GEOLOGICA CARPATHICA, 52, 4, BRATISLAVA, AUGUST 2001
195—203
DEPOSITIONAL ENVIRONMENT OF THE “OLD RED” SEDIMENTS
IN THE BRNO AREA (SOUTH-EASTERN PART OF THE
RHENOHERCYNIAN ZONE, BOHEMIAN MASSIF)
SLAVOMÍR NEHYBA, JAROMÍR LEICHMANN and JIŘÍ KALVODA
Department of Geology and Paleontology, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic;
slavek@sci.muni.cz
(Manuscript received January 18, 200l; accepted in revised form June 13, 2001)
Abstract: Lower Devonian monomict-quartzose coarse-grained clastics near Brno (on the Červený kopec Hill) are
interpreted as the deposits of an alluvial fan built up mainly by catastrophic sheetfloods. The main sources were probably
granites and gneisses, other components were derived from rhyolites, older siliciclastic sediments and low-grade meta-
morphic rocks. Abundant presence of muscovite reflects some role of an exotic source area. Rapid uplift, erosion domi-
nated by mechanical weathering and multiple redeposition are supposed within the drainage basin. The flat alluvial fan
was only slightly reworked and eroded during subsequent non-catastrophic overland flows (secondary processes). A
relatively mature stage of the evolution of the alluvial fan and drainage basin was accepted. A continental extensional
basin represents the most probably depositional setting of the studied deposits.
Key words: Early Paleozoic, monomict-quartzose clastics, conglomerates, sheetfloods.
Introduction and geological setting
The thick, siliciclastic unit that typically mantles the Neoprot-
erozoic crystalline rocks of Brunovistulicum (eastern margin
of the Bohemian Massif) has been described as the “Devonian
Basal Clastics“ or Moravian “Old Red“ in the Czech geologi-
cal literature. They were the subjects of numerous studies
(Dudek 1960; Dvořák 1993, 1998; Dvořák & Skoček 1997;
Batík & Skoček 1980; Jaroš & Mísař 1976; etc.). These sedi-
ments were assigned to the Devonian on the basis of their sim-
ilarity to Devonian rocks in the European neighbourhood.
However, the Devonian age of these clastics is proved by pale-
ontological findings (Chlupáč 1989; Havlíček & Mergl 1990;
Hladil 1985) or suggested by carbonate-clastic interfingering
in the Moravian Karst facies only for their uppermost part
(Chlupáč 1988; Galle et al. 1988; Hladil 1988, 1994). An as-
sumption of Cambrian age existed for some very thick clastic
sequences in SE Moravia (Roth 1981). Recent studies of acri-
tarchs in the boreholes Měnín-1, Němčičky-3 and Němčičky-6
indicated an Early Cambrian age (Jachowicz & Přichystal
1997; Fatka & Vavrdová 1998).
Basal Paleozoic Clastics (BPC), which seems to be the more
precise designation of the bulk of the rocks under consider-
ation, occur mainly in the subsurface. The greatest part is hid-
den below the Outer Carpathian units. The BPC have a highly
variable thickness (50 m up to > 1500 m), with several post-
Carboniferous erosion windows where the entire Paleozoic se-
quence is entirely removed (Adámek et al. 1980). The tectonic
environment influenced the thickness of the BPC as well
(Skoček 1980; Leichmann et al. 1999).
BPC rocks also differ in the composition and lithology. They
are commonly highly mature with a strong prevalence of quartz
and stable minerals. Quartz sandstones and conglomerates are
fairly abundant (Štelcl 1969). A generally decreasing amount of
quartz clasts stratigraphically upward was formerly accepted in
the Czech geological literature. The BPC were subdivided into
three types, mainly on the basis of petrographic studies. These
types are: (1) polymict clastics with a lower content of quartz,
Fig. 1. Location map of the Červený kopec Hill in Brno.
196 NEHYBA, LEICHMANN and KALVODA
Fig. 2. Variscan zones of the Bohemian Massif and position of in-
vestigated area.
(2) monomict-quartzose clastics, and (3) arcose and quart-
zose sandstones and mudstones (Skoček 1980). The BPC are
usually green or red coloured. The abundance of quartz clasts
corresponds to ultrastable composition of the heavy mineral
association. Argillaceous or clayey beds are relatively rare.
Pokorný (1948) and Přichystal (1993) described coarse-
grained, intermediate volcanic tuff layers within the BPC.
The presence of the BPC reflects the evolution of the
Brunovistulian Panafrican Terrane. The presence of Lower
Cambrian continental and marine siliciclastic sediments may
indicate extension related to the fragmentation of the Gond-
wana Panafrican margin. After the early Paleozoic accretion,
the Brunovistulian Terrane formed a Baltica promontory,
which was involved in an oblique convergence with the Ar-
morican group of terranes during the Devonian and Carbon-
iferous. In the first stage of convergence, a slab pull contrib-
uted to the widespread aegotype rifting on the Brunovistulian
passive margin and led to the formation of half-graben sub-
basins where Devonian Basal Clastics (DBC) were deposited
(Kalvoda 1995). These red continental rocks have been com-
pared to the Old Red facies of the British Isles. However, in
contrast to the typical British Old Red facies, they do not
represent a Caledonian molasse.
According to present knowledge, it is assumed that the
BPC originated in a mainly fluvial and lacustrine deposition-
al environment with occasional alternation with nearshore
marine sedimentation at the top of the sequence. Opinions
about an origin as residues, aeolian silts and sands or coastal
sabkha have been presented by Zádrapa & Skoček (1983)
and by Dvořák & Skoček (1997).
All these findings proved that besides the rough similarity
of the BPC, great differences in stratigraphy, depositional en-
vironments, source areas, tectonic and basinal settings, etc.
must be taken into account in the process of geological eval-
uation of these rocks.
The presented paper is focused on the nicely exposed pro-
file of the BPC (monomict-quartzose clastics) on the Čer-
vený kopec Hill in the southern part of the city of Brno. In
the locality studied here, the BPC is supposed to represent
the first member of the “Moravian Karst Development“
(Zukalová & Chlupáč 1982) which is characterized by the
predominance of shallow-water platform carbonates at the
top. The BPC can be studied both in the river Svratka bench
cut and in quarries on the hill. The basement is not exposed.
The area is situated in a N-S elongated depression that ex-
tends between Červený kopec Hill in the south and the Babí
lom Hill in the north (Fig. 1). The position of the Moravia in
the context of Paleozoic terrains geology is presented in Fig.
2, and geological development of this area during the Devo-
nian is described in Fig. 3.
The aim of the present study is to describe depositional
processes and environments and to contribute to the recogni-
tion of source areas.
Sedimentary facies and facies distribution
Five lithofacies (A—E) have been recognized within the
logged profile (Fig. 4) on the basis of textures, sedimentary
structures and geometry of bedding surfaces. The width of
the studied profile was limited (max. 10 m) and enabled the
study only in one direction.
Facies A
The most common facies (about 86 %) consists of rhyth-
mic conglomerate and sandstone planar couplets (Fig. 5A
and 5B). Almost planar beds of pebbly conglomerate (cob-
bles are very rare) are rhythmically interstratified with planar
beds of parallel laminated pebbly sandstone. This rhythmic
stacking of relatively coarse and fine beds is a most charac-
teristic feature of facies A. The thickness of each couplet
ranges between 8 cm and 30 cm.
Both conglomerate and sandstone beds are poorly sorted.
The conglomerates play a relatively more important role in
the couplets. They are clast-supported or show open-work
fabric. Pebbles and small cobbles are mainly subrounded to
rounded, although angular clasts have also been noted.
Quartz pebbles dominate, chert pebbles occur rarely. The
maximum length (A-axis) of clasts is 12 cm, but it averages
3—4 cm. Crude, preferred orientation of elongated pebbles,
dominantly perpendicular to, but also parallel to the sup-
posed transport direction can be traced. Vertically aligned
clasts were observed close to the base of a bed. Sandstones
are medium to very coarse grained, and contain scattered
pebbles up to 3 cm in size. Locally crude planar bedding with
aligned coarser elongated clasts can be found.
The bedding planes are mainly sharp, flat or erosive. Low-
relief scouring was observed on the base of beds. The beds are
laterally persistent on the scale of outcrop. In places they dis-
play broad convex-down shape (very broad and flat channels?).
These beds have almost continuous sheet-like geometry.
DEPOSITIONAL ENVIRONMENT OF THE “OLD RED” SEDIMENTS, BOHEMIAN MASSIF 197
Facies B
Laterally limited wedges of gravely sandstone with cross
or planar stratification belong to this facies (Fig. 6). The
sandstone is medium to coarse-grained and micaceous. Scat-
tered pebbles and angular clasts up to 0.7 cm in diameter are
more abundant towards the top of the beds. Cross-bedding is
slightly sigmoidal. Facies B is interfingering and interstrati-
fied with facies A. Beds of facies B are laterally discontinu-
ous and erosively cut by overlaying facies A. Facies B repre-
sents only 3.8 % of the logged profile and occurs only in the
upper part of the studied profile.
The orientation of the cross-beds is oblique to dip of bed-
ding planes and for that reason upfan-dipping (backsets) can
be supposed. The angle of cross bedding reaches 20°. Bed
thickness ranges from 10 to 30 cm, and cross-bedding is best
developed in the thickest beds.
Facies C
Facies C consists of beds of clast-supported conglomer-
ates, occasionally clast- to matrix-supported, ungraded, mas-
sive to crudely parallel bedded. Vertically aligned clasts are
present. Bed thickness ranges from 20 to 40 cm. The largest
clasts are 6 cm in diameter, dominantly about 3 cm. Facies C
occurs only interstratified with facies A and represents 3.4 %
of the studied profile.
Facies D
This facies is formed by medium to coarse-grained, granu-
lar or pebbly sandstone with coarser clasts concentrated near
the base of the bed (gravel lag?) and parallel bedding with
scattered coarser grains in the upper part (Fig. 7). Normal
grading can be observed due to fining upwards of sandstone
Fig. 3. Geological development of Moravia during the Lower Paleozoic.
grains and lower presence of pebbles towards the top. The
conglomerates are poorly sorted, with the maximum grain-
size about 1 cm, occasionally up to 3 cm. Both angular and
subrounded clasts have been observed. The content of angu-
lar, coarser clasts seems to be higher than in facies A. Bed
thickness ranges from 8 cm to 30 cm. Facies D represents
7.1 % of the studied profile and has been documented main-
ly near the base of the studied profile.
Erosive soles with broad convex-down shapes are typical.
The repeated occurrence of low-relief scours (up to 10 cm
depth and max. 50 cm width) has been observed along the
base of some coarser beds. Pebble preferred orientation is
rare. The beds of facies D cut each other erosively and are fi-
nally erosively cut by conglomerates of facies A.
Facies E
Facies E is formed by red mudstone or very fine sand-
stone, massive or parallel laminated. Sandstone is mica-
ceous. Facies E is extremely rare (0.5 % of the studied pro-
file) and occurs as interbeds within facies D. The beds are
only 2 to 7 cm thick. They occur either as small erosional
relics or as thin layer traceable for the distance of only 3 m.
Both lower and upper bedding planes are irregular. Tops are
erosive, locally with broad scourings. Small loading struc-
tures are rarely observed (Fig. 7).
Depositional processes and sedimentary
environment
The interfingering of facies A and B points to their common
origin. They are the products of sediment-charged, upper-
flow-regime sheetfloods of high capacity and competence that
expanded across the almost flat surface of a fan or its active
198 NEHYBA, LEICHMANN and KALVODA
lobes. Hence, depositional environment is interpreted as an al-
luvial fan mostly formed by catastrophic sheetfloods typified
by supercritical condition. Sheetfloods are instigated by the
rapid drainage of high volumes of water from the catchment
after heavy rainfall, rapid snowmelt or released stored water
(Blair 1999). Facies A and B are interpreted as having originat-
ed as upper-flow-regime antidune bedforms deposited on the
fan surface beneath evolving standing wave trains of high-dis-
charge sheetfloods (cf. Blair 1999; Blair & McPherson 1994).
Waves are autocyclically developed and destroyed many times
during a single flood and numerous sheetflood couplets may
have been deposited during one flash-flood event.
Facies B is typical for sedimentation during the growth
phase of a standing wave cycle, whereas facies A is the prod-
uct of a violent style of standing wave destruction. Details
about the origin of upper-flow-regime sheetfloods facies and
standing waves are described by Blair (1999). A sharp, rather
than gradational contact between conglomerate and sandstone
implies that coarse member deposition occurs in a rapid pulse,
followed by a more sustained phase of finer-grained fall-out of
the intermittent suspended load. The alternation of coarser and
finer material is caused by changing hydraulic conditions re-
lated to flow expansion and decreasing slope, as well as to in-
trinsic variations in depth and velocity typical of supercritical
flow.
The strong predominance of facies A over the facies B in the
studied fan indicates that the standing waves most commonly
underwent destruction by violent breakage and washout. The
Fig. 4. Lithological log through “Devonian Basal Clastics” on the Červený kopec Hill and facies distribution.
DEPOSITIONAL ENVIRONMENT OF THE “OLD RED” SEDIMENTS, BOHEMIAN MASSIF 199
relatively low preservation of facies B and the thickness of
single beds also reflect relatively shallow flows. Preservation
of cross-bedded antidune sets is most likely in the proximal
fan, where flow depth is greatest. The spatial distribution of
facies B supports the idea of a mainly distal part of the fan (or
its lobe) and its prograding.
The interpretation of facies C is difficult, because of uncer-
tainty regarding the shape of beds and their orientation on the
fan (ribs, clusters?). A close relationship to the facies A re-
flects a secondary reworking of the host sheetflood deposits.
The surface of the fan was reworked and partly eroded away
during subsequent non-catastrophic overland flows. These
flows are usually not strong enough to remove coarser gravel,
and tend to produce coarse clast lags by winnowing fine-
grained material. The very minor role of these deposits within
the studied profile suggests that such secondary processes only
slightly remoulded the shape of the fan. This is consistent with
rapid deposition on the fan and sufficient accommodation
space (tectonic subsidence?).
The deposits of facies D are interpreted as the products of
waning traction currents initially with high competence (Ne-
mec & Steel 1984). This suggests deposition within “distal
parts” of alluvial fan (or its temporarily inactive lobe). Facies
D has been produced either by overland flows (secondary pro-
cesses), or more probably by stream currents originated from
waning catastrophic flows (primary processes). The erosional
cuts of facies D beds itself and erosional contact with overlay-
ing facies A can represent important “bounding surface” re-
flecting progradation of the fan (tectonic or climatic cycles?).
This interpretation can be supported by the close relationship
of facies D and E (see Fig. 4).
Facies E represents suspended load deposition in quiet con-
ditions. It forms only erosional relics. Their presence provides
evidence of probably shallow and small depressions on the fan
surface. These depressions occurred in the more distal part of
the fan (or its inactive lobes) and were filled mainly during
overland flows (secondary processes). The minimal role of
these deposits in the studied section supports the opinion about
mud deficiency in the depositional system, which is primarily
connected with processes in the source area. It also supports
the minor role of secondary processes and relatively rapid dep-
osition (aggradation of the fan).
The sandstones (facies B) were studied in detail to add some
information about the source rocks. Quartz, plagioclase, K-
feldspar, biotite, muscovite, and pebbles of ryolites, pegma-
tites, slates and clasts of sandstones and siltstones formed the
main components. The cathodoluminescence (CL) study of
selected polished thin-section have provided some additional
information important for interpretation. Quartz and plagio-
clase as the dominant minerals were subjected to the CL
study (Fig. 8).
Six types of quartz were distinguished in the samples (Fig.
8). The first type exhibits bright red luminescence with clear
zoning. This feature is typical for high-temperature quartz
Fig. 5A, B. Rhythmic conglomerate and sandstone couplets.
Fig. 7. Erosional relic of red mudstone (facies E) within the medi-
um to coarse-grained granular to pebbly sandstone (facies D).
Fig. 6. Gravelly sandstone with well developed cross stratifica-
tion.
200 NEHYBA, LEICHMANN and KALVODA
derived from volcanic rocks, such as rhyolites. Some grains
exhibit bright blue luminiscence with indistinct zoning. This
population was probably derived from acid plutonic rocks
such as granites. The majority of quartz displays dark blue
luminescence. These grains were probably derived either
from granites or high-grade gneisses. The quartz grains with-
out CL or with dull purple-brown CL point to low-tempera-
ture source rocks, for example, older sediments or low-grade
metasediments. Quartz grains with medium blue rims formed
the 6-th type of quartz. Because the rims are developed over
all previously mentioned quartz types, they must be of diage-
netic origin.
Several types of plagioclase grains were also identified in
the rock (Fig. 8). The most common type exhibits bright blue
or yellow-blue CL. Some grains are normally zoned with the
yellow CL in the centre and blue CL at the rim. Other grains
with purple-magenta CL are strongly altered in the core. Both
types were probably derived from plutonic rocks. Some grains
exhibit only dull purple-blue CL, or are without CL due to al-
teration.
Discussion
Alluvial fans constructed principally by water flows have
been documented in both arid and humid weather conditions
(Nemec & Postma 1993; Blair & McPherson 1994), although
fans dominated by water-laid deposits are sometimes interpret-
ed as originating in humid conditions and fans dominated by
debris-flow deposits as originating in arid conditions. Numer-
ous factors can potentially affect fan sedimentation including
climate, tectonic conditions, catchment area and relief, vegeta-
tion type and density, fan area, density of fans in their catch-
ment, relief and drainage density, bedrock types in the catch-
ment area (Blair 1999).
The slope materials are transported to the fan as fluid gravi-
ty flows (i.e. water flows), in which sediment is moved by the
force of water. In the studied case, the primary fan processes
were represented by fluid gravity flows generated by destabili-
zation of colluvial slopes in the drainage basin (sheetfloods
and incised-channel floods). Fluid gravity flows result from
flashy concentration of runoff from snowmelt or rainfall over
colluvial slopes in drainage-basins, leading to sediment-laden
and catastrophic discharge downslope. Debris flows fail to be
generated in this situation, because of the low concentration of
clay in colluvium, insufficient sediment concentration, or a
slow rate of sediment entrainment by the flow. Colluvium can
be transported within these flows as bed load, or suspended
load, and the sediment content may range from low to hyper-
concentrated (Blair & McPherson 1994).
A casual relationship exists between the primary sedimenta-
ry processes active on alluvial fans and in drainage basins
(Blair & McPherson 1994; Nemec & Postma 1993). In the
studied case, a relatively mature stage of the evolution of the
alluvial fan and the drainage basin can be presumed. The
abundant presence of subrounded and rounded quartz pebbles
reflects multiple redeposition within the drainage basin before
the final deposition on the alluvial fan depositional lobe. The
absolute dominance of sheetflood deposits can be connected to
a relatively low fan slope angle. The relative absence of boul-
ders and predominance of pebbles, together with abundance of
coarse sand, can be explained by relative scarcity of coarse
gravel in the source area. The absence of incised channel fa-
cies can be explained by the distal position of the studied de-
posits with respect to the fan apex.
Though both debris-flow and sheetflood deposits can be
present on the same fan, most modern alluvial fans are domi-
nated by one of these. This is because lithological and weath-
ering conditions in the drainage basin usually promote one of
these processes to the near exclusion of the other (Blair &
McPherson 1994). The domination of sheetfloods over debris-
flows occurs on fans where: (1) the drainage-basin bedrock
weathers to produce clay-deficient sediment, or (2) the size,
storage capacity, and roughness of the catchment of the feeder
channel and channel gradient commonly incite deposition of
debris flows before they reach the fan site. The very low pres-
ence of mud material in the studied section is remarkable. It
can be explained by the deficiency of clay material within the
weathered source rock and by the further transport of such ma-
terial on the fan slopes (climatic control?). Clay-deficient col-
luvial sediments are commonly generated in drainage basins
underlain either by quartzose deposits or acid crystalline bed-
rock under arid conditions of weathering. The petrological
study indicates that the source area of the BPC was heteroge-
neous. Granites and possibly gneisses were the dominant
sources. Other components were derived from rhyolites, older
siliciclastic sediments and low-grade metamorphic rocks.
Only granites and small rhyolite bodies are exposed in the
broader vicinity of the studied section in the present-day ero-
sion level. However, muscovite is not a typical mineral for the
granites in the basement nearby. Some clasts, at least, must
therefore be interpreted as exotic with respect to the recently
known geological situation.
An important role can also be played by rapid uplift and ero-
sion under minimal chemical, but intense mechanical weather-
ing. In the studied case, the occurrence of such conditions is
supported by the presence of rounded quartz pebbles together
with angular clasts, mostly from granitic source rocks, rela-
tively fresh feldspars without traces of kaolinite weathering
features, fresh biotite, etc.
Fig. 8. Thin-section photomicrographs of BPC on Červený kopec
Hill. A – Fresh and non-zoned plagioclase with bright blue lumi-
nescence. LP (length of the photograph) is 1.2 mm, B – Plagio-
clase grain with magenta CL and altered core without CL. The
bright orange grains in the altered zone are carbonates. LP is 1.2
mm, C – Zoned plagioclase with very bright core (originally yel-
low CL), bright blue rim and a zone with dull blue CL in-between.
Plagioclase without CL could be found on the left side of the pho-
tograph. LP is 1.2 mm, D – The same area as in C, but with
crossed polars, E – The three main quartz types in CL image. The
most common grains exhibit dull blue luminiscence. Grains with
bright blue or bright red CL are not so abundant. Note that some
grains are rimmed by authigenic quartz with medium blue CL. LP
is 3.2 mm, F – The same area as in E, but with crossed polars, G
– Plagioclase with dull purple CL as a consequence of alteration
(left-right corner) and common plagioclase fragment with bright
blue luminescence (right down). LP is 1.2 mm.
▲
DEPOSITIONAL ENVIRONMENT OF THE “OLD RED” SEDIMENTS, BOHEMIAN MASSIF 201
202 NEHYBA, LEICHMANN and KALVODA
A down-fan change from debris flows to fluid flows is sup-
posed in some large fans (Ammorosi 1996; Leeder 1999;
Wells & Harvey 1987; Yoshida 1994). Facies sequences are in
that case dominated by stream channels deposits on various
scales. Such channels are probably absent in the studied case.
The depositional settings of the studied deposits can most
probably be associated with high-angle normal or strike-slip
faults within a continental extensional basin (cf. Busby & In-
gersoll 1995). The question of drainage catchment area, fan
slope and area is difficult to discuss because of insufficient
data.
Previous discussion is based mainly on comparison with
modern or Pleistocene fans. Some differences in sedimentary
processes and environments may be expected between modern
alluvial fans and the studied Lower Paleozoic ones, formed
before the appearance of abundant metazoans and land plants
(MacNaughton et al. 1997). Similar sedimentary structures
and facies associations have been observed in conglomerates
of Middle Devonian Pointagare Group (Old Red Sandstone se-
quences of Western Ireland) which are interpreted as alluvial
fan deposits (Richmond 1998).
Conclusions
Lower Devonian monomict-quartzose coarse-grained clas-
tics from Červený Kopec Hill near Brno are interpreted as the
deposits of an alluvial fan mainly formed by catastrophic
sheetfloods.
The mode of transport of the material was controlled both
by the source area (chemistry of source rocks, weathering con-
dition, extent of the drainage basin) and the alluvial fan itself
(shape, angle of the slope, rapid deposition and formation of
accommodation space, etc.).
The provenance of the deposits was heterogeneous and geo-
logically varied. The main source was probably granites and
gneisses, other components were derived from rhyolites, older
siliciclastic sediments and low-grade metamorphic rocks. The
important presence of muscovite reflects some role of an exot-
ic source area with respect to the recently known geological
situation. The abundant presence of subrounded and rounded
quartz pebbles reflects multiple redeposition within the drain-
age basin before the final deposition in the alluvial fan deposi-
tional lobe. The deficiency of clay material within the weath-
ered source rock, rapid uplift and erosion under intense
mechanical weathering together with the relatively low fan
slope angle were the most important factors for absolute domi-
nance of sediment transport by fluid gravity flows (sheet-
floods). These flows were relatively shallow.
Mainly the distal part of the fan (or its lobe) can be observed
in the studied profile. Five different lithofacies have been rec-
ognized in the logged profile on the basis of different grain-
size, sedimentary structures and shape of bedding-plains. The
absolutely dominant facies was formed by almost planar beds
of pebbly conglomerate rhythmically interstratified with pla-
nar beds of parallel laminated pebbly granular sandstone.
These couplets formed more than 80 % of the profile.
The surface of the fan was reworked and partly eroded dur-
ing subsequent non-catastrophic overland flows. These sec-
ondary processes played a minor role and slightly remoulded
the surface of the fan. A relatively complicated stage of the
evolution of the alluvial fan and drainage basin can be accept-
ed. The limited length and width of the profile and post-depo-
sitional tectonic did not allow us to reconstruct the shape and
orientation of the whole alluvial fan. Continental extensional
basin stage represents the most probably depositional settings
for the studied deposits which is in accord with the interpreta-
tion of the Devonian basal clastics as a record of the initial rift-
ing phase of the Brunovistulian foreland (Kalvoda 1995).
Acknowledgment: The study was supported by the Research
Project CEZ J07/98-1431000004.
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