S. Arcusa, T. Schneider, P. Mosquera, H. Vogel, D. Kaufman, S. Szidat, M. Grosjean
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引用次数: 6
Abstract
Lakes located downwind of active volcanoes serve as a natural repository for volcanic ash (tephra) produced during eruptive events. In this study, sediment cores from four lakes in Cajas National Park, southern Ecuador, situated approximately 200 km downwind of active volcanoes in the Northern Andes Volcanic Zone, were analysed to document the regional history of tephra fall extending back around 3,000 a cal BP. The ages of the lacustrine sedimentary sequences were constrained using a total of 20 AMS radiocarbon ages on plant remains. The tephra layers were correlated among the lakes based on their radiocarbon age, elemental composition, colour, and grain morphology. We found five unique tephra layers, each at least 0.2 cm thick, and further constrained their ages by combining the results from two age-depth modelling approaches (clam and rbacon). The tephra layers were deposited 3,034±621, 2,027±41, 1,557±177, 733±112, and 450±70 a cal BP. The ages of all but the youngest tephra layer overlap with those of known eruptions from Tungurahua. Some tephra layers are missing as macroscopic layers in several cores, with only two of the five tephra layers visible in the sediment of three lakes. Likewise, previous studies of lake sediment cores from the region are missing the four youngest tephra layers, further highlighting the need to sample multiple lakes to reconstruct a comprehensive history of fallout events. The newly documented stratigraphic marker layers will benefit future studies of lake sediments in Cajas National Park.
位于活火山顺风处的湖泊是火山爆发时产生的火山灰(tephra)的天然储存库。在这项研究中,研究人员分析了厄瓜多尔南部Cajas国家公园的四个湖泊的沉积物岩心,这些湖泊位于北安第斯火山带活火山的下风约200公里处,记录了回溯到大约3000 cal BP的tephra falls的区域历史。利用20个植物残体AMS放射性碳年龄对湖相沉积序列进行了年龄约束。根据放射性碳年龄、元素组成、颜色和颗粒形态,在湖泊之间对温层进行了对比。我们发现了五个独特的麻风层,每个至少0.2厘米厚,并通过结合两种年龄深度建模方法(蛤蜊和rbacon)的结果进一步限制了它们的年龄。温层沉积分别为3034±621、2027±41、1557±177、733±112和450±70 a cal BP。除了最年轻的火山层外,所有火山层的年龄都与已知的通古拉瓦火山喷发的年龄重叠。在几个岩心中,一些温层作为宏观层而缺失,在三个湖泊的沉积物中,只有两个温层可见。同样,先前对该地区湖泊沉积物岩心的研究也遗漏了四个最年轻的温层,这进一步强调了对多个湖泊进行采样以重建沉降事件的全面历史的必要性。新记录的地层标志层将有利于卡哈斯国家公园湖泊沉积物的未来研究。
期刊介绍:
This journal publishes original and review articles on geology and related sciences, in Spanish or English, in three issues a year (January, May and September). Articles or notes on major topics of broad interest in Earth Sciences dealing with the geology of South and Central America and Antarctica, and particularly of the Andes, are welcomed.
The journal is interested in publishing thematic sets of papers and accepts articles dealing with systematic Paleontology only if their main focus is the chronostratigraphical, paleoecological and/or paleogeographical importance of the taxa described therein.