Devonian of New York: Schoharie and the Helderberg Group

Adriane here–

When I was a PhD candidate at UMass Amherst, I was the teaching assistant for our geology department’s Historical Geology class. Every spring, weather permitting, we would take our students on a weekend field trip to upstate New York, to visit rock formations and outcrops that were of Ordovician to Devonian (~450 to 385 million years ago) age. These outcrops and rocks contain abundant fossils, but there was one outcrop in particular that I always found to be the most fascinating: the Middle Devonian rocks exposed near Schoharie, New York.

Now that I am a postdoc at Binghamton University, I’m only about 1.5 hours away from this incredibly cool outcrop! A few weekends ago, my husband and I decided to take a short road trip to go fossil collecting here, as it was the perfect activity to do during a pandemic (limited to no interactions with other people, ample outside time, but also close enough to home). Unfortunately the day was incredibly hot, and we were only able to stay for about half an hour before we felt as if we were roasting. Regardless, we brought home so cool finds, namely a slab of invertebrates, some brachipods, a horn coral, and a sponge!

The outcrop exposed near Schoharie is well-known to local fossil and mineral clubs and fossil enthusiasts. The location is secluded and quiet, there is a long and wide shoulder for parking, and the outcrop itself is set off the road a bit, which is great for students and kids! The outcrop itself is located on Rickard Hill Road, just east of the town of Schoharie.

Google Map of Schoharie, New York, with the location of the outcrop denoted by the yellow star.

The rocks here are part of the Helderberg Group, which are composed of limestones that were deposited in a shallow sea during the Middle Devonian. There are three rock formations that are present: the Coeymans Limestone, Kalkberg Limestone, and Becraft Limestone. The Coeymans Limestone is the oldest formation here. It is a medium to coarse grained limestone which is massively bedded, meaning the rock layers, or beds, themselves are quite thick. Fossils are present in this formation, however, because the formation is massively bedded, the fossils are hard to get out of the rock and are less easily eroded.

An image of the Rickard Hill Road outcrop. The Kalkberg Formation is the rock that makes up the slope of the outcrop which you can walk on and collect fossils. On the right side of the image, the small cliffs are mainly composed of the Becraft Limestone. Image from http://bingweb.binghamton.edu/~kwilson/Devonian/DevSites/Schoharie/Schoharie.htm

The Kalkberg Formation lies above the Coeymans, and is described as a thin to medium bedded limestone. This means the individual rock layers within the formation are smaller and not as thick as those observed in the Coeymans Limestone. This formation also contains shale layers, a very fine-grained rock. This formation was likely deposited in a deeper-water setting than the Coeymans Limestone. Several different species and types of fossils are found in the Kalkberg, including animals such as corals, conularia, bryozoa, crinoides, brachiopods, trilobites (which are very rare), bivalves, gastropods, and even straight-shelled cephalopods. When you get out of you car at the outcrop, the Kalkberg Formation is what you are walking on!

 

My pentamerid brachiopod from the Becraft Formation. The lines visible on the surface are from glaciers that flowed across this brachiopod, which was cemented into the rock!

The Becraft Formation is the youngest of the three formations exposed at the Schoharie outcrop, and sits atop the Kalkberg Limestone. Similar to the Coeymans Limestone, the Becraft is a more massively bedded, coarse-grained limestone that was likely deposited in shallower waters than the Kalkberg Limestone. Because this formation is more resistant to weathering, it forms the small cliffs at the outcrop location. This formation contains fossils, but again, because it is more massively bedded, the fossils are not always as easily eroded out from the rocks. Other collectors have found fossils such as crinoids, brachiopods, gastropods, and bivalves.

One of the things I absolutely love about the Becraft Formation is that it contains glacial striations at the top of the cliffs! Glacial striations are grooves left in rocks when the glaciers covered much of northern North American about 15,000–20,000 years ago. Striations are commonly found on metamorphic, sedimentary,and igneous rocks, and help geoscientists know which way the ice flowed. But that’s another fun story for later. One of my all-time favorite fossil finds came from the top of the Becraft Formation: a pentamerid brachiopod that was carefully sliced in half by glaciers, that contains glacial striations! The brachiopod was likely preserved as a whole specimen with two valves, much like a clam has two parts to its shell. The glaciers eroded just enough of the formation and brachiopod to cut it perfectly in half. Incredible!

A slab of limestone containing quite a few fossils, including brachiopods, bryozoa, and bivalves!

If you are in the area, I highly recommend stopping at the Rickards Hill Road outcrop and visiting the Helderberg Group. Collecting here is fun for all ages, is open to the public, and fossils are almost guaranteed 🙂

Additional Resources

Fossil digs in Upstate New York: 5 Good Places to Search
Lower Devonian Fossils near Schoharie, NY
USGS Helderberg Group 

 

 

 

 

 

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