Giant Foresets and Giant Sediment Waves in the Taranaki Basin, New Zealand.

Abstract

Sequence stratigraphic models are conventionally based upon transport of sediments from a terrestrial source via a fluvial distributary system to accommodation sinks on the shelf, slope and basin floor. As hydrocarbon exploration moves to exploit deepwater regions in basins around the world, knowledge of the controls on the nature and distribution of deep-water deposits should help to increase exploration success rates. Here we present a sequence stratigraphic model for the evolution of a giant clinoformal sedimentary wedge fed by oceanic currents and longshore drift and examine features present on the mid-lower slope. The Plio-Pleistocene Giant Foresets Formation of the Taranaki Basin, New Zealand is a rapidly prograding (up to 38 km/Ma) continental margin-scale clinoforms succession up to 1500m in height fed dominantly by sediment sourced from the uplift and erosion of New Zealand's South Island. This sediment was transported up to 500 km north across the shelf via a combination of longshore drift and the Westland Current. This study utilises regionally extensive, borehole calibrated, 2D and 3D seismic datasets to present the shelf margin architecture and sequence stratigraphy in context with recent advances in the understanding of Plio-Pleistocene Paleo-oceanography. Based on a combination of trajectory analysis and sequence stratigraphy, 19 sequences have been mapped from 2.4 Ma to present, with particular attention to along strike changes in character. Many sequences, but in particular the Early Pleistocene sequences 8 - 9 show a very distinctive discontinuous wavy seismic facies in the mid to lower slope in the central shelf area of the Taranaki Basin. This facies is interpreted as a thick succession of sediment waves similar to features recently described in the South China Sea. Individual waves show average wavelengths of 750 m forming an upslope migrating sediment wave package approximately 500 m thick (with a velocity of 2000 m/s) covering an area of approximately 1700 km2. Overall the sediment wave field is oriented perpendicular to the direction of shelf margin progradation suggesting influence from downslope processes. Sequence Stratigraphic interpretations place the sediment wave field across two depositional sequences indicating long lived sediment delivery to deep water regions of the Taranaki Basin.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017