Temporal and spatial variations of redox conditions in the middle Triassic Chang 7 member of the Yanchang formation, Ordos Basin, North China

doi:10.1016/j.marpetgeo.2025.107565

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	Temporal and spatial variations of redox conditions in the middle Triassic Chang 7 member of the Yanchang formation, Ordos Basin, North China
	Liu, Hanlin 1; Huang, Yuangeng 2; Zhao, Xiangdong 3; Wang, Wei 4; Qiu, Xincheng 2; Qiu, Zhen 1; Han, Juan 5; Shen, Zhen 1; Li, Yujie 6; Hua, Ganlin 7; Chen, Zhong-Qiang 2; Zou, Caineng 1
	2025-12-01
发表期刊	MARINE AND PETROLEUM GEOLOGY
ISSN	0264-8172
卷号	182 页码:12
通讯作者	Huang, Yuangeng(yghuang@cug.edu.cn) ; Zou, Caineng(zcn@petrochina.com.cn)
摘要	The Chang 7 member of the lower Yanchang Formation, situated within the Ordos Basin, dates back to the Ladinian stage of the late Middle Triassic. These strata, notable for their organic-rich black shales, serve as a key lacustrine hydrocarbon-bearing unit in China. The Chang 7 shales encompass a wide array of vertebrate, invertebrate, and plant fossils, offering valuable perspectives on the ecological recovery of lacustrine systems following the end-Permian mass extinction (EPME). Redox conditions within the water column play a critical role in influencing organic matter deposition and shaping lacustrine biodiversity. Nonetheless, prior investigations into redox dynamics during the formation of the Chang 7 shales have predominantly relied on single redox proxies or isolated sampling locations, which restrict a comprehensive understanding of the redox evolution across the entire Ordos Basin. For these reasons, this study employs framboidal pyrite size statistics, pyrite sulfur isotopes, major and trace element concentrations, and lipid biomarkers of five Ladinian-age wells from both deep and shallow sedimentary facies to rebuilt up evolutional patterns of redox conditions in the Basin. Our results reveal remarkable difference of redox conditions amongst deposition periods of three submembers. Notably during the formation of the Chang 73 submember (lower Chang 7 member), the Ordos paleo-lake exhibited progressively declining oxygen levels, transitioning from dysoxic to anoxic conditions in deeper facies. Dysoxic conditions prevailed in the deep facies, with transient anoxic conditions emerged. By contrast, evidence indicates that the Chang 72 submember (middle Chang 7 member) was primarily deposited under fluctuating dysoxic-oxic conditions, while the Chang 71 submember (upper Chang 7 member) was formed in predominantly oxic environments. Collectively, the Chang 7 member shows remarkable organic matter preservation, with an average total organic carbon (TOC) content of 11.02 wt%, and peak TOC levels reaching 35.8 wt % in the Chang 73 submember. These findings indicate that by the Ladinian, the Ordos paleo-lake had already achieved a high level of productivity, capable of sustaining a fully developed, trophically complex lacustrine ecosystem in the aftermath of the EPME. The relatively oxygen-depleted bottom waters during deposition of the Chang 73 submember provided favorable conditions for the preservation of the abundant and diverse biota. This comprehensive analysis offers valuable insights into the lacustrine paleoenvironmental conditions and biotic recovery following the EPME, and provides important clues for the formation environment of source rocks.
关键词	Yanchang formation Pyrite framboids Element geochemistry Biomarker Organic matter
DOI	10.1016/j.marpetgeo.2025.107565
关键词[WOS]	ORGANIC-MATTER ; DEPOSITIONAL ENVIRONMENT ; TECTONIC EVOLUTION ; ANOXIC EVENT ; BLACK SHALES ; RICH SHALES ; SEDIMENTS ; PRISTANE ; PROXIES ; OIL
收录类别	SCI
语种	英语
资助项目	National Natural Science Foundation of China[42222209] ; National Natural Science Foundation of China[42377205] ; National Natural Science Foundation of China[42302347] ; GuangDong Basic and Applied Basic Research Foundation[2024A1515012584] ; GuangDong Basic and Applied Basic Research Foundation[THEMSIE04010101]
项目资助者	National Natural Science Foundation of China ; GuangDong Basic and Applied Basic Research Foundation
WOS研究方向	Geology
WOS类目	Geosciences, Multidisciplinary
WOS记录号	WOS:001583590000001
出版者	ELSEVIER SCI LTD
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.205/handle/311034/24903
专题	中国科学院古脊椎动物与古人类研究所
通讯作者	Huang, Yuangeng; Zou, Caineng
作者单位	1.PetroChina Res Inst Petr Explorat & Dev, Beijing 100083, Peoples R China 2.China Univ Geosci Wuhan, State Key Lab Geomicrobiol & Environm Changes, Wuhan 430078, Peoples R China 3.Chinese Acad Sci, Inst Vertebrate Paleontol & Paleoanthropol, Key Lab Vertebrate Evolut & Human Origins, Beijing 100044, Peoples R China 4.Chinese Acad Sci, Nanjing Inst Geol & Paleontol, State Key Lab Palaeobiol & Stratig, Nanjing 210008, Peoples R China 5.Beijing Res Inst Uranium Geol, Beijing 100029, Peoples R China 6.China Univ Min & Technol, Coll Geosci & Survey Engn, Beijing 100083, Peoples R China 7.China Petr Enterprise Assoc, Beijing 100120, Peoples R China
推荐引用方式 GB/T 7714	Liu, Hanlin,Huang, Yuangeng,Zhao, Xiangdong,et al. Temporal and spatial variations of redox conditions in the middle Triassic Chang 7 member of the Yanchang formation, Ordos Basin, North China[J]. MARINE AND PETROLEUM GEOLOGY,2025,182:12.
APA	Liu, Hanlin.,Huang, Yuangeng.,Zhao, Xiangdong.,Wang, Wei.,Qiu, Xincheng.,...&Zou, Caineng.(2025).Temporal and spatial variations of redox conditions in the middle Triassic Chang 7 member of the Yanchang formation, Ordos Basin, North China.MARINE AND PETROLEUM GEOLOGY,182,12.
MLA	Liu, Hanlin,et al."Temporal and spatial variations of redox conditions in the middle Triassic Chang 7 member of the Yanchang formation, Ordos Basin, North China".MARINE AND PETROLEUM GEOLOGY 182(2025):12.