Geology Reference
In-Depth Information
2.2 Foredeeps
2.2.1 The Carpathian Foredeep
The sediment section in the mobile-belt internal foredeep zone is domi-
nated by metamorphosed chlorine-calcium brines with total salinity of
315
−
1,050 mg-equiv. (90
−
300 g/l). In some intervals it reaches 1,155
−
1,575 mg-equiv. (330
450 g/l). Not as common are salt waters and brines
of the chlorine-magnesium and hydrocarbonate-sodium type with the
salinity of 105
−
90 g/l). At some prospects the topmost
intervals exposed on the surface locally contain infiltration fresh and
brakish (17.5
−
315 mg-equiv. (30
−
−
35 mg-equiv. or 5
−
10 g/l) sulphate-sodium and alkaline
varieties (Table 2.15).
The region includes three major waterhead complexes:
1. The Paleozoic - Middle Jurassic complex. It is not penetrated
in wells. By analogy with the adjacent Central Carpathian,
Pannonian, Viennese and Trans-Carpathian basins (Bakirov,
Varentsov and Bakirov, 1970; Beka and Vysotsky, 1976;
Vadas, 1964; Varentsov, 1948) it is composed of compact and
strongly fractured volcanoclastic rocks;
2. Upper Cretaceous - Upper Oligocene flysh of alternating
clastic reservoir and impermeable members composing as a
whole a single fracture-porous natural reservoir;
3. The evaporite-molasses Lower Miocene complex.
The thickest and most water-abundant intervals in the flysh sequence are
massive thickly-laminated sandstones of the Yamen (Paleocene), Vygodsk
(Eocene) formations and Menilite (Lower-Middle Oligocene) Series. In the
Lower Miocene complex, individual water-saturated beds and lenses are
identified in the Vorotyshchen Series (Upper Aquitaine-Burdigalian Stage
of the lower Miocene), Stebnik and Balich formations (Helvetian Stage of
the Lower Miocene).
The spatial position of the lowermost regional permeability barrier is
not yet accurately placed in terms of its stratigraphy. It may be assumed that
its functions are carried by compact rocks of the Paleozoic basement. The
uppermost regional water barrier is formed by rocks of the Polyanitsa Fm.,
evaporites of the Vorotyshchen Series and clayey-salty rocks of the Stebnik
and Balich formations. A partial water-barrier within the flysh complex
is formed by mostly clayey Bystritsa (Upper Eocene) formation. They are,
however, sporadically developed over the area. At some prospects isolating
