Susan Barbour Wood, a Ph.D. student, studied an area in Cincinnati, Ohio, where abundant road cuts show outcrops well preserved along major highways and interstates. The outcrops studied are Ordovician in age. At the time the fossils in those outcrops were deposited approximately 450 million years ago, that land would have been located underwater in a tropical setting south of the equator in a prime storm area, she said. Potentially, any number of things could have disturbed the sea floor--organisms burrowing through it, storms, for example--but that doesn't appear to have happened.
"The fossils were preserved in a series of stacked or amalgamated horizons of rock totaling approximately one foot thick," Barbour Wood said. "The horizons are believed to have been produced by multiple storms over a long period of time. The oldest storm-derived deposits are preserved at the bottom of the horizon and the youngest at the top. During the Ordovician, storm waves and currents would have pounded against the ancient ocean shelf as they do today. The storms could have shifted or scrambled the ancient sea floor habitats across geographical space or potentially dug up buried deposits of mud and dead organisms and mixed them with live or recent ones (time averaging) or simply washed them away to another area."
Barbour Wood collected samples every 10 meters along a 130-meter-long outcrop, or transect, and at the same foot-thick horizon at four other locations in the area. "I analyzed spatial and microstratigraphic patterns of fossil distribution preserved in an amalgamated, multi-storm event Cincinnatian horizon that is traceable for a lateral distance of some 60 km," she said.
Contact: Susan Barbour Wood