Study Of Uranium-series Dating Of The Mouth-hole Sites In Yunnan

The appearance of anatomically modern Homo sapiens is a hotly debated issue in paleoanthropology. Specialists and lay people alike now tend to recognize two major models, i.e. "out of Africa" and "multiregional evolution". In China, there is a widely accepted "temporal gap" between 40-100 ka of human presence, which is recognized as an important evidence in favor of the "out of Africa" hypothesis. However, we thought it is only a false phenomenon due to methodological imperfections.Zhangkou Cave, located at the Jiuxiang Scenic Area in Yiliang County, Yunnan Province, is one of the numerous anthropologic cave sites in southern China. From the deposits inside the cavern, 40 hominid fossil teeth attributed to modern Homo sapiens together with -2,000 mammalian fossils representing 33 species have been discovered. Relics of prehistoric human activities, such as stone artifact and charcoal grains have also been found. There were two conventional 14C ages, 9965+110 years on charcoal grains from the upper strata and 14550+450 years on fossil bones from the lower part. Thus Zhangkou Cave was considered being Late Pleistocene to early Holocene in time. However, it is well known that classical 14C determination on fossil materials is of limited reliability. While U-series dating of compact and well crystallized cave calcites, with its fairly high reliability, is widely used for hominid fossil sites. Acorrding to the excavation report, in T| and T2 of Zhangkou Cave, there are 10 flowstone layers, which provide favorable materials for chronological studies.We have carried out 230Th/234U dating on several intercalated calcite samples. The results show that the capping flowstone layer and the second one are Holocene in time. The fourth flowstone layer is of an age of 55 ka, and the fifth one 110 ka. The cultural deposits which are bracketed by the two flowstone layers should be of an age between 55 and 110 ka. The sixth flowstone layer gave date of 300 ka, which is much too old compared with the previous 14C age of-15 ka on fossil materials.The results of our study imply that time span of deposits inside Zhangkou Cave is much greater than previously estimated, providing one more example for the under-estimated chronologies of Chinese Middle and Late Pleistocene sites. For abundant relics and favorable condition for chronological study, this site is likely to become a benchmark for correlative subjects research and provide important information on physcical and cultural evolution, stone implement civilization and climate since tens of thousands of years.