南海礁区大型底栖有孔虫Mg/Ca值微区分布及其应用潜力  

IN-SITU MG/CA MICROANALYSIS IN LARGER BENTHIC FORAMINIFERA FROM THE SOUTH CHINA SEA REEF REGION AND THEIR APPLICATION POTENTIAL

作　　者：黄晓婷 李玫 吴司琪 HUANG Xiaoting;LI Mei;WU Siqi(Guangxi Laboratory on the Study of Coral Reefs in the South China Sea,Guangxi University,Nanning 530004,China)

机构地区：[1]广西南海珊瑚礁研究重点实验室,南宁530004

出　　处：《微体古生物学报(中英文)》2025年第1期58-70,共13页Acta Micropalaeontologica Sinica

基　　金：国家自然科学青年科学基金项目(42402007);广西自然科学基金项目(2024GXNSFBA010231)。

摘　　要：生物碳酸盐Mg/Ca值是古水温的重要指标。然而作为珊瑚礁区沉积物重要组成部分的大型底栖有孔虫(LBF),其Mg/Ca指标的应用受到诸多限制。为探究礁区LBF Mg/Ca值在海水古温度重建方面的应用潜力,本研究使用微区分析方法,深入探讨了西沙群岛永乐环礁表层沉积物中两种有孔虫Amphistegina lobifera和Amphistegina lessonii壳内Mg/Ca值的分布规律,同时,比较了两种微区方法——电子探针(EPMA)和激光剥蚀电感耦合等离子质谱(LA-ICP-MS)的差异。另外,为了探究成岩作用对有孔虫Mg/Ca值的影响,选取永乐环礁羚羊礁及琛航岛岩心中的A.lobifera进行了测试。结果表明,两种LBF的Mg/Ca值展现出了极为相似的分布特征,沿着生长方向均呈现出清晰的周期性分布模式,这与初级和次级方解石层的交替生长有关,但二者的Mg/Ca值在次级方解石层边缘的变化模式略有不同。结合壳内分布规律及两种微区方法的差异,发现尽管有孔虫的Mg/Ca值受到初级方解石层影响,但通过选择合适的微区原位分析方法和打点位置,仍然具有反映海水温度变化的潜力。成岩作用对岩心深处有孔虫Mg/Ca值的影响不容忽视,实际应用时需加以考虑。通过与现代表层沉积物同种有孔虫的Mg/Ca值范围对比,同时结合扫描电镜观察结果,可以判断成岩作用影响程度。The Mg/Ca ratio in biogenic carbonates serves as a key indicator for paleotemperature reconstruction.However,the application of Mg/Ca ratio of larger benthic foraminifera(LBF),an important component of sediments in coral reef regions,is limited by various factors.To explore the application potential of Mg/Ca ratio in reef-dwelling LBF as a paleotemperature proxy,the intratest variation of Mg/Ca ratios of Amphistegina lobifera and Amphistegina lessonii obtained from the surface sediments of the Yongle Atoll in Xisha Islands was thoroughly investigated.Additionally,the differences between two methods[Electron Probe Microanalysis(EPMA)and Laser Ablation Inductively Coupled Plasma Mass Spectrometry(LA-ICP-MS)]were discussed.Furthermore,to examine the influence of diagenesis,the Mg/Ca ratios of A.lobifera from downcore samples of the Lingyang reef and the Chenhang Island in the Yongle Atoll were also analyzed.The results show that the Mg/Ca distributions of the two species exhibit notable similarities,both displaying a distinct periodic pattern along the growth direction,which is related to the alternate growth of primary and secondary calcite layers.However,the shifting trends in two species are slightly different near the edge of the secondary calcite layer.Combining the intratest distribution pattern and the differences between the two methods,it can be inferred that despite the influence of the primary calcite,the potential to reflect paleotemperature remains valid by selecting appropriate analytical methods and positions.The influence of diagenesis on the Mg/Ca ratio of downcore samples cannot be ignored and should be taken into account in applications.By comparing the Mg/Ca range with modern samples,and a thorough observation using scanning electron microscope,the extent of diagenetic influence can be assessed.

关 键 词：大型底栖有孔虫 Mg/Ca指标 原位微区分析 古温度 永乐环礁 

分 类 号：P736.4[天文地球—海洋地质] P736.2[天文地球—海洋科学]