Eh-pH Diagrams for Geochemistry

Brookins, Douglas G.

doi:10.1007/978-3-642-73093-1

Cited by 765 publications

(526 citation statements)

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“…Precipitation of Mn-oxide decreases with either decreasing Eh or decreasing pH. In the present open ocean (pH = 8.1, pθ 2 = 0.2, Eh = 0.4V), Mn 2+ is oxidized and precipitates as MnO 2 in nodules and crusts (Brookins, 1988;Mangini et al, 1990). Present oxygen levels in Pacific bottom water are sufficient to oxidize most organic matter; therefore, the Mn redox level is generally too deep within the sediment to allow Mn 2+ migration into the water column (Froelich et al, 1979;Emerson and Hedges, 1988).…”

Section: Manganese Depletion and Interstitial Water Conditionsmentioning

confidence: 87%

Jurassic through Early Cretaceous Sedimentation History of the Central Equatorial Pacific and of Sites 800 and 801

Ogg¹,

Stattegger²,

Behl³

1992

Proceedings of the Ocean Drilling Program, 129 Scientific Results

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Sedimentation in the central Pacific during the Jurassic and Early Cretaceous was dominated by abundant biogenic silica. A synthesis of the stratigraphy, lithology, petrology, and geochemistry of the radiolarites in Sites 801 and 800 documents the sedimentation processes and trends in the equatorial central Pacific from the Middle Jurassic through the Early Cretaceous. Paleolatitude and paleodepth reconstructions enable comparisons with previous DSDP sites and identification of the general patterns of sedimentation over a wide region of the Pacific.Clayey radiolarites dominated sedimentation on Pacific oceanic crust within tropical paleolatitudes from at least the latest Bathonian through Tithonian. Radiolarian productivity rose to a peak within 5° of the paleoequator, where accumulation rates of biogenic silica exceeded 1000 g/cm 2 /m.y. Wavy-bedded radiolarian cherts developed in the upper Tithonian at Site 801 coinciding with the proximity of this site to the paleoequator. Ribbon-bedding of some radiolarian cherts exposed on Pacific margins may have formed from silicification of radiolarite deposited near the equatorial high-productivity zone where radiolarian/clay ratios were high. Silicification processes in sediments extensively mixed by bioturbation or enriched in clay or carbonate generally resulted in discontinuous bands or nodules of porcellanite or chert, e.g., a "knobby" radiolarite. Ribbon-bedded cherts require primary alternations of radiolarian-rich and clay-rich layers as an initial structural template, coupled with abundant biogenic silica in both layers. During diagenesis, migration of silica from clay-rich layers leaves radiolarian "ghosts" or voids, and the precipitation in adjacent radiolarite layers results in silicification of the inter-radiolarian matrix and infilling of radiolarian tests. Alternations of claystone and clay-rich radiolarian grainstone were deposited during the Callovian at Site 801 and during the Berriasian-Valanginian at Site 800, but did not silicify to form bedded chert.Carbonate was not preserved on the Pacific oceanic floor or spreading ridges during the Jurassic, perhaps due to an elevated level of dissolved carbon dioxide. During the Berriasian through Hauterivian, the carbonate compensation depth (CCD) descended to approximately 3500 m, permitting the accumulation of siliceous limestones at near-ridge sites. Carbonate accumulation rates exceeded 1500 g/cm 2 /m.y. at sites above the CCD, yet there is no evidence of an equatorial carbonate bulge during the Early Cretaceous. In the Barremian and Aptian, the CCD rose, coincident with the onset of mid-plate volcanic activity.Abundance of Fe and Mn and the associated formation of authigenic Fe-smectite clays was a function of proximity to the spreading ridges, with secondary enrichments occurring during episodes of spreading-center reorganizations. Callovian radiolarite at Site 801 is anomalously depleted in Mn, which resulted either from inhibited precipitation of Mn-oxides by lower pH of interstitial waters in...

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Section: Manganese Depletion and Interstitial Water Conditionsmentioning

confidence: 87%

Jurassic through Early Cretaceous Sedimentation History of the Central Equatorial Pacific and of Sites 800 and 801

Ogg¹,

Stattegger²,

Behl³

1992

Proceedings of the Ocean Drilling Program, 129 Scientific Results

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“…As(III) concentrations are highest in the highest temperature SPR1-6 group, and these are the lowest pH spring waters sampled (pH = 6.42-6.75). At this pH, the As(III) will likely occur as the species H 3 AsO 3 (Brookins, 1988). were calculated for all of the spring waters using Geochemist's Workbench, suggesting saturation with this mineral, and that dissolution of this mineral gave rise to the F concentrations observed.…”

Section: Characteristics Of Spring Watersmentioning

confidence: 99%

Geochemistry of As-, F- and B-bearing waters in and around San Antonio de los Cobres, Argentina, and implications for drinking and irrigation water quality

Hudson‐Edwards¹,

Archer²

2012

Journal of Geochemical Exploration

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Spring, stream and tap waters from in and around San Antonio de los Cobres, Salta, Argentina, were sampled to characterize their geochemical signatures, and to determine whether they pose a threat to human health and crops. The spring waters are typical of geothermal areas world-wide, in that they are Na-Cl waters with high concentrations of As tot , As(III), Li, B, HCO 3 , F and SiO 2 (up to 9. 49, 8.92, 13.1, 56.6, 1250, 7.30 and 57.2 mg L -1 , respectively), and result from mixing of deep Na-Cl brines and meteoric HCO 3 -rich waters. Springs close to the town of San Antonio have higher concentrations of all elements, and are generally cooler, than springs in the Baños de Agua Caliente. Spring water chemistry is a result of mixing of deep Na-Cl brines and meteoric HCO 3 waters. Stream waters are also Na-Cl type, and receive large inputs of all elements from the springs near San Antonio, but concentrations decrease downstream through the town of San Antonio due to mineral precipitation. The spring that is used as a drinking water source, and other springs in the area, have As, F and B concentrations in excess of WHO and Argentinian drinking water guidelines. Evaluation of the waters for irrigation purposes suggests that their high salinities and B concentrations may adversely affect crops. The waters may be improved for drinking and irrigation by dilution with cleaner meteoric waters, mineral 2 precipitation or by use of commercial filters. Such recommendations could also be followed by other settlements that draw drinking and irrigation waters from geothermal sources.

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“…The calcium in the GLD is expected to originate from calcite as previous mineralogical analysis showed the presence of this mineral [8]. Calcite has low solubility in neutral and alkaline water but dissolves more readily in acidic water [31]. The calcium concentrations of the aged GLD at Rönnskär and Iggesund were similar to or greater than those of fresh GLD, indicating that the rainwater that had percolated through the GLD had not dissolved its calcite.…”

Section: Changes In Chemical Propertiesmentioning

confidence: 88%

Prediction of the long-term performance of green liquor dregs as a sealing layer to prevent the formation of acid mine drainage

Mäkitalo

Maurice

et al. 2016

Journal of Environmental Chemical Engineering

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Eh-pH Diagrams for Geochemistry

Cited by 765 publications

References 0 publications

Jurassic through Early Cretaceous Sedimentation History of the Central Equatorial Pacific and of Sites 800 and 801

Jurassic through Early Cretaceous Sedimentation History of the Central Equatorial Pacific and of Sites 800 and 801

Geochemistry of As-, F- and B-bearing waters in and around San Antonio de los Cobres, Argentina, and implications for drinking and irrigation water quality

Prediction of the long-term performance of green liquor dregs as a sealing layer to prevent the formation of acid mine drainage

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