THE PEDOGENIC EXPRESSION OF ACADIAN OROGENIC ACTIVITY IN THE APPALACHIAN BASIN: THE FORELAND-HINTERLAND CONNECTION

Soils form in response to five primary factors (climate, organisms, relief, parent material, and time) that manifest as particular soil features representing distinct processes and products, and which can be preserved in the geological record as paleosols. The Appalachian Basin preserves numerous paleosols reflecting variations in these factors throughout the Devonian, including relative changes in mean annual precipitation (climate), the paleobotanical revolution of terrestrial ecosystems (organisms), and variability in soil types as a function of proximity to stream channels and paleo-shorelines (relief and time). Of these factors, the influence of parent material on soil formation can be used as a proxy for the influence of volcanogenic activity associated with the Acadian Orogeny. Weathering of volcanogenic parent materials produces smectite which, when incorporated into soil profiles, results in expansion and subsequent contraction of the soil column with repetitive wetting events to form Vertisols, soils with very distinctive macroscopic and microscopic features. Vertisols are preserved in the Appalachian Basin and are intercalated with non-vertic paleosols, suggesting that they formed in response to episodic influxes of volcanogenic materials into the terrestrial environment. In contrast, constant erosion and input of smectite sourced from the orogen would promote a dominance of vertisols through time. The transition from vertic to non-vertic soils is accomplished by burial and subsequent isolation of the vertisol by smectite-poor materials until the next influx of volcanic ash. Although it is very likely that smectitic materials were recycled by fluvial processes, the relative proportion of vertic versus non-vertic paleosols throughout any given section of the foreland basin should be a reflection of the intensity of volcanic activity. While only a dozen or so distinct airfall volcanic tephras have been recognized from terrestrial environments of the Givetian to Frasnian (ca. 15 my), hundreds of vertisols are preserved throughout this same interval. As such, vertic soil activity in the foreland of the Appalachian Basin can serve as a proxy for volcanic activity in the hinterland, representing a much more detailed record of Acadian volcanism than provided by altered airfall tephras.