NIGPAS OpenIR
Depositional environment of Middle Triassic organic-rich shales in the Ordos Basin, Northwest China
Zhao, Xiangdong (赵向东)1,2,3; Wang, Wei (王伟)1,2; Xie, Guwei4,5; Pan, Songqi6; Jarzembowski, Edmund A.1,2,7; Zheng, Daran (郑大燃)1,2,8
2021-07-21
Source PublicationGEOLOGICAL JOURNAL
ISSN0072-1050
Pages12
Abstract

The Middle Triassic Tongchuan Formation in the Ordos Basin of northwestern China is a typical lacustrine deposit. A major component of this formation is thick layers of organic-rich shales that are probably a potential hydrocarbon source and preserve the earliest known Mesozoic-type lacustrine ecosystem. The exact depositional environment of the shales in the Tongchuan Formation, however, remains unknown. To address this question, we carried out high-resolution carbon (delta C-13(org)) and sulphur (delta S-34(py)) isotope analysis as well as undertook total organic carbon (TOC)/pyrite contents and pyrite morphology investigation, and framboidal pyrite size measurements in shales of the Bawangzhuang section of the southern Ordos Basin. Remarkably high TOC (23 +/- 9%) and pyrite (7 +/- 3%) contents were obtained from the shales, which indicate a large amount of organic carbon and pyrite burial during shale deposition. Framboids are the dominant pyrite morphology in the pyrite crystals and show large and variable mean diameters (7.0 +/- 1.7 mu m to 14.3 +/- 6.8 mu m) across the section, indicating oxic-dysoxic bottom water during shale deposition. delta C-13(org) and delta S-34(py) revealed narrow and less variable values, ranging from -31.8 parts per thousand to -28.1 parts per thousand, and -4.1 parts per thousand to 4.9 parts per thousand, respectively. The delta C-13(org) values suggest balanced and consistent carbon cycles. Integrated with pyrite content and morphological patterns, consistent delta S-34(py) values probably demonstrate a relatively open environment for the formation of sedimentary pyrite, and thus a shallow chemocline that was quite close to the water-to-sediment interface during shale deposition. Overall, the organic-rich shales of the Tongchuan Formation were probably deposited under oxic-dysoxic bottom-water conditions. Shallow chemocline depth combined with moderately high sedimentation rate and high primary productivity may have played crucial roles in the deposition and formation of the organic-rich shales in the Tongchuan Formation. The shallow chemocline also facilitates the fossil preservation in a lacustrine environment.

KeywordMiddle Triassic Ordos Basin organic-rich shales primary productivity redox condition
DOI10.1002/gj.4215
Indexed BySCI
Language英语
WOS KeywordSILURIAN HOT SHALES ; YANCHANG FORMATION ; VOLCANIC ASH ; GEOCHEMICAL CHARACTERISTICS ; ISOTOPE CHEMOSTRATIGRAPHY ; SEDIMENTATION-RATE ; SULFUR ISOTOPES ; BLACK-SEA ; CARBON ; PYRITE
Funding ProjectStrategic Priority Research Program of the Chinese Academy of Sciences[XDB26000000] ; Strategic Priority Research Program of the Chinese Academy of Sciences[XDA19050101] ; National Natural Science Foundation of China[42072036] ; National Natural Science Foundation of China[41688103] ; CAS President's International Fellowship Initiative (PIFI) ; Fundamental Research Fund from the China National Petroleum Company[2018D-500805] ; Leverhulme Emeritus Fellowship
WOS Research AreaGeology
WOS SubjectGeosciences, Multidisciplinary
WOS IDWOS:000675115100001
Funding OrganizationStrategic Priority Research Program of the Chinese Academy of Sciences ; National Natural Science Foundation of China ; CAS President's International Fellowship Initiative (PIFI) ; Fundamental Research Fund from the China National Petroleum Company ; Leverhulme Emeritus Fellowship
PublisherWILEY
Document Type期刊论文
Identifierhttp://ir.nigpas.ac.cn/handle/332004/38433
Collection中国科学院南京地质古生物研究所
Corresponding AuthorWang, Wei (王伟)
Affiliation1.Chinese Acad Sci, Nanjing Inst Geol & Palaeontol, State Key Lab Palaeobiol & Stratig, Nanjing 210008, Peoples R China
2.Chinese Acad Sci, Ctr Excellence Life & Paleoenvironm, Nanjing 210008, Peoples R China
3.Univ Chinese Acad Sci, Beijing, Peoples R China
4.Northwest Univ, Dept Geol, Xian, Peoples R China
5.PetroChina Co Ltd, Changqing Oilfield Branch, Inst Explorat Dev & Res, Xian, Peoples R China
6.PetroChina, Res Inst Petr Explorat & Dev, Beijing, Peoples R China
7.Nat Hist Museum, Dept Earth Sci, London, England
8.Univ Hong Kong, Dept Earth Sci, Hong Kong, Peoples R China
First Author AffilicationNanjing Institute of Geology and Palaeonotology,CAS
Corresponding Author AffilicationNanjing Institute of Geology and Palaeonotology,CAS
Recommended Citation
GB/T 7714
Zhao, Xiangdong ,Wang, Wei ,Xie, Guwei,et al. Depositional environment of Middle Triassic organic-rich shales in the Ordos Basin, Northwest China[J]. GEOLOGICAL JOURNAL,2021:12.
APA Zhao, Xiangdong ,Wang, Wei ,Xie, Guwei,Pan, Songqi,Jarzembowski, Edmund A.,&Zheng, Daran .(2021).Depositional environment of Middle Triassic organic-rich shales in the Ordos Basin, Northwest China.GEOLOGICAL JOURNAL,12.
MLA Zhao, Xiangdong ,et al."Depositional environment of Middle Triassic organic-rich shales in the Ordos Basin, Northwest China".GEOLOGICAL JOURNAL (2021):12.
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