Revisiting diagenesis on the Ontong Java Plateau: Evidence for authigenic crust precipitation in Globorotalia tumida
Revisiting diagenesis on the Ontong Java Plateau: Evidence for authigenic crust precipitation in Globorotalia tumida
复制标题
重新审视翁通爪哇高原的成岩作用：Globorotalia tumida 自生地壳沉淀的证据
DOI：
10.1002/2014pa002759
复制
发表时间：
2015
期刊：
影响因子：
--
通讯作者：
H. Elderfield
中科院分区：
文献类型：
--
作者：
O. Branson;E. Read;S. Redfern;C. Rau;H. Elderfield
有孔虫的方解石测试在海洋沉积物中存在了数千年至数百万年，然后进行分析以产生微量元素和同位素古代用记录。这些沉积物构成了与试验形成条件不同的物理化学环境。有孔虫方解石在沉积物中的储存可以通过成岩蚀变改变其微量元素和同位素含量，从而有可能混淆其古海洋学解释。先前对赤道太平洋西部Ontong爪爪岛高原的G. tumida的研究发现，高Mg室方解石的优先溶解和低Mg地壳的保存显著降低了整体测试Mg/Ca和Sr/Ca [Brown and Elderfield， 1996]。在这里，我们结合同步x射线计算机断层扫描（sXCT）和电子探针显微分析（EPMA）重新审视这些标本，以重新评估其成岩改变的性质。在sXCT数据中直接观察到高mg方解石随深度的溶解，证实了之前研究的推断。sXCT数据进一步揭示了方解石地壳的化学和结构随深度的不同而变厚。我们认为这些地壳具有成岩成因，是由高镁室方解石的同时溶解和由此产生的改性孔隙水溶液中低镁地壳的沉淀所驱动的。虽然研究的广度受到技术性质的限制，但对有孔虫方解石溶蚀和再沉淀的观察有助于证明两个同时发生的成岩蚀变过程的作用，并对由此产生的古代理信号产生重大影响。
The calcite tests of foraminifera lie in marine sediments for thousands to millions of years, before being analysed to generate trace element and isotope palaeoproxy records. These sediments constitute a distinct physio-chemical environment from the conditions in which the tests formed. Storage in sediments can modify the trace element and isotopic content of foraminiferal calcite through diagenetic alteration, which has the potential to confound their palaeoceanographic interpretation. A previous study of G. tumida from the Ontong Java Plateau, western equatorial Pacific, found that preferential dissolution of higher-Mg chamber calcite, and the preservation of a low-Mg crust on the tests significantly reduced whole-test Mg/Ca and Sr/Ca [Brown and Elderfield, 1996]. Here, we revisit these specimens with a combination of synchrotron X-ray computed tomography (sXCT) and electron probe micro-analyses (EPMA) to re-evaluate the nature of their diagenetic alteration. The dissolution of higher-Mg calcite with depth was directly observed in the sXCT data, confirming the inference of the previous study. The sXCT data further reveal a thickening of the chemically and structurally distinct calcite crust with depth. We propose that these crusts have a diagenetic origin, driven by the simultaneous dissolution of high-Mg chamber calcite and precipitation of low-Mg crust from the resulting modified pore-water solution. While the breadth of the study is limited by the nature of the techniques, the observation of both dissolution and re-precipitation of foraminiferal calcite serves to demonstrate the action of two simultaneous diagenetic alteration processes, with significant impacts on the resulting palaeoproxy signals.
影响因子：
5.3
作者：
Elderfield, H.;Yu, J.;Nyland, B.
通讯作者：
Nyland, B.