Caracterização das praias de Navegantes e Itajaí (SC) em relação às características sedimentológicas e composição dos minerais leves (quartzo e feldspato)

Resumen

This study collected sand samples at Navegantes and Itajaí beaches during all seasons of the year, and used the staining technique to determine the quartz/feldspar ratio (R(Q/F)). This parameter can be used to measure the maturity of sedimentary deposits. Samples were collected and the beach profile was measured at Gravatá, Meia-Praia, Navegantes Jetty; Atalaia, Cabeçudas and Praia Brava (3 profiles: Morcego, Salva-Vidas and Amores) at Itajaí. The staining technique was used to diferentiate between sediments that were visually similar but with different mineralogical composition. Using this technique it is possible to distinguish both due to a colored precipitate on the feldspars when exposed to a specific reagent. The results showed that dissipative beaches (Navegantes and Atalaia) were composed by thin, better selected and well rounded sediments, with a greater value of R(Q/F). Reflective (Cabeçudas) and intermediate beaches (Brava) were composed of medium sand, moderately selected and rounded, with lower values of R(Q/F). On the shoreface zone the sediment doesn’t suffer much weathering, being more coarse, not rolled, and with greater concentration of feldspars. This high concentration is due to the aquatic transport which is not predominant on the foreshore and the backshore that show aeolian transport. Higher values of R(Q/F) occurred during fall and spring, lower values during winter and summer. The staining technique proved to be an effective method for distinguishing quartz and feldspars. The amount of quartz found was much higher than feldspars, reiterating that beaches are sandy environments with mature sediments.