N. Fiet, 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), B SOC GEOL, 171(1), 2000, pp. 103-113
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.