Interacting Thrust Systems and Submarine Canyons During Taconian Deformation of the Ordovician Outer Shelf in the Champlain Valley, Vermont and New York

Paul A. Washington
University of Louisiana at Monroe, Monroe, LA

The outer edges of the Cambro-Ordovician carbonate shelf in the Champlain Valley were strongly segmented by submarine canyon systems at the onset of Taconian orogenesis. Many of the tributary canyons lay subparallel to the regional shelf edge, and some, but not all, were filled with synorogenic flysch prior to deformation. Recent careful mapping of the structural and stratigraphic relations in the central Champlain Valley has discovered the locations, lateral extents, and incision depths of many of these paleocanyons.

The submarine canyons strongly influenced the location of detachments and ramps during deformation, with many of the intervening carbonate banks being decapitated along detachments that intersected the forelandward canyon just above or below the canyon floor. Canyon collapse accounts for abrupt along-strike displacement discontinuities and cross-section balancing problems that plague this fold-and-thrust belt. Where the canyons were filled prior to initiation of thrusting, the valley-fill is preserved as extremely thick, intensely deformed, black shales lying along thrust block boundaries. Where valleys did not contain a shale fill, the canyons are marked by footwall stratigraphic beveling and complex thrust sheet geometries.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005