Miocene paleoenvironments and paleoclimatic reconstructions based on the palynology of the Solimões Formation of Western Amazonia (Brazil)

Abstract

The Neogene was a critical interval in the establishment of the modern geography and biotic composition of Amazonia. Because the region is covered with rainforest vegetation and lacks extensive outcrops, most of the understanding of its geological and evolutionary history relies on the study of rock cores. We studied the Miocene paleoenvironments and paleoclimate of borehole 1-AS-15-AM, drilled in western Amazonia, by analyzing the palynological content of 107 samples from the Solimões Formation. Graphic correlation indicates that the borehole spans palynological zones T13 to T16 (middle to late Miocene). We found 342 morphospecies of pollen and spores, including 280 angiosperm taxa and 62 pteridophyte taxa. Sixteen new species are described: 12 angiosperms and four pteridophytes. Pollen counts are dominated by elements associated with aquatic grasses, palms and ferns that can be associated with the Pebas ecosystem. We also found 11 morphospecies of dinoflagellate cysts and microforaminiferal linings between 115.4 m and 118.95 m that correlate with the middle Miocene marine flooding event of western Amazonia. Average Miocene temperature was estimated to be 24.9 °C (min = 14.40, max = 27.30) while precipitation was 1946 mm/y (min = 1,080, max = 3000), not significantly different from Holocene estimates.

Keywords:

• Amazonia
• Miocene
• systematics
• paleoenvironments
• graphic correlation
• marine flooding

Acknowledgements

The authors thank the reviewers for their suggestions and corrections that improved the first version of the manuscript; the Instituto Nacional de Pesquisas da Amazônia and Universidade Federal do Mato Grosso where this research was developed; the Departamento Nacional de Prospecção Mineral (DNPM) and Companhia de Pesquisas em Recursos Minerais (CPRM) for allowing the collection of sediment samples from well 1AS-15-AM; Damian Cárdenas for his help in the identification of dinoflagellate cysts and Cristian Camilo Solano for his help in the identification of acritarchs; the Smithsonian Tropical Research Institute for a research fellowship to Bianca T. Gomes; the Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) for a Produtividade em Pesquisa grant to Maria L. Absy (Proc. 308425/2016-2); and the Coordenação de Aperfeiçoamento de Pessoal em Nível Superior (CAPES) and CNPq for grants to Carlos D’Apolito (CAPES BEX 0376/12-4 and CNPq 150247/2020-6).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) [under grant numbers 308425/2016-2 and 50247/2020-6].