Multiple Ir anomalies in uppermost Triassic to Jurassic-age strata of the Blomidon Formation, Fundy basin, eastern Canada

Abstract: A detailed profile of Ir concentrations in continental strata of the Blomidon Formation ostensibly spanning the Triassic–Jurassic boundary confirms the existence of multiple anomalies, with a peak Ir concentration of 450 pg/g. The total amount of Ir deposited exceeds 4 ng/cm2, a value that requires an external source other than typical terrestrial sediment. Of the 10 other elements measure, only Zn and organic carbon are correlated to Ir. The organic carbon appears to be concentrated in mm-thick kerogenous laminae in greenish-grey to dark grey sediment layers that also host the Ir anomalies. The stratigraphic distribution of Ir and probably Zn appears to be controlled largely by redox boundaries conditions, with Ir probably forming organo-metallic complexes. We find no specific geochemical or sedimentological evidence for an extraterrestrial source for this enrichment, although we cannot exclude an impact origin. However, the close spatial and temporal relationship of the Ir anomalies in the Fundy and Newark basins to the basalts of the Central Atlantic Magmatic Province suggests alternative working hypotheses. Potentially, the volcanic rocks sourced the Ir through post-eruptive fluid mobilization into the surrounding sediments. Conversely, mantle outgassing and aerosol deposition during early stages of the eruptions may have been the source for the Ir anomalies. At this time, the data are insufficient to eliminate any of these hypotheses conclusively. [Copyright &y& Elsevier]