43 results on '"John M. McArthur"'
Search Results
2. Overlapping redox zones control arsenic pollution in Pleistocene multi-layer aquifers, the Po Plain (Italy)
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Elisa Sacchi, Rasmus Jakobsen, Veronica Nava, Letizia Fumagalli, Barbara Leoni, John M. McArthur, Chiara Zanotti, Tullia Bonomi, Giuseppe Etiope, Marco Rotiroti, Alessandra Sciarra, Rotiroti, M, Bonomi, T, Sacchi, E, Mcarthur, J, Jakobsen, R, Sciarra, A, Etiope, G, Zanotti, C, Nava, V, Fumagalli, L, and Leoni, B
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Environmental Engineering ,Peat ,010504 meteorology & atmospheric sciences ,Pleistocene ,Methanogenesis ,Iron ,Methanogenesi ,Geochemistry ,Aquifer ,010501 environmental sciences ,01 natural sciences ,GEO/05 - GEOLOGIA APPLICATA ,TEAP ,chemistry.chemical_compound ,Groundwater quality ,GEO/08 - GEOCHIMICA E VULCANOLOGIA ,Environmental Chemistry ,Organic matter ,Sulfate ,Waste Management and Disposal ,Holocene ,0105 earth and related environmental sciences ,chemistry.chemical_classification ,geography ,geography.geographical_feature_category ,Pollution ,chemistry ,Environmental science ,BIO/07 - ECOLOGIA ,Groundwater - Abstract
Understanding thefactors that control As concentrations in groundwater is vital for supplying safe groundwaterin regions with As-polluted aquifers. Despite much research, mainly addressing Holocene aquifers hosting young (12,000 yrs) groundwatersare not yet fully understood and so are assessed here through an evaluation of the redox properties of the system in a type locality, the PoPlain (Italy).Analyses of redox-sensitive species and major ions on 22 groundwater samples from the Pleistocene arsenic-affected aquifer in the Po Plain shows that groundwater concentrations of As are controlled by the simultaneous operation of several terminal electron accepters. Organic matter, present as peat, is abundant in the aquifer, allowing groundwater to reach a quasi-steady-state of highly reducing conditions close to thermodynamic equilibrium. In this system, simultaneous reduction of Fe-oxide and sulfate results in low concentrations of As (median 7 μg/L) whereas As reaches higher concentrations (median of 82 μg/L) during simultaneous methanogenesis and Fe-reduction. The position of well-screens is an additional controlling factor on groundwater As: short screens that overlap confining aquitards generate higher As concentrations than long screens placed away from them. A conceptual model for groundwater As, applicable worldwidein other Pleistocene aquifers with reducible Fe-oxides andabundant organic matter is proposed: As may have two concentration peaks, the first after prolonged Fe-oxide reduction and until sulfate reduction takes place, the second during simultaneous Fe-reduction and methanogenesis.
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- 2021
3. Identifying multiple deep aquifers in the Bengal Basin: Implications for resource management
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Peter Ravenscroft, John M. McArthur, and Muhammad Saifur Rahman
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geography ,geography.geographical_feature_category ,0208 environmental biotechnology ,BENGAL ,Resource management ,Aquifer ,02 engineering and technology ,Structural basin ,Water resource management ,Geology ,020801 environmental engineering ,Water Science and Technology - Published
- 2018
4. Dating late Miocene marine incursions across Argentina and Uruguay with Sr-isotope stratigraphy
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Sergio Martínez, Matthew F. Thirlwall, Claudia Julia del Río, Leandro Martín Pérez, and John M. McArthur
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010506 paleontology ,LATE MIOCENE ,Structural basin ,Late Miocene ,010502 geochemistry & geophysics ,01 natural sciences ,Aequipecten ,Ciencias de la Tierra y relacionadas con el Medio Ambiente ,Paleontology ,PALEOGEOGRAPHY ,URUGUAY ,Cape ,Geología ,Chronostratigraphy ,0105 earth and related environmental sciences ,Earth-Surface Processes ,ARGENTINA ,biology ,SR-ISOTOPE ,“Paranense” sea ,Geology ,Geoquímica y Geofísica ,biology.organism_classification ,Stratigraphy ,Facies ,Transgressive ,CIENCIAS NATURALES Y EXACTAS - Abstract
A Sr-isotope chronostratigraphy is presented for Miocene sediments deposited by the “Paranense” Sea along 1200 km of the southwestern Atlantic coast of Argentina and Uruguay. Numerical ages were obtained for shells of Aequipecten paranensis from the Argentinean Puerto Madryn Formation, Facies Balneario La Lobería, “Entrerriense Beds” of the Salado Basin, and Paraná Formation, and from the Camacho Formation (Uruguay). The 87Sr/86Sr ages fall into five age-groups that encompass the “Paranense” flooding in the latest Serravalian-Messinian interval. For the Puerto Madryn Formation, the ages span the latest Serravalian to the Tortonian and are stratigraphically coherent with the transgressive phase (11.9–10.4 Ma) and the regressive phase (10.2–9.82 Ma and 9.40–9.05 Ma) of that unit. Ages of 8.85–7.95 Ma for the “Entrerriense Beds” show them to be Tortonian while the Facies Balneario La Lobería, and the Paraná and Camacho formations span the age-range 7.50–6.00 Ma, comprising the Tortonian-Messinian interval. The regressive phase of the Puerto Madryn Formation, and the Facies Balneario La Lobería are respectively correlated with the basal and middle beds of the cliffs at Barranca Final, where the uppermost horizons of the Barranca Final Formation are exposed. The “Entrerriense Beds” are correlated with the “Cape Fairwheater Beds”. Dating the “Paranense” marine incursion permits a reappraisal of its paleogeography and differentiation of its deposits from those of the “Patagoniense” Sea. The flooding area was smaller than previously thought, with its northwestern-most boundary in the surroundings of the Santa Fe Province and its southernmost boundary in southern Santa Cruz Province. Moreover, the Paranaian Molluscan Bioprovince was coeval with the Valdesian Molluscan Bioprovince for 2.35 Ma and species included in the Aequipecten paranensis Zone lived for at least 5.90 Ma. Fil: del Río, Claudia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Martinez, Sergio. Universidad de la República; Uruguay Fil: Mc Arthur, John. University College London; Estados Unidos Fil: Thirwall M,. University College London; Estados Unidos Fil: Pérez, Leandro Martín. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina
- Published
- 2018
5. Arsenic and other water-quality issues affecting groundwater, Indus alluvial plain, Pakistan
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John M. McArthur and Sadaf Naseem
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Hydrology ,Irrigation ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Aquifer ,Groundwater recharge ,010501 environmental sciences ,01 natural sciences ,Anoxic waters ,Alluvial plain ,Evapotranspiration ,Environmental science ,Water quality ,Groundwater ,0105 earth and related environmental sciences ,Water Science and Technology - Abstract
Groundwater beneath the alluvial plain of the Indus River, Pakistan, is reported to be widely polluted by arsenic (As) and to adversely affect human health. In 79 groundwaters reported here from the lower Indus River plain, in southern Sindh Province, concentrations of As exceeded the WHO guideline value of 10 g/L in 38%, with 22% exceeding 50 g/L, Pakistan’s guideline value. The As pollution is caused by microbially-mediated reductive dissolution of sedimentary iron-oxyhydroxides in anoxic groundwaters; oxic groundwaters contain < 10 g/L of As. In the upper Indus River plain, in Punjab Province, localised As pollution of groundwater occurs by alkali desorption as a consequence of ion-exchange in groundwater, possibly supplemented by the use for irrigation of groundwater that has suffered ion-exchange in the aquifer and so has values > 0 for residual sodium carbonate. In the field area in southern Sindh, concentrations of Mn in groundwater exceed 0.4 mg/L in 11% of groundwaters, with a maximum of 0.7 mg/L, as a result of reduction of sedimentary manganese oxides. Other trace elements pose little or no threat to human health. Salinities in groundwaters range from fresh to saline (EC up to 6 mS/cm). High salinities result from local inputs of waste-water from unsewered sanitation, but mainly from evaporation/evapotranspiration of canal water and groundwater used for irrigation. The process does not concentrate As in the groundwater owing to sorption of As to soils. Ion-exchange exerts a control on concentrations of Na, Ca, and B, but not on As. High values of Cl/Br mass ratios (most » 288, the marine value) reflect the pervasive influence on groundwater of sewage-contaminated water from irrigation canals through seepage loss and deep percolation of irrigation water, with additional, well-specific, contributions from unsewered sanitation.
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- 2018
6. The effects of irrigation on groundwater quality and quantity in a human-modified hydro-system: The Oglio River basin, Po Plain, northern Italy
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Letizia Fumagalli, John M. McArthur, Elisa Sacchi, Marco Rotiroti, Barbara Leoni, Chiara Zanotti, Sara Taviani, Gennaro A. Stefania, Tullia Bonomi, M Patelli, Valentina Soler, Veronica Nava, Rotiroti, M, Bonomi, T, Sacchi, E, Mcarthur, J, Stefania, G, Zanotti, C, Taviani, S, Patelli, M, Nava, V, Soler, V, Fumagalli, L, and Leoni, B
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Irrigation ,Environmental Engineering ,010504 meteorology & atmospheric sciences ,Drainage basin ,010501 environmental sciences ,Lake Iseo ,Nitrate ,01 natural sciences ,Arsenic ,GEO/05 - GEOLOGIA APPLICATA ,Environmental Chemistry ,Waste Management and Disposal ,Surface irrigation ,Cl/Br ,0105 earth and related environmental sciences ,Stable isotopes ,Hydrology ,geography ,Hydrogeology ,geography.geographical_feature_category ,Groundwater recharge ,Pollution ,Infiltration (hydrology) ,Recharge/discharge ,Environmental science ,BIO/07 - ECOLOGIA ,Water quality ,Groundwater - Abstract
For several hundred years, farming in the Po Plain of Italy (46,000 km2, 20 million inhabitants) has been supported by intensive surface irrigation with lake and river water. Despite the longevity of irrigation, its effects on the quality and quantity of groundwater is poorly known and so is investigated here through seasonal measurements of hydraulic heads and water quality in groundwaters, rivers, lake, springs and rainwaters. In the north of the study region, an unconfined coarse-grained alluvial aquifer, infiltration of surface irrigation water, sourced from the Oglio River and low in NO3, contributes much to aquifer recharge (up to 88%, as evidenced by a δ2H-Cl/Br mixing model) and has positive effects on groundwater quality by diluting high concentrations of NO3 (decrease by 17% between June and September). This recharge also helps to maintain numerous local springs that form important local micro-environments. Any increase in water-use efficiency in irrigation will reduce this recharge, imperil the spring environments, and lessen the dilution of NO3 leading to increasing NO3 concentrations in groundwater. These findings can be extended by analogy to the entire Po Plain region and other surface-water-irrigated systems worldwide where inefficient irrigation methods are used and similar hydrogeological features occur.
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- 2019
7. Sr-Isotope Stratigraphy: Assigning Time in the Campanian, Pliensbachian, Toarcian, and Valanginian
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Neil H. Landman, Thomas Steuber, Kevin N. Page, and John M. McArthur
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Current time ,Astrochronology ,Paleontology ,010504 meteorology & atmospheric sciences ,Stratigraphy ,Isotope ,Geology ,010502 geochemistry & geophysics ,01 natural sciences ,0105 earth and related environmental sciences - Abstract
The trend of marine 87Sr/86Sr against stratigraphic level through sections, whether linear or not, can identify hiatuses and changing rates of sedimentation through those sections and so be a valuable constraint on attempts to assign numerical ages to sediments on the basis of astrochronology or U/Pb dating of zircons. Here we illustrate that value for the Campanian, Pliensbachian, Toarcian, and Valanginian ages by comparing 87Sr/86Sr profiles for different localities and comparing those to the 87Sr/86Sr profile through time. The analysis reveals possible problems both with current time scales and with some astrochronological calibrations. Our analysis is neither comprehensive nor final; rather, with a few examples, we show how Sr-isotope stratigraphy can be used to moderate other methods of assigning numerical ages to sediments.
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- 2016
8. Arsenic in Groundwater: The Deep Late Pleistocene Aquifers of the Western Bengal Basin
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U. Ghosal, J. D. Ball, John M. McArthur, and P. K. Sikdar
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Bromides ,Time Factors ,Pleistocene ,δ18O ,Water Wells ,0208 environmental biotechnology ,Geochemistry ,India ,Aquifer ,02 engineering and technology ,010501 environmental sciences ,Structural basin ,01 natural sciences ,Arsenic ,Chlorides ,Environmental Chemistry ,Groundwater ,Geomorphology ,Holocene ,0105 earth and related environmental sciences ,geography ,geography.geographical_feature_category ,Geography ,Sulfates ,General Chemistry ,020801 environmental engineering ,Arsenic contamination of groundwater ,Isotope Labeling ,BENGAL ,Oxidation-Reduction ,Water Pollutants, Chemical ,Geology - Abstract
in groundwaters from 145 wells across central West Bengal, India, those from Pleistocene aquifers at depths70 m beneath paleo-interfluves contain10 μg/L As. Pleistocene aquifers beneath deep paleo-channels typically host groundwaters containing 10-100 μg/L As at depths between 120 and 180 m. The depth profiles of As and SO4 and the conservative tracers Cl/Br, δ(18)O, and δ(2)H show that the As in Pleistocene groundwater beneath deep paleo-channels is relict and does not arise from migration downward of As-polluted groundwater in overlying aquifers. We postulate that the As was liberated in situ by reduction of minimal iron oxyhydroxides in the gray Pleistocene sands by organic matter infiltrating from riverbeds during late Pleistocene or earliest Holocene times. Mitigation of the widespread As-pollution in shallow aquifers through exploitation of deep Pleistocene aquifers would improve if guided by an understanding of the distribution of buried paleo-channels and paleo-interfluves and the knowledge that As may be present naturally in groundwater at depths150 m beneath deep paleo-channels.
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- 2016
9. Groundwater quality beneath an Asian megacity on a delta: Kolkata’s (Calcutta’s) disappearing arsenic and present manganese
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Melanie J. Leng, I. Sen, U. Ghosal, P. K. Sikdar, and John M. McArthur
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Delta ,0208 environmental biotechnology ,India ,chemistry.chemical_element ,02 engineering and technology ,Manganese ,010501 environmental sciences ,01 natural sciences ,Arsenic ,chemistry.chemical_compound ,Environmental Chemistry ,Groundwater ,0105 earth and related environmental sciences ,General Chemistry ,Contamination ,Pesticide ,020801 environmental engineering ,Megacity ,Paris green ,chemistry ,Environmental chemistry ,Environmental science ,Water Pollutants, Chemical ,Environmental Monitoring - Abstract
Kolkata, the capital city of West Bengal, exploits groundwater for public water-supply. The groundwater has been reported to be widely polluted by arsenic (As). Analysis for As in 280 groundwaters from across Kolkata, failed to detect As concentrations >10 μg/L from natural processes. Arsenic concentrations between 10 and 79 μg/L found in 14 of the 280 groundwaters are remnant from a pollution-plume emanating from a single factory site where Paris Green, an arsenical pesticide, was manufactured between 1965 and 1985. In 45% of groundwaters sampled, concentrations of Mn exceed 0.4 mg/L, a putative health guideline value for drinking water. Sporadic minor hazards are posed by Pb > 10 μg/L introduced into groundwater from well-fittings, from 4% of groundwaters with F concentrations between 0.75 and 1 mg/L, and the 14% of groundwaters containing more than 500 mg/L Na, concentrations that might contribute to excessive daily intake of Na. Compounding hazards from As, F, Mn, Na, and Pb, shows that 64% of public wells and 40% of municipal wells supply groundwater of suspect quality. Groundwaters comply with WHO Guideline Values for drinking water in terms of Cr, Cu, Co, NO2, NO3, Sb, Se, and U. Aesthetic guideline values for Fe, Mn, SO4, and Cl are exceeded for many groundwaters.
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- 2018
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10. Late Burdigalian (Miocene) age for pectinids (Mollusca-Bivalvia) from the Pirabas Formation (northern Brazil) derived from Sr-isotope (87Sr/86Sr) data
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Claudia Julia del Río, Matthew F. Thirlwall, Maria Inês Feijó Ramos, John M. McArthur, and Sergio Martínez
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010506 paleontology ,Fauna ,Central American Seaway ,Biostratigraphy ,010502 geochemistry & geophysics ,Neogene ,01 natural sciences ,Ciencias de la Tierra y relacionadas con el Medio Ambiente ,Paleontology ,STRONTIUM ,Geología ,Mollusca ,0105 earth and related environmental sciences ,biology ,Isotope ,Pectinoidea ,PIRABAS FORMATION ,Geoquímica y Geofísica ,biology.organism_classification ,Bivalvia ,BRAZIL ,SIS ,PECTINOIDEA ,87SR/86 SR ,Geology ,CIENCIAS NATURALES Y EXACTAS ,MIOCENE - Abstract
The faunas of the highly fossiliferous Pirabas Formation belong to the southern part of the biogeographical unit known as "Neogene Tropical America". This unit developed prior to the closure of the Central American Seaway by the Isthmus of Panama. Until now, the age of the Pirabas Formation was inferred only from biostratigraphy. The Sr-isotope (87Sr/86Sr) values of pectinid shells from the Pirabas Formation show that most parts of this unit were deposited during the Late Burdigalian (about 16-17 Ma ). This result does not contradict biostratigraphic data and it constrains the age of the Pirabas Formation more tightly than do previous estimates of age, it for future, more precise biogeographical comparisons. Fil: Martinez, Sergio. Universidad de la República; Uruguay Fil: Feijó Ramos, María Inês. Museo Paraense Emilio Goeldi; Brasil Fil: McArthur, John M.. University College London; Estados Unidos Fil: del Río, Claudia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Thirlwall, Matthew F.. Royal Holloway University Of London; Reino Unido
- Published
- 2017
11. Pollutant sources in an arsenic-affected multilayer aquifer in the Po Plain of Italy: Implications for drinking-water supply
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Gennaro A. Stefania, Elisa Sacchi, John M. McArthur, Marco Rotiroti, Letizia Fumagalli, Tullia Bonomi, Rotiroti, M, Mcarthur, J, Fumagalli, M, Stefania, G, Sacchi, E, and Bonomi, T
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Environmental Engineering ,010504 meteorology & atmospheric sciences ,Aquifer ,010501 environmental sciences ,01 natural sciences ,Arsenic ,Rainwater harvesting ,GEO/05 - GEOLOGIA APPLICATA ,Water Supply ,Cl ,Environmental Chemistry ,Groundwater discharge ,Groundwater ,Waste Management and Disposal ,Cl/Br ,0105 earth and related environmental sciences ,Surficial aquifer ,Hydrology ,geography ,geography.geographical_feature_category ,Drinking Water ,Outfall ,Environmental engineering ,Groundwater recharge ,Pollution ,Recharge ,Italy ,Wastewater ,Cremona ,Water Pollutants, Chemical ,Geology ,Environmental Monitoring - Abstract
In aquifers 160 to 260 m deep that used for public water-supply in an area ~ 150 km2 around the town of Cremona, in the Po Plain of Northern Italy, concentrations of arsenic (As) are increasing with time in some wells. The increase is due to drawdown of As-polluted groundwater (As ≤ 144 μg/L) from overlying aquifers at depths 65 to 150 m deep in response to large-scale abstraction for public supply. The increase in As threatens drinking-water quality locally, and by inference does so across the entire Po Plain, where natural As-pollution of groundwater (As > 10 μg/L) is a basin-wide problem. Using new and legacy data for Cl/Br, δ18O/δ2H and other hydrochemical parameters with groundwater from 32 wells, 9 surface waters, a sewage outfall and rainwater, we show that the deep aquifer (160–260 m below ground level), which is tapped widely for public water-supply, is partly recharged by seepage from overlying aquifers (65–150 m below ground level). Groundwater quality in deep aquifers appears free of anthropogenic influences and typically < 10 μg/L of As. In contrast, shallow groundwater and surface water in some, not all, areas are affected by anthropogenic contamination and natural As-pollution (As > 10 μg/L). Outfalls from sewage-treatment plants and black water from septic tanks firstly affect surface waters, which then locally infiltrate shallow aquifers under high channel-stages. Wastewater permeating shallow aquifers carries with it NO3 and SO4 which suppress reduction of iron oxyhydroxides in the aquifer sediments and so suppress the natural release of As to groundwater.
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- 2017
12. Tracing recharge to aquifers beneath an Asian megacity with Cl/Br and stable isotopes: the example of Dhaka, Bangladesh
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T. N. Molla, Mohammad A. Hoque, J. D. Ball, P. K. Sikdar, and John M. McArthur
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Hydrology ,education.field_of_study ,geography ,geography.geographical_feature_category ,Population ,Aquifer ,Groundwater recharge ,Connate fluids ,Salinity ,Infiltration (hydrology) ,Earth and Planetary Sciences (miscellaneous) ,Environmental science ,education ,Effluent ,Groundwater ,Water Science and Technology - Abstract
Dhaka, the capital of Bangladesh, is home to a population of 15 million people, whose water supply is 85% drawn from groundwater in aquifers that underlie the city. Values of Cl/Br >500 are common in groundwater beneath western Dhaka in areas
- Published
- 2014
13. Waste-water impacts on groundwater: Cl/Br ratios and implications for arsenic pollution of groundwater in the Bengal Basin and Red River Basin, Vietnam
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Mohammad A. Hoque, U. Ghosal, John M. McArthur, and P. K. Sikdar
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Bromides ,Pollution ,Environmental Engineering ,media_common.quotation_subject ,Drainage basin ,India ,Aquifer ,Wastewater ,Chloride ,Arsenic ,Chlorides ,Enterobacteriaceae ,Rivers ,Groundwater pollution ,Environmental Chemistry ,Organic matter ,Cl/Br ,Groundwater ,Waste Management and Disposal ,media_common ,Hydrology ,chemistry.chemical_classification ,Bangladesh ,geography ,Nitrates ,geography.geographical_feature_category ,Bengal ,Models, Chemical ,Vietnam ,chemistry ,Waste-water ,Seawater ,Water Pollutants, Chemical ,Geology ,Environmental Monitoring - Abstract
Across West Bengal and Bangladesh, concentrations of Cl in much groundwater exceed the natural, upper limit of 10 mg/L. The Cl/Br mass ratios in groundwaters range up to 2500 and scatter along mixing lines between waste-water and dilute groundwater, with many falling near the mean end-member value for waste-water of 1561 at 126 mg/L Cl. Values of Cl/Br exceed the seawater ratio of 288 in uncommon NO(3)-bearing groundwaters, and in those containing measurable amounts of salt-corrected SO(4) (SO(4) corrected for marine salt). The data show that shallow groundwater tapped by tube-wells in the Bengal Basin has been widely contaminated by waste-water derived from pit latrines, septic tanks, and other methods of sanitary disposal, although reducing conditions in the aquifers have removed most evidence of NO(3) additions from these sources, and much evidence of their additions of SO(4). In groundwaters from wells in palaeo-channel settings, end-member modelling shows that >25% of wells yield water that comprises ≥10% of waste-water. In palaeo-interfluvial settings, only wells at the margins of the palaeo-interfluvial sequence contain detectable waste water. Settings are identifiable by well-colour survey, owner information, water composition, and drilling. Values of Cl/Br and faecal coliform counts are both inversely related to concentrations of pollutant As in groundwater, suggesting that waste-water contributions to groundwater in the near-field of septic-tanks and pit-latrines (within 30 m) suppress the mechanism of As-pollution and lessen the prevalence and severity of As pollution. In the far-field of such sources, organic matter in waste-water may increase groundwater pollution by As.
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- 2012
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14. Reworked late Neogene Austrochlamys anderssoni (Mollusca: Bivalvia) from northern James Ross Island, Antarctica
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J. A. Crame, Duncan Pirrie, John M. McArthur, HA Jonkers, and John L. Smellie
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geography ,geography.geographical_feature_category ,Glaciology ,Outcrop ,Geology ,Glacier ,Late Miocene ,Oceanography ,Neogene ,Ecology and Environment ,Paleontology ,Clastic rock ,Phanerozoic ,Interglacial ,Earth Sciences ,Cenozoic ,Ecology, Evolution, Behavior and Systematics - Abstract
We report on the discovery of a new outcrop of fossiliferous Neogene sediments on northern James Ross Island, northern Antarctic Peninsula. Approximately 100 specimens of the pectinid bivalve Austrochlamys anderssoni (Hennig, 1911) were collected from the permafrost active layer. This bivalve species has a late Miocene to late Pliocene range and has previously been reported from both the glaciomarine Hobbs Glacier Formation and the interglacial Cockburn Island Formation in the James Ross Island area. The localized presence of abundant A. anderssoni within the permafrost suggests that the fossils have been frost heaved from an outcrop of either the Cockburn Island or the Hobbs Glacier formations, originally deposited on northern James Ross Island. The overall shell form, general absence of associated Antarctic Peninsula-derived clasts in the host sediment, and the measured 87Sr/86Sr isotope ratio of the shells (0.709050) which is indistinguishable from that for pectinid bivalves from the Cockburn Island Formation on Cockburn Island (0.709047) suggest that the shells were derived from a unit similar in age to the Cockburn Island Formation. This suggests that the Cockburn Island Formation was originally more laterally extensive than was previously known.
- Published
- 2011
15. Comment on 'Carbon-isotope record of the Early Jurassic (Toarcian) Oceanic Anoxic Event from fossil wood and marine carbonate (Lusitanian Basin, Portugal)' by Hesselbo S., Jenkyns H.C., Duarte L.V. and Oliveira L.C.V
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John M. McArthur
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Calcite ,Excursion ,Peniche ,Methane ,chemistry.chemical_compound ,Paleontology ,Geophysics ,chemistry ,Space and Planetary Science ,Geochemistry and Petrology ,Isotopes of carbon ,Anaerobic oxidation of methane ,Earth and Planetary Sciences (miscellaneous) ,Fossil wood ,Carbonate ,Geology - Abstract
Hesselbo et al. (2006; hereinafter HJDO06) present stable-isotopic profiles through lower Toarcian sediments at Peniche, Portugal, and interpret them as evidence of a massive injection to the atmosphere of isotopically-light CO2 derived from methane oxidation. The atmospheric inputs supposedly gave rise to negative isotopic excursions in all carbon reservoirs. The paper follows others proposing that environmental change in early Toarcian time was driven by the release to the atmosphere of methane, either from marine clathrates (Hesselbo et al., 2000; Kemp et al., 2005), or from organic-rich shales that were baked by Karoo–Ferrar intrusions (McElwain et al., 2005). The methane hypothesis was tested by van de Schootbrugge et al. (2005), who highlighted the existence of sections that lacked a negative excursion in aC in one or more sample media: amongst them is the section on the coast of Yorkshire, UK, used to erect the methane hypothesis by Hesselbo et al. (2000), which lacks a negative excursion in the δC of belemnite calcite (McArthur et al., 2000; van de Schootbrugge et al., 2005). As the excursion is not seen in these sections, it cannot represent a global event and so could not have resulted from methane release, which would have influenced all reservoirs of carbon. New data are now provided by HJDO06 for a section (Peniche
- Published
- 2007
16. Natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water: the example of West Bengal and its worldwide implications
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R. Purohit, S Houghton, David Lowry, John M. McArthur, Richard J. Howarth, Karen A. Hudson-Edwards, DK Chadha, D.M. Banerjee, Rosaline Mishra, A Chatterjee, T Talukder, P Ravenscroft, and A Cronin
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chemistry.chemical_classification ,geography ,geography.geographical_feature_category ,Piezometer ,Mineralogy ,Aquifer ,Pollution ,Anoxic waters ,Sedimentary depositional environment ,SEA-LEVEL CHANGES, DISSIMILATORY REDUCTION, UNITED-STATES, SULFATE REDUCTION, DRINKING-WATER, TRACE-ELEMENTS, BANGLADESH, IRON, MOBILIZATION, SORPTION ,chemistry ,Geochemistry and Petrology ,Environmental chemistry ,Environmental Chemistry ,Organic matter ,Dissolution ,Geology ,Groundwater ,Water well - Abstract
In order to investigate the mechanism of As release to anoxic ground water in alluvial aquifers, the authors sampled ground waters from 3 piezometer nests, 79 shallow (80 m) wells, in an area 750 m by 450 m, just north of Barasat, near Kolkata (Calcutta), in southern West Bengal. High concentrations of As (200-1180 mug L-1) are accompanied by high concentrations of Fe (3-13.7 mgL(-1)) and PO4 (1-6.5 mg L-1). Ground water that is rich in Mn (1-5.3 mg L-1) contains
- Published
- 2004
17. Strontium Isotope Stratigraphy: LOWESS Version 3: Best Fit to the Marine Sr‐Isotope Curve for 0–509 Ma and Accompanying Look‐up Table for Deriving Numerical Age
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T. R. Bailey, Richard J. Howarth, and John M. McArthur
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Paleontology ,Isotope ,Stratigraphy ,Lookup table ,Table (landform) ,Geology ,Isotopes of strontium - Abstract
An improved and updated version of the statistical LOWESS fit to the marine 87Sr/86Sr record and a revised look-up table (V3:10/99; available from j.mcarthur@ucl.ac.uk) based upon it enables straightforward conversion of 87Sr/86Sr to numerical age, and vice versa, for use in strontium isotope stratigraphy (SIS). The table includes 95% confidence intervals on predictions of numerical age from 87Sr/86Sr. This version includes the Triassic and Paleozoic record (0509 Ma) omitted from previous versions because of the paucity of adequate data at the time of preparation. We highlight differences between the previous versions of the table and the current version and discuss some aspects of the 87Sr/86Sr record that may have geological significance. We give examples of how the table can be used and where it has proven useful.
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- 2001
18. Definition of Late Cretaceous Stage Boundaries in Antarctica Using Strontium Isotope Stratigraphy
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John M. McArthur, J. A. Crame, and Matthew F. Thirlwall
- Subjects
Extinction event ,Inoceramus ,Paleontology ,Stratigraphy ,biology ,Stage (stratigraphy) ,Northern Hemisphere ,Macrofossil ,Geology ,biology.organism_classification ,Southern Hemisphere ,Cretaceous - Abstract
New 87Sr/86Sr analyses of macrofossils from 13 key marker horizons on James Ross and Vega Islands, Antarctica, allow the integration of the Antarctic Late Cretaceous succession into the standard biostratigraphic zonation schemes of the Northern Hemisphere. The 87Sr/86Sr data enable Late Cretaceous stage boundaries to be physically located with accuracy for the first time in a composite Southern Hemisphere reference section and so make the area one of global importance for documenting Late Cretaceous biotic evolution, particularly radiation and extinction events. The 87Sr/86Sr values allow the stage boundaries of the Turonian/Coniacian, Coniacian/Santonian, Santonian/Campanian, and Campanian/Maastrichtian, as well as other levels, to be correlated with both the United Kingdom and United States. These correlations show that current stratigraphic ages in Antarctica are too young by as much as a stage. Immediate implications of our new ages include the fact that Inoceramus madagascariensis, a useful ...
- Published
- 2000
19. Mechanism of arsenic release to groundwater, Bangladesh and West Bengal
- Author
-
WG Burgess, John M. McArthur, Kazi Matin Ahmed, Peter Ravenscroft, and R.T. Nickson
- Subjects
Pollution ,geography ,geography.geographical_feature_category ,media_common.quotation_subject ,Mineralogy ,chemistry.chemical_element ,Aquifer ,engineering.material ,chemistry ,Geochemistry and Petrology ,Environmental chemistry ,engineering ,Environmental Chemistry ,Environmental science ,Sedimentary organic matter ,Water treatment ,Pyrite ,Groundwater ,Arsenic ,media_common ,Water well - Abstract
In some areas of Bangladesh and West Bengal, concentrations of As in groundwater exceed guide concentrations, set internationally and nationally at 10 to 50 m gl ˇ1 and may reach levels in the mg l ˇ1 range. The As derives from reductive dissolution of Fe oxyhydroxide and release of its sorbed As. The Fe oxyhydroxide exists in the aquifer as dispersed phases, such as coatings on sedimentary grains. Recalculated to pure FeOOH, As concentrations in this phase reach 517 ppm. Reduction of the Fe is driven by microbial metabolism of sedimentary organic matter, which is present in concentrations as high as 6% C. Arsenic released by oxidation of pyrite, as water levels are drawn down and air enters the aquifer, contributes negligibly to the problem of As pollution. Identification of the mechanism of As release to groundwater helps to provide a framework to guide the placement of new water wells so that they will have acceptable concentrations of As. # 2000 Elsevier Science Ltd. All rights reserved.
- Published
- 2000
20. Statistics For Strontium Isotope Stratigraphy: A Robust Lowess Fit to the Marine Sr‐Isotope Curve For 0 to 206 Ma, With Look‐Up Table For Derivation of Numeric Age
- Author
-
Richard J. Howarth and John M. McArthur
- Subjects
Calibration (statistics) ,Statistics ,Nonparametric statistics ,Local regression ,Geology ,Replicate ,Scatterplot smoothing ,Table (information) ,Confidence interval ,Regression - Abstract
We provide a best‐fit curve to 1849 strontium isotope data for the period 0 to 206 Ma using the LOcally‐WEighted regression Scatterplot Smoother (LOWESS) method. This is a robust, nonparametric modern regression technique. Since it does not yield an explicit mathematical equation relating 87Sr/86Sr to time, a look‐up table to determine numeric age has been generated in steps of 1 × 10−6 in 87Sr/86Sr. The calibration uses the timescales of Shackleton and coworkers for 0‐7 Ma; Cande and Kent for 7‐72 Ma; Obradovich for 72‐95 Ma and Gradstein and coworkers for >95 Ma. The look‐up table includes 95% confidence intervals on the predictions of numeric age. When using this table, the uncertainty on the 87Sr/86Sr of the sample whose age is sought must be added to that inherent in the LOWESS regression. We show how to determine the uncertainty in 87Sr/86, i.e., how best to obtain the 95% confidence bounds on a single measurement of 87Sr/86 for a sample, and on the mean 87Sr/86 value for 2 or more replicate measure...
- Published
- 1997
21. Jellyfish Lake, Palau: Regeneration of C, N, Si, and P in anoxic marine lake sediments
- Author
-
William M. Landing, William C. Burnett, William H. Orem, Philip A. Chin, John M. McArthur, Robert M. Lent, and W. Berry Lyons
- Subjects
Terrigenous sediment ,Alkalinity ,Sediment ,Mineralogy ,Authigenic ,Aquatic Science ,Oceanography ,Anoxic waters ,Pore water pressure ,chemistry.chemical_compound ,chemistry ,Environmental chemistry ,Carbonate ,Seawater ,Geology - Abstract
Sediment cores from Jellyfish Lake were processed under an inert atmos phcre and the pore waters extracted and analyzed for the following parameters: pH, titration alkalinity (TA), Cl-, H4Si04, POd3-, NH4+, Ca2+, Mg2+, SOd2-, and H2S. Additionally, in one set of pore-water samples (core lo), the 613C of the X0, was also determined. The TA, H4Si04, POd3-, NH;+, and H,S increased with depth in the pore waters above anoxic bottom-water values. H,S values increased to 3.8 PM. In one case, both H,SiO, and POd3- concentrations increased to a maximum value and then decreased with depth, suggesting removal into solid phases. The H,SiO, concentrations are equal to or greater than pore-water values observed in sediments underlying upwelling areas. Pod3 - concentrations are, in general, lower than pore-water values from terrigenous nearshore areas but higher than nearshore carbonate pore-water values from Florida Bay or Bermuda. The Ca2+, Cl-, and Mg2+ : Cl- ratios show slight decreases in the top 15-20 cm, suggesting that authigenic carbonate may be forming. This suggestion is supported by the fact that the pore waters are saturated with respect to CaCO, due to the very high TAs. The 613C measurements of the pore-water X0, are from a shorter core. These measurements reach their most negative concentration at 72 cm and tilen become slightly heavier. This change is accompanied by a decrease in TA, suggesting the onset of methanogenesis at this location in this core.
- Published
- 1996
22. The palaeosol model of arsenic pollution of groundwater tested along a 32 km traverse across West Bengal, India
- Author
-
Mohammad A. Hoque, John M. McArthur, and P. K. Sikdar
- Subjects
Pollution ,Arsenic pollution ,Geologic Sediments ,Traverse ,Environmental Engineering ,media_common.quotation_subject ,Bengal Basin ,India ,Aquifer ,Arsenic ,Sequence (geology) ,Water Quality ,West Bengal ,Environmental Chemistry ,Palaeo-interfluve ,Waste Management and Disposal ,Groundwater ,media_common ,Well-colour ,Hydrology ,geography ,geography.geographical_feature_category ,Groundwater arsenic ,Palaeosol ,Models, Theoretical ,Paleosol ,West bengal ,Geology ,Water Pollutants, Chemical - Abstract
The distribution of As-pollution in groundwater of the deltaic aquifers of south-eastern Asia may be controlled by the subsurface distribution of palaeo-channel sediments (As-polluted groundwaters) and palaeo-interfluvial sediments (As-free groundwaters). To test this idea, termed the palaeosol model of As-pollution, we drilled 10 sites, analysed groundwater from 249 shallow wells (screened
- Published
- 2012
23. Strontium isotope stratigraphy in the Late Cretaceous: Numerical calibration of the Sr isotope curve and intercontinental correlation for the campanian
- Author
-
Andrew S. Gale, Matthew F. Thirlwall, William James Kennedy, M. Chen, and John M. McArthur
- Subjects
Inoceramus ,biology ,Scaphites ,Paleontology ,Baculites ,Biostratigraphy ,Oceanography ,biology.organism_classification ,Cretaceous ,Marsupites ,Belemnites ,Geology ,Belemnella - Abstract
The white Chalk exposed in quarries at Lagerdorf and Kronsmoor, northwestern Germany, provides a standard section for the European Upper Cretaceous. The Sr-87/Sr-86 values of nannofossil chalk and belemnite calcite increase upward through 330 m of section, from less than or equal to 0.70746 in the Upper Santonian to greater than or equal to 0.70777 in the Lower Maastrichtian. The data define three linear trends separated by major points of inflection at stratigraphic heights in the section of 162 m (75.5 Ma) in the Upper Campanian Galerites vulgaris zone and at -6 m (82.9 Ma), just above the base of the Campanian in the Inoceramus lingua/Goniateuthis quadrata zone. The temporal rate of change of Sr-87/Sr-86 was constant through each of the linear segments of our isotope ''curve'' when viewed at the resolution of our average sampling interval (0.15 m.y.). Fine structure, if rear, may record brief (
- Published
- 1993
24. Strontium isotope stratigraphy for the Late Cretaceous: a new curve, based on the English Chalk
- Author
-
Matthew F. Thirlwall, Andrew S. Gale, J. A. Burnett, A. R. Lord, David P. Mattey, John M. McArthur, and William James Kennedy
- Subjects
Paleontology ,Stratigraphy ,Macrofossil ,Geology ,Ocean Engineering ,Biostratigraphy ,Cenomanian ,Cretaceous ,Isotopes of strontium ,Water Science and Technology - Abstract
Marine 87Sr/ 86Sr decreases from 0.70775 in the Cenomanian to 0.70730 in the middle Turonian before increasing in a near-linear manner to >0.70775 in the early Maastrichtian. This variation has been defined using samples from the English Chalk that are closely integrated with the macrofossil and microfossil biostratigraphy of northwestern Europe. With this new isotope curve a stratigraphic resolution is attainable in correlation that is typically ±0.8 Ma for the Santonian and Campanian stages. Isotopic and biostratigraphic correlations between Dorset and Norfolk, in the UK, agree within the limit of analytical error in 87Sr/ 86Sr. © The Geological Society 1993.
- Published
- 1993
25. Localization of Quaternary slip rates in an active rift in 10(5) years: An example from central Greece constrained by U-234-Th-230 coral dates from uplifted paleoshorelines
- Author
-
Frances J. Cooper, John M. McArthur, P. van Calsteren, S Houghton, Patience A. Cowie, T Wigley, Ioannis Papanikolaou, Gerald P. Roberts, and Charlie J. Underwood
- Subjects
Atmospheric Science ,Soil Science ,Slip (materials science) ,Aquatic Science ,Fault (geology) ,Oceanography ,Geochemistry and Petrology ,Sea-level curve ,Earth and Planetary Sciences (miscellaneous) ,Sea level ,Holocene ,Earth-Surface Processes ,Water Science and Technology ,geography ,geography.geographical_feature_category ,Rift ,Ecology ,Paleontology ,Forestry ,Geophysics ,Space and Planetary Science ,Quaternary ,Cenozoic ,Geology ,Seismology - Abstract
Mapping, dating, and modeling of paleoshorelines uplifted in the footwall of the 1981 Gulf of Corinth earthquake fault, Greece (Ms 6.9–6.7), are used to assess its slip rate history relative to other normal faults in the area and study strain localization. The 234U-230Th coral ages from Cladocora caespitosa date uplifted shoreface sediments, and paleoshorelines from glacioeustatic sea level highstands at 76, (possibly) 100, 125, 175, 200, 216, 240, and 340 ka. Uplifted Quaternary and Holocene paleoshorelines decrease in elevation toward the western tip of the fault, exhibiting larger tilt angles with age, showing that uplift is due to progressive fault slip. Since 125 ka, uplift rates varied from 0.25 to 0.52 mm/yr over a distance of 5 km away from the fault tip. Tilting was also occurring prior to 125 ka, but uplift rates were lower because the 125 ka paleoshoreline is at 77% of the elevation of the 240 ka paleoshoreline despite being nearly half its age. Comparison of paleoshoreline elevations and sedimentology with the Quaternary sea level curve shows that slip rates increased by a factor of 3.2 ± 0.2 at 175 ± 75 ka, synchronous with cessation of activity on a neighboring normal fault at 382–112 ka. We suggest that the rapid localization of up to 10–15 mm/yr of extension into the narrow gulf (∼30 km wide) resulted from synchronous fault activity on neighboring faults followed by localization rather than sequential faulting, with consequences for the mechanism controlling localization of extension.
- Published
- 2009
26. Basinal restriction, black shales, Re-Os dating, and the Early Toarcian (Jurassic) oceanic anoxic event
- Author
-
Qin Li, B. van de Schootbrugge, Richard J. Howarth, John M. McArthur, and Thomas J. Algeo
- Subjects
Total organic carbon ,Extinction event ,Paleontology ,Water mass ,Sediment ,Structural basin ,Oceanography ,Anoxic waters ,Geology ,Posidonia Shale ,Chronology - Abstract
[1] Profiles of Mo/total organic carbon (TOC) through the Lower Toarcian black shales of the Cleveland Basin, Yorkshire, United Kingdom, and the Posidonia shale of Germany and Switzerland reveal water mass restriction during the interval from late tenuicostatum Zone times to early bifrons Zone times, times which include that of the putative Early Toarcian oceanic anoxic event. The degree of restriction is revealed by crossplots of Mo and TOC concentrations for the Cleveland Basin, which define two linear arrays with regression slopes (ppm/%) of 0.5 and 17. The slope of 0.5 applies to sediment from the upper semicelatum and exaratum Subzones. This value, which is one tenth of that for modern sediments from the Black Sea (Mo/TOC regression slope 4.5), reveals that water mass restriction during this interval was around 10 times more severe than in the modern Black Sea; the renewal frequency of the water mass was between 4 and 40 ka. The Mo/TOC regression slope of 17 applies to the overlying falciferum and commune subzones: the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years. The more restricted of the two intervals has been termed the Early Toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to NW Europe. Crossplots of Re, Os, and Mo against TOC show similar trends of increasing element concentration with increase in TOC but with differing slopes. Together with modeling of 187 Os/ 188 Os and d 98 Mo, the element/TOC trends show that drawdown of Re, Os, and Mo was essentially complete during upper semicelatum and exaratum Subzone times (Mo/TOC regression slope of 0.5). Drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of Re, Os, and Mo, via a low-salinity surface layer, created isotopic excursions of up to 1.3% in d 98 Mo and up to 0.6% for 187 Os/ 188 Os. Restriction thereby compromises attempts to date Toarcian black shales, and possibly all black shales, using Re-Os chronology and introduces a confounding influence in the attempts to use d 98 Mo and initial 187 Os/ 188 Os for palaeo-oceanographic interpretation.
- Published
- 2008
27. How paleosols influence groundwater flow and arsenic pollution: A model from the Bengal Basin and its worldwide implication
- Author
-
Anindya Sarkar, S. Sengupta, Karen A. Hudson-Edwards, P. Ravenscroft, R. Purohit, J. Milsom, S. Tonkin, Charlie S. Bristow, John M. McArthur, and D.M. Banerjee
- Subjects
Pollution ,Hydrology ,geography ,geography.geographical_feature_category ,Groundwater flow ,media_common.quotation_subject ,Geochemistry ,Aquifer ,Structural basin ,Paleosol ,Palaeochannel ,Sedimentary rock ,Geology ,Groundwater ,Water Science and Technology ,media_common - Abstract
In the Bengal Basin, the land surface exposed during the last lowstand of sea level around 20 ka, and now buried by Holocene sediment, is capped by an effectively impermeable clay paleosol that we term the Last Glacial Maximum paleosol (LGMP). The paleosol strongly affects groundwater flow and controls the location of arsenic pollution in the shallow aquifers of our study site in southern West Bengal and, by implication, in shallow aquifers across the Bengal Basin and As-polluted deltaic aquifers worldwide. The presence of the LGMP defines paleointerfluvial areas; it is absent from paleochannel areas. A paleosol model of pollution proposed here predicts that groundwater in paleochannels is polluted by arsenic, while that beneath paleointerfluvial areas is not: paleointerfluvial aquifers are unpolluted because they are protected by the LGMP from downward migration of arsenic and from downward migration of organic matter that drives As-pollution via reductive dissolution of As-bearing iron oxyhydroxides. Horizontal groundwater flow carries arsenic from paleochannels toward paleointerfluvial aquifers, in which sorption of arsenic minimizes the risk of pollution.
- Published
- 2008
28. Palaeoceanography: methane release in the Early Jurassic period
- Author
-
Paul B, Wignall, John M, McArthur, Crispin T S, Little, and Anthony, Hallam
- Subjects
Greenhouse Effect ,Carbon Isotopes ,Time Factors ,Oceans and Seas ,Temperature ,Reproducibility of Results ,Marine Biology ,Biodiversity ,Oceanography ,Carbon ,Oxygen ,Dinoflagellida ,Animals ,Seawater ,Methane ,History, Ancient - Abstract
Dramatic global warming, triggered by release of methane from clathrates, has been postulated to have occurred during the early Toarcian age in the Early Jurassic period. Kemp et al. claim that this methane was released at three points, as recorded by three sharp excursions of delta13C(org) of up to 3 per thousand magnitude. But they discount another explanation for the excursions: namely that some, perhaps all, of the rapid excursions could be a local signature of a euxinic basin caused by recycling of isotopically light carbon from the lower water column. This idea has been proposed previously (see ref. 3, for example) and is supported by the lack evidence for negative delta13C excursions in coeval belemnite rostra. Kemp et al. dismiss this alternative, claiming that each abrupt shift would have required the recycling of about double the amount of organic carbon that is currently present in the modern ocean; however, their measurements are not from an ocean but from a restricted, epicontinental seaway and so would not require whole-ocean mixing to achieve the excursions.
- Published
- 2006
29. Toarcian oceanic anoxic event: An assessment of global causes using belemnite C isotope records
- Author
-
John M. McArthur, James D. Wright, Kenneth G. Miller, B. van de Schootbrugge, Yair Rosenthal, and T. R. Bailey
- Subjects
biology ,Paleontology ,Oceanography ,biology.organism_classification ,Carbon cycle ,chemistry.chemical_compound ,Isotopic signature ,chemistry ,Isotopes of carbon ,Dissolved organic carbon ,Carbonate ,Sedimentary organic matter ,Photic zone ,Belemnites ,Geology - Abstract
Two hypotheses have been proposed to explain simultaneous large negative excursions (up to 7% PeeDee belemnite) in bulk carbonate (delta(13)C(carb)) and organic carbon isotope records (delta(13)C(org)) from black shales marking the Toarcian oceanic anoxic event (T-OAE). The first explanation envisions recycling of dissolved inorganic carbon (DIC) with a light isotopic signature into the photic zone from the lower levels of a salinity-stratified water mass, essentially requiring a regional paleoceanographic driver of the carbon cycle. The second involves the rapid and massive dissociation of methane from gas hydrates that effectively renders the T-OAE a global perturbation of the carbon cycle. We present C isotope records from belemnites (delta(13)C(bel)) sampled from two localities, calibrated with high-resolution ammonite biostratigraphy and Sr isotope stratigraphy, in Yorkshire (England) and Dotternhausen (Germany), that can be used to assess which model best explains the observed changes in carbon isotopes. Our records of the delta(13)C composition of belemnite calcite do not show the large negative C isotope excursions shown by coeval records of delta(13)C in sedimentary organic matter or bulk sedimentary carbonate. It follows that isotopically light carbon cannot have dominated the ocean-atmosphere carbon reservoir during the Toarcian OAE, as would be required were the methane release hypothesis correct. On the basis of an evaluation of available carbon isotope records we discuss a model in which the recycling of DIC from the deeper levels of a stratified water body, and shallowing of anoxic conditions into the photic zone, can explain all isotopic profiles. In particular, the model accounts for the higher C isotope values of belemnites that are characteristic of open ocean, well-mixed conditions, and the lower C isotope values of neritic phytoplankton communities that recorded the degree of density stratification and shallowing of anoxia in the photic zone.
- Published
- 2005
30. New234U-230Th coral dates from the western Gulf of Corinth: Implications for extensional tectonics
- Author
-
John M. McArthur, S Houghton, Ioannis Papanikolaou, Mabs Gilmour, and Gerald P. Roberts
- Subjects
geography ,geography.geographical_feature_category ,Cladocora caespitosa ,Coral ,Fault (geology) ,Tectonics ,Geophysics ,Oceanography ,Mediterranean sea ,General Earth and Planetary Sciences ,Extensional tectonics ,Marine terrace ,Normal fault ,Geology - Abstract
We derive rates of uplift of ∼0.7–0.8 mm/yr for the western end of the Gulf of Corinth, Greece, using geomorphic paleaoshoreline modeling. We calibrate the modeling with new 234U-230Th dates on the coral Cladocora caespitosa collected from raised marine terraces uplifted in the footwall of the active Psathopyrgos fault, the only major active normal fault, reported on published maps controlling the downthrown Rio Straits at the western end of the Gulf of Corinth. In this area of high (15–22 mm/yr) extension rates measured with GPS, the ratio of uplift-rate to extensional velocity is 0.025–0.035, much lower than values of 0.15–0.25 found further east in the gulf. These low values imply that if GPS extension rates are correct then mechanical/kinematic models developed for the eastern and central gulf may not be applicable to the western gulf.
- Published
- 2003
31. Fluorine-deficient apatite
- Author
-
John M. McArthur
- Subjects
Provenance ,010504 meteorology & atmospheric sciences ,Phosphorus ,Inorganic chemistry ,Fluorapatite ,chemistry.chemical_element ,Mineralogy ,010502 geochemistry & geophysics ,01 natural sciences ,Apatite ,Phosphorite ,chemistry ,Geochemistry and Petrology ,visual_art ,visual_art.visual_art_medium ,Fluorine ,Sedimentary rock ,Francolite ,0105 earth and related environmental sciences - Published
- 1990
32. Comment on 'Limited Temporal Variability of Arsenic Concentrations in 20 Wells Monitored for 3 Years in Araihazar, Bangladesh'
- Author
-
Peter Ravenscroft, Richard J. Howarth, and John M. McArthur
- Subjects
Environmental Chemistry ,General Chemistry - Published
- 2006
33. Strontium isotope stratigraphy for Late Cretaceous time: Direct numerical calibration of the Sr isotope curve based on the US Western Interior
- Author
-
Andrew S. Gale, Matthew F. Thirlwall, M. Chen, William James Kennedy, and John M. McArthur
- Subjects
Ammonite ,Paleontology ,Macrofossil ,Western Interior Seaway ,Biostratigraphy ,Oceanography ,language.human_language ,Cretaceous ,Stratigraphy ,language ,Mesozoic ,Cenomanian ,Ecology, Evolution, Behavior and Systematics ,Geology ,Earth-Surface Processes - Abstract
The 87Sr/86Sr of Sr in macrofossil carbonate from Upper Cretaceous strata deposited in the Western Interior Seaway, USA, provides a Sr-isotope curve for Late Cretaceous time (Cenomanian-Early Maastrichtian). The curve is calibrated biostratigraphically against the most refined ammonite zonation known for the interval, and calibrated numerically with 39Ar/40Ar dates for 20 bentonites within the sequence. Marine 87Sr/86Sr decreased from 0.70743 in the late Middle Cenomanian to a Late Cretaceous minimum of 0.70730 in the Late Turonian (89 Ma). From the minimum, 87Sr/86Sr increased through a Middle Campanian inflexion (minimum at 77 Ma, maximum at 78-80 Ma) to reach 0.70772 at the Campanian/Maastrichtian boundary. Thereafter 87Sr/86Sr increased through a very short inflexion in the latest Early Maastrichtian to the limit of our sampling in the earliest Late Maastrichtian. The inflexions provide global event markers for correlation. For most of the period covered by our curve resolution in dating and correlation of ≤0.8 Ma should be achievable with our 2 s.d. precision in measurement of ±18 × 10-6. Our 87Sr/86Sr data show no evidence of having been affected by influxes of freshwater into the US Western Interior Seaway from rivers, including those that drained the Sevier Orogenic Belt. © 1994.
- Published
- 1994
34. Reply: Arsenic poisoning in the Ganges delta
- Author
-
John M. McArthur
- Subjects
Delta ,Arsenic pollution ,Multidisciplinary ,Iron reduction ,Chemistry ,Environmental chemistry ,medicine ,Arsenic poisoning ,medicine.disease - Abstract
In their comments on our paper1, both Acharyya et al. and Chowdhury et al. refer to previous suggestions2,3 that iron reduction might be the source of arsenic pollution. Naming a process2, suggesting that it occurs on the basis of reasoned argument3, and providing objective evidence that it does1,4 are different things.
- Published
- 1999
35. Methane release in the Early Jurassic period
- Author
-
Anthony Hallam, Crispin T. S. Little, Paul B. Wignall, and John M. McArthur
- Subjects
Extinction event ,Total organic carbon ,Multidisciplinary ,δ13C ,Global warming ,Methane ,Paleontology ,chemistry.chemical_compound ,Oceanography ,Water column ,chemistry ,Period (geology) ,Arctic methane release ,Geology - Abstract
Arising from: D. B. Kemp, A. L. Coe, A. S. Cohen & L. Schwark Nature 437, 396–399 (2005); Kemp et al. reply Dramatic global warming, triggered by release of methane from clathrates, has been postulated to have occurred during the early Toarcian age in the Early Jurassic period1. Kemp et al.2 claim that this methane was released at three points, as recorded by three sharp excursions of δ13Corg of up to 3‰ magnitude. But they discount another explanation for the excursions: namely that some, perhaps all, of the rapid excursions could be a local signature of a euxinic basin caused by recycling of isotopically light carbon from the lower water column. This idea has been proposed previously (see ref. 3, for example) and is supported by the lack evidence for negative δ13C excursions in coeval belemnite rostra4. Kemp et al. dismiss this alternative, claiming that each abrupt shift would have required the recycling of about double the amount of organic carbon that is currently present in the modern ocean; however, their measurements are not from an ocean but from a restricted, epicontinental seaway and so would not require whole-ocean mixing to achieve the excursions.
- Published
- 2006
36. Joint discussion of sedimentary geochemistry data management systems that cross the waterline
- Author
-
John M. McArthur, Cinzia Cervato, Steven L. Goldstein, Kerstin Lehnert, and Ethan L. Grossman
- Subjects
Extinction event ,geography ,geography.geographical_feature_category ,Earth science ,Climate oscillation ,Geochemistry ,Deep sea ,Isotopes of oxygen ,Cretaceous ,Volcanic rock ,Precambrian ,General Earth and Planetary Sciences ,Sedimentary rock ,Geology - Abstract
Earth's evolution, its climate history, and the history of life are archived in the chemical and isotopic compositions of marine and terrestrial sediments and fossils found within them. This information provides evidence for crustmantle recycling, bolide impacts, mass extinction events, gas hydrate expulsion, climate cycles, and much more. Much of this geochemical evidence, such as the discoveries of oxygen isotope cycles in Quaternary sediments, enhanced iridium at the Cretaceous/Paleocene boundary and relationships between near-trench sediments and associated arc volcanics, have overturned paradigms, opened new avenues of inquiry, and helped launch international research programs (e.g., the Deep Sea Drilling Project [DSDP]). In addition to revealing much about important Earth events and processes, geochemical records preserved in marine and terrestrial sediments are increasingly important for the correlation of global records; indeed, for Precambrian and anoxic sediments, chemical and isotopic methods are indispensable and provide the main basis for correlation.
- Published
- 2004
37. Arsenic poisoning of Bangladesh groundwater
- Author
-
Kazi Matin Ahmed, MB Rahman, WG Burgess, John M. McArthur, Peter Ravenscroft, and R.T. Nickson
- Subjects
inorganic chemicals ,Iron ,India ,Arsenic poisoning ,chemistry.chemical_element ,Aquifer ,Arsenic ,Toxicology ,Water Supply ,medicine ,Water pollution ,geography ,Multidisciplinary ,geography.geographical_feature_category ,integumentary system ,Water Pollution ,medicine.disease ,Arsenic contamination of groundwater ,chemistry ,Environmental science ,Alluvium ,Water resource management ,Oxidation-Reduction ,Groundwater ,Water well - Abstract
In Bangladesh and West Bengal, alluvial Ganges aquifers used for public water supply are polluted with naturally occurring arsenic, which adversely affects the health of millions of people. Here we show that the arsenic derives from the reductive dissolution of arsenic-rich iron oxyhydroxides, which in turn are derived from weathering of base-metal sulphides. This finding means it should now be possible, by sedimentological study of the Ganges alluvial sediments, to guide the placement of new water wells so they will be free of arsenic.
- Published
- 1998
38. Strontium isotopes at K/T boundary
- Author
-
J. Burnett, John M. McArthur, and J. M. Hancock
- Subjects
Multidisciplinary ,Analytical chemistry ,Boundary (topology) ,Geology ,Isotopes of strontium - Published
- 1992
39. The composition and distribution of nodular monazite in the Lower Palaeozoic rocks of Great Britain
- Author
-
D. Read, John M. McArthur, and D. C. Cooper
- Subjects
Provenance ,Recrystallization (geology) ,010504 meteorology & atmospheric sciences ,Paleozoic ,Metamorphic rock ,Geochemistry ,010502 geochemistry & geophysics ,01 natural sciences ,Source rock ,Geochemistry and Petrology ,Monazite ,Sedimentary rock ,Pegmatite ,Geology ,0105 earth and related environmental sciences - Abstract
Millimetric, ellipsoidal monazite nodules found within Lower Palaeozoic sedimentary rocks in Wales, south-west England and Brittany are characterised by a pronounced zonation of light and heavy REE, an inclusion fabric of low-grade metamorphic minerals indistinguishable from the host rock and a low Th content. They are interpreted as the product of in situ recrystallization of detrital monazites derived from pegmatitic or granitic source rocks and are potentially useful as indicators of Lower Palaeozoic sedimentary rock provenance.
- Published
- 1987
40. Metal accumulation rates in sediments from Mid-Indian Ocean Ridge and Marie Celeste Fracture Zone
- Author
-
Henry Elderfield and John M. McArthur
- Subjects
Basalt ,geography ,Multidisciplinary ,geography.geographical_feature_category ,fungi ,Sediment ,Mid-ocean ridge ,Fracture zone ,Ferromanganese ,Hydrothermal circulation ,Oceanography ,Ridge ,Precipitation ,Geology - Abstract
THE existence of metalliferous sediments on mid-ocean ridges is well documented1 and the general conclusion is that they form by precipitation from submarine hydrothermal solutions. Pacific and Atlantic Ocean sediments have been studied in detail2–6. We describe here material from the Indian Ocean Ridge, collected during cruise 8/75 of RRS Shackleton, and compare metal accumulation rate data for ridge-crest and -flank sediments with those from other regions. The metalliferous sediments are present on the Mid-Indian Ocean Ridge, particularly near the Triple Junction7,8, and Bostrom and Fisher7 suggest that “there is a complete belt of iron-rich sediment along the entire length of the Indian Ocean–Pacific Ocean active-ridge system”. We have found ferromanganese encrustations on basalts from the median-valley wall and have recognised what are probably sulphides in decorated vesicles of basalts. The metal accumulation rate data argue against a hydrothermal source of metals in the ridge sediments, however, and suggest that metalliferous sediment accumulations in the Indian Ocean may be more local phenomena than previously realised.
- Published
- 1977
41. Pleistocene phosphorites off the west coast of South Africa
- Author
-
William C. Burnett, Gavin F. Birch, J. Thomson, and John M. McArthur
- Subjects
Multidisciplinary ,Oceanography ,Pleistocene ,Continental margin ,Phosphorite ,Upwelling ,Radiometric dating ,Sedimentary rock ,West coast ,Quaternary ,Geology - Abstract
We report here relatively modern phosphogenesis on the continental margin off South Africa, where palaeontologically old limestone (middle Eocene–middle Miocene) has been phosphatized in late Pleistocene times (62–76 kyr) in an area of only moderate and seasonal present-day upwelling1,2. Previously, modern phosphogenesis had been reported as occurring only off Namibia3–15, Peru/Chile16–21 and very recently, east Australia22,23. This report, and those describing the late Quaternary east Australia phosphorite22,23, suggest that, contrary to established opinion, strongly enhanced upwelling may not be necessary for phosphorite formation and that oceanic phos-phogenic models need not be based exclusively on localized oceanographie regimes such as exist off Peru and Namibia.
- Published
- 1983
42. Origin of sedimentary francolite from its sulphur and carbon isotope composition
- Author
-
John M. McArthur, Max Coleman, and Richard A. Benmore
- Subjects
Multidisciplinary ,Mineral ,δ34S ,chemistry ,Phosphorite ,chemistry.chemical_element ,Mineralogy ,Sedimentary rock ,Authigenic ,Francolite ,Carbon ,Chemical composition - Abstract
Francolite, the phosphorus-bearing mineral of nearly all sedimentary phosphorites, has a variable chemical composition which can be represented by (Ca, Mg, Sr, Na)10(PO4, SO4, CO3)6F2–3. It is now well established that this mineral can form authigenically in organic-rich muds1 or by replacement of precursor carbonate2 but the origin of some phosphorite deposits is still in dispute or unknown. Recently the isotopic composition of structural PO4–O, CO3–C+O, and SO4–S has been considered in attempts to resolve this problem3–9. Structural CO3–C has proved particularly useful in discriminating between phosphatized carbonates and authigenic phosphorites, the former preserving the δ13C of its precursor and the latter containing a substantial proportion of lighter carbon generated by anaerobic bacterial degradation of organic matter4,5. From new δ34S data we present here a more refined interpretation of the formational environment. δ34S values heavier than that of sea-water indicate that genesis has occurred within the bacterial sulphate reduction zone whilst δ34S values lighter than that of seawater delimit formation to a zone between sulphate reducing and overlying oxic conditions where isotopically light H2S is re-oxidized.
- Published
- 1983
43. Book Review: Monographs on Oncology: The Chest
- Author
-
John M McArthur
- Subjects
medicine.medical_specialty ,business.industry ,General surgery ,Medicine ,business - Published
- 1974
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