Abstract: Wrench Tectonics and Strain-Decoupling in the Kettleman Hills Anticlines Central California

Donald D. Miller

During the 1970s, the Kettleman Hills anticlines were interpreted as en echelon folds produced by an active wrench tectonic regime. During the 1980s, the same system of folds was thought to be related to the decoupling of oblique plate motion into a strike-slip component parallel to the San Andreas fault and a perpendicular component of shortening. This paper presents several lines of evidence that argue the validity and compatibility of both concepts in the structural development of the existing structures, which have been major oil producers in central California since 1928.

Several data sets can be used to argue that the Kettleman Hills and related anticlines initially formed at a higher angle with respect to the San Andreas fault and have been reoriented to their present sub parallel position. These include: (1) numerous small (less than 100 ft) and oblique normal-fault offsets mapped along a diagonal fault set in the Pliocene-Pleistocene Tulare Formation; (2) paleomagnetic data indicating at least 12° clockwise rotation during the Brunhes polarity chron (White, 1987); (3) surface drainage patterns; (4) and isochore maps that constrain the age and rates of a 24° clockwise rotation during the past 4.1 Ma at the nearby Lost Hills anticline (Julander, 1992). The timing of this structural change correlates with the change of Pacific plate motion a d horizontal stress field at about 3.5 Ma.

This interpretation explains the obliquity of the fracture anisotropy to the geometry of the present structure, which in turn affects permeability pathways and optimal orientation of horizontal wells on these and similar structures.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994