The petrology, geochemistry and age determination of impact melt from the USGS-ICDP drill core Eyreville-B from the late Eocene Chesapeake Bay impact structure

大型撞击坑将物质分布在全球各地，其喷出物层是重要的层位标志，使不同地点的沉积物相互关联，例如始新世晚期的沉积物早于始新世-渐新世边界的地球气候临界点。位于意大利马西尼亚诺的全球层型剖面和点（GSSP）包含三个富铱喷出物层，覆盖时间间隔为2 Ma，其中两个分别归因于切萨皮克湾（85 km宽）和波皮盖（100 km宽）撞击构造。目前，切萨皮克湾陨石坑的放射性年龄测定是基于玻璃陨石（远距离撞击玻璃）的总熔融Ar年龄。在初步的40 Ar-39 Ar工作中，我已经证明，这些玻璃陨石的精确Ar年龄不能通过全聚变实验获得，但需要逐步加热测量。我提出了一个系统的岩石学，地球化学和放射性研究的第一个发现的影响熔融岩石从内的切萨皮克湾陨石坑和完善的40 Ar-39 Ar年龄的相关玻璃陨石。这项研究将得到补充的40 Ar-39 Ar年龄测定的影响熔融岩石从其他三个晚始新世的影响结构，Popigai，Mistastin和Wanapitei。放射性测量和岩石学的结果，结合新的数值模型的影响喷出物分布的结果在年龄，成分和分布的全球标志层在晚始新世沉积物：一个基本的数据集，调查的继承事件早于地球气候的临界点。只有USGS-ICDP Eyreville B岩芯为这项研究的主要重点提供了样本材料：确定切萨皮克湾陨石坑的年代。

Large impact craters distribute material globally, and their ejecta layers present important horizon markers allowing inter-correlation of sediments from different sites, e.g. for late Eocene sediments pre-dating the tipping point of Earth’s climate at the Eocene Oligocene boundary. The Global Stratotype Section and Point (GSSP) in Massignano (Italy) contains three Iridium rich ejecta layers covering a 2 Ma time interval, with two being attributed to the Chesapeake Bay (85 km Ø) and Popigai (100 km Ø) impact structures, respectively. Current radiometric age determination for the Chesapeake Bay crater is based on total fusion Ar ages of tektites (distal impact glasses). In preliminary 40Ar-39Ar work, I have shown that precise Ar ages on these tektites cannot be acquired by total fusion experiments but require step heating measurements. I propose a systematic petrologic, geochemical and radiometric study of the first found impact melt rocks from within the Chesapeake Bay crater and refine the 40Ar-39Ar ages for the related tektites. The study will be complemented by 40Ar-39Ar age determinations of impact melt rocks from three other late Eocene impact structures, Popigai, Mistastin and Wanapitei. Radiometric and petrological results combined with new numerical models on impact ejecta distribution result in age, composition and distribution of global marker horizons in later Eocene sediments: a fundamental data set for investigations on the succession of events predating the tipping point of Earth’s climate. Only the USGS-ICDP Eyreville B drill core provides the sample material for the main focus of this research: dating the Chesapeake Bay crater.