Luncheon – March 21, 2003

Title: Natural Fractures in Strata Overlying a Laramide Thrust: Teapot Dome, Wyoming
Speaker: Scott P. Cooper, Sandia National Laboratories, Albuquerque, New Mexico
Publication: The Outcrop, March 2003, p. 4-5

Teapot Dome is an asymmetric, basement-cored, Laramide-age anticline. A systematic study of natural fractures indicates that lithology and structural position control outcrop and subsurface fracture patterns. Three throughgoing fracture sets were documented within this context. The oldest fracture set, containing relatively few fractures, is oblique to the hinge of the anticlinal fold. The majority of these fractures strike NW to WNW and abutting relationships indicate they predate fold-related fractures. A second set of fractures consists of bed-normal extension fractures striking subparallel to the fold hinge. A third set consists of bed-normal extension fractures striking normal to the fold hinge. In many areas this fracture set is spatially related and subparallel to NE-striking, normal dip-slip and normal oblique-slip faults that maintain a roughly perpendicular orientation to the fold hinge. Fractures, deformation bands and faults, all with conjugate geometries oriented such that they have a vertical bisector to the acute angle and strike subparallel or normal to the axis of the anticline and have a normal sense of displacement, are also observed.

Fracture abutting relationships and the spatial relationship of fractures, deformation bands, and faults relative to the fold indicate the deformation process was a dynamic interactive system, wherein progressive folding was driven by displacement on the basement-involved thrust fault. Fractures and normal faulting perpendicular and parallel to the fold hinge accommodated extension in both directions associated with the three-dimensional bending of beds across the fold. This bending was created by passive drape over the growing basement-cored thrust.

Recent analyses of 3-D seismic data allow mapping of subsurface structural features. Structural trends vary slightly with depth, suggesting a slight difference in orientation with depth of Laramide stresses. The interplay of these stresses with pre-existing basement structures are responsible for uplift of Teapot Dome.