RIFT BASIN STRUCTURE AND DEPOSITIONAL PATTERNS INTERPRETED USING A 3DREMOTE-SENSING APPROACH - THE BARINGO AND BOGORIA BASINS, CENTRAL KENYA RIFT, EAST-AFRICA

Following the 3D remote sensing study of the Bogoria area, Central Ken ya Rift, by GRIMAUD ef al. (1994), a similar morphostructural study al so using SPOT satellite imagery and a Digital Elevation Model (DEM) wa s undertaken for the Baringo - Marigat-Loboi area, directly north of B ogoria. This morphostructural analysis was completed through fieldwork . To begin with, the different types oi tectonic structures were obser ved at various scales in order to determine tile extension mechanisms of the ''Baringo-Bogoria half-graben'', which lies al the intersection of the N 140 degrees Proterozoic Aswa shear zone and the Kenya Rift w hich generally follows a N-S direction, The general structural framewo rk of the Baringo area has been defined, involving three major regiona l tectonic trends: N 0-10 degrees, N 150 degrees, and N 50 degrees, in terference of these trends at different scales within the Baringo area has produced several types of sigmoidal, S- and Z-shaped structures w hich define transverse zones with left-lateral and right-lateral compo nent movements. The combination of these lateral component movements w ith major normal movements on meridian faults is in agreement with a l ocal N 90 degrees direction of extension. These transverse zones seem to have been a major influence on the location of several volcanoes wi thin the Baringo-Bogoria area. These belong to a linear N 0 degrees-tr ending array of Pliocene to Recent volcanoes all located along the rif t axis. These volcanoes show regular spacing and good correlation with N 150 degrees transverse zones inherited from the ancient Aswa shear zone of the Proterozoic age. These observations clearly indicate that interactions-exist between the rift thermal history and the brittle de formation at shallow depth. The 3D study of the geometry of border fau lts and their associated alluvial fans of the Baringo area confirms a typical east-dipping half-graben structure for the Baringo - Marigat-L oboi Basin, and for the Bogoria Basin. The influence of the transverse zones led to the segmentation of two individual basins: (1) the rhomb -shaped, ''flexured'' Baringo Basin, 50 km long and 20 km wide, and 1 km deep; this is bounded to the east and west by major N O-10 degrees faults, and to the north and south by flexural zones superimposed on t wo N 150 degrees transverse zones; (2) the giant ''grid-fault basin'' of Bogoria, 20 km long x 5 km wide. Modern sedimentation in the Baring o and Bogoria Basins is briefly considered in terms of its significanc e for the petroleum potential of similar rift basins.