Granite Slab in Chesapeake Bay Crater Surprises Scientists

Scientists are rethinking their theories about the Chesapeake Bay impact crater after they drilled deeper into it than ever before and unexpectedly hit a huge slab of granite.

Crews penetrated 5,795 feet at the site, about five miles north of Cape Charles, Va., in drilling that began in September and ended last week.

An international team of scientists will analyze core samples as it tries to piece together what happened 35 million years ago when a meteorite smashed into what is now the mouth of the bay.

The mile-wide meteorite incinerated everything in its path and created a tsunami when it splashed into the sea, leaving a hole the size of Rhode Island.

The drills penetrated clay, sand and sediments before reaching pulverized stones known as suevite that were melted by the impact. One drill bit got stuck and two had to be replaced, so crews couldn’t reach their target depth, 7,200 feet.

What stalled them between the sediment and stones was a slab of granite that started at 3,600 feet and extended down to about 4,500 feet. How it got there is a mystery.

“The granite was a complete surprise to everybody,” said J. Wright Horton, a bay impact crater expert for the U.S. Geological Survey. “We had never anticipated this 900-foot block of granite, and we’re going to have to rethink and reinterpret some pretty big things about the crater structure.”

The granite is lodged between sedimentary material, which washed into the area after impact, and the suevite. One issue ripe for review is exactly what type of debris filled the hole in the sea floor moments after the meteorite hit, Horton said.

“It could mean new models of crater formation,” he said.

Experts are unsure whether the granite slid into the crater bed from the rim or was pushed there by massive shifting of the earth when the meteorite hit. Scientists also are unsure whether they’ve reached the bottom of the crater.

“We don’t exactly know what we have right now, even though the drilling phase is over,” Horton said. “We still have to go through the scientific phase and analyze all the material.”

The $1.5-million drilling project was funded by the Geological Survey, NASA and the International Continental Scientific Drilling Program, a consortium of scientists that pays for drilling projects at fault lines, volcanoes and craters around the world.

About 45 scientists from around the world will go to Geological Survey headquarters in Reston, Va., in the spring to collect core samples for research topics including how prehistoric climates changed, whether the meteorite was an asteroid or comet, and what types of microbes thrived in the boiling habitats created by the impact.

The bay crater is the largest in the United States and the sixth-largest of 170 known impact craters in the world.