Fine-Scale Structure of the Seawater Strontium Isotope Curve at the Cretaceous/Tertiary Boundary: ABSTRACT

Abstract

The fine-scale structure of the seawater strontium isotope curve near the Cretaceous/Tertiary boundary is of particular interest because it may reflect some of the unusual events that occurred at that time. The authors report an attempt to document that record, emphasizing experimental aspects relevant to strontium isotope stratigraphy. They used very small, well-documented samples of hand-picked foraminifera typically containing about 20 ng Sr. Thus, a fragment of one individual can be analyzed for large specimens, or several individuals for smaller ones. This makes it possible to examine each foram using the scanning electron microscope and reject obviously recrystallized samples. Furthermore, each sample represents a specific point in time rather than an average. However, definition of the curve is limited by age determinations and mechanical reworking. Reproducibility of each data point is well within the precision determined from repeat analyses of NBS 987. This was verified by 10 sets of duplicates and 18 intercore comparisons of samples with similar ages. Also, seven individually analyzed forams from one sample yielded a variation around the mean equivalent to the standard uncertainty. Applying this technique, they have found a statistically significant step function increase in {sup 87}Sr/{sup 86}Sr at the Cretaceous/Tertiary boundary. Recovery frommore » this perturbation was much faster than expected from the residence time of Sr in seawater, suggesting an influx of less radiogenic Sr, possibly from weathering of Cretaceous carbonates.« less