From all sediment lithotypes of the drill core a
first set of large-
scale (10 cm long) petrographic thin sections has been prepared, using
the freeze-drying method after
Werner (1966)
. Microscopic analyses
have been performed using a Carl Zeiss Axioplan microscope with
polarizing contrast, a Carl Zeiss Jenalumar for
fluorescence with
incident, broad-band blue light excitation, and a Leica DMC 480 digital
microscope camera for documentation.
Preparation of pollen samples followed methods described by
Berglund & Ralska-Jasiewiczowa (1986)
. Lycopodium spores were
added to each sample for calculation of pollen concentrations. Pollen
percentages were calculated on the basis of terrestrial pollen, exclud-
ing aquatics and spores.
Samples from nephelinitic host rock and crustal xenoliths from the
tuff-tephra deposit in the Mytina trench, as well as two lapilli and one
phyllitic sample (pebble) from MY-1 borehole (84
–85.5 m depth), see
Fig. 10
, were analysed for their chemical composition by X-ray
fluorescence (XRF) and inductively coupled plasma mass spectro-
metry (ICP-MS). Samples were ground in an agate mill to homo-
geneous rock powders of
b62 µm grain size. Major element oxides and
trace elements (Ba, Cr, Ni, Rb, Sr, V, Zn and Zr) were analysed by X-ray
fluorescence spectrometry on a Siemens SRS303AS spectrometer. The
rare earth elements (REE) + Y, Cs, Hf, Pb, Th and U were analyzed by
inductively coupled plasma-mass spectrometry (ICP-MS) on a Perkin-
Elmer/SCIEX Elan 5000 ICP mass spectrometer according to the
method and with precision and accuracy outlined by
Dulski (2001)
.
Total water and CO
2
were determined by IR-spectrometry (LECO CH
elemental analyser) or thermal conductivity measurements (vario EL)
after decomposition of the rock powder in a 1000 °C oxygen stream.
FeO was analysed by potentiometric titration using a modi
fication of
the Wilson procedure (
Wilson, 1955
).
Samples of 2 cm
3
each for geomicrobiological investigations were
taken immediately after the retrieval of the core of the MY-1 borehole
for enumeration of microbial cells by pushing cut-off syringes into
the centre of the core (
Smith et al., 2000
). Samples were
fixed at the
drill site in a solution containing 120 mg/L NaCl, 250 mg/L Na
2
SO
4
,
and 20 ml/L formalin. Also, 2 cm
3
samples of the drill
fluid were
taken in regular intervals and processed like sediment samples.
Samples were stored at 4 °C until analysis. For enumeration, small
aliquots of the sample were
filtered onto 0.2 µm pore size Whatman
Anodisc Filters and stained with SYBR Green I, according to
Noble &
Fuhrman (1998)
. No independent contamination control method,
like dyes, microspheres, or per
fluorocarbon (
Phelps et al., 1989
) was
employed.
4.3. Sediment microfacies
The main lithological pro
file (
Fig. 6
) exhibits a discontinuous record
of ca 82 m of lacustrine sediments below a 1.7 m thick cover of colluvial
Fig. 6. Lithological pro
file of the Mýtina 2007-1 (MY-1) well with indicated positions of preliminary pollen, thin section, and microbiological samples. Letters in brackets from the
legend refer to corresponding core photos from
Fig. 7
.
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–112
material (
Fig. 7A
). Visual inspection and amended preliminary smear-
slide and thin section analyses revealed that most of the sediments are
greyish, minerogenic
fine-grained lake deposits. Large parts of these
minerogenic sediments show faint lamination, but lack any signs of
clear gradation (
Fig. 7D
). Occasionally intercalated are horizons of
coarser clasts (
Fig. 7E
), composed of typical phyllitic-quartzitic rocks of
Fig. 7. Representative core photos of the main lithological types from M 2007-1 (MY-1). All depths given below are related to individual core barrels; scales with the photos are
related to the corresponding core barrel. A
— colluvial deposit with erratically distributed pebbles, B — silty clay, partly with faint lamination, with intercalations of dm-scale organic-
rich, non-laminated horizons, C
— mainly loose, medium- to coarse sand, D — silty clay, mostly with faint lamination, E — silty clay with some pebble-rich horizons, F, G — finely
laminated sediments with high organic content (F
— transition from silty clay into laminated organic sediments), H — mainly pebbles and cobbles with some silty clay.
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–112
Fig. 8. Mýtina sediment microfacies from thin sections. All photos, except A, are from laminated, organic-rich sediments of lithotype G (75.6
–75.86 m); photo A is from lithotype D. All
photos with
fluorescence taken with incident, broad-band blue light excitation. Arrows point to bottom. A — silty clay with faint lamination, caused by minerogenic grain size
variations, crossed polarizers, B
— alternation of minerogenic and organogenic laminae, partly crossed polarizers, C — lake sediments with high organic content, enrichments of
Chrysophyte cysts, Botryococcus colonies, and Pinus pollen, parallel polarizers, D
— same as C, but under fluorescence, E — laminated sediment with enrichments of Pinus pollen,
fluorescence, F — laminated sediment with enrichment of Botryococcus colonies, fluorescence, G — lamination with a single diatom bloom, parallel polarizers, oil immersion, H —
massive enrichment of Pinus pollen,
fluorescence.
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–112