Geology Reference
In-Depth Information
rigid complexes) and mud volcanism. The upper competent complex usu-
ally has nonuniform thickness. This results in the load differentiation on
the poorly lithified clay sequence. That results in the formation of grav-
ity faults in this sequence and generates a possibility for the formation of
crypto-diapir and diapir forms. Examples are found in the Lower Kura
and Djeirancheckmes Depressions, Western Apsheron (South Caspian
Depression), Anastasyev-Troitsk zone (Indolo-Kuban Trough), Minbu
Depression (in the Irrawaddy-Andaman Depression), folding of the
Trinidad Isl. (Orinoco Basin), etc. (Aliyev, 1960; Alferov and Kurenkov,
1973; Akhmedov, 1977; Geologic structure…, 1959; Krishnan, 1964;
Reference book…, 1976).
Geotectonic inversion typical of the fifth model makes the folding much
more complex. It results in a scale-like structure directly underneath the
upper structural barrier. It facilitates “twisting” of the clays, overturning
the argillized rock members, formation of tectonic fragmentation zones,
emergence and development of crushing deformations, faults, etc. Natural
hydraulic fracturing in the clay sequence plays a significant role there. It
determines the fracture development mostly within its lower, contact por-
tion. It also determines various dynamic effects causing vertical upward
displacement of the clay mass up to piercement of the upper competent
sedimentary series. It is believed that under these circumstances the for-
mation is possible within the clay sequence of inverted (transformed) fold-
ing in the areas where the troughs in the underlying rocks convert into the
uplifts in the process of fault-block motions.
Examples may be quoted from the Araks Depression (the Ararat
Depression: Oktemberyan, Erevan and Artashat troughs). There,
Quaternary volcanoclastic rocks overlie plastic Paleogene-Miocene
sequence over a mobile Mesozoic basement. Another example is the axial
zone over the southeastern plunge of the Caucasus Major Meganticlinorium,
etc. (Alferov and Kurenkov, 1973; Grigoriants, Muradian and Tagiyev,
1967; Grigoriants, Muradian and Tagiyev, 1969).
The sixth model includes the participation of lateral stress in the pro-
cess of folding. It is realized in some areas in the Central Kobystan (South
Caspian Depression), Internal zones of the Carpathian Trough, Tersk
and Sunzha zones of the Tersk-Caspian Trough, in California and Rocky
Mountains. It is characterized by maximum development of nappe type
horizontal clay sequence movements, intense structure formation and
fold overturning. Typical of these conditions is also the formation of large
nappe overthrust with horizontal rock offset of up to tens and even hun-
dreds of kilometers. These offsets occur due to balancing by pore water
high pressure of the gravity load from the overburden and decrease in
