Temporal calibration of the Aptian stage and related sub-stages by a cyclostratigraphic approach applied to the pelagic successions of the Umbria-Marche basin (central Italy)

A review of the standard time scales shows an important variability in the estimation of the Aptian duration (between 4 et 9 m.y.). From a pelagic and continuous succession, located in the Umbria-Marche basin, a cyclostratigr aphic study on the alternating rhythmic sedimentation has been carried out in order to refine the temporal calibration of this stage and related sub-s tages. The stratigraphic constraints are derived from palaeomagnetism, plan ktic foraminifera, calcareous nannofossils and dinokysts. A sedimentary org anization in three orders of cycles has been distinguished. They represent the expression of astronomical parameters: precession and eccentricity (fir st and second mode). This work permits to envisage a new duration of the Aptian stage, estimated as 6.4 +/- 0.2 m.y. From this calibration, the duration of Tethyan ammonit e zones in each sub-stage has been revised and a maximal duration of the OA E 1a proposed.