Il Pliocene del sottosuolo di Casale Monferrato (Piemonte, Italia Nord-Occidentale): dati preliminari

Preliminary lithologic and micropaleontological analisys, carried out on clayey silts cored in the Casale Monferrato area (Piedmont, north–western Italy), documents Middle Pliocene deposits, so far recorded only in deep cores of the western Po Plain but absent in the central and western Piedmont. The deepest foraminiferal assemblages are referable to the MPl4a subzone, Early Pliocene, on the basis of the occurrence of Globorotalia puncticulata and to the next MPl4b subzone, Middle Pliocene, on the occurrence of Globorotalia puncticulata padana, common in coeval Northern Apennines deposits. Within the same samples, benthic taxa (Cassidulina carinata, Cibicidoides spp. and Uvigerina peregrina) suggest an outer neritic paleodepth. The upper clayey silts are dated to the MPl5a subzone, Middle Pliocene, on the occurrence of Globorotalia bononiensis, G. aemiliana and Bulimina marginata. Benthic foraminiferal assemblages show increasing percentages of Ammonia beccarii and Elphidium spp. and document a shallow outer neritic zone for the uppermost silty layers. Miliolids, very rare in older Pliocene Piedmont deposits, are here common and well diversified. Strong winnowing from the inner neritic zone and hyathuses are inferred in the middle part of the succession. Quantitative variations of warm and cold water planktonic foraminifera suggest climatic changes, more frequent in the middle and upper part of the Pliocene succession.