Triangle Zone Traps - From Under-Represented Play Type in Fold-Thrust Belts
Recent discoveries within the Sevier Thrust Belt, Utah, such as the Covenant Field, indicate that trap structures within triangle zones are potentially more widespread than currently appreciated. An analog region for exploring the variation in thrust front structures is the along-strike continuation of the Sevier Thrust Belt; the Sawtooth Range, Montana. The Sawtooth Range is also located along-strike from productive triangle-zone fields within the Canadian Foothills.
The deformation front of the Sawtooth Range is marked by different structures along the strike of the belt. In the Teton Canyon region, the thrust front is characterised by a triangle zone structure, containing a complex stack of folds and thrusts. To the North, in the Swift Reservoir region, the deformation front is marked by a trailing-edge imbricate fan. Considerable variation in geometry and in thrust style is exhibited within the triangle zone folds, over a distance of approximately 10km. At the northern limit of this triangle zone, a number of structures have been drilled and two small fields related to the transition between the triangle zone and imbricate fan deformation styles have been discovered.
Analogue modelling experiments indicate that the geometry and spatial extent of an upper detachment horizon within the sedimentary pile can account for the variation in deformation front style observed in the Sawtooth Range. Specifically, the spatial extent of the upper detachment horizon with respect to the spatial extent of the deformed region is a key influence on the development of deformation front structures.
We suggest that this concept of such rapid variation in deformation style, related to the distribution of detachment horizons within the sedimentary pile, coupled with influencing factors such basement influence and foreland basin sedimentation, should be considered in the exploration and development of foreland fold-belt regions worldwide.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009