BIO-MAGNETO-STRATIGRAPHY OF THE LOWER MIOCENE “LA MORIA” SECTION (UMBRO-MARCHE APENNINE, CENTRAL ITALY)

Abstract

We present the results of a stratigraphic study carried out on the Lower Miocene “La Moria” section (43°30’13.9’’N, 12°35’39.1’’E), outcropping in the neighborhoods of the Cantiano village (Marche Region, Central Italy). The succession, about 55 m thick, shows in its lower part, the transition between the Bisciaro and the Schlier Formations (Auctorum). The first is represented by few meters of indurated marly limestones and the second by about 50 meters of blue marly clays, interbedded by thin calcareous horizons in the uppermost portion. According to the existing literature the succession yields the so-called “Piero della Francesca” horizon, a biotite rich level few centimeters thick, radiometrically dated at 17.1 Ma (Deino et al., 1997), occurring at about 24 meters from the base of the section. The succession has been sampled for both magnetostratigraphic and calcareous plankton analyses. In spite of the absence of magnetic signal in the first 12 meters of the section, satisfactory results have been obtained for most of the examined succession. The calcareous plankton content shows different degree of preservation, being better for the calcareous nannofossil and worse for the planktonic foraminifers. Nevertheless, a set of useful biohorizons have been detected, which have been dated through the integration with the magnetostratigraphic data. The present study provides interesting results whose value is amplified considering the scarsity of Miocene Mediterranean successions characterized by reliable magnetostratigraphic and biostratigraphic data. In addition, the correlation of the present results with those obtained in the DSDP Hole 608 succession (North Atlantic) gives the opportunity to evaluate the sinchroneity of the detected biohorizons and to establish correspondence between the Mediterranean and the Atlantic in the considered time interval.