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Carboniferous and Permian evaporites and associated rocks in Arctic regions are of current interest in terms of global paleogeography and petroleum exploration. In the Canadian Arctic Archipelago, 3 upper Paleozoic evaporite formations are present in the Sverdrup basin, a regional depression overlying the Franklinian geosyncline and containing 40,000 ft (13,000 m) of lower Carboniferous to Eocene sediments. Two of these formations are: the Otto Fiord Formation (upper Carboniferous) in the axial region of the basin, and the Mt. Bayley Formation (Lower Permian), which is closer to the eastern basin margin. A third, unnamed evaporite unit of Moscovian or younger age is present along the north coast of Ellesmere Island.
The Otto Fiord Formation consists of over 1,300 ft (430 m) of interbedded anhydrite (75% by thickness) and limestone (25%) at the type section, with interbedded sandstones in other sections. The formation overlies sandstones and conglomerates of the Borup Fiord Formation (Namurian?), grades laterally into carbonates of the Nansen Formation, and is overlain by carbonates or siltstones of the Hare Fiord Formation (Moscovian at base). The Otto Fiord evaporites extend for at least 400 mi (650 km) in a broad, northeast-trending belt characterized in the south by numerous large piercement structures. Namurian and Bashkirian ammonoids discovered in these diapirs now have been found at several levels in the Otto Fiord type section.
Apart from a few cubic crystal casts, there are no positive indications of halite in surface exposures of the Otto Fiord Formation; breccia zones in anhydrite and limestone are not extensive. The Otto Fiord anhydrite beds vary in fabric from indistinctly bedded nodular mosaics, to fabrics apparently pseudomorphic after coarsely crystalline gypsum. Fabrics and bedding of the anhydrite, the biota of limestone interbeds, and the associated lithofacies indicate a marine subaqueous mechanism of deposition for these evaporites.
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