Publication Date:
2021-06-16
Description:
The early–middle Miocene, marked by the Middle Miocene Climatic Optimum (MMCO) followed
by the Middle Miocene Climate Transition (MMCT) towards cooler temperatures, represents a crucial
period in Earth’s climate evolution. To understand this episode and reconstruct its origin and the regional impact
of the observed global changes, it is critical that high-resolution astronomical age models are developed
for climate sensitive regions around the world. One of these areas undoubtedly is the Mediterranean, but so
far no such an age model has been established for the interval of the MMCO. Nevertheless, this interval is
well exposed in the coastal cliffs along the Adriatic Sea near Ancona (Italy), where it is characterized by the
occurrence of 7 conspicuous limestone beds, termed megabeds, alternating with marl intervals. Here, we use
the Lower La Vedova Beach section to construct an astronomical time scale for the younger part of the
MMCO in the Mediterranean. The tuning to ~ 100-kyr eccentricity seems robust, but is less certain for
precession in some intervals, as a consequence of the less clearly developed internal structure of the basic
precession related cycles and uncertainties in the phase relation with climatic precession and insolation and
in the astronomical solution in terms of tidal dissipation and dynamical ellipticity values. The tuning nevertheless
provides astronomical ages for calcareous plankton events and magnetic reversals for the interval
between 16.3 and 15.0 Ma. Individual megabeds are related to the ~ 100-kyr eccentricity cycle corresponding
to eccentricity minima and the megabed interval itself is partly controlled by the 405-kyr cycle, as it marks
two successive minima and the maximum in between. However, no relation with very long period eccentricity
cycles (2.4 and 1 myr) is evident, and a link to regional tectonic processes (a major orogenic phase at the base
of the Langhian and the likely associated Langhian transgression) seems more plausible. The higher sedimentation
rate in the megabeds can be explained by the additional preservation of biogenic silica, which may also
account for the diluted planktonic foraminiferal assemblages. With the integrated magnetobiostratigraphy and
the tuning to eccentricity and to precession/insolation, the Lower La Vedova Beach section meets key requirements
for defining the Langhian GSSP.
Description:
Published
Description:
1-29
Description:
1A. Geomagnetismo e Paleomagnetismo
Description:
JCR Journal
Keywords:
Burdigalian/Langhian boundary, magnetobiostratigraphy, element geochemistry, astronomical tuning, Mediterranean, environmental changes
;
Stratigraphy
;
Mediterranean
;
Environmental changes
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
