SOLVING A CHESAPEAKE BAY CONUNDRUM: NEW CLUES TO THE SOURCE BEDS FOR NORTH AMERICAN TEKTITES

The Chesapeake Bay impact crater is generally accepted as the source of the North American (NA) tektite strewn field (which covers ~9 x 10⁶ km² in NW Atlantic, Gulf of Mexico, Gulf Coastal Plain, and Caribbean Sea). Geochemical analyses (major and trace elements; radiogenic isotopes [Rb/Sr, Sm/Nd]) of preimpact sedimentary beds inside and outside the crater have yielded generally good agreement with NA tektite geochemical signatures, but an exact match has yet to be found. A new seismostratigraphic cross section of the impact structure (6 coreholes; ~100 km of marine seismic reflection data) provides clues to the possible provenance of the NA tektites. The line of section begins in the lower reaches of the York River (~ 6 km NW of the outer sedimentary rim of the crater), crosses the annular trough, crystalline inner ring, inner basin, and central peak (the latter near Cape Charles, Virginia), and terminates on the continental shelf, ~60 km southeast of the Delmarva Peninsula shoreline. Shoreward extrapolation of the offshore stratigraphic succession indicates that a relatively thick section (400-600 m) of previously unsampled Jurassic, Lower Cretaceous and Upper Cretaceous sedimentary units covered the crystalline basement rocks at the target site prior to the impact. It is reasonable to expect that blocks and (or) smaller clasts of these unsampled units are present in the crater fill. Recent coring (completed in December, 2005) at Eyreville, Virginia (continuous coring to 1766 m) recovered a 652-m-thick section of sedimentary crater fill from the inner basin of the Chesapeake Bay crater. The Eyreville core, thereby, holds great potential for identifying clasts from these offshore units and specifying the exact source beds for NA tektites.