RECONSTRUCTING CRETACEOUS AND PALEOGENE PALEOENVIRONMENTS AND DRAINAGE PATTERNS OF CENTRAL AFRICA

Sedimentological investigations, in conjunction with paleontological studies, of late Mesozoic-early Cenozoic continental deposits in Central Africa were conducted in the Rukwa (Tanzania), N. Malawi, Mana Pools and Cabora Bassa (Zimbabwe) and southern Congo (Dem. Rep. of Congo) basins. Facies, paleocurrent (PC), detrital zircon (DZ), and paleosol/clay mineral analyses of outcrop and 18 new drill cores (Congo Basin) provide critical new data for improving regional correlations and reconstructing Cretaceous-Paleogene paleoenvironments, paleoclimate and paleodrainage patterns of Central Africa during and following break-up of Gondwana. These data suggest a semi-arid to arid climate with a network ephemeral lakes, flashy fluvial channels and patchy eolian dunes systems across the interior of Central Africa during the L. Jurassic to E. Cretaceous. Increasing tectonic activity and subsidence during the E. to mid Cretaceous is documented by the widespread deposition of thick fluviatile successions. Regional PC (N = >500) and DZ (N = 400+ U-Pb ages]) data from channel sandstones provide evidence for the development of a major E. to mid Cretaceous drainage divide near the present latitude of 15ºS. PC and DZ data show that a network of rivers flowed north out of E. Zambia, Malawi and N. Mozambique to form a major trunk river system that drained NW along the Rukwa Rift and into the Congo Basin. Previous studies in the central/northern Congo Basin provide evidence for the intermittent development of a marine embayment or large lake system in this region during the L. Jurassic-early L. Cretaceous. Paleosol/clay mineral analyses indicate that climate ameliorated from tropical semi-arid to tropical humid conditions during the E. to mid Cretaceous, which persisted into the L. Cretaceous and Paleogene. DZ data indicates a major drainage reversal during the mid to late Paleogene, with rivers draining out of the Congo Basin and down the Rukwa Rift (possibly into the Indian Ocean). Regional doming to the north, associated with initiation of the African Superswell, is suggested as the cause. By the late Paleogene, rifting and carbonatite volcanism was initiated, and an internally draining lake basin developed in the Rukwa Rift. A shift back to semi-arid climatic conditions marks this major tectonic event in Central Africa.