St. Clair County
Remnants Of The Past

Research Team visits Osceola-Weaubleau Impact Site

St. Clair County Courier
6 May 2005

On April 15, Kevin Evans, Assistant Professor of geology at Southwest Missouri State University, led a tour of SMSU and Central Missouri State University students around the meteor site located near Vista, and affecting a wide triangular area from Vista to Osceola and Weaubleau.
Evans was born in Versailles, Missouri. He received his B.S. in geology from SMSU, and a Ph.D. in Geology from the University of Kansas. His specialty is stratigraphy the study of layered sedimentary rocks.
Evans worked six years for the U.S. Geological Survey in Menlo Park, Calif. He said he considers it his service to the United States because he didn’t make much money. He was involved with a number of interesting projects including the coral reefs for Hawaiis, petroleum resources of the Alaska National Wildlife Refute in 1002 Area and the National Petroleum Reserve, Alaska, and salt-water intrusion into fresh-water aquifiers in the Los Angeles Basin. In 2001, he returned to Missouri and began teaching at SMSU as in instructor.
The Weaubleau-Osceola structure is about 340 million years old. Geologists refer to time period as the Mississippian Period. They know this because it deformed, folded and fractured limestones of that age but sandstones these are about 300 million years old; geologists refer to that time as the Pennsylvanian Period. It is sort of like a bookmark in the layered rocks that have recorded Earth’s history.
The Weaubleau-Osceola structure is unusual in that it is essentially complete and very well exposed. Evans used this analogy: meteorite impacts are like gunshots. They penetrate part of the Earth’s crust, but it would be difficult to tell when this event occurred except for the fact that it was covered fairly quickly afterward. If it remained completely covered, it would be difficult to recognize it. Erosion has exposed part of the structure to make it possible to study it in detail.
Twenty-seven impact structures are known in the United States. Two of the accepted impact structures are in Missouri: Decaturville about 10 miles north of Lebanon bordering LaClede and Camden counties and Crooked Creek about 10 miles south of Steelville in southwestern Crawford County. Both of these are fairly deeply eroded. The Weaubleau-Osceola structure is currently not on the list because researchers are still gathering evidence of the impact. It is virtually assured that it will be added to the list. Evans expects Weaubleau-Osceola to be added to the list of impact sites someday, Evans doesn’t claim to be an impact expert. He says, “I’m just kind of an interloper,” one who normally works on plain old sediment.
Conducting research in Antarctica had been one of the thrills of Evans’ career, but of the Weaubleau-Osceola discovery he says,
“This is the most exciting project I’ve ever been on.” The town of Vista, population “about 80”, is excited about nearly Weaubleau-Osceola site too, and is thinking of making it a tourist attraction. Evans enjoys talking to school children about the site. He said that he likes opening their eyes to the reality of asteroid impacts by pointing to the giant hole in their own backyard.
A half-mile wide asteroid strikes Earth on average every 500,000 years. Objects the size of an aircraft carrier hit 10 times as often, and football-field size rocks come every approximately 10,000 years. An asteroid that size moving at 20 miles a second can punch out a crater more than a mile wide, slamming into Earth with 80 megatons of energy, more than the largest hydrogen bomb ever exploded.
A three-mile-wide object still much smaller than the one that most likely killed the dinosaurs delivers more energy at the moment of impact than all our planet’s earthquakes, volcanoes, and tsunamis typically release over hundreds of years. Short of the sun going nova, an asteroid impact is the worst natural disaster that can befall us. Don’t take comfort in the frequency estimates, either: they are only statistical averages. Any of these things could happen tomorrow.
This is a cooperative research effort that involves geologists from SMSU, University of the Missouri, Missouri Department of Transportation, the Missouri Geological Survey, University of Oklahoma, Ohio State University, Appalachia State University, University of Vienna Austria, and Humboldt University Germany. Some of the principal features that support the idea that the Weaubleau-Osceola structure is a meteorite impact site include: two eccentric round topographic features that surround an area of intense geologic deformation. Crater and relict round features are common in many, but not all, impact structures. Rocks are intensely folded, fractured, and brecciated or broken to pieces in a localized area that is surrounded by relatively undisturbed rock. The breccia is rock that has completely mixed rock clasts and fossils from strata that include the limestones and rocks below. Quartz grains in the breccia rock have planar features that only form under extreme pressures. The element nickel is found in minerals that are in the breccia. Nickel is common in meteorites. Granite blocks have locally been lifted up to within 200 feet of the surface. Normally, these rocks are at 1,400 feet depth in this area. Uplifted areas are common in meteorite impact structures.
The meteorite impact hit in the shallow oceans, that covered this area during the Mississippian Period. Looking across the hills and hollows of the Ozarks, it may be hard to imagine but this area was once covered by oceans, but the fossils we see in many of the limestone rocks in this area demonstrate that this was once under the seas.
Geology is fascinating to study. We have such a limited perspective as humans. We live to be into our 80’s or 90’s if we are lucky. If we preserve the memories of those who have gone before, it may be up to four generations. With writings and sacred teachings, we can stretch history back a few thousand years. Yet we know humans lived and painted horses and cattle on cave walls some 40,000 years ago.
Homonids existed long before that but only a few tens of millions of years. Most of the rocks exposed in Missouri preserve records from much older times, when the continents were in different configurations. Still, these ancient events like a 340 million year old impact hold valuable information for us. We know that impacts have occurred in the past. They will happen again. What are the risks of future impacts? What sort of devastation occurs when they strike? Would a marine impact generate a deadly tsunami? How can we best survive future impacts? These are the sorts of questions where studies of an ancient impacts will help.
The conference will be held May 21-23, 2005. They will have a day of talks and poster presentations followed by two field trips. The first field trip is to the Weaubleau-Osceola structure on May 22. The second field trip will visit the Decaturville and Crooked Creek impact structures. They expect about 50-60 people from around the world to attend the conference.

Picture caption:
The Weaubleau-Osceola structure spans 19 km (the large circular drainage outlines the area of deformation above), but imagery and field data also indicate the extent of the transient crater is only 7 km.