Improving confidence in ferromanganese crust age models: A composite geochemical approach
Improving confidence in ferromanganese crust age models: A composite geochemical approach
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DOI：
10.1016/j.chemgeo.2019.03.003
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发表时间：
2019-05-20
期刊：
影响因子：
3.9
通讯作者：
Murton, Bramley
中科院分区：
文献类型：
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作者：
Josso, Pierre;Parkinson, Ian;Murton, Bramley
海洋铁锰结壳的精确年龄模型对于了解古海洋学变化和影响结壳生长速度及其横向连续性的当地环境因素的变化至关重要。然而，没有绝对的方法存在的年龄超过10百万年，这需要结合一些方法，这些存款。在这里，我们提出了一个复合年龄模型的15厘米厚的铁锰结壳样品通过独特的芯钻使用遥控车在水深1130米，在热带海山，在东北大西洋的首脑会议。该年龄模型是基于激光消融U-Pb定年、Co测时和Os同位素的交叉验证。这使得使用马尔可夫链蒙特卡罗（MCMC）模拟的贝叶斯统计建模的年龄-深度模型的鲁棒校准。结果表明，该铁锰结壳在晚白垩世73 ~ 77 Ma开始生长，生长速率为1 ~ 24 mm/Myr，平均4 mm/Myr。磷酸盐化的碳酸盐基底，覆盖热带海山和下面的大多数铁锰结壳，产生的U-Pb年龄为84 +/- 4百万年，并提供了年龄上限的模型。在地壳垂直剖面中，Os-188/Os-187的放射性偏移较小，因此可以确定始新世-渐新世和始新世-古近纪过渡期Os同位素海水曲线中的关键拐点。增长率估计从经验的合作计时器相结合的年龄包络定义的Os数据，并用于验证MCMC模拟。该模型确定了上新世期间发生的五个间断（2.5 +/- 1.9-5.3 +/- 1.7 Ma），早中新世（16 +/- 1-27 +/- 2 Ma）、渐新世（29 +/- 2-32 +/- 1 Ma）、始新世（41 +/- 2-52 +/- 0.6 Ma）和古新世晚期（55 +/- 1-59 +/- 1.4 Ma）。一个主要的磷酸盐化事件影响的铁锰核心可以追溯到始新世晚期（38 +/- 1.2马），这与全球海洋系统的记录变化，从温暖和缓慢的循环冷和积极的热盐驱动的南极冰川开始的赤道翻转。
Accurate age models for marine ferromanganese (Fe-Mn) crusts are essential to understand paleoceanographic changes and variations in local environmental factors affecting crust growth rate and their lateral continuity. However, no absolute method exists for dating these deposits beyond the age of 10 Myr, which requires the combination of a number of approaches. Here, we present a composite age model for a 15 cm thick Fe-Mn crust sample obtained by unique core drilling using a remotely operated vehicle at a water depth of 1130 m, on the summit of Tropic Seamount, in the north-east Atlantic. The age model is based on cross-validation of laser-ablation U-Pb dating, Co-chronometry and Os isotopes. These enable robust calibration of the age-depth model using the Bayesian statistical modelling of Markov Chain Monte Carlo (MCMC) simulations. The results show that this Fe-Mn crust commenced growth in the Late Cretaceous between 73 and 77 Ma, and grew at a rate between 1 and 24 mm/Myr, averaging 4 mm/Myr. The phosphatised carbonate substrate, capping Tropic Seamount and underlying most of the Fe-Mn crusts, yields a U-Pb age of 84 +/- 4 Myr, and provides the upper age limit for the model. Less radiogenic excursions of Os-188/Os-187 in the vertical profile through the crust permit the identification of key inflection points in the Os isotope seawater curve at the Eocene-Oligocene and Cretaceous-Paleogene transitions. Growth rates estimated from the empirical Co-chronometer are combined with the age envelope defined by the Os data and used to validate the MCMC simulations. The model identifies five hiatuses that occurred during the Pliocene (2.5 +/- 1.9-5.3 +/- 1.7 Ma), Early Miocene (16 +/- 1-27 +/- 2 Ma), Oligocene (29 +/- 2-32 +/- 1 Ma), Eocene (41 +/- 2-52 +/- 0.6 Ma), and the Late Paleocene (55 +/- 1-59 +/- 1.4 Ma). A major phosphatisation event affecting the Fe-Mn core can be dated to the Late Eocene (38 +/- 1.2 Ma), which coincides with a recorded change in the global oceanic system, from warm and sluggish circulation to cold and vigorous thermohaline-driven meridional overturn at the onset of Antarctic glaciation.