The Olorgesailie Drilling Project and the related Hominin Sites and Paleolakes Drilling Project in East Africa were initiated to test hypotheses and models linking environmental change to hominin evolution by drilling lake basin sediments adjacent to important archeological and paleoanthropological sites. Drill core OLO12-1A recovered 139 m of sedimentary and volcaniclastic strata from the Koora paleolake basin, southern Kenya Rift, providing the opportunity to compare paleoenvironmental influences over the past million years with the parallel record exposed at the nearby Olorgesailie archeological site. To refine our ability to link core-to-outcrop paleoenvironmental records, we institute here a methodological framework for deriving a robust age model for the complex lithostratigraphy of OLO12-1A. Firstly, chronostratigraphic control points for the core were established based on 40Ar/39Ar ages from intercalated tephra deposits and a basal trachyte flow, as well as the stratigraphic position of the Brunhes-Matuyama geomagnetic reversal. This dataset was combined with the position and duration of paleosols, and analyzed using a new Bayesian algorithm for high-resolution age-depth modeling of hiatus-bearing stratigraphic sections. This model addresses three important aspects relevant to highly dynamic, non-linear depositional environments: 1)correcting for variable rates of deposition, 2)accommodating hiatuses, and 3)quantifying realistic age uncertainty with centimetric resolution. Our method is applicable to typical depositional systems in extensional rifts as well as to drill cores from other dynamic terrestrial or aquatic environments. We use the core age model and lithostratigraphy to examine the interconnectivity of the Koora Basin to adjacent areas and sources of volcanism.
Bibliographical noteFunding Information:
We gratefully acknowledge support for the Olorgesailie Drilling Project from the National Museums of Kenya, the Oldonyo Nyokie Group Ranch, the Peter Buck Fund for Human Origins Research (Smithsonian), the William H. Donner Foundation (R.P.), the Ruth and Vernon Taylor Foundation (R.P.), Whitney and Betty MacMillan (R.P.), and the Smithsonian's Human Origins Program. Geochronological research was supported by National Science Foundation grant EAR 1322017 . R.D. acknowledges support of a Smithsonian Postdoctoral Fellowship and by Geo. X, the Research Network for Geosciences in Berlin and Potsdam, Germany. M. S. acknowledges support from the Swiss National Science Foundation (grant P300P2 158501 ). Fig. 1 is based on the TanDEM-X Science DEM, granted to S. Riedl by the German Space Agency ( © DLR 2017). Research and drilling permits were provided by the Kenyan National Council for Science and Technology, the Kenyan Ministry of Mines, and the National Environmental Management Authority of Kenya, and facilitated by the National Museums of Kenya. We thank DOSECC Exploration Services for drilling supervision, Drilling and Prospecting International (DPI) for drilling services, and the US National Lacustrine Core Facility (University of Minnesota) for core handling, processing and storage facilities. We thank R.B. Owen for his collaboration with the lithologic core description. We are grateful for discussions and ongoing contributions by our colleagues of the HSPDP research groups.
- Bayesian modeling
- East Africa
- Kenya Rift
- Radiogenic isotopes