Glass shards in Pinnacle Point Rock Shelter 5-6, South Africa: Are they from the last super-eruption of Toba

Cryptotephra, in the form of individual glass shards, have been discovered in paleoarchaeological site PP5-6 North at Pinnacle Point, Western Cape, South Africa. This marks the first documentation of cryptotephra in a South African paleoarchaeological site. PP5-6 North is a rock shelter in the cliffs along the coast of the Western Cape and is one of a series of caves and rock shelters at Pinnacle Point that were inhabited by early modern humans. The presence of cryptotephra at PP5-6 is an important discovery in terms of tephra preservation in cave deposits as well as the possibility of tephra being present in other nearby locations. The cryptotephra at PP5-6 presented numerous challenges in terms of extraction and analysis. Shards were less than 60 micrometers in size and were extremely low in abundance. Electron probe analyses show that the shards are rhyolitic in composition and optically stimulated luminescence dating of the host sediment indicates the shards are 73.7 ka. This leads to the conclusion that the cryptotephra in PP5-6 may represent an ultra-distal deposit, more than 5000 km from the source eruption, of the 74 ka Toba super-eruption in Sumatra, Indonesia. The Toba caldera is 8964 km away from Pinnacle Point, making Pinnacle Point the most distal deposit of this eruption.