Abstract

Rocks equivalent to the upper Devonian Pinyon Peak limestone and Victoria quartzite occur unconformably above older rock units in central and east-central Utah. This unconformity is perhaps most profound in the Stansbury Range where Pinyon Peak limestone overlies rocks as old as the upper part of the Tintic quartzite and as young as Simonson dolomite. A thick conglomerate occurs below the Pinyon Peak formation at the northern end of the range, and the conglomerate rests upon rocks as young as the Lake-town dolomite. To the south the conglomerate is thin and rests upon lower Simonson dolomite.

Pinyon Peak limestone overlies Victoria quartzite which is disconformable upon Simonson dolomite. A similar but much thicker arenaceous unit is exposed on Stansbury Island north of the core of the uplift.

The unconformity is present in the Oquirrh and southern Wasatch Mountains where Mississippian rocks rest unconformably upon Upper and Middle Cambrian units and generally rest lower in the section from southwest to northeast. Ophir shale, exposed below the Mississippian and lenticular Devonian rocks in the Central Wasatch southeast of Salt Lake City, represents an area of deep erosion. Northeast of Salt Lake City, the unconformity is at the base of the Upper Devonian clastic unit within the Three Forks or Jefferson formations. Younger rocks appear beneath the unconformity toward the north; a nearly complete and normal section occurs in the vicinity of Logan in the northeastern corner of the state.

The thick conglomerate of the Stansbury Range and the more widespread Upper Devonian sandstone, siltstone, shale, and silty carbonate units were probably derived from erosion of the uplifted area. Erosion, not nondeposition, probably accounts for much of the stratigraphic gap immediately below uppermost Devonian and lowermost Mississippian –rocks in the central part of Utah.

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