Estimation of the sediment thickness beneath the Southern Benue Trough in Nigeria by using gravity and borehole data

Abstract

Mapping the sediment-basement morphology represents a crucial part of the geophysical exploration of oil, gas, and mineral resources. In this study, authors estimated the sediment thickness in the area covering the Southern Benue Trough in Nigeria and parts of the Cameroon Volcanic Line using a high-resolution tailored gravity model together with sediment and bedrock samples taken from 113 logged boreholes. A 3-D inversion of the residual gravity data is done by applying a recently developed time-efficient gravity inversion software to determine a 3-D depth structure of the basement relief after regional-residual gravity separation. The estimated depths of the sediment-basement based on a 3-D gravity data inversion are compared with the measured sediment thickness data from drilling profiles to optimally select the gravity inversion parameters, particularly the mean sediment depth, and density contrast. Our numerical result indicates that the sediment thickness within the Southern Benue Trough study area and parts of the Cameroon Volcanic Line vary from 0.8 to 5.5 km, with a prevailing southwest trend of increasing sediment thickness while decreasing eastward. This trend closely mimics the known geological structure of the study area and generally agrees with localized estimates of the sediment thickness from previous studies. Moreover, the Bouguer gravity map of the study area exhibits a spatial pattern that indicates an existence of a high-density material, which could have led to the shallowing of sediments over and along the Abakaliki Anticlinorium. Based on these findings, the authors argued that these magmatic structures could influence hydrothermal fluid migration and might have entrapped enough sediments suitable for the maturation of mineral resources over time.