Geology of the Weber region, North Island, East Coast, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Earth Science, School of Agriculture and Environment

Abstract

Geological mapping of the East Coast Basin has tended to be at a broad scale with detailed mapping confined to a few specific areas of interest. The East Coast Basin is a petroliferous region and therefore of interest for petroleum exploration, however, further detailed mapping and sedimentological research is needed to have a better appreciation of the reservoir potential of the basin. Mapped geological boundaries are inferred based on broad tectonic features and structures, and little sedimentology has been undertaken. The current geological understanding is that this area contains a succession of Late Cretaceous (70 Ma) to Late Miocene (~5 Ma) sandstone, limestone, marl, flysch and mudstone facies. Few potential reservoir units are mapped or received detailed analysis and source rock has been an ongoing enigma due to known oil and gas seeps but low Total Organic Content results in most previously studied samples. The purpose of this research is to produce a high- resolution 1:25 000 geological map and undertake biostratigraphical, petrological, structural and paleo-environmental studies to help differentiate the Miocene aged geology of the area. Findings indicate the area is structurally complex with many faults, folds, including the Akitio Syncline, and local unconformities. Within the stratigraphic sequences identified both macro and micro fauna provide depositional environment and age control. Sedimentological and petrographic analysis of the major units also indicate variability in depositional environments from abyssal to shallow marine. Key areas have been located to provide accurate ages throughout the depositional sequence. This project will contribute to current research on the petroleum reservoir potential of the East Coast Basin.