Dados da Submissão

Título

GENESIS AND DEVELOPMENT OF THE NEGRO RIA, AMAZON RIVER BASIN

Texto do resumo

Fluvial rias are striking lake-like features of the Amazon Basin landscape.
Formed during the inundation of river valleys by rising sea levels during
interglacial periods, they register and offer key insights into environmental
changes of the last millennia. Discussions about Amazonian fluvial rias often
focus on the influence of sea-level change and tectonics in their formation, as
well as on aspects related to their morphology and sedimentation patterns.
However, few comprehensive efforts have aimed at understanding how major
changes in the Amazon River discharge may have affected sedimentation in
fluvial rias. In this study, we compared the chronology and major elements
distribution of three sediment cores obtained from the Negro Ria to investigate
factors contributing to major sedimentary changes at the lowermost Negro
River. Results were interpreted with the aid of endmember unmixing models
and principal component analysis and compared to data from other Amazonian
fluvial rias and floodplain lakes. Si/Al and Ti/Fe ratios show a significant and
synchronous decrease in grain size in the studied area after approximately 5.5
ka. We interpret this as the onset of the low-energy environment in the lower
Negro River that we observe today. Multivariate analysis and literature data
suggest that this shift may not necessarily be driven solely by environmental
changes in the Negro River Basin itself. Instead, it may primarily respond to
broader regional factors, possibly related to changes in Amazon River
discharge linked to precipitation in the western Amazon Basin. By integrating
our results with the chronology and geochemical profiles of other sediment
records, as well as with paleoclimate reconstructions, we aim to identify major
regional factors influencing fluvial rias across the Amazon Basin.

Palavras Chave

Negro River; Holocene; Fluvial Rias