Sedimentary facies and coal-bearing property of the Lower Cretaceous strata of Chuanba area in Coqen Basin,Tibet

The Coqen Basin has recently become one of the important areas of mineral exploration in Tibet, and the Chuanba area in northern Coqen Basin is the prospective area for coal resources. The lower Cretaceous strata in Chuanba area consist in upward succession of Zelong Group, Duoni Formation and Langshan Formation. On the basis of the outcrop section sedimentary facies analysis and the lithofacies type summarization in combination with regional data analysis, the lower Cretaceous strata can be divided into 7 sedimentary facies, i.e., neritic muddy shelf, carbonate platform, mixed platform, tidal flat, braided river delta, fan delta and braided river. Zelong Group, composed of pyroclastic rocks, fine conglomerate, pebbly sandstone and sandstone, develops fan delta sedimentary facies. Duoni Formation, composed of fine conglomerate, sandstone, siltstone, mudstone, limestone, carbon mudstone and coal, develops neritic muddy shelf, mixed platform, braided river delta and braided river facies. Langshan Formation, composed of limestone, mudstone, siltstone and fine stone, develops tidal flat, mixed platform and carbonate platform sedimentary facies. The study of coal accumulating process based on an analysis of sedimentary environment showed that the interdistributary bay of braided river delta plain in Duoni Formation was the main coal-forming environment. The Agesang-Chuanba area and its eastward extensional area are the main zones of coal accumulation in the study area.