Award Date

8-1992

Degree Type

Thesis

Degree Name

Master of Science in Geoscience

Department

Geoscience

First Committee Member

S. M. Rowland, Chair

Second Committee Member

F. W. Bachhuber,

Third Committee Member

D. L. Weide

Graduate Faculty Representative

J. B. Case

Number of Pages

103

Abstract

The Opd Unit of the Pogonip Group is a slope-forming carbonate sequence that crops out in the Arrow Canyon Range 75 miles north of Las Vegas, Nevada. It is composed mainly of grainstones, packstones, and intraformational conglomerates and also contains Calathium-bearing bioherms composed dominantly of wackestones. These rocks were deposited in a shallow-water, high-energy, subtidal, tropical marine environment. Nuia and Nuia-crinoid shoals developed on this shallow ramp and the area was frequently disturbed by storms.

Calathium-dominated carbonate mudmounds emerged on the Nuia and Nuia-crinoid shoals. Although Calathium dominated the mounds on a macroscopic scale, the mounds were build by unpreserved microorganisms. Calathium simply lived in the mounds and may have acted as sediment bafflers. Other mound dwellers included trilobites, crinoids, gastropods, nautiloids, brachiopods, and bryozoa.

The bioherms of the Opd Unit represent the transition from bioconstructions dominated by microorganisms during the Middle and Late Cambrian to those dominated by sessile benthonic macroorganisms during the Middle Ordovician.

Keywords

Carbonate rocks; Nevada – Arrow Canyon; Ordovician Geologic Period; Paleoecology; Sedimentation and deposition

Disciplines

Geology | Paleontology | Sedimentology

Language

English

Comments

Best copy available.

Signatures have been redacted for privacy and security measures.


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