FROM AN ESTUARY TO A FRESHWATER LAKE: A PALEO-ESTUARY EVOLUTION IN THE CONTEXT OF HOLOCENE SEA-LEVEL FLUCTUATIONS, SE BRAZIL

摘要

A sediment core was studied to characterize the influences of Holocene sea-level variations in the Barra Seca River valley, in the Atlantic rainforest, Linhares, Espirito Santo, southeastern Brazil. Biological proxies (pollen, spores, and sponge spicules), ~(14)C dating, granulometry, δ~(13)C, δ~(15)N, C/N and major chemical elements revealed the establishment and the evolution of a paleo-estuary during the interval from -7700-585 cal BP. During the interval ~7700~7000 cal BP, the study site was occupied by a bay-head delta, the inner portion of the paleo-estuary, presenting the most dense mangrove coverage of the entire record. In the interval -7000-3200 cal BP, the site was occupied by the central basin, possibly a consequence of the landward migration of the paleo-estuary. This interval presents reduced mangrove coverage, probably due to the permanent flooding of the valley. From ~3200 cal BP, the marine influence at the site decreased probably as result of the seaward migration of the coast line. From ~600 cal BP, the modern floodplain and freshwater lake were established. This interpretation is in agreement with the sea-level curves for the southeastern Brazilian coast, except for the fact that evidence of sea levels lower than the present at -4000 and -2500 cal BP as suggested by some authors were not found.