Geochemical characterization of the hydrous pyrolysis products from a recent cyanobacteria-dominated microbial mat

• Published in: Geologica acta Vol. 14; no. 4; p. 385
• Main Authors: Franco, N, Filho, J.G. Mendonca, Silva, T.F, Stojanovic, K, Fontana, L.F, Carvalhal-Gomes, S.B.V, Silva, F.S, Furukawa, G.G
• Format: Journal Article
• Language: English
• Published: Geologica Acta 01-12-2016
• Subjects: Biogeochemistry; Cyanobacteria; Geological research; Microbial mats; Pyrolysis
• ISSN: 1695-6133
• DOI: 10.1344/GeologicaActa2016.14.4.4

Hydrous pyrolysis experiments were performed on a recent microbial mat sample from Lagoa Vermelha, Brazil, to determine whether crude oil can be generated and expelled during artificial maturation of the Organic Matter (OM). The experiments were conducted at 280[degrees]C, 330[degrees]C and 350[degrees]C during 20h. Two types of liquid pyrolysis products, assigned as free oil and bitumen, were isolated and analyzed. Free oil represents free organic phase released by hydrous pyrolysis, whereas bitumen was obtained by extraction from the solid pyrolysis residue with dichloromethane. Changes in the OM maturity were determined using Rock-Eval parameters and biomarker maturity ratios of original sample and pyrolysis products. Biomarker compositions of original sample extract and liquid pyrolysates were used for determination of dominant bacterial source. The yields of free oil and bitumen showed that a microbial mat OM has a high liquid hydrocarbons generation potential. Rock-Eval maturity parameters, biopolymer and biomarker compositions indicate a significant increase of the OM maturity during hydrous pyrolysis. At 280[degrees]C the release of free, adsorbed and occluded compounds was observed; however, without a cracking of the OM. At 330[degrees]C the generation of bitumen and free oil is mostly related to the OM cracking. The highest yield of free oil was recorded at this temperature. Distribution of biomarkers in the extract of original sample and liquid pyrolysates confirms cyanobacteria-dominated microbial mats, whereas the identification of long chain n-alkane series, with maximum at [C.sub.26], and prominent [C.sub.30] hop-17(21)-ene additionally suggest the presence of sulfate reducing bacteria. KEYWORDS Microbial mat. Hydrous pyrolysis. Hydrocarbon potential. Biomarkers. Lagoa Vermelha.