H geomorfologiji Voglajnske pokrajine in Zgornjega Sotelskega

Abstract

In this article the area is discussed which extends east of the Lower
Savinja River Valley and which covers two larger regions: that of the
Voglajna River basin (a left tributary of the Savinja River into which it
flows at the town of Celje), and the basin of the Upper Sotla River which
extends as far as Podčetrtek, i. e„ the so-called Upper Sotla River Region
(Zgornje Sotelsko). In the north this area is limited by the Donat. Fault Zone
which represents the eastern extension of the Karavanke Mountains, with
Konjiška gora, Boč, Donačka gora, and Macelj; in the south it borders on
the eastern extension of the northern corner of the Trojane anticline with
the Rudnica Mountain, i. e., the northern fringeland of the Sava River Folds.
During our geomorpliological mappings 14 levels and 2 accumulative
terraces at a distance of ca 240—830 m have been established. The levels
300—320 m and 340—360 m are most widely spread and they show the best
state of preservation. Both occur exclusively in the Tertiary rocks, while the
levels above 360 m can also be found in the older fringeland. The most
important of these is the level 580—640 m, it is densely scattered in the
whole area here discussed and in all rocks, also in the limestone of the
Rudnica Mountain and in its Oligocene extension towards the west. The
changes in the reorientation of the liydrographic net can already be observed
in the level of 380—420 m, yet they were most important after the level of
340—360 m had already been formed, and partly also in the level 300-—320 m.
A special attention has been paid by the author of the present study to
the levels of up to ca 300 m. This is due to his main task which was that
he should try to find the traces of the ancient bed of the Savinja River
which according to a supposition proposed by Rakovec (13) flowed eastwards
into the contemporary Pannonian Sea viz. Lake. A later change of the flow
of the Savinja River towards south took place, according to I. Rakovec,
after the individual tributaries of the Sava River had created their own
effluxes; because of this change the present bed of the Savinja River forms a sharp bend near the town of Celje and turns from a generally east-west direction to that fro m north to south and the river flows now in a narrow
and deep valley transversing the Sava River Folds.
A stratigraphic section of the old Pannonian strata at Pristava and
Zibika betrays no traces of an eventual influ x of a larger river into the old
Pannonian Gulf . There could have been smaller rivers only that flew into
it fro m the neighbouring hinterland. There are, however, several elements
which seem to indicate that during the Pliocene and perhaps also during
a part of the Pleistocene the Savinja River flew towards the northeast in
the direction of the Drav a River Valley (Dravsko polje) and into the sea
viz. lake gulf closest to that area. This seems to be proved b y the large
incision that can be observed in the relief in the Oligocene sea rocks that
occur between the mountains of Boč and Konjiška gora at the village of
Lipoglav, an incision which is now used by the railway line Celje—Maribor;
the remains of the old levels are still preserved along this incision. Southwest of this passage, too, the levels are well preserved which can also be found on the slopes above it. Besides these facts, the composition of the
Dacian gravel in the Dravdnja River Hills near Slovenske Konjice (14, p. 175
and 176) and east of them (12, p. 265—266) whic h contains a considerable
quantit y of the carbonate gravel that does not, according to Rakovec (14,
p. 176), originate from the neighbouring Pohorje onl y "but it had rather
been also brought from the Eastern Kravanke Mountains, even from considerable distances" seems to prove that the Savinja River had once indeed
flown in the direction of the Drav a River Valley. The author thinks the
carbonate and partly also the siliceous gravel to be the result of an accumulation caused b y the Savinja River; in this way he disagrees with the proposition proposed b y I. Rakovec that waters flowing from the Eastern
Karavanke Mountains had also participated in the accumulation of the
Dacian gravel. The highest level reached by the Dacian gravel is 481 m.
The change in the direction of the flow of the Savinja River towards
the south had taken place, according to the present author, soon after the
formation of the level of 340—360 m. the highest part of the passage being
situated 355 m above sea level. He believes that this event can be placed
into the beginning of the Pleistocene or into the transition period between
the Pliocene and Pleistocene. He has been led to this conclusion b y the
results arrived at by some investigators who have considered the present
relief to be comparatively recent. In this way an important role has now
been attributed to the Pleistocene — including the transition period between
the Pleistocene and the Pliocene — in the formation of the present-day
relief. The author finds the most important support for his supposition i n
the chronology that was proposed by Winkler (17, p. 405^407) who places
the origin of the levels below 600 m above sea level into the so-called Praeglacial considering at the same time the levels of up to 150 m of relative height of the Goričko and Slovenske gorice areas to belong into the Quaternary (18). The young character of the relief has also been shown by the
newer results of the geologic investigation in the area here discussed and by
the recent geomorphologic investigations of the Quaternary development in
the Dravinja River Hills, in the Haloze Mountains, Šalek Valley, and in the
Upper Savinja River Basin.
In the eastern part of the area we find the hydrographic net connected with the important hydrographic knot at Pristava which stands in genetic connection with the old Pannonian Sea Gulf. Waters flew into it
from the whole source area of the present Sotla River and during an older
period even from the surroundings of Svetina from which there had also
flown a unitary river towards the west along the southern syncline and
north of the Rudnica anticline. This river was later cut off b y the Savinja
River, and its tributaries fro m the Oligocene continuation of the Rudnica anticline had their currents changed so that now they flew into the Savinja
River or, later, into the Voglajna River. Attention is called by the author to
the normal flow of waters in the eastern part of the area here discussed in
contrast to the asymmetric and geniculate flows that can be observed in its
western part and which are a consequence of the palaeohydrographic factors.
From under the southern slopes of the Boč Mountain and the western
part of the Macel j Mountain the waters flew originally towards the west
into the Mestinjščica Brook. Later only, when they came sufficientl y close
to the Sotla River they were absorbed directly by the latter.
The hydrographic net is strongly influenced b y the tectonic lines and
by the system of synclines, especially in the eastern part of the area. I n
this connection the Sotla River Fault has the most important role, it attracts
numerous brooks that flow from under the Donat Fault Zone as well as the
Sotla River itself as far as the town of Rogaška Slatina.
An important role is also attributed by the author to the selective erosion. Numerous valleys have been formed by the selective erosion caused.
also b y smaller waters; this is particularly true for the soft Sarmatian
rocks that occur at the bottom of the synclines, and for the low and broad
pass in the valley of the northern syncline between Voglajna and Sotla
Rivers above the town of Šmarje in Haler's Hil l (Halerjev breg) over which
the road goes that leads from Celje to Rogaška Slatina. All the structural
gradations that can be observed in contact zones of harder and softer
Tertiary rocks are also a product of selective erosion.
Earthflows — both recent and fossil earthflows -— had according to
the author had an important role in the formation of the slopes in the
Tertiary rocks. In some places, particularly in the harder Tortonian conglomerates and in limy sandstones where the slopes are steeper we find whole slopes exposed to earthflows so that during heavy rainfalls many
earthslides frequently occur. In such places the slopes are virtually washed
clean and because of this the older levels and the terraces above them are
also deformed or, on the other hand, we can find the material brought by
earthflows at the bottom of the slopes which can occasionally also make an
impression of a level or of a terrace.
In wider flat areas with the lithotamnian limestones, in the Tortonian
limestone conglomerates, and in limy sandstones Karstie phenomena have
partly been developed, especially the Karstie pot-holes. Karstie sources, and
even one Karstie swallow-hole (ponikva). Aft r the latter the village of
Ponikva has been given its name.