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Reconstructing the first moments after the Cretaceous-Paleogene boundary impact event: high-resolution petrography and geochemistry of proximal and distal Chicxulub impactites

par Kaskes, Pim
Président du jury Gao, Yue
Promoteur Mattielli, Nadine ;Fontijn, Karen
Co-Promoteur Claeys, Philippe;Goderis, Steven
Publication Non publié, 2023-04-26

Thèse de doctorat

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Résumé :

The Chicxulub meteorite impact, ~66 million years ago, marks one of the most catastrophic events inEarth’s history. This event is linked to abrupt climate change and the Cretaceous-Paleogene (K-Pg)boundary mass extinction, responsible for the demise of 75% of life including the iconic non-aviandinosaurs. Fractured, molten, and vaporized rocks from the impact site were rapidly ejected into theatmosphere. This likely triggered the environmental stress at the K-Pg boundary, but the timing and exactmechanisms of these impact-induced processes are still poorly understood. The ~200-km-wide Chicxulubimpact structure, buried below the Yucatán Peninsula in México, forms a unique natural laboratory toinvestigate these processes. This crater is the only impact structure on Earth associated with ejectapreserved worldwide, which allows for a direct comparison between material from the source area and itsglobal deposits. In this PhD thesis, I present new high-resolution geochemical and petrographic analysis onrocks from the Chicxulub crater region and on globally distributed and well-preserved K-Pg boundaryejecta deposits. This work allows for a detailed reconstruction of the sequence of geological and biologicalevents that occurred in the moments prior, during and in the direct aftermath (minutes to years) of theChicxulub impact.The first part of this thesis is centered around crater suevites (impact-melt-bearing breccias)obtained from the Chicxulub northern peak ring by the recent IODP-ICDP Expedition 364 drilling campaign.The peak ring, consisting of granitoid basement, pre-impact dikes and impact melt bodies, was formed dueto the downward and outward collapse of the central uplift and this process took place within the first tenminutes after impact. The ~100 m thick suevite sequence on top is likely formed within 1 day after impactby the rapid arrival of ocean water in the crater that interacted with the underlying melt and subsequentlyflooded the crater basin. The overlying sediments are capped by a marlstone that is rich in iridium, likelyformed by settling of meteoritic dust (<20 years after impact). Based on the novel clumped isotopethermometry technique, hot secondary carbonate phases formed deep within the Chicxulub crater, whichlikely represent the recombination of CaO and impact-released CO2. The second part of the thesis focuseson terrestrial K-Pg boundary sections at a distance of 2000-3000 km from the Chicxulub crater. Micro–Xrayfluorescence (μXRF) and grain-size analysis of the K-Pg boundary sediments are combined with climatemodelling. Our results show that not sulfur or soot but a massive plume of micrometer-sized silicate dustwith a long atmospheric lifetime of 15 years was a key factor driving the K-Pg impact winter, steering thephotosynthetic shutdown, and ultimately triggering the K-Pg mass extinction.