Abstract:

The Cretaceous-Palaeocene strata in the Simao Basin consists of the Mangang Formation (K₁m), the Pashahe Formation (K₁p), the Mengyejing Formation (K₂me) and the Denghei Formation (E₁d), which are primarily composed of sandstone and mudstone. Based on the geochemical research into detrital rocks of 19 pieces of samples from ErguanzhaiHepingzhai-Bashahedaoban section and 17 pieces of samples from drilling hole SHK4 in Mengyejing deposit of Jiangcheng, three conclusions have been drawn which are presented as follows. Firstly, in theses samples, δCe vs. δEu, δCe vs. ∑REE, CIA vs. Th/U, CIA vs. Th/Sc show no correlation, which imply that the Cretaceous-Palaeocene clastic rocks are mainly controlled by source region rather than chemical weathering and oxidationreduction conditions. Secondly, the distribution patterns of rare earth elements are basically the same; LREE/HREE ratios are high; Eu negative anomalies are evident, indicating the same source region of the Cretaceous-Palaeocene sediments with little mantle material adding. The rocks are mainly pro-granite felsic, and the parent rock debris comes predominately from the upper crust which is in accordance with the features displayed by the Hf-La/Th,La/Sc-Co/Th,REE-La/Yb,Hf-Co-Th discrimination diagrams. Thirdly, during the deposition of Mengyejing and Denghei Formations, a sudden rise of CaO content, Gd content, ICV, (Gd/Yb)N  ratio demonstrates that the provenance area is in an rapid uplift and erosion stage. The research provides a geochemical basis for the provenance of Cretaceous-Palaeocene strata in the Simao Basin.

Key words: Simao Basin, Cretaceous-Palaeocene, detrital rock, geochemistry, provenance property