Visions of ice sheets in the early Ordovician greenhouse world: Evidence from the Peninsula Formation, Cape Peninsula, South Africa

The depositional architecture within the Early Ordovician, Peninsula Formation, South Africa, indicates a three-tier stratal sequence hierarchy comprising likely 4th order autogenic, 3rd order allogenic and 2nd order regressive–transgressive sequence stacking pattern. Based on correlation with the global eustatic sea level curve, we interpret the 3rd order sequences, comprising predominantly lowstand braided fluvial deposits with thin early transgressive system tract marginally marine sandstones, as orbitally induced, glacioeustacy. Eustacy affected sand delivery, base level changes and discharge patterns. The Cape Peninsula lay at ~ 30°S during the Early Ordovician yet the primary control on sedimentation was the waxing and waning of ice sheets in the source area. We hypothesize the presence of an Early Ordovician ice sheet of 8–12 × 106 km3 and a Polar Front at ~ 40°S.