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Paper No. 148-4
Presentation Time: 2:20 PM
THE STRATIGRAPHIC CONTEXT OF THE MIDDLE STONE AGE IN THE KOOBI FORA FORMATION: MID-LATE PLEISTOCENE BASIN HISTORY OF THE NORTHERN TURKANA BASIN
The Koobi Fora Formation (eastern Turkana Basin, Kenya), represents a laterally extensive Plio-Pleistocene sequence of well-dated tuffaceous fluvial, lacustrine and aeolian deposits. The stratigraphic resolution contains volcanic ash beds which allows for a high chronostratigraphic framework and allows for the study early hominin evolution over time. However, an important time period in hominin development, the Middle Stone Age (MSA), is not well understood as it is stratigraphically situated in a highly eroded, unconformable Chari Member sediment unit (1.34 Ma to 10 ka). This complication is further compounded by lithologically localised and laterally discontinuous beds. Nevertheless, the existence of MSA-bearing beds have been reported by Kelly and Harris (1992) and noted in surveys conducted between the years 2015-2018.
Here, we present the stratigraphic investigation of MSA-bearing deposits noting occurrence and lithology across the sub-regions of the basin. The Ileret region represents at least two chronological occurrences of MSA-bearing deposits. The oldest, located in area 7, is situated between the Kale Tuff and the unnamed tuff (< 0.74 Ma) and overlain by a younger (undated) unconformable unit correlated across areas 4, 5, 6A and 7. Younger occurrences found in other regions were dated using Optically Stimulated Luminesce (OSL). These occurrences are situated in a laterally occurring deposit (~ 160 ka) in the Karare region and in two correlated deposits (30 - 60 ka) near Koobi Fora. The lithology of all three regions is sourced from underlying geology and represents deposition in near-shore environments as evident with arenaceous packages rich with gastropoda and bivalva, as well as upward fining sequences of flood plain beds. This near-shore environmental reconstruction represents a unique example of early modern human lacustrine habitation in eastern Africa. The preservation of occurrences represents localised depocentres and their preservation can be attributed to indurated sandstones, which cap the deposit during a repeatedly erosive time. This regional stratigraphic framework provides the first dated context of modern human occupation in the Turkana Basin and can ultimately elucidate the role of aquatic resource use in the development of modern human behaviour.