ESTUDOS MINERALÓGICOS, GEOQUÍMICOS E PALINOLÓGICOS DE SEDIMENTOS DE MANGUEZAIS DO NORDESTE DO ESTADO DO PARÁ

Mangroves constitute an expressive ecosystem in the northeastern Amazon region and one of the best examples of them is located in the marine coastal plain of Para State close do Braganca City in northern Brazil. They were the subjects of our multi-disciplinary researches carried out in past years. The gotten data included palynology, mineralogy, multi-element geochemistry and radiocarbon dating in order to get information about their formation conditions and transformation. This can help identify how this environment changed during the late Quaternary, mostly the paleoclimatic and continental-marine interaction in the region. The geological descriptions, the physicochemical data, the mineralogical and chemical composition and the multi-element geochemistry allow the identification of two zones in the 640-cm long drill core collected from the mangrove deposits. One acid, reduced and high salinity, rich in organic matter, clay minerals (smectite and kaolinite), halite, pyrite and feldspars from the surface up to 300 cm; and the other from 300 to 640 cm in depth, alkaline, oxidizing, with low salinity, and rich in diatoms and quartz. The chemical composition displays a signature of terrigenous material like latosol derived from the Barreiras Formation, and of marine influence (Sr, Ba, Na, K, Mg, Cl and F), as sources of material for the mangrove sediments. The pollen analyses and radiocarbon dates allow to identify three zones: the first two zones correspond to the near surface zone, deposited of low rates, in the last 1770 yr. The third zone can be correlated to alkaline and oxidizing zone. It was deposited from 2170 to 1770 yr. BP under high rates. The pollen diagram shows the domain of humid climate and the mineralogy and chemistry indicate a contribution of marine incursion and strong evaporation and oxidation close to the land surface.