REDOX CONTROL OF TRACE ELEMENT ENRICHMENT AT THE TRIASSIC-JURASSIC BOUNDARY, FUNDY BASIN, CANADA

Tanner and Kyte (EPSL 240: 641, 2005) described a pattern of PGE enrichment in continental strata of the Blomidon Formation ostensibly spanning the palynological Triassic-Jurassic boundary at Partridge Island, Nova Scotia. This earlier study found Ir concentrations exceeding 310 pg/g, at multiple levels near the top of the formation. We re-examined the trace element geochemistry of these strata at much higher resolution and confirm that Ir concentrations are elevated at several horizons in the uppermost meter of the formation. The level of Ir elevation correlates well with the concentration of organic carbon in the strata. Other trace elements, in particular Sc, Cr, Fe, Co, Ni, Zn, Cs, Ce and Eu display modest enrichment above baseline levels at approximately the same stratigraphic levels as the peak concentrations of Ir. The stratigraphic distribution of these elements appears to be controlled largely by redox boundary conditions, with some elements, such as Ir, probably forming organo-metallic complexes. We find no geochemical or sedimentological evidence for an extraterrestrial source for this enrichment, and propose mantle outgassing and aerosol deposition during eruptions of the flood basalts of the Central Atlantic Magmatic Province as an alternative source of this enrichment.