Characterizing oil, gas hydrate, and sedimentary systems via geochemistry, computational modeling, and global synthesis

At the highest level, this dissertation investigates marine systems from a geochemical, computational, and sedimentological perspective through the undertaking of six distinct contributions. Overall, the work detailed herein might perhaps be thought of as fitting under two central themes, being (i) investigations into the formation, evolution, and destruction of hydrocarbon systems and (ii) advancement and refinement of the understanding of global controls on deep-sea clastic depositional systems. These investigations have important bearing on the interplay of climate, tectonics, and paleoceanography and attendant modulation of deep-marine depositional systems and the oceanic carbon cycle—at local, regional, and global scales—throughout the Phanerozoic. Chapter 1 presents an organic geochemical assessment of petroleum quality using oil seep samples from underexplored regions of New Zealand's east coast. Analysis of biomarkers (including n-alkanes, isoprenoids, steranes, and terpanes) determines the degree to which oils have been biodegraded, while analysis of biomarker and diamondoid compounds enables evaluation of thermal maturity, oil-to-gas conversion, and hydrocarbon mixing. Chapter 2 presents a geochemical assessment of petroleum source rock depositional environment based upon expanded analysis of these oil samples. Analysis of biomarkers, stable carbon isotopes, and sulfur aids in the interpretation of source rock characteristics including organic matter type, redox conditions, sedimentary facies, and age. Chapter 3 examines the impact of tectonic uplift on the stability of subsea gas hydrate, with implications for ocean chemistry and the carbon cycle. Two-dimensional basin modeling of a structurally restored transect from New Zealand's Hikurangi margin predicts uplift-driven changes to hydrate system extent and thickness from the late Oligocene to present. Chapter 4 presents a compilation of shallow (~2 km subseafloor) sediment organic properties at 43 biogenic gas hydrate localities from five continental margins as an empirical assessment of the organic carbon (n = 2000+ analyses) and hydrogen (n = 500+ analyses) content required for methane hydrate formation. Chapter 5 assesses the response of deep-marine coarse-grained depositional systems to exceptionally warm climates and attendant high sea levels. This review compiles 59 examples of sand-rich systems (abundant on both active and passive margins—from all continents except Antarctica) emplaced during the early Eocene hothouse despite purportedly unfavorable conditions for deep-sea siliciclastic deposition, calling for reevaluation of the understanding of marine depositional systems at regional to global scales. Chapter 6 assesses the response of deep-marine clastic systems to major cooling, sea-level fall, and ocean circulation changes at the Eocene-Oligocene boundary—that is, during the transition from warm, largely ice-free conditions of Eocene hothouse and greenhouse worlds to the cool, glaciated conditions of the Oligocene to recent icehouse world. This synthesis compiles 93 locations—along the margins of all seven continents—where unconformities of Eocene-Oligocene age occur, with significant implications for the influence of major climatic transitions—and attendant changes to sea level and deep-sea circulation—on submarine erosion

Keywords: Geological and Environmental Sciences.
Advisor: Graham S. A. (Stephan Alan)
Moldowan J. M. (J. Michael)
Mukerji Tapan