Goldberg, KarinHumayun, M.2017-11-302017-11-30http://hdl.handle.net/2097/38351Citation: Goldberg, K., & Humayun, M. (2016). Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Parana Basin, southern Brazil. Brazilian Journal of Geology, 46(3), 377-393. doi:10.1590/2317-4889201620160001Paleoredox indicators were used to assess the depositional environment of the Permian Irati Formation, and discuss the controls on the accumulation of organic-rich sediments. Geochemical data were measured for 43 drill-core samples in southern Parana Basin. We infer that redox boundary was located at the sediment-water interface during the accumulation of these sediments. Trace-element data demonstrate that Irati shales were similar to average shales, except during deposition of two organic-rich beds in which U and Mo are enriched, suggesting fully anoxic conditions. The variable degree of oxygenation of bottom waters is also attested by DOPT, Fe-T/Al, and sedimentological indicators of episodic ventilation. DOPT and Fe and S correlation points to an iron-limited environment, where the main sulfur sink is organic matter rather than pyrite. Cu and Cu/Mo ratio suggests bottom-water anoxia driven by increased organic flux. The Irati Formation was probably deposited in a salinity-stratified body of water, with positive water balance. The main control on the accumulation of the organic-rich sediments was the high organic carbon flux resultant from high primary productivity in surface waters. Anoxia arose as a consequence of increased productivity, not as the primary driver in the formation of these organic-rich rocks.Attribution 4.0 International (CC BY 4.0)Black ShalesPaleoredox ProxiesIrati FormationPermianEarth-Element GeochemistryArticle