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川黔湘交境早寒武世“变马冲组”为一套陆源碎屑岩沉积，是在三角洲环境中形成的．该组相当于一个Ⅱ型三级层序，由陆棚边缘体系域、海侵体系域和高水位体系域组成，分别代表了三角洲发育、萎缩和再发育的３个演化阶段．陆棚边缘体系域期，发育河流相、三角洲前缘相和前三角洲相，以三角洲前缘相为主；海侵体系域期，发育三角洲前缘相和前三角洲相，以前三角洲相为主；高水位体系域期，发育三角洲平原相、前缘相和前三角洲相，以三角洲平原相为主．研究区西北部的秀山古岛是主要物源区，由此向东南呈现出水体渐深，沉积物渐细的变化趋势．
The trans-Cambrian “Qianmachong Formation” of Sichuan-Guizhou-Xiangshan is a set of terrigenous clastic sediments that formed in a delta environment. This group is equivalent to a type Ⅱ tertiary sequence and is composed of marginal system tract, transgressive system tract and highstand system tract, which respectively represent three evolution stages of delta development, atrophy and re-development. The marginal system tract, the developed fluvial facies, the delta front facies and the former delta facies are dominated by the delta front facies. In the transgressive system facies, the delta front and the former delta facies are developed, while the former delta facies dominated. In the high water system tract, the delta plain, the frontal facies and the former delta facies develop mainly in the delta plain. The Xiushan ancient island in the northwestern part of the study area is the main source area, thus showing the trend of gradual deepening and sediment thinning toward the southeast.