DISTAL IMPACT EJECTA FROM THE CHESAPEAKE BAY IMPACT STRUCTURE

^{Microtektites, belonging to the North American (N.A.) tektite strewn field, have been found in upper Eocene sediments on Barbados and in sediment cores from the Gulf of Mexico, Caribbean Sea, and NW Atlantic Ocean with the highest concentration in the NW Atlantic. Unmelted impact ejecta (e.g., quartz with planar deformation features, coesite, stishovite) have been found in the microtektite layer. A high-pressure polymorph of zircon also was discovered in the layer and has been given the name reidite. It has been proposed that the Chesapeake Bay impact structure (CBIS) may be the source crater for the N.A. tektites strewn field. DSDP Site 612, ~330 km NNE of the CBIS, contains an 8-cm-thick layer containing ~65% tektite glass and ~30% unmelted ejecta. At Ocean Drilling Program Site 904, ~4 km NNW of Site 612, the layer is ~5 cm thick and contains ~50% tektite glass and 40% unmelted ejecta. At ODP Sites 903 and 1040, ~13 km NNW of Site 612 and 62 km NNE of Site 612, respectively, an impact ejecta layer of equivalent age contains only unmelted ejecta. This suggests that the glass may be distributed in a ray pattern. In the Gulf of Mexico, Caribbean Sea, and on Barbados the estimated thickness (based on number of microtektites/cm2) of the microtektite layers ranges between 0.017 and 0.155 cm and the ejecta are composed of >99% glass. Thus, the thickness of the ejecta layer decreases and the percent glass increases away from the CBIS. In addition, the glass fragment/spherule ratio decreases away from the CBIS. The thickness of the N.A. microtektite/ejecta layer and its distance from the CBIS (at six sites) indicate that the source crater diameter should be ~46 ± 18 km. Considering the error, this is close to the diameter of the central basin of the CBIS.}