苏家村遗址烧土样品的过火温度研究

Determination of the thermal temperatures of burnt clay at Sujiacun site based on magnetic susceptibility

烧土制品作为最早的人工建筑材料,使人类的居住环境得到了根本性的改善。然而,学界关于烧土建筑的成因存在人为烘烤处理、缘自火焚、废弃习俗等多种观点。通过科技手段研究烧土制品的过火温度,有助于科学分析烧土建筑的成因,探讨与之相关的建筑工艺,丰富史前建筑史研究。磁学研究表明,考古遗址中的土壤及其他沉积物在受热后新生成了磁铁矿、磁赤铁矿等强磁性矿物导致磁性显著增强,且矿物成分和磁性几乎不会再发生变化;但当重烧的温度接近或大于原始烧成温度时,样品中原始矿物的破坏或新矿物的生成,会引起矿物磁性的改变。基于这一原理,实验室内分析受热黏土的磁化率随再加热温度的变化特征,可反映烧土制品的过火温度。苏家村遗址是大汶口文化晚期至龙山文化中期早段一处重要的聚落遗址,遗址中第5层为厚约20~40 cm的红烧土层且覆盖整个遗址,推测为房屋倒塌造成的建筑垃圾堆积层或人为堆积层,出土大量烧土块。本研究利用X射线衍射分析法、X射线荧光光谱分析法和磁化率法等对苏家村遗址出土的烧土样品开展了组成及构造特征和样品的过火温度的综合分析。结果表明,苏家村遗址烧土样品中的白灰层中人为地添加了白色陶土原料,土层中有意地添加了植物残骸作为羼和料,推测是为加强坯体的强度和粘结度的草筋泥,与该样品可能为房屋倒塌造成的建筑垃圾堆积的推测一致;烧土样品属于人为烧制,其等效过火温度区间为600~700℃;烧土内部未出现玻璃化,结构疏松,抗压强度较低,在制定烧土遗迹保护方案时,应根据烧土的过火温度,采取针对性的保护措施,从而取得最佳保护效果。苏家村遗址烧土制品的出现,使人类建造房屋的能力和水平跃上了新的台阶,对于了解山东新石器时代晚期建筑技术具有重要意义。磁化率法适用于这一类低温烧制酥松黏土样品的过火温度研究,进一步可尝试应用于早期陶器(尤其低温陶器)的烧成温度研究。

As the earliest artificial building materials,burnt clay products led to a fundamental improvement in the living environment of prehistoric human beings.There are many viewpoints on the causes of burnt clay buildings,such as artificial baking,accidental fire,and abandonment customs,etc.Determination of the firing temperatures of burnt clay materials in prehistoric architectural relics is helpful by providing important information on technical development and enriching research on the history of prehistoric buildings.Magnetic research shows that soil and other sediments at archaeological sites contain newly-formed magnetite,maghemite and other strongly magnetic minerals after being heated,resulting in significant enhancement of magnetism,and that the mineral compositions and magnetism hardly change thereafter.However,when the re-firing temperature is close to or greater than the original firing temperature,the destruction of original minerals or the formation of new minerals in samples causes a change in mineral magnetism.As a result,analysis in the laboratory of the characteristics of magnetic susceptibility variation of heated clay with temperature changes can reflect the firing temperatures of burnt clay products.Sujiacun site is an important settlement site from the late Dawenkou culture to the early middle Longshan culture.The fifth layer is a burnt clay layer with a thickness of about 20—40 cm that covers the whole site.It is speculated that the layer is a construction waste accumulation site or a man-made accumulation site caused by house collapse.In this study,the compositions,structural characteristics and firing temperatures of burned clay samples unearthed from Sujiacun site were analyzed by X-ray diffraction(XRD),X-ray fluorescence spectrometry(XRF)and magnetic susceptibility method.The results show that the white clay(kaolin)raw material was artificially added to the white ash layer of the burnt clay samples from the Sujiacun site,and that plant debris was intentionally added as an extender to the burnt clay layer.It is speculated that this is straw-reinforced mud used to improve the strength and adhesion of the body.This verifies the speculation that the samples may come from building materials.The burnt clay samples were artificially fired,with the firing temperatures ranging from 600℃to 700℃.There is no vitrification inside the burnt clay,the structure is loose and the compressive strength is low.When formulating a scheme for protection of burnt clay relics,we should take targeted protection measures according to the firing temperatures of burnt clay in order to achieve the best protection effect.The appearance of burnt clay products brought humans into a new level of skill in building houses.The study of burnt clay products is of great significance to understanding the architectural technology of the late Neolithic Age in Shandong Province.The magnetic susceptibility method is suitable for studying the firing temperatures of low-temperature-fired burnt clay samples and could be further applied to the study of the firing temperatures of early pottery(especially low-temperature pottery).