Variações Morfodinâmicas e Sedimentológicas Sazonais e Exoscopia de Grãos de Quartzo na Praia do Atalaia, Salinópolis, Pará, Brasil

Abstract

This work is a contribution to the knowledge of the actual beach dynamics in Pará, taking as example the Atalaia beach, municipality of Salinópolis, being supported by recent bibliography and the Atlas of Surface 41 of Quartz Grains, by W. Mahaney (2002). Atalaia beach is dissipative (SHORT, 2003), exposed to moderate to high waves, with low slope and having a wide surf zone. The beach profiling showed seasonal variations, with sand input and output. Samples were collected during rainy and dry periods in the eastern sector (At1) in the infratidal, intertidal and supratidal parts. The granulometry of 12 samples revealed very fine to fine (0.062 mm and 0.125 mm), quartz, unimodal, moderately selected, and positively asymmetric sands. The SEM analysis showed that the quartz grains of the intertidal zone are generally rounded, shiny and with V-shaped marks (reminiscent of water action), containing micro-textures of weathering, while the sands of the supratidal zone are partially formed by rounded and matte grains, with mechanical marks (conchoidal fractures, shock marks, striations, elongated depressions ...), characteristic of aeolian action, in addition to abundant chemical dissolution marks. However, the study of geomorphological processes (marine, aeolian, fluvial) still needs much more work before it is possible to hypothesize about the origin of the sands.