修正磁时线M0r起始年龄的年代地层和地质意义

　　美国威斯康星大学Youjuan Li和中国科学院朱日祥研究团队合作，报道了修正磁时线M0r的起始年龄的年代地层和地质意义。该项研究成果发表在2023年4月12日出版的《地质学》上。

　　研究人员基于两个天文钟(40 Ar / 39 Ar, U-Pb)和中国胶莱盆地青山群新发布的古地磁的数据，提出反极性区间的年代地层学框架。贝叶斯建模透长石是U-Pb锆石和40 Ar / 39 Ar 数据显示，反极性区间的最短持续时间为540±37k.y.(95%可信区间)。这些发现与M系列海底磁异常的天文年代模型相吻合，表明反磁化沉积物对应于磁时线M0r，而不是较短的“M-1r”。U-Pb锆石和40 Ar / 39 Ar 年龄的整合将M0r的起始限制在120.29±0.09 Ma，这比当前地质时间尺度(GTS 2020)中推断的时间年轻约 1 m.y。

　　这一发现也意味着白垩纪正常超时(CNS)始于119.70±0.12Ma ，正常超时期间的平均海底扩张速率比当前地质时间尺度推断的要高出约3.5%。研究结果强调，大洋缺氧事件1a始于 119.40±0.12 Ma，从而为探索这种碳循环扰动的主要触发因素提供了更新的年代学基础。

　　据悉，磁时线M0r的起始年龄及其持续时间存在争议，反映了一组有限的放射性同位素日期和不确定的磁性地层的相关性。

　　附：英文原文

　　Title: Revised onset age of magnetochron M0r: Chronostratigraphic and geologic implications

　　Author: Youjuan Li, Huafeng Qin, Brian R. Jicha, Magdalena H. Huyskens, Corey J. Wall, Robin B. Trayler, Qing-Zhu Yin, Mark Schmitz, Yongxin Pan, Chenglong Deng, Brad S. Singer, Huaiyu He, Rixiang Zhu

　　Issue&Volume: 2023-04-12

　　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.

　　DOI: 10.1130/G50873.1

　　Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50873.1/622182/Revised-onset-age-of-magnetochron-M0rredirectedFrom=fulltext