The coastal Holocene sedimentary environments of Loango Bay and Pointe-Noire, Congo: Previous works, recent development and synthesis

• Published in: The African Neogene – Climate, Environments and People Vol. 1; pp. 161 - 181
• Main Authors: Malounguila-Nganga, Dieudonné, Giresse, Pierre, Miyouna, Timothée, Boudzoumou, Florent
• Format: Book Chapter
• Language: English
• Published: CRC Press 2018
• Edition: 1
• Subjects: ITCZ; Late Paleocene Early Eocene; Hydromorphic Soils; Mangrove Swamp; Swampy Forest; Sea Level Curve; Precambrian Metamorphic Basement; Ivory Coast; Annona Glabra; Relative Sea Level Curves; Acrostichum Aureum; Peaty Deposits; NW SE Orientation; Holocene Transgression; Sedimentary Archives; Ammonia Beccarii; Beach Barriers; Vegetation Indicators; Sedimentary Unit; Forest Savanna Mosaic; Holocene Sea Level; Littoral Plain; WGS84 Coordinate System; Negative Carbon Isotope Excursion
• ISBN: 113806212X; 9781138062122
• DOI: 10.1201/9781315161808-9

This review focuses on Holocene swampy, estuarine and fluvial systems of the southern coast of Congo. These deposits can provide proxy data at various geographic and chronologic palaeoclimate scales. During the relative high stand of the MIS 3, about 45,000–35,000 years BP, an important thickness of peat deposited in mangrove swamp in the palaeo-valley of the Kouilou estuary. During MIS 2, the significant fall in the sea level led to the emersion of this site and to the important compaction of these peaty deposits. During MIS 1, the approach of the Holocene led new conditions favourable to the mangrove development. In the Bay of Pointe-Noire, the morpho-structural depression of the Upper Cretaceous between 9000 and 7000 years BP allowed the rapid deposition of more than 10 metres of not compacted peat. In Kouilou River palaeo-valley, it was only during the end of the Holocene that the bank deposition shows recurrent evidence of the mangrove proximity. Holocene palaeoclimatic changes of central Africa are now well documented, but there is evidence that landscape evolution of the coastal plain has also been affected by approach and then arrival of the marine transgression and its influence on hydrological process. From 7000–6000 years BP, the construction of large beach barriers by the oceanic drift allowed the definition of long and narrow depressions where Monopetalanthus swampy forests developed, thus allowing accumulation of peat and organic muds. Water table oscillations favoured an active podzol process of the littoral sands and development of hydromorphic soils (gley). Indications of a marked renewal of erosion, probably of climatic origin, are present on the scale of the last centuries. Finally, a more recent generation of beach barriers came to bury these paralic deposits. Today, very dynamic oceanic erosion is exposing these Holocene deposits and providing new opportunities to obtain more and better palaeoclimate databases. The equatorial West African continental margin comprises depot centres located offshore major river mouths. The Congo Holocene sea level curve is slightly above the global sea level curve without any specific characteristic. The high sea level being reached, the facies transition from low energy marine swamps in the north to lenses of sandy alluviums in the south is recognizable. The sedimentary archives of the lakes of Cameroon, Gabon and Congo supply the best Holocene biostratigraphic and palaeoclimatic information. Loango Bay shows a low coast lined with littoral barriers except near Pointe Indienne, where the “Série des Cirques” cliff approach the coastline. The littoral plain or at least a part of this one was occupied by a dense and periodically flooded rainforest with Syzygium that was long lasting, probably from the beginning of the Holocene. The Late Quaternary organic accumulation of the southern Congo coast was controlled first of all by the closeness of the oceanic water masses.