Eric A. Erslev¹, Peter H. Hennings², Chris K. Zahm³

(1) Colorado State University, Fort Collins, CO
(2) Phillips Petroleum Company, Bartlesville, OK
(3) Colorado School of Mines, Golden, CO

ABSTRACT: Kinematics and Structural Closure of Basement-Involved Anticlines in the Central Rocky Mountains Petroleum Province

The contractile foreland-basin system of the central Rocky Mountains is dominated by anastomosing basement arches that separate elliptical basins of early Tertiary age. Kinematic complexities associated with these first-order structural features generated an array of second-order structures, which form important hydrocarbon traps. Second-order anticlines can be differentiated on the basis of their primary, 2D mechanism of formation and their secondary, 3D mechanisms that produced structural closure. Primary mechanisms for the anticlines include (1) basement backthrusting causing rotation and folding in the hanging wall of basin-boundary thrusts (e.g., Oregon Basin and Rattlesnake Mountain anticlines), (2) stratal wedging caused by detachment and backthrusting of sedimentary strata in the hanging wall of basin-boundary thrusts (e.g., Oil Mountain anticline), (3) footwall thrusting on splays off basin-boundary thrusts, which commonly have large hanging-wall rotations indicating shallow-level detachment in the basement (e.g., Pinedale and Elk Basin anticlines), and (4) synclinal tightening in the backlimb of asymmetrical arches (e.g., anticlines in the backlimb of the Wind River arch), which can be attributed to rotational fault-bend folding on curved master thrusts at depth.

3D structural closure of these second-order features occurs mainly by three mechanisms: (1) large displacement gradients along strike; (2) intersection with other transversely-oriented, basement-rooted structural elements; and (3) development of tear faults. Classification of productive anticlines in the Wyoming foreland based on these criteria reveals that the interaction of anticlines formed by basement backthrusting and footwall thrusting with transverse structural elements constitute the most productive second-order anticlines in the central Rocky Mountains.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado