The Hornby Bay Group is a middle Proterozoic (1.8 to 1.2 b.y. ago), 2.5 km thick succession of terrestrial siliciclastics overlain by marine siliciclastics and carbonates. Deposition initially occurred in isolated intracratonic depocenters. Infilling of rugged basement topography by alluvial fans and braided rivers was followed by deposition of more than 500 m of mature quartzarenite on a low-energy braidplain. Three facies assemblages within this sequence are interpreted as eolian.

Facies A (80 to 200 m thick) interfingers with alluvial fan deposits. It displays low-angle tabular-planar cross-bed sets with wedge-shaped intrasets, ripple cross-lamination perpendicular to foreset dips, and climbing ripples proximal to the fan deposits and large trough cross-beds with wedge intrasets in distal parts of the basin. This facies records deposition in complex transverse bed forms. Facies B consists of lenses up to 40 m thick interlayered with low-energy fluvial deposits. Composed of 3 to 4 single low-angle trough cross-beds with numerous smaller intrasets, it is inferred to represent barchanoid

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dune deposition. Facies C is characterized by tabular-planar cross-beds, 3 to 4 m thick, interlayered with flat laminated fluvial arenites. It probably formed by migration of solitary transverse dunes across emergent parts of the braidplain. Paleocurrents in all facies are unimodal and parallel to the paleoslope, but commonly show a strong mode perpendicular to the paleoslope. The lack of duricrusts, silcretes, and ephemeral lake deposits suggests a semi-arid to humid paleoclimate.

The eolianites are distinguished from fluvial sediments by: (1) tabular-planar and trough cross-beds bounded by low-angle to horizontal planar surfaces, the cross-beds being composed internally of wedge-shaped intrasets that dip in the direction of the megaset foresets; (2) ripple cross-lamination perpendicular to the megaset foreset dip; and (3) large-scale cross-beds. An eolian origin is substantiated by association with braided river facies, dissimilarity of cross stratification compared to established fluvial facies models, and the tectonic setting.

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