Clearwater Formation
The Clearwater Formation is a stratigraphic unit of Early Cretaceous age in the Western Canada Sedimentary Basin in northeastern Alberta, Canada. It was first defined by R.G. McConnell in 1893 and takes its name from the Clearwater River near Fort McMurray.
Impermeable marine shales in the Clearwater Formation provided part of the trapping mechanism for the underlying Athabasca oil sands in the McMurray Formation. Sandstone units in the Clearwater Formation, including the Wabiskaw Member, can contain oilsand and heavy oil resources.
Nearly complete specimens of plesiosaurs and ichthyosaurs, as well as one ankylosaur, have been recovered from the formation during oilsand mining.
Lithology
The Clearwater Formation consists of primarily of black and green shale, with some interbedded grey and green sandstone and siltstone, and ironstone concretions. To the southeast of Cold Lake it includes massive hydrocarbon-bearing, glauconitic salt-and-pepper sandstones with interbedded shales.Wabiskaw Member
The Wabiskaw Member forms the base of the Clearwater Formation. It consists of glauconitic sandstones with interbeds of black fissile shale, and it includes oilsand and heavy oil in some areas. It was defined in well Barnsdall West Wabiskaw No. 1 by P.C. Badgley in 1952.Distribution
The Clearwater Formation is present in the subsurface of northeastern and central Alberta, and is exposed on lower course of the Athabasca River, as well as along the Christina River, a tributary of the Clearwater River southeast of Fort McMurray. It reaches a maximum thickness of on the Athabasca River, thins out to in the Cold Lake area, and wedges out towards the south. It is not present south of Edmonton.Relationship to other units
The Clearwater Formation is part of the Mannville Group. It is conformably overlain by the Grand Rapids Formation and conformably overlies the McMurray Formation. It is equivalent to the Bluesky Formation and the lower Spirit River Formation in the Peace River region, and may be equivalent to the Cummings Member in the Lloydminster region.Palaeontology
The Clearwater Formation was deposited in marine, near-shore and estuarine environments on the eastern side of the Western Interior Seaway, and it contains marine and, rarely, terrestrial fossils. Workers at mines near Fort McMurray have made a number of significant finds while removing Clearwater strata to expose underlying oilsand deposits. Plesiosaurs such as Nichollssaura and ichthyosaurs such as Athabascasaurus, some of them nearly complete, have been recovered at Syncrude Canada Ltd.'s mines.The well-preserved holotype specimen of the nodosaurid Borealopelta markmitchelli has also been recovered at the Suncor Millennium Mine. Plesiosaurs and ichthyosaurs were large marine reptiles, but the ankylosaur was an armoured dinosaur and represents a terrestrial animal that became entombed in the sea floor approximately from the nearest known paleo-shoreline. Its bloated carcass probably washed out to sea and floated for several days before sinking to the sea floor.
All of the specimens now reside at the Royal [Tyrrell Museum of Palaeontology].
Oil/gas production
The formation contains oilsand in the Cold Lake and Primrose Lake region. Heavy oil is produced from the loose sandstones of the Wabiskaw Member by means of horizontal drilling in the Wabasca oil field, and the Wabiskaw contains surface-mineable oilsand in the Fort McMurray area.The oilsands of the Clearwater Formation are more difficult to tap than those of the McMurray Formation. Cenovus Inc.'s Tucker thermal oilsands project which opened in 2006 began to post a modest return in 2013. Cenovus Inc., with its head office in Calgary, Alberta, Canada is an integrated oil and natural gas producer.