DACIAN BASIN - GeoEcoMar

1.2. Stratigraphy
poral limits of these “brackish stages” are different from one area to another. The
ecological facies pertaining to a brackish stage may occur in different space units
or time intervals. The best example is that of the “Pontian type” fauna or “Sarmatian
type” fauna from the Mediterranean area, faunas which have nothing in common
with the Paratethian Pontian or Sarmatian faunal assemblages. These aspects could
also create difficulties for the construction of the magnetostratigraphic scales.
1.2.2. Toward a reliable chronostratigraphic and geochronologic framework
of the Dacian Basin 1
Many contributions of Romanian and/or foreign researchers refer to the ages of the
Dacian Basin sedimentary deposits. Still, an unique (and unanimously accepted)
chronostratigraphic and geochronologic framework has not yet been achieved
(Fig.1.5). To reach a high-resolution dating of the Miocene and Pliocene (sub)stage
boundaries, various new techniques have been integrated with the traditional biostratigraphy,
principally magnetostratigraphy, astrochronology and cyclostratigraphy.
Reliable sampling techniques, sophisticated paleomagnetic laboratories, along
with an increasing number of data analysis methods and more refined criteria
were developed worldwide to retrieve the paleogeomagnetic fossile, i.e. the primary
Natural Remanent Magnetisation (NRM) component (Characteristic Remanent
Magnetisation/ChRM, isolated in laboratory). This magnetic signal, commonly
weak in the sedimentary deposits in which it is printed/”frozen”, may be affected by
noise from a number of perturbation processes or may be obscured subsequently
to rock formation, along their geological and geochemical history.
A breakthrough in age determination has been the astronomical dating (Hilgen,
1991, 1994, Hilgen et. al., 1995, Berggren et al., 1995, Krijgsman, 1996). An Astronomically
calibrated (Polarity) Time Scale [A(P)TS] has been constructed (first, for the
Pliocene – Pleistocene time interval; Lourens et al., 1996), and even incorporated in
the existing (very usable) standard Geomagnetic Polarity Time Scale (GPTS) of Cande
and Kent (1995; CK95). Since 2004, the Astronomical Tuned Neogene Time Scale
(ATNTS2004; Lourens et al., 2004), characterised by an unprecedented resolution
and accuracy, is in use.
In this shortly defined context, the geological time scales (GTS) in figure 1.5,
particularly the ages assigned to the chronostratigraphic boundaries, should be
carefully considered before adopting one of them. To compare and evaluate these
GTS’s (models A, B, C, D) with the intention of assuming a (reliable) version for
the Dacian Basin (possibly, a composite GTS), at least the following major aspects
should be taken into consideration:
1 Author: Sorin-Corneliu Rădan
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