Abstract Oceanic red beds were widespread during the Late Cretaceous in association with major climate perturbations. Despite their relevance to the debate concerning the effects of climate change on ocean redox, the detailed geochemistry (particularly with regard to Fe mineralogy) and the mechanism of formation of Cretaceous oceanic red beds remain poorly understood. Here we present a detailed examination of Fe partitioning in Cretaceous oceanic red beds. Our focus is on a transition from gray-black shales (the Barremian-Santonian Gyabula Formation) to overlying oceanic red beds (the Late Santonian-Campanian Chuangde Formation) from the Chuangde section, Gyangtze, South Tibet. A chemical sequential extraction method was applied to these two distinct rock types to acquire burial records for different operationally defined iron fractions. Carbonate-associated iron and pyrite are relatively enriched in the Gyabula Formation. When combined with total Fe-Al relationships, REE data, and trace-fossil occurrences, this implies deposition under conditions of relatively reduced dissolved oxygen. In contrast, pyrite was below detection limits and carbonate-associated iron was much lower in the red beds of the Chuangde Formation. Here, ferric iron oxides (largely hematite) are relatively enriched, and this enrichment likely occurred during deposition to early diagenesis. The ratio of ferric oxides to total iron (Feox/FeT) indicates an oxic depositional environment for the red beds. A comparison of records of reactive iron burial with proxies for paleo-productivity suggests that productivity decreased with increased Feox/FeT in the red beds. This implies that a feedback between oceanic redox and productivity (i.e., lower productivity under more oxic oceanic conditions), might be responsible for the prolonged formation of Cretaceous oceanic red beds in South Tibet. This feedback mechanism could have been fostered by increased ventilation of the ocean due to global cooling and a deep connection between the North and South Atlantic Ocean during Late Santonian-Early Campanian times. Key words:iron speciation, oceanic red beds, Cretaceous, Chuangde section, South Tibet