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The Cumberland basin of Nova Scotia has long been considered a structural basin by virtue of the elliptical outcrop and inward dip pattern of the Pennsylvanian outcrops. Recent data indicate that subsidence began in the Late Devonian perhaps resulting from a graben or rift. The Mississippian sediments which filled the growing depression were continental, lacustrine, and marine with evaporites. The cessation of the rift-forming processes are recorded by the alluvial swamp-type sediments of the Pennsylvanian which filled the depression. More than 25,000 ft of Carboniferous rocks are believed to be present in the deepest part of the basin. Starting with the rift hypothesis some speculations about the kinds of sediments and their locations, and about the structural features p esent beneath the Pennsylvanian surface may be ventured. From surface exposures and a limited amount of subsurface data, it is theorized that the Mississippian evaporites acted as glide zones which effectively divided the basin into 2 horizontal structural layers. The rocks above the evaporites, responding to Appalachian stresses, formed the long diapiric folds with cores of over-thickened evaporites. Below the evaporites the structures are related to movements of the rift floor, compaction closures, and structures formed by differential horizontal movements of the rift walls. In its deeper parts the rift probably contains more and a greater variety of marine rocks than the outcrops indicate. Should the rift hypothesis be correct, the possibility of finding hydrocarbons is enhanced.
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