iodine as a sensitive tracer for detecting influence of organic rich shale in shallow groundwater abstract public and regulatory agencies are concerned over the potential for drinking water contamination related to high volume hydraulic fracturing hydrofracking of the marcellus shale in pennsylvania and in new york state nys where exploitation of marcellus gas has not yet begun unique natural tracers are helpful for distinguishing the influence of formation water and or flow back water here we use halogen concentrations particularly bromine and iodine to characterize natural variability of baseline water chemistry in the southern tier of nys majority of streams and drinking water wells have br and i concentrations below 1 and 0 1 m respectively a range typical for relatively pristine surface water and shallow groundwater wells that have higher br and i concentrations are likely affected by formation waters br i ratios indicate two different sources of formation waters in these wells possibly controlled by geologic settings our results suggest that iodine combined with other halogens may be a novel and sensitive tool for fingerprinting trace levels of formation water signal in drinking water sources

lateral injection of oxygen with the bosporus plume fingers of oxidizing potential in the black sea saline and warm mediterranean water flowing through the bosporus strait maintains a permanent pycnocline with vertical separation of oxic o 2 suboxic absence of o2 and h2s and anoxic h2s zones in the black sea the stable suboxic zone implies restricted vertical mixing of the upper oxic and lower anoxic layers and limited vertical flux of oxygen that cannot balance the upward flux of sulfide we report data that directly confirm massive lateral injections 200 km from the bosporus of oxygen enriched waters of the bosporus plume created by the mixing of shallow cold intermediate layer black sea water with mediterranean water these plume waters are laterally injected into the oxic layer and more importantly into the suboxic and anoxic layers over several small vertical scales fingers of 5 m at water densities st from 15 0 to 16 4 o2 injection oxidizes mn ii to mn iii iv which then oxidizes h2s the onset of h2s detection occurs in deeper waters in the southwest 170 m st 16 4 relative to the west central black sea 110 m st 16 2 and coincides with increased mno2 and s8 formation in the southwest

louann salt geochemistry gulf of mexico sedimentary basin u s a a preliminary synthesis abstract samples of jurassic salt and anhydrite were obtained from throughout the gulf of mexico sedimentary basin salt samples have been analyzed for bromide content and 87 sr 86 sr of anhydrite inclusions and anhydrite for 87 sr 86 sr most samples of diapiric salt contain 87 sr 86 sr ratios are commonly radiogenic relative to the ratio in presumed coeval jurassic callovian seawater both these observations suggest that during deformation salt undergoes extensive rock water interaction losing bromide to the reacting brines and incorporating radiogenic sr similar behavior of anhydrite during deformation with respect to sr is also observed samples of deeply buried salt exhibit bromide concentrations consistent with the precipitation of marine halite but include several samples with extremely high values few 87 sr 86 sr ratios however seem to be characteristic of coeval callovian seawater samples with normal bromide content but radiogenic sr suggest primary deposition from or recrystallization in the presence of radiogenic fluids with marine like bromide content samples with extremely high bromide content and radiogenic sr values suggest recrystallization in fluids with elevated bromide content due to loss of bittern phases or extensive rock water interaction of bedded salt during deep burial the data suggest a dynamic system in which physical modification of evaporites during deformation and deep burial is accompanied by chemical modification

discovery of an anoxic basin within the strabo trench eastern mediterranean we report here the discovery of a basin which we call the tyro basin in the eastern mediterranean in which anoxic conditions exist and organic rich sediments are accumulating bottom water samples show extremely high salt concentrations a horizontal midwater sound reflector about 70 m above the basin floor was observed in a seismic reflection profile across the basin from shipboard observations we conclude that dissolution of messinian evaporites exposed by faulting in the sides of the basin causes stagnant bottom conditions this basin provides an opportunity to test some of the hypotheses concerning the formation of sapropels present in cores collected from the same area cores taken in an adjacent similar basin for which we propose the name kretheus basin indicate a recent change from anoxic to oxygenated conditions which was probably caused by tectonic activity associated with the strabo trench

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

trace metal distributions in seawater and anoxic brines in the eastern mediterranean sea abstract the vertical distribution of dissolved and particulate trace metals mn fe ni cu cd is reported for seawater and the anoxic brines of tyro and bannock basins in the eastern mediterranean in normal mediterranean seawater the distribution of dissolved trace metals is governed by water mass circulation as well as by local input sources for cd and possibly cu steady state behaviour is not a viable assumption probably as a result of anthropogenic sources in agreement with previous reports no correlation was observed between dissolved ni cu cd and the major nutrients at the seawater brine interface all trace metals show dramatic changes in concentration in the brines the concentrations of dissolved fe and mn are strongly elevated compared to overlying waters yet probably limited by formation of solid sulfide and or carbonate phases the distributions of dissolved fe and sulfide show a remarkable mirror image of those found previously in the orca brine gulf of mexico and the ionic concentration products are approximately the same in all three basins the difference in absolute fe and sulfide concentrations is thought to be caused by a high supply of fe to orca basin concentrations of dissolved ni cu and cd in the brines are at least one order of magnitude lower than in overlying waters most likely due to formation of solid sulfide phases we believe these data provide the first indication of substantial nickel sulfide co precipitation within an anoxic basin particulate metal concentrations are elevated at the seawater brine interface and are probably associated with the presence of solid sulfide phases in addition the extreme density gradient at the interface will slow the sinking rate of particles and lead to accumulation of particles at the interface due to accumulation

marine geochemical cycles of the alkali elements and boron the role of sediments abstract we have analysed the concentrations of li k rb cs and b and the isotopic ratios of li and b of a suite of pore fluids recovered from odp sites 1037 leg 169 escanaba trough and 1034 leg 169s saanich inlet in addition we have analysed dissolved k rb and cs concentrations for estuarine mixing of the ganges brahmaputra river system together these data sets have been used to assess the role of sediments in the marine geochemical cycles of the alkali elements and boron uptake onto clay minerals during estuarine mixing removes 20 30 of the riverine input of dissolved cs and rb to the oceans prior to this study the only other recognised sink of rb and cs was uptake during low temperature alteration of the oceanic crust even with this additional sink there is an excess of inputs over outputs in their modern oceanic mass balance pore fluid data show that li and rb are transferred into marine sediments during early diagenesis however modeling of the li isotope systematics of the pore fluids from site 1037 shows that seawater li taken up during marine sedimentation can be readily returned to solution in the presence of less hydrated cations such as nh4 this process also appears to result in high concentrations of pore fluid cs relative to local seawater due to expulsion of adsorbed cs from cation exchange sites flux calculations based on pore fluid data for a series of odp sites indicate that early diagenesis of clay sediments removes around 8 of the modern riverine input of dissolved li although nh4 rich fluids do result in a flux of cs to the oceans on the global scale this input only augments the modern riverine cs flux by 3 nevertheless this may have implications for the fate of radioactive cs in the natural environment and waste repositories

paleodepositional conditions in the orca basin as inferred from organic matter and trace metal contents abstract the orca basin located in the gulf of mexico is a highly stratified basin that collects sedimentary particles of clastic origin supplied by the mississippi river and of biogenic origin marine surface productivity the strong pycnocline induces anoxic bottom conditions that are expected to be favorable to organic matter om accumulation and prone to enrichment of sediments in redox sensitive trace metals here we report on om and trace metal contents in the upper 750 cm below sea floor cmbsf of core md02 2552 mostly holocene and deposited under permanently stratified bottom conditions the organic content is dominated by marine derived amorphous om contrary to expectations sedimentary om in the basin is highly degraded probably due to a long residence time of organic particles at the basin s basin s halocline at 2240 m also unexpected is the limited sedimentary enrichment of redox sensitive trace metals we suggest that the non enrichment in u and v could be explained by the so called basin reservoir effect that is limited metal availability because of low rates of water renewal in a strongly restricted subpycnoclinal water mass the non enrichment in cu could have the same cause plus the fact that the relatively degraded om may not readily form organometallic complexes however a marked enrichment is observed for mo and a moderate one for ni and cr which could be accounted for by sporadic presence of h 2 s in bottom waters such occurrences of h 2 s would not be sufficient to promote a detectable fes to fes 2 conversion but they would induce the capture of mo in the form of thiomolybdate and accessorily ni cr as ni cro 4 complexes

relative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the acores area abstract relative changes in geomagnetic field intensity over the last 280 kyears have been recovered from the study of three marine cores from the acores area one core was precisely dated by oxygen isotope study and the other two records were linked to it using light reflectance analysis which allowed precise correlation rock magnetic analysis shows that the main magnetic mineral is magnetite with a very homogeneous grain size distribution in the pseudo single domain range for the three cores changes in the amount of magnetite do not exceed a factor of 10 therefore these cores appear to be suitable for relative palaeointensity determinations two mineral magnetic components with periodicities of 23 and 18 kyears are present in the records of bulk magnetic parameters and natural remanent magnetisation nrm but the power at these frequencies is not significant at the 95 level for the normalised remanence records for each core normalisation of the nrm using different normalising parameters yields virtually identical results using saturation isothermal remanent magnetisation sirm as the normalising parameter the results of the three cores were then combined into a stacked curve squared coherence analysis between this stacked curve and bulk mineral magnetic parameters reveals that the 18 kyear component is still present in the record but that the power spectrum is barely above noise level at this frequency some of the features of this north atlantic record are consistent with the main characteristics already documented in other sedimentary or volcanic records for instance distinct periods of low intensity are observed around 40 120 and 190 kyears and periods of high intensity at 50 and 80 kyears because of the uniformity of the mineral magnetic characteristics of the three cores we suggest that this record may be a suitable palaeointensity reference curve for the central north atlantic ocean region

long term secular variation of the geomagnetic field during the last 200 kyr recorded in sediment cores from the western equatorial pacific we have conducted a paleomagnetic study of five hemipelagic clay cores of 4 7 m in length obtained from the west caroline basin western equatorial pacific the purpose of this study is to clarify the long term secular variation of the geomagnetic field during the last 200 kyr using both intensity and directional changes one core was dated using oxygen isotope ratios 18o and characteristic magnetic susceptibility variations of about a factor of four allowed precise correlation between all cores the magnetic mineralogy is estimated to be dominated by magnetite of single domain sd and or pseudo single domain psd state the magnetic mineralogy and grain size are uniform throughout the cores which enabled us to obtain relative paleointensity variations as well as directional changes remanent intensity normalized by anhysteretic remanent magnetization arm indicates that sharp intensity drops to 20 of the present field occurred at about 40 and 190 kyr b p with a broader decrease around 110 kyr b p the former two are accompanied by anomalous remanent directions suggesting short polarity reversals or excursions their ages are close to those of the previously reported laschamp excursion and biwa i event a prominent intensity peak occurred immediately preceding the possible excursion at 40 kyr b p our results are in general similar to the recently reported datasets spanning the last 80 140 kyr from the somali basin the mediterranean and the sulu sea 1 3 the inclination record shows long term cyclic changes of several degrees in amplitude the intervals of the recurring variation are 40 50 kyr which is longer than the core s memory and is close to the milankovitch frequency associated with the change in obliquity of earth s rotational axis we infer that an external force such as orbital forcing could be a cause of the long term secular variation

a detailed chronology of the australasian impact event the brunhes matuyama geomagnetic polarity reversal and global climate change a mechanism had been recently proposed to show how an impact event can trigger a geomagnetic polarity reversal by means of rapid climate cooling we test the proposed mechanism by examining the record from two high sedimentation rate 8 11 cm kyr deep sea sediment cores odp sites 767 and 769 from marginal seas of the indonesian archipelago which record the australasian impact with well defined microtektite layers the brunhes matuyama polarity reversal with strong and stable remanent magnetizations and global climate with oxygen isotope variations in planktonic foraminifera both odp cores show the impact to have preceded the reversal of magnetic field directions by about 12 kyr both records indicate that the field intensity was increasing near the time of impact and that it continued to increase for about 4 kyr afterwards furthermore the oxygen isotope record available from sediments at odp site 769 shows no indication of discernible climate cooling following the impact the microtektite event occurred in the later part of glacial stage 20 and was followed by a smooth warming trend to interglacial stage 19 thus the detailed chronology does not support the previously proposed model which would predict that a decrease in geomagnetic field intensity resulted from a minor glaciation following the impact event we conclude that the evidence for a causal link between impacts and geomagnetic reversals remains insufficient to demonstrate a physical connection

the enigma of prokaryotic life in deep hypersaline anoxic basins deep hypersaline anoxic basins in the mediterranean sea are a legacy of dissolution of ancient subterranean salt deposits from the miocene period our study revealed that these hypersaline basins are not biogeochemical dead ends but support in situ sulfate reduction methanogenesis and heterotrophic activity a wide diversity of prokaryotes was observed including a new abundant deeply branching order within the euryarchaeota furthermore we demonstrated the presence of a unique metabolically active microbial community in the discovery basin which is one of the most extreme terrestrial saline environments known as it is almost saturated with mgcl2 5 m

normalised natural remanent magnetisation intensity during the last 240 000 years in piston cores from the central north atlantic ocean geomagnetic field intensity or environmental signal we have examined in detail the stratigraphic variations in magnetic parameters of four cores from the north atlantic ocean in areas where the depositional environment has varied with climatic changes our objective is to assess whether normalisation of the natural remanent magnetisation nrm intensity can cancel the effect of climatically induced variations in magnetic mineral content and grain size and whether a reliable record of relative changes in geomagnetic field intensity can be obtained after selecting the core sections which meet published criteria for paleointensity normalisation we have attempted to obtain a record of the geomagnetic field intensity variations over the past 240 kyear using both arm and irm as normalising factors for the nrm the two methods yield overall similar results except for the interval 20 30 kyear where irm normalisation yields a record more consistent with previous sedimentary and volcanic results than does the more frequently employed arm normalisation the final intensity record docmments a picture of the dipole field moment which presents large similarities with profiles obtained from sediments deposited in different environmental conditions in various regions around the world we observe a major low at about 42 kyear which could correspond to the laschamp event a broad low in the interval 90 130 kyear possibly connected to the blake event and another low at about 190 kyear which could reflect the biwa i event the processes of acquisition of depositional and postdepositional remanent magnetisation and the physics of the normalising methods are still insufficiently understood however these results obtained from a region characterised by complex environmental dynamics confirm the potential of sedimentary deep sea cores for relative paleointensity determinations

sulfur and oxygen isotopic compositions of dissolved sulfate in the orca basin implications for origin of the high salinity brine and oxidation of sulfides at the brine seawater interface abstract analysis of sulfur and oxygen isotopic compositions of dissolved sulfate from a vertical water profile in the anoxic hypersaline orca basin provides important constraints upon the provenance of the sulfate results support a dissolution origin of the brine from a jurassic evaporitic salt however mass balance considerations and the observed minima in the vertical 18o sulfate profile at the brine seawater interface are not reconcilable with only a simple two box brine seawater mixing model instead the data imply contributions from the oxidation of sulfides

sources and mechanisms for the enrichment of highly reactive iron in euxinic black sea sediments the deep basinal euxinic sediments of the black sea are enriched in iron that is highly susceptible to sulfidization compared to oxic suboxic continental margin sediments in the black sea and oxic dysoxic continental margin and deep sea sediments worldwide a mass balance treatment of iron speciation data from three deep basin sediment cores shows that this enrichment is due to a combination of 1 highly reactive iron bearing phases sulfides and oxides whose ultimate source was by diagenetic mobilization from the shelf wijsman and others 2001 and 2 enhanced iron reactivity in the lithogenous component of deep basinal sediments the cause of the enhanced reactivity of lithogenous iron is problematical possible mechanisms include microbial oxidation of non reactive iron silicates and the preferential deposi tion of a fine grained reactive iron enriched lithogenous component in the deep basin by the fractionation of the lithogenous flux during transport across the shelf the application of paleoredox indicators based on iron reactivity degree of pyritization indicator of anoxicity should take into account that the availability of highly reactive iron and hence the concentration of reactive iron phases in the sediment is controlled by a variety of chemical physical and biological factors some of which are not related directly to redox conditions in the water column

reactivity of evaporites during burial an example from the jurassic of alabama the jurassic louann salt was the first significant sedimentary unit to accumulate in the gulf of mexico sedimentary basin br cl and sup 87 sr sup 86 sr ratios of halite from a single core into the top of the formation record the evaporation of normal seawater to bittern stage the bittern zone today consists of intergrown halite and sylvite the br and rb contents of the solid phases along with sup 87 sr sup 86 sr ratios and rb sr systematics are inconsistent with precipitation of the existing phases from seawater evaporated in jurassic time rather petrography and fluid inclusion and solid phase chemistry from the bittern zone is consistent with postdepositional water rock interaction which diagenetically modified a marine bittern assemblage to halite sylvite the chemistry of the br and rb rich saline formation waters characteristic of this area today likewise may reflect water evaporite interaction during burial

a precursor to the matuyama brunhes transition field instability as recorded in pelagic sediments abstract the period some 20 25 kyr just prior to the most recent generally recognized geomagnetic field polarity transition the matuyama to brunhes reversal appears to be marked by significant geomagnetic variability manifested as pronounced oscillations in intensity we compare several previously published paleomagnetic records with new high resolution paleomagnetic data obtained from five pelagic marine sites north atlantic dsdp hole 609b equatorial atlantic odp hole 665a and western equatorial pacific odp holes 803b 804c and 805b using standard rock magnetic normalization for all of the samples as well as a thellier thellier method on the sediments of hole 804c we consistently find a decrease in paleointensity dip of 1 approximately 15 kyr prior to the matuyama to brunhes transition in the five new records as well as in the previously published records despite sedimentation accumulation rates sar that range from 11 cm kyr to 1 cm kyr these sequences yield paleointensity curves that are broadly similar in form even at the lowest sars the intensity of the pre reversal low dip1 appears to be of the same magnitude as that of the transition itself dip2 of 1 in some of the records a directional excursion to nearly full normal polarity accompanies dip1 and remains after alternating field af and or thermal demagnetization whereas in other records the directional changes vanish with demagnetization and appear to be caused by overprinting a viscous remanent magnetization vrm contribution to nrm was identified in two of the records and until removed by af or thermal demagnetization was found to blur the double dip nature of the paleointensity profiles into an apparent single dip and also resulted in an apparent but erroneous sawtooth like post transitional sudden increase in paleointensity after appropriate normalization the magnitude of the post transitional recovery was much reduced the magnetic directions of three of the new records after cleaning and adjusting the stable declinations to either 0 normal or 180 reverse map to vgp positions lying in the pacific the directional variations however are far less consistent than the intensity variations the confirmed global existence of this dip so closely preceding a major reversal invites questions about its relation to the reversal itself the apparent normal character of this interval can also present problems for magnetostratigraphical interpretations based on coarse or incomplete sampling by mimicking the brunhes matuyama reversal some 15 kyr earlier in the section than its true location

mineral deposits and earth evolution mineral deposits are not only primary sources of wealth generation but also act as windows through which to view the evolution and interrelationships of the earth system deposits formed throughout the last 3 8 billion years of the earth s history preserve key evidence with which to test fundamental questions about the evolution of the earth these include the nature of early magmatic and tectonic processes supercontinent reconstructions the state of the atmosphere and hydrosphere with time and the emergence and development of life the interlinking processes that form mineral deposits have always sat at the heart of the earth system and the potential for using deposits as tools to understand that evolving system over geological time is increasingly recognized this volume contains research aimed both at understanding the origins of mineral deposits and at using mineral deposits as tools to explore different long term earth processes

alkali elements na k rb and alkaline earth elements mg ca sr ba in the anoxic brine of orca basin northern gulf of mexico abstract a profile of filtered seawater and brine samples was collected in the summer of 2003 from a depth of 1500 m down to the bottom of the anoxic hypersaline orca basin northern gulf of mexico using ion chromatography and inductively coupled plasma mass spectrometry icp ms these samples were analyzed for alkali cations na k rb alkaline earth cations mg 2 ca 2 sr 2 ba 2 and the major anions chloride cl and sulfate so 4 2 major ion concentrations in the brine are consistent with previous studies confirming that na plus cl make up more than 95 of its composition hence governing its density and hydrodynamic stability binary mixing plots across the interface between deep gulf of mexico seawater and the anoxic brine are generally linear but display substantial deviations from conservative behavior at the steepest part of the pycnocline for all analytes except na cl and ca negative deviations signify localized cation removal by an adsorption or ion exchange process probably associated with the dense layers of particles that are trapped there especially strong mg removal may be indicative of dolomitization whereby the concomitant release of ca counters its adsorption resulting in zero net ca removal a positive deviation for sulfate is attributed to bacterial sulfide oxidation concentrations of rb sr and ba in the homogeneous brine reported here for the first time are enriched by factors of 1 5 1 4 and 9 respectively with respect to the overlying seawater unlike ca and sr ba concentrations in the brine are clearly controlled by the solubility of its sulfate salt barite causing a maximum of 670 nmol kg at the interface several independent lines of evidence suggest that the brine is formed outside the basin most likely by the interaction of seawater with regionally extensive evaporite deposits a simple mass balance shows that the dissolution of about 280 g of halite per kg of seawater can account for the extreme concentrations of na and cl in the orca basin brine the same mass balance was applied to a number of minor constituents k rb mg ca sr so 4 br total iodine in order to calculate what abundances in the halite are required to reproduce their concentrations in the brine as measured in the present work and by others the results are entirely compatible with the composition of the jurassic louann salt specifically with the median of compositions published for a transect spanning early to late stage halites elevated abundances of k and rb point to contributions from bittern facies modified by prior diagenetic contact with seawater

vertical distributions and speciation of dissolved rare earth elements in the anoxic brines of bannock basin eastern mediterranean sea abstract vertical distributions of dissolved rare earth elements rees are presented for the anoxic highly sulfidic brines of bannock basin in the eastern mediterranean sea ree concentrations at the seawater brine interface are the highest ever recorded in the water column of an anoxic basin and comparable only to ree concentrations at depth in the porewaters of reducing sediments below the seawater brine interface throughout the upper of two chemically distinct brine layers ree concentrations decrease with depth as a result of scavenging while shale normalized ree patterns are characterized by little or no fractionation between the light rees lrees and the heavy rees hrees and by a positive ce anomaly throughout the lower of the two brine layers ree concentrations are constant while ree patterns are characterized by the same lack of lree or hree enrichment as well as by the absence of any ce anomaly a pronounced ree minimum at the interface between the two brine layers is apparently caused by uptake into dolomite that is formed through in situ recrystallization of ca carbonate a process that was previously reported to cause similar minima for mn and fe calculations of ree speciation incorporated into a model of ree scavenging developed by byrne and kim 1990 which uses ree complexation by monocarboxylic acids to represent ree adsorption onto particulate matter are surprisingly successful at reproducing the unusual shape of ree patterns in the brine this suggests that this shape although very different from that of ree patterns in the overlying seawater due to the very high ionic strength of the brine is the result of much the same processes that constitute ree scavenging in the open ocean

biogenic hydrocarbon gases and sulfate reduction in the orca basin brine the composition of light hydrocarbon gases in the orca basin an anoxic hypersaline intraslope depression on the continental slope of the northern gulf of mexico indicates that both methane and ethane are biogenic in nature with a c1 c2 c3 ratio of 730 and a 13c of methane of 73 relative to the pdb standard the concentrations of methane 750 mm and ethane 1300 mm in the orca basin brine are higher than any other marine anoxic basin these high levels result not from high rates of productivity but from the long residence time of the brine in the basin due to its high stability toward mixing with overlying seawater 1 z 3 2m both methane and ethane show well mixed distributions in the brine these distributions probably result from convective mixing of the isohaline brine pool due to normal heat flow from the basin sediments methane and ethane maxima above the pycnocline at the brine seawater interface reflect in situ production and or consumption in the aerobic water column concurrent maxima in suspended particulate material distributions in this region suggest methane may be produced there in anaerobic microenvironments associated with the suspended matter reduced rates of anaerobic decomposition including sulfate reduction in the brine sediments are inferred from preserved sargassum fronds in the sediments vertical sulfate profiles in most cores and the sediment organic carbon content which is two to three times higher in sediments below the high salinity brine than in the normal gulf sediments nearby

towards absolute calibration of sedimentary paleointensity records abstract using relative paleointensity estimates derived from twelve globally distributed pelagic sediment cores we assess whether they record a signal consistent with that expected from a dominant geocentric axial dipole the cores span the matuyama brunhes boundary and we normalize the observations by supposing that at the time the direction reverses the intensity low reflects only the non axial dipole contribution to the field we further assume that this non axial dipole contribution to the field is invariant with geographic location from absolute paleointensity compilations we estimate its size to be about 7 5 t this supplies the calibration for the axial dipole signal away from the extreme low in intensity the data predict the dipole field variation with latitude with similar accuracy to that observed in absolute paleointensity records and show similar behavior when transformed to virtual axial dipole moments

stratigraphic correlation of late palaeocene sand deposits in the sogne basin area of the danish and norwegian central north sea a stratigraphic analysis of late palaeocene sands of the sogne basin and the western part of the norwegian danish basin shows that the sand bodies are of differenct ages the geographic distribution of the sand deposits shows that they are related to underlying mesozoic structures suggesting a controlling effect of tertiary tectonics on the deposition of sand during the late palaeocene however the structural setting of various sand bodies varies from reactivation of older faults and reactivation of salt structures the local character of the structures active during the late palaeocene introduces minor depressions with no lateral connection the sand bodies which are interpreted as having been deposited in these depressions are thus in general separate bodies with no lateral connection the fennoscandian shield and eroded mesozoic sediments along the fennoscandian border zone are suggested as source area for the late palaeocene sand deposits

a method for precise analysis of trace element calcium ratios in carbonate samples using quadrupole inductively coupled plasma mass spectrometry an improved method has been developed using a quadrupole inductively coupled plasma mass spectrometer q icp ms to analyze carbonate samples for multiple trace element to calcium ratios problems alleviating shorter term drift have been overcome by manipulating the instrument to bracket each trace metal measurement with a calcium measurement while longer term drift is corrected by bracketing each sample analysis with external matrix matched standards of typical foram composition our method is optimized for measuring the ratios sr ca mg ca zn ca cd ca ba ca mn ca and u ca from a single carbonate sample but could be adapted to include a range of alternative ratios evaluation has shown the method to be extremely precise at less than 1 rsd 1 for 3 trace metal to calcium ratios we have achieved comparable precision to a sector field icp ms instrument and an advance over previous methods using the q icp ms instrument precision rsd for each ratio based on 96 sample analyses in 5 batches made over a period of 9 months using a 100 mg l ca standard is 2 2 for u ca 1 7 for cd ca 1 9 for zn ca 1 1 for ba ca 0 7 for mn ca and 0 7 and 0 6 for sr ca and mg ca respectively accuracy of the method is confirmed by comparing standard ratios with those obtained from an icp aes instrument and by comparing sample analyses of neap4b material from the north atlantic with data measured using thermal ionization mass spectrometry tims and flame atomic absorption spectroscopy faas

progressive dolomitization of florida limestone recorded by alkaline earth element concentrations in saline geothermal submarine springs 1 studies in the late 1970s revealed that the effluents of saline geothermal submarine springs on the west florida shelf have compositions nearly identical to seawater except for distinct ca enrichments and mg depletions probably resulting from dolomitization during annual visits between 1996 and 2003 we collected high purity effluents from four submarine springs and from warm mineral springs wms which is located on land filtered effluents were analyzed for major ions and for sr and ba these analyses confirm the seawater like composition of the effluents as well as the ca enrichment and mg depletion the alkaline earth elements sr and ba like ca and ra are significantly enriched in the effluents compared to ambient seawater by average factors of 1 6 and 3 8 respectively about 9 and 12 for wms the mg depletion and the sr and ba enrichments while invariant over the 7 year sampling period increase gradually from south to north consistent with progressive dolomitization of limestone along the purported convective flow path of the warm seawater the ca enrichment shows no obvious trend because besides dolomitization gypsum dissolution is an independent source of ca a simple mass balance indicates that the ca excess is fully accounted for by these two processes in all four submarine springs this is not the case for wms where a residual ca excess points to a third source of ca presumably limestone dissolution that occurs upon mixing of the modified seawater with fresh groundwater from the floridan aquifer system

gypsum precipitation from cold brines in an anoxic basin in the eastern mediterranean in 1968 hot brines from which gypsum had precipitated were discovered in the red sea in a divergent plate boundary setting with hydrothermal activity1 we now report the discovery of cold brines in an entirely different geodynamic situation a convergent plate boundary in the eastern mediterranean where the heatflow is very low2 and no hydrothermal activity occurs decimetric pure gypsum crystals precipitate from the cold brines which occupy the bottom of a rimmed anoxic basin near the southern edge of the mediterranean ridge close to the sirte abyssal plain nucleation of the crystals does not occur at the surface but from the deep brines because the salinity of the water is normal down to the depth of 3 000 m we propose the name bacino bannock for this basin after the consiglio nazionale delle ricerche r v bannock from which the bottom water brines were surveyed and sampled

absolute paleointensities between 60 and 160 kyear bp from mount etna sicily abstract paleointensity measurements were conducted on 17 distinct lava flows from mount etna sicily in order to obtain records of absolute paleointensities for the period covering the last 60 160 kyear a complementary aspect of this study was to improve and extend the calibration of relative paleointensities obtained for the same interval from sedimentary sequences based on absolute values of virtual axial dipole moments seventy three samples have been subjected to double heating thellier coe experiments under vacuum and care was taken to perform additional studies dealing with the magnetic mineralogy and to scrutinize the effects of heating upon magnetic minerals potassium argon k ar datings provided precise ages in most cases absolute paleointensities were obtained with success for ten lavas flows the succession of the virtual axial geomagnetic dipoles vadm oscillate between extrema centered around a mean value of 6 3 2 6 10 22 a m 2 this result is in good agreement with the sedimentary record published for the same period and confirms that there has been an appreciable decrease in geomagnetic field intensity between 80 and 150 kyear

paleointensity of the geomagnetic field during the last 80 000 years high resolution records of the relative paleointensity of the geomagnetic field have been obtained from five marine cores three duplicate records were used to estimate the regional coherency of the data within a single area tyrrhrenian sea while the two others document the field variations in the eastern mediterranean and the southern indian ocean careful investigations of distinct rock magnetic parameters have established the downcore uniformity of the sediments in terms of magnetic mineralogy and grain sizes the time depth control was provided by oxygen isotopes and small scale variations in the deposition rates were constrained by means of tephrachronology the synthetic curve calculated from the mediterranean records provides a continuous record of the intensity variations during the last 80 000 years 80 kyr which correlates well with the sparse volcanic data available for the period 0 40 kyr the fact that identical behavior is seen in both data sets and that they also compare quite well with results from a core collected in the pacific ocean establishes the truly dipolar character of these variations the dipole field moment is characterized by large scale changes as shown by the existence of pronounced drops at 39 and 60 kyr alternating with periods of higher intensity the record suggests a periodic nature for these intensity variations however the period studied is not sufficiently long to state this conclusively these results demonstrate the potential of sediments for such studies and constitute a first step towards obtaining a global paleointensity record over a long period of time

geochemical tracing and hydrogeochemical modelling of water rock interactions during salinization of alluvial groundwater upper rhine valley france in the southern upper rhine valley groundwater has undergone intensive saline pollution caused by the infiltration of mining brines a consequence of potash extraction carried out during the 20th century major and trace elements along with sr and u isotopic ratios show that groundwater geochemical characteristics along the saline plumes cannot reflect conservative mixing between saline waters resulting from the dissolution of waste heaps and one or more unpolluted end members the results imply the occurrence of interactions between host rocks and polluted waters and they suggest that cationic exchange mechanisms are the primary controlling process a coupled hydrogeochemical model has been developed with the numerical code kirmat which demonstrates that cationic exchange between alkalis from polluted waters and alkaline earth elements from montmorillonite present in the host rock of the aquifer is the primary process controlling the geochemical evolution of the groundwater the model requires only a small amount of montmorillonite between 0 75 and 2 25 which is in agreement with the observed mineralogical composition of the aquifer the model also proves that a small contribution of calcite precipitation dissolution takes places whereas other secondary mineral precipitation or host rock mineral dissolution do not play a significant role in the geochemical signature of the studied groundwater samples application of the model demonstrates that it is necessary to consider the pollution history to explain the important cl na and ca concentration modifications in groundwater samples taken over 2 km downstream of waste heaps additionally the model shows that the rapidity of the cationic exchange reactions insures a reversibility of the cation fixation on clays in the aquifer

variations of calcium carbonate organic carbon and iron sulfides in anoxic sediment from the orca basin gulf of mexico abstract sediment from the anoxic orca basin is highly laminated and enriched in iron sulfides and organic carbon unlike sediment from the surrounding northwest gulf of mexico continental slope black laminae are enriched in calcium carbonate 19 vs 15 organic carbon 1 8 vs 0 7 and iron sulfides 0 7 vs 0 4 compared to light gray laminae however more of the fes is converted to fes2 in the light gray laminae dark gray laminae of intermediate composition are also common the laminae probably reflect annual and longer term variations in organic matter supply to the basin and variations in mixing at the brine seawater interface

formation of hematite in the euxinic orca basin northern gulf of mexico abstract the orca basin is a depression in the northern continental slope of the gulf of mexico which is partially filled with hypersaline anoxic brine pool sediment cores taken from this basin show millimeters to centimeters thick red layers within typical dark anoxic muds chemical and x ray mineralogical analyses reveal that the red laminae are invariably enriched in iron in the form of hematite they are formed primarily by interaction of ferrous iron in the brine with dissolved oxygen from overlying seawater during isolated incidences of enhanced mixing a cross the normally stable oxic anoxic boundary the presence of hematite red layers within generally anoxic sediment cores would complicate interpretation in the sedimentary record and limit the usefulness of hematite as an indicator for environment of deposition it also demonstrates that the close association of iron formation with interbedded sulphic shales observed in many proterozoic iron formations is practically feasible the processes associated with the formation of hematite in red layers might affect the extent and nature of organic matter eventually deposited in the basin as well a fact of considerable significance for petroleum source bed formation

the evaporation path of seawater and the coprecipitation of br and k with halite brines and salt were sampled at the morton bahamas solar salt production facility on great inagua island in the bahamas the brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies at inagua calcium carbonate begins to precipitate at a brine concentration factor of 1 8 times that of seawater gypsum begins to precipitate at a brine concentration of 3 8 times seawater and halite at a concentration factor of 10 6 three of the most concentrated brines from inagua 40 times seawater were evaporated further in the laboratory magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater and potassium bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater the distribution of coefficients of br and k between brines and halite were determined by combining analytical data for the inagua brines with measurements of the br and k content of halites from inagua and of halite which had precipitated from inagua brines during storage the observed average value of dbr is 0 032 in good agreement with some of the previous measurements the measured values of dk are highly variable 0 001 to 0 021 dk for halite precipitated early in the halite facies is in the vicinity of 0 015

geochemical variations within a laminated evaporite deposit evidence for brine composition during formation of the permian castile formation texas and new mexico usa abstract the upper permian castile formation of the delaware basin in northwest texas and new mexico consists of up to 600 m of evaporites and is subdivided into units of anhydrite overlain by halite the castile formation has commonly been interpreted as a deep water deep basin deposit in which sediments were laid down in several hundred metres of water or brine recent textural observations within anhydrite units in which the thick bedded anhydrite horizons have been interpreted as being of shallow water origin have challenged this assumption this geochemical study of the oldest anhydrite unit in the castile formation the anhydrite 1 member attempts to resolve some of the problems regarding brine depth and evolution in the basin the anhydrite 1 member has been subdivided into five major cycles on the basis of the distribution of stratigraphic units of thick bedded anhydrite stable isotopic analyses of sulphur from anhydrite and oxygen and carbon from calcite show that the basin waters were chemically homogeneous during precipitation of anhydrite and do not indicate any significant input of meteoric continental derived waters throughout the section studied progressive enrichment of 18 o upwards within cored intervals indicates continuous evaporation of the water body carbon isotopes appear to indicate fluctuations in organic activity within the cycles trace elemental analyses of fe mg sr mn al ba zn pb and cu from the sulphate fraction of the samples show a very high variability there is a distinct increase in trace elemental abundances at the tops of cycles which may indicate variations in precipitation kinetics analyses of texturally defined cycles show that up core trends for many of the trace elements correlate with changes in 18 o indicating a progressive increase in the influence of evaporation in addition cyclical variations in trace elemental composition indicate changes in basin conditions with around a 350 year cyclicity these changes are independent of 18 o values the geochemical data do not provide conclusive proof of water depth during deposition of the castile formation the data are interpreted as reflecting small scale changes in conditions of deposition despite the fact that water input remained essentially constant in terms of chemical composition