A Middle Jurassic Radiolarite-Clastic Succession from the Medvednica Mt.

(NW Croatia) 

Josip HALAMI∆ 1, ©pela GORI»AN 2, Damir SLOVENEC 1 and Tea KOLAR-JURKOV©EK 3

1. INTRODUCTION

In the last few decades, especially after invention of

a method for the extraction of radiolarians from radiola-

rian cherts (DUMITRICĂ, 1970; PESSAGNO & NEW-

PORT, 1972; DE WEVER, 1982), investigation of radi-

olarian cherts in the Mediterranean area has intensified.

This is the consequence of their stratigraphic impor-

tance, bathymetry of their origin, and their common

occurrence with ophiolites. All the aforementioned is

extremely important for the palaeogeographic recon-

struction of this area. From this perspective, in the geo-

logical literature dealing with SW part of the Pannonian

Basin (i.e. NW Croatia) deposits of this kind were disre-

garded, and were only mentioned together with mag-

matic rocks (GORJANOVI∆-KRAMBERGER, 1908;

BABI∆, 1974; ©IMUNI∆ & ©IMUNI∆, 1979; ©IKI∆ et

al., 1979; BASCH, 1983). The age of the magmatic

rocks and associated sedimentary rocks of the north-

western part of the Medvednica Mt. has been, on the

basis of their common appearance together with Lower

Cretaceous clastic carbonate deposits (which usually

overlie them), previously determined as either Lower

Cretaceous (©IKI∆ et al., 1979; BASCH, 1983; ©IKI∆,

1995), or even Upper Cretaceous (CRNKOVI∆, 1963).

After the discovery of Triassic radiolarites together

with basic volcanic rocks from Kalnik and Medvednica

Mts. (Middle Carnian to uppermost Carnian - Norian -

HALAMI∆ & GORI»AN, 1995; HALAMI∆, 1998),

and Triassic limestones (peperites) in pillow lavas from

Medvednica Mt. (upper Anisian - lower Ladinian -

HALAMI∆ et al., 1998), it has been determined that

part of the magmatic rocks with pelagic sediments on

the Medvednica Mt. are of Triassic age, without regard

to its present geotectonic position (accretionary com-

plex - HALAMI∆, 1998). Furthermore, during these

studies it has been determined that part of siliceous

rocks are of Jurassic age (HALAMI∆ & GORI»AN,

1995; HALAMI∆ et al., 1995), and will be discussed in

detail in this paper. Jurassic radiolarites of the Medved-

nica Mt. alternate with shales, siltites, matrix-supported

conglomerates, or represent the matrix of olistostromes,

and therefore are very important for the palaeogeo-

graphic reconstruction of the SW part of the Pannonian

Basin in the Jurassic.

Jurassic mass-flow deposits containing olistoliths of

Triassic pelagic rocks are known from Hungary and

G EOL.  CR OAT. 52/1 29 - 57 17 Figs. 4 Tabs. 4 Pls. ZAGREB 1999

Key words: Radiolarite-clastic succession, Middle Jur-

assic, Radiolarians, Conodonts, Triassic olistoliths,

Geochemistry, Subduction, Accretionary complex,

Medvednica Mt., Croatia.

1 Institute of Geology, Sachsova 2, P.O. Box 268, HR-10000 Zagreb,

Croatia.

2 Ivan Rakovec Institute of Palaentology, ZRC SAZU, Gosposka 13,

SI-1000 Ljubljana, Slovenia.

3 Geological Survey of Slovenia, DimiËeva 14, SI-1000 Ljubljana,

Slovenia.

Abstract
On the NW part of Medvednica Mt. radiolarites with carbonate

olistoliths, shales and siltites, matrix-supported conglomerates and

basic volcanic rocks were investigated. This facies association is

informally named the Poljanica unit. Major element geochemical data

indicate deposition of radiolarites in the vicinity of the middle ocean-

ic ridge, while sedimentological data indicate deposition in an area

closer to the continent. Shales and siltites, as well as matrix-supported

conglomerates, were deposited in short periods characterised by

increased input of terrigenous material. Matrix-supported polymict

conglomerates are composed of silicified shales, lithic graywackes,

cherts and metabasalts, and were deposited by debris flow mecha-

nisms as a consequence of synsedimentary tectonic activity. Carbon-

ate olistoliths are composed of biomicrosparite, and jointly with

deformed radiolarian cherts compose an olistostrome. Basic volcanic

rocks represent high-Ti tholeiitic basalts formed in the MORB realm.

Micropalaeontological investigation of radiolarite samples pro-

ved the Middle Jurassic (latest Bajocian - early Bathonian to late

Bathonian - early Callovian) age of the Poljanica unit. Additionally, a

new radiolarian species Theocapsomma medvednicensis n.sp. has

been described. Conodont analyses from carbonate olistoliths in radi-

olarites proved their Triassic age.

The investigated radiolarite-clastic succession is the result of sub-

duction processes. Further continuation of this process caused incor-

poration of these deposits into the accretionary prism, where they

were brought in direct contact with Triassic volcanic rocks and radio-

larites (in the form of a tectonic mélange).

Based on the lithological similarities with the Middle Jurassic

turbidite-olistostrome successions in the Western Carpathians and

Northern Calcareous Alps, the study area is considered to be part of

the Meliata-Hallstatt Ocean. 



30 Geologia Croatica 52/1

Slovakia (KOZUR, 1984, 1991; KOZUR & MOCK,

1985, 1995, 1997; KOZUR et al., 1996), as well as

from Austria (MANDL & ONDREJI»KOVÁ, 1991,

1993; KOZUR & MOSTLER, 1992; GAWLICK,

1993).

3. BASIC GEOLOGICAL DATA

Medvednica Mt. is situated in the SW part of the

Pannonian Basin, and is incorporated as part of the geo-

dynamic unit Supradinaricum (HERAK, 1986) or Inner

Dinarides (HERAK et al., 1990). Tectonically, the

Medvednica Mt. belongs to the Mid-Transdanubian

Zone (sensu HAAS et al., 1988) or Zagorje - M i d -

Transdanubian Zone (as defined by PAMI∆ & TOM-

LJENOVI∆, 1998), which is bounded by the Balaton

Line in the north and the Zagreb-Zemplen (or Mid-

Hungarian) Line in the south.

The core of the Medvednica Mt. is composed most-

ly of low-grade metamorphic rocks (various metape-

lites, metapsammites, slate-phyllite, slates, quartzites,

marbles, ortho- and paragreenschists of Palaeozoic, and

partly Mesozoic age - BELAK et al., 1995), high-pres-

sure metamorphic rocks (blueschists - BELAK & TIB-

LJA©, 1998), magmatic rocks associated with sedimen-

tary rocks (CRNKOVI∆, 1963; ©IKI∆ et al., 1979; HA-

LAMI∆, 1998), and clastic-carbonate deposits of Trias-

sic, Lower Cretaceous and Upper Cretaceous - P a l a e o-

gene age (©IKI∆ et al., 1979; ©IKI∆, 1995). This core

is surrounded by younger Tertiary and Quaternary sedi-

ments (Fig. 1).

Rocks of the magmatic-sedimentary complex, inclu-

ding those described in this paper, outcrop in the NW

part of Medvednica Mt. over an area of approximately

25 km2. Towards the east they are in reverse tectonic

contact with low-grade metamorphic rocks, and tow-

ards the NE they are bounded from the low-grade meta-

morphic rocks by the normal fault. Along their SW

margin rocks of this complex are partly surrounded by

Lower Cretaceous and Upper Cretaceous - P a l a e o g e n e

sedimentary rocks, and are partly in contact with Lower

Triassic pelites and psammites and Middle and Upper

Triassic limestones and dolomites of the ZakiËnica

nappe (©IKI∆, 1995). Towards the NW, rocks of the

magmatic-sedimentary complex are disconformably

overlain by sedimentary rocks of the Neogene, which

are partly in tectonic contact with them. M a g m a t i c

rocks are mainly represented by greenish altered basalts

(spilites), with subordinate green-grey massive basalts,

pillow lavas, diabases and altered diabases in the form

of veins dissecting metabalts, and gabbro and metagab-

Fig. 1  Location map and geologi-

cal sketch map of Medvednica

Mt. (from HALAMI∆ et al.,

1998). Legend: 1) Tertiary sed-

imentary rocks; 2) Cretaceous-

Palaeogene sedimentary rocks;

3) investigated magmatic and

sedimentary rocks; 4) Triassic

clastic and carbonate rocks of

ZakiËnica nappe; 5) metamor-

phic rocks; 6) stratigraphic bo-

undary; 7) fault; 8) reverse fau-

lt; 9) thrust fault; 10) investiga-

ted area.



bro. Among the sedimentary rocks the most frequent

are matrix-supported conglomerates, conglomeratic

shales and siltites of brown, grey and dark grey colour,

composed of pebbles and blocks of sandstones (lithic

greywackes, lithic arenites, sublithoarenites), metaba-

salts and metagabbros. These sediments are most com-

mon above the main magmatic body of the NW Med-

vednica Mt., but are also found as decametre-sized

packages within basic volcanic rocks (HALAMI∆,

1998).

In the SW part of the magmatic-sedimentary com-

plex dark red, grey and green-grey shales, siltites and

radiolarian shales are abundant together with dark grey

and green-grey radiolarites, which are locally in direct

contact to spilites. Some radiolarites and pillow lavas

with pelagic limestones are of Triassic age (HALAMI∆

& GORI»AN, 1995; HALAMI∆ et al., 1998), and a

part of these siliceous and siliciclastic rocks is of Juras-

sic age.

3. PETROLOGY

3.1. SEDIMENTARY ROCKS

Siliceous rocks in the Poljanica creek were investi-

gated in detail at three localities, while palaeontological

and sedimentary-petrographic studies of outcrops of

these rocks south of Poljanica and towards the NE to

the Jelenja voda creek were subsequently performed

(Fig. 2).

The geological column P o l j a n i c a - A (Figs. 2 & 3a)

represents the sequence on the SW bank of the Poljani-

ca creek, on both sides of the forest road, approximately

600 m E of Poljanica village. The measured deposits

are 22.5 m thick. 

The lower 12 m of the column is composed of grey

and green-grey radiolarites characterised by very thin

bedding (1-5 cm thick, rarely to 15 cm), which is late-

rally persistive. Bedding surfaces are wavy but sharp.

Cherts are interbedded with mm- to cm-thick beds of

silicified shales and clayey silty cherts. The matrix of

the radiolarian cherts is composed of cryptocrystalline

quartz, while planparallel oriented white mica flakes

(?muscovite) averagely 0.01 mm, rarely up to 0.5 mm

in size, as well as silt-sized detrital quartz grains are

subordinate. An opâque mineral (?Fe-hydroxide) found

in the form of agglomerates up to 0.6 mm in size is an

accessory. These cherts are dissected by mm-thick qu-

artz veins and mutually connected mesh-like stylolites.

In the lower part, the rocks are characterised by a weak-

ly expressed, parallel laminated structure, while in the

upper part the structure is homogenous. Laminae com-

posed of skeletons and relics of radiolarians (up to 0.2

mm in diameter) are less than 2 mm thick. Most of the

radiolarian skeletons are recrystallized and filled with

microcrystalline quartz, while some are filled with radi-

al chalcedony. Gradation is not visible, both in the lam-

inated and homogenous types of radiolarian cherts.

In the middle part of the column there is a 1.7 m

thick bed of dark red and green-red conglomeratic

sandy-siltose shale. The deposit is characterised by a

slaty structure, and is weathered into cm-sized chips.

The rock is matrix-supported, and the matrix is com-

posed of clay minerals and cryptocrystalline quartz,

with small subrounded to rounded grains of the same

composition, detrital quartz grains (up to 0.1 mm in

size) and small rounded grains of quartz siltite. Pebbles

larger than 2 mm are irregularly distributed, and com-

posed of silty radiolarian cherts and lithic graywacke of

a green-grey colour.

The overlying interval is 1 m thick, composed of a

green-grey massive radiolarite, followed by a 2.6 m

thick bed of conglomeratic chert. Its lower boundary is

sharp and relatively flat, while the upper boundary is

sharp, irregular and uneven. Deformed grey-reddish

31HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

Fig. 2  Location map of analyzed

samples and sections.



32 Geologia Croatica 52/1

beds of chert have a slaty structure and contain up to

0.3 m large rounded fragments of light-grey carbonates

and reddish cherts. Carbonate fragments predominate in

the lower part of the bed, and chert fragments in the

upper part. Carbonates are represented by sporadically

silicified biointrasparrudites containing completely

recrystallized mollusc debris; these rocks were sampled

for conodont analyses (samples PA 16, PA 18 and PA

19 - Fig. 3).

The upper part of the column is composed of a

5.2 m thick succession of grey, homogeneous and lami-

nated radiolarite. The rock is intensely tectonised and

disintegrated. Laminae show no gradation, similar to

those in the lower part of the column.

The geological column Poljanica-B (Figs. 2 and 3b)

of the rocks on the SW bank of the Poljanica creek, east

of the Poljanica-A column, in a forest road-cut approxi-

mately 900 m E of Poljanica village, comprises a 9.6 m

thick succession.

The lower part of the column is composed of 4.2 m

of predominantly radiolarian cherts, with subordinate

silty radiolarian cherts of a dark red and reddish colour.

The rocks are thin-bedded (5-20 cm). Bed surfaces are

sharp and wavy. The matrix is composed of cryptocry-

stalline to microcrystalline quartz, containing radiolari-

an tests up to 0.15 mm in size, which are partly concen-

trated in mm-thick laminae and partly distributed irreg-

ularly. Tests are mostly filled with chalcedony, and

infrequently with microcrystalline quartz. Accesory

minerals are white mica and silt-sized detrital quartz

grains. An increased content of quartz, in the form of

mm-sized elongated lenses is present in silty radiolarian

cherts. Rocks are impregnated by Fe-hydroxides in the

form of pigments, resulting in the dark red and red

colour of the entire rocks. Lamination is the only struc-

tural characteristic represented in the sediment.

The middle part of the column is composed of a 0.8

m thick bed composed of lens-shaped fragments (up to

40 cm in diameter) of fine-grained limestones and radi-

olarian cherts. Limestones are represented by biomi-

crosparites, biomicrites, fossiliferous micrites and mic-

rosparites. Microsparite matrix, which is partially silici-

fied, in some samples contains 10 -20 % of completely

recrystallized 0.1-0.25 mm large grains, probably com-

pletely calcitized radiolarian tests. The radiolarian

cherts are very similar to those from the lower part of

the column. The matrix between carbonate and radio-

larian chert fragments is slaty, composed of silicified,

dark red shale.

The upper part of the column is composed of an

alternation of deformed layers of radiolarian cherts and

sandy radiolarian cherts. These deposits also contain a

Fig. 3  Geological columns in the

Poljanica creek (for location

see Fig. 2). Legend: 1) shales;

2) siltites; 3) sandstones; 4) pa-

raconglomerates; 5) cherts; 6)

radiolarian cherts; 7) micrites;

8) calcarenites; 9) sedimentary-

petrographical analysis; 10) pa-

laeontological analysis; 11) ge-

ochemical analysis.



33HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

carbonate olistolith, 1.75 m in size (Fig. 4), composed

of biocalcarenitic sandstone. The matrix of the radiolar-

ian cherts is composed of microcrystalline quartz with

infrequent white mica and quartz grains. The sandy

component is composed of quartz grains and mica

flakes up to 0.1 mm in size. Micro- and macrofossil

detritus, ooid fragments, complete radial ooids and mic-

rite intraclasts, with subordinate quartz, feldspar, micro-

quartzite, microcrystalline quartz and granitoid grains

comprise the biocalcarenite. Intergranular spaces are

filled with drusy calcite cement, which is sporadically

silicified. This level could be, according to its sedimen-

tary-petrographic and sedimentological characteristics,

correlated to the upper part of the Poljanica-A column.

The third locality studied is a geological section

Poljanica-C (Figs. 2 and 5), located on the N bank of

the Poljanica creek, approximately 800 m E of the Polj-

anica village.

The lower part of the section is composed of matrix-

supported conglomerates. The matrix is comprised of

brown-grey, slaty, sandy-silty shale. Up to 15 cm sized

pebbles are composed of grey and grey-green lithic

greywackes. There is no inner organisation of the sedi-

ment, which was probably deposited from a mud flow.

These conglomerates are followed by a 2 m thick suc-

cession of reddish, weakly silty, silicified, radiolarian

Fig. 4  Metre-sized olistolith of light-grey calcarenitic sandstone in

dark-red shale (geological column Poljanica-B). Scale bar = 1 m,

sample PB18.

Fig. 5  Geological section Poljanica-C (for location see Fig. 2). Legend: 1) shales; 2) sandstones; 3) cherts; 4) radiolarian cherts; 5) micrites; 6)

recrystallized and haematized limestones; 7) pillow lavas; 8) metabasalts; 9) sedimentary-petrographical analysis; 10) palaeontological

analysis; 11) chemical analysis; 12) reverse fault. Note: pillow lavas with shale intercalations in the lower part of the section could represent

an olistolith.



34 Geologia Croatica 52/1

shales, with sharp and wavy lower bedding surfaces.

The sediment is thin-bedded (up to 12 cm), and its

matrix is composed of clay minerals and subordinate

cryptocrystalline quartz, and impregnated with Fe-

hydroxides. A silt-sized component is composed of det-

rital quartz grains and white mica flakes. The matrix

comprises up to 5 % of relatively well-preserved radio-

larian tests, up to 0.15 mm in size, which are predomi-

nantly filled with a greenish mineral from the chlorite

group (?seladonite - Dragutin SLOVENEC, unpub-

lished). Infrequent tests are filled either with a ferrugi-

nous-clayey substance or radial chalcedony. These radi-

olarian shales are covered by a 15 m thick succession of

pillow lavas. The contact between the sedimentary and

volcanic rocks is sheared, as the result of differing com-

petence of the materials. Some pillows are more than

1 m in diameter (Fig. 6). These volcanic rocks will be

described in more detail later.

In the middle and upper part of the effusive succes-

sion there are a few decimetre thick beds of sediments

in contact with volcanic rocks. These are predominantly

haematized and silicified shales. Along with the clay

minerals, which constitute the rock matrix, there is a

silt-sized component composed of quartz grains and

planparallely oriented white mica particles, with zircon

as an accessory. Millimetre-sized veins filled with qu-

artz, plagioclase and calcite dissect the deposit. At the

shale/metabasalt boundary “tongues” of the sediment

penetrate into the volcanic rock (Fig. 7), the contact

surface is irregular, and joints in the metabasalt are

filled by haematized shale and volcanic fragments.

Since this outcrop is very restricted, the possibility

that the basalt with shale intercalations represents a

megablock within the sedimentary succession cannot be

excluded. On the Basic Geological Map (©IKI∆ et al.,

1977) basalts in the Poljanica creek are presented as

small isolated basalt bodies not exceeding 300 m in dia-

meter. This distribution also suggests that the basalt

bodies represent allochthonous blocks in a tectono-sedi-

mentary mélange.

After a 15 m thick covered interval the section is

continued with matrix-supported conglomerates, which

in the lower part are brownish-red, and in the upper part

dark red and greenish, partly silicified and partly cov-

ered by Mn or haematite-limonite crusts. In the lower

part the matrix is composed of sandy-silty shale, and

pebbles are represented by lithic greywackes and

almost completely calcitized cherts. Pebbles in the

upper part of paraconglomerates are represented by

brownish-green metabasalts, greenish lithic greywacke,

greenish vitreous and grainy chert and dark red siltite.

A further part of the section is composed of very thin-

and thin-bedded, deformed dark red radiolarian cherts.

Radiolarian tests in these radiolarites are, as in the low-

er part of the section, filled by a green, chloritic sub-

stance (?seladonite). Within the radiolarites irregularly

distributed pebbles, cobbles and smaller blocks (olis-

toliths) of light grey limestones can be found (Fig. 8).

These carbonates are composed of recrystallized, and

sporadically dolomitized biomicrosparites and intrabio-

microsparites.

Beside the aforementioned columns we have inves-

tigated several other localities. At the Pijesak locality

south of the Poljanica creek (sample VH 32 on Fig. 2)

there is an alternation of centimetre-decimetre thick

Fig. 7  Contact of haematized shale (up) and metabasalt (below). Note

“tongues” of shale filling fractures in metabasalts (Poljanica-C

section, below 113/2 sample).

Fig. 6  Outcrop of pillow lavas in the lower part of the Poljanica-C

geological section. Pillows up to 1 m in diameter are well

exposed (hammer for scale is 30 cm long).



35HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

beds of reddish radiolarian cherts, greenish cherts and

dark red fine-grained quartz arenites.

The radiolarian cherts are characterised by the same

composition as in the aforementioned successions. The

chert is composed of a cryptocrystalline quartz matrix,

and 0.03 mm long planparallel oriented sericite parti-

cles. Detrital, subrounded quartz grains from 0.04-0.22

mm in size, which compose submillimetre-thick lami-

nae, are subordinate, as well as rare radiolarian tests.

The chert is characterized by stylolitized bedding sur-

faces, stylolites being filled by a ferruginous substance.

Quartz arenites are characterized by a psammitic tex-

ture and homogenous structure. They are composed of

poorly sorted subrounded detrital grains of quartz, up to

0.5 mm in size, most of them exhibiting undulatory ext-

inction. Subordinate muscovite particles up to 0.5 mm

in size (longer grains are trapped between quartz grains

and fragmented) occur with rock fragments (chert and

quartzite) and amphibole. Zircon and garnet, as well as

opâque minerals are accessory, and a haematite-limo-

nite component fills interstices, causing the reddish

colour of the rock. The rock matrix is composed of cry-

ptocrystalline quartz and sericite (Fig. 9).

At the VH 891 locality (Fig. 2) interbedded matrix-

supported conglomerates were discovered, which are

greenish-grey in colour, and characterized by a slaty

structure. A greenish-grey silty shale matrix is com-

posed of clay minerals and cryptocrystalline quartz.

Subordinate silt-sized, rarely sand-sized detrital quartz

grains and white mica also occur. Zircon and opâque

minerals are accessory. Poorly-sorted fragments, 2-50

mm in size are found in the matrix, rarely exhibiting

orientation of the longer axis subparallel to the schistos-

ity. The matrix around fragments and pebbles show no

signs of their subsequent rotation, indicating that their

orientation originated during the flow of the mud mass.

Fragments are angular to subangular, partly rounded,

composed predominantly of dark grey, grey, grey-green

and yellow-green silicified shale. Some fragments are

covered by Mn and limonite crusts (Fig. 10). At this

locality radiolarian chert does not crop out; therefore,

these rocks are not dated (see Table 1).

The VH 967 locality is situated on the slope NE of

the Poljanica village (Fig. 2), and the eastern part of the

outcrop is composed of a breccia, which is towards the

west followed by grey radiolarites. The breccia matrix

is composed of calcarenite consisting predominantly of

radial ooids with silicified margins and partly visible

agglomeration, as well as fragments of recrystallized

fossiliferous micrites, cherts and scarce metabasalts in

recrystallized microsparite. Centimetre sized fragments

in the breccia are predominantly composed of grey and

light-grey, partly laminated radiolarian cherts. Subordi-

nate fragments include biomicritic limestones and

metabasalts. Radiolarites found in the western part of

the outcrop represent typical ribbon radiolarites com-

posed of chert beds ranging in thickness from a few to

ten centimetres.

The outcrop at the PE 1 locality is composed exclu-

sively of dark red radiolarite, which is tectonically

deformed and folded, and the contact with neighbour-

ing rocks is not visible.

Fig. 8  Decimetre-sized carbonate olistoliths within radiolarian cherts

in the upper part of the Poljanica-C section (objective cap is 55

mm in diameter).

Fig. 9  Quartz arenite bed within radiolarite (outcrop VH32, sample

VH32/4).

Fig. 10  Matrix-supported conglomerate. Pebbles are composed of

cherts and silicified and manganised shales (outcrop VH891).



36 Geologia Croatica 52/1

The PD 0 locality is situated in a small abandoned

quarry, where an olistolith composed of grey, recrystal-

lized and weakly silicified pelmicrite was found within

dark red and grey radiolarites. In the pelmicrite pellets

and small circular forms, up to 0.03 mm in diameter,

which could represent calcitized radiolarians were

found.

The PC 50 locality is situated approximately 400 m

up-stream of the Poljanica-B column (Fig. 2). The low-

er part of the outcrop is composed of grey, fractured

radiolarian chert covered by matrix-supported conglom-

erates.

An outcrop of grey to light grey radiolarian cherts at

the VH 113 locality (Fig. 2) lies toward the E, bounded

by a several metre wide tectonic zone of Upper Creta-

ceous(?) carbonate-clastic deposits, while towards the

W, the outcrops are covered by Quaternary deluvial

deposits.

Sample VH 882 (Fig. 2) was taken from a several

metre-sized outcrop of intensely folded dark red, mas-

sive, clayey radiolarian chert. The rock is at places inte-

nsely manganized.

Samples VH 141 and VH 147A (Fig. 2) were col-

lected from grey and dark red radiolarian cherts. The

associated rocks are radiolarites, polymict and monom-

ict matrix-supported conglomerates and metabasalts in

the form of pillow lavas. Towards the W these deposits

are covered by delluvium, while towards the E they are

in tectonic contact with Cretaceous calcisiltites and cal-

carenites.

Samples VH 558 and JV©P (Fig. 2) were taken from

grey, greenish and red radiolarites, associated with

matrix-supported conglomerates and metadiabase and

metabasalt blocks.

Rocks from these localities represent part of the Po-

ljanica lithostratigraphic unit, which is composed of

radiolarites, siltites and shales with limestone olisto-

liths, ?blocks of basic volcanic rocks and matrix-sup-

ported conglomerates. The footwall of this unit is not

defined, while the hanging-wall is composed of debrites

of the Markov travnik unit, which are in disconfor-

mable contact with the Poljanica unit. Deposits of these

units are allochthonous to neighbouring rocks, and rep-

resent parts of the accretionary complex (HALAMI∆,

1998).

3.2. VOLCANIC ROCKS

In the eastern part of the Poljanica-C section (Fig. 5)

basic volcanic rocks are present in the form of pillow

lavas. These rocks are green (in the lower part) to red

(upper part), characterised by irregular fracturing. The-

re are several textural varieties of metabasalts.

Metabasalt texture is predominantly microcrys-

talline, ophitic and porphyric-ophitic, and in the upper

part of the section towards the contact with shale also

divergent-radial. The structure in the lower part is amy-

gdaloidal, while towards the upper part it becomes mas-

sive. Vesicles are monomineralic, composed either of

calcite, chlorite or fine-grained quartz (up to 0.7 mm in

diameter). On the basis of textural and structural char-

acteristics the following varieties of metabasalts were

separated: ophitic, porphyric-ophitic and divergent-

radial. These varieties contain the mineral association

of albite ± altered clinopyroxene ± secondary minerals.

Albite in the groundmass has a twig-like habit, com-

monly ranging 0.1-0.9 mm in size, and rarely occurs in

the form of phenocrysts up to 1.6 mm in length. Grains

are mostly inhomogenous because of small inclusions

of chlorite, calcite and minerals from the zoisite-epidote

group. Albite originated from the alteration of basic

plagioclases, by the albitization process under the hyd-

rothermal influence during the postmagmatic phase.

Clinopyroxenes were found exclusively in the upper

part of this sequence as small skeletal relics of yellow

augite. In other parts of the succession, albite interstices

are filled with completely weathered contours or aggre-

gates of former pyroxenes, which were postmagmati-

cally hydrothermally altered into an aggregate of chlo-

rite and blurred cryptocrystalline mass of ?clinozoisite-

epidote.

Interstices in the upper part of the sequence, near

the contact with shale, contain finely dispersed haema-

tite, and on the surface (weathering crust) also limonite,

and sporadically radial prehnite, formed by alteration of

basic plagioclases. Besides chlorite, which is the most

abundant alteration product, there is secondary, fine-

grained calcite which substitute other constituents of

the rock, forming irregular aggregates or filling numer-

ous veins. Opâque minerals, finely dispersed magnetite

and skeletal ilmenite are accessory.

Besides the Poljanica-C section, basic volcanic

rocks in the contact with red shales and cherts were

investigated at two other localities. Locality VS 94 is

situated in the Poljanica creek valley, 350 m E of Polja-

nica village, and locality VH 1001/1 is located on the

NE bank of the nameless creek, in the area called

PopovËica, approximately 500 m south of Oreπje vil-

lage (Fig. 2). These rocks are green, and according to

their microphysiographic properties they are identical

to the aforementioned rocks from the Poljanica-C sec-

tion. Due to their ophitic texture and massive structure

they were determined as ophitic metabasalts. Main

rock-forming minerals, especially pyroxenes, are com-

pletely altered, predominantly into chlorite and calcite.

Associated sedimentary rocks from these localities

were not dated.

4. STRATIGRAPHY

4.1. RADIOLARIAN DATING

Twenty samples of red and green chert were exam-

ined for radiolarians. They were prepared using stan-

dard HF methods. The location of all samples is shown

on the map (Fig. 2), the stratigraphic position of the

samples from the Poljanica-C (samples 113A), Poljani-



37HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

ca-A (samples PA), and Poljanica-B (samples PB) sec-

tions is shown in Figs. 3 and 5.

Small nassellarians predominate in all samples, spu-

mellarians are represented by rare Bernoullius and Emi -

l u v i a in addition to some indeterminable fragments

(spines, rays). Planktonic foraminifera were found in

sample PD 0.

The radiolarian dating (Table 1) is based on the

zonation of BAUMGARTNER et al. (1995b). Eight

samples correspond to the UAZ 5 and two to the UAZ

7. The assemblages in the other samples do not contain

species or pairs of species characteristic of one zone

and allow only a broader age assignment corresponding

mainly to UAZs 5 to 7. The minimum range of the

Poljanica unit is thus latest Bajocian - early Bathonian

(UAZ 5) to late Bathonian - early Callovian (UAZ 7).

Theocapsomma cucurbiformis was found in the

sample VH 882/1, which is assigned to the UAZ 5 bas-

ed on the co-occurrence of Guexella nudata and T h e o -

capsomma cordis with Unuma latusicostatus . This as-

sociation suggests that the range of T. cucurbiformis

(UAZ 6 to 7) should be extended. T. cucurbiformis i s

therefore not considered indicative of UAZ 6 and UAZ

7 in the other samples. Another example is Xitus mag -

nus, supposed to make its first appearance in the UAZ 8

but already occurring in the UAZ 7 (see sample VH

967) in association with Dictyomitrella ? k a m o e n s i s,

Stichocapsa naradaniensis and Tricolocapsa conexa .

The shortened ranges of T. cucurbiformis and X. mag -

nus in the zonation of BAUMGARTNER et al. (1995b)

are due to a small number of records for these two

species in their database.

Tricolocapsa plicarum s.l. ranges from UAZ 3 to

UAZ 8 while both subspecies T. plicarum plicarum and

T. plicarum ssp. A, range only from UAZ 4 to UAZ 5.

This discrepancy exists because in the oldest and youn-

gest samples containing T. plicarum, this species was

not introduced at subspecific level in the database of

BAUMGARTNER et al. (1995b). The proposed ranges

of T. plicarum plicarum and T. plicarum ssp. A are

therefore not considered reliable and were not used for

age determination.

The sample PA 15 comes from a deformed, brec-

ciated chert bed. In addition to C y r t o c a p s a a f f . m a s -

toidea, Stichocapsa robusta a n d Tricolocapsa tetrago -

n a , which first appear in the UAZ 5, it also contains

Cyrtocapsa mastoidea , which is restricted to UAZs 3

and 4 and seems to be reworked. The UAZ 5 or young-

er age of this sample is also evidenced by its strati-

graphic position above the UAZ 5 (sample PA12).

4.1.1. Systematics of radiolarians

Basic synonymy is provided for the species which

are not included in the catalogue of BAUMGARTNER

et al. (1995a). Theocapsomma medvednicensis n.sp. is

introduced; a short description is given for the species

in open nomenclature.

We retained the generic names (see species list in

Table 1) commonly used in the literature on Jurassic

radiolarians, although some of these names are not in

agreement with ICZN rules. Two examples of incorrect

generic assignment have recently been discussed by

KOZUR et al. (1996). Most of these taxonomic prob-

lems are not satisfactorily solved yet and would need a

more thorough revision, which is beyond the scope of

this paper.

Canoptum sp. A

(Pl. III, Figs. 18-22)

1985 C a n o p t u m sp. - YAMAMOTO et al., p. 34, pl. 3,

fig. 10.

D e s c r i p t i o n : Test multicyrtid, conical, with well pro-

nounced constrictions. Surface rough, covered with

small irregularly arranged nodes. Minute pores pre-

sent on circumferential ridges. A thin spongy mesh-

work is developed on some specimens (Pl. III, Fig.

18) suggesting that C a n o p t u m is closely related to

S p o n g o c a p s u l a PESSAGNO. The pitted surface of

the circumferential ridges on some specimens rese-

mbles that of Cinguloturris carpatica D U M I T R I-

CĂ. It seems that S p o n g o c a p s u l a and C i n g u l o t u r r i s

evolved from Canoptum.

Cyrtocapsa aff. mastoidea YAO

(Pl. I, Fig. 24)

1994 Cyrtocapsa a f f . mastoidea YAO - GORI»AN, p.

65, pl. 9, fig. 20.

1995a Stichocapsa sp. E - BAUMGARTNER et al., p.

524, pl. 4042.

Obesacapsula magniglobosa AITA

(Pl. III, Figs. 6, 7 a-b)

1987 Obesacapsula magniglobosa n. sp. - AITA, p. 71,

pl. 2, figs. 4a-b; pl. 9, figs. 10-11.

Parvicingula ? cappa CORTESE

(Pl. III, Figs. 8-9)

1993 Parvicingula cappa n. sp. - CORTESE, p. 176, pl.

4, figs. 1-4.

Protunuma fusiformis ICHIKAWA & YAO

(Pl. II, Figs. 14-16)

1976 Protunuma fusiformis n. sp. - ICHIKAWA &

YAO, p. 116, pl. 2, figs. 1-4.

Protunuma ? lanosus OÆVOLDOVÁ

(Pl. II, Figs. 20-22)

1996 ?Protunuma lanosus OÆVOLDOVÁ n. sp. -

SYKORA & OÆVOLDOVÁ, p. 23, pl. 2, fig. 13;

pl. 3, figs. 1-6.

Genus: Theocapsomma HAECKEL, emend.

FOREMAN

Theocapsomma medvednicensis GORI»AN n. sp.

(Pl. I, Figs. 12a-b, 13, 14a-b, 15-16)

1997 T h e o c a p s o m m a sp. A - ARAKAWA, pl. 6, fig.

17.



38 Geologia Croatica 52/1

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39HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

Holotype: Pl. I, Fig. 12a-b; sample PA 12.

Etymology: The species is named after its type locality,

Medvednica Mountain, northern Croatia.

D e s c r i p t i o n : Test composed of three segments. Cepha-

lis small, hemispherical. Thorax and abdomen much

larger, hemispherical; abdomen distally constricted,

having a circular aperture. The lumbar stricture well

marked. Thorax and abdomen bear small circular

pores. Thorax and lumbar stricture covered with

vertical ridges, the distal part of the abdomen is

nodose.

R e m a r k s : Theocapsomma medvednicensis n.sp. differs

from T. cordis KOCHER (KOCHER, 1981, p. 100,

pl. 17, figs. 2-4) by having ridges on the thorax and

at the lumbar stricture. It differs from T. cucurbifor -

m i s BAUMGARTNER (BAUMGARTNER et al.,

1995a, p. 574, pl. 3047) and T. bicornis B A U M-

GARTNER (BAUMGARTNER et al., 1995a, p.

572, pl. 3276) by having no horn.

Measurements (in µm, based on 13 specimens): total

height - holotype: 90, minimum: 75, maximum:

115, average: 91; width of thorax - holotype: 50,

minimum: 45, maximum: 60, average: 52; width of

abdomen: holotype: 63, minimum: 55, maximum:

75, average: 64.

Tricolocapsa sp. A sensu YAMAMOTO et al.

(Pl. II, Figs. 5-6)

1985 Tricolocapsa sp. A - YAMAMOTO et al., p. 39,

pl. 8, figs. 6a-c.

1991 Striatojaponocapsa sp. - KOZUR, pl. 3, fig. 3.

1997 Protunuma (?) sp. A - ARAKAWA, pl. 5, fig. 7.

Tricolocapsa sp. A

(Pl. II, Figs. 10-12)

1993 Tricolocapsa sp. - MAATÉ et al., fig. 3/14, 15.

D e s c r i p t i o n : Test composed of three segments. Cepha-

lis and thorax small, partly encased in the abdomen.

Abdomen subspherical, inflated. Thorax and abdo-

men perforate, and covered by longitudinal plicae.

On the thorax, the plicae are connected with trans-

verse ridges. Several rows of small circular pores

present between adjacent plicae and transverse rid-

ges.

Unuma darnoensis KOZUR

(Pl. II, Fig. 13)

1991 Unuma darnoensis n.sp. - KOZUR, pl. 2, fig. 2.

1994 Unuma darnoensis KOZUR - GORI»AN, p. 95,

pl. 10, figs. 7-8, 9a-b.

Williriedellum marcucciae CORTESE

(Pl. I, Figs. 26-28)

1993 Williriedellum ( ? )marcuccii n.sp. - CORTESE, p.

180, pl. 7, figs. 6-7.

1995a W i l l i r i e d e l l u m sp. A sensu MATSUOKA -

BAUMGARTNER et al., p. 628, pl. 4060, and syn-

onymy therein.

Xitus sp. A.

(Pl. III, Figs. 1-4)

1993 Xitus (?) sp. A - CORTESE, p. 181, pl. 7, fig. 8.

1997 X i t u s sp. - MATSUOKA & BAUMGARTNER,

pl. 3, fig. 16.

Description: Test short, conical. Cephalis smooth, pore-

less, bearing a stout apical horn. Thorax and the fol-

lowing segments with pores. Prominent tubercles

are developed on the post-thoracic segments.

4.2. CONODONT DATING

4.2.1. Material and methods

Seven samples between 0.5 to 1.5 kg were collected

and processed for conodonts by dissolving them in 15%

acetic acid following standard conodont techniques.

After laboratory treatment only four samples proved to

contain conodont elements. The frequency of conodonts

is low, mostly of fragmentary preservation.

The fossil material is stored at the Geological Sur-

vey of Slovenia, catalogue numbers IGGG 3139-3141.

The figured conodont specimens were photographed on

an EM GEOL by Dr. K. DRA©LAR (Institute of Biolo-

gy, University of Ljubljana). The location of investigat-

ed samples is shown in Figs. 2 and 3.

4.2.2. Conodont fauna

Sample PA 16A (IGGG 3128)

The sample yields a microfauna that includes

foraminifera (Toplypammina discoidea T R I F O N O V A ) ,

ostracods (Polycope sp.), echinoderm ossicles as well

as conodont elements Norigondolella steinbergensis

(MOSHER) (Pl. IV, Fig. 2) and Epigondolella ex gr.

postera (KOZUR & MOSTLER) (Pl. IV, Fig. 1). 

Age: Middle - Upper Norian. In Slovenia, diagnostic

Norian elements Epigondolella postera and N o r i -

gondolella steinbergensis have been recognized in the

p o s t e r a -A.Z. (Alaunian) and b i d e n t a t a-R.Z. (Sevatian)

(KOLAR-JURKOV©EK, 1991). 

R e m a r k s : The elements which are characterized by

a narrow platform, about half of the total unit length

and denticles arranged on the anterior part of the plat-

Table 1  Occurrence of radiolarian species in the samples studied. The first column gives zonal ranges of species according to BAUMGART-

NER et al. (1995b), the age of the samples is shown in the bottom row. The radiolarian dating indicates that the Poljanica unit spans at least

from the latest Bajocian -early Bathonian (UAZ 5) to the late Bathonian - early Callovian (UAZ 7). Note that the sample PA 15 contains a

mixed radiolarian assemblage.



40 Geologia Croatica 52/1

form are here assigned to E p i g o n d o l e l l a ex gr. p o s t e r a

(KOZUR & MOSTLER). Similar elements were sepa-

rated from the E. postera population of Canada (ORC-

HARD, 1983) and described as E. elongata O R C H A-

RD where it is a name-bearer of the Middle Norian

elongata zone (ORCHARD, 1991b).

Sample PA 18 (IGGG 3130)

The sample produced a small microfauna including

ramiform conodont elements and rare but diagnostic

platform conodont elements of Paragondolella foliata

BUDUROV.

Age: The species is characteristic of Upper Langob-

a r d i an - uppermost Julian (KOVÁCS, 1983) and has

been reported from the Tethyan realm except for the

West Mediterranean province (KOZUR, 1973; KOV-

ÁCS, 1983).

Sample PA 19A (IGGG 3131)

The microfauna contains numerous ramiform and

platform conodont elements, however mainly of frag-

mentary preservation. The elements of Neocavitella s p .

and Paragondolella tadpole (HAYASHI) (Pl. IV, Fig.

3) are recognized. 

A g e : Stratigraphic range of Paragondolella tadpole

(HAYASHI) is the Cordevolian - Lower Tuvalian inter-

val (KOVÁCS & KOZUR, 1980; KOVÁCS, 1983).

Sample PB 18 (IGGG 3134)

A small microfauna is represented by rare foramini-

fera and a single conodont element referred to Norigon -

dolella navicula (HUCKRIEDE).

Age: Stratigraphic range of Norigondolella navicula

is confined to the Norian stage (KOVÁCS & KOZUR,

1980; KOZUR, 1990) and it is regarded as definitive of

the basal Norian (ORCHARD, 1991a).

4.2.3. Summary of the conodont dating

Triassic conodont faunas are recorded from Mt.

Medvednica, Croatia. Element P. foliata is recognized

in the sample PA 18. It is an index species of the f o l i -

a t a -R.Z. that in Slovenia encompasses Upper Lango-

bardian and Lower Cordevolian (KOLAR-JURKOV-

©EK, 1991). The sample PA 19A is characterized by

the Carnian species P. tadpole . The presence of the

Ladinian-Carnian and Carnian conodont elements has

been hitherto proved in several locations of Mt. Med-

vednica (–UR–ANOVI∆, 1973; BELAK et al., 1995).

Norian conodonts were collected in two outcrops. The

element N. navicula was recovered from the sample PB

18 thus proving a Norian age. A diverse fauna of the

sample PA 16A contains E. ex gr. postera and N. stein -

b e r g e n s i s . In Slovenia, E. postera is recorded in the

Middle and Upper Norian (KOLAR-JURKOV©EK,

1991).

5. GEOCHEMISTRY

5.1. RADIOLARITES

Geochemical analyses were undertaken on the radi-

olarian cherts from the radiolarite succession, which

were dated as Jurassic on the basis of radiolarians.

Additionally, shale samples were collected for correla-

tional purposes. The position of samples in columns

and sections, as well as in the field, is presented in Figs.

2, 3 and 5.

Major elements in sedimentary rocks were deter-

mined by standard wet chemical analyses. The Ca,

F e2O3, Mg and Al contents were analysed complexo-

metrically by EDTA with corresponding indicators; Ti,

Mn and P were analysed spectrophotometrically from

the same solution. The K and Na contents were deter-

mined by flame photometry, while the Fe2+ and Si con-

tents were determined gravimetrically. Volatiles were

measured by loss of ignition at 1150 °C.

Trace elements were done by the ICP-AES method

at ACME Analytical Laboratories Ltd. (Vancouver).

Rock samples were milled into powder and homoge-

nized in an agate mill. A sample of 0.25 gr. was digest-

ed with 10 ml HClO4-H N O3-H Cl- HF at 200 °C to

fuming and diluted to 10 ml with diluted aqua regia.

This leach is partial for magnetite, chromite, barite,

oxides of Al, Zr and Mn and massive sulphide samples.

Recalculated contents of major elements on 100 %

without volatiles, trace elements contents, as well as

various ratios between major- and trace elements are

presented in Table 2. In addition, the table contains

average values of major- and trace element contents of

the Triassic radiolarian cherts and shales (HALAMI∆

& GORI»AN, 1995; HALAMI∆, 1998).

Chemical elements can be divided into three groups

according to their origin in siliceous deposits. The first

group comprise biogenic silica, originating from silice-

ous tests, spicules and other skeletal detritus. The sec-

ond group is of terrigenous origin, comprising elements

which are predominately related to clay minerals: SiO2,

T i O2, Al2O3, FeO*, MgO, Na2O, K2O, Cr, Rb and Zr.

The third group of so-called hydrogenous elements

( F e2O3, MnO, Cu, Ni, V and Zn) comprise elements

which are predominantly precipitated directly from

marine water (MATSUMOTO & IJIMA, 1983).

Alternation of radiolarian cherts and shale beds in

radiolarites results from the mutual influence of several

processes. It has been undoubtedly proven that during

diagenesis there is a segregation of silica from siliceous

mud into nodules, lenses and beds (TADA, 1991;

MURRAY et al., 1992a, b, c; DE WEVER, 1994;

MURRAY, 1994 and cited literature). However, beside

diagenetic processes, during the deposition of mud

there is an alternation of periods characterised by incre-

ased bioproductivity (e.g. radiolarians) with the con-

stant sedimentation rate of clastic detritus, or increased

input of clastic detritus with constant bioproduction

(DECKER, 1991; DE WEVER, 1994). Furthermore,



41HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

partial redeposition of sedimented material by contour

currents or low-density turbidite currents is indicated by

the sedimentary structures preserved in radiolarian

cherts, like gradation, horizontal and wavy lamination

and load casts on lower bedding surfaces (NISBET &

PRICE, 1974; FOLK & McBRIDE, 1978; VECSEI et

al., 1989; HALAMI∆ & GORI»AN, 1995).

Investigations of recent and ancient oceanic silice-

ous deposits have shown, that during diagenesis, frac-

tionation and migration of some elements occur, which

partly result in the formation of radiolarian chert/shale

alternation. During these processes important mobiliza-

tion of biogenic SiO2 takes place, which migrates into

beds enriched in silica, and from these beds Mn, Ca,

RADIOLARIAN CHERTS SILICEOUS SILTY SHALES

VH PA1 PA5 PA20 PB2 VH x SD X* VH VS VS 113/3 PA PB x SD X*
558/4 882 n=5 558/2 941) 103/11) 14C 01) n=5

SiO2 89.37 91.70 88.42 91.45 95.40 91.00 91.22 2.41 91.27 78.38 70.11 62.72 64.27 79.09 87.15 73.62 9.53 79.97
TiO2 0.21 0.20 0.24 0.28 0.12 0.24 0.22 0.05 0.18 0.44 0.61 0.73 0.30 1.44 0.22 0.62 0.44 0.42
Al 2O3 0.40 1.80 2.57 2.90 1.55 0.94 1.69 0.95 2.93 9.22 12.38 13.27 5.69 3.96 5.47 8.33 3.89 7.03
Fe2O3 6.40 4.13 6.86 3.03 2.03 4.98 4.57 1.89 2.87 5.97 7.09 9.71 10.67 6.42 3.31 7.20 2.67 5.33
MnO 0.36 0.05 0.13 0.10 0.05 0.05 0.12 0.12 0.13 0.03 0.12 0.09 0.37 0.20 0.15 0.16 0.12 0.12
MgO 1.07 0.59 0.49 0.59 0.28 0.37 0.57 0.28 0.78 0.92 1.45 1.73 16.33 0.62 0.57 3.60 6.25 1.58
CaO 1.72 0.32 0.69 0.37 0.20 0.23 0.59 0.58 0.79 0.73 1.41 0.93 1.87 2.81 0.97 1.45 0.78 1.68
Na2O 0.13 0.15 0.15 0.12 0.08 1.23 0.31 0.45 0.35 0.45 1.25 5.41 0.98 0.86 0.31 1.54 1.93 0.87
K2O 0.68 1.21 0.70 1.29 0.41 1.19 0.91 0.36 0.80 4.05 5.68 5.53 1.20 4.87 1.94 3.88 1.89 3.10
P2O5 0.02 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.02 0.00 0.02 0.01 0.01 0.01 0.01

CaCO3 2.92 0.46 1.06 0.49 0.27 0.34 0.92 1.02 1.23 0.77 1.77 0.92 2.81 4.50 1.41 2.03 1.41 2.50

Al 2O3 / TiO2 1.91 9.00 10.71 10.36 12.92 3.92 8.14 4.28 16.28 20.95 20.30 18.18 18.97 2.75 24.86 17.67 7.67 16.74

Fe2O3 / TiO2 30.48 20.65 28.58 10.82 16.92 20.75 21.37 7.31 15.94 13.57 11.62 13.30 35.57 4.46 15.05 15.60 10.47 12.69

100x
Fe2O3 /SiO2

7.16 4.50 7.76 3.31 2.13 5.47 5.06 2.18 3.14 7.62 10.11 15.48 16.60 8.12 3.80 10.29 4.91 6.66

100x
Al 2O3 / SiO2

0.45 1.96 2.91 3.17 1.62 1.03 1.86 1.05 3.21 11.76 17.66 21.16 8.85 5.01 6.28 11.79 6.44 8.79

Fe2O3 /
100-SiO2

0.60 0.50 0.59 0.35 0.44 0.55 0.51 0.09 0.33 0.28 0.24 0.26 0.30 0.31 0.26 0.28 0.03 0.27

Al 2O3 /
100-SiO2

0.04 0.22 0.22 0.34 0.34 0.10 0.21 0.12 0.34 0.43 0.41 0.36 0.16 0.19 0.43 0.33 0.12 0.35

Al 2O3 /
Al 2O3+Fe2O3

0.06 0.30 0.27 0.49 0.43 0.16 0.29 0.16 0.51 0.61 0.64 0.58 0.35 0.38 0.62 0.53 0.13 0.57

Si / Si+Al+
Fe+Ca 0.88 0.91 0.86 0.92 0.95 0.91 0.91 0.03 0.91 0.79 0.72 0.67 0.72 0.81 0.87 0.76 0.07 0.81

Al / Al+
Fe+Mn 0.04 0.25 0.22 0.41 0.36 0.12 0.23 0.14 0.43 0.54 0.56 0.51 0.28 0.31 0.54 0.46 0.13 0.47

Ba 51 104 98 92 71 85 84 20 130 206 239 276 35 229 100 181 93 297
Th 2 2 3 3 < 2 3 2 1 2 7 9 11 5 10 3 8 3 7
Nb 2 5 4 4 2 2 3 1 3 6 8 7 3 10 4 6 3 7
Sr 37 35 37 58 14 25 34 15 24 49 49 60 16 38 32 41 16 45
Y 9 6 6 10 2 6 7 3 4 10 14 25 11 18 12 15 6 10
Zr 7 23 21 22 6 15 16 8 13 21 39 58 23 53 20 36 17 38
Sc 4 5 6 7 2 6 5 2 4 13 19 23 7 17 7 14 7 12
Cr 15 18 25 26 9 20 19 6 16 60 73 97 42 85 30 65 26 37
Ni 48 23 26 32 10 44 31 14 20 45 56 116 200 86 32 89 62 54
Cu 35 41 55 59 25 47 44 13 51 20 68 81 9 113 65 59 39 88
Pb 27 <5 < 5 7 < 5 6 9 9 7 11 20 29 < 5 < 5 7 13 10 15
Zn 67 32 44 20 11 55 38 21 33 52 48 118 46 117 33 69 38 72
Co 25 7 6 23 5 26 15 10 8 13 7 31 21 28 12 19 10 15
V 25 31 34 45 15 35 31 10 21 93 115 159 107 142 47 111 39 50
La 6 9 13 13 3 10 9 4 7 23 30 36 11 31 13 24 10 18

Th/Sc 0.50 0.40 0.50 0.43 0.50 0.50 0.47 0.04 0.50 0.54 0.47 0.48 0.71 0.59 0.43 0.54 0.10 0.58

Table 2  Major element content (%), recalculated on 100% without volatiles and some trace elements (mg/kg) in radiolarian cherts and radiolari-

an shales. Major element analysis were performed by classical silicate-chemical method at the Institute of Geology, Zagreb; analyst: Vlasta

JURI©I∆-MITROVI∆. Trace elements were measured by ICP-AES at ACME Laboratories, Vancouver, Canada. Legend: x) average value;

SD) standard deviation; X*) average values of Triassic sediments (after HALAMI∆ & GORI»AN, 1995). 1) Shale samples are not dated

because of the lack of fossil material; however, they are attributed to the Poljanica unit since they contact dated cherts.



42 Geologia Croatica 52/1

Mg, P, Sr and Ba are remobilized and removed (MUR-

RAY, 1994). Manganese is especially subject to these

processes, and its migration is further enhanced during

subductional-accretional processes involving pelagic

sediments. During diagenesis moderately migrative ele-

ments entering into chert beds are K, Na, Ge, Co and B,

while V migrates out. On the basis of these facts MUR-

RAY (1994) proposed that only Al, Ti, Fe and rare

earth elements should be used as the most reliable for

determination of the geotectonic position of radiolarites

and radiolarian chert origin with discrimination dia-

grams (GIRTY et al., 1996).

As a result of the important migration of SiO2 d u r-

ing the diagenetic processes, radiolarian tests within

shale beds should be weakly preserved (MURRAY et

al., 1992a). However, microscopic examination of thin-

sections prepared from samples of silicified shale beds

of Jurassic radiolarites of Medvednica Mt. and similar

rocks of Triassic age from Kalnik and Medvednica

Mts., has shown that radiolarian tests in these rocks are

best preserved (HALAMI∆ & GORI»AN, 1995; HAL-

AMI∆, 1998). Therefore, for estimation of the biogenic

silica contents in radiolarites we used a value of the

Si / Si+ Al+Fe+Ca ratio (RANGIN et al., 1981; RUI-

TZ-ORTIZ et al., 1989), while for calculation of CaCO3

we used a method after BALTUCK (1982).

Examination of the major element contents in the

analysed samples (Table 2) revealed that some of the

shale samples are characterised by significantly incre-

ased SiO2 contents, and therefore could be determined

as siliceous shales. Furthermore, shales have much

higher values of all major elements than the cherts

(except SiO2, FeO and MnO contents), which is the

result of the quantity and variability of terrigenous

material composing the shales. The Fe content of shales

is generally significantly higher than that of the cherts.

Results of trace element analysis of shales show

generally higher values of all trace elements in respect

to cherts, which is caused by the higher clay minerals

content of shales.

The Si / Si+Al+Fe+Ca ratio presents information

on the content of biogenic silica with respect to alumi-

nosilicates and ferrugenous and calcic minerals (RAN-

GIN et al., 1981; RUITZ-ORTIZ et al., 1989). Rocks

rich in biogenic silica have ratio values between 0.8 -

0.9. Investigated radiolarian cherts have an average

ratio value on the upper boundary of this range (0.9 -

see Table 2), indicating that the major part of silica in

cherts originates from siliceous tests and biogenic

siliceous detritus. The principal portion of silica in sha-

les is also of biogenic origin (high values of the ratio -

0.76), which is further indicated by well preserved radi-

olarian skeletons in shales.

Calculated values of the Fe2O3/TiO2, Al2O3/(Al2O3+

Fe2O3), 100xFe2O3/SiO2, 100xAl2O3/SiO2, Fe2O3/100-

SiO2 and Al2O3/ 100-SiO2 ratios (Table 2) were inserted

into discrimination diagrams after MURRAY (1994).

This author suggested the aforementioned major ele-

ment ratios as the most reliable for the determination of

depositional environments for siliceous rocks. His

chemical sedimentary model distinguished three areas

on these diagrams: a) spreading ridge - proximal or near

ridge, b) pelagic (including parts of the sedimentary

area closer to the continent, but topographically protect-

ed from more important terrigenous input) and c) conti-

Fig. 11  a) Diagram of Fe2O3 /A l2O3 ratio normalized on SiO2. Points

representing analyzed samples bundle in the field indicating

vicinity of the mid-oceanic ridge; b) Diagram representing

F e2O3 /A l2O3 ratio normalized on 100 -S i O2. The analyzed sam-

ples also bundle in the field indicating vicinity of the mid-ocean-

ic ridge; c) Diagram showing bundling of Jurassic radiolarite

samples near the field indicating vicinity of the mid-oceanic

ridge, but are below it because of the increased Ti values. To a

lesser extent samples fall within the field of pelagic environment.

*) average value for Triassic cherts (n=5; after HALAMI∆ &

GORI»AN, 1995).



43HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

nental margin (back-arc basins, marginal seas, epiconti-

nental seas and open continental shelves) (MURRAY,

1994, p. 218).

On the basis of calculation of the aforementioned

major element ratios, investigated Jurassic radiolarites

fall within the fields of the area near the mid-oceanic

ridge (Fig. 11a and b). Figure 11c shows a certain dissi-

pation of a minor part of the data into the pelagic area,

while the major part is grouped in the area which corre-

sponds to the vicinity of the mid-oceanic ridge.

Since they are connected with aluminosilicates, Al

and Ti are good indicators of a terrigenous influence.

The Al2O3/T i O2 ratio for the analysed cherts ranges

from 1.91-12.92 (average value 8.14 - see Table 2),

indicating that detrital material in cherts may have orig-

inated from an undifferentiated magmatic arc charac-

terised by a predominance of basic magmatic rocks

over acid varieties (Al2O3/ T i O2 ratio values for these

areas are ≤14 - GIRTY et al., 1996). However, the pos-

sibility of a detrital origin from the accretionary prism

comprising parts of the MORB cannot be excluded.

Values of the Th/Sc ratio for Jurassic cherts (Table 2)

also indicates an origin of the material from a magmatic

arc, but also a possible origin from oceanic island arcs.

Despite the fact that manganese is very mobile dur-

ing diagenetic and later processes (as previously dis-

cussed), we took values of the Al/Al+Fe+ Mn ratio for

evaluation of the hydrothermal influence on the origin

of the siliceous sediments (BALTUCK, 1982; ADA-

CHI et al., 1986), i.e. for estimation of the contribution

of continental material in respect to the oceanic materi-

al (RUITZ-ORTIZ at al., 1989). Removal of manganese

from this calculation would not significantly change

values of this ratio (because of its small contents in the

rocks - from 0.05-0.36%, average 0.12%), while in this

case it would not be possible to compare our results

with published data. The value of this ratio for typical

continental material is 0.619 (average value for shale),

for marine biogenic material 0.391, for basaltic material

of the Eastern Pacific rift 0.00815 (BALTUCK, 1982),

and for pelagic clays 0.54 (WEDEPOHL, 1969). The

studied Jurassic cherts exhibit much lower average val-

ues (0.23) than for continental material, which indicate

a large distance from the continental mass to the sedi-

mentary area, i.e. weaker terrigenous influence. In con-

trast, debris flow beds and siltite and shales indicate a

more important input of terrigenous material.

Increased values of Al /Al+Fe+Mn ratio in shales

in respect to cherts represent a consequence of the high-

er contents of clay minerals.

5.2. VOLCANIC ROCKS

Geochemical analysis were performed on 4 samples

of magmatic rocks (Figs. 2 and 5). Samples VS113/1

and VS113A4 were collected on the Poljanica-C geo-

logical section (Fig. 5). Samples VS94 and VH1001

from separate localities (Fig. 2) are taken from rocks

which are in contact with dark red haematized shales

without any fossil remains, and therefore they were not

stratigraphically determined; however, on the basis of

geological relationships they are attributed to the Polja-

nica unit.

Major element and some trace element (Rb, Sr, Y,

Nb and Ba) analyses were performed by the XRF

method at XRAL Laboratories (Canada). Other trace

elements were analysed by the ICP-AES method in

ACME Analytical Laboratories (Canada). Results of

these analyses are presented in Table 3, and the CIPW

normative composition and petrochemical indices in

Table 4.

Sample VH VS VS VS VH VS VS VS Average
1001 94 113/1 113A4 10011) 941) 113/11) 113A41) *MORB

SiO2 46.90 37.00 48.10 44.30 51.01 42.08 52.25 49.25 49.10 ± 1.50

TiO2 2.13 1.44 0.93 1.11 2.31 1.64 1.03 1.23 1.17 ±0.05

Al 2O3 13.10 16.60 14.00 15.40 14.25 18.88 15.50 17.12 15.60 ± 1.60

Fe2O3 3.63 2.94 2.43 2.61 3.95 3.34 2.69 2.90 2.60 ± 1.40

FeO 9.51 9.77 2.95 6.27 10.34 11.11 3.27 6.97 6.70 ± 1.70

MnO 0.29 1.60 0.29 0.83 0.32 1.82 0.32 0.92 0.16 ±0.03

MgO 7.90 9.39 5.68 11.10 8.59 10.68 6.29 12.34 8.20 ±2.30

CaO 5.06 5.81 12.00 4.67 5.50 6.61 13.28 5.19 11.80 ± 1.40

Na2O 3.03 3.06 3.55 3.47 3.29 3.49 3.93 3.86 2.40 ± 0.50

K2O 0.17 0.03 0.26 0.06 0.18 0.03 0.29 0.06 0.20 ±0.19

P2O5 0.23 0.29 0.14 0.12 0.25 0.33 0.15 0.13 0.12 ± 0.05

LOI 6.35 11.20 8.20 9.50

Total 99.40 100.30 99.00 100.30

Ba 213 298 189 124

Cr <50 312 364 780

Nb 8 18 12 8

Sr 116 52 169 73

V 458 168 238 213

Y 51 34 24 25

Zr 151 106 75 81

Table 3  Chemical compo-

sition of metabasalts

(wt. %) and some trace

elements (mg/kg). 
1) Recalculated on 100

% without volatiles.

*MORB) middle-ocea-

nic ridge basalt (WED-

EPOHL, 1988).



44 Geologia Croatica 52/1

According to their SiO2 contents on the TAS dia-

gram (Le BAS et al., 1986) samples VH1001 and

VS113A4 represent basic rocks, sample VS94 ultraba-

sic, while sample VS113/1 falls within the field of neu-

tral rocks, but very close to the border with basic rocks

(Fig. 12). On the same diagram two analyzed samples

fell within the basalt field, and sample VS113/1 in the

field of basaltic andesite, as a consequence of increased

S i O2 contents resulting from the presence of quartz

vesicles. Sample VS94, which represents the most alte-

red rock, falls within the field of basanite and tephrite

because of the low SiO2 contents, which is a conse-

quence of the presence of a large quantity of chlorite,

pumpellyite(?), and less prehnite, the formation of

which caused migration of the surplus silica from the

rock.

According to the normative CIPW composition

(Table 4), most of the samples contain normative

hypersthene, except sample VS94 which contains nor-

mative nepheline and belong to the alkali basalts. Fur-

thermore, normative olivine is present in most samples,

and is especially high in sample VS94, where it is stat-

ed instead of chlorite. High values of normative nephe-

line and olivine in sample VS94 are caused by high Na

contents, which is introduced in the rock by hydrother-

mal solutions with insufficient Si. In normative anor-

CIPW norms Petrochemical indices

Sample VH VS VS VS VH VS VS VS
1001 94 113/1 113A4 1001 94 113/1 113A4

qz 2.01 - - - AI 5.3 1.0 6.8 1.7

c - 1.89 - 1.58 FI 38.7 34.7 24.1 43.0

or 1.09 0.20 1.70 0.39 MI 62.5 57.5 48.7 44.4

ab 27.88 21.48 33.25 32.64 SI 33.1 37.7 38.8 47.7

an 23.53 30.63 23.80 24.89 DI 31.0 26.0 34.9 33.0

ne - 4.32 - - VSM Th Th CA CA

diwo 0.89 - 17.16 - VSIB B PB B B

dien 0.53 - 13.12 -

difs 0.31 - 2.24 - CA - calc-alk.
hyen 20.86 - 1.20 11.55 Th - tholeiite
hyfs 12.18 - 0.21 3.79 B - basalt
olfo - 18.64 0.94 13.45 PB - picrite basalt
olfa - 14.15 0.18 4.86

mt 5.72 4.58 3.90 4.21

hm - - - -

il 4.40 3.11 1.95 2.34

ap 0.58 0.76 0.36 0.31

norm Pl. (%an) 46 52 42 43

Table 4  CIPW normative

composition and petro-

chemical indices.

Fig. 12  TAS diagram (Le BAS et al., 1986). Legend: 1) basanite and

tephrite; II) phonotephrite; III) tephriphonolite; IV) basaltic tra-

chyandesite; V) trachybasalts; VI) basalts; VII) basaltic andesite;

VIII) andesite.

Fig. 13  TiO2 vs. Zr /P2O5 diagram (WINCHESTER & FLOYD,

1976).



45HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

thite part of the calcium from the zoisite-epidote group,

as well as prehnite and rarely augite is included; these

minerals are very common, and therefore increase the

anorthite contents.

By comparison of some major elements contents

with the average major element contents in oceanic

tholeiites of mid-oceanic ridges (MORB; Table 3)

increased Na2O contents (as a consequence of postcon-

solidational changes) and decreased K2O contents may

be noted. In sample VH1001 TiO2 is increased, in sam-

ple VS94 MnO is increased, while in sample VS113/1

the Fe2 + content is significantly decreased. Contents of

other major elements are within the range of average

values for MORB.

On the TiO2 vs. Zr /P2O5 diagram (WINCHESTER

& FLOYD, 1976) all samples fall within the field of

tholeiite, except sample VS-94 which belongs to the

alkali basalts (Fig. 13). On the basis of SiO2 v s .

( N a2O + K2O) ratio (MIYASHIRO, 1974) it is visible

that samples VH1001 and VS113/1 fall within the field

of subalkalic basalts, and samples VS94 and VS113A4

within the field of alkali basalts (Fig. 14). However, on

the SiO2 vs. FeO*/ MgO diagram (MIYASHIRO, 1974)

samples VS113/1 and VS113A4 fall within the field of

calc-alkali basalts, sample VH1001 in the field of the

tholeiitic series, and sample VS94 in the same field,

although outside the diagram (because of decreased

SiO2 contents).

Contents of some typical trace elements were used

for the interpretation of geotectonic regime in which

basic magmas were produced. On the Ti-V diagram

(SHERVAIS, 1982) all rocks belong to high-titanium

basalts formed in the MORB realm (Ti /V ratio > 2 0 ) ,

except sample VS94, which, due to decreased value of

V, falls outside the area (Fig. 15). A similar situation is

present on the Zr :T i / 1 00 :Yx3 diagram (PEARCE &

CANN, 1973), where all analyzed rocks are concentrat-

ed within the MORB field (Fig. 16). On the Zr/4:2 Nb:

Y diagram (MESCHEDE, 1986) analyzed samples mo-

stly fall within the E-MORB type field, except for one

sample which falls within the N-MORB field (Fig. 17).

Due to the small number of samples, processes of

hydrothermal alteration, spilitization and low-grade

metamorphism, together with the enhanced mobility of

some major elements, the analyzed rocks concerning

the magma character show two different results: they

belong to alkalic, but also to tholeiitic rock series. Fresh

rocks belong to the tholeiitic series, which suggests

their primary tholeiitic character.

In the geotectonic sense analyzed metabasalts belo-

ng to the tholeiitic basalts of the MOR.

6. DISCUSSION

Radiolarian cherts in radiolarites show no sedimen-

tary structures except lamination. A lack of other struc-

tures indicates the “normal” deposition, i.e. alternation

of periods with increased bioproduction or periods with

Fig. 15  Ti-V discrimination diagram (SHERVAIS, 1982). Legend: I)

arc tholeiite; II) calc-alkali basalts; III) MORB and BAB; IV)

continental flood basalts; V) ocean-island and alkali basalts.

Fig. 14  Variation diagram

F e O* /MgO vs. SiO2

and TAS diagram (MI-

YASHIRO, 1974).



46 Geologia Croatica 52/1

increased input of terrigenous material. The difference

in silica contents in different layers is further increased

by diagenetic processes (TADA, 1991; MURRAY et

al., 1992a; MURRAY, 1994).

Centimetre-thick layers of quartz arenite within

radiolarite are the consequence of rapid deposition by

gravity flows, while the angularity of grains indicates

relatively short transport. On the basis of mineral com-

position (predominantly undulatory quartz, microquar-

tzite, garnet and mica, and only subordinate magmato-

genic quartz) it may be concluded that the continental

source area was composed mostly of metamorphic

rocks, and subordinately of acid magmatic rocks.

Metre-thick layers of matrix-supported conglomer-

ates within the radiolarites described from the VH891

locality (Fig. 2), as well as from other localities, are the

consequence of tectonic activity within the depositional

area or on its margin, which resulted in debris flows of

unconsolidated sediments.

In the study area radiolarites s. str. are subordinate

to shales and siltites, and are found as metre-decametre

thick packages within pelitic sediments. This indicates

that: a) periods with increased input of terrigenous

material were much longer than those with increased

bioproductivity, or b) that significantly increased input

of terrigenous material took place in a short period.

Debris flow layers support the latter assumption. Geo-

chemically analyzed radiolarite samples fall within the

diagrammatic fields suggesting the vicinity of the ridge

(Fig. 11a-c). This might be related to some sediment

input from the oceanic crust or accretionary wedge as

also suggested by metabasalt clasts in conglomerates.

On the basis of the appearance of decimetre-metre

sized carbonate olistoliths of Triassic age in radiolar-

ites, it may be concluded that parts of the Triassic car-

bonate platform were, during the Middle Jurassic, locat-

ed close to the sedimentary realm where siliceous rocks

were deposited. Carbonate rocks formed the relatively

steep slopes of the sedimentary basin, and their parts

disintegrated and fell into unconsolidated siliceous

mud. Additionally, these tectonically uplifted parts rep-

resented a barrier to a greater input of terrigenous mate-

rial into the sedimentary basin. This described arrange-

ment of elevated areas and a deeper-water sedimentary

basin is a consequence of subduction processes which

were already active in this area (HALAMI∆, 1998).

Further subduction caused more severe disintegra-

tion of the described deposits and resulted in formation

of a tectonic mélange, which also incorporated parts of

the Triassic oceanic crust (basic magmatic rocks) as

well as parts of the Triassic siliceous rocks.

Similar Middle Jurassic successions composed of

chert, shale, sandstone and olistostromes with clasts of

Triassic rocks were described from the Western Carpa-

thians (KOZUR & MOCK, 1985, 1995, 1997; KOZUR,

1991; KOZUR et al., 1996) and from the Northern Cal-

careous Alps (MANDL & ONDREJI»KOVÁ, 1991,

1993; KOZUR & MOSTLER, 1992). These facies

associations are considered the most characteristic low-

er Mesozoic tectofacies of the Meliaticum (KOZUR &

MOCK, 1997). HALAMI∆ & GORI»AN (1995) corre-

lated the Triassic radiolarites overlying basic volcanic

rocks in the study area, with those of the Meliata Unit.

The presence of a Middle Jurassic (uppermost Bajo-

Fig. 16  Zr: T i / 1 00 : Yx3 diagram (PEARCE & CANN, 1973). Leg-

end: A) island-arc tholeiites; B) MORB; C) calc-alkali basalts;

D) within-plate basalts.

Fig. 17  Zr/4 :2 Nb :Y diagram (MESCHEDE, 1986). Legend: AI)

within-plate alkali basalts; AII) within-plate alkali basalts and

within-plate tholeiite; B) E-type MORB; C) within-plate tholeiite

and volcanic-arc basalts; D) N-type MORB and volcanic-arc

basalts.



47HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek: A Middle Jurassic Radiolarite-Clastic Succession...

c i an - lower Bathonian to upper Bathonian - lower Cal-

lovian) radiolarite-clastic succession further supports

the idea that the study area was part of the Meliata-

Hallstatt Ocean. HALAMI∆ & GORI»AN (1995) poin-

ted out that the Triassic basalts are younger in the Med-

v e d n i ca - Kalnik area (Middle Carnian to uppermost

C a r n i an - Norian than in the Meliata Unit (Ladinian to

Lower Carnian). More recently, HALAMI∆ et al.

(1998) proved that some pillow lavas of MORB type in

Medvednica Mt. are as old as upper Anisian to lower

Ladinian. The age difference between the basalts in the

Meliata Unit and the Medvednica-Kalnik area is thus

minor and does not contradict the assignment of the

studied Mesozoic succession to the Meliata-Hallstatt

Ocean.

HALAMI∆ & GORI»AN (1995) correlated the

M e d v e d n i ca - Kalnik area also with the Vardar Zone in

Serbia, based on the occurrence of Carnian - N o r i a n

basic volcanics in both areas. The ophiolite-bearing

clastic succession (ophiolitic mélange) of the Vardar

Zone is assignable to the Middle and Upper Jurassic as

evidenced by its stratigraphic position (DIMITRIJE-

VI∆, 1995). Due to the lack of more precise biostrati-

graphic data for the Jurassic successions of the Vardar

Zone, a reliable correlation with the Poljanica unit is

still not possible.

7. CONCLUSIONS

Siliceous and siliciclastic deposits from the area

between the Poljanica and Jelenja voda creeks in NW

Medvednica Mt. consist of radiolarites s. str., shales and

siltites, radiolarian cherts with carbonate olistoliths and

matrix-supported conglomerates. These rocks were

attributed to the Poljanica informal lithostratigraphic

unit.

On the basis of radiolarians it is concluded that the

analyzed radiolarites were deposited from the latest

B a j o c i an - early Bathonian (UAZ 5) to late Bathonian -

early Callovian (UAZ 7). Furthermore, study of con-

odonts from the carbonate olistoliths proved their late

Ladinian - Carnian, Carnian and Norian age.

Geochemical scatter diagrams of major elements

indicate that the radiolarites were deposited in the area

close to the mid-oceanic ridge. However, sedimentolog-

ical characteristics indicate significant input of terrige-

nous detritus (matrix-supported conglomerates, siltites

and shales), which suggests proximity to the continent.

For comparison, diagrams include data for Triassic che-

rts from the same area (HALAMI∆ & GORI»AN,

1995), which were, according to geochemical data, also

deposited in marginal areas, i.e. in the area closer to the

continental mass.

Several textural varieties of metabasalts associated

with siliceous rocks were analyzed petrographically.

Geochemical analysis of these rocks indicated that

these high-titanium tholeiitic basalts were generated in

the area of the mid-oceanic ridge. It should be noted

that the age of these metabasalts has not been proven. It

is possible that they represent large olistoliths or off-

scraped blocks in the mélange and could thus be Middle

to Late Triassic in age.

Investigated Middle Jurassic radiolarites with Trias-

sic carbonate olistoliths, shales and siltites, matrix-sup-

ported conglomerates and basic volcanic rocks were

incorporated in an accretionary prism, where they were

brought in direct contact with Triassic volcanic rocks

and radiolarites (tectonic mélange).

Based on the lithological similarities with Middle

Jurassic turbidite - olistostrome successions in the

Western Carpathians and in the Northern Calcareous

Alps, the study area is considered to have been part of

the Meliata - Hallstatt Ocean. This palaeogeographic

location is also suggested by previously documented

Triassic basic volcanics (HALAMI∆ & GORI»AN,

1995; HALAMI∆ et al., 1998).

Acknowledgements

The authors are grateful to Drs. H. KOZUR (Buda-

pest), L. DOSZTÁLY (Budapest), S. KOVÁCS (Buda-

pest), L. PALINKA© (Zagreb) and I. VELI∆ (Zagreb)

for their critical reading and improvement of the manu-

script. The authors are indebted to Dr. M.J. ORCHARD

(Vancouver) for critical reading of the conodont dating

section. We wish to thank I. LAPAJNE (Ljubljana) and

M. GRM (Ljubljana) for processing the scanning elec-

tron micrographs of radiolarians.

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50 Geologia Croatica 52/1

MURRAY, R.W., JONES, D.L. & BUCHHOLTZ TEN

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PLATE I

Radiolarians

For each illustration the sample number, SEM-negative number, and magnification are indicated. The scanning

electron micrographs were taken on a JEOL JSM-330A at the Institute of Palaeontology, Scientific Research Centre

of the Slovenian Academy of Sciences and Arts. Rock samples, residues and SEM negatives are stored in the col-

lection of the second author.

1-2 Eucyrtidiellum ptyctum(RIEDEL & SANFILIPPO), 1: VH 558/5, 961022; 2: VH 967, 971905; 200x.

3 Eucyrtidiellum nodosum WAKITA, VH 967, 971906, 200x.

4 Eucyrtidiellum unumaense pustulatum BAUMGARTNER, 113 A13, 962111, 200x.

5 Bernoullius cristatus BAUMGARTNER, JV©P, 971006, 200x.

6-7 Guexella nudata (KOCHER), 6: PA 12, 960716; 7: JV©P, 971026; 200x.

8-9 Stylocapsa oblongula KOCHER, 8: PE 1, 960113; 9: VH 967, 971934; 200x.

10-11 Theocapsomma cucurbiformis BAUMGARTNER, 10: PA 15, 961603; 11: VH 882/1, 961733; 200x.

12-16 Theocapsomma medvednicensis GORI»AN n. sp., 12 (holotype): PA 12, a: 960718, b: antapical view,

980101; 13: PB 18A, 960332; 14: PB 18A, a: 960326, b: antapical view, 980115; 15: PA 12, 960527; 16:

PD 0, 961101; 300x. 

17-19 Theocapsomma cordis KOCHER, 17: JV©P, 971005; 18: VH882/1, 961735; 19: VH 967, 971914; 300x.

20 Stichocapsa himedaruma AITA, PD 0, 961035, 300x.

21 Tricolocapsa? fusiformis YAO, PA 15, 961614, 300x.

22 Tricolocapsa? aff. fusiformis YAO, PD 0, 961207, 300x.

23 Cyrtocapsa mastoidea YAO, PA 15, 961534, 200x.

24 Cyrtocapsa aff. mastoidea YAO, PA 15, 961535, 200x.

25a, b Stichocapsa robusta MATSUOKA, PB 18A, 25a: 960321; 25b: antapical view, 960320; 200x.

26-28 Williriedellum marcucciae CORTESE, 26: VH 882/1, 961722; 27: PA 12, 960611; 28: PA 12, 960609;

200x.



51HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek PLATE I



52 Geologia Croatica 52/1

ORCHARD, M.J. (1991b): Upper Triassic conodont

biochronology and new index species from the

Canadian Cordillera.- Geol. Survey of Canada Bull.,

417, 299-335, Vancouver.

PAMI∆, J. & TOMLJENOVI∆, B. (1998): Basic geolo-

gical data from the Croatian part of the Zagorje -

Mid-Transdanubian Zone.- Acta geol. Hungarica,

41/4, 389-400, Budapest.

PEARCE, J.A. & CANN, J.R (1973): Tectonic setting

of basic volcanic rocks determined using trace ele-

ment analyses.- Earth Planet. Sci. Lett. 19, 290-300.

PESSAGNO, E.A. & NEWPORT, R.L. (1972): A tech-

nique for extracting Radiolaria from radiolarian

cherts.- Micropaleontology, 18/2, 231-234.

RANGIN, C., STEINBERG, M. & BONNOT-COUR-

TOIS, C. (1981): Geochemistry of the Mesozoic

bedded chert of Central Baja California (Vizcaino-

Cedros-San Benito): implications for paleogeo-

graphic reconstruction of an old oceanic basin.-

Earth Planet. Sci. Lett., 54, 313-322.

RUITZ-ORTIZ, P.A., BUSTILLO, M.A. & MOLINA,

J.M. (1989): Radiolarite sequences of the Subbetic,

Betic Cordillera, Southern Spain.- In: HEIN, J.R. &

OBRADOVI∆, J. (eds.): Siliceous Deposits of the

Tethys and Pacific Regions. Springer Verlag, 107-

127, New York, Berlin, Heidelberg, London, Paris,

Tokyo.

SHERVAIS, J.W. (1982): Ti-V plots and the petrogen-

esis of modern and ophiolitic lavas.- Earth. Planet.

Sci. Lett., 59, 101-118. 

SYKORA, M. & OÆVOLDOVÁ, L. (1996): Lithocla-

sts of Middle Jurassic radiolarites in debris flow

sediments from Silica Nappe (locality Bleskovy pra-

men, Slovak Karst, Western Carpathians).- Miner-

alia Slovaka, 28, 21-25.

©IKI∆, K. (1995): Prikaz geoloπke grae Medvednice.-

In: ©IKI∆, K. (ed.): Geoloπki vodiË Medvednice.

PLATE II

Radiolarians

For each illustration the sample number, SEM-negative number, and magnification are indicated. The scanning

electron micrographs were taken on a JEOL JSM-330A at the Institute of Palaeontology, Scientific Research Centre

of the Slovenian Academy of Sciences and Arts. Rock samples, residues and SEM negatives are stored in the col-

lection of the second author.

1 Tricolocapsa plicarum plicarum YAO, PA 15, 961608, 200x.

2 a, b Tricolocapsa plicarum ssp. A sensu BAUMGARTNER et al., PD 0, 2a: 961116; 2b: antapical view,

961115; 200x.

3-4 Tricolocapsa conexa MATSUOKA, 3: PA 12, 960510, 4: PB 18A, 960317; 200x.

5-6 Tricolocapsa sp. A sensu YAMAMOTO et al., 5: PA 12, 960532; 6: VH 882/1, 961727; 300x.

7-8 Tricolocapsa tetragona MATSUOKA, 7: PD 0, 961129; 8: PB 18A, 960310; 200x.

9 Stichocapsa naradaniensis MATSUOKA, VH 967, 971912, 300x.

10-12 Tricolocapsa sp. A, PA 12; 10: 960518; 11: 960713; 12: 960520; 200x.

13 Unuma darnoensis KOZUR, 113 A3, 961913, 200x.

14-16 Protunuma fusiformis ICHIKAWA & YAO, 14: VH 967, 971908; 15: PA 15, 961612; 16: PA 15, 961613;

200x.

17-18 Unuma latusicostatus (AITA), 17: PA 12, 960524; 18: PD 0, 961219; 200x.

19 Protunuma turbo MATSUOKA, PB 7, 961504, 200x.

20-22 Protunuma? lanosus OÆVOLDOVÁ, 20: PD 0, 961208; 21: PA 12, 960515; 22: PB 6, 961409; 300x.

23-24 Protunuma? ochiensis MATSUOKA, PA 12, 23: 960615; 24: 960721; 200x.

25-27 Archaeodictyomitra? amabilis AITA, 25: PD 0, 961114; 26: PD 0, 961212; 27: PA 12, 960604; 200x.



53HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek PLATE II



54 Geologia Croatica 52/1

Inst. za geol. istraæ. and INA-Naftaplin, 7-30, Za-

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©IKI∆, K., BASCH, O. & ©IMUNI∆, An. (1977): Osn-

ovna geoloπka karta 1:100.000. List Zagreb L38-

80.- Inst. za geol. istraæ. Zagreb (1972), Sav. geol.

zavod, Beograd.

©IKI∆, K., BASCH, O. & ©IMUNI∆, An. (1979): Osn-

ovna geoloπka karta SFRJ 1:100 000. TumaË za list

Zagreb L33-80.- Inst. za geol. istr. Zagreb (1972),

Sav. geol. zavod, Beograd, 81 p.

©IMUNI∆, Al. & ©IMUNI∆, An. (1979): Litofacijelno

raπËlanjivanje mezozojskih naslaga KalniËkog gor-

ja.- Zbornik radova 4. god. Znan. skupa Sekcije za

primjenu geol., geofiz., geokem. Znan. savjeta za

naftu Jugosl. Akad. znan. i umjet., StubiËke Toplice

(1978), 125-137, Zagreb.

TADA, R. (1991): Compaction and cementation in sili-

ceous rock and their possible effect on bedding

enhancement.- In: EINSELE, G., RICKEN, W. &

SEILACHER, A. (eds.): Cycles and Events in Stra-

tigraphy. Springer Verlag, 480-491, Heidelberg,

New York.

VECSEI, A., FRISCH, W., PIRZER, M. & WETZEL,

A. (1989): Origin and tectonic significance of radio-

larian chert in the Austroalpine rifted continental

margin.- In: HEIN, J.R. & OBRADOVI∆, J. (eds.):

Siliceous Deposits of the Tethys and Pacific Regi-

ons. Springer Verlag, 65-80, New York, Berlin,

Heidelberg, London, Paris, Tokyo.

WEDEPOHL, K.H. (1969): Composition and abun-

dance of common sedimentary rocks.- In: WEDE-

POHL, K.H. (ed.): Handbook of Geochemistry, Vol.

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WEDEPOHL, K.H. (1988): Spilitization in the ocean

crust and seawater balances.- Fortschr. Miner., 66/2,

129-146.

PLATE III

Radiolarians

For each illustration the sample number, SEM-negative number, and magnification are indicated. The scanning

electron micrographs were taken on a JEOL JSM-330A at the Institute of Palaeontology, Scientific Research Centre

of the Slovenian Academy of Sciences and Arts. Rock samples, residues and SEM negatives are stored in the col-

lection of the second author.

1-4 Xitus sp. A, 1: PD 0, 961125; 2: PD 0, 961102; 3: PC 50, 962228; 4: VH 147A, 960229; 200x.

5 Xitus magnus BAUMGARTNER, VH 967, 971928, 150x.

6-7a, b Obesacapsula magniglobosa AITA, 6: PB 18A, 960413; 7: PD 0, a: 961033; b: antapical view, 961034;

200x.

8-9 Parvicingula ? cappa CORTESE, 8: 113 A13, 962030; 9: PB 18A, 960334; 300x.

10-11 Parvicingula dhimenaensis BAUMGARTNER s.l., 10: PA 12, 960635; 11: PA 12, 960631; 200x.

12  Ristola procera (PESSAGNO), VH 967, 971921, 200x.

13-16 D i c t y o m i t r e l l a? k a m o e n s i s MIZUTANI & KIDO, 13: PA 12, 960621; 14: PA 18A, 960427; 15: PA 18A,

960428; 16: PD 0, 961209; 200x.

17  Ristola? turpicula PESSAGNO & WHALEN, PA 12, 960720, 200x.

18-22 Canoptum sp. A, 18: PB 18A, 960403; 19: PB 18A, 960410; 20: PA 12, 960727; 21: PD 0, 961221; 22: PB

18A, 960415; 200x.

23-24 Stichomitra? takanoensis AITA gr., 23: PB 7, 961503; 24: PA 12, 960728; 200x.

25-26 Cinguloturris carpatica DUMITRICĂ, 25: VH 967, 971923; 26: VH 967, 971926; 200x.

27  Transhsuum brevicostatum (OÆVOLDOVÁ) gr., VH 141, 962233, 200x.



55HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek PLATE III



56 Geologia Croatica 52/1

PLATE IV

Conodonts

Scale bar = 100 µm.

1 E p i g o n d o l e l l a ex gr. postera (KOZUR & MOSTLER), sample PA 16A (IGGG 3128), 1a: oblique oral view,

1b: aboral view.

2 Norigondolella steinbergensis (MOSHER), sample PA 16A (IGGG 3128), 2a: oral view, 2b: lateral view, 2c:

aboral view.

3 Paragondolella tadpole (HAYASHI), sample PA 19A (IGGG 3131), 3a: oblique oral view, 3b: lateral view,

3c: aboral view (anteriormost platform broken off).

WINCHESTER, J.A. & FLOYD, P.A. (1976): Geo-

chemical magma type discrimination: Aplication to

altered and metamorphosed basic igneous rocks.-

Earth Planet. Sci. Lett., 28, 459-469.

YAMAMOTO, H., MIZUTANI, S. & KAGAMI, H.

(1985): Middle Jurassic radiolarians from Blake

Bahama Basin, West Atlantic Ocean.- Bull. Nagoya

Univer. Museum, 1, 25-49.

Manuscript received May 18, 1998.

Revised manuscript accepted May 28, 1999.



57HalamiÊ, GoriËan, Slovenec & Kolar-Jurkovπek PLATE IV



58 Geologia Croatica 52/1