UPPER EOCENE TEKTITE AND IMPACT EJECTA LAYER ON THE CONTINENTAL-SLOPEOFF NEW-JERSEY

During Leg 150 of the Ocean Drilling Project (ODP), two sites (903C an d 904A) were cored that have sediments of the same biostratigraphic ag e as the upper Eocene tektite-bearing ejecta layer at Deep Sea Drillin g Project (DSDP) Site 612. Core 45X from ODP Site 904A (similar to 4 k m north of Site 612) contains a 5 cm thick tektite-bearing ejecta laye r, and Core 56 from Site 903C (similar to 8 km north-northwest of Site 904) contains a 2 cm thick layer of impact ejecta without any tektite or impact glass. Shocked quartz and feldspar grains, with multiple se ts of planar deformation features (PDFs), and abundant coesite-bearing grains are present at both sites. The major oxide contents, trace ele ment compositions, and rare earth element (REE) patterns of the Site 9 04 tektites are similar to those of the Site 612 tektites and to North American tektites (especially bediasites). The epsilon(Sr) and epsilo n(Nd) values for one composite tektite sample from Site 904 fall withi n the range previously obtained for the Site 612 tektites, which defin es a linear trend that, if extrapolated, would intersect the values ob tained for North American tektites. The water contents of eight tektit e fragments from Site 904 range from 0.017 to 0.098 wt%, and, thus, ar e somewhat higher than is typical for tektites. The heavy mineral asse mblages of the 63-125 mu m size fractions from the ejecta layers at Si tes 612, 903, and 904 are all similar. Therefore, we conclude that the ejecta layer at all three sites is from the same impact event and tha t the tektites at Sites 904 and 612 belong to the North American tekti te strewn field. Clinopyroxene-bearing (cpx) spherules occur below, or in the lower part of, the main ejecta layer at all three sites. At al l three sites, the cpx spherules have been partly or completely replac ed with pyrite that preserved the original crystalline textures. Site 612, 903, and 904 cpx spherules are similar to those found in the Cari bbean Sea, Gulf of Mexico, central equatorial Pacific, western equator ial Pacific, and eastern Indian Ocean. The cpx event appears to have p receded the North American tektite event by 10-15 ka or less. The fini ng-upward sequence at all three sites and concentration of the denser, unmelted impact ejecta at the top of the tektite layer at Sites 612 a nd 904 suggest that the tektite-bearing ejecta layers are not the resu lt of downslope redeposition and that the unmelted ejecta landed after the glass. Geographic variations in thickness of the tektite-bearing ejecta layer, the lack of carbonate clasts in the ejecta layer, and th e low CaO content of the tektite glass suggest that the ejecta (includ ing the tektite glass) were derived from the Chesapeake Bay structure rather than from the Toms Canyon structure. A sharp decline in microfo ssil abundances suggests that local environmental changes caused by th e impact may have had adverse effects on benthic foraminifera, radiola ria, sponges, and fish as well as the planktic foraminifera.