Microscale imaging of the preservation state of 5,000-year-old archaeological bones by synchrotron infrared microspectroscopy

Abstract

Archaeological bone materials record characteristic markers of life in prehistoric times (dating, climate, environment, diet, human migration) in their isotopic and chemical composition in addition to palaeontological, archaeozoological, anthropological and palaeogenetic information. Thus, the discovery and conservation of archaeological bone materials is of great importance to get access to this information. However, archaeological materials are altered by different postmortem processes and it appears necessary to estimate if the archaeological information is still reliable or if it has been modified during burial. As archaeological bone materials present a high structural hierarchy at the micro- and nanoscale, changes induced by diagenetic phenomena have to be observed at these scales. One method for revealing post mortem changes of the bone structure and composition at the microscale is synchrotron radiation micro-FTIR imaging (SR micro-FTIR). Thus, thin sections of about 5,000-year-old archaeological bones have been analysed in transmission mode at the IRIS beamline (BESSY II, HZB Berlin) to determine markers of the state of bone preservation at the microscale. The archaeological bone material comes from station 19 of the Neolithic site of the Chalain Lake. By using SR micro-FTIR it was possible to image characteristic bone structures, e.g. osteons (the constitutive histological unit of cortical bone), using the absorption band ratios corresponding to different chemical bone constituents (collagen content and quality, phosphate crystallinity, carbonate content). These data allow us to precisely evaluate the state of preservation of a 5,000-year-old bone at the histological level.

Informative Potential of Multiscale Observations in Archaeological Biominerals Down to Nanoscale

“…The drying process must be as slow as possible and a high humidity should be maintained as long as possible to avoid bursting. Additionally and also observed on other biological tissues, the alteration features within an object might be variable depending on the environmental conditions and the advancement of alteration (Godfrey et al 2002;Lafontaine and Wood 1982;Chadefaux and Reiche 2009;Large et al 2011;Reiche et al 2003Reiche et al , 2010.…”

“…Such multi-scale analytical approach combining different complementary methods was recently adapted to determine the preservation state of archaeological elephant ivories and bone. The investigation allowed characterizing both, the mineral and organic phase of ivory, with 2D and 3D structural information on the small samples at all length scales of the hierarchical tissue (Chadefaux and Reiche 2009;Large et al 2011;Müller and Reiche 2011;Reiche 2009aReiche and Chadefaux 2009;Reiche et al 2003Reiche et al , 2007Reiche et al , 2010Reiche et al , 2011aAlbéric et al 2014). …”

“…These methods were developed on modern and experimentally altered (heated) bone samples, and applied to archaeological samples. Particularly, FTIR micro-spectroscopy imaging using synchrotron light was first performed on histological thin sections (<2 µm thick) in transmission mode to investigate qualitatively and quantitatively the mineral (mineral crystallinity, carbonate content, presence of authigenic minerals) and organic phases (collagen alteration state and content) in samples (Lebon et al 2011a;Reiche et al 2010). FTIR micro-spectroscopy in Attenuated Total Reflexion (ATR) mode was later applied to be able to analyse hard and brittle samples impossible to cut in very thin sections (Lebon et al 2016).…”

“…Nowadays, two and sometimes three-dimensional (2D and 3D) elemental, molecular, structural and isotopic imaging of entire objects has becomes possible owing to recent technological developments off ocused analytical probes used in scanning mode and detectors (e.g. Lebon et al 2011a;Reiche et al 2011aReiche et al , 2003Reiche et al , 2010Reiche and Chalmin 2008;Anne et al 2014;Bergmann et al 2010;Gueriau et al 2014;Gourrier et al 2007bGourrier et al , 2010.…”

Towards a Better Understanding of Alteration Phenomena of Archaeological Bone by a Closer Look at the Organic/Mineral Association at Micro- and Nanoscale. Preliminary Results on Neolithic Samples from Chalain Lake Site 19, Jura, France

“…Background spectra were collected under identical conditions in constant intervals. Th e spectrum acquisition has been performed by using the OMNIC AtlμsTM software [39]. Spectral data analysis was performed using the OMNIC 7.4 (Th ermo) and OPUS (Bruker Optic GmbH) software.…”