Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 21. 2003. (Budapest, 2003)
FRAGMENTA PALAEONTOLOGICA HUNGARICA 21, BUDAPEST, 2003 Palaeocommunity studies on Eocene larger Foraminifera of the Bakony Mountains (Transdanubia, Hungary) by Tibor KECSKEMÉTI Abstract — The paper introduces five Nummulites-pzlaeocommumties which succeeded each other in the seas of the Bakony region during the Early Lutetian to Latest Eocene to Earliest Oligocène time interval. Two of the palaeocommunities are Lutetian, two others are Bartonian and one is Priabonian. Their reconstruction below is presenting the composition, the dominant population, the density, the diversity and also the relation of nummulits to the most important other large formainifers. Tracing of the changes in the palaeocommunities received a special respect. From the factors inducing the changes, those are discussed which are connected to tectonism, global sea-level changes, climate, and water chemistry (salinity, Sr-content). Formation of the so-called "monospecific" faunas and the possible influence of ontogenetic and phylogenetic factors, independent from the environment are also discussed. Key words — Nummulites, Eocene, palaeocommunities, Bakony Mountains, Hungary. KECSKEMÉTI, T. (2003): Palaeocommunity studies on Eocene larger Foraminifera of the Bakony Mountains (Transdanubia, Hungary). — Fragmenta Palaeontologica Hungarica, 21: 33-41. Introduction In Hungary no palaeocommunity studies have been done so far on larger Foraminifera. Consequently, no home literature was available. The majority of the more and more numerous relevant papers published abroad are dealing with general problems, interrelations, of the evolution and the ecosystems, and investigations on the higher macrobenthos. Few papers have been published on palaeocommunities of benthic and planktonic small foraminifera. Some of these concern recent faunas (HlLTERMANN & TÜXEN 1974; GRÜNIG & HERB 1980; HlLTERMANN, BRONNIMANN & ZANINETTI 1981; HlLTERMANN 1982; GRÜNIG & HERB 1984; HOFFMANN & KlTCHELL 1984; HERB 1988). Beside these, I have found many interesting, mainly ecological data, in papers on reef communities (FRAGERSTROM 1987; COPPER 1988). ROLLINS, CAROTHERS & DONAHUE (1979) published interesting observations concerning succession changes brought about by sea level changes (transgressions, regressions). The two main aims of the studies summarized in the present paper were: - to define the taxonomic composition of the Nummulites communities in the Bakony Mountains, — to trace the changes occuring in the palaeocommunities from the Early Lutetian to the Eocene/Oligocene boundary. In order to attain the first aim, it was necessary to establish the dominant Nummulites populations, as well as their relations to the stratigraphically and palaeoecologically most important other genera of larger Foraminifera. In order to approach the second aim, it was necessary to consider all the environmental factors that affect the Nummulites communities. It had to be studied, how do they effect the composition of the communities, the areas of individual populations, their bathymétrie distribution, living conditions, and their relations to other foraminifer genera. Furthermore, attention had to be paid also to evolutionär}' factors and effects that operate independentiy of the environment, because these may have played the role of an "internal engine" in the changes and evolution of the communities. The starting point was the factual evidence accumulated during the previous studies of taxonomic, stratigraphical, palaeoecological and palaeobiogeographical nature. Out of these, the palaeogeographical data (KECSKEMÉTI 1978) proved to be the most useful (areas, relationships, provinciality, diversity etc.). Relying upon these, I selected five profiles out of the more than 50 profiles which had been thoroughly investigated, in a way that they should represent a fair areal coverage of the Eocene formations of the Bakony Mountains. The representative profiles are Eocene core columns of boreholes Somlóvásárhely 1. (S v. 1.), Csehbánya 1. (Cseh. 1.), Pénzesgyőr térképező 31 (Pgyt. 31.), Dudar 218. (D. 218.) and Balinka 219 (Ba. 219.). In a next step, intervals were chosen, each of which represents a chronostratigraphic unit, i.e. a zone. The Nummulites laevigatus Zone of the Lower Lutetian is represented by the following depth intervals: 829.0 m in borehole Sv. 1., 181.2-183.6 m in borehole Cseh. 1. The Nummuites lorioli Zone in represented by the interval 146.2—148.2 m in borehole Cseh. 1. The Nummulites perforates Zone of the Bartonian is represented by core 780.0 m in borehole Sv.l., as well as by the intervals of 56.0— 59.6 m in borehole Pgyt. 31., 172.2—172.7 m in borehole D. 218., and 443.0-443.3 m in borehole Ba. 219. The Nummulites millecaput Zone of the Bartonian is sented by the core 759.9 m of borehole Sv. 1. and of the interval
