The Boltysh meteorite impact, Ukraine: verification of a KT boundary multi imapct hypothesis.

在过去的25年里，科学家们逐渐认识到大型陨石对地球和太阳系其他行星的影响的重要性。陨石撞击不仅牵涉到大灭绝，它们还形成了石油和天然气的圈闭，在地球和火星的早期历史中，它们可能是生命的重要栖息地。6500万年前，乌克兰的博尔泰什陨石坑形成于平坦大陆架上的一个非常浅的海域，与墨西哥的奇克苏鲁布陨石坑形成的时间相同，不过，目前还无法确定这两个陨石坑是否在同一时间发生。撞击后，火山口很快被一个淡水湖填满。在接下来的1500万年里，这个湖充满了细微的沉积物和生活在湖里或被河流冲刷进来的动植物的有机遗迹。Boltysh仍然是平坦大陆架上的一个洞，这意味着它拥有关于KT界线和早古近纪的独特和几乎连续的记录。我们已经知道了很多关于陨石坑的情况，因为它是在20世纪60年代至80年代钻探的，但核心在随后的政权更迭中丢失了，除了我们在开始这项工作之前能够研究的一些零散的碎片。该项目的目的是钻两个洞，并从陨石坑底部回收岩心沉积物，直到大约5000万年前海洋入侵陨石坑的时候。我们能从这些沉积物中学到什么？首先，我们应该能够更准确地确定年龄，或许可以确定它是在KT界线上形成的，是早于它，还是实际上是在它之后。我们之前的工作表明，博尔泰什陨石坑是在距离边界50万年的范围内形成的，但地球上每100万年就至少形成一个这种大小(直径24公里)的陨石坑，所以这可能是巧合。如果它确实是同时形成的，这将是几颗陨石落在KT边界的令人信服的证据，我们可能不得不重新考虑我们对白垩纪末期发生的事情的看法。即使这两次撞击不是同时发生的，我们也将能够利用沉积物中的信号来限制KT事件。其次，撞击后不久沉积的沉积物将告诉我们火山口湖保持高温的时间。这将是一个重要的结果，因为撞击坑可能为早期火星上的生命提供了重要的栖息地，也可能为地球上的生命提供了栖息地。当行星还很年轻的时候，有更多的撞击，温暖的火山口湖可能是早期生命形式得以生存的地方。在非洲(加纳的博苏姆特维)火山口进行的一项类似研究将与这项工作相结合，以模拟早期地球和火星上的火山口湖泊。早期生命也与我们的最终目标有关，我们的最终目标是利用沉积物中保存的花粉、孢子和藻类来揭示重大陨石撞击事件后的破坏和生物恢复过程。我们可以通过记录植物孢子、花粉和藻类化石来了解湖泊周围的环境，并测量有机分子和碳同位素的变化，这些变化可以告诉我们更多关于当时气候的信息。我们对广泛的灭菌和营养贫乏区域的生物重组知之甚少，例如Boltysh喷射物毯子，目前的模型基于较小的火山成因景观，这些景观不能直接相似，因为它们的营养更丰富。对博尔泰什陨石坑的研究将使我们能够为撞击事件后的生态系统恢复建立一个详细的模型，为陆地陨石喷射场创建一个比较装置。最后，岩芯将提供几乎连续的中欧和亚洲气候记录。在未来，我们和其他科学家将能够利用它来发现大陆地区的气候与其他地方看到的海洋信号之间的关系。

In the last 25 years, scientists have come to understand the importance of large meteorite impacts on the Earth and other planets in the solar system. Not only are meteorite impacts implicated in mass extinctions, they form traps for oil and gas, and in the early history of the Earth and Mars, they may have been important habitats for life. The Boltysh crater in Ukraine was formed in a very shallow sea on a flat continental shelf 65 million years ago, at the same time as the Chicxulub crater in Mexico, though it has not been possible to determine whether the two happened at exactly the same time. After the impact, the crater was quickly filled with a fresh water lake. Over the next 15 million years the lake filled with fine sediment and the organic remains of the flora and fauna which lived in the lake, or were washed in by rivers. The fact that Boltysh remained a hole in the ground on the flat continental shelf means that it holds a unique and near continuous record of the KT boundary and early Paleogene period. We already know a lot about the crater because it was drilled in the 1960s - 1980s but the core has been lost in subsequent regime changes, apart from a few scattered pieces we have been able to study before starting this work. This project is intended to drill two holes and recover cored sediments from the crater floor up to the point when the sea invaded the crater around 50 million years ago. What can we learn from these sediments ? Firstly, we should be able to establish the age more precisely, and perhaps whether it formed at the KT boundary, predates it or indeed post-dates. Our previous work shows that the Boltysh crater formed within about half a million years of the boundary, but at least one crater of this size (24 km diameter) forms on Earth every 1 million years so it might be coincidence. If it did form at the same time, it would be convincing evidence that several meteorites fell at the KT boundary, and we might have to reconsider our ideas about what happened at the end of the Cretaceous. Even if the two impacts were not simultaneous, we will be able to use signals in the sediments to constrain the KT events. Secondly, sediments deposited soon after impact will tell us how long the crater lake remained hot. This will be an important result because impact craters may have provided an important habitat for life on the early Mars and also possibly on Earth. There were more impacts when the planets were young and warm crater lakes may have been places where early forms of life could survive. A similar study being undertaken in a crater in Africa (Bosumtwi in Ghana) will combined with this work to model crater lakes on early Earth and Mars. Early life is also related to our final aim, which is to use pollen, spores and algae preserved in the sediments to uncover about the processes of devastation and biotic recovery after a significant meteorite impact event. We can do this by recording the fossil plant spores and pollen and algae which tell us about the environments surrounding the lake, and by measuring the variations in organic molecules and carbon isotopes which tell us more about the climate at the time. We know very little about biotic reassembly of a wide sterilised and nutrient poor zone such as Boltysh ejecta blanket, current models being based on smaller volcanogenic landscapes which are not directly analogous because they are richer in nutrients. Studying the Boltysh crater will allow us to produce a detailed model for ecosystem recovery following the impact event, creating a comparator for terrestrial meteorite ejecta fields. Finally, the cores will provide an almost continuous record of the climate in central Europe and Asia. In the future we and other scientists will be able to use it to discover how climate in continental areas relates to the oceanic signal seen elsewhere.