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

Abstract

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, n = 284; Holocene, n = 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.