Characteristics of the Milankovitch cycles and lake-level changes in the Ganchaigou Formation of the Kaitemirike area, western Qaidam.

At present, the research on Milankovitch cycles in the Qaidam Basin is generally based on the discussion of the shallow-water sedimentary facies strata in the piedmont, but it remains to be explored whether the Milankovitch cycle characteristics are recorded in the deep-water facies strata. In this study, the Milankovitch sedimentary cycles of deep lacustrine strata in the Kaitemilik area in the west of the basin have been discussed through spectral analyses and filter analyses of natural gamma logging curves of the upper Ganchaigou Formation (N₁)and the upper part of lower Ganchaigou Formation (E₃²) in Well K2. The results show that the stratigraphic cycles of the upper Ganchaigou Formation (N₁) and the upper part of lower Ganchaigou Formation (E₃²) in this area have a good correlation with the earth's orbital cycle parameters of Milankovitch, indicating that the astronomical orbital cycle had a significant effect on the stratigraphic deposition in this area. On this basis, the Fischer plot and the sedimentary characteristics of the strata indicate that the lake level near the upper and lower boundary of Ganchaigou Formation (~38.1-32.8 Ma) experienced a relatively long period of fluctuation. The upper part of lower Ganchaigou Formation was formed in the rising stage of the lake level, which was mainly controlled by the eccentricity cycle in the Milankovitch cycle, and the climate was relatively warm and humid, corresponding to the high stage of lake level. The upper Ganchaigou Formation was deposited in the falling stage of the lake level, which was mainly controlled by the axial slope cycle in the Milankovitch cycle, and the climate was relatively cold and dry, corresponding to the low stage of lake level.