Carbonate–sulphate–redbed facies and cyclic sedimentation of the Windsorian Stage (Middle Carboniferous), Maritime Provinces

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Abstract
After the late Devonian orogeny, thick Carboniferous, mainly continental redbeds, derived from intrabasinal horsts, accumulated in a complex rift-valley system called the Fundy basin. During the mid-Carboniferous Windsorian Stage, generally hypersaline seas flooded repeatedly into the tortuously interconnected, intrabasinal grabens. The resulting carbonate–sulfate blankets intertongue laterally with increasingly coarser redbeds and even basalt adjacent to the horst. Macrofaunal, microfaunal, insoluble residue, heavy-mineral, and trace-element analyses and Irwin-logs have limited success in identifying remnants of each particular blanket. Nevertheless, a Windsorian facies model is constructed from detail microscopy and Recent analogues, including field work in Bermuda.Windsorian carbonates are mainly shallow marine to supratidal; calcium sulfate is mainly diagenetic and supratidal, precipitated within, not on, subaerial salt flats; and redbeds are mainly subaerial and diagenetic, pigmented by post-depositional alteration of iron-rich detrital minerals. Dolomitization was both penecontemporaneous within the salt flat by influxing lagoonal water, and also secondary within buried, permeable, basinward lithosomes by refluxing brine. Gypsum–anhydrite nodules metamorphose on stress from mosaic, through penemosaic structures, and finally to massive, porphyroblastic plutons.Floodings in the Antigonish–Mabou basin were from the north–the present Gulf of St. Lawrence. Cyclic sedimentation was probably due to fluctuating supply of terrigenous detritus into a continually subsiding basin.

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