Roberts, Eric, Jelsma, Hielke A., and Hegna, Thomas (2015) Mesozoic sedimentary cover sequences of the Congo Basin in the Kasai region, Democratic Republic of Congo. In: de Wit, Maarten J., Guillocheau, François, and de Wit, Michiel C.J., (eds.) Geology and Resource Potential of the Congo Basin. Regional Geology Reviews . Springer, Heidelberg, Germany, pp. 163-191.

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Abstract

The Congo Basin represents one of the largest and least studied continental sedimentary basins in the world. The stratigraphy of cover sequences across the basin is poorly resolved and a somewhat simple stratigraphy has generally been applied with gross subdivision of the Mesozoic-Cenozoic cover sequences into a number weakly correlated units. Although these subdivisions are useful for broad, regional-scale correlations, investigation of drill cores and outcrop in the shallow, southern Kasai part of the basin, from Tshikapa to Kabinda, reveals considerable facies, provenance and thickness variations, suggesting a more complex depositional and stratigraphic history than previously recognized. This study now permits the subdivision of the sedimentary cover in the Kasai portion of the Congo Basin into five distinct depositional sequences consisting of (1) P1: Permo-Carboniferous glacio-lacustrine deposits correlative to the Lukuga Group; (2) J1: Jurassic-age arid to semi-arid laminated shales and siltstones and aeolian sandstones, interpreted as ephemeral lake and sand dune sequences with interspersed loess deposits and rare fluvial channel sequences (considered part of the historic Lualaba-Lubilash Supergroup—the lacustrine facies likely correlates with the Stanleyville Group, DRC and the Continental Intercalar Group, Angola); (3) C1 & C2: Lower Cretaceous locally heavy mineral-rich fluvial sandstone deposits and variably present basal conglomerate (correlated to the Loia Group, DRC and the Calonda Formation, Angola); (4) C3 & C4: Upper Cretaceous conglomerates of alluvial fan origin that grade upward into laminated shales and siltstones or well-sorted and rounded, fined grained sandstones representative of a semi-arid to arid depositional setting dominated by ephemeral lakes and small aeolian dunes, (equated to the Kwango Group, DRC and Angola) and (5) T1: fluvial, aeolian and lacustrine sediments of Paleogene age (correlated with portions of the Kalahari Group). The results convincingly suggest that this part of the Congo Basin is more structurally complex than previously appreciated, with multiple fault-bounded basement highs and depocenters that strongly influenced regional sedimentation patterns. Prolonged and sporadic displacement appears to have taken place along these faults, leading to heavily bisected basin morphology with uneven thickness and depth distributions between sequences. The deposition of Cretaceous sequences was coeval with two episodes of kimberlite emplacement, the first at ~120–130 Ma in northern Angola, and the second at ~70–80 Ma in the DRC, with gravel horizons within the Cretaceous fluvial successions (C1 and C3) known for their alluvial diamond concentration. The models developed provide a regional context for evaluation of alluvial diamond source areas and prospectivity.

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