Fig. 5: Mercury isotopic signature variation across the Triassic–Jurassic transition.

Cross-plots depicting Δ¹⁹⁹Hg (MIF = mass-independent fractionation) plotted against a mercury over total organic carbon correction (Hg/TOC), b δ²⁰²Hg (MDF = mass-dependent fractionation), c Δ²⁰¹Hg and d spore malformations for the Schandelah-1 core. a Pathways for Hg-enrichment in relation to Δ¹⁹⁹Hg (MIF). The shaded gray bars represent background Hg concentrations (<50 ppb/wt%). The red square indicates the position of the volcanic endmember, based on the highest measured Hg/TOC (vertical red line = 309.36 ppb/wt%) and zero MIF (Δ¹⁹⁹Hg = ~0‰) of volcanogenic Hg. The black dashed arrow indicates the predicted path of volcanic Hg-enrichment based on volcanic-related intervals (squares) and the estimated volcanic endmember. The blue dashed arrow indicates the path of terrestrial Hg-enrichment. The position of the terrestrial-input endmember is assumed to be the highest value for Hg/TOC in the Hettangian interval and Δ¹⁹⁹Hg values similar to the background (~−0.1‰ to −0.3‰). The yellow diamond represents an outlier data point. The range of Hg-MIF reservoirs is depicted in boxplots. b Relative variation of Δ¹⁹⁹Hg (MIF) versus δ²⁰²Hg (MDF) for three separate intervals (excluding the Sinemurian measurements) with the slopes of the respective linear relations depicted with the dashed lines. c Three Δ¹⁹⁹Hg/Δ²⁰¹Hg ratios based on total, Rhaetian, and Hettangian intervals (dashed lines) showing variation in mass-independent fractionation (MIF). d The relation of Δ¹⁹⁹Hg and the corresponding relative abundances of spore malformations. Average spore malformations were calculated using three samples closest to the Hg-isotope measurements if sample rates did not match. Error bars represent standard deviation (2σ).