Geology of Saskatchewan - Phanerozoic Western Canadian Sedimentary Basin

Phanerozoic Western Canadian Sedimentary Basin

There were three depositional stages for the Western Canada Sedimentary Basin which were dependent on plate tectonics of the era. Present-day North America was identified to lay upon the Proterozoic super-continent, Rodinia.

This continent broke apart about 700 million years ago and formed other continents, one of which was Laurentia or the North American Craton. Laurentia drifted south of the equatorial zone. As this new smaller continent was smaller than Rodinia, it had some surface area under water level, including area designated as the Phanerozoic basin. Cambrian 544-505 Ma to Mississippian 362-320 Ma period laid down base clastics, then platform carbonates and evaporites. These deposits form the origins of potash evaporites for the potash industry. Laurentia began to rise at the close of the Cambrian Period. Huge flooding occurred during the Middle Ordovician period 505-441 Ma. Laurentia had shifted again, and the region of Saskatchewan was now north of the equator and some raising exposing the land again. Re-flooding in the Late Ordovician age with warm water increased calcium carbonate sedimentation, and marine life.

The Williston basin was formed creating a lowered land area during this period filling with the Winnipeg Sea. The Williston basin was mainly south of Saskatchewan but extended north into the Saskatchewan plains area.

Laurasia was created near the end of the Silurian Period. Laurasia was formed from the joining of Laurentia with Gondwana and two smaller continents which had broken off Rodinia. The orogeny between Laurasia and Gondwana created the Appalachian Mountains, and an exodus of water from the Laurasian land surface. In the early Devonian Period 418-361 Ma, Laurasia separated from Gondwana, creating a depressions or land separations through the continent. One low-lying area occurred along the edge between the Cambrian shield and the Phanerozoic basin, the other trough lay along southwestern Saskatchewan extending east and west along the plains areas we know today. The Saskatchewan region was again south of the equator and under water, with reefs forming. A major barrier reef formed in the area now known as British Columbia, creating higher salinity levels east of the reef. Calcium carbonate, halite, gypsum, and potash were clastic deposits. The Antler orogeny on the southwest coast of Laurassia caused upheavals.

Following this orogeny, during the Carboniferous Period in the Mississippian epoch 362-320 Ma the Williston Basin again subsided and the area of the Phanerozoic basin was again mainly under tropical marine water. Oil production of southeastern Saskatchewan emerges mainly from Mississippian rocks.

During the Pennsylvanian epoch 320-286 Ma of the Carboniferous period, Laurasia joined with Gondwana to become Pangea. This supercontinent rose above sea level, in an equatorial zone producing desert-like conditions. The late Triassic 245-208 Ma or early Jurassic 208-144 Ma to Jura-Cretaceous 208-66 Ma where red clay beds and marine clastics were deposited. Pangea began to separate during the Jurassic period.

The Kimberlite Volcanoes of this period produce the Kimberlite diamonds which are mined today. Near Fort à La Corne (FALC) were Kimberlite volcanoes in Archean cratons.

The Cretaceous 144-66 Ma to Miocene periods deposited clastic sediments from the Cordilleran orogeny. This period saw 40% of the region now called North America below sea level under the Rocky Mountain Seaway which comprised the Western Interior Seaway and the Hudson Seaway, and Labrador Seaway. The Cretaceous period rocks produce medium and heavy gravity oil in the Lloydminster region, and of the western province. The Laramide orogeny episode near the end of the Cretacsous and early Tertiary period caused larger gravels to be deposited from the newly formed Rocky Mountains when the Kula and Farallon Plates subducted below the North American plate. In the Cypress Hills area and southern Saskatchewan, lignite deposits developed from the marshes of these Tertiary rivers. The sea waters have retreated from the areas known as Saskatchewan. The Ravenscrag formation, Cypress Hills, and Wood Mountain Formations were notable gravel deposits from the Tertiary period. The Williston Basin affects this region at the southern edge. Tectonic movements and global changes in the sea level have given rise to a source of oil, natural gas, and coal.