Geochemistry

Backflushing Midcontinent Basins

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Science  24 May 2002:
Vol. 296, Issue 5572, pp. 1367
DOI: 10.1126/science.296.5572.1367b

Pleistocene glaciations have had dramatic effects on surface hydrology across North America and Europe, such as the formation of the Great Lakes and the establishment of the courses and flows of most of the major rivers in the Northern Hemisphere. In addition, glaciations have affected deep groundwater flow in many areas of this region and have even influenced the production of natural gas.

McIntosh et al. document an example from the midcontinent basins of North America. Several large basins filled with sedimentary rocks formed hundreds of millions of years ago, and these relatively stable formations developed a local system of groundwater flows. Pores in the rocks contained saline groundwater as well as some gas and petroleum. This area was covered repeatedly by continental ice sheets during the past 1 million years. Melt waters from the base of the ice sheet apparently penetrated into some of the basins, which reversed the directions of flows and reduced the salinity in much of the upper ground waters. Black shales along the margins of some basins experienced microbial production of methane in response to the influx. — BH

Geochim. Cosmochim. Acta66, 1681 (2002).

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