Geological Characterization of Fractures in the Structural and Tectonic Units of the Atacora Range in North-Western Benin

Abstract

Access to groundwater, particularly in the base zone, is a real problem. Located in the northwest of Benin, the structural and tectonic units of the Atacora chain are composed of fractured sedimentary and crystalline formations. The objective of this study is to dimension fractures on the scale of the Atacora Tectonic Unit and its foreland. The Landsat OLI 09 TIRS images have been processed in order to enhance the linear elements considered as lineaments. The lineaments obtained were compared with high-flow drilling data in order to identify fractures in the lineament network. In total, 417 fractures of various sizes (0.33 - 34.10 km) and orientations (NNE-SSW, NE-SW, ENE-OSO, ESE-ONO, SE-NO, and SSE-NNO) were identified. The distribution of fracture orientations shows a certain heterogeneity of fracturing in the study area. The statistical analysis shows that the fractures are numbered in the ESE-WNW directions: 146 fractures of length between 0.5 - 34.10 km and density between 7.87 × 10 −5 - 2.50 × 10 − 3 km/km 2 ; NE-SW, a total of 121 fractures with a length between 0.335 - 14.41 km and a density between 2.49 × 10 −5 - 1.07 × 10 − 3 km/km 2 ; ENE-OSO, 91 fractures with a length between 0.5 - 14.10 km and density between 3.78 × 10 −5 - 1.04 × 10 − 3 km/km 2 ; and for NNE-SSW, there are 39 fractures with a length between 0.33 - 6.74 km and a density between 2.88 × 10 −5 - 5.01 × 10 − 3 km/km 2 . All the results contribute to a better understanding of fracture networks and the functioning of groundwater in the structural and tectonic units of the Atacora chain.