Early Mississippian ocean anoxia triggered organic carbon burial and late Paleozoic cooling: Evidence from uranium isotopes recorded in marine limestone
Early Mississippian ocean anoxia triggered organic carbon burial and late Paleozoic cooling: Evidence from uranium isotopes recorded in marine limestone
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DOI：
10.1130/g46950.1
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发表时间：
2020-04-01
期刊：
影响因子：
5.8
通讯作者：
Romaniello, Stephen J.
中科院分区：
文献类型：
--
作者：
Cheng, Keyi;Elrick, Maya;Romaniello, Stephen J.
早密西西比期（图尔奈期）正三角洲C-13偏移（图尔奈期中期碳同位素偏移[TICE]）是中生代最大的偏移之一，与其发展相关的有机碳（OC）埋藏被假设为增强了晚古生代的冷却和冰川作用。我们测试的假设，扩大海洋缺氧驱动广泛的OC埋藏使用铀同位素（三角洲U-238）的下密西西比海灰岩作为全球海水氧化还原代理。三角洲U-238趋势记录了一个大的图尔奈负偏移，持续时间类似于100万年。三角洲U-238值和相变以及局部沉积和成岩影响的代理之间缺乏协变，表明三角洲U-238趋势代表全球海水氧化还原信号。负三角洲U-238偏移与第一个TICE正偏移一致，支持扩大的海洋缺氧事件控制OC埋藏的假设。这些结果提供了来自全球海水氧化还原代用品的第一个证据，即海洋缺氧事件驱动了图尔奈阶OC埋藏并控制了早密西西比期的冷却和冰川作用。铀和碳模拟结果表明：（1）富氧海底面积增加了6倍，（2）OC埋藏最初是由富氧扩张驱动的，随后是缺氧/亚氧条件的扩张，（3）OC埋藏质量比其他主要海洋缺氧事件期间的封存质量大4- 17倍。
The Early Mississippian (Tournaisian) positive delta C-13 excursion (mid-Tournaisian carbon isotope excursion [TICE]) was one of the largest in the Phanerozoic, and the organic carbon (OC) burial associated with its development is hypothesized to have enhanced late Paleozoic cooling and glaciation. We tested the hypothesis that expanded ocean anoxia drove widespread OC burial using uranium isotopes (delta U-238) of Lower Mississippian marine limestone as a global seawater redox proxy. The delta U-238 trends record a large Tournaisian negative excursion lasting similar to 1 m.y. The lack of covariation between delta U-238 values and facies changes and proxies for local depositional and diagenetic influences suggests that the delta U-238 trends represent a global seawater redox signal. The negative delta U-238 excursion is coincident with the first TICE positive excursion, supporting the hypothesis that an expanded ocean anoxic event controlled OC burial. These results provide the first evidence from a global seawater redox proxy that an ocean anoxic event drove Tournaisian OC burial and controlled Early Mississippian -cooling and glaciation. Uranium and carbon modeling results indicate that (1) there was an similar to 6x increase in euxinic seafloor area, (2) OC burial was initially driven by expanded euxinia -followed by expanded anoxic/suboxic conditions, and (3) OC burial mass was similar to 4-17x larger than that sequestered during other major ocean anoxic events.