Miocene Palynology of the Solimões Formation (Well 1-AS-105-AM), Western Brazilian Amazonia

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.