The Neoproterozoic Katanga Supergroup (D. R. Congo): State-of-the-art and revisions of the lithostratigraphy, sedimentary basin and geodynamic evolution

Abstract

Abstract In the last 25 years, successive revisions were introduced in the lithostratigraphy of the Neoproterozoic Katanga Supergroup, which hosts the Katanga Copperbelt (KCB, D.R.Congo). The evolving changes in nomenclature and definitions of the formations and subgroup/group relationships, superposed with the different previous classifications, are clarified and summarized in the present stage of knowledge. Moreover, revisions are proposed based on lithologic and sedimentary considerations. The R.A.T. Subgroup, at the bottom of the succession, is re-named “Musonoi” based to one of the two sites where this unit is best observed in drill cores. The R.A.T. Grises are included in the Musonoi Subgroup as the topmost formation of this succession displaying similar sedimentary conditions. The Dipeta Subgroup is re-named as the Fungurume Subgroup, and defined as containing five formations: the R.G.S. (re-named “Kwatebala”) at the base, overlain by the alternating dolomite and siltstone beds of the Dipeta and Tenke formations, and by two dominantly carbonate sequences at the top, the Mofya and Kansuki formations. The Mofya Formation and the transition to the Kansuki Formation is still poorly documented. The sedimentary, lithologic and recent geochronological data on diagenetic and metamorphic-hydrothermal minerals clearly confirm that the Musonoi (former R.A.T.), Mines and Fungurume (former Dipeta) subgroups are part of the Roan sedimentary pile as a typical Congo facies, and cannot be interpreted as a Kundelungu-foreland deposition. Supported by a ∼765 Ma geochronological age of Kansuki lavas in northwestern Zambia, the basal conglomeratic beds of the Kamoya Formation (bottom of the Mwashya Subgroup) are interpreted as a diamictic deposition that corresponds to the Kaigas glacial event (∼770-735 Ma). The Mwale and Kyandamu diamictites are considered as separate formations from the overlying Muombe and Gombela subgroups at the base of the Nguba and Kundelungu groups, respectively. In addition to previous revision of the Nguba Group, the “Dolomie Tigree” cap-carbonate succeeding the Mwale Formation is introduced as a new formation at the base of the Muombe Subgroup. Inversion from an extensional to a compressional orogenic regime is marked by a group of metamorphic peaks at ∼595 Ma that probably correspond to the first D1 folding deformation phase of the Lufilian orogeny at the end of the Gombela Subgroup deposition. The second D2 main deformation phase between ∼550 and ∼530 Ma and the final collision is marked by hydrothermal-metamorphic crystallisations or remobilisations associated with the paroxysms of this compressive period. Thrusting and bending of the Lufilian arc probably occurred between these two main metamorphic events. The Mongwe and Kiubo formations, that represent the upper part of the Kundelungu Group (or Ngule Subgroup), belong to the folded Katangan and are interpreted as sediments filling northward-prograding foreland basins, north of the thrusting. The sub-horizontal Sampwe Formation that was deposited at the final stage of the thrusting, probably represents the only autochthonous Kundelungu rocks in the KCB. The overlying Biano tabular sediments are interpreted as a group distinct from the Kundelungu Group, and is possibly of Cambrian age.