Aspects of carbonate sedimentation?

Abstract

A dolomitic sediment of grain size too small to permit optical determination of the minerals is forming today in many shallow water lagoons and at the closed shallow end of the Coorong in the South‐East of South Australia. Relative amounts of calcian dolomite, magnesian calcite and shell calcite have been indicated by X‐ray powder diffraction patterns, and strontium is found to be present (in celestite). It is considered that these are formed inorganically, though seasonal effects and organisms may have played big parts in providing the right physico‐chemical conditions for precipitation. There is no simple relationship between salinity and carbonate precipitation, but the carbonates have been observed forming in salinities ranging from less than 1–6 per cent, to more than 14 per cent., with pH varying from 8–5 to 9–0, and with reducing conditions being suggested by associated sulphur‐bearing muds. It is suggested, therefore, that the physical conditions of shallow waters favour the precipitation of dolomite.