华南地区新石器早中期动物骨中羟磷灰石的污染鉴别及机制——以广西桂林甑皮岩遗址为例

DIAGENESIS AND MECHANISM OF BONE APATITE FROM EARLY AND MIDDLE NEOLITHIC ANIMALS IN SOUTH CHINA——CASE STUDY FROM ZENGPIYAN CAVE SITE IN GUANGXI

了解古代人(动物)骨羟磷灰石的污染,是对其开展C、O稳定同位素分析以揭示其食物来源和栖息环境的前提条件。目前,我国在此方面开展的研究较少,华南地区尚无报道,由此导致我们对此区域人群生存方式的变迁以及农业的产生与扩散等一些重要考古学问题,仍缺乏深入的了解。本文以广西桂林甑皮岩洞穴遗址(新石器早中期)出土的20例动物骨为研究对象,以10例现代骨为参照,对以上原始样品以及预处理后的样品进行了红外光谱分析,并对预处理后的样品进行了C、O稳定同位素分析,以期实现骨羟磷灰石的污染鉴别和探讨其机制。根据已发表数据和本研究10例现代骨的红外光谱及其指标(IRSF、CO3/PO4、FW85%),未经化学处理前的原始样品中,3例样品检测出明显的外源污染(方解石),剩余17例原始样品中仅余3例为未受污染样品。经预处理后,含方解石样品(n=3)红外谱图显示,其结构内仍有方解石残存;剩余17例不含方解石的样品中,12例样品的红外指标皆已符合现有标准(IRSF≤4.2和CO3/PO4≤0.6),样品可用数量显著提升。20例骨羟磷灰石的C、O稳定同位素分析进一步显示,去污染样品与污染样品的δ13C和δ18O值存在明显差异,污染样品的同位素数据更多反映了埋藏环境对其的影响。骨羟磷灰石的污染机制可能主要与华南地区特有的石灰岩地质环境密切相关。由此,进一步完善华南地区出土骨样的预处理方法并挑选出未受污染的样品,是今后开展稳定同位素分析的必经之路。

Assessment of human or animal bone diagenesis from archaeological sites is the prerequisite for stable isotope(C,O)analysis to reveal their diets and habitat.To date,the diagenesis research in China has been rarely reported in South China,hindering us to probe into the subsistence strategy of the prehistoric people.Zengpiyan cave(25°21’87.84″N,110°29’83.52″E)is a limestone cave site located in Guilin Guangxi.It was excavated in 1965~1979 and in 2001 by Archaeological Team of the Guangxi Zhuang Autonomous Region,Cultural Relic Survey Team of Guilin City and Institute of Archaeology Chinese Academy of Social Science.The site was dated to 12000~7000 a B.P.,belonging to early to middle Neolithic.The human and animal bones at the site were generally poorly preserved.In order to assess and discuss the diagenetic effects and mechanism on isotopic data of bone apatite,10 modern animal bones and 20 animal bones from Zengpiyan site before and after the pretreatment were analyzed by FTIR(Infrared spectrometers).In addition,carbon and oxygen isotope analysis were undertaken.According to the previously published data as the criteria to determine the bone contamination and 10 modern animal bone apatite as references,20 archaeological animal bones were divided into Group A(before pretreatment)and Group B(after pretreatment)to judge the diagenetic effects on bones.The infrared spectra of Group A showed the existence of exogenous substances(calcite)in 3 bones.On the other hand,only 3 of the remaining 17 animal bones in Group A can be regarded as the uncontaminated given their IRSF≤4.2 and CO3/PO4≤0.6.After pretreatment with 2%sodium hypochlorite and 1 M acetic acid,the infrared spectra of Group B showed 12 bones were in accord with the uncontaminated even though calcite still existed in 3 bones.This strongly indicates that the pretreatment significantly reduced the diagenetic effects of bone apatite,which greatly increased the availability of sample numbers for isotopic analysis.Carbon and oxygen isotope analysis of bones in Group B shows that there exist significant differences ofδ13 C andδ18 O values between contaminated and uncontaminated bones.The isotopic data of the contaminated bones might be biased by its post-mortem contamination.We call on the need to improve the pretreatment methods and try the best to diminish the bone diagenesis in South China in the near future,which will be quite beneficial to fill up the gap of the evidence on human subsistence strategy during the prehistoric era.