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夏威夷大学的Gregory Ravizza，1998 - 0843930摘要一个广泛的，但不完全保存的，对地球上的撞击坑的记录表明，来自太空的大型抛射物多次撞击地球？s表面。虽然大约6 600万年前的第三纪大灭绝与过去5亿年中已知的最大撞击事件恰好吻合，但对许多其他大型撞击事件的环境后果仍然知之甚少，也没有记录在案。为了研究地球系统对这些大的、突然的扰动的反应，必须能够在整个沉积物记录中可靠地识别全球范围内的影响范围。目前，最常用的是提高铱（Ir）浓度，以试图识别远离撞击地点的撞击层，但结果往往是模糊的。该奖项支持的研究将测试结合测量锇（Os）同位素比（187 Os/188 Os）与Os和Ir浓度的有用性，以可靠地确定撞击层位，并估计抛射体的大小。这将通过在经过充分研究的海洋沉积物序列中进行这些分析来实现，这些沉积物序列是已知在大型撞击坑形成期间积累的。一些待研究的地点相对靠近撞击地点，而另一些则位于数千公里之外。PI以前的工作使用Os同位素识别主要由碳酸钙微体化石组成的深海沉积物中的撞击事件，取得了令人鼓舞的结果。在这项新的研究中，他将调查成分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个新的和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加。如果前者是真的，这项工作将作出持久的贡献事件地层学和全球相关的沉积物记录，以及了解地球的气候系统的突然扰动的大的影响事件。

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.