Comparison Between Subtropical And Temperate Carbonate Elemental Composition: Examples From The Great Barrier Reef, Shart Bay And Tasmania, Australia And The Persian Gulf, UAE

The Persian Gulf (United Arab Emirates) is renowned for subtropical carbonates. Extensive subtropical (Great Barrier Reef and Shark Bay) to temperate (Tasmania) carbonates are also forming in shallow seas around Australia. These carbonates differ in the types and proportions of skeletal to non-skeletal grains and cements, and are forming in normal to hypersaline shallow-marine environments. The elemental composition of subtropical carbonates differs from that of their temperate counter-parts mainly because of differences in seawater temperature, carbonate mineralogy, salinity, rate of precipitation and the proportion of skeletal to non-skeletal grain composition. Differences in the Mg concentrations of the bulk carbonates result from variations in the temperature of sea water and carbonate mineralogy. Sr concentrations are higher in subtropical carbonates relative to temperate ones because of a higher proportion of aragonite in the tropical carbonate and calcite mineralogy. Na values increase with increases in salinity and rate of precipitation. Under reducing conditions appreciably higher Mn and Fe concentrations enter the calcite lattice compared with aragonite. The results from this study demonstrate that modern subtropical carbonate elemental composition differs distinctly from that of temperate carbonates. Thus, these differences can be used in the recognition of the ancient spectrum of subtropical to temperate carbonates based on the relative concentrations of elements and their ratios.