Oldest Body Seawater Discovered Under Chesapeake Bay

A team of scientists have discovered in what could be the oldest body of seawater in the Chesapeake Bay. The ancient seawater is about 100-145 million years old.

Nearly 1,000 meters deep under the Chesapeake Bay, the largest estuary in the United States, scientists have discovered the high salinity groundwater that is actually water from the Early Cretaceous North Atlantic Sea. Dating some 100-145 millions years, the discovery of the ancient seawater makes it the oldest sizeable body of seawater worldwide.

The well-preserved ancient sea water is twice as salty as the modern seawater.  According to U.S. Geological Survey press release, about 35 million years ago, a huge comet or meteorite collided with the planet, which led to plenty of debris entering the Earth's atmosphere with one creating a 56-mile wide hole in the ocean floor. This formed the Chesapeake Bay that trapped the ancient seawater.  The collision also gave rise to chain of tsunamis that reached more than 100 miles, as far as the Blue Ridge Mountains

The 56-mile Chesapeake Bay impact crater is the largest crater to be discovered in the U.S. and is one of the few oceanic impact craters that have been documented worldwide till date. The average depth of this Bay is 46 feet and goes to a maximum of 208 feet.

"Previous evidence for temperature and salinity levels of geologic-era oceans around the globe have been estimated indirectly from various types of evidence in deep sediment cores," Ward Sanford, a USGS research hydrologist and lead author of the investigation, said in a statement. "In contrast, our study identifies ancient seawater that remains in place in its geologic setting, enabling us to provide a direct estimate of its age and salinity."

Researchers believe that this impact distorted the arrangement of the water bearing rocks called aquifers. The impact also deformed the layers of confining units that curb the flow of groundwater. Virginia's 'inland saltwater wedge' phenomenon is a current example that is associated with impact crater, where the outer rim of the crater appears to overlap the boundary that separate the salt water from the fresh groundwater.

"We knew from previous observations that there is deep groundwater in quite a few areas in the Atlantic Coastal Plain around the Chesapeake Bay that have salinities higher than seawater," said Jerad Bales, acting USGS Associate Director for Water. "Various theories related to the crater impact have been developed to explain the origin of this high salinity. But, up to this point, no one thought that this was North Atlantic Ocean water that had essentially been in place for about 100 million years."

This study assures the researchers that they are dealing with Earth's ancient seawater and also increases the understanding of the geological framework of the Chesapeake Bay.

The study is published in the journal Nature.