Geoscience Reference
In-Depth Information
Fig. 2.21
Regional scheme,
nearest earthquake fault-plane
solution and geological
background of the Orlova
Chuka Cave area (North
Bulgaria). The fault-plane
solution for Hlebarovo
Earthquake (M
s
= 4.7) is
based on the data published
by Shanov et al. (1988). The
geological map is based on
Sheet ''Byala'' from the
Geological Map of Bulgaria
in scale 1:100 000 (Filipov
1992
) 1—Loess cover;
2—Aptian limestones (Lower
cretaceous); 3—fault
information. The maps of the known karst galleries are
necessary to make the most possible realistic conclu-
sions for the features of the karst formation and evo-
lution in the area concerned.
An example from the Moesian Platform (Northern
Bulgaria) is presented below.
limestones and calcareous sandstones. According to
Radulov (
2002
), the morphological features of the cave
galleries suggest a phreatic origin. The cave system lies
just below an old river terrace at elevation about 60 m
above the present floodplain of Cherny Lom River,
tributary of Danube River. Terrace at 60 m corre-
sponds to an erosion surface formed in the southern
margin of the so-called Dacian Basin during the Plio-
cene and Early Pleistocene. Erosional surface is cut
2.59 Ma BP, and the alluvium deposits over it extend
to the beginning of loess formation in NE Bulgaria.
The main phreatic stage of cave formation should be
assigned to the same time span. Brunhes/Matuyama
geomagnetic boundary (0.78 Ma BP) has been found
Orlova Chuka Cave, North Bulgaria
The cave Orlova Chuka (means Eagle rocky peak) is
located on the left bank of Cherni Lom River
(Fig.
2.21
). The cave is a complex system of galleries,
caves, and large and small halls. It is the second in
Bulgaria by the total length of its galleries—13,437 m.
The cave is formed in Cretaceous (Aptian-Urgonian)
