[M-IS14] Paleoclimatology and paleoceanography

[MIS14-P21] Spatio-temporal paleoenvironmental change in the Indian Ocean during Cretaceous OAEs and Paleogene PETM via µXRF analysis of ODP/IODP cores (Preliminary results)

*Ryudai Kotobuki¹, Hitoshi Hasegawa¹, Masafumi MURAYAMA¹, Takashi Hasegawa⁴, Erika Tanaka¹, Kazutaka Yasukawa³, Hironao Matsumoto², Junichiro Kuroda³ (1.Kochi University , 2.Tsukuba University, 3.University Tokyo, 4.Kanazawa University)

Keywords:ocena anoxic event, Paleocene Eocene Thermal Maximum, Indian Ocean, Ocena Circulation, global warming, paleoenvironment

The mid-Cretaceous Ocean Anoxic Events (OAEs) and the Paleocene-Eocene Thermal Maximum (PETM) are notable “hothouse" periods in Earth's history, characterized by extreme warming and disruptions in the carbon cycle due to the massive release of greenhouse gases into the atmosphere-ocean system. Reconstructing the paleoenvironmental changes during these past “hothouse” periods is significant for predicting the Earth’s system response to on going global warming. While numerous studies have been conducted to reconstruct paleoenvironmental changes during the OAEs and PETM intervals in the Atlantic and Pacific Oceans (João et al., 2010; Takashima et al., 2011; Elisabeth et al., 2012), records from the Indian Ocean remain limited (Dickson et al., 2016; Wolfgring et al., 2024). Paleoclimate model studies suggest that deep water formation sites were located in the Indian Ocean during the mid-Cretaceous and early Eocene (Donnadieu et al., 2016; Zhang Y et al., 2022) making this region critical for understanding ocean circulation during “hothouse” periods. This study focuses on ODP/IODP cores drilled in the Indian Ocean, which contain stratigraphic sequences corresponding to OAE2 and PETM. Using a µXRF machine (Bruker JETSTREAM), we investigated variations in elemental composition across multiple sites for the same interval to reconstruct spatio-temporal changes in oceanic environments during periods of extreme warming.
The samples analyzed for the OAE2-equivalent interval include ODP Leg 122-762C-75X (hereafter 762C) and ODP Leg 122-763C-2R (hereafter 763C) from the Exmouth Plateau, ODP Leg 183-1138A-69R (hereafter 1138A) from the Kerguelen Plateau, and IODP Exp 369-U1516D-4R (hereafter U1516D) from the Mentelle Basin. The 762C core includes sediments from the black shale layer of OAE2 through the recovery phase, while the 763C core covering a temporary cooling event (Plenus Cold Event, PCE) within extremely warm interval of OAE2. The 1138A core fully covers the OAE2 intervals, while the U1516D core contains sequences from the initial phase of OAE2, including the PCE. For the PETM interval, we analyzed IODP Exp 353-U1443A-35X (hereafter U1443A) from the Ninety East Ridge and ODP Leg 119-738C-11R (hereafter 738C) from the southern Kerguelen Plateau.
The results show that the Mn/Fe ratio (a redox proxy) and the K/Ti ratio (a chemical weathering proxy) decreased at all sites in the OAE2 and PETM intervals. The S/Ti ratio (a redox proxy) and Ba/Ti ratio (a productivity proxy) increased in the OAE2 intervals of 763C and U1516D, but decreased in the OAE2 interval of 762C and the PETM intervals of 738C and U1443A. The results of osmium isotope stratigraphy (Matsumoto et al., in preparation) suggest that there is a hiatus at the base of OAE2 interval. Thus, oxic conditions and decreased productivity during the OAE2 interval of 762C may have been influenced by the strengthening of deep-water circulation associated with PCE cooling. For the PETM intervals of U1443A and 738C, elemental compositions suggest more oxic bottom water environment and reduced biological productivity may have occurred compared to OAE2.
We plan to conduct statistical analyses using Independent Component Analysis (ICA) to examine the spatio-temporal variations in elemental composition among each region and to further investigate the environmental changes that occurred in the Indian Ocean during the OAE and PETM intervals.