eocene sedimentation and tectonics in the hampshire basin sedimentary evidence in the eocene cuisian lutetian of the hampshire basin indicates important intra eocene movement on the isle of wight and purbeck monoclines and on the ridgeway fault evidence for syn depositional movement includes jurassic and cretaceous chert and flint pebbles in the eocene the distribution of which suggests derivation from both e and w at whitecliff bay two units of cross bedded sand have northward directed palaeocurrents and may have been deposited as localized fans of debris reworked from earlier tertiary sediments on the upwarped side of the monocline three units of laminated muds are intercalated with marine sediments in the eastern part of the basin and suggest periods of low salinity tideless conditions these episodes are attributed to the periodic isolation of the hampshire basin from the fully marine dieppe basin to the se this may have been the result of intermittent movement on a tectonic barrier to the se of selsey the onset of uplift and subsequent exposure of the chalk along the southern margin of the basin proceeded unevenly from early cuisian to late lutetian times movement on the portsdown anticline probably occurred over a similar period the isle of wight and purbeck monoclines are the superficial expressions of faults in the palaeozoic basement and not the result of lateral alpine pressures a minor series of syn depositional folds trend nw se across the basin and may reflect a component of sinistral strike slip on basement faults

geochemistry and isotope systematics of sulphur in the mixing zone of bahamian blue holes abstraet a profile of aqueous s species concentrations and stable isotope compositions is presented for the mixing zone of cousteau s blue hole north andros bahamas together with similar but less detailed results from two other blue holes these data show that s o and s 2 are produced by bacterially mediated sulphate reduction near the base of the mixing zone and that these species are reoxidized at shallower levels acidity generated by oxidation can contribute to corrosion of limestone walbrock estimated rates of such corrosion range up to 1200 mm wall rock recession per 10 ka at cousteau s blue hole equivalent to 16 porosity generation per l0 ka and are comparable with rates of dissolution caused by inorganic mixing corrosion

the nature of mineralizing fluids of the kipushi zn cu deposit katanga democratic repubic of congo quantitative fluid inclusion analysis using laser ablation icp ms and bulk crush leach methods fluid inclusions from the epigenetic zn cu deposit of kipushi central african copper belt katanga democratic republic of congo have been subjected to an integrated microthermometric bulk crush leach and laser ablation inductively coupled plasma mass spectrometric la icp ms study to elucidate the physicochemical conditions of ore formation and the origin of the mineralizing fluids the kipushi deposit is hosted in carbonates and partly in siliciclastic rocks that have undergone regional low grade greenschist facies metamorphism and which were strongly deformed during the lufilian orogeny main deformation phase 550 ma investigation of host rock gangue and ore samples enabled reconstruction of the paragenesis of ore deposition the main zn cu ge pb sulfide mineralization was accompanied by three generations of hydrothermal dolomite and a generation of coarse grained quartz primary and pseudosecondary fluid inclusions in these minerals contain predominantly halite saturated aqueous brines 30 43 wt nacl equiv with locally unidentified trapped solids these inclusions mostly decrepitate upon heating before total homogenization which could suggest that they also trapped excess carbonic vapor they show petrographic and microthermometric evidence for postentrapment reequilibration prohibiting their use as accurate geothermometers and geobarometers previous studies on chlorite and sphalerite geothermometry framed the formation temperature of the kipushi cu zn deposit between 290 to 380 c younger fluids are present as secondary inclusions in the gangue minerals and as primary fluid inclusions in sphalerite from a minor secondary mineralization phase these two phase aqueous inclusions have a slightly lower salinity 23 31 wt nacl equiv and have homogenization temperatures ranging from 170 to 80 c in successive fluid inclusion assemblages sporadically some mixed aqueous carbonic and gaseous co2 ch4 inclusions are present but their genetic position is un clear and they are insignificant with regard to the mineralization process as a whole crush leach bulk analysis of the fluid inclusions show that the mineralizing fluids had a molar cl br ratio close to or somewhat higher than the seawater value which rules out a major contribution from bittern brines and suggests that the fluids gained their salinity primarily by the dissolution of evaporites younger fluids that circulated through the deposit after the main phase of ore formation have cl br and na br signatures indicative of a greater involvement of halite dissolution brines values much higher than that of seawater la icp ms analyses of the mineralizing fluids reveal that they have molar li na ca na mg na mn na and sr na in the range of natural high salinity fluids in metamorphic environments worldwide however they have relatively high molar fe na zn na pb na and especially very high ba na ratios their molar k na is also somewhat higher than for other low grade metamorphic fluids but is nevertheless in agreement with the values predicted by the k na geothermometer at the conditions of ore formation this suggests that the major element composition of the fluids was buffered by fluid mineral equilibria their relatively high metal contents ba zn fe and pb suggest that they interacted with and leached these elements from felsic basement rocks at higher temperatures whatever the origin of the fluids their salinity and the metals their uniformly high ba and ore metal content together with the absence of barite and the occurrence of ba silicates at kipushi indicates that sulfide mineralization occurred when the metal bearing fluids encountered a reducing h2s rich reservoir the ubiquitous presence of preexisting metamorphosed carbonic material shungite in the sulfides and host rock and a sulfur isotope signature of the ores in agreement with thermogenic sulfate reduction suggests that this condition was likely created due to the high initial reduced carbon content of the host rocks at kipushi which seems to be exceptional in the copper belt therefore we postulate that a critical factor in the formation of major vein type zn cu mineralization was the presence of a hydrocarbon rich facies of the lower nguba carbonates at kipushi

the structural development of the wessex basin the mesozoic and cenozoic structures of southern england form part of a system of disturbances which extends across the channel into northern france they are reviewed in the light of published data from south dorset basin development started with permo triassic rifting and is believed to have continued through the jurassic and early cretaceous with intermittent growth on deep seated listric normal faults probably associated with roll over anticlines this regime had ceased by the aptian and the basin passed through a period of relative stability in the late cretaceous followed by tectonic inversion and in the miocene by northwards compressive movement along the former normal faults this partially restored the earlier separative displacement at depth and probably accentuated pre existing roll over anticlines it was expressed in the surficial upper cretaceous palaeogene sequence as monoclinal flexuring the early rifting and the change from overall n s crustal stretching to compression may reflect plate tectonic events in the north atlantic region

extension tectonics in the wessex basin southern england the permian to cretaceous tectonic evolution of the wessex basin was controlled by horizontal tensional and vertical isostatic forces within the lithosphere the gross morphologies of its constituent structures were governed by the location of variscan thrust and wrench faults in the upper and middle crust which suffered extensional reactivation in tensional stress fields oriented approximately nw se several episodes of crustal extension can be resolved in early permian early triassic early jurassic and late jurassic early cretaceous times these were characterized by the rapid subsidence of fault bounded basins and commonly by erosion of adjacent upfaulted blocks superimposed upon the fault controlled subsidence dominant during periods of fault quiescence and becoming increasingly important with time a component of regional subsidence is considered to have a thermal origin this suggests that crustal extension was accompanied by some form of not necessarily uniform lithospheric thinning subsidence analyses assuming local airey isostasy give cumulative crustal extension factors of 20 28 beneath the grabens a more reasonable assumption of regional airey compensation indicates basinwide crustal extension of 13 17 which is consistent with birps offshore deep seismic reflection data

multiple generations of high salinity formation water in the triassic sherwood sandstone wytch farm oilfield onshore uk abstract the origin and heterogeneity of oilfield formation water in the lower triassic sherwood sandstone at wytch farm in the wessex basin uk have been investigated using production data detailed water geochemistry and o s and h stable isotope data the formation waters are highly saline nacl type brines with tds values of up to 230 000 mg l there is a general decrease in salinity from the flanks of the field to the crest with cl decreasing from about 136 000 to 109 000 mg l the cl br ratio of the water shows that salinity was largely derived from the dissolution of upper triassic continental evaporites found off structure to the west and north of the field the water in the field had a meteoric source although variation in 2h values suggests that there may be meteoric waters of different ages in the oilfield reflecting recharge under different palaeoclimatic conditions at the crest of the field aqueous so 4 2 resulted from dissolution of anhydrite in the reservoir in contrast in other parts of the field there is an indication that some of the dissolved so 4 2 was derived from oxidation of pyrite at some point on the recharge path of meteoric water to the field there were two meteoric influx events bringing different cl concentrations and different 2h values the first was probably before the eocene oil influx and could have occurred in the lower cretaceous or early tertiary the second meteoric influx event probably occurred after or during oil migration into the wytch farm structure since the second meteoric water is found at the flanks of the field adjacent to the regions where salt is found in the stratigraphy the preservation of heterogeneities in oilfield formation water compositions suggests that there has been little aqueous fluid movement or diffusive flux for over 40 million years mass flux has been restricted by density stratification within the aquifer and the very low effective permeability for the aqueous phase in the oil filled reservoir

br cl na systematics in illinois basin fluids constraints on fluid origin and evolution the authors present here bromide chloride and sodium data for fluids from reservoirs of ordovician through pennsylvania age in the illinois basic which suggest that remnant marine fluids contribute significantly to fluid cl budgets cl br and nabr ratios for ordovician through devonian formation fluids are relatively uniform and near those for seawater despite greater than a factor of ten range in cl concentration in contrast fluids from mississippian and pennsylvanian reservoirs separated from older reservoirs by the new albany shale group have more variable fluid cl br and na br ratios most of which are significantly greater then those of seawater the 1 1 stoichiometry of cl and na increases for mississippian and pennsylvanian formation fluids is consistent with halite dissolution nevertheless br systematics and mass balance considerations indicate that he overall cl budget of illinois basin formation fluids appears to be more significantly influenced by the contribution from subaerially evaporated seawater than by halite dissolution

the structure and evolution of the wessex basin southern england an example of inversion tectonics abstract the wessex basin of southern england consists of four main sub basins each sub basin is thought to be fundamentally controlled by the normal reactivation of hercynian basement thrust and wrench or transfer faults post hercynian polyphase reactivation of both east west thrust and northwest southeast transfer faults tended to compartmentalise the basement thereby leading to the initiation of discrete permian cretaceous depocentres while rifting was confined to the western portions of the area during the permo triassic easterly migration in the mesozoic allowed the initiation of the weald and channel basins the sub basins represent therefore simple sinistral pull apart basins opening along northwest southeast faults this same fault direction is postulated to have also played a major role in controlling and or modifying the development of european basins in general major pre aptian uplift and erosion is largely attributed to the thermal effects and hence the isostatic uplift of the basin associated with continental rifting of the bay of biscay and the north atlantic margins major inversion and hence basin destruction began in the late cretaceous early tertiary with the uplift of the channel weald and vale of pewsey basins and culminated in the oligocene miocene synchronous with the helvetic phase of alpine deformation wessex basin inversion was facilitated by the thrust reactivation of variscan faults above an intracrustal detachment surface the same surface which allowed upper crustal extension and hence basin initiation in the permo triassic the structural development of the wessex basin both during extension basin formation phase and compression inversion phase was ultimately controlled by the plate motion of africa relative to europe such plate motions successfully predict the observed nw se sinistral motion from the stephanian to the aptian e w sinistral motion during the aptian cenomanian and largely nw se dextral motion from the cenomanian to the present day

impurity sources of f cl no3 and so4 2 in greenland and antarctic precipitation five polar impurity sources are proposed anthropogenic no3 and so42 in recent greenland but not antarctic snow marine aerosols the dominant cl source volcanic eruptions which produce detectable but variable peaks in so42 f and or cl concentrations biogenic sulfurous gases from soil and coastal waters the dominant source for so42 in nonvolcanic strata an unidentified source of background nitrate which is more active in the northern hemisphere and which displays a summer concentration maximum solar activity and supernova events do not modulate no3 concentrations in greenland snow

ichnology paleosols and palimpsests surfaces in the tinat member of the nuayyim formation unayzah group subsurface saudi arabia trace fossils and genetic stratigraphy in continental settings abstract the nuayyim formation of the unayzah group is widespread in subsurface central saudi arabia and constitutes a laterally variable stratigraphic unit with a complex mosaic of facies sedimentation for the tinat member took place majorly in a continental setting dominated by aeolian processes that resulted in dunes interdunes ephemeral stream deposits terminating with regional development of paleosols facies ichnofacies and palynological analysis suggest an arid to semi arid setting with biogenic activity in the form of continental fauna and plants in deposits associated with pedogenetical alteration in paleosol horizons therein burrowing exhibits elements of the scoyenia ichnofacies in beds with sparse to abundant bioturbation tectonic uplift and subaerial exposure resulted in the exhumation of previously buried substrates leading to the formation of burrowed palimpsests surfaces associated with paleosols at the end of unayzah deposition prior to the onset of the khuff formation progressive thermal updoming is interpreted to have occurred during the latest portion of the unayzah group sedimentation cycle in the arabian plate culminating in the regional pre khuff unconformity at the top of this megacycle recognized in this study by biogenically demarcated diastems ichnological and sedimentological observations outlined in this study are significant because they i refine existing interpretations of the paleoenvironmental history in the study area ii document diastems marking breaks in sedimentation and iii outline several soil forming cycles that allowed the establishment of a trace fossil suite with continental affinities thus demarcating the end of an entire sedimentation cycle the recognition and delineation of burrowed horizons associated with paleosols provides a tool to understand the tectono stratigraphic evolution of similar successions in the rock record

sedimentologic palaeoecologic taphonomic and ichnologic criteria for high resolution sequence analysis a practical guide for the identification and interpretation of discontinuities in shelf deposits abstract we classify stratigraphic bounding surfaces defined by sedimentologic palaeoecologic or taphonomic and ichnologic criteria our case study refers to a particularly well preserved outcrop of miocene sedimentary rocks on the pacific coast of central costa rica these rocks mainly fine sandstones accumulated in a tropical shallow marine strongly subsiding sand swamped forearc coastal embayment sedimentary bounding surfaces or lithofacies bounding surfaces can be subdivided into erosional and non erosional boundaries between depositional systems in our case study erosional boundaries angular unconformities and erosional disconformities were produced by block tilting tectonic reactivation of cliffs or wave and tidal ravinement during sea level rises and are interpreted as sequence boundaries and bases of parasequence sets respectively non erosional transitions delimit genetically closely related depositional systems sharp contacts are considered as bases of parasequence sets diffuse transitions are interpreted as parasequences palaeoecologically and taphonomically defined fossiliferous bounding surfaces or layers mostly occur within depositional systems they seldom coincide with erosional lithofacies bounding surfaces two types can be distinguished autochthonous and allochthonous fossil concentrations autochthonous fossil concentrations can be grouped into layers with epifaunal and semi infaunal molluscs in growth position layers with infaunal bivalve associations in growth position and coprolith concentrations the majority of these layers is developed as concretion horizons autochthonous fossil concentrations invariably signal a relative rise of sea level and are interpreted as bases of parasequences or parasequence sets allochthonous fossil concentrations can be grouped into fossil concentrations produced by non turbulent shelf currents driftwood concentrations tempestite fossil concentrations fossil concentrations produced by near shore turbulent flow regimes and fossil concentrations produced by tidal currents they are only seldom developed as concretion horizons the appearance of allochthonous fossil concentrations in certain intervals of a given section and disappearance in others is clearly a signal of shallowing or deepening seas fossil concentrations produced by non turbulent shelf currents and driftwood concentrations can be interpreted as bases of parasequences ichnofabrics can be used as an additional tool for the identification and interpretation of bounding surfaces erosional boundaries may be marked by well known features such as gastrochaenolites sequence boundaries may be preceded by thalassinoides boxworks strongly thickened by concretionary growth at non erosional boundaries however trace fossils commonly fail to mark the crucial turning point yet they seem to record environmental changes for instance a coming transgression far earlier than any sedimentary phenomenon or body fossil after prolonged swamping with sand during a relative sea level lowstand they explode in diversity during the following transgression before this transgression produces its own typical sediment equally after the dumping of organic matter during the transgression trace making organisms announce the coming highstand by reworking their habitat to the degree of total destratification before the highstand deposits proper force them to keep up with aggradation which results in the typical highstand selection of deep tier structures thus the degree of reworking by bioturbation seems to be a very good and easily recognizable indicator of the internal architecture of parasequences and parasequence sets

ichnofabrics and geometric configurations of ophiomorpha within a sequence stratigraphic framework an example from the upper cretaceous us western interior ichnofabric in the upper cretaceous sego sandstone and anchor mine tongue of east central utah can be differentiated into two components 1 discrete ophiomorpha and 2 mottling and other trace fossils the ichnofabric index method was employed to evaluate spatial variability of the ichnofabrics within depositional sequences and component systems tracts indices were logged for amount of bioturbation caused solely by ophiomorpha oii and that represented by all other biogenic features bii values of oii 1 are more pervasive in lowstand systems tracts compared to transgressive systems tracts this is consistent with the predominance of marginal and nearshore marine sand dominated settings that are characteristic of lowstands which are favourable habitats for colonization by ophiomorpha producers ichnofabric index values vary both vertically and laterally within any given systems tract reflecting differences in physical and biological parameters operating in the palaeoenvironment these parameters include the total number and behaviours of organisms occupying the substrate as well as substrate texture and grain size and rates of sedimentation the architectural style of ophiomorpha was examined within five depositional facies shelf storm deposit lower shoreface shoreface and estuarine inclinations of individual burrow elements were approximated relative to bedding planes categorized as either vertical inclined or horizontal and then plotted on ternary diagrams based on the types of facies present these results suggest that variations in the geometric configurations of ophiomorpha are controlled primarily by physical energy levels and the rate and nature of sedimentation results of this study have broad implications for understanding the physical factors affecting facies variability within sequences and systems tracts when coupled with sedimentologic data recognition of variations in the distribution of ichnofabrics and architectural style of ophiomorpha can provide additional information useful for characterizing depositional environments and therefore could be integrated with other basin analysis techniques to test and refine sequence stratigraphic interpretations

fossil wood in middle upper jurassic marine sedimentary cycles of france relations with climate sea level dynamics and carbonate platform environments abstract vegetation climate and sea level oscillations interact in complex ways intuition suggests that climatic variations are recorded in geological deposits by both fossil phytoclasts and sediments therefore investigation of palaeobotanical remains within a precise sedimentological framework may help to decipher this much debated interaction a database of 129 jurassic bathonian oxfordian fossil wood samples from france is used here as a case study the palaeoenvironment freshwater swamp carbonate lagoon shoreface argillaceous offshore and the second order relative sea level phases were determined for each datum there is no correlation between the wood genera distribution and second order relative sea level cycles however 66 of the fossil wood samples were found within transgressive parts of cycles or at maximum flooding surfaces versus 34 in their regressive counterparts by contrast there is a close correlation between wood distribution and palaeoenvironment for agathoxylon and brachyoxylon the two most common genera although both genera occur in the four main depositional systems agathoxylon is the more common in offshore facies whereas brachyoxylon predominates in protected lagoon environments a model of wood deposition preservation is proposed it is shown that 1 the distribution of wood is not controlled by climate but by environmental processes related to relative sea level changes 2 the abundance of wood in transgressive deposits may be related to ravinement of previously emerged areas and or to the high preservational potential associated with increased accommodation space 3 carbonate platforms were probably inhabited by low diversity brachyoxylon xylofloras whereas offshore environments received a more diversified probably multi source flora from emergent land areas periods of bathonian callovian and oxfordian subaerial exposure of carbonate platforms may not have been conducive to the establishment of a diverse stable climax xyloflora

crustal structure beneath southern england from deep seismic reflection profiles seismic reflection events from recently acquired profiles in southern england are interpreted in terms of stratigraphic and structural interfaces between rock units in particular evidence is brought forward that a series of reflection events dipping between 22 and 27 with azimuth averaging 160 represents 2 major thrust zones occurring in the variscan floor beneath mesozoic cover a geological model based upon borehole information and regional geological considerations is presented the tentative recognition of crystalline basement overlain and overstepped by late proterozoic rocks of variable thickness suggests that basement in this area was unstable from late precambrian times the mesozoic structural evolution can be related to tectonic re activation of major concealed thrust zones in the palaeozoic 9basement9

chemical composition of ice containing tephra layers in the byrd station ice core antarctica abstract the chemical composition of ice containing tephra volcanic ash layers in 22 sections of the byrd station ice core was examined to determine if the volcanic eruptions affected the chemical composition of the atmosphere and precipitation in the vicinity of byrd station the liquid conductivity acidity sulfate nitrate aluminum and sodium concentrations of ice samples deposited before during and after the deposition of the tephra layers were analyzed ice samples that contain tephra layers have on average about two times more sulfate and three to four times more aluminum than nonvolcanic ice samples the acidity of ice samples associated with tephra layers is lowered by hydrolysis of silicate glass and minerals average nitrate sodium and conductivity are the same in all samples because much of the sulfur and chlorine originally associated with these eruptions may have been scavenged by ash particles the atmospheric residence time of these volatiles would have been minimized therefore the eruptions probably had only a small effect on the composition of the antarctic atmosphere and a negligible effect on local or global climate

origin of cacl brines in devonian formations western canada sedimentary basin abstract the majority of waters in devonian formations of the western canada sedimentary basin are high salinity ca cl brines this relatively rare type of brine is of economic interest because of its association with both oil and hydrothermal ore deposits these brines are important sources of ca2 mg2 and ore metals in sedimentary basins it is possible to generate the ca cl brines by modification of residual evaporite brines the evaporation of devonian sea water produced large quantities of gypsum and halite such as the prairie formation residual brines were not retained in the evaporating system quantities of dense halite saturated brine sufficient to account for the high salinity formation waters in the basin were lost syndepositionally the cl and br content of waters within devonian formations in the basin can be explained by dilution of the residual evaporite brines brine composition was modified as a result of density driven reflux to depths of several kilometers this placed concentrated brines in contact with precambrian basement rocks at elevated temperatures 100 300 c the most important reactions between the brine and basement rocks appear to involve albitization of feldspars further modification of the brines occured as cements formed in devonian carbonates volumetrically the most important of these is dolomite in addition some devonian carbonates were dolomitized during ascent along faults mg2 was lost from hot brines as dolomite formed

volcanic ash from the 1362 a d oraefajokull eruption iceland in the greenland ice sheet a continuous record of electrical conductivity measurements ecm was made on site during the drilling of a 200 m ice core at summit greenland and was used to identify horizons in the ice that might be linked to volcanic eruptions in one detailed section that we studied a large peak in the number of particles two orders of magnitude above the background was measured the particle peak was not associated with an ecm peak however the particles were identified as volcanic ash on the basis of both particle morphology and chemical composition the ash composition suggests an explosive rhyolitic eruption and is believed to have originatedfrom oraefajokull in iceland in 1362 a d

attributes of the wood boring trace fossil asthenopodichnium in the late cretaceous wahweap formation utah usa abstract a common macroscopic wood boring trace fossil occurs in the upper cretaceous braided and meandering stream deposits of the upper and capping sandstone members of the wahweap formation in grand staircase escalante national monument utah upon detailed examination this trace warrants assignment to asthenopodichnium thenius 1979 asthenopodichnium is a scoop shaped pouch like trace that is preserved as iron hydroxide rind casts of wood fragments and logs the long axes of the scoops are typically aligned parallel or sub parallel to the long axis of the preserved wood in the upper and capping sandstone members asthenopodichnium characteristically occur in dense clusters in which pouches overlie one another although they are found as isolated individual traces and tight clusters of multiple individuals as well the asthenopodichnium trace maker has been purported to be the possible product of mayfly nymphs developed in moving fresh water as a fresh water trace asthenopodichnium may be used in conjunction with teredolites a marine or brackish indicator to delimit the brackish fresh water limit in estuarine deposits

a north atlantic tephrostratigraphical framework for 130 60 ka b2k new tephra discoveries marine based correlations and future challenges abstract building chronological frameworks for proxy sequences spanning 130 60 ka b2k is plagued by difficulties and uncertainties recent developments in the north atlantic region however affirm the potential offered by tephrochronology and specifically the search for cryptotephra here we review the potential offered by tephrostratigraphy for sequences spanning 130 60 ka b2k we combine newly identified cryptotephra deposits from the ngrip ice core and a marine core from the iceland basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time interval forty three tephra or cryptotephra deposits are incorporated into this framework twenty three tephra deposits are found in the greenland ice cores including nine new ngrip tephras and twenty separate deposits are preserved in various north atlantic marine sequences major minor and trace element results are presented for the new ngrip horizons together with age estimates based on their position within the ice core record basaltic tephras of icelandic origin dominate the framework with only eight tephras of rhyolitic composition found new results from marine core md99 2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits tephra based correlations in the marine environment provide independent tie points for this time interval and highlight the potential of widening the application of tephrochronology further investigations however are required that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes in order to trace coeval events between the two depositional realms

mesozoic fluorite veins in ne spain record regional base metal rich brine circulation through basin and basement during extensional events abstract basinal brines are commonly involved in the formation of hydrothermal base metal ore deposits in sedimentary basins although in many instances the source of metals is often thought to be the underlying basement rocks the evidence of brine infiltration through the basement is sometimes directly found in vein systems in fracture zones crosscutting the basement that is the case of the fluorite barite base metal veins found throughout the hercynian basement of europe north africa and the appalachians a geochemical study of brines trapped in these veins can reveal their origin and evolution but also their mineralizing potential and coupled with the timing of fluid circulation can give clues to elucidate the role of these or similar brines in the genesis of base metal mineralizations together with their possible links to tectonic events the sm nd dating of fluorite samples from one of these veins in ne spain the rigros fluorite vein has yielded an age of 137 25 ma 2 mswd 0 40 the vein formation took place during the late jurassic early cretaceous rifting event in the western european basins which is related to the opening of the atlantic inclusion fluids in samples from rigros and another vein system from the same region the berta fluorite vein have been studied with microthermometry crush leach and la icp ms the brines trapped in the two studied vein systems are na ca cl k mg brines with homogenization temperatures 120 c and salinities up to 25 equiv mass nacl the source of this salinity is related to evaporated seawater at least in the halite precipitation field and to the leaching of mesozoic halite and gypsum sequences by seawater and or meteoric water the basinal brines later evolved through water rock interaction with the crystalline basement resulting in some sodium loss and potassium calcium strontium the latter inferred from isotope data and barium enrichment the analyzed brines have concentrations of zn between 3 and 790 ppm of pb between 3 and 995 ppm and of fe between 27 and 2639 ppm which are similar to those reported in comparable hydrothermal veins and mississippi valley type deposits but higher than in most present day sedimentary brines despite the fact they were able to transport large amounts of metals no significant precipitation of sulfides occurred in the veins and consequently the mineralizing potential of these brines was still preserved after fluorite vein formation

pb isotope evidence for the role of mesozoic basins in the genesis of mississippi valley type mineralization in somerset uk the mendip bristol veinfield is one of a number of british mississippi valley type deposits the genesis of which has never been fully explained the mendip bristol pb zn ba vein mineralization is hosted in carboniferous permo triassic and jurassic sediments the metal sources involved during mineralization were investigated using pb isotope analysis of vein galenas 206 pb 206 pb values range from 18 311 to 18 594 207 pb 204 pb values from 15 601 to 15 688 and 208 pb 204 pb values from 38 257 to 38 565 the data show three isotopically different mineralizing fluids which it is suggested reflect fluid expulsion from adjacent mesozoic sedimentary basins as a result of overpressuring due to rapid subsidence in the triassic jurassic

volcanism and the greenland ice cores the tephra record abstract in recent years increased awareness of the considerable potential offered by tephrochronology in palaeoclimatic studies has fuelled a renewed interest in the tephra record preserved within the greenland ice cores this renewal has occurred in tandem with the development of continuous flow analysis techniques which provide high resolution volcanic aerosol records these chemical records are of considerable value for identifying tephra horizons composed of glass shards and also provide the basis for a new high precision ice core timescale thus allowing ages to be assigned to volcanic events tephra horizons of glass shards in the ice cores play a critical role for 1 testing and building chronological frameworks for the ice cores and other sequences 2 synchronising disparate palaeoclimatic sequences and testing phase relationships 3 atmospheric pathway reconstruction and 4 verifying the source of volcanic aerosol peaks here we review the results of over 25 years of research into tephra horizons in the grip gisp2 and ngrip cores we provide high precision ages for horizons based on recently developed timescales and draw together geochemical characterisations of the products of 45 volcanic events deposited on the greenland ice sheet and identified in the cores there is a clear disparity between the number of volcanic aerosol peaks and the number of tephra horizons of glass shards identified thus far however this synthesis highlights the critical role of the greenland ice cores firstly in the reconstruction of the history of icelandic volcanic eruptions and secondly the considerable value of some tephra horizons in facilitating the correlation of these key climatic archives to north atlantic marine sequences other noteworthy issues include the potential of these cores to preserve tephra horizons from more distal volcanic sources such as north america to resolve the debate surrounding the thera eruption and the observation that some tephra horizons are preserved within the ice without coeval volcanic aerosol signals

soluble impurities in the byrd station ice core antarctica their origin and sources polar ice cores contain long and detailed records of paleoatmospheric composition paleoclimate and their evolution through time by making a complete ionic balance in melted samples of ice it is possible to evaluate the origin identification of chemical compounds and sources continental marine volcanic extraterrestrial of soluble impurities contained in these ice cores once these are known an attempt can be made to try and explain the cause of any observed changes in this paper we present results of analyses of the major soluble impurities h na nh4 k so4 no3 cl made on bulk samples selected at approximately 50 m intervals down the length of an ice core from byrd station antarctica 80 01 s 119 31 w 1530 m most samples are in ionic balance and it is therefore possible to suggest with which compounds the ionic impurities are linked these compounds include an important contribution from both sea salts nacl and na2so4 and strong acids approximately equal amounts of hno3 and h2so4 the cl na mole ratio is found to be quite stable throughout the core and hovers about the expected bulk sea water ratio in general the marine derived components at byrd station decreased by a factor of 2 between the late glacial maximum and holocene while the gas derived acid components decreased by a factor of only 1 5 some possible causes of these variations are suggested

isotopic evidence for anoxic pyrite oxidation and stimulation of bacterial sulphate reduction in marine sediments pore water sulphate concentrations show marked increases at depths 50 m at odp sites 888 and 890 889 from the cascadia margin accretionary wedge in the uppermost 10 m sulphate concentrations decrease with depth and sulphate 34 s and 18 o increase as sulphate is removed by bacterial sulphate reduction isotopic data show that sulphate formed below 50 m results from oxidation of early diagenetic pyrite and that oxygen in the sulphate molecules is derived from pore water fe 3 in the sediment is the probable oxidizing agent the increased sulphate concentrations stimulate bacterial sulphate reduction at depths of 70 250 m and are thus important in sustaining deep bacterial activity

distribution and mineralogical controls on ammonium in deep groundwaters abstract compositional data from published sources environmental monitoring and new analyses demonstrate that for a wide range of water types oilfield water coal mine water landfill leachate nh 4 is present in amounts up to 2200 mg l oilfield waters from alberta canada contain 1 1000 mg l nh 4 coal mine water uk surface discharges 1 45 mg l nh 4 and landfill leachates uk up to 2200 mg l nh 4 ammonium contents generally show a positive correlation with k and increase with increasing salinity geochemical modelling of sufficiently complete data using solmineq88 demonstrates that nh 4 activities vary systematically and are consistent with a mineralogical control sodium k exchange divides the entire sample suite into at least 4 groups controlled by reaction temperature and reaction with either albite k feldspar or illitic clay minerals in contrast comparison of nh 4 and k divides the sample suite into 2 groups on the basis of geological setting these correspond to k nh 4 exchange involving illitic illite muscovite clays and possibly feldspars for samples from natural sources and to exchange involving smectitic clays for samples from landfill sites this study demonstrates the importance of nh 4 as a constituent of natural groundwaters requiring that this reservoir of n is taken into account in detailed discussion of hydrological components of the n cycle

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

dropstones pseudoplanktonic forms and deep water decapod crustaceans within a lutetian condensed succession of central istria croatia relation to palaeoenvironmental evolution and palaeogeography abstract in central istria western croatia a middle eocene unit some tens of metres thick marks the transition from shallow water carbonate to deeper water clastic sedimentation this unit consists of a basal interval rich in macrofossils made of clayey fossiliferous wackestones and packstones known as marls with crabs and of an overlying marly interval globigerina marls integrated paleontological sedimentological and petrographical analyses of three key sections supplemented with data from several other sites reveal the history of the depositional environment and the changes that occurred up section in the carbonate deposition and the faunal assemblages palaeobathymetric reconstruction based on the benthic and planktonic foraminiferal assemblages shows a rapid deepening upward from the base palaeodepth is about 200 m to the top about 1000 m of the unit the base of the unit represents a condensed section that contains abundant macrofossils consisting of autochthonous mainly decapod crustaceans and deep water mollusks and allochthonous macroforaminifers and shallow water mollusks benthic as well as pelagic nautiloids and nektonic remains and pseudoplanktonic teredinids and ostreids forms the abundance of decapod crustaceans probably represented by only one species that lived in deep water can be correlated with the substantial arrival of plant organic detritus at the bottom the further deepening of the environment caused the disappearance of most of the benthic autochthonous forms dropstones wood boring bivalves and other pseudoplanktonic forms and vegetation remains are mainly found within and just above the basal fossiliferous horizon the abundance of vegetation remains and teredinids reflects the input of wood into deep marine environments and condensation associated with sediment starvation both related to a phase of sea level rise dropstones were transported by vegetation rafting and probably at a lesser rate by kelp rafting petrologic studies of the dropstones provide information on the source areas deltaic areas of the collio region ne italy and on the little known palaeogeography of the southern alps and outer dinarides during the lutetian tectonic phase of regional relevance

fossil travertine system and its palaeofluid provenance migration and evolution through time example from the geothermal area of acquasanta terme central italy abstract the geothermal area of acquasanta terme has often been studied for its active and fossil travertine deposits to elucidate fluid origin geodynamic and hydrological setting even though present day thermal springs are usually used to obtain most information the three travertine terraces bordering the tronto river contain a plethora of information a combination of elemental and isotope analyses 18o 13c and 87sr 86sr ratio fluid inclusion microthermometry and u th dating is used to verify the hydrogeology and its timing these analyses point out two fluid reservoirs with distinctly different fluids one with low salinity of 0 7 wt nacl eq and another with 28 5 wt nacl eq which corresponds to the fluid composition of present day spring fluids furthermore it is demonstrated that geothermal sources were intermittently active in the past 221 ka mainly during uneven numbered marine isotope stages which are related to humid interglacial periods and resulted in three different travertine terraces around 210 5 126 5 and 36 5 ka accordingly an uplift rate for this area could be estimated at around 1 mm ka the fluids were tapped at a depth of approximately 3 km in the tectonized cataclastic fraction of the triassic anidriti di burano formation the calcare cavernoso formation and are originally meteoric based on geochemical evidence of a uniform 87sr 86sr ratio of 0 707914 0 00019 and a 18oaragonite value of 11 90 0 34 which has been depressed by elevated precipitation temperatures between 22 2 and 50 c the characterization and dating of fossil travertine deposits gives valuable data providing insights in long term fluid flow and orogenic uplift rates adding valuable information to present day spring fluid characterization

teredolites wood substrates and sea level dynamics allochthonous logs and or teredolites clavate borings produced within xylic wood substrates occur in extraordinary abundance as sedimentary components in transgressive marine shelf deposits of the lower paleocene clayton formation in western alabama it is pro posed herein that the abundance and preservational state of these components were controlled by 1 an influx pulse of xylic substrates into marine and marginal marine environments 2 hydraulic concentration of substrates during ravinement and 3 condensation associated with sediment starvation all three of which are induced by sea level rise the proposed relations among fossil wood ichnofossils produced therein and sea level dynamics may be of use in the discrimination of sequence stratigraphic packages and their bounding surfaces these relations also have implications for paleobotanical prospecting and the biological evolution and stratigraphic distribution of marine organisms that inhabit xylic substrates

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

gas souring by thermochemical sulfate reduction at 140 c reply natural gas in the permian triassic khuff formation of abu dhabi contains variable amounts of h2s gas souring occurred through thermochemical sulfate reduction of anhydrite by hydrocarbon gases sour gas is observed only in reservoirs hotter than a critical reaction temperature 140 c petrographic examination of core from a wide depth range showed that the anhydrite reactant has been replaced by calcite reaction product only in samples deeper than 4300 m gas composition data show that only reservoirs deeper than 4300 m contain large quantities of h2s i e 10 at present day geothermal gradients 4300 m is equivalent to 140 c fluid inclusion analysis of calcite reaction product has shown that calcite growth only became significan at temperatures greater than 140 c thus three independent indicators all show that 140 c is the critical temperature above which gas souring by thermochemical sulfate reduction begins the previously suggested lower temperature thresholds for other sour gas provinces 80 130 c derive from gas composition data that may not allow adequately either for the reservoir temperature history or for the migration of gas generated at higher temperatures into present traps conversely published proposals for higher threshold temperature 180 200 c derive from short duration experimental data that are not easily extrapolated to geologically realistic temperatures and time scales therefore the temperature of 140 c derived from our study of the khuff formation may be th best estimate of temperature required for in situ thermochemical sulfate reduction to produce the high h2s concentrations encountered in deep carbonate gas reservoirs

magmatic and phreatomagmatic volcanic activity at mt takahe west antarctica based on tephra layers in the byrd ice core and field observations at mt takahe abstract the morphology grain size characteristics and composition of ash particles in 30 ka to 150 ka tephra layers from the byrd ice core were examined to characterize the eruptions which produced them and to test the suggestion that they were erupted from mt takahe a shield volcano in marie byrd land west antarctica volcanic deposits at mt takahe were examined for evidence of recent activity which could correlate with the tephra layers in the ice core coarse and fine ash layers have been recognized in the byrd ice core the coarse ash layers have a higher mass concentration than the fine ash layers and are characterized by fresh glass shards 50 m diameter many containing elongate pipe vesicles the fine ash layers have a lower mass concentration and contain a greater variety of particles typically mt takahe is the favored source for the tephra because a chemical analyses of samples from the volcano are distinctive being peralkaline trachyte and similar in composition to the analyzed tephra b mt takahe is a young volcano a speculative eruptive history for mt takahe is established by combining observations from mt takahe and the byrd ice core tephra initial eruptions at mt takahe were subglacial and then graded into alternating subaerial and subglacial activity the tephra suggest alternating subaerial magmatic and hydrovolcanic eruptions from 30 to 20 ka b p followed by a sustained period of hydrovolcanic eruptions from 20 to 14 ka b p which peaked at 18 ka b p

salinization processes in the unconfined aquifer of bou areg ne morocco a geostatistical geochemical and tomographic study hydrogeological and geochemical data in conjunction with the results of an electrical imaging tomographic survey were examined to determine the main factors and mechanisms controlling the groundwater chemistry and salinity of the unconfined aquifer of bou areg on the mediterranean coast of ne morocco in addition statistical and geochemical interpretation methods were used to identify the distribution of the salinity multivariate statistical analysis cluster and principal component factors revealed the main sources of contamination groups a b and c in the cluster analysis and factors 1 3 factor 1 ce cl k so42 and mg2 factor 2 ca2 hco3 and ph factor 3 no3 represent the signature of seawater intrusion in the coastal zone the influence of marly gypsum outcrops in the upstream zone and anthropogenic sources respectively the ionic delta the ionic ratio the saturation index and stuyfzand s method were applied to evaluate geochemical processes the results obtained indicate on the one hand the phenomenon of salinization in both the coastal and the upstream zones and on the other the dilution of groundwater by recharge cation exchange is shown to modify the concentration of ions in groundwater locally with respect to salinization processes in the coastal zone the results of electrical imaging tomography show that salinity increases both with depth and laterally inland from the coastline due to seawater intrusion

use of isotope fractionation of sulfate sulfur and sulfate oxygen to assess bacterial desulfurication in a sandy aquifer abstract the unconfined aquifer of the fuhrberger feld consists of 20 30m sands and gravelly sands with unevenly distributed reduced sulfur compounds and small lignitic pebbles in vertical direction two hydrochemically different zones with specific solute transformations are present an upper portion with bacterial denitrification with reduced sulfur compounds as electron donors and a deeper portion with hydrochemical indications of reduction of the aqueous sulfate in the study area ten multilevel groundwater sampling wells were installed sampling and interpretation was based on a two dimensional vertical plane groundwater flownet and on the knowledge of the landuse upgradient of the multilevel wells the concentration and isotopic composition of the sulfate at the entrance into the zone of sulfate reduction is controlled by sulfate of groundwater recharge as well as sulfate formed during denitrification the recharge sulfate shows clear landuse specific differences in concentration and isotopic composition under arable land an average concentration of 60 mg so 4 l 1 with values of 34 s close to 3 cdt diablo meteorite standard canon and of 18 o about 8 standard mean ocean water smow was measured whereas under coniferous forest an average of 100 mg so 4 l 1 with 34 s 2 and 18 o 4 5 was found in the denitrification zone no significant sulfur isotope fractionation occurs during oxidation of reduced sulfur the oxygenisotopic composition of the newly formed sulfate denitrification sulfate depends on the 18 o content of nitrate acting as oxygen donor and on the 18 o content of groundwater in which the oxidation occurs under certain assumptions a 18 o 0 54 was calculated for the oxygen of the newly formed sulfate consequently with increasing sulfate concentrations i e with the admixture of denitrification sulfate a decrease of the 18 o values from about 8 to 2 was observed in the zone of sulfate reduction both the 34 s and 18 o values of the residual sulfate increase with decreasing sulfate concentrations thus proving the existence of bacterial reduction of the aqueous sulfate this sulfate reduction follows a rayleigh process with calculated enrichment factors of 34 9 7 for 34 s and 18 6 for 18 o respectively a plot of 34 s vs 18 o gives a good linear correlation with a slope close to 1 1 4 data on concentration and isotopic composition of sulfate and on the hydraulically derived groundwater age are used for kinetic considerations the results of a multilevel well for depths between 10 and 17m are given as an example the bacterial reduction can be considered as first order reaction with a half life between 75 and 100 years

the thermal and mechanical development of the wessex basin southern england summary the wessex basin of southern england is an e w trending late palaeozoic to tertiary extensional basin formed on early palaeozoic variscan crust extension occurred over a protracted period from late carboniferous to cretaceous times resulting in the evolution of four main depocentres or sub basins the channel basin winterborne kingston trough vale of pewsey and weald basins each sub basin was controlled fundamentally by the normal reactivation of basement thrust faults and wrench or transfer faults the basement faults represent primary structures associated with the fold and thrust terrain of the devonian carboniferous variscan orogeny subsequent but synchronous reactivation of both thrust and transfer faults tended to compartmentalize the basement leading to discrete depocentres and the production of general rhomboidal shaped sub basins characteristic of pull apart basins in strike slip terrains to investigate the thermo mechanical properties of the lithosphere during basin formation 50 boreholes within the wessex basin were back stripped to isolate the driving tectonic subsidence responsible for basin formation the resultant driving subsidence is characterized by a gentle sometimes negative exponential form with superimposed rapid discrete subsidence events as the geological development of the wessex basin was characterized by polyphase extension and the utilization of crustal detachments the lithospheric model used to determine crustal extension above the detachment and stretching below the detachment included the effects of depth dependent stretching and finite re rifting from the back stripping analysis the basin wide averaged upper crustal extension and lower crustal sub crustal lithospheric stretching were 11 and 5 respectively the distribution of is strongly influenced by the location of growth faults and hence basement thrust fault reactivation suggesting that is reflecting the brittle failure and collapse of hanging wall blocks repeated slip and block collapse resulted in the polyphase extension responsible for renewed basin subsidence in contrast is uniformly distributed across the basin suggestive of a ductile failure of the lower crust and responsible for the low magnitude thermal subsidence strain compatibility between the upper crust and lower crust sub crustal lithosphere is maintained partly within the basin 5 and partly external to the basin as the variscan basal thrust was the fundamental relay in the sense of wernicke responsible for the wessex basin formation we postulate that strain balancing induced a cumulative essentially thermal isostatic uplift of 60 m under the northern margin of the armorican massif

event beds or condensed unit analysis of a wood log concentration in the upper jurassic of the kachchh basin western india abstract the 2 m thick wood log bed is a highly ferruginous middle oxfordian rock unit exposed in the dry bed of the river tramau in the wagad uplift of the eastern kachchh basin western india and composed of several layers the bed contains at several levels permineralised conifer wood logs seeds carpolites cones araucarites leaves brachyphyllum podozamites possible bennettitalean flowers williamsonia and abundant wood debris in a poorly sorted muddy sandstone with scattered coarse quartz grains the wood concentration is interpreted as the result of episodic flash floods in the hinterland situated in the east associated with the wood fossils are abundant ammonites which together with the ferruginous nature of the sediment point to offshore sediment starvation decay of the plant material might have led to widespread anoxia at the sea floor which restricted the benthic macrofauna for much of the time thus the wood log bed is the product of two processes episodic flash floods and sediment starvation signs of these processes can be seen in age equivalent sediments throughout the kachchh basin

controls on stable isotope profiles in the chalk aquifer of north east norfolk uk with special reference to dissolved sulphate groundwater samples were collected at a site in n norfolk uk comprising a borehole penetrating upper chalk and piezometers open within the overlyinf glacial deposits and intervening weathered putty chalk the samples were analyzed for 18o water 34s and 18o so4 and 13c hco3 as well as major ions variations in solute concentration and isotopic composition with depth were found to be caused by limited groundwater circulation at the site and incomplete flushing of old groundwater the isotopic data prove the existence of a mineralized palaeowater at depth which has undergone so4 reduction and is being slowly modified by mixing with recent groundwater circulating at a shallow depth in a more transmissive chalk horizon one measured 18o h2o value of 8 25 vsmow represents the lightest value reported for the norfolk chalk aquifer and is evidence for a component of late pleistocene recharge trapped at depth the wide range of observed isotope ratios at the site e g 34s and 18o so4 between 7 8 to 27 8 cdt and 5 2 to 20 0 ovsmow respectively demonstrates the importance of vertical stratification of solutes and the implications this has for interpreting spatial hydrochemical surveys of groundwater

volcanic deposits in antarctic snow and ice major volcanic eruptions are able to spread large amounts of sulfuric acid all over the world acid layers of volcanic origin were detected for the first time a few years ago by hammer in greenland ice the present paper deals with volcanic deposits in the antarctic the different methods that can be used to find volcanic acid deposits in snow and ice cores are compared electrical conductivity sulfate and acidity measurements numerous snow and ice samples collected at several antarctic locations were analyzed the results reveal that the two major volcanic events recorded by h2so4 fallout in antarctic ice over the last century are the eruptions of krakatoa 1883 and agung 1963 both located at equatorial latitudes in the southern hemisphere the volcanic signals are found to be particularly well defined at central antarctic locations apparently in relation to the low snow accumulation rates in these areas it is demonstrated that volcanic sulfuric acid in snow is not even partially neutralized by ammonia the possible influence of antarctic volcanic activity on snow chemistry is also discussed using the three recent eruptions of the deception island volcano as examples only one of them seems to have had a significant effect on the chemistry of snow at a location 200 km from this volcano it is concluded that antarctic volcanic ice records are less complicated than greenland records because of the limited number of volcanos in the southern hemisphere and the apparently higher signal to background ratio for acidity in antarctica than in greenland

origin and evolution of formation water at the jujo tecominoacan oil reservoir gulf of mexico part 2 isotopic and field production evidence for fluid connectivity abstract the chemical and isotopic characterization of formation water from 18 oil production wells extracted from 5200 to 6100 m b s l at the jujo tecominoacan carbonate reservoir in se mexico and interpretations of historical production records were undertaken to determine the origin and hydraulic behavior of deep groundwater systems the infiltration of surface water during late pleistocene to early holocene time is suggested by 14c concentrations from 2 15 to 31 86 pmc and by 87sr 86sr ratios for high salinity formation water 0 70923 0 70927 that are close to the composition of holocene to modern seawater prior to infiltration the super evaporation of seawater reached maximum tds concentrations of 385 g l with lowest 18o values characterizing the most hypersaline samples minor deviations of formation water and dolomite host rocks from modern and jurassic 87sr 86sr seawater composition respectively suggest ongoing water rock interaction and partial isotopic equilibration between both phases the abundance of 14c in all sampled formation water 87sr 86sr ratios for high salinity water close to holocene present seawater composition a water salinity distribution that is independent of historic water cut and a total water extraction volume of 2 037 mmm3 1 83 4 07 excludes a connate oil leg origin for the produced water of the jurassic cretaceous mudstone dolomite sequence temporal fluctuations of water chemistry in production intervals the accelerated migration of water fronts from the reservoir flanks and isotopic mixing trends between sampled wells confirms the existence of free aquifer water below oil horizons vertical and lateral hydraulic mobility has probably been accelerated by petroleum extraction the combination of interpreting historical fluctuations of salinity and water percentage in production wells with chemical isotopic analysis of formation water resulted in a successful method to distinguish four groundwater bodies stratified vertically within the jujo tecominoacan reservoir two with low tds from 10 to 23 g l are preserved in the upper reservoir section mainly in lower cretaceous and kimmeridgian strata for the deeper part of the reservoir 87sr 86sr trends indicate an affiliation of most samples to two independent mixing trends between intermediate saline tds 200 g l and hypersaline 350 g l groundwater end members

ichnological analysis in high resolution sequence stratigraphy the glossifungites ichnofacies in triassic successions from the betic cordillera southern spain this study integrates ichnological and sedimentological data in order to refine sequence stratigraphy and interpretations of sea level dynamics for the ladinian middle triassic muschelkalk succession siles formation in the betic cordillera southern spain facies analysis was integrated with a detailed ichnological study focused on the middle part of the lower member of the muschelkalk succession transgressive systems tract which is characterized by an abundant and conspicuous trace fossil assemblage seven lithofacies were recognized recording sediment accumulation in tidal flat and inner to outer marine carbonate ramp depositional environments thin bedded marly limestones with bioclastic shelly beds facies e middle ramp with storm influence are characterized by diplocraterion and rhizocorallium diplocraterion is protrusive usually eroded on top and mainly recorded in the marly limestone intervals rhizocorallium preserves well defined scratch marks and is commonly emplaced in bioclastic shelly beds the assemblage represents the glossifungites ichnofacies sedimentological and ichnological data are interpreted to record a complex transgressive context associated with high frequency sea level dynamics that allowed formation of transgressive surfaces of erosion tse i e ravinement surfaces of different orders major tse associated with continuous bioclastic shelly beds delimit parasequences the absence of the glossifungites suite reveals that there was little time between erosion and deposition intermediate tse associated with discontinuous shell beds are related to comparatively less significant sea level rises and occur within parasequences the glossifungites suite reveals colonization of firmgrounds during relatively prolonged times between erosion and deposition related to intermediate tse minor order tse recorded between the intermediate tse are related to punctuated highest frequency sea level changes phases of colonization by the diplocraterion tracemaker and protrusive capped structures reveal more or less stillstand phases tse stillstand phases and minor order erosional phases

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

tephra layers in the byrd station ice core and the dome c ice core antarctica and their climatic importance abstract volcanic glass shards from tephra layers in the byrd station ice core were chemically analyzed by electron microprobe tephra in seven layers have similar peralkaline trachyte compositions the tephra are believed to originate from mt takahe on the basis of their chemical similarity to analyzed rocks from mt takahe and because dated rock samples from the volcano are younger than 250 000 years old glass shards from 726 m deep in the dome c ice core which is 2400 km from byrd station are composed of peralkaline trachyte and may have also been derived from mt takahe the tephra could have resulted from eruptions which were triggered by increased ice loading during the late wisconsin glaciation preliminary grain size data suggest the eruptions were only minor and they were unlikely to have instantaneously altered global climate as have explosive eruptions in the tropics nevertheless the effect of this localized volcanic activity upon the antarctic energy budget warrants further investigation

basin scale evolution of formation waters a diagenetic and formation water study of the triassic chaunoy formation paris basin abstract formation waters and their movements within basins are commonly attributed with responsibility for patterns of cementation and porosity loss within reservoirs and aquifers it is thus important to understand when and how waters move in the subsurface we have studied the evolution and movement of formation water in the triassic chaunoy formation of the paris basin nw europe to define the way in which the water has evolved and to interpret water movement patterns using mineral isotope and fluid inclusion data in conjunction with detailed formation water analyses the chaunoy formation is cemented with different types of dolomite calcite and quartz cement we have studied the evolution of waters in terms of oxygen carbon and strontium isotopes and salinity connate waters were meteoric in origin but strongly influenced by the proximity of a playa lake input of palaeo meteoric water which entered the chaunoy via eastern halite bodies resulted in highly saline formation water for the majority of the chaunoy formation from about 100 ma until and for some time after maximum burial saline waters spread into the aquifer initially taking a west north west trajectory and then switching to a west south west pattern in the eocene following the alpine orogeny and localised uplift of the basin margin the southern portion of chaunoy received fresh low salinity meteoric water it is likely that formation water was lost from the chaunoy in a more central part of the basin via sub vertical cross formational flow to the mid jurassic dogger formation to accommodate the influx of fresh water

diagenesis and reservoir quality of the sherwood sandstone triassic corrib field slyne basin west of ireland abstract the triassic sherwood sandstone in the corrib field slyne basin west of ireland on the european continental margin is a dry gas reservoir with a mercia mudstone top seal petrographic analysis combined with x ray diffraction stable isotope fluid inclusion and core analysis have been used to assess timing of growth and origin of mineral cements whether sandstone diagenesis involved mass flux the controls on reservoir quality and how reservoir quality is likely to vary in more deeply buried sections depositional and early diagenetic characteristics of the sherwood in corrib are typical of a semi arid fluvial environment containing groundwater of meteoric origin early diagenesis included the development of copious dolomite cement in the form of dolocrete as well as the formation of abundant clay while less volumetrically important grain coating haematite and k feldspar cement also grew burial diagenesis witnessed the initial growth of minor chlorite and albite quartz overgrowths and ankerite followed and are the most important burial cements growing over a temperature interval between 100 and 1165 c albite commenced growth at about 90 c quartz cement at 100 c and ankerite at 110 c these cements reached the zenith of their development at 105 110 c for albite 125 130 c for quartz and 135 145 c for ankerite siderite and anhydrite are relatively minor late stage cements the formation water has been consistently highly saline during burial and in terms of mineral cement derived oxygen stable isotope values is likely to be a diagenetically evolved version of the initial depositional water suggesting long term stagnation of the pore fluids the diagenetic reactions that formed burial cements all seem to be essentially isochemical including the ankerite that has carbon isotope characteristics of the cannibalisation of dolocrete reservoir quality is mainly controlled by early diagenetic dolomite and clay although grain size is also important because only sandstones with 200 m grain size have 50 md permeability both shallower and deeper sections than corrib may have similar porosity and permeability since temperature dependent diagenetic controls on reservoir quality e g quartz and illite cement are peripheral

re evaluation of alleged bees nests from the upper triassic of arizona published records of supposed triassic bees nests are based on trace fossils in silicified wood and in sandstone in upper triassic strata of the chinle group in petrified forest national park arizona a critical firsthand restudy of these trace fossils indicates that they lack diagnostic features of bees nests such as cells with smooth linings and spiral closure caps indeed many of the observations claimed to identify these traces as bees nests cannot be replicated instead the putative triassic bees nests can be classified as 1 clavate borings in petrified wood somewhat similar to teredolites these borings preferentially penetrate heart rot fungus polyporites and are mostly likely larval chambers of wood boring beetles 2 cylindrical vertical burrows in sandstone assignable to skolithos these are almost certainly arthropod produced the recognition that the chinle group trace fossils are not bees nests eliminates them as evidence that decouples bee origins from the cretaceous origin of angiosperms the triassic trace fossils in silicified wood are also a new and unique record of likely beetle borings in triassic wood

reaction of the accumulation zone portions of glaciers to climatic change the response of the accumulation regions of glaciers to changes in accumulation rate and in surface temperature is calculated by considering perturbations to the ice flow the analysis is limited to glaciers in which flow is dominated by internal shear and not by bottom sliding and for which flowlines are geographically parallel in general glaciers begin to alter thickness immediately after a change in accumulation rate but the effect of a change in surface temperature is delayed by the time for this temperature change to penetrate to depth in the glacier a warming leads to glacial thinning the amount and timing of the response is very different for different glaciers characteristic times are on the order of tens of years for mountain glaciers and tens of thousands of years for the east antarctic ice sheet as an example the theory is applied to the ice sheet near byrd station antarctica for hypothetical changes in surface accumulation rate and temperature rates and amounts of thickness change are calculated and it is found that the measured thinning is probably too fast to have been caused by climatic variation alone the effects of hypothetical climatic variations on the depth age and depth temperature relationships through the ice sheet are also calculated it is hoped that the theory will prove valuable in the interpretation of future drill hole results