The Ellis Group is a stratigraphic unit of Bajocian-Oxfordian age in Alberta, Saskatchewan, Montana and Wyoming in the Western Canadian Sedimentary Basin. It takes the name from Fort Ellis, Montana, and was first described in outcrop in the Rocky Creek Canyon by A.C. Peale in 1893.Peale, A.C., 1893. The Paleozoic section in the vicinity of Three Forks, Montana. United States Geological Survey, Bulletin 110, p.9-56.
Lithology The Ellis Group is composed of shale and sandstones deposited in a marine and transitional environment.
Hydrocarbon production Oil is produced from the Sawtooth Formation in southeastern Alberta.
Distribution The Ellis Group laterally occurs in the subsurface in southern Alberta and northern and central Montana. It is typically , but thickens on either side of the Sweetgrass Arch and reaches up to in southeastern Alberta.
Subdivisions The Ellis Group includes the following formations, from top to bottom:
Sub-unit Age Lithology Max.thickness Notes Swift Formation Oxfordian marine shale, transitional shale, siltstone and sandstone Rierdon Formation Bathonian to Callovian marine shale and limestone Sawtooth Formation Bajocian to Bathonian quartzose sandstone with shale Piper Formation Middle Jurassic sandy limestone (top)papery shalesiltstone and shalegrey limestonewhite gypsum (base)
Relationship to other units The Ellis Group is unconformably overlain by the shales and sandstones of the Mannville Group and rests on the carbonates of the Rundle Group. It grades westwards to the shales of the Fernie Group, and eastwards to the shale, sandstones and limestones of the Vanguard and Shaunavon Formations.
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