Upper Cenomanian Foraminifers from the Southern Part of the San Juan Basin, New Mexico U.S. GEOLOGICAL SURVEY BULLETIN 1808-N AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with the last offerings, are given in the current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List" Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. 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Residents of Alaska may order maps from FAIRBANKS, Alaska-New Federal Building, 101 Twelfth U.S. Geological Survey, Map Sales Ave. 101 Twelfth Ave., Box 12 Fairbanks, AK 99701 Chapter N Upper Cenomanian Foraminifers from the Southern Part of the San Juan Basin, New Mexico By MARY ALICE CAREY A multidisciplinary approach to research studies of sedimentary rocks and their constituents and the evolution of sedimentary basins, both ancient and modern U.S. GEOLOGICAL SURVEY BULLETIN 1808 EVOLUTION OF SEDIMENTARY BASINS SAN JUAN BASIN U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government UNITED STATES GOVERNMENT PRINTING OFFICE: 1992 For sale by Book and Open-File Report Sales U.S. Geological Survey Box 25425 Denver, CO 80225 Library of Congress Cataloging-in-Publication Data Carey, Mary Alice. Upper Cenomanian foraminifers from the southern part of the San Juan Basin, New Mexico : a multidisciplinary approach to research studies of sedimentary rocks and their constituents and the evolution of sedimentary basins, both ancient and modern / by Mary Alice Carey. p. cm. (Evolution of sedimentary basins San Juan Basin ; ch. N) (U.S. Geological Survey bulletin ; 1808-N) Includes bibliographical references. Supt. of Docs, no.: I 19.3:R1808N 1. Foraminifera, Fossil San Juan Basin (N.M. and Colo.) 2. Paleontology Cretaceous. I. Title. II. Series. III. Series: U.S. Geological Survey bulletin ; 1808-N. QE75.B9 no. 1808N [QE772] 557.35 dc20 91-42291 [563'.12'097895] CIP CONTENTS Abstract Nl Introduction Nl Method of study N3 Stratigraphy N3 Micropaleontology N4 Whitewater Arroyo Tongue N4 Lower Member of the Mancos Shale at Laguna N6 Hartland Member-lower member, Chama Basin N7 Significance of planktonic foraminifers N8 Faunal and environmental interpretations N9 Paleogeographic theories Nil Late Cenomanian stratigraphy and ammonite zones N12 Conclusions N13 Taxonomic notes on selected species N14 References cited N16 Appendix Description of localities N17 PLATES [Plates follow text] 1-3. Scanning electron microscope photomicrographs of selected specimens from study area. FIGURES 1. Cross section showing intertonguing rock units of Dakota Sandstone and Mancos Shale N2 2. Index map showing sample localities in study N2 3. Chart showing stratigraphic nomenclature of middle Cenomanian to lower Turanian rocks in parts of New Mexico and southeastern Colorado N3 4-10. Charts showing distribution of foraminifers: 4. Hyde Mine N4 5. Casamero Lake N5 6. Cubero N5 7. L-Bar N6 8. Type section near Two Wells N16 9. Laguna N7 10. Heron Reservoir N7 11. Chart showing foraminiferal zones and stratigraphic nomenclature as related to the Laguna and Heron Reservoir localities N8 12. Maps showing distribution of foraminifers in the Western Interior during latest Graneros time and middle Hartland time Nil 13. Sketch showing the general outcrop boundary of the Twowells Tongue and deltaic headland that served as source for offshore bars and shoreface sands of the Twowells N12 Contents III 14, 15. Maps showing general positions of shorelines: 14. Late Cenomanian N13 15. Middle Cenomanian N13 16. Chart showing foraminiferal zones and subzones, ammonite zones, and stratigraphic nomenclature of study area N14 IV Contents EOLUTION OF SEDIMENTARY BASINS SAN JUAN BASIN Upper Cenomanian Foraminifers from the Southern Part of the San Juan Basin, New Mexico By Mary Alice Carey Abstract characterize a deeper water environment and record a major incursion of the southern ocean into the Western Interior. The The Cenomanian Whitewater Arroyo Tongue of the foraminiferal fauna of the Hartland Member-lower member of Mancos Shale is the upper shale in an intertonguing sequence the Mancos in the Chama Basin correlates with that of the consisting of five Dakota Sandstone units and two Mancos Hartland Shale Member of the Greenhorn Limestone of the Shale units. This sequence is best developed in the vicinity of Great Plains. Laguna, New Mexico, where the Whitewater Arroyo is 90 ft Differences in the foraminiferal assemblages between the thick. Overlying the Whitewater Arroyo is the Twowells Whitewater Arroyo Tongue and the lower member of the Tongue of the Dakota, which separates the Whitewater Arroyo Mancos imply that a variety of bottom conditions and water- from the lower member of the Mancos in the southern part of mass circulation patterns existed within the Whitewater Arroyo the San Juan Basin. These two tongues, the Whitewater Arroyo sea and that an abrupt change in water depth occurred at the and the Twowells, are the most laterally extensive units of the beginning of deposition of the lower member of the Mancos, a Dakota-Mancos sequence and thus provide a basis for regional change caused by rapid subsidence and (or) rapid sea-level environmental interpretation. rise. Foraminifers recovered from six outcrops of the White- water Arroyo Tongue and from one outcrop of the basal part of the lower member of the Mancos Shale show that the White- INTRODUCTION water Arroyo represents a shallower, nearshore, better oxygenated bottom environment than does the lower member. Despite considerable studies on middle and late Although both planktonic and arenaceous and calcareous benthic foraminifers were recovered from the Whitewater Cenomanian foraminifers from the central, most open- Arroyo, some nearshore localities in the middle Cenomanian marine part of the Cretaceous seaway (Richer, 1969; Eicher Seboyeta bay produced only arenaceous specimens. The and Diner, 1985; Eicher and Worstell, 1970), little work has greatest abundance and diversity of foraminifers in the White- been done to correlate these foraminiferal faunas with those water Arroyo assemblage at the Laguna section indicate a of the more shoreward facies of the seaway. A complex northerly flow of southern ocean waters and an increase in intertonguing rock sequence of Dakota Sandstone and vertical circulation of the sea that produced an oxygenated sea Mancos Shale units exposed in west-central New Mexico floor. In contrast, the dominance of planktonic foraminifers in represents a segment of the shoreward facies and is coeval the lower member of the Mancos at Laguna indicates a deeper with the middle and late Cenomanian and Turonian water, open-marine environment and oxygen-reduced sea Greenhorn Limestone of southeastern Colorado and central floor. Kansas. The foraminifers from this intertonguing