Expedition 364 Chicxulub: Drilling the K-Pg Impact Crater

墨西哥的希克苏鲁布撞击坑是独一无二的。它是唯一已知的与大规模灭绝事件直接相关的陆地撞击结构，也是唯一具有全球喷出物层的陆地撞击。在地球上三个最大的撞击结构中，希克苏鲁布是保存最好的。希克苏鲁布也是唯一已知的具有完整、明确的地形“峰环”的陆地撞击结构。希克苏鲁布在K-Pg大灭绝中的作用及其特殊的保存状态使其成为研究地球和其他行星上大型撞击坑形成以及大型撞击对地球环境和生态影响的重要天然实验室。我们对撞击过程的理解还远未完成，尽管经过了30多年的激烈辩论，我们仍在努力回答为什么这次撞击如此灾难性的问题。364号探险队是第一个钻入完整地形峰环的钻孔，也是第一个穿透希克苏鲁布陨石坑近海部分的钻孔。峰环是类地行星上大型撞击盆地中突出于火山口底部的一圈山丘，关于它们的形成机制或形成它们的岩石的性质，目前还没有共识。地球物理数据表明，希克苏鲁布的峰环是由速度和密度较低的岩石形成的，对此的一种解释是，它们高度破碎和多孔。撞击后，山峰环立即淹没在水下，并位于一个厚厚的热融岩池附近。因此，我们预计峰环内会有强烈的热液活动。这种活动可能为外来生命形式提供了一个适当的生存环境，就像海洋中的热液喷口系统一样。钻峰环将确定形成它的岩石的起源，岩性和物理状态，使我们能够区分峰环形成的竞争模型，以及记录热液系统和任何相关的微生物学。撞击后，海洋在局部可能是无菌的。我们将使用撞击后沉积物的核心来研究海洋的退化，包括：什么生物群首先回来（底栖生物，腰鞭毛虫，专家与通才），以及恢复正常状态需要多长时间？拟议的钻探直接有助于实现国际海洋发展方案在以下方面的目标：深层生物圈和海底下海洋以及环境变化、过程和影响，特别是希克苏鲁布造成的环境和生物扰动。

The Chicxulub impact crater, Mexico, is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event, and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic "peak ring". Chicxulub's role in the K-Pg mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets, and the effects of large impacts on the Earth's environment and ecology. Our understanding of the impact process is far from complete and, despite over 30 years of intense debate, we are still striving to answer the question as to why this impact was so catastrophic.Expedition 364 is the first drill hole into an intact topographic peak ring, and the first to penetrate the offshore portion of the Chicxulub crater. Peak rings are a ring of hills that protrude through the crater floor within large impact basins on the terrestrial planets, and there is no consensual agreement on either their formational mechanism or the nature of the rocks that form them. Geophysical data indicate that the peak ring at Chicxulub is formed from rocks that have a low velocity and density, and one explanation for this is that they are highly fractured and porous. Immediately after impact the peak ring was submerged under water, and located adjacent to a thick pool of hot melt rocks. Hence, we would expect intense hydrothermal activity within the peak ring. This activity may have provided a niche for exotic life forms, in a similar way that hydrothermal vent systems do in the oceans. Drilling the peak ring will determine the origin, lithology, and physical state of the rocks that form it, allow us to distinguish between competing models of peak-ring formation, as well as document the hydrothermal systems and any associated microbiology. Immediately after impact the ocean is, locally, likely to have been sterile. We will use core through the post-impact sediments to examine the recolonization of the ocean, including: what biota came back first (benthic, dinoflagellates, specialists vs generalists), and how long did it take to return to normal conditions? The proposed drilling directly contributes to IODP goals in the: Deep Biosphere and the Subseafloor Ocean and Environmental Change, Processes and Effects, in particular the environmental and biological perturbations caused by Chicxulub.