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of stratigraphically younger intervals with waters appropriate for older
intervals; the presence at great depths of low-salinity alkaline and hard
«transitional» waters. In particular, ground water salinity decline with
depth was recorded at the Tanyava and Strutyn prospects. Shchepak
believes that the reason is the overthrust structure of the foredeep (as in
some anticlines water salinity increases from younger to the older sedi-
ments and the inversion occurs only when an uplifted structure is thrust
over the subsided underthrust structure. Shchepak justifiably believes that
the inversion was caused by tectonics, by the overthrusting. In other words,
the normal hydrochemical profile which existed prior to the overthrusting
was disrupted, so it is just an ostensible inversion. Shchepak believes that
the ostensible inversion on the whole was caused by the ancient infiltration
water-exchange which affected highs of the Internal zone of the Foredeep
even before the Upper Miocene overthrusting. In a number of sections
were recorded traces of Oligocene and Lower Miocene erosions. In our
view it supports the probable subsidence to great depths of the rocks satu-
rated with ancient infiltration low-salinity waters.
The validity of such interpretation is supported by the results of spe-
cial study of buried waters in the oil and gas accumulations conducted
by Lozinsly (1968). He established the following features in the relic
waters preserved in the oil-saturated reservoirs in the flysh complex of the
Dolinsk field: hydrocarbonate-sodium type, quite low total salinity values
(35-175 mg-equiv. or 10-50 g/l); relatively high contents of carbonate-
and bicarbonate-ions (2.0-4.0 mg-equiv.); Na/Cl =1.0-1.5. At the same
time the proper formation waters in the same intervals are usually more
metamorphosed, higher salinity (160-620 mg-equiv. or 45.7-177.3 g/l)
and higher hardness. It is noteworthy that the buried waters in the Dolinsk
Field in their component composition, extent of metamorphism and the
pattern of changes with depth are similar with the formation waters of the
adjacent Obolon structure which does not include commercial hydrocar-
bon accumulations.
These authors agree with the view of Shchepak, Lozinsky and Bankovsky
that the buried water chemistry specifics in the Dolinsk area were deter-
mined mostly by the paleo-hydrogeological environment during the last
hydrogeological cycle. At that time, during Oligocene paleo-infiltration
waters were forming. They substantially flushed-through the productive
sequence of the flysh complex. Based on the thickness decrease of the
Menilite Series (which is believed to be a result of the intraformational ero-
sion), the northeastern and northwestern areas of the subject territory had
undergone the most intense flush-through by the paleo-infiltration waters.
These areas include the North Dolinsk, Dolinsk, Dzvinyach and Gvizdetsk
