Geomorphological investigations of sediment traps on Lanzarote (Canary Islands) as a key for the interpretation of a palaeoclimate archive off NW Africa

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 Ma and especially during the Early/Middle Holocene.

Loess-like and palaeosol sediments from Lanzarote (Canary Islands/Spain) — Indicators of palaeoenvironmental change during the Late Quaternary

“…Loess-like layers in particular show ferromanganese concretions up to 2 cm in diameter or calcified nests of ground-nesting anthophora bees (Fig. 2). The upper parts of the sequences are characterised by anthropogenically influenced colluvial deposits of varying thickness, some containing ovicaprid bones (Zöller et al, 2003;von Suchodoletz et al, 2009). Details of the studied sites are listed in Table 1.…”

“…As shown by von Suchodoletz et al (2009), valley base sediments derive from Saharan dust and volcanic material, either deposited as aeolian fallout or as colluvially reworked material derived from the slopes. Taking the vega of Femés, we find a catchment area/valley base ratio of 5.4:1 (see Table 1), meaning that only 18% of all sediments deposited in the total catchment area were directly deposited as aeolian fallout in the valley base.…”

“…However, 57% of the total sediment found in the vega system is now stored in the valley base. Thus, most of these sediments were originally deposited and stored somewhere in the catchment area and subsequently colluvially transported into the valley base, yielding a ratio between material deposited as aeolian fallout in the valley base and that deposited as reworked material from the slopes of 1:2.2 or 30:70% (von Suchodoletz et al, 2009). Consequently, most (70%) of the reddish/clayey material found in the vega base must be regarded as soil sediment whose properties are mainly derived from pedogenetic processes active along the slopes.…”

“…The loess-like sediments found in the sediment traps on Lanzarote are mainly composed of Saharan dust with a minor contribution of local volcanic fallout, both either directly deposited as aeolian fallout or as hill-wash material (von Suchodoletz et al, 2009). These sediments underwent intense pedogenesis during humid periods which also affected the magnetic minerals.…”

“…We propose that the alternation of loess-like yellowish/silty and reddish/clayey layers reflects differing periods of weathering on the island, regardless of the geomorphic position of the material (slope, valley) during weathering. Therefore, these sequences should reflect climatic changes, where properties such as reddish color and high clay content developed during more humid periods (Zöller et al, 2003;von Suchodoletz et al, 2009).…”