松辽盆地松科1井上白垩统嫩江组三～五段沉积序列厘米级精细刻画:岩性·岩相·旋回

Centimeter-scale sedimentary sequence description of Upper Cretaceous Nenjiang Formation(upper numbers 3-5): Lithostratigraphy,facies and cyclostratigraphy,based on the scientific drilling(SK1) borehole in the Songliao Basin

中国白垩纪大陆科学钻探松科1井连续取嫩江组三～五段岩心长532.07m,岩心收获率为94.8%,是迄今获取的最连续完整的沉积记录。文章对此进行了厘米级沉积地质描述(分层厚度2～5cm)。嫩三～五段沉积时期与坎潘阶中期对应。通过对松科1井嫩三～五段岩心的精细描述,揭示其岩性-岩相-旋回的沉积序列及其过程。嫩三～五段识别出9种岩石类型,发育曲流河、湖泊和三角洲3种沉积相,河道、堤岸、河漫、三角洲前缘和浅湖5种沉积亚相以及河床滞留、点砂坝、天然堤、决口扇、决口水道、河漫滩、河漫湖、河口砂坝、水下分流河道、水下天然堤、分流间湾、远砂坝、浅湖静水泥、临滨砂坝、浊流15种沉积微相。在岩相序列上共识别出9种共417个米级旋回(六级旋回),94个五级旋回,26个四级旋回,3个三级旋回。连续的组段厘米级刻画为高精度沉积过程研究提供了可能,嫩江组五段厘米级刻画识别出的陆相红层为全球白垩纪富氧事件研究提供了可能的立典剖面,嫩江组三、四段的厘米级刻画为松辽盆地黑帝庙油层的研究与开发提供了不可替代的精准地质资料。

China Cretaceous Continental Scientific Drilling （CCSD） in the Songliao Basin, called SIK1 project, collects 532.07 m of members 3 - 5 of the Upper Nenjiang Formation which correspond to the middle Campa nian. 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, distrihutary mouth hat, subaqueous distributary channels, subaqueous natural levee, subaqueous inter-distributary bay, distal bar, mudstone of still water, adbacent 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 depi〈tion of the core-section revealed some previ- ously 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 Neniiang Formation is significant for their further exploration in the Songliao Basin.