Late Quaternary human occupation of the Kilwa coast (Tanzania): OSL ages and paleoenvironmental proxies from isotope geochemistry

We report new geochronologic and paleoenvironmental data for Mnaraeka 01, a prehistoric site located in the Kilwa district of coastal Tanzania. The oldest trace of human activity at the site comes from a context dated to 71 ± 6 thousand years ago (ka) where flaked stones but techno-typologically non-diagnostic were uncovered. Stratigraphic units dated to 43.9 ± 2.4 ka and 41.8 ± 2.1 ka have revealed stone artifacts broadly characteristic of the Middle Stone Age (MSA) while a context dated to 10.0 ± 0.6 ka has produced artifacts referrable to the Later Stone Age (LSA). Eight soil samples from the site subject to stable carbon and nitrogen isotope analyses reflect grassy-woodland habitat during the settlement episodes with δ¹³C values ranging from −19.3‰ to −27.8‰ (vs. VPDB). The results demonstrate the persistence of coastal woodland vegetation and human foraging populations in coastal East Africa during the onset of the cold Marine Isotope Stage (MIS) 4, between the cold spells of Heinrich Events 4 and 5, and during the Holocene Climatic Optimum. Our study shows that the Stone Age archaeology of coastal Tanzania has the potential to shed light on the role of coastal ecozones as potential refugia for human populations during variable climate conditions of the late Quaternary. Furthermore, the emergent datasets from Mnaraeka 01 open a window into the deep human history preserved in the Kilwa basin.