Arid climate 2.5 Ma in the Plio-Pleistocene Valdarno Basin (Northern Apennines, Italy)

摘要: Abstract Distinctive, eolian-dominated sandy deposits 35 m thick exposed along the SW margin of Plio-Pleistocene Valdarno Basin in Northern Apennines, Italy, reflect an unusually arid period region. Paleomagnetic investigation and 40 Ar/ 39 Ar dating a tephra layer, 10 above eolian sand, suggest that sand was deposited between about 2.7 2.4 Ma. This age is coeval with global climatic deterioration occurred at Middle–Upper Pliocene transition. Eolian sediments are represented by cross-bedded rippled horizontal-bedded sand. The alluvial deposits, associated sediment, consist sheet-like beds coarse erosively based, pebbly bodies. together fluvial formed medial–distal portion system, represents Rena Bianca Sand Unit. arranged into sedimentary cycles (2–6 thick), displaying wetting–drying–wetting upward trend recording second-order oscillations ca. ka. Each cycle enclosed major bounding surfaces, defined iron mineral encrustations. These surfaces represent periods reduced accumulation caused rising water table. During 2.5 Ma cooling, experienced conditions owing to influence cold dry easterly northeasterly winds. In contrast, during Pleistocene, uplift Pratomagno Ridge protected from winds, giving rise relatively warm wet conditions, mitigating regional changes.