GSA Connects 2021 in Portland, Oregon

Paper No. 145-11
Presentation Time: 10:35 AM


HIRNIAK, Jayde1, SMITH, Eugene2, JOHNSEN, Racheal2, REN, Minghua2, CAMPISANO, Christopher1 and MAREAN, Curtis1, (1)School of Human Evolution and Social Change, Institute of Human Origins, Arizona State University, 900 Cady Mall, Tempe, AZ 85281, (2)Department of Geoscience, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010

Tephra deposits have been instrumental in constructing the chronostratigraphic framework at east African archaeological and paleontological sites for decades. However, the use of tephrochronology at archaeological sites in South Africa has not been used in the past due to the lack of visible volcanic deposits. The recent discovery of the 74 ka Youngest Toba Tuff (YTT) as cryptotephra in South African archaeological sites Pinnacle Point (PP) 5-6N and Vleesbaai demonstrated the potential for this technique. The YTT eruption deposited cryptotephra across eastern and southern Africa, providing an isochron useful for linking human behavioral and cultural changes between archaeological sites and for testing existing age models. The YTT shards are rhyolitic with SiO2>75 wt. %, FeO < 1.0 wt. % and K2O/Na2O>1. Trace elements of deposits throughout South Africa are nearly identical to those from distal YTT present at Lake Malawi and Malaysia, providing strong evidence for a widespread isochron.

While the YTT is commonly the subject of discussion, the 26.5 ka Oruanui (New Zealand) eruption was also extremely explosive (VEI = 8) and likely deposited tephra in South Africa within weeks following the eruption based on atmospheric tephra transport models. Therefore, this paper will report on evidence of the YTT as well as a younger cryptotephra population, potentially sourced to the Oruanui eruption, present at the Kathu Pan 6 archaeological site in Northern Cape Province, South Africa. Shards from Kathu Pan 6 are rhyolite with FeO >1.0 wt. % and higher trace element abundances than YTT, indicating that this cryptotephra is a separate population from YTT. These findings demonstrate the potential of a larger tephrochronological framework throughout this region, which is essential for age control in archaeological and geological studies, particularly for understanding the temporal-spatial sequence of technological and behavioral changes of modern humans in southern Africa.