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Evidence of tilting of the U.S. coast
Accurate sea level markers
Roe Plains, Australia
The team’s first expedition
Researchers take advantage of a celestial collision
Uplift exposes a repository of Pliocene sediments
Researchers study crater of hydrogen bomb test
The Roe Plains, a crescent-shaped scrubland on Australia’s southern shore, dates to the mid-Pliocene. It was created by the scouring action of waves that, over millions of years, planed down a thick layer of limestone deposited during an earlier era. The Pliomax team explored numerous quarries and road cuts in the region in July 2009 and 2010. They had chosen Australia as their first research site due to its aridity—which preserves fossils—and the widespread belief that the region is relatively free of vertical motions that could otherwise confound past sea level measurements. Australia is distant from polar ice sheets that deform Earth’s crust when they advance and retreat. It’s also far from the colliding and spreading edges of the moving plates that support the continents. (Australia is in the middle of what’s called the Indo-Australian plate, thousands of miles from the nearest plate boundary.) Interactions between plates vertically displace land near the edges. Staying away from such boundaries was a priority.
The team found shells and corals indicating shorelines, some as high as 27 meters (90 feet) above current sea level. Samples at several sites have subsequently been dated in the laboratory as 3 million years old. The researchers expected that shells marking shoreline sites of the same age would be at the same elevation everywhere. But three-million-year-old shells on one end of the Roe Plains were lower than those at the other. The researchers have now concluded that they have evidence that Australia’s southern shoreline has tilted since the Pliocene. They will take this and other vertical movements into account when assessing Pliocene sea level.