TECTONOSTRATIGRAPHIC HISTORY OF THE CUMBERLAND BASIN, NOVA SCOTIA: EXTENSION, SHORTENING, AND SALT TECTONICS IN A “STRIKE-SLIP” BASIN

The Cumberland Basin of mainland Nova Scotia is part of the Late Paleozoic Maritimes Basin, and lies north of the Cobequid-Chedabucto Fault Zone, the boundary between the Meguma and Avalon Terranes of the Northern Appalachians.  The basin has been interpreted variously as a rift, a pull-apart related to strike-slip faulting, or as a product of Meguma-Avalon convergence.  

High-quality seismic lines indicate a more complex tectonostratigraphic history.  Sedimentation likely began in the Tournaisian with deposition of the Horton Group, although these strata are not exposed at surface and poorly imaged at depth. During the Viséan, deposition of as much as 3 km of Windsor Group evaporites and clastics accompanied movement along basement-cutting normal faults. Syndepositional minibasins within the Windsor Group and overlying Mabou Group (Viséan-earliest Namurian) indicate that extension continued throughout the Mississippian and that fault movement nucleated minibasin formation. Although disconformable at the surface, the contact between these Mississippian units and the overlying Cumberland Group (Pennsylvanian) is marked by a pronounced angular unconformity in the subsurface deformation presumably related to movement along the Cobequid-Chedabucto fault zone. Following the mid-Carboniferous deformation, the Boss Point Formation (Yeadonian-Langsettian) uniformly blanketed the basin and partially onlaped the adjacent crystalline massifs. The overlying Early to Middle Pennsylvanian coal-bearing succession exhibits marked thickness changes caused by salt tectonism. Folding and faulting of the Cumberland and overlying Pictou Group (Stephanian), together with tilting of basement rocks in the Cobequid Highlands, indicate that reverse faulting accompanied, and possibly triggered, Pennsylvanian halokinesis.  

This complex history is consistent with an overall environment involving significant dextral strike-slip motion on bounding faults of the Maritimes Basin, alternating between overall transtension (leading to extensional tectonics and minibasin formation) and overall transpression (leading to reverse faulting) during final stages in the docking of the Meguma Terrane. Younger parts of the basin-fill were profoundly influenced halokinesis triggered by these changes in tectonic style.