Paleoenvironments of the last 24,000 years on the extreme northern Rio Grande do Sul coastal plain, southern Brazil

Abstract

In the northernmost of Rio Grande do Sul coastal plain, southern Brazil, the first comparative palynological study of the sedimentary profiles of two present-day Atlantic rainforests was conducted in Torres municipality: Pirataba forest (29°15′ S, 49°51′ W), 17 km from the coastline, and Faxinal forest (29°21′ S, 49°45′ W), 2 km from the coastline. Ten radiocarbon dates and additional grain influx diagrams allowed for a more accurate analysis. The results suggested that regional and local events affected the northern coastal plain vegetation. The inner coastal plain of the Pirataba site was characterized by a cold, dry regional climate and a small number of pioneer forest species at the end of the last glacial stage (24,000–10,000 bp); a regionally variable temperature increase with slightly humid and dry phases in the early/mid-Holocene (10,000–6700 bp); and regional high temperature and humidity, and expanding Atlantic rainforests, in the mid-Holocene (6700 bp onwards). Near the coastline in the Faxinal site, the following were detected: marine transgression and damage to herbaceous marsh plants, and elevated temperature in the mid-Holocene (7000–6700 bp); regional marine regression, gradual soil desalination and scarce herbaceous marsh in the mid/late Holocene (6700–3500 bp); and regional high temperature and humidity, with forest expansion over the desalinated herbaceous marsh in the late Holocene (3500 bp onwards). The Pirataba and Faxinal forests expanded because of the high temperatures, an even greater increase in regional rainfall, and improved soil conditions at the end of the late Holocene (1500 bp onwards). The hydrosere occurring due to a water reservoir in Faxinal highlights the importance of preserving the lacustrine bodies of the region as generators of coastal forests.