ABSTRACT

Vertical movement of the north-south Boothia Uplift affected regional sedimentation in the central Arctic Islands during Early Devonian time. Synorogenic and postorogenic clastic wedges derived from the uplift and deposited in flanking basins include the Snowblind Bay Formation of Cornwallis Island.

The Snowblind Bay Formation, 578 m thick, has been divided into three facies associations based on constituent lithologies, sedimentary structures and biota. The fine-grained facies association (70-220 m thick) contains less than 10% conglomerate and occurs at the base of the formation. The sequence is noncyclic and shows evidence for an intertidal depositional environment, including a probable Skolithos ichnofauna, ostracoderm fragments, abundant soft-sediment deformation structures, pinstripe bedding and rare resedimented conglomerate units. A nearshore mud-flat facies assemblage can be broadly distinguished from a more offshore sand flat - tidal flat facies assemblage by the presence of terrestrial conglomerate units, scarcity of faunal elements, higher mud content, and a relatively higher abundance of low-energy bedforms and stratification.

The overlying conglomerate-sandstone facies association (120-300 m thick) contains 10-90% conglomerate. Lithofacies display sheet-form geometry and are arranged into two distinct types of fluvial cycle, one sand-dominated, the other gravel-dominated. The gravel-dominated sheet-flood cycle (average 3.7 m thick) formed from higher-discharge events.

The capping conglomerate facies association (210-240 m thick) contains more than 90% horizontally bedded conglomerate. The succession is dominated by conglomerate-sandstone flood cycles (1-6 m thick) arranged in coarsening-upward and coarsening-, then fining-upward sequences (7-30 m thick). The depositional environment is interpreted as the midreaches of an alluvial-fan complex. The sheet-braided and sheet-flood cycles in the conglomerate-sandstone facies association represent the distal-fan equivalent of the mid-fan flood cycles.

The Snowblind Bay Formation is interpreted as a coastal-fan complex that was derived from a north-northwest source, possibly from reactivated fault scarps that also may have controlled the Ordovician - Upper Silurian basin (Cape Phillips Formation) to shelf (Allen Bay Formation, Read Bay Group) facies change in the Laura Lakes district.