A Study On The Sedimentary Environment Of Xiannao Cave In Tangjiahe Section Of Drum Township In

Micang Mountain Uplift, which is located in the boundary of Sichuan Province and Sharxi Province of northern Sichuan basin, is a geological subdivision of north margin of Yangtze Platform. The Cambrian strata and lithology in Micang Mountain are well exposed and great changes. The lower Cambrian, which consists of the Kuanchuanpu Formation, Guojiaba Formation, Xiannudong Formation, Yanwangbian Formation and Kongmingdong Formation, comprises mostly clastic rock, carbonate and hybrid sediment. Xiannudong Formation and its adjacent stratas comprise micrite, multi-types of oolitic grainstone, microbial limestone, rudstone and calcareous sandstone or mud. Eleven sedimentary facies were divided according to the macro-micro features such as geometry, sedimentary structure and the changing grainsize in the Xiannudong Formation and its upper or lower stratas of Micang Mountain area. These eleven facies were grouped into four sedimentary facies, which represents neritic shelf, platform marginal slope, platform marginal mound and shoal and restricted platform environment singly by analyzing the environment which sedimentary facies characterizes and the relationship among the all facies. There are also some kinds of sub-environment had found after studying vertical sedimentary facies sequence. The total depositional environment of the Xiannudong period of early Cambrian in Micang Mountain was interpreted as the old-land-closed rimmed platform to marginal slope to shelf environment with hybrid carbonate sediment which was linked the land.The bottom of Xiannudong Formation was considered as the platform marginal slope environment because of the regional background research. Then the different types of sedimentary environment in different depth were represented by simulative four sedimentary facies. As a result, the perspective of deformation structures in southwest Micang Mountain, which means deformed slump caused by gravity factors on the background of syndepositional fault and the formation of the particular analogous-nodular limestone and slump rudstone, has been discussed via the deformed ribbon, collapsed rock and slope mud mound. In addition, three periods microbe buildups, such as slope algae-thrombolytic mound, platform marginal algae-thrombolytic mound and back platform marginal archaeocyath mound, in the different sedimentary environment and in different depth of water in Xiannudong Formation of Micang Mountain, have been summarized by contrasting the global microbes and their distribution. Hence, the difference of surviving and breeding among the different microbes and the models of the mounds they build have been established.