Evidence of Saharan dust in upper Pleistocene reworked palaeosols of North‐west Sardinia, Italy: palaeoenvironmental implications

Abstract

A multi‐disciplinary approach was followed to investigate two thick palaeosol strata that alternate with wind‐blown dominated deposits developed along the Alghero coast (North‐west Sardinia, Italy). Optically stimulated luminescence ages reveal that both palaeosols were developed during cooler drier periods: the first one at around 70 ka Marine Isotope Stage 4 and the latter around 50 ka (Marine Isotope Stage 3). In contrast, the pedological features indicate that the palaeosols underwent heavy weathering processes under warm humid to sub‐humid conditions, characteristic of the Sardinian climate during the last interglacial stage (Marine Isotope Stage 5e). To reconcile this apparent data discrepancy, a range of sedimentological and pedological analyses were conducted. These analyses reveal that the palaeosols possess a complex history, with accumulation and weathering occurring during Marine Isotope Stage 5e, and erosion, colluviation and final deposition taking place during the following cold stages. Thus, even if these reddish palaeosols were last formed during the glacial period, the sediments building up these strata probably record the climate of the last interglacial stage (Marine Isotope Stage 5e). Trace element and X‐ray diffraction analyses, together with scanning electron microscope images, reveal the presence of Saharan dust in the parent material of the palaeosols. However, no evidence of any far‐travelled African dust has been observed in the Marine Isotope Stage 4–3 aeolian deposits. It is possible to conclude that in the West Mediterranean islands, Saharan dust input, even if of modest magnitude, is preserved preferentially in soils accumulated and weathered during interglacial stages.

Evolution and architecture of a West Mediterranean Upper Pleistocene to Holocene coastal apron‐fan system

“…Similar mechanisms of fine material production and transport were proposed for reworked palaeosol strata of similar age ( ca 70 ka) that crop out in the nearby Alghero area (Andreucci et al ., ). This interpretation is further supported by evidence of erosion and colluviation of weathered MIS 5 materials during the beginning of the MIS 4 glacial phase reported for palaeosol sequences in Tuscany, Central Italy (Mirabella et al ., ), south–east Spain and Mallorca (Ortiz et al ., ; Muhs et al ., ).…”

“…Madsen & Murray, ; Thiel et al ., ), whereas less consistent results have been obtained for fluvial and alluvial deposits. Nevertheless, many OSL applications to fluvial and alluvial deposits have been successful (Bøe et al ., ; Buylaert et al ., ; Martins et al ., ; Pérez Alberti et al ., ; Andreucci et al ., ).…”

“…The required correction on the D r values for cementation (lithified samples) were taken into account and calculated following Andreucci et al . (). A weighted average between the present‐day and saturation values was selected as lifetime water content since the time of deposition for each sample (Table ).…”

Sr and Nd isotopes as tracers in pedogenic studies: Evidence for Saharan dust contribution to the soils of Muravera (Sardinia, Italy)

“…Later, Le-Bolloch et al (1996) estimated that the present-day dust deposition on southern Sardinia ranges between 6 and 13 g/m 2 . The Saharan contribution, although of modest magnitude, was also documented in paleosoils from the island by Genova et al (2001) and Andreucci et al (2012).…”

Pedogenic and palaeoclimatic evidence from an Eemian calcrete in north‐western Sardinia (Italy)

“…The OSL dating method has been applied to terrigenous siliciclastic deposits of various aeolian, fluvial and shallow marine environments (Andreucci et al, 2012;Pascucci et al, 2014). This dating method is conventionally applied to quartz grains (Murray & Wintle, 2003); however, in recent years a method based on K-feldspar grains has been developed and applied successfully to coastal and alluvial deposits (Buylaert et al, 2012;Andreucci et al, 2014).…”