About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 68 (1984)

Issue: 4. (April)

First Page: 490

Last Page: 490

Title: Depositional Environments of Devonian Cairn Formation, Rocky Mountain Foothills, Alberta, Canada: ABSTRACT

Author(s): Ian G. Hunter, Graeme R. Bloy, Sidney R. Leggett

Abstract:

The Cairn Formation is a carbonate sequence of Frasnian (Late Devonian) age that is the stratigraphic equivalent of the major oil-producing Leduc Formation of southern Alberta. During the summers of 1982 and 1983, detailed stratigraphic sections were measured near Canmore where the Cairn Formation is a platform sequence of carbonates approximately 50 km (31 mi) from the nearest reef edge.

The entire sequence consists of sediments deposited in a subtidal environment. No evidence of intertidal or supratidal deposition was found. The formation consists of very fine to medium crystalline, buff to dark gray dolomite, in which original textures (usually mudstones, grainstones, and stromatoporoid floatstones) often can be identified. The sequence contains fair to good intercrystalline, biomoldic, and vuggy porosity. Some of the vuggy porosity has been infilled by very late, coarse crystalline dolomite and calcite.

Individual beds typically are composed of a consistent lithologic character throughout. These beds are usually 10 cm to 2 m (1 in. to 6 ft) thick, and are virtually always bounded by disconformities. Some individual beds can be seen to swell and pinch out.

The stromatoporoid floatstones are composed of 10-40% fossils consisting of Amphipora, Euryamphipora, bulbous stromatoporoids (5-20 cm, 2-8 in.), tabular stromatoporoids, horn corals, and colonial corals. All organisms are not in place but have only moved a short distance.

Some thin beds consist of a black bituminous dolomite and probably represent a restricted lagoon environment of deposition.

Although most beds are horizontal, some constructional bioherms up to 5 m (16 ft) in relief have been recognized in the sequence.

End_of_Article - Last_Page 490------------

Copyright 1997 American Association of Petroleum Geologists