6-8 Record of a dynamic, fluctuating lacustrine margin from the Turkana Basin, Kenya

Session: Integrating 20 Years of Scientific Drilling in the East African-Syrian Rift: A Session In Honor of Andrew Cohen, Part I

Presenting Author:

Catherine Beck

Authors:

Beck, Catherine C.¹, Feibel, Craig S.², van der Lubbe, Jeroen³, Lupien, Rachel⁴, Alexander, Emily⁵, Campisano, Christopher J.⁶, Cohen, Andrew S.⁷

(1) Hamilton College, CLINTON, NY, USA, (2) Rutgers University, Piscataway, NJ, USA, (3) Vrije Universiteit, Amsterdam, Netherlands, (4) Aarhus University, Aarhus, Denmark, (5) Wake Forest University, Winston-Salem, NC, USA, (6) ASU, Institute of Human Origins, Tempe, AZ, USA, (7) University of Arizona, Dept Geosciences, Tucson, AZ, USA,

Abstract:

Scientific drill cores from continental eastern Africa provide proxy records, which contextualize the paleoclimate and paleoenvironment in which hominins evolved. However, without thorough sedimentological context, these records cannot be interpreted to their full potential. Here we present a detailed facies analysis of the West Turkana Kaitio (WTK) core (~1.9-1.4 Ma) retrieved from northern Kenya as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP). The sedimentology, including biologic components such as macro- and microfossils were described for the core from direct observation and with the aid of high-quality color images and smear slides. From the lithology, fossil record, and sedimentary structures, 11 facies were defined. The individual facies were subsequently grouped into common, repeating facies associations to better understand patterns including trends and cyclical changes throughout the record. The facies associations reveal an up-core trend of a lake regression, shown most dramatically in a color change from greenish gray to reddish brown at ~1.5 Ma (60 m below surface). Superimposed on this first order regression are 126 shorter (cm-scale) fluctuations from lacustrine laminated clays that become increasingly pedogenically modified moving up core. The dominant depositional environment of the drill site is interpreted as a dynamic fluctuating lacustrine margin that was subaqueous during transgressive events but sub-aerially exposed and forming weak soils during regressions. Significantly, the core location was extremely sensitive to high-frequency climate cycles that cannot be easily resolved in a deeper water record from the lake center. These fine-scaled cycles are on the order of 2-3 kyr and due to their high-frequency are interpreted to reflect lake level changes in response to climatic variability. This archive demonstrates the opportunity, unprecedented in outcrop, to resolve sub-Milankovitch scale cyclicity for lake levels in the Turkana Basin. These results also challenge the long held conceptual model of the Turkana Basin that predicted deep, stable lacustrine conditions for paleo-Lorenyang Lake along the western shore from ~2.0 to 1.5 Ma. Further, this has implications for regional ecosystems, including the nearby hominin fossil localities such as the Nariokotome Boy (KNM-WT 15000) and the earliest documented use of the Acheulian technology (Kokiselei). Hominins potentially utilized these dynamic lake margins because of the diversity of resources they presented.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8635

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