Date of Award:

1984

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

Peter T. Kolesar, Jr.

Abstract

The Middle Cambrian Ute Formation was studied in the Bear River Range and the Wellsville Mountains of north-central Utah and southeastern Idaho. The depositional textures and sedimentary structures found within the rocks were compared with similar modern sediments and ancient rocks to determine depositional environments, paleogeography, and diagenetic alterations.

The rocks of the Ute Formation were divided into five basic types. These five rock types were formed within four identifiable lithofacies: 1) elastic marine shelf; 2) carbonate marine shelf; 3) agitated shoal; and 4) quiet-water shoal.

The sequence of elastic and carbonate sediments is believed to have been deposited in a shallow, subtidal environment. Clastic sediments from the east and northwest periodically prograded over the carbonate sequences. A major regression marks the base of the Ute Formation. This was followed by a series of transgressions and regressions, until a major transgression occurred near the end of the deposition of the Ute.

Paleomagnetic and faunal evidence suggest the study area was within 10° of the equator during the Middle Cambrian. Clay mineralogy of insoluble residues indicates a humid, tropical climate.

Primary diagenetic features are compaction, micritization, and cementation. Secondary diagenetic changes include the inversion of high-magnesium calcite to low-magnesium calcite, aggrading neomorphism, stylolitization, fracturing, and calcite infilling.

Partial dolomitization of grains and/or matrix is believed to result from the release of magnesium due to the decomposition of magnesium-rich, organic matter. The formation of a lens-shaped body of dolostone may have resulted from dolomitization by a magnesium-rich fluid circulating along faults.

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