Abstract

The Visean–Serpukhovian transition in Atlantic Canada was marked by a general humidification of the climate as the region drifted towards equatorial latitudes. It also corresponds to a time when ice volume was increasing on Gondwana, which marked the end of Mississippian marine incursions in the region. Glacioeustatic fluctuations of greater magnitude are thought to have increased the response of the regional climate to third-order cyclicity from orbital forcing. In the Cumberland Basin, fluvial grey beds of the lower Serpukhovian Shepody Formation were deposited in sub-humid conditions during highstands, whereas red playa deposits of the same unit were deposited under semi-arid conditions during lowstands. Basin reconstruction suggests that this unit was sourced from the fault-bounded Cobequid and Caledonia highlands and deposited in two separate salt-withdrawal minibasins. This fluvial system was seemingly discharging to the north into the broad lake that deposited the contemporaneous Hastings Formation. A disconformity separates the Shepody Formation from mid-Serpukhovian red beds of the Claremont Formation and is tentatively associated with another increase in ice volume on Gondwana followed by a recrudescence of fault activity and basin subsidence. A prolonged time of aridity, floral crisis, non-deposition, deep weathering and karstification in late Serpukhovian to early Bashkirian times is contemporaneous with abundant glacial deposits in higher latitudes, suggesting that globally low sea levels may have been at play in creating a situation of greater continentality in the study area.

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