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AN ABSTRACT OF THE THESIS OF Thomas Lee De Keyserfor the degree of Doctor of Philosophy in Geology presented on September 18, 1978 Title: THE EARLY MISSISSIPPIAN OF THE SACRAMENTO MOUNTAINS, NEW MEXICO - AN ECOFACIES MODEL FOR CARBONATE SHE MARGIN DEPOSITION Abstract approved: Redacted for privacy 7 J. Y'Jhnson This study involves a combined ecosystem-modeling approach to clarification of organism-substrate-erivironnient relationships.The methodology developed - ecofacies analysis - combines three submodels (paleontological, sedimentological, stratal) into a single ecofacies model for the reef ecosystem, the links between the submodels being provided by analogy with the Holocene reef ecosystem. Analysis of the Devonian and Mississippian depositional se- quences in the Sacramento Mountains, New Mexico, necessitates a clarification and reinterpretation of the included stratigraphic units and requires several revisions in the stratigraphic nomenclature: (1) the Middle Devonian Oate Formation was deposited as a thin blanket throughout the Sacramento Mountains; it was draped over a pre-Oiate structural (?) high, separating a shallow, silled basin on the north from a deeper, offshore basin on the south; (Z) the early Late Devonian Sly Gap and late Late Devonian Percha. (?) formations, the Early Mississippian Kinderhookian Caballero Formation,and the Early Mississippian Osagean Andrecito Member of the Lake Valley Formation filled the silled basin and prograded beyondthe buried pre-O'ate high as several successive elastic shelfmargins; (3) an abrupt reduction in the supply of terrigenous elasticsediment due to a postulated rise in sea level allowed coLonization bythe pioneer communities of the reef ecosystem. The reefslocalized north of a buried Percha (?) paleoshoreline and south of thesilled basin, above the pre-Oiate high and the Caballero and Andrecito shelf margins; (4) reefs north of the Percha (?) paleoshoreline co- alesced to form a carbonate shelf; those south of the silledbasin did not and are preserved as pinnacle reefs; (5) the previouslydescribed Alarnogordo, Nunn, and Tierra Blanca members o the LakeValley are facies of the reefs; they have nochronostratigraphic value and their use is discontinued; (6) tIe superjacent Arcente andDona Aria members of the Lake Valley are separated from the remainderof the formation by an unconformity; they are removed fromthe Lake Valley and raised to forrnational rank; (7) the Arcente wasdeposited below the tops of the Lake Valley (restricted) reefs, further reducing the water depth around them; (8) with a return to clear-water condi- tions and reef growth, the shelf margin prograded to a positionat or near the Lake Valley pinnacle reefs. Community analysis of the Lake Valley (restricted) brachiopod fauna does not permit identification of particular communitiesof stable composition.It does recognize an upward, intra-reef community succession, from a deep, below-wave-base communityof diverse, small, thin-shelled brachiopods to a shallow, above-wave-base corn- munity of large, thick-shelled brachiopods, dominated by Spinier app., Imbrexia app., Unispirifer app., Marginatia sp. A, andPseudosyrinx missouriensis.Description of the brachiopod fauna within this ecofacies framework allows clarification of many ecologic relationships between species and suggests that intraspecific variation isgenenally much greater than has been supposed. Two new species are described: Coledium sugarloafensisand Cranaena longicrura.Serial sections are illustrated for most of the 47 species described and, in the case of two species ofterebratu].ids (Cranaena longicrura and Beecheriasp. A), these are supplemented by isometric drawings of the loop and cardinalia.This is a new technique in brachiopod illustration. 1978 THOMAS LEE DE KEYSER ALL RIGHTS RESERVED The Early Mississippian of the Sacramento Mountains, New Mexico - an Ecofacies Model for Carbonate Shelf Margin Deposition by Thomas Lee De Keyser A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed September 18, 1978 Commencement June 1979 APPROVED: Redacted for privacy Pr,fe4or of Geology ( J in eof major Redacted for privacy Head of Department of G4bgy Redacted for privacy Dean of Graduate School Date thesis is presented n-ir.ey\ Typed by Opal Grossnicklaus for Thomas Lee De Keyser FRONTISPIECE Photo of a large block of weathered reef core, Little Sugarloaf Mound, showing complex depositional tex- ture and apparently encrusting growth forms ACKNOWLEDGEMENTS Numerous individuals and institutions have contributed to this study.Special thanks are due to the members of my thesis committee, consisting of Drs. J. G. Johnson (principal advisor), R. S. Yeats, K. F. Oles, and A. G. Carey, for careful reading of this dissertation and for their many helpful criticisms and comments. Many of the ideas expressed and the concepts developed grew out of numerous discussions with and several courses taught by Dr. Johnson.Drs. H. Richard Lane and Allen R. Ormiston of Amoco Production Co., Research Center, provided useful in.formation and constructive criti- cism during the initial planning for the project, in the field, and throughout its progress.In addition, Lane, who had recently pub- lished the Faunal Unit scheme used in this study, provided conodont identifications for many samples critical to the interpretations presented. Also influential in the planning and execution of the study were Drs. Lowell R. Laudon and Lloyd C. Pray of the University of Wisconsin, Madison. The former served as my advisor for both my Bachelor of Science and my Master of Science degrees and, as the author, with Dr. A. L. Bowsher, of the first detailed stratigraphic study of the Mississippian strata in the Sacramento Mountains, pro- vjded much valuable information during formal and informal discussions; the latter not only introduced me to the study of carbonate rocks, but is the author of the first and still the most accurate geologic map of the Sacramento Mountains escarpment. Expenses for all field work were paid by Amoco Production Co., Research Center, Tulsa, Oklahoma. Valuable field assistance was provided by Alex Kilby, Randy Ames, and John Stroud, all of Amoco, and by Jed Day and Steve Durkee of Oregon State University. Thanks are also due to Dr. G. A. Cooper and Frederick J. Collier of the U. S. National Museum for their assistance in obtaining comparative specimens for use in the taxonomic portion of this study. Finally, acknowledgement must be given to William F. Koch, II, for many stimulating discussions and valuable criticisms of the con- ceptual framework developed herein.His own dissertation study, in many ways, conceptually parallels my own. TABLE OF CONTENTS INTRODUCTION I METHODOLOGY 6 LOCALITIES 8 RESTORED CROSS-SECTION OF SHELF-BASIN TRANSECT 11 STRATIGRAPHY OF DEVONIAN FORMATIONS 16 Oxate Formation 16 Sly Gap Formation 18 Percha (?) Formation 22 STRATIGRAPHY OF MISSISSIPPIAN FORMATIONS 31 Caballero Formation 31 Lake Valley Formation 34 Arcente Formation 43 Dona Ana Formation 49 EARLY MISSISSIPPIAN (T?WAULSORTIANII) REEFS IN THE SACRAMENTO MOUNTAINS: STRATIGRAPHIC RELATIONSHIPS AND CONFIGURATION 54 Tepee Mound 55 Alamo Mound 58 Muleshoe Mound 60 Phantom Mound 63 Little Sugarloaf Mound 64 San 4Andres Mound 65 REEF GROWTH AND SHELF DEVELOPMENT IN THE LAKE VALLEY FORMATION - AN ECOFACIES MODEL 77 Introduction 77 Stratigraphic Submodel 79 Sedimento1ogiaI Submodel 80 Paleontological Submodel 81 Inception of Reef Growth 82 Colonization 82 Localization 87 Upward Growth to Wave Base 87 Attainment of Wave Base - Inception of Flank Bed Deposition 91 Wave Base 94 Ecofacies Distribution 103 Progradation and Coalescence of Centers of Reef Growth 104 Progradation of the Carbonate Shelf Margin 106 SUMMARY AND CONCLUSIONS 110 REFERENCES CITED 113 APPENDIX A: SYSTEMATIC PALEONTOLOGY 124 Phylum BRACHIOPODA Class ARTICULATA Order ORTHIDA Suborder DALMANELLIDINA Superfamily ENTELETACEA Family SCHIZOPHORIIDAE Subfamily SCHIZ OPHORIINAE Genus Schizophoria Schizophoria cf. chouteauensis 1 24 Superfamily DALMANELJLACEA Family RHIPIDOMELLIDAE Genus Rhipidomella Rhipidomella tenuicostata 1 25 Order STROPHOMENIDA Suborder STROPHOMENIDINA Superfamily STROPHOMENACEA Family LEPTAENIDAE Genus Leptagonia Leptagonia cf analoga 128 Suborder PRODUCTIDINA Superfamily PRODUCTACEA Family LEIOPRODUC TIDAE Genus Productina Productina sampsoni 130 Family OVERT ONIIDAE Subfamily OVER TONIINAE Genus Geniculifera Geniculifera boonensis 131 Genus Rhytiophora Rhytiophora cf. blairi 131 Rhytiophora cf. calhounensis 132 Rhytiophora sp. A 133 Rhyohora sp. B 133 Genus Stegacanthia Stegacanthia bowsheri 134 Family BUXTONIIDAE Subfamily BUSTONIINAE Genus Marginatia Marginatia sp A 134 Order RHYNCHONELLIDA Superfamily RHYNC9ONELLACEA Family TRIGONIEH?NCHONIIDAE Genus Ptychomaletoechia ychomaletoechia (?) sp. A 135 Family PUGNACIDAE Genus Shumardella Shumardella obsolescens 137 Family YUNNANELLIDAE Genus Paraphorhynchus Paraphorhynchus sp. A 139 Superfamily STENOSCISMATACEA Family ATRIBONIIDAE Subfamily ATRIBONIINAE Genus Atribonium Atribonium (?) sp A 141 Family STENOSCISMATIDAE Subfamily ST ENOSCISMATINAE Genus Coledium Coledium sugarloafensis 144 Superfamily RHYNCHOPORACEA Family RHYNCHOPORIDAE Genus Rhynchopora Rhynchopora sp. A 147 Rhynchopora sp. B 147 Rhynchopora sp C 149 Rhynchopora sp D 153 Order SPIRIFERIDA Suborder RETZIIDINA Superfamily RETZIACEA Family RETZUDAE Genus Hustedia Hustedia (?) sexplicata 153 Suborder ATHYRIDIDINA

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