CHARACTERIZATION OF RECENT SEDIMENTARY DEPOSITS FROM THE UPPER PORTION OF THE MARAJÓ BAY (EASTERN MARGIN OF PÁRA RIVER, AMAZONIA)

Abstract

This study aims at characterizing the distribution of bottom surface sediments in the lower course of Pará river, more precisely in the area of influence of the Vila do Conde Port, Barcarena region, state of Pará. Based on the available bathymetric map, a grid of 254 points was established for collecting bottom surface sediments. The samples were then submitted to classical particle size analysis (sieving and centrifugation) to enable textural characterization, and were analyzed for grain size distribution and organic matter. The chart of bottom sediment distribution shows a dominance of litoclastic medium sand, and litoclastic sand with gravel. The distribution of bottom sediments is closely related to the bottom morphology and indicates high to very high hydrodynamic conditions for this area. The poorlyselected, medium, coarse and very coarse sands with gravel occur in the channel to the Port of Vila do Conde, characterizing it as the sector of highest hydrodynamic energy. Other areas of deposition of coarse sediments correspond to the river banks associated with sediment input due to erosive action. The northern portion of the study area features the highest percentages of organic matter, which would be closely related to the higher adsorption capacity of its muddy sediments. The contribution of organic matter is mainly due to the local input of vegetation from floodplain areas, and secondarily to organic debris from the urban area of Vila dos Cabanos. The relevance of this study is to portrait the current sedimentological features of Vila do Conde Port area for future comparison with eventual changes related to natural and/or anthropogenic variants, due to recurrent industrial and port activities in the area.