Bedrock outcrops in the central Appalachian Mountains make up ridgelines that define watershed boundaries and thus influence landscape evolution. However, erosion rates of these rock exposures are poorly constrained over the course of thousands of years. Samples from over 70 outcrops were collected and concentrations of the isotope, 10-Beryllium, were measured to determine the amount of time the rock material has been exposed at Earth's surface before being eroded away. The spatial patterns of erosion were also analyzed in an effort to understand how different parts of the varied landscape are evolving through time. Eric Portenga and colleagues find that bedrock ridgelines are eroding on average at nine meters per million years -- a rate slower than river drainage-basins in the Susquehanna and Potomac River watersheds. Our findings suggest that the central Appalachian landscape is in disequilibrium and still adjusting to hydrological changes. The presented erosion rates are similar, though, to denudation rates determined by other means indicating that the pace of landscape evolution in the central Appalachian Mountains is slow, and has been since the rifting of the supercontinent, Pangaea.
A century of U-Pb geochronology: The long quest towards concordance
F. Corfu, University of Oslo, Dept. of Geosciences, Postbox 1047 Blindern, N-0316 Oslo, Norway. Posted online 31 October 2012; http://dx.doi.org/10.1130/B30698.1.
The uranium-lead method for dating rocks and minerals is based on the radioactive decay of 238U to 206Pb and 235U to 207Pb. Trace amounts of uranium are incorporated in minerals such as zircon at the time of their formation. Geochronologists separate such mi
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Geological Society of America