Transient electromagnetic mapping of clay units in the San Luis Valley, Colorado

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Abstract

Transient electromagnetic soundings were used to obtain information needed to refine hydrologic models of the San Luis Valley, Colorado. The soundings were able to map an aquitard called the blue clay that separates an unconfined surface aquifer from a deeper confined aquifer. The blue clay forms a conductor with an average resistivity of 6.9 ohm‐m. Above the conductor are found a mixture of gray clay and sand. The gray clay has an average resistivity of 21 ohm‐m, while the sand has a resistivity of greater than 100 ohm‐m. The large difference in resistivity of these units makes mapping them with a surface geophysical method relatively easy. The blue clay was deposited at the bottom of Lake Alamosa which filled most of the San Luis Valley during the Pleistocene. The geometry of the blue clay is influenced by a graben on the eastern side of the valley. The depth to the blue clay is greater over the graben. Along the eastern edge of valley the blue clay appears to be truncated by faults.

Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Transient electromagnetic mapping of clay units in the San Luis Valley, Colorado
DOI 10.4133/1.3445428
Year Published 2010
Language English
Publisher Society of Exploration Geophysicists
Contributing office(s) Crustal Geophysics and Geochemistry Science Center
Description 11 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Symposium on the Application of Geophysics to Engineering and Environmental Problems 2010
First page 154
Last page 164
Conference Title Symposium on the Application of Geophysics to Engineering and Environmental Problems 2010
Country United States
State Colorado
Other Geospatial San Luis Valley