Abstract The organic geochemistry of organic-rich facies including shales, marls, and carbonates (Assistência Member) of the Irati Formation, Paraná Basin, Brazil, were analyzed to evaluate the thermal effects of igneous intrusions upon the kerogen present in these facies. Total organic carbon (TOC) content and hydrocarbon source potential (S2) of the Irati source rocks range from 0.03 to 20.4% and 0.01 to 112.1 mg HC/g rock, respectively, indicating excellent potential as a source for hydrocarbon generation. Hydrogen index (HI) values reveal that the kerogen is predominantly type I (HI: up to 892.6 mg HC/g TOC) and, therefore, an oil source, except for samples having low TOC content due to severe maturation caused by the heat from diabase intrusions. The thickness of igneous intrusions in the 64 wells investigated in this study ranged from 2 to 231 m. They clearly had a major impact on TOC, HI, and S2 values, which decrease in the vicinity of intrusions, indicating a gradual increase in maturation toward the igneous body. In wells without the influence of igneous intrusions, Tmax values of Rock-Eval pyrolysis and %Ro indicate that the organic matter is immature for the generation of hydrocarbons.

A baía de Camamu, importante pólo turístico, pesqueiro e mineiro, está localizada na Região Litoral Sul do Estado da Bahia. Esse corpo hídrico é bordejado por extensa floresta de manguezal e tem se tornado alvo de uma série de estudos geoambientais. O objetivo desse trabalho é apresentar parte dessas investigações, que corresponde a uma avaliação mineralógica nos sedimentos do manguezal estudado. O estudo semiquantitativo realizado mostrou que, nas estações próximas à zona de mineração, o sedimento é rico em quartzo, barita e argilas, além de pequeno percentual de pirita e jarosita. Nas demais estações, a mineralogia é composta predominantemente por quartzo e argilas, com percentuais variados de barita, pirita e gipsita em determinadas estações. Nos sedimentos de manguezal estudados, os minerais identificados parecem estar intimamente relacionados aos processos geológicos ocorrentes localmente: seja através de processos intempéricos da zona de alimentação ou processos antropogênicos com posterior transporte, seja através de modificações mineralógicas in situ provenientes das condições físico-químicas impostas ao ambiente.

The Camamu Bay, an important fishing, mining and tourist site, is located at the South Coastal Region of the State of Bahia, Brazil. This large water body is surrounded by extensive mangrove forest and has been the object of many geo-environmental studies. The objective of this work is to present partial results of one of these studies, a mineralogical evaluation in the sediments of the Camamu Bay's mangrove. This semi-quantitative study showed that in the stations next the mining zone the sediment is rich in quartz, barite and clays, with small percentage of pyrite and jarosite. However, for the majority of the stations, the mineralogy is predominantly: quartz and clays, with a variety of percentages of barite, pyrite and crude gypsum in some stations. The results obtained in this work indicated that, for this studied mangrove, the mineralogical composition of the sediments seems to be intimately related to the geologic processes occurring locally. The processes can be: either weathering processes in situ, or man made processes with posterior carriage; or through mineralogical modifications in situ, resulting from the physical-chemical conditions operating at the environment.