Paleocurrents and Depositional Environments of the Dakota Group (Cretaceous), San Miguel County, New Mexico Item Type text; Thesis-Reproduction (electronic) Authors Bejnar, Craig Russel Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the Antevs Library, Department of Geosciences, and the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author or the department. Download date 10/10/2021 09:59:36 Link to Item http://hdl.handle.net/10150/244084 PALFACURRENTS AND DEPOSITIONAL ENVIRONMMT5 OF THE DAKOTA GROUP (CRETACEOUS), SAN MIGUEL COUNTY, NEW MEXICO by ,Crag Ru.s s el Bejnar A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 1975 STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of re- quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests . for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judg- ment the proposed use of the material is in the interests of scholar- ship. In all other instances, however, permission must be obtained from the author. SIGNED: APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: 4/-Am..d RIC " F. WILSON Associate Professor of Geosciences ACKNOWLEDGMENTS I want to thank Dr. Richard F. Wilson, my thesis director, for his visit in the field, suggestions, and critical review of the manu- script. Thanks are also extended to Dr. Joseph F. Schreiber, Jr., and Dr. Gerhard O. W. Kremp for their help and critical review of the manus c rip t. I gratefully acknowledge the help given by my fellow graduate students: William Sulkoske for his generous aid in pollen preparation and for numerous helpful suggestions, Art Trevena forour many fruit- ful discussions, Bill Purves for the initial computer programs, and Steven Wampler for the computer plotter routines. Special thanks goes to Dr. Schumacher who unselfishly gave his time to helpme with the photographic work. My thanks are extended to Jan Drlik, my valuable field assistant, and Louise Drlik for typing the manuscript. I acknowledge with appreciation the financial assistance for the summer field work provided by Waldemere Bejnar and Associates,Inc. iii TABLE OF CONTENTS Page vi LISTOF ILLUSTRATIONS. LISTOF TABLES . ix x ABS'MA CT . INTRODUCTION. i Location i Scope of Investigation . i Geomorphology and Structure . 3 Regional Concepts of the Dakota Group. 4 STRA.TICRAPHY . 9 Field Problems . 9 Generalized Section. il Lower Sandstone Unit 11 Middle Shale Unit. 19 Upper Sandstone Unit 21 SEDIMENTARYSTRUCTURES . 25 Stratification 25 Cross- Stratification . 26 Ripple Marks . 30 Soft Sediment Deformation. 34 PALEONTOLOGY. 38 Root Casts . 38 Trace Fossils. 40 Pollen and Spores . 44 Sample Collection. 46 Maceration Procedure 46 Identification . 48 PALEOCURRENTDIRECTIONS. 51 Sampling Procedure . 51 Data Reduction 53 iv v TABLE OF CONTENTS-Continued Page Cross- Strata Variability . 55 Paleoslope and Shoreline Strike. 57 HEAVYMINERAL ANALYSIS . 60 Methods 60 Results. 61 Provenance . 65 Paleoclimate . 67 INTERPRETATION OF DEPOSITIONAL ENVIRONMENTS. 69 Lower Sandstone Unit . 70 Middle Shale Unit. 73 Upper Sandstone Unit . 74 Paleote ct onic Setting. 75 Depositional History . 77 APPENDIX A: MEASURED SECTIONS . 80 APPENDIX B: CROSS -STRATIFICATION MEASUREMENTS . 107 APPENDIX C: STATISTICAL DATA ON CROSS -STRATIFICATION. 133 REFERENCES. 145 LIST OF ILLUSTRATIONS Figure Page 1. Index Map and Location of Study Areas . 2 2. General View of the Three Units in the Dakota Group in North- Central New Mexico. 12 3. Basal Cretaceous Strata in North -Central New Mexico ..in pocket 4. Photomicrograph of Sandstones in the Lower Sandstone Unit 13 5. Limonite- Cemented Nodules (right) Grading into Con- tinuous Cementation (left) in Lower Sandstone Unit at Coyote Creek 15 6. Secondary Quartz Veinlets in Lower Sandstone Unit at Montezuma 15 7. Maximum Size of Pebbles in Lower Sandstone Unit of the Dakota Group . 16 8. Photomicrograph of Chert Pebble Containing Foramini- fera in Conglomerate from the Lower Sandstone Unit (plain light). 1$ 9. Chert Pebbles Displaying White Tripolitic Weathering in the Lower Sandstone Unit at Box Canyon. Scale is in Inches 1$ 10. Intercalated Green Shales and Sandstones at the Con- tact of the Pajarito Shale and the Lower Sand- stone Unit of the Dakota Group at the Trujillo Section. 20 11. Photomicrograph of Sandstone in Middle Shale Unit at Romeroville Gap. Dark Areas Are Carbona- ceous Matter - . 20 12. Middle Shale Unit at Coyote Creek. Note the Channel Sandstone (center right) 22 vi v]..7. LIST OF ILLUSTRATIONS Continued Figure Page 13. Textural Changes in a Poorly Sorted, Fine-Grained, Carbonaceous Sandstone Produced by Burrow(left) in Upper Sandstone Unit at Romeroville . 24 14. Wood Fragment Molds in Bedding Plane in Upper Sand- stone Unit at Sapello. 24 15. Principle Types of Cross -Stratification: Tabular - Planar (left) and Trough (right) . 26 16. Trough Cross -Stratification in the Dakota Group . 28 17. Tabular- Planar Cross -Stratification in the Dakota Group. 29 18. Ripple - Marked Set of Cross -Strata in the Lower Sand- stone Unit at Kearny Gap Looking Toward the North- west. Hammer Gives Scale. 31 19. Symmetrical Wave Ripples in Float from the Upper Sandstone Unit at Montezuma. 35 20. Soft Sediment Deformation: Load Casts and Overturned Cross- Stratification . 36 21. Sand- Filled Root Casts in Middle Shale Unit at Coyote Creek. 39 22. Skolithos Tubes in Upper Sandstone Unit at McAllister Lake between Location 9 and 10 (Figure 1) 39 23. Ophiomorpha Burrows in Upper Sandstone Unit . o . 41 24. A Block Diagram Showing U -in -U Tubes with Spreiten (From MacKenzie, 1968, p. 11) O 42 25. U -in -U Burrows in the Upper Sandstone Unit. 43 26. U -Tube in Upper Sandstone Unit at Montezuma. Pencil is 15 cm long. 45 27. Planolites in Bedding Plane in the Upper Part of the Lower Sandstone Unit at Arroyo Hermanos. 45 28. Pollen and Spores in the Dakota Group . 49 viii LIST OF ILLUSTRATIONS - -Continued Figure Page 29. Paleocurrent Directions in Lower Sandstone Unit of the Dakota Group in North -Central New Mexico. Arrows show Locality Mean Direction and 95 Percent Confidence Level. 54 30. Comparison of Cross -Stratification Directions in Lower and Upper Sandstone Units of the Dakota Group in North- Central New Mexico. 5$ 31. Compass Rose Diagrams of Cross -Stratification in in Lower Sandstone Unit. .in pocket 32. Variation in Current Direction within the Lower Sandstone Unit at Box Canyon 59 33. Percentage of Opaque and Non -Opaque Fractions of Heavy Minerals in Each Unit at Romeroville Gap 62 34. Average Composition of the Non - Opaque Heavy Minerals from All Intervals Plotted Against Grain Size. 62 35. Photomicrograph of Well Rounded and Euhedral Zircon (Four Phi Size). 64 36. Hypothetical Models Illustrating Textural and Geo- metrical Characteristics of Common Alluvial En- vironments. A. Piedmont Formed of Alluvial Fans; B. Braided Streams; C. Low Sinuosity Stream; D. Strongly Meandering Stream 71 37. Paleotectonic Map of the Western Interior of the United States during Early Cretaceous Time. o 76 LIST OF TABLES Table Page 1. Nomenclature of Basal Cretaceous Strata of the Western Interior of the United States . 5 2. Measurements and Orientations of Ripple Marks at Kearny Gap........................... 32 3. Ripple Mark Indices at Kearny Gap Compared with Indices of Particular Environments . 34 4. Maceration Procedure. 47 5. Non-Opaque Heavy Mineral Composition Percentages. 63 6. Varieties of Zircon and Tourmaline in Each Phi Size Class . 66 ix ABSTRACT The Dakota Group surrounding Las Vegas, New Mexico, consists of three units: 1) a basal, predominately trough cross- stratified, con- glomeratic sandstone, 2) middle intercalated, thin- bedded sandstone and carbonaceous shale, and 3) upper, predominately tabular- planar cross - stratified, sandstone containing trace fossils. These units represent, respectively, 1) a fluvial piedmont plain, 2) fluvial coastal plain, and 3) a beach, littoral, and shallow marine complex. The cross- stratification in the lower sandstone unit indicates an easterly paleo- slope. The cross -stratification in the upper sandstone unit has a bi- modal distribution almost at right angles to the paleoslope, suggesting deposition by longshore currents. The standard deviation of the cross- stratification in the lower sandstone unit of 78° is typical of fluvial deposits. The standard deviation in the upper sandstone unit of 97° indicates a marine origin. x INTRODUCTION The basal Cretaceous Dakota Group has been wellstudied in many places. This thesis examines the Dakota Group's southernmost occurrence along the Front Range ofthe Rocky Mountains. An under- standing of this area is critical to the eventual understanding of the relationships of the basal Cretaceous strata to the southeastin the Tucumari basin. Location The area of this study is located in north-central New Mexico in the vicinity of Las Vegas, New Mexico (Figure 1) .Study was con- centrated on two overlapping areas, one along the north trending Creston Ridge for about 28 miles from La Cueva to Romeroville, the other extending 32 miles eastward from Romeroville to Trujillo (Figure 1). Scope of Investigation Stratigraphic sections, spaced a few miles apart, were measured and described during the summer of 1974. Laboratory pro- cedures involved study of thin sections, heavy minerals, and palyn- morphs in an attempt to differentiate the stratigraphic units within the Dakota Group.