Depth and latitudinal characteristics of sedimentological and geochemical variables in temperate shelf carbonates, eastern Tasmania, Australia

In eastern Tasmania temperate shelf carbonates occur in latitudes between 40°30' and 44°S in water depths from approximately 14 to 250 m. Increasing water depths correspond to decreasing water temperatures and salinities. Bryozoans (total, not species) increase with increasing water depth, bivalves are high in shallow-depths, foraminifera are high in mid-depth and gastropods are mostly located around 130 m. The amount of calcite relative to aragonite increases with increasing water depth due to decreasing water temperatures. The Mg, Sr and Na values increase with increasing water depth due to changes in carbonate mineralogy, the type of biota and the temperature. Mn and Fe values in bulk carbonates decrease with increasing water depth, due to the decreasing of terrigenous content. The δ18O values of bulk sediments, bryozoans, benthic foraminifera and brachiopods increase with increasing water depth, due to decreasing seawater temperatures and salinity, and the changes in carbonate mineralogy. The δ13C values of most of these carbonates increase with increasing water depth, mainly due to mixing of water masses and decreasing seawater temperatures. Latitudinal variations in sedimentology, carbonate elemental and isotopic compositions and mineralogy caused by seawater temperatures and salinities are small when compared to changes caused by increasing water depth. Combining present oceanographic features with those deduced from sedimentological and geochemical properties enables better understanding of the paleoceanography off Tasmania since the Last Glacial Maximum, related to seawater temperatures, salinity, mixing of water masses, sea-level changes, sedimentation and diagenesis.