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 key to continuing with studies that contribute to a better assessment of the consequences of future disturbances, such as landscape transformation and climate change

Caracterización geofísica de técnicas de explotación de nódulos de sílex en el yacimiento de la Leandra (La Muela, Zaragoza).

En el yacimiento de La Leandra (La Muela, Zaragoza) afloran unidades miocenas lacustres que incluyen habituales niveles de especial concentración de nódulos de sílex. Éstos han sido explotados durante varios periodos y, dadas las características climáticas y demográficas, conservan en ocasiones la topografía original desde su explotación. Con el objetivo de evaluar desde el punto de vista geofísico la estructura de una zona explotada del yacimiento, se realizó prospección geofísica por magnetometría, medidas de susceptibilidad magnética de los materiales y prospección geofísica por georradar que fueron integrados en la información obtenida de un vuelo de dron en la zona. La integración de datos obtenida permite identificar una dinámica de explotación a través de pozos verticales, continuidad lateral de las zonas de explotación generando explanadas horizontales cuando existían niveles de interés, o el abandono y posterior relleno de los huecos de explotación generados en el avance de la explotación. El caso analizado permite inferir a partir de los cambios geométricos y estructurales la progresión de las explotaciones de época previsiblemente neolítica y la identificación de una rutina de explotación a modo de minería de transferencia. In La Leandra archaeological site (La Muela, Zaragoza) Miocene lacustrine deposits outcrop and usually present levels with high concentration of silex nodules. These nodules have been exploited during several periods, and due to the weather and demographic characteristics, original topographical features related to their exploitation usually persists. With the aim of evaluating the site exploitation from a geophysical point of view magnetometry, magnetic susceptibility survey and ground penetrating radar were integrated with the obtained information from a drone flight. This analysis permits to identify an exploitation progression from vertical pits, lateral continuity of the excavation when profitable levels were found through horizontal platforms and the later filling of the excavated pits during the excavation progression. The studied case permits to infer from geometrical and structural changes the mining progression from an expected Neolithic quarry and the identification of an exploitation routine through transfer mining