Determination on ~(87)Sr/~(86)Sr ratio and stratigraphic dating of single-grain foraminifera

摘要

The Sr isotopic composition of foraminifera has been used in studies of chronstratigraphy and sedimentary geochemistry. However, it is difficult to sample foraminifera without overprinting of later diagenesis, which contains enough amount of Sr for isotopic measurement. Analysis of single-grain foraminifera was successively conducted by a combination of low Sr procedural blank and high precision determination of ~(87)Sr/~(86)Sr ratio. This combination of single-grain foraminifera can be significant for the study and application of Sr isotopic composition of foraminifera. Measured foraminifera of this study, having a size between 250 mu m and 400 urn, were sampled from the carbonate basement of a ferromanganese crust in western Pacific. Mean value of ~(87)Sr/~(86)Sr ratios of the analyzed single-grain foraminifera is 0.709150 + - 0.000013 with internal , precision between 4 ppm and 8 ppm for each measurement run. Average value of total procedural blank of Sr is 14 pg. It is significant but difficult to date foraminifera in carbonate basements of ferromanganese crusts. Based on the obtained value of ~(87)Sr/~(86)Sr ratio, the analyzed foraminifera can be dated at 0.91 +0.33/-0.39 Ma.