FORMATION OF PYRITE IN THE WALDRON SHALE (NIAGARAN-SILURIAN), DAVIDSON COUNTY, TENNESSEE

The appearance of pyrite (FeS₂) in the Waldron Shale is not a new one. Pyrite has been identified in the formation replacing fossils around its type locality in Indiana. However, the concentration and formation of pyrite roughly three hundred miles to the south in Tennessee, along the edge of the Nashville Dome, indicates that the mineral is not localized. Pyrite replacement of fossils in the Waldron is less complete in Tennessee than in Indiana, and mean crystal size is smaller. Tennessee pyrite is euhedral and in some instances displays octahedral habit. Towards upper portions of the formation, pyrite is oxidized into hematite (Fe₂O₃) and pseudomorphs are seen. High amounts of organic material resulted in bacterial sulfate reduction, which in turn formed pyrite. The existence of pyritized burrows in the limey units of the upper Waldron suggest that the pyrite was depositional. Fractured pieces of fossils in areas of the formation indicate higher energy environments which allowed oxygen to convert existing pyrite into hematite. Additionally, the burrows allowed oxygen to reach lower into the Waldron, arising in iron oxide precipitation.