CONSTRAINING PALEOENVIRONMENT AND PALEOWATER DEPTH USING BENTHIC FORAMINIFERAL ASSEMBLAGES FROM CARBONATE SEDIMENTS (ODP LEG 194, MARION PLATEAU, NE AUSTRALIA)

The Marion Plateau is a carbonate platform complex on the passive northeast Australia margin. During ODP Leg 194, a series of eight sites, on two transects, was drilled through Oligocene to Holocene mixed carbonate and siliciclastic sediments that record the depositional history of the Marion Plateau. This project reconstructs paleoenvironments, including paleowater depths, on the Miocene-aged carbonate platform sequences of the Marion Plateau using quantitative benthic foraminiferal presence, absence, morphology and assemblage data as indicators for environmental conditions at the time of deposition. Benthic foraminifers were counted from thin sections made from samples taken from three drilling sites from ODP Leg 194: bryozoan-dominated intervals at sites 1193 and 1194 (Northern Marion Plateau) and coralline red algae-dominated Site 1196 (Southern Marion Plateau). Multivariate analysis of benthic foraminiferal assemblages revealed three paleoenvironmentally relevant groups of taxa. The first group consisted primarily of Amphistegina, and Lepidocyclina, found at Site 1193 and 1196 and transported in to site 1194, and is interpreted to be representative of deposition in shallow water. The second group consisted primarily of Cycloclypeus, Operculina and planktonic foraminifers. This group was commonly found at sites 1193 and 1194 and is interpreted as representing deposition in deep-euphotic shelf/reef slope environments. The third group, consisting of small miliolids, soritids, alveolinids, Austrotrillina and Flosculinella, was found in sediments from Site 1196, and is interpreted to represent deposition in a restricted shallow marine environment, consistent with a sea grass meadow.