The Sequence Stratigraphic Division and Depositional Environment of the Jurassic Yan’an Formation in the Pengyang Area, Southwestern Margin of the Ordos Basin, China

Lianfu Hai, Caixia Mu, Qinghai Xu, Yongliang Sun, Hongrui Fan, Xiangyang Xie, Xiangcheng Wei, Chao Mei, Haibin Yu, Walter Manger and Jun Yang
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Lianfu Hai: Mineral Geological Survey Institute of Ningxia Hui Autonomous Region, Yinchuan 750021, China
Caixia Mu: Mineral Geological Survey Institute of Ningxia Hui Autonomous Region, Yinchuan 750021, China
Qinghai Xu: School of Geosciences, Yangtze University, Wuhan 430100, China
Yongliang Sun: Mineral Geological Survey Institute of Ningxia Hui Autonomous Region, Yinchuan 750021, China
Hongrui Fan: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Xiangyang Xie: School of Geology, Energy, and Environment, Texas Christian University, Fort Worth, TX 76129, USA
Xiangcheng Wei: Mineral Geological Survey Institute of Ningxia Hui Autonomous Region, Yinchuan 750021, China
Chao Mei: Mineral Geological Survey Institute of Ningxia Hui Autonomous Region, Yinchuan 750021, China
Haibin Yu: Mineral Geological Survey Institute of Ningxia Hui Autonomous Region, Yinchuan 750021, China
Walter Manger: Department of Geosciences, University of Arkansas, Fayetteville, AR 72701, USA
Jun Yang: School of Geosciences, Yangtze University, Wuhan 430100, China

Energies, 2022, vol. 15, issue 14, 1-14

Abstract: Coal and organic-rich shale in the Yan’an Formation in the southwestern margin of the Ordos Basin are widely developed, which is an important fact for oil and gas exploration in China that has been widely explored for a long time. In this paper, detailed sequence division and sedimentary environment analyses of the Yan’an Formation in the Pengyang area on the southwestern margin of the Ordos Basin were conducted using field outcrops, drilling cores, logging, wavelet transform and organic geochemistry. The results showed that the succession consists of some units with distinctly different characteristics. Based on the petrographic assemblage and transform wavelet characteristics, the Yan’an Formation in this area can be divided into a long-term cycle, five medium-term cycles, and eleven short-term cycles, among which coal and carbonaceous shale were mainly developed in the short-term cycles I 2 , III 1 , III 2 , V 1 and V 2 . Coal and organic-rich mud shale have been developed in the Yan’an Formation and plant debris in mudstone and coal is common, indicating the development of swamps and shallow water-covered depressions in this area. The sandstones showed parallel bedding, cross-bedding and scours, thus indicating fluvial deposits. The saturated hydrocarbon gas chromatographic parameters of mud shale showed that the pristane/phytane (Pr/Ph) ratio is 2.24–6.22, the Ph/nC18 ratio is 0.15–0.93, and the Pr/nC17 ratio is 0.97–2.78, supporting the finding that the organic matter has mainly originated from terrestrial sources.

Keywords: Ordos Basin; Pengyang; Yan’an Formation; sequence classification; peat environment (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: 2022
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