GeolCarp_Vol52_No6_327

GEOLOGICA CARPATHICA, 52, 6, BRATISLAVA, DECEMBER 2001

327 — 342

GEOCHEMISTRY OF TRIASSIC RADIOLARIAN CHERTS

IN NORTH-WESTERN CROATIA

JOSIP HALAMIĆ

, VESNA MARCHIG

and ŠPELA GORIČAN

Institute of Geology, Sachsova 2, HR-10000 Zagreb, Croatia; jhalamic@yahoo.com

Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30631 Hannover, Germany; v.marchig@bgr.de

Institute of Paleontology, ZRC SAZU, Gosposka 13, SI-1000 Ljubljana, Slovenia; spela@zrc-sazu.si

(Manuscript received April 18, 2001; accepted in revised form October 5, 2001)

Abstract: The analysed Triassic (Illyrian, Lower Fassanian, Upper Carnian) radiolarian cherts on Žumberak, Ivanščica,
Kalnik and Medvednica Mts (NW Croatia) are rocks with high SiO

content (mean >90 %) and the major part of silica is

of biogenic origin. Besides this siliceous component, two others stand out in the radiolarian cherts. One of them is detritic
(terrigenous input) and it consists mainly of Al, Ti, K, Zr, Hf, Cr, Th, Rb, Nb and Sc. The other, hydrothermal one, is
composed of Fe, Mn, P, Cu, Pb, Zn, Ni, Co and Sr. The terrigenous component is a significant REE carrier. The radiolar-
ian cherts on Kalnik and Medvednica Mts show a positive Ce-anomaly (Ce/Ce*) which indicates a sedimentation in a
narrow trough relatively close to the continent. The negative Ce-anomaly on Žumberak and Ivanščica Mts suggests a
reduced terrigenous input. The radiolarian cherts in the last mentioned areas are sedimented directly onto the dolomites
and limestones of the carbonate platform. This means that the terrigenous input was probably weaker, because of the
width of the disintegrated carbonate platform (larger distance to the continent) or because of a topographically higher
position (bypass of fine terrigenous material) with respect to Medvednica and Kalnik.

Key words: South-western Pannonian region, NW Dinarides, Croatia, Triassic, radiolarian cherts, geochemistry, major
and trace elements, REE.

Introduction

The area of north-western Croatia is situated within the south-
western part of the Pannonian region (Fig. 1). Because of its
placement in relation to the Alps, Dinarides and Pannonian
Basin it is essential for solving the tectonic and paleogeo-
graphic relationships of this part of the Tethys.

The radiolarites are especially interesting, forming the upper

part of an ophiolitic sequence (geophysical layer 1 – Wilson
1989). In north-western Croatia they often occur in the Middle
and Upper Triassic marine sediments. On Žumberak Mt and
part of Ivanščica Mt (Fig. 1) these rocks are part of the Middle
Triassic volcano-sedimentary formation and they occur togeth-
er with pyroclastics and basic volcanites within the carbonate
complex (Šikić et al. 1979; Basch 1983; Šimunić et al. 1981;
Šimunić & Šimunić 1980, 1997; Bukovac et al. 1995; Grgaso-
vić et al. 2000). During the Late Jurassic and Early Creta-
ceous, the Middle to Upper Triassic siliceous rocks from
Kalnik Mt, part of Ivanščica and Medvednica Mts were incor-
porated into an accretionary prism (subductional complex) and
today they represent part of an ophiolitic melánge (Halamić &
Goričan 1995; Halamić 1998; Pamić & Tomljenović 1998; Gr-
gasović et al. 2000).

In the past the Triassic siliceous rocks were described only

sporadically and their age was determined on the basis of their
superpositional relation to the other sedimentary rocks defined
by their fossil content. The exact stratigraphic position of the
radiolarites has been documented in the recent publications
(Halamić & Goričan 1995; Halamić 1998; Grgasović et al.
2000).

Up to now, the chemical composition (major and trace ele-

ments and REE) of these rocks was poorly known. In recent

publications, Halamić & Goričan (1995) and Halamić (1998)
tried to determine the original tectonic and depositional envi-
ronment of the radiolarites from the Kalnik and Medvednica
Mts on the basis of the chemical composition of major ele-
ments and their ratios.

In this paper we show detailed geochemical study (major,

trace, and rare earth elements) of radiolarian cherts from radi-
olarite succession of selected localities in north-western Croat-
ia and try to explain depositional environment of radiolarian
oozes. Due to the tectonic position of the investigated area, we
consider that this paper is an important contribution to better
understanding of the geological evolution of this part of the
Tethys during the Triassic which will enable comparison with
similar siliceous rocks in the Alps, Dinarides, Hellenides, Pan-
nonian region and Carpathians.

Geological setting, basic geological data and

petrographical outline

The investigated area is situated in the SW part of the Pan-

nonian  region  (Fig.  1).  According  to  Haas  et  al.  (1990,  1995,
2000), it represents the SW extension of the Mid-Transdanubian
Terrain, that is the Zagorje-Mid-Transdanubian Zone (Pamić &
Tomljenović  1998).  This  terrain  is  separated  towards  the  SE
from  the  Tisza  Megaunit  by  the  Zagreb-Zemplen  lineament
(Kovács et al. 1988) and towards NW from Transdanubian Cen-
tral  Range  subunit  by  the  Periadriatic  lineament  (Fig.  1).  Ac-
cording to Herak (1986) this area represents a part of the Supra-
dinaric geodynamic unit, or Inner Dinarides (Herak et al. 1990).

The major part of north-western Croatia is covered by Ceno-

zoic sediments. Under this cover there are Mesozoic rocks

328 HALAMIĆ, MARCHIG and GORIČAN

forming the cores of the Žumberak, Kalnik, Medvednica, and
Ivanščica Mts. The central part of the Medvednica Mt consists
of Paleozoic-Mesozoic metamorphic rocks (Fig. 1).

During the preparation of the Geological Map of the Repub-

lic of Croatia (scale 1:50,000), the representative geological
sections of Triassic deep-water sediments were investigated on
Žumberak Mt (Kolići and Bezjak sections), Ivanščica Mt (Bel-
ski dol 1 and 2 sections), Kalnik Mt (Jazvina, VHK, Kestenik
sections) and Medvednica Mt (PC and PF sections) (Bukovac
et al. 1995; Halamić & Goričan 1995; Šimunić & Šimunić
1997; Halamić 1998; Grgasović et al. 2000). In these papers
basic geological data on these rocks was presented and on the
basis of paleontological results the age was determined.

For present investigation only radiolarian cherts from radi-

olarite succession (chert/shale couplets) were sampled at nine
sections  which  were  representative  for  the  investigated  area.
Only samples which were determined as Triassic (42 in total)
by  previous  research  were  selected  for  chemical  analysis
(Halamić  &  Goričan  1995;  Halamić  1998;  Grgasović  et  al.
2000).

The Kolići section (KL) (1 on Fig. 2). The red radiolarian

cherts were found in the lower part of the section with interca-
lations of siltites and pyroclastites. The analysis of the radi-
olarian fauna shows its Late Anisian to Early Ladinian age.

The matrix of cherts is composed of microcrystalline quartz

and recrystallized radiolarian tests. White micas and clay min-

erals form clastic detritus. Preserved radiolarian tests are filled
up with microcrystalline quartz and radial chalcedony. Acces-
sory minerals are rounded zircon, opaque mineral grains and
apatite. There are preserved parts of microcrystalline calcite in
the matrix (sample KL-70).

The Bezjak section (BZ) (2 on Fig. 2). The interval of sili-

ceous rocks was found in the lower part of the section. It is
composed of cm- to dm-beds of greenish-gray radiolarian
cherts with interstratified tuffitic siltstones. The Late Anisian
(Illyrian) age is determined on the basis of radiolarians.

Siliceous rocks are determined as dolomitized radiolarian

cherts. The rock matrix is built of microcrystalline quartz with
relics of microcrystalline calcite and dolomitization is visible
in the form of small dolomite crystals. In the matrix, there are
recrystallized and partly dolomitized radiolarian skeletons.
The accessory minerals are apatite, hematite and rare rounded
zircon.

The Belski dol-1 section (BD-II) (3 on Fig. 2). The silici-

fied grayish pelecypod limestones, greenish pyroclastites and
red radiolarian cherts in alternation overlie carbonate breccias
with “pseudooncoidal” structure. Cherts are found in the lower
part of the interval and their age is defined as Early Ladinian
(Early Fassanian).

The rock matrix consists of microcrystalline quartz and is

rich in ferruginous substance. Radiolarian skeletons are filled
with granular quartz. In the matrix, there are also submillimet-

Fig. 1. Location map and geological sketch map of north-western Croatia (according to Pamić & Tomljenović 1998, supplemented) with
locations of analysed sections. Legend: 1 – Neogene and Quaternary fill of the Pannonian Basin; 2 – Late Cretaceous-Paleocene fly-
sch; 3 – Hauterivian to Cenomanian pelagic limestones and calcareous turbidites; 4 – Ophiolitic melánge; 5 – Late Triassic platform
carbonates; 6 – Late Paleozoic and Triassic clastics and carbonates interlayered with volcanics and tuffs; 7 – Paleozoic-Triassic meta-
morphic complex; 8 – Section position.

GEOCHEMISTRY OF RADIOLARIAN CHERTS IN CROATIA 329

ric laminae of microquartz, 0.5 to 1 mm in length. The rock is
determined as hematitic radiolarian chert.

The Belski dol-2 section (BD) (4 on Fig. 2). Red radiolar-

ites are overlying brecciated and dolomitized grayish pelecy-
pod limestones. In the lower part of the siliceous interval there
are cm- to dm-thick layers of dark red radiolarian chert in alter-
nation with cm-thick layers of mudstones. In the upper part of
the package the cherts are greenish. The age of the lower carbon-
ate part is documented with algae and foraminifers (Upper Ani-
sian) and the age of cherts with radiolarians (Lower Ladinian).

All samples from the siliceous interval are determined as ra-

diolarian cherts. The rock matrix is granular microquartz. The
radiolarian skeletons are mainly affected by the recrystalliza-
tion and calcitization processes. The radial chalcedony has

been found only in some skeletons. Clastic detritus is repre-
sented by quartz and white mica. The accessory minerals are
zircon,  tourmaline,  biotite  and  opaque  mineral  grains.  The
matrix  is  enriched  in  ferruginous  and  manganese  substance.
Sample 35 is determined as a weakly tuffitic radiolarian chert.
The rock matrix is also composed of granular microquartz and
mica  (sericite?).  Accessory  minerals  are  apatite,  zircon,  and
opaque mineral grains. The entire rock is slightly calcitized.

The Jazvina section (JA) (5 on Fig. 2). The lower part of

the section is composed of calcitized, weakly porphyric ophit-
ic metabasalts. The pillow lavas are interlayered with light-
green basic tuff. The sediments which overlie the effusive
rocks are composed of red silty shale and silicified redish radi-
olarian microsparite in the lower part, and greenish-gray silty

Fig. 2. Detailed geological sections of Žumberak Mt (sections 1 and 2), Ivanščica Mt (sections 3 and 4), Kalnik Mt (sections 5, 6 and 7)
and Medvednica Mt (sections 8 and 9). Legend: 1 – pillow lava; 2 – metabasalt with amygdaloidal structure; 3 – shale xenolith in me-
tabasalts; 4 – metabasalt, massive; 5 – pyroclastic rocks; 6 – platform dolomite, massive; 7 – limestone, massive; 9 – limestone
with Pelecipoda; 10 – limestone with “oncoidal like” structure; 11 – calcarenite; 12 – siltstone; 13 – shale; 14 – tuffitic shale; 15 –
calcitized shale; 16 – silicified reddish radiolarian limestone; 17 – silty shale; 18 – marl; 19 – radiolarite; 20 – greenish-gray radi-
olarian chert interlayered with pyroclastic rock; 21 – Mn-enriched beds; 22 – sample position (time scale see Fig. 9).

330 HALAMIĆ, MARCHIG and GORIČAN

radiolarian chert in the upper part. According to radiolarians,
the chert is Upper Carnian—Middle Norian.

The silt-sized component of shale is composed of quartz

grains, white mica, and subordinate chlorite. The accessory
minerals are rounded zircon and apatite. The radiolarian tests
in silty cherts are irregularly distributed, and mostly complete-
ly recrystallized into microcrystalline quartz.

The VHK section (6 on Fig. 2). The interval of siliceous

rocks, from 4.5 to 5 m thick, is intercalated within the pillow
lavas. The contact towards the underlying deposits is covered,
and towards the overlying deposits it is easily visible. The
chert contains Early Ladinian radiolarians.

The lower part of the section is composed of silty radiolari-

an greenish cherts. The matrix of the rock is composed of mi-
crocrystalline  quartz,  white  micas  and  grains  of  resorbed
quartz. The accessory minerals are apatite, epidote, zircon and
opaque mineral grains. In the upper part of the section the silt-
clayey  component  decreases;  therefore  the  rock  is  mainly
composed  of  radiolarian  chert.  In  the  uppermost  part  of  the
sedimentary  succession  there  is  silicified  tuffitic  radiolarian
shale. The rock matrix consists of microcrystalline quartz with
parallel flakes of white mica. The accessory green mineral be-
longs to the zoisite group.

The Kestenik section (KE) (7 on Fig. 2). Red siliceous

rocks are found between underlying pillow lava (ophitic me-
tabasalt) and overlying calcitized vesicular metabasalt. The
age of sediments lying directly over the effusives is deter-
mined as Middle to Late Carnian, and by the top of the section
as Late Carnian.

The lower interval is composed of a green-gray silty sili-

ceous shale. The matrix is made up of clay minerals and cryp-
to- to microcrystalline quartz. The silt-sized components con-
sist  of  quartz  grains,  phyllosilicates  and  feldspars,  while
rounded  zircons,  apatite  and  opaque  ferruginous  grains  are
subordinate. The middle and upper part of the sediments are
composed of alternating dark red radiolarian cherts with milli-
metre  to  centimetre  thick  interbeds  of  very  thinly  laminated
silty shales. The matrix of the radiolarian cherts is made up of
microcrystalline quartz.

The “PC” and “PF” sections (8 and 9 on Fig. 2). The

foot-wall of the reddish radiolarite sequences is unknown,
due to intense tectonics (tectonic melánge), while the hang-
ing-wall is represented by disconform Paleocene calcitic silt-
stones. The radiolarites from “PC” and “PF” sections are as-
signed to Upper Ladinian or base of Carnian and Upper
Carnian.

The matrix of the radiolarite is composed of microcrystal-

line  quartz  with  millimetre  radiolarian  enriched  laminae,
while  quartz  grains,  muscovite/illite,  apatite  and  zircon  are
accessory. Very small fractures are filled with calcite. Within
the “PC” section, Mn-enriched laminae occur from few-mil-
limetre to 2 cm thick. Manganese is probably a consequence
of hydrothermal activity during or immediately after volca-
nic effusion on the sea floor. In the middle part of the “PF”
section a bed of green-gray, homogeneous tuffitic radiolarian
silty  shale  has  been  observed.  The  matrix  is  composed  of
clay minerals, cryptocrystalline quartz and subordinate chlo-
rite.  The  accessory  components  include  apatite,  zircon  and
hematite.

Analytical methods

For the microscopic analysis thin sections of all radiolarite

samples were made (42 in total).

Pieces of chert in all samples with obvious Fe-Mn coatings

and calcite veins were hand-picked and removed to avoid the
contamination. The remaining samples were powdered in ag-
ate mortar. Chemical analysis of the sediments was performed
by X-ray fluorescence (XRF). Philips PW 1400 and PW 1480
instruments were used to determine the concentrations of the
major  and  trace  elements.  The  method  of  sediment  analysis
was  calibrated  with  106  international  standards  and  24  syn-
thetic  standards  for  elements  or  ranges  of  concentration  not
covered  by  international  standards.  Analytical  precision  was
better  than  2 %  for  major  elements  and  better  than  5 %  for
trace elements.

Rare earth elements (REE), as well as some of the trace ele-

ments which were below the detection limit of XRF analysis,
were  determined  by  inductively  coupled  plasma  mass  spec-
trometry  (ICP-MS)  with  SCIEX,  model  250,  apparatus,  fol-
lowing the pressure dissolution in hydrofluoric acid. Analyti-
cal  precision  was  better  than  5 %.  The  completeness  of
dissolution was checked by dissolving and analysing lithium
tetraborat/metaborat melt glasses used by XRF.

contents were determined in selected samples (Table 1)

with indication of carbonate occurrence. We used modified
pressure-sensitive method of Klosa (1994). The analytical pre-
cision is 1 % if 100 mBar pressure is reached in the reaction
vessel.

Results and discussion

The major and trace elements are listed in Table 1 and Table

2. The raw analytical data of major elements were recalculated
on a volatile-free basis. The rare earth analytical data and REE
ratios were reported in Table 3. The correlation coefficient (r)
values for major elements are shown in Table 4. The problem
of compositional data (close data) of major elements and the
dilution effect of the other elements with SiO

was solved by a

log-ratio transformation log (x/y) (Aitchison 1986), with the
SiO

being used as a denominator for all variables. The same

procedure was also used for the trace elements (Aitchison
1986; Swan & Sandilands 1996).

Major elements

The silica content in all analysed radiolarian cherts is high

(>90 % for the majority of the samples; Table 1). On Kalnik
Mt it varies from 77 to 97 %, and on Medvednica Mt from 89
to 97 %. In cherts on Žumberak Mt the silica content varies
from 77 to 98 % and on Ivanščica Mt from 74 to 92 %. Lower
silica content (74 to 79 % SiO

) and increased content of car-

bonate (3 to 14 % CaO) was registered in all samples lying
closer to the carbonate bedrocks (limestones, dolomites) (Ta-
ble 1: samples BZ-8, BD-12 and BD-II/4). In the radiolarian
cherts on Žumberak Mt (section Bezjak) along with calcium,
there is an increas of MgO which indicates the existence of do-
lomitization processes.

GEOCHEMISTRY OF RADIOLARIAN CHERTS IN CROATIA 331

The Si/Si+Al+Fe ratio (Rangin et al. 1981) was calculated

to  evaluate  the  origin  of  silica  in  the  radiolarian  cherts.  Be-
cause  of  the  increased  content  of  secondary  carbonate  in
cherts, the Si/Si+Al+Fe+Ca ratio (Ruiz-Ortiz et al. 1989) was
not used. The values for Si/Si+Al+Fe in the radiolarian cherts
of  north-western  Croatia  are  higher  than  values  obtained  for
the Mediterranean cherts (0.8—0.9; Ruiz-Ortiz et al. 1989), and
are above 0.91 for the majority of the samples. Although such
high values indicate biogenic origin of SiO

, they also show

additional  silica  enrichment  in  the  radiolarian  cherts  (from
shale in chert/shale couplet) and dilution of the other compo-
nents during diagenesis. The high negative correlation coeffi-
cient between silica and the majority of other major elements
indicates  the  process  of  dilution  especially  in  cherts  on  the
Kalnik  and  Medvednica  Mts  (Table  4).  The  same  process  is
not so evident in the cherts of Ivanščica Mt, and values of the

correlation coefficient, although mostly negative, are not sig-
nificant. The situation on Žumberak Mt is quite similar to the
one on Ivanščica Mt.

Because of the aforementioned diagenetic migration and the

dilution effect of the other elements, SiO

is inappropriate for

paleogeographic consideration of the position of the sedimen-
tary basin during the radiolarian chert genesis (Murray 1994).

Aluminium, titanium and potassium

are abundant in clay

minerals and aluminosilicates and are good indicators of the
clastic and detritic component in sediments (terrigenous input)
(Murray 1994). In all analysed radiolarian cherts aluminium,
titanium and potassium show a high mutual correlation (Table
4) which is also well defined on the diagram (Fig. 3).

The contents of Al

are relatively high in all chert sam-

ples. Its highest content was registered on Kalnik Mt (range
1.7 to 9.74 %) in sections “VHK” and “JA” (Table 1). Al

Table 1: Major element data (wt. % – volatile free; CO

measurements after Klosa 1994; Stdv = Standard deviation; geomean = geometric

mean; Fe

* = Fe

total

SiO

TiO

MnO

MgO

CaO

Kalnik
KE-0/98

90.84

0.164

4.44

1.79

0.056

1.31

0.11

0.31

0.95

0.028

KE-1/98

93.51

0.104

3.08

1.22

0.050

1.10

0.09

0.21

0.61

0.015

KE-2/98

92.83

0.128

3.45

1.37

0.069

1.16

0.11

0.22

0.67

0.016

KE-3/98

91.52

0.143

3.86

1.71

0.079

1.63

0.08

0.22

0.74

0.024

JA-0/98

90.53

0.167

4.69

1.83

0.147

1.24

0.14

0.38

0.88

0.035

JA-1/98

85.37

0.283

7.91

2.48

0.110

1.47

0.15

0.47

1.71

0.057

JA-2/98

96.55

0.051

1.70

0.67

0.072

0.32

0.20

0.08

0.33

0.012

JA-3/98

88.13

0.205

6.12

2.62

0.085

1.04

0.13

0.34

1.28

0.049

JA-4/98

94.64

0.078

3.09

0.81

0.050

0.44

0.08

0.15

0.64

0.020

VHK-215

91.87

0.154

3.74

1.52

0.119

0.56

1.07

0.22

0.74

0.018

VHK-215/1

77.31

0.678

8.20

5.17

0.163

2.06

3.07

0.43

2.69

0.230

1.89

VHK-215/3

93.99

0.092

2.38

0.83

0.139

0.29

1.68

0.15

0.44

0.012

VHK-215/4

95.63

0.084

1.86

0.66

0.068

0.30

0.85

0.14

0.39

0.018

VHK-215/5

80.86

0.464

9.74

3.73

0.179

2.41

0.22

0.36

2.00

0.041

Geomean

90.09

0.155

4.02

1.57

0.091

0.88

0.25

0.24

0.83

0.027

Stdv

5.60

0.173

2.49

1.28

0.044

0.67

0.87

0.12

0.69

0.056

Medvednica
PF-1

92.06

0.110

3.54

1.24

0.220

1.49

0.56

0.21

0.53

0.035

PF-5

90.64

0.115

3.28

3.52

0.320

0.64

0.62

0.14

0.68

0.039

PF-7

91.98

0.141

3.42

2.55

0.176

0.68

0.18

0.22

0.62

0.039

PF-11

97.44

0.050

1.32

0.25

0.067

0.27

0.28

0.08

0.21

0.020

PC-2

92.62

0.120

3.18

1.02

0.249

0.65

1.36

0.16

0.63

0.013

PC-6

89.14

0.209

5.42

2.01

0.179

1.34

0.19

0.38

1.11

0.030

PC-10

90.93

0.130

4.48

1.48

0.320

1.35

0.16

0.30

0.84

0.018

PC-14

90.85

0.117

3.95

1.12

0.368

0.98

1.65

0.19

0.77

0.021

PC-19

94.49

0.104

2.67

1.04

0.118

0.57

0.30

0.17

0.53

0.015

PC-23

95.24

0.101

2.31

1.00

0.058

0.48

0.09

0.18

0.53

0.021

PC-24

91.18

0.173

4.44

1.59

0.106

1.14

0.18

0.29

0.88

0.028

Geomean

92.39

0.118

3.26

1.28

0.169

0.78

0.33

0.20

0.62

0.024

Stdv

2.41

0.041

1.13

0.89

0.107

0.41

0.52

0.08

0.23

0.009

Žumberak
BZ-8

77.20

0.030

1.06

0.70

0.045

6.88

13.77

0.05

0.24

0.026

14.33

BZ-10

85.88

0.036

1.20

1.01

0.030

4.23

7.24

0.10

0.23

0.025

8.79

BZ-14

95.75

0.025

0.74

0.21

0.019

0.83

2.24

0.06

0.12

0.020

2.55

BZ-33

86.95

0.162

4.13

1.26

0.024

2.64

3.45

0.11

1.23

0.043

4.27

BZ-37

90.40

0.232

5.19

1.37

0.023

0.82

0.36

0.15

1.42

0.042

KL-13

98.50

0.021

0.67

0.17

0.006

0.02

0.41

0.08

0.12

0.007

KL-18

96.05

0.035

1.12

0.22

0.010

0.36

1.82

0.10

0.27

0.013

KL-24A

93.81

0.136

3.09

1.46

0.010

0.36

0.10

0.15

0.86

0.047

KL-28

93.78

0.101

2.87

1.53

0.018

0.40

0.09

0.14

1.02

0.048

KL-70

97.37

0.022

0.59

0.17

0.005

0.01

1.61

0.08

0.12

0.016

Geomean

91.34

0.054

1.55

0.57

0.015

0.44

1.12

0.10

0.36

0.024

Stdv

6.59

0.074

1.64

0.58

0.012

2.28

4.33

0.04

0.51

0.015

Ivanščica
BD-12

79.51

0.170

4.11

2.73

0.500

0.67

10.99

0.07

1.19

0.057

7.78

BD-16

84.38

0.102

2.25

3.74

1.111

0.39

7.40

0.06

0.51

0.053

5.50

BD-21

92.00

0.155

3.62

1.26

0.176

0.39

1.29

0.12

0.95

0.039

BD-25

90.32

0.170

3.72

1.30

0.463

0.56

2.36

0.17

0.89

0.046

2.33

BD-35

88.72

0.210

4.54

2.50

0.510

0.70

1.38

0.09

1.31

0.051

BD-II/4

74.09

0.155

3.66

17.27

0.340

0.57

2.51

0.05

1.28

0.076

1.80

BD-II/4A

85.34

0.104

2.42

4.38

0.631

0.30

5.69

0.09

0.80

0.246

3.83

Geomean

84.70

0.148

3.38

3.16

0.468

0.49

3.36

0.09

0.95

0.065

Stdv

6.33

0.038

0.84

5.64

0.293

0.15

3.66

0.04

0.29

0.074

Table 2: Trace element data (mg/kg; Stdv = Standard deviation; geomean = geometric mean).

332

HALAMIĆ, MARCHIG and GORIČAN

As Ba Co Cr Cs Cu Ga Hf Li Nb Ni Pb Rb Sc

Ta Th Tl U V W Y Zn Zr

Kalnik

KE-0/98

3.31 81.1 7.2 21.6 2.75 29.4 5.91 1.00 64.5 3.9 19.4 6.1 34.0 4.2 11.5 0.29 3.08 0.220 0.65 21.9 0.52 5.66 48.5 36.6

KE-1/98

2.79 56.9 5.4 14.0 2.23 24.7 3.82 0.53 70.6 2.2 15.4 5.3 23.2 2.3 11.4 0.15 1.85 0.160 0.54 14.5 0.38 2.98 36.2 20.9

KE-2/98

0.03 95.7 4.4 10.7 1.89 24.3 3.59 0.47 15.4 1.9 16.8 3.9 29.8 2.8 8.5 0.13 1.91 0.180 0.38 26.2 0.29 4.08 23.3 18.1

KE-3/98

1.32 67.1 5.6 18.9 2.58 49.5 5.27 0.80 100.0 3.0 21.5 3.0 27.8 3.2 9.4 0.22 2.72 0.180 0.82 21.5 0.47 3.85 43.2 30.6

JA-0/98

1.57 109.0 11.5 26.1 2.69 65.3 6.29 0.98 29.6 3.9 31.5 23.8 37.8 5.0 9.9 0.28 3.98 0.240 0.53 29.4 0.90 9.39 67.3 36.1

JA-1/98

0.78 179.0 14.3 35.6 4.33 104.0 9.67 1.70 21.3 6.5 43.8 3.0 53.8 7.5 10.9 0.50 6.53 0.460 0.78 42.0 0.93 11.20 57.0 59.7

JA-2/98

0.28 54.5 2.8 9.6 1.04 15.4 2.17 0.28 12.7 1.1 10.7 3.7 14.0 1.2 6.4 0.08 1.16 0.110 0.45 6.9 0.29 2.94 14.5 10.2

JA-3/98

1.35 147.0 10.8 27.3 3.66 16.2 7.34 1.20 18.4 5.0 40.6 21.5 55.5 5.7 8.9 0.36 4.95 0.350 0.66 25.1 1.03 8.47 64.7 42.9

JA-4/98

1.64 62.2 4.8 16.9 2.31 23.1 4.24 0.65 74.8 2.6 18.4 4.2 24.4 2.5 9.5 0.21 2.27 0.210 0.71 17.9 0.50 3.72 34.1 23.3

VHK-215

2.44 75.8 4.2 18.0 3.48 27.3 5.16 0.89 57.0 3.2 11.8 7.0 31.3 3.2 15.8 0.24 2.57 0.190 1.02 20.1 0.61 6.22 37.7 31.0

VHK-215/1

4.30 119.0 8.6 63.2 8.54 39.9 10.80 1.93 41.3 10.8 33.9 7.8 77.6 11.0 25.7 0.72 3.21 0.360 0.54 64.9 1.49 16.10 51.8 77.9

VHK-215/3

2.04 47.0 2.4 13.2 1.83 16.3 2.93 0.57 60.5 1.9 6.7 3.9 18.2 1.8 13.6 0.14 1.63 0.120 0.43 11.1 0.40 5.38 28.1 21.3

VHK-215/4

1.44 43.5 2.5 9.7 1.58 12.1 2.48 0.63 57.3 2.4 9.6 3.3 15.4 1.5 10.5 0.20 1.77 0.110 0.38 11.2 0.35 4.68 30.6 22.7

VHK-215/5

3.15 171.0 14.7 60.3 10.20 36.9 12.90 2.26 62.4 8.8 46.6 4.5 70.8 10.3 22.0 0.66 6.62 0.460 2.60 57.8 1.41 13.00 83.2 80.6

Geomean

1.26 84.3 6.0 20.4 2.88 28.8 5.15 0.85 41.1 3.4 19.8 5.6 32.1 3.6 11.6 0.25 2.77 0.214 0.65 22.1 0.59 6.03 40.3 31.3

Stdv

1.20 45.4 4.2 17.4 2.65 24.8 3.25 0.59 26.3 2.8 13.4 6.7 20.2 3.2 5.4 0.20 1.76 0.121 0.56 17.2 0.40 4.08 19.0 21.8

Medvednica

PF-1

0.51 66.7 6.2 12.3 1.59 27.7 4.27 0.58 57.5 2.4 17.1 2.6 22.7 2.9 21.5 0.19 2.05 0.140 0.46 16.7 0.44 5.17 33.8 21.6

PF-5

1.00 62.5 7.6 9.4 1.16 20.9 3.24 0.52 41.3 2.3 19.4 12.0 16.0 1.4 25.7 0.15 1.91 0.120 0.78 26.1 0.54 3.17 25.1 19.9

PF-7

13.60 93.4 5.5 15.2 2.79 33.9 4.74 0.82 42.1 3.6 17.0 4.7 33.1 3.1 25.5 0.26 2.63 0.290 0.86 15.6 0.98 5.15 30.3 30.4

PF-11

1.34 27.6 1.4 8.2 0.41 13.8 1.43 0.34 22.2 2.4 6.3 1.5 7.1 0.8 14.1 0.10 0.95 0.058 1.79 20.3 0.25 1.86 10.3 13.2

PC-2

2.91 70.9 6.8 14.8 1.71 58.2 4.04 0.70 35.6 2.8 10.6 3.5 27.8 2.5 17.7 0.21 2.25 0.200 0.89 20.2 0.91 3.71 25.2 24.0

PC-6

31.30 99.8 17.6 14.2 2.97 33.8 6.22 1.44 29.9 5.4 16.6 6.1 39.1 3.5 21.6 0.49 4.96 0.370 1.31 20.6 2.18 7.22 36.9 44.2

PC-10

19.10 76.9 17.7 15.8 2.08 28.1 4.73 0.91 37.5 3.2 23.2 3.5 29.9 2.1 16.8 0.27 3.35 0.270 0.90 9.7 4.07 3.64 31.2 28.7

PC-14

10.80 85.7 5.1 9.1 1.88 26.1 4.47 0.76 34.5 3.7 11.8 4.7 28.2 2.3 19.6 0.25 2.31 0.250 0.73 12.8 0.84 4.62 28.2 27.5

PC-19

10.10 60.0 3.7 9.5 1.43 23.8 2.94 0.65 30.2 2.8 12.2 4.7 21.4 1.9 18.2 0.20 2.07 0.190 0.81 11.9 0.93 3.79 22.2 22.2

PC-23

8.26 63.4 3.2 9.8 1.30 24.1 2.60 0.65 24.0 2.1 10.4 4.8 19.5 1.6 15.8 0.17 1.85 0.160 1.05 11.4 0.76 3.58 17.8 21.1

PC-24

2.96 94.7 7.2 15.1 2.23 28.7 5.08 1.11 30.0 3.7 21.0 6.1 34.2 3.1 18.4 0.31 3.11 0.260 0.88 17.7 0.93 5.94 37.5 36.5

Geomean

4.94 69.4 6.0 11.8 1.60 27.4 3.73 0.72 33.8 3.0 14.1 4.3 23.3 2.1 19.2 0.22 2.31 0.189 0.90 16.0 0.88 4.11 25.7 25.1

Stdv

9.45 20.6 5.4 3.0 0.73 11.2 1.33 0.30 9.8 0.9 5.2 2.7 9.2 0.8 3.7 0.10 1.04

0.089 0.35 5.0 1.08 1.47 8.2 8.6

Žumberak

BZ-8

0.07 14.8 0.4 4.7 0.64 6.9 0.81 0.28 21.6 0.4 3.8 1.6 7.3 0.8 26.4 0.11 0.56 0.096 0.91 12.2 0.08 5.40 11.9 6.8

BZ-10

0.75 15.6 1.5 13.6 0.51 16.6 1.22 0.23 30.0 0.6 23.1 2.2 5.9 0.7 15.3 0.07 0.68 0.089 1.67 4.6 0.11 3.43 11.4 8.4

BZ-14

0.47 12.1 1.1 3.0 0.18 9.0 0.64 0.15 11.5 0.4 2.5 8.4 3.1 0.5 3.2 0.04 0.43 0.040 0.62 4.3 0.09 3.22 11.6 4.9

BZ-33

0.73 61.1 3.8 23.8 2.47 23.4 4.55 0.94 22.9 3.0 12.3 26.5 36.7 3.9 19.4 0.28 3.05 0.180 0.79 30.1 0.54 8.76 50.8 30.5

BZ-37

6.50 96.5 3.8 28.0 3.41 22.9 6.57 1.47 41.4 4.6 15.8 9.9 43.8 4.8 24.4 0.36 4.14 0.250 0.89 35.5 0.72 8.93 39.5 52.5

KL-13

0.32 15.9 0.7 6.0 0.24 3.5 0.73 0.11 16.0 0.4 3.6 4.9 3.1 0.6 0.6 0.03 0.34 0.062 0.97 3.3 0.40 1.47 40.8 4.3

KL-18

0.93 17.4 0.4 3.1 0.64 11.9 1.66 0.20 40.6 0.6 1.5 179 6.1 0.6 6.6 0.05 0.57 0.044 0.64 4.1 0.14 2.76 310 6.8

KL-24A

0.54 61.5 2.3 14.2 2.63 33.8 3.77 0.76 37.0 2.5 8.3 3.8 27.8 2.3 24.1 0.18 2.19 0.130 0.66 22.8 0.45 10.20 19.8 26.7

KL-28

0.81 54.5 1.6 10.1 1.91 29.4 3.33 0.52 43.0 1.6 6.4 4.5 24.9 2.7 21.2 0.13 1.53 0.099 0.82 19.4 0.30 10.30 21.3 18.9

KL-70

0.80 12.4 0.1 1.8 0.20 2.8 1.10 0.13 11.0 0.7 1.6 8.7 3.0 0.2 1.6 0.03 0.44 0.028 0.95 2.6 0.25 6.34 6.2 7.7

Geomean

0.65 26.8 1.0 7.6 0.77 12.0 1.78 0.33 24.6 1.0 5.4 7.9 9.8 1.1 8.6 0.09 0.95 0.083 0.86 9.1 0.24 5.13 25.2 11.8

Stdv

1.88 29.9 1.3 9.1 1.20 11.0 2.02 0.45 12.6 1.4 7.1 54.6 15.6 1.6 10.3 0.11 1.32 0.069 0.30 12.3 0.22 3.30 91.8 15.7

Ivanščica

BD-12

1.45 55.6 2.3 12.4 3.71 21.6 3.85 1.02 10.7 2.9 17.6 41.2 37.8 3.5 27.5 0.26 3.53 0.180 0.50 21.2 4.08 14.80 53.2 32.9

BD-16

16.40 66.7 2.3 5.7 1.87 55.7 2.38 0.64 12.1 1.9 20.3 130 19.0 2.3 37.2 0.15 1.95 0.090 0.35 45.9 1.40 24.80 30.6 26.4

BD-21

3.17 65.9 4.2 10.1 2.86 26.7 4.40 1.18 13.2 3.5 16.1 12.8 34.6 2.7 10.3 0.24 3.09 0.190 1.07 23.1 0.86 14.20 32.8 56.4

BD-25

5.61 115 3.4 14.1 2.88 16.1 4.34 0.97 14.6 3.8 11.4 8.1 35.0 3.0 28.1 0.27 3.26 0.190 0.98 24.1 1.28 14.20 30.2 38.8

BD-35

29.30 90.3 4.7 26.8 4.59 72.1 6.26 1.30 18.1 4.7 37.8 16.0 58.3 5.3 15.1 0.32 3.80 0.220 0.73 32.6 1.25 16.30 40.2 60.9

BD-II/4

4.32 77.6 6.9 13.9 2.88 155.0 6.12 1.33 15.6 5.0 74.4 26.3 62.8 4.8 22.5 0.26 3.30 0.250 0.83 70.3 10.3 22.10 161.0 82.8

BD-II/4A

3.80 51.0 7.8 7.9 1.67 57.3 2.90 0.67 9.4 2.2 43.2 18.1 34.9 2.7 36.7 0.16 2.17 0.200 0.35 59.4 1.04 32.20 44.7 27.8

Geomean

5.73 72.0 4.1 11.7 2.77 44.2 4.10 0.98 13.09 3.2 26.0 23.7 37.8 3.3 23.3 0.23 2.94 0.181 0.63 35.7 1.88 18.89 46.4 42.9

Stdv

10.15 22.1 2.2 6.8 1.01 47.7 1.47 0.28 2.99 1.2 22.3 42.8 15.2 1.1 10.2 0.06 0.69 0.049 0.29 19.5 3.45 6.88 47.0 20.9

GEOCHEMISTRY OF RADIOLARIAN CHERTS IN CROATIA 333

in those samples is mainly connected to the white mica, clay
minerals? and epidote-coisite mineral group. The radiolarian
cherts on the Medvednica and Ivanščica Mts have approxi-
mately the same content of Al

. On Žumberak Mt, the con-

tent of aluminium is the lowest except for two samples, which
were microscopically determined as clayey radiolarian cherts.
Similar to the TiO

the aluminium is positively correlated with

elements which mainly originated from the detritic compo-
nent.

TiO

is mostly contained in the heavy mineral fraction. Its

content in the Kalnik, Medvednica and Ivanščica Mts radiolar-
ian cherts is more or less equal, and ranges between 0.05 and
0.67 %, while it is lower on Žumberak Mt and ranges between
0.02 and 0.23 %. TiO

on Žumberak Mt shows a very high

correlation to Al

and K

O and a high correlation to Na

All these elements are, like titanium, connected to the detritic
component in the radiolarian cherts. Similar values of the cor-
relation coefficients to the same elements were obtained for
the cherts on the Kalnik and Medvednica Mts. On Ivanščica
Mt TiO

shows a high positive correlation only to Al

, and

lower correlations to K

O and MgO.

O content in the analysed rocks varies from 0.12 to 2.69 %.

The highest contents were registered in the Kalnik radiolarian
cherts (section VHK). Potassium is, like aluminium, mainly
connected to aluminosilicates (white micas) and is a part of the
clastic component.

Iron and phosphorus.

Increased iron contents can indicate a

strong hydrothermal influence during sedimentation. In this
case the iron content decreases with distance from the spread-
ing ridge.

The content of iron is highest in the Ivanščica Mt radiolarian

cherts (max. value 17.27 %), while it is significantly lower on

the Kalnik and Medvednica Mts (Table 1). The lowest values
of Fe are registered in the Žumberak cherts. In sample KL-70
(Žumberak Mt) a portion of Fe can also be found in veins
along with calcite.

The increased content of iron on Ivanščica Mt is not fol-

lowed by an increase of aluminium which is an indicator of its
hydrothermal origin. The REE spectra also support the conclu-
sion that the hydrothermal iron has been precipitated from sea-
water.

The iron on Kalnik Mt shows a very high correlation to

TiO

, and a high correlation to K

O, Al

and Na

O (Fig. 3;

Table 4) which indicates that part of the iron in the radiolarian
cherts is also connected to the terrigenous material. In the oth-
er three investigated areas the Fe shows high correlation to the
phosphorus.

The phosphorus content on the Kalnik, Medvednica and

Žumberak sections is relatively uniform and low, while it is in-
creased only in Ivanščica radiolarian cherts (Table 1). The rel-
atively low contents were conditioned by diagenetic SiO

dilu-

tion or silicification. The origin of phosphorus in these rocks is
not clear and could be equivocal. The first possibility is that
the phosphorus is of biogenic origin, and the other is that the
phosphate from seawater was adsorbed onto ferric hydroxide
which was precipitated from the hydrothermal fluids on the di-
vergent plate margins (Berner 1973) (the content of Fe on
Ivanščica Mt rises up to 17 %!). During diagenesis the phos-
phate is transformed to apatite which is hard to distinguish
from the biogenic type. Biogenic apatite has a higher content
of Sc, Y, La, and REE (Marchig et al. 1982). The consideration
of the contents of the aforementioned elements on the studied
sections shows that the content of Y, La and

REE is almost

two times higher on Ivanščica Mt than on the Kalnik, Medved-

Fig. 3. Cluster analysis diagrams of major elements (Tree clustering; Linkage rule = Ward’s method; Distance measure = 1-Pearson r).

334 HALAMIĆ, MARCHIG and GORIČAN

nica and Žumberak Mts. The Ivanščica radiolarian cherts show
a high correlation of phosphorus only to Y, while there is no
correlation to Sc, La and

REE. Based on that, and also on the

explicit correlation of P to Fe on Kalnik, Medvednica,
Žumberak Mts and indirectly on Ivanščica Mt (Fig. 3; Table
4), it can be concluded that the phosphorus in the analysed Tri-
assic radiolarian cherts is mostly bound to hydrothermaly sup-
plied iron.

Calcium, magnesium and manganese.

The carbonate con-

tent in the Kalnik and Medvednica radiolarian cherts is rela-
tively low (Table 1). The higher content in a few samples is the
consequence of secondary calcite which appears in the form of
submillimetre veins. CaO shows correlation to Mn on
Medvednica, while on Žumberak it also correlates to MgO
(Fig. 3; Table 4). There is a highly negative correlation to sili-
ca on Žumberak Mt (Table 4), which is mainly the result of di-

agenetic silicification of carbonate mud. The MgO content on
Kalnik and Medvednica Mts is low (Table 1). The slightly in-
creased magnesium contents in samples VHK-215/1 and 215/5
(2.06 and 2.41 % respectively) can originate from the epidote-
coisite mineral group. Contrary to that, the calcium and mag-
nesium contents on Žumberak and Ivanščica Mts are signifi-
cantly higher, especially in the “BZ” section (see Table 1). The
high content of those elements in these sections is the result of
the dolomitization of the radiolarian cherts that lie closer to the
dolomite bedrock. The significantly lower MgO content on
Ivanščica Mt is caused by limestones and carbonate breccia
that underlie the cherts. The CaO content is significantly high-
er for the same reason.

Manganese content is relatively low in the cherts with the

exception of some Ivanščica samples (Table 1). Although
there were layers enriched by manganese oxide found in one

Table 3: Rare earth contents (mg/kg) and Rare earth ratios (Normalization: NASC = North American shale composit; Gromet et al. 1984).

Sum

(Σ)

(La/Yb)n

n=NASC

Ce/Ce*

n=NASC

Kalnik
KE-0/98

8.7

19.40

1.88

6.65

1.22

0.25

1.16

0.18

0.98

0.20

0.59

0.088

0.57

0.092

41.96

1.53

1.17

KE-1/98

5.0

12.20

1.03

3.60

0.62

0.13

0.59

0.09

0.50

0.11

0.32

0.045

0.32

0.054

24.65

1.56

1.32

KE-2/98

4.2

15.10

1.06

4.20

0.89

0.19

0.89

0.14

0.72

0.14

0.42

0.057

0.36

0.061

28.39

1.17

1.65

KE-3/98

5.0

13.70

1.14

4.03

0.73

0.16

0.73

0.12

0.65

0.13

0.42

0.063

0.41

0.072

27.36

1.22

1.40

JA-0/98

8.9

31.10

2.22

8.45

1.89

0.42

1.92

0.29

1.71

0.34

0.95

0.140

0.86

0.140

59.35

1.04

1.65

JA-1/98

14.9

48.20

3.75

13.90

2.86

0.65

2.83

0.42

2.17

0.42

1.24

0.180

1.13

0.200

92.85

1.32

1.54

JA-2/98

2.5

8.05

0.59

2.21

0.47

0.12

0.56

0.10

0.56

0.11

0.31

0.043

0.26

0.041

15.88

0.96

1.57

JA-3/98

10.7

34.70

2.59

9.71

1.95

0.41

1.92

0.29

1.65

0.32

0.95

0.150

0.88

0.150

66.37

1.22

1.56

JA-4/98

4.7

13.50

1.17

4.33

0.81

0.16

0.81

0.12

0.65

0.13

0.39

0.060

0.39

0.063

27.26

1.21

1.37

VHK-215

8.4

18.00

1.94

7.26

1.48

0.26

1.46

0.21

1.15

0.23

0.65

0.094

0.59

0.099

41.79

1.43

1.06

VHK-215/1

14.3

29.80

3.64

14.50

3.08

0.81

3.34

0.51

2.88

0.57

1.62

0.230

1.32

0.210

76.81

1.08

0.95

VHK-215/3

5.0

11.10

1.17

4.43

0.99

0.20

1.08

0.18

1.02

0.19

0.52

0.073

0.45

0.071

26.46

1.11

1.08

VHK-215/4

5.0

12.90

1.26

4.82

1.00

0.21

1.04

0.16

0.85

0.17

0.45

0.063

0.37

0.062

28.33

1.35

1.21

VHK-215/5

17.6

37.80

4.00

14.70

2.73

0.57

2.65

0.41

2.35

0.47

1.40

0.210

1.35

0.230

86.47

1.31

1.08

Geomean

7.1

19.01

1.68

6.27

1.26

0.27

1.28

0.20

1.09

0.22

0.63

0.092

0.57

0.095

39.73

1.24

1.31

Stdv

4.64

12.23

1.13

4.30

0.88

0.22

0.90

0.13

0.76

0.15

0.43 0.06

0.38 0.06

25.53

Medvednica
PF-1

6.2

16.10

1.51

5.65

1.15

0.27

1.10

0.17

0.91

0.17

0.51

0.070

0.41

0.072

34.29

1.51

1.25

PF-5

3.4

7.72

0.81

3.06

0.63

0.15

0.61

0.10

0.52

0.11

0.34

0.055

0.36

0.064

17.88

0.95

1.10

PF-7

6.6

16.20

1.59

6.07

1.28

0.25

1.19

0.18

0.97

0.20

0.55

0.080

0.51

0.082

35.72

1.30

1.17

PF-11

3.2

9.04

0.69

2.45

0.45

0.10

0.43

0.07

0.35

0.07

0.20

0.030

0.18

0.033

17.29

1.78

1.48

PC-2

5.0

10.90

1.13

4.16

0.84

0.16

0.77

0.12

0.65

0.14

0.39

0.059

0.38

0.064

24.74

1.32

1.10

PC-6

12.0

24.60

2.63

9.41

1.80

0.35

1.74

0.27

1.45

0.29

0.88

0.130

0.83

0.140

56.52

1.45

1.06

PC-10

5.1

11.30

1.32

4.79

0.82

0.16

0.83

0.13

0.66

0.14

0.41

0.066

0.42

0.073

26.21

1.22

1.05

PC-14

5.0

14.00

1.44

5.61

1.23

0.25

1.22

0.18

0.98

0.19

0.50

0.070

0.44

0.070

31.20

1.14

1.21

PC-19

5.5

13.70

1.41

5.35

1.12

0.21

1.09

0.16

0.83

0.17

0.45

0.068

0.41

0.064

30.52

1.34

1.16

PC-23

4.4

11.80

1.21

4.53

0.94

0.19

0.91

0.14

0.75

0.15

0.41

0.060

0.38

0.063

25.95

1.16

1.21

PC-24

7.4

18.90

1.97

7.47

1.49

0.31

1.49

0.21

1.16

0.22

0.63

0.092

0.59

0.098

42.03

1.26

1.17

Geomean

5.4

13.33

1.34

5.00

1.00

0.21

0.97

0.15

0.79

0.16

0.45

0.067

0.42

0.071

29.37

1.29

1.17

Stdv

2.41

4.81

0.53

1.94

0.39

0.08

0.38

0.06

0.31

0.06

0.17 0.02 0.16 0.03

11.20

Žumberak
BZ-8

6.6

8.85

1.39

5.32

0.96

0.24

1.02

0.15

0.85

0.17

0.46

0.061

0.38

0.059

26.49

1.74

0.69

BZ-10

3.9

4.72

0.91

3.57

0.68

0.15

0.71

0.10

0.57

0.11

0.31

0.042

0.23

0.038

16.01

1.70

0.58

BZ-14

3.3

5.14

0.76

3.10

0.55

0.12

0.63

0.09

0.48

0.10

0.28

0.040

0.25

0.041

14.90

1.32

0.74

BZ-33

14.4

21.30

3.89

14.90

2.70

0.54

2.45

0.34

1.68

0.32

0.91

0.130

0.76

0.120

64.44

1.90

0.67

BZ-37

13.0

20.70

3.29

12.50

2.39

0.47

2.16

0.30

1.61

0.32

0.93

0.130

0.82

0.130

58.75

1.59

0.75

KL-13

3.3

4.06

0.82

3.05

0.54

0.11

0.48

0.07

0.30

0.05

0.16

0.020

0.14

0.025

13.16

2.36

0.59

KL-18

3.2

4.81

0.82

3.11

0.55

0.15

0.56

0.08

0.45

0.09

0.25

0.034

0.20

0.032

14.30

1.60

0.70

KL-24A

29.4

25.30

5.54

18.90

3.39

0.68

3.04

0.42

2.02

0.36

0.99

0.130

0.74

0.120

91.03

3.98

0.49

KL-28

37.4

26.80

7.46

24.50

4.73

0.95

3.82

0.52

2.33

0.39

1.02

0.130

0.77

0.110 110.9

4.86

0.41

KL-70

1.5

1.81

0.46

2.03

0.46

0.09

0.61

0.10

0.64

0.16

0.46

0.066

0.42

0.073

8.916

0.43

0.37

Geomean

7.0

8.62

1.66

6.30

1.18

0.25

1.16

0.16

0.87

0.17

0.48

0.065

0.39

0.064

28.38

1.80

0.58

Stdv

12.41

9.92

2.43

8.04

1.51

0.30

1.22

0.17

0.74

0.13

0.34 0.05

0.27 0.04

36.94

Ivanščica
BD-12

17.4

25.50

4.86

19.30

3.81

0.79

3.97

0.57

3.00

0.58

1.55

0.200

1.26

0.200

82.99

1.38

0.64

BD-16

19.0

13.10

4.91

20.60

4.55

1.05

5.30

0.81

4.83

0.97

2.61

0.360

2.09

0.320

80.50

0.91

0.30

BD-21

23.0

28.00

6.16

24.60

5.13

0.94

4.96

0.67

3.29

0.60

1.51

0.190

1.13

0.180

100.4

2.04

0.54

BD-25

17.5

22.80

4.60

18.40

3.67

0.71

3.74

0.52

2.80

0.55

1.47

0.200

1.26

0.200

78.42

1.39

0.58

BD-35

22.4

25.60

4.90

19.10

3.64

0.76

3.82

0.55

3.02

0.60

1.69

0.240

1.49

0.230

88.04

1.51

0.57

BD-II/4

61.8

58.60

12.80

49.00

8.85

1.70

8.20

1.05

4.96

0.92

2.68

0.390

2.61

0.430 213.99

2.37

0.49

BD-II/4A

20.0

12.50

5.26

24.10

5.70

1.39

7.05

1.02

5.68

1.11

2.93

0.390

2.27

0.360

89.76

0.88

0.26

Geomean

23.26

23.53

5.81

23.58

4.81

1.00

5.07

0.71

3.80

0.73

1.98

0.268

1.65

0.261

98.34

1.41

0.46

Stdv

15.99

15.40

2.95

10.86

1.85

0.37

1.73

0.22

1.18

0.23

0.64 0.09

0.59 0.10

48.67

GEOCHEMISTRY OF RADIOLARIAN CHERTS IN CROATIA 335

section on Medvednica Mt (Halamić & Goričan 1995), its
content in the radiolarian chert beds is relatively low as a re-
sult of its diagenetic migration, and accumulation in centime-
ter thick layers which were avoided by sampling. This element
shows connection only to calcium in all sections, and also to
magnesium on Žumberak Mt (Fig. 3). But it shows significant
negative correlation to SiO

in almost all sections and that in-

dicates its replacement by silica, so that its use as a paleogeo-
graphical indicator is questionable (Murray 1994).

Trace elements

Comparing the contents of particular trace elements of anal-

ysed radiolarian cherts to recent oceanic radiolarian oozes
(Gundlach & Marchig 1982; Marchig et al. 1982, 1986, 1987;
Murray et al. 1992b) it is evident that the majority of the val-
ues in the cherts are significantly lower than in recent radiolar-
ian oozes. The decreased contents in the studied cherts are the
result of an enrichment in SiO

. Besides that, during the silici-

fication of carbonate sediments, for example, the Ba and Sr

were removed from the host sediment (Murray 1994). Because
of that effect, the Ba, Sr, V and Co contents do not correspond
to the primary contents and should be considered with caution.

Cr, Zr, Hf, Rb, Th and in part V, and major elements Al, Ti

and K are mainly incorporated in the detritic and clastic com-
ponent  of  the  sediment.  Their  increased  content  indicates  a
more intense terrigenous input. However, Cr can be partly mo-
bile and enriched in the hydrothermal precipitates (Marchig et
al. 1982). In all analysed radiolarian cherts Cr shows a high or
relatively  high  correlation  to  the  other  aforementioned  ele-
ments,  and  this  shows  that  it  is  mainly  bound  to  the  terrige-
nous component.

Individual diagrams for the Žumberak, Ivanščica, Kalnik

and Medvednica Mts on the basis of Pearson’s correlation co-
efficient were constructed to understand the relationships and
mutual connections between major and trace elements.

Ivanščica Mt. The trace elements on the diagram are sepa-

rated into two groups (Fig.

4). The first one consists of Zr, Hf,

Th, Cr, Rb, Sc and Nb which are characteristic of the terrige-
nous input in the form of detritic component, as is also proved
by the stronger correlations of the named elements to Al

Table 4: Correlation coefficient (r) values for major elements (significant correlations at p < 0.05; Kalnik: —0.54 < r > 0.54; Medvednica:
—0.63 < r > 0.63; Žumberak: —0.75 < r > 0.75; Ivanščica: —0.77 < r > 0.77; (—) indicates negative correlation; Fe

* = Fe

total

Kalnik

SiO

TiO

MnO

MgO

CaO

SiO

1.00

TiO

-0.97

1.00

-0.95

0.86

1.00

-0.98

0.98

0.90

1.00

MnO

-0.71

0.70

0.65

0.66

1.00

MgO

-0.86

0.79

0.86

0.84

1.00

CaO

-0.44

0.59

1.00

-0.84

0.74

0.88

0.80

0.55

0.77

1.00

-0.99

0.97

0.94

0.98

0.64

0.81

0.84

1.00

-0.80

0.88

0.60

0.85

0.54

0.75

0.60

0.84

1.00

Medvednica

SiO

TiO

MnO

MgO

CaO

SiO

1.00

TiO

-0.82

1.00

-0.93

0.91

1.00

-0.65

1.00

MnO

-0.66

1.00

MgO

-0.74

0.63

0.84

1.00

CaO

0.64

1.00

-0.73

0.91

0.79

1.00

-0.90

0.93

0.96

0.69

0.89

1.00

0.76

1.00

Žumberak

SiO

TiO

MnO

MgO

CaO

SiO

1.00

TiO

1.00

0.99

1.00

0.78

0.82

1.00

MnO

-0.96

1.00

MgO

-0.96

0.93

1.00

CaO

-0.88

0.86

0.97

1.00

0.80

0.79

1.00

0.97

0.99

0.85

0.81

1.00

0.80

0.83

0.96

0.75

0.87

1.00

Ivanščica

SiO

TiO

MnO

MgO

CaO

SiO

1.00

TiO

1.00

0.98

1.00

-0.82

1.00

MnO

1.00

MgO

0.87

0.88

1.00

CaO

1.00

0.77

1.00

0.81

0.87

0.78

1.00

336 HALAMIĆ, MARCHIG and GORIČAN

TiO

and K

O. The same group of trace elements is less

strongly correlated to Ba and As which correlate positively to
Na

O, which means that Ba and As are, at the least, in part of

terrigenous origin. The second group consists of Cu, Zn, Ni,
Co, V and Y, which represent the hydrothermal component,
and correlate positively to major elements such as Fe and P.
The connection of Sr and Pb to Mn and Ca is the result of di-
agenetic processes.

Kalnik Mt. In this area, similar as on Ivanščica, the trace

and major elements characteristic of the terrigenous source are
separated in two groups with the difference that the iron, phos-
phorus, sodium and magnesium are in greater part contained in
the detritic component (Fig. 4). The second group consists of
Ni, Co, Zn, Cu, Ba, Th and Na

O which reflects a hydrother-

mal activity. The Pb, As and Sr are correlated to Ca and Mn
and that is in greater part the result of diagenetic migration.

Medvednica Mt. The trace elements on the diagram are

separated into three different groups (Fig. 4). The first, terrige-
nous group is correlated to Al

, TiO

, K

O, Na

O and MgO,

while the second hydrothermal group correlates to Fe, P and
Mn (probably adsorbed on Fe-Mn hydroxide precipitates). The
third group consists of V, Co, Y and As, and indicates an en-
richment of these elements during the diagenesis.

Žumberak Mt. The diagram (Fig. 4) shows two different

groups of trace elements. In contrast to the previously dis-
cussed areas with predominant terrigenous major elements
(Al

, TiO

and K

O), the trace elements Cu, Sr and Y are

strongly correlated to iron and phosphorus indicating a possi-
bly weaker hydrothermal activity (together with Ni, Cr, Ba, As

and Na

O) and increased terrigenous input of these elements

along with Zr, Hf, Th, Cr and others. The second separated
group consists of Zn, Pb, Ca, Mg and Mn. The grouping of
these elements is more the result of migration during diagenet-
ic and postdiagenetic processes (silicification, dolomitization)
than of direct magmatic activity.

We normalized the major and trace elements to Al, and

placed them into relationship to NASC (“North American
shale composite”; Gromet et al. 1984) (Fig. 5). This diagram
shows the enrichment of SiO

in all samples, which confirms

the aforementioned diagenetic migration. K, Ti and Rb con-
centration have quite similar normalized values according to
the NASC. Mg, Fe and Na also belong to the same group. Fe
on the Ivanščica Mt is enriched and reflects a hydrothermal in-
put into the sediment (high Fe content; Table 1). Ca is depleted

Fig. 5. Al-normalized major and trace elements distribution rela-
tive to NASC (NASC values from Gromet et al. 1984; detailed de-
scription see text).

Fig. 4. Cluster analysis diagrams of major and trace elements (Tree clustering; Linkage rule = Ward’s method; Distance measure = 1-Pear-
son r).

GEOCHEMISTRY OF RADIOLARIAN CHERTS IN CROATIA 337

Fig. 6. Cluster analysis diagrams of major elements and

REE (Tree clustering; Linkage rule = Ward’s method; Distance measure = 1-Pear-

son r).

on the Kalnik and Medvednica Mts, which indicates sedimen-
tation  without  a  carbonate  component  (probably  below  the
CCD). Increased ratios of Ca on Ivanščica and Žumberak Mts
reflect the influence of carbonate host sediment. However, a
portion of CaO is of secondary origin because of the underly-
ing  carbonate  sediments  (limestones  and  dolomites)  which
partly  migrated  in  cherts  during  diagenesis.  Manganese  en-
richment in relation to NASC is probably ambiguous. This en-
richment starts with a hydrothermal input of Mn, and it contin-
ues with a remobilization and reprecipitation in more oxidic,
or  as  carbonate  in  reducing  conditions.  Phosphorus  on  the
Kalnik and Medvednica Mts is quite similar to NASC contents
and is here probably of terrigenous origin (apatite as a heavy
mineral),  while  the  increased  contents  on  the  Ivanščica  and
Žumberak Mts indicate an additional source (adsorption on Fe
and Mn hydroxide).

REE

The content of the majority of REE in the analysed radiolar-

ian cherts is relatively low (<1mg/kg) (Table 3).

While analysing the correlation ratios of

REE to major ele-

ments (Fig. 6) it can be concluded that the REE on the Kalnik,
Medvednica and Žumberak Mts are positively correlated to
Al, Ti, K and Na, which means that the aluminosilicates are
significant carriers of REE in radiolarian cherts. Additionally,
the high correlation coefficient of

REE to Zr and Ti indicates

that the heavy minerals from the terrigenous component are
partly carriers of rare earths. REE in the analysed cherts show
no correlation to Mn (besides a weaker correlation on Kalnik
Mt; r = 0.71, not shown), which is the result of diagenetic frac-
tionation of Mn and its migration from silica rich layers. On
the other hand, there is a significant connection of

REE to Fe

on the Ivanščica Mt (Fig. 6), while it is weaker to P and Fe in
the other three areas. This indicates that a part of REE was ad-
sorbed onto Fe-hydroxide from sea water during sedimenta-
tion (in sample BD-II/4 on the Ivanščica Mt

REE is 213.99

mg/kg with a 17.27 % of iron) and probably onto Mn (the Mn
content in the sample BD-16 is >1 %).

We normalized our REE data to NASC (normalization val-

ues from Gromet et al. 1984). These average shale values are
the best representatives of the upper continental crust REE
values and of the REE distribution of average values for terres-
trial material in the oceans (Condie 1991).

REE distribution patterns for the Kalnik and Medvednica ra-

diolarian cherts are relatively flat, but show slight LREE en-
richment compared to HREE (Fig. 7) (average of ratio La

/Yb

1.24 and 1.29 respectively; Table 3). The radiolarian cherts on
the Ivanščica and Žumberak Mts show a stronger enrichment
of LREE compared to HREE (average of ratio La

/Yb

1.41

and 1.80 respectively; Table 3). There is a difference in REE
content between the studied sections on Žumberak Mt, but
their basic characteristics are quite similar (Fig. 7). The LREE
values on the Kalnik and Medvednica Mts are quite similar to

338 HALAMIĆ, MARCHIG and GORIČAN

the proposed values of La

/Yb

for the marine sediments

(Sholkovitz 1990; La

/Yb

= 1.33+/—0.15), but they are higher

on Ivanščica and Žumberak Mts.

It is significant for Ivanščica and Žumberak radiolarian

cherts that they have a distinctive negative Ce anomaly (Ce/
Ce*) (mean for Ce/Ce* 0.46 and 0.58; Table 3), while this
anomaly is positive on Kalnik and Medvednica Mts (mean for
Ce/Ce* 1.17 and 1.31). It is well known that the Ce/Ce* does

not change during diagenetic processes in most cases, so the
difference of registered values presents a variation in the pri-
mary sediment (Murray et al. 1992a). The marked negative Ce
anomalies are characteristic of deep sea sediments (Shimizu &
Masuda 1977; Toyoda et al. 1990; Murray et al. 1990, 1991).

The positive Ce anomaly could be caused by an increased

terrigenous input (Murray et al. 1992a). We could give two ex-
planations for the positive Ce anomaly on Kalnik and Med-

Fig. 7. NASC normalized REE distribution diagrams for all samples. The values on the diagram in the middle are geometric means values
for individual areas.

GEOCHEMISTRY OF RADIOLARIAN CHERTS IN CROATIA 339

vednica Mts (1) the deposited radiolarian oozes originally had
a negative Ce anomaly. During the diagenetic processes the
partial depletion of LREE occurred except for Ce, which was
followed by the development of a positive Ce anomaly (Mur-
ray et al. 1991) and (2) the positive Ce anomaly could be the
result of an “oxygen minimum zone” (OMZ), which develops
close to a continent in narrow basins as a result of a high pri-
mary plankton production in connection with increased oxy-
gen consumption for oxidation of organic matter (Murray et al.
1990). It should be mentioned that almost all analysed samples
from Kalnik and Medvednica Mts are red in colour and were
probably deposited below the OMZ. A direct influence of the
OMZ to the positive Ce anomaly in these rocks thus cannot be
confirmed.

Depositional environments

Bedded cherts (radiolarites s.str.) originate in specific geo-

tectonic conditions and are connected to specific evolution
phases of ocean basins and continental margins. In most cases
they are the only sediments in the ophiolite sequence with a

Fig. 8. La

/Ce

vs. Al

/ Al

+Fe

discrimination diagrams for individual investigated areas (individual fields after Murray 1994).

valid fossil content. Besides that, the chert sequences can to-
day  often  be  found  in  structurally  alochthonous  packages,
whereby  they  represent  carriers  of  important  information
about the evolution of the sedimentary basin, and play an im-
portant role as a stratigraphic and depositional indicator for the
paleogeographical  reconstruction  of  particular  areas  or  re-
gions.

In the past decade, the use of chemical methods has gained

significance, and today these methods represent an important
tool for solving the problems of depositional environments of
radiolarian cherts, and simultaneously for determination of the
paleogeographical position of sedimentary basins during their
genesis.

Because of the diagenetic chemical fractionation and the mi-

gration of Si, Mn, Ca, Mg, P, Sr and Ba out of silica rich lay-
ers, these elements are inappropriate for the determination of
depositional environment. Therefore we used only the dia-
grams based on Al, Fe, La and Ce proposed by Murray (1994).

On the La

/Ce

vs. Al

/(Al

+Fe

) diagram (La and

Ce NASC normalized) (Fig. 8), the Kalnik and Medvednica
samples are grouped in the continental margin field. A smaller
part of Žumberak radiolarian cherts belong to the pelagic field,

340 HALAMIĆ, MARCHIG and GORIČAN

but the majority is outside of all fields. Such a distribution is
conditioned by the increase of the La

/Ce

ratio and by a lower

content of Ce in those samples. The samples on Ivanščica Mt
are divided into two groups. One group is closer to the pelagic
field, with a lower Al

/(Al

+ Fe

) ratio due to increase

of Fe content, and a decrease of Ce content. Three samples are
grouped closely to the field of the mid-oceanic ridge. The dis-
tribution of these samples is the result of a further increase of
Fe content, and the decrease of Ce content (Table 3), which
caused an increase of the La/Ce ratio.

The sample distribution on the diagrams is not completely in

concordance with the geological data. In fact, the radiolarian
cherts on Kalnik Mt lie between basic effusive rocks or direct-
ly on them, and in the diagrams they belong to the continental
margin field. This is a result of the width of the sedimentary
basin (increased terrigenous input in a narrow sedimentary
trough). The radiolarian chert samples on Ivanščica Mt lie on
carbonate sediments (Fig. 2), while a part of the samples on
the discussed diagrams show a strong influence of the ocean
ridge (Fig. 8). Lower terrigenous input is a consequence of the

sedimentary basin’s size, as the disintegrating carbonate plat-
form created a larger distance to the continent.

Based on geological data from previous studies (Halamić &

Goričan 1995; Bukovac et al. 1995; Halamić 1998; Grgasović
et al. 2000) and geochemical data in this paper, we constructed
a simplified evolutionary model of the sedimentary basin dur-
ing the Triassic in which the studied radiolarian cherts were
sedimented (Fig. 9).

The disintegration of the carbonate platform in the studied

areas  started  probably  in  Middle  Anisian  (rifting),  which  is
documented by a sudden facies change (sections on the Žum-
berak and Ivanščica Mts). The subsequent disintegration and
deepening  of  the  sedimentary  basin  during  the  Late  Anisian
and  Early  Ladinian  was  accompained  by  magmatic  activity
(MOR-basalts on Medvednica Mt; Halamić et al. 1998 and the
VHK  section  on  Kalnik  Mt).  The  magmatic  activity  on
Žumberak and Ivanščica Mts is registered only in the form of
tuffs and tuffites. During the following spreading and lateral
drift of the sedimentary basin the Žumberak and Ivanščica ar-
eas stayed at the basin’s margin (passive continental margin),

Fig. 9. Simplified disintegration model of the carbonate platform and position of investigated radiolarian cherts during the Triassic (leg-
end see Fig. 2).

GEOCHEMISTRY OF RADIOLARIAN CHERTS IN CROATIA 341

while the Medvednica and Kalnik Mts were located in the
deeper part of the same basin. The most distinctive differentia-
tion between the Žumberak and Ivanščica Mts on the one side
and the Medvednica and Kalnik Mts on the other, happened
from Late Ladinian (Late Carnian?) when the carbonate sedi-
mentation on Žumberak and Ivanščica Mts was renewed. At
the same time on the Medvednica and Kalnik Mts the magmat-
ic activity and sedimentation of radiolarian siliceous mud con-
tinued.

Conclusions

All of the analysed radiolarian cherts are rocks with high

SiO

content (mean SiO

= 90.05 %). The major part of SiO

is of biogenic origin (radiolarian tests). The SiO

enrichment

of particular layers in the radiolarite and the shale/chert alter-
nation is the result of diagenetic chemical fractionation of
SiO

and its migration (Murray et al. 1992c; Murray 1994).

Statistical analysis (correlation) and the normalization to Al
compared to NASC of major and trace elements showed that
besides the siliceous component, two other components stand
out in the radiolarian cherts. One of them is detritic (terrige-
nous input) and it consists of Al, Ti, K, Cr, Hf, Zr, Th, Rb, Sc
and Nb. All these elements show a relatively high mutual cor-
relation (Fig. 3 and 4). The other component (hydrothermal)
consists of iron, manganese and phosphorus, which precipitat-
ed into the precursor sediment on the divergent plate margins,
in the form of hydroxides with a high adsorption capability.
Phosphate is adsorbed onto Fe-hydroxide. Subsequently, dur-
ing diagenesis goethite was formed from Fe-hydroxide and ap-
atite from phosphate. In this process, manganese is more sen-
sitive to redox conditions than iron, and is therefore dissolved,
removed and reprecipitated and now shows no significant cor-
relation to Fe and P.

The La/Ce vs. Al/Al+Fe ratios (Fig. 8) suggest that (1) the

radiolarian cherts from the Kalnik and Medvednica Mts were
sedimented  near  a  continental  margin  (narrow  sedimentary
trough). That is also indicated by a positive Ce anomaly which
ranges from 1.17 to 1.31 (Table 3) and these values are charac-
teritic  for  sedimentary  basins  lying  closer  to  the  continental
masses  (Murray  et  al.  1990),  (2)  the  Ivanščica  radiolarian
cherts  were  deposited  in  a  pelagic  environment  with  mid-
ocean  ridge  influence  and  (3)  the  siliceous  rocks  from
Žumberak  Mt  were  sedimented  in  an  open  sea  environment
without mid-ocean influence.

The distinctive negative Ce-anomalies on Ivanščica and

Žumberak Mts indicate a reduced terrigenous input, or an open
sea sedimentary environment (Ce/Ce* from 0.46 to 0.58).
Since the cherts on those two terrains are sedimented directly
onto the dolomites and limestones of the carbonate platform
(Bukovac et al. 1995), the radiolarian cherts were not neces-
sary sedimented in a deep water environment (a negative Ce
anomaly was also registered in Triassic carbonate sedimented
on a 50 m depth; Liu et al. 1988). The terrigenous input in this
part of the sedimentary basin was probably weaker, because of
the width of the disintegrated carbonate platform (greater dis-
tance from the continent) or because of a topographically high-
er position (bypass of fine terrigenous material) with respect to
Medvednica and Kalnik.

Acknowledgment: The authors are grateful to Dr. J. Michalík
(Bratislava),  Dr.  S.  Kovács  (Budapest),  Prof.  I.  Rojkovič
(Bratislava)  and  two  anonymous  reviewers  for  critical  com-
ments that have improved this manuscript. The work was done
in the framework of the geological mapping of Croatia (scale
1:50,000)  with  support  of  the  Croatian  Institute  of  Geology
and  Croatian  Ministry  of  Science  and  Technology,  Project
01810106.

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