The Cretaceous deep-water carbonate to siliciclastic transition in the Senegal Basin – insights into provenance, sediment routing and depositional mechanisms from outcrop and core.

Provenance and biostratigraphic data from a recent fieldwork campaign characterising the Mesozoic lithostratigraphy of Ilha de Maio, Cabo Verde has been integrated with legacy data from DSDP sites 367 and 368. These study sites are situated along a 600 km north-south transect of the western margin to the prospective Senegal Basin off NW Africa. Together they record predominantly Cretaceous sedimentation overlying supposedly Late Jurassic oceanic crust basalts. Of particular interest is the character, evolution and depositional mechanism of distal siliciclastic sedimentation from the Upper Cretaceous in the study area. Key questions are (1) whether these sediments represent gravity flows in distal fan fringe deposits or contourites and (2) whether regional sediment routing patterns can be inferred.

The provenance character of previously unreported up-to-coarse-grade sandstones from has been assessed via a combination of petrographic, conventional HM and U-Pb zircon data. Detailed logs of type sections from Maio provide improved constraint on the thickness and composition of the Lower to Upper Cretaceous rock record onshore. A particular focus is the mid Cretaceous carbonate to silicilastic transition and the extent to which depositional setting can be reliably interpreted in heavily dyked successions. The significance and stratigraphic context of sandstones outcropping on Maio is reassessed with respect to Robertson (1984), and compared to correlative sequences in the offshore. A revised litho/biostratigraphic correlation linking the Cape Verde outcrops to the offshore sequences has also been assembled. Finally, the sedimentology of the studied sections is compared to recent models developed from seismic data (Mourlot et al., 2018), which emphasise the dominance of contourites in the distal Senegal Basin in the Turonian-Maastrichtian.

This study forms a subset of a regional reassessment by CASP of provenance and sediment routing in the Senegal Basin.

References:

• Robertson, A.H.F. (1984) Mesozoic deep-water and Tertiary volcaniclastic deposition of Maio, Cape Verde Islands: implications for Atlantic paleoenvironments and ocean island volcanism (hot-spot activity). Geological Society of America Bulletin, 95, 433-453.
• Mourlot, Y., Calvès, G., Clift, P.D., Baby, G., Chaboureau, A.C., Raisson, F. (2018) Seismic stratigraphy of Cretaceous eastern Central Atlantic Ocean: Basin evolution and palaeoceanographic implications, Earth and Planetary Science Letters, 499, 107-121.