Abstract The geological paradox of at least two Neoproterozoic glacial intervals at tropical latitudes intercalated within carbonates remains an unsolved puzzle. Several conceptual models have been proposed to explain these apparent rapid swings between climatic extremes and the associated isotopic changes in sea-water chemistry. In Oman, post-glacial transgressive sedimentary successions represent important hydrocarbon source rocks. Source rock characteristics of Neoproterozoic post-glacial successions in other parts of the world (even if not directly correlatable) are, therefore, of special economic interest. This paper concentrates on the Ghaub Formation diamictite interval in northern Namibia and the major environmental change in the aftermath of the assumed glaciation. The relationship of the post-glacial sediments with the underlying different types of cap carbonate and diamictite successions is discussed, and a model of the succession of events is presented. The palaeotopography, caused mostly by ongoing tectonic activity including uplift on the scale of thousands of metres, strongly influenced the petroleum system created and played an important role for the hydrocarbon prospectivity of this post-glacial succession. Tectonic activity on the shelf of the southern margin of the Congo Craton was repeated, and different sub-basins were created before, during and after the Ghaub glaciation. The newly formed relief was flooded, and the different sub-basins were affected by restricted circulation for quite some time. This general scenario bears many similarities to the late Ordovician–early Silurian petroleum system, also formed during post-glacial sea-level rise.

Abstract Lithospheric cusps occur where arcs are joined end to end. Where a subducting plate moves directly into a cusp, the slab experiences lateral constriction due to the cusp geometry. Buckled slabs of Cenozoic age occur at cusps (also known as ‘syntaxes’) in the Arabian, Indian, Pacific, Juan de Fuca and other plates. Here I report an Ediacaran example from the cusp of the Congo Craton where Pan-African collision zones meet at a right angle in NW Namibia. The craton was blanketed by syn- and post-rift Neoproterozoic marine carbonate, disconformably overlain by collision-related foredeep clastics. The disconformity has little stratigraphic relief in a 900 km-long fold belt rimming the craton, except within 60 km of the cusp apex where foredeep deposits bury a megakarst landscape floored by exhumed crystalline basement. Forebulge uplift, estimated from palaeokarst relief, was ≥1.85 km. This far exceeds characteristic forebulge heights of c. 0.5 km and matches the deepest part of the Grand Canyon of Arizona (USA). Coeval with megakarst development, map-scale mass slides moved coherently westwards and southwards towards the advancing accretionary prisms. Rapid burial by foredeep clastics preserved the megakarst palaeosurface and associated mass slides; folding them brought protection from complete destructive resurfacing for eons.