August 2009 Geology and GSA Today media ...(timony tellurium and lead while copper-r...)

Date:7/31/2009

timony, tellurium, and lead, while copper-rich zones are depleted in these elements. These zones are interpreted to result from invasion of the pyrite-forming fluid by magmatic vapors. The close association of arsenic with gold and silver strongly suggests that these three elements may be transported by hydrothermal vapor separately from copper-rich vapor. Comparison of the analytical data to experimental studies of elemental partitioning, and analyses of fumaroles and fluid inclusions from magmatic-hydrothermal systems, suggests that the arsenic-rich vapor formed at high and possibly magmatic temperatures, whereas the copper-rich vapor formed at lower temperatures, possibly during migration of the original magmatic vapor.

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Paradox of late Paleozoic glacioeustasy
Daniel E. Horton and Christopher J. Poulsen, Dept. of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA. Pages 715-718.

The ice age of the late Paleozoic (326-267 million years ago) was a period of dynamic climatic fluctuation, a time period in which southern Pangea saw the waxing and waning of massive continental ice sheets while low-latitude Pangean sedimentary sequences recorded multiple 100-m eustatic fluctuations. This cyclicity is thought to have been driven by changes in Earth's orbit with relation to the sun. Horton and Poulsen employ a coupled ice sheet-atmospheric general circulation model in an attempt to simulate both observed glacioeustatic changes and inferred ice sheet volumes. Their simulations present paradoxical results. While ice volumes of similar size to those implied by proxy evidence are simulated, sea-level changes brought about by cyclic variations in Earth's orbit are minuscule. It is only with large perturbations to atmospheric greenhouse gas concentrations that observed sea-level changes are simulated. Current geological evidence does not support such drastic greenhouse gas fluctuations, leaving the driving fact
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Contact: Christa Stratton cstratton@geosociety.org 303-357-1093 Geological Society of America Source:Eurekalert

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