Weathering Products of a Dismantled VariscanBasement. Minero-Chemical Proxiesto Insight on CretaceousPalaeogeography and Late NeogenePalaeoclimate of Sardinia (Italy)

This study compares, for the first time, the mineralogy and geochemistry oftwo residual-clay deposits in NW Sardinia (Nurra district)that formed at differenttimes in tropical and sub-tropical climates. Both depositsrepresent palaeosolswith deep-weathered residual profiles and overlie Mesozoiccarbonate rocks thatwere deposited on the south European palaeomargin. The older alterite isCenomanian–Turonian in age and grades upward into a horizonof karstic bauxite,whereas the younger unit occurs within alluvial deposits ofLate Neogene age. TheCretaceous palaeosol represents the precursor of the overlying bauxite and formed fromunknown sedimentary parent rocks. In contrast, the Messinian weathering productsformed by alluvium that was sourced from the Variscan metamorphic basement.Chemical Index of Alteration values, REE fractionation index values, and the results ofR-mode factorial analysis suggest a common initial weathering path and a commonprecursor for the deposits. However, the latter stages of weathering of the Cretaceouspalaeosols resulted in lateritic alteration and bauxite production, whereas weathering ofthe Late Neogene palaeosols produced 2:1 clay minerals under less extreme conditions.Comparison of these residual products constrains the parental material and weatheringtrends and allows insight into the relationship between palaeoclimate and regional/localpalaeogeography of southern Europe during Upper Cretaceous and during Messinian.