Effect of Mesozoic volcanic eruptions in the western Liaoning Province, China on paleoclimate and paleoenvironment
Effect of Mesozoic volcanic eruptions in the western Liaoning Province, China on paleoclimate and paleoenvironment
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DOI：
10.1360/03yd0071
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发表时间：
2003-12-01
期刊：
影响因子：
--
通讯作者：
Wang, XL
中科院分区：
文献类型：
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作者：
Guo, ZF;Liu, JQ;Wang, XL
在中国辽西义县组下部夹有凝灰岩和凝灰岩的湖泊沉积物中发现了保存完好的中生代脊椎动物化石。四合屯发掘剖面的中酸性火山矿床中保存了富含化石的地层。本文在对剖面采集的凝灰岩和凝灰岩样品进行岩相研究的基础上，通过电子探针分析测定了斑晶和基质玻璃中熔体包裹体的主量元素浓度和挥发性成分。通过比较喷发前后的挥发物浓度来估算排放到大气中的挥发物（S、F、Cl 和 H2O）含量。辽西地区的挥发物排放量（除水外）远高于历史上火山喷发的排放量，对气候和环境产生了重大影响。根据辽西火山喷发释放的气体的性质和数量，我们提出了一个假设，即富含挥发物的火山活动可能会通过向平流层注入大量挥发物（例如SO2、H2S、HCl、HF和H2O）而导致研究区域的脊椎动物大量死亡，从而引发环境和气候的突然变化并改变湖泊化学成分。从挥发物排放物含量来看，辽西火山喷发可细分为以下三类。第一类以高频排放为主，它对古气候和古环境产生了致命但可能短暂的影响，最终导致了原始鸟类的大规模死亡。第二组的卤素排放浓度最高。然而，喷出的氯含量高于释放的氟含量。活性氯化合物可能导致臭氧层消耗，从而导致大多数脊椎动物（包括鱼类、海龟和恐龙）大量死亡。第三种主要是释放的含硫气体（主要是SO2和H2S）。它们降低了地表温度并形成了大规模的有毒酸雨。最终，这种环境创伤杀死了许多陆地和淡水脊椎动物，并形成了脊椎动物（包括有羽毛的兽脚亚目恐龙）化石丰富的层。结果表明，辽西地区中生代火山活动无论是大规模还是频繁的中规模火山活动都可能导致脊椎动物大量死亡。
Well-preserved Mesozoic vertebrate fossils were found from lacustrine deposits interbedded with tuff and tuffites in the lower part of the Yixian Formation, western Liaoning Province, China. The fossil-rich layers were preserved in the intermediate-acid volcanic deposits in Sihetun excavating profile. Based on the petrographic studies of samples of the tuff and tuffites collected from the profile, this paper determines major element concentrations and volatile compositions of the melt inclusions in phenocrysts and matrix glasses with electron microprobe analysis. Volatile (S, F, Cl and H2O) contents emitted into the atmosphere were estimated by comparing pre- and post-eruptive volatile concentrations. Amount of volatiles (except for water) emitted in western Liaoning are much higher than those in the historic eruptions which had a substantial effect on climate and environment. Based on the nature and amount of the gases emitted in the eruptions of western Liaoning, we present a hypothesis that volatile-rich volcanism could result in mass mortality of vertebrates in the study area by injecting a large amount of volatiles (e.g., SO2, H2S, HCl, HF and H2O) into the stratosphere that would have triggered abrupt environmental and climate changes and altered lake chemistry. In terms of contents of volatile emissions, the eruptions in western Liaoning can be subdivided into the following three categories. The first group is dominated by HF emission, which had a fatal but possibly short-lived effect on paleoclimate, and paleoenvironment and finally caused the mass mortality of the primitive birds. The second group presents the highest halogen concentrations emitted. However, contents of chlorine erupted is higher than those of fluorine emitted. The reactive chlorine compounds probably led to the ozone layer depletion and, therefore, caused mass mortality of most of all vertebrates including fishes, turtles and dinosaurs. The third one consists mainly of sulfur gases (primarily SO2 and H2S) released. They declined the surface's temperatures and formed large-scale toxic acid rains. Eventually, such environmental trauma killed many land- and freshwater-based vertebrates and formed vertebrate (including feathered theropod dinosaurs) fossil-rich layers. The results show that the Mesozoic volcanic activities on either a large scale or frequent moderate scales in western Liaoning could lead to mass mortality of the vertebrates.