New Paleoenvironmental Proxies for the Permian Irati Black Shales Based on Acidic O1 and O2 Compounds Assessed by FT-ICR-MS

Summary Variations of the acidic polar composition of the Early Permian Irati black shales and Serra Alta shales were assessed by ESI(-) FT-ICR-MS to investigate their significance for the paleoenvironmental studies by comparison with known features in the northeastern and central-eastern Parana Basin (Brazil). The high O>2 classes in the Serra Alta shales points to high input of terrigenous OM deposited in oxic waters. In addition, seven parameters based on O1 and O2 compounds are proposed as new paleoenvironmental proxies: phenol index (%DBE 4; O1 class); C27/C28 DBE 4 (O1 class); C27/C28 DBE 5 (O1 class); Even/OddFA; TARFA Odd (terrigenous/aquatic ratio); C36 hopanoic acid index; and hopanoic/steranoic acids ratio. Higher values of the phenol index and the TARFA indicate higher land plant input during the final black shale deposition, and higher Even/OddFA to northeastern basin samples reflects their higher content of terrigenous OM. Furthermore, variations of C27/C28 (DBE 4) and C27/C28 (DBE 5) is useful to reconstruct paleosalinity, in which higher values indicate higher salinity. The C36 hopanoic acid index is higher for the marine hypersaline basal samples from the northeastern basin, while a significant bacterial biomass signal is stored as a higher hopanoic/steranoic acids ratio for central-eastern basin samples.