The Characteristics of Lithofacies and Depositional Model of Fine-Grained Sedimentary Rocks in the Ordos Basin, China

Zhenhong Chen, Xincheng Li (), Hao Chen, Zhennan Duan, Zhen Qiu, Xiaoqian Zhou and Yuguang Hou
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Zhenhong Chen: PetroChina Exploration and Development Research Institute, Beijing 100083, China
Xincheng Li: Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China
Hao Chen: PetroChina Exploration and Development Research Institute, Beijing 100083, China
Zhennan Duan: SINOPEC Gudong Geological Research Institute, Dongying 257000, China
Zhen Qiu: PetroChina Exploration and Development Research Institute, Beijing 100083, China
Xiaoqian Zhou: Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China
Yuguang Hou: Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China

Energies, 2023, vol. 16, issue 5, 1-22

Abstract: In order to clarify the characteristics of fine-grained sedimentary lithofacies and the depositional models in lacustrine environments of the Chang 7 Member of the Upper Triassic Yanchang Formation in the Ordos Basin, we focus on the lacustrine lithofacies classification and controlling factors. Based on the typical field sections of the southern Ordos Basin, combined with the methods of organic geochemical analysis, polarizing microscopic observation, XRD and elemental geochemistry, we summarize the main controlling factors of the lithofacies under different sedimentary environments and establish the sedimentary model under different sedimentary backgrounds. Results show that the Chang 7 Member of the Ordos Basin includes six major lithofacies types, i.e., quasi-laminated clayey shale facies, blocky silty mudstone facies, quasi-laminated silty shale facies, laminated silty shale facies, blocky mixed mudstone facies, and laminated argillaceous siltstone facies. Al 2 O 3 , MgO, CaO, Na 2 O, K 2 O, and SiO 2 are relatively depleted, while TiO 2 , TFe 2 O 3 , and P 2 O 5 are relatively enriched in the Chang 7 2+3 . Meanwhile, the trace elements are relatively enriched in Cd, Cu, Mo, U, and V. The fine-grained sedimentary facies were influenced by various sedimentary environments, such as paleoclimate, redox conditions, productivity and terrigenous input. According to lithofacies types and genetic mechanisms of the Chang 7 Member in the study area, two types of lithofacies assemblages are identified. The rapid rise in lake level during the deposition of the Chang 7 2+3 resulted in an anoxic water column, high productivity, and low terrigenous input under a humid climate and weak-to-moderate weathering conditions. Therefore, clayey shale lithofacies assemblage is developed in the lower Chang 7 Member.

Keywords: lithofacies; sedimentary model; elemental geochemistry; Yanchang Formation; Ordos Basin (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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