由暗云遭遇驱动的白垩纪末冷却和mass extinction
End-cretaceous cooling and mass extinction driven by a dark cloud encounter
摘要：
我们在886 C站点深海海底取芯的约5米厚的远洋沉积物中发现了铱，此外，在与希克苏鲁伯小行星撞击有关的K-Pg边界处发现了明显的铱峰值。我们通过Co-Ir图解区分了地球外物质在沉积物中的贡献和地球物质的贡献，称之为“地球外物质指数”fEX。这个新的指数揭示了希克苏鲁伯峰周围广泛的铱异常。地球表面的任何物质混合物都不能解释广泛的铱成分。另一方面，我们发现太阳系与巨大分子云的相遇可以恰当地解释这一成分，特别是如果分子云的大小约为100 pc，中心密度超过2000个质子/cm ^3。Kataoka et al.（2013，2014）指出，与暗云的相遇将导致环境灾难，导致大规模灭绝。来自假设的暗云的固体颗粒将与地球的全球环境结合，在平流层中保留至少数月或数年。据估计，乌云的遮阳效应高达-9.3 W m^-2，因此在白垩纪最后800万年期间，乌云将导致全球气候变冷，这与氧中稳定同位素比的变化一致（Barrera和Huber，1990; Li和Keller，1998; Barrera和Savin，1999; Li和Keller，1999）和锶（Barrera和Huber，1990; Ingram，1995; Sugarman等人，1995年）。大陆冰盖的增长也导致了海平面的下降。全球变冷似乎与化石多样性的减少有关，最终导致了K-Pg边界的大灭绝。
英文摘要：
We have identified iridium in an ~5 m-thick section of pelagic sediment cored in the deep sea floor at Site 886C, in addition to a distinct spike in iridium at the K-Pg boundary related to the Chicxulub asteroid impact. We distinguish the contribution of the extraterrestrial matter in the sediments from those of the terrestrial matter through a Co-Ir diagram, calling it the "extraterrestrial index" fEX. This new index reveals a broad iridium anomaly around the Chicxulub spike. Any mixtures of materials on the surface of the Earth cannot explain the broad iridium component. On the other hand, we find that an encounter of the solar system with a giant molecular cloud can aptly explain the component, especially if the molecular cloud has a size of ~100 pc and the central density of over 2000 protons/cm^3. Kataoka et al. (2013, 2014) pointed that an encounter with a dark cloud would drive an environmental catastrophe leading to mass extinction. Solid particles from the hypothesized dark cloud would combine with the global environment of Earth, remaining in the stratosphere for at least several months or years. With a sunshield effect estimated to be as large as -9.3 W m^-2, the dark cloud would have caused global climate cooling in the last 8 Myr of the Cretaceous period, consistent with the variations of stable isotope ratios in oxygen (Barrera and Huber, 1990; Li and Keller, 1998; Barrera and Savin, 1999; Li and Keller, 1999) and strontium (Barrera and Huber, 1990; Ingram, 1995; Sugarman et al., 1995). The resulting growth of the continental ice sheet also resulted in a regression of the sea level. The global cooling, which appears to be associated with a decrease in the diversity of fossils, eventually led to the mass extinction at the K-Pg boundary.
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