Combining the HSPDP West Turkana Core with Outcrop Samples to Provide a Climate Framework

Combining the HSPDP West Turkana core with outcrop samples to provide a climate framework for hominin evolution between ca. 2.1 -1.4 Ma

Josephine Joordens, Craig Feibel, Guillaume Dupont-Nivet, Andy Cohen, Catherine Beck, Jeroen van der Lubbe, Mark Sier, Cor Langereis, Hubert Vonhof

The Turkana Basin (Kenya, Ethiopia) is famous for the discovery of large numbers of hominin fossils. Especially the time period between ca. 2.1 and 1.4 Ma, when several early Homo species together with Paranthropus boisei roamed the landscape around paleolake Lorenyang, is considered to be a key interval in hominin evolution. The aim of our study is to provide a cyclostratigraphic climate framework for hominin evolution between ca. 2.1 and 1.4 Ma. In summer 2013, the ICDP Hominin Sites and Paleolakes Drilling Project (HSPDP) succesfully drilled a 215 m long core in paleolake Lorenyang deposits in West Turkana. After drilling, complementary outcrop fieldwork by our team yielded a set of high-resolution paleomagnetic and sediment samples covering the complete Lorenyang lake interval (253 m). We will apply a climate proxy, which combines strontium isotope stratigraphy (measuring 87Sr/86Sr of fish and ostracod fossils sampled from core and outcrop sediments) with magnetostratigraphy providing the required age tie points to resolve precession-forced wet-dry climate cycles. Previously, this approach has been employed in the lowermost part of paleolake Lorenyang in the East of the basin (Joordens et al., 2011, 2013). There we demonstrated the strength of the method to resolve precession cycles and showed that hominins persisted in both dry and wet phases of the cycles. However, the younger (< 1.87 Ma) Lorenyang deposits in East Turkana are not suitable to capture climate cycles due to basin configuration.Now, the unique combination of core and outcrop samples from West Turkana will for the first time allow us to construct a climate framework for the whole time period between ca. 2.1 and 1.4 Ma, which may include episodes of orbitally-forced extreme climate variability, as well noncyclic variability leading to a generally drier climate in the younger part of paleolake Lorenyang. These climatic changes are expected to have exerted a strong influence on hominin evolution and dispersal.

Joordens, J.C.A., Dupont-Nivet, G., Feibel, C.S., F. Spoor, Sier, M.J., van der Lubbe, H.J.L., Kellberg Nielsen, T., Knul, M.V., Davies, G.R., Vonhof, H.B., 2013. Improved age control on early Homo fossils from the upper Burgi Member at Koobi Fora, Kenya. Journal of Human Evolution, accepted.

Joordens, J.C.A., Vonhof, H.B., Feibel, C.S., Lourens, L.J., Dupont-Nivet, G., van der Lubbe, H.J.L., Sier, M.J., Davies, G.R., Kroon, D., 2011. An astronomically-tuned climate framework for hominins in the Turkana Basin. Earth and Planetary Science Letters 307: 1-8.