Abstract
Sodium, chlorine, manganese and strontium in fresh shells of pecten collected from the Enoshima-Bay, Miyagi Prefecture were determined by nondestructive neutron activation analysis to study changes in statistical distribution of chemical elements of shells by diagenesis. Samples of the fresh shell consist of three groups, i. e., different parts of the same growth stage in the same disc (group A), different parts of the same disc along a central radial rib (group B), and similar parts of different discs (group C). In order to compare with the fresh shell, data of the Recent shells reported in the previous works were also examined as leached shells (group D). Samples of group D consist of similar parts of different discs, but their locality and buried period were not the same.
Geometric means of sodium, chlorine, manganese and strontium contents in each group were calculated, and the fitting of lognormal distribution to data for manganese and strontium was illustrated. Each element in group A exhibited the least relative standard deviation. These values were much the same as the experimental errors of γ -ray spectrometry. Medium variations observed in groups B and C may be reflections of environmental and individual variations of living shells, respectively. On the other hand, group D showed large variations in contents of all the elements. Large differences in the distribution of elements between the fresh shells (groups A, B and C) and the leached shells (group D) are perhaps due to the versatility in diagenesis in the latter. These results seems to be of importance for the study of paleoenvironment by trace elements in fossil shells, because similar phenomena may also have happened among fossil shells during the process of fossilization.
