U-Th dating of a Paleolithic site in Guanyindong Cave, Guizhou Province, southwestern China

Guanyindong Cave in southwestern China has received considerable attention in the investigation of Paleolithic hominin origins and evolution in China, due to its rich archaeological finds composed of thousands of stone artifacts and a unique fauna with 23 species of mammalian fossils found. However, despite earlier extensive excavations and descriptive studies, debates still centre around the conflict between previous radiometric age data and evidence from biostratigraphic correlations. In this study, we carried out detailed field investigations and sampling, and obtained 35 U-Th dates on flowstone layers and other datable materials from the cave. The age results from materials in stratigraphic context provide a robust chronological framework of the cave. The data suggest that the deposition of Group B sediments and fossil assemblages widely distributed within the cave should have occurred after ~370 ka but before ~70 ka, with the bulk of the sediments and associated fossils laid down during 200–140 ka. Our new U-Th dates of in situ flowstone layers intercalated with one rhinoceros tooth and several other fossil fragments near the Hall at the centre of the cave constrain the deposition ages of these mammalian fossils to the period between 469 ± 37 and 336 ± 7 ka. Combined our U-Th data with recent OSL dates of Hu et al. (2019), we suggest that Group A sediments and associated fossils were likely deposited episodically from ca. 90 ka to <40 ka. Overall, our data indicate that the cave development started >469 ± 37 ka ago, whilst the cave system framework took shape as we see today >340 ± 10 ka ago. Subsequently, the cave might have experienced several flooding and washout events, resulting in recycling and mixing of older sediments and fossils into younger sequences, a hypothesis consistent with tight clustering of both U-Th ages of speleothems in this study and the OSL dates of clastic sediments (Hu et al., 2019). This would reconcile the contradiction between the great antiquity of mammalian fossils inferred from biostratigraphic correlation and the much younger radiometric dates of materials in stratigraphic context, and explain the lack of technological advance despite an apparently long presence of the “Guanyindong culture”, as well as the presence of the Levallois technologies. In this regard, our U/Th age data, combined with other recent studies, have resulted in an improved understanding of Paleolithic hominid evolution and stone technologies in south China.