Sunday, January 25, 2015

Ohio in the Silurian Age

The Silurian Period lasted from about 443 million years ago until 416 million years ago during the Paleozoic Era (Hansen).  Glacial formations began melting off, causing the deposition of rock across the state as well as a rise in sea levels. As the water began getting deeper reef environments sprang to life, giving this time period the nickname “the Age of Corals.” With the proximity to the equator being so close, Ohio was a tropical paradise abundant with many life forms that had previously not inhabited the area (Fischer). However, one of the most interesting aspects of Ohio during this time was not its ancient animals, but its rocks. Silurian rocks on the subsurface were predominantly salt and sandstone and were in what is now Eastern Ohio (Hansen). On the western side of Ohio, the rocks were completely different. Rocks such as limestone, dolomite, shale, and gypsum were abundant and remained on the surface (“Silurian”). All of these rocks were formed from chemical precipitation because of the sodium chloride, halite, hematite, and calcium in the warm, shallow, water (Coogan). As a result of numerous reefs developing that restricted the water from flowing naturally, the salt from the sea deposited into the ground after it evaporated and made the rocks chemically precipitate (“Silurian”). The rocks formed in Clark County developed in the Silurian Period. (Behrensmeyer, 438-408) In this period there were low continental elevations and a high global standing sea level. The area was geologically filled with siltstone and limestone. There was also shale and gray mudstone sediment.

Silurian history of Ohio:
Generalized nomenclature and relationships of Silurian rocks in various parts of Ohio and their relationships to underlying and overlying geologic systems. Rocks in region 4 (eastern Ohio) are in the subsurface. Names in quotation marks are drillers' terms. my = millions of years.

Map on left shows region of Silurian outcrop (green) and stratigraphic column areas.

Behrensmeyer, A.K., J.D. Damuth, W.A. DiMichele, R. Potts, H.D. Sues, and S.L. Wing. 1992. Terrestrial  Ecosystems Through Time: Evolutionary Paleoecology of Terrestrial Plants and Animals. University of Chicago Press, Chicago.
Coogan, Alan H. Ohio's Surface Rocks and Sediments.1996. PDF.
Fischer, Dan, Tammy Liu, Emily Yip, and Korsen Yu. "The Silurian Period." The Silurian Period. University of California Museum of Peleontology, 5 July 2011. Web. 20 Jan. 2015. <>.
Hansen, Michael C. "Geology of Ohio--The Silurian." Ohio Department of Natural Resources. Divison of Geological Survey, 8 Feb. 2000. Web. 20 Jan. 2015.
"Silurian Period - Ohio History Central." Silurian Period - Ohio History Central. Web. 18 Jan. 2015.

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