Guidebook - Ispra

Volume n° 1 - from PR01 to B15
B12
B12 -
Leader: M. Sandulescu
Stop 7.5:
Bela Reka valley. Middle Lias.
Upstream the Bela Reka valley, black shales with
gritty intercalations of the Middle Lias crop out,
characteristic for the Gresten facies. Their age is constrained
by faunas with Ostrea cymbium, Belemnites
paxillosus, Pholadomya sturi. Upwards they grade
into the Upper Lias, with Posidonia bronni (Codarcea
et al., 1961).
Stop 7.6:
Timiș valley between Teregova and Sadova Veche.
Armeniș Formation of the Lotru Series.
The lowermost term of the Lotru Series consists of
nodular sillimanite-bearing biotite gneisses, pearlgneisses,
quartz-feldspar gneisses, amphibolites and
amphibole-gneisses, marbles and calc-silicate rocks
(Savu, 1970; Săbău, 1994). Pegmatite veins are frequent.
The top of the formation is represented by the
thin Piatra Scrisă amphibolite level, overlain by almandine,
kyanite and staurolite bearing micagneisses
and schists (Săbău, 1994).
Stop 7.7:
Moniom. Relations between the Getic Reșiţa
Nappe and the Supragetic Moniom Nappe.
Leaving Moniom, the (Westphalian C.) Doman Beds
of the Reșiţa Nappe will be crossed up to the Cârșie
Hill, where they are overthrust by the metamorphic
rocks of the Moniom Nappe along the Oraviţa tectonic
line. The uppermost term of the Reșiţa Nappe is
represented by the Carboniferous Cârșie Formation.
It consists of metaconglomerates, metasandstones and
phyllites. In the former, the pebbles decrease in size
westwards. The stretching lineations are materialized
by the N30 - 40°E / 10 -30°NE trending elongations
of the pebbles. Analysis of the finite strain put in
evidence its high intensity (Rf > 2,5) and its plane
character. The Oraviţa tectonic line represents a post-
Supragetic Nappe dextral transcurrent fault, inducing
a simple shear in the Carboniferous formations (M.
Dimitrescu, 2000).
Westwards along the Bârzava river, the Devonian
Valea Satului Formation of the Moniom Nappe consists
of chlorite-epidote-actinolite-albite schists (±
quartz, sericite, calcite) representing mylonitic basic
metatuffs, metatuffites and metaaglomerates, with
intercalations of carbonatic and graphitic rocks, acid
metatuffs also being present, as well as metagabbroic
intrusions.
The described formations exhibit subhorizontal ini-
tial stratification surfaces (S 0 ) and almost vertical S 2
cleavages.
The Valea Satului Formation was parallelized with
the Leșcoviţa “Series” exposed along the Danube (V.
Iancu, in: Năstăseanu et al., 1981).
Stop 7.8:
Colţan tunnel. Bocșa Nappe overthrust onto the
Moniom Nappe.
Along the Bârzava valley, above the Colţan railway
tunnel, the Valea Satului Formation of the Moniom
Nappe is overthrust by the Bocșiţa-Drimoxa Formation
of the Bocșa Nappe. The latter formation consists
of muscovite-chlorite-albite plagiogneisses, with biotite
and garnet relics ( mainly enclosed in plagioclase
porphyroblasts); it crops out about 200 m west of the
forest chalet. The rocks exhibit intrafolial transposition
folds, the limbs of which are cut by a S2 foliation
with a westward dip. Westwards, the plagiogneisses
alternate with rare microcline augengneisses and
orthoamphibolites (V. Iancu, in: Năstăseanu et al.,
1981).
The Mesozoic cover of the basement formations is
represented by marbles, the age of which is ascribed
to the Middle-Upper Jurassic-Lower Cretaceous.
The Bocșiţa-Drimoxa Formation was parallelized
with the Locva “Series” exposed along the Danube
(V. Iancu).
Stop 7.9:
Bârzava valley - Bocșa Nouă. Banatitic massif.
The contact zone between the Bocșa banatitic pluton
and the intruded Supragetic augen-and plagiogneisses
is exposed. A first intrusion of micromonzodiorite
porphyry is penetrated by a granodiorite, carrying
xenoliths of both crystalline schists and eruptive
rocks. The micromonzodiorite porphyry of the early
magmatic stage (Western Unit) contains large hornblende
and biotite phenocrysts. The monzogranites
and granodiorites Medium Unit consists of zoned
plagioclase (20-35 % An), microcline, quartz, biotite
and hornblende (Russo-Săndulescu et al., 1975; in
Năstăseanu et al., 1981).
The respective K - Ar ages of the succesive intrusions
are 87 m.y. (B 1) and 80 - 81 m.y. (B2) that is, intra
- Senonian.
Acknowledgements
The authors would like to express their gratitude to
Dr. Mihaela Dimitrescu, Miss Elena Negulescu and
Miss Delia-Georgeta Dumitraș (Geological Institute