WHY LOMEKWI? THE GEOLOGY AND DEPOSITIONAL CONTEXT OF THE LOMEKWI 3 ARCHAEOLOGICAL SITE IN KENYA: A SEDIMENTARY FACIES ANALYSIS

The Lomekwi Member is part of the Nachukui Formation, a Plio-Pleistocene sedimentary exposure west of Lake Turkana in northwestern Kenya. Over the last 30 years, much fieldwork has been conducted around the Lomekwi member, resulting in many 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 site. The Nachukui Formation was formally named and described in 1988 by Harris et al., but to date, there has been no high-resolution facies analysis or paleoenvironmental reconstruction of the Lomekwi member.

During the summer of 2016, in association with the West Turkana Paleo Project, 14 stratigraphic sections were measured and facies analyzed in each of the LO fossil collection areas. Additionally, previously measured stratigraphic sections around the LOM3 archaeological site were assessed in the field for facies classifications and associations. The analyses of the Lomekwi Member and its environs indicate 21 facies classifications and eight facies associations. The high-resolution facies analysis combined with the correlation of the stratigraphic sections provide a window into this complex depositional regime.

Rapid accumulation of muds and soils lent to the excellent preservation of fossils and artifacts 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. Analyses also indicate several lacustrine intervals, to include smaller ponds and oxbow lakes. Forthcoming analyses of pedogenic carbonate and phytoliths should speak to the climate of this area, and hopefully provide insight as to why these hominins chose to inhabit this area. Additionally, further analyses of tephra collected should serve to more tightly constrain the time period over which the Lomekwi member spans. Finally, understanding the paleoenvironment of this fossiliferous and artifact-rich location will help direct future researchers to similar areas in which to study.