Characteristics, genetic mechanism and hydrocarbon accumulation of inverted structures in the Doseo Basin, Chad

Abstract

Based on two-dimensional/three-dimensional seismic and logging data, combined with the analysis of low-temperature thermochronology data, the unconformity surface characteristics and the patterns and dynamic mechanisms of inverted structures in the Doseo Basin in the Central and West African rift systems are systematically analyzed. Seismic profiles reveal two key inversion unconformable surfaces in the basin, i.e. the T₅ interface within the Upper Cretaceous and the T₄ interface at the top of the Cretaceous, which control the development of inverted structures in the basin. Four types of inverted structures, i.e. fault-associated, thrust, fold, and back-shaped negative flower, are identified. Spatially, they form six inverted structural belts trending in NE-NEE direction. The thermal history simulation of apatite fission track reveals two rapid cooling events in the late Late Cretaceous (85–80 Ma, cooling by 15 °C) and the Eocene–Oligocene (30–40 Ma, cooling by 35 °C), corresponding respectively to the formation periods of the T₅ and T₄ interface. The dynamics analysis of structural inversion indicates that the structural inversion in the Late Cretaceous was controlled by the subduction and long-range compression within the Tethys Ocean in the north of African Plate, while the structural inversion in the Eocene–Oligocene was drived by the stress transmission from the African–Eurasian collision. The two events were all controlled by the continuous tectonic regulation of the intracratonic basin by the evolution of the Tethys tectonic domain. The two periods of structural inversion enhanced the efficiency of oil and gas migration by controlling the types of traps (anticline and fault-related traps) and fault activation, precisely matching the hydrocarbon generation peaks of the Lower Cretaceous source rocks in the Late Cretaceous and Eocene, thereby controlling the formation of large-scale oil and gas reservoirs in the Doseo Basin. This geological insight provides a critical basis for the theoretical research on the evolution and hydrocarbon accumulation of inverted structures in discrete strike-slip rift systems.