GeolCarp_Vol49_No4_271

GEOLOGICA CARPATHICA, 49, 4, BRATISLAVA, AUGUST 1998

271287

PECULIAR TYPES OF THIN VEINS IN THE MESOZOIC

CARBONATES AND SILICITES OF THE WESTERN CARPATHIANS

MILAN MIÍK

Department of Geology and Paleontology, Faculty of Science, Comenius University, Mlynská dolina,

842 15 Bratislava, Slovak Republic

(Manuscript received March 9, 1998; accepted in revised form June 16, 1998)

Abstract: Many veinlets in carbonate rocks considered as open crack fillings, are the result of recrystallization (dashed

veinlets formed by the shear, whitened veinlets). Synsedimentary and early diagenetic veinlets may be folded in a soft

sediment deformation or deformed by brittle fragmentation. They may also fill desiccation cracks, bedding parallel

joints and synsedimentary cracks with internal sediment (microdykes). Synaeretic cracks in bedded silicites and nodular

cherts can be filled with calcite partially infiltrating the still reactive silica mass (pearl-string type veinlets, bordered

veinlets), filled by chalcedony, or can disappear being healed by neighbouring silica mass. Relative dating of veinlets

with regard to the formation of authigenic minerals, formation of chert nodules, conglomerate deposition, calcite

twinning, microstylolites etc. is possible. Authigenic quartz, feldspars, pyrite, illite, baryte, fluorite and galena found

in calcite veinlets are mentioned. From the commonly occurring dedolomitized saddle dolomite in calcite veinlets, the

burial depth of the Krína Nappe was estimated.

Key words: Western Carpathians, Mesozoic, silicites, limestones, dolomites diagenesis, synsedimentary cracks, veinlets.

Introduction

Veinlets register a lot of the geological history of carbonate and

silicite complexes since their deposition through early diagene-

sis and deep burial up to their final uplift to subsurface depth.

They reflect strain field, tectonic events, render possible the es-

timation of the burial depth, record changes in the composition

of fluids. This contribution is focused upon the types of vein-

lets derived from thin-section study and the perspectives for

further investigations. The types of veinlets recognized in the

following paper are summarized in the Fig. 1.

Questions concerning veins are dispersed in many pa-

pers. A review of them can be found in Groshong (1988).

Types of veinlets

Recrystallization veinlets. According to the current

opinion thin veins in limestones originated by the filling of

opened cracks that is by filling of an empty space. In an older

contribution (Miík 1971) I demonstrated that a considerable

part of these veinlets of millimetres thickness was formed by

recrystallization. That is clear mainly in such cases when

fossils (bioclasts) cross the veinlet without being torn and

both their ends put off, e.g. the aptychus at the Pl. I: Fig. A.

The upper veinlet seems to be formed still in the unlithified

sediment and the fossil could have been torn off the matrix.

Relics of echinoderm plates are frequently preserved in the

recrystallized veinlets (Pl. I: Fig. B). They originated mostly

as so-called dashed veinlets (see in the further text). The pen-

etration of the echinoderm plate into the veinlet on Pl. I:

Fig. C is clearly visible, the recrystallization (removal of in-

clusions) was perfect and the dashed structure totally disap-

peared. Another veinlet (Pl. I: Fig. D) also seems to repre-

sent a normal filled crack but it branches by entering the

crinoidal plate and so betrays its origin by the coalescence

of thin veinlet array.

Several veinlets caused only lightening of the crossed part

of fossil (aptychus Pl. I: Fig. E, echinoderm plates and

ooids Pl. I: Fig. F), see further as whitened veinlets. The

fibrous calcite aggregate of the veinlet crossed by undis-

turbed juvenile bivalves (Pl. II: Fig. A) also belong to the re-

crystallization veinlets.

Dashed veinlets (definition by Miík 1971) originated by

recrystallization, by amalgamation of an array of subparallel

hair-thin veinlets formed by the shear. Their origin was later

explained by Ramsay (1980) by the crack-seal-mechanism (re-

peated cracking and sealing). Bons & Jessell (1997) suggested

an alternative explanation of fibrous veins, formed by diffu-

sional transport, by dissolution-precipitation creep, without

fracturing. Our cases indicate the origin of dashed veins from

an array of thin subparallel cracks which is not compatible

with the process supposed by Bons & Jessell (1997).

A considerable part of the thickness of dashed veins pro-

ceeds from the recrystallization of the micritic host rock. The

remnants of micrite dividing former subparallel veinlets are

concentrated in stripes or only as inclusion trails parallel to

the vein (Pl. II: Figs. BE; Pl. III: Fig. A). Some larger cal-

cite grains were totally cleaned of these remnants during the

recrystallization (aggrading neomorhism, Folk 1965), while

they are well preserved in the neighbouring grains(Pl. II: Fig.

C). The new-formed aggregates use to have a columnar or fi-

brous structure with fibres normal to the veinlet walls. The

origin of the asbestos-like calcite aggregate could probably

have been initiated by the process of forming the array of

very thin veinlets as can be seen in Pl. III: Figs. B, C. Some

272 MIÍK

of dashed, originally fibrous veinlets can acquire after re-

crystallization an aspect of elongated-blocky veins of Fisher

& Brantley (1992).

The mutually cut dashed veinlets register the change in the

direction of extension (Pl. II: Fig. F). The dashed veinlets are

sometimes folded (Pl. III: Fig. D), perhaps contraction af-

fected still semiconsolidated and later compacted sediment.

The dashed veinlets also occur in dolomites. In the two fol-

lowing cases the remnants of dashed structure were preserved

due to authigenic quartz replacing a part of the veinlet before

its final recrystallization (e.g. in a Carboniferous dolomite

Pl. II: Fig. E and the Triassic dolomite Pl. III: Fig. F).

These examples again show that the recrystallized veinlets are

much more wide spread than was estimated before, because

frequently no phantoms of their dashed nature were preserved.

Recrystallized dashed veinlets also occur in silicites, e.g.

quartz veinlet in Triassic radiolarites (Pl. IV: Figs. A, B), cal-

cite veinlet in Oxfordian radiolarites (Pl. IV: Figs. CE). An

albitic dashed veinlet was exceptionally found in the acid tuf-

fites. Similar veinlets were illustrated by Ramsay & Huber

from greywackes (1987, Fig. 25.16) and calcareous phyllites

(Fig. 25.17). Augustithis (1973, Fig. 12.12) illustrated dashed

veinlets from granites; he explained them surprisingly as col-

loform structures.

Bordered veinlets belong to a rare type. They represent a

combination of normal veinlet with recrystallization veinlet.

Their central part originated by filling of an empty space

(open crack) and lacks inclusions. The recrystallization part

was developed along both sides by replacement of the sedi-

ment and therefore is full of inclusions. Bordered veinlets

were found in limestones (Pl. IV: Fig. F), radiolarites (Pl. IV:

Fig. G), and chert nodules (Pl. V: Fig. A).

Whitened veinlets. In these cases the recrystallization is

manifested by whitening (removal of inclusions during the

recrystallization) of the matrix, ooids and bioclasts crossed

by the veinlet in limestone (Pl. I: Fig. F). In another case the

recrystallization veinlet cleared an aptychus by removing of

its pigment without tearing it (Pl. I: Fig. E).

Limpid phantom veinlets occur very frequently in the do-

lomites (Pl. V: Fig. B). They possess sharp boundaries but

pass independently of the new-formed mosaic of larger

grains (aggrading neomorphism). They are phantoms of nor-

mal veinlets filled with clear dolomite cement which lost

their individuality during the recrystallization of the dolo-

mite rock. The same explanation was suggested by Bose

(1979, p. 690, Fig. 8F).

Granulation veinlets in dolomites, in contrast to the pre-

ceding category, originated by degrading neomorphism (Folk

1965). They represent thin zones of the tectonic trituration of

a coarser-grained dolomite (Pl. V: Fig. C). The pseudodolo-

micritic matrix of dolomite tectonic breccias originated by

increasing the amount of their products.

Syngenetic (or very early diagenetic) veinlets deserve spe-

cial attention. Five types of them will be described.

Veinlets folded by compaction are frequent in marls and

marly limestones (Pl. III: Fig. D), but also occur in rapidly

accumulated silicites. Two examples will be mentioned. Tri-

Plate I: Thin-section microphotographs in plane-polarized light.

Fig. A. Aptychus crosses the upper recrystallization veinlet without

being disturbed; it was partly dislocated in the lower one. Upper Ti-

thonian limestone, Manín Unit, klippe Butkov, 6. gallery. Magn.

. Fig. B. Recrystallization veinlet formed by the coalescence of

parallel hairline cracks shown by the remnants of dashed structure

in the place where it is crossed by the crinoidal plate. Liassic lime-

stone, Krína Nappe, Donovaly, Nízke Tatry Mts. Magn. 55

Fig. C. Partial penetration of an echinoderm plate in a calcite re-

crystallization veinlet shows that it did not originate from an open

crack. Upper Tithonian limestone, Manín Unit, Butkov, borehole

LC-5, 25 m. Magn. 55

. Fig. D. Recrystallization veinlet penetrat-

ing the crinoidal plate. The ghosts of its pore structure and preced-

ing thin veinlets array are visible inside the veinlet. Liassic lime-

stone, Krína Nappe, Donovaly, Nízke Tatry Mts. Magn. 43

Fig. E. Recrystallization veinlet crossed by aptychus. At the cross-

ing the aptychus lost pigment during the recrystallization (whitened

veinlet). Tithonian limestone, Krína Nappe, Padlá Voda near Smo-

lenice, Malé Karpaty Mts. Magn. 43

. Fig. F. Whitened veinlets

with phantoms of crossed ooids and bioclasts (their pigment was

partly removed during the recrystallization). Rhaetian limestone,

Krína Nappe, loc. 114 near Rajec, Malá Fatra Mts. Magn. 20

Fig. 1. Described types of veinlets.

PECULIAR TYPES OF THIN VEINS IN THE MESOZOIC CARBONATES AND SILICITES 275

assic radiolarites of the Meliata Unit are sometimes associ-

ated with hematite and baryte deposits proceeding from hy-

drotherms penetrating through the ocean bottom. Deforma-

tions of the net of chalcedony veinlets caused by the

movement of non-consolidated mass have been found at the

locality Bradlo (Pl. V: Fig. D). Another case is represented

by the Oxfordian radiolarites (Pl. V: Fig. E), from the locali-

ty Trstená bowling alley (Miík et al. 1991a). The participa-

tion of hydrotherms in the silica accumulation was docu-

mented there by rare baryte crystals, roof-like lifting of

radiolarite laminae by ascending fluids (Pl. V: Fig. F) and

large spheroids (their sole locality in Slovakia). From the

folded vertical veinlet (Pl. V: Fig. E) compaction at least 20

% can be deduced. In other localites radiolarites were depos-

ited slowly (about 5 mm/1000 y) and do not contain such

compactional deformations.

Extremely folded calcite veinlets were found in a Mn-crust

from the Oxfordian limestone (Pl. VI: Figs. A, B). It is an ex-

ceptional case for Mn-crust. The early filled dehydratation

cracks were deformed by the movement of semiconsolidated

colloidal mass rapidly accumulated by supposed hydrotherms.

Fragmented veinlets originated by breaking of a rigid

veinlet within the semiconsolidated mass. The doubling of

part of a veinlet may be documented from the above men-

tioned radiolarite locality Bradlo (Pl. VI: Fig. C). The second

locality for radiolarites at Trstená bowling-alley also con-

tains fragmented syngenetic veinlets (Pl. VI: Fig. E). Such

broken veinlets also illustrated Soták & Ovoldová (1993,

pl. XXXII: Figs. 12) from the radiolarites of the Car-

pathian Flysch Belt and Hattori et al. (1996, Fig. 6A, p. 169)

from the Japanese Miocene silicites. Fragmented syngenet-

ic veinlets rarely occurred in spiculite limestone (Pl. VI:

Fig. D) and fresh-water Upper Cretaceous limestone (Pl. VI:

Fig. E with imbricated fragments).

Desiccation veinlets were formed during temporary emer-

sion, e.g. circular veinlets from dehydratation cracks in

fresh-water limestone (Pl. VI: Fig. G), or from cracked litho-

clasts in the Keuper Dolomite (Pl. VII: Fig. C). Veins paral-

lel to the bedding filled with prismatic or fibrous calcite ag-

gregate were named sheet cracks by Fischer (1964, p.114).

In the Western Carpathians they occur in dolomites (Pl. VII:

Fig. D); the cases of their partial erosion support their origin

near the surface.

Dewatering veinlets and voids may be formed within the

covered sediment, e.g. circular cracks in a coal fragment (Pl.

VII: Fig. A), in limestone (Pl. VII: Fig. B perhaps

formed due to fluid overpressure). Subaqueous shrinkage

cracks were described Donovan & Foster (1972).

Veinlets from the dehydratation of opal-chalcedony

mass. Shrinkage cracks sealed usually by chalcedony occur

in radiolarites (Pl. V: Fig. D) or chert nodules (Pl. VII: Fig.

E some parts of the veinlets are filled with calcite, others

with chalcedony). More examples will be demostrated fur-

ther by discussing syngenetic veinlets in chert nodules.

Syngenetic neptunic microdykes also represent the prod-

ucts of syngenetic cracking of sediment. If such cracks were

partly filled by sediment and the remaining space by calcite,

a polarity structure originated (Pl. VII: Fig. F). Neptunian

microdykes filled with sediment of a different age (Pl. VIII:

Fig. A) are not the subject of this contribution. A special case

was registered in Pl. VII: Fig. G where the infilling of a mi-

crodyke was repeatedly cracked forming an array of very

thin veinlets parallel to the microdyke walls.

Timing of veinlet formation

Timing of veinlets in the conglomerates. It is possible to

discern three groups of veinlets: (1) preconglomerate veinlets

occur only in the pebbles, they reflect older tectonic process-

es (Pl. VIII: Fig. D), (2) synchronous with the deposition

these veinlets proceed from the cracking of pebbles under the

load (Miík et al. 1991a,b,c), the matrix was entrained in the

cracks and the rest eventually filled by calcite cement (Pl.

VIII: Figs. A, C), (3) post-depositional veinlets formed after

the solidification of the conglomerate; they cross not only

pebbles but also the matrix in parallel systems.

Timing of veinlets formation in chert nodules. Three

groups can be defined:

(1) Pre-chert calcite veinlets limit in straight lines the

chert nodules in thin sections; they represented an obstacle to

the growth of the nodule and stopped the migrating silica so-

lutions (Pl. VIII: Figs. E, F). They are very frequent. The op-

posite case of pre-chert shear joints serving for the small

chert accumulations was observed only once (Pl. IX: Fig. A).

It might be a case of diastasis cracks (Cowan & James 1992)

originated by differential mechanical behaviour of interlay-

ered stiff mud under stress.

(2) Syngenetic veinlets, already mentioned (Pl. VII: Fig.

E), were formed in the stage when silica accumulation con-

tained a considerable amount of water and was still reactive.

Solutions of calcium bicarbonate penetrated in the submicro-

scopic synaeretic cracks, calcite rhombs grew from them as

if hanging on a string (Pl. IX: Figs. C, E) pearl-string

type of veinlets (Miík 1971, 1993). Radiolarians were filled

by calcite monocrystal but only in their immediate neigh-

bourhood (Pl. IX: Fig. D).

Plate II: Fig. A. Shells of juvenile bivalves cross the recrystalliza-

tion veinlet, formed by fibrous calcite, without being torn in two

pieces. Middle Triassic limestone, Choè Nappe, quarry near Èierna,

Stráovské vrchy Mts. Magn. 43

. Fig. B. Dashed veinlets with par-

allel inclusions of the marly micritic limestone, originated by re-

crystallization from parallel hairline fractures (crack-seal mecha-

nism). Neocomian limestone, Manín Unit, Butkov. Magn. 43

Fig. C. Vestige of dashed structure; the impurities were partly re-

moved by aggrading crystallization. The same locality. Magn. 43

Fig. D. Rare remnants of the dashed structure make it possible to

identify a recrystallization veinlet. Thin section from a pebble of

Barremian Lower Aptian limestone in the Cenomanian conglom-

erate. Shear cracks with the following recrystallization veinlet were

formed in the time span Upper Aptian Albian. Manín Unit,

Praznov. Magn. 43

. Fig. E. Remnants of dashed structure near the

lower margin of the veinlet and neighbouring parallel hairline vein-

lets betray the recrystallization. Neocomian marly limestone, Kysu-

ca Unit of the Klippen Belt, Horné Sànie. Magn. 43

. Fig. F. Array

of subparallel veinlets penetrated by a dashed veinlet. Neocomian

limestone, Manín Unit, Butkov, gallery 6, 32 m. Magn. 23

PECULIAR TYPES OF THIN VEINS IN THE MESOZOIC CARBONATES AND SILICITES 281

Plate III: Fig. A. Another thin vein which did not originate by the filling of an open crack. The true extension was only about half the thick-

ness of this dashed veinlet. Pebble of the Upper Tithonian limestone from the Eocene Strihovce Conglomerate, Magura Unit of the Flysch

Belt. Starina. Magn. 30

. Fig. B. New-formed calcite fibres approximately perpendicular to the array of hairline veinlets. Pebble of the Se-

nonian limestone from the Lower Miocene Jablonica Conglomerate. Prievaly. Magn. 30

. Fig. C. Calcite fibres (pseudosparite) grown per-

pendicularly to the array of hairline cracks. Norian Hallstatt Limestone, Silica Nappe, Silická Brezová. Magn. 55

. Fig. D. Folded dashed

veinlet indicates that the crack-and-seal mechanism took place still in a non-consolidated sediment. Lower Tithonian marly limestone, up-

permost nappe, quarry in ipkovský Haj near Krajné, Èachtické Karpaty Mts. Magn. 30

. Fig. E. Thin calcite vein partially replaced by au-

thigenic quartz (white). Remnants of the dashed structure are preserved only in quartz due to the early replacement. Upper Visean Lower

Namurian dolomite, Gemeric Superunit, Ochtiná. Magn. 30

. Fig. F. Part of a carbonate veinlet in dolomite was early replaced by the authi-

genic quartz; its dashed structure was preserved only there. Pebble of Triassic dolomite in the Albian Ludrová Conglomerate, Tatric Super-

unit, Malá Magura Succession. Èavoj-20. Stráovské vrchy Mts. Magn. 95

Plate IV: Fig. A. Quartz dashed veinlet in the radiolarite. Ladinian-Carnian of the Meliata Unit, Bradlo, South-Slovak Karst. Magn. 55

. Fig.

B. The same in cross-polarized light; perpendicularly recrystallized quartz grains are clearly visible. Fig. C. Dashed calcite veinlet in the ra-

diolarite, formed by coalescence of hairline cracks. Oxfordian radiolarites of the Pieniny Succession, Klippen Belt, Dúbrava near Stará Turá.

Magn. 48

. Fig. D. Dashed calcite veinlet in the radiolarite. Oxfordian of the Pieniny Succession, Klippen Belt, Trstená bowling alley. Magn.

. Fig. E. Calcite dashed veinlet in a radiolarite. Recrystallization of hairline veinlets to perpendicular calcite fibres and prismatic grains

eliminated the dashed structure except for some remnants of host rock in the calcite vein. The same locality. Magn. 30

. Fig. F. Bordered

veinlet in dolomitic limestone. Its pigmented margins were formed by syntaxial growth of calcite grains from the veinlet at the expense of the

host rocks, partially dolomitized limestone. Anisian Gutenstein Limestone, Tatric Succession, Ve¾ký Kriváò, Malá Fatra Mts. Magn. 25

Fig. G. Bordered calcite veinlet in radiolarite. Its clear middle part was formed by the filling of an open fracture with chalcedony. Grey pig-

mented borders were formed by calcite replacing the host Oxfordian radiolarite. Pieniny Klippen Belt. Trstená, bowling alley. Magn. 48

Plate V: Fig. A. Bordered veinlets in the chert nodule are syngenetic with the chert forming process. Their middle limpid parts had been

open cracks filled by calcite. Its grains grew syntaxially through the walls into the surrounding silica mass with high content of water. The

replaced margins are grey, filled by inclusions. Chert nodule in the Upper Tithonian limestones of the Kysuca Succession, Peniny Klippen

Belt, quarry near Brodno. Magn. 55

. Fig. B. Lightened veinlets in dolomite do not disturb the grain mosaic. They are ghosts of normal vein-

lets (open cracks filled by limpid dolomite) in the completely recrystallized dolomitic rocks with grains full or inclusions. Ladinian dolomite

of the Krína Nappe, Demänová, Pod Lúèkami, Nízke Tatry Mts. Magn. 136

. Fig. C. Network of granulation veinlets in dolomite repre-

senting fine cracks filled by cataclastic pseudodolomicrite. Triassic dolomite breccia. Vojtová Valley near Rajec, Stráovské vrchy Mts.

Magn. 13

. Fig. D. Synsedimentary folded network of chalcedony veinlets in radiolarite. After the filling of thin synaeretic cracks, sliding

of non-consolidated silica mass took place. The hydrothermal activity caused the rapid accumulation of silica. Ladinian-Carnian radiolarite

of the Meliata Unit, Tri Peniaky, Bradlo, South Slovak Karst. Magn. 14

. Fig. E. Compactional deformation of the chalcedony veinlet in

distal turbidite intercalation within the Oxfordian radiolarites. Pieniny Succession, Klippen Belt, Trstená bowling alley. Magn. 30

. Fig. F.

Vertical veinlet filled with chalcedony penetrating laminated radiolarite. The filling proceeds from a hydrothermal source at the bottom; the

ascending fluids heaved the uppermost part of the sediment which was not yet consolidated. The same locality. Polished section, slightly

magnified (1.7

Plate VI: Fig. A. Ptygmatic folding of calcite veinlets in a hardground Mn-crust occurred during the Albian. Early filled dehydratation

cracks were deformed by the movement of semiplastic colloidal manganese mass. Czorsztyn Succession, Vratec-castle klippe. Magn. 48

Fig. B. The same. Magn. 16

. Fig. C. Fragmented chalcedony veinlet formed by the breaking of its consolidated filling within still semiplas-

tic silica mass; fragments are partially overthrust. Ladinian-Carnian radiolarites of the Meliata Unit, Bradlo Tri Peniaky. Magn. 43

. Fig.

D. Early vertical calcite veinlet (perpendicular to the lamination) fragmented during compaction. Liassic limestone pebble from the Eggen-

burgian conglomerate, quarry near Podbranè (material of I. Baráth). Magn. 14

. Fig. E. Fragmented veinlet with early consolidated chalce-

dony filling, broken by extension of the still semiplastic silica sediment. Oxfordian radiolarites, Trstená, bowling alley, Pieniny Succession.

Magn. 30

. Fig. F. Syngenetic fragmented calcite veinlet with partial imbrication of its fragments, diagonally crossed by a set of thin young-

er veinlets. Fresh-water Coniacian limestone, pebble in the Santonian-Campanian conglomerate. Dobinská ¼adová jaskyòa. Magn. 30

. Fig.

G. Circular veinlets originated by the calcite filling of desiccation cracks in fresh-water Lower Coniacian limestone. Betlanovce, Stratenská

hornatina Mts. Magn. 7

Plate VII: Fig. A. Dewatering circular calcite veinlets (filled desiccation cracks) in a coal fragment. Senonian marlstone with silt lami-

nae. Borehole Gajary G-125, 4842 m, basement of the Vienna Basin. Magn. 13

. Fig. B. Dewatering veinlets synsedimentary cracks

filled with calcite cement and partly by younger micrite. Upper Berriasian limestone of the Horná Lysá Succession, Pieniny Klippen Belt,

Vratec. Magn. 22

. Fig. C. Desiccation veinlets (thin cracks formed during temporary emersion) with dolomitic infilling in a dolomite

intraclast. Norian Keuper dolomite of the Krína Nappe, quarry between diar and Tatranská Kotlina. Magn. 11

. Fig. D. Desiccation

veins of the sheet-crack type. Stratabound joints filled by asbestos-like calcite fibres, locally affected by the erosion. Ladinian Wetter-

stein Limestone, quarry near Krásna Ves, Stráovské vrchy Mts. Polished section, natural size. Fig. E. Network of syngenetic dehydrata-

tion veinlets in a chert nodule. Synaeretic cracks were partially filled with calcite and partially refilled with silica mass. Chert from the

Upper Tithonian limestone of the Kysuca Succession, Pieniny Klippen Belt, quarry near Brodno. Magn. 20

. Fig. F. Neptunic veinlets

(microdykes) syngenetic cracks filled partially by internal micritic sediment; the remaining empty space was sealed by calcite cement.

Polarity structure shows inclination with regard to the laminated infilling of a void, larger than the figure. Callovian-Oxfordian lime-

stone, klippe Kostelec. Magn. 6

. Fig. G. Neptunic microdyke formed as an open vertical fracture in Berriasian limestones with tintin-

nids which was filled by red Albian marl with Hedbergella and Ticinella. The microdyke filling was later disturbed by a set of hairline

veinlets subparallel to the fracture. Czorsztyn Succession, Klippen Belt, quarry near Kamenica. Magn. 30

PECULIAR TYPES OF THIN VEINS IN THE MESOZOIC CARBONATES AND SILICITES 283

(3) Post-chert veinlets represent younger tectonic phe-

nomena. They originated by cracking of already non-reactive

solidified chert nodules. These open joints were filled with

clear calcite aggregates. Due to the higher plasticity of the

limestone compared to the silicite, the veinlets in chert nod-

ules are always thicker and more frequent (Pl. IX: Fig. B).

Timing of veinlets with regard to authigenic minerals

and other diagenetic phenomena. If the authigenic quartz

or feldspar is younger than the veinlet, it extends from the

rock into the veinlet (Pl. X: Figs. C, D). The veinlet is cut by

the younger stylolite (Pl. IX: Fig. F). A younger vein filled

an opened stylolite after the change of compression into ex-

tension (Pl. X: Fig. A); the opposite explanation is impossi-

ble, because the coarse-grained filling of the veinlet would

not render possible the formation of a stylolite. Similar solu-

tions exist in relation to veinlets and microslickensides. If the

grains of a limestone were affected by pressure twinning, the

veinlets older than twinning will also be affected; the calcite

filling of the younger veinlets would not be disturbed.

Influence of veinlets on the colour of limestones. Calcite

veinlets formed an obstacle to the late diagenetic migration

of pigments (Pl. X: Fig. B). On the other hand, veinlets

younger than the pigment of the red limestones cause the

well-known decoloration (or green coloration) in their imme-

diate surrounding, due to the reducing nature of fluids.

Some other minerals from veinlets

Veinlet minerals other than calcite were not the subject of

this contribution, therefore only some examples from the

Western Carpathians will be presented. Authigenic quartz lim-

ited to the calcite veinlets is not rare; macroscopic crystals oc-

cur in the Liassic Borinka limestones (Turan & Vavro 1970),

Liassic limestone of the Oreany Succession, quarry NW from

Dolany, Malé Karpaty Mts. and in Paleogene sandstones

(Marmarosch diamonds Hurai et al. 1995). Authigenic

feldspar (microscopic size) is exceptional, e.g. Neocomian

limestones, locality Butkov. Pyrite is frequent, baryte rare (e.g.

in Keuper Dolomite, Zázrivá), fluorite exceptional (e.g. Car-

nian Opponitz Limestone, basement of the Vienna Basin,

borehole Závod-93, in the depth 5306 m), galena occurred only

once in a calcite veinlet from Liassic limestones of the Malá

Fatra Mts. (Miík 1964, p. 85). Albite veinlets in radiolarites

are probably connected with postvolcanic activity (Triassic ra-

diolarites of the Meliata Unit, Jaklovce Pl. X: Fig. E, and in

a pebble of Jurassic radiolarites from Strihovce conglomerates,

Flysch Belt Miík et al. 1991b, p. 23, Pl. III: Fig. 1).

Illite veinlets do not attract due attention in spite of their

frequency. In the Western Carpathians they occur mainly in

Liassic and Tithonian-Neocomian limestones. They consist

of large light-brown aggregates with uniform extinction, ori-

ented parallel to the walls of veinlets; their birefringence is

comparable with that of the illite. The material from a vein-

let about 1 mm thick from Neocomian limestones was iden-

tified (V. ucha personal communication) by X-ray analysis

as a mixture of illite and chlorite. It is probable that at least

some of the illite veinlets represent microslickensides. The

material for the new-formed illite probably originates from

the tiny submicroscopic clastic illite in limestone, mobilized

during pressure solution.

Veinlets with dedolomitized saddle dolomite. They of-

fer possibility of approximate estimation of temperature.

The temperatures from isotopic study of host limestones are

much lower than those from the calcite of veinlets, for exam-

ple the red nodular Hallstatt Limestone, locality Silická Bre-

zová (Kantor & Miík 1992) had

0 = 0.87 , the calcite

from a veinlet of the same specimen

0 = 7.38 corre-

sponding to the temperature of about 60

The Jurassic and Cretaceous limestones of the Krína

Nappe frequently contain veins (up to 2 cm in thickness) filled

by a mixture of white calcite and brown carbonate grains. In

all the analyzed cases the brown grains belonged to the dedo-

lomitized baroque dolomite (Pl. X: Figs. F, G). The saddle or

baroque dolomite originated under temperatures mostly be-

tween 90 and 160

C (Spötl & Pitman 1992) which reflects

the minimum burial depth. Supposing an average value of 33

m/1

C the burial depth could be estimated as 2.34.6 km.

The baroque dolomite with characteristic curved crystal

planes and sweeping exctinction was in all cases dedolo-

mitized, and replaced by secondary calcite. The brown co-

lour proceeds from Fe

isomorphe admixture in Mg

which

was liberated by the calcification and oxidized. The dedolo-

mitization was caused by groundwaters charged with sul-

phate ions during the erosional uprise to subsurface level.

Summary

The modern methods for studying thin veins such as stable

isotope analyses, cathodoluminiscence, microprobe analyses

of calcite, study of inclusions and structural measurements

must be preceded by a serious thin-section study. Various

Plate VIII: Fig. A. Neptunic microdykes cracks in the Oxford-

ian limestone filled with Albian limestone sediment with Hedber-

gella and Ticinella. Czorsztyn Succession, Vratec-castle klippe.

Magn. 43

. Fig. B. Veins in synsedimentary cracked pebble filled

with the matrix of the conglomerate. Limestone pebble from the

Paleocene Proè Conglomerate, Pieniny Klippen Belt, Beòatina.

Natural size. Fig. C. Synsedimentary cracks in a limestone pebble

were filled with the not yet consolidated matrix. These clastic

veinlets, synchronous with the deposition of conglomerate, are pe-

culiar for the abundant quartz grains totally absent in the sur-

rounding limestone. Their distal wedging-out parts were filled by

calcite cement. Pebble of the Paleocene biohermal limestone in the

Eocene Strihovce Conglomerate, Flysch Belt. Matiaka. Magn.

. Fig. D. Pre-conglomerate veinlet in the pebble of Middle Tri-

assic limestone from the Coniacian Upohlav Conglomerate of

the Kysuca Succession, Pieniny Klippen Belt. The calcite veinlet

was formed in the time span Upper Triassic Middle Cretaceous

probably during the Cretaceous tectonics in the accretionary

wedge. Zádubnie. Magn. 20

. Fig. E. Pre-chert calcite veinlets

originated in the micritic radiolarian limestone before the forming

of chert nodules. They acted as obstacles for the migrating silica

and limit the chert nodule in straight lines. Neocomian cherty

limestone, Manín Unit, quarry Butkov. Magn. 23

. Fig. F. Another

pre-chert veinlet. Berriasian-Valanginian Horná Lysá Limestone,

Kysuca Succession, Vratec. Magn. 13

286 MIÍK

Plate X: Fig. A. The calcite veinlet is younger than the stylolite. During the compressional phase the stylolite was formed. In the course

of the following extension the stylolite was opened and the crack sealed by coarse-grained calcite aggregate. Tithonian limestone of the

Kysuca Succession, quarry near Brodno. Polished section, natural size. Fig. B. The vertical calcite veinlet was an obstacle for the late di-

agenetic migration of pigment-bearing solutions. Stromatolitic limestone (loferite) with desiccation pores partly filled with internal sedi-

ment. The right side and the left side of the same layer are differently coloured. Norian limestone from the basement of the Vienna Basin.

Borehole Studienky-95, 4195 m. Magn. 30

. Fig. C. The authigenic idiomorph quartz is younger than the calcite veinlet. Ladinian Rei-

fling Limestone of the Choè Nappe. Hradkovo, Choè Mts. Magn. 136

. Fig. D. The authigenic feldspar is younger than the calcite vein-

let. Rhaetian limestone pebble from the Cenomanian-Turonian conglomerate of the Klape Unit. Oravský Podzámok. Magn. 136

. Fig. E.

Albite veinlet in the Carnian radiolarite of the Meliata Unit, probably formed by post-volcanic activity of near by diabase (basalt) bodies,

approximately of the same age. Jaklovce. Magn. 30

, crossed polars. Fig. F. Dedolomitized (calcified) grains of saddle dolomite with

curved crystal planes, pigmented by iron hydroxides. They partially replaced the older calcite filling of the veinlet. Liassic limestone of

the Krína Nappe, Kraviarske, Malá Fatra Mts. Magn. 27

. Fig. G. Dedolomitized saddle dolomite grains (dark) replacing the older cal-

cite filling of the vein. Neocomian limestone, Krína Nappe, Motyèky, Nízke Tatry Mts. Magn. 26

Plate IX: Fig. A. Pre-chert veinlets filled with silica. Tensional cracks inclined to the stratification were probably formed in the not yet

consolidated calcareous sediment and immediately used by the migrating silica solutions. Upper Tithonian limestone of the Choè Nappe,

ipkovský háj near Krajné. Polished slab, natural size. The photo is rotated 90

. Fig. B. Set of post-chert calcite veinlets is limited to the

chert nodule. The rigid chert was disturbed by extensional fractures in difference to the more plastic host limestone. Neocomian cherty

limestone, Hradská Valley near Podhradie, Ve¾ká Fatra Mts. Polished slab, natural size. Fig. C. Veinlet of the string-pearl type syngenetic

with the chert. The solutions of calcium bicarbonate penetrated through the synaeretic cracks in the time when the silica mass rich in wa-

ter was still reactive. Calcite grains usually of rhombic shape grew from the cracks replacing the silica mass. Upper Jurassic cherty lime-

stone, Pieniny Succession, Klippen Belt, Lubina. Magn. 55

. Fig. D. Another veinlets syngenetic with the chert nodule. Molds of radi-

olarians in their immediate neighbourhood were also filled by calcite; other radiolarians in the chert were dissolved mostly without any

trace. Tithonian cherty limestone of Kysuca Succession, Klippen Belt, quarry near Brodno. Magn. 43

. Fig. E. Pearl-string type veinlets

syngenetic with the chert nodule in dolomite. They consist of a row of calcite rhombs replacing silica (their calcitic nature was verified

by the staining with alizarine). Red chert nodule in Norian Keuper dolomite. Magn. 95

. Fig. F. Microstylolite is younger than the veinlet

in Middle Jurassic radiolarites of the Meliata Unit. Meliata, near the mill. Magn. 45

types of veinlet are described in this contribution (Pls. IX

and Fig. 1).

It was shown that a lot of veinlets regarded as normal

(open cracks originated by extension) are really the recrystal-

lized veinlets formed by shear. Recrystallized veinlets can

be identified by fossils traversing them without being torn,

by remnants of an array of coalescing hairline shear veinlets

(dashed or crack-and-seal veinlets), by whitening removal

of inclusions during the recrystallization.

Synsedimentary veinlets in carbonate and silicic rocks

may be deformed in the semiplastic state of sediment (duc-

tile deformation) or by brittle fragmentation. Syngenetic

and very early diagenetic veinlets fill desiccation cracks,

beddingparallel joints (sheet cracks), neptunic microdykes

(partly filled with internal sediment), subaqueous dewatering

cracks, synaeretic cracks in silicites (bordered veinlets with

replacement margins and pearl-string type).

We are handicapped by the impossibility of calcite radio-

metric dating (except of Quaternary calcites), therefore nu-

merous possibilities for relative dating of veinlets must be

used: with regard to authigenic minerals, formation of nodu-

lar cherts, deposition of conglomerates, calcite twinning, for-

mation of microstylolites etc.

The large extension of dedolomitized saddle dolomite in

calcite veinlets within the Mesozoic limestones of Krína

Nappe shows the burial depth about 2.34.6 km. The abun-

dance of thin illite veinlets in the studied limestones is su-

prising. The formation of albite veinlets in Triassic radiolar-

ites are considered to be a post-volcanic feature.

A team study of thin veins can substantially contribute to

the deciphering of the diagenesis, subsidence, fluid migra-

tion and tectonic history of carbonate and silicite complexes.

Acknowledgements: The author is indepted to Prof. Franz

Neubauer (University Salzburg) and Doc. RNDr. Duan

Plaienka,CSc. (Geological Institute of Slovak Academy of

Science) for many improvements of the manuscript.

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