Environmental control on shell structure and composition of agglutinated foraminifera along a proximal–distal transect in the Marmara Sea

The study of benthic foraminifera in a complex marine system, like the Marmara Sea, is a key for understanding the influence of environmental factors on foraminiferal species, density, assemblage composition, and shell construction. This kind of study is important for further extensive use of foraminifera-based investigation of water mass and sediment exchange between the eastern Mediterranean and Black Sea through the Marmara Sea. Based on proximal–distal transect from the southwest coast of the Erdek Bay to the top of canyon close to the North Anatolian Fault, this study aims at defining the geochemical conditions at the seafloor and identifying the sediment constraints that act upon agglutinated test construction for selected species (Eggerelloides scaber, Textularia agglutinans, Textularia sagittula, Textularia truncata and Textularia bocki). Grain size, mineralogical, and chemical analyses of their shells were investigated and confronted with the main geochemical conditions prevailing during deposition and within the sediment. Among grains used to construct the agglutinated foraminiferal tests from available grains, both grain size selection and sorting have been evidenced. This suggests that the mineralogical composition is related to the species and the sample localization within the basin. Our observations further suggest that bottom water conditions of the Marmara Sea do not have a significant influence on agglutinated foraminiferal shell development, which is primarily driven by sediment characteristics. Our results are thus transposable to other environments.

► We study sediment parameter effects on foraminiferal agglutinated test.
► Bottom water redox conditions play no detectable role on grain selectivity.
► The test chemical composition shows a “fractionation” relative to bulk sediment.
► Respective to bulk-sediment mineralogy and grain size, forams select specific grains.