Middle to Late Holocene paleoenvironmental changes in the coastal plain of southern Brazil

摘要

The coastal plain of southern Brazil documents several environmental changes mainly related to sea-level fluctuation and climatic variations during the Quaternary. Comprehensive studies have been carried out, of local and regional scope, in order to improve the knowledge about the geological evolution of this portion of the South American. In this paper we present the results of stable isotope, palynological and palynofaciological analysis of the PSC-03 core (7744 cal yr BP - Modern) was performed to provide the sedimentary evolution of the Santa Catarina coastal plain. Palynological and palynofacies analyses revealed abundant and diversified palynological associations, including terrestrial palynomorphs (spores, pollen grains, fungi, and freshwater algae), marine elements (dinoflagellate cysts and foraminiferal linings), besides abundant phytoclasts and amorphous organic matter. Based on the combined analysis of delta C-13 isotopes (-20.7 parts per thousand to -29.6 parts per thousand) and the C/N ratio (15.5-68) of the selected samples, we deduce that the organic matter is derived from marine phytoplankton and terrestrial C3 plants. The integrated approach of palynofacies and stable isotopes (delta C-13 and C/N) analyses revealed three distinct intervals, which characterize the environmental evolution of this portion of the coastal plain. The Interval I (7744 to 2844 cal yr BP) is related to a marginal marine environment, followed by the Interval II (2857 to 2276 cal yr BP), which indicates shallow water conditions, with wetland or soggy soils, while the Interval III (2124 cal yr BP to Modern) shows a subaerial scenario, strongly influenced by arboreal forms of the Atlantic Forest. Comparisons with other sites in southeastern South America were carried out, especially from Uruguay and Argentina, showing similarities in the palynological succession, as response to broader climatic conditions.