Basalt weathering as the key to understand the past human use of hematite-based pigments in southernmost Patagonia. (December 2019)

• Record Type: Journal Article
• Authors: Oriolo, Sebastián; Ozán, Ivana L.; Schmidt, Burkhard C.; Charlin, Judith E.; Manzi, Liliana M.; Techmer, Kirsten
• Is Part Of: Journal of South American earth sciences. Volume 96(2019)
• Publication Date: 2019-12
• Subjects: Raman spectroscopy -- μXRF -- Pali aike rock art -- Red ochre -- Chemical alteration -- Hematite crystallinity; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2019.102376
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: The present work aims at understanding the composition and source of the red rock art pigments used by hunter-gatherer groups during the late Holocene in southern Patagonia (southernmost South America), by combining micro X-ray fluorescence (μXRF) and Raman spectroscopy. In the first place, μXRF geochemical data do not reveal any significant compositional contrast between anthropogenic pigments and altered basalts but, instead, only different degrees of basalt alteration. Thus, past human populations inhabiting the Pali Aike volcanic field might have locally found the raw material to obtain red pigments from highly weathered basalt outcrops and/or at less than 20 cm depth, where basalt-derived saprolite is widespread. On the other hand, Raman spectroscopy allows distinguishing different hematite populations based on the width and position of the 226 cm −1 band, being the former a proxy of hematite crystallinity. Natural hematite, derived from basalt alteration, shows a relatively low crystallinity and a wide spectrum of Raman parameters, whereas anthropogenic hematite from red rock art pigments shows higher crystallinity and more clustered Raman parameters, indicating possible heating processes of the latter. In addition, the low crystallinity recorded in hematite from an archaeological grindstone suggests that it was used to grind the raw material, a step prior to heating. Highlights: Micro X-ray fluorescence and Raman spectroscopy were applied in red rock art. Geochemistry reveals a basalt weathering trend of both natural and anthropogenic samples. Weathered basalts of the Pali Aike volcanic field constitute the red pigment source. Anthropogenically heated hematite has higher crystallinity than natural hematite. Natural hematite-rich raw material might probably be ground prior to heating.