Variability of carbonate diagenesis in equatorial Pacific sediments deduced from radiogenic and stable Sr isotopes
Variability of carbonate diagenesis in equatorial Pacific sediments deduced from radiogenic and stable Sr isotopes
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从放射成因和稳定锶同位素推断赤道太平洋沉积物中碳酸盐岩成岩作用的变化
DOI：
10.1016/j.gca.2014.10.001
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发表时间：
2015
影响因子：
5
通讯作者：
Eisenhauer A.
中科院分区：
文献类型：
--
作者：
Voigt J;Hathorne E. C;Frank M;Vollstaedt H.;Eisenhauer A.
碳酸盐沉积物的重结晶（溶解-沉淀）已被成功地模拟，以解释在全球海洋的不同位置的孔隙水Sr浓度和放射成因Sr同位素组成的配置文件。然而，很少有系统的研究试图更好地了解影响碳酸盐重结晶变异性的因素的相对重要性。在这里，我们提出了一个多组分的研究结果，从综合大洋钻探计划（IODP）远征320/321太平洋赤道年龄样带（PEAT），在类似的初始组成的沉积物已受到不同的成岩history.The PEAT网站调查显示可变的孔隙水Sr浓度梯度最大的梯度在最年轻的网站的沉积物重结晶。放射成因Sr同位素表明，重结晶相对较快，与其他沉积柱的建模一致，因为87 Sr/86 Sr比值与同期海水87 Sr/86 Sr比值无法区分（在2σ不确定度内）。散装碳酸盐沥滤液和相关的孔隙沃茨的站点U1336有较低的87 Sr/86 Sr比同期海水沉积年龄大于20.2 Ma的最有可能导致从旧重结晶碳酸盐的Sr向上扩散。在102.5 rmcd（修正后的复合深度）以下，U1336站点的重结晶似乎仍在进行，这表明重结晶处于后期阶段。此外，较低的Sr/Ca比的散装碳酸盐的站点U1336相比，其他PEAT网站建议更广泛的成岩蚀变较少的Sr被纳入次生方解石。与其他PEAT地点相比，U1336推断具有更大的热梯度和更高的碳酸盐含量。在这项研究中，我们首次研究了富含碳酸盐的深海沉积物的稳定Sr同位素。孔隙水δ88/86 Sr随深度增加（从0.428‰到0.700‰），记录了重结晶过程中的同位素分馏过程。次生方解石优先结合较轻的Sr同位素（86 Sr），使孔隙沃茨同位素较重。碳酸盐岩本身的δ88/86 Sr值显示出更均匀的值，没有可检测到的随深度的变化。碳酸盐岩的Sr含量和总Sr存量比孔隙沃茨高得多，这意味着孔隙沃茨比碳酸盐岩对分馏过程更敏感。δ88/86 Sr结果表明，孔隙水稳定Sr同位素具有指示碳酸盐沉积物重结晶作用的潜力。
The recrystallisation (dissolution–precipitation) of carbonate sediments has been successfully modelled to explain profiles of pore water Sr concentration and radiogenic Sr isotope composition at different locations of the global ocean. However, there have been few systematic studies trying to better understand the relative importance of factors influencing the variability of carbonate recrystallisation. Here we present results from a multi-component study of recrystallisation in sediments from the Integrated Ocean Drilling Program (IODP) Expedition 320/321 Pacific Equatorial Age Transect (PEAT), where sediments of similar initial composition have been subjected to different diagenetic histories.The PEAT sites investigated exhibit variable pore water Sr concentrations gradients with the largest gradients in the youngest sites. Radiogenic Sr isotopes suggest recrystallisation was relative rapid, consistent with modelling of other sediment columns, as the87Sr/86Sr ratios are indistinguishable (within 2σ uncertainties) from contemporaneous seawater87Sr/86Sr ratios. Bulk carbonate leachates and associated pore waters of Site U1336 have lower87Sr/86Sr ratios than contemporaneous seawater in sediments older than 20.2 Ma most likely resulting from the upward diffusion of Sr from older recrystallised carbonates. It seems that recrystallisation at Site U1336 may still be on-going at depths below 102.5 rmcd (revised metres composite depth) suggesting a late phase of recrystallisation. Furthermore, the lower Sr/Ca ratios of bulk carbonates of Site U1336 compared to the other PEAT sites suggest more extensive diagenetic alteration as less Sr is incorporated into secondary calcite. Compared to the other PEAT sites, U1336 has an inferred greater thermal gradient and a higher carbonate content. The enhanced thermal gradient seems to have made these sediments more reactive and enhanced recrystallisation.In this study we investigate stable Sr isotopes from carbonate-rich deep sea sediments for the first time. Pore water δ88/86Sr increases with depth (from 0.428‰ to values reaching up to 0.700‰) at Site U1336 documenting an isotope fractionation process during recrystallisation. Secondary calcite preferentially incorporates the lighter Sr isotope (86Sr) leaving pore waters isotopically heavy. The δ88/86Sr values of the carbonates themselves show more uniform values with no detectable change with depth. Carbonates have a much higher Sr content and total Sr inventory than the pore waters meaning pore waters are much more sensitive to fractionation processes than the carbonates. The δ88/86Sr results indicate that pore water stable Sr isotopes have the potential to indicate the recrystallisation of carbonate sediments.
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DOI：
--
发表时间：
2006
期刊：
影响因子：
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DOI：
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2000
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修订了复合深度尺度以及 IODP 站点 U1331-U1334 和 ODP 站点 1218-1220 的集成
DOI：
10.2204/iodp.proc.320321.201.2012
发表时间：
2012
期刊：
影响因子：
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作者：
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通讯作者：
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影响因子：
3.9
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