Compositional and diversity comparisons between the palynological records of the Neogene (Solimões Formation) and Holocene sediments of Western Amazonia

Western Amazonia underwent dramatic changes in its landscape and environments during the Neogene, which led to its extant, hyperdiverse, tropical rainforest. Although the palynological fossil record has been the most useful proxy for understanding the history of the Amazonian biome, the floristic composition and diversity of the Neogene and the present Amazonian environments have never been thoroughly compared. In this work, we present preliminary comparisons of the pollen content of a Miocene core from the Solimões Formation in western Amazonia (Brazil) with the pollen content of Holocene sediments from flooded environments (várzeas and lake margins) near the Miocene site. We found a total of 463 pollen and spore types (Miocene, <i>n</i> = 284; Holocene, <i>n</i> = 231), only 52 of which were shared. The Holocene flooding environments displayed distinct palynological signals; both the Holocene and Miocene palynofloras have pollen primarily sourced from the local, flooded environments, with no significant differences in within-sample pollen diversity. The Holocene palynoflora was more heterogeneous in composition than the Miocene palynoflora, probably because the Miocene wetlands (the Pebas System) were highly homogeneous at a continental scale, far more than modern western Amazonia, thus implying that the spatial vegetation turnover was much lower than in modern ecosystems.

西亚马孙（Western Amazonia）在新近纪（Neogene）期间经历了景观与环境的剧烈变革，最终形成了现存的超多样化热带雨林。尽管孢粉化石记录（palynological fossil record）是解析亚马孙生物群系（Amazonian biome）演化历史的最实用代用指标，但学界始终未对中新世（Miocene）与现代亚马孙环境的植物区系组成及多样性开展全面对比。本研究对取自巴西西亚马孙地区索利蒙伊斯组（Solimões Formation）的一枚中新世岩芯的孢粉组分，与该中新世遗址附近全新世（Holocene）泛滥环境（瓦尔泽亚（várzeas）与湖岸）沉积物的孢粉组分进行了初步对比。本研究共识别出463种花粉与孢子类型：中新世样品含284种（n=284），全新世样品含231种（n=231），其中仅52种为两类样品共享。全新世泛滥环境展现出独特的孢粉信号；两类样品的孢粉植物群（palynofloras）均主要源自局地泛滥环境，且样内花粉多样性无显著差异。全新世孢粉植物群的组成异质性强于中新世孢粉植物群，这可能是因为中新世湿地（佩巴斯系统（Pebas System））在大陆尺度上具有高度均一性，远超现代西亚马孙地区，由此表明当时的空间植被更替率远低于现代生态系统。