Presentation Information
[T18-O-10]Geochemical Stratigraphy of the Chicxulub Impact and Deccan Trap Volcanism in Indian Ocean IODP Cores★2026年度学生優秀発表賞受賞★
*Hayu Ota1, Junichiro Kuroda1, Maria Luisa Tejada2, Katsuhiko Suzuki2, Yusuke Kubo3, Akira Ishikawa4 (1. Atmosphere and Ocean Research Institute, the University of Tokyo, 2. Japan Agency for Marine-Earth Science and Technology, 3. Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 4. Department of Earth and Planetary Sciences, Institute of Science Tokyo)
Keywords:
K-Pg boundary,Chicxulub impact,Deccan flood basalt eruption,Osmium isotope ratio,Indian Ocean
The Cretaceous–Paleogene (K–Pg) boundary, approximately 66 million years ago, is characterized by a large extraterrestrial impact that formed the Chicxulub crater on the Yucatán Peninsula in the present-day Gulf of Mexico. This impact caused abrupt changes in Earth’s surface environments and is thought to have led to the extinction of up to 75% of species. In addition, large-scale eruptions of the Deccan flood basalts occurred on the Indian subcontinent around the same time and are considered to have influenced global climate change. To understand the global and regional environmental responses associated with these events, it is essential to establish high-resolution K-Pg boundary stratigraphy worldwide and to correlate them precisely among different regions.
In this study, we focus on the Indian Ocean, a geographic gap in K-Pg studies, and conduct a stratigraphic investigation of marine drilling cores from two sites based on osmium isotope ratios (187Os/188Os) and platinum-group element (PGE) concentrations. Concentration peaks of PGEs, such as osmium (Os) and iridium (Ir), have been identified in K-Pg boundary layers worldwide (e.g. Alvarez et al., 1980). In addition, decreases in 187Os/188Os ratios in marine sediments are among the most reliable geochemical indicators of extraterrestrial impacts and volcanic activity, and have been widely used for correlation of K-Pg boundary layers (e.g. Ravizza & Peucker-Ehrenbrink, 2003).
The first study site is Ocean Drilling Program (ODP) Site 761 Hole B (16°44.23'S, 115°32.10'E), drilled on the Wombat Plateau off northwestern Australia. This core yields a highly continuous 187Os/188Os record, and its variation pattern is in good agreement with records from the Pacific and Atlantic oceans (Westerhold et al., 2025). Therefore, this core is likely to provide an important record for constructing a high-resolution reference curve of seawater 187Os/188Os variations during the latest Cretaceous Maastrichtian. We plan to complete analyses of all samples by the time of the conference presentation and to discuss their relationship to Deccan volcanism.
The second study site is International Ocean Discovery Program (IODP) Site U1514 Hole C (33°7.24'S, 113°5.48'E), drilled in the Mentelle Basin off southwestern Australia. In this core, a distinct PGE concentration peak and a decrease in 187Os/188Os ratios were observed at the biostratigraphic K-Pg boundary. These results indicate that one of the few continuous K-Pg boundary intervals in the high southern latitudes is preserved at this site. On the other hand, the timing of the 187Os/188Os decrease during the Maastrichtian does not coincide with the Pacific and Atlantic records. This discrepancy is likely due to significant uncertainties in the age model based on paleomagnetic reversals. We plan to complete carbon isotope analyses by the time of the conference presentation and to conduct a more detailed stratigraphic investigation by comparing the carbon isotope record with the 187Os/188Os variations.
Together, these results provide a stratigraphic framework for the K-Pg boundary and the interval of Deccan volcanism in the Indian Ocean, enabling high-resolution correlations with other ocean basins. This study provides an important basis for understanding both global and regional environmental changes across the K-Pg boundary.
【References】
Alvarez, L. W. et al. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208, 1095–1108 (1980).
Ravizza, G. & Peucker-Ehrenbrink, B. Chemostratigraphic evidence of Deccan volcanism from the marine osmium isotope record. Science 302, 1392–1395 (2003).
Westerhold et al. Earth orbital rhythms links timing of Deccan trap volcanism phases and global climate change. Sci. Adv. 11 eadr8584 (2025).
In this study, we focus on the Indian Ocean, a geographic gap in K-Pg studies, and conduct a stratigraphic investigation of marine drilling cores from two sites based on osmium isotope ratios (187Os/188Os) and platinum-group element (PGE) concentrations. Concentration peaks of PGEs, such as osmium (Os) and iridium (Ir), have been identified in K-Pg boundary layers worldwide (e.g. Alvarez et al., 1980). In addition, decreases in 187Os/188Os ratios in marine sediments are among the most reliable geochemical indicators of extraterrestrial impacts and volcanic activity, and have been widely used for correlation of K-Pg boundary layers (e.g. Ravizza & Peucker-Ehrenbrink, 2003).
The first study site is Ocean Drilling Program (ODP) Site 761 Hole B (16°44.23'S, 115°32.10'E), drilled on the Wombat Plateau off northwestern Australia. This core yields a highly continuous 187Os/188Os record, and its variation pattern is in good agreement with records from the Pacific and Atlantic oceans (Westerhold et al., 2025). Therefore, this core is likely to provide an important record for constructing a high-resolution reference curve of seawater 187Os/188Os variations during the latest Cretaceous Maastrichtian. We plan to complete analyses of all samples by the time of the conference presentation and to discuss their relationship to Deccan volcanism.
The second study site is International Ocean Discovery Program (IODP) Site U1514 Hole C (33°7.24'S, 113°5.48'E), drilled in the Mentelle Basin off southwestern Australia. In this core, a distinct PGE concentration peak and a decrease in 187Os/188Os ratios were observed at the biostratigraphic K-Pg boundary. These results indicate that one of the few continuous K-Pg boundary intervals in the high southern latitudes is preserved at this site. On the other hand, the timing of the 187Os/188Os decrease during the Maastrichtian does not coincide with the Pacific and Atlantic records. This discrepancy is likely due to significant uncertainties in the age model based on paleomagnetic reversals. We plan to complete carbon isotope analyses by the time of the conference presentation and to conduct a more detailed stratigraphic investigation by comparing the carbon isotope record with the 187Os/188Os variations.
Together, these results provide a stratigraphic framework for the K-Pg boundary and the interval of Deccan volcanism in the Indian Ocean, enabling high-resolution correlations with other ocean basins. This study provides an important basis for understanding both global and regional environmental changes across the K-Pg boundary.
【References】
Alvarez, L. W. et al. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208, 1095–1108 (1980).
Ravizza, G. & Peucker-Ehrenbrink, B. Chemostratigraphic evidence of Deccan volcanism from the marine osmium isotope record. Science 302, 1392–1395 (2003).
Westerhold et al. Earth orbital rhythms links timing of Deccan trap volcanism phases and global climate change. Sci. Adv. 11 eadr8584 (2025).
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