The evolution of a Middle Miocene deep-water sedimentary system in northwestern New Zealand (Taranaki Basin): Depositional controls and mechanisms

摘要

Through the Oligocene and Miocene, New Zealand basins underwent widespread subsidence, related to the evolution of the convergent plate boundary between the Pacific and Australian plates. In Taranaki Basin on the western margin of the North Island, a deep water siliciclastic sedimentary system developed in response to basin subsidence and hinterland uplift. Basinward of the evolving shelf, basin floor sandstones and mudstones were deposited, some of which constitute important petroleum reservoirs and seals. Extensive 3D reflection seismic coverage has enabled us to map the character and distribution of basin floor sedimentary units and to develop a comprehensive sequence stratigraphic model. The stacking patterns of depositional sequences reflect an overall progradation of basin floor sedimentary facies and change in geometries through time, while associated elements such as fan lobes and channel systems increased in dimension. Structural change and southward progressing tectonic uplift most likely controlled increasing sediment input into the basin. In addition, an intensification of bottom current activity led to the development of sediment drifts, which we suggest was related to oceanographic changes at the end of the Middle Miocene Climatic Optimum. While turbidite depositional systems were dominant during lowstands, sediment reworking by shore parallel currents is interpreted to have been a dominant process during highstands. We document a change from sand-dominated to more mud-dominated deposits through the Middle Miocene and propose that this change in sediment character may be related to a higher degree of chemical weathering on land, possibly related to the northward migration and intensification of westerly winds.