Distribution patterns of trace elements in fossil molluscan shells

In order to study the diagenetic change of chemical constituents in shells during the course of fossilization, the relations between the trace elements contained in shells and the geological age of shells were examined from a statistical point of view. Twenty six minor or trace elements in shells of Pelecypoda collected from the Miocene, Pliocene, Pleistocene and the Holocene deposits in the northeastern Japan were determined by neutron activation analysis. In dealing with the results statistically, the writers applied the lognormal distribution law. In the case of the Recent leached shells, the lognormal curves of trace element concentration in aragonitic shells are similar to those of calcitic ones except sodium. The concentration range of sodium in aragonitic shells is very narrow and that of calcitic ones is wide. Most of the examined elements show the lowering tendencies of peak height of lognormal curves with the geological age. However, the highest peak of a few elements is recognized in samples of the Pleistocene or the Pliocene-Miocene. From these facts, it is concluded that there is no simple relationship between the trace element concentration in fossil shells and the geological age. The relative abundance ratios of the trace element contents to the scandium content in shells were compared with those of crust of the earth. These values were examined in connection with the geological age. (author)