DEPOSITIONAL ENVIRONMENTS AND ALLUVIAL ARCHITECTURE OF THE SPRINGHILL MINES FORMATION (PENNSYLVANIAN), CUMBERLAND BASIN, NOVA SCOTIA

The Pennsylvanian Springhill Mines Formation crops out along the southern shore of Chignecto Bay in northwestern Nova Scotia. Although this 714-m-thick unit represents a significant part of the newly designated “Joggins Fossil Cliffs” World Heritage Site, this study provides the first detailed measurements and descriptions of this unit since the work of William Logan in the 1840s.

The Springhill Mines Formation can be subdivided into open water, peat-forming wetland, and seasonally-oxidizing floodplain facies associations. The open-water facies association occurs only in the basal 16.9 m of the section (2.4% of formation thickness) and consists of laminated grey mudstones and interbedded sharp-based sandstones (up to 0.9 m thick). The overlying 697 m of section consists of alternations between the peat-forming wetland and seasonally-oxidizing floodplain facies associations. The six occurrences of the peat-forming wetland facies association range from 3.2 to 74.7 m thick and have a total thickness of 127.4 m (17.8% of formation thickness). Common facies include green and gray mudstones, thin coals (up to 0.18 m thick), channel bodies, sheet sandstones, and heterolithic sandstone-mudstone packages. The eight occurrences of the seasonally-oxidizing floodplain facies association range from 20.8 to 156.8 m thick and have a total thickness of 508.3 m (71.2% of formation thickness). Common facies include red mudstones, channel bodies, sheet sandstones, and heterolithic sandstone-mudstone packages.

Notable formation-scale changes include a progressive decrease in the thickness and abundance of wetland deposits and an increase in channel body abundance, thickness, and grain size. Alternations between peat-forming wetland and seasonally-oxidizing floodplain deposits may represent a subdued expression of the cyclic sedimentation patterns (cyclothems?) present in the underlying Joggins Formation. Given the profound influence of tectonism in the Cumberland Basin, the progressive decrease in wetland deposits and increase in channel body abundance/grain size probably records progradation of fluvial systems into the basin and aggradation of the alluvial surface.