GEOLOGIJA 30, 123-148 (1987), Ljubljana
UDK 551.763.781.8:552.52(450.36,497.12) = 20
Flyschoid deposits of Goriška Brda (Collio)
between Soča (Isonzo) River and Idrija (ludrio)
River - facies and paleoenvironments
I depositi flyschoidi dei Colli Goriziani (Goriška Brda) tra il fiume Isonzo
(Soča) e fiume ludrio (Idrija) - facies e condizioni paleoecologiche
Flišoidni sedimenti iz Goriških Brd med Sočo in Idrijo - faciesi in
paleoekoloske razmere
Giorgio Tunis
Istituto di Geologia e Paleontologia dell'Università degli studi
Piazzale Europa 1, 34127 Trieste, (Italia)
Camilla Pirini Radrizzani
Istituto di Geologia dell'Università di Genova
Corso Europa 30, 16132 Genova, (Italia)
Abstract
Presented is the interpretation of environments of main facies associations
types in Goriška Brda. The high diversity of studied depositional facies bears
evidence of profound differences of environments during deposition of flyschoid
beds. Environments from relatively deep sea to those of the external margin of the
platform, and those of delta (delta front and delta plain) can be established.
Riassunto
Viene qui fornita l'interpretazione ambientale delle principali associazioni di
facies riconosciute nel Collio. La grande varietà delle facies sedimentarie esami-
nate testimonia una altrettanto varia diversificazione ambientale dei depositi
flyschoidi del Collio. Si è riscontrata un'evoluzione da condizioni di ambiente
marino relativamente profondo, ad ambiente di piattaforma esterna ed intema, ad
ambiente di delta (fronte deltizio e piana deltizia).
Kratka vsebina
Podana je razlaga okolja ob nastajanju osnovnih tipov faciesov v Goriških
Brdih. Velika raznolikost preučevanih sedimentacijskih faciesov kaže na velike
razlike v okolju med nastajanjem flišoidnih kamnin. Opazujemo razvoje od rela-
tivno globokega morja do zunanjega roba platforme in do delte (čelo delte in
prodelta).
124	Giorgio Tunis & Camilla Pirini Radrizzani
Introduction
The area under examination is situated between the Soča (Isonzo) River and the
Idrija (ludrio) River and straddles the Italian - Yugoslav border; specifically it lies
between Korada (Corada), Medeja (Mt. Medea) and Sabotin (Mt. Sabotino). The
outcrops of this area are mainly represented by Tertiary clastic sediments ranging in
age from Early Ilerdian (Cimerman et al., 1974) to Early Lutetian.
Older deposits obviously outcrop here. An example are the Podsabotin beds
(Campanian-Maastrichtian - Early Eocene)^ situated in the south-eastern sector near
Sabotin (see Šribar, 1966; Pavšič, 1977 and 1979). Near Kožbana, both on the
southwestern side of the Cretaceous anticline (Cousin, 1981) and on the
northeastern flank (Cimerman et al., 1974) there is a flysch rich in conglomerates
dating back to the Late Thanetian. As far as younger beds are concerned. Cousin
(1981) also reports the presence of Biarritzian in two outcrops, one near Subida
(Cormons) and the other near Ponte del Torrione (Gorizia).
This paper will deal mostly with the flyschoid sediments lying above the olisto-
strome of Plave which could correspond chronologically to the "Megastrato di M.
loanaz", as we have defined it in the subdivision of flyschoid units in eastern Friuli
(Pirini et al., 1986).
In the history of the sedimentary evolution of the Slovenian (or Friulan) basin, the
sedimentation was influenced, during the Middle - Late Paleocene and Early Eocene
by a particularly active syndepositional tectonism caused by orogenesis involving the
innermost zones, in conjunction with an abrupt subsidence and with the collapse and
break-up of a wide sector of the Friulan-Karstic platform. The beginning of the
flyschoid sedimentation in the area in question is ascribed to this phase, at first with
prevailing chaotic facies, megabeds, paraconglomerates and so on, then with predo-
minant siliciclastic turbidites. Outside the area examined, these facies are well
exposed, particularly in the Natisone valley ("Flysch di Canebola", Pirini et al., in
press) and in the Idrija (ludrio) valley ("turbidites and associated coarse facies",
Tunis & Venturini, 1984). Near Anhovo (Kuščer et al., 1976; Buser & Pav-
šič, 1978; Skaberne, 1987) they are represented by a cyclic sequence containing
megabeds and siliciclastic distal turbidites interbedded with calcareous proximal
turbidites.
This was followed in the examined area in the Middle-Upper Cuisian by a phase
of less intense orogenetic activity up to the Late Cuisian-Early Lutetian. According
to the world-wide global eustatic model (Vail et al., 1977) during the Lutetian
a transgressive phase began, but in the zone we have not clear elements of this event.
We should like to stress that, in the area examined, from north to south the
outcrops progressively show a pronounced facies association change (a lateral facies
variation is also evident inside the lower calcareous-marly-arenaceous facies) indica-
tive of a wide variety of sedimentary environments. These range from relatively deep
sea environments in the northern zone, where the oldest turbiditic sediments and the
mainly coarse associated lithofacies were deposited, to transitional up to shallow
water environments in the southern zone where the youngest sediments are clearly
related to a fluvio-deltaic complex.
This area has been studied by several authors, mainly from the paleontological
and pedological point of view (see Martinis, 1962, for the bibliography). Recent
studies deal mainly with micropaleontology and biostratigraphy (Piccoli
Flyschoid deposits of Goriška Brda (Collio)	125
& Proto Decima, 1969; Cimerman et al., 1974; Pavšič, 1977 and 1979;
Cousin, 1981).
With regard to the exact chronological attribution of the Tertiary detrital forma-
tions of eastern Friuli and western Slovenia there is no complete agreement among
the various authors (see, for example. Tab. XIII, p. 286, Cousin, 1981). It must
therefore be presumed that the large number of depositional environments makes
very difficult to define the exact biostratigraphic correlations on a regional scale.
Tab. 1 shows a comparison^ of the various Paleogene detrital (and carbonatic)
formations and units in eastern Friuli and western Slovenia.
Tunis and Venturini (1984) have studied the sedimentological characteristics
of the thick flyschoid (and preflyschoid) Maastrichtian-Early Paleocene sequence in
the upper ludrio (Idrija) valley. The terrains of this valley above the "Flysch di Calla"
(Early Paleocene) and especially those bounded by the "Megastrato di Mt. loanaz"
(Early Ilerdian) and the "Megastrato di Vernasso" (Early Cuisian) are being studied
at the time of writing, as are the younger Cuisian sediments which are also turbiditic.
The characteristic sequence of turbidites and megabeds in the Natisone valleys is
also under study. This is being carried out in the Faedis-Attimis area, where the best
outcrops are to be found.
In Cousin's subdivision (1981) the reason for his positioning of the base of the
Medana beds is not clear. The author himself states: "la limite entre ces deux
formations (Kožbana beds and Medana beds) est un peu arbitraire" (p. 277). The
criteria by which he distinguishes the lower from the upper Medana beds are equally
unclear. The reasons for his stratigraphie and chronological attribution of the
younger deposits in the eastern Friuli hills are, in our view, even more tenuous. In the
highest beds of the stratigraphie sequence of the Flysch di Cormons^ we have never
found any faunal associations more recent than Early Lutetian.
We gather from Pavšič (1979) that red marls with sandstone interbeds (Late
Maastrichtian - Danian-Montian) are present in the vicinity of Lig, Colnica and
Kanalski vrh. These beds are entirely similar to the coeval beds of the "Flysch di
Calla", an important marker which may be followed from Breginj (Pavšič, 1985)
along all the Natisone valleys as far as the Isonzo (Soča) river. P a v š i č ' s account
(profile Lig-Vrhovlje), however, does not make it clear where the Kožbana beds begin
and what their relationship is to the underlying flysch.
The biostratigraphic study of these terrains is undoubtedly difficult, but the
environments in sedimentary rocks can be defined not only by their faunal content,
but also by their sedimentary structures, the geometry of their deposits and regional
changes of thickness and facies.
A working team recently set up by researchers at the Ljubljana and Trieste
Universities, with the aim of studying the flysch of the Goriška Brda and Vipava
valley, indicated the following objectives as the most important ones: 1 - to give
a more detailed description and more definite environmental interpretation of these
beds; 2 - to provide a stratigraphy based on the correlation of the facies sequences
within the depositional cycles, after a revision and a synthesis of the stages and
members proposed by previous authors; 3 - to recognize the distribution of the
sedimentary facies and to carry out paleogeographic reconstructions. Work on
' Our comparison takes account only of the most recent studies.
2 The flysch di Cormons, which lies in the hilly area between Brazzano and Gorizia, was
named by Martinis (1962), who distinguished the following facies in it: marly facies, marly-
sandy facies, sandy facies and conglomeratic facies.
126	Giorgio Tunis & Camilla Pirini Radrizzani
Flyschoid deposits of Goriška Brda (Collio)	127
objective^ has begun on the Italian side of the border and a well-defined depositional
suite has been recognized in the upper strata of the Flysch di Cormons (Late Cuisian
- Early Lutetian).
The aim of this study is therefore sedimentological. It is one of the first attempts
at a paleoenvironmental reconstruction of the area, essentially by means of the
recognition and investigation of the sedimentary facies. We should state at the outset
that we do not have a deep knowledge of the Kožbana beds and mostly of the Medana
beds which mainly outcrop on Yugoslav territory, especially compared to the know-
Fig. 1. Distribution map of the main facies associations
1. Podsabotin beds, 2. Megabed of Plave, 3. Megabeds and lower calcareous-marly-sandy facies,
4. Upper calcareous-marly-sandy facies, 5. Marly facies, 6. Marls with sandstone interbeds and
sandstones with marl interbeds facies, 7. Sandstones, conglomeratic sandstones and sandstones
with gravel facies. The arrows 8. show directions of currents during the turbiditic sedimenta-
tion in the Kožbana zone
128	Giorgio Tunis & Camilla Pirini Radrizzani
ledge we have acquired about the Flysch di Cormons, where a bed by bed study of 400
small outcrops was carried out (Nardon, 1982).
From base to top of the stratigraphie sequence five facies associations were
identified (Fig. 1), some of which include further subfacies: megabeds and lower
calcareous-marly-arenaceous facies; upper calcareous-marly-arenaceous facies;
marly facies; marls with sandstone interbed and sandstones with marl interbed
facies; sandstones; conglomeratic sandstones and sandstones with gravel facies. The
text contains comparisons between these associations of facies and the formations,
facies, subdivisions and "zones" proposed by ComeP (1927), Martinis (1962),
Cimerman et al. (1974) and Cousin (1981). To simplify the chronological interpre-
tation and stratigraphie attribution of the facies associations, the most significant
correlations may now be roughly summarized.
The Kožbana beds (Thanetian-Ilerdian) comprise megabeds and lower calcare-
ous-marly-arenaceous facies; the lower Medana beds (Early Cuisian) correspond, in
our view, to the upper calcareous-marly-arenaceous facies; the upper Medana beds
(Late Cuisian) comprise the marly facies and, partially, the marls with sandstone
interbeds''. The marls with sandstone interbed and sandstones with marl interbed
facies (Flysch di Cormons) represent the passage from Cuisian to Lutetian, while
sandstones, conglomeratic sandstones and sandstones with gravel facies (Flysch di
Cormons) are probably of Early Lutetian.
The Main Facies Associations: Description and Interpretation
Megabeds and lower calcareous-marly-arenaceous facies
These facies correspond to marly conglomeratic formation (Cousin, 1981) and
pelitic-sandy-conglomeratic flysch (Cousin, 1981), to the lower and upper part of
the Kožbana flysch of Cimerman et al. (1974) and to the "transitional zone" of
Comel (1927).
Near Plave (along the Plave-Šmartno road) there is a well exposed outcrop of
megabreccia, characterized by undefined stratification and by marly matrix, which
contains coarse to very coarse clasts of rudist limestone (hence the name of "conglo-
merato pseudocretaceo" given by Taramelli, 1870), pebbles of chert, outsize rip-
up mudstone clasts (red and gray marls) and blocks of plastic formations i. e.
turbidites up to 5 m in diameter. The fabrics of these sediments prove that they have
been instantaneously remobilized from their original position. The thickest portion of
this outcrop is given by thick bedded calcarenite, calcilutite and marl which directly
overlie the breccia and represent the grading upwards. The megabed of Plave could
correspond to the "Mt. loanaz Megabed" (Pirini et al., 1986). Above it, massive
calciruditic-calcarenitic big beds are widespread, particularly on the southern flanks
of the Mt. Korada (along the cartway Senik-Mt. Planina); they are characterized by
the rareness of internal structures and slow grading upwards. In this part of the
stratigraphie sequence sandstones with marl interbeds of turbiditic origin are fairly
3 In his pioneer study Comel (1927) proposed the first division of the Goriška Brda into
"zones". This study is entirely devoid of chronological attributions, but its lithological descrip-
tions and pedological informations proved to be extremely useful, particularly in the study of
the oldest terrains.
* We thus assume that the upper Medana beds correspond to the lower-middle part of the
Flysch di Cormons.
Flyschoid deposits of Goriška Brda (Collio)	129
common; they are represented by thin-medium layers. The complete T a-e Bouma
sequence very rarely may be found.
Then, from west to east between Bucovizza, Mt. Brischis, Cladrecis, Stregna di
Prepotto, Fragielis Mernicco, Restocina, Serió (Italy), Vrhovlje pri Kožbani, Kož-
bana, Brdice, Brezovk^ Slapnik, Nožno, Belo, Breg, Krasno, Vrhovlje pri Kojskem,
Brestje, Vamorje (Yugoslavia) and probably S. Mauro and the upper Piumizza valley
(Italy), several facies are present with rapid variations: megabeds, calcarenites,
siliciclastic turbidites, sandy calcarenites, marls and marly limestones, paraconglo-
merates, fine breccias consisting of subangular calcareous and cherty clasts, rare
microbreccias rich in nummulites, etc.
A characteristic of the above mentioned zone is the concurrence and local
interfingering of several lithofacies, none of which clearly predominates over the
others.
This peculiarity is more evident because nearby there are areas in which just one
or two lithofacies predominate (the southern flanks of Mt. Korada, for example).
In Fig. 2 two sections of the Flysch of Kožbana are sketchily illustrated: Hlevnik-
Mt. Korada (on the left) and cross road for Kožbana-Brdice (on the right). As far as
the megabeds are concerned, the underlined letters make reference to internal organi-
zation of a megabed proposed by Segur e t et al. (1984): Dl = poorly sorted carbonate
megabreccia (or olistostrome); D2 = carbonate breccia; D3, D4, D5, = thick sequence,
grading from calcirudite (D3) to graded calcarenite (D4), to calcareous mudstone (D5).
The letters c and d refer to classification of turbidites (both siliciclastic and carbo-
nate) given by Mutti and Ricci Lucchi (1972). Dr. S. Buser kindly furnished
the fundamental biostratigraphic informations for these sections.
Four megabeds are visible along Hlevnik-Mt. Korada section. The most spectacu-
lar megabed outcrops near to Brdice. This megabed, with a thickness of up to
50-60 m, has a sheet-like geometry and consists of a very thick basal division which
contains very large slabs of ripped up turbidites (Fig. 3) and paraconglomerates
(Fig. 4). The other big beds are mainly carbonate and of smaller dimension.
Among the siliciclastic turbiditic layers, in terms of the Bouma sequence, the
graded coarse intervals are poorly represented (Belo, Nozno, to the north of Hlevnik,
along the cartway Brdice-Kožbanjšček R.), while the Bouma base-missing sequences
bee and cde are very frequent. The thickness of the sandy beds varies normally
between 5, 10 to 20cm; the sand/marl ratio is approximatively equal to 1 or lower.
Sometimes, small marly clasts concentrated in distinct lenses are found in the
sandstones (Vrhovlje pri Kojskem). Several paleocurrent directions measured in the
sandstone beds (north of Hlevnik, Kožbana, Brdice, Slapnik, Nozno, Belo, Krasno,
Vrhovlje pri Kojskem) reveal a southeastward direction of the turbidites. This trend
coincides roughly with the longitudinal axis of the basin of the Flysch of Friuli.
Broad, low relief channels are occasionally seen (north of Belo, Kožbana, Kožbanjš-
ček R. and G. Brezovk); channel (Fig. 5) and interchannel facies are well exposed near
Brdice and Kožbana.
Thick beds of calcarenites are observed to be either interbedded to sandstones and
marls or developed in thick to massive individual beds (big beds). The former are
calciturbidites, mainly with the complete Bouma sequence. In the second case the
internal structures are quite scarce.
Sandy calcarenites of turbiditic origin are common. Some types of calcarenite-
sandstone couplets are observed along the Slapnik-Nozno-Belo loose surface road.
The lower member of most couplets is composed of carbonate (graded calcarenite or
9 - Geologija 30
130	Giorgio Tunis & Camilla Pirini Radrizzani
Flyschoid deposits of Goriška Brda (Collio)	131
coarse calcarenite), while the capping member consists of quartzose or lithic material.
The relative thickness of carbonate and terrigenous members of such couplets is
variable, but the sandstones invariably have a smaller thickness. There is often an
abrupt junction between the two lithologies (Fig. 6).
The paraconglomerates consisting of subrounded clasts of limestone and sand-
stone up to 35 cm in diameter and smaller, well rounded chert pebbles are quite
common. The fine nummulitic breccias (Belo) also contain limestone pebbles ranging
from a few mm to 1-2 cm; these levels are highly cemented by calcareous cement
unlike the nummulitic microbreccias interbedded in the marly facies (Vipolže and
Russiz).
Discussion and interpretation
From the observed coarsest facies the depositional mechanism of these seems to
have been caused by very rapid processes of resedimentation that occurred in a deep
marine environment, but relatively close to the carbonate platform. At present it is
rather difficult to define exactly the depositional environment (slope and/or basin's
border) due to the lack of a detailed analysis and mapping of the different facies. We
think, however, that the interpretation given by Pavlovec (1969) for the central
Istria deposits could be acceptable also for most of these deposits. This author, on the
basis of several paleoecological indicators and of the mixing of faunas of different
ages and environments, hypothesized a relatively narrow and deep basin. One of the
edges of the basin was an active slope connected to a carbonate platform; the slope
was capable, because of the tectonics, of discharging huge masses of sediments. The
slope on the other edge was either more gentle, or less tectonically active. We suppose
that the more active side was situated near Banjšice (see also Cousin, 1981 and
Skaberne, 1987).
Explanation as to the genesis of the megabeds is sought in the notable paleosei-
smicity of the area and in the high mobility of the basin. The outcrops of the Kožbana
- Korada area are comparable in their affinities of characteristics to the Stregna
Flysch Venzo & Brambati, 1969).^ However, these outcrops of chaotic facies are
generally less wide, less thick and less frequent compared to the coeval ones in the
area situated near Stregna, Canalutto, Clap or Canebola.
A last problem rises from the examination of the Paleocene facies outcropping
near Mt. Sabotin, between Podsenica and Podsabotin, and in Piumizza valley where
marly calcareous lithotypes predominate and near Groppai and S. Mauro where thin
sandstones with marly interbeds (turbidites?) prevail. This is interpreted as lateral
facies change. The relationship between the turbiditic facies and big beds to the west
and these last facies, which may be observed in the easternmost area, is not clear.
5 We would like to point out that the term "Flysch di Stregna", whose biostratigraphic
description was unsatisfactory, is currently being abandoned.
Fig. 2. Columnar section of the sequence with turbidites and megabeds outcropping
along Hlevnik-Mt. Korada road and cross road for Kožbana-Brdice
1. Marls and marly limestones, 2. Calcisiltites, 3. Sandy calcarenites (turbidites), 4. Siliciclastic
turbidites (classification according to Mutti & Ricci Lucchi, 1972), 5. Calciturbidites, 6. Fine
breccias consisting of calcareous and cherty clasts, 7. Paraconglomerates, 8. Megabeds (internal
organization according to Seguret et. al., 1984), 9. Carbonate big beds, 10. Faults
132
Giorgio Tunis & Camilla Pirini Radrizzani
Fig. 3. Well exposed basal unit of Brdice megabed (Flysch of Kožbana)
mainly consisting of large deformed rip up layers of turbidites
Fig. 4. Channel-like body composed of matrix supported conglomerate
within the basal unit of the Brdice Megabed (Flysch of Kožbana). The light
colored limestone blocks and cobbles are predominantly platform limesto-
Flyschoid deposits of Goriška Brda (Collio)
133
Fig. 5. Channelized sandy body in the Flysch of Kožbana (Kožbana village)
Fig. 6. Photograph of a limestone - lithic sandstone couplet from Kožbanjš-
ček-Brdice cartway (Flysch of Kožbana). The limestone rests on an eroded
surface of marl. Note irregular base and poor grading of the sandstone unit
134	Giorgio Tunis & Camilla Pirini Radrizzani
The development and distribution of the eastern facies have probably been
conditioned by paleomorphology and by syndepositional and postdepositional tecto-
nics.
Upper calcareous-marly-arenaceous facies
These facies, described by Tunis (1976), could correspond to the lower marly-
arenaceous facies and the middle marly-arenaceous facies p. p. of Comel (1927), and
to the lower and middle parts of the Medana Flysch of Cimerman et al. (1974).
Calcarenites, calcilutites, sandstones with marl interbeds and marls outcrop
along a belt extending from Pojanis, south of Serió, Dolegna, Lonzano (Italy) up to
Kojsko and the S. Floriano area through Hlevnik, Hruševlje, Pristava, Slavce,
Višnjevik, Vedrijan, Imenje, Šmartno and Gonjače. Calcarenites and calcilutites are
mainly present in the lower part of the sequence associated with marly-arenaceous
interbeddings of turbiditic origin and marls (having marked lateral continuity), and
with very rare individual beds of fine breccia.
The marl sandstone interbeddings in comparison with those of the lower calcare-
ous-marly-arenaceous facies, are thinner, finer and less rich in internal structures
and sole marks.
Going up the stratigraphie sequence (south of Lonzano, Vencò, Ruttars, Neblo,
etc.), thin bedded sandstones and marls are still present with a sand/marl ratio
generally lower than 1, while the calcarenitic beds become gradually rarer and less
thick and the calcilutites and marls progressively predominate.
Discussion and interpretation
This facies association could be considered as belonging to the lower calcareous-
marly-arenaceous facies and to the superimposed marly facies, and objectively, at
our current level of knowledge, it would be difficult to define its exact stratigraphie
limits. Nevertheless, all these facies or subfacies - they can probably be defined and
mapped one by one - are discussed here because they have several common distinc-
tive features. First of all they are Lower-Middle Cuisian in age and contain Paleogene
faunas only, while the lower facies (lower calcareous-marly-arenaceous facies) are
characterized by a mixing of Cretaceous and Paleocene faunas (Cimerman et al.,
1974). A rarefaction, from gradual to abrupt, of conglomeratic and calcarenitic beds
was noted, as already observed by Comel (1927) and Cousin (1981). To these
peculiarities must be added a progressive rareness of the turbidites, which disappear
near to Lonzano.
In the above mentioned area important tectonical disturbances are visible. There
is a lot of evidence of these: the beds appear verticalized, suddendly folded, someti-
mes disrupted and often broken along a line from Pojanis Hill (Italy) to Kojsko,
through Mounts Candia and Komnina, the Gradno Hills, Višnjevik and Vedrijan (see
also Carobene, 1984). South of this alignment, the sporadic appearance of turbiditic
layers, in the light of the above, could represent also the result of displacements of
turbiditic deposits caused by tectonical processes (see also Amato et al., 1976;
Placer, 1981: Fig. 7). To the south of the faulted and "overthrusted" zone, the
prevalence of marls point to a quiet marine environment; most of the facies here
would have originated from a slow fall-out of fine material. The presence of 50 to
150 cm thick fine grained sandstone beds in the upper part of the sequence seems to
Flyschoid deposits of Goriška Brda (Collio)	135
be linked mostly with physical factors (storm waves and/or currents) rather then
with paleotectonics (faint pulsations inside the basin) whose characteristics are
lacking.
Marly facies
This facies was described by Martinis (1962) as a part of the Flysch of Cormons.
It corresponds to the upper part of the Medana Flysch of Cimerman et al., 1974 (see
also Buser 1968 and 1973; Drobne, 1979). The marls represent one of the most
widespread lithotypes in the examined area. They outcrop in the area around
Ruttars, Brazzano, at the foot of Mt. Quarin, on the Croce Hills, between Spessa and
Russiz di sopra, at Blanchis, Giasbana, from Gradiscutta to Oslavia in Italy and at
Barbana, Fojana, Dobrovo, Biljana, Medana, Vipolže, G. Cerovo in Yugoslavia. This
facies is represented by thick beds of marly limestones and silty marls which are
compact, vertically monotonous and structureless. When washed, these marls leave
a residue of quartz grains and, to a lesser extent, mica flakes, small well rounded
chert grains, limonitic concretions, pyrite crystals and scarce elements of light
limestone.
In the middle part of the stratigraphie sequence of the marly facies, fine calcare-
ous subgraywackes appear in layers up to 1 metre thick, vertically graded, extensi-
vely rippled and wavy, with plane parallel and low angle lamination and with sharp
contacts both at the base and at the top (hummocky layers).
Very thin layers of fine sandstone are interbedded in the marls; they are frequent,
although not ubiquitous.
It is common to find (Case Limband, Russiz, Subida, D. Cerovo, Vipolže) 10 to
25 cm thick layers of microbreccia with interstitial marly-calcareous cement, compo-
sed mainly of macroforaminifera and subordinately by well rounded cherty and
calcareous clasts. Often in such layers Nummulites and Assilinae are found in bands
parallel to the stratification.
Inside the marly facies, carbonate breccia (or a calcareous belt) with alveolinas,
nummulites, assilinas and discocyclinas are occasionally found (south of Ruttars,
Tunis, 1976; east of Vipolže, Cimerman et al., 1974).
Layers of pebbly marls are frequent at the top of the marly facies. They are
mainly composed of chert pebbles ranging from 3-4 mm to, exceptionally, 30 cm, quite
well sorted and well rounded.
At the very top of this sequence there are pebbly mudstone outcrops with a rich,
macro and micro invertebrate fauna. The fossils are in various states of preservation,
molluscan shells are often abraded. The fauna has some affinities with tropical
faunas and consists of several species; corals both colonial (of large size) and isolated,
gastropods, bivalves and very abundant macroforaminifera. These deposits, because
of the abundance of macrofaunas and of chert pebbles and due to their areal extent,
could be considered as a subfacies, called here "fossiliferous pebbly marls".
The assemblages of the microfossils found in this marly facies are not very rich in
species and in specimens. Among the planktonic foraminifera, Globorotalia (Acari-
nina) crassata densa is present throughout the section; the globigerinae are always of
small size. Among the benthic foraminifera Nodosarinidae, Buliminidae and Anom-
nalinidae are constantly present. The Bosco di Corrado fossiliferous outcrop, rich in
Nummulites (N. friulanus, N. quasilaevigatus) and Assilinae (A. ex gr. spira and A. ex
gr. exponens), is of particular interest.
136
Giorgio Tunis & Camilla Pirini Radrizzani
Fig. 7. Tectonic map of southeastern Friuli (a- Amato et al., 1976) and of
southwestern Slovenia (b- Placer, 1981)
1. Quaternary deposits, 2. Eocene - Paleocene - Late Cretaceous flysch, 3. Tertiary and
Mesozoic rocks, 4. Geological boundary, 5. Overthrust and reverse fault, 6. Main fault, 7.
Boundary of uplifted platform, 8. Boundary of nappe and thrust sheet, 9. Anticlinal axis, 10.
Synclinal axis, 11. Well, 12. Boundary of nappe and thrust sheet, 13. Assumed thrust plane, 14.
Reverse fault, 15. Fault concealed, 16. Fault identified by means of photogeology, 17.
Brachyanticline, 18. Brachysyncline
Discussion and interpretation
On the whole, the sediments seem to have been deposited slowly from a suspen-
sion of fine material, in a quiet marine environment, mostly below the normal wave
base level. The presence of hummocky layers at about the middle of the stratigraphie
sequence suggests that occasionally the seafloor was agitated. The scale of the
structures, from medium to large, could relate them to storm waves.
Flyschoid deposits of Goriška Brda (Collio)	137
The thin interbeddings of fine sandstones, structureless and bioturbated, can be
attributed to a wave-induced bottom sediment surge.
The presence of nummulitic microbreccias with generally well preserved speci-
mens is attributed to the reworking, over short distances, of nummulitic bars
prosperous at reduced bathymetries near the shoreline.
The frequent coarse size and the general high sphericity of . the pebbles in the
pebbly marls suggest their previous reworking (fluvial or marine) and certainly their
transport by wave motion along a shoreline. Flint (1983) explains a similar facies as
a result of an offshore migration of a pebble beach. As the geometry of this pebbly
body is tabular on the whole and considering the presence of the marl, it seems
plausible to consider instead a mass gravity transport mechanism, such as debris
flow. The large amount of marl would also have favoured the preservation of the
macrofaunas involved in the mass flow.
Finally, an interesting tectonical problem, now under study, is posed by the
presence of outcrops of breccias with alveolinas and nummulites.
138_Giorgio Tunis & Camilla Pirini Radrizzani
Maris with sandstone interbed and sandstones with marl interbed facies
These facies were described by Martinis (1962) in the Cormons Flysch as sandy
marl and sandstone facies respectively; the sandy marl facies probably corresponds
with the uppermost part of the Medana Flysch of Cimerman et al. (1974).
On the top of the marly facies there is a gradual transition towards sandy facies
through sandstones and marls interbeddings at first of 10-30 cm and then of 30 to
100 cm.
The bed by bed investigation of about a hundred outcrops shows a succession of
marly and sandy layers with a progressive increase of sandiness upward. The
sandiness must be understood as growing up of thickness of the sandy layers and
coarsening upward.
The marls with sandstone interbed facies include the outcrops in which the
thickness of the psammitic portion is higher than 3 cm, while the sand/marl ratio
ranges costantly between 1 and 0,5.
The widest outcrops are near S. Giorgio di Brazzano, Mt. Quarin, S. Mauro, Mt.
Galuz, Pubrida, on the slopes of Mt. Calvario and on the southern foothills of the
Goriška Brda.
From the pétrographie point of view the marls have the same characteristics as in
the marly facies, except for their higher quartz content.
The sandstones are quartz-siliceous with calcareous cement; they consist of an
association of angular and subangular quartz grains (predominant) and minor
carbonate grains which are nearly all fossil fragments, often strongly reworked, of
a highly diverse nature (echinoids, molluscs, larger foraminifera and algae). Other
carbonate grains are structureless intraclasts; grains of chert, quartzite and mica are
also present. The grain size is fine.
Primary sedimentary structures are rarely visible because of cementation and
intense bioturbation; where present, they are gradation and plane parallel or low
angle laminations.
Tracks and burrows are present everywhere and the latter sometimes cross
several beds. Finely comminuted plant debris is also very common; bits of vegetal
detritus are frequent especially at the top of sandy marl facies. Fauna is almost
absent in the sandy beds, except for occasional nummulites, while in the marly beds
a poor planktonic microfauna is present. A few nummulitie microbreccias are
interbedded with the marls.
The sandstones with marl interbed facies is also a monotonous alternation of
sandstones and marls. Thin layers (10-30 cm) prevail in the lower part, while in the
upper part the thickness increases to 30-100 cm. The sand/marl ratio is always higher
than 1, generally it is around 2, occasionally 4.
Sandstones with marl interbed facies is frequent in the area of S. Giorgio, Mt.
Quarin, Croce Alta, Budignacco, Bienich, Valleris, Mt. Calvario and Forte nel Bosco.
Grain size is fine to medium fine, coarse at the top where the sandstones are scarcely
cemented and immature from the textural point of view.
Two types of sandstone are generally present. The prevailing type has fine grain
size with infrequent sedimentary structures as plane laminations, both horizontal
and gently inclined, and a few very small scale ripples. The rock is bioturbated and
rich in comminuted plant debris.
The second type has medium fine grain size; it is structureless and scarcely
bioturbated. At a few levels it has an erosive base and contains small cherty clasts,
clay chips and reworked nummulites.
Flyschoid deposits of Goriška Brda (Collio)_17
In both types the grains are angular and subangular and well sorted, the lateral
continuity of the beds is considerable, the lower contacts are sharp flat but, occasi-
onally, concave and erosional unlike the sandstone in the marls with sandstone
facies.
In comparison with marls with sandstone interbed facies, in the sandstones of this
latter facies the quartz content is higher, while the bioturbations are less strong and
decreasing or vanishing towards the top of the sequence. Fine and reworked carbona-
ceous plant remains are very frequent and distributed throughout the stratigraphie
sequence.
At Case Limband there are silty to fine sandy beds, with roots in some cases,
impregnated with bitumen of vegetal origin. Marinoni (1881-86) reported the
presence of a large lens of dark lignite which was subsequently excavated and
utilized.
As far as the marly part is concerned a further increase of the quartz content is
observed with rarefaction and disappearance of the pyrite crystals and of the mica
lamellae, while the kaolinite, in the clayey fraction, increases.
Also in this facies the microfauna is absent in the sandstones and poor in the
marls where were found small size Globigerinae and Globorotalia (G. Acarinina) ex
gr. crassata densa). Nummulitic microbreccias also are present with similar charac-
teristics to those described for the marly facies.
Discussion and interpretation
The prevalence of mud in the marls with sandstone interbed facies leads to an
interpretation of deposition in a low-energy setting. Most of the sandy sediments are
mixed and homogenized because of the strong bioturbation and, probably, due to the
activity of the waves. The occasional finding of nummulitic microbreccias and of thin
layers of graded and laminated sandstone caused by resuspension and concentration
of sand by wave motion would appear to indicate periods of activity of the waves
alternated with periods of calm.
The higher proportion of quartz grains and the lower proportion of mica lamellae
in the marly portion compared with the marly facies could depend partially on
a grain size differentiation towards the shore. The lower marly facies would therefore
represent a depositional environment »further offshore« and deeper in comparison
with marls with sandstone interbed facies.
The increase of the quartz percentage in the sandstone beds suggests a mixed
petrographical assemblage progressively changing towards the top of the stratigrap-
hie sequence. In fact the limestone components of shallow marine origin are in
gradual decrease upward and the allochthonous terrigenous components increase
proportionally. The bioturbation would exclude high rates of sedimentation even
though the observation of vertical systems of burrows crossing several beds shows
the presence of organisms adapted to survive in environments subject to quick
sedimentation and erosion, and therefore on an unstable substrate (Seilâcher,
1967). This facies could be traced to a prodelta environment or to a deltaic front (see
Homewood & Allen, 1981), but, in any case, to a relatively nearshore environ-
ment with shallow bathymetry and connected to a delta system. The thin tabular
sand bodies would represent the fringes of a delta front. The idea of a shoreface may
be ruled out because of the rareness of high energy indicators such as primary
sedimentary structures, fossil tracks and grain size characteristics.
140	Giorgio Tunis & Camilla Pirini Radrizzani
As far as the sandstones with marl interbed facies is concerned, the laminated
sandstones at the base still show evidence of wave motion. The intercalations of
marls and sandstones organized in thickening and coarsening upward sequences are
indicative of proximality conditions accompanied obviously by reduced bathymetry
caused by deltaic aggradation. It is not easy to define carefully the specific depositi-
onal environments. The global sedimentological characteristics could denote a pro-
gressive paleoenvironmental evolution from a submarine deltaic front up to a deltaic
plain or at least to a "transition zone" (sensu Wescott & Ethridge, 1983). In
these types of environments the delicate balance of sedimentation, subsidence and
sea level changes can give rise to an extremely differentiated scenery which is more
or less stable in the time (Ricci Lucchi et al., 1981). The thickest sandstone beds
are seldom bioturbated, and it should be pointed out in a speculative way that this
may reflect either a continuous physical reworking of the sediments, which the
scarcity of current marks makes improbable, or unfavourable biotic conditions (Eh,
pH, or salinity), or, more probably, higher rates of sedimentation. In this area
a coastal shifting could have taken place as it is indicated by the sandstone beds with
erosional base, clay chips and small pebbles, and by the prograding of sand bodies
sedimentologically characterized by slight coarsening upward, i. e. mouth bars,
lagoonal barriers, etc.
Lastly, in the upper beds the association with lignites suggests a deposition in
shallow water or in semiemergent conditions (lakes, marshes and ponds of coastal
plain). Generally, lignites all deposit in restricted nearshore brackish basins (Flint,
1983) where material can accumulate while a dense vegetation develops.
Sandstones, conglomeratic sandstones and sandstones with gravel facies
The sandy facies and the conglomeratic sandstone facies are extremely limited
(Prati Grandi, Mt. Calvario, Mt. Quarin, hill 242 of Mt. Quarin).
The former (sandy facies) consists of medium to coarse sandstone beds up to
120 cm thick, with a high sand/mud ratio. The sandstones are generally structureless,
except for the normal graded bedding. Near to Gorizia and Nova Gorica, sequences
of strata of the sandy facies show pinch outs; the most frequent structures are
gradation, cross planar stratification and perhaps festoons.
The latter (conglomeratic and microconglomeratic sandstones facies) consists of
subangular to sub rounded cherty and calcareous clasts, from 2 to 10 mm. The
thickness of the beds is around 30-50 cm, the hardness is variable in relation to the
different proportions of sandy matrix and of calcareous cement. Gradation, crude
lamination and minor pebble imbrication are occasionally seen in the conglomeratic
sandstones. Thin levels of pebbles of larger size, nummulites and, exceptionally,
reworked and broken macrofossils are confined to the bottom of some beds (coqui-
noid graded beds are present near Case Peressin).
In both facies the base of the beds is flat or concave.
The gravelly sandy facies outcrops in the Bosco di Flessiva, Mt. Quarin, at altitude
240, Subida, the Croce hills, between Valleris and Uclanzi, Rožna dolina and
Okroglica (Pavlovec, 1963). It consists of gravel and pebble beds, mostly matrix
supported (with pelitic - sandy matrix) and subordinately clast supported. In this
last case the poor sorting and the random distribution of the clasts give a misleading
appearance of a matrix supported conglomerate. These conglomerates are disorgani-
zed and not stratified. The clasts, generally well rounded, have size ranging from 0,5
to 3-4cm up to a maximum of 20cm. They are of various origins: chert (largely
Flyschoid deposits of Goriška Brda (Collio)	141
predominating), several calcareous lithotypes (Voice limestone), marly limestones
and sandstones. It is not possibile to make accurate observations about the geometry
of the beds, but it is our impression that the tabular unchannelized deposits prevail.
Discussion and interpretation
The depositional history of these sediments denotes increasing fluviatile influence
and indicates an interaction of marine and fluvial processes, initially with the
prevalence of the former. We are not yet in possession of sufficient data to suggest
any other hypotheses about the sandy and conglomeratic sandstones facies. Clifton
(1973) interpreted similar conglomeratic sandstones and fossiliferous sandstones
with horizontal stratification as shoreface and foreshore deposits. In the area exami-
ned, the conglomeratic sandstones are segregated from the sandstones in which they
are interbedded; lateral transitions between the two lithotypes were never observed.
These characteristics, according to Clifton, indicate a "wave worked gravels as
opposed to fluvial gravels which are lenticular and not well segregated into discrete
laminae".
The presence of disorganized conglomerate (gravelly - sandy facies) with abun-
dant pelitic matrix may be related to transport mechanisms of debris flow even
though they are not characterized by a high flow competence. The unusually high
sphericity of the cherty clasts suggests their strong fluvial reworking. The probable
tabular shape of the gravel beds would also suggest reworking caused by wave
motion, albeit quite moderate. The chert is derived from limestones with chert
nodules and sheets of Malm, Early Cretaceous and Late Cretaceous (Soča Valley).
This facies, on the basis of the existing models, could be referred to as a "non
channelized deltaic plain environment" (Ricci Lucchi et al., 1981).
Paleogeographic Evolution
In accordance with what has already been said, it is possible to infer that the
clastic deposits of the Goriška Brda represent a wide range of environments that
successively embrace: (i) relatively deep sea conditions of lower slope and/or border
of basin (megabeds and lower calcareous-marly-arenaceous facies and upper calca-
reous-marly-arenaceous facies p. p.), (ii) mixed siliciclastic and carbonate external
and internal platform (upper calcareous-marly-arenaceus facies p. p. and marly
facies), (iii) deltaic front (marls with sandstone interbed facies, sandstones with marl
interbed facies) and (iv) deltaic plain (sandstones, conglomeratic sandstones and
sandstones with gravel facies).
Regarding the deep sea facies we suppose (see also Pirini et al., 1986) that there
was a "ridge" originated by tectonical structures already existing at the time of the
sedimentation of the Flysch of Kožbana. This morphostructural element was placed
transversally and partially laterally with respect to the NW-SE basin axis of the
Friuli flysch and separated the turbiditic deposits (Kožbana beds) from the non
visible deposits of a carbonate platform subsequently covered by terrigenous sedi-
ments (upper Medana beds and Flysch of Cormons). We think that this could explain
the turbiditic facies zonation in Friuli and Goriška Brda with the decrease of the
coarsest lithofacies from NW to SE, the difficulties of wide scale correlations of the
megabeds and some lateral facies association changes in the Goriška Brda region.®
® The lateral facies variation, from turbidites and megabeds in the west to thin marl with
sandstone interbeddings in the east, in the lower calcareous-marly-arenaceous facies stated
previously.
142	Giorgio Tunis & Camilla Pirini Radrizzani
Inside the upper calcareous-marly-arenaceous facies the deposits show important
tectonical disturbances. Here (between Pojanis and Kojsko) there are overthrusts and
faults (Amato et al., 1976; Placer, 1981) which also display the NW-SE direction.
With reference to the overthrusts of southwestern Slovenia, Placer (1981) gives the
distances and displacement directions of the main structural units (the Trnovo
nappe, for example, which affects also the Goriška Brda, was driven for 29 km in the
area of Trnovo forest).'' We are not able to express an opinion on this remarkable
thrust length but we would stress the importance of the fact that above the Thanetian
Kožbana megabeds there is no sign of the thick Cuisian sequence (over 1000 m thick)
with turbidites and megabeds found in Friuli in the whole sector north of the line
Faedis-Cividale.
The supposed presence of the overthrusts, together with the fact that the greatest
shortening in the entire area took place between Mt. Sabotino and Gorizia, makes it
very difficult to locate the position of the ridge (which we have postulated) and
complicates all the problems connected with the turbiditic and non-turbiditic depo-
sits.
At present we only have fragmentary knowledge concerning the zone of transition
between the northern area, where the older deposits (turbidites and megabeds) are to
be found, and the southern area where a "relatively" shallow water clastic terrige-
nous regime was established during the Early Eocene.
To return to the paleogeographic evolution, the deposition of the Flysch of
Medana (upper part) and of the Flysch of Cormons (lower part) was affected by
subsidence, which probably had its origin in the load which caused a general uplift of
the northern areas, the main source region of the siliciclastic materials. The uplift
gave rise to a sedimentary cycle from the Late Cuisian to the Early Lutetian (mainly
regressive) which is well documented, mostly by the study of the marls with sand-
stone interbed facies and sandstones with marl interbed facies.
Before and during the regressive phase, small transgression-regression fluctuati-
ons, due to oscillatory basin subsidence, are probably present (marly facies). The
fossiliferous pebbly marl subfacies (inside the marly facies), in fact, records a marine
transgression. As the shoreface equivalent of the marly facies (which instead belongs
to the external platform) has not been found, we would postulate an offshore shift of
a pebbly beach: the waves reworked near the coast fluvial deposits from an alluvial
delta, building up pebble-sand mixed beaches. A probable pre-indication on this
shifting is given by very thin monotonous rhythmic intercalations of sandstones and
marls in the marly facies. These last ones could represent either lower shoreface
deposits (Bourgeois, 1980) or prodelta deposits ( S arntheim & Walger, 1973,
Cason et al., 1980, Ricci Lucchi et al., 1981).
The marls with sandstone interbed facies is also indicative of a calm water
environment, interrupted by phases of weak wave winnowing. The seabottom on the
whole does not seem to have been strongly agitated even when the bathymetry is very
low; this could be connected to waves of extremely limited fetch.®
The monotonous sequence of thin sandstone and marl beds, in shallow sea con-
ditions, indicates a phase of steady equilibrium between subsidence and deposition.
There is not a great deal of field evidence (in the southern Goriška Brda) of the second,
more southern, thrust plane proposed by Placer. In the Ruttars area there is, however, an
important disturbance; in Cà delle Vallade there is an other fault (probably inverse).
8 The only exception is represented by the ripple and wavy laminated calcareous subgray-
wackes, ascribed to storm waves, found approximately in the middle of the marly facies sequence.
Flyschoid deposits of Goriška Brda (Collio)	143
Afterwards, with the sandstones with marl interbed facies, sedimentation overco-
mes the effect of subsidence, causing a decrease in the bathymetry almost to the point
of emersion. The moderate action of synsedimentary tectonics during the building up
of the delta front (that corresponds with the sandy-marl and marly-sandstone facies
deposition) allows us to attribute little importance to this factor in our estimation of
the sedimentation rate. Considering a thickness of 500 m and a time interval that
could range from 2 to 4 MY a value of 10-20 cm/1000 yr is obtained; this could
indicate a moderate or not too high amount of material input. Even if a regressive
phase is generally not very preservative, breaks in the sedimentation have not yet
been observed.
There are no substantial differences between the microfaunas of the examined
sequences and they do not therefore offer clear elements with which to define the
association zones.
On the one hand this suggests the hypothesis that the building of the delta
happened in a relatively short period, and on the other hand would confirm an
assumption of Wescott and Ethridge (1980), but with regard to fan deltas.
According to these authors, the biostratigraphic criteria are inadequate for the
differentiation of the fan delta paleoenvironments.
In the upper part of the stratigraphie sequence the sandstones and conglomeratic
sandstones facies are connected to a generic delta plain environment; the limited
areal extent of the outcrops and the lack of other data prevent, for the present, the
recognition of specific subenvironments. The characteristics of the gravelly sandy
outcrops, as said before, seem to show a moderate energy fluvial system with not very
high solid discharge (small river with low longitudinal gradient and/or with mode-
rate flow competence?).
Cousin (1981) reports the presence of Biarritzian in Subida (presumably in the
gravelly-sandy facies) and near to Nova Gor .ca. We have not yet sufficient data for
dating both the conglomeratic sandstones and the gravelly-sandy facies, but we think
that they are nearly coeval to the underlying marly sandstone facies.
An other important control factor of the sedimentation, that is the sediment
dispersal, further supports the paleoenvironmental reconstruction proposed here. In
fact there is strong evidence of an interdependence between the different sedimen-
tary facies and the geochemical and mineralogical characteristics. The vertical
decrease in the carbonate content (and the proportional increase of the quartz
content) follows the depositional suite verj' well®. Inside the sandy facies a sharp
increase of the kaolinite, a typical mineral of some fluvial areas (Flügel, 1981), is
also observed in the clayey fraction, but in this case it was not noted whether the
increase is progressive along the stratigraphie sequence.
With reference to the origin of the terrigenous non turbiditic material, the few
paleocurrent directions measured, mainly from N, NE and NW (see also Bus er,
1973), are not to be considered as decisive. A more important contribution is offered
ä From north to south it is possible to note a decrease of the calcareous lithotypes and an
increase of the arenaceous lithotypes. This ratio coincides both stratigraphically and chemi-
cally, as noted by Comel in 1927. Inside the sandy portion, in the upper part of the
stratigraphie sequence, the thickness of the beds increases gradually together with a general
increase of the grain size from fine and medium sandstones up to coarse sandstones and
conglomeratic sandstones. From the geochemical point of view, the total carbonate percentage
ranges from 80-90% in the calcareous facies to about 50% in the marl with sandstone facies
and to 10% in the coarse sandstones collected near Subida (0.5 in a sample of conglomeratic
sandstone).
144	Giorgio Tunis & Camilla Pirini Radrizzani
Flyschoid deposits of Goriška Brda (Collio)
145
Fig. 9. Orientative paleogeographic scheme of the Late Cuisian - Early Lutetian (sources: Buser,
1973; Cousin, 1981; Drobne, 1977; Engel, 1974; Orehek, 1972; Pavlovec, 1963)
1. Areas emerging or already emerged, 2. Submarine areas directly influenced by deltaic
systems, 3. Shallow areas affected by clastic inputs, 4. Relatively deeper areas characterized by
calcareous turbidites (megabeds) and sometimes by siliciclastic turbidites, 5. Carbonate plat-
form, locally emerged
Fig. 8. Early Cuisian paleogeography
1. Carbonate platform, 2. Area emerging or already emerged,5. Lower slope, 4. Basin filled with
turbidites and chaotic facies, 5. Platform characterized by clastic input, 6. Postulated position
of the submerged ridge, 7. "Friulan" inputs, 8. "Prealpine" and "Carnic" inputs, 9. Probable
northeastern deltaic inputs
10 - Geologija 30
146_Giorgio Tunis & Camilla Pirini Radrizzani
by the geochemical and sedimentological data of maris with sandstone interbed and
sandstones with marl interbed facies and by the distribution of conglomerates over
the area. The decrease of the total carbonate content from N-NE to S-SW and the
processing of sedimentological parameters in order to get information about the
intensity and the variability of the energy levels allow us to assume a northern
provenance of the materials (from the uplifted area), rather than a northwestern one.
We cannot definitively exclude the hypothesis that the usual northwestern input of
Friuli flyschoid turbiditic deposits influenced, in this period and in this area too, the
development of the depositional system, but, on the basis of the whole facies
distribution, this is pratically impossible to back up.
The distribution of the upper facies is asymmetrical; the conglomerates are
thicker to the west (Cormons, Rosazzo and Noax)!" while the sandstones outcrop most
widely in the area around Gorizia. This could be connected to the system morphology
and geometry and also to the erosive processes which occurred later on; coarse facies
in fact are moderately well developed near Nova Gorica.
The last depositional environment here described corresponds to the conventional
picture of those deltas, characterized by non coarse sedimentation, most of which are
placed near narrow coastal plains bordered by young mountains. On this subject it is
worth noting that, during the Eocene, similar fluvio-deltaic systems were active in the
Tarcento area (Frattins, Cesarris, Monteaperta) and perhaps in the Pivka Valley (see
also Pavlovec, 1963, Orehek, 1972), while in the Oligocene they were also active in
the Tremugna Valley on the west of the Tagliamento R. (Sarti, 1979).
The Ajdovščina flysch basin shows, on the contrary, evidence of sediments
deposited in relatively deep sea environments during the Cuisian (see for example,
the megabeds described by Engel, 1974).
Figs. 8 and 9 show the paleogeographic situation of the eastern Friuli area and
southwestern Slovenia area in the Earlyand Late Cuisian respectively (from
Pirini et al., 1986).
In conclusion, the Julian Prealps were emerging in the Middle Eocene, while the
hilly strip between Tarcento and Gorizia was by this time an alluvial plain. In what is
now the Friuli plain, marine clastic sedimentation took place during the Late Eocene
and continued to the Oligocene. In fact, southwest of the Udine-Buttrio line a new
basin with flyschoid deposition grew, as can be deduced from the stratigraphy of
the AGIP well Terenzano 1 and from the seismic lines pubblished in Amato et al.
(1976). This basin was rapidly deepening since the Lutetian.
With regard to this matter, in the Late Cuisian and Early Lutetian the characteri-
stic carbonate platform facies in southwest Slovenia and Istria shifted southwards;
the same occurred to the flysch basin of Central Istria (Drobne, 1977; Magdale-
nić, 1972).
Acknowledgements
We wish to thank Prof. Mario Pleničar and Dr. Katica Drobne who supervised this
paper, and Prof. Rajko Pavlovec for his help and suggestions. A particular thank to
Prof. Stanko Buser for providing us precious biostratigraphic data and for his help.
We think that also the flyschoid deposits of the Rocca Bernarda hills (Martinis, 1955;
Castellarin & Zucchi, 1963) a few km northwestward are related to the same fluvio-
deltaic environment.
Fig. 8 ilustrates the hypothesis that in the area between Kožbana and Plave the deposition
of turbidites and other coarse sediments continued during the Cuisian.
Flyschoid deposits of Goriška Brda (Collio)	147
We thank also Prof. Francesco Massari (Università di Padova) for the criticisms of
the early draft of this paper and Drs. Sergio Nardon and Sandro Venturini (Agip,
Milano) for their valuable discussions about several problems. This research was
supported by financial funds of M. P. I. "Litosfera Carso" (Director C. Pirini
Radrizzani) and M. P. L "Evoluzione della Tetide - Flysch del Friuli orientale"
(Director G. Catani).
Literature
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1976, Geodynamic outline and seismicity of Friuli-Venetia Julia Region. Boll. Geof. Teor. Appi.,
72, 217-256, Trieste.
Bourgeois, J. 1980, A transgressive shelf sequence exhibiting hummocky stratification:
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