Geochimica et Cosmochimica Acta ( IF 5 ) Pub Date : 2021-08-02 , DOI: 10.1016/j.gca.2021.07.031 Nan Sun 1 , Alan D. Brandon 1 , Steven L. Forman 2 , Michael R. Waters 3
One of the prevailing hypotheses for the origin of the Younger Dryas (YD) cooling event is that it resulted from a bolide impact or airburst. Purported impact markers peak at or near the YD basal boundary layer at Northern Hemisphere locations. In this study, the 187Os/188Os ratios and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundances in a well-dated sediment section through the Younger Dryas at the Debra L. Friedkin site, Texas are reported. Unradiogenic 187Os/188Os peaks, which could be mantle-derived or extraterrestrial, have been found above, within, and below the YD basal boundary layer. Mass balance mixing models using chondrites or iron meteorites with upper continental crust fail to duplicate the chondrite-normalized HSE patterns of the sediment samples. These HSE signatures in the Friedkin site section replicate those found in Hall’s Cave, Texas. The new results here thus independently confirm that the HSE abundances in the unradiogenic Os layers are likely a fingerprint of volcanic gas aerosols derived from large Plinian eruptions and not extra-terrestrial materials. To better constrain the lithological origins of YD sediments from the Friedkin and Hall’s Cave sites, Texas, trace elements are presented here. The rare earth elements (REE) patterns and Ir, Ni, Ti and Zr abundances are also characterized with terrestrial signatures as opposed to impact melt rocks. An age profile correlation between the two study sites, further shows that three unradiogenic Os peaks overlap in time. The results are inconsistent with the extraterrestrial hypothesis and support instead an episodic and volcanic origin for the observed geochemical anomalies at the Debra L. Friedkin and Hall’s Cave sites, Texas.
中文翻译:
新仙女木事件沉积物中火山特征的地球化学证据
新仙女木 (YD) 冷却事件起源的流行假设之一是它是由火流星撞击或空爆引起的。据称的撞击标记在北半球位置的 YD 基底边界层处或附近达到峰值。在这项研究中,187 Os / 188 Os 比率和高度亲铁元素(HSE:Os、Ir、Ru、Pt、Pd、Re)在 Debra L. Friedkin 站点通过 Younger Dryas 的一个年代久远的沉积物剖面中的丰度,得克萨斯州报道。非放射性187 Os/ 188在 YD 基底边界层的上方、内部和下方都发现了 Os 峰,它们可能来自地幔或来自地外。使用球粒陨石或铁陨石与上大陆地壳的质量平衡混合模型无法复制沉积物样品的球粒陨石标准化 HSE 模式。弗里德金站点部分中的这些 HSE 签名复制了德克萨斯州霍尔洞穴中的签名。因此,这里的新结果独立地证实,非放射性 Os 层中的 HSE 丰度可能是源自普林尼亚大喷发而非外星物质的火山气溶胶的指纹。为了更好地限制来自德克萨斯州弗里德金和霍尔洞穴遗址的 YD 沉积物的岩性起源,这里介绍了微量元素。稀土元素 (REE) 模式和 Ir、Ni、Ti 和 Zr 丰度也具有陆地特征,而不是撞击熔岩。两个研究地点之间的年龄分布相关性进一步表明,三个非放射性 Os 峰在时间上重叠。结果与外星假设不一致,而是支持在德克萨斯州德布拉·弗里德金和霍尔洞穴遗址观察到的地球化学异常的偶发性和火山起源。