sulfur record of rising and falling marine oxygen and sulfate levels during the lomagundi event carbonates from approximately 2 3 2 1 billion years ago show markedly positive 13c values commonly reaching and sometimes exceeding 10 traditional interpretation of these positive 13c values favors greatly enhanced organic carbon burial on a global scale although other researchers have invoked widespread methanogenesis within the sediments to resolve between these competing models and more generally among the mechanisms behind earth s most dramatic carbon isotope event we obtained coupled stable isotope data for carbonate carbon and carbonate associated sulfate cas cas from the lomagundi interval shows a narrow range of 34s values and concentrations much like those of phanerozoic and modern marine carbonate rocks the 34s values are a close match to those of coeval sulfate evaporites and likely reflect seawater composition these observations are inconsistent with the idea of diagenetic carbonate formation in the methanic zone toward the end of the carbon isotope excursion there is an increase in the 34s values of cas we propose that these trends in c and s isotope values track the isotopic evolution of seawater sulfate and reflect an increase in pyrite burial and a crash in the marine sulfate reservoir during ocean deoxygenation in the waning stages of the positive carbon isotope excursion

joint inversion of 2d resistivity and seismic travel time data to image saltwater intrusion over karstic areas the simultaneous inversion of multiple geophysical data types has been proven to be a powerful tool to both improve subsurface imaging and help in the interpretation process the main goal of this paper was to develop joint inversion strategies to provide improved resistivity and seismic velocity images for delineating saline water zones in karstic geological formations the cross gradient constraint approach was adopted to jointly invert resistivity and seismic first arrival data the basic idea of this approach is to quantitatively estimate the structural similarity between resistivity and seismic velocity models using the cross product of their gradients and to achieve a unified geological model which satisfies both data sets initially synthetic data were employed to help develop a joint inversion strategy to be used over such complex geological structures the proposed strategy uses a weighting factor for the cross gradient constraints and separate damping factors for the resistivity and seismic data this strategy was applied successfully on field data from the karstic region of stilos crete greece

fluid inclusions in the stripa granite and their possible influence on the groundwater chemistry fluid inclusions in quartz and calcite of the proterozoic stripa granite central sweden demonstrate that the rock and its fracture fillings have a complex evolutionary history the majority of inclusions indicate formation during a hydrothermal stage following emplacement of the stripa pluton total salinities of quartz inclusions range from 0 18 eq wt nacl for unfractured rock and from 0 10 eq wt for fractured rock vein calcites contain up to 25 eq wt nacl but the inclusion size is larger and the population density is lower homogenization temperatures are 100 150 c for unfractured rock and 100 250 for fractured rock pressure corrections assuming immediate post emplacement conditions of 2 kbar give temperatures about 160 c higher measurements of fluid inclusion population densities in quartz range from about 108 inclusions cm3 in grain quartz to 109 inclusions cm3 in vein quartz residual porosity from inclusion densities has been estimated to be at least 1 which is two orders of magnitude greater than the flow porosity breakage and leaching of fluid inclusions is proposed as an hypothesis for the origin of major solutes na ca cl in the groundwater evidence for the hypothesis is based on 1 mass balance only a small fraction of the inclusions need to leak to account for salt concentrations in the groundwater 2 chemical signatures brcl ratios of fluid inclusion leachates 0 0101 match those ratios for the deep groundwaters 0 0107 3 leakage mechanisms micro stresses from isostatic rebound or mining activities acting on irregular shaped inclusions could cause breakage and provide connection with the flow porosity and 4 experimental studies water forced through low permeability granites leach significant quantities of salt this hypothesis is consistent with the available data although alternate hypotheses cannot be excluded

groundwater salinity influenced by holocene seawater trapped in incised valleys in the red river delta plain brackish to salty waters have been found in inland areas of delta aquifers geophysical data and modelling suggest that salty groundwater in the red river delta originates from trapped seawater contained in underlying holocene marine deposits

delineation of saltwater intrusion zones using the time domain electromagnetic method the nabeul hammamet coastal aquifer case study ne tunisia the time domain electromagnetic method tdem is applied to monitor to delineate and to map the saltwater intrusion zones in the mediterranean plio quaternary aquifer forty two tdem soundings were carried out in the coastal plain of nabeul hammamet region ne tunisia tdem resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater seawater transition zone the geoelectric sections showing the vertical configuration of seawater intrusion with the brackish salty saturated zones have a resistivity ranging from 0 1 to 5 m and are detected at a depth lower than 1 5 m the salinized zones are located at nabeul sidi moussa sidi el mahrsi al gasba and mrazgua and at hammamet touristic zone of hammamet north and south baraket essahel and reached a distance of 4 km from the coastline indicating a severe state for the aquifer in these zones these tdem results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells moreover in the northeastern part the presence of a saltwater front located far from the coast and along the nw se major surface fault can be explained by two hypothesis i this fault seems to provide a conduit for seawater to move readily towards the water wells and ii the clay and gypsum infiltration of marine messinian deposits through the fault plane leads to low resistivities finally it comes out from this study that tdem survey has successfully depicted salinized zones of this coastal aquifer copyright 2012 john wiley sons ltd

resistivity imaging reveals complex pattern of saltwater intrusion along monterey coast abstract electrical resistivity tomography data were acquired along 40 km of the monterey bay coast in central california these data resulted in electrical resistivity images to depths of approximately 280 m b s l which were used to understand the distribution of freshwater and saltwater in the subsurface and factors controlling this distribution the resulting resistivity sections were interpreted in conjunction with existing data sets including well logs seismic reflection data geologic reports hydrologic reports and land use maps from the region interpretation of these data shows a complex pattern of saltwater intrusion resulting from geology pumping and recharge the resistivity profiles were used to identify geological flow conduits and barriers such as palaeo channels and faults localized saltwater intrusion from individual pumping wells infiltration zones of surface fresh and brackish water and regions showing improvements in water quality due to management actions the use of ert data for characterizing the subsurface in this region has led to an understanding of the spatial distribution of freshwater and saltwater at a level of detail unattainable with the previously deployed traditional well based salinity mapping and monitoring techniques alone significant spatial variability in the extent and geometry of intrusion observed in the acquired data highlights the importance of adopting continuous subsurface characterization methods such as this one

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

aquifer characterization using shallow geophysics in the keritis basin of western crete greece effective management of groundwater resources is a well known problem in several areas around the world it is especially important to areas suffering from an intrinsic lack of fresh water such as islands detailed study of available aquifers is of particular interest in the highly touristic greek island of crete the increasing water demand makes water resources management extremely important for sustainable development this is the case in the prefecture of chania in western crete where there has been a lack of success of many different groundwater management plans that have been produced over the years and submitted for application to water management authority the inefficiency of the management plans is verified by the continuous water shortage reported every year which forces the public authorities to transfer water from far away sources and wells until today there are only geological data as well as information from the borehole logs therefore the current work is focused to study in detail the tectonic and hydrogeological characteristics of the keritis watershed to make a correlation of the available geoenvironmental information with the geophysical data of the study aquifer transient electromagnetic soundings were conducted to obtain detailed information about the tectonic hydrogeological hydrolithological and geometrical characteristics of the aquifer under investigation in addition optimum areas of water well drilling were identified to minimize the uncertainty and the total cost economical managerial etc of future groundwater surveys

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

early cretaceous denudation related to convergent tectonics in the baikal region se siberia we present 24 new apatite fission track aft ages and 18 track length measurements from the baikal region se siberia most samples have aft ages between 140 and 100 ma with relatively high mean track lengths c 13 2 m the relationship between aft ages elevation and mean track lengths indicate that the samples record rapid cooling during the early cretaceous 140 120 ma as also shown by thermal history inversion of track length distributions cooling took place during a late jurassic early cretaceous orogenic phase related to closure of the mongol okhotsk ocean and reflected in the exhumation of metamorphic core complexes followed by thrusting and reverse faulting basin inversion and large vertical motions the variation in aft ages throughout the study area can be partly explained by differences in geothermal structure but differential denudation also played a role minimum amounts of early cretaceous denudation are estimated at 2 3 km

seawater strontium isotopic perturbation at the permian triassic boundary west spitsbergen and its implications for the interpretation of strontium isotopic data brachiopod shell samples from the kapp starostin formation west spitsbergen provide evidence for a large and rapid drop in seawater strontium isotopic ratios close to the permian triassic boundary the strontium isotopic shift is associated with similarly dramatic declines in carbon and oxygen isotope curves recorded in the same samples this pattern can be explained by a paleoceanographic model that we have proposed previously a model in which there is replacement of a largely stagnant stratified ocean by a vigorously mixed one at the permian triassic boundary

stable carbon and oxygen isotope shifts in permian seas of west spitsbergen global change or diagenetic artifact we performed petrographic cathodoluminescence electron microprobe and isotopic analyses of brachiopod shells from the permian kapp starostin formation in west spitsbergen to reevaluate the 9 negative shift in 13c and 18o values reported in 1989 by m gruszczynski s halas a hoffman and k malkowski the 13c and 18o values within shells typically decrease with increasing luminescence indicating diagenesis nonluminescent nl shell 13c and 18o values are 4 3 and 6 2 higher respectively than those of associated cements and matrix for the same stratigraphic interval 13c and 18o values of the nl shells are equal to or substantially greater than those reported by gruszczynski et al for the interval where those authors saw a 10 13c shift our mostly nl spiriferella polaris shells only yield a 1 5 shift gruszczynski et al reported a 9 18o shift whereas we observe almost none our results strongly suggest that the 9 isotopic shifts reported in gruszczynski et al are diagenetic artifacts on the other hand their kazanian tatarian 13c maximum of 7 5 is substantiated by our data this late permian 13c maximum represents the highest spiriferid brachiopod 13c values in the phanerozoic and within stratigraphic uncertainty correlates with the whole rock 13c maximum in east greenland and northwestern europe the 13c shift may reflect changes in global storage of organic carbon indicated by coal volume changes in the late permian

a brachiopod calcite record of the oceanic carbon and oxygen isotope shifts at the permian triassic transition the permian triassic p t mass extinction was the most dramatic of all such events but its cause has thus far remained elusive1 3 carbon and oxygen isotope analyses may offer clues to this puzzle because their results identify major changes in the earth s exosystem4 5 several studies have already dealt with carbon and oxygen isotope records at the p t transition2 6 11 but we present here empirical data derived from the brachiopod shell calcite whose isotope composition generally corresponds to that of the sea water in which the animals lived originally12 15 these data allow us to assess quantitatively the magnitude of changes in the earth s exosystem during that critical time interval

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

an inverse method of modeling thermal histories from apatite fission track data abstract apatite fission track ft ages and track length distributions are important sources of information about the thermal histories of rocks recent advances in the understanding of track annealing in apatite provide a solution to the forward problem of predicting ft ages and track length distributions that result from a given thermal history in this paper a method is presented to address the inverse problem estimation of the thermal history from ft data the inverse method uses an iterative approach the downhill simplex to systematically modify a starting thermal history to achieve satisfactory statistical agreement between the predicted and observed ft age and track length distribution however because of analytical uncertainties a unique thermal history does not exist monte carlo simulations are used to take into account the uncertainties in the data and yield a spectrum of possible thermal histories the results are based on the isothermal annealing model of laslett et al 1 chem geol isot geosci sect vol 65 but because the method uses forward predictions and not an analytical formula specific to a single annealing model alternative annealing models could be used within the same framework this method is an improvement in interpreting fission track data because the range of thermal histories permitted by the data can be evaluated to demonstrate the method it is applied to several sets of test data created by forward modeling of idealized thermal histories the results show that the age at which the sample cooled through its closure temperature and the most general features of the thermal history are revealed however data from partially annealed samples have wide spectra that reflect large uncertainties in the form of the thermal history for such samples ft data alone are not likely to provide strong tests of geologic hypotheses conversely geologic information may play a crucial role in constraining the thermal history spectrum in application to uplift related cooling this inverse method can provide much more realistic assessments of the cooling rate and its uncertainty than are otherwise possible

salinity mapping of coastal groundwater aquifers using hydrogeochemical and geophysical methods a case study from north kelantan malaysia integrated hydrogeochemical and geophysical methods were used to study the salinity of groundwater aquifers along the coastal area of north kelantan for the hydrogeochemical investigation analysis of major ion contents of the groundwater was conducted and other chemical parameters such as ph and total dissolved solids were also determined for the geophysical study both geoelectrical resistivity soundings and reflection seismic surveys were conducted to determine the characteristics of the subsurface and groundwater contained within the aquifers the ph values range from 6 2 to 6 8 indicating that the groundwater in the study area is slightly acidic low content of chloride suggests that the groundwater in the first aquifer is fresh with an average concentration of about 15 8 mg l and high geoelectrical resistivity 45 ohm m on the other hand the groundwater in the second aquifer is brackish with chloride concentration ranging from 500 mg l to 3 600 mg l and very low geoelectrical resistivity 1 000 mg l the groundwater in the third aquifer is fresh with chloride concentrations generally ranging from 2 mg l to 210 mg l and geoelectrical resistivity of greater than 45 ohm m fresh and saltwater interface in the first aquifer is generally located directly in the area of the coast but for the second aquifer both hydrogeochemical and geoelectrical resistivity results indicate that the fresh water and saltwater interface is located as far as 6 km from the beach the considerable chloride ion content initially suggests that the salinity of the groundwater in the second aquifer is probably caused by the intrusion of seawater however continuous monitoring of the chloride content of the second aquifer indicated no significant changes with time from which it can be inferred that the salinity of the groundwater is not affected by seasonal seawater intrusion schoeller diagrams illustrate that sulphate concentrations of the groundwater of the second aquifer are relatively low compared to those of the recent seawater therefore this result suggests that the brackish water in the second aquifer is probably from ancient seawater that was trapped within the sediments for a long period of time rather than due to direct seawater intrusion

application of ert and gpr for demarcating the saline water intrusion in coastal aquifers of southern india to investigate the pathways for saline water intrusion into fresh water aquifers the electrical resistivity tomography ert and ground penetrating radar gpr have been pooled for nagapattinam area of southern india the study area has two river sub basins uppanar river basin urb and cauvery river basin crb ert carried out in urb shows very low resistivity ranging from 0 003 to 1 5 m at shallow depth indicating saline water whereas the resistivity ranges away from the river stream are 1 7 5 0 m cauvery river basin shows resistivity range varying from 3 6 to 150 m indicating a salt fresh water mix similarly few gpr profiles were carried out along ert profiles to confirm the saline water intrusion and its pathway besides the hydrochemical study reveals the same signature of saline and fresh water zones in both river basins water samples collected during field investigation show high total dissolved solids tds content near urb and crb river course ert data was correlated with gpr data to distinguish fresh and saline water zones more accurately urb has more saline water zones at shallow depth nearer to river course and intermediate depth of saline water zones away from the river course while crb is having fresh water towards the inland

δ18o values 87sr86sr and sr mg ratios of late devonian abiotic marine calcite implications for the composition of ancient seawater abstract late devonian frasnian abiotic marine calcite has been microsampled and analyzed for 87 sr 86 sr ratios 18o and 13c values and minor element concentrations portions of marine cement crystals from the alberta and canning basins have escaped diagenetic alteration and preserve original marine 18o values 4 8 0 5 pdb 13c values 2 0 to 3 0 pdb 87 sr 86 sr ratios 0 70805 3 and sr mg weight ratios 0 04 to 0 05 marine 87 sr 86 sr ratios are globally consistent and can be correlated within the alberta basin and among the alberta canning and williston basins correlation of isotopic and chemical data strengthen the conclusion that marine cements from the leduc formation preserve original marine 18o values which are 3 to 4 lower than those of modern marine cements these low 18o values are best explained by precipitation from 18o depleted seawater and not by elevated seawater temperature or diagenetic alteration for comparison with devonian data analogous data were collected from holocene mg calcite and aragonite marine cements from enewetak atoll marshall islands mg calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater and mg calcite cements are homogeneous with respect to sr and mg contents empirically derived homogeneous distribution coefficients for mg and sr in modern abiotic mg calcite from enewetak atoll are 0 034 and 0 15 respectively an equation describing the dependence of dsr on mg content was based on a compilation of sr and mg data from holocene abiotic marine calcite dsr 3 52 10 6 ppm mg 6 20 10 3 unlike that derived from experimental data this sr mg relation is consistent over a range of 4 to 20 mol mgco3 and may represent precipitation phenomena which are minimally controlled by kinetic effects comparison of sr and mg contents of analogous devonian and holocene marine cements suggests that the mg ca ratio of late devonian seawater was significantly lower and that the sr ca ratio was significantly higher than that of modern seawater

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

present day heat flow thermal history and tectonic subsidence of the east china sea basin the east china sea basin is located in the convergence area between the eurasian plate the pacific plate and the philippine sea plate and consists of two depressions the taibei depression in the west and the xihu depression in the east heat flow measurements show that the east china sea basin is characterized by present day heat flow around 70 6 mw m 2 varying between 55 and 88 mw m 2 no significant difference in heat flow is observed between the xihu and the taibei depressions thermal history reconstruction using vitrinite reflectance suggests that the thermal history was however different in the taibei and the xihu depressions paleo heat flow values when the pretertiary formations experienced their maximum temperature at the end of the paleocene reached a mean of 82 mw m 2 in the taibei depression much higher than the present day value the lower tertiary sediments in the xihu depression experienced maximum temperatures at the end of oligocene 35 4 23 3 ma and reached a mean paleo heat flow value of 83 mw m 2 tectonic subsidence analysis shows that the timing of the major rifting episode was different across the east china sea basin the rifting occurred from the late cretaceous w65 ma to the early eocene w55 ma in the taibei depression followed by thermal subsidence from the late eocene to the end of miocene 23 3 5 2 ma in contrast in the xihu depression the initial subsidence lasted until the early miocene and thermal subsidence to the end of miocene from pliocene to the present an accelerated subsidence took place all along the west pacific margin of asia significant thicknesses of strata were removed from the unconformities in the basin the mean amount of erosion was 1147 m from the paleocene and 1208 m above the oligocene in the taibei depression and 1409 m from the oligocene in the xihu depression q 2004 elsevier ltd all rights reserved

fission track evidence for quaternary uplift of the nanga parbat region pakistan the north striking nanga parbat haramosh massif protrudes into the northwestern himalaya along the axis of a great syntaxis1 2 fig 1 where the hindu kush karakorum and himalayan ranges converge as the indus suture zone3 enters this region from the east it bifurcates into two branches encircling what may be a docked island arc terrane4 the southern branch the main mantle thrust crops out on both flanks of the nanga parbat massif forming a tight structural loop5 this massif and the adjacent terrane contain some of the highest peaks in the himalaya nanga parbat and the indus river located just 20km away define the world s greatest continental relief 6 930 m we report here the discovery of unexpectedly young sphene zircon and apatite fission track dates from the nanga parbat haramosh massif these dates as low as 1 3 myr for zircon and 0 4 myr for apatite imply that during the pleistocene the nanga parbat region was uplifted and eroded at nearly 1 cm yr 1

the relationship between track shortening and fission track age reduction in apatite combined influences of inherent instability annealing anisotropy length bias and system calibration abstract the relationship between reduced track density 0 and reduced mean confined track length l l 0 during annealing has been studied for both spontaneous and induced tracks in four apatite samples with different chemical composition compositional range and origin and with spontaneous tracks giving mean confined track lengths varying from 14 5 m down to 12 3 m in all four apatites induced tracks show a relationship between l l 0 and 0 composed of two regions at higher values the two appear to be equal while at lower values l l 0 is greater than 0 this can be understood qualitatively in terms of the anisotropy of annealing and the bias against revelation of short tracks data from three apatites of uniform composition show near identical relationships in a sample showing a range of apatite compositions the point of divergence from the 1 1 relationship is somewhat higher than in the uniform composition apatites because individual grains anneal at different rates and the presence of highly annealed grains affects the track density more strongly than the mean track length spontaneous tracks show similar relationships to those observed for induced tracks in each sample when the data are renormalised to allow for the natural annealing present in the spontaneous tracks previous studies which led to the idea of length reduction without density reduction for spontaneous tracks did not renormalise density data as well as length data thereby distorting the apparent relationship data for the multi compositional apatite sample where annealing has taken place in geological conditions also agrees with the laboratory annealing data for both spontaneous and induced tracks this consistency suggests that a single process is responsible in all three cases implying that a laboratory based description of annealing can be applied to geological conditions with confidence recognition that spontaneous tracks in apatite are commonly annealed suggests that in general the fission track age should be interpreted as a reflection of both the time over which tracks have been retained and the distribution of etchable track lengths since the latter is a manifestation of the thermal history the fission track age should be interpreted in similar terms

the internal structure of an active sea floor massive sulphide deposit the hydrothermal circulation of sea water through permeable ocean crust results in rock water interactions that lead to the formation of massive sulphide deposits these are the modern analogues of many ancient ophiolite hosted deposits1 4 such as those exposed in cyprus here we report results obtained from drilling a series of holes into an actively forming sulphide deposit on the mid atlantic ridge a complex assemblage of sulphide anhydrite silica breccias provides striking evidence that such hydrothermal mounds do not grow simply by the accumulation of sulphides on the sea floor indeed the deposit grows largely as an in situ breccia pile as successive episodes of hydrothermal activity each form new hydrothermal precipitates and cement earlier deposits during inactive periods the collapse of sulphide chimneys dissolution of anhydrite and disruption by faulting cause brecciation of the deposit the abundance of anhydrite beneath the present region of focused hydrothermal venting reflects the high temperatures 150 c currently maintained within the mound and implies substantial entrainment of cold sea water into the interior of the deposit these observations demonstrate the important role of anhydrite in the growth of massive sulphide deposits despite its absence in those preserved on land

on the salt water intrusion into the durusu lake istanbul a joint central loop tem and multi electrode ert field survey durusu lake is the biggest and most important freshwater source supplying drinking water to the european side of istanbul in this study electrical resistivity tomography ert and transient electromagnetic tem measurements were applied to detect a possible salt water intrusion into the lake and to delineate the subsurface structure in the north of durusu lake the ert and tem measurements were carried out along six parallel profiles extending from the sea coast to the lake shore on the dune barrier tem data were interpreted using different 1 d inversion methods such as occam marquardt and laterally constrained inversion lci ert data were interpreted using 2 d inversion techniques the inversion results of ert and tem data were shown as resistivity depth sections including topography the sand layer spreading over the basin has a resistivity of 150 400 omega m with a thickness of 5 10 m the sandy layer with clay silt and gravel has a resistivity of 15 100 omega m and a thickness of 10 40 m followed by a clay layer of a resistivity below 10 omega m when the inversion of these data is interpreted along with the hydrogeology of the area it is concluded that the salt water intrusion along the dune barrier is not common and occurs at a particular area where the distance between lake and sea is very close using information from boreholes around the lake it was verified that the common conductive region at depths of 30 m or more consists of clay layers and clay lenses

why the oxygen isotopic composition of sea water changes with time the oxygen isotopic composition of oxygen in minerals and oxygen in water this sea water is determined by interactions with equilibrium fractionation is a strong function of fresh silicate rocks interactions at high temperature varying for many minerals from about

two dimensional inversion of direct current resistivity data incorporating topography by using finite difference techniques with triangle cells investigation of kera fault zone in western crete in this study we suggest the use of a finite difference fd forward solution with triangular grid to incorporate topography into the inverse solution of direct current resistivity data a new inversion algorithm was developed that takes topography into account with finite difference and finite element forward solution by using triangular grids using the developed algorithm surface topography could also be incorporated by using triangular cells in a finite difference forward solution initially the inversion algorithm was tested for two synthetic data sets inversion of synthetic data with the finite difference forward solution gives accurate results as well as inversion with finite element forward solution and requires less cpu time the algorithm was also tested with a field data set acquired across the kera fault located in western crete greece the fault location and basement depth of sedimentary units were resolved by the developed algorithm these inversion results showed that if underground st

the jameson land basin east greenland a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime abstract the late mesozoic and cenozoic thermal history of the jameson land basin is constrained by new apatite and zircon fission track ft data of surface permian to jurassic sedimentary rocks the results show a general regional thermal evolution related to burial to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval 125 c followed by cooling mainly due to cenozoic uplift and erosion faulting and differential movements in the basin generally occurred after cooling below the apatite partial annealing zone paz 75 125 c however in the northern part of the basin the data suggest a thicker sediment cover or localized heating related to an earlier fracture zone both apatite ft analysis and vitrinite reflectance values reveal a postmature signature for the studied rocks in the northeastern jameson land and premature to mature for the western central and southern jameson land rocks with respect to generation of hydrocarbons the chemical variations of apatite enhance the possibility of recognizing sample positions near maximum temperatures in the paz furthermore the pb zn mineralization pattern closely follows the tertiary maturity trend given by the ft data the type and distribution of mineralization suggest that it was influenced by the regional thermal evolution of the basin in the northeast domain circulating fluids may have overprinted the regional thermal record before ca 20 ma basaltic dyke and sill intrusions 55 45 ma locally caused resetting of apatite ft ages but generally the direct influence from upper crustal magmatic activity played only a minor role the thermal evolution in northeast jameson land is related to the late tectonic evolution of the northeast atlantic involving a change in ridge position at ca 25 ma which followed the passage of the proto icelandic mantle plume at 63 40 ma

the isotopic composition of strontium and sulfur in seawater of late permian zechstein age abstract the paleozoic minima of 87 sr 86 sr ratios and 34 s values in seawater are observed in anhydrite layers of the stassfurt a 2 and aller a 4 cycles of evaporation of late permian age in germany these minima were probably caused by extremely low rates of continental runoff and bacterial sulfate reduction thereafter conditions changed suddenly with a steeply increasing supply of radiogenic sr and of nutrients into seawater the latter induced a large growth in the production of organic material in bacterial activity in sediments and in the flow of isotopically heavy sulfur back into the oceans this large change in the cycles of s and sr as well as of c and o within the relatively short zechstein period 2 5 ma reflects a considerable modification of the plate tectonic and environmental conditions shortly before the beginning of the mesozoic era the ochoan deposition in the usa is probably of the same age as the stassfurt leine evaporation in w europe

global geochemical cycles of carbon sulfur and oxygen time resolved data on the carbon isotopic composition of carbonate minerals and the sulfur isotopic composition or sulfate minerals show a strong negative correlation during the cretaceous carbonate minerals are isotopically heavy during this period while sulfate minerals are isotopically light the implication is that carbon is being transferred from the oxidized carbonate reservoir to the reservoir of isotopically light reduced organic carbon in sedimentary rocks while sulfur is being transferred from the reservoir of isotopically light sedimentary sulfide to the oxidized sulfate reservoir these apparently oppositely directed changes in the oxidation state of average sedimentary carbon and sulfur are surprising because of a well established and easy to understand correlation between the concentrations of reduced organic carbon and sulfide minerals in sedimentary rocks rocks rich in reduced carbon are also rich in reduced sulfur the isotopic and concentration data can be reconciled by a model which invokes a significant flux of hydrothermal sulfide to the deep sea at least during the cretaceous

thermal history and tectonic subsidence of the bohai basin northern china a cenozoic rifted and local pull apart basin the bohai basin is a part of the larger bohai bay basin a cenozoic rifted intraplate basin heat flow measurements show that the bohai basin is characterized by present day heat flow varying between 53 and 74 mw m 2 with a mean of 63 mw m 2 however thermal history analyses derived from vitrinite reflectance vr and apatite fission track aft data indicate that tertiary cooling took place following a period of much higher paleo heat flow 70 90 mw m 2 prior to 25 million years to the present furthermore tectonic subsidence analysis reveals that the bohai basin experienced episodic sub rifting processes from the eocene to the end of the oligocene the post rift thermal subsidence was superimposed by intensified subsidence from the late miocene 12 million years in the bozhong depression and from the early quaternary 2 4 million years in the east liao bay indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike slip faults the present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the bohai basin the bohai basin is an early cenozoic rifted and local pull apart sub basin of the larger bohai bay basin 2001 elsevier science b v all rights reserved

dynamic feedback between a continentlike raft and thermal convection seismic observations of the mantle which include long wavelength structure a k 1 dependence of heterogeneity on harmonic k and a heterogeneous upper boundary layer and supercontinent kinematics may be explained by the dynamic interaction between a continent like raft and thermal convection we have formulated finite element models of convection with rafts simulating continental plates in a cylindrical geometry the azimuthal interconnectivity of this geometry is vital to resolve the two way dynamics between rafts and convection computations show that 1 raft motion is periodic 2 long wavelength thermal structure is significant within both thermal boundary layers and the fluid interior and 3 the large scale thermal structure with a wavelength longer than the width of raft is responsible for raft motion these three results which are observed for a range of rayleigh numbers internal heating rates and raft sizes are a direct consequence of the dynamic interaction between the raft and convection the physical processes for a model with a rayleigh number of 10 5 are representative when the raft is stationary due to the less efficient heat transfer through the raft and instabilities from the bottom boundary layer heat accumulates beneath the raft and results in long wavelength thermal anomalies the long wavelength thermal anomalies enhance raft motion accompanying the enhanced raft movement the long wavelength thermal anomalies diminish and the raft velocity decreases or the raft comes to rest since convection models without rafts generate less long wavelength heterogeneity compared to the models with rafts or continental plates we suspect that continental plates may play a crucial role in mantle dynamics interestingly raft motion with a period of about 10 transit times is usually significant 10 transit times is about 600 m y if scaled to the earth this is close to the observed 300 500 m y period of supercontinent aggregation and dispersal

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

extremely acid permian lakes and ground waters in north america evaporites hosted by red beds red shales and sandstones some 275 265 million years old extend over a large area of the north american mid continent1 they were deposited in non marine saline lakes pans and mud flats2 settings that are typically assumed to have been alkaline here we use laser raman microprobe analyses of fluid inclusions trapped in halites from these permian deposits to argue for the existence of highly acidic ph 1 lakes and ground waters these extremely acidic systems may have extended over an area of 200 000 km2 modern analogues of such systems may be natural acid lake and groundwater systems ph 2 4 in southern australia3 4 5 6 7 8 9 both the ancient and modern acid systems are characterized by closed drainage arid climate low acid neutralizing capacity and the oxidation of minerals such as pyrite to generate acidity the discovery of widespread ancient acid lake and groundwater systems demands a re evaluation of reconstructions of surface conditions of the past and further investigations of the geochemistry and ecology of acid systems in general

determination and evaluation of saltwater intrusion on bafra plain joint interpretation of geophysical hydrogeological and hydrochemical data saltwater intrusion and its spatial distribution using a multidisciplinary approach were investigated on the northeast coast of bafra plain which is one of the most important delta plains in turkey intensive agricultural activity in the study area which supplies the local and international market with agricultural products is increasing the importance of this ecosystem even the groundwater potential and supply are high the main problem is the groundwater degradation due to salinization moreover local lithological tectonic and hydrological complexities increase the uncertainty in the interpretation of the collected chemical geophysical etc data providing an inaccurate geomodel specifically in the study area there are mixtures of freshwater saltwater aquifers and geological units containing clay lenses thin layers and fine grained alluvium at the same time these geological formations have similar resistivity responses and the ambiguity of the collected electric and electromagnetic geophysical data is high therefore a third geophysical method seismic refraction which is sensitive to different physical parameters to constrain the uncertainty in the interpretation was used in this study the salinization of bafra plain and complex aquifer system was revealed with the combined use of direct current resistivity and transient electromagnetic data constrained by seismic refraction data and guided by hydrogeological and hydrochemical data using information obtained from multidisciplinary study we inferred that the intrusion is monitored inland up to 3 5 km the intrusion is traced after approximately the first 10 m depth in the central part of the plain additionally in some areas it was concluded that the intrusion is interrupted by clay lenses also drainage channels constructed in the plain have brought soil salinization under control but have not completely succeeded in controlling the saltwater intrusion into the deeper aquifer the saltwater intrusion can move more inland if groundwater pumping is not controlled especially in areas close to the river

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

sr and nd isotopes at the prmian triassic boundary a record of climate change abstract we present a detailed curve of seawater 87sr 86sr for the middle permian to triassic based on analyses of conodonts from overlapping sections in the u s a pakistan correlated using conodont biostratigraphy the isotope ratio decreased in the middle permian at an average rate of 0 000062 ma 1 reached a minimum in the capitanian 257 258 ma and increased in the late permian at an average rate of 0 000097 ma 1 the late permian rate of increase was roughly two and a half times greater than the average increase over the past 40 ma and approximately equal to the highest cenozoic rates which occurred over much shorter time intervals modeling results suggest that decreasing middle permian 87sr 86sr ratios were driven by changes in the riverine sr flux to the oceans while increasing ratios in the late permian triassic are attributed to both increased riverine 87sr 86sr and flux the reduced middle permian riverine flux coincides with extreme continental aridity associated with the formation of pangea and recorded by massive evaporite deposits in addition mountains in the equatorial region of pangea may have created a rain shadow thereby minimizing precipitation in regions that currently contribute the bulk of chemical weathering products to the ocean increasing riverine 87sr 86sr in the late permian is suggested by the observation that 143nd 144nd values decrease at the same time however the source of radiogenic sr is not known frequently cited mechanisms for increasing 87sr 86sr in runoff such as glaciations and continent to continent collisions coincide instead with decreasing seawater 87sr 86sr in the middle permian one possible source may have been deep erosion into older orogens associated with a dramatic increase in chemical weathering in the late permian the cause of enhanced weathering appears to have been increased levels of atmospheric co2 with associated global warming and increased humidity proposed sources of co2 include dissociation of gas hydrates and oxidation of organic matter during extreme sea level regression as well as volcanic emissions from siberian traps eruptions continental floral and faunal distributions are consistent with this interpretation as are oceanic 13c patterns and variations in shallow water sediment lithologies

environmental isotope systematics of the groundwater system of southern kuwait the carbonate dammam formation of eocene age and the unconformably overlying clastic kuwait group of rocks of mio pliocene age are the two aquifers that provide useable groundwater salinity 5000 mg l or less in kuwait these aquifers extend beyond the political limits of the country to saudi arabia and iraq a detailed environmental isotopic 2 1h 18 16o 13 12c 3h 14c characterization of the groundwater system of southern kuwait a regional aquifer extending beyond the political limits of the country to saudi arabia and iraq has been carried out to understand its hydrodynamics so as to evolve a better conceptual flow model of the aquifer system from the study it was observed that the groundwater salinity of the kuwait group aquifer increases generally from south west to north east although locally a few of them show low values groundwater samples from the dammam formation aquifer are characterized by a relatively low mineralization compared with those of kuwait group aquifer the water in the kuwait group aquifer in the south western part of the country is na cl type and in the dammam formation aquifer is na cl to so4 na cl so4 type a wide range of d excess of the groundwater samples was seen kuwait group aquifer 16 0 to 20 6 dammam formation aquifer 22 8 to 19 6 indicating that the groundwater system contains more than one type of water with different origin recharge area and history time evaporation climate in both the aquifers the groundwater samples from south and central parts and along the coast showed negative d excess values with heavier 18o and 2h indicating older recharge and greater degree of evaporation prior to recharge the 18o and 2h of the initial recharge waters respectively are 8 8 and 40 for the kuwait group aquifer and 7 2 and 32 for the dammam formation aquifer the corrected 14c ages tamer s model of groundwater samples of kuwait group aquifer ranged from 5000 to 24 000 a b p and that of dammam formation aquifer ranged from 6000 to 20 000 a b p the intermediate groundwater in the south west and central parts of kuwait group aquifer is recharged during humid period 5000 to 10 000 a b p whereas deeper groundwater in the south is recharged during arid period 9000 16 000 a b p the recharge to the dammam formation aquifer mostly occurred during a cooler humid phase in the past the dammam formation aquifer water is hydraulically well mixed below 350 m depth interconnection between the two aquifers established near the coast and south west border of the country the results of the study were used to refine the existing conceptual groundwater flow model for the aquifer system

igneous origin of co2 in ancient and recent hot spring waters and travertines from the northern argentinean andes abstract thermal travertines are an archive of co2 sources and sinks in hydrothermal systems two major regional factors control travertine precipitation water availability and co2 supply thus travertines form a valuable archive of hydrodynamic variability and sources of main contributions to dissolved inorganic carbon dic it is relevant to determine the main dic sources of thermal waters i e organic matter degradation recycled from older carbonates emission of deep seated magmatic co2 as they are key inputs to calculate the lithosphere atmosphere co2 budget the antuco travertine from the central andes represents one of such archives with a 500 ky record of accretionary periods dated as 425 320 260 and 155 ky bp related to high hydrothermal activity of hot springs it consists of two travertine units 1 a lower massive unit displaying large calcite pseudomorphs after aragonite that precipitated in proximal ponds with abundant water and 2 an upper stratified unit showing more distal facies bearing siliciclastics and manganese and iron oxides the replacement of aragonite by calcite in the lower unit was related to the decrease of water salinity in the thermal system through time in the antuco travertine dic 13c values of travertine parental waters of around 9 suggest that co2 was related to igneous processes and volcanic activity and released along deep seated faults relative water rock ratios derived from 18o values and fluid inclusion microthermometric data from travertine carbonates are consistent with an interpretation of greater water availability in the hydrothermal system during the late pleistocene than at present the different petrographic features and isotopic signatures are interpreted to reflect increased water availability during more humid periods in the altiplano which triggered precipitation of travertine bodies travertine growth took place during interglacial humid climate periods between marine isotope stages mis 3 and 9 which correspond to highstand events in large lakes of the andean altiplano results of this study illustrate that volcanic activity furnishing rather constant co2 and heat fluxes were the key controls of thermalism in the altiplane region during the quaternary whilst climatic changes humid vs arid periods in the late pleistocene controlled mineralogy facies and architecture of the travertines the combined use of 13c and 87sr 86sr signatures in carbonate precipitates has been proven to be of major relevance to evaluate the co2 sources along fault zones in this study

strontium isotopic composition of mid cretaceous seawater the 87sr 86sr ratio in fish teeth separated from mid cretaceous marl and black shale from the northeastern apennines and venetian alps italy define three periods of low 87sr 86sr ratio at 121 to 124 million years ago ma 110 to 115 ma and 89 to 91 ma the 87sr 86sr excursions correspond to oceanic anoxic events represented by the livello selli livello 113 livello urbino and livello bonarelli black shale marker beds and probably reflect an increase in the low 87sr 86sr hydrothermal strontium flux associated with the emplacement of the ontong java and kerguelen plateaus 120 to 110 ma and the caribbean plateau 89 to 91 ma the modeled flux is consistent with the volumes and eruption rates of the oceanic plateaus but is far smaller than expected from the proposed cretaceous crustal production rates of 50 to 100 percent greater than modern

thermal annealing of fission tracks in fluorapatite chlorapatite manganoanapatite and durango apatite experimental results it is well known that the optically measured lengths of fission tracks in apatite crystals are a function of etching conditions crystallographic orientation of the track composition of the crystal and the state of thermal annealing in this study we standardize etching conditions and optimize track length measurability by etching until etch pits formed at the surface of each apatite crystal reached widths of about 0 74 m etching times using 5m hno3 at 21 c were 31 s for otter lake quebec fluorapatite 47 s for durango mexico apatite 33 s for portland connecticut manganoanapatite and 11 s for bamle norway chlorapatite an etching experiment using two etchant strengths 5m and 1 6m hno3 revealed that despite significant differences in etch pit shape fission track length anisotropy with respect to crystallographic orientation of the tracks is not a chemical etching effect a series of 227 constant temperature annealing experiments were carried out on nuclear reactor induced tracks in orient

an atmospheric pco2 threshold for glaciation in the late ordovician the late ordovician glaciation differs from other major phanerozoic glaciations because of its short duration 1 m y a satisfactory explanation for this glaciation must be able to account for its sudden initiation short duration and rapid termination mechanisms operating on tectonic time scales appear to be precluded given recent studies of a major perturbation in the carbon cycle during the glaciation a climate model investigation of the sensitivity of the late ordovician climate to changes in atmospheric p co2 was undertaken under the condition of a 4 5 reduction in solar luminosity permanent snow cover taken as a key indicator of potential for glaciation is dramatically different between five experiments the range of 18x present atmospheric level co2 ice free to 8x runaway icehouse lies within the uncertainty of previous geochemical estimates of late ordovician atmospheric p co2 the strong sensitivity to the modest direct forcing from p co2 changes is due to the ice albedo feedback a plausible increase in organic carbon burial could have drawn down enough atmospheric co2 to have briefly lowered the climate system below a critical glacial inception threshold at the end of the ordovician conversely a high p co2 is required for the rest of the early paleozoic which was essentially ice free

coastal aquifer assessment based on geological and geophysical survey northwestern crete greece groundwater preservation comprises a major problem in water policy the comprehension of the groundwater hydraulic systems can provide the means to approach this problem generally drilling is expensive and time consuming on the other hand new techniques have been applied during the last few decades that provide useful information on the depth and quality of aquifers among them transient electromagnetic method tem is an appealing method that provides fast results with minimum field crew and solves several hydrogeological problems many portable systems for single site measurements are commercially available the tem fast 48hpc was used for acquiring 106 soundings in the northwestern crete in greece for defining the hydrogeological characteristics of the study area since there were no available data from boreholes detailed geological hydrolithological and tectonic survey was applied prior to the geophysical measurements all the data were integrated to produce a secure and reliable hydrogeological model for the study area prior to any future hydrowell specifically geometrical and hydraulic data of the study area groundwater were acquired two unconnected aquifers were detected and their possible contamination due to saltwater intrusion was analyzed and eliminated moreover a location for borehole construction and groundwater pumping based on the potential of the aquifer system was proposed finally the contribution of tem and electrical resistivity tomography geophysical methods in studying complex coastal aquifers is shown by this work

reply to the comment by s t petsch on carbon isotope ratios of phanerozoic marine cements re evaluating global carbon and sulfur systems

saltwater intrusion in an irrigated agricultural area combining density dependent modeling and geophysical methods saltwater intrusion is one of the most important water quality problems in coastal aquifers especially in areas with increased water demands geophysical techniques can provide a non invasive and cost effective approach for determining the geometrical characteristics of an aquifer and for guiding the saltwater intrusion modeling process and in turn reducing the model s inherent uncertainty in this work the above concept was applied in the tympaki basin in heraklion greece the transient electromagnetic method was used to obtain an accurate 3 d geomodel bedrock geometry and fault detection of the basin this in turn was used to guide the construction of a density dependent groundwater flow and transport simulation model the results show significant advancement of the saltwater intrusion front in the northern part of the study area while the phenomenon is less pronounced in the central and southern parts this is mainly attributed to the combined effect of the fault in the northern part of the basin the uplifted neogene deposits in the central part and the freshwater inflow from the festos corridor in the southern part

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton

consolidation and break up of the south american platform in southeastern brazil tectonothermal and denudation histories the different tectonic stages that occurred at the end of the proterozoic and during the phanerozoic have an important bearing on the tectonothermal history of the south american platform and its consolidation geochronological data u pb monazite 40ar 39ar whole rock and apatite fission track analysis from precambrian rocks of the southeastern brazilian coastline permit the modeling of a long term thermal history of the crust and constrain variable denudation rates using these data a temperature time diagram reflects a period of accelerated exhumation during the end of the brasiliano orogeny followed by long stability and reactivation of the platform during the rifting phase of the south atlantic ocean u pb zircon and monazite blocking temperature of ca 650 c data from a series of igneous bodies suggest that a tangential and transpressional tectonic regime occurred between 625 and 610 ma during the following escape tectonics between 610 and 590 ma the exhumation process indicates cooling rates of ca 12 c ma 40ar 39ar biotite ages between 540 and 510 ma ca 300 c and a corrected fission track age on apatites 100 c of 480 ma indicate an exhumation event related to block tectonics with huge vertical displacement along shear zones a long stabilization phase with low exhumation and cooling rate around 0 25 c ma was recorded from the cambro ordovician to the mesozoic at 65 ma an acceleration of the exhumation through denudation and reworking of the south american surface with cooling rate of 1 5 c ma is observed the uplift of the mantiqueira and serra do mar mountain ranges along the southeast brazilian coastline works as a climatic barrier provoking lateral erosional processes causing long term scarp retreat combined with intense but progressive denudation towards the continent a denudation of 2 5 to 4 km was calculated for such processes this lateral retreat of escarpments and flexural response can provide important insights regarding marginal isostatic uplift and the evolution of offshore sedimentary basins of southeast brazil

integrated geophysical geochemical and hydrogeological investigation of shallow groundwater resources in parts of the ikom mamfe embayment and the adjoining areas in cross river state nigeria information generated from geophysical geochemical and hydrogeological data has been used in assessing the groundwater resource potential quality and usability and in mapping flow directions within the shallow subsurface of the mamfe embayment cross river state nigeria the electrical resistivity technique in which the schlumberger s vertical electrical sounding field procedure has been adopted was the geophysical method employed lithology logs from drilling records discharge rates static water level information were the hydrogeological information utilized while the geochemical techniques involve analyses of water samples apparent resistances were measured using different resistivity meters including oyo mcohm model 2115 abem terrameter sas300b and sas1000 models and igis ssp ats mrp model with maximum current electrode separation reaching 1 km in some communities geological information was used as control in the modelling and interpretation of all geophysical data the physico chemical parameters of the water samples from the different water sources in the area were determined using different analytical techniques and in some cases by in situ direct measurement of some parameters measured values of electrical conductivity static water level available aquifer discharge information and calculated sar and na were integrated into the geophysical and hydrogeological results the shallow subsurface of the area is segmented into four hydrogeological provinces crystalline basement province cbp cross river plain province crpp nkporo afikpo shales province nasp and alluvial buried river province abrp with localized groundwater flow patterns results indicated that the alluvial discharge rate of 3 83 l s fractured sandstone discharge rate of 2 43 l s and basement discharge rate of 1 80 l s aquifers are more yielding than the aquifers in areas covered with deformed shales discharge rate of 0 62 l s and siltstone aquifers discharge rate of 0 97 l s the aquifer horizons are inhomogeneous and anisotropic with topography and lithology exerting significant influence on groundwater flow direction however there appears to be some high yielding aquifers at depths greater than 100 m in the crpp areas although researches on their distribution are still ongoing precipitation is the major source of recharge and the water is enriched with na k ca2 mg2 text hco 3 cl text so 4 2 and text no 3 throughout the year graphical analyses of hydrochemical data using piper and stiff diagrams show that ca mg co3 hco3 is the dominant water facies results from ec sar and na show that the water is fresh and belongs to the good to excellent class and is therefore suitable for domestic agricultural and industrial use

a numerical model of the evolution of ocean sulfate and sedimentary sulfur during the last 800 million years abstract a reservoir model describing the time evolution of the sedimentary cycle of sulfur over the past 800 my has been developed as a first approximation the ocean sulfate concentration is assumed to be time independent with this assumption the model is integrated backward in time and a new initialization procedure is derived in order to calculate the present state of the system which must be compatible with both observational data and model equations the effects of a variation of the present state of the cycle on its past evolution are investigated it is found that when the present gypsum reservoir content is too low or when the weathering rate constants are too high no acceptable solution can be obtained for the evolution of the cycle since one reservoir is forced to depletion the sensitivity of the model to the mean isotopic composition of the sedimentary system and to the fractionation factor during pyrite formation is also studied moreover a model with time dependent ocean sulfate concentration was developed the existence of an acceptable solution appears to be linked to the steady state hypothesis for ocean sulfate since a model with no acceptable steady state solution may be integrated until t 800 my without any problem of reservoir depletion when the time dependent equations are used a tentative evolution of the ocean sulfate concentration is calculated it is shown that this concentration is negatively correlated to the 34s of seawater sulfate the carbon cycle is modelled in order to compare the calculated 13c of carbonate deposits to the observational data