A terrestrial auxiliary stratotype point and section for the Plio-Pleistocene boundary in the Turkana Basin, East Africa

Abstract

The Turkana Basin of northern Kenya and southern Ethiopia preserves an extensive record of terrestrial sediments and fossils dating from the Oligocene through the Holocene. Of particular significance is the Plio-Pleistocene Omo Group, which documents changes in environments and faunas through the Pli-Pleistocene. Omo Group strata have been intensively studied for nearly three decades, and a tightly constrained stratigraphic framework has been developed. The lithostratigraphic sequence shows that a fluvial system dominated the basin for most of the past five million years, with six relatively short but significant intervals of lacustrine deposition. The sequence is punctuated by some 130 tephra, most of which have been geochemically characterized, and can be used as a basis for local and inter-basinal correlation. These tephra reach as far as the Gulf of Aden and the Indian Ocean, providing a means of tightly correlating the marine and terrestrial records. Isotopic dating and magnetic polarity stratigraphy allow good temporal control on the sequence, with over 30 control points in the interval from 4.35 to 0.6 Ma. Extensive paleontological collections from this context provide critical calibration of East African biostratigraphic markers. The Plio-Pleistocene boundary can be closely constrained in the Omo Group deposits based on magnetic polarity stratigraphy. This allows the boundary to be related to components of the stratigraphic framework recognized in the terrestrial sequence there, and thence related to other East African terrestrial localities by a variety of correlation tools. Establishment of the Omo Group sequence as an Auxiliary Stratotype Point for the Plio-Pleistocene boundary will thus allow close relation of these terrestrial localities on the basis of tephro- and biostratigraphy, the most useful correlation tools in the East African terrestrial record.