Date of Award:

5-1982

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

Peter T. Kolesar, Jr.

Committee

Peter T. Kolesar, Jr.

Committee

Don Fiesinger

Committee

Davie Liddell

Abstract

The Lower Middle Cambrian Langston Formation was studied in the Bear River Range of north-central Utah and southeasternmost Idaho and the Wellsville Mountains of north-central Utah. The depositional textures and sedimentary structures preserved within the rocks were compared with characteristics of similar modern sediments and ancient rock to determine environments of deposition, paleogeography, diagenetic alteration and pattern of dolomitization.

The rocks of the Langston Formation were divided into eleven different rock types. These eleven rock types were formed within four recognizable lithofacies: 1) upper peritidal; 2) inner carbonate shelf; 3) inner clastic shelf; and 4) outer clastic shelf.

The general depositional environment is inferred to have been a shallow subtidal to subaerial carbonate shoal complex. Clastic sediments from the east and north or northwest periodically prograded over the carbonate complex during times of relatively slow subsidence. The deposition of the Langston Formation mudrocks and carbonates occurred during the first Cambrian grand cycle.

During Langston time the study area was located near the outer edge of an equatorial epeiric sea. Clay mineralogy of the insoluble residues indicates a relatively humid climate, yet the humidity was low enough to permit precipitation of sulfate minerals.

Eogenetic diagenetic features include birdseye structures, relict evaporite structures, fibrous rim cement, compaction, and the begining of dolomitization. Mesogenetic diagenesis is characterized by dolomitization and pressure solution. Telogenetic diagenesis is limited to fracturing and calcite infilling.

Dolomitization is believed to have resulted mainly from downward reflux of hypersaline brines, as indicated by relict evaporite structures, zoned dolomite rhombs, and a general association of dolomite with upper peritidal facies. The hypersaline brines formed in the upper peritidal environment, and percolated downward through underlying porous sediments. The greater density of the hypersaline brines displaced less-dense interstitial fluids. These brines were periodically diluted by normal marine water or fresh water.

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