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Use of surface and borehole geophysics to delineate the glacial-drift stratigraphy of northeastern St. Joseph County, Indiana

Water-Resources Investigations Report 95-4041

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Abstract

Inverse models of direct current electrical- resistivity sounding data and normal-resistivity and natural-gamma logs were used to assist delineation of the glacial-drift stratigraphy in a 580-square- kilometer area of northeastern St. Joseph County, Indiana. Unconsolidated deposits in the study area are composed of glacial-drift, including outwash, till, and lacustrine sediments; thicknesses range from about 15 to more than 70 meters. The glacial outwash deposits are mostly composed of sand and gravel and are the primary source of drinking water to northeastern St. Joseph County. The glacial till and glacio-lacustrine deposits contain a larger fraction of clay than the outwash deposits and may retard ground-water flow between shallow and deeper sand and gravel aquifers. Results of the geophysical measurements collected during this study indicate that glacial-drift deposits in the area north and east of the St. Joseph River are mostly composed of sand and gravel with inter-layered clay-rich deposits that are laterally discontinuous. In the area south of the St. Joseph River, the thickness of sand and gravel deposits diminishes, and clay-rich deposits dominate the stratigraphy. The presence of an electrically conductive bedrock, the Ellsworth Shale, beneath the glacial-drift deposits is identified in inverse models of direct current electrical-resistivity sounding data.

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Use of surface and borehole geophysics to delineate the glacial-drift stratigraphy of northeastern St. Joseph County, Indiana
Series title:
Water-Resources Investigations Report
Series number:
95-4041
Edition:
-
Year Published:
1995
Language:
ENGLISH
Publisher:
U.S. Geological Survey ; USGS Earth Science Information Center, Open-File Reports Section [distributor],
Description:
iv, 42 p. :ill., maps ;28 cm.