.) (Anderson and Arthur, 1983). For 25 comparison, marine sedimentary organic matter yields a carbon isotopic ratio of about -23%o PDB, and the value of modem seawater is 0% o PDB (Anderson and Arthur, 1983). The only naturally occurring physicochemical process that isotopically fractionates marine carbon to very negative values during carbonate precipitation (range o f —30 to -80% o PDB for combined thermogenic and biogenic methane reservoirs) is the process of methane oxidization, which spontaneously occurs, for example, when methane-rich seep-fluids come into contact with seawater (e.g., Hudson, 1977; Schoell, 1980; Anderson and Arthur, 1983; Hoefs, 1987). Site #2, the Vernonia-Timber Locality, Oregon. A 20-m high road cut on the Vernonia-Timber Road in northwestern Oregon, exposes a fossil cold-seep site in the Keasey Formation of Late Eocene age (~36-40 m.y. old) (Campbell and Bottjer, 1990; 1993a; Niem etal., 1992; Nesbitt etal., 1994) (Figures 1, 6, 7, Table 2). The Vernonia- Timber locality (Figure 6) is characterized by several pyramidal to irregularly shaped mounds of gray limestone; immediately adjacent to the mounds are carbonate nodules, lens shaped pods and a small chimney structure (Figure 7). The carbonates are well-exposed in cross-section along the road cut (e.g., Figure 8). They are surrounded by glauconitic, thin- bedded siltstone, sandy siltstone, and massive mudstone typical of the lower member of the Keasey Formation (van Atta, 1971; Hickman, 1976). Overall, the Keasey Formation comprises up to 700 m of buff to gray-colored tuffaceous marine siltstone and mudstone discontinuously exposed in quarries, road and railroad cuts, and along major drainages in the upper Nehalem River basin in Oregon (Hickman, 1976). The deep-water aspect of the Formation has been established based on the taxonomic structure of fossil assemblages compared with Recent molluscan communities (Hickman, 1974; 1984). In particular, Hickman (1976) noted that "[t]he percent species composition of turrids [gastropods] in the Keasey Formation (55%) clearly identifies it with modem bathyal composition" (p. 25). The Late Eocene age of the Keasey is based on megafauna characteristic of the Bathybembix colutnbiana Zone, lower Galvian Stage; whereas, benthic foraminifera are 26 Holcomb '(Site #3) Centralia' WASHINGTON Naselle Astoria Longview OREGON Vemonia - Timber v (Site #2) i Timber, Portland 20Km Figure 6. Geographic locality map for Vernonia-Timber site (#2), along Nehalem River, northwestern Oregon and for Holcomb site (#3), along Willapa River, southwestern Washington. Modified from Nesbitt et al. (1994). 27 mound 3 gliu co n jtic i j » r »imd«tonc ~ W mound 1 luclold-rlch m lcrltlc llm cilone ch lm n c - C f - carbouatt uodulti [glauconitic illtito n e N ---------- 10 m Figure 7. Outcrop sketch (to scale) of Vernonia-Timber carbonate morphotypes and their stratigraphic positions with respect to surrounding fine-grained siltstone strata of the Keasey Formation (late Eocene). Mound 1 schematic of this figure is shown in photograph of Figure 8. to 00 Figure 8. Field photograph of one seep-carbonate mound (above person's head) at Vernonia-Timber site (#2), northwestern Oregon. assigned to the Refugian Stage, and planktonic foraminifera to worldwide zones P15-P17 (Durham, 1944; Armentrout, 1981; Nesbitt etal., 1994). Typical mega-invertebrate taxa collected from lower-member Keasey siliciclastics at the Vernonia-Timber locality include scaphopods (dentalid), gastropods (Bathybembix columbiana, Exilia lincolnensis, Cancellaria sp., Cotius sp.), and bivalves (Acila nehaleinensis, Yoldia chehalisemis, Crenella porterensis, Neocardium weaveri, Nuculana sp., Macoina sp., Delectopecten sp.) (Hickman, written communication, 1990; personal observations). The 140 m long Vernonia-Timber outcrop grades laterally from highly resistant gray-green glauconitic sandy siltstone beds at the north end to eroding reddish-brown siltstone deposits at the south end, the latter of which enclose three gray carbonate mounds and numerous associated carbonate lenses and nodules (Figure 7). The abundant presence of glauconite mineral grains within the siltstone and carbonates indicates a marine sedimentary setting with generally low sedimentation rates. Pumice layers in isolated pods suggest pulses of arc-related volcanism during marine sedimentation. The carbonate mounds grew 2-3 m high and measure up to 4 m wide at base (Figures 7 ,8). Mound Hanks tend to be brccciated, which indicates instability of relatively steepened flanks during mound growth. Evidence for sulfur, a necessary component of chemosynthesis, is present in two forms: 1) faint halos of fine-grained yellow material with a strong sulfurous odor surround the carbonates in the sandy siltstone immediately adjacent to the mounds; and 2) framboidal pyrite (c.f. Berner, 1970; 1983) is finely disseminated in the carbonate cement. The carbonate mounds consist of micrite rich in glauconite and detrital grains, and contain numerous specimens of the large fossil bivalve Thyasira sp. cf. T. disjuncla (Durham, 1944; C. Hickman, personal communication, 1990) (Figure 9). Although a few of these thyasirid clams are found in the surrounding siltstone deposits, they are mostly restricted to the carbonates along with rare Solemya willapaensis and lucinid bivalves. All three of these fossil molluscs are considered core taxa, and are part of Hickman's (1984) recurring molluscan association in Cenozoic deep-water units throughout the Pacific Northwest. The 30 Figure 9. Carbonate slab from mound in Figure 8 , illustrating micrite lithology with glauconite grains (black flecks), and two large specimens of the bivalve Thyasira. 31 Vernonia-Timber carbonates also preserve evidence of anomuran crab activity, in the form of distinctive fecal pellets (Favreina) with distinctive tubules that are common in mound carbonates (Figure 10). Such decapod crustaceans are typical hydrothermal vent-associates today (e.g., Tunnicliffe, 1992). The distribution and morphologies of Vernonia-Timber carbonates suggest variations in fluid seepage "strength" during deposition (cf. Kulm and Suess, 1990). For example, in a composite vertical transect through a typical mound (e.g., Figures 7 ,8), the presence of carbonate nodules, globular bunch-of-grape-like masses, and small lenses below the base of the deposit indicate that early seepage was relatively diffuse. These carbonate forms arc replaced stratigraphically by features suggestive of more concentrated fluid flow, such as larger limestone slabs, pipes (to 50 cm long, 15 cm wide; similar to Haggerty, 1991, her Figure 3, p. 298), a chimney structure, and finally a massive mound (cf. Han and Suess, 1989; Kulm and Suess, 1990). Petrographically, the 18 cm high carbonate chimney (Figure 11) can be divided into two sedimentologically distinct regions. The bulk of the chimney volume is comprised of an outer, massive micrite which contains rounded, sand-sized grains of glauconite, framboidal pyrite, and detrital material (angular quartz, feldspar, and wood debris derived from terrigenous surroundings). The smaller, central chimney portion is comprised of concentric layers (to 4 cm diameter) of detritrus- free, fibrous calcite cement that presumably surrounded a fossil fluid-conduit (Figure 12). Ritger etal. (1987) reported similar features in chimney structures from the modem Oregon seeps— especially detritus-free, authigenic, radial fibrous aragonite in chimney centers— which they suggest may have formed above the sediment-water interface (Ritger etal. , 1987, their Figure 5C, p. 150). Hence the outcrop-scale, vertical stratigraphic sequence of carbonate morphotypes and the inner fabric of the fossil chimney structure imply changes in fiuid-flow rates— from diffusive, toadvective, to cessation of growth altogether— during the development and evolution of seep-carbonates at the Vernonia-Timber site. 32 Figure 10. Distinctive fecal pellets (Favreina) from anomuran decapod- crustaceans (longitudinal and cross-sectional views) from late Eocene Vernonia- Timber site; modem crabs that form such pellets are common at hydrothermal vents today. Pellets ^ 2 mm in diameter; to 0.5 cm long. 33 Figure 11. Eocene carbonate chimney (18 cm high) collected adjacent to carbonate m oundof Figure 8 at Vemonia-Timber locality. Note conduit openings on top and left side of chimney (chimney in stratigraphic "up" position). 34 Figure 12. Entire thin-section view (3.5 cm across) of cross-section through carbonate chimney of Figure 11, depicting concentric layers of cement around central fluid-flow conduit, Vemonia-Timber site. 35 Site #3, the Holcomb Locality, Washington. Lithologically similar and time-equivalent to the lower member of the Keasey Formation in NW Oregon (e.g., Site #2, above) are the well-known Willapa River "Keasey" Beds exposed near Holcomb, southwestern Washington (Durham, 1944; Hickman, 1976), which preserve anomalous carbonates in the fine-grained siliciclastics (Figures 1, 6, 13, Table 2). The Willapa River section is actually part of the Late Eocene portion of the Lincoln Creek Formation of southwestern Washington, and is well-exposed along the river (1500 m total thickness) between Holcomb and Menlo (Figure 6) (Beikman etaL, 1967; Armentrout, 1973). Although the heavily forested terrain of the Pacific Northwest impedes direct lithostraligraphic correlation between outcrops at Holcomb (site #3) and Vemonia-Timber (site #2) (Figure 6), Armentrout (1973) and Hickman (1976) reported the same deep-water molluscan fauna in both areas, which are at least partially equivalent to the Turicula (=Bathybembix) columbiatia megafaunal zone of Durham (1944). Microfossil comparisons between forearc siliciclastic strata of the two regions also revealed similar foraminiferal assemblages that are typical of bathyal depths (Rau, 1951; Hickman, 1976). Beikman el al. (1967) described the lowermost part of the Lincoln Creek Formation exposed in the area (417 m thickness), within which anomalous carbonates occur: The basal part of the formation is basaltic, glauconitic granule sandstone as much as 50 feet thick and is overlain by predominantly tuffaceous siltstone about 1,200 feet thick in which bedding is generally well developed. Calcareous concretions, many of which contain megafossils, occur sporadically in beds and zones throughout this siltstone. (Beikman etaL, 1967, p. 18) The Holcolmb outcrop, which contains a portion of these lower Lincoln Creek siltstone deposits along the Willapa River section, consists of a somewhat poorly exposed (vegetated, eroded), -1 0 m high bluff (-30 m wide) along a bend in the Willapa River. Most of the bluff comprises poorly bedded, sandy siltstone with granules of glauconite and weathered basalt clasts. Abundant micritic carbonate nodules and bunch-of-grape carbonate masses (to 25 cm diameter) dominate the siltstone in places (Figure 13). Megafossils collected at the locality include Thyasira sp. aff. T. disjuncta, Solemya and Figure 13. Field photograph illustrating occurrence of white carbonate nodules (3-15 cm diameter) at Holcomb locality, which are embedded in glauconitic siltstone of "Keasey Beds" (=Lincoln Creek Formation). Pocket knife for scale. 37 Bathybembixr; Armentrout (1973) also reported Macoma, Neocardium, Conns, Cyclostremella, Epitoniinn and Margarites from this site. Site #4, the West Fork Satsop Locality, Washington. The West Fork of the Satsop River cuts across an anomalous carbonate deposit in Grays Harbor county, Washington, at the base of the Olympic Mountains (Campbell and Bottjer, 1993a) (Figures 1, 14, Table 2). The limestone deposit occurs in massive siltstone and tuffaceous sandstone of the Lincoln Creek Formation (Late Eocene through Oligocene age), which attains a thickness of over 4,000 m in the West Fork of the Satsop River region of southwestern Washington (Rau, 1966). When Rau (1966) mapped the lithostratigraphy and foraminiferal biostratigraphy of the area, he described nine informal members of the Lincoln Creek Formation, of which Member Tl-7 contains a large, unusual carbonate outcrop: Member Tl-7 is primarily a massive siltstone unit that ranges from 900 to 1,400 feet in thickness. The central part contains a considerable amount of tuffaceous sandstone, most of which is thin-bedded.... A limestone bed some 100 feet thick occurs within the central part of this member. It forms a strike ridge on the east side of the West Fork of the Satsop River immediately south of the mouth of the Little River. It appears to have been formed as the result of solution and redeposition of calcium carbonate in the form of aragonite. This bed can be traced along the strike for about a quarter of a mile south of the Little River, but it was not found in any other part of the area. (Rau, 1966, p. 15) On strike with the unusual limestone ridge, one hundred meters southwest across the river, Rau (1966) collected fossil foraminifera in Lincoln Creek siltstone including the genera Dentalina, Globigerina, Karreriella, Usterella, Nodosaria, Robulus and Uvigerina of the Zemorrian Stage. At the locality, the West Fork of the Satsop River flows around the ridge of limestone (Figure 14, labeled "LR"), that has at its top three probable carbonate mounds (conical, to 4 m high; Figure 14, black arrowheads; personal observation) which are covered by dense vegetation. In addition to the main limestone ridge (LR), a smaller, separate white limestone block is exposed just to the north of the ridge at river level, 160 m upstream of the confluence with Little River (labeled "LB" in Figure 14; LB exposed over a 38 V7 sN . M p and Lincoln C m k gaobgy basad on Ffcu. 1 966; Imaitona gaobgy bf O tx**I and Botljar. para, obaarvalbns. 1091 WEST FORK SATSOP RVER LOCALITY EXPLANATION < D a ® S» U > o o O ) LR Limestone ridge LB Limestone block, ?allochthonous Tl Lincoln Creek Formation mostly massive to thin-bedded siltstone _________ geologiocontactdotted where approximate ------------- topographiccontour N river x strike/dip symbol (map dips: 15‘ -52‘ SE) countour interval = 40 ft scale 1.6 km Figure 14. Geographic and geologic locality map for West Fork of the Satsop River site (#4), southwestern Washington. Seep-carbonates (shaded) occur both as a limestone ridge (LR) with three conical mounds at its top (black arrowheads), and as a smaller allochthonous block (LB), exposed at river level. The limestones are surrounded by deep-water siltstone and sandstone deposits of the Oligocene Lincoln Creek Formation (Tl) of the southern Olympics area, southwestern Washington. Figure modified after Rau (1966). O J V O ~5 m x 5 m surface area, Figure 15). Overall, the site is spectacular in the sheer volume of carbonate produced over the effective lifetime of the seep. The carbonates present are composed of lime mudstone and fibrous cements; internal fabrics are massive to highly irregularly laminated. The limestone block outcrop (LB) is similar in lithology to the main ridge (LR), but also displays a complex array of brecciated fabrics. The limestone block appears to be allochthonous and may have originally formed on an unstable flank of a larger carbonate deposit where downslope transport of carbonate debris was common. Dense vegetation and poor exposures at river level today obscure potential evidence that might distinguish whether the block (LB) is a Recent block-fall off the main ridge (LR) or if it was stratigraphically emplaced as an allochthonous block while Lincoln Creek silts accumulated during Late Eocene time. Presently, a low bank of Lincoln Creek siltstone (LCS) that lies on strike with the limestone ridge (LR), dips away from the allochthonous block (LB) and toward the ridge (LR) at the mouth of Little River (Figures 14, 15). Fossils are not abundant at the West Fork Satsop locality, although the mussel Modiolus is found with some frequency in the smaller limestone block. Reasons for such a minor biotic component present at the site are unclear but may be related to high fluid-flow and carbonate precipitation rates. A limestone doughnut also was discovered at the site (Figure 16), which is a relatively common feature known from modem seeps offshore of Oregon and from Papua New Guinea that represent carbonate precipitation around a fluid- flow conduit (compare to Niem, 1989, his Figure 10, p. 191, and to Kulm and Suess, 1990, their Figures 6, 7, p. 8905-8906). Site #5, the Paskenta Locality, California. In rolling hills 35 km west of Corning and five kilometers northwest of the town of Paskenta, northern California, is a thick succession of fine-grained turbidites, wherein lies "a mass of limestone about 10 feet thick and not much more than 100 feet long" (p. 17, Stanton, 1895) that strikes parallel to regional bedding and is situated adjacent to a large, regional fault zone (Figures 1, 17, 18, Table 2). Stanton (1895) described numerous megafossils from the site, including several 40 Figure 15. Field photograph of person standing on small allochthonous limestone block (LB of Figure 14) situated along the bank of the West Fork of Satsop River, southern Olympic Mountains. Allochthonous block is located just above the confluence of the Little River, upstream of the large limestone ridge (LR of Figure 14). River bank strata in background comprised of Lincoln Creek siltstone. 41 Figure 16. Oligocene limestone doughnut-shaped structure from West Fork of Satsop River locality; such fluid-conduit features are common at modem methane-seep sites offshore Oregon today (e.g., Kulm and Suess, 1990). Pocket knife for scale. 42 LOWERMOST GREAT VALLEY GROUP m ap area California LEGEND Qt Tertiary cover GREAT VALLEY GROUP IK Lower Cretaceous strata uJ Upper Jurassic strata *■ Paskenta fossil seep locality ____________ fault * i ■ < — *— thrust fault --------------------- contact ____________creek • town of Paskenta @ county road 5 km i ______ i Figure 17. Geologic, structural, and stratigraphic locality map for Paskenta site (#5) (star), adjacent to synsedimentary Paskenta Fault zone, northern California. Mesozoic arc-trench system preserved in series of north-south trending outcrop belts: Sierra Nevada Batholith = remnant volcanic arc; CRO, Coast Range Ophiolite = serpentine thrust sliver of oceanic crust; Franciscan Group = melange and broken formation of accretionary prism; Great Valley Group = forearc basin turbidites. Ages of Great Valley strata based on ammonites and Buchia bivalve zonations. Figure modified after Jones et al. (1969), and Moxon (1990). 43 Figure 18. Field photograph of two low relief carbonate mounds (light-colored: left foreground; right background) at Paskenta site, surrounded by slope turbidites (dark-colored) of Great Valley Group (Stony Creek Formation, Tithonian). 44 that are stratigraphically restricted to the two low relief, light gray carbonate mounds present (Figure 18) (also see Campbell and Bottjer, 1991; 1993a; Campbell etal., 1993; Sandy and Campbell, 1994). Fossil core taxa include Solemya occidentalis, Lucina ovalis, and Lucina colusaensis. The ubiquitous presence of the bivalves Buchia piochii and B. Jischeriana, in both the limestone and surrounding shale, indicate a Late Jurassic (Tithonian) age for the locality, and places the site lithostratigraphically within the Stony Creek Formation of the Great Valley Group (Jones etal., 1969; Ingersoll, 1978; 1983). The geographic position of the Paskenta white limestones (star) is illustrated in Figure 17 with respect to generalized Upper Jurassic and Lower Cretaceous megafaunal zones based on occurrences of the bivalve Buchia (Jones etal., 1969). Also shown (Figure 17) is the syndepositional Paskenta Fault zone (Suchecki, 1984; Moxon, 1990), along which fluids presumably migrated (Campbell etal., 1993). Other invertebrate fossils reported from the white limestone (Stanton, 1895) include the gastropod genera Turbo (?), Arnberleya, Hypsipleura and Cerithiunr, the bivalve genera Nucula, Cardinopsis, and Corbula', the cephalopod genera Phyloceras and Belemnites-, and the brachiopod "Rhynchonella" {-Cooperrkynchia; Sandy and Campbell, 1994). The carbonates at the Paskenta locality were originally thought by Anderson (1945) to have formed in shallow-water, derived from dissolution of the shells of the brachiopod Cooperrhynchia common at the site. Subsequent tectonic, stratigraphic, and sedimentologic studies of the Great Valley Group overall have established its forearc basin setting and deep-water, turbidite-dominated character (e.g., Hamilton, 1969; Dickinson, 1971; Ingersoll and Dickinson, 1981; Ingersoll, 1983). In particular, the fine-grained turbidites that surround the Paskenta carbonates were likely deposited at slope depths, along with most of the Upper Jurassic strata exposed along the western Sacramento Valley (Ingersoll, 1978; Suchecki, 1984). Detailed observations from the limestone mounds at Paskenta indicate that precipitation was in situ within an offshore, deep-water marine setting, based on the presence of articulated, non-abraded megafossils, the presence of deep-water microfossils, and lack of sedimentary fabrics within the carbonate indicative of slumping or transport. Furthermore, petrographic and stable isotopic analysis of shell material and carbonate fabrics at Paskenta indicate that these carbonates have not undergone significant recrystallization or alteration (see Chapter 2); hence, the mounds could not have been derived from brachiopod shell dissolution. Several outcrop-scale, sedimentological and paleoecological features of Paskenta mound carbonates are typical of those reported for other cold-seep sites, both modem and ancient. These features include carbonate nodules and lucinid bivalves found clustered around mound peripheries in the adjacent siliciclastics (c.f. Rolin etal., 1991). Moreover, isopachous fibrous cements occur in complex, cylindrical bodies, with concentric fibrous layers in cross-section (to 4 cm diameter, 12 cm long) (Figure 19). Similar small carbonate fluid-flow conduit features form on the seafloor today in association with dewatering of the modem Marianas forearc (e.g., Haggerty, 1987; compare Figure 19 herein with her Figures 5, 6, p. 179-180). Site #6, the Cold' Fork of Cottonwood Creek Locality, California. Twenty kilometers west of Red Bluff, California, a large gray limestone lens (260 m long, 2-3 m wide, and 1-2 m apparent thickness) is exposed along a low ridge above the Cold Fork of Cottonwood Creek, surrounded by deep-water turbidites of the Lodoga Formation, Great Valley Group (Ingersoll, 1983) (Figures 1, 20,21, Table 2). Bailey and Jones (1973) mapped this carbonate lens close to the juncture of the regional Sulphur Spring and Cold Fork faults (Figure 20), and they assigned an early Cretaceous (Albian) age to the locality based upon the occurrence of the ammonite Leconteites cf. L. deattsi (Jones and Bailey, 1973). Stanton (1895) reported the core bivalves Modiolainajor (e.g., Figure 5) and a lucinid from the limestone, as well as limpets and Turbo (?) gastropods. Giant, poorly preserved Modiola major specimens (internal molds, to ~22 cm length) also are housed in U.S. Geological Survey (Menlo Park) invertebrate fossil collections; they were collected from the Cold Fork of Cottonwood Creek limestone by Survey geologists in the 46 Figure 19. Concentric, double fluid-conduit feature lined with isopachous, fibrous cement. Paskenta locality, California. Coin for scale. Cold Fork Cottonwood Creek H-B Pettyjohn . / JCenoM Weemasoul Fbad [Ftett yjohn W A W # . W oodyard/ Creek evenson ftttyjohn '♦<Ceno W A l b X V „ h -b Cold Fork Cottonwood Figure 20. Geographic, structural, and biostratigraphic locality map for Cold Fork of Cottonwood Creek site (#6) (star), near juncture of large, regional Cold Fork and Sulfur Springs Faults, northern California. Carbonate lens (star) is 260 m long and strikes parallel to regional bedding (turbidites). Biostratigraphic boundaries based on ammonites and molluscs. Val = Valanginian, H-B = Hauterivian-Barremian, Apt = Aptian, Alb = Albian, Ceno = Cenomanian. Modified after Bailey and Jones (1973). Figure 21. Field photograph of 260 m long limestone lens (blocky boulders in trees) at Cold Fork of Cottonwood Creek locality, surrounded by turbidites (grassy hill-slope) of Great Valley Group (Lodoga Formation, Albian). 49 late 19th century (e.g., USGS locality 1070; Appendix I). In addition, in places the limestone fabric is crowded with areally extensive masses of thin tubes (Figure 22), which are elliptical to circular in cross-section (to 0.5 cm diameter, to 20 cm long) and are cement- lined, sediment-filled, or pyrite-coated. The tubes are interpreted as biogenic remains because they maintain relatively constant diameters (with slight taper at bottom ends) and they aggregate in spotty clumps (Figure 22). Moreover, in rare cases smaller individuals display very thin, organic tube-wall linings that are preserved by irregular yellow calcite cement coatings (Figure 23). These biogenic fabrics probably represent the preserved remains of fossil tube worms, possibly Pogonophorans, which are chemosymbiotic taxa commonly present in both modem and ancient cold-seep and hydrothermal vent environments (e.g., Banks, 1985; Haymon and Koski, 1983; Lonsdale, 1977; Sucss etal., 1985; Dub<5, 1988; von Bitter etal., 1990). The carbonates at the Cold Fork of Cottonwood Creek site display fabrics similar to those found at Paskenta. Most of the lens is comprised of carbonate mudstone and marine cements with wavy laminated fabrics, which are morphologically similar in places to modern microbially induced structures (e.g., Kempe etal., 1991). Fossils are volumetrically less significant than at Paskenta, except for the tube-like structures. These biogenic remains are patchy in their distribution, as in modem examples (e.g., MacDonald etal., 1989), but when present they dominate the fabric. Site #7, The Wilbur Springs Locality, California. Forty-two km west of Williams and one kilometer south-southeast of Wilbur Springs, northern California, several scattered limestone blocks (1-10 m long, up to 5 m wide) are exposed in close association with foliate serpentine breccias (Carlson, 1981) (Figures 1, 24, 25, Table 2). These sedimentary serpentinites are interbedded with deep-water turbidites of the Stony Creek Formation, Great Valley Group (Ingersoll, 1983; Campbell etal., 1993) (Figure 24). The Early Cretaceous (Hauterivian) age assignment for the site is based upon the stratigraphic position of the limestone blocks just above the highest occurrence of the bivalve Buchia 50 Figure 22. Mass of tube worm remains, longitudinal and cross-sectional views. Cold Fork of Cottonwood Creek site. Edge of pocket knife for scale. 51 Figure 23. Thin section photomicrograph displaying rare preservation of thin, dark brown, organic tube-vvall lining. Cold Fork of Cottonwood Creek locality, California. Tube wall coated extemalK u uh thin isopachous layer of yellow calcitc cement (arrows); tube interior filled with cloudy, fibrous calcite cement. Diameter of lube = 0.5 mm. 52 122°22'30" I 122 25 h 39°02'30" 2 Km - 39°00' undifferentiated Great Valley Group foliate serpentinite breccia limestone serpentinite melange belt (Coast Range Ophiolite) Peregrinella locality ---------- fault geologic contact ■0------- > anticlinal fold axis, J ------->■ synclinal fold axis, with plunge plunge road Figure 24. Geologic, structural, and geographic locality map for Wilbur Springs site (#7), northern California. Peregrinella-bearing limestone block surrounded by sedimentary serpentinite and turbidite slices. Sedimentary serpentinite represents product of subjacent oceanic plate dewatering and diapiric rise of fluid- rich material (brecciated) to seafloor. Black dots indicate locations where Peregrinella fossils found, brachiopods extremely abundant in limestone; scattered, low abundance in sedimentary serpentinite, where diapiric material flowed into basin via turbidity currents. Modified after Carlson (1984). Figure 25. Field photograph of quarried white limestone at Wilbur Springs locality. Scattered blocks in foreground; small pit in middleground. 54 pacifica (a Valanginian form) in the area (Lawton, 1956; Biemat, 1957; Imlay, 1959; Jones et al., 1969). Prior to quarrying, Stanton (1895) described the Wilbur Springs locality as a fossiliferous bed of white limestone, and noted the great abundance of the rhynchonellid brachiopod Peregrinella whitneyi, as well as various molluscan groups represented. In particular, Modiola major, Solemya occidenlalis and Lucina colusaensis are three core bivalves present; other associated mega-invertebrate taxa include several species of the gastropod Turbo and pectinid bivalves (Stanton, 1895). The carbonates exposed near Wilbur Springs (Figure 25) were originally described as transported, patch-reef limestone coquinas of shallow-watcr origin (Lawton, 1956). Later structural and stratigraphic studies of the surrounding serpentinite deposits revealed that the foliate serpentine breccias originated as deep-water, protrusive submarine flows derived from a nearby mass of serpentinite— a mass tectonically emplaced by diapiric processes and actively mobile during Hauterivian time (Carlson, 1981, 1984). The "reefoid" Peregrinella-carbonate occurrences originated on a serpentinite substratum, as evidenced by abundant ultramafic detritus found within the limestones. Carlson (1981) proposed emplacement of the source protrusion as a seamount on the developing trench- slope break in the outer forearc to explain limestone origins at "shoaling" water depths affiliated with the seamount, within an overall deep-water setting. At Wilbur Springs, the subsequent discovery of vent-type mega-invertebrate fossils (Campbell and Bottjer, 1991), in association with poorly preserved radiolaria from various textural microfacies of the carbonates, now allows for a stratigraphically more consistent interpretation of the Peregrinella-bearing limestones as deep marine in origin, which represent vent-type paleocommunities related to fluids escaping from the extruded, submarine serpentinite flows (Campbell et al., 1993). Owing to truncation of the western margin of the Great Valley Group, the serpentine diapir source (derived from the Coast Range Ophiolite) is not preserved; only tongues of sedimentary serpentinite flows are present in the Wilbur Springs region (Figure 55 24) to mark this pulse of Hauterivian, subduction-driven tectonic activity (Carlson, 1984). Interfingered with the serpentinites are turbidite deposits which represent the ambient surrounding deep-sea environment into which the submarine protrusions advanced (Carlson, 1984). The carbonate mounds likely formed atop or on the flanks of the source protrusion, as fluids were brought to the seafloor by diapiric activity. Subsequently, the carbonate mounds were rafted away from the source protrusion by mobile, foliate serpentine breccia flows that advanced eastward to interfinger with terrigenous turbidites of the axial floor of the forearc basin (see Campbell etal., 1993, their Figure 7, p. 44). A modern marine analog to the Wilbur Springs protrusive submarine serpentinites is the occurrence of serpentine seamount diapirs in the outer forearc of the Marianas (Fryer and Hussong, 1983; Fryer and Fryer, 1987; Fryer, 1992). Haggerty (1987; 1991) reported authigenic carbonates associated with the modem Marianas sedimentary serpentine deposits. As in the Paskenta and Cottonwood Creek occurrences, the limestone blocks at Wilbur Springs preserve two broad carbonate fabric types: a fossiliferous, peloidal micrite, and wavy-laminated, irregular yellow and isopachous fibrous cements. Laminated layers of dark gray, micritic, thin, irregular tubules and tiny, dark micrite clots are evident in thin section (see Chapter 2); these layered fabrics may represent the preserved remains of mat like, sulfur bacterial structures in the sediment (e.g., see Kempe et al., 1991). Site #8, the Rice Valley Locality, California. Exposed 8.5 km southeast of Lake Pillsbury in the central part of the northern Coast Ranges, California, is an outlier (or remnant) of Great Valley equivalent and Tertiary marine strata (Lower Cretaceous through Paleocene age; -1550 m thick), that crops out within the Eastern Belt of the Franciscan Group (Berkland, 1973) (Figures 1, 26, Table 2). One of four known structural outliers of similar strata in the area, the Rice Valley Outlier (2 km^) is synclinally folded and has a Lower Cretaceous (Hauterivian) basal portion which consists of sandstone, shale and rare, fossiliferous white limestone deposits, all of which are in fault 56 contact with serpentinite slivers and chaotic terrane (melange) (Berkland, 1973) (Figure 26). The tectono-stratigraphic context of the Rice Valley Outlier is interpreted as forearc sediments structurally emplaced onto oceanic crust and trench materials (=Franciscan Group), the latter of which were tectonically mixed in a friction carpet during subduction beneath the Great Valley forearc (Berkland, 1973; S. Phipps, personal communication, 1992). In detail, Hauterivian-age strata in Rice Valley comprise mainly arkosic sandstone and greenish-gray to dark gray siltstone turbidites which contain variably sized lenses of fossil-rich light gray limestone (to 5 m diameter) (Berkland, 1973). Berkland (1973) observed: The most striking fossiliferous rocks at Rice Valley are coquinoid pale-gray limestone lenses from shales within 100 feet of the ultramafic belt [serpentinites] along the west side of Rice Valley. The limestones produce a strongly foetid odor when struck with a hammer and have yielded the following Hauterivian Stage megafossils: Peregrinella whitneyi, Turbo wilburensis, Belemnites sp., and a modiolid pelecypod. (Berkland, 1973, p. 2395) More recent field reconnaissance during this study also has yielded Solemya and fossil tube worm remains in these Rice Valley carbonates. Berkland's (1973) geologic map of the Rice Valley area (northwest part of Potato Hill 7^2 minute quadrangle) depicts two limestone outcrops in lower Cretaceous shale, at the depositional contact with upper Cretaceous sandstone; both units are down-faulted along their outer margins against ultramafic rocks (Berkland, 1973, his Figure 2, p. 2394). USGS field geologists also recorded two additional outcrops of fossiliferous limestone (localities M 6395and M6396, Appendix I) about 700 m southeast of Berkland's (1973) finds, along the western wall of Rice Valley. Some of these reported limestones were located during the course of this investigation, but they are poorly exposed and several are encased in dense underbrush, and they are as yet only poorly studied. 57 RCE VALLE/ OUTLER LOCALITY— EXPLANATION Pillsbury ^ Rbe Kgr- V a lle y ' • Outlier Rotter V alley^ 10 km m □ N geologic contact fault; te e th = thrust stream Rice Valley and Middle Mountain Outliers, Q e a t Valley Q oup equivalents (Kgv); and, Great Valley Q oup sensustri c to (J/ K) (shale and thin-bedded sandstone turbid it es; in Rice Valley, rare limestone lenses to 5 m diam. with Peregrinella whitneyi) [= fore arc basin] Eastern Belt metamorphosed Franciscan Q'oup rocks (J / K) (foliatedand/or blueschist facies, m etam orphosedgrayw acke, siltstone, greenstone) [= accretionary prism] Central Belt melange of Franciscan Qoup rocks (J/ K ) (highly deformed chaotic mix of blueschist facies in sheared shale matrix ) [= accretionary prism] ultramafic rocks (J/ K) (serpentinized harzburgite and dunite); CFD = Coast Flange Cphiolit e [=t hrust slic es of oceanic crust] Geolog c m ap and I ithologies based onB erkland (1 9 7 3 ) Figure 26. Geologic, structural, and geographic locality map for Rice Valley Outlier site (#8), northern California. Rice Valley and Middle Mountain outliers (Kgv) are Cretaceous-early Paleocene age thrust slivers, equivalent to portions of the Great Valley Group sensu stricto. The Great Valley-type outliers are enclosed within Eastern and Central Belt rocks (blue schists, melanges) of the Franciscan Group, and both outliers contain isolated outcrops of anomalous white limestones. Great Valley forearc sedimentation and Franciscan accretionary prism accumulation were roughly coeval (late Jurassic- late Cretaceous). Within Early Cretaceous age turbidites of the Rice Valley Outlier, fossil-rich limestone lenses contain o o the brachiopod Peregrinella and core seep-type taxa. Modified after Berkland (1973). Other Reported or Suspect-Seep Localities from the Northeast Pacific Convergent Margin Site #9, the Humptulips Locality, Washington. As described by Goedert and Squires (1990), a carbonate mound (15 m thick, 30 m long, 15 m wide) represents a fossil cold-seep site within deep-water siltstone deposits of the Humptulips Formation of late Middle to Late Eocene age (35-40 m.y. old), exposed along the East Fork of the Humptulips River in southwestern Washington (Figure I). Abundant core fossil invertebrates include the bivalves Acharax cf. A. dalli, Modiolus (Modiolus) willapaensis, Calyptogena chinookensis, and 77tyasira (Conchete) folgeri, and ?vestimentiferan worm tubes (Goedert and Squires, 1990; Squires and Goedert, 1991). Associate fossil taxa from the limestone include gastropods (Homalopomal, fissurellid?, patelliform limpet, and naticid), a scaphopod (Dentalium), a pitarid bivalve and decapod fragments (Goedert and Squires, 1990; Squires and Goedert, 1991). Site #10, the Bear River Locality, Washington. An abandoned limestone quarry on the Bear River preserves a fossil cold-seep site in the informally named siltstone of Cliff Point of Late Eocene age (~40 m.y. old), exposed near the town of Chinook in southwestern Washington (Goedert and Squires, 1990) (Figure 1). A limestone mound that was once 15 m thick, 68 m in length and 38 m wide (Danner, 1966) is composed of a fine-grained carbonate mudstone with a vuggy fabric which is filled with fibrous marine cement and siltstone. The Bear River deposit is extremely fossiliferous and unusual in that the carbonates contain a diverse and abundant megafauna including core taxa such as Modiolus (Modiolus) willapaensis, Calyptogena chinookensis, Acharax cf. A. dalli, and ?vestimentiferan tube worms, and other affiliated fossil taxa such as the siliceous sponge Aphrocallistes polytretos, a pitarid bivalve, and gastropods (Margarites (Pupillaria) columbiana, ?patelliform limpet, naticid, ?buccinid) (Goedert and Squires, 1990; Squires and Goedert, 1991). Site #11, the Menlo Locality, Washington. An abandoned bend in the Willapa River exposes a fossil seep-carbonate in siltstone of the Lincoln Creek Formation 59 of Late Eocene age (~40 m.y. old), exposed near the town of Menlo in southwestern Washington (Goedert and Squires, 1990) (Figure 1). Several low relief, white limestone mounds 1-3 meters in diameter (Campbell and Bottjer, 1993a, their Figure 9, p. 337) contain relatively abundant core specimens of Modiolus (Modiolus) willapaensis, Calyptogena chinookensis, and Thyasira (Conchele) folgeri (Goedert and Squires, 1990; Squires and Goedert, 1991). Site #12, the Shipwreck Point Locality, Washington. A small, allochthonous, fossiliferous limestone block (2.5 m long, 2.5 m wide, 0.75 m high) is enclosed in deep-water sandstone and siltstone deposits of the Early Oligocene portion of the Makah Formation at Shipwreck Point, Straits of Juan de Fuca on the Olympic Peninsula (Goedert and Campbell, 1995) (Figure 1). The overall depositional setting of the Makah Formation is that of a deep-water, terrigenous submarine-fan setting (Snavely et a!., 1980). The limestone block at Shipwreck Point, which contains seep-related taxa, is positioned stratigraphically within basin-plain and fan-fringe deposits of the Makah Formation, but the block originally formed further up-slope and subsequently slid or slumped into deeper parts of the Makah basin to its final place of deposition (Goedert and Campbell, 1995). The limestone block contains an abundant and diverse assemblage of core and associate fossil taxa. Mega-invertebrate taxa with extant chemosymbiotic relatives include Modiolus (Modiolus) willapaensis, Calyptogena (Calyptogena) chinookensis, Lucinoma hannibali, Acharax sp., IVesicomya sp., IThyasira sp., and ?vestimentiferan worm tubes; additional taxa affiliated with the limestone block include bivalves (Nuculana, Macoma), gastropods (Provanna, "Admete," Margarites, Aforia, ISolariella, and hyalogyrinid, naticid, marginellid, scaphandrid, turrid, buccinid representatives), and polyplacophorans (Leptochiton) (Goedert and Campbell, 1995; Squires, 1995). Associate fossil gastropods from Shipwreck Point that recur in other modem and ancient hydrothermal vent or cold-seep settings include Margarites (Pupillaria) cohunbiatta, hyalogyrinids, and limpets (Goedert and Campbell, 1995, and references therein). 60 The limestone block at Shipwreck Point can be characterized petrographically (Goedert and Campbell, 1995) as composed predominantly of a gray-brown micrite, which contains abundant woody debris, and quartz and feldspar grains. Relatively homogeneous regions of micrite are commonly disrupted by irregular intraclasts of micrite with diffuse boundaries, or by angular to rounded brecciated micrite fragments. Blocky, clear spar and carbon isotopically depleted, isopachous fibrous cements fill pore spaces between micritic fragments, but the micrite/cement ratio is high (Goedert and Campbell, 1995). Some of the terrigenous organic material has been replaced by pyrite and mytilid shells are coated with pyrite. Site #13, Fossil whale falls, Washington. Early Oligocene age (~35 m.y. old) basin-plain and outer-fan fringe deposits of the Makah Formation, Straits of Juan de Fuca, northern Olympic Peninsula, are typically fossil-poor (Snavely etal., 1980). An exception is the discovery within the Makah of three fossil whale skeletons preserved in concretions, and associated with vent-type fossil molluscs (Squires etal., 1991) (Figure 1). The fossil whales are small, primitive baleen and toothed species; immediately surrounding the skeletons or lodged in their skull cavities are core bivalves Lucinotna hamiibali, Modiolus sp., and Thyasira sp. (Squires etal., 1991). Modem analogous whale falls with vent-type faunas living off whale bone-oil have been described from the California Borderland basins (Smith etal., 1989), and large marine reptile fossil "falls" (e.g., Icthyosaurus) have been described from the Mesozoic which were coated with ?chemosynthetic microbial mats as they decayed on the seafloor (Martill, 1987). Site #14, Twin River Locality, Washington. In and near Twin Quarry (Ideal Cement Company), northern Olympic peninsula, Washington (Figure 1), in dark siltstone strata of the Pysht Formation, Twin Rivers Group (Snavely etal., 1978), are large numbers of Solemya, Tliyasira, and Lucinoma. Rare, irregular micritic carbonates were collected in float from the quarry, but none were found in place. Without further study, 61 this site can only be considered seep-suspect or gradational toward a deep-water basinal deposit that is dominated by core taxa. Site #15, Canyon River Locality, Washington. In a large meander bend of the Canyon River, southern Olympic Mountains (Figure 1), gray-brown siltstone of the Oligocene part of the Lincoln Creek Formation contains abundant nodules of micritic carbonate and large numbers of Solemya, Lucinoma and Thyasira. This site is CR-10 of Armentrout (1973), and it is located downstream of several small seep-carbonate edifices recently discovered by Goedert (personal communication, 1994). Detailed petrographic and isotopic analyses of the nodular carbonates are required to clearly elucidate the paleoenvironmental origin of the deposit. Site #16, San Luis Dam Locality, California. Exposed along the eastern margin of the Diablo Range, near Romero Creek on the San Luis Dam, central California (Figure 1), is a thick section of Tithonian-Maastrichtian age strata of the Great Valley Group (eastern part of San Jose 1:100,000 quadrangle; Elder and Miller, 1993). Near the base of the Mustang Shale Member of the Moreno Formation, Elder and Miller (1993) reported limestone lenses of Late Campanian age based on the presence of Metaplacenticeras cf. M. pacificum. Elder and Miller (1993) reported core bivalves Thyasiracretacea and Solemya sp., and inferred a submarine spring origin for these limestones. USGS invertebrate collections also contain the following associate taxa for the locality (USGS M6991; Appendix I): Udonoearca sp., a tetragonitid ammonite, heterodont bivalves, unidentified inoceramid (W. Elder, written communication, 1990). Site #17, Humboldt area, California. Pliocene deep-water terrigenous strata of the Rio Dell Formation, Wildcat Group, contain at least two suspect localities where recurring core taxa have been reported (Figure 1). First, great abundances of Lucina acutilineata, Solemya ventricosa and Thyasira disjuncta are reported from the South Fork of the Elk River, southeast of Eureka (Ogle, 1953). Second, along the Centerville sea cliffs, on both the north and south side of False Cape, Martin (1916) and Talmadge (1974) 62 reported abundant lucinids and thyasirids. As yet, neither suspect-seep locality has been investigated by field reconnaissance. Site #18, Santa Cruz Mountains locality, California A limpet similar to Aom ea simplex has been reported (Dickerson, 1917) in some limestones at the head of the San Lorenzo River in Santa Cruz County (Figure 1). The seep-suspect aspect of these carbonates has yet to be investigated. Site #19, Irishman's Flat Locality, California. A 650 m long, 10 m thick limestone lens at Irishman's Flat, Potter Valley, contains the lucinacean bivalve Thyasira cretacea (USGS M5066; Appendix I) (Figure 1). Other associated early Campanian invertebrate fossils in the USGS collection include Spkenoceramus schmidli and ICrassaiella sp. Attempts to locate this large limestone lens in the Middle Mountain outlier of Great Valley Group strata (cf. Berkland, 1973) (Figure 26) thus far have been unsuccessful. Site #20, Potter Valley, California. A white limestone harboring abundant thyasirid bivalves is reported along the Eel River, Potter Valley, Mendocino County, California (USGS locality M2818; Appendix I). W. Elder (written communication, 1990) considered the locality to be most likely Santonian in age based on the presence of Sphenoceramus cf. S. nawnanm. Other fossil taxa in the USGS collection at Menlo Park include Crassatella sp, Baculites sp., and gastropods. The site was originally reported on by California Department of Fish and Game surveyors and has not been visited since. Site #21, Lowrey's Locality, California. Stanton (1895) reported the following invertebrate taxa from a "small limestone exposure" and adjacent shales between Elder Creek and Paskenta, 5 km south of Lowrey's Ranch (Figure 1): Solemya occidentalis, Buchia crassicollis, Nttcula gabbi, Astarte trapezoidalis, Turbo trilineatus, and Oleostephanus mutabilis. As yet, this suspect-seep limestone has not been found. Site #22, Devil's Kitchen Locality, California. Fossil core taxa reported by Wagner and Schilling (1923) from their locality #3195 (Appendix I) in the San Emigdio 63 Formation include Thyasira (Conchele) folgeri, Modiolus mulliradiatus, Lucinoma hiflata, Lucitioma gaylordi,; associate taxa include the bivalve ISemele sp. and gastropod Ampullospira sp. This locality is considered to be seep-suspect, but it has not yet been re located. DISCUSSION AND SUMMARY Use or a palcoecological approach to search for and identify ancient cold-seeps in western North America has revealed that these unusual habitats generally were more common in the geologic past than recognized previously (e.g., Table 2; also, review in Campbell, 1992). In westernmost North America alone, identification of ancient cold-seep deposits has increased from one Mio-Pliocene discovery in 1989 to 22 known or suspected fossil cold-seep sites reported in this study. Over a dozen additional Cenozoic cold-seep deposits recently have been discovered in Washington State by J. Goedert and K. Kaler (personal communication, 1994), and studies of these new sites are underway. Many core and associate taxa recur in these ancient chemosynthetic settings that have direct affinities with modern hydrothermal vent and cold-seep taxa. The similarity in taxa suggests that many of these faunal elements were evolutionarily conservative. Recurring core taxa include probable vestimentiferan or pogonophoran tube worm remains, and the bivalves Solemya, Acharax, Calyptogena, Vesicomya, Thyasira, Modiola, Modiolus, Lucina, and Lucinoma (Gabb, 1869; Stanton, 1895; Campbell, 1989; 1992; Goedert and Squires, 1990; 1993; Squires and Goedert, 1991; Campbell and Bottjer, 1993a, b; Campbell etal., 1993; Goedert and Campbell, 1995). Recurring associate fossil invertebrate components from western North American sites that are common in (but not restricted to) modem and ancient hydrothermal vent and cold-seep habitats include anomuran decapod fecal pellets, serpulid worm tubes, and the gastropods Margarites, Provanna, hyalogyrinids, and various limpets (e.g., Squires and Goedert, 1991; Goedert and Campbell, 1995; Squires, 1995). Taxonomic similarity is also a characteristic of modem vent-seep ecosystems (e.g., 64 Tunnicliffe, 1992; review in Lutz and Kennish, 1993). The evolutionary significance of these observations, as summarized by Hecker (1985) for present-day chemosynthetic settings, can also be applied to ancient vent-seep habitats: The notable taxonomic similarity between the seep and vent faunas presents several evolutionary implications for the origin and maintenance of sulfide-based communities. At the very least, this similarity points to an evolutionary conservatism in the taxa that have adapted to sulfide-enriched environments. However, the familial and generic similarity between seep and vent taxa points to an even stronger relationship, namely that of a common origin and subsequent evolutionary history. (Hecker, 1985, p. 470) However, many details of the evolutionary processes that have influenced these patterns of similarity remain obscure, and await further analysis in both modem and ancient chemosynthetic settings. The localities share other strikingly similar seep-to-seep characteristics in carbonates. Based on field observations, sedimentologic and strati graphic evidence for ancient fluid seepage among all sites includes: carbonates (mounds, lenses, nodules) characteristically enclosed within fine-grained siliciclastic deposits, strati graphically adjacent structures (faults, diapirs) to transmit fluids, sulfur-rich halos around mounds, preserved fluid-flow conduits (carbonate chimneys, pipes, doughnuts, concentric cement linings, etc.), and fossils zoned with respect to broad fiuid-fiow features (see Haggerty, 1987; 1991; Howe, 1987; Kulm and Suess, 1990; Rolin etal., 1990; von Bitter etal., 1990, 1992; Campbell and Bottjer, 1992a; 1993a; Campbell etal., 1993). Even finer-scale petrographic evidence for ancient fluid seepage is outlined in Chapter 2. Reconnaissance of seep-suspect sites during the course of this investigation has yielded a continuum of deposits that may range from "true" seeps (characterized by relatively vigorous fluid flow parameters) to ?dysaerobic reduced sediments that contain core taxa. For example, at least four sites have been located during the course of this investigation-Quinault (Site #1), Holcomb (Site #3), Twin River (Site #14), and Canyon River (Site #15)— that contain a strati graphically restricted Thyasira-Lucinoma-Solemya association but preserve relatively minor amounts of carbonate, in the form of scattered 65 nodules and shell-fill. These sites may represent the products of relatively diffusive fluid seepage rather than the vigorous fluid-flow features typified by "end member" cold-seep limestone lenses and mounds of greater dimensions. Moreover, other stratigraphic sequences from Hickman's (1984) list contain fossil core taxa, but do not contain unusual carbonates. Armentrout (1973) also recognized recurring faunules dominated by Thyasira, Lucinoma, Modiolus and Solemya bivalves in many Cenozoic deep-water deposits across the Pacific Northwest (e.g., Nye Mudstone, Astoria Formation, Lincoln Creek Formation, Blakeley Formation, Twin River Formation, shale below Quimper Sandstone, Marrowstone Shale, Townsend Shale) (Figure 27). A few of these sequences (e.g., Lincoln Creek Formation) yield "true" seep-carbonates with core taxa in some exposures, but in other areas of outcrop of the same formations, core taxa are present in variable concentrations within fine-grained siliciclastics (i.e., no carbonates). These latter deposits may represent ancient, low-oxygen, somewhat restricted, and/or organic-rich environments which today support chemosymbiotic invertebrates (for example, in marine grass banks, mud flats or fjords, or at oxic-anoxic boundaries of oxygen-deficient marine basins; Cavanaugh, 1985; Cary etal., 1989), and which are gradational with diffusive or end- member cold-seep deposits. At all potentially diffusive-seeps or gradational reduced- sediment sites, a methane influence during sedimentation must be corroborated via detailed stratigraphy, sedimentology and stable isotopic study, as in the Quinault example (Campbell, 1992), if the locality is to be classified as a "true" ancient cold-seep deposit. As yet, no formal criteria have been established to clearly define the continuum of deposits which contain fossil core taxa. Such gradations, from "end-member" cold-seep deposits, to diffusive, "leaky" seeps, to reduced-sediment deposits, may eventually be used to establish relative fluid flow rates through tectonically active marine basins along continental margins. Because the modem analogous associations were unknown until the late 1970's, many ancient hydrothermal vent and cold-seep deposits in the geologic record overall, and 66 124» 1200 48 Olym pia iftCO LN CREEK F M - ‘if. VA N CO U V ERstJ^v ISLAND SOOKE FM TWIN RIVERS Flo. 2. Portland Sal am Yaquina NNEL POINT FM BASTENDORF FM fMARROW STONE SH J q u i m p e r SS (TOWNSEND SH BLAKELEY FM Seattle N W A S H I N G T O N O < a- "MUDSTONI OF OSWAL WEST* Tillamook Undifferentiated Oligocane Rock* NYE FM YAQUINA FM "SILTSTONE OF ALSEA' NESTUCCA FI GRIES RANCH BEDS SCAPPOSE FORMATION PITTSBURG BLUFF FM KEASEY FM O R E G O N 0 5 0 1 — 4—I I ■ ,, I miles 100 __J Figure 27. Map of Pacific Northwest showing outcrop extent of deep-water Cenozoic strata that contain "gradational" (see text), reduced-sediment deposits with the Thyasira-Lucinoma-Solemya fossil bivalve association. From Armentrout (1973). 67 in western North America in particular, have either gone unrecognized or have been misidentified in previous studies (e.g., Danner, 1966; Hickman, 1984). Before a deep- water, in situ, seep-carbonate paradigm was established, many earlier workers had to rely on a more limited suite of facies models to explain fossiliferous carbonate deposition in deep-water siliciclastic depositional environments. Bottjere/a/. (1995) examined the impact of uniformitarian facies models for seep-carbonate deposition on the interpretation of several unusual carbonate bodies, such as the Tepee Buttes of the Pierre Shale (Campanian), Colorado. The Tepee Buttes are exposed as resistant, conical carbonate mounds in fine-grained siliciclastics, and were once thought to represent marine grass banks (e.g., Petta and Gerhard, 1977; Bretsky, 1978). More recently the Tepee Buttes have been interpreted as submarine-spring deposits (e.g., Arthur etal., 1982; Howe, 1987; Kauffman and Howe, 1991; see also Gaillard et al., 1985). In another example from Cenozoic strata of the Pacific Northwest, limestones are considered rare in the sandstone- and mudstone-dominated sedimentary sequences that fill ancient forearc basins. From this study, however, it is evident that limestone lenses of variable size and morphologies (see Chapter 3) contain fossils of organisms now recognized to have modem chemosymbiotic representatives. Many of these deposits were ignored by earlier workers or interpreted as shallow-water deposits because no seep-carbonate model was available for comparative study. For example, Danner (1966) described the large Bear River limestone deposit (Site # 10) as a reef or bank based on the exceptionally fossiliferous character of the carbonate (Figure 28) and its misconstrued shallow-water aspect. Deep-water siliceous sponges (Aphrocallistes) were misidentified as dasycladacean algae, and the bivalve Solemya was mistaken for the shallow-water razor clam Solen (Danner, 1966) (Figure 28). Moreover, in the Jurassic-Cretaceous age turbidites of the Great Valley Group, California, isolated, fossiliferous "white limestones" with anomalous mega-invertebrate taxa have been known since the late 19th century (e.g., Figure 5) (Gabb, 1869; Stanton, 1895). The earlier interpretation that the vast quantities of fine-grained siliciclastics of the Great Valley Group 68 Figure 28. Carbonate slab illustrating diversity and abundance of Bear River (Eocene) cold-seep megafossils. Along top portion of slab are siliceous sponge Aphrocallistes (A), and large chemosymbiotic bivalves of the genus Calyptogena (C). Micrite matrix of slab contains modiolid and thyasirid bivalves, gastropods, and serpulid worm tubes. 69 were shallow-water deltaic deposits (Anderson, 1945) cemented the early notion that the unusually fossiliferous "white limestones" were nearshore "reef" deposits. Even after the deep-water turbidite aspect of this Mesozoic forearc basin was recognized, geologists still postulated localized shallowing mechanisms to explain isolated carbonate deposits in an overall deep-water setting (e.g., Carlson, 1984), because in situ, seep-carbonates were not yet well-known in the geologic record. I predict, as have others, that over the next decade or so, isolated, anomalous carbonate bodies in syntectonic deposits worldwide likely will be re-evaluated and interpreted with the fossil cold-seep paradigm model, so that a more accurate picture of the ubiquity and extent of chemosynthetic paleoenvironments finally may be realized from the stratigraphic record. New discoveries of ancient vent-seep deposits worldwide are likely to come from regions with a geologic history of subduction or rifting contemporaneous with sedimentation, such as the Caribbean, New Zealand, Japan, Alaska, and the western areas of Central and South America. Overall, the results of this study demonstrate that once ancient cold-seep sites are identified in their proper tectono-stratigraphic context, the presence and environmental significance of seep deposits can provide a new dimension to understanding the geological and biological development of ancient sedimentary marine environments. Before the study of fossil cold-seeps began, appreciation was lacking for the influence that expulsion of reduced fluids from the seafloor might have on the paleobiogeography and evolution of benthic marine faunas in the geologic record. Discerning how particular ancient seeps developed, and how they have varied in time and space, will also lead to a better understanding of the interactions between tectonics and sedimentation that previously has been unavailable from other sources of geological information on marine sedimentary sequences deposited in geologically active regions throughout the Phanerozoic. Although we have barely begun to consider the influences of submarine fluid- seepage and chemosynthesis on the Phanerozoic history of life, many of the fascinating evolutionary, paleoecologic and geological mysteries surrounding chemosynthetic 70 ecosystems will be answered only through historical analysis. Moreover, continued exploration for additional ancient hydrothermal vent and cold-seep sites will lead to a more complete characterization of the environmental context of evolution in chemosymbiotic benthic invertebrates. Only by this interdisciplinary approach can we begin to understand the paleoecologica] and geochemical framework of fossil vent-seep habitats through time, and the concomitant evolution of their constituent core and associate taxa. 71 CHAPTER 2. MICROFACIES ANALYSIS AND FAUNAL-SEDIMENTOLOGICAL PATTERNS OF SELECTED MESOZOIC SEEPS OF NORTHERN CALIFORNIA INTRODUCTION Recurring, unusual faunal-carbonate associations in siliciclastic forearc sequences of western North America display broad regional indications as well as outcrop-scale evidence for cold-seep palcoenvironmental origins (e.g., Chapter 1; Campbell and Bottjer, 1993a). Nonetheless, a more detailed microfacies analysis (cf. Fliigel, 1982; Carozzi, 1989) of seep-suspcct carbonates is required to demonstrate: 1) that the geochemical fuels of chemosynthesis (hydrogen sulfide, methane) were contemporaneous with carbonate development, and 2) that these fuels had an observable influence on biotic activity at fossil cold-seep sites. In general, the microfacies approach has been applied to many classic, photosynthetically based, marine carbonate settings (e.g., reefs, platforms, etc., e.g., Carozzi, 1989, and references therein). However, very few studies of ancient chemosynthetically based ecosystems have utilized this technique of paleoenvironmental analysis (notable exceptions are von Bitter etal., 1990; 1992; and Beauchamp and Savard, 1992). The purpose of this chapter is to outline the methods and results of microfacies analysis applied to three Mesozoic seep-carbonate deposits of northern California, including preliminary stable isotopic analyses. Fossil faunas at these localities are restricted to particular carbonate cement types and microfabrics, as classified herein. In addition, a recurring cement stratigraphy can be delineated for the Tithonian-Albian age deposits in California; this same cement stratigraphy was first recognized in Albian age, methane- derived seep-carbonates of the Canadian Arctic (Beauchamp and Savard, 1992; Campbell et 72 «/., 1993). Herein, I discuss the potential physical, chemical and biological processes that may have influenced organism distribution patterns in the local seep environment, and I present a generalized model to explain recurring cement/fabric sequences that record the geochemical evolution of scep-mound development. METHODS Once field associations and outcrop-scale observations confirmed the probable seep-origin of certain limestone deposits (cf. Chapter 1), the carbonates then were analyzed pctrographically, paleontologically and isotopically via microfacies analysis of thin- sections. In general, the goal of a microfacics approach is toward recognition of an integrated paragenetic sequence, or cement stratigraphy— a recurring sequence of particle components, cements and fabrics as observed in thin-sections— that may be interpreted in terms of the overall faunal-sedimentological and geochemical evolution of fossil cold-seep deposits. A definition and sampling strategy for microfacies analysis are outlined below. Also discussed in this section are other analytical techniques that were applied in this study, including thin-section mapping, petrographic observations, and stable isotopic evaluation. Microfacies Analysis D efinition. Microfacies analysis is application of the classic facies concept on a microscopic scale (Brown, 1943). This approach therefore provides fundamental information about the sedimentary environment, habitat of fossil organisms, and diagencsis, and is particularly useful for study of carbonate rocks, which can be mistaken easily in outcrop as being monotonous and unexceptional. Specifically, the microfacies approach is defined as the study of the sum total of all paleontological and sedimentological criteria which can be classified from thin-sections, peels and polished slabs (Fltigel, 1982). To allow for a more complete characterization of a particular microfacies and its inferred environment of deposition, Carozzi (1989) extended the definition of microfacies analysis to include: "the total of the mineralogic, paleontologic, textural, diagenetic, geochemical, 73 and petrophysical features of a carbonate rock" (p. 24). Herein, I use such a microfacies approach to classify three western North American, seep-carbonate deposits of Mesozoic age— the Paskenta, Cold Fork of Cottonwood Creek, and Wilbur Springs sites (Figures 29, 30). A recurring cement stratigraphy is recognized for the various components and fabrics. Further, I test the proposed microfacies classification by comparing petrographic observations with integrated regional field data, paleoecological interpretations, and stable isotopic evidence. Field Framework and Sampling. As a framework for finer-scale microscopic studies, the necessary prerequisites for microfacies analysis are geological field studies and measured strati graphic sections, with particular emphasis on facies criteria (e.g., lithology, rock colors, grain size and shape, particle types, bedding and lamination, sedimentary structures and textures, fossil content, stratigraphic and structural relationships, geometry of carbonate bodies, etc.) (Fliigel, 1982). The geologic, bio-, and litho-stratigraphic context of the Paskenta (Tithonian), Cold Fork of Cottonwood Creek (Albian), and Wilbur Springs (Hauterivian) localities arc described in Chapter 1 and in Figures 17, 20, 24, 29 and 30. Figure 29 depicts the three sites in their tectono-stratigraphic setting— within the voluminous forcarc turbidites of the Jurassic-Cretaceous Great Valley Group that are exposed in a north-south outcrop belt juxtaposed between a Mesozoic arc (Sierra Nevada Batholith) and trench (Franciscan Group) in northern California (e.g., Ingersoll and Dickinson, 1981). The stratigraphic context of several known or inferred fossil cold-seep localities (Tithonian-Cenomanian age) within the Great Valley Group are illustrated in Figure 30. Once located for this study (Chapter 1), seep-suspect carbonate lenses and mounds were sampled vertically and laterally as discrete, isolated units within fine-grained turbidite sequences. The number of samples collected for petrographic and isotopic analysis depended upon outcrop exposure, and the type/thickness of carbonate bodies, which are commonly lens- or mound-shaped. Future investigations that build on this microfacies 74 120“ W 42°W Cold Fork Cottonmod Creek Wilbur Springs Sac S F S N \ \ N ^ / / / / \ \ \ \ ' / / / / / . \ \ \ N V f f * f * v v v v v FRANCISCAN COMPLEX GREAT VALLEY GROUP SIERRA NEVADA BATHOLITH 50 100 km -j U l Figure 29. Great Valley Group fossil cold-seep localities and simplified geologic map of late Mesozoic arc-trench belts exposed in north-central California. Great Valley Group turbidites mark locus of forearc sedimentation, juxtaposed between remnant arc Sierra Nevada igneous rocks to the east and accretionary prism rocks of the Franscican Complex to the west. Wilbur Springs, Paskenta and Cold Fork of Cottonwood Creek localities represent isolated, ancient cold-seep carbonates that are the subject of a detailed microfacies analysis, described herein. Also shown are other seep-suspect limestone deposits (discussed in Chapter 1) as lettered circles: a — Lowrey's Ranch, between Elder Creek and Paskenta; b — Irishman's Flat, Potter Valley; c — Eel River, Potter Valley; d — Rice Valley; e — San Luis Dam. Figure modified after Campbell et al. (1993). LIMESTONE CHEMOSYNTHETIC STAGE LOCALITY SUSPECT TAXA lucinid and solemyid bivalves San Luis Oam CMP 8 0 - SAN Potter Valley lucinid bivalves CON 9 0 - TUR CEN 100 - mussels and lucinid bivalves, ? worm tubes c n C ottonw ood Creek ALB LU 110 - cc APT 120 - BRM mussels and lucinid bivalves 1 3 0 - Wilbur Springs HAU VLG 1 4 0 - BER mussels, lucinids and solemyids TTH P askenta 1 5 0 - K IM Figure 30. Summary of stratigraphic context of Great Valley Group fossil cold- seep localities (Tithonian-Cenomanian) with respect to current nomenclature. Compiled from Stanton, 1895; Bailey and Jones, 1973; Carlson, 1984; W. Elder, written communication, 1990). 76 investigation will use a larger number of randomly collected samples (cf. Fliigel, 1982). In the present study, samples were collected for all three sites along transects at uniformly spaced intervals (Carozzi, 1989) (e.g., Figure 31); sample volumes were held constant by the filling of same-sized sample bags (bag dimensions: 30 cm x 17 cm). Carbonate rock hand samples were cut on slab saws; thin-sections were made from sub-sample surfaces. For the three sites, the number of bulk samples collected (#), outcrop sample interval (s.i.), and number of thin-sections analyzed (t.s.) are as follows: Paskenta (two mounds, 1 m thick, 3-7 m wide, 20 m long outcrop extent)— 26 #, 50 cm s.i., 39 t.s.; Cold Fork of Cottonwood Creek (one lens 1-2 m thick, 2-3 m wide, 260 m long outcrop extent)— 26 #, 10 m s.i., 31 t.s.; Wilbur Springs (several mounds, quarried, 1-5 m wide, to 20 m long apparent extent)— 32 #, random float from quarry rubble, 16 t.s. Thin Section Maps The recognition and classification of various carbonate cement and fabric types were facilitated by the mapping of such features onto 8 " x 10" black and white photographs of entire thin-sections. Petrographic characteristics, and boundary and spatial relationships among cements and fabrics were easily delineated by this method. Also mapped onto the photos were microdrill sites for isotopic investigations. Petrographic Analysis Petrographic observations were recorded on a Nikon Optiphot-Pol petrographic microscope (from 1-40X magnification) using transmitted, reflected, polarized, or ultraviolet (UV) light. Limited cathodoluminescence (CL) observations also were made with aTechnosyn cold-cathode Luminoscope; this technique is typically utilized to document growth zonation or recrystallization of cements at fine scales (e.g., Popp etal. , 1986; Carpenter and Lohmann, 1989; Hurley and Lohmann, 1989). Polarized light was especially useful for determining particle, cement, and fabric types, as well as direction of cement growth in cavities. Reflected light was utilized primarily to distinguish metal 77 Thomes Camp Road (Paskenta 5 km SE) ■O— ------------ telephone pole fence PN1-1 PN1-5 / pi PN2-5 l & Q n 0 PN2* 4 PN1-6 PN1-13 oak trees • ^ T 2-3 V T VPN2-2 ^ P N 2-1 o o North Paskenta Mound 0 meters N PS 1-0 ~ Q O o H n p s 1 - 1 PS1-5 o<* ©PS1-6 P S 1 - 7 ^ PS1-9 South Paskenta Mound Figure 31. Transects for bulk carbonate sample collection, Paskenta cold-seep deposit. 78 sulfides (pyrite). At high magnification, UV light delineated fluid inclusion composition in certain cement phases. Stable Carbon and Oxygen Isotopes Stable carbon and oxygen isotopes were utilized in this study to aid in determination of the origin of carbonate carbon, to identify potential mixing of end-member cement types and/or geochemical differences of source-fluid reservoirs, and to recognize recrystallization (e.g., Anderson and Arthur, 1983; Popp etal., 1986; Haggerty, 1987; R itgere/a/., 1987). Once individual cement components were identified by petrographic and CL study, components were separated from rock chips with a microdrill assembly under a binocular microscope and fiber-optic lighting set-up. Each individual phase was analyzed as follows. Powdered, weighed samples (150-400 pg) of shell or cement components (i.e., fossil shell material, yellow calcite, fibrous calcite, blocky spar, calcite veins) were roasted in vacuo at 375° C for one hour, and then placed in an automated carbonate device attached to a VG Prism II stable isotope ratio mass spectrometer, where they were reacted with orthophosphoric acid (90°C) to release C02(g). Working standards of Ultissima marble were interspersed with samples and analyzed during the automated runs to test precision of analyses during a run. Stable carbon and oxygen isotopes for the sample material and Ultissima standards were measured with the mass spectrometer. Results, below, are reported in per mil (%c) units using delta (6) notation, where, for example, 6 ^ c = [(^c/l^Q gajjjpig + (13c/12c)standaK i - l] x 1000, where standard = Pee Dee Formation Belemnite (PDB) (Hoefs, 1987). Average laboratory precision is better than 0.1 %o for both carbon and oxygen (L. Stott, personal communication, 1991). RESULTS Petrographic analysis of Mesozoic seep-carbonates in northern California allowed for identification of distinctive carbonate phases in a predictable paragenetic sequence. Fossils tend to be restricted to certain microfacies (e.g., Campbell and Bottjer, 1992b). 79 Evidence for the presence of hydrogen sulfide during carbonate precipitation also was observed for all three sites. Stable isotopic signatures of certain cement components suggest they were derived from methane-rich pore-waters. Shell material values are more similar to typical sea water values. Petrographic Observations of Carbonate Cement Components and Other Fabric Types At the outcrop-scale of observation, seep-carbonate mounds and lenses are comprised of two broad carbonate types: 1) fossiliferous micrite, and 2) wavy laminated, layered cements. Layered fabrics and cavity-fill features are common. Spatially, micritic fabrics are typically preserved around mound margins; whereas, wavy laminated cements are most common in mound interiors. Within this geologic context, detailed petrographic mapping of thin-sections revealed five major recurring carbonate types, described below, from the three Mesozoic cold-seep localities: a) fossiliferous micrite, b) irregular yellow calcite cement, c) isopachous to botryoidal, transparent-gray fibrous cement, d) peloidal yellow calcite, and e) blocky, clear calcite spar. Other recurring fabrics include pyrite- coated corrosion surfaces; internal sediment fill; and thin, dark-gray micritic tubes, linings, and clotted fabrics. Each fabric component type is characterized, and its potential origin discussed below. F o ssilifero u s m icrite. Evidence for biogenic activity is almost entirely restricted to the micrite microfacies. At all three localities, this microfacies is characterized by a brown to gray microcrystalline calcite (4-30 /<m diameter crystals) that is typically detrital-, organic- and pyrite-rich. Figure 32 illustrates a gastropod-rich micritic fabric from the Paskenta locality that is burrow mottled, especially with numerous circular, micrite- Iined and -filled gastropod burrows. In places, peloids are also very common in the micrite microfacies. The source of the micrite is somewhat problematic (see Bathurst, 1975, for a discussion of the overall problem of the origin of micrite in marine environments) but was probably deposited in relation to methane-rich fluid seepage and bacterial activity (I. Montanez, personal communications, 1993; see also model and discussion below). Figure 32. Gastropod fossils, their burrows, and overall bioturbate, mottled texture of fossiliferous micrite microfacies from Paskenta locality. Entire thin- section view, long dimension = 3.5 cm. 81 Irregular yellow calcite cement. A second fabric type is an irregular yellow calcite, which is an ubiquitous cement that fills spaces, and crusts and coats existing grains. It is organic- and pyrite-rich, and, in places, contains numerous, small dissolution cavities filled with clear spar. For example, the irregular yellow calcite cement coats fossil tube worms (Figure 23), and lines larger vugs (Figure 33). This cement type was first described for Early Cretaceous methane-seep carbonates of the Canadian Arctic, and appears to be a seep-indicator cement that is unknown from other marine settings (Beauchamp et al„ 1989; Beauchamp and Savard, 1992; von Bitter etal., 1992). Fibrous cement. Commonly, irregular yellow calcite cements exhibit a gradation toward fibrous cements, the third fabric type (e.g., Figure 33). The gray to translucent fibrous cements are typically isopachous, botryoidal or concentric in their growth patterns (e.g., Figures 19, 33, 34). Figure 34 illustrates a transition from irregular yellow calcite to translucent, fibrous calcite cement. The latter cement is comprised of fibrous crystal bundles that exhibit undulose extinction under polarized light. Two bundle- sets radiate out from a growth surface in Figure 34, and join along a discontinuity surface. Organic-rich inclusions are incorporated into the fibrous cements at Paskenta in two modes (Figure 34a): 1) as black streaks that occur parallel to subcrystal boundaries, and 2) as brown globules that are encased within the cements, concentrated along consecutive, arcuate growth lines. The organic-rich black and brown materials fluoresce bright yellow under UV light epifluorescence (Figure 34b), and are therefore interpreted to represent hydrocarbon inclusions, which formed during cement precipitation {i.e., brown globules), or which migrated into the fibrous cements following subcrystal formation {i.e., black streaks). The irregular yellow calcite cement does not contain hydrocarbon inclusions (Figure 34b). Fibrous cements identical to those found at Paskenta (Figures 19,33, 34) also occur at the Cold Fork of Cottonwood Creek and Wilbur Springs localities, but they are somewhat recrystallized and appear to have lost their hydrocarbon inclusions during burial diagenesis. 82 Figure 33. Vug (5 mm across) lined with irregular yellow calcite cement (y), followed by fibrous cement (f) growth into cavity, and lastly, filled with clear, blocky calcite spar (s). 83 Figure 34. Transition from irregular yellow calcite cement (upper left comer) to radiating bundles of fibrous cement sub-crystals. Fibrous cements contain organic-rich, hydrocarbon inclusions, observed in (a) plain light and (b) UV light. In plain light (a), hydrocarbon inclusions preserved as black streaks along sub crystal boundaries, or as brown globules along concentric growth lines within crystals. In same field of view under blue-light epifluorescence (b), both types of hydrocarbon inclusions fluoresce bright yellow; the irregular yellow calcite cement does not contain hydrocarbons. Scale mark = 0.1 mm. 84 Peloidal deposits. A fourth fabric type is a peloid-rich deposit with a background replacement cement matrix of either irregular yellow calcite, or fibrous calcite, or both (Figure 35). Where it appears with clotted micrite, the fabric is commonly referred to as structure grunieleuse (Bathurst, 1975, his Figure 350, p. 505). As in Bathurst's (1975) discussion of this fabric type, a complete gradation exists from "pure" micrite to structure grunieleuse to pelsparite. The origin of structure grumeleuse is controversial and has been attributed to mechanical deposition of peloids or micrite relics in neomorphic spar (Bathurst, 1975). More recently, MacIntyre (1985) addressed the peloidal question in general for submarine cements from photosynthetic settings, and concluded that most peloids were inorganically produced in place, although he did not discount the pelletizing action of cryptic (i.e. bacterial) organisms. Peloids "drowning" in spar are an extraordinarily abundant microfabric feature of fossil cold-seep deposits worldwide (e.g., see figures in Beauchamp etal., 1989; Gaillard eta!., 1992; von Bitter etal., 1992) yet their origin(s) remains a mystery. Formation of peloids and structure grumeleuse in seep- carbonates must be studied in greater detail to take into consideration the probable influence of bacteria, which are common in modem hydrothermal vent and cold-seep settings (e.g., Jannasch, 1983; 1985). From this study, peloidal deposits appear to be an in situ replacement phase of micrite during seep-mound formation. Aggrading, irregular yellow calcite appears to have "consumed" micrite patches, commonly leaving behind the presumably more resistant, ?mucus-lined peloids (Figure 35, upper right comer; see also Beauchamp and Savard, 1992, their Figure 8a, p. 440). During a subsequent or contemporaneous pulse of hydrocarbon-rich fluid through the system, fibrous cements typically grew radially around peloid surfaces (Figure 35). Blocky calcite spar. The fifth major fabric type is a blocky, clear calcite spar, which fills fossil tests and cavities (e.g., Figure 33). The clear spar is usually the last cement to fill once-open, irregular cavities, and it likely filled remaining pore spaces during burial diagenesis. These vugs (e.g., Figure 33) are typically regionally extensive and 86 Figure 35. Peloidal fabric type; peloids surrouned by a region of aggrading irregular yellow calcite cement (y) whieh "consumed" micrite (upper right diagonal of photomicrograph). Two large peloids (p) (~0.8 m diameter) may have resisted in situ replacement by yellow calcite owing to mucus (?) linings. Peloids subsequently served as growth substrates for radial fibrous cement growth (0 - 87 appear to be dissolution features that were opened during seep-mound formation, and then later were filled by continued precipitation of irregular yellow calcite, fibrous calcite, and clear calcite spar cements during mound growth. Pyrite-coated corrosion surfaces. The two broad carbonate fabric types detected at the outcrop-scale of observation at the three Mesozoic Californian sites— fossiliferous micrite vs. various cements (yellow, fibrous, clear blocky)— are commonly separated from one another by irregular surfaces coated by thin, dark layers of an isotropic mineral (Figure 36), identified in thin-sections as pyrite by reflected light microscopy (brassy reflection). The pyrite coatings clearly formed immediately following a corrosion event, since the irregular surfaces cut across all fabric features of the micrite (e.g., fossil shells are commonly intact within micrite regions up to the pyrite-coated boundary, where the remaining shell material is dissolved away). In places, corrosion events left behind peloids, or pyrite-coated micrite "islands" that became surrounded by a sea of later- precipitated, light-colored cements (Figure 36). The association of corrosion surfaces and pyrite coatings implies that pulses of acidic, sulfide-rich fluids interrupted carbonate formation in the paleoseep environment. Beauchamp and Savard (1992) reported a similar petrographic association in Early Cretaceous seep-carbonates of the Canadian Arctic. Acidic, H2S-rich fluids are generally highly corrosive to carbonates and, upon auto-oxidation in seawater in the presence of iron, will precipitate iron-sulfide minerals (Pauli and Neumann, 1987; Stoessell, 1991). From a biogeochemical standpoint, the presence of pyrite is significant because it is direct evidence that a source of sulfide was available to the sulfide-oxidizing bacteria that must have been present in order to drive chemosynthesis in the ancient seep environment. Internal sediment. Some vugs and most fossil tube worms contain partial linings or total in-fillings of internal sediment. In hand sample, internal sediment commonly appears as a golden-yellow-colored siltstone (e.g., Figure 4, which is also published in color in Campbell and Bottjer, 1993a, their Figure 5, p. 332). In rare cases, Figure 36. Pyrite-coated corrosion surfaces (arrows). Earlier-formed micrite (m) dissolved by corrosion event (arrows), leaving behind micritic islands and peninsulas. Following corrosion event, pyrite precipitated onto irregular dissolution surfaces. Subsequent to this H 2S-event, lighter-colored irregular yellow calcite and fibrous gray calcite cements precipitated. Scale bar: 2 mm. 89 the siltstone is iron-rich and reddish in color. Microscopically, internal sediments are typically comprised of silt-sized lithic fragments, with some larger quartz and feldspar grains. Figure 37 illustrates such a partial siltstone infill of tube worm structures across an entire thin-section from the Cold Fork of Cottonwood Creek limestone (note passive meniscate fill, arrow). In this photomicrograph, tube worm pore-space is filled or lined with internal sediment, followed by clear, blocky calcite cement spar. This mode of siltstone occurrence in tubes, commonly observed in outcrop across the entire 260 m length of the limestone lens, suggests that the internal sediment washed into worm pore spaces after overall carbonate cement precipitation ceased, but before the last clear, blocky spar filled the remaining void space (e.g., geopetal structure with passive fill, Figure 37). The origin of the internal sediment is most likely from the surrounding turbidite-dominated, siliciclastic sedimentary environment. M icrobial fabrics. Certain dark-gray, morphologically distinctive, micritic fabrics arc relatively common throughout all three Mesozoic seep-carbonate deposits. They occur as dark micritic tubules, laminated mat-like layers, and clotted fabrics that are commonly associated with but are distinct from the micrite microfacies. These mat-like layers are texturally and morphologically similar to microbial features reported elsewhere (examples abound in the literature; some of the more interesting are found in Larsen and Chilingar, 1979; Fliigel, 1982; Tsien, 1985; Bume and Moore, 1987; Kempe etal., 1991). The microbial fabrics from the Californian sites exhibit the following distinctive characteristics: 1) they are generally less regionally continuous than the micrite microfacies on a thin-section scale; 2) in places, they form thin, layered coatings that extend over and across one or several adjacent surfaces (gastropods, bivalves, tube worms, corrosion surfaces) (Figure 38a); 3) in places, they "hang" in clots inside enclosed spaces such as cavities or shell chambers (Figure 38b); 4) in places, they are finely laminated in mat-like layers (Figure 39a), or are commonly intercalated at a fine-scale with pyrite horizons and irregular yellow and fibrous calcite cements (Figure 39b); 5) at higher magnification, these 90 Figure 37. Internal sediment infill of preserved tube worm structures, entire thin- section view (3.5 cm length), Cold Fork o f Cottonwood Creek limestone. Two tubes in longitudinal section diagonally cut across photomicrograph (from upper right to lower left); several circular tube cross-sections preserved on left side of photomicrograph. Dark detrital infill material of silt-size grains partially fill or line tubes (note passive meniscate fill, arrow); remaining tube pore space was subsequently cemented with late, blocky clear spar (white). 91 Figure 38. Microbial fabrics associated with outer or inner tube worm surfaces: (a) Clots thinly coating outside of tube (longitudinal section of tube = 4.1 mm); (b) Clots (c) forming clumps inside tube pore space, following or contemporaneous with decay of worm organic material (width of circular tube wall cross-section = 4 mm). Note in (b) that microbial features are preserved throughout significant portion of cement sequence: micritic clots (c) "hanging" from roof of tube interior, and thin microbial coating over fibrous cement growth inside tube (arrows) — clear, blocky spar is last material to fill tube (no microbial association). Thin isopachous coating of yellow calcite cement defines original tube wall surface (a,b). Surrounding tube in (a) are peloidal carbonate fabric and adjacent gastropod (upper left comer). 92 93 Figure 39. Microbial fabrics preserved as finely laminated, mat-like layers from Paskenta locality, (a) Microbial mat (arrows) encrusting peloidal micrite "island" that formed during corrosive H2S event. Layered microbial fabric (intercalated at a fine scale with thin pyrite and yellow calcite layers) directly overlies pyrite- coated corrosion surface. Long dimension of peloidal micrite island = 3.9 mm. (b) Fine-scale layering of clotted microbial micrite (arrows), yellow calcite, and fibrous calcite cements. Field of view = 3 mm, long dimension. 94 occurrences exhibit clumping tendencies and/or display diffuse boundaries within the small, dark micritic clots, as compared to the sharply bounded and internally more homogeneous, larger peloids typical of the micrite microfacies or peloidal deposits; and finally, 6) the inferred microbial fabrics are typically gray-black in color rather than displaying the brownish hue characteristic of the lime mudstone present in the micrite or peloidal microfacies. Cathodoluminescent Observations Cursory cathodoluminescent (CL) observations of Paskenta seep-carbonate fabric types imply that the carbonate phases are primarily nonluminescent, or essentially unaltered (Barker and Kopp, 1991); this inference is corroborated by petrographic observations. The Cold Fork of Cottonwood Creek and Wilbur Springs carbonates show petrographic evidence of recrystallization— e.g., color loss in irregular yellow calcites, absence of hydrocarbons in fibrous cements, micrite grading into microspar, greater frequency of calcite veining— which should be confirmed with CL mapping and comparisons of brightness patterns with similar carbonate phases from different localities. Any anomalous brightness patterns identified during future, more detailed CL mapping of carbonate components from these sites will delineate redox zonation during cement growth (bright luminescent regions, layered, with sharp boundaries), or recrystallized phases (mottled luminescence). These areas then can be sampled in greater detail or be avoided in future isotopic analyses (cf. Popp etal., 1986). Paragenetic Sequence Initial petrographic examination of thin-sections from Paskenta, the Cold Fork of Cottonwood Creek, and Wilbur Springs sites yielded the following paragenetic sequence, listed from early to late in a relative sense; 1) deposition of micrite and (when present) peloids, with contemporaneous biotic activity (fossiliferous, bioturbated); 2) corrosion event(s), marked by irregular dissolution surfaces and cavity formation; 3) precipitation of pyrite on some corrosion surfaces; 4) precipitation of irregular yellow calcite cement in void 96 spaces and around peloids; 5) growth of gray to translucent, fibrous cement in void spaces and around peloids; 6) internal sediment fill of voids; and 7) remaining pore spaces filled by late, clear, blocky calcite spar. Various segments of the sequence may repeat several times, or be missing altogether, depending upon timing of periods of sedimentation, corrosion and cementation (e.g., portion of sequence [#4,5,7] preserved in Figure 33). Microbial fabrics are not restricted to a particular, relative microstratigraphic position in the paragenetic sequence. Instead, evidence for microbial activity is preserved over a significant portion of the geochemical history of seep-mound development. Earlier formed microbial fabrics (post-corrosion, event #2, above) are mat-like, and are preserved as laminae on primary surfaces (gastropod shells, bivalve shells, corroded micrite surfaces, coating outside of tube worms) (e.g., see Figures 38, 39a). Later formed microbial fabrics (post-yellow-calcitc, event #4, above) are clumped, clotted, and restricted to enclosed microenvironments (inside vugs, tube worms, other shells), but definitely pre-date the final (burial) sparry cement-fill event (event #7). For example, the relative sequence of events in worm tube-fill for Figure 38b is as follows: a) worm tube living in environment where peloidal micrite was forming; b) organic tube wall-lining was coated with thin rim of yellow calcite cement during life of worm; c) worm dies; d) fibrous calcite cement partially fills empty tube; e) clotted microbial micrite fabrics "hanging" inside tube-void; 0 continuation of a minor amount of fibrous calcite growth; g) thin, dark microbial layer lining last fibrous calcite blades; and, h) remaining tube-pore volume filled by clear, blocky calcite spar. Hence, microbial activity is present throughout a large portion of the history of seep-carbonate formation, from the early presence of mega-invertebrates to just before the last pore spaces were filled by late blocky spar. All three Mesozoic sites display similar relative cement stratigraphies, with slight variation. The similarity in carbonate types and in cement stratigraphies for the Mesozoic sites span at least 30 million years of Californian forearc history (Tithonian-Albian), over a regionally widespread area (120 km) (Figure 29), and suggest similar geochemical 97 processes of seep-carbonate formation. Beauchamp and Savard (1992) report a comparable sequence of microfacies events for methane-seep carbonates (Albian) of the Canadian Arctic (see discussion section, below). Stable Isotopic Analysis of Cement Components Once the cement-stratigraphic framework for the Californian seep-carbonates was established, individual carbonate cement-components could be separated and analyzed for their stable carbon and oxygen isotopic signatures. The results of these preliminary isotopic studies: 1) confirm the methane-derived origin of the fibrous cements; 2) suggest elevated seep-fluid temperatures during cement precipitation; 3) corroborate textural observations that the Wilbur Springs and Cold Fork of Cottonwood Creek carbonates have undergone diagenetic alteration; and, 4) generate further questions which may be answered with additional isotopic and trace elemental studies. Tabulated in Table 3 is a preliminary compilation of measured stable carbon and oxygen isotopic values for various carbonate components from Paskenta, Cold Fork of Cottonwood Creek, and Wilbur Springs sites. Paskenta carbonate components show textural evidence for the least amount of diagenetic alteration, and are therefore considered as a template for isotopic comparison with the other sites. Paskenta carbon and oxygen values are plotted in Figure 40. Lime-mudstone (micrite) components were not evaluated for this investigation because the impure, sulfur-rich micrites tainted the common acid bath on the automated carbonate device, and adversely affected the isotopic signatures of the Ultissima standard runs. Micrites will be measured in future studies utilizing a variable temperature trap to separate SO2 and CO2 gases off-line of the mass spectrometer. Systematic assessment of cements will also be made at a later date which will incorporate a greater number of samples and trace element analyses of components. For Paskenta, the range in stable carbon and oxygen isotopic values for some of the various cements in the paragenetic sequence are illustrated in Figure 41. In general, strongly depleted 6 ^ C values from Paskenta locality cements indicate a methane 98 Table 3. Summary of stable carbon and oxygen isotope data on carbonate phases (shells, fibrous calcite cement, irregular yellow calcite cement, clear blocky calcite spar) for Paskenta, Cold Fork of Cottonwood Creek and Wilbur Springs localities (Tithonian-Albian), northern California, (t.s.) = sample drilled from thin-section chip; (h.s.) = sample drilled from surface of hand sample. Extraction techniques described in methods section and significance of values discussed in text. 99 SAMPLE NO. CARBONATE PHASE d 13 C d 18 O PASKENTA PN1-9B-1 fibrous -4 0 .1 2 -2.01 PN1-9A-3 fibrous -4 1 .3 7 -0 .7 3 PN1-11B-2 fibrous -3 4 .4 4 -3 .4 4 PN1-12B-2 fibrous w/ yellow -3 7 .1 8 -5 .4 6 PN1-5B-1 fibrous -3 6 .1 5 -6 .8 5 PN2-3A-3 fibrous -41.01 -0 .9 2 PSK-1 fibrous, conduit -3 4 .5 4 -3 .9 2 PSK-3 fibrous, conduit -3 6 .4 7 -3 .3 3 PSK-4 fibrous, conduit -3 9 .6 3 -0 .5 3 PSK-5 fibrous, conduit -4 3 .7 6 -1 .1 5 PSK-6 fibrous, conduit -3 5 .9 6 -3 .8 4 PN1-9A-1 irregular yellow -3 7 .8 -9 .1 4 PN1-9B-3 irregular yellow -3 6 .5 3 -7 .9 8 PN1-7B-1 irregular yellow -36.11 -7 .2 8 PN1-9A-2 irregular yellow -3 8 .0 4 -7.41 PN1-11B-1 irregular yellow -35.1 -8 .1 7 PN1-13A-1 irregular yellow -3 2 .4 7 -6 .4 5 PN2-2A-1 irregular yellow -3 5 .7 4 -7.41 PC1 brachiopod shell -2 .4 3 -0 .6 3 PC2 brachiopod shell -0 .7 0 .0 7 PB2 bivalve shell 2 .1 5 -0 .9 5 PN1-5A-1 clear blocky sp ar -3 8 .3 6 -1 3 .8 PN1-9B-2 clear blocky sp ar -2 7 .8 7 -1 3 .4 4 PN1-7B-2 clear blocky spar -3 7 .2 -1 2 .8 3 PN1-9A-4 clear blocky spar -3 7 .4 5 -1 3 .4 PN1-9A-5 clear blocky spar -3 3 .2 7 -1 3 .5 PN1-12B-1 clear blocky spar -2 9 .0 3 -1 2 .8 5 COLD FORK COTTONWOOD CREEK CC-80-5-2 fibrous -2 1 .7 5 -5 .1 4 CC-80-4-2 fibrous -2 0 .0 7 -4 .2 9 CC-20-1-2 fibrous -2 3 .3 8 -2 .9 9 CC-80-5-1 irregular yellow -2 0 .5 7 -7 .9 7 CC-80-4-1 irregular yellow -2 1 .4 2 -8 .9 3 CC-60-5-1 clear blocky spar -2 0 .3 -1 1 .2 6 WILBUR SPRINGS WS-2-1 micrite -1 9 .2 5 1 .4 9 WS-7-1 fibrous -22.31 2 .1 6 WS-6-1 fibrous -2 3 .9 4 1 .2 8 W S-7-3 fibrous -2 2 .2 1 .9 5 W S-9-2 fibrous -2 1 .6 9 2 .2 7 WS-14-11 fibrous -2 4 .3 4 1 .8 2 WS-14-1H fibrous -2 1 .3 2 1 .0 9 WS-8-1 fibrous -2 1 .6 9 2 .2 7 W S-16-2 brachiopod shell, t.s. 0.51 0 .6 9 W S-17-1 m ussel shell, h.s. -21.31 -5 .5 2 W S-17-2 brachiopod shell, h.s. -6 .7 7 0 .2 W S-17-3 brachiopod shell, h.s. -2 .1 7 0 .0 5 WS-4-1 clear blocky sp ar -1 9 .3 7 -5 .1 9 WS-5-2ii clear blocky sp ar -1 9 .5 4 0 .8 W S-12-1 clear blocky sp ar -2 1 .7 7 2 .2 2 10 CEMENTS AND SHELL VALUES FROM PASKENTA Q P l , w u ro t H to 0 - 10 - 20 -30 4 0 -50 + + i.+ + %a u a qP □ -15 -10 - 5 5180 (%c), PDB 0 o fibrous calcite cement a in*egular yellow calcite + late, clear blocky spar • shell Figure 40. Plot of S ^ C and 6 ^ 0 values for Paskenta carbonate components. Carbonate carbon values of cements are strongly depleted, implying a methane component during cementation; shell carbonate carbon values are slightly depleted with respect to typical seawater values (S ^C ~ 0 % o PDB). Carbonate oxygen values vary systematically. Shell material and fibrous cement 8 ^ 0 values are similar to modem seawater signatures. Irregular yellow calcite and clear blocky calcite cements are more depleted in 8 ^ 0 values, which suggest higher pore-fluid temperatures during precipitation, burial diagenetic effects, or both. Figure 41. Photomicrograph of paragenetic sequence of Paskenta fabrics, shown with range in stable isotopic values measured for cements. Carbon and oxygen values for irregular yellow calcite, fibrous calcite, clear blocky spar cements. See text for interpretations. 102 813c 5^8q Cement type -32.5%c to -38.0%e -6.5%c to -9 .1 % o irregular yellow calcite -34.4%o to -43.7%o -3.9% t> to -0.5%o fibrous gray calcite -27.9%< to -38.4%f - 12.8%c to - 13.8%c blocky clear spar i k v ■ ’V * ^ a - ‘M y y t ;.4 ? - component during cementation, especially for fabrics that consistently range from -27% o to -43% o PDB (Figures 40, 41, Table 3) (as in Arthur etal., 1983; Hudson, 1977; Ritger el al., 1987; Suess and Whiticar, 1989). By comparison, other available sources of marine carbon are more enriched in the isotope; for example, marine sedimentary organic matter yields a carbon isotopic value of approximately -23%o, and sea water records a 6 ^ C value of approximately 0% o PDB (Arthur etal., 1983). The only naturally occurring process that leads to very negative 5 ^ c values (—30% o to -80%o) is precipitation of abiotic carbonates from oxidation of biogenic or thermogenic methane, which occurs, for instance, when methane-rich fluids come into contact with seawater (e.g., Suess and Whiticar, 1989). Fibrous cements yielded the most negative b ^ c values (-34.4%o to -43.7%<? PDB) (Figures 40,41). Stable carbon isotopic values for the irregular yellow calcite cement also yielded signatures more negative (-32.4%o to -38.0% o PDB) than typical organic carbon values (Figures 40, 41; Table 3). Late, clear blocky spar signatures range from -27.8% o to -38.4%o PDB (Figures 40,41; Table 3), indicative of a residual methane influence during even late cementation phases. Shell carbonate carbon rendered values of -2.4%o to 2.2% o PDB, slightly deviated from typical sea water carbon signatures (Figure 40; Table 3). Slight carbon isotopic depletion or enhancement of modem vent-bivalve shells (to ±3.5 % o PDB) have been reported and attributed to chemosymbiotic life habits of the clams (e.g., Rio et al., 1992), but yet to be implemented are systematic comparative studies of well- preserved fossil shells from ancient seep deposits. Stable oxygen isotopic values from Paskenta fossil shells and cements (Figures 40, 41; Table 3) indicate fluid source/temperature variabilities among the various fabric types that are in need of further study. Shell 6 ^ 0 values hover near typical sea water signatures (Figure 40); therefore, shell secretion probably occurred in near isotopic equilibrium with sea water. The fibrous methane-derived calcite cement likely precipitated near ambient conditions; whereas, the blocky clear spar, which invariably fills vugs at a late-stage in precipitation history, yields strongly depleted oxygen isotopic values typical for meteoric- 104 influenced or late-burial fluids (e.g., Land, 1989). However, I cannot rule out the potential influence of hydrothermal fluids on the 6 ^ 0 signature of the blocky clear spar. The irregular yellow calcite cements may have precipitated at warmer fluid temperatures under more sulfide-rich conditions than ambient seawater, as indicated by: 1) their depleted oxygen isotopic signatures (Figures 40,41; Table 3), and 2) their petrographic similarity to peculiar sulfide-rich yellow cements reported from Cretaceous seep-carbonate mounds of the Canadian Arctic (Beauchamp and Savard, 1992). Alternatively, the 6 ^ 0 values of these unusual yellow cements could suggest burial diagenesis; however, at Paskenta, the yellow calcite exhibits no textural or cathodoluminescent indications of significant recrystallization, and appears "pristine" in thin-sections. More detailed isotopic study of these carbonate components, in conjunction with trace element analysis, should more clearly elucidate the geochemical evolution of Paskenta carbonates. (See discussion section below for a geochemical-environmental model for seep-mound development.) Preliminary stable carbon and oxygen isotopic analysis of the Cold Fork of Cottonwood Creek (CFCC) seep-carbonates (Table 3) indicates that these carbonate components were affected by recrystallization, probably during burial diagenesis. For example, carbonates from the Cold Fork of Cottonwood Creek display a small range of 6 values that fluctuate near - 21 % o PDB, which suggests either a re-setting of original values during recrystallization, or implies that all cement components precipitated from fluids with a similar carbon reservoir source. It is deemed unlikely that these texturally distinct limestones precipitated from the same carbon reservoir, especially since the carbonate types and cement stratigraphy are identical to those preserved in Paskenta carbonates, the latter of which display distinct stable isotopic fields for the different cement phases (Figures 40, 41). Oxygen isotopic values for CFCC fibrous cements corroborate a recrystallization influence, since 6 ^ 0 values are more depleted (- 4% o to - 5 %o PDB) than signatures from fibrous cements at Paskenta (— 2 % o PDB), yet CFCC fibrous cements are consistently more positive in 6 ^ 0 than the other cement types, just as in Paskenta 105 examples (Table 3). In other words, a residual stable isotopic signature may be present in CFCC limestones that partly reflects original formation conditions. Wilbur Springs carbon and oxygen values from carbonates are variable, and do not show the strong depletion in as do some Paskenta cements. Texturally, Wilbur Springs carbonates and shells are recrystallized, and the isotopic signatures could reflect diagenetic alteration. However, the tectono-stratigraphic setting of this locality is unusual, and Wilbur Springs cements also may have been isotopically affected by anomalous fluid flow patterns in the environment associated with localized serpentine diapirism. For example, Wilbur Springs cements display a variable range in oxygen isotopes, which is not surprising considering the inferred paleoenvironment of formation of these seep-carbonates atop a submarine serpentine diapir that entrained deep-seated fluids from a subducted, dcwatering slab of oceanic crust (Campbell et al., 1993). In a modem analogous tectonic regime of the Marianas forearc, Haggerty (1991) measured carbon and oxygen isotopes from aragonite slabs precipitated from fluids seeping out of diapiric serpentine seamounts. She reported a range in carbonate carbon 6 ^ C values from 0 % o to - 20 % o PDB, which she attributed to mixing between sea water and methane reservoirs (Haggerty, 1991). In comparison, 6 ^ C values measured from Wilbur Springs carbonate phases range from about - 19%o to -24% o PDB (Table 3), even more depleted, in general, than modem Marianas seep-carbonates. Carbonate 6 ^ 0 signatures from modem Marianas carbonates are reported in the range of +2 % o to + 8 % o PDB, which Haggerty (1991) interpreted to represent formation from cold waters. In contrast, 6 ^ 0 values from Wilbur Springs seep-carbonate phases exhibit a range from about - 5 % o to + 2 % o PDB (Table 3). Because the inferred, ancient fluid-sedimentation history at Wilbur Springs is presumed to be relatively complex, a more detailed, systematic, regional isotopic assessment of these carbonates is necessary, one which would incorporate measurements from the adjacent, carbonate-cemented serpentinite deposits, as well as from more recently deposited, nearby 106 hot springs precipitates that may have affected regional groundwater systems long after Hauterivian-age formation of the seep-carbonates. Fossil Faunal-Carbonate Microfacies Associations Most faunal elements (both core and associate taxa) are restricted to the micrite microfacies at all Californian Mesozoic sites. An exception, however, is the occurrence of tube worms; when present (e.g., at Cold Fork of Cottonwood Creek [CFCC]), they tend to be associated with wavy cement regions or with peloidal cement patches in the seep- carbonate mounds (e.g., Figures 23, 37, 38). The vast majority of the tubes are preserved in intimate association with a complex array of cements that outline the original morphology of a tube-like organism that possessed no hard parts (e.g., Figure 23, 38). In particular, circular to elliptical tube cross-sections are defined by thin rims of yellow calcite cement that coated the outside of the tube while the organism was alive— otherwise, the perfect tube-like shape would not be so consistently preserved (Figure 42). In some examples, tubes also are commonly coated with pyrite and/or dark microbial linings (Figures 23,37, 38,42). Once the organism died, other cements and internal sediments eventually filled the tube pore-space left open by soft-part decay. For example, Figure 42 illustrates a partial thin-section view (3.5 cm longest dimension) of fossil tube worms (two sizes: small [~ 1 mm diameter], and large [~4 mm diameter]) preserved in wavy laminated fibrous and irregular yellow calcite cements, or in peloidal cement fabrics from the Cold Fork of Cottonwood Creek site. Large tubes (1) are preserved in longitudinal and cross-sectional views. Most tube structures display thin coatings of yellow calcite cement, except for two longitudinal large tubes, which are coated with pyrite (p). Following the demise of the organism, tube pore spaces were filled with fibrous cement, microbial clumps, internal sediment, and/or clear blocky spar (Figures 38b, 42). Besides the tube worms, only one other invertebrate taxon is found outside of the fossiliferous micrite microfacies— unidentified gastropods are abundantly associated with CFCC tube worm remains (e.g., Figure 38a, upper left comer of photomicrograph; Figure 107 Figure 42. Entire thin-section view (3.5 cm across) of fossil tube worms (defined by thin rims of yellow calcite cement) in two sizes: small (~ 1 mm diameter cross-section, e.g., upper left portion of photomicrograph) and large (to 0.5 cm diameter cross-section, e.g., two tubes in upper center of photomicrograph). Tube worm remains enclosed by layers of fibrous and irregular yellow calcite cements, or by peloidal fabrics; Cold Fork of Cottonwood Creek site. Large tubes are preserv ed in both longitudinal and cross-sectional views. Two large tubes in longitudinal section (upper right and lower right, diagonal) are coated with pyrite (p). Subsequent to death of tube worms, tube pore spaces were filled with fibrous cement, microbial clumps, internal sediment, and/or clear blocky spar. 108 43). The gastropods are commonly preserved "attached" to or closely affiliated with tube worm surfaces, and were presumably grazing on microbial mats that coat some tube outer walls (Figure 43). Grazing gastropods, and microbial and iron sulfide coatings on tube worms arc well-documented from modem hydrothermal vent settings (Tunnicliffe and Fontaine, 1987; Lutz and Kennish, 1993). Figure 44 summarizes the observed fossil-carbonate microfacies associations for California Mesozoic sites: I. Early phase. Most core and associate taxa restricted to the micrite microfacies. II. Later Phase. Fossil tube worm remains (and gastropods) associated with irregular yellow calcite, microbial features, or pyrite on living tube worms, followed by post-mortem precipitation of fibrous methane-cement growing on and inside of empty worm tubes (Figure 44). The spatial relationship at the outcrop-scale between these two phases of faunal-gcochemical activity is illustrated in Figure 45 in a schematic drawing of a typical Californian Mesozoic site (based on general observations for all sites, and data from Appendix II for the Paskenta site hand samples [relative micrite:cement ratios]). Fossiliferous micrites tend to be preserved on the peripheries of seep-carbonate mounds and lenses; in addition nodular carbonates and core taxa also are preserved around mound edges and out into the adjacent siliciclastics (Figure 45). These features (micrite, nodules) may collectively indicate relatively diffuse fluid-flow conditions at seep margins which may have been conducive to enhanced biogenic activity, as in modem sites. Wavy laminated yellow calcite and fibrous calcite cements tend to be preserved at mound centers (Figure 45), and may represent relatively vigorous fluid-flow that was not ideal for biotic colonization (or, the fossil remains were dissolved or otherwise removed during vigorous fluid-flow phases that produced the cements). A general model to explain fossi 1-carbonate microfacies and spatial associations in terms of the overall geochemical evolution of Californian Mesozoic seep deposits is discussed in greater detail below. 109 Figure 43. Gastropod (g) nestled between two tube worms that are preserved in longitudinal section (v-shaped in thin section view) and are coated with microbial mat (arrows). Sequence of microfabric features observed for tubes (best seen in tube on right) are as follows, from outside to inside: affiliated gastropod, thin (dark) microbial mat (arrows), thin layer of yellow calcite (y), internal sediment (siltstone lining or fill, s), clear blocky spar (white). Fuzzy dark line in lower right comer of photomicrograph is scratch on glass. Length of gastropod along axis (apex to aperture) = 2.4 mm. 110 RELATIONSHIP BETW EEN CARBONATES AND S E E P TAXA I . FOSSILIFEROUS M IC R IT E c > II. ALTERNATING CEM ENTS / TUBE W ORM S ?CH4 fibrous cement yellow cement, microbial coating, pyrite coating CH4 H 2S, C H 4 Figure 44. Schematic diagram illustrating distribution of fossils with respect to microfacies components for Californian Mesozoic seep-carbonates. Most core and all associate taxa are affiliated with the early formed micrite microfacies (I). Fossil tube worms are preserved in cements with a distinctive fine-scale cement sequence (II). Specifically, tube walls are lined with fabrics indicative of geochemicaUy reduced microenvironmental conditions: yellow calcite cement rims, pyrite, microbial coatings. I l l SITE DISTRIBUTION OF SEEP TAXA AND CARBONATE FABRICS PLAN VIEW fossiliferous micrite alternating cements {tube worms) 9i fossiliferous micrite H2S Figure 45. Spatial association of fossiliferous micrite microfacies and wavy- laminated cements at outcrop-scale for California Mesozoic seep carbonates. Outcrop sketch (approximately 20 m across in plan view) of Paskenta seep- carbonate lenses and distribution of micrite-dominated vs. cement-dominated fabrics. Micrite-dominated fabrics are fossil-rich and are preserved at mound peripheries; cement-dominated fabrics are found in mound interior areas. Outcrop observations corroborated by estimates of relative micritexement ratios in hand samples (logged in Appendix II). 112 DISCUSSION The observed microfacies separation of seep taxa— core/associate taxa in micrite, tube worms in cements (Figure 44)— can be explored genetically by examining the potential physical-chemical-biological mechanisms that produced the different types of enclosing carbonate fabrics. These mechanisms include the affects of relative fluid-flow rates, the significance of microbial mat growth, and the changing geochemical conditions recorded in pore microenvironments during the life of a developing seep-mound. In studies of fluid flow through modem and ancient accretionary prisms, micrite is typically reported as an early lime mud associated with diffuse fluid flow through surrounding sediments; whereas, fibrous or coarsely crystalline cements are commonly associated with features delineating advective fluid flow (e.g., Ritger etaL, 1987; Kulm and Suess, 1990; Orange eta l.t 1993a). In particular, cement-lined conduit features such as chimneys and doughnuts appear to represent more vigorous fluid flow rates (e.g., see Figures 11, 12, and 19); whereas, slabs and lenses composed of micrite likely represent more diffusive fluid flow conditions (e.g., Kulm and Suess, 1990). It is probable that ancient microfacies distributions may reflect differential rates of fluid flow at Mesozoic sites as they do in modem examples (e.g., Grassle, 1985; MacDonald el al., 1989;Arquit, 1990; Lutz and Kennish, 1993; Robison and Greene, 1993). For example, at modem petroleum seeps in the Gulf of Mexico, MacDonald el al. (1989; 1990) reported seep mussel distributions at "dying" seep sites, or in areas of diffuse fluid flow; whereas, tube worms were found to cluster in areas of very active fluid venting. In a review, Lutz and Kennish (1993, p. 231) noted that the "(t)ube worms, Riftia pachtyptila, are limited to vent openings, thriving in areas of strong vent flow." Childress et al. (1993) recently provided a possible biochemical explanation for the observed distribution of modern hydrothermal vent tube worms in areas of high sulfide concentrations (and therefore, also associated with vigorous venting). They described the metabolic requirement for particularly high inorganic carbon uptake by tube worms (to fuel 113 their Calvin-Benson cycle metabolism) because the bacterial symbionts in this organism are physically far-removed from the environment (Childress etal., 1993). In order for the bacteria residing in the worm-trunk troposome tissues to obtain access to environmental H2S through the worm's plume, the organism appears to situate itself physically in areas of relatively vigorous fluid venting. In this particular microenvironment, deep-seated symbiont uptake of H2S is facilitated by high environmental pC 02 (Childress el al., 1993), a condition prevalent near advcctive, vent-fluid effluent areas (Grassle, 1985). In California Mesozoic examples, fossil tube worms, when present, appear to be associated with fabrics indicative of reducing microenvironmental conditions, as described for similar fabrics from Cretaceous-age seeps of the Canadian Arctic (Beauchamp and Savard, 1992). Specifically, as described above, the tube cross-sections are defined by thin rims of yellow calcite cement, and are commonly coated with pyrite and/or dark microbial linings (Figures 23, 37,38,42, 44). For Cretaceous Canadian Arctic seeps, Beauchamp and Savard (1992) reported similar fabrics: pyrite and irregular yellow calcite cement coat serpulid worm tubes, followed by botryoidal fibrous cement precipitation. They suggest that these fabrics represent fluctuating pore-fluid redox conditions between aerobic and H2S-frec (i.e., methane oxidation and precipitation of botryoidal cements) and anaerobic and H2S-rich (i.e., corrosive events and precipitation of sulfur-rich, irregular yellow cements). At the Cold Fork of Cottonwood Creek site in California, the yellow cement, pyrite coating, and microbial lining association with fossil tube worms (Figure 44) is compelling, since all three fabric types apparently are common in reduced microenvironments (Berner, 1970; Beauchamp and Savard, 1992). For similar features in the Cretaceous of the Canadian Arctic, Beauchamp and Savard (1992) proposed that yellow calcite may have precipitated beneath bacterial mats under localized anaerobic conditions (Figure 46). However, no remnants of these supposed microbial features are preserved in the Canadian examples. At Paskenta, however, I have found evidence for bacterial mat growth over yellow calcite, which overlies pyrite-coated corrosion surfaces (e.g., Figures 114 BOTRYOIDAL & SPLAYED CALCITE-II | CORROSION I PYRITE | Figure 46. Part of Beauchamp and Savard's (1992) model of paragenetic events leading to chemosynthetic mound development for Cretaceous (Albian) methane seeps of the Canadian Arctic. Beauchamp and Savard (1992) recognized two phases of mound development: a) an early phase (not shown here), characterized by anaerobic micrite development, followed by aerobic biogenic activity within micrite deposits; and, b) a later phase, shown here, that models yellow cement formation beneath bacterial mats postulated to have existed within an anaerobic microenvironment. In detail, circular drawing depicts late-stage anaerobic events (5, 6 ,7 , 8) that produced (in order): corrosion, flourishing of biogenic activity (serpulid worm tubes), pyrite-coating of serpulids, and precipitation of yellow calcite. Formation o f yellow calcite is envisioned as follows: "[establishment] of sulfur-oxidizing bacterial mat, corrosion, development of serpulid-rich life oasis, anaerobic precipitation of pyrite and organic matter- and pyrite-rich methane- derived yellow calcite beneath mat" (p. 448, Beauchamp and Savard [1992]). A return to aerobic conditions and precipitation of botryoidal calcite cement (event 9) was concurrent with the demise of the postulated mat. Microfabrics from Mesozoic seeps of California show display the same paragenetic sequence and may have formed in a similar manner. 115 38,39). This localized paragenetic sequence affiliated with preserved worm tubes (Figure 44) suggests that there may indeed be a close microenvironmental link between the formation of pyrite, yellow calcite and bacterial mat under reduced conditions at certain times during seep-mound formation. The closely associated growth of fibrous cement outside and inside of tube wall linings following phases of pyrite, yellow calcite and bacterial activity (Figures 23,38,42, 44), may mark a return (post-worm) to aerobic, methane-oxidizing conditions, and relatively more vigorous fluid-flow rates in the mound environment. Hence, this model for seep-carbonate development for Californian Mesozoic sites (Figure 44) is a modified version— that includes actual microbial mat preservation— of Beauchamp and Savard's (1992) scenario (Figure 46) for the geochemical evolution of Cretaceous chemosynthetic mounds in Arctic Canada. Several aspects of the above model for faunal-carbonate associations at Californian Mesozoic seep sites (Figure 44) remain to be tested more completely. Future studies: 1) will incorporate methods to analyze C and O isotopes of sulfur-rich carbonate phases, such as the micrite microfacies; and 2) will examine the use of sulfur isotopes to distinguish origins of preserved bacterial mats, micrite, and irregular yellow calcite cements. These objectives are significant because crucial data are missing for the isotopic-cement sequence scenario of Figure 41. Without stable isotopic signatures for the micrite microfacies components, for example, no geochemical information is available for the preserved record of most of the biogenic activity at these cold-seep sites. Furthermore, the general problem of the origin of micrite must be more fully addressed, which is a difficult problem already identified for other modem and ancient marine environments (discussed earlier in this chapter). Another problem to be resolved is that, for the Canadian Arctic example, Beauchamp and Savard (1992) attribute early-phase, fossiliferous micrite development and later-phase yellow calcite cement development to the same mechanism: anaerobic precipitation beneath bacterial mats (mats not preserved at their sites). It is difficult to envision how two distinctly different types of marine carbonate fabrics could be formed by 116 precisely the same biogeochemical process. Trace element and stable isolopic studies for Californian carbonate components, including the yellow calcites and microbial mats/clumps that are preserved at Paskenta, may yield important geochemical information to solve this problem. It is also necessary to attempt sulfur isotopic studies of sulfur-rich components at Paskenta (e.g., pyrite-coatings, and sulfur-rich micrites and irregular yellow calcite cements), since there are at least two possible sources for hydrogen sulfide in this setting: H2S formed as a product of sulfate-reducing bacterial activity in connate waters, and H2S formed from deep-seated ?igncous sources. For instance, iron sulfides in marine settings have been attributed to both inorganic (e.g., Stoessell, 1991) and bacterial (e.g., Rickard, 1969) origins. Finally, future studies might further explore the use of oxygen isotopes as relative temperature indicators during seep-mound development. At present, it appears that certain Paskenta cement components were precipitated from warm seep-fluids, or have undergone diagenetic alteration during burial. Wilbur Springs and Cold Fork of Cottonwood Creek carbonate components are identical in fabric and cement stratigraphy to Paskenta, but textural and isotopic evidence suggests the former components have been partially recrystallized. Data compiled in Table 3 hint at the potential to unravel the difference between temperature and diagenesis, but detailed future studies must be undertaken that would incorporate more isotopic measurements with cathodoluminescent and trace clement investigations. A more comprehensive geochemical analysis of seep-carbonates has the potential to uncover the underlying processes driving seep-carbonate formation and their geochemical evolution. In addition, such a study has implications for examining the probable gradation in physicochemical conditions between hydrothermal vent settings (e.g., von Bitter etal., 1990; 1992) and "warm" cold-seep paleoenvironments. 117 CHAPTER 3. INHERENT VARIABILITY OF ANCIENT COLD-SEEP DEPOSITS INTRODUCTION Despite general similarities, western North American fossil cold-seep sites are variable in morphology and volume of carbonate deposits, and in diversity and abundance of faunal constituents (Campbell and Bottjer, 1992a). Spatial and temporal heterogeneity is well-documented in modern hydrothermal vent and cold-seep settings, and it typically reflects the dynamic interplay between the organism-sedimentary system and fluctuating geochemical and physical parameters, both locally at a given site, and also regionally across an entire tectono-sedimentary system (e.g., Hessler and Smithey, 1983; Grassle eta l., 1985; Fustec etal., 1987; Juniper and Sibuet, 1987; Juniper etal., 1990; MacDonald etal., 1989; 1990; Arquit, 1990; Van Dover and Hessler, 1990; Lutz and Kennish, 1993; Robison and Greene, 1993). Lutz and Kennish (1993) reviewed the ecology of deep-sea hydrothermal vent communities, and summarized the origin and impact of variability on the vent ecosystem as follows: The biological communities occupying the vast and relatively stable soft bottom habitats of the deep sea are characterized by low population densities, high species diversity, and low biomass. In contrast, those inhabiting the generally unstable conditions of hydrothermal vent environments exhibit high densities and biomass, low species diversity, rapid growth rates, and high metabolic rates....Fluxes in vent flow and fluid chemistry cause changes in growth rates, reproduction, mortality, and/or colonization of vent fauna, leading to temporal and spatial variation of the vent communities. Vent populations that cannot adapt to modified flow rates are adversely affected, as is evidenced by high mortality or lower rates of colonization, growth, or reproduction. Substantial changes in biota have been witnessed at several vents, and successional cycles have been proposed for the Galapagos vent fields. Dramatic temporal and spatial variations in vent community structure may also relate to variations in larval dispersal and chance recruitment, as well as biotic interactions. (Lutz and Kennish, 1993, p. 211) 118 The purpose of this chapter is to compare and contrast the variability inherent in the cold-seep deposits thus far discovered along the convergent margin of western North America, using the character and hierarchy of modem vent-seep variability as a measure for comparison. The results presented herein are qualitative in nature; quantification of these observations awaits future investigations. Variability among ancient cold-seep sites is manifested (and preserved) as differences in 1) geo-tectonic setting, 2) paleocommunity composition, diversity and abundance of taxa, and 3) seep-carbonate composition, volume, and geometry. The levels at which this variability persists— regional-, outcrop-, and microfacies-scales— are similar for both modem and ancient vent-seep settings, and may reflect relative large-scale continuity (geographically and temporally) of regionally active tectono-sedimentary systems, despite the ephemeral nature of individual vent-seep habitats. This chapter also explores the potential physical-chemical-biological processes that may have produced such variability, including tectonic regime, changing fluid flow rates, changing sedimentation rates, and the mechanisms and timing of biotic colonization. BACKGROUND: MODES AND LEVELS OF VARIABILITY IN MODERN HYDROTHERMAL VENT AND COLD-SEEP ENVIRONMENTS Several levels of temporal and spatial variability have been observed for modem hydrothermal vent systems (Figure 47), including the following levels: fine-scale (within individual vent-seep site), local or outcrop-scale (among clusters in vent-seep field), and regional or global-scale (across vent-seep tectono-sedimentary system) (Van Dover et al., 1988; MacDonald elal., 1990; Van Dover and Hessler, 1990; Tunnicliffe, 1991). Some of the broad characteristics that differentiate each level are outlined in three sub-sections below, as a background for the types and levels of variability one might expect to be discernible in ancient cold-seep deposits. Overlap exists between levels, since certain physical-chemical-biological factors operating at one level can impinge on and affect vent communities locally, or across the global distribution of vent biotas worldwide. At the 119 \ S Itm VENT FIELD CLUSTERS ami valley S O km OSC ~ C tt RIDGE SEGMENTS 500 m VENT FIELDS hith iemo. — y— r—’ y . lemp VENTS Figure 47. Three-tiered hierarchical context for observations of spatial heterogeneity in modem hydrothermal vent systems: (1) individual vent in vent field, (2) clusters of vent fields along spreading axis, and (3) regional ridge segments. Underlying this spatial hierarchy is a gradient in the probability of vent megafaunal dispersal and genetic exchange. At global and regional scales, these processes most likely control the faunal composition of vent communities. From Van Dover and Hessler (1990). Similar scales are apparent in ancient cold-seep settings of western North America. finest scale of observed variability, individual vent sites contrast in local physical-chemical- biological features, such as faunal differences between high temperature and low temperature vents within the same vent field (Figure 47, [1]). At intermediate levels of observation, variability can be examined among vent fields (Figure 47, [2]). Finally, different oceanic vent-segments can be compared regionally at a global scale (Figure 47, [3]). At all scales, the geochemical and geological constraints on modem vent-type faunas result in faunal assemblages that are spatially discrete, geographically isolated, and ephemeral. Despite the fundamentally ephemeral nature of vent-seep habitats, similarity in faunas persists, and may reflect the physiological and behavioral adaptations of their constituent taxa to fluctuating environmental conditions. Modem cold-seeps in sedimentary basins have not been as well-studied as hydrothermal vent systems, but variable faunal and tectono-sedimentary characteristics can be discerned from individual and regional studies (e.g., Hecker, 1985; Suess etal., 1985; Hovland and Judd, 1988; MacDonald etal., 1989; 1990). Finc-Scale Levels of Variability at Individual Modem Vent-Seep Sites Locally, both physico-chemical gradients and biological interactions (recruitment, competition, predation) appear to control faunal composition and relative abundance of species at individual vent-seep sites. Specifically, individual hydrothermal vent sites exhibit "variable concentrations of vent animals with gradients in biotas distributed in halos around vent openings" (p. 363, Tunnicliffe, 1991). This zonation is probably regulated by the physical and geochemical characteristics of individual sites: from 1) a central point- source area of high temperature, vigorous flow with an associated vent-obligate fauna, to 2) a more peripheral zonation of areally diffuse flow with an associated "near-field" vent fauna (i.e., suspension-feeding and grazing species that depend on primary chemosynthetic production via free-living microbes or on short, localized food webs) (Grassle etal., 1985; Arquit, 1990; Van Dover and Hessler, 1990; Desbruyfcres etal., 1994). 121 For example, in a submersible study of spatial variability at a single modem hydrocarbon cold-seep in the Gulf of Mexico, MacDonald etal. (1989) identified two levels of tube worm and mussel distribution at the site, coarse-scale and fine-scale. At the coarse-scale over the entire site, organisms displayed a patchy distribution but generally clustered spatially around a fault that is seeping hydrocarbons above a rising salt diapir. Other factors that might explain coarse-scale faunal distributions were suggested— e.g., substrate-topography heterogeneity, current patterns, differential larval settling rates, predation— but the degree to which these factors affect zonation are unknown at present (MacDonald et al., 1989). At a fine-scale, tube worm abundances were found to correlate with high pore-water sulfide concentrations, and mussel abundances correlated with high methane concentrations (MacDonald et al., 1989). This result is consistent with physiological requirements of the mega-invertebrates: tube worms contain sulfur oxidizing bacterial symbionts whereas seep mussels contain methylotrophic bacterial symbionts (Childress etal., 1986; 1993; Brooks etal., 1987; Fisher etal., 1987). Thus, modem Gulf of Mexico hydrocarbon seeps exhibit spatial distribution of faunas that are linked to fine-scale differences in local seep fluid chemistry. Organisms also must be able to respond to the ephemeral nature of the vent habitat, or perish; therefore, the variable temporal component (e.g., life and death of vents, changing fluid-flow, vagaries in dispersal) at the scale of an individual site is also extremely significant in the ordering of vent community composition and structure. For instance, a return visit to the Rose Garden hydrothermal vent site near the GaMpagos after six years (Hessler etal., 1988) yielded the following general changes: concomitant with a decrease in fluid-flow rates was an observed decline in the population of the tube worm Riftia (which flourishes in relatively high-fiow regions), and an increase in the populations of the bivalves Bathymodiolus and Calyptogem, as well as galatheid crabs, and turrid gastropods (groups known for their more mixotrophic strategies at modem vent sites). Not only do fluid-flow rates change over time, but other physical factors induce variability in 122 the local vent environment, such as the fluctuating nature of temperature change, which in itself may be more important to the vent inhabitants than the mean temperature regime that the organisms experience overall (Hessler et al., 1985; Johnson etal., 1988). Furthermore, temporal recruitment experiments at vent fields in the Galdpagos and East Pacific Rise indicate that colonization of hydrothermal vent habitats is intermittent or continuous, rather than comprising a single, episodic recruitment event (Van Dover etal., 1988a). Meso-Scale Levels of Variability among Modem Vent-seep Fields At the intermediate scale of the vent-field, relative abundances of vent-seep species are most likely controlled by local physico-chemical parameters (flow rates, fluid chemistry, age of site, stochastic events) characteristic to the field itself; and biological interactions are postulated to affect species composition of vent-seep fields, but are not known in detail (MacDonald etal., 1990; Van Dover, 1990; Van Dover and Hessler, 1990). In particular, where meso-scale processes and patterns have been explored, hydrothermal vent fields along particular vent segments appear to share a similar species p>ool, yet display clear differences in the relative abundance of primary vent species (Van Dover and Hessler, 1990). For example, comparisons of megafaunal composition of seven vent fields along an 11-km length of the Galdpagos spreading axis revealed abundance differences among Riftia pachyptila, Bathymodiolus thennophilus, and Calyptogena tmgnifica that "seem to reflect habitat differences, especially the availability of vent water, but [abundance differences] may be secondarily influenced by biological interactions [e.g., overcrowding of certain niches]" (p. 258, Van Dover and Hessler, 1990). Similar meso-scale associations have been observed along clusters of East Pacific Rise vents (Hessler et al., 1985). At modem hydrocarbon cold-seep fields across the Gulf of Mexico, several meso- scale biofacies have been recognized based on biomass-dominant taxa (MacDonald etal., 1990; Callender and Powell, 1992). In general, the methanotrophic mussel, 123 Bathymodiolus, "occurs in areas of high methane concentrations, usually associated with fresh oil on or near the surface, and brine seepage" (p. 390, Callender and Powell, 1992). Tube worm associations are more common in sulfide-rich areas, on grabens or half grabens at the crests of diapirs (MacDonald et al., 1989; 1990). Further away from active seepage areas occur the three bivalve biofacies of Calyptogena, Vesicomya and Iucinids (Callender and Powell, 1992). For these modern cold-seeps, "[c]ommunity development appears to be determined by whether seepage provides methane or sulfide compounds to the benthos and by the geological characteristics of the surface sediments" (p. 251, MacDonald et al., 1990). Large-Scale Levels of Variability across Modem Oceanic Regions Now that modern hydrothermal vents are understood as a relatively ubiquitous phenomenon worldwide, researchers are beginning to compare various ridge segments across the oceans to understand large-scale spatial and temporal differences among vent systems. Although at higher taxonomic orders [e.g., family level and higher], there is remarkable global consistency in the megafaunal composition of vent communities, these communities appear to respond to differences in the tectonic and volcanic character of regional hydrothermal activity (Van Dover, 1990; Van Dover and Hessler, 1990; Tunnicliffe, 1992). In one study of regional-scale differences among oceanic vent segments, Juniper etal. (1990) compared features of Northeast Pacific, East Pacific Rise, and Gulf of Aden vents and communities, and found that fluid physiochemical properties, mineral deposition, vent field geology, and recent volcanic history vary considerably among regions. For example, the extensive sulfide mineral deposition that is particularly characteristic of Northeast Pacific ridge sites profoundly influences community composition and structure, as well as the distributions of vent-type species with respect to active vent areas (Tunnicliffe and Fontaine, 1987; Juniper et al., 1990). Only certain taxa can withstand the constant rain of sulfide precipitates. In contrast, widespread low- temperature venting is characteristic of rifting activity associated with the opening of the 124 Gulf of Aden. Brine pools and iron-hydroxide gel precipitation characterize these relatively newer vents, which contain dense aggregations of non-vent-type faunas (Juniper et al., 1990). Chemosymbiotic mega-invertebrates have yet to colonize these young vent systems. Finally, along the fast-spreading East Pacific Rise, numerous well-established hydrothermal vents separate out into distinct, spatially separated high-temperature (200- 350°C white and black smokers) and low-temperature (<30°C diffuse emissions) zones with differentiated, well-developed community assemblages (Juniper et al., 1990). These three oceanic vent systems ultimately reflect temporal and spatial variability in fluid mixing between hot, highly reducing "primary" vent-fluids and cold, oxidizing bottom seawater that has penetrated the upper part of the oceanic crust (Juniper et al., 1990). Hence at a global scale, geology and tectonics affect the regional biotic response. Temporal and spatial variability are inextricably interwoven at all levels of observation in modem vent-seep systems, and such variability is manifest at the broadest, regional scale by global differences in faunas that have experienced long-term isolation and geographic separation. For modem hydrothermal vents, any given ridge segment appears to draw its vent-fauna from a shared pool of species; vent fields from different ridge segments have overlapping species pools but the amount of genetic exchange between segments is poorly understood (Van Dover, 1990; Van Dover and Hessler, 1990). This underlying gradient in the probability of dispersal and genetic exchange among populations probably drives the observed variations in composition of vent faunas at global-scales (Van Dover and Hessler, 1990). In some cases, community composition is remarkably similar between vastly separated ridge segments— e.g., >3000 km separates Galdpagos and East Pacific Rise spreading centers, which contain the same dominant vent species (tubeworms, mussels, giant white clam Calyptogena) (review in Van Dover, 1990). In other cases, several distinctive communities exist that reflect specific geographic regions, such as the shrimp-dominated vents at the Mid-Atlantic Ridge, and the symbiotic gastropod-dominated vents at Marianas and Fiji back-arc basins (e.g., Van Dover etal., 1988b; Desbruybres et 125 al., 1994). Geographic barriers to larval dispersal and gene flow across oceanic vent systems exist spatially, "in the form of deep, offset transform faults and hydrothermally quiescent segments of ridge axes" (p. 244, Van Dover, 1990). Large-scale temporal barriers also exist: for example, the plate tectonic history of the Eastern Pacific includes plate consumption and separation of the large ancestral Farallon oceanic plate into the smaller Juan de Fuca and Nazca Plates 25 m.y. ago, when an originally contiguous eastern Pacific spreading center encountered the continental margin of western North America (Atwater, 1989; Duncan and Kulm, 1989). Today, hydrothermal vent communities on the northern ridges (Juan de Fuca, Gorda and Explorer), share few species but have many genera in common with vents on the southern ridge (East Pacific Rise), in an apparent case of endemism, with continued speciation, that originated when the initial ridge segment was split during the Cenozoic (Tunnicliffe, 1988; Van Dover, 1990). Nonetheless, even "isolated" oceanic vent islands such as the west-central Marianas region show evidence for significant faunal interchange with the global mid-ocean ridge system (Hessler and Lonsdale, 1991). Thus, additional mechanisms for dispersal must be sought to explain global faunal congruities. Whale falls, cold-seeps, and dysaerobic settings all might have served to provide "stepping stones" for dispersal for similar taxa across vast oceanic regions, while still allowing for faunal differentiation at the species level to occur within global vent-seep systems. It is probable that the mechanisms controlling global variability among vent-seep regions will only be elucidated through a combined approach: 1) of continued studies of genetic differentiation among modern vent- seep invertebrate populations, and 2) through continued investigations of the physical- chemical-biological characteristics and biogeography of modem and ancient vent-seep systems. 126 VARIABILITY PRESERVED IN THE GEOLOGIC RECORD OF SEEP PA LEOEN VIRONMENTS Although studied sites are consistently characterized by recurring fossil core taxa and unusual carbonates, the ancient cold-seep examples of western North America also are variable with respect to geo-tectonic settings, composition and diversity of associated paleocommunities, and volume and morphology of carbonate masses. This preserved variability is similar to the environmental patchiness observed for modem vent-seep settings (see above), and in the past was likely related to physical-chemical-biological differences in depositional setting from site to site, such as changing strength and composition of seep fluid flow, relative sedimentation rates, seep longevity, and potential for and duration of biotic colonization (Campbell and Bottjer, 1992a). Patterns of faunal- sedimentological variability can be recognized at several scales of observation for the almost two dozen confirmed or suspected cold-seep deposits of the present study. Forearc basin strata that were deposited within this convergent margin setting are well-represented both temporally (~150 m.y., Tithonian - Pliocene interval) and spatially (1600 km along continental margin) (e.g. Figure 1; Chapter 1). Preserved cold-seep deposits within these strata display distinct differences, both within a given fossil seep site (microfacies-scale differences), and among fossil seep sites (outcrop-scale distinctions) in a similar overall tectono-sedimentary system over time. On a larger scale, these western North American fossil chemosynthetic settings can be compared in order to recognize system-wide and global differences in faunal-sedimentologic components and geo-tectonic regimes. Fine-Scale Levels of Variability at Individual Ancient Seep Sites Within-seep variability (cf. Figure 47[1]) can be recognized from faunal- sedimentological patterns in several well-exposed cold-seep deposits (described in Chapter 1) that can be used to decipher coupled fluid-faunal associations preserved at fine-scale levels of observation (e.g., Campbell and Bottjer, 1993b). For example, the carbonate deposits at Paskenta were sampled in transects (Figure 31), and they reveal a distinct spatial zonation of different carbonate fabric types, as defined in Chapter 2. Hand-sample description data from these transects are logged in Appendix II (see also Figures 31,45; note that north and south lenses were once contiguous, based on field observations). These data document that the central portions of the outcrop area are dominated by cement fabrics indicative of relatively vigorous fluid-flow regimes (Appendix II; lower relative micrite:cement ratio). In contrast, the outer margins of the limestone lenses are dominated by micritic fabrics which grade into nodular micrite at mound edges, indicative of more diffuse fluid-flow conditions (Appendix II; higher relative micrite:cement ratio). At Paskenta, and at all other cold-seep deposits thus far discovered, micrite is the dominant carbonate fabric that is associated with evidence for biological activity at these sites, such as associated body fossils, bioturbation, fecal pellets (see also Chapters 1, 2). Conversely, all carbonate morphotypes that have been attributed to vigorous fluid-flow activity (chimneys, doughnuts, concentric conduits) are comprised mostly of cement-rich fabrics (irregular yellow cement, fibrous methane-derived cements, late calcite spar) (see also Chapters 1,2). Hence, fossil cold-seeps record zonation of physico-chemical parameters of the ancient environment that are mirrored by seep-associated fossil distributions. In greater detail, a comparison of microfacies-scale carbonate-fossil associations at Californian (Paskenta, Cold Fork of Cottonwood Creek) and Canadian Arctic sites reveals differences in tube worm-cement associations vs. all other taxa-micrite associations (see also Chapter 2). Specifically, tube worms at Cottonwood Creek are defined by thin, isopachous rims of yellow calcite cement (Figure 23) that coated the organism during life (as in Tunnicliffe and Fontaine, 1987). This unusual, seep-restricted yellow calcite cement (Beauchamp and Savard, 1992; von Bitter etal., 1992) has been attributed to anaerobic, sulfate-reducing conditions in Cretaceous Canadian Arctic seep deposits (Beauchamp and Savard, 1992). Tube worm remains at Cottonwood Creek also are associated with pyrite and microbial linings (e.g., Figure 38), which corroborate interpretations of an apparently localized, reduced, sulfide-rich microenvironment during worm tube growth (Figure 44). 128 The remaining core taxa and almost all faunal associates are restricted to the fossiliferous micrite, the origin of which is uncertain, but these micrite fabrics most likely represent more diffusive fluid-flow and possibly dysaerobic conditions in the mound environment (Figures 44,45,46; discussion in Chapter 2; model in Beauchamp and Savard, 1992). Detailed trace element and additional stable isotopic analyses should further elucidate these relationships. Nonetheless, it appears that fine-scale features are preserved in ancient seeps which may record detailed, coupled fossil-carbonate associations. Meso-Scale (Outcrop-Scale) Levels of Variability among Ancient Seep Fields Despite many similarities, fossil seep carbonates and taxa vary widely among outcrops and localities (cf. Figure 47[2]) in several key respects. For instance, carbonates vary in form and dimensions, ranging from scattered, localized nodules (Figure 48a) to large mounds (Figure 48b), to linear ridges up to 0.5 km in length (Figure 14) (Campbell and Bottjer, 1992a; 1993a). Volume, extent, and morphology of carbonate deposits have been used to describe variable fluid-venting relationships from cold-seep settings associated with modem subduction zones (e.g., Kulm and Suess, 1990). In addition, fossil seep taxa arc variable at the outcrop level in terms of diversity and abundance of core (=chemosymbiotic) vs. associate (=non-chemosymbiotic) taxa present. The faunas generally exhibit a patchy distribution, from scattered to concentrated. They also range in taxonomic diversity, although vent-type taxa are usually present and are stratigraphically restricted with respect to the surrounding siliciclastic strata. In particular, some sites are characterized by great abundances of a virtually monospecific core assemblage (e.g., Vemonia-Timber locality, dominance of Thyasira cf. T. disjuncla\ Figure 9); whereas, other sites arc diverse in their faunal composition (e.g., Bear River locality; Figure 28). The variability in paleoseep faunal and sedimentological characteristics at the outcrop level and between outcrops reflects geologic, biologic, and tectono-sedimentologic differences in the paleoenvironmental setting from seep to seep. These differences likely can be explained by such phenomena as dispersal potential of larvae, seep longevity, structural-stratigraphic 129 Figure 48. Range in carbonate volume from western North American ancient cold-seep sites: (a) small "blebs" from storm-shelf si Its tone of Mio-Pliocene Quinault Formation, Washington (Site #1); and (b) large limestone mound from Bear River Quarry (Site #10, in Eocene siltstone of Cliff Point, Washington). See text for explanation. 130 conduit type, and relative rates of clastic sedimentation versus seep fluid-flow and carbonate production. For western North American ancient seep sites, meso-scale variability among outcrops can be distinguished clearly from fine-scale, microfacies variability within an individual seep; however, it is difficult to explicitly differentiate among the potential mechanisms that likely produced the varying faunal-carbonate patterns. However, a few "end-member" mechanisms can be identified in some cases. For example, Figure 48 illustrates two end-member examples of variability in preserved carbonate volume for the Quinault (Site #1, Figure 48a) and Bear River (Site #10 , Figure 48b) localities. Within the outer storm-shelf siltstone and sandstone deposits of the Quinault Formation, carbonate is preserved as low-volume wispy "blebs," small nodules, and burrow/shell-fill (Figure 48a; Campbell, 1992). Storm-shelf sequences are typified by high rates of siliciclastic sedimentation that, in this case, probably "swamped" the methanc-seepage signal, and therefore allowed preservation of only minor amounts of limestone. The duration of fluid seepage at the Quinault site is unknown. At the opposite volumetric extreme, the massive, quarried limestone deposit at Bear River (Figure 48b) was once the largest limestone resource of western Washington, and originally measured 15 m in thickness, 68 m in length and 38 m in width (Danner, 1966). The deposit is characterized by a diverse and abundant fauna (e.g., Figure 28; Goedert and Squires, 1990; Squires and Goedert, 1991), and by a primarily micritic carbonate fabric throughout. The large volume of micrite present, and the great number of diverse taxa evidently suggest slow, diffuse fluid flow rates, relatively long-lived fluid seepage, and long-term colonization of the Bear River seep habitat, although the exact contribution of each process cannot yet be determined. The West Fork of Satsop River locality (Site #4) is the other volumetrically spectacular seep- carbonate deposit of the present study. It is nearly devoid of fossils altogether, but the site is typified by a cement-dominated carbonate fabric that may indicate relatively vigorous fluid-flow rates that either precluded colonization or removed evidence of earlier 132 colonization. In the West Fork example, it is likely that deposition of a large volume of carbonate was associated with rapid, effusive fluid-flow in the local seep environment. In a final example illustrating that some differentiation of processes and products of environmental variability, the seep-mounds at Vemonia-Timber, Oregon, preserve a striking vertical sequence of carbonate morphotypes that represent increasing relative fluid- flow rates: from nodules and bunch-of-grape concretions at the base of the deposit, to slabs and vertical pipes, to chimney and larger mound features at the top of the deposit (Figure 7; Campbell and Bottjer, 1993b; Nesbitt et al., 1994). The preservation of such a detailed sequence of carbonate morphotype features was likely possible only because siliciclastic sedimentation rates appear to have been very low at this site— glauconite grains are extraordinarily abundant throughout the seep-carbonate and surrounding siltstone, and imply low sedimentation rates and reduced geochemical conditions (e.g., McRae, 1972). Moreover, if the nearly monospecific and abundant presence of large thyasirid bivalves at the Vernonia-Timber locality represents long-term colonization of the seep-habitat, then the lack of faunal diversity at the site may be explained by factors such as limited dispersal from other areas, or local physico-chemical conditions that prevented mound colonization by other taxa. Hence, in several ancient seep-deposits, some meso-scale processes can be elucidated that likely contributed to the observed outcrop-level variability in fossils and carbonates. Large-scale variability in Ancient Cold-Seep Systems of Western North America Although ancient cold-seeps continue to be discovered along the western North American convergent continental margin (J. Goedert, personal communication, 1994), enough sites have been characterized to date to begin a synthesis of large-scale differences across the 150 m.y. duration and 1600 km length of the entire tectono-sedimentary system (cf. Figure 47[3]). Within this suite of known cold-seep deposits, at least three types of regional differences are recognized: 1) large-scale temporal and spatial patterns in seep-site 133 distributions; 2) broad contrasts in geo-tectonic regimes; and 3) changes in dominant mega invertebrate taxaover time. First, pulses in tectonic activity may be indicated by the spatial and temporal distribution of western North American seep deposits recognized to date (Figure 1). The Ccnozoic examples in particular were deposited in forearc settings, and tend to cluster in age around the Eocene-Oligocene boundary, with numerous examples located in Washington State (also, many of Goedert's new localities are late Eocene to early Oligocene in age; personal communication, 1994). Curiously absent are Cenozoic cotd- seep deposits from Oregon (Figure 1). In late Eocene and early Oligocene time (~35 m.y. ago), the offshore Pacific Northwest area was subjected to a significant pulse of volcanic activity in the arc (Duncan and Kulm, 1989, p. 425), which is recorded regionally in the voluminous accumulation of tuffaccous, fine-grained marine sediments. The increase in volcanic arc activity is probably coupled with a period of major convergence that is recorded in the Eocene accretionary tcrrane of the Olympic Mountains (Snavely and Kvenvolden, 1989, p. 3). In general, plate convergence at this time was directed orthogonally to the continent (Duncan and Kulm, 1989), unlike today's orientation of oblique subduction, so that stronger compressional forces within the Eocene-Oligocene forearc may have generated increased fluid seepage into marine depositional basins. As more ancient seep sites are discovered along the northeast Pacific convergent margin, it should be possible to more fully characterize their temporal and spatial relationships to the evolving, active tectonic regime of the time. In addition, other climatic, oceanographic and preservational factors should be considered to fully explain the concentration in numbers of seep sites of Eocene-Oligocene age in the Pacific Northwest. Furthermore, cold-seep deposits of western North America are preserved in ancient forearc strata, unlike modem examples worldwide, which tend to be associated with accretionary prism regimes. For example, cold-seep deposits have not been reported from ancient accretionary prism deposits from California to Washington (e.g., Jurassic-Cretaceous Franciscan Group, Eocene-Miocene Hoh Rocks Assemblage). Given that accretionary prisms dewater large volumes of pore fluids into overlying marine settings during their development (Langseth and Moore, 1990), the absence of seep carbonates in ancient accretionary prisms of western North America may reflect either lack of recognition or a fundamentally low preservation fostered by transient fluid sources and paths within dynamically deforming and accreting wedges (Campbell etal., 1993). Along convergent margins worldwide, many modem cold-seeps are directly associated with oceanic plate convergence fronts and accretionary prism settings (e.g. Suess etal., 1985; Hashimoto etal., 1989; Moore and Vrolijk, 1992). By contrast, the numerous Ccnozoic and Mesozoic fossil cold-seeps of western North America are preserved in forearc settings (e.g., Campbell, 1992; Campbell and Bottjer, 1993a, and references therein), with cold-seep examples from ancient accretionary deposits reported thus far only from the Pliocene Japanese examples (Niitsuma etal., 1989) and an Eocene Barbados deposit (Speed, 1990). Second, broad contrasts in geo-tectonic settings indicate that Mesozoic Californian (Great Valley Group) seep carbonates are preserved in two regionally distinct settings— siliciclastic, turbidite-hosted deposits, and serpentinite, protrusion-hosted deposits— which reflect different fluid sources, fluid-flow regimes, and large-scale tectono-scdimentary controls (Campbell etal., 1993). Campbell etal. (1993) suggested that the relatively numerous turbidite-hosted seeps were quasi-continuous and long-lived throughout the duration of Great Valley forearc sedimentation. Conversely, the less common serpentinite- hosted seeps are interpreted to delineate a specific episode of oceanic plate dewatering and diapiric activity that disrupted "normal" forearc sedimentation in this region during Hauterivian times. In particular, Campbell etal. (1993) described these two different host- geology types as having been controlled by two fundamentally different types of tectonic dislocations that were contemporaneous with carbonate deposition, and which served as active fluid conduits in each host-type situation. These structural features are: 1) syndepositional, regional-scale, extensional faults at the Paskenta and Cold Fork of 135 Cottonwood Creek sites (turbidite-hosted), and 2) structurally controlled protrusive serpentinite mounds at Wilbur Springs and possibly Rice Valley sites (serpentinite-hosted). When considered within the overall tectono-stratigraphic context for the Mesozoic arc- trench system, the turbidite-hosted, Great Valley seep-carbonates occur repeatedly along strike over 120 km of the basin (Figure 29) and span at least 50 million years of geologic history. In a regional sense for the turbidite-hosted cases, fluids generated within or beneath the forearc basin could have escaped upward 1) along lithologically controlled permeable horizons, 2) via faults within the basin, or 3) along the inclined tectonic contact of the forearc sediments against the accretionary wedge (Campbell el al., 1993). In contrast in the Wilbur Springs area, contractional features (e.g., Wilbur Springs Antiform) are associated with voluminous serpentinite protrusion during -Hauterivian to Albian time (Carlson, 1984). These features record a major deformational and hydration event in the hanging wall of the subduction zone. High-pressure metamorphic blocks entrained by the foliate serpentinite breccias during their diapiric rise require an origin deep within the metasomatized peridotite wedge of the upper plate (Campbell et al., 1993). Although now the lone preserved example of serpentine protrusion in the late Mesozoic, numerous serpentine seamounts like the one exposed at Wilbur Springs today may have once dotted a wider region of the outer forearc and trench-slope break, analogous to the field of submarine serpentine extension in the modem outer Marianas forearc basin (Fryer, 1992; Campbell et al., 1993). Therefore, two different geo-tectonic regimes are recorded across the entire suite of western North American cold-seep deposits— quasi-continuous fluid seepage along faults and coarse-sediment layers throughout the basin (turbidite-hosted seeps), and punctuated, event fluid-seepage above serpentine diapiric episodes (serpentinite-hosted seeps). Finally, the entire suite of western North American ancient cold-seeps indicate that changes occurred in dominant fossil taxa during the ~150 m.y. interval of recorded seepage and sedimentation. Specifically, bivalves with modem chemosymbiotic counterparts dominate mid-Cretaceous age and younger seeps; whereas, articulate brachiopods are abundant in cold-seep deposits older than Early Cretaceous in age (e.g., Paskenta [Tithonian, rhynchonellid Cooperrhynchia]; Wilbur Springs and Rice Valley [Hauterivian, rhynchonellid Peregrinella] (Campbell 1994; Campbell and Bottjer, 1994; in press; in review; Sandy and Campbell, 1994). This age-related pattern of bivalve- vs. brachiopod- dominated taxa in western U.S. sites is also preserved in other Phanerozoic cold-seep and hydrothermal vent deposits worldwide (Campbell, 1994; Campbell and Bottjer, in press; in review), and is described in detail in Chapter 4. SUMMARY Spatial and temporal variability is reported from all scales of observation in modem and ancient hydrothermal vent and cold-seep environments. Variability is manifest at all levels: fine-scale (within individual vent-seep site), local or outcrop-scale (among clusters in vent-seep field), and regional or global-scale (across vent-seep tectono-sedimcntary system). Western North American ancient cold-seeps are variable in morphology and volume of carbonate deposits, and in diversity and abundance of faunal constituents. Physical-chemical-biological processes that likely produced such variability include geo- tectonic regime, changing fluid-flow rates, changing sedimentation rates, and the mechanisms and timing of seep colonization. Individual Mesozoic seep-carbonates in California display a distinct spatial zonation of different carbonate fabric types, where the central portions of the limestone deposits generally are dominated by cement fabrics (indicative of relatively vigorous fluid-flow regimes); and, the outer margins of the deposits tend to be micritic (indicative of more diffuse fluid-flow conditions). Micrite also is the dominant carbonate type associated with biological activity at all sites. An exception is the faunal-carbonate affiliation of fossil tube worms. When present in Mesozoic examples, fossil tube worms are associated with 137 sedimentologic indicators of a sulfide-rich, reduced microenvironment, such as yellow calcite cements, and coatings of microbial mats or pyrite. Among-seep variability in faunal and sedimentological characteristics at the meso- scale (outcrop) level for these cold-seep deposits reflects seep-to-seep differences in geology, biology, and tectono-sedimentologic framework. Some examples reflect importance of one or more processes, such as dispersal potential of larvae, seep longevity, structural-stratigraphic conduit type, and relative rates of clastic sedimentation versus seep fluid-flow and carbonate production. Variations in these parameters explain end-member differences in carbonate volume, and diversity-abundance of seep-type taxa, but in many cases, these processes cannot be separated from one another (e.g., such as abundance of taxa owing to seep-longevity vs. ideal geochemical conditions for coexistence of biotas). Together, the suite of western North American ancient cold-seeps cluster spatially and temporally in distinctive patterns, with Mesozoic localities occurring in northern California, and Cenozoic localities occurring mostly in western Washington. Most Cenozoic sites cluster in age around the Eocene-Oligocene boundary, which may reflect an increase in arc-trench activity at this time, or could be caused by other factors. Furthermore, all cold-seep deposits identified in this study are preserved in deep-water, forearc basin sequences. Ancient accretionary prism strata have yet to yield cold-seep deposits in this region. This discrepancy in occurrence may reflect the fundamentally transient nature of fluid release in accretionary prisms, with rapid deformation and dissolution resulting in low preservation potential of prism seep-carbonates. Modem convergent margin cold-seeps typically occur in accretionary prism tectonic regimes. The Mesozoic Great Valley Group cold-seep carbonates and vent-type biotas of northern California occur in two distinct tectono-sedimentary associations: siliciclastic- hosted and serpentinite-hosted settings. The siliciclastic-hosted carbonate deposits are the predominant ancient occurrence and are thought to represent quasi-continuous, large-scale fluid migration out of an evolving forearc basin throughout its history. The sedimentary 138 serpentinite-hosted seep carbonates appear to represent a temporally restricted, punctuated, diapiric event of active expulsion of foliate serpentinite breccias and their associated deeply- sourced fluids onto the outer forearc. 139 CHAPTER 4. BRACHIOPODS AND CHEMOSYMBIOTIC BIVALVES IN PHANEROZOIC HYDROTHERMAL VENT AND COLD-SEEP ENVIRONMENTS INTRODUCTION In life habit and history, brachiopods are predominantly filter-feeding, sessile, epibenthic marine invertebrates with an excellent fossil record that spans the early Cambrian to the present (Rudwick, 1970). During the Paleozoic, brachiopods were diverse and abundant members of most major marine paleoenvironments such as reefs and muddy continental shelves; however, following the Permian-Triassic mass extinction the phylum suffered a considerable decline from which it has never fully recovered (Rudwick, 1970; Thayer, 1986). Living representatives of the articulate brachiopods tend to be restricted to hard substrates in relatively obscure habitats such as the polar oceans, deep sea basins, cryptic reef microenvironments, submarine caves, and coastal fjords (Rudwick, 1970; Rhodes and Thompson, 1993). In addition, brachiopods are absent from the modern hydrothermal vent fauna of the deep-sea, which is taxonomically dominated by annelids, molluscs and arthropods, with tube worms forming a major biomass component (Van Dover, 1990;Tunnicliffe, 1992). In contrast, bivalves have a distinctly different overall Phanerozoic history from that of brachiopods. Bivalves first appeared in the early Paleozoic fossil record as relatively minor components of Paleozoic invertebrate assemblages, but displayed increasing abundance and diversity after the Permian-Triassic mass extinction (e.g., Gould and Calloway, 1980). Living bivalves are commonly found in almost all benthic marine environments and are adapted to a wide variety of substrate niches and trophic strategies 140 (Stanley, 1970). The discovery of chemoautotrophic bacterial symbionts in gill tissues of modem chemosymbiotic bivalves (e.g., "gutless" Solemya\ Cavanaugh, 1985, and references therein) further illustrates the evolutionary plasticity of the group under varied environmental conditions. Living chemosymbiotic bivalves occur in five families (Vesicomyidae, Mytilidae, Solemyidae, Thyasiridae, Lucinidae) and are found in various habitats with reduced sediments (e.g., seagrass beds, oxygen-deficient basins, sewage outfalls), as well as hydrothermal vents and cold-seeps (e.g., Cavanaugh, 1985; Hovland and Judd, 1988). In the geologic record, fossil bivalves with modem chemosymbiotic counterparts have been used in a taxonomic uniformitarian approach to identify ancient cold-seep and hydrothermal vent deposits (e.g., see Chapter 1). However, fossil brachiopods have been considered to be neither typical nor significant faunal components of hydrothermal vent or cold-seep deposits, despite scattered reports in recent years of their presence and even dominance at some Paleozoic and Mesozoic sites (e.g., Lemoine etal., 1982; Noll etal., 1984; Dubd 1988; Beauchamp etal., 1989; von Bitter et al., 1990; Campbell etal., 1993). One reason brachiopods may have been virtually ignored in ancient vent-seep settings is that, until recently, paleontological studies of these paleoenvironments have been focused on comparisons with modem, chemosymbiotic bivalve-dominated faunas (e.g., Clari etal., 1988; Squires and Goedert, 1991; Campbell, 1992; Gaillard etal., 1992; Campbell and Bottjer, 1993a,b). But application of a uniformitarian model for paleoecological analysis of fossil vent-seep taxa is limited for older, pre-Early Cretaceous deposits (cf. Bottjer etal., 1995), where biotic similarities with modern chemosynthetically-based faunas tend to fade with temporal distance from the present (e.g., Poole etal., 1983; Moore etal., 1986; Poole, 1988; Beauchamp and Savard, 1992; von Bitter et al., 1992; Campbell, 1994; Campbell and Bottjer, 1994; in press; in review). Moreover, brachiopods also may have been overlooked in ancient hydrothermal vent or cold-seep paleoenvironments because, until recently (e.g., Campbell and Bottjer in review, and herein), restriction of specific 141 brachiopods to vent-seep deposits had not been demonstrated, so that chance colonization from surrounding habitats could not be ruled out in many cases. This chapter comprises a synthesis, to date, of the changing geologic history of occupation of Phanerozoic hydrothermal vent and cold-seep paleoenvironments by dominant mega-invertebrate taxa, particularly articulate brachiopods and bivalves with modem chemosymbiotic counterparts (also in Campbell and Bottjer, in press; in review). The first part of this chapter is a description of the peculiar depositional settings and characteristics of "certain large, thick-shelled brachiopods in the Mesozoic which occur in anomalous ways and which seem to require a special explanation" (p. 157, Ager, 1965), with special emphasis on Early Cretaceous Peregrinella, a rhynchonellid genus with scattered, global representation from California to Tethyan Eurasia. I explore the origins, adaptations, paleogeography, and potential phylogenetic affinities of Peregrinella, the largest of all Mesozoic rhynchonellids, which has long puzzled paleontologists because of its unusual morphology, stratigraphic occurrence, and distribution patterns. These features now can be explained by the restricted stratigraphic association of Peregrinella with fossil cold-seeps during the Neocomian (-145-130 Ma; Harland etal., 1990) (Campbell and Bottjer, in review). The second part of this chapter is a compilation of occurrence data for dominant mega-invertebrates preserved in 42 fossiliferous Phanerozoic marine deposits interpreted to represent ancient hydrothermal vent or cold-seep habitats (also in Campbell and Bottjer, in press). This compilation reveals that articulate brachiopods, particularly rhynchonellids and terebratulids, were relatively common constituents of vent-seep paleoenvironments from the Devonian through the Early Cretaceous, but were rare in such settings from the Late Cretaceous to the present. In addition, the overall Phanerozoic record of bivalves with modem chemosymbiotic representatives in vent-seep deposits indicates that these molluscs: 1) entered the vent-seep habitat during the Late Jurassic; 2) then overlapped with brachiopods at some sites until the Early Cretaceous; and 3) since the late Mesozoic, 142 chemosymbiotic bivalves have been dominant in vent-seep settings to the present-day. I close this chapter with a discussion of the implications of these findings for brachiopod and bivalve evolution overall in marine paleoenvironments throughout Earth history. PEREGRINELLA: AN EARLY CRETACEOUS COLD-SEEP-RESTRICTED BRACHIOPOD Peregrinella is a globose, coarse-ribbed rhynchonellid brachiopod (Family Dimerellidae) that ranges in age from possibly latest Berriasian to certainly Hauterivian (Biemat, 1957; Ager etal., 1972) (~140-130 Ma; Harland et al. 1990). Peregrinella has long been viewed as a paleontological curiosity because of its distinctive morphology, anomalous stratigraphic associations, and extensive, yet discontinuous paleogeographic distribution throughout Early Cretaceous continental margin areas of western North America and Tethyan Eurasia (e.g., Ager, 1965; 1967; 1968; 1986) (Figure 49). For example, its relatively colossal proportions (to 9.8 cm long, 12 cm wide, 5.6 cm thick; Biemat 1957) qualify Peregrinella as the largest of all Mesozoic rhynchonellids. Its characteristic features (most notably its internal mergifer crura, or elongate calcareous supports for the lophophore) cannot be mistaken for any other genus (Ager, 1965; 1968). This articulate brachiopod has been reported from over a dozen isolated localities in California, France, Italy, Germany, Switzerland, Poland, the Czech Republic, Romania, southwestern Russia, and Tibet (e.g., Gabb, 1869; Viola and Cassetti, 1893; Macovei and Atanasiu, 1934;TrUmpy, 1956; Biernat, 1957; Ager, 1965; Thieuloy, 1972; Berkland, 1973; Hou and Wang, 1984; Sun, 1986) (Figure 49; Table 4). At each of these sites, Peregrinella is nearly monospecific, and occurs in great abundances across all ontogenetic stages. Worldwide, lithofacies associations of Peregrinella-bearing strata are reportedly very similar and are considered anomalous by most workers with respect to the surrounding stratigraphy. Fossils are enclosed in carbonate lenses or blocks of limited 143 Figure 49. Paleogeographic map for the Early Cretaceous (Hauterivian) (from Smith and Briden, 1978) depicting 13 worldwide localities of the fossil seep-restricted, cosmopolitan brachiopod genus Peregrinella (black dots) along the margin of the Tethys Ocean. "+" indicate former technically active areas along continental margins where exact paleogeography is uncertain. From Campbell and Bottjer, in review. Table 4. Summary of heretofore unrecognized seep-suspect aspects of the stratigraphy, sedimentology, structure and biotic associations for 13 ?Late Berriasian-Hauterivian age Peregrinella occurrences worldwide, as reported in original references. Each occurrence represents one to several individual Peregrinella-bearing limestone deposits of the same age, stratigraphy and geotectonic/geographic region. Some original age designations of Peregrinella- bearing strata are probably accurate; others were derived using Peregrinella as a "classic" Hauterivian taxon, and therefore must be viewed with some caution (discussions in TrUmpy, 1956; Biemat, 1957). Fossil seep-associated faunas are defined as 1) taxa commonly affiliated with modem hydrothermal vents or other environments (e.g. Serpula worm tubes), or 2) taxa with extant chemosymbiotic descendants (=core taxa, e.g. certain bivalves in the families Solemyidae, Vesicomyidae, Mytilidae, Lucinidae, Thyasiridae). Standardized ages follow Harland et al. (1990). 145 TA B LE4 LOCATION STRATIGRAPHIC A G E SEDIM ENTOLOGIC, PEREG RINELLA : CON TEX T STRUCTURAL SEEP-ASSOCIATED* CONTEXT FAUNA 1. M usenalp, near Treberen nappe o f the Alps, Switzerland Prdalpes M edians 2. Gongboxue D istrict, Sangxiu Formation N agarze Co., Xizang (Tibet), China 3. E. o f Lhasa, Xainza Co., Xizang (Tibet), China 4. Krondstadt (Brasov), Romania ?Late B enia- hemipelagic chalk; sian to Early ?"oncolites" Valanginian Valanginian Chebo Form ation Valanginian Sinaia Beds, in M oldavian Flysch (internal zone) limestone lenses in gray-yellow (?sulfur) silty shale, sandstone (bathyal) gray limestone lens (20-30 m thick, 200- 300 m wide) in tuffaceous shale; ?microbial lam inae Peregrinella m u lticarin ata subsilvana Peregrinella gongboxueensis Peregrinella cheboensis, P. bifurcata, P. baingoinensis, P. dongqoensis Valanginian- yellow-gray to gray Peregrinella Hauterivian limestone intercalated multicarinata with micaceous sandstone and shale A C \ 5. W ilbur Springs (Colusa Co.), Rice Valley outlier (Lake Co.), N. Califom ia,U.S.A . 6. Sites at Rottier, ChUtillon-en-Diois (Quintet), Ddvoluy, Cum ier, dept. Drfime, Vocontien Basin, SE France Stony Creek Fm., Great Valley G roup, and equivalent Olcostephanus (Jeannoticeras) jeannoti (d'Otb.) zone; Hoplites angulicostatus zone Hauterivian limestone blocks (1- Peregrinella 10 m long, to 5 m wide) in turbidites, adj. to serpentinite diapir, microbial fabric, irregular yellow calcite cement whitneyr, worm tubes, M odiola major, Solemya occidentalis Hauterivian various limestone Peregrinella lenses, ’’blocks" in multicarinata; deep-water calcareous Pseudomiltha shales; along syndepositional faults o r faults assoc, with diapir REFERENCES Triimpy 1956; Boiler 1963; Ager eta l. 1972 H ou Honfei and W ang Jinxing 1984; Sun Dongli 1986 Sun Dongli 1986 T oula 1911. M acovei 1927, in B iem at 1957; M acovei and A tanasiu 1934; Bancila 1941; Onescu 1943; Ager 1965 G abb 1869; Stanton 1895; Berkland 1973; Campbell et al. 1993 Kilian 1913, in B iem at 1957; Thieuloy 1972; Lemone et al. 1982 T A B L E 4 LOCATION STRATIGRAPHIC A GE CON TEX T 7. Bois de la Valette, near M ontpellier, dept. Herault, SE France 8. Raciborsko, near upper Grodziszcze W ieliczka, Carpathian beds (Silesian Unit) M ins., Poland 9. Silesia, Beskidy Range, Poland 10. M ahren, near Freiberg transported, (M oravia), Beskidy origin uncertain Range, Czech Republic 11. Oubinc Valley, W. Kuban, N. Caucasus, Russia 12. W erle District, M ecklenburg, Germany 13. Monte Gargano, Puglia, Italy Hauterivian Hauterivian Hauterivian Hauterivian Hauterivian Hauterivian Neocomian SEDIM ENTOLOCIC, STRUCTURAL CONTEXT "detached limestone blocks" with pyrite in fine-bedded calcareous sandstone isolated limestone block in yellow (?sulfur) argillaceous soil calcareous bed inter calated with mottled marls fossil-rich limestone fragments from borehole PEREG RINELLA : SEEP-ASSOCIATED* FAUNA Peregrinella multicarinata; Serpula recta Peregrinella multicarinata Peregrinella silesica Peregrinella multicarinata Peregrinella multicarinata var. typica, var. pingus Peregrinella multicarinata Peregrinella multicarinata; Serpula recta REFERENCES Roman 1857, in Biem at 1957 Biem at 1957 Ascher 1906, in Biemat 1957; Ager 1965; Sun Dongli 1986 Remes 1903; Biemat 1957 Rcnngartcn 1924; Biem at 1957; Ager 1965; Sm irnova 1972 Biem at 1957; C hryploff 1958 Viola and Cassetti 1893; B iem at 1957 Table 4. continued areal extent, which in tum typically are surrounded by more regionally extensive, deep- water deposits of dark mudstone or gray-black argillaceous limestone (Stanton, 1895; Biemat, 1957; Ager, 1965;Thieuloy, 1972; Berkland, 1973; Hou and Wang, 1984; Sun, 1986; Campbell etal., 1993) (Table 4). Previous explanations for the global occurrence of these isolated, brachiopod-rich carbonates within fossil-poor, fine-grained siliciclastic strata include transport (sliding, slumping) into deeper water from a shallow-water setting, non preservation of a restricted habitat, or deposition atop sea-mounts with the brachiopods seen as "hopping" across the ocean basins (e.g., Biemat, 1957; Ager, 1965; 1967; 1986; Hou and Wang, 1984). Recently in northern California and southeastern France, several Mesozoic Peregrinella-bearing limestone deposits have been reexamined and interpreted as fossil cold-seeps (Lemoinc etal., 1982; Campbell etal., 1993). The pertinent details of these studies arc outlined below. The dozen other Early Cretaceous, geographically widespread deposits which contain Peregrinella (Figure 49) contain heretofore unrecognized seep- suspect features which are summarized from the literature in Table 4 (see also below). It is proposed herein (and in Campbell and Bottjer, in review) that all worldwide Peregrinella occurrences record restriction of this brachiopod genus to a particular, unusual habitat- ancient cold-seeps— during the ~10 Ma Neocomian interval of the Early Cretaceous. Early Cretaceous Paleoenvironments of Pereerinella The Wilbur Springs and Rice Valley Localities, Northern California. Sedimentary strata at Wilbur Springs (Colusa County) and Rice Valley (Lake County), northern California (Figures 24, 26,49; Table 4), were deposited as fine-grained, siliciclastic turbidity flows in a narrow, deep forearc basin (-Great Valley Group) that was situated parallel to the convergent continental margin of western North America during the Mesozoic (e.g., Ingersoll and Dickinson, 1981) (general geologic description of sites [#7,8] discussed in Chapter 1). Several scattered, brachiopod-rich, white limestone "blocks" (1-10 m long, up to 5 m wide) occur at both localities; the limestones are 148 surrounded by turbidites and also are closely affiliated with foliate serpentine breccias (=sedimentary serpentinites) (Berkland, 1973; Carlson 1984). At the better-exposed Wilbur Springs site, the serpentinites have been interpreted as the products of rising diapirs which pierced the submarine sea floor of a deep marine forearc basin, driven by dewatering of the underlying, subducting oceanic plate (Carlson, 1984). The intimately associated fossiliferous carbonates are inferred to have formed atop or adjacent to the serpentine diapir as it released reduced fluids to the surrounding seafloor (Campbell etal., 1993; Chapters 1, 3). A modem analogous tectonic regime, associated submarine fluid seepage, and seep- carbonates occur today above active serpentine diapirs in the outer Marianas forearc (e.g., Haggerty, 1987; Fryer, 1992). The fossiliferous Early Cretaceous limestones of Wilbur Springs and Rice Valley, California, arc typified by great abundances of the rhynchonellid brachiopod Peregrinella whitneyi Gabb 1869. In addition, the strati graphically restricted core fauna includes fossil worm tubes and the bivalves Modiola major, Solemya occidentalis and Lucina colusaensis (Stanton, 1895; Berkland, 1973; Campbell etal., 1993), which are inferred to have been chemosymbiotic (Campbell etal., 1993). In places, articulated specimens of Peregrinella whitneyi are closely associated with mussels (Modiola major) (Figure 50). The Rice Valley locality consists of several scattered small outcrops, whereas the Wilbur Springs locality has been quarried so that outcrops once exposed over several tens of meters now consist of piles of loose rubble. Nevertheless, faunal counts were made at Wilbur Springs from the surfaces of random, loose, fossiliferous Wilbur Springs blocks (e.g., Figure 50) to estimate relative abundances of Peregrinella and Modiola. From these counts Peregrinella ranges from 500-5,000 individuals/m2, and Modiola ranges from 0-80 individuals/m2 (Campbell and Bottjer, in review). Evidence preserved in the carbonates for the presence of sulfide and methane— the geochemical fuels of chemosynthesis— include micritic microbial fabrics, pyrite-coated corrosion surfaces, irregular yellow calcite, and fibrous methane-derived cements typical of 149 Figure 50. Hauterivian rhynchonellid brachiopod Peregrinella whitneyi Gabb 1869 (right) and core mytilid Modiola major (left) from Wilbur Springs, California ancient cold-seep. Note internal mold of muscle scar near umbo of Modiola. Abundant fragments and broken, articulated specimens of Peregrinella in micrite matrix. Length of mussel = 2.5 cm. 150 ancient seeps (cf. Beauchamp and Savard, 1992; Campbell etal., 1993; Chapters 1, 2). The age of the Wilbur Springs site is likely Hauterivian, based upon the stratigraphic position of the limestone blocks just above the highest occurrence of the Valanginian bivalve Buchiapacifica in the surrounding Great Valley Group turbidites (Lawton, 1956; Imlay, 1959; Jones etal., 1969). By analogy, the age of the.less well-exposed Rice Valley carbonates is inferred to be Hauterivian, since Peregrinella is present and Buchia is absent from this deposit. The Rottier, Chatillon-en-Diois, Devoluy and Curnier Localities, Southeastern France. During the Late Jurassic through Early Cretaceous interval in southeastern France, fine-grained hemipelagic and pelagic sediments were deposited in deep marine basins of the Ligurian Tethys, the western extensional arm of the greater Tcthys Ocean (Lemoine et al., 1982; 1986). The rifted opening of the Ligurian Tethys separated European and African geo-tectonic domains and produced basin subsidence, block faulting, and regional hydrothermal activity under the European passive margin (Lemoineetal., 1982; 1986; Robertson and Boyle, 1983). Lemoine etal. (1982) presented an inventory of a variety of Jura-Cretaceous geologic units in the western Alps region which appear to preserve evidence for submarine paleo-hydrothermalism. Specifically, during the Hauterivian, the muddy "bassin vocontien" of southeastern France (Ferry, 1984) was disrupted by a series of synsedimentary faults and/or fault-bounded diapirs, where unusually fossil-rich lime muds accumulated with abundant Peregrinella multicarinata Lamarck 1819 (Thieuloy, 1972; Lemoine etal., 1982) (Figure 49; Table 4). In an early biostratigraphic study of the Tentilles h Pdrt-grinelles," Thieuloy (1972) considered beds at Rottier and Chattilon-en-Diois to represent a "peculiar sedimentation zone which may [have] occurred] on a shoal, widely open to the influx of the surrounding pelagic area" (p. 6, Thieuloy, 1972). However, Thieuloy (1972) avoided investigation of any Peregrinella horizons exposed in structurally complex areas because of their lack of stratigraphic continuity. For example, there has been no detailed analysis to date of the 151 Cumier locality, which is situated along a bundle of synsedimentary faults (e.g., faille de Trente-Pas-Condorcet) associated with the flank of an active Cretaceous diapir (Thieuloy, 1972). Overall, the Peregrinella-bearing carbonates contain a relatively diverse and abundant fauna which includes ammonites, mesogastropods, and Pseudomiltha, a lucinid bivalve; these beds are among the most fossiliferous of all of southeastern France (Thieuloy, 1972; Lemoine etal., 1982). In general, across the preserved stratigraphic record of Mesozoic rifting within the passive continental margin of southeastern France, anomalous fossil concentrations occur sporadically thoroughout the muddy, deep-marine basinal deposits. For example, Lemoine etal. (1982) considered both the Hauterivian Peregrinella horizons, described above, and older Callovian bivalve-sponge constructions near Beauvoisin to represent submarinc- spring "oases de vie" (life oases). The latter deposits recently have been studied in detail by others and their fossil seep (=pseudobioherm) origin confirmed (Gaillard etal., 1985; 1992; Gaidon etal., 1988; Rolin etal., 1990). The Early Cretaceous Peregrinella limestones have yet to be studied to the same degree as the Late Jurassic bivalve-sponge pseudobioherms, but there are some indications from earlier reports that the younger, brachiopod-rich carbonates preserve evidence of sulfides and fabrics typical of fossil cold- seep deposits (e.g., Thieuloy, 1972; Table 4). Other Localities of Eurasia. Based on the fossil seep-identification criteria outlined previously, Table 4 summarizes the hitherto unrecognized seep-suspect aspects of the stratigraphy, sedimentology, structure, and biotic associations for 11 additional known Peregrinella occurrences throughout Europe and Tibet (Figure 49), as determined from literature reports. Most of the Peregrinella-bearing beds consist of isolated carbonates of limited areal extent surrounded by regionally widespread, deep-water, fine-grained siliciclastic or marly sequences. Most of the original paleontological reports contain few detailed descriptions of associated sedimentology, however certain seep-suspect features noted for some deposits include presence of ?microbial laminites, pyrite, and yellow 152 (sulfur-rich?) carbonate or siliciclastic deposits (Table 4). In addition, some benthic taxa found with Peregrinella are common to modem hydrothermal vents and cold-seeps, such as serpulid worm tubes and lucinid bivalves. Implications for Brachiopod Paleobiology Phylogenetic A ffinities of Peregrinella. Several rhynchonellid brachiopods from the Paleozoic and early Mesozoic bear remarkable morphologic similarity to Neocomian Peregrinella. Ager (1968) observed that "although externally these Devonian [forms] [Dzieduszyckia, 1 Eoperegrinella ] are very close to the Triassic genus [Halorella ], transverse sections showed an even more remarkable resemblance to the Cretaceous genus Peregrinella . . . from [the] French Alps" (p. 60-61). Indeed, in dispute for many years have been the phylogenetic affinities among Dzieduszyckia (Late Devonian), Eoperegrinella (="Halorella") (Late Devonian), Halorella sensu stricto (Triassic), and Peregrinella (Early Cretaceous) (e.g., Termier, 1938; Termier and Termier, 1949; Ager, 1965; Biemat, 1967; Ager, 1968; Cloud and Boucot, 1971; Ager et al., 1976). It now appears that these morphologically similar rhynchonellids also share, to some extent, a common palcoenvironmental habitat in chemosynthetically based settings (details below). For example, Dzieduszyckia (Famennian) of Nevada and Mexico is now recognized from barite-rich sedimentary exhalative deposits (i.e., low-temperature hydrothermal "white smokers") in extensional settings (e.g., Poole etal., 1983; Noll etal., 1984; Dubd, 1988; Poole, 1988; Poole etal., 1991). Eoperegrinella (also described as "Halorella" and Dzieduszyckia by early workers) (Famennian) occurs in anomalous, isolated carbonate lenses surrounded by deep-water turbidites in the central Hercynian massif of Morocco (Termier, 1938; Termier and Termier, 1949; Hollard, 1967; Hoi lard et al., 1970; Hollard and Morin, 1973; Ager etal., 1976; Pique and Michard, 1989). Unfortunately, no overall consensus on the systematic classification of Paleozoic and Mesozoic rhynchonellid families has emerged (Harperetal., 1993) so that the phylogenetic affinities remain obscure among apparently vent-seep-related brachiopod 153 groups. Ager et al. (1972) acknowledged the antiquity of the Eoperegrinella-Peregrinella "lineage" and lamented the lack of any brachiopod genera in the latest Paleozoic which appear to be closely related to these rhynchonellids. Some morphologically similar Mesozoic genera from other habitats that may help to fill the gap include Carapezzia, Anarhynchia, and Peregrinelloidea (Ager et al., 1972). Similarly, Ager (1968) identified potential affinities between Peregrinella and Halorella s.s. The latter represents a cosmopolitan rhynchonellid genus of Late Triassic age that occurred in various paleoenvironments from the Alps to central-southeast Asia. Hence, with further study, part of the phylogenetic history of this larger group of ?related rhynchonellids may turn out to pass in and out of vent-seep habitats during the course of the Phanerozoic. Adaptations of Brachiopods to Chemosynthetic Settings. The probable restriction of Peregrinella to Early Cretaceous cold-seeps leaves open to question the potential life strategies of this as well as other ancient vent-seep-associated brachiopods. It is probable that Peregrinella grew to large sizes in such great abundances because of a richly organic, localized food supply generated by fluid seepage and bacterial chemosynthetic activity at the Tethyan sites. Peregrinella probably represents either an extinct chemosymbiotic brachiopod or, like modem articulates, filtered the presumably high concentrations of free-living bacteria from seep-suspensate. Living brachiopods are not known to harbor chemosymbiotic bacteria in their tissues. However, modem articulates appear to be well-adapted to environmental conditions typical of vent-seep settings. They commonly are termed "metabolic minimalists," and some have been reported from areas of relatively low oxygen and high sulfide concentrations, or have been shown experimentally to be sustained under these "stressed" conditions (Rudwick, 1970; Hammen, 1977; Thayer, 1986;Tunnicliffe and Wilson, 1988; Curry etal., 1989; James etal., 1992). For example, modem terebratulids have recently been discovered in great abundances at a modem cold-seep in Monterey Bay, California, in association with carbonate crusts, seeping methane, and sulfide-rich fluids along the submarine trace of the San Gregorio 154 Fault (Barry etal., 1993; Orange etal., 1993; personal observations, 1993). Hence, it seems likely that many ancient vent-seep-associated brachiopods also were at least sulfide- tolerant if not sulphophilic and chemosymbiotic. Environmental Origins of Brachiopods in Chemosynthetic Settings. Tunnicliffe (1992) recognized four broad sources from which the modem hydrothermal vent invertebrate fauna (over 200 species) originates: "taxa from the surrounding deep-sea, generalized opportunists, sulphophilic biotas, and an endemic [relict], in situ fauna" (p. 346). Whereas some other fossil vent-seep-articulates may have been derived from surrounding paleoenvironments or entered chemosynthetic settings as generalized opportunists, Cretaceous Peregrinella does not appear to have colonized the fossil seep- habitat via these routes, because the genus appears to be restricted to seep deposits worldwide during the Ncocomian. Therefore, Peregrinella may have been sulphophilic, or at least sulfide-tolerant, but was not necessarily chemosymbiotic. Finally, restriction of Peregrinella to cold-seep deposits also might be explained by the status of this brachiopod as a Mesozoic relic of a long-lived "lineage" of vent-seep associated rhynchonellids from the Paleozoic (cf. McLean, 1981; Newman, 1985), but major gaps in the stratigraphic record between these Paleozoic rhynchonellid occurrences (i.e., from Famennian forms [Eoperegrinella , Dzieduszyckia] to Neocomian Peregrinella), and the lack of rigorous phylogenetic analysis for these groups preclude a clear resolution of the environmental origin(s) of vent-seep-brachiopods at present. Paleogeography and Mode of Larval Development. A fossil cold-seep interpretation succinctly resolves the problem of the discontinuous paleogeographic distribution of Peregrinella-bearing limestones worldwide (Ager, 1965), because it accounts for the origins of the deposits as the products of localized, methane-rich fluid seepage to the deep sea floor (cf. Ritger et al., 1987). Unresolved, however, is the manner of dispersal for Peregrinella across the Tethys Ocean (Figure 49) over the ~10 million year duration of the existence of the genus. Ager's (1986) hypothesis of sea-mount-hopping by 155 certain Mesozoic brachiopods to explain their disjunct and far-flung paleogeographic patterns can be modified to take into consideration the unusual paleoenvironmental setting o f Peregrinella. Current hypotheses invoked to explain the distribution of modem vent- type taxa typically model the vents along oceanic ridges as "stepping stones" for organism dispersal (e.g. Hecker, 1985; Van Dover, 1990; Lutz and Kennish, 1993). An examination of age designations for the 13 Peregrinella occurrences around the globe (Table 4) suggests that the oldest populations may have originated in the western Alps and Tibet (Figure 49). Regionally, this apparently seep-restrictcd brachiopod seems to have occupied Tethyan margin areas of Europe throughout the duration of its existence, with its most extensive geographic representation in Tethyan cold-seeps during the Hauterivian. Tectonically, this time interval represents the greatest extent of Ligurian Ocean extension and basinal sedimentation, before this smaller arm of the Tethys Ocean began to close in the late Cretaceous to make room for the expanding central Atlantic Ocean and onset of northward migration of Africa (Lemoine et al., 1986). Meanwhile, Tibetan forms originating in the Valanginian may have dispersed across the Pacific along unknown routes to reach California by Hauterivian times. The larval mode of fossil articulates is not known with certainty because early stages of development are not preserved in the brachiopod shell (James et al., 1992). However, all living articulate brachiopods have nonplanktotrophic larval development; therefore, capabilities for dispersal are somewhat limited (Valentine and Jablonski, 1983; James etal., 1992). Nonetheless, Valentine and Jablonski (1983) have postulated that some Paleozoic articulate brachiopods may have been planktotrophic based on paleobiogeographic diversity patterns, although many of these lineages subsequently must have died out following the end-Permian mass extinction. Planktotrophy in Peregrinella could readily explain its patchy, circum-Tethys distribution. However, planktotrophy is not required for the spread of Peregrinella across widely separated fossil seeps during the Neocomian since extended organism dispersal occurs along modem hydrothermal vent 156 "islands" in the deep sea, where benthic faunas display both larval-mode types (Lutz and Kennish, 1993). BRACHIOPODS AND CHEMOSYMBIOTIC BIVALVES IN PHANEROZOIC VENT- SEEP SETTINGS Data and Results Figure 51 summarizes data on occurrences of fossil brachiopods as well as bivalve genera with extant chemosymbiotic descendants from 37 fossiliferous hydrothermal vent and cold-seep deposits of Ordovician to Pliocene age. Each single recorded "appearance" in Figure 51 represents one to several individual ancient hydrothermal vent or cold-seep deposits (criteria for recognition described previously) of similar age, stratigraphy and geo- tectonic/geographic region. For example, the methane seeps of Late Cretaceous age exposed in Colorado and Kansas number in the hundreds to thousands, and occur in Pierre Shale outcrops over a distance of hundreds of kilometers, but are included here as one occurrence (Figure 51). Data collection revealed an additional five fossiliferous hydrothermal vent sites (high-temperature "black smokers") that predominantly preserve only tube worms and are therefore excluded from Figure 51. Of the appearances plotted, many have previously been identified as fossil vent-seep deposits, and others are included through an interpretation of published data on these sites (referenced for each site in the caption of Figure 51). The lack of identified vent-seep deposits during the Permian and Triassic might be explained by the formation of Pangaea at this time, and subsequent reduction of global plate tectonic activity, which also might have led to a reduction in compression-related fluid seepage within marine basins worldwide. Of the 37 fossiliferous Phanerozoic vent-seep occurrences included in Figure 51, 20 have been reported to contain articulate brachiopods. The brachiopods are predominantly rhynchonellids or terebratulids, are nearly monospecific at each site, occur in great abundances, and all but one of the 20 deposits with brachiopods are as old or older 157 Figure 51. Occurrence of brachiopods as well as bivalves with extant chemosymbiotic descendants in Phanerozoic hydrothermal vents and cold-seep paleoenvironments (ages after Harland et al., 1990). Brachiopod occurrences documented from the Ordovician (O) ("methane" pockmarks and mounds, Ontario, Canada: Hovland, 1989), Silurian (S) (cold- seep, Hercynian Massif, Morocco: Ager etal., 1976), Devonian (D) ([low-temperature hydrothermal vents, Sonora, Mexico: Poole et al., 1983; 199 Noll etal., 1991] [low- temperature hydrothermal vent, Nevada, U.S.A.: Dubd, 198;- ’ oole, 1988] [cold-seeps, Hercynian Massif, Morocco: Ager et al., 1976]), Mississippian (M) ([low-temperature hydrothermal vent, Newfoundland, Canada: von Bitter etal., 1990; 1992] [low- temperature hydrothermal vents. Nova Scotia and New Brunswick, Canada: Boehner et al., 1989; McCutcheon et al., 1989; von Bitter et al., 1992]), Pennsylvanian (Pn) (low- moderate-temperature hydrothermal vent, Alaska, U.S.A.: Moore etal., 1986), Jurassic (J) (Malm) (methane seep, California, U.S.A.: Campbell and Bottjer, 1993; Campbell et al., 1993), Early Cretaceous (EC) ([cold-seeps, California, U.S.A.: Berkland, 1973; Campbell etal., 1993] [cold-seeps, Xizang (Tibet), China: Hou and W ang,1984; Sun, 1986] [cold-seeps, southeastern France: Thieuloy, 1972; Lemone etal., 1982] [cold-seep, Carpathian Mountains, Poland: Biemat, 1957] [cold-seep, Puglia, Italy: Biemat, 1957] [cold-seep, Swiss Alps: Biemat, 1957; Ager, 1965] [cold-seep, Romania: Biemat, 1957; Ager, 1965] [cold-seep, Caucasus Mountains, Kuban, Russia: Renngarten, 1924; Biemat, 1957] [cold-seep, former Czechoslovakia: Biemat, 1957; Ager, 1965] [methane seeps, Canadian Arctic: Beauchamp etal., 1989]), and Tertiary (T) [cold seep, Nagano, Japan: Tanaka, 1959]. Bivalve occurrences documented from the Jurassic (Malm) ([cold-seeps, southeastern France: Gaillard et al., 1985; Rolin et al., 1990] [methane seep, California, U.S.A.: Campbell and Bottjer, 1993; Campbell et al., 1993] [methane seep, Antarctic Peninsula: Kelly et al., in press]), Early Cretaceous ([cold-seeps, California: Campbell and Bottjer, 1993; Campbell et al., 1993] [cold-seep, southeastern France: Thieuloy, 158 Figure 51, continued 1972]), Late Cretaceous (LC) ([cold-seeps, California, U.S.A.: Campbell etaL, 1993; Elder and Miller, 1993] [methane seeps, Colorado, Kansas, U.S.A.: Elias, 1931; Arthur et al., 1982; Howe, 1987]), and Tertiary ([methane seeps, Washington, U.S.A.: Goedert and Squires, 1990; Campbell, 1992; Campbell and Bottjer, 1993; Goedert and Campbell, in press ([cold-seep, Oregon, U.S.A.: Campbell and Bottjer, 1993] [cold-seep, eastern Barbados: Speed, 1990] [methane seeps, Apennines, Italy: Clari etal., 1988; Aharon et al., 1993] [cold-seep, Nagano, Japan: Tanaka, 1959] [cold-seeps, Nigata, Japan: Kanno et al., 1989] [cold-seep, Kanagawa, Japan: Niitsuma etal., 1989]). No hydrothermal vent or cold-seep deposits are yet reported from Permian (P) orTriassic (Tr) strata. "Methane" designation indicates use of stable isotopic data in original study. Each single recorded appearance represents one to several individual ancient hydrothermal vent or cold-seep deposits (criteria for recognition described in text) of same age, stratigraphy and geotectonic/geographic region (e.g., methane seeps of Late Cretaceous age in Colorado and Kansas are numerous and occur in Pierre Shale outcrops over a distance of hundreds of kilometers, but are included here as one appearance). 159 1 ■V ■ ’ . * ■ * / S ■ S * S - S ■ S- S ' . S - % " _ S ■ _ S % ■ _ % ' . S ' S VVVV ■ /■ V 'V * /■ • ■ ■ W W W W * W l W i — i — r i 12 S « V ^ * \ * % ■ % ■ % ■ \ i * L > % ■ \ ■ % ■ % ■ * . *S • \ H 0 i — i — i — r 4 8 12 Brachiopods Chemosymbiotic Bivalves Number of Appearances in Hydrothermal Vents and Cold Seeps than Early Cretaceous in age. The single Tertiary cold-seep occurrence in Japan with the brachiopod Coptolhyris sinanoensis is dominated numerically by bivalves with modem chemosymbiotic representatives (Tanaka, 1959). The brachiopods that occur at Paleozoic vent-seep sites include Dubaria (Ager et al., 1976), Dzieduszyckia (Cloud and Boucot, 1971; Poole, 1988; DutxS, 1988; Poole etal., 1983; 1991; Noll etal., 1984), Eoperegrinella (Ager et al., 1976), and Beeclteria (Boehner et al., 1989; McCutcheon et al., 1989; von Bitter etal., 1990; 1992). Mesozoic vent-seep brachiopods include Cooperr/iynchia, Modestella, and Peregrinella (Lemoine etal., 1982; Campbell eta l., 1993; Sandy, 1990; Sandy and Campbell, 1994). The greatest number of vent-seep appearances with brachiopods for any one time is during the Early Cretaceous (Valanginian-Hauterivian) (Figure 50), a time when the apparently seep-restricted Peregrinella was relatively common worldwide (Campbell and Bottjer, in review). Bivalve genera with extant chemosymbiotic descendants are present in 21 of the 37 Phanerozoic appearances (Figure 51). For this study, a fossil bivalve genus with extant chemosymbiotic descendants is defined as a genus which exists in modem environments with chemosymbiotic representatives. A report of "vesicomyid-like bivalves" in a Devonian hydrothermal vent deposit from the Urals of Russia (Kuznetsov etal., 1988; 1990) is not included in this compilation; further systematic work is needed on these specimens, because the range of the Family Vesicomyidae is currently known to extend into the geologic past only to the late Eocene (Squires and Goedert, 1991). Thus, the oldest occurrence of bivalve genera with extant chemosymbiotic descendants in an ancient hydrothermal vent or cold-seep deposit appears to be an unnamed lucinid in Late Jurassic (Bathonian-Oxfordien) cold-seeps from southeastern France (Figure 51; Gaillard etal., 1985). Fossil bivalves with modem chemosymbiotic representatives and articulate brachiopods overlap in their distribution in vent-seep deposits, particularly during the Late Jurassic-Early Cretaceous interval (Figure 51). In some cases where both groups are present, brachiopods dominate the vent-seep fossil assemblage (e.g., deposits at Wilbur Springs and Rice Valley, California); in other cases of overlap, fossil chemosymbiotic bivalves represent the dominant taxa at a site (e.g., Paskenta, California). The peak in distribution of chemosymbiotic bivalves in vent-seep habitats is probably in present day settings (not plotted); however, these molluscs are well-represented in mid-late Mesozoic and Cenozoic vent-seep deposits as well (Figure 51). All of the fossil chemosymbiotic bivalve appearances examined in this study were found to be from cold-seep deposits (Figure 51); lucinids and thyasirids are most abundant. Only three ancient, fossiliferous (tube worm-rich) hydrothermal vent sites of Jurassic or younger age are known (excluded from Figure 51); none of these high-temperature "black smoker" deposits contain bivalves or brachiopods (Oudin and Constantinou, 1984; Oudin etal., 1985; Haymon and Koski, 1985). Discussion and Implications of the Contrasting History of Brachiopods and Chemosymbiotic Bivalves in Vent-Seep Paleoenvironments As in so many other Phanerozoic marine paleoenvironments (Rudwick, 1970), articulate brachiopods are well-represented in hydrothermal vent and cold-seep habitats during the Paleozoic and the early to mid-Mesozoic, but subsequently are comparatively rare in younger settings (Figure 51), with only one post-Early Cretaceous rhynchonellid occurrence, and two known modern cold-seep sites that contain terebratulids (Hovland and Judd, 1988; Barry etal., 1993). Furthermore, fossil bivalve genera with extant chemosymbiotic descendants become dominant over brachiopods in ancient vent-seep settings in the late Mesozoic (Figure 51). For non-vent-seep marine paleoenvironments, the contrasting pattern of dominance between brachiopods and bivalves in the Phanerozoic paleontological record has been extensively documented, but explanations for the cause(s) of this change have been controversial. It is generally agreed that the long-term, post-Paleozoic shift in level- bottom, benthic marine paleocommunity composition— from brachiopod- to bivalve- dominated— was certainly at least in part caused by the Permian-Triassic boundary mass extinction, which preferentially selected against articulates. However, disagreement exists as to the link, if any, between relative abundance changes between the two metazoan groups over time. Some maintain that the shift in dominance was a consequence of brachiopods and bivalves following separate evolutionary paths punctuated by differential resetting of diversities by independent random events (i.e., mass extinctions; Gould and Calloway, 1980). Others have proposed that more deterministic factors such as brachiopod adaptations and their biotic interactions were more important (i.e., Phanerozoic increase in bioturbation and predation, direct bivalve-brachiopod interactions, etc.; e.g., Thayer, 1986; Rhodes and Thayer, 1991; Rhodes and Thompson, 1993; Sepkoski, 1994). Although the classic problem of deciphering which factors contributed to the Phanerozoic decline of brachiopods and the not-necessarily-coupled rise of the bivalves remains contentious, this study suggests a variety of new avenues of research in a previously unstudied paleoenvironmental setting where both groups have had historical representation. For example, in the vent-seep habitat local chemosynthetic primary production allows for partial ecosystem decoupling from surficial photosynthetic processes. Thus, hydrothermal vents and cold-seeps have been considered to be relatively resistant to the effects of mass extinctions, and are thought to serve as refugia for relict taxa today (e.g., McClean, 1981; Newman, 1985; Kauffman and Howe, 1990). From this study, certain seep-associated rhynchonellid brachiopods appear in the record both before and after the end-Permian mass extinction; however, it is difficult to assess if these seep "lineages" survived the event better than brachiopods from other paleoenvironments because of the significant hiatus in vent-seep appearances before and during the extinction interval. However, it is probable that the demise of Cretaceous Peregrinella in particular was caused by factors other than a mass extinction because of the disappearance of this genus during the Hauterivian, a time not associated with any of the major mass extinction events (Raup and Sepkoski, 1982). 163 Moreover, the vent-seep setting introduces the novel factor of chemosymbiosis into any set of adaptive explanations for the contrasting brachiopod-bivalve history in this environment, worthy of further exploration. For example, brachiopods always may have been uniformly non-chemosymbiotic, but some perhaps were well-suited to Paleozoic and Mesozoic vent-seep settings as "metabolic minimalists" (i.e., adapted to low-oxygen and high-sulfide concentrations; e.g., James etal., 1992, and references therein). Possibly, the Mesozoic entrance of chemosymbiotic bivalves to the vent-seep habitat allowed them to become competitively superior to brachiopods in these environments. Therefore, the similarity of brachiopod and bivalve histories for both vent-seep and other, non-vent marine paleoenvironments during the Phanerozoic could be fortuitous. Within both types of settings, each group's history ultimately may have been influenced by distinctly different mechanisms. However, any explanations of change from brachiopod to bivalve dominance within Phanerozoic vent-seep settings should incorporate the Mesozoic interval where both metazoan groups mutually occurred in some seep deposits (Figures 50, 51). During this time, bivalve genera with living chemosymbiotic counterparts first appear in vent-seep habitats and they co-occur with brachiopods at three late Jurassic to Early Cretaceous sites (Thieuloy, 1972; Campbell and Bottjer, 1993; Campbell etal., 1993), before chemosymbiotic bivalves became the dominant benthic invertebrate faunal components at most younger chemosynthetically based localities. For example, co-appearance of mytilids with Peregrinella at some of the cold-seep sites is of interest, because studies of modem mussels demonstrate that they can out-compete articulate brachiopods for space (Thayer, 1985). However, preliminary abundance analysis of Peregrinella and the mussel Modiola major at the Wilbur Springs site (e.g., Figure 50) indicates that Peregrinella appears to dominate Modiola at this particular locality. Thus, one hypothesis for the demise of Peregrinella in particular is that further evolution of competitive interactions between Peregrinella and core taxa, such as these mussels, ultimately caused the demise of these 164 rhynchonellids in cold-seep settings. However, detailed studies of the paleoecological relationships between Modiola and Peregrinella at other seep sites, and investigations of other potential bivalve-brachiopod associations in this transitional late Jurassic to Early Cretaceous interval are necessary. Studies of seeps with brachiopod-chemosymbiotic bivalve overlap may provide key evidence toward understanding causes for the contrasting history of dominance of each of these metazoan groups within chemosynthetic settings, and the degree to which their history in this distinctive habitat is coupled with the overall history of the brachiopods and bivalves in Phanerozoic marine paleoenvironments. Continued study of ancient cold-seeps and hydrothermal vents promises to lead to the discovery of additional organisms, such as Peregrinella^ which do not have representatives in modem oceans. Ultimately a detailed Phanerozoic history of metazoan occurrences in cold-seep and hydrothermal vent settings will be possible. Such a biotic history for chemosynthetic settings will be invaluable for comparison with well-studied, photosynthetically based ecosystems, such as reefs (e.g., Fagerstrom, 1987) or soft- substrate, level-bottom settings (e.g., Bottjer and Ausich, 1986). Detailed histories of mctazoans that inhabited chemosynthetic and/or photosynthetic habitats through time will lead toward a better understanding of the processes, biotic and abiotic, that have affected life's development through the Phanerozoic. 165 CHAPTER 5. CONCLUSIONS 1) Jurassic-Pliocene age siliciclaslic strata deposited in forearc basins along the convergent margin of western North America were the targets of a search for ancient cold- seep paleoenvironments. Anomalous carbonates and associated mega-invertebrate fossils inferred to have been chemosymbiotic were the sedimentologic and faunal criteria used to identify eight hitherto unknown cold-seep deposits. Fourteen additional sites reported on by others in northern California, Oregon and Washington bring the present total of known cold-seep deposits in this region to 22 localities that span ~150 m.y. of subduction-related geologic history, and that include the oldest (Tithonian age) yet reported ancient cold-seep from a convergent margin tectonic setting. These deposits are broadly analogous to modern methane seep environments offshore of Oregon today. 2) Core taxa (= descendants are chemosymbiotic in modem vent-seep settings) are similar across all ancient cold-seeps of western North America. This observation is consistent with modern vent-seep studies, where similarities at both higher and lower taxonomic levels imply a common origin and similar subsequent evolutionary history. Fossil core taxa identified include: probable pogonophoran tube worm remains, and the bivalves Solemya, Acharax, Calyptogena, Vesicomya, Thyasira, Modiola, Modiolus, Lucina, and Lacinoma. Recurring associate taxa (= non-obligate taxa common in modem and ancient vent-seep settings) in these seep deposits include: anomuran decapods (inferred from fecal pellet remains), serpulid worm tubes, and the gastropods Margarites, Provanna, hyalogyrinids, and various limpets. 3) Deep-water seep-carbonates display outcrop geometries characteristic of point- source fluid seepage; they tend to be lens-, mound- or conical-shaped. In addition, the carbonates contain fluid-flow features such as chimneys, dough-nuts, and conduits 166 concentrically lined with fibrous cements. Comparison of relative seep-carbonate volume among the 22 sites indicates that a gradation of fluid-seepage conditions may have existed: from "end-member" cold-seep deposits (relatively large volume of carbonate exposed in mounds, lenses), to diffusive, "leaky" seeps (minor volume of carbonate preserved as blebs, nodules), to reduced-sediment deposits (no carbonates). Within the voluminous siliciclastic sequences of western North America, many of the isolated masses of Mesozoic- and Cenozoic-age carbonate deposits herein interpreted as ancient seeps have been known for quite some time, but these limestones have been misidentified in previous studies as shallow shoal, reef or bioherm facies because a deep-water seep-carbonate model has only recently been applied to such deposits in the geologic record. 4) Pctrographic and isotopic investigations of three Mesozoic seep-carbonate deposits demonstrate that the geochemical fuels of chemosynthesis were present in the local marine environment during carbonate formation. Pyrite-coated corrosion surfaces delineate acidic, H2S conditions. Fibrous and other cements that are isotopically depleted in carbon (to —43%o PDB) indicate a methane influence during cementation. Microbial fabrics, both layered and clotted, are relatively common in these carbonates, and are implied to be the product of chemosynthetic bacterial activity. 5) Mesozoic seep-carbonates of northern California (Tithonian-Albian) exhibit a recurring cement stratigraphy similar to the paragenetic sequence reported from methane- derived seep-carbonates of the Canadian Arctic (Albian) (Beauchamp and Savard, 1992),' which suggests that similar geochemical processes of seep formation may have been operating globally in some ancient seep systems. Especially distinctive are irregular yellow calcite cements that appear to be indicators of anaerobic, sulfide-rich conditions locally; whereas, gray fibrous cements may mark phases of aerobic, methane-rich fluid pulses to the local seep environment (cf. model in Beauchamp and Savard, 1992). 6) Fine-scale associations between fossils and carbonates are observed for Mesozoic sites in California. Specifically, most biogenic activity (bioturbation; core and 167 associate taxa) is restricted to the early-formed micrite microfacies. One key exception is the fossil tube worm association which commonly is affiliated with certain cement phases (e.g., irregular yellow calcite cement rims around original tube walls). The implications of this division in faunal-carbonate associations are 1) that most ancient seep faunas lived optimally under diffuse fluid flow conditions (typical during micrite formation), and 2) that fossil tube worms were adapted to more vigorous fluid-flow regimes and/or higher concentrations of sulfide in the local microenvironment (as indicated by fibrous cements, irregular yellow calcite affiliations). In general, lime mudstone is more common at mound peripheries, and cements are more prevalent in mound interiors, although some sites contain only micrite or only cements. Analogous distribution patterns of faunas and fluids concentrations are found in modem vent-seep environments. 7) Spatial and temporal variability is inherent at microfacies-, outcrop-, and regional-scales of observation. Ancient seeps of western North America are variable in volume and morphology of carbonate deposits, and in diversity and abundance of faunal constituents, as produced by differences in geo-tectonic regime, changing fluid-flow rates, changing sedimentation rates, and the mechanisms and timing of seep colonization. Some of these processes and products can be differentiated within certain outcrops. For example, Mesozoic cold-seep sites in California occur in two regionally distinctive tectono- stratigraphic associations: 1) quasi-continuous (Tithonian-Campanian), turbidite-hosted settings, and 2) a punctuated fluid-seepage event (Hauterivian) affiliated with diapirism in serpentinite-hosted settings. Temporal clustering of ancient seep sites occurs regionally, with most Cenozoic sites in Washington found at the Eocene-Oligocene boundary. 8) The Early Cretaceous (Neocomian) rhynchonellid brachiopod Peregrinella has long been viewed as a paleontological curiosity because of its distinctive morphology, status as the largest Mesozoic brachiopod, anomalous stratigraphic associations, and widespread, yet discontinuous paleogeographic distribution. Peregrinella is present in abundance at two Mesozoic cold-seeps in this study, the Wilbur Springs and Rice Valley 168 localities. Examination of all worldwide Peregrinella occurrences (13) implies restriction of this rhynchonellid to ancient cold-seeps. It is probable that Peregrinella grew to large sizes in such great abundances because of a rich localized food supply generated by fluid seepage and bacterial chemosynthetic activity at cold-seep sites. Living brachiopods are not known to harbor chemosymbiotic bacteria in their tissues; however, direct chemoautotrophic utilization of reduced fluids by Peregrinella cannot be dismissed nor demonstrated at present. Although Peregrinella occurs at widely separated fossil seeps during the Neocomian (e.g., California, Tibet, Europe), its mode of dispersal and larval development is unknown; whereas, in modem hydrothermal vents of the deep-sea, organism dispersal occurs along oceanic ridges, where benthie faunas display both planktotrophic and nonplanktotrophic larval-mode types. Peregrinella might represent a Mesozoic relic of a long-lived "lineage" of vent/seep associated rhynchonellids from the Paleozoic (e.g., lEoperegrinella, Dzietluszyckia), but major gaps in the stratigraphic record between these rhynchonellid occurrences, and the lack of rigorous phylogenetic analysis for these groups preclude a clear resolution of the origin(s) of vent-seep brachiopods at present. 9) A compilation of 42 fossiliferous Phanerozoic marine deposits interpreted to represent ancient hydrothermal vent or cold-seep habitats worldwide reveals that articulate brachiopods, particularly rhynchonellids and terebratulids, were relatively common constituents of these chemosynthetic settings from the Devonian through the Early Cretaceous, but were rare in such settings from the Late Cretaceous to the present. Late Devonian (Famcnnian) hydrothermal vents and cold-seeps were dominated by rhynchonellids (Dzieduszyckia, lEoperegrinella ) of remarkable morphological similarity to Cretaceous seep-restricled Peregrinella, all of which are purported to be phylogenetically related. Bivalve genera with extant chemosymbiotic descendants first appeared in vent/seep deposits during the Jurassic and were prevalent therein after the Early Cretaceous. These bivalves include members of five families (Vesicomyidae, Mytilidae, Solemyidae, Thyasiridae, Lucinidae); lucinids and thyasirids are the dominant groups represented, 169 especially in ancient cold-seeps. 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Wells, R.E., Engebretson, D.C., Snavely, P.D., Jr., Coe, R.S., 1984, Cenozoic plate motions and the volcano-tectonic evolution of western Oregon and Washington: Tectonics, v. 3, p. 275-294. Whidden, K.J., 1994, Paleogeography of the southern California forearc basin in the Late Cretaceous and Early Paleogene: Evidence from paleomagnetism and carbonate facies analysis: Ph.D. Thesis, University of Southern California, Los Angeles, CA, 324 p. Wilson, J.L., 1975, Carbonate Facies in Geologic History: Springer-Verlag, NY, 471 p. 192 APPENDIX I. Geographic Locality Information. Museum abbreviations used below: United States National Museum (USNM); United States Geological Survey, Menlo Park invertebrate collections (USGS); Los Angeles County Museum of Natural History, invertebrate paleontology collections (LACMNHIP); California Academy of Sciences (CAS), University of California, Berkeley (UCB). Ordered alphabetically by site name. B ear R iv er Pacific County, Washington. Abandoned quarry, south side of bend in the Bear River, 2.25 miles northeast of Columbia River, southeast 1/4 of southeast 1/4 of section 20, T. 10 N., R. 10 W., U.S. Geological Survey, 7.5 minute, Chinook Quadrangle. LACMNHIP 5802. Canyon River: Pacific County, Washington. Cliff on south and southwest side of Canyon River immediately above bridge in big meander bend, southeast 1/4 of southeast 1/4 of section 13, T. 21 N,. R. 7 W., U.S. Geological Survey, 15 minute, Grisdale Quadrangle. This is Armentrout's field locality CR-10; USGS 25764. Cold F ork o f Cottonwood C reek: Tehama County, California. 1 mile up Cold Fork of Cottonwood Creek from Pettyjohnn ranch house, northeast of Stevenson Peak and due west o f Wilcox Flat, section 29, T. 27 N., R. 7 W., U.S. Geological Survey, 15 minute, Col year Springs Quadrangle. U SG SM 2676,1070. Devil's Kitchen: Kern County, California. Small hogsback which joins cliff south of Devil's Kitchen, southeast comer of section 31, T. 10 N., R. 21 W., U.S. Geological Survey, 7.5 minute, Eagle Rest Peak Quadrangle. To be curated into LACMNHIP collections. Holcomb: Pacific County, Washington. Bluffs on north side of Willapa River at the big bend, 1/2 mile southwest of Holcomb. 900 ft. north of southeast comer o f section 36, T. 13 N., R. 8 W. (46.2* N, 123.2* W), U.S. Geological Survey, 15 minute, Raymond Quadrangle. Known in literature as Willapa River "Keasey Beds" (=LincoIn Creek Formation). UCB A-64; USGS 25024. Hum ptulips: Grays Harbor County, Washington. Hill cut by abandoned meander of East Fork of Humptulips River in northwest 1/4 of section 4, T. 20 N., R. 9 W., U.S. Geological Survey, 15 minute, Quinault Lake Quadrangle. LACMNHIP 12385. Irishm an's Flat: Mendocino County, California. In Irishman's Flat, northeast 1/4 of section 10, T. 17 N., R. 11 W., U.S. Geological Survey, 7.5 minute, Potter Valley Quadrangle. USGS M5066. M enlo: Pacific County, Washington. North bank of the Willapa River adjacent to the Chehalis-Raymond highway 1.9 miles southeast of Menlo, southwest 1/4 of northwest 1/4 of section 24, T. 13 N., R. 8 W., U.S. Geological Survey, 7.5 minute, Raymond Quadrangle. LACMNHIP 12326. Paskenta: Tehama County, California. 3.2 miles (4.8 km) northwest of Paskenta by Thornes Camp Road, on knoll between road and Digger Creek, southeast 1/4 of section 25, T. 24 N., R. 7 W., U.S. Geological Survey, 7.5 minute, Paskenta Quadrangle. USNM 23205,23245, 23051 (see also Stanton, 1895; some collections housed at USGS). P otter Valley: Mendocino County, California. On east side of Eel River, 2100 ft SW of junction with Thomas Creek, 1000 ft. N and 2100 f t W e rf" southeast comer of section 26, 193 T. 19 N., R. 12 W., U.S. Geological Survey, 15 minute, Potter Valley Quadrangle. USGS M2818. Rice Valley: Lake County, California. Several nearby sites within Rice Valley or along the "walls" of Rice Valley. "SW Rice Valley Wall", 1950' N, 1600' west of southeast comer of section 10, T. 17 N., R. 9 W., U.S. Geological Survey, 7.5 minute, Potato Hill Quadrangle. USGS M6010. (see also 15 minute, Lake Pillsbury Quadrangle). Other U.S. Geological Survey locality data describes white limestones ("John Suppe's Fossil Rock") in northwestern part of Potato Hill Quadrangle, Lat 39*20'23" N., long. 122"51'15" and Lat 39°20'26" N., long. 122°51T1." USGS M6395, M6396, M6986. San Luis Dam: Merced County, California. North side of mouth of Romero Creek at south end of small point, about 800 ft. east of center of section 26, T. 9 S., R. 8 E., U.S. Geological Survey, 7.5 minute, San Luis Dam Quadrangle; USGS M6991. More recent collection by Elder and Miller (1993), map no. 160, M8766: On slope 200 m W of California Aqueduct, 400 m N of Romero Creek SW center of NE 1/4 of section 26, T. 9 S., R. 8 E. Twin Rivers: Clallam County, Washington. In Twin Quarry (Ideal Cement Company), seacliff exposure above dirt road leading westward to quarry and loading dock, northwestern shore of Straits of Juan de Fuca, near mouth of Twin Rivers, northeast 1/4 of southwest 1/4 of section 23, T. 31 N., R. 10 W., U.S. Geological Survey, 15 minute, Lake Crescent Quadrangle. CAS 2368, 223, 575; USGS M4038, M4034; LACMNHIP 6146, 6147. V ernonia-Tim ber: Columbia-Washington County line, Oregon. Prominent bluff along Nehalem River, east side of Vernonia-Timber road, 0.3 mi north (by road) of Columbia- Washington Co. line, 45.2* N, 123.1* W of southwestern 1/4 of section 35, T. 4 N., R. 5 W., U.S. Geological Survey, 15 minute, Birkenfeld Quadrangle. UCB 4198; Hickman's "Thyasira cut" = USGS 25028; Vokes' USNM 15265. W est Fork of Satsop River: Pacific County, Washington. U.S. Geological Survey, 15 minute, Grisdale Quadrangle. To be curated into LACMNHIP collectk r (see also Rau, 1966). W ilbur Springs: Colusa County, California. On hill immediately south of Wilbur Hot Springs Resort, above Sulphur Creek, Lat 39*N, long. 122° W, 1000 ft. north, 300 ft. east of southwest comer of section 28, T. 14 N., R. 5 W., U.S. Geological Survey, 7.5 minute, Wilbur Springs Quadrangle. USGS M7012; USNM 20173, 20174, 23263, 23265 (see Stanton, 1895; some collections housed at USGS). 194 A P P E N D IX I I . R e la tiv e m ic rite x e m e m ratio s an d fossil ab u n d an ce s fo r bu lk sam p les co llected in tra n se c ts at P a sk e n ta se e p -c a rb o n a te lo cality , n o rth ern C a lifo rn ia (re fe r to F ig u re 31 for sa m p le lo catio n s). A = ab u n d an t; C = c o m m o n ; F = few ; R = rare; N = not p resen t. N orth ( P N l, P N 2 ) an d sou th (P S I) m ounds a p p e a r to re fle c t h ig h e r re lie f areas o f a larg er, c o n tig u o u s lim esto n e bo d y th at c o n tin u e s at g ro u n d su rface through the o a k tree area. M o u n d areas w h ich are p re d o m in a n tly m icritic in co m p o sitio n are relativ ely m o re ab u n d an t in fo ssils o r b io tu rb a tio n . T h ese fo ssilife ro u s m ic ritc a re a s (= d iffu siv e flu id flow co n d itio n s) m ak e up th e larg er m o u n d perip h ery (e.g . P N l - l . P N 1 -3 , P N 1-3, P N 2 -3 , P N 2 -4 , P N 2 -5 . PS I -0 th ro u g h PS I -9). In c e n tra l p o rtio n o f larg er m o u n d (w h ere ex p o sed ; see F ig u re 3 1 ), the m ic rite x e m e n t ra tio is m u ch lo w e r and fo ssils a re rare to a b se n t (e.g ., P N l-5 th ro u g h P N l -13, P N 2 -I, P N 2-2). H ence b io g en ic a c tiv ity a p p e a rs low w h e n c e m e n ts (= v ig o ro u s flu id flo w rates) are th e d o m in an t fabric. S A M P L E N O . M K R IT E C E M EN I E Q S S 1 L S P N l- l A R A P N l -2 A R F P N l-3 A N C P N 1-4 A N N P N l -5 C C N P N 1-6 A C N P N l -7 A c N P N l -8 C c N P N l -9 C A N P N I-1 0 C C N P N l- l 1 C A N P N 1 -I2 C C N P N t-1 3 c C N P N 2 -I c C R P N 2-2 c C N P N 2 -3 A c A P N 2 -4 A N A P N 2-5 A R A PS 1-0 A C A P S I- I A R C PS 1-2 A R A P S 1-3 A R C PS I -4 A C A P S 1-5 A C F P S 1 -6 A R A PS 1-7 A C A P S I -8 A C R P S 1 -9 A R A
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Dynamic Development Of Jurassic-Pliocene Cold-Seeps, Convergent Margin Of Western North America
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