Pirita como Proxy de ambientes lagunares

Abstract

Coastal lagoons are common ecosystems in all continents and represent important areas of human occupation and use. Are water bodies whose characteristics vary depending on the influence of the tide, coastal typology and climate. Are environments with low water circulation that are conducive to the formation of pyrite (FeS2). The formation of pyrite occurs in the presence of iron and sulfate from seawater, so this mineral can be used as an indicator of marine influence. The objective of this work was to prove the marine origin Lagoon Paradise in the city of Jijoca Jericoacoara, Ceará, the analysis of iron associated with pyrite. Was used for the analysis sedimentary material from the bottom of the pond, collected in January 2013, in triplicate, in two distinct points, P1 and P2. The data pH and Eh were measured in situ. Fractions clay, silt, sand and gravel were separated by gravimetry, and pyritic iron quantification was performed by sequential extraction of iron and atomic absorption spectrometry. Was also determined content of organic matter by burning in a muffle furnace. According to the results, the sediment of the lagoon is basically composed of sand (90%), the concentrations of Fe-Fe-reactive and pyritic are low (<3 mol and <1 mol) and the degree of pyritization (DOP) did not exceed 35%. The environment of the lagoon is oxic, is undergoing acidification process and there is little organic matter in the sediment (<1%). The results of particle size indicated that there was influence of dunes in the isolation of the basin and the presence of pyrite confirmed that there was contact with the Paradise Lagoon adjacent sea, characterizing it as an ancient coastal lagoon.