Palaeoclimatic cyclicity in central Mediterranean Pliocene sediments: the mineralogical signal

A high resolution X-ray mineralogical study of four Pliocene sediment sections from the central Mediterranean (Punta Piccola, Sicily; Monte Singa and Vrica, Calabria; ODP Hole 964 A, Ionian Sea) shows cyclic opposite abundance variations of two groups of clay minerals. The first is dominated by palygorskite and kaolinite, whose abundance maxima can be interpreted as resulting from periods of aridity on the African continent, allowing their transport as wind-blown dust. The second is dominated by smectite, whose abundance maxima can be interpreted as indicative of periods of abundant rainfall on the Mediterranean borderlands. These variations in abundance show a 22 ky cyclicity, implying a control by the precession of the Earthʹs orbit. Sapropels and sapropelic layers always occur in the smectite-rich beds, and therefore appear to have been deposited during the wet periods.