Ostracod faunas as palaeoenvironmental indicators in marginal marine environments

Abstract

Ostracod species diversity in marginal marine environments is markedly lower than in non- and fully marine ecosystems. This largely reflects the physiological burden encountered during diurnal tidal cycle (e.g. salinity changes). These environments encompass not only the open-marine systems but also settings that undergo marked environmental variability over a range of timescales. The abundance of individuals in marginal marine environments can reach very high levels resulting in near monospecific faunas of specialised taxa. The ostracods must tolerate varying parameters such as salinity, temperature and dissolved oxygen levels over a range of temporal scales and even short periods of exposure. Given the often poor preservation potential of organisms in marginal marine environments there may appear to be limited potential for ostracods in Quaternary research, however, in this work we review the utility of these organisms in reconstructing past sea-levels and salinity regimes in marginal marine settings, based on criteria such as sieve-pore shape, noding, shell size and shell chemistry. In the following pages we outline the range of modern environments from which marginal marine ostracods have been investigated, discuss their preservation potential and illustrate (where possible) examples of similar environments from Quaternary deposits. Subsequently we discuss the reconstruction of past marginal marine environments from individual specimens, particular species or a fossil assemblage. Finally, we give two case studies of the use of ostracods in reconstructing past marginal marine environments from Holocene sediments in Norfolk, eastern England and from Menorca, Balearic Islands in the Mediterranean.