Mineralogy of agglutinated benthic foraminifera; implications for paleo-environmental reconstructions

Benthic foraminifera of recent salt marsh environments are often dominated by species with an agglutinated test. The grains used for test construction by these foraminifera are collected from their surrounding environment. In this study we investigated the role of sediment grain size and mineralogical composition for richness, population density and taxonomic composition of agglutinating foraminifera. Foraminifera from 15 stations of the tidal marsh of the Canche estuary (Pas-de-Calais, France) were studied. The species richness depends on the grain size of the sediment, whereas the density is not related to sediment grain size. The distribution of foraminifera species throughout the tidal marsh may depend on many environmental parameters such as OM as well as tidal elevation, already largely discussed in literature. The mineralogical composition of the agglutinated grains in Trochammina inflata and arenoparrella mexicana is very different from that of sediment; the composition of Jadammaina macrescens is generally different from that of the sediment with some exceptions, and in Miliammina fuca, Paratrochammina haynesi and Remaneica plicata the mineralogical compositions are similar to those of sediment. The studied species may be able to select their preferred grains based upon composition even if a particular mineral is scarce in the sediment.