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Seismic information for Lake Superior on CD-ROM

Deep reflection seismic profiles in Lake Superior, shot by Grant Norpac, Inc., and leased by Argonne National Laboratory, are now available to the geological research community in the digital report Seismic Reflection Profiling and Tectonic Evolution of the Midcontinent Rift in Lake Superior, published by the Wisconsin Geological and Natural History Survey.

As a consequence of major geologic events, such as plate convergence and continental glaciation, one of Earth’s largest lakes, Lake Superior, is now superposed over the axis of one of Earth’s largest rifts, the Midcontinent Rift System. The superposition of a lake over a rift permitted deep seismic reflection sounding data to be acquired in a marine mode, resulting in particularly high-quality data.

A grid of seismic reflection profiles in Lake Superior, which cover approximately 20 percent of the length of the Midcontinent Rift, provided a comprehensive data set that assisted structural and stratigraphic analysis of the rift beneath the lake. The data allowed the report’s authors, L.D. McGinnis and M.G. Mudrey, Jr., to identify several distinct basins and interconnecting troughs, a large anticlinal structure, and major boundary faults and folds. In addition, they were also able to revise locations and characteristics of previously known boundary faults and their relationship to rifted blocks.

Integration of information obtained from outcrops with data presented in this report contributes to a better understanding of not only Precambrian rift processes in the vicinity of Lake Superior, but of the interaction of the rift with the Grenville orogeny to the east and to Precambrian tectonism in other parts of the world.

The report, Survey Miscellaneous Paper 91-2, is available on CD-ROM for $25. The CD-ROM contains an electronic version of the report as well as scanned images of the 15 plates of seismic lines. Come in to the Map Sales office or order from the Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, Wisconsin 53705-5100; telephone 608/263.7389. MasterCard and Visa customers may telephone their orders between the hours of 8 am and 4:30 pm, Monday through Friday. Shipping and handling charges are extra; refer to our order form, which is in Adobe® Acrobat® format.