late miocene holocene canyon incision in the western altiplano northern chile tectonic or climatic forcing abstract major fluvial incision 600 1000 m affecting the coastal cordillera and central depression of northern chile is analysed to evaluate supposed coeval uplift of the altiplano and or climatic changes in the atacama desert the timing of the beginning of incision is constrained by the age of deposition of the central depression top in the north 18 19 s this top corresponds to fluvial gravels accumulated between 11 9 0 6 ma and 8 3 0 5 ma which are genetically related to semiarid climate and to an eastward poorly dissected parallel drainage network that developed between 15 0 0 6 and 11 2 0 6 ma thus gravel deposition ended at 11 9 11 2 ma to the south 19 20 s the central depression top corresponds to c 6 ma alluvial deposits stratigraphically determined canyon ages and knickzone locations indicate that southward dissection began later and or developed under a regime of lower erosion capacity owing to drier climate vertical incision rate evolution is compatible with eastward knickzone migration dissection required a considerable altitude difference between ancient and present day river base levels which was achieved predominantly by basin infill on an already partially elevated bedrock therefore subsequent incision would have been triggered by local semiarid climatic periods rather than by contemporaneous surface uplift exoreic canyons occur when climatic conditions in the catchments are arid semiarid whereas endoreism is developed when these conditions in catchments are hyperarid

calcite dissolution in sediments of the ceara rise in situ measurements of porewater o2 ph and co2 aq in situ electrode measurements of porewater oxygen and ph from four sites on the ceara rise in the western tropical atlantic unequivocally demonstrate that calcite dissolution driven by metabolic co2 produced within the sediments is a significant part of the diagenesis of sedimentary calcite dissolving at least 20 of the calcite rain to the seafloor the first ever in situ absorbance based measurements of porewater co2 aq support the dissolution estimates based on models of the observed ph distributions and are incompatible with scenarios excluding metabolic co2 driven dissolution our dissolution estimates are consistent with those estimated by an independent study of porewater calcium and alkalinity profiles martin and sayles 1996 at this location the consistency of these disparate porewater measurements and our ability to interpret them with simple models of respiration and dissolution implies that no special mechanism is required to describe this process the calcite dissolution rate constant in the sediments of the deepest station in this study is significantly higher than determined by in situ studies at other locations values approach those determined by early laboratory measurements the dissolution rate constant here must be at least two orders of magnitude higher than for calcite in sediments on the ontong java plateau based on in situ electrode measurements there hales and emerson 1996 the calcite solubility consistent with these data is not compatible with that consistent with the ontong java data the reason for this difference is currently unresolved but may be due to the high order of the empirical dissolution rate law assumed in this study

an evaluation of lohmann s foraminifera weight dissolution index down water column traverses of core top weights for three planktonic species confirm lohmann s 1995 relationship between foraminifera shell weight loss and bottom water carbonate ion content however they also suggest that the initial shell thickness varies with growth habitat and that the offset between bottom water and pore water carbonate ion concentration varies even on small space scales

demonstration of two pulses of paleogene deformation in the andes of peru abstract new radiometric ages of about 25 m y on volcanic materials in a marine intercalation within clastic continental strata of the upper moquegua formation near caraveli southern peru together with an age of 25 3 0 4 m y obtained by tosdal et al from a locality about 300 km to the ese show that the formation contains strata of late oligocene as well as miocene age and demonstrate that the coastal region was at a low elevation during latest oligocene time because the unconformities between the upper moquegua formation and the underlying lower moquegua formation and between the lower moquegua formation and underlying paleocene rocks cannot both represent the same tectonic event two discrete paleogene events must be present in the andes of peru although the exact timing of these events is uncertain the unconformities are likely to be of paleocene and middle eocene age or possibly of middle eocene and oligocene age

planktic foraminiferal sedimentation and the marine calcite budget 1 the vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal cac0 3 budget is presented test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget highlighting the importance of ecological autecological e g reproduction and biogeochemical conditions that determine the presence or absence of species to complete the open marine particulate caco 3 inventory the contribution of coccolithophores pteropods and calcareous dinophytes is discussed based on the studied regions the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1 3 3 2 gt yr 1 equivalent to 23 56 of the total open marine caco 3 flux the preservation of tests varies on a regional and temporal scale and is affected by local hydrography and dissolution during most of the year off peak periods many tests dissolve above 700 m water depth while settling through the water column with on average only 1 3 of the initially exported caco 3 reaching the deep seafloor pulsed flux events mass dumps of fast settling particles yield a major contribution of tests to the formation of deep sea sediments on average 25 of the initially produced planktic foraminiferal test cac0 3 settles on the seafloor the total planktic foraminiferal contribution of caco 3 to global surface sediments amounts to 0 36 0 88 gt yr 1 32 80 of the total deep marine calcite budget

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

progress toward a multi basin calibration for quantifying deep sea calcite preservation in the tropical subtropical world ocean article i nfo the development of a quantitative and multi basin deep sea calcite preservation proxy is important for a better understanding of the marine carbonate system both in modern sediments and in down core work we present caco3 preservation data from 89 core top samples in tropical and subtropical areas of the pacific atlantic and indian oceans we observe that the globorotalia menardii fragmentation index mfi has potential to trace deep sea caco3 dissolution quantitatively across the tropical subtropical world ocean this is evident in the robust relationship between mfi and bottom water calcite under saturation in six depth transects with markedly different bottom water co3 2 saturation states we also found a strong relationship between mfi and modeled estimates of percent caco3 dissolved at our core top locations corroboration for mfi s dissolution trend in the subtropics comes from the concurrent drop in size normalized shell weight of globorotalia truncatulinoides specimens with increasing co3 2

changes in opal flux and the rain ratio during the last 50 000 years in the equatorial pacific abstract changes in the orgc caco3 ratio in particles sinking from the surface to the deep ocean have the potential to alter the atmospheric pco2 over the span of a glacial interglacial cycle recent paleoceanographic and modern observational studies suggest that silica is a key factor in the global carbon biogeochemical cycle that can influence the flux ratio especially at low latitudes through silicic acid leakage brzezinski m pride c franck m sigman d sarmiento j matsumoto k gruber n rau r coale k 2002 a switch from si oh 4 to no 3 depletion in the glacial southern ocean geophysical research letters 29 5 to test this hypothesis we reconstruct biogenic fluxes of caco3 orgc and si for three equatorial pacific cores we find evidence that a floral shift from a sio2 based community to a caco3 based occurred starting in mid marine isotope stage mis 3 24 59 cal ka and declining toward mis 2 19 24 cal ka this could reflect the connection of the peru upwelling system to the subantarctic region and we postulate that excess silica was transported from the subantarctic via the deep equatorial undercurrent to the eastern equatorial pacific in the eastern equatorial pacific only we document a significant decrease in rain ratio starting mid mis 3 toward mis 2 this decrease is concomitant with a significant decrease in silica accumulation rates at the seabed this pattern is not observed in the pacific influenced by equatorial divergence and shallow upwelling where all reconstructed fluxes caco3 orgc and opal increase during mis 2 we conclude that the overall calcium carbonate pump weakened in the eep under peru upwelling influence

biogenic budgets of particle rain benthic remineralization and sediment accumulation in the equatorial pacific abstract budgets of organic c corg cac03 and opal have been constructed for the palisades ny pacific equatorial region at 140 w between 5 n and 5 s measurements of the rain and benthic remineralization rate of biogenic materials have been adjusted and normalized to account for sampling biases sea surface temperature serves as a master variable in normalizing sediment trap and benthic remineralization data to average conditions the rain and remineralization rates for corg are nearly equal 0 40 0 05 and 0 46 0 06 mmol m 2 d 1 respectively thus only a minor fraction of this constituent is buried rain and dissolution rates for biogenic opal are similarly balanced 0 3 0 06 and 0 36 0 01 mmol m 2 d 1 and consistent with the value for opal burial 0 0 0 004 the cac03 budget appears to have changed during the holocene the best estimates of modern cac03 dissolution 0 58 0 03 mmol m 2 d 1 and rain rate 0 61 0 06 are consistent with230th normalized carbonate accumulation rates for the late holocene 0 1 mmol m 2 d 1 however the balance between dissolution and rain is not consistent with early holocene carbonate accumulation 0 3 mmol m 2 d 1 and this imbalance suggests 1 a recent increase in the rate of cac03 dissolution on the sea floor or 2 a decrease in the rain rate of carbonate particles modeling230th profiles in sediments from this region define the last 3000 years as the duration of increased dissolution or decreased particle rain 231pa 230th ratios in sediments indicate that particle rain rates have remained constant or possibly increased slightly through the holocene two potential causes for increased dissolution were investigated a change in deep water carbonate saturation or a change in co g cac03 rain ratios a model describing carbonate dissolution as a function of the degree of undersaturation and the amount of organic carbon oxidation within sediments indicates that the recent increase in dissolution is more likely due to changes in bottom water chemical composition we propose that pacific ocean bottom water carbonate ion concentration has decreased by 10 15 m over the last 3000 years

accurate estimation of sea surface temperatures using dissolution corrected calibrations for mg ca paleothermometry 1 paired 18o and mg ca measurements on the same foraminiferal shells offer the ability to independently estimate sea surface temperature sst changes and assess their temporal relationship to the growth and decay of continental ice sheets the accuracy of this method is confounded however by the absence of a quantitative method to correct mg ca records for alteration by dissolution here we describe dissolution corrected calibrations for mg ca paleothermometry in which the preexponent constant is a function of size normalized shell weight 1 for g ruber 212 300 m mg ca ruber 0 025 wt 0 11 e0 095t and b for g sacculifer 355 425 m mg ca sacc 0 0032 wt 0 181 e0 095t the new calibrations improve the accuracy of sst estimates and are globally applicable with this correction eastern equatorial atlantic sst during the last glacial maximum is estimated to be 2 9 0 4 c colder than today

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

abundance and distribution of fluoride concentrations in groundwater la ballenera catchment southeast of buenos aires province argentina high concentrations of fluoride have negative effects on human health and it is one of the most widespread contaminants in groundwater having being found in high concentrations in different countries over the entire world fluoride concentrations exceeding the drinking water levels are very frequent in the region known as pampa plain in argentina associated with loess like sediments bearing volcanic shards and calcium carbonate concretions in this study the behavior of fluoride in the catchment of la ballenera creek is performed to contribute to the understanding of the processes controlling its distribution at catchment scale the catchment is around 100 km2 mostly in a flat landscape outflowing into the atlantic ocean the concentration of major ions silica and fluoride was measured on 34 groundwater and 9 surface water samples obtained in october 2013 all the samples both streamwater and groundwater were sodium bicarbonate type with an average ph of 8 and 7 3 respectively the fluoride concentrations in groundwater ranged between 1 1 and 2 5 mg l with an average value of 1 9 mg l fluoride concentrations in streamwater were close to groundwater concentrations indicating the predominance of baseflow on surface water composition the variations in the contents of fluoride are due to two main factors one geological geomorphological and the other geochemical the first one is related to the dominance of loess like sediments formed by minerals bearing fluoride and the second one is related to the control resulting on calcite precipitation adsorbing fluoride ions

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

response of supergene processes to episodic cenozoic uplift pediment erosion and ignimbrite eruption in the porphyry copper province of southern peru the jurassic to middle eocene porphyry copper deposits and prospects exposed on the pacific slopes of the central andean cordillera occidental of southern peru between latitudes 16 309 and 18 s record a protracted ca 30 m y history of supergene processes that were fundamentally controlled by the evolving local geomorphologic environment itself a response to successive regional tectonic events including the late eocene incaic the late oligocene to earliest miocene aymara and the middle to late miocene quechuan events weathering of the porphyry centers also overlapped temporally with the local resumption of arc volcanism in southern peru at 25 5 ma following a 27 m y amagmatic interval and supergene processes were variously interrupted or terminated by ignimbrite blanketing although in several locations supergene profiles were preserved by such cover the landform chronology for the area surrounding the cuajone quellaveco and toquepala deposits ca 17 s is revised and extended northwestward through field mapping to the cerro verde santa rosa district ca 16 309 s the 40 ar 39 ar incremental heating dates of supergene alunite group minerals from the angostura 38 1 and 38 8 ma and posco 38 8 ma prospects and the cerro verde deposit 36 1 38 8 ma demonstrate that supergene processes were underway in the late eocene beneath a subplanar topography resulting from uplift and erosion during the incaic orogeny now represented by a regional unconformity in the cenozoic volcanic sedimentary rock succession broadly contemporaneous supergene processes were probably active in the cuajone quellaveco toquepala district slow erosion and the accumulation of clastic sediments through the tectonically quiescent early to mid oligocene are envisaged to have caused a rise in the water table and the widespread preservation of the incaic supergene profiles aymara uplift subsequently led to the incision of the 23 8 to 24 ma altos de camilaca and the 18 8 to 19 1 ma pampa lagunas pediplains and their regional correlatives the ensuing water table lowering was associated with intense leaching and sulfide enrichment from the late oligocene 24 4 28 ma natroalunite at cerro verde 26 27 ma natroalunite at santa rosa and 28 6 ma jarosite at la llave to the early miocene 23 ma alunite and 21 ma natroalunite at cerro verde and 19 2 ma jarosite at la llave and was plausibly responsible for much of the upgrading of the cuajone and toquepala deposits and thr quellaveco prospect which are intersected by both the altos de camilaca pediplain and erosional features representing upslope extensions of the pampa lagunas pediplain the younger supergene profiles were widely superimposed on the remnants of those generated during the incaic orogeny middle miocene 14 2 ma biotite age chuntacala formation flows protected the cuajone supergene profile from destruction by erosion but at 13 0 ma interrupted supergene processes at quellaveco revision of volcano stratigraphic relationships in the latter area reveals that subsequent erosion of the chuntacala formation ignimbrites and part of the supergene profile took place prior to the deposition of a 10 1 ma ash flow tuff of the asana formation elsewhere supergene activity persisted at the cachuyito prospect through 11 4 ma and minor jarosite development occurred at least until 4 9 ma both there and at cerro verde during and following the multiple pediment landform stage ca 7 9 15 0 ma the occurrence of relics of late eocene alunite group minerals within considerably younger late oligocene to late miocene supergene alteration profiles suggests that the overall physiographic configuration of the pacific piedmont of southern peru remained remarkably consistent from the late eocene to the middle miocene moreover the new age data confirm that as in northern chile semiarid climatic conditions prevailed along much of the plate boundary from the mid eocene until the late miocene or early pliocene onset of hyperaridity the local geomorphologic and volcanic conditions in southern peru however conspired to generate more complex supergene profiles with lower aggregate enrichment factors relative to the strongly enriched profiles in the late eocene to early oligocene porphyry copper belt of northern chile which underwent supergene upgrading over relatively brief periods

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

sedimentation tectonism and volcanism relationships in two andean basins of southern peru the intermontane basins of the central andes formed from the first episode of the andine tectonic peruvian phase santonian are characterized by a clastic continental sedimentation settled in a compressive tectonic context and containing volcanic intercalations

importance of accessory minerals for the control of water chemistry of the pampean aquifer province of buenos aires argentina abstract the pampean aquifer in south east argentina is mainly constituted of loess like sediments these are clastic sediments mainly composed of quartz and aluminosilicates and calcrete concretions its hydrochemistry is generally studied assuming a chemical equilibrium between mineral phases and the aqueous fluids the phases forming the matrix of this aquifer are considered to be the reactive phases responsible for the chemistry of the groundwater in the present study batch dissolution experiments were performed on calcrete and loess to better understand the source of the pampean aquifer water chemistry and to measure the benefit of applying water rock interaction models that use kinetic rate laws instead of thermodynamic equilibria the different minerals composing the loess and calcrete samples were calculated using quantitative rietveld refinement of x ray powder diffraction xrd patterns this analysis showed that the major phases of loess are quartz 30 wt and feldspars 70 wt the main components of calcrete are calcite 95 wt and quartz 5 wt scanning electron microscopy with energy dispersive x ray microanalysis sem edxs was used to provide detailed information about the chemical composition of the powder samples revealing the presence of traces of minerals like halite barite and fluorapatite which were not detected by xrd the kinetic code kindis was used to carry out simulations using the minerals identified previously in their relative proportions to identify the signature of those geochemical phases on water chemistry experimental data from batch dissolution experiments were compared to simulated data this investigation showed that water reached pseudo steady state concentrations due to the presence of fast dissolving phases like halite barite gypsum plant phytolith these phases appeared to be of major importance in controlling the chemical composition of the pampean groundwater furthermore this work showed that the kindis software can be used on all kinds of aquifers as it is very easy to modify the parameters of the simulation to adapt it to numerous situations the modeling is a very important tool for thermodynamic and kinetic studies of groundwater chemistry it enables the prediction of water quality and can help to understand the impact of anthropic or natural contamination on the groundwater

geochemistry and health aspects of f rich mountainous streams and groundwaters from sierras pampeanas de cordoba argentina symptoms of dental fluorosis have been observed in rural communities located in the sierras pampeanas de cordoba a mountainous area in central argentina the clinical assessment was performed in the charbonier department where the fluoride f intake was determined to be 3 90 0 20 mg day 1 n 16 in this community mild and severe fluorosis reach an incidence of 86 7 total teeth surface 636 teeth among the children population to determine the origin and distribution of fluorine in natural waters from the charbonier department and nearby regions sampling was performed in the area covering the san marcos river basin the obtained results show that f concentrations vary between 1 to 2 5 mg l 1 with an outlier value of 8 mg l 1 the spatial distribution of f shows that the lowest concentrations are found at the basin s catchments maximum values are located in two sectors of the basin the charbonier depression in the eastern part and at the san marcos village downstream the main collector in the western part of the basin in these two regions the f contents in ground and surface waters are 2 0 mg l 1 and nearly constant dissolved f in natural waters from the study area has its origin in the weathering of f bearing minerals present in the region s dominant lithology the extent of mineral weathering is mostly determined by the residence time of water within the aquatic reservoir longer residence times and a major solid water interaction lead to enhanced release of f this explains the higher f concentrations found in basin areas with lower run off the removal of f from water appears to occur by neither fluorite precipitation nor by adsorption hence variations in f concentrations seem to be more related to regional hydrological conditions

hydrogeochemistry of arsenic and other inorganic constituents in groundwaters from la pampa argentina groundwaters from quaternary loess aquifers in northern la pampa province of central argentina have significant quality problems due to high concentrations of potentially harmful elements such as as f no3 n b mo se and u and high salinity the extent of the problems is not well defined but is believed to cover large parts of the argentine chaco pampean plain over an area of perhaps 106 km2 groundwaters from la pampa have a very large range of chemical compositions and spatial variability is considerable over distances of a few km dissolved as spans over 4 orders of magnitude 4 5300 g l 1 and concentrations of f have a range of 0 03 29 mg l 1 b of 0 5 14 mg l l v of 0 02 5 4 mg l 1 no3 n of 0 2 140 mg l 1 mo of 2 7 990 g l 1 and u of 6 2 250 g l 1 of the groundwaters investigated 95 exceed 10 g as l 1 the who guideline value and 73 exceed 50 g as l 1 the argentine national standard in addition 83 exceed the who guideline value for f 1 5 mg l 1 99 for b 0 5 mg l 1 47 for no3 n 11 3 mg l 1 39 for mo 70 g l 1 32 for se 10 g l 1 and 100 for u 2 g l 1 total dissolved solids range between 730 and 11400 mg l 1 the high values resulting mainly from evaporation under ambient semi arid climatic conditions the groundwaters are universally oxidising with high dissolved o2 concentrations groundwater phs are neutral to alkaline 7 0 8 7 arsenic is present in solution predominantly as as v groundwater as correlates positively with ph alkalinity hco3 f and v weaker correlations are also observed with b mo u and be desorption of these elements from metal oxides especially fe and mn oxides under the high ph conditions is considered an important control on their mobilisation mutual competition between these elements for sorption sites on oxide minerals may also have enhanced their mobility weathering of primary silicate minerals and accessory minerals such as apatite in the loess and incorporated volcanic ash may also have contributed a proportion of the dissolved as and other trace elements concentrations of as and other anions and oxyanions appear to be particularly high in groundwaters close to low lying depressions which act as localised groundwater discharge zones concentrations up to 7500 g l 1 were found in saturated zone porewaters extracted from a cored borehole adjacent to one such depression concentrations are also relatively high where groundwater is abstracted from close to the water table presumably because this zone is a location of more active weathering reactions the development of groundwaters with high ph and alkalinity results from silicate and carbonate reactions facilitated by the arid climatic conditions these factors together with the young age of the loess sediments and slow groundwater flow have enabled the accumulation of the high concentrations of as and other elements in solution without significant opportunity for flushing of the aquifer to enable their removal

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

geomorphologic environment and age of supergene enrichment of the cuajone quellaveco and toquepala porphyry copper deposits southeastern peru copper ore grades of the cuajone quellaveco and toquepala porphyry cu mo deposits situated at 3 000 to 4 000 m a s l on the pacific slope of the cordillera occidental of southernmost peru lats 17 degrees 02 17 degrees 15 s have been markedly increased by supergene sulfide enrichment following the emplacement of the hypogene mineralization in the early eocene 52 57 ma as the terminal stage in the development of the toquepala group continental volcano plutonic terrane this andean transect was gradually reduced by erosion in a semiarid climate to a low altitude topography unroofing of the deposits had taken place by the mid oligocene the initiation of cordilleran uplift at ca 25 to 26 ma accompanied by the episodic eruption of felsic ash flow tuffs at the oceanward front of the volcanic arc led to more rapid erosion and the conversion of the mid tertiary landscape into the subplanar altos de camilaca surface this regionally extensive pediplain constitutes the major landform component of the present precordillera surrounding the porphyry centers its final configuration was attained at ca 18 to 19 ma ash flow tuff eruption was widespread and frequent at this time supergene enrichment began in the late oligocene during the progressive lowering of topography and continued through the more abrupt water table depression resulting from the latest oligocene to early miocene uplift however the distribution of chalcocite sensu lato in the three porphyry deposits and the local postmineralization landforms and volcanic histories differed significantly during the latter interval at toquepala and to a lesser extent quellaveco the landform regimes were dominated by open valleys and ignimbrite blanketing was short lived whereas the exposed cuajone deposit was both the site of aggressive early miocene valley incision and the deposition of an unusually thick in part welded ash flow tuff at 22 8 or 0 7 ma as a result the enrichment blanket at cuajone remained relatively thin and was even partially eroded in the early miocene whereas the blankets at quellaveco and toquepala were thickened continued strong uplift in the mid miocene ca 8 15 ma generated the array of apron and terrace pediments of the multiple pediment stage which dominates the lower cordilleran slopes and in the mineralized areas led to the deepening of existing valleys and the development of new fluvial channels ignimbrite eruption persisted throughout the miocene again local regimes of erosion and volcanism proved inimical to supergene activity at cuajone but enrichment continued at quellaveco and particularly toquepala where there is no record of later miocene ash flow accumulation uplift in this period was apparently also most extensive in the vicinity of the toquepala deposit which experienced the formation of a deep chalcocite blanket while the extant enrichment zone at quellaveco was thickened the development of enriched assemblages containing massive chalcocite had clearly terminated by 13 1 or 0 4 ma at cuajone and by 9 5 or 0 5 ma at quellaveco the timing of later enrichment at toquepala is less constrained but a mid miocene age is probable supergene upgrading of the three peruvian deposits was contemporaneous with that of copper mineralization in northernmost and northern chile as at chuquicamata and la escondida and in the copiapo mining district in all of which areas a late oligocene to mid miocene age has been inferred for supergene alteration this major and regionally developed metallogenic episode took place during and between two major periods of cordilleran uplift under semiarid climatic conditions the termination of intense enrichment along this 2 000 km stretch of the cordillera occidental in the late miocene was a direct result of marked climatic desiccation which not only reduced the overall supergene activity but focused fluvial erosion leading to the incision of steep walled canyons less favorable for supergene alteration than the earlier subplanar landforms

occurrence and formation of high fluoride groundwater in the hengshui area of the north china plain although high f groundwater was observed in the hengshui of the north china plain the depth dependence of groundwater f and its relation to aquifer sediments remains unknown both shallow groundwater and deep groundwater were collected for chemical and isotopic characterization sediments were taken from different depths down to 130 m for total element analysis and f form determination with sequential extraction procedure results show that f concentration ranges from 0 37 to 3 28 mg l and from 0 28 to 3 6 mg l in shallow and deep groundwater respectively high f water from shallow aquifers are of cl so4 na mg hco3 cl so4 na and so4 cl na mg types while hco3 so4 cl na and cl so4 na types are from deep aquifers high f waters are mainly found at the depths of 50 200 and 300 m along the flow path groundwater shows an increasing trend in f concentration from the northwest to the southeast isotopes of 18o and d in deep groundwater are more depleted in comparison with shallow groundwater suggesting that shallow and deep groundwater replenish through different ways with longer retention time of deep groundwater 13c of dissolved inorganic carbon are between 11 9 and 8 8 in shallow groundwater and between 10 6 and 7 5 in deep groundwater respectively which indicates that groundwater dic comes from both rock weathering and biodegradation of organic matter fluoride content in the sediment ranges from 140 to 1690 mg kg showing a decreasing trend with depth good correlations between f and al2o3 and fe2o3 are observed demonstrating that f contents in sediments are significantly influenced by the minerals containing fe2o3 and al2o3 in terms of adsorption sequential extraction procedure shows that exchangeable f form f1 and fe mn oxides bound f f3 generally decrease with depths while organic matter or sulfide bound f f4 keeps relatively stable and carbonate bound f f2 exhibits highly variable the relationships between f concentration and fe or mn imply that f in f1 is more inclined to be scavenged by fe and mn oxides hydroxides which have a stronger affinity for f although a variety of hydrogeochemical processes affected f concentrations dissolution precipitation is a vital process in the study area in comparison with shallow groundwater cation exchange may exhibit more significantly effect on f enrichment in deep groundwater competitive adsorption of hco3 and oh with f leads to the release of f from aquifer matrix into solution which increases groundwater f concentration evaporation is another control on f concentration especially in shallow groundwater

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

arsenic and fluoride in a loess aquifer in the central area of argentina the objective of this study is to analyze the geochemical conditions associated with the presence of arsenic as and fluoride f in the phreatic aquifer of coronel moldes in the central sector of the argentine chacopampean plain the studied aquifer is composed of silty sand sediments of aeolian origin typically loess like sediments the geochemical composition of water varies from sodium bicarbonate to sodium sulfate chloride water as contents range from low concentrations below detec tion level to 250 lg l high values of f up to 12 mg l were recorded a high as f correlation was found r 2 0 84 the ph varied from 7 31 to 8 85 and the nitrates reached concentrations up to 200 mg l indicating an oxidant environment the highest values of as and f agreed with sodium bicarbonate waters as well as with the highest values of ph recorded there was a high correlation between as and f as well as between as and the na ca ratio the composition and texture of loess low permeability and hydraulic gradients together with the geochemical features of sodium bicarbonate waters are proper conditions for the mobilization of as and f in groundwater in the central area of argentina

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

concept of continuum as opposed to periodic tectonism in the andes abstract results of a study of various andean sedimentary basins that are distinct in terms of age and geodynamic position allow us to postulate the idea of a compressional tectonic continuum as opposed to the short tectonic events which have so far been considered as one of the main features of the dynamic evolution of the andean belt in these basins the development of kilometre scale synsedimentary folded structures implies the existence of compressional stress over a period of several million years the existence of tectonic events of long duration allows us to modify the interpretation of the classic andean tectonic model the timing of the continuum tectonism is perhaps dependent on the variation in the convergence rate between the farallon nazca and south american plates

the andean orogenic period and its major structures in central and northern peru the andean orogenic period began in the albian and consisted of at least 6 discrete compressional phases which are albian to late miocene in age deformation migrated progressively toward the amazonian foredeep the major andean structures in central and northern peru are related to the eocene incaic early miocene quechua 1 and late miocene quechua 3 phases the maranon thrust and fold belt mtfb which bounds the western cordillera to the ne rose in the eocene it was reactivated partly by the quechua 1 phase which also folded the altiplano farther e and possibly part of the eastern cordillera the sub andean thrust and fold belt stfb is related to the quechua 3 phase in both mtfb and stfb the imbricate thrusts merge at depth in large decollement faults gravity sliding does not play a dominant role for these faults have to be rooted westward in the pre andean basement the corresponding crustal shortening played a significant part in the creation of the sialic root of the andes

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

late quaternary hydroclimatology of a hyper arid andean watershed climate change floods and hydrologic responses to the el nino southern oscillation in the atacama desert abstract although certain characteristics of the el nino southern oscillation enso are well known on contemporary timescales less is known about the magnitude frequency relationships of this atmospheric phenomenon on longer timescales or its relationship to widespread flooding especially in its core zone along the sub tropical andes where la nina or el nino episodes control regional hydroclimatology using a combination of stratigraphic evidence geochronologic dating 14c and osl stable isotope analyses and water geochemistry along the rio moquegua in the northern fringes of the atacama desert we assemble a paleoflood chronology for mainstem and tributary sections for the past ca 20 ka and ascertain the variation in enso frequency and magnitude because of the inherent watershed structure and regional hydroclimatology mid valley tributaries of the rio moquegua only flood during el nino episodes and thus provide an important proxy of extreme el ninos while mainstem stratigraphy records both la nina and el nino episodes el nino floods appear to have been pronounced during the late pleistocene and up to at least the younger dryas 12 000 cal yr bp while stratigraphic evidence of large el nino floods is lacking in tributary systems during the mid holocene flood stratigraphy in a 2 ka 7 m high terrace along the mainstem indicates an increased frequency and magnitude of large floods between ca 700 and 1610 ad as compared to the period from ca 160 bce to 700 ad with mega ninos occurring ca 1330 ad and ca 1650 ad water geochemistry and radiocarbon dating indicate that at least two major aquifers exist with wells and springs in the mid valley dating to 710 and 3100 14c yr bp respectively while water from a spring in the headwaters dates to 10 320 14c yr bp this range in dates suggests that groundwater flow in the mid valley is neither fossil water nor exclusively recharged from local precipitation while the older date for headwater sections suggests a more fossil groundwater source and lack of contemporary recharge the 18o similarity between groundwater in the mid valley and the regional meteoric water line mwl suggests a pacific moisture source and the role of el nino precipitation in recharging local aquifers thus el ninos and pacific sourced moisture are an important component of the regional hydroclimatology and the variation in enso frequency and intensity has significant social and hydrologic repercussions in these hyper arid settings

quality and hydrochemistry of groundwater used for drinking in lahore pakistan analysis of source and distributed groundwater more than 7 million people of lahore city pakistan use groundwater for drinking and other household purposes the quality of drinking water from source and distribution system was investigated and the hydrochemical characteristics and formation mechanisms of groundwater were analyzed statistical summary showed higher mean values of major descriptors in distributed groundwater samples compared with source groundwater samples a total of 50 drinking water samples 16 from source and 34 from distribution system were examined for physical chemical and bacteriological parameters including ph turbidity electrical conductivity total dissolved solids total hardness total alkalinity ca2 mg2 na k so42 cl no3 f arsenic as chromium cr iron fe copper cu zinc zn cadmium cd and lead pb varying concentrations of trace amounts of cr in 8 samples fe 18 samples cu 18 samples zn 13 samples and pb 14 samples were detected however the detected trace elements were within the who permissible limits for drinking water except pb where 5 out of 14 samples showed higher than who limit value pb 0 01 mg l 19 out of 50 samples 6 from source and 13 from distributed samples showed high values of alkalinity 250 mg l all of 16 groundwater samples from source exceeded 0 01 mg l who limit value for arsenic as on the basis of bacteriological analysis 42 samples 12 from source 55 from distribution did not meet who guidelines and were unsafe for drinking especially distributed groundwater samples mg hco3 contents predominated the groundwater type followed by ca hco3 carbonate weathering was revealed to be the dominant process controlling dissolution precipitation processes phreeqc modeling showed that the aqueous phase was undersaturated with respect to significant gypsum halite and mirabilite while equilibrium to saturated with respect to aragonite calcite and dolomite was observed principal component analysis pca revealed that the concentration of as was strongly associated with that of so42 reductive dissolution and ph dependent desorption are the plausible processes responsible for the observed high as concentrations in lahore

carbonate preservation in marine sediments mid to higher latitude quantitative proxies 1 observations of carbonate preservation in marine sediments have long been used to infer changes in ocean circulation or biogenic production when combined with measures of organic carbon rain and calcite accumulation rates quantitative estimates of changes in preservation can reveal variation in biogenic fluxes the org c to calcite flux ratio and saturation state of bottom waters here we develop quantitative dissolution proxies for mid to higher latitudes based on foraminiferal test fragmentation examining surface sediments we find that fragmentation in g bulloides and g truncatulinoides is linear with increasing seabed dissolution rate and can be used to quantify changes in carbonate preservation g truncatulinoides shows a constant relationship of fragmentation to dissolution however we observe that although linear to dissolution rate the fragmentation in g bulloides depends on which morphotype is present other species such as g inflata have complex responses to increasing dissolution and are less direct preservation indicators

characterization of loess in central spain a microstructural study the purpose of this paper is to characterize the materials developed in the middle tajo river valley central spain these sediments are loess the characterization of which has not been reported in the international bibliography the sediments are related to the next geological context and their characterization is indispensable to locate the said material in the adequate environment a few different methods have been employed in this study such as the pipette method for determining the grain size and separation of the light and heavy minerals of the sand fraction by using bromoform the mineralogical composition was determined by xrd and textural study was accomplished by sem edx the loessic materials are silt clay or sandy silt that are quite unstable the mineralogical composition shows quartz feldspar calcite and clay minerals some samples show gypsum this mineral and calcite present dissolution and stability problems the heavy minerals starting from the sand fraction are tourmaline zircon garnet staurolite sillimanite and biotite associations the studies carried out with sem show that the quartz grain surfaces present etch pits typical of the wind blown origin

k ar geochronology of the late cenozoic volcanic rocks of the cordillera occidental southernmost peru abstract twenty four k ar radiometric ages are presented for late cenozoic continental volcanic rocks of the cordillera occidental of southernmost peru lat 16 57 17 36 s rhyodacitic ignimbrite eruptions began in this transect during the late oligocene and continued episodically through the miocene the development of andesitic dacitic strato volcanoes was initiated in the pliocene and continues to the present the earliest ignimbrite flows 25 3 22 7 ma are intercalated in the upper coarsely elastic member of the moquegua formation and demonstrate that this sedimentary unit accumulated in a trough parallel to andean tectonic trends largely in the oligocene more voluminous ash flow eruptions prevailed in the early miocene 22 8 17 6 ma and formed the extensively preserved huaylillas formation this episode was coeval with a major phase of andean uplift and the pyroclastics overlie an erosional surface of regional extent incised into a paleogene volcano plutonic arc terrain an age span of 14 2 8 9 ma mid late miocene is indicated for the younger chuntacala formation which again comprises felsic ignimbrite flows largely restricted to valleys incised into the pre huaylillas formation lithologies and at lower altitudes an extensive aggradational elastic facies the youngest areally extensive ignimbrites constituting the sencca formation were extruded during the late miocene in the earliest pliocene the ignimbrites were succeeded by more voluminous calcalkaline intermediate flows which generated numerous large and small stratovolcanoes these range in age from 5 3 to 1 6 ma present day or holocene volcanism is restricted to several large stratovolcanoes which had begun their development during the pleistocene by 0 7 ma the late oligocene early miocene ca 22 23 ma reactivation of the volcanic arc coincided with a comparable increase in magmatic activity throughout much of the cordilleras occidental and oriental of the central andes

hydrogeochemistry of fluoride in the quequen river basin natural pollutants distribution in the argentine pampa fluoride pollution is a widespread problem in argentina as it is in many areas of the world former investigations have demonstrated that the dissolution of volcanic glass disseminated in the loess like sediments is the main source of fluoride in the argentine pampas nevertheless fluoride distribution is erratic and the factors controlling it are not yet well known a large amount of hydrochemical data collected in the quequen grande river catchment is used in order to contribute to the understanding of fluoride distribution and mobility in groundwater in the argentine pampas the quequen grande river catchment is 10 000 km2 it extends between two low hills ranges of precambrian metamorphic rocks and sedimentary paleozoic rocks filled by a thick sequence of cenozoic sediments mainly silts and silt clayed with sand layers these sediments form a multilayer phreatic aquifer which is recharged from precipitation infiltration discharging through streams directly into the sea fluoride concentration in surface water n 353 ranges between 0 and 6 5 mg l with an average value of 2 14 mg l groundwater concentration n 135 is from 0 up to 5 7 mg l with an average of 1 84 mg l considering the statistic distribution of fluoride two groups of samples can be determined a dominant group between 0 and 3 mg l with a mean value around 1 5 mg l corresponding to samples widely distributed in the catchment and a second one group with fluoride contents between 3 and 6 mg l corresponding to a smaller area in the central west border two different sources are proposed volcanic glass dissolution is responsible for dominant values in the catchment while the weathering of biotite from the paleozoic bedrock can be assumed to account for the higher concentrations in the second group

assessment of processes controlling the regional distribution of fluoride and arsenic in groundwater of the pampeano aquifer in the del azul creek basin argentina abstract groundwater in the upper 50 m of the pampeano aquifer in the del azul creek basin argentina has f and as contents above the who safe drinking levels this basin is situated to the se of the chaco pampean plain in buenos aires province the pampeano aquifer is a major water source for all uses the aim of the study is to assess the primary processes controlling the regional distribution of f and as in the most exploited part of the aquifer the study involved sampling for chemical and isotopic analyses interpretation of data with different methods diagrams bivariate analyses mineral saturation states principal component analysis and deduction of leading processes information about aquifer mineralogy and hydrogeochemical processes involved in f and as solubilization in the aquifer has been taken from previous works of the same and other authors groundwater salinity increases to the ne in the direction of the regional groundwater flow chemical types evolve from ca mg hco 3 in the upper part of the basin to na hco 3 in the middle part and to na clso 4 and na cl in the lower part the regional distribution of f is controlled by hydrogeochemical processes the distribution of as is controlled by two types of processes dominating in different areas hydrogeochemical controls prevail in the low to moderately mineralized groundwater of the middle and lower parts of the basin hydrogeological controls lead to the ne of the lower basin and beyond it in the last zone there are abundant lagoons and seasonal flooding is frequent making evapoconcentration an important process for groundwater mineralization the main hydrogeochemical processes involved in both f and as distribution are cation exchange with na release and ca uptake carbonate dissolution and ph increase arsenic release induced by redox processes may play to the ne but its results would be masked by the effect of evaporation

hydrochemistry and quality of groundwater in alluvial aquifer of karonga malawi this study highlights the quality of groundwater for both drinking and irrigation in karonga north where subsistence and commercial farming is practiced all major groundwater quality descriptors and selected trace elements iron manganese arsenic and aluminum were studied the study demonstrated evidence of higher concentrations of bicarbonates 60 590 mg l total iron 2 2 5336 g l total manganese 0 1 804 g l and total arsenic 0 4 14 5 g l in certain samples with low values of eh 32 0 to 25 8 and no3 8 2 mg l against who standards thirty six percent of samples were rated as poor using the water quality index wqi criteria no scaling potential was observed using the langelier analysis the majority of samples were of the mixed bicarbonate type with the abundance order of cations as ca2 na mg2 k carbonate dissolution silicate weathering and cation exchange were identified as possible main geochemical control mechanisms the sources responsible for fluoride and nitrate include anthropogenic activities and rock water interaction dissolution precipitation and ph control the levels of as fe and mn

box cores from the equatorial pacific 14c sedimentation rates and benthic mixing abstract carbon 14 determinations on box cores of calcareous ooze from the western and eastern equatorial pacific suggest that patterns of mixed layer ages sedimentation rates and mixed layer thicknesses are controlled by gradients of carbonate dissolution and fertility and by small scale redeposition processes mixed layer ages range from 3000 to 7000 years with a mode between 4000 and 5000 years sedimentation rates range from 0 8 to 2 4 cm 1000 years mixed layer depths calculated according to the box model of mixing range from 7 cm to 16 cm observed thicknesses are about one fourth smaller than calculated ones

sources distributions of fluoride in waters and its influencing factors from an endemic fluorosis region in central guizhou china the use of high fluoride content coal caused the severe coal burning endemic fluorosis in zhijin county guizhou province china the long term mine exploitation in this region is as an important source of acid mine drainage amd and leads to the release of potential fluoride f into the surrounding waters aiming to investigate the source hydrogeochemical characteristics and influencing factors of fluoride in waters of this area a hydrogeological and geochemical research has been conducted in this study samples of various types of waters were collected and analyzed for major cations major anions and tfe al selected coal and gangue samples were analyzed for fluoride contents the f concentration in amd or amd affected waters ranged from 0 27 to 4 94 mg l and f was mainly enriched in na so4 and mg so4 waters but a relatively low f concentration was found in the ca so4 water the f concentration in the ca hco3 water without being affected by amd ranged from 0 01 to 0 20 mg l the elevated f contents were found in the amd which is mainly influenced by the local coal mining activities and it is resulted from the dissolution of fluoride bearing minerals in coal bearing clastic rocks as well as the low ph values high al and fe concentrations high total dissolved solids and high al f ratio of the amd in addition the dissolution precipitation of carbonate rocks and special hydrogeological conditions determined the f concentration in surface water meanwhile the climate is also an influencing factor that cannot be ignored to affect the f concentrations of surface water and groundwater

age and regional tectonic and metallogenetic implications of igneous activity and mineralization in the andahuaylas yauri belt of southern peru