origin and evolution of oilfield waters in the tazhong oilfield tarim basin china and their relationship to multiple hydrocarbon charging events abstract we conducted a chemical and isotopic study of oilfield waters from ordovician limestone reservoirs in the tazhong oilfield tarim basin china to trace the origin and evolution of the waters and to demonstrate their possible relationship with hydrocarbon charging the elemental chemistry cl br so4 i k na ca mg and sr and multiple isotopic compositions d 18o 87sr 86sr and 129i i of the oilfield waters were determined the results show that these oilfield waters contain basinal brines that infiltrated in three stages along with a lesser contribution from meteoric water the meteoric water appears to have infiltrated downwards during the late silurian and carboniferous the earliest brine had very low i contents 50 mg l was derived from cambrian argillaceous source rocks and migrated upwards into ordovician reservoirs this stage was related to the main period of migration of crude oils out of the source rocks into reservoirs during the silurian and devonian both of these brines incorporated constant levels of fissiogenic 129i from the limestone reservoir rocks 11 8 47 0 atom l finally brine with very low i contents but higher 129i 106 491 atom l began to migrate upwards and infiltrate reservoirs given the relatively high fissiogenic 129i this stage may have occurred during the late cenozoic and was associated with migration of dry gas from the same source rocks our results combined with those of a previous study of other oilfields in the basin suggest that the evolutionary of oilfield waters can be used to constrain hydrocarbon accumulation events and both of which were ultimately controlled by regional tectonism and local geological factors

iodine 129 87sr 86sr and trace elemental geochemistry of northern appalachian basin brines evidence for basinal scale fluid migration and clay mineral diagenesis evidence for basin scale brine migration and clay mineral diagenesis in the northern appalachian basin was investigated using elemental and isotope 129i i 87sr 86sr geochemistry of formation waters collected from the middle to upper devonian section of the northern basin margin in western new york northwest pennsylvania and eastern kentucky one sample from each of the mississippian berea sandstone and the silurian medina sandstone were analyzed for comparison measured iodine ratios range between 28 to 1 890 10 15 and are anomalously high compared to cosmogenic iodine sourced from devonian age organic matter iodine 129 in the waters was largely derived from fissiogenic sources the spontaneous fission of 238u to produce 129i with estimated 129i i values up to 270 10 15 which occur locally in the organic rich shales there are three water samples that have values of 490 10 15 860 10 15 and 1 890 10 15 which are above the range for local fissiogenic 129i and may be accounted for by topographically driven basin scale fluid flow through a regionally high fissiogenic source relatively large uranium occurrences lie along the structural front of the appalachian basin in the blue ridge province and are situated within hypothesized flow paths parallel to the main compressional direction of the alleghanian orogeny estimated 129i i values for these uranium occurrences are in excess of 55 000 10 15 the strontium isotope composition and sr concentration of brines display a mixing trend between a highly radiogenic end member 0 7210 with low sr 51 mg l and a non radiogenic 0 7100 high sr 4789 mg l end member potassium and boron concentrations are notably depleted relative to evaporated paleozoic seawater the hypothesized source of appalachian basin brines the k rb values of formation waters are depleted relative to seawater values but in some cases are well above values indicative of water rock reactions the sr isotopic composition k and b depletion and intermediate k rb ratios are consistent with smectite diagenesis and paleo temperatures that are likely greater than approximately 150 c these temperatures may be high given the burial history of the study area and support the flow of formation waters from deeper within the basin the combined isotopic and elemental results of formation waters provide compelling evidence for basin scale fluid migration in the northern appalachian basin and are consistent with previously published evidence documented from the rock record including clay mineral diagenesis and ore deposition

potential salinity driven free convection in a shale rich sedimentary basin example from the gulf of mexico basin in south texas we investigate the plausibility of salinity driven free thermohaline convection in sedimentary rocks of the south texas part of the gulf of mexico basin using salinity data rayleigh number calculations and numerical models previous studies speculated that free convection could account for high fluxes evidently required for diagenesis in the basin but low permeability shales are calculated to be a barrier to free convection in the study area salinity inversions occur either above or within the transition zone from hydropressures to overpressures the positioning of brines over less saline fluids provides a significant buoyancy force rayleigh number calculations and numerical simulations suggest that homogeneous shaly systems are unstable near the high end of the expected ranges of shale permeability 10 15 10 16 m2 numerical simulations show that the influx of brine into the permeable layers and permeability heterogeneity in the shales are both conducive to free convection simulations indicate that salinity driven free convection can occur at lower permeabilities 10 16 10 18 m2 that may approximate the permeabilities of shales in the zone of extreme overpressures over geologic time simple rayleigh numbers are inadequate to predict the occurrence of free convection in heterogeneous systems salinity driven free convection at depths in some large sedimentary basins such as the gulf of mexico may be more common than expected

comparison of stable isotopes ratios of 36cl cl and 129i 127i in brine and deep groundwater from the pacific coastal region and the eastern margin of the japan sea abstract fifty three samples including brines associated with oil and natural gas reservoirs and groundwater samples from deep boreholes were collected from the pacific and japan sea coastal regions in japan the 129 i 127 i and 36 cl cl ratios and stable isotopes d and 18 o are compared to investigate differences related to the geotectonic settings of the two regions the d and 18 o data indicate that brine and groundwater from the pacific coastal region reflect mixing of meteoric water with connate seawater in the pores of sedimentary rocks on the other hand brine and groundwater from the japan sea coastal region have been hydrothermally altered in particular brines associated with petroleum accumulations at niigata and akita showed the same isotopic characteristics as fluids found in the kuroko deposits of the green tuff region in northeastern japan there is little difference in the 36 cl cl ratios in brine and groundwater from the pacific and japan sea coasts most brine and some deep groundwater except those from the pleistocene kazusa group have already reached the average secular equilibrium ratio of 9 9 2 7 10 15 for their mudstone and sandstone reservoirs there was no correlation between the 36 cl cl ratios and differences in geotectonic setting between the pacific and the japan sea coast the molar i br ratio suggests that the i in all of water samples was of biogenic origin the average 129 i 127 i ratio was 290 130 10 15 to 294 105 10 15 in both regions showing no relationship to the different geotectonic settings the uncontaminated brine and groundwater samples are likely to have retained the original 129 i 127 i ratios of marine i released from the old organic matter stored in sedimentary rock

physical and chemical controls on the composition of waters in sedimentary basins abstract the composition of subsurface waters is determined not only by diagenetic reactions but also by physical processes of fluid convection and hydrodynamic dispersion the south west louisiana gulf coast provides an instructive field example of the net effects of diagenetic reaction and solute transport on pore water compositions in a regional siliciclastic sequence most formation waters here have compositions totally unlike the compositions of the connate meteoric and marine fluids that were buried with their host sediments at the time of deposition dissolved chloride has been generated by the subsurface dissolution of salt domes and has been pervasively transported by fluid flow throughout most of the upper 3 km of the sedimentary section the simultaneous systematic variation in dissolved na k mg ca and alkalinity with chloride in these waters supports the hypothesis that metastable thermodynamic buffering by silicate carbonate mineral assemblages is a first order control on fluid compositions the chemical potential of chloride or alternatively total anionic charge appears to be a master variable which ranks in importance with such other variables as pressure and temperature in driving diagenesis in this region this variable is controlled largely by physical processes of advection and dispersion in the upper 3 km of the section and by dehydration reactions in deeper mudstone dominated sediments where the composition of the fluid is largely rock buffered the ultimate origin of the fluid and its pathway of chemical evolution may be obscured at least in terms of major solute composition non buffered components such as cl and br or isotopic compositions are more likely to retain information on original end member fluid compositions and reaction pathways

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

halogen concentrations in pore waters and sediments of the nankai trough japan implications for the origin of gas hydrates abstract presented here are halogen concentrations cl br and i in pore waters and sediments from three deep cores in gas hydrate fields of the nankai trough area the three cores were drilled between 1999 and 2004 in different geologic regions of the northeastern nankai trough hydrate zone iodine concentrations in all three cores increase rapidly with depth from seawater concentrations 0 00043 mmol l to values of up to 0 45 mmol l the chemical form of i was identified as i in accordance with the anaerobic conditions in marine sediments below the so 4 reduction depth the increase in i is accompanied by a parallel although lesser increase in br concentrations while cl concentrations are close to seawater values throughout most of the profiles large concentration fluctuations of the three halogens in pore waters were found close to the lower boundary of the hydrate stability zone related to processes of formation and dissociation of hydrates in this zone generally low concentrations of i and br in sediments and the lack of correlation between sediment and pore water profiles speak against derivation of i and br from local sediments and suggest transport of halogen rich fluids into the gas hydrate fields differences in the concentration profiles between the three cores indicate that modes of transportation shifted from an essentially vertical pattern in a sedimentary basin location to more horizontal patterns in accretionary ridge settings because of the close association between organic material and i and the similarity of transport behavior for i and ch 4 the results suggest that the ch 4 in the gas hydrates also was transported by aqueous fluids from older sediments into the present layers

rates of iodine remineralization in terrigenous near shore sediments much of the sedimentary geochemistry of iodine has been surmised from analyses of solid phase distributions without direct documentation of reactions or reaction rates it is shown here that the anoxic production rate of dissolved i in nearshore terrigenous sediments decreases rapidly below the sediment water interface and is strongly temperature controlled an apparent activation energy of 19 3 kcal mole comparable to that found for other microbially mediated reactions describes the temperature dependence of release production of dissolved iodide is zeroth order with respect to natural ranges of pore water concentrations and apparently first order with respect to a reactive i component in the solid phase first order reaction coefficients in sediments from mud bay south carolina and long island sound connecticut u s a are strongly depth dependent varying from 6 9 yr in the top few centimeters to an average of 0 011 yr over the upper 70 cm about 90 of the dissolved i flux comes from the top 10 cm with estimated values of 15 and 29 moles m2 day at 22 23 c in mud bay and long island sound respectively the i c net release ratio of decomposing material changes rapidly below the sediment surface when temperature corrections are made i remineralization rates from nearshore sediments below the bioturbated zone appear to be similar to those observed in deep water sediments underlying oxygenated waters

petrogenesis of the concordia granite gneiss and its relation to wmo mineralization in western namaqualand south africa abstract the 1 1 ga concordia granite gneiss cgg is part of the late to postorogenic spektakel suite in the western namaqualand metamorphic complex south africa it intruded synkinematically with respect to the main d2 deformation event into lower to middle crustal rocks and granite emplacement was more or less coeval with the peak of granulite facies metamorphism 800 c 5 kbar several genetically related rock types megacrystic garnet bearing granite minor aplitic leucogranites and pegmatites are distinguished all varieties are sio 2 rich 69 79 wt peraluminous granites and show subalkaline monzonitic magma characteristics geochemical differences in whole rock chemistry between megacrystic granite and aplitic leucogranites e g lower al 2 o 3 mgo cao ba zr higher k 2 o rb nb w rb sr ga al and the decrease of e g cao mgo fe 2 o 3 ba zr th u with increasing sio 2 in the megacrystic granites as well as the variation in fe mn of magmatic garnets are best explained with crystal fractionation processes fractional crystallization of plagioclase produced potassium and silica rich residual melts characterised by very high rb sr rb ba u th mn fe ratios and higher concentration of w cu and zn crystal fractionation processes also resulted in a relative lree depletion and hree enrichment megacrystic granite la lu cn 8 87 31 67 aplitic leucogranite and pegmatites la lu cn 0 71 1 44 and evolution of pronounced negative eu anomalies the crystallization sequence near solidus crystallization of biotite prior to alkali feldspar suggests that the cgg magmas were h 2 o undersaturated over a long period of their evolution water saturation during late stage crystallization is however indicated by coarse late stage eutectic mineral textures pegmatites and w mo bearing siliceous rocks furthermore the economic potential of the cgg is supported by its geochemical signature e g high u th contents which is similar to evolved high heat production hhp granites the granitic magmas are attributed to partial melting of peraluminous crustal source rocks and are tentatively interpreted as fractionated s type granites the w mo deposits represent vein type and pegmatitic deposits genetically related to a deep seated granitic system

origin of iodine in the anadarko basin oklahoma an 129i study iodine comes almost exclusively from organic matter in sedimentary basins and therefore can be used as a source indicator for hydrocarbons the long lived half life 15 7 m y cosmogenic and fissiogenic isotope 129i has been applied to tracing brine migration in the anadarko basin oklahoma because all of the likely source formations for i are paleozoic the cosmogenic 129i component has decayed to undetectable levels and all of the measured 129i is of fissiogenic origin comparison of 129i 127i ratios measured in 12 brines from the platform area of the anadarko basin with ratios determined for potential source rocks reveals that the woodford shale is the probable source formation for the extremely high i concentr tions observed in these brines if the woodford shale is the exclusive source for i the time of expulsion can be constrained to between 2 and 90 ma although this date is much later than most estimates of expulsion time derived from conventional methods a case is presented for more recent expulsion in the northern part of the basin which was the sample area

palynology of the bryn mawr formation miocene insights on the age and genesis of middle atlantic margin fluvial deposits abstract the ages of fluvial deposits at the head of chesapeake bay thought to be the updip chronostratigraphic equivalents of a well dated late oligocene to quaternary marine sequence in the salisbury embayment are poorly known we present data regarding a new occurrence of a palynoflora recovered from the bryn mawr formation in cecil county maryland the floral assemblage for the bryn mawr formation includes at least 40 taxa at the generic level where quercus cupuliferae ilex carya taxodium and pinus are important elements most of the taxa identified from the bryn mawr formation palynoflora are extant and occur within the modern middle atlantic coastal plain however several important taxa such as alangium engelhardia sciadopitys tricolporopollenites sp and cupuliferoidaepollenites sp are at present either extinct or exotic to the middle atlantic coastal plain comparison of the bryn mawr formation palynoflora to well dated marine deposits of the salisbury embayment suggests a late middle to early late miocene age late serravallian early tortonian for bryn mawr formation phase 2 deposition supporting previously proposed genetic links to the marine deposits of the choptank formation in the subsurface of the delmarva peninsula relative abundances of common extant taxa such as quercus carya pinus and nap the total non arboreal pollen vary considerably throughout late cenozoic deposits of the middle atlantic coastal plain we present data for common extant taxa in a ternary diagram to define discrete palynofacies that discriminate among middle miocene late miocene pliocene and pleistocene palynofloras these results show that relative abunances of common easily identifiable extant pollen may be as diagnostic as exotic taxa in assigning ages to middle atlantic coastal plain deposits the bryn mawr formation palynoflora like other middle to late miocene palynofloras of the middle atlantic coastal plain suggests terrestrial climatic cooling in the larger temporal scale of climate change throughout the cenozoic this change in miocene climate is one of three major events that may have had a significant impact on the rate of sediment yield from the appalachians as recorded in the volume of offshore basin sediments

geochemistry of highly saline fluids in siliciclastic sequences genetic implications for post variscan fluid flow in the moravosilesian palaeozoic of the czech republic ubiquitous post variscan dolomites occur in zn pb cu veins at the nizk jesenik mountains and the upper silesian basin lower and upper carboniferous siliciclastics at the eastern part of the bohemian massif crush leach stable isotope oxygen and carbon and microthermometry analysis of the fluid inclusions in dolomites enable understanding the geochemistry origin and possible migration pathways of the fluids homogenisation temperatures of fluid inclusions range between 66 and 148 c with generally higher temperatures in the nizk jesenik mountains area than in the upper silesian basin the highest homogenisation temperatures up to 148 c have been found near major regional faults and the lowest in a distant position or at higher stratigraphic levels highly saline 16 6 28 4 eq wt nacl h2o nacl cacl2 mgcl2 fluids occur in inclusions na cl br systematics of trapped fluids and a calculated oxygen isotopic fluid composition between 0 9 and 3 0 v smow indicate that the fluid was derived from evaporated seawater stable isotopic modelling has been used to explain stable isotopic trends isotopic values 13c 6 0 2 0 v pdb 18o 15 5 22 5 v smow of dolomites resulted from fractionation and crystallisation within an open system at temperatures between 80 and 160 c rock buffering explains the isotopic composition at low w r ratios organic matter maturation caused the presence of isotopically light carbon in the fluids and fluid rock interactions largely controlled the fluid chemistry k li br and na contents k cl i cl and li cl molar ratios the fluid chemistry reflects well the interaction between the fluid and underlying limestones as well as with clay and organic rich siliciclastics no regional trends in temperature or fluid geochemistry favour a fluid migration model characterised by an important vertical upward migration along major faults a permeable basement and fractured sedimentary sequence enhanced the general nature of the fluid system fluid characteristics are comparable with the main post variscan fluid flow systems in the polish cracow silesian ore district and german sedimentary basins

chemical constraints and origins of four groups of gulf coast reservoir fluids discussion the authors take to task stoessell and moore s 1983 review of some previous ideas on the origin of gulf coast formation fluids taking specific exception to their interpretation of data from the edwards formation six points are emphasized edwards brines are significantly enriched in bromide relative to chloride over seawater evaporated to halite saturation edwards brines have significantly higher k c1 and ca mg c1 ratios than seawater evaporated to halite saturation edwards brines cannot achieve molar ca mg ratios of 16 by dolomization progressive stabilization of metastable dolomite by updip fluid cannot raise the magnesium content of edwards water in the absence of dolomite dissolution the volume of brine contained in the cretaceous section exceeds any reasonable volume of hypothetical connate mesozoic brine and isotopic differences between edwards brines and jurassic seawater evaporated to halite saturation are extreme and therefore preclude recognition of any primary jurassic component in the current brines

kilometer scale upward migration of hydrocarbons in geopressured sediments by buoyancy driven propagation of methane filled fractures several lines of evidence support kilometer scale upward migration of fluids in the gulf of mexico basin discharge of hypersaline brines at the sea floor long term natural hydrocarbon seeps and microseeps gas chimneys lead zinc mineralization in salt dome cap rocks and allochthonous brines in cenozoic sediments we explore the hypothesis that upward fluid transport in geopressured sediments is caused by buoyancy driven propagation of isolated methane filled fractures in other words instead of fluid migrating along a fixed network of interconnected pores or fractures fluid enclosed within an isolated fracture is transported upward by hydrofracturing the mechanically weak geopressured sediments thus the fluid filled fracture propagates upward through the sediments hydrofracture is driven by the pressure difference buoyancy between the enclosed methane and the surrounding sediments our results show that methane filled fractures with half lengths of a few meters should propagate upward through geopressured sediments with velocities of hundreds of meters per year or higher as methane filled fractures increase in volume and decrease in density with decreasing confining pressure they develop the potential to entrain and transport more than 1000 kg m3 of oil or brine methane filled fractures should propagate to the surface unless they are trapped beneath a layer that has high fracture toughness such as salt or are absorbed when they intersect a permeable 10 md sand layer

the o okiep copper district namaqualand south africa a review of the geology with emphasis on the petrogenesis of the cupriferous koperberg suite the o okiep copper district is the oldest formal mining area in south africa between 1852 and 2002 the 2 500 km2 area yielded two million tons of copper from 32 mines ranging in ore tonnages from 140 000 to 37 million tons this paper summarizes the calendar of events from the formation of the first primitive crust 1 700 2 000 ma ago to early cambrian times 500 ma ago with particular emphasis on the namaquan grenville orogeny notably the o okiepian episode 1 180 1 210 ma ago of alpine type folding regional granite plutonism and granulite facies metamorphism and the klondikean episode 1 020 1 040 ma ago of open and tight folding and the intrusion of the rietberg granite and the koperberg suite almost all of the copper in the o okiep district occurs in the koperberg suite of which there are 1 700 small bodies that constitute 0 7 of the outcrop area the suite comprises jotunite anorthosite biotite diorite and hypersthenic rocks ranging from leuconorite to hypersthenite and it is one of only two world examples of economic copper mineralization in rocks of the anorthosite charnockite kindred the second example is caraiba brazil high isr and low end for a 1 030 ma intrusion age and high 2 of 10 1 for koperberg rock types indicate a crustal progenitor for the suite and the presence of jotunite suggests a subducted crustal source at ca 40 50 km depth the magmatic sulphide paragenesis in the koperberg suite is chalcopyrite pyrrhotite narrap type ore that in a number of ore bodies has been inverted under upper amphibolite facies conditions to bornite ti free magnetite carolusberg type ore meteoric fluids resulted in supergene cu enrichment in koperberg bodies to 500 m below the pre nama peneplane and lower greenschist facies metamorphism 500 570 ma ago is reflected by inter alia hoits type ore bearing second generation bornite chalcopyrite covellite chalcocite

constraints on the amplitude of mid pliocene 3 6 2 4 ma eustatic sea level fluctuations from the new zealand shallow marine sediment record ice volume calibrations of the deep ocean foraminiferal delta18o record imply orbitally influenced sea level fluctuations of up to 30m amplitude during the mid pliocene and up to 30 per cent loss of the present day mass of the east antarctic ice sheet eais assuming complete deglaciation of the west antarctic ice sheet wais and greenland these sea level oscillations have driven recurrent transgressions and regressions across the world s continental shelves wanganui basin new zealand contains the most complete shallow marine late neogene stratigraphic record in the form of a continuous cyclostratigraphy representing every 41 and 100ka sea level cycle since ca 3 6ma this paper presents a synthesis of faunally derived palaeobathymetric data for shallow marine sedimentary cycles corresponding to marine isotope stages m2 100 ca 3 4 2 4ma our approach estimates the eustatic sea level contribution to the palaeobathymetry curve by placing constraints on total subsidence and decompacted sediment accumulation the sea level estimates are consistent with those from delta18o curves and numerical ice sheet models and imply a significant sensitivity of the wais and the coastal margins of the eais to orbital oscillations in insolation during the mid pliocene period of relative global warmth sea level oscillations of 10 30m were paced by obliquity

iodine 129 chronological study of brines from an ordovician paleokarst reservoir in the lunnan oilfield tarim basin abstract previous studies have shown that brines in an ordovician paleokarst reservoir of the lunnan oilfield in the tarim basin china are the product of mixing of paleo evaporated seawater in the east with paleometeoric waters in the west in order to put time constraints on the brine and related hydrocarbons in this field 10 brine samples were collected for which the iodine concentrations and 129 i i ratios were measured and discussed the iodine concentration 3 70 31 2 mg l and the 129 i i ratio 189 897 10 15 show that the iodine in the paleoseawater and meteoric water mw had different origins and 129 i characteristics the paleoseawater has a high iodine content 31 mg l indicating that iodine was introduced into the reservoir along with thermally generated hydrocarbons possibly in the cretaceous from the caohu sag in the eastern area based on consideration of all possible origins of iodine and 129 i in the brines it is suggested that the meteoric water maintained its initial iodine content 0 01 mg l and 129 i i ratio 1500 10 15 whereas the iodine enriched paloseawater ipsw exhibited a secular 129 i equilibrium n sq 39 atom l as a result of fissiogenic 129 i input in the reservoir over a long period of time the model of brine evolution developed on that basis confirmed that meteoric water entered the reservoir in the miocene at about 10 ma and partially mixed with the iodine enriched paleoseawater the movement of meteoric water was facilitated by faults created during the himalayan orogeny then became more dense after dissolving paleogene halite and infiltrated into the reservoir at high pressure the iodine and 129 i concentration in the brine contains information about the path and history of the fluid in the reservoir this may be useful in oil exploration since the movement of water was to some extent related to hydrocarbon migration

variations in 129i 127i ratios in recent marine sediments evidence for a fossil organic component abstract the value of the pre bomb 129 i 127 i ratio in the hydrosphere is important for the use of this isotope system for dating and tracing purposes in order to determine this value and to examine spatial variability 129 i 127 i ratios were measured in 25 sediment samples from five cores taken at geographically distinct coastal areas the results indicate a pre anthropogenic 129 i 127 i ratio of 1500 10 15 in good agreement with values derived from previous sediment and groundwater studies results from shallow sediments show that the layer of bioturbation is dominated by the addition of anthropogenic 129 i the good agreement between results for this layer from different cores supports the understanding that marine iodine is isotopically homogeneous and associated with organic material which is actively remineralized at the sediment water interface lower ratios down to 354 10 15 corresponding to an age of 32 5 ma and larger variations than expected were found in sections of the cores below the layer of bioturbation these observations can be explained by the presence of refractory fossil organic material transported by rivers to the sediments from uplifted continental shales the results suggest that marine iodine is present in two forms a labile component which is isotopically homogeneous and a refractory component which is associated with kerogen or other fossil organic compounds whose 129 i 127 i ratio reflects the age of these compounds 129 i 127 i ratios can be used to identify and date fossil organic material in recent sediments the presence of which can alter the assumptions underlying models of the global carbon cycle

chemical constraints and origins of four groups of gulf coast reservoir fluids pitzer s method for computing activity coefficients has been applied to reported fluid compositions in four groups of gulf coast reservoirs the mississippi and arkansas smackover formation the texas edwards group the texas frio formation and the louisiana miocene sequence the activity quotients in fluids from carbonate reservoirs imply a reaction relation between calcite and disordered dolomite in which ordering increases at higher temperatures this relationship indicates that an increasing mg ca molality ratio with decreasing temperature does not necessarily imply dolomite dissolution by an updip moving fluid instead it may reflect an approach to equilibrium between calcite and metastable dolomite activity quotients in fluids from clastic reservoirs imply a rea tion relation between chlorite illite potassium feldspar and quartz at temperatures above 100 c 212 f present fluid compositions in the smackover and the edwards appear to be related to the updip movement of louann brines from the gulf coast basin accompanied by dolomitization in particular bromide plots for the edwards fluids indicate simple dilution of louann brines with interstitial fluids similar plots for fluids from the smackover show the complicating effects of illite formation sylvite dissolution and halite recrystallization albitization may have occurred during fluid movement through clastics prior to entering the smackover and edwards present fluid compositions in the frio and miocene are apparently not related to louann brines the compositional data reflect the effects of halite dissolution the subsequent albitization of plagioclase and potassium feldspar and the dissolution of carbonates during secondary porosity formation

steep structure formation in the okiep copper district south africa bulk inhomogeneous shortening of a high grade metamorphic granite gneiss sequence abstract subhorizontal gneissosities and lithologies of the 1200 1000 ma granulite facies granite gneiss terrane of the okiep copper district south africa are cut by narrow discontinuous e trending cusp like and or monoclinal structures in which the regional gneissosity has been rotated to subvertical attitudes closely associated migmatization and charnockitization indicates that these steep structures formed during high grade metamorphic conditions in this paper we present a model which relates the deformational style strain and orientation of the steep structures to bulk inhomogeneous shortening the development of steep structures can be described as a progression from initial folding via explosive fold amplification to the progressive obliteration of folds by a subvertical e trending intensely developed transposition fabric this fabric is parallel to the axial planes of regional scale open folds shortening in the structures is mainly accommodated by a vertical material extrusion resulting in the commonly upward pointing steep structure geometries and volume loss the strain compatibility with surrounding rocks is maintained by bounding shear zones the progressive development of steep structures illustrates the close relationship between buckle folding and the formation of internal induced anisotropies during deformation of the high grade metamorphic granitic gneisses the apparent discrepancy between large scale open folding and simultaneously developed steep structures recording large finite shortening strains is interpreted to be the result of a large component of internal layer parallel shortening and strain partitioning

natural iodine 129 as an environmental tracer abstract iodine 129 t 1 2 16 my is a naturally occurring tracer which can be used to study hydrologic and geologic processes on time scales up to 100 my the pre bomb atmospheric ratio 129 i i should have been constant in time and space and is the starting value in ground water recharge subsequent ratio changes in ground water should be determined by isotope contributions from three sources recharge water iodine leached from the formation and in situ uranium fission the mathematical expression of these time dependent processes forms the basis for dating and tracing applications the expected behavior of natural 129i in ground water is compared to results from field studies ground water samples from the great artesian basin australia provide an estimate of the atmospheric equilibrium ratio 6 10 13 down gradient changes in water up to 1 my old suggest that subsurface production can be significant the usefulness of 129i as an indicator of brine source and age is verified in brines collected in and around louisiana salt domes the method leads to ages of 7 and 9 my for two brine pockets trapped within jurassic salt and 32 to 40 my for oil field brines in miocene sands adjacent to the domes the results demonstrate the capability of tandem accelerator mass spectrometry to measure as few as 107 atoms of 129i in 10 mg i with 10 precision although such atom sensitivity can be achieved otherwise the accelerator technique is necessary to measure naturally low pre 1945 cosmogenic isotope ratios

atlantic coastal plain exploratory drilling in the atlantic coastal plain region decreased in 1980 seven wells were drilled five of which were completed for a total footage of 80 968 ft 24 679 m six of the wells were located in the baltimore canyon trough and one was located in the southeast georgia embayment no exploratory wells were drilled in the georges bank basin or in the onshore portion of this region in 1980 tenneco and exxon reported gas shows in two wells in the baltimore canyon trough the remaining completed wells were reported as dry holes no lease sales were held in 1980 but two sales are scheduled for 1981 in the middle and south atlantic

sources sinks and long term cycling of iodine in the hyperarid atacama continental margin abstract the atacama region in northern chile hosts the driest desert on earth and is the world s premier iodine production province the origin of iodine enrichment in atacama is controversial and fundamentally different processes have been invoked over the years that involve marine eolian and more recently deep sedimentary fluid and groundwater sources as a result of the very limited geochemical iodine data in atacama and the western south american margin the origin of iodine enrichment in this region still remains elusive in this study we present a comprehensive survey of iodine concentrations and isotopic ratios 129i i of different reservoirs in the atacama desert of northern chile including nitrate soils supergene copper deposits marine sedimentary rocks geothermal fluids groundwater and meteoric water nitrate soils along the eastern slope of the coastal cordillera are found to have mean iodine concentrations of at least three orders of magnitude higher than the mean crustal abundances of 0 12 ppm with a mean concentration of 700 ppm soils above giant copper deposits in the central depression are also highly enriched in iodine 100 s of ppm range and cu iodide and iodate minerals occur in the supergene enrichment zones of some of these deposits further east in the precordillera jurassic sedimentary shales and limestones show above background iodine concentrations the latter averaging 50 ppm in the southern portion of the study area the highest iodine concentrations in fluids were measured in groundwater below nitrate soils in the coastal range 3 5 10 ppm and in geothermal waters 1 3 ppm along the volcanic arc although highly variable the iodine isotopic ratios 129i i of jurassic marine sedimentary rocks 300 600 10 15 nitrate soils 150 1500 10 15 and waters 215 10 15 are consistently low

dating of pore waters with 129 i relevance for the origin of marine gas hydrates pore waters associated with gas hydrates at blake ridge in the atlantic ocean were dated by measuring their iodine 129 iodine ratios samples collected from sediments with ages between 1 8 and 6 million years ago consistently yield ages around 55 million years ago these ages together with the strong iodine enrichment observed in the pore waters suggest that the origin of iodine is related to organic material of early tertiary age which probably is also the source of the methane in the gas hydrates at this location

late quaternary uplift rates of marine terraces on the pacific coast of north america southern oregon to baja california sur abstract marine terraces are common landforms along the pacific coast of north america from southern oregon to southern baja california we report 60 new uranium series ages of marine terrace corals hydrocorals and other fossils terraces representing the ca 80 ka and ca 125 ka high stands of sea are the most common along the pacific coast and we have used these ages along with terrace shoreline angle elevations and paleo sea level estimates to calculate late quaternary uplift rates uplift rates in the forearc region of the cascadia subduction zone range from 0 45 1 08 m kyr farther south along most of the coast west of the san andreas fault zone uplift rates range from 0 15 0 35 m kyr but some areas have significantly higher rates of uplift and others have apparently experienced little or no uplift in the last 125 ka in baja california sur west of the east pacific rise little or no uplift has occurred during the late quaternary on average the magnitude of rates of uplift for the tectonic regimes is as follows cascadia subduction zone san andreas fault zone region east pacific rise region

rare earth element geochemistry of an anorthosite diorite suite namaqua mobile belt south africa abstract a swarm of small dyke like plutons ranging in composition from anorthosite through diorite and norite to hypersthenite and glimmerite occurs in the western part of the namaqua mobile belt south africa known as the koperberg suite these rocks host important magmatic sulphide deposits zircon ages of approximately 1100 ma suggest that the suite was emplaced after the peak of the regional high grade metamorphism dated at 1200 ma a postulated comagmatic origin for the various rock types is confirmed by the ree distributions of anorthosite leucodiorite diorite hypersthenite and glimmerite the koperberg suite resembles the well known massif anorthosite complexes typified by the adirondack suite in most properties except for the dispersed mode of occurrence it is now shown that the similarity also holds for the ree spectra thus the predominant anorthosite and leucodiorite of the koperberg suite are comparable to similar rocks of the adirondacks and the burwash area ontario albeit more enriched in lree more mafic rock types such as norite mica diorite and glimmerite are substantially enriched in lree compared to mafic differentiates of massif anorthosites apatite is abundant in the mafic rocks and stores large proportions of the lanthanides the occurrence of apatite and mica rich assemblages indicates source magmas enriched in k ree and p a few intrusives exhibit excessively enriched ree patterns which are attributed to late hydrothermal alteration or metasomatism the ree data for syenite and two pyroxene assemblages from the copper district argue against a genetic relationship to the koperberg suite in spite of close spatial association

on the identification of a pliocene time slice for data model comparison the characteristics of the mid pliocene warm period mpwp 3 264 3 025 ma bp have been examined using geological proxies and climate models while there is agreement between models and data details of regional climate differ uncertainties in prescribed forcings and in proxy data limit the utility of the interval to understand the dynamics of a warmer than present climate or evaluate models this uncertainty comes in part from the reconstruction of a time slab rather than a time slice where forcings required by climate models can be more adequately constrained here we describe the rationale and approach for identifying a time slice s for pliocene environmental reconstruction a time slice centred on 3 205 ma bp 3 204 3 207 ma bp has been identified as a priority for investigation it is a warm interval characterized by a negative benthic oxygen isotope excursion 0 21 0 23 centred on marine isotope stage km5c km5 3 it occurred during a period of orbital forcing that was very similar to present day climate model simulations indicate that proxy temperature estimates are unlikely to be significantly affected by orbital forcing for at least a precession cycle centred on the time slice with the north atlantic potentially being an important exception

tracing crustal fluids applications of natural 129i and 36cl the two cosmogenic isotopes 129i and 36cl have half lives and geochemical characteristics that make their application of interest in the tracing of crustal fluids oil field brines and geothermal fluids the focus of this review is to compare 129i data from volcanic fluids with those from mud volcanoes and gas hydrate locations associated with the same subduction zone in order to demonstrate that fundamentally different hydrologic systems are present in active margins whereas 129i i ratios in volcanic fluids are site dependent and show a relation to the ages of subducting marine sediments ratios in fore arc fluids are similar in all sites investigated and are independent of the ages of the host sediments and the age of the subducting slab volcanic fluids contain iodine transported in sediments from the trench to the main volcanic zone whereas iodine in fore arc fluids is derived from organic material stored in the upper plates of subduction zones

isotopic characteristics of brines from three oil and gas fields southern louisiana abstract abstract isotopic analyses of twenty brine samples from two salt diapir related oil fields and one growth fault related gas field in southern louisiana lend support to the model proposed by workman and hanor this volume that brines from the zone of geopressure are mixing with hydropressured formation waters along the flanks of the iberia salt dome and within the limits of the sampling suggest that this hydrodynamic process may be characteristic of the region 18o d and 87sr 86sr determinations suggest that formation fluids above 2000 m 6500 ft depth have partly equilibrated with terrigenous clastic rocks fluids below 2000 m 6500 ft appear to be mixed oligocene miocene seawater and clay mineral water or evolved hydrocarbon bearing water these fluid compositions vary with depth due to mixing and possibly to temperature variations some samples may contain constituents derived from salt dissolution

distribution of trace elements in crude oils from southern germany the concns of s v cr fe co ni zn se br i ag and hg were detd in 45 crude oil samples of 17 oilfields originating from 9 different mesozoic or tertiary reservoir rock formations in the southern german alpine foreland furthermore the concns of na mg s cl ca fe co cu zn br sr and i were detd in 15 oilfield water samples the main anal technique was instrumental neutron activation anal to a minor degree x ray fluorescence spectrometry at absorption and emission spectrometry and titrimetric methods were applied the amts of s v ni and se are relatively const in the different oilfields therefore they are suitable for distinguishing between different classes of oil the crudes can be divided into 3 groups by their concns of s v and ni triassic and lower jurassic crudes of the western molasse basin crudes from the bausteinschichten lower chattian in the western molasse except the one from aitingen and crudes from priabonian sands malm and lower cretaceous in the eastern molasse and secondary altered crudes of the ampfinger schichten in the eastern molasse basin the crudes of aitingen are exceptional with their high content of s and v being enhanced 3 and 20 times resp relations between trace element distributions in crudes and in accompanying oilfield waters could not be found only the amts of i in crudes are significantly correlated with those from the corresponding oil field waters

migration of crude oil from the smackover source rock to jurassic and cretaceous reservoirs of the northern gulf rim abstract migration of distinctive crude oils from the upper jurassic smackover source rock across the northern gulf rim began at various times during the cretaceous regional source rock differences resulted in two compositional subfamilies of smackover crude oils type i crude oils in upper smackover reservoirs of east texas arkansas louisiana and mississippi reflect an origin from algal derived kerogen deposited in an anoxic environment type ii crude oils in upper smackover reservoirs of alabama and florida reflected an origin from kerogen preserved in a less anoxic environment with a terrestrial component comparison of molecular and carbon isotopic compositions of crude oils suggests that vertical migration of type i smackover crude oils charged many overlying upper jurassic lower cretaceous and upper cretaceous reservoirs some lateral migration to cretaceous reservoirs north of the updip limit of the smackover formation also occurred both type i smackover crude oils and geochemically dissimilar cretaceous sourced oils are found in upper cretaceous tuscaloosa and woodbine reservoirs because of impermeable barriers to migration especially in alabama vertical migration of type ii crude oils was less significant

iodine 129 constraints on residence times of deep marine brines in the canadian shield canadian shield brines are characterized by high concentrations of both stable iodine and 1 2 9 i the former reflecting its concentrated but diagenetically modified seawater origin and the latter its long subsurface residence time within its host shield rocks stable iodine concentrations in the yellowknife brine are as high as 18 mg l requiring the contribution of iodine from an external marine reservoir this reservoir likely comprised organic rich marine sediments in the basin where the brine was produced diagenesis of these sediments released iodine to the brine during its infiltration into the subsurface 1 2 9 i concentrations in the yellowknife brine are as high as 3 4 x 10 8 atom l and are due to the fission of 2 3 8 u in the rock matrix and subsequent diffusion of the radiogenic 1 2 9 i into the fracture fluids this concentration is close to the predicted secular equilibrium concentration for a fluid in basaltic rock with a uranium concentration of 1 mg kg after the residence time of 80 m y required for secular equilibrium has been attained this time period is interpreted as the minimum residence time of the yellowknife brine in the shield but it may be much greater possibly dating back to middle devonian time when most of the present day shield was covered by seawater similarly high stable iodine and 1 2 9 i concentrations measured in the sudbury brine support a generic ancient marine hypothesis for the origin of shield brines stable iodine and 1 2 9 i concentrations in the shallower mine waters are the result of mixing between the brine and low iodine modern meteoric recharge that is enriched in 1 2 9 i due to global fallout from nuclear fuel waste reprocessing activities

the influence of humic substances on the geochemistry of iodine in nearshore and hemipelagic marine sediments iodine is characteristically enriched at the surface of hemipelagic and nearshore sediments deposited under oxygenated conditions in such sediments bulk i corg ratios usually decrease with depth to values which are characteristic of anoxic sediments reflecting a preferential release of i during early diagenesis there is some debate as to whether sedimentary i is associated with the iron oxyhydroxide phase or with the organic fraction and whether the decrease in i corg with depth is due to the dissolution of the iron oxyhydroxides or the decomposition of labile organic matter it is shown that in a surficial hemipelagic sediment sample and in a nearshore sediment core i is mainly associated with the organic fraction and moreover that humic substances are involved in the surficial iodine enrichment laboratory experiments on the uptake and release of i by and from sedimentary humic substances also suggest a mechanism whereby humic materials reduce iodate at the sediment water interface to an electrophilic i species which further reacts with the organic matter to produce iodinated organic molecules during burial this excess i could be displaced from the organic matrix by nucleophiles such as sulphide ions or thiosulphate thus providing a possible explanation for the decrease in i corg ratio with depth observed in many nearshore and hemipelagic sediments

correlation between dissolved 4he concentration and 36cl in groundwater at aspo sweden abstract tunnel excavation at aspo island sweden has caused severe groundwater disturbance gradually extending deeper into the tunnel as present day baltic seawater intrudes through fractures connecting to the surface however the paleo hydrogeochemical conditions have remained in the deep highly saline waters that have avoided mixing a correlation has been observed between dissolved 4he concentration and cl ion concentration measured every two years from 1995 to 2001 at aspo groundwater mixing conditions can be examined by the correlations between 1 cl 36cl cl and 3h concentrations subsurface production is responsible for the majority of the 36cl and excess dissolved 4he of interstitial groundwater in fractures the secular equilibrium ratio of 36cl cl in rock was theoretically estimated to be 5 05 0 82 10 14 based on the neutron flux intensity a value comparable to the measured 36cl cl ratio in rock and groundwater the degassing crustal 4he flux was estimated to be 2 9 10 8 1 3 10 6 ccstp cm2a using the hto diffusion coefficient for the aspo diorite the 4he accumulation rate ranges from 6 8 10 10 for the in situ accumulation rate to 7 0 10 9 ccstp gwater a considering both 4he in situ production and the degassing flux assuming 4he is accumulated constantly in groundwater by comparing the subsurface 36cl increase with 4he concentrations in groundwater the 4he accumulation rate was determined from data for groundwater arriving at the secular equilibrium of 36cl cl the 4he accumulation rate was found to be 1 83 0 72 10 8 ccstp gwater a without determining the magnitude of degassing 4he flux

genesis of the precambrian copper rich caraiba hypersthenite norite complex brazil caraiba the largest brazilian copper deposit under exploitation consists mostly of disseminated and remobilised bornite and chalcopyrite hosted in early proterozoic norite and hypersthenite the mafic igneous complex comprises multiple intrusions of dykes veins and breccias of norites and hypersthenites with minor proportions of amphibolised gabbronorite and peridotite xenoliths transported by the magma from deeper levels in the lithosphere the country rocks are high grade gneisses granulites and metasediments compositions of plagioclase an60 40 and orthopyroxene en70 60 fall in a narrow range similar to the koperberg suite from the okiep copper district south africa and to that in many massif type anorthosites whole rock major and trace element geochemistry indicate a parental magma enriched in fe lree p k and cu negative nb anomalies on multi element plots and fractionated ree patterns along with sulphide sulphur isotopes in the range 34s 1 495 to 0 643 suggest a primary mantle lithosphere source although a lower crustal source for the gabbronorite and peridotite xenoliths cannot be excluded geochronological and field evidence indicate that both norite and hypersthenite are likely to have been emplaced during a major sinistral transcurrent partly transpressional shearing event associated with the waning stage of evolution of the early proterozoic salvador curaca orogen

origin and history of waters associated with coalbed methane 129i 36cl and stable isotope results from the fruitland formation co and nm abstract the fruitland formation of the san juan basin was deposited during the late cretaceous and is associated with significant reservoirs of coalbed methane cbm the purpose of this study is to determine the origin and history of waters associated with the formation using long lived cosmogenic and stable isotope systems ratios of 129 i i and stable isotope values d and 18 o were determined in waters from close to 100 wells 36 cl cl ratios for a subset of these samples a significant group of samples has 129 i i ratios between 100 10 15 and 200 10 15 indicating minimum iodine ages close to 60 ma if these ages are corrected for the addition of fissiogenic 129 i they are compatible with the depositional age of the fruitland formation late cretaceous several sets of waters are clearly present within the data a group dominated by infiltration of recent surface waters is restricted to the uplifted basin margins with a lateral extent of less than 5 km from outcrop and is characterized by 129 i i ratios in excess of 1500 10 15 and meteoric d 18 o and 36 cl cl signatures the rest of the basin is characterized by several subsets of formation waters which have undergone variable degrees of iodine enrichment through diagenesis as well as variable degrees of dilution the first subgroup is found in coals of relatively low vitrinite reflectance and moderate enrichment of iodine this subgroup predominantly consists of entrapped pore fluids although it may also contain waters which infiltrated the coals at the time of the laramide uplift between 25 and 30 ma a second subgroup consists of formation waters associated with coals of high vitrinite reflectance despite subsequent uplift the high iodine concentrations and low 129 i i ratios of this subgroup as well as a moderate depletion of deuterium relative to 18 o suggest that these waters were not significantly altered since the time when diagenetic reactions occurred in the deepest portion of the basin a third subgroup with higher d and 18 o values as well as higher 129 i i ratios extends roughly west to east at the new mexico colorado state line and corresponds to a region of extensive fracturing of the coalbeds in this case the higher 129 i i ratios are probably due to contributions of fissiogenic 129 i through fracture flow perhaps from deeper formation waters our results do not support models of subsequent basin wide groundwater migration in the fruitland formation the combined use of 129 i and 36 cl with stable isotope studies provides valuable information as to the hydrologic history of coalbed methane deposits as well as their potential for commercial exploitation

influence of subduction zone settings on the origin of forearc fluids halogen concentrations and 129i i ratios in waters from kyushu japan abstract fluid migration in subduction zones is one of the key phenomena to understand the global mass transfer system while active volcanoes provide the most recognizable conduits for fluid flow in active margins the existence of a large number of active fluid seepages demonstrates that other forms of fluid release are also important in subduction zone settings the authors collected fluid samples from springs and wells across the forearc area in kyushu a southwestern island of japan covering hot spring activities associated with active volcanism and the median tectonic line mtl a major fault system present in the southwestern part of japan in order to determine sources of these fluids halogen concentrations as well as 129 i i and 36 cl cl ratios were measured in samples from several locations while cl concentrations of the forearc fluids in kyushu range between seawater and meteoric water value i concentrations are considerably higher than seawater value fluids in the miyazaki area are much higher in i and somewhat higher in br than waters in the oita area which is closely associated with the mtl the differences between those two areas are also pronounced in 129 i i ratios which range between 800 and 900 10 15 in the oita area and between 100 and 360 10 15 in the miyazaki area the 129 i i ratios obtained from the oita area are compatible with an i derivation from subducting marine sediments similar to findings from an earlier investigation of fluids collected from satsuma iwojima an active volcano south of kyushu island in the miyazaki area on the other hand i ages are too old to be derived from currently subducting marine sediments and point to a derivation from old organic rich materials in the upper plate of the forearc region the results demonstrate the presence of very different fluid systems in the forearc area of kyushu old ch 4 rich fluids dominate in the seaward side of the forearc while fluids close to the mtl and the quaternary volcanic front demonstrate derivations from subducting marine sediments the latter fluids in the mtl area probably are transported through the fractures associated with the fault activities suggesting that this fault system reaches the transition zone between upper and lower plates in this region

129i and 36cl concentrations in waters of the eastern clear lake area california residence times and source ages of hydrothermal fluids abstract the clear lake area of northern california is the location of hot spring activity some of which is associated with the formation of au and hg deposits we measured 129 i i and 36 cl cl ratios in nine warm springs formation springs six cold springs with elevated levels of cl and i mineral springs and five springs of recent meteoric origin dating of the i in the formation waters indicated that sources of i in these waters are formations with minimum ages between 60 and 80 ma this age range is in good agreement with the ages of the franciscan complex and the great valley sequence the dominant formations in this area because the mineral waters are essentially formation waters diluted with meteoric water i in these waters is of the same origin residence times of the waters were calculated based on the build up of129i and 36cl as a consequence of the presence of u and th in the crust the residence time of the formation waters in the great valley sequence the location for most of these springs was probably not longer than 84 000 yr the concentrations found for 36cl and 129i in the mineral waters indicate that these waters have residence times of similar magnitude in formations such as the franciscan complex or the clear lake volcanics which have slightly higher levels of u and th than the great valley sequence

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

halogen systematics in the mallik 5l 38 gas hydrate production research well northwest territories canada implications for the origin of gas hydrates under terrestrial permafrost conditions abstract the authors report here halogen concentrations in pore waters and sediments collected from the mallik 5l 38 gas hydrate production research well a permafrost location in the mackenzie delta northwest territories canada iodine and br are commonly enriched in waters associated with ch4 reflecting the close association between these halogens and source organic materials pore waters collected from the mallik well show i enrichment by one order of magnitude above that of seawater particularly in sandy layers below the gas hydrate stability zone ghsz although cl and br concentrations increase with depth similar to the i profile they remain below seawater values the increase in i concentrations observed below the ghsz suggests that i rich fluids responsible for the accumulation of ch4 in gas hydrates are preferentially transported through the sandy permeable layers below the ghsz the br and i concentrations and i br ratios in mallik are considerably lower than those in marine gas hydrate locations demonstrating a terrestrial nature for the organic materials responsible for the ch4 at the mallik site halogen systematics in mallik suggest that they are the result of mixing between seawater freshwater and an i rich source fluid the comparison between i br ratios in pore waters and sediments speaks against the origin of the source fluids within the host formations of gas hydrates a finding compatible with the results from a limited set of 129i i ratios determined in pore waters which gives a minimum age of 29 ma for the source material i e at the lower end of the age range of the host formations the likely scenario for the gas hydrate formation in mallik is the derivation of ch4 together with i from the terrestrial source materials in formations other than the host layers through sandy permeable layers into the present gas hydrate zones

recycling of iodine in fore arc areas evidence from the iodine brines in chiba japan the distribution of iodine in the earth s crust is dominated by its accumulation in marine sediments if fluxes between terrestrial and marine compartments are considered however a significant imbalance exists between known sources and sinks of iodine we present here evidence from the fore arc area near chiba japan the world s largest brine iodine producing area that iodine is mobilized from marine sediments during the early stages of subduction based on detailed chemical analyses of 22 brines and 129i dating of 13 of these samples collected from the kazusa formation we show that iodine in these fluids is derived from organic rich marine sediments with a minimum age of 50 myr geochemical characteristics of the brines and the age of the iodine indicate that the iodine enrichment is caused by mobilization from subducting marine sediments and not by derivation from the host formation age 1 2 myr the direct return of iodine from marine sediments into the oceans during the subduction of oceanic plates could provide the missing link in the iodine cycle and be an important pathway also in the marine cycle of carbon

petrology geochemistry and geochronology of the chilka lake igneous complex orissa state india abstract the chilka lake igneous complex of orissa the largest known anortosite massif of the indian shield occurs in a catazonal environment of high grade metamorphics of the eastern ghats precambrian orogenic province the syntectonic massif consists of the anorthositic balugaon dome leuconoritic rambha lobe and quartz mangeritic kallikota cover a completely gradational suite comprising anorthosite leuconorite norite minor jotunite the anorthositic suite constitutes most of the complex the subordinate of suite of acid rocks spatially associated with this is of a broad quartz mangeritic lithology with minor granitic rocks the acidic suite geochemical evolution of the complex in the sequence anorthosite leuconorite norite jotunite acidic rocks shows moderate iron enrichment in the noritic jotunitic stage and is marked by an overall decrease in al 2 o 3 cao mgo ni co sr ba k rb and increase in sio 2 k 2 o v ni k ba and rb sr such progressive variation in geochemical parameters appears i essentially gradual and frequently overlapping in rock members of the intergradational anorthositic suite and ii rather abrupt across transition zones between the anorthositic suite and the acidic suite due to near absence of intervening intermediate lithologies rb sr whole rock isochron studies indicate that the complex was emplaced ca 1400 ma ago the initial 87 sr 68 sr 0 70661 implies limited hybridisation of the parent magma prior to emplacement a critical appraisal of all the available evidence suggests that i the anorthositic suite of rocks form a perfectly consanguinous and comagmatic assemblage and ii the spatially associated acidic suite emerged through a convergence of magmatic and metasomatic processes the latter brought about by contact anatexis of the host rocks the complex as well as the host metamorphics are intruded by an atectonic suite of noritic dykes emplaced ca 850 ma ago

lower tertiary and upper cretaceous source rocks in louisiana and mississippi implications to gulf of mexico crude oil the lower tertiary sparta formation wilcox group and the midway group in southern louisiana include organic rich source facies that generate crude oil at relatively high thermal maturities the wilcox group is an important source of wilcox crude oil and regional kerogen variations explain two crude oil subfamilies wilcox crude oils in downdip areas of southern louisiana migrated short distances but long range lateral migration about 150 km best explains wilcox crude oils far updip from mature source rocks crude oils in oligocene and younger reservoirs in southern louisiana migrated vertically from deep lower tertiary source rocks some crude oils in upper cretaceous tuscaloosa reservoirs were emplaced by long range lateral migration from tuscaloosa source rocks g ven little evidence of upper tertiary source rocks and the overmaturity problems of mesozoic source rocks most crude oils in upper tertiary and pleistocene reservoirs of the gulf continental shelf are best explained by vertical migration from deep lower tertiary source rocks even so it is simplistic to assume an exclusive lower tertiary origin many tertiary and pleistocene crude oils of this study probably include an overprint of high maturity hydrocarbons from mesozoic sources

evidence for vertical movement of fluids gulf coast sedimentary basin sediments between 10 and 15 km thick have prograded approximately 400 km into the small oceanic basin which formed along the southern margin of north america subsequent to early mesozoic rifting redistribution of mass during burial diagenesis and the chemistry of present day formation waters in jurassic through pleistocene formations document local kilometer scale and in cases basin scale vertical fluid transport within the sedimentary wedge fluid flow is in part driven by porosity reduction which takes place by both physical and chemical processes during burial vertical and horizontal transport also occurs as the result of thermally and salinity generated buoyancy effects input of fluids into the sedimentary wedge from the underlying crust is predicted but not documented

contrasting copper and chromium metallogenic evolution of terranes in the palaeoproterozoic itabuna salvador curaca orogen sao francisco craton brazil new zircon shrimp and sm nd model ages and their significance for orogen parallel escape tectonics abstract the northern segment of the palaeoproterozoic itabuna salvador curaca collisional orogen in the sao francisco craton brazil comprises two high grade terranes separated by the 150 km long n s trending itiuba syenite the curaca terrane to the west contains copper sulphide deposits hosted by hypersthenite norite complexes e g caraiba body whereas the jacurici terrane to the east contains chromite deposits hosted by peridotite norite sills e g medrado body shrimp u pb dating of zircons combined with a significant major element compositional gap indicates that the caraiba 2580 10 ma and the medrado 2085 5 ma mafic ultramafic complexes are not related by fractional crystallisation as previously thought depleted mantle nd model ages for the regional gneisses are also distinct with the curaca terrane having younger ages 2 4 2 8 ga than the jacurici terrane 2 9 3 2 ga suggesting that they represent two independent fragments of continental crust accreted during the palaeoproterozoic orogeny emplacements of the itiuba syenite ca 2084 ma and of the medrado complex were apparently coeval probably controlled by orogen parallel block displacement or escape tectonics following continent continent collision

geochemical and isotopic characteristics of different types of anorthosite in the namaqua mobile belt south africa abstract anorthosite genesis in the proterozoic namaqua mobile belt of south africa encompasses a range of intrusive histories including massif type as in the occurrences of plat sjambok and possibly koperberg suite and layered type as at oranjekom different compositional ranges at all levels of analytical resolution mineralogical geochemical and isotopical are revealed there is a spectrum from orthopyroxene dominance and extremely high lree koperberg suite to clinopyroxene horn blende dominance with normal ree patterns oranjekom plat sjambok and low iron oranjekom isotopic data for the various complexes rb sr sm nd indicate differences in magma evolution the oranjekom complex represents a depleted mantle origin with low to moderate contamination sr 6 to 9 nd 7 to 9 while the plat sjambok complex reflects a depleted mantle origin with a noticeable contribution from a crustal component sr 40 to 150 nd 5 to 1 in contrast the koperberg suite sr 300 nd 9 if derived from the mantle would require mixing between a highly enriched mantle source and an extremely enriched crustal contaminant high sr 700 to 800 nd 2 resulting in an unusual isotopic trend with a positive slope the waterkop pluton that has in the past been regarded as related to the plat sjambok complex represents a quite different syenitic magma from a slightly enriched mantle source with very little contamination and is not a cogenetic with the latter collectively the analytical data support original magma generation from different mantle sources followed by various intrusive histories ranging from rapid transit between source and emplacement in the upper crust oranjekom to prolonged travel and differentiation involving considerable crustal contamination koperberg suite the fact that the different intrusive types occur in different suspect terranes of the mobile belt may reflect originally contrasting tectonic settings during a late proterozoic continental collision that played a role during the assembly of rodinia

in situ neutron flux 36cl production and groundwater evolution in crystalline rocks at stripa sweden the meteoric input of36cl due to cosmogenic or nuclear weapon produced36cl cannot contribute significantly to the36cl present in the saline groundwaters up to 700 mg l 1 cl from the stripa granite the extent of in situ production of36cl has been estimated on the basis of the neutron fluxes within the granite and its surrounding leptite the36cl present in the groundwaters is attributed to either admixture of labelled cl from the leptite with cl from the granite or to the total derivation of groundwater chlorinity within the leptite followed by radiochemical ingrowth of36cl during subsequent groundwater residence within the granite the chloride derived from the leptite may be either matrix chloride or chloride from an external source which has had a long residence time within the leptite the implications of36cl in situ production for the estimation of groundwater residence times and for the geochemical evolution of groundwater chlorinity are discussed

petrographical characteristics of the koperberg suite south africa an analogy to massif type anorthosites a swarm of anorthositic dioritic intrusives collectively termed the koperberg suite is scattered over an area of about 3000 km2 in the northwestern cape province namaqualand south africa the intrusive suite is renowned for its associated magmatic copper sulphide deposits transgressive field relationships and the preservation of primary igneous features suggest emplacement of the suite after the main metamorphic event which has been dated at c 1200 ma the distribution of the intrusions seems to have been controlled by vertical shearing which is manifested by antiformal disruptions steep structures in the country rocks post intrusion movement along some of these structures is deemed responsible for metamorphic textures in some mafic bodies igneous breccias associated with some intrusions present evidence of explosive tectonics at the time of emplacement the rock types which compose the mafic suite include andesine anorthosite leucodiorite hypersthene and mica diorite hypersthenite and glimmerite the occurrence of composite intrusions with two or more mafic varieties and the modal gradation between the rock types suggest consanguinity the anorthosite appears to be the oldest member of the series followed by increasingly more mafic varieties such as leucodiorite hypersthene diorite norite and hypersthenite owing to the presence of virtually monomineralic rock types various differentiation trends are recognized series that are dominated by hypersthene brown mica iron titanium oxides and amphibole can thus be delineated microprobe analyses of the major silicates indicate plagioclase compositions of andesine en58 68 for hypersthene and brown mica compositions on the biotite phlogopite boundary the predominance of anorthosite and leucodiorite in the suite suggest an affinity with the massif type anorthosite kindred this relation is supported by other criteria such as the preponderance of hypersthene the age of emplacement the sequence of intrusion en an ratios of plagioclase and hypersthene and the association of syenitic rocks as well as iron titanium oxide and apatite rich assemblages it is provisionally proposed that the okiep district represents the lower levels of an anorthosite complex of the massif type

halogen geochemistry of the mcmurdo dry valleys lakes antarctica clues to the origin of solutes and lake evolution abstract we have determined the halogen and boron concentrations in the ice covered lakes of taylor valley antarctica to better establish the sources of salts and evolutionary histories of these unusual water bodies in addition we report on a series of 129 i measurements that were compared with previous 36 cl data that also help constrain the source of solutes and histories of the lakes the new data when put into context of previous work on these systems over the past forty years allow us to make the following conclusions the primary source of solutes to lake hoare the youngest of the lakes is the dissolution of marine aerosols and aeolian salts and the chemical weathering of dust on the glaciers the geochemistry of lake fryxell the brackish water lake is primarily dominated by the diffusion from a halite saturated brine at the sediment water interface and the recent infilling of the lake by glacier meltwater these waters have chemical weathering and marine aerosols components lake bonney has two distinct lobes whose hypersaline hypolimnia have different chemistries both of the lobes are remnants of ancient marine waters that have been modified by the input of weathering products this lake has also been modified by periods of cryogenic concentration when solutes have been lost via mineral precipitation thus the geochemistry of lake bonney owes its unusual geochemistry in part to variations in the climate in the taylor valley over at least the past 300kyr the 129 i data from the taylor valley are similar to those from fracture fluids in crystalline rocks from the northern hemisphere

using iodine isotopes to constrain supergene fluid sources in arid regions insights from the chuquicamata oxide blanket although iodine is rare in crustal settings previous studies have documented its occurrence in the supergene zones of base and precious metal ore deposits in arid environments in this report we present a novel application of the iodine 129 129i isotope tracer to iodine rich samples from the world s largest supergene cu profile at the chuquicamata deposit in northern chile where anomalous concentrations of this element have been reported all supergene marshite cui samples from chuquicamata and iodine rich soil above the mansa mina deposit have 129i i isotope ratios 190 560 10 15 that are significantly lower than those of surface waters i e 1 500 10 15 indicating that iodine was most likely derived from a reservoir of marine origin rather than a meteoric and or atmospheric source geochemical modeling shows that the long term dilution of iodinerich deep formation waters by meteoric water during the main stage of supergene alteration 40 10 ma resulted in fluid 129i i ratios that are within the range of mineral soil 129i i ratios observed at chuquicamata strongly suggesting that iodine was remobilized from the lower jurassic to mid cretaceous marine basement results from this study show that iodine isotopes can be successfully applied to trace the origin and nature of supergene fluids in iodine rich oxide blankets leach caps and soils above buried cu deposits and also to constrain the timescales of fluid circulation during supergene enrichment

reservoir fluids and their migration into the south eugene island block 330 reservoirs offshore louisiana this study in the well documented pliocene pleistocene south eugene island block 330 sei330 field offshore louisiana unravels a complex petroleum system by evaluating both the inorganic and organic geochemical characteristics of reservoir fluids the brines at sei330 dissolved halite prior to entering the reservoirs and equilibrated with reservoir sediments exchanging sodium for calcium magnesium and other cations the systematically varying extent of brine sodium depletion in two reservoirs defines south to north flow in those sands these sands were filled from a fault that bounds the reservoirs on the south oil compositional parameters also show north south variation across these reservoirs the sei330 oils and gases each had different sources in contrast to published jurassic sources for oil carbon isotope data indicate that sei330 hydrocarbon gases probably sourced from early tertiary or cretaceous sediments after oil had migrated through them distribution of biodegraded vs unbiodegraded oils indicates the reservoirs filled much more recently than formation of the salt weld beneath the field oil compositions indicate that some sei330 oils were partially stripped of low molecular weight compounds by their dissolution in a mobile vapor phase gas washed by large volumes of gas several hundred meters below the deepest reservoir modeling of this gas oil interaction aids in identifying deep potential targets in which gas washing occurred hydrocarbon distribution combined with oil chemistry and reservoir pressures indicate reservoirs filled from fault systems on both the north and south sides of the field the fault feeders are wide 100 m structurally complex zones that can direct different types of fluids into different reservoirs

comparison of amino acid racemization geochronometry with lithostratigraphy biostratigraphy uranium series coral dating and magnetostratigraphy in the atlantic coastal plain of the southeastern united states the results of an integrated study comprising litho and biostratigraphic investigations uranium series coral dating amino acid racemization in molluscs and paleomagnetic measurements are compared to ascertain relative and absolute ages of pleistocene deposits of the atlantic coastal plain in north and south carolina four depositional events are inferred for south carolina and two for north carolina by all methods the data suggest that there are four pleistocene units containing corals that have been dated at about 100 000 yr 200 000 yr 450 000 yr and over 1 000 000 yr some conflicts exist between the different methods regarding the correlation of the younger of these depositional events between charleston and myrtle beach lack of good uranium series dates for the younger material at myrtle beach makes the correlation with the deposits at charleston more difficult

determination of natural and anthropogenic 129i in marine sediments sup 129 i concentrations in two sediment cores from the continental slope near cape hatteras were determined with tandem accelerator mass spectrometry tams the natural sup 129 i sup 127 i ratios in these cores are approximately 10 sup 12 the input of anthropogenic sup 129 i has increased this ratio to values close to 10 sup 10 at the surfacee of the sediments the observed natural level of sup 129 i is about two orders to magnitude above the current detection limit with tams which opens up to possibility for applications of sup 129 i in the marine system such as dating of sediments and crude oils and tracing of slow water movement in sediments

iodine dating of pore waters associated with gas hydrates in the nankai area japan the nankai hydrate field japan is an example of gas hydrate deposits associated with an active subduction zone in order to determine the origin of gas hydrates in this area 129i i ratios together with halogen concentrations were measured in a set of pore water samples collected from two boreholes in the nankai hydrate field iodine concentrations are between 100 and 230 m i e strongly enriched compared to seawater while cl concentrations were found to be close to that of seawater except for one sample 129i i ratios are between 180 and 520 10 15 giving minimum ages between 24 and 48 ma because these ages are considerably older than present host sediments 2 ma and subducting marine sediments 21 ma in this area iodine and by association methane in the gas hydrates must have been derived from source formations located in the continental side of the subduction zone the results do not support derivation of gas hydrates from present host sediments or currently subducting sediments but could be related to release and long time recycling of fluids from marine formations of early tertiary age

introduction pliocene climate processes and problems climate predictions produced by numerical climate models often referred to as general circulation models gcms suggest that by the end of the twenty first century global mean annual surface air temperatures will increase by 1 1 6 4 c trace gas records from ice cores indicate that atmospheric concentrations of co 2 are already higher than at any time during the last 650 000 years in the next 50 years atmospheric co 2 concentrations are expected to reach a level not encountered since an epoch of time known as the pliocene uniformitarianism is a key principle of geological science but can the past also be a guide to the future to what extent does an examination of the pliocene geological record enable us to successfully understand and interpret this guide how reliable are the retrodictions of pliocene climates produced by gcms and what does this tell us about the accuracy of model predictions for the future these questions provide the scientific rationale for this theme issue

south carolina interglacial sites and stage 5 sea levels abstract amino acid and other studies have been made on the 30 km pleistocene sections of the intracoastal waterway between myrtle beach and little river south carolina our ratios differentiate the long established waccamaw oldest canepatch and socastee formations the ratios from the four laboratories that have worked in this area agree very well and apparent conflicts with u series dates may merely reflect an abundance of reworked corals our amino acid correlations with u series coral dates in south carolina bermuda and the mediterranean all argue that the classical canepatch and its horry clay date from isotope stage 5e and not as has been implied from stage 7 9 11 or 13 excavations and erosion have increased position fixing problems along the waterway and canepatch amino acid ratios and u series dates 460 000 100 000 yr b p at icw5 may be from an older unit the canepatch shows the double marine transgression visible in many stage 5e deposits pollen shows that the second transgression occurred late in the interglaciation and stratigraphic studies show that it reached 14 m it therefore fits very well antarctic ice surge models of stage 5 sea level and climate the socastee adds to the evidence for one or more sea levels above 0 m late in stage 5

mineral chemical and isotopic studies of namaqualand granulites south africa a grenville analogue the northwestern part of south africa and southern south west africa namibia is amongst the most extensive granulite terranes in africa this work reports the results of electron microprobe studies of minerals from two pyroxene cordieriteorthopyroxene gedrite sapphirine and garnet and or cordierite parageneses from namaqualand in the n w cape province of south africa determined pt conditions of prograde metamorphism based on thermodynamic calculations are 800 900 c and ca 6 7 kb and it is argued that rocks of unusual composition notably cordierite orthopyroxene rocks are restites after the extraction of granitic liquid from former argillites this interpretation is consistent with previously published data on similar rocks and with mccarthy s 1976 suggestion of extensive partial melting in the quartzofeldspathic rocks in the area

loss of provenance information through subsurface diagenesis in plio pleistocene sandstones northern gulf of mexico abstract subsurface alteration of plagioclase potassium feldspar and a variety of nonopaque heavy minerals has substantially modified the detrital composition of plio pleistocene sediments in the northern gulf of mexico albitization of plagioclase and dissolution of unstable grains are the two principal mechanisms of grain alteration grain alteration increases progressively with depth and has taken place without the influence of significant amounts of meteoric fluids the degree to which strictly subsurface grain alteration has affected these young sediments suggests that grain assemblages in older rocks should be viewed most skeptically with regard to their state of preservation

potassium distribution and metasomatism in pelites and schists how and when relation to postdepositional events a large global database for over 9000 archean to holocene pelites in numerous basins has been developed to evaluate diagenetically unaltered and altered compositions the mineralogy and geochemistry of quaternary muds and ancient mudstones provide first order controls on diagenetic potassium metasomatism in pelites clay mineralogy of quaternary muds is dominated by smectite and kaolinite with minor detrital mica and illite thus k2o is 4 k al is 0 25 and k rb is 220 in most quaternary muds with diagenetic alteration of clays to illite smectite and illite k2o content increases to 4 8 and k al rises to 0 2 0 5 or more in extreme potassium metasomatism authigenic k feldspar develops sources of potassium are internal to shale sandstone units wherein detrital k feldspar is dissolved during diagenesis providing k for clay illitization in closed system isochemical alteration as in some gulf coast and north sea basin cases potassium in amounts greater than that available from closed system alteration is provided from extraformational circulating brines in open system diagenesis k rb with diagenesis varies according to whether the metasomatizing fluid was relatively poor in rb seawater derived brines or richer in rb as in many hydrothermal waters diagenetic fluids may originate from seawater or meteoric water enriched in cations by water rock interactions along their subsurface migration paths and or by dissolution of evaporites potassium metasomatizing fluids penetrate low permeability pelites through faults fractures and microfractures and by diffusion in the mineral matrix typically k metasomatism possibly with pb zn cu ba and f mineralization occurs long after sediment deposition and burial at temperatures of 50 to 150 c related to tectonic activity and fluid movement different modes of metasomatism are recognized and correlated with geological setting in the passive margin gulf coast tertiary basin open system k metasomatism where present is limited to areas adjacent to steeply dipping growth faults which act as conduits for episodic pulses of altering fluids migrated upward from deeper basin sources in contrast widespread pervasive open system k metasomatism produced by continuous long term gravity advective and diffusive flow of brine from the late paleozoic appalachian ouachita wichita mountains highland to altered earlier paleozoic shales plus sandstones bentonites and carbonates in the illinois and anadarko ardmore foreland basins this mode of k alteration following major mountain building events is characteristic of many precambrian and paleozoic collision orogens and associated foreland basins another mode is in rift basins with no external drainage in which indigenous waters are evaporated to brines these brines cause albitization of k feldspar to yield potassium for illitization of detrital clays

geochemical constraints of the petrogenesis of the o okiep koperberg suite and granitic plutons in namaqualand south africa a crustal source in namaquan grenville times the namaquan grenville orogeny late mesoproterozoic in the o okiep district is characterized by two tectono magmatic episodes the o okiepian episode 1210 1180 ma with the intrusion of batholitic granites and the klondikean episode 1040 1020 ma which includes the intrusion of the copper bearing koperberg suite and the rietberg granite this study focuses on the geochemistry major and trace elements sr and nd isotopes of intrusive rocks of the o okiep terrane to provide better constraints on their source rock characteristics and on their petrogenesis the o okiepian granites belong to the k rich granite kindred with shoshonitic affinities the concordia granite results from dehydration melting of a pelitic source the rietberg granite shows geochemical similarities with post collisional magmatic series the anorthosites and related rocks of the koperberg suite are cumulates their ree distribution is controlled by their apatite content a new rock type jotunite has been identified in the koperberg suite it is analogous to the rogaland chilled jotunite a characteristic which gives strong evidence that the koperberg rocks belong to the massif type anorthosite suite inversion modelling of plagioclase ree compositions from anorthosite permits the reconstruction of melt compositions and places constraints on the melting process and on the characteristics of the source rocks the occurrence of jotunite in the koperberg suite is strong additional evidence for a crustal source because jotunite is produced by remelting of gabbronorite under dry conditions the various intrusions in the koperberg suite show distinct isotopic signatures which resulted from isotopic heterogeneities of the crustal source and from minor contamination with the country rocks the characteristic negative end 1030 ma values 5t o 11 can be explained by remelting at 1030 ma of a 1900 ma old oceanic crust protolith with an enriched morb ree distribution the large range in sr initial ratios 0 709 0 748 may reflect hydrothermal alteration of the oceanic crust a process which may also explain the cu enrichment the koperberg intrusions were produced by forceful injection of cumulate crystal mush which were differentiated in deeper magma chambers or in conduits

129i and 36cl in dilute hydrocarbon waters marine cosmogenic in situ and anthropogenic sources abstract the long lived halogen radioisotopes 129 i and 36 cl provide valuable information regarding the source of fluids in hydrocarbon systems and in localized areas where infiltration of younger meteoric water has occurred despite the utility of these two isotopes in providing time signatures for fluid end members considerable uncertainty remains regarding the interpretation of intermediate age waters in hydrologic systems these waters are likely the result of the combination of two or more halogen sources at some time in the past each with its own characteristic concentration and isotopic composition in order to unravel the evolution of these intermediate age waters the effect that infiltration of meteoric water has on the isotopic composition of older formation waters is modeled also evaluated is the effect that the timing of dilution has on 129 i and 36 cl signatures observed in the present specifically the hypothesis that halogen isotopic signatures imparted by the mixing of brine and meteoric waters early in the development of a sedimentary basin are quantitatively different from those imparted by the mixing of old brines with recent meteoric waters the modeled results are compared to previously published isotopic data from production wells in the fruitland formation coalbed methane system portions of the basin preserve enough of the original brine source to retain 129 i i ratios roughly recording the age of deposition of organic matter 73 76 ma even where some degree of dilution by meteoric water has occurred however the 129 i signatures of waters that presently contain less than 10 of the original formation water component indicate that mixing has occurred within the past 10 ma consistent with recently published 4 he data both 36 cl concentrations and 36 cl cl ratios show that waters containing more than 10 formation water are all in secular equilibrium with the host formation coals in contrast waters with less than 1 of the original formation water s cl content all have 36 cl cl ratios which are greater than secular equilibrium values indicating the migration of meteoric water into the coal formation more recently than 2 ma although 36 cl signatures in the fruitland formation are not significantly affected by anthropogenic input 129 i i ratios in a subset of samples that retain less than 1 of the initial formation water component suggest input of anthropogenic 129 i during the past 50 a

tectonic cycles in southern africa abstract the recurrence of major geological events within the 3600 ma stratigraphic record of southern africa suggests a periodicity of320 25ma for at least the last 3200 ma this periodicity is reflected in major episodes of continental volcanism granitoid plutonism orogeny reciprocity of terrestrial and marine dominated sequences platform carbonate sedimentation glaciation and first order changes in sea level these serve to define 11 completed megacycles each introduced by a major rifting event accompanied by listric faulting alluvial sedimentation in restricted fault bound troughs volcanism and a type granitoid plutonism prior to 3200 ma continental rift magmatism occurred subaqueously due to very high early archean sea levels resulting in pillow lavas and a lack of interbedded terrigenous siliciclastics the long term reciprocity of terrestrial and marine dominated sequences records eustatic first order changes in sea level with highstands characterized by generally humid warm continental climates low relief and tropical afforestation on the other hand lowstand climates were hot and arid with high relief and widespread desertification thick marine sequences accumulate in areally extensive epeirogenic basins without significant volcanism or faulting and commonly are divided into an early phase of open shelf sedimentation followed by deposition in a brackish marine foreland basin within openshelf environments an early phase of biochemical precipitation and or siliciclastic reworking along linear shorelines is separated from a later phase involving rapid deposition of immature siliciclastics along lobate shorelines evolution of the foreland basin is related to orogenic activity and the isolation of an epeiric sea which sometimes developed the characters of a barred basin marine dominated sequences display a deterministic stacking of lithofacies important glacial epochs commonly occur midway through first order regression sometimes with lesser events closely following peak transgression potentially they display 320 ma periodicity but with an unexplained mid proterozoic gap glaciation is related to the combined effect of climatic cooling associated with first order regression and depletion of atmospheric co2 by biological uptake associated with platform carbonate development terrestrial volcanism is believed to be the main contributor of atmospheric co2 climatic change is accompanied by cyclical patterns of cratonic weathering and pedogenesis

determination of source ages and migration patterns of brines from the u s gulf coast basin using 129i abstract the long lived cosmogenic and fissiogenic isotope 129i has been applied to the study of source ages and migration patterns of oil field brines from the u s gulf coast basin 129 i i ratios were measured in sixty samples of saline formation water from depths of 660 4503 m in several oil fields in southeast texas south central louisiana and offshore louisiana comparisons between measured ratios and the decay curve for surface hydrospheric 129i result in minimum source ages much older than present host formation ages indicating vertical migration of brine from older deeper sources conservative corrections for a fissiogenic component due to spontaneous fission of 238u in the subsurface result in the following median source ages iberia field 55 ma port barre field 53 ma and eugene island blocks 316 and 330 55 ma pointing to wilcox group shales as source formations mesozoic sources cannot be ruled out due to the uncertainties in estimating the fissiogenic component some of the ratios measured in texas gulf coast brines show evidence of a greater fissiogenic component which indicates that the brines have resided in formations with locally high u concentrations

evidence for large scale vertical migration of dissolved fatty acids in louisiana oil field brines iberia field south central louisiana abstract abstract there is considerable interest at the present time in the origin and distribution of dissolved volatile fatty acids vfas in oil field brines this interest has developed as a result of the recognition of the role these compounds may play 1 in subsurface acid attack and porosity enhancement 2 as precursors of natural gas and 3 as possible proximity indicators of hydrocarbon accumulations the detailed study of the distribution of dissolved vfas on a field scale provides much useful information on processes of generation transport and degradation of these compounds at the iberia oil field one of several fields we have studied in the tertiary section of south central louisiana spatial variations in pore water compositions and temperatures indicate the presence of an on going dynamic subsurface circulation system deep brines with vfa levels in excess of 150 mg 1 are migrating up the south flank of the iberia salt dome a vertical distance of at least 2 km 6000 ft the vfas in these waters are dominated by acetate and propionate as these waters ascend they mix with an ambient mass of water having total vfa concentrations of 20 mg 1 or less and dominated by n butyrate preferential decarboxylations of acetate and propionate relative to iso and n butyrate and iso and n valerate are occurring in this system the byproducts of these decarboxylation reactions should be methane ethane and bicarbonate temperatures are cool enough 80 c in the shallower parts of the sequence to permit the existence of bacteria that coud break down acetate through fermentation the spatial distribution of individual dissolved vfa s is complex but systematic and must ultimately be related to the rates of advective transport dispersive mixing and chemical reaction we believe that a potential new application of the study of these dissolved organic compounds lies in helping to unravel the dynamics of some types of subsurface flow systems

the copper bearing basic rocks of namaqualand south africa copper mineralisation is associated with rocks of basic intermediate composition which occur as a widespread swarm of relatively small irregularly shaped bodies within the gneissic terrain of the okiep district these basic rocks comprise the so called koperberg noritoid suite of namaqualand and constitute one of the three major copper producers in south africa while a metasomatic origin was briefly favoured for the noritoids most researchers have emphasized the cross cutting nature of the noritoids relative to their host rocks and prefer an origin involving magmatic injection high noritoid 87sr 86sr initial ratio values indicated to some workers that mobilisation of suitable crustal materials was more attractive than intrusion of mantle derived melts to account for the origin of the noritoid suite the present study has shown that the structure texture and mineralogy of the noritoids do not lend themselves to interpretation of the noritoids as pristine intrusive rocks and indicate that the noritoids have undergone high grade metamorphism after emplacement the geochemistry of the noritoid suite reveals a pronounced alkaline affinity and mineralogical control of the chemistry characterises the rocks as cumulates the dimensions of the noritoids appear unfavourable for development of cumulate rocks and it is considered possible that the present configuration of the noritoids results from dismemberment of larger intrusive bodies as a result of shear deformation during high grade metamorphism it has not been possible to identify a magma parent to the noritoid suite but we believe the parent to have been an alkaline mantle derived magma which suffered contamination by granitic anatects in the lower crust recognition of the metamorphic history of the namaqualand noritoids renders a comparison between them and the caraiba noritoids of interest

rise and demise of the bahama grand banks gigaplatform northern margin of the jurassic proto atlantic seaway abstract an extinct 5000 km long jurassic carbonate platform and barrier reef system lies buried beneath the atlantic continental shelf and slope of the united states a revised stratigraphic framework a series of regional isopach maps and paleogeographic reconstructions are used to illustrate the 42 m y history of this bahama grand banks gigaplatform from its inception in aalenian early middle jurassic time to its demise and burial in berriasian valanginian time early early cretaceous aggradation progradation rates for the gigaplatform are comparable to those of the familiar capitan shelf margin permian and are closely correlated with volumetric rates of siliciclastic sediment accumulation and depocenter migration siliciclastic encroachment behind the carbonate tracts appears to have been an important impetus for shelf edge progradation during the early cretaceous sea level changes combined with eutrophication due to landward soil development and seaward upwelling and the presence of cooler upwelled waters along the outer shelf appear to have decimated the carbonate producers from the carolina trough to the grand banks this allowed advancing siliciclastic deltas to overrun the shelf edge despite a notable reduction in siliciclastic accumulation rates however upwelling did not extend southward to the blake bahama megabank so platform carbonate production proceeded there well into the cretaceous subsequent stepwise carbonate abatement characterized the blake plateau basin whereas the bahamas have maintained production to the present the demise of carbonate production on the northern segments of the gigaplatform helped to escalate deep water carbonate deposition in the early cretaceous but the sudden augmentation of deep water carbonate reservoirs in the late jurassic was triggered by other agents such as global expansion of nannoplankton communities

stable isotopic evidence for crustal contamination and desulfidation of the cupriferous koperberg suite namaqualand south africa abstract the middle proterozoic koperberg suite occurs as a swarm of differentiated mafic dikes in a granulite facies terrane in the northwestern cape province of south africa rock types include pyroxenite norite anorthosite diorite and glimmerite and host an important repository of copper ore this paper reports petrographic and stable isotope data that places new constraints on the magmatic and metamorphic evolution of the koperberg suite and associated copper mineralization oxygen isotope ratios of the basic bodies are significantly enriched in 18 o 18 o plag 6 2 to 9 6 18 o opx 6 2 to 7 4 and 18 o rock 5 9 to 8 3 relative to mantle derived basic rocks this enrichment appears to be the result of crustal contamination granite gneiss country rocks exhibit 18 o values in the range from 7 8 8 7 the systematics of oxygen isotope data for coexisting minerals suggest that in addition to crustal contamination further modification took place due to low temperature post peak metamorphic exchange involving circulating fluids that had undergone isotopic exchange with the surrounding gneisses these fluids are probably related to the upper greenschist grade metamorphism associated with the regional pan african orogeny 500 550 ma this is indicated by the lack of temperature concordancy based on 18 o values of several mineral pairs involving orthopyroxene plagioclase biotite and magnetite sulfur isotope ratios from diorite and norite hosted sulfides are light relative to mantle values and co genetic mineral pairs show a lack of temperature concordancy the ranges in 34 s values for the sulfides are 34 s cpy 1 5 to 3 8 0 34 ss bo 1 9 to 4 1 0 and 34 s po 1 9 to 2 5 0 bulk ore samples show a systematic decrease in 34 s values with increasing cu s ratios this is seen as being diagnostic for an oxidation process and the degassing of a so 2 rich vapour phase petrographic observations and mineral chemistry data support this conclusion and indicate that the devolatilization event was caused by granulite facies metamorphism followed by a later lower temperature alteration event in our genetic model we envisage a mantle origin for the koperberg suite the original magma was modified through assimilation and fractional crystallization processes later modification occurred at the level of emplacement through differentiation and metamorphism crustal contamination can explain the origin of the enriched o isotope values the high levels of incompatible trace elements as well as the high initial 87 sr 86 sr ratios in the basic bodies

tundra environments in the neogene sirius group antarctica evidence from the geological record and coupled atmosphere vegetation models the neogene meyer desert formation sirius group at oliver bluffs in the transantarctic mountains contains a sequence of glacial deposits formed under a wet based glacial regime within this sequence fluvial deposits have yielded fossil plants that along with evidence from fossil insects invertebrates and palaeosols indicate the existence of tundra conditions at 85 s during the neogene mean annual temperatures of c 12 c are estimated with short summer seasons with temperatures up to 5 c the current published date for this formation is pliocene although this is hotly debated reconstructions produced by the triffid and biome 4 vegetation models utilizing a pliocene climatology derived from the hadam3 general circulation model running with prescribed boundary conditions from the us geological survey prism2 dataset also predict tundra type vegetation in antarctica the consistency of the model outputs with geological evidence demonstrates that a pliocene age for the meyer desert formation is consistent with proxy environmental reconstructions and numerical model reconstructions for the mid pliocene if so the east antarctic ice sheet has behaved in a dynamic manner in the recent geological past

the geochemistry and petrogenetic relationships of two granites and their inclusions in the keimoes suite of the namaqua mobile belt south africa abstract the colston and straussburg plutons consist of two dissimilar granites belonging to the proterozoic 1100 1200 ma keimoes suite along the eastern margin of the namaqua mobile belt the intrusives and their enclaves were investigated to establish their genetic relationships the peraluminous colston granite exhibits s type characteristics while the strausaburg intrusive shows marked similarity with i type granites one set of quartz rich melanocratic inclusions are present in the colston granite the corresponding melanocratic enclaves in the straussburg pluton are comprised of a porphyritic type and a non porphyritic type while leucocratic inclusions are also abundant field relationships mineralogical and chemical compositions as well as ree patterns point to a strong genetic relationship between the granites and their enclaves genetic models involving fractional crystallization wall rock assimilation two magma mixing and minimum melt restite mobilisation were considered to explain the nature and origin of the inclusions and the host granites and the observed ree characteristics make most of the models unlikely it is concluded that the quartz rich melanocratic inclusions in both plutons formed as products of partial batch melting from a common source possibly a basic or intermediate gneiss or granulite under relatively high xco 2 conditions after the intrusion and consolidation of the first melts water undersaturated granitic magmas intruded as a secondstage incorporating the first melt products as melanocratic inclusions the different crystallization conditions of the melanocratic inclusions and the host granites are highlighted by the difference in chemical composition of the biotites as for instance illustrated in ti al diagrams the biotite is accompanied by hornblende in all the rock types with the exception of the colston granite and the leucocratic inclusions of the straussburg granite the leucocratic enclaves in the straussburg granite are interpreted as depleted restite material which formed at a pressure near 5 kbar and which was transported to the surface by the granite magma when the compositions of the granitic rocks are compared with the experimental results for the haplogranitic ab or an q system they prove to be quite near the expected minimum melt compositions for a total pressure of 5 kbar

u series and amino acid racemization geochronology of bermuda implications for eustatic sea level fluctuation over the past 250 000 years abstract bermuda is a stable mid oceanic carbonate platform for which a particularly complete record of late pleistocene eustatic sea level fluctuation has been reconstructed from a detailed study of geological field relationships combined with an extensive programme of u series and amino acid racemization geochronology only twice in the past 250 000 yr has sea level in bermuda been above its present level once at approximately 200 k y when it stood at about 2 m and most recently at 125 4 k y when it stood at 5 1 m these times of interglacial high sea level are characterized by the development of patch reefs and marine calcarenites at elevations above present sea level episodes of lower sea stand onto the bermuda platform at elevations higher than 20 m are observed within the two interglacial periods and are characterized by the deposition of eolianites by contrast glacial periods are times of residual soil formation and deposition of speleothems in caves at elevations below present sea level excellent correlation is observed between the bermuda glacio eustatic sea level record and other marine and terrestrial paleoclimate records

identification of organic rich lower tertiary shales as petroleum source rocks south louisiana abstract comprehensive organic geochemical evidence of organic rich marine shales in the lower part of the middle eocene claiborne group and the lower eocene paleocene wilcox group of south louisiana is now available that influences models for gulf coast petroleum origin the shales are the only post cretaceous age sediments in the northern gulf of mexico that meet recognized criteria for oil source rocks many organic rich paleogene shales contain terrestrially derived amorphous kerogen altered by microbial activity and display pyrolysis results consistent with type ii iii kerogen shelf edge depositional environments favor preservation of hydrogen rich kerogen seismic and sedimentologic interpretations suggest that marine character and thickness increase on the paleogene continental slope to the south the shales at burial depths in the 3050 4600 m depth range are at present thermally immature to late mature with respect to oil generation detailed geochemical analysis of extractable organic matter and kerogen isolates suggest an oil source correlation with tertiary reservoired oils in south louisiana and offshore in the adjacent gulf of mexico biomarkers of selected samples display high concentrations of c28 bisnorhopane and 18 oleanane that are also found in tertiary reservoired oils the key 18 oleanane biomarker is absent or not reported in gulf crude oils from cretaceous and jurassic source rocks burial and thermal history models suggest the timing of oil migration from paleogene source rocks is consistent with emplacement of oils in tertiary reservoirs the lower tertiary source rocks described here could offer new insight to understanding the origin of oil in other tertiary deltas

geochemistry and petrogenesis of the laramie anorthosite complex wyoming abstract a geochemical investigation of the laramie anorthosite complex determined that monsonite associated with the complex are characterized by positive eu anomalies and display a regular variation in composition with distance from the monzonite county rock contact anorthositic rocks have major and trace element abundance typical of similar complexes the internal variations in the monzonite were produced by in situ fractionation and contamination the data indicate that anorthosite and monzonite cannot be comagmatic it is proposed that the anorthosite and monzonite of the complex evolved from two distinct magmas and that two stages of anatectic melting contributed to the evolution of the monzonite an initial stage of partial melting was induced by intrusion of a gabbroic anorthosite magma into the lower crust a second partial melting event occurred after emplacement where heat from the intrusions melted country rocks resulting in extensive contamination ofthe monzonite

origin of hydrocarbons in the green tuff region of japan 129i results from oil field brines and hot springs in the akita and niigata basins abstract the akita and niigata basins are part of the green tuff region of honshu japan which hosts major occurrences of oil and gas and of hydrothermal sulfide sulfate kuroko deposits the green tuff formation is associated with the opening of the japan sea which occurred in the early miocene and was accompanied by large scale volcanic activities we measured halogen concentrations and 129i i ratios in oil and gas field brines and hot springs in order to determine the origin of iodine and indirectly of hydrocarbons in this area and their association with geological processes during the formation of the japanese island arc based on the concentration of iodine these samples fall into three categories type a i 190 m type b 150 m i 90 m and type c i

origin and age of pore waters in an actively venting gas hydrate field near sado island japan sea interpretation of halogen and 129i distributions abstract a gas hydrate field with highly active venting of methane was recently found near sado island in the eastern japan sea piston cores were collected from active venting sites and nearby locations in the umitaka spur joetsu knoll area during two cruises in 2004 ut04 and 2005 ky05 08 we report here halogen concentrations and 129 i i ratios in pore waters associated with gas hydrates from these expeditions the strongly biophilic behavior of i and to a lesser degree of br together with the presence of the long lived iodine radioisotope 129 i allow evaluation of potential source materials for methane in gas hydrate systems depth profiles of all three halogens particularly the very rapid downward increases of br and i concentrations strongly suggest input of deep fluids enriched in br and i but the profiles also display the effects of gas hydrate formation and dissociation although the 129 i i ratios are modified by 129 i from seawater and sediments at shallow depth likely ratios of the deep fluids are estimated to be between 400 10 15 and 600 10 15 equivalent to a late oligocene to early miocene age ages in the active methane venting sites typically are closer to the old end of this range than those in the reference sites this age range suggests that the methane associated with venting and gas hydrate formation in this area is derived from organic materials accumulated during the initial opening of the japan sea the umitaka spur joetsu knoll gas hydrate field demonstrates the movement of deep fluids associated with the release of significant amounts of methane from the seafloor processes which might be important components of mass transfer and carbon cycle in the shallow geosphere

the record of major quaternary sea level changes in a large coastal plain estuary chesapeake bay eastern united states abstract seismic reflection surveys of the chesapeake bay combined with geologic mapping and analysis of boreholes on the delmarva peninsula provide evidence of at least three generations of the susquehanna river system and three generations of the chesapeake bay the evidence for ancient courses of the susquehanna river is preserved as three distinct paleochannels and evidence for ancient versions of the chesapeake bay is preserved as three sets of paleochannel fill beneath the bay and three generations of barrier spit deposits on the southern delmarva peninsula the paleochannels represent relative sea level minima and the channel fill and barrier spit deposits represents relative sea level maxima a history of three major marine transgressions is recorded in the stratigraphy preserved in the filled paleochannels and in the overlying barrier spit complexes three systematic progressions from fluvial to estuarine to bay or nearshore marine environments this sea level record seems to be compatible with the saw toothed pattern of the marine oxygen isotope record and with the concept of glacial interglacial terminations it also seems to have a climax character in which most of the preserved evidence is related to the largest terminations and to the extreme sea level positions that bound those terminations the three paleochannel fill and barrier spit complexes appear to correspond to oxygen isotope stages 1 5 and either 7 or 11 the three related paleochannels correspond to stages 2 6 and either 8 or 12

chemical osmosis reverse chemical osmosis and the origin of subsurface brines abstract calculations using recently tabulated values of density and osmotic coefficient for nacl h2o indicate that overpressuring is more than adequate to overcome chemical osmosis and drive reverse chemical osmosis in sedimentary sequences the best demonstrated overpressuring mechanism is the rapid deposition of fine grained sediments the dehydration of gypsum contributes to overpressuring for brief time intervals at shallow depths whereas water evolved during the protracted conversion of smectite to illite is probably a subordinate but continuing contributor to overpressuring at greater depth occurrences of overpressuring in sedimentary sections older than cretaceous indicate that post depositional mechanisms such as tectonic compression and aquathermal pressuring must also operate the latter may be of major importance in geothermal areas with adequate low permeability seals and a nontrivial contributor in areas of normal geothermal gradient because of shales that sharply decrease normal fluid flow the strongest arguments for the importance to present day brine compositions of membrane concentration of sea water solutes are 1 1 the correlation of d values of water molecules of pore fluid with those of local meteoric water 2 2 the need for major sources of mg2 and cl in apparently evaporite free basins even where dissolution of halite is a major contributor of solute reverse chemical osmosis still operates to leak relatively dilute water of the associated diagenetic chemical reactions that of mg2 with limestone to form dolomite is particularly effective in generating concentrated cl brines rich in ca2 it decreases the concentration of mg2 increases that of ca2 and decreases those of both so42 and co32 by precipitating caco3 and caso4 because of the ca2 common ion effect

a new chronology for the age of appalachian erosional surfaces determined by cosmogenic nuclides in cave sediments the relative chronology of landscape evolution across the unglaciated appalachian plateaus of kentucky and tennessee is well documented for more than a century geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide valley straths and smaller terraces constraining the timing of river incision into the appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials today burial dating using the differential decay of cosmogenic 26al and 10be in clastic cave sediments reveals more than five million years of landscape evolution preserved underground multilevel caves linked hydrologically to the incision history of the cumberland river contain in situ sediments equivalent to fluvial deposits found scattered across the eastern highland rim erosional surface cave sediments correlate with 1 thick lafayette type gravels on the eastern highland rim deposited between c 5 7 and c 3 5 ma 2 initial incision of the cumberland river into the eastern highland rim after c 3 5 ma 3 formation of the parker strath between c 3 5 ma and c 2 0 ma 4 incision into the parker strath at c 2 ma 5 formation of a major terrace between c 2 0 ma and c 1 5 ma 6 shorter cycles of accelerated incision and base level stability beginning at c 1 5 ma and 7 regional aggradation at c 0 85 ma initial incision into the appalachian uplands is interpreted as a response to eustasy at 3 2 3 1 ma incision of the parker strath is interpreted as a response to eustasy at 2 5 2 4 ma a third incision event at c 1 5 ma corresponds with glacial reorganization of the ohio river basin widespread aggradation of cave passages at c 0 85 ma is interpreted as the beginning of intense glacial interglacial cycling associated with global climate change copyright 2006 john wiley sons ltd