The present paper deals, in detail, with the stratigraphy, lithology, sedimentary facies and evolution in the first member of the Upper Triassic Xujiahe Formation in Hexidong, Beibei, Chongqing in the light of field outcrop observation, typical profile measurement, sample collection and laboratory analysis. The lithology in the first member of the Xujiahe Formation consists of grey and brownish grey fine-grained sandstone and dark grey, grayish black shale and silty mudstone intercalated with thin coal seams in which carbonized plant remains and siderite nodules are observed. The sandstones are composed of feldspathic lithic quartz sandstone and feldspathic litharenite with large-scale trough cross-bedding, parallel bedding, horizontal bedding, and ripple lamination. The first member of the Xujiahe Formation is interpreted to be deposited in the shallow-water delta environment including the sedimentary subfacies such as the delta plain, delta front and prodelta subfacies, and the sedimentary microfacies such as the distributary channel, swamp, interdistributary bay and channel mouth bar microfacies. The vertical sequences indicate the evolution of sedimentary environments from the delta plain through the delta front to the prodelta and finally to the delta plain.%对重庆北碚上三叠统须家河组一段地层特征、岩性特征、沉积相及演化规律进行了系统研究.研究区须一段以灰色、褐灰色细砂岩及深灰色、灰黑色页岩、粉砂质泥(页)岩夹薄煤层为主,见炭化植物碎片及菱铁矿结核,砂岩类型主要为长石岩屑石英砂岩及长石岩屑砂岩,大型槽状交错层理、平行层理、水平层理及沙纹层理发育.综合分析认为研究区须一段属浅水三角洲沉积环境,包括三角洲平原、三角洲前缘和前三角洲3种亚相,可进一步划分出水上(水下)分支河道、沼泽、支流间湾、河口砂坝等沉积微相.其垂向序列反映了沉积环境三角洲平原-三角洲前缘-前三角洲-三角洲平原的演化过程.
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