THESIS TIMING and GENESIS of FRACTURES in the NIOBRARA FORMATION, NORTHEASTERN FRONT RANGE and DENVER BASIN, COLORADO Submitted

THESIS TIMING AND GENESIS OF FRACTURES IN THE NIOBRARA FORMATION, NORTHEASTERN FRONT RANGE AND DENVER BASIN, COLORADO Submitted by Cody Lee Allen Department of Geosciences In partial fulfillment of the requirements For the Degree of Master of Science Colorado State University Fort Collins, Colorado Summer 2010 COLORADO STATE UNIVERSITY April 30th, 2010 WE HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER OUR SUPERVISION BY CODY L. ALLEN ENTITLED TIMING AND GENESIS OF FRACTURES IN THE NIOBRARA FORMATION, NORTHEASTERN FRONT RANGE AND DENVER BASIN, COLORADO BE ACCEPTED AS FULFILLING IN PART REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE. Committee on Graduate Work ____________________________________ Wayne Charlie ____________________________________ Sven Egenhoff ____________________________________ Bryan Richter ____________________________________ Advisor: Eric Erslev ____________________________________ Department Head: Sally Sutton ii ABSTRACT OF THESIS TIMING AND GENESIS OF FRACTURES IN THE NIOBRARA FORMATION, NORTHEASTERN FRONT RANGE AND DENVER BASIN, COLORADO Naturally-occurring fractures in foreland basins, particularly in self-sourced resource plays, are critical to the production of hydrocarbons from low permeability reservoirs. Both shear and extensional fractures commonly cause reservoir anisotropy as well as providing critical tests of tectonic hypotheses. The objective of this research is to determine the mechanisms and timing of naturally-occurring fractures in the upper Cretaceous Niobrara Formation along the northeastern Front Range and in the Denver Basin of the Rocky Mountain Foreland. Previous hypotheses for the origin of fractures within the Denver Basin have focused largely on mechanisms invoking basement reactivation either by vertical block motion or by Laramide subhorizontal shortening. Contrasting hypotheses include multidirectional slip, regional and/or local detachment, and post-Laramide extension in the direction of previous compression. This study analyzes the kinematics, modes and mechanisms of deformation in the Niobrara Formation from fractures examined along the northeastern Front Range and from faults identified in 3D seismic data from the Denver Basin. Surface fracture data collected from 61 locations include minor faults, joints, calcite-filled fractures, and pressure solution stylolites. Subsurface data includes two 3D seismic surveys (Sooner Field and Dana Point) were fault geometries were examined. iii In outcrops, ideal σ1 analysis of strike–slip and thrust fault data document a subhorizontal Laramide compression with an average attitude of 086°-08⁰. Normal faults identified through the study are highly variable with an average slip direction of 183⁰- 73⁰. Normal dip-slip reactivation of right-lateral shear planes indicates normal faults are younger. Two joint systems are observed throughout the study area with J1 joints averaging 078⁰ and later J2 joints averaging 171⁰. Subsurface 3D seismic data show listric and planar normal fault sets cut the Niobrara and lower Pierre formations. Calculated fault dip angles at Sooner Field average 8⁰, and those at Dana Point average 27⁰. These low fault dip angles suggest layer-parallel detachment, but diverse fault strikes are problematic and suggest multiple slip directions. No basement-to-Cretaceous faults were identified in either volume, casting doubt on basement reactivation hypotheses. Fracture sets in the Niobrara Formation show evidence for four different fracture mechanisms. Initial faulting generated by Laramide subhorizontal compression (086°) was followed by later, but still Laramide, ENE- to E-W-striking J1 splitting joints. Post- Laramide extension is indicated by NNW to N-S-striking J2 joints. Lastly, low-angle listric and planar normal faults in seismic data are interpreted to be post-Laramide. They were probably caused by local detachment, but their mechanisms and timing require further investigation. Cody Lee Allen Department of Geosciences Colorado State University Fort Collins, CO 80523 Summer 2010 iv ACKNOWLEDGMENTS This project was supported by a research assistantship through Noble Energy Inc., and the Duncan A. McNaughton memorial grant from the American Association of Petroleum Geologists. Echo Geophysical Inc. graciously donated access to the Dana Point 3D seismic survey. I would like to express my sincere gratitude and thanks to my advisor, Dr. Eric Erslev, for his patience and guidance throughout my graduate studies at Colorado State University. Eric, your expertise and scientific enthusiasm greatly enhanced my ability to test complex geologic hypotheses, and fostered a renewed appreciation for field research, and the Colorado outdoors. I would also like to thank Dr. Sven Egenhoff and Dr. Wayne Charlie for being on my graduate committee, as well as fellow students and staff at Colorado State University for their instruction, and friendship. Special thanks go to Dr. Bryan Richter of Noble Energy Inc. who was also on my committee, for being a great mentor, friend, and sounding board for new ideas and hypotheses. Field data presented in this thesis could not have been collected without the permission of many public and private landowners. I would like to thank Holcim Inc, Cemex Inc., and the many private land owners who allowed access to outcrop along the northeastern Front Range. Last but not least, I would like to express my sincere gratitude and appreciation to my mother Jacqi and father Terry for their support and encouragement. To my wife Charity, thank you for your emotional and financial support, understanding, patience, and bright smile after long field days. I couldn’t have done it without you. v TABLE OF CONTENTS Page Title Page …………………………………………………………………………. i Signature Page……………………………………………………………………..ii Abstract of Thesis………………………………………………………………….iii Acknowledgements……………………………………………………………….. v Table of Contents………………………………………………………………….vi 1. INTRODUCTION………………………………………………………….…... 1 2. STRATIGRAPHIC SUMMARY……………………………………………….8 Precambrian…………………………………………………………………8 Paleozoic……………………………………………………………………10 Mesozoic……………………………………………………………………12 Cenozoic……………………………………………………………………18 3. PREVIOUS WORK……………………………………………………………20 Laramide Tectonic and kinematic Models…………………………………20 Post-Laramide Tectonic and Kinematic Models…………………………...26 Previous Structural Interpretations of the Northeastern Front Range ……...28 Subsurface Denver Basin Fracture Studies………………………………...32 4. METHODS OF DATA COLLECTION, SURFACE FRACTURE OBSERVATIONS AND ANALYSIS………………………………………….....40 Fault and Shear Sense Data Collection Methods…………………………...41 Fracture and Bedding Data Collection Methods……………………………42 Methods of Analysis of Minor Fault Data……………………………….....42 Methods of Analysis of Joint, Calcite Fracture, Stylolite, and Pencil Cleavage Data…………………………………………………………………………44 Geologic Observations……………………………………….......................44 Livermore Quadrangle……………………………………………...53 Laporte Quadrangle………………………........................................56 Horsetooth Reservoir Quadrangle…………………………………..63 Masonville Quadrangle……………………………………………..67 Carter Lake Reservoir Quadrangle………………………………….73 Hygiene Quadrangle………………………………………………...76 Boulder Quadrangle………………………………………………....81 Observations Summary……………………………………………...88 5. DETAILED FRACTURE ANALYSIS………………………………………...90 Minor Fault Slickenlines and Ideal σ1 Axes………………………………...90 Stylolite Data Analysis……………………………………………………...98 Joint Data and Analysis……………………………………………………..99 Calcite filled Fracture Analysis……………………………………………..104 Conclusions from Fracture Analysis………………………………………..105 vi TABLE OF CONTENTS (CONT.) Page 6. 3D SEISMIC FAULT ANALYSIS………………………………………….….107 Previous Subsurface studies and hypotheses………………………………..107 Methods of 3D Seismic Fault Analysis……………………………………..111 Sooner Field 3D Seismic Observations and Fault Analysis………………...113 Dana Point 3D Seismic Observations and Fault Analysis…………………..120 Conclusions………………………………………………………………….128 7. CONCLUSIONS………………………………………………………………...132 Questions for Future Research………………………………………………137 References Cited……………………………………………………………………139 Appendices………………………………………………………………………….153 Appendix One: Shear Fracture Data Tables..........................................................154 Appendix Two: Extensional Fracture Data Tables……………………………....159 Appendix Three: Calcite-Filled Fracture Data Tables……………………...…...165 Appendix Four: Stylolite Data Table………………………………………….......169 Appendix Five: Pencil-Cleavage Data Table……………………………………...170 Appendix Six: Borehole Breakout Data Table ……………………………...…....171 Appendix Seven: Formation Micro-Image Log Fracture Data Tables……….....172 Appendix Eight: Sooner Field 3D Seismic Fault Data Tables……… ……..…....175 Appendix Nine: Dana Point 3D Seismic Fault Data Tables………………...……186 vii Chapter 1 Introduction Foreland basins develop on continental crust along the length of collisional plate margins or along compressional destructive margins (Beaumont, 1981; Blackstone, 1986; Jordan, 1981; 1995; DeCelles and Giles, 1996; Leeder, 1999). They are the most studied type of sedimentary basin because they lie adjacent to Earth’s major mountain chains and contain geological data with which orogenic belts can be reconstructed. Retro-arc foreland basins such as the active basins east of the Andes and the eastern forelands of the Rocky Mountains lie on continental crust of the overriding plate at destructive margins on the continental side of orogenic belts away from the subducting plate (Leeder, 1999; Allen and Allen, 1990, Ramos

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