Number 31 January 1998 Newsletter of the Subcommission on ...

that are generally related to a
“Namurian-Stephanian” interval. They infilled a
large number <strong>of</strong> fault-bounded and
intramountainous narrow and subsiding basins,
which were mainly concentrated along and near
<strong>the</strong> most mobilized marginal areas <strong>of</strong> <strong>the</strong> Moesia
and Balkan terranes.
On <strong>the</strong> basis <strong>of</strong> <strong>the</strong> vertical and lateral distribution
<strong>of</strong> <strong>the</strong>se early Late Palaeozoic products, we
are led to recognize that deposition was possibly
cyclical.
The first, or older Upper Carboniferous cycle
encompasses <strong>the</strong> “Namurian-Westphalian” sediments,
from <strong>the</strong> boundary with <strong>the</strong> Variscan substratum
up to about <strong>the</strong> top <strong>of</strong> <strong>the</strong> Series. Thus,
this cycle appears to be confined between two
unconformities, which presumably coincide with
<strong>the</strong> widely reported “Sudetian” and “Asturian”
tectonic phases.
The second, or younger Carboniferous cycle
begins with “Stephanian” sediments, and ends
during <strong>the</strong> Lower Permian. Specifically, this cycle’s
presence is suggested by a general switching <strong>of</strong>
<strong>the</strong> depositional areas, which generated new basins
and extensively abandoned o<strong>the</strong>r areas. It is
highly probable, in this case too, that <strong>the</strong> Uppermost
Carboniferous-Lowermost Permian cycle
developed between two unconformities, which
more or less coincide, respectively, with <strong>the</strong>
younger one <strong>of</strong> <strong>the</strong> previous cycle and ano<strong>the</strong>r
located inside <strong>the</strong> overlying Rotliegend units. In
Bulgaria, according to Yanev (1981), <strong>the</strong> latter
unconformity marks <strong>the</strong> boundary between <strong>the</strong>
Lower and Upper Rotliegend, and is followed both
by a progressive or abrupt disappearance <strong>of</strong> <strong>the</strong>
igneous, intrusive and extrusive deposits, and by
<strong>the</strong> onset <strong>of</strong> differing sedimentary and structural
features. In a Permian excursus, this unconformity
could be reasonably correlated with <strong>the</strong> main
“Saalian” tectonic phase proposed by German
authors.
The subsequent third cycle, which includes <strong>the</strong>
Upper Rotliegend sediments, probably extended
from undefined Early Permian times to <strong>the</strong> beginning
<strong>of</strong> Late Permian. It is delimited by <strong>the</strong> second
<strong>of</strong> <strong>the</strong> aforementioned unconformities and by ano<strong>the</strong>r
one, which expresses itself markedly and
extensively in <strong>the</strong> present Bulgaria and abroad.
This younger unconformity is generally related
to a plate structural reorganization <strong>of</strong> vast European
regions, which was probably caused by a
major extensional activity. In o<strong>the</strong>r European regions,
this discontinuity has variously been identified
with <strong>the</strong> “Palatine” tectonic phase (e.g.,
Kozur, 1980), and with <strong>the</strong> “post-Saalian” or <strong>the</strong>
“Altmark” phases (e.g., H<strong>of</strong>fmann et al., 1989).
As a consequence, <strong>the</strong> overlying Upper Per-
Figure 3. Schematic, non-palinspastic sections through <strong>the</strong> Permian <strong>of</strong> Bulgaria, before deposition <strong>of</strong> Lower Triassic clastic redbeds. Section traces
in Fig.2B; lateral and vertical distances not in scale. Symbols: Pz = Palaeozoic; O1 = Lower Ordovician; D = Devonian; C1 = Lower Carboniferous;
C1V2 and C1V3 = Lower Carboniferous - Visean; C2 = Upper Carboniferous; C2N = Upper Carboniferous - Namurian; C2S = Upper Carboniferous -
Stephanian; P1 = Lower Permian; P11 = Lower Rotliegend; P12 = Upper Rotliegend; P2 = Upper Permian; T = Triassic.
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