黑龙江省小南山遗址受热历史的考古磁学证据

Archaeomagnetic evidence for heating history of the Xiaonanshan archaeological site in Heilongjiang Province, northeastern China

考古磁学技术为考古遗址的受热历史研究提供了重要的定性/定量分析方法.黑龙江省东北部的小南山是中国东北地区重要的史前遗址之一,该遗址记录的最早人类活动可以追溯到更新世末期.遗址揭露了距今约16 ka以来序列性的人类生活遗物及遗迹,包括大量的石制品和少量的陶片,以及与当时人类生活方式相关的疑似用火遗迹.本文对小南山遗址内疑似用火区及周边的散土样品进行了一系列岩石磁学测试,包括低频磁化率、逐步磁化率随温度变化曲线(χ-T)、磁滞回线、等温剩磁获得曲线、反向场退磁曲线和一阶反转曲线(FORC)等,旨在通过磁学指标为遗址受热温度、受热范围等信息提供定量化证据.实验结果显示,采样区域内两处疑似用火区(ZB、ZC)磁化率普遍偏高、逐步χ-T曲线在400~600℃之间表现出较好的热稳定性、饱和等温剩磁偏强、FORC信号偏强;而表层烧土被清理后的疑似用火区(ZA)和非疑似用火区磁化率普遍偏低、逐步χ-T曲线显示样品在加热过程中逐渐发生热变化、饱和等温剩磁和FORC信号偏弱.这些磁学特征意味着ZB、ZC两处疑似用火区曾受过加热烘烤,而从ZA采集到的样品和疑似用火区外的样品则可能没有受热.逐步χ-T曲线结果显示疑似用火区高磁化率样品在400~600℃之间表现出较好的热稳定性,而当温度达到700℃时则发生明显的热转化,指示样品历史最高受热温度应该在600~700℃之间.

Archaeomagnetic techniques provide important qualitative and quantitative analysis methods for heating history of archaeological sites.The Xiaonanshan site,located at northeastern Heilongjiang Province,is one of the most important prehistoric sites in northeast China.The earliest discovered human activity relics on this site trace back to the Late Pleistocene.The site unearthed series of remains and relics of human activity since 16 ka,including many stone artifacts,some potteries,and a few remains of suspected fire use related to human lifestyles.In this study,we collected soil samples from the suspected fire areas and surround area,and conducted a series of rock magnetic experiments,including low-frequency magnetic susceptibility(χLF),step-wise variation of susceptibility versus temperature(χ-T),hysteresis loop,isothermal remanent magnetization(IRM)acquisition curves,back field demagnetization curves(BFD)and first order reversal curve(FORC)diagrams,to provide quantitative data for the heating history,e.g.,heating temperature and heating range,of the site.The results indicate that the two suspected fire areas(ZB,ZC)show higherχLF,higher saturation IRM,stronger signal of FORC,and better thermal stability between 400~600℃,while the suspected fire area ZA,with surface soil removed during excavation,and surrounding area show lowerχLF,lower saturation IRM,weaker signal of FORC,and gradually thermal alteration during the heating process indicated byχ-T curves.The rock magnetic results support the two suspected fire areas ZB and ZC were burnt,while ZA and surrounding areas were probably not heated,at least not to high temperatures as ZB and ZC.The thermal stability between 400~600℃and obviously thermal transformation at 700℃of theχ-T curves indicate that the historical heating temperatures of firing areas are about 600~700℃.