Research On Sequence Stratigraphy And Sedimentary Facies Of Carboniferous To Lower Permian In The Central Tarim Basin

Central Tarim uplift located in the middle part of Tarim basin, which has a great potential for oil and gas exploration. The predecessors have done some researchs on this area, however, there are still a lot of problems unsolved, especially on the aspects of sedimentary environment and sequence stratigraphy, various concepts are exsit.Guided with the theories and methods of sedimentology, sequence stratigraphy and logging geology, seismic stratigraphy, various kinds of sequence boundaries of regional unconformity, sedimentary environment transforming interface,sequence stacking mode transforming interface and maximum flooding surface has been identified on the basis of the tectonic paleogeomorphology framework,comprehensive outcrop and logging data and seismic profiles materials in Tarim basin. These kinds of boundaries contain two 1st-order, three 2nd-order, and four 3rd-order sequence boundaries, which divide the Carboniferous to Lower Permian into 1 supersequences, 3 tectono-sequences, 7 sequences. The development characteristics of each sequence are controlled by sea-level changes.Based on logging sedimentary facies and outcrop analysis, combining the core observation, well logging, and the testing data of the study area, 6 kinds of mainly developed sedimentary facies have been identified, which are evaporate platform, restricted platform facies, tidal flat facies, meandering river delta, meandering river and shoreside facies. The Carboniferous-lower Permian in the study area is predominantly composed of a set of restricted platform - tidal-flat sedimentary system under marine background. Besides Bachu and Xiaohaizi Fomations in which there contain three sets of marine carbonate, the carboniferous is overall for clastic sedimentary background. The depositional environments change from the marine into continental at the upper Lower Permian, and meandering river delta, meandering river facies are developed. The paleogeography from Carboniferous through Lower Permian has been constructed in the sequence stratigraphic framework, and the depositional evolution is discussed. The control factors of sedimentation include paleogeomorphology, sediment supply, climate, tectonic activity and the tectonic subsidence and sea-level fluctuation, etc. Due to the tectonic framework of central uplift is basicly stable, the influence of aleogeomorphology, sea-level fluctuation, and climate are the most predomiant ones.