Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 19. 2001. (Budapest, 2001)

Middle Triassic (Anisian) nautilid cephalopods from Aszófő (Balaton Highland, Hungary) by Attila VÖRÖS Abstract — A nautilid fauna of medium abundance (38 specimens) was collected from the Aszófő section, well known for its rich ammonoid (Balatonites) fauna, and its biostratigraphic importance (one of the best secdons for the Pelsonian Substage). The naudlid fauna is diverse: ten species were determined. Systematic description of the ten species is given; from among them Encoiloceras balatonicum sp. n., Fncoiloceras lajosi sp. n. are new. Keywords — Triassic, Anisian, Balaton Highland, Hungary, Nautilida, systematic descriptions. VÖRÖS, A. (2001): Middle Triassic (Anisian) nautilid cephalopods from Aszófő (Balaton Highland, Hungary). — Fragmenta Palaeontologica Hungarica, 19: 1-14. Introduction After its golden ages in the Paleozoic, the subclass Nautiloidea reached a secondary flourishng period in the Triassic (see DZIK 1984). Nautilid cephalopods are subordinate to ammonoids in Tethyan Middle Triassic marine sediments, but they are frequently found around the Tethyan region, in the Germanic (MUNDLOS & URLICHS 1984) and the Sephardic provinces (e.g. PARNES 1986, GOY & MARTINEZ 1996) and even in the Arctic basin (SOBOLEV 1989). The Alpine-Mediterranean area is especially rich in Middle Triassic nautilids (HAUER 1887, 1892, 1896, MOJSISOVICS 1882). Surprisingly, the Balaton Highland, which is among the best known and richest fossil localities of the Alpine Middle Triassic, provided very limited knowledge on Nautiloidea. Apart from some early descriptions of orthoconic forms ("Orthoceras cfr. lateseptatum" in STÜRZENBAUM 1875), coiled nautiloids (Nautilida s.str.) were rarely mentioned and never figured or described. In his voluminous geological description ("Balaton Monograph") LÓCZY (1913, 1916) mentioned the following four species of Anisian Nautilida in faunal lists: Vkuronautüus Mösts MOJS. Vkuronautüus ambiguus ARTH. Vkuronautüus cf. Ko liiert ARTH. Vkuronautüus sp. ind. ex. äff. ptycboides ARTH. In the last decades the Hungarian Geological Institute carried out a detailed geological mapping of the Balaton Highland. The results of this mapping were published recendy (BUDAI et al. 1999). The Middle Triassic paleogeography (sedimentation and paleotectonics) of the Balaton Highland was dealt with by BUDAI & VÖRÖS (1992) and HAAS & BUDAI (1995); a complex paleogeographical picture was outlined in the paper by VÖRÖS et al. (1997). The biostratigraphy of the most important localities and sections have been described and their ammonoid faunas have been listed by VÖRÖS (1998). In the course of the fieldwork, supported both by the Hungarian Natural History Museum and the National Scientific Research Fund, a great amount of fossils was collected, mainly by T. BUDAI, L. DOSZTÁLY, I. SZABÓ and the present author. The collecting were focused on the ammonoids, but, besides the frequent brachiopods, bivalves and gastropods, some dozens of nautiloids were also found in the Middle Anisian to Upper Ladinian interval. Orthoconic and coiled groups are both represented; the coiled Nautilida are especially diverse. The richest assemblage of Nautilida was collected in the Aszófő section (Pelsonian to Early Illyrian: Balatonicus to Binodosus Subzones); this fauna is described in the present paper. Locality Aszófő lies at the central segment of the Balaton Highland (Figure 1). Here the Middle Triassic basinal sequence is extremely thick (see BUDAI & VÖRÖS 1992, VÖRÖS et al. 1997). The Aszófő section is located on the slope of the Farkó-kő (Farkó Hill) about 2 km north of village Aszófő near the forestry road leading to Balatonszőlős. The section was excavated, after the assignment by I. SZABÓ, in two parallel, partly overlapping trenches of 50 m length. The limestone sequence, exposed in about 20 m thickness is underlain by the Megyehegy Dolomite Formation. The lower part of the sequence is dolomitic, then becomes more and more calcareous, marly and nodular; in the yellow-motded beds (Beds 11/40-42) poorly preserved ammonites (Balatonites ottonis, Acrocbordiceras sp.) have been found. The next part of the sequence is dominated by pebbly mudstones and biodetrital limestones "Recoaro limestones"), interpreted