SIMILARITIES AND PALEOGEOGRAPHY OF LATE PALEOPROTEROZOIC TERRESTRIAL SANDSTONE DEPOSITS ON THE CANADIAN SHIELD: PRODUCT OF HUDSONIAN OROGENESIS

Studies by Al Fraser and colleagues at the Geological Survey of Canada in the 1960s and 1970s proposed that several large and now geographically separate sedimentary basins might be remnants of a formerly continuous blanket of sand that was deposited unconformably across the Canadian Shield ca. 1.7-1.6 Ga. Subsequent provenance and coupled sedimentological studies suggest that these sands were deposited by a vast contemporaneous river system that drained northwestward from the 1.9-1.8 Ga Trans-Hudson orogeny. Subsequent uplift and erosion isolated the deposits within the Athabasca, Thelon, Hornby Bay and Elu basins, interpreted to represent intracontinental sags possibly formed by the thermal insulating effects of supercontinent Nuna. Similarities of these basins include their large size, thickness and dish-like geometry. Each is composed of a lower succession of relatively immature alluvial fan and gravel-bed-dominated braided stream deposits that are confined to rifts. Above are thicker, more widely distributed and mature, sand-bed dominated deposits with cross-bedding that defines west- to northwesterly flowing, mainly braided rivers. The fluvial strata are intercalated with very large-scale cross-bedded, medium-grained quartz arenite interpreted as eolian deposits (except in Athabasca Basin). Provenance studies employing detrital zircon analysis show a source region composed of a broad variety of protolith ages but with a dominant component of 1.9-1.8 Ga zircon grains. This age is characteristic of the Trans-Hudson orogeny, which trends northeastward across central Laurentia and is interpreted to have a huge mountain chain from which the late Paleoproterozoic river deposits were derived. In all basins, the terrestrial sandstones pass upward through marginal marine mixed siliciclastic and carbonate strata into thick stromatololitic platformal carbonates.