Along-strike variations and internal details of chevron-style, flexural-slip thrust-propagation folds within the southern Livingstone Range anticlinoriurn, a paleohydrocarbon reservoir in southern Alberta Foothills, Canada

摘要

The Livingstone Range anticlinoriurn marks a hanging-wall ramp across which the Livingstone thrust cuts up eastward approximately 1000 m (~3280 ft) between regional decollements in the Devonian and the Jurassic strata. It is well exposed and provides actualistic models for exploration of analogous subsurface structures. More than 30 km (>19 mi) of detailed mapping along strike reveals generally gradual changes, punctuated by abrupt terminations or offsets of structures at northeast- to east-trending tear faults, interpreted to be reactivated basement faults. Some folds plunge out at tear faults, forming domal culminations between them. Hinge zones of chevron-style, flexural-slip thrust-propagation folds display a distinctive pattern of ramp-flat thrusting comprising stacked detachment thrusts, each of which emerges from a different zone of interbed slip in the backlimb and deflects the hinge zone eastward. Each successively lower detachment thrust dies out in the hinge zone just below an overlying one. Displacements on the detachments, rotation of fold limbs, and interbed fiexural slip were integrated kinematically. Thrust-propagation folding involved a form of cataclastic flow: individual blocks of rock delimited by faults, joints, and sheared bedding surfaces underwent minor relative displacements with little or no internal deformation, despite large translations and rotations of the thrust sheet. Pressure solution and vein formation were widespread but were minor components of the deformation. Complex fracturing within the anticlines is dominated by conspicuous widely spaced (~ 150 m [~490 ft]) transverse (east-northeast-striking) zones of intense fracturing that transect hinge zones and limbs. These permeable zones likely originated by reactivation of basement faults, and their significance may not be predictable by curvature analysis.