Preservation and Paleoenvironmental Significance of a Footprinted Surface on the Sandai Plain, Lake Bogoria, Kenya Rift Valley

Abstract

An exhumed late Pleistocene land surface on the deltaic Sandai Plain north of Lake Bogoria, Kenya, preserves traces of bovids, suids, birds, and at least one hominid. The host sediments (Loboi Silts) are reddish brown, poorly bedded siltstones, mudstones and silty sandstones that were probably deposited in a shallow closed-basin lake. Most of the prints were impressed on exposed, moist lake-marginal mudflats. Print distribution is patchy due to a complex interaction between biogenic and sedimentological factors. The preservation of a single hominid track provides a fortuitous addition to the sparse hominid track record in East Africa. Field, petrographic, and mineralogical analyses of the fossil substrate were undertaken to determine how the footprinted surface was preserved. Comparison with modern lake-marginal processes suggests that the prints were initially stabilized by desiccation, soil-crusting, and organic films, followed by cementation of the surface sediments by calcite and analcime, with minor authigenic clay minerals and Fe-Mn-oxihydroxides. The zeolites formed by reaction of detrital silicates with saline, alkaline groundwater; calcite was precipitated from dilute runoff and fresher groundwaters. Cementation likely occurred during a prolonged period of relatively low, stable lake level. Following cementation, the surface was buried by Holocene lake sediments, then recently exhumed.

Keywords:

• Paleoichnology
• vertebrate tracks
• hominids
• Kenya Rift
• taphonomy
• diagenesis

ACKNOWLEDGEMENTS

This research has been supported by an NSERC Research Grant (RGPIN629) to R.W.R, and a HKBU Grant (#FRG/02–03/II-15) to R.B.O. We thank the Government of Kenya for granting research permission; Mr. William Kimosop, Senior Warden of the Lake Bogoria National Reserve, for his continuing support; Jenna Cole and Michael Kimeli for advice and field assistance; Gail Ashley and Vicky Hover for helpful discussions and assistance in the field; and Andy Cohen and Martin Lockley for their helpful, insightful and thought-provoking reviews of the manuscript. Thank you also to Martin Lockley for the invitation to submit to this special volume.