[S-GL19] Frontier research on chronostratigraphic unit boundaries

[SGL19-03] Age and duration of the Aptian OAE1a determined by integrated carbon, osmium isotope, and planktonic foraminiferal stratigraphy and U-Pb dating in the Yezo Group, Hokkaido.

*Reishi Takashima¹, Li Youjuan², Bradley S. Singer², Mark Schmitz⁴, Luca Podrecca⁵, Bradley B Sageman⁵, David Selby³, Toshiro Yamanaka⁷, Michael T. Mohr⁴, Keiichi Hayashi⁶, Taiga Tomaru¹, Katarina Savatic⁵ (1.Tohoku University, 2.Wisconsin University, 3.Durham Univeristy, 4.Boise State University, 5.Northwestern University, 6.Hokkaido Research Organization, 7.Tokyo University of Marine Science and Technology)

Keywords:Cretaceous, OAE1a, Aptian, Yezo Group

The age of Aptian OAE1a and its relationship with the emplacement of the Ontong Java Nui remain major unresolved issues. The stratigraphy of OAE1a has long been studied in detail in the Tethys area of Europe (Italy, France, and Spain), where the lower Cretaceous is continuously exposed. In these areas, integrated stratigraphy using fossils and carbon and osmium isotopies has enabled detailed international stratigraphic correlation, e.g., OAE2 (Bottini et al., 2012; Du Vivier et al., 2014; Martínez-Rodríguez et al., 2021) and OAE1a (this study). Furthermore, prominent negative excursion in osmium and carbon isotopes at the onset of OAE1a has been regarded as supporting evidence for the emplacement of the Ontong Java Nui as the trigger of OAE1a. On the other hand, various age-models have been proposed for OAE1a, and there are maximum differences of about 5 million years among the models (Erba et al., 2015). Recent reexamination of the ⁴⁰Ar/³⁹Ar ages of the basalts from the Ontong Java Plateau revealed that they are much younger than the previously proposed OAE1a ages, raising questions about the relationship between OAE1a and emplacement of the Ontong Java Nui (Davidson et al., 2023).
The Yezo Group, exposed in Hokkaido, is considered to have been deposited in the fore-arc basin, which was emplaced along the Asian active continental margin in the northwest Pacific. The Aptian interval of the Yezo Group, exposed in the upper stream of Soashibetsu River, is suitable for constructing an OAE1a age model because it contains numerous felsic tuffs in mudstone-dominated strata. In this study, the basal part of the Yezo Group exposed in the Soashibetsugawa River was correlated in detail with representative European Aptian strata based on planktonic foraminiferal, carbon isotopic and osmium isotopic stratigraphy, and new CA-ID-TIMS U-Pb zircon age determinations have been obtained from 19 tuffs from the Yezo Group. Our result demonstrates that onset and termination of OAE1a are 119.456 + 0.053/-0.032 and 118.440 + 0.097/-0.136 Ma, respectively, which is ∼1 Ma younger than inferred in GTS 2020 (Gale et al., 2020). The duration of OAE1a is estimated to be 1016 ka, which is consistent with that inferred from astronomical age model (Charbonnier et al., 2023). In addition, since an occurrence of Leupoldina cabri, a foraminifer found capping the uppermost Ontong Java basalts, has a U-Pb age of ~118.8 Ma in the Yezo Group, we contend that Ontong Java Plateau volcanism remains a strong candidate for the trigger of OAE1a.
Rerferences
Bottini et al., 2012. Geology, 40, 583–586; Du Vivier, 2014.Earth. Planet. Sci. Lett. 389, 23–33; Martínez-Rodríguez et al., 2021, Glob. Planet Change 207, 103652; Erba et al., 2015. The Geological Society of America Special Paper 511, 271–303; Gale et al., 2020. Geologic Time Scale 2020, 1023–1086.; Davidson et al., 2023. Science 380, 1185–1188; Charbonnier et al., 2023. Earth. Planet. Sci. Lett. 610, 118104.