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Volume 21 Issue 9 (September 2011)

GSA Today

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Article, pp. 10-12 | Full Text | PDF (160KB)

Recent advances in the hydrostratigraphy of Paleozoic bedrock in the Midwestern United States

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Kenneth R. Bradbury1*, Anthony C. Runkel2

1 University of Wisconsin–Extension, Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, Wisconsin 53705, USA
2 Minnesota Geological Survey, 2642 University Avenue W, St. Paul, Minnesota 55114, USA

PREFACE: (open/close)
Special 2011 Annual Meeting–Themed Science Article Section

In a departure from GSA Today’s usual single lead science article format, the following four articles are meant to familiarize you with the span of geologic time represented in the Upper Midwest and the expertise of its geoscience community as we prepare to assemble at the Annual Meeting in Minneapolis. These articles also emphasize the critical role geologists are being asked to play in a society that is increasingly focused on sustainable resource use and the long-term resilience of the planet.

The first two papers treat geologic events from opposite ends of the timeline as a controlled experiment that can be studied to help understand, and thereby forecast, system responses. The latter two speak directly to our role in society.

The EarthScope USArray is currently deployed in Minnesota. Seth Stein and colleagues describe how the information coming in regarding the failed, 1.1-Ga midcontinent rift, frozen in time, will provide a way to test the two leading theories about the fundamental cause of rifting.

Next, Karen Gran and colleagues describe Holocene valley evolution. A well-constrained downcutting event is driving continuing adjustment on tributaries to the Minnesota River, the history of which has a strong influence on modern sediment loads and direct resource-management implications.

Ken Bradbury and Tony Runkel, geologists with two state surveys, partnered up for the third article, which examines how the mechanical behavior of Paleozoic rocks affects groundwater flow systems. This information is critical for sustainable groundwater use in the face of challenges ranging from the presence of live viruses deep beneath Madison, Wisconsin, USA, to evolving cones of depression that change hydraulic gradients.

Finally, Cathy Manduca introduces readers to the process of producing an educated citizenry (and a well-prepared geoscience community) that understands the ways that Earth and society are linked. The article also illustrates the need to act collectively to share experiences, develop them into classroom activities, and accurately diagnose student challenges.

Carrie Jennings, Minnesota Geological Survey
Vice Chair, 2011 Annual Meeting Organizing Committee

Relatively undeformed Paleozoic bedrock forms the most widely used aquifers in Minnesota and Wisconsin (Fig. 1). Increasing demand for groundwater and concerns about contamination of deep aquifers have led to the need for a more comprehensive understanding of the hydrogeologic attributes of these strata than was deemed suitable just a few decades ago. Modern field techniques, coupled with advances in numerical modeling, are providing new insights into bedrock groundwater flow systems and redefinition of the classic divisions of the section into regional aquifers and aquitards. In Minnesota and Wisconsin, we commonly undertake borehole flowmeter logging, optical and acoustical borehole imaging, temperature profiling, short-interval packer testing, multi-level hydraulic head measurement, and dye tracing to evaluate the hydrogeology of bedrock formations. These techniques are widely available today but were beyond the reach of most field hydrogeologists only a few years ago.

Manuscript received 21 Mar. 2011; accepted 21 Apr. 2011

DOI: 10.1130/G122A.1