ARCHAEOLOGICAL SITES RECORD LATE HOLOCENE CLIMATE CHANGE IN THE EAST AFRICA RIFT VALLEY

The Holocene was a time of cultural change in East Africa from hunter-gatherer and fishing to pastoralism and ultimately sedentary settlement. Recent excavations in paleoshoreline deposits of Lake Turkana, Kenya (4°N) provide new archaeological materials, a high-resolution stratigraphic and paleoenvironmental data set, OSL and radiocarbon dates, and cultural records. These archaeological materials in the context of documented environmental change (falling lake levels), provide insights about climate change in East Africa. Climate shifted from wetter in the Early-Mid Holocene (>5000 BP) to drier in Late Holocene followed by slight reversal in moisture levels at ~1000 BP. Archaeological material from Late Holocene sites (obsidian microliths, Nderit pottery sherds, wild and domestic mammal bones, and fish bones) are a proxy record of environmental change. Rather than a progressive change in subsistence strategies with increasing drought, a mixture of subsistence strategies (hunting and gathering, fishing, and herding animals) were all used.

Geoarchaeological study of sites provide evidence of environmental change. Dates (4.23 ± 0.27 ka) confirm that GaJj4 (Dongodien), a beach site on the Koobi Fora cuspate foreland, was the earliest site in East Africa to have domestic animals. Drying climate opened up a tsetse-free corridor between North and South Africa and falling lake levels exposed rich pasture land for domestic herds on the lake margin. This site is stratified and dates indicate that it was chosen for reoccupation (2.38 ± 20 ka). The site borders rich fishing grounds associated with nearby areas of lacustrine upwelling.

A complete buried skeleton (4.4 ± 0.28 ka), unfortunately with no grave goods, was uncovered at FwJj27. Late Holocene climate change is recorded in the palimpsest record of FwJj5 (0.90 ± 0.06 ka) in a small river valley containing a groundwater seep. Stone bowls, lithic artifacts, bone harpoons, fish bones, and domesticated cattle remains at this site located 5 km from the lake suggests a “cultural melting pot” of inhabitants. The archaeology indicates occupation by people who may have covered distances up to several km in accessing resources, but were likely drawn to an environmental refugia of a freshwater spring during times of regional aridity.