A Deep‐Time Dating Tool for Paleo‐Applications Utilizing Obliquity and Precession Cycles: The Role of Dynamical Ellipticity and Tidal Dissipation
A Deep‐Time Dating Tool for Paleo‐Applications Utilizing Obliquity and Precession Cycles: The Role of Dynamical Ellipticity and Tidal Dissipation
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DOI：
10.1029/2021pa004349
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发表时间：
2022-01
影响因子：
3.5
通讯作者：
R. Zeebe;L. Lourens
中科院分区：
文献类型：
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作者：
R. Zeebe;L. Lourens
古海洋学和古气候学中使用的前更新世年龄模型通常依赖于沉积记录中天文计算的偏心率周期和其他太阳系频率的印记（例如，405、173和100 kyr）。然而，在这些时间段内，使用行星和岁差周期（目前为4.1万年和2.2万年）仍然具有挑战性，主要是由于过去地球动力学椭圆率（艾德，引力形状）和潮汐耗散（Td，地球自转的减速）的变化，这影响了天文计算。在这里，我们提出了一种将艾德和Td结合到天体年代学中的深时记录的定年方法。我们的方法的关键是结合对Td的约束（从而间接地对艾德）与基于太阳系频率的年龄模型优化，再加上调整到地磁/岁差频率，同时改变Td和Ed。重要的是，我们的目标是深时间间隔，其中Td显示出显着的影响，但高质量的沉积记录可用（新生代早期）。我们包括一个快速入门指南，并将我们的代码和预先计算的解决方案免费提供给用户。为了证明我们的方法的实用性，我们将我们的工具应用于两个使用早始新世和中始新世深海记录的案例研究。我们的研究结果证实了非常准确的年代学的沉积记录，从始新世早期（1056 -54马），但建议显着改善中始新世（1040 -39马）。对于始新世早期，我们的方法提供了绝对地质年龄，估计不确定度为±20-40 kyr，小于或等于最近放射性40 Ar/39 Ar定年的典型不确定度。
Pre‐Pleistocene age models used in paleoceanography and paleoclimatology often rely on the imprint of astronomically calculated cycles of eccentricity and other solar system frequencies in sedimentary records (e.g., 405, 173, and ∼100 kyr). However, use of obliquity and precession cycles (at present ∼41 and ∼20 kyr) remains challenging for these periods, mostly due to past changes in Earth's dynamical ellipticity (Ed, gravitational shape) and tidal dissipation (Td, slowdown of Earth's rotation), which affect the astronomical calculations. Here, we present a dating method for deep‐time records by integrating Ed and Td into astrochronology. The key to our approach is the combination of constraints on Td (and thus indirectly on Ed) with age model optimization based on solar system frequencies, plus tuning to obliquity/precession frequencies, while varying Td and Ed. Importantly, we target deep‐time intervals where Td shows significant effects but high‐quality sedimentary records are available (early Cenozoic). We include a quickstart guide to our approach and make our code and pre‐computed solutions freely available to users. To demonstrate the practical utility of our approach, we apply our tool to two case studies using deep‐sea records from the early and middle Eocene. Our results confirm very accurate chronologies of sedimentary records from the early Eocene (∼56–54 Ma) but suggest significant improvement for the middle Eocene (∼40–39 Ma). For the early Eocene, our method provides absolute geologic ages with an estimated uncertainty of ±20–40 kyr, which is smaller than or equal to typical uncertainties from recent radiometric 40Ar/39Ar dating.