The complex prograded Cassino barrier in southern Brazil: Geological and morphological evolution and records of climatic, oceanographic and sea-level changes in the last 7–6 ka

Abstract This paper presents the geological and morphological evolution of the prograded Cassino barrier during the middle and late Holocene. A special focus is given on the presentation and discussion of records of environmental changes that occurred during barrier progradation. The results demonstrated that variable rates of progradation were produced by environmental changes that affected the coastal sediment budget, such as changes in the wave climate. The total progradation of 18 km recorded for the Cassino barrier is probably the highest extension of progradation registered for a ridge plain associated with a coastal barrier. Sea-level changes during barrier progradation were accessed by the high difference between the degree of compaction of the foredune and backshore/foreshore deposits detected by the drilling system applied in this study and were confirmed by the limit of those deposits, which were also revealed by GPR records. During most of the time of barrier progradation, an overall sea-level fall of approximately 2 ± 1 m occurred. Six sets of relict foredune ridges were identified, and the limits between them were well marked by ridge truncations and the formation of transgressive dune sheets (TDS). Optically stimulated luminescence ages show that the TDS were formed under the driest climate conditions, with age periods very close to 3.8, 3.5, 1.9, 1.5, 0.22 and 0.09 ka ago, interspersed with ages of known wetter conditions in southern Brazil. The modern phases of TDS formation, with ages varying from 0.25 to 0.22 ka ago, were coincident with the time period of the younger pulse of the Little Ice Age (LIA), which was characterized by arid and cold conditions in southern South America. A comparison with prograded barriers located 350 to 600 km to the north suggests the existence of teleconnections, with phases of TDS and parabolic dunes that formed with a time interval of approximately 405 to 583 years.