Erika R. Elswick

Changes in productivity and redox conditions in the Panthalassic Ocean during the latest Permian

The Gujo-Hachiman section in central Japan provides a rare window into environmental conditions within the Panthalassic Ocean, which encompassed more than half the Earth’s surface at 251 Ma. The section is characterized by a sharp transition from green-gray organicpoor cherts to black siliceous shales in the uppermost Permian. Normalization to the clay fraction demonstrates that apparent increases in the concentrations of organic matter and trace metals above this transition were due primarily to the loss of a diluent biogenic (radiolarian) silica fl ux and only secondarily to a small shift toward more reducing bottom waters. In the black shale, pyrite abundance increases by a factor of ~30× and is dominated by framboidal grains of probable syngenetic origin. These observations suggest that the expansion of lowoxygen conditions within the Panthalassic Ocean was focused within the oxygen-minimum zone rather than at the seafl oor. Such a pattern implies that (1) changes in nutrient fl uxes and primary productivity rates, rather than stagnation of oceanic circulation, were a key factor infl uencing oceanic redox conditions around the Permian-Triassic boundary, and (2) large regions of the Panthalassic Ocean underwent only limited redox changes, providing potential refugia for marine taxa that survived into the Triassic.

Sulfur isotopic studies of continental flood basalts in the Noril’sk region: implications for the association between lavas and ore-bearing intrusions

Previous studies of both ore and non-ore-bearing intrusives in the Permo-Triassic flood basalts of the Siberian platform in the Noril’sk area have shown that high-grade Ni–Cu–platinum group elements (PGE) mineralization is associated with anomalously high δ34S values of ∼8 to 12‰. In addition, several researchers have proposed that observed depletions in the Cu, Ni, and PGE content of basaltic lavas of the Nadezhdinsky (Nd) Formation are related to diffusional exchange with, and upgrading in metal tenor of, sulfides in the volcanic conduit system. Sulfur isotopic studies of the lavas at Noril’sk were initiated to determine if interaction with crustally derived sulfur in the conduit system was evident, and if the Nd lavas in particular were characterized by an anomalous isotopic signature. δ34S values of the lavas range from −4.5 to 8.7‰ Vienna Canon Diablo Troilite (VCDT), with S concentrations from <40 to 1373 ppm. The majority of δ34S values range from 0 to 4‰, and are similar to those from S-poor intrusions in the Noril’sk area. Although textural data are not supportive of early sulfide saturation and the presence of immiscible sulfide droplets in the lavas, recrystallization may have erased expected mineralogical and textural evidence. Mineralogical data indicate that hydrothermal alteration of the lavas has occurred, but S redistribution has been restricted to localized areas and δ34S values have not been affected. The relatively low S concentrations of the lavas are thought to be due in large part to degassing of the lavas in the shallow conduit system and during eruption. Our calculations are consistent with the premise that degassing of basaltic magmas at temperatures in excess of ∼900°C at QFM leads to only minor 34S-depletion of sulfur remaining in the melt, and decreases in δ34S values of less than 2‰ at 90% degassing. For this reason all lavas with δ34S values in excess of ∼ 2‰ require a contribution of 34S-enriched country rock sulfur. Because of the high S content and δ34S value (∼ 16–20‰) of evaporites in the country rocks at Noril’sk, contamination of less than 0.5% is required to explain the most 34S-enriched lavas. The Nd lavas have an average δ34S of 2.9‰, but show no difference in S isotopic composition relative to the other lavas, suggesting that metal depletion involved only limited S transfer, or that exchange between mantle-derived S and S of crustal origin buffered δ34S values to less than ∼5‰. Anomalously positive δ34S values, similar to those of the ore-bearing intrusives in the Noril’sk region, are not consistently found in low-S rocks, either lavas or intrusives. Although the mechanism for the derivation of sulfide in the ore-bearing intrusions remain speculative, it is clear that the formation of sulfide ores characterized by high metal tenors proceeded only in the presence of sulfur of crustal origin.

Evidence for a diachronous Late Permian marine crisis from the Canadian Arctic region

A high-resolution chemostratigraphic study of a 24-m-thick section at West Blind Fiord on Ellesmere Island (Canadian Arctic) documents stepwise environmental deterioration in the marine Sverdrup Basin during the late Changhsingian (late Late Permian) as a result of volcanic disturbances to surrounding landmasses. A horizon within the upper Lindstrom Formation (datum A) is characterized by increased Fe-oxyhydroxide fl uxes and weathering intensity as well as modest shifts toward more reducing watermass conditions and higher marine productivity, recording an initial disturbance that washed soils into the marine environment. The contact between chert of the Lindstrom Formation and silty shale of the overlying Blind Fiord Formation, which is 1.6 m higher and ~50 k.y. younger than datum A, records a large increase in detrital sediment fl ux, more strongly enhanced marine productivity, and a regional extinction of siliceous sponges, herein termed the “Arctic extinction event.” The horizon equivalent to the latest Permian mass extinction of Tethyan shallow-marine sections is 5.6 m higher and ~100 k.y. younger than the Arctic extinction event, demonstrating the diachronous nature of the marine biotic and environmental crisis at a global scale; it is associated with intensifi ed anoxia and possible changes in phytoplankton community composition in the study section. Marine environmental deterioration in the Sverdrup Basin, probably triggered by terrestrial ecosystem deterioration and elevated detrital sediment fl uxes, was under way by the early part of the late Changhsingian, well before the onset of main-stage Siberian Traps fl ood basalt volcanism. The event sequence at West Blind Fiord may record the deleterious effects of early-stage explosive silicic eruptions that affected the Boreal region, possibly through deposition of toxic gas and ash within a restricted latitudinal band, while having little impact on marine ecosystems in the peri-equatorial Tethyan region.

Further Investigation of the Impact of the Co-combustion of Tire-derived Fuel and Petroleum Coke on the Petrology and Chemistry of Coal Combustion Products

Abstract A Kentucky cyclone-fired unit burns coal and tire-derived fuel, sometimes in combination with petroleum coke. A parallel pulverized combustion (pc) unit at the same plant burns the same coal, without the added fuels. The petrology, chemistry, and sulfur isotope distribution in the fuel and resulting combustion products was investigated for several configurations of the fuel blend. Zinc and Cd in the combustion products are primarily contributed from the tire-derived fuel, the V and Ni are primarily from the petroleum coke, and the As and Hg are probably largely from the coal. The sulfur isotope distribution in the cyclone unit is complicated due to the varying fuel sources. The electrostatic precipitator (ESP) array in the pc unit shows a subtle trend towards heavier S isotopic ratios in the cooler end of the ESP.

Reflectance of dispersed vitrinite in shales hosting Pb-Zn-Cu ore deposits in western Cuba: comparison with clay crystallinity

Abstract The Pinar del Rio district of western Cuba contains several examples of stratiform Pb–Zn mineralization underlain by stockwork Cu mineralization. Similar deposits in Canada and Australia have been variously interpreted as products of seafloor hydrothermal systems or of much later hydrothermal activity associated with peak metamorphism during deep burial. The Cuban deposits are Jurassic in age and are less overprinted by later tectonic events than other deposits of this type, so they offer a useful opportunity to resolve these controversies. Vitrinite reflectance and illite and chlorite crystallinity were studied from cores and mine exposures from several localities in western Cuba. Dispersed vitrinite in host shales shows a sharp increase in thermal maturity over three distinct stages from host-rock to stratiform mineralization to stock-work mineralization. Based on vitrinite data from modern hydrothermal systems, the paleotemperatures are 175, 250, and 300 °C. The clay mineral results also show a step-wise increase in the crystallinity of illite and chlorite. In addition, there is an increasing dominance of chlorite over illite. When compared to burial diagenetic trends, chlorite crystallinity in the Cuban samples matches values expected from R r , whereas illite tends to yield lower-than-expected crystallinities. The clay results indicate that chlorite is an ore-stage mineral that equilibrated at the same temperature/pressure conditions as the vitrinite, whereas the illite is largely detrital and only incompletely recrystallized in the relatively short times available. These results are best explained as reflecting relatively low amounts of heating of shales in the country rock by burial diagenesis, progressing to intermediate heating by exhalative seafloor hydrothermal fluids in the stratiform portion of the deposits, and finally to still higher temperatures in the sub-seafloor stockwork portion.

Physical and Geochemical Characteristics of Soils from Angel Mounds State Historic Site, Indiana, including a Case Study of Sherds from Unit A

Abstract Using physical and chemical characteristics of soil to evaluate archaeological artifacts and their preservation potential along with associated features is well established. The soil characteristics and geochemistry of the Angel Mounds site (12Vg1) indicate the soil geochemistry is very homogenous and composed of loams and silt loams with a range of pH values from 4.69 to 6.17, mean value of 5.40 ± 0.47. The slightly acidic nature of the soil favors the preservation of pollen and soil diatoms, with minor corrosion potential for the bone, shell, and sherd artifacts. A comparison of the geochemistry of the soils from Unit A and site-wide sampling to sherds from Unit A suggests that elevated phosphorus (P) in the sherds is either the result of the addition of a P-rich temper material or from the sourcing of nonlocal clay-rich sediment, and not from use-derived residue or from the soils themselves.