Abstract

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 cyclostratigraphic study on the alternating rhythmic sedimentation has been carried out in order to refine the temporal calibration of this stage and related sub-stages. The stratigraphic constraints are derived from palaeomagnetism, planktic foraminifera, calcareous nannofossils and dinocysts. A sedimentary organization in three orders of cycles has been distinguished. They represent the expression of astronomical parameters: precession and eccentricity (first and second mode). This work permits to envisage a new duration of the Aptian stage, estimated as 6.4+ or -0.2 m.y. From this calibration, the duration of Tethyan ammonite zones in each sub-stage has been revised and a maximal duration of the OAE 1a proposed.

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