Origem e distribuição dos beachrocks na costa cearense e a sua influência na dinâmica costeira

Abstract

Located in northeastern Brazil, the coast of Ceará is characterized by geological and geomorphological features that directly influence coastal dynamics, among which beachrocks stand out. The main objective of this study was to map and analyze the characteristics of these deposits, based on samples collected from selected beaches along the Ceará coast, investigating their genesis and evaluating their role in shoreline protection and stability, as well as in coastal marine habitats. The influence of coastal dynamics was discussed through multitemporal satellite image analysis, geological–geomorphological mapping, and field observations of the interaction between beachrock outcrops and the prevailing hydrodynamic processes. To achieve these objectives, a bibliographic review focused on beachrocks was conducted, combined with geological and geomorphological mapping, including stratigraphic characterization, spatial distribution, and relationships with other rocks and sedimentary deposits, in addition to sampling and petrographic analyses. The results indicate a wide distribution of beachrocks along the Ceará coast, highlighting their interaction with coastal processes and the influence of marine and fluvio-marine environments on coastal evolution over different periods. These outcrops act as natural barriers, promoting wave energy dissipation, the formation of hydrodynamic shadow zones, and sediment retention, thereby contributing to shoreline protection and stability and to the development of more sheltered marine environments. Petrographic analyses revealed a diversified mineralogical composition, with a predominance of quartz and feldspar in different stages of weathering, indicating sediment supply from both proximal and distal sources subjected to varying degrees of sedimentary reworking. The identification of successive episodes of erosion, deposition, and lithification of new beachrock layers evidences the evolutionary dynamics and resilience of these formations. The occurrence of beachrocks over erosional platforms developed on argillaceous–ferruginous rocks and sediments of the Barreiras Formation indicates the action of variable physicochemical conditions over time, reinforcing the importance of beachrocks as key elements in controlling coastal dynamics along the Ceará coast.