Keywords: 
• sequence classification /
• Ordos basin /
• transgressive coal formation

Abstract: The identification of sequence boundaries is the key point for sequence stratigraphic classification. Both the higher-order sequences and the units within the sequences are bounded with the key sediments or isochronous surfaces. It is common that regional erosion and event sedimentation, resulting from transgression occurred in epicontinental sea basin infill. So, water flow washing surface originated from the overspreading and shrinking of water over a large area, the large scale switchover surfaces between depositional systems and the filling surface of incised valley caused by rejuvenated river and flow washing during basin inversion are the important surfaces in classifying sequences. The forming of a coal seam is a special event that could be the end or start of an event and then could become the basis for sequence classification. It is classified into nine third-order sequences and three second-order sequences from Benxi formation to Xiashihezi formation. The four-order sequence of epicontinental sea basin is composed of two units, that is, the Transgressive System Tract (TST) and Highstand System Tract (HST).Both the infill sequence during basin inversion and that of continental basin are composed of three parts: Low system tract, water invasion system tract and highstand system tract. Transgressive coal forming and coal forming under  event are the essential features of Late Palaeozoic coal accumulation in Ordos basin.