西藏措勤盆地川巴地区下白垩统沉积相及含煤性研究

措勤盆地是西藏近年来矿产勘查的重要地区之一,其北部川巴地区是目前的煤炭资源调查远景地区。川巴地区下白垩统由下而上可划分为则弄群、多尼组和郎山组。在对川巴地区下白垩统露头剖面沉积特征研究的基础上,结合区域地质资料,共识别出浅海泥质陆棚、碳酸盐岩台地、混积台地、潮坪、辫状河三角洲、扇三角洲和辫状河7种沉积相。则弄群岩性主要为火山碎屑岩、细砾岩、含砾粗砂岩、砂岩,发育扇三角洲相;多尼组岩性主要为细砾岩、含砾粗砂岩、砂岩、泥岩及灰岩,夹炭质泥岩和薄煤层,发育辫状河、辫状河三角洲、混积台地和浅海泥质陆棚相;郎山组岩性主要为灰岩,夹细砂岩、粉砂岩及泥岩,发育潮坪、混积台地和碳酸盐岩台地相。基于沉积相分析的聚煤规律研究,指出川巴地区主要成煤环境为多尼组辫状河三角洲平原分流间湾,阿格桑至川巴一线及其以东一带地区,是本区主要的聚煤作用带。

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.