抄録
A detailed understanding and quantitative evaluation on the mechanism of elemental and isotopic fractionation in biogenic calcium carbonate are essential for a reliable past environmental reconstruction. Biogenic calcium carbonate has characteristic skeletal micro-structure which is strongly controlled by biomineralization. Elemental distribution pattern associated with skeletal micro-structure likely provides unique information on biological elemental fluctuation which can not be accessed by bulk scale analysis, because smaller spatial scale likely reflects more primary processes. To study the elemental fractionation mechanisms, the author has been studied micro scale elemental distribution patterns of coral skeletons, bivalve shells, and foraminiferal shells, and compared the patterns with skeletal micro-structure, sulfur distribution and organics. The micro-analytical studies have revealed that there are following two characteristic patterns that are common in all studied biogenic calcium carbonates, even though the studied specimens are different in phylum level.
(1) Significant compositional heterogeneities that cannot be explained by changes of ambient environment.
(2) Strong correlation of “Metal/Ca” ratios with the sulfur distribution, skeletal microstructure or organics, or some of them.
Based on such common features, I suggest the general mechanism of elemental fractionation applicable to the most biogenic calcium carbonates, namely, both soluble and insoluble organic composition and/or concentration in the calcifying fluid can facilitate a preferential elemental incorporation into biogenic calcium carbonate.
