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 Kolesar

Committee

Peter Kolesar

Committee

Donald Fiesinger

Committee

Robert Oaks

Abstract

The dolostones and dolomitic limestones of the Middle Cambrian Blacksmith Formation were studied in the Bear River and Malad Ranges and the Wellsville Mountains of north-central Utah. The depositional textures and sedimentary structures retained within the rocks form the basis of subdivisions of measured sections, interpretation of depositional paleogeography, and reconstruction of environments.

Other studies of modern carbonate environments and their ancient analogues provided the basis for interpretation of the depositional textures found within the rocks of the Blacksmith Formation. Four identifiable lithofacies were recognized within the study area. These facies include: (1) oolite shoal; (2) restricted lagoon; (3) low- to middle-intertidal; and (4) high-intertidal to supratidal environments. These four facies have an areal distribution that was controlled by the interactions of: (1) vertical buildup of carbonate platform; fluctuation of sea level; and (3) subsidence.

The general environment of deposition is inferred to have been an isolated carbonate bank located in a marginal sea west of the craton. The carbonate bank was characterized by low-lying tidal flats surrounded by low- to middle-intertidal regions and a restricted lagoon, with oolite shoals forming a barrier that limited water movement on the bank.

Early diagenetic features include fibrous rim cement, fenestral fabric, and minor compaction. Secondary diagenetic changes are dominated by the dolomitization of most of the Blacksmith Formation within the study area.

Dolomitization is believed to result from downward reflux of hypersaline brines. The hypersaline brine formed in the intertidal and supratidal environments and percolated into the porous carbonate sediments. Due to the density of the brine, the descending brine displaced marine and other less dense pore waters. The dolomite distribution is in part due to facies control of the brine movement. Outward movement of the brine, and subsequent decrease in the Mg:Ca ratio, are also inferred to be controlling factors in the distribution and extent of the dolomitization.

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