Interaction of Multiple Deepwater Sediment Pathways With Evolving Seafloor Topography: Implications for Intra-Slope Reservoir Architecture, With Examples From the East Coast Basin of New Zealand

Abstract

Intra-slope, deep-marine depositional systems are of major importance for the petroleum industry in many settings, e.g. the Gulf of Mexico and NW Borneo. However studies have typically focused on single-source distributary systems, which present simple models of basin fill and spill hierarchy. Here we examine multi-source, accretionary wedge traversing systems in discrete sub-basins of the East Coast Basin, New Zealand. Understanding how multiple systems interact with seafloor topography and each other gives better understanding of reservoir architecture, connectivity and ultimately slope basin prospectivity.

High resolution outcrop studies from the exhumed portion of the trench-slope system are allied with bathymetric studies and analysis of 2D seismic data from across the system. Outcrop studies in the innermost sub-basins identified a heterogeneous range of architectural elements. Seismic scale elements include discrete axial channels within sub-basins, vertically stacked lobe complexes up to 200 m thick within the centre of the sub-basins and fill of a transverse canyon >5 km wide that connected the outcropping sub-basins. The distribution of elements and palaeocurrent data demonstrate numerous sediment input and output pathways linking sub-basins. Seafloor data allow us to examine modern sediment pathways and their interaction with developing growth structures, demonstrating the ability of canyons to directly cut multiple active growth structures to deliver sediment to outboard sub-basins. Bathymetry also highlights the influence of slope gradient on basin linkage. Seismic data allow investigation of the large scale architecture of sub-basins, revealing how multiple systems interact and compensationally stack. The influence of MTCs in generating and negating topography is apparent across all datasets.

These results demonstrate the interplay of both inherent and external controls on the evolution of deepwater sediment pathways. The reservoir potential of sub-basins is greatly enhanced by the development of autogenically-controlled sediment bypass to relatively distal areas through structure-breaching basin linkages, even in actively deforming basins. However, the positioning of such conduits is ultimately controlled by allogenic factors such as slope gradient and sediment flux.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018