长白山千年大喷发泉阳泥炭沉积物记录

TEPHRA RECORD FROM QUANYANG PEAT OF THE CHANGBAISHAN MILLENNIUM ERUPTION

长白山千年大喷发火山灰覆盖面积极广,广泛分布于日本海及日本半岛等地,在9 000km以外的格陵兰地区也有这层火山灰的产出,是1个非常重要的等时标志层。文中在长白山NW约45km泉阳泥炭沉积物(64cm)中发现一火山灰层,放射性14C定年结果为886—1013cal AD(95. 4%),火山玻璃主量元素的地球化学特征显示其为碱流质,与长白山千年大喷发火山灰碱流质端元十分吻合,确定为长白山千年大喷发的产物。文中的研究结果说明,这次火山喷发产生的火山灰向NW向已经飘散至约45km以外的泉阳地区,另外,鉴于火山灰中浮岩颗粒粒径可达0. 3cm,说明此次火山喷发产生的火山灰可能向W飘散至更远的地区,从而在更广大的区域上形成等时标志层。千年大喷发泉阳泥炭火山灰与四海龙湾、日本等地以及格陵兰冰芯中的火山灰具有不完全一致的火山玻璃主量元素组成,泉阳泥炭中的火山物质在成分上与典型的空降浮岩有所不同,而是与此次火山喷发的松散火山碎屑流更为接近。

Tephra,usually produced by explosive eruptions,is deposited rapidly,hence,it can serve as a distinctive and widespread synchronous marker horizon correlating terrestrial,marine and ice core records.The tephra from Changbaishan Millennium eruption,a widely distributed tephra,is an important marker bed across the Japan Sea,Japan Islands and even in the Greenland ice cores9 000 km away from volcanic vent.In this study,a discrete tephra was identified in the Quanyang peat^45 km northeast to the Changbaishan volcano.Radiocarbon14 C dating on the plant remains constrains an age of 886—1013 cal AD(95.4%)to the tephra layer,which can correspond to the Millennium eruption of Changbaishan in time.In addition,there was no similar volcanic eruption in the surrounding areas except Changbaishan at the same time.This tephra shows rhyolitic glass shards major element compositions similar to those rhyolitic tephra from Millennium eruption.This study illustrates that tephra from Millennium eruption has been transported to Quanyang peat^45 km northwest to the Changbaishan volcano.Additionally,the diameter of the pumice lapilli is up to0.3 cm,implying that the tephra must be transported more distal away from Quanyang peat and formed a widely distributed isochronic layer.Glass geochemistry of the Quanyang tephra,different from the distal tephra recorded at Sihailongwan,Japan,and Greenland ice,shows a close affinity to the pyroclastic flow deposits of the Millennium eruption while not from fall deposits.This may indicate that distribution of the Millennium eruption of Changbaishanin in different directions may be controlled by different stages of eruption.This layer with well-defined annual results can be used to optimize the chronological framework of the corresponding sedimentary environment,thus facilitating more accurate discussion of corresponding environmental changes,which can achieve the contrast of the ancient climate records in the whole Northeast China-Japan and arctic regions.