Ellis Group

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.

Lithology

The Ellis Group is composed of shale and sandstones deposited in a marine and transitional environment.

Hydrocarbon production

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 papery shale siltstone and shale grey limestone white gypsum

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.