IDENTIFICATION OF SULFATE IN NATURAL CARBONATES BY X-RAY ABSORPTION SPECTROSCOPY

Abstract

We have analyzed sulfur K-edge X-ray absorption near-edge structures (XANES) and demonstrated, with a high degree of certainty, that sulfur is present in a variety of biogenic and diagenetic carbonates as sulfate. The sulfate is clearly not in the form of gypsum or anhydrite inclusions, and there is good evidence that the sulfate substitutes for carbonate. This finding validates systematic investigations of sulfate distribution in modern and ancient carbonate minerals. Further, it documents that carbonate sedimentation is a sink for marine sulfate, accounting for perhaps 15% of the annual sulfur sedimentary depositional flux.