Exotic clasts of organodetritic algal limestones from lithosomes of the Babica Clay, Skole Unit (Outer Flysch Carpathians, Poland)

Annales Societatis Geologorum Poloniae (1998), vol. 68: 225-235.

EXOTIC CLASTS OF ORGANODETRITIC ALGAL LIMESTONES FROM LITHOSOMES OF THE BABICA CLAY, SKOLE UNIT

(OUTER FLYSCH CARPATHIANS, POLAND)

J a c e k R A J C H E L & J o la n ta M Y S Z K O W S K A

Zakład Geologii Ogólnej i Matematycznej, Wydział Geologii, Gebfizyki i Ochrony Środowiska Akademii Górniczo-Hutniczej im. Stanisława Staszica, al. Mickiewicza 30, 30-059 Kraków

Rąjchel J. & Myszkowska J. 1998. Exotic clasts o f organodetritic algal limestones from lithosomes of the Babica Clay, Skole Unit (Outer Flysch Carpathians, Poland). Ann. Soc. Geol. Polon., 68: 225-235.

A bstract: The paper deals with exotic clasts o f Lithothamnium calcarenites and calcirudites occurring in the central part o f the Skole Unit. The clasts are confined exclusively to those lithosomes o f the Babica Clay (upper Paleocene) which occur within the Variegated Shale Formation, overlying the Bircza Lithothamnium Limestone Bed (BLLB). The exotic clasts represent fragments o f talus deposits, formed due to degradation o f algal reefs which were situated along the northern margin of the Skole basin. They were transported into the basin by dense cohesive flows that built pebbly mudstones lithosomes of the Babica Clay. Exotic clasts of calcarenites contain silicified cores formed after clast deposition. The age o f exotic rocks was determined as the turn o f the Early and Late Paleocene basing on foraminifers.

A bstrakt: Scharakteryzowano grupę litotamniowych, kalkarenitowych i kalcyrudytowych egzotyków, z central­

nej części jednostki skolskiej. Występują one tylko w tych litosomach iłów babickich (późny paleocen), które usytuowane są w obrębie formacji pstrych łupków, powyżej warstwy litotamniowego wapienia z Birczy /wt/.

Egzotyki te są fragmentami stożków nasypowych, formujących się z degradacji raf glonowych usytuowanych wzdłuż północnej krawędzi zbiornika tej jednostki. Ich transport w głąb zbiornika odbywał się w gęstych, kohezyj­

nych spływach żwirowców ilastych formujących litosomy iłów babickich. Egzotyki kalkarenitowe posiadają zsylifikowane jądro, utworzone po ostatecznej depozycji egzotyka. Na podstawie zawartej w egzotykach mikro­

fauny otwornicowej określono ich wiek na przełom wczesnego i późnego paleocenu.

Key words: Skole Unit, Babica Clay, organodetritic exotic clasts, calcareous algae, silicification, cherts, Paleo­

cene, Outer Flysch Carpathians.

Manuscript received 6 December 1996, accepted 28 November 1998

INTRODUCTION

The object o f this study are clasts o f organodetritic algal limestones which fall into the category o f exotic rocks (cf.

Jaroszewski et al., 1985). The clasts have been found in li­

thosomes o f the Babica Clay occurring in the central part o f the Skole Unit (Fig. 1), between Rzeszów and Ustrzyki Dol­

ne (Rajchel, 1976a, 1989, 1990). The lithosomes with exotic rocks occur only above the Bircza Lithothamnium Limesto­

ne Bed (BLLB; Gucik, 1961; Kotlarczyk, 1978; Rajchel, 1976a, 1989; c/! Figs. 2,3).

The Babica Clay represents strongly differentiated de­

posits o f the pebbly mudstone type. They have been distin­

guished first by Kropaczek (1917a, b) near Babica village on the Wisłok River, and later described under this name from numerous sites of Upper Cretaceous-Low er Palaeoge­

ne strata in the Skole Unit. At present, the name “Babica Clay” is applied exclusively to those deposits o f this type which occur in lense-like lithosomes within Paleocene strata

o f the Wola Korzeniecka Member, Ropianka Formation, and in the Paleocene sequence of the Variegated Shale For­

mation of the Skole Unit (Kotlarczyk, 1978; Rajchel, 1990).

The majority of exotic rocks studied do not show close resemblance to the older allodapic limestones o f the BLLB (Rajchel & Myszkowska, in press). Some specimens resem­

ble, in turn, carbonate conglomerates from the top o f the Ro­

pianka Fm, occurring in the north-eastern and central parts o f the Skole Unit (Fig. 2; cf. Rajchel, 1976a, 1989; Kotlar­

czyk, 1988a).

The aim o f our paper is to characterise the lithology of exotic rocks and to compare them with deposits o f similar type and age. Such a comparison could help in documenting differences in appearance and mode o f sedimentation of these deposits, as well as to confirm the exotic character of the clasts studied. Basing on foraminifer tests preserved within exotic rocks, the age o f parent rocks has also been

226

RZESZÓW

DUBIECKO.

Pr z e m y ś l

12

11

10

9 8

Fig. 1. Locations o f exotic clasts o f organodetritic Lithotham- niura limestones in the Skole Unit (after Swidziński, 1958 and Rajchel, 1990; simplified and modified). 1 - Variegated Shale and Hieroglyphic Fm, 2 - Spas Shale Fm, Dolhe Fm, Ropianka Fm, Menilite Fm and Krosno Fm, 3 - Quaternary sediments, 4 - principal thrusts: a - Carpathian over thrust, b - other thrusts, 5 - extent of the Babica Clay lithosomes at the base o f the Variegated Shale Formation, 6 - extent o f exotic organodetritic limestones within lithosomes o f the Babica Clay, weathering regolith, collu- via and alluvia, 7 - extent of the Bircza Lithothamnium Limestone Bed, 8-9 - outcrops o f exotic clasts o f organodetritic limestones: 8 - in situ, 9 - within weathering regolith. Sites: 1 - Zabratówka Wieś, 2 - Siodmówka, 3 - Przedmieście Dynowskie, 4 - Kosz­

towa, 5 - Drohobyczka Dolna, 6 - Skopów, 7 - Skopów Buczacz, 8, 9 - Bachów, 10 - Jureczkowa, 11 - Żohatyn, 12 - vicinities of Bircza

determined.

Our study makes it possible to reconstruct sedimentary environment of the northern margin o f the Skole basin in Late Paleocene times, i.e. before its closing due to the Early Styrian orogenic movements (Kotlarczyk, 1988a).

BABICA CLAY LITHOSOMES:

CHARACTERISTICS

Lithosomes o f the Babica Clay were formed due to co­

hesive flows shed from the northern slope o f the Skole basin (Bukowy, 1957a, b; Gucik et a i, 1962; Kotlarczyk & Śli­

wowa, 1963), wherefrom only the largest flows could have reached the axial part o f the basin (Fig. 1; cf. Rajchel, 1990, fig.8). Moreover, the western part o f the Skole Unit bears traces o f the Babica Clay flows, derived from the southern basin margin (Szymakowska, 1961; Jasionowicz, 1962; Gu­

cik et al., 1962). The dispersive phase o f such flows was usually composed o f strongly sandy, black, carbonate clayey substance. Their dispersed phase, in turn, were iitho- logically differentiated exotic rocks, as well as rocks eroded from the base o f the flow, occurring in variable proportions and showing different sizes. The dispersive phase usually dominates over the dispersed one, although the reverse situ-

7

6

5

4

3

, a

A

Fig. 2. Schematic lithostratigraphy o f upper part o f the Ro­

pianka Fm and Variegated Shale Fm o f the central part of Skole Unit (after Kotlarczyk, 1978 and Rajchel, 1990; modified and supplemented, not to scale). 1-5 - Ropianka Fm: 1 - thin-bedded sandstones and calcareous shales, 2 - thick-bedded calcareous sandstones, 3 - thin- and medium-bedded sandstones with interca­

lations of conglomerates and submarine slump deposits, a - Bacu- lites marls, 4 - thin-bedded brittle sandstones and noncalcareous shales, a - Lithothamnium calcareous conglomerates and calciru- dites, 5 - variegated shales markers, 6 — Babica Clay, a - exotic clasts of organodetrital limestones, 7-12 - Variegated Shale Fm: 7 - Boguszówka Sandstone Member, 8 - Bircza Lithothamnium Limestone Bed, 9 - Zohatyn Variegated Shale Member, 10 - Kosztowa Sandstone, 1 1 - variegated shales of the Lower Eocene, 12 - Trójca Variegated Shale Member

ation can also be encountered (Fig. 3). The Babica Clay de­

posits rarely contain olistoliths.

The submarine slump origin o f the Babica Clay results in the presence o f irregularly spaced lense-like lithosomes o f variable size and thickness up to 30 m.

The petrographic inventory o f exotic rocks comprised in the Babica Clay can be reconstructed on the basis of nu­

merous papers (Bukowy, 1956, 1957a, b; Kotlarczyk, 1961;

EXOTIC CLASTS OF ALGAL LIMESTONES

227

9

10

WWl-VtAA/V

Fig. 3. Detailed lithostratigraphy of the lower part o f the Vari­

egated Shale Fm bearing lithosomes of the Babiea Clay with exotic clasts of organodetrital Lithothamnium limestones: A - site 4 (Kosztowa), B - site 10 (Jureczkowa). 1-2 - layers associated with the Bircza Lithothamnium Limestone Bed: / - limestones with a high admixture of inorganic material, as well as sandstones and conglomeratic sandstones with large proportion of calcareous ma­

terial, 2 - chert-bearing limestones with low admixture o f noncal- careous material; 3 - very fine-grained white sandstones, 4 - ash-coloured-green mudstones, 5 - greyish red clayey shales, 6 - green clayey shales, 7 - grey clayey shales, 8 - deep-blue clayey shales. 9 - Babica Clay: black, calcareous, sandy shales with interlayers of clayey sandstones, 10a - exotic clasts o f organode- tritic limestones, 10b - clasts o f limestones derived from the Bircza Lithothamnium Limestone Bed, 10c - clasts of black shales, lUd- other exotic rocks

Fig. 4. Polished slab of an exotic organodetritic Lithothamnium limestone of calcarenitic type. Irregular outer surface is visible along with central cherty core which reflects the shape of the surface and contain equally-spaced enclaves of unsilicitied rock (arrowed). Site 4 (Kosztowa): bar scale in centimetres

G eroch & K otlarczyk, 1963; K otlarczyk & Śliw ow a, 1963;

N owak, 1963; Dżulyński et al., 1979; Skulich, 1986; Raj- chel, 1989, 1990). The Ś tram berk-type lim estones are the dom inant com ponent. D olom ites, m arls, phyllites, porphy- res, andesites, granites and other igneous rocks occur subor- dinately, alongside with clasts derived from the substratum , i.e. sandstones, shales and m arls o f the R opianka Fm, and lim estones originated from the BLLB. Exotic sandstones, conglom erates, quartzites and m etam orphic rocks, as w ell as fragm ents o f C arboniferous coal occur m ore rarely. These exotic rocks display highly variable sizes and diversified de­

gree o f roundness. The B abica Clay deposits also contain unusually abundant m acrofauna o f bivalves, gastropods, bryozoans, and corals, as well as fragm ented and som etim es not dism em bered Lithotham nium rodoliths.

Fig. 5. Section through exotic rock built up of highly psamitic, organodetritic calcarenite. Clast pierced by borings produced by organisms (a), 6 cm deep and 1.5 cm in diameter, as well as a tunnel (b) of similar diameter. On the left - asymmetric silicifica- tion area (c), postdating the borings. Site 12 (vicinity of Bircza);

from collection of Prof. Dr. J. Kotlarczyk; bar scale in centimetres

LITHOLOGY OF EXOTIC ORGANODETRITIC LIMESTONES

The object o f our study is a set o f several tens o f exotic rocks representing algal calcarenites and calcirudites. These clasts are usually prolate or circular, 10 to 30 cm in diam e­

ter. M ost o f them do not show any regular arrangem ent o f com ponents. Singular specim ens (K osztow a, site 4) display poorly m arked horizontal lam ination or grading. Infrequent specim ens bear hollow s o f different depth and diam eter (Fig. 4 & 5), left by boring organism s.

The population studied is dom inated by calcarenite- type exotic rocks, the m ajority o f w hich contain a central cherty core (Fig. 4). C arbonate com ponents o f these exotics are beige in colour algal biocalcarenites o f variable content o f sand fraction (C zerm iński, 1955) (Fig. 6). Such a sedi-

228

Fig. 6. Exotic clast of biocalcarenite from Kosztowa, site 4.

Rounded fragments of coralline algae (a), cemented by calcite blocky cement (b), with isolated quartz grains (c). Thin section; 1 N

ment is usually w ell-sorted (diam eters from 0.1 to 0.6 mm, som etim es up to 2.3 m m ), its principal com ponent being fragments o f calcareous red algae from C orallinaceae, rarely Squam ariaceae fam ilies, w hich m ake up 30 to 50% o f all the fragm ents. Algal rem ains show w ell-preserved internal m i­

crostructure, although they are usually strongly fragm ented.

This fragm entation preclude identification, even at the ge­

nus level. The rem aining, non-algal organodetritic m aterial constitutes up to 10% o f the rock m ass, and included frag­

ments o f echinoderm s (crinoids, echinoids), bryozoans and polychaetes (Serpula and D itm pa), as w ell as planktonic and benthic' foram inifers. Fragm ents o f brachiopods and thick-shelled bivalves occur sporadically. All the above ele­

m ents are preserved as oval grains o f rounded edges, more rarely as angular grains.

The content o f terrigeneous m aterial, m ostly quartz, varies from 2.7 to 27% o f the rock. Its poorly rounded grains are 0.1 to 0.5 mm, rarely up to 1.5 mm in diam eter. They are accom panied by clasts o f organodetritic lim estones, gneis­

ses, and granitoids (0 .1 -0 .8 % ).

Blocky calcite cem ent dom inates, although the m ajority o f sam ples contain also syntaxial cem ent grow ing around echinoderm s, as well as scalenohedral and isopachous ce­

ment. The latter occurs in incipient intragrain voids, mostly w ithin bryozoan zoecia and foram iniferal tests, rarely out­

side the tests.

Exotic rocks o f the calcirudite structure are gray or white, do not contain siliceous cores (Fig. 7), and are poorly sorted. Bimodal distributions o f grain size are frequently ob­

served. O ne o f grain size classes is represented by clasts 1 to 6 cm in diam eter w hich are usually rounded fragm ents o f gray and beige, m icritic and fine-sparitic lim estones (Fig. 7).

A nother class is represented by w hite, angular clasts o f lim estones, a fraction o f a m illim etre to 3 -5 mm across, dom inated by the rem ains o f coralline algae (4 0 -4 5 % ). The latter belong m ainly to the genus Lithothamnion (form erly Lithothamninnr, vide Studencki, 1988; B osence, 1991), rarely Archaeolithothamnium. They are accom panied by single specim ens o f algae from the S quam ariaceae fam ily,

Fig. 7. Polished slab of an exotic clast o f organodetritic Li- thothamnium calcirudite. a - clasts of different limestones, b - psefitic clasts o f Lithothamnia, c - quartz and rock fragments. Site 4 (Kosztowa); bar scale in centimetres

represented by Personnelia and Ethelia genera. Apart from psam m itic grains o f algae o f unidentified growth form, pse­

fitic fragm ents were observed o f branching and crustose thalli, with borings filled either by cem ent or organodetritic material. Fragm ents o f algal-bryozoan biolites are also fre­

quent. G rains o f organic origin com prise as well the remains o f bryozoans, echinoderm s (crinoids, echinoids), worm tubes (Serpula and Ditrupa genera), foram inifers and iso­

lated fragm ents o f calcareous sponges. The above grains, com prising a few percent o f the total num ber o f grains, are rounded, oval or circular in cross-section, som etim es also ir­

regular.

The adm ixture o f non-carbonate grains varies from 6 to 7%. These are relatively frequent aggregates o f glauconite, as well as o f terrigeneous m aterial, m ostly quartz and feld­

spars, rarely lithic grains (dolom ite-bearing glauconitic claystones, quartzites, m icritic and organodetritic lim esto­

nes, rarely interm ediate and mafic igneous rocks). The ter- rigenic m aterial show s a broad spectrum o f grain sizes, from a fraction o f a m illim etre to a few m illim etres. Psefitic com ­ ponents are better rounded.

Exotic clasts o f calcirudites contain cem ent types sim i­

lar to those o f calcarenites. Intergranular cavities are filled w ith blocky cem ent, accom panied by syntaxial cem ent. In- tragranular voids com prise, in turn, scalenohedral and isopa­

chous cement.

SILICIFICATION OF CALCARENITIC EXOTIC ROCKS

Siliceous cores form ing the interior o f exotic clasts o f calcarenites usually reflect the outer shape o f the latter. The size o f cores vary in relation to the diam eters o f exotic rock, and usually occupies 1/2 to 3/4 o f the surface o f the greatest section o f the clast (Fig. 4). C om pletely silicified exotics, found in alluvia, probably represent cherty cores separated due to recent w eathering. C herts are alw ays dark-beige or brown show ing planar or conchoidal fracture, rough, som e­

EXOTIC CLASTS OF ALGAL LIMESTONES

229

0.2 m m

lig . S. Poorly si 1 icitied exotic clast o f a calcarcnite; site I 1 (Zohatyn). Quartz grains (a), unsilicified organodetritic grains (b), cemented by calcite (c) and partly by silica (d) visible. Thin section. N X

Fig. 9. Cherty core of an exotic calcarenite. Site 5 (Drohobycz ka). Strongly silicified rock with relics of organic grains (a), vis­

ible as shadows. Thin section, 1 N

tim es splintery, earthy or sm ooth, with transparent splinters.

The cherts usually contain m acroscopically visible, sin­

gle, non-silicified carbonate grains, as well as irregular en­

claves o f unsilicified parent rock, several m illim etres in di­

am eter. The surfaces o f cherty cores show som etim es hol­

lows filled with carbonate m aterial. A characteristic feature is the lack o f silicification w ithin borings resem bling those left by boring organism s (Fig. 5).

The features m entioned above suggest that silicification postdates both cem entation o f the sedim ent and the borings, the latter probably form ed in the littoral zone (R adw ański, 1969). This silicification represents a m etasom atic process prograding from the centre o f exotic rock outw ards, w ithout rem obilising the silicified m aterial. The central position o f cherty cores, w hich adjust th eir shape to clast surface, testi­

fies to their form ation after rounding and deposition w ithin a lithosom e o f the Babica Clay. This silicification proceeded d ue‘to changes in pH, m odified by the decay o f organic m at­

ter present both in exotics and in surrounding clays (K w iat­

kowski, 1996).

A sim ilar type o f pebble silicification has been de­

scribed from the central part o f the Skole Unit, w ithin lim e­

stones clasts derived from the Dynów' M arl M em ber. The lim estones rest w ithin a sand (low, im m ediately overlying the m em ber (R ajchel, 1976a).

The silicification show s variable advancem ent w ithin the individual clasts, as show n by the presence o f different num ber o f carbonate grains or by the occurrence o f concen­

tric zones show ing slightly different silica contents (K oszto­

wa, site 4; D rohobyczka D olna, site 5; B achów , site 8; Ju- reczkow a, site 10; Żohatyn, site 11).

In poorly silicified exotic rocks (Z ohatyn, site 11), the o f replacem ent affects m ainly the m atrix (Fig. 8). O rganic rem ains preserve their original com position and contain som etim es only sm all im pregnations o f silica. W ithin exot­

ics o f m acroscopically visible silicification (cf. Kosztow a, site 4; D rohobyczka Dolna, site 5; Jureczkow a, site 10) the silica replaces, besides m atrix, m ost o f the organic rem ains (Fig. 9). C alcite occurs only as relics, reflecting som e fea­

tures o f the internal grain structure. O nly fragm ents o f echi- noderm s and isolated foram inifers, together w ith surround­

ing syntaxial and isopachous cem ent, rem ain unchanged. At the more advanced level o f silicification (K osztow a, site 4;

vicinity o f Bircza, site 12), the process o f replacem ent o f parent rock by chalcedony affects both the m atrix and the clasts, except fragm ents o f echinoderm s. The internal m i­

crostructure o f skeletal elem ents becom es destroyed. In ex­

trem e cases their identification becom es im possible. Despite strongly advanced silicification, depositiqnal structures are still visible due to the presence o f inclusions which mark prim ary grain m argins (Fig. 9), and ow ing to differences in crystallinite o f silica. O riginal carbonate grains are, hence, replaced by m icrocrystalline chalcedony, w hereas inter- granular voids are filled w ith spherulites.

The source o f such abundant silica supply is still uncer­

tain. It cannot be represented by the exotic m aterial itself, because it contains no siliceous organism s. The quartz grains cannot be considered either, since they show negli­

gible corrosion. M ost probably, the source o f silica was pro­

vided by siliceous organism s, m ainly radiolarians, occurring w ithin the matrix o f the B abica Clay deposits and w ithin the surrounding variegated shales (M orgiel & Szym akow ska, 1978). It is also possible that part o f silica m ight have been derived from pelitic fraction o f the B abica C lay (Gaweł,

1951).

AGE OF EXOTIC ORGANODETRITIC LIMESTONES

Stratigraphic position o f the exotic rocks studied here indicates that they are older than host lithosom es o f the Babica Clay. The P aleocene age is com m only accepted, on the basis both o f foram iniferal m icrofauna (M orgiel, 1959;

S zczechura & Pożaryska, 1974; M orgiel & Szym akow ska, 1978) and the m acrofauna (K rach, 1963). Som e other opin­

ions resulted from erroneous assignm ent o f the Babica Clay lithosom es to the lithologically sim ilar Eocene C zudec Clay

230

Table 1

Foram inifers from exotic L ithotham nium lim estones and their stratigraphic ranges (based on O lszew ska et al., 1996)

(Rajchel, 1990) or to U pper M a astric h tia n -L o w er Paleo- cene lithosom es o f the M akow ka slum p debrite (K otlarczyk,

1978, 1988a, b).

A n attem pt o f direct dating these exotic rocks, basing on foram inifers, has been m ade by B. O lszew ska. T aking into account the com pactness and silicification, the determ ina­

tions have been m ade in the m icroscopic thin sections. The follow ing foram inifer species (Table 1) and genera have been identified: Bolivinasp., Gavelinella sp., Haplophrag- moides sp., Cibicides sp., Ammobaculites sp., Gaudryina sp., Polymorphinidaesp., Discocyclinasp., as well as frag­

m ents o f large foram inifers.

Irrespectively o f variable lithology, the age o f exotic rocks, deduced from foram iniferal m icrofauna, can be as­

signed to the turn o f the E arly and Late Paleocene. This as­

sem blage is stratigraphically younger in respect to the in situ occurring deposits o f the BLLB (R ajchel, 1990).

EXOTIC ORGANOGENIC LITHOTHAMNIUM LIMESTONES IN OTHER OUTER CARPATHIAN UNITS

Exotic clasts o f organodetritic L ithotham nium lim e­

stones from the Babica C lay o f the Skole U nit show petro-

graphic sim ilarity to num erous exotic rocks o f the other O uter C arpathian units, both P aleocene and younger in age.

The closest analogues are organodetritic rocks o f the K rosno Beds, at the B ystre slice, in the south-eastern part o f the Silesian Unit. These exotics are, how ever, not silicified.

They are em bedded together w ith other exotic rocks within subm arine slum p deposits, sim ilar to that o f the Babica Clay. Som e o f them represent fragm ents o f a Lithotham - nium -bryozoan reef. The source area o f these exotics were Cordilleras situated farther to the south-east (Ślączka, 1959).

The other, sim ilar to the above-described, exotic clasts o f biosparitic and biom icritic lim estones with coralline al­

gae and m inor rhodolites occur in pebbly m udstones and conglom erates o f the C iężkow ice sandstone (P a leo c en e - Early Eocene), o f the Silesian Unit. T hey display com para­

ble size and chaotic texture, although show ing no silicifica­

tion phenom ena (Leszczyński, 1978).

Exotic organodetritic L ithotham nium -bryozoan-num - m ulitic lim estones o f Palaeogene age have also been de­

scribed from num erous sites throughout the w estern part o f the M agura Unit. They w ere encountered in the upper part o f the R opianka beds, as w ell as in the M agura Beds, Pasier- biec Sandstone and C iężkow ice S andstone. T heir source ar­

eas w ere situated on both m argins o f the M agura basin. Ex­

otic Lithotham nium lim estones are also known from the K rynica zone o f the M agura Unit, from the Hieroglyphic Beds o f Early Eocene age that are exposed near Stary Sącz (O szczypko, 1975) and w hich have been transported from the south-eastern margin o f the M agura basin.

The Fore-M agura zone also contains exotic clasts o f S enonian-P alaeogene organodetritic lim estones with cal­

careous red algae and bryozoans that have been shed from the Silesian cordillera (B urtan e t a l., 1984).

LITHOLOGICAL PROPERTIES OF ORGANODETRITIC EXOTIC ROCKS AND AUTOCHTHONOUS PALAEOGENE

LIMESTONES OF THE SKOLE UNIT:

A COMPARISON

The exotic rocks studied show som e resem blance to the older, autochthonous carbonates o f the Skole Unit.

Exotics o f calcarenites are sim ilar to som e o f the lim e­

stones derived from the BLLB (G ucik, 1961; K otlarczyk, 1961). The m ain difference consist in the turbiditic origin o f the latter, w hereas sim ilarities refer to the character and ori­

gin o f detrital m aterial. The principal com ponent o f the two types o f rocks are the rem ains o f coralline algae. Echino- derms, foram inifers, fragm ented bryozoans and polychaetes are also present. In contrast, the BLLB lim estones are white or w hite-greenish due to significant adm ixture o f glauconite and clasts o f green glauconitic claystones. M oreover, they show grading and characteristic horizontal lamination, w hereas the exotic lim estones are m assive. O rganic rem ains o f the BLLB lim estones show poorer roundness, as com ­ pared to analogous grains from exotic rocks; they also con­

tain a more differentiated spectrum o f terrigenic m aterial, including quartz, feldspars, m icas, glauconitic claystones, granitoids, gneisses, and schists (R ajchel & M yszkow ska, in

fo ram in ifers

Late C re ta ­

ceous Early P aleo ­

cen e Late P a le o ­

c en e Early M iocene

M iddle M iocene

Rzehakina cf.

fissistoinala (G rz y b .) Spiropleclinella a ff.

denial a (A 1th) Planorbulina cf.

cretae (M arsso n ) Lobatida cf. carina I a (T erq w cm )

Dorothia cf. crassa ( M arsso n) Discocyclina sp.

Parasnbbotina pseudobulloides

Plum m er) Eoglobigerina cf.

spiralis (B o lli) Acarinia ex gr angulata (W h ite ) A. aff. intermedia S u bbotina

A. cf. nitida (M a rtin) Subbotina triloculinoides ( P lum m er)

S. Iriva/is (S u b b o tin a) Igorina pusilla (B o lli)

EXOTIC CLASTS OF ALGAL LIMESTONES

231

press). D ifferences in chert structure are also noticeable.

Cherts derived from the BLLB lim estones show traces o f horizontal lam ination, are usually carbonate-free and dis­

play lense-like shapes.

Exotic clasts o f calcirudites are m acroscopically sim ilar to the carbonate conglom erate (breccia) w hich occurs in the Skole Unit near Przem yśl, in the upper part o f the Ropianka Fm. This conglom erate is com posed o f clasts o f the Śtram - berk-type lim estones, quartzites, green phyllites, as w ell as flysch-derived m arls and shales, cem ented by carbonate ma­

trix m ade up o f dism em bered green shales (W ójcik, 1907;

Bukow y & G eroch, 1957; D żułyński et al., 1979). Strati- graphic position o f the conglom erate is not precisely deter­

mined, its age being established from the presence o f M aas- trichtian to Early Paleocene m icrofauna (B ukow y & G e­

roch, 1957; Dżułyński et al., 1979; K otlarczyk, 1988a).

A nother type o f rock, sim ilar to exotic calcirudites, is represented by locally exposed, isolated beds o f breccias or conglom erates in the top o f the R opianka Fm (Rajchel, 1976a, 1989, 1990). The psefitic carbonate m aterial is com ­ posed here m ainly o f fragm ents o f L ithotham nium colonies, up to 2 cm in diam eter or larger, as well as o f clasts o f green shales o f com parable size. The psam m itic fraction is dom i­

nated by quartz w ith variable adm ixture o f glauconite.

Coarse-grained varieties o f these conglom erates, particu­

larly the chaotic ones, are sim ilar to exotic clasts o f calciru­

dites. This sim ilarity consists m ainly in grain-size com posi­

tion and texture. The conglom erates in question are or- ganodetritic grainstones, com prising as a main com ponent fragm ents o f calcareous red algae from the C orallinaceae family. The coexisting assem blage o f skeletal grains is analogous to that described from the exotic lim estones o f the Babica Clay, and contain relict o f bryozoans, echinoderm s, polychaetes and foram inifers, as well as fragm ents o f algal- bryozoan biolites. Poor sorting is another com m on property.

Sim ilarly to exotic calcirudites, clasts o f the conglom erates in question range in size from the aleuritic to psefitic frac­

tion, although carbonate clasts several centim etre across are lacking. The conglom erates described differ also in higher and more differentiated adm ixture o f terrigeneous material (quartz, quartzites, glauconitic claystones, chlorite-quar- tzose and quartz-m uscovitic schists, acid and igneous rocks) and glauconite.

In the light o f the above com parison one can infer that none o f the autochthonous rocks described can be consid­

ered as a potential source rock for the studied exotic clasts.

SEDIMENTARY ENVIRONMENT AND SOURCE AREAS OF EXOTIC ORGANODETRITIC LIMESTONES

Sedim ents o f the C arpathian geosyncline becam e en­

riched in phytogenie carbonate m aterial in different areas and at different stages o f developm ent (A lexandrow icz et al., 1966). This m aterial, transported by turbidity currents, w as dispersed together with terrigeneous m aterial. O nly ex­

ceptionally larger accum ulations o f L ithotham nium detritus could have been form ed, and on extrem ely rare occasions this detritus could build carbonate rocks. A few exam ples

are provided, i.e. by the S kalnik lim estone occurring in Me- nilite Fm o f the Dukla U nit (M ałecki, 1963; Ślączka, 1971;

Ślączka & W alton, 1992), and by the B ircza lim estone (Gu- cik, 1961; K otlarczyk, 1961, 1978). The phytogenic algal m aterial is also a com ponent o f the above-m entioned exotic clasts w hich occur in Palaeogene and older strata o f the Flysch C arpathians (Ślączka, 1959; Leszczyński, 1978;

Burtan et al., 1984).

It can be proposed that in the Paleocene, and particu­

larly in its younger part, a regional trend to the w idespread developm ent o f calcareous red algae and the form ation o f shallow -w ater organodetritic lim estones in the marginal parts o f flysch basins occurred. The clim ax o f developm ent o f calcareous algae, how ever, took place in the final stage o f the C arpathian orogen evolution, on the northern m argin o f the Badenian sea w hich filled the foredeep (Radw ański, 1969, 1973), as well as on the southern m argin o f the nearly com pletely form ed orogen (R ajchel, 1976a, b; G olonka,

1979, 1981).

N orm ally, the environm ent for calcareous red algae grow th is the littoral zone and the upper part o f th e neritic one, down to a depth o f a few tens o f m etres. This zone be­

cam e an alim entary area for carbonate phytogenic detritus w hich w as accum ulated in the m iddle and low er parts o f the neritic zone. Both these zones could have been situated upon deform ed and tectonically uplifted parts o f the geosyncline, as e.g. in the m argins o f the Tatra island in the Eocene (M ałecki, 1956; R oniew icz, 1969). M ore frequently, how ­ ever, such accum ulation p roceeded upon banks associated with geosynclinal Cordilleras, even up to 15 km w ide (U n­

rug, 1979). Such occurrences w ere described, for exam ple, from the southern part o f the M agura Unit, at its contact with the geanticlinally uplifted Pieniny K lippen Belt. L ithotham ­ nium detritus occurs here both in the Z łatne sandstone, be­

longing to the P ieniny K lippen Belt (B irkenm ajer, 1979), and in coeval sandstones o f the M agura U nit, know n from Krościenko and O chotnica (A lexandrow icz et al.,1966; G o­

lonka, 1974).

The Silesian cordillera played a sim ilar role o f alim en­

tary centre during Palaeogene tim es (K siążkiew icz, 1951;

G u c ike t a i , 1962). This centre supplied Lithotham nium de­

tritus both southw ards, to the M agura basin, and northw ards, to the Silesian basin (Leszczyński, 1978; Ślączka & W alton, 1992). A nother, m inor centre was located over the A ndry­

chów K lippes swell (K siążkiew icz, 1951). The latter was a source o f the L ithotham nia-rich S zydłow iec Sandstone o f the Subsilesian Unit. The lithostratigraphy o f the klippes zone includes bryozoan-L ithotham nium lim estones at the turn o f the C retaceous and T ertiary. T hese lim estones were deposited in a very shallow sea (K siążkiew icz, 1951). The other Lithotham nia-rich deposits in the Subsilesian Unit are represented by the sandstones exposed in the Ż yw iec tecto­

nic window , coeval with the S zydłow iec Sandstone (G e­

roch & G radziński, 1955).

The source area for studied exotic clasts has not been preserved. This zone w as p robably situated north o f the geo­

synclinal Skole basin. A long the recent C arpathian arc, at least betw een the D ębica U plift and the R zeszów area, the zone was the m arginal cordillera. (G ucik et al.,1962; K siąż­

kiewicz, 1975; Unrug, 1979; B rom ow icz, 1986). Farther to

232

14

Fig. 10. Reconstruction of the northern margin of the Skole ba­

sin in Late Paleocene times (not to scale). 1 - basement, 2 - sandy-clayey sediments of the littoral and neritic zones, 3 - algal reef, 4 - talus o f algal calcarenite, 5 - talus o f algal calcirudite, 6 - gravity cohesive flow (lithosomes of the Babica Clay), 7 - exotic clasts of organodetritic limestones, 8 - other exotic rocks derived from the littoral zone, 9 - limestone clasts derived from the Bircza Lithothamnium Limestone Bed, 10 - Zohatyn Variegated Shale Member, 11 - Bircza Lithothamnium Limestone Bed, 12 - Li­

thothamnium breccia or conglomerate from the top of the Ropianka Fm, 13 - Wola Korzeniecka Member, 14 - Leszczyny Member

the east, neat' Przem yśl, the continental slope with sh elf zone w ere developed (K otlarczyk, 1988a).

The exotic clasts w ere transported as fragm ents o f pre­

lim inarily lithified rock perpendicularly to the northern m ar­

gin of the Skole basin (Figs. 10, 11). They w ere m oved in dense gravity flow s o f the Babica C lay, dow n to the axial zone o f the basin (B ukow y, 1957a; G ucik et al., 1962; K ot­

larczyk & Śliw ow a, 1963; R ajchel, 1990). The w estern part of the source zone supplied loose, clastic, phytogenic m ate­

rial that now builds the BLLB, and w as transported N W -S E i.e. along the basin (G ucik et al., 1962; Brom ow icz, 1974;

K otlarczyk, 1978, 1988a, b).

The lim estone from w hich exotic clasts w ere derived, have originated from accum ulations o f fragm ented benthic organism s, dom inated by calcareous red algae. The detrital grains w ere fragm ents o f single thalli o f coralline algae. O c­

casionally branching thalli and fragm ents o f crustose thalli w ere be identified.

The organodetrital grains w hich form the exotic clast- sdo not contain corals, contrary to recent reefs w here corals coexist w ith1 calcareous red algae, p laying the role o f bound­

ing, cem enting and encrusting organism s (W ray, 1977).

This may indicate that the studied m aterial was derived from an area dom inated by bryozoan-algal f a d e s (M cK enzie et al., 1978). This f a d e s recently proceeds south and north o f the tropical zone, and outside the coral-algal fa d e s dom ain.

Fig. 11. Palacogeographic sketch o f the Skole basin at the turn of Early and Late Paleocene (after Gucik et al., 1962; modified). I - variegated marls, 2 - variegated and green shales, 3 - Inoceramian beds grading upwards into variegated shales, 4 - Babica Clay, 5 - occurrences of the Babica Clay lithosomes within the Variegated Shale Fm, above the Bircza Lithothamnium Limestone Bed, 6 - extent o f exotic clasts of organodetritic Lithothamnium lime­

stones, 7 - boundary o f the Skole basin, 8 - cordilleras and Lithothamnium reefs, 9 - recent Carpathian margin

A ccording to this m odel, the mass growth o f different or­

ganic form s depends on surface w ater tem perature which is a function o f depth and latitude. C alcareous red algae are cosm opolitic form s and coexist abundantly with corals only in low -latitude seas. O utside the tropical zone, the number o f corals decreases m arkedly. The reverse relationship is true for bryozoans, w hich show m axim um developm ent in colder w aters at higher latitudes.

An equivalent o f the bryozoan-algal fa d e s in the M edi­

terranean Sea is the “co ralligene” fa d e s (B osence, 1983, 1985), com posed o f bottom -stabilising sea organism which shown considerable species differentiation, and dom inated by calcareous red algae (B osence, 1983; Studencki, 1988).

The resulting buildups occur in littoral and sublittoral zones, down to 160 m (Bosence, 1985). T hey are up to 4 m high and 50 m in diam eter. A t their base, carbonate sands and gravels derived from re e f disintegration are accum ulated.

Such reefs are cavernous structures; and include tunnels and galleries that form suitable ecological niches for num erous penetrating, burrow ing and encrusting organism s (Bosence,

1985).

The fragm entation o f algae that build the exotic clasts indicates that, at a certain stage o f developm ent, the ree f en­

tered the range o f destructive activity o f w aves or currents.

Bioerosion m ust have been also im portant. As a result o f such processes, bioclastic m aterial o f variable size was pro­

duced and accum ulated upon the talus form ed at shallow depth, at ree f base. This is indicated by m icroborings, adapted to the littoral zone conditions (R adw ahski, 1969).

This material w as then recycled on the bottom by waves and currents, and consolidated during early diagenesis in shal­

low, marine, phreatic environm ent. The resulting material was fragm ented into clasts o f variable size w hich, after rounding and subsequent borings, becam e incorporated into gravity flow s o f the Babica Clay.

PRZEMYŚL RZESZÓW

--- 7

^ 6 M b

czb nnm 2

f W l U l i 1

EXOTIC CLASTS OF ALGAL LIMESTONES

233

CONCLUSIONS

1. The exotic clasts described in this study represent fragm ents o f organodetritic L ithotham nium lim estones w hich originated as talus deposits around sm all algal reefs.

The reefs developed upon the sh e lf o f the northern margin o f the Skole basin.

2. Algal reefs and related organodetritic deposits cannot be observed at the northern m argin o f the basin due to tec­

tonic m odification.

3. The host rocks for exotic clasts w ere represented by organodetritic algal lim estones o f calcarenite and calcirudite types.

4. The littoral provenance o f the deposits in question is indicated by the presence o f num erous shallow -w ater organ­

isms within the clasts, as well as by the lack o f turbiditic structures.

5. The deposits studied w ere form ed at the turn o f Early and Late Paleocene, as indicated by th e stratigraphic posi­

tion o f exotic clasts and, first o f all, by the preserved foram i- nifers and - to som e extent - the assem blage o f calcareous algae.

6. The extensive developm ent o f calcareous algae took place som ew hat earlier, i.e. during the final stages o f depo­

sition o f the Ropianka Fm in Early P aleocene tim es. As a result, individual beds o f calcirudites with phytogenic car­

bonate m aterial w ere form ed in the upper part o f this form a­

tion.

7. Silicification processes, leading to the form ation o f chert}' cores, affected only exotic clasts o f calcarenitic struc­

ture, and took place after their deposition w ithin lithosom es o f the Babica Clay.

8. The m ethod used in this study allow s to reconstruct the environm ent o f m arginal zones o f geosynclinal basins that w ere subsequently destructed during orogenic m ove­

ments.

A c k n o w le d g e m e n ts

The authors would like to express their thanks to Prof. Dr. J.

Kotlarczyk who provided a very interesting exotic clast from the vicinity of Bircza, to Assoc. Prof. Dr. B. Olszewska for microfos­

sils identification and permission to use the unpublished materials, and to Dr. M. Muszyński for his help in microscopic study. We arc also grateful to Mr. A. Górny for cutting the exotic clasts, Mr. A.

Szumny for preparation of thin sections and excellent polished slabs, Dr. M. Wit and Mr. S. Klimowski for taking photographs, and to Mr. J. Kępiński for preparation o f drawings.

This study has been carried partly within the frame o f re­

search activity of the Department o f General and Mathematical Geology, Faculty of Geology, Geophysics and Environmental Pro­

tection of the University of Mining and Metallurgy in Kraków, Project No. 11.140.50 Geological studies of deposits o f the Outer Carpathian units: mineralprospeclion and cognitive aspects.

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S tre s z c z e n ie

EG ZO TYK I O R G A N O D E T R Y T Y C Z N Y C H W A PIEN I LITO TAM NI O W Y C H Z L IT O S O M Ó W

IŁÓW BA BICK IC H JE D N O S T K I SK O L SK IE J (K A R PA T Y FL ISZ O W E , PO L SK A )

Jacek Rajchel & Jolanta Myszkowska

Opisano egzotyki organodetrytycznych wapieni glonowych z centralnej części jednostki skolskiej (Fig.l). Występują one tylko w tych litosomach iłów babickich (późny paieocen), które usytuo­

wane są w obrębie formacji pstrych łupków, powyżej warstwy li- totamniowego wapienia z Birczy /wt/ (Fig. 2, 3).

Badane egzotyki mają średnicę od 10 do 30 centymetrów i zwykle są kształtu wrzecionowatego lub kulistego (Fig. 5, 7). Ich zewnętrzna powierzchnia posiada nierówności rzędu 2-3 cm, a niekiedy z obecnością wydrążeń (Fig. 5). Biorąc pod uwagę frak­

cję materiału okruchowego wyróżniono 2 odmiany egzotyków:

dominujące biokalkarenity (Fig. 5) i znacznie rzadsze biokalcyru- dyty (Fig. 7). Obie odmiany są bezstrukturalne i odpowiadają swym składem wapieniom, ewentualnie wapieniom słabo lub sil­

nie zapiaszczonym.

Egzotyki kalkarenitowe są fragmentami dobrze wysortowa- nego osadu (Fig. 6), składającego się ze szczątków krasnorostów (rodzina Corallinaceae, Squamariaceae) i towarzyszących im ele­

mentów szkieletowych szkarlupni, mszywiolów, wieloszczetów i otwornic. Materiał terygeniczny to głównie kwarc, sporadycznie okruchy skal. Składniki detrytyczne, tworzące zwarty szkielet ziarnowy, spojone są kalcytowym cementem blokowym, lokalnie syntaksjalnym lub skalenoedrycznym-izopachytowym.

Egzotyki kalcyrudytowe reprezentują osad źle wysortowany (Fig. 7). o bimodalnym rozkładzie wielkości ziarn. Jedną klasę stanowią składniki o średnicy od I do 6 cm, będące głównie ok­

ruchami wapieni. Druga klasa to elementy frakcji psamitowo-aleu- rytowej reprezentowane najliczniej przez szczątki krasnorostów (rodzina Corallinaceae, Squamariaceae), mszywiolów, szkarlupni, wieloszczetów oraz otwornice, kwarc, a także okruchy biolitytów glonowo-mszywiołowych. Egzotyki kalcyrudytowe wykazują teksturę ziarnową i zawierają analogiczne rodzaje cementu jak od­

miana kalkarenitowa.

Egzotyki kalkarenitowe na ogół zawierają centralnie umiesz­

czone krzemienne jądro, odwzorowujące ich zewnętrzne zarysy (Fig. 4). Sylifikacja ta jest procesem późniejszym od cementacji (brak kompakcji ziarn) i od wydrążeń (“omijanie” ich przez syliti- kację; Fig. 5). Proces ten zachodził po ostatecznej depozycji egzo­

tyków w litosomach iłów babickich. Potwierdza to m.in. kształt krzemiennego jądra, zgodny z zewnętrznymi zarysami egzotyków (Fig. 4). W poszczególnych egzotykach proces sylifikacji jest róż­

nic nasilony. W próbkach najsłabiej zsylifikowanych spoiwo ulega zastępowaniu w pierwszej kolejności (Fig. 8). Przy bardziej zaa­

wansowanej sylifikacji wypierany jest węglan wapnia budujący ziarna, w miejscu których pozostają brunatnawe wrostki lub relik­

ty węglanu wapnia (Fig. 9). Źródłem krzemionki były prawdopo­

dobnie radiolarie zawarte w iłach babickich i w otaczających je pstrych lupkach (Fig. 2).

Wszystkie egzotyki są fragmentami organodetrytycznych wa­

pieni krasnorostowych, powstałych jako osad stożków nasypo­

wych wokół niewielkich raf glonowych. Budowle te były usytuo­

wane w płytkim środowisku wzdłuż północnej krawędzi zbiornika jednostki skolskiej (Fig. 10. 11). Potwierdzeniem litoralnego miej­

sca sedymentacji tych utworów jest obecność w badanych egzoty­

kach szczątków szeregu organizmów płytkowodnych, a także brak struktur turbidytowych, charakterystycznych dla wapieni alloda- picznych. W wyniku tektonicznej modyfikacji wspomnianej kra­

wędzi, utwory te nie są dostępne współczesnej obserwacji. Trans­

port egzotyków w głąb zbiornika odbywał się prostopadle do jego krawędzi w gęstych, kohezyjnych spływach, docierających do jego osiowej strefy.

Utwory macierzyste dla egzotyków powstały na przełomie wczesnego i późnego paleocenu, na co wskazuje obecna w nich mikrofauna otwornicowa i w pewnym stopniu zespół wapiennych glonów. Są one mniej więcej równowiekowe z warstwą organode- trytyczncgo, wapienia litotamniowego z Birczy /wt/ (Fig. 2, 10).

Rozwój glonów wapiennych, w podobnym usytuowaniu ale na mniejszą skalę, nastąpił w basenie skolskim również nieco wcześ­

niej, czyli pod koniec sedymentacji formacji ropianieckiej /fm/, wc wczesnym paleocenie. Doprowadziło to do powstania pojedyn­

czych ławic kalcyrudytowych i zlepieńców z domieszką węglano­

wego materiału fitogcnicznego w stropie tej formacji.