Comparative Study On Stratigraphy And Sedimentary Facies Of The Xujiahe Formation In Sichuan Basin And The Yanchang Formation In Ordos Basin

Sichuan Basin and Ordos Basin are located to the south and north of QinlingMountains respectively. Both of basins are the important oil-gas-bearing resources.The Xujiahe Formation of the Upper Triassic Series in Sichuan Basin is an importantexploration target layer. Ordos Basin, as the best-preserved, and has the mostabundant Mesozoic fossil energy resources among oil and gas-bearing inland basinsin Western China. The Yanchang Formation of the Triassic Series in Ordos Basin hasbeen studied for a long time and is very rich in oil and gas. Based on outcrop data,well data and seismic data, this thesis systematically studies and compares thesequence stratigraphy and sedimentary facies of Xujiahe Formation and YanchangFormation, explores the differences and similarities of the different basins in basindevelopment, sedimentary evolution and sequence division, etc. It will not onlyprovide new ideas and new momentum for further exploration for the oil field, butalso enrich and develop the terrestrial lacustrine sedimentary theory.Based on the sequence stratigraphy and sedimentology, various types ofsequence boundaries at different levels are recognized using the outcrops data,well log data and seismic data. According to those boundaries, the author dividesthe sequence of both formations. The Xujiahe Formation in Sichuan Basin isdivided into3super long-term cycles,6long-term cycles,21medium-termcycles and hundreds of short-term cycles. The Yanchang Formation in OrdosBasin is divided into5super long-term cycles,18long-term cycles and hundredsof medium-term cycles. The study found that although Xujiahe Formation andYanchang Formation were regarded as the continental basins in late Triassic andlocated to each side of Qinling Mountains, there are huge disparities between thetwo in sequence development. In particular, there are major differences in theduration of the two layers, the sequence division scheme (especially the superlong-term cycles), the average length of the long-term cycles, and the main typesof sequence boundaries. In addition, there are some differences in tectonicbackground, development time, the sequence overlapping style, and so on. As for the sedimentary, both Xujiahe Formation in Sichuan Basin andYanchang Formation in Ordos Basin were mainly developed in continentalsedimentary. Xujiahe Formation in Sichuan Basin is the outcome ofquasi-foreland basin background. The distribution pattern of sedimentary faciesbelt is strictly controlled by the tectonic movement. It mainly developed alluvialfan-braided river-braided river delta-lakes depositional system. YanchangFormation in Ordos Basin is a product of typical depression lacustrine basinwhich mainly developed braided river-braided river delta-lakes depositionalsystem, and its lacustrine facies is stable and deposited for a wide range.Finally, this paper analyzes and contrasts comprehensively the nature ofeach basin, their tectonic evolution, their sequence stratigraphy, their sedimentarysystems， and the main factors controlling the basin development of SichuanBasin and Ordos Basin.