Development of a simple and versatile ultrafiltration system for the fractionation of aquatic humic substances

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Carboxylic acids of marine evaporitic oils from Sergipe-Alagoas Basin, Brazil

A. suite of 10 different marine evaporitic oil samples from Sergipe-Alagoas Basin, Brazil was studied for its biomarker content, in particular its acidic constituents. The oils showed different molecular distributions and relative abundances of n-alkanoic, isoprenoid and hopanoic acids. The observed differences were assigned to the incorporation of immature organic matter in the oils and fractionation along the migration pathway. The diagenetic precursor functionality (alcohol/ether or acid) was proposed based on the comparison of the relative abundances of the neutral and acidic biomarkers (hopanoids, isoprenoids, alkyl-steranes, monoaromatic alkyl-steroids). In the acidic fraction, 3 series of steroid-alkanoic acids and monoaromatic steroid-alkanoic acids (steroid-methanoic, ethanoic and propanoic acids and monoaromatic steroid-methanoic, ethanoic and propanoic acids) were detected, while in the neutral fraction only 2 series of each corresponding class could be observed (methyl and ethyl-steranes and monoaromatic methyl and ethyl-steroids). These carbon shifts suggest that decarboxylation is an important process in the formation of the alkyrsteranes and monoaromatic alkyl-steroids, and we infer that carboxylic acids are the diagenetic precursors of these classes of compounds. When alcohol or ether are the diagenetic precursors (isoprenoids and hopanoids), no significant differences in the molecular distributions between neutral and acidic fractions were observed. (C) 2000 Elsevier B.V. Ltd. All rights reserved.

Evidence for euphotic zone anoxia during the deposition of Aptian source rocks based on aryl isoprenoids in petroleum, Sergipe-Alagoas Basin, northeastern Brazil

Four crude oil samples from the Sergipe-Alagoas Basin, northeastern Brazil, were analyzed using full scan gas chromatography-quadrupole mass spectrometry (GC-qMS) for biomarkers, in order to correlate them using aromatic carotenoids thereby enhancing knowledge about the depositional environment of their source rocks. The geochemical parameters derived from saturated fractions of the oils show evidence of little or no biodegradation and similar thermal maturation (Ts/(Ts+Tm) for terpanes, C29 αββ/(αββ+ααα), C27, and C29 20S/(20S+20R) for steranes). Low pristane/phytane ratios and the abundance of gammacerane and β-carotane are indicative of an anoxic and saline depositional environment for the source rocks. Moreover, we identified a large range of diagenetic and catagenetic products of the aromatic carotenoid isorenieratene, including C40, C33, and C32 diaryl isoprenoids and aryl isoprenoid derivatives with short side chains and/or additional rings. These results indicate anoxia in the photic zone during the deposition of the source rocks. © 2013 The Authors.