Date of Award:

1994

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

Dr. James P. Evans

Abstract

Surface geology is combined with abundant industry seismic-reflection and drill­-hole data in the central Bear River Range and Bear Lake Plateau to depict the forms and interactions of the Paris-Woodruff-Willard, Laketown-Meade-Home Canyon, and Crawford thrust faults. Displacement on the Paris thrust diminished to the south, and died out in splays where displacement was transferred to the Willard thrust. West of Woodruff, Utah, splays of the Laketown thrust deformed a complex footwall imbricate of the Willard thrust. To the east, a major northeast-striking Crawford thrust splay exhibits a change in slip vectors from east to southeast. Reorientation of these slip vectors is recorded by an imbricate stack of thrusts in the Willard thrust footwall to the west. The sharp bend in the surface trace of the Crawford normal fault southeast of Randolph, Utah, reflects the separation of the south-southeast-trending surface traces of the Crawford thrust and this northeast-trending splay.

Cross sections indicate that the Sheep Creek thrust, a major splay off the basal decollement at the base of the Crawford thrust sheet, accommodated displacement during the transition from thrusting on the western thrust system (Paris-Woodruff-Willard, and Laketown-Meade-Home Canyon) to the structurally lower eastern thrust system (Crawford, Absaroka, and younger thrusts). The Sheep Creek thrust trends northeast and folded the Laketown thrust in the central Bear River Range. Shortening in the northeast part of the study area was accommodated by the Home Canyon thrust along a detachment in the Jurassic Twin Creek Limestone. Several splays from this thrust extensively folded the footwall of the Meade thrust and rocks of the Bear Lake Plateau, and thereby formed a series of hanging-wall anticlines that have been extensively drilled for hydrocarbons.

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