Depositional Age, Provenance And Sedimentary Environment Of Madian Formation In Southern North China Craton

There is a set of clastic rock strata composed of phosphorus-containing argillite and breccia between dolomites of Jiudingshan Formation (or the third Member of Sidingshan Formation) of Neoproterozoic Erathem and Houjiashan Formation of second Series of Cambrian. Its depositional age and petrogenesis are still controversial among different scholars. Many stratigraphic names and grouping schemes have been used to the set of strata, such as Fengtai Formation and Yutaishan Formation et al., and the Madian Formation as well as its scheme of four members proposed by Dai et al. is adopted in this thesis.Zircon U-Pb dating results show that the youngest ziron Pb/U ages of M21 and M22 samples from second member of Madian Formation are 637 ± 18Ma and 640 ± 18Ma respectively. Consequently, depositional age of Madian Formation should be younger than 637Ma, and Madian Formation should belong to second Series of Cambrian combined with fossil evidence of third and fourth members.Comparison of U-Pb dating patterns between the second and third member of Madian Formation and basement of North China Craton (NCC) demonstrates that terrigenous sediment to form Madian Formation should mainly come from inside of the NCC. Besides, evidence of grain constituents suggests that provenance of conglomerate of the second member was partially from underlying Neoproterozoic stata of carbonate. Geochemical analyses indicate that shale mainly was from provenance of quartzite sediment while hot-water chemical sediment was insufficient. Shale deposited in oxygen-deficient passive continental margin environment.According to field sedimentary facies and microscopic micro-faces, it is inferred that conglomerate in second Member of Madian Formation might form by carbonate debris flow or turbidite deposition. Madian Formation was in a transgressive systems tract on the whole. The sedimentary facies of first member was marine basin fan, and the second member was marine slope-fan. The third member was characteristic of shelf facies deposits under weakened hydrodynamic conditions below sea-level, where large masses of organic matter start to be preserved for lack of supplement of terrigenous sediment and anoxic environment. The third member indicated the beginning of initial transgression, and deposition of the fourth member was significantly speeding with gradual slide of sediments towards the bottom of the slope under the conditions of continental margin environment.