Microbialites and Environmental Change at the Permian-Triassic Boundary: An Overview

摘要

Carbonate microbialites that formed directly after the end-Permian mass extinction are widespread in low to mid latitudes, especially abundant in the Tethys Ocean. Current biostratigraphic constraints indicate that some begin slightly before the Permian-Triassic boundary (PTB), others after, suggesting diachroneity of base of microbialites, to be confirmed. PTB microbialites are mostly stromatolites and thrombolites. Most thrombolites are extensively recrystallised with the constructing elements poorly preserved. Identification of possible cyanobacteria is limited to coccoid structures sparsely distributed in largely sparitic (often partly dolomitised) structures, but coccoid structures are not proven to be organic. Nevertheless, there seems little doubt that the majority of PTB microbialites were organic, from their constructional architecture. In most cases they have sharp margins in contact with sediment, so the overall macrofabric is preserved.