GEOLOGICA CARPATHICA, 51, 2, BRATISLAVA, APRIL 2000
PYRITIZED RADIOLARIANS FROM THE MID-CRETACEOUS
DEPOSITS OF THE PIENINY KLIPPEN BELT A MODEL OF
PYRITIZATION IN AN ANOXIC ENVIRONMENT
MARTA B¥K and ZBIGNIEW SAW£OWICZ
Institute of Geological Sciences, Jagiellonian University, Oleandry 2A, 30-063 Kraków, Poland; email@example.com
(Manuscript received August 24, 1999; accepted in revised form March 15, 2000)
Abstract: Excellently preserved, pyritized radiolarian skeletons have been found within the Upper Cenomanian de-
posits in the Pieniny Klippen Belt (PKBCarpathians, Poland). On the basis of a study of their chemical composi-
tion, structure of replacing skeletons and exceptional preservation of all morphological details, we propose a new
model where the pyritization process took place not in sediment but while the radiolarian skeletons were suspended in
the anoxic water column. The radiolarians rich in organic matter, sinking through the upper (iron-rich) part of an
anoxic water column, became the sites of organic matter decomposition and enhanced bacterial sulphate reduction.
Dissolved iron in this zone diffused into the radiolarians and precipitated as iron sulphides replacing the opaline
skeletons. This process was controlled by the rates of opal dissolution and of bacterial sulphate reduction, and the
availability of dissolved iron. The preservation of radiolarians in the Upper Cenomanian deposits from different depth
sub-basins of the PKB was compared. We found that the extent of pyritization and preservation of radiolarian skel-
etons may be dependent on the depth of the basin and the position of the oxic-anoxic interface.
Key words: Carpathians, Pieniny Klippen Belt, anoxic event, pyritization, Radiolaria.
Pyritized organic remains are common in the sedimentary
record. Pyrite may form moulds of diatoms (Geroch 1978;
McNeil 1990), fill empty spaces and/or replace carbonates in
echinoderms (Jensen & Thomsen 1987), ammonites (Hudson
1982), gastropods and bivalves (Fisher 1986) or whale bones
(Bang 1994), delineate tubes and burrows of polychetes
(Thomsen & Vorren 1984) and replace soft-bodied trilobites
(Briggs et al. 1991). Pyrite has also been found in recent fora-
minifers (Seiglie 1973). Pyrite can adopt various forms, from
massive to aggregated, euhedra and framboids. Generally py-
rite replaces the organic matrix (soft parts) and carbonate
skeletons during all stages of sediment burial history. Excel-
lent descriptions of mechanisms of fossil pyritization (but not
of silica skeletons) were given by Canfield & Raiswell (1991),
Briggs et al. (1996) and Raiswell (1997).
While pyritized radiolarian skeletons are relatively com-
mon (e.g. Pessagno 1977; Thurow 1988; M. B¹k 1995,
1996b), this phenomenon has only been recorded in the taxo-
nomic literature. In this paper we present the results of the
first non-taxonomic study and propose an original model of
radiolarian pyritization in the water column. Perfectly and
poorly preserved pyritized radiolarian skeletons from the up-
per Cenomanian deposits of different successions in the Pol-
ish part of the Pieniny Klippen Belt were also compared.
The Pieniny Klippen Belt (PKB) represents a zone of
strongly deformed Mesozoic and Paleogene sedimentary rocks
which separates two major structural units of the Carpathians:
the Inner and the Outer Carpathians (Fig. 1). During the Creta-
ceous, the Pieniny Klippen Basin consisted of several sub-ba-
sins representing realms from the outer shelf (the Czorsztyn
Succession), to the lower and middle bathyal zones, (the
Branisko and Pieniny successions) (Birkenmajer 1977;
Birkenmajer & Gasiñski 1992; K. B¹k 1993). The Upper Cen-
omanian deposits in the Pieniny Klippen Basin, which belong
to the foraminiferal Rotalipora cushmani Zone are represented
by two facies. These are black marly shales with radiolarians
(Birkenmajer 1977; Birkenmajer & Jednorowska 1987), which
can be correlated with an anoxic event, well developed in the
Pieniny and Czorsztyn successions, and grey-green shales
with thin sandstone intercalations represented by the shaly fly-
sch deposits belonging to the Branisko Succession (Birkenma-
jer 1977; K. B¹k 1993). All these deposits contain pyritized ra-
diolarians (M. B¹k 1995, 1996a,b, 1999). For the purpose of
this study the rocks belonging to the Czorsztyn, Branisko and
Pieniny successions were sampled and the pyritized radiolari-
an skeletons compared.
The material studied includes 33 samples, from four profiles
in the Polish part in the Pieniny Klippen Belt. Eleven samples
have been taken from black shales of the Magierowa Member
in the Magierowa Ska³a section of the Pieniny Succession (M.
B¹k 1999). Ten samples have been taken from grey-green
shales of the Jaworki Formation (Trawne Member and
Snenica Siltstone Member) in the Kietowy stream section of
the Branisko Succession (M. B¹k 1995, 1996a), and twelve
92 B¥K and SAW£OWICZ
samples have been collected from black shales of the Altana
Shale Bed in two profiles of the Czorsztyn Succession
(Szaflary quarry and Lorencowe Klippes sections see M.
B¹k 1996b). The samples were collected in the sections ev-
ery 10 to 80 cm (depending on the changes of lithology and
the quality of exposure), especially near lithological bound-
aries. Marls and marly shales were the dominant lithotypes.
A few samples were taken from mudstones.
Samples of about 1 kg were taken for preparation. Each
sample was broken into pieces 12 cm across and dried out
under a temperature of 105 °C. Next the samples were
soaked in a hot solution of glauberic salt and boiled, usually
for several days. Hard cemented parts of samples were
soaked in hot acetic acid for 78 hours. Then the residue
was washed through a 63
Radiolarians were first examined under a binocular mi-
croscope. They were picked out manually from the residue
(maximum 300 specimens per sample). The best preserved
specimens were mounted on Scanning Electron Microscope
(SEM) stubs for photography.
Radiolarian association and description
of pyritized skeletons
Radiolaria are generally common in the samples studied.
Specimens are well to poorly preserved, silicified or pyri-
tized. The above mentioned data suggest, that the type of
preservation of pyritized radiolarian skeletons depends on
the depth at which they were formed in the sub-basins.
Radiolarian skeletons from the black marly shales of the
Pieniny Succession (the deepest part of the PKB) (Fig. 2A)
are usually moderate to poorly preserved. Pyritized skeletons
with poorly preserved outer structures (due to dissolution)
dominate in the radiolarian association which consists of nu-
merous Nassellaria (mostly cryptocephalic and cryptothorac-
ic forms), belonging to genera such as Holocryptocanium,
Hemicryptocapsa, Squinabollum) with only a few forms of
Spumellaria (genera Archaeocenosphaera, Orbiculiforma).
Siliceous skeletons are rare here. Pyrite microconcretions,
possibly pseudomorphs after radiolarian skeletons, are also
Radiolarian skeletons from the black shales of the
Czorsztyn Succession (the shallowest part of the PKB ba-
sin) (Fig. 2C) are usually poorly preserved (although often
sufficiently for taxonomic determinations), and seem to be
formed exclusively of pyrite. However, the examination of
cross-sections shows that irregular masses of pyrite grains
cover various parts of the majority of the siliceous skeletons
of radiolarians. This radiolarian association comprises both
Nassellaria (genera Holocryptocanium, Hemicryptocapsa,
Dictyomitra, Stichomitra) and Spumellaria (genera Patellu-
la, Crucella, Cavaspongia) (forming about 60 and 40 per
cent of the association, respectively).
The majority of the radiolarians in one sample (Kietowy
section sample Ki-14 see M. B¹k 1995) from the grey-
green shales of the Branisko Succession (Fig. 2B) (lower to
middle bathyal, K. B¹k 1993) consist of pyrite, with only a
few siliceous skeletons. The radiolarian assemblage consists
predominantly of Nassellaria. The pyritized forms belong
mostly to the cryptothoracic Nassellaria (Pl. I) such as Holo-
cryptocanium barbui, Hemicryptocapsa tuberosa and Hemi-
cryptocapsa prepolyhedra. Xitus mclaughlini and Thanarla
pulchra are less abundant. The rare siliceous specimens, all
corroded, also include the Nassellaria (Cryptamphorella co-
nara, Sethocapsa sp.) (Pl. II: Fig. 2), with only one specimen
of Spumellaria (Haliommura sp.). The above mentioned radi-
olarian taxa do not occur in both siliceous and pyritized
forms. Pyrite very faithfully replaces all the original silica
skeletons in the studied sample, even the finest details of or-
namentation (Pl. II: Figs. 3, 4). Even in cryptothoracic forms
with a thick abdomen wall (e.g. H. barbui, H. tuberculatum)
of four layers, the internal layers are perfectly preserved (Pl.
II: Figs. 7, 8). SEM-EDS study showed that pyrite is actually
the only sulphide mineral present, without the presence of sil-
ica or silicates. At lower magnifications (below 1000
images reveal very even surfaces of pyritized skeleton ele-
ments. However, higher magnifications (500010000
that these skeletons are built of masses of small irregular
grains of pyrite (size about 0.5
m), intergrown or closely
packed, sometimes with pores (Pl. II: Fig. 1). Secondary dis-
solution of the pyritized skeletons caused corrosion, resulting
in fine to coarse-granulated surfaces, or partly destroyed
walls (Pl. II: Fig. 6). Dissolution sometimes enhances a pri-
mary granulated structure of the walls. The observations of
corroded surfaces of some preserved silica skeletons suggest
that the primary skeletons were built of silica grains of the
similar size to the pyrite grains. Pyrite framboids are common
in the pyritized radiolarian skeletons. They typically occur in
Fig. 1. The geological position of the Polish part of the Pieniny
Klippen Belt (P.K.B.) within the Carpathians. Tectonic elements
mainly after M. Ksi¹¿kiewicz, simplified by K. Birkenmajer (1985);
A: Location of the investigated sections in the Pieniny Klippen Belt
(geology after Birkenmajer (1977) simplified). Designation of
the sections: Ki Kietowy, Lor Lorencowe Klippes, Sz
Szaflary quarry, Mag Magierowa Ska³ka.
PYRITIZED RADIOLARIANS FROM THE MID-CRETACEOUS DEPOSITS 93
Plate I: Pyritized Radiolaria: Fig. 1. Hemicryptocapsa tuberosa Dumitricã. Fig. 2. Holocryptocanium tuberculatum Dumitricã. Fig. 3.
Holocryptocanium barbui Dumitricã. Fig. 4. Hemicryptocapsa prepolyhedra Dumitricã. Fig. 5. Xitus mclaughlini Pessagno. Fig. 6. Tha-
narla pulchra (Squinabol).
94 PLATE II
PYRITIZED RADIOLARIANS FROM THE MID-CRETACEOUS DEPOSITS 95
Plate II: Fig. 1. Pyrite octaedra (with growth defects or partly dis-
solved) forming microconcretions replacing radiolarian skeleton.
Fig. 2. Siliceous, partly corroded, skeleton of Sethocapsa sp. Fig. 3.
Inner side of abdomen chamber with aperture, perfectly replaced by
pyrite. Fig. 4. Pyritized, partly removed the external layer and com-
pletely preserved the internal layer of abdomen wall (H. barbui)
with pyrite framboids inside of the pores. Fig. 5. Granulate pyritized
surface of abdomen wall of H. tuberosa, with pyrite framboid in a
pore. Fig. 6. Partly corroded pyritized surface of H. barbui, reveal-
ing granulated texture, also seen in a pore, note the similar size of
grains forming abdomen wall and framboid in a pore. Fig. 7. Interi-
or of the abdominal chamber of H. barbui, with individual fram-
boids and their clusters attached to the inner surface. Fig. 8. A
cross-section of the abdomen wall of H. barbui with lamp chimney
shape of pores, sometimes hosting a pyrite framboid.
Fig. 2. An idealized cross-section through different depths of sub-basins of the PKB showing various modes of radiolarian skeleton preser-
vation (species Holocryptocanium barbui, magnification for all illustrated forms:
300). The most faithful replacement by pyrite is expected
where the chemocline is just below the SiO
dissolution zone (Branisko Succession); A Pieniny Basin example of pyritized, poorly
preserved skeleton; B Branisko Basin excellently preserved, pyritized skeleton; C Czorsztyn Basin siliceous skeleton covered by
pyrite grains. 1 black shales, 2 grey-green shales; D place of ideal pyritization of radiolarian skeletons in an anoxic water column.
two different positions: (1) in channels (pores) (Pl. II: Figs.
4, 5, 8); (2) inside the abdomen of cryptothoracic forms, at-
tached to an internal surface, often at a channel exit (Pl. II:
Fig. 7). The size of framboids is around 5
m. The average
size of grains and crystals in the framboids is similar to that of
the opal grains, forming the radiolarian skeleton. Sometimes
the framboids contain silicate minerals in the interstices. In
some pyrite skeletons pores are filled by aggregations of alu-
A 0.5 mg combined sample of excellent pyritized radiolar-
ian skeletons was subjected to a sulphur stable isotope study
(preparation after Robinson & Kusakabe (1975), analysed on
a modified MI-1305 mass spectrometer). The
was 1.88 ± 0.07 .
96 B¥K and SAW£OWICZ
Proposed model of radiolarian pyritization
Pyrite can be formed either directly or indirectly (via iron
monosulphides, mainly mackinawite and greigite) although
the latter pathway is more typical for sediments (Rickard
1975; Howarth 1979; Berner 1980; Rickard et al. 1995). Py-
rite may also form in an euxinic water column but its forma-
tion during diagenesis is more common.
We assume that the pyritization of skeletons resulting in ex-
cellent preservation of the radiolarians described here took
place in the anoxic water column. A comparison of the de-
grees of preservation of skeletons from different environ-
ments suggests that such perfect (exceptionally well pre-
served details, etc.) and clean (no silicate admixtures or
silica remains), replacement of silica by pyrite as observed in
the sample (Ki-14) of the Branisko Succession is unlikely to
have occurred in a sediment during and/or after burial. This
origin is supported by observations on the formation of sul-
phides and pyrite framboids in the anoxic water column of
the Black Sea and Framvaren Fjord (Skei 1988; Canfield et
al. 1996). Sulphur isotope data from the Black Sea also sug-
gest a rapid water-column formation of Fe-S (Lyons 1997).
Further evidence for pyritization of radiolarian skeletons in
water column could be derived from close spatial and genetic
association of skeletons with pyrite framboids. Pyrite fram-
boids typically form in euxinic water column and/or during
early diagenesis in a sediment (Lyons 1997; Wilkin & Barnes
1997). Their occurrence in pores or attached to the internal
surface of pyritized radiolarian skeletons suggests that pyriti-
zation of skeletons took place before framboids formation. If
framboids formed in siliceous radiolarian skeletons, the sub-
sequent process of skeleton pyritization would caused infill-
ing of framboid interstices, overgrowths on framboid or fram-
boid growth to euhedra (see Saw³owicz 1993) which was not
observed in the studied sample.
It has been suggested that settling organic matter becomes
sites for elevated rates of sulphate reduction (Muramoto et al.
1991; Canfield et al. 1996). We propose that siliceous radi-
olarian skeletons, rich in organic matter, settling in the upper
(iron-rich) part of an anoxic water column were the sites of
organic matter decomposition and enhanced bacterial sul-
phate reduction (BSR), producing sulphide (Fig. 3). Dis-
solved iron in this zone diffused into the radiolarians and pre-
cipitated as iron sulphides replacing the opaline skeletons.
The chemical properties of the water column were important
factors in the pyritization. The process requires a water col-
umn undersaturated with respect to SiO
and saturated with
respect to iron sulphides (appropriate ratios of iron to sul-
phide, see Canfield & Raiswell 1991). According to Raiswell
(written comm. 1997), the amount of dissolved iron in the res-
ervoir below the oxic/anoxic interface would only need negli-
gible sulphur for saturation. Thus, as opaline skeletons with
organic matter sink through the Fe-rich zone, they are re-
placed by Fe-sulphides. A simplified reaction could be: SiO
O, although pyrite forma-
tion was probably preceded by formation of mackinawite and
greigite. It is possible that only iron monosulphide formation
took place in the water column with subsequent pyritization
during/after burial. On the basis of the similarity between siz-
Fig. 3. Model of pyritization of radiolarian skeletons in an anoxic
water column. Pyritization, resulting from H
S formation in the or-
ganic matter of the radiolarian and iron supply from the Fe-rich
water column, must be matched by dissolution of the opal skele-
ton; 1 organic matter; 2 siliceous skeleton; 3 pyritized
parts of the skeleton.
es of grains forming the silica and pyrite skeletons, we suggest
that replacement of opal by iron sulphides could be grain for
grain. The primary and necessary condition for excellent
preservation is that the living level of radiolarians (the begin-
ning of the opaline skeleton dissolution process), the rate of
sulphide production by BSR and the oxic/anoxic interface
with the iron-rich zone below (low in H
S and with relatively
high pH) must be correlated (Fig. 2B). Typical dissolution of
radiolarians begins in the upper hundreds of meters of the wa-
ter column, which suggests that the pyritization process began
very early and high up in the water column. For comparison,
the oxic/anoxic interface in the Black Sea varies from 60 to
200 m depth (Brewer & Spencer 1974). If the chemocline is
much below a silica dissolution level, then well pyritized but
poorly preserved skeletons (or microconcretions), without
preservation of all morphological details (Fig. 2A), result from
the pyritization of silica remnants during sinking or in the sed-
iment. On the other hand, pyrite encrustation on silica skele-
tons may form when the chemocline is high in the water col-
umn (pyritization proceeds opal dissolution), or when
skeletons are buried before dissolution, for example in a shal-
low basin (Fig. 2C). The processes described above are also
controlled by the ratios of dissolved sulphide and iron concen-
trations (compare with the diffusion-with-precipitation model
of Raiswell et al. 1993).
In discussing the main factors influencing the model pre-
sented above, we are aware that most available data are re-
PYRITIZED RADIOLARIANS FROM THE MID-CRETACEOUS DEPOSITS 97
lated to the present day ocean, and that care is required when
applying them to past environments.
The most difficult problem is to evaluate a possible rate of
opaline skeleton dissolution, especially as the available data
are often contradictory. Present day oceans are highly un-
dersaturated with dissolved silica. The mean concentration
of silicon in seawater is 1
mol/kg (Broecker & Peng
1982). Dissolution of the silica in radiolarians during settling
through the water column is a very common process. The
amorphous mineralogically unstable opal, which forms ra-
diolarian skeletons, is dissolved in a silica-undersaturated
marine environment (Hurd 1974). However opal skeletal re-
mains have a variable resistance to dissolution, due to dif-
ferences in structure, chemical composition, geometrical
construction and specific surface area (Bohrmann 1986).
According to Goll & Bjorklund (1974) most biologically
produced opal in the oceans dissolves before reaching the
bottom and, for example, in the present central Pacific, radi-
olarians suspended in the water column dissolve most rapid-
ly in the upper 250 metres. On the other hand, Broecker &
Peng (1982) found that only a little silica dissolution occurs
during settling of the particles through the water column,
and inferred that most of the opal dissolution occurs on the
sea floor. There is a possible relationship between radiolari-
an opal preservation and oxygen minima in the water col-
umn (Goll & Bjorklund 1974). A semi-closed anoxic basin
with little exchange and increased concentrations of dis-
solved silica may probably lower silica undersaturation in
the water column and slow down dissolution. The rate of
opal dissolution could also be modified by some other fac-
tors. Production of HCO
O + SO
S + 2HCO
inside radiolarians during organic matter decomposition and
bacterial sulphate reduction may enhance opal skeleton dis-
solution. On the other hand, the early formation of iron sul-
phide coatings may slow down dissolution. It is interesting to
note that higher concentrations of iron salts may reduce the
solubility of radiolarians (Lewins experiments with diatoms
see Goll & Bjorklund 1974). The depth of the Branisko
Basin has been estimated at approximately 1500 m (K. B¹k
1993). Radiolarians which are not transported in fecal pelets,
reach the bottom during several days to about one month,
based on sinking rates and residence time calculated by Ta-
kahashi & Honjo (1983), and Berger & Piper (1972). This
seems to be a reasonable period of time for pyritization of
skeletons to proceed.
Bacterial sulphate reduction is the most common source of
sulphide for pyrite formation and often occurs at the site of the
decomposing organic matter (Berner 1980). Decay of readily
metabolizable organic matter in radiolarians produces an anaer-
obic microenvironment in which sulphates from surrounding
seawater are being reduced by anaerobic bacteria (Berner 1970,
1984). As the skeleton of living radiolarians is encased in a soft
cytoplasm, not even the most protruding parts of the skeleton
are ever in direct contact with seawater. The proteinaceous ma-
terial comprising the soft bodies of radiolarians decomposes
rapidly, probably together with symbiotic bacteria and algae.
There is no consensus as to the rate of organic matter decompo-
sition, estimates ranging from days to years, depending on dom-
inant organic compounds (Westrich 1983). Studies of Radiolaria
from the South Atlantic suggest that bacterial decay of cyto-
plasm may progress to completion long before burial (Goll &
Bjorklund 1974). Canfield et al. (1996) explained a process of
iron mineral sulphidation in the euxinic Black Sea as the result
of local sulphate reduction during decomposition of settling
organic material. H
S generation could be a very localized
process restricted to radiolarians, especially when coupled
with contemporaneous iron sulphide formation. In such a case
the water column would be iron-rich and anoxic but not euxin-
ic. Concentration of the free H
S in the water column would
have to be low otherwise the samples would contain extensive
pyrite framboids formed in the water column or at the sedi-
ment-water interface, which was not observed.
of Upper Cretaceous seawater sulphate was
about +17 (Claypool et al. 1980). The typical maximum of
microbial sulphate reduction fractionation varies from 45 to
60 (Goldhaber & Kaplan 1974), but it is much lower in
the absence of the oxidative sulphur cycle (Canfield & Tham-
drup 1994). In our study,
S is around 2 indicating frac-
tionation of about 19 . It is worth stressing that a readily me-
tabolizable proteinous material stimulates higher rates of
sulphate reduction, which in turn may cause a smaller fraction-
ation. Thus, fractionation of around 20 could be typical for
pyritization of radiolarians. It is also possible that the radiolar-
ians themselves could form a semi-closed system to sulphates.
Part of the isotopically light H
S formed during BSR may be
removed from the radiolarians faster than the rate of iron sul-
phide formation. Thus, heavier residual sulphates remain in
the radiolarian body and are used for continued BSR. As the
result, the pyritized skeleton may be relatively enriched in
heavy sulphur. It cannot be excluded that
S varies across
the skeleton wall.
The concentration of iron in recent ocean water is generally
very low and varies from 0 to 0.007 mg/l, with mean concen-
tration of 1
mol/kg (Broecker & Peng 1982). However,
high maxima are typically found in an iron-rich zone below
the oxic/anoxic interface, reaching 50 ppb in the Black Sea
(Brewer & Spencer 1974). Iron concentrations in some anoxic
basins may conform to mackinawite-greigite solubility limits
(Morse et al. 1987). The major sources of iron could be iron
oxides, like goethite, hematite, lepidocrocite and ferrihydrite
(Canfield 1989), which are then reduced in the anoxic water-
column. Some iron may be adsorbed on radiolarians (especial-
ly those still covered with organic material) as oxides and hy-
droxides and dissolved in situ.
Pyritization of only specific radiolarian species may be ex-
plained by their variable living levels and/or different skele-
ton structure. The position of the living zone in relation to the
chemocline could be crucial for the degree of pyritization and
preservation. We cannot exclude radiolarian taxa selection by
bottom currents, but the diversity of the shapes (e.g. spheres
and cones) of pyritized skeletons speaks rather against this
Pyrite framboids present in Radiolaria were probably
formed after the pyritization of skeletons. They occur in free
spaces within the skeletons and could form during diagenesis
(even late diagenesis if only BSR was active) of the sediment,
like pyrite concretions. The latter could replace the silica of ra-
diolarians or recrystallize earlier pyritized radiolarians during
98 B¥K and SAW£OWICZ
diagenesis. Pyrite encrustation on silica skeletons could form
both during the short period of sinking in shallow water, or lat-
er, after burial.
The results of the studies presented here are based on mi-
cropaleontological and mineralogical analyses of radiolari-
an skeletons from 33 samples from four profiles.
For the purpose of this study the Upper Cenomanian de-
posits belonging to the Czorsztyn, Branisko and Pieniny
successions were sampled and the radiolarian skeletons
Samples have been taken from black shales of the Magier-
owa Member (Pieniny Succession), grey-green shales of the
Jaworki Formation (Branisko Succession), and black shales
of the Altana Shale Bed (Czorsztyn Succession).
Radiolarian skeletons from the Pieniny Succession are
usually moderately to poorly preserved. The pyritized skele-
tons with poorly preserved outer structures (due to dissolu-
tion) dominate the association. Siliceous skeletons are rare
here. Pyrite microconcretions, possibly pseudomorphs after
radiolarian skeletons, are also present.
Radiolarian skeletons from the Czorsztyn Succession are
usually poorly preserved and seem to consist exclusively of
pyrite. The examination of skeleton cross-sections show
that irregular masses of pyrite grains cover various parts of
the majority of siliceous skeletons of radiolarians.
Excellently preserved, pyritized radiolarian skeletons
have been found within the grey-green shales of the Branis-
ko Succession. On the basis of a study of their chemical
composition, structure of replacing skeletons and exception-
al preservation of all morphological details, we proposed a
new model where the pyritization process took place not in
sediment but while the radiolarian skeletons were suspend-
ed in the anoxic water column. The radiolarians rich in or-
ganic matter, sinking through the upper (iron-rich) part of an
anoxic water column, became the sites of organic matter de-
composition and enhanced bacterial sulphate reduction.
Dissolved iron in this zone diffused into the radiolarians and
precipitated as iron sulphides replacing the opaline skele-
tons. This process was controlled by the rates of opal disso-
lution and of bacterial sulphate reduction, and the availabili-
ty of dissolved iron.
Preservation of radiolarians in the same deposits from dif-
ferent depth sub-basins of the Pieniny Klippen Belt (Pien-
iny, Branisko, and Czorsztyn) was compared. We found that
the extent of pyritization and preservation of radiolarian
skeletons may be dependent on the depth of the basin and
the position of the oxic-anoxic interface.
Acknowledgements: The authors wish to thank D.E.G.
Briggs, M. Piasecki and R. Raiswell who thoroughly read a
draft version of the manuscript and made constructive criti-
cisms. Thanks are due to CoBabe, D.H. McNeil, L. Ovol-
dová, I. Rojkoviè, W. Oschmann and an anonymous reviewer
for their suggestions. We thank K. B¹k for information on the
foraminiferal assemblage and discussion, J. Szaran for the sul-
phur isotope analysis and J. Faber for the SEM photographs.
Bang B.S. 1994: Framboidal pyrite and associated organic matrices.
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(Ed.): Surface Treatment: Cleaning, Stabilisation and Coat-
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