stable isotope geochemistry of crude oils and of possible source rocks from new zealand 2 sulfur abstract the sulfur isotopic composition of new zealand low s crude oils and components asphaltenes absorptive filtration fractions and source rock components extracted hydrocarbons kerogen pyrite sulfates were determined oils from the taranaki basin have 34s values from 3 to 14 o the lower values possibly represent plant assimilation of fresh water sulphate higher values particularly those from the west coast basin around 20 suggest closed ocean basin conditions or fast sedimentation rate whereas negative 34s values from east coast basin suggest open ocean or low sedimentation rate conditions it is suggested than an oil source rock relation should show as a similarity in 34s values for total oil and source rock extract kerogen and pyrite shale samples analysed plot outside the corresponding oil range and cannot be considered as possible source rocks however coal samples from the maui 4 well and nelson outcrops show strong isotopic correlations with the taranaki oils

evidence for bacterial degradation of hydrocarbons in uranium deposits the biodegradation of free hydrocarbons migrated in reservoir faaes has often been observed in petroleum exploration this bacterial alteration is characterized by the progressive removal of different classes of hydrocarbons one of the most important consequences of biodegradation is the reduction of sulphate as noted in several pb zn deposits biodegradation of oils spatially associated with uranium deposits has also been observed in lodeve france grand canyon arizona usa temple mountain utah usa and leads to the transformation of fluid oils into solid bitumens within this study emphasis has been laid on the relationships between the effects of biodegradation on organic matter oxidation or aromatization and the nature of aqueous solutions analysed in fluid inclusions trapped in authigenic minerals different mechanisms are proposed to explain the transformations of organic matter during biodegradation and their possible links with ore forming processes

physically based modeling of bedrock incision by abrasion plucking and macroabrasion 1 many important insights into the dynamic coupling among climate erosion and tectonics in mountain areas have derived from several numerical models of the past few decades which include descriptions of bedrock incision however many questions regarding incision processes and morphology of bedrock streams still remain unanswered a more mechanistically based incision model is needed as a component to study landscape evolution major bedrock incision processes include among other mechanisms abrasion by bed load plucking and macroabrasion a process of fracturing of the bedrock into pluckable sizes mediated by particle impacts the purpose of this paper is to develop a physically based model of bedrock incision that includes all three processes mentioned above to build the model we start by developing a theory of abrasion plucking and macroabrasion mechanisms we then incorporate hydrology the evaluation of boundary shear stress capacity transport an entrainment relation for pluckable particles a routing model linking in stream sediment and hillslopes a formulation for alluvial channel coverage a channel width relation hack s law and exner equation into the model so that we can simulate the evolution of bedrock channels the model successfully simulates various features of bed elevation profiles of natural bedrock rivers under a variety of input or boundary conditions the results also illustrate that knickpoints found in bedrock rivers may be autogenic in addition to being driven by base level fall and lithologic changes this supports the concept that bedrock incision by knickpoint migration may be an integral part of normal incision processes the model is expected to improve the current understanding of the linkage among physically meaningful input parameters the physics of incision process and morphological changes in bedrock streams

variscan and post variscan lead zinc mineralization rhenish massif germany evidence for sulfide precipitation via thermochemical sulfate reduction a mechanical decrepitation device coupled with a gas chromatograph has been used to characterize the molecular composition of gaseous and liquid hydrocarbons contained in minerals application of this technique allows the identification of low molecular weight n alkanes and some aromatic hydrocarbons in sulfides and gangue minerals from epigenetic variscan and post variscan lead zinc deposits in the rhenish massif germany based on the analysis of 200 samples variscan and post variscan mineralization can be distinguished by the composition of associated hydrocarbons variscan sulfides and gangue minerals contain high abundancies of methane in contrast n alkanes in the c2 c9 range and aromatic hydrocarbons benzene toluene are dominant in post variscan mineralization the absence of high molecular weight hydrocarbons in ore minerals suggests highly mature gas associated with hydrothermal activity during which hydrothermal fluids caused an increase in thermal maturation of organic matter and the generation of low molecular weight hydrocarbons in the adjacent organic rich rocks the hydrocarbon compositions contained in fluid inclusions of variscan and post variscan minerals are probably governed by the maturation level of the potential source rocks in variscan time tectonic brines t 175 c generated predominantly methane whereas basement brines t 175 c expelled higher molecular weight hydrocarbons wet gases condensates aromatic hydrocarbons from adjacent rocks during the mesozoic event the specific role of hydrocarbons in sulfide precipitation via thermochemical sulfate reduction is indicated by geochemical characteristics of organic matter associated with the plombieres pb zn deposit in eastern belgium intense alteration phenomena were observed in near ore kerogens compared with unaltered kerogens far from the ore body as well as by a very high maturity 5 40 ro a systematic depletion in 12c towards the vein type mineralization high atomic s c ratios 0 49 and by low atomic h c ratios 0 29 the data suggest that hydrothermal solutions caused a drastic increase in the thermal maturation of organic matter within the adjacent wall rock increased thermal maturation resulted in increased 13c values of organic carbon due to the preferential release of 12c the change in the organic matter to a h depleted and s enriched bulk composition in association with sulfide ores strongly suggests that thermochemical sulfate reduction was responsible for organic degradation thus thermochemical sulfate reduction probably triggered base metal sulfide precipitation in variscan and post variscan ore deposits of the rhenish massif finally based on data from this study and previous investigations new genetic models are presented for both variscan and post variscan mineralization in the rhenish massif

chronology of pleistocene glacial advances in the central rocky mountains the distribution and ages of moraines in the wyoming type localities for pre pinedale rocky mountain glacial deposits are not well known through morphostratigraphic mapping river terrace longitudinal profile analysis and tephrochronology we place the age of sacagawea ridge moraines in the dinwoody lakes type area at about 660 ka outwash and river terrace deposits in the bull lake type area previously considered to be sacagawea ridge are actually older by one or two glacial cycles in the bull lake type locality 15 individual moraines are divided into 4 groups on the basis of relative age criteria using 36cl 10be cosmogenic dating of boulders the two older groups must be 130 ka the younger groups are given age ranges of 130 to 100 ka and 120 to 95 ka a terrace along wind river can be morphostratigraphically traced to the youngest of these moraine groups 36cl dating of boulders on the terrace provides an age range of 125 to 100 ka the combined relative age and cosmogenic nuclide chronology is consistent with previously published evidence from yellowstone national park demonstrating that mountain glaciers advanced not only prior to and during the later portion of marine isotope stage 6 but also during marine isotope stage 5d in contrast with some other areas of the rocky mountains we found no evidence for advances during marine isotope stage 4 at bull lake pinedale moraines that have a 36cl 10be age range of 23 to 16 ka suggest that glacial advances were limited to the later part of marine isotope stage 2 a river terrace that can be traced to these moraines has an age range of 23 to 16 ka a possible glacial advance during early marine isotope stage 2 is indicated by a river terrace whose age range is estimated by incision rate modeling at 46 to 28 ka but no moraines were identified along wind river there are eight terrace levels capped with outwash that are older than sacagawea ridge although the terraces are the record of early to middle pleistocene climatic cycles there are no correlative moraines preserved at the land surface

rapid formation of river terraces in non welded ignimbrite along the hishida river kyushu japan abstract river terraces are well preserved in the middle to lower reaches of the hishida river that flows through the extensive ignimbrite field produced by the large scale ito eruption about 24 500 years ago from aira caldera in southern kyushu japan the terraces are erosional and formed during dissection of the initial topography of the ito ignimbrite these occur within the upper non welded zone of the ito ignimbrite about 20 60 m below the depositional surface and usually more than 20 m above the welded zone streams associated with terrace formation were ephemeral because perennial streams are considered highly unlikely within the porous non welded ignimbrite all tephra layers on the original ignimbrite depositional surface also cover the terraces this indicates that the formation of terraces preceded the accumulation of the oldest tephra the age of which is about 23 000 years old high erodibility of the non welded ito ignimbrite and absence of vegetation on the initial surface would have permitted a rapid dissection of the initial topography and the formation of the river terraces thus it is interpreted that the river terraces were formed very rapidly in a period of far less than 1500 years immediately after the deposition of the ito ignimbrite and before cover of new vegetation on the depositional surface

relation between the thermal behaviour and the structure of kerogen in the goesan uranium deposit korea abstract the study of kerogens associated with mineralized and non or poorly mineralized samples shows that 1 1 the organic matter reached a high rank of evolution namely pre graphitic to graphitic 2 2 kerogens of mineralized samples differ from those of non mineralized samples by their behaviour under pyrolysis conditions the kerogens associated with mineralized samples display a higher pyrolysable and oxidizable fraction under the conditions of measurement of the organic carbon content in the rock eval ii pyrolyser i e by heating up to 600 c than kerogens associated with non or poorly mineralized samples 3 3 under transmission electron microscopy all kerogens appear to be highly coalified they are all made of a mixture of partially graphitized shell like sub concentric particles semi graphites and lamellae of graphite samples from mineralized areas u 100 ppm contain relatively more and smaller shelly particles than samples from poorly mineralized zones p in conclusion the thermal behaviour of kerogen particles up to the maximum temperature 600 c of rock eval ii pyrolysis could discriminate particles associated with uranium whose crystallinity would be less perfect than that of particles of high crystallinity found in uranium poor samples

association of pyrobitumen with copper mineralization from the uchumi and talcuna districts central chile abstract pyrobitumen has been shown to be an essential component in formation of some chilean manto type strata bound copper deposits and its presence has been observed in a number of other deposits but has received limited investigation in this paper we present paragenetic and geochemical data from two central chilean manto type deposits from the uchumi and talcuna districts where solid pyrobitumen residual petroleum is intimately associated with copper sulfides pyrobitumen in the uchumi deposit occurs in pore space within the host conglomerates and is adjacent to a granitoid stock pyrobitumen predates bornite chalcocite mineralization and may have reduced subsequent mineralizing fluids pyrobitumen from the manto delirio deposit talcuna district fills the cores of early sphalerite veins and was partially replaced by later cu as mineralization pyrobitumen is petrographically intergrown with cu fe sulfides and light 13c values of gangue calcite indicates the interaction of pyrobitumen with the mineralizing fluid the presence of pyrobitumen within the ores of other manto type copper deposits in the lower cretaceous basin of chile suggests that degraded petroleum reservoirs in particular if biodegradation generated authigenic pyrite can be important controls for metallic mineralization derived from hydrothermal solutions of different sources

sulfidation of organic matter associated with gold mineralization pueblo viejo dominican republic the pueblo viejo district is one of the largest producers of precious metals in the world yielding more than 11 000 kg of au annually gold mineralization at pueblo viejo is hosted in spilite and coarse elastic and finely laminated fine grained carbonaceous sedimentary rocks of the lower cretaceous los ranchos formation mineralization was accompanied by sulfidation as evidenced by i the occurrence of siderite distal to mineralization and pyrite proximal to mineralization 2 increased s fe ratios associated with au mineralization 3 the occurrence of native s in and adjacent to mineralization and 4 the presence of sulfidized organic matter organo s compounds in mineralized rocks organic matter in the carbonaceous sedimentary rocks comprises vitrinite and pyrobitumen rock eval pyrolysis data indicate that this organic matter is overmature hi 55 the organic matter is s rich up to 14 wt s in rocks where all fe has been sulfidized to pyrite x ray absorption near edge structure xanes analysis indicates that the c bonded s is thiophenic early disseminated au mineralization is postulated to have occurred in response to sulfidation of ferrous fe to form pyrite the consequent decline in the activity of h2s in the mineralizing fluid would have destabilized au bisulfide complexes and caused deposition of gold the restriction of s rich organic matter to rocks in which all fe occurs as pyrite indicates that sulfidation of organic matter postdates sulfidation of ferrous fe and therefore deposition of much of the au

geochemical and carbon isotopic studies of crude oil destruction bitumen precipitation and sulfate reduction in the deep smackover formation abstract crude oil generated by the lower smackover source facies migrated to upper smackover reservoirs where slow thermal cracking of crude oil resulted in the formation of gas condensate and late solid bitumen ultimately only pyrobitumen methane and nonhydrocarbon gases including hydrogen sulfide persist in the deepest smackover reservoirs the carbon isotopic compositions of crude oils became heavier during crude oil destruction the carbon isotopic compositions of asphaltenes nso compounds and saturated hydrocarbons in late solid bitumen and the lower smackover source facies became isotopically lighter during crude oil destruction it is suggested that some isotopically light components from crude oils were incorporated in late solid bitumen by reactions involving thermochemical sulfate reduction thermochemical sulfate reduction and crude oil destruction occurred over a long span of geologic time at temperatures in the 120 150 c range

natural and human induced landsliding in the garhwal himalaya of northern india after the march 28 1999 garhwal earthquake 338 active landslides including 56 earthquake induced landslides were mapped in a 226 km 2 study area in the garhwal himalaya northern india these landslides mainly comprised shallow failures in regolith and highly weathered bedrock involving avalanches slides and flows the total volume of active 33 landslide debris in the region was estimated to be 1 3 million m including 0 02 million m 2 of the total volume moved during and within a few days of the earthquake the denudation produced by the active landsliding within the study area is equivalent to a maximum landscape lowering of 5 7 mm if active landsliding persists for a duration of between 1 and 10 years then denudation due to landsliding is in the order of 0 6 6 mm a y1 approximately two thirds of the landslides in this region were initiated or accelerated by human activity mostly by the removal of slope toes at road cuts suggesting that human activity is accelerating denudation in this region three ancient catastrophic landslides each involving 1 million m 3 of debris were identified and two were dated to the early middle holocene using cosmogenic radionuclide 10 be and 26 al cosmogenic radionuclide 10 be and 26 al were also used to date strath terraces along the alaknanda river in lower garhwal himalaya to provide an estimate of 4m m a y1 for the rate of regional denudation throughout the holocene natural landsliding therefore contributes 5 50 of the overall denudation in this region and is important as a formative process in shaping the landscape q 2001 elsevier science b v all rights reserved

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

cordilleran metamorphic core complexes in arizona a contribution from geomorphology cordilleran metamorphic core complexes consist of granitic cores surrounded by in an outward direction mylonite chloritic breccia and microbreccia these rocks are separated by a low angle detachment fault from typically unmetamorphosed but normally faulted rocks rocks above the detachment fault have been transported relative to the core rocks in one consistent direction giving a distinct lineation to rocks below the detachment fault dome shaped metamorphic core complex mountains show considerable structural control of landforms mylonitic rocks develop triangular dome facets around the margins and low relief areas in the central parts of the complexes chloritic breccia is much less resistant to erosion and has been almost completely removed from many complexes drainage patterns in metamorphic core complexes are mainly radial but an older set of drainage lines parallel to mylonitic lineation especially channels that drain down the crests of antiformal ridges suggests that drainage developed on a ramp on the detachment fault and the underlying breccia prior to lineation parallel arching

organic geochemistry of the san vicente zinc lead district eastern pucara basin peru abstract isotopic and chemical studies of organic matter of the san vicente mississippi valley type zn pb district hosted in the dolomitic units of the eastern pucara basin peru provide insight into the source of organic matter and of the organic matter ore relationship a large scatter exists in the 13c and 15n values of the highly mature kerogens these bulk data were combined with 13c covariations of the saturated and aromatic fractions of the rock extracts to indicate a contribution of continental higher plant lipids to the marine algal source of the organic matter disseminated in the host carbonate rocks an enrichment in 15n of the kerogens of mineralized samples compared to barren samples suggests that isotopically heavy nitrogen compounds were introduced to the ore fluid the fluid likely leached these compounds from the underlying clastic rocks and other detrital units of the pucara the extracts from mineralized samples are enriched in 13c compared to the associated kerogens this suggests that the rocks in the mineralized areas were stained by a mixture of extrinsic and indigenous bitumens by the use of novel instrumentation such as a gas chromatograph gc coupled to a stable isotope ratio mass spectrometer irms through a combustion c interface gc c irms stable carbon isotope analyses of individual hydrocarbons were also obtained both the molecular and isotopic signatures of the individual hydrocarbons are related to mineralization the variability in the organic molecular parameters and the 13c values of the individual n alkanes and isoprenoids indicate mixing of indigenous hydrocarbons with extrinsic 13c depleted microbially derived hydrocarbons the extrinsic source hydrocarbons were introduced to the mineralization site by the ore fluid or later fluids using the same porosity network oxidative alteration of the migrating hydrocarbons was involved in the thermochemical reduction of sulfate to h2s and precipitation of pyrobitumen large differences 12 in the carbon isotope compositions of long chain c20 n alkanes can be utilized in distinguishing sources of organics in the barren and mineralized samples

manetoe facies a gas bearing megacrystalline devonian dolomite yukon and northwest territories canada the manetoe facies is a broadly stratiform and regionally developed 38 000 km2 or 15 000 mi2 body of white sparry dolomite hosted in lower and middle devonian strata and is the northwestward continuation of the similar but better known presqu ile facies dolomite several large gas fields have been discovered within anomalously thick developments of the manetoe dolomite close to the northwest limit of the devonian elk point basin of alberta the external geometry of the manetoe facies indicates that it may have been a cavern or karst system excavated in the late middle devonian by a large vertically confined coastal aquifer the local regions of anomalously thick manetoe facies may have developed where the aquifer stoped upward into strata above the confining aquiclude of the headless formation shale dolomite cementation may have occurred during any of three possible episodes of large scale fluid movement fluid inclusion and strontium isotope data favor the hypothesis that manetoe dolomites precipitated from heated 150 210 c or 300 410 f hypersaline evaporitic brines that have interacted with the underlying precambrian crust probably in the late devonian lead isotope data support the general concept of pre mesozoic dolomite cementation and largely preclude a late early tertiary deep burial setting spectacular zones of detrital dolomite cement within the manetoe are most readily accommodated by a near surface very early middle devonian aquifer mixing model origin but the presence of these zones does not preclude the other possible origins carbon and xygen isotope data from the manetoe facies support the concept that the presqu ile and manetoe facies are physically continuous and had a common origin

stream incision and terrace development in frijoles canyon bandelier national monument new mexico and the influence of lithology and climate abstract the record of stream incision and terrace development in frijoles canyon nm was investigated to examine the controls on channel evolution in this region frijoles canyon developed after deposition of the voluminous ignimbrites of the tshirege member of the bandelier tuff at ca 1 22 ma which provides excellent temporal constraints on canyon evolution base level fall along the rio grande the master drainage in the region contributed to initial incision of the stream development of a major knickpoint in basalt near the rio grande however has effectively isolated most of the stream channel from direct effects of this base level change since the early or middle pleistocene late quaternary evolution of the channel has included development of strath and fill terraces that record the effects of climatic variations and local lithologic variations within the tuff on channel processes a fill terrace underlain by up to 13 m of coarse gravelly alluvium records significant aggradation in the early to middle holocene following a major regional climate change aggradation probably resulted from large increases in sediment supply in the holocene relative to the late pleistocene which was perhaps related to variations in intense summer rains rapid incision in the middle to late holocene has stranded the underlying strath up to 21 m above the modern channel and local rates of incision of up to 4 m ka are more than 10 times the average rates since 1 22 ma holocene incision displays great spatial variability associated with local lithologic variations and results in a stream profile that has evolved rapidly in the last 10 000 years the high rates of incision occur where easily eroded nonwelded tuff is exposed in the canyon bottom whereas a more resistant vapor phase altered tuff unit upstream has impeded incision incision may also have been affected by migration of knickpoints within the tuff paired strath terraces record periods of local base level stability and lateral erosion that were terminated by episodes of downcutting the downcutting was probably controlled by rare high magnitude floods capable of stripping the pervasive gravel armor and exposing nonwelded tuff beneath the stream bed no tectonic influence on late quaternary terrace development or stream incision has been recognized despite frijoles canyon being crossed by the pajarito fault zone a major bounding structure of the rio grande rift instead climatic influences on sediment supply and flood characteristics mediated by lithologic variations in the canyon bottom have controlled late quaternary stream profile evolution

role of organics and methane in sulfide ore formation exemplified by kupferschiefer cu ag deposits poland abstract organic material has been involved in the formation of the kupferschiefer cu ag sulfide deposits in poland in several different ways and at several stages in their development during sedimentation a mixture of continental humic material and marine algal material was concentrated in the euxinic peri marine kupferschiefer black shale environment 6 c org having the black shale directly on the continental redbeds below effected a strong redox gradient across which the ore is located early diagenetic pyrite marcasite framboids and nodules were formed through bacteriogenic reduction of sulfate from seawater derived pore waters metal zones and variations in organic composition indicate that upwelling oxidized ore fluids were reduced by organic material and fe sulfides in the shale inducing the precipitation of cu sulfides a network of natural hydrofractures formed by generation of hydrocarbon related gases in the shale allowed the ore fluids to penetrate the otherwise impermeable caprock and concentrate sulfides natural gases also migrated up from carboniferous coal source beds and accumulated in the c org free eolian sandstone below the kupferschiefer shale geologic and cathode luminescence evidence indicates that the ch 4 reacted with anhydrite cement to form distinctive calcite cements and h 2 s which precipitated cu sulfide cements although 13 c and 34 s values are inconclusive quartz replacement concomitant with sulfide formation in the kupferschiefer and proterozoic nonesuch ores michigan u s a and in athabasca oil sands canada provides field support that silica organic complexing is a mechanism that accelerates dissolution and increases solubility of quartz at low temperature and neutral ph

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

thermal history of alberta deep basin comparative study of fluid inclusion and vitrinite reflectance data the thermal history of the alberta deep basin the gas saturated westernmost part of the western canadian sedimentary basin has been studied by analyzing aqueous and hydrocarbon fluid inclusions in diagenetic cements and comparing the results with coal maturity data results indicate that most of the diagenetic quartz druse precipitated from low salinity fluids 2 3 wt at a temperature of 170 195 c calcite cement precipitated after quartz druse during uplift and cooling at temperatures of 108 169 c inclusions rich in larger hydrocarbon molecules occur in cements that precipitated at 150 c whereas methane rich inclusions occur in cements that precipitated at 165 c or at lower temperatures after significant uplift and cooling of the b sin maximum burial temperatures tmb calculated from vitrinite reflectance data using the lopatin waples tti ro calibration are significantly lower 150 c than the temperature at which quartz druse precipitated in the same area 190 c an equation directly relating tmb and ro proposed by barker and pawlewicz in 1986 yields maximum burial temperatures 200 210 c only slightly higher than the fluid temperatures the results from this study suggest that hot fluids migrated updip along permeable conglomerates and bedding plane fractures to produce unexpectedly high geothermal gradients 38 c km in the western part of the study area the apparent restriction of hot fluids to the western part of the study area sugge ts that convective heat transfer by fluids may have operated on a scale of only tens of kilometers in lower cretaceous rocks of the alberta deep basin

observations on the role of lithology in strath terrace formation and bedrock channel width field observations from western washington and eastern tibet indicate a strong lithologic influence on strath terrace formation and highlight the response of bedrock channel width to spatial gradients in bedrock erodibility and or rock uplift rates measurements of local bedrock bed and bank erosion rates together with observations of the role of weathering processes on erosion of siltstones and sandstones illustrate a mechanism that underlies a conceptual model that predicts a strong lithological control on strath terrace formation direct measurements of bedrock erosion rates in lithologies susceptible to accelerated erosion upon sub aerial exposure show that lateral rates of bedrock bank erosion can substantially exceed vertical incision below the perennial flow level due to an asymmetry in erodibility between perennially submerged rock and rock exposed to cyclic wetting and drying on bedrock channel walls under such conditions the rapid weathering mediated lowering of bedrock exposed above baseflow promotes development of a beveled bedrock platform that could become a strath terrace upon abandonment in contrast to previous studies channel widths measured across a substantial gradient in lithology slope and long term erosion rates in eastern tibet do not follow conventional relations where channel width scales as a power law function of drainage area instead as they flow across a zone of rapid uplift these channels systematically narrow relative to the predicted width extrapolated from traditional power law relations field studies from a wide range of geological settings and lithologies support the interpretation that in general strath terraces tend to be more extensive in rivers flowing over weak sedimentary rock and tend to be poorly developed and or preserved where rivers flow over hard erosion resistant rock

formation of coarsely crystalline hydrothermal dolomite reservoirs in the presqu ile barrier western canada sedimentary basin late stage coarsely crystalline replacement dolomite and associated saddle dolomite cement form a widespread diagenetic facies in the middle devonian presqu ile barrier that extends southwestward from pine point to the subsurface of the foothills in northeastern british columbia these dolomites create hydrocarbon reservoirs in otherwise tight limestones in the subsurface of the northwest territories and northeastern british columbia and host mississippi valley type deposits at pine point the coarsely crystalline replacement dolomite and saddle dolomite cement are interpreted to have formed during burial because they replace blocky sparry calcite cements occur continuously across the sub watt mountain unconformity postdate stylolites and earlier replacement dolomites and overlap sulfide mineralization the dgr18o values of both replacement and saddle dolomites increase eastward updip along the presqu ile barrier from 16 pmil pdb in the deeper subsurface of northeastern british columbia to 7 pmil pdb at pine point whereas the corresponding homogenization temperatures of saddle dolomite fluid inclusions decrease from 178 to 92 c the 87sr 86sr ratios of coarsely crystalline and saddle dolomites decrease eastward along the pres u ile barrier from about 0 7106 in the subsurface of northeastern british columbia to 0 7081 at pine point these geochemical trends suggest a possible basin scale migration of hot radiogenic dolomitizing fluids updip eastward along the presqu ile barrier such large scale fluid movements probably were related to western canada sedimentary basin tectonic compression and sedimentary loading which occurred at least twice during early burial between the late devonian and early carboniferous and during deep burial between the late jurassic and early tertiary

processus d alteration thermique physico chimique et biologique de constituants organiques et genese d une mineralisation sulfuree le gite zn pb de la florida cantabria espagne the la florida lead zinc deposit cantabria spain which is hosted by urgonian carbonates is located on the border of the basco cantabric lower cretaceous basin the stratiform orebody which is composed of sphalerite galena and barite in iron dolostones occurs in an envelope of dolostone organic matter studies have been carried out on samples from this deposit to understand its genesis and later evolution the results of this work reveal the immatury of the autochthonous organic matter despite a slight paleothermal anomaly centred on the deposit various alteration processes have affected the hydrocarbons associated with autochthonous organic matter and or allochthonous bitumens namely geochromatographic fractionation water washing and biodegradation together with previous geological work the results of this study are consistent with epigenetic and or diagenetic emplacement of the mineralization the proposed genetic scheme involves hydrothermal fluids that would have acquired at least so

thermal comparison of mississippi valley type lead zinc deposits and their host rocks using fluid inclusion and conodont color alteration index data fifteen north american mississippi valley type districts distributed from the arctic archipelago to arkansas and in host rocks ranging in age from late cambrian to early carboniferous were selected for abroad test survey of mississippi valley type district thermal histories for each district in which data were collected histograms of homogenization temperatures for the ore minerals were compared with the temperature range of the corresponding host rocks as indicated by color alteration index cai determinations on conodonts in the host rock carbonates although a special effort was made to collect conodonts from the upper cambrian bonneterre formation host rock to the southeast missouri district all samples were devoid of conodonts thus only 14 districts were used in the final analysis comparison of fluid inclusion homogenization temperatures in main stage ore minerals with color alteration index determined host rock temperatures reveals that a majority of mississippi valley type districts pine point newfoundland zinc mascot jefferson city copper ridge sweetwater central missouri northern arkansas and tri state are representative of group 1 i e they are in thermal equilibrium with their host rocks insofar as could be determined by the color alteration index method ore minerals in group 2 districts upper mississippi valley polaris and central tennessee are significantly hotter than surrounding host rocks and as such define a positive thermal anomaly host rocks to the austinville ivanhoe northern newfoundland and robb lake deposits group 3 revealed the highest color alteration index values of north american mississippi valley type districts with host rock temperatures greatly exceeding ore mineral fluid inclusion temperatures negative thermal anomaly with respect to major tectonic elements of north america group 3 deposits cool ore in hot rocks are positioned within orogenic belts but on the continental side some group 1 deposits ore temperature host rock temperature are well within the continental interior but others are adjacent to orogenic belts on the continental side group 2 deposits hot ore in cool rocks are all within the continental interior current hypotheses regarding the formation of mississippi valley type deposits and simultaneous heating of their host rocks invoke the migration of hot brines set into motion craton ward by the hydraulic gradient produced by orogenic uplift at the craton edge once the ore bearing fluids entered the foreland carbonate platforms they traveled through sedimentary aquifers of the continental interior raising the temperature of the thinly covered carbonate rocks the fluids left as evidence of their passage elevated color alteration index values and group 1 mississippi valley type deposits distributed with decreasing homogenization temperatures away from the orogenic front the correspondence between host rock and ore temperatures suggests that group 1 deposits were deposited essentially within their own aquifers group 2 deposits were formed when the same or genetically similar fluids rose from the regional aquifer s into structurally controlled conduits in the continental interior possibly developed as a result of synorogenic doming and arching this upward channeling of the fluids resulted in rapid and localized fluid flow which precluded or at least inhibited wide spread heating of the host rocks by ore fluids consequently color alteration index values in group 2 districts record only maximum burial depths of the host rocks and bear little relation to temperatures of the ore fluids although the cause of the unusually high color alteration index values 4 5 of group 3 districts is not fully understood it is noted that these districts occur near the extreme outward edge of foreland platforms near or within the leading margins of orogenic belts whether these group 3 host rocks were heated by simple tectonic burial or by passage of heated fluids under shallower conditions is not known

the relationship between bitumens and mineralization in the south pennine orefield central england like many examples of mississippi valley type mineralization the south pennine orefield is well known for the occurrence of hydrocarbons within hydrothermal mineral veins bitumens from this area along with oils from the east midlands have been characterized using standard organic geochemical techniques and compared with potential source rocks lower namurian mudstones from the widmerpool gulf and the gainsborough and goyt troughs were rejected as possible sources for the bitumens and oils on the grounds of lack of sufficient thermal maturity and or essential biomarker correlation lower namurian mudstones with type ii kerogen from the edale gulf are proposed to offer a likely hydrocarbon source for the area with a minor more localized contribution from organic rich type ii mudstone partings within the dinantian limestones simple geochemical models consistent with recent sequence stratigraphic interpretation suggest a late carboniferous age for hydrocarbon generation where geothermal gradients were slightly higher c 50 c km 1 than the present day microthermometric analysis of fluid inclusions from fluorite and calcite allowed three fluid types to be distinguished one na ca cl bearing fluid was discerned to be dominant throughout the orefield being of low temperature uncorrected t h 70 110 c and high salinity c 20equiv wt nacl a second high salinity na ca cl fluid uncorrected t h 70 120 c c 24equiv wt nacl distinguished from the first by varying na ca contents was observed in the westernmost extremities of the orefield a third nacl bearing fluid of higher temperature t h 100 145 c and lower salinity 4 wt nacl was detected in the northernmost part of the orefield hydrocarbon bearing inclusions were not observed in any of the three fluids in this study sulphur isotopic analyses performed on a selection of sulphides sulphates and bitumens to gauge the role of organic matter in sulphate reduction reactions proved inconclusive the mineralization is thought to have occurred as several events that in the north is thought to be derived from the dewatering of the edale gulf towards the end of the carboniferous whilst other mineralization events occurred from the early permian onwards with the ore fluids having more distal sources predominantly from the east with a minor input from the west the main phases of hydrocarbon generation and mineralization appear to be unrelated

preliminary organic geochemical study of an anoxic upper triassic sequence from w hungary abstract the anoxic upper triassic kossen marl was studied with standard organic geochemical techniques leco ir lc gc rock eval pyrolysis and the different forms of sulfur were also analysed the rocks contained an immature sulfur rich type ii kerogen the limy marls contain less pyrite and their kerogen is richer in sulfur than that of the marls the increase in sulfur content of the kerogen is related to the increase in carbon normalized extract content extract composition is partially dependent on lithology the kossen marl has proven to be an excellent oil source rock

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

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

organic geochemistry of the pine point lead zinc ore field and region northwest territories canada middle devonian barrier complex within the pine point lead zinc ore field located within the immature to marginally mature zone with respect to petroleum generation certain of the host rocks of the ore field were deposited in highly reducing conditions such that organic matter of algal or microbial origin has been preserved to a remarkable degree yields of extractable soluble material relative to organic carbon are extremely high which has resulted in the local migration of immature bitumens and heavy oil within the shallow regime polymerization of nitrogen sulfur and oxygen compounds and asphaltenes biodegradation of bitumens is a relatively late process the question of a genetic relationship between lead zinc sulfide and organic matter remains open modified journal abstract

organic geochemistry and mineralogy i characterisation of organic matter associated with metal deposits abstract as geochemical appraisals of mineral regions of commercial prospectivity evolve the organic matter associated with metal rich ores has attracted greater attention petroleum basin and modern seafloor hydrothermal vent studies have suggested that organic matter can have a significant influence on the behaviour of mineralising fluids there have been many isolated reports of certain organic compositional or morphological e g pyrobitumen features showing an apparent relationships with hydrothermal fluids or minerals raising expectations that organic based parameters might be useful to mineral exploration however the understanding of organic inorganic relationships in earth systems is far from complete for example the detailed mechanics of the interaction of organics with hydrothermal fluids over geological time remain largely undefined organic geochemistry studies have traditionally involved the measurement and interpretation of the hydrocarbon composition of sedimentary rocks here we review the types of aliphatic hydrocarbons aromatic hydrocarbons and metalloporphyrins often detected from organic geochemical investigations in mineral rich regions such molecular data can be particularly diagnostic of biochemical sources and the palaeo environments at the time mineral associated organic matter was deposited sub surface trends of hydrocarbon alteration may also reflect major biogeochemical processes such as thermal maturity and biodegradation organic geochemistry data can also occasionally provide information about the nature e g origin composition temperatures and migration pathways of hydrothermal fluids and can make a contribution to holistic ore genesis models the well preserved organic matter associated with the economic here s your chance pb zn ag mine paleoproterozoic barney creek formation mcarthur basin australia and the transition metal rich early permian kupferschiefer formation germany poland have attracted significant attention a more detailed summary of the organic character of these deposits is provided to highlight the contribution organic geochemistry can make to understanding mineralisation processes most organic geochemical studies of highly mineralised regions however have not adequately addressed the significance of organic matter to mineralisation a slightly different analytical focus than traditionally used for exploration appraisal of petroleum hydrocarbons may be required to properly evaluate the significance of organic species to the mobilisation transport and deposition of ore metals the characterisation and subsequent thermodynamic modeling of organic substances and complexes within metalliferous hydrothermal systems will contribute to a better understanding of the nature and role of organic inorganic fluids or other affiliated organics in ore systems

the trace metal geochemistry of pore water brines from two hypersaline lakes abstract pore water brines from modern hypersaline lake sediments have been analyzed to determine the nature of brine trace metal interaction in these environments brine samples were collected from the surface waters and sedimentary pore waters of two hypersaline lakes solar lake eastern sinai and goto meer bonaire netherlands antilles metal concentrations in the oxic brines appear to be related to the strength of their respective chloride complexes with pb and zn more enriched than cu pore water cu zn and fe concentrations increased across the sediment water interface in both lakes all three metal profiles follow a similar pattern with depth in the pore water higher concentrations were observed in the goto meer brines strontium isotopes were utilized to qualify better the mixing of the brines in solar lake although these metals were observed at higher concentrations than sea water in these sulfidic brines their concentrations are not close to what is needed for the formation of ore deposits

review and update of the applications of organic petrology part 2 geological and multidisciplinary applications abstract the present paper is focused on organic petrology applied to unconventional and multidisciplinary investigations and is the second part of a two part review that describes the geological applications and uses of this branch of earth sciences therefore this paper reviews the use of organic petrology in investigations of i ore genesis when organic matter occurs associated with mineralization ii the behavior of organic matter in coal fires self heating and self combustion iii environmental and anthropogenic impacts associated with the management and industrial utilization of coal iv archeology and the nature and geographical provenance of objects of organic nature such as jet amber other artifacts and coal from archeological sites and v forensic science connected with criminal behavior or disasters this second part of the review outlines the most recent research and applications of organic petrology in those fields

thermal alteration of gilsonite due to bushfire an example from southwest iran abstract heat affected fragments of bitumen with distinctive properties which can be interpreted as being produced by local heating were found in gilsonite deposits in the vicinity of an asphaltic pool southwest iran the coke fragments consist of multi phase isotropic to anisotropic thermally altered fragments the morphology of the coke fragments is described and an attempt is made to correlate these fragments with laboratory carbonized products of natural bitumen the presence of natural coke in bitumen deposits suggests redeposition of coke following its initial production the formation of natural bitumen coke probably resulted from heat generated by bushfire s in the area in recent times

age and origin of the well preserved organic matter in internal sediments from the silesian cracow lead zinc deposits southern poland the molecular and petrographic characteristics of organic matter in internal sediments from the mississippi valley type lead zinc deposits in southern poland reveal immature and well preserved organic matter huminite reflectance values of organic matter in all internal sediments are low with a mean value of 0 29 corresponding to a lignite range of coalification most organic compounds in the organic matter e g cadalene retene simonellite perylene and sitosterol and its transformation products stigmastanol and stigmasta 3 5 dien one as well as lignin degradation compound products e g benzoic acid vanillin 4 benzaldehyde benzenedicarboxilic acids and hydroxybenzoic acids are of terrestrial origin monosaccharides with dominant and glucose were identified as possible remnants of cellulose degradation products suggesting an excellent state of organic matter preservation given that monosaccharides are preserved only under conditions of limited oxygen after sedimentation resulting from the rapid accumulation of internal sediments in meteoric paleokarst cavities followed by insignificant diagenesis petrologic and palynological data on internal sediments clearly indicate a middle triassic age for organic matter and for the development of a triassic meteoric karst system immediately after anisian carbonate sedimentation

sediment hosted zn pb cu deposits in the central african copperbelt abstract stratabound epigenetic sulphide zn pb cu ore deposits of the central african copperbelt in the democratic republic of congo and zambia are mostly hosted in deformed shallow marine platform carbonates and associated sedimentary rocks of the neoproterozoic katanga supergroup economic orebodies that also contain variable amounts of minor cd co ge ag re as mo ga and v occur mainly as irregular pipe like bodies associated with collapse breccias and faults as well as lenticular bodies subparallel to bedding kipushi and kabwe in the democratic republic of the congo and zambia respectively are the major examples of carbonate hosted zn pb cu mined deposits with important by products of ge cd ag and v in the lufilian arc a major metallogenic province famous for its world class sediment hosted stratiform cu co deposits the carbonate hosted deposits range in age from neoproterozoic to early palaeozoic 680 to 450 ma the formation of the relatively older neoproterozoic deposits is probably related to early collision events during the lufilian orogeny whereas the younger palaeozoic deposits may be related to post collisional processes of ore formation fluid inclusion and stable isotope data indicate that hydrothermal metal bearing fluids evolved from formation brines during basin evolution and later tectonogenesis ore fluid migration occurred mainly along major thrust zones and other structural discontinuities such as karsts breccias and faults within the katangan cover rocks resulting in ore deposition within favourable structures and reactive carbonates of the katangan supergroup

chemical transformations of type iii organic matter associated with the akouta uranium deposit niger geological implications abstract pure vitrinites from the akouta uranium deposit niger have been characterized using rock eval pyrolysis c h o analysis infrared and raman spectroscopies and reflectance measurements the organic matter sampled in the sandy guezouman formation is land derived type iii elemental analyses plotted in a h c vs o c diagram define three types of evolution the first one corresponds to a maturation trend and has been related to a w e geothermal gradient the second one corresponds to a slow rate diagenetic oxidation affecting organic matter located far from the ore zone the third one can be compared with a late oxidation it is related to the mineralizing process and results from both oxidation reduction and radiolysis effects the different alteration trends have been compared to mineralogical and microthermometric data in order to draw geological implications

organic geochemical indicators of biological sulphate reduction in early diagenetic znpb mineralization the bois madame deposit gard france abstract at bois madame gard france zn pb s mineralization zn pb 4 occurs in dolomitized kimmeridgian carbonates very near layers which are rich in organic matter of planktonic origin previous geological and geochemical studies have suggested early syn or diagenetic ore deposition controlled by sulphate reducing bacteria the metals probably having originated from regionally mineralized triassic or liassic formations rock eval pyrolysis data complemented by biomarkers show that the organic matter reached only the organic diagenesis catagenesis transition owing to burial pb deposit as in many pb zn s deposits the hydrocarbons almost certainly autochthonous show no indication of relatively late alteration by biodegradation or water washing the presence of hopanes c 27 35 with high abundance in the c 27 32 range indicate that intense bacterial activity occurred during early diagenesis under su ic anoxic conditions this interpretation is reinforced by the presence of n alkanes in the range n c 22 to n c 28 dominated by compounds with an even number of carbon atoms which may have derived from the reduction of bacterial fatty acids except for these even number n alkanes the organic geochemical evidence for sulphate reducing bacteria during early diagenesis must remain equivocal

grain size of granite and derived grus enchanted rock pluton texas abstract twenty five samples of grus from non vegetated weather pits in granite were sieved and found to be mostly pebble gravel average content of gravel sand and mud was 76 16 and 18 respectively by weight primary grain size modes were between 2 8 23 0 mm and most grus was composed of granite rock fragments twelve granite cores drilled in the same weather pits from which grus was collected were studied in thin section with 856 grains identified mineralogically and measured for size these measurements were recast as sieve data grain size comparisons for each granite grus pair showed that the grain size mode of grus did not follow the crystal size of parent granite granite with average crystal sizes of 23 0 and 4 0 mm formed grus with a primary grain size mode of 5 7 mm for two different sample pairs granite with crystal sizes of 4 0 and 1 0 mm yielded grus with primary grain size modes of 5 7 and 11 6 mm modal size measurements were pooled for the twelve granite grus pairs and the average crystal size of parent granite was found to be 3 4 mm and the average grain size model of derived grus was 5 7 mm folk and patton 1982 have documented micro sheet fracturing of granite as the earliest stage of weathering which explains the lack of correspondence between granite texture and grain size of grus at enchanted rock

the spar lake strata bound cu ag deposit formed across a mixing zone between trapped natural gas and metals bearing brine ore formation at the spar lake red bed associated strata bound cu deposit took place across a mixing and reaction zone between a hot oxidized metals transporting brine and a reservoir of sour h2s bearing natural gas trapped in the host sandstones fluid inclusion volatile analyses have very high ch4 concentrations 1 mol in most samples and a sample from the fringe of the deposit has between 18 and 36 mol ch4 the ratio of ch4 co2 in fluid inclusions appears to vary regularly across the deposit with the lowest ch4 co2 ratios from high grade chalcocite bearing ore and the highest from the chalcopyrite bearing fringe the helium r ra isotope ratios 0 23 0 98 and concentrations define a mixture between crustal and atmospheric helium the volatiles in fluid inclusions ch4 co2 h2s so2 h2 h2o and other organic gases and values of f o2 and temperature calculated from the volatiles data all show gradations across the deposit that are completely consistent with such a mixing and reaction zone other volatiles from the fluid inclusions hcl hf 3he 4he n2 ar characterize the brine and give evidence for only shallow crustal fluids with no magmatic influences the brine entered the gas reservoir from below and along the axis of the deposit and migrated out along bedding to the southwest northeast and northwest metals transporting brines may have been fed into the host sandstones from the east fault but that remains uncertain abundant ore stage fe and mn calcite cements from the reduced fringe have 13c values as low as 18 4 and many values less than 10 which indicate that significant carbonate was generated by oxidation of organic carbon from the natural gas the zone of calcite cements with very low 13c values approximately envelopes chalcocite bearing ore sulfur isotope data of cu pb and fe sulfides and barite indicate derivation of roughly half of the orebody sulfide directly from sour gas h2s that sour gas h2s had developed in steps known from other sedimentary basins starting with 1 bacterial sulfate reduction bsr of seawater sulfate having 34s of about 20 and sequestering of the sulfide in organic matter in source rocks stratigraphically below the deposit host rocks followed by 2 maturation of the sulfide bearing organic matter into liquid petroleum with relatively homogeneous sulfide having 34s of 5 5 then by 3 thermal cracking of the oil to ch4 and h2s with relatively homogeneous sulfide having 34s closely distributed about 6 the ch4 and h2s migrated and were trapped in sandstones of the upper member of the revett formation where they were later met by the 200 c metals transporting brine there was additional contribution of sulfide to ore from later thermochemical sulfate reduction tsr operating on sulfate 34s of 20 to 29 in both formation waters and metals transporting solutions a large range of 34s in sulfides resulted as the 6 sour gas sulfide was supplemented with varying proportions of 20 to 29 sulfide from tsr

introduction to geochemistry of metalliferous black shales 1 metalliferous black shales metalliferous black shales exhibit a wide range of physical and chemical characteristics they can be enriched in many different metals and the metals can be in a variety of geochemical states depositional and geological histories of these shales are diverse some metalliferous black shales contain relatively high concentrations of organic matter whereas others do not because of elevated carbonate contents some are calcareous shales or marlstones metal enrichments can result from redox reactions mediated by bacteria during early diagenesis and also from those associated with hydrothermal processes after deep burial however unifying characteristics of metalliferous black shales are sufficiently well established to justify combining a diverse number of fine grained sedimentary rock types under a common term that reflects enhanced metal content dark color and an inferred association with organic matter e g huyck 1990 moreover the term metalliferous black shales is sufficiently accepted that working group 254 of the international geological correlation program igcp has that title and focus this special issue of chemical geology brings together reports describing characteris

weathering and vegetation effects in early stages of soil formation abstract bedrock surfaces in the ouachita mountains arkansas exposed by spillway construction and which had not previously been subjected to surface weathering environments developed 15 20 cm thick soil covers in less than three decades all open bedrock joints showed evidence of weathering and biological activity rock surfaces and fragments also showed evidence of significant weathering alteration the results suggest a soil production function whereby weathering and increases in thickness are initially rapid the rapid initial rate 5 to 10 mm year 1 is facilitated by a weathering favorable regional climate local topography favoring moisture and sediment accumulation and aggressive vegetation colonization the ages of the trees on the bedrock benches suggests that a short period

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur