INOCERAMID EXTINCTION IN THE GUBBIO BASIN (NORTHEASTERN APENNINES OF ITALY) AND RELATIONS WITH MID-MAASTRICHTIAN ENVIRONMENTAL-CHANGES

A detailed study of five representative Maastrichtian sections of deep -water pelagic limestones in the Umbria-Marche Apennines of Italy show s that inoceramids became extinct synchronously throughout this region some 3.5 Ma before the Cretaceous/Tertiary boundary. The decline and disappearance of these bivalves are immediately preceded by two closel y spaced peak abundance zones, and are linked with an important change in environmental conditions during the mid-Maastrichtian period, as i s indicated by modifications in the delta(13)C composition of sea wate r and variations in planktonic foraminiferal assemblages. The restorat ion of stable environmental conditions after this biotic crisis took a bout half a million years in this region. Excursions of the delta(13)C Signal contemporaneous to the extinction of inoceramids in other Maas trichtian basins throughout the world (i.e. Basque Country and souther n oceans) indicate that these bivalves were extremely sensitive to env ironmental changes. However, accurate magneto-and biostratigraphic cor relations between the Italian, Basque, and southern hemisphere section s unambiguously indicate that the extinction of inoceramids was widely diachronous throughout the world of as much as 4 Ma. (C) 1998 Elsevie r Science B.V. All rights reserved.