Near Infrared Spectroscopy between social archaeology and geochemistry. A transdisciplinary experiment from a Swedish Mesolithic dwelling site

Near Infrared Spectroscopy (NIRS) is a well-known analytical method largely applied to various research fields as punctual measurements or chemical imaging. This remote sensing technique is used in pharmaceutics and food quality control as well as in agricultural and forest sciences and geology. In archaeology the use of Near Infrared bands is usually limited to the detection of archaeological features through UAV or satellite imagery. This approach can be integrated by close range spectroscopy and hyperspectral imaging (HSI) to analyze various archaeological materials. In particular NIRS can be used in provenance studies and soil geochemistry to help detecting and mapping intangible properties. Applying chemical imaging and portable spectroscopy it is possible to collect empirical data to track production and use of stone artifacts over time as well as detecting the concentration of certain compounds in the soil. These invisible records must be collected and analyzed in order to define the ecological system of humans and the space in which they live. Stones and soils, as we see them in the archaeological context, are the result of a long chain of interactions embedded in their physicality. The material qualities of these objects are the center of a network of social relations and exchanges with the environment. The life story of items is registered in their primary material properties and physical alteration from contact with other agents.

We will discuss few different case studies in which the application of NIRS is combined with spatial analysis, study of techniques and archaeology of buildings, the data gathered are treated through statistical analysis and compiled in tridimensional database platforms (3D GIS).

In particular we will focus on the example of a Mesolithic pit house in northern Sweden. The site of Lillsjön, Ångermanland (RAÄ 260), was excavated in 2010-2012 by a team of researchers and students from the University of Umeå, uncovering a dwelling feature and the surrounding settlement area. Within the project it was possible to analyze more than 820 soil samples through various techniques (NIRS, X-Ray Fluorescence, Inductively Coupled Plasma optical emission spectrometer, total organic content, magnetic susceptibility and phosphate content). Lithic tools were classified according to the technology and the raw materials using hyperspectral imaging. The documentation from the excavation has been compiled into a geodatabase together with the geochemical data. Through the analysis of this big dataset it was possible to understand the spatial organization of the site.