Mounting evidence suggests that the Archaic Southeast shell mound builders had large‐scale trade networks and engaged in social aggregations. Here, incremental 87 Sr/ 86 Sr values were measured by laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) in third molar enamel samples of 11 individuals interred in the Middle Archaic Harris Creek shell burial mound in St. John's River Valley (SJRV), Florida. Results reveal that SJRV residents engaged in short‐term, long‐distance mobility up to the Piedmont margin and excursions into coastal areas, consistent with direct trading and social gatherings. Two individuals are interpreted as migrants from central Tennessee, suggesting a link to the Ohio River Valley shell mound builders.
A global carbon-isotope curve for the Late Triassic has the potential for global correlations and new insights on the complex and extreme environmental changes that took place in this time interval. We reconstruct the global δ13Corg profile for the late Norian, improving on sparse published data from North American successions that depict a "chaotic carbon-isotope interval" with rapid oscillations. In this context, we studied three sections outcropping in the Lagonegro Basin (southern Italy), originally located in the western Tethys. The carbon-isotope profiles show four negative excursions correlatable within the Lagonegro Basin. In particular, a negative shift close to the Norian/Rhaetian boundary (NRB) appears to correlate with that observed in the North American δ13Corg record, documenting the widespread occurrence of this carbon cycle perturbation. The 87Sr/86Sr and 187Os/188Os profiles suggest that this negative shift was possibly caused by emplacement of a large igneous province (LIP). The release of greenhouse gases (CO2) to the atmosphere-ocean system is supported by the 12C enrichment observed, as well as by the increase of atmospheric pCO2 inferred by different models for the Norian/Rhaetian interval. The trigger of this strongly perturbed interval could thus be enhanced magmatic activity that could be ascribed to the Angayucham province (Alaska, North America), a large oceanic plateau active ca. 214 ± 7 Ma, which has an estimated volume comparable to the Wrangellia and the Central Atlantic Magmatic Province (CAMP) LIPs. In fact, these three Late Triassic igneous provinces may have caused extreme environmental and climate changes during the Late Triassic.
Dissolved Zr and Hf distributions have been determined for five stations located across the shelf break in the northeastern Atlantic Ocean on the Celtic Approaches. For stations in deep water, the range in Zr concentrations has been found to be 70–180 pmol/kg, and the range in hafnium concentrations 0.4–1.1 pmol/kg. The distributions with depth are indicative of a nutrient-like scavenging-regeneration behavior in seawater, although the dissimilarity with silicate and nitrate for samples below the nutricline suggest that other mechanisms are also important in defining the oceanic distribution of these elements. In contrast, the concentrations of Zr and Hf at the station located closest to land are highest in surface waters and decrease with depth, although salinity does not indicate dilution of seawater with freshwater with high Zr and Hf concentrations. The ratio of dissolved Zr to Hf in seawater is higher and more variable than is found for the majority of terrestrial rocks, or predicted from thermodynamic considerations. Fractionation due to small differences in their interactions with particulate material is implicated.
Abstract We analyzed the first Cu isotopes in primary cupreous pyrite and orpiment, from modern CO2-degassing, seafloor massive sulfide diffuser vents (“KCO2Ds”), from the Kolumbo submarine volcano, Hellenic volcanic arc. Samples came from six KCO2Ds that are actively boiling. Pyrite comprises colloform pyrite-I and euhedral pyrite-II, which occur erratically distributed within the KCO2Ds and are contemporaneous with barite and spatially concurrent with the chalcopyrite that is lining narrow internal conduits, respectively. Orpiment occurs on the outer walls of the KCO2Ds with barite and stibnite. The δ65Cupyrite-I values show high variability, ranging from +2.93‰ to +6.38‰, whereas the δ65Cupyrite-II and δ65Cuchalcopyrite values vary from −0.94‰ to +0.25‰ and −0.45‰ to –0.09‰, respectively. The range of δ65Cuorpiment between +1.90‰ and +25.73‰ is the most extreme ever reported from any geological setting. Pyrite-I is concentrically layered, with a core comprising random crystallites, whereas the mantle crystallites have grain-size, shape, and orientation variability between layers. Pyrite-II forms aggregates of uniform euhedral pyrite crystals. Pyrite-I has higher concentrations of Cu (≤21,960 ppm) compared to pyrite-II (≤4963 ppm), and both have incompatible and volatile metal(loid)-rich composition and low Sb/Pb (<0.5) and Tl/Pb (<0.03) ratios. When combined with evidence for significant magmatic contributions at Kolumbo and geochemical and micro-textural evidence for recurrent intense boiling and/or flashing or gentle and/or non-boiling, the measured extreme δ65Cu values are consistent with transport of Cu by vapor that is preferentially enriched by heavy 65Cu and controlled by continuous Rayleigh distillation–type Cu fractionation. Boiling-induced Cu vapor transport can generate extreme Cu isotope fractionation.
Published Sn isotope data along with 150 new analyses of cassiterite and four granite analyses constrain two major tin isotope fractionation steps associated with (1) separation of tin from the magma/orthomagmatic transitional environment and (2) hydrothermal activity. A distinct Sn isotope difference across deposit type, geological host rocks, and time of ore deposit formation demonstrates that the difference in the mean δ124Sn value represents the operation of a unified process. The lower Sn isotope values present in both residual igneous rocks and pegmatite suggest that heavier Sn isotopes were extracted from the system during orthomagmatic fluid separation, likely by F ligands with Sn. Rayleigh distillation models this first F ligand-induced fractionation. The subsequent development of the hydrothermal system is characterized by heavier Sn isotope composition proximal to the intrusion, which persists in spite of Sn isotope fractionating towards isotopically lighter Sn during hydrothermal evolution.
Abstract Submarine groundwater discharge is increasingly recognized as an important component of the oceanic geochemical budget, but knowledge of the distribution of this phenomenon is limited. To date, reports of meteoric inputs to marine sediments are typically limited to shallow shelf and coastal environments, whereas contributions of freshwater along deeper sections of tectonically active margins have generally been attributed to silicate diagenesis, mineral dehydration, or methane hydrate dissociation. Here, using geochemical fingerprinting of pore water data from Site J1003 recovered from the Chilean Margin during D/V JOIDES Resolution Expedition 379 T, we show that substantial offshore freshening reflects deep and focused contributions of meteorically modified geothermal groundwater, which is likely sourced from a reservoir ~2.8 km deep in the Aysén region of Patagonia and infiltrated marine sediments during or shortly after the last glacial period. Emplacement of fossil groundwaters reflects an apparently ubiquitous phenomenon in margin sediments globally, but our results now identify an unappreciated locus of deep submarine groundwater discharge along active margins with potential implications for coastal biogeochemical processes and tectonic instability.
'/%3e%3cuse xlink:href='%23a' transform='scale(-1 1)'/%3e%3c/g%3e%3cuse xlink:href='%23b' transform='rotate(72)'/%3e%3c/g%3e%3cuse xlink:href='%23b' transform='rotate(-72)'/%3e%3cuse xlink:href='%23c' transform='rotate(144)'/%3e%3c/svg%3e)
