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Abstract

AAPG Bulletin, V. 102, No. 8 (August 2018), P. 1429-1453.

Copyright ©2018. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/1107171616617170

Neoproterozoic–Cambrian petroleum system evolution of the Micang Shan uplift, northern Sichuan Basin, China: Insights from pyrobitumen rhenium–osmium geochronology and apatite fission-track analysis

Xiang Ge,1 Chuanbo Shen,2 David Selby,3 Guozhi Wang,4 Zhao Yang,5 Yongjun Gong,6 and Suofei Xiong7

1Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, 388 Lumo Road, Hongshan District, Wuhan 430074, Hubei, China; Department of Earth Sciences, Durham University, Science Labs, South Road, Durham, DH1 3LE, United Kingdom; [email protected]
2Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, 388 Lumo Road, Hongshan District, Wuhan 430074, Hubei, China; [email protected]
3Department of Earth Sciences, Durham University, Science Labs, South Road, Durham, DH1 3LE, United Kingdom; [email protected]
4Faculty of Earth Sciences, Chengdu University of Technology, No. 1 Erxianqiao Road, Chenghua District, Chengdu 610059, Sichuan, China; [email protected]
5Department of Geology, Northwest University, No. 229 North Taibai Road, Xi’an 710069, Shanxi, China; [email protected]
6Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, 388 Lumo Road, Hongshan District, Wuhan 430074, Hubei, China; [email protected]
7State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Resources and Collaborative Innovation Center for Exploration of Strategic Mineral Resources, China University of Geosciences, 388 Lumo Road, Wuhan 430074, China; [email protected]

ABSTRACT

The Neoproterozoic strata of the Sichuan Basin are a key target for oil and gas. To evaluate the hydrocarbon evolution and its relationship with tectonic events in the Micang Shan uplift, northernmost Sichuan Basin, we apply solid bitumen geochemistry (bitumen reflectance and fluorescence) and Re-Os geochronology.

The geochemistry of the solid bitumen indicates that it is highly mature pyrobitumen that formed contemporaneously with dry-gas generation during oil thermal cracking. The pyrobitumen is enriched in both Re (∼106–191 ppb) and Os (∼3030–5670 parts per trillion). The Re-Os isotope data imply an Early Jurassic date for pyrobitumen formation, which coincides well with age estimates from fluid-inclusion data and basin modeling. The Re-Os date for pyrobitumen formation coupled with previously presented apatite fission-track (AFT) analysis show that exhumation of the Neoproterozoic strata occurred during the Cretaceous in the Micang Shan uplift. This extensive uplift led to the erosion of any potential gas reservoirs and surface exposure of bitumen-bearing Neoproterozoic strata. In contrast, the more southern and central portions of the Sichuan Basin have experienced less severe exhumation and, as a result, Neoproterozoic-sourced gas systems are present. This study shows that, through the combined application of Re-Os and AFT methodologies, the timing of gas generation and subsequent erosion of any potential gas reservoirs in the Micang Shan uplift, northern Sichuan Basin, can be quantified. Moreover, the Re-Os and AFT data illustrate the potential to constrain the timing of gas generation in petroleum systems worldwide.

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