Kalahari Gr

The classical ‘Kalahari type-section’, as first described in Botswana by Passarge (1904). The Group is generally subdivided into two (Cahen and Lepersonne 1952): An upper Sables Ocres Fm and the underlying Gres Polymorphes Fm (de Wit et al., 2015).

Synonym: Kalahari Sands, Kalahari Sands Gr

Reference: Colin 1994; Cahen and Lepersonne 1952; De Wit et al.,2015; Grekoff 1958; Kadima et al., 2011; Leriche 1927; Polinard 1932; Passarge,1904

[Fig 1. Simplified geological map of the Congo Basin, compiled from various published map. The stratigraphic units have been assembled into major sequences (Late Neoproterozoic, Paleozoic and Cenozoic)]

[Fig 2. Tectonic setting of the Neoproterozoic basins of present-day Central Africa, compiled from the 1: 2M geological map of the Zaire (Lepersonne, 1974) and the 1: 4M map Geology and Major Ore Deposits of Africa (Milesi et al., 2006)]

[Fig 3. Lithostratigraphic synthesis for the Neoproterozoic to Early Paleozoic period. Compiled after various authors. Dotted lines between Banalia, Alolo and Galamboge formations: stratigraphic transition by recurrences]

[Fig 4. Lithostratigraphic columns for the Congo Basin established using data from the 4 wells in the central part of the basin and outcrops on its NE margin (Lindi-Ubangi and Kisangani-Kindu region), compared with the West-Congo and Katanga stratigraphy]

[Fig 5. Simplified geological map of Sub-Saharan Africa showing the Neoproterozoic basins on and around the Congo Shield (modified after De Waele et al. 2008). (LC) Lower Congo Basin, (Co) Comba Basin, (Sa) Sangha Basin, (Ny) Nyanga-Niari Basin, (An) Angola Basin, (SO) Semb-Ouesso Basin, (Ba) Ubangui Basin, (LiB) Likki-Bembe´ Basin, (Bk) Bakouma Basin, (Fou) Fouroumbala Basin, (Li) Lindi Basin, It Itombwe Basin, (Ma) Malagarazi-Bukoban Basin, (Mb) Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin, (Lu) Luamba Group, (Kat) Katanga Basin, (RB) Ruwenzorian Belt, KaB) Karagwe-Ankole Belt, (RuB) Ruzisian Belt, (KiB) Kibaran Belt,(UB) Ubendian Belt, IB Irumide Belt]

[Fig 6. Northern margin of the Congo Shield. (A) Geological sketch map of the Lindi Basin (modified after Verbeek 1970; Poidevin 1985)]

[Fig 7. Stratigraphic logs of the Lindi Supergoup in the DRC (modified after Verbeek 1970). (C and D) Stratigraphic logs of the Lindi Supergoup in CAR (modified after Poidevin 1985). cc cap carbonates, SG Sturtian Glaciation, MG Marinoan Glaciation]

[Fig 8. Stratigraphic correlation between the Neoproterozoic sedimentary basins in Central Africa. Correlations based on Sr isotopic data, radiometric age constraints and revised lithological relationships]

At the type section of the Kalahari Group, it ranges between about 100 m and 300 m thick (de Wit et al., 2015). At the type-section, consists of basal gravels (the Botletle Beds), calcretized or silcretized sandstones and marls (‘Kalahari Limestones’) and aeolian sands (‘Kalahari Sands’). A significant part of the Kalahari Group has been argued to have resulted from in-situ weathering of its basement rocks, further hampering construction of a robust stratigraphy (McFarlane et al. 2010).

Sables Ocres Fm: The Neogene consists of sequence of unconsolidated sands, up to 120 m thick, overlies another weathering surface, marked by ferricrete deposits at the top of the ‘Polymorph Sandstones’ (Cahen and Lepersonne 1952; de Wit et al., 2015). This sequence comprises fine ochreous sands, silts and kaolinitic muds devoid of stratification, possibly due to intense bioturbation, and which are interpreted as sheet wash deposits (De Ploey 1968; de Wit et al., 2015). Origin of sands might be predominantly fluvisl plus aeolian.

Gres Polymorphes Fm: The Paleogene consists of siliceous sandstones (Kadima et al., 2011). It is made up of massive sequence comprises 60–80 m thick extensively silicified ‘limestones’, calcareous sandstones and silcretes with chalcedony, known as the ‘Polymorph Sandstones’ (C.f. Lepersonne 1945; de Wit et al., 2015). These rocks are often cavernous, bioturbated and fossiliferous with shells that display early silicification (De Ploey 1968). Origin of sands might be predominantly aeolian.

Ostracods (Cypris farnhami, C. lerichei, Erpetocypris sp., Gomphocythere? sp., Oncocypria sp. and Stenocypris bunzaensis; Leriche 1927; Polinard 1932; Grekoff 1958; Colin 1994) and other lacustrine fossils, e.g., charophytes (Grambastichara) and gastropods (de Wit et al., 2015).

Eocene (Linol et al., 2015, Fig. 11.4)

Aeolian – fluviatile depositional environment