PYRITE MINERALIZATION IN DEVONIAN-AGE BLACK SHALE IN SOUTHWEST VIRGINIA: IMPLICATIONS FOR ACID DRAINAGE AND PALEOENVIRONMENTAL RECONSTRUCTION
In this study we present results of an ongoing investigation of ARD, pyritization and paleoenvironment reconstruction of the Middle Devonian Millboro Shale exposed near Radford in southwestern Virginia. We extracted a total of 368 cm of the Millboro Shale strata using a portable, gasoline-operated, concrete-cutting saw. Prior to the extraction of the stratigraphic column, a total of 30 pyritic nodules, pyritized worm burrows, and various other occurrences of pyrite were sampled and analyzed for their paleoenvironmental information.
In lab, strata were analyzed for parameters including - patterns of lamination, ichnofabric indices (i.e. levels of bioturbation), point-counts of pyrite flecks and type of macro- and micro-sedimentary structures. Samples were also examined with a Scanning Electron Microscope (SEM) and a Z-stacking Dissecting Microscope (ZDM) for ascertaining primary and secondary crystal morphologies. Results highlight overall relationships between levels of bioturbation, erosional surfaces, pyrite distribution and events of benthic oxygenation possibly related to storm surge events in this setting of the Appalachian Basin.