Geology Reference
In-Depth Information
Table 2.4
Ground water salt composition in the Paleogene-Miocene deposits of
the South Caspian
Depression.
Hydrochemical
parameters
Ground
water
type
Formation, horizon
Maikopian
Chokrackian
Diatomaceous
From
To
From
to
From
to
Hard
Alkaline
30.2
24.0
126.0
32.8
60.0
35.4
145.0
58.2
61.8
32.6
241.0
136.0
Σ
а+k
, mg-equiv.
S
1
, %-equiv.
Hard
Alkaline
65.6
54.3
96.5
94.0
88.3
59.2
93.2
93.1
80.2
54.0
95.7
95.4
S
2
, %-equiv.
Hard
1.14
24.5
2.32
7.42
0.28
19.5
А
, %-equiv.
Alkaline
2.6
39.6
5.8
34.6
1.4
44.3
Within the local structures is recorded rather significant increases
of water salinity and calcium and magnesium chloride contents from
intensely-faulted crestal zones toward the flanks and plunges. Regionally,
the trend is clear of the increased water salinity and its replacement by the
chlorine-calcium type in the direction of the regional dip (Figure 2.2). It
may be the result of the following two factors. First, it may be associated
with the improved isolation in this direction of the water-saturated res-
ervoirs from surface infiltration (due to the Maikopian being overlain by
younger sediments). Second, it may be affected by a decrease of the faulting
in the same direction, which limits the hydrodynamic communication of
the structures with the underlying rocks where low-salinity alkaline waters
are common.
The waters in the
Chokrackian
horizon (Middle Miocene) are mostly
of the hydrocarbonate-sodium type wherever the faulting is strong and
there are no hydrocarbons (Southwestern Kobystan). Wherever there are
no hydrocarbons and the structure is relatively quiescent (the western
part of Apsheron), the waters are of the chlorine-calcium and chlorine-
magnesium type. Their salinity in the former case is 35 to 60 mg-equiv.
(10-17.2 g/l); in the latter case it is much higher and reaches 60-150 mg-
equiv. (17.2-43 g/l). Chlorine content in the horizon's water is 10-70 mg-
equiv.; the water is practically devoid of sulphates (their presence, however,
is quite possible in the areas subjected to the present-day infiltration).
Total alkalinity reaches 8 mg-equiv. (its minimum value is 0.2 mg-equiv.).
Water-soluble salts of organic acids, the same as in the Maikopian Fm.,
are associated with the hydrocarbons; their content, however, does not
