Abstract:

China Cretaceous Continental Scientific Drilling (CCSD) in the Songliao Basin, called SK1 project, collected 20902 m of Sifangtai Formation which correspond to middle to late Campanian. The borehole got a highly continuous core section with recovery of 97.5%，that is the most complete and precise sedimentary records up to now in the basin. Thicknesses of the description can be as thin as 25 cm for the interbedding sequences. We described in cmscale the sedimentary sequence, lithology, lithofacies and cyclic stratigraphy at the drilling spot. Eleven lithotypes were recognized in the section. Sedimentary facies are predominantly meandering river and lacustrine that can be subdivided into ten microfacies including point bar, natural levee, crevasse splay, crevasse channel, floodplain, flood lake, nearshore bar，mudstone of still water, and turbidite. The whole sequence is composed of 174 meterscale cycles (sixthorder cycle), 43 fifthorder cycles, 13 fourthorder cycles and 2 thirdorder cycles. Centimeter scale description of the section revealed some previously unknown horizons such as special kind of mudstone, favorable sand reservoir of the formation. The new found evidences are very important for us to interprete basin evolution features such as lake oxic and the reservoircap rock assemblages in shallow stratigraphy. That is to say, the scientific drilling provides us with powerful insight in to the basin. Researchers who are interested in the basin can do their reasonable analysis about the basin based on the precise original materials of the paper.

Key words: Songliao Basin, SK1, Sifangtai Formation, sedimentary facies, sedimentary sequence, cyclostratigraphy