Role of transverse faulting in along-strike termination of Limestone Mountain Culmination, Rocky Mountain thrust-and-fold belt, Alberta, Canada

Abstract

Surface geology, well data, and ∼100 km of 2D seismic reflection data delineate the 3D geometry of Limestone Mountain Culmination (LMC). The lower lithotectonic package of the culmination is a SE-plunging antiformal stack of four thrust sheets of Paleozoic platform carbonates that is detached from and folds the upper package of NE-verging thrust sheets of Mesozoic siliciclastics, tilting these imbricates toward the foreland. LMC abruptly loses 1.5 km of structural relief along strike in less than 2 km across a NE-striking blind transverse fault that changes from a NW-dipping lateral ramp in the southwest to a steep tear fault in the northeast. It soles into the Brazeau Thrust and merges upward into the roof thrust of LMC. An extension fault that soles into the steepest portion of the transverse fault cuts moderately SW-dipping Mesozoic rocks that drape over the tear fault, thereby juxtaposing Mesozoic siliciclastics against Paleozoic carbonates of the Brazeau sheet. Synchronous thrusting is suggested by preferential imbrication over the forelimb of the antiformal stack, by offset of the roof thrust, and by folded and unfolded thrust segments in the stack. A Precambrian basement structure beneath this transverse fault may have acted as a buttress during the Laramide Orogeny.