María Marta Sampietro-Vattuone

Geomorphology of the alluvial fans in Colalao del Valle-Quilmes area (Santa María Valley, Tucumán Province, Argentina)

ABSTRACT The geomorphological map of the alluvial fans in the Colalao del Valle-Quilmes area represents the first detailed map of the Santa María Valley, Northwest Argentina. The map was made using photointerpretation of aerial photographs and Google Earth images. The initial working scale was 1:10,000 and then reduced to 1:27,000 to fit ISO A1 size. Final drawings were produced using FreeHand 11. The area is characterized by the presence of coalescent alluvial fans developed on four levels. These fans end at the floodplain of the Santa María River. Sand mantles and dunes are present in this area, with old channels of the main river forming abandoned wetlands. A Holocene fault affects the distal area of some fans, whilst the apices of several alluvial fans have archaeological settlements. This study area presents an excellent example of regional Holocene evolution. Recent and present fluvial dynamics, aeolian activity, and the Holocene fault show high geomorphological activity. As a consequence, the information contained in the geomorphological map may be relevant to the establishment of risk areas for human settlements. Moreover, the map could be useful for planning conservation measures for the Prehispanic villages.

Fluvial and aeolian dynamics of the Santa María River in the Cafayate depression (Salta Province, NW Argentina)

ABSTRACT A geomorphological cartography of the Cafayate depression (NW Argentina) at a scale of 1:20,000 is presented. The Main Map was made with satellite images from 2009 to 2016 and aerial photographs from various dates. The area was classified into three categories of geomorphological dynamics according the type of fluvio-aeolian interaction. Anastomosing channels and crevasse splays are dominant in the southern section of the Santa María River, while meandering channels develop in the northern section. Extensive dune fields interacting with fluvial deposits have developed in the central sector of the depression. The Main Map also reflects the main human features and can be used as a tool for preparing hazard maps.

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.