Lions Hole Uranium Series Dating And The Baise Basin In Guangxi Youjiang Ⅲ Level Terrace S Of The First

Baise Basin in Guangxi Autonomous Region, covering an area of-800km2, is dissected by the Youjiang River from northwest to southeast. Terraces II-IV along the river preserve concentrations of Paleolithic stone artifacts. Their chronological position has been difficult to define because of the lack of suitable samples for dating.Previously fission track and40Ar/39Ar dating of tektites buried in T4gave ages of-733and803ka, respectively. However, no isotopic dating on T3has ever been carried out.Bubing Basin is a small basin subordinate to the larger one of Baise. Shizi Cave is located in the karstic peaks which constitute the former basin’s southern border. The cavern’s depositional sequence can be divided into two layers:upper fossiliferous sandy-clay and lower weathered sandstone gravels, which resembles the dualistic structure of fluvial terraces. The sample of SZD-3, taken from a thin flowstone layer at the boundary of the two depositional layers, gives a high precision MC-ICP-MS U-series date of366±19ka, which coincides well with the dates with alpha spectrometry. Another sample ca.1.4m higher, SZD-4, taken from calcite drapery adhered to a projecting rock of the cave wall, dates to517±42ka, representing the maximum age of the deposits inside the cave.Being situated at the same elevation of140-150m above sea level, the deposits inside Shizi Cave should be coeval with the third terrace of Bubing Basin. Based on the highly reliable mass spectrometric U-series dating of pure and dense cave calcites with definite stratigraphic provenience, and on the recognition that the evolution of Bubing Basin has been contemporaneous with Baise Basin, the age of the third terrace of Baise Basin may be bracketed in the range of366-517ka.The results here presented represent the first radioisotopic age assigned to this terrace, and render support to the reliability of previous dating of T4. Moreover our results mark an important step forward in systematic studies of geomorphological and archaeological evolution in the region.