OSL dating of a carbonate island in the Chobe Enclave, NW Botswana

Abstract

Abstract Carbonate platform islands are important landscape features in the northeastern part of the Okavango Delta region of Botswana, the Chobe Enclave. However, the formation processes and the timing of these “Chobe Islands” remain unclear. They are assumed to be the result of late Quaternary hydrological changes. Records of such changes are poorly preserved, though the occurrence of beach ridges in the Middle Kalahari Basin attests to the existence of large paleo-lakes in the past. Carbonate rocks from the Chobe Island appear to be relics of palustrine environments, but their relationship with the other hydrological archives is still unclear. Here, we report optically stimulated luminescence dating of key sedimentary beds in and around a single Chobe Island. It was necessary to model dose rate evolution for each sample individually, taking into account post-depositional changes in the sediment chemistry and its burial depth. The resulting ages suggest that the dated units were deposited between MIS6 to MIS1. The carbonate platform itself appears to have been deposited in two phases, separated by either an unexpectedly long (∼40 ka) depositional hiatus or an episode of erosion. This study demonstrates the potential of using luminescence dating in such settings, and offers the possibility of linking sedimentary processes within the Chobe Enclave to regional paleo-hydrological records.