Geology Reference
In-Depth Information
Dolinsk and Dolinsk fields, in the Vygodsk and Manyavsk formations the
ground water salinity changes in individual fault-blocks by 50
100 g/l
(Zinenko, 1975; Lozinsly and Bankovsky, 1972). An example of a regional
comparison is hydrochemical data for the Menilite Series of the Borislav-
Pokut zone and Tanyav Depression. It shows almost ubiquitous presence
in the former region of chlorine-calcium brines with the salinity around
300 g/l and greater, whereas in the latter are common chlorine-calcium,
chlorine-magnesium and hydrocarbonate-sodium varieties with salinity of
30
−
150 g/l (Lozinsly and Bankovsky, 1972).
Ground water distribution vertically within the local structures and
regionally shows the presence of a complex hydrochemical zoning. The
authors conducted the probabilistic statistical analysis of the data. It was
shown for the region as a whole that the ground water salinity first declines in
the section from 1,470-1,575 mg-equiv. (420-450 g/l) in the Balich, Stebnik
formations and Vorotyshchen Series to 525-980 mg-equiv. (150-280 g/l) in
the Polyanitsa and 315 mg-equiv. (90 g/l) in the Upper- and Middle-Menilite
formations; and then it regularly increases through 700-770 mg-equiv.
(200-220 g/l) in the Lower Menilite to 875-1120 mg-equiv. (250-320 g/l)
in the Bystritsk, Vygodsk, Manyavsk (Eocene), Yamnen (Paleocene) and
Stryy (Upper Cretaceous) formations. The elements of inverse zoning
appear in the interval Lower Miocene - Middle Oligocene. The main reason
may be the presence in the Upper Oligocene-Lower Miocene interval (the
Aquitaine, Burdigalian and Helvetian Stages) of a thick evaporite sequence.
Its brines formed in the course of the salt dissolution. One more reason may
be the presence of regular depositional waters in the underlying clastics of
the Lower Oligocene-Upper Cretaceous stratigraphic range. It is obvious
that the apparently inverted hydrochemical profile of the upper section is
completely determined by its evaporite nature.
Thus, the general background is the salinity increase down the strati-
graphic section in the interval Middle Oligocene-Upper Cretaceous. A
somewhat different picture is recorded in the ground water salinity within
a single stratigraphic unit. Kolody (1983) showed for the Menilite Series a
water salinity increase to a depth of about 3,000 m (up to 200-250 g/l) and
then its decline to 50-100 g/l a depths of over 3,000 m. The latter is accom-
panied by the increase in concentration of the carbonate- and bicarbonate-
ions, Na/Cl values and replacement of the hard varieties by alkaline ones.
These authors recorded a similar phenomenon for the Eocene intervals.
The specifics of hydrochemical zoning in the Internal part of the
Carpathian Foredeep are the local inversion anomalies. They are mani-
fested by several factors: the presence on some structures or in their fault-
blocks of less saline waters below the more saline ones; sporadic saturation
−
