Sedimentation in a fluvially infilling, barrier‐bound estuary on a wave‐dominated, microtidal coast: the Ouémé River estuary, Benin, west Africa

摘要: The Oueme River estuary is located on the seasonally humid tropical coast of Benin, west Africa. A striking feature this microtidal presence a large sand barrier bounding 120 km2 circular central basin, Lake Nokoue, that being infilled by heterogeneous fluvial deposits supplied relatively catchment (50 000 km2). Borehole cores from lower show basal Pleistocene lowstand alluvial sediments overlain Holocene transgressive–highstand lagoonal mud and transgressive to probably early highstand tidal inlet flood-tidal delta deposited in association with non-preserved barriers. change estuary-mouth sedimentation barrier-inlet system regressive reflects regional modifications marine supply cross-barrier flux associated systems. As formation led an increasingly rectilinear shoreline, longshore drift cell matured, ensuring voluminous eastward transport Volta Delta Ghana, major purveyor sand, embayment, 200 km east. Concomitantly, number inlets, hitherto interlinked coast, diminished. Complete sealing Nokoue has produced large, permanently closed estuary, where intrusion assured through interconnected coastal lagoon via 60 km Since 1885, tides have entered directly artificial outlet cut across barrier. Although precluding seaward loss sediments, permanent closure especially deprived potentially important component estuarine infill wave-dominated coasts. In spite significant sediment supply, been moderate, because size basin. Estuarine resulted two co-existing suites, limited admixture, marine-derived, upland-derived back-barrier sediments. This situation differs mature estuaries characterized active fluvial-marine mixing facies interfingering.