The formation, alteration and significance of pyrogenic magnetic fabric in mid-paleolithic burnt cave facies

Trabajo presentado en: Magiber XI, 4-7 de septiembre de 2019, Condeixa a NovaB. Bradák acknowledges the financial support of project BU235P18 (Junta de Castilla y Leon, Spain) and the European Regional Development Fund (ERD)

Saving Bones: a direct comparison of FTIR-ATR, whole bone percent nitrogen, and NIR

89th Annual Meeting of the American-Association-of-Physical-Anthropologists (AAPA), Los Angeles, CA, APR 15-18, 202

Magnetic fabric and archaeomagnetic analyses of anthropogenic ash horizons in a cave sediment succession (Crvena Stijena site, Montenegro)

An archaeomagnetic, rock magnetic and magnetic fabric study has been carried out on seven anthropogenic ash horizons in theMiddle Palaeolithic sedimentary level XXIV at the rock shelter of Crvena Stijena (‘Red Rock’), Montenegro. The study has multiple goals, including the identification of iron bearingminerals formed during combustion, assessment of the suitability of these combustion features for recording the Earth´s magnetic field direction, revelation of the magnetic fabric and its significance in the characterization of cave (rock shelter) burnt facies, and identification of post-burning alteration processes. Magnetite has been identified as themain ferromagnetic component of the ash. The ash layers exhibit a high thermomagnetic reversibility in contrast to the irreversible behaviour of their subjacent burnt black layers which is related to the different temperatures attained. Seven mean archaeomagnetic directions were obtained with acceptable statistical values indicating that these features recorded the field direction at the time of burning. However, some of them are out of the expected range of secular variation for mid-latitude regions suggesting post-burning alterations. The magnetic fabric of the ash was characterized by anisotropy of low field magnetic susceptibility measurements. Statistical analysis (box and whisker plot) of the basic anisotropy parameters, such as foliation, lineation, degree of anisotropy and the shape parameter, along with the alignment of the principal susceptibilities on stereoplots, revealed variation among the ash units. The diverse, oblate to prolate, lineated or strongly foliated, quasi-horizontally and vertically oriented fabrics of the units may indicate different slope processes, such as orientation by gravity, solifluction, run-off water, quasi-vertical migration of groundwater and post-burning/post-depositional alteration of the fabric by rockfall impact. In sum, the magnetic characterization of the ash layers has shown the occurrence of different post-burning alteration processes previously not identified at the site. Alteration processes in prehistoric combustion features are often identified from macroscopic observations but our study demonstrates that multiple processes can affect them and are usually unnoted because they take place on a microscopic scale. Their identification is critical for a correct chronological and cultural interpretation of a site (e.g. collection of samples for dating, stratigraphic displacement of remains), especially if significant alterations are involved. Magnetic methods are therefore a powerful but underutilized tool in palaeolithic research for the identification and evaluation of taphonomic processes affecting prehistoric fires.BU235P18 (Junta de Castilla y León, Spain) and the European Regional Development Fund(ERDF) and the CGL2016-77560- C2, PID2019-108753GB-C21 and PID2019-105796GB-I00 of the Agencia Estatal de Investigación (AEI/10.13039/501100011033). AHL gives thanks to Junta de Castilla y León (Spain) and European Social Fund for the financial support during her predoctoral period. Micromorphological investigations by CM are funded by ERC Consolidator Grant project ERC-2014-CoG- 648871-PALEOCHAR

Lithic raw material units based on magnetic properties: A blind test with Armenian obsidian and application to the Middle Palaeolithic site of Lusakert Cave 1

Classification of lithic artifacts’ raw materials based on macroscopic attributes (e.g., color, luster, texture) has been used to pull apart knapping episodes in palimpsest assemblages by attempting to identify artifacts produced through the reduction of an individual nodule. These classes are termed “raw material units” (RMUs) in the Old World and “minimum analytical nodules” in the New World. RMUs are most readily defined for lithic artifacts in areas with distinctive cherts and other siliceous raw materials, allowing pieces from different nodules to be recognized visually. Opportunities to apply RMUs, however, are strongly limited at sites where lithic material visual diversity is low. The magnetic properties of obsidian, which result from the presence of microscopic iron oxide mineral grains, vary spatially throughout a flow. Consequently, obsidian from different portions of a source (i.e., different outcrops or quarries) can vary in magnetic properties. This raises the possibility that magnetic-based RMUs (mRMUs) for obsidian artifacts could be effective to distinguish individual scatters from multiple production episodes and offer insights into spatial patterning within a site or specific occupation periods. First, we assess the potential of mRMUs using obsidian pebbles from Gutansar volcano in Armenia. Second, we evaluate the validity of this approach based on a double-blind test involving an experimental assemblage of Gutansar obsidian flakes. Cluster analysis can successfully discern flakes from obsidian specimens containing high concentrations of iron oxides. Obsidian with more magnetic material has more opportunities for that material to vary in unique ways (e.g., grain size, morphology, physical arrangement). Finally, we apply the mRMU approach to obsidian artifacts from the Middle Palaeolithic site of Lusakert Cave 1 in Armenia and compare the results to traditional RMU studies at contemporaneous sites in Europe. In particular, we seek – but do not find – differences between retouch flakes (which re