Type Locality:

North side of point, East Arm of Moose Lake, 10.9 km (6.6 mi) south of the Narrows (approximately Lsd. 4, Sec. 32, Twp. 55, Rge. 16WPM), Manitoba. The lower East Arm sandy beds, which are not exposed at the type section are well exposed in a newly accessible small cliff on Highway 6, 48.3 km (30.2 mi) north of Grand Rapids. Suggested reference core hole is Freeport Clearwater Lake No. 6, in 23-53-16WPM), between approximately 12 and 28.7 m (40 and 94.2 ft)

Distribution:

Stearn originally estimated a total thickness of 15.2 m (50 ft), but recent core hole and outcrop data show that the lower silty and sandy unit is 7 to 9 m (23 to 29.5 ft) thick. Since no sandy beds are reported at the 13 m (42.6 ft) thick type section, the total East Arm thickness is at least 20 to 25 m (66 to 82 ft) (the top of the unit is difficult to define in core). The name is applied only in the northern part of the Manitoba outcrop belt. Extensive, newly accessible outcrops occur intermittently along Highway 6 for 64 km (40 mi) north of Grand Rapids, and also as near-shore cliffs at the south ends of both Little Limestone and William Lakes.

Lithology:

A varied sequence of yellowish grey, very fine- to medium-grained, oolitic, fossiliferous and predominantly algal dolomite with interbedded algal breccia. A zone containing isolated sand grains occurs near the base of the formation.

Relationship:

The unit conformably overlies the brown, vuggy Atikameg Dolomite, although the contact may be locally disconformable. It is overlain disconformably by crinoidal dolomites of the Cross Lake Member of the Cedar Lake Formation. In the subsurface of the Williston Basin the lower sandy beds of the East Arm comprise the basin-wide marker zone defining the top of the lower Interlake Group (Porter and Fuller, 1959) or the upper Brandon Formation of the Interlake Group (King, in Cowan, 1971); the upper East Arm dolomites comprise the basal part of the middle Interlake, or the basal Cedar Lake as re-defined by King (1964, in Cowan, 1971).

Other Citations:

Baillie, 1951; King, in Cowan, 1971; Porter and Fuller, 1959; Stearn, 1956.