The Chesapeake Bay impact structure was formed by a meteorite crashing to Earth during the late Eocene, about 35.5 million years ago (Ma). In May 2006, a scientific drilling project, sponsored by the International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS), completed a deep coring program into the impact structure. The deep drilling produced one of the most complete geologic sections ever obtained in an impact structure, and studies of the core samples will allow scientists to understand a shallow-marine impact event and its consequences at an unprecedented level.

This buried structure is the seventh largest, and one of the best preserved, of the known impact structures on Earth [Poag et al., 2004]. It consists of a 38-kilometer-wide, highly deformed central zone, which approximates the dimensions and location of the transient impact crater, surrounded by a shallower outer zone of sediment collapse known as the annular trough [Horton et al., 2005]. Together, these zones have a diameter of about 85 kilometers and a distinctive shape similar to an ‘inverted sombrero.’