Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 14. 1989. (Budapest, 1989)
FRAGMENTA MINERALOGICA ET PALAEONTOLOGICA 14. BUDAPEST, 1989 p. 73-82 Bathymétrie significance of Recent Larger Foraminifera: an example of application to the Eocene of Hungary By T. KECSKEMÉTI (Received December 16, 1988) Abstract: A distribution model is presented for Eocene sedimentary rocks of Bakony Mts. formed under different water depths, based on bathymétrie significance of larger foraminifers, using backward extension of modern sea investigation's data. A shallow marine environment developed by rapid transgression during the Early Lutetian time. A deepening trend resulted in more pelitic sedimentation and decrease of larger foraminifers reached shallow bathyal depth range during the Late Lutetian time. Larger Foraminifers as benthic organisms offer excellent information concerning several environmental factors, like rock quality of the basement, currents and water depth. At present this latter is of primary importance for us. Our purpose is to supply bathymétrie data for the reconstruction of the geological evolution of the Transdanubian Paleogene basins, and to provide ideas, based on observations of larger Foraminifera. This task is rather complicated. Among the several factors the following two are of the most importance: determination of the depth range of the larger Foraminifers and evaluation of their role as depth-indicators. The difficulty of the problem is clearly shown by the fact that the depth-range of the different genera and species of larger Foraminifera is in correspondance with several ecological factors. Transillumination of the water should also be considered, since the larger Foraminifera, being primarily symbiont-bearing, need the light to a great extent - according to an important (biological) discovery of the past decade (DIETZELBRÀCHTER 1971, RÖTTGER 1972, HOTTINGER and DREHER 1974, LEUTENEGGER 19771, The symbionts are mostly algae, and their assimilation requires proper light intensity, but its quality is also important. The depth range depends also on the basement. Of the several factors a direct one is the epiphyte coverage of the bottom (food and habitat preferencel, and an indirect one is the nutrient content of the sediments (organic detritus etc. ) and the pore volume facilitating or hindering the penetration into the bottom. Several observations and data are available for these relations and mutual effects on the basis of recent marine biological and ecological investigations. At the present treaty L. HOTTINGER's two model areas are considered (HOTTINGER 1984). One of them is in an open ocean environment on one of the Maldive Islands in the Indian Ocean, while the other is a more closed marine region, the NE bay of the Red Sea, the Elat (or Akaba) Bay. For both sites no actual model is elaborated, that serves as a good basis for the comparison of Recent and fossil material, and for finding analogies of present conditions and processes in the geological past. Analysis and up-dating is made more solid by the fact that species of genera that existed already in the Paleogene, or more precisely in the Eocene were mostly observed. These are: Nummulites cummingi , Operculina ammonoides, Heterostegina depressa , Borelis melo
