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首页> 外文期刊>Geochemistry, geophysics, geosystems >Identifying cryptotephra units using correlated rapid, nondestructive methods: VSWIR spectroscopy, X-ray fluorescence, and magnetic susceptibility
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Identifying cryptotephra units using correlated rapid, nondestructive methods: VSWIR spectroscopy, X-ray fluorescence, and magnetic susceptibility

机译：使用相关的快速，无损方法鉴定隐足单位：VSWIR光谱，X射线荧光和磁化率

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摘要

Understanding the frequency, magnitude, and nature of explosive volcanic eruptions is essential for hazard planning and risk mitigation. Terrestrial stratigraphic tephra records can be patchy and incomplete due to subsequent erosion and burial processes. In contrast, the marine sedimentary record commonly preserves a more complete historical record of volcanic activity as individual events are archived within continually accumulating background sediments. While larger tephra layers are often identifiable by changes in sediment color and/or texture, smaller fallout layers may also be present that are not visible to the naked eye. These cryptotephra are commonly more difficult to identify and often require time-consuming and destructive point counting, petrography, and microscopy work. Here we present several rapid, nondestructive, and quantitative core scanning methodologies (magnetic susceptibility, visible to shortwave infrared spectroscopy, and XRF core scanning) which, when combined, can be used to identify the presence of increased volcaniclastic components (interpreted to be cryptotephra) in the sedimentary record. We develop a new spectral parameter (BDI1000VIS) that exploits the absorption of the 1 mu m near-infrared band in tephra. Using predetermined mixtures, BDI1000VIS can accurately identify tephra layers in concentrations >15-20%. When applied to the upper approximate to 270 kyr record of IODP core U1396C from the Caribbean Sea, and verified by traditional point counting, 29 potential cryptotephra layers were identified as originating from eruptions of the Lesser Antilles Volcanic Arc. Application of these methods in future coring endeavors can be used to minimize the need for physical disaggregation of valuable drill core material and allow for near-real-time recognition of tephra units, both visible and cryptotephra.
机译：了解爆炸性火山喷发的频率，幅度和性质对于危害规划和缓解风险至关重要。由于随后的侵蚀和掩埋过程，陆地地层的特菲拉记录可能不完整且不完整。相比之下，海洋沉积记录通常会保留更完整的火山活动历史记录，因为单个事件被记录在不断积累的背景沉积物中。尽管通常可以通过沉积物颜色和/或质地的变化来识别较大的提夫拉层，但也可能存在较小的沉降层，而肉眼看不到。这些隐头目通常较难识别，并且经常需要耗时且破坏性的点计数，岩相学和显微镜检查工作。在这里，我们介绍了几种快速，无损和定量的岩心扫描方法（磁化率，短波红外光谱可见和XRF岩心扫描），当组合使用时，可用于识别火山碎屑成分增加（解释为隐密岩）在沉积记录中。我们开发了一个新的光谱参数（BDI1000VIS），该光谱参数利用了特非拉中1微米的近红外波段的吸收。使用预定的混合物，BDI1000VIS可以准确地识别浓度> 15-20％的提菲拉层。当将其应用到来自加勒比海的约270年记录的IODP核心U1396C的上部记录中，并通过传统的点计数进行验证时，发现了29个潜在的隐胎群层是源自小安的列斯火山弧的喷发。这些方法在将来的取芯工作中的应用可用于最大程度地减少对有价值的钻芯材料进行物理分解的需要，并允许近实时识别可见和隐球菌的特非拉单位。

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