July 2008 GEOLOGY and GSA Today media ...(using numerical models. This uplifted ar...)

Date:6/20/2008

using numerical models. This uplifted area is cut by some of the world's biggest fjords. Scoresbysund fjord alone is up to 60 km wide and cuts 400 km into the land and more than 4 km down from the peaks of the region. Glacial erosion and fjord formation has thus removed significant loads from the upper crust, which are compensated by uplift due to buoyancy forces, which act from the deep earth. These forces, however, are smoothed out by the flexural rigidity of the lithosphere. Therefore, the isostatic readjustment results not only in smaller subsidence of topography in the eroded fjord, but also in the uplift of the surrounding non-eroded area. To quantify this effect, Medvedev et al. construct a numerical model and analyze the erosional process backward in time. They estimate that an average of almost 1.2 km of bedrock was eroded in the region during past 20 million years. Their model demonstrates that rocks in the central Fjord Mountains may be uplifted up to 1.1 km due to erosional unloading and flexural isostasy. Thus, these effects should be a main mechanism responsible for the uplift in central East Greenland and probably represent a model applicable to other deeply eroded and recently uplifted coastal ranges.

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A new constraint on the antiquity of anaerobic oxidation of methane: Late Pennsylvanian seep limestones from southern Namibia

Daniel Birgel et al., MARUM - University of Bremen, Leobener Strasse, D-28359 Bremen, Germany. Pages 543-546.

Molecular fossils enclosed in Late Pennsylvanian seep limestones from southern Namibia reveal that prokaryotes oxidized methane by the same process that is still dominant at modern marine seeps. Birgel et al. show that the anaerobic oxidation of methane was performed by methanotrophic archaea and associated sulfate-reducing bacteria. Birgel et al.'s finding extends the record of a major biogeochemical process by approximately 150 million years.

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Crustal evolut
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Contact: Christa Stratton cstratton@geosociety.org 303-357-1093 Geological Society of America Source:Eurekalert

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