Stratigraphy of the Fungurume Group - evolving foreland basin succession in the Lufilian fold-thrust belt, Neoproterozoic-Lower Palaeozoic, Democratic Republic of Congo

Abstract

The Lufilian arc (Neoproterozoic-Lower Palaeozoic) is a Pan-African orogen that lies between the Kalahari Craton in the south and the Congo Craton in the north. North vergent thrusting of its Katangan metasedimentary succession formed a fold-thrust belt in the northern sector of the arc. The belt contains prominent bodies of fragmental rocks including thrust sheets and megablocks of older Katangan strata, some of which contain Cu-Co mineralisation. These fragmental rocks were traditionally considered as tectonic friction breccias formed underneath the advancing Katangan nappes. This paper presents the stratigraphic implications of a recent reinterpretation of these breccias as sedimentary conglomerates in the fold-thrust belt of the Lufilian arc. The Katangan succession in Zambia and the Democratic Republic of Congo (DRC) is traditionally subdivided into four main lithostratigraphic units: Roan, Mwashya, Lower Kundelungu and Upper Kundelungu. It has been considered that that the Roan, Mwashya and Lower Kundelungu strata were deposited in a progressively opening rift basin, then folded and thrust northwards during Upper Kundelungu times. No syntectonic sedimentation associated with this orogenesis was previously recognised. Megabreccias within the Kundelungu succession in the northern part of the fold-thrust belt are interpreted here to be sedimentary complexes of synorogenic conglomerates derived from the orogenic front advancing from the south and deposited in a newly recognised foreland basin to the north. The sedimentary origin means that the ‘megabreccias’ should be classified as new lithostratigraphic units of the Katangan succession. The Fungurume Group (new unit), which unconformably overlies older strata, represents foreland basin fill and is subdivided into three formations. The Mutoshi Formation is characterised by continental red beds, previously called RAT. A facies association of hematite-rich, marginal marine, mixed clastic and carbonate rocks constitutes the Dipeta Formation. The Kambove Formation comprises olistostromes deposited by subaqueous sediment-gravity flows. The Mutoshi and Dipeta Formations were previously correlated with the rift-related Roan Group of Zambia. The Cu-Co-bearing Roan-derived strata, traditionally called the Mines Group, occur only as allochthonous blocks embedded in any of the above formations. Therefore, the Mines Group does not form a legitimate lithostratigraphic unit, and it is excluded herein from the revised stratigraphy of the Katanga Supergroup. The undeformed continental molasse of the Plateau Group fills the youngest foreland basin, extending ahead of the fold-thrust belt.