Neogene siliciclastic deposition and climate variability on a carbonate margin: Australian Northwest Shelf

Abstract

The Bare Formation represents a unique episode of Neogene siliciclastic deposition on the carbonate-dominated Australian Northwest Shelf (NWS). Seismic interpretation coupled with age control from International Ocean Discovery Program (IODP) Expedition 356 Sites U1462, U1463 and U1464 allow us to constrain the timing of siliciclastic deposition and the associated sedimentary processes. The Bare Formation is preceded by middle to late Miocene shelf exposure and karstification (~12 Ma). Elongate sandbars deposits with small lobate deltas developed during the late Miocene. Fluvial deposition increased markedly in the Zanclean (5.3–3.6 Ma), resulting in development of a large wave dominated delta, with evidence of channels, comprising the thickest component of the Bare Formation. Siliciclastic input decreased in the Piacenzian (3.6–2.58 Ma), leading to margin retreat and final termination in the early Pleistocene (~2.39 Ma). The results correlate with regional climate and sedimentary records from Sites U1463 and U1464, which indicate an arid middle to late Miocene on the NWS, followed by a humid interval in the Zanclean and a return to arid conditions during the Piacenzian. We suggest that fluctuation of surface runoff patterns in the continental hinterland was the primary control on Bare Formation evolution. Sedimentary and climate transitions are linked to reorganization of Indian Ocean paleoceanography, accompanying northward migration of the Australian continent and progressive restriction of the Indonesian Throughflow.