THE INKISI FORMATION (WEST CONGOLIAN SUPE RGROUP) IN CENTRAL-AFRICA (CONGO AND LOWER ZAIRE) - PALEOZOIC DELTA FILLING A LARGE BASIN

The Inkisi Formation (West Congolian Supergroup) corresponds to a larg e deltaic body, which extends through Congo, Lower Zaire and Angola. I n the Congo and Lower Zaire areas, the lower part of this formation is characterized by a fluvial conglomerate with elliptic pebbles. The re d arkosic, channelized series from the Brazzaville-Kinshasa area invol ves delta plain distributary channels and delta front sequences. The t ransport direction of continental material is from north to south and the source area is the Chaillu basement. Glacial quartzitic pebbles ar e probably reworked from the fluvio-lacustrine Upper Diamictite Format ion. The classical subdivisions of the Inkisi Formation - basal conglo merate (I-o), Lower part (I-1) and Upper part (I-2) - are not used. Th ese subdivisions correspond to a fluvial conglomerate and to delta fro nt and delta plain fades. The coastal onlap progressively covered the conglomerate and the distributary channels in the delta plain was prog rading onto the delta front. The prodelta sequence could correspond to the Upper level of the Mpioka molassic Formation. The Inkisi delta wa s on the northern edge of an extensional basin controlled by NE-SW nor mal faults. The extension phase is clearly post Pan-African and occurr ed during the Palaeozoic, probably in relation to the Permian Karoo ph ase, and is also known in Angola.