Sedimentary tectonic pattern of Wufeng and Longmaxi Formations in the northern margin of Sichuan Basin, South China

ABSTRACT

Organic-rich black shales in the Sichuan Basin from the Upper Ordovician and Lower Silurian are considered excellent source rocks and unconventional reservoirs of hydrocarbons in South China. The Wufeng and Longmaxi Formations in the Micangshan – Dabashan areas of the northern margin of Sichuan Basin were taken as the research objects. The purpose of this study is to reconstruct the sedimentary tectonic pattern of the Wufeng and Longmaxi Formations in the study area. First, the stratigraphic framework correlation and sedimentary facies analysis of Wufeng and Longmaxi Formations in the study area were carried out. Then, Mo/TOC and Al-Co[EF]×Mn[EF] geochemical indicators were used to identify the degree of water restricted during the deposition period. It was found that the thickness of black shale was relatively small near the uplift area. However, far away from the uplift area, from west to east, the black shale thickened and the TOC content increased gradually, which were controlled by the upwelling of continental margin and intracontinental depression. The results show that: (1) At the front edge of Micangshan, during the deposition period of Wufeng Formation, Fucheng and Qiaoting profiles were located in the intersection area of upwelling formed by two kinds of monsoon, which led to the long-term influence of upwelling in this area. The sedimentation period of Longmaxi Formation was mainly affected by ‘Xixiang Rise’, which led to the uplift of Wangcang and Nanjiang areas into islands. (2) At the front edge of Dabashan and Western Hubei – Eastern Chongqing areas, the Wufeng Formation presented a tectonic pattern of alternating uplift and depression. Due to the continuous compression of the Cathaysian Block from southeast to northwest, the Shizhu – Wuxi areas continued to subside during the deposition period of Longmaxi Formation, and the black shale was quite thick.

KEYWORDS:

• Wufeng–Longmaxi Formations
• Upper Ordovician-Lower Silurian
• upwelling
• sedimentary tectonic pattern
• Sichuan Basin

Highlights

(1) During the deposition period of the Wufeng Formation, the influence of upwelling was obvious in the coastal area of the front edge of Dabashan.

(2) The Wufeng Formation in the northern margin of Sichuan Basin presented a tectonic pattern of alternating uplift and depression, with relatively small range of uplift and depression.

(3) During the deposition period of Longmaxi Formation, the Shizhu area was characterized by a deep water restricted environment, while the Chengkou-Wuxi area was affected by the seasonal upwelling of the continental margin.

(4) The distribution of TOC content was obviously controlled by sedimentary tectonic pattern.

Acknowledgments

Thanks for the help of Sinopec Exploration Company in the process of drilling data collection.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

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Additional information

Funding

This work was supported by the National Science and Technology Major Project of China (grant no. 2017ZX05005003-007) and the National Natural Science Foundation of China (grant no. 41602153). We also appreciate the support of Project supported by the discipline innovation team of Liaoning Technical University (grant no. LNTU20TD-14, LNTU20TD-30);National Natural Science Foundation of China [41602153];Project supported by discipline innovation team of Liaoning Technical University [LNTU20TD-14, LNTU20TD-30];