| Geological exploration in Yangxia region began in the 1990 s. After many years of exploration, several gas reservoirs which reserves more than one hundred billion cubic natural gas, and other petroleum structures had been found in our region,and Jurassic Ahe Formation was the important target formation. A systematic research in provenance and sedimentary facies of Ahe Formation in our area based on geology, seism and logging data is significant for the exploration potential evaluation and favorable exploration targets screening.On the basis of the outcrop and core analyses, logging, seism and laboratory testing data, this paper did comprehensive study in the provenance and the types of sedimentary facies and marks, establishing facies models.The result of our study shows that the sediment of Ahe Formation in the study area comes from recycled orogenic zone, most likely from the Tianshan Mountains, and that the Ahe Formation is deposited in a braided river delta environment which can be further divided into braided river delta plain and front, including braided channels, alluvial plain, underwater distributary channels, underwater interdistributary bays and subaqueous mouth bars. In the early time when lower Ahe Formation was deposited, environment in the study area was almost the braided delta plain, and most of the sediment was the braided channel coarse sandstone and conglomerate. The characteristics of middle Ahe Formation were similar to that of lower segment, but the range of the braided river delta reduced compared with the invironment in the early time. In the later Ahe Formation the range of the braided river delta continued to shrink, especially the plain, and the environment included plain braided channels, front underwater distributary channels, underwater interdistributary bays and subaqueous mouth bars. Though braided river delta was the main environment in the whole stage of Ahe Formation, the range of it continuously shrank, with continuous lake invasion. |
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