Geology Reference
In-Depth Information
to 62 g/l) chlorine-calcium waters. These chlorine-calcium waters are clear
derivatives of a lengthy alteration process of the marine ooze waters under
the known ground water metamorphism schemes after Valyashko (1964)
and Kapchenko
et al
. (1972).
The post-Cretaceous stratigraphic intervals were mostly deposited
under the fluvial, deltaic, lagoon, lacustrine (Paleocene, Miocene and
Pleistocene) and marine bay brackish- and freshwater (Eocene, Oligocene)
environments (Young, Bellis and Rentz, 1959; Miller, Edwards and Walcott,
1961; Mencher E., Fichter, 1953). They correspond with a formation's
hydrochemical medium of low-salinity (11.8
16.8 g/l) hydrocarbonate-
sodium-type waters bearing in their composition clear indications of their
connection with surface agents. It appears that a relatively low salinity of
these waters was caused not only by the initial fresh-water or brakish nature
of the depositional basins but also to a certain extent by paleo-infiltration
of fresh meteoric waters. This infiltration occurred during numerous depo-
sitional gaps, in particular, between Paleocene and Eocene, Eocene and
Oligocene, Middle and Late Miocene, Miocene and Pliocene (Young, Bellis
and Rentz, 1959; Miller, Edwards and Walcott, 1961).
Primary hydrocarbonate-sodium type of the syngenetic ground waters
within the post-Cretaceous section was formed during the deposition and
early deposit diagenesis. At those stages the desalinated pore solutions in
the lithifying rocks came into contact with alkaline minerals. These miner-
als emerged from weathering of the granite-gneisses in the depositional
basin's provenance areas and were enriched in the carbonate and bicar-
bonate ions. This process was facilitated by a gradual increase in the water
bodies of the surface waters enriched in the atmospheric СО
2
.
An additional factor in the subsequent ground water alkalinity increase
appears to have been the catagenic hydrochemical effect. It was imple-
mented in the present-day elevated temperature environment in the
process of thermochemical filtration rock leaching in the reservoirs in
accordance with the models after Kissin (1967), Kissin and Pakhomov
(1970), Kononov (1965) and Krasintseva (1968).
Origins of the “transitional” ground water varieties were determined to
have been the result of mixing in different proportions of the syngenetic
alkaline waters from the Cenozoic complex hydrochemical background
with the invading hard water solutions from the lower stage. This conclu-
sion is based on a number of factors. They include:
−
t
accounting for the distribution areas in the post-Cretaceous
complexes of “transitional” chlorine-calcium, chlorine-
magnesium, sulphate- and hydrocarbonate-sodium waters;
