GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 147-6
Presentation Time: 2:55 PM


SCHALLER, Morgan F., Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Jonsson-Rowland Science Center 1W19, 110 8th Street, Troy, NY 12180-3590, TURRIN, Brent, Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854, FUNG, Megan K., Department of Earth and Environmental Sciences, California Lutheran University, 60 West Olsen Rd, Thousand Oaks, CA 91360 and KATZ, Miriam E., Dept. of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, 110 8th St, Troy, NY 12180

We report 40Ar-39Ar step-heating ages of P-E boundary impact spherules from Atlantic Margin coastal plain and open ocean sites. We test the hypothesis that the P-E spherules are reworked from an earlier event (e.g., K-Pg impact at ~66 Ma), which predicts a cooling age discordant from their depositional age of 55.93 ± 0.05 Ma at the P-E boundary. Isochrons from the step heating analyses yield 40Ar-36Ar intercepts in excess of the modern in most cases, indicating that the spherules have inherited radiogenic Ar (40Ar*), typical of impact glasses incompletely degassed before solidification. The weighted mean of the isochron-corrected plateau age is 54.1 ± 3.4 Ma (1s), and their isochron age is 55.4 ± 4.0 Ma, both indistinguishable from their P-E depositional age, not supporting the K-Pg reworking hypothesis. This is consistent with all other stratigraphic and geochemical evidence for an impact at the P-E boundary and ejecta distribution by air-fall.