A CULTURAL REVOLUTION IN HUNTER-GATHERER SUBSISTENCE STRATEGIES LIKELY LINKED TO HOLOCENE CLIMATE CHANGE: APPLICATIONS OF OSL DATING TO ARCHAEOLOGY

The Holocene was a time of dramatic climate change in East Africa, shifting from wetter climate characterized by high lake levels in the Early-Mid Holocene (>5000 BP) to drier climate with lower lake levels in the Late Holocene. By ~4500 BP the area was headed into drought and the lake level lowered leaving successively younger shorelines (Galana Boi Fm.) stranded as beach, delta and coastal dune sediments. Archaeological data indicate that the Early to Late Holocene was a time of cultural change from hunter-gatherers and fishing folk to agro-pastoralists, but dating these important cultural adaptions in the absence of organic-rich sediments has been difficult. Thus, the cause and effect link between climatic conditions and type of subsistence practices has remained elusive. Recent excavations of sediments along the shores of Lake Turkana (4º N) yielded archaeological materials, high-resolution stratigraphy and paleoenvironmental analyses, quartz-OSL dates and new insights into the timing of cultural change in the context of documented environmental change.

Dongodien (GAJI 4) along the eastern shore of L. Turkana is an unusually well preserved sequence of sub-lacustrine, beach and sub-aerial lake margin sediments. The 12 m stratified section contains two archaeologically-rich beds (A & B). The lower bed (B) comprised of coarse sand has an OSL age of 4.23 ± 0.27 ka. This date is supported by uncalibrated radiocarbon ages (ka) of charcoal from fire pits: 4.18 ± 0.04, 4.24 ± 0.04 and 4.18 ± 0.04. Archaeological material (obsidian microliths, Nderit pottery sherds, cut-marked bones of wild and domestic mammals, and fish bones) suggests a mixture of subsistence strategies (hunting and gathering, fishing, and herding animals) as climate turned from wet to dry. The OSL dates confirmed that Dongodien was the earliest site in East Africa to have domestic animals. The upper bed (A) of medium sand has a younger OSL age of 2.78 ± 0.19 ka consistent with its stratigraphic position. In contrast to data from other luminescence dating attempts elsewhere in the East African Rift System, quartz OSL for samples from this locality and from sites FwJj5 and FwJj25 ~40 km NW have a dominant fast component and robust intrinsic characteristics. OSL dating has been shown to be a valuable dating tool for archaeological sites with organic-poor sediments.