The Allerod-Younger Dryas iridium anomaly: comet impact or volcanism

最近的科学报告提出，大约12900年前，一颗彗星或陨石撞击了地球，造成了大面积的植被燃烧。这导致了北美许多大型哺乳动物的灭绝，如猛犸象和剑齿虎，并因此影响了该大陆最早的一些殖民人类文化。有人进一步提出，陨石撞击导致北半球气候迅速冷却，并在北纬地区恢复到冰川状态，持续了大约1400年。这一观点的部分证据是，相对于背景值，在一个特定的地平线上发现了过量的铱，这与有机物或木炭的丰度增加有关。这与6500万年前发生的希克苏鲁伯陨石撞击有关的铱异常相似，希克苏鲁伯陨石撞击是地质记录中记录最充分的陨石撞击之一。然而，提出的彗星撞击的证据受到了其他科学家的质疑，这个话题仍然是许多争议的主题。人们还认识到，大型火山爆发可能在短期内影响气候，我们建议火山作用作为另一种解释。这项研究的目的是通过使用一种简单的诊断测试来澄清这一立场，该测试能够区分陨石和火山特征。人们发现，陨石中铂族元素（铱、铂、钯、铑、钌、铼和锇）的丰度高于普通的地壳岩石，其比例与最原始的陨石群相似，被认为是太阳系形成的代表物质。相反，由于铂族元素的化学行为和性质不同，火山作用往往会产生更多变的铂族元素丰度剖面。我们的目标是测量从北美、欧洲和北大西洋沉积物钻探岩芯中收集的富有机质层中铂族元素的丰度，其中包括先前报道的铱异常。此外，我们还将寻找陨石撞击的其他诊断证据，如震荡石英，增强的亲铁元素丰度和富镍尖晶石。

Recent scientific reports have proposed a comet or meteorite struck the Earth about 12,900 years ago causing widespread vegetation burning. This lead to the extinction of many large mammals in North America such as the mammoth and sabre toothed cats and consequently effected some of earliest colonizing human cultures of that continent. It is further proposed that the meteorite impact caused a rapid cooling of the Northern hemisphere climate and a return to glacial conditions in northern latitudes which lasted for about 1,400 years. Part of the evidence presented for this idea is an excess of Iridium, relative to background values, found at one particular horizon and which is associated with an increased abundance of organic matter or charcoal. This is similar to the Iridium anomaly associated with the Chicxulub meteorite impact which occurred 65 million years ago and remains one of the best documented meteorite impacts within the geological record. However the evidence presented for a comet strike has been contested by other scientists and the topic remains the subject of much controversy. It is also recognized that large volcanic eruptions may effect climate in the short term and we suggest volcanism as an alternative explanation. This research aims to clarify the position by using a simple diagnostic test capable of distinguishing a meteoritic from a volcanic signature. Meteorites are found to have higher abundances of the platinum group elements (Iridium, Platinium, Palladium, Rhodium, Ruthenium, Rhenium and Osmium) than ordinary crustal rocks and in proportions similar to those of the most primitive meteorite groups, thought to be representative of material from which the solar system formed. In contrast volcanic processes tend to produce a more variable abundance profile for the platinum group elements because of the different chemical behaviour and properties of each element within this group. We aim to measure the platinum group element abundances in material collected from the organic rich layers, with a previously reported iridium anomaly, from across North America, Europe and from sediment drillcores in the North Atlantic. In addition we will also search for other diagnostic evidence of a meteorite impact such as shocked quartz, enhanced siderophile element abundance and nickel-rich spinels.