Foraminifera and microfacies of the type-Priabonian

Abstract

The Priabonian is generally recognized and accepted as a stage name for the uppermost Eocene. The name is derived from the small village ofPriabona in the North Italian province of Vicenza (fig. 1). Since the underlying and overlying stages of the idealized chronostratigraphic scale are based on sections in completely different sedimentation areas in northwest Europe which are remote from each other and from Priabona, the correlation between the type sections, especially at the Eocene-Oligocene boundary has been a subject of much discussion. The predominantly carbonate facies of the Priabonian deposits contain abundant larger foraminifera, and were therefore of great interest to paleontologists at the beginning of the 20th century. Unfortunately the groups represented belong to poorly defined lineages without distinct or sufficiently well-known evolutionary trends. In addition, the scarcity of planktonic organisms means that the type Priabonian is not very promising as a basis for establishing modern biostratigraphic correlations. The primary object of this study is to provide an illustrated record of the smaller foraminifera, both benthonic and planktonic. The widest possible range of habitats was obtained by investigating the contents of three sections: the Buco della Rana section, thought to lie close to the Late Eocene shallow carbonate platform; the off-shore Bressana section; and the Priabona section, paleogeographically situated in an intermediate position on the slope between platform and off-shore area. An additional study has been carried out involving microfacies analysis of the carbonates ~nd quantitative investigations of the benthonic faunas from intercalated marls. The purpose of this study was to obtain a better appreciation of the environments of the deposition and a correct biostratigraphic correlation of the three sections. The original intention was to give a thorough account of biometrical data on the larger foraminifera, but this had to be restricted to a detailed study of certain assemblages of the Discocydinidae.