Ca isotope stratigraphy across the Cenomanian-Turonian OAE 2: Links between volcanism, seawater geochemistry, and the carbonate fractionation factor
Ca isotope stratigraphy across the Cenomanian-Turonian OAE 2: Links between volcanism, seawater geochemistry, and the carbonate fractionation factor
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DOI：
10.1016/j.epsl.2015.02.001
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发表时间：
2015-04-15
影响因子：
5.3
通讯作者：
Sageman, Bradley B.
中科院分区：
文献类型：
--
作者：
Du Vivier, Alice D. C.;Jacobson, Andrew D.;Sageman, Bradley B.
海洋碳酸盐岩的钙同位素组成提供了潜在的重建在地质过去的环境变化的驱动力。这项研究报告了新的，高精度的钙同位素记录（Δ Ca-44/40; 2 sigma sp = +/- 0.04千分之一），跨越了白垩纪海洋气候系统的主要扰动称为海洋缺氧事件2（OAE 2）：中央科罗拉多，美国（波特兰#1核心），法国东南部（蓬特d 'Issole），和北海道，日本（大夕张，Yezo集团）。此外，我们生成了来自英格兰伊斯特本（English Chalk）的选定样品的新数据，其中先前的Ca同位素研究使用不同的方法完成（Blather等人，2011年）。Yezo组的地层含有少量碳酸盐（类似于1重量%）。平均），因此没有产生清晰的Δ Ca-44/40信号。波特兰岩芯和蓬特德伊索剖面显示出相当的δ Ca-44/40值，在OAE 2开始时增加约0.10-0.15 ppm，然后在整个事件中降低至接近初始值。伊斯特本δ Ca-44/40值高于先前报告的值。它们也高于波特兰岩心和蓬特德伊索剖面的δ Ca-44/40值，但定义了类似的模式。根据海洋Ca循环的数值模型，升高的热液输入对海水三角洲Ca-44/40值的影响很小。高架河流（化学风化）输入产生一个短暂的负同位素漂移，显着不同的正同位素漂移观察到的波特兰，蓬特德伊索莱，和伊斯特本记录。碳酸盐分馏系数幅度的降低为δ Ca-44/40值的正移提供了最好的解释，特别是考虑到偏移的快速性质。由于分馏因子的降低对应于海水Ca/CO 3比值的增加，我们暂时将正Ca同位素偏移归因于瞬时海洋酸化，即，在CO2吸收过程中CO 32-的浓度降低。最近的研究利用了各种同位素替代物，例如，钕，锇，铅，牵连喷发的加勒比大火成岩省增加二氧化碳的可能来源。此外，C，Ca和Os同位素数据的整合揭示了OAE 2发作期间事件发生时间的新信息。(C)2015作者由爱思唯尔公司出版
The Ca isotope composition of marine carbonate rocks offers potential to reconstruct drivers of environmental change in the geologic past. This study reports new, high-precision Ca isotope records (delta Ca-44/40; 2 sigma sp = +/- 0.04 parts per thousand) for three sections spanning a major perturbation to the Cretaceous ocean-climate system known as Ocean Anoxic Event 2 (OAE 2): central Colorado, USA (Portland #1 core), southeastern France (Pont d'Issole), and Hokkaido, Japan (Oyubari, Yezo Group). In addition, we generated new data for selected samples from Eastbourne, England (English Chalk), where a previous Ca isotope study was completed using different methodology (Blather et al., 2011). Strata of the Yezo Group contain little carbonate (similar to 1 wt.% on average) and accordingly did not yield a clear delta Ca-44/40 signal. The Portland core and the Pont d'Issole section display comparable delta Ca-44/40 values, which increase by similar to 0.10-0.15 parts per thousand at the onset of OAE 2 and then decrease to near-initial values across the event. The Eastbourne delta Ca-44/40 values are higher than previously reported. They are also higher than the delta Ca-44/40 values for the Portland core and the Pont d'Issole section but define a similar pattern. According to a numerical model of the marine Ca cycle, elevated hydrothermal inputs have little impact on seawater delta Ca-44/40 values. Elevated riverine (chemical weathering) inputs produce a transient negative isotope excursion, which significantly differs from the positive isotope excursions observed in the Portland, Pont d'Issole, and Eastbourne records. A decrease in the magnitude of the carbonate fractionation factor provides the best explanation for a positive shift in delta Ca-44/40 values, especially given the rapid nature of the excursion. Because a decrease in the fractionation factor corresponds to an increase in the Ca/CO3 ratio of seawater, we tentatively attribute the positive Ca isotope excursion to transient ocean acidification, i.e., a reduction in the concentration of CO32- during CO2 uptake. Recent studies utilizing a variety of isotope proxies, e.g., Nd, Os, and Pb, implicate eruption of the Caribbean Large Igneous Province as a likely source of increased CO2. Moreover, integration of C, Ca, and Os isotope data reveals new information about the timing of events during the onset of OAE 2. (C) 2015 The Authors. Published by Elsevier B.V.