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Anatomy and evolution of a pull-apart basin, Stellarton, Nova Scotia

John W.F. Waldron^,1

¹ Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada

The Stellarton Basin is a late Paleozoic pull-apart basin located close to the Meguma-Avalon terrane boundary in the Canadian Appalachians, at the stepover between the Cobequid and Hollow strike-slip faults. The basin contains 3 km of rapidly deposited Pennsylvanian clastic sedimentary rocks representing lacustrine and deltaic environments, extensively documented through coal-related mining and drilling. Coal seams and oil shales allow stratigraphic correlation within the basin, permitting reconstruction of basin subsidence and structural evolution. Coal seams represent approximately paleo–horizontal surfaces; thickness variations (corrected for tilt and compaction) in the most coal-rich part of the basin fill show that the south basin margin subsided rapidly during deposition, acting as a trap for coarse sediment and allowing coal-forming mires to develop in the north. Abundant soft- sediment deformation structures reflect synsedimentary tectonic activity. North-striking normal faults dissected the basin fill during and soon after deposition, early in the diagenetic history. Contouring of mine plans allows fault heaves to be identified and also shows that both coal seams and faults were folded by east- to northeast-trending folds, consistent with (1) an environment of deformation involving dextral strike-slip motion and (2) clockwise rotation of fault blocks during progressive strain. Later, north-northeast–striking contractional structures within the basin, and a positive flower structure at the northwest margin, probably represent a transition from transtension to transpression. The basin illustrates the role of rotational progressive strain in the reorientation of structures generated during transtension. It displays evidence for changes in tectonic style through time, from transtension to transpression, that may typify basins developed on major strike-slip faults.

Key Words: strike-slip faults • pull-apart basins Basin • Canadian Appalachians • Maritimes Basin • coal

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