Paleoenvironments of Coniacian Age Outcrops in the Congo Coastal Sedimentary Basin

Hilaire Elenga,Nehl Dorland Kobawila,Dieudonne Maurice Malounguila Nganga,Princesse Zatonga,Timothée Miyouna

doi:10.19026/rjees.12.6047

Abstract

The study of the Turonian formations outcropping along the Congolese coast was undertaken in the order of to understand the sequential organization of the deposits as well as the evolution of the paleoenvironments. The study consisted of a detailed description of the lithofacies in the field and in the laboratory. This study shows that these formations are essentially made up of silty dolomites, formed in a littoral environment where the waters were favorable to the multiplication of planktonic foraminifers, Lamellibranchs and Brachiopods. The sedimentological characteristics indicate a sudden retreat from the shore, witnessed by the various regressive elementary sequences. These elementary sequences each begin with a layer of thanatocenosis which would be due to a sudden change of environment, consequence of an important arrival of detrital terrigenous sediments. This terrigenous detrital contribution disrupts each time the physicochemical characteristics of the environment (oxygen deficiency, absence of light, high turbidity). The fauna of these formations exhibits a coniacian affinity. The sequential evolution of the deposit shows a large ravine unconformity on the top of the mega sequence. The composition of the fauna and the sedimentological characteristics confirm the existence of a regressive sedimentation model of the Lower Coniacian age.

Highlights

The Congo coastal basin is part of the central segment of the Gulf of Guinea, of the African Atlantic margin, whose evolution is linked to the opening of the South Atlantic during the lower Cretaceous, establishing the separation of the African and South American continents (Le Pichon and Hayes, 1971; Larson and Ladd, 1973)
It shows an alternation of horsts and grabens lying globally NW-SE. These hens and ditches are interspersed with normal, globally oriented NE-SW (Read, 1988). It is organized into three large lithostratigraphic units representative of the three major tectono-sedimentary phases that mark the evolution of the Atlantic margin (Guiraud and Maurin, 1992; Grosdidier et al, 1996; Séranne and Anka, 2005)
There is an alternation of bioclastic dolomite levels of bioturbated bioclastic dolomite accumulation, with bioclastic dolomites for the creation of young, or mature, Lamellibranch, packed in sparite cement rich in quartz and feldspars silts. This alternation ends with a silty and sandy marl inter-stratum indicating a deepening of the basin and a sudden change in the dynamic conditions of the environment where the waters become less oxygenated and very turbid, causing the reef to be botched

Summary

Introduction

The Congo coastal basin is part of the central segment of the Gulf of Guinea, of the African Atlantic margin, whose evolution is linked to the opening of the South Atlantic during the lower Cretaceous, establishing the separation of the African and South American continents (Le Pichon and Hayes, 1971; Larson and Ladd, 1973). According to Belmonte et al (1965), the structure of the basin is roughly monocline It shows an alternation of horsts and grabens lying globally NW-SE. These hens and ditches are interspersed with normal, globally oriented NE-SW (Read, 1988). It is organized into three large lithostratigraphic units representative of the three major tectono-sedimentary phases (pre-salt, salt and post-salt) that mark the evolution of the Atlantic margin (Guiraud and Maurin, 1992; Grosdidier et al, 1996; Séranne and Anka, 2005). The post-rift series presents two large superimposed units, Aptian to Eocene age aggradation Units and propagation Units of Miocene to the Present Age, separated by a major Oligocene-age erosion of 10 to 15 Ma (Séranne et al, 1992)

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Discussion

Conclusion