Pyrogenic organic matter from palaeo-fires during the Holocene: A case study in a sequence of buried soils at the Central Ebro Basin (NE Spain)

We studied the fire record and its environmental consequences during the Holocene in the Central Ebro Basin. This region is very sensitive to environmental changes due to its semiarid conditions, lithological features and a continuous human presence during the past 6000 years. The study area is a 6 m buried sequence of polycyclic soils developed approximately 9500 years ago that is exceptionally well preserved and encompasses four sedimentary units. The content and size distribution of macroscopic charcoal fragments were determined throughout the soil sequence and the analysis of the composition of charcoal, litter and sediments via analytical pyrolysis (Py-GC/MS). The high amount of charcoal fragments recovered in most horizons highlights the fire frequencies since the beginning of the Neolithic, most of which were probably of anthropogenic origin. In some soil horizons where charcoal was not found, we detected a distribution pattern of lipid compounds that could be related to biomass burning. On the other hand, the low number of pyrolysates in the charcoal could be attributed to high-intensity fires. No clear pattern was found in the composition of pyrolysates related to the age of sediments or vegetation type. The most ancient soil (Unit 1) was the richest in charcoal content and contains a higher proportion of larger fragments (> 4 mm), which is consistent with the burning of a relatively dense vegetation cover. This buried soil has been preserved in situ, probably due to the accumulation of sedimentary materials because of a high-intensity fire. In addition, the pyrogenic C in this soil has some plant markers that could indicate a low degree of transformation. In Units 2-4, both the amount of charcoals and the proportions of macrofragments > 4 mm are lower than those in Unit 1, which coincides with a more open forest and the presence of shrubs and herbs. The preservation of this site is important to continuing with studies that contribute to a better assessment of the consequences of future disturbances, such as landscape transformation and climate change.Fil: Armas Herrera, Cecilia María. Universidad de Zaragoza. Facultad de Filosofía y Letras; EspañaFil: Pérez Lambán, Fernando. Universidad de Zaragoza. Facultad de Filosofía y Letras; EspañaFil: Badia Villas, David. Universidad de Zaragoza. Facultad de Filosofía y Letras; EspañaFil: Peña Monné, José Luis. Universidad de Zaragoza. Facultad de Filosofía y Letras; EspañaFil: González Pérez, José Antonio. Universidad de Zaragoza. Facultad de Filosofía y Letras; EspañaFil: Picazo Millán, Jesús Vicente. Universidad de Zaragoza. Facultad de Filosofía y Letras; EspañaFil: Jiménez Morillo, Nicasio T.. Universidad de Zaragoza. Facultad de Filosofía y Letras; EspañaFil: Sampietro Vattuone, Maria Marta. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Laboratorio de Geoarqueología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Alcolea García, Marta. Universidad de Zaragoza. Facultad de Filosofía y Letras; Españ