Revised Onset Age of Magnetochron M0r: Chronostratigraphic and Geologic Implications
Document Type
Article
Publication Date
6-2023
Abstract
The timing of the onset of magnetochron M0r and its duration are disputed, reflecting both a limited set of radioisotopic dates and uncertain magnetostratigraphic correlations. We present a chronostratigraphic framework for a reversed polarity interval based on two chronometers (40Ar/39Ar, U-Pb) and newly published paleomagnetic data from the Qingshan Group, Jiaolai Basin, China. Bayesian modeling of U-Pb zircon and 40Ar/39Ar sanidine dates suggests a minimum duration of 540 ± 37 k.y. (95% credible interval) for the reversed polarity interval. These findings are compatible with an astrochronologic age model for M-sequence seafloor magnetic anomalies, indicating that the reversely magnetized sediments correspond to magnetochron M0r rather than the shorter chron “M-1r.” Integration of U-Pb and 40Ar/39Ar ages constrains the onset of M0r to 120.29 ± 0.09 Ma, which is ~1 m.y. younger than that inferred in the current geologic time scale (GTS 2020). This finding also implies that the Cretaceous normal superchron (CNS) began at 119.70 ± 0.12 Ma and that the average seafloor spreading rate during the CNS was ~3.5% higher than that inferred from GTS 2020. It also suggests that oceanic anoxic event 1a began at 119.40 ± 0.12 Ma, thereby providing an updated chronologic basis for exploring the primary trigger of this carbon cycle perturbation.
Publication Information
Li, Youjuan; Qin, Huafeng; Jicha, Brian R.; Huyskens, Magdalena H.; Wall, Corey J.; Trayler, Robin B.; Yin, Qing-Zhu; Schmitz, Mark; Pan, Yongxin; Deng, Chenglong; Singer, Brad S.; He, Huaiyu; and Zhu, Rixiang. (2023). "Revised Onset Age of Magnetochron M0r: Chronostratigraphic and Geologic Implications". Geology, 51(6), 565-570. https://doi.org/10.1130/G50873.1