Miller Ana Z, De la Rosa José M, Jiménez-Morillo Nicasio T, Pereira Manuel F C, González-Pérez José A, Calaforra José M, Saiz-Jimenez Cesareo
Instituto de Recursos Naturales y Agrobiología de Sevilla, Consejo Superior de Investigaciones Científicas (IRNAS-CSIC), Av. Reina Mercedes 10, 41012, Sevilla, Spain.
Instituto de Recursos Naturales y Agrobiología de Sevilla, Consejo Superior de Investigaciones Científicas (IRNAS-CSIC), Av. Reina Mercedes 10, 41012, Sevilla, Spain.
J Chromatogr A. 2016 Aug 26;1461:144-52. doi: 10.1016/j.chroma.2016.07.038. Epub 2016 Jul 16.
This study comprises an innovative approach based on the combination of chromatography (analytical pyrolysis and pyrolysis compound-specific isotope analysis (Py-CSIA)), light stable isotopes, microscopy and mineralogy analyses to characterize the internal layering of coralloid speleothems from the Ana Heva lava tube in Easter Island (Chile). This multidisciplinary proxy showed that the speleothems consist of banded siliceous materials of low crystallinity with different mineralogical compositions and a significant contribution of organic carbon. Opal-A constitutes the outermost grey layer of the coralloids, whereas calcite and amorphous Mg hydrate silicate are the major components of the inner whitish and honey-brown layers, respectively. The differences found in the mineralogical, elemental, molecular and isotopic composition of these distinct coloured layers are related to environmental changes during speleothem development. Stable isotopes and analytical pyrolysis suggested alterations in the water regime, pointing to wetter conditions during the formation of the Ca-rich layer and a possible increase in the amount of water dripping into the cave. The trend observed for δ(15)N values suggested an increase in the average temperature over time, which is consistent with the so-called climate warming during the Holocene. The pyrolysis compound-specific isotope analysis of each speleothem layer showed a similar trend with the bulk δ(13)C values pointing to the appropriateness of direct Py-CSIA in paleoenvironmental studies. The δ(13)C values for n-alkanes reinforced the occurrence of a drastic environmental change, indicating that the outermost Opal layer was developed under drier and more arid environmental conditions.
本研究采用了一种创新方法，将色谱法（分析热解和热解化合物特定同位素分析（Py-CSIA））、轻稳定同位素、显微镜和矿物学分析相结合，以表征智利复活节岛阿纳赫瓦熔岩管中珊瑚状石笋的内部层理。这种多学科代理方法表明，石笋由结晶度低的带状硅质材料组成，具有不同的矿物成分和大量有机碳。蛋白石-A构成了珊瑚状石笋最外层的灰色层，而方解石和无定形镁水合硅酸盐分别是内部白色和蜜棕色层的主要成分。这些不同颜色层在矿物学、元素、分子和同位素组成上的差异与石笋形成过程中的环境变化有关。稳定同位素和分析热解表明水分状况发生了变化，表明富含钙的层形成期间气候更湿润，滴入洞穴的水量可能增加。观察到的δ(15)N值趋势表明平均温度随时间升高，这与全新世所谓的气候变暖一致。对每个石笋层进行的热解化合物特定同位素分析显示出与整体δ(13)C值相似的趋势，表明直接Py-CSIA在古环境研究中的适用性。正构烷烃的δ(13)C值强化了剧烈环境变化的发生，表明最外层的蛋白石层是在更干燥和干旱的环境条件下形成的。
