Abstract
In the Koobi Fora region of the northeast Lake Turkana Basin (Kenya) dozens of archeological sites have been studied for decades 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 particularly rich locality is collection Area 130. 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, few published studies provide a detailed chronostratigraphy for Area 130. The lack of a detailed chronostratigraphy has contributed to conflicting interpretations for the dates of the hominin fossils and archaeological sites. Here we present new geochronologic and paleomagnetic data to develop a chronostratigraphic framework that allows us to directly assess the age of the sediments, fossils, and artifacts from Area 130. Individual pumices from the Orange Tuff marker level and a previously unnamed tuff exposed near the FxJj 18 (referred here as the FxJj 18 tuff) archaeological site complex were collected for high precision single crystal 40Ar/39Ar dating. Concurrently, we collected orientated paleomagnetic samples from stratigraphic levels of the KBS Member in Area 130 and used them to develop a magnetostratigraphic section. Our findings allow 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 Lake Turkana Basin. Our data show that the first appearance of the Developed Oldowan for Koobi Fora does not correlate with any obvious evolutionary changes represented by the local hominin hypodigm nor with the arrival of a cognitively advanced hominin. Therefore we speculate that the advent of this more sophisticated type of stone tool was a response to a change in the diet of the genus Homo.
Highlights
Within the northeast part of the Lake Turkana Basin (Kenya) (Figure 1), dozens of archeological sites from the Koobi Fora Region have been studied since the late 1960s (Harris and Isaac, 1976)
KNM-ER 1805 and KNM-ER 1806 are the only hominin fossils recovered from the outcrops of Area 130 that we have examined for our study (Wood, 1991)
Yielding K-feldspar are consistent and have been combined together to obtain our best estimate for the age of the Orange Tuff at 1.763 ± 0.007 Ma (Figure 5). This age is consistent with the stratigraphic position of the Orange Tuff in Area 130 below the FxJj 18 tuff and above the KBS Tuff (∼1.87 Ma)
Summary
Within the northeast part of the Lake Turkana Basin (Kenya) (Figure 1), dozens of archeological sites from the Koobi Fora Region have been studied since the late 1960s (Harris and Isaac, 1976) Data collected from these sites have been important for interpreting the manufacture styles of Oldowan stone-tool users, hominin dietary preferences, and processes of Early Stone Age site formation (Rogers et al, 1994; Braun et al, 2008; Pobiner et al, 2008). The KBS Member from northeast to southwest varies from fluvial sands, conglomerates, and mudstones to a series of lake-margin, lacustrine, and alluvial deposits across a distance of ∼30 km (Lepre et al, 2007; Lepre, 2017) These difficulties have hampered efforts of dating archeological sites and hominin fossils, and well as underscore the need to individualize chronostratigraphic information for different geographic areas
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