Print this pageStructural and Tectonic Evolution of the Garoua Basin in Cameroon, Central Africa, as Derived from Geological and Seismic Data
The Garoua basin is the eastward branch of the Benue Trough to the north into Cameroon, Central Africa. It is an asymmetric WNW-ESE oriented trough. Previous studies based mostly on gravity and magnetic data have concluded to an uplifted Moho under this basin due to lithospheric extension (Kamguia et al, 2005). The mantle uplift has also been alluded in surrounding regions (Dorbath et al., 1986; Poudjom Djomani, 1993; Poudjom Djomani and Diament, 1997 and Noutchogwé, 2004).
The present paper using both geological as well as 2D seismic data (more than 1000 km), is the first attempt to illustrate the exhumation of the Garoua basin in Late Cretaceous due to the uplift of the upper mantle in response to isostatic compensation.
Structurally, this basin is bounded by normal faults trending N100°E, probably Early Cretaceous in age, intersected by younger faults trending N10°-20°E with sinistral wrenching. Physiographically, the Garoua basin is a plain with disseminated numerous mounts of flat lying sedimentary rocks of Lower to Middle Cretaceous in age. The dominant sedimentary facies are indurated conglomeratic to coarse grained alluvial sandstones with siliceous cement often rich in iron oxides and in places numerous intercalations of reddish ferruginous sandstones are observed. The western parts of the basin exhibits many volcanic necks of Cainozoic age (Bea et al, 1990; Ngounouno et al, 1997; Ngounouno et al, 2005) whereas veins of basic rocks are observed to the east.
Average seismic velocities observed in the Garoua basin are abnormally higher (more than 5,000 m/sec at depths of 2,000 m) than those indicated at the same depths in the Logone Birni basin to the north (3,000 m/sec) and the neighbouring Doba basin to the east (3,400 m/sec). Moreover, some lateral discrepancy is deciphered from average seismic velocities which are much higher in the eastern part ( 5,200 m/sec at depths of 2,000 m) than in the western part of the basin.
These data although attributable to important compaction and primary porosity reduction by iron oxides enrichment of the sedimentary pile estimated at 4,000 metres, are compatible with the interpretation of that the Garoua basin was exhumed in Late Cretaceous as a consequence of an uplifted Moho under the basin , with more thinning of the crust observed to the west.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil