Preliminary observations on the Upper Cretaceous rudist communities from the Alburni Mts. (southern Italy)

摘要

The aim of this paper is to present some results of biostratigraphical and paleoecological analyses made on the Upper Cretaceous rudist bearing carbonate sediments from the south-eastern Alburni Mts. (southern Apennines). The study of several sections exposed along the roadway cutting leading from S. Arsenio village to Mt. Carmelo allowed us to define a stratigraphic succession (about 200 m thick) referred to the Santonian age on the basis of benthonic foraminifers and rudist assemblages. Facies analyses evidenced a depositional style typical of an open shelf; the lithotypes are dominated by fine to coarse-grained skeletal packstone-grainstones, floatstones and less frequently rudstones. In these loose sediments, rudists exhibit solitary and different constructing habits according to the recognized deepening and more open upward trend. The lower portion of the succession is characterized by a prevailing presence of radiolitids either isolated or forming small clusters. In the upper portion, large specimens of Vaccinites and Sauvagesia, forming thickets of densely packed specimens, characterize lens-shaped rudist-rich bodies. Sidewise, in grain supported sediments, isolated specimens of hippuritids, radiolitids and caprinids together with colonial corals are present. Sedi-mentological features also support the deepening trend: storm events and current winnowing are more frequent in the lower and shallower part of the succession. Furthermore, the stratigraphic frequency of rudist beds increases going upward as well as the bed's thickness. The Santonian age-assignment was established by the occurrence of Dicyclina schlumbergeri Munier-Chalmas and, in the upper part of the succession, of Keramosphaerina tergestina (Stache) among benthic foraminifers and Jerinella klinae Pejovic, Sauvagesia tenuicostata Polsak, Durania apula Parona, Plagioptychus paradoxus Math-eron, Hippurites colliciatus Woodward, H. nabresinensis Futterer, Vaccinites boehmi (Douville), V. fortisi (Ca-tullo), V. sulcatus (Defrance), V. vredenburgi (Kuehn) among rudists.