Postmortem transport and resedimentation of foraminiferal tests: relationsto cyclical changes of foraminiferal assemblages

Cyclical changes in microfossil (mainly foraminiferal) assemblages were ana lysed for sixteen boreholes from three stratigraphical levels in the Lower and Middle Miocene of the Central Paratethys. The following characteristics of assemblages were quantified and used for interpretation of cyclical cha nges in assemblages: (I) abundance of foraminifers, calcareous nannoplankto n, sponge spicules and diatoms; (2) similarity, diversity and epifauna/infa una ratio of benthonic foraminiferal assemblages; (3) planktic/benthic rati o of foraminiferal assemblages. The palaeoecology (mainly palaeobathymetry) fluctuations were interpreted from the species composition of assemblages. Values of the mentioned quantitative characteristics as well as palaeoecol ogical interpretations may be influenced by postmortem transport and resedi mentation of foraminiferal tests. Therefore, prior to the interpretation of cyclical changes of quantitative characteristics, the studied sections wer e classified on the basis of the intensity of taphonomical changes in foram iniferal assemblages. Three different categories of sections were obtained. For every category, those quantitative characteristics of foraminiferal as semblages were chosen which reflect cyclical changes most efficiently: (1) cyclical changes of abundance of foraminifers, calcareous nannoplankton and sponge spicules, as well as the fluctuations in palaeobathymetry for secti ons dominated by indigenous foraminifers; (2) percentage of indigenous, sus pension-transported, bedload-transported and reworked foraminiferal tests a nd changes in the abundance of indigenous tests for sections dominated by t ransported tests; (3) different modes of test preservation used for the ide ntification of a cycle boundary for sections with only transported or rewor ked tests. The distinguished cycles were interpreted predominantly as manif estations of relative sea-level changes. if comparable data exist from othe r Paratethys regions, the determined cycles can be correlated with the othe r basins. (C) 1999 Elsevier Science B.V. All rights reserved.