GEOCHRONOLOGY AND STRATIGRAPHY FOR PALEOANTHROPOLOGY SITES FROM EAST-CENTRAL AREA 130, KOOBI FORA, KENYA

In the Koobi Fora region of the northeast Lake Turkana Basin (Kenya) dozens of archeological sites have been excavated in order to understand the behavior of Early Pleistocene hominins. Data collected from these sites have been important for demonstrating the manufacture styles of Oldowan stone-tool users, hominin dietary preferences, and processes of Early Stone Age site formation. A well-known and particularly rich locality is collection Area 130 of Koobi Fora. Area 130 is noteworthy for hominin fossils KNM-ER 1805 (Homo) and 1806 (Paranthropus) as well as the FxJj 18 site complex, which represents one of the type localities for the Developed Oldowan of Koobi Fora. However, despite research beginning in the late 1960s, and several revisions to the stratigraphy and dating of the Koobi Fora Formation, there are few studies that have attempted to provide the fossil and archaeological sites of Area 130 with a sequence and chronology. The lack of a detailed chronostratigraphy for the Area 130 succession has contributed to conflicting interpretations for the dates of KNM-ER 1805 and 1806 hominin fossils.

Here we present new geochronology and paleomagnetic data used to develop a chronostratigraphic framework that allows us to directly assess the age of the sediments, fossils, and artifacts from Area 130. Single pumices from the Orange Tuff marker level and an unnamed tuff exposed near the FxJj 18 archaeological site complex have been dated by high precision single crystal ⁴⁰Ar/³⁹Ar dating on k-feldspar separates. Concurrently we collected orientated paleomagnetic samples from the fine-grained strata in Area 130 from stratigraphic positions situated between the KBS Tuff and the of the Okote tuffaceous siltstone complex and used them to develop a magnetostratigraphic section for Area 130. Our findings allows us to better constrain the stratigraphy of the analyzed sections and can be used to refine the sequence and chronology of the archaeological and fossils sites from Area 130 and other penecontemporaneous sites within the Koobi Fora Formation and elsewhere in the Lake Turkana Basin.