K-Ar dating of an early Middle Pleistocene age distal tephra in the interglacial varved succession of Pianico (Southern Alps, Italy).

A distal tephra has been discovered in the varved lacustrine succession of Pianico-Sellere, one of the best-preserved interglacial sedimentary assemblages, south to the Italian Alps. The K/Ar dating of the juvenile glass fraction gives an age of 779 ± 13 ka. This age is supported by the observation of a reverse paleomagnetic direction, probably recorded before the Matuyama-Brunhes transition dated at 780 ka. The tephra belongs to the shoshonite series and the volcanic source is likely located in Southern Italy. The age of 779 ± 13 ka is much older than that of the `Riss-Wurm' interglacial, which was previously suggested on the basis of geological setting and macroflora studies. The Pianico tephra represents the first stratigraphical marker of an interglacial so far unsettled in the Southern Alps.