Stratigraphic analysis of the Sterkfontein StW 573 Australopithecus skeleton and implications for its age.
StW 573, Little Foot, is the most complete Australopithecus skeleton yet discovered, with many of its bones found in their correct anatomical position. Since the discovery of the in situ skeleton in the Silberberg Grotto in 1997, several teams have attempted to date the fossil. This appeared a simple process because several flowstones are inter-bedded in the breccia above and below StW 573. Dating of these flowstones, using U-Pb (uranium-lead) isotope decay techniques, gave younger results than expected from the fauna and stratigraphic position, around 2.2 Ma (millions of years). Our recent stratigraphic, micromorphological and geochemical studies revealed that the stratigraphy is much more complicated than was previously thought, with localized post-depositional processes leading to the creation of voids within the breccia around the skeleton. These voids were then filled by multiple generations of flowstone growth. The research we present here demonstrates that the proposed dates based on the flowstone deposition can give only a minimum age for StW 573 and that the flowstone formation came after, and probably long after, the breccia deposition. If one takes account of the long evolution of these karst fillings, StW 573 appears to be significantly older than 2.2 Ma.
French National Institute for Preventive Archaeological Research (Inrap), 561 rue Etienne Lenoir, km delta, 30900 Nîmes, France; University of Toulouse, UMR 5608 du CNRS (TRACES), Maison de la Recherche, 5 Allées Antonio Matchado, F-31058 Toulouse, France; School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa. Electronic address: laurent.bruxelles@inrap.fr.
Laurent
L
Bruxelles
Evolutionary Studies Institute, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa. Electronic address: ronald.clarke@wits.ac.za.
Ronald J
RJ
Clarke
University of Bordeaux, UMR 5185 ADES, CNRS, 3 Maison des Suds, 12 Esplanade des Antilles, F-33607 Pessac cedex, France. Electronic address: rmaire@ades.cnrs.fr.
Richard
R
Maire
University of Bordeaux, CENBG, UMR 5797, F-33170 Gradignan, France; CNRS, IN2P3, CENBG, UMR 5797, F-33170 Gradignan, France. Electronic address: ortega@cenbg.in2p3.fr.
Richard
R
Ortega
School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa. Electronic address: dominic.stratford@wits.ac.za.
Dominic
D
Stratford
D000818:Animals; D001106:Archaeology; D005075:Biological Evolution; D001842:Bone and Bones / Q000737:chemistry; D002910:Chronology as Topic; D005580:Fossils; D019015:Geologic Sediments / Q000737:chemistry; D015186:Hominidae; D007856:Lead Radioisotopes / Q000737:chemistry; D010163:Paleontology; D055110:Radiometric Dating; D013019:South Africa; D014501:Uranium / Q000737:chemistry
D007856:Lead Radioisotopes; D014501:Uranium
Geochemistry; Geochronology; Little Foot; Micromorphology; Pliocene; Silberberg Grotto; South Africa