Deep-water facies and depositional environment in Chang 7 of Yaoqu in the south Ordos basin

In-field detailed sectional records and measurements indicate that 5 major facies have developed in Chang 7 of Yaoqu in the south Ordos basin, including deep-water autochthonous facies, tuffaceous facies, sandy clastic-flow facies, turbidite facies, and slump facies. These facies constitute four vertical combination patterns: A, B, C and D. We comprehensively analyzed the lithologic characteristics, facies combinations, sedimentary structures, and biological remains there. Based on the results, we divided the study area into two major depositional systems: the lake system and the channel-type gravity flow system. The lake system was subdivided into semi-deep lake/deep-lake subfacies, and semi-deep lake/deep-lake mud microfacies. The channel-type gravity flow system was subdivided into proximal channels, distal channels, banks, and front lobes, including 4 microfacies of sandy clastic flow deposits, turbidite deposits, slump deposits, and autochthonous deposits. Section profile analysis shows that the high-quality hydrocarbon source rocks and gravity flow sandbodies in the study area are favorable for the production of excellent lithologic oil-gas reservoirs.