Geometries and Kinematics of Laramide Basement- Involved Anticlines

A. B. Fisher
Colorado State University, Department of Earth Resources, Fort Collins, CO

Mechanical and kinematic understanding of anticlinal folds is essential to describing reservoir characteristics and hence the efficient exploitation of anticlinal hydrocarbon traps. This research will detail the geometry and deformation of a series of Laramide basementinvolved anticlines southeast of the Bighorn Mountains. These asymmetric anticlines are defined by the Tensleep Formation, a major hydrocarbon reservoir, and provide an excellent surface analog of nearby oil fields.

Defining the geometries of the anticlines by section—forelimb, hinge, and backlimb—will help describe the kinematic and mechanical development of the folds. Deformation within the forelimb and hinge of anticlinal structures has been attributed to several mechanisms. One new hypothesis being modeled at CSU proposes trishear forelimb deformation (within a triangular shear zone) and rotational fault-bend folding (rotation and translation along a curved fault plane) for the backlimb with possible flexural slip in upper strata of the hinge.

EK, Gardner, and Fraker Mountains, optimally exposed near Kaycee, Wyoming, will be used to test the fold models. The fold geometries, fracture patterns, and directions and intensity of primary stress through the folds will be compared to those of the fold models to determine the kinematics of the structures.

This work proposes to better define fracture zones and deformation in basement-involved anticlines containing the petroliferous Tensleep Formation. An accurate definition of the geometry of the anticlines can be used to characterize basement-involved hydrocarbon traps. The anticipated results from this work can be applied to subsurface structures to infer deformation occurring within the fold and hence the heterogeneity of the reservoir.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid