The Beaufort Sea Fold-and-Thrust Belt, Northwestern Canada: Implications for Thrust-Belt Evolution

ROOT, KEVIN G., Shell Canada Limited, Calgary, Alberta, Canada

The northeasternmost segment of the Cordilleran thrust belt of western North American underlies the Beaufort Sea continental margin. Folds and associated northeast-directed thrusts in this region formed synchronously with Tertiary sedimentation. As a result, the times of fold development can be determined from reflection seismic data by analyzing lateral thickness changes in stratigraphic sequences of known ages, and onlap and truncation relationships at unconformities.

Thrust faulting occurred throughout the late Paleocene-Pliocene. The abundant temporal data indicate the deformational sequence was significantly different from the simple, steplike, foreland-propagating model formulated in other less well-dated thrust belts. Many thrusts were active simultaneously, especially during the late Eocene, when the region of active thrusting had an across-strike width of greater than 200 km. This observation calls into question the popular concept that only one thrust moves at a time as a thrust belt develops.

The thrust belt propagated along, as well as across, strike. During the late Paleocene-middle Eocene, the area of active thrusting was bounded on the southeast by poorly imaged zones of right-lateral strike-slip faults that apparently are the northern offshore continuation of the Rapid fault array. During the late Eocene-Pliocene these strike-slip zones were largely inactive, and the southeastern boundary of the belt shifted along strike about 100 km southeast to the right-lateral Donna River fault. The change in the age of thrusting along strike results in no obvious geometrical anomalies and could not be deduced without timing information. This has an important implication: temporal data cannot necessarily be projected along strike in a thrust belt.

AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)