Caracteriza?§?￡o geoqu?-mica com ind?-cios paleoambientais de folhelhos da Forma?§?￡o Pimenteiras, estado do Tocantins, Bacia do Parna?-ba, Brasil

摘要

The discovery of natural gas in siliciclastic deposits of the Parna?-ba Basin has motived new research to understand the petroleum??system, to characterize source rock intervals, as well as to improve the paleoenvironmental characterization. Since??the deposition of the main source rock in the Parna?-ba Basin, the Pimenteiras Formation, occurred during the Devonian,??associated with global anoxic event at the Fransnian, shales samples of Devonian were collected from outcrops of Pimenteiras??Formation and analyzed using the geochemical techniques of total organic carbon, total sulfur, Rock Eval pyrolysis??and stable carbon isotopes. Analysis results of 27 source rock samples indicated that 67% of the samples have a minimum??total organic carbon content required to produce hydrocarbons. Approximately 77% of the samples had the potential to??generate gas, while the remaining percentage are those corresponding to the samples with the potential to generate oil or??gas. The maximum pyrolysis temperature suggests thermal immaturity of the samples. The geochemical data correlation allowed??recognizing signs of changes in the depositional paleoenvironment of the outcrops studied, probably by sea flooding.