Luminescence dating of weathered sediments from the Paleolithic site of Fengshuzui in northern Hunan province, China

Abstract

Abstract South China is an important region for the investigation of the origin of modern humans and the dispersal of Homo sapiens in Asia. However, the accurate dating of Paleolithic sites, especially for open-air sites, in the region has been difficult due to the lack of datable materials like bones that were destroyed due to intense chemical weathering. In this study, we applied optically stimulated luminescence (OSL) dating techniques to the Paleolithic site of Fengshuzui in south China, in which the deposits are intensely weathered. We first investigated the degree of chemical weathering of the deposits and the effect of weathering on dose rate, and then measured the equivalent dose of quartz extracts from five sediment samples from a ∼5\u202fm thick archaeological section. The contents of mobile and immobile elements determined by different analysis methods show that the studied sediments are homogenous in chemical and mineral compositions. Enrichment or depletion of major and trace elements including U and Th were not detected. The sediments consist of ∼60% quartz, ∼30% illite and ∼6% feldspars, ∼3% kaolinite and ∼2% hematite. The calculated chemical weathering indices show that the sediments have been intensely weathered, and the weathering degree of the five studied samples at different depths are similar. Radioactive disequilibrium in the uranium decay series caused by weathering was not detected. All these indicate that the effect of chemical weathering on dose rate is negligible for our samples. The quartz extracts displayed excellent luminescence characteristics, and the five samples, from bottom to top, were dated to 123\u202f±\u202f7, 98\u202f±\u202f5, 98\u202f±\u202f4, 81\u202f±\u202f3, 68\u202f±\u202f2 ka, respectively. The ages of the cultural layers range from 100 to 70 ka, mainly corresponding to MIS 5. This also implies that the OSL techniques can be employed to date open-air sites in south China, but the effect of weathering on dose rate should be investigated on a case by case basis.