Guidebook - Ispra

Volume n° 1 - from PR01 to B15
B12
B12 -
Leader: M. Sandulescu
The top of the sequence consists of massive greyishwhite
Wetterstein limestones.
The detritic formation presented above gives evidence
of a continental environment deposition, the
limestone pebbles and the violet clays possibly representing
a karst infilling.
Some hundreds of meters upriver, the Wetterstein
limestones overthrust by Codru Granitoids and
migmatites of the Gârda Nappe are transformed into
calcite mylonites (Bleahu et al., 1981).
Stop 5.4:
Scărișoara - Gârda. Upper Carboniferous-Lower
Permian of the Gârda Nappe.
After crossing laminated Codru granitoids and migmatites
and a horst exposing Wetterstein limestones in
a half-window, the road reaches the first sedimentary
term of the Gârda Nappe, namely the Laminated Conglomerates,
the Upper Carboniferous-Lower Permian
age of which was evidenced by palynology. They consist
of flattened, mainly quartz pebbles in a violaceous
slaty matrix. An oblique foliation may sometimes be
obseved. Upsequence follows laminated violet or
green rhyolitic ignimbrites and violet shales with
interbeds of red micaceous sandstones (with hyeroglyphs)
(Bleahu et al., 1981).
Measurement of the pebbles has shown that the strain
was predominantly an extensional one, but in places
the main deformation was flattening (Dimitrescu,
1995).
Stop 5.5:
Gârda de Sus - confluence with Iarba Rea. Lower
Permian of the Gârda Nappe.
After crossing again, due to the Gârda major fault,
the Anisian dolomites of the Bihor Unit, the road
continues across the formations of the Gârda Nappe,
the place of the Laminated Conglomerates being
taken by a breccia consisting of fragments reaching
20 cm in length of gneisses, muscovite, schists quartz
and quartzites included in a shaly matrix. They are
believed to be an alluvial deposit, without fluvial
transport and present a striking similarity to the “Conglomerati
di Dosso dei Galli” of the Southern Alps
and with the Medódoly (Kopersady) breccias of the
Tatrides (Bleahu et al., 1981).
Stop 5.6:
Confluence with the Buciniș valley. Arieșeni Nappe
overthrusting the Gârda Nappe.
After crossing a spectacular gorge cut across a syn-
cline of Skythian violaceous quartz conglomerates
and sandstones overlying the Permian micaceous or
feldspathic sandstones and shales, at the confluence
with the Buciniș valley the contact between the Gârda
and the Arieșeni Nappes is exposed. The former is
represented by laminated conglomerates, sandstones
and rhyolites, while the latter consists of green phyllitic
schists of Lower Carboniferous age, the attitude
of their schistosity being about EW with southern dip
(Bleahu et al., 1981).
Stop 5.7:
Arieșeni. Greenschist Formation
(Upper Carboniferous).
From the front of the Arieșeni Nappe overthrust examined
at the previous stop, the road crosses exclusively
the Lower Carboniferous greenschists of this
unit. The large outcrops reveal the schistosity of the
Arieșeni Formation showing various dips, generally
towards W and NW.
At km 40 + 350 m of main road nr. 75, in an exposure
about 10 m long on the left side of the Arieșul Mare,
a subhorizontal exposure may be observed consisting
of weakly metamorphosed conglomerates with
strongly rolled pebbles, composed predominantly of
quartz and with greyish-green quartzitic matrix; the
metaconglomerates admit an intercalation of greyish-green
sandstone and overlie green pelitic schists
cropping out just at the water level. The alternation
of the lithological horizons expresses the S 0 bedding
of the rocks, on the planes of which no foliation has
developed; the attitude of the graphically determined
bedding is approximately N 45° W / 12° SW. Directly
measurable foliation planes correspond to a schistisity
S 1 (flow cleavage) oblique with respect to the bedding;
its attitude here is N 70°W / 45°SW. Along this
foliation small faultings of the lithologic horizons occur
locally. The intersection lineation trends N 67°W
/ 04°NW.
The regional trend of the stretching lineations, marked
by the elongation of the pebbles in the Greenschist
Conglomerates of the Arieșeni Nappe, is NW, signalling
the direction of Alpine tectonic transport in the
Northern Apuseni (Dimitrescu, 1995).
Stop 5.8:
Arieșeni. General view of the Biharia Massif.
The whole crest of the Biharia Massif is built up of
the formations of the Biharia Nappe consisting of the
Biharia crystalline series. It overlies horizontally the
Poiana Nappe made up of a narrow strip of metacon-