Guidebook - Ispra

Volume n° 1 - from PR01 to B15
B12
B12 -
Leader: M. Sandulescu
section lineation: N53°E/ 36°SW). The regional trend
of the stretching lineations marked by the elongation
of the pebbles in the Laminated Conglomerates of the
Arieșeni Nappe is also north-western, confirming the
direction of the Alpine tectonic transport.
The strain of the pebbles was exclusively an extensional
one, as measurement of their shape has shown,
the intensity of deformation being medium.
Comparing the Es parameters for the pebbles of the
Greenschist conglomerates with those of the Laminated
Conglomerates in the Arieșeni Nappe, it may
be concluded that the former were more intensely
deformed (Es = 0.55 - 1.22 versus 0.55 - 0.80), having
undergone an older Midcarboniferous tectonic phase
that did not affect the latter. On Flinn’s diagram, the
majority of the pebbles shows a k~1, the strain having
been a plane one in the Laminated Conglomerates of
the Arieșeni Nappe (Dimitrescu, 1995).
Stop 5.10:
Bubești Hill. Permian Vermicular
Formation. Banatitic sill.
At km 32 + 120 m, on the left slope of the valley
above the road, the Permian is represented by red
micaceous sandstones and argillaceous shales. In the
sandstones, bioglyphs of burrow - fillings type can
be observed. The Permian is pierced by a banatitic
andesite sill.
Stop 5.11:
Piatra Muncelului. Lamprophyre dykes crossing
Urgonian limestones.
After reaching the main watershed of the Apuseni
Mountains, the road leaves the Arieș hydrographic
basin and enters the Crișul Negru basin, intersecting
reddish Permian and quartzitic Lower Triassic
formations.
After a number of road windings and hair-pin bends
across Lower Jurassic detrital formations changed
into hornfelses (“Black Series”), a fault is traversed
and then white massive limestones of Barremian in
Urgonian facies belonging to the lowermost Bihor
Unit are continuously exposed.
At km 21 + 50 m, three almost vertical lamprophyre
dykes striking about NS are intruded into the limestones.
The thickness of the dykes ranges between
1 and 3 m; the eastern one presents at its contact a
breccia about 1 m thick, composed of angular fragments
of white limestones (recrystallized as marbles)
and of igneous rocks, enclosed in a calcareous-gritty
cement.
The lamprophyres correspond to odinites, consisting
of basic plagioclase and augite, the ground-mass
having an intergranular texture. It is worth noting the
presence of pyroxenes as phenocrysts (Bleahu et al.,
1981).
Stop 5.12:
Arieșeni - Băiţa road. Contacts Arieșeni
Nappe / Următ Nappe / Bihor Unit.
In the last outcrops of the limestones (km 20 + 60 m)
numerous Coral traces as well as remnants of Megalodonts
are to be observed; then, at the road surveyor’s
cabin, the road crosses from the Bihor Unit into the
Următ Nappe. The latter consists of slight micaceous
shales, yellowish quartz sandstones and greyish calcarenites,
all of them assigned to the Lower Jurassic.
Further on, the road leads again into the Arieșeni
Nappe consisting mainly of the Permian violaceous
rocks. Red coloured rocks are gradually replaced
by black coloured ones (“Black Series”) due to the
thermal action of the banatitic body intruded here at a
small depth (Bleahu et al., 1981).
Stop 5.13:
Băiţa Bihorului. Rhyolites in the black Permian.
On entering the old mining locality of Băiţa Bihorului,
opposite the first houses, on the right slope, a
rhyolitic body is exposed. Its colour is light grey, due
to thermal metamorphism with very slight violaceous
hues at places. The rock presents a feebly pronounced
foliation; the attitude of the layering is approximately
N 20°E / 40°SE; two main joint systems are observable.
The footwall consists of blackish vermicular
micaceous sandstones, while in the hanging wall, the
contact with black argillites and quartzites may be
observed (“Black Series”).
Past the town of Băiţa, on the right-hand side, the formation
of the Bătrânescu Nappe appear contacting the
Arieșeni Nappe along a fault. Skythian quartzites followed
by dolomites and limestones of Middle Triassic
age can be noticed. Finally the road reaches the Beiuș
Depression with outcrops of Pliocene.
Stop 5.14:
Vașcău. Permian ignimbritic rhyolites.
Ignimbritic rhyolites are exposed about 400 m west of
the Vașcău railway station. White feldspar and quartz
crystals about 1-3 mm in size are conspicuous, as well
as leafy biotite, included in a greenish-grey schistose
matrix. Characteristic “fiamme” are often noticed in
the latter (N. Stan in Borcoș et al., 1980).