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Abstract

AAPG Bulletin, V. 105, No. 5 (May 2021), P. 919-944.

Copyright ©2021. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/11182019167

Thermal history reconstruction from apatite fission-track analysis and vitrinite reflectance data of the Bongor Basin, the Republic of Chad

Lirong Dou1, Renchong Wang2, Jingchun Wang3, Dingsheng Cheng4, Paul F. Green5, Xiaodong Wei6

1China National Oil and Gas Exploration and Development Company, Ltd., Beijing, People’s Republic of China; Key Laboratory of Exploration Technologies for Oil and Gas Resources, College of Resources and Environment, Yangtze University, Ministry of Education, Wuhan, Hubei, People’s Republic of China; [email protected]
2China National Oil and Gas Exploration and Development Company, Ltd., Beijing, People’s Republic of China; [email protected]
3China National Oil and Gas Exploration and Development Company, Ltd., Beijing, People’s Republic of China; [email protected]
4Research Institute of Petroleum Exploration and Development, PetroChina, Beijing, People’s Republic of China; [email protected]
5Geotrack International Pty., Ltd., West Brunswick, Victoria, Australia; [email protected]
6CNPC Geophysical Company, Ltd., Zhuozhou, Hebei, China; [email protected]

ABSTRACT

The Bongor Basin in southern Chad is one of the Cretaceous–Paleogene rift basins developed on the Precambrian crystalline basement and has been confirmed as a petroliferous basin in the last decade. Less than 400 m of Cenozoic unconsolidated sediments are separated by an unconformity from an underlying section of Lower Cretaceous units, in turn separated by another unconformity from underlying Precambrian basement. In addition, there is a locally low-angle unconformity within the Cenozoic section. A synthesis of apatite fission-track analysis data in four wells from the basin reveals two cooling episodes from Late Cretaceous to early Paleocene (beginning between 75 and 60 Ma) and mid-Miocene, respectively. The results suggest that regionally synchronous cooling is a likely scenario. The first exhumation between 75 and 60 Ma affected the whole basin, and the magnitude of uplift and erosion was approximately 1100–1250 m across the whole basin. In contrast, the second exhumation during the Miocene affected mainly the northern part of the basin while the magnitude was weak and could not be detected in the southeast of the basin. Potential trapping structures, for example, fault blocks and synsedimentary anticlines, formed prior to and inverted anticlines as a result of the first cooling phase of exhumation (strong compressional inversion) and were available for hydrocarbon migration and accumulation during the main phase of hydrocarbon generation. The Miocene exhumation was less pronounced and had weak or no impact on the hydrocarbon generation and accumulation.

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