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Estimation of Thickness of Sediments and Delineation of Subsurface Geologic Structures Within Anambra Basins, Southeaster Nigeria Using Spectral Analysis and Euler Deconvolution Techniques on Gravity and Aeromagnetic Data

Abstract

Estimation of thickness of sediments/Depth to the Basement within Anambra Basin South eastern Nigeria using Spectral Depth and Euler techniques on gravity and aeromagnetic data have been carried out. Data were filtered with first vertical derivative to infer lineaments and to elucidate the subsurface geological structure of the study area from the aeromagnetic data. The spectral depth analysis was applied to the residual anomaly of the study area. The result of Spectral analysis reveals three depths sources of shallow, intermediate and deep. The first magnetic layer (shallow depth) could be attributed to the effects of shallow basement materials occur in form of sills or dyke which occurred interstratified within the cretaceous sediment. The second magnetic which is the intermediate depth is probably due to near – surface or shallow basement. The third magnetic sources layer (deeper depth) which is the area of concerned in this study. The depths of 4.58 km and 13.48 km represent the average depth to the intermediate- and deep-seated basement respectively occurred around Odeke. This layer shows the deep estimate depths which could be attributed to effect of sandstone, shale and clay from the study area. The standard Euler deconvolution method was applied to residual magnetic intensity map of the study area. The Euler solutions were obtained for varying Structural Index (SI) values of 0.5 and 1.0 with maximum % tolerance and window size respectively. The result of Euler solutions for structural index agreed with the spectral depth technique. The result of Euler solutions for structural of 0.5 have their depths ranges from 14.0 m to 13090 (0.014 to 13.09 km). For the Euler solutions with structural index of 1.0 depths range from 76.34 m to 13750 (0.076 to 13.75 km) are obtained. Their patter of anomalous source location of Northeast – Southwest coincides with the Pan African Basement trends. The estimated depths provided by the Euler deconvolution and Spectral analysis result will aid in exploitation of the hydrocarbon deposit in the study area.