primary sink and source of geogenic arsenic in sedimentary aquifers in the southern choushui river alluvial fan taiwan abstract this work characterized the sink and source mobility of as in the as affected sedimentary aquifers of the southern choushui river alluvial fan central taiwan major mineral phases and chemical components were determined by xrd and x ray photoelectron spectroscopy xps the partitioning of as and fe among cores were determined by sequential extraction based on xps results the primary forms of fe were hematite goethite and magnetite sequential extraction data and the xrf analysis indicated that fe oxyhydroxides and sulfides were likely to be the major sinks of as particularly in the distal fan furthermore fe oxyhydroxides retained higher as contents than as bearing sulfides the reductive dissolution of fe oxyhydroxides which accompanied high levels of hco 3 and nh 4 concentrations was likely the principal release mechanism of as into groundwater in this area the dual roles of fe oxyhydroxides which are governed by the local redox condition act as a sink and source in the aquifer ionic replacement by po 4 3 and hco 3 along with seasonal water table fluctuation caused by monsoons and excessive pumping contributed specific parts of as in the groundwater the findings can be used to account for the inconsistency between fe and as concentrations observed in groundwater

high precision u pb geochronology and a new chronostratigraphy for the canadon asfalto basin chubut central patagonia implications for terrestrial faunal and floral evolution in jurassic abstract the fluvial lacustrine and tuffaceous sedimentary succession of the canadon asfalto continental basin exposed in the argentinean chubut province of central patagonia preserves an extraordinary record of jurassic fauna and flora that marks key events in the evolution of dinosauria early mammals and major south american plant groups however basin wide correlation of the fossiliferous units is complicated by fault displacements unconformities and repetitive lithofacies new u pb analyses of zircon ca tims method from five primary tuff beds interstratified with the lacustrine strata establish a new chronostratigraphic framework for the sedimentary and volcanic units of canadon asfalto basin constraining ca 33 m y of depositional history and biotic evolution that spans nearly all three epochs of the jurassic five major vertebrate and plant rich stratigraphic intervals have been identified and are being actively investigated that range in age from pliensbachian to kimmeridgian or younger our combined biostratigraphic and high precision geochronologic results indicate that the major faunal turnover of the sauropodomorph dinosaurs which led to the rise of the eusauropods took place in the early jurassic earlier than previously recognized similarly the first successful radiation of the ornithischian dinosaurs heterodontosaurids as well as the evolutionary diversifications of the araucarian conifers and the osmundaceous ferns all occurred before the end of the early jurassic the diverse palynofloral assemblage of the canadon calcareo formation that was once considered to be early cretaceous in age is now entirely constrained to the late jurassic

tectono sedimentary characteristics of late miocene quaternary extensional basins of the northern apennines italy abstract extensional and compressional regimes exist at the same time in adjacent parts of the northern apennines italy and the former regime succeeded the latter at the same place as the thrust mountain front moved eastward since miocene times numerous extensional basins have developed west of the present mountain divide the westernmost ones formed over attenuated continental crust since late miocene and have been subjected to several subsidence and uplift events with rates of subsidence generally faster than rates of sedimentation they contain continental deposits overlain by gypsum bearing upper miocene marine sequences and siliciclastic marine pliocene deposits these basins were affected by shallow magmatism and are still experiencing high geothermal gradient and late to post magmatic activities such as in the renowned thermal region of larderello to the east closer to the present mountain divide the extensional basins formed later from pliocene to quaternary contain continental fluvial and lacustrine deposits and have not experienced near surface magmatic activities the sedimentary fill architecture of the apennine extensional basins is similar to that of other european american and african extensional or transtensional systems for instance a common characteristic is the prevalence of large alluvial fan deposits at the hanging wall shoulder of half grabens coarser smaller alluvial fans at the footwall shoulder and some fluvial deposits introduced longitudinally unlike the african rifts though the sedimentary facies distribution of extensional basins which developed in active orogenic zones such as in the apennines may be strongly affected by uplifting steep mountain slopes and can have large thick coarse alluvial fans also on the footwall side of the half grabens

evolution of the san jorge basin argentina the san jorge basin although small is the most important hydrocarbon producing basin in argentina remaining untested potential is high because of the presence of good source rock favorable structural complexity and multiple reservoirs reservoir quality is commonly low because of the highly tuffaceous sandstones the sedimentary fill of the basin is closely related to its tectonic history northwest southeast trending grabens formed and filled during a triassic and early jurassic early rift phase climaxing with a pervasive middle jurassic volcanic episode continued growth and filling of the basin occurred during a late jurassic earliest cretaceous late rift phase and cretaceous early and late sag phases late cretaceous early tertiary extension set up many of the present day structural traps along normal faults middle tertiary andean compression produced the narrow north south san bernardo structural belt which exhibits reversed movement on older normal graben bounding faults and on local low angle thrust faults marked early to middle tertiary erosion produced a significant unconformi y within cretaceous beds around basin margins origin of upper jurassic and lowermost cretaceous sedimentary fill is primarily lacustrine or fluvial in origin lacustrine organic rich black shales are fringed by oolitic and other limestones and fluvial deltaic sandstones derived mostly from the north a significant southern source of sand existed during the valanginian interbedded marine shales occur mostly to the west toward a presumed marine seaway connection to the northern magallanes basin middle to upper cretaceous sedimentary rocks sourced mostly from the north are mainly fluvial sandstone shale successions with some minor lacustrine influence reservoir quality glauconitic sands were deposited during a late cretaceous early tertiary marine incursion from the atlantic after development of a lower tertiary regional unco formity relatively undisturbed younger tertiary sediments completed the basin fill lower cretaceous lacustrine shales of the d 129 formation are the best source rocks yet identified however most hydrocarbon production occurs above the source in middle and upper cretaceous sandstones along the basin flanks the most obvious hydrocarbon emplacement mechanism is vertical migration along reactivated graben faults

paleomagnetism of jurassic and cretaceous rocks in central patagonia a key to constrain the timing of rotations during the breakup of southwestern gondwana abstract a paleomagnetic study in jurassic and cretaceous rocks from the canadon asfalto basin central patagonia indicates the occurrence of about 25 30 clockwise rotation in upper jurassic lowermost cretaceous rocks whereas the overlying mid cretaceous rocks do not show evidence of rotation this constrains the tectonic rotation to be related to a major regional unconformity in patagonia which in turn seems to be close in time with the early opening of the south atlantic ocean the sense and probably the timing of this rotation are similar to those of other paleomagnetically detected rotations in different areas of southwestern gondwana suggesting a possible relationship between these and major tectonic processes related with fragmentation of the supercontinent on the other hand the mid cretaceous rocks in the region yield a paleopole located at lat 87 south long 159 east a95 3 8 this pole position is consistent with coeval high quality paleopoles of other plates when transferred to south american coordinates implying it is an accurate determination of the aptian circa 116 ma geomagnetic field in south america

large cretaceous sphenodontian from patagonia provides insight into lepidosaur evolution in gondwana sphenodontian reptiles successfully radiated during triassic and jurassic times but were driven almost to extinction during the cretaceous period1 the sparse early cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards their suspected ecological successors2 however recent discoveries in late cretaceous beds in patagonia partially modify this interpretation numerous skeletons of a new sphenodontian priosphenodon avelasi gen et sp nov were collected from a single locality in the cenomanian turonian candeleros formation where it is more abundant than any other tetrapod group recorded in the quarry for example crocodyliformes serpentes dinosauria and mammalia 3 4 adult specimens of priosphenodon reached one metre in length larger than any previously known terrestrial sphenodontian here we propose using available evidence that sphenodontians were not a minor component of the cretaceous terrestrial ecosystems of south america and that their ecological replacement by squamates was delayed until the early tertiary the new discovery helps to bridge the considerable gap in the fossil record around 120 million years that separates the early cretaceous sphenodontians5 6 7 from their living relatives sphenodon

the downward continuation of magsat crustal anomaly field over southeast asia a general method for the local downward continuation at ground level of geopotentials measured by low orbiting satellites at different altitudes is proposed such a continuation is the inverse solution of the external dirichlet problem the stability of the solution with respect to the altitude and the distribution of data points is discussed principal component analysis is shown to perform well and leads to a stable solution the method proposed has the advantage of being directly applicable to measured data points which are not evenly spaced and at different altitude as an illustration it is applied to magsat data over southeast asia two independent maps of the vertical component of the anomaly field at a constant altitude near ground level are derived for dawn descending orbits and dusk ascending orbits data separately the two maps reveal similar anomalies and confirm the correlation of the magsat derived anomaly field with the mosaic structure of the continental crust in southeast asia stable continental blocks are associated with positive anomalies and intervening collision belts correspond to well defined negative anomalies a very prominent low is observed above the himalaya and extends over the tibet plateau confirming an anomalous crustal and thermal structure of the plateau

tectonic evolution of the north patagonian andes 41 44 s through recognition of syntectonic strata abstract the north patagonian fold thrust belt 41 44 s is characterized by a low topography reduced crustal thickness and a broad lateral development determined by a broken foreland system in the retroarc zone this particular structural system has not been fully addressed in terms of the age and mechanisms that built this orogenic segment here new field and seismic evidence of syntectonic strata constrain the timing of the main deformational stages evaluating the prevailing crustal regime for the different mountain domains through time growth strata and progressive unconformities controlled by extensional or compressive structures were recognized in volcanic and sedimentary rocks from the cordilleran to the extra andean domain these data were used to construct a balanced cross section whose deep structure was investigated through a thermomechanical model that characterizes the upper plate rheology our results indicate two main compressive stages interrupted by an extensional relaxation period the first contractional stage in the mid cretaceous inverted jurassic lower cretaceous half graben systems reactivating the western canadon asfalto rift border 500 km away from the trench at a time of arc foreland expansion for this stage available thermochronological data reveal forearc cooling episodes and global tectonic reconstructions indicate mid ocean ridge collisions against the western edge of an upper plate with rapid trenchward displacement widespread synextensional volcanism is recognized throughout the paleogene during plate reorganization retroarc paleocene eocene flare up activity is interpreted as product of a slab rollback and fore to retroarc oligocene slab asthenospheric derived products as an expression of enhanced extension the second stage of mountain growth occurred in miocene time associated with nazca plate subduction reaching nearly the same amplitude than the first compressive stage extensional weakening of the upper plate predating the described contractional stages appears as a necessary condition for abnormal lateral propagation of deformation

the sauropod diversity of the la amarga formation barremian neuquen argentina abstract a study of the abundant and undescribed isolated and associated bones and teeth from the la amarga formation barremian of neuquen argentina permitted the recognition of additional clades of sauropod dinosaurs basal titanosauriforms both basal and derived titanosaurs and rebbachisauroid diplodocoids which are now added to the already known dicraeosaurids and a recently published basal diplodocoid these forms substantially increase the knowledge on the early cretaceous sauropod diversity in gondwana

on utility of space borne vector magnetic measurements in crustal studies abstract the magsat data over india and contiguous regions for quiet periods kp 3 have been analysed to isolate components of crustal origin the main field contribution was removed with mgst 4 81 13th degree and order spherical harmonic expansion the external current contributions were estimated using the h and z components directly and assuming the potential to have p1 cos dependence a quadratic polynomial for each satellite pass had to be removed to make residuals from adjacent passes agree with each other these residuals over 2 2 blocks were averaged to prepare the anomaly maps the anomaly maps exhibit better resolution than langel et al features associated with the indian ocean geoid low clearly appear in the results a test on internal consistency of reduction techniques was made by synthesizing b map through the projection of three vector maps and comparing the same with the map obtained from direct measurements it is noticed that near the dip equator the features of z map are not reflected in the b map we conclude that in those regions where the main field direction is such that one or two of its components x y or z become zero or very small the crustal anomaly in that direction will not influence the b anomaly for it would have no projection in the direction of the main field

initial scalar magnetic anomaly map from magsat a scalar magnetic anomaly map between 50 geographic latitude was derived from magsat data acquired during the november 1979 to june 1980 mission lifetime separation of anomaly fields from core and external fields was accomplished utilizing techniques developed for pogo data mayhew 1979 langel et al 1980 comparison with a similar map from pogo data shows that the basic anomaly patterns are essentially reproducible except in a few regions such as the atlantic and pacific at latitudes south of 15 increased resolution due to a lower measurement altitude is evident in the magsat map

application of ridge regression in inversion of low latitude magnetic anomalies derived from space measurements abstract anomalies in total field horizontal and vertical components over the indian region derived from magsat measurements have been inverted through the ridge regression method basically to test 1 the application of the method in deriving a stable estimate of crustal magnetisation and 2 the relative amount of information on crustal magnetisation contained in scalar vis a vis vector data results show that the instabilities in magnetisation solution that appear when mayhew s conventional method is applied in low latitudes could be removed through the ridge regression technique it was also noticed that magnetisation distribution estimated through the inversion of the total field b does not relate well with the geological features in the equatorial region inversion of thez anomaly alone gives realistic results for the equatorial region but not over higher latitudes we conclude that a joint inversion ofx andz anomalies provides a magnetisation estimate consistent with known geological features both for equatorial and higher latitudes

why no anomaly is visible over most of the continent ocean boundary in the global crustal magnetic field abstract it is generally believed that an anomaly should be expected over the continent ocean c o boundary in the global magnetic anomaly maps however such maps prepared at satellite altitude do not show an anomaly over most of the c o boundary we address this issue by a forward modelling technique we use a geographic information system gis technique to integrate information of the various geological units of continents and oceans the seismic crustal structure and standard susceptibility values of the rock types and compute a global vertically integrated susceptibility vis model in addition a remanent magnetisation model is used for the oceanic crust combining the induced and remanent magnetisation models the crustal field anomaly is predicted at a satellite altitude of 400 km for spherical harmonic degrees 16 80 the results show that an anomaly is indeed not predicted over the c o boundaries where the oceanic crust is flanked by continental regions phanerozoic in age we demonstrate that largely a c o anomaly over these regions is not even expected in the global magnetic anomaly map for degrees 1 80 confirming that it is not a long wavelength feature masked by the core field an anomaly however is predicted over some parts of the c o boundary where the flanking geological provinces over the continents are precambrian in age we argue that the vis values for the continents and oceans are largely comparable and therefore no anomaly is expected over most of the c o boundary

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

copper production at baratti populonia southern tuscany in the early etruscan period 9th 8th centuries bc abstract populonia is commonly regarded as one of the most important iron working centres in europe in the 1st millennium bc however multiple layers of copper slags have been recently discovered at the bottom of the slag deposit occurring along the shoreline of the underlying baratti gulf copper slag layers have been radiocarbon dated to the 9th 8th centuries bc i e to an early metallurgical stage predating the later large scale iron production the overall features of copper slags indicate a single step smelting process of copper rich ores containing variable amounts of zn and pb chemical and textural features of copper slags indicate an optimised high efficiency metallurgical process

impact of ancient metal smelting on arsenic pollution in the pecora river valley southern tuscany italy abstract a significant as anomaly has been reported in the literature for stream sediments and unlithified quaternary deposits of the pecora river valley in southern tuscany extending from the colline metallifere pyrite base metals district to the tyrrhenian sea the as anomaly spreads over several square kilometers around a core that exceeds 500 ppm several source contributions from natural to anthropogenic have been invoked to explain the observed as distribution in the pecora valley including the metal working industry which was active in this area particularly in etrusco roman times and in the middle ages in order to evaluate the contribution of ancient mining and metallurgical activities in the pecora valley to elevated as concentrations in the environment a detailed mineralogical and geochemical survey of metallurgical slags and smelted ore minerals was undertaken from six different sites through the pecora valley poggio butelli etrusco roman iron slags sata creek arialla marsiliana forra and cascata sites all medieval base metals slags the as content of etrusco roman slags is relatively low few tens of ppm whereas medieval slags show variable but higher amounts of base metals ag ranging from tens to tens of thousands ppm and as up to 267 ppm with average contents of about 40 ppm arsenic is mostly partitioned in sulfides disseminated through the glassy groundmass rather than in solid solution with the glassy matrix remnants of the ore used for base metal and ag smelting during the middle ages had the highest as contents up to about 1000 ppm the overall as concentration in the slags independent of age and type is generally lower than that found in stream sediments and quaternary alluvial deposit outcrops of the upper pecora valley textural observations indicate that exogenous alteration of slags is minor and mostly confined to superficial exposures of matte droplets or along fractures metal particles embedded within the glassy groundmass even those located a few micrometres from the surface appear to be unaltered it is suggested therefore that as and contaminant metal contributions to the pecora valley by archaeometallurgical slags was minor at least for slags from the last 2500 to 700 a bp similarly based on gross mass balance calculations airborne release of as due to smelting roasting operations in the past cannot account for the observed extent of the as anomaly in stream sediments and quaternary deposits although residues of unsmelted or partially smelted fe cu pb zn charges or fluxes for base metal metallurgy contain much greater amounts of as than smelting slags their relatively low abundance would limit the overall input of as into the pecora river valley on the other hand concurrent research seems to indicate a major geogenic contribution to the as anomaly in the pecora valley

extension and compression in the northern apennines italy hinterland evidence from the late miocene pliocene siena radicofani basin and relations with basement structures 1 the northern apennines na hinterland area is characterized by a complex neogene quaternary tectonics where both crustal extension associated with the tyrrhenian basin opening and crustal shortening in the onshore area took part in the deformation analysis of synorogenic deposits preserved in the nnw trending siena radicofani basin srb extending along a large part of the na hinterland documents the evolution of deformation of this sector during the last 9 ma information from subsurface geology deep seismic lines commercial seismic lines and deep wells surface geology mapping and structural analysis and from analogue modeling was integrated and used to infer the tectono sedimentary history of the srb and its relation with structures in the substratum as well as the possible implications for the evolution of the na hinterland the results we obtain indicate that the srb and the adjoining hinterland basins were bounded by thrust anticlines controlling basin development and deformation seismic lines across the srb display various examples of compressional structures affecting the basin fill and the substratum such as thrust anticlines and reverse faults notably these basin scale structures exhibit a good correlation with those observed in the field and are consistent with the kinematics of the outcrop scale compressional structures the thrust anticlines bounding the basins are often cored by triassic evaporites burano formation suggesting that this weak layer decoupling the sedimentary cover from the underlying crystalline basement controlled their evolution in this circumstance three series of scaled brittle ductile physical models have been used to investigate the development of a basement cover system with a decollement ductile layer at the base of the sedimentary cover these models simulate the evolution of the northern apennines hinterland where the basement is involved in the thrusting and the sedimentary cover is shortened above a basal ductile layer given by the burano formation longitudinal models cross sections display similar deformation patterns to those observed in the na hinterland such as characteristic wavelength of both basement and cover structures as well as detachment and fault propagation folding in the cover extensional tectonics is instead found to control sedimentation in the southern part of the srb at 8 ma or representing recent deformation the older extensional event is here related to the forelandward propagation of tyrrhenian related extension that could reactivate suitably oriented basement thrusts transfer zones produced a differential propagation of extension such that along strike sectors of the hinterland were eventually deformed by different stress fields analysis of the srb and of other adjoining basins reveals that the na hinterland experienced alternated periods of forward and backward migration of the compression extension transition in our interpretation the competition between extension and compression in the hinterland is related to the nnw directed africa pelagian indentation responsible for the lateral extrusion of the na and the contemporaneous opening of the tyrrhenian basin in the inner zone increased marginal loading at the foreland promoting reactivation of hinterland thrusts may have influenced this process as well

induced magnetization of the oceanic lithosphere and ocean continent magnetization contrast inferred from magsat anomalies a petromagnetic forward model of induced magnetization of iceland plateau is presented magnetic susceptibilities of icelandic rocks from the literature are placed in a vertical stratigraphic context according to a model of igneous and metamorphic layering of the icelandic crust that is compatible with seismic and other geophysical data curie isotherm depths for the magnetic forward model are based on the geothermal gradients measured in drill holes and those derived from magnetotelluric surveys the petromagnetic model is used to predict the satellite altitude 400 km magnetic field of iceland plateau comparison of calculated and magsat anomalies shows that the total induced magnetization the vertically integrated induced magnetization in the surrounding oceanic lithosphere is 2300 a this value is very similar to independent estimates based on rock magnetic models of the oceanic crust rockall plateau is a precambrian microcontinent largely surrounded by oceanic crust a few hundred kilometers south and east of iceland the size age and location of this plateau are ideally suited to characterize the ocean continent magnetization contrast the total induced magnetization contrast between the plateau and its surroundings estimated from the magsat anomaly of rockall plateau is 14 000 a

high precision u pb zircon geochronology of the late triassic chinle formation petrified forest national park arizona usa temporal constraints on the early evolution of dinosaurs the triassic successions of the colorado plateau preserve an important record of vertebrate evolution and climate change but correlations to a global triassic framework are hampered by a lack of geochronological control tuffaceous sandstones and siltstones were collected from the upper triassic chinle formation exposed in the petrified forest national park arizona usa within a refined stratigraphic context of 31 detailed measured sections u pb analyses by the isotope dilution thermal ionization mass spectrometry id tims method constrain maximum depositional ages for nine tuffaceous beds and provide new insights into the depositional history of the chinle fluvial system the base of the blue mesa member of the chinle formation is placed at ca 225 ma and the top of the petrified forest member is placed at 208 ma or younger bracketing an 280 m thick section that spans nearly the entire norian stage of the late triassic estimated sediment accumulation rates throughout the section reflect extensive hiatuses and or sediment removal by channel erosion the new geochronology for the chinle formation underscores the potential pitfalls of correlation of fluvial units based solely on lithostratigraphic criteria a mid norian age ca 219 213 ma for the distinctive sonsela conglomeratic sandstone bed constrains the adamanian revueltian land vertebrate faunachron boundary our new data permit a significant time overlap between the lower chinle sequence and the dinosauromorph rich ischigualasto formation of northwestern argentina near contemporaneity of the trans american deposits and their faunal similarities imply that early dinosaur evolution occurred rapidly across the americas

natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water the example of west bengal and its worldwide implications 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 50 mug l 1 of as the composition of shallow ground water varies at the 100 m scale laterally and the metre scale vertically with vertical gradients in as concentration reaching 200 mug l 1 m 1 the as is supplied by reductive dissolution of feooh and release of the sorbed as to solution the process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit in well waters thermotolerant coliforms a proxy for faecal contamination are not present in high numbers 10 cfu 100 ml in 85 of wells showing that faecally derived organic matter does not enter the aquifer does not drive reduction of feooh and so does not release as to ground water arsenic concentrations are high much greater than50 mug l 1 where reduction of feooh is complete and its entire load of sorbed as is released to solution at which point the aquifer sediments become grey in colour as feooh vanishes where reduction is incomplete the sediments are brown in colour and resorption of as to residual feooh keeps as concentrations below 10 mug l 1 in the presence of dissolved fe sorbed as released by reduction of mn oxides does not increase as in ground water because the as resorbs to feooh high concentrations of as are common in alluvial aquifers of the bengal basin arise because himalayan erosion supplies immature sediments with low surface loadings of feooh on mineral grains to a depositional environment that is rich in organic mater so that complete reduction of feooh is common c 2004 published by elsevier ltd

controls on elevated fluoride and arsenic concentrations in groundwater from the yuncheng basin china chemical analysis of groundwater and sediments was carried out to investigate causes of elevated f 1 5 6 6 mg l and as concentrations 10 27 mu g l one sample affected by local contamination with 4870 mu g l as in groundwater from the yuncheng basin northern china groundwater from 9 out of 73 wells contains both f and as concentrations above world health organisation safe drinking guidelines 1 5 mg l and 10 mu g l respectively f concentrations above safe levels are more widespread than as 27 vs 12 wells the elevated as and f concentrations represent a significant health risk as groundwater is widely used to supply agricultural and domestic water in the region high f and as concentrations occur in shallow groundwater affected by agriculture and deep groundwater with long residence times 13 ka that shows little sign of anthropogenic influence the strong positive correlation between groundwater f cl and as cl ratios r 2 0 98 and 0 77 in shallow and deep groundwater respectively indicates that these elements are mobilized and enriched by common processes positive correlations between f and as concentrations and na ca ratios r2 0 67 and 0 46 respectively indicate that groundwater major ion chemistry plays a significant role in mobilizing f and as mobilization likely occurs via de sorption of as and f anions e g haso 4 2 and f from hydrous metal oxides moderate positive correlations between ph and as and f concentrations r 2 0 36 and 0 17 respectively indicate that high ph may favour de sorption while hco 3 may act as a sorption competitor high groundwater na ca ratios likely result from cation exchange while ph and hco 3 contents are predominantly controlled by carbonate weathering reactions sediments from the area were reacted with various water solutions producing f concentrations between 0 49 and 2 7 mg l and as concentrations between 0 51 and 16 7 mu g l up to 45 more f and 35 more as were released when sediments were reacted with a na rich ca poor solution compared to a ca rich solution this is consistent with increased mobilization of f and haso 4 2 by na rich ca poor groundwater increasing f and as concentrations across a wide area caused by high levels of pumping is a potential future health concern c 2011 elsevier ltd all rights reserved

high resolution chronostratigraphy of the cerro barcino formation patagonia paleobiologic implications for the mid cretaceous dinosaur rich fauna of south america abstract the cretaceous cerro barcino formation chubut group of central patagonia argentina has yielded a remarkable fossil vertebrate fauna which form important components of the south american mid cretaceous fauna including titanosauriform sauropod dinosaurs theropod dinosaurs crocodyliforms turtles and lepidosauromorphs however a lack of robust chronostratigraphic framework for its fossil occurrences has so far hampered a full realization of their paleobiologic significance this contribution presents new stratigraphic sedimentologic and u pb isotopic age data from 11 localities throughout the patagonian somuncura canadon asfalto basin and analyzes the evolutionary characteristics of the cerro barcino fauna within the biostratigraphic context of the cretaceous of gondwana four new high precision 206pb 238u zircon dates by the ca id tims method range from 118 497 0 063 ma to 98 466 0 048 ma 2 internal errors and limits the puesto la paloma cerro castano and las plumas members of the cerro barcino formation largely to the aptian albian and cenomanian stages of the cretaceous respectively accordingly the majority of the cerro barcino vertebrates fall within a 118 110 ma time interval in the latest early cretaceous which makes them the oldest documented component of the mid cretaceous faunal assemblage of gondwana paleobiologic analyses of the latter assemblage suggests a 10 m y period of faunistic stability characterized by only minor evolutionary novelties or faunal turnovers

quaternary sediment geochemistry as a proxy for toxic element source a case study of arsenic in the pecora valley southern tuscany italy abstract the valley of the pecora river southern tuscany italy hosts a very large 25 km 2 arsenic anomaly with rock values up to 1000 mg kg its origin natural or anthropogenic is still debated a systematic study of a well developed neogene quaternary sequence in the middle pecora valley mpv reveals that each formation of the sequence has a distinctive definite range of arsenic contents specifically all but one upper messinian sands and gravels m2 formation show 4 39 mg kg as mean 20 sd 12 the overlying quaternary alluvial deposits p1 have the highest contents 142 1157 mg kg mean 647 sd 288 and the topmost calcareous tufa p2 show intermediate contents 83 243 mg kg mean 159 sd 50 except for a single silica rich sample having 420 mg kg this distribution cannot be explained by any anthropogenic practice and points to a geogenic origin of the anomaly we suggest that the arsenic anomaly of mpv is basically the result of erosion and fluvial transport processes of country rocks hosting vein mineral deposits this hypothesis is fully consistent with a recent reconstruction of the paleogeographic evolution of the pecora river catchment moreover a recent study pointed out a similar anomaly in the neighboring val di cornia thus the mpv anomaly could be just a part of a larger system an implication of this study is that mobilization of arsenic in shallow systems may be related to gravitational transport of clastic sediments causing a memory effect that may be preserved for relatively long times this process of mobilization may involve very large rock volumes resulting in regional scale anomaly

patagonian broken foreland and related synorogenic rifting the origin of the chubut group basin abstract the central patagonia is characterized by prominent continental deposits that belong to the cretaceous chubut group basin whose tectonic setting remains controversial it has been interpreted as a foreland basin an extensional basin and even as a sag stage of a rift event related deposits outcrop as part of the patagonian broken foreland east of the patagonian andes particulary the san bernardo fold and thrust belt between 42 and 48 s as the main sector of the broken foreland constitutes a nnw trending intraplate belt located 450 km away from the trench coincidentally at these latitudes 1200 km east of the trench intraplate deformation has caused tectonic inversion of mesozoic basins presently located at the atlantic offshore area additionally at the san jorge gulf area this orogenic system interferes with a conspicuous e w extensional system transversally disposed to the andean strike mainly active between the late early cretaceous and late paleocene we carried out an integrated analysis from structural 2 d and 3 d seismic data at the san bernardo ftb and the adjacent rio mayo basin studying sections of the chubut group basin to unravel the different evolutionary stages thus surface and subsurface evidence of syn compressional deposition indicate the development of a broken foreland basin related to the formation of the san bernardo ftb suggesting an initial growth during the late early cretaceous and probably up to the late paleocene our results imply that the cretaceous compression acted in concert with transversal foreland extension hence we propose a syncontractional rift reactivation of a potential lithospheric anisotropy triggered by regional contraction finally the origin of compression during this time is discussed in relation to multiple processes that go from high convergence between plates and trenchward motion of south america collision of mid ocean ridges to potential dip changes in the subducted slab as suggested by arc expansion

chemodynamics of an arsenic hotspot in a west bengal aquifer a field and reactive transport modeling study abstract extremely high as concentrations in drinking water of the ganges delta west bengal and bangladesh has emerged as an issue of great concern in the past decade because of its serious impact on the health of millions of people the distribution pattern of as concentrations in the ganges delta region is patchy and there are numerous as hotspots the present study is perhaps the first attempt in west bengal to characterize such a hotspot by geophysical and geochemical methods and to model the transport of the enrichment plume using a 1d reactive transport model phreeqc the study site is located along the hooghly river 60 km north of kolkota city near the city of chakdaha total as concentrations in the groundwater range from 0 5 to more than 6 mol l 1 the who recommended maximum drinking water concentration is 0 13 mol l 1 i e 10 g l 1 results show groundwater is in chemical equilibrium with siderite and calcite a mineral phase previously shown to be an efficient trap for as iii groundwater redox potential is controlled by the fe oh 3 am fe2 couple the as iii versus as v distribution 42 as iii and 58 as v on average is not at equilibrium with measured eh values no evidence of sulfide solid phases such as as rich pyrite or arsenopyrite was found although amorphous fe dissolution is confirmed to play an important role in the release of as selective dissolution extractions indicate that adsorption of as on carbonates and micas may also be an important component of as cycling in the sediment modelling results demonstrate the role of po 4 3 hco 3 and fe ii in mobilizing the as plume thereby increasing the threat to the 75 000 inhabitants of chakdaha

detrital zircon provenance from the neuquen basin south central andes cretaceous geodynamic evolution and sedimentary response in a retroarc foreland basin the surface response in terms of drainage pattern changes to the cretaceous geodynamic reorganization of the andean subduction zone between 36 s and 41 s is reconstructed through the geochronology based provenance study of alluvial detrital zircons the age spectra obtained by 500 spot u pb ages record an eastward provenance of detritus coming from the foreland during the early cretaceous backarc extensional stage followed by westward sourced clastics coming from the cordillera during the cenomanian this drainage pattern reversal fits the regional unconformity in the sedimentary record that is linked to the geodynamic reorganization of the continental margin from an extensional to a compressional regime forcing the neuquen basin to evolve from a retroarc to a foreland stage after this inversion the clastic systems progressively returned to be mainly fed by the foreland due to the uplift of the peripheral bulge as a consequence of the late cretaceous thrust front migration this tectonic evolution of the neuquen basin and the related response of the drainage pattern are thought to be the surface expression of the dip decrease of the benioff subduction zone

experimental simulation of arsenic desorption from quaternary aquifer sediments following sea water intrusion abstract alluvial sediments from the coastal area in southern tuscany italy characterized by a significant as anomaly as 500 mg kg are subjected to seawater intrusion due to groundwater exploitation sequential extractions and kinetic experiments were carried out on quaternary alluvial sediments to quantify the interaction between as oxianions adsorbed on mineral surfaces and cl in solutions and to establish if this mechanism may contribute to the release of as in groundwater the natural water rock interaction in the aquifer was simulated in two experiments by saturating the samples with four solutions with increasing chlorinity for different time firstly a rapid change in the aquifer salinity e g fast seawater intrusion groundwater over pumping was simulated by an interaction sediment solution of 24 h solutions with cl 2000 mg l extracted up to 76 g kg of as while seawater sol 4 24 cl 18 500 mg l extracted up to 161 g kg of as in a second experiment the ingression of water with increasing salinity in the acquifer followed by the withdrawal of the water after progressively longer interaction times with the aquifer sediments was simulated the timing of the as cl reaction was constrained by saturating the samples with four solutions with increasing salinity sol1 84 cl 0 mg l sol2 84 cl 250 mg l sol3 84 cl 2000 mg l sol4 84 cl 15 886 mg l that interacted with the sediment samples for longer saturation times up to 21 days for each solution after saturation with the previous three solutions up to 62 g kg of as were extracted by seawater following a salinity increase from 2000 mg l cl to a chlorinity close to seawater representing 60 of the exchangable as fraction in the sediments our results constrained the timing of sediment solution interaction of as desorption and showed that after a rapid intrusion of seawater or after a relatively long period of interaction with saline solutions an aquifer with similar geology releases in groundwater concentrations of as exeeding the 10 g l limit for drinking water also this study estimated the potential effects caused by the ingression of seawater in lowland alluvial coastal areas induced by groundwaters exploitation or by extreme weather events such information is crucial for management authorities to mitigate and predict the effects of as hazard in groundwater driven by changes in the environmental aquifer conditions e g seasonal fluctuations of the water table and or changes in salinity of coastal aquifers which are becoming increasingly frequent as consequence of climate change

definition of the continent ocean boundary of india and the surrounding oceanic regions from magsat data abstract magsat studies over the indian region and adjoining areas show that the continental oceanic contrasts appear more distinctly in the equivalent magnetization solution than in the anomaly maps the vertical component z is found to be more useful for the equatorial regions it is also noted that in general the continental crust has a higher magnetization than the oceanic crust further the continental crust seems to extend into the arabian sea across a part of the west coast a similar continuation is seen in the northern part of the bay of bengal the west coast result is corroborated using land and marine bouguer gravity anomalies

continent like crustal thickness beneath the bay of bengal sediments observed dispersion of fundamental mode rayleigh and love waves across the bay of bengal to wwssn and indian seismograph stations suggests increasing crustal thickness northward from an approximate 15 km thick oceanic crust south of the latitude of the southern tip of india to a more continent like thickness of approximately 25 km at 20 n and over 35 km at the northernmost part of the bengal fan the dispersion data are not consistent with models which simply add the increasing sedimentary thickness on top of a normal oceanic crust the sediment thicknesses and crust velocities are controlled by extensive seismic refraction results and are in agreement with clearly observed sedimentary higher mode waves recorded at the indian seismograph stations madras and vishakapatnam several hypotheses might explain this surprising result 1 1 the blanketing effect of the sediments with consequent temperature rise has brought about differentiation of basalt to increase the crustal thickness r n singh personal communication 2 2 the change in moho depth represents dynamic isostatic adjustment such as a phase change boundary which is lowered because of temperature or pressure perturbations from the sedimentary blanket or from pressure perturbations of plate collision 3 3 the collision has underthrust a wedge of low velocity material beneath the oceanic crust 4 4 the northern bay of bengal is actually fortuitiously continental or continent like possibly as a result of the influence of the 90 ridge especially in the northern part if the explanation is 1 2 or 3 the result is important to our understanding of crust and upper mantle dynamics it is suggested that further controlled studies be performed to verify the result

south american reference pole for the mid cretaceous further constraints in the interpretation of andean paleomagnetic data a paleomagnetic study of the aptian cerro barcino formation in central patagonia showed the presence of a stable magnetization with a positive tilt test the obtained pole position lat 85 s long 181 e 95 5 6 n 11 differs from reliable early and late cretaceous south american cratonic poles the cerro barcino pole overlaps coeval poles from the chilean andean fore arc previously interpreted to record crustal block rotations this new result indicates that previously published andean tectonic models must be reviewed

groundwater resource degradation in coastal plains the example of the cecina area tuscany central italy abstract the paper describes the degradation of the groundwater resources in the cecina area where seawater intrusion b contamination and no 3 pollution are all affecting the heavily exploited pleistocene aquifer over pumping has brought water levels to about 0 m a s l as far as about 7 km from the shore line thereby promoting the seawater intrusion the intrusion which is characterized by cation exchange phenomena and ca cl type waters enters the plain mostly through the shallower horizons the saline front which advanced from 0 5 to 1 km in 4 a has by now reached the foot of the hills to the east of the town where it is also affecting wells of the local aqueduct boron contamination linked to past discharge of industrial waste transported downstream by the river reached concentrations as high as 3 5 mg l in the mid 1980s although a decreasing trend is now under way b content is still close to 1 mg l the presence of high no 3 which together with the seawater intrusion represents a major issue for groundwater management in the area is linked to the widespread utilization of fertilizers nitrate concentration which reaches a maximum of about 300 mg l in the shallow aquifer horizons and then decreases rather regularly with depth is strongly influenced by precipitation however irrigation also contributes significantly to transporting the no 3 contamination to depth as clearly shown by 18 o data the severe decline in the quality of the groundwater resource in the cecina area is further compounded by an overall decrease in water availability in the region of tuscany as evidenced by long term monitoring of precipitation and fluvial discharge

magsat scalar anomaly map of india and a part of indian ocean magnetic crust and tectonic correlation magnetic scalar anomaly maps over india and a part of the indian ocean are prepared from the magsat data using an average of the observed field in a grid of 1 1 the magsat scalar anomaly map thus obtained is characterised by highs over the indian shield and large lows over the himalayas centered over tibet plateau a ne sw magnetic trend emanating from ne india and spreading almost over the entire peninsular shield is the single most prominent feature of the map which might be related to the stress system or deepseated structural trends associated with plate motion the deccan traps are reflected by nosing of the magnetic contours the shillong massif is characterised by a separate anomaly which deflects the ne sw magnetic trend referred to above a magnetic crustal map prepared from this magsat scalar anomaly using the principles of harmonic inversion yields a thickness of 30 km under the cambay basin and the western part of the narmada son lineament for a magnetization of 2a m suggesting a higher subsurface thermal gradient in this area and therefore a tectonically active region a maximum thickness of 40 42 km is found under the regions of aravallis singhbhum and south of the narmada son lineament which are precambrian stable cratons major lineaments and faults are reflected as variations in the thickness of the magnetic crust along these lines the himalayas are chaaracterised by an average thickness of 35 36 km with a thickening of 2 4 km under the tibet plateau and shillong massif the magsat anomaly in the northern part of the indian ocean can be accounted for by a thickening of 8 km in the magnetic crust the center of this crustal thickening derived from the magsat anomaly after appropriate correction for the inclination of the earth s magnetic field in this region coincides with the wellknown indian ocean gravity and geoid lows

crustal magnetisation model of the indian subcontinent through inversion of satellite data abstract an apparent magnetisation model of the indian subcontinent and the adjoining regions has been obtained through the inversion of magsat total field scalar and vertical field data a staggered 4 4 grid pattern with a constant continental crustal thickness of 40 km yielded magnetisation values over a 2 2 grid over the major part of the indian subcontinent the magnetisation picture brings out a prominent high sandwiched between the eastern ghats and the main boundary fault of the himalayas in contrast the identity of the western ghats comprising mainly deccan traps is missing while a distinct magnetisation low is observed over the known hot spot region of the saurashtra peninsula two magnetisation highs one over the shillong massif and the other over the central part of india covering aravallis and the bundelkhand massif are obtained interestingly even at a height of 400 km the well known narmada son lineament is clearly reflected in the total intensity map as well as in the corresponding magnetisation map the bay of bengal and the himalayas ara characterised by magnetisation lows

new remains and new insights on the gondwanan meiolaniform turtle chubutemys copelloi from the lower cretaceous of patagonia argentina abstract new cranial and postcranial remains of the gondwanan meiolaniform turtle chubutemys copelloi gaffney rich vickers rich constantine vacca and kool 2007 from the lower cretaceous puesto la paloma member of the cerro barcino formation chubut province patagonia argentina are presented described and compared in this contribution carapace and plastral remains pectoral and pelvic girdle cervical and thoracic vertebrae and the left maxilla and jugal are the new recovered elements from c copelloi these new remains were found in 2008 in turtle town locality the same site where the holotype and referred specimens of c copelloi had been found in 1997 the facies analysis of the sedimentary succession in turtle town and surrounding areas suggests a paleoenvironment constituted by a broad alluvial plain with influx of volcanic ash falls whose deposits were disturbed by pedogenesis or reworked by current flows that supplied water and sediment in ponded areas the presence of a very thin shell broad vertebrals broader than pleurals the presence of a shallow nuchal notch with the vertebral 1 almost reaching the anterior border of the carapace the presence of costo peripheral fontanelles and the presence of an ectepicondylar canal in the humerus are the most notable features provided by the new remains a cladistic analysis has been performed to test the phylogenetic position of c copelloi this phylogeny corroborates the basal position of c copelloi among meiolaniformes the plausible phylogenetic relationships of the clade meiolaniidae with other gondwanan e g otwayemys cunicularius gaffney kool brinkman rich and vickers rich 1998 or laurasian lower cretaceous taxa e g sinochelyids are also discussed in this contribution taxa included in meiolaniformes have been mainly found in gondwana and as the most basal taxon was found in patagonia paleobiogeographic studies suggest this clade originated in south america due to the basal position of c copelloi among meiolaniformes the discovery of more and previously unknown remains of this species sheds light on the origin and early evolution of this curious clade

effective middle surface of lithosphere representation of the lithosphere by an equivalent elastic plate is a common method in earth sciences when the mechanical behaviour of the lithosphere is investigated the equivalent plate is determined by two parameters thickness and configuration of the middle surface named as effective elastic thickness eet and effective middle surface ems of the lithosphere eet is related to the flexural deformation of the lithosphere to vertical loading while ems controls the lithosphere s response to lateral force variations eet has been well investigated whereas ems remains in the shadow in geophysics the present paper proposes a mathematical formulation for the ems allowing to calculate it theoretically from a stress strain distribution the equilibrium equation of the equivalent elastic plate is derived from the general rheologically independent equilibrium equation for the lithosphere it contains a member proportional to the ems curvature which describes pre existing flexure of the equivalent elastic plate it must be included in flexural calculations with non zero in plane forces because it is an integral part of the equilibrium ems like eet depends on the lithosphere s structure constitution and thermal state contrasting with eet bending and mechanical layering do not substantially affect ems temperature exerts the strongest influence on ems change in thermal regime may shift ems vertically by 50 km possible deflection of ems due to variations of other parameters is usually lower than 10 km tectonically ems reveals through stress induced vertical movements their amplitude may be detectable even under the action of moderate intraplate force the most pronounced effect of ems variation is expected at continental rifts and orogens 1999 elsevier science b v all rights reserved

calibrating the guadalupian series middle permian of south china abstract the guadalupian epoch represents one of the most critical intervals during the earth history which is characterized by a series of global geological and biological events however it is poorly constrained by radioisotopic ages in comparison with the high precision dates from the lopingian and lowest triassic in south china and the cisuralian in southern urals russia in this study we report combined ca id tims and sims u pb zircon geochronology for three ash beds from the base and lower part of the kuhfeng formation in the chaohu area southeastern china zircons from ash beds a c and d were initially analyzed by sims and yielded weighted mean 206pb 238u dates of 269 0 1 4 ma mswd 1 03 n 31 266 3 2 2 ma mswd 2 2 n 29 and 262 2 1 7 ma mswd 1 0 n 20 in ascending order however high precion u pb geochronology of the same ash beds by the ca id tims method point to important inaccuracies in the sims results due to pb loss in zircons ash beds a and c yielded two tims weighted mean 206pb 238u dates of 272 95 0 11 ma mswd 1 9 n 7 and 271 038 0 097 ma mswd 2 2 n 8 respectively the depositional age of 272 95 0 11 ma for ash bed a is postulated as the traditional cisuralian guadalupian boundary cgb age in south china our new geochronology suggests that the guadalupian series in south china had a total duration of 13 85 0 52 myr given a guadalupian lopingian boundary glb age of 259 1 0 5 ma the new age calibration of the base of the guadalupian series is ca 0 65 0 51 myr older than and improves upon the previous estimates for the cgb age and the duration of the guadalupian epoch based on the 2016 international chronostratigraphic chart icc and the 2012 geologic time scale gts