Abstract:

This paper researched coal-bearing strata depositional systems of Paleogene System in Qiongdongnan basin. The main depositional systems in the study area are alluvial fan(fan delta)abyssal fan system, shore marine and middle-deep lake and turbidite fan system, braided stream-braided channel deltasubsea apron system, tide flatlagoon system, offshore-epeiric sea-turbidite fan system, etc. Among the above depositional systems, the braided stream-braided channel delta-subsea apron system and tide flat-lagoon system have undergone great coal-forming actions. With high resolution sequence stratigraphy theory and technology, the middleand shortterm basal levels were identified. The main boundary types of shortterm basal level are erosion and the overlying lag sediments, soil sediments and peatification event sediments, microfacies and lithofacies types or facies group changes in vertical, abrupt interfaces in well logging curves, etc. In the Paleogene strata of Qiongdongnan basin, the shortterm basal level cycle types, controlled by different genetic feature boundaries,are deepeningupward asymmetric shortterm basal level cycle（type A）, shallowing-upward asymmetric shortterm basal level cycle（type B） and symmetric shortterm basal level cycle（type C）.

Key words: basal level cycle；short term；Paleogene System, China seas