| Establishing an unambiguous
timescale for the Late Neogene deposits of the Eastern Paratethys region
has been a problem for years caused by contradicting paleomagnetic results
and local biostratigraphic schemes. This work aimed to create a reliable
magnetostratigraphy for key sections in Azerbaijan. |
In the
past 7 Myr, the Caspian Basin has been characterized by large lake-level
variations with differing amplitudes. After the restriction during the
deposition of the Mio-Pliocene Productive Series, a number of important
transgressions took place in the Plio-Pleistocene.
The earliest of these
large transgressions of the Caspian Sea is the Pliocene Akchagylian transgression,
which marks the end of the Productive Series and the beginning of the Pliocene
Akchagylian deposition in the Caspian Sea. This transgression has at present
an age of 3.4 Ma. A similar transgression is found at the boundary between
the Apsheronian and Bakunian regional stages.
|
Some suggested time scale solution
|
The origin of the these
transgression has been linked to eustatic highstands, that caused overflow
of marine waters into the Caspian Sea. Younger (Late Pleistocene) transgressions
have been interpreted in terms of overflow of pro-glacial lakes during
extensive glaciations when land-ice blocked the north-flowing rivers from
Scandinavia to Siberia. A detailed age for these transgressions allows
for discriminating between a glacial and marine origin, which is the scope
of my Msc-project.
Lokbatan
section (Azerbaijan, near Baku)
Creating a reliable magnetostratigraphy
for key sections in Azerbaijan, is a first step. The boundary between uppermost
Productive Series and the Akchagylian regional stages, as observed in the
Lokbatan section, has in the most likely scenario an age of 2.5 Ma, which
is radically different from the existing age. The younger regional stages,
the Apsheronian and the Bakunian, yield ages for their lowerboundary of
older than 1.8 Ma, and 0.88 Ma.
| Transgressions at
the base of both the Akchagylian and the Bakunian fall within cold intervals
of the Pleistocene (marine isotope stages 100 and 22 respectively), and
are thus likely to have an origin related to northern hemisphere glaciation.
Existing models for Late Pleistocene ice-dammed lakes and reverse driver
drainage (and possibly increased precipitation) stretching from Scandinavia
to West Siberia are hypothesized for these transgressions, and may prove
that there was at times a connection between the Arctic Ocean and the Caspian
Sea. Existing biostratigraphic data does not contradict this hypothesis,
or does, in the case of the Caspian seal, even strongly support it.
Model
of the glacial-interglacial drainage hypothesis as used for the Akchagylian
transgression.
|
|
