Sand injection and polygonal faulting in the Great South Basin, New Zealand

Subsurface sediment remobilization phenomena, including sand injection complexes and mud volcano systems, have been recognized to play a significant role in basinal fluid flow and in some cases are an important part of petroleum systems. Seismic-scale wing-like anomalies, interpreted as sand injections based on their similarities with North Sea examples, have been identified within the upper Paleocene sediments of the Great South Basin (GSB), New Zealand. The structures were observed on three-dimensional seismic data at about 2.5-2.7 seconds two-way time beneath the seabed. The sand injections occur below a well-developed polygonal fault system within the uppermost Paleocene sediments. The wing-shaped sand injections are often located near the downward extent of polygonal fault tips, possibly implying that the injections affected polygonal fault formation. This is the first time that a seismic scale sand injection complex has been described in the south-eastern hemisphere. The study adds to an emerging realization that sand injection complexes occur in many deep-water basins and has direct implications for basin evolution and hydrocarbon exploration in the Great South Basin.