Sequence Stratigraphy of Late Paleozoic Coal-Bearing Measures in Northeastern Ordos Basin

By the identified the regional unconformity, sedimentary system conversion, tectonic stress conversion and exposed surface, the authors divided the Late Paleozoic coal-bearing measures in northeastern Ordos basin into seven 3rd sequences. Based on the study, the ternary texture of epicontinental sequence indicate that they also consist of lowstand systems tract, transgressive systems tract and highstand systems tract. Some fluvial sandbodies developed in the northern Ordos basin characteristic by filling of valley-incised in the lowstand systems tract that is sheet sandstone such as Jinci sandstone, Qiaotou sandstone and Beichagou sandstone. The position of coal seams in the sequence framework has relationship to the transformation time of sea level change, and develops mainly at the lower part of transgressive systems tract in epicontinental sequence and the upper part of highstand systems tract in nonmarine sequence.