Diniz, D. and Medeanic, S., 2013. Palynomorph records from the core of Rio Grande Cone, Brazil: approaches for palaeoenvironmental and palaeoclimatic reconstructions in the Middle Holocene.
Palynomorphs are an important tool for understanding palaeoclimatic and palaeoenvironmental changes in the past. There are no studies in Brazil based in palynomorphs in deep sea oceans. Based on core REG-973, the objective of this study was to determine changes in palaeoenvironments during the Middle Holocene in the Rio Grande Cone, southern Brazil. A total of 39 samples were collected from the core, with intervals of 4 cm. Samples were treated using methodology for palynological analysis. There was 14C dating at three samples (20, 100, and 200 cm depth) with absolute ages of 2290, 4080 and 5050 ± 40 yr BP, respectively. The analysis of palynomorphs revealed three distinct origins: marine, terrestrial, and freshwater. Much of this material was allochthonous, transported by aquatic currents of palaeorivers and palaeochannels, which were present on the continental shelf of Rio Grande do Sul (RS) in periods when the mean sea level (MSL) was lower than today. The analysis of the taxonomic variety of palynomorphs showed five Palynomorph Zones. These zones were admitted as corresponding to five stages of palaeoclimatic and palaeoenvironmental development. The constant presence of marine indicators pointed out the formation of such sediment in a marine environment but with influences of coastal surroundings. It was concluded that sediment was generated in a marine environment but always influenced by terrestrial material. The preservation of palynomorphs reflected the MSL oscillations. When the source area was more distant, the preservation level was worse. The generation of sediments was found to be very complex, influenced by factors affecting both the terrestrial and marine environments.
