Study On The Buried Dating Of Al / ¹⁰ Be In The Bailongdong Ruins Of Yunxi, Hubei Province

26Al/10Be burial dating is a new dating method emerged at the boundary between earth and physics sciences over the past dozen years. In situ cosmogenic nuclides are produced when secondary cosmic-ray particles penetrate the ground surface and react with nuclei within mineral grains.26Al and 10Be are two important cosmogenic nuclides. The 26Al/10Be ratio of about 6.75 remains nearly constant and is independent of varying altitude and geomagnetic latitude. If quartz minerals, after a long period of exposure near the ground surface, are suddenly washed into a cave or deeply buried, the production of cosmogenic nuclides drastically slows and the inherited radionuclide concentrations decay exponentially over time with an apparent half-life of 1.48 Ma.Bailong Cave is located at Yunxi County, Hubei Province in central China. Two excavations between 1977 and 1982 lead to the discovery of five human teeth, about twenty stone artifacts and a number of mammalian fossils. Judging by morphological and metric features, the human teeth were classified as Homo ereucts. Based on the faunal composition, the age of Bailong Cave was proposed as in the Middle Pleistocene. However for the lack of suitable dating method, the radiometric dating of the locality has been blank. Cosmogenic 26Al/10Be burial dating has been successfully applied to studying the chronology of Paleolithic hominin cave sites. Here we report the results of 26Al/10Be burial dating of Bailong Cave.The deposits inside the cave are divided into eight layers. All of the hominin teeth and stone and bone artifacts, and most of the mammalian fossils were unearthed from the deposits of Layer 2. We took three quartz samples from below the Layer 2. Three 26Al/10Be measurements of two quartz samples give ages of 0.65 ± 0.11 Ma、 0.67 ± 0.10 Ma and 0.81 ± 0.09 Ma (±1σ), corrected for insufficient coverage to 0.69 ± 0.12,0.70 ± 0.10 and 0.86 ± 0.10 Ma, respectively, with a weighted mean of 0.76 ± 0.06 Ma.Main conclusions are as follows:1. Taking into account possible bias of the dating method, stratigraphic order and evidence of rapid sedimentation, the cultural deposits of the site should be younger than 0.76 ± 0.06 Ma.2. The results of this paper potentially push the human coexistence with Stegodon-Ailuropoda fauna to an earlier time, and here the human actor on the stage is a later representative of H. erectus.3. Further studies are needed to refine the chronology of the site. Notably as the Brunhes-Matuyama magnetic reversal is within error range of the proposed date, paleomagnetic analyses may provide an effective means to narrow the uncertainties. Also, by washing dozens of kilograms of excavated deposits during a small scale excavation, we may possibly be able to obtain enough coarse quartz grains for a direct 26Al/10Be dating of the cultural Layer 2. Finally, if additional samples were collected it might be possible to carry out isochron 26Al/10Be burial dating to circumvent possible geological uncertainties.