The rate and consequences of Sr diagenesis in deep-sea carbonates
The rate and consequences of Sr diagenesis in deep-sea carbonates
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DOI：
10.1016/0012-821x(93)90102-f
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发表时间：
1993-06
影响因子：
5.3
通讯作者：
F. Richter;Yan Liang
中科院分区：
文献类型：
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作者：
F. Richter;Yan Liang
我们使用了深海碳酸盐岩成岩过程中 Sr 交换的扩散平流反应模型来确定 6 个 DSDP 站点（590B、575、593、516、305 和 289）处孔隙水和块体碳酸盐之间 Sr 交换的速率和后果，这些站点中间隙水所需的 Sr 浓度和同位素组成数据可从文献中获得。该模型可以通过调整溶液再沉淀引起的 Sr 交换速率作为沉积物年龄的函数，来重现每个地点孔隙水中的 Sr2+ 和 87Sr/86Sr 剖面。我们发现，所有地点的溶液再沉淀率对于最年轻的沉积物而言最高（1-10%/m.y.），并且在前 10 m.y. 中下降了大约一个数量级。的沉积年龄。这种交换对大量碳酸盐性质的影响是使 Sr 含量降低 5-25%（主要取决于沉积速率），并使 87Sr/86Sr 与沉积物首次沉积时的值相比移动多达 0.00004。与目前的分析不确定性相比，这种幅度的同位素变化很大，因此在使用散装碳酸盐 87Sr/86Sr 进行地层对比时应进行校正。研究的碳酸盐剖面的平均 Sr 损失约为 15%，由此我们得出结论，从碳酸盐沉积物到上覆海洋的 Sr 通量约为河流 Sr 通量的 15%。我们还表明，成岩 Sr 通量的同位素组成始终非常接近同期海水值，因此该通量在决定海水 Sr 同位素组成的总体 Sr 预算中起着非常小的作用。我们计算的成岩作用导致散装碳酸盐的 Sr 损失范围太小，无法解释中上层碳酸盐中 Sr 含量随年龄变化的典型下降（在前 100 m.y. 中约 70%）。我们的结论是，这种减少不是成岩作用的结果，并且一定涉及海洋本身的某些变化。
We have used a diffusion-advection-reaction model for Sr exchange during deep-sea carbonate diagenesis to determine the rate and consequences of Sr exchange between porewaters and bulk carbonate at six DSDP sites (590B, 575, 593, 516, 305 and 289) where the required Sr concentration and isotopic composition data for the interstitial waters are available from the literature. The model can reproduce both the Sr2+and87Sr/86Sr profiles in the porewaters at each of the sites by adjusting the rate of Sr exchange due to solution-reprecipitation as a function of sediment age. We find that the rate of solution-reprecipitation at all of the sites is highest for the youngest sediment (1–10%/m.y.) and decreases by about an order of magnitude over the first 10 m.y. of sediment age. The effect of this exchange on the properties of the bulk carbonate is to reduce the Sr content by 5–25%, depending primarily on the sedimentation rate, and shift the87Sr/86Sr by as much as 0.00004 from the value the sediment had when first deposited. Isotopic shifts of this magnitude are large compared to present analytical uncertainties and therefore should be corrected for when using bulk carbonate87Sr/86Sr for stratigraphic correlation. The average Sr loss in the carbonate sections studied is about 15%, from which we conclude that the Sr flux from carbonate sediments to the overlying ocean is of the order of 15% of the riverine Sr flux. We also show that the isotopic composition of the diagenetic Sr flux is at all times quite close to the contemporaneous seawater value and therefore this flux plays a very minor role in the overall Sr budget that determines the Sr isotopic composition of seawater. The range of Sr losses from bulk carbonate due to diagenesis that we calculate is too small to account for the typical decrease in Sr content seen in pelagic carbonates as a function of age (about 70% over the first 100 m.y.). We conclude that this decrease is not the result of diagenesis and must involve some changing property of the ocean itself.