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Initial 40 Ar‐ 39 Ar Ages of the Paleocene‐Eocene Boundary Impact Spherules
Author(s) -
Schaller Morgan F.,
Turrin Brent D.,
Fung Megan K.,
Katz Miriam E.,
Swisher Carl C.
Publication year - 2019
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2019gl082473
Subject(s) - isochron , geology , radiogenic nuclide , isochron dating , sedimentary depositional environment , ejecta , geochronology , isotopes of argon , radiometric dating , paleontology , plateau (mathematics) , geochemistry , mineralogy , mantle (geology) , argon , astrophysics , physics , atomic physics , mathematical analysis , mathematics , structural basin , supernova
We report 40 Ar‐ 39 Ar step‐heating ages of Paleocene‐Eocene (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 analysis yield 40 Ar‐ 36 Ar intercepts in excess of the modern in most cases, indicating that the spherules have excess radiogenic Ar ( 40 Ar*), typical of impact glasses incompletely degassed before solidification. The weighted mean of the isochron‐corrected plateau age is 54.2 ± 2.5 Ma (1σ), 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.