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首页> 外文期刊>Precambrian Research >Oceanic redox conditions in the Late Mesoproterozoic recorded in the upper Vazante Group carbonates of Sao Francisco Basin, Brazil: Evidence from stable isotopes and REEs
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Oceanic redox conditions in the Late Mesoproterozoic recorded in the upper Vazante Group carbonates of Sao Francisco Basin, Brazil: Evidence from stable isotopes and REEs

机译：巴西圣弗朗西斯科盆地上Vazante组上碳酸盐中记录的中元古代晚期的海洋氧化还原条件：来自稳定同位素和REE的证据

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摘要

The Vazante Group consists of a late Mesoproterozoic (similar to 1.0-1.1 Ga) carbonate-dominated marine platform sequence in east-central Brazil. The upper part of the sequence consists of a glaciomarine diamictite unit overlain by a cap carbonate. The delta C-13 profile of the upper Vazante shows significant negative plunges, one preglacial (drop of similar to 5.5%. VPDB) and two postglacial (drops of similar to 9 and 5 parts per thousand VPDB, respectively). The C-isotope plunge in the preglacial carbonates is correlated with low Th/U ratios (0.1-1.4) and a negative Ce/Ce* shift (similar to 0.4), suggesting deposition under relative reducing conditions. In contrast, the C-isotope plunges in the postglacial carbonates are associated with high Th/U ratios (>2) and positive Ce/Ce* shifts (up to similar to 1.5), thus reflecting oxidizing conditions. Variations in the redox conditions of the late Mesoproterozoic ocean, reflected by changes in the Th/U and Ce/Ce* ratios, are likely attributable to a combination of both global and local climatic and oceanographic changes, similar to what has been inferred for the Neoproterozoic oceans. (c) 2008 Elsevier B.V. All rights reserved.
机译：Vazante组由巴西中东部的中元古代（类似于1.0-1.1 Ga）碳酸盐岩为主的海洋平台层序组成。该序列的上部由覆盖有盖碳酸盐的冰川海洋铁矾土单元组成。上瓦赞特的δC-13剖面显示出明显的负暴跌，一个冰期前（下降了约5.5％，VPDB）和两个冰期后（下降了分别约9和5千分之一VPDB）。冰川前碳酸盐中的C同位素下降与低的Th / U比（0.1-1.4）和负的Ce / Ce *位移（类似于0.4）相关，表明在相对还原条件下沉积。相比之下，冰川后碳酸盐中的C同位素突降与高Th / U比（> 2）和正Ce / Ce *位移（最高接近1.5）相关，从而反映了氧化条件。 Th / U和Ce / Ce *比值的变化反映了中元古代晚期氧化还原条件的变化，这可能归因于全球和局部气候变化和海洋学变化的共同作用，与先前推断的相似。新元古代海洋。 （c）2008 Elsevier B.V.保留所有权利。

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