Research Article| January 01, 1985 10Be analysis of a Quaternary weathering profile in the Virginia Piedmont M. J. Pavich; M. J. Pavich 1U.S. Geological Survey, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar Louis Brown; Louis Brown 2Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D.C. 20015 Search for other works by this author on: GSW Google Scholar J. Nathalie Valette-Silver; J. Nathalie Valette-Silver 2Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D.C. 20015 Search for other works by this author on: GSW Google Scholar Jeffrey Klein; Jeffrey Klein 3Tandem Accelerator Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104 Search for other works by this author on: GSW Google Scholar Roy Middleton Roy Middleton 3Tandem Accelerator Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104 Search for other works by this author on: GSW Google Scholar Geology (1985) 13 (1): 39–41. https://doi.org/10.1130/0091-7613(1985)13<39:BAOAQW>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. J. Pavich, Louis Brown, J. Nathalie Valette-Silver, Jeffrey Klein, Roy Middleton; 10Be analysis of a Quaternary weathering profile in the Virginia Piedmont. Geology 1985;; 13 (1): 39–41. doi: https://doi.org/10.1130/0091-7613(1985)13<39:BAOAQW>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Samples from a residual weathering profile in the Virginia Piedmont have been analyzed for cosmogenic 10Be. Concentrations are highest in clay-rich soil and decrease exponentially to a depth of about 15 m. Despite uncertainties about the processes by which 10Be may be intercepted before entering the solum and eroded after incorporation, a minimum age may be calculated for the regolith. This calculation is based on the delivery rate of 10Be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 × 105 yr. The calculated minimum age may be within a factor of 2 of maximum-age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite. The vertical distribution of 10Be in the profile could result from a steady-state balance of deposition, weathering, radioactive decay, and erosion. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
There can be no satisfactory knowledge of when humankind began to wonder about the age of the Earth, but given the multitude of answers proffered in the world's religions and myths, one must assume it was very early. Answers supported by some kind of objective questioning of the evidence observed in the Earth and the solar system are, however, relatively recent, dating from the Age of the Enlightenment. In 1748 conjectures by Benoit de Maillet from (wrong) interpretations of fossil evidence contradicted the biblical periods, indeed suggesting an age of 2.4 billion years. Numerous attempts were made during the following century and a half based on the cooling of the Earth and Sun, solar orbital physics, ocean chemistry, erosion and sedimentation. The only common element of these attempts was that all were orders of magnitude greater than what was found in Genesis. The discovery of radioactivity at the end of the nineteenth century altered things substantially in the minds of the investigators of the time by providing a method for determining the ages of rocks and by disposing of Kelvin's age estimates, which had been derived from erroneous assumptions calling for much shorter ages than geology required. Radioactivity provided a heat source within the Earth, and presumably within the Sun, that evaded the heat flow problem.
Abstract The problem of identifying areas of accelerated erosion in a dynamic landscape is complicated. The limited history of sediment yield measurements makes this task difficult even if geomorphic evidence is available. Beryllium‐10, a cosmogenic isotope produced by cosmic rays interacting with the earth's atmosphere and surface, has chemical and physical properties that make it useful as a tracer for erosion and sediment transport processes. The rarity of the stable isotope, 9 Be, allows 10 Be to be detected with accelerator mass spectrometry in natural materials at extremely low levels. Backgrounds for rocks and sediments below 10 5 atom per g are now attainable, a value to be compared with an average deposition rate of 1.3 × 10 6 atom cm −2 yr −1 . The affinity of Be for the components of soil and sediment is sufficiently high that it is effectively immobilized on contact, thereby allowing 10 Be to function as a tracer of sediment transport. To a good approximation all the 10 Be transport out of a drainage basin is on the sediment leaving it. The number of 10 Be atoms passing the gauging station can be determined by measuring the concentration of the isotope in the sediment, if the annual sediment load is known. The ratio of the 10 Be carried from the basin by the sediment to that incident upon it, called the erosion index, has been determined for 48 drainage basins within the same physiographic province, which allows them to be reasonably compared, all of which have sediment yield data. Basins located in the Atlantic coastal plain have an average index of 0.3 with the maximum observed being 0.9. Basins located between the fall line and the mountains, a region called the Piedmont, have an average value of 2.2 with individual values ranging from 0.6 to 6.7; this marked difference is thought to result from two centuries of farming on land of moderate gradient. Basins in the highland regions reflect local conditions with low indices for those in grass and timber and high indices associated with destructive land use. The data allow an estimate of the erosion index for the pre‐colonial Piedmont, which then allows the pre‐colonial sediment yield to be calculated. A number of basins have also been examined world wide with similar conclusions derived. An important deviation from the rule is noted for rivers that erode large regions of loess, such as the Mississippi, Hwang Ho, and Yangtze. Large aeolian deposits were laid down during the ice age in these basins, deposits that brought inherited 10 Be with them and that are easily eroded.
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