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Manorkill Formation
The Devonian aged Manorkill Formation is comprised of red sandstone and shale that overlies the Plattekill Formation and underlies the Oneonta Formation. The formation is ~151 feet thick and thickens to southeast, becoming ~220 feet deep in the Durham quadrangle. The formation thins and wedges out southwestward from Schoharie Valley.

Location
The Manorkill Formation outcrops on the northern edge of the Appalachian Basin Geologic Province. In New York the formation is adjacent to the Schoharie Reservoir, located in the Druham quadrangle in southeastern, New York. Exposure of the Manorkill Formation is visible in the area along Platte Clove Road, between Tannersville and West Saugerties. These exposures consist of laterally continuous sandstone bodies that fine upwards.

Tectonics
The Manorkill Formation was formed during the Middle Devonian following the deposition of the Plattekill Formation and before the deposition of Oneonta Formation. These three formations are composed of sandstone and mudrock of fluvial-deltaic origin. Plattekill, Manorkill and Oneonta Formations are terrestrial deposits that formed as part of a clastic wedge dervied from the Acadian Mountains adjacent to the Appalachian basin. The Acadian Orogeny was caused by the collision between the island arc Avalon and the proto-North American continent, Laurentia as the Iapteus ocean closed in the mid-late proterozoic.

Depositional Conditions
The Manorkill Formation is composed of fine-grained fluvial overbank deposits formed primarily from aggrading, river systems that formed on a low-relief alluvial plain. The terrestrial strata reveal a landscape influenced by rainfall seasonality, tectonically driven changes in sedimentation and the onset of a forested ecosystem. The Devonian climatic conditions in this region are interpreted as tropical and seasonally wet to semi arid which would explain the strata influenced by changes in rainfall.

Fluvial systems were the primary method of sediment delivery into the Appalachian Basin during the Middle Devonian (Woodrow, 1985; Willis and Bridge, 1988). Fluvial sedimentation was likely influenced by the same factors that caused changes in marine sedimentation, such as paleoclimate change, sea level change or from tectonic forces controlling basin subsidence and sedimentation. The thicker fine-grained floodplain successions, which occur several times throughout the Plattekill and Manorkill Formations are most likely related to the marine carbonates present in the Appalachian Basin during this time period.

Regional Paleoenvironment
The forest environment evident in the Manorkill Formation, which contains stump casts and attached root systems, is thought to have decreased atmospheric carbon dioxide concentrations in the Middle Devonian. The fossilized forests exhibit both single and multi-generation growth that formed both in wet and dry environments. The occurrence of these diverse forested landscapes in the Givetian directly correlates to the onset of the steady decrease in atmospheric CO2 concentrations that have been tied to the Paleozoic glaciations.