Stratigraphic Revision and Depositional Environments of the Upper Cretaceous Toreva Formation in the Northern Black Mesa Area, Navajo and Apache Counties, Arizona U.S. GEOLOGICAL SURVEY BULLETIN 1685 Stratigraphic Revision and Depositional Environments of the Upper Cretaceous Toreva Formation in the Northern Black Mesa Area, Navajo and Apache Counties, Arizona By KAREN J. FRANCZYK Stratigraphic revision, sedimentology, and depositional history of Upper Cretaceous units in northern Arizona U.S. GEOLOGICAL SURVEY BULLETIN 1685 DEPARTMENT OF THE INTERIOR DONALD PAUL MODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1988 For sale by the Books and Open-File Reports Section U.S. Geological Survey Federal Center Box 25425 Denver, CO 80225 Library of Congress Cataloging-in-Publication Data Franczyk, Karen J. Stratigraphic revision and depositional environments of the Upper Cretaceous Toreva Formation in the northern Black Mesa area, Navajo and Apache counties, Arizona. (U.S. Geological Survey bulletin ; 1685) Bibliography: p. 1. Toreva Formation (Ariz.) 2. Geology Stratigraphic Cretaceous. 3. Sedimentation and deposition. 4. Geology Arizona Black mesa (Navajo Coun­ ty and Apache County) I. Title. II. Series: Geological Survey bulletin ; 1685. QE75.B9 no. 1685a [QE688] 557.3 s 86-600212 [551.7'7'0979135] CONTENTS Abstract 1 Introduction 1 Location and acknowledgments 2 Methods of study 2 Geologic and structural setting 3 Previous work and nomenclatural history of the Toreva Formation 4 Upper part of the Mancos Shale and lower sandstone member of the Toreva Formation 6 Description 6 Upper part of the Mancos Shale 6 Lower sandstone member of the Toreva Formation 6 Interpretation 9 Middle carbonaceous member of the Toreva Formation 11 Description 11 Interpretation 13 Upper sandstone member of the Toreva Formation 14 Description 14 Interpretation 16 Lower carbonaceous member of the Wepo Formation 18 Description 18 Interpretation 19 Wind Rock Tongue of the Mancos Shale and the Rough Rock Sandstone of Mesaverde Group 20 Description 20 Wind Rock Tongue of the Mancos Shale 20 Rough Rock Sandstone 22 Interpretation 26 Depositional history and regional correlations 27 References cited 31 PLATE 1. Stratigraphic cross sections through measured sections in northeastern Black Mesa, Arizona In pocket FIGURES 1. Location map of Black Mesa and study area 2 « 2. Location map of measured sections and cross sections 3 3. Diagram of the structural setting of the Black Mesa basin 3 4. Diagram showing correlations of the Toreva Formation across Black Mesa 5 5. Photograph of outcrop of Cretaceous units within the study area 6 6. Diagram of the mineral composition and classification of sandstone within the upper part of the Mancos Shale and the lower sandstone and middle carbonaceous members of the Toreva Formation 6 7. Photograph of large ball and pillow structures in the upper part of the Mancos Shale 8 8. Photograph of sheetlike sandstone bodies in the lower sandstone member of the Toreva Formation 9 Contents III FIGURES 9. Diagram of the sediment transport directions from the lower sandstone member and the middle carbonaceous member of the Toreva Formation 10 10. Diagram of the combined sediment transport directions from genetic units in the lower sandstone and middle carbonaceous members of the Toreva Formation 10 11. Schematic diagram of distribution of delta centers during deposition of the lower sandstone member of the Toreva Formation 11 12. Photograph of sandstone geometries of the upper sandstone member of the Toreva Formation 14 13. Photograph of the upper sandstone member of the Toreva Formation overlying the lower sandstone member of the Toreva Formation 15 14. Diagram of the mineral composition and classification of sandstone in the upper sandstone member of the Toreva Formation and the lower carbona­ ceous member of the Wepo Formation 16 15. Diagram of the sediment transport directions from the upper sandstone member of the Toreva Formation 16 16. Diagram of the type locality of the Wind Rock Tongue of the Mancos Shale 20 17. Photograph of intensely burrowed sandstone at the transgressive unconform­ ity between the Wind Rock Tongue of the Mancos Shale and the lower carbonaceous member of the Wepo Formation 21 18. Photograph of pebble lag marking the transgressive unconformity 22 19. Diagram of the distribution of the Wind Rock Tongue and the Rough Rock Sandstone on Black Mesa 22 20. Diagram of the type section of the Rough Rock Sandstone 23 21. Photograph of weathering differences between sheetlike and scour-based sandstones in the Rough Rock Sandstone 24 22. Photograph of laterally extensive scour-based sandstone at the top of the Rough Rock Sandstone 25 23. Diagram of the mineral composition and classification of the Rough Rock Sandstone 25 24. Diagram of the sediment transport directions from the Rough Rock Sandstone 26 25. Chart of faunal zones of the lower part of the Upper Cretaceous 28 26. Schematic of the paleogeography of the southwestern part of the western interior Cretaceous basin during the middle Turonian regressive cycle 28 27. Diagram of middle Turonian through Coniacian units in the southern part of the San Juan basin 28 28. Diagram of the relation of units in the Straight Cliffs Formation, southeastern Kaiparowits basin, Utah 29 TABLES 1. Location of measured sections 2 2. Comparison of sandstone types in the upper sandstone member of the Toreva Formation 17 IV Contents Stratigraphic Revision and Depositional Environments of the Upper Cretaceous Toreva Formation in the Northern Black Mesa Area, Navajo and Apache Counties, Arizona By Karen J. Franczyk Abstract Rough Rock Sandstone was deposited along a prograding barrier-island complex, which may have been flanked on the Detailed examination of the Upper Cretaceous Toreva northwest by a deltaic system. Formation resulted in recognition of six mappable lithologic units previously included in the Toreva Formation. Three of these units present at the type locality on the southwest side INTRODUCTION of Black Mesa are, in ascending order, the lower sandstone, the middle carbonaceous, and the upper sandstone members of the Toreva Formation; three of these units formerly assigned Interpretation of depositional environments and to the Toreva on the northeast side of Black Mesa are assigned mapping of facies changes within the Upper Cretaceous to the lower carbonaceous member of the Wepo Formation, Toreva Formation from the southwestern part of Black the Wind Rock Tongue (new name) of the Mancos Shale, and Mesa to the northeastern part of Black Mesa have resulted the Rough Rock Sandstone (new name) of the Mesaverde in revised correlations of the Toreva across the mesa, the Group. These six Stratigraphic units record two episodes of renaming of strata that were formerly included in the up­ marine regression separated by a period that included (1) base per part of the Toreva in northern Black Mesa, and the level lowering and channel erosion, (2) fluvial deposition, and establishment of better correlations of Cretaceous rock (3) marine transgression. units between the Black Mesa basin and the San Juan During the first regressive event, a prograding, wave- Basin to the east and the Kaiparowits basin to the north­ dominated deltaic system deposited the lower sandstone west. Also, this study of rock sequences within the Toreva member of the Toreva Formation. This regressive delta-front sandstone is overlain by delta-plain deposits of the middle car­ has provided information on the response of depositional bonaceous member of the Toreva Formation. A lowering of systems to regional events such as tectonism, eustatic base level, possibly initiated by both tectonic uplift and eustatic changes, and recurrent transgression and regression of drop, caused a period of channel erosion that removed a signifi­ the Cretaceous sea. cant thickness of the middle carbonaceous member in the study Nomenclatural problems have plagued the Toreva area. When deposition resumed, northeast-flowing, meander­ Formation since Repenning and Page (1956) formally ing and braided rivers deposited the upper sandstone member named it. The problems resulted from correlating the rock of the Toreva Formation. During deposition, a gradually rising units at the type locality of the Toreva (in the sea level caused the change from higher to lower energy fluvial southwestern part of Black Mesa), across an area of more systems, the landward shift in alluvial and coastal-plain en­ than 60 mi (97 km) where numerous facies changes oc­ vironments, and the transgression of the sea into the Black Mesa cur, to the northern part of Black Mesa. Repenning and area. The lower carbonaceous member of the Wepo Forma­ tion shows an upward change from alluvial to coastal-plain Page's (1956) interpretation of the facies changes across depositional environments. The transgression of the sea back Black Mesa led them to include in the Toreva Formation into the Black Mesa area resulted in the deposition of the newly the rock units in the northern part of Black Mesa that named Wind Rock Tongue of the Mancos Shale. During the are not present at the type locality and to assign different regressive event following this transgression, the newly named member names to the Toreva units in the northern part Introduction 1 of the mesa. When the depositional environments and the mesa, and there are few dirt roads to the cliffs at the base sequence of depositional events of these rock units are of the mesa. Most of the outcrops in the study area are known, the correlation problems caused by the facies accessible only on foot. changes are more easily understood and solved. The Navajo Tribe granted permission to conduct field studies on their land. Margaret Traylor and Alice Gross assisted in collecting the field data, and A. R. Kirk LOCATION AND ACKNOWLEDGMENTS and Fred Peterson of the U.S. Geological Survey and R. J. Weimer and J. C. Home of the Colorado School Black Mesa, located in the northeastern corner of of Mines provided helpful discussion and advice through­ Arizona, is a southwest-dipping cuesta, nearly circular out the study.