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Cretaceous/Paleogene Boundary Spherules

Source:Material on this page refers to and stems from the paper
Ebel, D.S., and L. Grossman (2005) Spinel-bearing spherules condensed from the Chicxulub impact-vapor plume. Geology, 33: 293-296.
html at Geology site,
PDF at Geology site,
preprint (not under copyright).

PDF versions of supplementary material:
Table DR1: K/P spinel data, weight fractions of oxides (F. Kyte, 1998, personal commun.)
Table DR2: Abundances of elements (atoms) in initial vapor plume.
P-T curve (temperature-pressure path)
.......... Portion of T-P path for expanding dunite sphere with appropriate internal energy (Melosh, pers. comm.).

Related Links:
Elizabetta Pierazzo's impact modeling pages (good graphics)
Jan Smit's paleostratigraphy pages

Spinel-bearing spherules precisely mark the Cretaceous-Paleogene (K-P) 65Ma stratigraphic boundary, coincident with a severe mass extinction event and with the Chicxulub impact that produced a superheated vapor plume. Impact simulations and well log data yield the initial composition of the plume, which circled the globe and deposited the Ir-rich boundary layer. In this paper, thermodynamic models of condensation are used to produce the most detailed picture yet of the complicated chemistry of the expected vapor. Silicate liquid droplets would condense at high temperature. Spinel crystals with compositions very similar to those in K-P boundary spherules would crystallize from the liquid droplets. The highly oxidizing nature of the plume, due to the thick carbonate and sulfate layers in the impact target, is crucial to this outcome. Compositions of spinels found in the Atlantic and Europe are consistent with their crystallization at higher temperatures than spinels found in Pacific drill core.

Last modified February 15, 2006