HIGH-RESOLUTION SEISMIC IMAGING OF THE CHESAPEAKE BAY IMPACT INNER CRATER RIM STRATIGRAPHY

Results from a high-resolution seismic reflection experiment across the inner crater rim of the Chesapeake Bay Impact Crater (CBIC) will be presented. This crater is the seventh largest impact crater on earth, formed during the Late Eocene when a meteorite struck the eastern continental shelf of North America. Although the impact structure is exceptionally well preserved, it is buried by about 500 m of post-impact deposits and cannot therefore be studied directly. The objective of this project was to image the transition from the inner to outer crater of the CBIC and to study the effect of the impact on the pre-impact stratigraphy and post-impact deposition on the continental shelf. About 3.4 km of seismic reflection data were collected in 3 profiles near Exmore, Virginia. One profile was acquired using a 120-geophone array at 5 m spacing. The other 2 profiles were collected using 24 channels at 10 m spacing. The source was a Betsy seisgun and sensors were 40-Hz geophones. Data were processed using Globe Claritas software, and processing steps included trace editing, refraction statics, spherical divergence correction, filtering, deconvolution, AGC, velocity analysis, NMO correction, and coherency filtering post-stack.

The resulting seismic sections show continuous and strong reflections down to 400 - 500 ms. These reflections show the post-impact stratigraphy, with a strong reflection from the top of the Chickahominy Formation at about 400 ms. Reflections from the syn-impact section are discontinuous with significant scattering. Basement reflections are not observed in the profiles. Although basement is not imaged on these lines, the depth of the post-impact sediments, and the fact that their thickness increases at the south end of the southernmost profile suggest that this profile crosses the inner crater rim.