Analysis of Salt-Sediment Interaction

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ANALYSIS OF SALT-SEDIMENT INTERACTION ASSOCIATED WITH STEEP DIAPIRS AND ALLOCHTHONOUS SALT: FLINDERS AND WILLOURAN RANGES, SOUTH AUSTRALIA, AND THE DEEPWATER NORTHERN GULF OF MEXICO

by Thomas E. Hearon, IV Copyright by Thomas E. Hearon, IV 2013 All Rights Reserved A thesis submitted to the Faculty and Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Geology).

Golden, Colorado Date

Signed: Thomas E. Hearon, IV

Signed: Dr. Bruce D. Trudgill Thesis Advisor

Golden, Colorado Date

Signed: Dr. Paul M. Santi Professor and Interim Department Head Department of Geology and Geological Engineering

ii ABSTRACT

The eastern Willouran Ranges and northern Flinders Ranges, South Australia contain Neoproterozoic and Cambrian outcrop exposures of diapiric breccia contained in salt diapirs, salt sheets and associated growth strata that provide a natural laboratory for testing and refining models of salt-sediment interaction, specifically allochthonous salt initiation and emplacement and halokinetic deformation. Allochthonous salt, which is defined as a sheet-like diapir of mobile evaporite emplaced at younger stratigraphic levels above the autochthonous source, is emplaced due to the interplay between the rate of salt supply to the front of the sheet and the sediment- accumulation rate, and may be flanked by low- to high-angle stratal truncations to halokinetic folds. Halokinetic sequences (HS) are localized (<1000 m) unconformity-bound successions of growth strata adjacent to salt diapirs that form as drape folds due to the interplay between salt rise rate (R) and sediment accumulation rate (A). HS stack to form tabular and tapered composite halokinetic sequences (CHS), which have narrow and broad zones of thinning, respectively. The concepts of CHS formation are derived from outcrops in shallow water to subaerial depositional environments in La Popa Basin, Mexico and the Flinders Ranges, South Australia. Current models for allochthonous salt emplacement, including surficial glacial flow, advance above subsalt shear zones and emplacement along tip thrusts, do not address how salt transitions from steep feeders to low-angle sheets and the model for the formation of halokinetic sequences has yet to be fully applied or tested in a deepwater setting. Thus, this study integrates field data from SouthAustralia with subsurface data from the northern Gulf of Mexico to test the following: (1) current models of allochthonous salt advance and subsalt deformation using structural analysis of stratal truncations adjacent to outcropping salt bodies, with a focus on the transition from steep diapirs to shallow salt sheets in South Australia; and (2) the outcrop-based halokinetic sequence model using seismic and well data from the Auger diapir, located in the deepwater northern Gulf of Mexico. Structural analysis of strata flanking steep diapirs and allochthonous salt in South Australia reveals the transition from steep diapirs to shallowly-dipping salt sheets to be abrupt and involves piston-like breakthrough of roof strata, freeing up salt to flow laterally. Two

iii models explain this transition: 1) salt-top breakout, where salt rise occurs inboard of the salt flank, thereby preserving part of the roof beneath the sheet; and 2) salt-edge breakout, where rise occurs at the edge of the diapir with no roof preservation. Shear zones, fractured or mixed ‘rubble zones’ and thrust imbricates are absent in strata beneath allochthonous salt and adjacent to steep diapirs. Rather, halokinetic drape folds, truncated roof strata and low- and high-angle bedding intersections are among the variety of stratal truncations adjacent to salt bodies in South Australia. Interpretation and analysis of subsurface data around the Auger diapir reveals similar CHS geometries, stacking patterns and ratios of salt rise and sediment accumulation rates, all of which generally corroborate the halokinetic sequence model. The results of this study have important implications for salt-sediment interaction, but are also critical to understanding and predicting combined structural-stratigraphic trap geometry, reservoir prediction and hydrocarbon containment in diapir-flank settings.

iv TABLE OF CONTENTS

ABSTRACT...... iii LIST OF FIGURES...... ix LIST OF TABLES...... xiii ACKNOWLEDGMENTS...... xiv CHAPTER 1 INTRODUCTION...... 1 1.1 Halokinetic Growth Strata...... 3 1.2 Allochthonous Salt...... 6 1.3 South Australia and the Gulf of Mexico...... 9 1.3.1 Basin Types and Evolution...... 14 1.3.2 Salt Composition and Deformation...... 19 1.3.3 Depositional Environments...... 20 1.4 Summary of Chapters...... 20 1.4.1 Chapter 2: Geology and tectonics of Neoproterozoic salt diapirs and salt sheets in the eastern Willouran Ranges, South Australia...... 20 1.4.2 Chapter 3: Allochthonous salt initiation and advance in the Flinders and eastern Willouran Ranges, South Australia: Using outcrops to test subsurface-based models from the northern Gulf of Mexico...... 21 1.4.3 Chapter 4: Testing the applicability of an outcrop-based halokinetic deformation model in a deepwater depositional setting: Auger diapir, Garden Banks 427, northern Gulf of Mexico...... 22 1.5 References Cited...... 22 CHAPTER 2 GEOLOGY AND TECTONICS OF NEOPROTEROZOIC SALT DIAPIRS AND SALT SHEETS IN THE EASTERN WILLOURAN RANGES, SOUTH AUSTRALIA ...... 28 2.1 Abstract...... 28 2.2 Introduction...... 29 2.3 Geologic Setting of the Flinders and Willouran Ranges...... 31 2.3.1 Regional Tectonic History...... 32 2.3.2 Stratigraphy...... 34

v 2.3.3 Callanna Group Breccia...... 38 2.4 Observations...... 39 2.4.1 Structural Geometries...... 43 2.4.2 Stratal Geometries...... 45 2.5 Interpretation...... 48 2.5.1 Autochthonous Salt Structures...... 48 2.5.2 Allochthonous Salt Structures...... 51 2.5.3 Delamerian Orogeny...... 54 2.5.4 Salt and Minibasin Evolution...... 55 2.6 Discussion ...... 59 2.7 Conclusions...... 63 2.8 Acknowledgments...... 64 2.9 References Cited...... 65 CHAPTER 3 ALLOCHTHONOUS SALT INITIATION AND ADVANCE IN THE FLINDERS AND EASTERN WILLOURAN RANGES, SOUTH AUSTRALIA: USING OUTCROPS TO TEST SUBSURFACE-BASED MODELS FROM THE NORTHERN GULF OF MEXICO...... 75 3.1 Abstract...... 75 3.2 Introduction...... 76 3.3 Geologic Setting of the Flinders and Willouran Ranges...... 79 3.4 Description of Stratal and Structural Geometries...... 83 3.4.1 Pinda Diapir...... 83 3.4.2 Patawarta Diapir...... 88 3.4.2.1 Southeast End...... 88 3.4.2.2 Northwest End...... 91 3.4.3 Eastern Willouran Ranges...... 94 3.4.4 Summary...... 98 3.5 Interpretation...... 99 3.5.1 Structural Analysis...... 99 3.5.2 Pinda Diapir...... 101 3.5.3 Patawarta Southeast...... 103

vi 3.5.4 Patawarta Northwest...... 103 3.5.5 Eastern Willouran Ranges...... 105 3.6 Allochthonous Salt Initiation and Advance...... 107 3.6.1 Initiation and Breakout...... 109 3.6.2 Advance...... 113 3.7 Discussion...... 115 3.8 Conclusions...... 123 3.9 Acknowledgments...... 125 3.10 References Cited...... 125 CHAPTER 4 TESTING THE APPLICABILITY OF AN OUTCROP-BASED HALOKINETIC DEFORMATION MODEL IN A DEEPWATER DEPOSITIONAL SETTING: AUGER DIAPIR, GARDEN BANKS 427, NORTHERN GULF OF MEXICO...... 134 4.1 Abstract...... 134 4.2 Introduction...... 135 4.3 Geologic Setting...... 142 4.4 Methodology...... 148 4.5 Description and Analysis...... 151 4.5.1 Stratal Geometries...... 154 4.5.2 Well Correlations...... 156 4.6 Discussion...... 158 4.6.1 Comparison to CHS Model...... 159 4.6.2 Additional Diapir Flank Truncations...... 160 4.6.3 Application to Allochthonous Salt...... 161 4.6.4 Limitations, Implications and Future Work...... 161 4.7 Conclusions...... 162 4.8 Acknowledgments...... 163 4.9 References Cited...... 163 CHAPTER 5 IMPLICATIONS AND CONCLUSIONS...... 168 5.1 Limitations...... 170 5.2 Exploration and Development Ramifications...... 171

vii 5.3 Suggestions for Future Work...... 172 5.3.1 Willouran and Flinders Ranges, South Australia...... 172 5.3.2 Northern Gulf of Mexico and other Global Salt Basins...... 172 5.4 References Cited...... 173 APPENDIX A CO-AUTHOR PERMISSIONS...... 174

viii LIST OF FIGURES

Figure 1.1 End-member styles of halokinetic sequences...... 4

Figure 1.2 Hook (i of Figure 1.1) and wedge (ii of Figure 1.1) end-member halokinetic sequence types (HS) stack vertically to form tabular (a) and tapered (b) end- member composite halokinetic sequence (CHS) types...... 4

Figure 1.3 Different geometric stacking patterns of composite halokinetic sequences...... 5

Figure 1.4 Conceptual model of an extrusive salt sheet connected to a primary salt diapir rooted in the autochthonous salt level...... 7

Figure 1.5 Controlled Beam Migration (CBM) of a 3-D PSDM seismic line from the northern Gulf of Mexico that illustrates two primary salt diapirs bounding a primary minibasin with an expulsion rollover and megaflap to the right, a partially welded allochthonous canopy with two allosutures (vertical red dashes) and suprasalt minibasins...... 8

Figure 1.6 Schematic model of scarp failure above a ramping salt sheet and the deposition of a debris flow deposit outboard of the sheet, later overridden by advancing salt...... 10

Figure 1.7 Schematic model for the advance of a salt glacier...... 11

Figure 1.8 Basal shear model for allochthonous salt advance showing a thrusted shear zone adjacent to and beneath the salt sheet...... 12

Figure 1.9 Uninterpreted and interpreted seismic examples of the frontal edge of advancing salt sheets showing thrust faults that link to the seafloor...... 13

Figure 1.10 Major geologic provinces and Delamerian structures of South Australia...... 15

Figure 1.11 Approximate location of mapped diapirs within the Adelaide Fold Belt...... 16

Figure 1.12 Generalized Neoproterozoic and Cambrian stratigraphy present in the Adelaide Fold Belt...... 17

Figure 1.13 Sequential plate restoration of the Gulf of Mexico...... 18

Figure 2.1 Major geologic provinces and Delamerian structures of South Australia...... 33

ix Figure 2.2 Generalized Neoproterozoic and Cambrian stratigraphy present in the Adelaide Fold Belt...... 35

Figure 2.3 Generalized Neoproterozoic stratigraphy of the eastern Willouran Ranges, South Australia...... 37

Figure 2.4 Approximate location of mapped diapirs within the Adelaide Fold Belt...... 40

Figure 2.5 Uninterpreted false color composite image of 128-band HyMap (4 m resolution) colored similarly to a Landsat 7 FCC 741 RGB image and false color 431 image of 4-band Quickbird (0.6 m resolution) imagery of the eastern Willouran Ranges...... 41

Figure 2.6 Interpreted version of Figure 2.5...... 42

Figure 2.7 Comparative schematic stratigraphic columns illustrating the variable distribution of omitted stratigraphic section...... 49

Figure 2.8 Geologic map of the eastern Willouran Ranges...... 50

Figure 2.9 Geologic cross-sections A through E...... 52

Figure 2.10 Schematic evolution of the minibasins, diapirs and allochthonous salt of the eastern Willouran Ranges...... 56

Figure 2.11 Controlled Beam Migration (CBM) of a 3-D PSDM seismic line from the northern Gulf of Mexico...... 60

Figure 2.12 3-D PSDM seismic profile of an encapsulated minibasin bounded by branching welds and an allochthonous diapir...... 61

Figure 3.1 Generalized location map of the Adelaide Fold Belt...... 80

Figure 3.2 Generalized Neoproterozoic and Cambrian stratigraphy present in the Adelaide Fold Belt, along with relevant tectonic cycles...... 81

Figure 3.3 Pan-sharpened Landsat 7 ETM+ satellite image of the north-central Flinders Ranges...... 84

Figure 3.4 Neoproterozoic stratigraphy flanking the Pinda and Patawarta diapirs...... 85

Figure 3.5 Geologic map of the Pinda diapir...... 86

Figure 3.6 Simplified regional geologic map of the area surrounding the Patawarta diapir and Narrina Basin...... 89

x Figure 3.7 Geologic map of the southeastern end of the Patawarta diapir...... 90

Figure 3.8 Oblique aerial photo of stratal geometries flanking the Patawarta diapir...... 92

Figure 3.9 Geologic map of the northwestern end of the Patawarta diapir...... 93

Figure 3.10 Geologic map of the eastern Willouran Ranges...... 95

Figure 3.11 Oblique aerial photo of the Witchelina syncline flanking the Witchelina diapir in the eastern Willouran Ranges...... 97

Figure 3.12 3-D block diagram of a ramping salt sheet with a flanking halokinetic drape fold showing key lines and planes that provide the basis for deriving three- dimensional orientations from map-view relationships...... 100

Figure 3.13 Down-plunge cross-section of the Pinda diapir and salt tongue constructed using the halokinetic fold axis of the Brachina Formation (Nsb) (46/163)...... 102

Figure 3.14 Down-plunge cross-section of the ramping salt sheet at Patawarta constructed using the halokinetic fold axis of the Wonoka anticline-syncline fold pair (Nww) (41/104)...... 104

Figure 3.15 Schematic composite cross-section of the Patawarta diapir that combines relationships observed on the northwestern and southeastern ends...... 106

Figure 3.16 Models of the transition from steep diapirs to allochthonous salt, all of which involve piston-like breakthrough of roof strata and crestal erosion...... 110

Figure 3.17 Three models of allochthonous salt advance...... 114

Figure 3.18 Two scenarios of further thrust advance after pinned inflation and halokinetic drape folding...... 116

Figure 3.19 Wide-azimuth, prestack depth-migrated 3-D seismic profile from the northern Gulf of Mexico showing a steep primary diapir that transitions abruptly to a low-angle allochthonous salt sheet without any apparent flanking halokinetic folding (salt-edge breakout)...... 118

Figure 3.20 Wide-azimuth, prestack depth-migrated 3-D seismic profile from the northern Gulf of Mexico showing a steep diapir that transitions upward to a low-angle allochthonous salt sheet, but with a short segment of roof preserved above a shoulder in the edge of salt (salt-top breakout)...... 119

xi Figure 3.21 Wide-azimuth, prestack depth-migrated 3-D seismic profile from the northern Gulf of Mexico showing a salt sheet with: (1) a base-salt flat with no apparent underlying folding; (2) a mock ramp flanked by a tapered composite halokinetic sequence (CHS); (3) a true ramp flanked by a tabular CHS; and (4) an upper base-salt flat with frontal imbricate thrust faults...... 120

Figure 3.22 Wide-azimuth, prestack depth-migrated 3-D seismic profile from the northern Gulf of Mexico showing a steep, primary salt diapir that gradually flares as it transitions upward into a shallowly-dipping allochthonous salt sheet...... 121

Figure 4.1 Surprising drilling results at the Tahiti field...... 136

Figure 4.2 Hook (a) and wedge (b) end-member halokinetic sequence types (HS) stack vertically to form tabular (a) and tapered (b) end-member composite halokinetic sequence (CHS) types...... 138

Figure 4.3 Different geometric stacking patterns of composite halokinetic sequences...... 139

Figure 4.4 Multibeam bathymetry image of the northern Gulf of Mexico continental shelf and slope...... 143

Figure 4.5 Subregional top salt map of the Auger area, which shows the Auger diapir positioned between the Auger and Andros minibasins...... 144

Figure 4.6 Interpreted wide-azimuth, prestack depth-migrated 3-D seismic profile of the Auger diapir and flanking downdipAuger (left) and updip Andros (right) minibasins...... 145

Figure 4.7 Wide-azimuth, prestack depth-migrated 3-D seismic profiles of theAuger diapir and flankingAuger minibasin...... 147

Figure 4.8 Detailed wide-azimuth, prestack depth-migrated 3-D seismic profile of CHS, cusps separating CHS and condensed sections present at CHS boundaries...... 149

Figure 4.9 Example of three-step method for two-dimensional restoration of CHS...... 150

Figure 4.10 Interpreted wide-azimuth, prestack depth-migrated 3-D seismic profile showing the vertical distribution of tapered and tabular CHS on the northeastern and southwestern flanks of theAuger diapir...... 155

Figure 4.11 Top: Different geometric configurations of stacked composite halokinetic sequences (CHS) around Auger diapir. Bottom: interpreted wide-azimuth, prestack depth-migrated 3-D seismic profiles of CHS flanking theAuger diapir display similar configurations of stacked CHS...... 157

xii LIST OF TABLES

Table 3.1 Metrics compiled from map and stereonet analysis of diapirs and salt sheets in the northern Flinders Ranges and eastern Willouran Ranges, South Australia.....108

Table 4.1 Metrics compiled from present day and restored configurations of each composite halokinetic sequence (CHS) flanking theAuger diapir in the northern and southern domains...... 152

Table 4.2 Metrics compiled from the integration of biostratigraphic data and decompacted thicknesses of composite halokinetic sequence (CHS) intervals, which yields sediment accumulation rate (m/1000 yrs) for each CHS...... 153

xiii ACKNOWLEDGMENTS

First, I would like to thank my parents, Faye and Tommy, for pushing me towards the Ph.D. track and for their encouragement, support and help along my path to higher education. I couldn’t have done it without you! My eldest sister, Elizabeth, my brother-in-law, Joshua, and my middle sister, Mary Kent, are also thanked for their encouragement and support during my tenure at CSM. This project could not have been completed without the generosity of Katherine Giles and the Salt-Sediment Interaction Research Consortium at the Institute of Tectonic Studies at the University of Texas at El Paso, which provided full support of my field research in South Australia. Present and past members, including Anadarko, BHP-Billiton, BP, Chevron, Cobalt, ConocoPhillips, Devon, ENI, ExxonMobil, Hess, Marathon, Maxus (Repsol-YPF), Nexen, Samson, Shell, Statoil and Total are thanked for their interest and funding. Additional field funding was kindly provided by the AAPG Arthur Meyerhoff Grant, the RMAG Norman H. Foster Grant, the GCAGS Student Research Grant, GCSSEPM Ed Picou Fellowship Grant and the CSM Department of Geology and Geological Engineering. My tuition and fees were graciously sponsored by BP, Encana and the ConocoPhillips SPIRIT Scholarship. I’d like to give a big thanks to Kate an all of these organizations for their generosity and support. The Saler and Morphett families and the Nature Foundation are thanked for access to Callanna and Witchelina stations in the eastern Willouran Ranges, South Australia. Steve and Brenda Coulter allowed unrestricted access to the Pinda Reserve and I appreciate all of the great times spent at Steve’s cabin and at the Pinda Hut. Tony and Lisa Nicholls, Ian Johnson and the Nepabunna Community Council are also thanked for access to Pinda. Ian and Di Fargher and Keith and Lisa Slade allowed our group access to Patawarta and many wonderful evenings were spent at the Prairie Hotel in Parachilna with Ross and Jane Fargher. I would also like to thank Brian and Kate Williams for their kindness and hospitality during the numerous weeks spent mapping at Oladdie Station, which mostly consisted of cold, windy and damp field days! Bill Hart, Nick Burke, Jacek Jaminski, Cindy Yeilding and Jay Thorseth and the Gulf of Mexico Exploration Team at BP Americas are thanked for their technical expertise and help with

xiv obtaining seismic data from the Auger diapir. CGG is thanked for allowing me to show the data in this thesis. Art Waterman and PaleoData are thanked for access to biostratigraphic data. Richard Allmendinger and Midland Valley are thanked for the use of Stereonet 8 and Move software, respectively. To all of my dear friends at Mines: Jane Stammer, Patrick Geesaman, Nick Kerr, Justin Palmer, Mike Doe, David Broughton and Murray Hitzman, I would like to thank you for your patience, laughter, willingness to listen and technical abilities. I would also like to thank Simon Baker, Carl Fiduk, Evey Gannaway, Eric Gottlieb, Tyler Hannah and Rachelle Kernen for their keen insight, field support and lively technical discussions during many months spent in the outback of South Australia. Wallace Mackay is thanked for sharing the results of his Ph.D. research on the Callanna Group breccia in the northern Willouran Ranges. Jerry Smith, Amy Opperman, Jennifer Nix and Daniel Smith at DigitalGlobe are thanked for the use of Quickbird satellite imagery over several areas in South Australia, including Pinda and Patawarta. Terry and Peter Cocks of HyVista in Sydney are thanked for the donation of a HyMap dataset over the Pinda diapir. Mark Pickard generously provided use of a helicopter and flight time to acquire oblique aerial photos at the Pinda and Patawarta diapirs. Ian Fargher was kind enough to allow doors-off flying in his Cessna 172 to obtain aerial photos throughout the various field areas in the Flinders and Willouran ranges…cold, but great experiences! I would also like to thank Pam Aagaard, John Keeling, Alan Mauger, Sandy Menpes, Wolfgang Preiss and Peter Waring from the Minerals and Energy Resources Division at the Department for Manufacturing, Innovation, Trade, Resources and Energy (DMITRE) in Adelaide, South Australia. I appreciate Tobi Payenberg, Carmen Krapf, and Blaise Fernandes for introducing me to the Flinders Ranges in 2006, along with Kate Giles, Tim Lawton and Mark Rowan. Thanks to Bob Dalgarno for sharing his keen insight of Flinders Ranges geology with me. Kathryn Amos, Maureen Sutton, Eileen Flannery and the staff at the Adelaide School of Petroleum at the University of Adelaide are thanked for their logistical support over the last several years. Debbie Cockburn, Marilyn Schwinger and Summer Jackson of the CSM Geology and Geological Engineering Department are thanked for making my tenure at CSM smooth and seemingly effortless from the administrative side. Lastly, I would like to give a special thanks to Nila Matsler at the University of Texas-El Paso, who tirelessly worked in the background to make our field seasons in South

xv Australia run smoothly. A big thanks is owed to my committee who helped guide me through this research project: Bruce Trudgill, Mark Rowan, Jennifer Aschoff, John Humphrey and Dag Nummedal. Many thanks especially go to Bruce, who served as my advisor. Bruce helped me through the research project and included me on a number of sponsored activities, including numerous trips to Moab to learn and teach about Paradox salt tectonics. Countless discussions about salt tectonics and general structural problems were had during field excursions to Utah and South Australia. Thanks again for being my cohort, Bruce! I would like to thank Jen Aschoff for her keen insight into thinking about the big picture and how my research applies to multiple aspects of geology, not just salt tectonics. John Humphrey is thanked for his insight into the world of carbonates and making me think about the importance of SUC’s! I would like to thank Dag Nummedal for his ‘outside-the-box’ approach to geologic uncertainties, especially those associated with the Neoproterozoic. I owe a very special thanks and a debt of gratitude to Mark Rowan, who was technically invested in this research project from day one and was a main driver behind our understanding of South Australian salt tectonics. Mark’s unselfish assistance throughout this research project helped me to become a better scientist and I really appreciate his help. Not only do I view my committee members as technical advisors, but they are also my friends and I appreciate their help throughout my tenure at CSM.

xvi CHAPTER 1 INTRODUCTION

Over the past two decades, allochthonous salt bodies and flanking stratal truncations have become increasingly important due to the increase in subsalt exploration drilling in salt- dominated passive margin and rift basins. In the deepwater Gulf of Mexico and along the South Atlantic margins, for example, hydrocarbon reservoirs flanking steep to vertical salt diapirs and beneath allochthonous salt bodies account for significant oil and gas reserves (e.g., McGee et al., 1994). Stratal truncations, including halokinetic growth strata, adjacent to salt diapirs and beneath allochthonous salt are forensic indicators of salt-sediment interaction and are a critical factor to hydrocarbon exploration. Specifically, the increased upturn of hydrocarbon-bearing stratigraphic units adjacent to a salt diapir can cause reservoir volumes to decrease significantly (e.g., hydrocarbon-bearing Lower Tertiary Wilcox Group, Gulf of Mexico). Additionally, reservoir-scale features, radial faults and diapir-flanking stratigraphy, which are not well-imaged seismic due to their proximity to salt, are also extremely important to exploration, development, risk analysis and overpressure prediction. Borehole stability and lithological and pressure uncertainties have also become major concerns in the risking of hydrocarbon prospects beneath allochthonous salt bodies. Competitive business strategies between hydrocarbon exploration companies, resolution limitations inherent in the subsalt realm, one-dimensional well sampling and the paucity of onshore basins that contain exposed diapirs, salt-sheets and canopies have resulted in a dearth of publicly available knowledge of allochthonous salt tectonics and halokinetic growth strata (e.g., Swanston et al., 2011). These issues, along with drilling hazards and reservoir prediction, reinforce the need for integrated outcrop- and subsurface-based investigations. A holistic approach combining field mapping, structural analysis, sedimentological characterization of outcropping diapirs, allochthonous salt, salt welds and related minibasin strata with subsurface data around similar features in a variety of depositional settings is necessary to test existing models of halokinetic deformation and allochthonous salt emplacement. Previous studies and models of halokinetic growth strata and allochthonous salt

1 emplacement are solely based on either two-dimensional outcrop data or seismic and one- dimensional well data, respectively (e.g., Fletcher et al., 1995; Giles and Lawton, 2002; Hudec and Jackson, 2006; Giles and Rowan, 2012). While these investigations have stressed the importance of salt-sediment interaction, rarely have outcrop and subsurface data been combined to test critical questions such as whether outcrop studies in shallow water settings are valid in deepwater settings, and whether additional stratal geometries may exist and are preserved during the initiation, breakout and advance of shallowly-dipping allochthonous salt from steep diapirs. To this end, this study combines subsurface data from the northern Gulf of Mexico with outcrop data from the eastern Willouran Ranges and northern Flinders Ranges, South Australia in order to test the model of halokinetic growth strata formation and the evolution of steep to vertical diapirs to shallowly-dipping allochthonous salt, respectively. This study addresses two noteworthy problems: (1) current models of allochthonous salt advance and subsalt deformation, many of which are based on seismic and limited well data, do not address how salt transitions from steep feeders to low-angle sheets; and (2) the halokinetic sequence model, which was defined and characterized from outcrops of steep salt diapirs present in shallow water to subaerial depositional environments, has yet to be tested in a deepwater setting using seismic and well data. Stratal geometries flanking allochthonous salt and steep diapirs, including halokinetic sequences, are often poorly imaged, even on high quality seismic, due to the proximity to salt faces, overlying salt wings or bodies. To address some of the aforementioned uncertainties and problems, the methods used in this field-to-subsurface project were two-fold: (1) field mapping and structural analysis of several steep salt diapirs and shallowly-dipping salt sheets in the northern Flinders Ranges and eastern Willouran Ranges, South Australia, which enabled current allochthonous salt emplacement models to be tested; and (2) interpretation of a high-resolution three-dimensional seismic dataset combined with well data and structural restorations of composite halokinetic sequences around the Auger diapir, northern Gulf of Mexico, which were used to test the outcrop halokinetic sequence model (sensu Giles and Rowan, 2012). Outcrop-scale salt-sediment deformation features in South Australia represent comparative analogs to similar seismic-scale geometries present in hydrocarbon-rich, salt-dominated basins, such as the Gulf of Mexico and along the South Atlantic margins.

2 This study provides geologists working salt-truncation hydrocarbon plays with the following: (1) additional possibilities for stratal geometries flanking salt bodies; (2) new methods for allochthonous salt initiation and breakout; and (3) greater confidence in the presence of halokinetic sequences in deepwater settings. This information can ultimately be combined with previous seismic, field and laboratory studies and used as a set of predictive tools during prospect evaluation, exploration and development in deepwater, salt-dominated basins.

1.1 Halokinetic Growth Strata Growth strata adjacent to steep to vertical salt diapirs and allochthonous salt are defined as halokinetic sequences (HS), which are localized (<1 km) unconformity-bound successions of thinned and folded strata that form as drape folds due to the interplay between salt rise rate (R) and sediment accumulation rate (A) (e.g., Giles and Lawton, 2002; Rowan et al., 2003; Giles and Rowan, 2012). The width of stratal upturn, width of thinning and degree of folding define two different end-member geometries of halokinetic growth strata: 1) hook halokinetic sequences (i of Figure 1.1); and 2) wedge halokinetic sequences (ii of Figure 1.1). Whereas hook HS have a narrow zone of stratal upturn (50-200 m), high angular discordance and common mass-wasting deposits, wedge HS have broad zones of stratal upturn and thinning (300-1000 m) (Figure 1.1). Hook and wedge HS stack vertically to form tabular and tapered composite halokinetic sequences (CHS), which form under relatively high and low ratios, respectively, of R and A. Tabular CHS have subparallel base and top boundaries and a narrow zone of thinning adjacent to a diapir, whereas tapered CHS have convergent base and top boundaries and a broad zone of thinning (Figure 1.2). CHS may stack vertically into a variety of different geometric configurations, which display offset axial traces (Figure 1.3). Depending on the configuration of stacked CHS, salt flank irregularities may be present (i.e., cusps). The width of the halokinetic drape fold is controlled by the thickness of the sedimentary roof atop a diapir (Giles and Rowan, 2012). Tabular CHS develop when the roof is thin, whereas tapered CHS develop when the sedimentary roof is thick. CHS may develop adjacent to steeply- dipping to vertical salt diapirs and salt walls, inclined salt feeders and ramp to flat transitions adjacent to allochthonous salt sheets (e.g., Giles and Lawton, 2002; Rowan et al., 2010; Giles and Rowan, 2012; Kernen et al., 2012; Hearon et al., 2012), but are unlikely to occur beneath

3 (i) (ii) nisabiniM nisabiniM ripaiD ripaiD Hook Wedge

50-200m 300-1000m

Figure 1.1. End-member styles of halokinetic sequences: (i) hook halokinetic sequence; and (ii) wedge halokinetic sequence (modified from Giles and Rowan, 2012).

(a) Zone of stacked (b) Zone of stacked monoclinal axial traces monoclinal axial traces

ook SHH egdeW SH Diapir Diapir Hook HS Wedge HS

Hook HS Wedge HS Tabular CHS Hook HS Wedge HS Tapered CHS

m002-05 m0001-003

Figure 1.2. Hook (i of Figure 1.1) and wedge (ii of Figure 1.1) end-member halokinetic sequence types (HS) stack vertically to form tabular (a) and tapered (b) end-member composite halokinetic sequence (CHS) types (modified from Giles and Rowan, 2012).

4 a) b)

Tabular-CHS Tabular-CHS diapir diapir

Tabular-CHS

Tapered-CHS

c) d)

Pronounced Tapered-CHS Pronounced Tapered-CHS cusp cusp diapir diapir

Tabular-CHS Tapered-CHS

Figure 1.3. Different geometric stacking patterns of composite halokinetic sequences (CHS): (A) tabular CHS over tabular CHS; (B) tabular CHS over tapered CHS; (C) tapered CHS over tapered CHS; and (D) tapered CHS over tabular CHS (Giles and Rowan, 2012).

5 broad, sub-horizontal salt sheets. The formation of upturned halokinetic sequences adjacent to salt diapirs and allochthonous salt is not ascribed to drag folding or vertical attenuation of bedding (e.g., Alsop et al., 2000), rather to drape folding due to the intricate balance between sediment accumulation rate and salt rise rate under passive, gravitational conditions (e.g., McGuinness and Hossack, 1993; Giles and Lawton, 2002; Giles and Rowan, 2012). Halokinetic growth strata have similar geometric characteristics as traditional growth strata formed under the progressive advance and unroofing of thrust sheets (e.g., Riba, 1973) and minibasin-scale growth sequences that develop due to deeper salt evacuation (e.g., Prather et al., 1998; Giles and Rowan, 2012). However, differences in geometry, width of thinning, degree of upturn and proximity to salt bodies distinguish halokinetic growth strata from traditional, larger-scale growth strata (>1 km) (e.g., Riba, 1976; Prather et al., 1998). CHS are bounded by angular unconformities that become conformable away from salt bodies. These boundaries, which form during periods of maximum topographic relief, have been tentatively linked to third-order transgressive systems tracts in shelf depositional settings as the concepts of CHS formation are derived from outcrops present in shallow water to subaerial depositional environments in La Popa Basin, Mexico and the Flinders Ranges, South Australia. Outcrop examples of CHS in a variety of depositional environments (i.e., subaerial, shallow water, outer shelf and deepwater) suggest the formation of CHS is independent of depositional environment, however because their development is tied to the formation of roof strata, CHS may be more likely to form and be preserved in shallow water to deepwater depositional environments as subaerial environments are more generally prone to higher erosion rates and lower probability for roof development and preservation.

1.2 Allochthonous Salt Allochthonous salt is defined as a sheet-like body of mobilized evaporite or layered evaporite sequence emplaced at younger stratigraphic levels above the original autochthonous source (e.g., Jackson and Talbot, 1991; Hudec and Jackson, 2006; Hudec and Jackson, 2011) (Figures 1.4 and 1.5). Allochthonous salt may be derived from a single salt feeder and then emplaced during lateral spreading as a solitary salt sheet or salt tongue, which can coalesce with other salt sheets to form larger canopies and nappes in a variety of depositional settings ranging

6 Figure 1.4. Conceptual model of an extrusive salt sheet connected to a primary salt diapir rooted in the autochthonous salt level (Hudec and Jackson, 2011).

7 supra-salt minibasin supra-salt minibasin

weld salt canopy

salt diapir primary minibasin salt diapir

Explanation

Suture

autochthonous salt Salt weld Stratigraphic horizons

Salt contact 5 km Figure 1.5. Controlled Beam Migration (CBM) of a 3-D PSDM seismic line from the northern Gulf of Mexico that illustrates two primary salt diapirs bounding a primary minibasin with an expulsion rollover and megaflap to the right, a partially welded allochthonous canopy with two allosutures (vertical red dashes) and suprasalt minibasins. Salt bodies and welds (indicated by pairs of dots) are outlined in blue and subsalt horizons are in green, red and orange. Data courtesy of WesternGeco and C. Fiduk.

8 from deepwater to subaerial (e.g., northern Gulf of Mexico; Zagros Mountains, Iran). The angle at which allochthonous salt is emplaced is a function of the interplay between sediment accumulation rate and salt rise rate (e.g., McGuinness and Hossack, 1993; Yeilding et al., 1995; Giles and Rowan, 2012). Salt sheets are generally asymmetric and subhorizontal to moderately dipping, whereas salt diapirs can be more symmetrical, bulb shaped and more steeply dipping. Allochthonous salt has been described most commonly from passive margin settings (e.g., Mohriak et al., 1995; Rowan, 1995; Hudec and Jackson, 2004, 2006), although early accounts documented allochthonous salt in orogenic belts (e.g., Mrazac, 1907; Lees, 1927; Van der Fliert, 1953). Stratal truncations in subjacent strata to salt sheets may include halokinetic growth folds, unfolded roof strata and high- and low-angle bedding juxtapositions against salt, all of which record the style of allochthonous salt movement and emplacement. A number of mechanisms have been suggested to account for the emplacement and spreading of allochthonous salt (mostly based on newly acquired seismic data, well data and physical and numerical models) have been suggested over the last two decades, including slump failure and surficial glacial flow (McGuiness and Hossack, 1993; Fletcher et al., 1995) (Figures 1.6 and 1.7), advance above subsalt shear zones (Harrison and Patton, 1995; Harrison et al., 2004) (Figure 1.8), and emplacement along tip thrusts (Hudec and Jackson, 2006, 2009) (Figure 1.9). These models, however, do not discuss the transition form steep diapirs to low-angle salt sheets, thus two additional models for allochthonous salt initiation and breakout, which involve piston-like rise of a diapir, termed salt top and salt edge breakout, are discussed in more detail in Chapter 3 of this thesis.

1.3 South Australia and the Gulf of Mexico The following sections highlight differences in terms of basin type and evolution, salt composition and deformation and depositional environments for the Adelaide Fold Belt and the northern Gulf of Mexico. Overall, the two basins have markedly different geologic histories, however, despite these differences, the Adelaide Fold Belt and the northern Gulf of Mexico have remarkably similar stratal geometries and features related to salt-sediment interaction. The geologic setting of the Adelaide Fold Belt and the northern Gulf of Mexico are discussed in more detail in Chapters 2, 3 and 4.

9 Figure 1.6. Schematic model of scarp failure above a ramping salt sheet and the deposition of a debris flow deposit outboard of the sheet, later overridden by advancing salt (modified from McGuinness and Hossack, 1993).

10 A)

Figure 1.7. Schematic model for the advance of a salt glacier (modified from Fletcher et al., 1995). (A) initial surface spreading; (B) lateral spreading of the shallowly-dipping salt sheet is roughly coeval with sedimentation; and (C) sedimentation outpaces salt advance thus wthe base of salt is steeper.

11 Figure 1.8. Basal shear model for allochthonous salt advance showing a thrusted shear zone adjacent to and beneath the salt sheet (Harrison and Patton, 1995; modified in Hudec and Jackson, 2011).

12 Figure 1.9. Uninterpreted and interpreted seismic examples of the frontal edge of advancing salt sheets showing thrust faults that link to the seafloor (Hudec and Jackson, 2009).

13 1.3.1 Basin Types and Evolution The northern Flinders Ranges and eastern Willouran Ranges are located within a north- south trending fold belt located approximately 450 km (280 mi) north of Adelaide, South Australia (Figure 1.10), commonly referred to as the Adelaide Geosyncline (e.g., Sprigg, 1952; Preiss, 1987), the Adelaide Basin (e.g., Preiss, 2000) or the Adelaide Fold Belt (e.g., Scheibner, 1973; Jenkins, 1990). Throughout the Early Neoproterozoic to Early Cambrian, this area evolved as a multi-stage aulacogen during a series of five consecutive rift episodes associated with the breakup of the Rodinian supercontinent, as western Laurentia broke away from Australia (Moores, 1991; Preiss, 2000). A layered evaporite sequence deposited during early rift stages was mobilized into salt diapirs and localized salt sheets during loading by a thick succession of nonmarine and marine sedimentary basin fill. More than 100 diapiric structures are exposed in the Flinders Ranges (Figure 1.11). Diapirism and allochthonous salt spreading was primarily passive (i.e., driven by differential loading) throughout the evolution of the Flinders Ranges salt system, although an early phase of the Delamerian Orogeny (see Lemon, 1988) may have caused allochthonous salt breakout in some areas. Rifting and thermal subsidence was immediately followed by thin- and thick-skinned inversion and deformation during the Upper Cambrian- Ordovician (~500 Ma) Delamerian Orogeny (Figure 1.12). Thus, the map-view patterns of two- dimensional outcrop exposures in all of the research areas represent oblique cross sections. In contrast, the Gulf of Mexico evolved as a passive margin during Mesozoic rifting and counterclockwise rotation of the Yucatan microplate and the North American plate (e.g., Pindell and Dewey, 1982; Hudec et al., 2013b) (Figure 1.13). Widespread Jurassic evaporites were deposited during rifting and mobilized into a complex array of salt diapirs and extensive multi-level sheets, canopies and salt welds during progressive loading by late Jurassic through Cenozoic sedimentary fill in a network of primary and secondary minibasins (e.g., Diegel et al., 1995; Peel et al., 1995; Galloway, 2009). Unlike South Australia, the Gulf of Mexico is dominated by gravity-driven structures and has not been subjected to large-scale basin inversion. However, in addition to gravitationally-driven salt movement, previous workers have documented a pulse of shortening during the Miocene, which increased salt rise rates during gravity spreading of allochthonous salt (Peel et al., 1995; Mount et al., 2007).

14 O O O O 137 139 141 O 135 Peake 143 Location Map 28O Inlier + 28O PEAKE DENISON+ + + RANGES + + + + QUEENSLAND MULOORINA AUSTRALIA + + NORWEST FAULTRIDGE + Mount + Babbage + MARREE Inlier + + + Mount + + + Painter T + L Inlier WONOMINTA O U O 30 + A F V BLOCK 30

+ + + TORRENS + + A V + N A CURNAMONA

FLINDERS L BENAGERIE V + A R + A V + PERNATTY P V + + NEW SOUTH WALES V + + + + + + CRATONIC

UPWARP RIDGE + + + + + + +

+ + HINGE MACDONALDNUCLEUS + Explanation + + + + + + + + STUART + + + Relatively undeformed ADELAIDE + + + + + O + SHELF + O 32 + + 32 GAWLER FAULT + + FOLD BELT + Willyama + Adelaidean and early CRATON Inlier + RANGES + + + A‘ Paleozoic cratonic cover + + Olary region + ZONE + ++ ++ + + Pre-Adelaidean rocks + ARC ++ + + + + ANTICLINAL + + + (largely outcropping) + + + NACKARA + + + HOUGHTON + ? Post-Delamerian Paleozoic + + + + ZONE + + ? rocks of western Victoria + + + SHELF O + MOUNT LOFTY O and New South Wales (Late 34 ? 34 + + v v Cambrian to Devonian)

+ SPENCER + MURRAY ADELAIDE ? BASIN + + Inferred area of Delamerian fold belt + TROUGH ?

+ + ARC Largely outcropping + + + + FLEURIEU ?

VICTORIA KANMANTOO + Largely concealed

SOUTHAUSTRALIA O O 36 + + + + 36

+ + KANGAROO ++ + Delamerian granitoids ISLAND ? + ? V v v V Cambrian volcanics V v + V ++ V + ++ + Major faults

0 100 200 V 38O V 38O Kilometers Major syncline axes in Adelaidean

O O O 135O 137 139 141 143O and early Paleozoic sediments

Figure 1.10. Major geologic provinces and Delamerian structures of South Australia (redrafted from Preiss, 1987).

15 O 136 INSET

O 28 PEAKE AND DENISON RANGES

O 138 O Mirra Marree 141 Clara St Dora Witchelina Breaden Hill Chintapanna O 30 South Hill Lyndhurst Burr Ideyaka Tourmaline Hill Loch Ness Copley LAKE Mucatoona Beltana Pinda LAKE FROME Nilpena Patawarta Frome Blinman Wirrealpa TORRENS Enorama Oraparinna Moralana NSW Upalinna Ilka Arkaba Windowarta intrusive breccias of

Worumba Anticline O Baratta 32 Wirreanda Uroonda Round Hill Yanyarrie Port Augusta Olary Oladdie

Coomooroo Walloway Paratoo Mount Vickery Rock Remarkable Whyalla Bulyninnie Oak Park

Port ADELAIDE Pirie FOLD BELT

Burra GULF

O 34 SPENCER RIVER Tamma VIC MURRAY

0 100 ADELAIDE KILOMETERS

Diapir

Basement inlier

O 36

Figure 1.11. Approximate location of mapped diapirs within the Adelaide Fold Belt (redrafted from Coats and Preiss, 1987; Dyson and Rowan, 2004).

16 Chronostratigraphic Units Major Lithostratigraphic Units Regional Tectonics Salt Tectonics 514+5 Ma Lake Frome Group Middle Cambrian Wirrealpa Limestone Kanmantoo Group 526+4 Ma Billy Creek Formation

Early Hawker Group Normanville Moralana

Cambrian Supergroup Group

Uratanna Formation diapir squeezing Delamerian Orogeny Pound Subgroup Ediacaran Wilpena 588+35 Ma Group Major hiatus Yerelina Marinoan Umberatana Willochra Subgroup Subgroup

Group thermal subsidence 657+17 Ma Farina Subgroup minibasin formation and diapirism

Sturtian Heysen Supergroup Yudnamutana Subgroup Major hiatus Belair Subgroup Burra Bungarider Subgroup Group Mundaillio Subgroup Emeroo Adelaidean Proterozoic Precambrian Torrensian River Wakefield Subgroup rifting 777+7 Ma Subgroup 802+10 Ma Curdimurka Local Warrina Supergroup Warrina Callanna Subgroup Willouran Group Arkaroola Hiatus

827+6 Ma Subgroup evaporite deposition Major unconformity pre-Adelaidean Archean to early Proterozoic metamorphic complexes; mid-Proterozoic granites, volcanics and sediments

Figure 1.12. Generalized Neoproterozoic and Cambrian stratigraphy present in the Adelaide Fold Belt, along with relevant tectonic cycles based on Preiss (1987), Preiss (2000), Rowan and Vendeville (2006) and Backe et al., (2010).

17 Figure 1.13. Sequential plate restoration of the Gulf of Mexico (Hudec et al., 2013b).

18 1.3.2 Salt Composition and Deformation The Willouran-aged Callanna Group (~850-800 Ma) is an assemblage of brecciated, siliciclastic, carbonate and mafic igneous to volcanic rocks that were originally interbedded with evaporites, which are now absent at the surface in South Australia (Preiss, 2000). A minimum of 6000 m of evaporites and associated facies of the Callanna Group was originally deposited as semi-coherent stratigraphy in a layered evaporite sequence, but was subsequently fragmented and mixed by entrainment in evaporitic diapirs such that much of the Callanna Group forms breccia, now leached of its former evaporite, consisting of clasts ranging in diameter from centimeters to hundreds of meters (e.g., Dalgarno and Johnson, 1968; Lemon, 1985; Preiss, 1987). Blocks of Callanna Group lithologies originally intercalated with evaporite form breccia bodies that represent salt diapirs, salt sheets and remnant allochthonous salt canopies. Outcrop relationships suggest that allochthonous salt primarily formed localized salt tongues (several kms) or small canopies (10’s kms). While the Callanna Group breccia is vastly different in composition than more pure evaporite sequences, it appears to have mobilized in a similar fashion to the Louann Salt of the northern Gulf of Mexico and is informally referred to as a mobile substrate (i.e., ‘salt’). In contrast to the Callanna Group breccia, the Jurassic Louann Salt in the Gulf of Mexico is estimated to be nearly pure halite with subordinate amounts of anhydrite, pyrite, dolomite, quartz and potassium salts (Hazzard et al., 1947; Salvador, 1987, 1991). Stern et al. (2011) reported igneous xenoliths contained within three onshore salt diapirs from southern Lousiana, however these inclusions have not been observed elsewhere. The original thickness of the Louann Salt is highly variable due to the original basin architecture and is thus difficult to measure due to post-depositional loading and evacuation by progradation of mainly Cenozoic sediments and subsequent downdip movement (e.g., Hudec et al., 2013a). In the northern Gulf of Mexico, the Louann Salt comprises extensive and widespread allochthonous salt sheets and canopies covering tens of thousands of square kilometers. Evolution of the Louann Salt has occurred over the last 160 Ma, whereas the salt system in South Australia was longer-lived, having evolved over a period of at least 250 Ma.

19 1.3.3 Depositional Environments Directly overlying the autochthonous Callanna Group in South Australia is a stratal succession predominantly deposited under shelfal, peritidal and periodically subaerial conditions in a marginal marine or lacustrine setting. Peritidal to shoreface siliciclastics and carbonates dominate a majority of post-salt Neoproterozoic through early Cambrian stratigraphy, with subordinate deepwater shales and sandstones. Thus, diapirs and allochthonous salt in the Flinders Ranges may have developed only a thin roof or even no roof at times, and subaerial dissolution may have decreased topographic relief. On the other hand, Cenozoic deepwater siliciclastics and subordinate carbonates were deposited in the northern Gulf of Mexico in a succession of 29 depositional episodes (Galloway, 2009). In deepwater depositional environments, hemipelagic sedimentation typically generates a thin veneer of carapace or roof strata atop diapirs and allochthonous salt, which generally protects salt from dissolution (Fletcher et al., 1995). Deepwater strata comprise a significantly larger number of primary, secondary and encapsulated minibasins spread over a much larger scale basin than in South Australia, thus adding to the overall complexity of the northern Gulf of Mexico.

1.4 Summary of Chapters The following sections provide a brief summary of three manuscript-style chapters included in this thesis. The first two chapters (Chapters 2 and 3) summarize outcrop studies of salt diapirs, allochthonous salt and associated stratal geometries from South Australia, while the final chapter (Chapter 4) focuses on a subsurface study of halokinetic growth strata on a 3D WAZ seismic dataset from the Auger diapir, northern Gulf of Mexico. Chapter 2 is currently in review with Basin Research, while Chapters 3 and 4 will be submitted to the AAPG Bulletin and Interpretation, respectively.

1.4.1 Chapter 2: Geology and Tectonics of Neoproterozoic Salt Diapirs and Salt Sheets in the Eastern Willouran Ranges, South Australia Neoproterozoic diapirs, allochthonous salt, welds and associated minibasin strata in the eastern Willouran Ranges, South Australia, provide insight into allochthonous salt advance and display key geometries related to salt-sediment interaction. This chapter details a variety of

20 stratal geometries contained in sub- and suprasalt minibasins that flank primary and secondary diapirs and a remnant salt canopy presently delineated by subhorizontal, inclined and steep salt welds. Minibasins contain strata present in both sub- and suprasalt positions and are similar in size to minibasins present in the northern Gulf of Mexico. Beneath allochthonous salt, there is no evidence for sheared strata, thrust faults or rubble zones and debris flow deposits are rare. Instead, halokinetic folds and truncated roof strata are present at the transition from steep, primary and secondary diapirs to shallowly dipping allochthonous salt. Shortening during the Delamerian orogeny tilted the entire eastern Willouran Ranges such that minibasin strata, diapirs and allochthonous salt are well exposed in map view as an oblique cross section.

1.4.2 Chapter 3: Allochthonous Salt Initiation and Advance in the Flinders and Eastern Willouran Ranges, South Australia: Using Outcrops to Test Subsurface-based Models from the Northern Gulf of Mexico Stereonet analysis of multiple diapirs, salt sheets and halokinetic sequences was used to derive three-dimensional information from two-dimensional outcrops and to evaluate ten examples of the transition from steep diapirs to salt sheets, three instances of ramp-to-flat geometries and two of flat-to-ramp transitions in the northern Flinders Ranges and eastern Willouran Ranges, South Australia. A variety of stratal truncations, ranging from a minibasin- scale megaflap to halokinetic drape folds to high-angle truncations, are adjacent to feeder diapirs. Regardless of the truncation type, the transition from steep diapirs to salt is abrupt and involves piston-like breakthrough of roof strata, freeing up salt to flow laterally. Based on this work, we suggest two models to explain the transition from steep diapirs to subhorizontal salt: 1) salt- top breakout; and 2) salt-edge breakout. Stratal geometries exposed in these field areas display similar features as those observed on seismic and well data in deepwater settings, namely the northern Gulf of Mexico.

21 1.4.3 Chapter 4: Testing the Applicability of an Outcrop-based Halokinetic Deformation Model in a Deepwater Depositional Setting: Auger diapir, Garden Banks 427, Northern Gulf of Mexico Poor seismic resolution and surprising well results typify subsalt salt-truncation hydrocarbon plays in basins such as the northern Gulf of Mexico, where topography generated by salt diapirs and allochthonous salt controls the development of localized (<1 km) halokinetic growth strata. Halokinetic growth sequences, which may flank salt bodies, are forensic indicators of salt-induced topography through time and provide insight into salt-sediment interaction, reservoir prediction, trap geometry, hydrocarbon containment and drilling hazards. Interpretation of ten composite halokinetic sequences flanking the deepwaterAuger diapir, northern Gulf of Mexico on wide-azimuth, prestack depth-migrated 3-D seismic data coupled with biostratigraphic data and structural restorations generally corroborate the outcrop-based halokinetic sequence model. In this deepwater setting, stratal geometries, widths of thinning, sedimentation accumulation rates and stacking patterns of composite halokinetic sequences are similar to diapir-flanking strata present in shallow water depositional settings.

1.5 References Cited Alsop, G. I., J. P. Brown, I. Davison, and M. R. Gibling, 2000, The geometry and deformation mechanisms of drag zones adjacent to salt diapirs: a case study from Cape Breton Island, Nova Scotia: J. Geological Society London, v. 157, p. 1019-1029.

Dalgarno, C. R., and J. E. Johnson, 1968, Diapiric structures and Late Precambrian-Early Cambrian sedimentation in Flinders Ranges, South Australia, in J. Braunstein, and G. D. O’Brien, eds., Diapirs and diapirism: AAPG Memoir 8, p. 301-314.

Diegel, F. A., J. F. Karlo, D. C. Schuster, R. C. Shoup, and P. R. Tauvers, 1995, Cenozoic structural evolution and tectono-stratigraphic framework of the northern Gulf coast continental margin, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., Salt tectonics: a global perspective: AAPG Memoir 65, p. 109-151.

Drexel, J. F., W. V. Preiss, and A. J. Parker, 1993, The geology of South Australia, Volume 1, The Precambrian: Geological Survey of South Australia Bulletin 54, 242 p.

Dyson, I. A., 1998, The ‘Christmas tree diapir’ and salt glacier at Pinda Springs, central Flinders Ranges: Division of Minerals and Energy Resources of South Australia (MESA) Journal, v. 10, p. 40-43.

22 Forbes, B. G., 1980, Three sections measured in Lower Adelaidean (Proterozoic) rocks, Southeastern CURDIMURKA area: Department of Mines and Energy South Australia, Report Bk. No. 79/159, D.M No. 252/72.

Fletcher, R. C., M. R. Hudec, and I. A. Watson, 1995, Salt glacier and composite sediment-salt glacier models for the emplacement and early burial of allochthonous salt sheets, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., Salt tectonics: a global perspective: AAPG Memoir 65, p. 77-108.

Galloway, W. E., Depositional evolution of the Gulf of Mexico sedimentary basin, in A. D. Miall, The Sedimentary Basins of the United States and Canada: Elseview, p. 505-549.

Giles, K. A. and Lawton, T. F., 2002, Halokinetic sequence stratigraphy adjacent to the El Papalote diapir, northeastern Mexico: AAPG Bulletin, v. 86, p. 823-840.

Giles, K. A., and M. G. Rowan, 2012, Concepts in halokinetic–sequence deformation and stratigraphy, in G. I. Alsop, S. G. Archer, A. J. Hartley, N. T. Grant, and R. Hodgkinson, eds., Salt Tectonics, Sediments and Prospectivity, Geological Society of London Special Publications, v. 363, p. 7-31, doi: 10.1144/SP363.2.

Harrison, H. L., and B. Patton, 1995, Translation of salt sheets by basal shear, in C. J. Travis, H. Harrison, M. R. Hudec, B. C. Vendeville, F. J. Peel, and B. F. Perkins, eds., Salt, sediment, and hydrocarbons: 16th Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 99-107.

Harrison, H., L. Kuhmichel, P. Heppard, A. V. Milkov, J. C. Turner, and D. Greeley, 2004, Base of salt structure and stratigraphy-Data and models from Pompano field,VK 989/990, Gulf of Mexico, in P. J. Post, D. L. Olson, K. T. Lyons, S. L. Palmes, P. F. Harrison, and N. C. Rosen, eds., Salt-sediment interactions and hydrocarbon prospectivity: Concepts, applications, and case studies for the 21st century: 24th Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 243-270.

Hazzard, R. T., W. C. Spooner, and B. W. Blanpied, 1947, Notes on the stratigraphy of the formations which underlie the Smackover Limestone in south Arkansas, northeast Texas, and north Louisiana: Shreveport Geological Society 1945 Reference Report, v. 2, p. 483- 503.

Hearon, T. E., IV, R. A. Kernen, M. G. Rowan, and K. A. Giles, 2012, Outcrop examples of subsalt structure related to allochthonous salt breakout, Flinders and eastern Willouran Ranges, South Australia (abs.): AAPG Annual Meeting Program, v. 21, CD-ROM.

Hudec, M. R., and M. P. A. Jackson, 2004, Regional restoration across the Kwanza Basin, Angola: Salt tectonics triggered by repeated uplift of a metastable passive margin: AAPG Bulletin, v. 88, p. 971– 990.

23 Hudec, M. R., and M. P. A. Jackson, 2006, Advance of allochthonous salt sheets in passive margins and orogens: AAPG Bulletin, v. 90, p. 1535-1564, doi: 10.1306/05080605143.

Hudec, M. R., and M. P. A. Jackson, 2009, The interaction between spreading salt canopies and their peripheral thrust systems: Journal of Structural Geology, v. 31, p. 1114-1129, doi: 10.1016/j.jsg.2009.06.005.

Hudec, M. R., and M. P. A. Jackson, 2011, The salt mine: a digital atlas of salt tectonics: The University of Texas at Austin, Bureau of Economic Geology, Udden Book Series No. 5, AAPG Memoir, v. 99, 305 p.

Hudec, M. R., M. P. A. Jackson, and F. J. Peel, 2013a, Influence of deep Louann structure on the evolution of the northern Gulf of Mexico: AAPG Bulletin, v. 97, p 1711-1735.

Hudec, M. R., I. O. Norton, M. P. A. Jackson, and F. J. Peel, 2013b, Jurassic evolution of the Gulf of Mexico salt basin: AAPG Bulletin, v. 97, p. 1683-1710.

Jackson, M. P. A., and C. J. Talbot, 1991, A glossary of salt tectonics: The University of Texas at Austin: Bureau of Economic Geology Geological Circular, 91-4, 44 p.

Jenkins, R. J. F., 1990, The Adelaide fold belt: tectonic reappraisal, in J. B. Jago, and P. S. Moore, eds., The Evolution of a Late Precambrian-Early Paleozoic Rift Complex: The Adelaide Geosyncline: Geological Society of Australia Special Publication, v. 16, p. 396- 420.

Kernen, R. A., K. A. Giles, M. G. Rowan, T. F. Lawton, and T. E. Hearon, 2012, Depositional and halokinetic-sequence stratigraphy of the Neoproterozoic Wonoka Formation adjacent to Patawarta allochthonous salt sheet, Central Flinders Ranges, South Australia, in G. I. Alsop, S. G. Archer, A. J. Hartley, N. T. Grant, and R. Hodgkinson, eds., Salt Tectonics, Sediments and Prospectivity, Geological Society of London Special Publications, v. 363, p. 81-105, doi: 10.1144/SP363.5.

Lees, G. M., 1927, Salzgletcher in Persien: Mitteilungen Geologische Gesellschaft Wien, v. 20, p. 29-34.

Lemon, N. M., 1985, Physical modeling of sedimentation adjacent to diapirs and comparison with late Precambrian Oratunga breccia body in Central Flinders Ranges, South Australia: AAPG Bulletin, v. 69, p. 1327-1338.

Lemon, N. M., 1988, Diapir recognition and modeling with examples from the late Proterozoic Adelaide Geosyncline, Central Flinders Ranges, South Australia: Ph.D. thesis, University of Adelaide, Adelaide, South Australia, unpublished.

24 McGee, D. T., P. W. Bilinski, P. S. Gary, D. S. Pfeiffer, and J. L. Sheiman, 1994, Geologic Models and geometries of Auger field, deep-water Gulf of Mexico,in P. W. Weimer, A. H. Bouma, and B. F. Perkins, eds., Submarine Fans and Turbidite Systems-Sequence Stratigraphy, Reservoir Architecture, and Production Characteristics: 15th Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 245-256.

McGuinness, D. B., and J. R. Hossack, 1993, The development of allochthonous salt sheets as controlled by the rates of extension, sedimentation, and salt supply, in J. M. Armentrout, R. Bloch, H. C. Olson, and B. F. Perkins, eds., Rates of geological processes: 14th Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 127-139.

Mohriak, W.U., J. M. Macedo, R. T. Castellani, H. D. Rangel, A. Z. N. Barros, M. A. L. Latgé, J. A. Ricci, A. M. P. Mizusaki, P. Szatmari, L. S. Demercian, J. G. Rizzo, and J. R., Aires, 1995, Salt tectonics and structural styles in the deep-water province of the Cabo Frio region, Rio de Janeiro, Brazil, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., Salt tectonics: a global perspective: AAPG Memoir 65, p. 273-304.

Moores, E. M., 1991, Southwest U.S.-East Antarctic (SWEAT) connection: A hypothesis: Geology, v. 19, p. 425-428, doi: 10.1130/0091-7613(1991)019<0425:SUSEAS>2.3.CO;2.

Mrazec, L., 1907, Despre cute cu simbure de strapungere [On folds with piercing cores]: Romania, Society of Stiite Bulletin, v. 16, p. 6–8.

Peel, F. J., C. J. Travis, and J. R. Hossack, 1995, Genetic structural provinces and salt tectonics of the Cenozoic offshore U.S. Gulf of Mexico: A preliminary analysis, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., Salt tectonics: A global perspective: AAPG Memoir 65, p. 153-175.

Pindell, J., and J. F. Dewey, 1982, Permo-Triassic reconstruction of western Pangea and the evolution of the Gulf of Mexico/Caribbean region: Tectonics, v. 1, p. 179–211.

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26 Yeilding, C.A., C. J. Travis, E. J. Ekstrand, D. M. Urban, M. T. May, and J. D. Boyd, 1995, Salt tectonics and depositional architecture of the continental slope, northeastern Gulf of Mexico, in C. J. Travis, H. Harrison, M. R. Hudec, B. C. Vendeville, F. J. Peel, and B. F. Perkins, eds., Salt, sediment, and hydrocarbons: 16th Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 307-308.

27 CHAPTER 2 GEOLOGY AND TECTONICS OF NEOPROTEROZOIC SALT DIAPIRS AND SALT SHEETS IN THE EASTERN WILLOURAN RANGES, SOUTH AUSTRALIA

A paper submitted to Basin Research

Thomas E. Hearon, IV, Mark G. Rowan, Timothy F. Lawton, P. Tyler Hannah, Katherine A. Giles

2.1 Abstract Allochthonous salt structures and associated sub and suprasalt minibasins recorded in Neoproterozoic strata of the eastern Willouran Ranges, South Australia, provide insights into allochthonous salt advance and associated salt-sediment interaction. Long-lived passive diapirism (>250 m.y.) began shortly after deposition of the Callanna Group layered evaporite sequence (~850-800 Ma), now represented by bodies of megabreccia. A primary minibasin containing an expulsion rollover structure and megaflap in lower Burra Group strata is flanked by two vertical diapirs. The diapirs fed a complex, multi-level canopy containing an encapsulated minibasin and suprasalt basins filled by upper Burra Group strata and younger Sturtian glacial- outwash deposits. Associated stratal relationships include omitted stratigraphic section, composite halokinetic sequences and diapir-derived detritus in salt-flanking strata. The area was subsequently deformed during the Late Cambrian-Ordovician Delamerian Orogeny (~500 Ma). Presently, the remnant salt canopy is segmented by multiple salt welds, which have varying lengths and orientations. Beneath allochthonous salt, small-scale structures such as subsalt shear zones, fractured or mixed ‘rubble zones’ and thrust imbricates are absent. Instead, halokinetic drape folds that include diapir roof strata are common directly below the transition from steep salt to base-salt flats, but are not present beneath the base-salt flats. Allochthonous salt breakout occurred first on steep faults that cut the overlying roof and was followed by lateral salt flow, resulting in variable preservation of the subsalt drape fold. Lateral salt emplacement was on roof-edge thrust faults,

28 or because of the shallow depositional environment, via open-toed advance or extrusive advance, but without associated subsalt deformation. The stratal geometries and salt-strata relationships exposed in the eastern Willouran Ranges can be applied as analogs when interpreting subsurface data in salt basins with allochthonous salt such as the Gulf of Mexico. Our field data and interpretations allow us to test models of allochthonous salt emplacement and associated salt-sediment interaction in these other well-documented salt basins.

2.2 Introduction Allochthonous salt is defined as a sheet-like body of mobile evaporite emplaced at younger stratigraphic levels above the original autochthonous source (e.g., Jackson and Talbot, 1991; Hudec and Jackson, 2006; Hudec and Jackson, 2011). Allochthonous salt can be derived alternatively from a single salt feeder and emplaced during lateral spreading as a solitary salt sheet, or individual sheets may coalesce to form larger canopies. The angle at which allochthonous salt is emplaced is a function of the interplay between sediment-accumulation rate and salt-rise rate (e.g., McGuinness and Hossack, 1993; Yeilding et al., 1995). Allochthonous salt is present in a variety of tectonic and depositional settings ranging from offshore fold-and-thrust belts to deepwater passive margins and was first recognized in the Romanian Carpathians by Mrazec (1907). Subaerial salt extrusions from Iran were described by Lees (1927), Busk (1929) and De Böckh et al. (1929) and later interpreted as salt glaciers or emergent salt diapirs by Ala (1974) and Kent (1979). Amery (1969) utilized sparker-profile surveys to confirm earlier hypotheses (Ewing and Antoine, 1966; Uchupi and Emery, 1968) of allochthonous salt along the Sigsbee Escarpment in the northern Gulf of Mexico. Other investigators documented lateral salt flow and the evolution of allochthonous salt and minibasins developed on salt as a function of sediment loading on the continental slope (e.g., Humphris, 1978, 1979; Worrall and Snelson, 1989). Initially, D’Onfro (1988), Nelson and Fairchild (1989) and Wu et al. (1990) proposed lateral injection of salt between bedding planes to account for the relatively shallow dip of allochthonous salt sheets in the northern Gulf of Mexico. More recently, newly acquired seismic data, well data and physical and numerical models have led to various theories of allochthonous salt emplacement, including surficial glacial flow (McGuinness and

29 Hossack, 1993; Fletcher et al., 1995), advance above subsalt shear zones (Harrison and Patton, 1995; Harrison et al., 2004), or emplacement along tip thrusts (Hudec and Jackson, 2006, 2009). Over the past two decades, allochthonous salt bodies have become increasingly important due to the increase in subsalt exploration drilling in basins such as the deepwater Gulf of Mexico and offshore West Africa. Poor seismic resolution of subsalt strata, borehole stability and lithological and pressure uncertainties have become major concerns in the risking of hydrocarbon prospects beneath allochthonous salt bodies. Stratigraphic geometries flanking passive salt diapirs and allochthonous salt sheets control reservoir geometry and trap configuration and may influence hydrocarbon migration and seal. For example, the amount of upturn within halokinetic sequences adjacent to salt diapirs can impact hydrocarbon containment and column heights and thus reservoir volumes (e.g., Wilcox Group, northern Gulf of Mexico) (e.g., Giles and Rowan, 2012). The presence of anomalous, commonly overpressured “rubble zones” or “gumbo zones” directly beneath allochthonous salt sheets and canopies has also plagued subsalt exploration. This zone, when present, may contain overturned stratigraphy, local repeat of section, mixed biostratigraphic ages and structurally repeated strata. Theories proposed to explain this subsalt structural complexity include: (1) subsalt basal shear; (2) imbricate thrusts in front of the advancing salt sheet; and (3) debris shed off the topographic scarp created by the advancing allochthon (i.e., slumped carapace) (e.g., McGuinness and Hossack, 1993; Harrison and Patton, 1995; Harrison et al., 2004; Jackson and Hudec, 2004; Alexander et al., 2005; Kilby et al., 2008; Hudec and Jackson, 2009). Competitive business strategies between hydrocarbon exploration companies, the ambiguity of seismic in the subsalt realm and the paucity of onshore basins that contain exposed salt-sheets and canopies have resulted in a dearth of publicly available knowledge about allochthonous salt tectonics. Because of the limitations inherent in subsalt seismic imaging and one-dimensional well sampling, there is a need for outcrop-based studies to test these models. Previous field studies in the Zagros Mountains, Iran, the Katangan Copperbelt, Democratic Republic of the Congo, southern Spain and Arctic Canada have yielded valuable insight into the advance and emplacement of allochthonous salt (e.g., Ala, 1974; Flinch et al., 1996; Jackson et al., 2003; Jackson and Harrison, 2006). Detailed outcrop analysis of reservoir-scale features,

30 subsalt geometries and diapir-flanking facies, which are not imaged well on high-quality seismic data, provide a better understanding of salt-sediment interaction and permit greater exploration success and evaluation of potential subsalt plays in global hydrocarbon-rich basins. Bodies of Callanna Group breccia in the Flinders and Willouran ranges, South Australia are generally interpreted as the outcrop expression of salt diapirs (e.g., Webb, 1960; Dalgarno and Johnson, 1968; Lemon, 1985; Dyson, 1996). Dyson (1998, 2004, 2005) was the first to recognize allochthonous salt sheets composed of diapiric breccia in the Flinders and eastern Willouran Ranges, an interpretation corroborated in the latter case by Hearon (2008), Hannah (2009) and Hearon et al. (2010a). Well-exposed outcrops of Neoproterozoic strata in this area contain some of the world’s oldest evidence for evaporite deposition, diapirism, lateral emplacement and subsequent evacuation. A wide variety of salt features and geometries including passive salt diapirs, primary and secondary minibasins, allochthonous salt tongues, sheets and canopies, multi-level salt welds and stacked composite halokinetic sequences are present in this area. These salt structures and associated geometric features and depositional sequences display compelling evidence for a complex, multi-phase salt history and make this area an important one in which to study salt tectonics and salt-sediment interaction. This paper builds on the pioneering work by Mawson (1927), Sprigg (1949), Webb et al. (1963), Murrell (1977) and Forbes (1990) and more recent work by Dyson (2004) and Mackay (2011) in the Willouran Ranges. We explain the geometry, timing, emplacement and history of an allochthonous salt system present in the eastern Willouran Ranges by investigating field-scale relationships. Many of our field observations are below seismic resolution, with a sampling density not possible with one-dimensional well data. This paper will aid in understanding the stratigraphy and tectonic evolution of the northern Adelaide Fold Belt and will also have implications for hydrocarbon-bearing analogs in the deepwater Gulf of Mexico and offshore Brazil and West Africa.

2.3 Geologic Setting of the Flinders and Willouran Ranges In the following three sections, we describe the regional tectonic setting and history of the eastern Willouran Ranges, provide an overview of Neoproterozoic stratigraphy and outline the Callanna Group breccia and its significance as a mobile substrate.

31 2.3.1 Regional Tectonic History The Willouran Ranges, located southwest of Marree, South Australia, approximately 560 km north of Adelaide, form a northwestern extension of the northern Flinders Ranges (Figure 2.1). The Flinders Ranges comprise a north-south trending tectonic province that, along with several other nearby ranges, including the Willouran, Mount Lofty, Peake and Denison Ranges, constitute the Adelaide Fold Belt (Scheibner, 1973; Jenkins, 1990), also referred to as the Adelaide Geosyncline (Sprigg, 1952) and the Adelaide Basin (e.g., Preiss, 2000). The north-south trending Torrens Hinge Zone is a transition lineament, marked by mild deformation and faulting, which separates the Adelaide Fold Belt from plutonic and metamorphic basement rocks of the Gawler Craton and relatively undeformed Stuart Shelf to the west (Preiss, 2000) (Figure 2.1). The Adelaide Fold Belt is bounded to the east by faults and to the northeast and southeast by the mostly undeformed Curnamona Province and the Murray Basin, respectively. During the Neoproterozoic-Early Cambrian, the Adelaide Fold Belt is interpreted to have been a rift or aulacogen between the Gawler Craton and Curnamona Province (Sprigg, 1952; Scheibner, 1973; von der Borch, 1980; Preiss, 1987). Initial rifting in South Australia began between 1000 Ma and 827 Ma and is thought to have occurred in five consecutive cycles throughout the Neoproterozoic as western Laurentia separated from Australia during the breakup of the Rodinian supercontinent (Moores, 1991; Preiss, 2000). Rift basins are thought to have been highly segmented and oriented northwest-southeast as a result of northeast-southwest extension (Rowlands et al., 1980; Preiss, 1987; Preiss, 2000). A minimum thickness of 6000 m of Callanna Group evaporites and associated facies were deposited in subsiding rift basins (Forbes, 1990; Mackay, 2011). During later periods of rifting and thermal subsidence, a thick succession (~9000 m) of nonmarine and marine strata accumulated as sedimentary basin fill (Coats, 1965; Forbes, 1990) in a series of partitioned basins (Murrell, 1977; Hearon et al., 2010a). Murrell (1977) suggested Burra Group rocks within the Willouran Ranges were deposited within a northwest-southeast trending trough less than 50 km wide. Continued rifting and thermal subsidence persisted until the Early Cambrian and was immediately followed by the Upper Cambrian-Ordovician (~500 Ma) Delamerian Orogeny (Preiss, 2000). The Delamerian Orogeny was a contractional event that consisted of complex

32 O O O O 137 139 141 O 135 Peake 143 Location Map 28O Inlier + 28O PEAKE DENISON+ + + RANGES + + + +

THIS STUDY QUEENSLAND MULOORINA AUSTRALIA + + NORWEST FAULTRIDGE + Mount + Babbage + MARREE Inlier + + + Mount + + + Painter T + L Inlier WONOMINTA O U O 30 + A F V BLOCK 30

+ + + TORRENS + + A V + N A CURNAMONA

FLINDERS L BENAGERIE V + A R + A V + PERNATTY P V + + NEW SOUTH WALES V + + + + + + CRATONIC

UPWARP RIDGE + + + + + + +

+ SPENCER + MURRAY ADELAIDE ? BASIN Inferred area of Delamerian fold belt + + + TROUGH ? + + Largely outcropping ARC + + + + FLEURIEU ? Largely concealed

VICTORIA KANMANTOO +

SOUTHAUSTRALIA O O 36 + + + + 36 + + Delamerian granitoids + KANGAROO ++ ISLAND ? v v + ? v Cambrian volcanics V V V Major faults + V ++ V + ++ + Major syncline axes in Adelaidean

0 100 200 V and early Paleozoic sediments 38O V 38O Kilometers Approximate location of the O O O 135O 137 139 141 143O eastern Willouran Ranges

Figure 2.1. Major geologic provinces and Delamerian structures of South Australia (redrafted from Preiss, 1987). Eastern Willouran Ranges are denoted by the red rectangle.

33 deformation, metamorphism and crustal shortening of Neoproterozoic to Cambrian strata throughout the Flinders Ranges (Foden et al., 2006). Shortening orientation varies widely and was formerly interpreted as the result of two phases of deformation: (1) early north-northwest- directed shortening created folds which trend east-northeast; and (2) later east-west-directed shortening created north-northwest trending folds (Preiss, 1987, 2000; Drexel and Preiss, 1995). In contrast, Rowan and Vendeville (2006) suggested the varying structural trends represent shortening of an array of preexisting salt diapirs and ridges. The Willouran and surrounding ranges were subject to both thin and thick-skinned shortening (Preiss, 1993a, 2000). In the northern Flinders Ranges, including the Willouran Ranges, complex thick-skinned deformation dominated in the form of basement-involved structures during reactivation of pre-existing extensional faults (Paul et al., 2000). These reactivated faults likely accommodated most of the shortening during the Delamerian Orogeny, such that growth stratigraphy and breccia bodies presently exposed in the eastern Willouran Ranges experienced only moderate deformation (Paul et al., 1999). However, Sprigg (1949) interpreted large fold structures (e.g., Witchelina Syncline) adjacent to Callanna Group breccia as drag structures resulting from regional thrusting and Mackay (2011) suggested a majority of structural features related to the Callanna Group breccia formed as shortening features during multiple phases of deformation in the Willouran Ranges.

2.3.2 Stratigraphy Exposed strata in the Willouran Ranges are Neoproterozoic, but elsewhere in the Flinders Ranges they range from Neoproterozoic to Cambrian (Preiss, 2000). Neoproterozoic rocks in the Adelaide Fold Belt are chronostratigraphically subdivided into four series: Willouran, Torrensian, Sturtian and Marinoan (Mawson and Sprigg, 1950; Sprigg, 1952; Webb, 1960; Rowlands et al., 1978; Preiss, 1987) (Figure 2.2). These rocks are lithostratigraphically divided into three supergroups that comprise the Adelaidean Supergroup: (1) the Warrina Supergroup contains the Callanna Group and the Burra Group; (2) the Heysen Supergroup includes glacio-marine strata of the Umberatana and Wilpena Groups; and (3) the Maralana Supergroup consists of Cambrian rocks (Thomson et al., 1964; Preiss, 1982, 1987) (Figure 2.2). Pre-Adelaidean basement rocks in South Australia include Archean and Mesoproterozoic metamorphic complexes and igneous rocks (Preiss, 1987).

34 Chronostratigraphic Units Major Lithostratigraphic Units Tectonic Cycle 514+5 Ma Lake Frome Group Early Delamerian Middle orogeny Cambrian Wirrealpa Limestone Kanmantoo Group 526+4 Ma Billy Creek Formation

Early Hawker Group Normanville Moralana

Cambrian Supergroup Group Uratanna Formation Rifting Pound Subgroup Ediacaran Wilpena 588+35 Ma Group Major hiatus Yerelina Rifting Marinoan Umberatana Willochra Subgroup Group Subgroup Sag 657+17 Ma Farina Subgroup

Sturtian Heysen Supergroup Yudnamutana Subgroup Rift Major hiatus Continental breakup Belair Subgroup Burra Bungarider Subgroup Group Mundallio Subgroup Rifting Emeroo Adelaidean Proterozoic Precambrian Torrensian River Wakefield Subgroup

777+7 Ma Subgroup Rifting 802+10 Ma Curdimurka Local Warrina Supergroup Warrina Callanna Subgroup Willouran Evaporite deposition Group Arkaroola Subgroup Hiatus 827+6 Ma Rifting; Major unconformity Rodinia break-up pre-Adelaidean Archean to early Proterozoic metamorphic complexes; mid-Proterozoic granites, volcanics and sediments

Figure 2.2. Generalized Neoproterozoic and Cambrian stratigraphy present in the Adelaide Fold Belt (redrafted from Preiss, 1987; after Preiss, 2000, Backé et al., 2010). Light blue box denotes stratigraphy represented in this study.

35 Burra Group rocks, which comprise the basal Emeroo Subgroup, the Mundallio Subgroup and the Bungarider Subgroup, conformably overlie the Callanna Group (e.g., Forbes, 1990; Parker et al., 1990) (Figure 2.3). Burra strata contain features that indicate deposition in a shelfal environment, primarily in a shallow-water, peritidal setting for most of its evolution, punctuated by brief episodes of deepening. The stratigraphy of the Emeroo Subgroup constitutes a succession of shallow-marine and non-marine sandstone with subordinate siltstone, dolostone and limestone. The Mundallio Subgroup is dominated by dolostone and shale with subordinate sandstone. The Bungarider Subgroup is mostly composed of shallow marine and nonmarine sandstone, dolostone and siltstone with polymict and monomict conglomerate. Polymict conglomerate beds containing clasts of diapiric breccia dominate the lower to middle section of the lower member of the Myrtle Springs Formation. The youngest unit exposed in the eastern Willouran Ranges is the Lower Umberatana Group of Sturtian Age (i.e., late Cryogenian), which is composed mostly of nonmarine to marginal marine siltstone, sandstone and diamictite. Alternating beds of tillite and fine-grained, massive siltstone are interpreted as glacial outwash and loessite deposits, respectively (Preiss, 1987; Kendall et al., 2006; Preiss, 2006). Facies and variations in stratal thickness of the Burra and Umberatana groups in the eastern Willouran Ranges area were most recently described by Hearon (2008), Hannah (2009) and Hearon et al. (2010a), but a number of other workers have also described these units in this area (e.g., Belperio, 1987, 1990; Preiss, 1987; Forbes, 1990). The principal units of interest include the Witchelina Quartzite, three members of the Skillogalee Dolomite (the lower Camel Flat Shale Member, the middle Twenty Mile Hill Member and the upper Old Mount North West Member) and the lower and upper members of the Myrtle Springs Formation (Figure 2.3) (see Hearon et al., 2010a for full description). Forbes (1990) partially attributed lateral thickness changes in the Burra Group north and south of Willouran Hill to post-depositional erosion or tectonic disruption. Conversely, Hearon et al. (2010a) interpreted local variations in sedimentary units in the eastern Willouran Ranges as a result of rift basin partitioning and the emplacement of a multi-level allochthonous salt canopy.

36 Generalized Neoproterozoic stratigraphy of the eastern Willouran Ranges, South Australia Lower Umberatana Group Undifferentiated (Nuu) (2200+ m) Diamictite consisting of well-rounded, pebble to boulder conglomerate with clasts of granite, granite porphyry, quartzite and dolostone; polymict, basal pebble conglomerate interpreted as tillite deposits; dolomite-rich siltstone interpreted as loessite deposits Tindelpina Shale Member (0-25 m) Group Lower 10000 Black shale, pyritic, carbonaceous with meter-scale dolomitic dropstones Heysen Supergroup

Umberatana Myrtle Springs Formation (Ndm) (0-1435 m) upper member (Ndm2) (0-335 m) Siltstone, rusty-pale green weathered, green on fresh surfaces and very thin bedded to laminated 9000 lower member (Ndm1) (0-1100 m) Centimeter-scale, polymict to monomict conglomerate, dark blue-gray; contains quartz arenite, calcareous, sandy dolostone and dolostone, dark blue-gray; cryptalgal laminites common in centimeter-scale beds Subgroup Bungarider

Diapiric breccia (br3) (0-350 m) 8000 Skillogalee Dolomite (Nms) (0-2510 m) Old Mount North West Member (Nmso) (0-1040 m) Quartz arenite, calcareous, blue-gray to gray, weathering red-brown, thin- to medium- bedded to thinly laminated, well indurated to flaggy, fine- to medium- grained, with ripple cross-lamination, hematitic. Beds 5-10 cm thick form upward-fining successions. Contains interbeds of sandy dolostone and dolostone, dark blue-gray, weathering brown, with 7000 chert nodules, desiccation cracks, cryptalgal laminites centimeter-scale beds; abundant cubic casts containing remnant

iron oxide in quartz arenite beds; suprasalt minibasin fill; Interbedded diapiric breccia (br3) (0-150 m) near basal Nmso

Diapiric breccia (br3) (0-150 m) Mundallio Subgroup Twenty Mile Hill Member (Nmst) (0-1350 m) Sandy dolostone, dark blue-gray, brown weathering, fine grained and laminated dolostone; interbedded with subordinate 6000 quartz arenite, gray, red-brown weathering, thin bedded to flaggy, fine grained

Camel Flat Shale Member (Nmsc) (0-120 m) Shale, dark gray to green, laminated; interbedded with subordinate dolostone and quartz arenite

5000

meters Witchelina Quartzite (Now) (0-2400 m) Subarkose to quartz arenite, gray to tan, fine-coarse grained, well sorted, medium

Burra Group bedded, flaggy, ripple cross laminations, clay intraclasts and desiccation cracks; 4000 interbedded with subordinate ripple cross-laminated siltstone and shale, dark gray-black; less common tidal channels Warinna SupergroupWarinna

3000

Willawalpa Formation (Noz) (0-2250 m) Quartz arenite, thin-bedded, flaggy, ripple cross laminations, shale intraclasts, desiccation 2000 cracks, cross bedding and lenticular bedding; interbedded with subordinate siltstone, dark

Emeroo Subgroup Emeroo gray; rare stromatolitic dolostone, dark gray

1000 Top Mount Sandstone (Not) (0-950 m) Quartz arenite, gray-tan, medium- to coarse-grained, medium bedded, ripple cross laminations, desiccation cracks and lenticular bedding; interbedded with subordinate siltstone, dark gray, thinly laminated; rare dolostone and limestone, gray 0 Diapiric breccia (br3) (6000+ m; Adelaidean, ~850-800 Ma) Undifferentiated Curdimurka and Arkaroola subgroups: megabreccia consisting of a mixed assemblage of unsorted centimeter to decameter scale blocks of mafic volcanics, dolostone, quartzite supported by light blue-gray to greenish matrix; some folded blocks, evaporite replacement minerals, salt hoppers, brecciated, hydrothermally altered; some Group

Callanna blocks contain cryptalgal laminites and stromatolites in centimeter-scale beds; autochthonous evaporite source

Figure 2.3. Generalized Neoproterozoic stratigraphy of the eastern Willouran Ranges, South Australia (modified from and after Belperio, 1986; Preiss, 1987; Forbes, 1990; Drexel et al., 1993; Hearon et al., 2010a). Unit colors match those on the geologic map, comparative stratigraphic section, cross-sections and schematic restoration (Figures 2.7-2.10).

37 2.3.3 Callanna Group Breccia The Willouran-aged Callanna Group (~850-800 Ma) is an assemblage of brecciated siliciclastic, carbonate and mafic intrusive to volcanic rocks originally interbedded with evaporites. Over time, the evaporites were either dissolved or altered so that they are now absent at the surface (Preiss, 2000). The Callanna Group, which is divided into the Arkaroola and Curdimurka subgroups, represents the lowermost strata of the Adelaide Fold Belt sedimentary sequence and nonconformably overlies Archean and Mesoproterozoic crystalline basement (Forbes, 1990). Most of the Callanna Group in the Flinders and Willouran ranges crops out as breccia, now leached of the former evaporite, containing clasts ranging in size from pebbles to clasts several kilometers long and several hundred meters thick. Bodies of Callanna Group breccia, herein termed diapiric breccia (br3 of Figure 2.3), crosscut and are intercalated with post- Callanna Group stratigraphy throughout the Willouran and Flinders ranges (e.g., Webb, 1960; Coats, 1964; Forbes, 1990). The origin of diapiric breccia has been the subject of much debate for over six decades. Numerous authors, including Sprigg (1949), Howard (1951), Spry (1952), Reyner (1955) and Reyner and Pittman (1955) interpreted the Callanna Group breccia in the Willouran and Flinders ranges as a product of thrust faults and thrust-fault complexes. Burns et al. (1977) interpreted the formation of these breccias as a result of tectonic décollements. In contrast, Webb (1960) suggested the breccia was emplaced diapirically due to a density contrast between mobile breccia and the overlying stratigraphy, while Mount (1975) argued for emplacement of diapiric breccia during the Delamerian Orogeny. Brittle deformation was also suggested as an origin for the Callanna Group breccia by Preiss (1987), Kreig et al. (1991) and Mendis (2002). Murrell (1977) recognized syndepositional folds and unconformities in the Willouran Ranges, but argued against diapiric intrusion in favor of synsedimentary slumping as the mechanism of breccia formation. Throughout the Flinders and Willouran ranges, the presence of growth geometries, unconformities, diapir-derived detritus and pseudomorphs after evaporite minerals in strata adjacent to diapiric breccia bodies demonstrates the origin of the Callanna Group breccia as evaporite diapirs in which salt is no longer exposed at the surface (e.g., Webb, 1960; Dalgarno and Johnson, 1968; Mount, 1975; Lemon, 1985; Dyson, 1996). The breccia represents a caprock assemblage of a layered evaporite sequence, with clasts of insoluble lithologies in a matrix

38 of anhydrite and gypsum that has been altered to silty dolomite (e.g., Rowlands et al., 1980; Preiss, 1987; Hearon, 2008; Hannah, 2009). Currently, there is a general consensus amongst investigators that most of the diapiric breccia throughout the Flinders Ranges represents passive diapirs that grew at or just beneath the ground surface or sea floor due to an intricate balance between salt-supply rates and sediment-accumulation rates (e.g., Coats, 1964; Dalgarno and Johnson, 1968; Lemon, 1985; Dyson, 1998, 2004; Rowan and Vendeville, 2006; Hearon et al., 2010a, 2010b; Kernen et al., 2012). More than 100 diapiric structures are exposed in the Flinders Ranges (Figure 2.4). Similarly, cross-cutting diapiric-breccia bodies and surfaces containing diapiric breccia exist in the eastern Willouran Ranges (Coats and Preiss, 1987; Forbes, 1990; Drexel et al., 1993; Dyson, 2004; Hearon et al., 2010a). According to Rowlands et al. (1980), the presence of minerals that occur only in hypersaline environments and the mixed facies assemblage of the Callanna Group suggest a continental rifting environment recorded by two coeval depositional systems: (1) a continental shallow marine to sabkha environment; and (2) widespread rift-related volcanism and extrusion of basic lavas (Forbes, 1980; Preiss, 1987; Forbes, 1990; Preiss, 1993b). Salt diapirs and remnant allochthonous salt canopies are delineated based on the presence of blocks of Callanna Group lithologies that were originally intercalated with evaporite. Thus, the Callanna Group breccia is informally referred to here as a mobile substrate (i.e., ‘salt’) with similar properties as mobile evaporite (e.g., Jurassic Louann salt, Gulf of Mexico).

2.4 Observations In the following two sections, we first describe the exposed geometries of diapiric-breccia bodies and associated discordant and concordant surfaces, and then we describe the variable geometries of strata in the Burra and Umberatana groups. In both cases, we proceed generally up-section stratigraphically and from large-scale to small-scale features. In order to facilitate the descriptions below, high-quality Quickbird satellite imagery and HyMap aerial imagery (Figure 2.5) were interpreted and annotated with roman numerals (diapiric-breccia bodies) and capital letters (discordant surfaces) on Figure 2.6.

39 O 136 INSET

O 28 PEAKE AND DENISON RANGES

O 138 O Mirra Marree 141 Clara St Dora Eastern Willouran Breaden Hill Chintapanna Ranges O 30 South Hill Lyndhurst Burr Ideyaka Tourmaline Hill Loch Ness Copley LAKE Mucatoona Beltana Pinda LAKE FROME Nilpena Patawarta Frome Blinman Wirrealpa TORRENS Enorama Oraparinna Moralana NSW Upalinna Ilka Arkaba Windowarta intrusive breccias of

Worumba Anticline O Baratta 32 Wirreanda Uroonda Round Hill Yanyarrie Port Augusta Olary Oladdie

Coomooroo Walloway Paratoo Mount Vickery Rock Remarkable Whyalla Bulyninnie Oak Park

Port ADELAIDE Pirie FOLD BELT

Burra GULF

O 34 SPENCER RIVER Tamma VIC MURRAY

0 100 ADELAIDE KILOMETERS

Diapir

Basement inlier

O 36

Figure 2.4. Approximate location of mapped diapirs within the Adelaide Fold Belt. Location of the eastern Willouran Ranges is outlined in black (redrafted from Coats and Preiss, 1987; Dyson and Rowan, 2004).

40 Regional Map of the Adelaide Fold Belt

Eastern Willouran Ranges

0 0.5 1 2 4

kilometers

Figure 2.5. Uninterpreted false color composite image of 128-band HyMap (4 m resolution) colored similarly to a Landsat 7 FCC 741 RGB image and false color 431 image of 4-band Quickbird (0.6 m resolution) imagery of the eastern Willouran Ranges. HyMap imagery over the area was collected with six flight paths of 1.5 x 15 kilometers with an overlap of ~0.25 kilometers. Processing by HyVista used the proprietary Hycorr correction for atmospheric conditions and 3 arc second SRTM data to gain true reflectance. Inset shows location approximately 560 km north of Adelaide, South Australia.

41 Boorloo Mine Composite Quickbird and HyMap image of the eastern Willouran Ranges, South Australia Explanation br Umberatana Group Undifferentiated 3 II Diapiric breccia body Nuu IV Burra Group Undifferentiated iv Fold iv Nbu Breaden Structural discontinuity Hill Mine Bungarider Subgroup A br 3 Myrtle Springs Formation Contact, dashed where Ndm2 upper member approximately located IV Ndm1 lower member Structural discontinuity

Mundallio Subgroup Fault Skillogalee Dolomite Not Nmst Nmso Old Mount North West Member Mine Nmst Twenty Mile Hill Member Hut, tank, bore or br3 Tank landmark Nmsc Camel Flat Shale Member Nmsc br3 Emeroo Subgroup Witchelina Quartzite Now Noz Now Willawalpa Formation

Noz I Top Mount Sandstone A N 7°MN Umberatana-Myrtle Not Springs minibasin Nuu Callanna Group Undifferentiated Thomas E. Hearon, IV Colorado School of Mines Willouran br3 Diapiric breccia vi Hill July 2013

C v br West 3 br Willouran 3 VI Mine Trial Hole

Nmso Nmso E viii Ndm1 br3 D B VII V

br3 Nuu

Tank

VIII Ndm2

Nmst ix F br3 G

Old Mount Now North West Homestead IX Nmso iii Nmst Noz

Mount Norwest br3 Not Gorge Nuu ii

Regional Map of the Adelaide Fold Belt Burra minibasin Ndm2 Nmsc Nmso Eastern Yards br3 Ndm1 Willouran vii Ranges

i Tank Twenty Mile Hill III Now Nmst Nmsc

Witchelina Syncline Spring Bore

ii Now

Delusion Hill

Delusion minibasin Noz

Not

Adelaide 0 0.5 1 2 4

kilometers

Figure 2.6. Interpreted version of Figure 2.5. Yellow lines are stratigraphic contacts and green lines are faults, and formations are labeled using the abbreviations in Figure 2.3. Diapiric breccia bodies (pale yellow shading) and discordant surfaces (red lines) are identified by capital Roman numerals and letters, respectively, and lower-case Roman numerals denote folds. See text for description.

42 2.4.1 Structural Geometries Mappable bodies of diapiric breccia range from structurally concordant and stratigraphically conformable, to structurally concordant but stratigraphically disconformable, to structurally discordant. In the former case, the Callanna Group breccia is conformable with lowermost Burra Group stratigraphy and is thus in its original depositional position along the western and southern margins of the research area (I of Figure 2.6). Diapiric breccia is discordant to bedding in the northwestern (II), and southeastern (III) parts of the area, where two large bodies of Callanna Group breccia (24-28 km2) are flanked by laterally thinned, rotated Burra Group beds. In map view, both bodies have hour-glass shapes, first narrowing and then flaring stratigraphically upward. Both are connected to the conformable diapiric breccia in its proper stratigraphic position below the flanking Burra stratigraphic section (I). Smaller bodies of diapiric breccia (<1 km2) are also present at younger stratigraphic levels in the eastern Willouran Ranges (IV-IX). Some of these are strongly discordant and others are more structurally concordant with upper Burra Group stratigraphy and separate different levels and types of strata. Based on structural attitudes of underlying and overlying strata, the shallow zones of mostly concordant diapiric breccia range in thickness from approximately 25 m to 350 m. Surfaces with structural and stratigraphic discordance connect various bodies of diapiric breccia and commonly contain clasts of Callanna Group breccia that are below map-scale resolution. South of Breaden Hill, the stratigraphically lowest surface extends approximately 5.5 km from the southern end of an elongate body of Callanna Group breccia (IV) and contains 0 to <100 m of breccia along its length (A). Missing stratigraphic section is evident in the Twenty Mile Hill Member in this area, where the surface locally cuts slightly downsection. More importantly, although the surface remains approximately parallel to bedding on both sides for much of its length, all strata of the Old Mount North West Member and Myrtle Springs Formation are missing in this area. Surface B is a southern extension of surface A and curves to the southeast to intersect a lower tip of a 0.5 km2 body of Callanna Group breccia (V). This segment is a zone of moderate deformation <50 m wide, contains no diapiric breccia and cuts out only a minimal part of the Old Mount North West Member, although some diapiric breccia was mapped in this area by Forbes and Coats (1963), Forbes (1990) and Dyson (2004). Another surface (C) that is highly discordant to the flanking strata branches off from the transition

43 between surfaces A and B and extends 1.2 km to the east-northeast to the base of a body of Callanna Group breccia located approximately 1.5 km northwest of Trial Hole (VI). Surface C cuts steeply upsection, juxtaposes the Old Mount North West Member against the Lower Umberatana Group and contains randomly spaced meter-scale clasts of diapiric breccia along its length. Callanna Group breccia body VI separates the Old Mount North West Member from the Lower Umberatana Group. Toward the south and south-southeast, this body of diapiric breccia bifurcates and is present above and below beds of the lower member of the Myrtle Springs Formation. The southern branch makes a transition into another surface (D) that is slightly discordant to underlying and overlying Burra stratigraphy and extends for 1 km to the south towards another small body of diapiric breccia (0.14 km2; VII), which is highly discordant to bedding within the Old Mount North West Member. To the north of this small domain of diapiric breccia, missing stratigraphic section in the Old Mount North West Member and extra section in the lower member of the Myrtle Springs Formation are evident below and above this upper surface, respectively. Upper beds of the Old Mount North West Member are discontinuous and are truncated by this surface, whereas lower beds of the lower member of the Myrtle Springs Formation onlap this surface from north to south. From Callanna Group breccia body VII, surface D continues to the south and connects to the same body of breccia (V) that is at the southeastern termination of discordant surface B. Further to the southeast is a series of small diapiric breccia bodies (VIII and IX) and linking surfaces (F and G) that separate the Old Mount North West Member and the lower member of the Myrtle Springs Formation and ultimately connect to the large Callanna Group breccia body III. Returning to diapiric-breccia body VI west of Trial Hole, a final and uppermost discordant surface (E) extends for 1 km to the southeast before becoming structurally conformable. It separates truncated strata of the lower member of the Myrtle Springs Formation beneath from onlapping strata of the overlying Lower Umberatana Group, which locally contains clasts of diapiric breccia in its conglomerate beds. No fragments of diapiric breccia are observed along this surface. In summary, the eastern Willouran Ranges display complicated geometries of diapiric-

44 breccia bodies and linking discordant surfaces that usually contain minor amounts of Callanna Group breccia (Figure 2.6). In ascending stratigraphic order, we have identified: (1) a structurally and stratigraphically conformable body of Callanna Group breccia in its original stratigraphic position (I); (2) two large bodies of diapiric breccia at the northern and southern margins of the research area that cut up-section and flare to the east and northeast (II and III); and (3) a complex array of small diapiric breccia bodies and associated surfaces (IV-IX and A-G), with single levels (albeit at different positions in the stratigraphy) to the north and southeast, adjacent to the two large Callanna breccia bodies (II and III), and three levels in the center of the study area west- southwest of Trial Hole. With a few exceptions, bodies of breccia and discordant surfaces throughout the eastern Willouran Ranges are associated with effectively no small-scale deformation in directly adjacent strata. We observed no zones of shear along the boundaries of breccia bodies, no tectonic brecciation of surrounding strata and few small-scale faults. Several faults of uncertain origin occur directly below diapiric-breccia body VIII, and several apparent normal faults intersect strata beneath diapiric-breccia body V. In addition, there is minor disruption of bedding in a zone less than 50 m wide along discordant surface B.

2.4.2 Stratal Geometries Correlative strata of variable thickness and differing growth geometry within the Emeroo, Mundallio and Bungarider subgroups are present on the southeast and northwest flanks of the large Callanna breccia body III in the southeast corner of the research area (Figure 2.6). On the southeast side, Emeroo Subgroup strata gradually thin toward the diapiric breccia over a distance of 3.5 km, from approximately 2300 m to 980 m thick directly adjacent to diapiric breccia body III. The Camel Flat Shale Member, at the base of the Mundallio Subgroup, is truncated within 1.5 km of the breccia beneath the Twenty Mile Hill Member, which maintains uniform thickness and orientation to within 700 m of the breccia margin. Strata of the Twenty Mile Hill and Old Mount North West members are then deformed into an anticline-syncline pair (i of Figure 2.6) that plunges shallowly to the northwest and within which bedding thins dramatically within 400 m of the breccia contact. The base of the upper part of diapiric breccia body III structurally overlies uppermost beds of the Old Mount North West Member on a concordant contact. Strata

45 of the Myrtle Springs Formation maintain constant thickness and orientation from southeast to northwest towards the diapiric breccia but are abruptly truncated at or near the breccia contact, where exposure is poor. The Lower Umberatana Group concordantly overlies the Myrtle Springs Formation and covers the top of the diapiric breccia in this area. Stratal geometries northwest of diapiric breccia body III are entirely different from those on the southeast side. From Willouran Hill (west of surface A), strata strike south for approximately 5 km, curve to a southeast strike for another 10 km and terminate in the southeast at the nearly isoclinal, north- to northeast-plunging Witchelina syncline (ii) (Figure 2.6). On the western limb of the syncline, the Top Mount Sandstone and Willawalpa Formation thin toward the fold hinge and onlap diapiric breccia body I, with only the upper Willawalpa Formation extending through the hinge to the eastern limb. Conversely, the overlying Witchelina Quartzite and lower two members of the Skillogalee Dolomite markedly expand into the hinge of the Witchelina syncline, and thin dramatically toward the breccia on the eastern limb, where they are approximately concordant to the breccia margin. The thinned Witchelina Quartzite and Camel Flat Shale Member are overturned adjacent to breccia body I. At the top of the eastern limb of the syncline, the three members of the Skillogalee Dolomite are folded toward the east to form a small northwest-plunging anticline (iii), with strata truncated to the east at a high angle and overlain to the north by diapiric breccia. Emeroo and lower Mundallio group strata also thin northward from near Willouran Hill toward Callanna Group breccia body II, near the Breaden Hill Mine (Figure 2.6). Moreover, the Twenty Mile Hill Member of the Skillogalee Dolomite is folded into a tight southeast-plunging syncline (iv), near the breccia body. However, unlike the Witchelina syncline to the south, there is no stratal thickening of any unit into the syncline, bedding remains upright through the fold and no associated anticline is present in this area. The fold continues across diapiric-breccia body IV, albeit with no reduced amplitude, into overlying Umberatana Group strata. A number of other folds are present within supra-Callanna Group stratigraphic units. First, a syncline (v) within Umberatana Group strata adjacent to surface C plunges very shallowly toward the northeast. Second, a fold pair (vi) is present within the upper Callanna Group breccia body I and directly superjacent lower Burra Group strata near the West Willouran Mine. Third, an isoclinal fold pair (vii) is confined to the Top Mount Sandstone on the western

46 limb of the Witchelina syncline. Fourth, an anticline (viii) plunges to the east between discordant surface B and the deepest portion of diapiric-breccia body VII. Fifth, an anticline-syncline pair (ix) plunges to the east just north of the Old Mount North West Homestead. Sixth, a syncline (x) that is offset from the trend of the Witchelina syncline plunges north-northeast directly southeast of the Old Mount North West Homestead. Finally, there are smaller-scale folds (below map- scale resolution) associated with the diapiric-breccia bodies that crosscut the Old Mount North West Member (V and VII). On three of the four flanks of diapiric breccia bodies VII and V, strata downturn as they approach the breccia, forming small anticlines. On the southern flank of breccia body VII and also 750 m to the southeast of the southern end of breccia body V, strata turn up and thin toward the breccia bodies before reversing again, thereby forming syncline-anticline pairs. These are equivalent to, but smaller then, the large fold pair of the Witchelina syncline and the shallower anticline adjacent to Callanna Group breccia body III. The lower member of the Myrtle Springs Formation north and northeast of the Old Mount North West Homestead has the most complex stratal geometries of any unit in the area. The base of the member has significant relief, resulting in prominent onlap and other thickness variations. Moreover, there are several small-scale anticlines and synclines, some which exhibit growth strata. The lowest part of the Myrtle Springs Formation, as well as the Old Mount North West Member just across the intervening zone of breccia bodies and linking surfaces, contain extraclast-rich conglomerate beds with extensively altered igneous clasts and dolomite clasts thought to be derived from the Callanna Group (Hearon, 2008). In contrast, the upper member of the Myrtle Springs Formation contains no such conglomerates, displays relatively minor thickness changes along strike, onlaps the lower member to the north and intersects diapiric- breccia body III to the southeast with little to no deformation. Three discontinuous, variably oriented blocks ranging from 170-250 m thick of the Twenty Mile Hill Member are present at the top of diapiric-breccia body III and unconformably overlain by the southeastern end of the Myrtle Springs Formation termination (Figure 2.6). These blocks are equivalent to the thinned beds of the Twenty Mile Hill Member present on the northeastern limb of the small anticline (iii) at the top of the Witchelina syncline. In summary, there is a broad panel of Burra Group stratigraphic units between the large Callanna Group breccia bodies II and III. This panel is separated from the younger Umberatana

47 strata that overlie the large breccia bodies by a complex array of smaller breccia bodies and linking discordant surfaces. Along this array are five prominent areas of omitted stratigraphy (Figures 2.7 and 2.8): (1) the Old Mount North West Member and the Myrtle Springs Formation are missing along discordant surface A east of Willouran Hill (Figure 2.7, column A); (2) there is minor omission of the lower Old Mount North West strata along discordant surface B (Figure 2.7, column B); (3) the uppermost Old Mount North West Member and lowermost Myrtle Springs member are variably absent along surface D and the linked breccia bodies VIII and IX at the top of the Old Mount North West Member (Figure 2.7, columns B and C); (4) surface C juxtaposes the Old Mount North West Member and Lower Umberatana Group strata so that the Myrtle Springs Formation is missing (Figure 2.8); and (5) lowermost Umberatana Group strata are missing along surface E and along the Myrtle Springs-Umberatana contact to the south and southeast (Figure 2.7, columns B-D).

2.5 Interpretation In the following sections, we interpret starting from the autochthonous salt level, moving upwards to the allochthonous salt level and finally the Delamerian overprint. Lastly, we offer an interpretation for the evolution of the eastern Willouran Ranges salt system.

2.5.1 Autochthonous Salt Structures The elongate Callanna Group breccia body I, on the western edge of the research area, is interpreted as the autochthonous salt level because it is stratigraphically concordant with the overlying Top Mount Sandstone, which is oldest Burra Group unit in the Willouran Ranges and northwestern Flinders Ranges (Preiss, 1987). This autochthonous breccia connects to the bases of the two large hourglass-shaped diapiric-breccia bodies II and III, which are interpreted as primary salt diapirs the northern Breaden Hill diapir (II) and the southeastern Witchelina diapir (III) (Figure 2.8). Stratal thinning of all Burra Group units towards both diapirs and stratal terminations against the diapirs demonstrate that they grew as passive diapirs, with diapir inflation coeval with minibasin subsidence and deposition of growth strata. The Burra and Delusion minibasins, on either side of the Witchelina diapir, represent primary minibasins (sensu Pilcher et al., 2011) because they conformably overlie autochthonous

48 A B C E

Nuu Nuu Nuu Nuu Group Lower unconformity? unconformity? Umberatana Surface E Ndm2 Ndm2 Ndm2 Ndm2

Subgroup Ndm1 Bungarider Ndm1 Ndm1 Ndm1

Surface D Surface D

Nmso Nmso Nmso Nmso

Surface B Surface A Mundallio Subgroup Nmst Nmst Nmst Nmst

Nmsc Nmsc Nmsc Nmsc

Now Now Now Now Burra Group

Not Not Not Not Emeroo Subgroup Emeroo

Noz Noz Noz Noz

br3 br3 br3 br3 Group Callanna Missing stratigraphic section

Figure 2.7. Comparative schematic stratigraphic columns illustrating the variable distribution of omitted stratigraphic section (see also Hearon et al., 2010a). Columns A, B, C and E have the same locations as cross sections A, B, C and E, respectively, in Figures 2.8 and 2.9.

49 137° 58’ 00” E 138° 02’ 00” E 138° 06’ 00” E To Marree Boorloo 12.5 km Mine North Dam North Gate B83

Nuu br 3 Geologic Map of the eastern

Breaden Hill Willouran Ranges, South Australia

diapir (II)

o Explanation

27 o s o 68

33 Umberatana Group Undifferentiated Overturned bedding 53 o o v 39 Nuu

40 Strike of vertical o Breaden Burra Group Undifferentiated bedding

35 o Nbu o Hill Mine 32 Strike and dip

41 of bedding br3 Bungarider Subgroup (IV) Myrtle Springs Formation Contact, dashed where approximately located Ndm2 upper member o Bedding trace 43 Tank and yards Ndm1 lower member Weld (iv) Mundallio Subgroup Skillogalee Dolomite Fault or discontinuity Not Nmst Nmso Old Mount North West Member 29° 48’ 00” S pCbu Anticline, indicating Nmst Twenty Mile Hill Member plunge, dashed where approximately located

Nmsc Camel Flat Shale Member Syncline, indicating plunge, dashed where Emeroo Subgroup approximately located Tank Witchelina Quartzite A’ Now Cross section A Nmsc o Umberatana- 68 Willawalpa Formation br3 (I) Myrtle Springs minibasin Noz Mine Now Top Mount Sandstone Noz 4WD track Not Ephemeral river Callanna Group Undifferentiated Hut, tank, bore or salt weld A N 7° br3 Diapiric breccia MN landmark

modified from Forbes and Coats (1963), 0 500 1000 2000 Belperio (1987, 1990), Forbes (1990), Dyson (2004), Forbes et al. (2009); Hearon et al. (2010) North Well meters

Nuu Kingston diapir Willouran Hill A’ A (vi) (v) o27 o o o 26 25 o26 o 50

o o 32 30 o22 o 34 o 21 22 br o o 3 o o 51 o 27 39 West 28 (VI) 30 br3 o Willouran 40

o Creek Trial Hole o 29° 52’ 00” S 82 Mine salt 33

weld C o salt weld E 30 o an 30 o ur o

o 46 ill 42 o W 42 o salt weld B o salt weld D 23 Nmso

60 o o 57

44 40

o o B’ 37 o o 45 Ram diapir

45 15 (viii) br3

o 53 (VII)

o B o 39 o 25

30 o o 46 32 51 58 Willawalpa 66 diapir (V) Umberatana- 59 61 o 60 C’ Myrtle Springs

60 o 23 o o 45 minibasin 52 47 br (I) br3 o o 3 o30 27 o o o 43 58 o 30 23 o52 Nuu o 75 o o 43 50 25 o o36 56 o o 33 o Tank 42 VIII 35 Ndm2 Nmso o

(ix) o30 42

o salt welds 41

minibasin Nmst o

o F & G o 26 o 55 34 50 D’

? o54

o48 ? br3 o o 48 Old Mount 56 IX Ndm1 60 o o 53o 45 North West 73 o Now o61 62 o 80 Hmstd 80 45 Burra o o49o 55 o o (iii) o

81 66

o 66

73 o o

o64 (x) o 61 Nmst Noz 53 o o 29° 56’ 00” S

55 44o

Mount Norwest br3 Gorge o Not 59 o 33 60 o Nuu (ii) s o v 71 63 v s s72 o 32

br3 (I) 55 o s Witchelina

v 24 o v o diapir (III) 70

(i) Ndm2 56 o43 br3 C v o o 45o 10 Nmso 70 o 82 Nmsc o o 48 43 38 Yards pCbu o oo 70 o o 37o Ndm1 57 33 o Chintapanna 67 40 E’ 60 o 48 o o 35 o62 o52 o o Dam 71 o

(vii) o80 o

38 o 51 42 o40 18 v

58 o o o v40 42 o38 o 64 o o 42 o40 o o41 63 o56 o 57 53

oo o53 o 34 36 oTank

37 35 o o 43 60 o o o 76 o

br v 40 o38 40 Twenty Mile Hill 3 35 o o45 o v o o52 52 48 43 57 o oo o43 o54 57 50 44

o o 27 o54 o o 46 o o o 48 Nmst 75 50 Bungarider fault o52 o o o 48 30 40 41 o o 63 38 o58 Nmsc o45 v o 47 oo o

Witchelina o60 56 o 52 44 v o 57 o36 76 78 57 syncline o o v

61 o

37 v 50 Spring Bore s o32 o o30 (ii) o30 v s47 o 32 s30 o 31 o Now s 43 85 34 o 33 o o o 33 D s57 o o 40 minibasin

s36 47 Delusion Hill o 53 61 s 36 o 60 s43 65 70 27 s 57 s

o o79 o 53 Nuu o 45

80 60 o Noz

39 o

o o50

o s E 50 o60 72 70 s o62 Not Delusion

br o83

3 30° 00’ 00” S s 28

61 o 49 42

57 o o

77 o 47 46

s o o o60

74 o s

o 61

74 s

48 o pCbu 81o 85

o 80 s

To Farina Witchelina Homestead 14.5 km

Figure 2.8. Geologic map of the eastern Willouran Ranges based on Forbes and Coats (1963), Belperio (1987, 1990), Forbes (1990), Dyson (2004), Forbes et al. (2009) and modified with new field work by Hearon (2008), Hannah (2009) and Hearon et al., 2010a). Red dashed lines indicate comparative stratigraphic sections and geologic cross-sections (Figures 2.7 and 2.9), black lines with pairs of dots denote salt welds, and Roman numerals and letters are the same as in Figure 2.6. Unit colors and abbreviations match those on the stratigraphic column (Figure 2.3).

50 Callanna Group breccia, are flanked by passive diapirs and relatively little stratigraphic omission (Figures 2.8 and 2.9). In the Burra minibasin, the southeastward thinning of the Top Mount Sandstone and the Willawalpa Formation, the thickening of younger Emeroo and Mundallio subgroup strata in the same direction and the progressive lateral shifting of synclinal hinge toward the Witchelina diapir are all characteristic of an expulsion rollover structure (e.g., Ge et al., 1997) formed during migration of salt from beneath the minibasin (Figure 2.9D). The near vertical strata turned up over a length of about 4 km adjacent to the Witchelina diapir form a megaflap (sensu Giles and Rowan, 2012; Graham et al., 2012). Instead of forming as a composite halokinetic sequence, which is an unconformity-bound succession of upturned strata within 1 km of the shallower parts of a vertical diapir (e.g., Giles and Lawton, 2002; Rowan et al., 2003; Giles and Rowan, 2012), the Witchelina syncline represents large-scale subsidence of a primary minibasin and inflation of a broad diapir that gradually evolved into a narrower, more vertical diapir during the early stages of minibasin development soon after deposition of the Callanna Group. Similarly, large-scale stratal thinning at the northern end of the Burra minibasin and within the Delusion minibasin is interpreted to represent early, minibasin-scale differential subsidence rather then the development of localized composite halokinetic sequences.

2.5.2 Allochthonous Salt Structures The shallow diapiric-breccia bodies (IV to IX) and linking discordant surfaces (A-G) are interpreted as remnants of a multi-level allochthonous salt canopy system, with the surfaces representing allochthonous salt welds. Stratal truncations above and below these surfaces and variably missing stratigraphy are compatible with both weld and fault interpretations. However, their interpretation as welds, rather than faults, is supported by several observations: (1) the presence of small, discontinuous outcrops of diapiric breccia along the surfaces; (2) local halokinetic folds beneath and above the linked surfaces and diapiric-breccia bodies; and (3) the presence of Callanna Group breccia clasts in superjacent and subjacent conglomerates. Henceforth in the paper, we refer to the previously described surfaces as welds (Figure 2.8). There are three distinct levels of allochthonous welds and associated diapiric breccia. The oldest, comprising diapiric-breccia body IV and welds A and B, is approximately parallel to bedding near the top of the Twenty Mile Hill Member and base of the Old Mount North West

51 A. A Burra minibasin Umberatana-Myrtle Springs minibasin A’ W E 1 km Burra Group salt weld A Lower Umberatana Group 500 500

m 0 0 m Not Noz Now Nmst Nuu 500 Nmsc 500 br3

1000 autochthonous br3 1000

Umberatana-Myrtle B Burra minibasin B’ B. W Springs minibasin E 1 km Burra Group 500 salt weld B salt weld D salt weld E 500

m 0 0 m

Not Noz Now Nmst Nmso Ndm1 Nuu 500 500 Nmsc br3 1000 1000 autochthonous br3

Umberatana-Myrtle Burra minibasin Springs minibasin C. C SW NE C’ Lower 1 km Myrtle Springs 500 Burra Group Umberatana 500 Formation Group m 0 0 m Nmso Ndm1 Ndm2 Not Noz Now Nmst Nuu 500 Nmsc 500

1000 1000 autochthonous br3

allochthonous br3

D. D D’ SW Lower NE 500 Burra Group Umberatana 500 Group m 0 Nmst 0 m Not Noz Now Nmsc Nuu Nmst 500 500 br3

1000 autochthonous Witchelina 1000 Witchelina br diapir 3 syncline 1500 1500

1 km 2000 2000

E. E SW NE E’ 1 km Delusion minibasin 500 500 Burra Group Nuu Ndm2 m 0 Ndm1 0 m Nmso Not Noz Now Nmst 500 500 Nmsc autochthonous br 1000 3 1000

Figure 2.9. Geologic cross-sections A through E, from north to south (see Figure 2.8 for location), constructed with no down-plunge projection except for D. Thick solid black lines represent approximate formation contacts, whereas thick dashed black lines represent inferred contacts. Thin black lines are intraformational bedding planes, solid where approximate and dashed where projected. Short red lines indicate measured bedding dips. Unit colors and abbreviations as in Figures 2.3 and 2.8. No vertical exaggeration.

52 Member (Figures 2.8, 2.9a and 2.9b). In this two-dimensional view, this surface represents a zone formerly occupied by a subhorizontal salt sheet fed at least in part by the Breaden Hill diapir, but it may in fact be a steeper ramp in three dimensions. The intermediate level, consisting of welds D, F and G and diapiric-breccia bodies V to IX, represents an allochthonous salt sheet that cuts up and down section in the upper Old Mount North West Member (Figures 2.8, 2.9B, 2.9C). The upper level is more localized and is a weld (surface E) that extends southeastward from diapiric-breccia body VI (Figures 2.8 and 2.9B). It is correlative with an unconformity at the top of the Myrtle Springs Formation that continues to the southeast to merge with a prong of diapiric breccia at the top of the Witchelina diapir. Although it is possible that the unconformity is in reality an extension of the upper weld, we favor an interpretation as a simple disconformity because there is no angular discordance and no diapiric breccia present along the boundary. Moreover, the equivalent unconformity occurs at the top of the Delusion minibasin, where Burra Group strata and middle Umberatana Group strata are structurally concordant (Figures 2.8 and 2.9E). Similar unconformities between strata of the Burra and Umberatana groups that occur at great distances away from diapiric breccia bodies have been identified throughout the central and northern Flinders Ranges by Webb (1960) and Coats (1964, 1965). The northern end of the deepest canopy level connects to the top of the Breaden Hill diapir and the southeastern end of the middle canopy level connects to a prong of diapiric breccia near the top of the Witchelina diapir (Figure 2.8), indicating that these two primary diapirs were feeders to the multi-level canopy. The deep and intermediate levels of the canopy are connected in two places: (1) by weld C, which is interpreted as a vertical weld due to the presence of diapiric breccia and halokinetic folding (fold v); and (2) by diapiric-breccia body V, here termed the Willawalpa diapir (Figure 2.8). The Willawalpa diapir represents a keel, which is structural low at the base of a salt sheet or canopy, as does diapiric-breccia body VII, which is called the Ram diapir. The fold beneath the Ram diapir (fold viii) and the normal faults beneath the Willawalpa diapir are somewhat enigmatic expressions of complex three-dimensional allochthonous salt geometries and associated deformation. The succession of Old Mount North West strata bounded by the lower and intermediate canopy levels, vertical weld C and Willawalpa diapir represents an encased or encapsulated minibasin sensu Pilcher et al. (2011) and Rowan and Inman (2011). The youngest Old Mount

53 North West strata in this encapsulated minibasin, directly beneath diapiric-breccia body VI (Figure 2.8), constitutes an allosuture (Dooley et al., 2012) where two salt sheets from separate feeders coalesced. Another allosuture occurs in a similar stratigraphic position at the top of the primary Burra minibasin just to the east-northeast of the Old Mount North West Homestead (Figure 2.8). Halokinetic drape fold monoclines (sensu Giles and Rowan, 2012) with upturned beds, albeit at different scales, are associated with the canopy system in several places: in Umberatana strata adjacent to vertical weld C (fold v), and within Old Mount North West strata on the southern flank of the Ram diapir and beneath the intermediate canopy level to southeast of the Willawalpa diapir. However, strata are turned down slightly in other places: the northern flank of Ram diapir, both flanks of Willawalpa diapir, and the edge of the upper part of the Delusion minibasin (Figure 2.8). These downward inflections may reflect minor extension or local dissolution collapse features along the edges of the diapirs. Salt dissolution may also have been responsible for randomly oriented blocks of the Twenty Mile Hill Member near the northwestern edge of the Witchelina diapir, which could also represent condensed carapace (sensu Hart et al., 2004) atop the diapir that was later extended and abandoned during allochthonous salt breakout (Figures 2.8 and 2.9D). In summary, the area between the Witchelina and Breaden Hill diapirs contains the primary Burra minibasin capped by a multi-level salt canopy that includes an encapsulated minibasin. In the two-dimensional view provided by the outcrops, the canopy was emplaced to the south from the Breaden Hill diapir near the end of Twenty Mile Hill Member deposition and to the northwest somewhat later, during Old Mount North West deposition. Other feeders and complicated salt features are certainly possible in three dimensions. Above the canopy, the Myrtle Springs Formation and the Umberatana Group comprise a suprasalt minibasin with a diachronous base. No canopy is evident to the southeast of the Witchelina diapir.

2.5.3 Delamerian Orogeny In the eastern Willouran Ranges, no large or obvious Delamerian structures exist other than the Norwest and Bungarider faults, which detach in the autochthonous Callanna Group breccia on the western margin of the research area, below the Burra minibasin. These thrust

54 faults were responsible for general tilting of exposed strata toward the northeast and the varying regional strikes as exemplified by Umberatana Group strata, which curve from a roughly north- south trend in the north to a northwest-southeast trend in the southeast (Figure 2.8). We interpret minor folds near the West Willouran Mine (fold vi) to have originated during the Delamerian Orogeny, and the regional shortening likely modified the syncline near the Breaden Hill Mine (fold iv) and the Witchelina syncline as well. However, preserved growth folding adjacent to diapirs and salt welds is almost certainly not related to shortening, but rather to long-lived passive diapirism. One anomalous fold pair is at the base of the Burra minibasin (fold vii), which, because it is confined entirely to the Top Mount Sandstone, is unlikely to have been caused by either Delamerian shortening or passive diapirism. Instead, it may represent gravity- driven deformation during early subsidence of the minibasin.

2.5.4 Salt and Minibasin Evolution The observed salt and weld geometries and the age and thickness patterns of minibasin strata record a complex history of autochthonous and allochthonous salt tectonics in the eastern Willouran Ranges. Stratal relationships and age estimates suggest this salt system evolved over a period of at least 200 m.y. in this area. Because the map view is effectively a warped, oblique, strike-oriented cross section, we use it to reconstruct this history in one two-dimensional cut. We first removed the effects of Delamerian deformation in three steps: (1) straightening out the regional strikes of the base Lower Umberatana Group by variable vertical axis rotation of three different segments of the map; (2) correcting stratal thicknesses for regional dip to the east and northeast; and (3) removing the effects of local folds considered to be of Delamerian origin. We then qualitatively reconstructed the history back though time (Figure 2.10). Due to the likelihood of movement into and out of the plane of the reconstruction, a more quantitative restoration was not attempted. In the following discussion, we describe the evolution moving forward through time. Early movement and initial inflation of diapiric breccia initiated immediately after salt deposition, with minibasin-scale thinning and onlap of lower Emeroo Subgroup at the base of the Burra and Delusion minibasins (Figure 2.10A). Initial salt pillows were likely broad and possibly subaerially exposed with little topographic relief, as suggested by marginal marine to

55 A - End Willawalpa Formation

megaflap

B - End Camel Flat Shale Member expulsion rollover

carapace

megaflap

C - Near end Twenty Mile Hill Member

carapace

allosuture allosuture

megaflap

D - End Old Mount North West Member

allosuture

E - End Myrtle Springs Formation

N SE Myrtle Springs Formation

br Umberatana Group 3 br Old Mount 3 Old Mount br North West Mbr 3 North West Mbr

Twenty Mile Hill Mbr Breaden Camel Flat Shale Mbr Witchelina Hill diapir diapir

Witchelina Qtzite

br 3 Willawalpa Fm 0 1 2 4 Top Mount Sdst F - End Umberatana Group kilometers

Figure 2.10. Schematic evolution of the minibasins, diapirs and allochthonous salt of the eastern Willouran Ranges. Salt area is not preserved because of almost certain flow from out of the plane of section. See text for methodology and explanation. Formation colors and salt annotation as in Figures 2.8 and 2.9.

56 lacustrine depositional environments present during deposition of the Top Mount Sandstone and the Willawalpa Formation and a lack of diapir-derived detritus in these units. Flank collapse of the initial Burra minibasin adjacent to the Witchelina diapir formed an expulsion rollover geometry (Figures 2.10B and 2.10C). The shift from a broad pillow to a steeper diapir occurred during deposition of the Witchelina Quartzite and continued during Camel Flat and Twenty Mile Hill time as successive depocenters shifted laterally towards the Witchelina diapir. Rotation of strata off the top of the growing diapir and ongoing minibasin subsidence resulted in the formation of a megaflap, where strata are draped along the steep flank of the diapir for up to 4 km (Figure 2.10C). By the end of Twenty Mile Hill deposition, both the Breaden Hill and Witchelina diapirs had thicker roofs (Figure 2.10C). Allochthonous salt breakout occurred at this time at the Breaden Hill diapir, but slightly later on the northwestern flank of the Witchelina diapir. The salt first broke through the roofs on steep faults, but back from the diapir edges so that some roof was preserved, and then flowed laterally (Figure 2.10D). Salt from Breaden Hill (or sources out of the plane) formed a flat at the top of the Twenty Mile Hill Member, a gentle ramp in the lowermost Old Mount North West Member north-northwest of the Willawalpa diapir, and another flat and then ramp in the middle of the Old Mount North West Member farther to the southwest. Salt emplaced to the northwest from the Witchelina diapir first formed a flat near the base of the Old Mount North West Member and then a ramp higher in the section before merging with salt advancing from the opposite direction to form an allosuture near the top of the Old Mount North West Member close to the Witchelina diapir. Randomly oriented blocks of the Twenty Mile Hill Member presently above the Witchelina diapir represent condensed carapace (Figure 2.10C) preserved behind and above the breakout point (Figure 2.10D). On the southeastern side of Witchelina diapir, a smaller breakout and lateral extrusion occurred slightly later, near the top of the Old Mount North West Member, although earlier extrusion may have occurred out of the plane of section. A suprasalt minibasin containing Old Mount North West strata formed as coeval deposition continued in the subsalt minibasin (Figure 2.10D). The subsalt minibasin was flanked by the growing Willawalpa diapir to the south and inflating salt sourced from Breaden Hill to the north. The underlying salt evacuated into the flanking diapirs, each of which in turn fed salt

57 laterally over the top of the suprasalt minibasin until they merged at another allosuture (directly west of Trial Hole on Figure 2.8). The final geometry at the end of Old Mount North West deposition shows a multi-tiered canopy emplaced over a large primary basin and containing a smaller encapsulated minibasin. The thinner equivalent section of the Old Mount North West Member in the Delusion minibasin may represent the edge of a minibasin that thickens out of the plane of section. The Myrtle Springs suprasalt minibasin subsequently formed atop the salt canopy to the southeast (Figure 2.10E). Complex onlap and top-salt geometries indicate a diachronous onset of salt evacuation or possibly some dissolution, but continued deposition partially evacuated the canopy. Inflated salt to the north partly overrode the northern end of the Myrtle Springs suprasalt minibasin (Figure 2.10E). Subsequently, the same inflated salt collapsed, forming another suprasalt minibasin filled with the lowermost Lower Umberatana Group strata and floored by a subhorizontal salt weld (surface A of Figure 2.6). No equivalent deposition took place atop the Myrtle Springs Formation, where erosion of the upper part of the adjacent salt is indicated by diapiric breccia clasts within onlapping beds of Lower Umberatana Group strata near Trial Hole. Eventually, deposition took place across the entire area and the canopy was buried (Figure 2.10F). Later deformation of the eastern Willouran Ranges during the Delamerian Orogeny tilted the minibasins and associated salt bodies to their present-day orientation (Figure 2.8). In addition, several prominent folds occurred in addition to the regional-scale warping as evidenced by the changing strike of Umberatana beds. First, the southern edge of the Breaden Hill diapir, the northern end of the Burra minibasin, the salt canopy and the overlying Umberatana strata were all folded into an anticline-syncline pair. (Figure 2.10F). Second, the other end of the Burra minibasin was also folded, enhancing the Witchelina syncline and associated megaflap, but this was decoupled from shallower deformation by the allochthonous salt and weld. Evidence that this fold was modified during the Delamerian includes the change in syncline geometry between the Twenty Mile Hill and Old Mount North West members and the lack of synclinal thickening in the Old Mount North West Member.

58 2.6 Discussion The large-scale geometries and features outcropping in the eastern Willouran Ranges are remarkably similar to salt and minibasin geometries in the northern Gulf of Mexico and, to a lesser degree, other salt basins with allochthonous salt such as the South and Central Atlantic. For example, the northern Gulf of Mexico contains analogous features and geometries such as vertical feeders, expulsion rollovers, megaflaps, carapace, composite halokinetic sequences, omitted and additional stratigraphic section, allochthonous salt, multi-level and branching salt sheets and welds, and primary, suprasalt and encapsulated minibasins (e.g., Schuster, 1995; Diegel et al., 1995; Rowan, 1995; Rowan et al., 2003; Hart et al., 2004; Pilcher et al., 2011; Rowan and Inman, 2011). Figure 2.11 shows a large primary minibasin between two diapirs, an expulsion rollover and megaflap at one end of the primary minibasin, a partially welded allochthonous salt canopy with two sutures and a supra-salt minibasin of differing ages and thicknesses. Figure 2.12 shows an encapsulated minibasin separated from a younger minibasin by a branching allochthonous weld that is situated between two allochthonous salt sheets. Allochthonous salt development is driven by a higher ratio of salt-rise rate to sediment- accumulation rate, which may happen due to an increased load and a decrease in sedimentation or due to shortening-induced squeezing of diapirs (e.g., McGuinness and Hossack, 1993; Hudec and Jackson, 2006). The drive for lateral salt emplacement in the eastern Willouran Ranges remains unexplained. There is no local or regional evidence for orogenic shortening at this time as age constraints for the lower Burra Group and Lower Umberatana Group strata suggest allochthonous salt breakout in the eastern Willouran Ranges to have been during the late Torrensian, i.e., between approximately 700 and 650 Ma, which predates Delamerian shortening by over 100 m.y. (Figure 2.2). There is also no evidence in the stratigraphic record during this time for prolonged periods of slower sedimentation except during deposition of the Camel Flat Shale Member, before allochthonous salt breakout. A possibility, especially given that allochthonous salt emplacement was rather abrupt as evidenced by the sharp change from a steep salt interface to a subhorizontal base of salt, is that there was local shortening induced by gravity gliding and/or spreading within the rift basin. However, there is no unequivocal supporting evidence for this scenario in the existing two-dimensional exposures. Whereas a number of large-scale geometries in the eastern Willouran Ranges are similar

59 supra-salt minibasin supra-salt minibasin

weld salt canopy

salt diapir primary minibasin salt diapir

Explanation

Suture

autochthonous salt Salt weld Stratigraphic horizons

Salt contact 5 km Figure 2.11. Controlled Beam Migration (CBM) of a 3-D PSDM seismic line from the northern Gulf of Mexico that illustrates two primary salt diapirs bounding a primary minibasin with an expulsion rollover and megaflap to the right, a partially welded allochthonous canopy with two allosutures (vertical red dashes) and suprasalt minibasins. Salt bodies and welds (indicated by pairs of dots) are outlined in blue and subsalt horizons are in green, red and orange. Data courtesy of WesternGeco and C. Fiduk.

60 encapsulated minibasin

Explanation

Salt weld 2 km Salt contact 2 km

Figure 2.12. 3-D PSDM seismic profile of an encapsulated minibasin bounded by branching welds and an allochthonous diapir (modified from Rowan and Inman, 2011). Salt is in blue and welds are indicated by pairs of dots. Black line represents a fault. No vertical exaggeration. Data courtesy of CGG and C. Fiduk. Republished by permission of the Gulf Coast Association of Geological Societies, whose permission is required for further publication use.

61 to those seen on seismic data in basins like the Gulf of Mexico, small-scale features that are usually below seismic resolution limits are also present in the research area. Thus, exposed relationships were used to test ideas of allochthonous salt emplacement and the nature of salt- sediment interaction beneath salt sheets. Evidence of fault displacement, including shearing, rubble zones or thrust imbricates (e.g., Harrison and Patton, 1995; Harrison et al., 2004; Hudec and Jackson, 2006, 2009), is universally absent adjacent to diapirs and salt welds in the eastern Willouran Ranges. There is also a complete absence of slumps or debris-flow deposits directly below allochthonous salt sheets, as has been suggested from other basins where allochthonous salt bodies are known from seismic data (e.g., McGuinness and Hossack, 1993; Orange et al., 2004; Kilby et al., 2008). Instead, two different subsalt geometries are present at the transition from steep diapirs to allochthonous salt sheets. First, halokinetic anticline-syncline fold pairs that contain thinned and rotated minibasin strata in subsalt positions often exist in areas such as along the upper, western flank of Witchelina diapir. While these fold pairs occur at a variety of scales, ranging from megaflaps to small composite halokinetic sequences, the similar geometries suggest scale independence. When the ratio of sediment-accumulation rate to salt-rise rate is high, a drape fold forms atop and adjacent to a diapir, but when the ratio decreases, i.e., salt rise greatly exceeds sediment accumulation, salt breaks out somewhere on the drape fold and resumes lateral flow (Rowan et al., 2010; Kernen et al., 2012). There will be variable preservation of the subsalt drape fold depending on where the fault and/or salt breaks out on the salt-induced bathymetric scarp (Rowan et al., 2010; Kernen et al., 2012). The second subsalt geometry, such as on either flank of the Willawalpa diapir, is the absence of subsalt halokinetic folds at the transition from steep diapirs to salt sheets. In these cases, there is simply an abrupt change in base-salt dip without any change in subsalt stratal geometry. The outcrops of the eastern Willouran Ranges are effectively two-dimensional and are thus of limited use in trying to understand the three-dimensional geometry of the allochthonous salt system. 3-D seismic data, for example from the northern Gulf of Mexico, are better suited to this purpose. Nevertheless, the observed geometries in the two basins are remarkably similar. The value of the field exposures, of course, lies in the ability to see features that are below seismic-resolution limits but that are key components to companies drilling through and beneath

62 salt canopies and equivalent welds. No small-scale deformation, such as shearing, fracturing, or pervasive faulting, or possible deformation related facies other than very rare, intraformational debris flow deposits are present. Thus, salt advance in the eastern Willouran Ranges was accommodated neither by subsalt basal shear (Harrison and Patton, 1995; Harrison et al., 2004) nor by the development of thrust imbricates (Jackson and Hudec, 2004; Hudec and Jackson, 2009). Instead, it is likely that advance was accommodated either on roof-edge thrusts, resulting in no subsalt halokinetic folds, or by pinned inflation and then break-through on salt-roof thrusts, resulting in preservation of subsalt halokinetic drape monoclines (Hudec and Jackson, 2006, 2009; Rowan et al., 2010). Furthermore, because of the shallow water depths, open-toed advance and extrusive advance of exposed salt (Hudec and Jackson, 2006) were probably much more common than in the deepwater northern Gulf of Mexico, where salt sheets are almost always covered by a carapace of condensed hemipelagic sediment (Hart et al., 2004). Relatively thin or absent roof strata may also explain the scarcity of slump deposits that would have lain originally in front of, and subsequently beneath, the advancing salt sheets. Regardless of the style of advance, there was little to no deformation of subsalt strata other than halokinetic folding.

2.7 Conclusions The eastern Willouran Ranges, South Australia, contain one of the world’s oldest records of salt diapirs and salt sheets and provide a unique opportunity to study a two-dimensional view of complex three-dimensional allochthonous salt tectonics and associated stratal geometries. We have demonstrated that: • The observed outcrops of Callanna Group breccia result from a combination of autochthonous, diapiric and allochthonous salt tectonics, as originally proposed by Dyson (2004). • Although rift-basin inversion modified the original geometries, the allochthonous salt system was well established prior to the Delamerian Orogeny. • At the autochthonous level, a large primary minibasin between two passive diapirs contains an expulsion rollover with a near-vertical megaflap along one diapir flank. • A complex array of diapiric-breccia bodies and linking discordant surfaces within upper Burra Group strata is interpreted as the remnants of an allochthonous salt

63 canopy, with the surfaces representing salt welds. The canopy includes stacked and branching salt levels that surround an encapsulated minibasin. • There is little to no subsalt deformation such as thrust imbricates, subsalt basal-shear zones, or increased fault or fracture development. Instead, subsalt strata are either undeformed or are folded into halokinetic anticline-syncline fold pairs just beneath the transition from passive diapirs to salt sheets. • Allochthonous salt emplacement likely occurred via a combination of pinned inflation and roof-thrust breakout and, because of the shallow water depths, open-toed and/or extrusive advance.

The field exposures in the easternWillouran Ranges provide high-resolution spatial and stratigraphic information unobtainable from subsurface 3-D seismic data or one-dimensional well data. Thus, they provide improved understanding of salt-sediment interaction beneath allochthonous salt sheets that can aid exploration and development efforts in global hydrocarbon- rich salt basins such as the northern Gulf of Mexico.

2.8 Acknowledgments We would like to thank former Witchelina Station owner, Kandy Saler, Alex Nankivell of the Nature Foundation, SA, and George and Anne Morphett for access to the eastern Willouran Ranges. We also thank Wolfgang Preiss, John Keeling, Alan Mauger and Sandy Menpes for though-provoking discussions regarding Flinders Ranges geology. Field support and spirited debate were generously provided by Simon Baker, Carl Fiduk, Eric Gottlieb, Rachelle Kernen and Bruce Trudgill. HyMap and Quickbird images were acquired by HyVista Corporation and DigitalGlobe. WesternGeco, CGG and Carl Fiduk are thanked for the use of the seismic profiles in Figures 2.11 and 2.12. Rick Almendinger and Midland Valley are thanked for the use of Steronet 8 and 2DMove. We thank Tobi Payenberg, Carmen Krapf, Kathryn Amos, Blaise Fernandes and the staff at the Australian School of Petroleum for their logistical assistance. Major financial support was generously provided by past and present sponsors of the Salt- Sediment Interaction Research Consortium (SSIRC) originally at New Mexico State University and currently at the University of Texas-El Paso: Anadarko, BHP-Billiton, BP, Chevron, Cobalt,

64 ConocoPhillips, Devon, ENI, ExxonMobil, Hess, Marathon, Maxus (Repsol-YPF), Nexen, Samson, Shell, Statoil and Total. The American Association of Petroleum Geologists Grants- in-Aid and the Geological Society of America Student Research Grants also contributed to the financial support of this project.

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Amery, G. B., 1969, Structure of Sigsbee Scarp, Gulf of Mexico: AAPG Bulletin, v. 53, p. 2480- 2482.

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Belperio, A. P., 1990, Palaeoenvironmental interpretations of the Late Proterozoic Skillogalee Dolomite in the Willouran Ranges, South Australia, in J. B. Jago, and P. S. Moore, eds., The Evolution of a Late Precambrian-Early Paleozoic Rift Complex: The Adelaide Geosyncline: Geological Society of South Australia Special Publication 16, p. 85-104.

Burns, K. L, O. Stephansson, and J. R. White, 1977, The Flinders Ranges breccias of South Australia-diapirs or decollement?: Journal of the Geological Society of London, v. 134, p. 363-384.

Busk, H. G., 1929, Earth flexures; their geometry and their representation and analysis in geological section with special reference to the problem of oil finding: Cambridge, Cambridge University Press, 106 p.

65 Coats, R. P., 1964, The geology and mineralization of the Blinman dome diapir: Report of Investigation 26, Geological Survey of South Australia, 52 p.

Coats, R.P ., 1965, Diapirism in the Adelaide Geosyncline: Australian Petroleum Exploration Association Journal, v. 5, p. 98-102.

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74 CHAPTER 3 ALLOCHTHONOUS SALT INITIATION AND ADVANCE IN THE FLINDERS AND EASTERN WILLOURAN RANGES, SOUTH AUSTRALIA: USING OUTCROPS TO TEST SUBSURFACE-BASED MODELS FROM THE NORTHERN GULF OF MEXICO

A paper to be submitted to AAPG Bulletin

Thomas E. Hearon, IV, Mark G. Rowan, Katherine A. Giles, Rachelle A. Kernen, Cora E. Gannaway, Timothy F. Lawton, Joseph C. Fiduk

3.1 Abstract The northern Flinders Ranges and eastern Willouran Ranges, South Australia, expose Neoproterozoic salt diapirs, salt sheets and associated growth strata that provide a natural laboratory for testing and refining models of allochthonous salt initiation and emplacement.The diapiric Callanna Group (~850-800 Ma) comprises an assemblage of highly brecciated rocks originally interbedded with evaporites that are now absent. Using stereonet analysis to derive three-dimensional information from two-dimensional outcrops, we evaluate ten examples of the transition from steep diapirs to salt sheets, three instances of ramp-to-flat geometries and two of flat-to-ramp transitions. Stratal geometries adjacent to feeder diapirs range from a minibasin-scale megaflap to halokinetic drape folds to high-angle truncations and appear to have no relationship to subsequent allochthonous salt development. In all cases, the transition from steep diapirs to salt is abrupt and involves piston-like breakthrough of roof strata, freeing up salt to flow laterally. We suggest two models to explain the transition from steep diapirs to subhorizontal salt: 1) salt- top breakout, where salt rise occurs inboard of the salt flank, thereby preserving part of the roof beneath the sheet; and 2) salt-edge breakout, where rise occurs at the edge of the diapir with no roof preservation. Lateral emplacement of salt sheets is dependent on the interplay between the rate of salt

75 supply to the front of the sheet and the sediment-accumulation rate. When the ratio of salt-supply rate to sediment-accumulation rate is high to moderate, thrust advance results in base-salt flats and true ramps, respectively. Halokinetic folds are absent because the thrust emerges at the base of the sea-floor scarp and mass-transport complexes are rare. If the ratio is low, pinned inflation leads to drape folding of the top salt and cover into a mock ramp, with occasional slumping of the sheet and its roof and further breakout on thrust or reverse faults. In the shallow-water depositional environments of South Australia, lateral emplacement occurred through some combination of thrust advance, extrusive advance, and open-toed advance, with no evidence for subsalt thrust imbricates, shear zones or continuous rubble zones. In deepwater environments such as the northern Gulf of Mexico, thrust imbricates and rubble zones, which represent slumped carapace, are more common. This is due primarily to higher topographic relief related to thicker hemipelagic roofs, a lack of dissolution and basinward transport of overburden due to gravitational failure above large canopies.

3.2 Introduction Allochthonous salt, which is defined as a sheet-like salt diapir composed of mobile evaporite that is emplaced at younger stratigraphic levels above the original autochthonous source (e.g., Jackson and Talbot, 1991; Hudec and Jackson, 2006; Hudec and Jackson, 2011), has been recognized globally, from field exposures in the Zagros Mountains, Iran (e.g., Kent, 1979; Jackson et al., 1990), the Sverdrup Basin, Canada (e.g., Jackson and Harrison, 2006), the Katangan Copperbelt, Democratic Republic of the Congo (e.g., Jackson et al., 2003) and the Flinders Ranges, South Australia (e.g., Coats, 1973; Dyson, 2004a, 2004b; Hearon et al., 2010a, 2010b), to subsurface settings such as the deepwater Gulf of Mexico and the South Atlantic margins (e.g., Worrall and Snelson, 1989). Allochthonous salt may flow laterally as a single sheet sourced from a single feeder, or coalesce with sheets sourced from multiple feeders to form a larger canopy. The base of allochthonous salt typically has a ramp-flat geometry, which forms as a result of variations in sediment-accumulation rate and salt-rise rate (e.g., McGuinness and Hossack, 1993; Yeilding et al., 1995). Salt ramps are the steeply inclined segments of a base salt contact that cut up stratigraphic section, whereas salt flats are the gently inclined segments of a base salt contact that are parallel to sub-parallel with underlying strata (Hudec and Jackson,

76 2011). Several mechanisms have been suggested to account for the emplacement and spreading of allochthonous salt, most of which are based on seismic and limited well data. Early investigators in the northern Gulf of Mexico suggested subhorizontal allochthonous salt was intruded or injected into surrounding strata as sills (e.g., D’Onfro, 1988; Nelson and Fairchild, 1989; Wu et al., 1990). McGuiness and Hossack (1993) and Fletcher et al. (1995) suggested allochthonous salt extrudes onto the seafloor as a salt glacier, advancing laterally with or without a sedimentary roof. More recently, Hudec and Jackson (2006, 2009) proposed that allochthonous advances along thrust faults that link its leading edge to the seafloor. Structural and stratigraphic complications in subsalt strata, commonly referred to as “rubble zones” or “gumbo zones,” are frequent directly below allochthonous salt in the northern Gulf of Mexico. These zones may contain local repeat of section, overturned strata and blocks of mixed biostratigraphic ages. A number of theories have been proposed to explain these observations: (1) subsalt basalt shear, in which the advance of salt is accommodated at least in part by shearing and thinning of subsalt strata (Harrison and Patton, 1995; Harrison et al., 2004); (2) imbricate thrusting forming an antiformal stack beneath salt that has already been emplaced (Jackson and Hudec, 2004; Alexander et al., 2005); (3) imbricate thrust faults ahead of the salt tip that get overridden when the salt advances one of the more hinterland thrusts (Hudec and Jackson, 2006, 2009); and (4) debris-flow deposits, in which carapace on the frontal scarp faults and subsequently gets overridden (McGuinness and Hossack, 1993; Kilby et al., 2008; Hudec and Jackson, 2009). Subsalt rubble zones are not ubiquitous, however some wells exit the base of salt sheets into undeformed minibasin strata and others encounter coherent upturned or overturned strata (Kilby et al., 2008). Because of the limitations inherent in subsalt seismic imaging and one-dimensional well sampling, however, there is a need for outcrop-based studies to test the various models for allochthonous salt advance and subsalt deformation. Moreover, these models do not address how salt transitions from steep feeders to low-angle sheets. Here, we use detailed observations and analysis from several field locales in the northern Flinders Ranges and easternWillouran Ranges, South Australia, which contain a variety of allochthonous salt bodies ranging from isolated tongues to ramping sheets to multi-tiered canopies. Allochthonous diapiric breccia was identified

77 during early mapping of the Flinders Ranges, specifically at the Pinda diapir, which was first described by Coats (1973) as having a ‘Christmas tree’ shape. This was later corroborated by Dyson (1997, 1998), who was also the first to suggest the presence of allochthonous salt in the eastern Willouran Ranges (Dyson, 2004b) and several diapirs in the northern Flinders Ranges including Patawarta and Loch Ness (Dyson, 2005). More recently, our research team has investigated these and other allochthonous salt bodies extensively (Hearon, 2008; Hannah, 2009; Rowan et al., 2010; Hearon et al., 2010a, 2010b; Kernen, 2011; Kernen et al., 2012; Hearon et al., 2012; Hearon et al., in review). The purpose of this paper is to present new data from the Pinda and Patawarta diapirs and the eastern Willouran Ranges to develop new models of allochthonous salt initiation and breakout, and to test existing models of allochthonous salt advance. Outcrops in these areas display transitions from primary diapirs to laterally spreading sheets and transitions from base- salt ramps to flats and flats to ramps. Although only two-dimensional (map-view) exposures are present, we use stereonet analysis to unravel key aspects of the three-dimensional geometry of salt-sediment interaction. We focus on the variety of stratal geometries and truncations and small-scale deformation that are present along the flanks of steep diapirs and directly beneath allochthonous salt. Specifically, we examine ten examples of the transition from steep to low-angle salt that record the initiation and breakout of allochthonous salt sheets from either primary or secondary diapirs. The transition is invariably abrupt rather than gradual and we interpret the observations to represent piston-like breakthrough of salt through its roof. We also present three examples of ramp-to-flat transitions and two examples of flat-to-ramp transitions along the base of allochthonous salt. After salt breakout, subsequent lateral emplacement is through some combination of extrusive advance, open-toed advance, thrust advance or pinned inflation and breakthrough (Hudec and Jackson, 2006), with no evidence for subsalt shear zones, imbricate thrusts or continuous rubble zones. The results of our study are relevant to oil companies doing subsalt exploration and production in passive-margin basins such as the Gulf of Mexico, the Lower Congo Basin and offshore Brazil. We discuss similarities and differences between the geometries observed from outcrops in South Australia and those imaged on seismic data from the northern Gulf of Mexico.

78 While exploring an offshore salt basin, companies may drill through allochthonous salt on their way to deeper hydrocarbon targets. In other instances, traps are against the base of allochthonous salt, in which case stratal geometries can control reservoir distribution and trap configuration and influence hydrocarbon charge and seal. In all cases, subsalt seismic imaging may be obscured by overlying salt and some key geometries are simply beyond the resolution limits of even high quality seismic data. As a result, a plethora of drilling uncertainties and surprises are common, including the presence and thickness of rubble zones, steep to overturned strata and multiple salt penetrations. We hope that our results will help geoscientists better understand the processes of allochthonous salt initiation and advance and, consequently, allow them to predict with more confidence what exploration and production wells may encounter directly beneath salt sheets and equivalent salt welds.

3.3 Geologic Setting of the Flinders and Willouran Ranges The northern Flinders Ranges, located approximately 450 km (280 mi) north of Adelaide, South Australia, and the eastern Willouran Ranges, 125 km (75 mi) farther northwest, are located within a broadly north-south trending fold belt commonly referred to as the Adelaide Geosyncline (e.g., Sprigg, 1952; Preiss, 1987), the Adelaide Basin (e.g., Preiss, 2000) or the Adelaide Fold Belt (e.g., Scheibner, 1973; Jenkins, 1990) (Figure 3.1). A thick succession of Neoproterozoic and Cambrian strata (>15 km, or 9 mi) was deposited during the multi-stage development of an aulagocen, as western Laurentia separated from Australia, during breakup of the Rodinian supercontinent (Preiss, 2000) (Figure 3.2). The area was later subjected to thin- and thick-skinned inversion and deformation during the Delamerian Orogeny, which is generally considered to have occurred during the Upper Cambrian-Ordovician (~500 Ma) (e.g., Preiss, 1987; Sandiford et al., 1998; Paul et al., 2000; Foden et al., 2006), but may have initiated as early as the latest Neoproterozoic to early Cambrian (e.g., Lemon, 1988; Jenkins, 1990; Rowan and Vendeville, 2006). The oldest sedimentary unit in the northern Flinders and eastern Willouran ranges is the Callanna Group (~850-800 Ma). When present in its correct stratigraphic position, it comprises a layered to brecciated sequence of nonmarine and marine siliciclastics, carbonates and volcanics, all of which was originally interbedded with evaporites (e.g., Preiss, 1987). In most cases,

79 136°E 138°E 140°E 28°S Peak and Explanation Denison Ranges Lake Eyre Adelaide Fold Belt

William Road Creek N 0 100 200 Marree km Eastern Willouran Figure 3.10 Ranges 30°S Mt Painter Inlier Northern Arkaroola Flinders Ranges Gammon Leigh Creek Ranges Lake Frome Stuart Shelf Lake Torrens Central Flinders Curnamona Ranges Province Figure 3.3

Southern 32°S Flinders Ranges

Port Augusta

rc A ra a k c a Gawler Craton N

34°S M

o Murray Basin Spencer u n

Gulf o

g e

Adelaide s

Kangaroo Island 36°S

Figure 3.1. Generalized location map of the Adelaide Fold Belt based on MacKay (2011). Inset map shows approximate location within Australia. Gray shaded area represents the Adelaide Fold Belt; dashed rectangles indicate the north-central Flinders Ranges, which include the Pinda and Patawarta diapirs (Figure 3.3) and the eastern Willouran Ranges (Figure 3.10).

80 Chronostratigraphic Units Major Lithostratigraphic Units Regional Tectonics Salt Tectonics 514+5 Ma Lake Frome Group Middle Cambrian Wirrealpa Limestone Kanmantoo Group 526+4 Ma Billy Creek Formation

Early Hawker Group Normanville Moralana

Cambrian Supergroup Group

Uratanna Formation diapir squeezing Delamerian Orogeny Pound Subgroup Ediacaran Wilpena 588+35 Ma Group Major hiatus Yerelina Marinoan Umberatana Willochra Subgroup Subgroup

Group thermal subsidence 657+17 Ma Farina Subgroup minibasin formation and diapirism

827+6 Ma Subgroup evaporite deposition Major unconformity pre-Adelaidean Archean to early Proterozoic metamorphic complexes; mid-Proterozoic granites, volcanics and sediments

Figure 3.2. Generalized Neoproterozoic and Cambrian stratigraphy present in the Adelaide Fold Belt, along with relevant tectonic cycles based on Preiss (1987), Preiss (2000), Rowan and Vendeville (2006) and Backe et al., (2010).

81 however, outcrops of Callanna Group form breccias to megabreccias that are slightly to strongly discordant with overlying and underlying strata, with chaotic and heavily oxidized meter- to kilometer-scale blocks of Callanna Group lithologies surrounded by a blue-gray carbonate matrix that contains rounded, pebble-sized carbonate clasts (e.g., Webb, 1960; Coats, 1964; Preiss, 1987; Forbes, 1990; Preiss, 2000). Over 180 bodies of Callanna Group breccia are present throughout the Flinders Ranges and surrounding ranges (Lemon, 2000). While a tectonic (Delamerian) origin has been suggested for the Callanna Group (e.g., Mount, 1975; Burns et al., 1977; Mendis, 2002), many previous workers have cited evidence for long-lived passive growth of salt diapirs (e.g., Coats, 1965; Dalgarno and Johnson, 1968; Lemon, 1985; Preiss, 1987; Dyson, 1996, 1998; Lemon, 2000; Rowan and Vendeville, 2006; Hearon et al., 2010a, 2010b; Kernen et al., 2012). Studies of diapirs in the eastern Willouran Ranges and northern Flinders Ranges have yielded abundant evidence, including halokinetic growth strata and unconformities, pseudomorphs after evaporite minerals and diapir-derived detritus in adjacent strata that demonstrates the origin of the Callanna Group breccia as a mobilized layered evaporite sequence in which halite and other evaporites are no longer exposed at the surface and gypsum has been altered to the carbonate matrix (e.g. Webb, 1960; Dalgarno and Johnson, 1968; Lemon, 1985; Dyson, 1996, 2004b; Hearon, 2008; Hannah, 2009; Hearon et al., 2010a, in review). The breccias, referred to as diapiric breccia, represent steep salt diapirs, generally lower- angle salt sheets and incomplete salt welds, with younger non-evaporite strata partitioned into intervening minibasins. Directly overlying the autochthonous Callanna Group is the Neoproterozoic Burra Group, which comprises the oldest suprasalt stratigraphy in the Adelaide Fold Belt. Burra Group strata, which mostly comprise sandstone and dolomite, with subordinate shale, are interpreted to have been deposited in a shallow water, peritidal environment (e.g., Preiss, 1987; Preiss and Cowley, 1999; Hearon et al., 2010a; Hearon et al., in review). The overlying Sturtian-aged Umberatana Group contains alternating beds of non-marine to marine tillite and fine-grained, massive siltstone, interpreted as glacial outwash and loessite deposits, respectively (e.g., Preiss, 1987; Kendall et al., 2006; Preiss, 2006). The uppermost Neoproterozoic Wilpena Group contains a shallowing upward succession of shelfal fine-grained siliciclastics and carbonates to shoreface sandstone and shallow-water peritidal carbonates (e.g., Haines, 1987, 1988; Preiss, 1987). The

82 oldest units in the Wilpena Group comprise strata deposited during world-wide glaciation, while the youngest units contain fossils of the Ediacaran fauna. Overlying the Wilpena Group are Lower and Middle Cambrian strata, including the Hawker and Lake Frome Groups, which comprise turbiditic and locally reefal limestone units and minor interbedded clastics (Figure 3.2). Burra and lowermost Umberatana group strata flank the salt bodies of the eastern Willouran Ranges and include the Witchelina Quartzite, Skillogalee Dolomite and Myrtle Springs Formation. Further to the southeast, the Pinda and Patawarta diapirs, which are located approximately 50 km (31 mi) to the southeast of Leigh Creek and 15 km (9 mi) to the northeast of Blinman, respectively (Figure 3.3), are flanked by younger stratigraphic units of theWilpena Group, including the Brachina Formation, ABC Range Quartzite, Bunyeroo Formation, Wonoka Formation, Bonney Sandstone and Rawnsley Quartzite (Figure 3.4).

3.4 Description of Stratal and Structural Geometries In the following sections, we summarize our observations at the Pinda and Patawarta diapirs in the northern Flinders Ranges and near the Witchelina and Breaden Hill diapirs in the eastern Willouran Ranges. Because of Delamerian tilting, the map-view patterns of outcrop exposures in all cases represent oblique cross sections. For each area, we describe the large- scale geometry of diapiric breccia, the geometries of flanking strata and any relevant small- scale features. We refer to composite halokinetic sequences (CHS), which are large-scale, unconformity-bound sequences of upturned strata adjacent to diapirs (Giles and Rowan, 2012). Tabular CHS comprise stacked hook halokinetic sequences, in which the folding occurs within 200 m of the salt-sediment interface and internal unconformities can have up to 90º of angular truncation. Tapered CHS are composed of stacked wedge halokinetic sequences, with folding occurring over a distance of up to 1 km and internal unconformities with up to 30º of angular truncation.

3.4.1 Pinda Diapir The Pinda diapir (4 km2, or 2.5 mi2) comprises three intersecting, elongate bodies of diapiric breccia surrounded by strata dipping moderately to the southeast (Figure 3.5). Two of them form a diapir that cuts steeply upsection. The base of the diapir, which is adjacent to

83 Lyndhurst Arkaroola

Leigh Creek Loch Ness coalfield

Copley Angepena Leigh Creek

Pinda Figure 3.5

Patawarta Narrina Basin Figure 3.6

Blinman

Parachilna

Diapir N Road

25 km

Figure 3.3. Pan-sharpened Landsat 7 ETM+ satellite image of the north-central Flinders Ranges. Dashed white lines represent roads and red boxes denote the Pinda and Patawarta research areas (Figures 3.5 and 3.6) with yellow stars indicating the location of studied diapirs. Image courtesy of the Global Land Cover Facility.

84 Generalized stratigraphy adjacent to the Pinda and Patawarta diapirs, South Australia

Wilkawillina Limestone (Chw) (1170 m) 8000 Sandy dolostone, dark blue-gray, brown weathering, fine grained and laminated dolostone; interbedded with subordinate quartz arenite, gray, red-brown weathering, thin bedded to flaggy, fine grained Group

Hawker Parachilna Formation (Chp) (0-350 m) Sandy dolostone, dark blue-gray, brown weathering, fine grained and laminated dolostone; interbedded with subordinate quartz arenite, gray, red-brown weathering, thin bedded to flaggy, fine grained 7000 Rawnsley Quartzite (Nwr) (0-630 m) Subarkose to quartz arenite and quartzite, white, cross bedded and rippled; regionally contains Ediacara fauna

Bonney Sandstone (Npb) (0-750 m) Subarkose to quartz arenite, reddish brown to yellowish tan, fine- to medium-grained, massive to laminated, 10-15 cm thick low angle trough cross beds, beveled ripples, fining upward sequences, green reduction spots; interbedded with subordinate conglomerate, 1-2 cm thick beds, discontinuous, clast-supported, minor scoured 6000 bases, occasional imbrication, elongate to well-rounded dolomite, quartz arenite, igneous and chert clasts, <1-5 cm long; diapiric breccia present at the Wonoka-Bonney contact

Patsy Hill Member (Npbp) (0-640 m) Thinly laminated green shale and cherty dolomite overlain by brown to orange weathered, dark yellow-orange Pound Subgroup fresh, fine grained, thinly bedded to laminated quartz arenite to calcareous sandstone; brown to gray weathered limestone to silty limestone with conglomerate and stromatolites dominate the upper Npbp 5000 Wonoka Formation (Nww) (0-730 m) Limestone, dolomite and dolomitic siltstone, tan-light tan to tan-greenish fresh, algal laminations

Wearing Dolomite Member (Nwww) (0-50 m) Tan-creamy weathered, pink fresh limestone, thin bedded to horizontally laminated with large flat limestone pebbles, specular hematite and malachite horizons and calcite fracture fills

4000 Bunyeroo Formation (Nwb) (0-980 m) Siltstone and shale, reddish brown to purple weathered, occasionally greenish-gray, brown fresh, thin

meters bedded to laminated, ripple cross laminations, cross bedding; interbedded with subordinate massive orange-brown sandstone; occasional conglomerate, 0.3 to 0.45 m thick beds, pinkish rectangular, elongate sandstone clasts and white rounded clasts; minor discontinuous lenses of dark brown dolomite; interbedded diapiric breccia at Pinda (br3) (0-640 m) Depot Springs Subgroup ABC Range Quartzite (Nsa) (0-120 m) Quartz arenite, pinkish-gray, fine- to medium-grained, flaggy to medium bedded, low angle trough 3000 and tabular cross bedding and ripple cross laminations; prominent ridge-former Wilpena Group

2000 Brachina Formation (Nsb) (0-3350 m) Quartz arenite, reddish-brown weathered, orange-gray fresh, fine-grained, medium bedded to flaggy, trough cross bedding and ripple cross laminations; interbedded with subordinate siltstone and shale, thinly laminated, desiccation cracks; minor conglomerate, 0.1-0.5 m thick beds, monomict, angular to elongate, rectangular clasts, sandstone to quartzite, <1-5 cm long

Sandison Subgroup 1000

0 Diapiric breccia (br3) (0-2500 m; Adelaidean, ~850-800 Ma) Undifferentiated Curdimurka and Arkaroola Subgroups: megabreccia consisting of a mixed assemblage of unsorted centimeter to decameter scale blocks of mafic volcanics, dolostone, quartzite supported by light blue-gray to greenish matrix; some folded blocks, pseudomorphed evaporite minerals, salt hoppers, brecciated, hydrothermally altered; some blocks contain cryptalgal laminites

Group and stromatolites in centimeter-scale beds; autochthonous evaporite source Callanna

Figure 3.4. Neoproterozoic stratigraphy flanking the Pinda and Patawarta diapirs based on Belperio (1986), (Preiss (1987), Forbes (1990), Drexel et al. (1999) and Hearon et al. (2010b). Unit colors match those on geologic maps, oblique aerial photos and cross-sections of the Pinda and Patawarta diapirs (Figures 3.5, 3.7-3.9 and 3.13-3.15).

138° 55’ 00” E

21 o

o Geologic Map of the Pinda diapir, o

18 24

North-central Flinders Ranges, South Australia o 25

19o

Explanation 65 o o 26 o

Hawker Group s o 68 26

Overturned bedding 44 21

Chw Wilkawillina Formation o o o o 54 v 32 35

Chp Strike of vertical Nwb 21 Parachilna Formation o

bedding

Wilpena Group o o73 o 23

o o

32 Strike and dip o47 63 o Pound Subgroup 30 o

of bedding

o 29

Nwr 27 33

Rawnsley Quartzite Nsa o o

65 o

Contact, dashed where 37 o

approximate o o Npb Bonney Sandstone o55 72 o66 54 35

o o

41 23

Bedding trace o

Npbp Patsy Hill Member o o

v o 31 35 o

70 75 35 o Depot Springs Subgroup Fault, dashed where o o approximate v 33 78 36 Nww Wonoka Formation 66o 45 Syncline axial trace o o Nww 81 78 Nwww Wearing Dolomite Member (plunge/trend) v

Diapiric caprock o o o

77 o Nwb Bunyeroo Formation Nsa o 42 o 75 65 48 41 v v Sandison Subgroup 2 Location discussed 80 in text o

Nsa ABC Range Quartzite N 72 o Mine 65

Nsb Brachina Formation 4WD track o

84 v o

Umberatana Group Undifferentiated Ephemeral 70 o

river o o

o 51

Nuu 68

Nuu 73 70 64 50 o

0 250 500 1000 o 42

o Callanna Group Undifferentiated o

o 40 o 50

meters o

br3 65 58 Diapiric breccia o

72 o

37 o 54 o

modified from Coats (1973), Dyson (1998) 70

o 45

73 o

53 48 53 o

56 o

o 49 o

76 o

s 80 45

v 40

48 o

71 o

v s o

57 o 38

o Nsb 34 o

52 o o 44

o 69 65 50 o 50

63 Nww

Nsa 57o o

56 60 o

76 o

o Nwww o

v 63 Npbp

Nwb 70 68

80 o

o 62 o

68 o

75 72 o o

76 84 o o o 1

o 70 55

o 55

o 75 30° 46’ 00” S

78 81 o

30° 46’ 00” S o

73 68 62 o o o 78

o Npb

65 o 55

73 o

68 v

67 79 40

o o

o 55 o o o 70

51 46

67 v 49

o 52 69 o 80

base of diapir 71 o 81 o caprock Npb

87 66 v 51

s o 3 o

o 73 62/152o

55 80 62 o

o 53

73 s v o

74 s 50

Nsb o

o 45 o

66 s o o o

o 4 o

54 78 o o 17 v 72 o

74 81 v 51 51 o

s 85 45

v 76 49 50 v

o 82 br o 45 Npr

37 s

o o 3 s

82 s s o 78 v 40 48 o

v o

br3 80 65 o 74o s 38 o

s 57

70 s 74 45 70 o

o 45

s 52 31 o

Pinda diapir o 55 53 o

o 47

o 40 50 s 46/163 43/124

2 s

60 81 o 65

s 64

s 49/150

71 65 o Chp

Nwb 70 o34 5 30 o o

o 57 55

o 40/203 55 o

31 o

o o 48

55 65 v 27 o

o 41

84 o 53 51 o o

o 80 44 50 v o

o 50/111 32 46 o 67

37/119 o

21 64 o 80

41 s

33 o 51 o

Nww o Npr Chw

25 Npb

38 42 o o

o 34

20 33 o

o 34

35 o 138° 55’ 00” E

o o

o Npbp

26 o o 40

28 o Chp

30 37 o 33 30 o 29 35 85 82 o o 40

Figure 3.5. Geologic map of the Pinda diapir based on Coats (1973) and Dyson (1998) and modified with new field work by Hearon et al. (2010b). Numbers in gray boxes indicate locations discussed in text. Unit colors and abbreviations match those on the stratigraphic column (Figure 3.4).

86 the oldest strata to the west, is triangular-shaped and narrows up-section in the Wilpena Group towards the east-southeast. The diapir curves to the northeast and then back to the southeast as it continues to cut upsection, terminating beneath a large syncline composed of Lower Cambrian strata. Where the diapir curves back to the southeast, the third elongate body, a 200-500 m (650- 1600 ft) thick, 6.6 km (4 mi) long tongue of diapiric breccia, extends to the northeast entirely within the Bunyeroo Formation (Figure 3.5, Location 1). CHS flank both sides of the steep diapir. Exposed only on the north side of the Pinda diapir and below the lateral tongue of diapiric breccia, the Brachina Formation, ABC Range Quartzite and lower Bunyeroo Formation fold regionally over a distance of about 750 m (2500 ft) from the diapir but then form a succession of tabular CHS as beds display strongly overturned bedding and high-angle internal unconformities within 250 m (800 ft) of the diapir margin (Figure 3.5, Location 2). Younger stratigraphic units of the Wilpena Group are present along both flanks of the diapir and have similar CHS development on each side, with highly variable but systematic thinning and upturn anywhere from 50 to 1000 m (160-1600 ft) of the diapir margin. The upper Bunyeroo and Wonoka formations together form a tapered CHS (Figure 3.5, Location 3), the lower Bonney Sandstone forms a tabular CHS (Figure 3.5, Location 4) and the overlying upper Bonney Sandstone and Rawnsley Quartzite form another tapered CHS (Figure 3.5, Location 5). Individual CHS display offset synclinal axial traces that trend mostly towards the southeast with one exception that trends towards the southwest. Prominent salt-edge cusps are present where the lower and upper bounding unconformities of the tabular CHS intersect the diapir. The 6.6 km (4 mi) long lateral extension of diapiric breccia is flanked on either side by mostly concordant strata of the Bunyeroo Formation. On its western, stratigraphically older margin, the base salt truncates Bunyeroo strata at a low angle towards the tip of the breccia, whereas the upper contact is onlapped by upper beds of the same formation. No CHS flank the lateral breccia extension along its length. Along the upper margin, directly below the Bunyeroo Formation, is a series of dolomite-rich blocks composed of diapiric caprock up to 500 m (1600 ft). We observe no evidence of shear, faults or rubble zones in strata flanking the Pinda diapir, whether the steep portion of the diapir or that extending into the Bunyeroo Formation.

87 Nor is there a weld surface or thrust fault at the tip of the lateral breccia body. The only anomaly other than the halokinetic folds are local conglomerate beds in the Bunyeroo Formation above the lateral tongue of diapiric breccia, at the base of the Bonney Sandstone on the north side of the diapir and within the lower Bonney Sandstone on both sides of the Pinda diapir. These conglomerates contain abundant sandstone and caprock clasts with rare igneous clasts, are diapir proximal and dissipate several hundred meters to one kilometer away from the diapir, suggesting local derivation. Sandstone clasts likely originated from a roof of Bonney Sandstone atop the diapir or from the recycling of older Brachina Formation rocks, whereas caprock clasts and rare igneous clasts were derived from the Callanna Group breccia during periods of brief diapiric exposure.

3.4.2 Patawarta Diapir The Patawarta diapir is a 15 km2 (9 mi2), crescent-shaped body of diapiric breccia that is split into two small segments on its northwestern end, widens into one single diapir up to 2.5 km (1.5 mi) wide towards the southeast, narrows to less than 5 m towards the east-southeast and ultimately expands again toward the southeast (Figure 3.6). Two northeast-southwest trending faults and one east-west trending fault, all of which have a left-lateral sense of motion (Lemon, 1988), extend away from the northwest and southeast ends of the diapir and connect the diapir to other domains of diapiric breccia. The diapir is flanked by Wilpena-aged strata that generally dip moderately to the northeast. The following two sections will focus on the southeast and northwest ends of the Patawarta diapir, which are two areas of more detailed mapping and analysis.

3.4.2.1 Southeast End (Figure 3.7) On the northern flank of the southeastern end of the Patawarta diapir, the Bonney Sandstone through Lower Cambrian strata are conformable to the edge of salt, young away from the diapir toward the northeast and form the southwestern edge of the Narrina Basin. In contrast, the southern edge of diapiric breccia cuts upsection from the older Bunyeroo Formation through younger Lower Cambrian strata. The Bunyeroo Formation and the overlying Wonoka Formation and Patsy Hill Member of the Bonney Sandstone display broad thinning within about 550 m

88 138° 40’ 00”E

10 35 20

20 Nsa 35

40 Nwb Nsb 35 15 Npu

30 30 65 Nww 30 25 30 Npu 25 Nww Nsa 70 60 Figure 3.9 61 Nsb Chu Narrina Basin 54 75 45 br3 25

25 30° 56’ 00” S 30° 56’ 00” S Nww 30 br Nsa 35 3 15 15 Patawarta 35 Simplified Geologic Map of the Patawarta area 10 35 diapir 45 Flinders Ranges, South Australia Explanation 50 Qpap Pooraka Formation Strike and dip of bedding Patawarta Hawker Group

Chu Hawker Undifferentiated Contact, dashed where Nwb Hill approximate Wilpena Group Pendulum 52 Pound Subgroup Bedding trace Springs 57 Npu Pound Undifferentiated Nsb Fault, dashed where 46 br Depot Springs Subgroup approximate 3 Nww Wonoka Formation NwwNww 40 Diapiric caprock Nwb Bunyeroo Formation Npu 50 Sandison Subgroup br3 Nsa N Figure 3.7 Qpap

ABC Range Quartzite 138° 40’ 00”E 35 Nsb Brachina Formation 5000 1000 2000 Chu Callanna Group meters 60

br3 Diapiric breccia modified from Lemon (1988) and Coats (2009) 40

Figure 3.6. Simplified regional geologic map of the area surrounding the Patawarta diapir and Narrina Basin (modified from Lemon, 1988; Coats, 2009). Dashed boxes show locations of detailed maps in Figures 3.7 and 3.9.

89 138° 42’ 40”E Chw Geologic Map of Patawarta diapir SE, o 30 North-central Flinders Ranges, South Australia o35 Explanation Hawker Group s 68 Overturned bedding Chw Wilkawillina Formation v Strike of vertical Npr Wilpena Group bedding Pound Subgroup o 32 Strike and dip Nwr Rawnsley Quartzite of bedding Contact, dashed where Npb Bonney Sandstone Patawarta Hill approximate o Bedding trace 50 Npbp Patsy Hill Member Inferred halokinetic Depot Springs Subgroup sequence boundary Nww Wonoka Formation Fault, dashed where Patawarta diapir approximate Nwww Wearing Dolomite Member Anticline axial trace Npb Nwb Bunyeroo Formation Syncline axial trace Callanna Group ! ! Salt weld

br3 Diapiric breccia Diapiric caprock

0 250 500 N

o meters 4WD track

br3 oo o 39

86 v o o 72

81 s modified from Coats (1973), Hall et al. (1986), Ephemeral

v 79 v o

52 v 81v o51 Coats (2009), Kernen (2011) and Kernen et al. (2012) river

o v

o 67 48 o

caprock o s 75

s v

45 66 o o

o 81 o o o o o

45 o v o

o o v o

60 o

o 59

o 30 72 o o 44 40o 59 40 o45

40 v

28 55 36 71 v o o 74 o v

o v o o

31 o 48 58 o 47 o 47 o 45 36 o o

o 22 70 o 43 o o

42 54 45 59 43 31 43 o 50 o 62

o 42 45o

38 o 34

o o 50

57 o 40 50

o o o 38 o o o o 34

Wonoka o 55 o o 33 42

19 31 o 35 o

o 21 o o 40 o 36o

19 o 34 o 37

o o 38 50

12 syncline 43 35 30 35 o o o 34 37 o Npb o o 32 o40 16 44 34 21 25 Npbp

o o o o49 15 20 o 32 40 o o o o 43 39 o31 49 15 o o o 48 30 o 28 o 33 br3 38° 58’ 15” S o 33 o37 38° 58’ 15” S o 40 o o o58 o33 42 40 33 o o o 34 o 25o o o36 o 34 40 o 38 Nww 32 o 49 o31 56 o 46 o o 41 40 o 18 o 45 46 o38 o29 o35 o o34 o43 o 46 40o o o45 44 o 49 o37 45 o o 40 o o 59 36 Npr 32 o 37 o27 o o 40 o 32 38 o o 34 50 Nwww o 40o 39 o 47o o 35 o o

38 22 39 o

o o 26 37 o 36 o 27 Nwb 31 o o 44 30

o o 25 o 138° 42’ 40”E 40 45 o 30 o 41 o 35

Figure 3.7. Geologic map of the southeastern end of the Patawarta diapir based on Coats (1973), Hall et al. (1986) and Coats (2009) and modified with new field work by Kernen (2011) and Kernen et al. (2012). Black lines with pairs of dots denote salt welds. Unit colors and abbreviations match those on the stratigraphic column (Figure 3.4).

90 (1800 ft) of the diapir and form two stacked tapered CHS with offset fold axial traces that trend approximately east (Kernen et al., 2012). The northwestern limbs of these synclines contain steep to nearly vertical strata that are effectively parallel with the edge of the Patawarta diapir. Separated from the Bunyeroo Formation by a local, high-angle halokinetic unconformity (~70°), lower beds of the Wonoka Formation onlap this surface and contain conglomerate with abundant diapir-derived caprock clasts. Diapiric caprock, which parallels the Bunyeroo Formation along the southern and southeastern margin of the Patawarta diapir, is truncated at the Bunyeroo- Wonoka unconformity. At the top of the Wonoka syncline, steep to overturned strata of the middle and upper Wonoka Formation thin dramatically and are folded into a small anticline that trends east-southeast (Figure 3.8). The edge of the diapir curves to follow bedding attitudes in the anticline and then truncates Wonoka strata at a high angle. The Patsy Hill Member, which onlaps the middle and upper Wonoka Formation, contains conglomerate beds with limestone clasts of older Wonoka Formation strata that extend several hundred meters away from the Patawarta diapir (Kernen et al., 2012). The overlying Bonney Sandstone is unfolded and also truncated at a high angle against diapiric breccia. The truncation angle decreases in the uppermost Bonney Sandstone, increases through the Rawnsley Quartzite and continues in a ramp-flat manner through overlying Lower Cambrian strata. Diapir-flanking stratigraphy range from concordant to the edge of breccia, but overturned, to highly discordant, to concordant and upright. Regardless of the relationship, there is no evidence for diapir-parallel shear zones or rubble zones adjacent to the breccia. One minor fault with apparent reverse offset and associated folding is bedding-parallel in the Bonney Sandstone and ramps up into the lower Rawnsley Quartzite; whether is connects to the diapiric breccia is uncertain.

3.4.2.2 Northwest end (Figure 3.9) The northwestern end of the Patawarta diapir displays complex map-view relationships between diapiric breccia and Wilpena Group strata. The diapir bifurcates into two domains, with the southern domain connected to the east-west trending fault surface (Figure 3.9, Location 1). To the south of the southern domain, the Brachina Formation, ABC Range Quartzite and Bunyeroo Formation form a broad syncline that plunges to the south and there is no change

91 Rawnsley Rawnsley Qtzite Qtzite Bunyeroo allochthonous Bonney Patsy Hill Mbr Fm breccia Sdst

suprasalt subsalt minibasin minibasin

Wonoka anticline Wonoka Fm Wonoka syncline Bonney Sdst

Patawarta diapir

diapiric Bunyeroo breccia Fm

caprock 500 m

Figure 3.8. Oblique aerial photo of stratal geometries flanking the Patawarta diapir. View is toward the south-southeast. Thick dashed white lines represent the boundaries of the diapiric breccia; solid white lines are formation contacts; thin dashed white lines are bedding traces within mapped formations; solid pair of white circles denotes a salt weld. Unit colors and abbreviations match those on the stratigraphic column (Figure 3.4).

92 o

138° 55’ 00”E o o 24 45

Geologic Map of Patawarta diapir NW, o 32 North-central Flinders Ranges, South Australia o o 29 Explanation 43 o o s 58 o 68 53 Overturned bedding o75 Wilpena Group v 47 o Strike of vertical o 65 Pound Subgroup bedding 78 Nwr Rawnsley Quartzite o 32 Strike and dip o Npbp o 64 of bedding 56 Npb Bonney Sandstone o Contact, dashed where o o approximate Nww 60 39 Npb Npr Npbp Patsy Hill Member o o 54 69 82 Bedding trace Depot Springs Subgroup Nwb o 77 Inferred halokinetic Nww o Wonoka Formation sequence boundary o 58 o Nsa 70 66 o 63 Nwb Bunyeroo Formation Fault, dashed where approximate o o64 Callanna Group Undifferentiated Syncline axial trace 62 o 40 br (plunge/trend) 3 Diapiric breccia Nsb o o80 o 77 Diapiric caprock 81 o 0 250 500 70 2 Location discussed N in text o meters o61 70 4WD track o o modified from Coats (1973), Hall et al. (1986), 75 Coats (2009) and Gannaway (2013) Ephemeral o river o 58 50 o o o 77 71 o 61 86 72 o o 69 70 o82 o55 o o

v 83

o 70 s o s o 50 67

75 o o 56 o53 80 v 83 o 64 54/003 o o northern 78 o76 o 4 80 o 74 62 domain 74

v o v 67 65o o70 o 19 o v 69 o 75 o o o36 o 78 o60 75o o77 61 50

o65 o77 o73 o

3 v 5 o 57 74 38° 55’ 00” S o54 55o southern v v 38° 55’ 00” S 1 v o

v domain o 62

v 87

o s o

56 o 82 o 86

45 44 o

o o

o v o 42 52 51 o 51 52 67

o 61

2 Nsb br3 8 o o 44 o 50 Nsa

Nwb o 51 13 o

138° 55’ 00”E 70 o

10 60 o

Figure 3.9. Geologic map of the northwestern end of the Patawarta diapir based on Coats (1973), Hall et al. (1986) and Coats (2009) and modified with new field work by Gannaway (2014). Unit colors and abbreviations match those on the stratigraphic column (Figure 3.4).

93 in bedding attitude close to the breccia (Figure 3.9, Location 2). On the western margin of the southern domain, the lower part of the Brachina Formation is folded into a tight syncline with vertical to overturned strata in the diapir-parallel limb. Upturn occurs within 450 m (1500 ft) of the diapiric breccia, making this a tapered CHS. On the northern margin of the southern domain, the upper part of the Brachina Formation onlaps diapiric breccia at a low angle with minor folding (Figure 3.9, Location 3). The overlying ABC Range Quartzite maintains constant thickness towards the diapir and is then truncated at a high angle by diapiric breccia. A thin veneer of the Bunyeroo Formation is present atop the ABC Range Quartzite. The southwestern margin of the northern domain of diapiric breccia cuts strata of the Bunyeroo Formation at a low angle upsection toward the northwest (Figure 3.9, Location 4). Diapiric caprock is present at the tip of the northern domain of diapiric breccia and forms a discontinuous veneer along the northeastern flank where it is in contact with the upper Bunyeroo Formation. Low-angle onlap and minor halokinetic folding is present along the northeastern margin in the Bunyeroo Formation (Figure 3.9, Location 5). The overlying Wonoka Formation and Patsy Hill Member thin southward atop the main part of the Patawarta diapir (Figure 3.9, Location 5). In similar fashion to the southeastern end of the Patawarta diapir, the northwestern end displays no evidence for shearing or rubble zones in strata adjacent to diapiric breccia. Minor normal faults offset the Wonoka Formation and Patsy Hill Member northeast of the northern domain, but growth strata are absent within individual fault blocks.

3.4.3 Eastern Willouran Ranges The eastern Willouran Ranges contains two large hour-glass shaped primary diapirs, two flanking primary minibasins and a multi-level allochthonous canopy with several secondary diapirs and an encapsulated minibasin (Figure 3.10) (see Hearon et al., in review for further details). There are numerous examples of the transition from steep salt-sediment interfaces to lower-angle interfaces. These occur at different scales and may be at the tops of primary diapirs or within the complex canopy. 1) On the southeast side of the Witchelina diapir in the Delusion minibasin (Figure 3.10, Location 1), the Top Mount Sandstone, Willawalpa Formation and Witchelina

94 137° 58’ 00” E 138° 02’ 00” E 138° 06’ 00” E To Marree Boorloo 12.5 km Mine North Dam North Gate B83

Nuu br 3 Geologic Map of the eastern

Breaden Hill Willouran Ranges, South Australia

diapir

o Explanation

27 o s o 68

33 Umberatana Group Undifferentiated Overturned bedding 53 o o Nuu v

3 39 40 Strike of vertical o Breaden Burra Group Undifferentiated bedding

35 o Nbu o Hill Mine 32 Strike and dip

41 of bedding br3 Bungarider Subgroup Myrtle Springs Formation Contact, dashed where approximately located Ndm2 upper member o Bedding trace 43 Tank and yards Ndm1 lower member Weld Mundallio Subgroup Skillogalee Dolomite Fault or discontinuity Not Nmst Nmso Old Mount North West Member 29° 48’ 00” S pCbu Anticline, indicating Nmst Twenty Mile Hill Member plunge, dashed where approximately located Nmsc Camel Flat Shale Member Syncline, indicating plunge, dashed where Emeroo Subgroup approximately located Tank Witchelina Quartzite Now Location discussed 4 in text Nmsc o Umberatana- 68 Willawalpa Formation br3 Myrtle Springs Mine minibasin Noz Now Top Mount Sandstone 4WD track Noz Not Ephemeral river

Callanna Group Undifferentiated Hut, tank, bore or salt weld A N 7° landmark br3 Diapiric breccia MN modified from Forbes and Coats (1963), Belperio (1987, 1990), Forbes (1990), 0 500 1000 2000 Dyson (2004), Forbes et al. (2009); Hearon et al. (2010); Hearon et al. (in press) North Well meters

Nuu Kingston Willouran diapir Hill

o27 o o o 6 26 26 25 o o 50

o o 32 30 o22 o 34 o 21 22 br o o 3 o o 51 o 27 39 West 28 30 br3 o Willouran 40

o Creek Trial Hole o 29° 52’ 00” S 82 Mine salt 33

weld C o salt weld E 30 o an 30 o ur o

o 46 ill 42 o W 42 o salt weld B o salt weld D 23 Nmso

60 o o 57

44 40

o o 37 o o 45 45 15 br3 Ram diapir

5 o 53 o

o 39 o 25

30 o o 46 32 51 58 Willawalpa 66 diapir Umberatana- 59 61 o 60 Myrtle Springs

60 o 23 o o 45 minibasin 52 47 br (I) br3 o o 3 o 27 30 4 o o 58 o 43 o 30 23 o52 Nuu o 75 o o 43 50 25 o o36 56 o o 33 o Tank 42 35 Ndm2 o

o30 42

o salt welds 41

minibasin Nmst o

o F & G o 26 o 55 34 50

? o54

o48 ? br3 o o 48 56 Ndm1 Old Mount 60 o o 53o 45 North West 73 o Now o61 62 o 80 Homestead 80 49 45 Burra o oo 55 o o o

81 66

o 66

Nmso 73 o o

o64 o 61 Nmst Noz 53 o o 29° 56’ 00” S

55 44o

Mount Norwest br3 Gorge o Not 59 o 33 60 o Nuu s o v 71 63 v s s72 o 32

br3 55 o s Witchelina

v 24 o v o diapir 70

Ndm2 56 o43 br3 v o o 45o 10 Nmso 70 o 82 Nmsc o o 48 43 38 Yards pCbu o oo 70 o o 37o Ndm1 Chintapanna 57 33 o 60 o67 48 40 o o 35 o62 o52 o o Dam 71 o

o80 o

38 o 51 42 o40 18 v

58 o o o v40 1 42 o38 o 64 o o 2 42 o40 o o41 63 o56 o 57 53

oo o53 o 34 36 oTank

37 35 o o 43 60 o o o 76 o

br v 40 o38 40 Twenty Mile Hill 3 35 o o45 o v o o52 52 48 43 57 o oo o43 o54 57 50 44

o o 27 o54 o o 46 o o o 48 Nmst 75 50 Bungarider fault o52 o o o 48 30 40 41 o o 63 38 o58 Nmsc o45 v o 47 oo o

Witchelina o60 56 o 52 44 v o 57 o36 76 78 57 syncline o o v

61 o

37 v 50 Spring Bore s o32 o o30 o30 v s47 o 32 s30 o 31 o Now s 43 85 34 o 33 o o o 33 s57 o o 40 minibasin

s36 47 Delusion Hill o 53 61 s 36 o 60 s43 65 70 27 s 57 s

o o79 o 53 Nuu o 45

80 60 o Noz

39 o

o o50

o s 50 o60 72 70 s o62 Not Delusion

br o83

3 30° 00’ 00” S s 28

61 o 49 42

57 o o

77 o 47 46

s o o o60

74 o s

o 61

74 s

48 o pCbu 81o 85

o 80 s

To Farina Witchelina Homestead 14.5 km

Figure 3.10. Geologic map of the eastern Willouran Ranges (modified from Forbes and Coats, 1963; Belperio, 1987, 1990; Dyson, 2004b; Forbes et al., 2009; Hearon et al., 2010a; Hearon et al., in review). Weld labels are from Hearon et al. (in review) and numbers in gray boxes indicate locations discussed in text.

95 Quartzite gradually thin toward the Witchelina diapir over a distance of 3.5 km (2 mi). There is a cusp in the edge of the breccia, and the uppermost Witchelina Quartzite and overlying Twenty Mile Hill and Old Mount North West members are folded into an anticline-syncline pair. Above the cusp, strata first display low-angle truncations against the breccia and then high-angle truncations. The breccia is then concordant to and overlies the top of the Old Mount Northwest member for a distance of ~700 m before ramping up through the Myrtle Springs Formation. 2) The minibasin flank northwest of theWitchelina diapir is dominated by the nearly isoclinal, north- to northeast-plunging Witchelina syncline (Figure 3.10, Location 2), which represents the combination of an expulsion rollover and a megaflap of strata coming far up the side of the diapir (Hearon et al., in review). The Witchelina Quartzite, Camel Flat Shale Member and Twenty Mile Hill Member markedly expand into the hinge of the syncline and then thin dramatically over a distance of 4 km (2.5 mi) toward the breccia on the eastern limb, where they are overturned and approximately concordant to the breccia margin (Figure 3.11). The top of the eastern limb of the syncline is folded along with the edge of the breccia into a small northwest-plunging anticline, and the thinned strata are then truncated by breccia to the east initially at a high angle and then at a low angle. 3) On the opposite end of the Burra minibasin, adjacent to the Breaden Hill diapir, the Twenty Mile Hill Member, which displays no stratal thickening on this end of this minibasin, is folded into a tight southeast-plunging syncline with no associated anticline (Figure 3.10, Location 3). Beds in the lower Twenty Mile Member are truncated by the breccia, whereas the upper part of the member is concordant to the breccia and maintains constant thickness on the northeastern limb of the syncline. This section is truncated by breccia to the east at a high angle, with more breccia concordantly above the Twenty Mile Hill Member and also folded in the syncline. 4) Strata of the Old Mount North West Member on both sides of the secondary Willawalpa diapir (Figure 3.10, Location 4) downturn slightly and are truncated against the diapir at a high angle, forming small, open anticlines. Breccia then concordantly overlies the truncated strata on both sides.

96 diapiric breccia Witchelina syncline Primary Burra minibasin Witchelina Qtzite

Camel Flat Shale Mbr

Twenty Mile Hill Mbr

Witchelina diapiric Old Mount diapir breccia North West Mbr upper anticline Lower Member Myrtle Springs Fm Secondary Myrtle Springs- allochthonous 500 m Umberatana minibasin breccia

Figure 3.11. Oblique aerial photo of the Witchelina syncline flanking the Witchelina diapir in the eastern Willouran Ranges. View is toward the south. Thick dashed white lines represent the boundaries of diapiric breccia; solid white lines are formation contacts; thin dashed white lines are bedding traces within mapped formations; solid pairs of white circles denote salt welds.

97 5) The northern flank of the Ram diapir (Figure 3.10, Location 5) also displays minor stratal downturn and nearly orthogonal truncation adjacent to the diapir. The southern flank, however, contains a small syncline-anticline pair in the flanking Old Mount North West Member. In similar fashion to the Willawalpa diapir, breccia is then concordantly above the flanking strata. 6) Lower Umberatana Group strata are folded into a shallow northeast-plunging syncline on the northwestern side of salt weld C (Figure 3.10, Location 6). On the southeastern side, Old Mount North West strata are truncated against breccia at a high angle, with more breccia concordantly above the truncated strata.

The eastern Willouran Ranges also include one example of a transition from an apparent low-angle base salt to a secondary diapir. The weld beneath the encapsulated minibasin (Figure 3.10, weld B) ramps up into the Willawalpa diapir, but the relationships are unfortunately obscured by faulting at the base of the diapir.

3.4.4 Summary A variety of folds and stratal truncations are present adjacent to steep flanks of diapiric breccia throughout the three field areas. These range from a minibasin-scale megaflap with strata overturned and broadly concordant to breccia, to tapered and tabular CHS with upturned, concordant strata, to unfolded strata with high-angle truncations against diapiric breccia. Sometimes there is an abrupt transition to overlying breccia that is concordant to strata or cuts upsection at low angles; in other cases, the steep breccia edge and adjacent strata form small anticlines, with the diapir-proximal limb truncated at a high angle before the transition to low- angle stratal cutoffs. In all cases, there is an absence of shear zones, rubble zones and thrust faults adjacent to or beneath steep or concordant diapiric breccia, respectively. Occasional conglomerates that contain diapir-derived detritus are present in strata adjacent to steep diapiric breccia bodies but are rare to absent beneath breccia bodies that overlie strata concordantly or at a slight truncation angle.

98 3.5 Interpretation The map view of each field area is effectively an oblique cross section due to regional tilting during the Delamerian orogeny. Thus, outcrop exposure represent only a two-dimensional cut through what is most certainly different and more complicated in three dimensions. For example, what is an apparent low-angle truncation in map view, may actually be a high-angle truncation in three-dimensions. Thus, in order to interpret the observations properly and to understand the evolution of diapirs and allochthonous salt present in each field area, we need to determine the true orientation of the salt-sediment interface. In the following sections, we will first describe a methodology for calculating the three-dimensional relationships from two- dimensional outcrops of salt diapirs and flanking strata and then apply this methodology to each of the diapirs present at Pinda and Patawarta and in the eastern Willouran Ranges.

3.5.1 Structural Analysis We use stereonet analysis of bedding attitudes coupled with reasonable assumptions associated with halokinetic drape-fold theory to calculate the original orientation of the salt- sediment interface. Where there is not halokinetic fold, the analysis is not possible. The key assumption is that the fold axis of a halokinetic drape fold is parallel to the associated salt face because the edge of the rising or advancing salt is controlling the geometry of the draped roof (Figure 3.12). The methodology entails the following six steps: 1) Calculate the plane of the minibasin adjacent to the salt body by taking the average orientation of regionally tilted strata outside of the zone of drape folding. 2) Calculate the halokinetic fold axis by using attitudes within the drape fold and assuming the fold is locally cylindrical. 3) Calculate the present-day orientation of the plane of the salt-sediment interface by using two lines that define the plane: the halokinetic fold axis and the map-view azimuth of the edge of salt (the intersection of the salt face with the horizontal). 4) Determine the original dip of the salt-sediment interface by measuring the angle between the calculated salt-face plane and the minibasin plane. 5) Determine whether the salt was dipping outward or flaring outward by examining whether beds lengths measured from a line perpendicular to the bedding in the

99 condensed drape-fold roof strata monocline

salt emplacement direction

diapir plane of diapir face plane of minibasin halokinetic fold axis strata

Figure 3.12. 3-D block diagram of a ramping salt sheet with a flanking halokinetic drape fold showing key lines and planes that provide the basis for deriving three-dimensional orientations from map-view relationships. See text for explanation.

100 minibasin increase or decrease, respectively, upward. 6) For low-angle allochthonous salt, calculate the current direction of salt advance by assuming it was perpendicular to the halokinetic fold axis in the plane of the minibasin. 7) Determine the original orientation of the salt face and the direction of allochthonous salt advance by removing Delamerian tilting.

3.5.2 Pinda Diapir Using the halokinetic fold axis of the upper Brachina Formation on the northern side, the original salt-sediment interface dipped outward at 77° and steepened upward to near vertical in the lower Bunyeroo Formation. Bed lengths lengthen slightly above a small cusp, indicating minor onlap of original roof (Figure 3.5, Location 1). The edge of salt is then steep again before an abrupt transition to allochthonous salt with a base salt dip of 13°. We use the halokinetic fold axis to construct a down-plunge section that depicts the approximate cross-sectional geometry prior to Delamerian tilting (Figure 3.13, Pinda down plunge). In map view, the length of the allochthonous salt tongue is 6.6 km (4 mi). However, the minimum extent is actually 5.5 km (3.4 mi) when measured using the calculated emplacement direction. When Delamerian tilting is removed, the paleo-emplacement direction was 059°. Thus, due to the oblique cut of the section, what appears as the frontal tip of a salt tongue in map view is actually the lateral edge of a tongue that advanced to the northeast from a position that is currently in the air (eroded) into the plane of map. The lateral body of diapiric breccia was first interpreted as an allochthonous salt body by Coats (1973), then as a subaqueous salt glacier by Dyson (1998, 2004a) and finally as an allochthonous salt tongue by Hearon et al. (2010, 2010b). The absence of diapir-derived detritus in the underlying Bunyeroo Formation suggests that the allochthonous salt tongue advanced with a thin sedimentary veneer and not as a subaqueous salt glacier, which advances freely without a roof (e.g., Fletcher et al., 1995; Jackson and Hudec, 2011). Finally, Delamerian shortening, which was responsible for tilting the Pinda area to the southeast, most likely also generated smaller-scale folds. We suggest that the kilometer-scale, non-halokinetic folding of the base of the allochthonous salt tongue and subjacent strata near the

101 ENE Chw WSW Chp Projected dip Npr 1 Npb km Chp Npb Npr Npbp

Nww Nwww Npb

Delamerian br Nwb Allochthonous 3 fold salt tongue Npbp Pinda diapir Nww Nsa

br3 Nwb Nsb

Nsa

Nsb

Figure 3.13. Down-plunge cross-section of the Pinda diapir and salt tongue constructed using the halokinetic fold axis of the Brachina Formation (Nsb) (46/163). Thick and thin black lines show formation contacts and intraformational bedding, respectively (solid where approximate, dashed where inferred). Short red lines indicate measured bedding attitudes. Unit colors and abbreviations as in Figures 3.4 and 3.5. No vertical exaggeration.

102 breakout point was a product of later contraction.

3.5.3 Patawarta Southeast Using the halokinetic fold axis of the Wonoka Formation beneath the southeastern end of the Patawarta diapir, the original salt-sediment interface was a base salt that dipped inward at 62° (Figure 3.14, Patawarta down plunge). The subjacent overturned strata represent original roof, so that the base-salt ramp is the rotated top salt. Some of the roof is preserved in the upper monoclinal fold limb above the folded salt-sediment boundary. This limb is truncated by a steep salt-sediment interface that ramps up at 72° through the lower Bonney Sandstone with no halokinetic folding. Directly above, there is an abrupt transition to a base-salt dip of 20° before the same ramps up steeply through the Rawnsley Quartzite and then at a lower angle through Lower Cambrian strata. The lack of halokinetic folding at these levels does not allow us to employ stereonet analysis to determine the true relationships. The southeastern portion of the Patawarta diapir is an allochthonous salt sheet with a ramp-flat geometry, with strata on the north and south sides representing the suprasalt and subsalt minibasins, respectively. Stereonet analysis indicates that the sheet was originally advancing to the south (000°). Whether the ramp adjacent to the Bunyeroo Formation extends all the way to the autochthonous level or shallows again in the subsurface cannot be determined from exposures in this area.

3.5.4 Patawarta Northwest The northwestern end of the Patawarta diapir exposes a deeper level of stratigraphy than the southeastern end. Stereonet analysis of the halokinetic fold within the Brachina Formation at the western end of the southern breccia domain indicates a roughly vertical salt-sediment interface (83°), with overlying roof strata onlapping diapiric breccia at a low angle (26°). At the eastern end of this roof, diapiric breccia truncates the ABC Range Quartzite and overlying thin veneer of Bunyeroo Formation at 51°, with no evidence of folding, then abruptly transitions to a northwest-directed salt tongue with a base salt dip of 5°. The southern margin of the southern domain of breccia is not a diapiric salt-sediment interface but is, instead, interpreted as a fault offset of the diapir edge. This is part of the regional

103 NNW SSE Chw Npr Npb Chw

Allochthonous Npr suprasalt minibasin salt sheet br3

Npb weld Npbp

Nww

br 3 subsalt minibasin Nwww Patawarta diapir 1 km Nwb caprock Projected dip

Figure 3.14. Down-plunge cross-section of the ramping salt sheet at Patawarta constructed using the halokinetic fold axis of the Wonoka anticline-syncline fold pair (Nww) (41/104). Thick and thin black lines show formation contacts and intraformational bedding, respectively (solid where approximate, dashed where inferred). Black lines with pairs of dots denote salt welds and short red lines indicate measured bedding dips. Unit colors and abbreviations as in Figures 3.4 and 3.7. No vertical exaggeration.

104 tear fault system (Lemon, 1988) in which the Patawarta diapir has been squeezed or thrusted at a restraining bend. The western end and northern edge of the same breccia domain represent the flank and top, respectively, of the diapir. The onlapping roof was cut at a high angle just below where the breccia broke out and advanced as a salt tongue toward the west-northwest (284°). We use the older relationships exposed on the northwestern end of the Patawarta diapir to speculate about the deeper geometries at the opposite end of the Patawarta diapir. Specifically, since allochthonous salt was emplaced near the base of the Bunyeroo Formation to the northwest, we assume that the same occurred to the southeast since this was the primary advance direction. Thus, we suggest that the observed ramp-flat geometry in the upper Bunyeroo andWonoka formations is rooted in another base-salt flat in the lower Bunyeroo Formation (Figure 3.15, composite Patawarta cartoon).

3.5.5 Eastern Willouran Ranges Using the fold axis calculated for the Witchelina Quartzite, Camel Flat Shale Member and the Twenty Mile Hill Member on the northwest side of the Witchelina diapir, the original salt-sediment interface dipped outward at 64°. The syncline forms a megaflap in which strata thin towards the diapir Witchelina over a distance of 4 km (e.g., Giles and Rowan, 2012; Hearon et al., in review). The anticline at the upper part of the megaflap represents the original roof draped over the edge of the inflated salt. The roof strata are parallel to the top of the diapir and are truncated by breccia, with no halokinetic folding, with the salt-sediment interface dipping inward at 73°. Above is an abrupt transition to allochthonous salt with a base-salt dip of 33° with no halokinetic folding in the underlying Old Mount North West Member. Salt emplacement was toward 190°. There are similar relationships on the opposite flank of theWitchelina diapir, but with several differences. First there is no megaflap but only gradual thinning of minibasin strata toward the diapir, which dipped outward at 34°. Second, the roof deposited atop the shoulder of the diapir is shorter and onlaps the breccia before it its truncated more steeply. Third, allochthonous salt breakout on this side of the diapir was at the top of the Old Mount North West Member and extended only a short distance. The origin of the anticline-syncline pair is enigmatic but may be due to Delamerian deformation or dissolution of underlying salt.

105 Cu Cu Npr Npr

Npb Npb

Nww br3 Nww

Nsa Nwb Nsa Nwb

Nsb Nsb

Figure 3.15. Schematic composite cross-section of the Patawarta diapir that combines relationships observed on the northwestern and southeastern ends. Solid black lines along salt flanks are oriented according to stereonet analysis, whereas dashed diapir flanks are inferred. Formation thicknesses are approximate and were measured from structural attitudes from geologic maps (Figures 3.7 and 3.9).

106 At the northern end of the Burra minibasin along the southern flank of the Breaden Hill diapir there is a thin, rotated beam of the Twenty Mile Hill Member. The syncline is Delamerian, since it also affects the overlying breccia and Lower Umberatana Group strata. When the folding is removed, the beam represents original roof that is truncated at a high angle and then overlain by allochthonous diapiric breccia. Using the halokinetic fold axis calculated for the small syncline-anticline pair in the Old Mount North West Member on the south side of the Ram diapir, the original salt-sediment interface flared outward at 77°. The northern limb of the anticline represents original roof that was truncated at a high angle by salt, which broke out and advanced with a base-salt dip of 22° in the direction 030°. There are four transitions from steep salt to shallow salt with an absence of folds: on the south side of salt weld C, the north side of the Ram diapir and both sides of the Willawalpa diapir. In each case, the Old Mount North West Member is truncated at a high angle by diapiric breccia and is then overlain by allochthonous diapiric breccia. Although fold analysis is not possible for these areas, the true angle between the steep and shallow salt must be between the angle observed in the two-dimensional map view and 90°, regardless of whether the angle is acute or obtuse.

3.6 Allochthonous Salt Initiation and Advance We combine our observations from the various field areas in the Flinders and eastern Willouran Ranges into a general model for allochthonous salt emplacement in South Australia. We distinguish between the initiation and breakout of allochthonous salt from either primary or secondary feeders and the advance of salt sheets along ramp-flat trajectories. The model for initiation and breakout is based on common features at ten different examples of the transition from a steep salt-salt sediment interface to a gently-dipping base salt (Table 3.1), including one from the Loch Ness diapir in the northern Flinders Ranges that is not described in detail here. Positive dip values are outward dipping salt edges, whereas negative dip values are inwardly dipping base-of-salt surfaces. In four of the examples, the transition is abrupt. In the other six, however, minibasin strata extend over a shoulder of the diapir to form a roof that is truncated at a high angle just beneath the low-angle base salt. There appears to be no correlation

107 Table 3.1. Metrics compiled from map and stereonet analysis of diapirs and salt sheets in the northern Flinders Ranges and eastern Willouran Ranges, South Australia. Positive and negative numbers refer to outwardly dipping and flaring/overhanging salt, respectively; ∆ is the dip change; CHS is composite halokinetic sequence.

Diapir/ramp Breakout- Fault-sheet Emplacement Roof Roof Drape Diapir type Sheet/flat dip Dip change Roof Fold type Thickness (m) dip fault dip dip change Azimuth Thickness (m) Length (m) Folding Witchelina SE 34 - - - 90<Δ<123 - Yes 400 500 No Minibasin 1850 Witchelina NW Primary 64 -33 97 -73 140 190 Yes 480 730 Yes Megaflap 2700 Breaden Hill S - - - - 68<Δ<90 - Yes 170 1200 No - - Pinda 77 -13 90 -78 115 059 Yes 120 160 Yes Tabular CHS <200 Primary? Patawarta NW 83 -5 88 -51 134 284 Yes 100 730 Yes Tapered CHS 400 Willawalpa N - - 90<Δ<115 - - - No - - No - - Ram S -77 -22 125 ? - 030 Yes - - Yes Tabular CHS 40 Ram N Secondary - - 90<Δ<132 - - - No - - No - - Salt weld C - - - - 90<Δ<114 - No - - No - - Loch Ness 58 -2 60 - - 050 No - - No Tabular CHS 230 Patawarta SE -62 -20 138 -72 128 000 Yes 150 270 Yes Tapered CHS 850 Patawarta ESE Ramp-to-Flat - - 90 - - - No - - No - - Willawalpa S - - 90 - - - No - - No - -

108 between the presence or style of folding adjacent to the steep salt and the different breakout styles. The model for the advance of salt sheets is based on observations from three examples of ramp-to-flat transitions (Table 3.1) and two of flat-to-ramp transitions. Flats invariably have no underlying halokinetic folds, whereas ramps may have adjacent folds or strata that simply abut against the base of salt without any folding

3.6.1 Initiation and Breakout The record of the initiation and breakout of allochthonous salt is present at five primary diapirs and five secondary diapirs.A primary origin is evident in the eastern Willouran Ranges because the connections between the Witchelina and Breaden Hill diapirs and the autochthonous diapiric breccia level are exposed (Hearon et al., in review). There is less certainty about the direct connection of the Pinda and northwestern flank of the Patawarta diapir to the autochthonous Callanna Group, but given the size of the flanking minibasins and the large wavelength of Delamerian folds adjacent to these areas (i.e., Narrina basin), these diapirs are likely to be primary. The secondary diapirs include those within the complex canopy in the eastern Willouran Ranges (Willawalpa and Ram diapirs and Weld C of Figure 3.10) and the Loch Ness example. We offer several simple models for allochthonous salt initiation and breakout from steep diapirs. The first model, here termed salt-top breakout, attempts to explain two key features of the six diapirs with a bit of preserved roof beneath the salt sheet (Table 3.1): the sudden change from drape folding to truncation of the roof and the sudden change from steep salt rise to subhorizontal emplacement. This sudden change is delineated by high angle stratal cutoffs at the transition from steep diapirs to shallowly-dipping allochthonous salt, whereas more gradual transitions may have lower angle stratal cutoffs against a flaring diapir, as opposed to one that has steep flanks. We begin with a steep to flaring diapir that has an overlying roof, regardless of the presence or type of folding adjacent to the diapir (Figure 3.16, model 1). The salt then rises by piston-like uplift, breaking through the roof of the diapir, possible on a reactivated normal fault, some distance back from the edge of the salt. Because we observe no beds of slumped roof strata, we invoke ongoing erosion of the roof during uplift of the diapir. This continues until

109 1) salt sheet

diapir diapir diapir diapir

2a) salt sheet

diapir diapir diapir diapir

2b) salt sheet

diapir diapir diapir diapir

Figure 3.16. Models of the transition from steep diapirs to allochthonous salt, all of which involve piston-like breakthrough of roof strata and crestal erosion (see text). Model 1 illustrates salt-top breakout, where salt breakthrough occurs inboard of the salt flank, thereby preserving part of the roof beneath the sheet. Models 2a and 2b illustrate variations of salt-edge breakout, where salt breakthrough occurs at the edge of the diapir: Model 2a begins with a drape fold of the roof; Model 2b, the roof is already bounded by a fault.

110 the top salt is exposed at the sea floor, allowing salt to break out and flow laterally. The style of lateral emplacement could be via extrusive, open-toed or thrust advance, depending on the amount and location of any preserved roof above the salt. There are several ways to explain the four examples where there is a sharp transition from a steep diapir without any preserved roof to an overlying salt sheet (Table 3.1). First, it is possible that there was no roof in the first place due to the top of the diapir being subaerial.An increase in salt-rise rate could then result in lateral flow via extrusive advance.Alternatively , there may have been a roof that was removed by erosion. The second model we present, here termed salt-edge breakout (similar to double-flap active diapirism sensu Schultz-Ela et al., 1993), we again start with steep diapir with a drape fold and thin roof (Figure 3.16, model 2a), but in this case piston-like uplift of the diapir occurs at the edge of the salt, fully decapitating the halokinetic drape fold and lifting the entire roof. As in model 1, continued uplift and erosion leads to exposure of the top salt and subsequent lateral flow. A variation invokes no shift from drape folding to piston-like rise; instead, the roof is bounded by a fault for an extended period of salt rise and an increase in either rise rate or crestal erosion frees the salt to flow laterally (Figure 3.16 model 2b). Again, lateral salt emplacement could be via extrusive, open-toed or thrust advance. We have shown that some diapirs display preserved roof, where the boundary of piston-like rise is back from the salt edge, while other diapirs do not display preserved roof and allochthonous salt breakout occurs at the edge. There are several possible factors that may explain why salt-top or salt-edge breakout occurs. First, if the top of the diapir is arched and covered by a wedge of overburden, it may be easier to break through some distance back from the edge where the roof is thinner; in contrast, a flat-topped diapir may breakout at the edge. Second, the plan-view shape of the diapir may be irregular such that breakout may not follow the exact irregularities in the edge of salt, resulting in along-strike transitions from salt-top to salt- edge breakout. Third, the presence or absence of non-evaporite clasts, such as rocks composed of dolomite or volcanics, may influence where breakthrough of the roof occurs. Finally, although it might be possible that the dip of the diapir edge (narrowing vs. flaring upward) plays a role, we see no such relationship (Table 3.1). In the case of salt-top breakout (Figure 3.16, model 1), why is there a sudden change

111 from gradual salt inflation and drape-folding to fault-bounded, piston-like active diapirism?We observe no obvious correlation with lithology or apparent sediment accumulation rate because both types of breakout occur in the same stratigraphic units. Nor can we say anything about the thickness of the roof (which ranges from 100-480 m where it is preserved) since it has been removed in the case of salt-edge breakout. One possibility is a sudden increase in salt-rise rate regardless of the sediment accumulation rate (i.e., absolute strain rate). More rapid rise might lead to more brittle deformation of the roof and thus fault-bounded breakthrough of the roof. Sudden breakout of allochthonous salt occurs at specific stratigraphic levels: in the Old Mount North West Member in the eastern Willouran Ranges and in the Bunyeroo Formation at the Pinda and Patawarta diapirs. There was presumably a relatively high ratio of salt-rise rate versus sediment-accumulation rate during deposition of the Bunyeroo mudstones, which may have enabled allochthonous salt breakout at Pinda and Patawarta. In the eastern Willouran Ranges, however, there was breakout not during the deposition of the Camel Flat Shale Member but during the relative faster deposition of the Old Mount Northwest Member. Moreover, a phase of slow deposition explains neither the change from drape folding to piston-like rise nor the sudden transition from steep diapirs to salt sheets. One possibility is shortening-induced increases in salt-rise rates. An early phase of the Delamerian Orogeny (see Lemon, 1988) may have caused allochthonous salt breakout at Pinda and Patawarta, but there is no regional evidence for early tectonic shortening in the eastern Willouran Ranges. However, the occurrence of early gravity-driven deformation in the eastern Willouran Ranges cannot be discounted. Although allochthonous salt breakout was broadly correlative at the different field areas of the eastern Willouran Ranges and later at Pinda and Patawarta, the exact timing of initial lateral flow is not equivalent. Breakout occurred during early deposition of the Bunyeroo Formation at Patawarta but higher in the same unit at Pinda. In the eastern Willouran Ranges, breakout occurred immediately prior to and during early deposition of the Old Mount North West Member at Breaden Hill diapir, slightly higher in the same strata on the western flank of the Witchelina diapir, and during latest deposition of the unit on the eastern flank of Witchelina diapir and within the salt canopy. While we would expect synchronous piston-like uplift on both flanks of one diapir, for example the Witchelina diapir, exposure of the salt and consequent lateral flow may have been diachronous due to variations in roof thickness.

112 3.6.2 Advance Once allochthonous salt breaks out, how does subsequent lateral flow occur and what impact does it have on subjacent strata? Our model is based primarily on exposed relationships in South Australia but also is similar to and incorporates concepts originally published by Hudec and Jackson (2006, 2009). First, we do not observe subsalt basal shear zones, individual or imbricate thrust faults, or continuous or discontinuous rubble zones. Beneath base-salt flats or low-angle ramps (dips of up to approximately 30°), there is an absence of halokinetic folding and diapir-derived detritus. Where the base salt dips more steeply, two styles are present: 1) high-angle stratal truncations, also with no halokinetic folds or debris (e.g., Rawnsley Quartzite at Patawarta SE); and 2) composite halokinetic sequences with steep to overturned strata and local conglomerate beds with diapir-derived detritus (e.g., Bunyeroo and Wonoka formations at Patawarta SE). Our models, again building on those of Hudec and Jackson (2006, 2009), emphasize the interplay between salt-supply rate and sediment-accumulation rate. Salt-supply rate here is defined as the lateral supply of salt to the front of the advancing sheet, which may be driven by further rise of salt from underlying feeders, secondary minibasins atop the salt sheet expelling salt laterally, or gravitational failure of the canopy resulting in net basinward movement of salt and roof strata. Although the models (Figure 3.16) show the sheet always covered by a roof, extrusive and open-toed advance are also possible in the shallow-water depositional environment of the study area. We offer three models that vary depending on the ratio of salt-supply rate to sediment- accumulation rate (Rowan et al., 2010). First, when the ratio is high (Figure 3.17a), the sheet is emplaced via thrust advance, forming a base-salt flat or low-angle ramp depending on the exact ratio. The thrust emerges at the base of the seafloor scarp so that there is no halokinetic folding preserved beneath the salt and at most only minor inflation and slumping. Second, if the interplay between salt-supply rate and sediment-accumulation rate is more balanced (Figure 3.17b), thrust advance still occurs but at a steeper angle (45º if the ratio is equal to 1), forming a true ramp. Again, the thrust emerges at the base of the salt-induced scarp, resulting in no subsalt folding and at most minor inflation and slumping. Third, when the ratio is low (Figure 3.17c), the tip

113 c)

a) b)

Salt-supply rate >> Sediment accumulation rate Salt-supply rate ≈ Sediment accumulation rate Salt-supply rate << Sediment accumulation rate

Figure 3.17. Three models of allochthonous salt advance (from Rowan et al., 2010, based in part on Hudec and Jackson, 2006, 2009). The style of advance depends on the ratio between salt-supply rate and sediment-accumulation rate: (A) a high ratio leads to thrust advance, a base-salt flat and no halokinetic folding; (B) a balanced ratio also results in thrust advance but at a steeper angle, thereby forming a true ramp; and (C) a low ratio leads to pinned inflation and development of a halokinetic drape fold that progressively rotates the top salt and overlying strata into a base-salt configuration termed a mock ramp.

114 of the frontal thrust gets buried by sediment. Further salt supply leads to pinned inflation and development of a halokinetic drape fold, progressively rotating the top salt and onlapping roof strata into a base-salt configuration that we term a mock ramp. Slumping of roof and diapiric material is more common than in the other two scenarios. Typically, the salt will break out again, possibly on a salt-roof thrust (Hudec and Jackson, 2009) that cuts the drape fold or, in the case of Patawarta SE, piston-like rise on a steeper fault. The resulting geometry will depend on when and where during inflation and folding the salt breaks out on a new fault, yielding anything from a large mock ramp with a decapitated halokinetic fold (i.e., Patawarta SE; Figure 3.18a) to a zig- zag base of salt (Figure 3.18b, not actually observed in the study area). In all cases where there is a roof, the thrust fault extending from the tip of salt becomes the base salt, so that the ramp-flat base of salt represents an original thrust ramp-flat geometry (see also Hudec and Jackson, 2009). There is a discrete surface of advance at the very tip of the salt, but what occurs where the salt is thicker? Conceptually, there are three possibilities: 1) subsalt basal shear, in which some of the advance is accommodated by shear in underlying strata (Harrison and Patton, 1995; Harrison et al., 2004); 2) base-salt detachment, where slip on the frontal thrust continues as slip on the base salt; and 3) intrasalt basal shear, with a zone of concentrated shear near the base of the salt sheet. We see no field evidence supporting subsalt basal shear and a base-salt detachment is incompatible with viscous drag near the boundary of a salt layer unless the boundary is somehow lubricated. Therefore, we envision a transition near the front of an advancing salt sheet from a discrete detachment right at the tip of salt to a zone of intense shear within and near the base of the salt, as observed in fold-and-thrust belts detached on salt (e.g., Cross, 2012).

3.7 Discussion We have presented and evaluated multiple examples of the initiation and continued emplacement of allochthonous salt in the northern Flinders and eastern Willouran ranges of South Australia. However, the real value in our work lies in its applicability as a supplement to seismic and well data in subsurface salt basins. The field exposures provide information that is simply not resolvable with subsurface methods, thus the question then arises as to the suitability of the South Australian outcrops to understanding other areas and testing existing

115 a)

Figure 3.18. Two scenarios of further thrust advance after pinned inflation and halokinetic drape folding from Rowan et al. (2010): (A) mock ramp configuration with breakout on a salt-roof thrust decapitating the flanking halokinetic drape fold (see also Hudec and Jackson, 2009); and (B) breakout at an earlier stage of inflation and halokinetic folding creates a zig-zag base-salt geometry.

116 models. In order to assess this, we examine below the similarities and differences between South Australia and the northern Gulf of Mexico (GoM), where many of the concepts and models for allochthonous salt were developed. The northern GoM contains stratal and structural geometries associated with diapirs and allochthonous salt that are analogous to specific outcrop examples in the northern Flinders Ranges and eastern Willouran Ranges. For example, the abrupt transition from steep diapirs to salt sheets, whether via salt-edge or salt-top breakout, is also apparent in the northern GoM (Figures 3.19 and 3.20). In the examples shown here, the abrupt breakout is probably due to a pulse of shortening, and thus increased salt-rise rates, during gravity spreading in the Miocene (e.g., Peel et al., 1995; Mount et al., 2007). Regardless of the cause of abrupt breakout, the various patterns we observe in the northern Flinders and eastern Willouran ranges suggest that it is impossible to predict stratal geometries beneath the transitions since the presence and type of folding does not appear to be relevant. There are also similarities between the northern GoM and the northern Flinders and eastern Willouran ranges in the geometries associated with allochthonous salt advance. True ramps with no halokinetic folding are difficult to image with confidence on seismic data. For example, strata just beneath the very shallow tongue in Figure 3.19 appear to truncate at a true ramp, but subtle irregularities in the salt-sediment interface may represent cusps associated with local hook halokinetic folds that are below seismic resolution. Having said that, wells in the northern GoM have exited the salt into undeformed strata, showing that true ramps exist (e.g., Kilby et al., 2008). In addition, seismic data do illustrate mock ramps, where the ramp represents the rotated top salt (Figure 3.21), as well as zip-zag base-salt geometries (J. Western, 2009, pers. comm.) The relative proportions of true and mock ramps are unknown. One style that we do not observe in South Australia but that is fairly common in the northern GoM is the gradual flaring, rather than abrupt transition, of a steep diapir into a low- angle salt sheet (Figure 3.22). This might be expected in the absence of a sudden pulse of more rapid salt rise, for example if there is a gradual increase in differential load over time, thereby increasing the pressure on salt and consequently the rate of salt rise. This geometry also suggests that the roof was never breached so that there was no abrupt onset of lateral flow of salt with or without its roof.

117 supra-salt minibasin

salt sheet

salt diapir

primary minibasin

autochthonous salt

Explanation

Salt weld 3 km Salt contact

Figure 3.19. Wide-azimuth, prestack depth-migrated 3-D seismic profile from the northern Gulf of Mexico showing a steep primary diapir that transitions abruptly to a low-angle allochthonous salt sheet without any apparent flanking halokinetic folding (salt-edge breakout). No vertical exaggeration. Data courtesy of WesternGeco.

118 supra-salt minibasin

salt sheet

primary minibasin salt diapir

Explanation autochthonous salt Salt weld 3 km Salt contact

Figure 3.20. Wide-azimuth, prestack depth-migrated 3-D seismic profile from the northern Gulf of Mexico showing a steep diapir that transitions upward to a low-angle allochthonous salt sheet, but with a short segment of roof preserved above a shoulder in the edge of salt (salt-top breakout). No vertical exaggeration. Data courtesy of WesternGeco.

119 imbricate thrusts

4 3 cusp Tabular CHS

2 Tapered CHS salt sheet

No halokinetic deformation 1 km

1 km

Figure 3.21. Wide-azimuth, prestack depth-migrated 3-D seismic profile from the northern Gulf of Mexico showing a salt sheet with: (1) a base-salt flat with no apparent underlying folding; (2) a mock ramp flanked by a tapered composite halokinetic sequence (CHS); (3) a true ramp flanked by a tabular CHS; and (4) an upper base-salt flat with frontal imbricate thrust faults. No vertical exaggeration. Data courtesy of CGG.

120 supra-salt minibasin

salt sheet

primary minibasin salt diapir

autochthonous salt Explanation

Salt weld 3 km Salt contact

Figure 3.22. Wide-azimuth, prestack depth-migrated 3-D seismic profile from the northern Gulf of Mexico showing a steep, primary salt diapir that gradually flares as it transitions upward into a shallowly-dipping allochthonous salt sheet. No vertical exaggeration. Data courtesy of WesternGeco.

121 There are two key differences between allochthonous salt features in South Australia and the northern GoM: 1) subsalt thrust faults are absent in South Australia but sometimes observed in the GoM (Jackson and Hudec, 2004; Alexander, 2004; Hudec and Jackson, 2006, 2009); and 2) slumped carapace preserved beneath salt sheets appears to be much more common in the northern GoM (Kilby et al., 2008). Therefore, below, we examine some of the primary known differences between the two areas in an attempt to further understand salt-sediment interaction in allochthonous salt tectonics. First, while the Callanna Group breccia was originally a layered evaporite sequence comprising various evaporites interbedded with siliciclastic, carbonate and igneous rocks, the Jurassic Louann salt of the Gulf of Mexico is estimated to be nearly pure halite (Hazzard et al., 1947; Salvador, 1987). Similarly, the Aptian layered evaporite sequence of offshore Brazil contains little to no non-evaporite lithologies but contains mostly halite with varying amounts of anhydrite, carnallite and other evaporite minerals (e.g., Karner et al., 2000; Meisling et al., 2001; Gamboa et al., 2008; Fiduk and Rowan, 2012). Despite these differences in composition, the Callanna Group appears to have mobilized in a similar fashion to the GoM and South Atlantic evaporites. However, the nature of the Callanna Group breccia and the similarity of its clasts to minibasin lithologies in terms of composition may explain in part the apparent absence of slumped material (‘rubble zone’). If the South Australian salt sheets had little to no roof due to shallow water or even subaerial exposure (see below), slumping or spalling of the front of the sheet may have produced rubble that is indistinguishable from the Callanna Group breccia itself. Second, the depositional environments of the GoM and South Australia were different. Salt sheets in the northern GoM were generally emplaced in a deepwater environment, where there is typically a hemipelagic carapace developed atop allochthonous salt. Not only is the roof perched above the salt at the frontal scarp, it also protects the salt from dissolution (Fletcher et al., 1995). In South Australia, because the depositional environment was predominantly shelfal to periodically subaerial, salt diapirs and sheets may have developed only a thin roof or even no roof at times, and subaerial dissolution may have decreased topographic relief. Third, allochthonous salt sheets and canopies in the northern GoM are extensive and widespread, covering tens of thousands of square kilometers and commonly serving as shallow detachments for gravity spreading, with often significant amounts of shortening at their toes

122 (e.g., Diegel et al., 1995; Peel et al., 1995; Rowan et al., 2012). In contrast, allochthonous diapiric breccia in the Flinders Ranges was almost certainly more localized. Allochthonous salt has limited map-view extent, most minibasins form long-wavelength, broad synclines suggesting they are deep primary minibasins, and there are no normal faults or growth strata compatible with gravitational failure. The outcrop relationships suggest that allochthonous salt primarily formed localized salt tongues or small canopies. One could argue that the differences between South Australia and the northern GoM cited above mean that there are distinct processes of allochthonous salt breakout and advance in the two areas. Again, however, there are apparently similar geometries and relationships; the principal differences are the increased presence of rubble zones and imbricate thrusts in the northern GoM. We ascribe these primarily to the amount of topographic relief at the frontal scarps. The deepwater environment and thus increased amount of hemipelagic roof, the lack of dissolution, and the basinward transport of overburden all tend to increase the relief and consequently the likelihood of mass transport complexes, frontal thrust imbricates and thrust advance in the GoM. Therefore, we suggest that the common rubble zones in the northern GoM represent not subsalt basal shear but slumped carapace as originally proposed by McGuinness and Hossack (1993) and interpreted from well data by Kilby et al. (2008). In contrast, in the northern Flinders and eastern Willouran ranges, lower topographic relief caused by dissolution, thin roof or no roof at all, more common erosion, smaller canopies and basinward transport of overlying roof all serve to diminish the likelihood of slumping and increase the probability of intermittent extrusive or open-toed advance.

3.8 Conclusions Outcrops at the Pinda and Patawarta diapirs and the eastern Willouran Ranges, South Australia, which contain some of the world’s oldest records of salt diapirs and allochthonous salt, provide a unique opportunity to study a salt system that evolved over a period of at least 250 Ma. The two-dimensional views of complex three-dimensional allochthonous salt bodies and associated stratal geometries yield important insights into the initiation, breakout and advance of allochthonous salt. Using ten examples of the transition from steep diapirs to salt sheets, three examples of ramp-to-flat geometries and two examples of flat-to-ramp geometries, we have

123 demonstrated and suggested the following: • Thrust faults, shear zones or rubble zones do not exist beneath allochthonous salt in South Australia. • There is no correlation between the presence or style of halokinetic folding adjacent to steep diapirs or beneath salt sheets and the processes of allochthonous salt breakout and advance. • The initiation of allochthonous salt spreading from a steep diapir is abrupt and is caused by piston-like breakthrough of the diapir roof, freeing the salt to flow laterally via open-toed, extrusive or thrust advance depending on roof presence and thickness. • In salt-top breakout, the salt breaks through its roof on a fault some distance inboard of the diapir margin, preserving part of the roof beneath the salt sheet. • In salt-edge breakout, the roof is fully decapitated as piston-like rise occurs at the edge of the steep diapir. • The style and geometry of allochthonous salt advance is dependent on the interplay between salt-supply rate to the front of the sheet and sediment-accumulation rate. • High and moderate ratios of salt-supply rate and sediment-accumulation rate generate base-salt flats and true ramps, respectively, with little development of slumped carapace. • A lower ratio results in pinned inflation, halokinetic folding and periodic slumping of the roof, and further breakout on a salt-roof thrust or a steeper fault. • The geometries and processes of allochthonous salt initiation and advance are similar in South Australia and the northern Gulf of Mexico. • The more common presence of subsalt rubble zones and imbricate thrusts in the deepwater environments of the northern Gulf of Mexico is attributed to greater relief at frontal scarps due to thicker hemipelagic roofs, a lack of significant dissolution, and more extensive canopies and consequent gravity spreading of the overburden.

Despite some differences between the northern Gulf of Mexico and South Australia, observations and models derived from two-dimensional outcrops of diapirs and allochthonous salt in the northern Flinders and eastern Willouran ranges are helpful in understanding and

124 exploring the northern Gulf of Mexico and other basins with allochthonous salt. The stratal and structural relationships exposed in South Australia, which are at a scale often below seismic resolution, have implications for building salt models in seismic imaging, drilling out of allochthonous salt, and exploring and developing three-way closures against salt sheets and the upper portions of their feeder diapirs.

3.9 Acknowledgments We thank former Witchelina Station owner, Kandy Saler, Alex Nankivell of the Nature Foundation, SA, and George and Anne Morphett for access to the eastern Willouran Ranges; Steve and Brenda Coulter, Tony and Lisa Nicholls, Ian Johnson and the Nepabunna Community Council for access to the Pinda diapir; and Ian and Di Fargher and Keith and Lisa Slade for access to the Patawarta diapir. Mark Pickard generously provided use of a helicopter and flight time to acquire oblique aerial photos at the Pinda and Patawarta diapirs. We thank CGG and WesternGeco for the use of seismic data from the northern Gulf of Mexico. Lively technical discussions were had with Patrick Geesaman, Tyler Hannah, Wolfgang Preiss and Bruce Trudgill. Aubrey Collie assisted with fieldwork. TH would like to thank Rick Almendinger for use of Stereonet 7 and Midland Valley for the use of 2DMove. This project could not have been completed without the generosity of the Institute of Tectonic Studies’ Salt-Sediment Industry Research Consortium (SSIRC) (present and past members, including: Anadarko, BHP- Billiton, BP, Chevron, Cobalt, ConocoPhillips, Devon, ENI, ExxonMobil, Hess, Marathon, Maxus (Repsol-YPF), Nexen, Samson, Shell, Statoil and Total) originally at New Mexico State University and currently at the University of Texas-El Paso and financial awards from the following funds: AAPG Grants-in-Aid, GSA Student Research Grants, GCSSEPM Ed Picou Fellowship, GCAGS Student Grants

3.10 References Cited Alexander, R. J., T. W. Bjerstedt, and S. L. Moate, 2005, Edge-Sigsbee folds, Gulf of Mexico, U.S.A., in J. H. Shaw, C. Connors, and J. Suppe, eds., Seismic Interpretation of Contractional Fault-Related Folds: AAPG Studies in Geology, v. 53, p. 2.20-2.21.

125 Backé, G., G. Baines, D. Giles, D., W. Preiss, and A. Alesci, 2010, Basin geometry and salt diapirs in the Flinders Ranges, South Australia: Insights gained from geologically constrained modelling of potential field data: Marine and Petroleum Geology, v. 27, p. 650-665.

Belperio, A. P., 1986, Stratigraphy and sedimentology of the Precambrian Skillogalee Dolomite, Northern Flinders Ranges: Geological Survey of South Australia Eighth Australia Geological Convention, 15:29.

Belperio, A. P., 1990, Palaeoenvironmental interpretations of the Late Proterozoic Skillogalee Dolomite in the Willouran Ranges, South Australia, in J. B. Jago, and P. S. Moore, eds., The Evolution of a Late Precambrian-Early Paleozoic Rift Complex: The Adelaide Geosyncline, Geological Society of South Australia Special Publication, v. 16,, 85-104.

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133 CHAPTER 4 TESTING THE APPLICABILITY OF AN OUTCROP-BASED HALOKINETIC DEFORMATION MODEL IN A DEEPWATER DEPOSITIONAL SETTING: AUGER DIAPIR, GARDEN BANKS 427, NORTHERN GULF OF MEXICO

A paper to be submitted to Interpretation

Thomas E. Hearon, IV, Mark G. Rowan, Katherine A. Giles, William H. Hart

4.1 Abstract Halokinetic sequences (HS) are localized (<1000 m) (3300 ft) unconformity-bound successions of growth strata adjacent to salt diapirs that form as drape folds due to the interplay between salt rise rate (R) and sediment accumulation rate (A). Hook and wedge HS stack vertically to form tabular and tapered composite halokinetic sequences (CHS), respectively. Tabular CHS have a narrow zone of stratal upturn (50-200 m) (160-500 ft), whereas tapered CHS have a broad zone of stratal upturn and thinning (300-1000 m) (1000-3300 ft). Tabular and tapered CHS form under relatively high and low ratios, respectively, of R and A. CHS boundaries, which form during times of maximum topographic relief, have tentatively been linked to third-order transgressive systems tracts in shelf depositional settings as the concepts of CHS formation are derived from outcrops in shallow water to subaerial depositional environments in La Popa Basin, Mexico and the Flinders Ranges, South Australia. These concepts have yet to be fully applied or tested in a deepwater setting. Three dimensional wide-azimuth seismic data, well and biostratigraphic data and structural restorations were combined to document a vertical succession of ten well-imaged CHS adjacent to the Auger diapir in the deepwater northern Gulf of Mexico. We observe variations in CHS geometry with depth and around the diapir flanks. For example, where the northwestern (updip) flank is dominated by tapered CHS, the southeastern flank contains a nearly equal proportion of tabular and tapered CHS. As suggested by the HS model, tabular and tapered

134 CHS stack vertically into four different geometric configurations. Tabular CHS have narrow zones of stratal upturn and thinning (<100 m) (<300 ft), whereas tapered CHS have wider zones (240-1260 m) (780-4000 ft). Rates of sediment accumulation for tabular CHS (2.0-4.6 m/ kyr) (6-15 ft/kyr) are generally lower than those for tapered CHS (1.5-19 m/kyr) (5-64 ft/kyr). CHS depositional intervals appear to occur on the fourth-order depositional cycle (130kyr to 940kyr), instead of third-order cycles, with CHS boundaries generally corresponding to sequence boundaries, when topographic relief is greatest. Halokinetic unconformities around Auger are more subtle than field analogs would suggest. Our findings generally corroborate established halokinetic sequence criteria, showing that some concepts learned from outcrops of diapirs in shelfal to subaerial depositional environments apply to deepwater settings. The results are critical to understanding and predicting combined structural-stratigraphic trap geometry, reservoir prediction and hydrocarbon containment in diapir-flank settings.

4.2 Introduction Elements of salt-sediment interaction have broad implications for the understanding of inherently complex structural and stratigraphic relationships present in passive margin and rift basin settings. In petroleum basins such as the Gulf of Mexico, sedimentary depocenters and reservoir distribution can be influenced by topographic relief created by passive salt diapirs and allochthonous salt sheets. Stratigraphic growth geometries flanking passive salt diapirs and allochthonous salt sheets control reservoir geometry and trap configuration and influence hydrocarbon development, migration and seal. In diapir-flank settings, where hydrocarbons are often trapped, an understanding of growth strata development and deformation may yield further insight into controls on gross depositional environments, reservoir proximity to salt faces and stratal upwarps against salt faces. Typically, localized growth strata adjacent to salt bodies are often difficult to image, even with the most current seismic acquisition techniques and surprising well results, such as steeper stratal dips, unexpected older stratal intersections, the presence of debris flows and the absence of sand bodies, reinforce the need for integrated outcrop and seismic studies of salt-sediment interaction (e.g., Swanston et al., 2011) (Figure 4.1). Halokinetic growth sequences are localized (<1 km), “unconformity-bound successions

135 A) B)

1000 m 1000 m

Figure 4.1. Surprising drilling results at the Tahiti field: (A) WEM seismic image; and (B) RTM seismic image; both indicating the well path of Well 1 and the post-drill interpretation of converging bedding towards the adjacent salt body (modified from Swanston et al., 2011). Republished with permission from the Society of Exploration Geophysicists.

136 of genetically related growth strata influenced by near-surface diapiric or extrusive salt rise” that become conformable away from salt bodies (Giles and Lawton, 2002). Giles and Rowan (2012) characterized two geometric end-member types of halokinetic sequences (HS), which stack vertically to form composite halokinetic sequences (CHS). Hook HS and wedge HS stack to form tabular CHS and tapered CHS, respectively (Figure 4.2). CHS are generally present adjacent to steep to vertical, often mature diapirs and ramping allochthonous salt and may stack vertically to form a variety of distinct geometric configurations (Figure 4.3). Conceptual sequence stratigraphic models for the formation of CHS were developed based on the relative rates of diapir rise (R) and sediment accumulation (A). When diapir rise rate exceeds sediment accumulation rate (R>A), tabular CHS form, whereas tapered CHS form when sediment accumulation rate exceeds diapir rise rate (R1 km) (e.g., Riba, 1976; Prather et al., 1998). While the former is caused by the interaction between a subsiding basin and an advancing thrust sheet and the latter is caused by evacuation of deeper salt, neither of these are attributed to local interactions with vertically rising bodies of salt that form halokinetic sequences. Concepts that explain the formation of halokinetic growth sequences adjacent to salt

137 (a) Zone of stacked (b) Zone of stacked monoclinal axial traces monoclinal axial traces

ook SHH egdeW SH Diapir Diapir Hook HS Wedge HS

Hook HS Wedge HS Tabular CHS Hook HS Wedge HS Tapered CHS

m002-05 m0001-003

Figure 4.2. Hook (a) and wedge (b) end-member halokinetic sequence types (HS) stack vertically to form tabular (a) and tapered (b) end-member composite halokinetic sequence (CHS) types (modified from Giles and Rowan, 2012). See text for description and geometric classification of each end-member CHS.

138 a) b)

Tabular-CHS Tabular-CHS diapir diapir

Tabular-CHS

Tapered-CHS

c) d)

Pronounced Tapered-CHS Pronounced Tapered-CHS cusp cusp diapir diapir

Tabular-CHS Tapered-CHS

Figure 4.3. Different geometric stacking patterns of composite halokinetic sequences (CHS): (A) tabular CHS over tabular CHS; (B) tabular CHS over tapered CHS; (C) tapered CHS over tapered CHS; and (D) tapered CHS over tabular CHS (Giles and Rowan, 2012).

139 diapirs are mostly derived from outcrops of shallow water, fluvial and subaerial depositional environments. Outcrop studies in La Popa Basin, northern Mexico established the theory of halokinetic deformation adjacent to steep salt diapirs (Giles and Lawton, 2002; Rowan et al., 2003; Giles and Rowan, 2012) and continued field studies in the Flinders Ranges, South Australia have documented halokinetic growth strata associated with steep to vertical diapirs and ramping allochthonous salt. Salt-dominated hydrocarbon provinces such as the Pricaspian Basin and the North Sea contain diapirs and depositional settings analogous to La Popa Basin and the Flinders Ranges and are directly applicable to the model for halokinetic sequence formation. However, the only documented field example of deepwater strata adjacent to a salt diapir is that of Rowan et al. (2012), which described CHS from outcrop exposures at the Bakio diapir in the Basque Pyrenees, northern Spain and further corroborated the CHS model. Composite halokinetic sequences have tentatively been linked to third-order depositional sequence cycles (several 100kyr to several Ma) in shelf depositional settings from the aforementioned areas (e.g., Giles and Rowan, 2012; Kernen et al., 2012), however the lack of detailed biostratigraphic data makes such correlations uncertain. In all of the field examples used to define halokinetic sequences, limited outcrop exposure, two-dimensional map view and inadequate age constraints have reinforced the need to test these concepts in a deepwater settings, such as the northern Gulf of Mexico hydrocarbon province, where biostratigraphic and well data are abundant and three-dimensional seismic data allow analysis of the full development of CHS around an evolving, mature salt structure. Diapir-proximal halokinetic sequences have undoubtedly been recognized and documented in unpublished studies throughout the northern Gulf of Mexico and other offshore salt-dominated basins by numerous previous investigators (e.g., Ermine Dome, Gulf of Mexico shelf). While we expect similar halokinetic geometries to form under similar rates of sediment accumulation and salt-rise in deepwater environments and to form independent of depositional setting, there is a need for outcrop-based halokinetic deformation concepts to be fully tested in this setting using high resolution three-dimensional seismic data combined with well and biostratigraphic data. Limited publicly available knowledge about the linkage between halokinetic sequences present in outcrop and in the subsurface also further supports the need to test this model. One of the many benefits of examining a deepwater diapir is that abundant

140 biostratigraphic well data will allow the correlation to be tested and constrained, thereby extending the usefulness of sequence-stratigraphic theories. To that end, this paper is one of the first attempts to link field-based halokinetic deformation concepts to subsurface data in a salt-dominated deepwater basin. In order to test whether these concepts are appropriate in a deepwater setting, we examined the Auger diapir, located in the northern Gulf of Mexico, which is a relatively straight-sided, mostly vertical diapir that lends itself to excellent subsurface seismic imaging. Unlike field outcrops, strata flanking Auger are not limited to a two-dimensional study, rather a three-dimensional is possible, where a vertical succession of well-imaged CHS is present around the diapir flanks. Utilizing a combination of high-resolution three-dimensional wide azimuth depth-migrated seismic data, well and biostratigraphic data, along with structural restorations, we suggest a methodology for characterizing CHS in the subsurface that will ultimately help define the extent of reservoirs in salt-flank settings. We conclude a number of key findings from this study, many of which corroborate the concepts of halokinetic deformation derived from outcrop studies in La Popa Basin, Mexico (e.g., Giles and Lawton, 2002; Giles and Rowan, 2012) and in the Flinders Ranges (e.g., Kernen et al., 2012; Hearon et al., in review B): 1) similar CHS end-member geometries and vertical stacking patterns of CHS observed in outcrop are present in Pliocene-Pleistocene-aged strata in three-dimensions around the Auger diapir flanks; 2) thinning and stratal upturn of CHS are within 1 km of the diapir contact; 3) sediment accumulation rates, determined from well and biostratigraphic data in the Auger area, generally coincide with specific end-member CHS geometries; 4) individual CHS may morph in geometry around the diapir flanks, from tabular to tapered and vice versa, between updip to downdip domains; 5) CHS intervals occur on 4th order depositional sequence cycles instead of 3rd order depositional sequence cycles; 6) older CHS are sequentially deformed by overlying CHS through bedding parallel slip such that deeper CHS exhibit higher fold elevations (i.e., steeper stratal upturn) than younger ones; and 7) present day structural upturn of halokinetic sequences is due to a combination of both depositional thinning and mechanical deformation.

141 4.3 Geologic Setting The Gulf of Mexico is a Triassic-Early Cretaceous rift basin formed during spreading and counterclockwise rotation of the Yucatan microplate and the North American plate (e.g., Pindell and Dewey, 1982; Hudec et al., 2013b). Initial deposition of the Middle Jurassic Louann Salt, which is estimated to nearly pure halite, occurred on transitional crust in a single broad basin that eventually split into two during further widening of the gulf (e.g., Hazzard et al., 1947; Humphris, 1978; Salvador, 1987; Galloway, 2009; Pindell and Kennen, 200l; Hudec et al., 2013a). The debate regarding the exact timing of rifting with relationship to early salt deposition and evolution is still ongoing (e.g., Buffler, 1989; Salvador, 1991; Peel et al., 1995; Hudec et al., 2013a, 2013b). In the northern Gulf of Mexico, thick evaporites of the Louann Salt were mobilized into a complex array of salt diapirs and multi-level sheets, canopies and salt welds during progressive loading by Mesozoic to Cenozoic sedimentary fill in a network of primary and secondary minibasins. The Auger diapir is located 350 km (200 mi) southwest of New Orleans, Louisiana, in the northeastern quadrant of the Garden Banks protraction area (GB 427), on the upper slope of the northern Gulf of Mexico in 600 m (2000 ft) of water (Figure 4.4). The mostly vertical secondary diapir has a diameter of 2 km (1.2 mi) and is located at the northwestern end of a northwest-southeast trending allochthonous salt ridge (East Auger Ridge) that partially separates the Andros and Auger minibasins (Figure 4.5). Near-surface Louann Salt that composes the Auger diapir produces bathymetric relief at the seafloor and extends vertically into the subsurface approximately 6 km (20000 ft). While the diapir is mostly vertical, it leans slightly to the south and exhibits a minor amount of flaring in the uppermost 1 km (3300 ft).The Auger and Andros minibasins are deep, young salt withdrawal basins, which accommodated Upper Miocene, Pliocene and Pleistocene strata during downbuilding into tabular, allochthonous salt bodies that presently bound the minibasins on all sides (Figure 4.5) (Booth et al., 2000). Stratigraphic intervals present along the diapir flanks display greater thickness variations near the diapir base, but become progressively similar with shallower depths. A deep, upturned 5 km (3 mi) long subparallel succession of strata is present on the southwestern side of the diapir and comprises the base of the Auger minibasin (A of Figure 4.6), which is onlapped by younger, large-scale (>1000 m) (>3300 ft) growth wedges that become

142 New Orleans Houston

Shelf

study area

Slope

Sigsbee Escarpment Alaminos Keathley Canyon Canyon Bryant 100 km Canyon

Figure 4.4. Multibeam bathymetry image of the northern Gulf of Mexico continental shelf and slope. White box indicates the location of the Auger diapir. Image courtesy of the National Ocean and Atmospheric Administration (NOAA).

143 4.7 &

Figures 4.6

allochthonous salt Habanero

t al s s u o Llano n o Auger th Andros h diapir c o Basin ll a

basin Auger Cardamom

East Auger Serrano Ridge

allochthonous Auger salt Basin Extent of data Oregano Commercial N discovery Platform

Macaroni 5 mi / 8 km

Figure 4.5. Subregional schematic cartoon top salt map of the Auger area, which shows the Auger diapir positioned between the Auger and Andros minibasins. Warmer colors are shallower depths, whereas colder colors are deeper depths.

144 diapir

Figure 4.8

megaflap A 2 km

allochthonous canopy 2 km

Figure 4.6. Interpreted wide-azimuth, prestack depth-migrated 3-D seismic profile of theAuger diapir and flanking downdip Auger (left) and updip Andros (right) minibasins (modified from Giles and Rowan, 2012). Three stratal successions are interpreted: (A) megaflap; (B) minibasin-scale thinning; and (C) conformable minibasin strata that display thinning and upturn within 1 km (3300 ft) of the Auger diapir. Red dashed box indicates the approximate location of Figure 4.8.

145 conformable towards the basin center, as described in detail by Prather et al. (1998) (B of Figure 4.6). Based on scale, uniform thickness and onlapping younger strata, Giles and Rowan (2012) defined this large-scale basal stratal interval as a megaflap (i.e., carapace of Hart et al., 2004). The megaflap is strongly upturned against the diapir flank and exhibits no demonstrable lateral thickness changes towards its crest, where it is truncated by an arcuate low-angle, north-dipping normal fault, at approximately 5.5 km (18000 ft). This depth is where the Auger diapir transitions from the allochthonous salt ridge into a mostly circular and vertical diapir. Above this depth, younger strata are generally conformable in the center of the Auger and Andros minibasins, but thin and upturn within 1 km (3300 ft) of the diapir flanks (C of Figure 4.6 and Figure 4.7).Two shallower arcuate-shaped, steeply dipping normal faults, which trend approximately NW-SE and dip towards the ENE, occur above the salt ridge, intersect the southern diapir flank and offset younger strata above the 5 km (3 mi) long megaflap. Middle Pliocene paleogeography for the Auger diapir has been suggested as approximately 100 km (60 mi) downdip of the paleo-shelf edge (e.g., Booth et al., 2003). Biostratigraphic information from the adjacent Green Canyon area, to the east of Auger, suggest paleowater depths during the Late Pliocene to Late Pleistocene (2.4-0.7 Ma) to be mostly lower bathyal (1300-1800 m) (4200-6000’) (Weimer et al., 1998). Such water depths are indicative of the depositional environments active during deposition of diapir-flanking strata at Auger. Eight high frequency, glacio-eustatic sea level cycles have been documented during the Pliocene to Pleistocene (5.2 Ma to present) and record water depth fluctuations on the order of approximately 50-100 m (160-300 ft) (Pulham, 1993; Prather et al., 1998). Facies assemblages in the Auger area vary between ponded to bypass (e.g., Prather et al., 1998; Winker and Booth, 2000), however the majority of strata examined in this study are within the bypass facies assemblage. Ponded strata generally refer to basin floor and slope submarine-fan complexes with higher sand content, whereas bypass strata refer to muddy turbidites and overbank deposits consisting of mudstones with subordinate interbedded sand (Prather et al., 1998). A number of productive oil fields surrounding the Auger diapir, including Auger, Cardamom, Macaroni, Serrano and Oregano, tie back to the Auger platform, which has been under sole operation by Shell since 1994 (McGee et al., 1994). These fields produce from a series of stacked Pliocene-Pleistocene turbidite reservoirs (e.g., Booth et al., 2000; Booth et al.,

146 (a)(a) (b)

Tapered Tapered Tabular

Tabular Tabular?

Tapered

Tapered? 1 km Tapered

1 km

Figure 4.7. Wide-azimuth, prestack depth-migrated 3-D seismic profiles of the Auger diapir and flanking Auger minibasin: (a) uninterpreted and (b) interpreted (modified from Giles and Rowan, 2012).Variably folded, stacked tapered and tabular CHS separated by unconformities (red) are present along the flanks of the diapir, which create a rugose edge-of-salt. Vertical exaggeration is 1.5:1.

147 2003) present along the allochthonous salt ridge in the intermediate stratal succession between the megaflap and younger conformable minibasin strata that thin and upturn within 1 km of the Auger diapir (B and C of Figure 4.6). For the purposes of this manuscript, the uppermost stratal succession above the megaflap and onlapping minibasin-scale growth wedges (seafloor to 5500 m) (seafloor to 18000’) was chosen as the primary zone of interest to test the outcrop halokinetic sequence model (Figures 4.6 and 4.7) (sensu Giles and Lawton, 2002; Giles and Rowan, 2012) based on the following criteria: (1) minimal overhanging salt yields high seismic resolution of diapir-flanking growth strata geometries; (2) abundant, publicly-available biostratigraphic information yields interval sediment accumulation rates and depositional time scales; and (3) previous research on stratigraphic architecture, depositional cycles has provided insight into the integration of sequence stratigraphic concepts with the formation and deformation of deepwater diapir-flanking growth strata (e.g., Prather et al., 1998; Booth et al., 2003).

4.4 Methodology Using concepts derived from the halokinetic sequence model (sensu Giles and Lawton, 2002; Giles and Rowan, 2012), ten unconformities that separate upturned diapir-flanking stratigraphic intervals were interpreted on a 350 km2 (225 mi2) three dimensional wide-azimuth (WAZ) depth-migrated seismic data volume. These unconformities, which separate and delineate individual composite halokinetic sequences (CHS), generally appear as bright pairs of continuous amplitudes and represent condensed hemipelagic mud deposited between third- order low-stand systems tracts (Figure 4.8) (e.g., Prather et al., 1998; Weimer et al., 1998; Giles and Rowan, 2012). Gamma-ray wireline data and ages of benthic foraminifera and calcareous nannoplankton biostratigraphy from the GB-471 well (API#: 608074004500), located 3.5 km (2 mi) south-southwest of Auger, were calibrated with interpreted unconformities to determine the age and rate of sedimentation for each unconformity-bound CHS interval and to correlate unconformities with depositional sequences. A three dimensional geobody of the Auger diapir was created by interpreting multi-z horizons of the diapir margin to gain spatial understanding and resolution of diapir flank irregularities (e.g., cusps and stratal upturn), as the resolution of the original velocity model was insufficient for creating a detailed geobody.

148 condensed section diapir minibasin diapir margin condensed section

thinned strata

cusp angular truncation thinned conformable strata strata

Figure 4.8. Detailed wide-azimuth, prestack depth-migrated 3-D seismic profile of the NE flank of theAuger diapir displaying CHS, cusps separating CHS and condensed sections present at CHS boundaries. From the diapir margin to the right side of the image is 2 km. Data provided courtesy of CGG.

149 A)

pin seafloor

width of apparent taper diapir 630 m

26°

425 m original CHS 41°

inflection point

diapir 650 m decompacted CHS 500 m

500 m

C) width of depositional taper 313 m pin 56° restored 650 m restored CHS taper angle

inflection point

diapir 500 m

500 m

Figure 4.9. Example of three-step method for two-dimensional restoration of CHS: (A) Present- day, deformed state of tapered CHS showing the apparent width of taper; (B) decompacted tapered CHS; (C) restored tapered CHS showing width of depositional taper and restored taper angle. In this example, folding is expected 630 m from the diapir edge, but thinning does not actually start until 300 m from the flank. Data provided courtesy of CGG.

150 Because the present-day geometry of CHS around Auger has been modified by erosion and slip along bedding planes and bounding unconformities during downbuilding, the original geometry of individual CHS is obscured. Simple seismic flattening of unconformity-bound intervals is not a proper restoration tool, so each CHS present on the well-imaged north and south flanks of the diapir was decompacted and structurally restored using flexural slip in order to obtain the closest pre-deformation, pre-erosion geometry (Figure 4.9). This process allowed us to differentiate the deformed, present-day geometry of CHS from original depositional geometry and to establish the following key metrics: (1) original depositional taper angle; (2) width of thinning; and (3) interval thickness. Vertical decompaction of CHS intervals was carried out using the decompaction algorithm in 2DMove, which is based on Sclater and Christie (1980) and follows that exponential decay of porosity (Φ) that occurs with increasing depth (c-factor) for system composed of equal sand and shale. C-factor referes to the rate of change in porosity with depth (Sclater and Christie, 1980). Original depositional taper angle and width of thinning were measured from the inflection point where taper and thinning begins and interval thickness was measured between the top and bottom of each CHS. Once these metrics were established, we attributed each stratigraphic interval to a CHS geometric classification as suggested by Giles and Rowan (2012). By differentiating present-day geometry from original depositional geometry, we suggest applying this methodology of characterizing geometric aspects of CHS on high- resolution seismic data where zones of stratal convergence are well imaged adjacent to salt faces.

4.5 Description and Analysis In the following two sub-sections, we describe and analyze ten stratigraphic intervals on the northeast and southwest flanks of theAuger diapir. Around the flanks of the diapir, the present day geometry of these intervals varies in terms of width of the folded and tapered zone, taper angle and folding elevation. Two tables display key metrics critical to classifying and interpreting each CHS and the overall CHS pattern along the Auger diapir flanks (Tables 4.1 and 4.2). Stratigraphic intervals are labeled from deepest to shallowest in alphabetical order (A-J).

151 Table 4.1. Metrics compiled from present day and restored configurations of each composite halokinetic sequence (CHS) flanking the Auger diapir in the northern and southern domains. Width of folded zone was measured from the start of present-day bedding upturn (inflection point in A of Figure 4.9) to the tip of each CHS. Width of thinning was measured from the restored inflection point to the tip of each CHS (inflection point in C of Figure 4.9). Present day taper angle was calculated by taking the difference between the upper and lower angles of each CHS (inflection point in A of Figure 4.9) and restored taper angle is the measurement of the angle from the start of bedding upturn to the tip of each CHS (inflection point in C of Figure 4.9).

North-Northwest Flank South-Southeast Flank Present Day Restored Present Day Restored Width of Width of Width of Width of Interval CHS Type folded zone Taper Angle Elevation (m) Taper Angle Interval CHS Type folded zone Taper Angle Elevation (m) Taper Angle thinning (m) thinning (m) (m) (m) J Tapered 1232 15 180 883 15 A Tapered 1760 17 260 1267 12 I Tapered 600 20 280 665 22 B Tapered 580 18 245 423 35 H Tapered 710 18 275 378 41 C Tabular <100 26 upt 285 100 - G Tabular <100 47 upt 530 100 - D Tabular <100 - 300 100 - F Tapered 630 15 390 313 55 E Tabular 620 31 upt 390 100 - E Tabular 594 24 upt 300 100 5 F Tapered 450 26 330 240 64 D Tapered 650 24 560 285 59 G Tapered 600 19 630 488 61 C Tapered 700 19 460 650 56 H Tapered 560 23 640 580 75 B Tapered 830 22 660 670 57 I Tapered 630 37 435 680 61 A Tapered 815 16 560 470 49 J Tapered 560 23 602 660 67

152 Table 4.2. Metrics compiled from the integration of biostratigraphic data and decompacted thicknesses of composite halokinetic sequence (CHS) intervals, which yields sediment accumulation rate (m/1000 yrs) for each CHS. Time (Ma) based on calcareous nannoplankton and foraminifera ages from the GB-471 well. Biostratigraphic data courtesy of A. Waterman and PaleoData.

North-Northwest Flank South-Southeast Flank Sed accum rate Present Decompacted Sed accum rate Present Decompacted Interval CHS Type Time (m.y.) Interval CHS Type Time (m.y.) (m/1000 yrs) Thickness (m) Thickness (m) (m/1000 yrs) Thickness (m) Thickness (m) J Tapered 0.084 4.4 370 370 A Tapered 0.084 5.6 472 472 I Tapered 0.046 6.3 242 289 B Tapered 0.046 8.8 347 406 H Tapered 0.202 1.7 290 342 C Tabular 0.202 2.0 305 408 G Tabular 0.178 2.1 305 380 D Tabular 0.178 2.5 300 440 F Tapered 0.13 5.0 425 650 E Tabular 0.13 4.6 420 600 E Tabular 0.141 3.8 365 534 F Tapered 0.141 4.4 415 626 D Tapered 0.055 17.8 682 980 G Tapered 0.055 19.5 670 1070 C Tapered 0.174 4.4 507 766 H Tapered 0.174 4.9 526 850 B Tapered 0.944 1.3 800 1226 I Tapered 0.944 1.5 890 1405 A Tapered 0.436 1.5 380 636 J Tapered 0.436 3.0 800 1290

153 4.5.1 Stratal geometries Table 4.1 summarizes both the present-day and restored geometric parameters of each interval, including present-day width of folded zone (m), taper angle and fold elevation (m) and restored thinning width (m) and taper angle, which are based on two-dimensional restorations of each interval on both the northeastern and southeastern flanks of theAuger diapir. Around the diapir flanks, a total of nine angular unconformities separate a succession of ten well-imaged stratigraphic intervals that form synclines within 1 km of the diapir flank, extend from the seafloor to approximately (5500 m) (18,000’) and correlate along strike around the diapir (Figure 4.10). With the exception of two unconformities present along the deepest flanks of the diapir, seven unconformities are present at similar depths between the Auger and Andros minibasins. Both subtle and pronounced angular unconformities, which generally correlate to bright pairs of continuous amplitudes, truncate underlying strata, separate individual stratigraphic intervals and often intersect the diapir at minor flank irregularities (i.e., cusps) (Figure 4.8), separate each interval. Individual stratigraphic intervals are upturned against the diapir contact and display variable widths of thinning and folding, offset axial traces and, in most cases, basal onlap. Present-day widths of folding vary between <100 m to 1760 m (<300-5700 ft) and taper angles vary between 15° to 47°. Restored thinning widths range from <100 m to 1260 m (<100-4000 ft) with negligible to 75° taper angles. Deeper intervals display a greater amount of present- day upturn (up to 660 m) (2100 ft) with increasing depth whereas shallower intervals exhibit less upturn (<200 m) (<650 ft). For example, the uppermost unit that covers the Auger diapir indicates very little folding and deformation, whereas deeper units are progressively upturned with greater depth (Figure 4.10). Based on the end-member geometric classification of CHS sensu Giles and Rowan (2012), intervals that display sub-parallel interval boundaries, narrow zones of restored thinning (<100 m) (<300 ft) and negligible taper are classified as tabular CHS, which account for 25% of growth strata adjacent to Auger. Conversely, intervals that exhibit converging top and basal boundaries, wide zones of restored thinning (240-1260 m) (780-4000 ft) and large taper angles (12°-75°) are categorized as tapered CHS, which account of the remaining 75% of growth strata around Auger. Individual CHS represent drape fold monoclines originally deposited atop the

154 tapered (J) diapir tapered (J) tapered (I) tapered (I) tabular (H) tapered (H) tabular (G) tabular (G)

tabular (F) tapered (F) tapered (E) tabular (E) tapered (D) tapered (D) tapered (C) tapered (C) tapered (B)

tapered (A) tapered (B)

tapered (A)

2 km

Figure 4.10. Interpreted wide-azimuth, prestack depth-migrated 3-D seismic profile showing the vertical distribution of tapered and tabular CHS on the northeastern (right) and southwestern (left) flanks of the Auger diapir. Blue domains refer to tabular CHS, whereas red domains refer to tapered CHS. Individual CHS A-J are labeled oldest to youngest. Data provided courtesy of CGG.

155 diapir but have been subsequently eroded and folded during passive diapirism and minibasin downbuilding. We observe various geometric stacking patterns of CHS (Figure 4.11), which form local cusps that intersect CHS-bounding unconformities along the diapir flank depending on the configuration of stacked CHS. Stacked tabular over tabular and tabular over tapered exhibit little in the way of diapir flank rugosity at Auger, whereas tapered over tapered and tapered over tabular produce pronounced cusps along the diapir edge. Tapered over tabular stacking patterns exhibit greater amounts of flank irregularity when compared to tapered over tapered stacking patterns. While smaller cusps may exist, they are below the resolution limits capable with the acquisition and processing techniques of this dataset. The lower flanks of the diapir are exclusively tapered CHS, whereas a mix of tapered and tabular CHS is present at shallower levels (Figure 4.10). The northern flank is dominated by tapered CHS, whereas the southern domain is still dominated by tapered CHS, but exhibits a slightly higher number of tabular CHS. A majority of CHS are the same on both flanks, however 30% morph from tapered into tabular in three dimensions. The southern, more basinward domain of the Auger diapir is tabular-dominant, whereas the updip, northern domain is more tapered- dominant.

4.5.2 Well correlations Table 4.2 summarizes a number of different metrics that were calculated for each CHS using a combination of present-day interval thickness and decompacted interval thickness and benthic foraminifera and calcareous nannoplankton age dates from the GB-471 well (API#: 608074004500), including interval thickness (m), sediment accumulation rate (m/kyr) and duration (Ma). First, CHS intervals generally display similar thickness around the Auger diapir flanks, but differ mostly near the base of the diapir, where units on the northern flank, in the Andros minibasin are 45-150 m (150-500 ft) thicker than those on the south-southwest flank, in the Auger minibasin (Figure 4.10). We observe a range of present-day thicknesses for the various stratigraphic intervals from 242 m to 890 m (790-2900 ft), which range in thickness from 289 m to 1405 m (950-4600’) when decompacted. Second, CHS sediment accumulation rates vary between 1.5 to 19 m/kyr (5-60 ft/kyr). While there are outliers, sediment accumulation rate generally appears to correlate to CHS

156 a) b)

Tabular-CHS Tabular-CHS

diapir diapir

Tabular-CHS

Tapered-CHS

c) d)

Pronounced Tapered-CHS Pronounced Tapered-CHS cusp cusp

diapir diapir

Tabular-CHS Tapered-CHS

diapir diapir

tabular tabular tapered tabular tabular tabular tapered tapered

diapir diapir tapered tabular cusps tapered

tabular

tapered tapered cusps tapered tapered 4000

tapered

Figure 4.11. Top: Different geometric configurations of stacked composite halokinetic sequences (CHS) around Auger diapir: (A) tabular CHS over tabular CHS; (B) tabular CHS over tapered CHS; (C) tapered CHS over tapered CHS; and (D) tapered CHS over tabular CHS (Giles and Rowan, 2012). Bottom: interpreted wide-azimuth, prestack depth-migrated 3-D seismic profiles of CHS flanking the Auger diapir display similar configurations of stacked CHS. Thinning and upturn of CHS are within 1 km of the diapir interface. Data provided courtesy of CGG.

157 geometry type, where faster sediment accumulation rates promote the formation of tapered CHS (R < A) and slower accumulation rates promote development of tabular CHS (R > A). Tapered CHS sediment accumulation rates have a narrower range of variation between 2.0 to 4.6 m/kyr (6.5-15 ft/kyr), whereas tabular CHS sediment accumulations rates have a wider range between 1.5 to 19.5 m/kyr (5-60 ft/kyr). Varying CHS geometries reflect overall changes in the rates of sediment accumulation and diapir rise. For example, tapered CHS are generally associated with high sediment accumulation rate relative to salt-rise rate, however two of the lowermost tapered CHS have very low sediment accumulation rates relative to shallower tapered CHS. Because salt rise rates were likely very low during the initial formation of the Auger and Andros minibasins due to lower differential pressure on salt, tapered CHS formed during this time in the presence of very low sediment accumulation rate. Third, most CHS were deposited over time scales ranging between 130kyr and 940kyr, while rare CHS were deposited over 46kyr and 55kyr time scales. Tabular CHS time intervals are clustered between 130kyr to 200kyr, whereas tapered CHS have a much broader time interval between 46kyr and 940kyr. In any case, all CHS were deposited on 4th order depositional time scales, which occur on time scales between 0.1-1.0 m.y., rather than 3rd order depositional cycles as suggested by the halokinetic sequence model sensu Giles and Rowan (2012).

4.6 Discussion We observe both tabular and tapered CHS along the margins of the Auger diapir, which display a range of restored taper angles and varying widths of thinning. Tabular CHS upturn within 100 m of the diapir interface and exhibit a narrower radius of thinning, whereas tapered CHS upturn within 240-1260 m and display a wider radius of thinning. Restored taper angles for tabular CHS are negligible (<5°), whereas tapered CHS have a range of 12°-75°. Multiple configurations of geometric stacking patterns produce varying amounts of rugosity along the diapir flanks in two dimensions. In three dimensions, however, individual CHS change geometry (i.e., tapered into tabular and vice versa) around the diapir flanks producing local flank irregularities that are dependent on the configuration and location of stacked CHS.The southern side of the diapir exhibits a higher percentage of tabular CHS, whereas the northern side contains a higher percentage of tapered CHS. Deeper flanks are dominated by tapered CHS that have

158 higher fold elevations, whereas shallower flanks exhibit a combination of tapered and tabular CHS that display lower fold elevations. Based on biostratigraphic ages from well data, tapered CHS have higher rates of sediment accumulation versus lower rates for tabular CHS.

4.6.1 Comparison to CHS Model The outcrop-based halokinetic sequence model presented by Giles and Rowan (2012) generally applies to the successions of growth strata flanking the deepwaterAuger diapir. Tapered and tabular CHS around Auger are bounded by both high angle and low angle angular unconformities and have similar amounts of upturn and widths of thinning as published examples of CHS from La Popa Basin and the northern Flinders Ranges (e.g., Giles and Rowan, 2012; Hearon et al., in review B). Other published outcrop examples from La Popa Basin (e.g., Giles and Lawton, 2002; Giles and Rowan, 2012), the northern Flinders Ranges (e.g., Kernen et al., 2012; Hearon et al., in review B), the Paradox Basin (e.g., Lawton and Buck, 2006; Shock et al., 2012) and the Bakio diapir (e.g., Rowan et al., 2012) also document composite halokinetic sequences flanking steep to vertical diapirs, but in a variety of depositional settings. The aforementioned examples display both types of CHS in outcrops ranging from deepwater turbidites and mass transport complexes, outer shelf, shallow marine, lacustrine, fluvial to subaerial environments, suggesting that CHS form independent of depositional environment. In similar fashion to Giles and Rowan (2012), we interpret sand bodies terminate closer to diapir flanks in tabular CHS due to a thicker roof and greater topographic relief, whereas sand bodies terminate further away from diapir flanks in tapered CHS, however a plethora of well data coupled with high resolution seismic are needed to fully document the variety of internal CHS geometric possibilities. While all of the published CHS examples, including this study, have similar properties to those presented by Giles and Rowan (2012), there are some key differences. Rowan et al. (2012) presented outcrop data from the Bakio diapir, northern Spain, which display abundant debris flow deposits in a tapered CHS that was controlled by a thick, preexisting carbonate roof, rather than a high ratio of sediment accumulation rate to diapir-rise rate. At the Patawarta diapir, South Australia, a tapered CHS is present in subjacent strata to ramping allochthonous salt instead of a vertical diapir (Kernen et al., 2012; Hearon et al., in review B). Well data at the Auger diapir

159 suggests CHS were deposited on 4th order depositional cycles as opposed to 3rd order cycles, as suggested by Giles and Rowan, 2012. We expect debris flow deposits at CHS unconformities due to continuous hemipelagic deposition of roof strata atop the diapir, oversteepening of the diapir flank during times of slow sedimentation and subsequent failure, however these deposits are not evident on seismic data or on available well data, which could be due to the resolution of seismic directly adjacent to the salt flank and the location of the well relative to the diapir flank. Geometric differences in CHS on opposite flanks of the Auger diapir may be the result of differential salt rise in three-dimensions, whereby salt rise rate was faster on the southern flank than the northern, resulting in a slightly higher number of tabular CHS. In the same regard, we suggest individual CHS that morph geometry around the diapir flanks in three dimensions are the result of variable salt rise rates. The upward change from tapered-dominated to mixed tapered and tabular not only indicates variance in local salt rise rates and sediment accumulation rates but also progressive increased differential pressure on salt below the Auger and Andros minibasins. However, in the presence of equal sediment accumulation rate on all sides of the diapir, increased differential pressure caused by progressive stacking of CHS may have caused the shift from tapered-dominated along the lower half of the diapir to mixed CHS along the upper half of the diapir.

4.6.2 Additional Diapir Flank Truncations While the mature, mostly circular and symmetrical Auger diapir is flanked by CHS, numerous diapirs in the subsurface and in outcrop are asymmetrical and are not bounded by CHS. Instead, they are bounded by a variety of stratal truncations including faults, high-angle truncations, megaflaps and truncated roof. For example, in the Grand Isle and Bay Marchand- Terrebonne areas of the northern Gulf of Mexico shelf, basinward-leaning diapirs are bounded and linked by counterregionally-dipping normal faults instead of CHS, some of which display high angle stratal truncations adjacent to diapirs. In the eastern Willouran Ranges, South Australia, several steep diapir flanks do not contain halokinetic folds, rather minibasin scale folding, high-angle stratal truncations and a megaflap are present (Hearon et al., in reviewA). A myriad of stratal truncations, including tight folds, high angle truncations, laterally onlapping strata and rare CHS, flank elongate salt walls in the Paradox Basin (e.g., Matthews et al., 2007;

160 Trudgill, 2011; Giles et al., 2012; Shock et al., 2012) and growth strata in the Kayenta Formation flank the circular Upheaval Dome structure, which has been postulated to be a pinched-off salt diapir but no evaporite is present (e.g., Jackson et al., 1998; Geesaman et al., in prep). Lastly, where a rotated carapace or roof block is present along the margin of a diapir, the development of roof strata may be hindered as the carapace block obstructs the salt-sediment interface, which prohibits the development of drape folding and the formation of CHS but still allows for minibasin strata to onlap the carapace block.

4.6.3 Application to Allochthonous Salt Although CHS are thought to develop primarily along the margins of steep, mature diapirs, they also may be present beneath and along the flanks of allochthonous salt, whereby the angle of the ramp determines whether or not CHS will develop and be preserved. Outcrop and seismic examples of allochthonous salt commonly display shallow stratigraphic truncations beneath shallowly-dipping salt sheets and canopies, whereas steeply dipping primary and secondary diapirs connected to allochthonous salt may or may not be flanked by subsalt CHS. Outcrop examples in the northern Flinders Ranges exhibit partially to fully decapitated CHS at ramp to flat transitions, the latter appearing in outcrop as high angle stratal truncations instead of an intact CHS. Hearon et al. (in review B) demonstrated two additional models of allochthonous salt initiation, whereby salt transitions from steep to vertical diapirs to laterally spreading salt sheets via salt-top or salt edge breakout. Both models invoke piston-like rise of a diapir (sensu Schultz-Ela et al., 1993), but salt top breakout occurs inboard of the salt-sediment interface, preserving most of the adjacent CHS, whereas salt edge breakout occurs along the diapir flank, decapitating the entire flanking CHS.

4.6.4 Limitations, Implications and Future Work While there are limitations inherent in any subsurface study, including availability and precision of biostratigraphic and well data, enhanced velocity modeling of salt and flanking sediments and recent advances in seismic technology and acquisition techniques have vastly improved the ability to image stratal truncations adjacent to salt diapirs, thus refining the understanding the evolution of minibasins, steep to vertical diapirs and allochthonous salt.

161 Additionally, the pitfalls of simple seismic flattening indicate the need for structural restorations of growth strata in salt-flank settings and further reveals restoration as an essential tool for understanding salt-sediment interaction, especially to aid in the geometric classification of deformed CHS. A plethora of well data is needed in order to determine the precise termination of sand bodies within individual CHS in relationship to any given salt flank, which will improve the understanding of reservoir presence adjacent to salt bodies. Also, higher resolution seismic imaging is needed for detailed interpretation of the variety of internal geometries present within individual CHS. While this study has primarily focused on the structural aspects of the halokinetic sequence model, higher resolution well data coupled with high-resolution sequence stratigraphic data is needed in order to test whether CHS unconformities around Auger tie to regional sequence boundaries. The deposition of Pliocene-Pleistocene strata flanking Auger was heavily influenced by glaciation, thus detailed studies of other diapirs with different aged strata are needed to determine whether CHS in deepwater depositional environments were deposited on 4th order cycles.

4.7 Conclusions The results of this study are mostly compatible with the outcrop-based halokinetic sequence model sensu Giles and Rowan (2012). Tapered and tabular CHS are present in three dimensions around the flanks of the deepwater Auger diapir. While geometries vary, tapered CHS is the dominant geometric end-member along the lower diapir flanks, whereas mixed tapered and tabular CHS are present at shallower depths. Tabular CHS have a narrower radius of thinning (<100 m) and negligible taper (<5°), whereas tapered CHS have a wider radius of thinning (240 m-1260 m) and variable taper (12°-75°). Tapered CHS have generally higher sediment accumulation rates, whereas tabular CHS have generally lower sediment accumulation rates and biostratigraphic data suggests CHS were deposited on 4th order depositional sequences (130- 940kyr). Halokinetic folding is not dependent on specific depositional environments and may form adjacent to allochthonous salt, as well as vertical diapirs. The details of this study have a number of practical exploration and development ramifications for hydrocarbon prospects adjacent to salt bodies. First, while stratal upwarps, unconformities and salt cusps associated with CHS may pose drilling challenges near salt

162 bodies, the details of this study help improve the understanding of poorly imaged zones adjacent to steep diapirs and allochthonous salt. Second, because tapered and tabular CHS geometries impact sand distribution and reservoir proximity to salt faces and are forensic indicators of salt-induced topography through time, the results of this study can be used to build better, more realistic reservoir models. Lastly, a better understanding of stratal upwarps adjacent to salt bodies can add clarity to salt-truncation traps, local seals, hydrocarbon migration, reservoir compartmentalization and connectivity.

4.8 Acknowledgments We thank CGG for permission to show seismic data around the Auger diapir; Nick Burke was instrumental in obtaining access to the data. We also thank Art Waterman and Paleodata for access to biostratigraphic information and well data. Robust technical discussions were had with Carl Fiduk, Rachelle Kernen and Bruce Trudgill. A majority of the data presented in this paper was collected by TH during an internship at BP and we would like to thank Jacek Jaminski, Cindy Yeilding, Jay Thorseth and BP management for the opportunity to publish these results.

4.9 References Cited Alsop, G. I., J. P. Brown, I. Davison, and M. R. Gibling, 2000, The geometry and deformation mechanisms of drag zones adjacent to salt diapirs: a case study from Cape Breton Island, Nova Scotia: J. Geological Society London, v. 157, p. 1019-1029.

Booth, J. R., A. E. Duvernay, III, D. S. Pfeiffer, and M. J. Styzen, 2000, Sequence stratigraphic framework, depositional models, and stacking patterns of ponded and slope fan systems in the Auger basin: central Gulf of Mexico slope, in P. Weimer, R. M. Slatt, J. Coleman, N. C. Rosen, H. Nelson, A. H. Bouma, M. J. Styzen, and D. T. Lawrence, eds., Deep- Water Reservoirs of the World: 20th Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 82-103.

Booth, J. R., M. C. Dean, A. E. Duvernay, III, and M. J. Styzen, 2003, Paleo-bathymetric controls on the stratigraphic architecture and reservoir development of confined fans in the Auger Basin: central Gulf of Mexico slope: Marine and Petroleum Geology, v. 20, p. 563-586.

163 Buffler, R. T., 1989, Distribution of crust, distribution of salt, and the early evolution of the Gulf of Mexico basin, in Gulf of Mexico Salt Tectonics, Associated Processes and Exploration Potential: 10th Annual Gulf Coast Section, SEPM Foundation Research Conference, p. 25-27.

Galloway, W.E., 2008, Depositional evolution of the Gulf of Mexico sedimentary basin, in A. D. Miall, ed., The sedimentary basins of the United States and Canada: The Netherlands, Elsevier, p. 505-549.

Geesaman, P., 2013, Structural observations and stratigraphic variability in Jurassic strata, Upheaval Dome, Canyonlands National Park, Utah, USA: Master’s thesis, Colorado School of Mines, Golden, Colorado, 137 p.

Giles, K. A., and T. F. Lawton, 2002, Halokinetic sequence stratigraphy adjacent to the El Papalote diapir, northeastern Mexico: AAPG Bulletin, v. 86, p. 823-840.

Giles, K. A., T. F. Lawton, A. Shock, R. A. Kernen, T. E. Hearon, IV, and M. G. Rowan, 2012, A halokinetic drape-fold model for caprock in diapir-flanking and subsalt positions (abs.): AAPG Annual Convention Program, v. 21, CD-ROM.

Gradstein, F. M., J. G. Ogg, A. G. Smith, F. P.Agterberg, W. Bleeker, R. A.Cooper, V. Davydov, P. Gibbard, L. A. Hinnov, M. R. House, L. Lourens, H-P. Luterbacher, J. McArthur, M. J. Melchin, L. J. Robb, P. M.Sadler, J. Shergold, M.Villeneuve, B. R.Wardlaw, J. Ali, H. Brinkhuis, F. J. Hilgen, J. Hooker, R. J. Howarth, A. H. Knoll, J. Laskar, S. Monechi, J. Powell, K. A. Plumb, I. Raffi, U. Röhl, A. Sanfilippo, B. Schmitz, N. J. Shackleton, G. A. Shields, H. Strauss, J. Van Dam, J. Veizer, Th. Van Kolfschoten, and D. Wilson, 2004, Geologic Time Scale 2004: Cambridge University Press, 589 p.

Hart, W., J. Jaminski, and M. Albertin, 2004, Recognition and Exploration Significance of Supra- salt Stratal Carapaces, in P. J. Post, D. L. Olson, K. T. Lyons, S. L. Palmes, P. F. Harrison, and N. C. Rosen, eds., Salt-sediment interactions and hydrocarbon prospectivity: Concepts, applications, and case studies for the 21st century: 24th Annual Gulf Coast Section, SEPM Foundation Research Conference, p. 166-199.

164 Hearon, T.E., IV, M. G. Rowan, T. F. Lawton, P. T. Hannah, and K. A. Giles, in review A, Geology and tectonics of Neoproterozoic salt diapirs and salt sheets in the eastern Willouran ranges, South Australia: Basin Research.

Hearon, T. E., IV, M. G. Rowan, R. A. Kernen, K. A. Giles, C. E. Gannaway, T. F. Lawton, and J. C. Fiduk, in review B, Allochthonous salt initiation and advance in the Flinders and Willouran Ranges, South Australia: using outcrops to test subsurface-based models from the northern Gulf of Mexico: AAPG Bulletin.

Hudec, M. R., M. P. A. Jackson, and F. J. Peel, 2013a, Influence of deep Louann structure on the evolution of the northern Gulf of Mexico: AAPG Bulletin, v. 97, p 1711-1735.

Hudec, M. R., I. O. Norton, M. P. A. Jackson, and F. J. Peel, 2013b, Jurassic evolution of the Gulf of Mexico salt basin: AAPG Bulletin, v. 97, p. 1683-1710.

Jackson, M. P. A., D. D. Schultz-Ela, M. R. Hudec, I. A. Watson, and M. L. Porter, 1998, Structure and evolution of Upheaval Dome: A pinched-off salt diapir: Geological Society of America Bulletin, v. 110, p.1547-1573.

Kernen, R. A., K. A. Giles, M. G. Rowan, T. F. Lawton, and T. E. Hearon, 2012, Depositional and halokinetic-sequence stratigraphy of the Neoproterozoic Wonoka Formation adjacent to Patawarta allochthonous salt sheet, Central Flinders Ranges, South Australia, in G. I. Alsop, S. G. Archer, A. J. Hartley, N. T. Grant, and R. Hodgkinson, eds., Salt Tectonics, Sedimentation and Prospectivity: London, Geological Society of London Special Publication, v. 363, p. 81-105, doi: 10.1144/SP363.5.

Lawton, T. F., and B. J. Buck, 2006, Implications of diapir-derived detritus and gypsic paleosols in Lower Triassic strata near the Castle Valley salt wall, Paradox Basin, Utah: Geology, v. 34, p. 885-888, doi: 10.1130/G22574.1.

Matthews, W. J., G. J. Hampson, B. D. Trudgill, and J. R. Underhill, 2007, Controls on Fluvio- lacustrine reservoir distribution and architecture in passive salt diapir provinces: insights from outcrop analogs: AAPG Bulletin, v. 91, p. 1367-1403.

McGee, D. T., P. W. Bilinski, P. S. Gary, D. S. Pfeiffer, and J. L. Sheiman, 1994, Geologic Models and geometries of Auger field, deep-water Gulf of Mexico,in P. W. Weimer, A. H. Bouma, and B. F. Perkins, eds., Submarine Fans and Turbidite Systems-Sequence Stratigraphy, Reservoir Architecture, and Production Characteristics: 15th Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 245-256.

165 Peel, F. J., C. J. Travis, and J. R. Hossack, 1995, Genetic structural provinces and salt tectonics of the Cenozoic offshore U. S. Gulf of Mexico: a preliminary analysis: AAPG Memoir, v. 65, p. 153-175.

Pindell, J., and J. F. Dewey, 1982, Permo-Triassic reconstruction of western Pangea and the evolution of the Gulf of Mexico/Caribbean region: Tectonics, v. 1, p. 179-211, doi:10.1029/TC001i002p00179.

Pindell, J., and L. Kennan, 2001, Kinematic evolution of the Gulf of Mexico and Caribbean, in R. H. Fillon, N. C. Rosen, P.Weimer, A. Lowrie, H. Pettingill, R. L. Phair, H. H. Roberts, and B. van Hoorn, eds., Petroleum systems of deep-water basins: Global and Gulf of Mexico experience: 21st Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 193-220.

Pulham, A. J., 1993, Variations in slope deposition, Pliocene-Pleistocene, offshore Louisiana, northeast Gulf of Mexico, in P. Weimer and H. W. Posamentier, eds., Siliciclastic sequence stratigraphy: AAPG Memoir 58, p. 199-236.

Riba, O., 1973, Las discordancias sintectonicas del Alto Cardener (Prepirineo catalan), ensayo de interpretacion evolutiva, Acta Geologica Hispana, v. 8, p. 90-99.

Riba, O., 1976, Syntectonic unconformities of the Alto Cardener Spanish Pyrenees: a genetic interpretation: Sedimentary Geology, v., 15, p. 213-233.

Rowan, M. G., K. A. Giles, E. Roca, P. Arbues, and O. Ferrer, 2012, Analysis of growth strata adjacent to an exposed deepwater salt diapir, northern Spain (abs.): AAPG Annual Convention Program, v. 21, CD-ROM.

Salvador, A., 1987, Late Triassic-Jurassic paleogeography and origin of Gulf of Mexico basin: AAPG Bulletin, v. 71, p. 419-451.

Salvador, A., 1991, Origin and development of the Gulf of Mexico basin, in A. Salvador, ed., The Gulf of Mexico basin: Geological Society of America, The Geology of North America, v. J, p. 389-444.

Schultz-Ela, D. D., M. P. A. Jackson, and B. C. Vendeville, 1993, Mechanics of active salt diapirism: Tectonophysics, v. 228, p. 275-312.

166 Sclater, J. G., and P. A. F. Christie, 1980, Continental stretching: An explanation of the post-mid- Cretaceous subsidence of the Central North Sea Basin: Journal of Geophysical Research, v. 85, p. 3711-3739.

Shock, A., T. F. Lawton, and K. A. Giles, 2012, Origin and implications of diapir-flanking caprock associated with the salt-sediment interface at Castle Valley salt diapir, Utah (abs.): AAPG Annual Convention Program, v. 21, CD-ROM.

Swanston, A. M., M. D. Mathias, and C. A. Barker, 2011, Wide-azimuth TTI imaging at Tahiti: Reducing structural uncertainty of a major deepwater subsalt field: Geophysics, .v 76, p. WB67-WB78.

Trudgill, B. T., 2011, Evolution of salt structures in the northern Paradox Basin: controls on evaporite deposition, salt wall growth and supra-salt stratigraphic architecture: Basin Research, v. 23, p. 208-238.

Waterman, A. S., M. W. Center, R. A. George, N. S. Vallette, A. F. Porter, Jr., T. M. Reilly, R. A. Weber, R. V. Roederer, J. Schmieder, J. A. Sarao, R. H. Fillon, 2012, Neogene Biostratigraphic Chart: PaleoData.

Weimer, P., P. Varnai, F. M. Budhijanto, Z. M. Acosta, R. E. Martinez, A. F. Navarro, M. G. Rowan, B. C. McBride, T. Villamil, C. Arango, J. R. Crews, and A. J. Pulham, 1998, Sequence stratigraphy of Pliocene and Pleistocene turbidite systems, Northern Green Canyon and Ewing Bank (offshore Louisiana), Northern Gulf of Mexico: AAPG Bulletin, v. 82, p. 918-960.

Winker, C. D., and J. R. Booth, 2000, Sedimentary dynamics of the salt dominated continental slope, Gulf of Mexico: Integration of observations from the seafloor, near surface, and deep subsurface, in P. Weimer, R. M. Slatt, J. Coleman, N. C. Rosen, H. Nelson, A. H. Bouma, M. J. Styzen, and D. T. Lawrence, eds., Deep-Water Reservoirs of the World: 20th Annual Gulf Coast Section, SEPM Foundation Bob F. Perkins Research Conference, p. 1059-1086.

167 CHAPTER 5 IMPLICATIONS AND CONCLUSIONS

The northern Flinders Ranges and eastern Willouran Ranges of South Australia contain one of the oldest records of salt diapirs and salt sheets, and are natural laboratories that provide a unique opportunity to study two-dimensional views of complex three-dimensional steep diapirs, allochthonous salt bodies and associated stratal geometries exposed in Neoproterozoic strata. Field mapping and structural analysis of diapirs and allochthonous salt in the eastern Willouran Ranges and Pinda, Patawarta and Loch Ness study areas (Chapters 2 and 3) provide important insights into the evolution of steep diapirs and the initiation, breakout and advance of allochthonous salt in a system that evolved over a period of at least 250 Ma. While the conclusions of the individual field-based allochthonous salt studies were outlined in Chapters 2 and 3, general conclusions regarding allochthonous salt in South Australia include: 1) Allochthonous salt is commonly linked to steep diapirs in the northern Flinders Ranges, however in the eastern Willouran Ranges, a complex array of discordant surfaces links diapiric-breccia bodies to steep diapirs; interpreted as the remnants of an allochthonous salt canopy, with discordant surfaces representing salt welds (Figures 2.6, 2.8, 2.9, 3.5 and 3.13). 2) There is little to no deformation such as thrust imbricates, shear zones, or rubble zones in strata beneath allochthonous salt in all of the study areas (Figures 3.5, 3.7 and 3.9). 3) Preserved stratal geometries at the transition from passive diapirs to salt sheets include minibasin-scale folding, tabular and tapered composite halokinetic sequences and unfolded strata. Strata beneath base-salt flats of subhorizontal salt sheets are always undeformed (Figures 2.8, 3.5, 3.7, 3.9 and 3.14). 4) The initiation of allochthonous salt spreading from a steep diapir is abrupt and is caused by piston-like breakthrough of the diapir roof, freeing the salt to flow laterally via open-toed, extrusive or thrust advance depending on roof presence and thickness (Figure 3.16).

168 5) Two models that explain the initiation of allochthonous salt spreading in South Australia are salt-edge breakout and salt-top breakout (Figure 3.16). 6) In salt-top breakout, the salt breaks through its roof on a fault some distance inboard of the diapir margin, preserving part of the roof beneath the salt sheet. 7) In salt-edge breakout, the roof is fully decapitated as piston-like rise occurs at the edge of the steep diapir. 8) The style and geometry of allochthonous salt advance is dependent on the interplay between salt-supply rate to the front of the sheet and sediment-accumulation rate (Figure 3.17). 9) High and moderate ratios of salt-supply rate and sediment-accumulation rate generate base-salt flats and true ramps, respectively, with little development of slumped carapace (Figure 3.17a and 3.17b). 10) A lower ratio results in pinned inflation, halokinetic folding and periodic slumping of the roof, and breakout on a salt-roof thrust or a steeper fault. 11) The geometries and processes of allochthonous salt initiation and advance are similar in South Australia and the northern Gulf of Mexico (Figure 3.17c).

Interpretation and structural analysis of ten well-imaged composite halokinetic sequences (CHS) flanking the deepwaterAuger diapir, northern Gulf of Mexico, yielded important metrics that generally corroborate the outcrop-based halokinetic sequence model (sensu Giles and Rowan, 2012). The following general conclusions provide insight into how this case study answers some of the key questions regarding the validity of applying an outcrop-based model in a subsurface setting: 1) The deepwater Auger diapir is flanked by both end-member CHS geometries (tabular and tapered), which have similar geometric characteristics to those CHS present in La Popa Basin and the Flinders Ranges (sensu Giles and Rowan, 2012) (Figures 4.6, 4.8 and 4.10). 2) As suggested by Giles and Rowan (2012), similar geometric patterns of vertically stacked CHS are present around the Auger diapir. All four stacking patterns were observed (Figure 4.11).

169 3) The integration of biostratigraphic data with individual CHS end-member geometries generally indicates that tabular CHS form when the ratio of salt rise to sediment accumulation is high, whereas tapered CHS form when the ratio is low (Table 4.2). 4) 3-D variations in CHS geometry around the flanks of theAuger diapir may be the result of differential salt rise in three-dimensions. 5) The formation of halokinetic sequences is independent of depositional environment as CHS are present in rocks deposited in environments ranging from shallow marine to outer shelf to deepwater (Figures 3.13 and 4.10). 6) In additional to steep diapirs, CHS may also flank allochthonous salt (Figure 3.7, 3.14 and 3.21), however CHS only represent a subset of salt-flanking stratal truncations. Other truncation types include megaflaps, faults, high angle truncations and truncated roof.

5.1 Limitations The Adelaide Fold Belt and the northern Gulf of Mexico have limitations to salt tectonics research. First, in the Flinders Ranges, outcrop exposures represent only one two-dimensional cut of what is most certainly a more complex salt system in the subsurface. A dearth of reliable, high quality subsurface data in this area confines research to geological mapping, structural analysis, characterization of stratigraphy and limited geochemical studies, Second, while subsurface data, including gravity and magnetic surveys, bathymetric seafloor surveys, borehole information and modern three-dimensional seismic data have improved the understanding of the Gulf of Mexico, the current resolution of these data and the fact that no outcrops exist creates uncertainty. Given these limitations, however, well-exposed outcrops of salt structures and associated stratal geometries in South Australia are helpful in understanding and exploring the northern Gulf of Mexico and other basins with complex salt histories. Additionally, well-imaged salt structures and related stratal geometries on high-quality seismic data from the northern Gulf of Mexico allow outcrop models to be tested and further calibrated, and vice versa.

170 5.2 Exploration and Development Ramifications Outcrop exposures display high-resolution spatial and stratigraphic information unobtainable from high-quality 3-D seismic data or one-dimensional well data in subsurface settings. Field-based studies, therefore, are crucial element in the understanding of complex geological systems, especially salt tectonics. Field exposures of steep diapirs, allochthonous salt and associated stratal geometries in South Australia and well-imaged CHS along the flanks of the Auger diapir, northern Gulf of Mexico provide important insight into salt-sediment interaction and have critical ramifications to hydrocarbon exploration and production in worldwide salt- dominated basins. Despite some differences between the northern Gulf of Mexico and South Australia, observations and models derived from two-dimensional outcrops of diapirs and allochthonous salt in the northern Flinders and eastern Willouran ranges are helpful in understanding and exploring the northern Gulf of Mexico and other basins with allochthonous salt. The stratal and structural relationships exposed in South Australia, which are at a scale often below seismic resolution, have implications for building salt models in seismic imaging, drilling out of allochthonous salt, and exploring and developing three-way closures against salt sheets and the upper portions of their feeder diapirs. The combination of drilling challenges in strata directly flanking salt bodies and the scarcity of well-imaged CHS along the flanks of steep salt feeders make theAuger diapir case study essential for the application of salt-sediment interaction to hydrocarbon exploration. The details of the Auger case study have a number of practical exploration and development ramifications for hydrocarbon prospects adjacent to salt bodies. First, because stratal upwarps, unconformities and salt cusps associated with CHS often pose drilling challenges near salt bodies, the details of this study help improve the understanding of poorly imaged zones adjacent to steep diapirs and allochthonous salt. Second, because tapered and tabular CHS geometries impact sand distribution and reservoir proximity to salt faces and are forensic indicators of salt-induced topography through time, the results of this study can be used to build better, more realistic reservoir models. Lastly, a better understanding of stratal upwarps adjacent to salt bodies can add clarity to salt-truncation traps, local seals, hydrocarbon migration, reservoir compartmentalization and connectivity.

171 5.3 Suggestions for Future Work Outcrop-scale salt-sediment deformation features in South Australia represent comparative analogs to similar seismic-scale geometries present in hydrocarbon-rich, salt- dominated basins, such as the Gulf of Mexico and along the South Atlantic margins. However, the details of specific features, such as megaflaps and their formation, remain ambiguous. Primary feeders, secondary diapirs and salt walls present in other basins, such as the South Atlantic margins, may be flanked by CHS thus making the Auger diapir a relevant analog for future studies in other salt-dominated basins. For example, while this study has focused on the external characteristics of CHS, questions remain about the different possibilities of internal CHS geometries.

5.3.1 Willouran and Flinders Ranges, South Australia The Witchelina syncline, located along the NW flank of the Witchelina diapir is interpreted as a megaflap (see Chapter 2 for explanation) (Figures 2.8 and 2.9).The presence of megaflaps are well-known from the northern Gulf of Mexico, however a number of questions remain about their formation and importance to salt-sediment interaction and hydrocarbon exploration: (1) What are the specific geometric criteria for megaflaps, and more importantly what are the characteristics that make this type of geometry important to a petroleum system like the northern Gulf of Mexico?; (2) What is the driver(s) that creates such an elongate succession of strata along the flank of a steep diapir for distances of up to 4-5 km?; (3)Are megaflaps formed purely under gravitational or shortening conditions, or is the formation driven in part by both?; (4) In the case of the Witchelina megaflap, why is it present only on one flank of the Witchelina diapir, while absent on the opposite flank?; (5) Are megaflaps present only in the basal parts of primary minibasins, or can they be present at the bottom of secondary minibasins?

5.3.2 Northern Gulf of Mexico and other Global Salt Basins The Auger diapir case study is the first attempt to link the outcrop-based halokinetic sequence model to a subsurface setting using high-quality 3D seismic and biostratigraphic data. However, continued refinement of the CHS model requires additional studies of diapirs, feeders

172 and salt walls in different global basins coupled with further integration of well data, including higher resolution biostratigraphic data, well logs, dip-meter data and pressure data. While this study focused on the external character of CHS, questions still remain about the internal geometries of CHS and the proximity of sand to salt bodies. CHS flankingAuger display a wide array of internal geometric patterns, which range from parallel, concordant beds to beds that display convergence and onlap. Some CHS around Auger display one distinct internal geometric pattern, whereas others are more complex and contain multiple stacked patterns. Regardless of the configuration, internal patterns record intricate variations in salt rise and sediment accumulation rate and erosion. A better understanding of the internal character of CHS may help to gain better resolution on sand proximity and distribution adjacent to diapirs and salt sheets. Because near-surface salt can generate local topographic relief, distribution and facies variations of salt-proximal reservoir strata in near-salt may be affected. Tying seismic facies in adjacent minibasins to individual CHS geometries may help to understand and possibly predict how facies change from the interior of a minibasin towards a topographic high, such as a salt diapir. Additionally, the integration of a plethora of well data is needed in order to determine the precise termination of sand bodies within individual CHS in relationship to any given salt flank, improving the understanding of reservoir presence adjacent to salt bodies. While this study has primarily focused on the structural aspects of the halokinetic sequence model, higher resolution well data coupled with high-resolution sequence stratigraphic data are needed in order to test whether CHS unconformities around Auger tie to regional sequence boundaries. The deposition of Pliocene-Pleistocene strata flanking Auger was heavily influenced by glaciation, thus detailed studies of other diapirs with different aged strata are needed to determine whether CHS in deepwater depositional environments were also deposited on 4th order cycles.

5.4 References Cited Giles, K. A., and M. G. Rowan, 2012, Concepts in halokinetic–sequence deformation and stratigraphy, in G. I. Alsop, S. G. Archer, A. J. Hartley, N. T. Grant, and R. Hodgkinson, eds., Salt Tectonics, Sediments and Prospectivity, Geological Society of London Special Publications, v. 363, p. 7-31, doi: 10.1144/SP363.2.

173 APPENDIX A CO-AUTHOR PERMISSIONS

10/21/13 Gmail - Willouran manuscript co-author permissions.

Thomas Hearon

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Timothy Lawton Mon, Oct 21, 2013 at 4:35 PM To: Thomas Hearon

Dear Mr. Hearon,

As a coauthor and noncommittee member, I, Timothy Lawton, give Thomas Hearon permission to publish Chapter 2 of Hearon's dissertation entitled 'Geology and tectonics of Neoproterozoic salt diapirs and salt sheets in the eastern Willouran Ranges, South Australia.

The signature line below constitutes my signature for this purpose.

With best Regards, Timothy Lawton

Timothy Lawton Titular Investigador B Centro de Geociencias Universidad Nacional Autónoma de México (UNAM) Blvd. Juriquilla No. 3001 Querétaro, 76230, México tel: 011 52 44 2238 1104 ext. 108

10/22/13 Gmail - Willouran manuscript co-author permissions.

Thomas Hearon

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Hannah, Tyler Mon, Oct 21, 2013 at 2:17 PM To: Thomas Hearon

I, Tyler Hannah, give Thomas Hearon permission to publish Chapter 2 of Hearon's dissertation entitled 'Geology and tectonics of Neoproterozoic salt diapirs and salt sheets in the eastern Willouran Ranges, South Australia.'

Cheers,

Tyler

https://mail.google.com/mail/ca/u/0/?ui=2&ik=9647eb4dcf&view=pt&search=inbox&msg=141dd287d7706dcdFrom: Thomas Hearon [mailto:[email protected]] 1/1 Sent: Monday, October 21, 2013 3:14 PM To: Timothy Lawton; Hannah, Tyler; Kate Giles 174 Cc: Mark Rowan Subject: Willouran manuscript coauthor permissions.

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Thomas Hearon

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Giles, Katherine A Tue, Oct 22, 2013 at 10:53 AM To: Thomas Hearon

I, Katherine Giles, give Thomas Hearon permission to publish Chapter 2 of Hearon's dissertation entitled 'Geology and tectonics of Neoproterozoic salt diapirs and salt sheets in the eastern Willouran Ranges, South Australia.

Katherine A. Giles Lloyd A. Nelson Professor Director, Institute of Tectonic Studies Department of Geological Sciences The University of Texas at El Paso El Paso, TX 79968-0555 Office Phone: (915) 747-7075

On Oct 21, 2013, at 2:14 PM, Thomas Hearon wrote:

Hey everyone, 10/22/13 Gmail - Allochthonous chapter co-author permission As a formality for my thesis and because you are coauthors, I need a written email statement from each of you saying that you give me permission to publish the Willouran chapter. This does not include you, Mark, since you're on the committee. Thomas Hearon Here's the verbiage from the Graduate School: "If the material was co-authored by authors other than the candidate's advisor or thesis committee Allochthonousmembers, the chapter candidate mustcoauthor obtain permission permission from each co-author who is not on the candidate's committee to reproduce the material as part of the thesis or dissertation." Giles, Katherine A Tue, Oct 22, 2013 at 10:55 AM To: ThomasCan Hearon go something like this:

I, KatherineI, your Giles, name, give give Thomas Thomas Hearon Hearon permission permission to topublish publish Chapter Chapter 3 of2 ofHearon's Hearon's dissertation dissertation entitled entitled 'Allochthonous'Geology salt and initiation tectonics and of advanceNeoproterozoic in the Flinderssalt diapirs and and eastern salt sheetsWillouran in theRanges, eastern South Willouran Australia: using outcropsRanges, to test Southsubsurfacebased Australia.' models from the northern Gulf of Mexico.' Katherine A. Giles If you want, or care, here's the link where you can read more about it (all the way at the bottom of Lloyd A. Nelson Professor the page): https://inside.mines.edu/Copyright Director, Institute of Tectonic Studies DepartmentThanks of Geological so much Sciences and sorry for the hassle. The University of Texas at El Paso El Paso,Cheers, TX 79968-0555 Thomas Office Phone: (915) 747-7075 Thomas E. Hearon, IV PhD Candidate | salt tectonics, structure Dept Geology and Geological Engineering On OctColorado 21, 2013, School at 2:21 of PM, Mines Thomas Hearon wrote: https://mail.google.com/mail/ca/u/0/?ui=2&ik=9647eb4dcf&view=pt&search=inbox&msg=141e115bf47f56a4&dsqt=1[Quoted text hidden] 1/2

175

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Thomas Hearon

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[email protected] Mon, Oct 21, 2013 at 3:51 PM To: [email protected]

I, Rachelle Kernen, give Thomas Hearon permission to publish Chapter 3 of Hearon's dissertation entitled 'Allochthonous salt initiation and advance in the Flinders and eastern Willouran Ranges, South Australia: using outcrops to test subsurfacebased models from the northern Gulf of Mexico.'

From: Thomas Hearon [mailto:[email protected]] Sent: Monday, October 21, 2013 3:22 PM To: Kate Giles; Kernen, Rachelle A SEPCOUAX/D/GOMA; Timothy Lawton; Evey Gannaway; Carl Fiduk Cc: Mark Rowan 10/21/13 Gmail - Allochthonous chapter co-author permission Subject: Allochthonous chapter coauthor permission

[Quoted text hidden] Thomas Hearon

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Evey Gannaway Mon, Oct 21, 2013 at 4:09 PM To: Thomas Hearon

As a coauthor, I, Cora Gannaway, give Thomas Hearon permission to publish Chapter 3 of Hearon's dissertation entitled 'Allochthonous salt initiation and advance in the Flinders and eastern Willouran Ranges, South Australia: using outcrops to test subsurfacebased models from the northern Gulf of Mexico.'

On Mon, Oct 21, 2013 at 5:01 PM, Evey Gannaway wrote: [Quoted text hidden] [Quoted text hidden]

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https://mail.google.com/mail/ca/u/0/?ui=2&ik=9647eb4dcf&view=pt&search=inbox&msg=141dd112e41fb8d0 1/1 10/21/13 Gmail - Allochthonous chapter co-author permission

Thomas Hearon

Allochthonous chapter coauthor permission

Timothy Lawton Mon, Oct 21, 2013 at 4:36 PM To: Thomas Hearon

Dear Mr. Hearon,

As a coauthor and noncommittee member, I, Timothy Lawton, give Thomas Hearon permission to publish Chapter 3 of Hearon's dissertation entitled 'Allochthonous salt initiation and advance in the Flinders and eastern Willouran Ranges, South Australia: using outcrops to test subsurfacebased models from the northern Gulf of Mexico.'

The signature line below constitutes my signature for this purpose.

With Best Regards, Timothy Lawton

Timothy Lawton Titular Investigador B Centro de Geociencias Universidad Nacional Autónoma de México (UNAM) Blvd. Juriquilla No. 3001 Querétaro, 76230, México tel: 011 52 44 2238 1104 ext. 108

10/28/13 Gmail - Allochthonous chapter co-author permission

Thomas Hearon

Allochthonous chapter coauthor permission

Joseph Carl Fiduk Mon, Oct 28, 2013 at 10:43 AM To: Thomas Hearon

In case it needs to follow the more formal statement:

I, Carl Fiduk, give Thomas Hearon permission to publish Chapter 3 of Hearon's dissertation entitled 'Allochthonous salt initiation and advance in the Flinders and eastern Willouran Ranges, South Australia: using outcrops to test subsurfacebased models from the northern Gulf of Mexico.'

Cheers, https://mail.google.com/mail/ca/u/0/?ui=2&ik=9647eb4dcf&view=pt&search=inbox&msg=141dd2a4fc510dac 1/1 Carl

From: Thomas Hearon [mailto:[email protected]] Sent: Monday, October 21, 2013 3:22 PM 177 To: Kate Giles; Rachelle A. Kernen; Timothy Lawton; Evey Gannaway; Joseph Carl Fiduk Cc: Mark Rowan Subject: Allochthonous chapter coauthor permission

Hi everyone,

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https://mail.google.com/mail/ca/u/0/?ui=2&ik=9647eb4dcf&view=pt&search=inbox&msg=141fff2c488e66c2 1/1 10/22/13 Gmail - Auger chapter co-author permission

Thomas Hearon

Auger chapter coauthor permission

Giles, Katherine A Tue, Oct 22, 2013 at 10:54 AM To: Thomas Hearon

I, Katherine Giles, give Thomas Hearon permission to publish Chapter 4 of Hearon's dissertation entitled 'Testing the applicability of an outcropbased halokinetic deformation model in a deepwater depositional setting: Auger diapir , Garden Banks 470, northern Gulf of Mexico.'

10/24/13On Oct 21, 2013, at 2:16 PM, Thomas HearonGmail wrote: - Auger chapter co-author permission

Hi Kate and Bill, Thomas Hearon As a formality for my thesis and because you are coauthors, I need a written email statement from each of you saying that you give me permission to publish the Auger chapter. This does not Auger include chapter you, Mark,coauthor since you're permission on the committee. Here's the verbiage from the Graduate School: Hart, Bill H Thu, Oct 24, 2013 at 10:22 AM "If the material was co-authored by authors other than the candidate's advisor or thesis committee To: Thomas Hearon members, the candidate must obtain permission from each co-author who is not on the candidate's committee to reproduce the material as part of the thesis or dissertation." Thomas, Can go something like this:

I, your name, give Thomas Hearon permission to publish Chapter 4 of Hearon's dissertation entitled Yesterday,'Testing Jay Thorseth,the applicability BP North of an America outcropbased Exploration halokinetic Director, deformation gave verbal model approval in a deepwater for me to grant co‐ authordepositional permission setting:to include Auger the diapirAuger , CGardenhapter Banksin you 470,dissertation. northern Gulf With of that, Mexico.'

I, WilliamIf you H. Hart,want, give or care, Thomas here's Hearon the link permission where you to can publish read Chaptermore about 4 of itHearon's (all the waydissertation at the bottom entitled of 'Testing the applicabilitythe page): of https://inside.mines.edu/Copyright an outcropbased halokinetic deformation model in a deepwater depositional setting: Auger diapir , Garden Banks 470, northern Gulf of Mexico.' Thanks so much and sorry for the hassle. I earnestly thank you for including me as a co‐author. Cheers, Thomas Bill Hart Thomas E. Hearon, IV BP America Inc. PhD Candidate | salt tectonics, structure Gulf of Mexico Exploration BU Dept Geology and Geological Engineering Mail Code: WL4 02081C Colorado School of Mines 200 WestLake Park Boulevard https://mail.google.com/mail/ca/u/0/?ui=2&ik=9647eb4dcf&view=pt&search=inbox&msg=141e116a3fed7b83&dsqt=1Houston, TX 77079 1/2 Phone: 2813662263; Fax: 2813663835 Email: [email protected]

178 From: Thomas Hearon [mailto:[email protected]] Sent: Tuesday, October 22, 2013 10:33 AM To: Hart, Bill H Subject: Re: Auger chapter coauthor permission

No immediate rush, Bill. If you would like a copy of the thesis chapter in question to make things easier with management, I can forward one along. The content will most certainly change for the submission to Interpretation, which I would really like for you to maintain your coauthorship.

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