THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS ARTICLE 58 (CRETACEOUS 3) PALEOECOLOGY AND DEPOSITIONAL ENVIRONMENT OF FORT HAYS LIMESTONE MEMBER, NIOBRARA CHALK (UPPER CRETACEOUS), WEST-CENTRAL KANSAS ROBERT W. FREY Department of Geology, University of Georgia, Athens The University of Kansas Paleontological Institute THE UNIVERSITY OF KANSAS PUBLICATIONS MAY 12, 1972 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Article 58 (Cretaceous 3), 72 Pages, 14 Figures, 15 Plates, 6 Tables PALEOECOLOGY AND DEPOSITIONAL ENVIRONMENT OF FORT HAYS LIMESTONE MEMBER, NIOBRARA CHALK (UPPER CRETACEOUS), WEST-CENTRAL KANSAS ROBERT W. FREY Department of Geology, University of Georgia, Athens CONTENTS PAGE ABSTRACT 5 Inoceramus deformis Meek, 1871 29 INTRODUCTION 6 Inoceramus browni Cragin, 1889 29 General statement 6 Inoceramus platinus, s. 1. 30 Purpose and scope 6 Genus Volviceramus Stoliczka, 1871 30 Discussion of the rocks and localities examined 7 Volviceramus grandis (Conrad, 1875) 30 General statement 7 Genus Pycnodonte Fischer de Waldheim, 1835 .... 31 Local setting 8 Pycnodonte congesta (Conrad, 1843) 31 Acknowledgments 10 Pycnodonte aucella (Roemer, 1849) 31 STRATIGRAPHY AND PETROGRAPHY 10 ?Teredine siphonal tubes 32 Physical stratigraphic setting 10 Miscellanea 33 Units in contact with the Niobrara 10 Boring organisms 33 Physiographic and geomorphic expression Problematica 34 of the Niobrara 10 Foraminifera and Ostracoda 34 Structure 11 Vertebrates 35 Subsurface distribution of the Niobrara 12 Plant fossils 36 Upper and lower contacts of the Fort Hays 12 Assemblage and population characteristics 36 Correlation of bedding units 14 Depositional setting 36 Petrology 16 Faunal assemblages 36 Major lithotypes 16 Population structures 37 Thickness and abundance of lithotypes 16 Orientation of bivalve shells 41 Color 17 DEPOSITIONAL ENVIRONMENT AND PALEOECOLOGY 43 Micrite petrology 17 General statement 43 Insoluble residues 19 Depositional setting 44 Authigenic and epigenetic minerals 20 The depositional regime 44 Skeletal aragonite preservation 20 Structural history 44 Primary sedimentary structures 21 The depositional surface 44 Diagenetic structures 23 Sedimentology 45 Biostratigraphy 24 Provenance 45 General statement 24 Rate of sedimentation 45 Regional setting 24 Hydrography 46 Biostratigraphic zonation of the Temperature 46 Fort Hays Member 26 Salinity 47 PALEONTOLOGY AND BIOMETRY 26 Bathymetry 47 General statement 26 Currents 49 Discussion of fossils 27 Turbidity 50 Genus Pyripora d'Orbigny, 1849 27 Water and sediment aeration 51 Pyripora shawi Frey & Larwood, 1971 27 Animal-sediment relationships 52 Genus Serpula Linné, 1768 27 Relationships between organisms 54 Serpula cf. S. semicoalita Whiteaves, 1889 27 Interspecific relationships 54 Serpula sp. 28 Intraspecific relationships 55 Genus Inoceramus Sowerby, 1814 28 Postmortem orientation of bivalve shells 56 lnoceramus cf. I. erectus Meek, 1877 29 DIAGENESIS 57 PAGE Consolidation of sediments 57 APPENDIX 1-LIST OF LOCALITIES EXAMINED 64 Taphonomy 57 Measured sections 64 SUMMARY OF OBSERVATIONS 58 Supplementary localities 65 Physical stratigraphy 58 APPENDIX 2—DESCRIPTIONS OF THREE Petrology 58 MEASURED SECTIONS 65 Sedimentary structures 58 Conventions in measurement and description 65 Diagenetic and postdiagenetic structures 58 Locality 1 65 Biostratigraphy 59 Locality 2 67 Systematic paleontology 59 Locality 3 68 Faunal assemblages 59 APPENDIX 3—QUANTITATIVE DATA ON THE CONCLUSIONS 59 Inoceramus deformis LINEAGE 69 REFERENCES 61 EXPLANATION OF PLATES 70 ILLUSTRATIONS FIGURE PAGE 1. General sediment distribution during peak 13. Size trends among members of the Inoceramus transgression of the Cretaceous epeiric sea, deformis lineage 41 Greenhorn cyclothem 6 14. Size-frequency distribution of valves within the 2. Fort Hays exposures examined in west-central Inoceramus deformis lineage 47 Kansas 7 3. Regional distribution of major facies during Niobrara deposition 8 PLATE FOLLOWING PAGE 72 4. Diagram of stratigraphic sections measured in 1. Stratigraphie aspects of the Fort Hays Member Trego County, Kansas 9 2. Stratigraphie, structural, and weathering features 5. Model for Cretaceous marine sedimentation in of the Fort Hays Member the Western Interior 11 3. Stratigraphie and petrographic aspects of the 6. Index map of major and minor Mesozoic struc- Fort Hays and Smoky Hill Member tures in central and western Kansas 13 4. Scanning electron photomicrographs of chalk 7. Stratigraphic section at Locality 1 15 and chalky limestone from the Fort Hays and 8. Stratigraphic distribution of major constituents Smoky Hill Members of chalky limestone and chalk at Locality 3 18 5. Inorganic and biogenic sedimentary structures 9. Diagrammatic reconstructions of burrow struc- in the Fort Hays Member tures from the Fort Hays 22 6. Current-influenced sedimentary structures in the 10. Stratigraphic ranges of macroinvertebrate fossils Fort Hays Member in the Fort Hays and basal Smoky Hill, Trego 7. Diagenetic and post-diagenetic structures in the County, Kansas 25 Fort Hays Member 11. Density and distribution of members of the 8-10. Fossils from the Fort Hays Member Inoceramus deformis lineage 39 11. Interior of articulated valves of Volviceramus 12. Comparison of vertical and horizontal quadrat grandis density data for members of the Inoceramus 12-14, 15. Fossils from the Fort Hays and Smoky deformis lineage 40 Hill Members TABLES TABLE PAGE 1. Stratigraphie units in the upper part of the 4. Colors encountered commonly among rocks of Upper Cretaceous Series, Western Kansas 12 the Fort Hays exposed in Trego County, Kansas 17 2. Thickness data for correlative Fort Hays strata 5. Inoceramid faunal zones for part of the Late in Gove, Trego, and Ellis Counties, Kansas 14 Cretaceous of the Western Interior of the United 3. Major lithotypes comprising the Fort Hays States 24 Member in Trego County, Kansas 16 6. Orientation of Inoceramus deformis valves in A. Definition of lithotypes 16 the Fort Hays Member, Trego County, Kansas 43 B. Thickness and proportion of lithotypes 16 Paleoecology of Fort Hays (Niobrara), West-Central Kansas 5 ABSTRACT In west-central Kansas the Fort Hays Limestone Member (lower Coniacian) of the Niobrara Chalk ranges in thickness from about 45 to 80 feet; it consists predominantly of thick to massive beds of nearly pure chalky limestone separated by very thin to thin beds of chalky shale. Beds of chalk and shaly chalk are considerably less abundant. Chalky limestones are texturally homogeneous and consist chiefly of cryptograined matrix, mostly coccoliths; subordinate constituents include foram iniferal tests, bivalve fragments, and authigenic iron compounds. Shaly chalks and chalky shales are thinly laminated to laminated and contain large quantities of clayey to silty terrigenous detritus. Strata of the Fort Hays are remarkably persistent laterally, and in Trego County each exposure of the member may be correlated on a bed-by-bed basis; this provides an excellent stratigraphic framework for sampling, and attests to a stable, geographically widespread depositional regime. Eleven macroinvertebrate species were observed in the Fort Hays and four in the lower part of the Smoky Hill. These include species of the bryozoan Pyripora, the annelid Serpula, and the bi- valves lnoceramus, Volviceramus, Pycnodonte, and ?teredine tubes. In addition, the following mis- cellanea are noteworthy in both members: sponge and barnacle borings, small tubular structures at- tached to inoceramid valves, planktonic foraminiferans and coccoliths, scattered fish remains, and diverse burrow structures. Lateral and vertical trends in density and distribution of both macro- invertebrates and trace fossils are correlative throughout Trego County. Three general assemblages are discernible among macroinvertebrates: 1) a gryphaeate Pycnodonte assemblage restricted essentially to the basal Fort Hays, dominated by P. aucella, 2) a bowl-shaped inoceramid assemblage ranging through most of the Fort Hays, dominated by Pycnodonte congesta and successive members of the lnoceramus deformis lineage, and 3) a rudist-like inoceramid assem- blage appearing at the top of the Fort Hays and ranging well into the Smoky Hill, dominated by Pycnodonte congesta and Volviceramus grandis. The last two assemblages are closely related; within them are numerous examples of inter- and intraspecific relationships. Various lines of physical and biological evidence indicate that 1) Fort Hays sediments in west- central Kansas were deposited far from shore, during maximum invasion of the Niobrara sea, 2) relatively little terrigenous detritus reached this part of the depositional basin, thus the sediments con- sisted essentially of pure carbonate mud, diluted periodically by brief influxes of clay and silt, 3) initial accumulation of Fort Hays sediments followed a long interval of nondeposition (latest Turonian through earliest Coniacian) in the Western Interior, 4) a regional slope and broad topo- graphic irregularities were present on the pre-Niobrara surface, 5) Fort Hays deposition in west- central Kansas commenced in shoal areas subject to wave scour but the waters deepened progres- sively through Fort Hays and early Smoky Hill deposition, probably attaining depths comparable to those of the present midshelf region off the Atlantic coast, 6) the nearly pure carbonates of the Fort Hays accumulated slowly and the clayey sediments comparatively rapidly, 7) the substrate remained soft and mechanically unstable until late