Biostratigraphy and isotope stratigraphy of Upper Eocene microtektites at Site 612: how many impacts?

Site 612, Core 21, Section 5 contains a tektite horizon. Ranges of magnetostratigraphically calibrated marker taxa firmly constrain the biostratigraphic position of these layers. 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. An alternative interpretation correlates the Barbados microtektites with the Site 612 tektites using ⁴⁰Ar/³⁹Ar age measurements and some compositional similarities; this requires that biostratigraphic first and last occurrences were diachronous. The late Eocene impact events do not correlate with climate changes inferred from the marine isotope record. -from Authors