J. Barry Maynard

Composition of modern deep-sea sands from arc-related basins

Summary Petrographic and chemical examination of modern deep-sea sands shows a clear distinction between active and passive plate-tectonic settings. Among active settings, sands from forearc basins of island arcs and basins from strike-slip continental margins can be distinguished, but those from other arc-related settings overlap considerably in composition. In particular, sands from continental margin subduction zones and those from the backarc of island arcs appear to be indistinguishable. Chemically, arc-related sands are very close in composition to ancient greywacke sandstones. For instance, sodium almost always exceeds potassium. Thus it is not necessary for sodium to be added to sands diagenetically to make greywackes, as has been suggested.

Heavy Metal Contamination in Soils of Urban Highways Comparison Between Runoff and Soil Concentrations at Cincinnati, Ohio

Rainfall runoff from urban roadways oftencontains elevated amounts of heavy metals in both particulate anddissolved forms (Sansalone and Buchberger, 1997). Because metalsdo not degrade naturally, high concentrations of them in runoffcan result in accumulation in the roadside soil at levels thatare toxic to organisms in surrounding environments. This studyinvestigated the accumulation of metals in roadside soils at asite for which extensive runoff data were also available.For this study, 58 soil samples, collected from I-75 nearCincinnati, Ohio, were examined using X-ray fluorescence, C-Sanalyzer, inductively coupled plasma spectroscopy, atomicabsorption spectrometry and X-ray diffraction. The resultsdemonstrated that heavy metal contamination in the top 15 cm ofthe soil samples is very high compared to local backgroundlevels. The maximum measured amount for Pb is 1980 ppm (at 10–15 cm depth) and for Zn is 1430 ppm (at 0–1 cm depth). Metal content in the soil falls off rapidly with depth, and metalcontent decreases as organic C decreases. The correlation toorganic C is stronger than the correlation to depth. The resultsof sequential soil extraction, however, showed lower amounts ofPb and Zn associated with organic matter than was expected basedon the correlation of metals to % organic C in the whole soil.Measurement of organic C in the residues of the sequentialextraction steps revealed that much of the carbon was not removedand hence is of a more refractory nature than is usual inuncontaminated soils. Cluster analysis of the heavy metal datashowed that Pb, Zn and Cu are closely associated to one another,but that Ni and Cr do not show an association with each other orwith either organic C or depth. ICP spectroscopy of exchanged cations showed that only 4.5%of Pb, 8.3% of Zn, 6.9% of Cu and 3.7% of Cr in the soil isexchangeable. Combined with the small amounts of metals bound tosoluble organic matter, this result shows that it is unlikelythat these contaminants can be remobilized into water. At thissite, clays are not an important agent in holding the metals inplace because of low amounts of swelling clays. Instead, insoluble organic matter is more important. Mass balancecalculations for Pb in soil showed that most of the Pb came fromexhausts of vehicles when leaded gasoline was in use, and thatabout 40% of this Pb is retained in the soil.This study shows that, highway environments being a relativelyconstant source of anthropogenic organic matter as well as heavymetals, heavy metals will continue to remain bound to organicmatter in-situ unless they are re-mobilized mechanically. Removalof these heavy metals as wind-blown dust is the most likelymechanism. Another possibility is surface run-off carrying themetals into surface drainages, bypassing the soil. This studyalso shows that for those countries still using leaded gasoline,important reductions in Pb contamination of soils can be achievedby restricting the use of Pb additives.

Use of statistical analysis to formulate conceptual models of geochemical behavior: water chemical data from the Botucatu aquifer in São Paulo state, Brazil

Water chemical data from the Botucatu Sandstone aquifer in the Sao Paulo State part of the Parana Basin, Brazil, was evaluated using geochemical methods and two statistical analyses: cluster analysis and factor analysis. The results were used to develop a conceptual geochemical model, in which three geochemical regions were identified, and their chemical behavior was modeled. The characteristic chemicals, changing from the recharge area to the center of the basin, are: SiO2—(HCO3− and Ca2+)—(Na+, CO32−, and SO42−). The distribution of the chemicals is interpreted as controlled by different water–rock interaction processes in the different regions. In the recharge area, dissolution of alkali–feldspar minerals in the sandstone is the main reaction observed; in the mid-section of the basin, calcite dissolution results in high calcium and bicarbonate concentration; in the center of the basin, leakage from underlying layers becomes the governing factor.

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.

Trace-metal covariation as a guide to water-mass conditions in ancient anoxic marine environments

Patterns of sedimentary trace-metal variation can provide information not only about benthic redox conditions, but also about other water-mass properties in ancient marine depositional systems. Trace metals such as Mo, U, V, and Re display conservative concentration profiles in the global ocean but varying concentration profiles in modern anoxic silled basins (e.g., the Black Sea, Cariaco Basin, and Framvaren Fjord) as a consequence of enhanced sedimentary uptake, water-mass mixing, microbial cycling, and other processes. Because basin-specific patterns of aqueous trace-metal concentrations can be recorded by the sediment, chemostratigraphic studies of ancient anoxic marine facies have the potential to provide information about the degree of water-mass restriction as well as secular changes in aqueous chemistry and basin hydrography. In the Upper Pennsylvanian Hushpuckney and Stark shales of midcontinent North America, strong positive covariation among major trace metals supports extraction from a water mass of unmodified “normal” seawater chemistry with control of sedimentary trace-metal uptake primarily by benthic redox variation. This inference is consistent with unrestricted renewal of deep waters of the Late Pennsylvanian Midcontinent Sea via lateral advection of oxygen-deficient intermediate waters of the eastern tropical Panthalassic Ocean through a deep-water corridor in the Greater Permian Basin region. In contrast, trace metals in the Upper Devonian Ohio Shale of eastern North America exhibit divergent stratigraphic trends: relative to total organic carbon (TOC), V and Zn increase, Ni is constant, and Mo and U decrease upsection. This pattern records secular evolution of the aqueous chemistry of the silled Appalachian Basin in response to an increase in restriction of deep-water exchange. Basinal restriction intensified during the later stages of deposition of the Ohio Shale as a consequence of the onset of a major glacioeustatic regression that culminated at the Devonian-Carboniferous system boundary. Analysis of trace-metal patterns in other ancient anoxic marine systems has the potential to yield new insights regarding hydrographic variables such as rates of deep-water renewal and the degree of evolution of water-mass chemistry, in addition to information about paleoredox conditions.

Isotopic evidence for organic matter oxidation by manganese reduction in the formation of stratiform manganese carbonate ore

Abstract Unlike other marine-sedimentary manganese ore deposits, which are largely composed of manganese oxides, the primary ore at Molango (Hidalgo State, Mexico) is exclusively manganese carbonate (rhodochrosite, Mn-calcite, kutnahorite). Stable isotope studies of the carbonates from Molango provide critical new information relevant to the controversy over syngenetic and diagenetic models of stratiform manganese deposit formation. Negative δ 13 C values for carbonates from mineralized zones at Molango are strongly correlated with manganese content both on a whole rock scale and by mineral species. Whole rock δ 13 C data fall into three groups: high-grade ore = −16.4 to −11.5%.; manganese-rich, sub-ore-grade = −5.2 to 0%.; and unmineralized carbonates = 0 to +2.5%. (PDB). δ 18 O data show considerable overlap in values among the three groups: +4.8 to −2.8, −5.4 to −0.3%., and −7.4 to +6.2 (PDB), respectively. Isotopic data for individual co-existing minerals suggest a similar separation of δ 13 C values: δ 13 C values from calcite range from −1.1 to +0.7%. (PDB), whereas values from rhodochrosite are very negative, −12.9 to −5.5%., and values from kutnahorite or Mn-calcite are intermediate between calcite and rhodochrosite. 13 C data are interpreted to indicate that calcite ( i.e . unmineralized carbonate) formed from a normal marine carbon reservoir. However, 13 C data for the manganese-bearing carbonates suggest a mixed seawater and organic source of carbon. The presence of only trace amounts of pyrite suggests sulfate reduction may have played a minor part in oxidizing organic matter. It is possible that manganese reduction was the predominant reaction that oxidized organic matter and that it released organic-derived CO 2 to produce negative δ 13 C values and manganese carbonate mineralization.

Lead and Zinc

Lead and zinc are found in two distinct associations in sedimentary rocks: carbonate-hosted and shale-hosted. The carbonate-hosted ores are generally agreed to be epigenetic, deposited from low temperature hydrothermal fluids. The shale-hosted deposits are more controversial, but most appear to be at least partly syngenetic. Shale-hosted orebodies can be exceptionally large, and are perhaps the most popular exploration targets among sedimentary ores at the present time. A transitional form between these two, one that is accordingly given considerable attention, is syngenetic ore in carbonate rocks, such as at Tynagh, in Ireland.

Extension of Berner's "New geochemical classification of sedimentary environments" to ancient sediments

Using stable isotopes of carbon and oxygen in siderite nodules and lithology of host shales, one can recognize geochemical environments proposed by Berner in Devonian-Carboniferous sediments of the Appalachian Basin. His oxic, post-oxic, and sulfidic diagenetic environments are well represented; sediments of the methanic environment may be present, but the evidence is equivocal. The sulfidic sediments can be further subdivided into well laminated and bioturbated, corresponding to the presence of H 2 S in the overlying water in the first case but confined to the sediment pore waters in the second.--Journal abstract.

Manganiferous Sediments, Rocks, and Ores

Manganese is of great interest in geochemistry because its minerals are both tracers of redox processes and accumulators of other elements of geochemical significance. The solubility of manganese compared to iron under reducing and mildly oxidizing conditions leads to its export from low-oxygen environments, be they basalt-hydrothermal systems or euxinic sedimentary basins, and its accumulation in oxidizing environments of the shallow ocean or in low-productivity areas of the deep sea. Therefore tracking Mn/Fe ratios provides us a means of reconstructing the oxidation structure of ocean basins, soils, or groundwater systems.

Speciation and distribution of vanadium in drinking water iron pipe corrosion by-products.

Vanadium (V) when ingested from drinking water in high concentrations (>15 μg L(-1)) is a potential health risk and is on track to becoming a regulated contaminant. High concentrations of V have been documented in lead corrosion by-products as Pb(5)(V(5+)O(4))(3)Cl (vanadinite) which, in natural deposits is associated with iron oxides/oxyhydroxides, phases common in iron pipe corrosion by-products. The extent of potential reservoirs of V in iron corrosion by-products, its speciation, and mechanism of inclusion however are unknown. The aim of this study is to assess these parameters in iron corrosion by-products, implementing synchrotron-based μ-XRF mapping and μ-XANES along with traditional physiochemical characterization. The morphologies, mineralogies, and chemistry of the samples studied are superficially similar to typical iron corrosion by-products. However, we found V present as discrete grains of Pb(5)(V(5+)O(4))(3)Cl likely embedded in the surface regions of the iron corrosion by-products. Concentrations of V observed in bulk XRF analysis ranged from 35 to 899 mg kg(-1). We calculate that even in pipes with iron corrosion by-products with low V concentration, 100 mg kg(-1), as little as 0.0027% of a 0.1-cm thick X 100-cm long section of that corrosion by-product needs to be disturbed to increase V concentrations in the drinking water at the tap to levels well above the 15 μg L(-1) notification level set by the State of California and could adversely impact human health. In addition, it is likely that large reservoirs of V are associated with iron corrosion by-products in unlined cast iron mains and service branches in numerous drinking water distribution systems.