A FLUCTUATING PLEISTOCENE LAKE MARGIN: UPDATES FROM THE HSPDP WEST TURKANA KAITIO DRILL LEG

The HSPDP West Turkana Kaitio (WTK) drill leg was completed in July 2013. While challenges were encountered during drilling, including penetrating a hydrothermal fracture system at ~197-207 m depth, ultimately this leg was successful as the entirety of the Pleistocene section from the KBS Tuff to the Natoo Tuff was recovered (2.0-1.45 Ma). Investigation of the stratigraphy and facies revealed a fluctuating lake margin with cycles of lacustrine clay transitioning into lacustrine clays with a weak soil overprint. Soils were recognized in cores by brecciated fabrics, sedimentary dikes, and slickensides on ped surfaces. While the section reflects a more marginal lacustrine environment than anticipated, the soil overprint does not compromise the quality of the record and no significant erosional surfaces were seen. The marginal lacustrine deposits may prove to be highly sensitive to climate induced lake level change as small-scale transgressions and regressions are preserved. An age model for this core comes from the robust tephrostratigraphic framework of the Turkana Basin. At present at least 5 tephra-rich intervals have been identified within the core. This allows for indirect dating through geochemical fingerprinting, and correlations with outcrop sections around the basin. The tephrochronology is coupled with a paleomagnetic record from the core. The stratigraphy and chronology provide the framework for multiproxy studies, including clay XRD, pollen, phytoliths, diatoms, ostracods and biomarkers. For example, a preliminary scan was conducted at ~3.2 m intervals to study the ostracods. Ostracod-rich samples primarily contained the genera Gomphocythere and Limnocythere. Samples with both abundant ostracods and pyrite have higher carapace preservation resulting in more articulated, whole valves and little to no staining. Ostracods are an ideal proxy as they have high preservation potential, are abundant throughout much of the section, and assemblage data can provide basis for paleolimnologic interpretations. The ecology and paleochemistry of paleo-Lake Turkana is linked to changes in the paleoclimate. The interval spanned by the WTK core is of great interest to the paleoanthropological community as it targets a relatively continuous sedimentary record from a time of significant evolutionary change.