STRUCTURAL JUXTAPOSITION OF DIFFERING STRATIGRAPHIC SUCCESSIONS IN THE CHAMPLAIN VALLEY

Despite providing many of the original reference sections for Cambro-Ordovician shelf stratigraphy, the shelf strata of the Champlain Valley have been the subject of recurring disputes concerning stratigraphic nomenclature, beginning with Emmons’ Taconic sequence and continuing to the present. A large part of this problem comes from the structural juxtaposition of three very different successions of shelf strata, with insufficient structural understanding to allow for the distinction of these various stratigraphic successions. Recent advances in our understanding of the structure now allows us to distinguish the three successions in large portions of the Champlain Valley, justifying the application of separate stratigraphic nomenclature for each of these successions. The Mohawk Valley-based terminology should only be applied to the inner shelf areas west of the normal fault systems that form the eastern boundary of the Adirondacks. The nomenclature for the outer shelf strata of the Champlain Thrust sheet, Green Mountain anticlinorium, and Vermont Valley should only be applied to those areas structurally at or above the level of the Champlain thrust surface, including those areas east of Stanley’s “Mesozoic” fault system. The remaining exposed portions of the Champlain megagraben, including the Champlain lowlands on both sides of the lake and the central portions of the supposed “Middlebury Synclinorium” west of the “Marble belt,” constitute the rich central shelf sequence that provided most of the original reference stratigraphic sections, and are distinct from the other two successions despite repeated attempts to override its stratigraphic nomenclature with stratigraphic names from the other two successions.