NEW DATA ON CEPHALOPOD LIMESTONE BIOFACIES FROM NORTHEAST HUNGARY

Kovács (1989) reported olistoliths from the Strázsahegyi Formation in the Uppony Mountains (northeastern Hungary) bearing nautiloid orthocones in profusion («orthoceratid lumachella») within the Ludlow Series (Gorstian) belonging to the Ozarkodina s. sagitta - Ancoradella ploeckensis conodont biozones. Gnoli (in Gnoli and Kovács, 1992) described and illustrated this faunule and, despite the poor preservation of the inner features in the available material due to slight metamorphism, recognized Michelinoceras 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). In addition to the following distinctive areas I would tentatively add a new Silurian region corresponding to the northeastern Hungarian Uppony Mountains because of its orthocone nautiloid content (Gnoli and Kovács 1992,). These strata–cropping out on the western ridge of the Strázsa Hill and locally called "Harka-tetö"–can be closely compared to the Plöcken facies of the Carnic Alps (Schönlaub 1979, 1980).

A manuscript entitled "Correlation of the Szendrö - Uppony Palaeozoic (Northeast Hungary) with the Carnic Alps - South Karavanken Alps and Graz Palaeozoic: some paleogeographic implications" by Ebner, Kovács, and Schönlaub (Kovacs, personal commun., 1995) exists which advanced one interpretation of these occurrence patterns: "The close similarities between these Variscan sequences suggest their original proximity on the southern (Apulian) carbonate shelf of the Alpine-Dinaric arm of Prototethys". These authors stated in the summary that: "The Silurian pelagic olistoliths of olistostrome derive, however, unambiguously from the coeval reddish pelagic carbonate formations of the Carnic Alps-South Karavanken Alps (Kok Limestone, Alticola Limestone)." According to these authors "The overlapping of the Carnic Alps, respectively Graz Palaeozoic characteristics in the Szendrö-Uppony Palaeozoic, indicate that the Periadriatic Lineament was not a paleogeographic boundary." Unfortunately, this manuscript was never published (Schonlaub, personal commun., 2002). Another possibility (Boucot, personal commun., 2002) is that the Carnic Alps and adjacent Karavanken might have been located near the southern end of the western Urals in the earlier Paleozoic. This assumes that their present position in the Early Carboniferous was linked to the exceptional coeval crustal shortening (Neugebauer 1988) which would explain some of the lithostratigraphy and also the `Uralian' nature of the Early Devonian faunas.

Looking at the paleogeographic reconstruction of Paris and Robardet (1990), Robardet et al. (1994) and Vai (1991), there are several circum-Mediterranean microplates besides the Variscan Terranes on the northern margin of Gondwana. These areas (Fig. 1) represent Silurian continental platforms (shelves) covered by relatively shallow water. From West to East they are: Tinduf Basin, Anti-Atlas, Ougarta Chains (Aulacogen), Cantabrian Mountains, Central Iberian Domain, French Massif Central, Mid-North Armorican Domain, Eastern Pyrenees-Aquitaine, Montagne Noire, Southwest Sardinia, Carnic Alps (may be equivalent to the Southern Urals), Prague Basin, Eastern Serbia - Suva Planina Mountains, Zebrina locality (Kríz and Veselinovic 1975), Uppony Mts. (northeastern Hungary), Western Macedonia (Bouček et al. 1968), and beyond the Armorican sea tongue and ?Rheic Ocean (Carls 2001) towards the East, the Podolia continental platform. The latter must, however, be considered as belonging to Baltica (Bullard et al. 1965). The nautiloid cephalopod fauna of the Ukraine (Podolia) is tentatively compared to those reported above to check with possible links on biogeography during Silurian-Early Devonian time. A Variscan crustal shortening of about a thousand kilometres is indicated. This shortening, plus the strong westward rotation of Gondwana, probably constitute exceptional events, particularly during the Carboniferous (Neugebauer 1988), necessitating revisions in previous paleogeographic reconstructions. The hypothetical Palaeozoic Hercynian Ocean separating Europe from Africa, somewhere south of the Tornquist Line, has been discovered by Vai (1991) because of the distribution of the circum-Mediterranean "Orthoceras" limestone (see also Berry and Boucot 1967; Kríz 1998).