LITHOSTRATIGRAPHY, SEDIMENTOLOGY AND FACIES ARCHITECTURE OF THE LATE CRETACEOUS SUCCESSION IN THE CENTRAL MAHAJANGA BASIN, MADAGASCAR.

New stratigraphical and sedimentological data are presented on the Late Cretaceous succession exposed in the central Mahajanga Basin (Andranolava-Berivotra area), western Madagascar. Eight lithostratigraphical units, Santonian to Maastrichtian in age, have been mapped in this area. These have been recognised on the basis of lithologies, sedimentary structures and fossil content. Particular attention was paid to the recognition of the surfaces separating these units, such as erosive, non-depositional and transgressive surfaces. The stratigraphical arrangement of these units can be placed tentatively in a sequence stratigraphical model and these units can be interpreted as elements of at least four depositional sequences. The comparison between this sedimentary succession and the latest Cretaceous volcano-sedimentary history of the other western Madagascar basins (Morondava and Diego-Suarez Basins) shows several analogies. The most striking are: north to south migration of basaltic volcanism and associated continental/transitional conditions; and definitive marine flooding of the western margin of Madagascar since the Maastrichtian. These features are thought to be related to the regional geodynamic events associated with the break-up of the Madagascar-lndia block. It is likely that uplift/subsidence pulses, more than sea-level variations, controlled the latest Cretaceous depositional patterns in the central Mahajanga Basin. (C) 1998 Elsevier Science Limited.