Techniques for the concentration of foraminifera from coastal salt meadow sediments

Abstract. INTRODUCTION

Concentration of modern foraminifera from sediment samples is commonly performed by the heavy liquid carbon tetrachloride (CCI₄) flotation method. From mainly inorganic, siliclastic sediments from marine habitats, about 94% of the foraminifera contained within a sample can be isolated in the first step (Lutze, 1968). This procedure is used in order to reduce the time taken to examine the foraminiferal content of a sample. However, it is not practical in all cases. Surface sediments of salt meadows from the west coast of the German Bight (southern North Sea) can be divided into two main types: (1) in seaward parts with only a patchy distribution of spermatophytes there is soft mud with a high content of detritus (faecal pellets and plant material) and low content of inorganic components (clay and finest sand); (2) in landward parts there is low moisture soil with a high content of living and dead plant roots similar to that of terrestrial meadows. Foraminifera of sediments of these kinds cannot be isolated by the flotation method for the following reasons.

For sediment of type 1, if fractions 60–1000 μm (all clay eliminated by washing) have been dried in order to submit them to the flotation method, a serious problem arises. Flocky/grainy detritus aggregates to a cement-hard mass which encloses all the foraminifera. This ‘cake’ cannot be disaggregated without damaging or destroying the foraminifera.

For sediment of type 2, when sediment treated the same way as sediment of type 1 is dried, fine plant remains, mainly . . .