Uncommon steranes in Brazilian marginal crude oils: Dinoflagellate molecular fossils in the Sergipe-Alagoas Basin, Brazil

Araújo, Bruno Quirino; Azevedo, Débora de Almeida

doi:10.1016/j.orggeochem.2016.06.004

Cited by 23 publications

(16 citation statements)

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“…40 The greater variation on maturity values from post-salt Brazilian crude oils are well known. 19,31,41 In general, the saturated biomarker parameters used to estimate the thermal maturity degree are shown to be contradictory, as previously observed for Brazilian crude oils. 29,31 With regard to the distribution of n-alkyltoluenes (m/z 106), the Sergipe-Alagoas oils show similar abundance patterns of meta and ortho isomers based on the m-ϕ T -C 15 /o-ϕ T -C 15 values (0.90 and 1.00 for SEAL1 and SEAL2, respectively), which indicates that both samples are thermally evolved.…”

Section: Resultsmentioning

confidence: 54%

“…32,33 Concomitantly, 4,23,24trimethylcholestanes (dinosteranes), which are important indicators of marine organisms such as dinoflagellates and diatoms, were detected only in the SEAL1 oil (Table 1), as previously noted for the Sergipe-Alagoas crude oils. 19 In addition, the aryl isoprenoids and related compounds were detected in both samples based on EIC m/z 134 and m/z 237 (Figure S2). Aryl isoprenoids, especially C 40 isorenieratane, and diagenetic compounds are indicators of organic matter contribution from marine sulfur bacteria (i.e., Chlorobiaceae).…”

Section: Resultsmentioning

confidence: 98%

“…28 The abundance of C 30 TPP is an indication of lacustrine fresh to brackish water depositional paleoenvironment, 30 as observed by Casilli et al 31 The TPP 30 /Dia 27 ratio <1, as observed for SEAL1, suggests a marine paleoenvironment. 16,19 The sterane profiles (SRM m/z 217, Figure S1) show high abundance of short-chain steranes (C 21 diginane, 21αββ) in SEAL2. Both samples presented C 27 sterane predominance in the class (C 27 > C 29 > C 28 ; C 27 /C 29 steranes >1.30; Table 1), and C 27 to C 29 diasteranes were identified in both samples.…”

Section: Resultsmentioning

confidence: 99%

“…The Sergipe-Alagoas Basin is divided into two sub-basins (Sergipe and Alagoas Basins) and encompasses 44 370 km 2 of the East Brazilian margin, 12 620 km 2 are onshore. The geological characteristics and biomarkers of Sergipe-Alagoas Basin (northeastern Brazil) are well documented. , In general, the Sergipe-Alagoas Basin developed during the Upper JurassicEarly Cretaceous period and its tectonostratigraphic record is represented by four mega-sequences. Biomarkers revealed five depositional paleoenvironments of the organic matter in the Sergipe-Alagoas Basin (lacustrine freshwater, saline lacustrine, marine evaporitic, marine carbonate, and open marine anoxic) …”

Section: Methodsmentioning

confidence: 99%

“…45 Recently, the abundance of phytanyl benzene and phytanyl toluene was reported in mudstones from Permian−Triassic Boundary sections, and its occurrence was associated to marine organic matter deposition in mid-paleolatitudes and microorganisms that could live under drastic paleoenvironmental conditions. 46 Several organic matter sources (Gloeocapsamorpha prisca, 20 Curtobacterium pusillum, 51 Alicyclobacillus spp, 52 and Phormidium ectocarpi 53 ) and biomass (i.e., olefin, triacylglycerol, fatty acids, macromolecules, and biopolymers) 4,5,19 may contribute to the formation of alkyl aromatics in geological samples.…”

Section: Energy and Fuelsmentioning

confidence: 99%

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An Assay on Alkyl Aromatic Hydrocarbons: Unexpected Group-Type Separation of Diaromatic Hydrocarbons in Cretaceous Crude Oils from Brazilian Marginal Basin

et al. 2019

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Numerous aromatic biomarkers such as aromatic carotenoids and aryl isoprenoids have been reported in Brazilian Cretaceous oils. The n-alkyl aromatics such as n-alkyl benzenes (ϕ-C n ), toluenes (ϕ T -C n ), xylenes, and mesitylenes have also been detected in geological samples and can be valuable tools in geochemical and environmental investigations. In this work, comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC−TOFMS) and GC−tandem MS (GC−MS/MS) were applied to identify the alkyl aromatic series in two crude oils from the Sergipe-Alagoas Basin, Brazil. Geochemical characteristics indicate a different depositional paleoenvironment for each sample, marine and lacustrine end-members. Aromatic compounds were identified using full mass spectrum information, diagnostic ions (i.e., m/z 92 for alkylbenzenes and m/z 106 for alkyltoluenes), selected reaction monitoring transitions, and coinjection with an authentic C 21 n-pentadecylbenzene standard. The Sergipe-Alagoas oils presented a series of n-alkylbenzenes and n-alkyltoluenes ranging from ϕ-C 7 to ϕ-C 33 and ϕ T -C 7 to ϕ T -C 30 , respectively. In addition, phytanyl arenes and a new series of α,ωbisphenylalkanes were identified for the first time in Sergipe-Alagoas oils. The n-alkylbenzene profile for marine crude oil resembles that of n-alkanes and n-alkylcyclohexanes, which suggests that they may have the same precursors. The investigation of aromatic fractions and detection of n-alkyl aromatic hydrocarbons in Brazilian Cretaceous oils provide new assignments to the contribution of organic matter and its geochemical significance.

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