Abstract
The Upper Benue trough of Nigeria consists of basins and horsts characterized by numerous structural features. Detailed study of one of the basins revealed sets of “centimetric”, riedel type “en-echelon” NE-SW trending strike slip faults contained in a number of brittle and ductile shear zones characterizing the basement/sediment boundary. Structural analysis suggests that the Moku sub-basin has been pulled apart along a releasing bend in between NE – SW strike slip faults and that three principal axes of stress were acting on the sub-basin during its formation. The maximum stress (1) with orientation 34/304 was responsible for the fault overlap (basin length), whereas the minimum stress (σ_3) with orientation 18/201 controlled the fault separation (basin width). These suggest a qualitative model showing the Moku sub-basin as a separate basin, which must have coalesced with adjacent sub-basins. Deposition of Bima sediments in the basin was closely controlled by tectonism. The immature B1 sediments are restricted mostly to the faulted margin of the basin. The more matured B2 and B3 sediments are distributed around the less disturbed areas.
Highlights
Most intracontinental basins are tectonically initiated and bounded by faulted rocks; striations on these rocks reveal different sense of movements that depict various fault types
The geometry and size of a fault-bounded basin depend on the bounding faults, normal faulting on both sides of a basin would result in a graben, while strike-slip faults along releasing or restraining bends could on a regional scale develop into pull-apart basins
It overlies the Precambrian shield of the West African mobile belt and is geographically divided into three regions, from southwest to northeast; the Lower, Middle and Upper Benue Trough which corresponds to different geological features (Allix and Popoff, 1983; Benkhelil, 1989; Maurin et al, 1986)
Summary
Most intracontinental basins are tectonically initiated and bounded by faulted rocks; striations on these rocks reveal different sense of movements that depict various fault types. The Benue Trough is an intracratonic Cretaceous basin about 1,000 kilometres in length and 50 to 100 kilometres wide elongated in the NE-SW direction (Guiraud et al, 1989) It overlies the Precambrian shield of the West African mobile belt and is geographically divided into three regions, from southwest to northeast; the Lower, Middle and Upper Benue Trough which corresponds to different geological features (Allix and Popoff, 1983; Benkhelil, 1989; Maurin et al, 1986). Field evidence indicates that a set of deep-seated faults is superimposed on the axial high and controlled the tectonic evolution of the Benue Trough (Benkhelil, 1989). Benkhelil (1989, 1986, 1982) and Maurin et al (1986) proposed that the basins and horsts structure of the Benue Trough were developed along releasing and restraining bends of the faults
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