Characteristic of Upper Paleozoic Sequence Stratigraphy in East-southern Ordos Basin

In east-southern Ordos basin, the Styles of third-order sequence boundary in Upper Paleozoic strata within can be districted as seven styles, including regional unconformity, structural system transformation surface, regional regression surface, channel erosion surface, regional leakage surface, coal bed, overlay-style transformation surface between limestone bottom and strata. Based on the analysis of sequence boundary characteristic, the Paleozoic stratigraphy, from Benxi Formation to Shihezi Formation, can be divided into two second-order sequences, namely the one (SS1) includes Benxi Formation, Taiyuan Formation and Shanxi Formation, the other (SS2) includes Shihezi Formation. Every second-order sequence is dominated by tectonic, including regional transgression and regression cycles. The second-order sequence can be divided into 11 third-order sequences, that is two third-order sequences (SQ1 and SQ2) in Benxi Formation, one (SQ3) in Taiyuan Formation, two (SQ4 and SQ5) in Shanxi Formation, six (SQ6 and SQ11) in Shihezi Formation. In which, the sequences of SQ1-SQ5 are marine and marine-continental sediments, while SQ6-SQ11 are lacustrine sediments on continental. With the characteristic of sequence stratigraphy, the sequence-filling model in east-southern Ordos Basin has been established in this paper, which has a guiding significance for further research in sedimentary system evolution, reservoir formation and gathering for gas.