Unit Name: Porcupine Hills Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Paleocene (65.5 - 55.8 ma)
Age Justification: At the type locality the Porcupine Hills Formation contains abundant fresh water mollusc remains of Paleocene age which have been correlated with similar assemblages in the upper part of the Paskapoo by Tozer (1956).
Originator: Dawson, G.M., 1883.
Outcrops in the Porcupine Hills area, southwestern Alberta. In the Gulf Spring Point 2-4-10-29W4M well, located near the south end of the hills the boundary between the Porcupine Hills and the underlying Willow Creek Formation was intersected at a depth of 545 m (1,778 ft).
Late Tertiary and recent erosion have confined the Porcupine Hills formation to southwestern Alberta, where it is recognized from the Porcupine Hills area to north of the Bow River. It reaches a thickness of up to 1,220 m (4,000 ft) in the type area, but because the upper boundary is an erosion surface the original thickness cannot be determined.
The Porcupine Hills Formation is composed of olive brown shales interbedded with fine- to coarse-grained brownish grey, cross-bedded limy sandstone and calcareous siltstone, in fairly well indurated beds from 6 to 15 m (20 to 49 ft) thick. The sandstones consist of detrital quartz, chert, nonvolcanic rock fragments and clastic carbonates. Sandstones at the base contain detrital coal fragments and a few calcareous pellets. The light grey shale contains calcareous concretions.
The Porcupine Hills Formation grades downward into recessive green, purple, maroon and brown shales of the Willow Creek Formation and is disconformably overlain by Quaternary deposits or is exposed at the surface. The Porcupine Hills Formation overlies and grades laterally into the Paskapoo Formation to the north and is believed to be the equivalent of the Ravenscrag Formation in southeastern Alberta and southwestern Saskatchewan.
Dawson (1883) gave the name "Porcupine Hills Series" to massive, cross-bedded sandstones with scattered shaly layers that outcrop in the Porcupine Hills of southwestern Alberta, and named the underlying beds which outcrop extensively in the surrounding plains, the "Willow Creek Series". In central Alberta Tyrell (1887) proposed the name "Paskapoo Series" for the beds overlying the "Edmonton Series" and then correlated the Paskapoo with Dawson's "Porcupine Hills", "Willow Creek" and all but the lowest 200 m (656 ft) of the "St. Mary's River Series". Dawson believed the beds of the "Porcupine Hills" to be equivalent to those outcropping along the Bow River, whereas Tozer (1956) arbitrarily defined all beds north of Twp. 13 in western Alberta as Paskapoo, thus obscuring the true relationship between the Porcupine Hills and Paskapoo. Recently, however evidence has been presented (Carrigy, 1971) to show that the Porcupine Hills Formation, which overlies the Willow Creek Formation in south western Alberta extends north beyond Calgary and also overlies the beds assigned to the Paskapoo Formation on the Bow River.
Carrigy, 1970, 1971; Dawson, 1883, Tozer, 1956; Tyrell, 1887.
Dawson, G.M., 1883. Preliminary report on the geology of the Bow and Belly river region, Northwest Territory, with special reference to the coal deposits. Geological Survey of Canada, Report of Progress for 1880-81-82, Part B.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: D.R. Turner
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 16 Dec 2008