Calcareous nannofossils play an important role in biostratigraphy and paleoecology, though their study is often complicated by their reduced size. The methodology presented herein allows to separate the nannofossil assemblage into granulometrically and taxonomically homogeneous fractions. This method permits :a) the concentration of rare taxa in order to simplify their morphometric study; b) the geochemical analysis (stable isotopes and trace elements) of these fractions. The latter is helpful in many cases, especially when the analysis of major or minor taxa constituent of the assemblage is greatly complicated by the reduced particles dimensions. In this way, it will be possible to bring light to the ecological parameters of these taxa, as calcification temperature and other ecological requirements (salinity, nutrient concentrations).