KARSTOGENESE DE LA GROTTE NDUNDU 1 DANS LA REGION DE MBANZA-NGUNGU AU KONGO CENTRAL

Abstract

Ndundu 1, situated near Mbanza-Ngungu (Kongo Central), constitutes a sink–resurgence system developed within massive dolomites. This study aims to characterise its morphology, lithostratigraphic and structural framework, and to propose an evolutionary model of its karstogenesis, taking into account the topography of the valley. The cavity displays fossil phreatic meanders, canyon sections, active galleries, speleothems, and brecciated deposits. Two families of subvertical fractures oriented NE–SW and NW–SE are dominant, whilst the overall trend of the cave is north–south. The micritic dolomites exhibit very low primary matrix porosity, with permeability being essentially controlled by fracturing. Morphological data suggest an initial development under phreatic conditions and a low hydraulic gradient, followed by vadose incision associated with the progressive lowering of the base level. Ndundu 1 corresponds to a polyphase tropical karst system controlled by fracturing, whose evolution results from interactions amongst inherited brittle tectonics, dolomitic lithology, and hydrological dynamics. This study highlights the importance of structural control, but also of topography, which directs flow and thereby governs the northward development of the cave along the steepest gradient towards the river below.