Abstract:

There is a set of high frequency cycles with lithological combination of purple red mudstone, grey siltstone and gypsiferous mudstone developing in the Kongdian Formation of Jiyang Depression.By using logging data, well logging, core observation and elemental geochemistry methods, this paper researched the deposition mechanism of high frequency cycles of the Kongdian Formation in Jiyang Depression.The research results show that the cyclic sedimentation record of Kongdian Formation in Jiyang Depression consist of color meter scale cycle, graded meter scale cycle, non-graded meter scale cycle and consist of 6 types of lithofacies assemblages which include 23 kinds of lithology combinations.The cyclic sedimentation record can be divided into 276 cycles, with the maximum thickness being 29.6m, the minimum thickness being 1.48m, and average thickness being 6.28m.Fisher diagrams and the spectrum analysis of logging curves reveal that the precession cycle is 19.2-23.4 ka, slope cycle is 39.1-51.4 ka, and eccentricity cycles is 95.3-403.1 ka.They are consistent with the period of ultra short term cycles, short-term cycle and medium-term cycles, respectively.So it is confirmed that the cyclic sedimentation record was controlled by the Milankovich cycle.In addition, it was also influenced by paleo-climate, sedimentary medium conjugate concussion and material supply.Finally, the cyclic-sedimentation dynamic model during low/high-stand period of Kongdian Formation in Jiyang Depression is established, and the original sedimentary dynamics and ancient environment of the cyclic sedimentation record under the control of Milankovich cycle are discussed.

Key words: high frequency cycle, deposition mechanism, Kongdian Formation, Palaeogene, Jiyang Depression