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我国下寒武统底部广泛发育磷结核、磷块岩等富磷沉积,为早寒武世最为重要的化学标志层之一,也代表了隐生宙—显生宙转折期地球表层系统的重大变革。当前对磷来源和富集机制的解释不一。为进一步明确该时期富磷沉积的形成机制,本文利用激光剥蚀电感耦合等离子体质谱联用技术(LA-ICP-MS)对贵州金沙地区牛蹄塘组黑色页岩中的磷结核进行多元素原位微区成像研究。结果表明:磷结核中各元素富集情况清晰地记录了磷结核形成过程中微环境的变化趋势。其中,磷结核内部Ca、P共富集以及Si亏损,指示P富集缘于自生磷灰石生成,P则来自于有机质含氧或厌氧降解释放;Mn、Zn与P共富集于磷结核内部,指示结核形成时的底部水体为含氧水体;As、Mo、V等元素主要富集于围岩或黑色页岩,指示缺氧含H_2S水体形成终止了结核生长。本研究显示,LA-ICP-MS原位多元素成像技术能够获取微区内丰富的地球化学信息,并提供高精度可视化证据,未来将在地质勘探和古环境研究等领域得到更广泛应用。
Phosphorus, Phosphorite and other phosphorus-rich deposits are extensively developed at the bottom of the Lower Cambrian in China, and are one of the most important chemical marker beds in the Early Cambrian. They also represent a significant part of the Earth’s surface system at the turn of the Miocene-Phanerozoic change. The current explanation of sources of phosphorus and enrichment mechanisms is mixed. In order to further clarify the mechanism of formation of phosphorus-rich sediment in this period, a multi-element elemental analysis was performed on the phosphorus nodules in the black shale of Niutitang Formation in Jinsha, Guizhou by using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) Micro-imaging of the area. The results showed that the enrichment of various elements in phosphorus nodules clearly recorded the changing trend of microenvironment during the formation of phosphorus nodules. Among them, Ca and P co-enrichment and Si loss in P-tuberculosis indicated that P enrichment was due to spontaneous apatite and P came from oxygenated or anaerobic degradation of organic matter. Mn, Zn and P co-enriched in phosphorus At the end of tuberculosis, the bottom water body when the tuberculosis was formed was oxygenated water body; elements such as As, Mo, V were mainly enriched in wall rock or black shale, indicating that the formation of H_2S water with hypoxia ended the tuberculosis growth. This study shows that the LA-ICP-MS in situ multi-element imaging technique can obtain abundant geochemical information in micro-regions and provide high-precision visualization evidence. It will be more widely used in geological prospecting and paleoenvironmental research in the future.