Algae Plant Fossils

Remains of aquatic, marine algae are found in Ohio's Paleozoic rocks but often these fossils are difficult to recognize and identify. Mound-shaped algal-sediment structures known as stromatolites or rounded ones known as oncolites, are found in some rocks in Ohio. They have been recognized from Silurian and Pennsylvanian rocks. Other, larger algae - seaweeds - have been found in Ordovician, Silurian, and Devonian rocks. Of particular note is a probable algal fossil known as Protosalvinia (formerly called Foerstia) that occurs in some abundance in a narrow zone in the Huron Member of the Ohio Shale. These fossils consist of shiny black, branched, lobed, or discoid structures preserved on bedding planes in fresh, unweathered shale.