CORRELATING KNOWN HOMININ SITES AND PALEOLANDSCAPES TO THE OGCP CORES, OLDUVAI GORGE, TANZANIA

During 2014 OGCP (Olduvai Gorge Coring Project) drilled 612 m of continuous core (recovery 94%) from four boreholes (1A, 2A, 3A, 3B) at three sites within the Olduvai Basin. These sites were selected to sample primarily lacustrine lithologies to deliver optimal paleoclimatic and paleoenvironmental proxy records. The deepest borehole penetrated the Naabi Ignimbrite, the oldest unit exposed in nearby outcrops, at a depth of ~110 m and continued another 135 m without reaching basement. More than 18 new pyroclastic units are identified in this new stratigraphic interval. We present OGCP methods to pinpoint core stratigraphic levels, corresponding to archeological levels. documenting evolutionary changes of hominin morphology, technology and behavior.

Tephrostratigraphic fingerprinting, radiometric dating, and magnetostratigraphy allow and will aid correlation to Tuffs that Hay (1976) recognized in exposures. Some outcropping hominin-related paleolandscapes can be readily correlated to the core based on tephrostratigraphy; e.g. FLK Level 22 (Zinjanthropus) and HWKE Level 1 (Oldowan hominin level) equate to the surfaces below Tuff IC and on top of Tuff IF, respectively. However other archeological levels (e.g., OH 9, OH 13) are not adjacent to Tuffs. We therefore utilize Sequence Stratigraphic concepts to define time-lines, allowing such hominin assemblage levels in their lake marginal, fluvio-deltaic and fan settings to be more precisely correlated from outcrop to cored lake sequences.

To illustrate our approach we feature correlation of Leakey's DK Oldowan assemblage, famous for its "Stone Circle", and set within a 3 m interval of lake marginal to alluvial fan sediments bracketed between the Bed I Basalt and Tuff IB, to its position in Borehole 2A. The equivalent interval is 18 m thick in Borehole 2A, and precise lithofacies correlation uncertain. However, using Sequence Stratigraphy, we correlate five "time-rock" parasequences at DK, each bound by unconformities and related to individual lake transgression and regression, as far west as the lake marginal FLK Fault. We correlate them to dolomite-topped time-rock units in Borehole 2A. By this means, the DK paleolandscape surface can be placed to ±50 cm within the core 2A succession.