重庆地区晚二叠世煤系层序地层与聚煤作用

重庆地区上二叠统包括龙潭组/吴家坪组和长兴组,主要发育海陆过渡相(海湾-泻湖-潮坪)及浅海碳酸盐沉积,其中龙潭组和吴家坪组为同期异相沉积。通过对区内钻井剖面及露头剖面的分析,在本区上二叠统中识别出区域性构造不整合面和沉积相转换面等地层界面,并将上二叠统划分为2个三级层序。基于近海煤盆地的背景,研究区厚煤层常靠近初始海泛面发育。总体来看,近海含煤盆地三级层序以海侵体系域聚煤最好。

Sequence stratigraphy and coal accumulation of Late Permian coal measures in Chongqing

Late Permian in Chongqing includes Longtan Formation (Wujiaping Formation) and Changxing Formation, mainly develops transitional facies(bay milieu(lagoon deposit)—tidal flat facies) and shallow marine carbonate facies. Longtan Formation and Wujiaping Formation are contemporaneous, but have different facies. We have conducted the sequence stratigraphic analysis on Late Permian in this area on the basis of boreholes and outcrop sections. Three sequence boundaries are identified which are represented by regional tectonic unconformities at the bottom of the Upper Permian, sedimentary facies reversal surface at the base of the No.16 coal in the Longtan Formation, and the event stratigraphic boundary at the top of the Upper Permian. Two third-order sequences are subdivided in the Upper Permian. Because the study area is located in the paralic basin, the thick coals tend to be developed near the transgressive surface. In overall, in the third-order sequences of paralic setting, the thickest coal seams tend to be developed in the transgressive system tract.