Abstract

A number of episodes in the post-orogenic history of the Adirondack Mountains and adjacent Paleozoic Lowlands are recognized. A late Hadrynian—early Cambrian tensional episode is suggested by the presence of nonmarine graben facies and extrusive volcanics. The Ottawa-Bonnechere graben was active at the initiation of Paleozoic deposition in the region. Subdued topography of the Adirondack massif had generally minor but locally important influence on early Paleozoic depositional patterns, as did minor basement faulting. Stratigraphic evidence suggests that the entire massif was covered by Cambrian-Ordovician cratonic sedimentary rocks. Following Cambrian-Ordovician sedimentation, a number of minor tectonic events can be recognized. These include renewed block faulting in the Ottawa-Bonnechere trend, normal faulting of pre-Silurian age on the southern Adirondack flank, post-Ordovician lead-zinc mineralization in Cambrian-Ordovician cover rocks, and intrusive activity of Jurassic-Cretaceous age. These later events may be related to either Taconian or Acadian orogenies. There is little evidence to suggest any major shortening of either basement or Paleozoic cover by post-Grenville tectonism in the region. Recent earthquake activity and Tertiary block faulting on the eastern Adirondack flank may be related to renewed uplift in the region.

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