Boletín de la Sociedad Geológica Mexicana Volumen 71, núm. 2, 2019, p. 383 ‒ 396 http://dx.doi.org/10.18268/BSGM2019v71n2a9

Combined study of archaeomagnetism and Raman spectroscopy of experimentally burnt limestones from the middle-palaeolithic site of Pinilla del Valle (Madrid, Spain) 

Ángel Carrancho^1,*, Susana E. Jorge-Villar^2,3, Laura Sánchez-Romero⁴, Theodoros Karampaglidis³

¹Área de Prehistoria, Dpto. Historia, Geografía y Comunicación, Plaza Misael Bañuelos S/N, Universidad de Burgos, 09001 Burgos, Spain.

²Área de Geodinámica Interna, Facultad de Educación, Universidad de Burgos, C/ Villadiego nº 1, 09001 Burgos, Spain.

³Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), Paseo Sierra de Atapuerca, 3, 09002 Burgos, Spain.

⁴Doctorado Interuniversitario de Evolución Humana, Paleoecología del Cuaternario y Técnicas Geofísicas Aplicadas a la Investigación, Universidad de Burgos, Juan de Austria 1, 09001 Burgos, Spain.

 ^*This email address is being protected from spambots. You need JavaScript enabled to view it. 

Abstract

Here we report the archaeomagnetic, rock-magnetic and Raman spectroscopy results of sample analysis from two types of limestones that were experimentally heated under controlled conditions. These lithologies have been commonly identified at the middle-palaeolithic sites of Descubierta Cave and Navalmaillo rock-shelter (Pinilla del Valle, Madrid, Spain). By means of a thermocouple system, maximum heating temperatures of 400 − 450 ºC were recorded during one hour. The main goal was to characterize the variations in the magnetic mineralogy and (in)organic compounds, and to study the record of the Earth´s magnetic field direction at the time of cooling. This allowed us to obtain a pattern that is potentially applicable to archaeological limestones in order to identify combustion structures at the site. All experiments were carried out on representative samples both before and after experimental heating. Before heating, both types of limestones were dominated by dolomite and calcite and as main iron oxides, goethite and magnetite. After heating, the original goethite persisted in samples heated to low temperatures (<200 ºC) whereas it transformed to haematite and/or magnetite in those heated to 450 ºC. Mineralogical alterations mostly focused on the outermost 1^st cm of depth. The neoformation of magnetite as intermediate step in the dehydration process of goethite to haematite has been barely documented and has palaeomagnetic implications. The mineralogical results obtained, their implications for the identification of fire at the site as well as potential applications to similar cases studies are discussed.

Keywords: iron oxides, experimental fires, geoarchaeology, hearths, Palaeolithic, thermal remanent magnetisation.