Chemostratigraphic characteristics of trace elements, biomarkers and clay mineralogy indicating environmental conditions within Aptian sediments of the Organyà Basin, North‐east Spain, prior to the onset of <scp>OAE</scp> 1a

Shifting palaeoceanographic and palaeoclimatic conditions together with fluctuating eustatic sea levels during the Early Cretaceous Aptian stage led to a globally widespread deposition of organic-rich marine sediments designated Oceanic Anoxic Event 1a. Here detailed lithostratigraphic geochemical study is presented for 35.6 m Cabó Formation, part Organyà Basin, North-east Spain, assess intermittent periods enhanced organic carbon preservation in Lower preceding The area contains well-exposed outcrops Mesozoic black dark grey marlstones limestones variable amount matter (OM) indicative oxygen-deficient conditions. Previous work section near town focussed on lithostratigraphy biostratigraphy assigned Barremian–Aptian age. This aims provide an updated age based isotope correlation established elsewhere, chemostratigraphic characteristics clarify environmental changes regarding oxygen deficient basin at that time. δ13Corg values fluctuate from −22.1 −24.4‰ showing concurrence results El Pui west studied section. Chemostratigraphic reveals within segment C2, Aptian. Redox-sensitive trace elements (V, Ni, Co, Cr, Cu, Mo) indicate heightened dysoxic five layers, here carbonaceous layers (TOC >2%), associated terrigenous fluxes coincident increased major (Al, Si Ti) these intervals. Biomarkers six showed n-alkane distributions chain lengths nC14 nC34, mostly below nC21 indicating predominance marine-derived OM. Climate inferred smectite, kaolinite content suggests humid-warm thus reveal Basin experienced intervals distinct oxygen-poor prior onset