STRUCTURAL ANALYSIS AND TECTONOSTRATIGRAPHIC EVOLUTION OF THE REINGA BASIN, OFFSHORE NORTHWESTERN NEW ZEALAND by Shawn P. Kramer A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Geology). Golden, Colorado Date: ________________ Signed: ________________________ Shawn P. Kramer Signed: ________________________ Dr. Bruce Trudgill Thesis Advisor Golden, Colorado Date: ________________ Signed: ________________________ Dr. M. Stephen Enders Professor and Department Head Department of Geology and Geological Engineering ii ABSTRACT The complex polyphase tectonic evolution of the southwest Pacific, from Late Cretaceous to Neogene time, was recorded by the various offshore sedimentary basins of greater Zealandia. The Reinga Basin, offshore of northwestern New Zealand, exemplifies the interaction between the regional tectonic evolution and local variations in the mode of structural and sedimentary responses. While the principal phases of the Reinga Basin’s evolution are well-established, the spatial and temporal migration of active structural and sedimentary reactions to tectonic events has not been the focus of an in-depth analysis. This study seeks to elucidate the locus and timing of active deformation through the lens of tectonostratigraphic seismic interpretations and sequential structural restoration. An integrated workflow of deliberately chosen methods and software solutions yields a set of diagnostic seismic sections, and a representative depth- converted and restored section. By these methods, a conceptual model is proposed for the dynamics of the Reinga Basin’s sedimentary and structural response to an evolving tectonic plate reconfiguration. A systematic development of both extensional and compressional deformational features is proposed that embraces both the kinematic aspects of deformation as well as the causative tectonic forces. The result of this research is an enhanced understanding of the local response to regional tectonic events in the southwest Pacific. Economic significance may be found in the further constrained evolution of principal petroleum reservoir system components. Furthermore, this study compliments the established record of Reinga Basin research, offers a new and pragmatic interpretation of a well-studied seismic data set, and reduces the negative influences of interpretational uncertainty. iii TABLE OF CONTENTS ABSTRACT ............................................................................................................................. iii LIST OF FIGURES .................................................................................................................. vii ACKNOWLEDGMENTS .......................................................................................................... xi CHAPTER 1 - INTRODUCTION............................................................................................... 1 1.1 Area of Interest .............................................................................................................. 1 1.2 State of the Basin........................................................................................................... 2 1.3 Research Objectives ...................................................................................................... 3 CHAPTER 2 - GEOLOGIC BACKGROUND ............................................................................ 4 2.1 Basin Overview ............................................................................................................. 4 2.2 Structural Framework .................................................................................................... 4 2.3 Tectonostratigraphic Evolution of Reinga Basin ............................................................ 6 2.3.1 Gondwana Convergent Margin Phase (Triassic to Early Cretaceous) ...................... 7 2.3.2 Rifting (Middle to Late Cretaceous) ........................................................................ 7 2.3.3 Passive Transgressive Phase (Late Cretaceous to Late Eocene) ............................... 9 2.3.4 First Compressional Phase (Late Eocene) ............................................................. 10 2.3.5 Second Subsidence Phase (Late Oligocene to Early Miocene)............................... 11 2.3.6 Second Compressional Phase (Middle-Late Miocene)........................................... 12 2.3.7 Tectonic Quiescence (Late Miocene to Present) .................................................... 12 iv CHAPTER 3 - DATA SETS ..................................................................................................... 18 3.1 Well Data .................................................................................................................... 18 3.2 Seismic Data ............................................................................................................... 20 3.3 Dredge Data ................................................................................................................ 22 CHAPTER 4 - SEISMIC INTERPRETATION ......................................................................... 24 4.1 Data Conditioning ....................................................................................................... 24 4.2 Seismic Stratigraphic Interpretation ............................................................................. 26 4.3 Structural Interpretation ............................................................................................... 30 4.4 TWT to Depth Conversion .......................................................................................... 36 CHAPTER 5 - RESTORATION ............................................................................................... 39 5.1 Restoration Workflow ................................................................................................. 40 5.2 2D Kinematic Modeling .............................................................................................. 43 5.2.1 Unfaulting ............................................................................................................ 43 5.2.2 Unfolding ............................................................................................................. 46 5.2.3 Decompaction and Isostasy ................................................................................... 47 5.3 Restorations................................................................................................................. 48 5.3.1 100 Ma (Middle Cretaceous)................................................................................. 48 5.3.2 ~ 90 Ma (Late Cretaceous) .................................................................................... 48 5.3.3 85 Ma (Late Cretaceous) ....................................................................................... 49 5.3.4 66 Ma (Top Cretaceous) ....................................................................................... 49 v 5.3.5 49 Ma (Early Eocene) ........................................................................................... 49 5.3.6 40 Ma (Late Eocene) ............................................................................................ 50 5.3.7 35 Ma (Top Eocene) ............................................................................................. 50 5.3.8 ~15 Ma (Middle Miocene) .................................................................................... 51 5.3.9 5 Ma (Top Miocene) ............................................................................................. 51 5.3.10 0.0 Ma (Present) ................................................................................................. 51 CHAPTER 6 - DISCUSSION ................................................................................................... 54 6.1 Review ........................................................................................................................ 54 6.2 Significance of Key Findings ....................................................................................... 54 6.2.1 Migration of Active Faulting................................................................................. 54 6.2.2 Economic Significance ......................................................................................... 63 6.2.3 Interpretational Uncertainty .................................................................................. 65 CHAPTER 7 - CONCLUSIONS AND RECOMMENDATIONS ............................................. 66 7.1 Conclusions ................................................................................................................. 66 7.2 Recommendations for Future Work ............................................................................. 67 REFERENCES ......................................................................................................................... 69 vi LIST OF FIGURES Figure 1.1 Bathymetry map of greater Zealandia and key tectonic elements (a), and physiography of the Reinga Basin and surrounding structures. The principal REI09 seismic survey, other key lines, and wells are shown (b). Bathymetry data comes from CANZ (2008). (Modified from Bache et al., 2013b) .................................................................................................................... 2 Figure 2.1 Structural map of the Reinga Basin highlighting two distinct