Quaternary paleosols and sediments on the Balearic Islands as indicators of climate changes. (Special Issue: Landscapes and soils through time.)

摘要

Paleosols and sediments are suitable objects for reconstructing paleoclimate. To obtain a high climatostratigraphic resolution in the Western Mediterranean, we investigated geoarchives with paleosols and sediment layers in cliff profiles of two alluvial fans on Mallorca, their pedostratigraphy covered the Late Pliocene, Pleistocene and Holocene. The sites were analysed in terms of colour, CaCO₃, delta 13C and delta 18O isotopes, and micromorphology. The sequence of El Toro (SW Mallorca) comprises 44 partly polygenetic paleosols and sediment layers, where redness is mostly pronounced in Late Pliocene and Early Pleistocene layers, but also partly in younger periods. The Eemian to Wurmian sequence of Colonia de Sant Pere (NE Mallorca) consists of yellowish-red beach sand deposits and fine red sediments, while the overlying brunified Holocene soil on loess follows shorter dry periods under moderate climate conditions with a declined pedogenetic intensity. Apart from iron weathering and hematite formation processes, soil reddening also requires polygenesis with frequent secondary climatic oscillations under distinctly alternating moisture conditions. Consequently, the current Mediterranean climate alone is not sufficient for soil reddening. Polygenetic development of the respective paleosols and sediments was underlined by micromorphological studies, showing an alternation of carbonate-rich sediments with predominantly decalcified, brunified and partly recalcified paleosols. Shrink-swell cracks reflect seasonal Mediterranean climate conditions already during the Early Pleistocene. Altogether, pedogenesis was most intense during the Late Pliocene and Early Pleistocene as enhanced by comparatively humid Mediterranean conditions, but then gradually decelerated. The sediments developed under comparatively drier and partly cooler climate conditions with a reduced open or even absent vegetation cover enhancing surface erosion. Paleosols and sediments on the Balearic Islands thus reflect a pronounced climatic cyclicity in the Western Mediterranean since the Late Pliocene.