The ikaite to calcite transformation: implications for palaeoclimate studies
The ikaite to calcite transformation: implications for palaeoclimate studies
复制标题
伊卡石到方解石的转变：对古气候研究的影响
DOI：
10.1016/j.gca.2022.08.001
复制
发表时间：
2022
影响因子：
5
通讯作者：
C. Korte
中科院分区：
文献类型：
--
作者：
Madeleine L. Vickers;Martin Vickers;R. Rickaby;Hanxiao Wu;S. Bernasconi;C. Ullmann;G. Bohrmann;R. Spielhagen;H. Kassens;Bo Pagh Schultz;C. Alwmark;N. Thibault;C. Korte
海相沉积伊凯石是绿泥石的母矿物，在地质记录中发现的星状假象大多由方解石组成。众所周知，Ikaite在地球表面的温度和压力下是亚稳定的，当暴露在温暖的(环境)条件下时，很容易分解成更稳定的碳酸盐多晶型。然而，伊开石转化为方解石的过程尚不清楚，关于地质记录中绿泥石的古气候意义也存在持续的争论。这项研究采用多种技术相结合的方法，在伊卡石生长介质之外考察了伊卡石分解为方解石的过程，并评估了伊卡石来源的方解石的稳定和块状同位素组成的古气候和古环境意义。粉末X-射线衍射表明，在空气中加热时，伊卡石经历了准固态转变为方解石，但当在高温差下转变时，伊卡石结构水也可能发生轻微的溶解-再结晶。在生成的方解石中没有观察到显著的转变温度的同位素平衡。因此，在伊卡石在空气中发生转化的情况下，可以用团块稳定同位素测温法重建伊卡石的生长温度。在古绿泥岩的例子中，伊开石在未知的时间尺度上与寄主沉积物的间隙水接触时发生了转变，因此不确定重建的团块同位素温度是否反映了伊开石的结晶或其转变温度。然而，块状稳定同位素测温法仍然可以保守地估计底水温度的上限。此外，稳定同位素以及元素/钙比值揭示了伊卡石生长的化学环境。我们的数据表明，在不同的海洋沉积地点，一系列(生物)地球化学过程可能促进了伊卡石的形成，包括细菌硫酸盐还原和甲烷的厌氧氧化。伊开石的颜色从浅棕色到深棕色，表明有机质含量很高，有利于细菌硫酸盐还原的高速率作为伊开石沉淀的主要驱动力。在最不稳定的伊卡石中发现了最高的镁钙比，表明镁对伊卡石结构起到了破坏作用。
Marine sedimentary ikaite is the parent mineral to glendonite, stellate pseudomorphs found throughout the geological record which are most usually composed of calcite. Ikaite is known to be metastable at earth surface temperatures and pressures, readily breaking down to more stable carbonate polymorphs when exposed to warm (ambient) conditions. Yet the process of transformation of ikaite to calcite is not well understood, and there is an ongoing debate as to the palaeoclimatic significance of glendonites in the geological record. This study uses a combination of techniques to examine the breakdown of ikaite to calcite, outside of the ikaite growth medium, and to assess the palaeoclimatic and palaeoenvironmental significance of stable and clumped isotope compositions of ikaite-derived calcite. Powder X-ray diffraction shows that ikaite undergoes a quasi- solid-state transformation to calcite during heating of samples in air, yet when ikaite transforms under a high temperature differential, minor dissolution-recrystallisation may also occur with the ikaite structural waters. No significant isotopic equilibration to transformation temperature is observed in the resulting calcite. Therefore, in cases of transformation of ikaite in air, clumped and stable isotope thermometry can be used to reconstruct ikaite growth temperatures. In the case of ancient glendonites, where transformation of the ikaite occurred in contact with the interstitial waters of the host sediments over unknown timescales, it is uncertain whether the reconstructed clumped isotope temperatures reflect ikaite crystallisation or its transformation temperatures. Yet clumped and stable isotope thermometry may still be used conservatively to estimate an upper limit for bottom water temperatures.Furthermore, stable isotope along with element/Ca ratios shed light on the chemical environment of ikaite growth. Our data indicate that a range of (bio)geochemical processes may act to promote ikaite formation at different marine sedimentary sites, including bacterial sulphate reduction and anaerobic oxidation of methane. The colours of the ikaites, from light brown to dark brown, indicate a high organic matter content, favouring high rates of bacterial sulphate reduction as the main driver of ikaite precipitation. Highest Mg/Ca ratios are found in the most unstable ikaites, indicating that Mg acts to destabilise ikaite structure.
水钙石 (CaCO3·6H2O) 沉淀随 pH、盐度、温度和磷酸盐浓度变化的实验室研究
影响因子：
3
作者：
Wolf-Gladrow;Dieckmann;Völker;Nehrke
通讯作者：
Nehrke
DOI：
10.1016/j.palaeo.2009.04.012
发表时间：
2009-07
期刊：
Palaeogeography, Palaeoclimatology, Palaeoecology
影响因子：
--
作者：
R. Spielhagen;A. Tripati
通讯作者：
R. Spielhagen;A. Tripati
托阿尔西亚海洋缺氧事件的温暖余辉推动了深度适应腕足动物的成功
影响因子：
4.6
作者：
Ullmann;Duarte;Hesselbo;Kasemann;Lenton;Piazza;Aberhan
通讯作者：
Aberhan