Distribution and Development of the Middle Miocene Moki Submarine Fans, Taranaki Basin, New Zealand

A dominantly sandy unit, the Moki Formation, was deposited during the Middle Miocene within the Taranaki Basin, offshore the west coast of the North Island of New Zealand. Several studies have been published on the Moki Formation in the southern Taranki Basin but none in the northern part of the basin. In order to determine the spatial distribution, evolution, and depositional settings of the Moki submarine sand bodies, this study utilized 3D seismic and well data. The study area covers about 1600 km² of the northern Taranaki Basin.

Seismic profiles reveal that the mound-shape reflectors of Moki fan deposits situated between continuous reflectors of underlying Oligocene carbonates and hemipelagic muds of the overlying Manganui Formation. The reflections of the Moki sandy fan deposits locally grade laterally into interlobal deposits of hemipelagic muds. Correlation between wells: Witiora-1, Taimana-1, and Arawa-1 verified the seismic interpretation. Well log correlation shows an overall thickness variation of fan deposits that ranges from a greater thickness in the middle part of the sand lobe accumulation towards diminished thicknesses on the flanks. Gamma ray facies show clear progradation then aggradation motif that confirms the results from the seismic analyses. Depending on seismic attribute maps, two paleochannels were distinguished in association with the sand bodies sharing a SE to NW flow direction. In the study area, the fan represent sand-rich deposits that developed and prograded from south to north with variations in lateral extent driven by three major shifts in sediment pathways as the feeder channel orientations changed. The Moki Formation is interpreted as basin floor fan deposits that accumulated during basinward migration of the shelf edge with supplied sediments sourced from the SSE.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California