Analysis of aeromagnetic data: Application to Early-Late Cretaceous events in parts of Lower Benue trough, Southern Nigeria

Abstract

The study of the sedimentary sequence in parts of the Nigerian lower Benue trough has been carried out to understand the sedimentary thickness and its structural framework using high resolution aeromagnetic gridded data. It represents background investigation for targeting new mineralization zones and probable locations for detailed petroleum system analysis in the study area. The first order vertical derivative and the horizontal gradient magnitude of the reduced to the magnetic equator anomaly map were derived while edge detection techniques such as analytic signal, tilt derivative and horizontal derivative of tilt were implemented. Quantitative interpretations such as three dimensional Euler deconvolution, spectral analysis, and Source Parameter Imaging were applied to the residual magnetic intensity anomaly map. The results obtained show the Abakaliki Albian Asu River Group, the Caniacian Awgu shale and the Agala / Amasiri sandstones of Agubala and Ngbo to be severely intruded by rocks suspected to be basic or ultrabasic plutonic rocks. The basement topography, the sedimentary thickness of about 3800 m characterized by moderate volcanic intrusions, and the presence of a prominent anticlinorium for hydrocarbons preservation in Okpoto and environs call for a detailed petroleum system analysis. Structures hosting Lead-Zinc-Copper mineralization were identified in Ishieke, Ekeriegwe, Ugbuloke, and Abakaliki during an onsite mapping of notable structures. The mineralized structures in the areas are generally of dual origins − hydrothermal and volcanic. The hydrothermal minerals are connected to lineament intersections and occur as veins and veinlets in sedimentary rocks and feldspars while volcanic related ones occur as grains and with gangues in volcanic rocks.