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Australian Great Barrier Reef Initiation Timing Constrained By Seaward Shallow-Water Sediment Drift Architecture (Odp Leg 194, Marion Plateau), Stephen P. Obrochta

USF Tampa Graduate Theses and Dissertations

I resolved the sedimentary architecture of a shallow water (< 500 m), hemipelagic sediment drift located on the Marion Plateau, seaward and downstream of the Great Barrier Reef (GBR). The drift responded increasingly to sea-level fluctuations during the Pleistocene. In the early Pleistocene, local climatic variations introduce a precessional rhythm to drift architecture that is out of phase with sea level-forced cyclicity. Beginning in the mid Pleistocene, sea level variations dominate drift architecture, with the highest carbonate and terrigenous fluxes likely occurring during highstand and transgression, respectively. At the sea-level transgression of MIS 15 and subsequent isotope stages, the phasing of maximum terrigenous flux corresponds to sea-level transgression, indicating siliciclastic sediment accumulated on the continental shelf behind an exposed barrier reef during the lowstand of MIS 16 and was remobilized by rising sea-level. These sedimentological data indicate GBR initiation occurred during MIS 17. The normal polarity exhibited by the central GBR and thick section of underlying sediments rules out initiation during MIS 19.

MIS 17 was the first of the asymmetric glacial cycles characteristic of the Late Pleistocene. If the Florida Keys and Belize barrier reef initiations were indeed simultaneous with that of the GBR, then the changing nature of cyclicity in global sea level and climatic fluctuations likely influenced the initiation of the world's major, modern barrier reefs.