Carbonate Shelf to Basin Architecture and Slope Seismic Geomorphology, Lower Miocene, Browse Basin, Northwest Shelf of Australia

Abstract

Renewed interest in carbonate slopes in both modern and ancient depositional environments has led to revise long-standing carbonate slope models to include canyons and channels with geomorphology similar to siliciclastic analogs. Using more than 50000 km² of contiguous 3D seismic-reflection data and industry and Ocean Drilling Program well data, we investigate the details of shelf to basin architecture of the lower Miocene carbonates in the Browse Basin of NW Australia. For more than 250 km along strike of the continental margin, the shelf to basin profile consists of a succession of six adjoining environments: (1) a wide inner shelf bordered by a thick carbonate platform, which developed at or near the shelf edge; (2) a low angle (1-3^o) upper slope between the carbonate platform margins and the main continental shelf break; (3) a steep (6-20^o) middle slope dissected by straight to low sinuosity canyons (1-3 km wide and up to 250 m deep); (4) a low angle (0.5-2^o) outer slope with an alternation of channel-levee and mass-transport complexes (MTC’s); (5) steep (25-40 ^o) escarpment between 1500 and 3500 m high that separated the outer slope; and (6) the Argo abyssal plain at >5500 m water depth where a >100 m thick succession of unconfined calciturbidites accumulated. These datasets image carbonate channel-levee complexes on the outer slope. These channels are 60-300 m wide and up to 75 m deep. They have associated levee-overbank deposits that are up to 3 km wide and 80 m high. The channel-levee complexes have variable sinuosity controlled by MTC confinement and slope angle. Common siliciclastic deep water channel-levee complex processes such as channel avulsion, channel axis lateral and vertical migration, lateral and down dip channel bend migration are interpreted in this deep water carbonate system. Channel development is commonly interrupted by MTC’s (0.2-20 km wide and 20-150 m thick). This unique dataset shows a complex shelf to basin morphology with several slope inflection points controlled by antecedent topography created by both previous tectonic events and pre-Miocene sedimentary accumulation. We document an almost complete section for more than 150 km from carbonate platform margins to a potentially >250 km² unconfined carbonate fan on the abyssal plain floor that can provide a new analogue for carbonate slope to basin profiles for exploring other continental margins in similar climatic and tectonic settings.

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