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- Title
Paleoambiente Deposicional de Folhelhos da Formação Pimenteiras da Borda Oeste da Bacia do Parnaíba, NE - Brasil.
- Authors
Caldas Abreu, Neila; Navarro de Andrade, Consuelo Lima; Roberto Cerqueira, José; Santos Garcia, Karina; Cordeiro de Oliveira, Olívia Maria; Portugal Severiano Ribeiro, Hélio Jorge
- Abstract
The shales of the Pimenteiras Formation deposited in a marine environment during the Devonian (Frasnian), are rich in organic matter and constitute the main source rock of the Parnaíba Basin. This work aims to characterize the depositional paleoenvironment of the Pimenteiras Formation based on the study of Organic Geochemistry and Palynofacies. Twenty-one rock samples were collected from an outcrop near the Aparecida do Rio Negro, on the western edge of the Basin, in the state of Tocantins, where there is a stratigraphic aspect of the contact between the Cabeças (Famenian) and Pimenteiras (Frasnian) Formations. Total organic carbon (TOC) contents range from 0.21 to 2.43% and Rock Eval pyrolysis results indicate predominantly type II and III kerogen, hydrocarbon source potential (S2) ranging from poor to medium (0, 41-6.13 mgHC / g rock), low concentration of free hydrocarbons (S1) and thermal immaturity (Tmax) for oil generation. The study of palynofacies allowed to identify and to quantify the particulate components of organic matter of palynomorphs, phytoclasts and amorphous organic matter (MOA) groups. A considerable number of prasinophytes of the genus Pterospermella, Cymatiosphaera, Durvenaysphaera, Leiosphaeridia, Tasmanites, Hemiruptia and Maranhites has identified, suggesting the flood surfaces possibly of Frasnian age. Throughout the outcrop the samples presented quantitative variation of terrestrial organic components, characterizing marine regressions, and other samples, suggesting marine transgressions, with the increase of prasinophytes and acritarchs. The organic carbon isotopes (d13C: -25.9 to -29.5?) and saturated biomarkers (C27-C28-C29 regular steranes and TPP / (TPP + DIA) ratios also suggest an alternation in the input of terrestrial and marine organic matter.
- Publication
Anuario do Instituto de Geociencias, 2020, Vol 43, Issue 2, p496
- ISSN
0101-9759
- Publication type
Academic Journal
- DOI
10.11137/2020_2_496_510