Ellis Group
Introduction Gypsum bed in the Piper Formation, Big Horn Basin of Wyoming.The '''Ellis Group''' is a stratigraphical 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.
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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