Study On Microbial Carbonates Of The Ediacaran In Southwestern Sichuan And Northwestern Tarim

South China Plate is at the same latitude as the Tarim Plate.They are both in similar depositional environment in the Ediacaran period.This paper focuses on the depositional characteristics of the microbial carbonate rocks in the Tarim Plate and South China Plate through microscope,high resolution scanning electron microscopy,cathodoluminescence and geochemical analysis.The research further discussed the depositional model of microbial carbonate rocks.The depositional model of stromatolite is discussed according to the texture of stromatolites,including layered,wavy,columnar,and cone.There are two different types for the depositional model of stromatolite.One is in situ and the other is ex-situ.The microbial structure of micrite carbonate thrombolite is carbonate lump.And the sparry carbonate cement is spread among the micrite carbonate lump.The microbial structure of sheath-like thrombolite is filamentous extending micrite carbonate.The deposition patterns of the two types of thrombolite are similar: rock-forming microorganisms can form microbial communities.Micrite carbonate particles can be formed by microbial agglutination and adsorption.The microbial reef is enriched in pores.In diagenesis,sprite carbonate cement fills pores.The microbial structure of cavity thrombolite is micrite carbonate particles.There are splendid carbonate cements.They both multi-phase crystallized inside and outside the boundary of micrite carbonate minerals.The genetic model is more inclined to the origin of ex-situ deposition.The internal cavity may be caused by independent bacterial body cavities or microbial holes.The botryoidal structure thrombolite form different sizes hemispherical convex,wavy cross section lace.The model of botryoidal structure could be described as follows.Microbial-bonded limestone formed during the interaction of microorganisms under the flat environment.There were a large number of pores inside the reef.The aragonite or high-magnesium calcite formed inward from the edge of the pores.The microbial-bonded limestone and encrustation received the quasi-synchronous dolomitization.During the burial stage,hydrothermal fluid was infiltrated into the pores forming the botryoidal structure core which was composed of saddle dolomite and striped pyrite.