ice sheet evolution in james ross basin weddell sea margin of the antarctic peninsula the seismic stratigraphic record the stratigraphic architecture of the james ross basin nw weddell sea continental shelf shows three major phases of deposition preglacial ice sheet growth and ice sheet dominated the preglacial phase shows stratigraphic sequences that are similar to low latitude margins during the ice sheet growth phase there is evidence for initial ice sheet grounding in the southern part of the basin which migrated in steps northward sediment supply was also high during the ice sheet growth phase during the ice sheet dominated phase both north and south parts of the basin inherited all the classic features indicative of glacial strata large glacial troughs hundreds of meters deep and tens of kilometers wide truncation of sequences overlain by chaotic seismic facies and topped with coherent laminated reflections and an oversteepened continental slope the james ross basin strata are divided into five units s5 s1 each unit is characterized based upon seismic facies and stratigraphic architecture and the age of each unit is inferred from a seismic stratigraphic age model end member strata s5 and s1 were drilled and dated during shaldril and help to constrain this age model in total 34 grounding events of the antarctic peninsula ice sheet apis are recorded on the continental shelf this is similar to the 31 grounding events imaged on the pacific side of the peninsula ice grounding on the continental shelf is shown to have occurred as early as late middle miocene to early late miocene in the southern part of the basin the ice sheet advanced northward to encompass the northern peninsula by late miocene time the seven oldest glacial unconformities are believed to predate all previously identified unconformities on the peninsula continental shelf an expanded section of late pliocene pleistocene deposits shows a minimum of 10 grounding events this record more closely matches the deep sea oxygen isotope record than previous seismic studies of antarctic margins have shown

reply to comment of d w g sears f a hasan b m myers and h sears on update on terrestrial ages of antarctic meteorites

the biotic record of events in the marine realm at the end of the cretaceous calcareous siliceous and organic walled microfossils and macroinvertebrates abstract the calcareous micro and nannoplankton were severely affected at the end of the cretaceous as known from numerous sections but the change was not quite as sudden or drastic as sometimes claimed the organic walled phytoplankton seem to have survived the k t boundary event s better than other plankton little is known about the fate of siliceous plankton from the relatively few more or less complete sections across the k t boundary that are rich in benthic macroinvertebrates it is clear that there was a striking change at species level in some groups which is apparently directly attributable to the disaster that overtook the plankton and hence requires no additional explanation other groups however were already in decline if not completely extinct before the end cretaceous catastrophe took place

groundwater geochemistry of the carbonate karst aquifer southcentral kentucky u s a abstract analyses of 441 water samples from 15 sample sites mainly springs and sinking creeks in the southcentral kentucky karst were used to determine hardness pco2 and state of saturation with respect to calcite and dolomite most of the waters are undersaturated with respect to calcite and more undersaturated with respect to dolomite in agreement with recent kinetic models time series data revealed chemical fluctuations on both weekly and seasonal time scales much of the short term variation and some of the seasonal variation in the hardness and saturation index parameters can be accounted for by dilution effects from storm and seasonal runoff seasonal cycles in co2 partial pressure arise from a dependence of soil co2 on temperature and the growing season waters from different locations in the aquifer system are chemically distinct and fit into the concept of a hydrochemical facies

relation between soil age and silicate weathering rates determined from the chemical evolution of a glacial chronosequence long term weathering rates rlt were determined from base cation depletion in soil profiles developed on six granitic glacial moraines varying in age from 0 4 to 297 ka in the wind river mountains wyoming weathering rates were found to decrease with soil age t according to the power law equation rlt 15 t 0 71 where rlt is in meq m 2 yr 1 and t is in ka comparable data from the literature are consistent with this function and it is similar to power law equations describing changes in laboratory weathering rates with time on the basis of our study we predict that for a catchment unaffected by anthropogenic inputs and in a steady state with respect to the organic and cation exchange pools rlt should be higher than present day weathering rates derived from stream fluxes rpd by a factor of about 3 4

the natural thermoluminescence of antarctic meteorites and their terrestrial ages and orbits a 2010 update abstract we have examined the relationship between natural thermoluminescence tl and 26al in 120 antarctic meteorites in order to explore the orbital history and terrestrial ages of these meteorites our results confirm the observations of hasan et al 1987 which were based on 23 meteorites for most meteorites there was a positive correlation between natural tl and 26al reflecting their similarity in decay rate under antarctic conditions and thus in terrestrial age for a small group with low tl and high 26al a small perihelion was proposed within this group natural tl decreases with terrestrial age as determined by 36cl measurements although the rate of tl decay is faster half life approximately 10 ka and the ages that can be determined are smaller 200 ka than for most meteorites the faster decay rate and lower natural tl levels are a reflection of recent exposure to higher radiation doses and higher temperatures since this history would populate less stable tl traps with smaller electron densities we sort the 120 meteorites by perihelion and terrestrial age the normal perihelion group range up to approximately 1000 ka and the small perihelion group range up to approximately 200 ka an intermediate perihelion group tends to have short terrestrial ages 20 60 ka there is acceptable agreement between most 34 out of 43 of our present terrestrial age estimates and those determined by isotopic means the exceptions reflecting complex irradiation histories long burial times in the antarctic or other issues

constancy of silicate mineral weathering rate ratios between natural and experimental weathering implications for hydrologic control of differences in absolute rates abstract inverse models which apportion watershed effluxes geochemical mass balance over estimated mineral surface area give weathering rates for individual silicate minerals e g feldspar 1 3 orders of magnitude slower than laboratory rates comparisons of rates calculated from several recent watershed geochemical mass balance studies with experimentally determined rates reveal that the ratio of mineral weathering rates for a given silicate mineral pair determined in an internally consistent field study equals the ratio of rates for the same minerals in any internally consistent set of laboratory experimental data thus the coefficient which corrects the weathering rate for any mineral from a laboratory data set to a field setting is identical to the corresponding coefficient for any other mineral in the same data sets the correction factor linking experimental and natural rates must be independent of composition physical e g hydrologic controls rather than compositional or chemical controls cause the difference between weathering rates in nature and the laboratory because flow in natural weathering profiles is spatially heterogeneous not all of the potentially available surface in natural systems actually participates in reactions with pore fluids

the surface area and reactivity of granitic soils i dissolution rates of primary minerals as a function of depth and age deduced from field observations surface area normalised dissolution rates of the primary minerals in two distinct granitic soils located in 1 the dartmoor national park england and 2 glen dye scotland were determined as a function of depth each soil was sampled to a depth of 1 m the maximum soil ages based on 14c analysis of the humin fraction of the soil are 15 600 and 4400 years for the dartmoor and glen dye soil profiles respectively the measured bet surface areas of the soil minerals are close to 5 m2 g in the b and c horizons but decrease to less than 1 m2 g close to the surface retrieved geometric surface area normalised mineral dissolution rates are most rapid at the surface and at the bedrock soil interface this behaviour is interpreted to stem from a combination of the approach to equilibrium of the soil waters with depth and more rapid dissolution rates of fresh versus weathered surfaces at the soil surface the relative mineral dissolution rate order is found to be quartz feldspar mica with quartz geometric surface area dissolution rates as fast as 2 6 to 4 1 10 13 mol m2 s as observed in a number of past studies field based rates obtained in this study are significantly slower than corresponding rates obtained from laboratory studies suggesting that these latter rates may not accurately describe the reactivity of primary minerals in soils

inverse and forward modelling of groundwater circulation in a seismically active area monferrato piedmont nw italy insights into stress induced variations in water chemistry municipality of nizza monferrato asti italy and the regional administration of regione piemonte italy

geochemistry of surface and ground water in guiyang china water rock interaction and pollution in a karst hydrological system the chemical compositions of the surface ground water of guiyang the capital city of guizhou province china are dominated by ca2 mg2 hco3 andso42 which have been derived largely from chemical weathering of carbonate rocks limestone and dolomite the production of so42 has multiple origins mainly from dissolution of sulfate evaporites oxidation of sulfide minerals and organic s in the strata and anthropogenic sources most ground water is exposed to soil co2 and therefore the h2co3 which attacks minerals contains much soil c in addition the h2so4 produced as a result of the oxidation of sulfides in s rich coal seams and or organic s is believed to be associated with the chemical weathering of rocks the major anthropogenic components in the surface and ground water include k na cl so42 andno3 with cl and no3 being the main contributors to ground water pollution in guiyang and its adjacent areas the seasonal variations in concentrations of anthropogenic components demonstrate that the karst ground water system is liable to pollution by human activities the higher content of no3 in ground water compared to surface water during the summer and winter seasons indicates that the karstic ground water system is not capable of denitrification and therefore does not easily recover once contaminated with nitrates

the natural thermoluminescence of meteorites 4 ordinary chondrites at the lewis cliff ice field natural thermoluminescence tl measurements have been made on 302 meteorites from the vicinity of the lewis cliff in the beardmore region of antarctica the data provide information on terrestrial age and unusual radiation and thermal histories which in turn are helpful in identifying fragments of a single fall and in understanding ice sheet movements and the mechanisms by which meteorite concentration occurs at this site the present data with data for induced tl class find location hand specimen descriptions and mineral composition have enabled 70 of the present samples to be assigned to 27 groups of paired meteorites with between 5 and 2 meteorites in each group the distribution of meteorites on the ice the shape of the fields of paired meteorites and trends in the natural tl data indicate that there is a western component to the movement of the ice at this location as well as the previously supposed movement to the north this western vector probably explains the concentration of meteorites along the western edge of the ice tongue meteorites at the northern end of the tongue the lower ice tongue and meteorite moraine to the east have relatively high natural tl and therefore young terrestrial ages while those on the upper tongue show a broad range of ages including a great many large ages details of the meteorite concentration are different on the upper and lower tongue and it might be that these two parts of the ice sheet are unrelated these new natural tl data identify several recent falls and several meteorites which probably had unusually small perihelia immediately prior to capture by the earth

thermoluminescence of meteorites and their terrestrial ages abstract a new technique is described in which the natural thermoluminescence tl in chondritic meteorites is normalized to the tl sensitivity of each meteorite the relationship between the normalized tl level and a meteorite s terrestrial age is examined the average normalized tl level measured in 45 ordinary chondrites of known terrestrial age decreases with increasing terrestrial age there is a factor of ten variation in the tl levels of fresh falls which is primarily due to differences in orbital temperatures melcher 1981 nevertheless it is possible to distinguish between recent falls and meteorites greater than a few hundred years old if they have been stored at the same temperature the decay characteristics of the tl are studied by means of initial rise experiments and isothermal decay experiments at elevated temperatures the tl levels of 11 antarctic meteorites are compared with the results of 14 c 26 al and 36 cl studies of the terrestrial ages of these objects there is a rough correlation between the low temperature tl levels and the radionuclide activities since the tl method is quick and requires as little as 10mg of material it is most valuable as a rapid screening process to select samples appropriate for study by other techniques

the role of dissolution kinetics in the development of karst aquifers in limestone a model simulation of karst evolution to model the development of karst aquifers from primary fissures in limestone rock a numerical model of solutional widening of such fractures by calcite agressive water is suggested the geological setting determines relevant geometrical parameters i e length of the fracture its initial width and the hydraulic gradient driving water from the input to the output to simulate the solutional widening as it proceeds in time the solution rates must be known as a function of concentration c of dissolved calcite they are given as a first order kinetic rate law for c leq k cdot c eq as f 1 alpha 0 c c eq for c k cdot c eq close to equilibrium a fourth order rate law becomes dominant f 4 beta cdot c c eq 4 the parameters alpha 0 beta and k depend on the chemistry of the carbonate system and rock chemistry the saturation concentration c eq with respect to calcite depends on the initial co 2 concentration of the inflowing solution

comment on update on terrestrial ages of antarctic meteorites by k nishiizumi d elmore and p w kubik comment and reply on the paper of k nishiizumi d elmore et p w kubik 1989 earth planet sci lett 93 299 313

basalt water interactions at high temperatures 1 dissolution kinetic experiments of basalt in water and nacl h2o at temperatures up to 400 c 23 mpa and implications abstract kinetic experiments of basaltic rock water and nacl h2o interactions at temperatures from 20 to 400 c were carried out using flow through a backed bed reactor experimental results indicate that all of the metal release rates vary with temperature and that the relative release rates for the various metals in the basaltic rock vary significantly at constant temperature the rock dissolution rate i e the release rate of si increased as the temperature increased from 20 c to 300 c and then decreased as the temperature continued to increase from 300 c to 400 c the release rate of si reached a maximum at 300 c at 350 c in nacl h2o the maximum release rate of al was reached at 350 c release rates of ca mg and fe decreased with increasing temperature from 20 to 300 c or 350 c and generally ca mg fe and al were dissolved more quickly than si at temperatures in the range from 25 to 300 c but more slowly in the range from 300 to 400 c our experiments demonstrated that si will be fixed on the rock surface at temperatures from 100 to 300 c al will be fixed at 200 300 c or 350 c but mg ca and fe will be fixed on the surface at temperatures from 300 to 400 c the experimental results can be used to illustrate the factors controlling alteration zoning in sub sea floor rocks at mid ocean ridges mor and in continental volcanic rocks in the luzong basin yangtze river valley china the results also demonstrate that alteration zoning in basaltic rocks in a geological profile with a temperature gradient is caused by the variable release rates for different metals with temperature strong variations in those release rates always occurred at 300 400 c which reflect changes in the properties of water as it passes from a sub critical to a supercritical state

dust impure calcite and phytoliths modeled alternative sources of chemical weathering solutes in shallow groundwater abstract in highly reactive carbonate terrains that constitute more than one fifth of critical zone landscapes quantifying bedrock weathering processes may require understanding the realities of carbonate mineral impurity on solubility biotically produced minerals as an integral part of leaky biogeochemical cycles and dust deposited minerals as important high surface area first contact solute sources the potential impact of these processes has not been thoroughly investigated as groundwater solutes are mostly thought to be sourced from chemical reactions with soil and bedrock although dust is often viewed as an important delivery mechanism of nutrients to other ecosystems including those in mountain and tropical settings we present results of computer and hand calculated manual inverse modeling of two years of stream water chemistry spanning a dry and a wet year for a groundwater fed headwater stream at the konza tallgrass prairie long term ecological research site in northeastern kansas weathering of the limestone and shale bedrock at the site provide a possible source of solutes to the groundwater fed stream but our modeling suggests an alternate source considering the pathway of groundwater recharge likely encounters highly reactive phases before encountering bedrock we used the mineralogy and geochemistry of local dust collected previously estimates of a possible chemical composition of phytolith containing potassium and an impure calcite representing measured limestone bedrock chemistry to show that chemical reactions with the current dust flux are adequate to account for the groundwater chemistry average annual amounts were about 1 380 kg ha 1 yr 1 dust dissolved 2 80 kg ha 1 yr 1 bedrock carbonate dissolved and 3 320 kg ha 1 yr 1 phytoliths precipitated small amounts of cation exchange were also required to balance the models there were only small differences between the computer and manual inverse models both methods resulted in up to 4 6 times more mass of dust dissolved than bedrock we suggest that dust weathering may be a process that occurs widely considering the ubiquitous dust flux in continental regions significance of research solutes in groundwater and in streams fed by groundwater are thought to be mostly derived from aquifer bedrock and soil water recharging the aquifer this paradigm may fail for landscapes that have been subaerially exposed for 10 s to 100 s of millions of years in terrains where relatively rapid dissolution of minerals dominates such as carbonate mineral dominated rocks like limestone here we test whether dust having high surface area and being the first inorganic solid encountered by meteoric precipitation could provide enough solutes water to reduce the amount of bedrock that dissolves extending the timeframe of landscape evolution we found through inverse modeling with phreeqc that dust can provide 4 6 times as much mass to stream water in merokarst than calcite and that the mass of dust dissolved was the same order of magnitude as local dust deposition these results give permissive evidence that dust is important to understanding groundwater chemistry

dissolution rates of actinolite and chlorite from a whole rock experimental study of metabasalt dissolution from 2 ph 12 at 25 c abstract the dissolution rates of the minerals actinolite and chlorite were determined from metabasalt element release rates measured at 25 c and 2 11 86 mol m 2 s mineral dissolution rates obtained in this study are within the range of corresponding values reported in the literature this observation suggests that the dissolution rates of major constituent minerals in a multi phase rock are not affected by the presence of the other minerals this conclusion validates the common assumption that the dissolution rate of an individual mineral is equal to that of the same mineral in a dissolving multi mineralogic rock at least for major constituents

the impact of dolomite and plagioclase weathering on the chemistry of shallow groundwaters circulating in a granodiorite dominated catchment of the sila massif calabria southern italy abstract this work is aimed at investigating the weathering processes of the granodiorites cropping out in a small catchment of the sila massif the mineral constituents in this granodiorite are plagioclase often zoned with a ca rich core and a na rich rim quartz chlorite k feldspar white mica and epidote during this study dolomite was discovered in local stream sediments as separate monomineralic grains probably resulting from erosion of veins cutting the crystalline rocks prevailing dissolution of foreign dolomite and a ca rich plagioclase is suggested by the ca mg hco3 chemical composition of local groundwaters and stream waters which is rather unexpected for waters interacting with granitoid rocks these qualitative observations are quantitatively confirmed by reaction path modelling of the weathering processes occurring in the study area which was carried out using the eq3 6 software package version 8 0 and the double solid reactant method indeed it was possible to ascertain that the release of both major dissolved constituents and several trace elements ba co cr fe mn ni pb sr v and zn from rocks to waters is chiefly controlled by the dissolution of foreign dolomite and the ca rich core of zoned plagioclases

experimental study of dissolution rates of actinolite in cacl2 hcl h2o up to 400 c abstract actinolite dissolution rates in aqueous hcl and aqueous cacl2 hcl have been measured at temperatures ranging from 25 to 400 c at 23 mpa under conditions far from equilibrium using a flow through reactor the relative release rates for the various elements in actinolite due to breaking of metal oxygen bonds are all different all of the release rates vary with temperature and ph the release rate of si increases as temperature rises from 20 to 300 c but then decreases at higher temperatures other metallic ions such as ca mg fe and al are all released more rapidly than si at temperatures between 25 and 300 c but more slowly at temperatures 300 c the ratios of mca msi and mmg msi in the effluent at 200 c are close to the stoichiometric proportions of these elements in actinolite but differ from stoichiometric values at temperatures both above and below 200 c actinolite dissolution in aqueous hcl at 100 c yields element ratios close to stoichiometric values in the mineral but again the ratios vary at higher and lower temperatures our experiments demonstrate that under conditions far from equilibrium dissolution rates depend on both ph and the activity of aqueous mi zi where zi is the valence of the metal mi in the mineral and mi zi refers to ca2 mg2 or al3 the ion exchange model suggests that metal hydrogen ion exchange reaction on the surface is a key step for mineral dissolution and that a si rich mi deficient precursor complex is formed on the mineral surface at temperatures r a exp e a rt a h zi a mi zi where is the order with respect to the ratio of activity of hydrogen ions and dissolved metal ions mi the mg h exchange coefficient is 0 55 at 100 c the apparent activation energy ea 14 4 kj mol and a 0 23 10 3 m cm 2 s 1 our results show that water properties vary strongly within the critical region which affects the dissolution mechanism thus the release rates for various elements at temperatures above 300 c are different from those at temperatures below 300 c high resolution transmission electron microscopy hrtem and scanning electron microscopy sem studies indicate that a fe al rich si deficient layer is formed on the surface at temperatures above 300 c x ray photoelectron spectroscopy xps analyses show that the surface layer that formed by reaction with aqueous hcl at 400 c is a hydrated silicate composed of si oh and mi oh as well as si o and mi o bonds

rates of mineral dissolution under co2 storage conditions abstract evaluating the potential of a sedimentary basin reservoir to securely store co 2 benefits from a comprehensive understanding of the geochemical reactions that take place once co 2 is injected into a formation in particular models that predict the transport and reaction of co 2 within a reservoir require a definition of the types of reactions affected by enhanced levels of co 2 and how the kinetics of these reactions will affect a heterogeneous mineralogy and formation waters within a reservoir over time in this review we evaluate rate models used to describe mineral dissolution kinetics and compare the range in values reported for the kinetic parameters used to describe the reactivity of various minerals relevant to mainly siliciclastic reservoirs parameters that have a significant impact on model results include the reactive surface area of a mineral the apparent activation energies used to extrapolate reaction rates to the temperatures of potential storage reservoirs c 50 125 c and the in situ ph of formation waters with elevated concentrations of dissolved co 2 the variation in reported values for these parameters can lead to predicted rates that span many orders of magnitude for a given mineral despite these uncertainties recent success with geochemical models has been made by applying a monte carlo approach to optimise the kinetic parameters for minerals where robust thermodynamic and kinetic data do not exist

a preliminary assessment of the hydrocarbon potential of the larsen basin antarctica abstract the larsen basin on the northwest margin of the weddell sea formed as a mesozoic ensialic basin during gondwana breakup deposition was either in half grabens on the extending weddell sea margin or in a restricted back arc basin at the northern end of this basin 5 6 km of sedimentary rock crop out on james ross island exposing elements of a large potential hydrocarbon system aeromagnetic and outcrop data suggest that the basin structure inferred from james ross island can be recognised at least as far south as 70 s upper jurassic anoxic marine strata deposited prior to the main phase of arc development form a rich potential source t o c up to 3 5 with both marine and terrestrial kerogens arc derived volcaniclastic sediments of barremian oligocene age form a regressive megasequence basal strata represent slope apron and rudaceous submarine fan deposits proximal to the margin fan conglomerates form lenticular bodies hundreds of metres thick and tens of kilometres across enveloped in slope apron mudstones late cretaceous fault reactivation and uplift led to dramatic shallowing of the basin with deposition of shelf facies although there are many potentially attractive reservoir targets there may be problems of pore occlusion due to the abundant labile volcanic grains however there is evidence of more quartzose sandstone towards the top of the section and inferentially toward the basin centre in the larsen basin there is moderate potential for oil generated from upper jurassic source rocks and reservoired in cretaceous and tertiary sandstones and conglomerates in large stratigraphic or structural traps caused by partial basin inversion during deposition

weathering plants and the long term carbon cycle the chemical weathering of ca mg silicate rocks is the principal process whereby co2 is removed from the atmosphere on long or multimillion year time scales at present vascular land plants exert an important influence on weathering by recycling water and by bringing about the secretion of acids and the buildup of high levels of co2 in soils before the spread of vascular plants on the continents during the mid paleozoic chemical weathering must have been achieved by higher levels of atmospheric co2 and or by the intercession of primitive land biota such as lichens and cyanobacteria from examination of several pre vascular weathering scenarios it is concluded that in order to prohibit unreasonably high levels of atmospheric co2 weathering during the precambrian and early paleozoic must have taken place under essentially closed system abiotic conditions linear feedback or via strong regulation by primitive biota preliminary examination of modern weathering by lichens over tens to thousands of years militates against the latter possibility however much more work needs to be done on the quantitative effect of both primitive biota and vascular plants on the rate of weathering and their response to changes in atmospheric co2 before anything more definitive can be said

continental rift to back arc basin jurassic cretaceous stratigraphical and structural evolution of the larsen basin antarctic peninsula the larsen basin developed in jurassic times as a result of continental rifting during the early stages of gondwana break up lower upper jurassic non marine sedimentary and volcanic rocks constitute a syn rift megasequence recording initial largely amagmatic extension and subsequent widespread extension related silicic volcanism a succeeding kimmeridgian early berriasian transgressive megasequence consisting largely of anoxic dysoxic hemipelagic mudstones is thought to have been deposited during a thermal subsidence phase when relative magmatic quiescence and peak jurassic eustatic sea levels served to maximize sediment starvation the fragmentary record for late berriasian barremian times suggests that a regressive megasequence may have developed in the earlier part of this period recording increased sediment yield to the larsen basin from the increasingly emergent antarctic peninsula arc subsequently strata in the southern but not the northern part of the basin underwent relatively intense eastward verging deformation possibly during the formation of a retro arc fold thrust belt where exposed the lower part of the succeeding aptian eocene megasequence consists of a deep marine clastic wedge deposited along the fault bounded western basin margin during a phase of arc uplift and related differential subsidence following partial basin inversion in late cretaceous times regression took place as reduced basinal subsidence rates allowed shallow marine facies to prograde basinward

review of the upper cretaceous lower tertiary sequence on seymour island antarctica the thick sequence of fossiliferous marine and non marine sandstones and siltstones on seymour i represents the most complete well exposed section of upper cretaceous to lower tertiary rocks known in the southern hemisphere the succession has been divided into the upper campanian to possibly lowermost tertiary marambio group comprised of the lopez de bertodano and sobral formations and the lower tertiary cross valley and la meseta formations of the seymour island group the lopez de bertodano formation consists of c 1067 m of medium grained to silty concretionary sandstones of middle campanian to possibly maestrichtian age and the sobral formation of c 210 m of medium to coarse grained glauconitic concretionary sandstones the precise age of the sobral formation is uncertain but may be maestrichtian to possibly danian the lower 110 m of the seymour island group consists of non marine gravelly to pebbly sandstones and tuffaceous plant bearing siltstones of the cross valley formation overlying which are 450 m of fine grained marine sandstones and siltstones with interbedded fossiliferous pebbly conglomerates recent studies of the diverse and abundant faunas and floras of the seymour island group have shown that they are older than previously thought the cross valley formation being palaeocene and the la meseta formation late eocene to possibly earliest oligocene

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

bridging the gap between laboratory measurements and field estimations of silicate weathering using simple calculations weathering rates of silicate minerals observed in the laboratory are in general up to five orders of magnitude higher than those inferred from field studies simple calculations show that even if the field conditions were fully simulated in standard laboratory experiments it would be impossible to measure the slow rates of mineral dissolution that are observed in the field as it is not possible to measure the dissolution rates under typical field conditions one should extrapolate the available data to the field conditions to do this a rate law for the dissolution of plagioclase in the field was formulated by combining the far from equilibrium dissolution rate of weathered natural oligoclase at 25 c with the effect of deviation from equilibrium on dissolution rate of fresh albite at 80 c in contrast to the common view that laboratory experiments predict dissolution rates that are faster than those in the field the simulation based on this rate law indicates that laboratory dissolution experiments actually predict slower rates than those observed in the field this discrepancy is explained by the effect of precipitation of secondary minerals on the degree of saturation of the primary minerals and therefore on their dissolution rate indeed adding kaolinite precipitation to the simulation significantly enhances the dissolution rate of the plagioclase moreover a strong coupling between oligoclase dissolution and kaolinite precipitation was observed in the simulation we suggest that such a coupling must exist in the field as well therefore any attempt to predict the dissolution rate in the field requires knowledge of the rate of the secondary mineral precipitation

update on terrestrial ages of antarctic meteorites abstract cosmic ray produced 36 cl half life 3 01 10 5 years has been measured in 90 antarctic meteorites by accelerator mass spectrometry the terrestrial ages of the meteorites were calculated from the results after excluding possible paired objects 138 terrestrial ages from 18 different locations are available from 14 c 81 kr and 36 cl measurements for application to antarctic meteorite and glaciological studies the terrestrial ages of allan hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of yamato meteorites and other antarctic meteorites the oldest allan hills meteorites were found close to the eastern edge and in the southeast of the main icefield among all antarctic meteorites measured to date only l and ll chondrites have terrestrial ages older than 370 000 years

modelling groundwater processes in a carbonate catchment a case study from the madonie area northern sicily abstract this study reports on the results of a hydrogeochemical survey carried out in the madonie area a carbonate massif located in palermo province northern sicily the large dataset 226 collected sites is used to highlight the processes controlling the distribution of dissolved chemicals in groundwaters and more importantly to develop a general model based on reaction path modelling and using the eq3 6 code of rock water reactions in a carbonate environment the investigated groundwater samples have conductivity between 31 7 and 8220 s cm their total dissolved solids tds content is higher near the coast area where the seawater contribution becomes important calcium and hco 3 excess concentrations in groundwaters with respect to the meteoric water seawater mixing line suggest that water rock interactions in carbonate aquifers play a major role on water chemistry using the dataset reaction path modelling is used to simulate the evolution of groundwaters upon interaction with carbonate rocks model simulations are performed in time mode taking into account the mineralogical composition of madonie carbonate rocks and the different dissolution rates of each dissolving mineral the model results of reaction path calculations are in fair agreement with analytical data for natural waters demonstrating the likelihood of model assumptions and supporting further the relevance of carbonate dissolution in determining the chemistry of fluids in the investigated area the developed model is useful for low temperature weathering of carbonate mineral in general and is thus likely to apply in a variety of geological contexts

additions to the diversity of elasmosaurid plesiosaurs from the upper cretaceous of antarctica abstract three specimens of elasmosaurid plesiosaurs sauropterygia plesiosauria from upper cretaceous beds of antarctica are described here these include postcranial remains of a single adult individual recovered from late maastrichtian beds of marambio seymour island possessing a distinctive combination of features cervical vertebrae having centra with a triangular outline in transverse section a vertical groove on the rostral and caudal edge of the neural spines and a deep articulation over the neural arch for the following postzygapophysis while the scapula shows an unusually large and anteriorly recurved dorsal process this combination of features is unknown in any adult postcranial elasmosaurid genus recovered to date in the upper cretaceous of the weddellian biogeographic province and could represent a new form additional specimens from james ross island comprise the first record of an aristonectinae plesiosauria elasmosauridae in late campanian beds being the oldest known record of this sub family finally a third specimen from the same age and locality reveals the presence of very long necked elasmosaurids with affinities to typical representatives from the upper cretaceous of the northern hemisphere these findings add to the known diversity of upper cretaceous elasmosaurids in high latitudes of the southern hemisphere

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

characterization of the reaction and transport properties of porous rhyolite and its application to the quantitative understanding of the chemical weathering rate abstract the chemical weathering of porous rhyolite from kozushima japan was studied and the factors controlling the weathering rate including advection diffusion and dissolution were characterized using laboratory experiments the results were used to analyze the reaction and transport rates and the relationship between the weathering rates obtained in the laboratory and field was evaluated a flow through dissolution experiment using a rhyolite core demonstrated that the dissolution rate r mol cm 2 s 1 in deionized water depends on time t days according to the relationship r 2 9 10 16 t 0 65 the dissolution rate was also dependent on the concentration of dissolved si according to the relationship r 1 n where c ceq ceq 230 mol l 1 and n 1 0 or 0 33 the hydraulic conductivity and diffusion coefficients were measured under water saturated and unsaturated conditions the saturated hydraulic conductivity was 10 times greater than the unsaturated conductivity and the saturated effective diffusion coefficient of dissolved si was 5 times greater than the unsaturated diffusion coefficient previous studies on the weathering of the rhyolites from kozushima have shown that the field dissolution rate over 52 000 years was 3 10 19 6 10 19 mol si cm 2 s 1 these values are 12 1000 times lower than the dissolution rates obtained in the laboratory over a reaction time of 277 days reactive transport analysis demonstrated that the effect of on the dissolution rate is enhanced as the water saturation decreases the rate decreasing effect of was large in the early stages of weathering and then gradually decreased with time the 52 000 year weathering period is inferred to have occurred following a decrease in the dissolution rate to a value close to the field rate during an early weathering stage and subsequent further decrease in the rate owing to the effect of

mebo70 seabed drilling on a polar continental shelf operational report and lessons from drilling in the amundsen sea embayment of west antarctica a multibarrel seabed drill rig was used for the first time to drill unconsolidated sediments and consolidated sedimentary rocks from an antarctic shelf with core recoveries between 7 and 76 we deployed the marum mebo70 drill device at nine drill sites in the amundsen sea embayment three sites were located on the inner shelf of pine island bay from which soft sediments presumably deposited at high sedimentation rates in isolated small basins were recovered from drill depths of up to 36 m below seafloor six sites were located on the middle shelf of the eastern and western embayment drilling at five of these sites recovered consolidated sediments and sedimentary rocks from dipping strata spanning ages from cretaceous to miocene this report describes the initial coring results the challenges posed by drifting icebergs and sea ice and technical issues related to deployment of the mebo70 we also present recommendations for similar future drilling campaigns on polar continental shelves

use of stream sediment chemistry to predict trace element chemistry of groundwater a case study from the bisagno valley genoa italy abstract irreversible water rock mass transfer accompanying the generation of the bisagno valley groundwaters starting from local rainwaters was simulated through reaction path modeling in reaction progress mode the simulations assumed bulk dissolution of local stream sediments i e without any constraint on their mineralogy and on the dissolution rates of primary solid phases and precipitation of chalcedony illite a smectite solid mixture a hydroxide solid mixture a trigonal and an orthorhombic carbonate solid mixtures concentrations of major chemical elements and several trace elements in groundwaters were satisfactorily reproduced thus in the system studied stream sediment data can be used as an initial condition in reaction progress calculations to predict the chemistry of groundwaters if this conclusion would be confirmed through other applications stream sediment data could be used to assess natural background levels in groundwaters and to identify pollution phenomena calculations similar to those carried out for the bisagno valley could be applied in many other areas given the large number of stream sediment data available throughout the world and the present efforts to generate worldwide geochemical databases a global geochemical database for environment and resource management recommendations for international geochemical mapping final report of igcp project 259 earth sciences 19 unesco paris 1995

limestone weathering rates accelerated by micron scale grain detachment the weathering of carbonate rocks plays a critical role in the evolution of landscapes the erosion of buildings and monuments and the global scale shifting of carbon from the atmosphere to the ocean chemical dissolution is often assumed to govern the rates of weathering of carbonate rocks although some studies have suggested that mechanical erosion could also play an important role quantifying the rates of the different processes has proved challenging in part due to the high degree of variability encountered across different scales in both field and laboratory conditions to constrain the rates and mechanisms controlling long term limestone weathering we analyze a lidar scan of the western wall a roman period edifice located in jerusalem we find that extreme erosion rates in fine grained micritic limestone blocks are as much as two orders of magnitude higher than the average rates estimated for coarse grained limestone blocks at the same site atomic force microscope imaging of dissolving micritic limestone suggests that these elevated reaction rates are likely to be the result of rapid dissolution along micron scale grain boundaries followed by mechanical detachment of tiny particles from the surface our analysis indicates that such grain detachment could be the dominant erosional mode for fine grained carbonate rocks in many regions on earth

dating of meteorite falls using thermoluminescence application to antarctic meteorites abstract the date of fall of a meteorite may be estimated from its thermoluminescence tl and in this paper the principle of a method of utilising tl to determine the terrestrial ages of eight antarctic meteorites allan hills 77 is described the tl in a meteorite is primarily induced by cosmic ray irradiation in space and once the meteorite is on the earth s surface it is shielded from further cosmic ray irradiation under these conditions the tl will decay at a rate governed by the thermal stability of the tl and by the environmental temperature an estimate of the decay rate may be arrived at by using recently calculated data for the trapping parameters associated with meteorite tl a major problem is the environmental storage temperature the effective storage temperature of the antarctic meteorites is unknown but appears to be greater than the mean annual temperature of the region of the meteorite find only upper limits to the terrestrial ages can be calculated because the tl at the time of the fall to earth is highly variable from sample to sample

geochemistry of high ph waters from serpentinites of the gruppo di voltri genova italy and reaction path modeling of co2 sequestration in serpentinite aquifers abstract the large number of geochemical data gathered on the gruppo di voltri springs confirm that progressive interaction of meteoric waters with ultramafic rocks variably affected by serpentinization leads initially to the formation of mg hco3 waters when the system is open to co2 and na hco3 and ca oh type water upon further interaction with the rock under highly reducing closed system conditions with respect to co2 as indicated by 3h data these high ph waters have had long residence times underground in deep aquifers hosted by serpentinitic rocks these waters are the only available evidence of the presence of such deep aquifers high pressure injection of co2 into these deep aquifers was simulated by reaction path modeling results indicate that this is a feasible methodology to reduce the inputs of anthropogenic co2 into the atmosphere serpentinitic rocks have a high capacity for co2 sequestration mainly through formation of carbonate minerals dissolution of serpentinitic rocks and precipitation of magnesite and silica minerals occurs naturally in areas of high terrestrial co2 fluxes such as in southern tuscany corroborating the feasibility of this methodology of co2 sequestration however this process causes a progressive decrease in the porosity of the aquifer at least under closed system conditions these side effects must be carefully evaluated by means of further laboratory tests and field activities

experimental study on water rock interactions at temperatures up to 435 c and implications for geophysical features in upper mid crust condition abstract globally observed zones of high conductivity and low seismic velocity in the mid crust remain enigmatic despite previous theoretical and experimental investigations we have carried out a series of dissolution experiments on mineral and rock samples in aqueous solutions using flow through reactors at temperatures as high as 435 c and at pressures of 23 36 mpa these experiments provide useful information for evaluating the behavior of crustal fluids and their role in the formation of geophysical detectible anomalies in the mid crust the steady state dissolution rates of minerals or rocks are measured as functions of temperature flow rate and pressure the maximum release rates of si for silicate minerals are always observed at 300 c or at 300 400 c for silicate rocks which results in strong leaching of si and the break up of silicate framework structures in minerals and rocks from a tectonic perspective plate motions are ultimately responsible for inducing cracking in rocks generating porosity decreasing pressure and moving fluids across and through continents these processes of decreasing pressure probably lead to the migration of aqueous fluid in the mid crust to locations where they are close to their critical state at temperatures ranging from 300 to 435 c therefore water rock interactions occurring in the crust will cause strong leaching of si breakage of silicate framework structures and rock collapse the strong water rock interaction will further lead to the generation of increased rock porosity and also drive fluid flow these hydrothermal events therefore have a significant role in enhancing the conductivity of rocks in the mid crust

using a reactive transport model to elucidate differences between laboratory and field dissolution rates in regolith the reactive transport model flotran was used to forward model weathering profiles developed on granitic outwash alluvium over 40 3000 ka from the merced california usa chronosequence as well as deep granitic regolith developed over 800 ka near davis run virginia usa baseline model predictions that used laboratory rate constants km measured fluid flow velocities v and bet volumetric surface areas for the parent material a o m were not consistent with measured profiles of plagioclase potassium feldspar and quartz reaction fronts predicted by the baseline model are deeper and thinner than the observed consistent with faster rates of reaction in the model reaction front depth in the model depended mostly upon saturated versus unsaturated hydrologic flow conditions rate constants controlling precipitation of secondary minerals and the average fluid flow velocity va unsaturated hydrologic flow conditions relatively open with respect to co2 g resulted in the prediction of deeper reaction fronts and significant differences in the separation between plagioclase and potassium feldspar reaction fronts compared to saturated hydrologic flow relatively closed with respect to co2 g under saturated or unsaturated flow conditions the rate constant that controls precipitation rates of secondary minerals must be reduced relative to laboratory rate constants to match observed reaction front depths and measured pore water chemistry additionally to match the observed reaction front depths va was set lower than the measured value v for three of the four profiles the reaction front gradients in mineralogy and pore fluid chemistry could only be modeled accurately by adjusting values of the product kma o m by assuming km values were constrained by laboratory data field observations were modeled successfully with tst like rate equations by dividing measured values of a o m by factors from 50 to 1700 alternately with sigmoidal or alinhibition rate models this adjustment factor ranges from 5 to 170 best fit models of the wetter hydrologically saturated davis run profile required a smaller adjustment to a o m than the drier hydrologically unsaturated merced profiles we attributed the need for large adjustments in va and a o m necessary for the merced models to more complex hydrologic flow that decreased the reactive surface area in contact with bulk flow water e g dead end pore spaces containing fluids that are near or at chemical equilibrium thus rate models from the laboratory can successfully predict weathering over millions of years but work is needed to understand how to incorporate changes in what controls the relationship between reactive surface area and hydrologic flow

end cretaceous mass extinction event argument for terrestrial causation the end cretaceous mass extinctions were not a geologically instantaneous event and were selective in character these features are incompatible with the original alvarez hypothesis of their being caused by a single asteroid impact that produced a world embracing dust cloud with devastating environmental consequences by analysis of physical and chemical evidence from the stratigraphic record it is shown that a modified extraterrestrial model in which stepwise extinctions resulted from encounter with a comet shower is less plausible than one intrinsic to the earth involving significant disturbance in the mantle

chemical and physical studies of type 3 chondrites viii thermoluminescence and metamorphism in the co chondrites the thermoluminescence properties of nine co chondrites have been measured with the exception of colony and allan hills a77307 alha 77307 whose maximum induced tl emission is at approximately 350 c co chondrites exhibit two tl peaks one at 124 7 c 130 c peak and one at 252 7 c 250 c peak the 130 c peak shows a 100 fold range in tl sensitivity 0 99 0 21 for isna to 0 010 0 004 for colony and correlates with various metamorphism related phenomena such as silicate heterogeneity metal composition and mcsween s metamorphic subtypes the peak at 250 c does not show these correlations and colony excepted varies little throughout the class 0 3 to 0 07 colony 0 018 0 004 mineral separation experiments and a series of annealing experiments on isna suggest that the tl properties for co chondrites reflect the presence of feldspar in two forms 1 a form produced during metamorphism and analogous to the dominant form of feldspar in type 3 ordinary chondrites and 2 a primary metamorphism independent form perhaps associated with the amoeboid inclusions if this interpretation is correct then the co chondrites have not experienced temperatures above the order disorder temperature for feldspar 500 600 c and they cooled more slowly than comparable i e type 3 5 type 3 ordinary chondrites colony and alha 77307 have atypical tl properties including very low tl sensitivity suggesting that phosphors other than feldspar are important they have apparently experienced less metamorphism than the others and may have also been aqueously altered

carbonate geochemistry of vadose water recharging limestone aquifers abstract thrailkill j and robl t l 1981 carbonate geochemistry of vadose water recharging limestone aquifers in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 195ndash 208 vadose water from lower carboniferous rocks in kentucky u s a was analyzed monthly in mammoth cave and in the caves and overlying soil at two other caves calcite saturation and equilibrium co 2 pressures of water were calculated after correcting for ion pairing and activity coefficients soil gas co 2 concentrations were determined directly both small flows of water which were usually depositing speleothems vadose seepages and larger flows vadose flows were studied some of the vadose seeps were often undersaturated with respect to calcite and showed little variation in ca content cv ca 7 while others were supersaturated and showed positive correlations between ca and soil co 2 or between ca and discharge at least some of the vadose seepages were believed to have been closed to co 2 introduction after leaving the soil zone in the soil co 2 varied with soil type moisture and season ca increased with depth but saturation with respect to calcite was not reached three types of vadose water may thus reach the aquifer undersaturated with respect to calcite 1 vadose flows which transit the vadose zone rapidly 2 low ca vadose seepage which is closed to co 2 as it transits the vadose zone and which may remain undersaturated with respect to calcite even after ventilation and 3 high ca vadose seepage which leaves the soil zone slightly undersaturated probably because of insufficient residence time

influence of rainfall quantity on the isotopic composition 18o and 2h of water in mountainous areas application for groundwater research in the yunquera nieves karst aquifers s spain abstract the isotopic composition 18 o and 2 h of rainwater and groundwater was determined in the yunquera nieves hydrogeological unit a karstic massif in s spain with complex orography and hydrogeology the aims were to identify 1 the source of the water 2 the main factors determining the isotopic content 3 the catchment area of the springs and 4 the aquifer behaviour the isotopic content of the sampled waters is of mixed atlantic mediterranean origin and is opposite to the quantity of rainwater distribution both in space and time spatially water is isotopically less depleted toward the eastern sector where rainwater quantity is lower which is locally affected by the orography thus it is possible to differentiate the catchment areas of the main springs aquifer recharge is produced by winter precipitation when rainfall water is isotopically more negative and evaporation is lower the decrease in rainfall quantity during the study period provoked an increase in 18 o and 2 h values both in rainwater and in groundwater the recorded variations of the isotopic content of the rainfall are rapidly evident in the spring waters which demonstrates a well developed karst network inside the carbonate aquifers and thus the existence of conduit flow systems

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

hydrogeochemical study of an ophiolitic aquifer a case study of lago southern italy calabria a hydrogeochemical survey was carried out in the area of lago calabria region southern italy and outcropping geological units were classified from the hydrogeological point of view to explain the evolution of local groundwaters in addition reaction path modeling was performed to simulate the evolution of groundwaters upon interaction with local metabasalts phyllites and serpentinites by means of the eq3 6 software package version 8 0 simulations were carried at constant temperature of 14 1 c which reproduces the average temperature of local groundwaters three different simulations have been performed for the average metabasalt fixing the fugacity of co2 at either 10 2 4 bar mean value 10 2 0 bar mean value 1 or 10 2 9 bar mean value 1 the simulation for the average serpentinite and phyllite was carried out at the mean value of the fugacity of co2 10 2 4 bar all evidences acquired in this study namely the hydrogeological framework the chemical analysis of local groundwaters and the results of reaction path modeling consistently point out that groundwater circulation under ordinary hydraulic gradient primarily occurs in the ophiolitic sub complex and that dissolution of metabasalts and serpentinites controls the chemical characteristics of the groundwaters from the study area

campanian maastrichtian cretaceous stratigraphy of the james ross island area antarctica one of the most important outcrops of uppermost cretaceous campanian maastrichtian sedimentary rocks in the southern high latitudes occurs within the james ross island group northeastern antarctic peninsula these rocks comprise a 1500 2000 m thick sequence of predominantly shallow marine clastic sediments that were deposited within a retro arc basin they are virtually undeformed and have yielded prolific invertebrate and vertebrate faunas and a wide range of plant taxa campanian maastrichtian strata are contained within two component formations of the upper cretaceous lower tertiary marambio group the lower santa marta formation is approximately 1100m thick and has three constituent members ammonites within the santa marta formation indicate an early to late campanian age assignment dinoflagellates suggest that the lower levels of the formation may range into the santonian stage in the northern james ross island to vega island region there is a conformable transition into the overlying lopez de bertodano formation here the basal cape lamb member is unconformably overlain by the sandwich bluff member although there are some lithological and fauna1 discrepancies which are attributed to marked lateral facies changes across the basin it is believed that the cape lamb member can be correlated with the lower to middle regions of the 1200 m thick sequence of undifferentiated lopez de bertodano formation lithologies exposed on seymour island molluscan data indicate a late campanian palaeocene age range for this upper formation dinoflagellates again suggest that the lowest beds may be slightly older the correlation presented provides the basis for a formal subdivision of the campanian and maastrichtian stages in the southern high latitudes it has also revealed two major basin shallowing events in the late campanian early maastrichtian and latest maastrichtian respectively and the existence of a major fault fault zone across southeastern james ross island the improved temporal framework will aid late cretaceous palaeoclimatic and palaeobiological studies in antarctica

application of geochemistry and radioactivity in the hydrogeological investigation of carbonate aquifers sierras blanca and mijas southern spain the chemical characteristics 3 h contents and radioactivity of groundwaters from the sierras blanca and mijas southern spain have been studied in relation to the chemical composition and radioactivity of the aquifer host rocks and the residence time of the water the sierras blanca and mijas are made up of calcitic and dolomitic marbles of triassic age the groundwaters that drain the calcitic marbles which outcrop principally in the western sierra blanca have less mineralization which descreases quickly with recharge as does the 3 h content and the gross alpha and beta activities are below detection limit this is due to the short residence time of water inside the aquifers which are conduit flow systems the waters of the dolomitic marbles eastern sierra blanca and sierra mijas have higher and less variable mineralization and contain greater concentrations of mg 2 sio2 and so 2 4 ions normally associated with slow flows the 3 h contents are more uniform with time indicating an older age and there is detectable natural radioactivity because the waters have a longer residence time in the aquifers which

water rock interaction in the bisagno valley genoa italy application of an inverse approach to model spring water chemistry abstract the chemical evolution of the bisagno valley spring waters ranging from initial ca hco3 towards final na hco3 composition is reconstructed with a reaction progress scheme defined by a fractional degree of advancement of the irreversible mass transfer process and attaining the continuum limit during water rock interaction the system is solved in terms of a transposed reaction rate vector introducing the experimental kinetic rate constants and solving for the surface areas of dissolving albite and k feldspar and precipitating carbonates this is also done by considering the activities of dissolved silica and al3 ion as constrained by the instantaneous equilibrium with quartz and kaolinite respectively the results of this inverse geochemical model are fully consistent with those obtained using the eq3nr eq6 forward code provided this last is run in iterative way changing progressively the surface areas of solid reactants and fco2 values accounting for the compositional dependence of the kinetic rate constants of plagioclase and alkali feldspar allows explanation of the progressive albitization of the mt antola formation through a kinetic phenomenon involving nowadays circulating fluids the comparison of computed surface areas with estimates based on the modal mineralogy grainsize and intergranular porosity of the arenitic siliciclastic beds outlines the importance of fracture driven flow in agreement with available lugeon flow tests

storm response of the karstic carbonate aquifer of southcentral kentucky abstract temperature and specific conductance were continuously measured in the downstream drainage of the turnhole spring subbasin in the southcentral kentucky karst precipitation was monitored with a rain gage network in the catchment area so that the storm response of specific conductance and temperature could be examined the aquifer feeding the turnhole spring is highly karstic with much of the discharge through integrated open conduits some of which carry water from surface sinking stream catchments both temperature and specific conductance fluctuate rapidly in response to storm events the conductivity curves and to a lesser extent the temperature curves show a sharp dip that lags some hours behind the storm pulse at the onset of the dip is a complicated sequence of fine structures that is interpreted to be the inputs from conduit tributaries to the master trunk drainage system the recovery curves have an exponential form that can be fitted to produce a characteristic response time for the conduit system

the natural thermoluminescence of meteorites i twenty three antarctic meteorites of known 26al content the level of thermoluminescence tl naturally present in 23 antarctic chondrites of known 26al content has been measured as a means of exploring their thermal and radiation history antarctic meteorites tend to have lower natural tl than non antarctic meteorites presumably because of their generally longer terrestrial ages seventeen of the meteorites lie on a band of increasing natural tl and 26al activity meteorites with 26al of 45 60 dpm kg have natural tl values normalized to the high temperature tl of 2 4 whereas those with 26al values of 30 45 dpm kg have normalized natural tl values of 1 2 and alha 76008 with an 26al content of 11 dpm kg has a tl value of 0 87 0 01 this suggests that the half life for tl decay is comparable to that of 26al the six meteorites not lying on the tl 26al trend have much lower tl than others of comparable 26al for two of them rkpa 79001 and rkpa 80202 which are tentatively paired the low natural tl probably reflects a recent severe shock while another alha 77294 has previously been measured in this lab and had tl consistent with the tl 26al trend the remaining three alha 78006 alha 77296 and alha 77297 of which the last two are probably paired have suffered a recent reheating such as would be expected from orbits of unusually small perihelia

hydrogeochemical modeling kirmat of spring and deep borehole water compositions in the small granitic ringelbach catchment vosges mountains france abstract this study presents the results of the coupled hydrogeochemical modeling of the geochemical compositions of spring and borehole waters from the ringelbach catchment which is located in the vosges mountains france this site has been equipped with 150 m deep boreholes facilitating the sampling of both rock and groundwater in the granitic bedrock the data point to very contrasting chemical compositions between spring and borehole waters which are discussed and explained in this study by the application of the coupled hydrogeochemical code kirmat using hydrological and geochemical data simulations were performed through two different water pathways which crossed different types of rocks within the ringelbach massif a subsurface and fast 2 5 mh2o yr 1 water flow which is more or less parallel to the slope for waters supplying the springs and a rather vertical and slower flow 0 5 0 1 mh2o yr 1 for the borehole waters the kirmat simulations make it possible to account for not only the geochemical differences between the spring and borehole waters but also the geochemical variations observed in waters in both contexts for borehole waters the model confirms the importance of the dissolution of minor mineralogical phases that are present in the granite here carbonates dolomites on the chemical budget of waters it also shows that the chemical differences between the waters collected in the two studied boreholes result from differences in the water flow in the granitic bedrock i e the difference between water flow in a regular porous medium and water flow in a porous medium crossed by a fracture this result likely highlights the role of geological inheritance on the hydrodynamical rock properties and the chemical compositions of waters circulating within the granitic bedrock for spring waters this model enabled us to constrain the nature of the rock in the pathway which is neither saprolite nor fresh granite but is instead weathered granite with a weathering age of several tens of thousands of years spatial and seasonal variations in the chemical compositions of spring water can be explained as the result of the same circulation pattern for which the water rock interaction time is determined by the length of the pathway and the water velocity especially in cases in which this interaction time is long enough the precipitation of clay phases is enabled which plays a major role in determining the chemical composition of the water despite the only one dimensional approach and the uncertainties linked to the geochemical complexity and the associated kinetic data the results obtained in this study demonstrate the effectiveness of using coupled hydrogeochemical modeling to better understand and quantify the weathering processes and the coupling that exists between water circulation dynamics and water rock interactions at the catchment scale

co2 diffusion into pore spaces limits weathering rate of an experimental basalt landscape basalt weathering is a key control over the global carbon cycle though in situ measurements of carbon cycling are lacking in an experimental vegetation free hillslope containing 330 m 3 of ground basalt scoria we measured real time inorganic carbon dynamics within the porous media and seepage flow the hillslope carbon flux 0 6 5 1 mg c m 2 h 1 matched weathering rates of natural basalt landscapes 0 4 8 8 mg c m 2 h 1 despite lacking the expected field based impediments to weathering after rainfall a decrease in co 2 concentration co 2 in pore spaces into solution suggested rapid carbon sequestration but slow reactant supply persistent low soil co 2 implied that diffusion limited co 2 supply while when sufficiently dry reaction product concentrations limited further weathering strong influence of diffusion could cause spatial heterogeneity of weathering even in natural settings implying that modeling studies need to include variable soil co 2 to improve carbon cycling estimates associated with potential carbon sequestration methods

thermoluminescence of meteorites and their orbits the thermoluminescence tl levels of 45 ordinary chondrites were measured to obtain information about the meteorite orbits the low temperature tl reaches equilibrium while the meteorite is in space and reflects the temperature of the meteorite at perihelion samples of pribram lost city and innisfree whose orbits are accurately known were used as control samples the tl levels in 40 out ot 42 meteorites are similar to the three control samples indicating that the vast majority of ordinary chondrites that survive atmospheric entry have perihelia similar to three known orbits i e in the range 0 8 1 au the effects of albedo and rotation are also considered a simple model indicates that temperature gradients of 1 2 k cm are possible in slowly rotating meteoroids and such a temperature gradient is consistent with the unusually large tl gradient measured in the farmville meteorite since slow rotation rates are improbable other possibilities are examined but no satisfactory explanation has been found the tl level measured in the malakal meteorite is two orders of magnitude lower than control samples and is best explained by thermal draining due to solar heating in an orbit with a small perihelion distance the perihelion is estimated to be 0 5 0 6au