Geology Reference
In-Depth Information
The largest lakes (Beyuk-Shor, Masazyr and others) reach 10 km
2
in areas
extent.
The formation of numerous lakes on Apsheron and of their ion-salt
composition has no single explanation. Various interpretations involve
meteoric, subsoil and depth-associated feed as major factors in the accu-
mulation of the lake water. In the latter case it would occur because of
replenishment by high-salinity ground waters of the Paleogene-Miocene
and Middle Pliocene - Productive Sequence complexes.
The available data indicate that the latter view is closest to reality. The
legitimacy of this conclusion is supported by Table 7.3, which lists the
water's chemical composition in the largest lakes. As the Table shows,
the water in most lakes belongs to chlorine-calcium-type brines and dis-
plays substantial similarity with ground waters in the Upper Group of the
Productive Sequence (Akhundov, Mekhtiyev and Rachinsky, 1976). This is
an unequivocal testimony to the fact that the fraction of desalinated and
meteoric subsoil waters (mostly sulphate-sodium and hydrocarbonate-
sodium) in the water-feed balance of the stated lakes is negligible
3
.
Also noteworthy in this respect is that the Apsheron Peninsula lakes are
usually located over the faulted areas of the local structures and zones of
large regional faults (Figure 7.1). In addition, a picture practically identical
in terms of lakes' origin and spatial position is noted in most other oil and
gas regions, in particular in California basins. Mostly alkaline lake water
medium (Table 7.4), lake location and their association with fields reflect
their regionally prevailing type and salinity of the formation solutions in
the Cenozoic section. As in the previous case, they may be interpreted as a
result of dominating depth feed of those water bodies in the process of the
underground fluid system's open surface discharge. The major cause of the
observed variations in lake water salinity and salt composition is likely a
differing effect of weathering factors and varying in individual cases rela-
tionships in the balance of the incoming depth water and evaporation of
lake water.
The conducted studies allow for the first approximation in the quantita-
tive estimate of the ground water discharge scale on the Apsheron Peninsula,
in the balance of the water emigration from traps and accumulation of
3
It is also supported by the fact that in most cases the lake waters are slightly more saline
than the formation waters and have lowered concentration of components
forming the com-
plex of secondary salinity (after Palmer). Under specific climate of the Apsheron Peninsula
(quite low natural precipitation) such outlook of the lake waters indicates rather their long
stay under the evaporation environment causing the sedimentation of calcium and magne-
sium sulphates and chlorides first (Gavrilov, 1939; Kedrova, 1962; Konstantov
et al
., 1929).
