The marine geochemistry of rehenium (Re) has attracted interest in recent years due to its extreme enrichment in reducing relative to oxygenated sediments and the utility of ReOs geochronometer for dating ancient black shales. Recent work has pointed out the essential features of its oceanic behavior, including its long residence time and conservative distribution in seawater. In this regard, Re is similar to Mo and U in its marine chemistry, all of which occur as oxo-ions or oxo-ionic complexes in oxic seawater. All three elements are also enriched in anoxic sediments relative to oxic sediments, by factors of 500 (for Re) to 5-50 (for Mo and U). It appears that Re is not enriched in any other sedimentary phase. Recent work has suggested that these elements (as well as V) may be used as indirect proxies for the redox state of ancient oceans, or of depositional environments. These suggestions follow one of two approaches: the first would utilize the sedimentary concentrations of the elements, while the second relies on records of their seawater concentration contained in foraminiferal calcite. This research will studt Re in the context of these other elements to determine whether it may be a useful indicator of paleoenvironment using either of the two approaches. Re concentrations will be measured in pore waters and sediments from a variety of depositional environments, including anoxic basins, low-oxygen hemipelagic sites, and fully oxygenated hemipelagic sites. The results of this investigation will attempt to answer basic questions about the mechanism of Re enrichment in anoxic sediments and relate Re behavior to environmental parameters.
