Am. Mus. Nat. Hist., United States

In view of recent controversy over the number and timing of late Eocene impact events, we evaluated biostratigraphic correlations at Deep Sea Drilling Project (DSDP)Site 612, New Jersey continental slope. Site 612, Core 21, Section 5 contains a tektite horizon which includes distinct microkrystite and microtektite layers (Glass, 1989). Ranges of magnetostratigraphically calibrated marker taxa firmly constrain the biostratigraphic position of these layers, although planktonic foraminiferal zonal criteria are equivocal for the upper Eocene at Site 612. Radiolarian and foraminiferal biostratigraphy indicate that the tektite layer at Site 612 is biostratigraphically older than a microtektite layer in Barbados which has been correlated with the North American strewn field. The Site 612 tektites are approximately 0.5-1.0 m.y. older than the Barbados microtektites. This conclusion is supported by compositional and isotope differences between the Site 612 tektites and the Barbados microtektites (Koeberl, 1988; Glass, 1989; Stecher et al., 1989), and requires that there were 3 or 4 separate late Eocene impact events. An alternative interpretation correlates the Barbados microtektites with the Site 612 tektites using (super 40) A- (super 39) Ar age measurements and some compositional similarities; this requires that biostratigraphic first and last occurrences were diachronous by approximately 0.7 m.y. or extremely high sedimentation rates at Site 612. Strontium and oxygen isotope stratigraphies are consistent with magnetobiostratigraphic correlations. The late Eocene impact events do not correlate with climate changes inferred from the marine isotope record.