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situated in the northern part of Vratsa Mountain are
draining the aquifer. Most of them are of ascending
type.
Typical precipices of different depths characterize
the zone along the northeastern border of the plateau.
The deeper one is Haydoushka Precipice, near the
Ivan Pousti Monastery. Its entrance begins with a
108 m deep well. Horizontal caves are also known,
some of them with springs. These ones are grouped
near the Saint Ivan Pousti Monastery, the longest cave
being of 546 m, and with a water stream inside. The
tectonic control of karst along the border of the pla-
teau is well expressed near Ivan Pousti Monastery
(Fig. 2.32 ).
The seven longest caves of the region include
75 % of the total length of the galleries. The ratio
between total vertical to total horizontal lengths
shows the domination of the vertical karstification
over the horizontal.
The karst formation began during the Early Mio-
cene and continued during Pontian and Pliocene time.
When Popov ( 1964 ) studied the genesis of Ledenika
Cave, he showed that its formation dates from the
beginning of the Dacian time, and it is related to the
Pontian level of denudation. The same period of for-
mation can be attributed to the caves and the preci-
pices in the high parts of the plateau.
Characteristics of the Karst of Vratsa Karst Region
The rainfalls are one of the most important factors
determining the active development of the karst pro-
cesses in the region. The classic type of karst is rep-
resented in the upper part of the mountain (Scorpil
and Scorpil 1895 , 1898 ; Radev 1915 ; Mishev and
Popov 1958 : Markowicz et al. 1972 ; Kostov 1997 ). Its
formation is also controlled by tectonic factors, as
well as by the geomorphological evolution of the area
(Ilieva et al. 1981 ; Angelova et al. 1995 , 1999 ).
Vratsa Karst Region represents a plateau with steep,
even vertical slopes, except the narrow band from the
south connecting it with the adjacent karst basin. It is
built by a north-northeast dipping monoclyne of
limestone layers of Late Jurassic and Early Cretaceous
age (Fig. 2.30 ). They are separated from the underly-
ing Iskar Carbonate Formation by a thin layer of non-
karstified rocks of Early Middle Cretaceous age. The
principal erosion basis is in the northeastern part of the
plateau. The principal karst springs appear at that
place. But, as a general rule for the entire area, the
boundary between the karstified and non-karstified
rocks is above the level of the local river network.
The principal part of the basin is characterized by
outcropping on the surface karst with abundant karst
forms. Some of the dolines are with dimensions
1-2 km 2 , the biggest one reaching 2-2.2 km 2 . The
underground karst forms are predominant. More than
70 caves and precipices are known in this area, most
of them in the limestones of Late Jurassic-Early
Cretaceous age. Some zoning can be traced from
southwest to northeast. The southwestern part con-
tains relatively little horizontal caves. Above them,
near the peaks Streshero and Ostria, there are con-
siderable and complicated as morphology precipices.
Here are the deepest Bulgarian caves Barkite 14, the
caves Beliar, Barkite 8, Mijishnitsa. All of them begin
from dolines and continue as a system of steps or
dipping generally toward northwest segments, fol-
lowing the upper boundary of the underlying karst
resisting rocks. Little water streams exist in every one
of the caves, their discharges are depending directly
from the atmospheric precipitation. The horizontal
projections of these caves on the surface are shown in
Fig. 2.30 .
Results from the Tectonic Stress Fields
Reconstructions
The reconstruction of the tectonic stress fields was the
first step of the study. The second one was to adjust
the received solutions in a tectonically logic scheme
for the time of manifestation of a given tectonic
strain. This scheme (Table 2.3 ) reflects the possible
temporal evolution of the tectonic stress axes orien-
tation for the area of Vratsa Block.
Looking at the performed reconstructions of the
tectonic stress fields, the most coinciding with the
described above tectonic deformations in macro scale
are these from the method using the shear joints.
The oldest deformations are detected on site No 5
where the Triassic limestones retain the ''memory''
for two impacts. The first one is related to the Early
Cimmerian Tectonic Phase (at the end of Upper Tri-
assic time), and the second—to the Late Cimmerian
Tectonic Phase (the second half of Upper Jurassic
time). The limestones of Polaten Formation (site No
4) were also deformed during the Late Cimmerian
Tectonic Phase. A second tectonic stress field is
reflected in the fracturing, and it was reconstructed on
sites No 1, 2, 3, and 6.
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