Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 18. 1996. (Budapest, 1996)

FRAGMENTA MINERALOGICA ET PALAEONTOLOGICA 18. BUDAPEST, 1996 p. 5-17 Environmental distribution and bathymétrie significance of Middle Triassic ammonoid faunas from the Balaton Highland (Hungary) by A. Vörös VÖRÖS, A. (1996): Environmental distribution and bathymétrie significance of Middle Triassic ammonoid faunas from the Balaton Highland (Hungary). - Fragm. Min. et Pal., 18: 5-17. Abstract: Large ammonoid faunas (more than two thousand specimens) have been collected from six sections of the Balaton Highland, encompassing the uppermost Anisian to Early Ladinian interval. Paleogeographically, three of the sections fall into basins, whereas other three have been on the top of pelagic plateaus. The environmental distribution of special morphogroups of ammonoids show that the proportion of "coronates" (strongly ornamented ceratitids) is consistently lower in the basins than in the pelagic plateaus, whereas "sphaerocones" (Ptychitidae + Arcestidae) show inverse relationship. During the studied interval, the proportion of "coronates" decreases, whereas the proportion of "sphaerocones" increases in time in the whole territory (both in the basins and on the pelagic plateaus). This relationship is used to estimate water depth and changes in bathymetry. INTRODUCTION The Ammonoidea, becoming extinct without present-day progeny, leave minor chance of uniformitarian approaches and pose delicate problems to the paleogeographer who would like to use them as tools in paleoenvironmental reconstruction. Nevertheless, since ammonoids are perhaps the most frequently found fossils in Mesozoic strata, paleontologists have never been satisfied with these excellent "guide fossils" and have always tried to obtain some paleoenvironmental information from them. Paleoecological analysis and habitat reconstruction became a rather widespread praxis in the case of Jurassic and Cretaceous ammonoid faunas (e.g. ELMI & ALMÉRAS 1984, MARCHAND et al. 1985, WESTERMANN 1990, CECCA et al. 1994) and the theoretical basis of these applications (from speculations to experiments) was also published in length (e.g. GÉCZY 1959, REYMENT 1973, EBEL 1985, see a review in WESTERMANN 1990). The Triassic is much less advanced in this respect. Apart from the traditional view that the "leiostracan" ammonoids (Ptychites, Monophyllites, Arcestes) were deep-water elements, hardly any detailed contribution has been given to ammonoid paleoecology until the recent paper by WANG & WESTERMANN (1993). This excellent study summarizes the autecology (morphotypes, habitats, siphuncle and septal strength) and