sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

zur systematik der kohlenstoff schwefel eisen verhaltnisse in auftriebssedimenten abundances of organic carbon sulfur and reactive iron in sediments of three upwelling environments peru oman and benguela suggest that organic carbon reduced sulfur ratios c s ratios in this category of marine sediments deviate considerably from previously established empirical ratios in normal marine sediments to clarify the discrepancies we investigated those components of the diagenetic system that limit the formation of pyrite sulfate concentrations and reduction rates in pore waters availability of reactive iron and the quantity and quality of organic matter all three limitations are evident in our sample pools the results suggest that c s ratios in recent and fossil marine sediments rich in organic matter may be unsuitable as paleoenvironmental indicators

recent localised sulphate reduction and pyrite formation in a fissured chalk aquifer abstract sulphate reduction and pyrite formation are well known diagenetic processes in marine sediments during the early stages of burial sulphate reduction has also been detected in aquifers however the identification of pyrite which was precipitated during the circulation of meteoric water is uncommon here we describe petrographic and sulphur isotope data which show that pyrite was formed in fissures while the aquifer contained meteoric water the occurrence of active sulphate reduction is demonstrated by the recovery of sulphate reducing bacteria srb s and detection of hydrogen sulphide hence organic matter may be metabolished and diagenetic minerals formed during late meteoric water diagenesis of sediments this process affects groundwater quality by removing sulphate fe and trace metals and by altering the redox state of the system

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

sedimentological characteristics heavy metal distribution and magnetic properties in subtidal sediments ria de pontevedra nw spain the rias of nw spain are coastal ecosystems of high biological productivity and great economic importance they are intensively exploited by man for fish and shellfish there are a number of important centres of population and industrial activity along their margins which serve as sources of contamination in this context it is desirable to achieve the best possible understanding of the physico chemical processes that control spatial and temporal variations in the geochemical mineralogical and sedimentological characteristics of near surface sediments in the ria de pontevedra and in particular the distribution and mobility of heavy metal contaminants thus adequate environmental planning can be achieved for this site and understanding gained for comparable contexts core samples were examined from the inner middle and outer parts of the ria grain size distributions reflect the presence of two main populations one dominated by silt and clay derived mainly from terrestrial sources and the other by fine sand to coarse silt which is derived mainly from continental shelf and ria mouth sources mineralogical analysis shows an abundance of terrestrial intensive weathering products near the ria head a dominance of shelf derived sediment towards the mouth and the presence of several diagenetic minerals whose nature varies with location within the ria in the inner ria the near surface sediments are slightly enriched in pb cu and zn from anthropogenic sources these sediments are fine grained and have a high organic content hence they have a higher potential to sorb contaminants than the coarser grained less organic rich sediments of the mid and outer ria the estimated sedimentation rates for the fine grained organic rich sediments from the inner part of the ria are about 1 mm year 1 the dominant authigenic minerals in the inner ria are iron sulphides whereas in the mid and outer ria iron silicates and oxyhydroxides are more important these differences in authigenic iron mineralogy are clearly reflected by the magnetic properties of the sediments

depositional environment of oil shale within the second member of permian lucaogou formation in the santanghu basin northwest china abstract the non marine santanghu basin in northwest china hosts one of the richest and thickest permian lacustrine source rock intervals in the world conventional oil in jurassic sandstone reservoirs and tight oil in the tuffaceous permian tiaohu formation were sourced from mudrocks in the underlying second member of lucaogou formation which also have tight oil potential proved by recent commercial discoveries based on inorganic and organic geochemistry organic petrography and stable isotope geochemistry the depositional environment and the tight oil potential of the second member of permian lucaogou formation were investigated the data imply a gradual evolution of the depositional environment from a stratified saline to a freshwater lake the succession can be subdivided into a lower middle and an upper unit each characterized by decreasing water salinity high bioproductivity has been caused by the bloom of algae and photosynthetic cyanobacteria water column stratification accelerated the activity of methanothrophs as indicated by low 13c values of hopanes biomarker composition provides evidence for decreasing contributions of cyanobacteria to the biomass and increasing abundance of prasinophytae compared to other algae with decreasing salinity enhanced terrigenous organic matter input appeared during periods of high freshwater inflow low total organic carbon toc contents in the lower unit are most likely caused by rapid sedimentation rate high bioproductivity and excellent preservation conditions resulted in high toc contents in the middle unit terrigenous organic matter input increased together with fresh water inflow in the upper unit resulting in high toc values during periods of possibly low sedimentation rates in a deep water column the samples of the second member exhibit a good to very good potential to generate conventional oil high toc and extractable organic matter yields together with the thickness of the fine grained sediments show that the middle and upper units of the second member of lucaogou formation hold significant tight oil potential mineralogical composition of this dolomite rich shale with respect to abundance of brittle minerals including quartz and carbonates and rare clay testifies a good tight oil potential

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

pore network analysis of brae formation sandstone north sea abstract in this work we apply digital rock physics drp to characterize the pore networks of the brae formation sandstones from two different wells in the miller field area north sea uk using x ray micro ct scans we calculate the porosity and permeability and generate pore network models to assess pore shape characteristics the porous samples are marked by macroporosities ranging from 4 9 to 15 2 with the effective porosities varying from 0 to 14 8 the samples also contained some microporosity hosted in secondary and accessory mineral phases varying between 2 6 and 10 7 pore network model results for total porosity indicate that the samples have median pore and throat radii ranging from 5 5 m to 16 8 m and 6 4 m 12 9 m respectively the throat length of all samples has a median value ranging between 36 3 m and 82 4 m the ratio between effective porosity and total porosity varies with total porosity following the exponential relation 0 98 e 0 032 0 028 pore network connectivity is established at a porosity of 3 and full communication is achieved at porosities exceeding 10 permeability was found to vary with total porosity with an exponent of 3 67 based on these observations and the results from our models the connectivity of the pore network has important implications for predicting reservoir performance during large scale subsurface projects such as hydrocarbon production and co2 storage

north atlantic sea surface temperatures for the last 1 1 million years summary a 1 2 ma time series of north east atlantic sea surface temperature sst has been assembled from the spliced record of piston core k 708 7 0 68 0 ma and hydraulic piston cores taken in nearby dsdp hole 552a 1 2 0 68 ma a no analogue fauna precludes making credible sst estimates in the interval 1 2 1 1 ma but the record above 1 1 ma is suitable for sst estimates and related time series analysis the amplitude of sst variation is considerably higher in the brunhes than in the upper matuyama this is due both to colder glacial sst minima after 0 85 ma and to increasingly warm interglacial sst maxima from 0 7 to 0 4 ma the dominant periodicity in the sst signal is centred near 95 000 years it increases in amplitude by a factor of four from the bottom of the record to the top with the largest increase occurring between 0 7 and 0 4 ma this suggests a relatively gradual evolution of 100 000 year power over half a million years of the late quaternary rather than a single abrupt change at 0 9 ma significant but progressively smaller spectral peaks occur at periods of 54 000 41 000 31 000 23 000 and 19 000 years both the 54 000 year and 31 000 year signals may be a response to insolation forcing by minor obliquity terms long term 18 o records show small responses by the ice sheets at or near these two periods indicating the probable initial response of the climate system to these insolation rhythms in phase relationships between 18 o and sst at these periods suggest that the ice sheets then impose these rhythms on the ocean with no lag the mechanism by which such small insolation and ice volume signals become enhanced in the sst record is not clear

geology and geochemistry of the sediment hosted cheshmeh konan redbed type copper deposit nw iran the several hundred m thick miocene upper red formation in northwestern iran hosts stratiform and fault controlled copper mineralization copper enrichment in the percent range occurs in dm thick carbonaceous sandstone and shale units within the clastic redbed sequence and consists of fine grained disseminated copper sulfides chalcopyrite bornite chalcocite and supergene alteration minerals covellite malachite and azurite the copper mineralization formed after calcite cementation of the primary rock permeability copper sulfides occur mainly as replacement of diagenetic pyrite which in turn replaced organic matter electron microprobe analysis on bornite chalcocite and covellite identifies elevated silver contents in these minerals up to 0 12 0 72 and 1 21 wt respectively whereas chalcopyrite and pyrite have only trace amounts of silver 0 26 and 0 06 wt respectively microthermometric data on fluid inclusions in authigenic quartz and calcite indicate that the cu mineralization is related to a diagenetic fluid of moderate to low temperature th 96 160 c but high salinity 25 38 wt cacl2 equiv the range of 34s in pyrite is 41 9 to 16 4 average 31 4 where framboidal pyrite shows the most negative values between 41 9 and 31 8 and fine grained pyrite has relatively heavier 34s values 29 2 to 16 4 consistent with a bacteriogenic derivation of the sulfur the cu sulfides chalcopyrite bornite and chalcocite show slightly heavier values from 14 6 to 9 0 and their sulfur sources may be both the precursor pyrite s and the bacterial reduction of sulfate bearing basinal brines carbonates related to the ore stage show isotopically light values of 13cv pdb from 8 2 to 5 1 and 18ov pdb from 10 3 to 7 2 indicating a mixed source of oxidation of organic carbon ca 20 and hco3 from seawater porewater ca 0 the copper mineralization is mainly controlled by organic matter content and paleopermeability intragranular space to large fracture patterns enhanced by feldspar and calcite dissolution the cheshmeh konan deposit can be classified as a redbed type sediment hosted stratiform copper ssc deposit

miller field a subtle upper jurassic submarine fan trap in the south viking graben united kingdom sector north sea the miller field is situated at a depth of 4 km in the south viking graben some 270 km northeast of aberdeen the field was discovered in 1983 in previously relinquished u k license blocks 16 7b and 16 8b the discovery can be attributed to a detailed understanding of the regional sedimentological and seismic velocity models which predicted the presence of submarine fan sediments within a structural nose some 10 km from the graben margin sediment source the miller field reservoir comprises up to 100 m of oil bearing upper jurassic brae formation turbidites core electric log and well test analyses show that the turbidites have excellent reservoir qualities porosity ranges from 12 to 23 and net gross ratios are typically greater than 0 75 the reservoir is highly productive with permeability typically ranging from 50 to 1200 md the reservoir fluid is an undersaturated co2 rich sour 37 5 api oil sourced from the kimmeridge clay formation which overlies and interfingers with the reservoir the oil is trapped by a subtle combination of structural and stratigraphic mechanisms thirty development wells will be drilled from a single platform a total of ten wells five producers and five injectors will be predrilled through a template prior to platform installation the first of these wells was spudded in march 1989 in preparation for first oil production in early 1992 ultimate recovery is estimated to be approximately 300 mmstb of oil and 0 57 tcf of associated gas end page 307

tracing bottom water redox conditions during deposition of lower and upper jurassic organic rich sedimentary rocks in the lusitanian basin portugal insights from inorganic geochemistry abstract the lower jurassic agua de madeiros am fm and vale das fontes vf fm formations and the upper jurassic cabacos formation cab fm are considered the most important units with petroleum source rock potential in the lusitanian basin and the likely sources for its widespread hydrocarbon occurrences nonetheless the bottom water redox conditions during their deposition remain debatable to resolve this controversy we investigated whole rock inorganic geochemical data of the most significant organic rich levels of the am vf and cab fms cropping out at basin scale significant variations in toc ts and redox sensitive elements contents and their ratios are evident within and between the organic rich levels of the studied units a positive covariation between primary productivity proxies toc enrichment and paleo redox proxies for the lower jurassic units clearly suggest an interdependence between enhanced primary productivity organic matter accumulation and bottom water redox conditions for the am fm the paleo redox proxies indicate that the black shales deposition took place beneath bottom waters that ranged from suboxic to strongly euxinic conditions with a clear predominance of the latter a toc threshold of 6 7 wt clearly separates samples deposited under suboxic to anoxic conditions from those deposited under true euxinic conditions and is interpreted as the minimum amount of organic matter om accumulation within sediments required to sustain h2s production at rates that outpaced its consumption through precipitation of sulphides and or om sulphurization allowing the diffusion of h2s to the bottom waters for the vale das fontes fm the paleo redox proxies suggest a prevalence of suboxic to anoxic bottom waters despite all black shales displaying toc contents greater than the above threshold the less reducing conditions relative to the am fm euxinic black shales are attributed to i a larger proportion of continental om ii lower reactivity of the om reaching the sediment water interface decreasing oxygen consumption and iii higher availability of reactive iron increasing the buffer effect to h2s produced through om remineralization by sulphate reducing bacteria both units display mo ef vs u ef covariation patterns that deviate from the field of sediments deposited under unrestricted open marine conditions towards higher mo enrichment relative to that of u indicating an accelerated transport of aqueous mo to the sediments consistent with the operation of a metal oxyhydroxide particulate shuttle linked to mn and fe redox cycling within the water column in a weakly restricted basin the mo cot regression line slope indicates a moderate degree of bottom water mass restriction with mo aq concentration of 60 70 of the present day seawater value and bottom water renewal times of 10 20 years akin to the present day cariaco basin the redox conditions of the cab fm organic rich levels are dependent on the location of the depositional environment in the basin with deposition taking place beneath oxygenated bottom waters at cabo mondego and under suboxic conditions at vale de ventos and pedrogao the latter denoting a larger degree of oxygen depletion than the former in this context the overall potential for om preservation should increase from cabo mondego to vale de ventos and pedrogao

carbon sulphur iron variations and sulphur isotope patterns of silurian graptolite shales black shale horizons graptolithenschiefer in silurian and lower devonian strata of the franconian thuringian highlands frankenwald thuringer wald of germany have high metal concentrations e g u v mo organic carbon sulphur and iron contents degree of pyritization dop and sulphur isotope ratios from the lower graptolite shales along with faunal and sedimentological evidence show that the depositional environment was anoxic although some data e g c s plots do not suggest completely euxinic conditions the dop versus c plot indicates a black sea type environment from the sulphur isotope data the environment fluctuated between open and closed with respect to sulphate supply with higher carbon contents reflecting an increased bacterial reduction of the available sulphate diagenetic effects were responsible for somewhat unusual plots of c s ratios though iron availability may have been influential

the effects of historic abstraction of groundwater from the london basin aquifers on groundwater quality abstract the basal sands and chalk aquifers in the lee valley and enfield haringey areaas of north london have considerable potential for artificial recharge having been dewatered by groundwater abstraction since the late 1800s trials have been undertaken periodically since the mid 1950s however one of the drawbacks is the potential for developing poor quality groundwater as a result of pyrite oxidation in the basal sands analysis of pumped groundwaters from the basal sands has confirmed the presence of relatively high concentrations of dissolved so4 along with k ca total fe and li porewater chemistry profiles have been obtained from fresh cores through the basal sands and underlying chalk at four sites the site with the highest so4 concentration up to 33 000 mg 1 1 had a porewater ph of 3 45 and has remained dewatered owing to overpumping for more than 70 a water pumped from the chalk showed little evidence of these extreme conditions there was no overall correlation between the bulk pyrite or gypsum content of the sediment and the porewater so4 concentration within the sediment the principal mechanism governing the generation of so4 is the oxidation of pyrite which is present in small amounts the extremely high concentrations of so4 in the porewaters indicate that the extent of oxidation is controlled by the entry of air rather than the input of dissolved oxygen or nitrate in the groundwater or recharge water abstraction from the chalk aquifer over many decades has resulted in the dewatering of the overlying basal sands aquifer allowing air entry and has led to the localized oxidation of pyrite and the accumulation of poor quality porewater in the basal sands the rate of oxidation is probably greatest near to wells and boreholes which allow ready access of air the solutes produced are only available for abstraction after the water table has risen dilution with native chalk groundwater will tend to minimize potential water quality problems future oxidation will be minimized by maintaining a high water table

the use of operationally defined sequential fe extraction methods for mineralogical applications a cautionary tale from mossbauer spectroscopy abstract reactive iron minerals are crucial components of global nutrient cycles directly controlling carbon transport and storage in marine sediments sequential selective extraction is frequently used for quantitatively characterising and chemically isolating individual fe mineral phases reagent specific mineral solubility is fundamental to the success of any sequential extraction but is strongly affected by the varying physical and chemical morphology intrinsic to natural mineral samples natural sediment rock and soil samples often contain a mineral mixture which further modifies solvent efficacy 57fe mossbauer spectroscopy only probes the hyperfine interactions between next nearest neighbouring atomic nuclei in the crystal lattice and is less affected by variation in mineral grain size and crystallinity than conventional x ray based methods in this study we used mossbauer spectroscopy in a novel context to cross calibrate and optimise a popular but frequently misused sequential fe extraction protocol our results showed that incomplete and premature removal of the target fe minerals could occur at nearly every stage of the extraction and in many cases the leachate fe content did not represent the target phase at all crystalline natural siderite and amorphous synthetic goethite were detected in the mossbauer spectrum of the ammonium oxalate extraction for magnetite after which all reactive fe minerals should have been removed consistent with previous studies and unlike many other clay minerals nontronite was extracted as part of the highly reactive fe pool and in fact our data indicate that this mineral was extracted by the initial na acetate extraction that targets carbonate bound fe matrix effects appeared to cause variable yield efficiencies synthetic goethite was successfully removed when present as an individual mineral yet persisted beyond its target extraction when present in an fe mineral mixture although suitable for the quantification of operationally defined fe pools we caution the unverified use of sequential fe extraction protocols for mineral specific applications the application of sequential fe extractions to define the reactive fe pools as a paleoredox proxy of depositional conditions appears relatively robust the premature removal of 2 line ferrihydrite observed in this study due to the use of the more aggressive na acetate extraction for crystalline siderite does not limit the quantitative use of the sequential fe extraction in ancient sediments where such easily reducible oxides are unlikely to persist in contrast attributing the outcomes of operationally defined fe pools to specific fe minerals is precarious and potentially entirely erroneous where fe mineral specificity or separation is required we recommend post extraction validation by another secondary technique mossbauer spectroscopy offers such a method that can independently verify extraction stages and assess mineral specificity

dating of late pleistocene interglacial and interstadial periods in the united kingdom from speleothem growth frequency abstract the growth of speleothems is indicative of interglacial and interstadial conditions in the united kingdom since their growth is dependent on two factors first the occurrence of significant diffuse groundwater recharge and second the biogenic production of carbon dioxide in the soil both are dependent on temperature and water availability the growth frequency of speleothems is examined using a cumulative distributed error frequency method applied to 341 uncontaminated uranium series age determinations the curves derived are shown to be statistically stable and the ages of the peaks are interpreted as the best estimates of the ages of interglacial and interstadial periods ten such periods are recognized during the interval 220 000 to 20 000 yr b p considerably more than are currently recognized in the uk pollen and coleoptera based quaternary stratigraphy correlations between the speleothem growth frequency peaks and last interglacial ipswichian sites can be made but correlations with last glacial devensian interstadial sites are limited because of the paucity of dates the speleothem growth frequency record provides a well dated terrestrial chronology for the past 140 000 yr b p which directly reflects regional palaeoclimatic conditions in britain and should prove very useful in unravelling the complex stratigraphy of the devensian and ipswichian stages

the hydrogeochemistry of methane evidence from english groundwaters the presence of methane ch4 in groundwater is usually only noticed when it rises to high concentrations to date rather little is known about its production or natural baseline conditions evidence from a range of non polluted groundwater environments in england including water supply aquifers aquicludes and thermal waters reveals that ch4 is almost always detectable even in aerobic conditions measurements of potable waters from cretaceous jurassic and triassic carbonate and sandstone aquifers reveal ch4 concentrations of up to 500 g l but a mean value of 10 g l however aquiclude and thermal waters from the carboniferous and triassic typically contain in excess of 1500 g l such high concentrations have so far only been found at redox eh potentials below 0 mv but in general ch4 concentration and eh value are poorly correlated this suggests a lack of thermodynamic equilibrium which is confirmed by comparing pe values calculated from the redox couple c 4 c 4 with those derived from eh genesis of ch4 appears to occur on two timescales a rapid if low rate of production from labile carbon in anaerobic microsites in the soil and a much longer millennium scale of production from more refractory carbon methane is rarely measured in groundwater there is no single ionic determinand which acts universally as a proxy but a combination of high hco3 and low so4 concentrations or the reverse is an indication that high amounts of ch4 may be present

ichnological characteristics and variability of miocene deposits in the cenozoic niger delta examples from cores in the coastal swamp and offshore depobelts abstract this work examines ichnological attributes and variability of core samples from four wells 1 4 within the coastal swamp and shallow offshore depobelts in the niger delta basin the cores consist of facies interpreted as mainly shoreface deposits these deposits are in successions and well developed the shoreface successions are divided up into a lower middle and upper shoreface the lower shoreface lies within fair weather wave base the ichnofossils assemblages characteristically represent a diverse and abundant cruziana ichnofacies the middle shoreface contains swaly and lesser hummocky cross stratified sandstones with an ichnofossil assemblage dominated by the skolithos ichnofacies the upper shoreface is dominated by planar and trough cross beddings ichnofossils are fairly abundant and consist of deeply penetrating structures of the skolithos ichnofacies these facies reveal a wide range of variability mostly limited to the lower and middle shoreface intervals this variability appears to be determined by relative storm dominance and the episodic character of associated storm bed deposition the successions are grouped into three 1 high energy shorefaces consist entirely of stacked storm beds with moderate bioturbation 2 moderate energy shorefaces comprises stacked laminated to burrowed intervals recording recurrent erosive storm bed emplacement followed by opportunistic colonization and normally overprinted by resident fair weather burrowing and 3 low energy shorefaces ordinarily exhibit intense bioturbation with low preservation of storm beds discrimination between lower and middle shoreface deposits is mainly based on the resident fair weather ichnofossil assemblage under increased energy settings in addition based on storm intensity relative water depth storm frequency and shoreline character the nature of coexistent lower and middle shoreface facies can differ significantly along strike in some cases the lower and middle shoreface differentiation was difficult

geochemical study of a crater lake lake pavin puy de dome france constraints afforded by the particulate matter distribution in the element cycling within the lake abstract suspended particles concentrations and settling particle fluxes collected by sediment traps were analyzed along a vertical profile in lake pavin france at the same time as dissolved element concentrations which are reported elsewhere viollier et al 1995 results for iron manganese cobalt vanadium molybdenum uranium barium rubidium and cesium are presented here particulate concentrations of all elements increase significantly just above the sediment water interface manganese iron and barium particulate concentrations exhibit a peak just above the oxic anoxic boundary molybdenum and uranium particulate concentrations increase drastically below the oxic anoxic boundary manganese and cobalt fluxes are at a maximum at 55 m depth above the oxic anoxic boundary for all other elements fluxes are at a maximum at 85 m depth just above the bottom of the lake in all cases settling particles fluxes are greater than buried fluxes indicating that a dissolution reaction occurs at the bottom of the lake particulate iron is essentially present as fe iii oxides in the mixolimnion as fe ii phosphates in the monimolimnion and as pyrite in the sediment the change in the fe bearing mineral leads to either important remobilisation or immobilisation of trace element into or from solution comparison of fluxes in the sediment trap at 85 m depth with dissolved concentrations gradients above the bottom leads to the rejection of the previous hydrodynamic model of the lake the fluxes and gradient data are consistent with the tritium data only if the arrival of sublacustrine waters occurs in the mixolimnion residence times of waters in monimolimnion in the model derived from the present study are about 20 times greater than the previous values the dissolved element concentrations profiles are explained only by eddy diffusion with a coefficient varying from about 20 m2 a at the bottom of the lake to 0 2 m2 a 1 at the mixolimnion monimolimnion boundary transport parameters obtained in this way allow a quantitative description of the element cycles within the lake and an estimation of the elemental ratio sedimentation versus exportation by the outlets

geochemical and petrographic investigation of triassic and late miocene organic rich intervals from onshore cyprus eastern mediterranean abstract in order to improve the understanding of potential petroleum systems in the still underexplored eastern mediterranean sea two field campaigns were performed to investigate potential source rocks onshore cyprus elemental data total organic toc and inorganic carbon tic total sulfur ts fe ni v rock eval pyrolysis biomarker and microscopic analysis organic petrography random vitrinite reflectance vrr palynofacies of the obtained mesozoic to cenozoic samples have proven the existence of organic matter om rich deposits within the following two geological formations 1 the triassic vlambouros formation fm of the mamonia complex comprises frequently occurring few centimeter thin clay layers interbedded between meter thick sandstone units the clay layers of this formation are characterized by toc contents of about 1 wt representing a type iii kerogen showing hydrogen index hi values of 48 mg hc g toc on average vrr values of 0 5 to 0 6 as well as several biomarker ratios indicate low thermal maturity the formation was deposited at the northern margin of gondwana and similar strata may be present in the basement of the levant basin and the eratosthenes seamount there thermal maturity would be higher and such rocks might contribute to thermogenic gas systems 2 in the miocene pakhna fm om bearing intervals are mainly present in the upper part of the formation in outcrops east of the troodos mountain while organic rich intervals are very scarce to absent in the south and southwest of the island the eastern outcrops show abundant fine grained marly mud to wackestones interbedded with coarser grained carbonates the fine grained intervals have toc contents of about 4 wt representing mainly type ii iii kerogen with hi values of 238 mg hc g toc on average the om is immature as indicated by vrr values between 0 3 and 0 5 ts toc 2 8 and several biomarker ratios indicate oxygen depleted even anoxic conditions during deposition a negative correlation between the toc and tic indicates that such conditions were reached during enhanced primary bioproductivity controlled by local and regional clastic derived nutrient input similar conditions may have been present along the southeastern margin of the eratosthenes seamount south of cyprus presence of abundant organic matter and high sedimentation rates during the miocene were favorable for microbial gas generation in the deeper parts of the basins

the sulfur system in anoxic subsurface brines and its implication in brine evolutionary pathways the ca chloride brines in the dead sea area abstract important elements in the evolutionary history of saline groundwater might be overlooked when they involve both sulfate removal through reduction and input of sulfate via dissolution these two simultaneous and apparently contrasting processes can result in a negligible net effect on the sulfate concentration isotopic composition of sulfur in sulfate and sulfide can be applied to identify the bacterial sulfate reduction bsr though the extent of the process is difficult to quantify saturation with respect to gypsum may suggest that gypsum dissolution also occurs however a more definite identification of these processes and their quantification can be achieved through the use of ammonium concentration in the anoxic brines this approach assumes that the ammonium is derived only from the oxidation of organic matter through bsr and it requires that the c n ratio in the oxidized organic matter be known a minimum estimate for the sulfate reduction can be obtained when the redfield c n ratio 106 16 is assumed several calculation methods are presented to identify the extent of sulfate reduction prior to concomitant with or following gypsum dissolution that are based on combining sulfur isotopic compositions rayleigh distillation equation and calculated gypsum saturation indices the required assumptions are presented and their validation is discussed the subsurface hypersaline ca chloride brines in the vicinity of the dead sea are taken as a case study here sulfur isotope compositions of sulfate and sulfide and high ammonium concentrations indicate bsr occurs in the subsurface the sulfur isotopic composition of the sulfate makes it possible to distinguish between two major groups of brine and their recent evolutionary histories 1 the qedem shalem thermal brines 34 s so4 21 24 which emerge as springs along the shores and are slightly undersaturated with respect to gypsum 2 dsif tappuah brines 34 s so4 30 60 which are found in shallow boreholes and are saturated to oversaturated with respect to gypsum calculations based on their ammonium content suggest that both groups of brine require apparent unreasonably high oversaturations with respect to gypsum prior to the onset of the reduction this implies that the groundwater systems were open with respect to sulfate and that the sulfate reservoir was replenished continuously or intermittently during the bsr the dsif tappuah brines continue to dissolve gypsum during their bsr the dissolving sulfate is derived from relatively isotopically enriched gypsums 34 s so4 20 such as found in the lisan formation these brines approach the steady state isotopic composition 34 s ss dictated by the combination of the 34 s of the dissolving gypsum and the fractionation factor accompanying bsr the sulfur isotopic composition of the qedem shalem brines implies that most of their ammonium content is derived from an earlier phase of bsr and that the last phase of bsr takes place during the brines rapid ascent to the surface prior to this stage they evolved through either 1 dissolution of gypsum with 34 s so4 20 which occurred after the main bsr in the subsurface 2 a previous phase in which the brines were part of a lake and later percolated to the subsurface as such their isotopic composition and ammonium content were determined by the combined effect of freshwater sulfate input to the lake and bsr in the stratified lake

origin of rollover rollover is the folding of hanging wall fault blocks by bending or collapse in response to slip on nonplanar commonly listric normal faults the shapes of rollover folds are controlled by a number of variables including 1 the shape of the fault 2 the total fault slip after a bed is deposited 3 the direction of relative particle motion in hanging wall collapse 4 the history of sedimentation rate relative to fault slip rate and 5 compaction the importance and role of each of these variables is illustrated by a two dimensional balanced structural modeling technique that treats continuously curved faults as though composed of a large number of straight fault segments in this modeling an active axial surface oriented parallel to the direction of relative p rticle motion in hanging wall collapse emanates from each fault bend and is the instantaneous locus of folding the quantitative correctness of this theory of rollover is tested by modeling natural structures from the gulf of mexico for which both fault shape and fold shape are known from high quality seismic and well sections the direction of hanging wall collapse commonly is in the antithetic or synthetic normal fault or coulomb shear orientations although sliding along weak bedding planes also is an important collapse mechanism in some regions collapse is in the antithetic shear direction for concave fault bends and in the synthetic shear direction for convex bends these collapse directions can be observed directly in some high quality seismic images as axial surfaces emanating from fault bends the shapes of rollovers within growth strata depend strongly on the sedimentation rate relative to fault slip rate as well as the total slip after a bed is deposited the crests of classic gulf coast rollovers are growth axial surfaces along which are abrupt changes in sedimentation rate within the growth st atigraphic interval these changes are produced by deformation of the sediment water interface along active axial surfaces compaction can substantially modify the relationship between fault shape and rollover shape however under certain common conditions the history of compaction can be neglected if the folding is modeled in the compacted state

phyllosilicates and zeolite assemblages in the carbonate periplatform of the great bahama bank origin and relation to diagenetic processes odp leg 166 sites 1006 and 1007 abstract the western flank of the great bahama bank drilled during odp leg 166 at seven sites represents a prograding carbonate sequence from late oligocene to holocene eberli et al proc odp init reports 166 1997 the signatures of the detrital input and of diagenetic alteration are evident in clay enriched intervals from the most distal sites 1006 and 1007 in the straits of florida mineralogical and chemical investigations xrd tem sem icp ms run on bulk rocks and on the clay fractions enable the origin and evolution of silicate parageneses to be characterized plio pleistocene silt and clay interbeds contain detrital clay assemblages comprising chlorite illite interstratified illite smectite smectite kaolinite and palygorskite the greater smectite input within late pliocene units than in pleistocene oozes may relate either varying source areas or change in paleoclimatic conditions and weathering intensity the clay intervals from miocene upper oligocene wackestone sections are fairly different with prevalent smectite in the fine fraction whose high crystallinity and mg contents that point towards an authigenic origin the lower miocene section below 1104 mbsf at depths where compaction features are well developed is particularly characterized by abundant authigenic na k clinoptilolite filling foraminifer tests the authigenic smectite and clinoptilolite paragenesis is recorded by the chemical trends both of the sediment and the interstitial fluid this diagenetic evolution implies si and mg rich fluids circulating in deeper and older sequences for lack of any local volcaniclastic input the genesis of zeolite and the terms of water rock interaction are discussed the location of the diagenetic front correlates with that of the seismic sequence boundary p2 dated as 23 2 ma this correspondence may allow the chronostratigraphic significance of some specific seismic reflections to be reassessed

low temperature sulphate reduction biological versus abiological sulphate is considered to have been a major source of sulphide in strata bound and stratiform base metal sulphide deposits many of these deposits however appear to have been formed at moderate temperatures 200 c which poses the question by what mechanism s was sulphate reduced to sulphide two modes of reduction have been established experimentally 1 catalysis by sulphate reducing bacteria which at present is only known to occur below ca 100 c and 2 abiological reduction by ferrous iron or organic matter which has only been clearly shown above ca 250 c several attempts have been made to demonstrate abiological reduction below 200 c and some new data are presented here although the results do not exclude the possibility that such a reaction may be geochemically significant there has been no unequivocal demonstration of nett sulphide formation from sulphate at these temperatures recent studies of the microbiology of hydrothermal regions have opened up the prospect of bacterial sulp

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

sedimentology and oceanography of early ordovician ironstone bell island newfoundland ferruginous seawater and upwelling in the rheic ocean abstract the bell island and wabana groups together comprise a ca 150 m thick succession of interbedded clastic and chemical sedimentary rocks composed of eight distinct lithofacies that accumulated along the northern margin of the rheic ocean lithofacies stacking patterns indicate that deposition occurred during a marine transgression with superimposed small scale sea level fluctuations producing at least six parasequences parasequences containing ironstone are 10 to 20 m thick and composed of hummocky cross stratified sandstone interbedded with organic rich mudstone and phosphatic fe silicate bearing siltstone which is overlain by hematitic granular ironstone capped by an erosive flooding surface this lithofacies association is interpreted to record the deposition of upwelling related ironstone on a storm dominated shelf the close relationship between fe silicates and phosphorite typical of upwelling systems suggests that fe was delivered from deep anoxic nutrient rich seawater that also stimulated high surface productivities the result was the precipitation of authigenic sedimentary apatite in anoxic organic rich sediments that accumulated near the upwelling front the gradual advection of fe rich waters away from the upwelling front initiated precipitation of fe silicate coated grains and cements in suboxic pore waters iron pumped into shallower environments through advection and fe redox cycling is interpreted to have precipitated fe oxyhydr oxide grains in sediment of the oxygenated middle shelf these coated grains were subsequently concentrated by fairweather and storm currents on the shoreface to create granular economic fe deposits we challenge conventional models of paleozoic ironstone deposition that rely on a continental source of fe by proposing a hydrothermal source that supplied fe2 to the shelf through upwelling it also highlights the potential connection between the delivery of anoxic ferruginous seawater to the margins of the rheic ocean and the early ordovician extinctions that punctuated the beginning of the great ordovician biodiversification event

palaeohydrogeological reconstructions of the north lincolnshire chalk uk for the last 140 000 years abstract the influence of climatic change on hydrogeology is investigated by studying the evolution of the north lincolnshire chalk aquifer system during the last 140 000 years a numerical modelling approach is adopted using a density coupled finite difference model to reconstruct past groundwater environments two major controls on groundwater circulation are considered the position of sea level which determines the base level condition and the amount of recharge associated with different climates the quaternary history of the region is used to define aquifer boundary conditions and climate analogue data are used to determine likely recharge amounts model results cannot be compared against groundwater flow volumes or head other than for the present day situation and so hydrochemical evidence is used to constrain the model simulations the main finding is that recharge to the chalk aquifer during the last 140 000 years has been restricted to periods when the climate and sea level position have been similar to those of the present day the devensian cold period experienced very minor recharge with no chalk permeability development forest clearance since about 5000 years ago is predicted to have permitted an increase in the volume of freshwater recharge which increased the rate of chalk permeability development the presence of saline water at depth in the aquifer is argued on the basis of the model behaviour to be contributed by a component of upward cross formational flow

framboidal and idiomorphic pyrite in the upper maastrichtian sedimentary rocks at gabal oweina nile valley egypt formation processes oxidation products and genetic implications to the origin of framboidal pyrite abstract the upper maastrichtian organic rich sediments studied at gabal oweina egypt are moderately enriched in syngenetic and diagenetic pyrite pyrite occurs mostly as layers or bands group of lamina lenses diagenetic intercalated pockets burrow fills and disseminated individual pyrite framboids and crystals within the host sediments the pyritic thin bands and lamina consist mostly of unconsolidated to compact oriented pyrite oriented along the bedding planes in gypsiferous clayey matrix and less common as poorly oriented pyrite crystallites in several cases pyrite crystals of the latter type depict zoning fracturing and micro concretions pyritic burrow fills are composed mainly of pyrite phosphatic ooids microfossils glauconitic grains poorly graphitized carbon and native sulfur pyrite replaces minerals other than gypsum sulfur or carbon it also replaces microfossils thus turning some of the phosphatic ooids and microfossils to pyritized pseudomorphs none of the studied phosphate ooids or framboids contains any mackinawite pyrrhotite or greigite based on the microscopic and sem observations of the micro textures of disseminated pyrite found at gabal oweina section four morphological forms of primary pyrite could be identified 1 grouped multiple framboids 2 individual framboids 3 pyrite idiomorphic crystal overgrowths on framboids and 4 single and aggregates of euhedral pyrite crystals the multiple framboid formation may have emerged from three successive processes nucleation and growth of individual aggregates of the microcrystals to form combined micro framboids the growth of framboids and followed by grouping of the several pyrite framboids direct pyrite nucleation shell formation crystallization and aggregation processes might complete a single framboid the disseminated single and aggregated euhedral pyrite crystals bear evidence indicating that their formation was via nucleation and growth of pyrite crystallites and their aggregation to individual framboids infilling in the interstices by additional pyritic material compaction and homogenization of all these materials furthermore we encounter for the first time in nature idiomorphic pyrite crystals that integrated numerous framboids using them as their nucleation and growth sites without erasing or modifying their pristine morphology elemental sulfur contains minor concentration of sb ni cd and cu strongly suggesting their presence as submicron sulfide crystallite inclusions sem and microprobe investigations revealed that goethite is present as a weathering product in all morphological types of pyrite however only an iron sulfate presumably melanterite was encountered as oxidation product of the multi framboids and the euhedral aggregate crystals the upper maastrichtian sediments not only contain a menagerie of pyrite morphologies but probably a complete record of the formation process and the geochemical conditions of the growth of framboids single pyrite crystals pyrite burrows pyritized mn fe oxide framboids and finally their weathered products the various pyrite forms strongly suggest a multistage process that led to their formation without any evidence for mackinawite pyrrhotite or greigite precursors there is also no evidence in the oweina sediments for post pyrite formation of mackinawite pyrrhotite or greigite the presence of elemental sulfur containing minor concentrations of sb ni cd and cu with pyrite framboids indicates that the pore solutions were geochemically supersaturated in sulfur thus inhibiting the crystallization of any iron sulfide other than pyrite this cast considerable doubt on the assumed mackinawite or greigite precursors as prerequisite for formation of pyrite framboids

formation of pyrite in freshwater sediments implications for c s ratios abstract the vertical distribution of pyrite acid volatile sulphide avs carbon and total s st were determined directly in the sediments of three lakes of different trophic status the results showed that freshwater pyrite formation reflects the redox status of the sediment or overlying waters it appears to form chiefly in reducing sediments which are subject to oxidizing influences by either a low turnover of organic carbon or periodic incursions of oxygen although there are high concentrations of avs in the near surface sediments of productive lakes very little is diagenetically converted to pyrite the feasibility of using sulphur ratios to diagnose whether rocks were formed in marine or freshwater environments is assessed new values for fes 2 fes of 0 5 5 show that this ratio does not provide a reliable test values of c sp where sp represents pyrite sulphur lie within the range of 160 700 and are much higher than previously measured ratios of c s t of 1 50 these new determinations show that if pyrite sulphur is unequivocally measured c s ratios may be a more sensitive indicator of salinity than had been previously thought

diagenesis in oxidising and locally reducing conditions an example from the triassic skagerrak formation denmark abstract diagenetic changes in red and white parts of the skagerrak formation triassic from onshore wells in denmark were analysed by scanning electron microscope electron microprobe and petrographic microscope in reflected and transmitted light the diagenetic sequences of the red and white parts of the skagerrak formation are in many ways the same early infiltration clays followed by precipitation of caliche calcite dolomite mixed layer illite smectite quartz feldspar kaolin minerals illite chlorite and anhydrite with increasing burial differences between the red and white parts of the skagerrak formation comprise oxidation stage in detrital minerals oxidation of glauconite in the red part and reduction of biotite in the white part the presence of eogenetic authigenic minerals pyrite and poikilotopic calcite in the white part hematite and red coatings in the red part the amount of mesogenetic authigenic kaolin minerals larger in the white part the chemistry of mesogenetic authigenic chlorite mg rich in the red part and fe rich in the white part and the preservation stage of detrital opaque minerals magnetite hematite chromite ilmenite show none or minor alteration in the red part whereas they have been almost completely altered in the white part as the differences between red and white areas are found both in early eogenetic and in mesogenetic authigenic minerals different oxidising conditions must have prevailed immediately after the deposition and continued into burial oxidising conditions were dominant in the arid triassic climate and the widespread red colour of the skagerrak formation was probably formed during early diagenesis due to precipitation of iron oxides or hydroxides locally reducing areas were formed probably by oxidation of organic material precipitation of oxidised iron minerals was thus prevented and the original white colour was preserved reducing conditions prevailed until the reducing agent was exhausted then an outer rim of the reduction spot might locally have been secondarily oxidised these changing redox conditions explain the occurrence of hematized authigenic pyrite and crandallite group minerals in red areas

magnetic iron nickel sulphides in the pliocene and pleistocene marine marls from the vrica section calabria italy abstract the rock magnetic properties of the late pliocene and early pleistocene open marine marls from the vrica section in calabria italy point to magnetic sulphide as the main magnetic mineral and remanence carrier the maximum blocking temperatures however are between 340 and 360 c which is too high for stoichiometric monoclinic pyrrhotite magnetic concentrates of the sediment are rich in iron sulphide grains and iron nickel sulphide grains microprobe observations show that most of the grains are of the order of 1 m in size and attached to iron bearing clay flakes microprobe analyses of the sulphides yield a large range of compositions ranging from pyrite through greigite pyrrhotite to sulphur deficient monosulphides and with ni contents varying from zero to a few atom percent in the pyrite grains and from zero to as much as 35 atm in the monosulphides the high ni content of many of the grains is extraordinary and has not been reported before in marine sediments most of the compositions cannot be directly connected with a known mineral phase the marine depositional environment of the marls imposes an authigenic origin for the sulphides and this is supported by several observations the great number of sulphide grains in the magnetic concentrates suggests that at least one of the sulphide compositions must have a ferrimagnetic structure possibly the sulphides with a metal to sulphur ratio close to that of monoclinic pyrrhotite and between 25 and 35 of the fe replaced by ni the ni substitution could possibly be the cause of the high blocking temperatures

role of organic matter and sulphate reducing bacteria for metal sulphide precipitation in the bahloul formation at the bou grine zn pb deposit tunisia abstract the origin of the bou grine zn pb deposit of tunisia was investigated during a geochemical study of the cretaceous bahloul formation the inorganic and organic chemical compositions of the bituminous marls and limestones as well as the light stable isotope ratios of organic carbon and carbonates were measured closely spaced samples were collected along two profiles at different distances from the enrichments in zn and pb which are best developed near the bou grine diapir the organic geochemical data suggest sulphide precipitation at the bou grine deposit by sulphate reducing bacteria srb srb utilized hydrocarbons derived both from the bahloul sediments and from external source rocks production of s ii by the bacteria was most probably limited by the availability of sulphate although sulphate was available to the bacteria in high concentrations in close proximity to the triassic salt dome ground waters evolved to hypersaline basinal brines by dissolution of salt and anhydrite at the contact of the diapir these brines would have been capable of leaching metals from the sedimentary sequences adjacent to the salt dome the triassic series has often been advocated as the source of the metals and the cretaceous sediments themselves are carriers of metallic elements ore deposition apparently resulted when metal bearing solutions that migrated upward into the roof zone of the diapir mixed with s ii bearing solutions those formed when srb oxidized the high amounts of hydrocarbons within the bahloul sediments and in the brines using so 4 2 from sulphate rich waters in the anhydrite caprock as an oxidant

processes responsible for the development of soft sediment deformation structures ssds in the paleoproterozoic gordon lake formation huronian supergroup canada abstract an exposure of the paleoproterozoic gordon lake formation in the bruce mines area ontario canada contains abundant soft sediment deformation structures ssds including load casts convolute bedding pseudonodules ball and pillow structures flame structures and one dewatering pipe these features are developed in siltstone to fine grained sandstone beds and are between 1 and 120 cm in width and 3 78 cm high the primary trigger mechanism is interpreted to be storm or tsunami activity however seismic shock overloading brought about by density inversions or a combination of these processes may have influenced the formation of ssds to a lesser degree several beds also contain flat to wavy carbonaceous laminae locally with a botryoidal texture and concentrations of heavy minerals which are interpreted as relicts of microbial mats microbial mats may have played a minor role in the formation of ssds but do not appear to have been a prominent driving mechanism soft sediment deformation structures observed in the baie fine flack lake and cobalt plains regions of ontario are smaller and not as abundant as in the study area suggesting that the deposits in the study area were either affected by local events or different magnitudes of sedimentary processes in contrast to the tidal flat paleoenvironment interpreted for the gordon lake formation in the flack lake area the stratigraphically lower beds at the studied outcrop more closely resemble shallow shelf deposits

geochemistry and mineralogy of marine and non marine namurian black shales from the tansley borehole derbyshire the namurian black shales studied have a good palaeontological control pyrite illite and organic matter are higher in the marine shales and siderite and kaolinite are higher in the non marine shales the distribution of the diagenetic iron minerals is attributed to anionic activities controlled by salinity the same control could account for the observed clay mineral distribution by differential flocculation the major element geochemistry closely reflects the above mineral variation mn and zr are higher in the non marine shales due to siderite and zircon respectively co cr rb y and ba are not significantly different and a detrital source mainly clay minerals is suggested in the marine shales the elements pb cu v ni sr and zn are significantly higher using a discriminant function analysis the palaeosalinity groups are separated and the contribution of each element to the separation is calculated the present element locations are thought from correlation analysis to be pyrite and organic matter by analogy with experimental work and modern environments the element enrichment is mainly attributed to reactions involving organic matter and oxyhydroxide material in environments in which salinity and slow rates of sedimentation were important factors the element enrichment cannot be related directly to seawater concentrations unlike some black shales and the accumulation rates for pb and cu are thought to be unusually high

formation of secondary pyrite and carbonate minerals in the lower williams lake tailings basin elliot lake ontario canada the lower williams lake tailings which resulted from u milling operations during the late 1950s and early 1960s cover an area of 2 ha in a small bog under partial water cover the tailings are underlain by a sand unit containing decaying organic material above the natural base consisting of sand till and gravel the tailings are composed predominantly of quartz muscovite k feldspar plagioclase and clinochlore residual pyrite grains displaying angular to subangular particles measuring less than 1 to 250 m occur in concentrations ranging from trace to approximately 6 wt framboidal pyrite has formed within the tailings basin in association with organic rich material the appearance of framboidal pyrite in the tailings indicates a reversal of the oxidation process and reprecipitation of fe sulfides in addition the tailings include calcite calcian siderite fe oxyhydroxides and fe si oxyhydroxides as secondary precipitates and replacement products groundwaters in the tailings and the underlying units are saturated with respect to gypsum and siderite these and the other saturation indices calculated for calcite goethite and barite are consistent with the secondary mineralogy of the tailings conditions promoting the formation of pyrite can be described as neutral to weakly alkaline and reducing assisted by microbial activity this study provides the first account of secondary carbonates and framboidal pyrite in the elliot lake tailings the existing environmental conditions at the site are favorable for the desired site rehabilitation

organic geochemistry of an anoxic cycle a case history from the oligocene section hungary total organic carbon extractable organic matter sulfur content kerogen type and saturated hydrocarbons have been determined in 25 core samples from an approximately 100 m thick section of the oligocene tard clay near budapest the tard clay records a five million year long anoxic cycle initiated by isolation of the sea development of a positive water balance and resulting density stratification and terminated by the re opening of access to the sea the lower non and moderately laminated shales record the build up of anoxia they contain 0 5 5 0 of organic carbon and type iii kerogen their saturated hydrocarbon fractions show high abundance of phyllocladanes biomarkers characterising coniferae derived organic matter the overlying moderately and strongly laminated sediments containing 1 5 5 0 organic carbon a predominance of hopanes over the n alkanes and type ii kerogen show the imprint of increased planktonic productivity the nutrients needed for this high productivity were liberated by alteration processes of contemporaneous volcanic glass the upper part of the strongly laminated shales containing a maximum of 2 organic carbon and type iii kerogen deposited after the termination of volcanic ash falls records a drop of planktonic productivity at the top of the tard clay the weak lamination and the low content 1 of organic carbon signifies the end of the bottom water oxygen depletion due to the destruction of density stratification of the water column

peat development sand cones and palaeohydrogeology of a spring fed mire in east yorkshire uk an archaeological dig near beverley east yorkshire uk revealed humified peat enclosing conical and cylindrical sand bodies sand cones which contained romano british greyware such sand cones have not been previously described in the literature below the peat upper and lower diamict units previously classified as holocene alluvium were reclassified as late devensian lodgement till and pre late devensian chalky head gelifluction deposits respectively enigmatic buried timbers dated dendrochronologically to 5840 bp were found partially buried within the till micromorphological evidence shows that the peat is autochthonous the sand cones are remains of former spring orifices which served as foci for groundwater discharge from the regional east yorkshire chalk aquifer which underlies the chalk head deposits in hydraulic continuity as a corollary it is suggested that the buried timbers subsided into the till penecontemporaneously with the death of the tree when an early period of vigorous groundwater discharge led to the temporary establishment of quicksand conditions peat accumulation and humification were intimately linked to variations in spring flows radiocarbon dates help to relate these variations to regional palaeohydrogeology in particular to holocene water table fluctuations which reflect changes in recharge rates a function of climatic change and sea level

groundwater chemistry in southeast suffolk u k and its relation to quaternary geology abstract east anglia has a complex pleistocene geological history having been affected both by major changes in the level of the adjacent north sea and by glacial processes the resulting geology has a profound effect on the distribution of water chemistry in the chalk aquifer which underlies the pleistocene deposits a detailed study of the chemistry of the chalk groundwater including strontium fluoride and iodide as well as major elements has shown that this chemistry results from three phases of saline intrusion early pleistocene to modern and at least two periods of freshwater flushing climatic changes and erosional history were important in controlling flushing periods

the magnetic structure and palaeomagnetic recording fidelity of sub micron greigite fe3s4 abstract we present the results of a finite element micromagnetic model of 30 nm to 300 nm greigite fe3s4 grains with a variety of equant morphologies this grain size range covers the magnetic single domain sd to pseudo single domain psd transition and possibly also the psd to multi domain md transition the sd psd threshold d 0 is determined to be 50 nm d 0 56 nm depending on grain shape the nudged elastic band method was used to determine the room temperature energy barriers between stable states and thus the blocking volumes it is found that in the absence of interparticle magnetostatic interactions the magnetisation of equant sd greigite is not stable on a geological scale and only psd grains 70 nm can be expected to carry a stable magnetisation over billion year timescales i e all non interacting sd particles are essentially superparamagnetic we further identify a mechanism for the psd to multi domain md transition which is of a continuous nature from psd nucleation up to 300 nm when structures typical of md behaviour like closure domains begin to form

estimating hydrogeological conditions over the last 120 ka an example from the sellafield area uk for a number of years united kingdom nirex limited investigated the suitability of the area around sellafield in nw england to assess its suitability to host a deep repository for intermediate level and some low level radioactive wastes resulting from britain9s nuclear programme the investigation programme collected a large amount of lithological hydrogeological and hydrochemical data from 18 boreholes up to 2000 m deep a potential route by which radionuclides may leave the repository and return to surface is the groundwater pathway it was recognized that the groundwater regime could be disturbed significantly by major climate changes particularly glacial interglacial cycles over the very long time scales considered in the assessment of the radiological safety of a repository available geological and hydrogeological data for the sellafield area are reviewed in the context of current thinking on glacial hydrogeology showing that disturbance of the hydrogeological regime is possible during glaciation and that there are significant uncertainties in determining the timing and magnitude of the effects caused by glaciation however the evidence available both from quaternary fracture filling minerals and from the chemistry of groundwater now present suggests that any disturbance to the deeper hydrogeological regime was relatively minor and that any subglacial recharge has been removed by the present flow regime there is a possibility that high hydraulic heads at depth in the low permeability basement rock considered as a host for the repository the borrowdale volcanic group of ordovician age beneath a cover of triassic sandstones may be residual

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

iron species determination to investigate early diagenetic reactivity in marine sediments iron speciation was determined in hemiplegic sediments from a high productivity area to investigate systematically the early diagenetic reactivity of fe a combination of various leaching agents 1 m hci dithionite buffered in citrate acetic acid hf h2so4 acetic cr ii was applied to sediment and extracted more than 80 of total fe subsequent fe species determination defined specific mineral fractions that are available for fe reduction and fractions formed as products of fe diagenesis to determine the fe speciation of sheet silicates we explored an extraction procedure hf h2so4 and verified the procedure by application to standard rocks variations of fe speciation of sheet silicates reflect the possible formation of fe bearing silicates in near surface sediments the same fraction indicates a change in the primary input at greater depth which is supported by other parameters the fe ii fe iii ratio of total sediment determined by extractions was compared with mossbauer spectroscopy at room temperature and showed agreement within 10 m6ssbauer spectroscopy indicates the occurrence of siderite in the presence of free sulfide and pyrite supporting the importance of microenvironments during mineral formation the occurrence of other fe ii bearing minerals such as ankerite ca fe mg carbonate can be presumed but remains speculative

the origin and isotopic composition of dissolved sulfide in groundwater from carbonate aquifers in florida and texas the 34s values of dissolved sulfide and the sulfur isotope fractionations between dissolved sulfide and sulfate species in floridan ground water generally correlate with dissolved sulfate concentrations which are related to flow patterns and residence time within the aquifer the dissolved sulfide derives from the slow in situ biogenic reduction of sulfate dissolved from sedimentary gypsum in the aquifer in areas where the water is oldest the dissolved sulfide has apparently attained isotopic equilibrium with the dissolved sulfate 34s 65 per mil at the temperature 28 c of the system this approach to equilibrium reflects an extremely slow reduction rate of the dissolved sulfate by bacteria this slow rate probably results from very low concentrations of organic matter in the aquifer in the reducing part of the edwards aquifer texas there is a general down gradient increase in both dissolved sulfide and sulfate concentrations but neither the 34s values of sulfide nor the sulfide sulfate isotope fractionation correlates with the ground water flow pattern the dissolved sulfide species appear to be derived primarily from biogenic reduction of sulfate ions whose source is gypsum dissolution although upgradient diffusion of h2s gas from deeper oil field brines may be important in places the sulfur isotope fractionation for sulfide sulfate about 38 per mil is similar to that observed for modern oceanic sediments and probably reflects moderate sulfate reduction in the reducing part of the aquifer owing to the higher temperature and significant amount of organic matter present contributions of isotopically heavy h2s from oil field brines are also possible

characterization of the reactivity of riverine heterogeneous sediments using a facies based approach the rhine meuse delta the netherlands large groundwater resources are found in densely populated lowland areas which consist often of young unconsolidated and reduced sediments when anthropogenic activities lead to oxygenation of the aquifer breakdown of the main reduced fractions i e sedimentary organic matter som and pyrite could lead to severe groundwater deterioration such as acidification heavy metal mobilization and increased hardness the characterization of the reactive properties of these sediments is important in predicting groundwater deterioration but is often complicated by the high degree of heterogeneity of these sediments in this study the potential reduction capacity prc based on som and pyrite content the potential buffer capacity pbc based on carbonate content potential acidification capacity pac based on the potential acid production by sulfide oxidation and the measured reduction capacity mrc of five facies which are typical of the riverine sediments in the rhine meuse delta the netherlands were determined a universal facies classification model was used to classify the deposits into more homogeneous sub units based on lithologic and geogenic properties with a further sub division into oxic or anoxic redox environment based upon groundwater data and field observations the bulk chemical data show strong variation across facies for the median values of prc 186 9093 mmol o2 kg 1 pbc 17 132 mmol o2 kg 1 and pac 36 1530 mmol h kg 1 the mrc was measured as reactivity to molecular o2 exposure and was 0 5 567 3 mmol o2 kg 1 steady state oxidation rates were in the wide range of 0 001 10 355 mmol o2 kg 1 day 1 but were typically about 3 8 times faster in fine facies than in coarse facies both the prc and mrc depend strongly on grain size but also on the syn post depositional environment and redox conditions the main part of the prc consists of som but pyrite reactivity is higher than som reactivity as shown by the relative depletion of pyrite in oxic subfacies and the preferential oxidation during the oxidation experiments some facies are very prone to acidification because the pac is higher than the pbc but the oxidation experiments also show that acidification could already start before the prc is fully exhausted this study is one of the few that combines bulk chemical data groundwater data and reactivity measurements and shows that a facies based approach is a practical tool in characterizing the reactivity of heterogeneous deposits 2007 elsevier ltd all rights reserved

reducing marine and warm climate conditions during the late cretaceous and their influence on organic matter enrichment in the oil shale deposits of north jordan abstract late cretaceous oil shales located in the yarmouk sub basin north jordan were analysed using techniques of organic and inorganic geochemistry coupled with a microfossil study results of this study were used to reconstruct the paleoenvironmental and paleoclimatic conditions during the late cretaceous and to investigate their influence on organic matter enrichment of the oil shale deposits the analysed oil shales have high toc and s total content values in the ranges of 2 11 12 85 wt and 1 83 8 81 wt respectively the high s total content and its relation with toc values indicate that the sulfur is associated with organic matter and that the oil shales were deposited in a marine environment under reducing conditions this is shown by petrographic observation and supported by biomarker distributions the microscopic investigation indicated that the oil shales contain abundant liptinitic materials i e alginite and amorphous organic matter and planktonic foraminifera the presence of these sapropelic materials and planktonic foraminifera assemblages further suggests a marine origin biomarker distributions are also known to reflect dominantly marine plankton algal and microorganisms source input water column stratification and low oxygen reducing conditions are indicated by narrow pr ph values relatively high v ni elemental ratios and the presence of gammacerane reducing conditions contribute to preservation of organic matter warm water periods during the late cretaceous are also indicated by dominant occurrences of warm water index microfossil taxa the warm climate combined with elevated phosphorus p are the major causes of excessive algae growth and led to enhanced biological productivity within the photic zone of the water column during deposition of the oil shale deposits this increased bio productivity in combination with good preservation of organic matter are the main mechanisms of organic matter enrichment within the late cretaceous oil shales in the north jordan

is the water still hot sustainability and the thermal springs at bath england the hot springs at bath are the largest natural thermal source in britain sustainable use of the waters for a spa requires maintenance of their temperature and flow rate together with smaller springs at hotwells bristol they form the outflow from a regional thermal aquifer that occurs where the carboniferous limestone is buried at depths 2 7 km in the bristol bath structural basin the aquifer is recharged via limestone outcrops forming the south and west portions of the basin rim current knowledge of the basin s structure is reviewed and important uncertainties identified concerning the hydrogeological role of thrust faults which may cut the limestone at depth a simple numerical model is used to determine the possible influence of thrusts upon groundwater flow within the thermal aquifer comparison of the modelled flow patterns with geochemical data and structure contours eliminates the hypothesis that thrusts completely disrupt the continuity of the aquifer the most successful model is used to simulate the possible impact of dewatering by large quarries at the limestone outcrops north and south of bath substantial reductions in modelled flow at bath result from proposed dewatering in the eastern mendips although the steady state approach adopted has severe limitations in that it does not take account of the incremental staging of actual dewatering nor allow for partial restitution of groundwater levels the geological uncertainties highlighted by the modelling could be addressed by future research into the effect of thrusts on the continuity of the carboniferous limestone more refined modelling to predict the timing of possible impacts of quarry dewatering will require measurements of the storativity of the thermal aquifer

mesozoic regional tectonics and south viking graben formation evidence for localized thin skinned detachments during rift development and inversion abstract a regional thin skinned model of south viking graben development is presented in which zechstein marginal evaporites and interpreted salt have acted as a key de collement horizon along which mechanical decoupling of post salt triassic and younger strata from pre salt basement has occurred the western margin of the south viking graben defines an asymmetrical late jurassic half graben controlled by episodic extension along a nne ssw trending eastward dipping fault system an initial minor phase of rifting in the triassic is suggested by the slight westward thickening and associated divergence of interpreted triassic sequences at depth the scarcity absence of upper triassic and lower jurassic sequences is believed to result from a subsequent phase of uplift which affected the region in the mid cimmerian attributed to the development of a thermal dome at the future site of a jurassic rift triple junction to the southwest the onset of large scale extension from the late callovian onwards marked the major phase of half graben formation and created a regional hanging wall tilt which locally caused gravity gliding of post salt section to the wnw with resultant low angle extensional faulting upslope and salt cored buckling downslope the late jurassic half graben was subsequently tightened by a phase of thin skinned inversion in the latest jurassic early cretaceous associated with back steepening of the western margin fault system with resulting reactivation of the extensional detachment system the effects of this inversion have been noted in many parts of the northern north sea within the south viking graben shortening estimates vary between 14 and 18 and are expressed on seismic data by localized hanging wall folds and the back steepening of faults along the western margin fault complex of the graben together with out of graben thrusting up the hanging wall dip slope variation in both the extension and inversion mechanisms appears to be controlled by interpreted nw se transfer systems which compartmentalize the graben into three subgraben within which differential zechstein basin development occurred

recent localised sulphate reduction and pyrite formation in a fissured chalk aquifer reply reduction oxidation reactions in the london basin aquifer system how may they be investigated

geochemical relationships of late paleozoic carbon rich shales of the midcontinent usa a compendium of results advocating changeable geochemical conditions abstract previous studies have shown that pennsylvanian black shales of the midcontinent us possess a more complex geochemical history than was once thought vine and tourtelot econ geol 65 1970 253 and coveney and glascock appl geochem 4 1989 347 note that the widespread nature of metalliferous pennsylvanian black shales and the diverse geological environments across the midwestern us pose the likelihood that metals contained in the black shales are of complex origins detailed geochemical and statistical representations using characteristics of numerous black shale members have shown that water depth may not have been uniformly deep as previously inferred by numerous workers earlier suggestions that these black shales were associated exclusively with anoxic depositional conditions have been challenged by a more realistic theory of multifaceted fluctuating environmental conditions a wide range of major and trace element concentrations combined with widely varying characteristics and diverse types of organic matter indicate the presence of fluctuating geochemical settings the presumption is that numerous associated chemical reactions occurred syngenetically one geochemical index degree of pyritization dop suggests a dysaerobic to aerobic setting for many of the shales whereas some other geochemical proxies i e v v ni indicate punctuated episodes of bottom water anoxia schieber abstr programs geol soc am 33 6 2001 a102 notes that in some black shales pyrite enrichment due to intermittent organic reworking explains the high dop values once thought to equate with extreme euxinic depositional conditions it seems likely therefore that even during apparent euxinic periods as indicated by bulk geochemistry oxygen deprived events were apparently short lived the seemingly euxinic fingerprint as shown by geochemical characteristics may result through time averaging abstr programs geol soc am 33 6 2001 a102 of intermittent euxinic events providing a misleading indication of dominant euxinic conditions thus detailed microstratigraphic sampling is necessary to delineate short punctuated occurrences of intermittent sub oxic episodes the midcontinent pennsylvanian shales may reflect a complex array of bottom water oxygenation variations and water depth fluctuations in response to climatic and localized events hatch j r and leventhal j s 1992 relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas usa in meyers p a pratt l m nagy b eds geochemistry of metalliferous black shales chem geol 99 65 82 complicated by post depositional events appl geochem 4 1989 347 this research examines the previous exclusively anoxic origin for midcontinent pennsylvanian black shales from a geochemical perspective and offers an alternative supported by detailed statistical presentations with the hypothesis that events of anoxia were punctuated by short lived dysaerobic or even near oxic events

hydrochemical evolution of the east midlands triassic sandstone aquifer england a detailed hydrogeochemical interpretation has been made of the red bed sherwood sandstone triassic aquifer of the east midlands of england on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water three distinct zones are recognised 1 i recent groundwater mainly 100 y oxidising dominated by congruent dissolution of dolomite and by inputs from atmospheric and anthropogenic sources 2 ii groundwater age 103 104 y predominantly reducing dominated by incongruent dissolution of dolomite 3 iii groundwater age 104 y reducing conditions approach to isotopic and chemical equilibrium in the carbonate system dominance of gypsum dissolution the minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history na cl f and b are controlled by atmospheric inputs sr2 and mn2 trends can be explained by carbonate and sulphate mineral dissolution ba2 is derived from carbonates but controlled by barite equilibrium fe so42 no3 and u are strongly influenced by redox reactions the concentrations of transition metals and other elements remain very low only li and k are considered to represent additions by reaction of silicate minerals the extent of direct anthropogenic influence is probably limited to enhanced so4 no32 and possibly cu zn and pb in zone i

hydrochemical trends palaeorecharge and groundwater ages in the fissured chalk aquifer of the london and berkshire basins uk the hydrochemical radiochemical stable isotope 14c and dissolved noble gas composition of groundwaters has been determined along two profiles across the confined fissured chalk aquifer of the london basin of southern england and for selected sites in the adjacent berkshire basin during downgradient flow in the london basin aquifer the groundwater chemistry is modified by water rock interactions congruent and incongruent reaction of the carbonate lithology resulting in enhanced mg ca and sr ca ratios and 13c contents with increased residence times redox and ion exchange reactions and towards the centre of the basin mixing with a residual saline connate water stored in the chalk matrix there is evidence from anomalous water chemistries for a component of vertical leakage from overlying tertiary beds into the confined aquifer as a result of historical dewatering of the aquifer dissolved noble gas contents indicate the climate was up to 4 5 c cooler than at present during recharge of the waters now found in the centres of both basins stable isotope 2h and 18o depletions correspond to this recharge temperature change for evolved waters having 13c 8 pdb a negative linear correlation is demonstrated between derived recharge temperatures and 13c values which is interpreted as mixing between relatively warm light isotopic fracture borne waters and cooler stored waters of the matrix having a 13c signature more or less equilibrated with the chalk from geochemical 14c 4he age estimates the abstracted water is interpreted as being either of wholly holocene post devensian glacial origin or an admixture of holocene and late pleistocene pre glacial cold stage interstadial recharge devensian pleniglacial stage waters of the last glacial maximum are not represented

characteristic trace fossils in nearshore to offshore sequences upper cretaceous of east central utah more than 20 trace fossil species occur in marine facies of the cretaceous star point and blackhawk formations in the book cliffs and wasatch plateau provinces of utah major genera include ancorichnus arenicolites aulichnites chondrites conichnus cylindrichnus medousichnus ophiomorpha palaeophycus planolites rosselia schaubcylindrichnus scolicia skolithos teichichnus teredolites and thalassinoides newly named taxa include ancorichnus capronus medousichnus loculatus and rosselia chonoides most trace fossils occur in characteristic albeit intergradational ichnofacies correlative with major lithofacies of regressive nearshore to offshore sequences the latter include foreshore foreshore shoreface transition shoreface and offshore facies landward facies are typified by clean well sorted well stratified sparsely burrowed sandstones seaward facies except where interrupted by hummocky bedded sandstones exhibit successively less pure less well sorted and stratified more intensely

hydrochemical and stable isotope evidence for the extent and nature of the effective chalk aquifer of north norfolk uk in eastern england the chalk aquifer is covered by extensive pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer in this study the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions 18o and 2h are interpreted to reveal the extent and nature of the effective chalk aquifer of north norfolk it is found that the chalk aquifer can be divided into an upper region of fresh groundwater with a cl concentration of typically less than 100 mg l 1 and a lower region of increasingly saline water the transition between the two regions is approximately 50 m below sea level and results in an effective aquifer thickness of 50 60 m in the west of the area but less than 25 m where the eocene london clay boundary is met in the east of the area hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the chalk where the chalk is confined by low permeability chalky boulder clay isotopically depleted groundwater 18o less than 7 5 is present in contrast to those areas of unconfined chalk where glacial deposits are thin or absent 18o about 7 0 the isotopically depleted groundwater is evidence for groundwater recharge during the late pleistocene under conditions when mean surface air temperatures are estimated to have been 4 5 c cooler than at the present day and suggests long groundwater residence times in the confined aquifer elevated molar mg ca ratios of more than 0 2 resulting from progressive rock water interaction in the confined aquifer also indicate long residence times a conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater occupying areas where confined groundwater dates from the late pleistocene is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body

groundwater sources and geochemical processes in a crystalline fault aquifer the origin of water flowing in faults and fractures at great depth is poorly known in crystalline media this paper describes a field study designed to characterize the geochemical compartmentalization of adeep aquifer system constituted by a graben structure where a permeable fault zone was identified analysesof the major chemical elements trace elements dissolved gases and stable water isotopes reveal theorigin of dissolved components for each permeable domain and provide information on various watersources involved during different seasonal regimes the geochemical response induced by performinga pumping test in the fault zone is examined in order to quantify mixing processes and contributionof different permeable domains to the flow reactive processes enhanced by the pumped fluxes are alsoidentified and discussed the fault zone presents different geochemical responses related to changes in hydraulic regime theyare interpreted as different water sources related to various permeable structures within the aquifer during the low water regime results suggest mixing of recent water with a clear contribution of olderwater of inter glacial origin recharge temperature around 7 c suggesting the involvement of watertrapped in a local low permeability matrix domain or the contribution of large scale circulation loops during the high water level period due to inversion of the hydraulic gradient between the major permeablefault zone and its surrounding domains modern water predominantly flows down to the deep bedrockand ensures recharge at a local scale within the graben pumping in a permeable fault zone induces hydraulic connections with storage reservoirs the overlaidregolith domain ensures part of the flow rate for long term pumping around 20 in the present case during late time pumping orthogonal fluxes coming from the fractured domains surrounding the majorfault zone are dominant storage in the connected fracture network within the graben structure mainlyensures the main part of the flow rate 80 in the present case reactive processes are induced by mixingof water from different sources and transfer conditions a specific approach is applied to quantify thereaction rate involved along the pumping time autotrophic denitrification coupled with iron mineralsoxidation is highlighted and water rock interaction is clearly enhanced by the flux changes induced bypumping

palaeohydrology and future climate change since the mid 1980s there has been growing concern that increasing concentrations of so called greenhouse gases will lead to global warming changes to regional climates and hence impacts on the environment society and economy the united nations environment program and the world meteorological organization in 1987 set up the intergovernmental panel on climate change ipcc which has reported on climate change predictions ipcc 1990a 1992a the possible impacts of climate change ipcc 1990b 1992b and strategies for mitigating the effects of climate change ipcc 1991 the ipcc second assessment is scheduled for publication in 1996 climate change science is essentially predictive it is trying to predict conditions during the twenty first century by far the most common approach is based around the use of global climate models gcms these numerical simulation models are used to predict the global and regional climatic effects of changing greenhouse gas concentrations and many climate change impact studies use scenarios based in some way on gcm simulations these scenarios are then used to perturb current climatic time series and fed through a catchment hydrological model to simulate river flows and other hydrological properties e g bultot et al 1988 lettenmaier gan 1990 arnell reynard 1993 and many others the two major problems with this approach lie in the definition of credible catchment scale scenarios from gcm simulations and the development of realistic hydrological simulation models the latter problem is fundamental to hydrological simulation whilst the former is peculiar to climate change impact assessments and arises for two reasons first gcms do not at present represent all the climatic processes in a realistic manner particularly those relating to the development of clouds and the interactions between the atmosphere and the land surface and second gcms operate at a very coarse spatial resolution some important atmospheric processes such as the development of meso scale circulation patterns and convective storms are therefore not simulated particularly well and whilst gcms can simulate large scale atmospheric features well regional and local climates are often not well reproduced the coarse spatial resolution also means that gcm output has to be interpolated down to the catchment scale a variety of techniques of varying degrees of sophistication have been used or proposed ranging from simple statistical interpolation through empirical relationships between large scale and local climate to the use of nested regional climate simulation models but all rely ultimately on the reliability of the gcm simulations of large scale climatic features arnell 1995a the other popular approach to climate impact assessment uses the past as an analogue for the future one variant uses the instrumental period in practice the last century another uses historical data and a third uses palaeoclimatic reconstructions

early diagenesis of the upper devonian escuminac formation in the gaspe peninsula quebec sedimentological and geochemical evidence abstract clay mineral investigations pyrolysis of organic matter and microscopic observation of palynomorphs are used to interpret the diagenetic conditions of the upper devonian escuminac formation quebec canada pyrolysis of kerogen vitrinite reflectance and the presence of smectite show that the sediments of this formation have been subjected only to a shallow burial diagenesis hence the geochemical signatures are informative on the palaeoenvironment concretions are observed in the escuminac formation sedimentological and geochemical evidence suggest that these concretions were formed during early diagenesis from biodegradation of organic matter the well known fish fauna of the escuminac formation show good preservation due in part to extensive early diagenetic carbonate cementation the occurrence of calcite cements and fibrous calcite is attributed to the early diagenetic transformation of pre existing organic matter

control of the preservation of organic matter by productivity and sulphate reduction in kimmeridgian shales from dorset uk abstract the kimmeridgian shales of dorset uk have a very wide range of total organic carbon toc content and hydrogen index hi these cyclic changes of organic carbon accumulation are usually interpreted in terms of biomass changes induced by variations in productivity the influence of such variations on the intensity of sulphate reduction and consequently on the preservation of organic carbon were studied the pyrite content does not reflect the full extent of sulphate reduction for sediments with a toc content greater than 10 when easily reducible iron is no longer available h 2 s is preferentially fixed as organic compounds in algal bodies a sulphate reduction index sri initial c org residual c org was calculated for each sediment on the basis of the sulphate reduction reaction stoichiometry and a drastic change in sulphate reduction intensity was seen for toc contents of about 10 above this value the sri is low and decreases with increasing toc content the sediments are rich in organic carbon composed of well laminated stacked algal bodies and were probably deposited at an oxygen depleted water sediment interface in this instance the quality and the amount of organic matter buried depends directly on the organic fluxes towards the redox interface it is assumed that the high relative input of organic matter which can be metabolized exceeds the availability of sulphate in the pore waters so that part of it escapes sulphate reduction and is probably degraded by other processes methanogenesis for toc contents less than 10 the sri is higher and variable the sediments show traces of burrowing and the depositional conditions are thought to be dysaerobic it is proposed that under such conditions bioturbation brings both sulphate and reducible iron into the sediment and that sulphate reduction mainly expressed by the presence of pyrite consumes all the available organic matter which can be metabolized the strong variability in the intensity of sulphate reduction depends on various parameters such as the genetic type of planktonic organic matter the method of transportation to the sediment and possibly the earlier oxic degradation during transportation

baseline geochemical conditions in the chalk aquifer berkshire u k a basis for groundwater quality management the chalk aquifer is the most important british aquifer and is also important over much of northern europe aquifer protection requires a sound knowledge of the baseline conditions and how these might vary or have varied with time this detailed geochemical study of a representative area of chalk in berkshire u k includes a consideration of several components 1 the inputs from the atmosphere 2 the interstitial water of the soil and the unsaturated zone 3 the interstitial water in the confined and unconfined sections of the aquifer and 4 the saturated mainly fissure flow along the hydraulic gradient which forms an important water supply of the thames valley region atmospheric inputs form an important source of some elements but the dominant chemical characteristics of the chalk groundwater are acquired during percolation through the soil and the upper unsaturated zone during saturated flow downgradient the chemistry is modified mainly by incongruent reactions of the carbonate matrix and by redox reactions and only to a minor extent by exchange reactions and mixing with residual saline connate water the incongruent reaction of carbonate results in a marked increase in the mg ca ratio and the sr and 13c contents of the groundwater with increased residence time oxygen concentrations are reduced mainly by oxidation of fe2 and the onset of reducing conditions allows dissolved fe2 to increase and rapid denitrification to occur the salinity profile through the confined chalk confirms that residual connate water up to one fifth sea water concentration still remains at depth and this accounts for some salinity increase in the confined groundwater resulting from fissure water pore water diffusional exchange timescales for groundwater movement have been established using tritium radiocarbon and indirectly using inert gas ratios and stable isotope ratios on balance it is concluded that all abstracted water is of holocene age although inert gas temperatures indicate cooler climatic conditions for recharge for some of the confined groundwater the implications for development and aquifer protection are discussed especially the prospect of natural in situ denitrification problems of fe solubility and the recognition of groundwater of different maturities