Constructing a Stratigraphic Framework for East African Hominid Localities: A Case Study in the Application of Tephrostratigraphy

Christopher J. Campisano¹ and Craig S. Feibel^2
1 Smithsonian Institution, Washington, DC
² Rutgers University, Piscataway, NJ

The dynamic and highly variable nature of terrestrial depositional environments often proves problematic when dealing with issues of lithostratigraphic correlation in basin analysis. While the construction of a proper chrono- or lithostratigraphic framework for intra-basin correlations is complicated enough, high-resolution inter-basin correlations based upon lithology or paleontology alone is often impossible. Tephrostragraphy, the geochemical correlation of volcanic ejecta in stratigraphic sequences, has proven an invaluable method for the correlation of widespread but often discontinuously exposed geologic strata preserving tephra deposits (ash, lapilli, and pumice). Tephra deposited via airborne or fluvial processes provides an isochronous marker across landscapes both proximal and distal to their original point of origin. As most tephra deposits have a unique geochemical “fingerprint”, tephrostratigraphy allows geologists to correlate sequences, establish temporal relationships, and construct long-term composite records from local sections.

One of the best examples of the utility of tephrostratigraphy comes from the Plio-Pleistocene paleontological and archaeological localities of the East African Rift. Here we demonstrate how the tephrostratigraphy of these deposits has provided a tightly resolved stratigraphic framework not only for highly variable intra-basinal deposits, but also for the correlation of deposits up to 1000 km apart. Well beyond the resolution provided by typical biostratigraphical analysis, the application of tephrostratigraphy revolutionized our ability to understand the pattern and timing of Plio-Pleistocene evolution in East Africa. As tectonically active regions with abundant explosive volcanism, such as the East African Rift, are often potential exploration targets, such a technique may also have significance to the petroleum industry.