The Relationship of Initial Flooding Depositional Facies to Global Sea Level and Climate on The Marion Plateau, NE Australia (ODP Leg 194)

The Coral Sea has been the host to a variety of large carbonate platforms over the geologic past and presently hosts the world\u27s largest system of coral reefs, the Great Barrier Reef, stretching more then 2,300 km along Australia\u27s northeast coast. The Marion Plateau, which today is the site of 400 m deep hemipelagic sediment drifts, once supported two large carbonate platforms that were precursors to reef growth on the central and southern Great Barrier Reef. Previous work examining the growth phases, drownings and rejuvenation of these platforms is extensive. The purpose of this research is to examine the factors controlling the earliest sedimentation on the margin and how it influenced early development of the carbonate platforms. One hundred and eighty-three samples were taken from the base of Hole 1195 B, that was drilled during the Ocean Drilling Program\u27s Leg 194. Analyses were performed using x-ray diffraction on the bulk powder and decalcified less than 2um size fraction smear slides. Four distinct sedimentary facies were defined on the basis of mineralogy and constituent grains. The initial marine transgression of the Marion Plateau was not a straightforward one where a shallow-water margin gradually transitioned into a deep-water margin. Instead, sediments record a complex history of unconformities, hardgrounds, and discrete sedimentary units. The initial flooding was complex as a result of its initially shallow depth at a time characterized by several glacio-eustatic sea-level changes. The data indicate that eustasy has been the strongest control on sediment deposition and clay mineral patterns on the Plateau. Falling sea level resulted in periods of increased detrital input and limited soil formation. Also, a decreasing kaolinite trend in the early Miocene, during a rising sea level, indicates that clays forming on land as a result of climate were not transported out onto the plateau