Composition and accretion rate of fossil micrometeorites recovered in Middle Triassic deep-sea deposits
Composition and accretion rate of fossil micrometeorites recovered in Middle Triassic deep-sea deposits
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DOI：
10.1130/g31866.1
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发表时间：
2011-06
期刊：
影响因子：
5.8
通讯作者：
T. Onoue;Tomoki Nakamura;T. Haranosono;Chika Yasuda
中科院分区：
文献类型：
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作者：
T. Onoue;Tomoki Nakamura;T. Haranosono;Chika Yasuda
微陨石是亚毫米大小的外星颗粒，能够在进入大气层后幸存下来，起源于彗星和小行星等产生尘埃的物体。尽管沉积岩中发现的古代微陨石作为太阳系流星体数量的历史记录具有重要意义，但它们非常罕见，而且容易遭受严重的化学风化。在这里，我们报告了在日本放射虫燧石中发现的保存完好的微陨石，其年龄超过 240 Ma。微陨石集合包括 258 个宇宙球体，这些宇宙球体是在进入大气层时完全熔化的颗粒，以及 2 个粗粒未熔化的微陨石。这些微陨石比沉积记录中任何先前的微陨石集合都要古老得多。利用这些数据，我们计算了中三叠世安尼阶阶段铁型宇宙球体对地球的吸积率。小于 125 μm 的 Anisian 铁型小球的估计吸积率为 25 ± 8 t yr -1 。对宇宙球体吸积率的分析还揭示了 0.74 m.y 的小球体 (~8-36 μm) 的高吸积率。安尼西亚晚期时期。然而，安尼纪晚期小宇宙球体吸积率的增加与地外物质流向地球的变化之间可能存在的联系需要进一步研究。
Micrometeorites, which are submillimeter-sized extraterrestrial particles that survive atmospheric entry, originate from dust-producing objects such as comets and asteroids. Although ancient micrometeorites found in sedimentary rocks are of key interest as a historical record of meteoroid populations in the solar system, they are rare and prone to severe chemical weathering. Here we report the recovery of well-preserved micrometeorites, older than 240 Ma, in radiolarian chert from Japan. The collection of micrometeorites comprised 258 cosmic spherules, which are particles that totally melted during atmospheric entry, and 2 coarse-grained unmelted micrometeorites. These micrometeorites are much older than any previous micrometeorite collection in the sedimentary record. Using this collection, we calculated the accretion rate of iron-type cosmic spherules to the Earth during the Anisian Stage of the Middle Triassic. The estimated accretion rate for Anisian iron-type spherules smaller than 125 μm is 25 ± 8 t yr −1 . Analysis of the accretion rate for cosmic spherules also reveals high accretion rates of small spherules (∼8–36 μm) for a 0.74 m.y. period in the late Anisian. However, the possible link between an enhancement in the accretion rate of small cosmic spherules in the late Anisian and variations in the flux of extraterrestrial matter to the Earth requires further scrutiny.