Investigation of Magnetotelluric Responses to Crustal Structure Beneath the Bida Basin, North Central Nigeria

The Bida Basin is a northeast-southwest trending intracratonic sedimentary basin straddling Niger and Kogi States, North Central Nigeria, whose crustal structure and basement depth configuration remain incompletely mapped, limiting understanding of its hydrocarbon and mineral resource potential. This study investigates the electromagnetic response of the Earth's crust beneath the Bida Basin using the magnetotelluric geophysical method, which measures natural electromagnetic field variations to derive subsurface electrical resistivity structure. Broadband magnetotelluric data were acquired at 24 stations distributed along two crossing profiles spanning the full width of the basin. Time series processing using the robust remote reference method was applied to extract impedance tensor and tipper vector responses in the period range 0.01 s to 1000 s. Two-dimensional inversion of the TE and TM mode impedances was performed using the OCCAM regularization algorithm. Results reveal a low-resistivity sedimentary package of 5 to 9 km thickness overlying a resistive basement, with basement depth increasing from the basin margins toward the axis. A moderately conductive mid-crustal anomaly at 15 to 25 km depth beneath the central basin is interpreted as a zone of partial melt or saline fluid infiltration associated with the Mesozoic rifting episode that formed the basin. The study provides new constraints on total sediment thickness and basement topography relevant to petroleum systems analysis in the Bida Basin. Keywords: magnetotellurics, crustal structure, Bida Basin, subsurface resistivity, geophysics