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A Quaternary geomagnetic instability time scale

机译：第四纪地磁不稳定时标

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Reversals and excursions of Earth's geomagnetic field create marker horizons that are readily detected in sedimentary and volcanic rocks worldwide. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to understanding several aspects of Quaternary climate, dynamo processes, and surface processes. For example, stratigraphic correlation between marine sediment and polar ice records of climate change across the cryospheres benefits from a highly resolved record of reversals and excursions. The temporal patterns of dynamo behavior may reflect physical interactions between the molten outer core and the solid inner core or lowermost mantle. These interactions may control reversal frequency and shape the weak magnetic fields that arise during successive dynamo instabilities. Moreover, weakening of the axial dipole during reversals and excursions enhances the production of cosmogenic isotopes that are used in sediment and ice core stratigraphy and surface exposure dating. The Geomagnetic Instability Time Scale (GITS) is based on the direct dating of transitional polarity states in lava flows using the ~(40)Ar/~(39)Ar method, in parallel with astrochronologic age models of marine sediments in which oxygen isotope and magnetic records have been obtained. A review of data from Quaternary lava flows and sediments gives rise to a GITS that comprises 10 polarity reversals and 27 excursions that occurred during the past 2.6 million years. Nine of the ten reversals bounding chrons and subchrons are associated with ~(40)Ar/~(39)Ar ages of transitionally-magnetized lava flows. The tenth, the Gauss-Matuyama chron boundary, is tightly bracketed by ~(40)Ar/~(39)Ar dated ash deposits. Of the 27 well-documented geomagnetic field instabilities manifest as short-lived excursions, 14 occurred during the Matuyama chron and 13 during the Brunhes chron. Nineteen excursions have been dated directly using the ~(40)Ar/~(39)Ar method on transitionally-magnetized volcanic rocks and these form the backbone of the GITS. Excursions are clearly not the rare phenomena once thought. Rather, during the Quaternary period, they occur nearly three times as often as full polarity reversals.
机译：地球地磁场的反转和偏移会产生标记层，这些标记层很容易在全世界的沉积岩和火山岩中检测到。这些地磁场不稳定的准确和精确的时间顺序对于理解第四纪气候，发电机过程和地表过程的多个方面至关重要。例如，高度解析的逆转和偏移记录使海洋沉积物和整个冰冻圈的极地冰记录之间的地层相关性受益。发电机行为的时间模式可能反映出熔融外核与固体​​内核或最低地幔之间的物理相互作用。这些相互作用可以控制反转频率并调整在连续的发电机不稳定性过程中出现的弱磁场。此外，在逆转和偏移过程中轴向偶极子的减弱会增强在沉积物和冰芯地层中以及地表测年中使用的宇宙成因同位素的产生。地磁不稳定性时标（GITS）基于熔岩流中过渡极性状态的直接测年（使用〜（40）Ar /〜（39）Ar方法）以及与氧同位素和已获得磁记录。回顾第四纪熔岩流和沉积物的数据，得出了一个GITS，其中包括在过去260万年中发生的10次极性反转和27次偏移。十个反转边界时间中的九个和子时间与过渡磁化熔岩流的〜（40）Ar /〜（39）Ar年龄相关。第十个高斯-玛图山时间边界由〜（40）Ar /〜（39）Ar过时的灰烬紧紧包围。在27个有据可查的地磁场不稳定性中，它们表现为短暂的偏移，其中14个发生在Matuyama年，13个发生在Brunhes年。已经使用〜（40）Ar /〜（39）Ar方法在过渡磁化的火山岩上直接进行了19次游览，这些游览构成了GITS的主干。游览显然不是曾经​​想过的罕见现象。相反，在第四纪期间，它们发生的频率几乎是完全极性反转的三倍。

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