NOAA/WDS Paleoclimatology - Earth Orbital 100 Million Year Precession and Tilt Solutions

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 (405, 173, and 100kyr). 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 for 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 (~56-54Ma) but suggest significant improvement for the middle Eocene (~40-39Ma). For the early Eocene, our method provides absolute geologic ages with an estimated uncertainty of +-20 to 40kyr, which is smaller than or equal to typical uncertainties from recent radiometric Ar/Ar dating.

古海洋学（paleoceanography）与古气候学（paleoclimatology）领域所采用的前更新世（Pre-Pleistocene）年代模型，通常依托沉积记录中经天文计算得到的偏心率（eccentricity）及其他太阳系轨道周期（405、173与100千年，kyr）的印记。然而，针对该时期使用斜度（obliquity）与岁差（precession）周期（当前约41与20千年）仍存在挑战，这主要源于地球动力扁率（dynamical ellipticity，Ed，即引力形状）与潮汐耗散（tidal dissipation，Td，即地球自转减速）的过往变化，二者会对天文计算造成影响。本文提出一种将Ed与Td整合入天文年代学（astrochronology）的深时（deep-time）记录定年方法。本方法的核心在于，将对Td的约束（进而间接约束Ed）与基于太阳系轨道周期的年代模型优化相结合，同时在调整Ed与Td的过程中适配斜度与岁差周期。尤为关键的是，本研究聚焦于Td影响显著且存在高质量沉积记录的深时时段——即新生代早期（early Cenozoic）。本文附带本方法的快速入门指南，并将代码与预计算结果对所有用户免费开放。为验证本方法的实际应用价值，我们利用始新世（Eocene）早期与中期的深海沉积记录开展了两项案例研究。研究结果证实，始新世早期（约5600万至5400万年前）沉积记录的年代学精度极高，同时表明本方法对始新世中期（约4000万至3900万年前）的定年结果有显著优化。针对始新世早期，本方法给出的绝对地质年龄估算不确定度为±20至40千年，小于或等同于近期氩-氩（Ar/Ar）放射性定年的典型不确定度。