T184 Human Evolution and Environmental History in Africa: 25 Years of Transformative Research (Posters)

Tuesday, 6 November 2018
9:00 AM - 6:30 PM
Halls J-K

GEOLOGY AND PALEOENVIRONMENTS OF FARRE, A LARGE OPEN-AIR MIDDLE TO LATE PLEISTOCENE ARCHAEOLOGICAL SITE IN EAST AFRICA

Paper number: T184-1
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Knowledge of the paleoenvironments associated with late-Middle and Late Pleistocene archaeological sites in East Africa is critical for understanding the broader context of the emergence of anatomically modern humans and their dispersal some 70 ka. One such site is Farre, a large open-air archaeology site in the arid (150 mm yr-1) and hyperthermic (>22ºC) Chalbi desert, northern Kenya. Farre is currently situated in a modern interdune pan. The site age is likely between 155 and 90 ka old and no younger than ca. 33 ka. Facies analysis, paleopedology and geochemistry suggest that Farre was positioned either in a medial/distal fan or littoral nearshore setting, proximal to paleo-lake Chalbi 155-90 ka. Paleopedology shows that the Farre soil is a complex relict paleosol that weathered under a range of climate conditions. Paleoprecipitation modeled using PPM provides a best estimate of 338 mm yr-1, but the error ranges from 0 to 852 mm yr-1, which limits our ability to interpret paleoclimate using this model. However, Si weathering rates of the Farre paleosol, -1.7x10-5 to -8.0x10-5 mol cm-2 yr-1, are similar to those found in the Sonoran Desert (340 mm), consistent with wetter paleoclimate conditions. Isotope-based canopy cover estimates are also consistent with this wetter climate and previous faunal analysis, where Farre was thought to have been vegetated under woody grassland. The modern-day Farre relict paleosol is likely sodic and has extremely alkaline pH, which is a testament to the modern hyper-arid conditions and possible dust influx sourced from the nearby saline clay pan. The hydrologic variability inferred from this complex polygenetic paleosol at Farre is consistent with regional paleoclimate records and shows that near-surface archaeology and fauna can be overprinted with younger weathering processes from contrasting environments, challenging paleoenvironmental interpretations. This work was supported by the National Science Foundation (BCS-1524036 and BCS-1524041)

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-323626

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