Cool-water carbonate sedimentology and eustasy; Pleistocene upper slope environments, Great Australian Bight (Site 1127, ODP LEG 182)

The southern Australian shelf is the largest area of the globe composed of cool-water carbonates and provides the basis for the development of actualistic models of such sediments. Ocean Drilling Program Leg 182 drilling of the sedimentary succession provides essential information to also decipher the dynamics of this depositional system. Sediment samples and geophysical logs from a core drilled on the Eucla Plateau off the coast of southern Australia (Site 1127) have been used to study sedimentary cyclicity in an 800-m-thick cool-water carbonate Pleistocene wedge. This periplatform succession is dominated by bioclastic packstone and wackestone with minor intercalations of bioclastic grainstone. Fluctuations of stable oxygen-isotope values in bulk carbonate samples parallel global climatic and related sea-level fluctuations as predicted in the SPECMAP-curve. The sea-level-controlled sedimentary cycles of the slope succession are several tens of meters thick. Lowstand deposits are relatively fine grained and include abundant sponge spicules, whereas highstand deposits are coarser grained and contain abundant high-Mg calcite bioclasts. Aragonite content makes up to 36% of the cool-water carbonates. Aragonite originates from tunicate spicules. Primary, sea-level-controlled carbonate mineralogical and textural changes are likely to promote facies-dependent differential diagenesis during later burial stages of such successions.