Report on Rumpel Lake stratigraphic test, Saskatchewan

The Athabasca Formation of middle Proterozoic age is an unmetamorphosed, cross-bedded, pure quartz sandstone occupying an oval, 38,000 square mile basin, more than 5,000 feet deep, in northern Saskatchewan. In 1968 Gulf Minerals continuously cored 4,776 feet of the Athabasca Formation and 340 feet of underlying basement near the basin centre, at Rumpel Lake, where the formation consists of two members. The Upper Member , 1,408 feet thick, is a well stratified , predominantly medium-grained, largely clay-cemented, purple, maroon and white, pure quartz sandstone containing less than 5% shale-siltstone. Cross-bedding and a strong textural lamination are characteristic. All clays are composed of illite and chlorite. Glauconite, altered to illite, and detrital green mica, as well as tourmaline, are the main accessories. The member was probably deposited in beach, barrier, lagoon and near- shore marine environments. The Lower Member, 3,368 feet thick, is a massive, pink and purple banded, cross-bedded, pure quartz sandstone with 24-foot thick basal conglomeratic zone. It possesses a strong textural lamination, is poorly sorted, has poor porosity and is very hard. The average grain size increases from medium-coarse at the top to very coarse at the base. Granules and small pebbles increase in quantity with depth. The sand is cemented with quartz, and clay composed of illite and kaolinite. Intraformational clay pebbles are common, and heavy minerals include tourmaline with zircon and magnetite at the base. The member was deposited in a fluviatile environment. The upper contact may represent a brief hiatus, and the lower contact is a major unconformity. Underlying the Athabasca at Rumpel Lake is a six-foot thick, red -maroon, clay regolith that represents the intense, in situ, chemical weathered zone at the top of the granitic basement complex. Locally the Athabasca is overlain, probably conformably, by the Carswell dolomite, and below, but nowhere in mutual contact is the thick, arkosic Martin redbed succession.