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Blast to the Past: Voyaging to the Ordovician Era

Written by: Donald Welsh

Undergraduate geology students went on a treasure hunt for fossils and geodes from the Ordovician Era in southern Indiana and Northern Kentucky as part of Professor Jeremy Fein's fall geology trip. Along the way, students discovered what the area was like 450 million years ago. 

This past semester I had the opportunity to experience some of the geology that helps explain the history of the Indiana/Kentucky area. Dr. Jeremy Fein led us on a trip to explore outcrops, caves, and waterfalls that reinforced concepts learned in class and provided an explanation on the geologic history of Notre Dame's surrounding area. 


Throughout the trip, we stopped at various outcrops filled with fossils that provided a look at the life that thrived on Earth around 350 to 450 million years ago. We used rock hammers to obtain samples containing fossils of brachiopods, crinoids, and corals. It was quite surprising to me how abundant the fossils were at the sites we visited- the limestone bedrock was full of them. Looking at these outcrops was a fantastic way to see firsthand that those places had previously been covered by a sea, as the fossils were from a shallow marine environment where life could thrive. We were also able to find geodes and stylolites at the outcrop sites. Stylolites are line formations that we found in the limestone, and they indicate which direction pressure was induced in the limestone. The geodes that we saw had beautiful formations of minerals precipitated in a cavity of the bedrock. Using rock hammers, we could break them open and take a look at the cool geologic phenomenon inside. 

Clifty Falls

Clifty Falls State Park provided an opportunity to learn about the geology of waterfalls. At the park, we could see the different layers of rock that the water flowed over. Specifically, we could see the more resistant layer of dolomite overlying a less resistant layer of shale, a classic feature of waterfalls (resistant rock on top of less resistant rock). We could also tell that the waterfall had retreated over time as the resistant layer was eroded away and that the waterfall will continue to erode and retreat into the future.

Marengo Cave

My favorite stop of the trip was the Marengo Cave in Marengo, Indiana. Here, we saw some classic features of karst topography- topography formed from the dissolution of soluble rocks such as limestone. The cave was filled with stalagmites and stalactites, as well as numerous ponds and caverns/rooms. Partway through the tour, the lights were turned off which provided a neat perspective into the life of cave-dwelling creatures and the sheer darkness that they lived in. This tour made me realize the vast amount of geology Indiana has to admire both above and below ground that can help to explain the history of this area.

A New Appreciation

This trip was truly awe-inspiring as I was able to look deep into the past of geologic time. I gained a better appreciation for rock outcrops, as now I know just how much information is stored in the layers of rock on the sides of the road. Despite the fact that most people would not think of Indiana as the most geologically interesting place in the world, it is clear that anywhere you look, geology will have a story to tell.

Donald Welsh is a sophomore earth sciences major with a minor in energy studies. Outside of his regular studies he is also conducting research for Professor Clive Neal's Lunar Petrology research group. 

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