PRONOUNCED CARBONATE DEPOSITION IN THE EARLY TRIASSIC DIENERIAN SUBSTAGE: WHO WAS THE CARBONATE PRODUCER?

At the Late Permian Mass Extinction (LPME) most marine carbonate producers were heavily affected or even terminated. After the event microbialites have been reported from the Griesbachian from many marine sections, however, without causing substantial thicknesses. The Dienerian in many Tethyan sections, though, is characterized by a huge increase in sedimentation rate due to the deposition of limestone mud, with only minor amounts of siliciclastic input. This is in contrast to the still missing “usual” (skeletal) carbonate producers that have not yet re-appeared after the extinction, and also in contrast to a steeply and constantly rising marine Sr-isotope curve. Peloidal textures observed in many of these Dienerian carbonate deposits indicate a planctic microbial origin of the carbonate mud, although additional inorganic carbonate precipitation in the water column also might have been possible. Thus the environmental conditions seem to have been optimal for a thriving planctic marine microbial biota and microbial carbonate precipitation. This observation/interpretation also indicates a non-acidic ocean, resulting in the accumulation of large amounts of planctic microbial and perhaps also some inorganic carbonate mud.