Let’s take a break today from mammals and talk about an impact in Chesapeake Bay about 35 million years ago, a few million years before the end of the Eocene Epoch. The area was offshore then as it is now, but the climate was probably at least sub-tropical if not tropical.
|Map from USGS|
The crater was unknown until 1983, because it is entirely in the subsurface, buried by later sediments. It was suspected because of the discovery of fused glass shards and shocked quartz grains in an exploratory oil well in New Jersey, and it was confirmed and defined in the 1990s though additional drilling. Once it was known, it became clear that its presence in the subsurface actually affects the courses of some modern rivers, including the York and James Rivers, which turn sharply at the buried rim of the crater. It also affects modern aquifer systems in the area, and the crater region is subsiding at a faster rate than the rest of the coastal zone, about 6 inches per hundred years. The crater also shows up in detailed gravity and magnetic surveys of the area.
|Cross-section from USGS|
—Richard I. Gibson
LINKS and References
Gravity and Magnetic expression
Crater map from USGS (public domain)
Cross-section from USGS (public domain)