STRONG SEASONALITY DURING EARLY FORESTATION on TECTONICALLY INFLUENCED LANDSCAPES IN THE MIDDLE DEVONIAN, APPALACHIAN BASIN, NEW YORK: RESOLVING CHANGES IN CLIMATE FROM BASE-LEVEL

Middle Devonian terrestrial strata deposited in the Appalachian Basin record very dynamic landscapes characterized by extreme rainfall seasonality and tectonically driven changes in sedimentation, contemporaneous with development of forest ecosystems. The Middle Devonian clastic wedge, derived from the Acadian orogen, was deposited during a series of tectophases as Avalon accreted onto the Laurentian continent. These tectophases have been recognized as a series of subsidence and sedimentation pulses in the Appalachian Basin that we have been able to identify in fluvial sections using fluvial cycle thickness and paleosol maturity. Several fluvial sequences are defined by increases in accommodation that coincide with a change in fluvial style from suspended-load-dominated sedimentation to a bed-load-dominated system. As accommodation within a sequence subsequently decreased, fluvial style returned to a suspended-load system with increased paleosol occurrence, maturity and drainage. Several soil orders are represented in these paleosols ranging from weakly-developed paleo-Entisols, moderately-developed paleo-Inceptisols and strongly-developed paleo-Vertisols and vary from poorly- to well-drained. Using the newly defined paleo-precipitation proxy CALMAG (a geochemical ratio from bulk soil material in fine-grained paleosols), the average mean annual precipitation (MAP) for the majority of these paleosols is estimated at ~1600 mm/year. Six paleosols, however, have lower estimates (ranging from ~850—1350 mm/year), as a result of elevated weight % CaO, which occurs at sequence boundaries in response to base-level fall or in extremely aquic paleosols. Carbonate-bearing vertic paleosols forming in a tropical climate suggest strong precipitation seasonality. Under seasonal climate conditions geochemical ratios from bulk matrix material in hydromorphic paleosols can be influenced by the average timing and duration of subaerial exposure that can result from changes in base-level or geomorphic position on the landscape. Using paleo-MAP proxies from geochemical ratios in vertic paleosols without contextual pedogenic and stratigraphic information may misrepresent changes in pedogenesis from geomorphic or hydrologic variability as changes in climate.