A fully calibrated astronomical time scale for the Cenozoic: Dating, climate forcing, and solar system chaos

为了确定海底沉积物和沉积岩的年龄，地质学家需要一个过去的“日历”。其中一种历法称为天文时标，它利用了行星轨道的可预测变化驱动地球气候的周期性变化这一事实。在这种方法中，观测到的沉积物组成周期与气候周期相匹配。这些周期的时间是通过计算行星轨道的时间向后计算的。天文时标是一个有价值的工具，因为轨道计算为地质记录提供了准确的年龄。PI最近的工作提供了新的天文计算，可以追溯到现在之前的5800万年（Myr BP）。然后将这些计算结果与深海沉积物记录进行比较。这些比较得出了始新世早期（距今5600万至5300万年）气候事件的新历史。他们还获得了关于太阳系混沌运动的新信息。这项拟议中的研究将提供一个经过充分测试的天文时间尺度和新的天文计算，可以追溯到古新世（6600万年至5600万年前）。天文计算将为沉积物记录提供一个时间尺度。同时，在沉积物中观察到的循环模式将限制行星轨道变化的计算。这一新的时间尺度将为追溯到白垩纪（1.45亿至6600万年前）的准确时间尺度铺平道路。它还将有助于改进使用放射性元素的测年方法。最后，它将提高我们对太阳系混沌演化的认识。该项目还将资助一名研究生，基于天文学解决方案的天文学时标的发展改变了地质档案的年代测定，是海洋旋回地层学和天文年代学重建地球历史的支柱。虽然稳定的405 kyr周期的地球轨道偏心率已被用来提供浮动（相对）年表跨越各种时间尺度，一个主要的挑战仍然是：发展绝对的，完全校准的天文时间尺度超过~50 Ma，迄今为止一直受到阻碍的事实，轨道解决方案不同意之前，由于太阳系的混乱。我们最近通过对深海沉积物档案（~58-53 Ma）进行测试，在提供~58 Ma的新天文解方面取得了进展，这也对始新世早期高温和太阳系混乱的年代学产生了重要的见解。该项目将开发和提供一个完全校准的ATS和一个新的天文解决方案，包括古新世（~66-56 Ma），结合我们最近的工作，将跨越整个新生代。我们研究的关键思想是利用海洋地质学来约束天文学，反过来，利用天文学来提供在海洋地质学中广泛使用的关键应用。超过58 Ma提出了新的挑战，这将需要分析多个地质记录和大量的计算资源。在~66-63 Ma的深海记录中解释旋回地层信号具有挑战性，为此，我们将在分析中整合陆基海洋剖面（例如，Zumaia，Spain）.地质档案中地球轨道偏心率的表达将指导我们使用太阳系轨道运动的数值（系综）积分来寻找天文学解决方案。具体来说，我们将使用海洋深海记录的颜色反射率和铁强度ODP站点1262和1209和旋回地层从陆基海洋部分（Zumaia）重建地球的轨道偏心率跨越临界间隔~66-56 Ma。根据记录中观测到的偏心率表达式，我们将寻找一个新的天文解，使我们能够将完全校准的天文时标扩展到~66 Ma。总之，我们的研究将（1）提供一个完全校准的新生代ATS，（2）帮助测量辐射测年校准，（3）测试偏心率振幅调制和古新世气候事件之间的相关性，（4）古新世气候-碳循环反馈的模型强迫，以及（5）该奖项反映了NSF的法定使命，并已被认为是值得通过使用评估的支持。基金会的学术价值和更广泛的影响审查标准。

To determine the ages of seafloor sediments and sedimentary rocks geologists need a “calendar” of the past. One such calendar, called the astronomical time scale, makes use of the fact that predictable changes in the orbits of the planets drive cyclic changes in Earth’s climate. In this approach observed cycles in sediment composition are matched to climate cycles. The timing of those cycles is then calculated by computing planetary orbits backward in time. The astronomical time scale is a valuable tool because the orbital calculations provide accurate ages for the geologic record. Recent work by the PI provided new astronomical calculations that stretch back to 58 million years before the present (Myr BP). Those calculations were then compared with deep sea sediment records. The comparisons yielded a new history of climate events during the early Eocene (56 to 53 Myr BP). They also yielded new information about the chaotic motions of the solar system. The proposed study will provide a fully tested astronomical time scale and new astronomical calculations extending back through the Paleocene (66 to 56 Myr BP). The astronomical calculations will provide a time scale for the sediment records. At the same time the cyclic patterns observed in the sediments will constrain calculations of the planets’ orbital variations. That new time scale will pave the way to an accurate time scale extending back through the Cretaceous period (145 to 66 Myr BP). It will also help improve dating methods that use radioactive elements. Finally, it will improve our knowledge of the chaotic evolution of our solar system. The project will also support a graduate student.The development of an astronomical time scale (ATS) based on astronomical solutions has transformed the dating of geologic archives and represents the backbone of marine cyclostratigraphy and astrochronology to reconstruct Earth’s history. While the stable 405-kyr cycle of Earth’s orbital eccentricity has been used to provide floating (relative) chronologies across various time scales, one major challenge remains: Development of an absolute, fully calibrated astronomical time scale beyond ~50 Ma, which has hitherto been hampered by the fact that orbital solutions disagree before that age due to solar system chaos. We have recently made progress in providing a new astronomical solution to ~58 Ma by testing against deep-sea sediment archives (~58-53 Ma), which also yielded critical insight into the chronology of early Eocene hyperthermals and solar system chaos. This project will develop and provide a fully calibrated ATS and a new astronomical solution including the Paleocene (~66-56 Ma), which, combined with our recent work, will then span the entire Cenozoic. The key idea of our study is to use marine geology to constrain astronomy, and, conversely, use astronomy to provide key applications widely used in marine geology. Reaching beyond 58 Ma presents new challenges, which will require analyses of multiple geologic records and significant computational resources. Cyclostratigraphic signals are challenging to interpret in deep-sea records across the interval ~66-63 Ma, for which we will integrate land-based marine sections in our analysis (e.g., Zumaia, Spain). The expression of Earth’s orbital eccentricity in the geologic archives will then guide our search for an astronomical solution, using numerical (ensemble) integrations of the orbital motion of the solar system. Specifically, we will use marine deep-sea records of color reflectance and iron intensities from ODP Sites 1262 and 1209 and cyclostratigraphy from land-based marine sections (Zumaia) to reconstruct Earth’s orbital eccentricity across the critical interval ~66-56 Ma. Based on the eccentricity expression observed in the records, we will search for a new astronomical solution that will allow us to extend the fully calibrated astronomically time scale to ~66 Ma. In summary, our study will (1) provide a fully calibrated ATS across the Cenozoic, (2) help gauge radiometric dating calibrations, (3) test correlations between eccentricity amplitude modulation and Paleocene climate events, (4) model forcing of Paleocene climate-carbon cycle feedbacks, and (5) transform our knowledge of the chaotic evolution of our solar system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.