Abstract Phytolith analysis has become a useful tool for paleoenvironmental studies. Phytoliths are produced by plants and are composed of biogenic silica, giving them higher resistance to diagenetic and oxidation processes that commonly occur in tropical sediments. Here, we analyzed the preserved phytolith assemblages in a sedimentary core recovered from an island in the Upper Parana River. Deposition and preservation of distinctive phytoliths of different vegetation types in the sedimentary facies have provided evidence of the formation of the fluvial island and the floral succession since the Late Pleistocene. Three distinctive phases were described in the island formation. The sandy base (Sr facies) of the core (240 cm) was dated to 14,620 cal yr BP. Most phytoliths in this phase were characteristic of the Podostemaceae family -- aquatic plants adapted to intense water flow. At 97 cm depth, organic sedimentary facies (Fm facies) were dated to 7382 cal yr BP. At this phase, the phytolith assemblage is composed mainly of parallelepipedal bulliform, cuneiform bulliform, and elongate psilate; such morphotypes are primarily produced by grasses. Towards the core top is a layer of massive fine sediments (Vm facies) with greater abundance of plant fragments. The assemblage is composed of short cells, predominantly the bilobate morphotype, which is characteristic of the Panicoideae subfamily (Poaceae) and indicative of soil humidity.

中文翻译：

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植硅体表明与巴西上巴拉那河古岛湖相分析相关的环境变化

摘要 植硅体分析已成为古环境研究的有用工具。植硅体由植物产生，由生物二氧化硅组成，使它们对热带沉积物中常见的成岩和氧化过程具有更高的抵抗力。在这里，我们分析了从上巴拉那河的一个岛屿回收的沉积岩心中保存下来的植硅体组合。沉积相中不同植被类型的独特植硅体的沉积和保存为晚更新世以来河流岛屿和花序的形成提供了证据。在岛屿形成过程中描述了三个不同的阶段。岩心（240 cm）的砂质基底（Sr 相）的年代为 14,620 cal yr BP。这个阶段的大多数植硅体是Podostemaceae科的特征——适应强烈水流的水生植物。在 97 cm 深度处，有机沉积相（Fm 相）的年代为 7382 cal yr BP。在这一阶段，植硅体组合主要由平行六面体大泡状、楔形大泡状和细长的甲状体组成；这种形态类型主要由草产生。靠近核心顶部的是一层具有更多植物碎片的块状细粒沉积物（Vm 相）。该组合由短细胞组成，主要是双叶形形态，这是 Panicoideae 亚科（禾本科）的特征并指示土壤湿度。植硅体组合主要由平行六面体大泡状、楔形大泡状和细长的甲壳状体组成；这种形态类型主要由草产生。靠近核心顶部的是一层具有更多植物碎片的块状细粒沉积物（Vm 相）。该组合由短细胞组成，主要是双叶形形态，这是 Panicoideae 亚科（禾本科）的特征并指示土壤湿度。植硅体组合主要由平行六面体大泡状、楔形大泡状和细长的甲壳状体组成；这种形态类型主要由草产生。靠近核心顶部的是一层具有更多植物碎片的块状细粒沉积物（Vm 相）。该组合由短细胞组成，主要是双叶形形态，这是 Panicoideae 亚科（禾本科）的特征并指示土壤湿度。