A SYNTHESIS OF MULTI-PROXY PALEOENVIRONMENTAL RECONSTRUCTION METHODS: THE DEPOSITIONAL ENVIRONMENTS OF THE LOMEKWI MEMBER, NACHUKUI FORMATION, WEST TURKANA

The Lomekwi Member is part of the Nachukui Formation, a Plio-Pleistocene sedimentary exposure west of Lake Turkana in northern Kenya, dated from 3.4 to 2.5 Ma. Over the last 30 years, fieldwork has been conducted around the Lomekwi member, resulting in fossil discoveries, including Kenyanthropus platyops and Paranthropus aethiopicus. In 2011, the West Turkana Archaeological Project discovered the oldest known stone tools at the Lomekwi 3 (LOM3) site, and the West Turkana Paleo Project has ongoing field work in the region regarding hominin fossils. The Nachukui Formation was formally named and described in 1988 by Harris et al., but to date, high resolution facies analyses of the Nachukui Formation have been lacking.

In the Lomekwi Member, rapid accumulation of muds and soils lent to the excellent preservation of fossils and artefacts found in the alluvial fan gravels, and large-scale cross bedding and climbing ripples found in the Tulu Bor tephra deposits indicate the short-term dynamics of rapid deposition. Additionally, the pure, coarse-grained tuff found in channels suggests a main depositional pulse of volcanics, whereas interbedded tuffaceous silts imply flowing rivers depositing over longer periods. Several lacustrine intervals, to include ponds and oxbow lakes have been preserved.

Pedogenic carbonate analyzed from the Lomekwi Member denote a mean δ¹³C_VPDB value of - 7.36±1.1%, suggesting the fraction woody canopy cover was about 0.50. Values of δ¹³C of faunal tooth enamel collected here show that between about 3.5 Ma and 2.5 Ma, there was a dietary shift from mainly C₃ – C₄ mixed feeders to C₄ grazers. The pedogenic carbonate analyzed came from the same stratigraphic level as the stone tools found at the LOM3 archaeological site, dated to 3.3 Ma. The change in dietary shift appears to occur after this time, about 3.0 Ma and Lomekwi Member spans this interesting change in behavior.

I present previously unmeasured stratigraphic sections and correlate them with published sections to create facies analyses and facies associations. I also present a map of the depositional environments, which I use to make a paleoenvironmental interpretation of the study area, which is a mainly fluvio-lacustrine environment, including alluvial fans and deltaic elements.