U.S. Atlantic Coast deformed unknown process

Plot Orangeburg scarp along the James River in Virginia (photo Harry Dowsett / USGS).

May 17, 2013. Compared with the western part of North America — a mountainous, volcanic and seismic — geologically quiet east coast received the name "passive continental margin."

However, new geological models suggest that the boiling bowels of the earth deform and distort this and many other so-called stable area.

Three million years ago, Earth was a few degrees warmer than today, and about the same temperature awaits us in 2100. Geologists want to know how the coastlines of continents looked at Pliocene, in order to predict the future change sea level. Scientists have speculated that the passive continental margin of the plains like the Atlantic coast and the nearby seabed pushed up by geological forces. It was thought that, on the contrary, the coast is lowered slowly and relentlessly, for rock beneath it cools, but the sand and the soil washed away from the land, fill the space vacated by the sinking of the continental margin. Consequently, the ancient shorelines should remain flat and horizontal, noting variations in sea level. One of these lines — the beach Pliocene-Orangeburg Scarp, which stretches from Florida to North Carolina. But it is not smooth, but lumps and creases that your carpet.

Maybe something is still pushing up land? Geologist David Rowley University of Chicago (USA) and his colleagues have developed a model of the motion of hot material in the Earth's mantle — a very viscous, while the solid layer of rock between the crust and the molten core. Such plumes (rising currents in the mantle) are responsible for Yellowstone geysers and volcanoes of Hawaii. The whole process is very similar to what Sunabout occurs gel lamp.

See also: In the Chesapeake Bay is sinking island

Group Mr. Rowley found subtle movement mantle beneath the eastern part of North America, including in the model layer of relatively liquid rock directly under the hard shell of the Earth — the asthenosphere. A model that does not account for the asthenosphere, showed that Orangeburg must sink. Clearly, however, it rises, and uneven — here and there. According to Mr. Rowley, a similar effect he modeled for Africa and the Colorado Plateau in the south-western United States. "The whole earth is going on a dynamic mantle," — he said.

Dynamic gown might skew the passive margins so that the researchers correctly read the geologic record of changes in sea level during the Pliocene and found them more sharp than they were in reality. Apparently, the authors of climate models have to be revised forecast of sea level rise in a warming world. (Dynamic topography, we note once again, does not change the level of the sea, but moves the mark by which to judge the climate of the Earth in the past.)

The findings suggest that the Atlantic coast can no longer be passive margin. "She's a passive-aggressive — says geologistKenneth Miller from Rutgers University (USA), who was not involved in the study. — And the new model provides insights on the mechanism of this aggression. " But the work of Mr. Rowley needs to be checked for compliance with the geological record, stressed Mr. Miller. He believes that the current large-scale models should be improved: at the present resolution of hundreds of kilometers, they are almost impossible to such a test.

Paleontologist Harry Dowsett of the U.S. Geological Survey, is also not involved in the study, sees evidence of innocence model Mr. Rowley in the distribution of surface rock outcrops: "It fits very well with geology, explaining what we are seeing."

A more accurate assessment of sea level during the Pliocene help geologists understand how much the ice sheets melted at that time, says Mr. Dowsett, and thus to look into our own future.

"But my work on this will not be easy — smiling specialist on the reconstruction of coastlines Pliocene based on microfossils. — On the contrary, become more difficult. "

The study is published in the journal Science.

Based on: ScienceNOW
Source: Kompyulenta

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