Caracterização sedimentológica do sistema estuarino-lagunar de Itarema, costa oeste do Ceará, Brasil

Abstract

Lagoons are transition environments between the continental and marine environments, and have no fluvial influence, however it is worth mentioning that there may be ephemeral drains. These are benefits on coastal plains and may be associated with sandy banks and barrier islands. They are environments that have an ecological, recreational and commercial importance. The lagoon environment adjacent to a locality of Porto dos Barcos in the municipality of Itarema, west coast of Ceará, has a coastal barrier and mangrove ecosystem. Thus, this study aimed to characterize the sedimentology of a lagoon in the estuarine-lagoon system in the municipality of Itarema, on the west coast of the state of Ceará. The methodology used consisted of going to the field, where two sedimentary cores (T1 and T2) were collected through tubes of 50 mm in diameter and 1 meter in length. Subsequently, the macroscopic description of the sedimentary cores was performed according to color, granulometry and presence of fragments of an organic and mineral nature. In the laboratory, a granulometric and geochemical analysis (quantification of the levels of calcium carbonate and organic matter) was performed. From the integration of the data, columnar profiles of the cores were elaborated. The results obtained indicated a variation color between shades of black, gray and green, in addition to some shades of white and blue in the T2 core. The presence of vegetable fragments was verified throughout all cores, as well as shell and root fragments in some fractions of the cores. The granulometry showed a predominance of the sand fraction in relation to other granulometric classes. However, muddy fractions were also identified in the cores, mainly in the T2 core. The statistical parameters of particle size (mean, standard deviation, skewness and kurtosis) showed a relative pattern between them. The calcium carbonate content in sediments varied from 0,90% to 26,84% and organic matter between 1,06% and 13,2%. The integration of the results obtained enabled the identification of sandy and sandy muddy bimodal sedimentary facies in the two cores, with a greater alternation between the facies in the T2 core, indicating a greater sedimentary dynamic in this lagoon sector. It is concluded that in the studied estuarine-lagoon plain, the presence of the analyzed facies is common, and the difference between the facies is related to sub-environments present in the estuarine-lagoon plain.