Kevin E. Nick

Abstract

The purpose of this study was to determine specific depositional environments of the Miocene Esmeralda Formation in Stewart Basin (Stewart Valley), Mineral County, Nevada. Previous workers have concentrated on paleontological aspects of the basin and have described in detail the molluscs, mammals and macroflora. Less work has been done on the diatoms and spores and none on the fish, algae, wood or ostracodes. Recently, seven lithostratigraphics units of the Esmeralda Formation have been mapped in Stewart Valley (Clausen, 1983).

Detailed lithofacies are described in each of the seven lithostratigraphic units. Lithofacies 1 is composed of porcelanite and diatomite containing plant fossils. Lithofacies 2a and 2b are volcanic conglomerates with fossil wood. Lithofacies 3a, 3b and 3c are varieties of feldspathic sandstones containing molluscs and fish. Thinly-laminated porcelanite, diatomite and dolomite comprise lithofacies 4. Articulated fish, plant and insect fossils are present. Massive and bedded porcelanite and silty diatomite dominate lithofacies 5. Lithofacies 6 is composed of dolomicrite.

A diagenetic origin for the porcelanite is proposed. The precursor is interpreted to be a silty qiatomite.

Depositional environments are proposed for six time intervals during the Miocene. In time A, limnetic and littoral environments and debris-flows existed. Lahars then covered previous sediments. During time C meandering and braided fluvial systems reworked the lahars and a paludal environment formed. A second limnetic environment then formed and transgressed over the littoral sediments during times D and E. The lake reached a size of 100 km 2 . During times A, D and E lake waters were generally fresh and moderately alkaline with periods of increasing salinity and alkalinity. The last major depositional period (time F) was regressive. The salinity and pH of the lake waters increased favoring the formation of evaporites and zeolites.

The Esmeralda Formation in Stewart Basin is an unusual example of a fresh to moderately saline-alkaline lake environment. The stratigraphic relationship of diatomaceous, volcaniclastic, stromatolitic, and dolomitic sediments provide new insights into ancient lake environments.

LLU Discipline

Geology

Department

Geology

School

Graduate School

First Advisor

H. Paul Buchheim

Second Advisor

Knut Andersson

Third Advisor

Ivan G. Holmes

Degree Name

Master of Science (MS)

Degree Level

M.S.

Year Degree Awarded

1983

Date (Title Page)

9-1983

Language

English

Library of Congress/MESH Subject Headings

Geology; Stratigraphic -- Miocene; Geology -- Nevada -- Mineral County; Paleontology -- Miocene -- Mineral County

Type

Thesis

Page Count

ix; 112

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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