My next post about the Geology of the National Parks Through Pictures is from a trip to Ohio shortly after we moved to New York for a memorial service for my dear friend Dale.
You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.
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Obligatory entrance sign shot.
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| Brandywine Falls |
The hike up to Brandywine Falls and the falls themselves show a wonderful cross section of the geology available within the park. As you can see in the image of the falls above, there are three main rock formations within the park. Starting with the bottom, and the oldest, is the Cleveland Shale, which sits at the base of the falls. The Cleveland Shale is Late Devonian in age (~350 to 400 million years old) and is mostly a black shale, meaning that it is rich in organic material (e.g. oil and gas). The Cleveland Shale is assumed to have been deposited in a fairly shallow water environment with low oxygen levels. These low oxygen levels have led to the preservation of a number of fossils within the formation including 22 species of jawed fishes, including the 40 foot long Dunkleosteus, and one of the earliest known sharks, Cladoselache.
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| Downward view of Brandywine Falls |
The uppermost layer that comprises the falls, and the capstone of the falls, is the erosion resistant Berea Sandstone. The resistance to erosion of this layer is what created the falls in the first place, preventing the breakdown of the much softer layers below (the Bedford Shale). The Berea Sandstone is also Late Devonian in age (~350 million years old), and continues the environmental shallowing seen in the lower Bedford Shale. The Berea Sandstone is made up of interbedded sandstones and siltstones, with mostly sandstone, that were deposited just offshore within the deltas of nearby rivers. This sandstone, because of the porosity of the rock (gaps in between the sand grains), makes this formation a valuable oil reservoir, when found deeper underground.
There are a few other geological formations within the park, most of which are related to the glacier deposits from the Ice Age, ~2 million to 10,000 years ago. However, we didn't see most of those. We were able to take a train ride along the Cuyahoga River, which makes its way across the entire park. Our train ride took us along the river for pretty much the entirety of the trip and it was definitely running very high/flooding while we were there. While the picture above you can't see how high the river really is, the picture below shows a little better the full extent of the water levels. The ancestor river to the Cuyahoga River first began to form 150 million years ago and continued to erode down into the landscape forming the prehistoric river valley until the glaciers damned up the river and filled that ancestral valley with till, i.e. glacial sediment.
As the glaciers started to melt away, the Cuyahoga River was reformed as a glacial outwash stream, flowing south away from the current Lake Erie. Due to the topography of the landscape, and despite the glaciers being towards the north blocking the way, the river still wanted to flow towards the direction of modern day Lake Erie. As this new Cuyahoga River carved down into the landscape as a glacial outwash stream, it eventually hit the topographical high around the city of Akron. When it hit this high it also rediscovered the ancestral river valley and was able to excavated the glacial sediments within it. Within the ancestral valley, the course of this new Cuyahoga River was redirected back towards the north from the City of Akron in a big U-shaped bend. This bend is what has caused the river to be known as the crooked path. Even the name of the valley is derived from what the Native Americans named the river, “Ka-ih-ogh-ha”, meaning crooked.
Alongside the river, the Ohio & Erie Canal was formed back in the 1800's and maintained through the early 1900's. This canal route contained several locks used to raise and lower boats along the waterway. Lock 29, along the Cuyahoga River, is a former Ohio & Erie Canal lock where the original construction sandstone blocks can still be seen. All the other locks had their sandstone blocks replaced in the early 1900's when their sandstone blocks had deteriorated. However, Lock 29 had it's masonry redone in 1882, and therefore the sandstone blocks were still in good condition during the renovation of the other locks. Therefore, while all those other locks were converted to concrete, we still have the original sandstone here. The sandstone used for these locks was the aforementioned Berea Sandstone. Because it could be quarried locally and was extremely durable (hence waterfall), it was chosen as the ideal rock to make the lock out of. Blocks of sandstone were taken from the nearby Deep Lock Quarry less than 2 miles away.
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