PALEOAPULIAN CARBONATE SHELF

In this region four main Silurian-Early Devonian cephalopod limestone biofacies can be recognized and linked to one another, including: (1) Carnic Alps, (2) Bistra Mts. in Western Macedonia (Bouček et al. 1968), (3) Suva Planina Mountains, Zebrina locality in Eastern Serbia (Kríz and Veselinovic 1975), and (4) Uppony Mt. in northeastern Hungary (Ebner et al. 1991; Gnoli and Kovács 1992).

Carnic Alps [K]

Here the 'Cellon Profil,' 'Rauchkofels,' and 'Plöckengebiet' represent the best-studied Silurian sections from a stratigraphical or paleontological point of view; as well as the Kok Limestone Section on the Italian side of the Carnic Alps. Ristedt (1968) reported the nautiloid species Merocycloceras declive, Michelinoceras (Sphaerorthoceras) carnicum, M. (S.) spp. ind. D and F sensu Ristedt, 1968, "Parasphaerorthoceras" accuratum, "P." spp. ind. A, C, D, F, and L, sensu Ristedt, 1968, Hemicosmorthoceras laterculum, and H. celloni Ristedt, 1968. At present, the author (in close cooperation with Dr. K. Histon, Geological Survey of Austria) has recognized the following Bohemian-type nautiloids (all Barrande's species unless otherwise specified) on the Italian side of the Carnic Alps (mainly from Mt. Cocco): Michelinoceras (M.) michelini, Michelinoceras? (M.) cf. nobile, M.? sp., Kopaninoceras? cf. jucundum, Plagiostomoceras gruenewaldti, P. sp., Arionoceras affine (Meneghini), A. submoniliforme (Meneghini), Columenoceras aff. grande (Meneghini), Geisonoceras sp., Akrosphaerorthoceras gregale Ristedt, Calorthoceras? cf. pseudocalamiteum, Orthocycloceras? cf. lynx, Kionoceras cf. carminatum, Parakionoceras originale, Rutoceras? mulus, and Oocerina cf. nuntius.

Gortani and Vinassa (1909) reported other Bohemian-type nautiloids from the Carnic Alps (Italian side), among which Michelinoceras amoenum, "O." alticola, Metaspyroceras subannulare (Münster 1840), Oonoceras potens, "O." pelagium, "O." firmum, Michelinoceras (M.) michelini, Plagiostomoceras cf. pleurotomum, Dawsonoceras dulce, "O." littorale, and Spyroceras pulchrum await systematic revision. Recently, in an unpublished PhD thesis, Dr. P. Serventi reported Hemicosmorthoceras cf. celloni Ristedt 1968, H. semimbricatum Gnoli 1983, H. aff. serratulum Ristedt 1968, Kopaninoceras jucundum, K. thyrsus, and Michelinoceras (Mich.) cf. currens, M. (Mich.) michelini from the Italian side of the Carnic Alps.

Many of the above reported Sphaerorthoceras and Parasphaerorthoceras–Ristedt's species occur on the Austrian side of the Carnic Alps–plus Kionoceras cf. carminatum, K. cf. electum, Akrosphaerorthoceras gregale Ristedt 1968, Sphooceras truncatum, Andigenoceras andigense Kiselev, Columenoceras? cf. duponti, Geisonoceras cf. nobile , G. rivale, Vericeras? cf. dorulites, and some indeterminable specimens of Armenoceras and Ormoceras. These last taxa were first described and figured by Serventi and Gnoli (2000). Serventi and Gnoli (2000) also pointed out the Silurian faunal affinities between the Carnic Alps and Central Bohemia (Perunica), with 18 of the 21 species in common. Histon (1999) revised the Silurian nautiloid cephalopods of the Heritsch (1929) collection previously collected by Stache mainly at "Kokberg" (Mt. Cocco) and stored in the Austrian Geological Survey, among which Oocerina? sp., Barrandeoceras sp., Uranoceras sp., and Lechritrochoceras cf. hoernesi (Barrande 1865) must be added to the Carnic Alps nautiloid assemblage.

Suva Planina Mountains, Eastern Serbia (Kríz and Veselinovic 1975) [L]

"Upper Silurian (Prídolí) and Lower Devonian (Lochkovian) carbonate rocks represent the core of the Suva Planina Mountains in eastern Serbia and are exposed in the upper part of Zli Do, east of Tuponica village and the Rebrina locality near the town of Ni." (Kríz and Veselinovic 1975, text-figs. 1, 2). In the latter area, in a little quarry, a black bituminous limestone crops out from which Bohemian-type bivalves were recovered, among with the nautiloids Orthocycloceras? fluminese (Meneghini 1857), and Parakionoceras sp. The detailed stratigraphic distribution of the cephalopod-bearing horizons in this locality is shown in Figure 4 after Kiselev (Kiselev, personal commun., 2002).

Bistra Mountains - Western Macedonia [M]

Bouček et al. (1968) wrote "In the mountain Bistra (2163) in Western Macedonia (the internal zone of Dinarides) near the locality named "Tonivoda." on the right side of the road Mavrovo-Galicnik, the clayey slates the age of which is not yet up to now determined with certitude were developed. Over this series the fine-grained gray limestones with Devonian Crinoids are lying. In the summer of 1963 a rather rich fauna containing relics especially of nautiloid shells followed by tentaculites, badly preserved ostracodes and rarely brachiopods was developed in the layers situated over the clayey slates, the lenses or intercalations of dark gray sometimes almost black limestones". In addition, the nautiloids Geisonoceras sp., Dawsonocerina sp. and Plagiostomoceras aff. pleurotomum (Barrande) also occur. According to Bouček et al. (1968, p. 8) these Lochkovian to Pragian rocks exhibit a close relationship with the typical Bohemian fauna.

Uppony(I) Mts. (Northeastern Hungary) (Gnoli and Kovács 1992) [N]

Gnoli in Gnoli and Kovács (1992) described and illustrated the following nautiloid orthocone taxa: Michelinoceras (M.) michelini Barrande, 1866, Mimogeisonoceras? cf. liberum Barrande, 1870, Kopaninoceras sp. sensu Gnoli in Gnoli and Kovács, 1992, Kionoceras? cf. adactum (Zhuravleva 1978), Leurocycloceras? or Dawsonoceras cf. dulce (Barrande 1868) and Columenoceras? cf. grande (Meneghini 1857), all of which are Lower to Middle Ludlow in age.

Ukraine - (former Podolia) continental platform [O]

This area was investigated by Kiselev, 1982, 1995, with summaries of Balashov and Kiselev, 1968; Kiselev, Mironova and Sinitsyna, 1987, who reported the Silurian-Devonian nautiloids: Kionoceras? canaliculatum (Eichwald 1839), K. decoratum (Eichwald 1861), K. loxias (Hall 1868), K.? ludense (Sowerby), K. neptunicum Barrande, 1868, K. scammoni (McChensney 1861), Harrisoceras abditum Kiselev, 1968, M. migrans (Barrande 1868), M. amoenum (Barrande 1867), Harrisoceras volkovense Kiselev, 1968, Mimogeisonoceras timidum (Barrande 1868), Eushantungoceras pseudoimbricatum (Barrande 1870), Brodekoceras dnestrovense Balashov, 1975, Mandaloceras ellipticum (McCoy 1854), "Orthoceras" seps Eichwald 1860, "Cyrtoceras" sp. ind. sensu Eichwald 1860, Dawsonoceras americanum (Foord 1888), D. annulatum (Sowerby 1816), D. dulce (Barrande 1868), Dawsonocerina barrandei Horný, 1956, D. althi (Venyukov 1899), D. hisingeri (Billings), D. kendalense (Blake), "Orthoceras" bacillus Eichwald, 1830, Polygrammoceras bullatum (Sowerby 1839), "Orthoceras" excentricum Sowerby 1839, Phragmoceras? arcuatum Sowerby, 1839, Gomphoceras pyriforme (Sowerby 1839), Anthoceras vaginatum (Schlotheim 1813), Protokionoceras multilineatum (Venyukov 1899), Peismoceras cf. asperum (Barrande 1865), Phragmoceras longum (Barrande 1865), Metarizoceras sinkovense Balashov, 1968, Uroniella cochleata (Schlotheim 1813), Parakionoceras? annulatocostatum (Billings)-suspected to have been authored actually by Boll 1857-Protokionoceras anticostiense Foerste in Twenhofel, 1928, P.? cf. virgatum (Sowerby 1839), Jovellania podolica (Siemiradzki), J. elliptica (Siemiradzki), Oocerina gorodokia (Balashov 1968), Mandaloceras? ellipticum (McCoy 1854), Gomphoceras pyriforme (Sowerby), Bickmorites? rapax (Barrande 1865), Ormoceras? cf. picteti (Barrande 1868), O. explanans (Barrande 1867), Metarizoceras? grave (Barrande 1867), "Orthoceras" roemeri Alth, 1874, Oonoceras? cf. nuntius (Barrande 1866), Oocerina? formidandum (Barrande 1867), Elrodoceras smotritchense Balashov, 1959, Eridites astrovae Zhuravleva, 1961, Harrisoceras volkovense (Balashov 1960), Pseudorthoceras amplum Kiselev, Rizoceras podolicum Balashov, 1968, Ormoceras rashkovense Balashov, 1968, O. seretense Balashov 1968, O. skalaense Balashov, 1968, O. dobroljanense (Balashov 1968), Podolicoceras giganteum (Balashov 1968), Umbeloceras tumescens (Barrande 1865), Armenoceras jupiterense Foerste, 1928, Bickmorites falcigerum (Eichwald 1857), Bickmorites podolicum Balashov, 1975, Gasconoceras planiventrum Foerste, 1936, Gordonoceras podolicum Balashov, 1975, Leurocycloceras bucheri Flower, 1941, L. brucense (Williams 1919), Metaspyroceras cf. ruedemanni (Foerste 1928), Polygrammoceras restevense Balashov, 1972, Protokionoceras anticoste Foerste, 1928, P. dnestrovense Balashov 1972, P. multilineatum (Venyukov 1839), and Sphooceras truncatum (Barrande 1860).

As outlined by Kiselev (1982, pp. 57-59) nautiloid faunas occur in the Ukraine with different assemblages in at least four stratigraphic stages: early Wenlock, mid-late Ludlow, Prídolí, and Lochkovian with a hiatus corresponding to the interval between the late Wenlock and early Ludlow. Detailed stratigraphic distribution of the cephalopod-bearing horizons in Ukraine Continental Platform are shown in Figure 4.

Faunal Similarity

The Raup and Crick (1979) statistical procedure was used to obtain a quantitative estimate of similarities between the different taxonomic content of these various nautiloid cephalopod faunas (Appendix I). This index ranges from 0 (no similarity) to 1 (identity). A matrix is presented with the comparisons between all pairs of associations. The Raup-Crick index (Raup and Crick 1979) uses a 'Monte-Carlo' randomization procedure, comparing the observed number of taxa occurring in both associations with the distribution of co-occurrences from 1000 random replicates.

In some localities (i.e., African and Eastern Europe) this index is very low despite the fact that the few taxa checked show identity at the species level and are also important from a stratigraphic point of view. Taking into account the value of this index for the Ukraine nautiloid assemblage, results indicate a certain similarity that can provide an idea of a possible assembling of the northern Gondwana margin belt. The median faunal similarity index (FSI) probability value of the Ukrainian Continental Platform nautiloid assemblage (shown in Appendix in red) compared with 12 other localities corresponds to 0.482. This result appears to support the present paleogeographic reconstruction of northern Gondwana.

To further probe faunal similarity between various tested localities, a Q-mode cluster analysis was also undertaken on a matrix of faunal similarities estimated by means of the Jacard coefficient. Results are shown in Figure 5. According to this approach, the greatest faunal similarity is recorded from southwestern Sardinia and the Prague Basin (0.89) followed by Carnic Alps and the last two (0.70). These are then followed by similarity between the Tinduf Basin and Anti-Atlas (0.60), between Carnic Alps and Montagne Noire (0.58), and between Eastern Pyrenees-Aquitaine and Suva Planina Mts. (0.50), followed by all others. Without more up-to-date and homogeneous systematics, it is only possible to make further conclusions if the same scientist checks the various nautiloid assemblages from the localities in which the so-called "Orthoceras Limestone" biofacies occurs.