Microarchaeology of hearths in tropical contexts by high-resolution FTIR microscopy

• Grant number: 24/13199-4
• Support Opportunities: Scholarships in Brazil - Support Program for Fixating Young Doctors
• Start date: August 01, 2024
• End date: July 31, 2025
• Field of knowledge: Humanities - Archeology - Prehistoric Archaeology
• Agreement: CNPq
• Principal Investigator: Ximena Suarez Villagran
• Grantee: Isabela Ferreira Sodré dos Santos
• Host Institution: Museu de Arqueologia e Etnologia (MAE). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 24/02117-7 - Microarchaeology of hearths in tropical contexts by high-resolution FTIR microscopy, AP.R

Abstract

Identifying combustion features (anthropogenic fires) in very ancient archaeological sites is challenging, primarily due to the susceptibility of burned sediments to reworking and diagenesis over time, which makes microarchaeology essential to document their composition, preservation, and function. The use of FTIR spectroscopy for the study of archaeological sediments was introduced in 2007 by Berna et al. and is well-established internationally in the field of microarchaeology. However, this approach has been virtually unexplored in the Brazilian context, reported only in the study conducted by Villagran et al. (2017) in investigations into the site formation process at Lapa do Santo shelter in central-eastern Brazil. In this work, combustion structures were investigated by monitoring heat-induced alterations in the molecular structure of the clay mineral kaolinite through chemical analyses using FTIR spectroscopy coupled with microscopy (FTIR microscopy). This research project aims to expand this approach by investigating combustion features identified in archaeological sites in different coastal and central regions of Brazil, with the main objective of addressing the need for the development of an analysis protocol that takes into account the complexity of tropical soils, predominantly composed of oxisols, whose intense weathering and leaching significantly alter the properties of minerals monitored in the investigations. A characterisation protocol based on high-resolution FTIR microscopy mapping, considered cutting-edge in this field of knowledge, will be employed to achieve this.In addition to conventional FTIR microscopes (equipped with MCT detector) for mapping, the results will be consolidated in further steps by analysis using state-of-the-art FTIR microscopes: (i) FTIR Microscope equipped with an FPA detector for imaging with higher resolution; and (ii) FTIR Microscope with synchrotron IR light source, whose high brightness and collimation allow conditions for working at very high resolution with high spectral quality. This detailed approach is expected to enhance the sensitivity of the currently employed methods in determining burning events near the kaolinite transition temperature (below 500 °C), as fires rarely produce higher temperatures in the soil, even near the surface, posing a challenge in this field of study. (AU)