Si isotope ratio of radiolaria across Triassic?Jurassic transition in a pelagic deep-sea bedded chert (Inuyama, Japan)
Si isotope ratio of radiolaria across Triassic?Jurassic transition in a pelagic deep-sea bedded chert (Inuyama, Japan)
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远洋深海层状燧石中三叠纪到侏罗纪过渡时期放射虫的硅同位素比（日本犬山）
DOI：
10.1016/j.gloplacha.2022.103882
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发表时间：
2022
影响因子：
3.9
通讯作者：
Ikeda Masayuki
中科院分区：
文献类型：
--
作者：
B?le Maximilien;Ushikubo Takayuki;Hori Rie S.;Baumgartner Peter O.;Nakai Yuki;Ikeda Masayuki
三叠纪末灭绝事件（ETE）是显生宙“五大”大灭绝事件之一，但全球范围内环境变化的时间和性质仍然难以捉摸。在这里，我们报道了一幅以模具形式保存的海面放射虫的毫米尺度高分辨率δ30Si剖面，该剖面跨越了日本犬山市胜山剖面的深海演替的三叠纪末放射虫更替期。三叠系—侏罗系放射虫的δ30Si值在- 0.6±0.5‰~ 2.6±0.3‰之间，与三叠系—新生代（包括现代样品）放射虫的δ30Si值有重叠。燧石中具有优势放射虫的Si的质量平衡高达90%，支持成岩作用对放射虫霉菌δ30Si的影响可以忽略不计。δ30Si的cm尺度变化最高可达2‰，总体上与二氧化硅含量变化有关。这里我们假设放射虫的δ30Si反映放射虫的生产力。我们在三叠纪末放射虫周转期（此处命名为SIE 1和SIE 2）内及以上检测到负硅同位素偏移。第一次SIE值为2‰，在紫斑岩段基底上方0 ~ 10 mm处测得，可能与中大西洋岩浆省（CAMP）的初始大规模火山活动有关，并与深海酸化和三叠纪末放射虫周转期的开始有关。在第一次SIE为负的基础上2‰（约10 mm）的后续SIE为正可能记录了生物硅质生产力的恢复，这可能与在放射虫周转期内侏罗纪放射虫分类群的首次出现有关。我们还在最下面的暗红色燧石层中检测到暗示SIE 2的数据，表明生产率也发生了类似的变化。这些负的si发生在~ 1 mm的间隔内，表明在三叠纪末放射虫周转期发生了kyr或更短尺度的剧烈环境扰动。
The end-Triassic extinction event (ETE) marks one of the “Big five” mass extinction events of the Phanerozoic, yet the timing and nature of environmental changes on a global scale remain elusive. Here we report a mm-scale high-resolution δ30Si profile of sea surface-dwelling radiolaria, preserved as moulds, spanning the end-Triassic radiolarian turnover interval of the deep-sea succession at the Katsuyama section, Inuyama, Japan. The δ30Si of the Triassic-Jurassic radiolaria between − 0.6 ± 0.5‰ and 2.6 ± 0.3‰ overlap with available radiolarian δ30Si data for Triassic to Cenozoic, including modern samples. The mass balance of Si with dominant radiolaria up to 90% in chert supports negligible impact of diagenesis on δ30Si of radiolarian moulds. The cm-scale δ30Si variations up to 2 ‰ are overall associated with changes in silica contents. Here we hypothesize that the δ30Si of radiolarian reflect radiolarian productivity. We detected negative silicon isotope excursions within and above the end-Triassic radiolarian turnover interval, named here the SIE 1 and 2. The first SIE of 2 ‰ is detected from 0 mm to 10 mm above the base of purple chert interval, probably linked with the initial massive volcanism in the Central Atlantic magmatic provinces (CAMP) and associated deep-sea acidification and the onset of the end-Triassic radiolarian turnover. Subsequent positive SIE up to 2 ‰ ca. 10 mm above the first negative SIEs may record recovery of biosiliceous productivity, which could may be related with the first appearance of several Jurassic radiolarian taxa within the radiolarian turnover interval. We also detected data that is suggestive of SIE 2 in the lowermost dusky red chert bed, suggesting similar changes in productivity. These negative SIEs occurred within ~ 1 mm interval, implying the occurrence of kyr- or shorter-scale drastic environmental perturbations across the end-Triassic radiolarian turnover interval.