Eifelian–Givetian (Middle Devonian) high-paleolatitude storm- and wave-dominated shallow-marine depositional systems from the Bidouw Subgroup (Bokkeveld Group) of South Africa

Abstract

ABSTRACTThe sedimentology of the Eifelian–Givetian (Middle Devonian) Bidouw Subgroup in the Clanwilliam Sub-basin of South Africa has been reassessed. Four distinct lithofacies associations are recognized (A–D) and are representative of the deposits of offshore (Os), offshore transition zone to distal lower shoreface (OTZ-dLSF), proximal lower shoreface (pLSF), and upper shoreface–beach (USF-Beach) paleoenvironments. These paleoenvironments are arranged as several T-R-controlled storm- and wave-dominated shallow-marine depositional systems. The presence of storm- and wave-dominated shallow-marine depositional systems in the Bidouw Subgroup, as well as the preceding Emsian–Eifelian (Early–Middle Devonian) Ceres Subgroup provides an alternative explanation to storm- and wave-dominated delta and mixed wave- and-tide-dominated delta models that have previously been proposed for the Bokkeveld Group. Sequence-stratigraphic analysis of the Bidouw Subgroup suggests that although sedimentation occurred during two large-scale second-order transgressive events, the succession was predominantly regressive. Third-order and fourth-order transgressive–regressive (T-R) sequences are more numerous with respect to the preceding Ceres Subgroup, suggesting that the driver for T-R cyclicity and relative sea-level change was more active during the Eifelian–Givetian than in the Emsian–Eifelian of South Africa. These data are important since relative sea-level change and its effects on paleoenvironmental change at high paleolatitudes during the Devonian Period are poorly known.