During the Miocene (23.03 to 5.33 Ma), western Amazonia experienced major changes in its geography and biodiversity as a response to Andean uplift. To better understand these changes, the palynology of the Solimões Formation (NW Brazil) is presented with the objective of providing age control, and establishing palaeoenvironments and pollen richness within the framework of geological and climatic events. The ninety-five palynological samples yield 491 palynomorphs, of which 76 pollen and 25 spores are new. Correlation with a nearby calibrated biozonation resulted in ages from 18.7 to 10.7 Ma (late early to earliest-late Miocene). The pollen associations are typical of Amazonian humid forests, with abundant palms, Bombacoideae, trees and grasses, and lack diverse and abundant herbs or dry forest indicators. Spikes in algae and dinoflagellates show phases of lake development and two marine incursions – one between 18.4 and 17.8 Ma, and another between 14.1 and 13.7 Ma. Statistical analyses of the data show inundations had no effect in the vegetation composition. Estimates of diversity using different metrics clearly show a diversity increase and community change at ca. 16 Ma, independent of lithofacies. This change is driven by the Middle Miocene Climatic Optimum and not correlated with any of the marine incursions. Altogether, the results bring more detail to the environmental history of western Amazonia, establishing two inundation events and furthering the climate diversification relationship in Neotropical biomes into the Miocene period
