SEDIMENTOLOGY OF THE PENNSYLVANIAN RAGGED REEF FORMATION, CUMBERLAND BASIN, NOVA SCOTIA

The Ragged Reef Formation (Pennsylvanian) crops out along the Bay of Fundy and represents the upper part of the newly designated “Joggins Fossil Cliffs” World Heritage Site. This study provides the first detailed measurement and description of the 891-m-thick type section.

The 46 channel bodies exposed in the cliffs range from 1.6 to 27.9 m thick and have a total thickness of 461 m (52% of formation thickness). Channel bodies are composed of medium-grained sandstone organized into lateral accretion deposits, trough cross-beds, and ripple cross-laminae. Channel bodies near the base of the formation have erosional surfaces lined with coarse-grained sandstone and quartz pebbles; maximum grain size and relative abundance of lag deposits increases upwards through the formation (cobbles in upper half of the formation). Sheet sandstones deposited adjacent to channel bodies range in thickness from 0.5 to 2.2 m (11.7 m total, 1% of formation thickness). Grayish red to dusky red mudstones and thin, interbedded sheet sandstones make up the majority of the overbank deposits (290 m total, 33% of formation thickness). These facies are interpreted to represent distal floodplain sediments deposited under seasonally-oxidizing conditions. Gray to grayish green mudstones and thin, interbedded sheet sandstones are common in the bottom 200 m of the formation (14 m total, 2% of formation thickness). These drab facies are interpreted as distal floodplain or wetland deposits.

The type section of the Ragged Reef Formation contains no coal and significantly less wetland deposits than the underlying formations in the Cumberland Group (Springhill Mines and Joggins formations). This progressive decrease in wetland deposits, both within the Cumberland Group and within the Ragged Reef Formation, most likely records long-term climate change or aggradation of the alluvial surface above local base level.