NEW LATE MIOCENE MAMMAL SITES CORRELATED WITH THE RADIOMETRIC SCALE FROM THE BICORP BASIN (EASTERN SPAIN)

The basin-fill sequence from the Tertiary Bicorp Basin (Eastern Spain) comprises a lower alluvial unit and an upper lacustrine unit. The low er part of the lacustrine unit includes a tuff bed, interbedded betwee n two mammal-bearing horizons which have yielded fossil rodents charac teristic of the MN 10 standard Mammal Unit (Late Vallesian, Late Mioce ne). K-Ar age determinations on the tuff have provided a radiometric a ge averaging 9.6 +/- 0.2 Ma (weighted average of two samples) for this ash fall deposit. The stratigraphic correlation between the fossil ma mmal sites and the radiometrically-dated tuff allows a more precise ca libration between the Late Miocene biochronologic and geochronometric scales. The Bicorp tie point constrains the calibration of the Late Va llesian to around 9.7 Ma, the ensemble of data suggesting ages of 10-1 1 Ma for the Early/Late Vallesian boundary and 9.5-8.5 Ma for the Vall esian/Turolian boundary.