10.6084/m9.figshare.3454310.v1
Ian McDougall
Ian
McDougall
Francis H. Brown
Francis H.
Brown
Precise <sup>40</sup>Ar/<sup>39</sup>Ar geochronology for the upper Koobi Fora Formation, Turkana Basin, northern Kenya
Geological Society of London
2016
sequence
KBS Tuff
Ma
Silicic tuffaceous horizons
Koobi Fora Formation
Ar
Geology
2016-06-21 12:02:40
Dataset
https://geolsoc.figshare.com/articles/dataset/Precise_sup_40_sup_Ar_sup_39_sup_Ar_geochronology_for_the_upper_Koobi_Fora_Formation_Turkana_Basin_northern_Kenya/3454310
<p>The Plio-Pleistocene Koobi Fora Formation, about 560 m thick, crops out east of Lake Turkana and is part of the much larger
depositional system of the Omo–Turkana Basin. The upper half of the Koobi Fora Formation from just below the KBS Tuff to above
the Chari Tuff is particularly notable for its wealth of hominid fossils and archaeological sites. Silicic tuffaceous horizons
have provided the basis for stratigraphic subdivision and correlation. Pumice clasts within the tuffs contain anorthoclase
phenocrysts, ideal for <sup>40</sup>Ar/<sup>39</sup>Ar single-crystal dating. Feldspars from pumice clasts in about 15 tephra within the stratigraphic interval from the KBS Tuff
to the Silbo Tuff have yielded precise ages that allow much finer definition of the numerical time framework for the sedimentary
sequence between the KBS Tuff (1.869 ± 0.021 Ma) and the Chari Tuff (1.383 ± 0.028 Ma) and to yet higher in the sequence to
the SilboTuff (0.751 ± 0.022 Ma). These results provide a precise and accurate time scale for the upper part of the sequence
in the whole of the Omo–Turkana Basin. A number of these tuffs are recognized elsewhere in East Africa; thus ages determined
at Koobi Fora also apply to the wider region.
</p>