Abstract

Re-evaluation of the sedimentology of the Emsian–Eifelian part of the Bokkeveld Group, the Ceres Subgroup, in the Clanwilliam Sub-basin of South Africa indicates that sedimentation occurred in an array of paleoenvironments that are related to three broad siliciclastic depositional systems in a marginal- to shallow-marine setting. These are: storm- and wave-dominated shallow marine depositional systems; transgressive barrier-island–lagoon depositional systems; and wave-influenced deltaic depositional systems. Storm- and wave-dominated shallow marine depositional systems comprise offshore, offshore transition zone to distal lower shoreface, proximal lower shoreface, and upper shoreface–beach complex paleoenvironments. This depositional system is present in the Gydo–Gamka and Voorstehoek–Hex River Formation intervals. A transgressive barrier-island–lagoon depositional system is present in the lower to middle Tra-Tra Formation and comprises back-barrier tidal-flat and lagoon and transgressive beach-barrier paleoenvironments. The wave-influenced deltaic depositional system is restricted to the top Tra-Tra–Boplaas Formation interval and comprises prodelta to distal delta-front and proximal delta-front paleoenvironments. The presence of these depositional systems and their constituent paleoenvironments provides an alternative explanation to existing storm- and wave-dominated delta and mixed wave- and tide-dominated delta models. High levels of variability in depositional environments along this coastal system constrain the effects of major changes in Devonian terrestrial environments on marginal and shallow marine sedimentation at high paleolatitudes. Application of sequence stratigraphy to the Ceres Subgroup has enabled recognition of environmental and relative sea-level change at high paleolatitudes during the Emsian–Eifelian.