Detection of Early-Middle Devonian biotic crises in East Gondwana, Paraná Basin, Brazil: An organic geochemical approach

• Published in: Organic geochemistry Vol. 181; p. 104629
• Main Authors: Rocha, Luiza Rodrigues, de Souza, Eliane Soares, Severiano Ribeiro, Hélio Jorge Portugal, Franco, Danielle Mitze Muller, Covas, Taynara, Gontijo Vaz, Boniek, da Cruz, Georgiana Feitosa
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2023
• Subjects: Depositional paleoenvironmental conditions; FT-ICR-MS; Kačák event; PAH; Perylene; Saturated and aromatic biomarkers; Kačák event; FT-ICR-MS; Perylene; Saturated and aromatic biomarkers; Depositional paleoenvironmental conditions; PAH
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2023.104629

•Changes in paleoenvironmental physicochemical conditions throughout Devonian events.•Zilchov, Daleje, Choteč, and Kačák events identified in Paraná Basin, Brazil.•Saturated and aromatic biomarker results indicating biotic crises in the Devonian.•Perylene as a marker of plant fungal degradation during Eifelian-Givetian.•FT ICR-MS analysis results contributed to biotic crisis events identification. Changes detected in the physicochemical conditions of the depositional palaeoenvironment of the Ponta Grossa Formation (Early-Middle Devonian), East Gondwana, were correlated with significant biotic crises that preceded the great Devonian extinction event (Frasnian-Famennian), culminating in the extinction of the Malvinokaffric fauna. The present study identified Zilchov, Daleje, Choteč, and Kačák biotic crisis events through geochemical analyses. Fifteen outcrop shale samples were analysed for the distributions of well-established geochemical parameters, such as those based on saturated and aromatic biomarkers and polycyclic aromatic hydrocarbons. Parameter results were correlated to polar compound distributions using atmospheric pressure photoionisation (APPI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in positive ionisation mode. A decrease in the summation of n-alkanes, αβC30 hopane, and gammacerane concentrations was observed at the Pragian-Emsian interval, related to the Zilchov event and the first decline of the Malvinokaffric fauna. At the Late Emsian, a severe change in paleoenvironment depositional conditions was detected by the increase in αβ C30 hopane, tetrahydrophenanthrene and gammacerane concentrations, suggesting water column stratification. Moreover, Tricyclic Index values indicated a change to a more freshwater lacustrine environment, which was confirmed by the occurrence ofn-alkyl cyclohexanes series. In addition, high percentages of O1 and N1 class compounds indicated that this interval was probably composed of a mixture of bacterial and terrigenous organic matter. These results indicated a large inflow of fresh and continental waters due to a regression related to the Daleje event and the second decline of the Malvinokaffric fauna. A significant decrease of the pristane/phytane ratio, summation of n-alkanes, αβ C30 hopane and gammacerane concentrations was observed, along with the absence of N1 compounds at the Emsian-Eifelian interval, representing a rapid transgression, corresponding to the Choteč event. At the Eifelian-Givetian interval, the detection of n-alkanes and biomarker low concentration values, low pristane/phytane values (anoxia), as well as the non-detection of N1 class compounds, indicated a great transgression related to the Kačák event and the disappearance of the Malvinokaffric fauna.