| Autor: |
Almeida LTG; Programa de Pós-Graduação em Química, Universidade Federal do Piauí/UFPI, Centro de Ciências da Natureza, Campus Ministro Petrônio Portella, s/n, Ininga, 64049-550 Teresina, PI, Brazil., Brito AS; Programa de Pós-Graduação em Química, Universidade Federal do Piauí/UFPI, Centro de Ciências da Natureza, Campus Ministro Petrônio Portella, s/n, Ininga, 64049-550 Teresina, PI, Brazil., Cioccari GM; Universidade Federal de Pelotas, Centro de Engenharias/CENG, Praça Domingos Rodrigues, 02, Centro, 96010-440 Pelotas, RS, Brazil., Souza AA; Programa de Pós-Graduação em Química, Universidade Federal do Piauí/UFPI, Centro de Ciências da Natureza, Campus Ministro Petrônio Portella, s/n, Ininga, 64049-550 Teresina, PI, Brazil., Mizusaki AMP; Universidade Federal do Rio Grande do Sul, Instituto de Geociências, Departamento de Paleontologia e Estratigrafia, Campus do Vale, Av. Bento Gonçalves, 9500, Prédio 43127, sala 112, 91501-970 Porto Alegre, RS, Brazil., Lima SG; Programa de Pós-Graduação em Química, Universidade Federal do Piauí/UFPI, Centro de Ciências da Natureza, Campus Ministro Petrônio Portella, s/n, Ininga, 64049-550 Teresina, PI, Brazil. |
| Abstrakt: |
The Irati Formation (Paraná Basin) is a mixed carbonate and organic-rich shale sequence intruded by Jurassic-Cretaceous basic rocks, featuring Brazil's most important oil shale deposits with different maturity levels. For the first time, the distribution of oil shale biomarkers from an outcrop section (quarry) of the Irati Formation in the northernmost Paraná Basin was analyzed by GC-MS and GC-MS/MS to determine the thermal evolution, organic matter origin and the depositional paleoenvironment. The organic-rich shale at the northernmost border of the basin has high similarity with the central and southernmost areas, indicating a primary control able to induce cyclic sedimentation in a broad (106 km2) and restricted environment. PCA and HCA analysis of bulk and molecular parameters showed changes in the organic matter composition and paleoenvironmental conditions throughout the stratigraphic column. Nonetheless, there are significant differences compared to the central-eastern and southern areas of the basin. Contrasting with the southern region, the north, predominates biphytane, low and medium gammacerane index. Pr/n-C17, Ph/n-C18, HI and OI values suggest type II/III kerogen from marine organic matter with freshwater input. Among the steranes, those of stereochemistry ααα 20R predominate over ααα 20S, and the presence of βTm indicates the shales are less thermally evolved. |
