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Channel Bodies of the Pennsylvanian Joggins Formation: A Unique Opportunity to Compare Internal Architecture and External Form

Michael C. Rygel1 and Martin R. Gibling2
1 University of Nebraska-Lincoln, Lincoln, NE
2 Dalhousie University, Halifax, NS

Coastal exposures of the Joggins Formation provide an excellent opportunity to describe the internal architecture and external form of channel bodies in the context of their depositional environment. Three general architectural patterns are present in this unit and each forms a distinct cluster in width versus thickness plots.

The 82 channel bodies described in this study were classified as fixed, meandering, and multistorey types; each is present in coastal wetland and interior dryland facies associations. Most channel bodies are of fixed type and single storey with low width/thickness (W/T) values between 2 and 20. A few channel bodies of meandering type consist of a single, broader (W/T 12 to 64) storey with extensive lateral accretion sets that onlap flat-lying channel bases. Multiple fixed and meandering channel bodies incise from the same level suggesting that these bodies represent anastomosing dryland systems or delta distributaries. Five multistorey bodies up to 9.2 m thick represent paleovalleys filled with the deposits of smaller fixed and meandering channels. Although the channel body types form statistically distinct clusters in W-T space, comparison of paleochannel geometries shows that the shapes of active channels were similar for all three types. Rapid subsidence in a fault-bounded basin allowed for preservation of the near-complete spectrum of fluvial forms.

Architectural element analysis provides an effective way of describing the channel body architecture and internal complexity, but clustering of the architectural types on W/T plots also supports the practice of identifying discrete channel types within the spectrum of possible fluvial forms.