Sedimentology, seismic geomorphology, and provenance investigations of deep-water deposits [electronic resource] : Taranaki Basin, New Zealand
Keywords: Geological Sciences.

This thesis investigates deep-water sediment transport and deposition from the perspective of three distinct depositional systems of the Taranaki Basin, New Zealand. Chapter 1 provides a general introduction to the scope of the thesis and the themes of each study. In Chapter 2, we investigate the initiation and evolution of submarine gullies and their role in sediment transport on a prograding continental slope in Pliocene time. Through three-dimensional seismic reflection interpretation and morphometric analysis, we document complex cycles of erosion, aggradation, and partial filling of gullies coincident with slope progradation. We evaluate multiple models for gully initiation, and our observations favor the concept of a dilute, sheet-like turbidity current characterized by alternating zones of erosion and sedimentation. We document the net-aggradational nature of the small-scale gullies observed in this study, and propose a possible process-based link between these features and the order-of-magnitude larger constructional canyons observed on other margins. Finally, we present a first-order quantitative metric that may distinguish net-aggradational submarine gullies from other seafloor channel features, but highlight the need for global morphometric datasets of gullies and other channels to bolster this finding. In Chapter 3, we examine the upper Miocene deep-water Mohakatino Formation, which was dominantly derived from submarine volcanoes associated with subduction at the Pacific-Australia plate boundary. Through centimeter-scale outcrop analysis and petrography, we identify a range of depositional styles that help constrain the geometry of the Taranaki Basin and characteristics of the offshore volcanoes. We also show that submarine volcanoes represent a previously neglected element of source-to-sink sediment transport analyses. We demonstrate that deeply submerged volcanoes may be significant sources of sediment that do not necessarily record the environmental signals of tectonic, climatic, and sea level change that source-to-sink studies attempt to identify in sedimentary records. Finally, in Chapter 4, we investigate the sediment provenance patterns of the Taranaki, King Country, and Wanganui Basins of the western North Island using detrital zircon U-Pb geochronology. By applying this technique to the complex, multi-cycle sedimentary systems of New Zealand, we present statistical methods for identifying key distinguishing age components in multi-modal zircon age spectra and for comparing detrital spectra against mixtures of potential sediment sources. With additional constraints from petrography and geological observations, we differentiate local vs. regional sources for numerous strata spanning Late Cretaceous to late Pliocene time. Our findings support nearly continuous contributions from the northwestern South Island across that time span, and a short-lived east-west drainage system in late Miocene time associated with increased exhumation in the southern Axial Ranges, which was terminated in early Pliocene time by southward migration of an intervening marine depocenter.