[S-GL19] Frontier research on chronostratigraphic unit boundaries

[SGL19-01] Astrochronology and radiometric ages for orbital-scale dynamics across the geologic stage boundaries

★Invited Papers

*Masayuki Ikeda¹, Nodoka Kuramoto¹, Aki Sakuma¹, Mizuki Tojima¹, Sota Niki¹, Hiroki Kamikura¹, Rio Miyata¹, Kentaro Izumi² (1.University of Tokyo, 2.Chiba University)

Keywords:geologic stage boundary, Milankovitch cycle, radiometric age, extinction, Triassic, Jurassic

The geologic stage boundaries are mainly defined by the occurrence or extinction of fossils. Massive volcanism and Bolide impact have been proposed as factors in boundary extinctions, but the cause of most stage boundaries is still a matter of debate. An important factor in elucidating the mechanism of the boundary events is the improvement of chronological resolution, which has been dramatically improved by radiometric dating and astrochronology using the Milankovitch cycle as a “pacemaker”. Milankovitch cycles are changes in the distribution of solar radiation on Earth associated with quasi-periodic changes in Earth's orbital parameters, which are widely accepted as the pacemaker for drastic environmental changes on ~100,000-year scales, such as glacial cycles (e.g., Hays et al., 1976). It is now clear that insolation also changes at even longer cycles, affecting ecosystems such as biodiversity and extinctions not only during the icehouse world but also in the ice-free greenhouse world (e.g., van Dam et al., 2005; Ikeda et al., 2020). In this presentation, we will combine astrochronology and absolute radiometric dating to improve the accuracy of geologic age boundary ages and introduce the influence of the Milankovitch cycle on boundary events, focusing on the Cenozoic (Pliocene-Pleistocene) and Mesozoic (Triassic-Jurassic) eras.