DEPOSITIONAL ARCHITECTURE, DRAINAGE PATTERNS AND GEOMORPHIC VARIABILITY OF A PALEOPROTEROZOIC FLUVIAL-COASTAL PLAIN: THE ELLICE FORMATION OF ELU BASIN (NUNAVUT, CANADA)

The three-dimensional architecture of Proterozoic fluvial deposits rarely has been integrated with sectorial paleocurrent analysis of discrete channel-bar complexes, so there remains scope to investigate the natural geomorphic variability of this alluvium. The ~1.7 Ga Ellice Formation of Elu Basin, Arctic Canada, is exposed along extensive coastal platforms and low cliffs scattered over an area of more than 1600 sq km, a configuration that allows architectural and paleoflow analysis of both planform and vertical sections. The Ellice Formation unconformably overlies the Archean Slave Province, and older Paleoproterozoic sedimentary rocks. Proximal facies are more frequent towards the southeast, while an increasing marine influence is evident toward the northwest. We investigate the morphodynamics of the Ellice Formation along different basin tracts, in concert with large-scale trends of facies distribution.

In the proximal, fluvial-dominated facies belt, larger channel bodies are up to 7-m thick and 200-m wide. A substantial portion of this facies belt appears to have been deposited along low-sinuosity channel belts dominated by compound mid-channel and side bars, in some cases preserving an original bar-top topography. These tracts exhibit ubiquitous downstream-directed cross-stratification, and both downstream- and lateral-accretion surfaces. High-sinuosity channel belts commonly are associated with eolian cross-bedded sandsheets. Along these high-sinuosity tracts, upbar-climbing cross-stratification and dispersed lateral-accretion surfaces suggest accumulation along short-lived meandering channels. In the distal, marine-influenced facies belt, smaller channelized units, up to 2-m thick and less than 50-m wide, occur alongside low-relief mouth bars interfingered with stromatolitic carbonates. Major distributary channels are in some cases attached to tidal bars with well-developed inclined heterolitic stratification. In synthesis, the sedimentary record of the Ellice Formation demonstrates how Proterozoic alluvial-coastal plains had greater geomorphic variability than previously expected.