--> --> Morphologies and Controls on Development of Pliocene-Pleistocene Carbonate Platforms: Northern Carnarvon Basin, Northwest Shelf of Australia

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Morphologies and Controls on Development of Pliocene-Pleistocene Carbonate Platforms: Northern Carnarvon Basin, Northwest Shelf of Australia

Abstract

The detailed morphologies, evolution and termination of Neogene tropical carbonate platforms on the passive margin of the Northern Carnarvon Basin (NCB) of the Northwest Shelf of Australia reveal information on the history of local oceanographic processes and changing climate. Cool-water carbonate deposition, dominant during the early-middle Miocene, was superseded by a siliciclastic influx, which prograded across the shelf beginning in the late-middle Miocene during a period of long-term global sea-level fall. The resulting prograding clinoform sets, interpreted as delta lobes, created relict topographic highs following Pliocene termination of the siliciclastic influx (Sanchez et al. (2012). These highs created a favorable shallow-water environment for subsequent photozoan carbonate production. A composite, commercial 3D seismic volume allows investigation of the temporal and spatial evolution of the resulting Pliocene-Pleistocene carbonate platforms. Initiation of carbonate development, in addition to being a response to cessation of siliciclastic influx and the existence of suitable shallow-water substrate, was also influenced by the development of the warm-water Leeuwin Current (LC), flowing southwestward along the margin. Four flat-topped platforms are mapped; each platform top is a sequence boundary defined by onlap above and truncation below the boundary. Successive platforms migrated southwestward, along-strike. The mapped platform tops reveal that these areas are large (= 10 km wide) have not identified in the subsurface before. Evidence of karst (e.g., troughs in v-shaped, lack seismically resolvable internal structures in seismic with up to ∼ 50m deep and ∼1km wide) on platform tops suggests episodic subaerial exposure. The progressive drowning and termination of platforms from northeast to southwest along strike may result from differential compaction of the deltaic substrate or differential tectonic subsidence caused by the collusion at the Banda Arc between the Australian and Pacific plates.