Abstract
On Lanzarote (Canary Islands) Late Quaternary Saharan dust and volcanic material were trapped in Miocence to Pliocene valleys dammed by volcanic lava flows. These trapped sediments are potentially interesting as they can be natural archives useful to reconstruct the terrestrial palaeoclimate history of the NW African margin. Nevertheless, slope wash processes altered the primarily eolian deposits, making climatic interpretation not straightforward. Geomorphological mapping, GIS calculations and sedimentological investigations were used to unravel these processes influencing the temporal resolution of the palaeoclimatic archive, demonstrating that they average the palaeoclimatic signal by some ka. Thus, despite the colluvial geomorphic environment, the valley fillings can be used for palaeoclimatic interpretation of events with a length of at least some ka. The youngest sediments, deposited since at least 2.5 ka, are anthropogenically triggered and thus cannot be used for palaeoclimatic interpretation. The results show that the input of Saharan dust at Lanzarote increased during the last 1.0 ka and especially during the Early/Middle Holocene.
Highlights
Loess–palaeosol sequences are an important type of terrestrial palaeoclimate archive
From a total volume of about 34 million m3 of sediment deposited in the vega system since damming 1.0 Ma ago a volume of 19.5 million m3 was deposited in the vega bottom, whereas 14.5 million m3 were deposited in storage positions of the catchment areas
Since only 18.4% of the total material could have been deposited in the area of the vega bottom itself as in situ aeolian fallout, there must have been a significant contribution of colluvial material from the slopes in order to get the recent proportion of 57.4% of total sediment stored in the valley btoom
Summary
Loess–palaeosol sequences are an important type of terrestrial palaeoclimate archive. When sediments were only partly directly deposited by eolian input and another part was later reworked by colluvial processes, the understanding of the link between erosional and depositional area and the type of material transport (high frequency/low magnitude or low frequency/high magnitude) becomes important for palaeoenvironmental interpretation. These issues are important since a weak link and low frequency/high-magnitude processes can cause a time lag between environmental signal and time of deposition or destroy older sediments (e.g. Lang, 2003; Fuchs et al, 2004; Rommens et al, 2006). Quantitative estimations from a selected sediment trap allow evaluating the dynamics of Saharan dust input during the Quaternary as well as the influence of anthropogenic activity on the local semiarid ecosystem
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