Abstract
In this study nitrogen markers (N-markers) were employed to evaluate the depositional paleoenvironment of the Candeias and Barreirinha Formations, Recôncavo and Amazonas Basins, respectively. Towards this end, twenty-one N-markers from carbazole (CA), benzocarbazole (BCA), indole (IND), acridine (ACR), and quinolone (QUIN) classes were determined by highly selective and sensitive gas chromatography-triple quadrupole mass spectrometry (GC–MS/MS). Twenty-four (24) samples was collected in vertical sections of outcrops of the Candeias Formation and of the Barreirinha Formation. The N-markers were efficient in evaluating distinctions and similarities between the source rocks and were able to define the origin and input of organic matter, the depositional paleoenvironment conditions of the samples. The samples from the Recôncavo Basin presented low concentrations of CA, methyl carbazole (MCA), and dimethyl carbazole (DMCA), and high concentrations of QUIN and 4-methyl quinoline (4-MQUIN), indicating a lacustrine environment. Samples from the Amazonas Basin present high concentrations of CA, MCA, DMCA, 2,4-dimethyl quinoline (2,4-DMQUIN), benzo[c]quinoline (B[c]QUIN), and ACR, typical of the marine environment. Although the formations are from different paleoenvironments, the organic matter input is similar. The proportions of the 1-, 2- and 4-methyl carbazole (1-MCA, 2-MCA, and 4-MCA), in addition to the low values for the 4-MCA/2-MCA ratio, allowed to affirm that algal input was predominant in the Candeias and Barreirinha formations. The relative concentration of DMCA and of the B[b]CA isomer also indicate the supply of terrigenous material for both formations. BCA concentrations were affected by the conditions of depositional paleoenvironment. Samples deposited under redox conditions presented low concentrations of BCA, and those deposited in oxidizing environments had higher amounts.
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