Abstract: Numerical ages have been derived from the 87 Sr/ 86 Sr values of well-preserved rudist shells from localities in Salento (S Italy)and Lefkas (Ionian Islands, Greece). Samples are from the platform margin (Salento) and from the toe of slope (Lefkas) of the former Apuliancarbonate platform. Rudists from both localities yielded a latest Maastrichtian age (66.4 Ma), and their rudist associations are the mostspecies-rich so far reported from the Mediterranean region so close to the Cretaceous-Paleogene (K-P) boundary. The abundance of large-size recumbent morphotypes of a taxon similar to Pseudosabinia is remarkable. Generally, the latest Maastrichtian rudist morphotypes ofthe Caribbean and of the Mediterranean region are very similar, although the faunas are highly endemic on the genus level. When comparedto the Turonian-Campanian, the increased abundance of aragonite in the shells of the dominant rudist taxa, and the higher abundance ofother originally aragonitic skeletal components, is discussed with respect to the major-ion composition of Cretaceous seawater. The nowwell-documented existence of species-rich rudist associations on both sides of the Atlantic argues for a catastrophic rather than a gradualextinction of the group.

Abstract During Aptian to Albian times a major influx of terrigenous material from the emerged Arabian Shield led to the deposition of the Nahr Umr Formation within the intracratonic Bab Basin. This argillaceous facies interfingers in northern Oman with sediments shed from reefal complexes. We studied a 100 km transect across the zone of facies intercalation extending from the margin of the Neo-Tethys (northern Jabal Akhdar) into the fringes of the Bab Basin in northern Oman (Foothills). The age of formation boundaries and key beds and surfaces in a reference section (Wadi Bani Kharus; I) was dated by use of the graphic correlation method. Graphic correlation indicates that the Nahr Umr Formation is of uppermost Aptian to Upper Albian age. Two types of stratigraphic markers were recognized: limestone marker beds, successions, and disconformity surfaces. Calcareous marker beds are probably related to increased carbonate production during sea-level lowstands. Investigations of the geochemistry (stable isotopes, fluid inclusions) and sediment petrography of limestones beneath disconformities revealed that they are of combined submarine and subaerial origin. Evidence for a subaerial exposure stage is recognized along the basin margin (northern and southern Jabal Akhdar) but is found less frequently in the basinward settings of the Foothills. Marker-bed successions and disconformity surfaces are correlated throughout the sections and indicate coeval deposition of the Nahr Umr Formation in northern Oman.