The Earliest Freshwater Trace Fossils and Their Depositional Environment in the Early Silurian (Llandoverian) Lower Massanutten Sandstone of Virginia

Alexandru M. F. Tomescu
Ohio University, Department of Environmental and Plant Biology
Athens, OH
at437491@ohio.edu

The goal of the proposed project is to characterize trace fossils that are potentially the oldest freshwater ichnofossils, and their depositional environments, in the Early Silurian (Llandoverian) lower Massanutten Sandstone of Virginia. These ichnofossils push back in time the colonization of freshwater habitats by at least 20 million years, and provide the first indication to the degree of development of early freshwater ecosystems. The trace fossil record was thus far suggesting that significant invasion of the freshwater ecospace did not begin until the end of the Silurian. Known Cambrian-Ordovician non-marine ichnofossils represent temporary colonization of marginal marine settings rather than true freshwater faunas, and no freshwater trace fossils were known prior to the Late Silurian. More importantly, the abundance of the Massanutten Sandstone ichnofossils indicates that by the Early Silurian continental ecosystems had reached unforeseen productivity levels, high enough to support well-developed freshwater communities. In-depth characterization of these trace fossils and their depositional environments will provide a rare glimpse at the type and intensity of interactions between freshwater and terrestrial ecosystems in an early stage of the colonization of continents. Ichnofacies are a useful tool in sequence stratigraphy. Documentation of Early Silurian freshwater ichnofossils will add a critical piece of information to continental ichnofacies models, with potentially important implications in sequence stratigraphic studies. Besides characterizing the oldest freshwater ichnofossils, this project will provide, for the first time, high resolution information on the sedimentology and depositional environments of the Llandoverian fluvial system that deposited the Massanutten Sandstone.