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Ancient Tsunami 'Hit New York'

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Author Topic: Ancient Tsunami 'Hit New York'  (Read 429 times)
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« on: May 03, 2009, 07:41:45 am »

High-speed wave

Dr Goodbred first proposed the link between the layers of unusual debris found in sediment cores and a tsunami while studying shellfish populations in Great South Bay, Long Island.

He extracted many mud cores with incongruous 20cm layers of sand and gravel.

Their age matched that of wood deposits buried in the Hudson riverbed and marine fossils in a New Jersey debris flow in cores gathered by other researchers.

The fist-sized gravel he found in Long Island would require a high velocity of water - well over a metre per second - to land where it did, said Dr Goodbred.

Among the fossils and shells sandwiched in the organic black mud of Sandy Hook Bay, New Jersey, Marine Geologist Cecilia McHugh of Queens College, City University of New York, discovered mud balls made from red clay that matched iron-rich sediments found onshore.

The balls form their spherical shape only through vigorous reworking, said Dr McHugh, and they do not form in small storms.

"I didn't think much about it until we dated the deposit and came up with the same date that Steve did on Long Island," she said.

It prompted her to check cores extracted from the upper continental slope 200km offshore.

She discovered a 2,200-year-old layer of sand and mud, on top of sedimentary layers 8,000 to 14,000 years old.

Dr McHugh says such relatively young debris is not found that far out on the slope, and the date is close to that of the New York and New Jersey samples.
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