A Long Time Ago...
By Matt Bayman
Fossil photographs by Matt Bayman.
Aerial photos by From Above Aerial Ohio.
Originally appeared in the winter
issue of This Local Life magazine.
at Fossil Beach in Tipp City
About 450 million years ago, Ohio was located 20-30 degrees south of the Equator beneath a shallow tropical sea that had flooded the continent of Laurentia, which would one day become North America. Scientists say the environment in Ohio resembled the Bahamas, with barren islands occasionally popping out of the warm water.
Laurentia was an ocean away from a super continent called Gondwana, which contained the land that eventually divided into Africa, Antarctica, the Arabian Peninsula, Australia, India and South America.
At this time, known as the Late Ordovician, there was no plant or animal life on land, and one of the warmest periods in Earth’s history was coming to an end. However, parts of the ocean were teeming with life, including the waters of Ohio.
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According to retired Ohio Department of Natural Resources geologist Michael C. Hansen in his paper, "The Geology of Ohio - The Ordovician," the two most conspicuous life-forms in Ohio at this time were bryozoans and brachiopods.
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Bryozoans are colonial animals that lived in branching, treelike colonies or flattened, encrusting masses. Brachiopods possess bivalved shells and lived on the bottom of the sea. In Ohio, these two species apparently lived in general harmony and abundance, along with a variety of other early aquatic life.
However, compared to most other life-forms from this time, what bryozoans and brachiopods had in common is that they used the warm sea water to produce calcium carbonate to construct their shells and skeletons. Upon death, these shells and hard parts collected on the bottom of the sea and eventually became cemented in finer calcium carbonate muds and, over time, turned into limestone rock.
This is why, today, the curious-at-heart can walk along a section of the Great Miami River in Tipp City and find not hundreds, but thousands of bryozoans and brachiopod fossils that date back half a billion years, as if a forest of these creatures lived and died at this location. It’s at an unofficial place known as Fossil Beach and it’s part of a fossil graveyard that sits beneath most of Ohio, but that is only exposed at the surface in the southwestern part of the state.
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While it is possible to find Ordovician-age fossils along many streams and rivers in southwest Ohio, including the much-sought-after trilobite, Fossil Beach stands out for its abundance of fossils – and its accessibility.
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ABOVE: The earth 458 million years ago with the continent of Laurentia at center left. Note that Ohio is flooded by an ancient sea. (Used with permission from Christopher Scotese, Scotese, C.R., 2001. Atlas of Earth History, Volume 1). BELOW LEFT: A depiction of bryozoans from Wikipedia Commons. BELOW RIGHT: A map to Fossil Beach in Tipp City.
A Collection in the Cobble
Fossil Beach is located in City Park not far from the second hole of the Frisbee golf course on the west bank of the Great Miami River. It’s not always easily accessible (a small stream with steep edges has to be crossed), and sometimes, due to flooding, it’s not even visible. But when conditions are right, and safe, about 1,200 feet (400 yards) of shoreline exposes thousands of chunks of limestone rocks filled with bryozoan and brachiopod fossils, among other rarer finds. There are even occasional pieces of frontier-era and Native American pottery.
The “beach” is located along a strong bend in the river and is noticeably different from the rest of the environment. When the sun is shining, the bleached rocks on the beach reflect the light like mirrors. These reflections can help lead hikers to the hidden location.
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Using Google Earth to view the beach from above, it appears as a banana-shaped formation hugging the west bank of the river, as if protruding from beneath City Park.
According to Ohio Department of Natural Resources Paleontologist Mark Peter, who viewed the images shown here and discussed the location via e-mail, the formation is a cobble bar, which is like a sand bar but made of cobble-sized stones (2.5-10.1 inches across) that have been rounded on the edges by water and tumbling against other stones.
Cobble bars form on the opposite sides of cutbanks (i.e. strong bends) in the river and collect and trap large amounts of rock, dirt and debris.
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At this particular cobble bar in Tipp City the trapped materials include a considerable amount of fossiliferous limestone, which itself was eroded away from an unabraded fossil source located somewhere upstream. Peter said that, along with bryozoans and brachiopods fossils, the cobble bar in Tipp City may also contain many other Ordovician-age fossils, including gastropods (snails), cephalopods, crinoid stem sections, and the occasional trilobite, among others.
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“Fossil Beach” is actually a cobble bar, which is an area along a river where rocks and other debris collect. In this photo above and to the left by From Above Aerial Ohio, it is clear that the massive cobble bar has influenced the flow of the Great Miami River. Along with rocks and debris, this particular cobble bar contains hundreds of tightly packed fossiliferous limestone, as seen at the top of the page. ABOVE RIGHT: A ground view of Fossil Beach by Matt Bayman. BELOW: Another view from above Fossil Beach by Above Aerial Ohio, this time, looking south.
The Ordovician Standard
When viewing a piece of limestone cobble from Fossil Beach, the first thing that becomes apparent is that most specimens contain not one or two fossils, but many, sometimes dozens. They often look almost plastered or stacked on top of each other, as if deposited in a mass grave.
According to Hansen, this abundance is what characterizes Ohio’s Ordovician-age fossils. It’s also why they’re considered world famous.
"Ordovician rocks in southwestern Ohio are world famous for the abundance, variety, and excellent preservation of the fossils they contain," Hansen writes, adding that these fossils “…define life of this geologic period, and the rocks of this region, the Cincinnatian Series, serves as the North American Upper Ordovician Standard.”
Hansen writes that many fossils in Ohio occur only in certain areas, one of which Fossil Beach is a part of.
"Many fossils occur only in certain beds or zones, and the serious fossil collector soon learns where to seek specific fossils among the thousands of outcrops in the tri-state area that centers on Cincinnati," he writes. "Anyone who has examined these rocks in the field immediately notes that, volumetrically, many beds are tightly packed with fossils."
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Tipp City is part of the Cincinnatian Series (seen on the map as the shark-tooth-like shape in southwest corner of the Ohio, which is filled with tightly packed Ordovician-aged fossils, seen at right.
Ancient Hurricanes?
Scientists are still working out the details about how and why so many dead creatures came to rest on the floor of Ohio’s ancient seas before turning into limestone, but part of the answer may have to do with hurricane cycles.
According to Hansen, large hurricanes were common during the Ordovician. They would form (likely to the north somewhere) and sweep across what would one day become the Miami Valley, where millions of bryozoan and brachiopod thrived.
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When this happened, the large storms would lift and then bury sea life on the sea floor, including large numbers of bryozoans and brachiopods.
As Hansen states in his paper, “The plants and animals living at the bottom of the sea were unearthed, dislodged, toppled and covered in the sediment. This shelly layer was then buried under a layer of finer-grained sediments that was in turn buried under a thin layer of mud. The process takes less than a day to complete and occurred countless times during the Late Ordovician.”
The result of this process is that there is over 900 feet of alternating, coarser-grained fossiliferous limestone and more sparsely fossilferous shale beds beneath southwest Ohio.
Hansen puts this in perspective, "It has been suggested that if all of the fossils could be removed from the Ordovician rocks of the Cincinnati area, Cincinnati would be below sea level."
Revealing Rivers
Although fossiliferous limestone is common beneath much of Ohio, the reason the fossils are visible at Fossil Beach (and many other places in the Miami Valley) has to do with the dynamics of the Great Miami River, and its predecessor, the ancient Teays River.
It needs to be remembered that during the Pleistocene glaciations (the Ice Age), Ohio was covered with hundreds of feet of glacial till (rocks and dirt deposited by advancing and receding glaciers). This covered up most of the limestone and shale layers that formed in southwestern Ohio during the Ordovician and later ages.
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In the case of Fossil Beach, Peter said that prior to the Pleistocene glaciations, the Miami Valley was part of the Teays River drainage system and that a river (probably a tributary of the Teays River, which flowed south to north) incised the Ordovician bedrock that contained the fossils that would one day end up at Fossil Beach.
Later, after being buried with glacial till for millennia and the end of the Ice Age, the Great Miami River cut through the till-filled valley and reached the Ordovician bedrock that had been exposed by the Teays River tributary eons before. When this happened, pieces of fossiliferous limestone dislodged into the streams and rivers, were rounded out by tumbling in the river, and eventually deposited as limestone cobble at Fossil Beach.
So, if you’re feeling adventurous, and the conditions are right, put on an old pair of shoes and seek out Fossil Beach, a place where some of the earlier forms of life on earth lived and died and where some of the most cherished fossils in the world are as common as stars in the night sky.
