Characteristics, nature, and formation of palaeosurfaces within dunes on Fuerteventura

Abstract

The appearances of palaeosurfaces intercalated into palaeo-dune fields on Fuerteventura are multifaceted. Although reddened layers in these dune sediments might suggest that strong soil-formation processes have taken place, the combination of aridity and parent material, namely biogenic carbonate sand of shelf origin, reveals that strong soil formation seems unlikely. These sediments rather represent de- and recalcification processes only. Solely in the case of admixed material of volcanic origin and dust deposits further soil-forming processes seem to be possible. Hematite-rich Saharan dust contributes to reddish colouration of the palaeosurfaces. In addition, CaCO3-coated iron particles appear to be ingredients of dust being leached after deposition and transformed to hematite. Overall, we propose much weaker soil-forming processes during the Pleistocene than previously postulated. Our findings support the relevance of local environments. Carbonate sands of shelf origin hinder strong soil formation and the reddish layers separating dune generations are palaeosurfaces, which mainly consist of Saharan dust. After deposition of allochthonous material, these layers are overprinted by weak soil-forming processes. The formation of palaeosurfaces primarily depends on morphodynamically stable periods during limited sand supply. Our data suggest a cyclicity of processes in the following order: (1) sand accumulation, (2) dust accumulation and weak soil formation, and (3) water-induced erosion. For the Canary Islands, we support the assumption of glacial maxima being periods of increased levels of moisture. In combination with rising sea level, we propose that favorable conditions of surface stability occur immediately after glacial maxima during periods of starting transgression, whereas regression periods immediately after sea-level high stands seem to yield the highest sand supply for the study area.

The antiquity of the Sahara Desert: New evidence from the mineralogy and geochemistry of Pliocene paleosols on the Canary Islands, Spain

“…Nevertheless, given its proximity to the Canary Islands, Africa is the simplest choice for the source of such sediments. This interpretation is supported by the abundant evidence for African dust inputs to Canarian soils and paleosols during the Holocene and Pleistocene (Muhs et al, 2010;Huerta et al, 2015;Menéndez et al, 2019;Roettig et al, 2019).…”

“…1a). African dust is reported as a component of modern soils on the Canary Islands (Muhs et al, 2010) and is also found in paleosols of Pleistocene age (Huerta et al, 2015;Muhs et al, 2016;Menéndez et al, 2019;Roettig et al, 2019). These studies have demonstrated the presence of an African dust component by identification of minerals exotic to the Canary Islands.…”

Rock magnetics of carbonate systems–investigating palaeodune archives on Fuerteventura (Canary Islands)

“…Based on Roettig et al (2017), the Quaternary aeolianites on northern Fuerteventura mainly consist of aeolian sands derived from the shelf, volcanic ash and long‐range transported dust. The formation of palaeosurfaces is related to periods of very weak soil formation (restricted to the processes of de‐ and recalcification as well as oxidation of iron and manganese) and dust imprint accompanied by a reduced supply of carbonate sands originating from the shelf (Roettig et al , 2019). The materials involved clearly influence the magnetic parameters and ratios.…”

“…Those materials shape the palaeosurfaces which were established during periods of little or no sand accumulation. Dust accumulation is assumed to be the dominant factor, whereas soil‐forming processes are expected to be of minor intensity (Roettig et al , 2019). These archives of alternating aeolianite–palaeosurface sequences offer the possibility to get a detailed understanding of the palaeoenvironmental conditions of the island.…”

“…These archives of alternating aeolianite–palaeosurface sequences offer the possibility to get a detailed understanding of the palaeoenvironmental conditions of the island. Faust et al (2015) and Roettig et al (2017, 2019) have already provided an interpretation of the archive's stratigraphy and chronology, advocating further detailed investigations. Due to the dominance of CaCO 3 ‐rich sands the dune archives are very sensitive in recording any kind of external input and secondary processes overprinting the primary sedimentary signal.…”