Two diatoms horizons in the Oligocene and (?)Lower Miocene of the Polish Outer Carpathians

Annales Societatis Geologorum Poloniae (1987), vol. 57: 143 — 188.

P L IS S N 0208-9068

TWO DIATOM HORIZONS

IN THE OLIGOCENE AND (?) LOWER MIOCENE OF THE POLISH OUTER CARPATHIANS

Janusz Kotlarczyk1 & Irena Kaczmarska2

1In stytu t Geologii i Surowców M ineralnych, Akadem ia Górniczo-Hutnicza, al. M ickiew icza 30,

v 30-059 Kraków, Poland

2Instytut Botaniki, Polska Akadem ia N auk, ul. L ubicz 45, 31-512 Kraków, Poland3

J. K otlarczyk & I. K aczm arska, 1987. Two diatom horizons in the Oligocene and (?)Lower M io­

cene o f the Polish O uter C arpathians. Ann. Soc. Geol. Polon., 57: 143—188.

A b s t r a c t : Two older o f the three diatom -rich horizons in the M enilite—K rosno series o f the Skole nappe, and their diatom s, are described. F u to m a horizon occurs in lower p a rt o f M eni­

lite Beds. I t consists m ostly o f lam inated diatom ites an d diatom aceous shales. It is m ore th a n 10 m thick in som e sm all areas (SSE o f Rzeszów, W and E o f Przem yśl) an d very thin or absent in between.

I t was accum ulated in local depressions o f the basin slope, during a period o f basin shallowing.

T h e diatom assem blage is alm ost autochtonous, slightly redistributed by bottom currents, carrying a ls o . som e freshw ater diatom s. I t is neritic-sublittoral, indicative o f an E arly Oligocene age.

Piątkow a horizon occurs at the transition between M enilite an d K rosno Beds, in the Niebylec shales. It consists o f m any thin, laterally discontinuous turbidite shales w ith diatom s, dispersed w ithin few tens o f m etres (or less) o f the host strata. D iato m assem blage is allochtonous, neritic- -su b litteral interpreted as latest Oligocene-earliest M iocene in age.

K e y w o r d s : diatom s, diatom ites, lam inated diatom ites, black shales, stratigraphy, taxa descriptions, botto m currents, turbidity currents, Oligocene, Low er M iocene, N o rth ern C arpathians, P oland.

M anuscript received January 1986, revision accepted December, 1986.

IN TR O D U C TIO N

Diatom-rich rocks occur at several horizons in Tertiary deposits o f the Skole nappe, the external tectonic and facies unit o f the Polish Outer C arpathians (K ot­

larczyk, 1958, 1966, 1982; Żgiet, 1961, 1963; Jerzm ańska & Jucha, 1963). They occur mainly in the youngest Oligocene—Lower Miocene, p art o f the Skole nappe sequence (distinguished informally as the M enilite—K rosno series) at three main horizons: (i) Futom a horizon in the lower p a rt o f the Menilite Beds, (ii) Piątkow a horizon a t the transition between the Menilite and K rosno Beds, mainly in the Niebylec shales, and (iii) Leszczawka horizon in the top p art o f the K rosno Beds (Fig. 1).

3 Present address: D ep artm en t o f Biology, M ount Allison University, Sackville, NB, EO A 3CO C anada.

1 4 4 J. K OTLA RCZYK J t 1. K ACZM ARSKA

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600

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Fig. 1. Stratigraphical position o f diatom horizons in area o f Błażowa an d Bircza (after Kotlar*

czyk, 1985, slightly modified). I — brow n clayey,-siliceous shales (J — unit 1, Jam m a m em ber;

B N — unit 6, Borek Nowy mem ber), partly with thin intercalations o f sandstones (R — unit 4, R udaw ka m em ber); 2 — cherts (K — unit 2, K otów m em ber) an d siliceous m arls (D — unit 3, D ynów m em ber); 3 — thick bedded quartzarenites; 4 — grey m arly shales; 5 — n orm al flysch;

6 — thick bedded calcareous sandstones; 7 — tuff horizons (num bers after Sikora et al., 1959);

8 — diatom horizons an d their stratigraphical extents; 9 — olisthostrom es; 10 — nannoplank- to n zones

Two types o f diatom -rich rocks are distinguished: diatomites ( > 4 0 volume

per cent o f diatom frustules and/or their fragments) and diatom aceous shales

( < 40%). Some diatom frustules and poor diatom assemblage were occasionally

found in black, bituminous, argillaceous-siliceous shales, the distinctive lithology

o f the Menilite Beds.

TW O D IA TO M H O R IZO N S 1 4 5

O ther microfossils (foraminifers and nannoplankton) are very rare in the Me- nilite Beds, so th a t precise biostratigraphic correlation or zonation of these strata is impossible. Diatom s have been successfully used for biostratigraphical purposes in many sequences (Barron, 1975; Dzinoridze et al., 1976; Hajos, 1976; M akarova &

K ozyrenko, 1966; Proshkina-Lavrenko et al., 1974; Sawamura & Yamaguchi, 1963;

Schrader & Fenner, 1976), including the shales o f the M aikop series o f the C au­

casus (Sheshukova-Poretskaya & Gleser, 1962), very similar to the Menilite shales.

The occurrence o f diatom s has been considered potentially useful for the biostrati­

graphy o f the Menilite-Krosno series in the Skole nappe.

This paper presents the descriptions of the Futom a and Piątkow a horizons and their diatom assemblages. D iatom taxa were determined by I. Kaczm arska.

The stratigraphical use o f diatoms must be based on well defined assemblages rather th an on individual taxa. F or this reason the interpretation o f the age and environm ental conditions o f deposition of the diatom-rich horizons are based on abundant taxa, i.e. those occurring in greatest numbers.

SA M PLIN G

The diatom-rich rocks are very similar to the argillaceous-siliceous shales ty­

pical o f the Menilite Beds and for this reason it is difficult to identify them in the field. The consistent position o f the diatom-rich rocks in the lithological succession helped to locate them in the outcrops.

Detailed sampling was done in all sections where diatom -rich rocks were observed macroscopically, or where their presence was expected from the position in the lithological succession. Samples for m aceration and sometimes also for thin sections, were taken from all layers o f shales similar to the diatom -rich shales. In the Piątkow a horizon all layers o f black (or dark) shales were sampled. In total 259 samples were taken from both horizons.

They were all disintegrated and placed in water-glycerine suspension. The pre­

sence o f diatom frustules and th eir fragments was checked under a microscope.

In the Futom a horizon 69 preparations, out o f 117, included diatoms. F or the Piątkow a horizon, this proportions is 52 of 142. The Piątkow a horizon was found in 11 sections o f the 24 investigated.

Water-glycerine preparations and thin sections were used to determine the ver­

tical extents o f the diatomite horizons in each section (see Figs 3, 5). Perm anent slides for detailed investigations were made o f 29 samples with diatom s; 12 from th e Futom a and 17 from the Piątkow a horizon.

LABORATORY TREA TM EN T

The studied rocks were strongly lithified and contam inated, so th at satisfactory

slides could not be obtained by the use o f standard methods. Special methods had

to be applied and these are described below.

1 4 6 J . K O TLARCZYK & I. KACZM ARSKA

F o r the soft diatomites and diatom -bearing shales a com bination o f the methods described by Jouse (1966) and M andra et al., (1973) was used. Samples o f few grams o f disintegrated rock were left in distilled water for 1/2 to 1 m onth, then decanted an d treated with 10% H C L and left for one or two days. Then the samples were washed several times in distilled water until the p H became neutral, heated several times on water bath, treated with 5% sodium carbonate and heated while a few mililitres of 30% H 20 2 were being cautiously added. The solution was kept boiling for several tens o f minutes, then cooled, decanted and several times washed in distil­

led water. The more resitant samples, which still contained non-disintegrated rock fragments, were divided in two parts. The p a rt with non-disintegrated material was boiled in 2% solution o f N aO H for 5 minutes, then quickly cooled and washed in distilled water to prevent dissolution o f the slightly silicified frustules in the alkaline medium. After each decantation and washing, decanted water was checked up under a microscope (at magnification 600 times or more) if all frustules settled down.

The diatom aceous shales, and also some diatomites included fine m ineral p a r­

ticles, which obscured details o f diatom frustules and precluded their identifica­

tions. The finest particles were eliminated by decantation, repeated up to 70 times.

The heavier particles were eliminated by flotation which was used also for samples containing small numbers o f diatoms.

H ard diatomites were prepared in a somewhat different way. The samples were treated with distilled water, then with HC1, and washed in distilled w ater until the p H o f the liquid was neutral, ju st as described above. Then the samples were treated with 30% H 20 2, mildly warmed several times, cooled and each tim e decanted.

I f nonm acerated particles still persited in the solution, they were separated from the sample and boiled in 10% N aO H or K O H from 10 to 30 minutes. The further pro­

cedure was the same as for the soft samples.

Three perm anent slides were made from each residuum by fixing it in pleurax j—

a highly refractive medium.

O ther methods o f m aceration were also tested, b u t appeared less useful. F or instance the m ethods used by Filipescu & Krestel (1959) for the C arpathian diato­

mites, consisting in repeated freezing and defreezing, or impregnation (e.g. with N a 2So4), crystallization and later solution o f the crystallizing substance, appeared highly destructive for the diatom frustules.

FU TO M A H O R IZ O N

L IT H O ST R A T IG R A PH Y AND D IST R IB U T IO N

The outcrops o f this horizon occur near Błażowa, SSE o f Rzeszów (Fig. 2), The outcrop at Futom a has been first described by Jerzm ańska & Jucha (1963).

The possibility o f occurrence o f diatom -rich rocks in the outcrops at Brzezówka.

TWO DIA TO M HORIZON S 1 4 7

Borek Nowy and Hermanowa was suggested by J. Badak and B. Kawalec (personal communications). The lithostratigraphic succesion within the lower part o f the Me- nilite Beds in this area includes the following lithologic units (from bottom to top, in brackets are given inform al names used for these units in Kotlarczyk, 1985):

1) black shales (Jam na member), sometimes with intercalations o f sandstones and conglomerates (Siedliska member), 2) cherts intercalated with black siliceous shales (Kotów member), 3) hard, partly silicified marls, light-coloured when weat­

hered (Dynów member), 4) black shales with interbeds of ripple-lam inated sandsto­

nes (Rudawka member), 5) light-coloured diatomites and diatom aceous shales with intercalations o f cherts, sandstones and shales (Futom a member), 6) siliceous paper-shales with th in layers o f cherts (Borek Nowy member). The m ore resistant chert and m arl horizons are useful m arkers in the field.

The diatom ite-bearing unit 5 is well individualized in the area about 10 km around Błażowa. Its thickness is m ore th an ten metres in the centre o f this area (Futom a, Borek Nowy) and decreases to a few metres at its periphery (H erm anow a, Brzezówka). Farther away from Błażowa, this unit quickly disapears, and only th in in te rca latio n s (from a few to m ore th an ten centimetres in thickness) o f dia- tom -rich rocks (e.g. at M alawa) replace this unit in the sequence. These intercala­

tions include the same diatom assemblage in all sections, and can be thus considered as one diatom horizon, nam ed Futom a horizon. Probably to this horizon can also be included the th in intercalations o f diatom -bearing shales found in D obra, Roz- pucie, Krościenko, Średnia and other localities (Kotlarczyk, 1982). O ther areas where the Futom a horizon has been found are situated west and south o f Przemyśl.

The diatomites described from the vicinities o f D obrom il (Gruzhiy & Ripun, 1970) also can be attributed to this horizon. The above data indicate th at the Futom a ho­

rizon is widely distributed over an area o f about 1.500 km 2.

Lithological sequences in the most im portant studied outcrops of the Futom a horizon are shown in Fig. 3 where the boundary o f the lithological units 5 and 6 is accepted as datum . The Futom a horizon is best developed in Futom a a n d its type section is exposed in a field road running along a hill crest between Futom a an d Ulanica (Fig. 4). The beds are dipping 10—30° towards SWW. The chert in­

tercalation at the base o f the Futom a horizon is situated about 13 m above th e to p o f the Dynów marls. The Futom a horizon is about 13 m thick, o f which the diatom -rich rocks, grouped in 3 complexes, occupy ca. 8 metres. The upperm ost complex o f diatom -rich rocks reveals features indicative o f submarine slumping.

The thickness o f the F utom a horizon is m uch lower in the investigated sections n ear Błażowa. In Borek Nowy in a slope east o f the road to Rzeszów, some 800 m south of the post office, a sequence, 6 m thick, o f the upper p a rt o f the Futom a horizon is exposed. A layer, 1.5 m thick, o f diatom ite mudflow, bearing granite granules and pebbles, occurs at the to p o f this sequence. The thickness o f the F u­

to m a horizon in H erm anow a is about 3.5 m, including about 2 metres o f white,

light diatomites. In Brzezówka (both escarpments o f the field road to Borówki)

th e section o f the Futom a horizon includes numerous thin — and some as thick

1 4 8 J. K OTLARCZYK & I. KACZM ARSKA

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TW O D IA TO M H ORIZO N S 1 4 9

FUTOMA BOREK N. HERMANOWA BRZEZOWKA

[STRATOTYPE]

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Fig. 3. Lithological colum ns o f F u to m a horizon. 1 — 7 — diatom -rich rocks: 1 — finely, wavy lam inated, white shales; 2 — thickly lam inated beige shales; 3 — platy, lam inated light brown sh ales; 4 — diam ictites; 5 — coarsely disintegrating, light brow n shales; 6 — non-lam inated, soft light brown shales; 7 — pale greenish-beige, som etim es indistinctly lam inated shales; 8 — brow n clayey-siliceous, hard shales (menilite shales), a — soft, brow n o r green shales; 9 — cherty shales; 10 — lam inated an d non-lam inated beige cherts; I I — light qu artz sandstones;

12 — sandy lam inae an d ripples; 13 — olistholite o f D yn6w m arl; 14 — frequency o f diatom s:

a — rare, b — frequent, c — a b u n d a n t; 15 — locations an d num bers o f investigated sam ples;

16 — boundaries o f F u to m a horizon

1 5 0 J. K O TLARCZYK & I. KACZM ARSKA

as 1.5 m — intercalations of brown cherts with white laminae. The cherts and dia- tomaceous shales replace the diatomites in this section. The horizon is here 9 m thick, and 5.5 m o f this are the diatom -rich rocks.

Fig. 4. Location o f type section o f F u to m a horizon. 1 — type section; 2 — m ain ro ad s; 3 — field ro ad s

A bout 30 km SE of Błażowa, at M alawa (exposure near a chapel by the Bir­

cza—M alawa road), the Futom a horizon is reduced to a few thin layers o f porcel-

lanite and white lam inated diatom -rich shale. These rocks occur ca 3.5 m above

the top of the Dynów m arls (unit 3). In the same area, 8 km east, in the section

o f the Menilite Beds in K rępak near Korzeniec (Fig. 2), only a layer one centimetre

thick was found, o f white shale composed o f diatomite micorclasts.

TW O D IA TO M HORIZON S 1 5 1

LITH O LO G Y OF DIATOM -RICH ROCKS

The Futom a horizon is mainly composed o f diatom-rich rocks and o f rocks which originated by diagenetic transform ation o f original diatom -rich sediments:

porcellanites, siliceous shales and cherts, also o f siliceous-argillaceous shales with scarce diatoms, and o f subordinate sandstones (Fig. 2). Characteristic features o f this horizon are the total lack o f calcium carbonate, and their colour, lighter than o f the surrounding lithological units.

The weathered diatomites are cream-white, light to dark beige, sometimes greenish beige or light brown. They are light (ca. 1 g/cm3), porous, brittle an d smear­

ing. Examinations o f thin sections reveal th a t one lithological variety may include rocks with either m ore o r less th an 40% o f diatom s in rock, so that macro- scopical distinction o f diatomites from diatomaceous shales is impossible. F or th is reason both types are considered together in the description o f lithological va­

rieties o f the diatom -rich rocks in the Futom a horizon. Seven lithological varieties o f diatom-rich rocks have been distinguished on the grounds of their macroscopic lithologic features:

1) finely lam inated, white or beige, with slightly undulating laminae o f sub- m illimetric thickness, differing in their shade o f colour, with good th in fossility;

2) thickly laminated, light an d dark beige, with horizontal lam ination (a lighter lam ina, several millimetres thick occurs every few, rarely few tens o f millimetres),

splitting into plates;

3) indistinctly lam inated, white and greenish beige, sometimes dark beige (each several millimetres occur poorly visible lighter laminae), with faint fissility, some­

tim es o f scaly type;

4) non-lam inated beige and light brown, light, porous, friable;

5) coarsely splitting brow n or dark brow n, with large content o f clay minerals, non-lam inated, heavier, more com pact and m ore resistant th an the form er varie­

ties, frequently with shell-like fractu re;

6) platy, differing from the form er only by its splitting into scale-like plates 1—3 cm thick, and by frequent lam inae o f fine quartz and glauconite sand;

7) layers o f mudflows, beige, falling into blocks, rich in quartz sand and lithic fragm ents.

There are no regularities in the vertical sequence of these rock types.

SEDIM ENTO LOGICAL OBSERVATIONS

The m ost conspicuous sedimentary feature in the Futom a horizon is the var-

ve-like horizontal lam ination o f the diatom -rich rocks. The light lam inae — white

o r light beige — are more constant in thickness th an the dark lam inae — beige

o r pale brown. In the finely and wavy lam inated varieties o f diatomites, the light

lam inae are thickner th an the darker, while in the thickly lam inated varieties they

are m uch thinner. The light lam inae are composed mainly o f diatom frustules and

th eir fragments, binded by opaline cement. The dark laminae, besides the diatom

frustules include significant admixture of clay minerals, quartz and glauconite

silt. Flakes o f clay minerals parallel the lam inae; also other terrigenous m aterial

1 5 2 J. K OTLARCZYK & I. KACZM ARSKA

is often accumulated in lam inae or lenses (ripples o f various size). Some diatomite laminae are thinning laterally; some are bent beneath ripples which sunk by loading, other are partly washed out, and some, sporadically, reveal ripple structure. Postde- positional interruptions o f laminae are frequent. Evident grading was not observed in sandstones, siltstones or diatomites.

The described features of the very fine-grained sediments suggest their succes­

sive deposition from slow bottom currents. These currents tem porarily moved the biogenous m aterial accumulating at the bottom and occasionally supplied some terrigenous material, mainly quartz silt and fine sand. Perm anent deposition could be limited to local depressions perched on the basin slope. In the remaining area, diatom frustules either did not accumulate at all or did only sporadically (e.g.

M alawa); the sediment could be winnowed away (e.g. at K rępak near Korzeniec).

Layers o f mudflow deposits and subm arine slumps occur in the higher part o f the F utom a horizon.

FREQUENCY DISTRIBUTION OF D O M IN A N T TAXA IN STUDIED SAM PLES A ND POSSIBILITIES

FOR LO C A L STRATIGRAPHY

Individual dom inant taxa occur with different frequency in the studied slides (min. 3 slides from each sample). A semiquantitative, 5-rank scale has been used to com pare the frequency of their occurrence (Table 1).

Each o f the four most numerous among the 30 dom inant taxa (Actinoptychus senarius (Ehr.), Chaetoceras compressus Land., Odontella cornuta (J. Brun.) Schra­

der, Paralia sulcata (Ehr.) Cleve), occurs in each sample. The frequencies o f some taxa (Grammatophora sp., Pyxilla prolongata Brun., Rhizosolenia sp., Stephano- p yxis turris (Grer. et Arn.) Ralfs) oscillate in the section. Other dom inant taxa ap­

pear or disappear in different parts o f the section.

In the type section, the diatom ite layers include the m ost diversified diatom assemblages, comprising usually about 20 dom inant tax a (Table 1). In samples from diatomaceous shales, the numbers o f taxa are m uch lower. A part from the type section, the same diatom assemblage was found in all studied sections in th e vicinity o f Błażowa (Fig. 2), and only five taxa from this assemblage have been found in M alawa, 30 km to SE (Fig. 1).

W ithin the generally uniform composition o f the diatom assemblage, some vertical changes have been ascertained. Comparisons of the composition of the dia­

tom assemblages in the nearest investigated layers of the stratotype section indicate th a t similarities become greater upwards. This may suggest progressive stabiliza­

tio n o f the biocenosis during its development. However, taking into account the

m ost frequent ( + + + + and + + + in Table 1) taxa, we find great dr differences

b oth in the lower (between samples 4 and 6) and in the upper (between samples

14 and 18, 18 and 21) parts o f the section. Com binatorical com parison o f the layer

groups (each to each) reveals greatest differences o f the num ber o f comm on taxa

between the bottom and to p layers, an d between layer 21 and the middle part of

th e section.

Table1 Frequencydistribution ofdominant taxain investigated samples fromFutoma (F),Hermanowa(H), Brzezówka (B),BorekNowy (BN) and Malawa (M)

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The vertical differences in the composition o f the diatom assemblages have been also used to verify the lithological correlation o f the other sections with the stratotype. The greatest similarities, coupled with the smallest num ber o f differences are found in the following couples o f samples (for sample location see Fig. 3):

BN7 — F14, H29 — F14, B29 — F I 8, H29 — BN7. These results generally agree with the lithological correlation.

Two sub-assemblages have been distinguished in the type section, characteristic for the lower and upper part, respectively.

F o r the lower p art o f the section characteristic are: Chasea ornata, Actino- ptychus senarius var. tamanicus, Paralia sulcata var. crenulata, Odontella fim briata, Thalassiosira baltica and Xanthiopyxis oblonga. The upper p art o f the section is cha­

racterized by Chaetoceros robustus, Hyalodiscus scoticus, Sceptroneis grunowii and Xanthiopyxis papillosus. However, in all other sections, few specimens of the taxa characteristic for the lower p art o f the horizon occurred in the upper p a rt o f the section (see Fig. 3 and Table 1).

E C O L O G Y AND A G E O F T H E D IA T O M A SSEM BLA GE

The diatom assemblage in the Futom a horizon (Table 2) is indicative o f neritic- -sublittoral environm ent and it lacks oceanic pelagic taxa. Besides stenohaline ones there occur taxa which can live also in brackish water (Hyalodiscus scoticus, Rapho- neis amphiceros, Thalassiosira baltica), one known from brackish and fresh water

Table 2 Environm ent an d age o f dom inant taxa in F u to m a horizon

N am e o f taxon

Environment: marine (M) brackish(B) fresh-water (F) Biotope Age

Neritie Littoral Planktonie Epiphytic 1 Recent Pleistocene Miocene Oligocene Eocene Paleocene Cretaceous

1. Actinocyclus loczyi

P ant. M +

2. Actinoptychus sena­

rius (Ehr.) Ehr. M + + + + 4* + + +

3. A . senarius var. ta­

manicus (Jouse)

H ajos M + + +

4. Cestodiscus inter­

sectus Brun M +

5. Chaetoceros com­

pressus Laud. M + + + +

6. Ch. robustus

M akar. M + + +

7. Chasea ornata H a­

jo s et Stradner M + + +

8. Coscinodiscus cf.

subtilis Ehr. M BF + +

156

J. K O TLA RCZYK & I. KACZMARSKA

cd. table

N am e o f taxon

Environment: marine (M) brackish(B) fresh-water (F) Biotope Age

Neritie Littoral Planktonie Epiphytic Recent Pleistocene Miocene Oligocene Eocene Paleocene

9. Grammatophora sp. 1

10. Hemiaulus cf. mal­

leolus P ant. M + + + +

11. Hemiaulus sporalis

Streln. M

12. Hyalodiscus scoticus

(Kiitz). G run. MB + + + + + + + +

13. M elosira architec-

turalis Brun M + +

14. M elosira praeislan-

dica Jouse F + +

15. Odontella cornuta

(J. Brun) Schrader M +

16. O. fim briata (Grev.)

Schrader M + +

17. Paralia sulcata

(Ehr.) Cleve M + + + + + + + +

18. Par. sulcara var.

crenulata (G run.)

Freng. M + + + +

19. Pseudopodosira w ittii (Schulz)

Veksh. M + +

20. Pyxilla prolongata

Brun M + +

21. Rhaphoneis amphi- ^-

ceros Ehr. MB + + + + +

22. Rhizosolenia sp., seta type o f Rh.

setigera Brigh. M

23. Stephanopyxis turris (G rev et Arn.)

Ralfs M + + + + + + + +

24. Sceptroneis gruno-

wii Anissim. M + +

25. Thallassiosira cf.

baltica (G run.) O st. MB + +

26. Triceratium conde-

corum Ehr. M + + + + +

27. T. tesellatum Grev. M + + + +

28. Trochosira spinosa

K itt. M + + + + +

29. Xanthiopyxis oblon­

ga Ehr. M + + +

30. X . papillosus H ajos M +

TWO D IA TO M H ORIZO N S 1 5 7

(Coscinodiscus subtilis) and one typically fresh water taxon (Melosira praeislandica).

The fishes found in the diatomites are exclusively neritic-sublittoral forms.

This character o f fossils suggests deposition in a shallow sea, possibly in vicinity o f a river m outh, during the Early Oligocene stage o f the general shallowing of the basin (cf. Kotlarczyk & Jerzm ańska, 1976).

The diatom assemblage in the Futom a horizon is not indicative o f precise age o f its host deposits. M ost taxa are long-ranging, usually known from the whole Tertiary. A bout one th ird o f the taxa are not hitherto known from strata older th an Neogene, while five taxa are considered not younger th an Oligocene (Table 2).

Here, the upper limits o f the stratigraphical extents o f the Palaeogene taxa are considered more significant for the conclusions regarding the age. The lower li­

mits o f the stratigraphical ranges o f the well studied Neogene taxa are frequently lowered with the increasing num ber o f studies on the Palaeogene assemblages (e.g. the extent o f Thalassiosira baltica and some other taxa must be extended down­

wards as a result o f our study). The Palaeogene age o f the diatom assemblage in th e Futom a horizon is suggested by Chasea ornata, Melosira architecturalis, Odon- tella fim briata, Pseudopodosira wittii and Pyxilla prolongata. The lack in this as­

semblage o f the forms, which accompany P. wittii in the U pper Eocene deposits in nearby localities in U kraine (Triceratium barbadensis and Melosira oamurensis), suggests the age not older th an Early Oligocene.

The diatom assemblage in the Futom a horizon is a very distinctive one, not similar to any hitherto described Oligocene assemblage. Some similarities occur to the diatom s described from the deposits o f the Norvegian Sea by D zinoridze et al. (1976). These authors distinguished Pyxilla prolongata zone in the lowermost p a rt o f Oligocene. The nom inal species o f this zone occurs in relatively large num ­ bers in all samples from the Futom a section. It should be noted however, th at other authors place Pyxilla prolongata zone in the U pper Oligocene (McCollum, 1975;

G om bos, 1976; Weaver & Gom bos, 1981; G om bos & Ciesielski, 1983).

O ther species comm on with the N orvegian Sea assemblage include M . architec­

turalis and X. oblonga (Dzinoridze et al., 1976) as well as Sceptroneis grunowii and Trochosira spinosa (Schrader & Fenner, 1976). The assemblage from Futom a has three Palaeogene taxa in comm on with the U pper Eocene—Lower Oligocene as­

semblage o f the SW Pacific Ocean (Hajos, 1976), one long-ranging taxon in common with the U pper Oligocene assemblage o f M angyshlak (Zhuze, 1978), and two long- -ranging taxa in comm on with the M aikop Bedsof the Shibik area, considered as Lo­

wer Miocene (Sheshukova-Poretskaya & Gleser, 1962).

PIĄTKOW A H O R IZ O N

L IT H O ST R A T IG R A PH Y AND D IST R IB U T IO N

The Piątkowa horizon does n o t constitute a separate lithologic unit. It occurs within transitional strata between the Menilite Beds and the K rosno Beds, in their p a rt traditionally named Niebylec shales. The Piątkowa horizon occurs in the p art

3 — A nnales S o cietatis 3-4/87

1 5 8 J . KOTLA RCZYK & I. KACZM ARSKA

o f the Niebylec shales which consists o f alternations o f grey m arly shales and cal­

careous sandstones typical o f the K rosno Beds, with subordinate layers o f black and brown, rarely green, siliceous-argillaceous shales and rare intercalations o f non-calcarous sandstones, both characteristic of the Menilite Beds. Characteristic for this strata are lenses o f ferrugineous dolomite and layers o f pyroclastic rocks, recognized as a m arker horizon (tuff horizon IV of Sikora et al., 1959).

There are several tens o f brown shale layers in the studied sections near Błażowa and Niebylec (Figs 2 and 5) and all are diatomaceous shales. Towards S and SE the num ber o f diatom-rich layers decreases and the diatom content diminishes.

Individual diatom-rich layers have been found, and their diatom s studied, at loca­

lities Lubno, D ąbrów ka Starzeńska, Jutna, Temeszów, K rępak (Fig. 1). Only in the last two sections the diatom s were num erous. D iatom s have been also found in the sections Szklary, Brzuska, Błażowa—Łęg II, Przylasek, Widaczów. In many investigated sections (Błażowa—Przedmieście, Błażowa—W ola, Borek Stary, N ie­

borów I and II, Dynów, K arolów ka, Leszczawa, Golcowa I and II, Barycz) no diatom s at all were found at the position o f the Piątkow a horizon.

The areal extent o f the Piątkow a horizon is about 1.000 km 2. Its type area is situated near Błażowa and Niebylec. There the intercalations o f diatomaceous shales may appear in the lower and m iddle parts o f the Niebylec shales (Piąt­

kowa) only in the middle part (Błażowa—Łęg), o r throughout the whole thick­

ness o f the Niebylec shales (Niebylec). The vertical distance between the extreme diatom -rich layers varies from 21 to 90 metres, respectively, and the total thickness o f the diatom -rich layers within the interval makes up 1 to 8 per cent o f the interval thickness. Away o f the type area, the diatom -rich layers appear either only in the lower p a rt o f the Niebylec shales (K rępak, Jutna, Temeszów) or in the middle and higher parts (Dąbrówka). Lithology o f the diatom -rich layers, their vertical sequence, and the lithology o f the accompanying rocks are highly variable laterally, even between closely spaced sections (see e.g. sections Piątkow a and Błażowa in

Fig. 5).

The Piątkow a horizon has no fixed position in the lithological sequence. The diatom horizon itself is defined as the totality o f the thin diatom -bearing layers which are intercalated within the Niebylec shales. Each diatom -bearing layer is o f a limited areal extent, but their occurrence in the section is vertically restricted and represents a short tim e o f diatom deposition.

There is no regularity in the m utual succession o f the diatom aceous shales and the pyroclastic layers. The latter occur as well am idst the diatom aceous shales (Błażowa—Łęg, Piątkowa) as beneath them (Niebylec), or above them (Dąbrówka Starzeńska). Although there is no direct p ro o f th at all the tuff layers belong to tuff horizon IV, and their lithology is different in different localities, but their occur­

rence within the same lithological division suggests their isochroneity (Żgiet, 1963).

This would corroborate the oppinion on the limited lateral extent and no fixed vertical position o f the individual diatom-rich layers.

The Piątkowa horizon is best developed in the Piątkow a I section which

is accepted as the horizon type section. The section is exposed in the escarpm ent

TW O H ORIZO N S D IA TO M 159

o f a hill-crest field ro ad between Ulanica and Piątkowa, running from the bench m ark 413.7 tow ards the ro ad to Rzeszów (Figs 5, 6). The beds are overturned and dip at 75—80° to NE. The diatomaceous layers are grouped in two clusters separated by a vertical distance o f 12 m. The lowermost diatom -rich layer is situated 11 metres above the top o f the Menilite Beds. The individual diatom-rich layers are 5 to 42 cm

PIĄTKOWA I

[ STRATOTYPE]

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110

120

130 140 150

Fig. 5. Lithological colum ns o f Piątkow a horizon. 1 — intercalations o f pyroclastic rocks; 2 — diatom aceous shales, a — diagenetic chert; 3 — calcareous K ro sn o sandstones; 4 — ochre- yellow, porous, diatom -poor shales; 5 — ankerite lenses; 6 — grey m arly K rosno shales; 7 — greenish clayey shales; 8 — brow n clayey-siliceous shales (menilite shales); 9 — non-calcareous quartzous sandstones (K liw a type); 10 — calcareous K rosno m udstones; 11 — frequency o f dia­

to m s:

a

— rare,

b

— frequent; 12 — hypothetical sequence o f stra ta in Niebylec section (recon­

struction); ovals with num bers locations and num bers o f investigated samples

1 6 0 J. KOTLARCZYK & I. KACZM ARSKA

Fig. 6. L ocation o f type section o f Piątkow a horizon. Explanations as in Fig. 4

thick; their to tal thickness is about 2.5 m. The same outcrop zone o f the Niebylec shales with diatom-rich intercalations was studied by Żgiet (1961, 1963) in prospec- tio n trenches. N atural exposures are scarce. A nother section (Piątkowa II), inclu­

ding only the lower p art o f the Niebylec shales is exposed in the field road running

TWO DIATOM H O R IZO N S 1 6 1

from the altitude m ark 389 m to Piątkow a village, some 1,600 m west o f the strato- type. It includes four thin (3—11cm ) layers o f diatom-rich shales, with total thickness o f 35 cm (Fig. 5).

The lower p a rt o f the Piątkow a horizon is more completely exposed at Błażo­

w a—Łęg locality, about 2 km away, in the opposite limb o f a syncline. In the es­

carpm ent of the field road running from the store by the road to the bench m ark 354 m, there are exposed 13 layers o f diatom-rich rocks. They are up to 44 cm thick; their to tal thickness is about two metres.

A t the periphery o f the type area, in Niebylec, the num ber o f the diatom-rich layers (see Fig. 5) is m uch lower (5—6), they are thinner (3—25 cm) and much more distant from one another (each 10 to 40 m). This section is now poorly exposed, south o f the tow n, in a field ro ad running to the hill 395. It was described earlier (Blaicher & N ow ak, 1963; Now ak, 1979) but without m entioning the diatom-rich layers.

L IT H O L O G Y O F T H E D IA T O M -R IC H RO CK S

The diatom-rich intercalations differ from the host rocks by their darker brown colour, dark beige with a violet shade when weathered, and higher porosity. These layers are well visible against the ash-grey or light-grey background o f the marly a n d clayey shales.

Five lithological varieties have been distinguished on the grounds o f litholo- gical features o f the weathered diatomaceous shales: ( 1) non-lam inated, beige or brow n, com pact (the most frequent); (2) spotted and banded, beige-brown, with the spots and bands irregular, sometimes lenticular (up to 1 cm in size), sometimes very small (size o f a comm a); shales are brittle, friable and p o ro u s; (3) parallel lam inated, brown, silty; white and beige laminae are up to 0.5 mm thick; (4) graded, brow n or beige; (5) clayey, brown or black, coarsely disintegrating into blocks, so­

metimes indistinctly lam inated, often slightly calcareous.

D iatom -poor shales found in the section o f the Piątkow a horizon resemble macroscopically the last variety. Sometimes they are yellow-ochre in colour.

SE D IM E N T O L O G IC A L OB SER V A TIO N S

Intercalations o f the diatomaceous shales are usually structureless. The spots, sometimes observed, are probably due to weathering and are porosity controlled.

Only in one case, in the section Błażowa—Łęg, the pattern o f the light spots seems to suggest th at these may be feeding channels. Thicker layers of diatom aceous shales are distinctly graded, and sometimes display Bouma sequences. Some sequences are incom plete: DE, CD, BC; they occur in thinner layers. M acroscopically discer­

nible sedimentary structures occur in 25—40% o f diatom aceous shales. The descri­

bed features indicate deposition by turbidity currents, as was suggested earlier by

Żgiet (1963). Light-coloured, quartzous non-calcareous sandstone occurs at base

o f some diatom -rich layers. Its petrographical type, similar to th at of the Kliwa

162

J. KOTLA RC ZY K & I. KACZM ARSKA

sandstones, suggests the same provenance i.e. from the northern (external) m argin o f the Skole basin.

There are no regularities in the contacts o f the diatom aceous shales with other rocks, including the pyroclastic layers.

D iagenetic silicification o f the diatom -rich rocks was occasional, only at two localities (Niebylec, Błażowa Wola) individual thin layers o f black cherts, adhering to black shale layers, have been found.

The Niebylec shales were laid down in a deep-sea environm ent, where biogenic and terrigeouns m aterial was supplied by turbidity currents from the shallower zones o f the basin.

FR EQ U EN C Y D IST R IB U T IO N O F D O M IN A N T TAXA IN STU D IED

SA M P L E S AND SE C T IO N S

The content o f diatom frustules in the studied samples was variable and the am ount of m ineral contam inations was significant. For this reason all samples were subject to flotation before the preparation o f slides. This resulted in fragm entation o f delicate frustules, so th at the semiquantitative analysis, similar to th at done for the Futom a horizon, was not attem pted. The inform ation about the 31 dom inant taxa is o f different type th an given in Table 1 for the Futom a horizon. Symbols in Table 3 denote the degree o f confidence in the identification o f the genera and spe­

cies.

The preservation o f diatom frustules in the diatom aceous shales was generally worse th an in the diatom-rich rocks o f the Futom a horizon, and in the shales with scarce diatom s it is poor or very poor. Some fragments found in the areas with the diatom horizon incompletely developed were determinable to the species, while in some sections (Lubno, Jutna, Temeszów and Niebylec) only genera could be determined.

The proportion o f diatom -bearing layers to the to tal num ber o f investigated black layers in individual sections was as follows: Lubno — 1:4, D ąbrow a Starzeńska — 2:8, Temeszów — 1:3, Jutna — 1:6, K rępak — 2:7, Brzuska — 2:11, Szklary — 1:3, Golcowa — 0:9, Bachórz — 0:5.

The diatom assemblage in the Piątkow a horizon is distinctive and uniform, both vertically and laterally (Table 3). Usually 18 to 27 taxa were found in indivi­

dual layers o f the diatomaceous shales after flotation; in individual layers o f the siliceous-argillaceous diatom -poor shales, from one to eleven taxa were found.

EC O LO G Y AND AGE O F D IA T O M S IN PIĄ TK O W A H O R IZ O N

The diatom assemblage in the Piątkowa horizon is indicative o f neritic-coastal, marine, normally saline environm ent (Table 4) but provides no indications on pa- aleoclimate. The assemblage consists mainly o f taxa with robust frustules. It re­

presents thus not a complete thanatocoenose but only its heavier fraction, th at o f

Frequency distributionofdominant taxain investigated samples ofPiątkowahorizon

TWO DIATOM H ORIZONS 1 6 3

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M 1 MB

S 2 S S S S s

— r - t f n r t i o v o r ^ o o o s o — 'fSr^lTj-lnVOr^

^{OO On} O — < N r>-> tT rH h M N N N N