FROST IN THE DEVONIAN? MICROMORPHOLOGY OF LATE DEVONIAN PERIGLACIAL ENVIRONMENTS IN THE APPALACHIAN BASIN.

The latest Devonian in the Appalachian Basin is characterized by glaciogenic deposits in the terrestrial realm and mass extinctions in the marine. The “red beds” of the late Famennian stage are preserved in the Catskill and Hampshire Formations in Pennsylvania and West Virginia, respectively. Overlying these formations are glacial diamictites often referred to as originating from a tidewater or alpine glacial source. Apparent relict periglacial macrostructures have been found in three upper red bed outcrops, including seasonal frost cracks (ground wedges) and a trough-like ice-wedge deformation structure. Thin sections of the latter structure reveal features characteristic of cold-region soils such as round to mamillated vesicles, lenticular microstructure, and silt cappings on grains. Such microscale features, while common to permafrost environments, can also occur under deep seasonal frost. Overall, these findings suggest that deep seasonal frost and/or permafrost could have been present in the Appalachian Basin during the Late Devonian at subtropical-tropical latitudes. The upper parts of the redbed formations belong to the LE/LN spore zones, contemporaneous with the onset of glaciation in Gondwana as well as the Hangenberg Crisis.