Type Locality:

None designated.

Distribution:

The upper of two white speckled, argillaceous units of widespread distribution across the northern Great Plains region and in the foothills of the Rocky Mountains, extensively used as stratigraphic markers in subsurface correlation. The unit is about 49 m (161 ft) thick in north-central Alberta, thinning to some 6 m (20 ft) or less in the Peace River area. Near the Fourth Meridian in the Cypress Hills area it is about 157 m (515 ft) thick and incorporates 44 m (144 ft) of largely noncalcareous shale 55 m (180 ft) below the top of the unit. The First White Speckled Shale is 40 to 50 m (131 to 164 ft) thick across much of southern Saskatchewan, but thins to less than 25 m (82 ft) in the central part of the province.

Lithology:

Mainly calcareous shale and mudstone with intercalated shaly chalk and skeletal calcarenite, as well as subordinate bentonite, accumulations of fish-skeletal debris, concretionary layers of calcite and siderite, nodular phosphorite and localized occurrences of noncalcareous shale, sandstone and siltstone. The calcareous shale and mudstone are regularly laminated and incorporate white, light grey and light bluish grey flakes composed of coccolithic debris up to several millimetres in diameter, and light grey chalk laminae. The argillaceous deposits are variably bituminous. Skeletal calcarenites occur as graded layers ranging in thickness from a few millimetres to several centimetres and composed of disaggregated Inoceramus prisms and foraminiferal tests. Sandstones and siltstones are variably muddy and bioturbated in layers up to several metres thick and also form monotonously repeated graded layers several centimetres thick and alternating in vertical sequence with shales and mudstones.

Relationship:

Marks the top of the Colorado Group in western Canada. In central and eastern Alberta and western Saskatchewan the First White Speckled Shale is overlain disconformably by shales of the Lea Park Formation and rests with very low angle, angular unconformity on a northeastward thinning, unnamed upper Colorado sequence of noncalcareous shales and mudstones. The noncalcareous deposits are not present in central Saskatchewan, so that the First White Speckled Shale rests unconformably on the Second White Speckled Shale to form a single, speckled argillaceous sequence. The contact between sandstones and siltstones of the overlying Milk River Formation and the First White Speckled Shale is gradational in southeastern Alberta and southwestern Saskatchewan. Furthermore, on and to the east of the Sweetgrass Arch, immediately north of the international boundary the unit incorporates the Martin Sandy Zone and the dominantly coarsening-upwards Medicine Hat Sandstone. In the Rocky Mountain foothills the unit is represented by the Thistle Member of the Wapiabi Formation, where its white speckled character is lost from east to west. In the plains of southern Alberta the unit occurs at the top of the Alberta Shale. In the Smoky River area it occurs in the middle of the Puskwaskau Formation of the Smoky Group, about 31 m (102 ft) above the Bad Heart Sandstone. In the McMurray-Athabasca area it occupies the upper part of the Labiche Formation. The First White Speckled Shale is correlated with the Boyne Member of the Vermilion River Formation in eastern Saskatchewan and southern Manitoba. It is also correlative with the upper Kevin Shale Member of the Marias River Formation in northwestern Montana and the Niobrara Formation of northeastern Montana and North Dakota.

Other Citations:

Caldwell et al., 1978; Fraser et al., 1935; Goodwin, 1951; Jeletzky, 1971, 1973; Nauss, 1947; Price and Ball, 1971, 1973; Simpson, 1975; Wall and Germundson, 1961; Wickenden, 1945; Williams and Burk, 1964.