Disentangling impact ejecta dynamics using micro–X-ray fluorescence (µ-XRF): a case study from the terrestrial Cretaceous-Paleogene (K-Pg) boundary

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Authors

Pim Kaskes , Roald Tagle, Mariia Rey, Steven Goderis, Sophie Decrée, Jan Smit, Philippe Claeys 

Abstract

This study presents a non-destructive geochemical and petrographic workflow to generate high-resolution chemostratigraphic records across key stratigraphic intervals, here exemplified by a terrestrial Cretaceous-Paleogene (K-Pg) boundary sequence. The geochemical records fingerprint specific Chicxulub related impact ejecta products and thereby further constrain the timeline of ejecta deposition. High-resolution (25 μm) micro-X-ray fluorescence (µ-XRF) mapping and quantitative integrated-area linescans in combination with ESEM-EDS analyses of the Starkville South sequence (Raton Basin, Colorado) reveal a complex microstratigraphy, in which additional sublayers can be identified than the classic ‘dual-layer’ succession, described in literature for US Western Interior K-Pg sites. First, a basal claystone is identified with abundant glassy impact spherules that have been altered over time to kaolinite and jarosite due to acidic and reducing conditions in a local swamp environment. This first lithology is followed by a carbonaceous shale interval rich in ejected quartz grains. These two ejecta intervals are interpreted to have formed by ballistic transport from the Chicxulub crater region and were likely emplaced within ∼1 hour after impact at Starkville. In the overlying lignite layer, pronounced enrichments in both zirconium and chromium are detected, hinting to a triple ejecta layer with a large part of the siderophile element anomaly being likely preserved in this coaly interval, including the famous iridium anomaly. These enrichments are attributed to fine-grained impact dust comprising of pulverized granitoid basement (Zr) and an admixture of meteoritic material (Cr, Ni and likely Ir), probably deposited <20 years after impact following slow atmospheric settling.

DOI

https://doi.org/10.31223/X5XQ5X

Subjects

Physical Sciences and Mathematics

Keywords

Cretaceous-Paleogene boundary, micro-X-ray fluorescence, Chicxulub, Ejecta, Event stratigraphy, trace elements

Dates

Published: 2024-12-31 08:32

License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
None

Data Availability (Reason not available):
All data on which this study is based are made available through the open-access database Zenodo.