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The elusive decollement of the Allegheny Plateau is identified by repeat stratigraphic sections on gamma-ray logs, and is mapped along the Southern Tier of New York. The detachment surface is found at three progressively lower stratigraphic levels from east to west within the Salina Group.
In the eastern counties, Chemung, Schuyler, Tompkins, and Tioga, Unit F (salt) sections of the Syracuse Formation are vertically repeated two and three times along splays of the main thrust fault residing within Unit F. Fault throws as great as 400 ft (120 m) are shown on gamma-ray logs. Correlations provide evidence for overthickened sections, which are accounted for by imbricate thrusting of the section, thereby stacking the salt beds atop each other over decollement. The three-dimensional dome shape of the Syracuse Formation with planar base supports a thin-skinned tectonic origin and negates the primary depositional genesis. The thrust was upward to the northwest, and subsurface faults are associated with folds at the surface.
In Steuben and Allegany Counties, the overthickened Unit E sections of the Syracuse Formation again suggest the presence of stacked repeat sections rather than a depocenter. The detachment surface is near the base of Unit E. Mapping indicates that the rocks from the northwest have slid and overridden those to the southeast in the central region.
To the west in Chautauqua County, decollement terminates in a structure with northeast strike, here named the "Chautauqua anticline." This prominent subsurface thrust zone is of smaller proportions, but structurally comparable to the Burning Springs anticline of West Virginia. At the northwest edge of the underlying salt beds, the horizontal decollement bends upward into the Upper Silurian and Lower Devonian rocks, eventually dying out in the fissile shales of the Hamilton Group. Thin-skinned slippage has occurred on at least two planes--those of the evaporite beds in the Syracuse and Vernon Formations. The Chautauqua anticline forms the structural trap for the targets of recent plays in the Bass Islands and Akron dolostones of the Rondout Group overlying the Salina.
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