Abstract:

China Cretaceous Continental Scientific Drilling (CCSD) in the Songliao Basin, called SK1 project, collects 53207 m of members 35 of the Upper Nenjiang Formation which correspond to the middle Campanian. The borehole gets a highly continuous core section with recovery of 948％，that is the most complete and precise sedimentary records obtained up to now in the basin. The minimum thickness of the subdivided layers is generally 2 to 5 cm for the whole drilling sequence. We describe  the sedimentary sequence in cmscale, revealing lithology, lithofacies and cyclic stratigraphy at the drilling spot. Nine lithotypes are recognized in the section. Sedimentary facies are predominantly lacustrine, delta and fluvial, which can be subdivided into fifteen microfacies including channellag deposit, point bar, natural levee, crevasse splay, crevasse channel, flood plain, flood lake, distributary mouth bar, subaqueous distributary channels, subaqueous natural levee, subaqueous interdistributary bay, distal bar, mudstone of still water, adjacent shore sand bar and lake turbidite. The whole sequence is composed of 417 meterscale cycles (sixthorder cycle), 94 fifthorder cycles, 26 fourthorder cycles and 3 thirdorder cycles. Centimeterscale depiction of the coresection revealed some previously unknown horizons such as special kind of mudstone, dolomite and volcanic ash of the formation. The red beds in the fifth member of Nenjiang Formation, being an important case study of midCretaceous continental red beds found in the northeast Asia, will become a standard of potential formulation section for the studies of late Cretaceous global oxygenenriched events. The detailed description of the third and fourth members of Nenjiang Formation is significant for their further exploration in the Songliao Basin.

Key words: Songliao Basin, SK1n, the Late Nenjiang Formation, sedimentary facies, sedimentary sequence, cyclostratigraphy, Cretaceous Campanian