Abstract
The Valanginian stage (Early Cretaceous) includes an episode of significant environmental changes, which are well defined by a positive δ13C excursion. This globally recorded excursion indicates important perturbations in the carbon cycle, which has tentatively been associated with a pulse in volcanic activity and the formation of the Paraná-Etendeka large igneous province (LIP). Uncertainties in existing age models preclude, however, its positive identification as a trigger of Valanginian environmental changes. Here we report that in Valanginian sediments recovered from a drill core in Wąwał (Polish Basin, Poland), and from outcrops in the Breggia Gorge (Lombardian Basin, southern Switzerland), and Orpierre and Angles (Vocontian Basin, SE France), intervals at or near the onset of the positive δ13C excursion are significantly enriched in mercury (Hg). The persistence of the Hg anomaly in Hg/TOC, Hg/phyllosilicate, and Hg/Fe ratios shows that organic-matter scavenging and/or adsorbtion onto clay minerals or hydrous iron oxides only played a limited role. Volcanic outgassing was most probably the primary source of the Hg enrichments, which demonstrate that an important magmatic pulse triggered the Valanginian environmental perturbations.
Highlights
Elemental mercury (Hg0), which is globally distributed due to a rather long atmospheric residence time (0.5–1 year)[28]
Since the pioneering work of Sanei et al.[25], anomalous enrichments in Hg contents observed in the geological records have been related to volcanic eruptions, such as the formation of the Siberian Traps leading to the end-Permian extinction event[31,33], central Atlantic magmatic activity inducing end-Triassic mass extinction[34], Karoo Ferrar LIP volcanism implied in the early Toarcian OAE29, and the build up of the Deccan Traps related to the K-T boundary extinction event[32,35,36,37]
The selected sections have not been the subject of significant diagenesis, benefit from a robust temporal frameworks, and the evolution of the Valanginian Weissert episode is well defined by δ13C stratigraphy[6,16,38,39,40]; Fig. S2 in the supplementary material)
Summary
Elemental mercury (Hg0), which is globally distributed due to a rather long atmospheric residence time (0.5–1 year)[28]. Hg is preferentially adsorbed onto organic matter, hydrous iron (Fe) oxides, and/or clay minerals[25,29,30,31,32] (Fig. S1 in supplementary material). The origin of sedimentary Hg anomalies is evaluated by discrmining between enrichments related to enhanced TOC, iron, and/or clay mineral contents and enrichments related to volcanic activity[29]. We investigate the distribution of Hg contents in four Valanginian reference sections located in pelagic and hemipelagic environments in the Central Tethyan Realm (Lombardian Basin, Breggia section), the northern Tethyan margin (Vocontian Basin, Orpierre and Angles sections), and the narrow seaway connecting the Tethyan and Boreal Oceans (Polish Basin, Wąwał core) (Fig. 1). For the samples with less than
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