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The timing and mechanisms of the climatic and environmental perturbations induced by the emplacement of the Deccan Traps large igneous province (India) and their contribution to the Cretaceous-Paleogene (K-Pg) mass extinction are still debated. In many marine sediment archives, mercury (Hg) enrichments straddling the K-Pg boundary have been interpreted as the signature of Deccan Traps volcanism, but Hg may also have been derived from the Chicxulub (Mexico) impact. We investigated the Hg isotope composition, as well as the behavior of iridium (Ir) and other trace elements, in K-Pg sediments from the Bidart section in southwest France. Above the K-Pg boundary, Ir content gradually decreases to background values in the Danian carbonates, which is interpreted to indicate the erosion and redistribution of Ir-rich fallouts. No significant enrichment in Ir and W, or Zn and Cu, is observed just below the K-Pg boundary, excluding the hypothesis of downward remobilization of Hg from the boundary clay layer. Positive Δ199Hg and slightly negative values in the upper Maastrichtian and lower part of the early Danian are consistent with the signature of sediments supplied by atmospheric Hg2+ deposition and volcanic emissions. Up section, large shifts to strongly negative mass-dependent fractionation values (δ202Hg) result from the remobilization of Hg formerly sourced by the impactor or by a mixture of different sources including biomass burning, volcanic eruption, and asteroid impact, requiring further investigation. Our results provide additional support for the interpretation that the largest eruptions of the Deccan Traps began just before, and encompassed, the K-Pg boundary and therefore may have contributed to the K-Pg mass extinction. [ABSTRACT FROM AUTHOR]

The element mercury (Hg) can develop large mass‐independent fractionation (MIF) (Δ199Hg) due to photo‐chemical reactions at Earth's surface. This results in globally negative Δ199Hg for terrestrial sub‐aerially‐derived materials and positive Δ199Hg for sub‐aqueously‐derived marine sediments. The mantle composition least affected by crustal recycling is estimated from high‐3He/4He lavas from Samoa and Iceland, providing an average of Δ199Hg = 0.00 ± 0.10, Δ201Hg = −0.02 ± 0.0.09, δ202Hg = −1.7 ± 1.2; 2SD, N = 11. By comparison, a HIMU‐type lava from Tubuai exhibits positive Δ199Hg, consistent with altered oceanic crust in its mantle source. A Samoan (EM2) lava has negative Δ199Hg reflecting incorporation of continental crust materials into its source. Three Pitcairn lavas exhibit positive Δ199Hg which correlate with 87Sr/86Sr, consistent with variable proportions of continental (low Δ199Hg and high 87Sr/86Sr) and oceanic (high Δ199Hg and low 87Sr/86Sr) crustal material in their mantle sources. These observations indicate that MIF signatures offer a powerful tool for examining atmosphere‐deep Earth interactions. Plain Language Summary: While Earth's mantle is continuously chemically and isotopically stirred by convection, some ocean island lavas preserve isotopic anomalies. Their most likely origin is the recycling of crustal material into Earth's mantle by subduction. A question is then whether these crustal materials originate from the ocean or the continents. By using mercury stable isotopic compositions, which have specific signatures in ocean and continent materials, we identify whether these anomalies are due to continental or oceanic crustal material in various ocean island basalts. Key Points: The Hg isotopic composition of the primitive mantle was determined by analyzing lavas from the Samoa and Iceland hotspotsKey samples from the canonical mantle end member were analyzed to track crustal recycling in the mantleWe demonstrate the presence of recycled oceanic and continental materials in the source of ocean island basalts [ABSTRACT FROM AUTHOR]

Abstract: We report Zn isotopic ratios (δ66Zn) of river suspended particulate matter (SPM) and floodplain deposits (FD) from the Seine basin, France, with a precision ⩽0.05‰. A decrease in δ66Zn from 0.30‰ to 0.08‰ is observed in SPM from the upstream to downstream parts of the fluvial system, associated with an increase in Zn concentration from 100ppm to 400ppm. The Zn/Al of SPM at the river mouth is up to five times greater than the Zn/Al of the natural background, and by normalizing to the later value we define a Zn enrichment factor. Suspended sediments from a temporal series of samples collected in Paris display a similar variation in δ66Zn of between 0.08‰ and 0.26‰, while showing an inverse relationship between the Zn enrichment factor and δ66Zn. The amount of Zn transported as suspended load varies from 10% to 90%, as a function of increasing discharge. The δ66Zn of SPM and the dissolved load are correlated, suggesting that adsorption processes are probably not the dominant process by which the Zn enrichment of SPM takes place. Instead, we interpret our data as reflecting the mixture of two main populations of suspended particles with distinct δ66Zn. The first is characteristic of natural silicate particles transported by erosion processes to the river, while the second likely represents anthropogenic particles derived from wastewater treatment plants or combined sewer overflows. Based on isotopic ratios, we calculate that 70% of Zn in SPM of the Seine River in Paris is of anthropogenic origin. [Copyright &y& Elsevier]

• Limited contribution of organic carbon to the Shuram Excursion. • The enhanced terrestrial input and the photic zone euxinia reduced the Δ199Hg. • The photic zone euxinia frequently occurred in the mid-depth ocean. • Macroscopic multicellular eukaryotes were poisoned by H 2 S. The Doushantuo negative carbon isotope excursion (DOUNCE), which corresponds to the worldwide mid-Ediacaran Shuram-Wonoka anomaly (567∼574 Ma), is characterized by a significant shift in carbonate-carbon isotopic values (δ13C carb) from ∼ 5‰ down to ∼ -12‰. It has been proposed to result from remineralizing a giant dissolved organic carbon (DOC) pool within the Ediacaran Ocean. However, direct geological proof confirming the existence and oxidation of such a large DOC reservoir is still scarce. The strong affinity of Hg for organic carbon in the surface environment could provide helpful information on the potential contribution of Hg-associated DOC to the DOUNCE. Here, Hg content and isotope values of marine sediments from the slope (Songtao) and basin (Fengtan) settings were measured and discussed with the previously published data from the shelf environment (Jiulongwan) in South China. The generally low Hg concentration and the absence of Hg/TOC (total organic carbon) anomaly within the DOUNCE carbonate from the proximal to distal sections argue against the massive contribution of DOC to the DOUCE. The gradually decreasing Δ199Hg but increasing δ202Hg in the proximal depositions would be indeed ascribed to the enhanced terrestrial input and the photic zone euxinia (PZE), which might hinder the development and expansion of macroscopic multicelluar eukaryotes via H 2 S poisoning. Our new Hg isotope data casts doubt on the DOC oxidation model, and contributions from other 12C-enriched reservoirs (e.g. recycled carbonatites) could be the cause of the most significant negative δ13C carb excursion in Ediacaran. [ABSTRACT FROM AUTHOR]

Mercury (Hg/TOC) spikes from eight Permian–Triassic boundary (PTB) sections in this study display patterns similar to each other across the so-called extinction interval as well as strong variation in sedimentation rates from section to section. Mercury may have been originated from the synchronous magmatism of the Siberian Traps Large Igneous Province (STLIP). At the GSSP in Meishan, China, Hg/TOC peaks were observed in the latest Permian mass extinction interval (LPME) and Early Triassic mass extinctions (ETME). The successions at Hovea-3 (Australia), Ursula Creek (Canada), Idrijca (Slovenia), Rizvanuša (Croatia) exhibit Hg/TOC peaks at the LPME and PTB. The Rizvanuša section displays one peak at the ETME horizon, Zal and Abadeh (Iran) successions at the LPME and ETME horizons, while Misci/Seres (Tyrol/Italy) section shows an enrichment at the LPME. The largest Hg/TOC peaks at the LPME, PTB and ETME are, perhaps, linked to the beginning of stage 2 (extrusive hiatus) of the Siberian Traps LIP. The meaning of the Hg/TOC spike between the LPME event and the PTB in seven of these sections is fuzzy. In the δ202Hg (MDF) vs Δ201Hg (MIF) cross plot, the majority of samples from the extinction interval appear within the volcanic-emission box and a few samples plot in the sediment/soil/peat box. Hg-isotope signatures resulted from mixing processes of volcanic and normal marine sediment Hg, generating four horizontal trends whose Δ201Hg shows negligible to no variation. Less terrigenous-Hg influx was noticed in the sections closer to the STLIP (Rizvanuša, Idrijca and Seres/Misci, all in Europe) in which Δ201Hg (MIF) is close to zero. Marked influence occurs in sections far distant from the STLIP (Meishan, Ursula Creek and Hovea-3) that exhibit negative Δ201Hg (MIF). The two sections from Iran, at intermediate distance from the STLIP, exhibit the highest, positive Δ201Hg values (Abadeh section) and the lowest, negative Δ201Hg values (Zal section). A Δ199Hg (MIF) vs Hg (n·ng−1) cross plot suggests that volcanic Hg has been contaminated by normal marine source-Hg influx in these sections helping to shape two major curved trends. The negative C-isotope excursions and Hg/TOC enrichments in the studied sections are nearly coeval and this supports the hypothesis of synchronism between the Permian–Triassic transition biotic crises (LPME and ETME) and the start of the stage 2 of the Siberian Traps (sill-intrusion style of magmatism). • Hg/TOC pathways across the extinction interval from eight PTB sections are similar. • Hg/TOC peaks at LPME, PTB and ETME are linked to stage 2 of Siberian Traps volcanism. • In δ202Hg vs Δ201Hg plot samples from the extinction interval plot in the volcanic box • Low terrigenous-Hg influx is noticed in sections closer to the STLIP. • High terrigenous-Hg influence occurs in sections far distant the STLIP. [ABSTRACT FROM AUTHOR]

Oceanic environments and biotas were in a state of near-continuous perturbation during the Early Triassic, the ~5-million-year interval following the latest Permian mass extinction (LPME), but the underlying cause(s) remain uncertain. The role of episodic volcanic or intrusive magmatic activity in triggering global-scale perturbations during this interval is suspected but has not been strongly evidenced to date. Here, we investigate the record of volcanism through the Early Triassic (with a focus on the Smithian-Spathian Boundary, or SSB) using mercury (Hg) concentrations in marine sediments as a proxy. This study examines five marine sections from three paleo-oceans (Paleo-Tethys, Neo-Tethys, and Panthalassa) representing a range of depositional settings from shallow platform to deep slope. Our results suggest that volcanic and magmatic activity of the Siberian Traps Large Igneous Province (STLIP) was most intense during the first ~1.3 million years following the LPME, and that termination of its most active stage was responsible for a sharp cooling event at the SSB. Variations in the intensity of STLIP activity are thus likely to account for the large (>8‰) fluctuations of δ13C carb and related changes in oceanic redox and environmental conditions that characterized the Griesbachian to Smithian substages of the Early Triassic in marine sections globally. We hypothesize that a strong reduction or cessation of STLIP activity at the SSB set the stage for the recovery of marine biodiversity and ecosystems in the Spathian and later. • First Hg concentration records spanning the full Early Triassic from five sections with a global distribution (581 analyses). • Hg data provide a proxy record of the timing and intensity of Siberian Traps volcanic activity during the Early Triassic. • Peak Hg inputs occurred around the Permian-Triassic boundary, when Hg/TOC rose to ~3–8× Late Permian background values. • High Hg inputs during the Griesbachian-Smithian, with a secondary peak coinciding with the Late Smithian Thermal Maximum. • Hg inputs were modest during the Spathian and returned to background levels at the Early/Middle Triassic boundary. [ABSTRACT FROM AUTHOR]

• Sediment Hg can be hosted by the organic, sulfide or clay fractions. • Hg uptake by sulfide fraction favored under strongly euxinic conditions. • TS > 1.0% and TS/TOC > 0.35 linked to dominant sulfide host phase. • Dominant host phase must be determined for correct normalization of Hg volcanic proxy. Mercury (Hg) concentration enrichments have become a widely used proxy for volcanic inputs to sediments, especially for investigation of ancient large igneous province (LIP) eruptions. Its application for this purpose requires normalization to an element representing the dominant host phase of Hg–generally total organic carbon (TOC) for the organic fraction, but occasionally total sulfur (TS) or aluminum (Al) for the sulfide or clay fractions, respectively. Hg studies generally assume an organic matter host, but recent work has demonstrated that sulfide or clay fraction host phases are not uncommon, making it essential to determine formation-specific Hg host phases. Here, we investigate Hg concentrations and their relationships to TOC, TS, and Al in four modern marine settings (Black Sea, Japan Sea, Saanich Inlet, and Peru Margin) and six ancient marine formations (from Lower Cambrian to Lower Jurassic). Multiple regression analysis (MRA) shows that the organic fraction is the dominant host of Hg in all of the modern marine sediments examined here, as well as in many ancient marine units, although in some of the latter Hg resides primarily in the sulfide fraction (i.e., lower Cambrian and Upper Ordovician units) or partly in the clay mineral fraction (Middle Permian) of the sediment. A sulfide host phase is more likely in strongly euxinic depositional facies, as reflected in high TS concentrations (>1.0%) and TS/TOC ratios (>∼0.35). This study thus demonstrates the importance of determining Hg host phases in sediments prior to normalization and use of Hg as a volcanic proxy. [ABSTRACT FROM AUTHOR]