Paleoecology of limnic ostracodes: A review of some major topics
Abstract The paleoecology of limnic ostracodes is reviewd in the context of the evolution of their environment. In order to understand why there is a rich ostracode fossil record we examine data such as the quantitative and qualitative distribution of living ostracode species and ostracode assemblages (ways of describing and limitations). Importance of biological and physico-chemical factors for the local accumulation of high numbers of ostracodes and diversified assemblages is emphasized. We discuss the limits of extrapolations of information from ecology to paleocology. We stress how paleontological knowledge can be applied to neontological studies. The possibility of using Holocene ostracodes as indicators of morphometric changes of lakes, temperature, salinity, eutrophication and as a criterion of meromictic conditions is demonstrated. Relationships between ostracodes and the chemical environment and particularly the morphological response of the carapace are considered: e.g., diversity and qualitative composition of assemblages and chemical stability, types of carapace mineralization and ornamentation and chemistry of bottom waters. These ideas, developed from studies on Recent material, are tested for limnic Cenozoic faunas. In the Mesozoic, the main questions arising from the study of nonmarine ostracodes deal with the possible evaluation of paleosalinities in marginal lagoonal environments (Purbeck-Wealden) and with evaluation of depth and hydrochemical and paleoclimatological regime in truly lacustrine intracratonic basins. Some peculiarities of Paleozoic nonmarine ostracode assemblages are described. The paleoecological cause of changes in diversity of several ostracode groups in the Carboniferous and Permian is emphasized.