DETRITAL ZIRCON GEOCHRONOLOGY OF SILURO-DEVONIAN SANDSTONES, ROCKY-MOUNTAINS, NORTHEASTERN BRITISH-COLUMBIA

Quartzose sandstones of latest Silurian to middle Devonian form the ba sal part of four unconformity-bounded, carbonate-dominated shelf succe ssions of the Alberta Basin in the Rocky Mountains of northeastern Bri tish Columbia - the Muncho-McConnell, Stone, Dunedin and Slave Point f ormations. The off-shelf equivalent to the Dunedin Formation is a mass ive channel deposit of quartzose sandstone that overlies basinal strat a along a 30-km wide re-entrant in the northern part of the Ospika Emb ayment (Halfway River map area). Paleocurrent measurements from basal sandstones of the Dunedin Formation, including the channel deposit, co ntain a northeast-directed component over a large ar ea and suggest po ssible sediment derivation from a western source area, perhaps reflect ing uplift during the early phases of the Antler orogeny. To test this hypothesis, we dated single detrital zircon grains, using the U-Pb te chnique, from sandstones of shelf (Muncho-McConnell and Slave Point fo rmations) and basinal settings (massive channel deposit) to examine th eir provenance. Twenty-nine single grain analyses from four different samples yielded a distinctive suite of U-Pb ages that are indistinguis hable regardless of paleogeographic setting and closely match the ages of basement terranes that underlie the Peace River Arch in the autoch thon to the east. These data support derivation of sediments of both b asinal and shelf association from the same source: the emergent Peace River Arch area to the east. Alternatively, to account for the northea sterly-directed paleocurrents, Dunedin-equivalent quartzose sandstones of the basinal association could have been derived from the west and acquired their detrital zircon provenance signature by recycling pre-D evonian sandstones.