Geology Reference
In-Depth Information
These results show conceptual likelihood of initiating and further evo-
lution of local structures under more significant natural rock load allevia-
tion phenomena if these rocks are elastic and have AHPP. Erosion, which
removes some gravity load, decreases the counter-pressure on the com-
pressed elastic clay rocks, thereby stimulating their motion in the verti-
cal direction, played an important role. The amplitude of this motion (the
amount of growth) depends on vertical pressure gradients emerging when
the erosion removes some gravity load.
Certainly, the amount of such undulations depends on the extent of the
erosion.
The association between the mechanism of emergence and formation of
local structures and load alleviation in elastic clay rocks may be supported
by examples of the intensity in quantitative structure evolution from the
areas of thick Paleogene-Miocene clay formation in the South Caspian,
Indolo-Kuban, Carpathian and other regions. As an example, in Kobystan,
in Kura and Iori interfluve, in the Baku Archipelago, Kerch-Taman zone
and other similar areas the number of folds per unit area is several times
greater than the same number in the areas of mostly competent rocks.
The role of plastic clay rocks with AHPP is even more significant in the
formation of complex fault tectonics, in the transfiguration of the structure
not only of the local highs but also of the entire areas.
While reviewing the role of plastic rocks in the emergence of the
described folded forms, it is important to emphasize a significant role
played by regression phenomena in the geologic evolution of depositional
basins. Due to regression and subsequent erosion of local highs, some of
the gravity counter-pressure is removed from elastic clay rocks with AHPP.
That in turn creates the conditions of their substantial load alleviation
(Durmishyan, Muradian and Rachinsky, 1982).
Together with significant decrease in the stated counter-pressure, the
denuding destruction of the crests on local highs results in substantial
weakening of the crestal portion of the structure. Combined with the pre-
vious factor it noticeably decreases tensile strength in the overlying com-
petent rocks and creates conditions for the intrusion into the emerged
dislocation by the underlying plastic mobile clay. Mirchink (1935) wrote
that “a plastic mass of the Paleogene, forcing apart disrupted anticlinal
crests, like a paint squeezed out of the tube, appeared on the surface sur-
rounded by foreign, much younger rocks of the flanks”.
We will now review this mechanism on a specific example of the
Neftyanye Kamni oil field (South Caspian Depression, the Apsheron-
Balkhan Sill).
