Expedition 364 Chicxulub: Drilling the K-Pg Impact Crater

墨西哥奇克苏鲁伯陨石坑是独一无二的。这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，也是唯一与全球喷射层有关的陆地撞击。在地球上三个最大的撞击结构中，奇克苏鲁布是保存最完好的。Chicxulub也是已知的唯一具有完整的、明确的地形“峰环”的陆地撞击结构。Chixulub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撞击对地球环境和生态影响的重要自然实验室。我们对撞击过程的了解远未完成，尽管进行了30多年的激烈辩论，但我们仍在努力回答为什么这次撞击是如此灾难性的问题。364探险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。峰环是从陨石坑底部突出出来的一圈山丘，位于类地行星上的大型撞击盆地中，对于它们的形成机制和形成它们的岩石的性质都没有达成共识。地球物理数据表明，奇克苏鲁布的峰环是由低速度和低密度的岩石形成的，对此的一种解释是它们高度破裂和疏松。撞击后，峰环立即被淹没在水中，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。这一活动可能为外来生命形式提供了一个生态位，就像海洋中的热液喷口系统所做的那样。钻探峰环将确定形成峰环的岩石的来源、岩性和物理状态，使我们能够区分峰环形成的相互竞争的模式，以及记录热液系统和任何相关的微生物。撞击后，当地的海洋很可能已经变得贫瘠。我们将使用撞击后沉积物中的岩心来研究海洋的再殖民化，包括：哪些生物群最先恢复(底栖生物、甲藻、专家和多面手)，以及需要多长时间才能恢复到正常条件？拟议的钻探活动直接有助于实现IODP在以下方面的目标：深层生物圈和海底海洋以及环境变化、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.