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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 8. (August)

First Page: 1361

Last Page: 1361

Title: Style of Deformation in Productive Fairway of Absaroka Plate: Southwest Wyoming and North-Central Utah: ABSTRACT

Author(s): Judy L. West

Article Type: Meeting abstract


Deformation of the Absaroka plate is characterized by two subparallel trends which result from ramp anticlines. Each thick competent unit in the stratigraphic section (Paleozoic carbonates, Thaynes Formation and Nugget/Twin Creek formations) forms hanging-wall ramp anticlines and productive structures. The western trend (anticline) is associated with truncation of the Paleozoic section against the Absaroka thrust, and the eastern trend (en echelon anticlines) with truncation of the Triassic/Lower Jurassic section.

Variations in the style of folding are different on the two trends. This variation results from the vastly different mechanical properties of their stratigraphic sections; 4,500 ft (1,370 m) of nearly continuous, competent Paleozoic carbonate and quartzite produce a single ramp anticline 50 mi (80 km) long. Imbricate faults at the base of this anticline (western trend) cause oscillations of closure along strike and minor strike offsets.


The eastern trend is dominated by folding rather than internal faulting. The Mesozoic section, which immediately overlies the thrust in the eastern trend, consists of alternating competent and incompetent units, each ranging from 750 to 2,500 ft (230 to 760 m) thick. Two competent mechanical units which form the ramp anticlines are the Thaynes Formation and the Nugget Sandstone/Twein Creek Limestone unit. Ramp anticlines develop from a single ramp through both competent units (producing one anticline) as well as stair-stepped ramps separated by a tread or "glide plane" in the incompetent unit between the Thaynes and Nugget formations (producing two anticlines). Additional folding may also result, apparently from simple compression which produces three anticlines stacked en echelon in he transport direction. These genetically related, stacked en echelon folds along an elongate zone of deformation are termed herein "imbricate folds" and are not associated with imbricate faulting.

Fold length along the eastern Mesozoic trend ranges from 1 to 6 mi (2 to 10 km). In contrast, oscillations in the 50-mi (80-km) long western anticline range from 5 to 15 mi (8 to 24 km). A clear relationship becomes apparent between both length and style of ramp anticlines and the thickness of the stratigraphic section traversed by the ramp.

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