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.

亚马逊西部（Western Amazonia）在新近纪（Neogene）期间经历了地貌与环境的剧烈变迁，最终形成了现存的超多样热带雨林。尽管孢粉化石记录（palynological fossil record）是探究亚马孙生物群区（Amazonian biome）演化历史最有效的代用指标，但此前从未有研究对新近纪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。本研究对巴西亚马孙西部索利蒙伊斯组（Solimões Formation）中新世（Miocene）岩芯的孢粉组分，与该中新世遗址周边淹水环境（含瓦尔泽亚泛滥平原（várzeas）及湖岸带）内全新世（Holocene）沉积物的孢粉组分进行了初步对比。本次研究共识别出463种花粉与孢子类型：中新世样本的样本量（*n*）为284，全新世样本的样本量（*n*）为231，其中仅52种为两类样本共有。全新世淹水环境呈现出独特的孢粉信号；两类样本的孢粉植物群（palynofloras）均主要来源于局地淹水环境，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高于中新世孢粉植物群，这可能是因为中新世湿地（佩巴斯水系（Pebas System））在大陆尺度上具有高度均一性，远高于现代亚马孙西部，这意味着当时的植被空间周转速率远低于现代生态系统。