Role of evaporite withdrawal in the preservation of a unique coal-bearing succession: Pennsylvanian Joggins Formation, Nova Scotia

Abstract

The Pennsylvanian Joggins Formation, in the Cumberland Group of Nova Scotia, is widely regarded as the world's best exposure of coal-bearing Carboniferous strata. This 1.5-km-thick coal-bearing unit is famous for upright fossil lycopsid trees, and is preferentially preserved in the Athol syncline in the western Cumberland basin. New seismic profiles show that the Athol syncline is atop a salt weld and that the Joggins Formation thins on the flanks of adjacent evaporite-cored anticlines. These observations indicate that during deposition of the Joggins Formation, at least 1 km of syndepositional subsidence was facilitated by flow of underlying salt into the adjacent anticlines. In contrast, halo-kinesis was mainly active during the Mississippian in the eastern Cumberland basin (Tatamagouche syncline); minibasins were filled by Mabou Group sediments, whereas the Cumberland Group is thin and lacks significant coals. This basinwide comparison shows that much of the subsidence responsible for the preservation of the coal-bearing Joggins Formation was the result of salt withdrawal at depth.