Abstract

The Precambrian Farmington Canyon Complex crops out in the Wasatch Mountains between Ogden and Bountiful, Utah. Additional exposures are present at Durst Mountain and at Antelope Island. These exposures form the northern Utah highland, a large basement uplift in north-central Utah.

Recent mapping in and around the highland, cast of the Wasatch Fault was combined with well data from the Henefer-Coalville area to provide a basis for interpretation of the basement uplift using a thin-skinned, piggy-back thrusting model. Three cross sections illustrate the inferred subsurface geometry of the northern Utah highland.

Correlation of the Ogden and Durst thrusts established a long, thin basement thrust sheet at a high structural position with 8 to 12 miles of eastward transport. The East Canyon thrust is interpreted as a westward-dipping thrust fault and correlated with the Ogden-Durst thrusts. The high structural position of these folded thrusts, compared to deeper thrusts encountered by drilling in the Henefer Anticline, indicates piggy-back motion on deeper basement-cored thrusts.

The basement thrusting is theorized as occurring late in the Willard-Paris thrust movement. The rise in basement temperature, due to thrust loading, weakened a steep Precambrian rift margin in the footwall that collapsed, producing basement-cored thrust sheets. The resulting culmination in the thrust belt is illustrated by the westward re-entrant in the Willard thrust trace west of Antelope Island and the parallel trend of structures and bedding around the margins of the highland.

The overall geometry of the northern Utah highland consists of a series of stacked basement thrust sheets. These basement-cored thrusts ramp eastward and connect with regional detachments in the overlying sedimentary pile.