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The Early Toarcian, organic-rich, black shales of the Cleveland Basin, Yorkshire UK, are the type sediments for the supposed early Toarcian oceanic anoxic event. The sediments have values of Cd/Mo that are 0.4. These values are typical of sediment deposited in modern basins that are hydrographically restricted and show that the Cleveland Basin was hydrographically restricted when depositing organic-rich sediments. These palaeo-proxies confirm earlier interpretations, based on Mo/TOC values, that argued for hydrographic restriction. The term Toarcian oceanic anoxic event can now be discarded.

During the Early Toarcian, volcanic gases released by the Karoo-Ferrar large igneous province are widely believed to have caused severe environmental disturbances, including ocean acidification. Here we show records of δ44/40Ca and δ88/86Sr through the Early Toarcian, as recorded in three groups of biogenic calcite: Megateuthididae belemnites, Passaloteuthididae belemnites, and brachiopods of the species Soaresirhynchia bouchardi. We evaluate the data to eliminate the influence on isotopic composition of varying temperature, calcification rate, and salinity, through the section that may mask the environmental signals. Neither δ44/40Ca nor δ88/86Sr show negative isotope excursions across the suggested acidification interval as would be expected had acidification occurred. A profile of δ11B, re-interpreted from a published study, shows no variation through the interval. Taken together, these data provide little support for ocean acidification at this time. In our belemnites, values of δ88/86Sr are independent of temperature or Sr/Ca. For brachiopods, too few data are available to determine whether such dependences exist. Values of δ44/40Ca show a weak temperature control of magnitude +0.020 ± 0.004 ‰/°C (2 s.d.). In belemnites, δ44/40Ca also correlates positively with Mg/Ca and Sr/Ca.

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

In 49 samples of groundwater, sampled in Muzaffargarh District of south-western Punjab, central Pakistan, concentrations of As exceeded the World Health Organisation provisional guideline value, and United States Environmental Protection Agency (USEPA) Maximum Contaminant Level (MCL), of 10 μg L−1 in 58% of samples and reached up to 906 μg L−1. In this semi-arid region canal irrigation has lead to widespread water-logging, and evaporative concentration of salts has the potential to raise As concentrations in shallow groundwater well above 10 μg L−1. In fact, in rural areas, concentrations stay below 25 μg L−1 because As in the oxic shallow groundwater, and in recharging water, is sorbed to aquifer sediments. In some urban areas, however, shallow groundwater is found to contain elevated levels of As. The spatial distribution of As-rich shallow groundwater indicates either direct contamination with industrial or agricultural chemicals, or some other anthropogenic influence. Geochemical evidence suggests that pollutant organics from unconfined sewage and other sources drives reduction of hydrous ferric oxide (HFO) releasing sorbed As to shallow groundwater. The situation is slightly less clear for seven wells sampled which tap deeper groundwater, all of which were found with >50 μg L−1 As. Here As concentrations seem to increase with depth and differing geochemical signatures are seen, suggesting that As concentrations in older groundwater may be governed by different processes. Other data on parameters of potential concern in drinking water are discussed briefly at the end of the paper.

In Bangladesh, concentrations of boron in groundwater reach 2.1 mg L −1 and are high regionally in alluvial aquifers of Late Pleistocene/Holocene age. Concentrations exceed 0.5 mg L −1 across approximately 6700 km 2 of the deep aquifer (>150 m depth) and 3000 km 2 of the shallow aquifer ( −1 and high values are widespread in the NE of the county. These concentrations exceed the regulatory guideline values for human consumption of 0.5 mg L −1 (WHO) or 0.9 mg L −1 (USA). The boron has desorbed from mineral surfaces as freshwater flushing displaces saline waters from the aquifers. In Bangladesh, desorption is driven by decreasing ionic strength, the equilibrium re-adjustment of mineral sorption sites to the low boron concentration in freshwater, and competitive exchange with HCO 3 /CO 3 . In deep Bangladesh aquifers in Barisal District (>250 m deep), boron enrichment delineates a buried estuary marking a previous course of the Ganges and/or Brahmaputra rivers. Boron enrichment is accompanied by ion-exchange that depletes Ca and enriches Na in the flushing freshwater. The patterns of enrichment and depletion indicate the direction of water quality change, in terms of salinization or freshening, with greater sensitivity than absolute chemical parameters.

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

Secular records of the elemental and isotopic composition of belemnite calcite were studied in Pliensbachian and Toarcian sections from the Yorkshire coast, UK, and Southern Germany, to investigate oceanographic change during an interval prior to and including the Toarcian Oceanic Anoxic Event (OAE). Records from Southern Germany are correlated to the UK stratigraphy using strontium isotope stratigraphy. The geochemical trends measured from belemnite calcite are consistent between the two sections, and are interpreted in terms of temperature and salinity of the northwest European epi-continental sea. The data suggest that a dramatic environmental change coincided with the Toarcian OAE. Belemnite Mg/Ca, Sr/Ca, and Na/Ca ratios increase by a factor of between 1.7 and 2 coincident with a 3‰ negative shift in δ18O from the mid-tenuicostatum zone until the lower falciferum zone of the UK ammonite biostratigraphy (a period of ∼0.6–0.7 Myr). Taken at face value, the Mg/Ca and δ18O data argue for an abrupt warming of 6–7°C and substantial freshening during this interval. Global warming accompanied by an accelerated hydrological cycle and increased runoff is proposed to explain these changes. Prior to these events, data from lower in the Yorkshire section suggest a possible cooling accompanied by a shift to more saline waters during the period from the upper Pliensbachian margaritatus zone to the Toarcian lower tenuicostatum zone. This earlier event may also have been important in causing density stratification in the northwest European epi-continental sea.

The preparation of samples for strontium isotope stratigraphy (SIS) by whole rock dissolution results in contributions of Sr from contaminant phases as well as from the target carbonate phase. Here we highlight and quantify the errors in 87Sr/86Sr values that might result when calcium carbonate is dissolved using an inappropriate method. We report the variation in 87Sr/86Sr value of Sr released from four samples of differing calcite content and degrees of cementation, when subject to different methods of dissolution. We show that errors of up to ±0.000076 in 87Sr/86Sr, which correspond to errors of ±3.68 Ma in age, can be avoided by careful preleaching of the samples.

We profile 87Sr/86Sr, δ13C, δ18O, Sr/Ca, Mg/Ca, and Na/Ca in belemnites through Pliensbachian and Toarcian strata on the Yorkshire coast, UK, which include the early Jurassic oceanic anoxic event. The 87Sr/86Sr profile shows that the relative duration of ammonite subzones differ by a factor of up to 30: the Lower Jurassic exaratum subzone is 30 times longer than the clevelandicum subzone because the exaratum subzone in Yorkshire, which contains the anoxic event, is condensed by a factor of between 6.5 and 12.2 times, relative to adjacent strata. Using our 87Sr/86Sr profile, the resolution in correlation and dating attainable in the interval is between ±1.5 m and ±15 m of section, and better than 0.25 Myr. In parts of the sequence, this stratigraphic resolution equals that attainable with ammonites. A new age model is provided for late Pliensbachian and early Toarcian time that is based on the 87Sr/86Sr profile. Through the sequence, the Sr/Ca, Mg/Ca, Na/Ca and δ18O of belemnite carbonate covary, suggesting that elemental ratios may be useful for palaeotemperature measurement. Our δ13Cbelemnite data splits into three the previously reported positive isotope excursion (to +6.5‰) in the early Toarcian. We speculate that the excursion(s) resulted from addition to surface waters of isotopically heavy CO2 via ebullition of methanogenic CO2 from the sediment during early burial of organic rich (>10% TOC) sediments

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.

Strontium isotope profiles, derived from minimally altered samples, across marine K/T boundary sequences exposed at Kjolby Gaard and Nye Klov, Denmark, and on Seymour Island, Antarctica, show neither the boundary excursions, nor the boundary spikes, in 87Sr/86Sr that have been reported for K/T boundary sequences from elsewhere. Nor do our data conform to modelled predictions of the Sr isotopic response of the oceans to a positive spike in 87Sr/86Sr at the terminal Cretaceous. Boundary values for 87Sr/86Sr (with 95% confidence intervals) are 0.707828±3 in Denmark and 0.707832±7 in Antarctica. Our data suggest that 87Sr/86Sr stopped increasing and started decreasing at least 90 ka before the K/T boundary.

The distribution of rare earth elements (REE) within the compositionally zoned Dartmoor pluton is used to constrain models of granite evolution and to assess the effects of pervasive hydrothermal alteration on REE mobility. The main process of magma evolution was crystal fractionation of early plagioclase, biotite, and accessory minerals (apatite, monazite, zircon, and xenotime). Concentrations of REE (particularly LREE and Eu) and other elements (Fe2O3t, MgO, CaO, TiO2, Zr, Ba, and Sr) decrease strongly with evolution of the pluton from 71 to 74% SiO2. These trends, and the inward zoning of the pluton, are compatible with differentiation by crystal fractionation at the level of emplacement, a process that gave rise to a marginal cumulate granite (CGM) modified by country rock assimilation, a body of inner granite (PM), and a late-stage evolved granite (FG) that intruded the earlier types. REE modelling of the Dartmoor granite types by fractional crystallization of REE-enriched accessory minerals from a parent PM-granite shows that the FG-granite cannot have formed from a residual liquid left by crystallizati on of the CGM-granite. Two discrete stages of crystallization occurred; side-wall cumulate CGM-granite crystallization dominated by LREE-enriched monazite fractionation followed by a late-stage mobile residual FG-granite in which fractionation was dominated by HREE-enriched apatite and zircon. Modelling supports the idea that largescale assimilation of country rock was not the dominant process during Dartmoor granite evolution. Pervasive hydrothermal alteration locally affected all Dartmoor granite types, altering primary plagioclase, biotite, apatite, monazite, and, to a lesser extent, zircon and xenotime. During pervasive sericitization, chloritization, and tourmalinization, REE were mobilized over distances of centimetres only and redistributed into the secondary alteration products seridte, chlorite, tourmaline, allanite, and sphene. Whole-rock REE abundances were not affected

In two distal carbonate turbidites (labelled a and e) from the Madeira Abyssal Plain oxidation of organic matter (OM) has been accompanied by a reduction in Hydrogen Index (HI) and change in the isotopic composition of carbon. Since the emplacement of turbidite α 0.5 ka ago 35% of the OM in the upper part has been oxidised by oxygen and nitrate diffusing from sea water into the sediment. There is an accompanying decrease of ≤ 0.3‰ in δ13C-OM, and a decrease of 25% in HI. Turbidite e was emplaced about 73 ka and was exposed to bottom water for 12.3 ka before being buried beneath later turbidites. During exposure oxygen and nitrate diffused into its upper part and oxidised 50% of the TOC without an accompanying change in isotopic composition; further oxidation of the more refactory organic components decreased TOC by a further 25% and decreased δ13C by 2.5‰. Oxidation also reduced HI by 50% from originally low values. Unless corrected for, the isotopic changes accompanying extended oxic and suboxic degradation of organic matter in sediments will give rise to erroneous estimates of marine-terrestrial OM ratios.

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.

In the southeastern part of Western Australia internal drainage and a semi-arid climate have resulted in extensive development of playas. The brines beneath the playas wedge outwards and force local infiltration to crop out at playa margins as discharge zones. The discharging water contains dissolved Fe2+, oxidation and hydrolysis (ferrolysis) of which generates very acidic water (pH ≥ 2.8). At least some of the alkalinity generated by the original reduction of Fe3+ has been sequestered as subsurface calcrete within local soils. The acidity causes the dissolution of kaolinite, which is abundant in playa sediments and as a thick capping on weathered bedrock, giving water with a low pH and high concentrations of dissolved Al and Si. Evaporation, and mixing with playa brines containing high concentrations of K and SO4, causes alunite to precipitate as pH rises from a minimum of 2.8, at chlorinities of 1 to 2 M, to > 6 at chlorinities of 4.8 M. The alunite deposits formed by this process are many orders of magnitude larger than occurrences elsewhere in the world. The large-scale mobilisation of Si during this process may be one mechanism for the formation of silica-cemented rocks (silcrete) that are widespread in the Australian regolith.

Authigenic and replacement francolites in modern phosphorite have values of {sup 87}Sr/{sup 86}Sr within error of that of modern marine Sr (0.70916 {plus minus} 2). During the phosphatisation of carbonate, Sr is not inherited from the carbonate but is totally exchanged with Sr in ambient water. The {sup 87}Sr/{sup 86}Sr in shallow marine pore waters is indistinguishable from the value for modern marine Sr, so authigenic francolite, which precipitates from pore water, accurately records the isotopic ratio of contemporary marine Sr. By comparing the {sup 87}Sr/{sup 86}Sr in francolite with published curves for the isotopic evolution of Tertiary marine Sr we have dated phosphogenetic events affecting the Chatham Rise (4.90 {plus minus} 0.35 Ma), the Nambian margin (1.15 {plus minus} 0.25 Ma and 4.70 {plus minus} 0.35 Ma), and the Sechura Desert, Peru (11.8 {plus minus} 0.5 Ma).

The concentrations of the major substitutents Na, Sr, CO 3 and SO 4 in the carbonate—fluorapatite phase of marine sedimentary phosphorites show large systematic variations between, and within, deposits now on land, whilst variations are minimal between, and within, present sea-floor deposits. These variations reflect the influence of weathering and suggest that all marine carbonate—fluorapatite originally has approximately the same chemical composition.

Phosphatic crusts and nodules recovered from the continental margin off Peru did not precipitate authigenically from anoxic pore water but were formed in post-Palaeogene times by phosphatisation of quartzitic and feldspathic carbonate-bearing sediments. The late Quaternary uranium-series and amino acid dates obtained for these phosphatic rocks are probably the result of secondary enrichment of organic matter and uranium and probably do not represent the times of phosphate mineralisation.

Uranium-series dating of phosphorites from the continental margin of South Africa shows that phosphogenesis has occurred during at least four periods — around 63, 83 and 250–800 ka, and between 800 ka and the middle Eocene. Petrographic study shows that five distinct apatite microfabrics can be recognised in our samples and confirms that several episodes of phosphatisation have occurred. Isotopic data for carbon and sulphur show that the phosphogenesis took place in oxic or post-oxic sediments and so was probably unrelated to enhanced coastal upwelling. The chemical composition of the francolite that formed between 91 and 62 ka differs from that in older samples. These differences possibly record variations in the composition of sea water during the late Tertiary.

Internal drainage in the south east of Western Australia are underlain by predominantly granitoid rocks. The regional shallow ground water are NaCl brines. Ratios of 87Sr/86Sr in the brines are 0.7155 ± 0.0015, which are close to the ratio of modern marine Sr (0.7092). A two-component isotopic mixing model, with end members of marine Sr and Sr from basement granitoid rocks, implies strongly that ⩽5% of the Sr is derived from rock weathering and ⩾95% is marine. The isotropic composition of S in gypsum crystallised from the brines is +19.8 ± 0.3ℵ CDT). This value is close to that of S in Recent evaporites (+21.5 ± 1CDT) and confirms that weathering of Archaean sulphides, with Δ34Sof0 ± 4ℵ (CDT), has contributed insignificant amounts of S to the brines. The isotopic data are compatible with a late Tertiary to Recent age for the Sr and S and, by implication, for the salts as a whole. The formation of alunite has been a major control on brine composition while gypsum and calcrete formation have been minor influences. None of the ground waters is saturated with halite which suggests the brines are immature and have evolved their present chemistry within the past few tens of thousands rather than millions of years. Marine aerosols are the main source of salt. Water sequestered in internal drainage basins, by a post-Middle Miocene regression, possibly provided a subordinate fraction.

Carbon isotope data are given for organic matter, calcite, and pore water in carbonate turbidites from the Madeira Abyssal Plain. The carbon isotope composition of dissolved inorganic carbon (DIC) in pore water is between 0.3 and 1%. heavier than modelled values. The δ13C of DIC added to the system is −5.5 to −6.9%., whereas the predicted value is −9.0%.. This difference does not result from isotopic fractionation of organic matter or calcite. During diagenesis, 31% of the organic matter is oxidized. The isotopic composition is −19.4 ± 0.1%. before and after oxidation. Depressurization artefacts affecting DIC occur at the sediment-water interface and at a lithologic discontinuity within the sediment.

Stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits. Values ofδ13C andδ34S in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions. The exceptions are concretionary francolite from Namibia, which has an isotopic composition in keeping with its formation within organic-rich sediments, and that from offshore Morocco, which has an isotopic signature of the anoxic/suboxic interface. Onshore deposits from Jordan, Mexico, South Africa and, possibly, the Permian Phosphoria Formation in the western U.S.A., are substantially depleted in18O: they appear to be too altered for deductions to be made about their environments of formation. In other onshore deposits which are unaltered, or minimally altered, the isotopic composition suggests that some formed within sulphate-reducing sediments (Sedhura, Morocco) whilst francolite from the Georgina Basin of Australia formed at the oxic/anoxic boundary, where oxidation of biogenic H2S decreases theδ34S of pore water. In general, pelletal samples show non-oxic isotopic signatures, whilst non-pelletal samples show oxic isotopic signatures, but samples from Namibia, Peru (Ica Plateau) and the Californian and Moroccan margins are exceptions to this rule. Morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature.

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.

The abundance of rare-earth elements (REE's) in francolite increases with increasing age as a result of post-depositional enrichment. Abundances are higher in pelletal samples than in non-pelletal ones because the higher surface/mass ratio of pelletal francolite promotes enrichment during diagenesis. Onshore francolite has higher REE abundances than that found offshore. Distribution patterns in francolite may be similar to those reported for open-ocean water or shale, depending upon the dominant source of the REE's: different patterns result from weathering and deep-burial diagenetic modification of the original patterns and abundances. Negative Ce anomalies occur in francolites containing structural sulphur that is isotopically indistinguishable from seawater of the same age; zero or positive anomalies occur in francolites which contain sulphur that is isotopically lighter than seawater.

Francolite in unaltered Tertiary phosphorites is highly substituted with about 1.2% Na, 0.25% Sr, 0.36% Mg and 2.7% SO4 within the structure in substitution for Ca and PO4. These substitutions reflect the composition of the solution from which francolite forms and are not influenced by the mechanism, rate or redox conditions of formation. The remarkably constant composition for a wide range of samples reflects the relative constant composition of sea water, during Tertiary times. Francolite in sulphate-reducing sediments forms in an uppermost zone where bioturbation maintains the concentrations of Na, Sr, Mg and SO4 at sea water concentrations. The structura-CO2 content of unaltered francolites vary from 1.4% to 6.3%, in response to variations in pH. The maximum level of carbonate substitution is limited by the disruption of the francolite structure at levels above 6.3% CO2. For the samples considered here F/P2O5 ratios vary with X-ray CO2 contents showing that PO43− is replaced by (CO32− + F−) and not by CO32− alone. In Phosphoria Formation francolite the Na/P2O5 ratios and X-ray CO2 contents show areal trends related to burial depth and thermal metamorphism. These two processes together with weathering and fresh water diageneses explain all observed variation in francolite composition.