Variations in fluvial style in the lower Cenozoic synorogenic sediments of the Canadian Arctic Islands

Abstract

The Eureka Sound Formation (Maastrichtian to Eocene or Oligocene) occupies seven intraplate basins in the Arctic Islands and equivalent beds form part of the continental-margin wedges flanking the Arctic Ocean and Baffin Bay. Shallow-marine, deltaic, fluvial and lacustrine facies are present. Fluvial assemblages can be subdivided into: (1) assemblage F: cyclic, generally fine-grained deposits with point bar crossbedding, deposited by high-sinuosity rivers; (2) assemblage G 1: noncyclic sandy sequences of Platte braided type; (3) assemblage G 2: cyclic sandy and conglomeratic assemblages of Donjek type; (4) assemblage H: laminated sandstone with minor crossbedding—ephemeral Bijou Creek or Malbaie type; and (5) assemblage J: cobble and boulder conglomerate deposited on alluvial fans—Scott type. Variations in fluvial style within and between basins are related to local tectonic and, possibly, climatic effects. Adjacent to active faults bounding two of the basins the deposits form coarsening-upward megasequences, showing transitions from assemblages E (deltaic) or F to G and H, and culminating in assemblage J. These sequences document the progradation of a braidplain and alluvial-fan complex in front of rising fault-bounded uplifts. Only at Strathcona Fiord in central Ellesmere Island does coal comprise a significant part of the formation. There the sediments also contain a rich vertebrate fauna. This and other broad facies variations may reflect local climatic differences generated by the rugged topography.