Microbial dolomite crusts from the carbonate platform off western India
Version of Record online: 27 AUG 2003
Volume 50, Issue 5, pages 819–830, October 2003
How to Cite
Rao, V. P., Kessarkar, P. M., Krumbein, W. E., Krajewski, K. P. and Schneider, R. J. (2003), Microbial dolomite crusts from the carbonate platform off western India. Sedimentology, 50: 819–830. doi: 10.1046/j.1365-3091.2003.00574.x
- Issue online: 27 AUG 2003
- Version of Record online: 27 AUG 2003
- Manuscript received 28 January 2002; revision accepted 26 March 2003.
- Carbonate platform;
- dolomite stromatolites;
- late Pleistocene;
- microbial processes;
- western India
Abstract The occurrence of Late Pleistocene dolomite crusts that occur at 64 m depth on the carbonate platform off western India is documented. Dolomite is the most predominant mineral in the crusts. In thin section, the crust consists of dolomitized microlaminae interspersed with detrital particles. Under scanning electron microscopy, these laminae are made up of tubular filaments or cellular structures of probable cyanobacterial origin. Dolomite crystals encrust or overgrow the surfaces of the microbial filaments and/or cells; progressive mineralization obliterates their morphology. Well-preserved microbial mats, sulphide minerals (pyrrhotite and marcasite) and the stable isotope composition of dolomite in the crusts indicate hypersaline and anoxic conditions during dolomite formation. The crusts are similar to dolomite stromatolites, and biogeochemical processes related to decaying microbial mats under anoxic conditions probably played an important role in dolomite precipitation. The dolomite is therefore primary and/or very early diagenetic in origin. The dolomite crusts are interpreted to be a composite of microbial dolomite overprinted by early burial organic dolomite. The results of this study suggest that a microbial model for dolomite formation may be relevant for the origin of ancient massive dolomites in marine successions characterized by cryptalgal laminites. The age of the crusts further suggests that the platform was situated at shallow subtidal depths during the Last Glacial Maximum.