Holocene deltaic sequence in the Saloum estuary, Senegal

Abstract

The 2250 km2 Saloum delta, south of Dakar, Senegal, consists of a Holocene sedimentary sequence deposited during five evolutionary stages: submerged postglacial ria, funnel-like estuary, barred estuary, cuspate delta, and reverse estuary. The passage from one stage to another was marked by the deposition of sedimentary units consisting of shelly sands, silty or sandy clays, and an extensive thick green mud. Muds in the lower strata, dating between 6130 and 3500 yr B.P., were deposited on a subtidal mudflat, while fine sands and silty clays characterize intertidal deposits. A drastic change in sedimentation patterns, resulting in the accumulation of a series of beach barriers, likely was associated with a major climatic change. The regional climate was then very dry, and silt and sand were trapped in the water behind the barriers in two stages, from 1990 to 1510 and 1020 to 600 yr B.P. Each event was accompanied by construction of shell middens that demonstrate the presence of humans who exploited newly available shallows and banks. Relative sea level did not change significantly between 6000 yr B.P. and the present. Morphological and sedimentological changes observed in the late Holocene sequences were apparently induced by a constraining climatic background.

Wave‐influenced deltas: geomorphological implications for facies reconstruction

“…However, these examples are atypical for deflected deltas, because much of the modern deltas of the Saloum and Senegal were built as bayhead deltas. The bays they grew in were protected by sandy spits formed of sediments eroded from updrift areas (Michel, 1968; Ausseil‐Badie et al ., 1991). Therefore, these spits were not necessarily deltaic before the bayhead deltas reached the open ocean, and these depositional systems bear more resemblance to the wave‐dominated estuaries of Dalrymple et al .…”

“…(A) Senegal delta, Senegal (after Michel, 1968). (B) Saloum delta, Senegal (after Ausseil‐Badie et al ., 1991). (C) Mahanadi delta, India (after Meijerink, 1982; Bharali et al ., 1991; Mohanti, 1993).…”

Subfossil diatoms from Bandiala (southern branch of the Saloum estuary, Senegal): Evidence of a wet period in the upper part of the Néma Ba core.

“…These two causes, which are moreover linked, seem to have played simultaneously in zone O of the Néma Ba core. The high sandy fraction in the lower part of the core is a known phenomenon in the first filling deposits of the Saloum estuary [8] . These authors indicated that between 6130 and 3500 years B.P.…”

“…The Saloum estuary has been the focus of several studies. They are based on the mangrove, its evolution and its deterioration [6,7] ; sedimentology [2,3,8,9] ; geomorphology, grain size, exoscopy and mineralogy [10,11] ; microfauna and macrofauna [12] ; salinity, rainfall and precipitation-evaporation [13][14][15][16] biology of fish community [17] and archaeology [4,18] . However, few studies have been devoted to the paleo-environment.…”