Fluviomarine processes associated with the genesis of Rasa island, south of Marapatá Bay, northeastern Pará, Brazil

Abstract

The islands take on significant prominence in the estuarine landscape of Pará State, although most of them present unclearly defined genesis. In order to investigate the formation factors of Rasa Island, located at the mouth of Tocantins, estuary of the Pará River, the present work is based on sedimentary features, identified in the sediment core taken by a Russian Sampler from a fluviomarine plain. In this study, the faciologic analysis and interpretation of sedimentary environments, in association with climatic events reported to the region, supported the proposition of a morphogenetic model. The model proposed here suggests that Rasa Island has late Holocene age and consisted of sandy bars that evolved under the effect of fluvial processes, inherent to the drainage basin, and coast processes articulated to sea-level changes and climate changes. These processes affected the sediment supply and distribution of vegetation cover, influencing the estuarine sector and contributing to the formation of proximal islands.

Keywords: sandy bars; estuary; relative sea level; sedimentary environment; Tocantins river.