STRIKE-SLIP FAULTS AND SALT TECTONICS IN THE EVOLUTION OF THE LATE PALEOZOIC MARITIMES BASIN, NORTHERN APPALACHIANS OF ATLANTIC CANADA

The Minas Fault System, or Cobequid-Chedabucto Fault Zone, coincides with the Early Paleozoic boundary between the Meguma and Avalon terranes of the Canadian Appalachians. This E-W boundary remained intermittently active, with mainly dextral motion, through the Mississippian-Pennsylvanian development of the Maritimes Basin, which is superimposed across all the earlier terranes of the orogen. Other major faults, with dextral components of slip, affect the NW and SE basin margins. The Maritimes Basin contains up to 12 km of late Paleozoic sedimentary strata, mainly fluvial and lacustrine clastics, but including thick marine evaporites of the Mississippian Windsor Group.

South of the Avalon-Meguma boundary, a thin Maritimes Basin succession onlaps the Meguma Terrane. Within about 20 km of the terrane boundary, the mainly Tournaisian Horton Group is intensely deformed and thrust south over younger Windsor evaporites. En-echelon folds and small-scale boudinage structures attest to a transpressional environment of deformation.

North of the terrane boundary, the Cobequid Highlands mark a strip of uplifted Avalonian basement. Immediately north of the Cobequids, the Cumberland sub-basin contains > 6 km of sedimentary rocks, including the famous Joggins succession, noted for the preservation of upright tree fossils. Industry seismic profiles indicate evaporite welds at depth, formed by the withdrawal of Windsor Group evaporites into E-W and NE-SW trending anticlines, developed concurrently with the rapid subsidence of late Mississippian and Pennsylvanian minibasins.

Stratigraphic relationships suggest that an initial thick layer of Windsor evaporites was present in the Cumberland sub-basin. Strike-slip motion along NE-SW major faults was probably associated with transtension along the northern margin of the Cobequids, triggering initial subsidence of extensional minibasins in late Mississippian time. Subsequent westward motion of the Meguma Terrane in the Pennsylvanian led to transpressional reactivation of these early-formed structures and further evaporite withdrawal.

Major tectonic features of the basin can thus be related to competing and alternating activity on two differently trending strike-slip fault systems, interacting with thick and mobile evaporites.