Bryozoan sediments in Cenozoic tropical environments

Studies of bryozoan faunas are generally regarded as a valuable source of information for reconstructing ecosystems of the geological past. Their occurrence and distribution patterns contribute essentially to the determination of various ecological factors like depth, water energy, temperature, salinity, sedimentation rate etc. and moreover yield considerable data for paleobiogeography. Realizing that Miocene bryozoan faunas from many parts of the Paratethys are understudied, not yet described at all, or described only briefly, one of the main goals of this project will be a thorough documentation of biodiversity of bryozoan faunas for the Miocene of Czech Republic, Slovakia and Hungary including detailed comparisons with Austrian faunas. For such comparisons exact biostratigraphical data are badly needed: studies of foraminifera as weil as of nannoplankton and dinocysts wi" yield sufficient data to confirm exact correlations of bryozoan faunas studied. Following the interpretations by many authors bryozoan-bearing sediments are regarded as indicative for cool- water environments. A high number of paleoecological data indicate however at least a subtropical climate for the Miocene of the Central Paratethys. Therefore one of the main items of this project will be to solve this obvious contradiction. Additional data, based on independent methods of paleotemperature measurements -oxygen-isotope determinations of bryozoan- bearing rocks or single bryozoan specimens -will be included in our studies too. To check the possibility of changes in food supply preliminary investigations concerning barium and other trace elements in some of the profiles will also be included. The results will hopefully contribute essentially to the distribution pattems for single bryozoan genera in the Central Paratethys and also enable a better understanding of ecological conditions under which bryozoan-bearing sediments have been deposited.

Bryozoa are a common, very often understudied faunal element in Recent seas and seas of the geological past. In the course of this project bryozoan faunas from Neogene sediments from the Central Paratethys have been investigated; our studies focussed on Moravian localities mainly, faunas mostly not studied since more than 100 years. In the course of our field work a number of new outcrops with bryozoan-bearing sediments were discovered. Beginning with a detailed documentation of the biodiversity of these faunas, problems of more general interest have been treated: the connection between local accumulations of rock-forming bryozoan skeletons and details of climatic development being one of the most challenging aspects. To yield informations of this kind profiles rich in bryozoan-bearing strata (e.g. bryozoan `reef` of Podbrezice) have been sampled layer by layer. The results enabled a reconstruction of paleoenvironments in the various states of development of these carbonate buildups. Realizing that the ecological background for such local accumulations of bryozoan skeletons could be either temperature changes and/or additional food supply (`high productivity events`), studies of stable isotopes of carbon and oxygen were performed. The results indicate that using bulk samples for this purpose, only diagenetic events can be testified; using bryozoan zoaria themselves however, the results show that a number of rather common bryozoan taxa can used for such studies in the sense of `paleothermometers`. Together with studies of foraminifera and calcareous nannoplankton in our samples a `multi-proxy` approach towards a detailed reconstruction of the development of local ecosystems in space and time could be achieved. In respect to possible `high productivity events` determination of barium traces in the profiles studied had been planned. This method is regarded as very useful for such purposes. Unfortunately however the co-operation necessary for these additional investigations did not work and we could not get the necessary data. The results of this project yielded a considerable increase of our knowledge of bryozoan faunas in the Central Paratethys with all consequences for ecological and biogeographical interpretations.