Análise dos sistemas deposicionais e dinâmica costeira do município de Aquiraz, Estado do Ceará, com auxílio de imagens de sensoriamento remoto

Abstract

The coastal area of the Ceará State, Brazil is locally represented by a natural landscape constituted by scarps developed in the Plio-Pleistocenic Barreiras Formation sediments and for extensive sandy deposits of eolian origin. The Barreiras Formation sediments due to lithologic variations, grain size and form, sedimentary structures and interfingering of facies were classified in three classes. The first class refers to the cyclical deposition of the sedimentary F1 and F2 facies described in the section of the profile PA8 in the District of Aquiraz. The F1 facies is characterized by the predominance of quartz pebbles in relation to sandy-clay matrix (orthoconglomerated) associated to channel and cut and fill sedimentary structures. In the F2 facies the matrix overcome in relation to the clasts, and the rock is classified as a diamictite. These coarse rocks facies and related structures are verified in the proximal segment alluvial fans, with alternations of droughts and humid climatic conditions. The second facies class includes the sandy-clay outcrops, of reddish color, massive aspect, with the presence of dispersed quartz grains (diameter > 3 mm) in the rock body. The sedimentation interpretation is related to intermediate portion of alluvial fans. The third class corresponds to the sandy-clay deposits of yellow reddish color and massive aspect that outcrops in plateau surface and in the majority of the cliffs in the districts of Beberibe, Aracati and Icapuí. The deposition was controlled by debris flow currents in semiarid conditions, and is interpreted as distal of the alluvial fans. The Barreiras Formation outcrop along the eastern coast of Ceará State are conditioned by the reactivation of tectonic structures in a neotectonic event. The quaternary sedimentation in the coastal plain of the District of Aquiraz is characterized by beach and aeolian deposits. Aeolian sandy dunes, show varied forms and are classified in active, partially active and inactive, in agreement with their morphologies and vegetable index covering. The cell of the beach face of the point of Iguape is characterized by the presence of extensive field of inactive parabolic dunes. In the cell of the foreshore beach there are a variety of dune types originated by reactivations of tectonic structures and by the processes of sedimentary by passing over the point of Iguape. The face of beach in the coast of Aquiraz is characterized by the dissipative stage (Barro Preto e Batoque beaches) and intermediate stage (Presidio, Prainha and Porto of the Dunes beaches). The amount of sediments involved in the costal dynamics reveals larger values for the areas situated in the beach face of the Iguape rocky point and smaller for the foreshore beach. The images interpretation of remote sensing allowed to discover submerged features in the delta of the Jaguaribe river and along the coastal plain of the District of Icapuí. The tax of migration of the active field dunes positioned in the margin of the Catú lake was calculated starting from the overlapping of aerial photography digitalized and images of the Ikonos - II satellite. The assessment of the variation of the line coast in the district of Aquiraz reveals that the area has been submitted to a small elevation of the relative level of the sea along the 36 last years. By this way the use of satellite images in the coastal researches becomes a tool of vital importance in the process of recognition of the physical processes involved in the coastal dynamics.