Magnetic Alteration of Soils by Late Holocene Hunter–Gatherer Groups (Tierra Del Fuego, South America)

Abstract

The present work aims to analyse the magnetic signature from the Late Holocene open‐air archaeological deposits of hunter–gatherer ephemeral occupations. For this purpose, two profiles were sampled at the Marazzi 2 site in the north‐western Isla Grande de Tierra del Fuego, Chile, in order to carry out studies of magnetic susceptibility, hysteresis cycles, back‐field remanent magnetization, isothermal remanent magnetization and thermal variation of magnetic susceptibility at high and low temperature. Despite short‐term occupations, the P1 profile shows a magnetic peak at a depth of ~30–70 cm due to magnetite, probably formed by anthropogenic activity related to combustion. The P2 profile instead yields an anomalous peak of coercivity (at a depth of 20–40 cm), which could also be anthropogenic, due to the presence of finely dispersed ancient ‘red ochre’. The red ochre is proposed to form anthropogenic thermal alteration of goethite associated with volcanic ash, the remnants of which were found in thin sections from the P2 subsoil.

Sediments vs. Historical narratives: The use of soil magnetic properties to evaluate the existence of a historical fire in an 18th century Spanish fort (Patagonia, Argentina)

“…A this regard, different analytical techniques were applied, such as clay X-ray diffraction, thermoluminensce, anthracology, soil micromorphology, geochemistry, FTIR spectroscopy and infrared analysis, among others (e.g., Karkanas et al, 2002;Berna et al, 2007Berna et al, , 2012Mallol et al, 2007;Goldberg et al, 2009;Brodard et al, 2012;March et al, 2014;Gur-Arieh et al, 2014;Morley, 2017;Villagran et al, 2017;Ozán et al, 2019;Shahack-Gross et al, 2018). To a lesser extent, past combustion features have been tackled by magnetic analyses to discuss paleotemperatures, the geomagnetic field evolution (i.e., archaeomagnetism) and postdepositional processes (e.g., Ellwood et al, 1998;Dalan, 2008;Brodard et al, 2012;Kapper et al, 2014;Morley, 2017;Ozán et al, 2015Ozán et al, , 2017Ozán et al, , 2019Shahack-Gross et al, 2018;Urban et al, 2019). Due to space-circumscribed combustions often took place repeatedly through time, they present a high archaeological visibility, whereas physicochemical characteristics of thermoaltered sediments contrast remarkably with the off-site or natural control area.…”

Magnetismo ambiental y cambio climático

“…1 Definición de los límites de áreas de actividad, funcionalidad de los espacios, estrategias de construcción de los mismos e intensidad de ocupación humana (Allen y Macphail, 1987;Oldfield et al, 1985;Clark, 1990;Gose et al, 1994;Ellwood et al, 1995;Dalan y Banerjee, 1998;Marmet et al, 1999;Orgeira et al, 2000;Macphail y Crowther, 2004;Rosendhal et al, 2014;Ozán y Orgeira, 2015;Ozán et al, 2017). Aquí vale mencionar el caso de la construcción de los famosos montículos de Cahokia (que alcanzan dimensiones de unos 30 metros de altura y 300 m de lado), ubicados en el suroeste del estado de Mississippi (Dalan, 1997;Dalan y Banerjee, 1998).…”

“…Adicionalmente la muestra ubicada a 73-80 cm de profundidad se destaca por sus valores relativamente altos en la señal magnética y su consistencia entre todos los otros parámetros. A esta profundidad no se observan componentes antropogénicos microscópicos (Ozán et al, 2017), ni aflora material arqueológico en el perfil. Este aumento de la señal probablemente se relaciona con el incremento de concentración de minerales magnéticos (magnetita y/o titanomagnetita) contenidos el abundante vidrio volcánico que se observa en las secciones delgadas (figura 11).…”

An experimental approach to the preservation potential of magnetic signatures in anthropogenic fires

“…: [54,55,63–65,79]), as well as identification of burning episodes (e.g. [16,71,80]), detection mechanical post-depositional processes affecting combustion structures (e.g. : [30,55,79]) and distinction of occupation events in Palaeolithic hearth-related assemblages [35].…”