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being of the youngest age, and they correspond to the
youngest (contemporary) tectonic stress field
(Table 2.2 ). The well-expressed thrust structures
(sites 3, 5, and 6) appear as relicts of the Laramian
tectonic phase deformations. In the zones of shearing
and mylonitization, there are conditions for formation
(mainly because of mechanical export of particles by
the water) of small horizontal cavities, which seldom
reach more than several tens of meters (for example at
sites 5 and 6). Their orientation is along the slip
surface.
During the Pyrenean Phase, strong normal faulting
along the ruptures of NE-SW direction and opening of
joints systems into the same direction occurred. Most
investigated vertical precipice caves developed on
these joints. It is worth to emphasize that they all
belong to zones with well- manifested faults.
Precipices near sites 10, 11, 12, and 16 are located
along morphologically well-manifested fault still not
shown on official maps. All these precipices are
located in brecciated zones with clear tectonic slic-
kensides and striations on them.
During the Pyrenean phase, tensile stresses varied
locally from NW-SE to NE-SW direction, and the
compression was oriented N-S or sub-vertically
(uplifting of the massif). The subvertical compression
lasted also during the Neotectonic stage when the
orientation of the minimum stress r 3 favored both the
existence of earlier formed open cracks of NW-SE
direction (sites 13 and 15—open karren and preci-
pices; in case of site 1—widely open karren up to
several meters). Some evidence of strike-slip dis-
placements can be seen on site 14. The controlling
role of the faults for the process of massif karstifica-
tion is best observed in areas of Upper Jurassic clay
sandstone, where caves could not exist without the
influence of the tectonic factor. Strong faulting and
crack opening favor mechanical export of debris and
the formation of typical karstic precipices.
The contemporary displacements are not so active
but in case of NW-SE orientation of r 1 they have led
to some clear strike-slip displacements along the
Dobromiri Fault. Besides that, the erosion rate obvi-
ously becomes dominating over the uplifting process,
and this results in sealing of many of the superficial
karstic forms with deluvial materials. Thus, in spite of
the high permeability for atmospheric waters into the
karstic
systems are conserved only within fault zones, where,
nevertheless, the young tectonic displacements do not
allow their fast colmatation with materials from the
rock weathering.
The sharp-shaped relief is a result not only of
tectonic displacements, but also of chemical destruc-
tion of limestones and dolomites by rains and snow.
The long lasting snow cover at this altitude (between
1,000 and 1,500 m) is a factor for chemical erosion
durability through the year. Special analyses in the
region for atmospheric waters aggression potential, as
well as of the snow covering melting waters have not
been done. Such an investigation would deepen the
analysis of the reasons for the strong superficial and
underground karstic processes in Albanian Dinarides.
2.3.2
Bulgaria: Tectonic Stress Fields
Studies in Karst Systems
Bulgaria covers an area of 111,000 km 2 . About 23 %
of this area consists of carbonate rocks (i.e., pure
limestone or dolomite) that host over 5,000 caves.
Carbonate rocks, in which the majority of karst is
developed, were formed during the Triassic, Jurassic,
Cretaceous, and Tertiary periods. Less extensive karst
with minor significance with respect to cave and
karst development exists in Proterozoic marbles of
Rila-Rhodopes area (Fig. 2.29 ).
Geomorphologically, there is an expressed dis-
tinction between the four principal regions (Popov
1982 ): (I) Danube Plain (Moesian Platform) in the
northern part of Bulgaria; (II) Stara Planina (Balkan)
Zone; (III) Intermediate Zone occupying the central
parts of the country; (IV) Rila-Rhodopes Zone in the
south (Fig. 2.29 ). The boundaries between the regions
are roughly coinciding with faults and fault segments
activated during the Neotectonic stage, some of them
active till now and controlling the contemporary ter-
rain morphology (USGS 2004 ). Only some of the
active faults are recognized by the method of Paleo-
seismology (Meyer et al. 2007 ; Vanneste et al.
Vanneste et al. 2006 ), the others are plotted on the
base of published data (Cadet and Funiciello 2004 ;
Georgiev et al. 2007 ; Kastelic et al. 2011 ; Radulov
et al. 2006 , 2011 , 2012 ; Tzankov et al. 1998 ;
Vapcarov et al. 1974 ; Vrablianski 1974 ), or verified
during field works for different projects.
massif,
the
vertical
type
of
open
karstic
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