Cosmogenic nuclide dating of <i>Australopithecus</i> at Sterkfontein, South Africa.

Abstract

Sterkfontein is the most prolific single source of <i>Australopithecus</i> fossils, the vast majority of which were recovered from Member 4, a cave breccia now exposed by erosion and weathering at the landscape surface. A few other <i>Australopithecus</i> fossils, including the StW 573 skeleton, come from subterranean deposits [T. C. Partridge <i>et al.</i>, <i>Science</i> 300, 607-612 (2003); R. J. Clarke, K. Kuman, <i>J. Hum. Evol.</i> 134, 102634 (2019)]. Here, we report a cosmogenic nuclide isochron burial date of 3.41 ± 0.11 million years (My) within the lower middle part of Member 4, and simple burial dates of 3.49 ± 0.19 My in the upper middle part of Member 4 and 3.61 ± 0.09 My in Jacovec Cavern. Together with a previously published isochron burial date of 3.67 ± 0.16 My for StW 573 [D. E. Granger <i>et al.</i>, <i>Nature</i> 522, 85-88 (2015)], these results place nearly the entire <i>Australopithecus</i> assemblage at Sterkfontein in the mid-Pliocene, contemporaneous with <i>Australopithecus afarensis</i> in East Africa. Our ages for the fossil-bearing breccia in Member 4 are considerably older than the previous ages of ca. 2.1 to 2.6 My interpreted from flowstones associated with the same deposit. We show that these previously dated flowstones are stratigraphically intrusive within Member 4 and that they therefore underestimate the true age of the fossils.