the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

the motion of rigid ellipsoidal particles in slow flows abstract preferred orientations of fabric elements in tectonites are usually interpreted with reference to two continuum models namely those of march 1932 and jeffrey 1922 it is argued that the first of these is usually inappropriate if the fabric elements are rigid inhomogeneities embedded in a deformable matrix jeffrey s model is more applicable but until recently its use has been limited to problems involving axisymmetric particles and simple flow geometries in this paper jeffrey s equations have been solved numerically in order to investigate the behaviour of more general systems the motions of two particle shapes one a prolate spheroid the other a triaxial ellipsoid are considered in parallel for four specified flow geometries which involve pure or simple shear and combinations of both any departures from particle axisymmetry or from simple flow geometries have a significant effect on particle behaviour compared with that predicted by spheroid simple flow solutions

contemporaneous early diagenetic formation of organic and inorganic sulfur in estuarine sediments from st andrew bay florida usa estuarine sediment samples were collected from nine stations in st andrew bay near panama city florida usa contrasting grain size and varying concentration of organic carbon allowed a comparative study of the relationships among organic degradation processes sulfur cycling and diagenetic removal of dissolved sulfide produced by bacterial sulfate reduction abundance and sulfur isotopic composition were determined for dissolved sulfide dissolved sulfate pyrite humic acid sulfur fulvic acid sulfur and elemental sulfur presence of free dissolved sulfide and enrichment in 34s of porewater sulfate in samples from organic rich muddy sediments of st andrew bay indicate high rates of sulfate reduction and anoxic conditions below 5 mm depth such conditions are not reflected in samples from organic poor sandy near shore sediments collected from highly productive areas occupied by seagrass beds in this estuarine system pyrite and fulvic acid sulfur are the largest sinks for sulfide produced by bacterial sulfate reduction strong correlation between abundances of pyrite and fulvic acid sulfur suggests coincident formation in the uppermost 10 cm of sediment large differences in isotopic composition between these two species and consistent enrichment in 34s of the fulvic acid fraction however indicate two different reaction pathways abundance and sulfur isotopic composition of humic acid and fulvic acid sulfur suggest that organic sulfur is derived from mixing between 1 34s depleted sulfur with an unknown oxidation state that was recycled from bacterial hydrogen sulfide and 2 34s enriched sulfur interpreted as primary biosynthetic sulfur originally assimilated from dissolved sulfate samples taken from sandy sediment localities where aquatic vascular plants are rooted in the anoxic zone show a strong depletion in 34s in the fulvic acid sulfur fraction suggesting recycled hydrogen sulfide as the dominant source of organic sulfur

experimental evidence for rapid biotic and abiotic reduction of fe iii at low temperatures in salt marsh sediments a possible mechanism for formation of modern sedimentary siderite concretions fe iii reduction is a key component of the global iron cycle and an important control on carbon mineralization however little is known about the relative roles and rates of microbial biotic iron reduction which utilizes organic matter versus abiotic iron reduction which occurs without carbon mineralization this paper reports on the capacity for salt marsh sediments which typically are rich in iron to support abiotic reduction of mineral fe iii driven by oxidation of sulphide sediment was reacted with amorphous fes under strictly anaerobic conditions at a range of temperatures in biotic and abiotic microcosm experiments fe iii reduction driven by sulphide oxidation occurs abiotically at all temperatures leading to fe ii and elemental sulphur production in all abiotic experiments in biotic experiments elemental sulphur is also the oxidized sulphur product but higher bicarbonate production leads to feco3 precipitation abiotic reduction of fe iii occurs at rates that are significant compared with microbial fe iii reduction in salt marsh sediments the solid phases produced by coupled abiotic and biotic reactions namely elemental sulphur and feco3 are comparable to those seen in nature at warham norfolk uk furthermore the rates of these processes measured in the microcosm experiments are sufficient to generate siderite concretions on the rapid time scales observed in the field this work highlights the importance of abiotic fe iii reduction alongside heterotrophic reduction which has implications for iron cycling and carbon mineralization in modern and ancient sediments

strain patterns in models of spreading gliding nappes three experiments have been carried out in order to study the progressive and finite strain in nappes where gravitational spreading and gliding occur together these experimental models were made from analogue materials able to collapse under their own weight on an inclined plane throughout most of the models the stretch trajectories in a vertical plane parallel to the flow show a low amplitude sigmoidal pattern consistent with a previous theoretical model other stretch trajectories exist at the front and back ends of each model the kinematic significance of all these trajectories is discussed in detail highest strain intensities are always found next to the base of the model strain paths calculated at different stages of flow indicate clearly that nowhere in the model is the motion simple there is a complex combination in time and space of simple and pure shear except at the base of the model where the motion approximates a simple shearing near the two parallel lateral sides of the model a lateral boundary effect can be observed from the strong curvature of the transverse markers surface grid and vertical layers strain paths have also been estimated in this complex zone where wrench shearing is superimposed upon vertical shortening and thrust shearing the geological implications of these experimental models are discussed in relation to recent theoretical studies and field work

late pleistocene to holocene environmental changes as recorded in the sulfur geochemistry of coastal plain sediments southwestern taiwan abstract a core drilled at san liao wan in the southwestern coastal plain of taiwan has been analyzed for total sulfur contents isotopic values as well as ratios of pyritic sulfur to organic carbon our results demonstrate a close relationship between late pleistocene sea level change and the proxies generated in this study the inorganic sulfur contents indicate that at our study site the holocene transgression started at 11 ka and remained under seawater for thousands of years until the late holocene corresponding to a depth of 20 m in the study core the uppermost 20 m of core shows relatively high total organic carbon toc and 34s of inorganic sulfur suggesting a transitional environment such as muddy lagoon or marsh before the site turned into a modern coastal plain in the lower part of the core at depths of 110 145 m corresponding ages of 12 30 ka low sulfur contents are recorded probably indicating fluvial sediments deposited during the oceanic isotope stage ois 2 a sea level lowstand the lower part of the core roughly within ois 3 records at least two transgressions although the transgressional signals may be somewhat obscured by subsequent weathering the reworked origin of organic matter reported in previous studies is confirmed by our organic sulfur data however the marine organic source was periodically dominant the modern high sulfate concentrations in pore water have no correlation to the other sulfur species in the sediments probably indicating that the sulfate migrated into the site subsequent to early diagenesis

a reappraisal of kerogen formation abstract comparative microscopical and chemical studies of recognizable entities in kerogen and their extant counterparts suggest a new and simple mechanism of kerogen formation which clarifies the interrelationships between extant biomass kerogen and fossil fuels

mechanism of crystal redistribution in a sheet like magma body constraints from the nosappumisaki and other shoshonite intrusions in the nemuro peninsula northern japan processes of crystal separation in a magma heavily laden with crystals without phase change are investigated from observations on frozen magma systems nosappumisaki and other shoshonite intrusions in the nemuro peninsula japan for which the origin of the crystals and the initial conditions are well constrained the nosappumisaki intrusion is 120 m in thickness and extends for more than 1 5 km it exhibits a wide range of lithological variation principally as a result of crystal redistribution after intrusion crystals in each lithology can be clearly divided into two kinds according to their composition and texture those present before the intrusion of the magma phenocrysts and those that crystallized in situ after intrusion from the vertical change in mode and size of phenocrysts it is shown that 1 augite phenocrysts were rapidly deposited with little overgrowth after intrusion by significant coagulation or clustering on a time scale of more than a few years and 2 plagioclase phenocrysts definitely denser than the melt but concentrated in the upper level floated by counter flow of massive deposition of augite phenocrysts these results indicate that in a magma heavily laden with crystals of a few millimeters in size 20 vol crystal crystal and crystal melt interaction play an important role in the separation of crystals from the host melt

organic sulfur compounds formed during early diagenesis in black sea sediments abstract sediments from units i and ii of the black sea were analyzed to assess the early diagenetic formation of organic sulfur compounds osc a series of isomeric c28 2 4 dialkylthiophenes was found at low concentrations in surface sediments osc with c25 highly branched isoprenoid rbi skeletons were not found in surface sediments even though there was a rapid decrease in the concentrations of c25 hbi alkenes in the same sediments nor were osc found which contained carbon skeletons derived from c37 c39 alkenes which are also abundant in the sediment as depth increased in unit i concentrations of the c28 2 4 dialkylthiophenes decreased while c25 and c30 hbi thiolanes appeared at the bottom of unit i and increased in concentration into unit ii treatment of macromolecular material from sediment extracts with raney nickel yielded phytane as the dominant hydrocarbon as well as series of c25 and c30 hbi hydrocarbons carotane and isorenieratane these latter two components were generally absent from the free hydrocarbon fractions these results indicate that sulfur incorporation into functionalized lipids can occur during the very early stages of sedimentary diagenesis even at the sediment water interface on the other hand the rapid loss of c25 hbi alkenes in surface sediments could not be accounted for by sulfur quenching and other potential osc precursors such as c37 c39 alkenes also apparently did not incorporate sulfur into readily analyzable material

selenium as paleo oceanographic proxy a first assessment abstract selenium se is an essential trace element which with multiple oxidation states and six stable isotopes has been suggested as a potentially powerful paleoenvironmental proxy in this study bulk se concentrations and isotopic compositions were analyzed in a suite of about 120 samples of fine grained marine sedimentary rocks and sediments spanning the entire phanerozoic while the se concentrations vary greatly 0 22 72 ppm the 82 76se values fall in a fairly narrow range from 1 to 1 relative to nist srm3149 with the exception of laminated black shales from the new albany shale formation late devonian which have 82 76se values of up to 2 20 black sea sediments holocene and sedimentary rocks from the alum shale formation late cambrian have se to total organic carbon ratios se toc and 82 76se values close to those found in modern marine plankton 1 72 0 15 10 6 mol mol and 0 42 0 22 for the other sedimentary sequences and sediments the se toc ratios show se enrichment relative to modern marine plankton additional input of isotopically light terrigenous se may explain the se toc and 82 76se data measured in recent arabian sea sediments pleistocene the very high se concentrations in sedimentary sequences that include the cenomanian turonian oceanic anoxic event oae 2 may reflect an enhanced input of volcanogenic se to the oceans as the latter has an isotopic composition not greatly different from marine plankton the volcanogenic source does not impart a distinct signature to the sedimentary se isotope record the lowest average 82 76se values are observed in the oae2 samples from demerara rise and cape verde basin cores 82 76se 0 14 0 45 and could reflect fractionation associated with microbial or chemical reduction of se oxyanions in the euxinic water column in contrast a limiting availability of seawater se during periods of increased organic matter production and burial may be responsible for the elevated 82 76se values and low se toc ratios in the black shales of the new albany shale formation overall our results indicate that to unlock the full proxy potential of marine sedimentary se records we need to gain a much more detailed understanding of the sources chemical speciation isotopic fractionations and cycling of se in the marine environment

eruptive style of the young high mg basaltic andesite pelagatos scoria cone southeast of mexico city the eruption of the pelagatos scoria cone in the sierra chichinautzin monogenetic field near the southern suburbs of mexico city occurred less than 14 000 years ago the eruption initiated at a fissure with an effusive phase that formed a 7 km long lava flow and continued with a phase of alternating and or simultaneous explosive and effusive activity that built a 50 m high scoria cone on the western end of the fissure and formed a compound lava flow field near the vent the eruption ended with the emplacement of a short lava flow that breached the cone and was accompanied by weak explosions at the crater products consist of a microlite rich high mg basaltic andesite samples were analyzed to determine the magma s initial properties as well as the effects of degassing induced crystallization on eruptive style although distal ash fallout deposits from this eruption are not preserved a recent quarry exposes a large section of the scoria cone detailed study of exposed layers allows us to elucidate the mode of cone building activity petrological and textural data combined with models calibrated by experimental work and melt inclusion analyses of similar magmas elsewhere indicate that the magma was initially hot 1 200 c gas rich up to 5 wt h2o crystal poor 10 vol fo90 olivine phenocrysts and thus poorly viscous 40 80 pa s during the early phase low magma ascent velocity at the fissure vent allowed low viscosity magma to degas and crystallize during ascent producing lava flows with elevated crystal contents at t 1 100 c and blocky surfaces later the closure of the fissure by cooling dikes focused the magma flow at a narrow section of the fissure this led to an increased magma ascent velocity rapid and shallow degassing 3 km deep triggered 40 vol microlite crystallization limited times for gas escape and higher magma viscosity 6 105 4 106 pa s drove strong explosions of highly 60 80 vol and finely vesicular magma coarse clasts broke on landing which implies brittle behavior due to complete solidification this requires sufficient time to cool and in turn implies ejection heights of over 1 km which is much higher than normal strombolian activity hence magma viscosity significantly impacts eruption style at monogenetic volcanoes because it affects the kinetics of shallow degassing the long lasting eruptions of jorullo and paricutin which produced similar magmas in western mexico were more explosive this can be related to higher magma fluxes and total erupted volumes implications of this study are important because basaltic andesites are commonly erupted to form monogenetic scoria cones of the trans mexican volcanic belt

porphyroblast rotation versus nonrotation conflict resolution data on foliation intersection and or inflection axes preserved in porphyroblasts fias indicate that no porphyroblast rotation occurs during ductile deformation relative to spatial coordinates this contrasts with 99 of investigations of rigid objects in non coaxially deforming media where the objects rotate when anastomosing shear zone formation around relatively strong objects in a weaker matrix is modeled no porphyroblast rotation occurs formation of these anastomosing zones controls the development of this phenomenon called gyrostasis if such zones are absent porphyroblasts rotate in weak materials the gyrostatic situation arises because the superposition of simple shearing deformation normal to initial coaxial shortening results in only small rotations of principal axes of stress since shear zones are controlled by the orientations of principal axes of stress initial anastomosing zones retain their orientations and positions during subsequent non coaxial deformation the porphyroblast is isolated from the embedding non coaxially deforming matrix but this material close to the porphyroblast continues to deform coaxially no local rotation occurs this has major tectonic significance because allowing for the effects of rotation due to brittle deformation porphyroblasts can now be routinely used to access lengthy structural and or metamorphic histories destroyed in the matrix by reactivation such as movement directions shear senses and extended pressure temperature time paths

sulphur cycling in organic rich marine sediments from a scottish fjord in this study the biogeochemical transformations of sulphur in organic rich marine sediments in a scottish fjord are investigated by a combination of pore water and sediment geochemistry with sulphide diffusive gradient thin film probes and sulphate isotopic data 34s and 18o particular attention is paid to sulphur cycling in the upper sediment profile where sulphate reduction occurs but free sulphide is below the detection limits of conventional pore water geochemical analysis but quantifiable by sulphide diffusive gradient thin film in the uppermost part of the sediment core 18o sulphate decreased from near sea water values to 7 indicating that anoxic sulphide oxidation dominated during this interval sulphate 34s remained unchanged as there was no net sulphate reduction i e reduction was balanced by re oxidation below 4 cm depth there was a slight increase in sulphate 34s from 20 to 23 associated with minor accumulation of iron sulphide the 18o of the sulphate also increased to around 10 at 10 cm depth as a result of the isotopic exchange of sulphate oxygen with pore water and or sulphur disproportionation reactions mediated during sulphur cycling these processes continued to increase the 18o of the sulphate to 14 at 20 cm depth with no further change in the 34s of the sulphate below 20 cm depth free sulphide is detectable in pore waters and both the 34s of the sulphate and sulphide increase with depth with an offset controlled by kinetic fractionation during bacterial sulphate reduction the 34s of the sedimentary organic fraction shifted towards lower more bacteriogenic values with depth in the profile without any increase in the size of this sulphur pool thus the organic sulphur fraction was open to interaction with bacteriogenic sulphide without the occurrence of net addition therefore caution should be exercised when using sulphur isotopic compositions to infer simple net addition of bacteriogenic sulphide to the organic sulphur fraction

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

magma evolution recorded in plagioclase zoning in 1991 pinatubo eruption products plagioclase the most abundant phenocryst at mount pinatubo displays varying textures and compositions within the 1991 eruption products in june 7 14 dome forming andesite plagioclase phenocrysts show prominent rims with higher mgo 0 04 0 06 wt jo fe20j 0 6 0 8 wt o and k20 at given an than the interiors the compositions of the rims are identical to those of microlites which are abundant in the groundmass glass white dacitic pumice the most voluminous product of the june 15 eruption contains partly corroded plagioclase phenocrysts but no prominent rims and no microlites the interiors of phenocrysts from the dacitic pumice and the dome forming andesite are remarkably similar in terms of textures and compositions they show oscillatory zoning mostly an35 6o low mgo 0 02 wtojo and fe20j 0 10 0 30 wt jo and similar k20 at given an this similarity indicates that the two types of plagioclase phenocrysts formed in the same rhyolitic melt the oscillatory zoning likely formed by temperature fluctuations in the convecting magma and incorporation and degassing of external fluids a portion of the felsic magma 800 c mixed with a mafic melt 1000 1100 c to become an andesitic magma that extruded to form the june 7 14 dome all plagioclase phenocrysts in the andesite were derived from the felsic magma the mixing caused destabilization of phenocrysts forming sieve textures dusty zones and partial resorption extrusion of the mixed magma resulted in overgrowths on once resorbed phenocrysts and the nucleation of plagioclase microlites in the groundmass glass in the unmixed remaining portion of the felsic magma some plagioclase underwent partial resorption but did not develop overgrowths this lack of overgrowths and the absence of micro lites in the groundmass glass of the june 15 dacitic pumice indicate rapid magma ascent during the eruption and a short time span between the injection of a mafic melt and the cataclysmic eruption supporting the linkage between the two

sulfur enrichment of humic substances in a delaware salt marsh sediment core abstract humic sulfur operationally defined as the sulfur extracted with humic substances in 0 l n naoh solution comprises up to 51 of the total sulfur inventory in a sediment core taken from a delaware spartina alterniflora marsh pyrite sulfur is the next largest fraction except at the near surface sediments where zerovalent sulfur concentrations are significant x ray photoelectron spectroscopy indicates that the humic sulfur consists of sulfoxides or sulfones and in a more reduced state organic sulfides and or organic polysulfides a subsurface decrease in the humic acid c s atomic ratio to 56 2 suggests that the upper 4 cm of marsh sediment is the locus for humic sulfur formation s alterniflora detritus and microbial biomass cannot fully account for observed sulfur enrichment of humic c s atomic ratios therefore the enrichment of humic substances by sulfur is probably via reaction of reduced sulfur compounds with organic matter a humic sulfur formation rate of 10 6 mol s cm 3 a 1 is calculated for the surface sediments and leads to an areal production of 18 mol s cm 2 a 1 of humic sulfur humic sulfur formation and preservation is enhanced by the limited availability of iron for the rapid precipitation of iron sulfide minerals and the apparent resistance of organic sulfur compounds towards reoxidation to sulfate especially in the upper 9 cm of marsh sediment where inorganic sulfur compounds are rapidly oxidized

compound tectonic fabrics in singly folded rocks from southwest virginia u s a abstract a compound tectonic fabric is associated with folded and faulted calcareous mudrock in the foreland fold and thrust belt of the appalachian orogen two approximately coplanar spaced cleavages evolved during one episode of folding an earlier close spaced 40 spacing domainal microfabric is overprinted by and transitional with a wider spaced 2 3 cm spacing spaced disjunctive cleavage development of the spaced cleavage from the domainal microfabric is considered due to a change in dominant deformation mode from controlled grain boundary sliding to pressure solution factors which determine whether single or compound cleavage fabrics develop in singly folded rocks may relate to the timing of cleavage forming deformation increments relative to metamorphic dehydration reactions at low metamorphic grade anchimetamorphism to low greenschist facies it is proposed that grain alignment cleavage will develop when reactions are concomitant with deformation whereas a spaced cleavage will develop when reactions are inhibited or have gone to completion compound tectonic fabrics result when reactions either undergo completion or are initiated during the period of cleavage formation there are three distinct geometrical associations of compound fabrics and folds these associations are determined by the relative timing of formation of the various cleavages with respect to the folding

garnet rotation and the development of axial plane crenulation cleavage rotated helicitic garnets syntectonically overgrowing axial plane crenulation cleavage on the limbs of folds show the opposite sense of rotation to that undergone by the folded foliation during the development of the fold the garnet rotation is inconsistent with simple minded shear models for the development of the crenulation cleavage and it is useful to consider this problem in order to understand the development of crenulation cleavage better various models are considered in an attempt to explain both garnet rotation and cleavage morphology earlier models were based on the assumption that garnet rotation is driven by shear parallel to s2 they were mostly unsatisfactory but one involving migration of the crenulation hinges is viable when combined with other models described here the new models proposed here are based on the assumption that garnet rotation is driven by shear on the crenulated surface s1 the new foliation s2 is considered to be a passive structure at least in the early stages of its development these models satisfactorily explain garnet rotation and development of the cleavage including differentiation and they can be used to predict the morphological evolution of the cleavage microstructure as it should be preserved in garnets comparison of observed and predicted helicitic structures strongly supports the proposed models evidence is presented to show that where a garnet has an se that is a schistosity and an si that is a crenulation cleavage the schistosity can have developed by unfolding of the crenulations

contrasting watermass conditions during deposition of the whitby mudstone lower jurassic and kimmeridge clay upper jurassic formations uk abstract the whitby mudstone formation wmf and kimmeridge clay formation kcf are both jurassic organic rich black shale units containing well preserved marine organic matter despite such gross similarities they exhibit opposite trends in 13 c toc versus wt decarbonated total organic carbon toc r 0 76 for wmf and 0 71 for kcf the 13 c toc versus toc trend also varies geographically within both units only the kcf data exhibit a positive correlation between 13 c toc and 15 n org r 0 76 and the presence of aryl isoprenoids probable indicators of photic zone anoxia maturity differences are insufficient to explain such contrasts bulk and compound specific isotopic variations in the kcf are interpreted largely as a reflection of primary productivity during deposition rather than a dominantly diagenetic signal due to incorporation of sulphurised carbohydrate the contrasts between the formations and the geographic variation in coeval shelf sediments are explained by a model stressing the relative positions and stabilities of the chemocline pycnocline nutricline and euphotic zone and the effect these have on productivity co 2 recycling and bacterial floras

an experimental study of the influence of oxygen fugacity on fe ti oxide stability phase relations and mineral melt equilibria in ferro basaltic systems

along strike structural variations in the southern patagonian andes insights from physical modeling abstract the southern patagonian andes between 48 and 53 sl offers a unique opportunity to study the results of orogenic growth superimposed over a previously rifted region in this sector the northern austral or magallanes basin was affected by late to middle jurassic extension followed by late cretaceous to neogene tectonic compression the resultant fold thrust belt displays significant along strike variations in width and lateral position of the structural domains that may be reflecting a first order control of the jurassic extensional depocenters as proposed in previous works this hypothesis is tested using a series of scaled sandbox analog models involving the positive inversion of two adjacent depocenters with different extensional rates accommodated by a transfer fault the correlation between structures in the southern patagonian andes and the features in the model have important first order similarities supporting the theory of a positively inverted extensional basin with a previous history of southward increase in extension moreover structural cross sections analyzed from field and seismic data have a geometry that is consistent with serial cross sections resulting from the models

sulphur speciation in anoxic hypersaline sediments from the eastern mediterranean sea abstract the anoxic hypersaline tyro and bannock basins are among the most sulphidic bodies of water in the marine environment h2s 2 mm we report the distribution of elemental sulphur acid volatile sulphur avs organic polysulphides humic sulphur 0 5 m naoh extractable and pyritic sulphur in the sediments from these basins pyritic sulphur appears to be the main phase of inorganic reduced sulphur 50 80 of the total sulphur pool and is at the same level about 250 moles per gram dry weight in cores recovered from the two basins remarkably humic sulphur has been found to account for 17 28 of the total sulphur pool in the tyro basin and for 10 43 in the bannock basin sulphur isotope data show negative 34s values for both pyritic sulphur 34s 19 c to 39 and humic sulphur 34s 15 to 30 this indicates that both pyritic and humic sulphur originate from microbially produced hzs neither basin shows a significant correlation between pyritic sulphur and organic carbon suggesting syngenetic pyrite formation additionally the degree of pyritization in these sediments dop is 0 62 indicates that pyrite formation is limited by the reactivity of fe humic sulphur correlates with the pyritic sulphur distribution and seems to be related with gelatinous pellicles bacterial mats at the interface between oxic seawater and brine both pyritic and humic sulphur can be formed in the water column at the interface of oxic seawater and brine by a syngenetic pathway about 5 of the pyrite is formed in the sediments by diagenetic processes the presence of a bacterial mat and high hzs content in the brines favour such conditions however most of the humic sulphur inventory can be supported by diagenetic processes although these basins differ in their major element chemistry their reduced sulphur species chemistry appears to be similar

transport and reduction of sulfate and immobilization of sulfide in marine black shales in fine grained sediments in which the amount of reduced sulfur retained in stable phases substantially exceeds that present initially in pore waters rates of sulfate reduction may have equaled or exceeded rates of sulfate transport resulting in enrichment of sup 34 s in pore waters and reduction products abundance and isotopic compositions of reduced sulfur compounds can be used to calculate the extent of sulfide retention and improve reconstructions of carbon sulfur oxidation reduction redox budgets the miocene monterey formation and upper devonian new albany shale represent distinct types of black shales that accumulated under different conditions of sulfate reduction our results suggest that the rate of sulfate reduction was controlled largely by mass transport in the monterey and by the reduction process itself in the new albany sulfide was more efficiently retained in the monterey thus each mole of sulfide in the new albany represents a greater amount of sedimented organic carbon removed during sulfate reduction 30 refs 4 figs 1 tab

porphyroblast inclusion trails the key to orogenesis detailed microstructural analysis of inclusion trails in hundreds of garnet porphyroblasts from rocks where spiral shaped inclusion trails are common indicates that spiral shaped trails did not form by rotation of the growing porphyroblasts relative to geographic coordinates they formed instead by progressive growth by porphyroblasts over several sets of near orthogonal foliations that successively overprint one another the orientations of these near orthogonal foliations are alternately near vertical and near horizontal in all porphyroblasts examined this provides very strong evidence for lack of porphyroblast rotation the deformation path recorded by these porphyroblasts indicates that the process of orogenesis involves a multiply repeated two stage cycle of 1 crustal shortening and thickening with the development of a near vertical foliation with a steep stretching lineation followed by 2 gravitational instability and collapse of this uplifted pile with the development of a near horizontal foliation gravitational spreading near coaxial vertical shortening and consequent thrusting on the orogen margins correlation of inclusion trail overprinting relationships and asymmetry in porphyroblasts with foliation overprinting relationships observed in the field allows determination of where the rocks studied lie and have moved within an orogen this information combined with information about chemical zoning in porphyroblasts provides details about the structural metamorphic p t t paths the rocks have followed the ductile deformation environment in which a porphyroblast can rotate relative to geographic coordinates during orogenesis is spatially restricted in continental crust to vertical ductile tear transcurrent faults across which there is no component of bulk shortening or transpression

fracture related hydrothermal alteration of metagranitic rock and associated changes in mineralogy geochemistry and degree of oxidation a case study at forsmark central sweden red staining of rocks due to fluid rock interaction during hydrothermal circulation in fractures is a common feature in crystalline sequences in this study red stained metagranitic rock adjacent to fractures in forsmark central sweden has been studied with emphasis on the mineral reactions and associated element mobility occurring during the alteration the main mineral reactions associated with the hydrothermal alteration are an almost complete saussuritization of plagioclase accompanied by total chloritization of biotite magnetite has been partly replaced by hematite whereas quartz and k feldspar were relatively unaffected by the hydrothermal alteration we show that redistribution of elements on the whole rock scale was very limited and is mainly manifested by enrichment of na2o and volatiles and depletion of cao feo and sio2 in the red stained rock however on the microscale element redistribution was more extensive with both intragranular and intergranular migration of e g ca k na al si fe ba cs rb sr ti and rees the altered rock shows a shift towards higher total oxidation factors but the change is smaller than 1 and the red staining of the rock is due to hematite dissemination rather than a significant oxidation of the rock an increase in the connected porosity is also observed in the altered rock

the effects of feo on the system cmas at low pressure and implications for basalt crystallization processes the common occurrence of olivine clinopyroxene and plagioclase in natural basalts may suggest that crystallization of these phases exerts important controls on the evolution of natural basalts at low pressure in order to understand the effects of such an assemblage on the evolution of basalt an experimental study of the divariant assemblage 1 an cpx ol in the system cmas feo was undertaken at 1 bar and under very reducing conditions experiments have been performed along three isothernal sections detailed electron microprobe data have been collected on all the coexisting phases combining these data with available data in the system cmas the compositions of all the coexisting phases have been described as functions of temperature and cao content in the melt by applying a multiple linear regression method this allows a quantitative characterization of the divariant assemblage 1 an epx ol in the system cmas feo from 1275 c to 1160 c with liquid compositions ranging from mg 1 to mg 0 28 knowing the composition temperature relationships the basic t x configuration of the assemblage 1 an cpx ol has been analysed and mass balance calculations have been performed to examine the feo effect on different crystallization processes addition of feo to the system cmas transforms the thermal divide in the assemblage 1 an cpx ol to a thermal ridge and shifts the spine of the thermal ridge towards sio2 poor compositions with decreasing temperature this indicates that tholeiitic basalts can be relatively silica poor and evolve towards slightly more silica poor compositions with increasing feo content pigeonite replaces ortheonstatite as a crystallizing phase along the silica rich boundary of the assemblage 1 an cpx ol in some iron and silica rich composition olivine possibly terminates its crystallization or even starts resorption prior to pigeonite precipitation this suppresses silica enrichment in the melt crystallization paths of the assemblage 1 an cpx ol are determined by the detailed t x relations of the thermal ridge with the melt evolving away from the spine the liquid evolution trend depends strongly on the initial compositions a tholeiitic liquid can follow a moderate silica enrichment path at the same very reducing condition of there is a high modal proportion of olivine a fenner mechanism therefore is at work at the same place as a bowen mechanism

magma evolution and open system processes at shiveluch volcano insights from phenocryst zoning phenocryst zoning patterns are used to identify open system magmatic processes in the products of the 2001 eruption of shiveluch volcano kamchatka the lavas and pumices studied are hornblende plagioclase andesites with average pre eruptive temperatures of 840c and fo2 of 1 5 2 1 log units above nickel nickel oxide nno plagioclase zoning includes oscillatory and patchy zonation and sieve textures hornblendes are commonly unzoned but some show simple multiple or patchy zoning apatite microphenocrysts display normal and reverse zoning of sulphur the textural similarity of patchy hornblende and plagioclase together with ba sr systematics in patchy plagioclase indicate that the cores of these crystals were derived from cumulate material plagioclase liquid equilibria suggest that the patchy texture develops by resorption during h2o undersaturated decompression when h2o saturated crystallization recommences at lower pressure reduced ph2o results in lower xan in plagioclase causing more al rich hornblende to crystallize plagioclase cores with diffuse oscillatory zoning and unzoned hornblende crystals probably represent a population of crystals resident in the magma chamber for long periods of time in contrast oscillatory zoning in the rims of plagioclase phenocrysts may reflect eruption dynamics during decompression crystallization increasing fe al in oscillatory zoned rims suggests oxidation as a result of degassing of h2o during decompression a general lack of textural overlap between phenocryst types suggests that different phenocryst populations were spatially or temporally isolated during crystallization we present evidence that the host andesite has mixed with both more felsic and more mafic magmas olivine and orthopyroxene xenocrysts with reaction or overgrowth rims and strong normal zoning indicate mixing with basalt sieve textured plagioclase resulted from mixing of a more felsic magma with the host andesite the mineralogy and mineral compositions of a mafic andesite enclave are identical to those of the host magma which implies efficient thermal quenching and thus small volumes of intruding magma mixing of this magma with the host andesite results in phenocryst zoning because of differences in dissolved volatile contents we suggest that small magma pulses differentiated at depth and ascended intermittently into the growing magma chamber producing incremental variations in whole rock compositions

the analysis of progressive deformation in rock analogues abstract two dimensional deformation experiments using analogue materials such as octachloropropane and camphor have proven to be a powerful tool in the investigation of microstructural development since they make it possible to observe the specimen throughout its deformation history the addition of dispersed marker particles makes it possible to trace the movement of material points during deformation from this information the flow and deformation can be interpolated for any point within the specimen at any time the geometry of the flow and deformation can then be visualized in the form of grids contour plots strain ellipses and other methods despite this apparently ideal setting for studying flow and deformation the need to use marker particles to trace material points introduces unexpected problems in the analysis we present a computer program to analyse the movement of marker particles digitization of the positions of the particles is improved by the use of video input and semi automatic digitization the use of polynomials to describe the complete path of marker particles and least squares best fit solving improves the analysis of the data

variable regimes in magma systems documented in plagioclase zoning patterns el misti stratovolcano and andahua monogenetic cones abstract magmas may experience closed or open system evolution during their ascent and evolution in the upper crust chemically closed system processes can involve heat transfer from underplating mafic magmas or decompression due to magma ascent on the other hand newly injected magmas can mix with the residing magma and hybridize plagioclase zonation patterns and electron microprobe major and trace element analysis constrain these contrasting scenarios for andesites from the 80 km3 el misti stratovolcano 5822 m and a field of relatively small monogenetic andahua scoria cones both in southern peru in particular fe concentration in plagioclase reveals valuable information within a magmatic system to explore the dominance of closed vs open system processes large and correlated anorthite fe contrasts at resorption zones identify compositional mixing related to recharge subhorizontal an fe variations record thermal or water induced effects el misti volcano a large but still relatively youthful stratovolcano is dominated during most of its approx 120 ka history by closed system effects during its evolution recharge and mixing mostly occurred cryptically as it is not recorded in drastic compositional changes in magmas or their phenocrysts a small volume erupted at el misti however is affected by strong open system behaviour as reflected in strongly correlated variations in an and fe contents of plagioclase compositions its crystal population is texturally and chemically very similar to lavas of the monogenetic cinder cones of the andahua volcanic field for the el misti magma reservoir resorption events caused by thermal effects or magma ascent are more frequent in comparison to the actual eruption frequencies many cycles of closed system evolution heat transfer and decompression therefore occurred without resulting in an eruption plagioclase zonations from lavas of the monogenetic andahua field indicate that any mafic batch that intruded the much smaller reservoirs immediately triggered an eruption by contrast a large magma system that feeds el misti volcano can easily accommodate a new batch without causing eruption

experimental investigation of the effects of fluid heterogeneity upon the motion of rigid ellipsoidal inclusions during bulk inhomogeneous shortening abstract an experimental study of the motions of rigid ellipsoidal inclusions within deforming homogeneous and heterogeneous fluid systems indicated that the time behaviour of such objects measured relative to the experimental apparatus can vary significantly between the two system types during inhomogeneous time dependent flow initially aligned ellipsoidal inclusions within a deforming homogeneous fluid were rotated in the same sense as an adjacent passive strain marker introduction of heterogeneity by partially enclosing the ellipsoidal inclusions with a less viscous fluid resulted in three different rigid body behaviours during deformation the behaviours observed for initially aligned ellipsoids in the system containing fluid heterogeneities were 1 opposite sense rotation to that of the strain marker 2 negligible rotation of the objects and 3 same sense of rotation as that of the strain marker a computerized time based analysis of the deformation possible through the incorporation of marker particles into each of the two different deforming systems revealed similar deformation kinematics for the two experimental types at both the system and sub system scale results of the experiments indicate that significant differences can occur in rigid body behaviour between apparently similarly deforming homogeneous and heterogeneous systems the results suggest that fluid flow theory as derived for rigid body behaviour in homogeneous fluids may be unsuitable for the purpose of qualitatively predicting rigid object behaviour within deforming rock systems that are highly anisotropic at the porphyroblast porphyroclast scale this notion is supported by an examination of the assumptions and simplifications upon which the theory relating to rigid body behaviour in homogeneous fluids was originally based

multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks pyritized plant tissues with well preserved morphology were studied in rocks from vanoise western alps france that experienced high pressure low temperature metamorphic conditions in the blueschist facies during the alpine orogeny organic and inorganic phases composing these fossils were characterized down to the nanometer scale by raman microspectroscopy scanning transmission x ray microscopy and transmission electron microscopy the graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and or thermal degradation during metamorphism various mineral phases are closely associated with this organic matter including sulphides such as pyrite and pyrrhotite carbonates such as ankerite and calcite and iron oxides a tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed the absence of traces of organic matter sulphurization the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional diagenetic environment of these metasediments was likely rich in reactive iron fe sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism in contrast iron oxides which form rims of 100 nm in thickness at the interface between organic matter and fe sulphides may result from metamorphic processes this study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism

erratum to the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate palaeogeogr palaeoclimatol palaeocol 165 2001 27 52 abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18 o and 13 c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuation maximum oxygen depletion and an extreme negative shift of 13 c org values 34 occurred during the early falciferum zone this is explained by the recycling of 12 c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18 o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18 o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

sulphur isotope geochemistry of pyrite from the upper cretaceous marshybank formation western interior basin abstract variations in the texture and sulphur isotopic composition of pyrite in the upper cretaceous marshybank formation are linked to depositional environment abundant framboidal and lesser euhedral pyrite precipitated in offshore marine rocks moderate quantities of pyrite also crystallized in brackish coastal plain rocks however in contrast to marine pyrite coastal plain pyrite is dominantly euhedral in texture reflecting direct precipitation from a porewater with a relatively low dissolved sulphide concentration in the marine rocks pyrite 34s values range from 35 7 to 27 4 avg 4 8 canyon diablo troilite cdt pyrite within carbonate concretions hosted in these marine rocks has a similar isotopic composition 49 8 to 10 6 cdt however isotopic values are often highly variable within individual concretions as a result of the heterogeneous nature of sulphate reduction and pyrite formation within marine sediments pyrite in coastal plain rocks is characterized by relatively high 34s values 4 2 to 35 5 avg 13 2 cdt while the overlying sideritized conglomerates have the lowest 34s values reported for cretaceous rocks from the western interior basin of north america 49 8 to 41 7 cdt very low 34s values which are only observed in the marine rocks are indicative of microbial sulphate reduction and pyrite formation in a sulphate replete i e open system higher 34s values up to 18 which were obtained for both the marine and coastal plain rocks are indicative of progressive pyrite crystallization in a sulphate limited i e closed system such conditions are expected in marine sediments as burial occurs and in brackish i e low sulphate sediments pyrite with very high 34s values 18 is common in the coastal plain rocks these high values are the result of influx of 34s enriched residual sulphide derived from overlying marine units a minor amount of 34s enriched pyrite is also present within and proximal to marine sedimentary unit h which was deposited at the same time as the coastal plain rocks we hypothesize that porewater containing 34s enriched residual sulphide flowed from the coastal plain and along unit h into the marine sediments thus producing anomalously high 34s pyrite

a simple three dimensional model of diffusion with precipitation applied to localised pyrite formation in framboids fossils and detrital iron minerals a three dimensional diffusion with precipitation model is constructed to estimate radial variations in the amounts of pyrite which precipitate where a spherical mass of organic matter producing h2s by sulphate reduction is enveloped in a dissolved iron bearing porewater the model indicates that higher rates of sulphate reduction more readily metabolisable organic matter and larger organic masses require increasingly high dissolved iron concentrations in order to confine pyrite or iron sulphide precipitation to the decay site the maximum size sphere of exceedingly metabolisable organic matter equivalent to fresh planktonic material which can be pyritised is about 50 m radius where decay occurs in porewaters with typical dissolved iron levels this radius is close to the maximum radius of framboidal pyrite the formation of which could involve model type processes fossil carcases although mainly composed of less readily metabolisable organic matter may be orders of magnitude larger and the model demonstrates that their pyritisation requires unusually high porewater dissolved iron concentrations these inferred chemical conditions are consistent with sedimentological observations of pyritisation in beecher s trilobite bed new york state at greater depths within the sediment pyritisation is controlled by the kinetics of iron mineral reactivity towards h2s sediments vary widely in their exposure times to h2s which can range at least from 50 to 106 years at low exposure times only iron oxides are pyritised whereas at high exposure times even the most refractory iron silicates can become pyritised

the rotation of garnet porphyroblasts around a single fold lukmanier pass central alps abstract the orientation of the straight internal foliation s i within large 5 mm garnet porphyroblasts has been measured relative to the orientation of the external foliation s e around a single antiform of 0 5 m wavelength which folds the dominant regional foliation the internal foliation is not constant in orientation but varies consistently both with position around the fold and with the porphyroblast ellipticity the dip of s i hinge dip taken as zero is consistently less than the dip of s e it increases with increasing dip of s e and with increasing ellipticity of the porphyroblasts s i effectively defines a fold with an opening angle greater than that in the external foliation the opening angle of this fold in s i decreases with increasing porphyroblast ellipticity the observed variation in the orientation of s i can be explained qualitatively by a flattened flexural flow model for fold development as could be expected for folding of a pre existing strongly anisotropic foliation the measurements clearly demonstrate that rotation of porphyroblasts relative to geographical co ordinates did occur during the development of this fold and that a model based on the classical theories of rotation of stiff inclusions in a weaker viscous matrix is most appropriate

experimental study of liquid evolution in an fe rich layered mafic intrusion constraints of fe ti oxide precipitation on the t f o 2 and t ϱ paths of tholeiitic magmas the newark island layered intrusion a composite intrusion displaying a similar fractionation sequence to the skaergaard has both dikes which preserved liquids fed into the intrusion and chilled pillows of liquids resident in the chamber this study reports experimentally determined one atmosphere liquid lines of descent of these compositions as a function of oxygen fugacity which varies from qfm quartz fayalite magnetite to 0 5 log10 units above iw iron wustite these experiments reveal a strong oxygen fugacity dependence on the order of appearance and relative abundances of the fe ti oxide minerals titanomagnetite saturates prior to ilmenite at qfm but the order is reversed at lower oxygen fugacities in the layered series of the newark island intrusion ilmenite arrives shortly before titanomagnetite and the titanomagnetite ilmenite ratio decreases monotonically after the cumulus appearance of titanomagnetite comparison of the crystallization sequence in the intrusion with that of the experiments requires that the oxygen fugacity in the intrusion increased relative to qfm before titanomagnetite saturation and decreased afterward but always remained between the qfm and iw buffers similar trends in the modes of the fe ti oxides ilmenite and titanomagnetite in the skaergaard kiglapait and somerset dam intrusions along with fe2o3 feo ratios in morbs suggest that such a temperature oxygen fugacity path may be typical of tholeiitic magma differentiation calculations of the temperature density paths of the experimental liquids indicate that at all possible oxygen fugacities the density must have decreased abruptly after fe ti oxide saturation accordingly liquids replenishing the intrusion after fe ti oxide saturation should pond at the bottom of the chamber quenching against older cumulates field observation at the newark island intrusion confirm this prediction the similarities in the fractionation paths of several other layered intrusions to that of the newark island intrusion suggest that the density of the liquids in these intrusions also decreased after fe ti oxide saturation experiments on a suggested initial skaergaard liquid are consistent with this model

new range data for marine invertebrate species across the early toarcian early jurassic mass extinction abstract we have reinvestigated the marine mass extinction interval that occurred during the early toarcian which was a time of widespread marine anoxia the ranges of marine benthic invertebrates are significantly altered using new observations from the cleveland basin uk goniomya rhombifera is reported for the first time from the whitby mudstone formation and together with an increased epifaunal bivalve diversity indicates a brief relatively oxygenated period towards the end of the event the new data together with published results suggest three apparent extinction horizons on a global scale the first is just above the pliensbachian toarcian boundary and the following two are in the semicelatum ammonite subzone as a result of the signor lipps effect there may be only one or possibly two true extinctions the youngest extinction horizon coincides with the first of the abrupt carbon isotope shifts that characterize this interval and with increases in sea surface temperature continental weathering rates and seawater anoxia pseudomytiloides dubius is the only abundant benthic macroinvertebrate during the most hostile environmental conditions but it and all other benthic species are almost entirely absent for many thousands of years immediately after each abrupt negative carbon isotope shift supplementary material a compilation of the late pliensbachian and early toarcian marine biotic changes and a discussion of the systematics of the key faunal elements are available at http www geolsoc org uk sup18353

sulphur incorporation in jurassic marine mudrocks and their bitumens at low thermal maturity cleveland basin england abstract the distribution of sulphur between pyrite kerogen elemental sulphur and the aromatic fraction of mudrock bitumens has been quantitated in two cored sections of immature marine kimmeridgian strata which have experienced different levels of thermal stress strata in the two boreholes ebberston and reighton were deposited in different basinal settings basinal marine and platform respectively and occasional euxinic laminated horizons are present at ebberston otherwise dysoxic deposition was the norm at both localities pyrite the dominant sulphur carrier in all the mudrocks has a sulphur isotopic composition consistent with mineralisation in a system mainly open to sulphate diffusion kerogens are mostly low sulphur atomic s c and account for between 5 and 10 of rock sulphur although occasionally up to 30 kerogen sulphur is closely correlated with toc and highest in laminated mudrocks consistent with most effective sulphurization of kerogen under anoxic conditions although kerogen compositions in both cores vary with organic richness no systematic differences in organic input between the borehole localities are recognised geochemically some thermal effects on sulphur geochemistry are therefore interpreted from a comparison of stratigraphically equivalent sections from the two cores bitumen yields and abundances of aromatic sulphur in the more thermally stressed ebberston section although variable are generally much higher than in the reighton section and are partly related to kerogen sulphur content this is tentatively attributed to thermal release of additional extractable bitumen from macromolecules elemental sulphur s0 in bitumen is unrelated in abundance to other sulphur species and isotopically heavier than coexisting pyrite overprinting of minor preserved diagenetic s0 by secondary oxidation of pyrite appears likely the distributions of individual sulphur aromatic compound classes have features related both to maturity and stratigraphy

pyrite geochemistry in the toarcian posidonia shale of south west germany evidence for contrasting trace element patterns of diagenetic and syngenetic pyrites authigenic pyrite grains from a section of the lower toarcian posidonia shale were analysed for their trace element contents and sulphur isotope compositions the resulting data are used to evaluate the relationship between depositional conditions and pyrite trace element composition by using factor analysis trace elements in pyrite may be assigned to four groups i heavy metals including cu ni co pb bi and tl ii oxyanionic elements as mo and sb iii elements partitioned in sub microscopic sphalerite inclusions zn and cd and iv elements related to organic or silicate impurities ga and v results indicate that trace element contents in pyrite depend on the site and mechanism of pyrite formation with characteristic features being observed for diagenetic and syngenetic pyrites diagenetic pyrite formed within anoxic sediments generally has a high heavy metals content and the degree of pyritization of these elements increases with increasing oxygen deficiency similar to the degree of pyritization of reactive fe the highest gradient in the increase of the degree of trace element pyritization with bottom water oxygenation was found for the elements ni cu mo as tl in contrast syngenetic pyrite formed within a euxinic water column typically is enriched in as mo and sb but is low in heavy metals and the geochemical variation reflects changes in sea water composition

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

formation of recumbent folds during synorogenic crustal extension austroalpine nappes switzerland in sedimentary rocks of the austroalpine nappes in eastern switzerland several generations of alpine cretaceous tertiary folds can be distinguished by overprinting relations the second generation d 2 probably late cretaceous in age includes spectacular kilometre scale folds refolding the earlier formed nappe pile d 2 folds are interpreted here as resulting from east southeast directed crustal extension rather than as previously assumed from north south crustal shortening for the following reasons 1 d 2 folds are restricted to a predominantly ductile layer underlying the brittlely extended orogenic lid and 2 d 2 folds are associated with structures indicating extension in a direction parallel to the extension direction of the brittle layer before the east southeast extension started the layering of the rocks was already steeply inclined owing to earlier d 1 folding the deformation producing the second phase folds probably had a noncoaxial component with a top to the east southeast shear sense and a component of coaxial deformation leading to shortening in the vertical direction and stretching in an east southeast horizontal direction the folds developed with axes oblique to parallel to the direction of bulk stretching i suggest that folding of initially nonhorizontal layers by ductile crustal extension is an important deformation mechanism in the austroalpine and possibly also in other parts of the alps initially steep orientations of layers resulted from transpressive deformation in the obliquely convergent alpine belt and crustal extension parallel to the chain resulted from gravitational spreading i propose that this process can lead to the often encountered phenomenon of stretching parallel to the axes of folds

a global perturbation to the sulfur cycle during the toarcian oceanic anoxic event abstract the mesozoic era was punctuated by intervals of widespread anoxia within the ocean termed oceanic anoxic events or oaes the chemostratigraphy of these intervals also contains evidence of transient perturbations to many biogeochemically important elemental cycles here we present high resolution sulfur isotope data from three stratigraphic sections spanning the toarcian oceanic anoxic event t oae of the early jurassic all sections show a similar increase in the sulfur isotope ratio of sulfate parallel to an overall positive excursion in carbon isotopes during the oae interval based on forward box modeling the sulfate s isotope excursion can be generated by transiently increasing the burial rate of pyrite in marine sediments likely deposited under euxinic i e anoxic and sulfidic conditions in the water column in addition modeling shows that prolonged recovery of the 34 s of seawater sulfate at least 8 ma after the initial rise associated with the oae was due to the relatively long residence time of sulfate in the jurassic ocean estimates from our modeling put the toarcian marine sulfate concentrations at 4 to 8 mm the similarity of the sulfur isotope records from the north european epicontinental or epeiric sea and tethyan continental margin suggests that local modification of the marine sulfur isotope signal was minimal a point explored with isotope mixing models importantly our results indicate that the sulfur isotope excursion reflects a globally significant perturbation in the sulfur cycle and that pyrite burial in the north european epeiric seaway alone cannot account for the excursion this study along with recent work from other phanerozoic intervals of widespread marine oxygen deficiency confirms that the sulfur cycle can be perturbed significantly by enhanced pyrite burial during periods of prolonged oceanic anoxia euxinia

humic sulfur in eutrophic bay sediments characterization by sulfur stable isotopes and k edge xanes spectroscopy abstract organic sulfur os is an important sedimentary sulfur pool in marine sediments and chemical extractions are often used for quantification of various os pools however os sources and mechanisms of os formation are not well understood in this study sulfur stable isotope and sulfur x ray absorption near edge structure xanes spectroscopy were combined to investigate the sources and speciation of humic acid sulfur ha s and fulvic acid sulfur fa s in sediments of eutrophic jiaozhou bay whilst there may be some indication that eutrophication has enhanced fa s burial in the sediment this has not substantially modified the characteristically low humic sulfur i e ha s fa s contents of the sediments sulfur isotopic compositions indicate that both ha s and fa s are mixtures of diagenetic and biosynthetic os in origin ha s is dominated by biosynthetic sulfur and fa s by diagenetic source sulfur isotopic compositions and contents of pyrite and diagenetic os indicate that inhibition of sulfurization by pyrite formation if any appears insignificant xanes analysis suggests that the contents of high oxidized os i e sulfones and ester sulfates and strongly reduced os species are comparable in the ha s whereas the fa s is dominated by strongly reduced os as a result of enhanced sulfurization

phase relations and liquid lines of descent in hydrous ferrobasalt implications for the skaergaard intrusion and columbia river flood basalts crystallization experiments using a hydrous ferrobasalt as starting material conducted at 200mpa 940 12008c at a wide range of water activities 0 1 1 and redox conditions qfm 3 to qfm 4 where qfm is the quartz fayalite magnetite oxygen buffer show that h2o influences significantly the differentiation history of ferrobasaltic magmas a combination of our data with published experiments on dry ferrobasalt at 1atm provides an extensive experimental database for modeling and quantifying crystallization and differentiation processes within a typical fe rich tholeiitic system under both dry and hydrous conditions the addition of h2o decreases liquidus temperatures and changes significantly the proportions temperature range and sequence of crystallizing mineral phases the dry liquidus is at about 11708c whereas the liquidus for h2o saturated melts is at 10608c the main phases crystallizing from h2o bearing ferrobasalt at the investigated conditions are olivine ol clinopyroxene cpx plagioclase pl magnetite mt hematite hm ilmenite ilm and amphibole am the phase assemblage is similar to that of the dry system except for the presence of hm at extremely oxidizing conditions and am at low temperatures 59508c and h2o saturated conditions the important observation made in this study is that the stability of fe ti oxides and in particular mt as well as the simultaneous coprecipitation of mtand ilm are almost independent of the activity of h2o ah2o in the system whereas the liquidus temperatures of the silicate minerals are dramatically depressed by increasing ah2o the stabilities of oxides are controlled mainly by the redox conditions prevailing in the system the most pronounced effect of ah2o on the liquidus temperatures of silicates is observed for pl which shows a considerable delay in crystallization with progressive magma differentiation early crystallization of fe ti oxides in h2o bearing ferrobasaltic compositions precludes any significant fe enrichment during differentiation as fe enrichment is a characteristic feature of the skaergaard intrusion it implies that the skaergaard parental magma did not contain considerable amounts of water on the other hand our experiments indicate that the differentiation of some ferrobasaltic series from the columbia river flood basalt province might have occurred in magmatic systems containing significant amounts of volatiles 0 5 3 wt h2o

boundary layer crystallization in a basaltic magma chamber evidence from rishiri volcano northern japan the evolution of basaltic magma by mushy boundary layer processes introduction in a magma chamber is documented for an alkali basalt kutsugata the evolution of magma chambers is of major petrologic lava from rishiri volcano northern japan on the basis of zoning interest and has been studied extensively experimental patterns of plagioclase phenocrysts and their spatial distribution in and theoretical studies that have investigated the cooling the lava plagioclase phenocrysts with complex zoning patterns can of magma chambers have demonstrated that a magma be divided into four types type 1 is characterized by an extremely chamber solidifies through formation of a mushy boundan rich core an71 90 which is commonly corroded and filled with ary layer composed of crystals and interstitial melt along sodic plagioclase type 2 has an ab rich core surrounded by a calcic the chamber walls e g brandeis jaupart 1986 turner mantle characteristic of partial dissolution type 3 is characterized by et al 1986 marsh 1988 tait jaupart 1992 layered igneous complexes e g morse 1969 shirley 1987 an ab rich core that is commonly surrounded by a reversely zoned mcbirney 1996 provide useful information on how slightly calcic mantle type 4 has an ab rich core without a calcic mafic magma chambers evolve and consolidate but they mantle the an rich cores of the type 1 plagioclase are too calcic do not offer much insight into the instantaneous state of to have crystallized from a liquid represented by any whole rock a chamber because those intrusions integrate processes composition at the estimated temperatures of the kutsugata magma that occurred over long solidification times mcbirney system the an rich cores are inferred to have been formed in a noyes 1979 tait 1988 volcanic products such as mushy boundary layer along the wall of a magma chamber where lava flows and tephra deposits can sample the inthe magma was relatively cool and rich in water because of significant stantaneous state of a magma chamber there are a few olivine fractionation and possibly because of addition of water studies along this line of approach tait 1988 de silva expelled from the chilled margin and or groundwater from the 1989 nakada et al 1994 these studies focused on surrounding crust the ab rich cores of types 2 4 plagioclase crystal aggregates in volcanic products and concluded phenocrysts are interpreted to have crystallized in the main magma that the crystal formation in a mushy boundary layer body of the reservoir the types 2 and 3 ab rich cores were brought plays a dominant role in magmatic evolution in a magma to the mushy layer by convection the temporal and spatial variations reservoir however these studies were mostly on silicic of zoning patterns of plagioclase phenocrysts in basaltic lava flows magmas and there are significant differences in physical give useful information on the evolution of mafic magma chambers and chemical features between silicic and mafic magma chambers in this paper the magmatic evolution of an alkali basalt kutsugata lava from rishiri volcano northern japan is studied the kutsugata lava is divided into three lava flows on the basis of whole rock chemical

microstructures of early jurassic toarcian shales of northern europe the toarcian early jurassic posidonia shale formation is a possible unconventional gas source in northern europe and occurs within the cleveland basin united kingdom the anglo paris basin france the lower saxony basin and the southwest germany basin germany and the roer valley graben the west netherlands basin broad fourteens basin the central netherlands basin and the dutch central graben in the netherlands outcrops can be found in the united kingdom and germany since the posidonia shale formation does not outcrop in the netherlands sample material suitable for experimental studies is not easily available here we have investigated lateral equivalent shale samples from six different locations across northern europe germany the netherlands the north sea and united kingdom to compare the microstructure and composition of toarcian shales the objective is to determine how homogeneous or heterogeneous the shale deposits are across the basins using a combination of ion beam polishing scanning electron microscopy and x ray diffraction the work presented here shows that the toarcian shales of northern europe display considerable homogeneity in mineralogy and microstructure in the different investigated samples and formations where the largest variability is the carbonate content ranging from almost zero up to 80 we conclude that the outcrop locations in germany and the united kingdom are suitable analogues with respect to their mineralogy and microstructure for experimental studies on the posidonia shale in the dutch subsurface 2016 the authors

behaviour of spherical rigid objects and passive markers during bulk inhomogeneous shortening of a fluid abstract quantitative analysis of the kinematics of an experimental gravity driven inhomogeneous time dependent flow showed that the kinematics of the flow varied both temporally and spatially the variation in kinematics of the flow included vorticity rotation sense reversals and the results provide possible insight into the kinematics of gravity spreading flows the variation of the kinematics reflected the influence of the boundary conditions upon the flow spherical inclusions and thin columnar passive markers placed within the fluid prior to deformation also allowed the fluid flow to be used to examine some of the possible relationships that may form between porphyroblasts and passive foliations in inhomogeneous time dependent flows comparison of initial and final orientations of several spherical inclusions suggested an apparent lack of rotation during deformation conversely comparison of the initial and final orientation of passive strain markers placed in close proximity to these inclusions suggested a non coaxial deformation environment rather than a coaxial environment the apparent lack of rotation of these inclusions resulted from a reversal in their rotation sense during deformation of the system the reversal in rotation sense of these inclusions was the result of time varying levels of spin and shear induced vorticity during deformation fold like structures were produced in the passive markers this allowed the flow to be used to examine possible relationships that may form between porphyroblasts and layers passively folded during inhomogeneous time dependent flow the inclusion passive marker relationships across the folds suggest that relationships between porphyroblasts with inclusion trails and foliations in rock layers passively folded by an inhomogeneous time dependent flow may contain similar relationships to folds that formed by layer buckling knowledge of the level of passive behaviour of the layers and boundary conditions during this type of deformation is essential for utilizing porphyroblast foliation geometry to evaluate deformation history

intermittent generation of mafic enclaves in the 1991 1995 dacite of unzen volcano recorded in mineral chemistry mafic enclaves in the 1991 1995 dacite of unzen volcano show chemical and textural variability such as bulk sio2 contents ranging from 52 to 62 wt and fine to coarse grained microlite textures in this paper we investigated the mineral chemistry of plagioclase and hornblende microlites and distinguished three enclave types type i mafic enclaves contain high mg plagioclase and low cl hornblende as microlites whereas type iii enclaves include low mg plagioclase and high cl hornblende type ii enclaves have an intermediate mineral chemistry type i mafic enclaves tend to show a finer grained matrix have slightly higher bulk rock sio2 contents 56 60 wt when compared with the type iii mafic enclaves sio2 53 59 wt but the overall bulk enclave compositions are within the trend of the basalt dacite eruptive products of quaternary monogenetic volcanoes around unzen volcano the origin of the variation of mineral chemistry in mafic enclaves is interpreted to reflect different degree of diffusion controlled re equilibration of minerals in a low temperature mushy dacitic magma reservoir mafic enclaves with a long residence time in the dacitic magma reservoir whose constituent minerals were annealed at low temperature to be in equililbrium with the rhyolitic melt represent type iii enclaves in contrast type i mafic enclaves result from recent mafic injections with a mineral assemblage that still retains the high temperature mineral chemistry taking temperature ca ca na ratio of plagioclase and water activity of the hydrous unzen magma into account the mg contents of plagioclase indicate that plagioclase microlites in type iii enclaves initially crystallized at high temperature and were subsequently re equilibrated at low temperature conditions compositional profiles of mg in plagioclase suggest that older mafic enclaves type iii had a residence time of 100 years at 800 c in a stagnant magma reservoir before their incorporation into the mixed dacite of the 1991 1995 unzen eruption presence of different types of mafic enclaves suggests that the 1991 1995 dacite of unzen volcano tapped mushy magma reservoir intermittently replenished by high temperature mafic magmas

evolutionary changes over the last 1000 years of reduced sulfur phases and organic carbon in varved sediments of the santa barbara basin california abstract sediments from the santa barbara basin sbb of the last 1000 years were analyzed for elemental sulfur se mineral sulfide sulfur sm lipid based organically bound sulfur sx residual organically bound sulfur so total organic carbon toc and total nitrogen tn the approximate annual resolution of the time series data permitted us to evaluate the influence of oceanic variables on the benthic environment and the accumulating varved sediment in the sbb a bacterial mat community at or near the sediment surface is influencing sediment porosity and the production and distribution of se early diagenesis dampens the amplitude of environmental signals in the geochemical time series the concentrations of sm and so increase with burial depth at the expense of decreasing concentrations of sx and se at depths greater than 5 5 cm corresponding to an age of 7 years sm becomes the largest pool of reduced sulfur it requires approximately 500 years of primarily bacterially mediated diagenesis equivalent to a burial depth of 1 4 m for sbb sediments to gradually approach and finally enter the region assumed to represent typical normal marine sediments on a plot of weight percent toc vs sm

the northwest africa 8159 nwa 8159 martian meteorite part 2 spinel orthopyroxene intergrowths a record of fo2 and crust basalt interactions abstract in part 1 of our examination of martian meteorite northwest africa 8159 nwa 8159 we illustrated many interesting mineralogical and textural attributes that make this martian basalt unique unlike the shergottites that illustrate a clear relationship between the extent of trace element and isotopic characteristics and oxygen fugacity reduced depleted magmas oxidized enriched magmas nwa 8159 illustrates a decoupling of this relationship as it has oxidized and depleted signatures in part 2 using a series of new observations and measurements cl isotopes xanes tem empirical modeling we use nwa 8159 to explore the interaction between mantle derived magmas and the martian crust the magnetite orthopyroxene intergrowths associated with olivine are a product of a martian subsolidus oxidation event near the qfm buffer and not a magmatic reaction in an oxidizing magma qfm 3 this subsolidus event is further supported by cr valence in the olivine alteration of p rich olivine and end member magnetite in the matrix of the meteorite although this subsolidus alteration makes it extremely difficult to determine the original fo2 of the parental magma for nwa 8159 there is evidence that during the initial stages of crystallization the fo2 was modestly reducing iw 1 potential manifestations of more reducing magmatic conditions include p rich cores in the olivine and low fe3 in silicates plagioclase pyroxene further if analogous to all other depleted shergottites nwa 8159 initially crystallized under reducing conditions this decoupling between oxygen fugacity and isotopic trace element characteristics suggests that basalts derived from the martian mantle interacted with the crust in ways that significantly influenced redox history and volatile element isotopic composition cl s without dramatically modifying many of its radiogenic isotope and trace element mantle fingerprints

kerogen asphaltene sulfur relationships in sulfur rich monterey oils abstract monterey oils in the santa maria basin onshore and offshore are generally low maturity oils because of low thermal exposure relatively shallow burial for short times they are generated as heavy high sulfur oils because of the composition of the unusual type ii source kerogens which are exceptionally rich in organic sulfur 8 14 these high sulfur kerogens which we designate type ii s appear to generate oil at significantly lower thermal exposures than ordinary type ii kerogens with less than 6 s in contrast to common type ii kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon carbon bonds eliminating co2 h2o and hydrocarbon fragments type ii s kerogens have an additional complement of weak bonds associated with bound sulfur the preferential cleavage at weak sulfur linkages tends to produce larger fragments leading to high initial amounts of asphaltenes resins and sulfur rich aromatics together with smaller amounts of saturated hydrocarbons elemental analyses of monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics this sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties initial asphaltenes have essentially the same atomic h c ratios as the source kerogen but have significantlyy lower o c ratios and slightly lower s c ratios the n c ratios are nearly the same for kerogens and their derived asphaltenes with increasing maturity the h c ratios in asphaltenes decrease much like maturation changes in kerogen the s c ratio also decreases significantly however the o c ratios initially low in asphaltenes and n c ratios increase slightly due to material balance caused by other losses these element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone this can be useful when potential source rock samples are not available for analysis and or when a choice between alternate source rock possibilities must be made

thermodynamic analysis of fe and mg partitioning between plagioclase and silicate liquid thermodynamic analysis of fe and mg bearing plagioclase and silicate liquid was carried out based on reported element partitioning data between plagioclase and silicate liquid in reduced conditions solution properties of ternary feldspar standard state properties of plagioclase endmembers and solution properties of multicomponent silicate liquid derived mixing properties of fe and mg bearing plagioclase are in harmony with estimated results from synthetic experiments in the systems caal2si2o8 cafesi3o8 and caal2si2o8 camgsi3o8 based on the determined solution properties of the plagioclase a computer program to calculate the element partition relationships between fe and mg bearing plagioclase and multicomponent silicate liquid was developed the feo mgo and mgo mgo feo in plagioclase predicted from known liquid compositions and pressure are in agreement with measurements within 0 2 wt 0 1 wt and 0 1 mol ratio respectively the fe3 content in plagioclase crystallized at high oxygen fugacity can be estimated with this program the fe3 total fe ratio in plagioclase crystallized near the quartz fayalite magnetite buffer ranges from 0 to 0 5 which is consistent with previous study on natural plagioclase in submarine basalt derived solution properties of the fe and mg bearing plagioclase are also used to calculate equilibrium composition relationship between olivine and plagioclase change of xfo in olivine coexisting with plagioclase affects mgo and feo contents in plagioclase greatly the present model predicts xfo of coexisting olivine from the chemical composition of plagioclase to 0 1 accuracy at given pressure and temperature

anomalous iron distribution in shales as a manifestation of non clastic iron supply to sedimentary basins relevance for pyritic shales base metal mineralization and oolitic ironstone deposits in previous investigations nearshore pyritic shale horizons in the mid proterozoic newland formation were interpreted to be due to non clastic colloidal iron supply by streams new data on the chemical composition of shales in the newland formation support this interpretation in these shales fe and al show a positively correlated trend that intercepts the fe axis above the origin these relationships suggest control of fe by clays via iron oxide coatings on clay minerals and the presence of an additional non clastic iron component shales from stratigraphic intervals during which pyritic shale horizons were deposited plot above the fe al trend typical for the remainder of the newland formation

origin of sulfur rich oils and h2s in tertiary lacustrine sections of the jinxian sag bohai bay basin china abstract very high s oils up to 14 7 with h 2 s contents of up to 92 in the associated gas have been found in the tertiary in the jinxian sag bohai bay basin pr china several oil samples were analyzed for c and s stable isotopes and biomarkers to try to understand the origin of these unusual oil samples the high s oils occur in relatively shallow reservoirs in the northern part of the jinxian sag in anhydrite rich reservoirs and are characteristic of oils derived from s rich source rocks deposited in an enclosed and productive stratified hypersaline water body in contrast low s oils as low as 0 03 in the southern part of the jinxian sag occur in tertiary lacustrine reservoirs with minimal anhydrite these southern oils were probably derived from less s rich source rocks deposited under a relatively open and freshwater to brackish lake environment that had larger amounts of higher plant inputs the extremely high s oil samples 10 underwent biodegradation of normal alkanes resulting in a degree of concentration of s in the residual petroleum although isoprenoid alkanes remain showing that biodegradation was not extreme interestingly the high s oils occur in h 2 s rich reservoirs h 2 s up to 92 by volume where the h 2 s was derived from bacterial so 4 reduction most likely in the source rock prior to migration three oils in the jinxian sag have 34 s values from 0 3 to 16 2 and the oil with the highest s content shows the lightest 34 s value this 34 s value for that oil is close to the 34 s value for h 2 s 0 it is possible that h 2 s was incorporated into functionalized compounds within the residual petroleum during biodegradation at depth in the reservoir thus accounting for the very high concentrations of s in petroleum

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

the early diagenetic formation of organic sulfur in the sediments of mangrove lake bermuda due to a low mineral content the sapropelic sediments depositing in mangrove lake bermuda provide an excellent opportunity to explore for possible additions of sulfur to organic matter during the early stages of diagenesis we evaluated early diagenetic organic sulfur transformations by monitoring the concentrations and stable isotopic compositions of a number of inorganic and organic sulfur pools thereby accounting for all of the sulfur in the sediments we have identified and quantified the following sulfur pools porewater sulfate porewater sulfide elemental sulfur pyrite sulfur hydrolyzable organic sulfur hyos chromium reducible organic sulfur cros and nonchromium reducible organic sulfur non cros of the organic sulfur pools the non cros pool is by far the largest followed by cros and finally hyos by 60 cm depth these pools contribute respectively to 85 7 9 and 3 6 of the total solid phase sulfur the hyos pool is probably of biological origin and shows no interaction with the sulfur compounds produced during diagenesis by contrast cros is produced most likely from the diagenetic addition of polysulfides to functionalized lipids in the upper h2s poor elemental sulfur rich region of the sediment a portion of this sulfur pool is unstable and decomposes on contact with the h2s rich porewaters the portion of cros that remains in the sulfidic waters appears to readily exchange sulfur isotopes with h2s while some of the non cros pool is of biological origin some is also formed by the diagenetic addition of sulfur to organic compounds in the upper h2s poor region of the sediment by contrast with cros non cros is not diagenetically active in the h2s rich porewaters overall somewhere between 27 and 53 of the organic sulfur buried in mangrove lake sediments is of diagenetic origin with the remaining organic sulfur derived from biosynthesis we extrapolate our mangrove lake results and calculate that in typical coastal marine sediments between 11 and 29 mol g 1 of organic sulfur will form during early diagenesis of which 2 5 mol g 1 will be chromium reducible

iron in plagioclase as a monitor of the differentiation of the skaergaard intrusion a discussion of christian tegner contrib mineral petrol 128 45 51

partition coefficients for iron between plagioclase and basalt as a function of oxygen fugacity implications for archean and lunar anorthosites abstract experimental studies were undertaken to determine d for feot between plagioclase and melt as a function of oxygen fugacity for a basaltic composition that occurs as matrices for plagioclase megacrysts that are similar to those in calcic anorthosites at liquidus conditions the d for feot between calcic plagioclase and tholeiitic basalt changes very little from 0 030 to 0 044 between the very low o 2 of the iron wustite buffer and that of the quartz fayalite magnetite qfm buffer at fugacities above qfm the value for d increases rapidly to 0 14 at the magnetite hematite buffer and 0 36 in air the increase in d results from the fact that nearly all of the fe is in the fe2 state at o 2 below qfm and the fe 3 fe 2 ratio in the melt increases rapidly above qfm causing more fe to enter the plagioclase which accepts fe3 more readily than fe2 there is essentially no change in values of d over cooling rates that vary by two orders of magnitude the d for feot of 0 030 at iron wustite is in good agreement with earlier studies at low o2 terrestrial calcic plagioclase matrix pairs display ds of about 0 043 in excellent agreement with the experimental value of 0 044 at qfm which is the accepted fugacity for terrestrial tholeiitic basalts application of the ds for feot and other components to terrestrial calcic anorthosites indicates that the anorthosites were in equilibrium with nearby coeval tholeiitic basalts at qfm as was expected lunar anorthosites however have anomalously low contents of feot as well as mgo and would be in equilibrium with melts that are several times lower in these components than expected the low values of feot and mgo in the plagioclase of lunar anorthosites are a result of subsolidus reequilibration with pyroxene olivine and other fe mg bearing phases during high temperature metamorphism as is the case in terrestrial anorthosites that have undergone granulite grade metamorphism the ds for k2o mgo and tio2 were determined as 0 21 0 044 and 0 033 respectively and show no variation with o 2 the value for k2o is in good agreement with natural assemblages the values for mgo and tio2 however are lower in natural assemblages but the high degree of mobility of mg and the very low contents of tio2 in plagioclase makes the reliability of the natural values rather low also the d for tio2 may be affected by rate of cooling attempts to determine the d for cr2o3 as a function of o 2 were made difficult by the low levels of cr2o3 300 to 500 ppm in the melt when saturation with a cr spinel occurred because the cr concentrations in plagioclase are nearly 100 times less than those in the melt it was not possible to obtain reliable analyses for plagioclase these uncertainties constrain the d for cr to be less than 0 07 at the qfm buffer

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

a study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis abstract the evolution of the sulphur content of humic acids extracted from a near shore sediment core was investigated special attention was taken to avoid s contamination of the humic materials during extraction the s c ratios increased continuously with depth to values which strongly suggest s addition to the humic matrix during early diagenesis by reactions between organic matter and h2s or its oxidation products their light isotopic composition supports this view however subsequent isotopic exchange has obscured the mechanism initially involved since a large fraction of the enrichment occurred above the sulphidic zone redox boundaries such as the interface of anoxic microniches within more oxidized zones or the sulphidic suboxic boundary of the sediment column must have been important sites for s addition bioturbation by increasing the contact between sedimentary zones of a different redox regime will likely enhance such processes

petrological insights into shifts in eruptive styles at volcan llaima chile tephra and lava pairs from two summit eruptions ad 2008 and 1957 and a flank fissure eruption ad 1850 are compared in terms of textures phenocryst contents and mineral zoning patterns to shed light on processes responsible for the shifts in eruption style during typical eruptive episodes at volcan llaima andean southernvolcanic zone chile the mineralogy and whole rock com positions of tephra and lavas are similar within eruptive episodes suggesting a common magma reservoir for strombolian paroxysms and lava effusion the zoning profiles and textures of plagioclase record successive and discrete intrusions of volatile rich mafic magma accompanied by mixing of these recharge magmas with the resident basaltic andesitic crystal mushes that are commonly present at shallow levels in the llaima system each recharge event destabil izes the plagioclase in equilibrium with the resident crystal mush melt and stabilizes relatively an rich plagioclase as is recorded by the numerous resorption zones lavas typically have 15 20 vol more phenocrysts than the tephra differences in plagioclase and olivine textures and zoning combined with different phenocryst contents indicate that a greater volume fraction of recharge magma is present in the explosively erupted magma than in subsequent effu sively erupted magma we propose that strombolian paroxysms at volcan llaima are triggered by interactions with large volume frac tions of recharge magma which decrease the bulk viscosity and in crease the volatile contents of the erupted magmas leading to the conditions required for the fragmentation of basaltic andesite lava effusion ensues from reduced interactions with the recharge magma after it has partially degassed and crystallized thereby impeding rapid ascent this process could be operating at other steady state basaltic volcanoes wherein shallow reservoirs are periodically re filled by fresh volatile rich magmas

a high resolution shallow marine record of the toarcian early jurassic oceanic anoxic event from the east midlands shelf uk the global deposition of organic rich mudrocks a mass extinction and marked geochemical changes in the sedimentary rocks and fossils deposited during the early toarcian indicates a period of extreme environmental change and an oceanic anoxic event this study investigates at a high resolution the environmental and biotic changes that occurred during the event in a shallow marine area using rocks deposited on the east midlands shelf uk we present a new graphic log geochemical data 13corg total organic carbon caco3 total sulphur and total nitrogen and benthic macroinvertebrate ranges from north quarry holwell leicestershire uk comparison of the ammonite ranges between the cleveland basin yorkshire and east midland shelf successions in the uk shows that there is a hiatus on the shelf across the dactylioceras semicelatum cleviceras exaratum subzone boundary the new high resolution geochemical data show that an 5 13corg excursion occurs similar to other lower toarcian sections in the world 13corg shifts a to c are missing in the hiatus but that 13corg shift d is present similar to the cleveland basin the c exaratum subzone of the east midlands shelf succession is dominated by three epifaunal bivalve species but their ranges differ significantly between the successions an increase in the faunal diversity occurs within the upper c exaratum subzone at holwell and other uk sections the biotic data indicate that conditions on the east midlands shelf were more hospitable than in the cleveland basin the bivalve populations on the shelf may have provided a source of new recruits for the basins

sulfur diagenesis and partitioning in holocene peru shelf and upper slope sediments abstract sediments of the peru margin were sampled in two transects across the shelf and upper slope 75 to 1000 m in october of 1992 this region is characterized by high surface water productivity and consequent high organic carbon fluxes low terrigenous inputs as well as an intense oxygen minimum zone omz impinging on the slope at depths between 75 and 550 m sediments analyzed in this study were collected from one ship deployed box core and five submersible deployed push cores organic carbon toc concentrations in surface sediments range from 1 to 18 on a dry weight basis formation of pyrite begins at the sediment water interface swi maximum concentrations of pyrite sulfur in the cores from this study range from 0 5 to 1 8 wt concentrations of pyrite are influenced by availability of reactive iron and an oxidant capable of converting avs to pyrite highly reactive iron is stripped from terrigenous detritus in the core of the omz some of this iron may contribute to glauconite formation in sediments near the base of the omz where it is concentrated into a glauconitic green sand as a result of reworking and winnowing in a shallow water site 109 m at the upper edge of the omz high concentrations of pyrite total iron and iron aluminum ratios indicate that easily reduced iron species are available for sulfidation at the swi pyrite formation at this site is nearly complete in the upper 4 cm of the sediment in contrast pyrite concentrations are slightly lower at the surface of two of the deeper water sites at 309 m in the center of the omz and to a lesser extent at 671 m at the bottom edge of the omz and appear to be influenced in part by availability of reactive iron concentrations of acid volatile sulfides avs are low in all sediments 0 04 wt but are slightly elevated in sediments from the center of the omz the ratio of organic sulfur s org to organic carbon toc at the sediment surface of the cores examined here is remarkably constant 0 012 0 002 and within the range observed in marine biota 0 01 to 0 02 suggesting that organic sulfur at the swi is dominantly biogenic although s org toc ratios increase downcore there is no clear correlation between concentrations of organic sulfur and organic carbon below the swi there is also no clear relation between concentrations of organic sulfur and total iron organic sulfur concentrations vary from site to site 0 06 to 0 33 wt but are relatively constant downcore at any given site maximum concentrations are in cores from the center of the omz

sulfonates a novel class of organic sulfur compounds in marine sediments abstract x ray absorption near edge structure spectroscopy xanes used to measure sulfur speciation in a variety of organic rich marine sediments has established sulfonates as a novel and major component of sedimentary organic sulfur the origins of sulfonates in sediments are not clear although both biological and geochemical mechanisms are possible the accumulation of oxidized sulfonate sulfur in reducing marine sediments was not known previously hence a new perspective in sulfur geochemistry is established the biogeochemical implications of the presence of sulfonates in marine sediments are discussed

recovery of benthic communities following the toarcian oceanic anoxic event in the cleveland basin uk during the toarcian oceanic anoxic event oae considerable environmental changes occurred that were associated with global warming perturbations to the c cycle and ocean deoxygenation which resulted in a mass extinction of marine fauna recovery of the biota after the event was protracted and has to date undergone limited study however understanding the patterns and processes of recovery are critical to anticipating ecosystem responses to the environmental changes predicted for the near future results showed that increases in benthic diversity and the re establishment of the toarcian infauna was gradual and followed the changing redox conditions pioneering infauna such as dacryomya ovum that dominated the seafloor after the event in the cleveland basin yorkshire uk can modify the physico chemical environment and thus facilitate ecological succession after disturbance the length of d ovum increased 8 mm throughout the bifrons zone and these body size changes were linked with total organic carbon toc content suggesting a link to primary productivity although only at intermediate levels of deoxygenation major changes in the phytoplankton and so food supply seem to have driven changes in bivalve body size across trophic guilds both during and after the event in yorkshire and on the mid to lower shelf in spain and france respectively primary productivity collapse seems then to have been a major driver of biotic change throughout the toarcian event as it was during the permian triassic triassic jurassic and cretaceous tertiary mass extinctions further investigation of both the palaeontological and geochemical changes that occurred within early successional toarcian infaunal communities are required to more fully understand the pattern of recovery after the oae

effect of mechanical interactions on the development of shape preferred orientations a two dimensional experimental approach abstract modifications in the development of preferred orientations of rigid particles due to mechanical interactions between particles are studied experimentally in two dimensions experiments in both pure shear and simple shear were performed and the results analysed using an easy and fast new automatic method for increased concentration of rigid particles the rotation of individual particles may be slowed down or even stopped due to collisions or disturbance of the flow in the matrix caused by neighbours in coaxial flow the fabric intensity is consequently reduced in simple shear flow the fabric evolution is no longer cyclic the intensity is on average weaker and the fabric axis rotates asymptotically toward the shear plane in the case of preferred orientations of particles having a low aspect ratio 2 5 the fabric rotates through the shear plane then undergoes a reverse rotation and rotates toward the shear plane again in the light of these experimental results we emphasize that quantification of finite strain based on such fabrics may lead to significant underestimates and calculated values should be taken as minimum estimates the kinematic significance of concentrated rigid particle preferred orientations in rocks is modified by interactions between particles techniques for qualitative or quantitative kinematic analysis may become unreliable for simple shear flows the concentrated population fabrics show an angular behaviour close to that of passive markers they tend to align parallel to the shear plane in simple shear flow

molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the early jurassic relatively brief periods of severe paleoenvironmental change during the jurassic and cretaceous were associated with the widespread accumulation of organic rich marine deposits termed oceanic anoxic events oaes these intervals involved abrupt global warming of 5 10 c higher rates of continental weathering elevated extinction rates and large scale perturbations to the global carbon cycle the major oaes also overlapped temporally the emplacement of large igneous provinces however despite being known as oaes the extent of seawater anoxia at those times is undefined and the causative processes remain unclear here we show how changes in seawater molybdenum isotope ratios a proxy for seawater anoxia during the toarcian early jurassic oae define the onset and expansion of oxygen deficient conditions our data also place constraints on the areal extent of marine anoxia during the event and demonstrate that anoxia expanded and contracted periodically broadly in line with precession driven changes in 13 corg despite their intermittent occurrence over geological history oaes have an important contemporary relevance because the magnitude and high rates of environmental change then were broadly similar to those occurring at the present day