The Pragian-Emsian conodont successions of the Barrandian area: search of an alternative to the GSSP polygnathid-based correlation concept

Geobios 37 (2004) 454–470 www.elsevier.com/locate/geobio

The Pragian-Emsian conodont successions of the Barrandian area: search of an alternative to the GSSP polygnathid-based correlation concept La succession de conodontes du Praguien à l’Emsien dans le Barrandien : recherche d’une alternative au concept de corrélation du GSSP basée sur des Polygnathides Ladislav Slavík Institute of Geology, Academy of Sciences of the CR, Rozvojova 135, CZ-16502 Praha 6, Czech Republic Received 19 December 2002; accepted 25 May 2003

Abstract Six Pragian-Emsian boundary sections in the Barrandian area, western of Prague, provided evidence of well detectable entries of Latericriodus fauna probably at the earliest Emsian beds (particularly Latericriodus bilatericrescens gracilis Bultynck). The chance to find icriodontid conodonts increases with latest part of Praha Fm., which is apparently of Emsian age, whereas polygnathids are sparsely preserved to absent. The high icriodontid/polygnathid ratio links together all these Barrandian sections, although their open-sea depositional environments range widely from deep troughs with rapid calciturbidite accumulation (Pod Barrandovem section) to relatively starving slope environments on elevations (Na Požárech sections). The reports on polygnathid occurrences around the Pragian-Emsian boundary beds of the Barrandian area are much biased by poor reproducibility of the results (the conodonts cannot be found again) as well as by different levels where they were randomly found and/or by major taxonomic problems with the “kitabicus” and “dehiscens” definitions and their stratigraphic use. Apart from the GSSP in the Zinzilban Gorge (Uzbekistan) and its “kitabicus” boundary, the newly introduced “gracilis” biostratigraphic-marker concept preserves the major volume of the Pragian and respects also approximately the base of the traditional Emsian. These “gracilis” entries are clustered around the dark-colored “graptolite-bearing interval” beds, which largely form a prominent lithological marker within the latest, light gray-colored Dvorce-Prokop Limestone of the Barrandian area. This “gracilis” biostratigraphic marker has a promising correlation potential relative to Spanish and Moroccan sections. © 2004 Elsevier SAS. All rights reserved. Résumé Six coupes de la limite Praguien-Emsien de l’aire Barrandienne, à l’ouest de Prague, mettent en évidence l’entrée des faunes à Latericriodus probablement dans les tout premiers niveaux emsiens (en particulier Latericriodus bilatericrescens gracilis Bultynck). La probabilité de trouver des conodontes icriodontides augmente dans la partie la plus haute de la Formation Praha, présumée d’âge Emsien, alors que les polygnathides y sont rares ou absents. Un rapport élevé d’Icriodontide/Polygnathide est commun à ces coupes barrandiennes, bien que leur environnement de dépôt de mer ouverte aille de fossés profonds caractérisés par des accumulations rapides de calciturbidites (Coupe Pod Barrandovem) à des environnements de talus sur des points hauts (Coupes de Na Požárech). Les occurrences de Polygnathides autour des bancs de la limite Praguien-Emsien de l’aire Barrandienne sont biaisées par la mauvaise reproductibilité des résultats. En effet les conodontes ne sont pas toujours retrouvés, ils peuvent aussi être représentés de façon aléatoire selon les niveaux et/ou leur détermination se heurte à des problèmes taxonomiques majeurs tels que les définitions de « kitabicus » et « dehiscens » et de leur utilisation stratigraphique. En dehors du GSSP de « Zinzilban Gorge » (Ouzbekistan) et de sa limite à « kitabicus », le nouveau concept biostratigraphique « gracilis » préserve

E-mail address: [email protected] (L. Slavík). © 2004 Elsevier SAS. All rights reserved. doi:10.1016/j.geobios.2003.05.002

L. Slavík / Geobios 37 (2004) 454–470

455

l’intégralité du Praguien et respecte approximativement la base du traditionnel Emsien. Les entrées de « gracilis » sont regroupées autour des « bancs foncés à Graptolites », qui forme un marqueur lithologique au sein du calcaire gris clair de « Dvorce-Prokop » de l’aire Barrandienne. Ce marqueur biostratigraphique « gracilis » montre donc un potentiel de corrélation prometteur pour les coupes d’Espagne et du Maroc. © 2004 Elsevier SAS. All rights reserved. Keywords: Conodonts; Lower Devonian; Biostratigraphy; Pragian/Emsian GSSP; Barrandian Mots clés : Conodontes ; Dévonien inférieur ; Biostratigraphie ; Praguien/Emsien GSSP ; Barrandien

1. Introduction The position of the Pragian/Emsian boundary and placement of its GSSP were subject to much discussion, particularly during the years 1989–1996 (cf. Yolkin et al., 1989, 1994), until the IUGS executive ratified the GSSP in the Zinzilban Gorge, Uzbekistan, where the leading correlation horizon should be the base of the kitabicus Zone (Riccardi et al., 1997; Yolkin et al., 1997). Although a taxonomic revision of relevant taxa around the Pragian/Emsian boundary were made (Yolkin et al., 1994), the established GSSP remained still rather problematic having inauspicious impact on the extent of the traditional Pragian and Emsian stratigraphic stages as well as on the quality of biostratigraphic correlation of the respective boundary. Nowadays, it is still clearer that the redefinition of the GSSP is inevitable in the near future. Therefore, all available biostratigraphic data and possibilities must be evaluated and considered prior to the new decision, despite the fact that the conodont record around this stratigraphic level is not very clear yet anywhere. The purpose of this paper is to provide the conodont data from the PragianEmsian boundary intervals from six sections of the Barrandian – the stratotype area of the Pragian stage – and to search for alternative potential correlation conodonts. 2. Pragian/Emsian GSSP – problems with position and conodont correlation The GSSP of the Pragian/Emsian (Pg/Em) boundary has been placed in the Zinzilban Gorge in Uzbekistan. The principal reason for the selection of this point was the hypothesis about phylogenetic succession (lineages) of early polygnathids (cf. Yolkin et al., 1989). The point itself was selected by the Subcommission on Devonian Stratigraphy in 1989 to match the level of the appearance of Polygnathus dehiscens – the supposed phylogenetic descendant of Polygnathus pireneae. Yolkin et al. (1994) established a new GSSP-defining taxon – Polygnathus kitabicus, on the basis of alleged morphological differencies from other polygnathids and systematic uncertainties and problems with the Australian holotype of P. dehiscens. In 1996 the recommendations of the Subcommission on Devonian Stratigraphy (SDS) and International Commission on Stratigraphy (ICS) were ratified by IUGS. The new “kitabicus concept” of Yolkin et al. (1994) for the boundary definition is still discussed by conodont workers

and its acceptance is not universal. Some authors regard P. kitabicus as a junior synonym of P. dehiscens, e.g., Mawson (1995) who considers the holotype of P. kitabicus to be a large specimen of P. pireneae, and the second specimen Figured (Yolkin et al., 1994: Pl. 1, Figs. 3–4) to belong to Polygnathus dehiscens in Australian sense. This is undoubtedly a serious disagreement in the conception of the index taxon. Another important point brought Carls and Valenzuela-Ríos (1999) who showed that the origin of the true P. dehiscens must be even in the middle Zlichovian and that this Australian species could be endemic, being different from much older P. excavatus – the taxon that was formerly often erroneously synonymized with P. dehiscens. However, whether the erection of P. kitabicus is well founded or not, there are also other important problems, that have been expressed recently. Carls and Valenzuela-Ríos (2002a) pointed out, on the basis of inter-regional correlations, that the GSSP lies actually in the early half of the original Pragian. This assertion is underpinned also by the synonymy of P. kitabicus, which occurs concurrently with taxa ranging in the earlier part of the original Pragian and that P. kitabicus is morphologically different from P. dehiscens. However, the roots of the problem are deeper. Even Polygnathus pireneae – alleged antecedent of the GSSP-defining taxon is not so stratigraphically reliable – first appearances are in the lower part of the Pragian in some regions (including the Barrandian), and its origin still unknown (Valenzuela-Ríos, 1997). The consequence of the difficulties mentioned above, apart from other problems, is the practical impossibility to find the end of the originally defined Pragian in its stratotype area and to approach the base of the classical Emsian.

3. Previous studies and constraints for recognition of the Pg/Em boundary in the Barrandian Complicated evolution of the Early Devonian sedimentary environment in the Barrandian area, which is still of primary stratigraphic significance, is documented by high facies diversity of Lower Devonian sediments (Chlupácˇ, 1957; Chlupácˇ et al., 1998), and, what is very distinctive, expressed also in the composition of conodont assemblages. Conodont data have long been deficient in the stratotype area, with the exception of several studies concentrated on stage boundaries (Pr/Lo, Lo/Pg, Pg/Em and Em/Ei) (cf. Klapper et al., 1978; Schönlaub in Chlupácˇ et al., 1985; Weddige, 1987;

456

L. Slavík / Geobios 37 (2004) 454–470

Jeppsson, 1988; Kalvoda, 1995) and two published papers (Slavík, 1998, 2001a) dealing with conodont data from continuous sections throughout the stages. A new regional conodont zonation of the Pragian in the Barrandian area was introduced by Slavík (in press), and this concept is used in the descriptions of the sections. Insufficient illustrations and descriptions of conodont specimens in some of the older papers cause difficulties in their placement within the present nomenclature. Previous conodont studies of the Pg/Em boundary, which faced the problem of scarcity of relevant conodont taxa, were not successful in regard of the location of the boundary. A typical representative of the Pragian stage in the Barrandian area is the Praha Fm., which is overlain by the Zlíchov Ls. (Zlíchovian – early Emsian age). The formation base (as well as the original biostratigraphic base) of the Zlíchovian was situated at the base of the first Kaplicˇka breccia (or Chapel Coral Horizon; cf. the Basal Zlíchovian Event; Chlupácˇ and Kukal, 1986). The corresponding end of the Pragian (in traditional sense) lies significantly higher than any of the first occurrences of taxa previously reported as “Polygnathus dehiscens” or “Po. Kitabicus” in the disputable concept of Yolkin et al. (1994), which lies much below the top of the Praha Fm. Moreover, the scarcity of specimens and dispersion of the first finds of taxa of the genus Polyg-

nathus seem to be a big problem for biostratigraphy around the Pragian/Emsian boundary in this region. A distinct lithological marker – the “graptolite-bearing interval” – and its equivalents split the uppermost portion of the Praha Fm. Unfortunately, this lithologically traceable horizon lies practically within the scatter of the entries of species that were probably erroneously regarded as Polygnathus dehiscens due to confusion in synonymy (cf. data by Kalvoda, Schönlaub and Weddige in Chlupácˇ and Lukeš, 1999) in the individual sections. With regard to the disputable “kitabicus” concept of Yolkin et al. (1994), it is stated here that no Po. kitabicus was found in the Barrandian sections. 4. New investigation – material and methods An extensive investigation of conodonts from the Pg/Em sections of the Barrandian area was undertaken in the past years. This paper presents conodont data from 6 selected sections at the following localities: “Pod Barrandovem” near ˇ eporyje), Praha-Hlubocˇepy, “Na Požárech” (Praha-R “Mramorka” near Chýnice, “Stydlé vody” near Bubovice and “Na Branžovech” near Lodeˇnice (see Fig. 1). The 55 samples produced approximately 200 conodont elements representing 19 taxa. Distribution of the taxa and abundance of conodont elements in samples is shown in detail in Fig. 2.

Fig. 1. A location map showing the outcrops of Pragian rocks and localities with the studied Pragian/Emsian sections situated in the central Barrandian synform. Fig. 1. Carte montrant les affleurements des terrains praguiens et les coupes étudiées du Praguien/Emsien situées sur la synforme Centrale Barrandienne.

L. Slavík / Geobios 37 (2004) 454–470

457

458

L. Slavík / Geobios 37 (2004) 454–470

Low conodont yields in samples (rarely more than 4 elements per 1 kg) are common but the number depends on facies. Accordingly, mostly large samples (from 6 kg to 8 kg) were treated to obtain representative numbers of specimens for biostratigraphic purposes (see Fig. 3). The buffered acetic acid method of Jeppsson et al. (1985) was used for sample dissolution and heavy liquids (tribromomethane and diiodomethane) were utilized for subsequent separation of conodont elements.

5. Studied sections – a brief description 5.1. Pod Barrandovem section The section is a steep quarried slope on the left bank of the Vltava River, on the southern periphery of Prague at Hlubocˇepy. It uncovers Lochkovian, Pragian and Zlíchovian strata. The section is exposed by an old roadcut and by many pits and quarries. The Pg/Zl interval is visible in the U Kaplicˇky Quarry. For detailed descriptions of the locality see Chlupácˇ et al. (1986), Chlupácˇ (1993) and Slavík and Hladil (2000). The Pragian beds represent a rapidly accumulated calciturbidite sequence, with calcisiltitic, lime-mud and pelagic components. Macrofauna is rare, late Pragian part contains thin black shale intercalations with scattered rostoconch and cephalopod shells, and first laminae of cherts appear with decline of the lenticular dissolution fabric. Previous conodont investigation focused only on the Pg/Zl boundary interval. Schönlaub (in Chlupácˇ et al., 1980) reported “Po. dehiscens” and “I. bilatericrescens” from the uppermost part of the Praha Fm., only 4 m below the lower boundary of the Chapel Coral Horizon (Zlíchovian). Conodont distribution from repeated sampling of the Pg/Zl interval is shown on Fig. 4. The upper limit of the celtibericus Zone is defined by the local appearance of the first polygnathids – Po. excavatus Carls and Gandl and Po. sokolovi Yolkin et al. The excavatus Zone is documented herein on the basis of this single occurrence of its name-bearer. These polygnathids occur, however, after thick interval (several tens of meters) without useful conodont record. It is presumable, that icriodontids, similarly like in other sections, should precede the polygnathids, but due to extreme scarcity of conodonts in this section, they have not yet been recorded. Because of that, the conodont data obtained from this section cannot be exhaustive. The complicated synonymy of Polygnathus excavatus in the sense of Yolkin et al. (1994) and differences in understanding

Fig. 3. Number and median weight of samples taken from the studied localities, and GPS location of the sampling sites. Fig. 3. Nombre et poids moyen des échantillons considérés pour chaque localité et localisation GPS des sites échantillonnés.

taxonomy expressed by various conodont workers makes the situation much confused – e.g., Bultynck (1999) regards the lower part of the excavatus Zone to correspond to the upper portion of the former standard dehiscens Zone. Accordingly, in this paper Po. excavatus is considered a form corresponding to Polygnathus webbi excavata described originally from Aragón by Carls and Gandl (1969). The index taxon of the dehiscens Zone – Polygnathus dehiscens dehiscens Philip and Jackson, 1967 (sensu Mawson, 1987) – was not recorded. Although several specimens were reported by Schönlaub (in Chlupácˇ et al., 1980: Pl. 21, Figs. 2–4, 6, 8–17) as Po. dehiscens, they are regarded here, at least by their platform shape, to be forms very close to Po. excavatus (Carls and Gandl). A few of the stratigraphically significant taxa of the Latericriodus bilatericrescens group were recorded in the uppermost part of the “traditional” Pragian (upper parts of the Praha Fm.). Noteworthy is the stratigraphic succession of individual members of this group. Similarly as in the Tafilalt, southern Morocco (Section Jbel Ou Driss; Bultynck, 1985), Latericriodus bilatericrescens gracilis Bultynck occurs at the lowermost position. Latericriodus b. bilatericrescens (Ziegler) was documented several meters higher. A mixed conodont assemblage is present immediately below the

Fig. 2. Presence and quantity of conodont taxa in samples from the Pragian/Emsian intervals of the studied sections. For detailed positions of samples in individual sections see Figs. 4–6 and 8–10. The following abbreviations for conodont genera and species names are used in the table: B. = Belodella; C. = Caudicriodus; L. = Latericriodus; N. = Neopanderodus; Oz. = Ozarkodina; P. = Panderodus; Po. = Polygnathus; b. = bilatericrescens; e. = excavata. Fig. 2. Présence et quantité des taxons de conodonte dans les échantillons Praguien/Emsien des coupes étudiées. La position détaillée des échantillons pour chaque coupe est donnée sur les Figs. 4–6 et 8–10. Abréviations utilisées pour les genres conodontes et nom d’espèces : B. = Belodella ; C. = Caudicriodus ; L. = Latericriodus ; N. = Neopanderodus ; Oz. = Ozarkodina ; P. = Panderodus ; Po. = Polygnathus ; b. = bilatericrescens ; e. = excavata.

L. Slavík / Geobios 37 (2004) 454–470

Fig. 4. Stratigraphical distribution of conodont taxa from the Pg/Em interval of the Pod Barrandovem section with schematic conodont zonation. The following abbreviations for species names are used occasionally throughout the Figs. 4–6 and 8–10: b. = bilatericrescens; e. = excavata; st. = steinhornensis. Fig. 4. Répartition stratigraphique des conodontes de l’intervalle Praguien/Emsien pour la section Pod Barrandovem en fonction de la zonation à conodonte proposée. Abréviations suivantes de noms d’espèces également utilisées pour les Figs. 4–6 et 8–10 : b. = bilatericrescens ; e. = excavata ; st. = steinhornensis.

Chapel Coral Horizon (of Zlíchovian age), combining different forms such as L. b. bilatericrescens, L. b. gracilis, L. b. aff. multicostatus (Carls and Gandl), Ozarkodina steinhornensis miae (Bultynck) and C. celtibericus. Their cooccurrence may be caused by reworking, and exceptional stratigraphical bias is related to small-scale tectonic structures below the base of the Chapel Coral Horizon. 5.2. Na Požárech sections The Požáry Quarries having two instructive Lower Devoˇ eporyje, SW of nian sections lie approximately 1 km E of R Prague. For a detailed description of the section see Chlupácˇ et al. (1986). The locality displays a typical facies development of the Pragian comprising all the principal facies members. In thin sections, most of these facies appear as differentiated but sequentially arranged calciturbidites with dacryoconarids and variable admixture of other reworked bioclasts. Fig. 5 shows a part of the Požár 2 section with

459

Fig. 5. Stratigraphical distribution of conodont taxa from the Pg/Em interval of the Na Požárech sections (Požár 2) with schematic conodont zonation. Fig. 5. Répartition stratigraphique des conodontes de l’intervalle Praguien/Emsien pour la coupe Na Požárech (Požár 2) en fonction de la zonation à conodonte proposée.

occurrences of important conodont species in the upper part of the Praha Fm., which consists mostly of varicolored micrites (Lodeˇnice Ls.) that are overlain by iron–rich nodular ˇ eporyje Ls.). However, only 10 meters of lime–mudstones (R these sediments are accessible in this section. Because of that, the upper part of the Praha Fm. was sampled in a large active quarry named Požár 3 (see Fig. 6), located east of the Požár 2 Quarry. About 1 m thick interval of seven packstone beds with calcareous shale intercalations is present in the uppermost part of the Praha Fm. (see Fig. 7(2)). This horizon has its analogue in several other studied sections (Na Branžovech, Mramorka and Stydlé vody), lying approximately at the same stratigraphic level. In the Stydlé vody section, this interval with dark shales yielded the youngest graptolite fauna in Europe (Boucˇek, 1966; Chlupácˇ et al., 1986), and is therefore named here the “graptolite-bearing interval” or “graptolite event” (Hladil and Kalvoda, 1997). Conodont fauna of the Lo/Pg interval was studied by Weddige (in Chlupácˇ et al., 1986). New data are shown in Figures 3 and 4. Conodont fauna within iron-rich limemudstones is usually very poor throughout Barrandian sections. Latericriodus bilatericrescens gracilis Bultynck and several other stratigraphically significant forms such as Latericriodus bilatericrescens bilatericrescens (Ziegler), C. celtibericus and C. curvicauda has been, however, recorded and enabled the identification of the celtibericus and gracilis zones in the upper part of the section Požár 2. The

460

L. Slavík / Geobios 37 (2004) 454–470

b. bilatericrescens occur in the uppermost parts of the Praha Fm. The occurrence of L. b. bilatericrescens proves that the base of the Dvorce-Prokop Ls. is well in Emsian. 5.3. Mramorka section

Fig. 6. Stratigraphical distribution of conodont taxa from the Pg/Em interval of the Na Požárech sections (Požár 3) with schematic conodont zonation. Fig. 6. Répartition stratigraphique des conodontes de l’intervalle Praguien/Emsien pour la coupe Na Požárech (Požár 3) en fonction de la zonation à conodonte proposée.

occurrence of L. b. gracilis in this section is very important, because this is its lowest position documented in the Barrandian and it may indicate the base of the Emsian in traditional sense. No representative of Polygnathus Hinde was found in the Požár 3 neither in Požár 2 sections. The studied interval of the uppermost beds of the Pragian in the Požár 3 section was predictably very poor in conodonts, however, Ozarkodina steinhornensis miae (Bultynck), C. celtibericus and L.

The Pragian/Zlíchovian boundary is well exposed in the old Mramorka Quarry near the village of Chýnice SW of Prague. The locality was described by Chlupácˇ et al. (1986), Vavrdová (1989), Kalvoda (1995) and Hladil et al. (1996), a.o. The upper part of the Praha Fm. is developed as the Dvorce-Prokop Ls. An equivalent of the “graptolite-bearing interval” is also present several meters below the lower Zlíchovian boundary, within the nodular lime-mudstones. The lowermost Zlíchovian is characterized by the onset of dark gray biomicrites devoid of nodular structure with thin shale intercalations. This 1.9 m thick interval, still bearing typical Pragian tentaculites, is overlain by gray, thickly bedded micritic limestone with cherts, containing Zlíchovian trilobites (Zlíchovian Ls.). Both the Pragian and Zlíchovian successions are represented by calciturbidites but differ in material composition and directions of deposition. The Pragian succession is formed by crinoidal slope debris and lime–mud calciturbidites with dacryoconarids, whereas the Zlíchovian succession is characteristically represented by calcilutitic – calcarenitic calciturbidites, lacking the breccia of the Chapel Coral Horizon. Conodont fauna from the Mramorka section was studied in detail by Kalvoda (1995), who recommended the base of the excavatus Zone sensu Yolkin et al. (1994) as a level for recognition of the lower Emsian boundary in the Barrandian. Several occurrences of conodont taxa were also presented by Chlupácˇ et al. (1986). Both the previous and new conodont data are summarized in Fig. 8. Conodont assemblages obtained from the Dvorce-Prokop Ls. are relatively poor, in spite of the big sizes of samples. Important are the yields of Caudicriodus celtibericus (Carls and Gandl), stratigraphically overlapping with C. curvicauda (Carls and Gandl). The upper boundary of the established celtibericus Zone is identified here by the first occurrence of Latericriodus bilatericrescens gracilis Bultynck, which indicates already the Emsian. The base of the Emsian (in traditional sense) may be expected several meters lower, below the “graptolite event” (cf. Požár 2 and Požár 3 sections). Higher in the section, the range of L. b. gracilis overlaps with Latericriodus bilatericrescens bilatericrescens (Ziegler) and Ozarkodina steinhornensis miae (Bultynck). The first Polygnathus reported by Weddige in Chlupácˇ et al. (1986) appears two meters above the first occurrence of L. b. gracilis in this section. Illustrations of forms reported as Po. dehiscens in Chlupácˇ et al. (1986) are not available and due to other problems with documentation it is difficult to consider these data without reservations. The incomplete specimen Figured as Polygnathus kitabicus by Kalvoda (1995: Pl. 2, Fig. 9) is regarded herein to be most likely Polygnathus excavatus (Carls and Gandl).

L. Slavík / Geobios 37 (2004) 454–470

461

462

L. Slavík / Geobios 37 (2004) 454–470

5.4. Na Branžovech section Lochkovian, Pragian and Zlíchovian rocks are exposed in a large active quarry about 2 km SE of Lodeˇnice near Beroun. The Pragian facies succession is typically complex, comprising the Koneˇprusy, Slivenec, Lodeˇnice, Rˇeporyje and the Dvorce-Prokop Ls. It is similar to that of the Na Požárech section but slightly differs in thickness of the individual members. More detailed description of this section is presented in Slavík (2001a). The previously published conodont data (Slavík, 2001a) are supplemented by results from repeated detailed sampling (Fig. 9). The lowest C. celtibericus was recorded within the Rˇeporyje Ls. It represents the only significant taxon at this stratigraphic level, while the solitary occurrence of Po. pireneae Boersma, 1973 in sample 25B doesn’t allow a definitive age designation (cf. Valenzuela-Ríos, 1997). The presence of the Emsian is proved by appearance of L. b. gracilis in the Dvorce-Prokop Ls., just below the “graptolite-bearing interval”. Therefore the base of the Emsian is presumed again a

few meters below this lithological marker. The uppermost beds of the Praha Fm. also contain C. celtibericus, C. curvicauda and Oz. st. miae. 5.5. Stydlé vody section The Stydlé vody quarry is located 1 km SW of the village of Bubovice. The fauna and lithology of the locality were studied by numerous workers (e.g., Boucˇek, 1966; Chlupácˇ et al., 1986; Kalvoda, 1995). The former quarry exposes a succession of various types of Pragian and Zlíchovian limestones. The studied interval starts with the onset of the micritic Dvorce-Prokop Ls., which is interrupted by several shale intercalations containing the youngest graptolites of Europe (described by Boucˇek, 1966). Sedimentology of this “graptolite-bearing interval” in Mramorka and Stydlé vody sections was studied in detail by Hladil et al. (1996). Conodont occurrences were previously reported by Chlupácˇ et al. (1986) and Kalvoda (1995). Both the previous

Fig. 7. Lithostratigraphy of the Pragian-Zlíchovian outcrops in northwestern limb of the central Barrandian synform. 1. An overall view of the active Požár 3 quarry near Rˇeporyje, situation in June 2001. Lodeˇnice and Slivenec limestone facies (stratigraphic members also) are developed in the south (left). These facies are characterized by scattered to accumulated, abraded and ferruginized crinoid ossicles but the structure is supported with microbial micrite and calcisiltite. Typical are rhythmical occurrences of submarine firmgrounds and/or varicolored laminar bands. The central part of the wall consists of lime-mud to calcisiltitic calciturbidites (micritic beds with abundant dacryoconarids and rare macrofossils – trilobites, cephalopods and gastropods). These Rˇeporyje limestones have typically purple to violet color (particularly if weathered) and serve as a relatively good, although swelling and moderately stratigraphically fluctuating, lithological marker. The dark-colored platy limestone beds and black shales of the “graptolite-bearing interval” separate the medium-gray lime-mud to calcisiltitic calciturbidites of the Dvorce-Prokop limestones into two parts (Dvorce-Prokop 1 and 2). The depositional style and fabrics of these ˇ eporyje Ls. The most typical feature is the presence of chemically altered “carbonate Dvorce-Prokop limestones are very similar to those of the underlying R milk” with flocs of clay minerals and iron oxides; the pronounced diagenetic dissolution produces secondary lenticular fabric (Dvorce type). The onset of the dark gray-colored, platy and cherty Zlíchovian beds is usually (but not unnecessarily) sharp. Fine-grained and well-sorted material of calciturbidites was largely derived from mechanically disintegrated carbonate rocks and fossils; basal Zlíchovian breccias are very rare in this northwestern Barrandian limb (practically absent). Most of the rock features in this “Zlichov” seem to be comparable with the classical Zlichov Ls. in the southeastern limb of the Barrandian (close to ˇ eporyje. The “graptolite-bearing interval” marker did not provide visible graptolite Prague). 2. Lithological detail of the beds in the active Požár 3 quarry near R stems but is very similar to classical outcrop in the Stydlé Vody (Paraple) quarry between Bubovice and Svatý Jan pod Skalou (where Monograptus dubius and M. yukonnesis have been collected). Beds with smooth surfaces consist usually of several distal turbiditic portions of sediment; the increased contents of glauconite and phosphate are also typical. 3. A comparable lithological detail from the Na Branžovech (Branžovy) quarry, which lies twelve kilometers to the WSW, but also in the northeastern limb of the central Barrandian synform – in the same tectonic stripe. Little differences concern the larger thickness of the Dvorce-Prokop 1 limestones, smaller thickness of these eight “graptolite-bearing interval” beds, and ostensibly gradual change in the upper Dvorce-Prokop-2 limestone facies toward the “Zlíchov” facies. The proper onset of the Zlíchov limestones is relatively sharp but not distinctly visible in detail. Fig. 7. Lithostratigraphie des affleurements du Praguien/Zlíchovien en bordure NO de la synforme centrale Barrandienne. 1. Vue générale de la carrière Požár ˇ eporyje en juin 2001. Les faciès calcaires de Lodeˇnice et Slivenec (membres stratigraphiques aussi) sont développés au Nord (gauche). Les 3 en activité près de R faciès sont caractérisés par des ossicles de crinoïde ferrugineux dispersés ou agglomérés mais une matrice micrite microbienne ou calcisilteuse. La présence régulière de sédiments indurés et de bandes laminées est typique. La partie centrale consiste en des calciturbidites (bancs micritiques avec d’abondantes ˇ eporyje sont de couleur pourpre à violet dacryoconarides et quelques rares macrofossiles (trilobites, céphalopodes et gastéropodes). Les calcaires R (particulièrement s’ils sont altérés) et peuvent être utilisés comme un repère lithologique fiable même s’ils fluctuent un peu sur le plan stratigraphique. Les bancs calcaires foncés en plaquettes et les schistes noirs de l’intervalle à graptolites séparent les boues carbonatées gris-clair et des calciturbidites silteuses des ˇ eporyje Ls. La calcaires Dvorce-Prokop en 2 parties (Dvorce-Prokop 1 et 2). Le type de dépôt et les fabriques de ces calcaires sont semblables à ceux de R caractéristique principale est la présence de « lait carbonaté » chimiquement altéré avec des flocons de minéraux argileux et d’oxyde de fer. La dissolution diagénétique prononcée induit une fabrique lenticulaire secondaire (de type Dvorce). La mise en place des bancs gris foncés du Zlíchovien est généralement (mais pas nécessairement) brutale. Les calciturbidites à grains fins et à matériel bien trié sont dérivées de la désagrégation mécanique des roches carbonatées et des fossiles ; les brèches de la base de Zlíchovien sont très rares voir absentes sur la bordure NO barrandienne. La plupart des caractéristiques de ces roches de « type Zlichov » sont comparables au classique Zlichov Ls, en bordure SE de la zone barrandienne (près de Prague). 2. Détails lithologiques des bancs de la ˇ eporyje. L’intervalle à graptolite n’a pas fourni de graptolites mais il est similaire à celui de l’affleurement classique de la carrière en activité Požár 3 près de R carrière de Stydlé Vody (Paraple) entre Bubovice et Svatý Jan pod Skalou (Monograptus dubius et M. yukonnesis ont été récoltés). Les niveaux avec les surfaces lissées sont généralement composés de sédiments turbiditiques distaux. L’augmentation en glauconie et phosphate est également caractéristique. 3. Détail lithologique comparable de la carrière Na Branžovech (Branžovy), qui s’étend sur 12 km vers l’OSO mais également sur la bordure NE de la synforme Barrandienne dans le même contexte tectonique. Les légères différences observées sont la plus grande épaisseur des calcaires Dvorce-Prokop 1, la plus petite épaisseur des 8 intervalles à graptolites et le changement graduel dans la partie supérieure d’un faciès calcaire Dvorce-Prokop-2 à un faciès « Zlíchov ». La mise en place des calcaires « Zlíchov » est relativement brutale mais pas visible en détail.

L. Slavík / Geobios 37 (2004) 454–470

Fig. 8. Stratigraphical distribution of conodont and tentaculite taxa in the Mramorka section with schematic conodont zonation. Fig. 8. Répartition stratigraphique des conodontes et des tentaculites pour la coupe de Mramorka en fonction de la zonation à conodontes.

463

464

L. Slavík / Geobios 37 (2004) 454–470

Fig. 9. Stratigraphical distribution of conodont taxa from the Pg/Em interval of the Na Branžovech section with schematic conodont zonation (occurrences of Belodella species are not included). Fig. 9. Répartition stratigraphique des conodontes de l’intervalle Pg/Em de la coupe de Na Branžovech en fonction de la zonation à conodontes proposée (présences de Belodella non précisées).

and new conodont data are summarized in Fig. 10. In spite of the big size of samples for conodonts, the new investigation was not more successful than the previous biostratigraphic studies. Only several specimens of Oz. e. excavata, Oz. st. miae, C. celtibericus, C. curvicauda, L. b. bilatericrescens and L. b. gracilis were obtained. The controversial Polygnathus kitabicus Yolkin et al. reported from the DvorceProkop Ls. by Kalvoda (1995) at a position near sample SV4 has not been figured, and no other Polygnathus were recorded by the new sampling. Conodont data from this section are still insufficient to trace the precise position of the Pg/Em boundary.

Fig. 10. Stratigraphical distribution of conodont and tentaculite taxa from the Pg/Em interval of the Stydlé vody section with schematic conodont zonation. Fig. 10. Répartition stratigraphique des conodontes et tentaculites de l’intervalle Pg/Em de la coupe Stydlé vody en fonction de la zonation conodonte proposée.

6. Systematic part Genus Latericriodus Müller, 1962. Type species Icriodus latericrescens Branson and Mehl, 1938. Latericriodus beckmanni (Ziegler, 1956). Fig. 11(6). I element. 1956. Icriodus latericrescens beckmanni nov. subsp. Ziegler, p. 102, Pl. 6, Figs. 1–5. 1967. Icriodus latericrescens beckmanni Ziegler - Ziegler, Pl. 8, Fig. 5. 1970. Icriodus latericrescens beckmanni Ziegler - Druce, Pl. 5, Figs. 7a, b. 1976. Latericriodus beckmanni (Ziegler) - Bultynck, p. 72, Pl. 9, Figs. 1–6.

L. Slavík / Geobios 37 (2004) 454–470

465

466

L. Slavík / Geobios 37 (2004) 454–470

1985. Latericriodus beckmanni beckmanni (Ziegler) Bultynck, Pl. 5, Fig. 8. 1988. Latericriodus beckmanni (Ziegler) - Grötsch, p. 165, Pl. 14, Figs. 39–40. 1990. Icriodus beckmanni Ziegler - Lazreq, Pl. 1, Figs. 1–4. 1994. Latericriodus beckmanni (Ziegler) - Benfrika, p. 121, Pl. 11, Figs. 15, 20. 1999. Icriodus beckmanni beckmanni Ziegler - Luppold and Wolfart, Pl. 6, Fig. 2, Pl. 7, Fig. 3. Material: 2 specimens (Pod Barrandovem, sample 33BA). Remarks: The Figured specimen bears three lateral processes on the posterior part of the platform element. Two distinct processes are well developed and the third one is rather incipient. The postero-lateral process is the longest and joints the main cusp at almost 90°. The presence of the third lateral process and a more expanded platform is, according to the original description, the main criterion for distinguishing this taxon from other members of the Latericriodus bilatericrescens group, although the character of

ornamentation on the upper part of the platform is very similar. Lateral processes in the figured specimen exhibit distinct ridges formed by rows of denticles on their upper part, which is typical for mature specimen. Latericriodus beckmanni was obtained from the Pod Barrandovem section, sample 33BA, where a mixed conodont assemblage is present (as it was mentioned above), just below the Chapel Coral Horizon. Accordingly, its stratigraphic position can be affected by reworking. However, this species frequently occurs in the upper part of the lower Emsian elsewhere in the world, e.g., in Morocco, Spain. Latericriodus sp. B. Fig. 11(18). Material: 4 specimens (Pod Barrandovem, sample 31BA; Požár 2, sample 20Po). Remarks: Morphologically distinct specimens were obtained from the sections of Požár 2 (sample 20Po) and Pod Barrandovem (sample 31BA) from the upper part of the Praha Formation. According to the accompanying fauna, the age would be lower Emsian. With respect to the incomplete-

Fig. 11. Caudicriodus celtibericus (Carls and Gandl, 1969): 1. Specimen 518M, I element × 44, upper view, Mramorka, sample M12. 2. Specimen 533SV, I element × 42, upper view, Stydlé vody, sample SV3. 3. Specimen 534SV, I element × 41, lateral view, Stydlé vody, sample SV3. Caudicriodus curvicauda (Carls and Gandl, 1969): 4. Specimen 451B, I element × 44, upper view, Na Branžovech, sample 26B. 5. Specimen 513M, I element × 40, upper view, Mramorka, sample M2. Latericriodus beckmanni (Ziegler, 1956): 6. Specimen 327BA, I element × 36, upper view, Pod Barrandovem, sample 33BA. Ozarkodina steinhornensis miae (Bultynck, 1971): 7. Specimen 321BA, Pa element × 37, upper view, Pod Barrandovem, sample 33BA. 8. Specimen 480B, Pa element × 40, upper view, Na Branžovech, sample 24B. 9. Specimen 501M, Pa element × 43, lateral view, Mramorka, sample M12. 10. Specimen 502M, Pa element × 50, lateral view, Mramorka, sample M11. 11. Specimen 504M, Pa element × 38, upper view, Mramorka, sample M11. 12. Specimen 503M, Sb element × 30, lateral view, Mramorka, sample M11. Latericriodus bilatericrescens bilatericrescens (Ziegler, 1956): 13. Specimen 340BA, I element × 34, upper view, Pod Barrandovem, sample 33BA. 14. Specimen 531SV, I element × 38, upper view, Stydlé vody, sample SV2. Latericriodus bilatericrescens cf. bilatericrescens (Ziegler, 1956): 15. Specimen 112Po, I element × 36, upper view, Požár 2, sample 19Po. 16. Specimen 074Po, I element × 38, upper view, Požár 2, sample 20Po. Latericriodus sp.: 17. Specimen 085Po, juvenile I element × 52, upper view, Požár 2, sample 20Po. Latericriodus sp. B. 18. Specimen 328BA, I element × 48, upper view, Pod Barrandovem, sample 31BA. Latericriodus bilatericrescens gracilis Bultynck, 1985: 19. Specimen 309BA, I element × 45, upper view, Pod Barrandovem, sample 33BA. 20. Specimen 310BA, I element × 44, upper view, Pod Barrandovem, sample 30BA. 21. Specimen 510M, I element × 48, upper view, Mramorka, sample M12. Latericriodus bilatericrescens aff. multicostatus (Carls and Gandl, 1969): 22. Specimen 311BA, I element × 48, upper view, Pod Barrandovem, sample 33BA. Latericriodus sp.: 23. Specimen 515M, I element × 42, upper view, Mramorka, sample M11. Ozarkodina sp. A: 24. Specimen 507M, Pa element × 41, lateral view, Mramorka, sample M10. Ozarkodina excavata excavata (Branson and Mehl, 1933): 25. Specimen 088Po, Pa element × 32, lateral view, Požár 2, sample 17Po. Polygnathus excavatus (Carls and Gandl, 1969): 26. Specimen 508M, Pa element × 36, lateral view, Mramorka, sample M11. 27. Specimen 509M, Pa element × 34, upper view, Mramorka, sample M11. 28. Specimen 338BA, Pa element × 30, upper view, Pod Barrandovem, sample 29BA. 29. Specimen 323BA, Pa element × 32, upper view, Pod Barrandovem, sample 29BA. Fig. 11. Caudicriodus celtibericus (Carls et Gandl, 1969) : 1. Spécimen 518M, I élément × 44, vue supérieure, Mramorka, échantillon M12. 2. Spécimen 533SV, élément I × 42, vue supérieure, Stydlé vody, échantillon SV3. 3. Spécimen 534SV, élément I × 41, vue latérale, Stydlé vody, échantillon SV3. Caudicriodus curvicauda (Carls et Gandl, 1969) : 4. Spécimen 451B, élément I × 44, vue supérieure, Na Branžovech, échantillon 26B. 5. Spécimen 513M, élément I × 40, vue supérieure, Mramorka, échantillon M2. Latericriodus beckmanni (Ziegler, 1956) : 6. Spécimen 327BA, I élément × 36, vue supérieure, Pod Barrandovem, échantillon 33BA. Ozarkodina steinhornensis miae (Bultynck, 1971) : 7. Spécimen 321BA, élément Pa × 37, vue supérieure, Pod Barrandovem, échantillon 33BA. 8. Spécimen 480B, élément Pa × 40, vue supérieure, Na Branžovech, échantillon 24B. 9. Spécimen 501M, élément Pa × 43, vue latérale, Mramorka, échantillon M12. 10. Spécimen 502M, élément Pa × 50, vue latérale, Mramorka, échantillon M11. 11. Spécimen 504M, élément Pa × 38, vue supérieure, Mramorka, échantillon M11. 12. Spécimen 503M, élément Sb × 30, vue latérale, Mramorka, échantillon M11. Latericriodus bilatericrescens bilatericrescens (Ziegler, 1956) : 13. Spécimen 340BA, élément I × 34, vue supérieure, Pod Barrandovem, échantillon 33BA. 14. Spécimen 531SV, élément I × 38, vue supérieure, Stydlé vody, échantillon SV2. Latericriodus bilatericrescens cf. bilatericrescens (Ziegler, 1956) : 15. Spécimen 112Po, élément I × 36, vue supérieure, Požár 2, échantillon 19Po. 16. Spécimen 074Po, élément I × 38, vue supérieure, Požár 2, échantillon 20Po. Latericriodus sp. : 17. Spécimen 085Po, élément juvénile I × 52, vue supérieure, Požár 2, échantillon 20Po. Latericriodus sp. B. 18. Spécimen 328BA, élément I × 48, vue supérieure, Pod Barrandovem, échantillon 31BA. Latericriodus bilatericrescens gracilis Bultynck, 1985 : 19. Spécimen 309BA, élément I × 45, vue supérieure, Pod Barrandovem, échantillon 33BA. 20. Spécimen 310BA, élément I × 44, vue supérieure, Pod Barrandovem, échantillon 30BA. 21. Spécimen 510M, élément I × 48, vue supérieure, Mramorka, échantillon M12. Latericriodus bilatericrescens aff. multicostatus (Carls et Gandl, 1969) : 22. Spécimen 311BA, élément I × 48, vue supérieure, Pod Barrandovem, échantillon 33BA. Latericriodus sp. : 23. Spécimen 515M, élément I × 42, vue supérieure, Mramorka, échantillon M11. Ozarkodina sp. A : 24. Spécimen 507M, élément Pa × 41, vue latérale, Mramorka, échantillon M10. Ozarkodina excavata excavata (Branson et Mehl, 1933) : 25. Spécimen 088Po, élément Pa × 32, vue latérale, Požár 2, échantillon 17Po. Polygnathus excavatus (Carls et Gandl, 1969) : 26. Spécimen 508M, élément Pa × 36, vue latérale, Mramorka, échantillon M11. 27. Spécimen 509M, élément Pa × 34, vue supérieure, Mramorka, échantillon M11. 28. Spécimen 338BA, élément Pa × 30, vue supérieure, Pod Barrandovem, échantillon 29BA. 29. Spécimen 323BA, élément Pa × 32, vue supérieure, Pod Barrandovem, échantillon 29BA.

L. Slavík / Geobios 37 (2004) 454–470

ness of the platform elements, it is difficult to assign them to a concrete species of Latericriodus (Müller), but the generic determination is obvious from the platform shape and the character of the basal cavity. A typical feature of this taxon is the marked prolongation of the distance between the last anterior transversal row and the anteriormost denticle. This feature is also typical for the specimens obtained from older stratigraphical levels (lower and middle Pragian) from the Požár 2 and Na Branžovech sections, which were determined as Latericriodus sp. A (Slavík, 2001b). This distinct feature is observed in much older forms of icriodontids, e.g., Icriodus lotzei (Carls, 1969) and Icriodus angustoides castilianus (Carls, 1969), described from Spanish Guadarrama. However, Latericriodus sp. B differs from Latericriodus sp. A in unusually more distinct prolongation observed also between the last transversal row and the rest of transversal rows on the spindle. Latericriodus sp. A bears a higher number of transversal rows than Latericriodus sp. B, which are arranged in a more tight configuration. Latericriodus bilatericrescens cf. bilatericrescens (Ziegler, 1956). Fig. 11(15, 16). Material: 4 specimens (Požár 2, samples 19Po and 20Po; Na Branžovech 30B). Remarks: The specimens bearing some common features with Latericriodus bilatericrescens bilatericrescens (Ziegler) described originally from the Harz Mts. were obtained from the section of Požár 2 (samples 19Po and 20Po) and Na Branžovech (sample 30B). Their stratigraphic range starts most probably in the lowest Emsian, because of the first occurrence recorded together with the first L. b. gracilis (in Požár 2 section, sample 19Po). The representative complete specimen is figured on Fig. 11(15). Posterior part of the element is almost identical with L. b. bilatericrescens, two well-developed lateral processes forming an angle of 180°. However, an indication of the third lateral process is present on the outer part of the platform. This feature is similar to Latericriodus beckmanni (Ziegler), much like the similar platform shape and the outline of the spindle on oral surface of the element. These characteristics would suggest to assign these specimens to transitional forms between L. b. bilatericrescens and L. beckmanni. Nevertheless, the denticles of the lateral rows of the spindle are, unlike in L. b. bilatericrescens and L. beckmanni, more flattened and have almost elliptical shape similar to that in older icriodontids, e.g., Caudicriodus vinearum (Carls, 1975) described from Celtiberia. The figured specimen (Fig. 11(15)) also exhibits a characteristic incurvation of the anterior tip of the spindle. Latericriodus bilatericrescens gracilis Bultynck, 1985. Fig. 11(19–21). I element. 1980. Latericriodus bilatericrescens bilatericrescens (Ziegler) - Bultynck and Hollard, Pl. 1, Figs. 22–24 only. 1980. Icriodus bilatericrescens Ziegler - Schönlaub (in Chlupácˇ et al.), Pl. 18, Fig. 4; Pl. 21, Fig. 1.

467

1985. Latericriodus bilatericrescens gracilis nov. subsp. Bultynck, p. 269, Pl. 5, Figs. 1, 2. 1994. Latericriodus bilatericrescens gracilis Ziegler Benfrika, p. 124, Pl. 11, Fig. 18. 1995. Latericriodus bilatericrescens (Ziegler) - Kalvoda, p. 36–37, Pl. 2, Figs. 5, 7. Material: 17 specimens (Pod Barrandovem, samples 30BA and 33BA; Na Požárech, sample 19Po; Na Branžovech, sample 26B; Mramorka, samples M4, M7, M8, M10, M11 and M12; Stydlé vody, samples SV2 and SV3). Description: The specimens obtained from the Barrandian sections correspond well to the material from the Dra Valley in southern Morocco. In mature specimens, the spindles are slender, moderately curved, bearing numerous transversal rows. The main lateral process is directed posteriorly and is situated on the outer part of the platform. Upper surface of the lateral process bears a narrow ridge or line formed by fusion of tiny denticles. The main axis of the spindle forms an angle of mostly 110° with the outer lateral process. The anteriorly oriented inner lateral process bears a similar ridge. In contrast to the original description, the junction of this process with the main axis of the spindle is located more posteriorly. Remarks: Typical specimens obtained from the Barrandian sections are figured on Fig. 11(19, 20). Denticles on the oral surface of the spindle are more separated from each other than in L. b. bilatericrescens (cf. Fig. 11(13, 14)). The specimens described by Kalvoda (1995, see the synonymy) from the Mramorka Quarry fully correspond to L. b. gracilis. The fact that Latericriodus bilatericrescens gracilis has been already described from the Barrandian confirms the relative abundance of these stratigraphically significant forms. L. b. gracilis represents the oldest subspecies of the Latericriodus bilatericrescens group including also L. b. bilatericrescens and L. b. multicostatus and, similarly as in other regions, it is the best indicator for approximating the base of the traditional Emsian in the Barrandian. Latericriodus bilatericrescens aff. multicostatus (Carls and Gandl, 1969). Fig. 11(22). I element. aff. 1969. Icriodus bilatericrescens multicostatus nov. subsp. - Carls and Gandl, p. 183–184, Pl. 17, Figs. 1–8. aff. 1980. Icriodus bilatericrescens Ziegler - Schönlaub (in Chlupácˇ et al.), Pl. 23, Fig. 6; Pl. 24, Figs. 6, 7. aff. 1990. Latericriodus bilatericrescens multicostatus (Carls and Gandl) - García-Alcalde et al., Fig. 10(8). aff. 1994. Latericriodus bilatericrescens multicostatus (Carls and Gandl) - García-López and Alonso-Menendez, Pl. 3, Fig. 1. aff. 2002. Icriodus bilatericrescens multicostatus Carls and Gandl - García-López et al., Pl. 3, Figs. 23, 24. aff. 2002. Icriodus bilatericrescens multicostatus Carls and Gandl - García-López and Sanz-López, Pl. 1, Fig. 7. Material: 2 specimens (Pod Barrandovem, sample 33BA).

468

L. Slavík / Geobios 37 (2004) 454–470

Remarks: A characteristic feature of L. b. multicostatus is the strong incurvation of the spindle, which is slender and long, the shape of the platform and the ornamentation of its oral surface. Denticles of the lateral rows are more robust than those of the middle row, and the number of transversal rows is normally much higher than in L. b. bilatericrescens (Ziegler) and L. b. gracilis Bultynck. However, the specimen Figured is not typical. It is small broken posteriorly and most likely juvenile. As a result, some characteristic features are hidden and this and the other non-Figured specimen cannot be assigned to L. b. multicostatus with certainty. Although only two specimens similar to L. b. multicostatus were obtained from the Barrandian area (Pod Barrandovem section, sample 33BA), the true presence of this species in the Barrandian is confirmed by the finds of Schönlaub (in Chlupácˇ et al., 1980) from the Srbsko roadcut section. Genus Ozarkodina Branson and Mehl, 1933. Type species Ozarkodina typica Branson and Mehl, 1933. Ozarkodina sp. A. Fig. 11(24). Material: 2 specimens (Mramorka, sample M10) Description: Platform elements have 5 to 6 large and very sharp flattened denticles, which are accompanied by a few alternating smaller denticles on the posterior part of the blade. The denticles are different from those of other ozarkodinas; their shape is distinctly triangular in lateral view and more sharp. The largest denticle is located just above the basal cavity, which is developed right in the middle of the unit and is restricted to a small and deep pit. The basal cavity has a typical, almost hemispherical shape and is not extended to the posterior or anterior end in the aboral part of the blade. Such shape of basal cavity does not resemble any of the so far described taxa belonging to the genus Ozarkodina from the Lower Devonian. In lateral view, the profile is rather high and symmetrical; in upper view the specimens are thin, with visible small semicircular platform lobes. Stratigraphic position: Both specimens were obtained from the section of Mramorka (sample M10), just above the upper boundary of the Dvorce-Prokop Ls., then well in the Emsian (Zlíchov Formation).

7. Icriodus concept – a discussion This paper is an attempt to trace and suggest an appropriate marker in order to better identify the Pragian/Emsian boundary in the Barrandian area. It is obvious that this task is rather complicated because the GSSP boundary does not correspond to the upper traditional Pragian boundary in its stratotype area, and that the “kitabicus” boundary is even cutting the traditional Pragian approximately in the middle (cf. Carls and Valenzuela-Ríos, 2002a). In addition, the base of the Emsian in its type area cannot be underpinned by conodonts. As shown by conodont data from the Barrandian

sections, both previous and newly obtained, the applicability of either Polygnathus “dehiscens” or P. kitabicus as a marker is impossible. In addition to that, the number of polygnathids occurring around the Pg/E boundary is very low, precluding any precise identification of the boundary. On the other hand, in contrast to problems with polygnathids, it is evident that better prospects could be found among icriodontids as regards as the solution of this problem. Individual representatives of the genus Latericriodus Müller and Caudicriodus Bultynck are present in all the sections described above and the number of obtained icriodontid specimens exceeds 100. This is in contrast with only 7 representatives of the genus Polygnathus, including the unique, and therefore stratigraphically unreliable record of P. pireneae. The correlation potential of icriodontids is much higher than it was believed for a long time. One of the reasons for the preference of polygnathids in the Lower Devonian biostratigraphy was the generalized assumption that icriodontids were restricted mostly to nearshore shallow-water environment. As has been remarked by Bultynck (2002), many early Devonian icriodontids occur rather in pelagic successions than on shoals. This observation corresponds well to sedimentary environments in the Barrandian sections, where these icriodontid conodonts occur together with pelagic dacryoconarids, cephalopods and graptolites, all embedded in lime-mud calciturbidites dominated by lithofacies with lenticular dissolution fabrics in comparison with gradually increasing proportion of laminar structures with Zoophycos and Chondrites. In the Barrandian, these icriodontids are most probably of fundamental stratigraphic significance. The lowermost and the uppermost Pragian conodont zones in the Barrandian – steinachensis and celtibericus – proposed recently by Slavík (in press) for the purpose of regional conodont zonation, are based on icriodontids. Apparent scarcity of early polygnathids in the Pragian and especially in the lowermost Emsian can be connected with conspicuous dearth of representatives of the genus Eognathodus Philip. Similar situation can be observed also in Spanish Pyrenees (Valenzuela-Ríos, 1994) and Moroccan Meseta (cf. Benfrika, 1994), where no Eognathodus has been found yet. This fact may support the idea that the origin of the genus Polygnathus evolved from the genus Eognathodus (cf. Mawson, 1998). There is, however, still not enough data up to now to confirm this hypothesis. The data from the Barrandian sections show that a promising alternative for the recognition of the Pg/Em boundary can be the entry of Latericriodus bilatericrescens gracilis Bultynck, 17 specimens were obtained from 5 sections. L. b. gracilis is most likely the oldest in the Latericriodus bilatericrescens group (e.g., Morrocan sections – Bultynck, 1985; Benfrika, 1994 and Barrandian sections – herein), and conodonts of this group provide a better indication of the earliest Emsian in the Barrandian than the polygnathids. L. b. gracilis first occurs in the Rˇeporyje Ls., i.e., well below the “graptolite-bearing interval” and mostly slightly below the entries of the representatives of the genus Polygnathus (except for Po. pireneae and one dubious refer-

L. Slavík / Geobios 37 (2004) 454–470

ence of “Po. kitabicus” in the Stydlé vody section). As was pointed out by Carls and Valenzuela-Ríos (2002b), worldwide correlations were based practically on Polygnathus excavatus (Carls and Gandl), formerly considered a junior synonym of P. dehiscens. According to Carls and ValenzuelaRíos (2002b), the entry of P. excavatus in Aragón is linked with the interval slightly below the traditional Emsian, although its origin can be older. If the oldest specimens of Polygnathus (except P. pireneae) reported from the Barrandian (by Schönlaub in Chlupácˇ et al., 1985; Kalvoda, 1995) belong to P. excavatus, the stratigraphic level of their entry, and consequently also the entry of L. b. gracilis must be close to the level of traditional base of the Emsian. Unlike the GSSP and the “kitabicus” boundary, this concept respects the major volume of the traditional Pragian and also the beginning of the traditional Emsian. Although more data are still needed, the position of the entry of L. b. gracilis could be in this respect promising beside Moroccan Meseta (Al Attamna section; Benfrika, 1994) and Tafilalt, southern Morocco (Section Jbel Ou Driss; Bultynck, 1985) also in SE Aragón (Carls and Valenzuela-Ríos, 2002b).

8. Conclusions Conodont data from the Pragian-Emsian boundary sections of the Barrandian area revealed that polygnathids are extremely scarce and stratigraphically useless component in this region and that they cannot be used for the identification of the lower Emsian stage boundary. A regular presence of L. b. gracilis in several sections allows suggest a new “gracilis Zone”. The base of this zone has a high potential for being a proxy for the identification of the lower Emsian boundary in the Barrandian and may enable a correlation with some other regions in the world. Stratigraphic importance of the icriodontid successions will be particularly strengthened after inevitable redefinition of the Pg/Em boundary in near future.

Acknowledgements The study was developed with the institute support (CEZ Z-3-013-912), and the final stage was possible due to a GA AV grant project (AA3013209 GACR). The primary thanks are addressed to J. Hladil for his useful consulting and guidance during my PhD. Special thanks are due to the CzechMoravian Cement Co. for co-sponsoring the conodont studies. I. Chlupácˇ for his excellent guidance in the field, and P. Bultynck, R. Mawson and P. Carls, for various and valuable discussions and suggestions about the conodonts. The paper has been critically read by J.I. Valenzuela-Ríos and E. Serpagli, whose suggestions in reviews are gratefully acknowledged. V. Sedlácˇek (density separation), A. Langrová (SEM) helped with the technical background of this study.

469

References Benfrika, M., 1994. Conodontes Siluriens et Dévoniens (Wenlock-Givétien) du Nord-Ouest de la Meseta marocaine : Systématique, stratigraphie et biofaciès. Katholieke Universiteit Leuven Thèse doctorale (unpublished). Boersma, K.T., 1973. Description of certain Lower Devonian platform conodonts of the Spanish central Pyrenees. Leidse Geologische Mededelingen 49, 285–301. Boucˇek, B., 1966. Eine neue und bisher jüngste Graptolithenfauna aus dem böhmischen Devon. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte 3, 161–168. Branson, E.B., Mehl, M.G., 1933. Conodont Studies. University of Missouri Studies 8 (1-4), 1–343. Branson, E.B., Mehl, M.G., 1938. The conodont genus Icriodus and ist stratigraphic distribution. Journal of Paleontology 12, 156–166. Bultynck, P., 1985. Lower Devonian (Emsian) – Middle Devonian (Eifelian and lowermost Givetian) conodont successions from Ma’der and the Tafilalt, southern Morocco. Courier Forschungsinstitut Senckenberg 75, 261–286. Bultynck, P., 1999. Succession within the conodont genus Polygnathus in Emsian-earliest Eifelian strata from the Bou Tchrafine area, (N-Eastern Tafilalt, Morocco). In: Feist, R., Talent, J.A., Orth, B. (Eds.), Abstract book, Errachidia meeting SDS-IGCP 421, pp. 6–7. Bultynck, P., 2002. Devonian Icriodontidae: Biostratigraphy and taxonomic, paleoecologic and paleogeographic considerations. Strata 12 (1), 23. Bultynck, P., Hollard, H., 1980. Distribution comparée de Conodontes et Goniatites dévoniens des Plaines du Dra, du Ma’der et du Tafilalt (Maroc). Aardkundige Mededelingen 1, 1–73. Carls, P., 1969. Die Conodonten des tieferen Unter-Devons der Guadarrama (Mittel-Spanien) und die Stellung des Grenzbereiches Lochkovium/ Pragium nach der rheinischen Gliederung. Senckenbergiana lethaea 50, 303–355. Carls, P., 1975. Zusätzliche Conodonten-Funde aus dem tieferen Unterdevon Keltiberiens (Spanien). Senckenbergiana lethaea 56, 399–428. Carls, P., Gandl, J., 1969. Stratigraphie und Conodonten des Unter-Devons der östlichen Iberischen Ketten (NE Spanien). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 132, 155–218. Carls, P., Valenzuela-Ríos, J.I., 1999. Faunas, correlations, various boundaries, and opinions concerning the early Emsian sensu lato and cancellata boundary. Web Page of the SDS-Emsian Working Party. http: //www.es.mq.edu.au/mucep/emsian/carls_and_ríos. Carls, P., Valenzuela-Ríos, J.I., 2002a. Pragian/Emsian boundary conodonts. Strata 12 (1), 24. Carls, P., Valenzuela-Ríos, J.I., 2002b. Early Emsian Conodonts and associated shelly faunas of the Mariposas Fm (Iberian Chains, Aragón, Spain). In: García-López, S., Bastida, F. (Eds.), Palaeozoic conodonts from Northern Spain. Instituto Geológico y Minero de España, serie Cuadernos del Museo Geominero, 1, pp. 315–333. Chlupácˇ, I., 1957. Facial development and biostratigraphy of the Lower Devonian of Central Bohemia. Sborník ústrˇedního ústavu geologického. Odd. geol 23, 369–485. Chlupácˇ, I., 1993. Geology of the Barrandian. A field trip guide. Senckenberg-Buch 69. Chlupácˇ, I., Havlícˇek, V., Krˇíž, J., Kukal, Z., Štorch, P., 1998. Palaeozoic of the Barrandian. Czech Geological Survey. Chlupácˇ, I., Hladil, J., Lukeš, P., et al., 1986. Field Conference of the ISDS Barrandian-Moravian Karst. A Field Trip Guide Book. Chlupácˇ, I., Krˇíž, J., Schönlaub, H.P., 1980. Silurian and Devonian conodont localities of the Barrandian. Guidebook and Abstracts, Second European Conodont Symposium /ECOS II/. Abhandlungen der Geologische Bundesanstalt, 30, pp. 147–180. Chlupácˇ, I., Kukal, Z., 1986. Reflection of possible global Devonian events in the Barrandian area, CSSR. In: Walliser, O.H. (Ed.), Global BioEvents. A critical approach: Lecture Notes in Earth Sciences, 8, pp. 169– 179.

470

L. Slavík / Geobios 37 (2004) 454–470

Chlupácˇ, I., Lukeš, P., 1999. Pragian/Zlíchovian and Zlíchovian/Dalejan boundary sections in the Lower Devonian of the Barrandian area. Czech Republic. Newsletters on Stratigraphy 37, 75–100. Chlupácˇ, I., Lukeš, P., Paris, F., Schönlaub, H.P., 1985. The LochkovianPragian boundary in the Lower Devonian of the Barrandian area /Czechoslovakia/. Jahrbuch der Geologische Bundesanstalt 128, 9–41. Druce, E.C., 1970. Lower Devonian conodonts from the Northern Yarrol Basin, Queensland. Bulletin of Bureau of Mineral Resources. Geology and Geophysics 108, 43–66. García-Alcade, J.L., Arbizu, M., García-López, S., Leyva, F., Montesinos, R., Soto, F., Truyols-Massoni, M., 1990. Devonian stage boundaries (Lochkovian/Pragian, Pragian/Emsian and Eifelian/Givetian in the Cantabric region (NW Spain). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 180, 127–207. García-López, S., Alonso-Menéndez, C., 1994. Conodontos del Grupo La Vid, Limites Praguiense/Emsiense y Emsiense Inferior/Emsiense Superior, Zona Cantabrica (NO de Espana). Revista Española de Micropaleontología 26, 81–97. García-López, S., Jahnke, H., Sanz-López, J., 2002. Uppermost Pridoli to Upper Emsian stratigraphy of the Alto Carrión Unit, Palentine Domain (Northwest Spain). In: García-López, S., Bastida, F. (Eds.), Palaeozoic conodonts from Northern Spain. Instituto Geológico y Minero de España, serie Cuadernos del Museo Geominero 1, pp. 229–257. García-López, S., Sanz-López, J., 2002. Devonian to Lower Carboniferous conodont biostratigraphy of the Bernesga Valley section. (Cantabrian Zone, N.W., Spain). In: García-López, S., Bastida, F. (Eds.), Palaeozoic conodonts from Northern Spain. Instituto Geológico y Minero de España, serie Cuadernos del Museo Geominero, pp. 163–205 1. Grötsch, J., 1988. Conodonten und Stratigraphie der unterdevonischen La Vid Formation (Kantabrische Gebirge, NW-Spanien). Erlanger geologische Abhandlungen 115, 155–198. Hladil, J., Cˇejchan, P., Gabašová, A., Táborský, Z., Hladíková, J., 1996. Sedimentology and orientation of tentaculite shells in turbidite lime mudstone to packstone: Lower Devonian, Barrandian, Bohemia. Journal of Sedimentary Research 66, 888–899. Hladil, J., Kalvoda, J., 1997. Dark, Graptolite-Bearing Level within the Earliest Emsian Beds of the Barrandian: Possible Event Correlation. EUG-9 Abstracts (European Union of Geosciences, Strasbourg, France). Terra Nova (Cambridge) 9, 282. Jeppsson, L., 1988. Conodont biostratigraphy of the Silurian-Devonian boundary stratotype at Klonk, Czechoslovakia. Geologica et Palaeontologica 22, 21–31. Jeppsson, L., Fredholm, D., Mattiasson, B., 1985. Acetic acid and Phosphatic Fossils – a warning. Journal of Paleontology 59, 952–956. Kalvoda, J., 1995. Conodont Fauna from the Pragian/Emsian boundary in the Mramorka and Stydlé vody Quarry (Barrandian, Czech Republic). Veˇstník Cˇeského geologického ústavu 70, 33–44. Klapper, G., Ziegler, W., Mashkova, T.V., 1978. Conodonts and correlation of Lower Middle Devonian boundary beds in the Barrandian area of Czechoslovakia. Geologica et Palaeontologica 12, 102–116. Lazreq, N., 1990. Devonian Conodonts from Central Morocco. Courier Forschungsinstitut Senckenberg 118, 65–79. Luppold, F.W., Wolfart, R., 1999. Fauna (Conodonta, Dacryoconarida, Trilobita), Biostratigraphie und Fazies von Hercynkalk-Vorkommen (Devon) in der westlichen Harzgeröder und in der Blankenburger Zone (Harz) – Eine Dokumentation. Geologisches Jahrbuch A155, 3–71. Mawson, R., 1987. Early Devonian conodont faunas from Buchan and Bindi. Victoria, Australia. Palaeontology 30, 251–297. Mawson, R., 1995. Early Devonian polygnathid conodont lineages with special reference to Australia. Courier Forschungsinstitut Senckenberg 182, 389–398.

Mawson, R., 1998. Thoughts on Late Pragian-Emsian polygnathid evolution: documentation and discussion. In: Szaniawski, H. (Ed.), Proceedings of the Sixth European Conodont Symposium (ECOS VI). Palaeontologica Polonica 58, pp. 201–211. Müller, K.J., 1962. Zur systematischen Einteilung der Conodonthophoridae. Paläontologisches Zeitschrift 36, 109–117. Philip, G.M., Jackson, J.H., 1967. Lower Devonian subspecies of the conodont Polygnathus linguiformis Hinde from southeastern Australia. Journal of Paleontology 41, 1262–1266. Riccardi, A.C., et al., 1997. Circular No. 92. International Subcommission on Stratigraphic Classification (ISSC) of the IUGS International Commission on Stratigraphy. http://www.geocities.com/issc_arg/ CIRC92.rtf. Schönlaub, H.P., 1980. Carnic Alps. In: Guidebook and Abstracts. Second European Conodont Symposium (ECOS II), Field Trip A, Abhandlungen der Geologische Bundesanstalt 35, pp. 5–57. Slavík, L., 1998. Early Devonian conodont succession from the section of the Cˇertovy schody Quarry (Koneˇprusy, Barrandian, Czech Republic). Veˇstník Cˇeského geologického ústavu 73, 157–172. Slavík, L., 2001a. Lower Devonian conodonts from the Karlík Valley and Na Branžovech sections in the Barrandian area, Czech Republic, and their significance for Pragian conodont zonation. Acta Geologica Polonica 51, 253–271. Slavík, L., 2001b. Konodontová fauna a zonace barrandienského pragu. Institute of Geology, Czech Academy of Sciences Ph.D. thesis Praha (unpublished). Slavík, L., (in press). A new conodont zonation of the Pragian in the stratotype area (Barrandian, central Bohemia). Newsletters on Stratigraphy. in press. Slavík, L., Hladil, J., 2000. Anatomy of the Pragian stratigraphic column: gamma spectrometric record throughout complete 170 m thick Pragian section in calciturbidite/hemipelagite facies (Prague, Section “Under Barrandov bridge”). Subcommission on Devonian Stratigraphy Newsletter 17, 46–47. Valenzuela-Ríos, J.I., 1994. Conodontos del Lochkoviense y Praguiense (Devónico Inferior) del Pirineo Central español. Memorias del Museo Paleontológico de la Universidad de Zaragoza 5, 1–142. Valenzuela-Ríos, J.I., 1997. Can Polygnathus pireneae be the index of a standard conodont Zone? Newsletters on Stratigraphy 35, 173–179. Vavrdová, M., 1989. Early Devonian palynomorphs from the DvorceProkop Limestone (Barrandian region, Czechoslovakia). Veˇstník Ústrˇedního ústavu geologického 64, 207–219. Weddige, K., 1987. The Lower Pragian boundary (Lower Devonian) based on the conodont species Eognathodus sulcatus. Senckenbergiana lethaea 67, 467–479. Yolkin, E.A., Apekina, L.S., Erina, M.V., Izokh, N.G., Kim, A.I., Talent, J.A., Walliser, O.H., Weddige, K., Werner, R., Ziegler, W., 1989. Polygnathid lineages across the Pragian-Emsian boundary, Zinzilban Gorge, Zerafshan, USSR. Courier Forschungsinstitut Senckenberg 110, 237–245. Yolkin, E.A., Kim, A.I., House, M.R., Weddige, K., Talent, J.A., 1997. Definition of the Pragian/Emsian stage boundary. Episodes 20, 235–240. Yolkin, E.A., Weddige, K., Izokh, N.G., Erina, M.V., 1994. New Emsian conodont zonation (Lower Devonian). Courier Forschungsinstitut Senckenberg 168, 139–157. Ziegler, W., 1956. Unterdevonische Conodonten, insbesondere aus dem Schönauer und dem Zorgensis-Kalk. Notizblatt des Hessischen Landesamtes-Amt Bodenforschung 84, 93–106. Ziegler, W., 1967. Zum höchsten Mitteldevon an der Nordflanke des Ebbesattels. Fortschritte in der Geologie von Rheinland und Westfalen 9, 519–538.