Environmental changes during the Upper Pleistocene–Holocene in Mediterranean NE Spain as recorded by the mineralogy and geochemistry of alluvial records

Landscape evolution and environmental conditions from Last Glacial Maximum (LGM) to Late Holocene times were reconstructed from the mineralogical and geochemical characteristics of the alluvial morphochronostratigraphy, recorded in Bardenas Reales Natural Park (Ebro Basin, NE Spain). Alluvial architecture includes a LGM-Holocene gravelly unit (≈22–9 ka BP), a Lower Holocene silty–muddy unit (≈9–7 ka BP), and an Upper Holocene sandy unit (≈5–0.1 ka BP). Increases in illite–smectite mixed layers, kaolinite, chlorite and modified Chemical Index of Alteration (CIA*), as well as the decrease in illite FWHM(E), are indicators of minor increases in the chemical weathering of the alluvial sediments. The results suggest that this area, although under broad semiarid conditions, underwent the following environmental evolution: i) an increasing trend in moisture availability in the Lower Holocene, and ii) a variable pattern in water disposal at the onset of the Upper Holocene, followed by a decrease in humidity during the last millennium. This reconstruction proves the usefulness of mineralogical and geochemical proxies as indicators of rapid environmental changes under Mediterranean conditions.