Sedimentology of alluvial fan deposits near Nature’s Valley, South Africa

• Published in: Journal of African earth sciences (1994) Vol. 216; p. 105301
• Main Authors: Hassan, Safiya M., de Wit, Maarten, Helper, Mark A., Hussein, Ahmed W.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2024
• Subjects: Alluvial fan; Braided stream; Enon formation; Mesozoic; Nature's Valley; South Africa; Enon formation; Mesozoic; South Africa; Braided stream; Alluvial fan; Nature's Valley
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2024.105301

Near Nature's Valley, South Africa, alluvial fan and braided-stream sandstones and conglomerates occur as a thin veneer unconformably overlying the Cape Supergroup's heavily weathered Ordovician Table Mountain strata. These deposits are similar to the Enon Formation of the Mesozoic Uitenhage Group. Two distinctive facies are recognized in outcrop: gravelly braided-stream and interbedded alluvial fan conglomerates and sandstones of mid-fan to distal fan affinity. Proximal alluvial fan deposits are not present. Clast-supported, structured pebble-boulder conglomerates with sandstone matrix dominate the braided-stream facies. Stratification and clast imbrication are common. The conglomerate clasts are mainly quartzite originating from the Table Mountain Group strata upon which they rest. The mid-fan to distal fan deposits are represented by interbedded cobble-boulder conglomerates and sandstones, mostly with erosive bases and with beds of a short lateral extent. A basal-lag boulder and cobble conglomerate grades upward to reddish, medium to thick sets of cross-bedded sandy conglomerates that pass upward to medium and fine-grained sandstone. The sedimentological characteristics and location of Nature's Valley fan suggest that its development was more influenced by tectonics than by climate fluctuations. The evolutionary history is likely to be dominantly a result of accumulation close to the foot of an active fault scarp. •Deposits near Nature's Valley represent an alluvial fan and braided fluvial system.•The Nature's Valley deposits are most similar to the Early Jurassic to Early Cretaceous Enon Formation.•The top of the Nature's Valley outcrops were eroded when a marine terrace formed, perhaps in the Late Miocene.