Timing of the onset of Devonian sedimentation in northwestern Poalnd: palynological evidence

TIMING OF THE ONSET OF DEVONIAN SEDIMENTATION IN NORTHWESTERN POLAND: PALYNOLOGICAL EVIDENCE

E lżbieta T U R N A U 1 & H anna M A T Y JA 2

1 Institute o f Geological Sciences; Polish Academy o f Sciences; Kraków Research Center, Kraków; Senacka I, 31-002 Kraków, Poland

2Polish Geological Institute, Rakowiecka 4, 00-975 Warszawa, Poland

T u m a u , E. & M aty ja, H ., 2001. T im in g o f the o nset o f D ev o n ian sed im en tatio n in n o rth w e stern P oland: paly n o - lo g ical evidence. A nnales Societatis Geologorum Poloniae, 71: 6 7 -7 4 .

Abstract: P aly n o m o rp h a sse m b la g es o f low tax o n o m ic d iv ersity are reco rd ed from the basal D ev o n ian strata in th ree b o reh o les in w e ste rn P o m eran ia and K ujaw y. T h e p aly n o flo ra is a ssig n e d to a y o u n g er, au to ch to n o u s assem b lag e, an d a n o ld er, re d ep o sited one. T he c o m p o sitio n o f the y o u n g e r assem b lag e sugg ests lo w e r to m iddle E ifelian. T he o ld e r p a ly n o m o rp h s are d eriv e d fro m (1) U p p e r O rd o v ic ian o r L o w e r S ilurian, and (2) p ro b a b ly from U p p e r Silurian d e posits.

Key words: N o rth w e ste rn P oland, O rdovician, S ilurian, D ev o n ian , sp o ro m o rp h s, stratig rap h y , redep o sitio n . M anuscript received 17 M ay 2001, accepted 4 August 2001

INTRODUCTION

In the Pom erania-K ujaw y region, the subsurface Devo­

nian deposits have been found in approximately hundred boreholes situated mainly w ithin the northeastern zone ex­

tending to SE o f Koszalin, and along the Baltic coast, west o f Koszalin (Fig. 1).

Dadlez (1978) was the first to propose an informal lithostratigraphic division o f the Devonian strata into basic units o f formation rank, w hich were termed complexes.

This author presented also his opinion on the spatial distri­

bution and correlation o f the rock bodies. The scheme was subsequently complemented by M ilaczewski (1986). Only for the well dated and well represented Upper Devonian succession the division has been formalized (Matyja, 1993).

The lithology, sedimentary structures and sedimentary envi­

ronment o f these deposits has been discussed recently by M atyja (1998). In the M iddle Devonian deposits 2 deposi- tional systems have been distinguished: a fluvio-deltaic one in the Jamno region and clastic/carbonate in the nearshore Miastko— Chojnice— Polskie Łąki area (comp. Fig. 1).

The basal Devonian strata concerned in this paper be­

long to the Jamno, Studnica, and Tuchola lithostratigraphic units. They have not, so far, been formally defined but in this paper they are termed formations for the sake o f sim ­ plicity.

The clayey carbonate U pper Devonian succession has been recognized in several tens o f wells, and it is well dated (see Matyja, 1993) on conodonts, other faunas, and mio- spores, contrary to the underlying Devonian clastics which are almost devoid o f stratigraphically important fauna.

These rocks, often coarse-grained and in m any cases occur­

ring at considerable depth are also, in many instances, unfa­

vourable for palynological studies. Because o f this, the tim­

ing o f the onset o f Devonian sedimentation in the area under discussion has been, so far, a m atter o f varying opinions.

These were based mainly on lithostratigraphic correlations and on comparisons with other regions. Lobanowski (1968) suggested that the basal Devonian strata from the M iastko 1 borehole represented Lower Devonian or Eifelian. In the opinion o f Dadlez (1978), the Devonian sedimentation in the marginal part o f the basin, close to the Jamno region (Fig. 1) commenced probably in late Siegenian (Pragian).

The age o f the Studnica Formation, known only from the Miastko 1 borehole, was suggested by Milaczewski (1979) to be Early Devonian. In subsequent paper (Milaczewski,

1986), this age was supposed to be either Emsian or Eife­

lian. In the opinion o f M ilaczewski (1979), to the north from Miastko (the Jamno region), the basal Devonian deposits are not older than the Eifelian, w hereas in the Chojnice area, they are even younger (Givetian). In a recent paper, Loba­

nowski (1990, p. 406, tab. 1) suggested that in the M iastko 1 borehole, the lowermost 60 m o f the Devonian sequence represent uppermost Silurian and Lower Devonian. This opinion was based on vertebrates (Thelodonti, Acanthodei) recovered from the basal few metres o f this sequence. This fauna was found in pebbles (Lobanowski, personal com m u­

nication, 1995), so it is reasonable to suppose that it had been redeposited. Some biostratigraphic information on the age o f the discussed deposits was provided by spore studies

68

POLSKIE ŁĄKI IG-1

F ig . 1. L o catio n o f d isc u sse d b o reh o les ag ain st the geo lo g ical m ap o f p re -P e rm ian d ep o sits in no rth w estern P oland. G e o lo g y a f­

ter M aty ja, 1993, 1998. In se rt - p o sitio n o f stu d y area

(Fuglewicz & Prejbisz, 1981; Tumau, 1995, 1996). The Studnica Formation was included in the Eifelian and Giv- etian, and the Jamno and Tuchola formations in the Giv- etian. But these results did not concern the lowermost strata (cf. Fig. 2) because either the samples processed were bar­

ren or cores were not available.

Recently, another attem pt has been made to obtain spores from the basal Devonian strata. The results are dis­

cussed below. The four wells which have been chosen are those in which the coring o f the relevant parts o f the D evo­

nian succession is almost complete. Even more important is the fact that in these sections the Ordovician/Devonian con­

tact is within the cored intervals.

LITHOLOGY AND SEDIMENTARY ENVIRONMENT

The subsurface Devonian deposits o f the Pomera- nia-K ujaw y region occur below various subsystems o f the Permian or Carboniferous, and they rest discordantly on Or­

dovician (mostly Caradoc) or Silurian strata. The Caledo­

nian substratum has been reached only in twelve boreholes or so.

Deposits o f the J a m n o F o r m a tio n occur only in the NE part o f western Pomerania. They are known, among others, from the Jamno IG-1 borehole where they overlie discor­

dantly Ordovician (Caradoc) deposits. The formation is de­

veloped as a sequence o f reddish and mottled, less com ­ monly grey clastics. These are alternating units representing either simple sedimentation cycles o f fining upwards grain size or reversed, coarsening up cycles. The former consist o f light grey, cross-bedded, coarse and medium-grained quartz sandstones containing layers o f well rounded but only m od­

erately sorted quartz pebbles. The sandstones o f some inter­

vals o f this lithofacies are massive and lack noticeable bed­

ding. This lithofacies passes upwards into medium grained sandstones displaying parallel mudstone bands.

F ig . 2. A ge an d stratig rap h ical n o m en clatu re o f M id d le D e v o ­ n ian fo rm atio n s o f b o reh o les studied. P ositio n o f E ife lian m io- spore asse m b la g es w ith Rhabdosporites and Grandispora is show n as w ell as p rev io u sly estab lish e d (T u m a u , 1995, 1996) p o ­ sitio n o f E ifelian R L an d G iv etian E x M io sp o re zo n es (sh ad ed a r­

eas)

Units o f coarsening up grain size include fine-grained quartz sandstones laminated levelly and paralelly with black claystones, and grey, very fine-grained quartz sandstones paralelly intercalated with dark grey mudstones. As a whole, the above formation represents fluvial and deltaic environments, and the lowermost interval concerned in this paper has entirely an alluvial origin (Paczesna in Matyja et al., 2000).

The S tu d n ic a F o r m a tio n , distinguished by Milaczew- ski (1986), has been known, so far, only from the Miastko 1 borehole. These deposits rest discordantly on Ordovician strata. They are reddish and pale grey siliciclastic-calca- reous and dolomitic sandstones and mudstones as well as claystones. The lower part o f the formation contains mainly coarse-grained sandstones displaying large-scale cross bed­

ding. These are overlain by a sequence o f fine grained sand­

stones with small-scale cross bedding and parallel lamina­

tion. Anhydrite nodules and layers occur within middle part o f the formation, and the presence o f linguloids and ostra- cods in clayey parts o f the formation was noted by Loba- nowski (1968), while micro- and megaspores are common in mudstones, except for the 60 lowermost part o f the for­

mation (Fuglewicz & Prejbisz, 1981; Tumau, 1995).

The basal part o f the formation, from which samples have recently been studied, represents sediments o f the lower part o f the delta plain, and, higher up, those o f the

delta front (Pacześna in M atyja et al., 2000)

The deposits o f the Tuchola Formation have been rec­

ognized only in the southeastern part o f the study area, among others in the Chojnice 5 and Polskie Łąki IG-1 bore­

holes (Figs 1, 2) where they rest on Ordovician strata. The unit thickness varies from 40 m in the latter borehole to about 200 m in Chojnice 5.

In the Chojnice 5 section the formation is developed as dark grey marls, marly and organodetritic limestones, the latter with abundant coralloids, remnants o f echinoderms, vermicular snails and large oncoids. There are also organo­

genic limestones with m assive stromatoporoids. The marly nature o f the sediment, presence o f characteristic fossils, large oncoids and vermicular snails suggests an inner car­

bonate ramp environment partly corresponding to a la- goonal one. In the Polskie Łąki borehole, the formation in­

cludes black claystones and fine laminated mudstones with laminite intercalations. The assemblage o f fossils is rather poor including ostracods and plant detritus. These are sedi­

ments o f clastic lagoon.

MATERIAL

The examined material was derived from the basal De­

vonian strata pierced in the Miastko 1, Jamno IG 1, Polskie Łąki IG 1 and Chojnice 5 boreholes (Figs 1,2). Twenty-one samples were processed using standard laboratory methods but only eight contained determinable palynomorphs. Sam­

ples from the Miastko 1 borehole were barren, m ost o f sam­

ples from the other three boreholes contained miospore as­

semblages.

PALYNOSTRATIGRAPHY

Eight samples yielded spores (see Table 1), few acri- tarchs, scolecodonts and fragmented chitinozoa. The domi­

nant palynological matter found in the slides was unstruc­

tured, and occasionally structured plant detritus supposedly representing in part comminuted spores. The spore preser­

vation was variable, large specimens were often frag­

mented, small specimens were rather well preserved, though those from the Chojnice 5 borehole were o f a high maturation level. The representation o f the particular forms was poor hence many taxa are in open nomenclature or are determined to the generic level only. Nevertheless, the stra- tigraphic conclusions based on the new findings are confi­

dent, at least those concerning the Polskie Łąki IG-1 and Jamno IG-1 boreholes.

The spore assemblages contain taxa which have contra­

dicting stratigraphic meaning. Small spores and crypto­

spores represented by tetrads, diads and monads indicate an older age, while species assignable to Rhabdosporites, Ca- marozonotriletes, Diatomozonotriletes and Coiystisporites suggest a much younger age. It is obvious that we deal with autochtonous and reworked palynomorphs. Specimens as­

signed to Retusotriletes sp., Cymbosporites sp., Apiculiretu- sispora sp. and Emphanisporites sp. may belong either to the autochtonous or to the reworked assemblage. As colour

T able 1 Distribution o f spore/cryptospore taxa in samples studied

BOREHOLE

Depth in m

Emsian/Eifelian taxa Apiculiretusispora brandtii Apiculiretusispora plicata Camarozonotriletes cf. sextantii

Rhabdosporites cf. parvulus Camptozonotriletes sp.

Retusotriletes sp.

Acinosporites cf. lindlarensis Retusotriletes cf. rugulatus Diatomozonotriletes sp.

Grandispora? sp.

Retusotriletes triangulatus Corystisporites sp.

Silurian taxa

Archaeozonotritetes chulus v. chulus

Apiculiretusispora sp.

Laevolancis divellomedium Cymbosporites sp.

Emphanisporites sp.

Chelinohilates sp.

Hispanaediscus? sp.

Ambitisporites dilutus Tetrahedraletes medinensis Nodospora sp.

Segestrespora sp.

Smooth diad/pseudodiad

Polskie Łąki IG-1

+ +

+ + + + +

+ +

+ + + + +

Chojnice 5

+ + + + + + +

indices (TAI) do not show differences in therm al maturity level o f spores derived from individual samples, the assig­

n m e n t to one or other assemblage has been made arbitrar­

ily based on spore diameter. Silurian spores are in generall small and the spore diameter increases during the Lower Devonian (Chaloner, 1967; Richardson, 1967). It was thus considered that specimens measuring about 30 fim belong rather to the older assemblage.

Autochtonous assemblage

The composition o f the autochtonous assemblage is given in Table 1, and the taxa are illustrated in Figure 3.

Stratigraphically most important is Rhabdosporites cf. par­

vulus Richardson. Rhabdosporites is a very distinctive pseu- dosaccate genus characterized by a very fine and dense sculpture o f rods and grana. Spores o f this genus, especially R. langii (Eisenack) Richardson, are important constituens o f spore assemblages o f early (but not earliest) and middle Eifelian age (Richardson & McGregor, 1986; Avkhi-

7 0 E. TURN AU & H. M A TYJA

Fig. 3. E ifelian spores. S p ecim e n s A , C , D are fro m P o lsk ie Ł ąk i IG -1, d ep th 427CM-271 m , slid e P Z N II/81; sp ecim en s B, G , K, ibi­

d em , slid e P Z N II/79; sp ec im en s F, N , M are from Jam n o IG -1 , d ep th 2 7 4 2 -2 7 4 3 m , slide P Z N II/6; sp ecim en s E, O are fro m P o lsk ie Ł ąki IG -1, dep th 4 2 6 9 -4 2 7 0 m , slid e P Z N I/100; sp ec im en H, ib id em , slide P Z N I/99; sp ecim en s I, J are fro m P o lsk ie Ł ąk i IG -ld e p th 4 2 7 3 ^ 2 7 4 m, slide PZ N 1/95; sp e cim en L is fro m C h o jn ice 5, dep th 4 7 0 1 -4 7 0 2 m , slide P Z N 11/64. A ll m ag n ifica tio n s x 500 e x ce p t w h en stated oth erw ise; A -B - Retusotriletes triangulatus (S treel) Streel, A - spore fragm ent; C - Retusotriletes sp.; D - Retusotriletes rugulatus R ieg el. frag m en t o f p ro x im al face; E - Apiculiretusispora brandtii Streel; F - A piculiretusispora plicata (A llen ) S treel; G - Diatom ozono- triletes sp.; H - Acinosporites lindlarensis R iegel, x 1000; I - Cam arozonotriletes cf. sextantii M c G re g o r & C am field, x 1000; J , N , O - Rhabdosporites c f .parvulus R ich ard so n ; K -L - G randispora! sp., M - Corystisporites sp.

movitch et al., 1993). The species Rhabdosporites parvulus is known from the M iddle Devonian, but it has been also re­

ported from the uppermost Emsian o f Canada (M cGregor &

Camfield, 1976). The earliest record o f Rhabdosporites is from the W iltz Beds in the Eifel region, Rheinisches Schiefergebirge. Riegel (1982) reported from these beds the first occurrence o f “small Rhabdosporites”, and A shraf et al. (1991) noted the appearance o f Rhabdosporites minutus Tiwari & Schaarschmidt in the upper part o f this unit corre­

sponding to the serotinus Conodont Zone (W eddige & Re- quadt, 1985). Rhabdosporites minis Arkhangelskaya is typical o f assemblages o f the latest Emsian Diaphanospora inassueta (DI) miospore zone for the central regions o f the

Russian Platform (Arkhangelskaya, 1985), and was also re­

ported from the DI Zone from Belarus (Obukhovskaya, 1999); the species range extends to the lower Eifelian (Avkhimovitch et al., 1993). Another Emsian record o f Rhabdosporites is from the Trebotov Limestone, Dalejan (the serotinus Conodont Zone), Barrandian region in the Czech Republic (McGregor, 1979). Rhabdosporites cf. par­

vulus from our material is quite different from R. minutus and R. mirus, but is closely comparable to Rhabdosporites parvulus, and to Rhabdosporites sp. from the Barrandian re­

gion (see Section Taxonomic Note).

In the Jamno IG-1 borehole, R. cf. parvulus was accom­

panied by Corystisporites sp. The oldest specimens assign-

F ig . 4. S ilu rian o r L o ch k o v ian spores. S pecim ens A , D, E are fro m C h o jn ice 5, d ep th 4 7 0 1 -4 7 0 2 m , slide P Z N 11/64; sp ecim en s В, С are from C h o jn ice 5, dep th 4 6 8 9 .7 ^ 4 6 9 0 .7 m , slide P Z N 11/61; sp ecim en s F, G, I, J, О, P are fro m P o lsk ie Ł ąk i IG -1 , d ep th 4 2 2 6 ^ 1 2 2 7 m, slide P Z N 1/88; specim en H is fro m C h o jn ice 5, d ep th 4 7 0 1 ^ -7 0 2 m , slide P Z N 11/67; sp ecim en s K , R are fro m P o lsk ie Ł ąk i IG -1 , depth 4 2 6 9 ^ 4 2 7 0 m , slid e PZ N 1/100; sp ecim en s Ł, M are fro m Po lsk ie Ł ąk i IG -1, dep th 4 2 7 0 -4 2 7 1 m , slide P Z N II/81; sp ecim en N , ibidem , slid e P Z N 11/79. A ll m ag n ifica tio n s * 1000; A - Nodospora sp.; B, F Tetrahedraletes m edinensis S tro th er & T raverse; С - Segestrespora sp.; D , E - sm o o th d iad /p seu d o d iad ; G - Laevolancis divellom edium (T ch ib rik o v a) B u rg ess & R ichardson; H - Laevolancisl divellome- dium?; I - Retusotriletes sp.; J - Am bitisporites dilutus (H o ffm eister) R ich ard so n et L ister; К - u n d e te rm in e d cry p to sp o re; L - Apiculire- tusispora sp.; M - Chelinohilates sp.; N - Archaeozonotriletes chulus C ram er; O - Cymbosporites sp.; P - E m phanisporites sp., R - Hispanaediscus sp.

able to this genus have been reported from the upper Emsian W iltz Beds in the Eifel (Tiwari & Schaarschmidt, 1975).

In the Polskie Łąki IG 1 borehole, R. cf. parvulus was accompanied by single specimens o f Camarozonotriletes cf. sextantii McGregor & Camfield and Diatomozonotri- letes sp. The species C. sextantii is known from Emsian o f Canada (McGregor & Camfield, 1976), Algerian Sahara, Germany and Belgium (see Steemans, 1989), and from the Barrandian region o f the Czech Republic (McGregor, 1979). The species is thought to disappear approximately at the top o f Emsian (Richardson & McGregor, 1986) but its exact range near the Lower/M iddle Devonian boundary has never been traced in a well dated section yielding well pre­

served and diversified miospore assemblages. Moreover, C.

cf. sextantii from our material m ay represent Camarozono­

triletes parvus Owens recorded from the Eifelian and Giv- etian (M cGregor & Camfield, 1982). The species Apiculire- tusispora plicata Allen, found in the strata under discussion from both Jamno IG-1 and Polskie Łąki IG-1 boreholes is a typical Lower Devonian taxon, but it extends to middle Eifelian (Richardson & McGregor, 1986). Spores o f Diato- mozonotriletes are quite common in the Biya Horizon (up­

permost Emsian and lowermost Eifelian) o f Bashkirya and western slopes o f the Urals (Tchibrikova, 1962), and are found in Middle Devonian o f Canada (M cGregor & Cam­

field, 1982) and Belarus (Kedo & Obukhovskaya, 1981).

72

B

F ig . 5. S ilu rian acritarchs. A ll sp ecim en s are from P o lsk ie Ł ąk i IG-1 b o re h o le , dep th 4 2 7 0 -4 2 7 1 m , slid e P Z N II/81. A ll m ag n ifi­

catio n s x 1000: A - Buedingiisphaeridium sp.; B - Moyeria cabotti (C ram er) M iller et E am es; C - Lophosphaeridium sp.; D - Leiosphaeridia sp.; E - D ictyotidium dictyotum E isenak; F - Gor- gonisphaeridium cf. bringwoodensis D o m in g

The species Acinosporites lindlarensis Riegel appears in uppermost Emsian and extends to the basal Givetian (M cGregor & Camfield, 1982; Riegel, 1982), and Retuso- triletes rugulatus Riegel appears in early (not earliest) Eife- lian (Riegel, 1982; Richardson & McGregor, 1986).

It may be thus concluded that the basal Devonian strata from the Polskie Łąki IG 1 and Jamno IG 1 boreholes are not older than the latest Emsian, the serotinus Conodont Zone.

In Polskie Łąki IG-1 borehole, a position not below lower Eifelian is indicated by the presence o f Retusotriletes rugulatus Riegel, but middle Eifelian where spores o f the Rhabdosporites langii - R. parvulus complex are veiy com­

mon can not been ruled out.

Poorly preserved (broken and dark) specimens o f pseu- dosaccate, apiculate spores (Grandisporal) were found in the basal strata o f the Tuchola Formation from the Chojnice 5 borehole. The presence o f spores featuring a spinose zona— pseudosaccus is first noted in Emsian spores (Rich­

ardson & McGregor, 1986). Consequently, these strata are not older than Emsian, and they may well be contemporane­

ous with the basal Devonian deposits from the Polskie Łąki IG-1 and Jamno IG-1 boreholes.

R e w o r k e d a s s e m b l a g e

The samples studied yielded also small trilete spores, cryptospores (see Table 1 and Figure 4), and few acritarchs.

Acritarchs occur as single representatives o f a few taxa (Fig. 5), o f Silurian, Silurian-D evonian or w ider ranges.

Cryptospores from the base o f the Tuchola Formation in the Chojnice 5 borehole (Tab. 1) may be derived from Upper Ordovician or Lower Silurian rocks which is indi­

cated by the presence o f Segestrespora sp. (see Burgess, 1991; Wellman, 1996).

The taxa recorded from the basal strata o f the Tuchola Formation from Polskie Łąki IG-1 borehole are known to first appear in the Ordovician or Silurian and extend into the Lower Devonian. The presence o f Laevolancis divellome- dium (Tchibrikova) Burgess & Richardson suggests that the assemblages are not older than W enlock (Richardson, 1996) and the presence of Emphanisporites indicates an age not older than Ludlow (Richardson & McGregor, 1986). The species Tetrahedraletes medinensis Strother & Traverse emend. W ellman & Richardson is common in Ordovician and Silurian, but has been noted also, though infrequently, from the Lochkovian (W ellman, 1993; W ellm an & Richard­

son, 1996). Thus, the spore/cryptospore data suggest that the reworked palynomorphs are probably derived from Lud­

low or Pridoli deposits but Lochkovian strata can not be en­

tirely ruled out. But the composition o f the derived acritarch assemblage, which includes Buedinghiisphaeridium sp., Moyeria cabotti (Cramer) M iller et Eames, and Gorgoni- sphaeridium bringewoodensis Doming, points to a Silurian age.

The first record o f redeposited fossils from the lower­

most Devonian deposits in western Pomerania was by Żbikowska (1974) who characterized assemblages o f Pri­

doli ostracods from limestone pebbles derived from the base o f the M iastko Formation in the M iastko 1 borehole. This, and the present data show that various Silurian fossils on secondary floor in the lowermost Devonian strata in western Pomerania are not exceptional. It is therefore very likely that the Pridoli-Lochkovian vertebrate fauna reported by Łobanowski (1990) from the Studnica Formation in M i­

astko 1 borehole section is not autochtonous. It is possible, therefore, that also in this borehole the basal Devonian strata are not older than latest Emsian or early Eifelian.

Łobanowski considered these strata as Silurian-Lochkovian transition beds, though the fauna was recovered from peb­

bles.

CONCLUSIONS

In the Polskie Łąki IG -1 and Jamno IG -1 boreholes, the basal Devonian strata are not older than latest Emsian, and the most likely age is early to middle Eifelian. In Chojnice 5 and M iastko 1 boreholes, these strata are probably o f the same age.

The redeposited palynomorphs are derived from Upper Ordovician or Lower Silurian rocks (Chojnice 5 borehole) and probably from higher Silurian strata (Polskie Łąki IG -1 borehole).

The Silurian-Lochkovian vertebrate fauna reported from the Miastko 1 borehole by Łobanowski (1990) is probably also reworked.

Acknowledgements

T hese are partial results fro m the p ro ject 6 .2 0 .1 3 1 4 .0 0 .0 fi­

n an ced by K o m itet B adan N a u k o w y c h , led by the P an stw o w y In- sty tu t G eo lo g iczn y .

APPENDIX - TAXONOMIC NOTE

Genus Rhabdosporites Richardson 1960 emend Marshall et Allen, 1982

Rhabdosporites cf. parvulus Richardson 1965 Fig. 3 J, N, O

Description: C avate, trilete spores. A m b su b trian g u lar, sides c o n ­ vex, apices rounded. T rilete ray s o b scu red b y folds e x ten d in g a l­

m o st to sp o re equator. E x o ex in e d e ta ch ed from intexine d istally and in eq u ato rial reg io n fo rm in g a bladder. R atio o f intexine to sp o re rad iu s is 6 9 -7 9 % . E x in e o rn a m e n te d b y d en sely pack ed , low elem en ts a b o u t 1/2 p m in d iam eter. D istal folds o f ex o ex in e p re s­

ent.

Size range: 5 8 -8 8 p m (5 specim ens).

Comparisons: the d escrib ed sp e cim en s are sim ilar to R. parvulus R ich ard so n (R ich ard so n , 1965, p. 5 88-589, pi. 93, figs 5-6) in size an d the sp o re/b o d y ratio but th e ir sp arcity and p o o r p re se rv a tio n do n o t a llo w a c o n fid en t assignm ent. T h e species Rhabdosporites mi- nutus T iw ari et S ch aarsch m id t (T iw ari an d S ch aarsch m id t, 1975, p. 39-40, pi. 2 1 , figs 4-6) re co rd e d from the E m sian is sm aller (4 5 -5 7 p m ), an d has m uch th ick e r, rig id exoexine. T he sp ecies R.

minis A rk h an g elsk ay a (A rk h a n g elsk ay a , 1985, p. 68, pi. 11, figs 4, 5; pi. X II, fig. 2) know n fro m the u p p erm o st E m sian /lo w erm o st E ifelian is larger, b u t o th erw ise sim ilar to the d iscu ssed form . A sp e cim en o f Rhabdosporites w as rep o rted (illu stra te d b u t n o t d e ­ scrib ed ) b y M c G reg o r (1979, pi. 22.3, fig. 87) fro m the u p p e r E m ­ sian. It ap p ears sim ilar to o u r sp ec im en s in size, sp o re/b o d y ratio, ex in e th ick n ess an d o rnam entation.

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o tw o ru P o lsk ie Ł ąk i to w a rzy sz ą im Apiculiretusispora plicata A l­

len i Retusotriletes m gulatus R iegel, z k tó ry ch p ierw szy z an ik a w śro d k o w y m e iflu a d ru g i p o jaw ia się p o raz p ierw szy w d o ln y m ei- flu. M o ż n a zatem tw ierd zić, że z b ad a n e u tw o ry n ie s ą starsze niż n ajm ło d szy em s a ich n ajbardziej p ra w d o p o d o b n y w ie k to w c ze ­ sny lub śro d k o w y eifel.

P o jed y n cze, słabo zach o w an e o k azy należąc e p ra w d o p o d o b ­ n ie do ro d z aju Grandispora (Fig. 3/K ) n a p o tk an o w je d n e j z d w ó ch p ró b e k z o tw o ru C h o jn ice 5. S p o r o takiej m o rfo lo g ii nie n o tu je się po n iżej em su.

S tarszy, re d ep o n o w a n y zesp ó ł z aw ierał m ały c h ro zm iaró w sp o ry i k ry p to sp o ry , o raz b ard zo n ieliczn e ak ritarch y . K ry p to sp o ry ze sp ąg u fo rm ac ji tuch o lsk iej z o tw o ru C h o jn ice 5 m o g ą re p re z en ­ to w ać g órny o rd o w ik lub d o lny sylur, o czym św iad czy o b ecn o ść o k azó w Segestrespora sp.

T ak so n y n ap o tk an e w p ró b k a ch z o tw o ru P o lsk ie Ł ąk i IG-1 p o ja w ia ją się po raz p ierw szy w o rd o w ik u lub sy lu rze. O b ecn o ść Loevolancis divellom edium (T ch ib rik o v a) B u rg ess & R ich ard so n su g eru je w ie k n ie starszy o d w en lo k u a o b ecn o ść Em phanisporites w sk azu je n a w iek nie starszy o d ludlow u. Tetrahedraletes m edinensis S tro th er & T rav e rse je s t p o sp o lity w o rd o w ik u i sy lu ­ rze, rzadziej sp o ty k an y je s t w lochkow ie. Z esp ó l a k rita rc h (F ig. 5), z aw ie ra ją cy m iędzy in n y m i Buedinghiisphaeridium sp., Moyeria cabotti (C ra m er) M ille r et E am es i Gorgonisphaeridium bringe- woodensis D o m in g sugeruje w ie k sylurski.

S tre sz c z e n ie

POCZĄTEK DEWOŃSKIEJ SEDYMENTACJI W PÓŁNOCNO-ZACHODNIEJ POLSCE:

PRZESŁANKI PALINOLOGICZNE

Elżbieta Tumau & Hanna Matyja

W iek k lasty c zn y c h u tw o ró w sta n o w iący ch n a jn iż sz ą część sukcesji d ew ońskiej n a P o m o rz u zach o d n im m a sła b ą d o k u m e n ­ tację b io straty g rafic zn ą z p o w o d u u b ó stw a sk am ie n iało ści, a p rzy- sp ąg o w a część ty ch osad ó w p o z b aw io n a b y ła do tej p o ry ja k ie g o ­ k o lw iek dato w an ia. S k u tk iem teg o o p in ie n a tem at czasu, w k tó ­ ry m n a stąp ił p o czątek sed y m en tacji d e w ońskiej n a ty m obszarze, w y rażan e w ostatn im trzy d z ie sto lec iu p rzez ró żn y ch a utorów , zn aczn ie się o d sieb ie ró żn iły . P rzed m io tem dyskusji b y ły szcze­

g ó ln ie o b ecn o ść lub b rak u tw o ró w d o ln eg o dew onu.

B a d an ia p alin o lo g iczn e , k tó ry c h re zu lta to m p o św ięco n y je s t n in ie jsz y arty k u ł, d o ty czy ły p ró b e k ze spągow ej części form acji tucholskiej z o tw o ró w P o lsk ie Ł ąk i IG-1 i C hojnice 5, form acji jam n e ń sk iej z o tw o ru Jam no IG-1 i z fo rm acji Stadnickiej z o tw o ru M iastk o 1 (Fig. 1, 2). P o zy ty w n e w y n ik i u zy sk an o z o śm iu p ró b ek p o ch o d zą cy c h z trzech o tw o ró w w y m ien io n y c h pow y żej w p ie r­

w szej kolejności.

P alin o m o rfy u zy sk an e z ty ch p ró b e k m ożna zaliczyć do d w ó ch ró ż n ią cy c h się w iek iem zesp o łó w . Z esp ó ł m ło d szy (T ab. 1, F ig. 3) m o żn a u zn ać za au to ch to n ic zn y , z esp ó ł sta rszy (T ab. 1, Fig.

4, 5) je s t n a d ru g im złożu.

W zesp o le m ło d szy m z o tw o ró w P o lsk ie Ł ąki IG-1 i Jam n o IG-1 n ap o tk an o Rhabdosporites cf. parvulus R ichardson, Acino- sporites lindlarensis R iegel, i C orystisporites sp. F o rm y te nie są zn an e z u tw o ró w starszych o d n a jm ło d sz eg o em su. W p ró b k a ch z