--> Abstract: Folding, Thrusting and Fracturing on Turtle Mountain Near Frank, Alberta, by C. Willem Langenberg and Dinu Pana; #90039 (2005)

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Folding, Thrusting and Fracturing on Turtle Mountain Near Frank, Alberta

C. Willem Langenberg and Dinu Pana
Alberta Geological Survey/EUB, Edmonton, AB

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 SSW 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. Type I fracture sets (in the ac geometric plane) and Type II fracture sets (in the bc geometric plane) can be distinguished and are variously penetrative. The west limb of the anticline on the crest of South Peak shows the best Type II fracture sets, which are also represented by the most prominent fissure direction (roughly parallel to the Turtle Mountain ridge) near South Peak. The east limb, on the eastern slope of the mountain, shows more prominent Type I fracture sets, which are represented by the less prominent fissures on South Peak and which are roughly perpendicular to the trend of the ridge.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005