A standard SEM-EDS methodology to determine the test microstructure of fossil agglutinated foraminifera

We propose a methodology as a possible standard approach for micropaleontological studies addressed to detect test microstructure and the chemical/mineralogical composition of grains used by agglutinated foraminifera. The methodology was tested on over 200 specimens of fossil agglutinated foraminifera, mostly belonging to the textulariid group, collected from Cenozoic successions of the Mediterranean region. The approach assesses the internal morphological and compositional features of agglutinated foraminifera by Scanning ElectronMicroscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses, performed on representative specimens that were embedded in epoxy resin and subsequently sectioned and polished.With respect to similar techniques that perform SEM and EDS analyses mostly on the agglutinated wall surface of free specimens or broken tests, this methodology provides the preparation of cross sections of isolated individuals. The use of cross sections has the advantages of: (i) documenting the internal chamber arrangement and other morphological elements (such as alcoves or canaliculi), even considering if the recognized features remain constant or change during ontogeny; (ii) measuring the testwall thickness and the grain distributionwithin the testwalls; (iii) detecting the chemical composition of the agglutinated grains and the cement in order to highlight mineralogical grain selectivity and arrangement; (iv) studying the agglutinated grains in their original position within the test wall and during test growth; and (v) the elemental compositional data collected from polished sections are more accurate than those collected on the rough surface of specimens.