Carbonate microfacies and sedimentary environment of the Middle Jurassic Buqu Formation in the Gongri area, eastern part of the Qiangtang basin, Tibet, China. Geological Bulletin of China

In the present paper, the Middle Jurassic Buqu Formation section containing asphaltum vein is studied in the Gongri area, eastern part of Qiangtang basin, Tibet，nine main types of carbonate micro-facies are distinguished in the deposits. They are lime marl, lamellar power-micrite limestone, calcarenite, pellet micrite-sparite packstone，oncoid lump packstone，bioclastic packstone, bioclastic wackstone, oosparite grainstone, bioclastic line marl. According to microfacies assemblage and sedimentary structure, carbonate rock of Buqu Formation mainly form three sedimentary environments: inner ramp, middle ramp and deep ramp. Four sedimentary cycles are recognized in the Buqu Formation, which constitue of a transgressive sequence, which is composed of entire sea-level cyclic sequence.