Geoscience Reference
In-Depth Information
Fig. 2.41
Geological map of the region of Karlukovo Village.
1—Roman formation rmK
a - al
(sandstones and marls); 2—Ter-
rigenous-carbonate formation 14K
cn - m
; 3—Kailaka formation
kK
m
13Pg
2
; 5—Ugarchin formation ugPg
2
(sandstones, clays, marls
and siltstones); 6—Opanets formation opN
b
(clays and lime-
stones); 7—fault covered by younger sediments; 8—flexure;
9—fault line according to gravimetric data; 10—studied territory
(limestones); 4—sandstones, siltstones, clays and marls
The summarized data on the shear joints from sites
1, 2, and 3 (302 measurements) were statistically
processed and as a result two tectonic stress fields
were reconstructed that had affected the Maastrichtian
limestones (Fig.
2.42
, diagrams A and B).
The first stress field is characterized by sub-hori-
zontal maximum compression in NW-SE direction,
while the minimum tectonic stress axis is also sub-hor-
izontal and NE-SW oriented. This situation is favorable
for opening of fissures dipping 75 northeastwards
(strike N 115). The strike is more or less coinciding
with the general direction of Karlukovo Fault.
In the second stress field, r
1
and r
3
are also sub-
horizontal, but the compression is NE-SW directed,
whereas the minimum stress axis strikes NW-SE. In
this case the fractures striking N 18 and dipping 80
are optimally oriented for opening and karstification.
These two fields have impacted the limestones
during the Late Alpine Tectonic Phase when the main
structures of the Balkan Montain were formed (45 Ma
ago). The local tectonic stress conditions provoked
the formation of Karlukovo Fault and the relative
uplift of its southern block. The initial conditions for
karst formation were created and they were more
active in the southern block being exposed to more
intensive denudation.
Later, probably during Neotectonic time, the gen-
eral N-S compression created conditions for devel-
opment of NNE-SSW fissures. The process was
relatively fast and lead to the formation of canyon
type valleys in the southern block, at some sites cut-
ting the older karst forms. During Neotectonic time,
the total uplift of the area is evaluated at about 300 m
(Vrablianski
1974
).
Studies of the electrical anisotropy were performed
at three sites (Fig.
2.42
) with array AB/2 = 30 m. Site
KE 1 and KE 3 have similar solutions and the long
axes of the electrical anisotropy ellipses are more or
less corresponding to the strike of Karlukovo Fault,
i.e., they reflect the first tectonic stress field. Site KE 2
is practically inside the fault zone, it has different
orientation of the anisotropy axis, corresponding
exactly to the second reconstructed stress field. The
possible interpretation is that it reflects superimposed
deformations of the trend of Karlukovo Fault leading
to its sinusoidal curvature.
