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Title:: Characteristics of Milankovitch Cycles in Deep Water Contourites—A Case Study of Upper Ordovician Zhaolaoyu Formation in Fuping Area of Shaanxi, China

Author(s):: FENG Bin; LI Hua; HE You-bin; SU Shuai-yi; 1. School of Geosciences, Yangtze University, Wuhan 430100, Hubei, China; 2. Research Center of Sedimentary Basin, Yangtze University, Wuhan 430100, Hubei, China; 3. Key Laboratory of Exploration Technologies for Oil and Gas Resources of Ministry of Education, Yangtze University, Wuhan 430100, Hubei, China

Keywords:: sedimentology; deep water deposit; Milankovitch cycle; contour current; orbital period; Zhaolaoyu Formation; Ordos Basin

Abstract:: The Upper Ordovician Zhaolaoyu Formation in Fuping area of Shaanxi develops the deep water autochthonous deposits, contourites and gravity-flow deposits, and the sedimentary environment is from the edge of the deep water basin to deep water slope. On the basis of the section measured in field and the lithofacies features, combined with Milankovitch theory, astrostratigraphy, paleoceanography, paleoclimatology and Fischer diagram, the relationships between the intensity of the contour current and changes of paleoclimate, sea level and paleosalinity were studied. The results show that Fischer diagram can reflect sea level changes objectively and accurately; the vertical combination of different grades of cycle in the deep water sediments and contourites records the characteristics of Milankovitch, showing that small scale cycles are superimposed in the vertical direction in the form of 1∶4 or 1∶5 to form the larger level of cycles; the contour current intensity is affected by Milankovitch cycle, which is reflected in the multi-cycle of weak-strong-weak change; the activity cycle of contour current is about 0.1 Ma.