Quaternary isolated carbonate build-ups in the Timor Sea (NW Australia) ? Understandings and Implications

Abstract

Distribution and growth history of isolated carbonate build-ups (ICBs) is controlled by complex interplay between various tectonic, eustatic, and oceanographic parameters. Quaternary ICBs in the Timor Sea (NW Australia) are located in tropical waters, and at present they form clusters of ~150 build-ups, developing 2 to 85 km from the edge of a wide continental shelf. The tectonic evolution of the Timor Sea lead to regional changes in the oceanography and flexural deformation of the NW Bonaparte Basin, which in turn had a major impact on the evolution of ICBs. Flexure-induced fault activity produced structural topography for the growth of ICBs over 'highs', while oceanic current through Timor Trough provided warm and nutrient-rich water. Our results demonstrate that, despite potentially good conditions for carbonate production, ICBs did not form until the Mid Pleistocene (ca. 0.582-0.8 Ma BP). This age corresponds to the onset of repeated, high-amplitude (+120 m) sea level fluctuations with rapid deglacial rises and slow falls. Thus, we infer that the NW Australia ICBs formed due to: (1) structural shaping of the margin; (2) oceanographic changes, and; most importantly, (3) onset of repeated short-term transgressions reactivating the carbonate production along isolated highs. The distribution and growth of ICBs could be useful to understand the evolution of ancient ICBs that formed along very wide shelves and epeiric seas.