ABSTRACT

Granite Wash is an informal term applied to the Paleozoic basal siliciclastic unit associated with the Peace River Arch, northwestern Alberta. The Granite Wash, which unconformably overlies Precambrian igneous and metamorphic rocks, consists of conglomeratic sandstone, sandstone and mudstone. The lithofacies distribution and depositional history of the Granite Wash have been determined in the Utikuma and Red Earth field areas. In these areas, Granite Wash clastics interfinger with open marine carbonates of the Keg River Formation (Middle Devonian) and form elongate trends that correspond to Precambrian structural trends.

Initial Granite Wash sediments in the Utikuma area consist of poorly sorted, dominantly unstratified, red, conglomeratic sandstones probably deposited in alluvial fans. The overlying succession consists of stacked, 10 to 20 m, coarsening-upward sequences interpreted as prograding fan deltas. The widespread lateral extent of these sequences suggests a probable allocyclic control on their development.

In the Red Earth area, initial Granite Wash sediments were confined to narrow, northeast-southwest trending paleovalleys that opened into a wider basin to the northeast. Conglomeratic sandstones were deposited in braided fluvial channels, alluvial fans(?), and deltas with a possible tidal influence. A transgressive event subsequently drowned the paleovalleys and resulted in the deposition of a widespread, black mudstone unit. Renewed progradation is indicated by the deposition of a 5 to 16 m coarsening-upward fluvio-deltaic sequence capped by a mudflat/tidal flat succession.

End_of_Record - Last_Page 183-------