Neogene-Quaternary sedimentary and paleovegetation history of the eastern Solimoes Basin, central Amazon region

摘要

Palynological and stratigraphical analyses were carried out on the outcrops of the Solimoes River to present new information about freshwater paleoenvironments of a fluvial-deltaic and meandering river system, evaluate the vegetation changes in the upper Solimoes and Ica Formations in the eastern Solimoes Basin, and the role of the Purus Arc in the evolution of central Amazon during the upper Neogene. The upper Miocene to Pliocene Solimoes Formation is related to a fluvial-deltaic system, with finegrained sediments of the prodelta-lacustrine environment supplied by meandering distributaries and delta front environment. The lake and distributaries were surrounded by extensive deltaic and floodplains colonized by lowland freshwater forests under wet climate conditions, persisting until the Pliocene. The lea Formation started to deposit unconformably on the Solimoes Formation during the Pleistocene, following the development of extensive meandering channels surrounded by floodplains of an essentially fluvial system linked to development of the present eastward direction of the Amazon River until the Atlantic coast. These floodplains were colonized by few palm species and pteridophytes of lowland freshwater forests during the Pleistocene. Additionally, no algae and fungi were observed, which may be related to drier climate conditions and/or different morphological conditions than the upper Solimoes Formation.