Earth Sciences Report 2007-03

Earth Sciences Report 2007-03

ESR 2007-03

Structural geology of Turtle Mountain near Frank, Alberta

Turtle Mountain forms part of the Livingstone Thrust sheet of the Foothills in Southwest Alberta and consists of Paleozoic carbonates and Mesozoic clastics. The dominant geological structures on Turtle Mountain are the Turtle Mountain Anticline and the Turtle Mountain Thrust. The rocks forming the top of the mountain are Paleozoic carbonates of the Banff, Livingstone, Mount Head, Etherington and Misty formations.

A detailed geological map of the South Peak area allows the construction of down-plunge cross sections, displaying the various structures. The Turtle Mountain Anticline changes geometry along its trend. Near the top of South Peak it forms a type of box fold with a 5 degrees south-southwest plunging fold axis.

The Turtle Mountain Anticline is a modified fault-propagation fold and can be described as a break-thrust fold. The rocks are extensively fractured. The Paleozoic carbonates are of most interest for the stability of the mountain and are only considered here. The majority of fractures are extension fractures with accompanying shear fractures related to the anticlinal fold.

Two main types of slope failure can be distinguished; i.e., sliding and toppling. Sliding along bedding planes along the east limb of the Turtle Mountain Anticline near South Peak could result in a major rock slide toward Bellevue. Normal faults are the main structures causing topple failure. They are slightly more likely to occur in the North Peak area and will generally be smaller in volume than the potential South Peak slide.

Langenberg, C.W., Pana, D.I., Richards, B., Spratt, D.A. and Lamb, M.A. (2007): Structural geology of the Turtle Mountain area near Frank, Alberta; Alberta Energy and Utilities Board, EUB/AGS Earth Sciences Report 2007-03, 46 p.