Significance of Green-Mineral or Verdine Facies from Upper Ordovician and Middle Mississippian Rocks in the Western Appalachian Basin, East-Central Kentucky

Modern green-mineral or verdine facies are currently known from relatively shallow (15-60 m) continental-shelf environments off the coasts of South America, Africa, India, and Australia. Here, we report the first Paleozoic verdine-facies rocks from the Upper Ordovician Terrill Bed of Ashlock Formation and the Middle Mississippian Nada and Renfro members of the Borden Formation in western parts of the Appalachian Basin in east-central Kentucky. In each setting, the facies occurs in a deeper open-marine unit with fossils and is found interbedded with overlying, peritidal, ferroan dolomitic mudstones. The verdine-facies is largely composed of diffusely pigmented, olive-green shales and mudstones with no characteristic form or fully formed grains; diffuse silty carbonate debris may be present and the coloration diffusely impregnates bioclasts as well. Although glauconite is locally present, its occurrence is distinct from the unusual green pigment. Current investigations suggest that this unusual green color is related to an abundance of chlorite or other clay minerals. Comparison with other nearby facies, as well as stratigraphic and paleogeographic occurrences, indicate that such facies develop in iron-rich waters where streams debouch into shallow, warm, oxidizing coastal or lagoonal settings. During subsequent transgression, these muds are commonly reworked into overlying peritidal environments and may contribute to later dolomitization. In Kentucky, these verdine-facies environments seem to occur during times of tectonic and eustatic transition from clastic-rich to carbonate-platform settings in the Appalachian Basin. Such units appear to be widespread and may reflect transitions that have significant correlative value.