Geology Reference
In-Depth Information
regional folding, formation of local structures, faults, “inverted” nappe tec-
tonics; isoclinal folds; diapirism; mud volcanism; mélange-like, “twisted”
layering of (“crushed”) clays, etc.
Rapid subsidence compensated by the deposition of thick clay intervals
(especially composed of smectite varieties), if accompanied by tectonic
motions, causes a number of effects. These effects include:
t Drastic slow-down in the pore fluid outflow and in deposit
compaction (that determines the generation of AHPP in
the deposits; sometimes these AHPP approach lithostatic
values).
t In turn, AHPP causes the development of natural hydraulic
fracturing combined with the formation of fracturing and
syndepositional faulting.
t The formation of disharmonious and diapir folding, mud
volcanism, etc.
The aforementioned is supported by numerous cases of spatial-genetic
association between the areas of mismatch in folding plans, diapirism, mud
volcanism and intense faulting, and regional development of thick under-
compacted Cenozoic clay formations with extreme AHPP manifestations.
In most contrasting form this kind associations are recorded in a number
of tectonically mobile basins. These basins are: South Caspian (Kobystan,
Baku Archipelago), Indolo-Kuban (Kerch-Taman area), Tersk-Caspian
(Tersk and Sunzha zones), Carpathian (Internal zone), Sea of Okhotsk
(Sakhalin Isl.), Irrawaddy-Andaman (Burma portion), Sumatra, Orinoco
(Trinidad Isl.). The sediment cover there is 75-95% clay. The thickness of
unconsolidated (uncompacted) clay series reaches 1,000-5,000 m, and in
some cases greater (Bagir-Zadeh, Kerimov and Salayev, 1988; Beka and
Vysotsky, 1976; Dolenko, 1962; Reference book…, 1976; Tectonics of
Azerbaijan, 1968).
Some tectonic deformations in all stated regions are caused by elasto-
plastic clay properties in the process of their lithostatic and geotectonic
consolidation (compaction). These deformations are transferred into the
overlying and underlying intervals with the formation of projected struc-
tures (drape folds, indentation/stamp folds, sag lows, etc.). They also con-
trol the formation of nappe folding that causes the mismatch of structural
plans in different complexes and is accompanied by cleavage and intense,
mostly fault tectonics. They are also responsible for the development of
diapirism and mud volcanism accompanied most commonly by normal
faults.
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