Geoscience Reference
In-Depth Information
Fig. 2.40
Remote view to
the entrance of Prohodna
Cave, Karlukovo Karst
Region, Central Balkan,
Bulgaria
highest cave entrance in Bulgaria (42.5 m) of Pro-
hodna Cave (Fig.
2.40
), as well as for the multiple
vertical and horizontal caves in the area.
• It was proven that a significant fault exists, named
Karlukovo Fault, striking NW-SE. The fault is
natural
westwards
prolongation
of
the
regional
Brestnik-Preslav Flexure (Fig.
2.41
);
• The fault is dividing the less karstified limestones
to the north from intensively karstified limestones
of the southern block. All important karst caves are
located directly south of the fault;
• Karlukovo Fault offers an explanation of the
hydrogeological features of the area, including the
karst springs;
• New unknown karst cavities were predicted to the
south of Karlukovo Fault and after a long period of
exploration of Bankovitsa Cave, the speleologists
discovered in 2008 new galleries with an under-
ground river. These galleries coincide with the
geophysical anomalies and their trend corresponds
to the reconstructed preferred directions of the open
fissures when analyzing the tectonic stress fields.
The scheme in Fig.
2.42
shows the main sites of
the performed structural and geophysical studies, as
well as the maps of the caves.
Geological Background
Karlukovo Karst Region is situated in Lukovit Syn-
cline. This is a well-expressed asymmetric structure in
the northern part of the Fore Balkan, affecting car-
bonate sediments of Campanian, Maastrichtian and
Paleocene age, and complicated by fold and faults
(Karagjuleva
1971
). The area of direct interest is
situated northwards of the village of Karlukovo
(Fig.
2.41
). Dominant sediments are the limestones of
Kailaka Formation—Late Maastrichtian; they build
the westernmost part of Lukovit Syncline. Aptian and
Albian sediments of Roman Formation (sands and
marls) occur southward.
Maastrichtian limestones are highly fractured and
karstified. This fact and the canyon type erosional
incisions suggest relatively young tectonic activity,
closely related to the karst processes. The faults,
crossing the area of interest, are not well recognized
geologically. The geophysical works during
1985-1986 (electrical profiling and WLF profiling—
personal unpublished data of S. Shanov) discovered
the existence of a covered fault, controlling the karst
in the area.
The most significant results from the performed
geophysical works were:
Tectonic Stress Fields Reconstructions
As in the above-discussed case studies, two methods
were applied to analyze the tectonic stress fields—
Nikolaev's Method (
1977
), based on the dispersion of
shear
joints
density,
and
studies
of
the
electrical
anisotropy.
