THE INFLUENCE OF CONVERGENT MARGIN STRUCTURE ON DEEP-WATER STRATIGRAPHIC ARCHITECTURE, PORE PRESSURE EVOLUTION, AND SOURCE ROCK MATURATION IN THE EAST COAST BASIN, NEW ZEALAND
A DISSERTATION SUBMITTED TO THE DEPARTMENT OF GEOLOGICAL AND ENVIRONMENTAL SCIENCES AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
Blair Nicole Burgreen August 2014
© 2014 by Blair Nicole Burgreen. All Rights Reserved. Re-distributed by Stanford University under license with the author.
This work is licensed under a Creative Commons Attribution- Noncommercial 3.0 United States License. http://creativecommons.org/licenses/by-nc/3.0/us/
This dissertation is online at: http://purl.stanford.edu/hm635pf1476
ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy.
Stephan Graham, Primary Adviser
I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy.
Donald Lowe
I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy.
Allegra Hosford Scheirer
Approved for the Stanford University Committee on Graduate Studies. Patricia J. Gumport, Vice Provost for Graduate Education
This signature page was generated electronically upon submission of this dissertation in electronic format. An original signed hard copy of the signature page is on file in University Archives.
iii ABSTRACT
The East Coast Basin (ECB) of the North Island, New Zealand contains active petroleum systems and has been explored intermittently since the late 1800s. Despite a few small discoveries, the basin is non-commercial largely due to stratigraphic and structural complexities associated with its development on the Hikurangi convergent margin. The major petroleum system risks are the presence of reservoir rock and good potential, mature source rock. Additionally, high overpressures have caused significant drilling problems, representing both a financial burden and a safety hazard for exploration. This dissertation investigates the petroleum system elements and processes of the ECB, and outlines the importance of convergent margin structure on reservoir architecture, overpressure generation and distribution, and source rock maturation. Each of the three chapters addresses aspects of the petroleum system. Chapter 1 focuses on the reservoir rock though stratigraphic and architectural analysis of an outcropping deep-water turbidite deposit, representing a reservoir analog for the basin. Chapter 2 establishes the structural and stratigraphic framework for the basin through geologic time, providing a means to understand and predict the development of overpressure. Lastly, Chapter 3 assesses the source rock maturation in the ECB through evaluation of the paleo-basal heat flow and structurally-controlled burial history. This dissertation integrates data from a variety of disciplines (sedimentology, structure, geomechanics, geochemistry) and scales (well samples, well logs, outcrop, seismic data) in order to provide a robust basin analysis of the ECB.
Chapter 1 presents a detailed outcrop interpretation and depositional model for the deep-water Hikuwai sandstone. The sandstone is interpreted to represent a deep-water frontal lobe system in a trench-slope setting based on stratigraphic and architectural analysis. Six lithofacies are defined from detailed stratigraphic measurements. A plan-form lobe model is proposed containing a distributary network of meter-scale erosional channels and scours on its surface. The model is based on
iv high-resolution outcrop data from this study, large-scale morphology data from analogous near-surface seismic images, and experimental and numerical modeling. The model suggests lobe lithofacies depend on their proximity to the sediment source, and their proximity to a distributary channel and/or scour. The basin setting is interpreted to be a weakly to moderately confining trench slope setting where sediment is directed through longitudinal corridors created by fault-controlled ridges. A depositional model is developed from architectural analysis of the lithofacies indicating the basin filled from north to south in four phases: 1) lobe aggradation related to healed slope accommodation, 2) retrogradation and lateral migration of the system 3) back-stepping of the system upslope causing reduced confinement and allowing flows to become wider, longer, and thinner, and 4) shut off of sediment supply and mass wasting, representing either renewed fault movement or equilibration of the system to the regional slope profile. The depositional model conceptually relates lobe lithofacies to stages of filling healed slope accommodation. This chapter was published in Marine and Petroleum Geology in February 2014, co-authored by Stephan Graham, who contributed to the conception of this study and the scientific interpretation. It presents detailed stratigraphic and architectural data useful for geomodeling analogous reservoirs. The relation of lithofacies to filling stages enables application of the depositional model to other healed slope deposits in weakly confined, elongate basins, including other trench slope settings, regions affected by mud diapirism, and submarine canyons such as offshore Brunei and the Niger Delta slope.
Chapter 2 examines the evolution of pore pressure and porosity in fault-bound pressure compartments in Hawke Bay of the ECB using two-dimensional basin and petroleum system modeling (BPSM). The smectite-rich Eocene Wanstead Formation forms an effective seal across the basin, creating high overpressure in the Cretaceous through Paleocene units below due to disequilibrium compaction. The chapter first establishes the basin framework through seismic interpretation, structural reconstruction, and pore pressure calibration to basin lithologies. Structural regimes
v are defined based on their style of deformation and structural and stratigraphic burial histories. The generation and distribution of overpressure is first modeled with a Terzaghi approach to examine the interplay of stratigraphic and structural elements on pore pressure evolution, including the influence of faults, erosion, structural thickening, and seal effectiveness of the Wanstead Formation. Results show that hydraulic fracturing is likely occurring in sub-Wanstead Formation source rocks, which is a favorable setting for potential shale gas plays. Models are then simulated with a poroelastic approach to investigate the potential impact of horizontal stress due to tectonic forces on pore pressure. Results show that bulk shortening modestly increases pore pressure. When 5% or greater shortening occurs, the horizontal stress may approach and exceed vertical stress for part of the basin history. Overpressure made the basin sensitive to subtle tectonic changes in the basin’s stress regime, promoting an evolution of structural deformational styles observed in the basin. This chapter will be submitted to Basin Research with Kristian Meisling and Stephan Graham as co-authors. Dr. Meisling provided significant assistance in the seismic interpretation and structural reconstruction of the modeled two-dimensional transect through Hawke Bay. Dr. Graham contributed to the conception and direction of this study. All authors contributed to the scientific interpretation. This paper is significant in that it demonstrates an attempt to quantify the impact of horizontal stress on pore pressure in a petroleum basin, which is often qualitatively suggested but rarely tested. It also supports the use of paleo-stepping models in complex structural regimes to best represent burial history and basin geometry, and model pore pressure evolution.
Chapter 3 evaluates the paleo-thermal regime and maturation of two prospective source rocks, the Waipawa Black Shale and Whangai Formation in Hawke Bay of the ECB using two-dimensional BPSM. The Waipawa Black Shale has the best source rock potential in the basin. The Upper Calcareous Member of the Whangai Formation has low source rock potential, but is also considered due to tentative correlation with onshore oil seeps. Three paleo-basal heat flow scenarios are
vi constructed based on calibration to vitrinite-inertinite reflectance and fluorescence analysis, apatite fission track analysis, Tmax from RockEval, the thermal alteration index, and present-day temperatures from wells. This study favors two of the paleo- basal heat flow scenarios because they are most consistent with the known tectonic history of the basin. We examine the impact of the paleo-basal heat flow on the timing and extent of source rock transformation for four distinct structural sections in Hawke Bay. BPSM results indicate that the timing and extent of source rock transformation depends both on the modeled heat flow scenario and the burial and uplift history associated with deformation in the structural section. For the two tested basal heat flow scenarios, source rock transformation is concurrent with the deposition of reservoir and seal rock and trap formation. Therefore, reservoir-seal targets in Hawke Bay need to be assessed in terms of their depositional age relative to their local burial history and their structural section to determine if there is a favorable timing of petroleum system events. This chapter will be submitted to AAPG Bulletin with co-authorship of Stephan Graham, who contributed to conception of the study and the scientific interpretation. Although the study is case specific to the ECB, it demonstrates the importance of incorporation of a structural model in BPSM to determine the timing of petroleum system events. The methodology outlined by this study can be applied to other structurally complex and overpressured basins, such as the California Coastal Ranges and Sacramento basin, the Barbados accretionary prism, and the Kutai Basin of Indonesia.
vii ACKNOWLEDGMENTS
My PhD in many ways has been a balancing act as I straddled two fantastic research groups through my research – the Stanford Project on Deep-water Depositional Systems (SPODDS) and the Stanford Basin and Petroleum System Modeling Group (BPSM). I certainly could never have pulled it off without significant help and support along my Ph.D. trek. First and foremost I would like to thank my advisor, Steve Graham, for letting me escape “Wall Street” to get back to my geology roots. Steve always provided me with excellent guidance, whether scientific-, academic-, career-, or life-related decisions. He always encouraged my scientific pursuits, and helped pull me out of rabbit holes when required. I feel so lucky to be a part of his group because in many ways they became my family in California. Don Lowe has been an unofficial advisor to me, and a large part of my development as a scientist. Don is possibly one of the greatest teachers I have come across ever both in and out of the field, and has helped me become an observant, methodical, and confident sedimentologist. Kris Meisling is the reason Chapters 2 and 3 came together in my thesis. Kris helped me tackle my first big seismic interpretation – the Hikurangi convergent margin, and taught me how to put lines on paper. Kris’s energy and enthusiasm for the science reinvigorated me throughout the process and I am eternally grateful for his support. I would also like to thank my two other committee members, Allegra Hosford Scheirer and Tapan Mujerki. Allegra has consistently been one of my fiercest supporters in making sure I had all the tools and resources I needed be a successful basin modeler. She has also been a great teacher and friend. Tapan always had his office door open to me and has greatly helped me to grow as an interdisciplinary scientist. His questions about my research always make me consider topics from new perspectives.
viii Many people from across the world in New Zealand require my acknowledgement and thanks. David Francis of Geologic Research Ltd was instrumental in introducing me to the field in the East Coast Basin. The support of numerous people from GNS Science also made this research possible, and I greatly value my relationships with these remarkable scientists. Rob Funnell supplied me with buried reports and articles on the East Coast Basin and many important contacts, setting me up with data to build a robust basin and petroleum system model. He has been a great friend and generous host to a graduate student in a foreign land. Martin Crundwell, Brad Field, Andy Nicol, Kyle Bland, Richard Sykes, and Peter King also provided both academic and logistical support in the field, for which I am grateful. They have been great resources to me throughout my Ph.D. Discussions with Jane Newman helped me to better understand the VIRF method and the significance of Hawke Bay-1 results. I really appreciated her enthusiasm for the project and her patience with me as I learned. Pop Milner of Titirangi Farm kindly provided me with access to the outcrops, looked out for me when weather got rough, and made me feel at home in Tolaga Bay. He also saved the day during a SPODDS field trip when numerous cars got stuck in the mud. I greatly miss my time spent at camp with Pop, Val, Ken, Mike, and Trina from Tolaga Bay. As interdisciplinary work goes, I relied on a number of excellent scientists from Stanford to complete my Ph.D. Les Magoon sat down with me for hours deciphering well reports to help me compile pressure data. Noelle Schoellkopf provided significant guidance with pressure calibration and the collection and correction of temperature data. Tim McHargue led several excellent discussion groups on deep-water systems, and I thank him for keeping me excited and engaged in the deep-water community. Ken Peters taught me the foundations of basin and petroleum system modeling through his course and provided direction to my BPSM projects. Carolyn Lampe helped me numerous times navigate problems in Petromod®. Oliver Schenk taught several excellent user courses for Petromod® software and was often the first line of defense when I came across software issues. Trevor Dumitru has been a great teacher and always made himself extremely available to me. He helped me
ix immensely with apatite fission track modeling, and also instructed me on zircon separation techniques. Schlumberger provided all of the software and software support used in this dissertation, including Petrel®, Dynel®, and Petromod®. They provided me with significant support for construction of the 2D Teclink Petromod® model. Andy MacGregor kindly invited me to work with the Petromod® experts in the Aachen office. Thorsten Joppen and Martin Neumaier were particularly helpful in development of the Teclink® model. Funding is a large part of the success of a research project, so I would like to thank the current affiliate members of the SPODDS and BPSM research groups. Current SPODDS affiliates include Aera, Anadarko, BHP Billiton, Chevron, ConocoPhillips, Hess, Karoon, Nexen, Oxy, Petrobras, RAG, Saudi Aramco, Schlumberger, Shell, Talisman Energy, Statoil, Eni, Reliance, and PTTEP. Current BPSM affiliates include Aera, BP, Chevron, ConocoPhillips, Great Bear Petroleum, Hess, Murphy Oil, Nexen, Oxy, Petrobras, Saudi Aramco, and Schlumberger. For several years I also received funding through the Chevron Fellowship, which was greatly appreciated. Additionally, I received funding for research projects and travel from the AAPG Grants-in-Aid, Chevron Grant, GSA Grant, ConocoPhillips, and GSA-USNC/GS Early Career Scientist Travel Fellowship Grant Award. I would like to specially thank the Stanford Sedimentary Research Group, SPODDS, and the BPSM group for some fantastic field trips. Our travels to the Book Cliffs, Death Valley, Saudi Arabia, Canadian Rockies, New Zealand, Ouachitas, and throughout California have left me with a rich store of geologic experiences and many great memories. In particular, the trip to Saudi Arabia was a once in a lifetime experience in terms of the geology, culture, and friendships formed with Middle Eastern students and faculty. I thank Don for his efforts in making this happen, and Saudi Aramco for the sponsorship of the Stanford-KFUPM trips. I have loved traveling to these places with such a dynamic and engaging research group, including Zane Jobe, Anne Bernhardt, Lisa Stright, Julie Fosdick, Katie Maier, Meng He, Danica Dralus, Jon Rotzien, Larisa Masalimova, Glenn
x Sharman, Lizzy Trower, Tess Menotti, Keisha Hazen, Theresa Schwartz, Matt Malkowski, Lauren Shumaker, Nora Nieminski, Wisam AlKawai, Inessa Yurchenko, Amrita Sen, Yao Tong, Danielle Zetner, Moy Hernandez, Nadja Drabon, Lauren Schultz, Zack Sickman, and Nilay Gungor, In particular I would like to thank Glenn Sharman, Katie Maier, Tess Menotti, Lauren Shumaker, and Nora Nieminski for providing excellent field assistance in New Zealand. All of them provided thoughtful discussion on the outcrop and excellent culinary support far exceeding my own ability (excepting Glenn, of course). A lot of work goes on behind the scenes, and I would like to thank a number of people in the GES Department including Yvonne Lopez, Stephanie James, Lauren Nelson, Alyssa Ferree, Tom Koos, Javier Illueca, Leslie Honda, and Lorraine Sandoval for their support. Last but not least, I would like to thank my family and friends for their support and encouragement from the beginning. Chris, my husband, left his job in New York to follow me here on this endeavor. He as always helped me keep my focus on the bigger picture (life), and has encouraged me to fulfill my own professional aspirations, even when it meant months apart for field work and summer internships. My parents, Larry and Alex Burgreen, have provided me with steady guidance throughout my life. I feel so lucky to have a very open and honest relationship with them. They have encouraged me when I needed encouraging, questioned me when I made decisions too fast, and stood behind me no matter what. My best friend, Nicole Cannizzaro, has remained one of my biggest cheerleaders despite living across the country, and regularly inspires me to be a better person in the world. And finally, my Grandma, for always remaining proud of me, and encouraging me to finish up as soon as possible. The day is here!
xi TABLE OF CONTENTS
ABSTRACT ...... IV
ACKNOWLEDGMENTS ...... VIII
TABLE OF CONTENTS ...... XII
LIST OF TABLES ...... XV
TABLE OF FIGURES ...... XV
LIST OF APPENDICES ...... XIX
CHAPTER 1 ...... 1
EVOLUTION OF A DEEP-WATER LOBE SYSTEM IN THE NEOGENE TRENCH- SLOPE SETTING OF THE EAST COAST BASIN, NEW ZEALAND: LOBE STRATIGRAPHY AND ARCHITECTURE IN A WEAKLY CONFINED BASIN CONFIGURATION ...... 1 ABSTRACT ...... 2
INTRODUCTION ...... 3 GEOLOGIC BACKGROUND ...... 5 Geologic Setting of the East Coast Basin ...... 5 Geologic Setting of the Hikuwai sandstone ...... 7 DATA AND METHODS ...... 8
LITHOFACIES ANALYSIS ...... 9 LF1: Thin- to medium-bedded sandstone and mudstone ...... 9 LF2: Thin- to very thick-bedded sandstone and mudstone ...... 10 LF3: Medium- to very thick-bedded sandstone and mudstone ...... 11 LF4: Thick- to very thick-bedded sandstone with mud clast conglomerate ...... 13 LF5: Chaotic and contorted sandstone, tuff, and mudstone ...... 14 LF6: Mudstone ...... 15
ARCHITECTURAL ANALYSIS ...... 15 Mahanga Stream (southern) section ...... 15 Tolaga Bay South (northern) section ...... 16 Cook’s Cove South (eastern) section ...... 17 Wairere and Waihi Beach section ...... 18
xii INTERPRETATION ...... 18 Environment of Deposition ...... 18 Lobe Morphology and Lithofacies Distribution ...... 20 Basin Configuration ...... 24 System Evolution ...... 25
CONCLUSIONS ...... 28
ACKNOWLEDGMENTS ...... 29 REFERENCES CITED ...... 30
FIGURES ...... 42
CHAPTER 2 ...... 67
BASIN AND PETROLEUM SYSTEM MODELING OF THE EAST COAST BASIN, NEW ZEALAND: A TEST OF OVERPRESSURE SCENARIOS IN A CONVERGENT MARGIN ...... 67
ABSTRACT ...... 68 INTRODUCTION ...... 69
GEOLOGIC BACKGROUND ...... 71 Present-Day Pore Pressure Distribution ...... 74 MODELING ...... 77 CM05-01 Interpretation ...... 78 Basin Modeling ...... 83
RESULTS ...... 88 Base Case, Terzaghi type model ...... 88 Poroelastic, Horizontal Compression Case ...... 93
DISCUSSION ...... 96 Terzaghi versus poroelastic models ...... 96 Stress Environment ...... 96 Seal Effectiveness ...... 97 Model Limitations ...... 98 Petroleum Implications ...... 99 CONCLUSIONS ...... 100
ACKNOWLEDGMENTS ...... 102
REFERENCES CITED ...... 103
xiii FIGURES ...... 120
TABLES ...... 148
CHAPTER 3 ...... 150
THERMAL REGIME EVALUATION AND SOURCE ROCK TRANSFORMATION IN HAWKE BAY, NEW ZEALAND ...... 150 ABSTRACT ...... 151
INTRODUCTION ...... 152
BACKGROUND ...... 154 Physiography ...... 154 Basin Stratigraphy ...... 154 Petroleum Systems ...... 155
BASIN AND PETROLEUM SYSTEM MODELING ...... 157 Structural Sections of CM05-01 ...... 157 Modeled Layers ...... 158 Source Rocks ...... 158 Boundary Conditions ...... 162
EVALUATION OF PALEO-BASAL HEAT FLOW ...... 162 Present-Day Thermal Regime ...... 162 Paleothermometers of the East Coast Basin ...... 163 Basal Heat Flow Calibration ...... 165 BASIN AND PETROLEUM SYSTEM MODELING RESULTS ...... 169 Transformation of the Waipawa Black Shale ...... 169 Transformation of the Whangai Formation ...... 172 DISCUSSION ...... 172 Prospective Source Rocks ...... 172 Evaluation of Paleo-Basal Heat Flow Scenarios ...... 173 Transformation of the Waipawa Black Shale ...... 174 Unconventional resource play potential ...... 175 CONCLUSIONS ...... 175
ACKNOWLEDGMENTS ...... 176 REFERENCES CITED ...... 177
FIGURES ...... 188
xiv TABLES ...... 200
APPENDICES ...... 201 CHAPTER 1 APPENDICES ...... 201
CHAPTER 3 APPENDICES ...... 227
LIST OF TABLES CHAPTER 2 Table 1: Lithologic properties for basin and petroleum system modeling ...... 148 Table 2: Heat flow scenarios ...... 149
CHAPTER 3 Table 1: Ages of horizons and paleosections ...... 200
TABLE OF FIGURES CHAPTER 1 Figure 1: Terraced slope and structurally defined tortuous corridors of the analogous offshore Oregon convergent margin ...... 42 Figure 2: Topographic and bathymetric map of the North Island, New Zealand, and geologic map of the Tolaga Bay study area: Topographic and bathymetric map of the North Island, New Zealand, and geologic map of the Tolaga Bay study area ...... 43 Figure 3: Two-dimensional seismic reflection data and interpretation of offshore Tolaga Bay demonstrating listric normal growth faults ...... 44 Figure 4: Geologic map of the Tolaga Bay area with measured section locations and paleocurrent data ...... 45 Figure 5: Generalized chronostratigraphy and lithostratigraphy around Tolaga Bay ...... 46 Figure 6: Quantitative description of lithofacies ...... 47 Figure 7: Lithofacies 1, thin- to medium-bedded sandstone and mudstone, stratigraphy and architecture at the Mahanga Stream field locality ...... 51
xv Figure 8: Lithofacies 2, thin- to very thick-bedded sandstone and mudstone, stratigraphy and architecture at the Mahanga Stream field locality ...... 52 Figure 9: Incisional surfaces in Lithofacies 2 at the Mahanga Stream field area ... 53 Figure 10: Lithofacies 3, medium- to very thick-bedded sandstone and mudstone, stratigraphy and architecture at the Hole in the Wall field locality ...... 54 Figure 11: Incisions and nested incisions in Lithofacies 4 at the Cook's Cove field locality ...... 55 Figure 12: Lithofacies 4, thick- to very thick-bedded sandstone with mud clast conglomerate, stratigraphy and architecture at the Hole in the Wall field locality ...... 56 Figure 13: Lithofacies 5, chaotic and contorted sandstone, tuff, and mudstone, lithology and architecture at the Cook's Cove field locality ...... 57 Figure 14: Photo-panoramas of lithofacies in the Mahanga Stream, Tolaga Bay, Cook's Cove South, and Waihi Beach field areas ...... 58 Figure 15: Examples of high-resolution photo-panoramas used for architectural analysis ...... 59 Figure 16: Stratigraphic section of the Cook's Cove South field area and identified lithofacies ...... 60 Figure 17: Stratigraphic section of the upper Mapiri Formation in the Wairere Beach field area ...... 61 Figure 18: Conceptual model of the Hikuwai sandstone lithofacies distribution across a lobe and comparison to amplitude extractions of lobe composites in offshore western Africa ...... 62 Figure 19: Possible basin configurations for deposition of the Hikuwai sandstone ...... 63 Figure 20: Conceptual model of the four phase evolution of basin fill ...... 64 Figure 21: Generalized 3D model of lithofacies distribution of the Hikuwai sandstone and Mapiri Formation in the Tolaga Bay area ...... 65
xvi CHAPTER 2 Figure 1: Geologic map of the East Coast Basin, North Island, New Zealand ...... 120 Figure 2: Tectonostratigraphy of the East Coast Basin ...... 121 Figure 3: Mud weight derived pore pressure for East Coast Basin wells ...... 122 Figure 4: Porosity - depth and porosity - permeability relationships from well samples ...... 123 Figure 5: Pore pressure summary of the Awatere-1 well ...... 124 Figure 6: Pore pressure summary of the Titihaoa-1 well ...... 125 Figure 7: Seismic stratigraphy and structural interpretation of the CM05-01 seismic line in offshore Hawke Bay ...... 126 Figure 8: Structural reconstructions of the CM05-01 line ...... 128 Figure 9: Present-day lithostratigraphy of the 2D basin and petroleum system model ...... 131 Figure 10: Porosity - effective stress relationships for modeled lithologies ...... 132 Figure 11: Porosity - permeability relationships for modeled lithologies ...... 133 Figure 12: Pressure calibration to the Hawke Bay-1 well ...... 134 Figure 13: Development of overpressure through time in the 2D basin and petroleum system model ...... 135 Figure 14: Effects of uplift and erosion on pore pressure ...... 140 Figure 15: Present-day modeled porosity preservation due to overpressure .... 141 Figure 16: Pore pressure evolution and stress to failure of the Whangai Formation ...... 142 Figure 17: Evolution of principal xx and zz stresses for the Whangai Formation in the Lachlan basin ...... 143 Figure 18: Leak off test data and mud weight derived pore pressure for East Coast Basin wells ...... 144 Figure 19: Present-day fracturing based on 2D basin and petroleum system modeling ...... 145 Figure 20: Stress to failure for the Wanstead Formation using poroelastic modeling ...... 146
xvii Figure 21: Present-day transformation ratios of the source rocks for high and low heat flow scenarios modeled ...... 147
CHAPTER 3 Figure 1: Map of hydrocarbon indicators and wells in the East Coast Basin, New Zealand ...... 188 Figure 2: Chronostratigraphy, petroleum system elements, and burial histories in Hawke Bay ...... 189 Figure 3: Structural sections of the Hawke Bay 2D basin and petroleum system model ...... 190 Figure 4: Source rock properties of the Whangai Formation ...... 191 Figure 5: Source rock properties of the Waipawa Black Shale ...... 192 Figure 6: Comparison of vitrinite reflectance analysis and vitrinite-inertinite reflectance and fluorescence analysis for Hawke Bay-1 and Opoutama-1 .. 193 Figure 7: Vitrinite-inertinite reflectance and fluorescence by geologic age for maximum burial depths ...... 194 Figure 8: Heat flow calibration using one-dimensional basin and petroleum system modeling ...... 195 Figure 9: Heat flow scenarios used in modeling through geologic time ...... 196 Figure 10: Paleo-temperatures for Opoutama-1 from apatite fission track modeling ...... 197 Figure 11: Transformation ratios through time for the Waipawa Black Shale and Whangai Formation for three basal heat flow scenarios by structural section ...... 198 Figure 12: Temperature and burial history of the Waipawa Black Shale through time for three basal heat flow scenarios by structural section ...... 199
xviii LIST OF APPENDICES CHAPTER 3 Appendix 1: Summary of biostratigraphic data ...... 201 Appendix 2: Biostratigraphic reports ...... 202 Appendix 3: Frequency factor and activation energies for modeled kinetics ...... 227 Appendix 4: Original and corrected temperature data used for present-day geothermal gradient estimation ...... 228 Appendix 5: Vitrinite-Inertinite Reflectance and Fluorescence Technique ...... 234 Appendix 6: Vitrinite-inertinite reflectance and fluorescence data used in heat flow calibration ...... 238 Appendix 7: One-dimensional basin and petroleum system models used for heat flow calibration ...... 240
xix CHAPTER 1
EVOLUTION OF A DEEP-WATER LOBE SYSTEM IN THE NEOGENE TRENCH-SLOPE SETTING OF THE EAST COAST BASIN, NEW ZEALAND: LOBE STRATIGRAPHY AND ARCHITECTURE IN A WEAKLY CONFINED BASIN CONFIGURATION
EVOLUTION OF A DEEP-WATER LOBE SYSTEM IN THE NEOGENE TRENCH-SLOPE SETTING OF THE EAST COAST BASIN, NEW ZEALAND: LOBE STRATIGRAPHY AND ARCHITECTURE IN A WEAKLY CONFIED BASIN CONFIGURATION
Blair Burgreen and Stephan Graham Geological and Environmental Sciences, Stanford University, Stanford, CA 94305
ABSTRACT This study presents a new depositional analysis of the stratigraphic architecture of a deep-water lobe system in a trench-slope basin setting by examining the upper Miocene Hikuwai sandstone and Mapiri Formation of the East Coast Basin (ECB) in the Tolaga Bay area, New Zealand. The Hikuwai sandstone is up to 385 meters thick and is enveloped by the mud-rich middle and upper Mapiri Formation. Stratigraphic sections measured at centimeter-scale and high-resolution photo-panoramas were collected from sea-cliff exposures for stratigraphic and architectural analysis and definition of six lithofacies. The Hikuwai sandstone is interpreted to represent a succession of frontal lobe deposits that contain a distributary network of meter-scale erosional channels and scours on their surface. Lobe lithofacies depend on their proximity to the sediment source, and their proximity to a distributary channel and/or scour. The late Miocene basin setting is interpreted to be a weakly to moderately confined trench-slope basin. The basin configuration controlled the development of the depositional system through elongate fault-controlled ridges that directed sediment dispersal pathways through longitudinal troughs. The basin filled from north to south in four phases: 1) lobe aggradation related to healed slope accommodation, 2) retrogradation and lateral migration of the system 3) back-stepping of the system upslope causing reduced confinement and allowing flows to become wider, longer, and thinner, and 4) shut off of sediment supply and mass wasting of the upper Mapiri Formation, representing either renewed fault movement or equilibration of the system to the regional slope profile.
2 This paper provides a detailed description of the internal structure of lobes in a trench- slope setting, and a depositional model that relates lobe lithofacies to the filling of healed slope accommodation. Therefore, this work presents an analog applicable for elongate basins, such as in the trench slope or settings with mud diapirism, where only seismic- scale or limited data is available.
INTRODUCTION Near-seafloor studies of modern to very young deep-water intra-slope deposits have shown that their distribution and shape vary dramatically depending on the slope gradient, basin geometry and bathymetric features, and sediment supply (Prather et al., 1998; Beaubouef et al., 2003; Booth et al., 2003; Laursen and Normark, 2003; Smith, 2004; Adeogba et al., 2005; Li et al., 2012; Prather et al., 2012a). Although slope basins can contain significant accommodation and host important hydrocarbon reservoirs, the centimeter to meter scale character of their fill and internal structure is poorly understood due to limited sedimentological and stratigraphic data in modern sea-floor studies. This makes prediction of reservoir quality and connectivity particularly challenging in slope settings. Intra-slope basins exhibit a range of morphologies depending on their tectonic setting. Smith (2004) identified three types of confined intraslope basins: (1) silled sub- basins that fully confine the flow, (2) partially silled basins with lateral escape paths, and (3) connected tortuous corridors that direct the flow basinward. Fill-and-spill depositional models for silled basins are well developed due to extensive studies in areas such as the Gulf of Mexico (Prather et al., 1998; Prather, 2000; Beaubouef and Friedmann, 2000; Prather et al., 2012a). Tortuous corridor basins can also be important reservoirs, and include regions such as the Niger Delta slope (Hooper et al., 2002; Steffens et al., 2003; Adeogba et al., 2005; Prather et al., 2012b) and offshore Brunei (Demyttenaere et al., 2000; Steffens et al., 2003) where mud diapirism and associated thrust faulting create mobile shale ridges separated by synclinal troughs (Wood et al., 2004). In addition to these basin settings, other elongate depressions on the slope, such as large submarine canyons, could also be considered as a type of tortuous corridor accommodation. Trench- slope basins, which also fall into the connected tortuous corridors category, are less well
3 studied. The trench-slope is typically characterized by margin-parallel, fault-controlled ridges that direct sediment longitudinally through their troughs (Fig. 1; Underwood and Bachman, 1982). Modern studies in this setting have been conducted in Indonesia (the Sunda Fore-arc), the Aleutian trench (Alaska), the Japan trench, and offshore Columbia using seismic data sets and piston cores (Moore et al., 1982; Underwood and Norville, 1986; Okada, 1989; Vinnels et al., 2010). While these studies have demonstrated the importance of slope morphology in dictating flow pathways and regions of deposition, they lack the stratigraphic resolution to develop a depositional framework. A few studies have utilized outcrops to address stratigraphic development in the trench-slope (McCrory, 1995; Lomas, 1999; Bailleul et al., 2007), but most studies are limited due to intense deformation of ancient convergent margin deposits (Underwood and Moore, 1995). Additionally, trench-slope deposits are not commonly exposed in outcrop and therefore opportunities for study are limited. Therefore, this study provides a rare opportunity to investigate the detailed stratigraphic architecture associated with deposition in the trench- slope. Deep-water deposits in trench-slope settings often have unusual shapes and dimensions due to the receiving basin configuration and evolution, which impacts the stratigraphy and architecture of the depositional elements. High-resolution seismic imagery has shown that deep-water lobe morphology is largely dependent on basin floor bathymetry (Gervais et al., 2006; Hay, 2012). Lobes are defined in this study as deposits where sediment gravity flows decelerate and deposit due to lack of confinement. With improvements in near-surface imaging technology, a new understanding of lobe systems has emerged. Many lobes have a complex distributary network on their surface (Nelson et al., 1992; Twichell et al., 1992; Adeogba et al., 2005; Jegou et al., 2008; Prather et al., 2012b), and several terms have been applied to describe this type of distributive lobe system, including “braided” marine fan (Belderson et al., 1984), distributary channel-lobe complex (Beaubouef and Friedmann, 2000), scoured lobe (Piper et al., 1999; Abreu et al., 2006), and distributary lobe complex (Hay, 2012). This depositional element has been recognized in modern studies of fully to weakly confined basins where flows diverge then reconverge into a single channel (Adeogba et al., 2005; Prather et al., 2012b), or continue to diverge and thin as confinement and slope gradient
4 is reduced (Hay, 2012). However, ancient deposits of distributive lobe systems are required to better quantify the dimensions of channelization and the character of its fill. In reservoir modeling, the extent of channelization and nature of the fill (i.e., mud-lined channels versus sand-on-sand contacts) within lobes will impact their connectivity (Snedden, 2013), and therefore it is important to understand their occurrence. This study presents a new stratigraphic and architectural analysis for the Hikuwai sandstone, a fine-grained Miocene deep-water unit interpreted to represent a system of lobes in the trench-slope setting of the East Coast Basin (ECB), North Island, New Zealand (Fig. 2). The Hikuwai sandstone is relatively undeformed, and therefore provides an uncommon opportunity to investigate the lithofacies, internal architecture, and stratigraphic evolution of a deep-water system in the trench-slope setting. This study develops a lithofacies scheme for the Hikuwai sandstone and the overlying mud-rich upper Mapiri Formation based on sedimentological, stratigraphic, and architectural data. A conceptual model of lithofacies distribution within the lobe is developed based on high-resolution outcrop data, large-scale morphology data from analogous near-surface seismic images, and experimental and numerical modeling. The lobe model is used as a building block to create a four-phase depositional model of the turbidite system as it filled slope accommodation, and then is linked to pseudo-wells through the outcrop to show corresponding lithofacies stacking patterns in different regions of the basin. The high-resolution lithofacies scheme developed in this study can be applied to the basin- scale and is readily transferable for reservoir modeling in the trench-slope and other similarly structured basin settings, such as basins dominated by mud diapirism.
GEOLOGIC BACKGROUND Geologic Setting of the East Coast Basin The ECB is a partly emergent forearc basin on the eastern side of the North Island, New Zealand (Fig. 2A). As part of a convergent margin setting, the basin is bordered by the Hikurangi trench to the east and by the Axial Ranges to the west. The basin formed around 23-25 Ma with the southward propagation of subduction along the Hikurangi trench (Ballance, 1976; Pettinga, 1982; Rait et al., 1991; Ballance, 1993). The ECB has a complex history including compressional and extensional tectonic regimes likely related
5 to changes in plate configuration, the subduction of seamounts and rugose seafloor, and other subduction processes such as accretion and subduction erosion (Davey et al., 1986; Lewis and Pettinga, 1993; Chanier et al., 1999; Collot et al., 2001; Lewis et al., 2004). Offshore seismic-reflection data to the south in Hawke Bay reveal a complex history of deformation including a shortening phase during early-mid Miocene time, followed by basin extension in mid-Miocene time, and finally basin inversion beginning by Pliocene time (Barnes et al., 2002; Barnes and Nicol, 2004). Although most of the basin is still experiencing compression, the Raukumara region, which includes the study area, is currently undergoing extension (Nicol et al., 2007). The offshore region may provide some insights for controls on sediment accumulation and basin configuration during Miocene time in the Tolaga Bay area. Offshore growth structures from listric normal faulting (Fig. 3) show that sediment accumulation was largely controlled by fault- generated seafloor topography, creating localized areas of accommodation (i.e., Timbrell, 2003). These extensional features result from subduction erosion in the northern portion of the ECB (Lewis and Pettinga, 1993; Barnes et al., 2010), and are likely post-Miocene in age (Nicol et al., 2007). Seafloor imaging of the offshore Wairarapa region shows numerous margin- parallel ridges related to the development of listric thrust faults, which construct intervening depressions on the order of 10-100 kilometers long (Fig. 2A, 2B; Field et al., 2006). The significance of these fault-created features in influencing paleo-sediment delivery pathways has been noted only locally in the Akitio Basin of the onshore Wairarapa region (Bailleul et al., 2007). However, the abundance of localized stratigraphic units in the ECB is likely a manifestation of the influence of faulting in subdividing the basin. These two distinct present-day structural regimes for the Raukumara and Wairarapa regions represent possible analogs for the basin configuration of the study area during Miocene time. Although the exact configuration cannot be reconstructed due to onshore structural complexity, erosion, and vegetative cover, small fault-controlled areas of accommodation along the slope likely influenced the deposition of the Hikuwai sandstone.
6 Geologic Setting of the Hikuwai sandstone The upper Miocene deep-water Hikuwai sandstone is exposed in the Tolaga Bay area with a total outcrop area of about 40 km long and 20 km wide (Fig. 2C). However, these measures only provide an approximation of the areal size of the sandstone because of documented compressional, extensional, and strike-slip faulting in the region that prevent correlation between outcrops. The Hikuwai sandstone is best exposed as part of a synclinal structure in coastal cliffs south of Tolaga Bay ranging up to 200 m high (Fig. 4). The base of the cliffs is accessible along 9 km of coastline and enables documentation of much of the approximately 385 m vertical section. In the Tolaga Bay study area, the Hikuwai sandstone is enveloped by the mud- rich middle and upper Mapiri Formation, which are early to late Tongaporutuan and late Tongaporutuan age (New Zealand Geologic Time Scale, (Hollis et al., 2010)) or approximately early to late Tortonian age (International Geologic Time Scale, (Gradstein et al., 2004)), respectively. They were deposited in lower bathyal water depths based on paleontological data from the New Zealand Fossil Record File held at GNS Science (Fig. 5; GNS, Fossil Record Electronic Database). Additional biostratigraphic data for the Tolaga Bay and East Coast region conducted for this study is in Appendices 1 and 2. The Mapiri Formation contains numerous interbedded arc-derived rhyolitic tuff layers that can attain several meters in thickness in the Tolaga Bay study area (Gosson, 1986). The middle Mapiri Formation transitions into the Hikuwai sandstone over about 10 cm, whereas the Hikuwai sandstone grades into the upper Mapiri Formation over about 10-20 m. The shelfal Tokomaru Formation unconformably overlies the upper Mapiri Formation. The unconformity extends throughout the Raukumara region and reflects a major uplift event (Buret et al., 1997). An older turbidite system of early Tongaporutuan age (or early Tortonian age), the Kaiaua sandstone, is exposed underlying the Hikuwai sandstone and middle Mapiri Formation to the north at Marau Point (Fig. 2C), although is not present in the Tolaga Bay study area (Francis, 2003). The Hikuwai sandstone is a very fine to fine-grained turbidite system largely comprised of partial Bouma sequences (Bouma, 1962). In the Tolaga Bay study area, the sandstone is exposed in its greatest thickness. Blom (1982) conducted the most recent detailed study of the Hikuwai sandstone, which recorded the mineralogy, sedimentology,
7 stratigraphy, and paleontology at sub-meter scale. She identified trace fossils, including Ophiomorpha, Zoophycos, Paleodictyon, and Chondrites, and foraminifera to help constrain paleodepth and age. Blom (1982) interpreted the sandstone to be deposited in a deep-water environment by turbidity currents. Updated biostratigraphic analysis of benthic foraminifera from the study area indicates that the basin subsided from middle bathyal depths to lower bathyal depths during the late Tongaporutuan (or late Tortonian; GNS, Fossil Record Electronic Database). Francis (2003) conducted a survey of the Hikuwai sandstone for petroleum services and mapped much of the unit’s outcropping extent. In previous studies, reports, and field maps, the Hikuwai sandstone is also referenced as the Kaiti sandstone and the Tokomaru Sandstone.
DATA AND METHODS This study focuses on the Hikuwai sandstone and upper Mapiri Formation in the Tolaga Bay study area, where the sandstone and mudstone is best exposed and accessible along the base of the sea cliffs. Taking advantage of an approximately east-west synclinal structure, a series of short, vertical sections were measured in the Hole in the Wall, Cook’s Cove, and Mahanga Stream field areas, while continuous vertical sections were collected in the Cook’s Cove South and Wairere Beach field areas. Thirty-nine stratigraphic sections of the Hikuwai sandstone were measured at cm-scale for a total of 309 m of measured section. Five sections of the upper Mapiri Formation were measured at dm-scale for a total of 86 m of measured section (Fig. 4). Bed thickness, sedimentary structures, and grain size were noted and measured in the field. Faulting was commonly observed, but the exact amount of offset was difficult to determine due to the lack of local marker beds and differential weathering in the stratigraphy. However, most faults are minor with meter to sub-meter scale displacement. High-resolution photo-panoramas of the cliffs were taken where section was measured and used in the field to document stratigraphy and architecture, and quantitatively assess degree of incision. Additional high-resolution photographs were taken from offshore for architectural analysis in order to achieve documentation of inaccessible portions of the coast and cliffs. Paleocurrent indicators and bedding attitudes were measured and reconstructed wherever accessible in order to determine the predominant direction of deposition and
8 assess for lateral and vertical changes. Paleocurrent directions were determined exclusively from ripples since sole marks and other paleocurrent indicators were not observed. Outcrop quality of the Hikuwai sandstone is limited inland due to vegetation. Inaccessibility due to coastal remoteness and/or short tide windows are limiting factors elsewhere. Additionally, because there are no key marker horizons within the Hikuwai sandstone, it is impossible to confidently correlate sections between field locations, thereby limiting their utility in developing a depositional model.
LITHOFACIES ANALYSIS We recognize six distinct lithofacies in the Hikuwai sandstone and Mapiri Formation based on stratigraphic sections: 1) thin- to medium-bedded (3 to 30 cm) sandstone and mudstone (LF1), 2) thin- to very thick-bedded (3 to greater than 100 cm) sandstone and mudstone (LF2), 3) medium- to very thick-bedded (10 to greater than 100 cm) sandstone and mudstone (LF3), 4) thick- to very thick-bedded (30 to greater than 100 cm) sandstone with mud clast conglomerate (LF4), 5) chaotic and contorted sandstone, tuff, and mudstone (LF5), and 6) mudstone (LF6). Bed thickness categories are based on the classification by Ingram (1954). LF1-LF4 represent a continuum of lithofacies and therefore their boundaries are typically represented by transition zones. The bed thicknesses of LF1-LF4 are very heterogeneous, and they have primarily been distinguished by their distribution of bed thicknesses. Although a given bed may have a thickness that falls within multiple lithofacies, its ultimate classification depends on the nature of the surrounding beds and degree of heterogeneity. Therefore, each bed can be uniquely classified as a particular lithofacies.
LF1: Thin- to medium-bedded sandstone and mudstone Description LF1 is primarily distinguished by its dominance of thin to medium beds, tabular architecture, and lack of incisional surfaces at the base of beds (Fig. 6A). Most beds range from 3 cm to 30 cm thick (Fig. 6Aiii), and it has an average net-to-gross of 67%. Mud clast conglomerate is uncommon, but occurs locally. This lithofacies has the
9 narrowest range of grain sizes with an average size of lower very fine to upper very fine sand and a maximum grain size of lower fine sand. Although most beds are weathered and/or bioturbated, climbing ripples and convoluted laminations are very common sedimentary structures in this lithofacies representing the Bouma Tc unit, with less common planar laminations, wavy laminations, and ripples. These beds typically have flat to gently undulating bases and lack significant incisional features. Lithofacies architecture is largely tabular and beds are laterally continuous (Fig. 7). They can be traced in some locations up to 1 km.
Interpretation This lithofacies represents deposits by low-density turbidity currents and are the lowest energy deposits within the Hikuwai sandstone. The high degree of bioturbation is due to quiescence between flows. Bioturbation surfaces are often useful in determining surfaces between event beds. Climbing ripples indicate high sedimentation rates during deposition and often grade into convoluted laminations through soft sediment deformation.
LF2: Thin- to very thick-bedded sandstone and mudstone Description LF2 is distinguished by its high degree of heterogeneity with beds ranging from thin to very-thick bedded, overall lateral continuity of beds, and infrequent but present incisional features at the base of beds (Fig. 6B). It contains beds from 3 cm to >100 cm thick and has an average net-to-gross of 82%. Mud clast conglomerate comprises about 4% of the lithology, making it slightly more common than in LF1. Grain size is typically upper very fine sand, and a maximum grain size of upper fine to lower medium sand occurs at the base of some beds. About a quarter of the beds measured are too weathered to see sedimentary structures. Of the non-weathered section, common sedimentary structures include convoluted laminations, wavy laminations, climbing ripples, and planar laminations. Although most of these beds appear to be laterally continuous, their thickness varies, and they contain shallow nested incisional features (Fig. 8). Incisional features are typically less than 1 m deep, but can be up to 2-3 m deep. The incisional
10 features in this lithofacies may either be mud-draped or lined with mud clast conglomerate at their base (Fig. 9).
Interpretation This lithofacies represents deposition predominantly by low-density turbidity currents, although of higher energy than those depositing LF1. Sedimentary structures primarily represent Bouma Tb and Tc units with the Tde units typically preserved, which include Tcde, Tbde, and Tbcde beds. The presence of incisional surfaces and very-thick beds indicates that occasional erosive turbidity currents passed through, although they are the exception rather than the norm. The nested nature of some of the incisional features indicates that flows focused their energy in a series of events before switching to another area of the system. The presence or absence of mud-draping incisional surfaces likely depended on the time lag between succeeding flows. Quickly succeeding flows were able to erode freshly draped mud from the previous flow. However, succeeding flows with a significant time lag provided time for the mud layer to harden, making it more difficult to erode. In Figure 8, the incisional surfaces and sedimentary fill show that sand was deposited both inside and outside of the incisional feature in two stages. The incision is filled by two convex deposits that connect to adjacent conformable sand deposits, possibly acting as minor levees. This geometry is similar to sedimentary deposits produced by a point-source jet-plume pair by Hoyal et al. (2003). In their study, the point source produced erosion and incipient levees, creating a flute-like feature with a similar cross sectional profile. This suggests that the incisional surfaces in Figure 8 represent scours.
LF3: Medium- to very thick-bedded sandstone and mudstone Description LF3 is primarily identified by its bed distribution, which ranges between medium- to very-thick bedded, common bed amalgamation, and common incisional features at the base of beds (Fig. 6C). Although LF3 shares some features with LF2, LF3 contains a negligible percentage of thin beds (Fig. 6Cii), a higher proportion of thick to very thick beds (70% as compared to 61% in LF2), and more frequent and deeper incisional features.
11 Beds range from 10 cm to >100 cm in LF3, and it has an average net-to-gross of 87%. Mud clast conglomerate is uncommon, but present locally. This lithofacies contains a range of grain sizes usually between lower very fine and lower fine sand. The maximum grain size occurring at the base of beds is upper fine to lower medium, the same as the thin to very thick-bedded sandstone and mudstone (LF2). This lithofacies primarily contains convoluted laminations, planar laminations, wavy laminations, and climbing ripples. Soft sediment deformation is prevalent and climbing ripples often grade into increasingly convoluted laminations. Planar laminations sometimes contain small mud clasts, and large dewatering structures are observed. Incisional features occur frequently in this lithofacies, and they are often deeper (typically 1-2 m, but can be >3 m) and more nested than the incisional features in LF2 (Fig. 10). Although most beds have preserved mudstone at their top, 14% of beds are amalgamated. Lateral continuity is difficult to assess due to the extent of exposure and faulting, but can often be traced up to 10s of meters.
Interpretation This lithofacies represents deposition by low-density turbidity currents, and most of the beds contain partial Bouma sequences Tcde, Tbde, or Tbcde. Incision is common and indicates the erosive nature of bypassing flows. The abundance of soft-sediment deformation reflects the high sedimentation rate and fluid entrainment during deposition. Ripple structures are particularly susceptible to soft-sediment deformation because they become loosely packed during avalanching as part of their formation process (Kolbuszewski, 1953), permitting additional space for pore fluids. Convoluted laminations are most commonly observed in the Tc division because of this mechanism, although can occur in other sedimentation units. Despite the high sedimentation rate, Bouma Tb and Tc divisions are much more common than Ta divisions. The lack of Ta units indicates that most grains underwent tractive movement as bed load prior to deposition. This is partly due to the fine-grained nature of the sandstone, which cannot fall out of suspension fast enough to suppress bed load movement.
12 LF4: Thick- to very thick-bedded sandstone with mud clast conglomerate Description LF4 is distinguished by its predominance of thick- to very-thick beds, significant mud clast conglomerate component, and laterally discontinuous architecture due to frequent incisional surfaces (Fig. 6D). It has an average net to gross of 92% and contains beds ranging from 30 cm to >100 cm. Mud clast conglomerate comprises 8% of the lithofacies, which is the highest percentage of all lithofacies. Grain sizes on average range from lower very fine to upper fine sand, and the maximum grain size of upper medium to lower coarse sand is the largest grain size observed in the Hikuwai sandstone. Common sedimentary structures in this lithofacies include convoluted laminations, wavy laminations, planar laminations, and massive/structureless units. Climbing ripples also occur but are less common. Soft sediment deformation is very common and may be present internally within a bed or across several beds (Fig. 11). Wavy and undulating contacts between beds are common, and incisional features can be >3 m deep, cutting across several beds. In Figure 12, the incisional surfaces contain mud clast conglomerate at their base and appear to step upward and leftward (northeastward) through time. Most beds (67%) are amalgamated, creating composite beds >4 m thick. Beds are highly discontinuous due to extensive incision and are often difficult to trace more than 20 m due the nature of the architecture and the extent of the outcrops.
Interpretation This lithofacies represents deposition by low-density turbidity currents and occasional high-density turbidity currents. It is the highest energy lithofacies of the Hikuwai sandstone. The degree and frequency of incision, large grain size, bed thickness, and sedimentary structures indicate that erosive turbidity currents carrying large sediment loads frequently passed through this area. The incisional surfaces in LF4 show greater internal organization and larger grain sizes than incisional surfaces observed in other lithofacies. This suggests the incisional surfaces in LF4 represent small erosional channels, which often develop through lateral migration and aggradation and contain the coarsest deposits in their thalweg (McHargue et al. 2011 and references therein). Additionally, this is the only lithofacies containing a significant proportion of massive Ta
13 Bouma divisions indicative of deposition by high-density turbidity currents (Lowe, 1982). The soft-sediment deformation and liquefaction here is directly related to the high sedimentation rate of the flows. Liquefaction occurs when there is an increase in pore fluid pressure due to deposition by a succeeding flow. Grains become temporarily supported by pore fluid, thereby altering existing sedimentary structures (Lowe, 1976; Owen and Moretti, 2011). If liquefaction occurs during or soon after deposition, the underlying and overlying bed will show different degrees of soft sediment deformation, whereas if liquefaction occurs post-deposition, a series of beds may undulate and deform as a single unit (Fig. 11).
LF5: Chaotic and contorted sandstone, tuff, and mudstone Description LF5 is present both in the Hikuwai sandstone and in the middle and upper Mapiri Formation, although has only a single occurrence within the Hikuwai sandstone. The lithofacies in the Hikuwai sandstone includes a contorted interbedded sandstone and mudstone facies with an overlying mud-dominated chaotic facies containing large bioclastic material (Fig. 13). The contorted interbedded sandstone and mudstone facies is comprised of deformed thin-bedded sandstone and mudstone. Sedimentary structures were not recognized likely due to liquefaction. The overlying mud-dominated chaotic facies is composed of matrix-dominated, structureless mudstone with sand grains and bioclastic material dispersed throughout the unit. The lithofacies in the middle and upper Mapiri Formation includes a mud- dominated chaotic facies and a more coherent facies of mudstone containing layers of rhyolitic tuff. The mud-dominated chaotic facies is comprised of matrix-dominated, structureless mudstone with meter-scale dispersed clasts of interbedded mudstone and tuff. The more coherent facies contains layers of mudstone and tuff beds that have been deformed and rotated along detachment surfaces.
Interpretation This lithofacies is interpreted to represent mass transport deposits (MTDs) produced by both debris flows (for the mud-dominated chaotic facies) and slumping (for
14 the contorted sandstone, tuff, and mudstone facies) both in the Hikuwai sandstone and in the Mapiri Formation. The occurrence of the MTD within the Hikuwai sandstone is observed close to the main area of deposition of LF4, and therefore its presence may be linked to regions where higher energy flows occur, although could be purely coincidental. The MTD within the Hikuwai sandstone is only locally observed therefore it is not known if it has any greater regional context for the system. The MTD within the upper Mapiri Formation is much more extensive and likely has regional significance in the basin.
LF6: Mudstone Description LF6 is present in the middle and upper Mapiri Formation and occurs as laminated mudstone with some interbedded rhyolitic tuff and sandstone. This lithofacies is extensively bioturbated and is mostly comprised of clay to silt size grains. Where the tuff layers are not completely bioturbated, they exhibit fining upward textures.
Interpretation This lithofacies is interpreted as deposited by very low energy turbidity currents and hemipelagic background suspension. The tuff layers reflect eruptions from the active volcanic arc and have also been deposited through suspension.
ARCHITECTURAL ANALYSIS Mahanga Stream (southern) section The Mahanga Stream section represents the base of the Hikuwai sandstone with the underlying middle Mapiri Formation exposed below (Fig. 14A). While the cliffs expose up to 150 m of the Hikuwai sandstone, only 35 m of vertical section from the base is accessible along the beach because the exposure is approximately parallel to the axis of the syncline and therefore there is minimal structural dip. Lithofacies from inaccessible portions of the cliff were determined based on high-resolution, photo-panoramas. Bed thickness and heterogeneity, lateral continuity of beds, and degree and amount of incision were the primary characteristics used to identify inaccessible lithofacies. However, since
15 high-resolution, photo-panoramas are still lower resolution than cm-scale measured sections, some smaller details were likely not identified. The underlying middle Mapiri Formation is primarily comprised of LF5 and LF6. The lowest 35 m of the Hikuwai sandstone section is predominantly LF2, with a thin layer of LF1 at the base. In the uppermost section of the cliffs, there is a brief occurrence of LF3 before returning back to LF2. The Mahanga Stream section continues around the corner to Waihi Beach (left side of Fig. 14D), where LF2 changes to LF1. This represents the complete stratigraphic section of the Hikuwai sandstone, albeit much of it is inaccessible. In the Mahanga Stream section, most beds exhibit tabular geometries, although some thin and pinch-out laterally at low angles or show lateral variations in thickness changing from about a meter thick to less than 20 cm thick in less than 10 meters laterally (Fig. 15A). Paleocurrent indicators in this section suggest a south-south eastern transport direction (Fig. 4).
Tolaga Bay South (northern) section The Tolaga Bay South section includes the Tolaga Bay Wharf, Cook’s Cove, and Hole in the Wall field localities (Fig. 14B). Like the Mahanga Stream section, the Tolaga Bay South section runs approximately parallel to the axis of the syncline with minimal structural dip, exposing about 175 m of vertical section along the cliffs. Although neither the top nor the base of the Hikuwai sandstone is exposed, this section represents the uppermost part of the sandstone based on inland mapping. The lowermost deposits in Cook’s Cove and Hole in the Wall correlate approximately to the uppermost deposits exposed in the Mahanga Stream area based on mapping. The Cook’s Cove and Hole in the Wall field areas expose the oldest stratigraphic section in Tolaga Bay South. The section becomes slightly younger to the west in the Tolaga Bay Wharf area. Following the section south into the Cook’s Cove South field area (Fig. 14C), the section youngs upward to the south to the top of the Hikuwai sandstone. Due to inaccessibility of the coast, only about 20 m of vertical section in the Cook’s Cove and Hole in the Wall field areas was accessible. The approximate stratigraphic positions of these sections were determined based on hanging them from the top of the Hikuwai sandstone exposed at Cook’s Cove South. High-resolution images obtained from the Tolaga Bay Wharf provided a basis for interpretation of lithofacies and architecture in the cliffs (Fig. 15B).
16 The lowest part of this section exposed at Cook’s Cove and Hole in the Wall are represented by LF4, the highest energy lithofacies in the Hikuwai sandstone. Moving up section both to the east and to the west, the lithofacies shifts into LF3. Following the section east, the coastline turns south and there is a continuation of LF3 (right side of Fig. 14C). Following the section to the west into Tolaga Bay Wharf, the section becomes inaccessible, but high-resolution photo-panoramas of the cliffs suggest that the beds continue to reflect waning energy, shifting into LF2 deposits. The uppermost part of the Tolaga Bay Wharf cliffs is represented by LF1. This LF2 to LF1 sequence is the same sequence identified in the uppermost exposure of the Mahanga Stream to Waihi Beach field areas and therefore can be used as stratigraphic marker for the top of the Hikuwai sandstone. Paleocurrent indicators suggest transport to the southwest and southeast (Fig. 4). The polymodal nature of the paleocurrent directions, based on ripple measurements, is likely due to variability in the direction of flows in this region.
Cook’s Cove South (eastern) section The Cook’s Cove South section transects the greatest continuous and accessible vertical exposure of the Hikuwai sandstone where an approximately 144 m section is exposed along the beach until it reaches the upper Mapiri Formation (Fig. 14C; Fig. 16). Some faulting and lack of exposure interrupt the section, but it nonetheless provides the most complete accessible record of temporal evolution. Because this section represents the top portion of the Hikuwai sandstone, the base (northern side) of the Cook’s Cove South section approximately correlates to the occurrence of LF3 in the Mahanga Stream field area. The Cook’s Cove South section is composed primarily of LF3, LF2, and LF1 (Fig. 14C; Fig. 16). Paleocurrent indicators suggest unidirectional transport to the southwest (Fig. 4). The lowermost portion of the section begins with LF3, which represents a continuation from around the corner at Cook’s Cove. LF3 briefly transitions into LF4 (Fig. 16), then into LF5, a localized mass transport deposit. LF5 is observed only in the Cook’s Cove South field area and therefore could not be used as a stratigraphic marker bed. The mass transport deposit is overlain by about 4 m of LF4, then the section transitions back to LF3. The section then exhibits two cycles of waning energy deposition. The first cycle consists of high energy deposits of LF3 for about 70 m,
17 which grade upward into LF1 for 12 m. The second, thinner cycle consists of a very thin (~4 m) unit of LF3 followed by 25 m of LF2, then 12 m of LF1. LF1 grades into LF6 of the upper Mapiri Formation just southwest of Cook’s Cove South in the Wairere Beach field area. Because there are few laterally continuous bed markers in this system, this capping pattern of LF1 overlain by the upper Mapiri Formation is used as the main stratigraphic datum for the top of the Hikuwai sandstone.
Wairere and Waihi Beach section Located in the center of the synclinal structure, the Wairere and Waihi Beach section represents the top of the Hikuwai sandstone and base of the overlying upper Mapiri Formation (Fig. 14D). Wairere Beach represents the northern side of the syncline, while Waihi Beach represents the southern side of the syncline, approximately. At Wairere Beach, the Hikuwai sandstone grades into the upper Mapiri Formation and is dominated by LF6 for the first 100 meters of upper Mapiri section (Fig. 17). While a few parts of this section show minor internal slumping, the main LF5 MTD deposit occurs at 103 meters into the upper Mapiri Formation. The MTD has a variable thickness, but reaches over 40 m thick in outcrop (Fig. 15D). It may have been deposited as multiple events since an intact section of LF6 is noted in some areas in the middle of the MTD (Fig. 14D). Most of the Waihi Beach section is comprised of LF5 and LF6 of the upper Mapiri Formation. The uppermost portion of the Hikuwai sandstone is exposed in Waihi Beach’s southernmost extent, represented by the LF2 to LF1 capping sequence based on photo-panorama mapping and a small area of accessible outcrop.
INTERPRETATION Environment of Deposition The stratigraphy and architectural styles observed suggest the system is predominantly depositional rather than a bypass region characterized by erosion. Most Hikuwai sandstone beds are laterally continuous and have a tabular appearance, which suggest deposition in an unconfined environment. This is particularly true for LF1 and LF2 deposits. The thick to very thick beds characterized by soft-sediment deformed structures indicate that sedimentation rate was very high. Thinner beds are often also
18 characterized by climbing ripples, another indicator of high sedimentation rate. These sedimentological and architectural observations suggest that the Hikuwai sandstone was deposited as part of a deep-water lobe system. Lobe architecture is commonly characterized as laterally continuous and lacking bounding erosional surfaces related to channelization (Deptuck et al., 2008; Prélat et al., 2009; Bernhardt et al., 2011). Although incisional features occur, they are typically less than 3 m deep and most do not have internal organization or major bounding surfaces (>10 m deep) as expected for channelized deposits (Clark and Pickering, 1996; Piper et al., 1999; McHargue et al., 2011; Sylvester et al., 2011). The base of most beds do not show bypass or lag deposits comprised of coarser bed load material characteristic of channels (McHargue et al., 2011), but instead contain sedimentary structures indicative of rapid deposition likely due to the loss of flow confinement. Paleocurrent indicators suggest a general southward direction of sediment transport, with no major deviations from this direction to suggest large channel meander bends or deposition perpendicular to flow on levees. Some of the spread in paleocurrents may be related to lateral deflections of flow (i.e., Kneller and McCaffrey, 1999) or radial deposition associated with loss of flow confinement (Normark, 1970). Because no other architectural elements are recognized (i.e., channel-levees, submarine canyons) and the outcrop extent is limited, the type of lobe setting (e.g., frontal, crevasse, overbank, intra- channel as defined in Posamentier and Kolla, 2003; De Ruig and Hubbard, 2006; Bernhardt et al., 2012) cannot be determined based on its position with respect to the rest of the system. However, the great thickness of the deposit (385 m) suggests that it is an aggradational frontal lobe as opposed to the other, more ephemeral types of lobes, although it may not represent the terminus of the system. The average sand net-to-gross from all measured sections is 81%. Although this is a typical net-to-gross for lobes (Nilsen et al., 2007), the 385 m thickness is exceptionally high for a single lobe system, which more commonly ranges from a few meters thick (Goyeneche et al., 2007; Prélat et al., 2009) to a few 10s of meters thick (Crevello et al., 2007; Saller et al., 2008). The sandstone lacks identifiable lobe packages that are separated by thick mudstone interbeds, which are thought to occur when the site of lobe deposition switches in association with channel avulsion and/or the topographic build-up of a lobe mound (Prélat et al., 2009;
19 Macdonald et al., 2011a). This lack of autocyclicity may be due to the influence of the slope topography where flows interacted with and built up against the boundaries of the local basin (Kneller and McCaffrey, 1999; Gervais et al., 2006). The paucity of Ta units is significant since these commonly occur in other fine- grained lobe systems such as the Lower Mount Messenger Formation of the Taranaki Basin (Masalimova et al., 2012), the Skoorsteenberg Formation of the Karoo Basin (Hodgson et al., 2006), and the Lower Brushy Canyon Formation of the Delaware Basin (Carr and Gardner, 2000). In the Hikuwai sandstone, sediments were not deposited as rapidly from suspension as compared to other lobe settings because tractive bed load movement occurred just before deposition. Possible factors contributing to a more gradually declining and depositing flow include: (1) the flows were never high-density flows, remaining low-density flows from inception to end, (2) a gradual decrease in slope, (3) a gradual widening from confined to unconfined flows (i.e., Felletti and Bersezio, 2010), (4) relatively low energy turbidity currents, (5) dilute turbidity currents, (6) a long transport distance/long duration of flow (i.e., Prélat et al., 2010) and/or (7) off-axis deposition. Although none of these parameters can be reconstructed for Miocene time, factor (6) is best supported by the elongate and tortuous nature of basins in the trench slope. However, factor (7) is best supported by the presence of LF4 exclusively in the easternmost position of the outcrop, likely representing the axis of the system.
Lobe Morphology and Lithofacies Distribution A conceptual model of lobe morphology and lithofacies distribution is developed here based on the observed lithofacies, experimental and numerical modeling of lobes, and plan-form lobe imagery from modern to recent systems. The model presents the range of lithofacies observed in outcrop in their approximate plan-form position (Fig. 18A). Incisional surfaces observed may represent small erosional channels creating a distributary network on the surface of the lobe (i.e., Nelson et al., 1992; Beaubouef and Friedmann, 2000; Posamentier and Kolla, 2003) or discontinuous scours representing localized bursts of turbulence as the flow spreads and thins (i.e., Normark et al., 1979; Satur et al., 2000; Wynn et al., 2002; Pyles and Jennette, 2009). These types of distributary networks are becoming increasingly recognized in recent deep-water lobe
20 systems due to technological advances in seismic imaging achieving meter-scale resolution. A high-resolution image from offshore western Africa shows an aggradational lobe that is dissected by a distributary system (Fig. 18B). However, when the image is scaled to the approximate size of a single lobe body of the Hikuwai sandstone, the channels in the image become less defined and their nature is less clear (Fig. 18C). Observations of the modern sea floor show that large scours (up to ½ to 5 kilometers wide and 10s-100s meters deep) often occur at the terminus of canyons and channels and may be related to hydraulic jumps in the channel-lobe transition area (Wynn et al., 2002; Macdonald et al., 2011b). While the channel-lobe transition zone is a net erosional region (Wynn et al., 2002), similar scouring processes may continue to occur at lower orders of magnitude on the lobe (e.g., Eggenhuisen et al., 2011). Recent studies of cyclic steps on the seafloor argue that scours are a precursor to channel formation, whereby a series of scours may eventually become a continuous, through-going conduit at a range of scales if erosion remains focused (Fildani et al., 2006; Fildani et al., 2013). Therefore, the scour surfaces identified in outcrop may represent both the channel and scour end-members, as well as their intermediaries. Distinguishing between continuous erosional channels and discontinuous scours is a challenge in outcrop-based studies, which typically do not provide extensive plan-form exposures. Similar to channels, scours can undergo multiple stages of cut-and-fill, and their infill can be out of phase with deposition outside of the scour (Macdonald et al., 2011b). Normark et al. (1979) suggested that scours may be differentiated from channels in outcrop on the basis of their fill. They suggest scours will contain local sediment similar to that with which they were cut, while channels should contain a coarser sediment fraction that has been transported from up-system. However, this assumes a grain size distribution in the deep-water system that enables such a distinction. LF4, thick- to very thick-bedded sandstone with mud clast conglomerate, is interpreted to represent the most proximal lobe area where flows are partially confined within erosional channels and/or scours. This region had extensive incision and remained a pathway for flows for the longest amount of time relative to more distal regions of the lobe. The proximal lobe region represents an area of both erosion and deposition (i.e., Gervais et al., 2006), and contains the highest energy beds and largest grain sizes (upper
21 medium to lower coarse, in this study; Alexander et al., 2008). The high sedimentation rates and incisional surfaces in LF4 suggest that the flow became unconfined near this locality. Mud clast conglomerates are commonly observed within the incisional features in LF4, and areas of nested incisions can be up to 5 m thick. Although nested incisional features are also associated with channels (Clark and Pickering, 1996), the lack of major bounding surfaces and levees suggests this is still a lobe environment or a transition zone between the two environments. In Figure 12, the incisional features appear to migrate up and to the left with time. This type of organization is commonly associated with the development of channels (McHargue et al., 2011 and references therein). Additionally, the polymodal nature of the paleocurrents in this area suggests flows were directed by channel development. Therefore, the nature of the incisional features, high percentage of mud clasts, and paleocurrent indicators in LF4 suggest that the incisional surfaces represent small erosional distributary channels that acted as conduits for several flows before switching to another region of the lobe. These conduits are interpreted to distribute sediment further down-system within the lobe. Bypass channels, which would feed sediment past the lobe, are not interpreted because incisional features of similar size and fill are not observed down-system. LF3, medium- to very thick-bedded sandstone and mudstone, is interpreted to represent the high-energy deposits associated with ephemeral channels and/or scours within a lobe. Although both erosion and deposition are reflected in LF3 and LF4, the LF3 region experienced significantly less erosion than LF4, and mudstone Tde Bouma divisions are more commonly preserved (Fig. 6C). While the incisional surfaces often show nesting, they lack the internal organization and significant mud clast component identified in LF4. Flume experiments (i.e., Luthi, 1981; Baas et al., 2004) have shown sedimentary structures reflect decreasing energy regimes from proximal to distal regions of a lobe, and this is reflected by a shift from mostly massive and laminated structures in LF4 to predominantly laminated structures in LF3 (Fig. 6C & 6D). Medium-grained sand and mud clasts are not present in LF3, and we interpret that the flow already deposited this grain size up-system. LF2, thin- to very thick-bedded sandstone and mudstone, is interpreted to represent a medial location within a lobe setting that is moderately scoured. The deposits
22 in this region of the lobe are laterally continuous with occasional interruptions by scours. Scours are interpreted to be predominant over through-going channels in the medial to distal region of the lobe due to a decrease in the nested nature of incisional features and a decrease in mud clast lag deposits. Scour zones spread laterally and did not commonly experience repeated cut-and-fill in this region of the distributary system. However, the scours acted as regions of flow acceleration (i.e., Macdonald et al., 2011b) and the thickness of each successive bed is interpreted to depend on its proximity to the nearest scour. This concept is in general concordance with the finger-like geometries observed and modeled in the Tanqua Karoo basin (van der Werff and Johnson, 2003; Groenenberg et al., 2010), and in agreement with the branching patterns on elongate lobes of the Amazon Fan (Jegou et al., 2008). As the distributary network on the lobe expands, the associated scours become smaller, more widely spaced, and only slightly nested to not nested at all. LF1, thin- to medium bedded sandstone and mudstone, represents the most distal region of a lobe setting. This contains the highest portion of mudstone and thinnest beds in the lobe (Fig. 6A; LF6 is not present in the Hikuwai sandstone so it is not considered here). Scouring is very uncommon and beds are laterally continuous for >1 km in LF1 because it represents the end of the distributary network. The lowest energy, thinnest, and finest-grained deposits characterize this region because most of the sediment load was already deposited up-system and the flow has become thin and fully unconfined (Luthi, 1981; Salaheldin et al., 2000; Baas et al., 2004). The conceptual model’s distribution of lithofacies is based on their distance from the point-source and distance from a feeder distributary channel and/or scour. This agrees with numerical modeling by Groenenberg et al. (2010), which shows that lobes have complex geometries and are comprised of unevenly distributed deposits. This explains the heterogeneity present in the described lithofacies scheme. Although higher energy, thicker deposits are more likely to occur in proximal regions of the system, they may still be present in more distal regions. Similarly, lower energy, thinner deposits are more likely to occur in the more distal (or laterally distal) regions, but may still be present in proximal regions. The bed thickness distribution of any given deposit will vary depending on the particular energy and size of a flow, the sediment source, the influence
23 of the underlying topography, and also the stochastic nature of deposition. This variation in bed thickness distribution directly corresponds to lithofacies distribution across the system. Although certain lithofacies will be more likely to occur in certain regions of the lobe, they will not necessarily be distributed in a perfectly predictive manner.
Basin Configuration Basin configuration of the study area during Miocene time is difficult to reconstruct due to tectonic erosion of much of the subduction wedge in the Raukumara region (Chanier et al., 1999). However, present-day offshore structures in the East Coast Basin offer possible analogs. In the southern Wairarapa region, the subduction wedge is wide and contains numerous margin-parallel, ridge-forming thrust faults (Fig. 2B). This type of setting may have characterized the Raukumara region during deposition of the Hikuwai sandstone, causing sediment to follow longitudinal dispersal pathways through moderately- to weakly-confining tortuous corridors along the slope. There is some evidence for middle to late Miocene thrusting in this region in support of this scenario (Chanier et al., 1999; Barnes et al., 2002; Barnes and Nicol, 2004), although most of the Miocene structures have been overprinted through tectonic erosion and recent extension. Alternatively, the Hikuwai sandstone may have been deposited within a subsiding region of the slope bound by a margin-parallel, listric normal fault. Comparable structures are observed in seismic data just offshore of the Tolaga Bay field location (Fig. 3), although are thought to be post-Miocene time in the Raukumara region (Nicol et al., 2007). However, extensional features as early as middle to late Miocene time are observed in the Hawke Bay region (Barnes et al., 2002; Barnes and Nicol, 2004). For either case, the faults would have produced longitudinal bathymetric relief along the slope and created localized accommodation for the Hikuwai turbidite system (Fig. 19). The limited areal extent, paleocurrent indicators, and aggradational nature of the Hikuwai sandstone provide further support of an axially draining, localized basin configuration. The limited extent of the Hikuwai sandstone exposed on land suggests a turbidite system on the order of ~40 km long and ~20 km wide (Fig. 2C). This represents a minimum estimation given that the lateral extent of a 385 m thick section is anticipated to be on the order of 55km long, estimating a system slope of 0.4°. However, it is
24 possible that simultaneous subsidence due to faulting decreased the typical slope of a lobe system. These dimensions are comparable to present-day dimensions of accommodation created by thrust and listric normal faulting in the Raukumara and Wairarapa regions, respectively (Fig. 2C, 3). The aggradational nature of the lobe deposits also suggests a confined basin setting. Lobes in these settings have higher average thickness to width ratios than lobes in unconfined settings and do not exhibit significant offset between lobe elements due to constriction by the basin margins (Prélat et al., 2010). Additionally, paleocurrent indicators show transport of sediments from approximately north to south, which is parallel to the basin margin. Axial sediment dispersal pathways are common in active basins associated with convergent tectonics (i.e., the Valparaiso Basin (Laursen and Normark, 2003), the Magallanes Basin (Hubbard et al., 2008), the Molasse Basin (De Ruig and Hubbard, 2006)) because the related structural fabric creates longitudinal topography that dictates sediment delivery pathways. Because the Hikuwai sandstone was deposited in a convergent margin setting, it was likely influenced by tectonic-related structures along the slope.
System Evolution A four phase depositional model for the Hikuwai sandstone and upper Mapiri Formation is developed based on the lithofacies distribution around the Tolaga Bay study area in context with the proposed trench-slope basin configuration. Therefore, the model incorporates both outcrop data and basin fill models previously developed for the intra- slope region. Prior to development of the Hikuwai turbidite system, mudstone (LF6) and MTDs (LF5) of the middle Mapiri Formation dominated deposition within the basin. MTDs also underlie a trench-slope turbidite system in the Wairarapa region of the ECB, and may be related to fault movement during the initial stages of basin formation (Bailleul et al., 2007). Phase 1 is represented by the basal Hikuwai sandstone deposits of LF2 observed at the Mahanga Stream section and signifies the beginning of sand-rich deposition by turbidity currents (Fig. 20; Fig. 21A). The Mahanga Stream area is interpreted to represent the medial region of a lobe environment, however correlative section from
25 Tolaga Bay South is not exposed. The deposits in this phase are aggradational, and therefore the basin configuration is interpreted to have been weakly to moderately confining (i.e., Prélat et al., 2010). Despite tabular geometry of the sandstone, the section still exhibits occasional incisional surfaces. The high net-to-gross suggests the sand-rich component of the flow was deposited in this area, while finer grained sediment continued down-system (i.e., flow stripping). Therefore, the flows were not fully contained by a silled basin configuration, and were likely deposited within healed slope accommodation (cf. Prather et al., 1998; Prather, 2000). Healed slope accommodation is defined as the difference between the total slope accommodation and ponded accommodation. Ponded accommodation represents silled space with full 3D closure, and total accommodation is defined by draping a 3D convex hull through the points of maximum curvature on the slope (Steffens et al., 2003). Because we do not interpret ponded accommodation for this deposit, healed slope accommodation can also be thought of as any depression along the slope that falls below the local slope equilibrium profile that is not fully enclosed (Fig. 21B). The deposits within the healed slope, also known as a perched basin (Beaubouef et al., 2003), can contain a variety of depositional elements including MTDs, sheet-sands, channel-levee complexes, and distributary lobe complexes (Booth et al., 2003; Beaubouef et al., 2003; Adeogba et al., 2005; Hay, 2012). Most studies of healed slope deposits are based on high-resolution seismic data of stepped slopes in salt-withdrawal mini-basins, slopes with shale remobilization, and rifted margins (i.e., Adeogba et al., 2005; Close, 2010; Li et al., 2010; Barton, 2012; Prather et al., 2012a; Prather et al., 2012b), and little is know about these deposits in the trench-slope. We suggest that the basin geometry of the trench-slope promotes development of sand-rich distributary lobe elements because flows will gradually lose confinement and velocity as they travel through the fault-bound tortuous corridors (Fig. 1, 19). Hay (2012) interpreted sand-rich distributary lobes as the dominant depositional element between salt-cored ridges in the offshore Kwanza Basin. Beaubouef and Abreu (2006) found the highest proportion of sand in the perched unit of Basin IV in the Brazos-Trinity slope system. Both studies provide further support of this concept. Phase 2 is represented by the high energy deposits (LF3 and LF4) in the northern Cook’s Cove section and the lower energy deposits (LF2 and LF3) in the southern
26 Mahanga Stream section. This suggests that the flows lost significant energy after moving ~5 km down-system due to increased loss of confinement and/or a reduction in slope gradient. The north side represents the proximal area of the lobe system, and the southern end represents its more distal deposits. The beginning of this phase is marked by the occurrence of LF3 in the Mahanga Stream section in conjunction with the occurrence of LF4 in the Cook’s Cove section, suggesting either progradation or lateral migration of the system to a more axial position. In Tolaga Bay South, LF4 represents the axis of the system and it transitions laterally to LF3 then to LF2 (Fig. 20). The brief reoccurrence of LF4 in Cook’s Cove South just below and above LF5, the MTD deposit, is likely associated with eastward lateral migration of the system. Although the phase is marked by initial progradation, the overall phase is retrogradational, with clear transitions from LF4 to LF3 to L2 in the Cook’s Cove, Hole in the Wall, and Tolaga Bay Wharf field areas (Fig. 20). This is associated with backstepping of the system as the healed slope accommodation filled (Fig. 21). The localized MTD in the Cook’s Cove South field area (Fig. 13; Fig. 20) contains distinct bioclastic material, indicating a different source than the encasing turbidite deposits. Therefore, the MTD is not derived from a levee or other mud-rich element of the turbidite system. It possibly developed as part of a collapse up- system or on the margin of the basin, which later became incorporated into the turbidite system. Phase 3 is represented by a thinning-upward succession from LF3 and LF2 to LF1 in the Cook’s Cove South and Tolaga Bay South sections, and by LF2 and LF1 deposits in the Mahanga Stream Section (Fig. 20). These deposits are interpreted to represent distributive lobe elements associated with continued slope healing. We interpret the overall thinning-upward deposits observed in the northern sections of Tolaga Bay to represent system retrogradation as the slope healed (Fig. 21). As slope healing reaches equilibrium, it causes an increase in the gradient of the deposits, a decrease in the change of gradient at the site deposition, and a reduction in the degree of basin confinement (cf., Covault and Romans, 2009). Therefore, the distributive lobe element dimensions are interpreted to become wider, longer, and thinner as the system back-steps. The lack of LF4 in this section may be due to backstepping of the system, or lateral migration of the system to the east. The cycle of LF3 to LF1 to LF2 to LF1 deposition in Cook’s Cove
27 South suggests that the system may have also continued to migrate eastward throughout its development (Fig. 20). The occurrence of LF2 encased by LF1 in Cook’s Cove South either indicates brief lateral system migration to the west during an overall phase of eastward migration, or a brief period of progradation during an overall retrogradational phase. Phase 3 is readily identifiable in the northern Cook’s Cove South and Tolaga Bay South sections where Phase 2 deposits transition to lower energy lithofacies and a thinning-upward succession. At the Mahanga Stream section, the transition from Phase 2 to Phase 3 is difficult to distinguish because it occurs within LF2 (Fig. 20; Fig. 21C). Phase 4 is represented by very low-energy, distal deposits of LF1 and LF6, and mass transport deposits of LF5. This is interpreted to represent the final stages of filling where the slope has fully healed and the flows are no longer confined in the basin. LF1 may represent very distal deposits associated with further retrogradation of the system, or represent levees associated with channelization and bypass of the region. The former hypothesis is favored here because there is no direct evidence of channel features. The Hikuwai sandstone gradually becomes more mud-dominated as it transitions into the mud-rich upper Mapiri Formation (Fig. 5, 16). Termination could be related to the gradual shut-off of sediment supply, sediment bypass, or channel avulsion upslope due to slope healing. Major slumping occurs in the upper Mapiri Formation, which is likely independent of the underlying deep-water system. The MTDs may represent the system’s equilibration to the regional slope profile or possibly renewed movement along nearby faults.
CONCLUSIONS The Hikuwai sandstone is a deep-water lobe system that was deposited in a weakly to moderately confined trench-slope basin setting. The basin underwent four phases of deposition that reflect the filling of healed slope accommodation. Initial deposition and aggradation of sand-rich distributary lobes occurred during Phase 1. The lobes are interpreted to contain a distributary network of small erosive channels and scours on their surface, similar to modern to recent lobes imaged on the seafloor. Phase 2 is marked by initial progradation in an overall retrogradational phase, and eastward lateral migration of the system. Slope healing continued into Phase 3 with associated
28 system backstepping and possible eastward lateral migration as the slope reached equilibrium. As the basin filled during this phase, it became less confined by the basin margins and the lobe deposits became wider and thinner. Phase 4 represents the gradual transition of the Hikuwai sandstone into the overlying mud-rich upper Mapiri Formation. Mass transport deposits in the upper Mapiri Formation represent either equilibration to the regional slope, or are possibly related to later fault movement. Trench-slope basins can act as major traps for sediment because they direct turbidity currents through their corridors, and therefore can be important intraslope reservoirs. This study provides a rich database of high-resolution lithofacies detail for distributive lobes in weakly to moderately confined basins, which is typically unavailable in these types of settings. The depositional model provides a means for mapping lithofacies to evolving configurations of healed slope accommodation as the basin fills, and to their corresponding position within a lobe. Therefore, this study provides a ready analog for elongate basins, such as trench-slopes and slopes with mud diapirism, where only seismic-scale data is available.
ACKNOWLEDGMENTS Funding for this research was provided by the affiliates of the Stanford Project on Deep-water Depositional Systems (SPODDS), with current members including Aera, Anadarko, BHP Billiton, Chevron, ConocoPhillips, Eni, Hess, Karoon Gas Austria LTD, Nexen, Oxy, Petrobras, RAG, Saudi Aramco, Schlumberger, Shell, Talisman Energy, Statoil, and Reliance. The AAPG Grants-in-Aid, Chevron Grant, and GSA Grant also provided additional funding for fieldwork. Martin Crundwell provided the paleontological interpretation through the support of GNS Science. The academic and field support of David Francis of Geological Research LTD was instrumental in the establishment of the project. This research has greatly benefited from discussion with Donald Lowe of Stanford University, and Martin Crundwell, Brad Field, Kyle Bland, and Andy Nicol of GNS Science. Glenn Sharman, Tess Menotti, Katie Maier, Nora Nieminski, and Lauren Shumaker are recognized for their excellent field assistance. Reviewers Bradford Prather, Rick Beaubouef, and Lorna Strachan, and editor Eric Hiatt provided insightful comments and significantly strengthened this paper. We
29 also thank James Milner, Manager of Titirangi Station, who kindly provided access to the coastal outcrops and logistical support during fieldwork.
REFERENCES CITED Abreu, V., Van Wagoner, J., Beaubouef, R., Hoyal, D.C.J.D., 2006. Scour Lobe: Fundamental Depositional Element of Deep-Water Distributary Systems. Abstracts of Annual Meeting. American Association of Petroleum Geologists, 151 pp. Adeogba, A.A., McHargue, T.R., Graham, S.A., 2005. Transient fan architecture and depositional controls from near-surface 3-D seismic data, Niger Delta continental slope. AAPG Bulletin 89, 627-643. Alexander, J.A.N., McLelland, S.J., Gray, T.E., Vincent, C.E., Leeder, M.R., Ellett, S., 2008. Laboratory sustained turbidity currents form elongate ridges at channel mouths. Sedimentology 55, 845-868. Baas, J.H., Van Kesteren, W., Postma, G., 2004. Deposits of depletive high-density turbidity currents: a flume analogue of bed geometry, structure and texture. Sedimentology 51, 1053-1088. Bailleul, J., Robin, C., Chanier, F., Guillocheau, F., Field, B., Ferriére, J., 2007. Turbidite systems in the inner fore-arc domain of the Hikurangi convergent margin (New Zealand); new constraints on the development of trench-slope basins. Journal of Sedimentary Research 77, 263-283. Ballance, P.F., 1976. Evolution of the upper Cenozoic magmatic arc and plate boundary in northern New Zealand. Earth and Planetary Science Letters 28, 356- 370. Ballance, P.F., 1993. The New Zealand Neogene forearc basins. Sedimentary Basins of the World 2, 177-193. Barnes, P.M., Lamarche, G., Bialas, J., Henrys, S., Pecher, I., Netzeband, G.L., Greinert, J., Mountjoy, J.J., Pedley, K., Crutchley, G., 2010. Tectonic and geological framework for gas hydrates and cold seeps on the Hikurangi subduction margin, New Zealand. Mar Geol 272, 26-48. Barnes, P.M., Nicol, A., 2004. Formation of an active thrust triangle zone
30 associated with structural inversion in a subduction setting, eastern New Zealand. Tectonics 23, TC1015. Barnes, P.M., Nicol, A., Harrison, T., 2002. Late Cenozoic evolution and earthquake potential of an active listric thrust complex above the Hikurangi subduction zone, New Zealand. Bulletin of the Geological Society of America 114, 1379-1405. Barton, M.D., 2012. Evolution of an intra-slope apron, offshore Niger Delta Slope: Impact of step geometry on apron architecture, in: Geology, S.S.f.S. (Ed.), Applications of the Principles Seismic Geomorphology to Continental Slope and Base-of-slope Systems: Case Studies from Seafloor and Near-Seafloor Analogues. Beaubouef, R.T., Abreu, V., 2006. Basin 4 of the Brazos-Trinity slope system: Anatomy of the terminal portion of an intra-slope lowstand systems tract. Gulf Coast Association of Geological Societies Transactions 56, 39-49. Beaubouef, R.T., Abreu, V., Van Wagoner, J.C., 2003. Basin 4 of the Brazos-Trinity Slope System, Western Gulf of Mexico: The Terminal Portion of a Late Pleistocene Lowstand System Tract, in: Roberts, H.H., Rosen, N.C., Filton, R.H., Anderson, J.B. (Eds.), Shelf Margin Deltas and Linked Down Slope Petroleum Systems: Global Significance and Future Exploration Potential. Gulf Coast Section SEPM Foundation, pp. 45-66. Beaubouef, R.T., Friedmann, S.J., 2000. High resolution seismic/sequence stratigraphic framework for the evolution of Pleistocene intra-slope basins, Western Gulf of Mexico: depositional models and reservoir analogs, in: Weimer, P., Slatt, R.M., Coleman, J., Rosen, N.C., Nelson, H., Bouma, A.H., Styzen, M.J., Lawrence, D.T., (Ed.), Deep-water Reservoirs of the World. GCS-SEPM Foundation, pp. 40-60. Belderson, R.H., Kenyon, N.H., Stride, A.H., Pelton, C.D., 1984. A 'braided' distributary system on the orinoco deep-sea fan. Mar Geol 56, 195-206. Bernhardt, A., Jobe, Z.R., Lowe, D.R., 2011. Stratigraphic evolution of a submarine channel-lobe complex system in a narrow fairway within the Magallanes foreland basin, Cerro Toro Formation, southern Chile. Mar Petrol Geol 28, 785-806. Bernhardt, A., Stright, L., Lowe, D.R., 2012. Channelized debris-flow deposits and
31 their impact on turbidity currents: The Puchkirchen axial channel belt in the Austrian Molasse Basin. Sedimentology 59, 2042-2070. Blom, W.M., 1982. Sedimentology of the Tokomaru Formation, Waiapu Subdivision, Raukumara Peninsula, New Zealand. Booth, J.R., Dean, M.C., DuVernay, A.E., Styzen, M.J., 2003. Paleo-bathymetric controls on the stratigraphic architecture and reservoir development of confined fans in the Auger Basin: central Gulf of Mexico slope. Mar Petrol Geol 20, 563- 586. Bouma, A.H., 1962. Sedimentology of some Flysch deposits; a graphic approach to facies interpretation, pp. 168-168. Buret, C., Chanier, F., Ferriére, J., Proust, J.N., 1997. Individualisation d'un bassin d'avant-arc au cours du fonctionnement d'une marge active; la marge Hikurangi, Nouvelle-Zelande. Individualization of a forearc basin during the active margin evolution; Hikurangi subduction margin, New Zealand. Comptes Rendus de l'Academie des Sciences, Serie II. Sciences de la Terre et des Planetes 325, 615- 621. Carr, M., Gardner, M.H., 2000. Portrait of a basinfloor fan for sandy deepwater systems, Permian lower Brushy Canyon formation, west Texas, in: Bouma, A.H., Stone, C.G. (Eds.), Fine-grained turbidite systems. SEPM / AAPG, pp. p. 215 - 232. Chanier, F., Ferriére, J., Angelier, J., 1999. Extensional deformation across an active margin, relations with subsidence, uplift, and rotations; the Hikurangi subduction, New Zealand. Tectonics 18, 862-876. Clark, J.D., Pickering, K.T., 1996. Architectural elements and growth patterns of submarine channels; application to hydrocarbon exploration. AAPG Bulletin 80, 194-221. Close, D.I., 2010. Slope and fan deposition in deep-water turbidite systems, East Antarctica. Mar Geol 274, 21-31. Collot, J.-Y., Lewis, K.B., Lamarche, G., Lallemand, S., 2001. The giant Ruatoria debris avalanche on the northern Hikurangi margin, New Zealand; results
32 from oblique seamount subduction. Journal of Geophysical Research 106, 19271- 19297. Covault, J.A., Romans, B.W., 2009. Growth patterns of deep-sea fans revisited: Turbidite-system morphology in confined basins, examples from the California Borderland. Mar Geol 265, 51-66. Crevello, P.D., Johnson, H.D., Tongkul, F., Wells, M., 2007. Lobe, channel-lobe, and channel deposits, Lok Kawi, Northwest Borneo, in: Nilsen, T.H., Shew, R.D., Steffens, G.S., Studlick, J.R.J. (Eds.), Atlas of Deep-Water Outcrops. The American Association of Petroleum Geologists, Shell Exploration and Production, Oklahoma, p. 504. Davey, F.J., Hampton, M., Childs, J., Fisher, M.A., Lewis, K.B., Pettinga, J.R., 1986. Structure of a growing accretionary prism, Hikurangi margin, New Zealand. Geology 14, 663-666. De Ruig, M.J., Hubbard, S.M., 2006. Seismic facies and reservoir characteristics of a deep-marine channel belt in the Molasse foreland basin, Puchkirchen Formation, Austria. AAPG Bulletin 90, 735-752. Demyttenaere, R., Tromp, J.P., Ibrahim, A., Allman-Ward, P., 2000. Brunei Deep Water Exploration: From Sea Floor Images and Shallow Seismic Analogues to Depositional Models in a Slope Turbidite Setting, in: Weimer, P., Slatt, R.M., Coleman, J., Rosen, N.C., Nelson, H., Bouma, A.H., Styzen, M.J., Lawrence, D.T., (Ed.), Deep-water Reservoirs of the World. GCS-SEPM Foundation, pp. 40- 60. Deptuck, M.E., Piper, D.J.W., Savoye, B., Gervais, A., 2008. Dimensions and architecture of late Pleistocene submarine lobes off the northern margin of east Corsica. Sedimentology 55, 869-898. Eggenhuisen, J.T., McCaffrey, W.D., Haughton, P.D.W., Butler, R.W.H., 2011. Shallow erosion beneath turbidity currents and its impact on the architectural development of turbidite sheet systems. Sedimentology 58, 936-959. Felletti, F., Bersezio, R., 2010. Quantification of the degree of confinement of a turbidite-filled basin: A statistical approach based on bed thickness distribution. Mar Petrol Geol 27, 515-532.
33 Field, B.D., Browne, G.H., Higgs, K.E., Pollock, R.M., Uruski, C.I., 2006. Reservoir plays of the East Coast Region, New Zealand Petroleum Conference, Auckland, NZ, p. 6. Field, B.D., Uruski, C.I., Institute of Geological & Nuclear Sciences Limited., 1997. Cretaceous-Cenozoic geology and petroleum systems of the East Coast region, New Zealand. Institute of Geological & Nuclear Sciences, Lower Hutt, N.Z. Fildani, A., Hubbard, S.M., Covault, J.A., Maier, K.L., Romans, B.W., Traer, M., Rowland, J.C., 2013. Erosion at inception of deep-sea channels. Mar Petrol Geol 41, 48-61. Fildani, A., Normark, W.R., Kostic, S., Parker, G., 2006. Channel formation by flow stripping: large-scale scour features along the Monterey East Channel and their relation to sediment waves. Sedimentology 53, 1265-1287. Francis, D., 2003. A study of Upper Miocene reservoir sandstone near Tolaga Bay, PEP38330, East Coast Basin, in: Zealand, M.o.E.D.N. (Ed.), Unpublished Petroleum Report 2839. Gervais, A., Savoye, B., Mulder, T., Gonthier, E., 2006. Sandy modern turbidite lobes: A new insight from high resolution seismic data. Mar Petrol Geol 23, 485- 502. Gosson, G.J., 1986. Miocene and Pliocene silicic tuffs in marine sediments of the East Coast Basin, New Zealand. Masters Thesis, Victoria University of Wellington, New Zealand. pp. 274. Goyeneche, C.J., Slatt, R.M., Witten, A.J., Young, R.A., 2007. Outcrop characterization, 3-D geological modeling, and upscaling for reservoir simulation of Jackford Group turbidites in the Hollywood Quarry, Arkansas, USA, in: Nilsen, T.H., Shew, R.D., Steffens, G.S., Studlick, J.R.J. (Eds.), Atlas of Deep-Water Outcrops. The American Association of Petroleum Geologists, Shell Exploration and Production, Oklahoma, p. 504. Gradstein, F.M., Ogg, J.G., Smith, A.G., Bleeker, W., Lourens, L.J., 2004. A new geologic time scale, with special reference to Precambrian and Neogene. Episodes 27(2), 83-100. Groenenberg, R.M., Hodgson, D.M., Prélat, A., Luthi, S.M., Flint, S.S., 2010. Flow-
34 Deposit Interaction in Submarine Lobes: Insights from Outcrop Observations and Realizations of a Process-Based Numerical Model. Journal of Sedimentary Research 80, 252-267. Hay, D.C., 2012. Stratigraphic evolution of a tortuous corridor from the stepped slope of angola, in: Applications of the Principles Seismic Geomorphology to Continental Slope and Base-of-slope Systems: Case Studies from Seafloor and Near-Seafloor Analogues. SEPM Society for Sedimentary Geology Special Publication of the International Association of Sedimentologists No. 99, 163-180. Hodgson, D.M., Flint, S.S., Hodgetts, D., Drinkwater, N.J., Johannessen, E.P., Luthi, S.M., 2006. Stratigraphic evolution of fine-grained submarine fan systems, Tanqua depocenter, Karoo Basin, South Africa. Journal of Sedimentary Research 76, 20-40. Hollis, C.J., Beu, A.G., Crampton, J.S., Crundwell, M.P., Morgans, H.E.G., Raine, J.I., Jones, C.M., Boyes, A.F., 2010. Calibration of the New Zealand Cretaceous- Cenozoic Timescale to GTS2004. GNS Science Report 2010/43, 20 p. Hooper, R. J., Fitzsimmons, R.J., Grant, N., Vendeville, B.C., 2002. The role of deformation in controlling depositional patterns in the south-central Niger Delta, West Africa. Journal of Structural Geology 24, 847-859. Hoyal, D.C.J.D., Van Wagoner, J., John, C., Adair, N.L., Deffenbaugh, M., Li, D., 2003. Sedimentation from jets; a depositional model for clastic deposits of all scales and environments. Annual Meeting Expanded Abstracts. American Association of Petroleum Geologists 12, 81 pp. Hubbard, S.M., Romans, B.W., Graham, S.A., 2008. Deep-water foreland basin deposits of the Cerro Toro Formation, Magallanes basin, Chile: architectural elements of a sinuous basin axial channel belt. Sedimentology 55, 1333-1359. Ingram, R.L., 1954. Terminology for the thickness of stratification and parting units in sedimentary rocks. Bulletin of the Geological Society of America 65, 937-938. Jegou, I., Savoye, B., Pirmez, C., Droz, L., 2008. Channel-mouth lobe complex of the recent Amazon Fan: The missing piece. Mar Geol 252, 62-77. Kneller, B., McCaffrey, W., 1999. Depositional effects of flow nonuniformity and
35 stratification within turbidity currents approaching a bounding slope: deflection, reflection, and facies variation. Journal of Sedimentary Research 69, 980-991. Kolbuszewski, J., 1953. Note on factors governing the porosity of wind deposited sands. Geological Magazine 90, 48-56. Laursen, J., Normark, W.R., 2003. Impact of structural and autocyclic basin-floor topography on the depositional evolution of the deep-water Valparaiso forearc basin, central Chile. Basin Res 15, 201-226. Lewis, K.B., Lallemand, S., Carter, L., 2004. Collapse in a Quaternary shelf basin off East Cape, New Zealand: evidence for the passage of a subducted seamount inboard of the Ruatoria giant avalanche. New Zealand Journal of Geology and Geophysics 47, 415-429. Lewis, K.B., Pettinga, J.R., 1993. The emerging, imbricate frontal wedge of the Hikurangi Margin. Sedimentary Basins of the World 2, 225-250. Li, L., Wang, Y., Xu, Q., Zhao, J., Li, D., 2012. Seismic geomorphology and main controls of deep-water gravity flow sedimentary process on the slope of the northern South China Sea. Science China Earth Sciences 55, 747-757. Li, L., Wang, Y., Zhang, L., Huang, Z., 2010. Confined gravity flow sedimentary process and its impact on the lower continental slope, Niger Delta. Science China Earth Sciences 53, 1169-1175. Lomas, S.A., Joseph, P., 2004. Confined turbidite systems. Geol Soc Spec Publ 222, 1-7. Lowe, D.R., 1976. Subaqueous liquefied and fluidized sediment flows and their deposits. Sedimentology 23, 285-308. Lowe, D.R., 1982. Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity current. Journal of Sedimentary Petrology 52, 279-297. Luthi, S.M., 1981. Experiments on non-channelized turbidity currents and their deposits. Mar Geol 40, M59-M68. Macdonald, H.A., Peakall, J., Wignall, P.B., Best, J., 2011a. Sedimentation in deep- sea lobe-elements: implications for the origin of thickening-upward sequences. Journal of the Geological Society 168, 319-332.
36 Macdonald, H.A., Wynn, R.B., Huvenne, V.A.I., Peakall, J., Masson, D.G., Weaver, P.P.E., McPhail, S.D., 2011b. New insights into the morphology, fill, and remarkable longevity (>0.2 m.y.) of modern deep-water erosional scours along the northeast Atlantic margin. Geosphere 7, 845-867. Masalimova, L.U., Lowe, D.R., King, P., Arnot, M., 2012. Cyclicity and hierarchy of the deep-water channel-lobe complex of the Lower Mount Messenger Formation, New Zealand, in: Romans, B.W., Covault, J.A., Hubbard, S.M. (Eds.), 2012 GSA Annual Meeting, Charlotte, NC, p. 631. Mazengarb, C., Speden, I.G., 2000. Geology of the Raukumara area; scale 1:250,000, New Zealand (NZL), pp. 60-60, 61 sheet. McCrory, P., 1995. Evolution of a trench-slope basin within the Cascadia subduction margin: the Neogene Humboldt Basin, California. Sedimentology 42, 223-247. McHargue, T., Pyrcz, M.J., Sullivan, M.D., Clark, J.D., Fildani, A., Romans, B.W., Covault, J.A., Levy, M., Posamentier, H.W., Drinkwater, N.J., 2011. Architecture of turbidite channel systems on the continental slope: Patterns and predictions. Mar Petrol Geol 28, 728-743. Moore, G.F., Curray, J.R., Emmel, F.J., 1982. Sedimentation in the Sunda Trench and forearc region. Geological Society, London, Special Publications 10, 245-258. Nelson, C.H., Twichell, D.C., Schwab, W.C., Lee, H.J., Kenyon, N.H., 1992. Upper Pleistocene turbidite sand beds and chaotic silt beds in the channelized, distal, outer-fan lobes of the Mississippi fan. Geology 20, 693-696. Nicol, A., Mazengarb, C., Chanier, F., Rait, G., Uruski, C., Wallace, L., 2007. Tectonic evolution of the active Hikurangi subduction margin, New Zealand, since the Oligocene. Tectonics 26, TC4002. Nilsen, T.H., Shew, R.D., Steffens, G.S., Studlick, J.R.J., 2007. Atlas of Deep-Water Outcrops. The American Association of Petroleum Geologists, Shell Exploration and Production, Oklahoma, p. 504. National Institute of Water and Atmospheric Research, 2008. New Zealand Region Bathymetry, in: Miscellaneous Series No. 85, Wellington, New Zealand. Normark, W.R., 1970. Growth patterns of deep-sea fans. The American
37 Association of Petroleum Geologists Bulletin 54, 2170-2195. Normark, W.R., Piper, D.J.W., Hess, G.R., 1979. Distributary channels, sand lobes, and mesotopography of Navy submarine fan, California Borderland, with applications to ancient fan sediments. Sedimentology 26, 749-774. Okada, H., 1989. Anatomy of trench-slope basins: examples from the Nankai trough. Palaeogeography, Palaeoclimatology, Palaeoecology 71, 3-13. Owen, G., Moretti, M., 2011. Identifying triggers for liquefaction-induced soft- sediment deformation in sands. Sedimentary Geology 235, 141-147. Pettinga, J.R., 1982. Upper Cenozoic structural history, coastal Southern Hawke's Bay, New Zealand. New Zealand Journal of Geology and Geophysics 25, 149-191. Piper, D.J.W., Hiscott, R.N., Normark, W.R., 1999. Outcrop-scale acoustic facies analysis and latest Quaternary development of Hueneme and Dume submarine fans, offshore California. Sedimentology 46, 47-78. Posamentier, H.W., Kolla, V., 2003. Seismic geomorphology and stratigraphy of depositional elements in deep-water settings. Journal of Sedimentary Research 73, 367-388. Prather, B.E., 2000. Calibration and visualization of depositional process models for above-grade slopes: a case study from the Gulf of Mexico. Mar Petrol Geol 17, 619-638. Prather, B.E., Booth, J.R., Steffens, G.S., Craig, P.A., 1998. Classification, lithologic calibration, and stratigraphic succession of seismic facies of intraslope basins, deep-water Gulf of Mexico. AAPG Bulletin 82, 701-728. Prather, B.E., Pirmez, C., Winker, C.D., 2012a. Stratigraphy of linked intraslope basins: Brazos-Trinity system Western Gulf of Mexico, in: Applications of the Principles Seismic Geomorphology to Continental Slope and Base-of-slope Systems: Case Studies from Seafloor and Near-Seafloor Analogues. SEPM Society for Sedimentary Geology Special Publication of the International Association of Sedimentologists No. 99, pp. 83-109. Prather, B.E., Pirmez, C., Sylvester, Z., Prather, D.S., 2012b. Stratigraphic response to evolving geomorphology in a submarine apron perched on the upper Niger Delta slope, in: Applications of the Principles Seismic Geomorphology to
38 Continental Slope and Base-of-slope Systems: Case Studies from Seafloor and Near-Seafloor Analogues. SEPM Society for Sedimentary Geology Special Publication of the International Association of Sedimentologists No. 99, pp. 145- 161. Pratson, L.F., Haxby W.F., 1996. What is the slope of the U.S. continental slope? Geology 24, 3-6. Prélat, A., Covault, J.A., Hodgson, D.M., Fildani, A., Flint, S.S., 2010. Intrinsic controls on the range of volumes, morphologies, and dimensions of submarine lobes. Sedimentary Geology 232, 66-76. Prélat, A., Hodgson, D.M., Flint, S.S., 2009. Evolution, architecture and hierarchy of distributary deep-water deposits; a high-resolution outcrop investigation from the Permian Karoo Basin, South Africa. Sedimentology 56, 2132-2154. Pyles, D.R., Jennette, D.C., 2009. Geometry and architectural associations of co- genetic debrite–turbidite beds in basin-margin strata, Carboniferous Ross Sandstone (Ireland): Applications to reservoirs located on the margins of structurally confined submarine fans. Mar Petrol Geol 26, 1974-1996. Rait, G., Chanier, F., Waters, D.W., 1991. Landward- and seaward-directed thrusting accompanying the onset of subduction beneath New Zealand. Geology (Boulder) 19, 230-233. Salaheldin, T.M., Imran, J., Chaudhry, M.H., Reed, C., 2000. Role of fine-grained sediment in turbidity current flow dynamics and resulting deposits. Mar Geol 171, 21-38. Saller, A., Werner, K., Sugiaman F., Cebastiant, A., May, R., Glenn, D., Barker, C., 2008. Characteristics of Pleistocene deep-water fan lobes and their application to an upper Miocene reservoir model, offshore East Kalimantan, Indonesia. AAPG Bulletin 92, 919-949. Satur, N., Hurst, A., Cronin, B.T., Kelling, G., Gürbüz, K., 2000. Sand body geometry in a sand-rich, deep-water clastic system, Miocene Cingoez Formation of southern Turkey. Mar Petrol Geol 17, 239-252. Smith, R., 2004. Silled sub-basins to connected tortuous corridors: sediment
39 distribution systems on topographically complex sub-aqueous slopes. Geological Society, London, Special Publications 222, 23-43. Snedden, J.W., 2013. Channel-body basal scours: Observations from 3D seismic and importance for subsurface reservoir connectivity. Mar Petrol Geol 39, 150- 163. Steffens, G.S., Biegert, E.K., Sumner, S. H., Bird, D., 2003. Quantitative bathymetric analyses of selected deepwater siliciclastic margins: receiving basin configurations for deepwater fan systems. Mar Petrol Geol 20, 547-561. Sylvester, Z., Pirmez, C., Cantelli, A., 2011. A model of submarine channel-levee evolution based on channel trajectories: Implications for stratigraphic architecture. Mar Petrol Geol 28, 716-727. Timbrell, G., 2003. Sandstone Architecture and Development of the Tunanui Slope Basin-Fill, Hikurangi Forearc, New Zealand. The University of Auckland, Auckland, New Zealand. Twichell, D.C., Schwab, W.C., Nelson, C.H., Kenyon, N.H., Lee, H.J., 1992. Characteristics of a sandy depositional lobe on the outer Mississippi fan from SeaMARC IA sidescan sonar images. Geology 20, 689-692. Underwood, M.B., Bachman, S.B., 1982. Sedimentary facies associations within subduction complexes. Geological Society, London, Special Publications 10, 537- 550. Underwood, M.B., Moore, G.F., 1995. Trenches and Trench-Slope Basins, in: Busby, C., Ingersoll, R.V. (Eds.), Tectonics of Sedimentary Basins. Blackwell Science, Cambridge, MA, pp. 179-219. Underwood, M.B., Norville, C.R., 1986. Deposition of sand in a trench-slope basin by unconfined turbidity currents. Mar Geol 71, 383-392. van der Werff, W., Johnson, S.D., 2003. Deep-sea fan pinch-out geometries and their relationship to fan architecture, Tanqua Karoo basin (South Africa). International Journal of Earth Sciences 92, 728-742. Vinnels, J.S., Butler, R.W.H., McCaffery, W.D., Paton, D.A., 2010. Depositional processes across the Sinu Accretionary Prism, offshore Columbia. Marine and Petroleum Geology 27, 794-809.
40 Wood, L.J., Sullivan, S., Mann, P., 2004. Influence of Mobile Shales in the Creation of Successful Hydrocarbon Basins, in: Post, P., Olson, D., Lyons, K., Palms, S., Harrison, P., Rosen, N. (Eds.), Salt Sediment Interactions and Hydrocarbon Prospectivity: Concepts, Applications, and Case Studies for the 21st Century: Proceedings of the 24th Annual GCSEPM Foundation Bob. F. Perkins Research Conference, p. 892–930. Wynn, R.B., Kenyon, N.H., Masson, D.G., Stow, D.A.V., Weaver, P.P.E., 2002. Characterization and recognition of deep-water channel-lobe transition zones. AAPG Bulletin 86, 1441-1462.
41 (Oregon Coast)
N
Figure 1. Compressional folds dominate the offshore Oregon convergent margin, creating a terraced slope with structurally defined tortuous corridors that direct sediment delivery pathways. Sediments partially bury the ridges due to ponding and slope healing. This setting is analogous to the present day convergent margin setting in the Wairarapa Region of the East Coast Basin, New Zealand (modified from Pratson and Haxby, 1996, Figure 1E).
42 B C A
Tokomaru Kilometers 0 30 60 Bay
Marau Point
48 mm/yr Raukumara Region Fig. 23 C Fig. 4 Hawke Bay Region
N=148 Wairarapa Region 43 mm/yr B Poverty Bay Seamount
Figure 2. A) Topographic and bathymetric map of New Zealand highlighting the major features of the current tectonic configuration of the East Coast Basin. The basin is bordered by the Axial Ranges to the west and by the Hikurangi Trench to the east. It contains numer- ous margin-parallel ridges and several major re-entrants into the continent (bathymetric map from NIWA, 2008). B) Close-up of struc- tural ridges related to thrust faulting. These ridges also represent possible analogs for basin configuration in the Raukumara region during late Miocene time. The intervening depressions between ridges range from around 10 to 30 km wide. C) Geologic map of mud- rich upper Miocene deposits and sand-rich upper Miocene deposits of the Hikuwai sandstone in the Tolaga Bay area. The approximate extent of the localized basin is 20 km by 40 km (geologic map from Mazengarb et al., 2000). 43 0 -1 W E growth strata possibly representing -2 turbidite deposition in a con ned, -3 margin-parallel basin -4 -5 TWT (s) -6 fault horizon -7 0 1 2 km -8 Figure 3. Listric normal growth faults offshore of the Tolaga Bay study area created a zone of accommodation ~11 km wide. Data quality becomes poorer landward, but this region may also be characterized by normal faulting, creating a confined, margin-parallel basin setting where localized deposition of turbidites occurred. This may represent the structural configuration of the study area in the onshore region, although Nicol et al. (2007) interpreted extension in the Raukumara region to be post-Miocene. See Figure 2A for line location (seismic data from Crown Minerals, 2005). 44 Tolaga Bay N = 35
South the Wall the
Hole in Hole 11 6D Cook’s Cove 12 ay Wharf 13 ga B 6C & 10 ola th T u 15B
So
e
v N = 67 6A o s C
15C ’
k
o
o C
h c a e B
e Mt. Titirangi r
aire W
15D
h
c
a
e
B
i
h
i
a W
6B & 8 15A 9A &B 7 N = 47 re am Mahanga St
Figure 4. DEM image overlain with a geologic map of the Tolaga Bay study area. Pink lines indicate measured sections’ locations. Paleocurrent data is based on ripple measure- ments. Numbers and arrows are provided for reference to figures. See Figure 2C for loca- tion of study area.
45 Intl. NZ Depositional Epoch Ma Depositional Style Formation Epoch-Stage (m) silt StageStage Setting clay v fine fine 3.6 Zanclean 1,000
Early Ramanui distal deep-marine 900 Tokomaru
Opoitian Pliocene Zanclean 5.3 Messinian Formation 800
Tokomaru outermost shelf Kapitean
Messinian 700 7.2 upper Mapiri deep-marine overbank upper Mapiri
Hikuwai turbidite complex 600 Formation
upper upper Tonga-
porutuan 9.0 middle deep-marine 500 Late Miocene Late late Miocene late Mapiri overbank
Tortonian Kaiaua turbidite complex 400
Upper
lower lower Tonga- porutuan lower deep-marine Hikuwai 11.0 Tortnian 300 11.6 Mapiri overbank sandstone middle Serra- Waiauan Miocene vallian 200 tuff sand clay conglomerate 100 middle Mapiri silt shells Lower A B 0 Formation Figure 5. A) Generalized chronostratigraphic column of the Tolaga Bay region. The depositional setting is primarily deep-water, although the Tokomaru Formation represents a brief period of shoaling and shelfal deposition (Field et al., 1997; Francis, 2003). B) Gen- eralized stratigraphy and lithology around Tolaga Bay. The Hikuwai sandstone grades into the overlying upper Mapiri Formation, which contains layers of rhyolitic tuff. The Tokomaru Formation unconformably overlies the upper Mapiri Formation. 46 47 (A), LF2(B), LF3(C),andLF4(D). SeeFigure4formeasured sectionlocationand Figure 16formeasured section legend. LF1 for section stratigraphic sample and scouring, of frequency and count bed by histogram thickness bed thickness, by thickness composition bed and composition structure sedimentary statistics, lithofacies including lithofacies of description Quantitative 6. Figure A
% of Total Beds 10 12 0 2 4 6 8 LF1: Thin- tomedium-bedded sandstoneandmudstone Sedimentary Process: Common Turbidite Divisions: Avg. Net:Gross: Max. grainsizeatbase: Avg. grainsize: bioturbation 42 63 84 05 26 48 69 98 92 86 80 74 68 62 56 50 44 38 32 26 20 14 8 2 weathered 24% 27% ripples 8% climbing ripples climbing 19% planarlaminations 5% N =372 Bed Thickness (cm) wavy laminations 6% laminations 10% convoluted convoluted dunes 1% dunes Low-density turbiditycurrents T 67% LF LVF -UVF cde , T Contains incisions at base incisions at Contains bcde Yes No medium-bedded bedded thick- 14% 62% bedded 24% thin- (iii) (ii) (iv)(i)
meters 10 11 9 0 1 2 3 4 5 6 7 8
silt LVF UVF LF2: Thin- to very thick-bedded sandstone and mudstone B (iv)(i) silt LVF UVF LF Avg. grain size: UVF Max. grain size at base: UF-LM 10 Avg. Net : Gross: 82% Common Turbidite Divisions: Tcde, Tbde, Tbcde 9 Sedimentary Process: Low-density turbidity currents bioturbation planar (ii) 8 3% laminations thin- 10% very bedded wavy thick- 9% 7 weathered laminations bedded 26% 15% 29% medium- convoluted bedded 6 ripples laminations thick- 30%
8% bedded meters climbing 26% 5 ripples 32% 12% N = 308 10 4 9 Contains incisions at base (iii) 8 unsure (base of section) 7 No 3 6 5 Yes 4 2
3
% of Total Beds Total % of 2 1 1 0 4 14 24 34 44 54 64 74 84 94 Bed Thickness (cm) 104 114 124 134 144 154 164 174 184 194 204 214 0 Figure 6 (continued) 48 11 C LF3: Medium- to very thick-bedded sandstone and mudstone (iv)(i) silt LVF UVF LF UF Avg. grain size: LVF - LF Max. grain size at base: UF - LM 10 Avg. Net : Gross: 87% Common Turbidite Divisions: Tcde, Tbde, Tbcde, 9 Sedimentary Process: Low-density turbidity currents bioturbation massive thin- 8 7% 1% (ii) weathered planar very bedded thick- 3% 11% laminations medium- 7 ripples 18% bedded 3% 26% bedded wavy 27% climbing ripples laminations 6 14% 16% thick- convoluted bedded laminations 44% meters 5 dunes 28% 2% N = 364 4 8 Contains incisions at base 7 (iii) No 6 3 5 Yes 4 3 2 2 % of Total Beds Total % of 1 1 0 6 16 26 36 46 56 66 76 86 96 106 116 126 136 146 156 166 176 186 196 206 216 226 236 246
Figure 6 (continued) 49 LF4: Thick- to very thick-bedded sandstone with mud clast conglomerate silt LVF UVF LF UF D (iv) 13 Avg. grain size: LVF - UF (i) Max. grain size at base: UM - LC 12 Avg. Net : Gross: 92% Common Turbidite Divisions: Tb, Tbc, Tab, Tabc 11 Sedimentary Process: high- and low-density turbidity currents 10 climbing ripples weathered medium- 6% dunes 1% bedded thick- (ii) 1% massive 9 10% 30% bedded planar 8% laminations 8 convoluted 14% laminations very thick-bedded 7 41% wavy laminations 91% 27% 6 N = 21 meters 5 24 Contains incisions at base 20 unsure (base of section) 4 16 No 3 12 Yes
8 2
% of Total Beds Total % of 4 1 0 0 50 100 150 200 250 300 350 400 450 500 550 600 Bed Thickness (cm) (iii) 0 Figure 6 (continued) 50 W E
lateral thinning
LF
UVF
LVF Silt
m 2
1 pinching out 1 m
0 Figure 7. Example stratigraphy and architecture of LF1 (thin-to medium-bedded sandstone and mudstone lithofacies) at the Mahanga Stream field locality. Beds are laterally continuous and can be traced up to 1 km. Thinning, thickening, and pinching out are observed. Incisional features are uncommon but occur locally. Colored horizontal lines are used to assist with visual bed tracing. Green vertical lines represent promontories and edges in the cliff (not faults) that create problems with perspective in bed tracing. 51 SW ow moving out of page NE ow moving into of page
m silt LVF UVF 4
3
incision 2 connected 2 to conformable bed lateral thinning 1
0 incision 1 connected to conformable bed Figure 8. Example stratigraphy and architecture of LF2 (thin- to very thick-bedded sandstone and mudstone lithofacies) at the Mahanga Stream field locality. Beds are heterogeneously stacked and the Tde layer is typically preserved. Bed thickness varies laterally, but appear to be relatively continuous. Lateral continuity cannot be quantified due to faulting and lack of marker horizons, but this section is at least continuous on the order of 10s of meters. Incisional features are common although not pervasive (red line indicates incisional surface). Incisions are usually less than 1 m deep, and in this example there were two cycles of incision followed by deposition. The sedi- ment deposited within each incisional feature is continuous with conformable deposits outside of the feature. 52 A B Laterally extensive mud layer Convoluted Onlaps
1 m Nested incisional surfaces
Mud clasts Convoluted beds 1 m
Incisional surface with thin mud drape W E W E
Figure 9. Incisional surfaces in LF2 at the Mahanga Stream field area. A) Incisional surface with numerous nested incisions containing mud clasts and a thick sandstone bed that laterally thins at the margin. Surface truncates liquefied turbidite beds and is capped by a later- ally extensive mud layer. B) Incision surface draped with 1 cm of mudstone. Incision-fill laps onto the incision margin. See Figure 8 for paleo-flow direction key. 53 NW SE conformable bed contact incisional surface 2 m amalgamation surface Tabular beds
Nested incisional surfaces
Figure 10. Stratigraphy and architecture of LF3, medium- to very thick-bedded sandstone and mudstone, at the Hole in the Wall field area. Incisions are nested and erode 1-3 meters into the underlying section. Most beds exhibit tabular geometries, although their lateral extent is difficult to assess due to faulting, lack of exposure, and incision. Beds are variably amalgamated. See Figure 8 for paleo-flow direction key. 54 S N
1 m Nested incisions with mud clasts at base
Dewatering structure bisecting amalgamation surface paleo- ow
Figure 11. Numerous incisions and nested incisions containing mud clasts at the base in LF4, thick- to very thick-bedded sandstone and mud clast conglomerate, at the Cook’s Cove field locality. A dewatering structure bisects an amalgamation surface of the above horizon, indicating deposition of the mud clast conglomerate was contemporaneous with dewatering.
55 Uninterpreted
Interpreted NE SW
1m paleo- ow Left-stepping nested incisional surfaces filled by mud clast conglomerate Figure 12. Stratigraphy and architecture for LF4, thick- to very thick-bedded sandstone with mud clast conglomerate, at the Hole in the Wall field locality. Incisional and amalgamation surfaces are very common and mud clast conglomerate frequently fills incisions. Beds are traced a few meters to a few 10s of meters due to their lenticular shape and common faulting. Total incision depth is often difficult to determine due to nested incisions, but they can be >3 m deep. The nested incisions are organized, stepping incrementally upward and to the left. The coarsest grain sizes in the Hikuwai sandstone are found in the base of this lithofacies. Incisional surfaces are marked in red, amalgamation surfaces are marked as a dashed line, bed contacts are marked as a black line, and sedimentary structures are in blue. 56 NE SW mud-rich debris ow
slumped interbedded sandstone and mudstone amalgamated turbidites lique ed sandstone 5 m paleo- ow LF3 LF4 LF5 Figure 13. Lithology and architecture of LF5, chaotic and contorted sandstone, tuff, and mudstone. This lithofacies includes both sand-rich and mud-rich mass transport deposits. Only one localized deposit is observed in the Hikuwai sandstone. The mass transport deposit occurs in the Cook’s Cove field locality in proximity to the highest energy lithofa- cies, LF4, thick- to very thick-bedded sandstone with mud clast conglomerate. LF5 also occurs in the middle and upper Mapiri Formation (see Figure 15D).
Figure 14 (following page). Uninterpreted and interpreted photo-panoramas of the lithofa- cies present in the Mahanga Stream field area (A), Tolaga Bay South field area (B), Cook’s Cove South field area (C), and Waihi Beach field area (D). A reference map for each panel is provided in (E). Field areas are approximately listed in order of most basal exposures to uppermost portions of the section.
57 W Mahanga Stream Field Area E A 150 m
Fig. 15A
lithofacies inferred above dashed line
B E Tolaga Bay South Field Area Tolaga Bay W Wharf Cook’s Cove Hole in the Wall 125 m Fig. 15B
C S Fig. 15C Cook’s Cove South Field Area N 100 m
D S Waihi Beach Field Area N E B Wairere Beach C Field Area ~140 m Fig. 15D
D Hikuwai sandstone - upper Mapiri Formation contact A LF1: Thin- to medium bedded sandstone and mudstone LF3: Medium- to very thick-bedded sandstone and mudstone LF5: Chaotic & contorted sandstone, tuff, and mudstone
58 LF2: Thin- to very thick-bedded sandstone and mudstone LF4: Thick- to very thick-bedded sandstone with mud clast conglomerate LF6: Mudstone Weathered/Covered A C 25 m
LF2 15 m
LF1 B D
5 m
~40 m
Figure 15. Examples of high-resolution photo-panoramas used for architectural analysis. A) Mahanga Stream field area: Beds are tabular and represent deposits of LF2, thin- to very thick-bedded sandstone and mudstone. B) Tolaga Bay South field area: Beds of LF2 are later- ally continuous, although contain minor incisional surfaces. C) Cook’s Cove South field area: Beds of LF1 and LF2 are laterally continu- ous and display an onlap surface where sub-parallel. Red vertical lines indicate faults. Green areas indicate vegetation. D) Wairere Beach section: Beds represent LF5 (chaotic and contorted sandstone, tuff, and mudstone) that contain slumped rhyolitic tuff beds, and LF6
59 (mudstone) in the upper Mapiri Formation. (m) (m) (m) (m) (m) (m) silt LVF UVF LF silt LVF UVF LF silt UVF silt LVF UVF silt LVF UVF silt LVF 24 48 72 LVF 96 120 144
F 23 47 71 95 119 143
F 22 46 70 94 118 142
21 45 69 93 117 141
20 44 68 92 116 140
43 19 LF3 67 91 115 139 LF4 18 42 66 90 114 138 F LF1 17 41 65 89 LF3 113 137
40 88 16 64 112 136 F
15 39 63 87 111 135 LF4 LF3 F 14 38 62 86 110 134
13 37 61 85 109 133 LF3 LF5 12 36 60 84 108 132 F LF1 LF2 11 35 59 83 107 131 LF2 LF3 10 34 58 F 82 106 130
9 33 57 81 105 129
8 32 56 80 104 128
7 31 55 79 103 127 LF3 LF1 6 30 54 78 102 126
5 29 53 77 101 125
4 LF5 28 52 76 100 124 LF4 3 27 51 75 99 123
F 2 26 50 74 98 122
1 25 49 73 97 121
0 24 48 72 96 F 120 wavy dunes faint climbing flame mudstone vegetation mud clasts ripples trough cross laminations ripples bedding structures sandstone F fault planar convolute climbing sand laminations laminations shells ripples bioturbation injections Figure 16. Stratigraphic section of the Cook’s Cove South field area and identified lithofa- cies. See Figure 4 for section location.
60 area. Sectionrecordedatadecimeterscale. SeeFigure4forsectionlocation. the Wairerein Formation Mapiri field upper Beach the of section Stratigraphic 17. Figure meters 10 11 12 13 14 15 16 17 18 19 20 0 1 2 3 4 5 6 7 8 9
clay-silt VF-F 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 20
clay-silt VF-F 50 51 52 53 54 55 56 57 58 59 60 40 41 42 43 44 45 46 47 48 49
clay-silt VF-F 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80
clay-silt VF-F 100 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
clay-silt VF-F 100 101 102 103 104 105 106 107 108 109 110 111 112 113 Inaccessible Rhyolitic tuff Sandstone Mudstone MTD
clay-silt 61 VF-F A B
5 km
5 km C
Erosional, nested channels Erosional channels or scours (thickness of line proportional to size) LF1: Thin- to medium-bedded sandstone and mudstone LF2: Thin- to very thick-bedded sandstone and mudstone Lf3: Medium- to very thick-bedded sandstone and mudstone LF4: Thick- to very thick-bedded sandstone with mud clast conglomerate Figure 18. A) A plan form conceptual model of Hikuwai sandstone lithofacies distribution across a lobe. The model portrays a lobe with deposits on the order of ~6 km long and 4 km wide. The Hikuwai sandstone is comprised of stacks of this single architectural element, although of changing dimensions and shapes. Incisions are interpreted to represent a distributary network of channels and scours acting as conduits and regions of focused flow for sediment dispersal throughout the lobe. Small, nested channels are more likely to occur in the proximal region of the lobe, while discontinuous scours with less common nesting are more likely to occur in the medial to distal regions. Average incision depth is also expected to decrease down-system. B) The conceptual model compares well to an amplitude extraction (10 ms window) of a deep-water lobe system from offshore western Africa. This image represents a composite of lobes, but clearly illustrates that channelization occurs throughout the system and at various scales (Reprinted from Sedimentary Geology, 232, Prélat A., Covault, J.A., Hodgson, D.M., Fildanic, A., Flint, S.S., Intrinsic controls on the ranges of volumes, morphologies, and dimen- sions of submarine lobes, 66-76, Copyright 2010, Figure 4, with permission from Elsevier). C) The medial area of the distributary com- plex is enlarged to highlight a region of comparable scale to the conceptual model. The distributive system continues to bifurcate with
62 increasing distance from the source, although the resolution is too low to determine if the erosional features become fractal continuous conduits or discontinuous scours. A B
Figure 19. Possible basin configurations for deposition of the Hikuwai sandstone. Dashed lines represent theoretical sediment delivery pathways. A) A small, margin parallel basin created between two ridges formed by thrust faults. This configuration is similar to the pres- ent day basin configuration in the southern Wairarapa region of the basin where there is a large subduction wedge, as shown in Figure 2B. B) A localized depression caused by listric normal faulting during extension of the basin. The basin is currently undergoing exten- sion in the Raukumara region as demonstrated by seismic data from offshore Tolaga Bay (Fig. 3). 63 VE = x4 LF1 LF2 LF3 LF4 Phase 3 LF5 Phase 4 LF6 Cook’s Cook’s Cove Hole in the Wall Tolaga Bay Cove South Wharf
Tolaga Bay South Wairere Beach N ? Phase 2
Waihi 0.25 km Beach Phase 1
1 km
1 km Mahanga Stream
Figure 20. Generalized 3D model of lithofacies distribution of the Hikuwai sandstone and Mapiri Formation in the Tolaga Bay area. The black line notes the outline of the outcrop and observed lithofacies boundaries. Locations of stratigraphic sections are noted in green. Interpreted lithofacies extent and correlation are noted with a gray dashed line.
64 Figure 21 (following page). A) Conceptual model of evolution of basin fill. The trench slope basin accommodation is controlled by a normal fault. Phase 1 begins with the initia- tion of sand-rich sedimentation by turbidity currents. Aggradational lobes with a distribu- tary network on their surface are deposited in healed slope accommodation. The lobes are elongate and approximately fill the width of the basin. Phase 2 is marked by initial progra- dation in an overall retrogradational phase, and eastward lateral migration. In Phase 3, the system begins to backstep, which reduces the degree of confinement and causes the depos- its to become wider, longer, and thinner. Continued lateral migration eastward may also occur. Phase 4 represents the gradual shut-off of the system with the loss of accommoda- tion and/or upstream avulsion of the feeder channel. Since the basin is no longer confined, flows that reach this area are very thin and are deposited over a wide region. In this final stage, the system is capped by increasingly distal turbidite deposits and mud-rich mass transport deposits. B) A cross-section of the healed slope accommodation configuration for each phase. C) Conceptual stratigraphic section of pseudo-wells from a proximal (PW-1) and distal (PW-2) region of the system. PW-1 shows a clear thinning upward pattern related to the overall backstepping of the system. This represents the generalized stacking pattern observed at Cook’s Cove. PW-2 has a stacking pattern that is much more uniform. Progradation, retrogradation, and lateral migration of the system are more difficult to detect in PW-2, making it a less able predictor of associated changes in accommodation configuration. A thinning upward stacking pattern occurs towards the top of both of the wells.
65 A Phase 1: Aggradational Phase 2: Initial progradation, Phase 3: Back-stepping Phase 4: Unconfined slope healing retrogradation and lateral migration and reduced confinement deposits/ MTDs Tokomaru Bay Tokomaru Bay Tokomaru Bay
a
Cook’s Cove Cook’s Cove Cook’s Cove PW-1 Cook’s Cove
Mahanga Stream Mahanga Stream Mahanga Stream Mahanga Stream PW-2
10 km
a’
thick thin mass transport deposit PW-1 PW-2
Phase 4: LF1 transi- tioning to LF6 Phase 4: LF1 tranisitioning to LF6 PW-1 PW-2 Phase 3: LF2 and LF1 a Phase 4 Phase 3: LF3 and LF2; grading into LF1 Phase 2: LF3 and LF2
Phase 3 400 m 400 Phase 2 Phase 2: LF3 and LF4 a’ 5 km Phase 1 Phase 1: LF2 Phase 1: LF3? (not exposed) B C 66 Figure 21
CHAPTER 2
BASIN AND PETROLEUM SYSTEM MODELING OF THE EAST COAST BASIN, NEW ZEALAND: A TEST OF OVERPRESSURE SCENARIOS IN A CONVERGENT MARGIN
BASIN AND PETROLEUM SYSTEM MODELING OF THE EAST COAST BASIN, NEW ZEALAND: A TEST OF OVERPRESSURE SCENARIOS IN A CONVERGENT MARGIN
Blair Burgreen, Kristian E. Meisling, and Stephan Graham Geological and Environmental Sciences, Stanford University, Stanford, CA 94305
ABSTRACT In the East Coast Basin (ECB), an active convergent margin of the North Island, New Zealand, the smectite-rich Eocene Wanstead Formation forms an effective seal across the basin, creating high overpressure in the Cretaceous through Paleocene units below due to disequilibrium compaction. This study examines the evolution of pore pressure and porosity in Hawke Bay of the ECB by first establishing a stratigraphic and structural framework through seismic interpretation and structural reconstructions of a regional two-dimensional seismic line. This framework is incorporated into a basin and petroleum system model to predict the generation, distribution, and dissipation of overpressure, and examine the influence of faults, erosion, structural thickening, and seal effectiveness of the Wanstead Formation on pore pressure evolution. We find that natural hydraulic fracturing is likely occurring in sub-Wanstead source rocks, which is a favorable setting for potential shale gas plays. We use poroelastic modeling to investigate the impact of horizontal bulk shortening due to tectonic compression on pore pressure and the relative order of principal stresses. We find that shortening modestly increases pore pressure. When 5% or greater shortening occurs, the horizontal stress may approach and exceed vertical stress in the last 4 m.y. of the basin’s history. Shortening impacts both the magnitude and relative order of principal stresses through geologic time. Due to the overpressured nature of the basin, we suggest that subtle changes in stress regime are responsible for the significant changes in structural deformational styles observed,
68 enabling compressional, extensional, and strike-slip fault regimes to all occur during the tectonic history and, at times, simultaneously.
INTRODUCTION Basin and petroleum system modeling (BPSM) is increasingly being used as a tool to understand and predict pore pressure in basins around the world (Düppenbecker et al., 1999; Swarbrick, 2002; Yu and Cole, 2003; Kunda et al., 2008; Helset et al., 2009). Pore pressure prediction is important to optimize field safety conditions for real-time drilling, and for paleo-modeling to provide a framework for development of the basin and petroleum systems. Pore pressure distribution affects migration of fluids and gases (England et al., 1987; Hantschel and Kauerauf, 2009), seal capacity and hydrocarbon column heights (Finkbeiner et al., 2001; Darby, 2002; Nordgård Bolås et al., 2005; Webster et al., 2011), the kinetics of vitrinite and hydrocarbon source rock maturation (Carr, 1999; Zou and Peng, 2001; Scotchman and Carr, 2005), and the evolution of basin structure (Hubbert and Rubey, 1959). BPSM provides a means for testing potential scenarios under which excess pressure above hydrostatic pressure, or overpressure, can develop, how overpressure may dissipate or be redistributed across the basin, and how overpressure impacts migration and seal capacity. Additionally, BPSM tracks the pore pressure throughout geologic time, providing a robust framework to understand the porosity and permeability evolution of the sediments based on predictions of effective stress through time (Swarbrick, 2002). The East Coast Basin (ECB) of the North Island, New Zealand is a primarily gas-prone basin in a convergent margin setting, and variably overpressured with depth (Fig. 1). Here, the term convergent margin sediments is used to refer to sediments between the arc and trench, which includes the forearc basin, trench slope, and accretionary subduction complex. The basin has been explored since the late 19th century with the discovery of oil and gas seeps onshore, however unanticipated shallow, near-lithostatic overpressures have been a problem for exploration, creating unsafe well conditions and hole instability (Darby and Funnell, 2001). The presence and magnitude of overpressure is variable throughout the basin, depending both on
69 local stratigraphy and structure (Darby and Funnell, 2001). Therefore, the ECB is an ideal system to explore how the interplay of stratigraphy and structure impacts the development of overpressure. In the ECB, disequilibrium compaction likely acts as the main mechanism generating overpressure (Darby and Funnell, 2001). The depth at which overpressure develops from disequilibrium compaction depends primarily on the sedimentation rate and permeability (Swarbrick et al., 2002). Horizontal stresses related to convergent margin tectonics may also increase pore pressure due to porosity reduction from compression (Walder and Nur, 1984; Cello and Nur, 1988), which is an important consideration for the ECB. However, limited data is available for petroleum basins in compressional settings, and the effect of compressional stress on pore pressure is poorly understood (Swarbrick et al., 2002). Most basin and petroleum system models assume Terzaghi’s model, which only account for vertical overburden stress in estimating pore pressure (e.g., Gusterhuber et al., 2014). As part of a convergent margin setting, overpressure from subduction-related mechanisms should also be considered in the ECB. Subducted sediments release fluids though compaction, the smectite-illite transformation, hydrocarbon generation, and deeper dehydration processes that transfer fluids to shallower levels through faults that sole out into the basal décollement (Saffer and Tobin, 2011). Accretionary prisms around the world are typically overpressured (von Huene and Lee, 1982; Moore and Vrolijk, 1992; Fisher and Zwart, 1996; Saffer and Tobin, 2011), although pore pressure within the forearc region is more variable because most fluid release occurs within 80 km of the trench (Saffer and Tobin, 2011). Although the subduction process cannot be accounted for presently in industry-standard BPSM software, it is worth consideration as an alternative overpressuring mechanism. The development of overpressure can have a large effect on rock strength and influence the structural development of the basin. Foroozan et al. (2012) numerically modeled the interplay between generation and dissipation of pore pressure in an actively shortening basin to demonstrate the resulting style and evolution of faulting and basin compartmentalization. In overpressured systems close to lithostatic pressure,
70 horizontal stress limits for extensional, strike-slip, and compressional environments approach vertical stress, and enable faulting with smaller differential stress requirements (Zoback, 2007). Although the style of faulting can still be predicted by Andersonian fault theory (Anderson, 1951), small changes in the stress state in overpressured systems can rearrange the order of principal stresses and change the style of faulting (Zoback, 2007). This is often seen in highly overpressured accretionary subduction complexes where spatial variations in stress orientations and magnitude promote both compressional and extensional structures (Byrne et al., 2009; Song et al., 2011). In this study, we aim to better understand the occurrence and distribution of overpressure in the ECB through BPSM by linking the stratigraphic and structural history of the basin to present-day pore pressure. The model allows hypothesis testing to examine the role of mudstones as seals, faults in basin compartmentalization, the structural history of uplift and erosion, and horizontal tectonic forces in a convergent margin setting.
GEOLOGIC BACKGROUND The stratigraphy of the ECB is closely linked to its tectonic development. The metasedimentary basement of the ECB formed during Permian to Early Cretaceous time as part of an accretionary subduction complex on the margin of Gondwana (Fig. 2; Mortimer, 2004). The subduction complex is known as the Torlesse Supergroup, which includes several elongate sub-terranes representing phases of accretion to the Gondwana margin (Mortimer, 2004). Structural boundaries between these terranes and deformation fabric of the Mesozoic subduction margin created preferred planes of weaknesses that were reactivated during the Cenozoic phase of deformation in the ECB (Field et al., 1997). Lower Cretaceous sediments conformably and unconformably overlie the Torlesse basement representing a less deformed overlap sequence of syn-tectonic deposits. These strata are typically turbiditic in nature and more heavily deformed on the eastern side of the basin (Field et al., 1997; Laird and Bradshaw, 2004).
71 Mesozoic subduction ceased around 100 Ma due to the collision of the Hikurangi Plateau, a ~35-km-thick basaltic oceanic plateau, with Zealandia (Davy et al., 2008; Reyners, 2013). The ECB entered a dormant convergent margin phase in which it experienced overall quiescence, coeval with the opening of the Tasman Sea (Ballance, 1993; Laird and Bradshaw, 2004). The mud-rich, siliceous Whangai Formation and Waipawa Black Shale, deposited during Late Cretaceous through Paleocene time, are considered prospective hydrocarbon source rocks in the region (Hollis et al., 2005 and references therein). They are overlain by the smectite-rich Wanstead Formation, deposited during Paleocene through Eocene time, followed by deposition of the Oligocene Weber Formation, a calcareous massive mudstone (Field et al., 1997). The west-dipping Kermedec-Hikurangi trench reactivated the ECB convergent margin around 25 Ma, defining the present-day eastern extent of the basin (Ballance, 1976; Rait et al., 1991; Kamp, 1999; Stern et al., 2006; Reyners, 2013). Although most of the plate convergence was accommodated on the subduction décollement (Nicol and Beavan, 2003), the upper plate also underwent internal deformation in the form of reverse, normal, and strike-slip faulting, as well as basin rotation (Nicol et al., 2007 and references therein). The basin experienced three phases of Neogene deformation including: (1) a compressional phase from 25 Ma through ~15 Ma resulting in extensive reverse faulting and uplift (Chanier, 1991; Rait, 1992; Bailleul et al., 2007), (2) an extensional phase from ~15 Ma through 5-6 Ma resulting in basin- wide normal faulting and subsidence (Chanier, 1991; Barnes et al., 2002), and (3) a renewed compressional phase from 5 - 6 Ma through present-day resulting in reverse faulting and uplift (Chanier, 1991; Nicol et al., 2002; Nicol and Beavan, 2003; Nicol et al., 2007). These phases of basin deformation are likely due to the upper plate’s response to subduction of the buoyant Hikurangi Plateau (Reyners, 2013). Although large amounts of strike-slip translation have previously been proposed for the North Island (King, 2000 and references therein), strike-slip faulting plays a relatively minor role in deformation east of the Axial Ranges (Fig. 1; Nicol et al., 2007). Throughout most of Neogene time, oblique subduction caused clockwise
72 rotation of the basin, with the greatest amount of rotation occurring in the Wairoa Domain during the last 10 Ma (Wallace et al., 2004). Increasing margin-parallel plate motion relative to margin-perpendicular plate motion caused a shift in deformational style from basin rotation to strike-slip displacement in the last 1-2 Ma (Nicol et al., 2007). The majority of the ECB was in deep-marine conditions during Neogene time. Stratigraphy of the Neogene section is spatially and temporally variable, however, and is closely linked to Cenozoic structural development. Out-of-sequence thrusting during compression created margin-parallel, elongate sub-basins with distinct sediment-filling histories (Chanier and Ferrièr, 1991; Barnes et al., 2002; Field et al., 2006; Bailleul et al., 2007; Bailleul et al., 2013; Burgreen and Graham, 2014). Although sedimentation was dominated by mudstone deposition, sand-rich turbidites were deposited within bathymetric lows and limestones are locally observed on structural paleo-highs (Bailluel et al., 2013). The dynamics of the ECB changed dramatically within the last 4 m.y. Significant uplift occurred over two Pliocene-Pleistocene intervals, from 2.5-3.7 Ma and after 1.5 Ma, which led to uplift of the Coastal Ranges, the Axial Ranges, and the Raukumara Peninsula (Melhuish, 1990; Beanland et al., 1998; Nicol et al., 2002; Nicol et al., 2007). These uplift events resulted in erosion that exhumed the western part of the basin. Uplift in the Raukumara Peninsula was caused by underplating associated with subduction (Walcott, 1987; Sutherland et al., 2009), which also resulted in overall extension of the region (Walcott, 1987; Cashman and Kelsey, 1990; Field et al., 1997; Mazengarb and Speden, 2000; Barnes et al., 2002; Barnes and Nicol, 2004; Nicol et al., 2007). The Hawkes Bay and Wairarapa regions of the ECB continue to exhibit deformation, predominantly on reverse and strike-slip structures, based on structural analysis (Nicol et al., 2007). The basin width from the Axial Ranges to the trench is up to 180 km (Barnes and Nicol, 2004), and is dominated by NE striking faults.
73 Present-Day Pore Pressure Distribution The ECB is known for having high overpressures that are difficult to predict (Darby and Funnell, 2001). Although some data from drill stem tests (DST), repeat formation tests (RFT), and modular dynamic tests (MDT) provide direct measurements of reservoir pressure, pore pressure data for non-hydrocarbon reservoir rocks are predominantly limited to mud weights recorded during drilling. Mud weights in the ECB are expected to be a good proxy for pore pressure because increases in mud weight were typically made in response to gas kicks and increases in connection gas, rather than the practice of drilling overbalanced in anticipation of higher pressures (Darby and Funnell, 2001). Overpressure is present in all regions of the ECB, but pressure versus depth profiles based on mud weight throughout the basin show that overpressure is highly variable in magnitude and depth (Fig. 3). High overpressures greater than 6 MPa were encountered at a depth of less than 400 m in the Rotokautuku-1 well. Wells of the Hawkes Bay and Wairarapa regions have lower overpressures than wells of the Raukumara and Northern Hawkes Bay regions, although there are also fewer wells in the Hawkes Bay and Wairarapa regions for comparison. Generally, the Cretaceous through Paleogene sequence is overpressured throughout the basin, whereas the Neogene sedimentary sequence is variably overpressured (Fig. 3; Darby and Funnell, 2001). The Quaternary section is not typically overpressured, which is not surprising given that it is most likely to be in hydraulic communication with the surface. The pressure distribution within the ECB is closely tied to lithostratigraphy (Darby and Funnell, 2001). In the Cretaceous through Paleogene section, the smectite- rich Wanstead Formation acts as an effective seal with very low permeabilities, creating cells of overpressure (Darby et al., 2000). The lithostratigraphy of the Neogene section is much more variable, and overpressure cells only develop where thick mudstones provide an effective seal (Darby et al., 2000). Examination of sandstone and siltstone porosity versus depth data reveals that potential hydrocarbon reservoir units do not follow hydrostatically-pressured compaction trends (Fig. 4), with both over- and under-compaction observed. Porosity preservation is commonly
74 associated with disequilibrium compaction, although it can also be associated with dynamic transfer of pressure in reservoir units (i.e., the centroid effect; Dickinson, 1953). Non-reservoir mudstone units are also overpressured based on observations from mud weight and sonic density logs, however, indicating disequilibrium compaction acts as the primary mechanism (Darby and Funnell, 2001). Load transfer mechanisms, such as gas generation and smectite to illite transformation, were not considered in this study because they are not typically associated with substantial porosity preservation (Yassir and Addis, 1998; Webster et al., 2011). Overcompaction is also observed, which could be related to uplift of sediments, horizontal compression, poorly sorted sediments, or cementation. To predict sediment porosity, the maximum effective stress through time must be estimated, which is a function of the overburden load, rock compressibility, and pore pressure (Hantschel and Kauerauf, 2009). For example, the Awatere-1 well in the northern Hawkes Bay region is located on a thrust-cored anticline (Fig. 1; Ian R Brown Associates Ltd, 1999a). Porosity values of sandstone samples above 1500 m depth are lower than anticipated, indicating overcompaction (Fig. 5). The fine-grained nature and poorly-sorted composition of the samples, which include sand, silt, and clay, may contribute to the low porosities. Figure 4 shows that sandstone samples from ECB wells have lower permeabilities for a given porosity than typical sandstone, consistent with the behavior of mud-rich sandstones (petrology not reported). However, a fine grain and mud-rich nature of the sandstone cannot fully explain the observed low porosity values, which are even lower than porosities for typical shale. Given the structural deformation that has occurred with the last 1-2 m.y., samples with extremely low porosities for a given depth may have experienced greater burial depths with higher effective stresses in the past. The current-versus-expected porosity curve indicates that 50-400 m of uplift and erosion may have occurred (Fig. 5). Below 2000 m depth, the Awatere-1 sandstone samples are above their expected porosity value, despite possible uplift. In this case, the sediments are undercompacted likely due to overpressure, which has reduced the effective stress. This zone of undercompaction is associated with signs of overpressure in the well’s sonic log. At 1225 m depth, there is a sharp decrease in velocity in the
75 sonic log associated with an increase in mud weight (Fig. 5). Velocity normally increases with depth as sediment becomes more compacted and releases water, however porosity preservation is associated with deviations in this trend. Additionally, there is a flattening to slight reduction in velocities with depth starting at around 1480 m. This is also associated with a deviation from the modeled sonic log for these lithologies under hydrostatic conditions. The top of overpressure is likely located between the sharp velocity decrease at 1225 m depth and the top of the reduced velocities at 1480 m depth. The Titihoa-1 well, located 211 km south of Awatere-1, also contains sandstone samples with higher than anticipated porosities given its burial depth (Fig. 6). Porosity preservation is associated with overpressure below a middle Miocene seal at 1800 m depth, represented by a sudden shift to lower velocities in the sonic log and a gradual increase in mud weight (Fig. 6; Darby and Funnell, 2001). In this case, the top of overpressure is stratigraphically correlated to the base of a calcareous mudstone unit. Although effective mud-rich seals and excessive overburden stress clearly play a role in the development of overpressure through disequilibrium compaction in these two representative wells, horizontal stresses likely also play a role as part of an active convergent margin. Compressional regimes are commonly associated with high overpressures, however, thus far, their relative impact on overpressure development in petroliferous sedimentary basins has been poorly quantified (Fisher and Zwart, 1996; Yassir and Addis, 1998; Swarbrick et al., 2002). In low permeability, normally- to under-consolidated mud-rock, shear stress can cause liquefaction, which reduces effective stress through pore collapse and generates additional overpressure (Yassir, 1999). Signs of liquefaction are present throughout the ECB including onshore and offshore mud volcanoes (Ridd, 1970; Law et al., 2010) and shale diapirs (Mazengarb, 1998; Nicol and Uruski, 2005; Zeyen et al., 2011). Compression-related uplift in the ECB is likely responsible for the near-lithostatic overpressures observed at shallow depths. Although uplifted sediments typically experience pore pressure reequilibration, they can maintain their pore pressure if volume-enhancing mechanisms, such as
76 porosity rebound and fracturing, are inhibited (Yassir, 1999; Darby et al. 2000). Darby and Ellis (2001) modeled a hypothetical uplifted region of the ECB and found that overpressure could only be maintained when lateral compression was accounted for. Although horizontal stresses have clearly impacted the ECB, it is important to distinguish the stress regime of the basin at present day versus throughout geologic time. The onshore central and southern regions of the basin are presently experiencing a transtensional stress regime based on focal mechanisms where the maximum principal horizontal stress is oriented approximately parallel to the margin in the Hawkes Bay area (Townend et al., 2012). Nicol et al. (2007) demonstrated that plate convergence dominated prior to 15 Ma, and there has been an increasing margin- parallel component of plate motion since 10 Ma. This suggests that vertical stress acted primarily as the least principal stress during the convergence-dominated phase associated with compressional structures, and then shifted to act primarily as the intermediate principal stress during the margin-parallel phase associated with strike- slip deformation. The northern region of the basin is an exception because it is presently characterized by extension (Walcott, 1987; Reyners and McGinty, 1999; Townend et al., 2012).
MODELING A 2D basin and petroleum system model was constructed for offshore Hawke Bay to test possible scenarios for generating overpressure. BPSM reconstructs basin history in the context of the timing of hydrocarbon generation, migration, and accumulation through forward modeling. Input for BPSM includes basin geometry, horizon ages, lithologies, fault properties, hydrocarbon source rock properties, basal paleo-heat flow, sediment-water interface temperature, and paleo-water depth. Seismic line CM05-01 of the MV Multiwave CM05 high-fold multichannel seismic reflection survey in offshore Hawke Bay was used to construct the basin and petroleum system model (Fig. 1; Multiwave, 2005). Along this line, the basin experienced compressional, extensional, and inversion tectonic regimes, making it an ideal vehicle to test the impact of deformational events on overpressure development.
77
CM05-01 Interpretation Seismic interpretation of line CM05-01 provides the essential framework for both structural restoration and BPSM, and therefore a robust interpretation that honors all available stratigraphic and structural constraints is paramount. The 124 km CM05- 01 seismic line was selected for interpretation because it is a long regional line, oriented perpendicular to the active margin, which ties the Hawke Bay-1 well. The seismic stratigraphy of CM05-01 is based on previous interpretation of nearby seismic lines by Barnes et al. (2002) and Barnes and Nicol (2004). The line is cut by numerous thrust and normal faults, of which the Lachlan fault is the largest and most active (Fig. 7). Quaternary kinematics of the Lachlan fault has been studied using uplift rates of marine terraces on the Mahia Peninsula and seismic sequence stratigraphy (Berryman, 1993a, 1993b; Barnes et al., 2002; Barker et al., 2009). The Lachlan fault acts as the principal thrust of a triangle zone (i.e., MacKay et al., 1996), where Kidnappers fault acts as the principal backthrust, creating a geometric wedge bound by opposite- dipping thrusts (Fig. 7; Barnes and Nicol, 2004). Complexly-imbricated thrust sheets along the Lachlan ridge expose Cretaceous and Paleogene rocks on the seafloor (Pettinga, 1982; Barnes and Nicol, 2004). In Barnes et al. (2002), mapped horizons are tied to rock dredge and gravity core samples, geometric projections of seismic reflections to outcrop, and the Hawke Bay-1 well. They recognized three main phases of deformation on the Lachlan ridge, including initial thrusting during early Miocene time, extensional faulting from middle Miocene to early Pliocene time, and Pleistocene to Holocene structural inversion. These three phases of deformation have also been identified in the CM05-01 seismic line (Fig. 2). In this study, eight tectonostratigraphic horizons were mapped based on interpretations by Barnes et al. (2002) on nearby seismic lines, and these horizons were used to reconstruct the structural history of the offshore Hawke Bay region.
78 Seismic Stratigraphy Many 2D and 3D basin and petroleum system model grids are based on seismic stratigraphy, and different model scenarios are built around the same seismic interpretation. Therefore, the interpretation of horizons, their stratigraphic ages, and the timing and degree of structural displacement are the foundation of the model. The seismic interpretation dictates the depth of the source rock, timing and depth of burial from both stratigraphic and structural thickening, and the timing and amount of erosion. The seismic stratigraphy is discussed from deepest to shallowest interpreted horizon, where the deepest horizons were picked with least confidence and the shallowest horizons were picked with most confidence. The basal décollement, or subduction zone thrust, is the deepest horizon interpreted in the seismic line, corresponding to the boundary between the undeformed sediments on the Hikurangi plateau of the subducting Pacific plate and the deformed sediments and accretionary basement of the overriding plate (Fig. 7). The top of the subducting Pacific plate is at a depth of between 12 and 25 km beneath Hawke Bay (Bannister, 1988; Ansell and Bannister, 1996; Barnes and Nicol, 2004). Identification of the décollement was based on the shallowest occurrence of continuous and undeformed, high-amplitude reflections interpreted to underlie the basal thrust. The Top of Torlesse Supergroup horizon and Top of Cretaceous horizon were difficult to follow due to poor data quality at depth. Subtle changes in amplitude and character were used to map the horizon tops, and reflection dip was used to guide structural geometry at depth. Significant uncertainty remains in these deep horizon picks, which translates into uncertainty in the eastward extent of the Torlesse Supergroup basement terrane. The Top of Paleogene, Late Miocene Unconformity, Top of Tongaporutuan, Top of Lower Pliocene, and Top of Pleistocene horizons were identified based on the interpretation of Barnes et al. (2002). Barnes et al. (2002) conducted a detailed analysis of the stratigraphy and structural evolution of the Hawke Bay region using 2D multichannel seismic profiles with an average line spacing of 3.5 km, and their interpretations were carried to the CM05-01 seismic line modeled in this study. The
79 horizon tops listed above correspond to Horizon 14 (~30 Ma; Top of Paleogene), Horizon 13 (ca. 9-8 Ma; Late Miocene Unconformity), Horizon 12 (ca. 7 Ma; Top of Tongaporutuan), Horizon 11 (4 Ma; Top of Lower Pliocene), and Horizon 8 (ca. 1 Ma; Top of Pleistocene), respectively, from their study. Figure 2 references these horizons to the tectonostratigraphy in the region. Horizons were correlated across faults based on their seismic character.
Sequence of Structural Deformation Structural reconstructions are an important part of basin and petroleum system modeling in tectonically complex regions because they provide geologically robust basin geometries through time that are critical to estimating burial history and predicting fluid migration pathways. Structurally reconstructed models work backwards in time from present-day geometry by removing progressively older sediment layers, restoring faults and unfolding structural deformation, and decompacting the underlying sediments at each successive time step. Structural reconstructions were completed using Dynel2D®, a geomechanically-based restoration and forward modeling software program using 2D finite element methods (Maerten and Maerten, 2006). Interpreted seismic horizons were converted to depth using a velocity model from GNS Science based on check-shot and sonobouy data (Funnell et al., 1999). The major faults were carefully restored, although some smaller faults were removed from the cross-section to simplify the reconstruction. Sediment layers were decompacted based on parameters for shale lithologies from Sclater and Christie (1980), as the ECB is predominantly mud-rich. Out-of-sequence faulting in the convergent margin was reconstructed in seventeen time steps, guided by the structural interpretation of Barnes and Nicol (2004). Time steps 1-9 (100 Ma, 92 Ma, 83 Ma, 75 Ma, 66 Ma, 60 Ma, 56 Ma, 34.6 Ma, 24 Ma) record the deposition of the pre-Miocene sediments, which generally define an eastward-thinning sediment wedge (Fig. 8). Time step 10 (18.8 Ma) records the initial low-angle thrusting along the proto-Lachlan fault, which occurred sometime during early to middle Miocene time. Syn-tectonic deposition of middle Miocene
80 sediments in the accommodation space created within the proto-Lachlan basin are rotated and thin on the flank of the rising Lachlan ridge. In time step 11 (13.6 Ma), continued deposition of mid Miocene sediments takes place, with most accommodation in the Lachlan basin and the region east of the Lachlan ridge. The Lachlan ridge is simultaneously eroded as it is uplifted, exposing Paleogene through Cretaceous sediments. Time step 12 (11.9 Ma) records continued uplift along the Lachlan ridge, as well as the initiation of extensional faulting that begins to open the Lachlan basin. Eastward-dipping listric normal faults dissect the basin in the last stages of fill prior to the Late Miocene unconformity (Horizon 13) depicted in time step 13 (8.5 Ma). Time step 14 (7 Ma) records the continued opening of the Lachlan basin through extensional faulting and deposition of associated growth strata. In time step 15 (4 Ma), the extensional faults in the Lachlan basin become less active, and the Lachlan fault becomes reactivated as a normal fault associated with the eastward thickening of the Pliocene interval in the Lachlan basin. In time step 16 (0.8 Ma), the Lachlan fault reverses motion again, causing renewed uplift of the Lachlan ridge and rotation and inversion of strata on both basinward and landward sides of the ridge. Outboard, uplift along the Ritchie ridge associated with subduction of a seamount (Barker et al., 2009) created additional accommodation space between the ridges. In the final time step 17 (present-day), a small amount of accommodation is created landward associated with continued uplift of the Lachlan ridge, and there is continued deposition outboard associated with development of Ritchie ridge, as well as the development of young imbricate thrust faults of the accretionary subduction complex to the east. Based on this structural and stratigraphic history, the basin is broadly divided into four main regions: 1) the Inboard region west of Kidnapper’s fault, 2) the Lachlan basin region between Kidnapper’s fault and Lachlan ridge, 3) the Outboard region between Lachlan ridge and Richie ridge, and 4) the Accretionary complex (Fig. 7). The Inboard region has undergone a steady rate of moderate burial since Neogene time and is characterized by high-angle low-displacement thrust faults. The Lachlan basin region has undergone more significant burial since Neogene time, and has experienced
81 both reverse and extensional faulting. Burial rate is highest in the last 10 m.y. due to accommodation created by the extensional faults. The Outboard region has also experienced significant burial similar to the Lachlan basin, although burial rates are highest within the last 5 m.y. in response to the more recent uplift of the Ritchie ridge. Unlike the Lachlan basin, accommodation rate is often higher than sedimentation rate in the Outboard region creating local under-filled basins. Structurally, the Outboard region is dissected by listric thrust faults. The Accretionary complex is located just outboard of Ritchie ridge and is characterized by numerous in-sequence thrust faults associated with the offscraping of subducting sediments. Across the entire reconstruction, there is a total shortening of 21 km since 24 Ma, with most shortening occurring during early Miocene time due to low angle thrusting within the basin and in the young accretionary complex to the east of Richie ridge. Excluding the accretionary complex, structural shortening is significantly less, totaling only 7 km since 24 Ma for the 0 to 95 km portion of the present-day section (Fig. 8). The Torlesse terrane shortens 8 km between 24 Ma and 18.8 Ma due to low- angle thrusting, but shortening is reduced to 7 km by 4 Ma due to extension in the Lachlan basin. Nicol et al. (2007) estimate 35 +/- 7 km of shortening in the offshore Hawke Bay region. The discrepancy between these estimates may be due to their use of the fault-parallel flow algorithm in 2DMove™ software, differences in seismic interpretation, or, most significantly, differences in estimation of eroded strata associated with unconformities. The interpretation presented in this study assumes minimum shortening and erosion in the reconstruction because this provides an end- member scenario for modeling, and also because there is no direct evidence for more significant erosion. Although there is no single solution for a structural reconstruction, these cross sections represent geologically reasonable solutions for stratigraphic and structural evolution of the basin, and are used as the geometric framework for the basin and petroleum system model. Throughout the reconstruction process, changes and simplifications were made to the structural interpretation to reduce complexity, while broadly honoring the sequence, timing, and overall geometry of regional structures documented by Barnes
82 and Nicol (2004). In one example, the faults associated with Kidnapper’s ridge were rooted into the main Lachlan fault, which was modified into a ramp-flat-ramp geometry that better enabled fault restoration. Additionally, the specific timing and magnitude of deformation honors the CM05-01 line, and therefore varies from the more general Hawke Bay tectonic events in Figure 2. For example, the CM05-01 line crosses the northern end of the Kidnapper’s ridge fault complex, where it is buried and has experienced significantly less vertical displacement than suggested by Barnes and Nicol (2004). Due to poor imaging, reconstruction of the accretionary complex east of Richie ridge was treated schematically and it does not account for the rate of subduction, true magnitude of shortening, or sequential imbrication of multiple thin thrust sheets. The accretionary complex was not the focus of this study because burial and temperature are considered insufficient to generate hydrocarbons. Time step 10 to time step 11 was particularly challenging to reconstruct, likely due to some structural movement in and out of the plane of the section. Numerous assumptions were made regarding the amount of erosion and shortening, as well as the paleobathymetric datum for each time step. Paleobathymetric estimations were based on biostratigraphic data and paleogeographic maps from Field et al. (1997).
Basin Modeling Horizons and faults from the structural reconstructions were transferred to PetroMod 2D Teclink (Version 2013.2)®. Typically, 2D basin and petroleum system models use an event-stepping method where sediments undergo layer-by-layer backstripping to determine an estimated initial thickness and basin geometry for subsequent use in forward modeling (Hantschel and Kauerauf, 2009). In regions where there has been significant horizontal offset of layers on faults, however, the event- stepping method leads to incorrect modeling of paleo-geometry (Neumaier et al., 2014). Additionally, event-stepping models cannot be used in thrust-faulted environments where a single horizon is duplicated along the z-axis of the model grid due to computational limitations.
83 In order to avoid these problems, a paleo-stepping model was used for this study. Paleo-stepping models require the user to specify basin geometry though time (Hantschel and Kauerauf, 2009), and are the only type of model that can handle complex thrusting geometries (e.g., Gusterhuber et al., 2014; Neumaier et al., 2014). In this case, the horizon and fault geometries reconstructed in Dynel 2D® were used as direct input for paleo-basin geometries for each time step. During the decompaction calculation, mass is added and/or removed from each layer at each time step in order to match the input layer thickness to the calculated state of compaction. Estimation of decompaction needs to occur prior to the input of each time step to the basin model in order to best approximate conservation of mass between time steps. Therefore, decompaction was carried out in this study during the structural reconstruction in Dynel® (e.g., Neumaier et al., 2014). A paleo-stepping model circumvents the problem of horizon duplication on the z-axis by dividing the model into numerous smaller models, or blocks, that do not violate this rule and can interact with each other. The user defines the number and geometry of the blocks, which enables the model to track the movement of the blocks (or mass) in the model through time. The blocks are tracked through parent-child relationships for each time step, where block properties from the parent are redistributed to the child in the sequential time step. The total number of blocks may change between time steps in the model as sometimes required due to thrust movement along faults. For example, a thrust fault may separate one block into two, and the properties of the parent block will be redistributed between the two new blocks based on their areas, geometry, and position relative to each other. Because the user defines each block’s geometry between time steps, more blocks means greater user control of the redistribution of properties between the parent and child blocks. However, the block geometries are defined by the user, so accurate redistribution of block properties depend on the users ability to track and geometrically define the blocks between time steps. Time steps in the basin model correspond to time steps in the structural reconstruction. Some modifications to the input geometries were made after the
84 reconstruction for compatibility and simplification in basin modeling, including the removal of overhanging layers associated with thrust faults and removal of the non- prospective accretionary complex. The time resolution of the basin and petroleum system model is dependent on the number of structural reconstruction steps, and additional time steps cannot be generated because they require structural geometries as input. Therefore, it is essential that the structural reconstruction include time steps significant to the petroleum system development (i.e., timing of expulsion, trap formation, deposition of source rock, reservoir rock, seal rock). Layer splitting for the Glenburn Formation, the Whangai Formation, Upper Calcareous Member of the Whangai Formation, Waipawa Black Shale, Wanstead Formation, Weber Formation, and Horizon 13 were conducted during the structural reconstruction in order to be able to include deposition and deformation of these layers as separate time steps in the basin model. Layer splitting was also conducted within the basin model, but was used to improve gridding geometries in the horizontal direction and did not change the number of time steps. Additional vertical grid resolution was required in the vicinity of high angle faults zones to improve fault and horizon geometries, but faults cutting through steeply dipping horizons cannot provide smooth geometries without excessive layer splitting. A summary of BPSM input at present-day is shown in Figure 9.
Lithologies Lithological properties were based on cuttings from Hawke Bay-1 and corresponding onshore and well stratigraphy as described in Field et al. (1997). The lithologies used are listed in Table 1 with their corresponding thermal conductivities, densities, total organic carbon (TOC), hydrogen index (HI), fracture pressure limit, and Poisson’s ratio. Porosity-versus-effective-stress relationships and porosity– permeability relationships of the modeled lithologies are presented in Figures 10 and 11. Lithologic properties are based on Athy’s compaction law (Athy, 1930) and the multipoint model (Hantschel and Kauerauf, 2009), with values based on comprehensive literature review by Hantschel and Kauerauf (2009). Although the porosity-depth relationships for sandstone and siltstone are useful to demonstrate the
85 impact of overpressure and uplift on porosity, they are poor calibration data because overpressure and uplift preclude estimation of maximum effective stress. Additionally, the basin is predominantly comprised of mudstone, but direct porosity measurements from shales are unavailable because non-reservoir units were not sampled in the wells. Accordingly, porosity-versus-depth trends for mudstones were analyzed in this study from bulk density logs and found to correspond to Athy’s Law of compaction (Athy, 1930), although trends were commonly offset to shallower depths due to uplift. Therefore, the porosity-versus-effective-stress relationships were modeled using Athy’s Law based on averaged properties of lithologic mixtures. Porosity–permeability relationships for Horizon 8, Horizon 11, Horizon 12, and Horizon 13 were calibrated to mud weight data from the Hawke Bay-1 well (Fig. 12). Mud weights show a build up of ~3 MPa excess pressure in the Neogene section (0.5-2.24 km below sea level). An additional increase in overpressure at the bottom of the well is associated with a major unconformity represented by a methane gas- bearing Oligocene limestone unit. This pressure kick was not used for calibration in the model, because the reservoir is too thin and of limited lateral extent for inclusion. The Oligocene limestone unit overlies the Wanstead Formation, which was not penetrated in the well because the bottom-hole-assembly became stuck in clay 100 m below the limestone (Heffer and Milne, 1976). The smectite-rich Wanstead Formation acts as a regional seal in the ECB, and is often associated with large overpressures. Darby et al. (2000) showed that the smectite content in the Wanstead Formation controls the porosity, permeability, capillary entry pressures, and fracturing behavior of the Formation, and can act as a significant barrier to flow. The Wanstead Formation was modeled with a 20% smectite content. This is lower than the 30% illite/smectite content measured by Darby (2002) on Wanstead-equivalent cuttings from the Mangaone-1 well. However, in this model, a 30% smectite content causes the Wanstead Formation to act as a near perfect seal and generate near-lithostatic overpressures at even shallow depths (Figs. 11, 12). This scenario is considered to be unrealistic because mud-weight data from the sub- Wanstead, Paleogene sections in most ECB wells suggest overpressure between
86 hydrostatic and lithostatic values, not approaching lithostatic pressure (Fig. 3). Sub-
Wanstead overpressure based on mud-weight data typically ranges between λp of 0.4 to 0.9, where λp is the ratio of pore pressure to lithostatic pressure. Because smectite content likely varies regionally, a smectite content of 20% was modeled in order to match observed overpressures within this λp range in the basin model. Hydrocarbon source rocks in the basin model included the Waipawa Black Shale and the Whangai Formation. These formations are modeled with TOCs of 3.6 wt. % and 0.56 wt. %, respectively, based on compiled data from Hollis et al. (2005). Although overpressure is often attributed to hydrocarbon generation, significant overpressure can only be achieved in areas immediately proximal to thermally-mature high-TOC source rocks (Swarbrick et al., 2002). Migration redistributes hydrocarbon- related overpressure throughout a permeability pathway, such that the total impact is typically an order of magnitude smaller than overpressure by disequilibrium compaction (Swarbrick et al., 2002; Hantschel and Kauerauf, 2009). Therefore, hydrocarbon-generated overpressure was not considered a major overpressure mechanism in the basin and not included in the calibration process.
Faults There are seventeen faults modeled through time as part of the CM05-01 basin and petroleum system model. Faults were modeled as closed (i.e., impermeable) for all time steps, because observed data shows that subsurface pore pressure has not dissipated despite surface breaching by many of the faults. In mud-rich systems, faults often have high seal potential due to high shale-gouge ratios (Freeman et al., 1998). Fault compartmentalization is common in many petroleum systems and is often identified by laterally distinct pressure regimes that have distinct pressure histories (Borge and Sylta, 1998; Borge, 2002; Williams and Madatov, 2005; Gibson and Bentham, 2003). Fault compartmentalization is also directly observed in the ECB, where there is an increase in pore pressure regime across a fault in Mangaone-1 at 1.3 km depth (Fig. 3).
87 Heat Flow Two heat flow scenarios of Funnell and Benchilla (2005) were modeled based on thermal calibration to the Hawke Bay-1 well (Table 2). Heat flow scenario 1 assumes a high heat flow history and incorporates a rifting event around 80 Ma associated with the opening of the Tasman Sea. Heat flow scenario 2 assumes a lower heat flow history and does not incorporate a rifting event.
RESULTS Base Case, Terzaghi type model In the base case model, only vertical stress is considered in accordance with Terzaghi type models (Terzaghi, 1923; Terzaghi and Peck, 1948), which is a typical simplifying assumption made in basin modeling even in many tectonically active environments (e.g., Gusterhuber et al., 2014). The base case modeling results show that overpressure begins to develop in the region soon after the deposition of the Wanstead Formation at 34 Ma (time step 8; Fig. 13). By 18.8 Ma (time step 10), excess overpressures from 1.5 MPa to 4.25 MPa develops in the Waipawa Formation (directly below the Wanstead Formation) in Blocks 1, 2, 3a, 3c, 7, 9, 10, 11, and 12, and up to 8.5 MPa in Block 9. Overpressure is due to disequilibrium compaction because fluid cannot escape laterally because of closed faults, or vertically because of the impermeable Wanstead Formation. Total overpressure in the model depends primarily on the depth of burial, because all of the lithologies are the same for each horizon across the blocks. Sedimentation rates are not high for any of the blocks, ranging from ~25 m/Ma to 180 m/Ma. The Wanstead seal rock prevents fluid from escaping and permits the generation of overpressure. Despite sedimentation rates within the same range, Blocks 3d, 4, 5, 6, and 8 do not experience any build-up of overpressure. These blocks are laterally connected to the surface due to thrusting, and excess pressure is able to dissipate. Although faults are modeled as closed (impermeable), pressure is able to leak off when formations have a direct hydraulic connection to the surface. This demonstrates the importance of the structural model in pore pressure development. Although the overhanging block geometry in Block 8 at
88 time step 10 is an artifact of the structural reconstruction, the sub-vertical beds of Blocks 3d, 4 and 5 are realistic geometries that may have permitted dissipation of pore pressure. Structural duplication in the model results in a component of structural thickening (tectonic overburden) throughout the basin, which as the same effect as very fast burial by sedimentation. Time step 12 at 11.9 Ma clearly depicts the impact of structural thickening in Blocks 6, 7, 8, and 9. Blocks 6 and 7 experience excess hydraulic pressures of 2.3 MPa and 5.2 MPa, respectively, directly beneath the Wanstead Formation. This represents a significant increase from the previous time step where the blocks experienced excess pressures of 0.4 MPa and 0.8 MPa, respectively. No sedimentation occurred between time step 11 and time step 12, and therefore all of the additional overpressure can be attributed to structural overburden. However, Block 8 in time step 12 experiences an effective sedimentation rate of 925 m/Ma where it underlies Block 5. The effect of the thrusted hanging wall is also clearly demonstrated in Block 9, where the region directly underlying the hanging wall experiences overpressures >30 MPa, while laterally contiguous layers without structural thickening experience overpressures <5 MPa directly below the Wanstead Formation. Minor uplift and erosion have also been incorporated into the model and exhibit the reverse effect to structural thickening (Fig. 14). Uplift and erosion reduce vertical stress, thereby reducing the required pore pressure to maintain equilibrium with the overlying column. This is demonstrated in the model between 11.9 Ma and 8.5 Ma (time steps 12 and 13), when about 800 m of section (Block 5 of time step 12) is eroded. Block 6 experiences excess pressure of 2.3 MPa at 11.9 Ma, which is then reduced to 0.9 MPa at 8.5 Ma (Block 7 in time step 13) post-erosion. Although this represents only a minor change in excess pressure, it demonstrates the ability of this mechanism to reduce pressure and its dependence on the input structural model. Luo and Vasseur (1995) found through modeling that impermeable, overpressured sediments underwent a pore pressure decrease along a trend larger than the hydrostatic gradient during uplift, allowing pressures to reach sub-hydrostatic levels in certain
89 cases. Uplift and erosion is commonly suggested as a mechanism of causing underpressure (Dickey and Cox, 1977; Law and Dickinson, 1985; Neuzil and Pollock, 1983; Doré and Jensen, 1996; Law and Spencer, 1998). Although sub-hydrostatic pressures are not noted in the model or in the basin, the reduction in pore pressure is in agreement with observations and modeling from other uplifted areas. As deposition continued through the Neogene, sub-Wanstead layers become increasingly overpressured with burial. Neogene sediments in the Lachlan basin begin to experience overpressure with the deposition of Horizon 12 due to disequilibrium compaction beneath a more effective seal (Fig. 11). Overpressure in Neogene sediments first develops in Block 5c at 7 Ma (time step 14), which experiences a high sedimentation rate up to 1400 m/Ma between 8.5 Ma and 7 Ma, achieving up to 2100 m of burial in the center of the Lachlan basin. The Neogene sediments outside of the Lachlan basin remain normally pressured due to low sedimentation rates. Overpressure begins to develop in Neogene layers outside of the Lachlan basin at 4 Ma (time step 15) due to disequilibrium compaction associated with burial in a shale- rich section. By present-day, excess pressures up to 2 MPa develop beneath Horizon 11, which represents the most effective seal within the Miocene section. However, overpressure is not as high as that observed beneath the Wanstead seal. The Miocene seals are less effective than the smectite-rich Wanstead Formation (Fig. 11), and therefore are unable to maintain the high >25 MPa overpressures occurring below the Wanstead Formation in the Cretaceous through Paleogene section. The highest excess pressure maintained in the Miocene section is just under 25 MPa, which occurs during the present-day step (time step 17) in Block 7c, at the center of the Lachlan basin at the base of the Neogene section. It is important to note that each stratigraphic layer in the Neogene is modeled with the same lithology for simplification and calibration to the Hawke Bay-1 well. The Neogene section, however, is likely significantly more complex and laterally variable (Fig. 2). The generation and preservation of overpressure depends on the distribution of mudstone, siltstone, and sandstone throughout the basin, and therefore improved stratigraphic modeling is required for more accurate predictions of pore pressure.
90 The development and distribution of overpressure varies throughout the basin due to compartmentalization by faults and top seal. In present-day (time step 17), pore pressure beneath the Wanstead Formation seal rock ranges from hydrostatic to 58 MPa of excess hydraulic pressure depending on the compartment. The sub-Wanstead excess pressure experienced in present-day depends both on the burial history and structural history of the block. Therefore, adjacent fault-bound compartments may have extremely distinct pore pressure versus depth profiles. For example, excess pressures of 21 MPa in Block 5 are juxtaposed against excess pressures of 56 MPa in Block 7. Blocks where the Wanstead Formation is deeply buried, such as Blocks 7a, 7c, 13, 15, and 16, exhibit the highest overpressures (>40 MPa) in present-day. Shallow blocks that have experienced pressure leakage to the surface in the past, such as Blocks 9 and 11, exhibit more moderate overpressures <10 MPa. Blocks that have been less deeply buried and retained overpressure throughout the basin’s history, such as Blocks 3, 4, and 5, exhibit intermediate overpressures between 17-22 MPa directly below the Wanstead Formation. Block 7e is laterally connected to the surface in present-day, and therefore is hydrostatically pressured. For most of the blocks, the top of overpressure corresponds with the geometry of the Wanstead Formation. Although pore pressure appears to be evenly distributed through each layer, layers in Present-Day Blocks 7d and 11 show overpressure corresponding more closely with depth. The Cretaceous through Paleogene stratigraphy is mud-rich and has poor permeability, preventing equilibration across the layer. This effect is less noticeable where there is minimal bed dip and overpressure generation is distributed more evenly. Horizontal permeability is greater than vertical permeability, and this effect is noted in Present-Day Block 5, where Cretaceous-Paleogene overpressure distribution is partly related to depth, and partly related to the geometry created by the deep structural anticline. The Neogene section is significantly less compartmentalized because many faults are no longer active and are buried, thereby hydraulically connecting sediments closer to the surface. The Neogene section can be viewed as a separate compartment from the underlying Cretaceous-Paleogene section because the degree of overpressure experienced by the Neogene section is not directly linked to the underlying
91 overpressures. Overpressure distribution in the Neogene depends primarily on the amount of burial and the presence, thickness, and quality of seal rock. To determine the impact of fluid expansion from hydrocarbon generation on pore pressure, the model was run first with generation only (no migration) to determine overpressure development exclusively from disequilibrium compaction. A second model was run using hybrid migration modeling. Hybrid migration assumes fluid flow is best modeled by Darcy flow in low permeability beds, and best modeled by flowpath migration in high permeability beds (>2.01 log(mD); Hantschel and Kauerauf, 2009). Results yielded no significant discrepancies in magnitude or distribution of overpressure between the two models for either heat flow scenario, confirming that hydrocarbon generation likely did not play a significant role in overpressure generation. Porosity preservation, or undercompaction, is a primary indicator of overpressure related to disequilibrium compaction. In Present-Day, many blocks exhibit undercompacted sediments due to overpressure (Fig. 15). For example, sediments directly below the Wanstead Formation in Blocks 3, 4, 5, 7a, 7c, 9, 13, 15, and 16 exhibit high porosities due to low effective stress in these regions. Unconsolidated, overpressured sediments are a common problem in drilling below the Wanstead Formation (Darby et al., 2000; Davies et al., 2000), and are likely also associated with the presence of shale diapirs in the basin (Field et al., 1998; Mazengarb, 1998; Nicol and Uruski, 2005). Porosity preservation depends not only on the distribution of overpressure in present-day, but the pore pressure history of the compartment. For example, Block 7d does not exhibit significant porosity preservation because it was only able to build-up overpressure starting at 11.9 Ma, when it became laterally disconnected to the surface through faulting. However, the Block had already reached close to maximum burial depth by this time, with only 500 m of additional burial to present-day, thereby limiting overpressure development. Block 7e shows overcompaction due to over 1500 m of uplift and erosion experienced in this area associated with thrusting on the Lachlan fault. Porosity preservation within the Neogene sediments is not as obvious as in the Cretaceous through Paleogene section,
92 although close inspection indicates that it is occurring. Block 14 experiences greater Neogene overpressures than Block 13, and therefore has higher porosities than sediments at the same depth in Block 13 just across the fault (Fig. 15). These results provide a reasonable start for understanding the distribution of overpressure in the ECB. However, it is important to note that as a two-dimensional model out of plane effects are not considered in this study.
Poroelastic, Horizontal Compression Case Although pressure calibration using Terzaghi-type models provides a good estimate of the vertical effective stress and pore pressure, it does not properly account for the stress regime in basins where horizontal stresses can approach or exceed vertical stress. Additionally, Terzaghi-type models use a very simple approach for predicting rock failure (Hantschel et al., 2011). Therefore, a poroelastic model was used instead of a Terzaghi model to incorporate horizontal stress in this convergent margin setting. The poroelastic model accounts for two time-dependent behaviors: 1) solid to fluid coupling in which a change in stress causes a change in pore pressure, and 2) fluid to solid coupling in which a change in pore pressure causes a change in volume (Wang, 2000). Terzaghi’s model for effective stress is, in fact, a special case of the poroelastic model in which pore pressure and stress are completely uncoupled (Wang, 2000). The poroelastic model assumes a fundamental relationship between stress, pore pressure, and strain that is based on the Biot coefficient and Poisson’s ratio (Hantschel et al., 2011). The model tests the impact of horizontal displacement scenarios on horizontal stress, thereby changing the mean stress. Therefore, increased shortening should increase the mean stress and decrease the porosity through compaction. Because plastic deformation is not accounted for in this model, there is no stress limit at which failure will occur, and therefore modeled pore pressures may be erroneous where stresses exceed the expected failure criterion (Hantschel et al., 2011). It is also important to note that horizontal shortening related to compression is different than shortening related to faulting. Shortening related to compression (bulk shortening)
93 affects the effective stress, pore pressure, and porosity within the sediment layers. Structural shortening accommodates shortening through sliding on faults, and although there may be more compression associated with or nearby the faults, the layers between the faults are not necessarily affected. One “no-shortening” and three compression-related shortening scenarios were tested to examine their impact on pore pressure. The present-day section is approximately 100 km long, so the scenarios include a 0% (0 km) shortening base case, a 1% (1 km) shortening case, a 5% (5 km) shortening case, and a 10% (10 km) shortening case. In each case, shortening occurs between 24 Ma and the present-day, contemporaneous with the Neogene convergent margin phase of the basin’s history. Given that most of the sediments have already experienced some amount of burial- related compaction, 10% shortening represents an uppermost end-member scenario. For deeply buried, low porosity (<1%) rocks, 10% bulk shortening is unrealistic and 1% shortening likely represents an uppermost end-member from compression. However, modeling limitations require the same magnitude of shortening be applied at all depths. The modeled section experiences compression in even increments through time since 24 Ma, the approximate onset of subduction. Model results show that the additional compressional stress modestly increases the pore pressure for the Whangai Formation (below the regional Wanstead seal rock) through time by varying amounts in each distinct structural regime of the basin (Fig. 16). The 10% shortening scenario results in the highest pore pressure because the basin experiences the greatest mean stress. Because compression is applied steadily from 24 Ma to 0 Ma, there is a gradual divergence in pore pressure from the base case through time. The 1% shortening scenario is almost indistinct from the base case scenario, although it results in a very modest pore pressure increase. In present-day, the 1% shortening scenario increases pore pressure from 0.1% to 0.8% relative to the base case. The 10% shortening scenario increases pore pressure from 2% to 6% relative to the base case. This represents a relatively modest increase in overpressure relative to the impact of disequilibrium compaction, which is clearly demonstrated in Figure 16 where compression-related shortening results in only a minor increase in
94 excess pressure. The beginning of overpressure generation is most closely associated with burial events, further indicating that disequilibrium compaction from vertical loading is the primary driver of overpressure. The Whangai Formation shows different amounts of sensitivity to shortening depending on location within the basin. In general, the areas with higher overpressures from vertical loading (i.e., Lachlan basin region and Outboard region) experience higher percentage increases in pore pressure due to horizontal compaction. Although the models provide good guidance for the expected pressure regimes associated with compression, they do not account for the effects of rock failure. The Whangai Formation in the Inboard, Lachlan basin, and Outboard regions is likely experiencing failure starting around the time of subduction (Fig. 16). Increasing compression actually reduces the magnitude of stress above the failure criterion because it increases the minimum principal stress (horizontal stress), thereby decreasing the deviatoric stress. A second set of scenarios was run where all shortening occurred between 24 Ma and 19 Ma, which represents the main period of thrust-related shortening. It is anticipated that bulk shortening is synchronous with structural shortening during this main compressional tectonic event. Although the effect on present-day pore pressure remains approximately the same regardless of timing, there is a distinct effect on the principal stresses acting in the basin through time (Fig. 17). For the Whangai Formation in the Lachlan basin, vertical stress always exceeds horizontal stress through time when no shortening is taken into account. When 5% shortening between 24 to 0 Ma is accounted for, horizontal stress exceeds vertical stress in present-day. When 5% and 10% shortening occurs between 24 to 19 Ma, horizontal stress very closely approaches vertical stress throughout the basin’s history, and exceeds vertical stress in present-day. This is an important consideration in terms of understanding the styles of faulting occurring in the basin through time.
95 DISCUSSION Terzaghi versus poroelastic models Both the Terzaghi and poroelastic models are useful in modeling the development of overpressure in the East Coast Basin. This study shows the importance of both lithostratigraphy and structure in generating and redistributing overpressure. Although the Terzaghi model is sufficient for many BPSM needs, the poroelastic model provides an improved means for describing the basin’s stress regime. This is particularly important when considering pore pressure development and the direction of principal stresses through time. Accurate estimation of these variables is important for understanding the timing and type of failure in overpressured sediments, seal effectiveness, and migration pathways. It is important to note that the Terzaghi model and the poroelastic model calculate effect stress and pore pressure differently, and therefore there are differences in modeled output even when no shortening or extension is assumed in the poroelastic model (Fig. 12). This is because the poroelastic model accounts for additional elastic rock properties, coupled pore pressure and stress compaction processes, and horizontal stresses. Although the lithologies are not recalibrated for the poroelastic model in this study in order to enable direct comparison to the Terzaghi model, they should be recalibrated if the poroelastic model will be used for additional BPSM.
Stress Environment The present-day stress environment of the ECB is reasonably well constrained by focal mechanism data, indicating a predominantly strike-slip stress regime with some regions of compression and extension (Townend et al. 2012). Regional variability of stress regimes is expected in strike-slip systems due to the curvature of the faults (Reading, 1980). Leak off tests provided additional constraints on the regional stress regime (Fig. 18). Leak off tests (LOTs) from Kauhauroa-2 and Tuhara- 1 have minimum principal stresses below lithostatic stress, and are therefore experiencing either extensional or strike-slip stress regimes. LOTs from Hawke Bay-1 and Tawatawa-1 show the minimum principal stress approximates vertical stress,
96 thereby indicating a reverse faulting environment. However, in wells where high overpressures exists, such as Hukarere-1 and Titihaoa-1, the difference between principal stresses required for failure significantly decreases due to reduced frictional strength (Zoback, 2007). Therefore, minor changes in the stress regime of these wells can change the style of failure. The Titihaoa-1 well also shows that the style of failure may depend on depth, where the upper part of the well is likely experiencing a strike- slip or extensional environment, and the lower part of the well is likely experiencing a reverse faulting environment. These observations are particularly important relative to the poroelastic modeling results, which permit the investigation of stress regime evolution in the context of basin development. When shortening is not accounted for in the model, the vertical stress exceeds the horizontal stress through time (Fig. 17). When shortening is accounted for from 24 Ma to 19 Ma, the stress regime varies between different Andersonian fault regimes (Anderson, 1951). The order and magnitude of the principal stresses impact both the type and degree of faulting in the basin. These findings help to explain the variety of fault styles that characterize the ECB, as well as the discrete deformational phases that have occurred throughout the basin’s evolution. In a highly overpressured setting, it is likely that relatively small changes in stress regime will significantly impact deformational style. In the ECB, the history of subduction of the Hikurangi Plateau likely significantly influenced the basin’s stress regime. Unfortunately, a complete stress regime cannot be incorporated in this model due to two-dimensional limitations.
Seal Effectiveness The build-up of extreme overpressures beneath the Wanstead seal rock raises concern regarding the seal integrity of the Wanstead Formation and whether leak points may exist regionally. Darby (2002) found that a Miocene seal in the Titihaoa-1 well anticlinal structure is likely acting as a regional leak point due to pore pressures attaining the seal fracture pressure at the top of the structure. Although the Wanstead Formation is more likely susceptible to ductile deformation, the extent of overpressure underneath the Wanstead Formation seal rock depends largely on the percentage of
97 smectite within the formation. Smectite content likely varies regionally, and bulk rock XRD measurements of the illite/smectite content suggest it could be upwards of 30% (Darby, 2002). Areas with reduced smectite content may also act as leak points for pressure compartments in the basin, whereas areas with increased smectite content are more susceptible to higher pore pressure and hydraulic fracturing. Two additional scenarios were modeled showing the impact of reducing the smectite content to 10% and increasing smectite content to 30%. These models show significant changes in excess hydraulic pressure underlying Hawke Bay-1. The base case model accumulates 17 MPa of excess pressure, while the 10% smectite scenario accumulates 5.5 MPa and the 30% smectite scenario accumulates 25 MPa. The model with 30% smectite reaches the estimated fracture pressure. This additionally has a significant impact on the preserved porosity, with greater porosity reduction in the scenarios with reduced smectite seals due to higher effective stresses (Fig. 12). When 30% smectite content is assumed in the Terzaghi model, fracturing is prevalent below the regional seal do to the build-up of excess pressure beyond the fracture gradient (Fig. 19). Although the poroelastic model does not achieve the same overpressure as the Terzaghi base case, even when shortening is included, results show that the Wanstead Formation experienced failure in the Lachlan basin by around 13 Ma (Fig. 20). Increasing the smectite content of the formation to 30% pushes the timing of failure to around 10 Ma.
Model Limitations Numerous limitations still remain in these models, most importantly that plastic deformation is not taken into account. A simplified fracture model based on the Griffith-theory is implemented for both the Terzaghi and poroelastic models, such that when pore pressure exceeds the fracture gradient (Table 1), fracturing occurs (Hantschel and Kauerauf, 2009). This increases the permeabilities and lowers the capillary entry pressures of the fractured rock. However, more advanced models that capture plastic deformation are not considered here. Another issue with the current modeling process is that decompaction is input from the structural reconstruction rather than calculated during the forward modeling
98 process. Although decompaction was accounted for during the structural reconstruction, the reconstruction does not account for porosity preservation associated with the development of overpressure. Therefore, compaction is likely overestimated during the structural reconstruction, causing a reduction in the appropriate amount of solid grain mass in the basin and petroleum system model for an overpressured and undercompacted layer. This problem is further exacerbated by the bulk shortening scenarios, which cannot truly shorten a paleo-stepping model and therefore will compensate by adding solid grain mass to the system. This problem can be addressed iteratively by conducting a second restoration using decompaction curves from the initial basin model (Neumaier et al., 2014). However, Neumaier et al. (2014) found that hydrostatic decompaction generally provided a reasonably balanced model with rock matrix mass between 80% to 120% of the backstripped rock matrix mass (as opposed to nondecompacted, which can be as low as 20% of the true rock matrix). Unbalanced decompaction most significantly impacts source rock thickness and stratigraphic burial depth in the model (Neumaier et al., 2014). Other uncertainties inherent in the study include the pitfalls of seismic interpretation in a frontier basin, the velocity model used to convert from time to depth, and the choices made in the structural reconstruction, all of which have non-unique, highly interpretive solutions. Lastly, the models described here are limited to two dimensions, and therefore do not account for processes occurring in and out of the plane. Three-dimensional models are particularly important in considering directions of fluid flow and potential leak points, as well as understanding the full stress regime. However, software tools for carrying out fully reconstructed 3D basin and petroleum system models is still undergoing development.
Petroleum Implications The development of overpressure below the Wanstead Formation has direct implications for petroleum exploration in the basin. The Waipawa Black Shale and Whangai Formation are directly underneath the regional seal and have experienced significant overpressure since early Miocene time. The Whangai Formation is a
99 prospective source rock, and, based on modeling results, has likely experienced natural hydraulic fracturing also during early Miocene time due to the build-up of overpressure (Figs. 16, 19). This is supported by the fractured nature of the formation in outcrop (Field et al., 2004). In contrast, the Waipawa Black Shale is more likely to undergo ductile deformation due to its more clay-rich lithology. An overpressured, naturally fractured source rock of high thermal maturity is a good candidate for shale- gas development (Curtis, 2002). Both scenarios show the Waipawa Black Shale and Whangai Formation reach transformation ratios between 50% to 95% in the Lachlan basin and in the footwall of the thrust just outboard of the Lachlan basin by present- day (Fig. 21), with most transformation occurring since late Miocene time. These are the most prospective regions of the basin for shale-gas plays because they are most likely to be generating gas. In modeling hydrocarbon generation and migration in shale reservoirs, pressure is also an important consideration because it can influence kinetic reactions and therefore impact present-day maturity (Zou and Peng, 2001; Scotchman and Carr, 2005). Pressure is also a significant factor in adsorption within the source rock and the in-situ phase of the hydrocarbons (Hantschel and Kauerauf, 2009). These are important considerations in evaluating the producibility of the shale gas reservoir.
CONCLUSIONS BPSM is increasingly being utilized as a tool to better understand and predict pore pressure in petroliferous basins. In structurally complex regions, pressure prediction can be particularly challenging due to variations in lithostratigraphy, distinct local basin-filling histories, and compartmentalization by faults. This study highlights the importance of including the structural evolution and stress regime in basin and petroleum system modeling, both of which are not commonly incorporated. Paleo-stepping models require a significant time investment, and therefore should be reserved for structurally complex regions where there has been significant movement along faults and structural burial. Although horizontal stress did not significantly impact pore pressure in this study, it has the capacity to generate overpressures on the
100 same order as compaction disequilibrium, and therefore should be considered in other compressional environments. Other structurally complex, overpressured basins that would be best modeded through paleo-stepping and poroelastic modeling include the Coastal Ranges and Sacramento basin of California (Unruh et al., 1992; McPherson and Garven, 1999), the Kutai Basin of Indonesia (Ramdhan and Goulty, 2010), and the Barbados accretionay complex (Westbrook and Smith, 1983). The dynamic tectonic history of the ECB has created a complex distribution of overpressure throughout the basin. Overpressure develops primarily due to disequilibrium compaction, and secondarily due to horizontal tectonic stresses. Incorporation of the basin’s structural history into the basin and petroleum system model permits an in-depth understanding of how overpressure develops in response to lithostratigraphy and structural events. Terzaghi-type basin modeling shows that overpressure develops almost universally beneath the smectite-rich Wanstead Formation, except where beds have been back-tilted, uplifted, and brought to the surface along the Lachlan fault. Overpressure in the Neogene section is more variable, and depends on the thickness of low permeability seal layers and the depth of burial. Overpressure in the Neogene is not as high as overpressure in the Cretaceous– Paleogene section at equal burial depths due to the lesser seal effectiveness in the Neogene. The basin can generally be divided into an overpressured, sub-Wanstead section, and a variably overpressured Neogene section that is the result of laterally variable stratigraphy not captured in the model. The magnitude of overpressure depends on the depth of burial and the presence (or absence) of pressure-releasing structural events. Both sedimentation and structural thickening are modeled to estimate total burial. Uplift and erosion reduces overpressure, although basin modeling calculates the history of maximum effective stress experienced. Porosity preservation is observed in areas that have experienced overpressure, and is directly related to the maximum effective stress experienced by the sediments. The impact of horizontal shortening was tested using a poroelastic basin and petroleum system model. Scenarios ranged from 1% shortening to 10% shortening,
101 and results showed increases in pore pressure in the Whangai Formation ranging from 0.8% to 6%, respectively. This represents only a minor contribution to the total overpressure in the formation, although it should be noted that the model does not account for plastic deformation. Rock stress modeling indicates the Whangai Formation has been experiencing rock failure since the beginning of the Neogene, therefore plastic deformation may be important to consider. Horizontal shortening also impacts the magnitude and rank of principal stresses in the basin, causing horizontal stress to approach and exceed vertical stress. This is particularly true for scenarios where most shortening occurs simultaneous with the main thrusting period between 24 Ma and 19 Ma. In overpressured basins where principal stresses are of similar magnitudes, the basin can easily go back and forth between different faulting regimes. The structural history of the ECB is likely significantly influenced by the high overpressures, which have enabled compressional, extensional, and strike-slip fault regimes to all occur during the tectonic history and, at times, simultaneously. The overpressure beneath the Wanstead Formation seal rock also sets up a potential shale gas play due to the natural hydraulic fracturing occurring within the Whangai source rock. The percentage of smectite in the Wanstead Formation is the main control on the magnitude of overpressure, and increases in smectite content promote fracture-inducing excess pressures. The Whangai Formation is a siliceous- rich source rock susceptible to brittle fracturing, and therefore may be a good candidate for shale gas resource plays where it has been buried deeply in the basin.
ACKNOWLEDGMENTS Funding for this research was provided by the affiliates of the Stanford Basin and Petroleum System Modeling research group, with current members including Aera, BP, Chevron, ConocoPhillips, Great Bear Petroleum, Hess, Murphy, Nexen, Oxy, Petrobras, Saudi Aramco, and Schlumberger. Schlumberger provided academic licenses and support for Petrel®, Dynel®, and Petromod®, which were essential in conducting this research.
102 The academic support of Rob Funnell, Andy Nicol, Martin Crundwell, and Brad Field of GNS Science were instrumental in the establishment of this project. This research also greatly benefited from discussions with Noelle Schoellkopf, Les Magoon, Allegra Hosford Scheirer, Carolyn Lampe, Mark Zoback, Oliver Schenk, Tim McHargue, Ken Peters, and Tess Menotti. The authors would also like to thank Andy MacGregor, Thorsten Joppen, and Martin Neumaier of Schlumberger for their extensive support in building the Teclink Petromod® model.
REFERENCES CITED Anderson, E.M. (1951) The Dynamics of Faulting and Dyke Formation with Applications to Britain, Oliver and Boyd, Edinburgh. Ansell, J.H. & Bannister, S.C. (1996) Shallow morphology of the subducted Pacific plate along the Hikurangi margin, New Zealand. Physics of Earth and Planetary Interiors, 93, 3-20.
ATHY, L.F. (1930) Density, porosity and compaction of sedimentary rocks. AAPG Bull., 14, 1-24. Bailleul, J., Robin, C., Chanier, F., Guillocheau, F., Field, B. & Ferrière, J. (2007) Turbidite systems in the inner fore-arc domain of the Hikurangi convergent margin (New Zealand): New constraints on the development of trench-slope basins. J. Sed. Res., 77, 263-283. Bailleul, J., Chanier, F., Ferrière, J., Robin, C., Nicol, A., Mahieux, G., Gorini, C. & Caron, V. (2013) Neogene evolution of lower trench-slope basins and wedge development in the central Hikurangi subduction margin, New Zealand. Tectonophysics, 591, 152-174. Ballance, P.F. (1976) Evolution of the upper Cenozoic magmatic arc and plate boundary in northern New Zealand. Earth Planet. Sci. Lett., 28, 356-370. Ballance, P.F. (1993) The paleo-Pacific, post-subduction, passive margin thermal relaxation sequence (Late Cretaceous-Paleogene) of the drifting New Zealand continent. In: South Pacific Sedimentary Basins, Sedimentary Basins of the World, 2 (Ed. by P. F. Ballance), pp. 93-110. Elsevier, Amsterdam.
103 Bannister, S. (1988) Microseismicity and velocity structure in the Hawkes Bay region, New Zealand: fine structure of the subducting Pacific Plate. Geophys. J., 95, 45-62. Barker, D.H.N., Sutherland, R., Henrys, S. & Bannister, S. (2009) Geometry of the Hikurangi Subduction thrust and upper plate, North Island, New Zealand. Geochem., Geophys., Geosyst., 10(2), Q02007. Barnes, P.M., Nicol, A. & Harrison, T. (2002) Late Cenozoic evolution and earthquake potential of an active listric thrust complex above the Hikurangi subduction zone, New Zealand. Geol. Soc. Am. Bull., 114, 1379-1405. Barnes, P.M. & Nicol, A. (2004) Formation of an active thrust triangle zone associated with structural inversion in a subduction setting, eastern New Zealand. Tectonics, 23(1), TC1015. Beanland, S., Melhuish, A., Nicol, A. & Ravens, J. (1998) Structure and deformational history of the inner forearc region, Hikurangi subduction margin, New Zealand. N. Z. J. Geol. Geophys., 41, 325-342. Berryman, K.R. (1993a) Age, height, and deformation of Holocene marine terraces at Mahia peninsula, Hikurangi subduction margin, New Zealand. Tectonics, 12(6), 1347-1364. Berryman, K.R. (1993b) Distribution, age, and deformation of late Pleistocene marine terraces at Mahia peninsula, Hikurangi subduction margin, New Zealand. Tectonics, 12(6), 1365-1379. Biros, D., Cuevas, R. & Moehl, B. (1995), Well Completion Report, Titihaoa-1, PPL38318, for Amoco NZ Exploration Co Ltd. Unpublished Open-File Petroleum Report 2081, Ministry of Economic Development, Wellington, New Zealand. Borge, H. (2002) Modelling generation and dissipation of overpressure in sedimentary basins: an example from the Halten Terrance, offshore Norway. Mar. Petrol. Geol., 19, 377-388. Borge, H. & Sylta, Ø. (1998) 3D modelling of fault bounded pressure
104 compartments in the North Viking Graben. Energy, Exploration, and Exploitation, 16(4), 301-323. Brown, B.R. (1960) Mangaone-1, for BP Shell and Todd Petroleum Development Ltd. Unpublished Open-File Petroleum Report 320, Ministry of Economic Development, Wellington, New Zealand. Burgreen, B. & Graham, S. (2014) Evolution of a deep-water lobe system in the Neogene trench-slope setting of the East Coast Basin, New Zealand: lobe stratigraphy and architecture in a weakly confined basin configuration. Mar. Petrol. Geol., 54, 1-22. Byrne, T.B., Lin, W., Tsutsumi, A., Yamamoto, Y., Lewis, J.C., Kanagawa, K., Kitamura, Y., Yamaguchi, A. & Kimura, G. (2009) Anelastic strain recovery reveals extension across SW Japan subduction zone. Geophys. Res. Lett., 36, L23310.
Carr, A.D. (1999) A vitrinite reflectance kinetic model incorporating overpressure retardation. Mar. Petrol. Geol., 16, 355-377. Cashman, S.M. & Kelsey, H.M. (1990) Forearc uplift and extension, southern Hawke's Bay, New Zealand: Mid-Pleistocene to present. Tectonics, 9(1), 23-44. Cello, G. & Nur, A. (1988) Emplacement of foreland thrust faults. Tectonics, 7(2), 261-271. Chanier, F. (1991) Le Prisme d'accrétion Hikurangi: Un témoin de l'évolution géodynamique d'une marge active péripacifique (Nouvelle-Zélande). Ph.D. dissertation, L’Université des Sciences et Techniques de Lille-Flandres-Artois, France. Chanier, F. & Ferrière, J. (1991) From a passive to active margin: tectonic and sedimentary processes linked to the birth of an accretionary prism (Hikurangi margin, New Zealand). Bull. Soc. Géol. France, 162(4), 649-660. Curtis, J.B. (2002) Fractured shale-gas systems. AAPG Bull., 86(11), 1921-1938. Darby, D., Funnell, R., Uruski, C.I. & Field, B.D. (2000). Patterns of Fluid Flow in the East Coast Basin. Proceedings of the 2000 New Zealand Petroleum Conference, Ministry of Economic Development, Wellington, New Zealand.
105 Darby, D. & Ellis, S. (2001). Evaluating Overpressure in Compressional Regimes Using Geomechanical Modelling. In: PESA Eastern Australasian Basins Symposium, Melbourne, Victoria, 613-620. Darby, D. & Funnell, R. (2001) Overpressure Associated with a Convergent Plate Margin: East Coast Basin, New Zealand. Petroleum Geoscience, 7, 291-299. Darby, D. (2002) Seal Properties, Overpressure and Stress in the Taranaki and East Coast Basins, New Zealand. In: Proceedings of the 2002 New Zealand Petroleum Conference, Ministry of Economic Development, Wellington, New Zealand, 363-372. Darley, J.H. & Kirby, K.F.S. (1969a) BP Shell Aquitaine Todd Petroleum Developments Ltd, Rakaiatai-1 Well Completion Report. In: Open-File Petroleum Report 330, Ministry of Economic Development New Zealand. Wellington, New Zealand, 80pp. Darley, J.H. & Kirby, K.F.S. (1969b) BP Shell Aquitaine Todd Petroleum Developments Ltd, Taradale-1. In: Open-File Petroleum Report 331, Ministry of Economic Development New Zealand. Wellington, New Zealand, 75pp. Davies, E.J., Frederick, J.B., Leask, W.L. & Williams, T.J. (2000). East Coast Drilling Results. New Zealand Petroleum Conference Proceedings, 19-22 March 2000. Ministry of Economic Development, Wellington, New Zealand, 11pp. Davy, B., Hoernle, K. & Werner, R. (2008) Hikurangi Plateau: Crustal Structure, Rifted Formation, and Gondwana Subduction History. Geochemistry, Geophysics, Geosystems, 9, 1-31. de Bock, J.F., Kelly, C., Lock, R. & Bulte, G. (1986) Petroleum Corporation of NZ Exploration Ltd, Well Completion Report Rere-1, PPL38-83. In: Open-File Petroleum Report 1231, Ministry of Economic Development, Wellington, New Zealand, 1202pp. Dickey, P.A. & Cox, W., C. (1977) Oil and Gas in Reservoirs with Subnormal Pressures. AAPG Bulletin, 61, 2134-2142. Dickinson, G. (1953) Geological Aspects of Abnormal Reservoir Pressures in Gulf Coast Louisiana. AAPG Bulletin, 37, 410-432.
106 Dobbie, W.A. & Carter, M.J. (1990) Petrocorp Exploration Ltd, Te Hoe-1 Well Completion Report PPL 38316. In: Open-File Petroleum Report 1835, Ministry of Economic Development, Wellington, New Zealand, 209pp. Doré, A.G. & Jensen, L.N. (1996) The Impact of Late Cenozoic Uplift and Erosion on Hydrocarbon Exploration: Offshore Norway and Some Other Uplifted Basins. Global and Planetary Change, 12, 415-436. Düppenbecker, S.J., Osborne, M.J., Bunney, J.R. & Duncan, R.A.B. (1999). Pre-Drill Pressure Prediction Provided by Multi-Dimensional Basin Modelling Techniques. International Conference and Exhibition, Birmingham, England, American Association of Petroleum Geologists. England, W.A., Mackenzie, A.S., Mann, D.M. & Quigley, T.M. (1987) The Movement and Entrapment of Petroleum Fluids in the Subsurface. Journal of the Geological Society, London, 144, 21. Field, B.D., Funnell, R., Lyon, G. & Uruski, C.I. (1998) Fluids, Migration Systems, and Diapirism, East Coast North Island, New Zealand. Water-rock Interaction: Proceedings of the 9th International Symposium on Water-Rock Interaction. (Ed. by G. B. Arehart & J. R. Hulston), International Association of Geochemistry, Taupo, New Zealand, 313-316. Field, B.D., Higgs, K.E., Chanier, F., Nicol, A. & Darby, D. (2004). Play Concepts for a Complex Margin: East Coast North Island, New Zealand. In: 2004 New Zealand Petroleum Conference Proceedings, Ministry of Economic Development, Auckland, New Zealand. Field, B.D., Uruski, C.I. & Institute of Geological & Nuclear Sciences Limited. (1997) Cretaceous-Cenozoic Geology and Petroleum Systems of the East Coast Region, New Zealand. Institute of Geological & Nuclear Sciences, Lower Hutt, New Zealand. Field, B.D., Browne, G.H., Higgs, K.E., Pollock, R.M. & Uruski, C.I. (2006). Reservoir Plays of the East Coast Region. 2006 New Zealand Petroleum Conference, Ministry of Economic Development, Auckland, New Zealand. Finkbeiner, T., Zoback, M., Flemings, P. & Stump, B. (2001) Stress, Pore Pressure,
107 and Dynamically Constrained Hydrocarbon Columns in the South Eugene Island 330 Field, Northern Gulf of Mexico. AAPG Bulletin, 85, 1007-1031. Fisher, A.T., Zwart, G. & Party, O.D.P.L.S. (1996) Relation between Permeability and Effective Stress Along a Plate-Boundary Fault, Barbados Accretionary Complex. Geology, 24, 307-310. Foroozan, R., Elsworth, D., Flemings, P., Bilotti, F. & Muhuri, S. (2012) The Role of Permeability Evolution in Fault Zones on the Structural and Hydro-Mechanical Characteristics of Shortening Basins. Marine and Petroleum Geology, 29, 143- 151. Francis, D., Johnston, J. & Langdale, S. (2002) Indo-Pacific Energy (NZ) Ltd, Waingaromia-2 Well Completion Report. In: Open-File Petroleum Report 2767, Ministry of Economic Development, Wellington, New Zealand, 23pp. Freeman, B., Yielding, G., Needham, D.T. & Badley, M.E. (1998) Fault Seal Prediction: The Gouge Ratio Method. Geological Society, London, Special Publications, 127, 19-25. Funnell, R. & Benchilla, I. (2005) 1D Basin Models in the East Coast Basin, New Zealand. In: Open-File Petroleum Report 3183, Ministry of Economic Development, Wellington, New Zealand, 24 pp. Funnell, R.H., Wood, R.A., Stagpoole, V.M., Uruski, C.I., Scadden, P., Killops, S.D., Cutress, G., Field, B.D. & Nicol, A. (1999) Thermal and Hydrocarbon Generation Modelling of the Hawke Bay Area (Pep38325, 38326, 38329). In: Unpublished Petroleum Report 4311, Ministry of Economic Development, Wellington, New Zealand, 91pp. Gibson, R.G. & Bentham, P.A. (2003) Use of Fault-Seal Analysis in Understanding Petroleum Migration in a Complexly Faulted Anticlinal Trap, Columbus Basin, Offshore Trinidad: Multidimentional Basin Modeling, Colorado Springs, CO, AAPG/Datapages Discovery Series, 7. Gusterhuber, J., Hinsch, R. & Sachsenhofer, R.F. (2014) Evaluation of Hydrocarbon
108 Generation and Migration in the Molasse Fold and Thrust Belt(Central Eastern Alps, Austria) Using Structural and Thermal Basin Models. AAPG Bulletin, 98, 253-277. Hantschel, T. & Kauerauf, A.I. (2009) Fundamentals of Basin and Petroleum System Modeling. Springer, New York. Hantschel, T., Wygrala, B., Fuecker, M. & Neber, A. (2011) Modeling Basin-Scale Geomechanics through Geological Time. In: International Petroleum Technology Conference, 15-17 November, International Petroleum Technology Conference. Bangkok, Thailand, IPTC 15286. Haskell, T.R. & Johnston, J. (1998) Asia Pacific Oil Co Ltd, Waitaria-1, -1a, and 1b Well Completion Report, PPL 38312. In: Open-File Petroleum Report 2340, Ministry of Economic Development, Wellington, New Zealand, 375pp. Heffer, K. & Milne, A.D. (1976) BP Shell Aquitaine Todd Petroleum Developments Ltd, Well Completion Report Hawke Bay-1. In: Open-File Petroleum Report 667, Ministry of Economic Development, Wellington, New Zealand, 191pp. Helset, H.M., Lüthje, M. & Ojala, I. (2009). Improved Pore Pressure Prediction by Integrating Basin Modeling and Seismic Methods. Basin and Petroleum System Modeling: New Horizons in Research and Applications (AAPG Hedberg Research Conference), Napa, California, AAPG Datapages/Search and Discovery, 3pp. Hollis, C.J., Manzano-Kareah, K., Crampton, C., Field, B., Funnell, R., Morgans, H. & Rogers, K. (2005) Source Rock Potential of the East Coast Basin (Central and Northern Regions). Institute of Geological and Nuclear Sciences Client Report 2005/118, 156 pp. Hollis, C.J., Beu, A.G., Crampton, J.S., Crundwell, M.P., Morgans, H.E.G., Raine, J.I., Jones, C.M. & Boyes, A.F. (2010) Calibration of the New Zealand Cretaceous- Cenozoic Timescale to Gts2004. GNS Science Report. G. Science. 2010/43, 20. Hubbert, K.M. & Rubey, W.W. (1959) Role of Fluid Pressure in Mechanics of Overthrust Faulting. Geological Society of America Bulletin, 70, 115. Ian R Brown Associates Ltd. (1998a) Kauhauroa-1 Well Completion Report, Pep
109 38329. Open-File Petroleum Report 2346. Westech Energy New Zealand Ltd, Ministry of Economic Development, Wellington, New Zealand, 815pp. Ian R Brown Associates Ltd. (1998b) Kiakia-1/-1a Well Completion Report, Pep 38329. Open-File Petroleum Report 2381. Westech Energy New Zealand Ltd, Ministry of Economic Development, Wellington, New Zealand, 334pp. Ian R Brown Associates Ltd. (1998c) Makareao-1 Well Completion Report, PEP 38329. Open-File Petroleum Report 2377. Westech Energy New Zealand Ltd, Ministry of Economic Development, Wellington, New Zealand, 295pp. Ian R Brown Associates Ltd. (1998d) Opoho-1 Well Completion Report, Pep 38329. Open-File Petroleum Report. Westech Energy New Zealand Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 314pp. Ian R Brown Associates Ltd. (1998e) Tuhara-1 Well Completion Report, Pep 38329. Open-File Petroleum Report 2401. Westech Energy New Zealand Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 259pp. Ian R Brown Associates Ltd. (1998f) Well Completion Report Kauhauroa-2, Pep 38329. Open-File Petroleum Report 2409. Westech Energy New Zealand Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 460pp. Ian R Brown Associates Ltd. (1999a) Awatere-1 Well Completion Report. Open File Petroleum Report 2365. Westech Energy New Zealand Ltd, Ministry of Economic Development. Wellington, New Zealand, 345pp. Ian R Brown Associates Ltd. (1999b) Kauhauroa-3 Well Completion Report. Open-File Petroleum Report 2445. Westech Energy New Zealand Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 462pp. Ian R Brown Associates Ltd. (1999c) Kauhauroa-4 & 4a Well Completion Report. Open-File Petroleum Report 2256. Westech Energy New Zealand Ltd, Ministry of Economic Development. Wellington, New Zealand, 296pp.
110 Ian R Brown Associates Ltd. (1999d) Kauhauroa-5 Well Completion Report. Open-File Petroleum Report 2431. Westech Energy New Zealand Ltd, Ministry of Economic Development. Wellington, New Zealand, 611pp. Ian R Brown Associates Ltd. (2000) Tuhara-1A Well Completion Report. Open-File Petroleum Report 2470. Westech Energy New Zealand Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 894pp. Ian R Brown Associates Ltd. (2001a) Hukarere-1 Well Completion Report. Open- File Petroleum Report 2656. Westech Energy New Zealand Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 385pp. Ian R Brown Associates Ltd. (2001b) Tautane-1 Well Completion Report Pep 38333. Open-File Petroleum Report 2637. Westech Energy New Zealand Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 296pp. Ian R Brown Associates Ltd. (2008) Waitihora-1 Well Completion Report. Open- File Petroleum Report 3783. Westech Energy New Zealand Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 77pp. Johnston, J. & Langdale, S. (2000) Speedy-1/1a Well Completion Report. Pep 38332. Open-File Petroleum Report 2537. Indo-Pacific Energy (NZ) Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 356pp. Johnston, J.G. & Francis, D.A. (1996) Kereru-1 Well Completion Report, Pep38328. Open-File Petroleum Report 2283. Indo-Pacific Energy (NZ) Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 569pp. Kamp, P.J.J. (1999) Tracking Crustal Processes by Ft Thermochronology in a Forearc High (Hikurangi Margin, New Zealand) Involving Cretaceous Subduction Termination and Mid-Cenozoic Subduction Initiation. Tectonophysics, 307, 313-343. King, P.R. (2000) Tectonic Reconstructions of New Zealand 40 Ma to the Present. New Zealand Journal of Geology and Geophysics, 43, 611-638. Kundu, N. & Basu, S. (2008). Application of Stratigraphy Specific Shale Compaction
111 Curves in Pore Pressure Prediction: A Basin Modeling Approach. GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain, American Association of Petroleum Geologists. Laing, A.C.M. (1972a) Rotokautuku-1. Open-File Petroleum Report 255. Alliance Petroleum NZ Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 112pp. Laing, A.C.M. (1972b) Te Horo-1. Open-File Petroleum Report 256. Alliance Petroleum NZ Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 150pp. Laing, A.C.M. (1972c) Te Puia-1. Open-File Petroleum Report 257. Alliance Petroleum NZ Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 183pp. Laird, M.G. & Bradshaw, J.D. (2004) The Break-up of a Long-Term Relationship: The Cretaceous Separation of New Zealand from Gondwana. Gondwana Research, 7, 273-286. Law, B.E. & Dickinson, W.W. (1985) Conceptual Model for Origin of Abnormally Pressured Gas Accumulations in Low-Permeability Reservoirs. AAPG Bulletin, 69, 1295-1304. Law, C.S., Nodder, S.D., Mountjoy, J.J., Marriner, A., Orpin, A., Pilditch, C.A., Franz, P. & Thompson, K. (2010) Geological, Hydrodynamic and Biogeochemical Variability of a New Zealand Deep-Water Methane Cold Seep During an Integrated Three-Year Time-Series Study. Marine Geology, 272, 189-208. Law, B.E. & Spencer, C.W. (1998) Abnormal Pressures in Hydrocarbon Environments. In: Abnormal Pressures in Hydrocarbon Environments: Aapg Memoir 70 (Ed. by B. E. Law, G. F. Ulmishek & V. I. Slavin), Memoir 70. The American Association of Petroleum Geologists, Tulsa, Oklahoma, USA, 1-11. Leslie, W.C. (1971a) Mason Ridge-1. PPL497. Open-File Petroleum Report 272. Beaver Exploration NZ Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 81pp.
112 Leslie, W.C. (1971b) Ongaonga-1. Open-File Petroleum Report 271. Beaver Exploration NZ Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 95pp. Leslie, W.C. (1971c) Takapau-1. Open-File Petroleum Report 273. Beaver Exploration NZ Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 84pp. Luo, X. & Vasseur, G. (1995) Modelling of Pore Pressure Evolution Associated with Sedimentation and Uplift in Sedimentary Basins. Basin Research, 7, 35- 52. MacKay, P.A., Varsek, J.L., Kubli, T.E., Dechensne, R.G., Newson, A.C. & Reid, J.P. (1996) Triangle Zones and Tectonic Wedges: An Introduction. Bulletin of Canadian Petroleum Geology, 44, 1-5. Maerten, L. & Maerten, F. (2006) Chronologic Modeling of Faulted and Fractured Reservoirs Using Geomechanically Based Restoration: Technique and Industry Applications. AAPG Bulletin, 90, 1201-1226. Mazengarb, C. (1998). Late Neogene Structural Development of Eastern Raukumara Peninsula: Implications for Oil Exploration. New Zealand Petroleum Conference Proceedings, Ministry of Economic Development, Wellington, New Zealand, 201-205. Mazengarb, C. & Speden, I.G. (2000) Geology of the Raukumara Area; Scale 1:250,000. New Zealand (NZL), 60-60, 61 sheet. McPherson, B.J.O. & Garven, G. (1999) Hydrodynamics and Overpressure Mechanisms in the Sacramento Basin, California. American Journal of Science, 299, 429-466. Melhuish, A. (1990) Late Cenozoic Deformation Along the Pacific-Australian Plate Margin, Dannevirke Region, New Zealand, PhD Dissertation, Victoria University of Wellington, New Zealand. Moore, C.J. & Vrolijk, P. (1992) Fluids in Accretionary Prisms. Reviews of Geophysics, 30, 113-135. Mortimer, N. (2004) New Zealand's Geological Foundations. Gondwana Research,
113 7, 261-272. Multiwave (2005) 05CM 2D Seismic Survey, Offshore East Coast - North Island. Open-File Petroleum Report 3136. Crown Minerals and GNS Science, Ministry of Economic Development New Zealand. Wellington, New Zealand. Neumaier, M., Littke, R., Hantschel, T., Maerten, L., Joonnekindt, J.P. & Kukla, P. (2014) Integrated Charge and Seal Assessment in the Monagas Fold and Thrust Belt of Venezuela. AAPG Bulletin, 98, 1325-1350. Neuzil, C.E. & Pollock, D.W. (1983) Erosional Unloading and Fluid Pressures in Hydraulically "Tight" Rocks. The Journal of Geology, 91, 179-193. Nicol, A., VanDissen, R., Vella, P., Alloway, B. & Melhuish, A. (2002) Growth of Contractional Structures During the Last 10 M.Y. At the Southern End of the Emergent Hikurangi Forearc Basin, New Zealand. New Zealand Journal of Geology and Geophysics, 45, 365-385. Nicol, A. & Beavan, J. (2003) Shortening of an Overriding Plate and Its Implications for Slip on a Subduction Thrust, Central Hikurangi Margin, New Zealand. Tectonics, 22. Nicol, A. & Uruski, C. (2005) Structural Interpretation and Cross Section Balancing, East Coast Basin, New Zealand. Unpublished Open File Petroleum Report 3184, Ministry of Economic Development. Wellington, New Zealand, 14pp. Nicol, A., Mazengarb, C., Chanier, F., Rait, G., Uruski, C. & Wallace, L. (2007) Tectonic Evolution of the Active Hikurangi Subduction Margin, New Zealand, since the Oligocene. Tectonics, 26, 24. Nordgård Bolås, H.M., Hermanrud, C. & Teige, G.M.G. (2005) Seal Capacity Estimation from Subsurface Pore Pressures. Basin Research, 17, 583-599. Ozolins, V. & Francis, D. (2000) Whakatu-1 Well Completion Report. Pep 38328. Open-File Petroleum Report 2476. Indo-Pacific Energy (NZ) Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 498pp. Pettinga, J.R. (1982) Upper Cenozoic Structural History, Coastal Southern
114 Hawke's Bay, New Zealand. New Zealand Journal of Geology and Geophysics, 25, 149-191. Rait, G., Chanier, F. & Waters, D.W. (1991) Landward- and Seaward-Directed Thrusting Accompanying the Onset of Subduction beneath New Zealand. Geology (Boulder), 19, 230-233. Rait, G. (1992) Early Miocene Thrust Tectonics on Raukumara Peninsula, Northeastern New Zealand, PhD Dissertation, Victoria University of Wellington. Ramdhan, A.M. & Goulty, N.R. (2010) Overpressure-Generating Mechanisms in the Peciko Field, Lower Kutai Basin, Indonesia. Petroleum Geoscience, 16, 367- 376. Reading, H.G. (1980) Characteristics and Recognition of Strike-Slip Fault Systems. In: Sedimentation in Oblique-Slip Mobile Zones (Ed. by P. F. Balance). Blackwell Scientific Publications, Oxford, England. Reyners, M. & McGinty, P. (1999) Shallow Subduction Tectonics in the Raukumara Peninsula, New Zealand, as Illuminated by Earthquake Focal Mechanisms. Journal of Geophysical Research, 104, 3025. Reyners, M. (2013) The Central Role of the Hikurangi Plateau in the Cenozoic Tectonics of New Zealand and the Southwest Pacific. Earth and Planetary Science Letters, 361, 460-468. Ridd, M.F. (1970) Mud Volcanoes in New Zealand. The American Association of Petroleum Geologists Bulletin, 54, 601-616. Saffer, D.M. & Tobin, H.J. (2011) Hydrogeology and Mechanics of Subduction Zone Forearcs: Fluid Flow and Pore Pressure. Annu. Rev. Earth Planet Sci., 39, 157- 186. Sclater, J.G. & Christie, P.A.F. (1980) Continental Stretching: An Explanation of the Post-Mid-Cretaceous Subsidence of the Central North Sea Basin. Journal of Geophysical Research, 85, 3711. Scotchman, I.C. & Carr, A.D. (2005). Effects of Transient Overpressure on the
115 Petroleum Systems of the Uk North East Atlantic Margin and Northern North Sea Areas: Implications for the Deep Water South Atlantic and Gulf of Mexico. Proceedings of the 6th Petroleum Geology Conference, Geological Society, London, 1247-1265. Song, I., Saffer, D.M. & Flemings, P.B. (2011) Mechanical Characterization of Slope Sediments: Constraints on in Situ Stress and Pore Pressure near the Tip of the Megasplay Fault in the Nankai Accretionary Complex. Geochemistry, Geophysics, Geosystems, 12, 1-20. Stern, T.A., Stratford, W.R. & Salmon, M.L. (2006) Subduction Evolution and Mantle Dynamics at a Continental Margin; Central North Island, New Zealand. Reviews of Geophysics, 44, RG4002(4001-4036). Strong, C.P., Scott, G.H. & Morgans, H.E.G. (1993) Biostratigraphic Review of Selected Drillholes, Hawke Bay - Gisborne Area. Science Report 93/19, Institute of Geological & Nuclear Sciences. Lower Hutt, New Zealand, 56pp. Sutherland, R., Stagpoole, V., Uruski, C., Kennedy, C., Bassett, D., Henrys, S., Scherwath, M., Kopp, H., Field, B., Toulmin, S., Barker, D., Bannister, S., Davey, F., Stern, T. & Flueh, E.R. (2009) Reactivation of Tectonics, Crustal Underplating, and Uplift after 60 Myr of Passive Subsidence, Raukumara Basin, Hikurangi-Kermadec Fore Arc, New Zealand: Implications for Global Growth and Recycling of Continents. Tectonics, 28, 1-23. Swarbrick, R.E. (2002). Developing Pressure Histories through Basin Modeling, In: Annual Meeting Expanded Abstracts, USA, American Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists, 10-13. Swarbrick, R.E., Osborne, M.J. & Yardley, G.S. (2002) Comparison of Overpressure Magnitude Resulting from the Main Generating Mechanisms. In: Pressure Regimes in Sedimentary Basins and Their Predictions (Ed. by A. Huffman & G. Bowers), AAPG Memior 76, 1-12. The American Association of Petroleum Geologists, USA. Tap Oil Limited. (2004) Tawatawa-1 Well Completion Report. Open-File
116 Petroleum Report 3067. T. O. Limited, Ministry of Economic Development New Zealand. Wellington, New Zealand, 873pp. Terzaghi, K. & Peck, R.B. (1948) Soil Mechanics in Engineering Practice. John Wiley, New York. Terzaghi, K.v. (1923) Die Berechnung Der Durchlassigkeitsziffer Des Tones Aus Dem Verlauf Der Hydrodynamischen Spannungserscheinungen. Sitz. Akad. Wiss. Wien, Abt. IIa, 132, 125-138. Townend, J., Sherburn, S., Arnold, R., Boese, C. & Woods, L. (2012) Three- Dimensional Variations in Present-Day Tectonic Stress Along the Australia– Pacific Plate Boundary in New Zealand. Earth and Planetary Science Letters, 353-354, 47-59. Unruh, J.R., Davisson, M.L., Criss, R.E. & Moores, E.M. (1992) Implications of Perennial Saline Springs for Abnormally High Fluid Pressures and Active Thrusting in Western California. Geology, 20, 431. von Huene, R. & Lee, H.J. (1982) The Possible Significance of Pore Fluid Pressure in Subduction Zones. In: Studies of Continental Margin Geology, 34, 781-791. AAPG Memior. Walcott, R.I. (1987). Geodetic Strain and the Deformational History of the North Island of New Zealand During the Late Cainozoic, Royal Society of London, London, United Kingdom. Walder, J. & Nur, A. (1984) Porosity Reduction and Crustal Pore Pressure Development. Journal of Geophysical Research, 89, 11539. Wallace, L.M., Beavan, J., McCaffrey, R. & Darby, D. (2004) Subduction Zone Coupling and Tectonic Block Rotations in the North Island, New Zealand. Journal of Geophysical Research, 109, B12406. Wang, H. (2000) Theory of Linear Poroelasticity with Applications to Geomechanics and Hydrogeology. Princeton University Press, Princeton, New Jersey. Watson, J.F. (1962) Ruakituri-1. Open-File Petroleum Report 324. BP Shell and Todd Petroleum Development Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 223pp.
117 Webster, M., O'Conner, S., Pindar, B. & Swarbrick, R. (2011) Overpressures in the Taranaki Basin: Distribution, Causes, and Implications for Exploration. AAPG Bulletin, 95, 339-370. Westbrook, G.K. & Smith, M.J. (1983) Long Decollements and Mud Volcanoes: Evidence from the Barbados Ridge Complex for the Role of High Pore-Fluid Pressure in the Development of an Accretionary Complex. Geology, 11, 279. Williams, K.E. & Madatov, A.G. (2005). Analysis of Pore Pressure Compartments in Extensional Basins. Petroleum Systems of Divergent Continental Margin Basins: 25th Annual, GCSSEPM Foundation Annual Bob F. Perkins Research Conference Proceedings, 25, 862-909. Yassir, N. & Addis, A.M. (1998) Relationships between Pore Pressure and Stress in Different Tectonic Settings. In: Pressure Regimes in Sedimentary Basins and Their Prediction (Ed. by A. R. Huffman & G. L. Bowers), AAPG Memoir 76, 79-88. AAPG/Houston Chapter of The American Association of Drilling Engineers, USA. Yassir, N. (1999) Overpressuring in Compressional Stress Regimes - Causes and Detection. In: Overpressure in Petroleum Exploration (Ed. by A. Mitchell & D. Grauls), Memoir 22, 13-18. Bulletin Centre Recherche Elf Exploration Production, Pau CEDEX, France. Yu, Z. & Cole, G. (2003). Application of 2-D Basin Modelling for Pre-Drill Pressure Prediction in the Gulf of Mexico and Offshore West Africa. Multidimensional basin modeling, AAPG/Datapages Discovery Series, 7, 362-363. Zeyen, H., Pessel, M., Ledésert, B., Hébert, R., Bartier, D., Sabin, M. & Lallemant, S. (2011) 3d Electrical Resistivity Imaging of the near-Surface Structure of Mud- Volcano Vents. Tectonophysics, 509, 181-190. Zimmermann, M.A., Faber, J. & Gouyet, J. (1967) Opoutama-1 Well Report. Open- File Petroleum Report 504. N. A. P. Ltd, Ministry of Economic Development New Zealand. Wellington, New Zealand, 973pp. Zoback, M. (2007) Reservoir Geomechanics. Cambridge University Press, New York.
118 Zou, Y.-R. & Peng, P.A. (2001) Overpressure Retardation of Organic-Matter Maturation: A Kinetic Model and Its Application. Marine and Petroleum Geology, 18, 707-713.
119 174˚E 176˚E 178˚E
New Zealand 38˚S Zone RAUKUMARA
Taupo Volcanic
Northern HAWKES BAY Mangaone-1 Wairoa Domain Awatere-1 Quaternary Mahia Hawke Peninsula Bay-1 Neogene CM05-01 Axial Ranges BAY HAWKE BAY HAWKES Paleogene Cretaceous Figure 2 Inset
40˚S Mz Basement Volcanics
WAIRARAPA Titihaoa-1
Hikurangi Trench
0 50 100 km
Figure 1. Geologic map of the East Coast Basin with selected wells and seismic line analyzed in this study. Geologic map based on Field et al. (1997).
Figure 2 (following page). Tectonostratigraphy of the East Coast Basin. Regional and Hawke’s Bay lithostratigraphy based on Field et al. (1997), chronostratigraphy based on Hollis et al. (2010), regional tectonics based on Ballance (1976), Ballance (1993), Laird and Bradshaw (2004), and Davy et al. (2008), seismic stratigraphy correlation based on Barnes et al. (2002) and Hollis et al. (2005), and offshore Hawke Bay structure based on Barnes and Nicol (2004). Structural inset map of Hawke Bay is modified from Barnes et al. (2002). See Figure 1 for map inset location.
120 Seismic Chronostratigraphy NE Regional Lithostratigraphy SW RegionalE Onshore Hawkes Bay W NW SE Hawkes Marl- Tectonics Stratigraphy O shore Hawke Bay Structure Ma PeriodEpochNZ Series NZ StageRaukumara Bay Wairarapa borough Lithostratigraphy Correlation
0 QuaternaryPleistocene Castlecli an Inversion Inversion Nukumaruan Horizon 8 Inversion Mangapanian Thrust backthrust Wanganui Waipipian & listric Pliocene Opoitian Horizon 11 duplex thrusting Inversion and Kapitean tectonic Horizon 12 Listric Listric TaranakiTongaporutuan Horizon 13 wedge and Listric and fault 10 ? ramp- ramp- Waiauan at reactivation ? at Extensional faults SouthlandLillburnian ? faults Clifdenian ? Altonian ??? Neogene Miocene Pareora low-angle Substantial 20 Otaian ? ? thrusting thrusting
Alloch- margin Convergent ? thon Horizon 14 Waitakian
Compressional (Weber Duntroonian Formation) Landon 30 Whaingaroan Oligocene ? Runangan Kaiatan ? Wanstead Arnold ? Formation 40 Bortonian
Porangan KIDNAPPERS RIDGE KIDNAPPERS FAULT BASIN LACHLAN RIDGE LACHLAN
Eocene Heretaungan Key: Black Shale 50 Paleogene Mangaorapan Calcareous/Limestone Waipawan ? Sandstone Waipawa Black Shale Interbedded sandstone ? and mudstone Dannevirke Upper Calcareous Member Erosion / No Deposition 60 Teurian Mudstone (Whangai Formation) Conglomerate Whangai Formation Siltstone Paleocene Breccia Glenburn Formation ? Key: 70 thrust Fault ? ? ? well (gas show) Haumurian Mata 80 Hawke Bay-1 Late Piripauan ? Teratan
90 Mangaotanean rifts Gondwana) (Zealandia from margin Dormant convergent ? Lachlan fault Arowhanan ? ? Raukumara CM05-01 Cretaceous Kidnappers ridge Ngaterian KidnappersLachlan fault basin 100 Torelesse Lachlan ridge Motuan Supergroup Ritchie
Clarence Urutawan Basement ridge
Early unknown margin 110 Taitai Korangan Hikurangi trench Convergent Convergent 121 Figure 2 122 Tap OilLimited,2004; IanRBrown Associates Ltd,2008) 1999c, 1999b, 1999a, 1998f, 1998e, 1998d, 1999d, 1998c, 2000; Johnston and Langdale, 2000; 1998b, Ozolins and Francis, 2000; 1998a, Ian R Brown Ltd, Associates Ltd, 2001a, 2001b; Associates Francis Brown et al., 2002; R Ian 1998; Johnston, and Haskell 1996; Francis, and Johnston Carter,1995; and al., Dobbie et 1986; Biros al., 1990; et Bock de 1976; HefferMilne, 1972c; and 1972b, 1972a, Laing, 1971c; 1971b, 1971a, Leslie, Kirby,1969b; and 1969a, Darley 1967; al., Watson,1960; et (Brown, Zimmermann reports 1962; assumes average shale properties based on literature review by Hantschel and Kauerauf (2009). Mud weight data is from open file well pressure Lithostatic level. sea to referenced are region. wells each All for age and depth by pressure pore based weight Mud 3. Figure
Depth (km) Depth (km) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 02 04 06 08 0100 90 80 70 60 50 40 30 20 10 0 02 04 06 08 0100 90 80 70 60 50 40 30 20 10 0 G e Paleogene Cretaceous Neogene Quaternary o l o g i c P e r i o d Raukumara
Hawke’s Bay
Mud WeightDerivedPorePressure (MPa) Mud WeightDerivedPorePressure(MPa)
Hydrostatic Hydrostatic
Lithostatic Lithostatic W W e Waitaria-1B Waitaria-1A Waitaria-1 Waingaromia-2 Puia-1 Te Te Horo-1 Ruakiture-1 Rotokautuku-1 Rere-1 e Whakatu-1 Titihaoa-1 Te Hoe-1 Taradale-1 Mason Ridge-1 Mason Kereru-1 Hukarere-1 Hawke Hawke Bay-1 l l l l
Depth (km) Depth (km) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 02 04 06 08 0100 90 80 70 60 50 40 30 20 10 0 02 04 06 08 0100 90 80 70 60 50 40 30 20 10 0 Northern Hawke’sBay Wairarapa
Mud WeightDerivedPorePressure (MPa) Mud WeightDerivedPorePressure(MPa)
Hydrostatic Hydrostatic
Lithostatic Lithostatic W e Takapau-1 Speedy-1A Speedy-1 Rakaiatai-1 Tawatawa-1 Tautane-1 Ongaonga-1 l l W e Kauhauroa-2 Tuhara-1 Opoutama-1 Opoho-1 Kauhauroa-1 Awatere-1 Mangaone-1 Makareoa-1 Kiakia-1 Kauhauroa-5 Kauhauroa-4 Kauhauroa-3 Waitahora-1 Tuhara-1A l l 200 Well Sample Porosity - Depth 4 Well Sample Porosity - Permeability 400 3 600 2 800 1 e 1000 ton nds 0 . sa 1200 Avg -1 1400
-2 1600
-3 1800 ne Well Depth (meters below mudline) Permeability (log(mD)) -4 to 2000 lts Awatere-1 g. si Hukarere-1 Av Kauhauroa-3 2200 -5 ne Kauhauroa-5 o t Kereru-1 s 2400 e -6 Tawatawa-1 l d ale Te Hoe-1 a n sh h a . Titihaoa-1 s s g Lithology -7 v 2600 . . A Sandstone Tuhara-1A g g Waitahora-1 v v Siltstone 2800 A A -8 Waitaria-2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Porosity (%) Porosity (%) Figure 4. Porosity-depth and porosity-permeability relationships for sandstones and siltstones from well samples. There is no clear relationship between porosity and depth, indicating the maximum effective stress must be determined to predict porosity. Sandstone and siltstone samples show lower permeabilities than average sandstone of the same porosity. The average sandstone and shale standards for comparison are from Hantschel and Kauerauf (2009) based on extensive literature review. The porosity versus depth model is based on
123 Athy’s Law of compaction (Athy, 1930), and the porosity versus permeability model is based on the multipoint model (Hantschel and Kauerauf, 2009). See Figure 3 for well data references. 124 and Kauerauf (2009). Athy’s compaction curve (Athy, 1930) is used to model the normal compaction trend based on extensive literature review by Hantschel (1993). al. et Strong from data Biostratigraphic 1999a. Ltd, Brown Associates R Ian from is Wellburial. data deeper previous despite due to deeper burial. Sandstone samples below this level exhibit undercompaction because overpressure has reduced the effective stress stone. Most sandstone samples above this level exhibit overcompaction because they have experienced higher effective stress in the past meters below sea level as identified by a reduction in velocity of the sonic log and a change in lithostratigraphy from sandstone to mud- Figure 5. Pore pressure summary of the Awatere-1 well (well location on Figure 1). Top of overpressure occurs between 1225 and 1480
metere below sea level 1400 1100 1000 1500 1200 1700 1600 1300 1900 1800 2000 2136 (TD) 2100 900 800 600 700 200 300 500 100 400 0 Siltstone Shale Limestone Sandstone
01 02 03 04 51 92 32 72 31 29 27 25 23 21 19 17 15 45 40 35 30 25 20 15 10 5 0 Hydrostatic Pressure Hydrostatic Pressure (MPa)
from mudweight Pore pressure estimate Lithostatic Pressure Lithostatic Top Miocene ofMiddle Top ofPliocene Top ofUpperMiocene Athy’s curve compaction Average sandstone Porosity (%) Athy’s curve compaction Average shale Top ofoverpressure
320 undercompaction
no compaction/ 300 280 260 240 compaction 220 normal trend compaction normal from core measured permeabilities SonicLog
200 (usec/ft) 180 160 140 120 100 80 60 2136 2100 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0
meters below sea level 125 et al.(1995). (RFT) data show that the formation is overpressured, which is responsible for the undercompaction of the samples. Well data from Biros TestFormation Repeat and weight Mud conditions. hydrostatic under depth given a for porosities average than higher exhibit samples lithology.sand-rich sandstone and Most mud- a to change and log sonic the in velocity in reduction sharp a by recognized is and level Figure 6. Pore pressure summary of the Titihoa-1 well (well location on Figure 1). Top of overpressure occurs at 1800 meters below sea
meters below sea level 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 0 Siltstone Shale
Limestone Sandstone 01 02 03 04 055 50 45 40 35 30 25 20 15 10 5 Hydrostatic Pressure Hydrostatic Pressure (MPa)
from mudweight Pore pressure estimate RFT Lithostatic Pressure Lithostatic Top ofUpperMiocene Top ofLower Pliocene Top Miocene ofMiddle 01 41 82 22 62 30 28 26 24 22 20 18 16 14 12 10 8 6 Athy’s curve compaction Average sandstone Porosity (%) Athy’s curve compaction Average shale 1750
overpressure 240 Top of
compaction 220 normal 200 Corrected Log Sonic Drift
180
160 (usec/ft) trend compaction normal from core measured permeabilities 140
120
100
80
60
3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 40 800 600 400 200 0 meters below sea level Figure 7 (following page). Seismic stratigraphy and structure of the CM05-01 line in offshore Hawke Bay (see Figure 1 for location). Top panel shows uninterpreted section and bottom panel shows interpreted section. Horizon 8, Horizon 11, Horizon 12, Horizon 13, and the Upper Cretaceous – Paleogene (Horizon 14) layers are based on horizon picks from nearby lines interpreted by Barnes et al. (2002) that have been tied to the Hawke Bay-1 well, onshore stratigraphy, and rock dredge samples. The lower Glenburn and Torlesse horizons are more poorly constrained as indicated by crossing white lines, and horizon tops are based primarily on the dip of seismic reflections and structural framework of the basin. The basin structure can generally be divided into Inboard, Lachlan Basin, and Outboard, and Accretionary Complex sections.
126 B A SE VE~x2 seamount Subducted Accretionary Complex Accretionary Horizon 13 Paleogene - U. Cret. Glenburn Torlesse Ritchie ridge Recent Horizon 8 Horizon 11 Horizon 12 Outboard Region Outboard
124 km Lachlan fault Lachlan sediment cover sediment Hikurangi Plateau and Hikurangi Plateau ridge Lachlan Lachlan Basin Region Lachlan basin
Kidnappers fault Kidnappers ridge Kidnappers 0 5 15 25 km Inboard Region Hawke Bay-1 NW
0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 TWT (sec) TWT (sec) TWT Figure 7.
127 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 Weber Formation Glenburn Formation (upper) Wanstead Formation 5 Glenburn Formation (middle) Waipawa Black Shale Glenburn Formation (lower) Upper Calcareous Torlesse Supergroup Member 10 Oceanic Crust and Cover Whangai Formation 15 24 Ma (Time Step 9) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 Horizon 13 (lower) LF 5
10
15 Horizon 13 (lower), 18.8 Ma (Time Step 10) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 LB Horizon 13 (middle)
5
10
15 1:1 Horizon 13 (middle), 13.6 Ma (Time Step 11)
Figure 8. Structural reconstructions of the CM05-01 line. Time Steps 1-8 represent deposition of a basinward thinning wedge and there- fore are not depicted here. The Cretaceous-Paleogene sections experience a total of 22 kilometers shortening since Neogene time. No vertical exaggeration. LF = Lachlan fault; LB = Lachlan Basin; LR = Lachlan Ridge; RR = Ritchie Ridge 128 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 LR
5
10
15 11.9 Ma (Time Step 12) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 Horizon 13 (upper)
5
10
15 Horizon 13 (upper), 8.5 Ma (Time Step 13) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 Horizon 12
5
10
15 Horizon 12, 7 Ma (Time Step 14)
Figure 8 (continued) 129 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 Horizon 11
5
10
15 Horizon 11, 4 Ma (Time Step 15) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 Horizon 8 RR
5
10
15 Horizon 8, 0.8 Ma (Time Step 16) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 km 0 Surface
5
10
15 Surface, 0 Ma (Time Step 17) Figure 8 (continued) 130 NW Inboard Region Lachlan Basin Region Outboard Region Accretionary Complex SE Hawke Bay-1 Kilometers 0 10 20 30 40 50 60 70 80 90 100 110 0 Surface Horizon 8 Horizon 11 2.5 Horizon 12 Horizon 13
5 Glenburn Formation 7.5 Surface: 15% sandstone, 15% siltstone, 70% shale Horizon 8: 10% sandstone, 15% siltstone, 75% shale 10 Horizon 11: 10% sandstone, 10% siltstone, 80% shale
Depth (km) Torlesse Horizon 12: 10% sandstone, 15% siltstone, 75% shale Supergroup Horizon 13: 10% sandstone, 15% siltstone, 75% shale 12.5 Weber Formation: 20% sandstone, 60% shale, 20% micrite Upper Oceanic Crust Wanstead Formation: 70% shale, 20% smectite, 10% micrite Waipawa Black Shale: 100% organic rich shale 15 Lower Oceanic Crust Upper Calcareous Member: 100% organic lean, siliceous shale Weber Formation Wanstead Formation Whangai Formation: 100% organic lean, siliceous shale 17.5 Waipawa Black Shale Glenburn Formation: 10% sandstone, 40% siltstone, 50% shale Upper Calcareous Member (Whangai Formation) Torlesse Supergroup: 25% sandstone, 25% shale, 25% slate, 25% schist Whangai Formation Upper Oceanic Crust: 100% oceanic basalt Lower Oceanic Crust: 100% oceanic gabbro
Figure 9. Present day lithostratigraphy and formation names of the basin and petroleum system model. Lithologic composition is the constant for the entire layer through time. The properties of compositional mixtures are based on extensive literature review by Hantschel and Kauerauf (2009). Stars correspond to time extractions in Figures 16, 17, and 20. The red star represents the Inboard Region, the green star represents the Lachlan Basin Region, and the blue star represents the Outboard Region. 131 Porosity (log%) 1 10 100 0
10
20
30
40
50 E ective Stress (MPa) Stress E ective
60
70
80 70% Shale, 20% Smectite, 10% Micrite Shale (Organic Rich) Shale (Organic Lean, Siliceous) 10% Sandstone, 10% Siltstone, 80% Shale 10% Sandstone, 15% Siltstone, 75% Shale 15% Sandstone, 15% Siltstone, 75% Shale 20% Sandstone, 60% Shale, 20% Micrite 40% Sandstone, 40% Siltstone, 50% Shale 25% Sandstone, 25% Shale, 25% Slate, 25% Schist Siltstone (typical) Sandstone (typical) Figure 10. Porosity-effective-stress relationships based on Athy’s compaction law (Athy, 1930) for modeled lithologies and lithologic standards. Most modeled lithologies exhibit a relationship between average shale and average siltstone. The 60% shale, 30% smectite, and 10% micrite lithology represents the Wanstead Formation, which acts as a regional seal in the basin. The porosity-effective-stress relationships represent mixtures of their litho- logic components based on literature review by Hantschel and Kauerauf (2009), and were not modified due to lack of calibration data.
132 Porosity (%) 0 10 20 30 40 50 60 70 80 106
104
102
1
10-2
10-4
10-6 Permeability (log(mD))
10-8
10-10
10-12 Surface Facies Glenburn Facies Horizon 8 Facies Torlesse Facies Horizon 11 Facies Sandstone (typical) Horizon 12 and 13 Facies Shale (typical) Weber Facies Wanstead Facies Siltstone (organic lean) Waipawa Facies (same as shale) Wanstead Facies 30% smectite Upper Calcareous Facies Wanstead Facies 10% smectite
Figure 11. Porosity-permeability relationships for modeled layer lithologies and lithologic standards using the multipoint model (Hantschel and Kauerauf, 2009). Relationships were calibrated to mud weight data from the Hawke Bay-1 well. Almost all porosity- permeability relationships are lower than typical siltstone, and the relationships are lower than typical shale for Horizon 8 and the Wanstead Formation, indicating their potential as effective seal rocks in the basin. In the Wanstead Formation, the 30% smectite content is the main driver of seal capacity. The porosity-permeability relationship is very sensitive to smectite content, and decreasing the smectite content down to 10% reduces its seal effec- tiveness. Porosity-permeability standards are based on literature review by Hantschel and Kauerauf (2009), although the properties of mixtures have been altered for calibration.
133 0 0 Hawke Bay-1 Hawke Bay-1 0.5 Pressure Scenarios Porosity Scenarios 1.0 1
1.5
2.0 2
2.5 Regional Seal Depth (km) 3.0 3 Depth (km)
3.5
4.0 4
4.5
5.0 5
0 10 20 30 40 50 60 70 80 90 100 110 0 10 20 30 40 50 60 70 Pressure (MPa) Porosity (%) Model Scenario Hawke Bay-1 Well Data Curve Measure Base Case (20% Smectite Seal) Leak Off Test Porosity Terzaghi 30% Smectite Seal Case Mud Weight Fracture Pressure Terzaghi 10% Smectite Seal Case Hydrostatic Poroelastic Model (No Displacement) Lithostatic Pore Pressure
Figure 12. Pressure calibration of the Terzaghi base case model to the Hawke Bay-1 well using mud weight data (see Figures 1 and 9 for well location). Very high overpressure is modeled to occur beneath the Wanstead Formation, which acts as a regional seal rock. The smectite content has a direct impact on the magnitude of overpressure maintained by the seal, and also a corresponding impact on the degree of porosity preservation. The poroelas- tic model assumes a 20% smectite content and there is significantly less preservation of excess pressure than the Terzaghi base case.
Figure 13 (following pages). Development of overpressure in the basin and petroleum system model by time step. Red dashed lines indicate model block boundaries required for representing thrusted geometries. Horizontal boundaries are all located on horizon tops. Vertical boundaries typically follow faults, although often extend vertically beyond the fault tip. Blocks are numbered from upper right to the lower left, and may change between time steps (i.e., the same block may have a different number between time steps). The Wanstead Formation, the main seal rock, is highlighted in white.
134 0 10 20 30 40 50 60 70 80 90 100km 110 0
2.5 1 2 5
7.5
10
12.5
15 17.5 34.6 Ma (Time Step 8) km 0 10 20 30 40 50 60 70 80 90 100km 110 0
2.5 1 2 5 Overpressure (MPa) 7.5 0 to 2 20 to 22 10 2 to 4 22 to 24 4 to 6 24 to 26 6 to 8 26 to 28 12.5 8 to 10 28 to 30 10 to 12 30 to 32 15 12 to 14 32 to 34 14 to 16 34 to 36 17.5 24 Ma (Time Step 9) 16 to 18 36 to 38 km 18 to 20 38 to 40 135 Figure 13 0 10 20 30 40 50 60 70 80 90 100km 110 0 5 4 2.5 6 1 2 3 7 14 5 a d 12 13 b c 8 10 11 9 7.5
10
12.5
15
17.5 km 18.8 Ma (Time Step 10) 0 10 20 30 40 50 60 70 80 90 100km 110 0 5 2.5 b 4 6 13 1 2 7 14 5 3 d 12 a 8 11 c 9 10 7.5 Overpressure (MPa) 0 to 2 20 to 22 10 2 to 4 22 to 24 4 to 6 24 to 26 12.5 6 to 8 26 to 28 8 to 10 28 to 30 15 10 to 12 30 to 32 12 to 14 32 to 34 17.5 14 to 16 34 to 36 13.6 Ma (Time Step 11) 16 to 18 36 to 38 km
136 18 to 20 38 to 40 Figure 13 (continued) 0 10 20 30 40 50 60 70 80 90 100km 110 0 5
2.5 b 4 e 6 1 13 2 7 14 5 3 a d 12 c 10 11 7.5 8 9
10
12.5
15 17.5 11.9 Ma (Time Step 12) km 0 10 20 30 40 50 60 70 80 90 100km 110 0 1 6 2.5 b 5 e 2 7 14 15 3 8 5 4 d 13 a c 12 9 11 7.5 10 Overpressure (MPa) 0 to 2 20 to 22 10 2 to 4 22 to 24 4 to 6 24 to 26 12.5 6 to 8 26 to 28 8 to 10 28 to 30 15 10 to 12 30 to 32 12 to 14 32 to 34 17.5 14 to 16 34 to 36 8.5 Ma (Time Step 13) 16 to 18 36 to 38 km 137 18 to 20 38 to 40 Figure 13 (continued) 0 10 20 30 40 50 60 70 80 90 100km 110 0 1 5 6 2.5 e b 7 2 14 3 8 15 d 5 4 13 c 9 a 11 12 7.5 10
10
12.5
15 17.5 7 Ma (Time Step 14) km 0 10 20 30 40 50 60 70 80 90 100km 110 0 5 6 1 7 8 2.5 13 2 3 9 15 16 10 17 5 4 18 11 7.5 Overpressure (MPa) 12 14 0 to 2 20 to 22 10 2 to 4 22 to 24 4 to 6 24 to 26 12.5 6 to 8 26 to 28 8 to 10 28 to 30 15 10 to 12 30 to 32 12 to 14 32 to 34 17.5 4 Ma (Time Step 15) 14 to 16 34 to 36 km 16 to 18 36 to 38 138 18 to 20 38 to 40 Figure 13 (continued) 0 10 20 30 40 50 60 70 80 90 100km 110 0 1 5 7 12 6 e 17 2.5 8 b 11 14 15 16 2 9 5 4 d a 3 c 7.5 10 13 10
12.5
15
17.5 km 0.8 Ma (Time Step 16) 0 10 20 30 40 50 60 70 80 90 100 110km 0 1 2 6 8 12 7 e 19 2.5 14 18 9 17 b 10 5 d 3 4 5 11 a c 13 16 7.5 15 Overpressure (MPa) 0 to 2 20 to 22 10 2 to 4 22 to 24 4 to 6 24 to 26 12.5 6 to 8 26 to 28 8 to 10 28 to 30 15 10 to 12 30 to 32 12 to 14 32 to 34 17.5 14 to 16 34 to 36 0 Ma (Time Step 17) 16 to 18 36 to 38 139 km 18 to 20 38 to 40 Figure 13 (continued) 0.9 MPa 2.3 MPa
km km 0 10 20 30 40 50 60 70 80 90 100 110 0 10 20 30 40 50 60 70 80 90 100 110 0 11.9 Ma 0 8.5 Ma 2.5 2.5
5 5
7.5 7.5
10 Overpressure (MPa) 10
Depth (km) 0 to 1.5 15 to 16.5 Depth (km) 1.5 to 3 16.5 to 18 12.5 3 to 4.5 18 to 19.5 12.5 4.5 to 6 19.5 to 21 6 to 7.5 21 to 22.5 15 7.5 to 9 22.5 to 24 15 9 to 10.5 24 to 25.5 17.5 10.5 to 12 25.5 to 27 12 to 13.5 27 to 28.5 17.5 13.5 to 15 28.5 to 30
Figure 14. Uplift and erosion occurs between 11.9 Ma and 8.5 Ma with the removal of Block 5 at 11.9 Ma (outlined in dashed red) during the 8.5 Ma time step. Sediment erosion results in a reduction in overpressure as the sediment re-equilibrates to the reduced vertical load.
140 Overpressure (MPa) Porosity (%)
0 10 20 30 40 50 60 70 80 90 100 km 0 1 0 Ma 6 8 2 e 12 2.5 7 14 9 17 18 19 b 10 16 d 13 5 15 3 4 5 11 a c 7.5
10
12.5 Porosity (%) 15 0 to 2 10 to 12 20 to 22 30 to 32 2 to 4 12 to 14 22 to 24 32 to 34 4 to 6 14 to 16 24 to 26 34 to 36 17.5 6 to 8 16 to 18 26 to 28 36 to 38 km 8 to 10 18 to 20 28 to 30 38 to 40
Figure 15. Map of porosity at present day. Present day modeled porosity is directly depen- dent on the effective stress (and overpressure) history modeled. Porosity is often preserved under the effective regional seal, the Wanstead Formation, as well as below late Miocene seals. The Wanstead Formation is highlighted in yellow. In the Miocene section, Blocks 14, 15, and 16 experienced higher magnitude overpressure relative to sediments in Block 13 at the same depth, resulting in porosity preservation (undercompaction).
141 Inboard Pore Pressure Lachlan Basin Pore Pressure Outboard Pore Pressure 150 0.0
130 0.9
110 1.8
90 2.7
MPa 70 3.6
50 4.5 Burial Depth (km)
30 5.4
10 6 Inboard Stress to Failure Lachlan Basin Stress Outboard Stress to Failure 4 to Failure
2
MPa Failure Line Failure Line Failure Line 0
-2 010203040506070 010203040506070 010203040506070 Time (Ma) Time (Ma) Time (Ma) Burial History Hydrostatic Pressure Lithostatic Pressure No Displacement Scenario 1% Displacement Scenario 5% Displacement Scenario 10% Displacement Scenario Figure 16. Pore pressure evolution and stress to failure of the Whangai Formation in the Inboard, Lachlan Basin, and Outboard regions of the ECB using the poroelastic model (see Figure 9 for extraction locations). Shortening from 24 Ma to present day cause increases in pore pressure. Failure occurs within the Whangai Formation around the beginning of short- ening, although the associated plastic deformation and effects on pore pressure are not modeled here.
142 150 Whangai Formation stresses with Whangai Formation stresses with shortening from 24 Ma to present shortening from19-24 Ma in the 125 day in the Lachlan Basin Lachlan Basin
100 Horizontal stress exceeds vertical stress at 0.4 Ma for 5%
MPa shortening scenario 75
50
25
010203040506070 010203040506070 Time (Ma) Time (Ma) Stress xx Stress zz Hydrostatic Pressure No Displacement Scenario 1% Displacement Scenario 5% Displacement Scenario 10% Displacement Scenario
Figure 17. Principal xx and zz stresses in the Whangai Formation within the Lachlan Basin (see Figure 9 for extraction location) through time based on poroelastic basin and petro- leum system modeling. Horizontal shortening causes increases in the xx stress experienced in the Whangai Formation. By present day, xx stress exceeds zz stress for the 5% and 10% shortening scenarios for both the 24 Ma to present day compression cases and 24 to 19 Ma compression cases. The 24 to 19 Ma compression cases show the xx stress is closer to the zz stress earlier on in the basin’s history.
143 Pressure (MPa) Pressure (MPa) Pressure (MPa) Pressure (MPa) 10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 0 10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 Waingaromia-2 Waitaria-1 Kauhauroa-2 Tuhara-1 0.5 1.0 1.5 2.0
Depth (km) 2.5 3.0 3.5 0 Hawke Bay-1 Hukarere-1 Whakatu-1 Speedy-1 0.5 1.0 1.5 2.0
Depth (km) 2.5 3.0 3.5 0 Tuatane-1 Tawatawa-1 Titihaoa-1 0.5 Waingaromia-2 Leak o test Waitaria-1 1.0 Hydrostatic Kauhauroa-2 Lithostatic Hawke Bay-1 Tuhara-1 1.5 Pore Pressure Hukarere-1 Whakatu-1 2.0 Speedy-1
Depth (km) 2.5 Tautane-1 Tawatawa-1 3.0 Titihaoa-1 3.5
144 Figure 18. Leak off test data and pore pressure estimate from mud weight for 11 wells, listed from north to south (see Figure 3 for refer- ences). Kilometers 0 Ma 0 10 20 30 40 50 60 70 80 90 100 0
2.5
5
7.5
10
Depth (km) Fracturing (MPa) 12.5 -0.1 to 0.0 0.9 to 1.0 0.0 to 0.1 1.0 to 1.1 0.1 to 0.2 1.1 to 1.2 0.2 to 0.3 1.2 to 1.3 15 0.3 to 0.4 1.3 to 1.4 0.4 to 0.5 1.4 to 1.5 0.5 to 0.6 1.5 to 1.6 17.5 0.6 to 0.7 1.6 to 1.7 0.7 to 0.8 1.7 to 1.8 0.8 to 0.9 1.8 to 1.9
Figure 19. Present day fracturing overlay where pressures greater than 0 MPa indicate potential fracturing due to excess pressures exceeding the fracture gradient (in Table 1). Results based on Terzaghi-type modeling with the Wanstead Formation composed of 30% smectite. The Wanstead seal rock (in white) and underlying formations are most likely to experience fracturing, as well as overpressured Neogene sediments in the Lachlan Basin. 145 4 Stress to failure of the Wanstead Formation in the Inboard Region 3
2 Poroelastic model (no displacement) with 20% smectite Wanstead Fm 1 Poroelastic model (no displacement) with 30% smectite Wanstead Fm 0 Stress to Failure (MPa)
-1
-2 50 40 30 20 10 0 Time (Ma) Figure 20. Stress to failure through time for the Wanstead Formation in the Inner region based on poroelastic modeling with no displacement. Location of extraction is directly above the Whangai Formation time extraction in the Inner region indicated in Figure 9. Negative values indicate no failure, while positive values have reached failure. Increasing the smectite content of the Wanstead Formation from 20% to 30% shifts the approximate timing of failure from 13 Ma to 12 Ma.
146 17.5 12.5 17.5 12.5 scenarios. both for basin the in buried deeply most is it where transformation 75% to 60% between reaches Formation Whangai The Table2). (see scenarios flow heat high and low the for basin the in rocks source potential for overlay ratio transformation day Present 21. Figure 7.5 2.5 7.5 2.5 15 10 15 10 0 5 5 km 0 km 02 04 06 08 0100km 90 80 70 60 50 40 30 20 10 0 02 04 06 08 0100km 90 80 70 60 50 40 30 20 10 0 High Heat FlowHigh Scenario Low Heat Flow Scenario Transformation (%) Ratio 45 to 50 40 to 45 35 to 40 30 to 35 25 to 30 20 to 25 15 to 20 10 to 15 5 to 10 0 to 5 95 to 100 90 to 95 85 to 90 80 to 85 75 to 80 70 to 75 65 to 70 60 to 65 55 to 60 50 to 55 147 148 149
CHAPTER 3
THERMAL REGIME EVALUATION AND SOURCE ROCK TRANSFORMATION IN HAWKE BAY, NEW ZEALAND
THERMAL REGIME EVALUATION AND SOURCE ROCK TRANSFORMATION IN HAWKE BAY, NEW ZEALAND
Blair Burgreen and Stephan A. Graham Geological and Environmental Sciences, Stanford University, Stanford, CA 94305
ABSTRACT This study uses basin and petroleum system modeling to examine the extent and timing of transformation of two prospective source rocks, the Waipawa Black Shale and the Whangai Formation, of the East Coast Basin (ECB) across a two- dimensional regional seismic line in Hawke Bay. The Waipawa Black Shale has the best source rock potential in the basin, and the Upper Calcareous Member of the Whangai Formation is considered despite low source rock potential because it may be responsible for onshore oil seeps. As part of a convergent margin, the basin has undergone a multiphase structural evolution. Early Miocene low angle thrust faulting caused structural thickening, and mid-to-late Miocene normal faulting created accommodation causing stratigraphic burial. The basin and petroleum system model is divided into four structural sections based on their distinct styles and timing of deformation. This study evaluates the likelihood of three possible paleo-basal heat flow scenarios, which are calibrated to vitrinite-inertinite reflectance and fluorescence analysis, Tmax, the thermal alteration index, apatite fission track analysis, and present- day temperatures. We support two heat flow scenarios based on their consistency with the basin’s tectonic history. We examine the impact of the paleo-basal heat flow on the timing and extent of source rock transformation for each structural section. Modeling results show transformation of the Waipawa Black Shale occurs from Miocene time to present day and is synchronous with respect to other petroleum system elements and events (reservoir rock, seal rock, and trap formation). We find that the exact timing of transformation is closely tied to the structural evolution of the basin, and dependent on
151 the structural section. The Lachlan footwall region experiences the earliest timing of transformation of the Waipawa Black Shale beginning at 19Ma due to early Miocene low angle thrust faulting, while the Lachlan basin region experiences transformation at 13 Ma associated with the onset of extensional faulting. Therefore, reservoir-seal targets in Hawke Bay need to be assessed in terms of their depositional age relative to their local structural history to determine whether the timing of petroleum system events is favorable.
INTRODUCTION The East Coast Basin (ECB) of the North Island, New Zealand is a frontier petroleum basin located on an active convergent margin where the Pacific Plate subducts obliquely beneath the Indo-Australian Plate at the Hikurangi trench (Fig. 1). As part of a convergent margin, the ECB is structurally and stratigraphically complex, and has presented a challenge for petroleum exploration. Nonetheless, the basin has been intermittently explored due to numerous structures and onshore and offshore oil and gas seeps. In the late 1800s, the Waingaromia borehole was drilled to 402 m depth and produced 20-50 barrels of oil per day until the derrick burned in 1888 (Field et al., 1997; Francis, 2000a). Since that time, numerous exploration wells have had dry gas shows, and, in 1998, there was a sub-commercial gas discovery in the Kauhauroa-5 well. However, there is currently no commercial production in the basin. Despite limited success in the basin, exploration continues both in the onshore and offshore regions. One of the main petroleum system risks is the maturation of the prospective source rocks. As part of a convergent margin setting, the thermal regime is anticipated to be depressed from subduction of cool oceanic crust (Dickinson, 1995). This implies deep burial (>4 km) of source rock is required for maturation. Despite the depressed geothermal regime, basins on convergent margins can be petroliferous under the right conditions, such as the Cook Inlet of Alaska, the Sacramento basin of California, and the Talara basin of Peru (Dickinson, 1995). Although ECB samples of prospective source rock from both outcrop and exploratory wells are thermally immature, samples from these locations typically have undergone less burial, thereby
152 representing a biased database. Additionally, the paleo-thermal regime may have been higher prior to subduction along the Hikurangi trench, suggesting prospective source rocks experienced maximum temperatures before present day. In order to fully assess the extent and timing of transformation of prospective source rocks, the paleo-thermal regime must be examined in context with the burial history. This is particularly challenging in the ECB because multiple phases of structural deformation have caused highly variable and localized burial and uplift histories across the basin. Basin and petroleum system modeling (BPSM) is a forward modeling technology that offers a comprehensive means to assess source rock maturation by integrating the basin history with source rock geochemistry through geologic time (Hantschel and Kauerauf, 2009). BPSM is increasingly being used to predict hydrocarbon generation, migration, and charge in basins worldwide (Lampe et al., 2006; Kuhn et al., 2012; Duran et al., 2013; Gusterhuber et al., 2014; Neumaier et al., 2014). Additionally, BPSM can incorporate the influence of structural deformation on development of the petroleum system, which is particularly important for the ECB and other structurally complex settings such as the Molasse fold and thrust belt of the Central Eastern Alps, Austria (Gusterhuber et al., 2014) and the Mongas fold and thrust belt of Venezuela (Neumaier et al., 2014). This study presents an assessment of source rock transformation in offshore Hawke Bay of the ECB along seismic line CM05-01 using two-dimensional BPSM. This study 1) evaluates the source rock potential of two prospective source rocks in the basin, 2) develops three possible paleo-basal heat flow scenarios through calibration to paleothermometers and present day temperatures, 3) examines the timing and extent of source rock transformation for the three heat flow scenarios in context with the rest of the petroleum system, and 4) investigates the impact of the local structural deformation on the source rock burial history and timing of transformation.
153 BACKGROUND Physiography The ECB developed in early Miocene time in response to subduction at the Tonga-Kermadec-Hikurangi trench where the Pacific plate obliquely subducts beneath the Indo-Australian plate (Ballance, 1976; Rait et al., 1991; Kamp, 1999; Stern et al., 2006; Reyners, 2013). The ECB is part of a convergent margin defined by a tapered wedge of sediments composed of an inboard, highly-overpressured Cretaceous to Oligocene sequence, an outboard accretionary subduction complex, and an overlapping, variably overpressured Miocene to Recent sedimentary sequence comprising the forearc and slope basin fill (Lewis and Pettinga, 1993; Mortimer and Parkinson, 1996; Field et al., 1997; Darby and Funnell, 2001). The basin is part onshore and part offshore, and is bordered to the west by the Axial Ranges and the Taupo Volcanic Zone (Fig. 1). Defining the forearc region of the modern day ECB is difficult because not all areas of the basin exhibit a clear trench-slope break (i.e., Dickinson, 1995). Therefore, the wedge of sediments between the Axial Ranges and Hikurangi trench is referred to as convergent margin sediments in this study for inclusivity. The focus of this study is in offshore Hawke Bay, which is part of the Hawkes Bay region.
Basin Stratigraphy The ECB experienced three main tectonic phases including a Permian to Early Cretaceous convergent margin phase, a dormant convergent margin phase from Late Cretaceous to Paleogene time, and a second convergent margin phase beginning in early Miocene time with the development of the Hikurangi trench (Fig. 2; Ballance, 1993; Field et al., 1997; Laird and Bradshaw, 2004). Corresponding basin stratigraphy begins with the Permian to Early Cretaceous Torlesse Supergroup, which is composed of metasediments from the ancient accretionary subduction complex of Gondwana and is the effective basement terrane (Mortimer, 2004 and references therein). Portions of the basement have experienced shale to schist grade metamorphism (Mortimer, 2004).
154 After subduction ceased around 100 Ma, the ECB experienced an overall quiescent period during which Zealandia rifted from Gondwana (Schellart et al., 2006; Reyners, 2013). The Upper Cretaceous Glenburn Formation was deposited in the Wairarapa and Hawkes Bay regions and is lithologically variable, comprised of interbedded sandstone, mudstone, siltstone, conglomerate, and pebbly sandstone (Field et al., 2005). Two prospective source rocks, the ~400 meter thick Upper Cretaceous through Paleocene Whangai Formation and the ~50 meter thick Paleocene Waipawa Black Shale were also deposited during this tectonically quiescent time (Fig. 2; Hollis et al., 2005 and references therein). This was followed by deposition of the smectite-rich Eocene Wanstead Formation, an effective seal rock, and by the calcareous mud-rich Weber Formation during Oligocene time (Field et al., 1997). With the onset of subduction at the beginning of Miocene time, coarser, more terrigenous sediment was supplied to the basin (Ballance, 1976; Pettinga, 1982; Rait et al., 1991; Mazengarb and Speden, 2000; Lee and Begg, 2002). Sandstone composition is dominantly fine-grained, representing crushed and sheared sedimentary rocks from the uplifting interior, and the volcaniclastic component is relatively minor despite the basin’s proximity to volcanic arcs (James et al., 2007). Turbiditic mudstone and sandstone were commonly deposited in elongate fault-bound depressions, whereas bioclastic limestones developed on paleo-structural highs (Bailleul et al., 2013; Burgreen and Graham, 2014). Although the Neogene deposits are predominantly mudstone, providing ample seal rock, turbiditic sandstone deposits are considered good reservoir rock. However, sand-rich turbidite deposits are often localized and ephemeral across the basin, depending primarily on the local uplift and subsidence history associated with the structural evolution (Field et al., 2005; Field et al., 1997).
Petroleum Systems At least three distinct petroleum systems exist in the ECB, including two thermogenic oil and gas systems and one biogenic gas system (Waples, 2001). Gas seeps are observed both onshore and offshore throughout the basin (Fig. 1). Oil seeps and stains are less common, but are observed onshore. Two oil families are recognized
155 based on biomarker and stable carbon isotope analyses of oil seeps and stain samples (Murray et al., 1994; Rogers et al., 1999). Family 1 oils are found in the Waitangi, Totangi, and Rotokautuku oil seeps and the Motu Valley, Isolation Creek, and Knights Stream oil stain locations (Fig. 1 – green diamonds; Rogers et al., 1999). Family 1 oils are the most widespread and have been tentatively tied to the Whangai Formation (Murray et al., 1994; Rogers at al., 1999; Waples, 2001; Hollis et al., 2005). Family 2 oils are found exclusively in the Wairarapa region in the Okau Stream, Westcott, and Tunakore Stream locations (Fig. 1 – blue diamonds). The Waipawa Black Shale is a proven source for Family 2 oils because the Okau Stream oil of Family 2 was sampled from sandstone enveloped by the Waipawa Black Shale (Rogers et al., 1999). This is further confirmed by isotopic and biomarker source rock and oil analyses (Murray et al., 1994; Rogers et al., 1999). Mixtures of Family 1 and 2 oils are present in the Tiraumea and Kerosene Rock locations (Fig. 1 – yellow diamonds; Rogers et al., 1999). Gas seeps occur throughout the onshore and offshore ECB, primarily releasing dry gas, although heavier gases (ethane – pentane) are often associated with the oil seeps (Lyon et al., 1991). Methane seeps in the onshore ECB are predominantly derived from thermogenic sources, although a biogenic component is also present in some samples (Hollis et al., 2005, and references therein). Methane seeps and gas hydrates are widespread offshore along the Hikurangi subduction margin (Plaza- Faverola et al., 2012). Geochemical analysis indicates that the offshore methane seeps are biogenic (Faure et al., 2010; Greinert et al., 2010; Law et al., 2010), although thermogenic methane may also contribute (Plaza-Faverola et al., 2012). In the onshore Raukumara and Wairarapa regions, Cretaceous and Miocene carbonate rocks containing chemosynthesis-based paleocommunities are evidence of paleo-methane seep sites (Campbell et al., 2008; Kiel et al., 2013). These paleo-seep sites are significant because they indicate hydrocarbon generation and expulsion has been ongoing since Cretaceous time, although a biogenic versus thermogenic source of the methane cannot be discerned (Coleman et al., 1981).
156 BASIN AND PETROLEUM SYSTEM MODELING A two-dimensional BPS model was constructed for Hawke Bay, where the basin geometry is reasonably well constrained by high quality seismic surveys and the offshore Hawke Bay-1 well, to assess the thermal maturity of prospective offshore source rocks. The BPS model was constructed using the 2D Petromod Teclink v2013.2® BPSM software. Modeling inputs include stratigraphic horizons for each geologic time step, stratigraphic ages of deposition and erosion, lithologies, source rock properties, paleo-basal heat flow, paleo-water depth, and sediment-water interface temperatures (SWIT). The model was run with three different basal heat flow scenarios to assess the timing and extent of transformation of prospective source rock for the distinct structural sections in the basin.
Structural Sections of CM05-01 Hawke Bay has undergone a complex structural history involving an early-to- mid Miocene phase of compression and shortening, a late Miocene phase of extension, and a Pliocene-to-present phase of inversion (Barnes et al., 2002; Barnes and Nicol, 2004). This study focuses on the CM05-01 seismic line from the MV Multiwave CM05 high-fold multichannel seismic reflection survey (Multiwave, 2005). The structural history and reconstruction is described in Burgreen et al. (in preparation). The 2D transect is sub-divided into Inboard, Lachlan basin, Lachlan footwall, and Outboard sections based on their distinct structural burial and uplift histories (Fig. 3). The Inboard section has undergone relatively steady burial of 2 to 4 km since Neogene time with limited vertical or horizontal displacement by faulting (Fig. 2). Mud diapirism likely affects the style of faulting in this region. The Lachlan basin experienced extensional faulting during mid-to-late Miocene time, achieving up to 6 km of burial in the center of the basin (Fig. 2). Inversion followed from Pliocene time to present, in which pre-existing listric faults were reactivated as reverse structures. The Lachlan footwall section is the just east of the Lachlan basin, which experienced up to 4 km of structural thickening during low angle thrusting events in early Miocene time (Fig. 2). Post-thrusting, the section experienced from 1 to 5 km of additional
157 burial by sedimentation. The Outboard section is dissected by listric thrust faults, which are inferred to have developed with the onset of subduction. Burial of the Outboard section during Neogene time ranged from 2 to 4 km, with around 1 km of burial occurring within the last 1 Ma (Fig. 2).
Modeled Layers The BPS model was constructed as a paleo-stepping model, in which layer geometries were defined for each modeled time step (Burgreen et al., in preparation). Layer geometries were provided for 17 time steps in the BPS model based on seismic interpretation and structural reconstruction of the CM05-01 seismic line (Table 1). Construction of the 2D BPS model is described in detail in Burgreen et al. (in preparation). The model includes 31 layers (Table 1). The layer lithologies are based on correlative onshore stratigraphy and cuttings from Hawke Bay-1. Each layer was modeled as a uniform lithology for simplicity and lack of additional lithologic data in Hawke Bay. Lithologic properties are based on extensive literature review by Hantschel and Kauerauf (2009) as described in Burgreen et al. (in preparation). Sediment compaction curves were calibrated for each layer based on regionally observed overpressure occurring below the smectite-rich Wanstead Formation, and mud-weight derived pore pressure from the Hawke Bay-1 well for Neogene sediments (Burgreen et al., in preparation).
Source Rocks Pre-Whangai Formation Source Rocks Although the Waipawa Black Shale and Whangai Formation are considered to be the two most prospective source rocks in the ECB, well and outcrop samples indicate these formations are primarily thermally immature (Figs. 4, 5). Therefore, the Upper Cretaceous Glenburn Formation is sometimes considered as a prospective source rock in the Hawke Bay region due to moderate to high total organic content (TOC) averaging around 2.0 wt.% and ranging up to 8.5 wt.%. However, hydrogen index (HI) values of thermally immature samples are only 25 mg/g TOC on average,
158 so source rock potential is poor (Hollis et al., 2005). Therefore, pre-Whangai Formation source rocks are omitted from this study.
Whangai Formation The Upper Cretaceous to Paleocene Whangai Formation is a siliceous source rock of low quality and richness (Fig. 4), but often considered to be capable of generating oil due to tentative geochemical ties with onshore seeps (Rogers et al., 1999). The Whangai Formation was deposited in a slowly subsiding basin accompanied by reduced terrigenous sediment supply and increased productivity of siliceous-rich phytoplankton (Moore, 1988). The Whangai Formation is comprised of the Rakauroa, Porangahau, Te Uri, and Upper Calcareous Members (Moore, 1988), and ranges between 300 to 500 m thick (Francis, 2000b). Although it is estimated around 400 m thick in the Hawke Bay region (Funnell and Benchilla, 2005), only a portion of this thickness likely represents potential source rock (Waples, 2001). Kerogen in the Whangai Formation is predominantly of marine origin based on biomarker analysis, although there is a small terrigenous component that varies by member (Hollis et al., 2005). A HI versus oxygen index (OI) plot indicates the Whangai Formation contains a mixture of Type II and Type III kerogens (Fig. 4), and therefore its main products are a mixture of oil and gas. Source rock potential also varies by member, and the 50 m thick Upper Calcareous Member has the best potential in the Hawke Bay region. However, the Upper Calcareous Member may transition into the less prospective Porangahau Member east of Lachlan ridge (Fig. 3; Moore, 1988). In this study, the Whangai Formation was separated into the Upper Calcareous Member and the less-prospective members of the Whangai Formation. The HI for the
Upper Calcareous Member was estimated from the best-fit linear slope of the S2 versus TOC plot from Angora Stream samples (Fig. 4). The HI was determined to be 305 mg/g TOC with an average TOC for these samples of 0.75 wt. %. TOC and HI values for the Whangai Formation did not need to be reconstructed due to low maturity. Although 1.0 wt.% TOC is a common baseline to be considered “good”
159 source rock (Peters et al., 2005), the actual TOC required for expulsion may be even higher (>2.4 wt.%) according to Lewan (1987). This is problematic for the Whangai Formation because all samples have measured TOC’s less than 1.7 wt. % (Hollis et al., 2005). In this study, we include the Upper Calcareous Member of the Whangai Formation as a prospective source rock only because it is tentatively tied to Family 1 oils in the basin. However, this implies the source rock richness must become higher in other areas of the basin in order for expulsion to occur. The rest of the Whangai Formation is considerably less prospective. HI calculated from samples of the Porangahau and Rakauroa Members at the Angora Stream Section estimate an HI of 58 mg/g TOC and a TOC of 0.1 wt. %. These members are considered non-source rock for this study. Upper Calcareous Member bulk kinetics are based on activation energies and frequency factor from an analysis conducted in 1994 by AGSO using samples from Kerosene Quarry (Appendix 3; C. Boreham, 2014, personnel communication).
Waipawa Black Shale The Waipawa Black Shale is the richest and highest quality known source rock in the region. The Waipawa Black Shale was deposited sometime between 58 Ma and 57 Ma within a short period of global cooling during an overall time of global warming (Hollis et al., 2005). The Waipawa Black Shale is thought to be associated with regional upwelling along the margin that created a narrow oxygen minimum zone between the outer shelf and upper slope (Killops et al., 2000; Rogers et al., 2001;
Waples, 2001). Kerogen is primarily marine-derived as evidenced by abundant C30 24- n-propylcholestanes indicating a chrysophyte microalgae source, and abundant amorphous algal material (Moldowan et al., 1990; Killops et al., 1996; Killops et al., 2000; Rogers et al., 2001). A variable amount of terrigenous kerogen is also present (Killops et al., 2000). Fuerst (2012) suggested that a marine transgression flooded near-shore swamps, locally providing additional terrigenous organic matter into the offshore oxygen minimum zone.
160 The thickness and lateral extent of the Waipawa Black Shale is poorly quantified due to faulting and incomplete sections, and its presence in Hawke Bay is uncertain because the Hawke Bay-1 well only reached Oligocene sediments. Measured sections of the Waipawa Black Shale range between 2-3 m to 50-60 m thick (Hollis et al., 2005 and references therein). However, most measured sections were incomplete and therefore represent minimum thickness. For simplicity, the Waipawa Black Shale is modeled as approximately 50 m thick in this study. TOC values range from 2 wt.% to 6 wt.% for immature samples of the Waipawa Black Shale (Fig. 5; Hollis et al., 2005 and references therein). HI is typically between 50 mg/g TOC to 500 mg/g TOC and is as high as 550 mg/g TOC in some areas (Hollis et al., 2005 and references therein). Tmax data indicates all of the samples are thermally immature, therefore these values represent original HI and TOC. A plot of HI versus OI indicates mainly kerogen types II and II/III (Fig. 5; Peters and Cassa, 1994), and therefore its main products include both oil and gas. To determine HI and TOC values of the Waipawa Black Shale for modeling, the Waipawa Black Shale was analyzed from outcrops in the Angora Stream,
Waitahaia River Gorge, and Te Weraroa Stream locations (Fig. 5). S2 versus TOC plots show that inertinite is present in the Angora Stream and Waitahaia River Gorge samples, which shifts the HI for a given TOC. To avoid underestimation of HI due to inert carbon, the HI was calculated from the best-fit linear slope of the S2 versus TOC plot for each sampled section. Because all three estimates of TOC and HI for the Waipawa Black Shale cluster together (Fig. 5), the TOC and HI values were averaged to an HI of 418 mg HC/g TOC and TOC of 3.7 wt. %. Bulk kinetics of the Waipawa Black Shale were modeled using activation energies and frequency factor from analysis by Applied Petroleum Technology (APT) in 2005 for GNS Science on samples from Black’s Quarry of the Northland region (Appendix 3; R. Sykes, personnel communication, 2014).
161 Boundary Conditions Paleo-water depth and SWIT are boundary conditions for the model. Paleo- water depth was determined from paleobathymetric maps by Field et al. (1997). The present-day SWIT is based on mean bottom water temperatures in Hawke Bay from Ridgeway (1969). The paleo-SWIT is based on surface temperature maps from Wygrala (1989) and temperature curves with depth from Beardsmore and Cull (2001).
EVALUATION OF PALEO-BASAL HEAT FLOW Heat flow through geologic time is an important parameter for modeling source rock maturation and is closely related to the tectonic history of a basin. The thermal regime controls the depth at which source rock generates and expels oil (i.e., the oil window), which typically ranges between 60°C to 160°C (Hunt, 1996). In this study, basal heat flow is calibrated to present-day geothermal gradients and temperatures, and paleothermometers including vitrinite-inertinite reflectance and fluorescence (VIRF), Tmax, the thermal alteration index (TAI), and apatite fission track (AFT) analyses. Calibration to both the present day and past thermal regime is particularly important in basins that may have cooled over time in order to predict the timing of maximum temperature experienced by the source rock.
Present-Day Thermal Regime The present-day thermal regime of the ECB is best constrained by temperatures measured in wells, present-day seawater temperature at the ocean floor, and bottom-simulating reflectors (BSRs). Well temperatures in the ECB are based on corrected bottomhole measurements, drill stem tests (DSTs), and temperature logs (Appendix 4). Thermal gradients were calculated for each well using corrected downhole temperatures and estimates of the sediment-water interface temperature. Calculated geothermal gradients were divided into three tiers based on their quality (Appendix 4). Tier 1 includes gradients calculated with Horner corrected bottomhole temperatures (Horner, 1951; Lachenbruch and Brewer, 1959; Dowdle and Cobb, 1975; Peters and Nelson, 2012) and DST temperatures with at least 100 barrels
162 of fluid flow (Peters and Nelson, 2012). Tier 2 includes gradients calculated with modified Horner corrected bottomhole temperatures with only two temperature readings and DST temperatures with less than 100 barrels of fluid flow. Tier 3 includes gradients calculated from temperature logs or “last resort” correction of BHT where 18°C was added to the temperature reading (Corrigan, 2003). Geothermal gradients in convergent margin settings are typically suppressed to below 15°C/km (Heasler and Surdam, 1985; Dumitru, 1988), and are characterized by low heat flow around 45 mW m-2 (Jessop, 1990; Allen and Allen, 2005). Tier 1 geothermal gradients indicate a gradient between 22°C/km to 34°C/km, which is surprisingly high. Tier 2 and Tier 3 geothermal gradients suggest even higher gradients unlikely for this tectonic setting, and were therefore omitted from the study. The high Tier 1 geothermal gradients may be due to out-of-equilibrium temperatures caused by recent uplift of many of the wells, which are located on structural highs. The high gradients may also be partly explained by the mud-rich nature of the basin. When thermal conductivities for shale and siltstone are assumed, the averaged Tier 1 geothermal gradient of 26 °C/km corresponds to present-day heat flows in the range of 42 mW m-2 to 53 mW m-2. The calculated heat flow increases significantly when additional sandstone lithofacies are assumed with higher thermal conductivities. BSRs also constrain the present-day heat flow in the offshore basin close to the trench, where temperatures are low and gas hydrates form (Sloan, 1990). Townend (1997) analyzed BSRs in the southern and central offshore margin of the ECB and determined a mean heat flow of 44 +/- 10 mW m-2 corrected for sedimentation, which is consistent with other convergent margin settings.
Paleothermometers of the East Coast Basin The thermal history of sediments in the basin provides important information regarding the burial history and paleo-heat flow. Vitrinite reflectance (VR) is the most commonly used petrographic method to assess thermal history. However, VR analysis has many recognized limitations, including incorrect identification of vitrinite macerals, vitrinite contamination from well cavings, VR suppression, VR retardation,
163 and recycled vitrinite from older formations (Wilkins et al., 1995; Carr, 2000). Due to the lack of non-marine intervals in the ECB, VR analysis has produced unreliable results because of the limited presence of normal vitrinite (Newman et al., 2000). In the Hawke Bay-1 and Opoutama-1 wells, two separate VR analyses were conducted for each well, resulting in distinct maturation profiles (Fig. 6). The inconsistency of these data indicate that VR analysis for other wells in the basin provide limited information on thermal history, and should be used with care. Instead, this study calibrates to paleothermometry data from VIRF analysis,
AFT analysis, Tmax, and the TAI. VIRF is a method developed by Newman (1997a, 1997b) and Newman et al. (2000) that uses fluorescence to identify normal vitrinite for VR analysis (see Appendix 3). The VIRF analysis conducted by Newman and Moore (2000) for the Opoutama-1 well shows a maturation trend that is significantly different from the original VR analyses conducted by Phillips Petroleum New Zealand Ltd (1976) and Jackson (1982) (Fig. 6). The original VR analyses overestimates maturity above 2400 m depth, possibly due to readings from inertinite that morphologically resembles the vitrinite, and underestimates maturity below 3000 m depth, possibly due to readings from suppressed vitrinite (Newman and Moore, 2000). A VIRF analysis conducted by Newman (2013) for Hawke Bay-1 for this study shows sediments are thermally immature and broadly corresponds to the VR analysis conducted by Lowe (1979). The VR analysis for Hawke Bay-1 by Phillips Petroleum New Zealand Ltd (1976) shows a maturation trend that is likely due to analyst selection bias. VIRF analysis is available for the Hawke Bay-1, Hukarere-1, Opoutama-1, and Tawatawa-1 wells in the ECB (Fig. 7; Appendix 4). AFT analysis and thermal modeling from Donelick (2001) of the Opoutama-1 well on eight samples of Late Cretaceous age are also considered. AFT modeling accounts for two kinetic variables (grain age and track length) and is considered to be a good paleothermometer in this study. However, there are significant complexities associated with AFT modeling due to distinct kinetics between age-length grain populations and partial annealing of fission tracks in the Opoutama-1 well (Donelick, 2001; Legg, 2010). Furthermore, the detrital apatite grains are likely derived from a
164 mixture of provenances from the metasedimentary basement terranes, which implies a distribution of original grain ages that further complicates modeling. However, these complexities are addressed as best possible by Donelick (2001) and the data quality is still considered to be good. The results from Donelick (2001) were reproduced with AFTSolve (Ketcham et al., 2000) using the same kinetic parameters as Donelick (2001) to be used in this study.
Other paleothermometry data used in this study includes Tmax data from the Hukarere-1, Rere-1, and Titihaoa-1 wells, and TAI data from the Titihaoa-1 well (Fig.
8). Tmax data was converted to equivalent VR based on the equation given by Jarvie et al. (2001). TAI was converted to an equivalent VR range based on an approximate relationship derived by Jones and Edison (1978).
Basal Heat Flow Calibration Basal heat flow was calibrated using one-dimensional BPSM for six ECB wells: Hawke Bay-1, Hukarere-1, Opoutama-1, Rere-1, Tawatawa-1, and Titihaoa-1, because these were the only wells with paleothermometric data considered in this study (Fig. 8; Appendix 7). It is important to note that although calibration can rule out certain scenarios, a calibrated basal heat flow scenario is non-unique. In these models, only one burial history scenario is presented for each well, although different burial, uplift, and erosion scenarios can also have a significant impact on heat flow calibration. VIRF and AFT analyses are considered to be the best quality calibration data in this study because they did not require conversion. Three heat flow scenarios were developed that best calibrate to the paleothermometric data and present-day temperatures (Fig. 9). Present-day thermal conditions were honored in all models, with geothermal gradients ranging between 19 °C/km and 33 °C/km for all heat flow scenarios. This is a slightly lower gradient range than the Tier 1 range due to limited maturation in several wells, which precluded higher present-day temperatures. The paleo-thermometry data is considered higher quality than the corrected present-day temperatures.
165
Apatite Fission Track (AFT) Scenario The AFT model provides thermal histories for each Upper Cretaceous sample in Opoutama-1 (Fig. 10), and shows a steady increase in temperature associated with burial from 90 Ma to 58 Ma. Partial annealing in the shallowest two samples and complete annealing in the six deepest samples suggest a brief but significant thermal event between 58 Ma to 49 Ma, peaking at 55 Ma. This AFT thermal event is not associated with additional burial, and its brevity suggests that it was related to a large intrusive or plutonic event or multiple events (Waples, 2001). AFT modeling indicates temperature and burial depth remained relatively steady through the rest of the Paleogene during the convergent margin dormancy period. At the beginning of Miocene time, the site where the Opoutama-1 well now sits experienced significant burial due to interior uplift and basin subsidence associated with the onset of subduction. Depsite additional burial, AFT data indicate temperatures dropped in the basin. The basal heat flow scenario calibrated to the AFT modeled temperatures for the Opoutama-1 well suggests several major shifts in thermal regime throughout the basin history (Fig. 9). During Late Cretaceous time, basal heat flow was steady at 35 mWm-2, which is below average global heat flow (ranging from 60 mWm-2 to 70 mWm-2) and a more typical heat flow for active convergent margins (Fig. 9; Allen and Allen, 2005). The AFT Paleocene thermal event requires an increase in basal heat flow to 80 mWm-2 at about 55 Ma. Volcanic or plutonic events, such as the Late Maastrichtian to early Paloecene dolerite and basalt flows and dikes observed in the eastern Wairarapa region (Moore, 1980) could produce a heat spike similar to this profile. However, no igneous intrusions have been recognized in the Hawkes Bay region either in outcrop or in seismic data. After the thermal event, AFT data require basal heat flow to gradually increase until early Miocene time, and then rapidly decrease to 23 mWm-2, suggesting extremely fast cooling associated with Pacific plate subduction. To slowly increase AFT temperatures during Pliocene uplift (Fig. 10), calibration required an increase in heat flow to pre-subduction levels to offset uplift-
166 related cooling. However, this Pliocene thermal heating event lacks apparent tectonic justification. The AFT heat flow scenario satisfactorily calibrates to other paleothermometric data from wells in the region (Fig. 8). The main discrepancies occur in the Paleogene and Neogene sections of the Opoutama-1 well, and in the uppermost late Miocene to Quaternary sections of the Titihaoa-1 well, where VR is underestimated in both cases. However, the AFT heat flow scenario is considered sub- optimal because calibration required several thermal events inconsistent with tectonic events in the basin.
55 mWm-2 with cooling at 15 Ma Scenario
Comparison of present-day temperatures with VIRF, Tmax, and TAI paleothermometers indicate many ECB wells experienced higher temperatures in the past. Sediment cooling is likely due to a combination of uplift (because many of the wells are drilled on structural highs) and a reduction in basal heat flow associated with the onset of subduction. Although subduction began in the ECB during or before early Miocene time, the shift in thermal regime appears to occur sometime between mid to late Miocene time, which is recognized in VIRF data by distinct thermal maturation trends in younger versus older sediments (Fig. 7) The “55 mWm-2 with cooling at 15 Ma” heat flow scenario reproduces this tectonic cooling with a reduction of heat flow at 15 Ma to 30 mWm-2 by present day, which is within the typical range of basal heat flow for a convergent margin setting (Fig. 9). Basal heat flow is steady at 55 mW/m-2 for the dormant convergent margin phase, which is slightly lower than global average heat flow. No thermal events are anticipated during this time because the basin was experiencing a tectonically quiescent phase. Although rifting occurred on the other side of the continent with the opening of the Tasman Sea, the ECB was likely too far to experience significant increased basal heat flow from this event. The “55 mWm-2 with cooling at 15 Ma” heat flow scenario calibrates to most paleothermometric data for each well except for the Rere-1 well, where thermal maturation is overestimated
(Fig. 8). However, only Tmax data are available for the Rere-1 well, which were
167 converted to equivalent VR. The “55 mWm-2 with cooling at 15 Ma” scenario also underestimates thermal maturity in the uppermost late Miocene to Quaternary sections of the Titihaoa-1 well based on Tmax and TAI data.
40 mWm-2 with cooling at 5 Ma Scenario The “40 mWm-2 with cooling at 5 Ma” scenario is similar to the “55 mWm-2 with cooling at 15 Ma” scenario, except that subduction-related cooling began during Pliocene time (Fig. 9). This scenario assumes that subduction-related cooling occurred well after the initiation of subduction during early Miocene time, and only once the Pacific plate was fully established beneath Zealandia. In reality, the exact timing of subduction-related cooling likely varies throughout the basin, where cooling was first experienced by the most outboard sediments followed by the more inboard sediments as the subducting plate migrated westward through time. In this scenario, the dormant convergent margin phase heat flow is lower at 40 mWm-2 because it is maintained through Miocene time when the basin experiences significant burial. Although this heat flow seems low for the dormant convergent margin phase, maintaining the higher heat flow of 55 mWm-2 from the “55 mWm-2 with cooling at 15 Ma” scenario would cause higher than observed temperatures in the deepest sediments. The “40 mWm-2 with cooling at 5 Ma” scenario calibrates reasonably well for most of the wells (Fig. 8). Although it slightly overestimates thermal maturity in the Rere-1 well, it calibrates significantly better than the “55 mWm-2 with cooling at 15 Ma” scenario. The “40 mWm-2 with cooling at 5 Ma” scenario underestimates thermal maturity in the Upper Cretaceous section of the Opoutama-1 well, and also underestimates thermal maturity in the uppermost Miocene to Quaternary sections of the Titihaoa-1 well, like the other two scenarios. The heat flow scenarios are calibrated to wells from different regions of the ECB and at different distances from the trench, therefore it is not surprising that none of the scenarios calibrate perfectly to all available maturity data. Although each scenario is plausible, the “55 mWm-2 with cooling at 15 Ma” and “40 mWm-2 with cooling at 5 Ma” scenarios are favored because they concur with the known tectonic
168 history of the basin. The “40 mWm-2 with cooling at 5 Ma” scenario overall calibrates better than the “55 mWm-2 with cooling at 15 Ma” scenario to the paleothermometers. However, the “55 mWm-2 with cooling at 15 Ma” scenario is better aligned with the anticipated global average heat flow during the dormant convergent margin phase (Fig. 9). Therefore, both the “40 mWm-2 with cooling at 5 Ma” and “55 mWm-2 with cooling at 15 Ma” heat flow scenarios are equally considered. Although the AFT heat flow scenario cannot be ruled out, more thermal analysis is required to confirm the Paleocene and Pliocene heat flow events because they lack tectonic justification. For simplification, the heat flow profiles are applied across the entire two-dimensional BPS model.
BASIN AND PETROLEUM SYSTEM MODELING RESULTS BPSM of the Waipawa Black Shale and Upper Calcareous Member of the Whangai Formation show that the timing and extent of source rock transformation is dependent both on the heat flow scenario and burial history associated with each structural regime (Inboard, Lachlan basin, Lachlan footwall, and Outboard sections). Timing and extent of source rock transformation is examined using 1D extracts from each structural section representing locations of maximum burial (Fig. 3).
Transformation of the Waipawa Black Shale Source rock transformation of the Waipawa Black Shale varies in each structural section by heat flow scenario (Fig. 11). The “55 mWm-2 with cooling at 15 Ma” heat flow scenario results in the earliest timing of transformation. In the Lachlan footwall, 10% transformation is reached by 17 Ma. This heat flow scenario also results in the most complete transformation. In the Lachlan footwall and Lachlan basin structural sections, the Waipawa Black Shale reaches near complete transformation by 4 Ma for the “55 mWm-2 with cooling at 15 Ma” scenario. The AFT heat flow scenario results in the most limited and latest transformation. The Waipawa Black Shale undergoes almost no transformation in the Inboard section with this scenario. In the Lachlan footwall, the Waipawa Black Shale reaches 10% transformation at 3 Ma
169 with the AFT heat flow, which is 14 m.y. later than the “55 mWm-2 with cooling at 15 Ma” scenario. Transformation begins between 6 to 4 Ma for the AFT heat flow scenario for the Lachlan basin, Lachlan footwall, and Outboard sections. This corresponds to the AFT scenario’s timing of increased basal heat flow from 23 mWm-2 to 39 mWm-2, which is observed in the AFT data although lacks an apparent tectonic justification (Fig. 9). BPSM shows that the Paleocene thermal event does not impact Waipawa Black Shale transformation. Despite high paleo-heat flow, the event is too brief and burial too limited for transformation to occur. Maximum temperature for the Waipawa Black Shale is attained during present day for the AFT scenario, not during the Paleocent thermal event (Fig. 12). The “40 mWm-2 with cooling at 5 Ma” heat flow scenario results in timing of transformation between the “55 mWm-2 with cooling at 15 Ma” and AFT heat flow scenarios (Fig. 11). For this scenario, the Waipawa Black Shale undergoes transformation in all structural sections, although to a more limited extent in the Inboard section. In the Lachlan footwall, the Waipawa Black Shale reaches 10% transformation at 10 Ma with the “40 mWm-2 with cooling at 5 Ma” scenario. The Waipawa Black Shale reaches near complete transformation in the Lachlan basin and Lachlan footwall structural sections by present day for this scenario. In addition to the modeled heat flow scenario, the timing of transformation is dependent on the structural section in Hawke Bay. The Inboard section achieves limited burial and therefore has the most limited transformation of the Waipawa Black Shale for all three heat flow scenarios (Figs. 11, 12). Despite reduction of basal heat flow at 21 Ma, 15 Ma, and 5 Ma for the AFT, “55 mWm-2 with cooling at 15 Ma”, and “40 mWm-2 with cooling at 5 Ma” heat flow scenarios, respectively, modeled temperatures of the Waipawa Black Shale continue to increase in the Inboard section until present day due to steady burial (Figs. 9, 12). In the Lachlan basin structural section, Waipawa Black Shale transformation begins earlier than the Inboard section. The Waipawa Black Shale reaches 50% transformation by late Miocene time for both the “55 mWm-2 with cooling at 15 Ma” and “40 mWm-2 with cooling at 5 Ma” heat flow scenarios (Fig. 11). This timing of transformation corresponds to extensional faulting in the Lachlan basin, which
170 increases accommodation and burial of the Waipawa Black Shale (Fig. 2). Temperature of the Waipawa Black Shale peaks at 4 Ma for both the “55 mWm-2 with cooling at 15 Ma” and “40 mWm-2 with cooling at 5 Ma” heat flow scenarios because of a reduction in basal heat flow, despite further burial (Fig. 12). For the “55 mWm-2 with cooling at 15 Ma” scenario, the Waipawa Black Shale reaches 95% transformation by this time, and undergoes limited additional transformation to present day. For the “40 mWm-2 with cooling at 5 Ma” scenario, the Waipawa Black Shale reaches 73% transformation by peak temperatures at 4 Ma, and then continues to undergo transformation, albeit at a slower rate, until it reaches 92% transformation at present day. For the AFT heat flow scenario, the Waipawa Black Shale experiences increasing temperatures through time and begins transformation during Pliocene time (Figs. 11, 12). Waipawa Black Shale transformation is earliest in the Lachlan footwall structural section (Fig. 11). Structural thickening occurs during early Miocene time due to low angle thrust faulting (Fig. 2). This enables transformation of the Waipawa Black Shale in early Miocene time for the “55 mWm-2 with cooling at 15 Ma” heat flow scenario because it has the highest basal heat flow during this time relative to the other scenarios (Figs. 9, 11). The “40 mWm-2 with cooling at 5 Ma” heat flow scenario does not undergo transformation until mid Miocene time because slightly more burial is required for the lower basal heat flow modeled. Temperature of the Waipawa Black Shale peaks at 4 Ma for the “55 mWm-2 with cooling at 15 Ma” and “40 mWm-2 with cooling at 5 Ma” scenarios due to basal heat flow reduction (Fig. 12). This corresponds to the timing of essentially complete Waipawa Black Shale transformation for the “55 mWm-2 with cooling at 15 Ma” scenario, and a decrease in transformation rate for the “40 mWm-2 with cooling at 5 Ma” scenario (Fig. 11). The AFT heat flow scenario only begins transformation during Pliocene time because its basal heat flow was too low for throughout Miocene time. In the Outboard section, Waipawa Black Shale transformation is incomplete for all modeled heat flow scenarios (Fig. 11). Temperature increases through time for all heat flow scenarios due to steady burial throughout the Miocene (Fig. 12).
171 Waipawa Black Shale transformation begins during mid to late Miocene time for the “55 mWm-2 with cooling at 15 Ma” and “40 mWm-2 with cooling at 5 Ma” heat flow scenarios. However, Waipawa Black Shale transformation begins much later at 1 Ma for the AFT heat flow scenario due to depressed basal heat flow throughout Miocene time. Although the Outboard section reaches burial depths greater than 5 km, similar to the Lachlan basin and Lachlan footwall sections, about 1 km of burial occurs only in the last 1 m.y. due to the timing of thrusting in this section (Fig. 12). Therefore, there is not enough time for significant Waipawa Black Shale transformation to occur despite a similar present day burial depth to the Lachlan basin and Lachlan footwall sections.
Transformation of the Whangai Formation Transformation results for the Upper Calcareous Member of the Whangai Formation show similar results in the relative timing of transformation and extent of transformation as the Waipawa Black Shale (Fig. 11). This is anticipated because the Upper Calcareous Member directly underlies the Waipawa Black Shale in the model and represents only an additional 50 m of burial. However, the exact timing and extent of transformation do vary between the two modeled source rocks, and the Upper Calcareous Member overall has undergone earlier and more complete transformation than the Waipawa Black Shale for all structural sections. This is because the bulk kinetics are different for the two source rocks, and the Upper Calcareous Member kinetics indicate source rock transformation at lower temperatures than the Waipawa Black Shale kinetics (Appendix 3). For example in the Outboard section, the “55 mWm-2 with cooling at 15 Ma” heat flow scenario models 10% transformation at 10 Ma for the Waipawa Black Shale and at 13.5 Ma for the Upper Calcareous Member.
DISCUSSION Prospective Source Rocks The Waipawa Black Shale and Whangai Formation represent the two most prospective source rocks in the EBC. However, analysis of source rock potential
172 indicates that only the Waipawa Black Shale has high enough richness to undergo expulsion. The Waipawa Black Shale’s match to Family 2 oils in the basin further supports its source rock potential. Although the Waipawa Black Shale has the potential to generate oil and gas, the basin is primarily gas-rich. This may be due to secondary cracking, or derivation from a different source rock, however neither scenario was modeled in this study. Although the Whangai Formation is thicker than the Waipawa Black Shale, it represents a very lean shale unlikely capable of generating hydrocarbons. The Upper Calcareous Member contains the most prospective source rock facies in the formation, and this study assumes its source rock effectiveness must improve in some regions of the basin to generate oils of Family 1. However, Family 1 oils may also be derived from another Cretaceous source rock that is perhaps distributed intermittently throughout the basin. Therefore, the source of Family 1 thermogenic petroleum system cannot be discerned from this study. The study focuses on transformation of the Waipawa Black Shale because of the limited prospectivity of the Whangai Formation.
Evaluation of Paleo-Basal Heat Flow Scenarios The three end-member paleo-heat flow scenarios developed by this study indicate there is still significant uncertainty in the paleo-thermal regime of the basin. VIRF data conflicts with data from AFT analysis, and there is no reason to doubt the credibility of either source. However, the AFT heat flow scenario is less favored over the “55 mWm-2 with cooling at 15 Ma” and “40 mWm-2 with cooling at 5 Ma” scenarios because it requires two basal heat flow events – one during Paleocene time and one during Pliocene time – that cannot be readily justified by the known tectonic history. Improved clarity on paleo-basal heat flow could be improved by additional analysis of paleothermometers in ECB wells that intersect these geologic sections. Additionally, the basal heat flow history likely varies regionally across the basin and based on its distance from the trench. Although over fifty wells have been drilled in the basin, only six wells have reliable paleothermometric data. Analyses of additional wells will help
173 distinguish regional heat flow profiles and trends in the timing of subduction-related cooling.
Transformation of the Waipawa Black Shale Results from this study show the Waipawa Black Shale is likely to be mature in Hawke Bay based on the “55 mWm-2 with cooling at 15 Ma” and “40 mWm-2 with cooling at 5 Ma” heat flow scenarios. Waipawa Black Shale transformation occurs primarily between mid to late Miocene time, which is concurrent with the timing of reservoir and seal rock deposition and trap formation (Fig. 2). This represents potentially favorable timing of petroleum system events for hydrocarbon charge. The “40 mWm-2 with cooling at 5 Ma” heat flow scenario, which indicates later transformation than the “55 mWm-2 with cooling at 15 Ma” heat flow scenario, is associated with the lowest risk because the petroleum system elements are more likely to be in place during hydrocarbon expulsion, migration, and accumulation. However, the depositional age of specific reservoir-seal targets needs to be considered relative to the structural section’s timing of transformation to fully assess the risks to hydrocarbon charge. BPSM results demonstrate the importance of incorporation of the type and timing of structural deformation into the BPS model. Each structural section experiences a distinct burial history related to phases of thrusting, listric normal faulting, and inversion in Hawke Bay (Fig. 2). Low angle thrusting occurs during early Miocene time, resulting in the earliest timing of transformation for the Waipawa Black Shale in the Lachlan footwall. Basin extension in the Lachlan basin occurs during mid Miocene time and is also associated with the onset of transformation. Therefore, it is important to consider the timing of these structural events in terms of prospective reservoir units and traps during exploration of the basin. The relative importance of burial history and heat flow scenario depend on the structural section and the specific heat flow profile anticipated. In the Inboard section, burial is limited and therefore Waipawa Black Shale transformation is low regardless of the heat flow scenario. When the AFT heat flow scenario is modeled,
174 transformation of the Waipawa Black Shale only occurs within the last 4 m.y. regardless of structural regime. However, for the other structural regimes and heat flow scenarios, timing of transformation is represented by an interplay of both burial history and heat flow history.
Unconventional resource play potential Results from this study and Burgreen et al. (in preparation) suggest that both the Waipawa Black Shale and Whangai Formation have many characteristics of unconventional resource plays. As described by the U.S. Geological Survey, common features of unconventional resource plays include a lack of obvious trap or seal, crosscutting lithologic boundaries, large areal extent, low matrix permeability, abnormal pressure, and close association with a source rock (Schmoker, 1999). Both the Waipawa Black Shale and Whangai Formation are present throughout most of the basin, have low permeability, and are experiencing very high, abnormal overpressure. They also have achieved significant maturity in the Hawke Bay region, although more regional modeling is required to estimate their maturity in other parts of the basin. The Whangai Formation is more likely to undergo brittle deformation due to natural hydraulic fracturing (Burgreen et al., in preparation), and may contain hydrocarbons both generated from within the source rock and from the Waipawa Black Shale through downward migration. Further basin and petroleum system modeling work is recommended to more fully assess the unconvential resource potential by the Waipawa Black Shale and Whangai Formation.
CONCLUSIONS The Hawkes Bay region of the ECB contains at least one prospective source rock, the Waipawa Black Shale. When paleo-heat flow is calibrated to VIRF data, the Waipawa Black Shale begins transformation during Miocene time and reaches near complete transformation by present day in the Lachlan basin and Lachlan footwall structural regimes. However when paleo-heat flow is calibrated to AFT data, the Waipawa Black Shale undergoes limited transformation even where it is most deeply
175 buried, with transformation beginning only with the last 4 m.y. Although the AFT heat flow scenario cannot be completely discredited, the heat flow scenarios calibrated to VIRF data are more consistent with known tectonic events in the basin and are therefore favored by this study. BPSM shows a potentially favorable timing of source rock transformation for VIRF-calibrated heat flow scenarios because deposition of reservoir and seal rock and timing of trap formation are concurrent in the basin history. However, specific reservoir-seal exploration targets should be considered in context with the timing of source rock transformation of their structural regime to determine potential risks to hydrocarbon charge. These considerations are relevant to other structurally complex petroleum basins, such as the Eastern Venezuela Basin (Neumaier et al., 2014), the Molasse fold and thrust belt of the Central Eastern Alps, Austria (Gusterhuber et al., 2014), and the South Caspian Basin of Azerbaijan(Feyzullayev and Lerche, 2009).
ACKNOWLEDGMENTS Funding for this research was provided by the corporate affiliates of the Stanford Basin and Petroleum System Modeling research group, with current members including Aera, BP, Chevron, ConocoPhillips, Great Bear Petroleum, Hess, Murphy, Nexen, Oxy, Petrobras, Saudi Aramco, and Schlumberger. Schlumberger provided academic licenses and support for Petromod®, which was essential to conduct this research. ConocoPhillips provided additional funding for vitrinite-inertinite reflectance and fluorescence analysis of samples from the Hawke Bay-1 well conducted by Jane Newman. The authors thank GNS Science for their support in providing kinetic data, providing logistical assistance for VIRF analysis, and directing us to additional resources. Specifically, Rob Funnell, Richard Sykes, Martin Crundwell, and Brad Field of GNS Science provided significant support of this research. This research also benefited from discussions with Jane Newman, Trevor Dumitru, Ken Peters, Les Magoon, Noelle Schoellkopf, Allegra Hosford Scheirer, and Gail Mahood.
176 REFERENCES CITED Allen, P. A., and J. R. Allen, 2005, Basin Analysis: Principles and Applications: Oxford, UK, Blackwell Science Ltd, 549 p. Bailleul, J., F. Chanier, J. Ferrière, C. Robin, A. Nicol, G. Mahieux, C. Gorini, and V. Caron, 2013, Neogene evolution of lower trench-slope basins and wedge development in the central Hikurangi subduction margin, New Zealand: Tectonophysics, v. 591, p. 152-174. Ballance, P. F., 1976, Evolution of the upper Cenozoic magmatic arc and plate boundary in northern New Zealand: Earth and Planetary Science Letters, v. 28, p. 356-370. Ballance, P. F., 1993, The paleo-Pacific, post-subduction, passive margin thermal relaxation sequence (Late Cretaceous-Paleogene) of the drifting New Zealand continent, in P. F. Ballance, ed., South Pacific Sedimentary Basins, Sedimentary Basins of the World, v. 2: Amsterdam, Elsevier, p. 93-110. Barnes, P. M., and A. Nicol, 2004, Formation of an active thrust triangle zone associated with structural inversion in a subduction setting, eastern New Zealand: Tectonics, v. 23, TC1015. Barnes, P. M., A. Nicol, and T. Harrison, 2002, Late Cenozoic evolution and earthquake potential of an active listric thrust complex above the Hikurangi subduction zone, New Zealand: Bulletin of the Geological Society of America, v. 114, p. 1379-1405. Beardsmore, G. R., and J. P. Cull, 2001, Crustal Heat Flow: A Guide to Measurement and Modeling: Cambridge, United Kingdom, Cambridge University Press. Biros, D., R. Cuevas, and B. Moehl, 1995, Well Completion Report, Titihaoa-1. PPL38318, Amoco NZ Exploration Co Ltd, Open-File Petroleum Report 2081, Wellington, New Zealand, Ministry of Economic Development New Zealand, 1096pp. Burgreen, B., and S. Graham, 2014, Evolution of a deep-water lobe system in the
177 Neogene trench-slope setting of the East Coast Basin, New Zealand: lobe stratigraphy and architecture in a weakly confined basin configuration: Marine and Petroleum Geology, v. 54, p. 1-22. Burgreen, B., K. E. Meisling, S. A. Graham, in preparation, Basin and petroleum system modeling of the East Coast Basin, New Zealand: A test of overpressure scenarios in a convergent margin. Campbell, K. A., D. A. Francis, M. Collins, M. R. Gregory, C. S. Nelson, J. Greinert, and P. Aharon, 2008, Hydrocarbon seep-carbonates of a Miocene forearc (East Coast Basin), North Island, New Zealand: Sedimentary Geology, v. 204, p. 83- 105. Carr, A. D., 2000, Suppression and retardation of vitrinite reflectance, Part 1. Formation and significance for hydrocarbon generation: Journal of Petroleum Geology, v. 23, p. 313-343. Coleman, D. D., B. J. Risatti, and M. Schoell, 1981, Fractionation of carbon and hydrogen isotopes by methan-oxiding bacteria: Geochimica et Cosmochimica Acta, v. 45, p. 1033-1037. Corrigan, J., 2003, Correcting Bottom Hole Temperature Data, ZetaWare, Utilities - BHT Correction Home Page, ZetaWare Inc. Darby, D., and R. Funnell, 2001, Overpressure associated with a convergent plate margin: East Coast Basin, New Zealand: Petroleum Geoscience, v. 7, p. 291- 299. Dickinson, W. R., 1995, Forearc Basins, in C. Busby, and R. V. Ingersoll, eds., Tectonics of Sedimentary Basins: Oxford, United Kingdom, Blackwell Science, p. 221-261. Donelick, R. A., 2001, Apatite Fission Track Dating, Opoutama-1, Unpublished Petroleum Report, Wellington, New Zealand, Ministry of Economic Development New Zealand, p. 96. Dowdle, W. L., and W. M. Cobb, 1975, Static Formation Temperature From Well Logs - An Empirical Method: Journal of Petroleum Technology, v. 27, p. 1326-1330.
178 Dumitru, T. A., 1988, Subnormal geothermal gradients in the Great Valley Forearc Basin, California, during Franciscan subduction: A fission track study: Tectonics, v. 7, p. 1201-1221. Duran, E. R., R. di Primio, Z. Anka, D. Stoddart, and B. Horsfield, 2013, 3D-basin modelling of the Hammerfest Basin (southwestern Barents Sea): A quantitative assessment of petroleum generation, migration and leakage: Marine and Petroleum Geology, v. 45, p. 281-303. Faure, K., J. Greinert, J. S. von Deimling, D. F. McGinnis, R. Kipfer, and P. Linke, 2010, Methane seepage along the Hikurangi Margin of New Zealand: Geochemical and physical data from the water column, sea surface and atmosphere: Marine Geology, v. 272, p. 170-188. Feyzullayev, A.A. & Lerche, I. (2009) Occurrence and Nature of Overpressure in the Sedimentary Section of the South Caspian Basin, Azerbaijan. Energy, Exploration, and Exploitation, 27, 345-366. Field, B. D., K. H. Higgs, R. Pollock, C. Jones, K. Beuth, and M. Arnot, 2005, Reservoir potential of the East Coast Basin (central and northern subregions), Institute of of Geological & Nuclear Scienes Client Report 2005/119, Wellington, New Zealand, Ministry of Economic Development New Zealand Unpublished Petroleum Report 3180. Field, B. D., C. I. Uruski, and Institute of Geological & Nuclear Sciences Limited., 1997, Cretaceous-Cenozoic geology and petroleum systems of the East Coast region, New Zealand: Lower Hutt, N.Z., Institute of Geological & Nuclear Sciences, 301 p. Francis, D., 2000a, Geology of the Waingaromia-Waitangi area. PEP38330 East Coast Basin, New Zealand, Indo-Pacific Energy (NZ) Ltd., Unpublished petroleum report 3117, Wellington, New Zealand, Mininstry of Economic Development New Zealand, 15 p. Francis, D. A., 2000b, Whangai Shale Distribution Report, Unpublished Petroleum Report PR4310, Wellington, New Zealand, Economic Development New Zealand, 17 p.
179 Fuerst, A. T., 2012, Trace metal variations through the Tartan and Waipawa formations: implications for the environment of deposition, Masters Thesis, Victoria University of Wellington, Wellington, New Zealand, 190 p. Funnell, R., and I. Benchilla, 2005, 1D Basin Models in the East Coast Basin, New Zealand, Open-File Petroleum Report 3183, Wellington, New Zealand, Ministry of Economic Development, 24 p. Greinert, J., K. B. Lewis, J. Bialas, I. A. Pecher, A. Rowden, D. A. Bowden, M. De Batist, and P. Linke, 2010, Methane seepage along the Hikurangi Margin, New Zealand: Overview of studies in 2006 and 2007 and new evidence from visual, bathymetric and hydroacoustic investigations: Marine Geology, v. 272, p. 6-25. Gusterhuber, J., R. Hinsch, and R. F. Sachsenhofer, 2014, Evaluation of hydrocarbon generation and migration in the Molasse fold and thrust belt(Central Eastern Alps, Austria) using structural and thermal basin models: AAPG Bulletin, v. 98, p. 253-277. Hantschel, T., and A. I. Kauerauf, 2009, Fundamentals of Basin and Petroleum System Modeling: New York, Springer. Heasler, H. P., and R. C. Surdam, 1985, Thermal evolution of Coastal California with application to hydrocarbon maturation: AAPG Bulletin, v. 69, p. 1386- 1400. Hollis, C. J., K. Manzano-Kareah, C. Crampton, B. Field, R. Funnell, H. Morgans, and K. Rogers, 2005, Source rock potential of the East Coast Basin (central and northern regions), Institute of Geological and Nuclear Sciences Client Report 2005/118, p. 156 pp. Horner, D. R., 1951, Pressure build-up in wells in Brill, E.J. (ed), Proceedings of the Third World Petroleum Conference, Section II, 30 May – 5 June, 1951: The Hague, Netherlands. Hunt, J. M., 1996, Petroleum Geochemistry and Geology: New York, W. H. Freeman and Company. Ian R. Brown Ltd, 2004, Hukarere-1 geochemistry, and its implications for
180 PEP38325, Westech Energy New Zealand Ltd, Unpublished Petroleum Report 2940, Wellington, New Zealand, Ministry of Commerce. Jackson, R. G., 1982, An assessment of the organic maturity of the well Opoutama- 1, East Coast, North Island, New Zealand, BP Oil Exploration Co. (NZ) Ltd, Unpublished Petroleum Report 903, Wellington, New Zealand, Ministry of Economic Development New Zealand. James, D. E., A. M. DeVaughn, and K. M. Marsaglia, 2007, Sand and gravel provenance in the Waipaoa River system: Sedimentary recycling in an actively deforming forearc basin, North Island, New Zealand, in J. Arribas, S. Critelli, and M. J. Johnsson, eds., Sedimentary Provenance and Petrogenesis: Perspectives from Petrography and Geochemistry, v. Special Paper 420, Geological Society of America, p. 253-276. Jarvie, D. M., B. L. Claxton, F. Henk, and J. T. Breyer, 2001, Oil and shale gas from the Barnett Shale, Fort Worth Basin, Texas: AAPG Annual Meeting, Programs and Abstracts, p. A100. Jessop, A. M., 1990, Developments in Solid Earth Geophysics, Thermal Geophysics, v. 17: Amsterdam, Elsevier. Jones, R. W., and T. A. Edison, 1978, Microscopic observations of kerogen related to geochemical parameters with emphasis on thermal maturation, in D. F. Oltz, ed., Symposium in geochemistry, Low temperature metamorphism of kerogen and clay minerals: Pacific Section, SEPM, p. 1-12. Kamp, P. J. J., 1999, Tracking crustal processes by FT thermochronology in a forearc high (Hikurangi margin, New Zealand) involving Cretaceous subduction termination and mid-Cenozoic subduction initiation: Tectonophysics, v. 307, p. 313-343. Ketcham, R. A., R. A. Donelick, and M. B. Donelick, 2000, AFTSolve: A program for multi-kinetic modeling of apatite fission-track data: Geological Materials Research, v. 2(1), p. 1-32. Kiel, S., D. Birgel, K. A. Campbell, J. S. Crampton, P. Schiøler, and J. Peckmann,
181 2013, Cretaceous methane-seep deposits from New Zealand and their fauna: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 390, p. 17-34. Killops, S., H. Morgans, and D. Leckie, 1996, The Waipawa Black Shale - A ubiquitous super source rock?: 1996 New Zealand Petroleum Conference Proceedings, p. 12-21. Killops, S. D., C. J. Hollis, H. E. G. Morgans, R. Sutherland, B. D. Field, and D. A. Leckie, 2000, Paleoceanographic significance of Late Paleocene dysaerobia at the shelf/slope break around New Zealand: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 156, p. 51-70. Kuhn, P. P., R. di Primio, R. Hill, J. R. Lawrence, and B. Horsfield, 2012, Three- dimensional modeling study of the low-permeability petroleum system of the Bakken Formation: AAPG Bulletin, v. 96, p. 1867-1897. Lachenbruch, A. H., and M. C. Brewer, 1959, Dissipation of the Temperature Effect of Drilling a Well in Arctic Alaska, Bulletin 1083-C, Washington, DC, p. 73- 109. Laird, M. G., and J. D. Bradshaw, 2004, The Break-up of a Long-term Relationship: the Cretaceous Separation of New Zealand from Gondwana: Gondwana Research, v. 7, p. 273-286. Lampe, C., K. Kornpihl, S. Sciamanna, T. Zapata, G. Zamora, and R. Varadé, 2006, Petroleum systems modeling in tectonically complex areas — A 2D migration study from the Neuquen Basin, Argentina: Journal of Geochemical Exploration, v. 89, p. 201-204. Law, C. S., S. D. Nodder, J. J. Mountjoy, A. Marriner, A. Orpin, C. A. Pilditch, P. Franz, and K. Thompson, 2010, Geological, hydrodynamic and biogeochemical variability of a New Zealand deep-water methane cold seep during an integrated three-year time-series study: Marine Geology, v. 272, p. 189-208. Lee, J. M., and J. G. Begg, 2002, Geology of the Wairarapa area: Institute of
182 Geological & Nuclear Sciences 1:250 000 geological map 11: Lower Hutt, New Zealand, Institute of Geological & Nuclear Sciences Limited, 1 sheet + 66 p. p. Legg, M. J., 2010, The tectonic and thermal evolution of Hawke's Bay Basin, New Zealand, Pennsylvania State University, State College, Pennsylvania, 72 p. Lewan, M. D., 1987, Petrographic study of primary petroleum migration in the woodfod shale and related rock units: Migration of Hydrocarbons in Sedimentary Basins, p. 113-130. Lewis, K. B., and J. R. Pettinga, 1993, The emerging, imbricate frontal wedge of the Hikurangi Margin: Sedimentary Basins of the World, v. 2, p. 225-250. Locarnini, R. A., A. V. Mishonov, J. I. Antonov, T. P. Boyer, H. E. Garcia, O. K. Baranova, M. M. Zweng, and D. R. Johnson, 2010, Temperature, in S. Levitus, ed., World Ocean Atlas 2009, v. Volume 1: Washington, D.C., NOAA Atlas NESDIS 68, U.S. Government Printing Office, p. 184. Lowe, S. P., 1979, Maturity and source rock richness of cuttings samples from New Zealand well: Hawke Bay No.1 in Well Completion report Hawke Bay-1, Unpublished Petroleum Report 667, Wellington, New Zealand, Ministry of Economic Development New Zealand, 160-162. Lyon, G. L., W. F. Giggenbach, and D. Francis, 1991, The stable isotope composition of some East Coast natural gases: New Zealand Oil Exploration Conference proceedings, p. 310-319. Mazengarb, C., and I. G. Speden, 2000, Geology of the Raukumara area; scale 1:250,000, New Zealand (NZL), p. 60-60, 1 sheet. Moldowan, M. J., F. J. Fago, C. Y. Lee, S. R. Jacobson, D. S. Watt, N.-E. Sloughui, A. Jeganathan, and D. C. Young, 1990, Sedimentary 24-n-Propylcholestanes, Molecular Fossils Diagnostic of Marine Algae: Science, v. 247, p. 309-312. Moore, P. R., 1980, Late Cretaceous-Tertiary stratigraphy, structure, and tectonic history of the area between Whareama and Ngahape, eastern Wairarapa, New Zealand: New Zealand Journal of Geology and Geophysics, v. 23, p. 167-177. Moore, P. R., 1988, Stratigraphy, composition, and environment of deposition of
183 the Whangai Formation and associated Late Cretaceous-Paleocene rocks, eastern North Island, New Zealand Lower Hutt, New Zealand, New Zealand Geological Survey. Mortimer, N., 2004, New Zealand's Geological Foundations: Gondwana Research, v. 7, p. 261-272. Mortimer, N., and D. Parkinson, 1996, Hikurangi Plateau: A Cretaceous large igneous province in the southwest Pacific Ocean: Journal of Geophysical Research, v. 101, p. 687. Multiwave, 2005, 05CM 2D Seismic Survey, Offshore East Coast - North Island. Open-File Petroleum Report 3136. Crown Minerals and GNS Science, Ministry of Economic Development New Zealand. Wellington, New Zealand. Murray, A. P., R. E. Summons, and C. J. Boreham, 1994, Geochemistry of oils and source rocks of the East Coast Basin and implications for the Taranaki Basin, New Zealand: 1994 New Zealand Petroleum Conference, p. 338-351. Neumaier, M., R. Littke, T. Hantschel, L. Maerten, J. P. Joonnekindt, and P. Kukla, 2014, Integrated charge and seal assessment in the Monagas Fold and Thrust Belt of Venezuela: AAPG Bulletin, v. 98, p. 1325-1350. Newman, J., 1997a, New approaches to detection and correction of suppressed vitrinite reflectance: APPEA Journal, v. 1997, p. 524-535. Newman, J., 1997b, VFT ™: Combined vitrinite and fluorescence: 7th New Zealand Coal Conference Proceedings, p. 490-498. Newman, J., 2013, VIRF analysis of samples from Hawke Bay-1, Christchurch, New Zealand, Newman Energy Research, p. 32. Newman, J., K. M. Eckersley, and N. A. Moore, 2000, Application of vitrinite- inertinite reflectance and fluorescence (VIRF) to maturity assessment in the East Coast and Canterbury Basins of New Zealand: 2000 New Zealand Petroleum Conference, 20 p. Newman, J., and N. Moore, 2000, Vitrinite-inertinite reflectance and fluorescence
184 analysis of samples from Opoutama-1, Westech Energy New Zealand Ltd, Unpublished Petroleum Report 3172, Wellington, New Zealand, Minitry of Economic Development New Zealand, 27 p. Newman, J., and N. Moore, 2002, Vitrinite-inertinite reflectance and fluorescence (VRF ®) analysis of samples from Hukarere-1, Ian Brown Associates Ltd, Unpublished Petroleum Report 2940: Hukarere-1 geochemistry, and its implications for PEP38325 prospectivity, Hawke Bay, New Zealand, Wellington, New Zealand, Ministry of Economic Development, p. 36- 67. Newman Energy Research Ltd, 2005, Vitrinite-inertinite reflectance & fluorescence (VRF®) analysis of samples from Tawatawa-1, Unpublished Petroleum Report 3076, Wellington, New Zealand, Ministry of Economic Development New Zealand, 873 p. NIWA, 2008, New Zealand 250m Bathymetry Grid: National Institute of Water and Atmospheric Research. Peters, K. E., and M. R. Cassa, 1994, Applied Source Rock Geochemistry, in L. B. Magoon, and W. G. Dow, eds., The petroleum system - from source to trip, AAPG Memoir 60, p. 93-117. Peters, K. E., and P. H. Nelson, 2012, Criteria to determine borehole formation temperatures for calibration of basin and petroleum system models, in N. B. Harris, and K. E. Peters, eds., Analyzing the Thermal History of Sedimentary Basins: Methods and Case Studies: Tulsa, Oklahoma, SEPM Special Publication No. 103, p. 5-15. Peters, K. E., C. C. Walters, and J. M. Moldowan, 2005, The Biomarker Guide Volume 1: Biomarkers and Isotopes in the Environment and Human History: New York, Cambridge University Press. Pettinga, J. R., 1982, Upper Cenozoic structural history, coastal Southern Hawke's Bay, New Zealand: New Zealand Journal of Geology and Geophysics, v. 25, p. 149-191. Phillips Petroleum New Zealand Ltd, 1976, Phillip's geochemical reports,
185 Unpublished Petroleum Report 737, Wellington, New Zealand, Ministry of Economic Development, 149 p. Plaza-Faverola, A., D. Klaeschen, P. Barnes, I. Pecher, S. Henrys, and J. Mountjoy, 2012, Evolution of fluid expulsion and concentrated hydrate zones across the southern Hikurangi subduction margin, New Zealand: An analysis from depth migrated seismic data: Geochemistry, Geophysics, Geosystems, v. 13, p. 1-21. Rait, G., F. Chanier, and D. W. Waters, 1991, Landward- and seaward-directed thrusting accompanying the onset of subduction beneath New Zealand: Geology (Boulder), v. 19, p. 230-233. Reyners, M., 2013, The central role of the Hikurangi Plateau in the Cenozoic tectonics of New Zealand and the Southwest Pacific: Earth and Planetary Science Letters, v. 361, p. 460-468. Ridgeway, N. M., 1969, Temperature and salinity of sea water at the ocean floor in the New Zealand region: New Zealand Journal of Marine and Freshwater Research, v. 3, p. 57-72. Rogers, K. M., J. D. Collen, J. H. Johnston, and N. E. Elgar, 1999, A geochemical appraisal of oil seeps from the East Coast Basin, New Zealand: Organic Geochemistry, v. 30, p. 593-605. Rogers, K. M., H. E. G. Morgans, and G. S. Wilson, 2001, Identification of a Waipawa Formation equivalent in the upper Te Uri Member of the Whangai Formation - implications for depositional history and age: New Zealand Journal of Geology and Geophysics, v. 44, p. 347-354. Scadden, P., M. Geddes, and A. Boyes, 2013, Petroleum Basin Explorer (PBE v2.0), Lower Hutt, New Zealand, GNS Science Limited. Schellart, W. P., G. S. Lister, and V. G. Toy, 2006, A Late Cretaceous and Cenozoic reconstruction of the Southwest Pacific region: Tectonics controlled by subduction and slab rollback processes: Earth-Science Reviews, v. 76, p. 191- 233. Schmoker, J.W. (1999) U.S. Geological Survey Assessment Model for Continuous (Unconventional) Oil and Gas Accumulations - the "Forspan" Model. U.S.
186 Geological Survey Bulletin 2168. L. Carter, U.S. Geological Survey. Denver, Colorado, 12. Sloan, E. D., 1990, Clathrate Hydrates of Natural Gas: New York, Marcel Dekker. Stern, T. A., W. R. Stratford, and M. L. Salmon, 2006, Subduction evolution and mantle dynamics at a continental margin; central North Island, New Zealand: Reviews of Geophysics, v. 44, p. RG4002(1-36). Sweeney, J. J., and A. K. Burnham, 1990, Evaluation of a Simple Model of Vitrinite Reflectance Based on Chemical Kinetics: American Association of Petroleum Geologists Bulletin, v. 74, p. 1559-1570. Townend, J., 1997, Estimates of conductive heat flow through bottom-simulating reflectors on the Hikurangi and southwest Fiordland continental margins, New Zealand: Marine Geology, v. 141, p. 209-220. Waples, D., 2001, An overview of source rocks and oils in the East Coast Basin, North Island, New Zealand, and reconstruction of the thermal history at Opoutama-1, Westech Energy New Zealand Ltd, Unpublished Petroleum Report 3173, Wellington, New Zealand, Ministry of Economic Development New Zealand, 64 p. Wilkins, R. W. T., J. R. Wilmhurst, G. Hladky, M. V. Ellacott, and C. Buckingham, 1995, Should fluorescence alteration replace vitrinite reflectance as a major tool for thermal maturity determination in oil exploration?: Organic Geochemistry, v. 22, p. 191-209. Wilkins, R. W. T., J. R. Wilmhurst, N. J. Russell, G. Hladky, M. V. Ellacott, and C. Buckingham, 1992, Fluorscence alteration and the suppression of vitrinite reflectance: Organic Geochemistry, v. 18, p. 629-640. Wygrala, B. P., 1989, Integrated study of an oil field in the southern Po Basin, Northern Italy: PhD thesis, University of Cologne, Germany.
187 Oil Family 1 Oil and gas show Oil Family 2 Oil show
Oil Families 1 & 2 Gas show Taupo Rotokautuku Gas Seep Dry hole Volcanic Motu Waitangi Miocene Paleo-seep Zone Valley RAUKUMARA nt Upper Pakarae e t Cretaceous Paleo-seep x Waingaromia e Rere-1 Borehole in s Totangi a b n r Kauhauroa-5 e t s Opoutama-1 Axial eRanges North Island, w Hawke Bay-1 te BAY a HAWKES Inboard CM05-01 New Zealand m i Hukarere-1 x Lachlan o Hawke r basin p Bay Outboard p A Lachlan footwall Knights Stream
Tunakore Stream Westcott
EAST COAST BASIN Tawatawa-1 Tiraumea Kerosene Rock Titihaoa-1 Okau Stream Hikurangi trench
WAIRARAPA
MARLBOROUGH Isolation Creek
Figure 1. Hydrocarbon summary map of the East Coast Basin, New Zealand. The CM05- 01 seismic line is the location of the two-dimensional BPSM presented in this study. Seep sites are based on locations from Hollis et al. (2005) and references therein. Well locations and well description are from the web-based Petroleum Basin Explorer (Scadden et al., 2013 and references therein). Miocene seep site locations are from Campbell et al. (2008) and Cretaceous seep site locations are from Kiel et al. (2013). Digital elevation map is from NIWA (2008).
188 ECB Hawke Bay Burial History for Waipawa Black Shale Chronostratigraphy Regional NW Modeled Hawke Bay Chronostratigraphy SE Source Seal Reservoir Trap Ma Period Epoch NZ Series NZ Stage Tectonics from CM05-01 2D seismic interpretation Rock Rock Rock Inboard Lachlan Basin Lachlan Footwall Outboard
0 Castlecli an Surface Quaternary Pleistocene Nukumaruan Mangapanian Wanganui Waipipian Horizon Pliocene Opoitian Inversion 8 Kapitean Horizon Taranaki Tongaporutuan 10 11 Waiauan Horizon
Southland Lillburnian Extensional 12 Clifdenian Altonian Horizon Neogene Miocene Pareora 13 20 Otaian Convergent margin Convergent Waitakian Compressional Duntroonian Landon Weber 30 Whaingaroan Formation Oligocene
Runangan Kaiatan Arnold 40 Bortonian
Porangan Wanstead
Eocene Heretaungan Formation
50 Paleogene Mangaorapan
Waipawan Waipawa Dannevirke 60 Teurian Upper Calcareous Member Black Shale (Whangai Formation) Paleocene Whangai Formation 70 (includes Te Uri, Rakuroa,
and Porangahau Members) 0.0 2.0 4.0 6.0 0.0 2.0 4.0 6.0 0.0 2.0 4.0 6.0 0.0 2.0 4.0 6.0 Haumurian Mata margin Dormant convergent Burial Depth Burial Depth Burial Depth Burial Depth (km) (km) (km) (km) 80 STRATIGRAPHIC SECTION LEGEND
Late sandy, silty mudstone BURIAL HISTORY LEGEND Piripauan Glenburn Teratan “40 mWm-2 with cooling at 5 Ma” Formation sandy, silt-rich mudstone 90 Mangaotanean Critical Moment Arowhanan sandy, micritic mudstone “55 mWm-2 with cooling at 15 Ma” Raukumara Cretaceous Critical Moment Ngaterian smectite-rich mudstone 100 Motuan meta-sedimentary basement
Clarence Urutawan Torlesse black shale Early margin Supergroup 110 Taitai Korangan Convergent Convergent siliceous shale Figure 2. Tectonostratigraphy and chart of petroleum system elements (source rock, reservoir rock, and seal rock) and processes (trap formation) of the CM05-01 2D seismic line in Hawke Bay. Timing of reservoir rock and seal rock deposition is schematic. Burial histo-
189 ries are from time extractions of the Waipawa Black Shale from the 2D model (see Figure 3 for locations of burial extractions). Stars represent critical moments from the basin and petroleum system models. Inboard 1D Lachlan Basin Lachlan Footwall Outboard Hawke Bay-1 Extract 1D Extract 1D Extract 1D Extract 0 10 20 30 40 50(km) 60 70 80 90 100 110 0 LR Surface Horizon 8 Horizon 11 2.5 Horizon 12 Horizon 13 OUTBOARD LACHLAN BASIN 5 INBOARD Glenburn Formation 7.5
10 LACHLAN
Depth (km) Torlesse FOOTWALL Supergroup 12.5 Upper Oceanic Crust 15 Lower Oceanic Crust Weber Formation Wanstead Formation 17.5 Waipawa Black Shale Location of 1D extractions from the Waipawa Black Shale Upper Calcareous Member Whangai Formation for burial histories in Figure 2
Figure 3. Stratigraphy of the present day 2D basin and petroleum system model for seismic line CM05-01 in Hawke Bay. The transect is sub-divided by a red dashed line into four structural sections: Inboard, Lachlan Basin, Lachlan Footwall, and Outboard. LR = Lachlan ridge. 190 A 800 B Upper Calcareous Member Porangahau and Type I Rakauroa Member 600 Type II
400
200 Angora
Hydrogen Index (mg HC/g TOC) Index (mg HC/g Hydrogen Type III Stream 0 0 100 200 300
Oxygen Index (mg CO2/g TOC) 26 Upper Calcareous Member C 24 Upper Calcareous Member D 500 Porangahau and Porangahau and Rakauroa Member 22 Rakauroa Member 20 400 18 16 300 14 12
(mg/g rock) 10 =3.05* TOC+(-)0.55
200 2 S 2 S 8 p-vale = <0.0001 6 HI = 305; Avg.S2 =0.58*TOC = 0.76 TOC+0.006 100 4 p-vale = < 0.0001 2 HI = 58; Avg. TOC = 0.1 Hydrogen Index (mg HC/g TOC) Index (mg HC/g Hydrogen Immature Mature Postmature 0 0 0 1.0 2.0 3.0 4.0 5.0 6.0 400 410 420 430 440 450 460 470 Tmax (°C) TOC (wt. %)
Figure 4. Source rock properties of the Whangai Formation including A) location map of samples, B) hydrogen index versus oxygen index plot, C) hydrogen index versus Tmax plot, and D) S2 versus TOC plot. HI and TOC are calculated for the Upper Calcareous, and the Porangahau and Rakauroa Members from the slope of the best fit line of S2 versus TOC from Angora Stream samples. RockEval sample data is from Hollis et al. (2005).
191 hydrogen index versus oxygen index plot, C) hydrogen index versus T index B) hydrogen C) plot, index oxygen versus index hydrogen samples, of map location A) including WBS the of properties rock Source 5. Figure leum systemmodeling.RockEvalsample data isfrom Hollisetal.(2005). petro- and basin for averaged were location each from values TOCand HI The locations. TOC for samples from the Angora Stream, Te Weraroa Stream, and Waitahaia River Gorge versus TOC plot. HI and TOC are calculated from the slope of the best fit line of S
100 Hydrogen200 Index (mg300 HC/g400 TOC) 500 A
400
410 maueMature Immature
420 Te Weraroa Stream T max 430 (°C)
440 Angora Stream
450
460 Gorge River Waitahaia
470 Postmature C
Hydrogen Index (mg HC/g TOC) Type I 100 200 300 400 500
S210 (mg/g12 14 rock)16 18 20 22 24 26 0 2 4 6 8 0 0 inertinite?
0 Sample Section Te Weraroa Stream Angora Stream Waitahaia RiverGorge due to O set O set Type II Avg. TOC =3.5 HI =456 =0.002 p-vale S2=4.56*TOC+0.95 50 1.0 Oxygen Index (mgCOOxygen Index 100 2.0 Avg. TOC =4.1 HI =396 =0.0005 p-vale S2=3.96 * TOC+(-)3.65 TOC (wt. %)
150
max 3.0 Type III Avg. TOC =3.4 HI =403 =0.008 p-vale S2=4.03 * TOC+(-)3.97
plot, and D) S D) and plot, 200 2 4.0 /g TOC) 250 2 versus 5.0 D 192 300 B 2
6.0 0 Hawke Bay-1 Opoutama-1 Overestimation - readings from inertinite?
400
800
1200 analyst selection bias? Overestimation -
1600
2000
2400 Depth (m below kelly bushing)
2800
3200
3600 Underestimation - suppressed vitrinite? 0.15 0.2 0.3 0.4 0.6 0.8 1.2 0.15 0.2 0.3 0.4 0.6 0.8 1.2 Ro (%) Ro (%) Hawke Bay-1 Legend: Opoutama-1 Legend: VR from Lowe (1979) VR from Jackson (1982) VR from Phillips Petroleum NZ Ltd (1976) VR from Phillips Petroleum NZ Ltd (1976) VIRF from Newman (2013) VIRF from Newman and Moore (2000) Figure 6. Comparison of VR and VIRF data for the Hawke Bay-1 and Opoutama-1 wells. VR and VIRF data from Phillips Petroleum New Zealand Ltd (1976), Lowe (1979), Jack- son (1982), Newman and Moore (2000), and Newman (2013).
193 al. (1995). Well locationsareshown onFigure 1.See Appendix 6for VIRF data. et Biros and (2005), Ltd Research Energy Newman (2013), al. et Scadden (2000), Moore and Newman (2004), Ltd Associates Brown R Ian (2002), Moore and Newman (2013), Newman from is data Calibration scenarios. flow heat Track”Fission “Apatite and Ma”, 15 at “Cooling Ma”, 5 at “Cooling the using models from kinetics (1990) Burnham and histories and boundary conditions). Each depth plot shows predicted VR based on Sweeny burial for 7 (see Appendix wells ECB for data reflectance vitrinite to scenarios flow heat three of calibration 1D for profiles depth versus VR Modeled page). (following 8 Figure Newman andMoore(2002),Energy ResearchLtd(2005),andNewman(2013). (2000), Moore and Newman from is Data uplift. to due well each for estimated burial is Maximum depth lines. dashed the by represented are regimes thermal distinct two The time. Pliocene to Miocene late from regime thermal lower a by followed time, Miocene maximum by wells late to mid to Cretaceous four Late from existed regime depth. early,thermal burial An higher for fluorescence and reflectance Vitrinite-inertinite 7. Figure Maximum burial depth (km) 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
0.225
0.25
0.275 0.3
0.33
0.36 W e Tawatawa-1 Opoutama-1 Hukarere-1 Hawke Bay-1 l 0.4 l
0.45 Ro% (normal)
0.5
0.55 Age ofDeposition Haumurian (LateCretaceous) Paleogene -midMiocene Miocene-Pliocene late 0.6 (Late Cretaceous) Arowhanan -Teratan 0.65 0.7
0.8
0.9
1.0
1.1 1.2 194 1.35 Hawke Bay-1 Hukarere-1 Opoutama-1 Rere-1 Tawatawa-1 Titihaoa-1
-400
0 early Miocene mid Miocene
400 Quaternary Quaternary Quaternary early 800 Miocene Oligocene Pliocene Pliocene Oligo- cene Pliocene
1200 Miocene late Eocene Eocene 1600 cene late Miocene late Paleo- cene Paleo- late Miocene late Miocene 2000 Oligo- cene
2400 Eocene Oligocene Depth below sea level (m) Late Cretaceous Late
2800 Paleo- cene mid Miocene Late Cretaceous Late
3200 Calibration Data Late Normal vitrinite Cretaceous TAI 3600 Tmax Modeled Vitrinite Reflectance
40 mWm-2 with cooling at 5 Ma Early Cretaceous 4000 55 mWm-2 with cooling at 15 Ma Apatite Fission Track 0.2 0.5 1 2 0.2 0.5 1 2 0.2 0.5 1 2 0.2 0.5 1 2 0.2 0.5 1 2 0.2 0.5 1 2 195 Vitrinite Reflectance Vitrinite Reflectance Vitrinite Reflectance Vitrinite Reflectance Vitrinite Reflectance Vitrinite Reflectance Figure 8 Dormant convergent margin (tectonic quiescence) Convergent margin 80 Heat Flow Scenario 40 mWm-2 with cooling at 5 Ma 70 55 mWm-2 with cooling at 15 Ma Apatite Fission Track
) Average global heat ow 2 60
50
40 Typical Heat Flow (mW/m convergent 30 margin heat ow 20 05101520253035404550556065707580859095100105 Time (Ma) Figure 9. The three profiles of basal heat flow through time modeled in this study. Global average heat flow (60 to 70 mWm-2) is compared to the period of tectonic quiescence in the ECB, and typical convergent margin basin heat flow is compared for the active margin phase beginning in Neogene time (average heat flows from Allen and Allen, 2005).
196 0 20 500 40 Thermal Cooling 1000 60 1500
2000 80 AFT Samples Temperature History 2500 100 2144 m depth Partial Annealing 2338 m depth Zone 3000 3049 m depth 120
3133 m depth 3500 Burial depth (m)
Temperature (°C) 3197 m depth 140 3271 m depth 4000 3379 m depth 4500 160 3528 m depth Rapid mid to 3656 m depth late Miocene 5000 180 Burial History Thermal Heating TD burial history Event burial 5500 05101520253035404550556065707580859095100105 Time (Ma) Figure 10. Modeled temperature histories based on AFT analysis for eight Upper Creta- ceous samples in the Opoutama-1 well based on Donelick (2001). The six deepest samples fully annealed during Paleocene time and remained in the partial annealing zone until early Miocene time. The shallowest two samples experienced partial annealing of apatite during Paleocene time. The partial annealing zone (in gray) is based on apatite fission modeling by Legg (2010) in the Opoutama-1 well.
197 100 80 Waipawa Black Shale 60 Heat Flow Scenario -2 40 40 mWm with cooling at 5 Ma TR (%) 55 mWm-2 with Inboard cooling at 15 Ma 20 Apatite Fission Track 0 100 80 60 40 TR (%) 20
Lachlan basin 0 100 80 60 40 TR (%) 20
Lachlan footwall 0 100 80 60 40 TR (%)
Outboard 20 0 024681012141618202224262830323436 Time (Ma) 100 80 Upper Calcareous Member 60 of the Whangai Formation 40 TR (%) Inboard 20 0 100 80 60 40 TR (%) 20
Lachlan basin 0 100 80 60 40 TR (%) 20
Lachlan footwall 0 100 80 60 40 TR (%)
Outboard 20 0 024681012141618202224262830323436 Time (Ma) Figure 11. Transformation ratios through time for each structural section (extract locations in Fig. 3) for the WBS and Upper Calcareous Member of the Whangai Formation source rocks for three heat flow scenarios. TR = transformation ratio.
198 Waipawa Black Shale 0.0 150 Heat Flow Scenario 40 mWm-2 with cooling at 5 Ma 2.0 55 mWm-2 with cooling at 15 Ma 100 Apatite Fission Track
Inboard Burial Depth 4.0 50 Temperature (°C) 6.0 0.0 150 2.0 100 4.0
Lachlan basin 50 Temperature (°C) 6.0 0.0 150 2.0 100 4.0 50 Burial Depth (km) Burial Depth (km) Burial Depth (km) Temperature (°C) Lachlan footwall 6.0 0.0 150 2.0 100
Outboard 4.0 50 Burial Depth (km) Temperature (°C) 6.0 04812162024283236404448525660 Time (Ma) Figure 12. Temperature and burial history through time for the WBS for three heat flow scenarios for each structural section (see Fig. 3 for locations of extracts).
199 Table 1. Ages of horizons and paleosections used in two-dimensional basin and petroleum system modeling. 200 Appendix 1. Summary of biostratigraphic data for the Raukumara Region conducted by Martin Crundwell for this study. 201 Appendix 2. Biostratigraphic reports by Martin Crundwell for collected samples from 2010 and 2011 field seasons
Biostratigraphy of samples collected by Blair Nicole Burgreen (Stanford University) from NZMS Y16 and Y17.
Martin Crundwell Paleontology and Environmental Change Section GNS Science PO Box 30368 Lower Hutt 5040 New Zealand
E-mail: [email protected]
05 May 2010
______Sample MRAR-1 NZ-FRF No. Z16/f76 GNS Lab No. F39010
Comment on fauna: Abundant moderately well preserved fauna. Misc: rare echinoid spines, bivalve shell fragments and microgastropods.
Age: Upper Tongaporutuan. Environment: 52% Planktics (Extra-neritic). Lower bathyal (1000-1500 m water depth).
Agglutinated sp. Ammodiscus sp. Karreriella cylindrica Haeuslerella morgani Vulvulina pennatula Sigmoilopsis schlumbergeri Lenticulina spp. Lenticulina calcar Nodosaria longiscata Nodosaria sp. Chrysalogonium verticale Vaginulina sp. Plectofrondicularia pohana Amphicoryna sp. Fissurina sp. Bulimina pyrula spinescens Bulimina striata Bolivina albatrossi Siphouvigerina canariensis Euuvigerina miozea Bolivinita pohana (compressed)
202 Bolivinita cf. elegantissima Cibicides deliquatus Cibicides molestus Cibicides robertsonianus Notorotalia taranakia Gyroidina sp. Anomalinoides sp. Anomalinoides parvumbilius Astrononion parki Sphaeroidina bulloides Pullenia cf. bulloides Oridorsalis tenera Hoeglundina elegans Osangularia culter Globoconella miotumida (43S:3D) Hirsutella cf. scitula (1S:0D) Neogloboquadrina pachyderma Globigerina bulloides Globigerina sp. Globigerinoides obliquus Zeaglobigerina nepenthes Zeaglobigerina druryi Zeaglobigerina woodi Zeaglobigerina sp. Globgerinita glutinata Orbulina universa
______Sample MRMP-2 NZ-FRF No. Z16/f77 GNS Lab No. F39011
Comment on fauna: Abundant well preserved fauna. Common pyrite. Misc: rare fish teeth, echinoid spines, ostracods and otoliths.
Age: Lower Tongaporutuan. Environment: 92% Planktics (Oceanic). Middle bathyal (600-800 m water depth).
Agglutinated spp. Ammodiscus sp. Karreriella cylindrica Martinottiella sp. Eggerella bradyi Sigmoilopsis schlumbergeri Quinqueloculina spp. Nodosaria longiscata Nodosaria sp. Dentalina spp. Mucronina sp. Pandaglandulina sp.
203 Stilostomella sp. Fissurina spp. Lagena cf. distoma Lagena sp. Globobulimina pacifica Bulimina pyrula spinescens Bulimina striata Trifarina sp. Siphouvigerina canariensis Euuvigerina sp. Bolivinita pohana (compressed) Cibicides ihungia Cibicides deliquatus Planulina cf. wuellerstorfi Planulinoides hamasuturalis Cancris sp.? Notorotalia cf. hurupiensis Gyroidina sp. Melonis cf. doreeni Sphaeroidina bulloides Pullenia bulloides Pullenia spp. Pleurostomella alternans Oridorsalis tenera Hoeglundina elegans Osangularia culter Globoconella miotumida (108S:6D) Menardella limbata (11S:0D) Globoquadrina dehiscens Neogloboquadrina pachyderma Globigerina bulloides Globigerina sp. Globigerinopsis obesa Zeaglobigerina nepenthes Zeaglobigerina druryi Zeaglobigerina woodi Zeaglobigerina sp. Globgerinita glutinata Orbulina universa
______Sample MRMP-296 NZ-FRF No. Z16/f78 GNS Lab No. F39012
Comment on fauna: Slightly weathered. Misc: abundant bivalve shell fragments, rare echinoid plate fragments, scaphopod shell fragments, otoliths, and bryozoan fragments.
Age: Lower Tongaporutuan to upper Lillburnian. Probably upper Waiauan.
204 Environment: 43% Planktics (Extra-neritic). Bathyal, probably lower bathyal (1000- 1500 m water depth). Abundant downslope reworking of shelfal material?
Haeuslerella sp. Karreriella cylindrica Eggerella bradyi Sigmoilopsis schlumbergeri Quinqueloculina spp. Lenticulina spp. Lenticulina calcar Nodosaria sp. Chrysalogonium verticale Stilostomella sp. Dentalina spp. Pseuodonodosaria symmetrica Plectofrondicularia pohana Fissurina sp. Globobulimina pacifica Bulimina sp. Bulimina striata Bolivina watti Siphouvigerina notohispida Siphouvigerina canariensis Euuvigerina cf. rodleyi Cibicides notocenicus Cibicides sp. Zeaflorilus parri Nonionella flemingi Elphidium charolottensis Elphidium sp. Notorotalia cf. hurupiensis Notorotalia sp. Gyroidina sp. Gyroidinoides zealandicus Melonis barleenum Anomalinoides subnonionoides Anomalinoides cf. parvumbilius Astrononion parki Pullenia bulloides Chilostomella ovoidea Hoeglundina elegans Globoconella miotumida Paragloborotalia mayeri s.l. (2% abundance) Globoquadrina dehiscens Globigerina sp. Sphaeroidinellopsis disjuncta Zeaglobigerina woodi Zeaglobigerina sp. Globigerinita glutinata Orbulina universa
205 Orbulina sp. (juvenile)
______Sample MRMP-297 NZ-FRF No. Z16/f79 GNS Lab No. F39013
Comment on fauna: Poor fauna. Weathered. Common rounded and polished shell fragments suggest a high-energy environment. Fauna consists largely of planktics, but overall specimen numbers are low.
Age: Poorly constrained. Tongaporutuan to upper Waiauan. Environment: Bathyal fauna, possibly reworked?
Dentalina sp.? Chrysalogonium verticale? Cibicides spp. Astrononion parki Globoconella miotumida (8S:0D) Zeaglobigerina nepenthes? Zeaglobigerina woodi Globigerina sp. Orbulina sp. (juvenile)
______Sample MRMP-5-M NZ-FR No. Z16/f80 GNS Lab No. F39014
Comment on fauna: Common, well preserved fauna. Planktics largely crust-free. Misc: rare echinoid spines.
Age: Lower Tongaporutuan. Environment: 78% Planktics (Sub-oceanic). Uppermost bathyal (200-400 m water depth). Minor reworking of deeper water taxa?
Eggerella bradyi (rare) Quinqueloculina spp. Pyrgo sp. Lenticulina spp. Nodosaria sp. Dentalina spp. Bulimina striata Siphouvigerina canariensis (rare) Euuvigerina miozea (rare) Bolivinita pohana Cibicides deliquatus Cibicides robertsonianus (rare) Notorotalia hurupiensis Gyroidina sp.
206 Astrononion parki Pullenia bulloides Alabamina sp. Globoconella miotumida (90S:3D) Menardella limbata? (1S:0D) Hirsutella cf. scitula Globoquadrina dehiscens Globigerina sp. Zeaglobigerina nepenthes Zeaglobigerina druryi Zeaglobigerina woodi Zeaglobigerina sp. Globgerinita glutinata Orbulina universa Orbulina sp. (juvenile)
______Sample WBTB-1 NZ-FRF No. Z16/f81 GNS Lab No. F39015
Comment on fauna: Abundant well preserved subtropical fauna. Misc: rare echinoid spines.
Age: Tongaporutuan, probably lower Tongaporutuan. Environment: 78% Planktics (Sub-oceanic). Lower bathyal (1000-1500 m water depth).
Agglutinated spp. Bathysiphon spp. Cyclammina sp. Karreriella cylindrica Haeuslerella morgani Eggerella bradyi Sigmoilopsis schlumbergeri Spiroloculina spp. Quinqueloculina sp. Lenticulina sp. Nodosaria longiscata Nodosaria sp. Stilostomella sp. Dentalina spp. Vaginulina sp. Pseudonodosaria symmetrica Amphicoryna sp. Fissurina spp. Proxifrons advena Bulimina striata Bulimina senta Hopkinsina mioindex
207 Siphouvigerina canariensis Euuvigerina spp. Bolivinita pohana Cibicides cf. deliquatus Cibicides novozelandicus Cibicides robertsonianus Melonis barleenum Pullenia sp. Pleurostomella alternans Oridorsalis tenera Osangularia culter Globoconella miotumida (57S:1D) Hirsutella scitula Globoquadrina dehiscens? Neogloboquadrina pachyderma Globigerina falconensis Globigerina sp. Turborotalita angustiumbilicata Sphaeroidinellopsis disjuncta Sphaeroidinellopsis seminulina? Globigerinoides quadrilobatus Zeaglobigerina nepenthes Zeaglobigerina druryi Zeaglobigerina woodi Zeaglobigerina sp. Orbulina universa Orbulina sp. (juvenile)
______Sample WBTB-4 NZ-FRF No. Z16/f82 GNS Lab No. F39016
Comment on fauna: Abundant, moderately well preserved fauna. Misc: rare echinoid spines and fish teeth.
Age: Upper Tongaporutuan. Environment: 88% Planktics (Sub-oceanic). Deep middle bathyal (800-1000 m water depth).
Agglutinated sp. Cyclammina spp. Martinottiella sp. Karreriella sp. Haeuslerella morgani Vulvulina pennatula Eggerella bradyi Sigmoilopsis schlumbergeri Pyrgo murrhina
208 Lenticulina calcar Lenticulina sp. Nodosaria longiscata Nodosaria sp. Dentalina spp. Stilostomella sp. Pseudonodosaria symmetrica Orthomorphina sp. Lagena spp. Fissurina spp. Bulimina pyrula spinescens Globobulimina pacifica Bulimina striata Bolivina sp. Bolivina affiliata Siphouvigerina canariensis Euuvigerina sp. Bolivinita pohana Cibicides finlayi Cibicides cf. deliquatus Cibicides molestus? Cibicides sp. Notorotalia taranakia Gyroidinoides neosoldanii Melonis barleenum Anomalinoides parvumbilius Sphaeroidina bulloides Pleurostomella alternans Oridorsalis tenera Osangularia culter Globoconella miotumida (78S:1D) Menardella limbata (1S:0D) Hirsutella cf. scitula (1S:0D) Neogloboquadrina pachyderma Globigerina sp. Sphaeroidinellopsis disjuncta Globigerinoides quadrilobatus Zeaglobigerina woodi Zeaglobigerina sp. Orbulina universa
______Sample MRCC-3 NZ-FRF No. Z17/f131 GNS Lab No. F39017
Comment on fauna: Abundant, moderately well preserved fauna. Misc: rare echinoid spines and fish teeth.
Age: Upper Tongaporutuan.
209 Environment: 93% Planktics (Oceanic). Lower bathyal (1000-1500 m).
Agglutinated spp. Bathysiphon sp. Cyclammina sp. Siphotextularia cf. wairoana Eggerella bradyi Sigmoilopsis schlumbergeri Pyrgo murrhina Lenticulina sp. Nodosaria longiscata Nodosaria sp. Dentalina spp. Pandaglandulina sp. Amphicoryna sp. Bulimina striata Bulimina cf. truncanella Bolivina sp. Trifarina sp. Siphouvigerina sp. Siphouvigerina notohispida Bolivinita cf. elegantissima Bolivinita cf. pohana Bolivinita compressa? Cibicides spp. Notorotalia hurupiensis Gyroidinoides cf. zealandicus Melonis cf. doreeni Astrononion parki Evolvocassidulina orientalis Cassidulina neocarinata Globoconella miotumida (123S:5D) Menardella limbata? (1S:0D) Neogloboquadrina pachyderma Globigerina bulloides Globigerina sp. Globigerinopsis obesa Zeaglobigerina nepenthes Zeaglobigerina sp. Orbulina universa Orbulina sp. (juvenile) Hirsutella cf. scitula (0S:2D)
______Sample MRMS-2 NZ-FRF No. Z17/f132 GNS Lab No. F39018
Comment on fauna: Common, moderately preserved fauna. Silty sediment, some dissolution related to grain contacts. Misc: rare echinoid spines.
210
Age: Upper Tongaporutuan? Environment: 81% Planktics (Sub-oceanic). Middle bathyal (600-800 m water depth).
Agglutinated spp. Bathysiphon sp. Ammodiscus sp. Karreriella cylindrica? Eggerella bradyi? Sigmoilopsis schlumbergeri Lenticulina spp. Dentalina sp. Stilostomella sp. Fissurina sp. Bulimina sp. Bulimina striata Siphouvigerina sp. Cibicides sp. Nonionella sp. Notorotalia sp. Gyroidina sp. Melonis barleenum Pullenia bulloides Pleurostomella sp. Globoconella miotumida (95S:5D) Neogloboquadrina pachyderma Paragloborotalia mayeri s.l.? Globigerina sp. Globgerinita glutinata Zeaglobigerina nepenthes Zeaglobigerina sp. Orbulina universa Orbulina sp. (juvenile)
______Sample MRMS-280 NZ-FRF No. Z17/f133 GNS Lab No. F39019
Comment on fauna: Abundant, well preserved fauna. Misc: rare echinoid spines.
Age: Upper Tongaporutuan. Environment: 93% Planktics (Oceanic). Lower bathyal (1000-1500 m water depth).
Agglutinated spp. Bathysiphon spp. Cyclammina sp. Eggerella bradyi Sigmoilopsis schlumbergeri Quinqueloculina sp.
211 Vaginulinopsis sp. Lenticulina calcar Lenticulina sp. Nodosaria longiscata Nodosaria sp. Dentalina spp. Stilostomella sp. Orthomorphina sp. Proxifrons advena Fissurina spp. Bulimina striata Bulimina truncanella Bolivinita pohana Cibicides robertsonianus Gyroidinoides neosoldanii Gyroidina sp. Melonis doreeni Melonis barleenum Sphaeroidina bulloides Pullenia bulloides Pleurostomella sp. Pleurostomella alternans Globoconella miotumida (109S:5D) Hirsutella scitula Neogloboquadrina pachyderma Globigerina bulloides Globigerina sp. Globigerinopsis obesa Globgerinita glutinata Zeaglobigerina nepenthes Zeaglobigerina woodi Zeaglobigerina sp. Orbulina universa Orbulina sp.
______Sample MRWB-289 NZ-FRF No. Z17/f134 GNS Lab No. F39020
Comment on fauna: Abundant, moderately well preserved fauna. Misc: rare echinoid spines and fish teeth.
Age: Upper Tongaporutuan. Environment: 89% Planktics (Sub-oceanic). Middle bathyal (600-800 m water depth).
Karreriella cylindrica Martinottiella sp. Siphotextularia sp. Eggerella bradyi
212 Sigmoilopsis schlumbergeri Spiroloculina sp. Pyrgo sp. Quinqueloculina sp. Lenticulina spp. Nodosaria longiscata Chrysalogonium verticale Dentalina sp. Bulimina striata Bulimina cf. truncanella Siphouvigerina canariensis Cibicides neoperforatus Cibicides sp. Planulina renzi Discorbis sp. (modern specimen) Gyroidina sp. Melonis barleenum Globocassidulina subglobosa Oridorsalis tenera Globoconella miotumida (93S:2D) Hirsutella scitula Globigerina bulloides Globigerina sp. Globgerinita glutinata Zeaglobigerina nepenthes Zeaglobigerina woodi Zeaglobigerina sp. Globigerinoides cf. trilobus Orbulina universa Orbulina sp. (juvenile)
______Sample MRWB-292 NZ-FRF No. Z17/f135 GNS Lab No. F39021
Comment on fauna: Abundant, well preserved fauna. Misc: rare echinoid spines and ostracods.
Age: Upper Tongaporutuan. Environment: 90% Planktics (Oceanic). Lower bathyal (1000-1500 m water depth).
Agglutinated spp. Bathysiphon sp. Cyclammina sp. Haeuslerella morgani Karreriella cylindrica Martinottiella sp. Eggerella bradyi Sigmoilopsis schlumbergeri
213 Quinqueloculina spp. Marginulina sp. Lenticulina sp. Nodosaria sp. Dentalina spp. Chrysalogonium verticale Stilostomella sp. Fissurina sp. Lagena sp. Oolina sp. Bulimina cf. aculeata (no spines) Bulimina striata Siphouvigerina notohispida Siphouvigerina canariensis Bolivinita pohana (compressed) Bolivinita cf. eleganitissima Cibicides deliquatus Cibicides neoperforatus Cibicides cf. robertsonianus Gyroidinoides neosoldanii Gyroidina sp. Melonis barleeenum Astrononion parki Pullenia bulloides Sphaeroidina bulloides Globocassidulina subglobosa Chilostomella ovoidea Oridorsalis umbonatus Osangularia culter Osangularia bengalensis Hoeglundina elegans Globoconella miotumida (100S:4D) Hirsutella scitula (0S:8D) Neogloboquadrina pachyderma Neogloboquadrina dutertrei Globigerinoides trilobus Zeaglobigerina nepenthes Zeaglobigerina druryi Zeaglobigerina woodi Globigerina bulloides Globigerina falconensis Globigerina sp. Globgerinita glutinata Turborotalita angustiumbilicata Orbulina universa Orbulina bilobata
______Sample MRWB-3 NZ-FRF No. Z17/f136
214 GNS Lab No. F39022
Comment on fauna: Abundant, well preserved fauna. Slightly weathered. Misc: rare bivalve fragments, echinoid spines and fish teeth.
Age: Upper Tongaporutuan. Environment: 89% Planktics (Sub-oceanic). Lower bathyal (1000-1500 m).
Agglutinated spp. Bathysiphon spp. Cyclammina sp. Haeuslerella morgani Haeuslerella sp. Martinottiella sp. Vulvulina sp. Textularia sp. Eggerella bradyi Sigmoilopsis schlumbergeri Spiroloculina sp. Lenticulina spp. Nodosaria longiscata Nodosaria sp. Dentalina spp. Chrysalogonium verticale Mucronina sp. Amphicoryna sp. Bulimina striata Siphouvigerina canariensis Bolivinita pohana (compressed) Bolivinita cf. elegantissima Cibicides cf. deliquatus Cibicides neoperforatus Cibicides robertsonianus Gyroidina sp. Melonis bareleenum Astrononion parki Sphaeroidina bulloides Pleurostomella alternans Hoeglundina elegans Osangularia culter Globoconella miotumida (87S:5D) Menardella limbata? (1S:0D) Neogloboquadrina pachyderma Globigerina sp. Globigerinopsis obesa Turborotalita angustiumbilicata Sphaeroidinellopsis disjuncta Sphaeroidinellopsis seminulina Zeaglobigerina nepenthes Zeaglobigerina druryi
215 Zeaglobigerina sp. Orbulina bilobata Orbulina universa Orbulina sp. (juvenile)
216 Biostratigraphy of samples collected by Blair Nicole Burgreen from NZMS: X18, Y18 and Z17.
Martin Crundwell Paleontology Department GNS Science PO Box 30368 Lower Hutt 5040 New Zealand
E-mail: [email protected]
21 September 2011
GBSB-353 Y18/f671 F39760 • Unwashed weight: 127.77 g • Washed weight: 0.12 g
• Age: More work is needed – possibly uppermost Pl? • Comment on age: The absence of Orbulina and Praeorbulina suggests • Water depth: Middle bathyal (600-800 m) • Oceanicity: 82% planktics (Suboceanic) • Water mass: Subtropical
Key age and environmentally significant taxa
Paragloborotalia cf. partimlabiata (22S:9D) 29% Dextral, aff. Gc. miozea Globoconella miotumida (3S:0D) Hirsutella cf. panda sinistral specimen Neogloboquadrina cf. nana Globoquadrina dehiscens Sigmoilopsis schlumbergeri Planulina renzi
______
GBSB-354 Y18/f672 F39761 • Unwashed weight: 71.15 g • Washed weight: 0.06 g
• Age: More work is needed – possibly uppermost Pl? • Water depth: not determined • Oceanicity: 89% Planktics (Suboceanic)
Key age and environmentally significant taxa
Paragloborotalia cf. partimlabiata (1S:0D) aff. Globoconella miozea
______
217 MRWB-355-1 Z17/f137 F39762 • Unwashed weight: 59.63 g • Washed weight: 1.12 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 91% planktics (Oceanic) • Water mass: Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (98S:1D) Hirsutella scitula Neogloboquadrina pachyderma Neogloboquadrina incompta Zeaglobigerina nepenthes Sphaeroidinellopsis cf. seminulina Globigerinoides obliquus Bolivinita pohana Siphouvigerina notohispida
______
MRWB-356-4 Z17/f138 F39763 • Unwashed weight: 91.04 g • Washed weight: 1.20 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 79% planktics (Suboceanic) • Water mass: Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (60S:1D) Menardella cf. limbata (0S:1D) Neogloboquadrina pachyderma (9% relative abundance) Zeaglobigerina nepenthes Sphaeroidinellopsis seminulina Bolivinita pohana Bolivinita cf. elegantissima Siphouvigerina notohispida Cibicides robertsonianus
______
MRWB-357-5 Z17/f139 F39764 • Unwashed weight: 142.30 g • Washed weight: 1.10 g • Comment on sample: iron-staining, slightly weathered
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens
218 • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 86% planktics (Suboceanic) • Water mass: Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (42S:1D) Hirsutella cf. ichinosekiensis (0S:1D) Menardella cf. limbata Neogloboquadrina pachyderma (6% relative abundance) Zeaglobigerina nepenthes Sphaeroidinellopsis seminulina Bolivinita pohana Bolivinita cf. elegantissima Hopkinsina mioindex Cibicides robertsonianus
______
MRWB-358-6 Z17/f140 F39765 • Unwashed weight: 151.59 g • Washed weight: 0.96 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 62% planktics (Suboceanic) • Water mass: Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (12S:0D) Menardella cf. limbata (0S:15D) Neogloboquadrina pachyderma (9% relative abundance) Neogloboquadrina dutertrei Zeaglobigerina nepenthes Bolivinita pohana (compressed) Bolivinita cf. elegantissima Siphouvigerina notohispida Cibicides robertsonianus
______
MRWB-360-7 Z17/f141 F39766 • Unwashed weight: 57.12 g • Washed weight: 0.13 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 54% planktics (Extra-neritic) • Water mass: Subtropical
Key age and environmentally significant taxa
219 Globoconella miotumida (23S:4D) 15% Dextral Neogloboquadrina pachyderma (5% relative abundance) Zeaglobigerina nepenthes Sphaeroidinellopsis seminulina Bolivinita pohana Siphouvigerina notohispida Cibicides robertsonianus
______
MRWB-361-12 Z17/f142 F39767 • Unwashed weight: 197.61 g • Washed weight: 49.02 g
• Age: lower Tk • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: outermost shelf (150-200 m) • Oceanicity: 46% planktics (Extra-neritic) • Water mass: Subantarctic/temperate
Key age and environmentally significant taxa
Globoconella conomiozea s.s. (27S:2D) 7% Dextral Neogloboquadrina pachyderma (23% relative abundance) Cibicides molestus Rectobolivina striatula
______
MRWB-362-10 Z17/f143 F39769 • Unwashed weight: 75.27 g • Washed weight: 14.55 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: middle bathyal (600-1000 m) • Oceanicity: 32% planktics (Extra-neritic) • Water mass: Temperate
Key age and environmentally significant taxa
Globoconella miotumida (7S:1D) 13% Dextral Neogloboquadrina pachyderma (17% relative abundance) Zeaglobigerina nepenthes (rare) Sigmoilopsis schlumbergeri
______
MRWB-312-9 Z17/f144 F39768 • Unwashed weight: 201.35 g • Washed weight: 0.60 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m)
220 • Oceanicity: 12% planktics (Inner neritic) • Water mass: Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (17S:0D) Neogloboquadrina pachyderma (7% relative abundance) Zeaglobigerina nepenthes Sphaeroidinellopsis seminulina Cibicides robertsonianus Sigmoilopsis schlumbergeri
______
MRWB-397-1 Z17/f145 F39771 • Unwashed weight: 144.07 g • Washed weight: 17.38 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 89% planktics (Suboceanic) • Water mass: Warm Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (94S:4D) Hirsutella scitula (0S:1D) Zeaglobigerina nepenthes Zeaglobigerina druryi Sphaeroidinellopsis seminulina Globigerinoides quadrilobatus Bolivinita pohana Siphouvigerina notohispida
______
MRWB-397-2 Z17/f146 F39772 • Unwashed weight: 183.66 g • Washed weight: 11.65 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 88% planktics (Suboceanic) • Water mass: Temperate?
Key age and environmentally significant taxa
Globoconella miotumida (62S:1D) Sphaeroidinellopsis seminulina (one specimen) Bolivinita pohana Siphouvigerina notohispida
______
221
MRWB-398-3 Z17/f147 F39773 • Unwashed weight: 215.16 g • Washed weight: 19.45 g
• Age: upper Tt • Comment on age: The absence of Globoquadrina dehiscens in nearby samples suggests the small specimen of Globoquadrina cf. dehiscens is a rare expatriate that has been transported in from a lower latitude population by the East Cape Current. • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 93% planktics (Oceanic) • Water mass: Warm Subtropical
Key age and environmentally significant taxa
Globoquadrina cf. dehiscens (small expatriate specimen?) Globoconella miotumida (63S:2D) Hirsutella scitula (0S:3D) Neogloboquadrina pachyderma (1% relative abundance) Zeaglobigerina nepenthes Sphaeroidinellopsis seminulina Globigerinoides obliquus Bolivinita pohana Bolivinita cf. elegantissima Siphouvigerina notohispida
______
MRWB-400-4 Z17/f148 F39774 • Unwashed weight: 239.15 g • Washed weight: 4.02 g
• Age: upper Tt • Comment on age: The absence of Globoquadrina dehiscens in nearby samples suggests the small specimen of Globoquadrina? is a rare expatriate that has been transported in from a lower latitude population by the East Cape Current. • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 88% planktics (Suboceanic) • Water mass: Warm Subtropical
Key age and environmentally significant taxa
Globoquadrina? (small expatriate specimen?) Globoconella miotumida (74S:1D) Zeaglobigerina nepenthes? Sphaeroidinellopsis seminulina Sphaeroidinellopsis disjuncta? Globigerinoides obliquus Globigerinoides quadrilobatus Bolivinita pohana Siphouvigerina notohispida
______
222
MRWB-401-5 Z17/f149 F39775 • Unwashed weight: 93.23 g • Washed weight: 1.57 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal? (1000-1500 m) • Oceanicity: 82% planktics (Suboceanic) • Water mass: Subtropical (warm?)
Key age and environmentally significant taxa
Globoconella miotumida (60S:4D) 6% Dextral Neogloboquadrina pachyderma (1% relative abundance) Neogloboquadrina incompta (rare) Zeaglobigerina nepenthes Globigerinoides obliquus Bolivinita pohana Bolivinita cf. elegantissima Cibicides robertsonianus Sigmoilopsis schlumbergeri
______
MRWB-402-6 Z17/f150 F39776 • Unwashed weight: 144.90 g • Washed weight: 2.09 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 88% planktics (Suboceanic) • Water mass: Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (67S:1D) Menardella cf. limbata (rare) Neogloboquadrina pachyderma (3% relative abundance) Zeaglobigerina nepenthes Globigerinoides obliquus Globigerinoides quadrilobatus Sphaeroidinellopsis seminulina Bolivinita pohana (compressed) Bolivinita cf. elegantissima Siphouvigerina notohispida
______
MRWB-405-9 Z17/f151 F39777 • Unwashed weight: 162.38 g • Washed weight: 2.80 g
• Age: upper Tt
223 • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 79% planktics (Suboceanic) • Water mass: Temperate (Globigerina > Zeaglobigerina)
Key age and environmentally significant taxa
Globoconella miotumida (40S:3D) 7% Dextral Neogloboquadrina pachyderma (3% relative abundance) Bolivinita pohana (compressed) Bolivinita cf. elegantissima Siphouvigerina notohispida Cibicides robertsonianus
______
MRWB-405-9 Z17/f152 F39778 • Unwashed weight: 171.38 g • Washed weight: 2.67 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 69% planktics (Suboceanic) • Water mass: Temperate/Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (26S:3D) 10% Dextral Menardella cf. limbata Neogloboquadrina pachyderma (1% relative abundance) Zeaglobigerina nepenthes Bolivinita pohana Siphouvigerina notohispida Cibicides robertsonianus
______
MRWB-408-12 Z17/f153 F39779 • Unwashed weight: 197.65 g • Washed weight: 6.87 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: middle bathyal (600-800 m) • Oceanicity: 34% planktics (Extra-neritic) • Water mass: Temperate?
Key age and environmentally significant taxa
Globoconella miotumida (33S:0D) 10% Dextral Globigerinoides quadrilobatus (one specimen) Bolivinita pohana (compressed) Sigmoilopsis schlumbergeri
224 ______
MRWB-411-14 Z17/f154 F39780 • Unwashed weight: 132.92 g • Washed weight: 2.01 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: middle bathyal (600-800 m) • Oceanicity: 22% planktics (Outer neritic) • Water mass: Temperate?
Key age and environmentally significant taxa
Globoconella miotumida (14S:1D) Bolivinita pohana (compressed) Sigmoilopsis schlumbergeri
______
MRWB-412-15 Z17/f155 F39781 • Unwashed weight: 76.74 g • Washed weight: 3.21 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal (1000-1500 m) • Oceanicity: 80% planktics (Suboceanic) • Water mass: Subtropical
Key age and environmentally significant taxa
Globoconella miotumida (78S:1D) Neogloboquadrina pachyderma (1% relative abundance) Zeaglobigerina nepenthes Zeaglobigerina cf. druryi Globigerinoides quadrilobatus? Sphaeroidinellopsis cf. seminulina Bolivinita pohana Siphouvigerina notohispida Sigmoilopsis schlumbergeri
______
MRWB-421-16 Z17/f156 F39782 • Unwashed weight: 64.33 g • Washed weight: 4.84 g
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: lower bathyal? (1000-1500 m) • Oceanicity: 84% planktics (Suboceanic) • Water mass: Subtropical
225 Key age and environmentally significant taxa
Globoconella miotumida (58S:2D) Zeaglobigerina nepenthes Sphaeroidinellopsis cf. seminulina Siphouvigerina notohispida? Sigmoilopsis schlumbergeri
______
NUOP-395 X19/f175 F39783 • Unwashed weight: 116.60 g • Washed weight: 8.61 g • Comment on sample: Profuse carbonized organic material
• Age: More work is needed to refine the age (upper Tt-uppermost Pl) • Comment on age: Poorly constrained. Very small planktics. • Water depth: Outermost shelf (150-200 m) near river estuary? • Oceanicity: 60% planktics (Suboceanic) • Water mass: Subtropical
Key age and environmentally significant taxa
Globoquadrina dehiscens Globoconella cf. miozea (4S:4D) Globoconella miotumida (1S:0D) Neogloboquadrina cf. incompta (questionable specimen) Sphaeroidinellopsis cf. seminulina Cibicides molestus Ammonia beccarii
______
MRWB-363-11 ?????? F39770 • Unwashed weight: 250.60 g • Washed weight: 17.54 g • Comment on sample: Iron-stained, weathered, taphonomically modified fauna
• Age: upper Tt • Comment on age: Based on the absence of Globoquadrina dehiscens • Water depth: Upper bathyal (400-600 m) • Oceanicity: 8% planktics (Suboceanic)
Key age and environmentally significant taxa
Globoconella miotumida (17S:0D) Karreriella cylindrica
______
226 Appendix 3. Kinetic data used for BPSM of the WBS and Whangai Formation from R. Sykes and C. Boreham (2014, personnel communication). Locations of samples indicated on map.
Black’s Quarry
Kerosene Blu
227 Appendix 4. Geothermal gradients derived from well temperature data and quality ranking (Tier 1 = best quality, Tier 2 = poor quality, Tier 3 = very poor quality). Data from open file well reports (Brown, 1960; Watson, 1962; Zimmermann et al., 1967; Darley and Kirby, 1969a, 1969b; Leslie, 1971a, 1971b, 1971c; Laing, 1972a, 1972b, 1972c; Newkumet and Hornibrook, 1972; Heffer and Milne, 1976; de Bock et al., 1986; Dobbie and Carter, 1990; Biros et al., 1995; Johnston and Francis, 1996; Haskell and Johnston, 1998; Ian R. Brown Associates Ltd, 1998a, 1998b, 1998c, 1998d, 1998e, 1998f, 1999a, 1999b, 1999c, 1999d, 2000; Ozolins and Francis, 2000; Ian R. Brown Associates Ltd, 2001a, 2001b; Tap Oil Limited, 2004; Ian R. Brown Associates Ltd, 2008).
228 Appendix 4 (continued)
229 References Cited Biros, D., R. Cuevas, and B. Moehl, 1995, Well Completion Report, Titihaoa-1. PPL38318, Amoco NZ Exploration Co Ltd, Open-File Petroleum Report 2081, Wellington, New Zealand, Ministry of Economic Development New Zealand, 1096 p. Brown, B. R., 1960, Mangaone-1, BP Shell and Todd Petroleum Development Ltd, Open-File Petroleum Report 320, Wellington, New Zealand, Ministry of Economic Development New Zealand, 232 p. Darley, J. H., and K. F. S. Kirby, 1969a, Rakaiatai-1 Well Completion Report, BP Shell Aquitaine Todd Petroleum Developments Ltd, Open-File Petroleum Report 330, Wellington, New Zealand, Ministry of Economic Development New Zealand, 80 p. Darley, J. H., and K. F. S. Kirby, 1969b, Taradale-1, BP Shell Aquitaine Todd Petroleum Developments Ltd Open-File Petroleum Report 331, Wellington, New Zealand, Ministry of Economic Development New Zealand, 75 p. de Bock, J. F., C. Kelly, R. Lock, and G. Bulte, 1986, Well Completion Report Rere-1 PPL38-83, Petroleum Corporation of NZ Exploration Ltd., Open-File Petroleum Report 1231, Wellington, New Zealand, Ministry of Economic Development New Zealand, 1202 p. Dobbie, W. A., and M. J. Carter, 1990, Te Hoe-1 well completion report PPL 38316, Petrocorp Exploration Ltd., Open-File Petroleum Report 1835, Wellington, New Zealand, Ministry of Economic Development New Zealand, 209 p. Haskell, T. R., and J. Johnston, 1998, Waitaria-1, -1A, and 1B well completion report, PPL 38312, Asia Pacific Oil Co Ltd, Open-File Petroleum Report 2340, Wellington, New Zealand, Ministry of Economic Development New Zealand, 375 p. Heffer, K., and A. D. Milne, 1976, Well completion report Hawke Bay-1, BP Shell Aquitaine Todd Petroleum Developments Ltd, Open-File Petroleum Report 667, Wellington, New Zealand, Ministry of Economic Development New Zealand, 191 p.
230 Ian R. Brown Associates Ltd, 1998a, Kauhauroa-1 Well Completion Report, PEP 38329, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2346, Wellington, New Zealand, Ministry of Economic Development New Zealand, 815 p. Ian R. Brown Associates Ltd, 1998b, Kiakia-1/-1A well completion report, PEP 38329, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2381, Wellington, New Zealand, Ministry of Economic Development, 334 p. Ian R. Brown Associates Ltd, 1998c, Makareao-1 Well Completion Report, PEP 38329, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2377, Wellington, New Zealand, Ministry of Economic Development, 295 p. Ian R. Brown Associates Ltd, 1998d, Opoho-1 Well Completion Report, PEP 38329, Westech Energy New Zealand Ltd, Open-File Petroleum Report, Wellington, New Zealand, Ministry of Economic Development New Zealand, 314 p. Ian R. Brown Associates Ltd, 1998e, Tuhara-1 Well Completion Report, PEP 38329, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2401, Wellington, New Zealand, Ministry of Economic Development New Zealand, 259 p. Ian R. Brown Associates Ltd, 1998f, Well completion report Kauhauroa-2, PEP 38329, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2409, Wellington, New Zealand, Ministry of Economic Development New Zealand, 460 p. Ian R. Brown Associates Ltd, 1999a, Awatare-1 well completion report, Westech Energy New Zealand Ltd, Open File Petroleum Report 2365, Wellington, New Zealand, Ministry of Economic Development, 345 p. Ian R. Brown Associates Ltd, 1999b, Kauhauroa-3 Well Completion Report, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2445, Wellington, New Zealand, Ministry of Economic Development New Zealand, 462 p. Ian R. Brown Associates Ltd, 1999c, Kauhauroa-4 & 4A Well Completion Report,
231 Westech Energy New Zealand Ltd, Open-File Petroleum Report 2256, Wellington, New Zealand, Ministry of Economic Development, 296 p. Ian R. Brown Associates Ltd, 1999d, Kauhauroa-5 Well Completion Report, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2431, Wellington, New Zealand, Ministry of Economic Development, 611 p. Ian R. Brown Associates Ltd, 2000, Tuhara-1A Well Completion Report, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2470, Wellington, New Zealand, Ministry of Economic Development New Zealand, 894 p. Ian R. Brown Associates Ltd, 2001a, Hukarere-1 Well Completion Report, Westech Energy New Zealand Ltd, Open-File Petroleum Report 2656, Wellington, New Zealand, Ministry of Economic Development New Zealand, 385 p. Ian R. Brown Associates Ltd, 2001b, Waitaria-2 Well Completion Report. PEP 38335, Westech Energy New Zealand Ltd, Unpublished Petroleum Report 2593, Wellington, New Zealand, Ministry of Economic Development New Zealand, 430 p. Ian R. Brown Associates Ltd, 2008, Waitahora-1 Well Completion Report, Westech Energy New Zealand Ltd, Unpublished Petroleum Report, Wellington, New Zealand, Ministry of Economic Development New Zealand, 77 p. Johnston, J. G., and D. A. Francis, 1996, Kereru-1 well completion report, PEP38328, Indo-Pacific Energy (NZ) Ltd, Open-File Petroleum Report 2283, Wellington, New Zealand, Ministry of Economic Development New Zealand, 569 p. Laing, A. C. M., 1972a, Rotokautuku-1, Alliance Petroleum NZ Ltd, Open-File Petroleum Report 255, Wellington, New Zealand, Ministry of Economic Development New Zealand, 112 p. Laing, A. C. M., 1972b, Te Horo-1, Alliance Petroleum NZ Ltd, Open-File Petroleum Report 256, Wellington, New Zealand, Ministry of Economic Development New Zealand, 150 p. Laing, A. C. M., 1972c, Te Puia-1, Alliance Petroleum NZ Ltd, Open-File Petroleum
232 Report 257, Wellington, New Zealand, Ministry of Economic Development New Zealand, 183 p. Leslie, W. C., 1971a, Mason Ridge-1. PPL497, Beaver Exploration NZ Ltd, Open- File Petroleum Report 272, Wellington, New Zealand, Ministry of Economic Development New Zealand, 81 p. Leslie, W. C., 1971b, Ongaonga-1, Beaver Exploration NZ Ltd, Open-File Petroleum Report 271, Wellington, New Zealand, Ministry of Economic Development New Zealand, 95 p. Leslie, W. C., 1971c, Takapau-1, Beaver Exploration NZ Ltd, Open-File Petroleum Report 273, Wellington, New Zealand, Ministry of Economic Development New Zealand, 84 p. Newkumet, P. J., and Hornibrook. N. de B., 1972, Waitangi Station-1, International Pacific Exploration Co. Ltd, Unpublished Petroleum Report 81, Wellington, New Zealand, Ministry of Economic Development New Zealand, 55 p. Ozolins, V., and D. Francis, 2000, Whakatu-1 Well Completion Report. PEP 38328, Indo-Pacific Energy (NZ) Ltd, Open-File Petroleum Report 2476, Wellington, New Zealand, Ministry of Economic Development New Zealand, 498 p. Tap Oil Limited, 2004, Tawatawa-1 Well Completion Report, Open-File Petroleum Report 3067, Wellington, New Zealand, Ministry of Economic Development New Zealand, 873 p. Watson, J. F., 1962, Ruakituri-1, BP Shell and Todd Petroleum Development Ltd, Open-File Petroleum Report 324, Wellington, New Zealand, Ministry of Economic Development New Zealand, 223 p. Zimmermann, M. A., J. Faber, and J. Gouyet, 1967, Opoutama-1 Well Report, NZ Aquitaine Petroleum Ltd, Open-File Petroleum Report 504, Wellington, New Zealand, Ministry of Economic Development New Zealand, 973 p.
233 Appendix 5: Vitrinite-Inertinite Reflectance and Fluorescence Technique In order to address vitrinite suppression, a few techniques have been developed using the fluorescence properties of vitrinite to determine the type of vitrinite and thermal maturity. Suppressed (perhydrous) vitrinite often has higher fluorescence intensities than normal chemistry (orthohydrous) vitrinite due to association with alginate and cutinite (Carr, 2000 and references therein). Paleothermometric techniques using fluorescence properties include (1) fluorescence alteration of multiple macerals (FAMMTM), which uses suppressed vitrinite fluorescing properties to estimate normal chemistry VR (Wilkins et al., 1992, 1995), (2) a simplified method based on FAMMTM by Quick (1994) which uses mean fluorescence to estimate reflectance of normal vitrinite, and (3) vitrinite-inertinite reflectance and fluorescence (VIRF) developed by Newman (1997a, 1997b) and Newman et al. (2000), which uses fluorescence to identify normal chemistry vitrinite for VR analysis. The VIRF method is considered to be the most direct approach to determine VR because reflectance is measured directly from normal chemistry vitrinite rather than derived from the fluorescence of suppressed vitrinite (Newman et al., 2000). VIRF has been conducted for numerous wells in the ECB and is used in this study. The VIRF technique distinguishes normal vitrinite from suppressed vitrinite, inertinite, and other sources of contamination through the relationship between reflectance and fluorescence as a proxy for chemistry of the organic matter (Newman et al., 2000). When dispersed organic constituents are analyzed together, suppressed vitrinite, normal chemistry vitrinite, and inertinite form a curved VIRF profile from high fluorescence and low reflectance (perhydrous vitrinite) to low fluorescence and high reflectance (inertinite) (Appendix 5 Fig. 1; Newman et al., 2000). VIRF provides a means to distinguish normal vitrinite from perhydrous vitrinite and inertinite macerals based on their position in this profile. VR can also be estimated from the trend of the VIFF profile in samples where normal chemistry vitrinite is absent. Caved and reworked vitrinite fall off of the VIRF profile and therefore are readily distinguished (Newman et al., 2000). VIRF analyses are available for four wells in the
234 ECB (Hawke Bay-1, Opoutama-1, Hukarere-1, and Tawatawa-1), and are considered in this study (Appendix 5). VIRF studies have found that normal chemistry vitrinite is rare in ECB sediments (Newman and Moore, 2002). Results from Newman (2013) for the Hawke Bay-1 well conducted for this study show that most sediments contain some normal chemistry vitrinite, but they also contain abundant perhydrous vitrinite, inertinite, chemically altered vitrinite, altered/caved vitrinite, and reworked/thermally altered vitrinite (Appendix 5 Fig. 1). Because vitrinite macerals are typically very small in the ECB and other macerals can have similar morphologies to normal chemistry vitrinite, other macerals were likely included in previous VR analyses conducted in the past.
References Cited Carr, A. D., 2000, Suppression and retardation of vitrinite reflectance, Part 1. Formation and significance for hydrocarbon generation: Journal of Petroleum Geology, v. 23, p. 313-343. Newman, J., 1997a, New approaches to detection and correction of suppressed vitrinite reflectance: APPEA Journal, v. 1997, p. 524-535. Newman, J., 1997b, VFT ™: Combined vitrinite and fluorescence: 7th New Zealand Coal Conference Proceedings, p. 490-498. Newman, J., 2013, VIRF analysis of samples from Hawke Bay-1, Christchurch, New Zealand, Newman Energy Research, 32 p. Newman, J., K. M. Eckersley, and N. A. Moore, 2000, Application of vitrinite- inertinite reflectance and fluorescence (VIRF) to maturity assessment in the East Coast and Canterbury Basins of New Zealand: 2000 New Zealand Petroleum Conference, 20 p. Newman, J., and N. Moore, 2002, Vitrinite-inertinite reflectance and fluorescence (VRF ®) analysis of samples from Hukarere-1, Ian Brown Associates Ltd, Unpublished Petroleum Report 2940: Hukarere-1 geochemistry, and its implications for PEP38325 prospectivity, Hawke Bay, New Zealand, Wellington, New Zealand, Ministry of Economic Development, p. 36-67.
235 Quick, J. C., 1994, Iso-rank variation of vitrinite reflectance and fluorescence intensity: Symposium Series, p. 64-75. Wilkins, R. W. T., J. R. Wilmhurst, G. Hladky, M. V. Ellacott, and C. Buckingham, 1995, Should fluorescence alteration replace vitrinite reflectance as a major tool for thermal maturity determination in oil exploration?: Organic Geochemistry, v. 22, p. 191-209. Wilkins, R. W. T., J. R. Wilmhurst, N. J. Russell, G. Hladky, M. V. Ellacott, and C. Buckingham, 1992, Fluorscence alteration and the suppression of vitrinite reflectance: Organic Geochemistry, v. 18, p. 629-640.
236 14 Hawke Bay-1 cuttings sample at 2335m Perhydrous vitrinite
12 Normal vitrinite Inertinite 10 Altered or caved Reworked or thermally altered 8 VIRF Profile Ro (normal) 0.30% Altered, caved, and reworked 6 vitrinite falls o of trend (n=8) Fluorescence % 4
2
0 0.0 0.5 1.0 1.5 2.0 Reflectance (random) %
Appendix 5 Figure 1. An example of determination of Ro (normal) at 2335m depth in the Hawke Bay-1 well using VIRF (modified from Newman, 2013). Inertinite, normal vitrin- ite, and suppressed vitrinite form a VIRF profile from high fluorescence, low reflectance to low fluorescence, high reflectance. In this example, normal vitrinite has fluorescence ranging from 1% – 4%. Thermally altered and reworked vitrinite falls above the VIRF profile (yellow triangles), and altered and caved vitrinite falls below the VIRF profile (red triangles). Only macerals identified as normal vitrinite are used to calculate Ro (normal).
237 Appendix 6. VIRF data used for thermal calibration from Newman and Moore (2000), Newman and Moore (2002), Newman Energy Research Ltd (2005), and Newman (2013).
238 References Cited Newman, J., 2013, VIRF analysis of samples from Hawke Bay-1, Christchurch, New Zealand, Newman Energy Research, p. 32. Newman, J., and N. Moore, 2000, Vitrinite-inertinite reflectance and fluorescence analysis of samples from Opoutama-1, Westech Energy New Zealand Ltd, Unpublished Petroleum Report 3172, Wellington, New Zealand, Minitry of Economic Development New Zealand, 27 p. Newman, J., and N. Moore, 2002, Vitrinite-inertinite reflectance and fluorescence (VRF ®) analysis of samples from Hukarere-1, Ian Brown Associates Ltd, Unpublished Petroleum Report 2940: Hukarere-1 geochemistry, and its implications for PEP38325 prospectivity, Hawke Bay, New Zealand, Wellington, New Zealand, Ministry of Economic Development, p. 36-67. Newman Energy Research Ltd, 2005, Vitrinite-inertinite reflectance & fluorescence (VRF®) analysis of samples from Tawatawa-1, Unpublished Petroleum Report 3076, Wellington, New Zealand, Ministry of Economic Development New Zealand, p. 562-585.
239 Appendix 7. Inputs for 1D BPS models for heat flow calibration.
240