GEOLOGIJA 33, 315-351 (1990), Ljubljana
UDK 551.762:550.4(497.12) = 20
Stratigraphy and geochemistry of Jurassic carbonate
rocks from Suha krajina and Mala gora mountain
(Southern Slovenia)
Christian Strohmenger
BEB Erdgas und Erdöl GmbH
Riethorst 12, D-3000 Hannover 51
Stevo Dozet
Geološki zavod Ljubljana, Dimičeva 14, 61000 Ljubljana
Abstract
Detailed sedimentological investigations have been carried out in the section
Kompolje-Ogorelec at the Mala gora mountain, and in the section Krka-Mali
Korinj at Suha krajina about 35 km SSE from Ljubljana (NW Yugoslavia). In both
sections a complete sequence of the Jurassic calcareous beds is exposed, including
the contacts between the Upper Triassic and the Lower Lias, and the Upper Malm
and the Lower Cretaceous. The field studies showed that at least the uppermost
part of Dogger was not deposited. The thickness of the Jurassic sequence is about
1500 m. The stratigraphie relationships have been established by means of micro
- and macrofossils, and by lithologie comparisions. The interpretation of microfa-
cies has been supplemented by geochemical, micropaleontological and some other
analyses. A polymict karst breccia within the Lower Malm beds proves a long
lasting emergence of the carbonate platform during the Upper Malm; it is appa-
rently the equivalent of the bauxite horizon commonly developed between the
Lower and the Upper Malm in Slovenia. The distribution of trace elements follows
the trends implied by the microfacies analyses.
Introduction
Jurassic carbonate deposits exposed SSE of Ljubljana consist of well developed
sequences of shallow subtidal, intertidal and supratidal fades. These carbonates
were studied at two different localities named section 1 and section 2 (Fig. 1). The two
sections are documented by about 800 samples. By means of aceton peels (all
samples), thin sections (selected samples), X-ray diffraction (all samples), scanning
electron microscopy and geochemical analyses (carbonate content and atomic ab-
sorption; all samples) the microfacies, diagenesis, geochemistry and the stratigraphy
of the carbonates were investigated.
The stratigraphie and tectonic evolution of the two sections is the main subject of
the present paper.
The appendix (section 1, section 2) gives a compilation of these studies together
with the results of the geochemical analyses.
316	Christian Strohmenger & Stevo Dozet
Section 1
Section 1 is situated in the Mala gora mountain about 35 kilometers SSE of
Ljubljana (Fig. 1). A series of carbonate rocks (Middle Lias to Upper Malm) is well
exposed directly at the path which starts near the village of Kompolje and leads up to
a site called Ogorelec (about 950 m).
Due to the strong tectonic overprint it is very difficult to determine the strati-
graphy of these carbonates.
Micropaleontological investigations and field observations helped to identify two
evident faults and two presumed ones within beds of the Lower Malm (Fig. 2,
Appendix: section 1, c-d, g). In addition, one fault separates the stromatolitic
carbonates of the Upper Malm from Lower Malm (Dogger?) carbonates with interca-
lated ooid grainstones (Fig. 2, Appendix: section 1, f). The latter were thought to be of
Upper Malm age by Strohmenger et al. (1987, b) but it is now clear (Buser, 1987
pers. com.) that they are upthrusted carbonate rocks of the Lower Malm (Fig. 3).
Beside these obvious repetitions of Lower Malm strata, also the contact of the Lower
Malm and the Upper Malm appears to be slightly tectonically overprinted (Fig. 2,
Appendix: section 1, e).
It is possible that section 1 contains some more minor faults which could not be
identified due to the locally insufficient outcrops.
These tectonical faults never represent overthrusts. They are on the contrary
clearly upthrow faults of which the net slip has an upward directed vertical compo-
nent.
Thicknesses of the Jurassic carbonate rocks are only of approximate values. Due
to the outcrop conditions the real thickness of the section can easily differ by some
tens of meters from the estimated value of about 1390 m.
Fig. 1. Location map of the investigated areas, section 1 and section 2;
Lj.: Ljubljana
stratigraphy and geochemistry of Jurassic carbonate rocks...	317
Fig. 2. Schematic column of the Jurassic carbonate rocks from Kompolje, section 1
U. L. Upper Lias; L. M. Lower Malm; Kimm Kimmeridgian; U. M. Upper Malm; D. Dogger
318	Christian Strohmenger & Stevo Dozet
Fig. 3. Upthrusted Lower Malm carbonate beds (left) juxtaposed to strongly tectoni-
zed Lower Malm strata (right). Section 1
Stratigraphy
By means of microfossils (foraminifera and dasycladaceans), corals and hydrozo-
ans (Tab. 1) it was possible to subdivide the carbonates in Middle Lias, Upper Lias?,
Dogger (Lower Dogger), Lower Malm and Upper Malm. In some cases it is not
possible to clearly separate the carbonates of the Dogger from those of the Lower
Malm. Therefore it cannot be excluded that parts of the Lower Malm (subdivided in
Lower Malm 1 to Lower Malm 4) are in fact belonging to the Dogger (Fig. 2,
Appendix: section 1).
Middle Lias
The subdivision of the Lias is very difficult due to the lack of good index fossils.
The subdivision presented here is done chiefly by lithostratigraphical considerations
(Fig. 2, Appendix: section 1, a-d).
Bus er (1974) describes the underlying and mostly dolomitic beds of section 1 as
Middle Lias. The only index fossil which could be found, the foraminifer Haurania
amiji Henson is not suitable to prove this assumption, but indicates that the descri-
bed carbonates are younger than Hettangian (Septfontaine, 1988).
Upper Lias?
The stratigraphie boundary between the Middle and Upper Lias is very arbitrary
(Fig. 2, Appendix: section 1, b). Unlike the ooid grainstones of the Middle Lais of
stratigraphy and geochemistry of Jurassic carbonate rocks...	319
Table 1. Index fossils of section 1
Age	Index Fossils
Middle Lias	Haurania amiji Henson
Upper Lias	-------
Lower Dogger Dictyoconus cayeuxi Lukas
^iraloconulus perconigi Allemann & Schroeder
Everticyclammina sp.
Mesoendothyra sp.
Mesoendothyra croatica GuSić
Lower Malm 1 Praekurnubia sp.
Kurnubia sp.
Kurnubia palastiniensis Henson
Heteroporella anici Nikler & Sokaö
Salpingoporella annulata Carozzi
Lower Malm 2 Praekurnubia sp.
Kurnubia sp.
Chablaisia sp.
Palaeosiphonium convolvens (Praturlon) Elliott ?
Cladocoropsis mirabilis Felix
Stylosmilia corallina Koby ?
Lower Malm 3 Praekurnubia sp.
Kurnubia sp.
Pfenderina sp.
Trocholina sp.
Trocholina gr. elongata Leupold
Trocholina elongata Leupold
Palaeosiphonium convolvens (Praturlon) Elliott
Juraella bifurcata Bernier ?
Cladocoropsis mirabilis Felix
Pleurophyllia sp. ?
Enhallhelia sp. ?
Chaetetopsis crinita Neumayr
Upper Malm	Labyrinthina mirabilis Weynschenk ?
Salpingoporella annulata Carozzi
Clypeina jurassica Favre
Parurgonina caelinensis Cuvillier
Aberrant Tintinnids:
Campbelliella striata (Carozzi) Bernier
* Campbelliella cf. milesi Radoičić
Dogger?	Siphovalvulina sp.
Lower Malm 4 Trocholina sp.
Trocholina gr. elongata Leupold
Trocholina elongata Leupold
Pfenderina sp. ?
Praekurnubia sp.
Kurnubia sp.
Valvulina a.ff . lugeoni Septfontaine
Cladocoropsis mirabilis Felix
Montlivaltia sp. ?
Stylosmilia corallina Koby ?
Parastromatopora Japónica Yabe & Sugiyama
section 2 which are extremely rich in microfossils (index fossils), the ooid grainstones
which overlay the dolomites of the Middle Lias (section 1) show nearly no biological
components. The ooid grainstones are followed by dark mudstones which pass into
dark wackestones/mudstones of undoubtedly Lower Dogger strata, until new data
are available, the oolitic beds and the overlying mudstones (which are also devoid of
index fossils) are attributed to the Upper Lias.
320	Christian Strohmenger & Stevo Dozet
Lower Dogger
The microfossils of the Dogger below the first presumed fault (Fig. 1, Appendix:
section 1, b-c) such as Mesoendothyra croatica Gušić, Spiraloconulus perconigi
Allemann & Schroeder Dictyoconus cayeuxi Lukas (synonym to Gutnicella cayeuxi
(Lukas) Gutnic & Moullade; Mo ul la de et al., 1981), all indicate to Lower Dogger
age or respectively to beds older than Callovian. The only indication of Upper Dogger
strata besides the foraminifer Praekurnubia sp. could give the alga Palaeosiphonium
convolvens (Praturlon) Elliott (see below).
Lower Malm
The carbonate rocks of the Lower Malm are strongly tectonized and can be
subdivided into four units (Lower Malm 1 to Lower Malm 4). They often contain an
obviously big quantity of foraminifera which, by use of the criteria stated by
Redmond (1964), must be ascribed to Praekurnubia sp. (Septfontaine, 1989
pers, com.). The absence of Kurnubia sp. makes Dogger age for large parts of these
carbonates very probable (see below).
Lower Malm 1
The carbonate rocks directly overlaying the beds of the Lower Dogger up to the first
evident fault are described as Lower Malm 1 (Fig. 2, Appendix: section 1, c-d). The
dominant fossil, however, is the foraminifer Praekurnubia sp. (Septfontaine,
1989 pers. com.) which is supposed to be of Dogger age, and not Kurnubia palastini-
ensis Henson (Radoičić, 1987 pers. com.) which is an index fossil of the Upper
Jurassic (Kimmeridgian). On the contrary, good indications of Lower Malm strata are
given by the alga Heteroporella anici Nikler & Sokač (Pl. 2, Fig. 1) and Salpingopo-
rella annulata Carozzi. The fossil assemblage of Heteroporella anici Nikler & Sokač,
Salpingoporella annulata Carozzi, Kurnubia palastiniensis Henson and/or Praekur-
nubia sp. seems very unusual. Keeping in mind the facies dependence of benthic
foraminifera, it may be suggested that the phylogenetic development of the species
Praekurnubia/Kurnubia is highly diachronous, which means that the species Pra-
ekurnubia in fact can be more frequent in Lower Malm carbonates than presumed.
The occurrence of Heteroporella anici Nikler & Sokač and Salpingoporella
annulata Carozzi as well as the microfacies development of these carbonates are
supporting the assumption that they are of Lower Malm age (probably Kimmerid-
gian: Radoičić, 1987 pers. com.).
Lower Malm 2
The carbonate rocks between the first and second evident faults (Fig. 2, Appen-
dix: section 1, d) are described as Lower Malm 2, despite the presence of Praekurnu-
bia sp., Chablaisia sp. and very probably Palaeosiphonium convolvens (Praturlon)
Elliott (Radoičić, 1987 pers. com.). Other fossils such as Kurnubia sp., Cladocorop-
sis mirabilis Felix (abundant) and Stylosmilia carollina Koby? as well as the facies
(hydrozoan-coral-oncoid boundstones) clearly indicate the Lower Malm age of the
unit.
stratigraphy and geochemistry of Jurassic carbonate rocks...	321
Lower Malm 3
The carbonate rocks of the Lower Malm 3 are juxtaposed to the previously
described ones (Fig. 1, Appendix: section 1, d-e). The lowermost micritic carbonates
of this sequence again are rich in the foraminifer Praekurnubia sp. and pass into
a thick succession of ooid grainstones (about 260 m) which is interrupted only by an
intercalation of hydrozoan-coral-oncoid boundstones. Within the lower part of the
ooid grainstones (about 100 m) the alga Palaeosiphonium convolvens (Praturlon)
Elliott could be identified. Elliott (1977, 1985) describes this alga as typical in the
Upper Dogger beds (Upper Bathonian to lowermost Callovian) within the realm of
the Tethys and (rarely) in extra-Tethyan deposits. R a d o i č i ć (1966) on the contrary
mentioned as range for Pseudocodium convolvens Praturlon (renamed by Elliott,
1985 as Palaeosiphonium convolvens (Praturlon Elliott) the uppermost Upper Dog-
ger to the lower parts of the Lower Malm. On my inquiries Mrs. Radoičić and Mr.
Elliott unfortunately could not give any new information concerning the age of this
alga (Radoičić, 1987 pers. com., Elliott, 1989 pers.com.).
It is therefore possible that the lower part of the relatively thick sequence (about
186 m) belongs to the Upper Dogger. Against this interpretation, however, argue the
following reasons:
-	Section 2 (Fig. 4, Appendix: section 2, e) shows an undisturbed transition of
definitely Lower Dogger (older than Callovian?) to Lower Malm strata (the upper-
most carbonate rocks of the Dogger contain the foraminifera Mesoendothyra
croatica Gušić and Dictyoconus cayeuxi Lukas).
-	Mudstones/wackestones of Lower Malm age are always intercalated between the
ooid grainstones of the Dogger and the ooid grainstones of the Lower Malm
(section 2; section 1: beneath and above the first presumed fault, above the second
evident fault). Those intercalations of Lower Malm mudstones/wackestones di-
rectly above the Dogger/Malm boundary are typical of the Jurassic beds of
Slovenia (Buser, 1987 pers. com.). On the other hand, the ooid grainstones
containing the alga Palaeosiphonium convolvens (Praturlon) Elliott are placed
above such an intercalation and pass without interruption into assured Lower
Malm ooid grainstones. No mudstones or wackestones are intercalated at this site.
-	B o s e 11 i n i et al. (1981) state a short drop of sea level during the Callovian which
has exposed large parts of the Friuli Platform and interrupted the formation of
ooids.
-	H a 11 a m (1978, 1988) assumes most important sea level falls in the Late Callovian
and in the end of the Bathonian.
Accordingly, the entire sequence of ooid grainstones, including those containing
the alga Palaeosiphonium convolvens (Praturlon) Elliott, are thought to be of Lower
Malm age.
Upper Malm
The contact between the beds of the Lower Malm and the Upper Malm also seems
to be slightly tectonically overprinted. The occurrence of the index fossil Clypeina
jurassica Favre above this fault (Fig. 2, Appendix: section 1, e-f), however, undoub-
tedly indicates the Upper Malm age of the superposed micritic and partly strongly
dolomitized carbonates. The dolomites as well as the calcareous dolomites of the
Upper Malm often show a pronounced cryptalgal lamination. Within the intercalated
bedded limestones and dolomitized limestones, abundant Salpingoporella annulata
Carozzi and aberrant Tintinnids (synonym to Campbelliella striata Carozzi; (Ber-
nier, 1974) can be found beside Clypeina jurassica Favre (PL 2, Fig. 3).
Fig. 4. Schematic column of the Jurassic carbonate rocks from Krka, section 2
U. T. Upper Triassic; M. L. Middle Lias; U. L. Upper Lias; L. D. Lower Dogger; L. C. Lower
Cretaceous
322	Christian Strohmenger & Stevo Dozet
stratigraphy and geochemistry of Jurassic carbonate rocks...	323
Lower Malm 4 ( Dogger?)
The Upper Malm carbonate beds are in tectonic contact (juxtaposed) with Dogger
and/or Lower Malm carbonates (Dogger?/Lower Malm 4; Fig. 2, Appendix: section 1,
f-h) which contain a thick intercalation of ooid grainstones (38,5 m). The abundance
of corals and hydrozoans within these oolites and in the superimposed beds (abun-
dant Cladocoropsis mirabilis Felix) clearly indicates the Lower Malm age of the
oolitic beds and the following micritic carbonates (Fig. 2, Appendix: section 1, g-h).
In the lowermost beds of the upthrusted carbonates (about 55 m) no index fossils
could be identified. This means that the stratigraphical position of these carbonates
is not defined. The microfacies development of the sequence, composed mostly of
micritic carbonates with thin oolithic intercalations, shows much similarities with
the carbonates (and microfacies types) of the Lower Dogger (Strohmenger, 1988).
It is therefore possible that also some parts of the Dogger (Lower Dogger?) are
upthrusted and juxtaposed to the Upper Malm carbonate rocks (Fig. 2, Appendix:
section 1, f-g).
A third presumed fault probably separates the upthrown oolites of the Lower
Malm from micritic carbonates of the same age (Fig. 2, Appendix: section 1, g) which
are rich in oncoids (oncoid boundstones), corals and hydrozoans {Cladocoropsis
mirabilis Felix).
Lithology
Limestones are the predominant carbonates of section 1. Dolomites occur only in
the Middle Lias and Upper Malm. Except of one very tectonized limestone intercala-
tion (about 10 m, lower part brecciated), the entire Middle Lias consists of dolomites
which are mostly brecciated.
The Upper Malm is built up by an alternation of limestones and (mostly) dolomi-
tes. The dolomites commonly show marked cryptalgal laminations.
Non-carbonate sediments are only present in the form of a 10 cm thick clay lens
which probably represents rather a diagenetically induced layer than a sediment
(Strohmenger, 1988).
The thicknesses of the beds vary between less than 10 cm (platy stromatolitic
dolomites. Upper Malm) and more than 1 m. The average thickness of the carbonate
beds is nevertheless less than 1 m.
Section 2
Section 2 is located near Krka, about 30 km SSE of Ljubljana (Fig. 1). An
undisturbed succession of carbonate rocks (Upper Triassic to Lower Cretaceous) is
exposed directly on or close to the path which leads from Krka to a hill with the small
village of Mali Korinj (about 750 m).
In contrast with section 1, the carbonate beds of section 2 are tectonically
undisturbed, but are in places very badly exposed. This is why the vertical transition
of the beds are not always visible. The real value of the thickness may therefore
deviate by some tens of meters from the estimated value of about 1270 m.
324	Christian Strohmenger & Stevo Dozet
Stratigraphy
With the exception of the boundaries betv^^en the beds ob the Lower Lias to the
Middle Lias and the Lower Malm to the Upper Malm the sections containing the
stratigraphical boundaries are well exposed and proved by index fossils (Tab. 2) and/
or field observations.
Section 2 can be easily subdivided into Upper Triassic (Main Dolomite), Lower
Lias, Middle Lias, Upper Lias, Lower Dogger, Lower Malm, Upper Malm and Lower
Cretaceous (Fig. 4, Appendix: section 2).
Lower Lias
The boundary of the Upper Triassic (Main Dolomite) to the Lower Lias is very
well exposed. The light gray dolomites of the Upper Triassic pass continiously into
the brownish limestones of the Lower Lias (Fig. 4, Appendix: section 2, a-c) which
contain the algae Palaeodasycladus mediterraneus Pia and Palaeodasycladus elonga-
tus Praturlon (PI. 1, Fig. 1).
Table 2. Index fossils of section 2
Age	Index Fossils
Main Dolomite	-------
Lower Lias	Palaeodasycladus sp.
Palaeodasycladus elongatus Praturlon
Palaeodasycladus mediterraneus Pia
Linoporella ? lucasi Gros & Lemoine
Gyroporella sp. ?
Middle Lias	Orbitopsella sp.
Orbitopsella cf. dubari Hottinger
Orbitopsella praecursor Gümbel
Mayncina termieri Hottinger
Glomospira sp. ?
Palaeodasycladus sp.
Palaeodasycladus mediterraneus Pia
Upper Lias	Palaeodasycladus mediterraneus Pia
Lower Dogger	Dictyoconus cayeuxi Lukas
Mesoendothyra sp.
Mesoendothyra croatica Gušić
Lower Malm	Protopeneroplis sp. ?
Trocholina elongata Leopold
Cladocoropsis mirabilis Felix
Meandrophyllia amedei EtalIon
Calamopnylliopsis flabellum Michelin
Thamnasteria sp.
Thamnasteria concina Goldfuss
Halisitastraea sp. ?
Stomatopora sp.
Upper Malm	Clypeina jurassica Favre
Clypeina cf. maslovi Praturlon
Salpingoporella annulata Carozzi
Aberrant Tintinnids:
Campbelliella striata (Carozzi) Bernier
*	Tintinnopsella besici Radoičić ?
*	Campbelliella sp.
Lower Cetaceous Clypeina solkani Conrad & Radoičić
stratigraphy and geochemistry of Jurassic carbonate rocks...	325
Middle Lias
The boundary between the Lower Lias and Middle Lias has been fixed with the
first appearance of Orbitopsella praecursor Gümbel (Fig. 4, Appendix: section 2, c;
PI. 1, Fig. 2). Connected with this stratigraphical change is also a petrographical
change from dolomites (Lower Lias) to limestones (Middle Lias) in which, beside
other index fossils, also Mayncina termieri Hottinger (PI. 1, Fig. 3) could be found. It
is of course, also possible that the boundary is situated somewhat lower within the
underlaying dolomites. Unfortunately, these dolomites contain no determinable
fossils.
Upper Lias
The delimitation of the Upper Lias beds is solely based on field observations (Fig.
4, Appendix: section 2, d). The part of the carbonate sequence overlaying the
uppermost Middle Lias with the Lithiotis-bioherms and underlaying undoubtedly
Lower Dogger carbonates (oolites with the index fossils) Dictyoconus cayeuxi Lukas
and Mesoendothyra croatica Gušić) is very well exposed and undisturbed. The
carbonates are built up by very dark micrites which are framed by intraclast-ooid-
peloid grainstones at the base (which contain Palaeodasycladus mediterraneus Pia
and abundant Codiacean fragments) and iron-ooid wackestones at the top. The latter
show a fossil assemblage (bentic foraminifera, ostracodes and strongly bored crinoid
fragments with thick micrite envelopes) that resembles typical Upper Lias fossil
assemblages (Radoičić, 1987 pers. com.) The thickness of the so-called Upper Lias
carbonates varies between 12m and 30m. This limited thickness and the ferriferous
ooid deposits at the top of the Upper Lias probably can be interpreted as a stratigrap-
hical gap between the Upper Lias and the Lower Dogger.
Lower Dogger
The Lower Dogger beds are exclusively developed as ooid grainstones which
laterally can also be somewhat dolomitized (Fig. 4, Appendix: section 2, d-e).
Although such thick oolitic series (about 84m) are thought to be typical of the Lower
Malm, the described sequence is of undoubtedly Lower Dogger age. The uppermost
beds of the ooid grainstones are rich in the foraminifer Dictyoconus cayeuxi Lukas
(Pl. 1, Fig. 4). According to Septfontaine (1988), the range of this foraminifer is
from Upper Aalenien (?) to Bajocian (Bathonian ?). Dictyoconus cayeuxi Lukas
together with Mesoendothyra croatica Gušić (which is also present within the ooid
grainstones) are well known index fossils of the Lower Dogger in the Dinarids
(Radoičić, 1966, Gušić, 1969). Outside Yugoslavia these foraminifera are known
from the Lower to Middle Dogger.
Oman and Spain: Dictyoconus cayeuxi Lukas together with Spiraloconulus
perconigi Allemann & Schroeder: Bajocian to Bathonian (Allemann & Schro-
eder, 1972, 1980)
West Thailand: Lucasella kaempferi Kemper, synonym to Dictyoconus cayeuxi
Lukas: Lower to Middle Dogger (Kemper, 1976; Hägen & Kemper, 1976;
Kemper et al., 1976)
By means of the index fossils it is well documented that at least the Callovian (or
the upper part of the Callovian) is not developed in the investigated area.
326	Christian Strohmenger & Stevo Dozet
Lower Malm
The Lower Malm beds mainly consist of different ooid grainstones which are
partly interrupted by breccias (Fig. 4, Appendix: section 2, e-g). The breccias are of
obviously polymict composition. They contain typical clasts of the Lower Malm (ooid
grainstones and/or oncoid-peloid packstones) as well as wackestones whose fossil
content {Clypeina jurassica Favre, Clypeina cf. maslovi Praturlon, Salpingoporella
annulata Carozzi and Campbelliella striata (Carozzi) Bernier) clearly identifies them
to be of Upper Malm age (Fig. 5). These breccias occur in three horizons within the
Lower Malm Carbonate rocks and are certainly wedging out laterally. The breccias
themselves and the adjacent limestone beds are often heavily dolomitized. The
polymict composition of the breccias (clasts of different composition and age) as well
as their confined occurrence as lenticular intercalations within the Lower Malm
strata allows the conclusion that they represent true karst breccias. Consequently,
they are interpreted to be the lateral equivalents of a bauxite horizon which often is
intercalated between the Lower and Upper Malm beds in the Dinarids and is also
present nearby the investigated carbonate succession (Buser, 1987 pers. com.).
Fig. 5. Karst breccia with clasts of Lower Malm (thick arrow: ooid grainstones) and
Upper Malm (thin arrows: mudstones and fossil wackestones). Section 2
Upper Malm
The boundary between Lower and Upper Malm (Fig. 4, Appendix: section 2, g) is
drawn beneath the uppermost (last) breccia which is of more monomict composition
(mudstones and fenestral mudstones). Clasts with typical Lower Malm carbonates
stratigraphy and geochemistry of Jurassic carbonate rocks...	327
(ooid grainstones and oncoid packstones) are missing. Unfortunately, the underlying
as well as the superposed carbonates are strongly to completely dolomitized. It may
therefore be possible that also this boundary is actually situated a little bit lower
within the underlying dolomites. At any rate, only the dolomites above the last
breccia show the typical cryptalgal lamination (»cryptalgalaminate carbonates«;
A i t k e n, 1967) which seems to be indicative for the Upper Malm (Strohmenger,
1988). Determinable index fossils {Campbelliella striata (Carozzi) Bernier, Clypeina
jurassica Favre, Salpingoporella annulata Carozzi) could only be found within the
dolomites situated above the last breccia (in the less dolomitized parts). Therefore, it
seems to be appropriate to define the boundary with the last occurence of the karst
breccia.
The Upper Malm is mostly developed in the form of bedded and partly stromatoli-
tic dolomites. Only the last 35m of the section (including Lower Cretaceous beds) are
built up of pure limestones (Fig. 4, Appendix: section 2, h). The lowermost parts of
these limestones contain the alga Clypeina jurassica Favre, Salpingoporella annulata
Carozzi and Campbelliella striata (Carozzi) Bernier (PI. 2, Fig. 4).
The boundary between the Upper Malm and the Lower Cretaceous is somewhat
controversial in the Dinarids. Some authors are drawing the boundary either with
the appearance of the aberrant Tintinnids (Radoičić, 1960, 1966), after the extinc-
tion of CZypezna jwrasszca (B u s e r, 1968, 1979; Turnšek & Buser, 1966) or a little
bit later after the extinction of the aberrant Tininnids (Sokač et al, 1978; Šribar,
1979a, b). A compilation of the literature concerning this problem is given by Šribar
(1979b) and Koch (1987). Nevertheless, one has to take into consideration that these
microfossils are also facies dependent (Radoičić, 1969). Only minor changes in the
environment may be responsible for a diachronous appearance or extinction of the
different algae. The investigated carbonates show no marked facies changes; for this
reason we place the boundary between the Upper Malm and the Lower Cretaceous
after the last appearance of the aberrant Tintinnids (which lies only about 4m above
the extinction of Clypeina jurassica Favre).
Lower Cretaceous (Berriasian)
The directly superposed limestones (9m) are free of index fossils but rich in
gastropods (Nerineae) and algal laminated, fenestral carbonate deposits at the top
(Fig. 4, Appendix: section 2, h). Above this series, within the uppermost exposed beds
(about 7m) of the section, an index fossil of the Lower Creataceous Clypeina solkani
Conrad & Radoičić could be identified (PI. 2, Fig. 2). The beds containig Clypeina
solkani as well as the underlaying limestones (totally about 16m) are therefore
supposed to be of Berriasian age.
Lithology
Section 2 is built up predominantly by limestones, but the content of dolomites is
much higher than in section 1. Large parts of the Lower Lias and the Upper Malm are
nearly completely formed by thick dolomite beds. In addition, the carbonate rocks of
the Lower Dogger (ooid grainstones) and Lower Malm (ooid grainstones, karst
breccias) are often laterally dolomitized. The dolomitized areas frequently show
a brecciated texture.
The thickness of the beds lies in the same range as for section 1.
328	Christian Strohmenger & Stevo Dozet
Geochemistry
The determined values of Mg, Sr, Fe, Mn, K (section 1 and 2) as well as Zn (section
2) and Al (section 2) in the investigated calcareous rocks demonstrate a significant
facies dependence:
-	relative high contents of all elements are typical for calcareous rocks of lagoonal
deposits (e. g. mudstones and wackestones)
-	high energy deposits (e. g. ooid grainstones) are, on the contrary, markedly
depleted in these elements.
The valeus of manganese and strontium are in some cases relatively low. The loss
of these elements might be explained by diagenetic processes.
The insoluble residue shows a good correlation with iron, manganese, potassium
and aluminium.
The measured elements in the two investigated sections reflect the environmental
conditions under which the calcareous rocks were deposited.
Similar geochemical results appear also in other Jurassic sections of the Slove-
nian Dinaric carbonate platform (O r e h e k & Ogorelec, 1979, 1981). According to
the literature they are within the general limits of calcareous rocks.
Conclusions
Section 1: the age of the carbonates above the beds containing definite index
fossils of the Lower Dogger is very uncertain (except for those of the Upper Malm).
The abundance of the foraminifer Palaeosiphonium convolvens points to Dogger age
for most of these carbonates (including a large proportion of the oolits). Nevertheless,
there are also hints for Lower Malm ages such as the occurrence of the alga
Heteroporella anici and the abundance of corals and hydrozoans (Cladocoropsis
mirabilis) within these carbonate beds. In addition, it cannot be excluded that under
siutable environmental conditions (e. g. restricted lagoon) Praekurnubia sp. can also
be frequent in Oxfordian and Lower Kimmeridgian carbonates, even when Kurnubia
sp. is missing. We therefore propose not to change the stratigraphy presented by
Strohmenger (1988), but to point to the possibility that the carbonates described
as Lower Malm might be partly of Dogger age, or respectively, that the range of
Praekurnubia sp. and Palaeosiphonium convolvens reaches also into the Lower Malm
(Kimmeridgian?) and therefore should be reinvestigated.
Section 2: the studied Jurassic carbonate rocks clearly indicate a stratigraphical
gap during the Dogger. The index fossils which could be identified point to an age
older than Callovian or older than Upper Callovian respectively. Perhaps the break
in sedimentation coincides with the assumed fall of sea level during the Callovian or
at the end of the Bathonian (Hallam, 1987, 1988; Bo ssellini et al., 1981). The
identified karst breccia (intercalated within Lower Malm carbonate rocks) contains
clasts of both Lower and Upper Malm. It therefore indicates a long-term emergence
of the carbonate platform during the Upper Malm.
The results of the geochemical analyses must be treated with care because of the
extensive fracturing of the carbonates. In relation to the sediment textures and
structures they are however useful indicators of the water conditions under which
the carbonates were formed.
stratigraphy and geochemistry of Jurassic carbonate rocks...	329
Acknowledgments
This study is based on the Ph. D. dissertation of the senior author and would not
have been possible without the support and cooperation of Prof. Dr. G. Müller
(Institut für Sedimentforschung, Heidelberg) and prof. Dr. R. Koch (Institut für
Paläontologie, Erlangen). The authors greatfully acknowledge Dr. R. Radoičić and B.
Sc. L. Šribar for the determination of the foraminifera and algae, as well as Dr. D.
Turnšek for the determination of the corals and hydrozoans. C. Strohmenger thanks
Dr. M. Septfontaine for the stimulating discussion and the determination of some
foraminifera. The senior author is particularly indepted to the Geološki Zavod
Ljubljana for providing access to the study area and for the financial support during
the field work. A very special acknowledgment from C. Strohmenger is extended to
Prof. Dr. S. Buser for his guidance, encouragement and helpful comments. We also
wish to thank Dr. A. Strasser for his critical review.
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Plate 1
1	Palaeodasycladus elongatus Praturlon, x 16. Lower Lias, thin section; section 2
2	Orbitopsella praecursor Gümbel, x 40. Middle Lias, thin section; section 2
3	Mayncina termieri Hottinger, x 40. Middle Lias, thin section; section 2
4	Dictyoconus cayeuxi Lukas, x 40. Dogger, thin section; section 2
stratigraphy and geochemistry of Jurassic carbonate rocks...	331
332	Christian Strohmenger & Stevo Dozet
Plate 2
1	Heteroporella anici Nikler & Sokač, x 40. Lower Malm 1 (Kimmeridgian?), thin section;
section 1
2	Clypeina? solkani Conrad & Radoičić and Miliolid foraminifer, x 40, Lower Cretaceous
(Berriasian); section 2
3	Parurgonina caelinensis Cuvillier (left) and Clypeina jurassica Favre (right), x 40. Upper
Malm, thin section; section 1
4	Campbelliella striata (Carozzi) Bemier (aberrant Tintinnids), x 16. Upper Malm, thin section;
section 2
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Explanation to the sections 1 and 2
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SECTION 1 (a, base)
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