CORRELATION OF SEQUENCE STRATIGRAPHIC SURFACES OF THE MID-CRETACEOUS DAKOTA GROUP FROM SUBSURFACE TO OUTCROP SOUTHERN DENVER BASIN, COLORADO by YAQOUB Y Y S M ALSAYED ALREFAEI Presented to the Faculty of the Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN GEOLOGY THE UNIVERSITY OF TEXAS AT ARLINGTON August 2011 Copyright © by Yaqoub Y Y S M Alsayed Alrefaei 2011 All Rights Reserved ACKNOWLEDGEMENTS My great gratitude is to Allah for his blessings and guidance. Then I‟m grateful to Dr. John Holbrook my thesis advisor and committee chairman for his unlimited help, assistance, advice and patience. Also, I would like to thank him for providing me with his well- logs, outcrop cross-sections, and papers which helped me greatly in my research. I would also like to thank my committee members Dr. John Wickham and Dr. Harold Rowe for their participation and help in my thesis. Special thanks to Kuwait University for sponsoring my scholarship and giving me the opportunity to peruse my higher education in the United States of America. Also a special thanks for Denver Earth Resource Library for giving me access to their well-log database and their journal and book collections. I would like to dedicate this thesis to my beloved family especially my parents (Yousef Alrefaei, Mariam Ali) whom I could not made it without and whose prayers and encouragement sustain me. Most of all, I wish to thank my dear wife Hanan and children Mariam and Yousef for their patience, sacrifices, help and endless support. May 9, 2011 iii ABSTRACT CORRELATION OF SEQUENCE STRATIGRAPHIC SURFACES OF THE CRETACEOUS DAKOTA GROUP FROM SUBSURFACE TO OUTCROP SOUTHERN DENVER BASIN, COLORADO Yaqoub Y Y S M Alsayed Alrefaei, M.S. The University of Texas at Arlington, 2011 Supervising Professor: John Holbrook The D and J sandstone of the Cretaceous Dakota Group are considered as the major oil and gas producing units within in the Denver Basin. Denver Basin is a sub-basin of the Early Cretaceous Western Interior Basin .These units are well understood within the northern Denver Basin and the linkage between the subsurface units and their equivalents in outcrop in the Front Range is well-established. These strata have gained less attention in southern parts of the basin and the linkage between the subsurface units and their equivalents in southern outcrop is not yet established. The main purpose of the study is to investigate the linkage between the subsurface Dakota Group units within the southern Denver Basin and their equivalents in outcrop of southeastern Colorado. This was achieved by correlating sequence stratigraphic surfaces within Dakota Group strata in the Denver Basin using well-log data and then correlating these surfaces with their age-equivalents in outcrop of southeastern Colorado. By proving this linkage, a better understanding for the correlation of Dakota Group strata from subsurface to outcrop is represented in the southeastern part of Denver Basin which can be used as a tool in future research in the area and can forward regional paleogeographic iv reconstruction for this time interval. Paleogeography, deposition and distribution of the J and D Sandstone were illustrated in the study using the Buffer and Buttress model. Valley intersection of different generation at the same stratigraphic level in both the J and D Sandstone were observed in the study area and were explained also by using the Buffer and Buttress model. The subsurface Huntsman Shale continuation in southern the Denver Basin to surface exposure in southeastern Colorado outcrops was supported based on thickness trend, fossil assemblage, and facies which constrained the correlation of the subsurface Dakota Group units with their surface equivalents in outcrop southeast Colorado. v TABLE OF CONTENTS ACKNOWLEDGEMENTS ................................................................................................................iii ABSTRACT ..................................................................................................................................... iv LIST OF ILLUSTRATIONS............................................................................................................. viii Chapter Page 1. INTRODUCTION……………………………………..………..….. ..................................... 1 1.1 The study area ................................................................................................. 4 1.2 Denver Basin .................................................................................................... 5 1.3 Purpose ............................................................................................................ 7 1.4 Background and previous work ........................................................................ 8 1.5 Dakota Group stratigraphy in Colorado ........................................................... 9 1.5.1 Surface Dakota Group nomenclature in Colorado ......................... 10 1.5.2 Subrface Dakota Group nomenclature in Colorado ....................... 11 1.6 Sequence stratigraphy and previously proposed depositional models of Dakota Group ........................................................... 14 1.6.1 Sequence stratigraphy of Dakota Group ........................................ 14 1.6.2 Previously proposed depositional models for Dakota Group in northern, western and central Denver Basin .................................................................... 16 2. METHODS ................................................................................................................... 20 2.1 Identification and correlation of sequence stratigraphic surfaces .................. 20 2.2 Correlation of marker beds and the X-bentonite ............................................ 21 2.3 Construction of strike and dip well-log cross-sections and isopach maps ........................................................................................ 21 vi 2.4 Correlation of subsurface well-log cross-section of Dakota Group with measured outcrop sections in southeastern Colorado .............................................................................. 21 3. DATA AND RESULTS ................................................................................................. 23 3.1 Dakota Group distribution and thickness variation......................................... 23 3.2 Strike and dip cross-sections of Dakota Group strata ................................... 24 3.3 Sequence Stratigraphic Surface correlation within the Denver Basin ........... 24 4. DISCUSSION ................................................................................................................ 30 4.1 Correlation of Dakota Group strata from subsurface Denver Basin to southeastern outcrop, Colorado .......................................... 30 4.2 Valley incisions and valley trends of the D and J Sandstone ........................ 36 4.2.1 Valley incisions and valley trends of the J Sandstone .................. 37 4.2.2 Valley incisions and valley trends of the D Sandstone ................. 37 4.3 Synchronous valleys vs. Asynchronous valleys ............................................ 38 4.4 Paleogeography of the J and D Sandstones ................................................. 39 5. CONCLUSION .............................................................................................................. 52 REFERENCES ............................................................................................................................... 54 BIOGRAPHICAL INFORMATION .................................................................................................. 59 vii LIST OF ILLUSTRATIONS Figure Page 1. The Cretaceous Western Interior Seaway extent during Late Cretaceous time .......................... 3 2. Location of the study area and outcrop sections that were used in the study: JM-101= John Martin‟s Reservoir section, H-100= Higbee section ........................ 4 3. Denver Basin outline and surrounding structural zones. ............................................................ 6 4. Surface nomenclature and sequence stratigraphy of mid-Cretaceous (Albian and Cenomanian) Dakota Group in northern and southeastern Colorado. .................... 11 5. Subsurface nomenclature and sequence stratigraphic surfaces of Dakota Group in Denver Basin, Colorado. ................................................................................. 13 6. Depositional model for the J “Muddy” Sandstone in northern Denver Basin proposed by Weimer (1988) and Weimer (1992) ............................................... 18 7. Depositional model for the D Sandstone in northern Denver Basin proposed by (Sonnenberg,1987) .................................................................................... 19 8. Isopach map of Dakota Group strata from the base of the J Sandstone (SB3) to the top of the D Sandstone showing the incision of the J Sandstone into the Skull Creek, valley trends and valley intersections ............................ 26 9. Isopach map of Huntsman Shale showing the incision of the D Sandstone into the Huntsman, valley trends and valley intersections ........................................................ 27 10. E-W strike and dip well-log cross-section of subsurface Dakota Group strata ....................... 28 11. N-S strike and dip well-log cross-section of subsurface Dakota Group strata ........................ 29 12. Longitudinal profile section