K-Ar date and biostratigraphic position of a volcanic ash-layer in the marine Pliocene of Crete, Greece

Abstract

Four of five size fractions of two biotite samples from a volcanic ash bed in the marine Pliocene Prassas section on Crete yielded almost concordant K-Ar dates of 3.20 to 3.25 Ma. The youngest date of 3.20 ± 0.03 Ma is interpreted to be a close estimate of the age of the ash. The tephra layer is situated in the lower part of the planktonic foraminiferal Globorotalia crassaformis Zone. In terms of calcareous nannofossil biostratigraphy, the ash bed can be assigned to the Discoaster surculus Zone (NN16) . The ash bed was also recognized in the nearby sections of Aghios Vlassios and Finikia and on the island of Koufonisi, SE of Crete. A tentative correlation with an ash level in the Mediterranean D.S.D.P. site 378 is proposed. The biochronologic scheme of the Mediterranean Pliocene, based on four K-Ar dates from volcanic intercalations in marine sequences, differs by its greater age estimates from the one commonly constructed on the basis of age-extrapolation of geomagnetic or biostratigraphic horizons from other areas.