WorldWide Drilling Resource

23 WorldWide Drilling Resource ® JULY 2014 Drilling Finds Ancient Seawater Adapted from Information by the U.S. Geological Survey U.S. Geological Survey (USGS) sci- entists drilled over half a mile under the Chesapeake Bay and found water from the Early Cretaceous North Atlantic Sea which is most likely over 100 million years old. It is the oldest body of seawater of this size to ever be found. The ancient seawater is twice as salty as modern seawater, and was pre- served with the help of a massive comet or meteorite which struck the area around 35million years ago, creating Chesapeake Bay. “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,” said Ward Sanford, a USGS research hydrologist and lead author of the investigation. “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.” The Chesapeake Bay impact crater is the largest crater ever discovered in the U.S. and is one of only a few oceanic impact craters ever documented. The 56-mile-wide hole was made when a gigantic rock or chunk of ice trav- eled through space to hit the shallow ocean floor near the modern-day mouth of the Chesapeake Bay. Huge amounts of debris were forced into the atmosphere when the object collided, spawning a chain of enormous tsunamis, probably reaching over a hundred miles away to the Blue Ridge Mountains. The arrangement of aquifers and layers of rock restricting the flow of groundwater at the time would have been broken up by the impact of the comet or meteorite. The “inland saltwa- ter wedge” in Virginia is a well-known phenomenon thought to be connected to the impact crater. The crater’s outer rim seems to coincide with the boundary separating fresh and salty groundwater. “We knew from previous observa- tions 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 associ- ate director for water. “Various theories This map shows the impact areas of a large asteroid or comet that struck the Chesapeake Bay some 35 million years ago. 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.” Bales also said researchers are confident they are working with seawa- ter from early in earth’s history; their understanding of the geologic history of Chesapeake Bay has been height- ened; and this study will improve over- all understanding of hydrology in the region.