Geology Reference
In-Depth Information
Thus, the hydrocarbonate-sodium waters are spatially associated with
faulted areas, mud volcano eruption apparatuses, contact zones between
crypto- and exo-diapir formations and the enclosing rocks, areas of litho-
logical unconformities (hydrogeological «windows»), etc. All these indicate
that relatively low-salinity alkaline waters within the Hauterivian-Pliocene
stratigraphic range on local structures are an injection-type hydrochemi-
cal anomaly against the general high-salinity chlorine-calcium water back-
ground of the surrounding geologic medium, and the post-Valanginian
interval per se is a discharge area of high-waterhead waters of the underly-
ing sediments.
This concept was applied to the section of the Apsheron oil and gas
area where lithology and thickness of the Middle Pliocene through
Valanginian-Middle Jurassic complex do not significantly vary (Tectonics
of Azerbaijan…, 1970; Khain, 1950; Khenkina, 1961, 1981). It was sug-
gested that the aforementioned association of the water type transition
zones on the individual structures with a certain distance from the base of
the Middle Pliocene is caused to a substantial extent by about equal in all
fields of the region hydraulic loss on the way of the foreign alkaline inva-
sion water from the Mesozoic (Rachinsky, 1970).
The described ground water distribution patterns by their origins,
chemical type and salinity enable certain conclusions about the inver-
sion of hydrochemical profile in the region's flank zones. A precondition
for the inversion is ubiquitous, independent of the structural-tectonic
situation fill-up of the section with waters of different chemism and of
salinity declining with depth. It was proposed that the inversion shows
up only at comparison of the Lower Cretaceous-Middle Jurassic inter-
vals with all other overlying stratigraphic intervals. In the latter, the alka-
line waters are present only in the composition of formation water mixes
genetically foreign to the enclosing rocks, have clearly secondary origin
and apparently represent a usual injection type hydrochemical anomaly
against the general background of the high-salinity chlorine-calcium
water medium.
Thus, a concept common in the geologic publications of the inverted
nature of the Middle Pliocene hydrochemical section needs to be modified.
The reason is that the profile is inverted only over the most faulted crestal
areas of local structures. And hard brines are found in all other subsided
areas of the structures. A typical model of such ground water distribution
and formation mechanism of hydrochemical zoning is the fields in the
Lower Kura Depression and Southwestern Turkmenistan where the alka-
line water distribution areas are relatively limited in size. In the Apsheron
oil and gas area the alkaline waters penetrate the greater territories. This
