Geology Reference
In-Depth Information
3.
Rachinsky—Durmishyan curve
, which represents an envi-
ronment of a substantially limited pore fluid outflow from
a thick (up to 4 km) Tertiary-Quaternary clay sequence
deposited within the intensely subsiding SE geosynclinal
area of the Kerch Peninsula (the axial and southern zones
of the Indolo-Kuban Trough). (Durmishyan and Rachinsky,
1976; Rachinsky, 1983).
Comparison of various curves with the type curves enables an evalu-
ation of the role played by each major factor in the clay compaction pro-
cess. It was possible, for instance, to make a quantitative determination
of the effect of permeable/impermeable thickness ratios for the same-age
compacting clays. It was also possible to determine the effect of geologic
time for the sections with identical lithofacies, and the effect of tectonic-
inversion and denudation factors for the lithologically similar sections of
the same age.
For the Pliocene sections of the Apsheron area and the Baku
Archipelago (South-Caspian Basin), the quantitative compaction param-
eters are significantly different depending on the permeable/imperme-
able rock thickness ratio. The pore fluids freely emigrate from frequently
alternating relatively thin (100 to 120 m) sand-clay layers in the Central
Apsheron. Their compaction rate is high (the curve is positioned between
the curves of Weller and Vassoyevich). In the Baku Archipelago area,
where the Pliocene section is highly clayey (up to 85-95%) and the clay
members are thick (up to 1,300-1,600 m at the Bulla-Deniz), compac-
tion occurs under a substantially restricted fluid outflow and is much
slower. The compaction curve is positioned between the Vassoyevich and
Rachinsky-Durmishyan correlation curves. The difference in clay porosity
at the same depth in the stated areas ranges from 2 to 10% (Figures 1 and
2, Tables 5.1-5.3; Rachinsky, 1983).
The Apsheron compaction curve is close to those of (1) Oligocene-
Miocene of western Fore-Caucasus region (Indolo-Kuban Trough),
(2)Â Cretaceous-Paleogene in the Crimean Plains (Scythian Plate), (3)
Pliocene intervals (up to 3 km deep) in the Western Turkmenistan (eastern
slope of the South-Caspian Basin), and (4) Cretaceous-Tertiary series (2 to
5 km deep) in the Venezuela and Columbia (Maracaibo Basin).
The compaction curves for the uniform, mostly clayey deposits over
the southern flank and axis in the Indolo-Kuban Trough, Tersk and
Sunzha zones in the Tersk-Caspian Trough, and Gulf Coast are similar
to those of the Baku Archipelago, with similar geological scenario, i.e.,
