Electron‐probe microanalysis of calcareous nannofqssils

Abstract

An electron‐probe microanalysis was undertaken to determine the presence and concentrations of trace elements in thirty nannofossils species representing most major Cenozoic morphological groups. Excellently preserved specimens from core samples from the Gulf of Mexico were analyzed with a combination scanning electron microscope and electron micro‐probe consisting of both dispersive and non‐dispersive X‐ray spectrometers. Any trace elements within the nannofossils examined are present only at levels below the limit of detectability of the instrument. The applications of trace element distributions in nannofossils to paleoecological or paleoenvironmental considerations do not appear promising. Compared to other calcareous algal groups, the nannoplankton are more discriminating against Mg and Sr uptake, and apparently they have been so throughout the Cenozoic. Other than that, biochemical evolutionary or phyletic relationships are not evident. It is also doubtful if nannofossils have been a major vector in the transport of trace elements into the pelagic realm. One of the factors that enhance the biostratigraphic utility of nannofossils is their relative resistance to dissolution during sedimentation. It is probable that the greater stability of the very low magnesium to pure calcite secreted by nannoplankton is one factor related to the higher degree of preservation of this group compared to other calcareous plankton.