渝南关坝地区上三叠统须家河组沉积特征

以渝南关坝地区上三叠统须家河组露头为研究对象,进行岩石学、沉积学分析,结果表明,须二段、须四段和须六段以灰白色中–粗粒长石岩屑砂岩为主,分选中等–较好,磨圆为次棱角状–次圆状,孔隙式胶结,大型斜层理及底冲刷面等沉积构造发育;须三段和须五段以灰–灰黄色泥页岩为主,水平层理等沉积构造发育。垂向上,须家河组"二元结构"非常发育,底层沉积厚度远大于顶层;横向上,砂岩被底冲刷面分割为透镜体及楔状体,并连续叠置成巨厚层–厚层砂体。综合研究表明,研究区须家河组须二段、须四段和须六段为辫状河三角洲前缘沉积,须三段和须五段为前辫状河三角洲沉积。

Sedimentary characteristics of upper Triassic Xujiahe formation in Guanba area of southern Chongqing

By taking the outcrop of the upper Triassic Xujiahe formation in Guanba area of southern Chongqing as the research object,the petrological and sedimentological analyses were carried out.The results show that the 2~(nd),4~(th) and 6~(th) member of the upper Triassic Xujiahe formation are mainly composed of grey-white medium to medium-coarse feldspathic lithic sandstones,with medium-well sorting,sub sharp-sub circle roundness pore cementation,large-scale inclined beddings and erosional basal surfaces.The 3~(rd) and 5~(th) member of the upper Triassic Xujiahe formation are mainly composed of grey and grey-yellow mud shale with horizontal bedding.In vertical direction,the'dual structure'is very developed in the Xujiahe formation,characterized by the thickness of the bottom layer being much larger than the top layer.In horizontal direction,sandstones are divided by erosional basal surfaces to lens-shaped and wedge-shaped sand body,which form large sand bodies by continuous superimposition.The comprehensive study shows that the 2~(nd),4~(th) and 6~(th) members of Xujiahe formation in the study area are braided delta front sedimentation,and the 3~(rd) and 5~(th) members of Xujiahe formation are braided river delta sedimentation.