Bollettino della Società Paleontologica Italiana, 49 (1), 2010, 65-74. Modena, 15 maggio 201065

A preliminary study of the upper Silurian nautiloid cephalopods from the Eggenfeld section (Graz Paleozoic, Austria)

Kathleen HISTON, Bernhard HUBMANN & Fritz MESSNER

K. Histon, Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio Emilia, Largo S. Eufemia 19, 41121 Modena (Italy); [email protected], [email protected] B. Hubmann, Institute for Earth Sciences (Geology & Palaeontology), University of Graz, Heinrichstrasse 26, A-8010 Graz (Austria); [email protected] F. Messner, Auenbruggergasse 8, A-8073 Feldkirchen bei Graz (Austria); [email protected]

KEY WORDS - Nautiloid cephalopods, upper Silurian, Austria, paleobiogeography, biostratigraphy.

ABSTRACT - The preliminary results of a systematic investigation of the nautiloid faunas from the upper Silurian (Pridoli) Eggenfeld section of the Graz Paleozoic are presented. A faunal list of the seven genera recognized to date, representing the families Oonoceratidae and Lechritrochoceratidae and subfamilies Michelinoceratinae, Kionoceratinae, Leurocycloceratinae is given and selected taxa illustrated. These genera document faunal exchange between the Graz Paleozoic, central Bohemia, the Carnic Alps, Sardinia, France (Montagne Noire), Spain (the Ossa Morena Zone) and Morocco during the late Silurian. The study adds a further contribution to the ongoing systematic description by diverse research groups of Silurian nautiloid cephalopods from the North Gondwana sector within a well defined biostratigraphic framework in order to elaborate their use as a tool for biostratigraphic correlation and paleobiogeographic reconstructions.

RIASSUNTO - [Studio preliminare dei cefalopodi nautiloidi del Siluriano superiore (Pridoli) della sezione di Eggenfeld (Paleozoico di Graz, Austria)] - Sono presentati i risultati preliminari di uno studio sistematico delle faune a nautiloidi del Siluriano superiore (Pridoli) provenienti dalla sezione di Eggenfeld nel Paleozoico di Graz. Il Paleozoico di Graz si trova nell’Austria orientale, ha un estensione geografica di circa 1250 km2 ed è suddiviso in tre gruppi di falde sulla base delle litologie, della posizione tettonica e della sovrapposizione metamorfica delle successioni: un gruppo basale, uno intermedio e uno superiore. Le faune a nautiloidi provengono dal gruppo di falde superiore - “Rannach- Hochlantsch Nappe” - di età compresa tra il Siluriano superiore e il Carbonifero Superiore. Le sequenze stratigrafiche indicano una varietà di ambienti di deposizione da un margine continentale passivo con vulcanismo intra-placca a sedimenti tipici di scogliere e piattaforme marine durante il Siluriano e Devoniano. La sezione di Eggenfeld fa parte dell’Eggenfeld Member della Kötschberg Fm. (Ludfordiano-Lochkoviano). I livelli K1, K2 and K3 sono dolomie grigio scure o dolomie localmente ricche di fossili. Le faune a conodonti indicano un’età compresa tra la biozona a P. siluricus (Ludlow superiore) e la biozona a I. woschmidti (Lochkoviano). Nonostante la fauna a nautiloidi presente sia risultata piuttosto ricca, questo lavoro rappresenta il primo studio sistematico effettuato nel Paleozoico di Graz. Viene presentato un primo elenco di sette generi appartenenti alle famiglie Oonoceratidae e Lechritrochoceratidae e alle sottofamiglie Michelinoceratinae, Kionoceratinae, Leurocycloceratinae. Vengono figurate sette specie, lasciate in nomenclatura aperta, appartenenti ai generi Michelinoceras Foreste, 1932, Merocycloceras Ristedt, 1968, Plagiostomoceras Teichert & Glenister, 1952, Parakionoceras Foerste, 1928, Orthocycloceras Barskov, 1972, Oonoceras Hyatt, 1884, e Lechritrochoceras Foreste, 1926. La segnalazione di questi generi nel Paleozoico di Graz, presenti anche in Boemia centrale, Alpi Carniche, Sardegna, Francia (Montagna Nera), Spagna (Ossa Morena) e Marocco (Tafilalt, Anti-Atlas) documenta l’interscambio faunistico dei nautiloidi durante il tardo Siluriano. Lo studio fornisce inoltre dati importanti per le descrizioni tassonomiche in fase di elaborazione da parte di diversi gruppi di ricerca sulle faune a nautiloidi raccolte in biozone (a conodonti e graptoliti) ben stabilite del Siluriano per tutta la fascia settentrionale del Nord Gondwana, con lo scopo di evidenziare la loro distribuzione paleobiogeografica e di scoprire la possibilità di applicare i dati ricavati, sia per le ricostruzioni paleobiogeografiche sia per le correlazioni biostratigrafiche.

INTRODUCTION Prague Basin (Marek, 1971; Kolebaba, 1975, 1977, 1999, 2002; Turek, 1975; Marek & Turek, 1986; Manda, In recent years there has been an increase in 1996, 2008; Gnoli, 1997; Stridsberg & Turek, 1997; systematic studies of Silurian nautiloid cephalopods from Manda & Kriz, 2006, 2007; Manda & Turek, 2009a, a variety of geographical settings and the observed 2009b, 2009c), South West Sardinia (Gnoli & Serpagli, temporal and spatial data from these faunas may now be 1977, 1991; Serpagli & Gnoli, 1977; Gnoli, 1990; Gnoli considered a reliable tool for paleobiogeographic & Serventi, 2006, 2009 and references therein), Spain reconstruction and tracing of migrational pathways of (Bogolepova, 1998b), France (Ristedt, 1968; Serventi & pelagic organisms. Concentrated efforts have been made Feist, 2009) and the Carnic Alps (Ristedt, 1968; Histon, to improve the knowledge of the distribution and 1997, 1998, 1999a, 1999b, 2002; Bogolepova, 1998a; taxonomy of Silurian nautiloid cephalopod faunas and Gnoli & Histon, 1998; Gnoli et al., 2000; Serventi & many existing collections have been revised using up to Gnoli, 2001; Serventi et al., 2006, 2010; Gnoli & date taxonomic criteria as well as collection of new Serventi, 2008). Tentative correlations are now possible material from horizons with precise biostratigraphic data. between Avalonia (British faunas) and North Gondwana In Europe the main work has been done in the British Isles (Carnic Alps, Sardinia, France and Spain) and Bohemia (Evans, 1994; Evans & Holland, 1995; Holland, 1998, and Baltica, although problems still exist in recognition 1999, 2000a, 2000b, 2000c, 2002, 2003, 2004, 2007; of faunas at both generic and specific level due to poor Holland & Stridsberg, 2004), Sweden (Stridsberg, 1985), preservation and lack of precise taxonomic diagnoses.

ISSN 0375-7633

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Fig. 1 - Location map of the Graz Paleozoic and other remnants of Paleozoic strata in Austria (Greywacke Zone, South Burgenland, Gurktal Nappe, Nötsch, the Carnic Alps, the Karawanken Mountains). The Periadriatic Line separates the Carnic Alps and the Karawanken Mountains (Southern Alps) from the Eastern Alps.

Detailed study of Silurian-Devonian nautiloid faunas from Fig. 2 - Simplified sketch of the Graz Paleozoic. Shaded patches correspond with outcropping area of the Rannach Nappe (Upper Morocco (Kröger, 2008) presented together with precise Nappe Group). Eggenfeld locality marked with arrow. stratigraphic and lithofacies data for the collection localities has highlighted further that correlation is feasible between the Peri-Gondwana Terranes and that nautiloid cephalopods are reliable paleobiogeographic indicators. This is the first detailed systematic study of the - The Basal Nappe System (“Schöckl-Hochschlag Nappe”; nautiloid fauna from the upper Silurian sections of the upper Silurian to Middle Devonian) was deformed under Graz Paleozoic area to be carried out even though upper greenschist facies conditions. Volcaniclastics nautiloids are to be found in abundance there (Ebner, dominate the late Silurian to Early Devonian interval, 1976a; Hiden, 1995). It is hoped that the results of the and carbonates the Middle Devonian time span. systematic investigation in progress will be of importance - The Intermediate Nappe System (“Laufnitzdorf Nappe for placing the nautiloid faunas from the Graz Silurian and Kalkschiefer Nappes”; lower Silurian to Upper within a global scenario both with regard to the Devonian) contains pelagic limestones, shales, implications from the faunal assemblage present for volcaniclastics as well as siliciclastics. paleobiographical reconstruction and patterns of faunal - The Upper Nappe System (“Rannach-Hochlantsch exchange along the North Gondwana margin but also with Nappe”; upper Silurian to Upper Carboniferous) is regard to their paleoecological and paleoenvironmental characterised by Lower to Middle Devonian settings which in some ways are similar to those in some volcaniclastic rocks, Lower to Middle Devonian areas of the Prague Basin (Manda & Kriz, 2006). siliciclastics and fossil-rich carbonates of near-shore environment followed by the pelagic sequences of late Givetian to Bashkirian age with shallow marine GEOLOGICAL SETTING sediments at the top. The stratigraphic sequence indicates a sedimentation The Graz Paleozoic located in eastern Austria (Fig. area changing from a passive continental margin with 1) extends over approximately 1250 km2 and is isolated intraplate volcanism to shelf and platform geometries from other low metamorphic Paleozoic occurrences by during Silurian to Devonian time (Fritz et al., 1992). tectonic borders to the north, east and west as well as by During Pragian to Givetian time deposition changed from its younger overlays in the south (Fig. 2). The near-shore facies to open platform environments, during northwestern and western parts of the Graz Paleozoic are the Frasnian the carbonate platform was drowned and bordered by polycrystalline units of the Austroalpine limestones were deposited. The “Variscan event” is Crystalline Zone, whereas in the south, Paleozoic indicated by mixed conodont faunas, stratigraphic gaps successions are transgressively overlain by Neogene and karstification (Ebner, 1976b). sediments of the “Styrian Basin”. The southwestern parts are unconformably covered by Upper Cretaceous sediments of the Kainach Gosau. STRATIGRAPHY AND ENVIRONMENTAL The Graz Paleozoic is divided into a basal, an ARCHITECTURE OF THE RANNACH NAPPE intermediate and an upper nappe group (Fritz & Neubauer, (UPPER NAPPE GROUP) 1990) based on lithological similarities, the tectonic position as well as the metamorphic superimposition of Volcaniclastics characterise the basal parts of all successions. nappe groups of the Graz Paleozoic. The sequence of the

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patch-reefs and monotonous mudstones (Kollerkogel Fm., Tyrnaueralm Fm., and Zachenspitz Fm.). During the uppermost Givetian to lower Frasnian the sedimentation of shallow platform carbonates was replaced by micritic cephalopod limestones (Steinberg Fm.). This sedimentation continued up to the Bashkirian (Sanzenkogel Fm., Forstkogel Group) with some interruptions caused by uplifting during the Variscan collision (Ebner, 1976b, 1978). Finally the sequence is terminated by shallow marine shales and limestones with birdseye structures (Hahngraben Fm.) (Hubmann & Messner, 2007).

THE EGGENFELD SECTION

The Eggenfeld section belongs to the Eggenfeld Member (Flügel, 2000) of the Kötschberg Fm. (Ludfordian - Lochkovian). The Silurian succession of the section (Fig. 4) at Eggenberg (hill north of the village of Eggenfeld) consists of greenish, massive diabase (V) at the base, which is followed by approximately a 2 m

Fig. 3 - Stratigraphic column of the Rannach Nappe. 1) Kehr Fm., Kötschberg Fm.; 2) Parmasegg Fm.; 3) Flösserkogel Fm., Bameder Fm.; 4) Plabutsch Fm.; 5) Kollerkogel Fm.; 6) Steinberg Fm.; 7) Sanzenkogel Fm.; 8) Höchkogel Fm.; 9) Hahngraben Fm.

Rannach Nappe starts with predominantly alkaline subordinately acidic metavolcanites (tuffs, lavas) of the Kehr Fm. (Fig. 3). A single finding of the graptolite Bohemograptus bohemicus tenuis (Boucek, 1936) within a tuffitic layer at the very top of the formation indicates an age not younger than Ludfordian (Neocucullograptus kozlowskii graptolite Biozone). The following Kötschberg Fm. comprises predominantly dolostones, argillaceous shales and silty shales of Ludlow to Lochkovian age (Ebner, 1976a; Hiden, 1995). Following the basal sequences dominated by volcaniclastics to fine-grained clastics sedimentation changes to platy crinoidal limestones intercalated with sandy marls and sand/siltstones of the Pragian age Parmasegg Fm. (Fritz, 1991). During Emsian times the peritidal Flösserkogel Fm. with monotonous light grey late diagenetic dolostones, reddish-purple to green volcaniclastics, pure quartz sandstones, marly dolomites and biolaminated dolomites of varying colours was formed (Fenninger & Holzer, 1978). A sea level rise resulted in the deposition of highly fossiliferous dark marly bioclastic limestones with reefal structures (coral-stromatoporoid-carpets), the Eifelian Plabutsch Fm. (Hubmann, 1993, 2003). This phase is terminated by a repetition of tidal flat deposits similar to the Flösserkogel Fm. and obviously caused by an eustatic Fig. 4 - Stratigraphy of the Eggenfeld Section. The haematite layer sea level fall. (R) separates rocks of the Kehr Fm. (below) from the Kötschberg During the Givetian renewed transgression resulted Fm. (above). V: diabase and tuffs; K: carbonates; S: tuffaceous in sequences with sharp (bio)facial contrasts between schists; D: dolomite.

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thickness of violet and greenish-grey unlayered tuffs, as macrofossils varies throughout the carbonate horizons well as thin bedded ash tuffs (Ebner, 1976a). Some (Ebner, 1976a): concretionary horizons with haematite occur. A K1 - crinoids, orthocerids (Kionoceras cf. bronni, moderately well preserved specimen of Bohemograptus Cyrtocycloceras cf. urbanum, Oonoceras? sp.), small bohemicus tenuis was recorded (Hiden, 1995) from one sized undeterminable brachiopods, Cardiolinka sp., of the ash tuff horizons. Above the volcaniclastic horizon gastropods, Favosites sp. which marks the boundary between the Kehr Fm. and the K2 - crinoids, orthocerids, Septatrypa subsecreta, overlying Kötschberg Fm. (Eggenfeld Member) a layer Syringaxon frame. of haematite (R) is developed at the contact between the K3 - crinoids, orthocerids, Septatrypa subsecreta, diabase and dolomite. This haematite level passes into a frequent loboliths of Scyphocrinites (Ø about 10 cm) 1 m thick succession of bedded dark grey dolostones occur. Brachiopods appear as pavements (Hubmann & which is overlain by fossil free tuffaceous schists and Suttner, 2007).

claystones (S1). Carbonate rocks K1, K2 and K3 of the Preservation of conodonts is excellent within the section are dark grey, bedded dolomites and/or dolomitic dolomites (see Ebner, 1976a) and these indicate a range limestones that are locally rich in fossils. They can be from the P. siluricus conodont Zone (upper Ludlow) to differentiated on the basis of their microfacies into: the I. woschmidti conodont Zone (Lochkovian). bioclastic dolosparites to biodolosparites, biodolosparites and biomicrites (microsparites). The bioclastic content (mainly crinoids, orthocerids, NAUTILOID FAUNAS brachiopods, rare solitary rugose corals) is subject to strong fluctuations, however, generally amounts are up The collection of nautiloid fauna being studied is to 15%. The fossil content of the biodolosparites likewise housed at the University of Graz under the accession reaches 15% but comprises exclusively crinoidal number series E.I-001-399. The material which to date

remains. Biomicrites contain up to 20% shell fragments, includes over 400 specimens, was collected from the K2 brachiopods, crinoids, trilobites and subordinate horizon at the Eggenfeld section locality and is being orthoconic nautiloids. The brachiopods are mostly prepared and photographed at the University of Graz. The preserved with both valves. The occurrence of specimens have to date been divided into 16 distinct taxa

EXPLANATION OF PLATE 1

Fig. 1 - Plagiostomoceras sp. Coll. n. E.I–329, external view of the specimen, showing fine, transverse ornament, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1cm.

Figs. 2, 9 - Lechritrochoceras sp. 2 - Coll. n. E.I–109, external view of the specimen, showing transverse ornament, prominent annulations and deep hyponomic sinus, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm. 9 - Coll. n. E.I–077, external view of the specimen, showing fine, transverse and longitudinal ornament and oblique annulations, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm.

Figs. 3, 10 - Parakionoceras sp. 3 - Coll. n. E.I–311, external view of the specimen, showing longitudinal ornament, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm. 10 -Coll. n. E.I–122, external view of the specimen, showing longitudinal ornament, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm.

Fig. 4 - Merocycloceras sp. Coll. n. E.I–001, external view of the specimen, showing slightly raised, transverse ornament, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm.

Figs. 5-7 - Michelinoceras sp. 5 - Coll. n. E.I–020, external view of the specimen, showing slender longiconic form, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm. 6 - Coll. n. E.I–001, external view of the specimen, showing slender longiconic form and fine, transverse ornament, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm. 7 - Coll. n. E.I–074, internal view of the specimen, showing cameral chambers and central siphuncle, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm.

Fig. 8 Oonoceras sp. Coll. n. E.I–079, external view of the specimen, showing slender cyrtoconic form and oblique septa, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm.

Figs. 11-12 Orthocycloceras sp. 11 -Coll. n. E.I–165, external view of the specimen, showing fine, transverse ornament and transverse annulations, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm. 12 -Coll. n. E.I–165, external view of the specimen, showing fine, transverse ornament and slightly oblique annulations, Pridoli, level K2, Eggenfeld section (Graz Paleozoic), scale bar 1 cm.

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however, this preliminary classification is based solely on external features, mainly ornament and conch form, and requires further verification based on internal features after sectioning of specimens has been completed. The preliminary data presented here includes a faunal list of the seven genera which have been ascertained to date and illustration of a selection of these specimens (Pl. 1, figs. 1-12). The higher taxonomic classification system of the Treatise (Moore, 1964) has been followed where possible with modifications from more recent systematic works when appropriate.

FAUNAL LIST Fig. 5 - Small block of cephalopod limestone E. I – 021, Pridoli, K2 Class CEPHALOPODA Cuvier, 1797 level, Eggenfeld section (Graz Paleozoic, Austria). Note well- Subclass NAUTILOIDEA Agassiz, 1847 preserved specimens on bedding surface showing two distinct Order ORTHOCERIDA Kuhn, 1940 perpendicular orientation directions. Scale bar 5 cm. Superfamily ORTHOCERATACEAE M’Coy, 1844 Family ORTHOCERATIDAE M’Coy, 1844 Subfamily MICHELINOCERATINAE Flower, 1945 has been considered in the past as unreliable as Genus Michelinoceras Foerste, 1932 paleobiogeographic markers (Westermann, 1998). Crick (Pl. 1, figs. 5-7) emphasized that much more detailed systematic work on nautiloid faunas with precise stratigraphic data was needed Genus Merocycloceras Ristedt, 1968 to facilitate their use for reliable paleobiogeographic (Pl. 1, fig. 4) reconstructions and as stated above the array of studies emerging in recent years has shown this to be feasible. Genus Plagiostomoceras Teichert & Glenister, 1952 The Silurian Cephalopod Limestone Biofacies (Kriz, (Pl. 1, fig. 1) 1998) is well developed in Spain, France, Sardinia, the Carnic Alps and Bohemia and has been famous since the Subfamily KIONOCERATINAE Hyatt, in Zittel, 1900 last century for its abundance of macrofossils, particularly of nautiloid cephalopods. Hence the name Genus Parakionoceras Foerste, 1928 ‘Orthoceras’ limestone was widely used in the literature (Pl. 1, figs. 3, 10) on these areas. A detailed multidisciplinary study of the occurrence of the Silurian Cephalopod Limestone Subfamily LEUROCYCLOCERATINAE Sweet, 1964 Biofacies at various sections in the Carnic Alps which, focused on obtaining data concerning the Genus Orthocycloceras Barskov, 1972 paleogeographical setting of the Carnic Alps during the (Pl. 1, figs. 11, 12) Silurian (Ferretti & Histon, in press), has shown that these horizons with rich nautiloid faunas may be traced all along Order ONCOCERIDA Flower, in Flower & Kummel, 1950 the northern Gondwana margin from Morocco, the Ossa Family OONOCERATIDAE Hyatt, 1884 Morena Zone (South West Spain), Montagne Noire (France), South West Sardinia, the Carnic Alps to the Genus Oonoceras Hyatt, 1884 Prague Basin. Kriz (1998) and Bogolepova (1998c) have (Pl. 1, fig. 8) outlined the distribution of cephalopod limestones during the Silurian along the North Gondwana margin, Perunica Family LECHRITROCHOCERATIDAE Flower, in Flower & and North Asia and Ferretti & Kriz (1995) did a detailed Kummel, 1950 microfacies study of diverse horizons of this biofacies in the Prague Basin identifying two distinct depositional Genus Lechritrochoceras Foerste, 1926 environments: one by surface currents and one within a (Pl. 1, figs. 2, 9) shallower setting affected by storm action. The cephalopod bearing limestone beds from the section being studied in the Graz Paleozoic also show diverse PALEOBIOGEOGRAPHY orientation of the nautiloid conchs on the bedding surface and taphonomic features which may be indicative of small The importance of nautiloid cephalopods for scale depositional cycles within this succession (Figs. biostratigraphy and paleobiogeography was highlighted 5-8). Uni-directional orientation of conchs (Figs. 6-7) by Crick (1990, 1993) who noted that Paleozoic nautiloid may indicate deposition by surface currents while the distribution was controlled by water depth, distance perpendicular orientation of conchs (Fig. 5) and distinct separating adjacent shelf seas, and water temperature. time-rich taphonomic features such as dissolution of Nautiloid cephalopods were also not subject to extensive shell material and disarticulation of septal chambers on post-mortem drift, the latter being a reason that this group the bedding surface (Fig. 8) may indicate deposition

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Fig. 6 - Small block of cephalopod limestone E. I – 001, Pridoli, K2 level, Eggenfeld section (Graz Paleozoic, Austria). Note well- Fig. 7 - Small polished block of cephalopod limestone E. I – 061, preserved specimens on bedding surface showing uniform orientation Pridoli, K2 level, Eggenfeld section (Graz Paleozoic, Austria). Note directions but opposed apex direction. Small orthoconic shells are well-preserved specimens on bedding surface showing uniform clustered near the large shell on the right. Scale bar 5 cm. orientation directions and telescoped specimens. Scale bar 5 cm.

within a shallower setting and periods of non-deposition. The preliminary results of the present study further The presence of the common Circum Mediterranean support this hypothesis as genera common to both the ‘Orthoceras’ Limestone and Scyphocrinites Carnic Alps, Sardinia, Spain (Ossa Morena Zone), France Communities (Vai, 1999) and the Dualina nigra- (Montagne Noire), Morocco (Tafilalt, Anti-Atlas) and Patrocardia bivalve subcommunity (Kriz, 1999) within Bohemia (Prague Basin) are found at the Eggenfeld the latest Pridoli of the Carnic Alps sections demonstrates locality of the Graz Paleozoic (Table 1). These in part that faunal exchange was taking place during this interval represent the more pelagic component of the fauna and between the Peri Gondwana terranes and Baltica (Histon, probably are the result of surface current transport. 2002). This may also be the case for the faunas of the However, some more benthonic elements may also reflect Graz Paleozoic. the closeness of these terranes during this time slice. Unfortunately there are few age comparable faunas Further study of the faunas and precise classification at described for considering exchange of the nautiloid species level should shed more light on this aspect. faunas between the North Gondwana terranes during the Pridoli as systematic revision, particularly of the Bohemian fauna, is still lacking. As outlined above many DISCUSSION authors have shown links between the Sardinian (Gnoli & Serpagli, 1977, 1991; Serpagli & Gnoli, 1977; Gnoli, It is hoped that the results of the systematic 1990; Gnoli & Serventi, 2006, 2009 and references investigation: therein) and Bohemian (Marek, 1971; Kolebaba, 1975, 1977, 1999, 2002; Turek, 1975; Marek & Turek, 1986; Manda, 1996, 2008; Gnoli, 1997; Stridsberg & Turek, 1997; Manda & Kriz, 2006, 2007; Manda & Turek, 2009a, 2009b, 2009c) Silurian nautiloid faunas within a broad stratigraphic framework while close relationships between the nautiloids of the Carnic Alps (Ristedt, 1968; Histon, 1997, 1998, 1999a, 1999b, 2002; Bogolepova, 1998a; Gnoli & Histon, 1998; Gnoli et al., 2000; Serventi & Gnoli, 2001; Serventi et al., 2006, 2010; Gnoli & Serventi, 2008) and both the latter areas has also been suggested. Histon (2002) contributed additional data to support the idea of faunal exchange between the Carnic Alps, in particular with Bohemia and Baltica during the late Silurian. The conclusion of the study was that the more shallow water, facies restricted, nautiloid species described were common to both areas possibly reflecting the closeness of the Carnic Alps to Bohemia where these forms are common in the Ludlow and/or Pridoli series Fig. 8 - Small block of cephalopod limestone E. II – 014, Pridoli, K2 (Marek & Turek, 1986; Manda & Turek, 2009c; Storch level, Eggenfeld section (Graz Paleozoic, Austria). Note preservation of specimens on bedding surface showing uniform orientation pers. comm.) while the more pelagic faunas in common directions and particular taphonomic features: disarticulation of septal reflected the exchange between the various North chambers, lack of outer shell, some specimens are represented by Gondwana terranes, Baltica and the Urals due to currents. only the internal siphonal and cameral deposits. Scale bar 5 cm.

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Tab. 1 - Comparison of upper Silurian nautiloid cephalopod genera from the Graz Paleozoic area with upper Silurian faunas from Morocco (Tafilalt, Anti-Atlas), Spain (Ossa Morena Zone), France (Montagne Noire), Sardinia, the Carnic Alps and Bohemia.

(1) will increase and add to the existing documentation Conference & 1998 Field Meeting, IUGS Subcommission on of the Silurian nautiloid fauna on a global scale and thus Silurian Stratigraphy. Temas Geologico-Mineros ITGE, 23: 63-66. make a further contribution towards the palaeobio- Bogolepova O.K. (1998c). Silurian Cephalopod Beds from North Asia. In Landing E. & Johnson M.E. (eds.), Silurian Cycles geographic knowledge of the position of this fragment Linkages of dynamic stratigraphy with atmospheric, oceanic of the North Gondwana terranes at a precise stratigraphic and tectonic changes. James Hall centennial volume. New York interval, the latest Pridoli; State Museum Bulletin 491: 199-207. (2) will add more data to support the idea of faunal Boucek B. (1936). Graptolitova fauna ceskeho spodniho ludlowu. exchange between North Gondwana terranes such as Rozpravy ceske Akademie ved a umeni, Trida 2, 46: 1-26. Morocco, the Ossa Morena Zone, Montagne Noire, Crick R.E. (1990). Cambro-Devonian biogeography of nautiloid cephalopods. In McKerrow W.S. & Scotese C.R. (eds.), Sardinia, the Carnic Alps, central Bohemia and Baltica Palaeozoic Palaeontology and Biogeography, Geological Society and the documentation of distinct nautiloid communities Memoir, 12: 147-161. within precise stratigraphic intervals; Crick R.E. (1993). Biogeography of Early and Middle Paleozoic (3) will be of great importance for placing the nautiloid nautiloid cephalopods: Evidence for barriers to dispersal and faunas from the Graz Silurian successions within a global evolution. Geobios, Mémoire Spécial, 15: 91-105. scenario. The results of the study of the systematics and Cuvier G. (1797). Tableau élémentaire de l’histoire naturelle des paleobiogeography of the fossil nautiloids will provide animaux. xvi and 710 pp. Paris. Ebner F. (1976a). Das Silur/Devon-Vorkommen von Eggenfeld - important information on regional paleogeography and ein Beitrag zur Biostratigraphie des Grazer Paläozoikums. possible migrational pathways for pelagic organisms. This Mitteilungen der Gesellschaft der Geologie und will yield further insights into the positioning of Bergbaustudenten, 37: 275-305. paleocontinents and seaways and mechanisms of Ebner F. (1976b). Die Schichtfolge an der Wende Unterkarbon/ paleooceanography during the Silurian. Oberkarbon in der Rannach-Fazies des Grazer Paläozoikums. Verhandlungen der Geologischen Bundesanstalt, 1976: 65-93. Ebner F. (1978). Stratigraphie des Karbon der Rannachfazies im Paläozoikum von Graz. Mitteilungen der Österreichischen ACKNOWLEDGEMENTS Geologischen Gesellschaft, 69: 163-196. Evans D.H. (1994). Irish Silurian Cephalopods. Irish Journal of This study is being funded by a grant from the Dr. Heinrich- Earth Sciences, 13: 113-48. Jörg Stiftung Karl Franzens Universität Graz. 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