A Study On The Stratigraphic Age Of The Maize Cave Archaeological Site In Wushan, Chongqing

Yumi Cave,located in the Wushan County of Chongqing is a newly discovered important prehistoric archeological site.Since it was excavated in 2011,a large number of archaeological findings such as mammal fossils and stone artefacts have been unearthed.In this study,43 dating samples collected from the Yumi cave were analyzed,including seven stalactite fragments,14 in-situ formed secondary carbonates,12 bone fossils,three charcoal debris and seven fossil teeth.Among them,the charcoal debris samples excavated from the fire relics at the T5 and T6 squares of the cave site and the three fine bones excavated from the upper strata?second layer?were used for the(AMS-¹⁴C)dating to obtain the direct age of the representative strata.Fossil teeth unearthed from the layers of 1,2,3…..were dated with the combined U-series and ESR dating method to obtain the direct ages of the representative strata.Bone fossils from the layers of 1,2,3…were dated by U-series method.Because they do not satisfy closed system for uranium and its daughters,the U-series dates of fossil bones were used here to define the minimum age of the corresponding layer.Secondary carbonates attached to the surface of breccia or clay were also dated by U-series method.Because they were deposited after the formation of the corresponding sedimentary layer,the U-series dates were also used to define the minimum age of the strata.In addition,stalactite fragments felling from the cave roof or cave wall were also dated by U-series method.Because the formation ages of these speleothem fragments are earlier than their burial ages,their U-series dates are used to define the maximum age of the strata.Finally,this study uses a hierarchical Bayesian model based on the Chrono Model software to combine the chronological results obtained by the above different methods with the stratigraphic order,in order to establish a complete of chronological framework for the Yumi Cave site.The Bayesian analysis results of this study show that the overall stratigraphic age range of the cave site is about 300,000 years from the late Middle Pleistocene to the Holocene.This is consistent with the biostratigraphic age.On the whole,the upper strata?between the second strata and the third strata?of the cave site have sedimentary discontinuities,and the lower strata are more continuous.