The Kentland Impact Crater is found in Indiana near a town called— you guessed it— Kentland. It is an active limestone and other aggregate quarry called Newton County Stone. This field trip was led by Dr. Nelson Shaffer of Purdue University who explained the geologic history of the site. It’s one of the only exposed ancient crater sites in the region - but it doesn’t have much topographic relief because it’s around 97 million years old and has been through several glaciations which have “shaved off” the top. It is a complex crater, meaning the impactor (meteorite) was big enough to cause the earth to rebound in the middle creating a central uplift. The remains of the site can be clearly seen thanks to the active quarrying and many structural features - which are completely alien to geologically boring Indiana - can be seen in the walls, including sharp folding and beds tilted in every different direction. In addition to the structural features, formations native to the region can be seen mushed together in the walls and included into other formations. Namely, the Saint Peter Sandstone - the same sandstone that Chicago used for an aquifer until it got too big - can be seen in one of the above photos which reportedly has grains of coesite - the high-pressure cousin of quartz. Other beds are composed of fossiliferous limestone and even glauconitic material, as well as shale, which was soft enough to basically turn into plastic cake frosting that squeezed into and through other formations. All of these muddle together to form a massive structural headache, especially for a quarry team! But they manage to make do and the quarry is apparently one of the better employment opportunities in the area.
If you aren’t familiar with AIPG (American Institute of Professional Geologists), you should definitely check them out, especially your regional section! Student membership is free and, at least in the IL-IN section, field trips are free for students as well! If you can’t get enough geology and being a kook by yourself in your backyard doesn’t satisfy your needs, consider AIPG.
Edited by Yi Z.