THE AGE OF THE POPIGAI IMPACT EVENT AND ITS RELATION TO EVENTS AT THEEOCENE OLIGOCENE BOUNDARY/

Ages ranging from the Late Cretaceous (similar to 65 Myr) to the Oligo cene (similar to 29 Myr) have been reported for the 100-km-diameter Po pigai impact structure(1,2) on the Anabar shield, central Siberia. The se ages(3-8) overlap the timing of several possible impact-related fea tures, including the Cretaceous/Tertiary and Eocene/Oligocene stratigr aphic boundaries, the North American tektites(9), and the recently rep orted occurrences of an iridium anomaly and shocked quartz in Late Eoc ene deposits in northern Italy(10). Here we report age determinations of several Popigai impact melt rocks using the Ar-40-Ar-39 step heatin g technique to constrain the age of the impact event. Our results are consistent with a Late Eocene impact age of 35.7 +/- 0.2 Myr (2 sigma) -coincident in time with the impact deposits found in Italy. As this a ge is also similar to that of the North American tektites, which have been associated with the Chesapeake Bay impact structure in the easter n United States(11-13) there seem to have been at least two large and essentially contemporaneous impacts during the Late Eocene.