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

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 sulfa te. The sulfate is clearly not in the form of gypsum or anhydrite incl usions, and there is good evidence that the sulfate substitutes for ca rbonate. This finding validates systematic investigations of sulfate d istribution in modern and ancient carbonate minerals. Further, it docu ments that carbonate sedimentation is a sink for marine sulfate, accou nting for perhaps 15% of the annual sulfur sedimentary, depositional f lux.