This map shows locations of Chesapeake Bay crater and coreholes; the black and red circular lines mark the outer edges of the inner and outer craters; the black circle marks the location of the deep corehole. Image credit: Sanford WE et al.
145-Million-Year-Old Seawater Found beneath Chesapeake Bay
A new study published in Nature provides chemical, isotopic and physical evidence that groundwater found more than 3,200 feet deep under the Chesapeake Bay is remnant water from the early Cretaceous North Atlantic Sea.
The seawater is up to 145 million years old and twice as salty as modern seawater. It was preserved like a prehistoric fly in amber, partly by the aid of the impact of a massive comet or meteorite that struck the area, creating Chesapeake Bay.
“Previous evidence for temperature and salinity levels of geologic-era oceans around the globe has been estimated indirectly from various types of evidence in deep sediment cores. 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,” said lead author Dr Ward Sanford of U.S. Geological Survey.
The Chesapeake Bay impact crater is one of only a few oceanic impact craters that have been documented worldwide.
About 35 million years ago a huge rock or chunk of ice traveling through space blasted a 56-mile-wide hole in the shallow ocean floor near what is now the mouth of the Chesapeake Bay.
The force of the impact ejected enormous amounts of debris into the atmosphere and spawned a train of gigantic tsunamis that probably reached as far as the Blue Ridge Mountains, more than 110 miles away.
The impact of the comet or meteorite would have deformed and broken up the existing arrangement of aquifers and confining units.
“This study gives us confidence that we are working directly with seawater that dates far back in Earth’s history,” said Jerad Bales, acting U.S. Geological Survey’s Associate Director for Water.
“The study also has heightened our understanding of the geologic context of the Chesapeake Bay region as it relates to improving our understanding of hydrology in the region.”