STRATIGRAPHY AND STRUCTURAL STYLE IN WINDSOR GROUP SALT DEPOSITS IN SOUTHWESTERN CAPE BRETON ISLAND, NOVA SCOTIA, CANADA

Deep core drilling provides stratigraphic and structural data for several major Windsor Group salt deposits which have been assessed as part of the joint Canada - Nova Scotia Targeted Geoscience Initiative (TGI). Documentation of bedded halite in rhythmic cycles of variable thickness in a succession reaching more than 2000 metres in aggregate thickness has important implications both for local resource extraction and for underground storage of hydrocarbons. Twenty deep wells cored to depths ranging from 700 - 1300 metres in three salt deposits reveal, a regionally comparable stratigraphic architecture complicated in each deposit by large scale fold repetition and faulting.

Rock salt comprises as much as sixty percent of the Viséan - early Namurian succession, ranging stratigraphically from the base to the top of the Windsor Group and extending into the lower portion of the overlying Mabou Group. Dissolution of halite in the near surface results in a variable depth to "first salt". The first salt intersected, because of the structural configuration of strata beneath the so-called "salt table", provides little stratigraphic information. The thickest halite interval, containing one significant potash horizon near the top, occurs low in the Windsor Group. This interval is soled by a major structural discontinuity below which the thick basal anhydrite of the Windsor Group is only moderately deformed. Above this structural break, interbedded carbonate rocks, anhydrite and halite with minor siltstones are folded in complex structures documented by overturned limbs reaching 600 metres in true thickness. In the most severely deformed deposit at McIntyre Lake, shear foliation within several major halite intervals is related to salt flow into broken fold axes. In contrast, thick halite/mudstone intervals at Malagawatch show only local shear-related flow and retain fine-scale depositional features in remarkable detail despite large-scale fold deformation. These deformed salt deposits suggest very significant structural shortening of the succession above the lower Windsor structural discontinuity, in part balanced by meso-scale boudinage and extension in equivalent strata to the northeast in the Sydney Basin.