Influences of Climate on Late Devonian Depositional Systems of the Central Appalachians

Late Devonian strata of the Appalachian Basin preserve dramatic lithologic differences between the Catskill Formation and overlying units.  These differences reflect a long-term replacement of climatic conditions from semi-arid to humid.  This gradual sedimentological changeover in Appalachian rocks is contemporaneous with the initiation of Late Devonian Gondwanan glaciation at paleo-high-latitudes of South America.  The Appalachian stratigraphic record of this long-term climate turnover reached its peak during the latest Devonian with deposition of the enigmatic Spechty Kopf diamictite of northeastern Pennsylvania and coeval Rockwell diamictite of western Maryland.  These extensive diamictite units are interpreted as piedmont glacial deposits formed in the paleo-mid-latitudes of the Appalachian Basin.  Strata correlative with these diamictites record a diverse assemblage of proglacial and periglacial depositional systems including glacial lake, outwash fan, and incised valley fillings.  The terrestrial sedimentologic signature of this peculiar interval is concurrent with evidence of increased precipitation and runoff fueling organic productivity in marine environments of Ohio and Kentucky.  The latest Devonian climate event appears to herald the deep time changeover from Middle Paleozoic greenhouse to Late Paleozoic icehouse conditions.