diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

carbonatization of oceanic crust by the seafloor hydrothermal activity and its significance as a co2 sink in the early archean abstract early archean 3 46 ga hydrothermally altered basaltic rocks exposed near marble bar eastern pilbara craton have been studied in order to reveal geological and geochemical natures of seafloor hydrothermal carbonatization and to estimate the co2 flux sunk into the altered oceanic crust by the carbonatization the basaltic rocks are divided into basalt and dolerite and the basalt is further subdivided into type i having original igneous rock textures and type ii lacking these textures due to strong hydrothermal alteration primary clinopyroxene phenocrysts are preserved in some part of the dolerite samples and the alteration mineral assemblage of dolerite chlorite epidote albite quartz actinolite indicates that the alteration condition was typical greenschist facies in other samples all primary minerals were completely replaced by secondary minerals and the alteration mineral assemblage of the type i and type ii basalts chlorite k mica quartz carbonate minerals albite is characterized by the presence of k mica and carbonate minerals and the absence of ca al silicate minerals such as epidote and actinolite suggesting the alteration condition of high co2 fugacity the difference of the alteration mineral assemblages between basalt and dolerite is probably attributed to the difference of water rock ratio that in turn depends on their porosity carbonate minerals in the carbonatized basalt include calcite ankerite and siderite but calcite is quite dominant the 13c values of the carbonate minerals are 0 3 1 2 and mostly within the range of marine carbonate indicating that the carbonate minerals were formed by seafloor hydrothermal alteration and that carbonate carbon in the altered basalt was derived from seawater whole rock chemical composition of the basaltic rocks is essentially similar to that of modern mid ocean ridge basalt morb except for highly mobile elements such as k2o rb sr and ba compared to the least altered dolerite all altered basalt samples are enriched in k2o rb and ba and are depleted in na2o reflecting the presence of k mica replacing primary plagioclase in addition noticeable co2 enrichment is recognized in the basalt due to the ubiquitous presence of carbonate minerals but there was essentially neither gain nor loss of cao this suggests that the co2 in the hydrothermal fluid seawater was trapped by using ca originally contained in the basalt the cao co2 ratios of the basalt are generally the same as that of pure calcite indicating that ca in the basalt was almost completely converted to calcite during the carbonatization although mg and fe were mainly redistributed into noncarbonate minerals such as chlorite the carbon flux into the early archean oceanic crust by the seafloor hydrothermal carbonatization is estimated to be 3 8 1013 mol yr based on the average carbon content of altered oceanic crust of 1 4 10 3 mol g the alteration depth of 500 m and the spreading rate of 1 8 1011 cm2 yr this flux is equivalent to or greater than the present day total carbon flux it is most likely that the seafloor hydrothermal carbonatization played an important role as a sink of atmospheric and oceanic co2 in the early archean

isorenieratane record in black shales from the paris basin france constraints on recycling of respired co2 as a mechanism for negative carbon isotope shifts during the toarcian oceanic anoxic event the prominent negative stable carbon isotope excursion in both carbonate and organic carbon recorded in organic rich sediments deposited during the toarcian oceanic anoxic event oae has commonly been explained by recycling of 13c depleted co2 the so called kuspert model more recently the massive release of 13c depleted methane or other forms of 13c depleted carbon was also proposed to account for the observed negative 13c excursions in organic carbon of terrigenous as well as of marine origin the occurrence of diagenetic products of the carotenoid isorenieratene isorenieratane and other aryl isoprenoids in toarcian black shales has been regarded as supporting evidence for the kuspert hypothesis as they point to strong stratification of the epicontinental seas a section of a drill core straddling the toarcian of the paris basin cirfontaineen ornois contained intact isorenieratane providing evidence that photosynthetic green sulphur bacteria were present at the time of deposition even prior to the oae however the isorenieratane abundances are very low in the section where the negative 13c excursion in organic carbon and phytane a chemical fossil derived from chlorophyll occurs the abundance of the isorenieratene derivatives increases once the 13c records have shifted to more positive values the 13c of isorenieratane generally circa 13 1 0 5 indicates that the respired co2 contribution at the chemocline was low and is thus not likely to be the main cause of the prominent up to 7 negative 13c shift recorded in toarcian organic carbon records

regional metamorphic controls on alteration associated with gold mineralization in the eastern goldfields province western australia implications for the timing and origin of archean lode gold deposits alteration assemblages associated with archean epigenetic gold mineralization in the menzies kambalda area of the yilgarn craton western australia vary systematically with regional metamorphic grade up to and including upper amphibolite facies rocks k metasomatism is recorded by the presence of muscovite biotite and k feldspar at progressively higher metamorphic grades high metamorphic grades are commonly developed in broad thermal aureoles around fate syntectonic granitic intrusions metamorphic recrystallization of alteration assemblages is common in the thermal aureoles these relations suggest broad contemporaneity among granitoid intrusion regional metamorphism and mineralization during the final stages of the tectonic evolution of the granite greenstone terrain late syntectonic granitoids acted as centers of heat and fluid flux in large scale synmetamorphic hydrothermal systems that deposited gold possibly from modified mantle derived fluids

geophysical evidence concerning the southern boundary of the london platform beneath the hog s back surrey the results of a gravity survey have been interpreted with seismic reflection and borehole data to show that a major change in the structure of the upper crust underlies the hog s back w of guildford surrey the pre mesozoic basement beneath the thin mesozoic succession n of the hog s back is of a lower density than that underlying the thick mesozoic succession to the s this lower density basement was probably the principal cause of the relative stability of the london platform during the mesozoic era the sourthern boundary of the london platform may have been initiated by variscan thrusting with subsequent reversal of displacement or may be inherited from an older crustal lineament

the multiple sulfur isotope architecture of the golden mile and mount charlotte deposits western australia the golden mile and mount charlotte deposits in the kalgoorlie terrane western australia display three main mineralization styles fimiston comprised of interconnected shear zones associated with ankerite pyrite hematite magnetite gold telluride alteration oroya made up of breccia bodies with v muscovite ankerite pyrite pyrrhotite gold telluride alteration and mount charlotte which consists of vein arrays with symmetrical ankerite sericite albite pyrite pyrrhotite gold alteration pyrite is in equilibrium with gold in all three mineralization styles and has been selected as a proxy to record the sulfur source of the mineralizing fluids as well as the nature of the hydrothermal processes the 34s 33s and 36s analyses on pyrite grains from the different mineralization styles including oxidized and reduced sulfide oxide assemblages reveal 1 a large variation in 34s from 12 6 to 23 5 and 2 a previously unrecognized occurrence of anomalous 33s and 36s signatures from 1 0 to 1 1 and from 2 3 to 0 9 respectively it is argued that the mineralizing fluids that formed the golden mile and mount charlotte deposits record mixing among three components mantle sulfur oxidized seawater sulfur e g so4 and reduced elemental sulfur e g s8 petrographic evidence in conjunction with 33s and 36s data suggest that mif s was acquired during the deposition of shales and basalts present in the kalgoorlie terrane and later mixed with mantle derived sulfur during the mineralization events the negative 34s values that predominate in fimiston style mineralization are consistent with a prevalence of oxidized fluids during the ore forming process as reflected by the presence of hematite pyrite magnetite gold assemblages conversely the positive 34s values that dominate in the mt charlotte and oroya mineralization styles reflect a reducing environment as reflected by the presence of pyrite pyrrhotite gold assemblages

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

molecular isotopic characterisation of hydrocarbon biomarkers in palaeocene eocene evaporitic lacustrine source rocks from the jianghan basin china immature organic matter in lacustrine source rocks from the jianghan basin eastern china was studied for distributions and stable carbon isotopic compositions 13 c of hydrocarbon biomarkers all of the bitumens contain isorenieratane 13 c ca 17 indicating the presence of chlorobiaceae and thus periods of euxinic conditions extended into the photic zone aliphatic hydrocarbon fractions are dominated by pristane and phytane and contain relatively low amounts of 4a and 4 methylsteranes c 30 13 c ca 16 believed to originate from 4 methylsterols in dinoflagellates 13 c values of gammacerane ca 24 and c 30 17 21 h hopane ca 23 are consistent with an origin from bacterivorous ciliates that fed on chlorobiaceae the bitumens contain low relative amounts of organo sulphur compounds one rock contains c 37 and c 38 n alkanes 13 c ca 36 derived from alkadienes and alkenones of prymnesiophytes the distributions of hydrocarbon biomarkers suggest that they were initially sulphurised during early diagenesis and later released during early thermal maturation

intermittent euxinia reconciliation of a jurassic black shale with its biofacies isorenieratane is ubiquitous in the organic carbon rich peterborough member callovian uk of the oxford clay formation indicating a temporal overlap of the euphotic and sulphidic zone in the water column

a 400 year record of environmental change in an euxinic fjord as revealed by the sedimentary biomarker record a 400 year sedimentary record of the euxinic kyllaren fjord was investigated using organic biogeochemical geochemical and sedimentological approaches accumulation rates of a suite of biomarkers and in some cases their stable carbon isotopic composition were determined biomarkers were separated into three different groups terrestrial derived general aquatic marine derived and aquatic marine derived but related to high primary productivity variations in bulk sediment parameters and biomarker accumulation rates with depth were used to interpret the sedimentary record we infer that in the first half of the 19th century an environmental change occurred caused by a change in either the precipitation regime vegetation and or land use the data also show that in the last century and especially in the last decades a distinct increase in primary productivity occurred most likely this is caused by a natural eutrophication due to the transformation of the fjord from an open to a confined system by the building of a partially open dam in 1954 possibly combined with anthropogenic eutrophication a concurrent shoaling of the fjord chemocline may have had a mediating effect in the change towards a higher productivity by enhancing nutrient and carbon recycling enhanced carbon recycling is reflected by decreased 13c values of several biomarkers

large sulphur isotopic perturbations and oceanic changes during the frasnian famennian transition of the late devonian the frasnian famennian transition of the late devonian was one of the most critical intervals in the phanerozoic sulphur isotopic pairs of carbonate associated sulphate and pyrite sulphide from coeval sections in south china and poland reveal frequent perturbations of sulphur cycling during this time interval these data suggest a sudden oceanic overturn during a rapid sea level fall probably induced by jerky block tilting in the latest frasnian this event was followed by long lasting photic zone euxinia during a rapid sea level rise in the earliest famennian large increases in continental nutrient fluxes and subsequent primary productivity and organic burial could have greatly enhanced bacterial sulphate reduction producing excessive sulphide through the water columns owing to iron depletion subsequently rapid ventilation of oceanic basins occurred dur ing which direct aerobic oxidation of sulphide into sulphate predominated in bottom waters and even surface sediments with minimal fractionation this oxygenation was probably induced by intensive climatic cooling and or large scale sea level fall the temporal coincidence of two extinction phases with the oceanic overturn and succeeding photic zone euxinia suggests that these extreme oceanic events played an important role in the severe biotic crisis furthermore photic zone euxinia coupled with subsequent climatic cooling may have delayed post extinction recovery of some taxa

a late cenozoic regional mesofracture system in southern england and northern france the upper cretaceous and palaeogene rocks of s england and n france are cut by a nw trending system of fractures characterized by swarms of vertical extension joints accompanied by conjugate sets of hybrid and shear joints and normal mesofaults many major photolineaments exhibit the same nw trend as the fractures and are particularly conspicuous in n france where they are coincident with rectilinear drainage channels suggesting a relationship between fracture orientation and physiography in s england this relationship is absent possibly because of the influence of additional fracture systems related to major flexures trending obliquely to the nw se direction these major e w trending flexures and associated fracture systems were formed during the oligocene to early miocene 9helvetic9 phase of deformation and are cross cut obliquely by fractures in the nw trending system the nw trending fractures and lineaments are parallel to neotectonic normal faults in the lower rhine embayment and become less well developed to the west with increasing distance from these major structures the lower rhine faults were reactivated and propagated into the quaternary cover as a consequence of ne sw regional tension generated during the late neogene to recent 9jura9 phase of nw se alpine convergence the nw trending extensional structures in s england and n france are considered to be of about the same age and related to the same stress regime as the neotectonic normal faults of the lower rhine embayment however because fractures of the nw system cutting palaeogene sediments in se england are truncated by the erosion surface beneath the plio pleistocene red crag deposits it is possible that in england fracture initiation did not continue into quaternary times

structure of blackdown pericline mendip hills from gravity and seismic data blackdown pericline is the western pericline of the mendip hills which were formed during the variscan orogeny at the end of the carboniferous unlike the more easterly periclines blackdown pericline has no associated magnetic anomaly indicating the absence of the silurian volcanic rocks responsible for the anomaly in eastern mendip the gravity field of blackdown pericline cannot be adequately modelled by the known geology of the mendip hills and requires the presence of an anomalously dense body at shallow depth the geometry of the body is inferred from a seismic reflection profile and is interpreted as a wedge of precambrian basement rocks its high density and negligible susceptibility may indicate an amphibolitic composition three models involving variscan thrusting and post variscan listric normal faulting are presented in explanation of the presence of the wedge the anomalous body is shown to be laterally continuous to west and east a linear negative gravity anomaly to the north of blackdown pericline is interpreted to be caused by a small occurrence of coal measures which have not before been described from this area

early to mid cretaceous tectonics and unconformities of the wessex basin southern england sediment distribution patterns time subsidence plots seismic data and outcrop analysis of the lower cretaceous ryazanian albian of the wessex basin southern england suggest that a number of unconformable horizons exist and that there is no single late cimmerian unconformity surface a tectonic change from areally restricted deposition in the weald and channel sub basins to extensive sedimentation across the whole of southern england began in the mid aptian this change ended with transgression of basement highs in the early albian of the dorset area and later albian of the devon and london platform basin margin areas its onset can be linked to the austrian tectonic phase of europe the onset of marine deposition in the aptian is coincident with periodic transgression of the margins of the wessex basin throughout the aptian albian mid late aptian and early mid aibian transgressions were preceded by periods of erosion the aptian albian lower greensand is characterized by transgressive regressive phases suggesting a short term controlling process third order eustatic changes or intra plate mechanisms tectonic changes in the mid aptian include uplift followed by widespread subsidence this change coincides with a time of plate reorganization in the european and north atlantic areas

isotopic biogeochemistry of the oxford clay formation jurassic uk a total of 165 samples was obtained from the oxford clay formation at seven different sites nearly all were from the peterborough member lower oxford clay but seven were from the stewartby and weymouth members middle and upper oxford clay respectively five samples from the underlying kellaways formation were also examined stratigraphic relationships were estimated on the basis of ammonite subzones and results from all locations can be placed along a single stratigraphic scale the following were determined for all samples abundance and isotopic composition of organic carbon abundances of carbonate carbon and total sulphur and the rock eval pyrolysis parameters hydrogen index oxygen index and t max for a subset of eight samples selected to be representative of geochemical and apparent palaeoenvironmental variations soluble organic compounds were extracted and the isotopic composition of pristane phytane and long chain n alkanes determined by isotope ratio monitoring gas chromatograph mass spectrometry concentrations of organic carbon in samples from the peterborough member ranged from 0 5 to 16 6 and values of total organic carbon toc ranged from 27 7 to 23 1 v pdb shales dominated by epifaunal bivalve assemblages have high concentrations of toc and values of h index approaching 800 indicating preservation of hydrogen rich organic material conversely shell beds and calcareous and silty clay beds have lower abundances of toc and values of h index dropping below 100 indicating extensive oxidation of the organic matter isotopic composition of pristane and phytane in the peterborough and stewartby members average 31 7 those in the weymouth member average 29 8 values of for long chain n alkanes average 28 together these results indicate values for primary inputs as follows terrestrial vascular plants 23 5 peterborough member algae 28 2 stewartby member algae 29 1 weymouth member algae 26 6 comparison of primary values to those of toc indicates that in some cases secondary processes enriched toc relative to primary inputs by as much as 4 palaeontological evidence in these same beds indicates development of extensive food webs and supports attribution of this isotopic enrichment to heterotrophic reworking

the carbon isotopic response of algae cyano bacteria archaea and higher plants to the late cenomanian perturbation of the global carbon cycle insights from biomarkers in black shales from the cape verde basin dsdp site 367 abstract the stable carbon isotopic compositions of free and sulfur s bound biomarkers derived from algae cyano bacteria archaea and higher plants and total organic carbon toc during the first phase of the late cenomanian turonian oceanic anoxic event oae were measured in black shales deposited in the southern proto atlantic ocean in the cape verde basin dsdp site 367 to determine the response of these organisms to this major perturbation of the global carbon cycle resulting from widespread burial of marine organic matter the average positive isotope excursions of toc and biomarkers varied from 5 1 to 8 3 the 13c values were cross correlated to infer potential common sources of biomarkers this revealed common sources for c31 and c32 hopanes but no 1 1 relationship for pristane and phytane the correlation of 13ctoc with the 13c value of sulfur s bound phytane is the strongest this is because s bound phytane is derived from phytol that originates from all marine primary producers algae and cyanobacteria and thus represents a weighted average of their carbon isotopic compositions the 13c values of s bound phytane and c35 hopane were also used to estimate pco2 levels before the oae burial event pco2 levels are estimated to be ca 1300 ppmv using both biomarkers and the independent maximum rubisco fractionation factors at times of maximum organic carbon burial rates during the oae reconstructed pco2 levels are estimated to be ca 700 ppmv however compared to other c t oae sections the positive isotope excursion of s bound phytane is also affected by an increased production during the oae when we compensate for this we arrive at pco2 levels around 1000 ppmv a reduction of ca 25 this indicates that burial of organic matter can have a large effect on atmospheric co2 levels

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

uranium and molybdenum isotope systematics in modern euxinic basins case studies from the central baltic sea and the kyllaren fjord norway abstract recent investigations have revealed significant fractionation of 238u 235u between organic rich sediments of anoxic marginal seas and seawater indicating redox dependent u isotope fractionation this study explores the conditions controlling u isotope fractionation in selected modern anoxic basins baltic sea landsort and gotland deeps and the kyllaren fjord in norway and compares u with mo isotope fractionation therefore the concentrations and isotope compositions of dissolved u and mo from the water column and organic rich sediments from three currently anoxic basins have been analysed the water column samples from the kyllaren fjord display a moderate depletion of u and a strong depletion of mo with increasing depth these variations are associated with a decrease in 238u and an increase in 98mo with depth from 0 35 to 0 70 and from 2 4 to 2 6 respectively from the u isotope composition of the deep euxinic water column of the kyllaren fjord a minimum value of 238ured 0 7 for the u isotope fractionation during reduction is inferred due to the high sedimentation rate in the kyllaren fjord surface sediment samples are only moderately enriched in u and mo 4 g g and 6 g g to 37 g g respectively and display 238u and 98mo averages of 0 26 0 10 and 2 18 0 21 respectively water column samples from the baltic sea display a minor decrease in the u and mo concentrations and only negligible u and mo isotope fractionation compared to open seawater the sediment layers from the baltic sea landsort deep which were deposited under mostly anoxic conditions are moderately enriched in u up to 8 g g and highly enriched in mo up to 222 g g however u and mo isotopic compositions are significantly lighter with 238u of 0 36 0 08 and 98mo of 0 04 0 11 than those of typical organic rich sediments from anoxic basins these findings reveal that compared to mo the u isotopic composition of sediments in restricted and strongly euxinic basins like the kyllaren fjord is significantly more dependent on 1 the extent of u removal from the water column which is lower than that of mo and on 2 the sedimentation rate i e the fraction of authigenic u relative to detrital u in the sediment which is also lower compared to that of mo in more open and only temporarily euxinic basins such as the investigated basins of the baltic sea strong mo is coupled with weak u isotope fractionation between water and sediment these signatures were likely the result of isotope fractionation under weakly sulfidic conditions and the generation of isotopically light mo during frequently occurring flushing events with oxygen rich water from the open sea this implies that mo and u isotope signatures of sediments only record paleo water column redox conditions of restricted basins if the water column was permanently stratified

a smooth negative shift of organic carbon isotope ratios at an end permian mass extinction horizon in central pelagic panthalassa abstract the end permian mass extinction is associated with a global perturbation in the carbon isotopic composition of carbonates and organic matter but such changes are not well documented from pelagic deep sea sediments one of the most continuous pelagic deep sea permian triassic boundary ptb sections the am 2 section is exposed in the accretionary complexes of japan new data for organic carbon isotope ratios 13corg were obtained from 36 samples from section am 2 the 13corg excursion curve exhibits a negative shift of 2 0 in the low latitude pelagic panthalassic ocean at the end of the permian which coincides with a radiolarian extinction the 13corg values of pelagic deep sea panthalassic sections and those of shallow water sections from panthalassic seamounts exhibit a smooth negative shift that lacks temporary increases like those reported from paleotethyan ptb sections absence of temporary 13corg increases at the ptb in panthalassa may reflect less algal and bacterial blooming in pelagic panthalassa compared to the shallow water paleotethys

thin skinned tectonics in the northern rhenish massif germany a network of profiles in the hercynian mountain system geo traverse rhenoherzynikum is needed to determine details of the geological structure and find the reasons for tectonic movements outstanding features within the mountain system such as the large fault zone along the southern boundary of the hunsruck1 and the left flank of the rhinegraben have already been investigated by reflection seismology2 3 we describe here a new reflection refraction experiment carried out in 1978 in the most northern part of the rhenish massif across the stavelot venn massif near aachen fig 1 while layers in the lower crust dip to the nnw a strong upper reflector at 3 4 km depth shows a slight dip to the sse and indicates a prominent fault zone near aachen known in belgium as the faille du midi here a comparable and apparently identical reflector was found some 100 and 175 km to the west of our profile we interpreted this reflector as a prominent and well lubricated thrust fault along which a huge horizontal nappe displacement took place during the last stages of the variscan orogeny

a euxinic southern north atlantic ocean during the cenomanian turonian oceanic anoxic event abstract during mid cretaceous times large amounts of organic carbon corg became sequestered in black shales possibly due to oceanic anoxic events characterized by the development of an extended oxygen minimum zone omz here we provide the first direct evidence for an open ocean omz in the cenomanian turonian c t southern north atlantic and in fact show that the base of the photic zone was euxinic as revealed by molecular fossils from photosynthetic green sulfur bacteria in c t black shales this together with evidence for bottom water anoxia and accumulation of redox sensitive trace metals and hydrogen rich organic matter indicates a continuously euxinic water column concurrent with the high corg accumulation rates which are 15 150 times greater in the southern than in the northern north atlantic and the low biological productivity this suggests that preservation controlled the accumulation of corg in c t black shales

a possible basaltic deep source of the south central england magnetic anomaly the group of large positive magnetic anomalies in south central england is shown to originate from two sources at different depths the shallow source originates from silesian basic igneous rocks the anomaly of the deeper source has been isolated by upward continuation and inverted via pseudofield transformation the magnetic model is interpreted as a large body of basaltic rocks intruding the middle crust it is proposed that the body was emplaced by buoyant ascent and may be the cause of the stability of the london platform during mesozoic times it is speculated that the basalt was intruded in a back arc environment during the period preceding the variscan orogeny

palaeocene oligocene tectonics of nw europe s u m m a r y during the palaeogene in nw europe a gallic subplate was very nearly created this plate was almost entirely bordered by plate boundaries although not of equivalent ages to the n the n atlantic began to open about 56 ma ago the alpine convergent boundary extended southwestwards to the pyrenean subduction zone on the ne side a n british pataeocene early eocene fracture dyke boundary appears to pass southeastwards across the north sea into a lutetian to burdigalian rift system there is an age disparity between the fracturing and nw dyke intrusion in britain and the fracturing and formation of the rhine graben the last dykes in britain ypresian were intruded not long before the important subsidence of the rhine graben earliest lutetian but their causes were different the british dyke fractures propagated southeastwards via the cleveland dyke towards the north sea whereas the rhine graben propagated northwards towards the zuider zee depression however the structures from both sides converged in the sole pit basin in the north sea with the result that a continuous though not coevally originated fracture system developed from nw scotland to the alps during the early tertiary there was a wide range of tectonic activity throughout nw europe fig 1 in nw britain lavas were extruded and plutonic complexes and extensive dyke swarms were intruded in the north sea tufts were deposited as a result of volcanism along the rockall faeroe rift reactivation of faults con trolled magmatism localization of gas fields devolatilization of coal and inversion of basins caused uplift deformation and erosion along the rhine graben doming subsidence and rift propagation took place in association with alka line volcanism and plutonism coevally with the meso alpine compressive deformations that oc curred in the alps faulting controlled sedimen tation patterns during inversion of basins in southern england the english channel northern france and holland old rift faults were reacti vated in the western approaches basin thrust faults formed in the southern bay of biscay contemporaneously with thrusting in the pyre nees and variscan massifs were tilted and uplifted along steep reverse faults the main tectonic activity lasted from about 60 ma to about 30 ma but it was diachronous generally earlier in the nw and later in the se the igneous activity in northern britain was related to the opening of the n atlantic in the late palaeocene but the formation of the rhine graben and the inversion of sedimentary basins in the north sea and near the english channel were caused by major orogenic events in the alpine region in the late eocene to mid oligocene frisch 1981 tectonic phenomena in the north sea provide the link between those in northern britain and those in the rhine graben the aim of this paper is to demonstrate that these movements from the atlantic and alpine sides almost fragmented the lithospheric plates of nw europe during the creation of a gallic sub block an earlier northern boundary from nw scotland to northern germany being transected by a later eastern boundary along the rhine graben

integrated geophysical geological modelling of the caledonian and precambrian basement of southern britian quantitative modelling of potential field data has been used to test and extend geological sections constructed for the new british geological survey tectonic map of britain and ireland three of the profiles cross part of the anglo brabant massif and provide new information on the nature of the pre mesozoic basement a profile across southern england passing just to the west of london suggests that a significant contribution to observed gravity variations in the region results from changes in the thickness of relatively low density lower palaeozoic rocks it also identifies a major deep seated body with relatively high magnetic susceptibility and low density which is interpreted as a precambrian cratonic core underlying the southeastern part of the midlands microcraton profiles across central and eastern england reveal major boundaries within the precambrian basement some of which coincide with structures mapped at surface a number of intrusions of probable caledonian age have been recognized including bodies beneath the widmerpool gulf and the wash those beneath the wash appear to lie in a discrete basement region which separates belts of more magnetic basement lying to the northwest and southeast

geochemical constraints on pliocene sapropel formation in the eastern mediterranean abstract seventeen eastern mediterranean pliocene sapropels from odp sites 964 966 967 and 969 some of which are coeval have been analysed for their geochemistry the sapropels are characterized by very high organic carbon contents up to 30 which are reported to be the result of both increased productivity and improved preservation although the organic matter in the sapropels is mainly of marine origin the 13 c org values and c n ratios appear terrestrial this is the result of anaerobic organic matter degradation which preferentially removed nitrogen and 13 c rich organic components a comparison with ti al profiles which mimic the precession index and a calculation of organic carbon accumulation rates indicate that sedimentation rates were at most 30 lower or at most 50 higher during sapropel formation thus sapropel formation lasted from between 2000 and 10 000 years at site 964 to between 4500 and 12 000 years at site 967 a synthesis of new data and a comparison with existing models indicates that productivity which increased due to extra nutrients supplied as a result of winter mixing and as a result of enhanced input by the nile was the driving mechanism behind sapropel formation the resulting sapropel formation was simultaneous at different depths but lasted longer in the part of the basin closest to the nile

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

relationships between carbon isotope evolution and variation of microbes during the permian triassic transition at meishan section south china this paper investigates kerogen carbon isotopes the difference between carbonate and kerogen carbon isotopes 13ccarb kero 13ccarb 13ckero and the difference between carbonate and n c19 alkane compound specific carbon isotopes 13ccarb n c19 13ccarb 13cn c19 during the permian triassic transition at meishan south china the results show that kerogen carbon isotopes underwent both gradual and sharp shifts in beds 23 25 and 26 29 respectively the differences between carbonate and organic carbon isotopes both the 13ccarb kero and 13ccarb n c19 which are mainly affected by co2 fixing enzyme and pco2 oscillated frequently during the permian triassic transition both the variations of 13ccarb n c19 and 13ccarb kero coupled with the alternation between cyanobacteria and green sulfur bacteria indicated by biomarkers the episodic low values of 13ccarb n c19 corresponded to episodic blooms of green sulfur bacteria while the episodic high values of 13ccarb n c19 corresponded to episodic blooms of cyanobacteria the relationships between the variation of carbon isotopes and biota show that the microbes which flourished after the extinction of macroorganism affected the carbon isotope fractionation greatly combining the carbon isotope compositions and the pattern of size variation of the conodont neogondolella this paper supposes that anoxia of the photic zone at bed 24 was episodic and it would be caused by the degradation of terrigenous organic matters by sulfate reducing bacteria in the upper water column considered together with results from previous research the high resolution variation of the biogeochemistry presents the sequence of the important geo events during the permian triassic crisis

the pattern of δ13corg versus hi oi relation in recent sediments as an indicator of geochemical regime in marine basins comparison of the black sea kara sea and cariaco trench an approach is suggested to evaluate the geochemical regime of marine basins by comparative study of the carbon isotopic composition of organic matter and its hydrogen index to oxygen index ratio in recent sediments a significant role of chemosynthetic bioproduction in the black sea and extensive oxidative diagenesis of the organic matter in the kara sea have been demonstrated the relative role of chemosynthetic production in the cariaco trench seems to be different compared to that in the black sea

biomarker evidence for intermittent photic zone euxinia in the aptian albian organic sedimentary record from the ionian zone epirus greece new biomarker evidence is presented that constrains the conditions of deposition and preservation of sediments rich in extractable organic matter from the aptian albian sedimentary record of the ionian zone in nw greece analyses were specifically carried out on total lipid extracts from 12 organic rich samples from the vigla shale member two of which represent the regional record for the early albian paquier event of oae1b in the aliphatic fractions compound groups such as n alkanes isoprenoid alkanes steroids hopanoids and terpenoids were recognized pointing to a mixed origin from algae and prokaryotes with an additional measurable contribution from terrigenous plant matter these compounds suggest deposition of the primary organic sediments under conditions of decreased bottom water oxygen concentrations mass spectral evidence from the aromatic fractions of most samples reveal the variable presence of diagenetic and catagenetic derivatives of carotenoid pigments including some with bound sulfur that are characteristic of photoautotrophic sulfur bacteria the presence of specific biomarkers originating from photosynthetic anaerobic microorganisms similar to those in ancient and contemporary euxinic basins such as the black sea suggest that photic zone euxinic conditions were intermittently operative in the aptian albian stages of the ionian basin but were not exclusively characteristic of the black shale representing the paquier event itself

recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach study of organic matter in immature sediments from a messinian evaporitic basin shows that consideration of structures modes of occurrence and carbon isotopic compositions of free and sulfur bound carbon skeletons allow identification of biochemical precursors detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way moreover unprecedented biochemicals were recognized these extend the horizon of biomarker geochemistry

archaean carbon reservoirs and their relevance to the fluid source for gold deposits it is commonly assumed1 2 that seawater derived carbon in altered volcanic rocks is the only major pre metamorphic carbon in carbonate reservoir in archaean greenstone belts thus carbonates from archaean gold deposits with stable isotope ratios too negative median 13c 3 to have been derived from such carbon 13c usually assumed to be near 0 have been interpreted as being derived from a local felsic magmatic source1 barley and groves3 however recognize two carbonate alteration styles that predate regional metamorphism and gold mineralization in the norseman wiluna greenstone belt of western australia evidence is summarized below these are seafloor alteration and fault controlled regional alteration which as shown below have completely different carbon isotope compositions the latter median 13c 4 8 implies a major juvenile carbon co2 flux from the mantle during greenstone belt evolution and is thus of fundamental importance in itself however here we show why the mere existence of two carbon in carbonate reservoirs and variation in carbon isotope ratios of carbonates between individual gold deposits in one area negate some of the fundamental assumptions used to support magmatic fluid models1

source of 1 2 3 4 tetramethylbenzene in asphaltenes from the tarim basin 1 alkyl 2 3 6 trimethylbenzenes and a high relative amount of 1 2 3 4 tetramethylbenzene ttmb have been previously detected in the marine oils and asphaltenes in the oils from the tarim basin in the present study the stable carbon isotopic compositions of ttmb and n alkanes in the pyrolysates of asphaltenes in the marine oils from the northern tarim basin and silurian tar sands from the tarim basin were determined ttmb has stable carbon isotopic compositions in the range from 23 to 24 and are about 12 more enriched in 13c than concomitant n alkanes 35 to 37 in the pyrolysates the results indicate a contribution from green sulfur bacteria chlorobiaceae to ttmb thus the depositional environments of the source rocks for the marine oils and the bitumen in tar sands from the tarim basin are characterized by periods of euxinic conditions within the photic zone

modelling earthquake rupture rates in fault systems for seismic hazard assessment the eastern betics shear zone abstract earthquake surface fault ruptures can show very complex geometries and involve different faults simultaneously consequently modern fault based probabilistic seismic hazard assessments psha need to account for such complexities in order to achieve more realistic modellings that treat fault systems as a whole and consider the occurrence of earthquake ruptures as aleatory uncertainties we use sherifs a recent approach of modelling annual rates of complex multi fault ruptures to obtain system level magnitude frequency distributions mfds for the eastern betics shear zone ebsz spain considering four fault rupture hypotheses we then analyze the consistency of each scenario based on data from the earthquake catalogue and paleoseismic studies the definition of the different rupture hypotheses was discussed within the frame of fault2sha esc working group and critical fault input data is extracted from previous published studies the four rupture hypotheses are defined as incremental scenarios based on fault geometry and kinematics with lengths varying from minimal fault sections to a rupture of nearly the whole system the results suggest that multi fault ruptures involving lengths up to single to several whole faults are consistent with the annual rates from both the instrumental catalogue and paleoseismic record the method does not allow to completely discard any hypothesis but it allows to weight the different models in a logic tree for seismic hazard assessment the approach is revealed as a practical tool for obtaining fault system mfds and as a useful tool for highlighting limitations and uncertainties in geological and paleoseismic data to be assessed this study aims to constitute a step forward in the consideration of complex multi fault ruptures for future seismic hazard assessments in the region

tertiary structures and hydrocarbon entrapment in the weald basin of southern england abstract the weald basin of southeast england was formed by rapid subsidence associated with thermal relaxation following early mesozoic extensional block faulting the basin appears initially to have taken the form of an easterly extension of the wessex basin but became the major depocentre during the upper jurassic and lower cretaceous with associated active faulting these movements appear to have ceased prior to albian times and a full upper cretaceous cover is believed to have been deposited in a gentle downwarp which extended far beyond the confines of the weald and wessex basins major inversion of the weald basin took place in the tertiary with both gentle regional uplift which in the eastern part of the basin is estimated to have exceeded 5000 feet 1525 metres and intense local uplift along pre existing zones of weakness which led to the formation of compressional features such as tight folds and reverse faults zones of tertiary deformation appear to have been strongly influenced by underlying particularly hercynian structural trends lower jurassic source rocks reached maturity in the early cretaceous and initial migration occurred at this time often over long distances into traps closed by pre aptian faults tertiary tilting and uplift led to the breaching of many of these pre existing traps and the formation of large folded closures a second phase of hydrocarbon migration particularly of gas took place at this time with significant vertical migration along fault zones major reservoirs located to date occur in middle jurassic carbonates and upper jurassic sandstones but deep burial in the basin has caused considerable destruction of primary reservoir characteristics changes in the temperature and pressure regimes and the mobilization of fluids within the basin resulting from the tertiary uplift caused further diagenetic changes particularly in the carbonate reservoirs exploration of the weald basin remains at a very early stage with a low drilling density to date the more recent drilling has focussed on earlier structures but traps formed or modified during the tertiary movements represent important exploration objectives although general deterioration in reservoir quality towards the centre and east of the basin makes large fold closures in these areas less attractive

vertical δ13corg gradients record changes in planktonic microbial community composition during the end permian mass extinction abstract the global carbon cycle experienced a major perturbation during the permian triassic transition reflected inter alia in a large increase in the vertical shallow to deep gradient of carbonate 13c 13ccarb in early triassic seas however the effect of this perturbation on the vertical gradient of organic matter 13c in seawater 13corg is less known to date here we examine geographic and secular variations in 13corg in late permian early triassic seas of the south china craton and their implications for contemporaneous changes in microbial community composition and paleoredox conditions vertical 13corg gradients document the existence of a narrow and relatively shallow oxygen minimum zone omz within the open ocean northern deepwater basin ndw and a deeper and thicker omz within the semi restricted nanpanjiang basin npjb for the pre extinction interval 13corg gradients between the shallow and intermediate watermasses of the ndb and between the shallow and deep watermasses of the npjb record contributions to the sediment of organic matter from bacteria living below the ocean surface layer these bacteria were mainly anaerobic chemoautotrophs that inhabited suboxic to anoxic waters of an omz and that produced more strongly 13c depleted organic matter than surface water eukaryotic algae thus increasing 13corg for the post extinction interval a reversed 13corg in the ndb is attributed to blooms of green sulfur bacteria or other anaerobic photoautotrophic bacteria that were resident in a deep chlorophyll maximum layer and that had smaller carbon isotopic fractionation than surface water algae although quantitatively important in intermediate to deep water areas during the early triassic such bacteria were absent in coeval shallow water sections reflecting water depth controls on microbial community composition a concurrent flatting of the 13corg gradient in the npjb was caused by a return of oxic conditions and or a decline of primary productivity in the surface ocean

geology and alteration in the golden mile kalgoorlie the giant kalgoorlie gold deposit 1 200 metric tons au recovered is surrounded by a wide wall rock alteration halo 1 x 3 km this alteration primarily represents the selectively pervasive formation of carbonate chlorite and localized intense pyrite and muscovite alteration which all formed synchronously with gold mineralization the carbonate alteration halo is interpreted as epigenetic because of evidence that carbonate chlorite assemblages overprint regional metamorphic fabrics furthermore the geometry of the alteration zone boundaries is controlled by ductile shear zones formed during regional deformation and the geochemistry of all the alteration zones suggests that one fluid was responsible for all assemblages there is no evidence of intense premetamorphic carbonation in the kalgoorlie area kalgoorlie is situated in the highly auriferous eastern goldfields province of the yilgarn block within a narrow corridor rift zone that contains several large gold deposits regional metamorphism has produced upper greenschist facies assemblages but has retained original rock textures at kalgoorlie the most important gold host is the golden mile dolerite 80 of gold produced a differentiated tholeiitic sill intruded between a lower mafic ultramafic pile including the paringa basalt the next most important gold host and overlying felsic rocks and metasediments the kalgoorlie syncline is the dominant tectonic structure in the main gold producing area of the golden mile adjacent to this infold of metasediments the golden mile dolerite and paringa basalt are the site of a number of ductile shear zones which formed synchronously with the syncline these zones and the many smaller shear zones between them have provided fluid channelways throughout the golden mile and are the site of most economic gold mineralization three alteration zones have been mapped in the golden mile dolerite on the basis of the mineralogic siting of fe i e the chlorite carbonate and pyrite zones the additional actinolite zone representing the unaltered regional metamorphic mafic assemblage has been converted to chlorite zone assemblages throughout the mined areas of the golden mile the carbonate zone bleached dolerite can be traced for 2 km through the main mineralized parts of the golden mile and to the full depth of lake view mine the boundary between the chlorite and carbonate alteration zones is locally sharp and controlled by ductile shear zones but is generally strata bound and preferentially developed in the more fe rich parts of the dolerite the pyrite zone which includes all economically gold mineralized areas is the site of the strongest muscovite alteration and is most intense and continuous in ductile shear zones the chlorite zone chlorite calcite or ankerite forms from mild carbonation of actinolite zone assemblages the carbonate zone ankerite siderite is a more local expression of this carbonation even after extensive carbonate alteration relative major element abundances are little changed and the main added components are limited to co 2 s k and rb the pyrite zone i e the gold lodes has ankerite muscovite quartz albite pyrite and minor siderite bearing assemblages it represents significant addition of sulfur the three alteration zones not only reflect differing degrees of alteration intensity but are also strongly influenced by host rock fe mg and this ratio largely determines the stability of chlorite favored by low fe mg and thus the distribution of the carbonate zone favored by high fe mg progressive deformation within the shear zones reworked existing mineralization kalgoorlie fits a metamorphic replacement model of gold formation by auriferous metamorphic fluids interacting with fe rich host rocks its great size is a function of a very well developed fluid channelway system via ductile shear zones and later fault zones and the favorable chemical nature of the host rocks especially the golden mile dolerite the full width of carbonation chlorite and carbonate zones reflects overlapping alteration envelopes around the closely spaced fluid pathways the processes responsible for the formation of most of the gold at kalgoorlie were essentially similar to those at several other archean gold deposits but on a larger scale

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

carbon isotopic evidence for chemocline upward excursions during the end permian event abstract a negative shift in marine inorganic carbon isotope composition 13 c carb during the end permian mass extinction has been used as evidence for several different extinction mechanisms changes to the 13 c of organic matter and the difference between it and 13 c carb 13 c 13 c carb 13 c org have been examined at few locations with conflicting interpretations we examine the changes to both organic and inorganic carbon isotopes across the permian triassic boundary at two marine sections from south china meishan and shangsi and compare these to data from other previously published sections through these analyses we demonstrate that a decrease in 13 c occurred during the extinction event throughout the paleo tethys ocean the extent and intensity of the decrease varies by location averaging a negative shift of 5 several possibilities as to the cause of this shift exist including siberian trap volcanism a change in the terrestrial marine organic carbon input to the system or a change in the dominant marine biota brought about through environmental changes such as widespread ocean anoxia euxinia the decrease in 13 c observed at many of these sections across the event horizon is here interpreted to represent a shift from algae cyanobacteria to less fractionating phototrophic sulfur bacteria in marine shelf environments resulting from upward excursions of the chemocline these chemocline upward excursions would release euxinic water to the photic zone allowing phototrophic sulfur bacteria to thrive the limited available biomarker data are consistent with this interpretation

the role of fluids in the metamorphism of komatiites agnew nickel deposit western australia the agnew nickel sulfide deposit is spatially associated with a lenticular body of ultramafic rocks which shows a concentric zonation in metamorphic mineralogy olivine tremolite chlorite cummingtonite enstatite assemblages occur at the margin of the ultramafic lens giving way to olivine anthophyllite olivine talc and olivine antigorite assemblages successively inwards these rocks are interpreted as having crystallized from komatiitic lavas and exhibit a spectrum of compositions from those of original flow tops to pure olivine adcumulates the relative modal abundances of metamorphic olivine tremolite and chlorite reflect original proportions of cumulus olivine and komatiite liquid in the protolith peak metamorphic conditions are estimated at 550 c based on garnet biotite thermometry at a maximum pressure of 3 kb this temperature falls within the narrow range over which metamorphic olivine may co exist with enstatite anthophyllite talc or antigorite depending upon the fugacity of water in the metamorphic fluid the observed mineralogical zonation is therefore attributed to infiltration by co2 rich fluids generated by decarbonation of talc carbonate rocks formed during pre metamorphic marginal alteration of the ultramafic lens metamorphic fluids were essentially binary mixtures of water and co2 with minor h2s having a maximum partial pressure less than 1 percent of total pressure enstatite bearing assemblages formed in the presence of co2 rich fluids at fluid rock volume ratios close to one while anthophyllite talc and antigorite bearing assemblages formed in the presence of progressively more water rich fluids at progressively lower fluid rock ratios

chlorobiaceae in palaeozoic seas revealed by biological markers isotopes and geology biomarker hydrocarbons in oils and sediments have considerable potential for assessing the nature of biological processes in the past but only a few can be uniquely related to particular organisms reef hosted oils in the silurian of the michigan basin canada and the devonian of western canada have high abundances of 1 alkyl 2 3 6 trimethylbenzenes their precise structures suggest that they are diagenetic products of aromatic carotenoids of the green sulphur bacteria individual components are enriched in 13c by 7 8 relative to the saturated hydrocarbons of the same oil an isotopic anomaly of this magnitude and direction correlates with a component of photosynthetic carbon assimilation by the reductive tricarboxylic acid cycle these results together with data on palaeoenvironments provide compelling evidence for the existence in ancient restricted seas of microbial communities containing chlorobiaceae organisms with distinctive biochemistry which leave morphologically identifiable remains

changes in palaeoenvironmental conditions during deposition of the permian kupferschiefer lower rhine basin northwest germany inferred from molecular and isotopic compositions of biomarker components abstract biomarker distributions based on gc and gc ms data supplemented by stable carbon isotopic compositions based on irm isotope ratio monitoring gc ms data have been used to investigate changes in depositional conditions in a number of samples from a 2 m core rheinberger heide covering the entire deposition of the permian kupferschiefer lower rhine basin northwest germany compound classes investigated are aliphatic and aromatic hydrocarbons and maleimides 1h pyrrole 2 5 diones the core has been previously divided into four sections ti tiia tiib and tiii based on lithology the biomarker distributions and the 13c values of components indicate contributions from cyanobacteria algae green sulphur bacteria and higher plants minor throughout kupferschiefer deposition all of the phytoplanktonic components show 13c enrichment in the lowest section suggesting a greater productivity the occurrence of components derived from green sulphur bacteria chlorobiaceae indicates that the entire deposition was characterised by periods of photic zone anoxia such conditions were rapidly established after the initial transgression of the zechstein sea and may have been productivity driven but were less prevalent during deposition of the upper core sections

molecular indicators of palaeoenvironmental conditions in an immature permian shale kupferschiefer lower rhine basin north west germany from free and s bound lipids a study of the distributions of free and s bound biomarkers and their 13c values in the extract of a bulk sample of the permian kupferschiefer from the lower rhine basin has been carried out to provide a more detailed characterization of the biological inputs the distributions and isotopic compositions of selected components released from nickel boride desulphurization have been compared with those of components in the free fraction the free biomarkers occur in greater abundance than their s bound counterparts the distribution and carbon isotopic composition of both free and bound components in the extract indicate a major cyanobacterial and algal input likewise the free and bound aromatic hydrocarbons contain components which reveal an origin from the carotenoids of chlorobiaceae green sulphur bacteria providing molecular evidence for the occurrence of photic zone anoxia in the water column most of the components in the complex mixture of mono di tri and tetra aromatics in the free aromatic hydrocarbon fraction result from cyclization and aromatization reactions

geochemistry of fluid inclusions from the mcintyre hollinger gold deposit timmins ontario canada type 1 h 2 o co 2 type 2 h 2 o co 2 type 3 ch 4 co 2 h 2 o and type 4 ch 4 fluid inclusions type 1 type 3 and some type 2 inclusions are primary or pseudosecondary in origin whereas type 4 and most type 2 inclusions are secondary the primary or pseudosecondary type 1 and 2 inclusions homogenized at temperatures of 220 degrees to 385 degrees c secondary type 2 inclusions homogenized at 160 degrees to 215 degrees c crushing tests confirm the presence of co 2 in samples with type 1 and 2 inclusions visually estimated x co2 values in type 1 inclusions range from 3 to 24 mole percent with bulk molar volumes of 19 to 28 cm 3 mole mineralizing fluids were at equilibrium with graphite at temperatures of 380 degrees to 480 degrees c and pressures of 1 to 3 kb calculated oxygen fugacities lie near the quartz fayalite magnetite buffer the mineralizing fluids differ compositionally from fluids in other types of ore deposits but resemble fluids derived from metamorphic rocks and deep level felsic intrusions modified journal abstract

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

a paired carbonate organic δ13c approach to understanding the cambrian drumian carbon isotope excursion dice abstract the middle cambrian cambrian series 3 drumian carbon isotope excursion dice represents a pronounced negative carbon isotopic excursion and has been proposed as a key chemostratigraphic marker for identifying the base of cambrian drumian stage and global correlation however the precise interbasinal correlation of the dice to the south china remains unsolved and the driving mechanism of the dice is to be further understood in this study we report new paired 13ccarb and 13corg data from the wangcun section in south china both 13ccarb and 13corg profiles capture a large negative excursion dice near the fad of p atavus we suggest that the parallel 13ccarb and 13corg negative excursions during the dice may have resulted from the shoaling of anoxic deep waters associated with the transgressive event shoreward and upward incursion of deep anoxic waters into oxygenated shallower water column during transgression could lead to the enhanced oxidation of dissolved organic carbon doc and introduce additional 13c depleted carbon to the surface water resulting in the parallel 13ccarb and 13corg negative excursions more importantly we use a box model to quantify the flux of doc oxidation needed to produce a carbon isotope excursion of the magnitude and duration of the dice we observed the model results indicate that oxidation of doc during the dice may require massive amounts of oxidants i e sulfate and oxygen probably causing further expansion of anoxia in the shallow marine environment we suggest that shoaling of anoxic water during the dice could have delayed the recovery of metazoan reef systems from the early middle cambrian mass extinctions

preservation of carbohydrates through sulfurization in a jurassic euxinic shelf sea examination of the blackstone band toc cycle in the kimmeridge clay formation uk a complete total organic carbon toc cycle in the upper jurassic kimmeridge clay formation kcf comprising the extremely toc rich 34 blackstone band was studied to investigate the controlling factors on toc accumulation compared with the under and overlying strata toc in the blackstone band was enriched by a factor of six and concomitantly the 13ctoc shows a 4 enrichment al normalized toc values indicated that the enhanced toc values were probably caused by increased toc accumulation and not by a decreased dilution with inorganic matter the amounts of short chain alkylated thiophenes and the sulfur rich unresolved complex mixture ucm in the kerogen pyrolysates as well as the toc al ratios correlated linearly with 13ctoc for sediments with toc al ratios 1 7 the alkylated thiophenes and sulfur rich ucm both originate from sulfurized carbohydrate carbon ccarb suggesting that the primary cause of the toc maximum is the enhanced contribution of ccarb to toc since carbohydrates can be substantially 13c enriched over lipids in biomass the enhanced contribution of ccarb explains the enriched 13ctoc values compound specific isotope data showed that primary productivity during deposition of the kcf toc cycle varied little while a two member isotopic mixing model showed that the preservation of ccarb relative to that of the lipid carbon may have increased by a factor of 10 in the blackstone band the enhanced preservation of ccarb was most likely caused by more frequent or longer lasting events of photic zone euxinia as revealed by the concentration of isorenieratene derivatives enhanced contributions of ccarb have also been observed in other kcf cycles suggesting that enhanced preservation of ccarb rather than an increase in primary production exerted direct control on the toc cycles of the kcf

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

carbon isotope characteristics of the diaromatic carotenoid isorenieratene intact and sulfide bound and a novel isomer in sediments abstract messinian marls from evaporitic cycle iv of the gessoso solfifera formation italy are known to contain in high abundance the diaromatic carotenoid isorenieratene of green sulfur bacterial chlorobiaceae origin along with a second diaromatic carotenoid the previous tentative assignment of the latter as a cis diastereomer of isorenieratene has now been confirmed this indicates that double bond isomerization occurs during early diagenesis and provides further evidence for the pathway proposed previously to link isorenieratene to a number of aromatic isoprenoid hydrocarbon biomarkers stable carbon isotopic data confirm the chlorobiaceae origin of the intact all trans isorenieratene isomer and indicate that the isomerization is accompanied by little or no kinetic isotope effect comparison of the 13c values of each of the isolated carotenoids measured as isorenieratane after hydrogenation with those of their sulfide bound counterpart in the polar fraction of the extracts also measured as isorenieratane indicates that sulfurization resulted in little depletion in 13c

biomarker geochemistry of a foreland basin the oligocene menilite formation in the flysch carpathians of southeast poland black shales of the menilite formation the source rock for oils in the carpathian overthrust belt display a large variability in their bulk and molecular geochemical parameters biomarker and stable carbon isotope analyses indicate a variable contribution from different algae particularly dinoflagellates and diatoms and cyanobacteria this is reflected by specific predominantly sulfurised biomarkers e g c35 homohopanoids c25 highly branched isoprenoids and marine n alkanes and by particular distributions of steranes and 4 methylsteranes comprising 24 nor and 24 methyl 27 norcholestanes and related novel steranes with a methylation at c 23 the presence of hopanoids of methanotrophic origin 13c up to 57 implies a temporarily enhanced full methane cycle in a marine environment which affected the isotopic composition of organisms dwelling in the upper photic zone the presence of isorenieratene derivatives indicate periods of euxinic conditions within the photic zone in all investigated sub basins

a multilayered water column in the ediacaran yangtze platform insights from carbonate and organic matter paired δ13c abstract large carbon isotope fluctuations have been systematically reported for ediacaran carbonate rocks the meaning of which remains controversial in order to better understand the mechanisms behind such variations we present new paired 13c data on carbonates 13ccarb and their associated organic matter 13corg from a shelf margin section yangjiaping of the doushantuo formation in this section the doushantuo formation starts with cap dolostones presenting 13ccarb values around 5 and 13corg values between 30 3 and 27 6 up section phased variations in 13ccarb and 13corg describe positive and negative excursions while their difference 13cdol org 13ccarb 13corg remains around 29 2 these new data allow the first reconstruction of lateral variations of 13ccarb 13corg and 13ccarb org for a shelf to basin cross section of the yangtze platform south china after integration with results reported previously for two other sections across the yangtze platform the isotope signals reveal strong lateral heterogeneities with complex variations of 13ccarb and 13cdol org in the inner shelf section phased variations in the shelf margin section with positive 13ccarb and 13cdol org close to 29 and dominantly negative 13ccarb with 13corg as low as 35 in the basin these variations are incompatible with the idea that the 13ccarb can systematically be used as a proxy of ocean surface waters assuming that 13ccarb are acquired in bottom waters and or upper sediments we show that the heterogeneous 13ccarb and 13cdol org are compatible with a stratified water column composed of up to three layers i an oxic surface layer where dissolved inorganic carbon dic is probably in isotope equilibrium with the atmosphere ii an intermediate euxinic layer with a lower 13cdic due to organic matter oxidation by ongoing sulphate reduction iii a bottom euxinic layer that seems to be restricted to the inner shelf lagoonal facies lacking sulphate containing methane and with a higher 13cdic due to dic production by methanogenesis if our model holds true it suggests that not only negative but also positive ediacaran carbon isotope excursions may reflect ocean stratification the positive excursion possibly recording a sulphate free methanogenic layer at the bottom of restricted basins

twentieth century proxy records of temperature and soil organic matter input in the drammensfjord southern norway abstract the drammensfjord in southern norway is an enclosed anoxic basin with a laminated sedimentary record the fjord is a transition area between the marine and terrestrial environments and thus its sedimentary archive contains information on both environments in order to reconstruct recent environmental changes in southern norway two sediment cores covering the last 90 years were analyzed we used the branched versus isoprenoid tetraether bit index as an indicator of terrestrial organic mater input and compared it to the stable carbon isotopic composition of total organic carbon 13 c toc the 13 c toc and bit index show opposing trends with 13 c toc indicating an increase in terrestrial input while the bit index suggests a decrease towards the present this contradiction is probably due to the different sources reflected by 13 c toc vegetation soil and anthropogenic input and the bit index only soil organic matter input in addition an increase in the recycling of respired co 2 within the fjord s water column could have depleted the 13 c toc of the marine component towards more negative values thus seemingly indicating an increase in terrestrial input whilst the bit index could have been affected by a reduction of riverine input and or an increase in archaeal biomass production the tetraether index of lipids with 86 carbons tex 86 was determined as a proxy for past water surface temperatures while some of the signal could be coming from the chemocline our results suggest that tex 86 indicates surface upper 25 m temperatures moreover tex 86 temperature patterns seem to follow variations in the historical record of averaged spring to fall oslo air temperature relatively closely suggesting the signal is produced during this period therefore tex 86 temperature records of fjord sediment cores can potentially be a useful tool in reconstructing past variations of coastal climates

carbon cycle perturbation and stabilization in the wake of the triassic jurassic boundary mass extinction event 1 the triassic jurassic boundary mass extinction event t j 199 6 ma is associated with major perturbations in the carbon cycle recorded in stable carbon isotopes two rapid negative isotope excursions in bulk organic carbon 13corg occur within the immediate boundary interval at multiple locations and have been linked to the outgassing of 12c enriched co2 from the central atlantic magmatic province in british columbia a positive 13corg excursion of 5 vienna peedee belemnite v pdb spans part or all of the subsequent hettangian stage here we examine the significance of these carbon isotope excursions as records of global carbon cycle dynamics across the t j boundary and test the link between carbon cycle perturbation stabilization and biotic extinction recovery patterns a combination of 13corg and palynological analyses from the late triassic to early jurassic in the mingolsheim core germany suggests that organic carbon isotope variations are best explained as the result of both compositional changes in terrestrial versus marine input and disturbance and recovery patterns of major terrestrial plant groups across the t j boundary a new high resolution 13ccarb record from the val adrara section in the southern alps italy spanning from the uppermost rhaetian through lower sinemurian does not exhibit a negative excursion at the t j boundary but does record a large positive 13ccarb excursion of 4 v pdb in bulk carbonate that begins at the t j boundary and reaches a local maximum at the early late hettangian boundary values then gradually decrease reaching 0 5 at the hettangian sinemurian boundary and remain relatively constant into the early sinemurian complementary 13ccarb data from 4 more sections that span the hettangian sinemurian boundary support carbon cycle stabilization within the upper hettangian our analyses suggest that isotope changes in organic carbon reservoirs do not necessarily require a shift in the global exogenic carbon reservoir and that the positive excursion in the carbonate carbon isotope record is best explained as the combined result of an increase in atmospheric pco2 leading to accelerated carbon cycling decreased skeletal carbonate production and increased organic carbon burial lasting several hundred thousand years the termination of the positive inorganic carbon isotope excursion coincides with the recovery of marine skeletal carbonate producers and coeval changes in terrestrial vegetation and reflects the gradual reduction in pco2 and the stabilization of the global carbon cycle during the sinemurian

reconstruction of δ13c of chemocline co2 aq in past oceans and lakes using the δ13c of fossil isorenieratene abstract high abundances of the diaromatic carotenoid isorenieratene derived from photosynthetic green sulfur bacteria chlorobiaceae were found just below the chemocline in an anoxic fjord in norway throughout the annual cycle the stable carbon isotope composition of this carotenoid co varied with the 13c of co2 aq and is independent of the co2 and isorenieratene concentration this constant isotopic fractionation p of isorenieratene versus co2 4 1 was subsequently used in the reconstruction of 13c of co2 at the chemocline in ancient oceans and lakes these reconstructions indicate that 13c of co2 at the chemocline is often influenced by isotopically light co2 formed by remineralization of organic matter this process can depending on the depth and stability of the chemocline also effect the isotopic composition of the phytoplankton and thus isotopic records of sedimentary inorganic and organic carbon

the nature of the variscan basement in southeast england evidence from integrated potential field modelling the variscides of southeast england are buried beneath post carboniferous cover interpretations of the basement are based mainly on deep boreholes geophysical signatures from the basement are contained within the regional gravity and magnetic data a gravity stripping exercise has been undertaken to remove the gravitational effect of the post variscan cover to generate a residual gravity map this map is interpreted along with integrated potential field modelling along four long interconnected profiles and compared with a revised pre permian subcrop map the magnetic evidence suggests that precambrian magnetic basement of the midlands microcraton has been buried southwards by north vergent variscan thusting over the foreland north of the variscan front short wavelength anomalies superimposed upon this deep precambrian source are due to shallower silurian and carboniferous volcanic rocks many residual gravity lows within the rhenohercynian zone may be related to thick low density devonian basins in the english channel a change in geophysical signature occurs north of the portland wight fault coinciding with phyllites in the basement models are presented in which the english channel magnetic anomalies originate within the pre permian basement comparisons with anomalies in the southwestern approaches suggest that the portland wight thrust is a terrane boundary possibly a subduction related suture implying southerly directed variscan subduction

sulphidic mediterranean surface waters during pliocene sapropel formation sapropels organic matter rich layers are common in neogene sediments of the eastern mediterranean sea the formation of these layers has been attributed to climate related increases in organic matter production1 2 3 and increased organic matter preservation due to oxygen depletion in more stagnant bottom waters2 3 here we report that eastern mediterranean pliocene sapropels4 contain molecular fossils of a compound isorenieratene known to be synthesized by photosynthetic green sulphur bacteria suggesting that sulphidic euxinic and therefore anoxic conditions prevailed in the photic zone of the water column these sapropels also have a high trace metal content which is probably due to the efficient scavenging of these metals by precipitating sulphides in a euxinic water column the abundance and sulphur isotope composition of pyrite are consistent with iron sulphide formation in the water column we conclude that basin wide water column euxinia occurred over substantial periods during pliocene sapropel formation in the eastern mediterranean sea and that the ultimate degradation of the increased organic matter production was strongly influential in generating and sustaining the euxinic conditions

sources of alkylbenzenes in lower cretaceous lacustrine source rocks west african rift basins abstract we conducted molecular biomarker and compound specific carbon isotope analyses of off line pyrolyzates from lacustrine samples recovered by onez 1 well the kissenda formation in the gabon basin and well a the maculungo formation in the kwanza basin in west africa pyrolyzates from onez 1 well contain isotopically depleted 1 2 3 4 tetramethylbenzene 1 2 3 4 tetramb 26 1 to 29 4 and 1 2 4 trimethylbenzene 1 2 4 trimb 26 4 to 29 7 which are isotopically similar to aryl isoprenoids 29 9 and 31 2 and carotane 28 5 to 31 3 identified in the bitumen fractions pyrolyzates from 3 samples in the lower sections of well a contain isotopically enriched 1 2 3 4 tetramb ca 16 and 1 2 4 trimb ca 14 consistent with an origin from diagenetic products of isorenieratene chlorobactene biosynthesized by green sulfur bacteria chlorobiaceae pyrolyzates from five samples in the upper sections of well a are characterized by the presence of intermediate carbon isotope values of 1 2 3 4 tetramb 20 7 to 22 8 and 1 2 4 trimb 19 3 to 21 2 and isotopically enriched isorenieratane ca 14 5 off line pyrolyzates from these lacustrine source rocks represent two distinct end members 13 c depleted diagenetic products of carotene derived from a lacustrine algal source and 13 c enriched diagenetic products of isorenieratene chlorobactene derived from green sulfur bacteria organic matter om from onez 1 well shows a significant proportion of algal biomass with a 13 c depleted composition the presence of 13 c enriched biomarkers derived from carotenoids of chlorobiaceae from samples in the lower part of well a indicates the development of photic zone euxinia and a significant biogeochemical role of sulfur in the upper section of well a the 1 2 3 4 tetramb and 1 2 4 trimb have 13 c values indicative of contributions from both chlorobiaceae and algae to the om

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

gold graphite association in granulite terrains implications for ore genesis abstract the gold occurrences of sri lanka are closely associated with the graphite deposits and are genetically related the quartz graphite margins of the vein graphite are shown to be metal accumulating the movement of co 2 rich fluids formation of graphite and the concentration of au are closely related whereas the co 2 rich fluids may well be the carbon carriers in the formation of graphite the original source of co 2 is still debated hydrothermal solutions when in contact with the graphite tend to activate the carbon thereby producing sites for the enrichment of gold the genetic link between the graphite veins and gold deposition has useful implications in the investigation of ore genesis in high grade metamorphic terrains and the exploration for gold

effects of an oceanic anoxic event on the stable carbon isotopic composition of early toarcian carbon the early toarcian transgression is marked by the occurrence of organic carbon rich shales in large parts of western europe and in other parts of the world as well based on the positive carbon isotope excursion of pelagic limestones in the middle to upper part of the falciferum zone in several of the tethyan sections the widespread occurrence of the early toarcian shales was explained by an oceanic anoxic event oae jenkyns 1988 jenkyns and clayton 1997 the rapid burial of large amounts of organic carbon which is rich in 12 c would have led to a relative enrichment in 13 c of the global carbon reservoir and hence to an increase in delta 13 c of the limestones in southwest germany and a number of other locations both organic and inorganic carbon display a negative isotope excursion in the upper part of the tenuicostatum zone and the lower part of the falciferum zone synchronous to black shale deposition and predating the positive isotopic excursion kuspert 1982 1983 it is presently unclear what the exact cause for this widespread negative isotopic excursion is jenkyns and clayton 1997 the objective of our study was to examine if the negative carbon isotope excursion of organic matter om in the southwest german toarcian shales can be attributed to compositional changes of the om or if the excursion is related to variations in delta 13 c sub co2 aq in the photic zone to this end we analyzed the molecular and stable carbon isotope composition of om in ten samples spanning the early toarcian toc 2 5 10 5 percent hi 350 700 biomarker distributions and kerogen pyrolysates differ only slightly among the samples and delta 13 c values of primary production markers follow closely those of associated carbonate and kerogen delta 13 c sub carb toc this strongly suggests that differences in delta 13 c toc are related to differences in delta 13 c of co 2 aq in the photic zone supporting kuspert9s model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters evidence for euxinic conditions extending into the photic zone was found by the presence of derivatives of carotenoids such as isorenieratane from anoxygenic phototrophic sulfur bacteria their concentrations are extremely low in black shales from the tenuicostatum zone but are significant in the falciferum and bifrons zone with a maximum in the exaratum subzone suggesting that photic zone euxinia pze was a common feature of the early toarcian sea in southwest germany our data therefore support the kuspert model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters to the upper part of the photic zone resulting in a negative isotope spike the enrichment in 13 c in the middle of the falciferum zone which followed the negative spike may be attributed to the burial of isotopically light organic matter through worldwide black shale deposition