PROVENANCE STUDY OF ORDOVICIAN SANDSTONES ALONG THE SOUTHEASTERN APPALACHIAN MOUNTAINS

The paleoclimate during the early Late Ordovician has not been clearly defined. Paleoceanographic conditions across the Turinian/Chatfieldian boundary are being studied within the eastern part of the North American continent in order to estimate early Late Ordovician paleotemperatures. In particular, the shallow epicontinental sea of Laurentia is of high interest, due to lithologic changes which suggests a warm-water to cool-water transition. This cooling, however, needs further explanation, as eastern North America was located in tropical to subtropical latitudes at this given time.

In order to understand the reasons for this cooling, a provenance study of different sandstones in the area is being conducted. By learning more about the basin evolution through U-Pb geochronology of detrital zircons, the study will seek to answer if the cooling was a product of global or local conditions. Initial results from the Dodson Mountain locale (Bays Formation; northeast Tennessee and southwest Virginia) showed Proterozoic detrital zircons, with ages ranging mostly between 1000-1500 Ma. These are compatible with previously reported ages of the Grenville Orogeny. The data supports previous work stating the dominance of Grenville-age detrital zircons from sandstones throughout the central and southern Appalachians, and their hypothesized, intricate fluvial drainage from Taconic highlands in the north. Previous results from Reed Road and Horseleg Mountain (northwest Georgia), while still showing a dominant Grenville-age signal, also show a second signal indicative of younger, possibly Taconic ages. This secondary signal points to at least two different sources for these Ordovician sandstones.