Tectono-sedimentary characteristics in the area with distributed normal faults: Lower Cretaceous Prosopis Formation in the northern slope of Bongor Basin, Chad

Abstract

Based on an integrated database (e.g., core observations, well logs, and seismic data), the characteristics of depositional systems, as well as the response to tectonics, are systemically delineated in the Prosopis Formation of the Lower Cretaceous at Bongor Basin, Chad. The tectonic setting of this study area experienced multiple, active sub-basins with narrow-spaced intra-basinal normal faults. The multiple normal faults formed in the initial rifted stage leading to the development of a corridor-shaped basin consisting of small-scale sub-basins. As this basin is attracting increased attention due to further hydrocarbon exploration, deciphering the process of sediment partition, especially in the initial rifted stage, would provide a further understanding of the tectono-sedimentary evolution in lacustrine rift basins. Based on core observations, well logs, and three-dimensional seismic data, fan-delta and sub-lacustrine-fan depositional systems are widely developed in this area. Two depositional systems (e.g., fan-delta and sub-lacustrine-fan) and three categories of slope break belts (single-faulted, step-faulted, and flexure types) have been identified. Overall, during the initial rifted stage, the formation of multiple normal faults mainly dominates the geomorphology and sediment supplies that generate the spatio-temporal features of depositional systems in semi-closed lacustrine basins. Climatic perturbations, furthermore, regulated the composition of sediments (coarse versus fine deposits). For the economic perspective, this study highlights the significance of fault systems in further hydrocarbon exploration during the initial rifted stage of lacustrine basins.