Potential dust source areas of Quaternary vega sediments on Lanzarote (Canary Islands)

On the eastern Canary Islands, several valleys exist that were dammed later on by volcanic activity. Since that damming, these valleys (locally called “vegas”) have acted as sediment traps. The deposited materials include volcanic material, redeposited (soil-)sediments from the surrounding slopes, and dust originating from the northern African continent. Due to intense postsedimentary calcification processes Vega sections are typically characterised by an alternation of pale-coloured, carbonate-enriched layers (PCL) and reddish, clay-enriched layers (RCL), forming recurring sedimentary sequences.

This study shall contribute to the reconstruction of palaeoenvironmental conditions during the formation of vega sections on Lanzarote, with particular emphasis on aeolian dust deposits. Therefore, we combine grain-size analyses, geochemical (XRF) and mineralogical analyses (XRD), and luminescence dating (IRSL) with a principal component analysis (PCA) to evaluate geochemical fingerprints and compositional end-members.

Four distinct clusters have been identified reflecting different sediment sources and transport pathways. A first cluster is characterised by increased Si, Zr, quartz and plagioclase contents and has been interpreted as short range (silt-dominated) aeolian dust input. A second cluster shows high Al, K and kaolinite loadings and indicates long range (fine-grained) aeolian dust derived from more southerly regions of northern Africa. A third cluster is defined by elevated Fe, Ni and Zn concentrations, which are typical for basaltic source rocks on the eastern Canary Islands and reflect locally derived material. In contrast, Rb–V–enriched samples define a distinct trend, as Rb substitutes for K in fine-grained mineral phases and V is associated with Fe-(hydr-)oxides, pointing to a fine-grained sediment component differentiated from the Ni–Zn–rich basaltic signal and possibly reflecting an additional aeolian contribution. The fourth cluster is associated with Ti and Cr, elements occurring both in Saharan dust and in local basaltic volcanics; however, the presence of K-feldspar suggests a predominantly allochthonous contribution.

The cyclic pattern (alternating PCLs and RCLs) within vega sections highlights the sensitivity of these archives to changing environmental conditions. While variations in grain size, mineralogical composition, and geochemical signatures indicate shifting potential source areas and pathways of dust, the carbonate redistribution in combination with the characteristics of clay-dominated sediment layers reflect changing hydrological and hence palaeoclimatic conditions on the Eastern Canary Islands. Finally, we hope to contribute on the one hand to the understanding of Late Quaternary conditions in an over regional scale and on the other hand to the individual behaviour of the different subterritories.