Postmortem transport and resedimentation of foraminiferal tests: relations to cyclical changes of foraminiferal assemblages

• Published in: Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 1999, Vol.145 (1), p.157-182
• Main Author: Holcova, K
• Format: Article
• Language: English
• Subjects: Central Paratethys; cyclical changes; Foraminifera; foraminifers; Neogene; sea-level fluctuation; taphonomy
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/S0031-0182(98)00100-X

Cyclical changes in microfossil (mainly foraminiferal) assemblages were analysed 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 changes in assemblages: (1) abundance of foraminifers, calcareous nannoplankton, sponge spicules and diatoms; (2) similarity, diversity and epifauna/infauna ratio of benthonic foraminiferal assemblages; (3) planktic/benthic ratio 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 palaeoecological interpretations may be influenced by postmortem transport and resedimentation of foraminiferal tests. Therefore, prior to the interpretation of cyclical changes of quantitative characteristics, the studied sections were classified on the basis of the intensity of taphonomical changes in foraminiferal assemblages. Three different categories of sections were obtained. For every category, those quantitative characteristics of foraminiferal assemblages 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 sections dominated by indigenous foraminifers; (2) percentage of indigenous, suspension-transported, bedload-transported and reworked foraminiferal tests and changes in the abundance of indigenous tests for sections dominated by transported tests; (3) different modes of test preservation used for the identification of a cycle boundary for sections with only transported or reworked tests. The distinguished cycles were interpreted predominantly as manifestations of relative sea-level changes. If comparable data exist from other Paratethys regions, the determined cycles can be correlated with the other basins.