During the Miocene, Andean tectonism caused
the development of a vast wetland across western Amazonia. Palynological
studies have been the main source of chronological and paleobotanical
information for this region, including several boreholes in the Solimões Formation in western Brazilian Amazonia. Here,
a palynological study of well core 1-AS-105-AM drilled in Tabatinga (Amazonas,
Brazil) is presented: 91 new taxa are erected (25 spores and 66 pollen,
including one new genus), 16 new combinations are proposed, and a list of botanical/ecological
affinities is updated. We recorded 23,880 palynomorphs distributed in 401
different types. Among pollen and spores, 62 extant families and 99 extant
genera were identified, which accounts for 39% and 30% of known botanical
affinities to the family and genus level, respectively. Individual samples have
pollen/spore counts with approximately 25% to 95% of known affinities to the
family level. Pollen associations are sourced primarily from the wetland
environments and to a minor extent from nonflooded forests. Palynological
diversity analyses indicate an increase from the early to the middle/early late
Miocene in core 1-AS-105-AM. Probable scenarios to explain this diversity
increase include a higher degree of environmental complexity from the middle
Miocene onwards, that is, a more heterogeneous riverscape, including broader
extensions of nonflooded forests, as opposed to the swamp-dominated early
Miocene. Additionally, the positive effects of the Miocene Climatic Optimum on
plant richness could explain the increase in pollen richness. We posit
hypotheses of forest diversification that can be tested as more botanical
affinities are established along with a longer Miocene record.