Petrogenesis of Neoproterozoic Allochthonous Reef Carbonates, Flinders Ranges, South Australia

Abstract

This study concentrates on the petrogenesis of carbonates in the Flinders Ranges with the view that they will give insight as to the nature of carbonate geochemistry with implications on the ocean geochemistry during the Neoproterozoic. The search for the reason for the paucity of dolomite in modern times compared to the Precambrian was one of the driving forces for Precambrian carbonate research to this day. By using petrology, cathodeluminescense, trace element analyses and stable isotope analyses, we hope to add to the growing field of evidence for a different ocean chemistry during the Precambrian. We suggest that dolomite is a common early diagenetic marine phase during the late Proterozoic. It has been found that there is a debris flow unit in the shales adjacent to the Balcanoona Formation (previously described as a submarine escarpment) near Oodnaminta Hut. At this stage we have identified several prominent fabrics in the partially dolomitised limestone blocks in this debris flow. Most of these fabrics involve some kind of biocementation by microbial structures. There are up to 4 geopetal generations found in these limestone blocks. With the 1st and 2nd generations being the most common. Preliminary studies show that there has been significant neomorphic replacement of aragonite to calcite and mimetic replacement of calcite by dolomite.