Stron tium iso tope dat ing of bi valve fau nas from the Up per Mio cene Cacela For ma tion , east ern Algarve , Por tu gal : ev i dence from Messinian bi valve

The study is fo cused on the de ter mi na tion of the geo log i cal age of bi valve fauna re cov ered from four fossiliferous se quences in the Cacela For ma tion of Algarve, south ern Por tu gal, by means of the stron tium iso tope stra tig ra phy. Forty two anal y ses of bi valve sam ples from Barroquinha, Ca banas, the Cacela River and Lacem were per formed. The es ti mated age based on the Sr/Sr ra tios in bi valve shell sam ples from the Cacela River (a ref er ence sec tion for the Cacela For ma tion) is 7.6 ± 0.4 Ma and is con sis tent with a late Tortonian age sug gested by micropalaeontological data (cal car e ous nannofossils and plank tonic foraminifers). More over, stron tium iso to pic data re cord that the old est age of the bi valves of the Cacela For ma tion (Lacem site) is at least 8.9 ± 0.4 Ma whilst the age of about 7.0 ± 0.5 Ma can be in ferred for bi valves from Barroquinha. An in trigu ing new da tum co mes, how ever, from the bi valve stron tium iso to pic data of the Ca banas sec tion which re cords the es ti mated age of about 6.7 ± 0.4 Ma and, there fore, an early Messinian age. This is the first re port of the early Messinian ma rine bi valve fauna in Por tu gal. Sixty one bi valve spe cies have been re cov ered in the Messinian of Ca banas. Four of them: Pseudopythina macandrewi (P. Fischer), Coripia corbis (Philippi), Glossus (Glossus) humanus (Linnaeus) and Cyathodonta dollfusi (Cossmann et Peyrot) have pre vi ously not been re ported from the Mio cene of south ern Por tu gal.