Yili Basin Tectonic Evolution And Sequence Characteristics Of The Carboniferous-Permian Strata

Yili Basin displays as a triangle superimposed basin in the West Tianshan tectonic belt. Its eastern part end in the junction of the north and south of Tianshan, and extends westward out of Chines frontier.On the basis of the field investigations and the geochemical analyses ,as well as previous studies by others, the regional geological background and tectonic evolution, as well as the sequence features and the capacity of hydrocarbon-generating in the Carboniferous and Permian are studied in this paper.The Carboniferous continental rift valley in the Yili block was formed by there duction of the oceanic basins to its north and south respectively in the early Carboniferous, and was closed in the late Carboniferous through the intracontinental orogenesis, which resulted in the end of ocean. In early Permian, Yili block experienced the second intracontinental extension alongwith the strong volcanic eruption, which makes the Yili block change to depression by the end of the Middle Permian. Up to late Permian, this region wasfolded with upliftand the lake was disappeared, all of which fixed the present tectonic pattern as we observe today.Combined with the Yili Basin tectonic evolution and the petrologiccharacteristics of the rock assemblages in outcrop, we discerned four long term base-level cycles and nine medium-term base-level cycles from Carboniferous-Permian strata by Cross's high-resolution principles of sequence stratigraphy. Among others, six medium-term base-level cycles have been studied by detailed analyses.Through all the analyses above, we obtained information about organic matter from Yili Basin, including abundances, the types and their maturity. The hydrocarbon-generating capacity of the Carboniferous - Permian strata is proposed as well.