Ancient meteorite impact in Iowa studied

Airborne surveys are providing an unprecedented look at a 470-million-year-old meteorite crater in Iowa concealed by bedrock and sediment, geologists say. The aerial surveys were conducted around Decorah, Iowa, within the past 60 days to map geologic structures and assess the mineral and water resources of the region, the U.S. Geological Survey said in a release Tuesday. "Capturing images of an ancient meteorite impact was a huge bonus," said Paul Bedrosian, a USGS geophysicist in Denver who is leading the effort to analyze the recently acquired geophysical data. "These findings highlight the range of applications that these geophysical methods can address." Iowa Department of Natural Resources geologists examined water well drill-cuttings in 2008-09 and recognized a unique shale unit preserved beneath and near Decorah. The extent of the shale defined a "nice circular basin" 3.4 miles in diameter, Robert McKay, a geologist with the Iowa Geological Survey, said. "The recognition of this buried geological structure was possible because of the collaboration of a local geologist, water well drillers, the USGS STATEMAP program, and the support of the Iowa DNR concerning research on fundamental aspects of Iowa geology," McKay said. The data show the impact as a nearly circular region distinct from the surrounding area to a depth of several hundred meters, the geologists said.