Abstract We report evidence for Milankovitch cycles in two drill cores from the Cambro–Ordovician Alum Shale Formation of Scandinavia. The signal is preserved in elemental abundances recorded at high stratigraphic resolution by core scanning XRF analysis (0.2 mm resolution). The new data enable us to establish a floating timeline calibrated to the stable 405 kyr eccentricity cycle for a ∼8.7 Myr interval across the Miaolingian–Furongian boundary. This interval spans the Steptoean Positive Carbon Isotope Excursion (SPICE), which is recorded in the δ 13 Corg in the studied drill cores. We calculate the durations of the Olenus Superzone to 3.4 ± 0.2 Myr, the Parabolina Superzone to 1.9 ± 0.3 Myr, the Leptoplastus Superzone to 0.33 ± 0.18 Myr, the Protopeltura Superzone to 0.51 ± 0.20 Myr, and the SPICE event straddling the Paibian and lower main part of the Jiangshanian Stage to 3.0 ± 0.2 Myr. The sedimentation rate shows similar trends at both drilling locations and is inversely correlated to eustatic sea level changes in certain time intervals, opening tantalizing new prospects of using cyclostratigraphic analyses of shales to track eustatic sea level variations. The identification of obliquity cycles enables us to calculate the Cambrian Earth–Moon distance as well as the day length at ∼493 Ma to 368.9 ± 2.3 ⋅ 106 m and 21.78 ± 0.29 hr, respectively.

中文翻译：

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晚寒武纪的天文强迫气候变化

摘要 我们报告了来自斯堪的纳维亚半岛 Cambro-Ordovician Alum 页岩地层的两个钻芯中米兰科维奇循环的证据。通过岩心扫描 XRF 分析（0.2 毫米分辨率），以高地层分辨率记录的元素丰度保留了信号。新数据使我们能够建立一个浮动时间线，校准到稳定的 405 kyr 偏心率循环，跨越苗陵阶 - 芙蓉阶边界约 8.7 Myr 间隔。该区间跨越 Steptoean 正碳同位素偏移 (SPICE)，记录在所研究的钻芯中的 δ 13 Corg 中。我们计算出 Olenus Superzone 的持续时间为 3.4 ± 0.2 Myr，Parabolina Superzone 的持续时间为 1.9 ± 0.3 Myr，Leptoplastus Superzone 的持续时间为 0.33 ± 0.18 Myr，Protopeltura Superzone 的持续时间为 0.51 ± 0.20 Myr，SPICE 事件跨越排边和江山阶下主要部分到 3.0 ± 0.2 Myr。两个钻井位置的沉积速率显示出相似的趋势，并且与特定时间间隔内的海平面变化呈负相关，这为使用页岩的旋回地层分析跟踪海平面变化开辟了诱人的新前景。倾角周期的识别使我们能够分别计算寒武纪地月距离以及 ∼493 Ma 到 368.9 ± 2.3 ⋅ 106 m 和 21.78 ± 0.29 小时的昼长。开启了利用页岩旋回地层分析追踪静海平面变化的诱人新前景。倾角周期的识别使我们能够分别计算寒武纪地月距离以及 ∼493 Ma 到 368.9 ± 2.3 ⋅ 106 m 和 21.78 ± 0.29 小时的昼长。开启了利用页岩旋回地层分析追踪静海平面变化的诱人新前景。倾角周期的识别使我们能够分别计算寒武纪地月距离以及 ∼493 Ma 到 368.9 ± 2.3 ⋅ 106 m 和 21.78 ± 0.29 小时的昼长。