The Congo-Gabon Source-to-Sink Project: Characterization of the Volume And Nature of the Cretaceous to Cenozoic Clastics Produced on the Uplifted Onshore Erosion Surfaces and Transported Offshore

Abstract

The source-to-sink (S2S) concept focuses on the quantification of the components of clastic sedimentary systems from initial sediment production in the source areas (i.e. onshore margin) through to their deposition within sedimentary sinks (i.e. offshore margin). The analysis of the clastics provenance contributes to a fundamental information about source and catchment areas as well as the sedimentary budget characterizing the offshore margin domain. Clastics production on the margin is controlled by the mechanical erosion and/or the chemical weathering of the onshore substrate. The intensity of the onshore erosion processes is mainly governed by the lithology of the substrate, the rate of tectonic uplift, and the nature of paleoclimate (hot humid climate privileging weathering versus cold dry climate favoring mechanical erosion). The main objective of the Congo-Gabon margin S2S project was to characterize (1) the factors controlling the intensity of the onshore erosional processes and (2) the volume and nature of the Cretaceous to Cenozoic clastics produced in the Congo-Gabon onshore domains and delivered to the offshore margin. The analysis of both surface and subsurface data highlighted the role of paleovalleys distributed along the border of the coastal sedimentary basin. These valleys (i.e. clastic entry points) funneled clastics produced onshore to the Congo-Gabon offshore depocenters. The sedimentary record in the basin, in particular the nature of the turbiditic sands, is consistent with the nature of the Cretaceous to Cenozoic clastics produced at the onshore margin (i.e. ultramature, mature to immature). The findings of this study are then two folds: First, the clastic volumes are directly controlled by the surface area of the different paleocatchment zones and distributed thanks to semi-perennials entry points. Second, the nature of the clastics is mainly governed by paleoclimate. Intensive chemical weathering of the hot and humid Senonian– Early Eocene paleoclimate constrains the onshore production of significant volumes of ultramature clastics (clays, quartzarenites and monogenic conglomerates) while the mechanical erosion and moderate weathering associated with the colder and less humid Late Eocene – Early Miocene paleoclimate caused the onshore production of immature clastics (quartz conglomerates, carbonates, fine to coarse-grained sands and clays).

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018