Fingerprinting the Cretaceous-Paleogene boundary impact with Zn isotopes

Ryan Mathur,Linda Godfrey,D Graham Pearson,Neil Landman,Francisca E Oboh-Ikuenobe,Brandon Mahan,Matthew Garb,Sheng-Ao Liu,Marissa Spencer

doi:10.1038/s41467-021-24419-8

Abstract

Numerous geochemical anomalies exist at the K-Pg boundary that indicate the addition of extraterrestrial materials; however, none fingerprint volatilization, a key process that occurs during large bolide impacts. Stable Zn isotopes are an exceptional indicator of volatility-related processes, where partial vaporization of Zn leaves the residuum enriched in its heavy isotopes. Here, we present Zn isotope data for sedimentary rock layers of the K-Pg boundary, which display heavier Zn isotope compositions and lower Zn concentrations relative to surrounding sedimentary rocks, the carbonate platform at the impact site, and most carbonaceous chondrites. Neither volcanic events nor secondary alteration during weathering and diagenesis can explain the Zn concentration and isotope signatures present. The systematically higher Zn isotope values within the boundary layer sediments provide an isotopic fingerprint of partially evaporated material within the K-Pg boundary layer, thus earmarking Zn volatilization during impact and subsequent ejecta transport associated with an impact at the K-Pg.

Highlights

Numerous geochemical anomalies exist at the K-Pg boundary that indicate the addition of extraterrestrial materials; none fingerprint volatilization, a key process that occurs during large bolide impacts
Geochronological, and geochemical evidence identify the existence of a bolide impact and the geological processes associated with this collision
An extraterrestrial impact component has been evidenced by the presence of a carbonaceous chondrite-like (CM2) Cr isotope anomaly (ε54Cr)[7], and Os isotopes have indicated that the Deccan traps volcanism preceded the K–Pg boundary, largely negating volcanism as the main driver of the K–Pg boundary mass extinction event, though debate persists[5,8]

Summary

Introduction

Numerous geochemical anomalies exist at the K-Pg boundary that indicate the addition of extraterrestrial materials; none fingerprint volatilization, a key process that occurs during large bolide impacts. Zn isotope compositions of K–Pg sedimentary rock layers have been characterized for five different locations, from proximal (up to 1000 km; Mississippi and Missouri sites) to intermediate distances from (1000–5000 km; Montana and New Jersey) the impact site at Chixculub crater in the Yucatan Peninsula.

Results

Conclusion