Geology Reference
In-Depth Information
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Dehydration of montmorillonite clays when substantial
fresh water amounts were released from the crystalline grid
of clay minerals («reborn» waters after Kartsev).
According to the theoretical model by Kapchenko (1978) and experimen-
tal data by Kolody (1985), the latter process at great depths, high tempera-
ture and elevated carbonate content of the Mesozoic section and the likely
presence of the depth СО
2
provides for the formation of hydrocarbonate-
sodium waters of low salinity. The feasibility of this process is supported in
studies by Blokh (1969), Kartsev (1973), Vagin (1973), Teodorovich (1970),
Bro (1980), Kapchenko (1978), Kolody (1985), Rachinsky (1983), Powers
(1976), Burst (1969), Perry and Hower (1972), Schmidt (1973) and others.
The stratigraphic association of the “reborn” waters in the region may
vary in its different parts as the necessary conditions for the formation of
dehydration processes are only the availability of the montmorillonite and
sufficient formation temperature. Therefore, the following becomes obvi-
ous. In the framework areas of the South Caspian Depression, the major
interval of the “reborn” waters is mostly the Middle Jurassic-Valanginian;
in these sediments are reached the needed formation temperatures of
120
С and higher. In the central areas (the South Apsheron shelf, southern
part of the Baku Archipelago and the Kyzylkum Trough) such function
may be performed by thick, mostly clayey Paleogene-Miocene formations
with about the same temperatures.
These considerations make it theoretically probable a gradual rise of
the reborn waters generation zone in the stratigraphic section down the
regional dip. It is possible that in the deepest subsided zone of the South
Caspian (the Central Basin) the waters of this origin could have formed in
part in the Middle Pliocene complex composed there of a clay lithofacies.
A special case of possible generation through this mechanism of the
alkaline waters in the Middle Pliocene of the South Caspian Depression
flank framework. It is suggested by Kartsev (1972) and naturally assumed
that the waters are syndepositional with the enclosing sediments. Special
studies showed that the clays in the entire Pliocene section (including its
deepest intervals) have a stable polymineral chlorite-kaolinite-montmo-
rillonite-hydromicaceous composition with the montmorillonite content
of 30
°
35% as a fine pelite fraction (Rachinsky and Kuliyev, 1984; Kheirov
and Daidbekova, 1981; Kheirov and Khalilov, 1972; Kheirov, Khalilov and
Kerimov, 1973). This indicates its restricted hydromication accompanied
by dehydration.
In particular, over 35% of clay minerals at depths exceeding 5 m in the
northern Baku Archipelago is montmorillonite possessing a rather high
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