Search

At Peniche, Portugal, the GSSP for the base of the Toarcian and in a Submediterranean province, a value of 0.707 073 ± 0.000 002 (2s.e., n = 13) is determined for 87Sr/86Sr at the base of the Toarcian. In Yorkshire, UK, a Subboreal province, the base of the Toarcian has an 87Sr/86Sr value of0.707 072 ± 0.000 002 (2s.e., n = 23). The similarity of the values shows that, within analytical uncertainty, these levels are exactly equivalent in time. At Peniche, the base of the Serpentinum (Falciferum/Levisoni) Chronozone has an 87Sr/86Sr value of 0.707 096 ± 0.000 003 (2.s.e). The value for this boundary in Yorkshire is 0.707 094 ± 0.000 002 (2s.e., n = 27). The similarity of the values shows that, within analytical uncertainty, these levels are exactly equivalent in time. The same ammonite successions occur through the lowermost Toarcian successions at Peniche and in Yorkshire. Between Peniche and Yorkshire, there is therefore an exact coincidence, within measurement uncertainty, between the Lower Toarcian, Tethyan Realm, Tenuicostatum (Polymorphum) [ammonite] Chronozone of Peniche and the Lower Toarcian, Boreal Realm, Tenuicostatum [ammonite] Chronozone of Yorkshire. The 87Sr/86Sr profile through the Tenuicostatum Subchronozone at Peniche reveals large variations in sedimentation rate, with lowest rates in a condensed basal 3 m of the zone, highest rates in mid-zone, with rates decreasing upward through the upper half of the zone. Apportioning time in proportion to 87Sr/86Sr shows that around half of Tenuicostatum time is condensed into the basal 3 m of the section.

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.

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

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.

The ages of carbonate rocks can be determined by comparing their 87Sr/86Sr ratios with the well-established seawater 87Sr/86Sr curve. Current models and databases provide no explicit solution to the problem of accurately assigning uncertainties to derived ages when the 87Sr/86Sr ratios of carbonate rocks contain analytical uncertainties. This is particularly concerning as significant amount of 87Sr/86Sr ratios are being measured by multi-collector inductively-coupled-plasma mass-spectrometry (MC-ICP-MS) which typically has a lower precision (1σ is typically several tens of ppm) compared with thermo-ionization mass-spectrometry (TIMs, 1σ can be as low as several ppm) used for calibrating the seawater 87Sr/86Sr curve. Deriving ages from carbonate 87Sr/86Sr ratios with large analytical uncertainties could introduce significant, sometimes asymmetric uncertainties in age estimates following a non-Gaussian distribution. More importantly, uncertainties in age estimates around the local maximum/minimum and saddle points on the Phanerozoic seawater 87Sr/86Sr curve are difficult to examine using conventional methods. In this study, we developed a rigorous mathematical framework (including perturbation and probability density methods) to estimate the 95% confidence interval (or any confidence interval of interest) of the derived age with any given analytical uncertainty. We applied this method to estimating uncertainties in derived ages for one version of the Phanerozoic seawater 87Sr/86Sr curve, assessing their sources and amplitudes. Our results indicates this method has the potential to be widely applied to estimating the uncertainties in ages derived from inversions using an empirical relationship. A Matlab program is presented that can calculate the age of carbonate rocks (based on their 87Sr/86Sr ratios and analytical uncertainties), the duration of intervals between ages, and the confidence interval of choice over the last 509 Ma (Version1 is available from zwang1@ccny.cuny.edu upon request).

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.

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.

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

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.

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.

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.

From 2002 to 2010 inclusive we monitored concentrations of arsenic (As) and major ions (Ca, Mg, Sr, Na, K, Fe, Mn, Cl, and SO(4)) in groundwater from 14 domestic wells and three piezometer nests in a shallow aquifer (60 m depth), and 3 wells in a deep aquifer (70 m depth), in southern West Bengal, India. In the deep aquifer, concentrations of As did not change over time despite increases in the concentration of Fe in two wells. The shallow aquifer occurs in two sedimentological settings: palaeo-channel and palaeo-interfluve. At the top of the shallow aquifer of the palaeo-channel, decreases in all constituent concentrations with time, and an (3)H/(3)He age of 1.4 years, proves that the aquifer is beginning to be flushed of pollutants. In As-polluted groundwater (50 microg/L As) tapped from deeper grey sands of the shallow, palaeo-channel, aquifer, concentrations of As were mostly stable over time, but both increases and decreases occurred with time in response to downward migration of the chemically-stratified water column. In groundwater tapped from Pleistocene brown sands, the concentration of As remained either low and stable (2 microg/L As), or increased at rates up to 34 microg/L per year. The increases were caused by the flow of As-rich groundwater either downward into brown sand at the base of palaeo-channels, or laterally into a confined, unpolluted, palaeo-interfluvial, aquifer of brown sand that lies regionally beneath a palaeosol. Under the present pumping regime, the prognosis for As-pollution in the shallow aquifer is complex. Wells in brown sand may become polluted over timescales of as little as 2 years, whilst some wells tapping As-polluted groundwater from grey sand will become fit for potable use (50 microg/L) within a few decades. The evidence of flushing, and of declining As in some of the groundwater from palaeo-channels, which are conduits for recharge of the confined, As-free, palaeo-interfluve aquifer, and probably also the deeper aquifer, offers hopes that the spread of As-pollution will be limited.

Eight samples of brachiopod shell material have been analyzed for their strontium isotope composition in order to more accurately date Lower to Upper Permian siliceous biogenic strata of Spitsbergen (Kapp Starostin Formation) and the southern Barents Sea (Roye Formation). The results are interpreted as showing a mid-Artinskian age for the basal Voringen Member of the Kapp Starostin Formation and a range of late Artinskian to Roadian for the overlying part of this unit. The upper part of the Roye Formation yields ages in the range Roadian to Wuchiapingian. These results are consistent with available biostratigraphic data and confirm the potential of strontium isotope stratigraphy for developing a more accurate chronology of the widespread spiculite deposits that characterize the northern margin of Pangea in late-Early Permian to Late Permian time and which constitute a potential target for petroleum exploration.

Detailed sedimentological and microtextural analyses of newly-discovered late Neogene diamictites and other coarse-grained facies, mostly sandwiched between hyaloclastite of the James Ross Island Volcanic Group and Cretaceous sandstone and mudstone, indicate deposition mainly by glacigenic debris flows. The deposits on James Ross Island (northern Antarctic Peninsula) constrain the depositional setting, ice–bed dynamics and regional palaeoclimate. The sequences on James Ross Island vary in age but are mainly late Miocene and Pliocene. Unlike Neogene sedimentary sequences elsewhere in Antarctica, those on James Ross Island are unusually well-dated by a combination of 40Ar/39Ar and 87Sr/86Sr analyses on fresh interbedded lavas and pristine bivalve molluscs, respectively. The Sr isotopic ages of the debris flows cluster around 4.74, 4.89, 5.44, 5.78, and 6.31 Ma and probably date relatively warm periods in the northern Antarctic Peninsula region, when the bivalves lived under ice-poor or seasonally ice-free conditions. The bivalves are often remarkably well-preserved, lack adhering lithified sediment and, in at least two locations, are large, mainly unfragmented and sometimes articulated, suggesting that they were alive immediately prior to their incorporation in subaqueous debris flows at the margins of an advancing glacier. These fossiliferous glacigenic debris flows signify episodes of ice expansion during relatively warm periods, or “interglacials”, of the late Miocene and Pliocene. The James Ross Island glacigenic sedimentary successions attain thicknesses of up to 150 m and extend over 4 km laterally. The high volume of glacigenic sediment delivery implicit in the James Ross Island successions indicates that a series of dynamic ice fronts crossed the region during the late Miocene and Pliocene epochs. Associated evidence, in the form of clast abrasion (including striations and faceting) and bedrock erosion, is indicative of basal sliding and subglacial sediment deformation active at the ice–bed interface and wet-based temperate or polythermal regimes, prior to remobilisation. The evidence further suggests two local ice caps on James Ross Island during the warm periods, as well as ice-overriding by the Antarctic Peninsula Ice Sheet from the west and northwest.

We test the hypothesis that the noise in belemnite records through time results from changing climate. We do so by comparing palaeo-proxies (Mg/Ca, Sr/Ca, Na/Ca, δ18O, δ13C) in two species of Toarcian belemnites, Acrocoelites (Odontobelus) vulgaris (14 specimens) and Acrocoelites (Acrocoelites) subtenuis (10 specimens), deposited in a period of time that was short relative to the timescale of climate change. The specimens are interpreted to have been regurgitated from the stomach of a marine predator and so were deposited together in a geological instant of Early Jurassic time. In A. (O.) vulgaris, isotopic and elemental palaeo-proxies group tightly, suggesting that this belemnite occupied a restricted environmental niche. In A. (A.) subtenuis, elemental and isotopic compositions spread more widely, suggesting that this species occupied a greater range of habitats. Possible sexual dimorphism in A. (O.) vulgaris is reflected in bimodal Mg/Ca and differing intra-rostral distribution of Mg in putative dimorphs; concentrations decline by 30% from apical line to rim in specimens with high Mg/Ca, but are largely invariant radially in specimens with lower Mg/Ca. Sexual dimorphism in A. (A.) subtenuis yields a bimodality in size, Mg/Ca, and intra-rostral distribution of Mg; larger specimens have a higher Mg/Ca, and Mg concentrations that increase along radial traverses from apical line to rim, whilst the smaller specimens show a mid-rostral minimum in Mg concentration. Radial profiles of concentrations for Sr and Na vary little in all forms. Toarcian belemnites of these species thus show strong biofractionation effects on Mg/Ca, and little or no observable biofractionation of Sr/Ca or Na/Ca. It follows that much of the noise in belemnite records results from biofractionation, and from a cosmopolitan life-style of some belemnite species, rather than climate-change. For Toarcian belemnites, we suggest that Sr/Ca is the best indicator of palaeo-temperature.

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

The Asmari Formation has been studied in the subsurface at the Bibi Hakimeh, Marun and Ahwaz oilfields and in an outcrop section from the Khaviz anticline. It consists of approximately 400 m of cyclic platform limestones and dolostones with subordinate intervals of sandstone and shale. The method of Sr-isotope stratigraphy is well suited for dating these strata because of the rapid rate of change of marine Sr-87/Sr-86 during Asmari deposition (roughly 32-18 Ma) and the common presence of well-preserved macrofossils.Profiles of age against depth in the four areas show a decrease from higher stratigraphic accumulation rates in the lower Asmari to lower rates in the middle to upper part of the formation. There is also a trend towards less open-marine depositional conditions and increasing early dolomitization and anhydrite abundance above the lower part of the formation. These changes reflect the dynamics of platform progradation across the areas studied, from early deposition along relatively high accommodation margin to slope settings to later conditions of lower accommodation on the shelf top.Ages of sequence boundaries are estimated from the age-depth profiles at each locality, providing a framework for stratigraphic correlation. Asmari deposition began in early Rupelian time (34-33 Ma) in the Bibi Hakimeh area, when the studied areas to the NW were accumulating basinal marl facies. Progradation of the platform across the Marun and Ahwaz areas took place in mid-Chattian time (27-26 Ma) and somewhat later (26-25 Ma) in the more basinward Khaviz area. Depositional sequences have durations of 1-3 Ma, whereas component cycles represent average time intervals of 100-300 Ky.Sr analyses of most dolomite, anhydrite and celestite samples plot close to or below the macrofossil age-depth trend for each locality, indicating formation from waters preserving seawater Sr-87/Sr-86 approximately contemporaneous with or slightly younger than the time of sediment deposition. Local deviations from this trend are interpreted as indicating episodes of seepage-reflux and also a contribution of Sr from non-marine sources during formation of the Gachsaran cap rock anhydrite.

New outcrops of Late Neogene sedimentary deposits discovered on James Ross and Vega islands, northern Antarctic Peninsula, are fossiliferous and contain mainly fragmented pectinids amongst other as yet unstudied biota. The sedimentary deposits are interbedded with fresh volcanic units, thus providing the unusual opportunity to investigate the ages of the sedimentary rocks using two independent isotopic systems (40Ar/39Ar and 87Sr/86Sr). The fossils record past periods of warmer conditions (interglacials) like today. However, our results demonstrate unequivocally that some of the macrofossils present in the sedimentary rocks are reworked and the host sediments are, in these cases, much younger than the ages of their included fossils would suggest. Nevertheless, the Sr ages date these records of interglacial events in the region independently of the age of the strata in which they occur. Conversely, the volcanic rocks show abundant field evidences that they are coeval with the underlying sedimentary deposits, and hence their Ar ages reliably date the timing of their deposition. Our results indicate that at least three generally warmer periods are represented in the James Ross Island region: at 6.5–5.9, 5.03–4.22 and< 0.88 Ma, although our data do not have the resolution for identifying Milankovitch-scale cyclicity. However, the Early Pliocene warm period is particularly well represented and the James Ross Island data may well be capturing a higher proportion of the longer-lasting interglacials that characterised that period. We also present evidence for an interglacial in the Late Pliocene (at 2.54 + 0.86/− 0.36 Ma). Our data suggest that both Antarctic Peninsula and the East Antarctic ice sheets responded in a similar way to long-term regional shifts in climate, but the Antarctic Peninsula is more sensitive to short-term warming, as occurs today.

Strontium-isotope stratigraphy has been used to examine the timing of depositional events and dolomitization in two Miocene carbonate platforms cored by Ocean Drilling Program (ODP) Leg 194, just seaward of the Great Barrier Reef. The results provide firm constraints for correlating surfaces and depositional stages between the two platforms and thereby relating seismic sequences previously defined in the off-platform sediments to the lithostratigraphic units described from cores in the seismically transparent platform-top sites. Oyster-bearing beds at the base of both platform successions yield early Oligocene ages (29–31 Ma), thus dating initial transgression of the Marion Plateau's volcanic basement. There followed a period of slow accumulation of shallow-water grainstones rich in quartz and phosphate grains in late Oligocene time (29–23 Ma; seismic Megasequence A). The main growth of the carbonate platforms took place in early to late Miocene time (23–7 Ma), comprising five depositional sequences. The first four of these (seismic Megasequence B) are common to both platforms and terminated with a possible karst surface at 10.7 Ma. Different sedimentologic expression of this megasequence in the two platforms reflects contrasting progradational versus aggradational geometries in the locations studied. The final growth stage (seismic Megasequence C) occurred only in the southern platform and terminated at 6.9 Ma. Both platform-demise events (10.7 and 6.9 Ma) approximately coincide with falls in global sea level combined with longer-term trends of decreasing water temperature. Sr-isotope ages of dolostones increase with depositional age, and older dolostones in the southern platform have more coarsely crystalline and fabric-destructive textures than overlying younger dolostones. These relationships are consistent with dolomitization by normal seawater shortly after deposition and overprinting of multiple times of dolomite recrystallization and cementation in the deeper strata.

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

We present new data on 87Sr/86Sr, δ13C and δ18O, and elemental compositions of belemnites from 85 m of Valanginian, Hauterivian and Barremian strata at Speeton, Yorkshire, eastern England. The 87Sr/86Sr data provide a global standard for 87Sr/86Sr isotopic dating, and correlation to the biostratigraphic schemes of NW Europe. Values of 87Sr/86Sr increase from 0.707380±0.000003, at the base of the Hauterivian, to 0.707493±0.000004 in the earliest Late Barremian Paracrioceras elegans ammonite Zone before decreasing thereafter towards an Aptian minimum. The downturn in the elegans Zone coincided with the onset of volcanism on the present Ontong Java Plateau. A linear interpretation of the 87Sr/86Sr profile shows that the relative durations of ammonite zones differ by a factor ≤18. The basal Hauterivian unconformably overlies Valanginian strata; the discontinuity in 87Sr/86Sr across this surface represents a gap in sedimentation of 2.0 myr. In our belemnites (mostly of the genera Hibolites, Acroteuthis, and Aulacoteuthis) the absence of a correlation between δ18O and δ13C suggests that strong non-equilibrium fractionation has not affected the isotopic composition of the calcite. Our δ18O values therefore approximate to a valid record of marine palaeo-temperatures. Specimens of the genus Hibolites have δ18O values that are 0.4‰ more positive than those of co-occurring specimens of the genus Acroteuthis. This offset may be explained as resulting from small (0.4‰) departures from equilibrium during precipitation of calcite, different depth habitats, or changing temperature in the Speeton sea in the time that elapsed between deposition of our individual belemnites. The averaged belemnite record of δ18O through the section shows that seawater warmed from around 11°C at the base of the Hauterivian to a maximum around 15°C in the middle of the Hauterivian regale Zone, and returned to a cooler temperature of around 11°C by the middle of the overlying inversum Zone, a temperature that persisted to the basal Barremian. Through the Barremian, temperature increased to a peak of 20°C in the early Late Barremian elegans Zone then, in the same zone, precipitately and temporarily decreased to around 14°C at about the time of onset of volcanism on the Ontong Java Plateau, before they returned to around 16°C in the uppermost part of the section. In specimens of Aulacoteuthis and Acroteuthis, a good correlation between δ18O and the content of Na, Sr, and Mg suggests that incorporation of these trace elements in these genera is largely controlled by temperature. The dependency of concentration on temperature ranges from 7 to 20% per degree Celsius, if equilibrium fractionation of oxygen isotopic composition is assumed, so the Mg, Na and Sr content of these genera may be used as palaeo-temperature proxies. The trace element content of Hibolites shows no relation to stable oxygen isotopic composition and so does not record palaeo-temperature.

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.

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.

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 ...

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

New 87 Sr/ 86 Sr dating allows the correlation of a marker horizon within the prolific Late Cretaceous Gunnarites antarcticus faunal assemblage of the Cape Lamb Member, Snow Hill Island Formation, Vega Island, Antarctica with reference sections in Europe and the USA. This horizon is between 81.5 and 96.5 m above the base of the G antarcticus assemblage. Replicate analysis of six macrofossils from within it yielded a mean value for 87 Sr/ 86 Sr of 0.707 735 9 ± 0.000 004 3 (± 2 s.e., n =17). This ratio in turn yields a numerical age of 71.0 ± 0.2 Ma when compared to the standard 87 Sr/ s6 Sr reference curve for the latest Cretaceous, for which the Campanian-Maastrichtian boundary is placed at 71.3 ± 0.5 Ma. The value of 0.707 735 9 ± 0.000 004 3 correlates to a level in the Belemnella lanceolata belemnite Zone of the Chalk of northwestern Germany that is 2.5 ± 5 m beneath the base of the overlying B. pseudobtusa Zone (and 7.5 m above the Campanian-Maastrichtian belemnite boundary), and to an interval within the ammonite zonation of the US Western Interior that spans the early Maastrichtian Baculites baculus and B. eliasi zones, but with a most likely level within the B. eliasi Zone. An earliest Maastrichtian age is thereby determined for the Antarctic horizon, and indeed for the entire G. antarcticus assemblage. Gunnarites, sensu lato, is an important ammonite marker for the base of the Maastrichtian throughout the southern high-latitude regions, and the associated large heteromorph ammonite Diplomoceras may comprise a macrofossil link back to the Maastrichtian type sections.

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.

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...

Strontium isotope stratigraphy is used to date two interglacial-marine deposits in the Antarctic Peninsula region. On King George Island, interglacial pectinid-rich sediments in the Low Head Member of the Polonez Cove Formation give a strontium isotope stratigraphy age of 29.0+0.7−0.6 to 29.8+0.8−0.7 Ma (mid-Oligocene), which, in conjunction with previous K–Ar dating of volcanic rocks, indicates a glacial episode in the Antarctic Peninsula between middle Eocene (42.0 ±1.0 Ma) and mid-Oligocene time. In addition, an inter-glacial deposit (Pecten Conglomerate) from tectonically-elevated exposures on Cockburn Island is dated as Pliocene (3.5–5.3 Ma). Published data suggest these latter sediments were deposited under shallow marine conditions, which were warmer than those of present-day Antarctica.

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.

Review of biostratigraphical evidence from different regions shows that criteria used by workers on various marine fossil groups to define the Santonian-Campanian boundary differ considerably in relative age and position. Probably the most widely recognizable of these criteria is the extinction of the distinctive crinoid Marsupites testudinarius (North America, Europe, Asia, north Africa, Australia), which, coincides exactly with two separate definitions of the boundary - appearances of the ammonite Placenticeras bidorsatum and the belemnite Gonioteuthis granulataquadrata - and may also coincide with a third - entry of the planktic foraminiferan Globotruncana elevata. A comparison of evidence from upper Santonian and lower Campanian successions in widely separated regions allows us to place a series of important biostratigraphical markers in correct order. Defining the boundary at the extinction of M. testudinarius corresponds to a 87Sr/86Sr of 0.707479, and a small positive excursion in δ13C. The base of magnetochron 33R, generally considered to coincide with, or fall just above the base of the Campanian, is shown to lie within the upper Santonian Uintacrinus socialis Zone.

In 140 metres of Maastrichtian White Chalk (nannofossil chalk) exposed near Hemmoor, NW Germany, values of 87Sr/86Sr increase from 0.707760 in the Belemnella sumensis Zone (Lower Maastrichtian) at the base of the section (-54.5 m; referred to 0 m at a prominent marl, M900) to 0.707821 in the Belemnella baltica/danica Zone (Upper Maastrichtian) at the top of the section (+84.5 m). A plateau in 87Sr/86Sr occurs between -5m and +50m in the section, probably as a result of a very high rate of sedimentation in this interval. A belemnite and associated nannofossil chalk have similar 87Sr/86Sr values, suggesting that there has been little diagenetic alteration of the 87Sr/86Sr ratios in the chalk, which therefore preserves its original 87Sr/86Sr. Comparison of 87Sr/86Sr and nannofossil zonations for sequences at Bidart, France, and DSDP Sites reveals discordance and so possible diachronism of the basal boundaries of nannofossil Zones CC25B and CC25C.

We find that the marine 87Sr/86Sr record shows a significant periodicity of m.yr. The 87Sr/86Sr record is out of phase with a 62 (±3)-m.yr. periodicity previously reported in the record of marine animal diversity. These periodicities are close to 58 (±4)-m.yr. cycles found for the number of gap-bounded sedimentary carbonate packages of North America. We propose that these periodicities reflect the operation of a periodic “pulse of the earth” in large-scale earth processes. These may be linked to mantle or plate-tectonic events, possibly uplift, which affects the earth’s climate and oceans and, thus, the geochemistry, sedimentation, and biodiversity of the marine realm.

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

An introduction to Sr-isotope stratigraphy can be obtained from several recent reviews (Elderfield, 1986; Veizer, 1989; McArthur, 1991, 1992a). The purpose of this article is not to repeat these reviews but to give to those not expert in the field, but who may be prospective users, a summary of aspects of the method not covered elsewhere, and some examples of recent applications of the technique and the problems that affect it. Highlighting problems inevitably means highlighting the publications in which they occur; I hope the authors will forgive me for spotlighting their work. Neither is this article intended to be a review of all that has been written on the use of Sr isotopes in low-temperature geochemistry; it concentrates on their use in stratigraphy and dating, rather than how they may be used to elucidate geochemical processes. Many excellent papers are thereby excluded from consideration. Implicit in this article is the view that the successful application of strontium isotope stratigraphy requires an application of good methodology in both geochemistry and stratigraphy.

This technical note examines the results of a nonlinear, finite‐strain consolidation analysis of a clay layer subjected to underdrainage at its base. It is shown that due to the nonlinearity of the soil properties the steady‐state pore‐water pressure cannot be defined until the end of consolidation. It is further shown that the steady‐state reference pore‐water pressure at the beginning and end of consolidation are different when the clay layer is loaded by a surcharge. The use of the excess pore‐water pressure as the dependent variable in a consolidation analysis is discussed.

Neodymium, samarium, and dysprosium concentrations were determined in groundwaters along a transect of Lake Gilmore sediments from the shoreline toward the playa center with the future intention of employing the whole suite of rare earth elements (REE). Two different water bodies were identified in the groundwater/playa system based on the neodymium, samarium, and dysprosium concentrations and associated pH and salinity values. Shallow groundwaters that discharge along the playa margins had the highest concentrations of these elements and the lowest pH and salinity. A more saline entrained brine was identified toward the middle of the playa with higher pH values and the lowest observed concentrations of neodymium, samarium, and dysprosium. Groundwaters with transitional neodymium, samarium, and dysprosium values, pH, and salinity were also recorded along the transect. The data suggest that the acidic shallow groundwaters remove REE from the surrounding granitic rocks of the Yilgarn block and introduce them into the playa where they are removed from solution as the pH of the system increases. Evaporative concentration does not appear to have a significant effect on the REE concentrations in the Lake Gilmore system. Other factors such as increasing pH and scavenging of REE by iron oxyhydroxides which precipitate as pH rises appear to exert more control on REE concentrations in the groundwaters by removing them from solution.

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 (

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.

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 the Boreal Chalk of northwestern Europe the base of the Maastrichtian Stage is defined by entry of the belemnite Belemnella. In the Kronsmoor section, in northwestern Germany, which is a standard section for the European Chalk, 87Sr/86Sr at the Campanian/ Maastrichtian (C/M) boundary is 0.707723±9 (10). An isotopic correlation of this boundary to the US Western Interior, for which a highly refined cephalopod biostratigraphy exists, suggests that this boundary, as defined at Kronsmoor, occurs within the Baculites jenseni zone. This correlationagrees with the latest placement based on biostratigraphic criteria. On87Sr/86Srcriteria the boundary at Kronsmoor correlates to the English Chalk at Trunch, Norfolk, UK, at a level 3.5 m lower than its position based on biostratigraphic criteria. At Kronsmoor, 87Sr/86Sr increases in a quasi-linear manner through much of the section, suggesting that, averaged over intervals of 1 Myr, the gross sedimentation rate and temporal rate of change of 87Sr/86Sr were approximately constant through the section. For US samples, zonally-plotted values of 87Sr/86Sr define a quasi-linear trend, which suggests a moderate uniformity of zonal duration from the Baculites compressus zone (73.2±0.7 Ma, 10) to the Baculites grandis zone (70.1±0.7 Ma, 10).

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.