Palynology of core 1-AS-20-AM from the Miocene and Quaternary of western Amazonia

The western Amazon landscapes evolved during the Neogene–Quaternary in response to the effects of the Andean orogeny and dynamic topography. During the Miocene, sedimentary basins accumulated hundreds of meters of sediments that harbor the biological history of the region and, consequently, the emergence of the amazonian biome. Palynology is the main source of biostratigraphic and paleobotanical information, its use has allowed placing sedimentary and biological events during the Miocene in a chronological framework. Here, we present palynological data from core 1-AS-20-AM, located in the northeastern portion of the Solimões Basin and exposing the Solimões and Içá formations of Miocene and Pleistocene ages, respectively. Pollen samples were collected throughout the 286 meters of core and processed following standard palynology methods. We report well-known index species from zonation schemes in Colombia and Venezuela, adapted for use in western Amazonia, and place the Solimões Formation in core 1-AS-20-AM into the Middle to Late Miocene. The occurrence of Cyatheacidites annulatus, marker of zone T17, confirms the presence of the latest Miocene in the basin, recorded for the first time in cores. The Içá Formation in core 20AM is only tentatively assigned to zone T18 of Pliocene/ Pleistocene age. We discuss the possibility of a six-million-year hiatus between the formations. Several species are recorded at a topmost extant (Holocene) sample and can serve as calibration for last appearance events. We also detected a Middle Miocene marine incursion along ~60 meters at the bottom of the core. Ten new taxa are erected formally, some of which had been recorded informally elsewhere and will be useful for future biostratigraphic correlations. The new species also document the first occurrences of two plant groups for the Miocene of Amazonia, they are related to Cabomba (Cabombaceae), and Eichhornia/Pontederia (Pontederiaceae). The new data from core 1-AS-20-AM will be key for regional biozonation schemes and analyses of biodiversity emergence.