Sedimentological Study of Alluvial Deposits on the Congolese Coast: Highlighting the Erosive Character of the Holocene Wet Climatic Phases

A granulometric, mineralogical, morphoscopic and exoscopic study and Rock-Eval analysis carried out on samples taken in the Loango Bay and at Kivesso on the Congolese coast have made it possible to highlight the highly erosive character of the well-documented wet phases ca 9000 - 3000 years B.P. and ca 320 B.P. in the sub-region. Supported by carbon-14 dating, total organic carbon analyses highlight two major phases of peat deposit emplacement. The first, ca. 7000 years B.P., corresponds to the beginning of the deposition of the yellow formation in the entire Loango Bay;the second, ca. 320 years B.P., is contemporary with the deposition of peat in the Kivesso sector. The granulometric analysis of the sediments shows that they are essentially sandy-clay and very poor in silt, alternating with beds of silty clay sometimes rich in organic matter. These sands have a predominant mode of 0.200 mm and an average varying between 0.150 and 0.300 mm. They constitute the flood phase of the carrier current. They are associated with a population of mode 0.125 mm sometimes 0.050 mm with an average varying between 0.100 mm and 0.126 mm which corresponds to the settling phase. Morphoscopic examination showed several varieties of quartz that argue for a source of supply close to the depositional sites.

Miocene Foraminifera Biostratigraphy and Interpretation North Deep Sea Block of the Congolese Atlantic Basin

This work is the subject of the biostratigraphic and palaeoenvironmental study of the North Deep Sea area of the Congolese Miocene Atlantic Basin. This study is made from samples of lateral cores, drill cuttings and electrical logs. Lithology generally exhibits an irregular alternation of weakly indurated grey clay, light grey siltstones, and whitish, quartzitic sand, medium to coarse-grained, sub-angular to rounded. The presence of glaucony indicates that sediments have been deposited in a calm and reducing environment. The entire formation is fossiliferous. Micropaleontological analysis revealed 120 species of foraminifera including 98 planktonic (81.67%) and 22 benthic (18.33%) species used for biozonation, dating and interpretation of palaeoenvironments. Similarly, the bio-events of plankton foraminiferal, characterized by the level of the first appearance of certain species, have made it possible to identify fifteen biozones (Globorotalia plesiotumida, Globorotalia merotumida, Globorotalia acostaensis, Globorotalia menardii, Globigerina nepenthes, Globorotalia siakensis, Globorotalia fohsi, Globorotalia praefohsi, Globorotalia peripheroacuta, Globorotalia peripheroronda, Praeorbulina sicana, Catapsydrax dissimilis, Globigerinatella insueta, Paragloborotalia kugleri and Globorotalia kugleri) corresponding to age between Aquitanian and Lower Pliocene. Biofacies analysis of foraminifera has identified palaeoenvironments that vary from open marine environments, bathyal to abyssal.