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A never solved problem in sedimentary petrology is the origin of sandstone consisting exclusively of quartz and most durable heavy minerals. The Congo River offers an excellent test case to investigate under which tectonic, geomorphological, climatic, and geochemical conditions pure quartzose sand is generated today. In both upper and lowermost parts of the catchment, tributaries contain significant amounts of feldspars, rock fragments, or moderately stable heavy minerals pointing at the central basin as the main location of the "quartz factory". In Congo sand, quartz is enriched relatively to all other minerals including zircon, as indicated by Si/Zr ratios much higher than in the upper continental crust. Selective elimination of old zircons that accumulated radiation damage through time is suggested by low percentages of grains yielding Archean U-Pb ages despite the basin being surrounded by Archean cratonic blocks. Intense weathering is documented by the lack of carbonate grains in sand and by dominant kaolinite and geochemical signatures in mud. In sand, composed almost entirely of SiO 2 , the weathering effect is masked by massive addition of quartz grains recycled during multiple events of basin inversion since the Proterozoic.Changes in mineralogical, geochemical, and geochronological signatures across Bas-Congo concur to suggest that approximately 10% of the sand supplied to the Atlantic Ocean is generated by rapid fluvial incision into the recently uplifted Atlantic Rise. The Congo River connects with a huge canyon ~ 30 km upstream of the mouth, and pure quartzose sand is thus funnelled directly toward the deep-sea to feed a huge turbidite fan. Offshore sediments on both sides of the canyon are not derived from the Congo River. They reflect mixed provenance, including illite-rich dust windblown from the arid Sahel and augite, hypersthene, and smectite ejected from volcanic centres probably situated along the Cameroon Line in the north.Because mixing of detritus from diverse sources and supply of polycyclic grains almost invariably occurs in the terminal lowland tract of a sediment-routing-system, no ancient sandstone can be safely considered as entirely first-cycle. Moreover, the abundance of pure quartzarenite in the rock record can hardly be explained by chemical weathering or physical recycling alone. The final cleansing of minerals other than quartz, zircon, tourmaline, and rutile requires one or more cycles of chemical dissolution during diagenesis, which operates at higher temperatures and over longer periods than weathering at the Earth's surface.

The acritarch assemblages of strata from the base of the Upper Proterozoic Sheepbed Formation to the base of the Lower Cambrian (Atdabanian) Sekwi Formation are described. The sections sampled are in southwestern (internal) structural units where erosion beneath the "sub-Cambrian"(?) unconformity is least evident. Problems of lithostratigraphic correlation of post-Sheepbed, pre-Backbone Ranges formations remain. Acritarchs indicate the age of the Sheepbed Formation and the Blue-flower Formation above it is latest Proterozoic (Vendian), whereas that of the Vampire Formation is Early Cambrian (Atdabanian). The Backbone Ranges Formation has not yielded datable acritarchs, but it is for the most part Cambrian in age, based on other fossil evidence. Comparisons are made with the Russian Platform and southern Canadian Rocky Mountains successions. The total number of acritarch genera increases markedly across the Precambrian–Cambrian transition.

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