| The establishment of a robust chronological framework for early Pleistocene hominin sites in East Asia is very important to the study of early human evolution and migration.However,due mainly to the lack of volcanic material for K/Ar(40Ar/39Ar)dating,almost all of these sites were dated by Paleomagnetism and Biostratigraphy,rather than any radioisotopic dating method.As a consequence,the chronology of most of these sites has remained controversial.26Al/10Be burial dating is a relatively still new dating technique.By analyzing the ratio of the two nuclides in quartz material,this method could provide age constraint for burial event occurred in the past 0.3-5.0 Ma.Since its establishment,simple burial dating method has been more and more widely applied in landscape evolution,archaeology and Paleoanthropology,and thus with potential for providing more robust chronological framework for the early Pleistocene sites in China.However,as its reliability is controlled by the validity of several prerequisites,this method is limited to fluvial,lacustrine and cave deposits with a thickness of overburden no less than 10 m.The isochron method has become a new approach for burial dating in the very recent years.By analyzing several samples from the same horizon level,and plotting their 26Al and 10Be data on the Cartesian coordinates,a straight line whose slope is dependent on the burial age could yielded through fitting,this provides a means to reveal the true burial age of the set of samples from shallower burial depths,and also offering a check for internal consistency.In this study,both of simple and isochron burial dating methods have been applied to Majuangou in Nihewan Basin and Gongwanling in Lantian,two important early Pleistocene sites in China.Based on Paleomagnetic study,the MJG-? layer of Majuangou site was previously dated to 1.66 Ma,being considered to be the earliest Paleolithic site in East Asia.In the present work,two 80 m-long sediment cores were drilled from the top of east bank of Majuangou gully.8 coarse quartz samples were retrieved from the cores,along with other 4 samples taken from the cross-sections of nature outcrop.The simple burial dating results of the core samples and the nature-outcrop samples are consistent with each other.According to these results,the Banshan layer should date back to 1.25± 0.08 Ma,a weighted mean age for MJG-??? layers is 1.67±0.06 Ma,consistent with the previous paleomagnetic age.This is the first evidence from radioisotopic dating that supports a human presence in East Asia as early as?1.7 Ma.The Gongwangling site was famous for the discovery of the Lantian man skull cap,one of the most important Homo erectus fossils found in China.In this study,we collected 7 samples from the top of the gravel layer,being 7 m below the finding layer of hominin fossils.Isochron burial dating on these samples yielded an age of 1.76 ±0.12 Ma,being consistent with the recently reported paleomagnetic polarity(Olduvai subchron)of this layer.Our result represents the age of the fifth terrace of Ba River,and marks the maximum age for the hominin fossils.It is compatible with the recent paleomagnetic age(1.63 Ma),however,could not exclude the possibility of a much younger age for the Gongwangling homininThis study provides the first radio-isotopic ages for Majuangou and Gongwangling site.Results confirmed the feasibility of simple burial dating method in hominin sites from Nihewan lacustrine sediment,and that of isochron burial dating method in hominin sites from aeolian deposits,thus lay the foundation for future series of studies in establishing a robust chronological framework for the early Pleistocene sites in East Asia by using 26Al/10Be burial dating method. |
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