DEFORMATION OF SEDIMENTARY ROCKS DURING LATE PALEOZOIC TRANSPRESSION ALONG THE AVALON-MEGUMA TERRANE BOUNDARY, NOVA SCOTIA

Devonian to Permian sedimentary successions in the Appalachians of Atlantic Canada record intense deformation in narrow zones related to intracontinental transform faults active during the assembly of Pangea.

On the south shore of the Minas Basin, Nova Scotia, Late Paleozoic deformation affects the Mississippian Horton and Windsor Groups, dominated by clastic lacustrine deposits and evaporites respectively. These rocks appear intensely deformed on the south shore of the Minas Basin (Bay of Fundy), immediately south of the Meguma-Avalon terrane boundary, within the Canadian Appalachians. Structures exposed in cliffs and on wave-cut platforms include reverse faults and tight folds with incipient axial-planar cleavage. A complex interference pattern was identified employing different map scales, recording a history of progressive deformation. Locally, overprinting has led to the development of downward-facing folds. Faults, marked by sheets of quartz with slickenfibres, were developed both before and after folding. In some instances, faults and folds are associated in outcrop-scale flower structures exposed in both cliff and wave-cut-platform view.

Low angle thrust faults and oblique strike-slip faults played a role in emplacing Horton Bluff Formation strata over younger strata of the Upper Horton Group and Lower Windsor Group. In seismic profiles, contorted reflections representing Windsor evaporites occur beneath areas mapped as older Horton Group, suggesting the presence of map-scale reverse faults or thrusts. Thrusting and strike-slip motion were followed by diapirism of Windsor evaporites, and probably also by solution-collapse, generating breccia zones in contact with Horton successions,.

This deformation was associated with transpressional motion along the boundary between the Meguma and Avalon terranes of the Appalachians. Stratigraphic relationships and isotopic ages obtained from dykes constrain the timing of deformation close to the Mississippian-Pennsylvanian boundary. The area provides an excellent opportunity to study and quantify the effects of transpression in deformed sedimentary rocks at very low metamorphic grade, and to document the behaviour of salt-detachment surfaces in transpressional environments.