GEOLOGICA CARPATHICA, AUGUST 2010, 61, 4, 293—308 doi: 10.2478/v10096-010-0017-0
Microfacies analysis of the Upper Triassic (Norian) “Bača
Dolomite”: early evolution of the western Slovenian Basin
(eastern Southern Alps, western Slovenia)
Geological Survey of Slovenia, Dimičeva ulica 14, SI-1000 Ljubljana, Slovenia; email@example.com
(Manuscript received November 3, 2009; accepted in revised form March 11, 2010)
Abstract: The Slovenian Basin represents a Mesozoic deep-water sedimentary environment, situated on the southern
Tethyan passive margin. Little is known about its earliest history, from the initial opening in the Carnian (probably
Ladinian) to a marked deepening at the beginning of the Jurassic. The bulk of the sediment deposited during this period
is represented by the Norian-Rhaetian “Bača Dolomite”, which has, until now, been poorly investigated due to a late-
diagenetic dolomitization. The Mount Slatnik section (south-eastern Julian Alps, western Slovenia) is one of a few
sections where the dolomitization was incomplete. Detailed analysis of this section allowed us to recognize eight
microfacies (MF): MF 1 (calcilutite), MF 2 (pelagic bivalve-radiolarian floatstone/wackestone to rudstone/packstone),
MF 3 (dolomitized mudstone) with sub-types MF 3-LamB and MF 3-LamD (laminated mudstone found in a breccia
matrix and laminated mudstone found in thin-bedded dolomites, respectively) and MF 3-Mix (mixed mudstone), MF 4
(bioturbated radiolarian-spiculite wackestone), MF 5 (fine peloidal-bioclastic packstone), MF 6 (very fine peloidal
packstone), MF 7 (bioclastic wackestone) and MF 8 (crystalline dolomite). The microfacies and facies associations
indicate a carbonate slope apron depositional environment with hemipelagic sedimentation punctuated by depositions
from turbidites and slumps. In addition to the sedimentary environment, two “retrogradation-progradation” cycles were
recognized, each with a shift of the depositional setting from an inner apron to a basin plain environment.
Key words: Norian, Slovenian Basin, “Bača Dolomite”, microfacies analysis, slope apron.
Winkler (1923) was the first to recognize the existence of a
Mesozoic deep-sea sedimentary environment in central
Slovenia, later named the Julian Trough, the Slovenian
Trough, the Tolmin Trough or the Slovenian Basin. Compre-
hensive research by Aubouin (1960, 1963), Cousin (1970,
1973, 1981) and Buser (1986, 1989, 1996) was recently im-
proved by Šmuc & Čar (2002), Goričan et al. (2003), Rožič
(2005, 2006, 2008, 2009), Rožič & Popit (2006), Rožič &
Šmuc (2006, 2009) Buser et al. (2008), and Rožič et al. (2009).
The Slovenian Basin was located on the south Tethyan
passive continental margin (Fig. 1A). It was situated be-
tween the Julian Carbonate Platform (the Julian High since
the Late Pliensbachian; Šmuc 2005) to the present north and
the Dinaric Carbonate Platform (Adriatic Carbonate Platform
of Vlahović et al. 2005) to the present south (Buser 1986).
The evolution of the Slovenian Basin can be divided into
two parts (Rožič et al. 2009). An initial opening during the
Carnian (probably already in the Ladinian or even Late
Anisian) and a progressive shallowing in the Carnian, was fol-
lowed by a marked deepening from the Late Triassic/Early
Jurassic to a final closure at the end of the Cretaceous (Buser
1986, 1989, 1996). The beginning of each stage was related
to extensional tectonics, probably related to the opening of
the Meliata part of the Neotethys to the east (Haas et al.
1995; Schmid et al. 2008) and the Piedmont-Ligurian Ocean
to the west (Bosellini 2004; Vlahović et al. 2005).
While the second phase of the evolution of the Slovenian
Basin has been greatly clarified by recent studies, the initial
stage of its evolution, during the Late Triassic, remains poor-
The Upper Triassic succession of the Slovenian Basin con-
sists of the Carnian “Amphiclina beds”, followed by the
Norian-Rhaetian “Bača Dolomite”, which in the northern-
most part of the basin laterally and vertically passes into
limestones of the Slatnik Formation of Late Norian—Rhaetian
age (Rožič et al. 2009).
The present paper focuses on the “Bača Dolomite”. Despite
its great thickness (around 300 m; Buser 1979) and basin-wide
presence, this informal lithostratigraphic unit has been poorly
investigated due to a strong late-diagenetic dolomitization,
which has almost completely obliterated primary sedimento-
logical structures and textures. However, as noted by Buser
(1986) and confirmed by Rožič (2006), in the most proximal
parts of the basin, lying adjacent to the Julian Carbonate
Platform, some limestone beds escaped dolomitization. They
are now intercalated between the dolomite beds of the “Bača
Dolomite”, offering an opportunity for a more detailed study
of the depositional environment. Such development is ex-
posed in the Mt Slatnik section (south-eastern Julian Alps,
western Slovenia) (Fig. 1B,C,D). Rožič (2006) examined the
upper 32 m of the Norian “Bača Dolomite” in this section. He
concluded that the deposition took place via turbidity currents,
and noted that grain composition points to a shallow-water
origin of the material (Rožič 2006; Rožič et al. 2009). However,
the predominant part of the “Bača Dolomite” in this section
The aims of this paper are:
– description of the total exposed sequence of the “Bača
Dolomite” from the Mt Slatnik section;
– presentation of the microfacies analyses of the “Bača
– comparison of the “Bača Dolomite” with the overlying
– interpretation of the results in terms of the depositional
Previous research on the “Bača Dolomite”
Kossmat (1901, 1914) was the first to describe the dark
dolomites and limestones with lenses and nodules of chert
(“Hornsteindolomit”). He placed them into the Carnian—
Norian, probably Rhaetian, according to their superposition
and rare fossil remains. Cousin (1973) placed the “Hornstein-
dolomit” or “dolomie siliceuse” into the Norian—Hettangian.
The name “Bača Dolomite” was introduced by Buser (1979).
Following this, Buser (1986) presented a more detailed study
of the “Bača Dolomite”, according to which it is usually do-
lomicritic, although coarser varieties can also be encoun-
tered. Its main characteristic is the abundance of black and
light grey chert in the form of layers and nodules up to
30 cm thick. Dolomitic breccias with clasts of dolomite and
chert are present locally (Buser 1986).
Rožič (2006) described the upper parts of the “Bača Dolo-
mite” from several sections from Mt Slatnik to Kobarid
(Fig. 1B). The bedded dolomites are locally intercalated with
breccias. The primary textures and structures are usually com-
pletely obliterated by the dolomitization. Parallel and wavy
lamination is commonly visible, reflecting different sizes of
dolomite crystals, as well as variations in the amount of clay
minerals (Rožič 2006). Silification took place prior to dolo-
mitization, so that primary textures were partly preserved in
the chert (Rožič 2006; Skaberne, pers. comm.). Rožič (2006)
concluded that sedimentation took place in calm, deeper water
as well as by settling from low-density turbidity currents. The
breccias were interpreted as intraformational, formed via slid-
ing/slumping and/or debris flows (Rožič 2006).
The Norian age for the lower part of the “Bača Dolomite”
has been proved by conodonts (Kolar-Jurkovšek 1982) and
the bivalve Halobia distincta Mojsisovics (Buser 1986). It
was previously assumed that the upper boundary of the “Bača
Dolomite” generally represents the Triassic/Jurassic bound-
ary. However, Rožič & Kolar-Jurkovšek (2007) and Rožič et
al. (2009) proved the Late Norian—Rhaetian age for several
tens of meters of limestones overlying the “Bača Dolomite” in
the northernmost part of the basin, which were previously
assumed to be of Early Jurassic age. They named this unit the
Slatnik Formation (Rožič et al. 2009). The “Bača Dolomite” is
thus proximal to the Julian Carbonate Platform of the Norian,
and distal from it of the Norian—Rhaetian age.
The Lower to Middle Norian (Lacinian 1 to Alaunian)
bedded dolomites with chert in the Hahnkogel (Klek) Unit in
the Southern Karavanke Mountains (Fig. 1B) were also
Fig. 1. A – The paleogeographic position of the Slovenian Basin,
the Julian and the Dinaric Carbonate Platforms during the Norian
(simplified after Haas et al. 1995). B, C – Position of the investi-
gated area. The smaller rectangle in B is shown in C. D – General-
ized nappe structure of the area shown in C (after Buser 1986; and
M. Demšar, pers. comm.). The Kobla, Rut and Podmelec Nappes
belong to the Tolmin Nappe, where rocks of the Slovenian Basin are
preserved. Triangles in B, C and D represent mountain summits.
MICROFACIES ANALYSIS OF THE UPPER TRIASSIC “BAČA DOLOMITE” (SLOVENIA)
named the Bača (“Baca”) Formation (Krystyn et al. 1994;
Lein et al. 1995; Schlaf 1996). A series of deposits around
170 m thick was interpreted as allodapic slope deposits
(Schlaf 1996). Krystyn et al. (1994) considered the Hahnkogel
Unit and the Slovenian Basin as parts of the same basin. This
theory remains to be proved since the time of opening of
these two units, as well as their lithological successions as a
whole, seem to differ (see also Rožič et al. 2009).
The studied Mt Slatnik section is situated in the Kobla
Nappe, which, with two more units (the Rut Nappe and the
Podmelec Nappe), is part of the higher-order Tolmin Nappe
(Buser 1986) (Fig. 1D), containing sedimentary rocks of the
Slovenian Basin. The succession of the Kobla Nappe was
deposited closest to the Julian Carbonate Platform, whereas
the succession of the Podmelec Nappe was formed relatively
far away from it (Rožič 2009).
The whole succession of the Kobla Nappe comprises the
Upper Triassic “Amphiclina beds”, the “Bača Dolomite” and
the Slatnik Formation, the Jurassic Krikov, the Perbla and
Tolmin Formations, the Upper Jurassic—Lower Cretaceous
“Biancone Limestone” and finally the Cretaceous “Lower
Flyschoid Formation” (Buser 1986; Rožič et al. 2009) (Fig. 2).
The Tolmin Nappe is overlain to the north by the Julian
Nappe, containing mainly sedimentary rocks of the Julian
Carbonate Platform and the Julian High. It is bordered to the
south by the Southalpine front, which separates it from the
External Dinarides with the sedimentary rocks of the Dinaric
Carbonate Platform (Placer 1999).
The original geometry of the basin was greatly obliterated
by the Late Eocene to Early Oligocene NE to SW Dinaric
thrusting and by the Middle Miocene and later Alpine N to S
thrusting (Placer & Čar 1998; Placer 2008). The tectonic
situation was further complicated by the Pliocene—recent
strike-slip deformation that displaced previous fold and
thrust structures (Vrabec & Fodor 2006; Kastelic et al. 2008;
Šmuc & Rožič 2009).
Fig. 2. A schematic stratigraphic column for the Slovenian Basin, with a short description of the units. For the references see the column on
the right. Informal stratigraphic units are placed in quotation marks. The grey bar in the stratigraphic column marks the schematic position
of the Mt Slatnik section. Note that only the “Bača Dolomite” part of the section is discussed in this paper.
Fig. 3. A – (Continued in Fig. 3B). The Mt Slatnik section. Only the “Bača Dolomite” is drawn, with indicated position of the overlying
Slatnik Formation, which is figured in Rožič et al. (2009). Though several faults are indicated, only the one separating the “Bača Dolomite”
from the Slatnik Formation is of a greater importance (Rožič, pers. comm.). The “Composition” and the “Sedimentary structures” refer to
the macroscopic observations only, whilst results of the microscope analysis are expressed as the microfacies (MF) types. Limestone beds
of the “Bača Dolomite” are shaded. See text for a detailed description of the section.
MICROFACIES ANALYSIS OF THE UPPER TRIASSIC “BAČA DOLOMITE” (SLOVENIA)
The studied section is exposed along the mountain path on
the southern flanks of Mt Slatnik (Y= 5420550, X= 5121670,
1609 m a.s.l.) (Fig. 1C; Fig. 7—1). The “Bača Dolomite” was
investigated bed-by-bed and 79 thin-sections of 47
in size were prepared for detailed investigation with an opti-
cal microscope. The textural classification followed Dunham
(1962). In wackestones and packstones at least 300 grains
were counted under the
×63 magnification using the area
method to determine relationships between individual grain
Fig. 3. B – Continued from Fig. 3A.
types. Grain-to-matrix relationships were estimated with the
comparison charts of Bacelle & Bosellini (1965 in Flügel
2004). Description of the dolomite crystals followed Sibley
& Gregg (1987). In Fig. 3, the field observations are separat-
ed from microscope observations (presented by microfacies
type) and are grouped in columns “Composition” and
Description of the “Bača Dolomite” from the
Mt Slatnik section
The Mt Slatnik section is exposed for around 330 m, only
slightly covered (around 6 %) with individual beds laterally
exposed for several meters (Fig. 7.1). It contains three lithos-
tratigraphic units: the “Bača Dolomite” (260 m), the Slatnik
Formation (50 m) and the Krikov Formation (20 m). This
study only focused on the “Bača Dolomite”. The upper 32 m
of the “Bača Dolomite” was already investigated by Rožič
(2006) and Rožič et al. (2009). Some minor faults are
present, but presumably without significant displacement
(Rožič, pers. comm.). The lower boundary of the “Bača Dolo-
mite” is not exposed. The older formations are not exposed
in the studied section. However, in a similar section not far
away, 40 m of grey limestones with mudstone and wacke-
stone, subordinately packstone textures, Carnian in age
(Kolar-Jurkovšek, unpublished) occur below the “Bača Dolo-
mite”. At its upper boundary the “Bača Dolomite” is separat-
ed from the Slatnik Formation by a minor thrust.
Based on the conodonts and supported by sponges, corals
and foraminifers, the overlying Slatnik Formation is of the
Late Norian to Rhaetian age (Rožič & Kolar-Jurkovšek
2007; Rožič et al. 2009). Accordingly, the exposed “Bača
Dolomite” can be assigned to the Norian, also confirmed by
ongoing foraminiferal research by the author.
The description of the profile is divided into two parts: the
first part is based solely on field observations, whilst the
second part describes thin-sections.
General description of the section
The investigated section was subdivided into ten intervals
(A—J, Fig. 3) by lithological characteristics. The characteris-
tics of each Interval are given in
Interval A: The basal part of the investigated section is
made up of 75 m of poorly sorted mud-supported breccias
with a light grey marly dolomicritic or dolomicrosparitic ma-
trix. The bedding planes are sharp, planar or chanellized
(Fig. 7.2). Massive (maximum thickness 1240 cm) and very-
thick beds predominate, but some thick (50—100 cm) and
medium-thick (10—50 cm) beds also occur. Oblique sigmoi-
dal laminae were also found in the matrix in the upper part of
one bed. Altogether, three types of clast are present. Very
elongated chips of marly dolomite with a parallel or cross-
lamination and normal grading mark the first group. They
show no preferred orientation, and can even be perpendicular
to the bedding plane. The second group of clasts is represent-
ed by more than 10 cm large clusters of angular pieces of
chert, that are slightly disintegrated chert nodules (“mosaic
chert”). Undeformed chert nodules are also present. Some
cherts contain clasts of older chert, or partly preserved pri-
mary sedimentary structures.
Interval B: In this, around 19 m thick interval consisting of
up to 60 cm thick beds, the marly content increases. The
breccias become subordinate and are only encountered as
medium-thick beds with convex-downwards lower and sharp
flat upper boundaries. The matrix is a light grey dolomi-
crospar, the clasts are mosaic cherts and elongated clasts of
marly dolomite with parallel lamination. Most beds are light
grey marly dolomicrosparites and occasionally dolosparites.
The boundary planes are flat and sharp; the individual beds
seem to be composed of several wavy thinner amalgamated
beds. Amalgamated units are separated by laminated marl-
stone up to 5 mm thick. Parallel and convolute lamination
can be seen. Most beds contain black, white, grey or red
chert nodules, sometimes with preserved parallel lamination.
Occasionally, only the outer rim of the nodule is silicified.
Beds of black, amalgamated and cherty microsparitic lime-
stone are also present.
Interval C: This interval represents an around 10 m thick
package of alternating thin beds of black, locally silicified
limestone, and light brown marlstone (Fig. 7.3). A cyclic
pattern was recognized. The cycles begin with thicker lime-
stone beds, upwards gradually becoming more clay-rich and
are capped by a more prominent marlstone bed. The individ-
ual cycles are 40 cm to 110 cm thick. The boundaries be-
tween the limestone beds are sharp, but wavy, often more
clayey. Parallel lamination is common and compactional sty-
lolites occur locally. The limestones are mudstones to pack-
stones. The latter contain juvenile thin-shelled bivalves,
forming lens-shaped coquinas. Individual shells are oriented
with their convex or concave sides upwards, or irregularly
grouped in clusters. In some cases they are silicified. Nod-
ules of black chert are present in the limestone as well as in
the marlstone beds. The marlstone beds are up to 5 cm thick
and usually laminated. Thicker beds can contain limestone
nodules. Fragmented terrestrial plant remains also occur.
Interval D: This interval measures 11.5 m in thickness.
The clay content is markedly reduced and medium—thick
beds predominate again. Some micritic to microsparitic bio-
turbated limestone beds in the lower part are amalgamated.
The bedding-plane boundaries are sharp, wavy or straight.
The limestones are texturally mudstones to wackestones.
Strongly recrystallized green algal thalli and normal grading
are visible. The rest of this interval contains light grey do-
losparites and dark grey dolomicrosparites. Parallel, cross or
convolute laminations can be found, especially in the latter.
The dolomites also contain chert nodules. An internal amal-
gamation of the individual beds becomes more prominent to-
wards the top of this interval.
Interval E: In this 11.5 m thick interval, limestones begin to
predominate again, although the bed thickness remains the
same. A lateral transition from limestone to coarse-grained do-
lomite was observed in one bed. The limestones are texturally
mudstones or wackestones. The bed boundaries are sharp,
straight or wavy, and sometimes dolomitized. Beds are inter-
nally amalgamated, sometimes with clayey laminae. Most
limestone beds contain chert nodules. Normal and inverse
grading, parallel, cross, and convolute laminations are com-
mon (Fig. 7.4). Possible ripples were observed in the upper
part of one bed. Load-casts and “sand”-balls were also found.
A geopetal structure was observed in an unidentified fossil
remnant with a circular cross-section (perhaps green algae).
Interval F: This interval consists of 13 m of very thick and
massive, up to 4 m thick, clast-supported breccia beds
(Fig. 3). The bedding planes are sharp and irregular. Along
with loose mosaics of chert clasts there are dolomite intrac-
lasts with clearly visible parallel and cross-laminations. The
dolomite clasts are abundant, especially near the base of the
breccia beds (Fig. 7.5). They are oriented approximately par-
allel to the lower boundaries and locally imbricated.
Fig. 4. Summarized characteristics of the individual Intervals distinguished in the “Bača Dolomite” from the Mt Slatnik section. See text
for more detailed descriptions.
MICROFACIES ANALYSIS OF THE UPPER TRIASSIC “BAČA DOLOMITE” (SLOVENIA)
Interval G: Interval F is followed by some medium-thick
coarse-grained dolomite beds with chert nodules, then by a
20 m thick succession of medium- to thick-bedded coarse dolo-
mites without chert, with only one massive dolomite bed and
two limestone packages. The lower one consists of thin and me-
dium—thick beds of a marly pink-grey micritic limestone with a
hardly distinguishable amalgamation. Parallel and convolute
laminations are visible, as well as a strong stylolitization. The
upper limestone package consists of a few medium to thick
beds with parallel lamination. Amalgamations are pronounced
near the lower and upper bed boundaries.
Interval H: This interval is 17 m thick. Chert nodules are
common. The succession consists of medium- to thick-bed-
ded coarse dolomites with chert, and a single massive bed.
Elliptical nodules of white, red or black chert are mostly lo-
cated near the lower bed boundaries.
Interval I: The following 47 m are dominated by medium-
bedded, light grey coarse dolomites. The limestone packages
are subordinate, and there are a few massive (up to 520 cm
thick) dolomite beds. Dolomite beds have sharp boundaries,
mostly flat, but in some cases convex downwards. Some beds
contain markedly more porous bands with straight boundaries,
up to 10 cm thick, laterally discontinuous and with a slightly
steeper dip. Within the beds normal grading and parallel lami-
nation were recognized. Limestone beds contain more sedi-
mentary structures. Parallel lamination was observed, which
passed upwards into a convolute lamination, followed by few
deformed clayey laminae. Parallel lamination and inverse
grading followed on top. The limestones have packstone or
wackestone textures. The individual beds are amalgamated.
Some are dolomitized near the upper or lower boundaries.
Interval J: This interval is separated from the rest of the in-
vestigated section by a minor fault (presumably without a
noteworthy displacement (Rožič, pers. comm.)). It starts
with a few thin limestone beds, some of them dolomitized in
the lower part, with mudstone to packstone textures. Some
of them exhibit cross-lamination and bioturbations (Diplo-
craterion). Juvenile ammonites were also found. Dolomiti-
zation obviously took place from the bed boundaries towards
the interior of the beds, sometimes extending only to the first
stylolite (Fig. 7.6).
A massive dolomite bed follows, then two thicker beds of
limestone, strongly stylolized. Small (1 cm thick) lenses with
a packstone texture and a normal grading occur within the
wackestones. The wackestones are typified by a parallel, cross
or convolute lamination, dolomitized at the upper boundary. A
single, seemingly massive (540 cm), bed follows, but different
textures (10 to 100 cm thick packstone and wackestone hori-
zons, separated by pronounced stylolites) indicate several dep-
ositional events, in a short time, with the sediment from each
being compressed together during compaction (i.e. pounded).
Parallel, cross-lamination and normal grading are visible. An-
other compacted bed follows, but with individual beds more
clearly separated into 10—15 cm thick parts with wackestone
and packstone textures.
Amalgamated medium—thick beds of dolomite, an amal-
gamated “massive” limestone bed and a massive (perhaps
pounded thinner beds) dolomite bed follow. The uppermost
part of the investigated section consists of medium—thick do-
lomite beds and some limestone (mudstone) beds.
Eight microfacies types (MF) were distinguished (Fig. 5):
MF 1 (calcilutite), MF 2 (pelagic bivalve-radiolarian float-
stone/wackestone to rudstone/packstone), MF 3 (dolomitized
Fig. 5. Summarized characteristics of the recognized microfacies (MF) types. Comparison with the Standard Microfacies Types (SMT) af-
ter Flügel (2004) is given in the last column.
mudstone) with three sub-types, MF 3-LamD (laminated brec-
cia mudstone matrix), MF 3-LamB (laminated mudstone of
bedded dolomites) and MF 3-Mix (mixed mudstone), MF 4
(bioturbated radiolarian-spiculite wackestone), MF 5 (fine pe-
loidal-bioclastic packstone), MF 6 (very fine peloidal pack-
stone), MF 7 (bioclastic wackestone) and MF 8 (crystalline
dolomite). Two of these, namely MF 3 and MF 8, represent
completely dolomitized samples. Accordingly, their primary
sedimentary textures are not preserved and their interpretation
is therefore speculative. The composition of the rest of the MF
types is summarized in Fig. 6.
MF 1 (calcilutite) (Fig. 8.1)
Characterization: Laminated calcilutite with rare echino-
Components: Echinoderm remains (5 %).
Detailed description: The MF 1 was found in the upper,
non-dolomitized, limestone microspar part of a 12 cm thick
bed of marly dolomite with chert nodules in Interval B. The
lower part of the same bed is dolomitized and included in the
MF 3-LamD. The MF 1 was also found in a thin limestone
bed in the lower part of Interval J (Fig. 3). The micritic
matrix is finely laminated. Echinoderm grains have syntaxial
overgrowths (neomorphic spar).
MF 2 (pelagic bivalve-radiolarian floatstone/wackestone
to rudstone/packstone) (Fig. 8.3)
Characterization: Alternations (less than 5 mm spacing)
of floatstones/wackestones with rare thin-shelled bivalves
and radiolarians and bivalve coquinas (rudstones/packstones
Components: Juvenile thin-shelled bivalves and radiolarians
are the main constituents. The bivalves (5—40 %, average 25 %
of an area) form up to 0.5 cm thick coquinas or are dispersed in
the micritic matrix. Their valves are up to 5 mm long but in
some horizons they are smaller than 500 µm (wackestone and
packstone). Valves are connected or separated. They are slightly
curved, with smooth or costate convex sides. The inner struc-
ture of the valves is occasionally preserved, with a thicker inner
prismatic layer composed of slightly curved calcite columns. In
other cases the shells are silicified and consist of microcrystal-
line quartz (subangular grains, up to 7 µm in diameter, some-
times elongated, with the longer axis perpendicular to the rim of
the valve) or fibrous chalcedony (in larger voids).
Around 100 (up to 500) µm large spheres, completely
filled by microcrystalline quartz or calcite spar were inter-
preted as radiolarians (1—30 %, on average 10 %). Simple
spines were observed in a few cases.
Peloids (1—15, on average 5 %), intraclasts, small benthic
foraminifers (nodosariids), echinoderm fragments and small
ostracods are subordinate. The peloids are well sorted,
rounded to subangular, up to 180 µm in size. Larger intra-
clasts consist of micritic matrix with radiolarians and sponge
The micritic matrix, on average, represents 60 % (locally
up to 98 %, but sometimes less than 40 %) of the area.
Detailed description: The MF 2 was recognized in
Interval C in thin-bedded black limestones with chert
nodules, intercalated with marlstones (Fig. 3; Fig. 7.3). Due
to the alternation of floatstone/wackestone and rudstone/
packstone textures, this microfacies is heterogeneous. The
transition from the bivalve dominated rudstone/packstone to
the bivalve-radiolarian floatstone/wackestone is sharp, but
the rudstone/packstone sometimes passes into the floatstone/
wackestone more gradually, probably due to a bioturbation.
The MF 2 has a distinctly laminated appearance also be-
cause of the horizontally oriented bivalve valves, which are
oriented with their convex sides up or down. Among the rare
foraminifers, lagenids and Variostoma sp. were recognized.
The former species is present in the coquina layers, while the
latter occurs directly beneath the coquina and in the float-
Some horizons are clearly bioturbated, with valves pushed
aside and oblique to the bedding plane. Shelter porosity was
often present beneath the valves, later filled with a spar
(Fig. 8.3). Silicification is restricted to very narrow horizons,
but does not seem to be related to the proportion of radiolari-
ans in thin-section. Calcitic and silicified laminae thus appear
close together. Small stylolites and dissolution seams are par-
allel or oblique to the bedding. Small euhedral crystals of do-
lomite usually occur in small quantities (less than 1 %), with
rare exceptions of almost totally dolomitized horizons. An en-
hanced dolomitization was observed among and along stylo-
lites, while the silicification seems to avoid dissolution seams.
Remarks: The MF 2 corresponds to the SMF 3-Fil (“Thin-
shelled pelagic bivalve (‘filaments’) wackestone”) of Flügel
(2004). The coquina horizons might represent periodic blooms
of pelagic bivalves (note that the bivalves are juvenile), alter-
nating with periods of only background deposition of hemipe-
lagic mud and radiolarians. The latter are also present in the
Fig. 6. Relative proportions of constituents in the distinguished MF
types (MF 3 and 8 are not shown, as no constituents could be distin-
guished due to the late-stage dolomitization).
MICROFACIES ANALYSIS OF THE UPPER TRIASSIC “BAČA DOLOMITE” (SLOVENIA)
Fig. 7. 1 – View of part of the Mt Slatnik section. Bedded dolomites with chert nodules of the “Bača Dolomite”. 2 – A channel (scour)
structure in the “Bača Dolomite”. 3 – Intercalations of marlstone, marly limestone and thin-bedded limestone with chert nodules. Lime-
stone beds are rich in small thin-shelled bivalves (MF 2). 4 – A limestone bed with numerous sedimentary structures, including parallel
lamination (P), load-casts (black arrow-head) and normal grading (N). Several closely-spaced depositional events are possible. Larger bio-
clasts (white arrow head) near the upper bedding plane probably settled late from suspension due to a larger buoyancy. 5 – Clast-supported
debris flow breccias. Clasts are angular cherts (C) and laminated fine-grained dolomites (intraclasts; I). 6 – Late-stage dolomitization,
advancing from the upper bedding-plane towards the interior of the limestone bed, but mostly stopped by the stylolite.
Fig. 8. 1 – A thin-section of MF 1 (calcilutite). Scale bar is 5 mm. 2 – A thin-section of laminated dolomite from the breccia matrix
(MF 3-LamB). Sedimentary structures are mostly visible, while textures are completely obliterated by dolomitization. Scale bar is 5 mm.
3 – The pelagic bivalve-radiolarian rudstone (MF 2). The shelter-type umbrella porosity is developed beneath valves. Radiolarians are calci-
fied. Scale bar is 1 mm. 4 – Radiolarian-spiculite wackestone (MF 4). A calcified radiolarian with simple spines is in the centre. Scale
bar is 200 µm. 5 – Fine peloidal-bioclastic packstone (MF 5) with a micritic matrix partly winnowed away. Peloids (P), green algal genicula
(G), small foraminifers (F), echinoderm fragments (E) and ostracod valve (O) can be seen. Note the point contacts between the grains (arrow
head) and the slight imbrications towards the right. Part of a large intraclast (MF 4) is visible at the bottom (I). Scale bar is 1 mm. 6 – Very
fine peloidal packstone (MF 6) with a micritic matrix partly winnowed away (perhaps recrystallized). Note the imbrications towards the right.
Scale bar is 200 µm. 7 – Bioclastic wackestone (MF 7) of the transitional character, having large allochthonous particles (mostly echinoderm
fragments; E) admixed with pelagic biota (in this case thin-shelled bivalves; B). Scale bar is 500 µm. 8 – Late-stage dolomite of MF 8. No
sedimentary structures and textures are preserved. Scale bar is 200 µm.
MICROFACIES ANALYSIS OF THE UPPER TRIASSIC “BAČA DOLOMITE” (SLOVENIA)
coquina layers, indicating that the (hemi)pelagic settling also
took place during the bivalve blooms. An alternative explana-
tion would be the presence of weak bottom currents, also indi-
cated by the parallel orientation of the valves and the
somewhat lens-shaped accumulations. Alternatively, the bi-
valve shells, as well as some radiolarians, could be accumulated
by storm waves, but no evidence (for example no hummocky
cross-stratification) for the latter has been found. The presence
of bottom currents, supplying oxygen to the sea bottom, could
also be indicated by intense burrowing.
Stylolites and dissolution seams that are parallel to the
bedding-plane are compactional in nature, whereas oblique
ones are tectonically induced. The majority of peloids are
probably micritized clasts or rip-up clasts (intraclasts).
The SMF 3 indicates a basin or an open deep-sea environ-
ment (Flügel 2004).
MF 3 (dolomitized mudstone)
Three submicrofacies types, which were greatly obliterat-
ed by dolomitization, are joined in microfacies type MF 3.
Sedimentary textures in MF 3 can no longer be recognized,
but unlike in MF 8, the structures are still visible. Submicro-
facies MF 3-LamB and MF 3-LamD are virtually indistin-
guishable in thin-sections. However, they are kept separated
as they occur in markedly different types of beds (namely in
different facies). All subtypes of MF 3 probably represent
autochthonous deep-water deposits which were in the case of
the MF 3-LamB deformed soon after deposition (i.e. prior to
total lithification, but after the formation of chert nodules, as
these are brecciated).
Submicrofacies MF 3-LamB (laminated mudstone breccia
matrix) (Fig. 8.2) and MF 3-LamD (laminated mudstone of
Characterization: Completely dolomitized microfacies
with recognizable (mostly parallel) lamination.
Components: No primary constituents were preserved.
Detailed description: The MF 3-LamB was found in the ma-
trix of the massive breccias in Interval A, whilst MF 3-LamD
was encountered in the thin-bedded marly dolomite of
Intervals B and J. It was also found in the dolomitized part of a
thin bed with MF 1 in its upper, limestone part. The lamination
is parallel or oblique to the bedding and is caused by differences
in size of the dolomite crystals, as well as by lenses and bands
(laminae) enriched in organic matter. Calcite veins are some-
times inserted in laminae partings. The dolomite crystals are
subhedral and closely linked together. Three size-classes were
recognized: 15—20 µm, 35 µm and 55—70 µm. Most of the
crystals have brown-stained cores. Stylolites are present.
Remarks: The MF 3-LamB could represent a dolomitized
equivalent of the SMF 1 (“Spiculite wackestone or pack-
stone, often with a calcisiltite matrix”) of Flügel (2004).
Submicrofacies MF 3-Mix (mixed mudstone)
Characterization: A completely dolomitized microfacies
with a mixed appearance, most probably due to a bioturbation.
Components: Not preserved, with the rare exception of
Detailed description: The subtype MF 3-Mix appears in
some thin- and medium-bedded dolomite and marly dolo-
mite beds. In one example, MF 3-Mix was in sharp contact
with MF 5. As in MF 3-Lam, different sizes of dolomite
crystals allowed recognition of probable bioturbations in
hand specimens. Convolute lamination cannot be excluded.
Subhedral dolomite crystals measure 15 µm, 35 µm, 50—60 µm
and 90 µm in diameter. Stylolites are present.
Remarks: Caution also regards this MF type. However, it is
possible, that the MF 3-Mix corresponds to Flügel’s (2004)
SMF 1-Burrowed (“Burrowed bioclastic wackestone with
abundant fine pelagic and benthic biodetritus”). Bioturbation
would indicate an oxygenated bottom. The SMF 1-Burrowed
occurs in basin, open-sea shelf and outer-ramp environment
MF 4 (bioturbated radiolarian-spiculite wackestone)
Characterization: Wackestone with radiolarians, sponge
spicules and rare thin-shelled bivalves, with an admixture of
allochthonous material, mostly echinoderms. Bioturbations
Components: The MF 4 is characterized by a large propor-
tion of micritic matrix (85—90 %), relatively numerous radio-
larians (4—7 %) and sponge spicules (0.5—3 %). The
radiolarians are calcified and 90—290 µm in diameter. Other
components include angular, 50 µm large peloids (3 %), sub-
angular, 160 µm large intraclasts, echinoderm remains
(7 %), thin-shelled bivalves, sparitic shell (bivalves) and
brachiopod fragments, and foraminifers.
Detailed description: The MF 4 often occurs in association
with MF 5 and the MF 6 in thin- or medium-bedded limestones
with a parallel lamination and a gradation in Intervals C, E, G
and J. When overlain by MF 5 or 6, the boundary is erosional.
The boundaries are sometimes stylolized. The MF 4 is often
bioturbated. Locally, lenses of MF 6 are present and sometimes
an imbrication occurs. A weakly expressed parallel lamination
is occasionally visible. Foraminifers Duotaxis nanus (Kristan-
Tollmann), trochamminids, Lenticulina sp. and Dentalina sp.
An intraparticle cement includes blocky, sometimes mosa-
Remarks: The MF 4 corresponds to the SMF 1-Burrowed
of Flügel (2004). The mixing of autochthonous and alloch-
thonous material might be the result of bioturbation and/or
weak current activity (as indicated by the lenses of MF 6 and
local imbrications). The bioturbation points towards an oxy-
genated bottom and relatively slow sedimentation.
MF 5 (fine peloidal-bioclastic packstone) (Fig. 8.5)
Characterization: Fine peloidal-bioclastic packstone, locally
with large intraclasts (floatstone), commonly graded and imbri-
cated. A micritic matrix is in places winnowed or recrystallized.
Components: Up to 20 µm large intraclasts, which repre-
sent 25 % of the thin-section area are characteristic of this
MF type. They are often limited to the basal part of MF 5
and closely resemble the other MF types, namely MF 1,
MF 4, MF 6 or dolomitized micritic clasts.
The majority of the volume is occupied by a fine (mean
size 125—250 µm) peloidal-bioclastic packstone. It consists of
40—50 % of matrix, 25—52 (average 40 %) of peloids, 1—5 %
(3 %) of echinoderms, 1—8 % (3.5 %) of recrystallized shell
fragments (molluscs), 1 % of foraminifers and 1 % of spheru-
lites. Intraclasts, ostracods and brachiopod fragments each
represent 0.5 % of the grains, while microgastropods, green
algae, sponge fragments and calcimicrobe ?Cayeuxia are
rarely found. The peloids are 40—450 µm large (mean size
250 µm), well sorted and rounded or subrounded. The bio-
clasts commonly have micritic envelopes and abraded
(rounded) edges. The spherulites are most probably radiaxial
ooids, up to 700 µm large, but mostly smaller than 200 µm.
Some concentric laminae are visible.
Detailed description: The MF 5 was recognized in
Intervals C, E, G, I and J in black, amalgamated, thin, medi-
um and in one case thick-bedded limestone, whose lower
part was completely dolomitized. It is closely associated
with MF 4 (MF 5 overlies MF 4 with a sharp, erosional con-
tact), MF 6 (MF 5 is below MF 6; the contact with MF 6 is
sharp, but probably not erosional) and MF 7 (MF 5 gradually
passes into MF 7). Intraclasts are most often directly derived
from the underlying MF 4 and represent the largest particles,
being in sharp contrast to the rest of the sediment as the latter
is very well sorted. Normal grading, imbrication and geo-
petal textures are most common, while inverse grading is
rare. Shelter porosity was later filled by cement. Several
normally-graded horizons up to 1 cm thick may follow one
another, or exchange with MF 6. Grains are in point or line
contacts. In the latter case, fragmentation of elongated grains
(namely brachiopod shells) is observed.
Several foraminiferal taxa were recognized, among them
Galeanella panticae Zaninetti & Brönnimann in Brönnimann,
Cadet, Ricou & Zaninetti, Galeanella tollmanni Kristan,
Palaeolituonella meridionalis (Luperto), Endotriada tyrrhenica
Vachard, Martini, Rettori & Zaninetti, Planiinvoluta deflexa
Leischner, Tolypammina sp. and Duostominidae.
Syntaxial overgrowth cement is common around echino-
derm fragments and intraskeletal spaces are filled with
blocky calcite. Where micrite is winnowed, grains are lined
with isopachous rims of equant calcite and the intergranular
spaces are filled with blocky spar, sometimes dolospar. A
microquartz locally replaces parts of the matrix (small patch-
es, bands). Euhedral dolomite crystals are locally abundant.
Some bioclasts, especially the central parts of echinoderm
plates and shells, are silicified. When present, stylolitization
is strong, with an amplitude of several centimeters, bringing
MF 5 into sharp, sutured contact with MF 4 and MF 6.
Remarks: Both MF 5 and MF 6 have a packstone texture, al-
though the micritic matrix is partly winnowed and the pores
are filled by orthospar or recrystallized into pseudospar. The
distinction between MF 5 and MF 6 is based on grain size.
The MF 5 corresponds to the SMF 4 (“Microbreccia, bio-
clastic-lithoclastic packstone or rudstone”) of Flügel (2004).
Arenaceous allochems in MF 5 are of a shallow-water ori-
gin, probably derived from an adjacent carbonate platform.
Sponges, ?Cayeuxia and some foraminifers in particular (for
example, Galeanella and Planiinvoluta) indicate the coeval
existence of a reef. Several reefs are indeed known to have
rimmed the Julian Carbonate Platform (Buser et al. 1982;
Turnšek & Buser 1991). Intraclasts, on the contrary, origi-
nate very close to the place of final deposition. A longer
transport path of the sandy material is indicated by its sorting
as well. Micritic envelopes, fragmentation and abrasion indi-
cate a pre-reworking taphonomic history for these particles.
Normal grading, the occurrence in laminae (sometimes in
several successive events) and small grain size correspond to
very distal turbidity current deposits (Tucker 2001). The im-
brications and the winnowed micritic matrix also point to-
wards some kind of current control (Watts 1987). The
inversely-graded horizons may be interpreted as modified
grain-flow deposits (Watts 1987).
The SMF 4 occurs in basinal and toe-of-slope settings
MF 6 (very fine peloidal packstone) (Fig. 8.6)
Characterization: Very fine, well-sorted peloidal pack-
stone. The micritic matrix is winnowed in places.
Components: Grains represent 50 % of the area and are domi-
nated by peloids (40 %). These probably include peletoids, as
well as true faecal pellets. Their average size is 70—90 µm.
Other constituents are subordinate: echinoderms (3 %), neo-
morphically altered shell fragments with micritic envelopes
(4 %), foraminifers, ooids and ostracods (each 1 %), very rare
intraclasts, brachiopods and gastropods.
Detailed description: The MF 6 is mainly found in thin-
and medium-bedded, often amalgamated, occasionally par-
tially dolomitized limestones in Intervals C, E, G, I and J. It
is in a sharp, planar contact with MF 4 or MF 5. It can also
appear as small lenses in MF 4. Inverse and normal grading
is visible, as well as imbrication. Peloids are well sorted and
in a point-contact. Some bioclasts have been silicified. Pores
are filled with syntaxial and blocky spar.
Remarks: The MF 6 corresponds to the SMF 4 of Flügel
(2004). It is interpreted as a distal turbidity deposit, finer-
grained than MF 5. The erosive potential was weaker than
that of MF 5, thus no rip-up clasts (intraclasts) were incorpo-
rated in the flow. Lenses of MF 6 in MF 4 could indicate re-
deposited material via bottom currents or bioturbation.
MF 7 (bioclastic wackestone) (Fig. 8.7)
Characterization: Wackestone with mixed shallow and deep-
water (radiolarians, spicules, thin-shelled bivalve) fossils.
Components: The micritic matrix represents 70—80 % of the
area. Grains are thin-shelled bivalves (7 %), peloids (11 %),
echinoderms (4.5 %), neomorphically replaced shell frag-
ments (1.5 %), foraminifers (0.5 %), brachiopods (0.5 %), ra-
diolarians, spicules and spherulites (ooids). Echinoderm
grains are the largest.
Detailed description: The MF 7 was found in Intervals C,
E, G, I and J. It often lies above MF 5 and MF 6. The transi-
tion from these two MF types is gradual, marked by an in-
crease in the matrix proportion, larger but fewer grains, and
MICROFACIES ANALYSIS OF THE UPPER TRIASSIC “BAČA DOLOMITE” (SLOVENIA)
the presence of pelagic fauna. A bioturbation is sometimes
visible, occasionally reaching into the underlying MF types.
Remarks: The MF 7 represents the transition from alloch-
thonous (MF 5, 6) to autochthonous deposition. The rate of
allochthonous deposition decreased and background hemipe-
lagic sedimentation took over, allowing benthos to populate
the sea bottom after disturbance by turbidites (MF 5, 6).
MF 8 (crystalline dolomite) (Fig. 8.8)
Completely dolomitized samples without preserved struc-
tures and textures were classified into this microfacies type.
It was found in Intervals B, D, G and I. Three types of dolo-
mite crystals were distinguished: 1) planar-euhedral, brown-
stained crystals; 2) subhedral crystals with polymodal size
distribution and 3) anhedral, vug-filling dolomite.
The planar-euhedral dolomite crystals were probably the
first to form. They are rhomb-shaped, with straight, planar
boundaries and brown-stained due to an increased Fe content.
The crystals are not in contact with each other and are either
rare or abundant. They are always included in the cores of the
dolomite crystals of the second generation, namely in the pla-
nar-subhedral dolomite crystals. These are predominant, in
close contact and completely obscure primary sedimentary
structures. Very few ghosts of echinoderms are found. Crys-
tals display a polymodal size distribution, with the main size
classes of 35 µm, 50 µm, 90 µm and 180 µm. When facing
pores (vugs), crystal faces are well developed. Banding in out-
er parts is sometimes visible in such cases, probably as the re-
sult of the evolving composition of pore fluid.
The separation of the first and the second generations of do-
lomite is based on the following arguments: not all subhedral
crystals contain euhedral cores; euhedral cores (first genera-
tion dolomite) have abundant inclusions of previous carbon-
ate, while these are rare in clear, subhedral crystals and in rare
cases subhedral crystals are poikilotopic, that is they include
several brown rhombic euhedral crystals of the first genera-
tion. The third generation of dolomite is rarely present in the
form of anhedral crystals filling rare vugs. The presence of at
least three generations of dolomite was recently confirmed
using cathodoluminescence, but more data is needed.
Several phases of silification are also present. The first
phase is characterized by the formation of chert nodules and
the silica-replacement of some fossils penecontemporane-
ously with the first dolomite generation. The second phase is
of a late-stage origin, filling voids after the second and possi-
bly the third generation of dolomite.
Sedimentary evolution of the Slovenian Basin during the
The observed MF types are strikingly similar to the associ-
ation from the Middle Triassic of the Dolomites, Italy (in
Flügel 2004). Unit A1 (“basal lithobioclastic grainstone”)
corresponds to MF 5 and is interpreted as a proximal calci-
turbidite. Unit A2 (“admixture of pelagic biota and echino-
derms”) and/or Unit D2 (“alternation of platform-derived
material and pelagic grains”) correspond to MF 7. Unit B
(“radiolaria packstone with bioturbations”) is equivalent to
MF 4, while Unit C (“lithobioclastic packstone” with small-
er and better sorted clasts than in Unit A) corresponds to
MF 6. Unit D1 (“coquina floatstone”) can be considered a
bioturbated version of MF 2.
Thin-sections of the matrix of the lower breccias
(Interval A) belong to MF 3-LamB. Chert nodules are brec-
ciated (brittle deformation), as they were lithified prior to
displacement, while the laminae of the matrix are only dis-
torted (plastic deformation), thus the sediment was not com-
pletely lithified. The fitting of the chert clasts (mosaic chert)
and the preserved lamination of the matrix indicate a rela-
tively minor internal deformation of the sediment and a very
short transport. Accordingly, the breccias may have been
formed via slides (only minor internal deformations) or
slumps (internally deformed), which had not yet progressed
into debris flows (see Stow et al. 1996). Nebelsick et al.
(2001) noticed slightly inclined, fine-bedding towards the
top of some of the debrites in the Oligocene of Austria, simi-
lar to oblique-to-bedding laminae at the top of one of the
breccia beds in the Mt Slatnik section.
The bedded dolomite above the breccias (Interval B), dis-
playing MF 3-LamD microfacies, possibly represents an un-
disturbed, stable sea-floor sediment, perhaps due to abated
tectonic activity or simply to a deeper depositional environ-
ment. The fine lamination suggests oxygen-depleted condi-
tions (Haas 2002), distal turbidites or (more likely) weak
The MF 2 is found only in limestones of Interval C. These
sediments were probably deposited in a quieter environment,
sporadically disturbed by distal turbidites (MF 5, 6, 7). A
similar alternation of hemipelagic limestones and marlstones
was recorded by Watts (1987). Siliciclastic intervals might
represent periods of reduced carbonate sedimentation, in-
creased carbonate dissolution or increased influx of terrige-
nous mud (Watts 1987). According to plant remains, the last
explanation seems the most likely in our case. Calcareous
mud with pelagic bivalves and radiolarians (MF 2) thus rep-
resents background sedimentation, occasionally punctuated
by turbidite deposition and increased river runoff. An en-
hanced terrigenous influx might indicate a period of a more
humid and seasonal (monsoonal) climate (Watts 1987).
The next few meters (Interval D) are made up of medium-
and thin-bedded cherty dolomite beds characterized by MF 3.
Virtually absent turbidite deposits and a predominance of
thin-bedded dolomites with chert might indicate deposition on
a basin plain. The limestone beds of Interval E contain MF 4,
5, 6 and 7, indicating enhanced turbidite deposition. The final
slope progradation is marked by the second breccias interval
(Interval F). Because the matrix is still laminated, the term
slump would be the most appropriate. The intraclasts are an-
gular, yet often plastically deformed and were not completely
lithified. The depositional basin started to progressively deep-
en for the second time. The predominant turbidity deposits
(MF type 6), interfingering with the autochthonous hemipe-
lagic sediments (MF 4, transitional MF 7 in Interval G), grad-
ually progressed into the cherty bedded-dolomites with
microfacies type MF 3 of Interval H. The predomination of
subtype MF 3-Mix indicates oxygenated sea-floor. The ap-
pearance of MF 5 and 6, interfingering with the autochthonous
deposits (MF 3-Mix, 4, 7), marks a new progradation phase
(Intervals I and J). Some of the turbidite sediments were re-de-
posited by grain flows, as indicated by the thin bands with
straight boundaries (around 205
m in Fig. 3). The deposition-
al system became shallower, with the “Bača Dolomite” pass-
ing upwards into the Slatnik Formation, which contains
thicker and coarser-grained limestone beds.
No transitional zone between the Slovenian Basin and the
Julian Carbonate Platform has been found so far for the
Upper Triassic, but Rožič & Šmuc (2006, 2009) have recog-
nized such a zone for the Jurassic sediments in the neigh-
bouring tectonic block, showing no by-pass zone. The
observed MF association fits into the Facies Zone 1 (“Deep
sea or cratonic deep-water basin”) of Flügel’s (2004) rimmed
carbonate slope apron model.
Two facies shifts (retrogressive-progressive cycles) were
recognized: from the inner apron with the mud-supported
debris flow breccias (“Facies F”), into the turbidite-dominat-
ed (“Facies D”) outer apron, and in turn to the basin plain
with the distal turbidites (“Facies D”) interbedded with the
peri-platform or pelagic oozes (“Facies G”), then back in
reverse order to finish each cycle.
A similar interpretation has been offered for the Upper Tri-
assic Hármashatár-hegy Basin in the Buda Hills of Hungary,
with proximal toe-of-slope (breccias), distal toe-of-slope
(fine-grained wackestones and turbidites), oxygen-depleted
basin (laminated carbonates and marlstones) and oxygenated
basin (peloidal wackestones, sponge-spicule, radiolarian and
bioturbated wackstones-packstones) settings (Haas 2002).
Several previously mentioned depositional features, namely
imbrication, the alignment of pelagic bivalve shells and spi-
cules, the occasionally observed cross-lamination and ripples,
bioturbation and the lack of a micritic matrix due to winnow-
ing, point towards occasionally present weak bottom currents.
The Dachstein-type reef-rims around neighbouring platforms
(Buser et al. 1982; Turnšek & Buser 1991) also imply good
water circulation (Iannace & Zamparelli 2002). The above
mentioned data, as well as the long-term existence of the
Slovenian Basin are in contrast to the shallower, more restrict-
ed intraplatform basins (see for example Cozzi & Podda 1998;
Iannece & Zamparelli 2002; Tomašových 2004).
Recognition of the regular variations in the input material,
namely in the redeposited grains of calciturbidites, as was
done by Reijmer et al. (1991), is probably not possible due to
dolomitization of most beds, but a strong predominance of
reef-derived foraminifers (see Senowbari-Daryan 1980;
Wurm 1982; Kuss 1983; Martini et al. 2009) in some of the
studied samples suggests that such variations do exist.
The “Bača Dolomite” compared to the Slatnik Formation
At the type locality (Mt Kobla; Fig. 1C) the Slatnik Forma-
tion consists of a finer-grained lower part (predominantly mi-
critic limestones and turbidites) and a coarser-grained upper
part (limestone conglomerates, calcarenites and hemipelagic
limestones) (Rožič 2006). At Mt Slatnik, following the de-
scribed section of the “Bača Dolomite”, the Slatnik Formation
predominantly consists of calcarenites, pebbly calcarenites
and clast-supported conglomerates, subordinately hemipelagic
limestones (Rožič et al. 2009). As the lower boundary with the
“Bača Dolomite” is a thrust, some doubt exists as to whether
only the upper part of the Slatnik Formation is preserved.
However, Rožič et al. (2009) concluded that the dislocation
along the thrust is minor. In any case, the Slatnik Formation at
Mt Slatnik contains thicker and coarser-grained beds. Deposi-
tion took place on the inner apron, passing to the upper slope
(Rožič et al. 2009), thus in a shallower environment than for
the underlying “Bača Dolomite” (this paper).
Furthermore, within the general trend of the progradation,
three lower-order retrogressive-progressive cycles were
recognized in the upper 32 m of the “Bača Dolomite” and
the Slatnik Formation. Based on the conodonts, the first of
these cycles is of the Late Norian (middle Sevatian) age
(Rožič et al. 2009). Combined with the two cycles recog-
nized in the investigated “Bača Dolomite” from the same
section, five lower-order cycles can be assumed for the
whole Norian-Rhaetian sequence.
The “Bača Dolomite” represents bedded or massive dolo-
mites with chert, deposited in the Slovenian Basin during the
Norian and Rhaetian (Buser 1986) and has been poorly in-
vestigated until now. In the Mt Slatnik section, some carbon-
ate beds within the “Bača Dolomite” have not been
dolomitized, offering a unique opportunity for research into
its depositional environment.
The following conclusions were reached:
– Eight microfacies types (MF) were recognized: MF 1
(calcilutite), MF 2 (pelagic bivalve-radiolarian floatstone/
wackestone to rudstone/packstone), MF 3 (dolomitized
mudstone) with three sub-types, MF 3-LamB (laminated
mudstone breccia matrix), MF 3-LamD (laminated mudstone
of bedded dolomites) and MF 3-Mix (mixed mudstone),
MF 4 (bioturbated radiolarian-spiculite wackestone), MF 5
(fine peloidal-bioclastic packstone), MF 6 (very fine peloidal
packstone), MF 7 (bioclastic wackestone) and MF 8 (crystal-
– The MF 1, 2, 3, 4 and 7 represent predominantly hemi-
pelagic sediments. The latter two types contain admixed re-
deposited clasts. The MF 5 and 6 formed via diluted,
low-density turbidite currents.
– Distribution of the MF types throughout the section cor-
responds to the facies distribution. Together they reflect shifts
in the depositional environment. Two complete retrogressive-
progressive cycles were recognized: from a proximal slope
apron (massive debris-flow breccias; MF 3-LamD), to a more
distal slope apron (hemipelagic deposits – medium-bedded
cherty dolomites or limestones of MF 1, 3-LamD, 4, 7 and
thin-bedded cherty coquina limestones of MF 2, exchanging
with distal turbidites – thin- to medium-bedded limestones
MICROFACIES ANALYSIS OF THE UPPER TRIASSIC “BAČA DOLOMITE” (SLOVENIA)
with or without chert and MF types 5 and 6), to a basin plain
(thin- and medium-bedded dolomites with chert, MF 3-Mix),
followed by the reverse trend.
– The “Bača Dolomite” was deposited in a more distal
setting than the overlying Slatnik Formation, thus a general
trend of progradation is proposed.
– Five lower-order retrogressive-progressive cycles were
recognized in the Norian and Rhaetian sediments of the Slo-
venian Basin, two of them being recorded for the first time.
Acknowledgments: This research was financially supported
by a grant from the Slovenian Research Agency. My sincere
thanks go to Dr. B. Rožič from the Faculty of Natural Sci-
ences and Engineering, University of Ljubljana, Dr. D.
Skaberne, Dr. B. Ogorelec and J. Atanackov from the Geo-
logical Survey of Slovenia for their guidance and for their
comments on the draft version of this paper. Special thanks
go to the reviewers, Dr. J. Michalík, Prof. Dr. J. Haas and Dr.
C. Scheibner for their very constructive remarks.
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