Lower Triassic stromatolites in Luodian County, Guizhou Province, South China: evidence for the protracted devastation of the marine environments.

摘要: Stromatolites are one of the oldest and most intriguing organosedimentary deposits. In contrast to stromatolites Precambrian Early Ordovician, Phanerozoic equivalents occurred episodically under specific conditions. A group previously undescribed in composition occur Lower Triassic (Olenekian) at Dajiang section Luodian region Guizhou Province, South China. We described textures these with aim determining genetic mechanisms revealing nature interactions between micro-organisms marine environments. Mesoscopic features show that consist several sets stacked slices, they embedded alternating beds fine coarse microsphere packstones include aggregates microspheres, forming grapestones lumps. Microscopically, spar- dolomite-infilled microspheres (average diameter, 100 μm), micrites, peloids, small-sized pyrite framboids 5.8 μm) fenestrae. Micrite-dominant intercalations accentuate laminated a mesoscopic level laterally continuous micrite-rich parts surrounding interstromatolites, indicating simultaneous, widespread deposition layers. The associated micrites were products situ microbial activity, probably sulphate-reducing or anoxygenic phototrophic bacteria, which led formation unusual stromatolites. Even during protracted period harsh conditions, carpets deposited intermittently on their surroundings severely anoxic/sulphidic presence subtle but important vertical variations texture provide record temporal changes conditions geobiologically critical intervals.