Geoscience Reference
In-Depth Information
Fig. 2.42
Scheme of the studied territory NE of the village of
Karlukovo with diagrams from the studied sites 1—Quaternary
deposits; 2—Maastrichtian limestones; 3—rock slope (canyon
type); 4—fault; 5—cave entrance and horizontal projection of
the galleries; 6—karst springs; 7—site of measuring of shear
joints; 8—site of study of the electrical anisotropy
Looking on the maps of the caves in the area
(Fig.
2.42
) it is clear, that the tendency of the cave
galleries is to follow one of the preferential directions
of open fractures, created by the principal tectonic
impacts on the Maastrichtian limestones.
Geological Background
The karst-rock complex consists of Triassic carbonate
rocks (Fig.
2.43
). They overlie red sandstones, con-
glomerates and siltstones. The siltstones were trans-
formed into quartzite at the contact zone of Vitosha
pluton. The carbonate rocks cover an area of 23 km
2
and are about 200 m thick. Thick packages (about
50 m) of argillite and siltstone divide the carbonate
rocks, playing the role of local aquicludes. The beds
situated below these packages consist of limestone,
and over them—of dolomite. Jurassic and Cretaceous
rocks locally occur in the NE part of the area. A set of
faults of different age of formation and activation has
complicated the tectonic structure of the area, and in
some cases, these faults control the relief, as well as
the features of the karst system. The relief is typically
mountainous—about 800 masl near the dam lake of
Studena and up to 1,400 m in the NE part. The waters
of Struma river principally, and also from other
smaller rivers in the area, are the main factor for the
karstification. The river loses its flow in the area of
the contact between sandstone and carbonate rocks, as
2.3.2.3 Intermediate Zone—Bosnek Karst
Region
The karst system in Triassic limestones near the vil-
lage of Bosnek (Southwestern Bulgaria) contains the
longest Bulgarian cave - Duhlata (more than 17 km of
total length of the galleries). Bosnek karst Region
(BOS—Fig.
2.29
), from tectonic point of view,
belongs to Golo Burdo thrust unit (Jelev
1982
;
Gochev
1983
; Zagorchev et al.
1994
). Important
structural and geophysical studies were done in this
area for understanding the tectonic control on the
karst formation and to explain better the hydrogeo-
logical features of the area (Benderev and Shanov,
1997
; Shanov et al.
2001
; Mihailova et al.
2006
).
Results from these studies will be analyzed and dis-
cussed below.
