关键词: 牙珐琅化石;电子自旋共振法测年;龙骨坡

Abstract: Huang et al ( 1995) reported the discovery of fossil hominid materials ( a single incisor and a bro ken mandible with P4— M1 ) and stone artifactsin the levels 7— 8 of the Longgupo profile, Wushan county. The publication has evoked much controversy. The main objections are: ( 1) the phylog enetic position of the mandibular dentition is not hominid, but hominoid and ( 2) the incisor belongs to late Homo sapiens and is intrusive into the old deposits.
This paper has the concern only with the dating problem of Longgupo Profile. Based on geomagnetic study of the profile and a single ESR age of a deer-tooth from the level 4, Huang assigned the Olduvai subchron to the magnetically normal levels 7— 8. However the published ESR age, 0. 75 Ma ( Early U-uptake) and 1. 02 Ma ( Lineal U-uptake) , could not exclude the possibility that the geological time of levels 7-8 fits Jaramillo subchron ( 0. 90— 0. 97Ma) .
In this work four animal tooth-enamel samples collected from levels 2-5 were dated with ESR method. The measured parameters and the final ESR EU and LU ages are summarized in the table 1. External gamma dose-rate was estimated from the average U, Th and K contents of the surrounding sediments which are 3. 14μg· g- 1 , 4. 3μg· g- 1 and 0. 5% respectively. Ka= 0. 15, radon loss= ( 30± 15)% and moisture= ( 10± 5)% were assumed in age calculation. The last three samples in table 1 show concordant EU ages of 1. 1— 1. 34Ma , but sample W -93002 is an exception, continuous U-uptake indicated by its low 230 Th /234 U ratio and higher U-content may account for its lower age.
The authors suggest that the ESR-EU ages of 1. 1— 1. 34M a serves only the lower limits of the true ages, because: ( 1) for samples of Earlier Pleistocene thermo-fading of paramagnetic centres in samples should be taken into consideration; ( 2) the real uranium uptake pattern is always bracketed by EU and LU uptake models, if no significant recent uranium leakage from samples detected ( this is the case for the samples studied in this work). Therefore the geomagnetically normal subchron of levels 7— 8 should be Olduvai Subchron ( or no younger than). Although the taxonomic classification of the`hominid’ fossils is still a matter of dispute and the certification of the artifacts is going on , the new ESR dating results may be helpful in understanding of this site and the evolution of the Longfupo fauna.

Key words: Tooth-enamel fossil, ESR dating , Longgupo