Synchronizing early Eocene deep-sea and continental records from the Bighorn Basin Coring Project@en

A consistent chronostratigraphic framework is required to understand the effect of major paleoclimate perturbations on both marine and terrestrial ecosystems. Transient global warming events in the early Eocene, 56-54 Ma ago, show the impact of large scale carbon input into the ocean-atmosphere system. Here we provide the first time-scale synchronization of continental and marine deposits spanning the Paleocene-Eocene Thermal Maximum (PETM) and the interval just prior to the Eocene Thermal Maximum 2 (ETM-2). Cyclic variations in geochemical data come from continental drill cores of the Bighorn Basin Coring Project (BBCP, Wyoming, USA) and from marine deep-sea drilling deposits retrieved by the Ocean Drilling Program (ODP). Both are dominated by eccentricity modulated precession cycles used to construct a common cyclostratigraphic framework. Integration of age models results in a revised astrochronology for the PETM in deep-sea records that is now generally consistent with independent 3He age models. The duration of the PETM is estimated at ~200 kyr for the CIE and ~120 kyr for the associated pelagic clay layer. A common terrestrial and marine age model shows a concurrent major change in marine and terrestrial biotas ~200 kyr before ETM-2. In the Bighorn Basin, the change is referred to as Biohorizon B, and represents a period of significant mammalian turnover and immigration, separating the upper Haplomylus-Ectocion Range Zone from the Bunophorus Interval Zone and approximating the Wa-4-Wa-5 land mammal zone boundary. In sediments from ODP Site 1262 (Walvis Ridge), major changes in the biota at this time are documented by the radiation of a \"2nd generation\" of apical spine-bearing sphenoliths species (e.g., S. radians and S. editus), the emergence of T. orthostylus, and the marked decline of D. multiradiatus.要揭示重大古气候扰动对海洋与陆地生态系统的影响，需构建统一的年代地层格架（chronostratigraphic framework）。距今56~54 Ma的始新世早期突发性全球变暖事件，直观展现了碳向海-气系统大规模输入所引发的环境效应。本文首次完成了横跨古新世-始新世极热事件（Paleocene-Eocene Thermal Maximum，PETM）以及始新世极热事件2（Eocene Thermal Maximum 2，ETM-2）之前时段的海陆沉积序列年代标尺同步工作。 本研究的地球化学旋回数据分别来自美国怀俄明州大角盆地钻探项目（Bighorn Basin Coring Project，BBCP）的大陆钻探岩芯，以及大洋钻探计划（Ocean Drilling Program，ODP）获取的深海沉积岩芯。两类数据集均以受偏心率调制的岁差周期为主要旋回特征，据此搭建了统一的旋回地层格架。 通过整合两套年代模型，本研究对深海记录中的PETM天文年代学（astrochronology）进行了修订，当前该修订结果与独立的氦-3（³He）年代模型基本吻合。其中，PETM伴随的碳同位素漂移事件（Carbon Isotope Excursion，CIE）持续时长约为200 kyr，与之伴生的远洋黏土层持续时长约为120 kyr。 统一的海陆年代模型显示，在ETM-2之前约200 kyr时，海洋与陆地生物群均发生了同步的重大转变。在大角盆地中，该转变被命名为生物层位B，代表了一次显著的哺乳动物类群更替与迁入事件，将上哈氏兽-外冠兽延限带与布诺兽间隔带分隔开，大致对应Wa-4至Wa-5陆生哺乳动物带的界线。 在大洋钻探计划1262站位（沃尔维斯海岭）的沉积物中，该时段的生物群重大转变被记录为：具顶刺的石星石藻物种的第二代辐射演化（如S. radians与S. editus）、T. orthostylus的首次出现，以及D. multiradiatus的显著衰退。