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Open-File Report 00-134

Preliminary Model of the Pre-Tertiary Basement Rocks Beneath Yucca Flat, Nevada Test Site, Nevada, Based on Analysis of Gravity and Magnetic Data

By Geoffrey A. Phelps, Edwin H. McKee, D. Sweetkind, and V.E. Langenheim

Thumbnail of and link to report PDF (1.7 MB)Introduction

The Environmental Restoration Program of the U.S. Department of Energy, Nevada Operations Office, was developed to investigate the possible consequences to the environment of 40 years of nuclear testing on the Nevada Test Site. The majority of the tests were detonated underground, introducing contaminants into the ground-water system (Laczniak and others, 1996). An understanding of the ground-water flow paths is necessary to evaluate the extent of ground-water contamination. This report provides information specific to Yucca Flat on the Nevada Test Site.

Critical to understanding the ground-water flow beneath Yucca Flat is an understanding of the subsurface geology, particularly the structure and distribution of the pre-Tertiary rocks, which comprise both the major regional aquifer and aquitard sequences (Winograd and Thordarson, 1975; Laczniak and others, 1996). Because the pre-Tertiary rocks are not exposed at the surface of Yucca Flat their distribution must be determined through well logs and less direct geophysical methods such as potential field studies.

In previous studies (Phelps and others, 1999; Phelps and Mckee, 1999) developed a model of the basement surface of the Paleozoic rocks beneath Yucca Flat and a series of normal faults that create topographic relief on the basement surface.

In this study the basement rocks and structure of Yucca Flat are examined in more detail using the basement gravity anomaly derived from the isostatic gravity inversion model of Phelps and others (1999) and high-resolution magnetic data, as part of an effort to gain a better understanding of the Paleozoic rocks beneath Yucca Flat in support of groundwater modeling.

First posted April 18, 2000

For additional information, contact:
Geology, Minerals, Energy, and Geophysics Science Center
U.S. Geological Survey
345 Middlefield Road, MS 901
Menlo Park, CA 94025-3591
http://geomaps.wr.usgs.gov/gmeg/

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Suggested citation:

Phelps, Geoffrey A., McKee, Edwin H., Sweetkind, D., and Langenheim, V.E., 2000, Preliminary Model of the Pre-Tertiary Basement Rocks Beneath Yucca Flat, Nevada Test Site, Nevada, Based on Analysis of Gravity and Magnetic Data: U.S. Geological Survey Open-File Report 00-134, 11 pp., http://pubs.usgs.ogv/of/2000/0134/.



Contents

Abstract

Introduction

Acknowledements

Data

Magnetic Field Analysis

Basement Gravity Modeling

Discussion

Conclusion

Future Work

References

5 Figures


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