Eolian coastal dune deposits and surrounding marine sandstones, Rocky Mountain Supergroup (Lower Pennsylvanian), southeastern British Columbia
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abstract
The Pennsylvanian Rocky Mountain Supergroup, in the Elk Range, B.C., includes three sandstone formations: Tyrwhitt (about 100 m thick), Storelk (about 95 m), and Tobermory (about 75). The Tyrwhitt consists mostly of structureless sandstones which prove to be bioturbated in X radiographs. There is an abundant trace fauna, as well as brachiopods. The second most abundant facies consists of medium scale (up to about 1 m) cross-bedded sandstones. The Tobermory is essentially similar to the Tyrwhitt but contains fewer structureless sandstones, and more beds with ripple cross-lamination and horizontal lamination. Both formations were probably deposited slowly in water deeper than fair-weather wave base (deeper than 10–15 m).The Storelk, sandwiched between Tyrwhitt and Tobermory, is dominated by large scale (up to 10.5 m) sets of cross-bedding. These occur in three members, separated by two structureless members. The Storelk structureless members are not mottled in X radiographs, and no trace fauna was found in the field. There is only one 1 m thick fossiliferous bed within the Storelk, which is otherwise barren of trace or body fossils. We reject fluvial and marine sandwave interpretations of the large scale cross-bedding, and suggest that the Storelk represents a coastal eolian dune complex. Paleoflow directions are dominantly toward south-southwest, similar to Pennsylvanian paleowind directions in the western United States. The Storelk structureless members possibly represent sand blown into standing bodies of water, one of which was connected to the open sea (the fossiliferous bed).
