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 OAE 1a. (28th April 2022)

• Record Type: Journal Article
• Authors: Herdocia, Carlos; Maurrasse, Florentin J‐M. R.
• Is Part Of: Depositional record. Volume 8:Number 2(2022)
• Page Start: 931
• Page End: 957
• Publication Date: 2022-04-28
• Subjects: Aptian -- dysoxic conditions -- marine redox conditions -- organic matter preservation -- Organyà Basin -- Spain -- terrestrial fluxes; Sediments (Geology) -- Periodicals; Sedimentology -- Periodicals; Sedimentation and deposition -- Periodicals; 552.5
• DOI: 10.1002/dep2.186
• Languages: English
• ISSNs: 2055-4877

Abstract

Abstract: 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 a detailed lithostratigraphic and geochemical study is presented for 35.6 m of the Cabó Formation, part of the Organyà Basin, North‐east Spain, to assess intermittent periods of enhanced organic carbon preservation in Lower Aptian sediments preceding Oceanic Anoxic Event 1a. The Organyà area contains well‐exposed outcrops of Mesozoic black to dark grey marlstones and limestones with variable amount of organic matter (OM) indicative of oxygen‐deficient conditions. Previous work in a section near the town of Organyà focussed on lithostratigraphy and biostratigraphy and assigned a Barremian–Aptian age. This study aims to provide an updated age based on carbon isotope correlation established elsewhere, and assess the chemostratigraphic characteristics of the Barremian–Aptian to clarify environmental changes regarding oxygen deficient conditions in the basin at that time. The δ 13 Corg values fluctuate from −22.1 to −24.4‰ showing concurrence with results at the El Pui section west of the studied section. Chemostratigraphic correlation of the δ 13 Corg reveals that the section is within segment C2, in the Lower Aptian. Redox‐sensitive trace elements (V, Ni, Co, Cr, Cu, Mo) indicate heightened dysoxic conditions at five organic‐rich layers, here designated carbonaceous layers (TOC >2%), associated with enhanced terrigenous fluxes coincident with increased major elements (Al, Si and Ti) during these intervals. Biomarkers from six levels showed n ‐alkane distributions with chain lengths from n C14 to n C34, mostly below n C21 indicating a predominance of marine‐derived OM. Climate conditions inferred from variable smectite, and kaolinite content suggests fluctuating humid‐warm conditions. The results thus reveal that the Organyà Basin experienced intervals of distinct oxygen‐poor conditions prior to the onset of Oceanic Anoxic Event 1a. Abstract : This study on 35.6 m of Lower Aptian deposits of the Cabó Formation assesses the geochemical characteristics regarding Barremian ‐ Aptian environmental changes. The results indicate a stratigraphic position within carbon isotope segment C2, n‐alkanes with Pr/Ph ratios between 0.57 and 1.54 indicate that the OM is not thermally overmature, and further highlight that the Organyà Basin experienced intermittent intervals of enhanced terrigenous fluxes associated with low oxygen conditions prior to the onset of OAE 1a.