Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi

Geological Survey of Finland, Special Paper 46
Pollen and IR-OSL evidence for palaeoenvironmental changes between ca 39 kyr to ca 33 kyr BP recorded in the Voka key
section, NE Estonia
Fig. 1. Location map of the study area (A) and the scheme of the Voka Clint Bay with locations of the outcrop V3 (B); 1– altitudes
above sea level in metres; 2 – Clint Bay boundary; 3 – outcrop; 4 – 20 m contour line; 5 – coastline; 6 – clint.
of soil formation, densely penetrated by roots and
fi lled krotovina-like irregular tunnels made probably
by burrowing animals. The boundary between units
A and B is marked by a gravel bed. The thickness
of unit A in the V3 section is about 10 m. unit A
in this section is characterised by alternating laminated
fi ne sand and clay with dispersed particles of
lower Ordovician Dictyonema argillite. Unit B is
represented by coarse-grained cross-bedded sands.
The maximum visible thickness of the unit (shown
only partly in Fig. 2) is about 15 m.
More than 90 samples were taken from unit A
of the V3 section and from overlying soil deposits
for detailed palynological analysis. In the present
study, the palyno-climatostratigraphic method was
applied to identify pollen zones in the record. The
standard palynological technique, which includes
treatment by 10% HCl, 10% KOH and acetolysis
solution, was applied for extraction of pollen and
spore grains from deposits (Grichuk & Zaklinskaya
1948). Samples of sands at the depths between 1.8–
5.0 m turned out to be poor in pollen and spores.
Since the deposits were devoid of macroscopic
organic remains, the infrared optically-stimulated
luminescence (IR-OSL) technique was applied to
produce an absolute chronology of the deposits.
Fifteen samples from unit A of the sections were
measured with IR-OSL and an age model was developed
(Molodkov 2007) to provide a time scale
for the unit and a temporal base for palaeoenvironmental
reconstructions (all IR-OSL ages reported in
this paper were obtained in the Research Laboratory
for Quaternary Geochronology, Tallinn; the IR-OSL
ages given here are in calendar years before present,
BP; the dating results obtained for unit A from the
Fig. 2. Stratigraphic column
of unit A of the V3 section at
the Voka site. The numbered
circles show the location of
the IR-OSL sampling points.
Shown to the right of the
columns are the positions
of pollen sampling points
and the variations with
depth of the Dictyonema
argillite distribution in the
deposits along the sections.
Calendar time scale for
unit A of the V3 section is
indicated on the left (for
detail see Molodkov 2007);
1 – soil; 2 – silt; 3 – sand; 4
– horizontally bedded sands;
5 – crossbedded sands; 6
– laminated clayey deposits;
7 – marker bed; 8 – IR-OSL
sampling points; 9 – interrupted
(a) and varve-like (b)
layers of Dictyonema-bearing
sediments.
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