maturation and bulk chemical properties of a suite of solid hydrocarbons abstract in this paper we present strong correlations of solid hydrocarbon reflectance shro to vitrinite reflectance vro and bulk chemical properties aromaticity tmax h c etc these correlations suggest that like kerogen in coals and sedimentary rocks solid hydrocarbons vary systematically during maturation as a consequence shro is especially useful as a maturity indicator in rocks lacking vitrinite such as pre devonian rocks and many organic rich marine rocks unlike other organic maturationv indicators the utility of solid hydrocarbons is not limited by botanical evolution but rather the generative potential of the petroleum system solid hydrocarbons also known as solid bitumen asphalt dead oil migrabitumen and pyrobitumen are genetically defined as solid phase accumulations of predominantly hydrocarbons produced by petroleum generation in source rocks they may occur over a range of concentrations in outcrop and well samples in all components of petroleum systems although accumulations of solid hydrocarbons from exhumed reservoirs are well reported the extent and utility of disseminated solid hydrocarbons in shales is less understood solid hydrocarbons are found in organic rich to very lean mature rocks as a residual product of generation disseminated solid hydrocarbons exhibit three optical forms anisotropic coked granular and relatively uniform homogenous only the homogenous solid hydrocarbons are recommended for correlation purposes with other thermal indicators

pyrite ooids in devonian black shales record intermittent sea level drop and shallow water conditions upper devonian black shales of the eastern united states contain in places unusual beds of pyrite ooids textural and geochemical studies show that these originated as chamositic iron ooids that were replaced by pyrite during early diagenesis pyrite mimics the laminated texture of the precursor grain yet inclusions of silicate minerals and instances of partial replacement reveal the secondary nature of the pyrite pyrite ooids occur above erosion surfaces that are considered sequence boundaries because of large lateral extent chamositic precursor ooids indicate an oxygenated water column and wave interaction with seafloor sediments at the time of their formation this scenario agrees with earlier work that stipulates that erosion surfaces in devonian black shales reflect lowering of sea level that allowed wave reworking and erosion of earlier deposited black shales pyrite ooid beds thus furnish direct evidence of significant sea level drops during the accumulation of upper devonian black shales in eastern north america

fingerprinting the water site in mantle olivine nominally anhydrous minerals such as olivine contain trace amounts of water and may accommodate the entire water budget of the upper mantle here we report for the first time synthetic olivines crystallized experimentally under upper mantle conditions that reproduce the most common and intense infrared hydroxyl stretching bands at 3572 and 3525 cm 1 observed in spinel peridotite mantle olivines these bands arise from water accommodated at point defects associated with the trace element ti and we suggest that this is the most important defect site in the shallow upper mantle additional hydrated defects may occur at higher pressures we also identify bands related to water associated with fe3 these are unlikely to reflect equilibrium with the mantle and indicate water incorporation during exhumation or retrogression water must be present at the defect site appropriate for the mantle at the conditions of interest for partitioning seismic wave speed and deformation experiments on hydrous olivine to be relevant

lithology and biostratigraphy of franciscan like chert and associated rocks in west central baja california mexico we present the result of biostratigraphic and lithologic studies of ribbon chert and associated rocks in a mesozoic subduction complex in west central baja california mexico the subduction complex terrane is divided into three subterranes each of which consists of an originally coherent sequence of interbedded oceanic rocks including ocean floor basalt terrigenous siliciclastic turbidites radiolarian ribbon chert and limestone parts of the original stratigraphy are preserved in the least deformed least metamorphosed subterrane ocean floor pillow basalt on cedros island is overlain by about 40 m of radiolarian ribbon chert ranging in age from early jurassic or older to early cretaceous the chert is overlain by thin bedded turbidites on san benito west island radiolarian ribbon chert is interbedded with volcanogenic rocks including a megabreccia that contains blocks of metabasites folded late jurassic early cretaceous chert and marble in a mid cretaceous radiolarite matrix chert samples from tectonically thinned sequences elsewhere on cedros and san benito islands contain late triassic to early cretaceous radiolarian assemblages the 40 m thick chert section on cedros island probably accumulated atop oceanic crust in a large ocean basin for at least 65 m y and was later capped by terrigenous turbidites as it approached the subduction zone along the western margin of north america faulted chert sections on cedros and san benito central and west islands are subsets of the main section on cedros island the chert megabreccia section on san benito west island is interpreted to have accumulated at the foot of a volcanic edifice on the ocean floor for example seamount fracture zone or during extension and normal faulting of the downgoing oceanic plate in a subduction zone sedimentary structures and stratigraphic relations indicate that all ribbon chert in this subduction complex was deposited by sediment gravity flows that is they are turbidites

a subsolidus olivine water solubility equation for the earth s upper mantle the pressure and temperature sensitivity of the two most important point hydrous defects in mantle olivine involving si vacancies associated to trace amounts of titanium tichu pd or exclusively to si vacancies si was investigated at subsolidus conditions in a fluid saturated natural peridotite from 0 5 to 6 gpa approximately 20 200 km depth at 750 to 1050 c water contents in olivine were monitored in sandwich experiments with a fertile serpentine layer in the middle and olivine and pyroxene sensor layers at the border textures and mineral compositions provide evidence that olivine completely recrystallized during the weeklong experiments whereas pyroxenes displayed only partial equilibration a site specific water solubility law for olivine has been formulated based on the experiments reconciling previous contradictory results from low and high pressure experiments the site specific solubility laws permit to constrain water incorporation into olivine in the subducting slab and the mantle wedge as these are rare locations on earth where fluid present conditions exist chlorite dehydration in the hydrated slab is roughly parallel to the isopleth of 50 20 ppm wt h2o in olivine a value which is independent of the pressure and temperature trajectory followed by the slab hydrous defects are dominated by si under the relevant conditions for the mantle wedge affected by fluids coming from the slab dehydration slab adjacent low viscosity seismic low velocity channel p 3 gpa in cold subduction zones at 5 5 km from the slab surface the storage capacity of the mantle wedge at depths of 100 250 km ranges from 400 to 2 000 ppm wt h2o

heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin of china this study characterizes the vertical heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin based on core description thin sections observation geological chemistry data interrogation and qemscan image analysis lithofacies associations mineralogy graptolite species occurrence rock fabrics as well as toc total organic carbon and gas content change noticeably and regularly in the lower silurian longmaxi marine shale within sequence stratigraphic framework lithofacies associations mainly include in situ graptolite rich and siliceous shale in the transgressive systems tract tst micro offsite graptolite rich shale and shale interbedded with siltstone laminaes in the early highstand systems tract ehst and micro offsite graptolite rich and carbonate rich shale in the late highstand systems tract lhst the tst has a greater abundance of diplogratus than ehst and lhst and has a lesser level of monograptus which is conversely higher in the ehst and lhst the tst shale is silica rich while the lhst shale is generally clay rich the ehst shale is more balanced in its silica and clay content than the tst and lhst are the sedimentary structure and fabric of shale shows that shale is homogenous in the tst with laminaes well developed in the ehst but decreasing in the lhst toc and gas content are highest in the tst and decrease upward the tst with high toc high gas content high brittle minerals silica rich and anoxic suboxic to dysoxic sedimentary environment is the most potential shale gas target interval in the study area our research also shows that the toc mainly controls shale gas accumulation and that the redox conditions mainly control the preservation of organic matter the silica also plays a significant role in shale gas content due to its contribution to hydraulic fracturing finally the study proposes a depositional and heterogeneity model for the lower silurian longmaxi marine shale in the study area

a depositional model for organic rich duvernay formation mudstones abstract the upper devonian duvernay formation of western canada is an organic rich shale formation now targeted as a hydrocarbon reservoir we present a detailed sedimentological analysis of the duvernay formation in order to better understand organic rich mudstone depositional processes and conditions and to characterize the vertical and lateral heterogeneity of mudstone lithofacies that affect petrophysical and geomechanical rock properties organic rich mudstone facies of the duvernay formation were deposited in a dynamic depositional environment by a variety of sediment transport mechanisms including suspension settling turbidity currents and bottom water currents in variably oxygenated bottom waters suspension settling dominated in distal relatively deep areas of the basin but evidence for weak turbidity currents and bottom water currents was observed in the form of graded beds and thin grain supported siltstone laminae organic enrichment primarily occurred in distal areas as a result of bottom water anoxia and low depositional rates of inorganic sediment in deep water locations near platform margins alternating silty sandy contourite beds and organic rich mudstone beds are present the former interpreted to have been deposited and reworked by bottom water currents flowing parallel to slope in shallower more oxygenated settings mudstone lithologies vary from calcareous to argillaceous these sediments were deposited from suspension settling turbidity currents and bottom water currents although primary sedimentary structures are often obscured by extensive bioturbation locally organic enrichment in dysoxic rather than anoxic bottom waters was driven by a slightly increased sedimentation rate and possibly also by aggregation of sedimentary particles in the water column due to interaction between organic matter and clay minerals large variations observed in sediment composition from siliceous to calcareous to argillaceous reflect multiple biogenic carbonate and clastic sediment sources sediment composition is influenced by basin morphology circulation patterns sea level variation and proximity to sediment sources

sea level highstand and lowstand shedding related to shelf margin aggradation and emersion upper eocene oligocene of maiella carbonate platform italy abstract sequence stratigraphic analysis of the upper eocene lower oligocene of the maiella carbonate platform allows the timing of shelf aggradation and erosion to be linked to shedding onto the slope and relative sea level stands the shelf was eroded during lowstands and the lowstand slope sediments are thin channelized lithic breccias with clasts eroded from an emerged reef tract highstand shedding of skeletal sands from the inner shelf resulted in thick coarsening and thickening upward successions of turbidites

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

thirtyone formation permian basin texas structural and lithologic heterogeneity in a lower devonian chert reservoir chert and carbonate reservoirs of the early devonian thirtyone formation comprise a major regional reservoir in the permian basin with more than 700 mbbl production to date and roughly an equal amount of potentially producible reserves remaining most major pools in the thirtyone formation were discovered several decades ago and are now in relatively advanced stages of enhanced recovery with significant variation apparent in response to waterflooding among different fields as shown by comparison between dollarhide and three bar fields reservoirs display significant heterogeneity due to structure and to depositional diagenetic factors affecting porosity development most studies of these fields to date have tended to emphasize depositional and diagenetic factors as the reason for observed variation in enhanced recovery performance however structural factors may be of nearly equal importance enhanced recovery at dollarhide field for example has been extremely successful with waterflood recoveries more than double those under primary production and a tertiary co2 flood expected to do nearly as well this extraordinary level of success is understood as a result of a combination of reservoir character and compartmentalization with the latter especially related to division of the field into several fault block portions mapping of these fault blocks and their related structures has been greatly advanced by a recent 3 d three dimensional seismic survey ultimate recovery at dollarhide is projected at 62 of original oil in place in comparison production history at three bar field shows a lower level of overall recovery yet a very similar increase between primary and secondary production reservoir heterogeneity related to depositional diagenetic factors appears more pronounced at three bar field than at dollarhide field but faulting is also significant with respect to division of the field into separate blocks with distinct productive histories a 3 d seismic survey may provide important discriminating data useful for a future co2 flood or other tertiary recovery project at three bar field

the origin of high frequency platform carbonate cycles and third order sequences lower ordovician el paso gp west texas constraints from outcrop data and stratigraphic modeling abstract the passive margin succession of the diablo platform lower ordovician west texas is represented by the second order sauk c supersequence set consisting of a basal transgressive clastic unit the bliss sandstone above the breakup unconformity marking the second order basal lowstand transgressive phase overlain by 750 m of drift related shallow marine platform carbonates the el paso group recording the second order highstand due to late paleozoic structuring of the gondwanan passive margin present exposures in texas are in an updip shelf position and lack internal stratal geometries across depositional strike so sequences and systems tracts are identified solely by the vertical stacking patterns of depositional subfacies and higher frequency fifth order cycles accommodation plots fischer plots of high frequency cycles gauge systematic shifts in third order accommodation of two complete third order sequences each about 2 m y long and 60 140 m thick within the el paso group this is expressed in the vertical succession of cycle types systematic changes in cycle thickness and variations in subfacies as revealed by histograms of subfacies types tied to fischer plots a complete el paso shelf sequence contains a thin lowstand systems tract of quartz arenite a thick transgressive systems tract dominated by upward thickening thrombolitic subtidal cycles and a highstand systems tract marked by dolomitic thinning upward peritidal cycles containing quartz sand the el paso third order depositional sequences have been correlated by biostrat graphy and cycle stacking pattern from the franklin mountains southeast to the diablo arch northeast into the ardmore basin and thence to the appalachian basin hence the third order sequences appear to be eustatic based on biostratigraphic correlation of accommodation plots around the periphery of gondwana time series analyses suggest that a strict allocyclic milankovitch driven glacio eustatic mechanism alone is insufficient to account for the higher frequency fifth order and lower frequency third order accommodation cycles we used a two dimensional forward computer simulation to compare allocyclic and autocyclic models for high frequency cycles the allocyclic simulation superimposes a deterministic milankovitch glacio eustatic driver on a lower frequency third order accommodation cycle and generates a two dimensional synthetic cross section composed of high frequency peritidal and subtidal cycles stacked into third order sequences the autocyclic simulation is generated by a ginsburg autocyclic mechanism for high frequency cyclicity triggered by third order accommodation changes the autocyclic simulation quantitatively replicates an autocyclic mechanism for fifth order cycle development linked to onshore sediment transport and seaward progradation of tidal flats the two dimensional internal facies architecture of a third order sequence and the high frequency cycle stacking patterns are simulated in both scenarios important differences in patterns of cycles and subfacies stacking in the simulations shed light on the interpretation of the diablo platform cycles and sequences as an alternative or a supplement to autocyclicity or milankovitch forced glacio eustasy we have studied stochastic models for driving high frequency changes in relative sea level these intriguing results maintain essentially all the features observed in the rock record our smoothed sto hastic simulations suggest that the cycle problem is much more complex than presently realized

pressure and temperature dependence of h solubility in forsterite an implication to water activity in the earth interior abstract we performed experiments at 2 5 6 and 9 gpa and temperatures ranging from 1000 to 1400 c in enstatite saturated conditions in the mgo sio 2 h 2 o system using a multi anvil apparatus and determined the dependence of oh solubility in forsterite as a function of pressure and temperature the abundance of oh in forsterite was determined using polarized fourier transform infrared spectroscopy the results show that oh solubility in forsterite increases with temperature only at 2 5 gpa at 6 and 9 gpa the oh solubility reaches a maximum at temperatures of 1175 to 1250 c depending on pressure and then decreases at higher temperatures such behaviour is explained by the change of water activity in the fluid due to dissolution of silicate component using oh concentrations measured on subsolidus samples we determined the thermodynamic parameters of oh incorporation in forsterite such as change in internal energy and entropy we find almost constant e of 37 1 6 7 kj mol and s of 82 8 6 8 j mol k these parameters together with a v solids of 10 6 cm 3 mol are used to calculate the fugacity of the real fluid i e water silicates and compare it to the fugacity of pure water our results imply that estimates of water storage capacity at mantle depths greater than 80 km and above 1250 c should be substantially reduced compared to models that assume that water is a pure fluid

hydrolytic weakening in olivine single crystals deformation experiments on single crystals of san carlos olivine under hydrous conditions were performed to investigate the microphysical processes responsible for hydrolytic weakening during dislocation creep hydrogen was supplied to the crystals using either talc or brucite sealed in nickel capsules with the crystal deformation experiments were carried out using a gas medium apparatus at temperatures of 1050 to 1250 c a confining pressure of 300 mpa differential stresses of 45 to 294 mpa and resultant strain rates of 1 5 10 6 to 4 4 10 4 s 1 for talc buffered i e water and orthopyroxene buffered samples at high temperatures the dependence of strain rate on stress follows a power law relationship with a stress exponent n of 2 5 and an activation energy of 490 kj mol brucite buffered samples deformed faster than talc buffered samples but contained similar hydrogen concentrations demonstrating that strain rate is influenced by orthopyroxene activity under hydrous conditions the values of n and dependence of strain rate on orthopyroxene activity are consistent with hydrolytic weakening occurring in the climb controlled dislocation creep regime that is associated with deformation controlled by lattice diffusion under hydrous conditions and by pipe diffusion under anhydrous conditions analyses of postdeformation electron backscatter diffraction data demonstrate that dislocations with 100 burgers vectors are dominant in the climb controlled regime and dislocations with 001 are dominant in the glide controlled regime comparison of the experimentally determined constitutive equations demonstrates that under hydrous conditions crystals deform 1 to 2 orders of magnitude faster than under anhydrous conditions

hydrographic conditions of the devono carboniferous north american seaway inferred from sedimentary mo toc relationships abstract deepwater anoxia developed widely within a series of silled intracratonic basins in north america during the middle devonian to early carboniferous but the hydrographic factors contributing to this development are virtually unknown the present study demonstrates that the degree of enrichment of strongly hydrogenous elements such as molybdenum mo in the organic rich shales that accumulated in these basins has the potential to provide information about paleohydrographic conditions most of the study units 49 of 55 exhibit significant positive covariation between elemental mo and toc concentrations yet there is substantial variation in the statistical parameters that define these relationships specifically the regression lines characterizing mo toc covariation have slopes m ranging from 2 to 65 10 4 although a majority of the study units yield m values between 10 and 25 10 4 the parameter m exhibits systematic stratigraphic variation within individual basins and geographic variation among basins suggesting that mo toc relationships were controlled by slowly evolving watermass characteristics of the devono carboniferous north american seaway a recent study of modern anoxic silled basins algeo t j lyons t w 2006 mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions paleoceanography 21 pa1016 doi 10 1029 2004pa001112 demonstrated that m is closely linked to the degree of restriction of the subpycnoclinal watermass as reflected in aqueous mo concentrations mo aq and deepwater renewal times dw these relationships reflect control of sedimentary mo enrichment by both the amount of sedimentary organic matter i e host phase availability and the concentration of aqueous mo i e source ion availability when applied to black shales of the devono carboniferous north american seaway these relationships permit both qualitative and quantitative inferences regarding the degree of restriction of deepwaters in cratonic basins and the evolution of hydrographic conditions through time black shales associated with early stages of sea level rise commonly exhibit low m values 1000 yr higher sea level stands resulted in more open marine conditions and enhanced deepwater renewal leading to deposition of black shales with m values up to 65 equivalent to mo aq 70 of the normal seawater concentration and dw

trace element budgets in the ohio sunbury shales of kentucky constraints on ocean circulation and primary productivity in the devonian mississippian appalachian basin abstract the hydrography of the appalachian basin in late devonian early mississippian time is modeled based on the geochemistry of black shales and constrained by others paleogeographic reconstructions the model supports a robust exchange of basin bottom water with the open ocean with residence times of less than forty years during deposition of the cleveland shale member of the ohio shale this is counter to previous interpretations of these carbon rich units having accumulated under a stratified and stagnant water column i e with a strongly restricted bottom bottom water circulation a robust circulation of bottom waters is further consistent with the palaeoclimatology whereby eastern trade winds drove upwelling and arid conditions limited terrestrial inputs of siliciclastic sediment fresh waters and riverine nutrients the model suggests that primary productivity was high 2 g c m 2 d 1 although no higher than in select locations in the ocean today the flux of organic carbon settling through the water column and its deposition on the sea floor was similar to fluxes found in modern marine environments calculations based on the average accumulation rate of the marine fraction of ni suggest the flux of organic carbon settling out of the water column was approximately 9 of primary productivity versus an accumulation rate burial of organic carbon of 0 5 of primary productivity trace element ratios of v mo and cr mo in the marine sediment fraction indicate that bottom waters shifted from predominantly anoxic sulfate reducing during deposition of the huron shale member of the ohio shale to predominantly suboxic nitrate reducing during deposition of the cleveland shale member and the sunbury shale but with anoxic conditions occurring intermittently throughout this period

inferring total organic carbon and major element geochemical and mineralogical characteristics of shale core from hyperspectral imagery hyperspectral systems that image drill core can capture detail mineralogical information at the millimeter scale and thus have the potential to enable investigators to characterize shale composition and heterogeneity complementing the direct chemical and x ray diffraction analysis of core samples and guiding detailed sampling this method provides insight into petrophysical and geomechanical properties because these properties are significantly correlated to rock composition we tested this approach on a continuous long core from the shale sequence of the horn river group in the horn river basin british columbia sampled at a spacing of 1 m 40 in and analyzed for geochemical composition these data enable the calibration of spectral imagery to rock composition and specifically predict total organic carbon toc and the abundance of sio2 al2o3 k2o and cao we then imaged nine samples from the woodford shale from the permian basin texas for a blind test to assess the predictive models the models were then used to predict toc and geochemical data over detailed imagery of 300 m 984 ft of horn river group shale core and portray their spatial variability downhole as images and profiles in its simplest form hyperspectral imagery can be enhanced to highlight fabric in shale core that otherwise is difficult to visualize because of low brightness in addition we show that spectral imagery of shale can also be processed to either convey mineralogical quartz clay and carbonate or geochemical information the resulting views can readily be used to guide the selection of samples and may provide tools for scaling reservoir properties from individual plugs to reservoir volumes

controls and development of late quaternary periplatform carbonate stratigraphy in walton basin northeastern nicaragua rise caribbean sea the late quaternary sedimentary record in periplatform oozes and muds deposited on the northern nicaragua rise results from the interplay of four main controls 1 input of pelagic carbonates and bank derived fine aragonite and magnesian calcite 2 input of siliciclastic sediments 3 dispersal and removal of sediments by the caribbean current and 4 partial seafloor dissolution of metastable carbonates high accumulation rates of the calcite coarse sediment fraction throughout the study area demonstrate that planktonic foraminiferal productivity peaked during interglacial stages neritic carbonate productivity also peaked during interglacial stages when bank and shelf tops along the nicaragua rise were submerged within the photic zone because the bank and shelf tops remained mostly exposed during glacial stages the surface area available for the neritic carbonate productivity was drastically reduced to a narrow band along the margins of pedro bank and the southern shelf of jamaica a large volume of siliciclastic sediments transported from the coastal area of south america and the eastern and western regions of jamaica were deposited during glacial stages within the eastern and western deep extensions of walton basin this finding contrasts with the input pattern of siliciclastic sediments in walton basin itself where the largest input of siliciclastic sediments occurred at each of the interglacial climatic optima corresponding to intervals of maximum sea level transgression finally cores in water depths exceeding 1100 m display during interglacial stages aragonite accumulation rates systematically lower than rates in cores from water depths shallower than 1100 m this indicates that some bank derived aragonite and magnesian calcite has been partially removed by seafloor dissolution in areas from water depths exceeding 1100 m results from this study on the northeastern nicaragua rise indicate that not only do offbank transport and water column saturation state influence the late quaternary record but also that the variable strength of the caribbean current and the proximity of sources for siliciclastic sediments have played a major role in the development of the late quaternary periplatform high resolution stratigraphy

radiolarians decreased silicification as an evolutionary response to reduced cenozoic ocean silica availability it has been hypothesized that increased water column stratification has been an abiotic universal driver affecting average cell size in cenozoic marine plankton gradually decreasing cenozoic radiolarian shell weight by contrast suggests that competition for dissolved silica a shared nutrient resulted in biologic coevolution between radiolaria and marine diatoms which expanded dramatically in the cenozoic we present data on the 2 components of shell weight change size and silicification of cenozoic radiolarians in low latitudes increasing cenozoic export of silica to deep waters by diatoms and decreasing nutrient upwelling from increased water column stratification have created modern silica poor surface waters here radiolarian silicification decreases significantly r 0 91 p 0 001 from 0 18 shell volume fraction in the basal cenozoic to modern values of 0 06 a third of the total change occurred rapidly at 35 ma in correlation to major increases in water column stratification and abundance of diatoms in high southern latitudes southern ocean circulation present since the late eocene maintains significant surface water silica availability here radiolarian silicification decreased insignificantly r 0 58 p 0 1 from 0 13 at 35 ma to 0 11 today trends in shell size in both time series are statistically insignificant and are not correlated with each other we conclude that there is no universal driver changing cell size in cenozoic marine plankton furthermore biologic and physical factors have in concert by reducing silica availability in surface waters forced macroevolutionary changes in cenozoic low latitude radiolarians

a sequence stratigraphic framework for the upper devonian woodford shale permian basin west texas criteria for recognizing stratigraphic sequences are well established on continental margins but more challenging to apply in basinal settings we report an investigation of the upper devonian woodford shale permian basin west texas based on a set of four long cores identifying sea level cycles and stratigraphic sequences in an organic rich shale the woodford shale is dominated by organic rich mudstone sharply overlain by a bioturbated organic poor mudstone that is consistent with a second order eustatic sea level fall interbedded with the organic rich mudstone are carbonate beds chert beds and radiolarian laminae all interpreted as sediment gravity flow deposits bundles of interbedded mudstone and carbonate beds alternate with intervals of organic rich mudstone and thin radiolaria rich laminae defining a 5 10 m 16 33 ft thick third order cyclicity the former are interpreted to represent highstand systems tracts whereas the latter are interpreted as representing falling stage lowstand and transgressive systems tracts carbonate beds predominate in the lower woodford section associated with highstand shedding at a second order scale chert beds predominate in the upper woodford section responding to the second order lowstand additional variability is introduced by geographic position wells nearest the western margin of the basin have the greatest concentration of carbonate beds caused by proximity to a carbonate platform a well near the southern margin has the greatest concentration of chert beds resulting from shedding of biogenic silica from a southern source a well in the basin center has little chert and carbonate here third order sea level cycles were primarily reflected in the stratigraphic distribution of radiolarian rich laminae

pore structure wettability and spontaneous imbibition of woodford shale permian basin west texas abstract even after more than 30 years of exploration and production low total recovery of shale gas

biostratigraphy of the caballos novaculite tesnus formation boundary marathon basin texas abstract the caballos novaculite is a radiolarian sponge spicule chert and siliceous mudstone which represents the final episode of a 200 ma span of dominantly biogenous hemipelagic sedimentation in marathon basin it is overlain by the tesnus formation an upward coarsening flysch sequence produced during the ouachita orogeny by the collision of laurasia and gondwana detailed radiolarian biostratigraphy of the boundary between these two units has provided greater age control as to the onset of flysch deposition and provides a greater understanding of the sedimentary patterns produced in ouachita basinal facies when switching modes of sedimentation from a passive to an active regime radiolarians and conodonts recovered from this interval show a hiatus equivalent to much of the early mississippian occurring in the vicinity of the boundary between the caballos and tesnus formations in three sections late mississippian meramecian radiolarians overlie earliest mississippian early kinderhookian radiolarians in an apparently conformable sequence of siliceous shale in a fourth section meramecian radiolarians overlie late devonian famennian radiolarians and conodonts separated by a conglomerate layer these data indicate that a hiatus equivalent to the late kinderhookian to osagean time period is present and that local erosion into the famennian part of the section occurred lithostratigraphically this hiatus is coincident with the caballos novaculite tesnus formation boundary in the central part of the basin while at the western margin it occurs 8 m above the base of the tesnus formation immediately above a clastic zone containing olistoliths results from this investigation show that localized deposition of olistoliths occurred in the western basin margin during the famennian late devonian followed by an interval of non deposition in the early mississippian finally basin wide flysch deposition in the meramecian

relative sea level cycles and organic matter accumulation in shales of the middle and upper devonian horn river group northeastern british columbia canada insights into sediment flux redox conditions and bioproductivity

hydrogen incorporation and retention in metamorphic olivine during subduction implications for the deep water cycle incorporation of hydrogen into metamorphic olivine during dehydration reactions in the subducting oceanic lithosphere provides a mechanism to replenish the deep mantle with water fourier transform infrared spectroscopy of metamorphic olivines formed at 2 5 gpa and 550 c through the reaction antigorite brucite olivine chlorite water shows water contents between 100 and 140 ppm h2o associated exclusively with silicon vacancies similar to the highest values found in peridotite xenoliths brucite involvement in the olivine forming reaction ensures h2o saturation and a low si activity favoring hydrogen incorporation into si vacancies the mapped water distribution in olivine is consistent with growth zoning and there is no evidence of water gain or loss thus even for metamorphic timescales of several million years at 550 c no ionic diffusion modification is observed in agreement with recent experimental findings metamorphic olivines formed by this dehydration reaction may contribute considerable amounts of water to the deep water cycle additionally olivine with abundant h in si vacancies are expected to be rheologically weaker than anyhdrous mantle olivine and might provide a weak interface between slabs and mantle wedges in subduction zones at conditions beyond the stability of hydrous phases

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

sedimentological and ichnological characterization of the middle to upper devonian horn river group british columbia canada insights into mudstone depositional conditions and processes below storm wave base abstract the middle and upper devonian horn river group in northeastern british columbia canada consists predominantly of organic rich mudstones that are typically described as black shales this stratigraphic unit has seen substantial exploration and development for natural gas during the last decade although black shales such as the horn river group have historically been interpreted as deposited in anoxic deep water basins detailed sedimentological and ichnological analyses of eleven horn river group cores indicate that the depositional conditions varied significantly with respect to paleoenvironments redox conditions and physical processes resulting in distinctive sedimentary facies this study integrates data on lithology and physical and biogenic sedimentary structures from detailed core descriptions combined with total organic carbon content to better understand depositional processes and conditions ten mudstone lithofacies and three lithofacies associations are identified massive mudstones and pyrite rich mudstones display very rare planar lamination and graded beds and scarce bioturbation bi 0 1 and are interpreted to represent anoxic waters below storm wave base swb with conditions of relatively low to moderate energy heterolithic laminated and more bioturbated lithofacies are interpreted to represent oxygenated waters below swb with relatively high energy conditions overall bioturbation intensity varies between moderate to intense bi 3 6 where these lithofacies are not intensely bioturbated oxygenated lithofacies show combinations of well preserved physical sedimentary structures including horizontal parallel lamination soft sediment deformation double mud drapes graded beds and current ripples a third lithofacies association represents conditions intermediate between anoxic and oxygenated lithofacies associations mainly based on local changes in the ichnological characteristics these lithofacies show either intense or sparse bioturbation bi 4 6 or bi 0 1 respectively depending on the core location possibly indicating local changes in the depositional conditions and processes e g variations in the oxygen content and or sedimentation rate they can also be found in thick anoxic and oxygenated deposits these lithofacies display intervals of faint lamination amalgamated current ripples and normally graded bedding the cores collectively display significant spatial and stratigraphic heterogeneity in lithology sedimentary structures and bioturbation that are related to relative water depth oxygen content sediment input and deep water currents we interpreted bioturbation intensity to vary mainly as a function of oxygen content related to proximity to the basin margin and sea level fluctuations although secondary stress conditions e g nutrient content and sedimentation rate may also be important unbioturbated and massive fabrics represent anoxic to dysoxic conditions current generated structures are present mainly in the central and distal parts of the basin and are interpreted to represent the presence of contour currents in the proximal parts of the basin laminated and heterolithic units are more common and more bioturbated than in the central and distal basin this study thus can provide significant insights into other shale basins that show similar lateral and vertical variations integration of multidisciplinary studies particularly sedimentology ichnology and total organic carbon aids in understanding and modeling the complexity of these systems

silica diagenesis porosity evolution and mechanical behavior in siliceous mudstones mowry shale cretaceous rocky mountains u s a quartz in mudstones of the mowry shale cretaceous rocky mountain region takes several forms extrabasinal detrital silt some with transported overgrowths replacement of skeletal debris minor overgrowth on detrital quartz and replaced radiolaria pore filling in the intragranular pores of allochems and authigenic microquartz that is dispersed through the clay size matrix the matrix dispersed microquartz has cl character similar to the overgrowths with which it is intergrown supporting the interpretation that it is authigenic and pore filling radiolaria are widely observed in these mudrocks but are poorly preserved by partial mineral replacement quartz dolomite calcite pyrite we interpret dissolved radiolaria and possibly now cryptic diatoms as the likely source of silica for the overgrowths and microquartz through a reaction pathway that entailed the formation of opal ct lepispheres that subsequently recrystallized to microquartz a newly devised variation of the igv intergranular volume concept a parameter igvm is applied for partitioning the causes of porosity decline in mudstones all of the samples examined contain authigenic microquartz which averages around 40 of the rock volume the large volume of microquartz together with the volumes of surviving intergranular pores and pore filling solid hydrocarbon constrain the porosity to around 50 at the time of initial lepisphere formation despite the exceptional abundance of cement overall porosity decline is compaction dominated the presence of significant volumes of cement has implications for mechanical rock properties in the mowry shale which is expected to manifest brittle behavior where cements are most prominently developed

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

minor and trace element and re os chemistry of the upper devonian woodford shale permian basin west texas insights into metal abundance and basin processes the trace and minor element and re os geochemistry of the upper devonian woodford shale are analyzed in order to characterize elemental abundances to identify associations among trace elements and to constrain paleoceanographic conditions and depositional processes this organic carbon rich mudstone in the permian basin west texas is a major source of hydrocarbons in the basin and is coeval with many other upper devonian shales in north america the woodford lacks enrichment in many trace metals only mo u s and se are significantly enriched other redox sensitive elements are depleted or similar to average shale composition including pb bi cr ti cu zn co and v elements associated with granitic sources such as rare earths th ce and tio2 are also depleted relative to average shale this appears to be related to be a source control a strong basin reservoir effect is noted among several redox sensitive elements including mo cu and ni which largely accounts for the depletion dilution by biogenic silica had an additional effect on metal concentrations multivariate factors analysis identified associations between elements including groupings of rare earth elements elements enriched in granitic crust silica varying antithetically with elements in carbonate minerals organic carbon mo and u v phosphate fe and s noteworthy among the results are the different behavior of redox sensitive elements suggesting different precipitation mechanisms or varying dependence on reservoir effects a strong redox effect is noted in the toc ptot ratio at approximately the frasnian famennian boundary indicating an abrupt transition to an anoxic column boundary that coincides with a short term significant fall in sea level this suggests that anoxia was induced by isolation of the basin from the global ocean however with the exception of the uppermost famennian initial 187os 188os values determined from re os geochronology for the permian basin are similar to correlative sections of the appalachian and peace river basins of north american and the rhenohercynian basin of europe this indicates that although the permian basin became restricted during the upper devonian and early mississippian ocean connectivity remained between regional and global basins

olivine hydration in the deep upper mantle effects of temperature and silica activity 1 although water controls the biology and geology of the surface hydrogen is perhaps the most poorly constrained compositional variable in the bulk earth its concentration in the upper mantle appears to be controlled by its solubility as hydroxyl in the nominally anhydrous silicate phases olivine pyroxene garnet wadsleyite and ringwoodite here we describe a series of experiments showing that the solubility of h2o in olivine at 12 gpa increases with temperature to 8900 ppm by weight at 1250 c and decreases at higher temperature with the onset of melting sample characterization by infrared spectroscopy indicates that the primary hydration mechanism is the substitution of 2h for mg2 similar results obtained from samples coexisting with clinohumite low silica and with clinoenstatite high silica indicate that silica activity has minimal effect on hydration under these conditions single crystal x ray diffraction measurements constrain the volume of hydration and indicate significant m site vacancies hydrogen thus appears to become a geochemically compatible element as depths approach 400 km

two stage models for lunar and terrestrial anorthosites petrogenesis without a magma ocean two stage diapiric models for lunar ferroan anorthosites and terrestrial massif anorthosites are examined the lunar model is developed to explain early lunar differentiation in the absence of a magma ocean if correct the terrestrial model serves as an analog for the development of lunar anorthositic diapirs there is field and textural evidence of transport of mostly crystalline anorthositic material within the terrestrial complexes this evidence combined with the absence of anorthositic lavas and phase equilibrium constraints inhibiting the production of hyperaluminous magmas is consistent with the detachment of plagioclase rich crystalline mushes from large uppermost mantle plutons and multiple diapiric intrusion of these mushes into the upper sialic crust with attendant anatexis rudimentary dynamical calculations suggest that a simple single layer source for the diapirs is improbable either there were several parental magma chambers or there was a single large chamber that was repeatedly replenished the lunar model is a development of wetherill s 1975 suggestion that following accretion the outer portion of the moon consisted of a stack of overlapping layered intrusions and that reheating of these intrusions mobilized their anorthositic layers which intruded upwards to produce the anorthositic lunar crust dynamical calculations show that gravitational instabilities in anorthositic layers 1 km thick could develop into diapirs on a reasonable time scale 50 100 m y only if the outer portion of the moon was partially remelted we suggest that partial melting of the interior due to the decay of long lived radionuclides with the subsequent onset of global convection heated the stack of intrusions from below thus causing melting and allowing the anorthositic diapirs to grow and ascend fairly rapidly as the convecting zone thickened a mass expulsion of anorthositic material out of the lunar interior may have occurred

geochemical and petrographic characteristics of wufeng longmaxi shales jiaoshiba area southwest china implications for organic matter differential accumulation abstract the organic matter rich shales in wufeng longmaxi formation have been considered to be a high quality source rock and a main shale gas producer in southern china as the material basis of shale gas the organic matter content in shales exhibits a notable vertical difference in the jiaoshiba area of fulin shale gas field this study integrated detailed geochemical analysis and sedimentary observations to investigate organic matter enrichment and depletion mechanism three intervals are identified by organic matter contents and their according variations six major lithofacies are identified based on mineral composition x ray diffraction xrd analyses microscopic observations and focused ion beam scanning electron microscopy fib sem data geochemical redox proxies mo ef u ef v cr and corg p indicate that organic matter rich shales of wufeng and bottom longmaxi formation are deposited in anoxic conditions whereas organic matter lean shales of the middle to top longmaxi formation are deposited in oxic environment this pattern is influenced by both worldwide marine transgression and regional tectonic movement the productivity proxies p al cu al ni al sio2 bio indicate that the organic matter rich wufeng longmaxi shales were deposited under moderate to high surficial primary productivity increasing terrigenous influxes dominated organic matter dilution and may have been promoted by regional tectonic uplift the organic matter enrichment or depletion mechanisms in each unit are controlled by different geological events enrichment was controlled by multiple reasons including both global and regional factors whereas depletion was mainly dominated by regional tectonic uplift additionally the sequence stratigraphic boundaries coincide with organic matter shifting interfaces indicating that high resolution sequence stratigraphy of fine grained sediments may have a certain effect on optimal reservoir predication conversely boundaries of toc and geochemical proxies may also help to subdivide sequence boundaries

recurring patterns of total organic carbon and source rock quality within a sequence stratigraphic framework sequence stratigraphy has been combined with total organic carbon toc analysis from well logs core and cuttings to develop a model of toc accumulation in marine source rocks routine well profiling of toc in marine source rocks has revealed that recurrent patterns in the vertical distribution of toc occur that can be explained with sequence stratigraphic concepts the model assumes that the principle controls on organic carbon accumulation are 1 the presence of low oxygen conditions at the sediment water interface and 2 sedimentation rate under these circumstances toc will vary inversely with terrigenous clastic influx if accommodation is high clastic influx is low in distal locations and the resulting weight percent toc in basinal sediments is increased th maximum toc in a vertical profile through a single marine sequence probably correlates to the maximum flooding surface toc decreases above this surface due to increasing sediment dilution during highstand progradation and decreases below it with the higher sedimentation rate of the older transgressive systems tract commensurate with toc increase towards the maximum flooding surface the organic matter type becomes more marine and therefore increasingly oil prone several marine source rock examples are presented as well as a lacustrine example which also conforms to the marine model

sequence stratigraphy and a revised sea level curve for the middle devonian of eastern north america abstract the well exposed middle devonian rocks of the appalachian foreland basin onondaga formation hamilton group tully formation and the genesee group of new york state preserve one of the most detailed records of high order sea level oscillation cycles for this time period in the world detailed examination of coeval units in distal areas of the appalachian basin as well as portions of the michigan and illinois basins has revealed that the pattern of high order sea level oscillations documented in the new york pennsylvania section can be positively identified in all areas of eastern north america where coeval units are preserved the persistence of the pattern of high order sea level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea level oscillation as opposed to autocylic controls such as sediment supply which would be more local in their manifestation there is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to milankovitch orbital variations with the short and long term eccentricity cycles 100 kyr and 405 kyr being the dominant oscillations in many settings relative sea level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism given that the middle devonian appears to record a greenhouse phase of phanerozoic history these new correlations lend strong support to a revised high resolution sea level oscillation curve for the middle devonian for the eastern portion of north america recognized third order sequences are eif 1 lower onondaga formation eif 2 upper onondaga and union springs formations eif giv oatka creek formation giv 1 skaneateles giv 2 ludlowville giv 3 lower moscow giv 4 upper moscow lower tully and giv 5 middle tully geneseo formations thus in contrast with the widely cited eustatic curve of johnson et al 1985 which recognizes just one major transgressive regressive t r cycle in the early mid givetian if prior to the major late givetian taghanic unconformity iia upper tully geneseo shale we recognize four t r cycles if restricted ig ih and ii we surmise that third order sequences record eustatic sea level fluctuations of tens of meters with periodicities of 0 8 2 myr while their medial scale fourth order subdivisions record lesser variations primarily of 405 kyr duration long term eccentricity this high resolution record of sea level change provides strong evidence for high order eustatic cycles with probable milankovitch periodicities despite the fact that no direct evidence for middle devonian glacial sediments has been found to date

ftir spectroscopy of ti chondrodite ti clinohumite and olivine in deeply subducted serpentinites and implications for the deep water cycle separated olivine grains from a deeply subducted serpentinized wehrlite changawuzi in the western tianshan ultrahigh pressure belt china were analysed with unpolarized transmission ftir and the ti contents were determined using la icp ms the major bands in the olivine spectra display striking similarities to ti clinohumite and are interpreted as oh in lamellae the quantification of the water content in lamellae requires calibration of the ir absorption for such bands we have obtained a new absorption coefficient for ti clinohumite of 0 125 0 017 ppm cm2 based on polarized ftir measurements on three orthogonal sections through a large single crystal of ti clinohumite from val malenco which has a known water content of 1 53 wt the resulting water content in olivine using this calibration factor ranges from 440 to 2 600 ppm and correlates positively with the ti content that ranges from 130 to 1 400 ppm for the quantification of the water content in ti chondrodite and ti clinohumite that are associated with olivine we developed a new method using attenuated total reflectance ftir spectroscopy ti chondrodite and ti clinohumite display similar ir bands at 3 562 3 525 and 3 583 3 586 cm 1 as in olivine the water content and ti content correlate in both ti clinohumite and ti chondrodite indicating an intergrowth of these minerals which has been confirmed by tem analyses our results confirm previous suggestions that there is a strong correlation between the ti content of ultramafic rocks and their capacity to transport water to the deeper mantle in subduction zones beyond conditions where hydrous phases are stable

evaluating re os systematics in organic rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments abstract successful application of the 187re 187os geochronometer has enabled the determination of accurate and precise depositional ages for organic rich sedimentary rocks ors as well as establishing timing constraints of petroleum generation however we do not fully understand the systematics and transfer behaviour of re and os between ors and petroleum products e g bitumen and oil to more fully understand the behaviour of re os systematics in both source rocks and petroleum products we apply hydrous pyrolysis to two immature hydrocarbon source rocks the permian phosphoria formation toc 17 4 type ii s kerogen and the jurassic staffin formation toc 2 5 type iii kerogen the laboratory based hydrous pyrolysis experiments were carried out for 72 h at 250 300 325 and 350 c these experiments provided us with whole rock extracted rock and bitumen and in some cases expelled oil and asphaltene for evaluation of re os isotopic and elemental abundance the data from these experiments demonstrate that the majority 95 of re and os are housed within extracted rock and that thermal maturation does not result in significant transfer of re or os from the extracted rock into organic phases based on existing thermodynamic data our findings suggest that organic chelating sites have a greater affinity for the quadravalent states of re and os than sulphides across the temperature range of the hydrous pyrolysis experiments both whole rock and extracted rock 187re 188os ratios show small variations 3 3 and 4 7 for staffin respectively and 6 3 and 4 9 for phosphoria respectively similarly the 187os 188os ratios show only minor variations for the staffin and phosphoria whole rock and extracted rock samples 0 6 and 1 4 and 1 3 and 2 2 these isotopic data strongly suggest that crude oil generation through hydrous pyrolysis experiments does not disturb the re os systematics in ors as supported by various studies on natural systems the elemental abundance data reveal limited transfer of re and os into the bitumen from a type iii kerogen in comparison to type ii s kerogen 0 02 vs 3 7 suggesting that these metals are very tightly bound in type iii kerogen structure the 187os 188os data from the pyrolysis generated phosphoria bitumens display minor variation 4 across the experimental temperatures with values similar to that of the source rock this indicates that the isotopic composition of the bitumen reflects the isotopic composition of the source rock at the time of petroleum generation these data further support the premise that the os isotopic composition of oils and bitumens can be used to fingerprint petroleum deposits to specific source rocks oil generated through the hydrous pyrolysis experiments does not contain appreciable quantities of re or os 120 and 3 ppt respectively in contrast to natural oils 2 50 ppb and 34 288 ppt for re and os respectively which may suggest that kinetic parameters are fundamental to the transfer of re and os from source rocks to oils from this we hypothesise that at the temperatures employed in hydrous pyrolysis re and os are assimilated into the extracted rock as a result of cross linking reactions

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions

fluvial sequence stratigraphy the wapiti formation west central alberta canada abstract outcrop exposures and high resolution subcrop data allow the description and mapping of four stratigraphic discontinuities in the fully nonmarine strata of the campanian maastrichtian wapiti formation western interior foreland basin alberta canada this framework defines four unconformity bounded depositional sequences a d based on sequence stratigraphic methodology well log patterns and facies analysis in ascending order sequence a records the transition from the underlying marine facies of the puskwaskau formation into the wapiti fluvial facies and consists of strongly progradational and aggradational stacking patterns sequences b and c show a similar pattern of basal amalgamated channel fill deposits that grade upwards into floodplain dominated strata finally sequence d is dominated by channelized sediments and extensive overbank facies an aggradational stacking pattern suggests deposition under high accommodation conditions maximum flooding surfaces are interpreted within fine grained deposits in the upper portions of sequences c and d they are tied to regionally extensive coals that accumulated more than 250 km away from the coeval shoreline this study provides new evidence that major coal seams may represent the extension of marine maximum flooding surfaces into the downstream controlled fluvial realm furthermore the new stratigraphic framework of subaerial unconformities and maximum flooding surfaces provides the means of subdividing the previously undifferentiated fully nonmarine wapiti formation into depositional sequences and component systems tracts

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

serpentinites of the zermatt saas ophiolite complex and their texture evolution the zermatt saas serpentinite complex is an integral member of the penninic ophiolites of the central alps and represents the mantle part of the oceanic lithosphere of the tethys metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean floor hydration subduction related high pressure overprint meso alpine greenschist facies metamorphism and late stage hydrothermal alteration the early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures the primary serpentine minerals were completely replaced by antigorite the stable assemblage in subduction related mylonitic serpentinites is antigorite olivine magnetite diopside the mid tertiary greenschist facies overprint is characterized by minor antigorite recrystallization textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high pressure metamorphism of up to 2 5 gpa and 650 c the zermatt saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth

high resolution sequence stratigraphic reconstruction of mud dominated systems below storm wave base a case study from the middle to upper devonian horn river group british columbia canada abstract the application of sequence stratigraphy to deep water mud dominated systems is more challenging than in shallow water siliciclastic settings largely because mudstones display subtle contrasts in grain size and lithology that make identification of facies and recognition of major stratigraphic surfaces difficult however the integration of sedimentology ichnology and geochemistry and an extensive suite of cores from the middle to upper devonian horn river group shales allow us to better understand how deep water mud dominated systems respond to fluctuations in the relative sea level manifested in sequence stratigraphic relationships the horn river group consists of in ascending order the evie member and otter park member of the horn river formation and the muskwa formation four systems tracts including highstand transgressive lowstand and falling stage systems tracts hst tst lst fsst respectively are identified and mapped highstand and transgressive systems tracts are both represented by dominantly massive mudstone lithofacies sparse bioturbation high mo al ratios and high toc values avg 3 1 and 3 4 wt respectively as well as low al2o3 concentrations they can be distinguished by upward increasing gamma ray values for transgressive systems tracts and upward decreasing values for highstand systems tracts the falling stage and low stand systems tracts display more heterolithic and laminated lithofacies sparse to intense bioturbation lower mo al ratio and lower toc values avg 1 2 and 1 7 wt respectively and high al2o3 concentrations and relatively low gamma ray readings sequence boundaries are represented by a transition from unbioturbated units to moderately or intensely bioturbated units suggesting increased bottom water oxygen levels which we infer to represent shallower waters they are gradational and clearly conformable contacts in distal parts of the basin they are sharp in more proximal settings but no erosional surfaces were identified that would indicate unconformable contacts maximum flooding surfaces are characterized by the highest toc contents and an increased gamma ray values our results suggest that the otter park member belongs to a long period sea level lowstand e g 2nd order cycle whereas the evie member and muskwa formation belong to long period sea level highstands

algal blooms and marine snow mechanisms that enhance preservation of organic carbon in ancient fine grained sediments abstract combined petrographic and geochemical methods are used to investigate the microfabrics present in thin sections prepared from representative organic carbon rich mudstones collected from three successions the kimmeridge clay formation the jet rock member of the whitby mudstone formation and the pebble shale and hue shale this study was initiated to determine how organic carbon rich materials were being delivered to the sediment water interface and what happened to them after deposition prior to deep burial analyses of the fabrics present shows that they exhibit many common attributes in particular they are all 1 highly heterogeneous on the scale of a thin section 2 organized into thin beds the organomineralic aggregates present in these mudstones are interpreted to be ancient examples of marine snow this marine snow likely formed in the water column particularly during phytoplankton blooms and was then transported rapidly to the seafloor the existence of the thin beds with homogenized tops and an in situ infauna indicates that between blooms there was sufficient oxygen and time for a mixed layer to develop as a result of sediment colonization by diminutive organisms using either aerobic or dysaerobic metabolic pathways these textures suggest that the constituents of these mudstones were delivered neither as a continuous rain of sediment nor were the bottom waters persistently anoxic in addition the presence of thin lags and sharp based beds suggests that the seafloor was being episodically reworked during deposition these fabrics indicate that conditions in the water columns and at the seafloors while these rocks were being deposited were very dynamic and episodic fluxes of high concentrations of organic carbon to the seafloor during phytoplankton blooms likely enhanced preservation of organic carbon

a sequence stratigraphic model for the organic rich upper devonian duvernay formation alberta canada abstract the upper devonian duvernay formation of western canada is a prolific source rock that in recent years has become an important exploration target for shale gas and oil we present a sequence stratigraphic model for the duvernay formation that characterizes relationships between sea level basin circulation lithofacies distribution and mechanisms for sediment transport and organic enrichment the study demonstrates lateral and stratigraphic variability in the character of sequence stratigraphic surfaces and systems tracts and interprets this variability in the context of sea level cycles at varying time scales correlation of 24 core descriptions to a network of 759 wells with wireline logs led to the creation of a basin scale sequence stratigraphic framework three 3rd order depositional sequences are identified the middle sequence straddles a 2nd order maximum flooding surface each systems tract shows unique trends in lithofacies rock properties and wireline character transgressive systems tracts are characterized by the increasingly widespread deposition of clay poor siliceous organic rich mudstones in the basin resulting from decreased clastic and carbonate input concentration of pelagic organic matter and siliceous radiolaria and low oxygen concentrations in basin center bottom waters highstand systems tracts are characterized by sustained radiolarian input and increases in carbonate sediment due to shedding of carbonate detritus during aggradation and progradation of platform margins and reefs lowstand systems tracts are more clastic rich and organic poor near reef complexes coarse carbonates locally mark the base of the lowstand systems tract bottom currents reworked mud and silt sized material in toe of slope locations and contributed to slope parallel progradation during regression

re os geochronology of organic rich sediments an evaluation of organic matter analysis methods rhenium and osmium in organic rich sedimentary rocks are dominantly hydrogenous but any nonhydrogenous component will influence the accuracy and precision of the re os date obtained to minimize the influence of any nonhydrogenous re and os we evaluate analysis of isolated organic matter from the whole rock together with whole rock analysis using a cro3 h2so4 digestion medium instead of inverse aqua regia for a black shale unit of the exshaw formation canada this unit previously returned a whole rock re os date of 358 10 ma model 3 geochim cosmochim acta 2002 using inverse aqua regia dissolution organic matter isolated from the whole rock matrix using the hf bf3 technique org geochem 20 1993 249 yields scattered data and a re os date of 449 220 ma model 3 mswd 616 the organic matter analyses show similar 187os 188os values but significantly lower 187re 188os values in comparison to the whole rock analyses we show that the re os systematics of organic matter are altered during chemical isolation and as such we suggest that the hf bf3 method should not be used for re os analysis of organic matter whole rock re os analysis using a cro3 h2so4 digestion medium yields significantly better regression analysis compared with the inverse aqua regia method and the re os data identify two distinct initial 187os 188os values for the sample set separate regressions of these data yield precise dates 366 1 9 6 mswd 2 2 and 363 4 5 6 ma mswd 1 6 model 3 which are indistinguishable from the age constraints for this formation 363 4 0 4 ma u pb monazite comparison of the re os dates obtained from aqua regia and cro3 h2so4 methods suggests that the former may contain nonhydrogenous re and os whereas the cro3 h2so4 method dominantly liberates hydrogenous re os from organic matter allowing for better stratigraphic age determinations and evaluation of the os isotope composition of seawater