The Response of the Marine Osmium Isotope Record to Impact Events

海洋臭氧同位素记录对撞击事件的响应夏威夷大学的格雷戈里·拉维扎，EAR-0843930大量但保存不完整的地球撞击坑记录表明，来自太空的大型抛射物曾多次击中地球表面？S。尽管大约6600万年前的白垩纪-第三纪大灭绝恰好与过去5亿年中已知的最大撞击事件重合，但许多其他大型撞击事件对环境造成的后果仍然缺乏了解和记录。为了研究地球系统对这些大的、突然的扰动的反应，至关重要的是能够在整个沉积物记录中可靠地识别全球范围内的影响地平线。目前，最常用的方法是识别远离撞击地点的撞击视界，但结果往往含糊不清。这项由该奖项支持的研究将测试将测量Os(Os)同位素比率(187Os/188Os)与Os和Ir浓度相结合的有用性，以可靠地确定撞击层位，并估计弹丸大小。这将通过对已知在大型撞击坑形成期间积累的经过充分研究的海洋沉积物序列进行这些分析来实现。一些待研究地点距离撞击地点相对较近，另一些地点则在数千公里外。Pi之前的工作是使用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，取得了令人振奋的结果。在这项新的研究中，他将调查不同成分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同位素记录是对地球历史上撞击事件的一种新的、无与伦比的记录，还是仅仅是对仅通过研究Ir浓度数据就可获得的往往模棱两可的撞击记录的适度增加。如果前者属实，这项工作将对事件地层学和沉积物记录的全球对比以及理解大撞击事件对地球气候系统的突然扰动做出持久的贡献。

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.