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The carbonate bank deposits of New York state's Trenton Group have been studied for nearly 150 yr. Curiously, it has been only recently that the facies patterns of the unit have been recognized. These facies patterns reveal that Trentonian epeirogeny was closely related to the regional inversions of topography that occurred at the beginnings of the Vermontian and Hudson Valley phases of the Taconic orogeny that was occurring in nearby New England. Each inversion resulted in a subsidence of the Trenton platform and an abrupt westward migration of the black shale facies derived from uplifting source lands.
Trentonian deposition began with the Vermontian phase. Carbonate-producing seas flooded onto a subsiding New York. The Napanee, Kings Falls, Sugar River, and lower Denley Limestones represent that transgression. At the same time, the shale facies migrated westward as far as Utica.
During the middle Trentonian, downwarping slowed markedly. Deposition was rapid enough to produce a shallowing facies pattern in the upper Denley and lower Steuben Limestones. During this time, the shale facies made no further westward advance.
The Hudson Valley phase began with a second, more intense, topographic inversion that would end Trentonian deposition. The upper Steuben and Hillier Limestones record a rapid subsidence. A brief, but puzzling, unconformity overlies the Trenton Group. Then, a final westward migration of the clastic facies buried the Trenton platform.
Thus, the upper and lower Trentonian strata were deposited in remarkably similar tectonic settings. The Vermontian phase initiated Trentonian deposition; the Hudson Valley phase brought that carbonate deposition to a close.
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