Document Type
Article
Publication Date
4-20-2026
Journal / Book Title
Chemical Geology
Abstract
The Cretaceous–Paleogene boundary (∼66 Ma) records the Chicxulub asteroid impact, a pivotal event in Earth's history that affected much of the Earth's surface. While products of this impact have been widely studied, the thermodynamics of the plume and formation mechanisms of certain impact materials remain unclear. This study investigates conditions within the intermediate fraction of the Chicxulub impact plume (pyrocloud) using K and Rb isotope signatures of Gorgonilla Island impact spherules with published δ25Mg data to trace evaporation and condensation processes during ejecta dispersion. The δ41K and δ87Rb signatures vary from −1.18 ± 0.04‰ to 0.43 ± 0.09‰ and − 0.35 ± 0.01‰ to 0.07 ± 0.03‰ relative to the UCC, respectively. Combined with δ25Mg, these variations indicate evaporation and condensation in the pyrocloud. A fractional condensation model involving Mg and K suggests recondensation of spherules between ∼2520–2130 K, with a K- and Rb-saturated vapor at the end of the condensation sequence. The δ41K, δ87Rb, and δ25Mg data imply that spherules formed mainly through recondensation and underwent secondary evaporation due to depressurization and fluctuating temperatures in turbulent convection cells. Decoupled recondensation and evaporation of K and Rb from Mg are required to explain their isotopic signatures. While Mg isotopes trace overall spherule formation, K and Rb isotopes reflect fine-scale physicochemical processes at the end of their formation. These results highlight the thermodynamically complex, yet key effects of turbulent convection cell environments in impact materials and emphasize the need to pair MVE isotope data with refractory element isotopes to better understand the formation of various impacts materials.
DOI
10.1016/j.chemgeo.2026.123309
MSU Digital Commons Citation
Rundhaug, Courtney Jean; Schiller, Martin; Bizzarro, Martin; Deng, Zhengbin; and Bermúdez, Hermann Dario, "Signatures of vapor evolution in turbulent convection cells recorded by K and Rb isotopes in Chicxulub impact spherules" (2026). Department of Earth and Environmental Studies Faculty Scholarship and Creative Works. 797.
https://digitalcommons.montclair.edu/earth-environ-studies-facpubs/797
Rights
This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Published Citation
Rundhaug, Courtney Jean, et al. “Signatures of Vapor Evolution in Turbulent Convection Cells Recorded by K and Rb Isotopes in Chicxulub Impact Spherules.” Chemical Geology, vol. 707, Apr. 2026, p. 123309. https://doi.org/10.1016/j.chemgeo.2026.123309.