The Response of the Marine Osmium Isotope Record to Impact Events

海洋锇同位素记录对撞击事件的响应格雷戈利·拉维扎（gregory Ravizza），夏威夷大学（university of hawaii）摘要：地球上大量但保存不完整的撞击坑记录表明，来自太空的大型抛射物曾多次撞击地球。年代的表面。虽然大约6600万年前的白垩纪-第三纪大灭绝恰好与过去5亿年来已知的最大撞击事件同时发生，但许多其他大型撞击事件对环境的影响仍然知之甚少，也没有文献记载。为了研究地球系统对这些大的、突然的扰动的响应，必须能够在整个沉积物记录中可靠地识别出全球的撞击水平。目前，提高铱（Ir）浓度最常用来试图识别远离撞击地点的撞击地平线，但结果往往是模糊的。该奖项支持的研究将测试将锇（Os）同位素比率（187Os/188Os）与Os和Ir浓度相结合的测量结果的有效性，以可靠地确定撞击范围，并估计弹丸大小。这将通过在研究充分的海洋沉积物序列中进行这些分析来完成，这些序列已知是在大型撞击坑形成期间积累的。一些被研究的地点离撞击地点相对较近，而另一些则位于数千公里之外。PI之前使用Os同位素识别主要由碳酸钙微化石组成的深海沉积物中的撞击事件的工作已经取得了很好的结果。在这项新的研究中，他将调查组成不同类型的海洋沉积物是否也能可靠地记录大型撞击事件的化学特征。这些研究目标的完成将表明，海洋Os同位素记录是否代表了地球历史上一种新的、无与伦比的撞击事件记录，或者仅仅是对仅通过研究Ir浓度数据获得的往往模棱两可的撞击记录的适度增强。如果前者是正确的，这项工作将对事件地层学和沉积物记录的全球相关性，以及对大型撞击事件对地球气候系统的突然扰动的理解做出持久的贡献。

The Response of the Marine Osmium Isotope Record to Impact EventsGregory Ravizza, EAR-0843930University of HawaiiABSTRACTAn extensive, but incompletely preserved, record of impact craters on the Earth demonstrates that large projectiles from space have repeatedly hit Earth?s surface. Although the Cretaceous-Tertiary mass extinction some 66 million years ago coincides precisely with the largest known impact event of the last 500 million years, the environmental consequences of numerous other large impact events remain poorly understood and documented. In order to study the response of the Earth system to these large, abrupt perturbations, it is essential to be able to reliably recognize an impact horizon globally throughout the sediment record. Currently elevated iridium (Ir) concentrations are most commonly used to try to recognize impact horizons far removed from the site of impact, but the results are often ambiguous. The research supported by this award will test the usefulness of combining measurements of Osmium (Os) isotope ratios (187Os/188Os) with Os and Ir concentrations to reliably identify impact horizons, and also to estimate projectile size. This will be accomplished by performing these analyses in well studied marine sediment sequences that are known to have accumulated during the time that large impact craters formed. Some of the sites to be studied are relatively close to the impact site while others are located thousands of kilometers away. PI's previous work using Os isotopes to recognize impact events in deep sea sediments composed mainly of calcium carbonate microfossils have yielded promising results. In this new study he will investigate if compositionally different types of marine sediments can also reliably record the chemical signatures of large impact events. Completion of these research objectives will show if the marine Os isotope record represents a new and unparalleled record of impact events through Earth history, or simply a modest augmentation of the often ambiguous record of impacts obtainable through the study of Ir concentration data alone. If the former is true this work will make lasting contributions to event stratigraphy and global correlations of the sediment record, as well as to understanding abrupt perturbations of Earth's climate system by large impact events.