Revised composite depth scale, Fe content and orbital tuning of Middle Eocene Climate Optimum samples from ODP Site 207-1260

A high-resolution stratigraphy is essential toward deciphering climate variability in detail and understanding causality arguments of events in earth history. Because the highly dynamic middle to late Eocene provides a suitable testing ground for carbon cycle models for a waning warm world, an accurate time scale is needed to decode climate-driving mechanisms. Here we present new results from ODP Site 1260 (Leg 207) which covers a unique expanded middle Eocene section (magnetochrons C18r to C20r, late Lutetian to early Bartonian) of the tropical western Atlantic including the chron C19r transient hyperthermal event and the Middle Eocene Climate Optimum (MECO). To establish a detailed cyclostratigraphy we acquired a distinctive iron intensity records by XRF scanning Site 1260 cores. We revise the shipboard composite section, establish a cyclostratigraphy and use the exceptional eccentricity modulated precession cycles for orbital tuning. The new astrochronology revises the age of magnetic polarity chrons C19n to C20n, validates the position of very long eccentricity minima at 40.2 and 43.0 Ma in the orbital solutions, and extends the Astronomically Tuned Geological Time Scale back to 44 Ma. For the first time the new data provide clear evidence for an orbital pacing of the chron C19r event and a likely involvement of the very long eccentricity cycle contributing to the evolution of the MECO.高分辨率地层学对于精细解析气候变率、厘清地球历史中各类事件的因果关系至关重要。活动特征极为显著的始新世中晚期，为逐渐趋缓的温暖世界背景下的碳循环模型提供了理想试验场，因此亟需精准的年代标尺以解码气候驱动机制。本文报道了大洋钻探计划（Ocean Drilling Program, ODP）第207航次1260站位的全新研究结果。该站位在热带西大西洋钻取了独特的展宽型始新世中期地层序列，对应磁极性时C18r至C20r，时代为路特阶晚期至巴顿阶早期，序列中包含C19r磁极性时对应的短暂超热事件以及中始新世气候适宜期（Middle Eocene Climate Optimum, MECO）。为构建精细的旋回地层学框架，我们通过X射线荧光（XRF）扫描该站位岩芯，获取了特征性的铁元素强度记录。我们对船上编录的综合剖面进行了修订，建立了旋回地层序列，并利用受偏心率调制的显著岁差周期开展轨道调谐。全新的天文年代学研究修订了磁极性时C19n至C20n的年龄，验证了轨道解中40.2 Ma与43.0 Ma处的超长偏心率极小值位置，并将天文校准地质年代标尺（Astronomically Tuned Geological Time Scale）延伸至44 Ma。本研究首次通过新数据为C19r磁极性时事件的轨道调控机制提供了明确证据，并表明超长偏心率周期可能参与了中始新世气候适宜期的演化过程。