Origins and genesis of loess deposits in central Spain, as indicated by heavy mineral compositions and grain‐size variability

Abstract

The formation of loess deposits strongly depends on the availability of deflatable dust-sized material. Identification of source areas and mechanisms of dust production is essential for an appropriate characterization of related palaeoenvironmental conditions. So far, little research has been done on loess deposits in the Mediterranean region and information about mechanisms of dust production is very rare. In this context, it is not clear from where the loess deposits from the upper Tagus Basin in central Spain originated. The main objective of this study was to find out whether these loess deposits were formed primarily by mountain processes and fluvial comminution, or whether they have their origin in the weathering of Tertiary marls in the centre of the Madrid Basin. A further concern was to link the determined source areas with loess formation mechanisms and concomitant environmental contexts. Following a comprehensive approach using heavy minerals and grain-size data, together with information on stratigraphic features and geomorphic positions, different local loess sources could be identified. This study shows that during the last 35 kyr a major proportion of the Tagus loess deposits was deflated from river floodplains, while the mountain region of the Iberian Range was identified as a significant source of respective floodplain sediments. Based on heavy mineral compositions and dating results, it was found that during Heinrich Stadial 3, sediment supply from the Iberian Range strongly increased, suggesting an environmental shift from initially warmer towards colder temperatures in late Marine Isotope Stage 3. Furthermore, it was found that grain-size patterns clearly indicate maximum wind strengths during Heinrich Stadial 3, followed by Heinrich Stadial 2 and Heinrich Stadial 1. These results demonstrate that the formation of dustsized particles in this part of the Mediterranean operated similar to many other places in temperate and continental regions, and that weathering processes linked to hot and dry environments were only of minor importance.

Atmospheric Dust Variations in the Ili Basin, Northwest China, During the Last Glacial Period as Revealed by a High Mountain Loess‐Paleosol Sequence

“…In fact, grains >50 μm could be suspended only if the wind is so strong that a dust storm occurs (Qiang, Chen, Zhang, et al, ). Thus, the changes in the sand fraction in NLK are suitable for evaluating the history of sand dust storm activity and the wind regimes, as the case of loess deposits in the Tagus River Valley, central Spain (Wolf et al, ). The higher percentages of sand fractions in the NLK loess are derived from more frequent stronger winds.…”

Disentangling Sedimentary Pathways for the Pleniglacial Lower Danube Loess Based on Geochemical Signatures

“…Heavy mineral assemblage data can be used to fingerprint loess deposits and compare them to potential source sediments. However, using heavy mineral distribution assemblages as a provenance proxy may bear the drawback of mixing multiple distinct sources (Mikulčić Pavlaković et al, 2011;Römer et al, 2016;Meng et al, 2019;Wolf et al, 2019). Recently, the advent of single-grain provenance techniques such as detrital zircon U-Pb dating allowed disentangling multiple dust sources and potentially sign specific proto-source terranes (Stevens et al, 2010;Újvári et al, 2012;Fenn et al, 2018;Pańczyk et al, 2020).…”

Geochemical signature of sources, recycling and weathering in the Last Glacial loess from the Rhône Valley (southeast France) and comparison with other European regions

“…Because of their sparser accumulation in the landscape, perimediterranean loess remain poorly documented except for some exceptions (Calvo et al, 2016;Profe et al, 2018). Recent studies in the Po plain (Wacha et al, 2018) the Ebro (Boixadera et al, 2015) and Tagus basins (Wolf et al, 2019) in Spain suggested, however, that Pleistocene loess covered vast parts of perimediterranean areas. The Rhône Valley (SE France) also recorded significant loess deposition during the Last Glacial (Bosq et al, 2018).…”