[B-CG05] Decoding the history of Earth: From Hadean to the present

[BCG05-P11] Paleoenvironmental reconstruction across the Cretaceous-Paleogene (K-Pg) boundary based on sulfur isotope compositions

*Nao Fujieda¹, Teruyuki Maruoka², Yoshiro Nishio³ (1.Masters Programs in Geosciences, School of life and Environmental Science, University of Tsukuba, 2.Faculty of Life and Environmental Sciences, University of Tsukuba, 3.Research and Education Faculty, Kochi University)

Keywords:Sulfur isotopes, Cretaceous-Paleogene boundary, Mass extinction, Stevns Klint, Acid rain, Environmental Perturbations

The mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary was induced by environmental perturbations just after the meteorite impact, but the details of such environmental perturbations have remained unclear [1]. The K-Pg boundary can be characterized by a clay layer enriched in siderophile elements as well as chalcophile elements [2]. The chondritic elemental ratios of siderophile elements in these layers revealed that the enrichment of siderophile elements resulted from the incorporation of meteorite condensates. However, as the ratios of chalcophile and siderophile elements (such as Zn/Ir, As/Ir, and Sb/Ir) are one to two orders of magnitude higher than those in chondrites, chalcophile elements in these clays included a component or components not related to the meteorite condensate [3]. As concentrations of chalcophile elements, such as copper and silver, were well correlated with those of siderophile elements, chalcophile elements in the K-Pg boundary clays must have been supplied to the oceans simultaneously with the meteorite condensate. This implies that chalcophile components not related to the meteorite condensate must have been supplied by the process or processes that occurred just after the K-Pg meteoroid impact. Maruoka et al. [4] recently found that chalcophile elements in the K-Pg boundary layer at Stevns Klint, Denmark, were enriched in two sulfur-containing phases: silver-sulfide and pyrite. Therefore, sulfur isotope analysis can be applied to both phases of chalcophile-enriched grains that might preserve environmental information immediately after the K-Pg meteorite impact. In this study, we determined sulfur isotopic compositions of sulfur fractions extracted from the samples across the K-Pg boundary of Stevns Klint, Denmark, such as water-soluble sulfate (WSS), acid volatile sulfide (AVS), chromium-reducible sulfur (CRS), and carbonate associated sulfate (CAS). The d³⁴S values of AVS, which should include silver-sulfide, could not be determined owing to their low concentrations, whereas those of CRS, which includes pyrite as a major constituent, and CAS could be determined for the samples across the K-Pg boundary. Negative shifts of d³⁴S for CRS and CAS were observed at the K-Pg boundary. Such negative shifts probably reflect the enhanced flux of terrestrial sulfur input to oceans, judging from the correlation with higher ⁸⁷Sr/⁸⁶Sr values [5]. Such enhancement might be induced by acid rain just after the K-Pg meteoroid impact [6].

References;
[1] Maruoka, 2019, in Yamagishi et al. (eds.), Astrobiology: From the Origins of Life to the Search for Extraterrestrial Intelligence, 303-320. [2] Kyte et al., 1980, Nature 288, 651-656; Schmitz, 1985, Geochim. Cosmochim. Acta 49, 2361-2370; Schmitz, 1988, Geology, 16, 1068-1072; Schmitz, 1992, Geochim. Cosmochim. Acta 56, 1695-1703. [3] Gilmour and Anders, 1989, Geochim. Cosmochim. Acta, 53, 503-511. [4] Maruoka et al., 2020, Geol. Soc. Am. Bull., 132, 2055-2066. [5] Frei and Frei, 2002, Earth Planet. Sci. Lett. 203, 691–708. [6] Maruoka and Koeberl, 2003, Geology 31, 489–492; Maruoka et al., 2002, Geol. Soc. Am. Spec. Pap. 356, 337–344.