Disentangling the Chicxulub Breccia; unravelling the formation of the suevite sequence in the IODP-ICDP 364 core by integrating major and trace elemental mapping with petrography

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Author(s): Kaskes, Pim; de Graaff, Sietze J.; de Beeck, Sander Op; de Winter, Niels J.; Smit, Jan; Goderis, Steven; Claeys, Philippe
Author Affiliation(s): Primary:
Vrije Universiteit Brussel, Department of Analytical, Environmental and Geo-Chemistry, Brussels, Belgium
Other:
Katholieke Universiteit Leuven, Belgium
Vrije Universiteit Amsterdam, Netherlands
Volume Title: European Geosciences Union general assembly 2018
Source: Geophysical Research Abstracts, Vol.20; European Geosciences Union general assembly 2018, Vienna, Austria, April 8-13, 2018. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English. 2 refs.
Summary: The joint IODP-ICDP 364 expedition in 2016 extracted a unique, continuous sequence of upper peak ring material from the Chicxulub impact structure in Mexico. The interval between core section 40R-1 and 95R-3 consists of a c. 130 m thick succession of suevite and impact melt rock that holds important clues about the composition and modification of the Chicxulub target lithologies (Morgan et al., 2017). The suevite unit is characterized as a polymict breccia that displays a generally gradual fining and a more well-sorted upward trend. This trend is most likely caused by the gradual decrease in settling velocity of ejecta after the asteroid impact. More subtle changes in the suevite succession, such as the transition between the fallback of ejecta material and the wash-back by tsunamis into the crater, are difficult to recognize. High resolution chemostratigraphy along the entire suevite sequence is therefore essential to identify the provenance of the various clasts and to link them to different formational processes. Micro X-ray fluorescence (µXRF) is an ideal technique for such a task, since it combines rapid, non-destructive elemental analysis such as semi-quantitative trace element mapping and quantitative line and point measurements at a 25 µm resolution (de Winter et al., 2017). Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) provides additional highly sensitive major and trace elemental analyses, which can be coupled to petrographic observations to further distinguish between different types of clasts and matrix. The main end-members discovered inside the Chicxulub suevite are (sub)angular clasts of fossiliferous limestone and chert in the top part versus clasts of granite and fragments of mafic lithologies that dominate the lower part. These clasts are remnants of a mixed target composed of a 2-3 km thick Mesozoic carbonate and evaporite platform and a Pan-African gneissic-granitic basement. The suevite matrix changes upward from green to grayish brown and represents a mixture of calcite and a clay component dominated by smectite (Morgan et al., 2017). Another important observation is the clear lack of sulfur in the entire suevite interval, which is suggested to be caused by the shock vaporization of major parts of the pre-impact evaporite platform on the Yucatan Peninsula. By integrating the XRF and LA-ICP-MS results with XRF and Computed Tomography scan data of the different core sections, it is possible to extrapolate microscopic data on the studied samples towards the entire core. This may shed light on the ongoing debate about emplacement mechanisms of suevite and on the relative contributions of the various lithologies to the Chicxulub pre-impact target. Morgan, J., et al., 2017. Chicxulub: Drilling the K-Pg Impact Crater. Proceedings of IODP, 364. https://doi.org/10.14379/iodp.proc.364.2017. de Winter N., et al., 2017. Trace element analyses of carbonates using portable and micro-X-ray fluorescence: Performance and optimization of measurement parameters and strategies. J. Anal. At. Spectrom., 2017, 32, 1211. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 02 Geochemistry; 05 Petrology, Igneous and Metamorphic; Atlantic Ocean; Breccia; Cenozoic; Chemical composition; Chicxulub Crater; Cretaceous; Expedition 364; Gulf of Mexico; ICP mass spectra; Impact breccia; Impactites; International Ocean Discovery Program; K-Pg boundary; Lower Paleocene; Major elements; Mass spectra; Mesozoic; Metamorphic rocks; North Atlantic; Paleocene; Paleogene; Petrography; Spectra; Stratigraphic boundary; Suevite; Tertiary; Trace elements; Upper Cretaceous; X-ray fluorescence spectra
Coordinates: N212701 N212701 W0895658 W0895658
Record ID: 2018093346
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany