Geology Reference
In-Depth Information
hydrocarbons in them. Their original in-place amounts within the stated
territory were about 1.6-2.0 km
3
. It is reasonable to assume that the forma-
tion of the accumulations resulted in the outflow from the reservoirs of
equal volumes of the depositional ground water syngenetic with the sec-
tion. Total amount of water currently in the salt lakes on the peninsula is
about 0.6 km
3
. The discharge occurred not only in the formation of surface
water bodies (both presently preserved and disappeared) but also through
a great number of ascending thermal sources, mud volcanoes, seeping out
of ground water with the formation of sabkhas, etc. That is why this value
(accounting for the evaporation since the time when accumulations were
formed, about 1 MMY) may be reasonably increased several times. Thus,
it may be about the same as total hydrocarbon amounts in the productive
sequences of the area.
Available data enable the evaluation of deep-origin hydrocarbonate-
sodium water discharge onto the surface. Total volume of the travertine
formations on the Apsheron Peninsula (in the area of Binagady, Kirmaku
Valley, Shubany, Bibieibat, etc.) is estimated at about 0.15 km
3
, and account-
ing for calcite veins, carbonate-filled fracture jointing , etc. (Surakhany,
Kala and Bibieybat fields) it is 0.3 km
3
. Travertine specific gravity is 2.5 g/
cm
3
, therefore their total weight is 7.5
10
8
tons. Average content of cal-
cium in the hydrocarbonate-sodium waters is 0.3 and of the bicarbonate-
ion is 1.05 g/l. At dissolved СО
2
release from water the decomposition of
calcium hydrocarbonate with the generation of carbon dioxide (escaping
into the atmosphere), water and calcium carbonate (or travertine) usually
occurs as follows:
⋅
Са(НСО
3
)
2
СаСО
3
+ Н
2
О + СО
2
.
↓
sediment
This reaction shows that the generation of the calcium carbonate takes
no more than half of the CO
3
−
available in the water. With total НСО
3
mass
of 1.05 g/l, the carbonate generation may theoretically take 0.52 g/l of
CO
3
−
. Actually, however, part of the calcium bicarbonate remains in the
water even after its significant degassing. So only about 0.3 g. of CO
3
−
was
expended for the travertine generation out of each liter of water. In the cal-
cium carbonate generation, this amount of CO
3
−
may be joined by about
0.2 g of calcium. Therefore, total mass of calcium carbonate forming from
one liter of water is about 0.5 g. Thus, the discharge of about 1.5 km
3
of
the hydrocarbonate-sodium composition water was needed for the genera-
tion of travertine, calcite veins and other hydrothermal formations. At that,
only a small portion of ancient travertines was preserved on the Apsheron
