TECTONIC INHERITANCE AND THE EVOLUTION OF THE CENTRAL SANTA CATARINA COAST, BRAZIL

The eastern margins of North and South America differ markedly due to differences in their tectonic history dating to the breakup of Pangaea. Whereas the passive margin of North America is a product of rifting, subsidence, and sedimentation, the evolution of South America encompassed a strong thermal event that resulted in uplift, magmatism, and rifting. Emplacement of 200,000 km³ of flood basalts in the Parana Basin in southern Brazil, Paraguay, Argentina and Uruguay during the early Cretaceous is a surface manifestation of the mantle plume that initiated the breakup of Gondwanaland. Normal faulting and a gentle downward flexure of the basement facilitated long-term rifting of southern Brazil from southern Africa and subsequent continental margin development. The hinge line of this flexure coincides with the coastal Serra do Mar mountains, a region of protracted uplift and sediment contribution to Santos Basin and coastal region. This tectonic history accounts for the > 800 m relief along much of the margin of southern Brazil. Within this region the central Santa Catarina coast is characterized by numerous bedrock headlands separated by reentrants and bays. Prograded beach ridge and chenier plains have partially smoothed the irregular coast. Origin of the strand plains is related to an abundant sediment supply combined with Late Pleistocene-Holocene sea-level changes. The most recent fall in sea level of 2 to 4 m during the past 5,600 years has been explained by geoid changes and/or sediment loading of the shelf causing flexure deformation of the adjacent coastal margin. Local sand delivery to the coast is from deeply weathered, coarse-grained Archaean to Proterozoic granitoids. The highly fractured nature of the quartz grains in these saprolites yields a variety of grain sizes, which partly explains the fine-grained beaches along much of the coast. Shelf sources of sand may have been derived from the Rio de la Plata and transported northward by a strong southeasterly wave regime that was operative during multiple transgressions and regressions.