Development and Deformation of the Late Paleozoic Cumberland Basin, Nova Scotia, Canada

John W. F. Waldron¹ and Michael C. Rygel^2
1 University of Alberta, Edmonton, AB
² Dalhousie University, Halifax, NS

The Cumberland Basin of Nova Scotia is a large depocenter in the Late Paleozoic Maritimes Basin, with a Carboniferous succession more than 8 km thick. Previous exploration has focused on anticlines cored by Mississippian Windsor and Mabou Groups, with targets in the underlying Horton Group. New seismic profiles in the Cumberland Basin show reflectors that can be traced to surface, allowing correlation with surface mapping.

In the western basin, the Joggins Formation, famous for preserved upright fossil trees, thins conspicuously eastward onto an evaporite-cored antiform at Springhill. At depth in the adjacent Athol syncline, reflectors identified as Namurian Mabou Group appear to rest directly on basal Windsor Group at an evaporite weld, indicating that the entire thickness of evaporites was evacuated. Early Westphalian evaporite withdrawal is largely responsible for the great thickness of coal-bearing Cumberland Group strata.

Farther east, a much thinner Cumberland Group overlies the Mabou Group with clear angular unconformity. Traced to depth, the Mabou also thickens into a synclinal 'minibasin', which subsided into evaporite-bearing Windsor Group.

Overall, subsidence and tectonism in the Cumberland basin were clearly controlled by differential flow of evaporites, which began in Visean or Namurian time and continued intermittently throughout the Pennsylvanian. The presence of coarse non-marine clastic units in synclinal minibasins, where they abut against adjacent evaporites or are truncated beneath internal unconformities, suggests several possible new exploration targets.

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