40AR/39AR GEOCHRONOLOGY OF MOCHENA BORAGO: REFINING THE OCCUPATIONAL PERIOD OF LATE PLEISTOCENE HUNTER-GATHERERS IN MOCHENA BORAGO ROCKSHELTER, SW ETHIOPIA

Mochena Borago Rockshelter is a Late Pleistocene and early Holocene archaeological site whose radiocarbon dates place prehistoric hunter-gatherer occupation of the site between 49-36 ka ago. This site’s abundance of lithic material and artifacts during a major period of homo sapien dispersal leads to greater questions of how these early hunter-gathers interacted with Mochena Borago Rockshelter and the role of the SW Ethiopian highlands during a period of climatic instability in Marine Isotope Stages (MIS) 4 and 3. The rockshelter is situated on the western flanks of Mt Damota, a trachytic volcano near the Southern Main Ethiopian Rift System that exhibits the same volcanic activity generally found in this part of the rift. Damota and the area adjacent to the rift have long experienced intermittent episodes of Quaternary-aged volcanic events shaping the depositional history of the site with definable volcanic stratigraphic layers and material interbedded between periods of human occupation. Mochena Borago Rockshelter has gone through intensive geologic processes including volcanic, aeolian, colluvial, and fluvial activity where these external and internal occurrences have impacted the stratigraphy of the site and defined its spatial complexity. Until recently, researchers at Mochena Borago have been limited in their assigning of chronological context to lithic assemblages and other artifacts found at the site due to the exceedance of the practical radiocarbon upper limit (approximately 50 ka). Under SWEAP (Southwest Ethiopian Archaeological Project), a collection of volcanics sitting within major stratigraphic units of the geologic sequence were collected during the most recent field season with the active excavation area, MB5, to be used for 40Ar/39Ar dating. The 40Ar/39Ar dates of this pyroclastic material will yield more insight into the spatial complexity of Mochena Borago’s archaeologic and geologic sequence and assign a more precise date to when early hunter-gatherers occupied the site.