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Homerian boundary beds (Wenlock) in the Prague Basin (Barrandian, Bohemia)
ELS EVI ER
Review of Palaeobotany and Palynology86 (1995) 135-145
REVIEW OF PALAEOBOTANY AND PALYNOLOGY
Chitinozoans from the Sheinwoodian/Homerian boundary beds (Wenlock) in the Prague Basin (Barrandian, Bohemia) Pavel Dufka Czech Geological Survey, Kl~rov 131/3, 118 21, Praha 1, Czech Republic Received 15 January 1993; revised and accepted 15 August 1993
Abstract
Sixteen chitinozoan taxa are identified in samples from the Sheinwoodian/Homerian boundary beds (Wenlock, Silurian) of the Kosov quarry (section 767) in the Prague Basin, Bohemia. Their stratigraphical range is correlated with graptolite data in the studied section. The distribution of some Wenlock index chitinozoan species (e.g. Cingulochitina cingulata, Gotlandochitina martinssoni, Conochitina gracilis) in section 767 is compared with their distribution in other regions around the world. The paleogeographic affinities of the Wenlock chitinozoans from the Prague Basin and the Baltica paleocontinent are stressed.
1. Introduction
In a preliminary study of the Lower Silurian chitinozoans of the Prague Basin (Dufka, 1992a), eleven chitinozoan taxa were reported from upper Wenlock strata. Two informal chitinozoan biozones (I and J) were proposed for various chitinozoan assemblages recorded in the upper Sheinwoodian and lower Homerian samples. The present study, based on more detailed sampling, focuses on chitinozoan distribution around the Sheinwoodian/Homerian boundary. The sampling was conducted in the large Kosov quarry near Beroun, Bohemia. Thirty-eight samples have been taken from both sides of the Sheinwoodian/Homerian boundary in section No. 767 exposed in the lower part of the quarry (see KfiZ, 1992, fig. 38 for sketch map). The section is represented by a continuous sequence of graptolite-bearing black shales with sporadic lenses of micritic limestone (Fig. 1). Numerous graptolite records in this section (Turek, 1989; Kfi~, 1992; Storch, 1992) provide a very good chronostrati0034-6667/95/$9.50© 1995ElsevierScienceB.V. All rights reserved SSDI 0034-6667(94)00102-P
graphic control (M. belophorus to C. lundgreni graptolite Biozones) to the samples investigated for chitinozoans (Fig. 1). All the processed samples yielded chitinozoans. The abundance and the diversity of the chitinozoans are generally higher with regard to those of other chitinozoan assemblages of similar age from the Prague Basin (Dufka, 1992a). The abundance of the chitinozoans in the shales ranges from several hundreds to 2000 specimens per gram of rock. Chitinozoans are badly preserved in shales and moderately preserved in micritic limestone. The fine processes and ornamentation of the majority of the thin-walled Lagenochitinidae forms as well as the carina of Cingulochitina genus are destroyed. Only one of 10,200 recorded specimens displays a morphological anomaly, represented by the bulging of an extremely elongate neck (Angochitina cf. echinata, sample No. 767/3). The ratio of chitinozoan malformations corresponds approximately to the general rate estimated by Jaglin and Paris (1992). Five chitinozoan taxa are reported for the first
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P. Dufka/Reviewof Palaeobotanyand Palynology86 (1995) 135-145 time in the Prague Basin and among them, two are particularly important for global biostratigraphic correlation, i.e. Cingulochitina cingulata and Gotlandochitina martinssoni. The other organic particles obtained by a separation with the 53 #m sieve are amorphous kerogen, fragments of graptolites, prasinophycean-like sphaeromorphs, scolecodonts, mazuelloids and different incertae sedis. Mazuelloids and scolecodonts were counted and their abundance is expressed in a number of specimens per gram of rock (Fig. 1).
2.1 List of species Aneyrochitina gr. ancyrea (Eisenack, 1931) (Plate I, 1)) Ancyrochitina primitiva Eisenack, 1964 (Plate I, 2) Ancyrochitina sp. A (Plate I, 8) Calpiehitina (Densichitina) sp. A (Plate II, 5) Cingulochitina sp. A (Plate I, 10, 11) Cingulochitina sp. B (Plate I, 6) Cingulochitina cingulata (Eisenack, 1937) (Plate I, 5,9) Conochitina cf. proboscifera Eisenack, 1937 Conochitina gracilis Laufeld, 1974 (=C. proboscifera forma gracilis) (Plate II, 10) Conoehitina tuba Eisenack, 1932 (Plate II, 12, 13) Gotlandochitina martinssoni Laufeld, 1974 (Plate I, 7) Linochitina cf. odiosa Laufeld, 1974 Linochitina cf. erratica (Eisenack, 1931) (Plate II, 1,2,9) Margachitina margaritana (Eisenack, (Plate II, 8, 11) ?Urnoehitina sp. A (Plate II, 3, 4, 6, 7)
Genus Urnoehitina Paris, 1981 Type: Desmochitina? urna Eisenack, 1934 ?Urnochitina sp. A (Plate II, 3, 4, 6, 7) Material: 65 three-dimensional (undeformed) specimens recorded in section Kosov-767, samples 767/31A, 767/31B, 767/32; T. testis Subzone. Dimensions: Based on 27 specimens. Measurements in/~m. Mean Range
2. Systematics
1937)
2.2 Description of selected taxa Order VROSOMATIFERAEisenack, 1972 Family DESMOCHITINIDAEEisenack, 1931; emend. Paris, 1981 Subfamily ~AR~ACmTrNINAE Paris, 1981
137
L 244 200-288
Dp 137 102- 166
Dc 78 65-100
Description: Vesicle with club to pear-shaped chamber; flexure and neck inconspicuous; short flaring collarette bordering the flat operculum. The basal margin is inconspicuous; base either flat with simple, narrow and low tim-like mucron or convex with a more distinct conical mucron. The mucron termination, usually uneven, suggests its partial destruction. Ornamentation consists of thin ruggae, irregularly convoluted or arranged more or less in a polygonal pattern (Plate II, 7). The ornamentation developed mainly on the anteapertural part of vesicle and fades away towards the aperture (Plate II, 3). Discussion: The characteristics of the individuals tentatively named ?Urnochitina sp. A do not compare with any generic definition. They cannot be assigned to Conochitina, due to the presence of an operculum, nor to Eisenackitina because of the absence of an echinate ornamentation, nor to Bursachitina because ?Urnochitina sp. A has usually a much more slender vesicle. Although neither distinct pedunculate copula nor chain-structure have been observed in these forms, they are referred herein to the genus Urnochitina in considering that a break-up of the copula of some specimens cannot be completely excluded. Furthermore, the generic classifications of several other Wenlock species are similarly not clearly defined, for example Conoehitina lagena from Estonia (Nestor, 1982, pl. 17, fig. 9), Conochitina gutta (Laufeld, 1974, fig. 25), and Kalochitina scabra (Schweineberg, 1987, pl. 8, figs. 3B, 4B). If
P. DuJka/Review of Palaeobotany and Palynology 86 (1995) 135 145
138
PLATE I
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P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135-145
well-preserved, these species exhibit a club-like chamber, distinct low mucron and characteristic chamber ornamentation ranging from rugulatereticulate (C. gutta, Urnochitina sp. A) to meshlike (C. lagena, K. scabra). The listed characteristics suggest that a new genus within the subfamily Eisenackitininae including these taxa would be useful. Genus Linochitina Eisenack, 1968 Type: Desmochitina erratica Eisenack, 1931 Linochitina cf. erratica (Eisenack, 1931 ) (Plate II, 1,2,9) Material: 940 specimens recorded in section Kosov-767, samples 767/13-766/32 (Fig. 1); C. perneri/C, ramosus Zone-T. testis Subzone. Dimensions: Based on 53 three-dimensional specimens and 120 flattened specimens, flattening corrected for Dc and Dp values by multiplying with a 0.7 coefficient. Measurements in #m. Mean Range
L Dp 184 45 142-256 38-53
Dc 33 30-40
139
Linochitina odiosa (Laufeld, 1974, p. 101) through the holotype of L. erratica (Eisenack, 1931, p. 92, L / D p = 3 ) to extremely long specimens of Linochitina sp. (Dufka, 1992a, pl. 3, fig. 6, L/Dp>4). Thus, based on this parameter Linochitina cf. odiosa is separated from L. cf. erratica rather artificially (Fig. 2). With reference to some previous discussions on Linochitina (Paris et al., 1981, p. 19; Schweineberg, 1987, pp. 31-32) the new data from the upper Wenlock of the Prague Basin indicate a close relationship, corresponding probably to intraspecific variations, between the Silurian species l. odiosa, L. erratica and L. klonkensis, with exception of the types with more or less distinct carina from Gotland (Laufeld, 1974, fig. 59) and from Estonia (Nestor, 1982, pl. 17, fig. 3). Subfamily PTEROCHITININAEParis, 1981 Genus Cingulochitina Paris, 1981 Type: Desmochitina cingulata Eisenack, 1937
Lcop 15-32
Description and remarks: Slender, elongated Linochitina distinctly varying in the vesicle length (L), however, the chamber diameter (Dp) is rather invariable. The L/Dp variations of herein described forms (Fig. 2) ranges continuously from typical
Cingulochitina sp. A (Plate I, 10, 11 ) Material: 393 flattened specimens recorded in section 767-Kosov, samples 767/la-767/4 (Fig. 1); M. belophorus-C, rigidus Zones. Dimensions: Based on 56 flattened specimens. Measurements in #m (Dp and Dc values corrected
PLATEI Wenlock chitinozoans of the Prague Basin. Section 767 of the Kosov quarry. Ancyrochitina gr. ancyrea (Eisenack). C. radians Biozone, sample 767/23, slide GSP-215. x 400. 1. Ancyrochitina primitiva Eisenack. C. radians Biozone, sample 767/20, slide GSP-209. × 350. 2. Angochitina cf. echinata Eisenack. C. rigidus Biozone, sample 767/I, slide GSP-164. 3,4. x 300. 3. x 350. 4. Cingulochitina cingulata (Eisenack). 5,9. C. rigidus Biozone, sample 767/2, slide GSP-241. x 400. 5. 9. C. radians Biozone, sample 767/25, slide GSP-221. x 350. Cingulochitina sp. B. C. rigidus Biozone, sample 767/lc, slide GSP-156. x400. 6. Gotlandochitina martinssoni Laufeld. C. perneri/C, radians Biozone, sample 767/7. x 325. 7. Ancyrochitina sp. A. C. perneri/C, ramosus Biozone, sample 767/6, slide GSP-179. x 350. 8. 10, 11. Cingulochitina sp. A. C. rigidus Biozone, sample 767/lf, slide GSP-164. x 350. 12. Linochitina cf. odiosa Laufeld. C. radians Biozone, sample 767/25, slide GSP-221. x 300.
P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135-145
140
PLATE II
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P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135-145
141
Dp 60 #
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Fig. 2. Diagram showing the variations of the chitinozoan vesicle length (L) with regard to the chamber diameter (Dp) of Linochitina cE odiosa Laufeld and Linochitina cf. erratica (Eisenack) in section 767 of the Kosov Quarry, Wenlock (Silurian), Prague Basin.
with the coefficient for restoring of original volume). Mean Range
L 194 170-260
Dp 43 34-49
Dc 36 31-44
Descr~t~n: Very slender Cingu~chitma
with slightly flexuous flanks about a half of the vesicle length. L/Dp ratio is more then 4 (average 4.5). Occurrence of a ring bordering the basal margin; however, no complete membranous carina has been observed in the available material similarly
as further morphological elements (operculum, collarette, anapertural mark). No twins nor chain-like structures have been observed. Discussion: The chamber outline, as well as the position of the carina in this species recalls Cingulochitina sp. aft. convexa described by Paris (1981, pp. 165-166) from the upper Wenlock of the Bugaco Formation, but Cingulochitina sp. A is longer (170-260/zm against 109 166 #m for C. sp. aft. convexa). In contrast, Cingulochitina sp. A is shorter and provided with a thinner wall when compared to a closely related form
PLATE II Wenlock chitinozoans of the Prague Basin. Section 767 of the Kosov quarry. Linochitina cf. erratica (Eisenack). C. radians Biozone, sample 767/23. 1,2,9. 1. Slide GSP-215. x 350. 2,9. Slide GSP-216. × 350. 3 , 4 , 6 , 7 . ?Urnochitina sp. A. T. testis Biozone, sample 767/31b. Slide GSP-238. x 250. 3. Slide GSP-239. × 250. 4,6,7. Calpichitina (Densichitina) sp. A. 72 testis Biozone, sample 767/31b, slide GSP-238. x 300. 5. 8,11. Margachitina margaritana (Eisenack). C. radians Biozone, sample 767/27, slide GSP-239. x 300. 8. 11. 7: testis Biozone, sample 767/32, slide GSP-242. x 350. 10. Conochitina gracilis Laufeld. C. perneri/C, ramosus Biozone, sample 767/12, slide GSP-194. x 200. 12, 13. Conochitina tuba Eisenack. 12. C. radians Biozone, sample 767/23, slide GSP-216. × 250. C. perneri/C, ramosus Biozone, sample 767/7, slide GSP-182. × 250. 13.
P. Dujka/Review of Palaeobotany and Palynology 86 (1995) 135-145
142
(Cyathochitina [ = Cingulochitina] sp. E), described by Schweineberg (1987, p. 86) from the Las Arroyacas Formation (upper Wenlock) in Spain.
by Schweineberg (1987, p. 84, fig. 6) from the Las Arroyacas Formation (upper Wenlock) in Spain.
Cingulochitina sp. B (Plate I, 6)
3. Biostratigraphy
Material: 286 flattened specimens recorded in section 767-Kosov; samples 767/la-747/4 (Fig. 1); M, belophorus-C, rigidus Zones. Dimensions: Based on 50 flattened specimens. Measurements in #m (Dp and Dc values corrected with the coefficient for restoring the original volume).
Long-ranging taxa of Ancyrochitina, e.g. Ancyrochitina ancyrea and Ancyrochitina primitiva,
Mean Range
L 166 147-192
Dp 53 49-60
Dc 40 34-47
Description: Most specimens have distinctly curved flanks (=originally slight flexure accentuated by flattening) and a widened aperture. The basal margin is ornamented by a short carina (probably partly destroyed). The vesicle surface is smooth. The base is usually destroyed and gone. Therefore, the anteapertural mark is indistinguishable. No specimens in chains have been observed. Remarks: Cingulochitina sp. B is longer than C. cingulata and less slender than Cingulochitina sp. A (see Fig. 3). Cingulochitina sp. B is very similar to Cyathochitina sp. C (= Cingulochitina) described
occur throughout section 767 of Kosov quarry. Margachitina margaritana, already reported from the C. murchisoni and T. testis graptolite zones (Wenlock) of the Prague Basin (Dufka, 1992a), occurs also sporadically from the base up to the top of the section. Conochitina tuba is not considered to be a significant index taxon for the Wenlock of the Prague Basin, due to frequent occurrence of transitional forms between this species and Conochitina cf. proboscifera (in the upper Sheinwoodian) and Conochitina claviformis (in the Homerian). Following chitinozoan taxa are proposed for Wenlock biostratigraphy of the Prague Basin: Cingulochitina sp. A, Cingulochitina sp. B,
Conoehitina gracilis, Cingulochitina cingulata, Gotlandochitina martinssoni, Linochitina cf. erratica and ?Urnochitina sp. A. (Fig. 1). Cingulochitina sp. A and Cingulochitina sp. B are commonly found in samples from M. belophorus and C. rigidus graptolite zones. Their preserva-
Cingulochitinasp. B
Dp
90
60
mmj ~*==~= "~=",~ f _ 1 Cingulochitinasp. A
Cingulochitinacingulata (82)
(56) 30 FLATTENED SPECIMENS t
o
i
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Fig. 3. Diagram showing the variations of the chitinozoan vesicle length (L) with regard to the chamber diameter (Dp) of Cingulochitina cingulata, Cingulochitina sp. A and Cingulochitina sp. B in section 767 of the Kosov quarry, Wenlock (Silurian), Prague Basin.
P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135 145
tion does not allow a good comparison with similar carina-bearing chitinozoans from other regions, except for some forms of Cyathochitina (= ?Cingulochitina) from the upper Wenlock in Spain (Schweineberg, 1987) which show some similarities with specimens from the Prague Basin (for details, see systematics). Extremely long and slender forms of Conochitina (L = 600-1100 /ira, L/Dp> 10), assigned herein to Conoehitina graeilis, range from the base of C. rigidus Zone to upper part of C. perneri/C, ramosus Zone in the section 767. Elsewhere in the basin, they are known only from the C. perneri/C, ramosus zone (Dufka, 1992a). In Gotland, where C. gracilis was originally described by Laufeld (1974, pp. 71-72), its occurrence is restricted to the basal Sheinwoodian in the Upper Visby beds and in the lowermost part of the Hogklint Beds. In the same area Conochitina leptosoma, a very similar species, ranges stratigraphically from the horizon with the last occurrence of C. gracilis up to the top of the Hogklint Beds (?rigidus Zone). Descriptions of both species suggest that their morphological diversity could correspond to intraspecific variations of a single species. Conochitina cf. leptosoma from lower Sheinwoodian of Estonia (Nestor, 1982, pl. 14, figs. 7, 8) which displays some morphological features common for both C. leptosoma and C. gracilis from Gotland, could be an intermediate form within the range of these morphological variations. Thus, if we compare the data from Estonia, Gotland and Bohemia, conspicuously elongated types of Conochitina are typical for the Sheinwoodian strata in these regions. The occurrence of closely related Conochitina (e.g. Rhabdochitina cf. minnesotensis, in Taugourdeau and de Jekhowsky, 1960, p. 1230, pl. 10, fig. 134) in the Lower Silurian subsurface sequences from Algeria suggests the wide distribution of this taxon. Cinguloehitina eingulata appears for the first time in sample 767/3 of the studied section in the upper part of the C. rigidus Zone and occurs in small number in all samples of the lower part of the C. perneri/C, ramosus Zone. In the Homerian, it was found only in two samples of the C. radians Subzone (767/25-26), but there it is rather abundant. The first occurrence of C. cingulata in the Prague Basin coincides with the first record of this
143
species from the mid-upper Sheinwoodian of Gotland (Laufeld, 1974), Estonia (Nestor, 1990), Great Britain (Doming, 1981), Belgium (Verniers, 1982) and also Libya and Algeria (Paris, unpubl. data). The absence of Cingulochitina around the Sheinwoodian/Homerian boundary and above the C. radians Zone in the section 767, as well as in other upper Wenlock sections in the Prague Basin (Dufka, 1992a; Kfi2 et al., 1993) could be related to the shallowing of the basin due to tectonic and volcanic activity as well as to eustatic movements (see Kfi2, 1991). This interpretation follows previous hypotheses that Cingulochitina is a genus indicating a deep water environment (Rombouts, 1978; Verniers, 1982). Gotlandochitina martinssoni occurs exclusively in samples (767/5-15) from the C. perneri/C, ramosus (= C. ellesae) graptolite Zone of the Prague Basin. It is a good marker of the upper Sheinwoodian and seems suitable for correlation between Bohemian and Baltic assemblages from Estonia (Nestor, 1990), Gotland (Laufeld, 1974) and England (Dorning, 1981). The genus Linochitina appears in the Prague Basin just below the Sheinwoodian/Homerian boundary (sample 767/12). The slender form referred herein to Linochitina cf. erratica is typical for chitinozoan assemblages of the C. lundgreni Zone in section 767. The occurrence of this form in this zone was already reported from several other localities in the basin (Eisenack, 1934; Dufka, 1992a; K~i2 et al., 1993). Linochitina erratiea is well known from Silurian strata both from Gondwana and Baltica (see Schweineberg, 1987, p. 31), but, in my opinion, the use of this species for interbasinal correlation is rather limited because of its confusing morphology and, therefore, an unclear taxonomy. ?Urnochitina sp. A was recovered in a studied section from the T. testis Subzone. It is so far the only occurrence of this species in the Prague Basin. Nevertheless, at least two other upper Wenlock forms, questionable Conochitina lagena from Estonia (Nestor, 1982, 1990) and Kalochitina scabra from Spain (Schweineberg, 1987), indicate a close generic affinity with ?Urnochitina sp. A.
144
P. Dufka/Review of Palaeobotanyand Palynology86 (1995) 135-145
and differ from each other only in complexity of surface ornamentation.
4. Conclusions Based on a recent study of section 767 in the Kosov quarry, the change in chitinozoan assemblages close to the Sheinwoodian/Homerian boundary of the Prague Basin appears to be less obvious than assumed previously (Dufka, 1992a,b). In fact, this boundary (= first occurrence of C. lundgreni in section 767) is characterized only by the disappearance of Gotlandochitina martinssoni. Linochitina cf. erratica, a fairly good marker for the lower Homerian of the basin, appears already in samples of the C. perneri/ C. rarnosus Zone. Two Wenlock index chitinozoan species are reported for the first time from the Prague Basin: Cingulochitina cingulata ranges from the C. rigidus Zone to the C. radians Zone, and Gotlandochitina martinssoni is restricted to the C. perneri/C, ramosus (= C. ellesae) Zone. The following remarks on the correlation and paleogeography of middle and upper Wenlock chitinozoans from the Prague Basin (Dufka, 1992a; KfiZ et al., 1993) take into account restrictions concerning the bad preservation of chitinozoans within the black shale facies in some regions (e.g. Bohemia and the Brabant Massif), poor independent biostratigraphic control of some North Gondwana chitinozoan assemblages (Algeria; northern Spain, Province of Leon; Florida; Brazil) and a lack of data on chitinozoans from regions paleogeographically related to the Prague Basin (e.g. Carnic Alps and Sardinia). Based on species spectra, the chitinozoan assemblages from the Prague Basin are characterised by (1) the c o m m o n presence of cosmopolitan species
(A. ancyrea, A. primitiva, M. margaritana, C. tuba, C. pachycephala, A. cf. echinata); (2) the occurrence of some Baltoscandinavian species (G. martinssoni, C. cingulata); and (3) the scarcity of typical N o r t h G o n d w a n a species, particularly of the genera Tanuchitina and PIectochitina. Only Cingulochitina sp. A and Cingulochitina sp. B exhibit some similarities with upper Wenlock cin-
gulate chitinozoans from Spain (Schweineberg, 1987). An additional characteristic feature of all Lower Silurian chitinozoan assemblages from the Prague Basin is the absence of distinct "endemic" species. Paleogeographical affinities of middle and upper Wenlock chitinozoans from the Prague Basin, just like those of Llandovery chitinozoans (Dufka, 1992a; D u f k a and Fatka, 1995) and acritarchs (e.g. Dufka, 1990, pp. 88, 93) in this region, indicate the intermediate position of the Prague Basin between the Gondwana and Baltica paleocontinents (see also Paris, 1993; Paris et al., 1995). Free exchange of paleoplankton between the Prague Basin and the Baltica's shelf seas is evident from the similar stratigraphic range of some species as well as of one genus (Cingulochitina).
References
Dorning, K.J., 1981. Silurian Chitinozoa from the type Wenlock and Ludlow of Shropshire, England. Rev. Palaeobot. Palynol., 34: 205-208. Dufka, P., 1990. Acritarchs of the Monograptus sedgwickii Zone (Zelkovice Formation, Llandovery) from Hyskov, Barrandian, Bohemian Massif. Acta Univ. Carol. Geol., 1990(1): 75-104. Dufka, P., 1992a. Lower Silurian chitinozoans of the Prague Basin (Barrandian, Czechoslovakia)-Preliminary results. Rev. Micropal6ontol., 35:117--126. Dufka, P., 1992b. Chitinozoansof the Sheinwoodian/Homerian boundary interval (Silurian) in the Prague Basin. 8th IPC, Aix-en-Provence, Abstr., p. 39. Dufka, P. and Fatka, O., 1993. Chitinozoans and acritarchs from the Ordovician Silurian boundary of the Prague Basin (Barrandian Area, Czechoslovakia). Spec. Pap. Palaeontol., 48: 17-28. Eisenack, A., 1934. Neue Mikrofossilien des baltischen Silurs III und neue Mikrofossilien des bohmischen Silurs I. Palaeontol. Z., 16: 52-76. Jaglin, J. and Paris, F., 1992. Examples de t6ratologie chez des Chitinozoaires du Pridoli de Libye et implications sur la biologie du groupe. Lethaia, 25: 151-164. Kfi~, J., 1991. The Silurian of the Prague Basin (Bohemia) tectonic, eustatic and volcanic controls on facies and faunal development. Spec. Pap. Paleontol., 44: 179-203. Kf%, J., 1992. Silurian field excursions: Prague Basin (Barrandian) in Bohemia. Natl. Mus. Wales Geol. Ser., 13, 111 pp. Kf'i~, J., Dufka, P. and Sch6nlaub, H.P., 1993. Wenlock Ludlow boundary in the Prague Basin, Bohemia. Jahrb. Geol. B. Wien, 136 (4): 809-839
P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135-145 Laufeld, S., 1974. Silurian Chitinozoa from Gotland. Fossils Strata, 5: 1-130. Nestor, V., 1982. Chitinozoan zonal assemblages (Wenlock, Estonia). In: D. Kaljo and E. Klaamann (Editors), Communities and Biozones in the Baltic Silurian. Valgus, Tallinn, pp. 84-97 (in Russian). Nestor, V., 1990. Silurian chitinozoans. In: D. Kaljo and H. Nestor (Editors), Field Meeting Estonia, 1990, an Excursion Guidebook. IUGS, Subcomm. Ordovician Silurian Stratigr., pp. 80-83. Paris, F., 1981. Les Chitinozoaires dans le Pal~ozoique du Sud-Ouest de l'Europe (Cadre grologique-Etude systrmatique-Biostratigraphie). Mrm. Soc. Grol. Minrr. Bretagne, 26: 1-412. Paris, F., 1993. Evolution pal~ogrographique de l'Europe au Palrozoique infrrieur: le test des Chitinozoaires. C.R. Acad. Sci. Paris, 316: 273-280. Paris, F., Laufeld, S. and Chlup~ir, I., 1981. Chitinozoa of the Siluria~Devonian boundary stratotypes in Bohemia. Sver. Geol. Unders. C, 51: 1-29. Paris, F., Verniers, J., AI Hajri, S. and Al-Tayyar, H., 1995.
145
Biostratigraphy and palaeogeographic affinities of Early Silurian chitinozoans from central Saudi Arabia. Rev. Palaeobot. Palynol., 89: in press. Rombouts, L.P., 1978. Factors controlling the distribution of Chitinozoa in the Gleedon chronozone (Wenlockian) of northern Europe. Ann. Soc. Geol. Belg., 105: 259-271. Schweineberg, J., 1987. Silurische Chitinozoen aus der Provinz Palencia (Kantabrisches Gebirge, N-Spain). G6tt. Arb. Geol. Paleontol., 33: 1-94. Storch, P., 1992. Facialni vyvoj, stratigrafie a korelace svrchniho ordoviku a spodniho siluru prazsk6 panve (Barrandien). Thesis. Geol. Surv. (unpubl., in Czech). Taugourdeau, P. and de Jekhowsky, B., 1960. R6partition et description des Chitinozoaires Siluro-Drvoniens de quelques sondages de la C.R.E.P.S. et de la S.N. Repal au Sahara. Rev. Inst. Fr. Prt., 15: 1199-1260. Turek, V., 1989: Comments to upper Wenlock zonal subdivision in the Silurian of Central Bohemia. Cas. Mineral. Geol., 35:337 353. Verniers, J., 1982. The Silurian chitinozoa of the Mehaigne area (Brabant Massif, Belgium). Belg. Geol. Dienst Prof. Pap., 192: 1-76.
Review of Palaeobotany and Palynology86 (1995) 135-145
REVIEW OF PALAEOBOTANY AND PALYNOLOGY
Chitinozoans from the Sheinwoodian/Homerian boundary beds (Wenlock) in the Prague Basin (Barrandian, Bohemia) Pavel Dufka Czech Geological Survey, Kl~rov 131/3, 118 21, Praha 1, Czech Republic Received 15 January 1993; revised and accepted 15 August 1993
Abstract
Sixteen chitinozoan taxa are identified in samples from the Sheinwoodian/Homerian boundary beds (Wenlock, Silurian) of the Kosov quarry (section 767) in the Prague Basin, Bohemia. Their stratigraphical range is correlated with graptolite data in the studied section. The distribution of some Wenlock index chitinozoan species (e.g. Cingulochitina cingulata, Gotlandochitina martinssoni, Conochitina gracilis) in section 767 is compared with their distribution in other regions around the world. The paleogeographic affinities of the Wenlock chitinozoans from the Prague Basin and the Baltica paleocontinent are stressed.
1. Introduction
In a preliminary study of the Lower Silurian chitinozoans of the Prague Basin (Dufka, 1992a), eleven chitinozoan taxa were reported from upper Wenlock strata. Two informal chitinozoan biozones (I and J) were proposed for various chitinozoan assemblages recorded in the upper Sheinwoodian and lower Homerian samples. The present study, based on more detailed sampling, focuses on chitinozoan distribution around the Sheinwoodian/Homerian boundary. The sampling was conducted in the large Kosov quarry near Beroun, Bohemia. Thirty-eight samples have been taken from both sides of the Sheinwoodian/Homerian boundary in section No. 767 exposed in the lower part of the quarry (see KfiZ, 1992, fig. 38 for sketch map). The section is represented by a continuous sequence of graptolite-bearing black shales with sporadic lenses of micritic limestone (Fig. 1). Numerous graptolite records in this section (Turek, 1989; Kfi~, 1992; Storch, 1992) provide a very good chronostrati0034-6667/95/$9.50© 1995ElsevierScienceB.V. All rights reserved SSDI 0034-6667(94)00102-P
graphic control (M. belophorus to C. lundgreni graptolite Biozones) to the samples investigated for chitinozoans (Fig. 1). All the processed samples yielded chitinozoans. The abundance and the diversity of the chitinozoans are generally higher with regard to those of other chitinozoan assemblages of similar age from the Prague Basin (Dufka, 1992a). The abundance of the chitinozoans in the shales ranges from several hundreds to 2000 specimens per gram of rock. Chitinozoans are badly preserved in shales and moderately preserved in micritic limestone. The fine processes and ornamentation of the majority of the thin-walled Lagenochitinidae forms as well as the carina of Cingulochitina genus are destroyed. Only one of 10,200 recorded specimens displays a morphological anomaly, represented by the bulging of an extremely elongate neck (Angochitina cf. echinata, sample No. 767/3). The ratio of chitinozoan malformations corresponds approximately to the general rate estimated by Jaglin and Paris (1992). Five chitinozoan taxa are reported for the first
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P. Dufka/Reviewof Palaeobotanyand Palynology86 (1995) 135-145 time in the Prague Basin and among them, two are particularly important for global biostratigraphic correlation, i.e. Cingulochitina cingulata and Gotlandochitina martinssoni. The other organic particles obtained by a separation with the 53 #m sieve are amorphous kerogen, fragments of graptolites, prasinophycean-like sphaeromorphs, scolecodonts, mazuelloids and different incertae sedis. Mazuelloids and scolecodonts were counted and their abundance is expressed in a number of specimens per gram of rock (Fig. 1).
2.1 List of species Aneyrochitina gr. ancyrea (Eisenack, 1931) (Plate I, 1)) Ancyrochitina primitiva Eisenack, 1964 (Plate I, 2) Ancyrochitina sp. A (Plate I, 8) Calpiehitina (Densichitina) sp. A (Plate II, 5) Cingulochitina sp. A (Plate I, 10, 11) Cingulochitina sp. B (Plate I, 6) Cingulochitina cingulata (Eisenack, 1937) (Plate I, 5,9) Conochitina cf. proboscifera Eisenack, 1937 Conochitina gracilis Laufeld, 1974 (=C. proboscifera forma gracilis) (Plate II, 10) Conoehitina tuba Eisenack, 1932 (Plate II, 12, 13) Gotlandochitina martinssoni Laufeld, 1974 (Plate I, 7) Linochitina cf. odiosa Laufeld, 1974 Linochitina cf. erratica (Eisenack, 1931) (Plate II, 1,2,9) Margachitina margaritana (Eisenack, (Plate II, 8, 11) ?Urnoehitina sp. A (Plate II, 3, 4, 6, 7)
Genus Urnoehitina Paris, 1981 Type: Desmochitina? urna Eisenack, 1934 ?Urnochitina sp. A (Plate II, 3, 4, 6, 7) Material: 65 three-dimensional (undeformed) specimens recorded in section Kosov-767, samples 767/31A, 767/31B, 767/32; T. testis Subzone. Dimensions: Based on 27 specimens. Measurements in/~m. Mean Range
2. Systematics
1937)
2.2 Description of selected taxa Order VROSOMATIFERAEisenack, 1972 Family DESMOCHITINIDAEEisenack, 1931; emend. Paris, 1981 Subfamily ~AR~ACmTrNINAE Paris, 1981
137
L 244 200-288
Dp 137 102- 166
Dc 78 65-100
Description: Vesicle with club to pear-shaped chamber; flexure and neck inconspicuous; short flaring collarette bordering the flat operculum. The basal margin is inconspicuous; base either flat with simple, narrow and low tim-like mucron or convex with a more distinct conical mucron. The mucron termination, usually uneven, suggests its partial destruction. Ornamentation consists of thin ruggae, irregularly convoluted or arranged more or less in a polygonal pattern (Plate II, 7). The ornamentation developed mainly on the anteapertural part of vesicle and fades away towards the aperture (Plate II, 3). Discussion: The characteristics of the individuals tentatively named ?Urnochitina sp. A do not compare with any generic definition. They cannot be assigned to Conochitina, due to the presence of an operculum, nor to Eisenackitina because of the absence of an echinate ornamentation, nor to Bursachitina because ?Urnochitina sp. A has usually a much more slender vesicle. Although neither distinct pedunculate copula nor chain-structure have been observed in these forms, they are referred herein to the genus Urnochitina in considering that a break-up of the copula of some specimens cannot be completely excluded. Furthermore, the generic classifications of several other Wenlock species are similarly not clearly defined, for example Conoehitina lagena from Estonia (Nestor, 1982, pl. 17, fig. 9), Conochitina gutta (Laufeld, 1974, fig. 25), and Kalochitina scabra (Schweineberg, 1987, pl. 8, figs. 3B, 4B). If
P. DuJka/Review of Palaeobotany and Palynology 86 (1995) 135 145
138
PLATE I
I
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J
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P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135-145
well-preserved, these species exhibit a club-like chamber, distinct low mucron and characteristic chamber ornamentation ranging from rugulatereticulate (C. gutta, Urnochitina sp. A) to meshlike (C. lagena, K. scabra). The listed characteristics suggest that a new genus within the subfamily Eisenackitininae including these taxa would be useful. Genus Linochitina Eisenack, 1968 Type: Desmochitina erratica Eisenack, 1931 Linochitina cf. erratica (Eisenack, 1931 ) (Plate II, 1,2,9) Material: 940 specimens recorded in section Kosov-767, samples 767/13-766/32 (Fig. 1); C. perneri/C, ramosus Zone-T. testis Subzone. Dimensions: Based on 53 three-dimensional specimens and 120 flattened specimens, flattening corrected for Dc and Dp values by multiplying with a 0.7 coefficient. Measurements in #m. Mean Range
L Dp 184 45 142-256 38-53
Dc 33 30-40
139
Linochitina odiosa (Laufeld, 1974, p. 101) through the holotype of L. erratica (Eisenack, 1931, p. 92, L / D p = 3 ) to extremely long specimens of Linochitina sp. (Dufka, 1992a, pl. 3, fig. 6, L/Dp>4). Thus, based on this parameter Linochitina cf. odiosa is separated from L. cf. erratica rather artificially (Fig. 2). With reference to some previous discussions on Linochitina (Paris et al., 1981, p. 19; Schweineberg, 1987, pp. 31-32) the new data from the upper Wenlock of the Prague Basin indicate a close relationship, corresponding probably to intraspecific variations, between the Silurian species l. odiosa, L. erratica and L. klonkensis, with exception of the types with more or less distinct carina from Gotland (Laufeld, 1974, fig. 59) and from Estonia (Nestor, 1982, pl. 17, fig. 3). Subfamily PTEROCHITININAEParis, 1981 Genus Cingulochitina Paris, 1981 Type: Desmochitina cingulata Eisenack, 1937
Lcop 15-32
Description and remarks: Slender, elongated Linochitina distinctly varying in the vesicle length (L), however, the chamber diameter (Dp) is rather invariable. The L/Dp variations of herein described forms (Fig. 2) ranges continuously from typical
Cingulochitina sp. A (Plate I, 10, 11 ) Material: 393 flattened specimens recorded in section 767-Kosov, samples 767/la-767/4 (Fig. 1); M. belophorus-C, rigidus Zones. Dimensions: Based on 56 flattened specimens. Measurements in #m (Dp and Dc values corrected
PLATEI Wenlock chitinozoans of the Prague Basin. Section 767 of the Kosov quarry. Ancyrochitina gr. ancyrea (Eisenack). C. radians Biozone, sample 767/23, slide GSP-215. x 400. 1. Ancyrochitina primitiva Eisenack. C. radians Biozone, sample 767/20, slide GSP-209. × 350. 2. Angochitina cf. echinata Eisenack. C. rigidus Biozone, sample 767/I, slide GSP-164. 3,4. x 300. 3. x 350. 4. Cingulochitina cingulata (Eisenack). 5,9. C. rigidus Biozone, sample 767/2, slide GSP-241. x 400. 5. 9. C. radians Biozone, sample 767/25, slide GSP-221. x 350. Cingulochitina sp. B. C. rigidus Biozone, sample 767/lc, slide GSP-156. x400. 6. Gotlandochitina martinssoni Laufeld. C. perneri/C, radians Biozone, sample 767/7. x 325. 7. Ancyrochitina sp. A. C. perneri/C, ramosus Biozone, sample 767/6, slide GSP-179. x 350. 8. 10, 11. Cingulochitina sp. A. C. rigidus Biozone, sample 767/lf, slide GSP-164. x 350. 12. Linochitina cf. odiosa Laufeld. C. radians Biozone, sample 767/25, slide GSP-221. x 300.
P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135-145
140
PLATE II
3
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. ~j,~iii •
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P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135-145
141
Dp 60 #
t, 30
i
"-'_I il,::,,,~, , ~air'll "-'-';" .r,'|n?'" ~ ~ • IIIlll • I I "~I
Linochitina of. odiosa
Linochitina cf. erratica
(31)
0
I
0
(160)
J
IO0
I
200 M
I
k
Fig. 2. Diagram showing the variations of the chitinozoan vesicle length (L) with regard to the chamber diameter (Dp) of Linochitina cE odiosa Laufeld and Linochitina cf. erratica (Eisenack) in section 767 of the Kosov Quarry, Wenlock (Silurian), Prague Basin.
with the coefficient for restoring of original volume). Mean Range
L 194 170-260
Dp 43 34-49
Dc 36 31-44
Descr~t~n: Very slender Cingu~chitma
with slightly flexuous flanks about a half of the vesicle length. L/Dp ratio is more then 4 (average 4.5). Occurrence of a ring bordering the basal margin; however, no complete membranous carina has been observed in the available material similarly
as further morphological elements (operculum, collarette, anapertural mark). No twins nor chain-like structures have been observed. Discussion: The chamber outline, as well as the position of the carina in this species recalls Cingulochitina sp. aft. convexa described by Paris (1981, pp. 165-166) from the upper Wenlock of the Bugaco Formation, but Cingulochitina sp. A is longer (170-260/zm against 109 166 #m for C. sp. aft. convexa). In contrast, Cingulochitina sp. A is shorter and provided with a thinner wall when compared to a closely related form
PLATE II Wenlock chitinozoans of the Prague Basin. Section 767 of the Kosov quarry. Linochitina cf. erratica (Eisenack). C. radians Biozone, sample 767/23. 1,2,9. 1. Slide GSP-215. x 350. 2,9. Slide GSP-216. × 350. 3 , 4 , 6 , 7 . ?Urnochitina sp. A. T. testis Biozone, sample 767/31b. Slide GSP-238. x 250. 3. Slide GSP-239. × 250. 4,6,7. Calpichitina (Densichitina) sp. A. 72 testis Biozone, sample 767/31b, slide GSP-238. x 300. 5. 8,11. Margachitina margaritana (Eisenack). C. radians Biozone, sample 767/27, slide GSP-239. x 300. 8. 11. 7: testis Biozone, sample 767/32, slide GSP-242. x 350. 10. Conochitina gracilis Laufeld. C. perneri/C, ramosus Biozone, sample 767/12, slide GSP-194. x 200. 12, 13. Conochitina tuba Eisenack. 12. C. radians Biozone, sample 767/23, slide GSP-216. × 250. C. perneri/C, ramosus Biozone, sample 767/7, slide GSP-182. × 250. 13.
P. Dujka/Review of Palaeobotany and Palynology 86 (1995) 135-145
142
(Cyathochitina [ = Cingulochitina] sp. E), described by Schweineberg (1987, p. 86) from the Las Arroyacas Formation (upper Wenlock) in Spain.
by Schweineberg (1987, p. 84, fig. 6) from the Las Arroyacas Formation (upper Wenlock) in Spain.
Cingulochitina sp. B (Plate I, 6)
3. Biostratigraphy
Material: 286 flattened specimens recorded in section 767-Kosov; samples 767/la-747/4 (Fig. 1); M, belophorus-C, rigidus Zones. Dimensions: Based on 50 flattened specimens. Measurements in #m (Dp and Dc values corrected with the coefficient for restoring the original volume).
Long-ranging taxa of Ancyrochitina, e.g. Ancyrochitina ancyrea and Ancyrochitina primitiva,
Mean Range
L 166 147-192
Dp 53 49-60
Dc 40 34-47
Description: Most specimens have distinctly curved flanks (=originally slight flexure accentuated by flattening) and a widened aperture. The basal margin is ornamented by a short carina (probably partly destroyed). The vesicle surface is smooth. The base is usually destroyed and gone. Therefore, the anteapertural mark is indistinguishable. No specimens in chains have been observed. Remarks: Cingulochitina sp. B is longer than C. cingulata and less slender than Cingulochitina sp. A (see Fig. 3). Cingulochitina sp. B is very similar to Cyathochitina sp. C (= Cingulochitina) described
occur throughout section 767 of Kosov quarry. Margachitina margaritana, already reported from the C. murchisoni and T. testis graptolite zones (Wenlock) of the Prague Basin (Dufka, 1992a), occurs also sporadically from the base up to the top of the section. Conochitina tuba is not considered to be a significant index taxon for the Wenlock of the Prague Basin, due to frequent occurrence of transitional forms between this species and Conochitina cf. proboscifera (in the upper Sheinwoodian) and Conochitina claviformis (in the Homerian). Following chitinozoan taxa are proposed for Wenlock biostratigraphy of the Prague Basin: Cingulochitina sp. A, Cingulochitina sp. B,
Conoehitina gracilis, Cingulochitina cingulata, Gotlandochitina martinssoni, Linochitina cf. erratica and ?Urnochitina sp. A. (Fig. 1). Cingulochitina sp. A and Cingulochitina sp. B are commonly found in samples from M. belophorus and C. rigidus graptolite zones. Their preserva-
Cingulochitinasp. B
Dp
90
60
mmj ~*==~= "~=",~ f _ 1 Cingulochitinasp. A
Cingulochitinacingulata (82)
(56) 30 FLATTENED SPECIMENS t
o
i
lOO
~
I
2oo g
t
L
Fig. 3. Diagram showing the variations of the chitinozoan vesicle length (L) with regard to the chamber diameter (Dp) of Cingulochitina cingulata, Cingulochitina sp. A and Cingulochitina sp. B in section 767 of the Kosov quarry, Wenlock (Silurian), Prague Basin.
P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135 145
tion does not allow a good comparison with similar carina-bearing chitinozoans from other regions, except for some forms of Cyathochitina (= ?Cingulochitina) from the upper Wenlock in Spain (Schweineberg, 1987) which show some similarities with specimens from the Prague Basin (for details, see systematics). Extremely long and slender forms of Conochitina (L = 600-1100 /ira, L/Dp> 10), assigned herein to Conoehitina graeilis, range from the base of C. rigidus Zone to upper part of C. perneri/C, ramosus Zone in the section 767. Elsewhere in the basin, they are known only from the C. perneri/C, ramosus zone (Dufka, 1992a). In Gotland, where C. gracilis was originally described by Laufeld (1974, pp. 71-72), its occurrence is restricted to the basal Sheinwoodian in the Upper Visby beds and in the lowermost part of the Hogklint Beds. In the same area Conochitina leptosoma, a very similar species, ranges stratigraphically from the horizon with the last occurrence of C. gracilis up to the top of the Hogklint Beds (?rigidus Zone). Descriptions of both species suggest that their morphological diversity could correspond to intraspecific variations of a single species. Conochitina cf. leptosoma from lower Sheinwoodian of Estonia (Nestor, 1982, pl. 14, figs. 7, 8) which displays some morphological features common for both C. leptosoma and C. gracilis from Gotland, could be an intermediate form within the range of these morphological variations. Thus, if we compare the data from Estonia, Gotland and Bohemia, conspicuously elongated types of Conochitina are typical for the Sheinwoodian strata in these regions. The occurrence of closely related Conochitina (e.g. Rhabdochitina cf. minnesotensis, in Taugourdeau and de Jekhowsky, 1960, p. 1230, pl. 10, fig. 134) in the Lower Silurian subsurface sequences from Algeria suggests the wide distribution of this taxon. Cinguloehitina eingulata appears for the first time in sample 767/3 of the studied section in the upper part of the C. rigidus Zone and occurs in small number in all samples of the lower part of the C. perneri/C, ramosus Zone. In the Homerian, it was found only in two samples of the C. radians Subzone (767/25-26), but there it is rather abundant. The first occurrence of C. cingulata in the Prague Basin coincides with the first record of this
143
species from the mid-upper Sheinwoodian of Gotland (Laufeld, 1974), Estonia (Nestor, 1990), Great Britain (Doming, 1981), Belgium (Verniers, 1982) and also Libya and Algeria (Paris, unpubl. data). The absence of Cingulochitina around the Sheinwoodian/Homerian boundary and above the C. radians Zone in the section 767, as well as in other upper Wenlock sections in the Prague Basin (Dufka, 1992a; Kfi2 et al., 1993) could be related to the shallowing of the basin due to tectonic and volcanic activity as well as to eustatic movements (see Kfi2, 1991). This interpretation follows previous hypotheses that Cingulochitina is a genus indicating a deep water environment (Rombouts, 1978; Verniers, 1982). Gotlandochitina martinssoni occurs exclusively in samples (767/5-15) from the C. perneri/C, ramosus (= C. ellesae) graptolite Zone of the Prague Basin. It is a good marker of the upper Sheinwoodian and seems suitable for correlation between Bohemian and Baltic assemblages from Estonia (Nestor, 1990), Gotland (Laufeld, 1974) and England (Dorning, 1981). The genus Linochitina appears in the Prague Basin just below the Sheinwoodian/Homerian boundary (sample 767/12). The slender form referred herein to Linochitina cf. erratica is typical for chitinozoan assemblages of the C. lundgreni Zone in section 767. The occurrence of this form in this zone was already reported from several other localities in the basin (Eisenack, 1934; Dufka, 1992a; K~i2 et al., 1993). Linochitina erratiea is well known from Silurian strata both from Gondwana and Baltica (see Schweineberg, 1987, p. 31), but, in my opinion, the use of this species for interbasinal correlation is rather limited because of its confusing morphology and, therefore, an unclear taxonomy. ?Urnochitina sp. A was recovered in a studied section from the T. testis Subzone. It is so far the only occurrence of this species in the Prague Basin. Nevertheless, at least two other upper Wenlock forms, questionable Conochitina lagena from Estonia (Nestor, 1982, 1990) and Kalochitina scabra from Spain (Schweineberg, 1987), indicate a close generic affinity with ?Urnochitina sp. A.
144
P. Dufka/Review of Palaeobotanyand Palynology86 (1995) 135-145
and differ from each other only in complexity of surface ornamentation.
4. Conclusions Based on a recent study of section 767 in the Kosov quarry, the change in chitinozoan assemblages close to the Sheinwoodian/Homerian boundary of the Prague Basin appears to be less obvious than assumed previously (Dufka, 1992a,b). In fact, this boundary (= first occurrence of C. lundgreni in section 767) is characterized only by the disappearance of Gotlandochitina martinssoni. Linochitina cf. erratica, a fairly good marker for the lower Homerian of the basin, appears already in samples of the C. perneri/ C. rarnosus Zone. Two Wenlock index chitinozoan species are reported for the first time from the Prague Basin: Cingulochitina cingulata ranges from the C. rigidus Zone to the C. radians Zone, and Gotlandochitina martinssoni is restricted to the C. perneri/C, ramosus (= C. ellesae) Zone. The following remarks on the correlation and paleogeography of middle and upper Wenlock chitinozoans from the Prague Basin (Dufka, 1992a; KfiZ et al., 1993) take into account restrictions concerning the bad preservation of chitinozoans within the black shale facies in some regions (e.g. Bohemia and the Brabant Massif), poor independent biostratigraphic control of some North Gondwana chitinozoan assemblages (Algeria; northern Spain, Province of Leon; Florida; Brazil) and a lack of data on chitinozoans from regions paleogeographically related to the Prague Basin (e.g. Carnic Alps and Sardinia). Based on species spectra, the chitinozoan assemblages from the Prague Basin are characterised by (1) the c o m m o n presence of cosmopolitan species
(A. ancyrea, A. primitiva, M. margaritana, C. tuba, C. pachycephala, A. cf. echinata); (2) the occurrence of some Baltoscandinavian species (G. martinssoni, C. cingulata); and (3) the scarcity of typical N o r t h G o n d w a n a species, particularly of the genera Tanuchitina and PIectochitina. Only Cingulochitina sp. A and Cingulochitina sp. B exhibit some similarities with upper Wenlock cin-
gulate chitinozoans from Spain (Schweineberg, 1987). An additional characteristic feature of all Lower Silurian chitinozoan assemblages from the Prague Basin is the absence of distinct "endemic" species. Paleogeographical affinities of middle and upper Wenlock chitinozoans from the Prague Basin, just like those of Llandovery chitinozoans (Dufka, 1992a; D u f k a and Fatka, 1995) and acritarchs (e.g. Dufka, 1990, pp. 88, 93) in this region, indicate the intermediate position of the Prague Basin between the Gondwana and Baltica paleocontinents (see also Paris, 1993; Paris et al., 1995). Free exchange of paleoplankton between the Prague Basin and the Baltica's shelf seas is evident from the similar stratigraphic range of some species as well as of one genus (Cingulochitina).
References
Dorning, K.J., 1981. Silurian Chitinozoa from the type Wenlock and Ludlow of Shropshire, England. Rev. Palaeobot. Palynol., 34: 205-208. Dufka, P., 1990. Acritarchs of the Monograptus sedgwickii Zone (Zelkovice Formation, Llandovery) from Hyskov, Barrandian, Bohemian Massif. Acta Univ. Carol. Geol., 1990(1): 75-104. Dufka, P., 1992a. Lower Silurian chitinozoans of the Prague Basin (Barrandian, Czechoslovakia)-Preliminary results. Rev. Micropal6ontol., 35:117--126. Dufka, P., 1992b. Chitinozoansof the Sheinwoodian/Homerian boundary interval (Silurian) in the Prague Basin. 8th IPC, Aix-en-Provence, Abstr., p. 39. Dufka, P. and Fatka, O., 1993. Chitinozoans and acritarchs from the Ordovician Silurian boundary of the Prague Basin (Barrandian Area, Czechoslovakia). Spec. Pap. Palaeontol., 48: 17-28. Eisenack, A., 1934. Neue Mikrofossilien des baltischen Silurs III und neue Mikrofossilien des bohmischen Silurs I. Palaeontol. Z., 16: 52-76. Jaglin, J. and Paris, F., 1992. Examples de t6ratologie chez des Chitinozoaires du Pridoli de Libye et implications sur la biologie du groupe. Lethaia, 25: 151-164. Kfi~, J., 1991. The Silurian of the Prague Basin (Bohemia) tectonic, eustatic and volcanic controls on facies and faunal development. Spec. Pap. Paleontol., 44: 179-203. Kf%, J., 1992. Silurian field excursions: Prague Basin (Barrandian) in Bohemia. Natl. Mus. Wales Geol. Ser., 13, 111 pp. Kf'i~, J., Dufka, P. and Sch6nlaub, H.P., 1993. Wenlock Ludlow boundary in the Prague Basin, Bohemia. Jahrb. Geol. B. Wien, 136 (4): 809-839
P. Dufka/Review of Palaeobotany and Palynology 86 (1995) 135-145 Laufeld, S., 1974. Silurian Chitinozoa from Gotland. Fossils Strata, 5: 1-130. Nestor, V., 1982. Chitinozoan zonal assemblages (Wenlock, Estonia). In: D. Kaljo and E. Klaamann (Editors), Communities and Biozones in the Baltic Silurian. Valgus, Tallinn, pp. 84-97 (in Russian). Nestor, V., 1990. Silurian chitinozoans. In: D. Kaljo and H. Nestor (Editors), Field Meeting Estonia, 1990, an Excursion Guidebook. IUGS, Subcomm. Ordovician Silurian Stratigr., pp. 80-83. Paris, F., 1981. Les Chitinozoaires dans le Pal~ozoique du Sud-Ouest de l'Europe (Cadre grologique-Etude systrmatique-Biostratigraphie). Mrm. Soc. Grol. Minrr. Bretagne, 26: 1-412. Paris, F., 1993. Evolution pal~ogrographique de l'Europe au Palrozoique infrrieur: le test des Chitinozoaires. C.R. Acad. Sci. Paris, 316: 273-280. Paris, F., Laufeld, S. and Chlup~ir, I., 1981. Chitinozoa of the Siluria~Devonian boundary stratotypes in Bohemia. Sver. Geol. Unders. C, 51: 1-29. Paris, F., Verniers, J., AI Hajri, S. and Al-Tayyar, H., 1995.
145
Biostratigraphy and palaeogeographic affinities of Early Silurian chitinozoans from central Saudi Arabia. Rev. Palaeobot. Palynol., 89: in press. Rombouts, L.P., 1978. Factors controlling the distribution of Chitinozoa in the Gleedon chronozone (Wenlockian) of northern Europe. Ann. Soc. Geol. Belg., 105: 259-271. Schweineberg, J., 1987. Silurische Chitinozoen aus der Provinz Palencia (Kantabrisches Gebirge, N-Spain). G6tt. Arb. Geol. Paleontol., 33: 1-94. Storch, P., 1992. Facialni vyvoj, stratigrafie a korelace svrchniho ordoviku a spodniho siluru prazsk6 panve (Barrandien). Thesis. Geol. Surv. (unpubl., in Czech). Taugourdeau, P. and de Jekhowsky, B., 1960. R6partition et description des Chitinozoaires Siluro-Drvoniens de quelques sondages de la C.R.E.P.S. et de la S.N. Repal au Sahara. Rev. Inst. Fr. Prt., 15: 1199-1260. Turek, V., 1989: Comments to upper Wenlock zonal subdivision in the Silurian of Central Bohemia. Cas. Mineral. Geol., 35:337 353. Verniers, J., 1982. The Silurian chitinozoa of the Mehaigne area (Brabant Massif, Belgium). Belg. Geol. Dienst Prof. Pap., 192: 1-76.