Geology Reference
In-Depth Information
The region has a Pre-Jurassic basement overlain by mostly clastic rocks
from Jurassic to Quaternary. Average thickness of the sediment cover is
11  km; the clay content is 53%. The Mesozoic complex over most of the
region is deep and poorly studied. The Jurassic was penetrated in a few
wells on the foredeep's periphery (over the southeastern plunge, in the
Kerch-Taman area). It is composed there of Oxfordian-Kimmeridgian
limestones. It is assumed by analogy with the adjacent areas on the north-
western plunge of the Caucasus Major meganticlinorium that the Jurassic
is up to 3,000 to 6,000 m thick. The Lower Cretaceous complex with a maxi-
mum thickness of 4,000 m is mostly a clay facies with interbeds of compact
sandstones and siltstones. The Upper Cretaceous is mostly carbonate up to
1,500-m thick. The Paleocene series (includes the Tsitse, Goryacy Klyuch
and Ilsk formations) is mostly composed of flyshoid rocks up to 1,600m
thick, alternating with clay, marls, sandstones and siltstones. The Eocene
complex (except for the Kuma Horizon of the Upper Eocene) is mostly
represented by a clay facies (the Zybin, Kutaisi, Kaluga, Khadyzhen and
Beloglin formations), up to 700-m thick. The Kuma Horizon (maximum
400-m thick) includes dark bituminous clays and marls and a clastic flysh,
which is one of the major reservoir intervals in the region. The Oligocene-
Lower Miocene interval and the entire overlying section are mostly clayey
with some reservoir (sandstone and siltstone) members, which are dis-
continuous and are replaced by clays at short distances. Its total thickness
reaches 6,500 m. The Meothic Stage forming a thick natural reservoir in
the central part of the region has elevated sand content.
The general lithofacies pattern in the Indol-Kuban Foredeep is the lens-
shaped reservoir geometry and the increase in clay content toward the axis
of the region.
The Foredeep is a complex structure. Its general architecture is defined
by the lengthwise and cross-faults causing the step-block nature of its
sediment cover over a block basement. The following cross-faults (anti-
Caucasus cuts) are identified in the Foredeep, east-to-west: the Kurdzhip,
Tsitsin, Afip, Gelendzhik, East Crimean, Zhigin, Marthov and West Kerch.
These faults determine the step profile of the region. The former five faults
provide for the sequential subsidence of the steps they form into the sub-
longitudinal (superimposed) Kerch-Taman trough from the east, and the
latter two, from the west. Three major lengthwise faults of the general
Caucasus trend are established in the foredeep. North-to-south they are:
the Novotitarev-North Kerch Fault and Anastasiyev and Akhtyr-Parpach
suture zones.
Both types of faults may exceed 1,000 m of throw.
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