14c offsets and apparently non synchronous δ18o stratigraphies between nannofossil and foraminiferal pelagic carbonates abstract multiple stratigraphies of subtropical south atlantic cores reveal significant stratigraphic discrepancies between the nannofossil and the foraminiferal carbonates variations in the stratigraphic signals carried in the nannofossil dominated 38 m fraction were measured with detailed stratigraphies of 18o 13c 14c grain size percentage carbonate percentage aragonite and taxonomic composition across the last deglaciation in inmd box core 111 no 9 three other cores inmd box cores 113 and 115 and v 22 174 also from the shallow flanks of the mid atlantic ridge in the south atlantic 10 17 s contain similar stratigraphies indicating that these cores represent regional patterns the onset of the deglacial 18o shift in foraminiferal carbonate occurs 6 to 20 cm deeper than the 18o shift in the nannofossil fraction nineteen accelerator mass spectrometer 14c dates of various fractions 355 m and g ruber from inmd box 111 show that the components within an individual core slice may differ by up to 4900 14c years twelve traditional 14c dates determined by beta counting of the 38 and

carbon dioxide reaction processes in a model brine aquifer at 200 c and 200 bars implications for geologic sequestration of carbon the reactive behavior of supercritical co2 under conditions relevant to geologic storage and sequestration of c is largely unknown experiments were conducted in a flexible cell hydrothermal apparatus to determine the extent of fluid rock reactions in addition to carbonate mineral precipitation that may occur in a brine aquifer aquitard system that simulates a saline aquifer storage scenario the system was held at 200 c and 200 bars for 59 days 1413 h to approach steady state then injected with co2 and allowed to react for another 80 days 1924 h in addition to magnesite precipitation silicate minerals quartz plagioclase microcline and biotite in the aquifer and the aquitard display textures etch pits mineralization indicating significant reaction changes in elemental abundances in the brine following addition of co2 include ph decrease and enrichment in cl partly due to supercritical co2 desiccation of the brine geologic sequestration systems have potential for geochemical reactions that extend beyond simple aqueous dissolution of co2 and precipitation of carbonate these reactions may produce geochemical and geotechnical consequences for sequestration and provide important characteristics for monitoring and evaluation of stored co2 a n understanding of multi phase equilibrium relationships between supercritical co2 and aquifer brine systems also raises new questions for a variety of geologic systems multi phase fluid equilibria may for example account for the large amounts and heterogeneous distributions of calcite cement in a wide variety of geologic systems particularly in sedimentary basin sandstones published by elsevier science ltd

progressive dissolution of fine carbonate particles in pelagic sediments abstract large systematic variations occur in the proportion of coccolith sized carbonate particles relative to other types of carbonate particles within the

geochemical evolution of groundwater in the carbonate aquifers of sierra de segura betic cordillera southern spain summary sierra de segura betic cordillera with a total area of over 3000 km 2 is the source of the two principal rivers in southern spain the guadalquivir and the segura due to the orographic effect of these mountains precipitations are considerably more abundant than in nearby lowland areas where the climate is semi arid sierra de segura is constituted of mesozoic and cenozoic sedimentary rocks among which there are thick limestone dolomitic formations which have given rise to extensive outcrops of permeable materials in geomorphological terms there is a large plateau intensively karstified that constitutes the main recharge area discharge takes place via a large number of springs of which the 50 most important add up to a mean spring flow of about 13 500 l s the active geochemical processes in aquifers of sierra de segura with their corresponding time sequence are dissolution of co 2 dissolution of calcite incongruent dissolution of dolomite dedolomitization exsolution of co 2 and precipitation of calcite more evolved water has higher temperature magnesium content and mg ca ratio therefore these parameters can be utilised as indicators of the degree of hydrochemical evolution in addition a good correlation between water temperature and magnesium concentration or mg ca ratio indicates that an increase in temperature accelerates the kinetics of the dissolution of dolomite finally the distribution of the temperatures in the vadose zone determined by atmospheric thermal gradient implies an apparent stratification of the predominant hydrochemical processes and of the groundwater physical and chemical characteristics

mercia mudstone formation caprock to carbon capture and storage sites petrology and petrophysical characteristics porous rocks in the subsurface are now used for carbon capture and storage ccs to help ameliorate the effects of greenhouse gas emissions these porous reservoir rocks require a caprock to retain the co 2 it is important to characterize caprock quality and its stability in the presence of elevated partial pressures of co 2 lower triassic sandstones are common in the uk and nw europe and are being considered for future ccs projects the caprock to these sandstones is the middle and upper triassic mercia mudstone group we have studied the mercia mudstone using mineralogy petrology and mercury injection porosimetry to assess its caprock quality detrital minerals are dominated by quartz k feldspar illite and chlorite diagenetic pore filling minerals are dominated by calcite dolomite and gypsum in samples with abundant clay minerals there are only small quantities of pore filling diagenetic cements porosity is broadly uniform for both clay rich and clay poor samples the cleaner clay poor samples had their initial pore spaces filled with early diagenetic pore filling carbonates and gypsum despite the broadly uniform porosity mean pore throat diameter displays a strong inverse correlation with clay content whereas threshold capillary entry pressure shows a strong positive correlation with clay content the more clay rich samples represent much better caprock than the coarser grained samples that contain abundant pore filling cement the samples could support potential column heights of supercritical co 2 between 70 and 540 m and have calculated permeabilities between 10 20 and 10 19 m 2 leakage would occur only on geological time scales assuming that these samples are representative of the whole caprock because caprock quality correlates with illite content and illite will be relatively immune to elevated partial pressures of co 2 the mercia mudstone probably represents a durable caprock for future lower triassic sandstone ccs projects

hydrogeochemical modeling of a thermal system and lessons learned for co2 geologic storage abstract geological storage of carbon dioxide is presently considered to be one of the main strategies to mitigate the impact of the emissions of this gas on global warming among the various alternatives considered for co 2 geological storage one of the main geological candidates for hosting injected co 2 in the long term are deep porous reservoir rock formations saturated with brackish or saline solutions although valuable information on the expected hydrogeochemical processes involved in the co 2 storage in such deep saline aquifers can be obtained in laboratory or modeling studies the only direct source of information about the long term behavior of geological storages for co 2 in deep aquifers is natural analogues in this work a classical and simple geochemical methodology is successfully applied to the study of the features and hydrogeochemical processes determining the evolution of a spanish thermal system the alhama jaraba complex which can be considered as a natural analogue for deep geological co 2 storage in carbonate rocks the geology structure depth and hydrogeochemistry of the alhama jaraba thermal system are very similar to the expected features of a potential co 2 reservoir in carbonate materials the processes determining the hydrogeochemical evolution in the alhama jaraba thermal system have been successfully identified and quantified with the assistance of ion ion plots speciation solubility calculations and mass balance calculations furthermore the feasibility of the proposed conceptual hydrogeochemical model for this system has been verified by using reaction path calculations mass balance calculation results have indicated that the observed hydrogeochemical evolution between springs is mainly due to halite dissolution and dedolomitization triggered by gypsum or anhydrite dissolution co 2 g mass transfer has been estimated to be negligible which suggests that the main processes responsible for the variation in the tic and the co 2 g pressure during deep circulation are dissolution and precipitation reactions for carbonate minerals all the processes identified in the alhama jaraba thermal system are relevant for the long term evolution of a deep co 2 storage site hosted by carbonate rocks as shown in this study the application of classical geochemical tools provides an excellent starting point for understanding the behavior of prospective storage systems moreover the existence of dedolomitization is very relevant for the hydraulic properties of carbonate aquifers potentially used for co 2 geological storage because of the effects on porosity and therefore permeability during the long term evolution of such systems furthermore dedolomitization may represent a mechanism of mineral trapping for co 2 sequestration under certain conditions

paleoceanographic implications of the difference in deep sea sediment mixing between large and fine particles more and more paleoceanographic studies are performed on different size fractions of deep sea sediments although it has been a controversial issue for some time the bioturbation process depends on the particle size and can in principle decouple paleoceanographic records obtained in the same core this problem is studied by using a simple mixing model which allows the derivation of analytical equations for both the expected phase shift and relative attenuation of signals carried by different size fractions depending on several parameters the time shift and relative attenuation can be on the order of a few millenia and 50 respectively however high sedimentation rates 10 20 cm kyr minimize these potential complications allowing us to study millenium scale events in well chosen sedimentary environments

recent increase in pacific caco3 dissolution a mechanism for generating old 14c ages abstract western equatorial pacific box cores taken from water depths greater than 4 km show increased dissolution and anomalously old 14c ages in the upper 8 cm the temporal response of the vertical distribution of sediment carbonate fraction and 14c age to a decrease in the dissolved carbonate ion concentration of the deep sea is examined with a diffusion advection dissolution model the nature of this response is highly sensitive to both the magnitude of the dissolved carbonate ion decrease and the rate of mixing of the upper few centimeters of sediment if the sediment is initially calcareous and the increase in undersaturation is sufficient to eventually dissolve away most of the solid carbonate the system relaxes on a very long time scale greater than 10 000 years the dissolution flux in such a case temporally is greater than the total sedimentation input and chemical erosion occurs the cumulative erosion is about 4 times greater for strong sediment mixing d 200 cm 2 ka 1 than for weak mixing d 2 cm2 ka 1 the chemical erosion causes old carbonate to be transferred into the sediment mixed layer as the interface moves downwards thus the 14 c 12 c ratio initially decreases when erosion decreases because the surface carbonate content is diminished the 14c age of the sediment continues to become older in the case of weak mixing but reverses itself and becomes younger in the presence of moderate or strong mixing an attempt to predict the observed caco3 and 14 c 12 c in west equatorial pacific sediment suggests that beginning a few thousand years ago the deep pacific was 20 more undersaturated than today for about 1500 yrs this could possibly have been caused by late holocene growth of coral reefs following after the deglaciation

chronology for climate change developing age models for the biogeochemical ocean flux study cores we construct age models for a suite of cores from the northeast atlantic ocean by means of accelerator mass spectrometer dating of a key core bofs 5k and correlation with the rest of the suite the effects of bioturbation and foraminiferal species abundance gradients upon the age record are modeled using a simple equation the degree of bioturbation is estimated by comparing modeled profiles with dispersal of the vedde ash layer in core 5k and we find a mixing depth of roughly 8 cm for sand sized material using this value we estimate that age offsets between unbioturbated sediment and some foraminifera species after mixing may be up to 2500 years with lesser effect on fine carbonate 10 mu m ages the bioturbation model illustrates problems associated with the dating of instantaneous events such as ash layers and the heinrich peaks of ice rafted detritus correlations between core 5k and the other cores from the bofs suite are made on the basis of similarities in the downcore profiles of oxygen and carbon isotopes magnetic susceptibility water and carbonate content and via marker horizons in x radiographs and ash beds

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

quaternary surface water stable isotope signal from calcareous nannofossils at dsdp site 593 southern tasman sea oxygen isotope values from calcareous nannofossils in four cores spanning the quaternary from dsdp site 593 in tasman sea are compared with the 18o signal of planktonic and benthic foraminifers from the same samples the classic mid late quaternary isotope stages are exhibited with stage 12 particularly well developed when 18o values of nannofossils are adjusted for coccolithophore vital effects they indicate larger by 1 6 c surface to bottom paleotemperature gradients and greater by 1 3 c changes in mean sea surface temperature between full glacial and interglacial conditions than do 18o values from planktonic foraminifers along with the foraminifers the nannofossils record a bimodal distribution of 18o between the early and mid late quaternary indicating a significant change in global ice budget the 13c of nannofossils also shows a bimodal distribution but is opposite to that for the foraminifers nannofossil 18o values record a shift of 0 8 at isotope stage 8 corresponding to a major reduction in abundance of the previously dominant gephyrocapsids a shift in 13c of 1 5 also occurs at stage 8 and a shift in 13c of 1 2 at around stage 14 the 18o shift in nannofossils is at least a pacific wide phenomenon the 13c shifts are possibly global the 13c signal of nannofossils exhibits an antipathetic relationship to that of benthic foraminifers back to isotope stage 18 but no significant correlation beyond this level to the base of the quaternary this is interpreted as reflecting local productivity dominating global influences on 13c since stage 18 at dsdp site 593 the difference between nannofossil and benthic foraminifer 13c signals 13c tends to be maximum during glacial stages and minimum during interglacials throughout the section showing a strong correlation with the nannofossil 18o signal the increased partitioning of 13c between surface and bottom waters during the glacial periods may indicate heightened productivity in surface waters in the southern tasman sea at these times

direct dating of the oxygen isotope record of the last deglaciation by 14c accelerator mass spectrometry major trends of quaternary global climate are reflected in the continental ice volume changes which have been reconstructed by oxygen isotope analysis1 2 18o records from deep sea sediments show that the net glacial build up occurs relatively slowly3 but that the end of an ice age occurs quickly in less than 10 000 yr implying a nonlinear response4 5 to simple milankovitch theory6 the latter observation suggests that the cause of the most recent deglaciation was the maximum in summer calorific radiation at the upper latitudes of the northern hemisphere centred around 11 000 yr ago a view supported by early studies7 later work has produced conflicting dates the main source of confusion being problems with obtaining accurate and reliable dates here by using accelerator mass spectrometry we have measured 14c for various species of foraminifera to produce a reliable timescale for the oxygen isotope record our results show that at the end of the last ice age continental ice sheets began to melt more than 4 000 yr before the northern hemisphere maximum of summer calorific radiation

two step deglaciation 14c dated high resolution δ18o records from the tropical atlantic ocean abstract eight box cores from the tropical atlantic were studied in detail with regard to foraminiferal oxygen isotopes radiocarbon and globorotalia menardii abundance a standard atlantic oxygen isotope signal was reconstructed for the last 20 000 yr it is quite similar to the west equatorial pacific signal published previously deglaciation is seen to occur in two steps which are separated by a pause onset of deglaciation is after 15 000 yr b p the pause is centered between 11 000 and 12 000 yr b p but may be correlative with the younger dryas 10 500 yr b p if allowance is made for a scale shift due to mixing processes on the sea floor step 2 is centered near 10 000 yr b p and is followed by a brief excursion toward light oxygen values this excursion the m event may correlate with the gulf of mexico meltwater spike

playa lake and sheetflood deposits of the upper cretaceous jindong formation korea occurrences and palaeoenvironments abstract lake model of the upper cretaceous jindong formation in korea was established on the basis of sedimentological and palaeobiological records of the playa lake and sheetflood deposits and their palaeoenvironmental implications the playa lake and sheetflood deposits of the jindong formation are characterized by the common presence of traces of vanished evaporites complicated polygonal desiccation cracks and rainprints the pedogenic carbonate development and the preservation of invertebrate traces and dinosaur and bird tracks the traces of vanished evaporites including halite and sulphate evaporite occur as evaporite pseudopmorphs and moulds the occurrence of all of the evaporite minerals as traces suggests that flooding stages persisted much longer than evaporation and desiccation stages invertebrates birds and dinosaurs inhabited the playa lake environment of the upper cretaceous jindong lake the jindong lake formed by the combination of humid source area and arid depositional site due to an orographic effect in fault bounded basin extensive development of the playa lake and sheetflood deposits with evaporite mineral casts and very limited association of shoreline deposits in the jindong formation are characteristic of closed lake and the jindong lake is compared to a lake formed in partly drained closed basin the aggradation of mudflat deposits indicates continued subsidence of the basin and continuation of an underfilled lake basin the jindong lake expanded and stabilized as a playa lake surrounded by dry to saline mudflats and palaeoclimate and subsidence rates changed little throughout the period of the jindong lake development

screening and ranking of sedimentary basins for sequestration of co2 in geological media in response to climate change sedimentary basins are suitable to different degrees for co2 geological sequestration as a result of various intrinsic and extrinsic characteristics of which the geothermal regime is one of the most important warm basins are less favorable for co2 sequestration than cold basins because of reduced capacity in terms of co2 mass and because of higher co2 buoyancy which drives the upward co2 migration a set of 15 criteria with several classes each has been developed for the assessment and ranking of sedimentary basins in terms of their suitability for co2 sequestration using a parametric normalization procedure a basin s individual scores are summed to a total score using weights that express the relative importance of different criteria the total score is ranked to determine the most suitable basin or region thereof for the geological sequestration of co2 the method is extremely flexible in that it allows changes in the functions that express the importance of various classes for any given criterion and in the weights that express the relative importance of various criteria examples of application are given for canada s case and for the alberta basin in canada

hydrogeochemical processes in clastic sedimentary rocks south korea a natural analogue study of the role of dedolomitization in geologic carbon storage abstract for long term mineral trapping of sequestered co 2 in deep saline aquifers base cations such as ca 2 and mg 2 are essential as a natural analogue study of geologic carbon storage in deep aquifers hosted in sedimentary formations we examined the hydrochemistry of sulfate rich up to 1140 mg l so 4 2 and moderately high p co 2 10 1 1 to 10 2 4 atm groundwater in a cretaceous non marine sedimentary basin in south korea with the objective to elucidate water rock interactions controlling the concentrations and behavior of base cations principal component analysis of the acquired hydrochemical data indicated that dissolution of carbonates calcite and dolomite and evaporite minerals halite and gypsum controls the chemical composition of groundwater resulting in substantial increases of the concentration s of ca 2 mg 2 na cl so 4 2 and total dissolved solids tds in deep groundwater na versus cl and ca 2 mg 2 versus hco 3 so 4 2 plots provided evidence for dissolution of halite and gypsum progressively increasing 34 s values of dissolved so 4 2 from 15 1 to 19 2 with increasing sulfate concentrations indicated gypsum dissolution ion ion plots esp mg 2 ca 2 ca 2 so 4 2 and mg 2 so 4 2 and saturation indices of calcite dolomite and gypsum suggest that the groundwater chemistry esp the concentrations of ca 2 and mg 2 is controlled by dedolomitization driven by gypsum dissolution groundwater in the study area does not reach complete equilibrium with respect to calcite and dolomite because of gypsum dissolution which controls the mg 2 ca 2 ratios of groundwater continued calcite precipitation triggered by an excess ca supply from gypsum dissolution reduces the concentrations of dissolved inorganic carbon dic in groundwater the increase of 13 c dic values from 11 1 to 6 5 concomitantly with increasing sulfate concentration was explained via geochemical modeling by dedolomitization under the rate constant ratio of about 0 038 between dolomite and calcite the model results agree well with the observed mg 2 ca 2 ratios and further suggest a potential increase of the void volume in the aquifer through dedolomitization by about 0 72 cm 3 l based on this analogue we suggest that dedolomitization in concert with dissolution of gypsum may constitute an important process releasing base cations for mineral trapping of injected co 2 in non marine clastic sedimentary strata containing carbonates and gypsum in south korea and elsewhere

stable isotopic fractionation among particles in quaternary coccolith sized deep sea sediments oxygen and carbon isotopic ratios of individual grain size splits of the 38 m fraction of deep sea carbonate particles vary systematically with size over a range of 1 25 4 0 most splits are dominated by just a few coccolith taxa and other types of particles the 18o and 13c values of individual splits are linearly related to each other with a slope of 1 5 13c 18o in all holocene and glacial samples analyzed although the observed variability is less than predicted from culture experiments of individual components compositional variations can significantly influence the stable isotopic stratigraphies measured on the nannofossil fraction

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

isotopic and biostratigraphical records of calcareous nannofossils in a pleistocene core knowledge of the species composition is essential for the isotopic record of polyspecific coccolith assemblages in deep sea sediments to be interpreted properly we have determined the carbon and oxygen isotopic composition as well as the relative abundance of coccolith species on the 3 25 m fractions of the caribbean core p6304 4 the dominant taxon in all samples is well preserved gephyrocapsa spp oxygen isotope variations clearly define glacial interglacial oscillations except in the upper part of the core carbon isotopic compositions are not related to the oxygen isotope stratigraphy the occurrence of three coccolith datum levels in the core correlates almost exactly with globally synchronous horizons1 the amplitude of the coccolith 18o record 2 4 is significantly greater than that for the planktonic foraminifera globigerinoides sacculifer in p6304 4 and adjacent cores2 4 we suggest here that selective dissolution or deep calcification during interglacials reduced the amplitudes of g sacculifer in these cores and that the coccolith record is a more reliable indicator of temperature and 18o changes in surface seawater

traces of evaporites in upper cretaceous lacustrine deposits of korea origin and paleoenvironmental implications abstract diverse types of halite and sulfate evaporite traces occur in the upper cretaceous lacustrine deposits of the jindong formation and the jangdong tuff in korea in which dinosaur tracks are common the halite traces usually occur as casts or moulds and they include traces of primary halite hoppers primary and intrasedimentary skeletal halite and intrasedimentary tiny halite the sulfate traces occur as intrasedimentary and displacive casts filled with sediments and sparry calcite and the casts occur as diverse modes from single crystal casts through nodular aggregates to massive aggregates some aggregates of the sulfate casts are aligned in crack pattern and selective occurrence of the laths in ripple troughs are observed soluble sulfate evaporite minerals such as gypsum glauberite or mirabilite are probable for the precursors of these traces these halite and sulfate traces are interpreted to have been formed in a saline lake and mudflats it is interpreted that meteoric water was responsible for the evaporite precipitation in the jindong lake and jangdong lake recycled brine produced by the repeated dissolution of evaporites might contribute to the evaporite precipitation in the paleo jindong lake and the paleo jangdong lake the development of saline lake deposits in the jindong formation and the jangdong tuff suggests that the southern part of the korean peninsula remained an inland continental area during the cretaceous resulting in semi arid paleoclimatic condition due to an orographic effect by the location of the korean peninsula on continental margin in mid latitude with topographic barriers during the cretaceous the occurrence of dinosaur tracks in the lake margin deposits of saline lake with frequent inflow of dilute meteoric water suggests that upper cretaceous dinosaurs inhabiting lakes on the korean peninsula might have drunken brackish water

palaeogroundwater evolution in playa lake environments sedimentary facies and stable isotope record palaeogene almazan basin spain the palaeogene history of the almazan basin is that of a non marine basin sediments derived from fluvial distributary systems and lateral playa lakes the coeval uplifting of the cameros massif and the aragonian branch of the iberian chain during alpine compression exposed triassic evaporites which became the main source of sulphates to the playa lake system as recorded by the bordalba formation this unit exhibits the classical facies distribution of gypsum precipitating playa lakes which can be grouped into two main settings 1 distal alluvial mud flat and 2 saline mud flat ephemeral lake the stable isotope data for gypsum from the distal alluvial mud flat areas 12 2 18osmow 16 5 10 8 34scdt 13 0 lie within the range of values of neighbouring triassic gypsum or are slightly lower for 34scdt this agrees with palaeogeographical interpretations suggesting that the triassic evaporites were the source of gypsum for the almazan basin the slightly lower values could be explained in terms of a minor contribution through the oxidation and dissolution of palaeozoic derived sulphides the isotopic values for gypsum of the saline mud flat ephemeral lake environments 19 8 18osmow 23 82 15 6 34scdt 19 9 are higher than those of the distal alluvial mud flat the higher 18osmow in the saline mud flat ephemeral lake environments is interpreted as being a consequence of the progressive evaporation of shallow groundwaters from proximal to distal areas the heavier values for the 34scdt in the saline mud flat ephemeral lake environments are interpreted as reflecting the activity of sulphate reducing bacteria which is evidenced by spheroidal dolomite aggregates on gypsum crystals and by the grey colours of the gypsum facies

direct assessment of stable isotope variability in planktonic foraminifera populations abstract a large number of tests of three species of planktonic foraminifera globigerinoides sacculifer orbulina universa and pulleniatina obliquiloculata were analyzed for stable oxygen and carbon isotopes in a western equatorial pacific box core estimates of population variance were calculated using a statistical technique known as the jackknife these estimates were used to generate sampling curves which provide the number of foraminiferal tests required in an isotopic analysis when precision and reliability criteria are specified the jackknife results have important sampling implications 1 a large number of foraminiferal tests are required to obtain statistically reliable isotope data for example given a machine precision standard deviation of 0 09in0 417 tests g sacculifer 355 420 m are required to obtain a 18 o precision of 0 1in0 with 90 reliability 2 variance is a function of test diameter with greater variance being found in larger size fractions 3 variance is dependent on foraminiferal species 4 variance differences between glacial and interglacial samples are not significant 5 in the size interval 600 900 m a systematic relationship is not seen between size and 18 o or 13 c 6 replicate analysis is a practical method of improving isotope data quality size and species related variance differences are probably related to a number of factors including depth habitat seasonal production of tests species vertical migrations and vital and or symbiosis caused effects knowledge of data variance permits error assessment in sediment unmixing analyses and optimization of spectral estimates

bioturbational mixing depth and carbon flux at the seafloor radiocarbon dating series bulk sediment and organic carbon flux from various atlantic deep sea regions reveal that the thickness of the bioturbated zone increases by 2 cm if food supply increases by 1 gcm 2yr 1 r 0 8 bulk sediment accumulation rates do not influence the depth of bioturbational mixing under normal pelagic sedimentary conditions we believe that this relationship between nutrient supply and benthic mixing can be used for a quantitative and time variable unmixing procedure to improve high resolution stratigraphic correlations and paleoclimatic interpretations of deep sea records

oriented chromite diopside symplectic inclusions in olivine from lunar regolith delivered by luna 24 mission abstract calcium chromium rich lamellae in olivine grain no 1611 from the luna 24 regolith were studied with feg empa and tem the lamellae consist of a worm like intergrowth of fecr 2 o 4 chromite chr and camgsi 2 o 6 diopside di with a chr di modal proportion of 1 3 the linear extension of the lamellae and crystallographic orientation relationships among the symplectite phases and the olivine suggest that the lamellae nucleated at deformation defects in the olivine host calcium depletion haloes surrounding the lamellae amount to about 75 m and indicate that the chromite diopside lamellae were formed by segregation of calcium and chromium from the host olivine into the lamellae without addition of calcium and or chromium from outside the olivine the segregation of calcium and chromium and consequently the growth of the symplectic lamellae were diffusion controlled the segregation of a calcium chromium component from the host olivine was associated with oxidation of divalent to trivalent chromium oxidation was facilitated by dehydrogenation which was driven by decompression and or a change in redox potential hydrogen point defects in the original olivine with h substituting for divalent cations on the m sites provided the necessary electron acceptors for the oxidation of chromium and after electron transfer left olivine as molecular h 2 the internal microstructure of the lamellae suggests that exsolution of the calcium chromium rich lamellae from the host olivine and formation of the chromite diopside symplectic intergrowth occurred simultaneously the time scale derived from diffusion modeling of the calcium depletion haloes around the lamellae indicates a thermal event on the order of several months to several hundred years at most symplectic inclusions found in olivine from lunar martian and terrestrial rocks are similar with respect to their shape crystallographic orientation relationships and internal microstructure of the spinel clinopyroxene intergrowth these features are inconsistent with dry olivine oxidation that is by the uptake of oxygen dehydrogenation of oh bearing precursor olivine is suggested as a general mechanism of oxidation accompanied by chemical segregation and phase separation resulting in symplectite formation

sodium sulphate deposits of neogene age the kirmir formation beypazari basin turkey the evaporite member of the kirmir formation was deposited in shallow lacustrine environments during the upper miocene the most soluble minerals of this member can be currently observed in the cayirhan mine the evaporite member which is composed of secondary gypsum at outcrop can be subdivided into a bedded lower unit and a massive upper unit in the bedded lower unit most of the gypsum throughout the basin can be identified as having been transformed from glauberite in the glauberite layers of the cayirhan mine some glauberite textures clear glauberite suggest a primary subaqueous free precipitation on a depositional floor more common however are the glauberite textures indicating an interstitial growth within a clayey magnesitic matrix in the thenardite layers accompanying the glauberite in the cayirhan mine some disruption structures can be assigned to synsedimentary dissolution these structures together with the textures of the thenardite suggest that the original sodium sulphate was mirabilite thenardite being a secondary phase which formed during early to moderate burial diagenesis the massive upper unit in which evidence of sodium bearing minerals is absent is characterized by laminated to banded gypsum and nodular gypsum in the marginal areas of the evaporitic basin whereas thick clast supported gypsum breccias prevail in the northern deeper part of the basin the brecciation of these calcium sulphate layers occurred as a result of synsedimentary gravitative slumping under tectonic control although the sulphur isotopic values d 34 s of the sulphates of the kirmir formation suggest a marine derived brine supply the oxygen isotopic values d 18 o and the strontium ratios 87 sr 86 sr do not support such a supply the origin of the mother brines the glauberite genesis the depositional model of the sodium sulphates and the salinity evolution are discussed d 2002 elsevier science b v all rights reserved

geochemistry of regional aquifer systems hosted by carbonate evaporite formations in umbria and southern tuscany central italy abstract in central italy mesozoic carbonates represent the principal reservoir of freshwater of the region the hydrogeological setting is linked to the geological evolution of the apennine chain and is generally characterised by a lower aquifer and one or more shallower aquifers separated by thin aquicludes in these systems groundwater composition is the result of a complex array of regional and local geochemical processes the main geochemical processes are the dissolution of calcite the influx of deeply derived co2 related to a regional process of mantle degassing dedolomitization and mixing with deep saline fluids the occurrence of saline fluids characterised by a na cl hco3 composition is related to the presence of a deep regional aquifer at the base of mesozoic carbonates the extremely high pco2 values computed for the saline waters suggest that the deep aquifer is also a structural trap for the mantle derived co2 during its ascent towards the surface in central italy geological and geophysical data highlight the presence of two different crustal sectors the eastern sector where the geometry of the apennine thrust belt is still preserved and the western sector where the compressive structures are dislocated by important extensional deformations in the western sector the normal faults disrupting the compressive structures allow the mixing of the deep na cl hco3 fluids with the shallow groundwater causing a salinity increase and the natural deterioration of groundwater quality

timing of deglaciation from an oxygen isotope curve for atlantic deep sea sediments the exact timing of deglaciation is an important issue in the context of climatic feedback involving the deglacial rise in atmospheric co2 seen in ice cores1 4 we have produced evidence from box cores taken in the equatorial atlantic that the last deglaciation occurred in two major steps which were separated by a brief pause5 here we propose that this pause is equivalent to the period of glacial readvance known as younger dryas which lasted from about 11 to 10 kyr bp if our correlation is correct then the initiation of deglaciation occurred after 14 kyr bp which disagrees with most other deep sea timescales

radiocarbon age of last glacial pacific deep water one of the most important projects envisaged ever since the possibility emerged of making tandem accelerator mass spectrometric radiocarbon determinations has been that of investigating changes in the radiocarbon age of the deep ocean1 initial attempts to achieve this2 were thwarted by difficulties imposed by bioturbation because these workers used core v28 238 with an accumulation rate of only 1 5 cm kyr 1 thus emphasizing the need to work in a core with a higher accumulation rate working in the glacial section of core tr163 31b with an accumulation of 10 cm kyr 1 we show here that the ventilation age of pacific deep water was about 500 years greater in last glacial times than it is today

the sedimentary record of pelagic biogeography abstract sedimentary remains of fossilizable marine organisms chiefly microplanktonic ones coccolithophorids silicoflagellates diatoms dinoflagellates radiolarians foraminifers have long been used for biogeographic surveys usually with the aim of unravelling paleoenvironmental settings utilization of bottom deposits rather than plankton samples has some advantages for this purpose thanatocoenoses require smaller sample sizes materials are more readily available and they eliminate the small time scale variability which obscures long term trends on the other hand the sedimentary imprint of planktonic distributional patterns is often severely distorted by fragmentation and dissolution of the biogenic remains reworking of sediments winnowing and lateral advection of shells especially toward lower latitudes seasonally and interannually variable output rates and the integration of vertically heterogeneous assemblages the biases derived from these processes are reviewed and the need for more information on selective dissolution vertical distribution patterns and planktonic reproduction and output rates is stressed given the assumptions used in paleoenvironmental studies distributional information drawn from sediment samples is less prone to yielding biased information when applied to these surveys than to bio or paleobiogeographic investigations albeit the former can also be significantly affected as a result of changes in the traits that govern the formation of biogenic sediments

preliminary estimates for the radiocarbon age of deep water in the glacial ocean radiocarbon ages for benthic and planktonic foraminifera from the late glacial sections of two atlantic and two pacific cores are reported the differences for benthic planktonic pairs suggest that the radiocarbon age for deep atlantic water was somewhat larger than today s i e 600 250 as opposed to 400 years and that the radiocarbon age for deep pacific water was also slightly larger than today s 2100 400 as opposed to 1600 years our results suggest that during glacial time the deep pacific was as it is today significantly depleted in radiocarbon relative to the deep atlantic as many questions remain unanswered regarding the reliability of this approach these conclusions must be considered to be preliminary

hydrothermal dedolomitisation of carbonate rocks of the paleoproterozoic zaonega formation nw russia implications for the preservation of primary c isotope signals abstract the paleoproterozoic zaonega formation in karelia nw russia has played a key role in understanding the environmental conditions postdating the great oxidation and lomagundi jatuli events its carbonate and organic rich rocks shungite define the postulated shunga event representing an accumulation of very organic rich sediments at c 2 ga and are central in ideas about changing ocean atmosphere composition in the wake of those worldwide biogeochemical phenomena our work focussed on a key interval of carbonate rocks in the upper part of the formation to i obtain new high resolution carbon oxygen and strontium isotope data complemented by detailed petrography and mineralogical characterisation and ii expand upon previous studies by using our data to constrain geochemical modelling and show in greater detail how magmatic hydrothermal fluids induced dedolomitisation and altered geochemical signals our findings show that the 13ccarb of calcite rich intervals are the most altered with values between 16 9 to 0 6 whereas the dolomite dominated parts retain the best preserved i e most original values those define a trend of steadily increasing 13ccarb from 6 to 0 5 which we interpret as a return to normal marine conditions and carbonate carbon values following the lomagundi jatuli event

alkenones as paleoceanographic proxies 1 alkenone derived estimates of temperature and co2 are contributing to our understanding of earth s climate history in order to increase confidence in alkenone based climate proxies we recommend the following actions first the sedimentary component or fraction containing alkenones should be identified in order to assess the impact of horizontal advection and vertical mixing on alkenone derived temperature and co2 estimates second differential mixing rates of alkenone containing particles and sand sized foraminifera should be quantified by independent dating of the two phases until that is accomplished apparent temporal offsets of climate proxies in the two phases should be interpreted cautiously third the stability of the unsaturation ratio and carbon isotopic compositions of alkenones during all phases of diagenesis should be confirmed both field and laboratory observations are required fourth future alkenone investigations should be coupled with other paleoclimate proxy measurements at high deposition rate sites in a variety of oceanographic settings in upwelling regions and in the vicinity of river plumes salinity and nutrient proxies should be measured since changes in these parameters may affect alkenone biosynthesis

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

asynchronous alkenone and foraminifera records from the benguela upwelling system abstract radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies including the investigation of temporal leads and lags the critical assumption is that temporal coupling between foraminifera and other sediment constituents including specific molecular organic compounds biomarkers of marine phytoplankton e g alkenones is maintained in the sediments to test this critical assumption in the benguela upwelling area we have determined radiocarbon ages of total c37 c39 alkenones in 20 samples from two gravity cores and three multicorer cores the cores were retrieved from the continental shelf and slope off namibia and samples were taken from holocene deglacial and last glacial maximum core sections the alkenone radiocarbon ages were compared to those of planktic foraminifera total organic carbon fatty acids and fine grained carbonates from the same samples interestingly the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples such age differences may be the result of different processes bioturbation associated with grain size effects lateral advection of recycled material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes based on the results of this study the age offsets between foraminifera and alkenones in sediments from the upper continental slope off namibia most probably do not result from particle selective bioturbation processes resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm s recorded near the core sites is the more likely explanation our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of alkenone based proxy data observed temporal leads and lags between foraminifera based data and data derived from alkenone measurements may therefore be secondary signals i e the result of processes associated with particle settling and biological activity

34s and 18o in dissolved sulfate as tracers of hydrogeochemical evolution of the triassic carbonate aquifer exposed to intense groundwater exploitation olkusz zawiercie region southern poland abstract the objective of this study was to determine the sources of so 4 2 in groundwater of the olkusz zawiercie major groundwater body the quality of groundwater was relatively good in the past but fluctuations of the water table level have caused degradation of water quality variations in the water table level and the formation of the depression cone have resulted from both groundwater withdrawal and zn pb mine dewatering as a result within the extended vadose zone of the aquifer weathering of pyrite and accompanying sulfides has taken place since 1992 the water table has risen and this process has been associated with an increase in concentrations of so 4 2 ca and mg at the same time the ph has decreased and periodically high fe concentrations have been detected high concentrations of mg and sr have been observed and since gypsum layers are known to be present a de dolomitisation process has been hypothesized the phreeqc program for windows was used to estimate saturation indices for calcite dolomite gypsum and epsomite isotopic data for so 4 2 dissolved in the groundwater and archival data on isotopic composition of ore sulfides were used to solve the isotope balance equation and to estimate the fraction of dissolved so 4 2 that originated from pyrite oxidation and gypsum dissolution the results have shown that dissolution of pyrite oxidation products has a significant influence on chemical composition of groundwater especially in the southern part of the cone of depression by solving the additional combined mass transfer and isotope balance equations it was inferred that a variation in isotopic composition of weathered sulfides must also occur

hydrogeochemistry of groundwaters from carbonate formations with basal gypsiferous layers an example from the mt catria mt nerone ridge northern appennines italy abstract the mt catria mt nerone mesozoic calcareous ridge contains a defined almost isolated hydrogeological system this system is composed of three main superimposed aquifers separated by marly and marly clayey aquicludes which developed in the calcareous and marly calcareous formations of the umbria marche series the lower water circulation occurs in the massiccio formation where ca mg hco 3 waters mix with underlying gypsum saturated waters due to the presence of triassic evaporites giving rise to ca mg hco 3 so 4 up to ca mg so 4 water types the mixing ratio between the two end members or the degree of gypsum dissolution depends on the depth of water circulation and depth of the top of the triassic evaporites recharge areas for these water types are located at the highest elevations on the ridge while discharge areas occur at springs along the slopes of the main reliefs as well as in two deeply eroded valleys waters recharged in the mt nerone area north western side of the ridge appear to be affected by gypsum and dolomite dissolution caused by a direct interaction at depth with the triassic evaporites followed by calcite precipitation in a closed p co 2 system dedolomitization conversely waters recharged in the mt catria area south eastern side of the ridge seem to be affected by gypsum dissolution and calcite precipitation in an open p co 2 system which produces fracture sealing of the upper parts 120 m of the massiccio formation and a confinement of the deep waters the consequent pressurization causes additional gypsum dissolution without calcite precipitation in a closed p co 2 system previous hypotheses of hydraulic continuity of the basal aquifer throughout the calcareous ridge are reconsidered here and a new interpretation based on hydrochemical data is provided

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

role of an impermeable layer in controlling groundwater chemistry in a basaltic aquifer beneath an agricultural field jeju island south korea abstract hydrochemical data major cations and anions and trace metals such as fe mn and v of groundwater n 144 were collected from 15 pre existing wells in the gosan area along the southwestern coast of jeju island south korea between january and october 2010 these were used to investigate the spatio temporal variability of groundwater quality in a basaltic aquifer beneath an agricultural field in the western part of the study area an impermeable clay rich layer gosan formation overlies the basaltic aquifer prohibiting direct recharge from rainwater infiltration and allowing a shallow perched aquifer to form above the formation robust principal component analysis robpca was performed to investigate the hydrochemical characteristics twenty seven outlying samples were separated from the total dataset among these 17 samples reflected seawater effects and seven samples reflected abnormally high impacts from agricultural contamination for the rest regular observations n 117 and a good leverage point robpca showed that principal component pc 1 effectively distinguishes uncontaminated water from those samples reflecting agricultural contamination variables with positive pc 1 loadings tds ca mg no 3 so 4 and cl indicate agricultural contamination while negative pc 1 loadings ph na k hco 3 and v possibly indicate basalt weathering samples with chemistry controlled by agricultural contamination are restricted to the eastern part of the study area while uncontaminated water is predominantly observed in the western part where the gosan formation occurs such a distinct spatial pattern indicates that overall groundwater quality is regulated by the occurrence of the impermeable formation groundwater samples from wells near the edge of the gosan formation show seasonal fluctuations in water quality with factor scores that indicates uncontaminated water in the dry season january to april and agricultural contamination in the wet season may to october this suggests that groundwater below the marginal part of the impermeable layer is seasonally contaminated by a temporal extension of the pollution front during the wet season even though the impermeable layer plays a role as a natural barrier to protect groundwater from the infiltration of surface contaminants this study also shows the advantage of robpca to successfully identify spatio temporal variation of groundwater quality in an area where diverse hydrochemical processes are coexisting and anormalous samples occur

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

comparison of fine fraction with monospecific foraminiferal stable isotopic stratigraphies from pelagic carbonates across the last glacial termination detailed 18o and 13c stratigraphies were measured through the last deglaciation on fine 38 m carbonate material in eleven atlantic two pacific and one caribbean core all cores show the characteristic glacial to holocene decrease in 18o values the mean amplitude of the glacial holocene 18o shifts in open ocean cores is1 57 0 19 pdb in the fine fraction and1 54 0 23 pdb in monospecific foraminifera only the caribbean core had a significantly greater amplitude 2 59 18o pdb thus isotopic stratigraphies of the calcareous nannofossil dominated fine fraction do not generally record an isotopic change which is significantly larger than is recorded in monospecific foraminiferal carbonates from the same cores the fine fraction 13c stratigraphies show no consistent glacial holocene trends

subaerial lenticular cracks in cretaceous lacustrine deposits korea abstract in the cretaceous lacustrine deposits of the yucheon group of korea lenticular cracks are commonly found in the interlaminated to thinly interbedded sandstone mudstone facies the general shape of the cracks is variable many having lenticular shape incomplete development and random distribution in places cracks are orthogonally intersected or polygonally interlinked elongate rhombic to subrhombic hemipyramidal bladed prismatic or swallow tail twin shaped cracks and square cuboid or rectangular sand patches are associated with the lenticular cracks which suggests the former presence of soluble evaporite minerals in the unit layers of the crack bearing deposits sandstones have sharp bases and grade upward into mudstones planar lamination low angle cross lamination and small scale ripples are present mudstone chips some of which preserve the cracks are present in the sandstones these crack bearing layers are interpreted as sheetflood deposits on the basis of these characteristics the lenticular cracks of the yucheon lacustrine deposits in korea are interpreted as subaerial desiccation cracks formed on dried mudflats the similarity between the yucheon lenticular cracks and those described from the devonian lacustrine deposits in scotland astin and rogers 1991 suggests that subaerial lenticular cracks associated with evaporite minerals are not rare in geologic time and space

dolomite dissolution rates and possible holocene dedolomitization of water bearing units in the edwards aquifer south central texas abstract rates of dolomite dissolution can be used to test the concept based on geomorphologic evidence that a major part of the edwards aquifer could have formed within the holocene a timeframe of approximately 10 000 years during formation of the aquifer in the edwards limestone cretaceous albian of the balcones fault zone dolomite dissolution and porosity development were synchronous and the result of mixing zone dedolomitization initiation of the mixing zone in the early holocene 11 000 years before present is suggested by the maximum age of formation of major discharge sites that allowed the influx of meteoric water into brine filled dolomitic preaquifer units dedolomitization the dissolution of dolomite and net precipitation of calcite has left aquifer units that are calcitic and 40 vol interconnected pore space the mass of dolomite missing is obtained by comparison of stratigraphically equivalent altered and unaltered units one dissolution rate 1 76 10 4 mmol dolomite kg h 2 o 1 yr 1 is determined from this mass 10 4 yr reaction time and a log linear function describing the increase in mass discharge three orders of magnitude during aquifer formation the second estimated dissolution rate is obtained from the mass transfer of dolomite to solution calculated from the increase in magnesium in pore fluids selected from the modern aquifer to represent a typical flowpath during aquifer formation a reaction time of 10 4 yr for this mass transfer yields a rate of 0 56 10 4 mmol dolomite kg h 2 o 1 yr 1 both of these rates are comparable to modern rates of dolomite dissolution 0 3 to 4 5 10 4 mmol dolomite kg h 2 o 1 yr 1 calculated from measured reaction times in the tertiary floridan aquifer system in florida and the madison aquifer in the mississippian madison limestone of the northern great plains similarity of these rates to the estimated paleo rates of dolomite dissolution supports a 10 4 yr reaction timeframe the holocene reaction time also can be compared to a series of reaction times calculated by assuming that the mass of dolomite missing from the edwards was removed at rates observed in the floridan and madison aquifers these reaction times for complete removal of dolomite range from 2700 to 58 500 yr and span the pleistocene holocene boundary finally an estimated dolomite reaction rate during dedolomitization of the edwards aquifer based on surface area of exposed dolomite mmol cm 2 s 1 millimoles per square centimeter per second may be approximated from reaction times this rate is directly a function of the mass of dolomite removed and the surface area exposed per pore volume passing through the rock the surface area is available from the observed dolomite rhomb size in unaltered rock the rate of pore fluid movement is obtained from the averaged annual discharge rates during formation of the edwards aquifer calculated from all reaction times range from 10 13 to 10 14 mmol dolomite cm 2 s 1 these rates are faster than rates 10 18 mmol cm 2 s 1 measured in the pure laboratory system camg co 3 2 co 2 h 2 o but slower than rates determined in an alpine stream study 10 10 to 10 11 mmol cm 2 s 1 where cold glacial melt water flows over dolostone dolomite dissolution rates from both the edwards and other aquifers support the concept that a major part of the edwards aquifer could have formed within the holocene