ABSTRACT

The northeasternmost segment of the Cordilleran Thrust Belt of western North America 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.

Many thrusts were active simultaneously during the Late Paleocene - Pliocene development of the thrust belt. 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 geometric 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.

The thrusts probably formed within a broad zone of right-lateral shear based on the presence, within the thrust belt, of northeast-striking right-lateral strike-slip faults, east-striking left-lateral antithetic strike-slip faults, and possible rotations of fault-bounded regions about vertical axes.

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