Morphological and depositional facies of transgressive dunefields in the Imbituba-Jaguaruna region, Santa Catarina State, southern Brazil

This paper presents a morphological (process-form) and depositional (process-product) facies analysis of two types of active transgressive dunefields (facies associations) in the mid-south coast of Santa Catarina State. The Ibiraquera dunefield (Imbituba) has parabolic geometry and about 5 kilometers of extension. It migrates inland and it's separated from the beach by a vegetated deflation plain. The influence of the vegetation on the dynamics of morphological facies in this dunefield is very common. The Grande do Sul dunefield (Jaguaruna) migrates parallel to the beach along tens of kilometers. It has a predominance of unvegetated morphological facies. When common facies to both dunefields are compared, the Grande do Sul's morphological facies are larger and their depositional facies are finer-grained. Two hypotheses can explain the differences between these dunefields. The first one involves a larger sand volume available to be transported by the wind at Grande do Sul beach: this sand volume comes probably from the adjacent inner shelf, which is wider and gentler on the Jaguaruna coast than on the Imbituba coast. The second hypothesis considers the angular relation between shoreline orientation and the effective wind direction. The maintenance of the eolian supply is favored in the beach-dunefield system that has an orientation more parallel to the prevalent wind from NE, i.e. Grande do Sul dunefield. The grain size differences are possibly related to the length of the dunefields: the tendence to finer and better sorted sediments in Grande do Sul dunefield than in Ibiraquera dunefield can be attributted to greater length and longer transport in the former.