sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

stability limits of hydrous minerals in sediment and mid ocean ridge basalt compositions implications for water transport in subduction zones phase relationships in hydrated natural sediment and mid ocean ridge basalt morb compositions were investigated experimentally from 6 to 15 gpa and 700 c to 1400 c in order to determine the stability of hydrous phases in subducting slabs and to constrain reactions resulting in the release of water from subduction zones to the mantle phengite and hydrous aluminum silicates topaz oh and phase egg are stable in the sediment composition at depths greater than 150 km and constitute h2o reservoirs similarly lawsonite is an h2o reservoir in morb composition at depths greater than 150 km according to mass balance calculations based on experimental run products the weight proportions of phengite and h2o at 6 gpa in the sediment are about 50 and 2 respectively at pressures from 8 to 12 gpa topaz oh al2sio4 oh 2 appears as the hydrous mineral and the sediment retains about 0 5 0 7 wt h2o at higher pressures phase egg alsio3 oh appears as the hydrous phase with a large stability field the h2o content in the sediment is about 0 5 wt at pressures greater than 12 gpa in natural morb compositions lawsonite is the hydrous phase at pressures lower than 10 gpa about 1 wt h2o in the morb composition is retained by lawsonite at 6 gpa and 800 c above 6 gpa a lawsonite out reaction is controlled by compositional changes of garnet and clinopyroxene if the oceanic crust descends with an overlying sediment layer water can be carried down into the transition zone by the sediment the amount of transported water is controlled by the chemical compositions of the subducting sediments water in the morb layer can be stored to 300 km in lawsonite for a cold subduction zone geotherm water release at depths greater than 200 km through progressive lawsonite breakdown can hydrate the overlying mantle causing the generation of a peridotite region including hydrous phases chondrodite clinohumite phase a and phase e if this hydrous peridotite is dragged down by the descending oceanic crust water can be transported into the transition zone by the subduction process the amount of transported water is controlled by the thermal state of the slab and the chemical composition of morb

the inorganic geochemistry of cretaceous black shales dsdp leg 41 in comparison to modern upwelling sediments from the gulf of california

the high pressure phase of lawsonite a single crystal study of a key mantle hydrous phase lawsonite caal2si2o7 oh 2 h2o is an important water carrier in subducting oceanic crusts and the primary hydrous phase in basalt at depths greater than 80 km we have conducted high pressure synchrotron single crystal x ray diffraction experiments on natural lawsonite at room temperature up to 10 0 gpa to study its high pressure polymorphism we find that lawsonite remains orthorhombic with cmcm symmetry up to 9 3 gpa and shows nearly isotropic compression above 9 3 gpa lawsonite becomes monoclinic with p21 m symmetry across the phase transition the ca polyhedron becomes markedly distorted and the average positions of the h2o molecules and hydroxyls change the changes observed in the h atom positions under compression are different than the low temperature changes in this material we resolve for the first time the h bonding configuration of the high pressure monoclinic phase of lawsonite a bond valence approach is deployed to determine that the phase transition from orthorhombic to monoclinic is primarily driven by the si2o7 groups and in particular their bridging oxygen atoms o1 the changes in the structure strongly indicate that entropy increases across the symmetry lowering transition and hence that the slope of the phase transition is negative monoclinic lawsonite is thus stable under the pressure and temperature conditions that exist in the earth and is likely to be a major water carrier in colder deep subducted slabs monoclinic lawsonite also likely has enhanced electrical conductivity along its c axis due to its dynamically disordered hydrogen atoms

lawsonite composition and zoning as tracers of subduction processes a global review abstract lawsonite is an abundant hydrous mineral in oceanic crust sediments and metasomatic rocks at depths of 45 to 300 km in most subduction zones but it is rarely preserved in the geologic record because it commonly transforms to epidote and other minerals during prograde or retrograde metamorphism owing to the significance of lawsonite for water and element cycling in subduction zones occurrences of fresh lawsonite in blueschist and more rarely eclogite provide important opportunities to determine lawsonite composition zoning and inclusion suites and to use this information to reconstruct reaction history during subduction and exhumation in this review we use new and published data to document lawsonite composition in eight of the nine known lawsonite eclogite localities in which fresh lawsonite coexists with garnet omphacite in the rock matrix as well as the composition of lawsonite inclusions in six of seven known sites in which lawsonite occurs only as inclusions in garnet in eclogite facies rocks that lack matrix lawsonite as lawsonite blueschist is much more common than lawsonite eclogite we survey the composition of lawsonite in representative localities of blueschist including blueschist associated with eclogite lawsonite bearing epidote bearing and blueschist not associated with eclogite at current exposure levels included in this review are metabasaltic rocks silica and carbonate rich metasedimentary rocks metasomatic rocks and lawsonite rich veins this dataset demonstrates that lawsonite composition is a sensitive indicator of reaction history during subduction and exhumation and specifically of fluid rock interaction with implications for element cycling in subduction zones furthermore most exhumed lawsonite eclogite records slab surface conditions that correspond to the location where the slab mantle interface transitions from decoupled to coupled and therefore provides key insights into the thermal history and dynamics of subduction zones

selenium enrichment in carboniferous shales britain and ireland problem or opportunity for shale gas extraction research was partly supported by nerc grants ne l001764 1 and ne m010953 1 mrs a sandison provided skilled technical support barnett shale was kindly provided by hu qinhong the manuscript was improved by the helpful comments of a reviewer

paleoceanographic applications of trace metal concentration data abstract recent studies have identified a range of new applications of trace metal concentration data in the analysis of paleoceanographic systems in restricted anoxic marine systems trace metal toc ratios can provide insight into the degree of watermass restriction and estimates of deepwater renewal times in such systems secular changes in sediment trace metal ratios may provide evidence of the chemical evolution of basinal deepwaters in response to differential rates of trace metal removal to the sediment the degree of deepwater restriction in silled basins is generally controlled by eustatic elevations with higher lower sea levels resulting in lesser greater watermass restriction short term ca million year drawdown of the trace metal inventory of seawater has occurred repeatedly in conjunction with oceanic anoxic events which result in elevated rates of trace metal removal to widespread anoxic facies long term eon scale changes of the trace metal composition of seawater have occurred in response to secular changes in atmospheric oceanic redox conditions and their effects on trace metal cycling caution must be exercised in evaluating trace metal patterns in paleomarine systems however 1 hydrographic analyses based on trace metal toc relationships can be undertaken only on systems that had anoxic deepwaters and 2 the influence of redox variation on trace metal accumulation patterns outweighs that of hydrographic factors in some paleomarine systems

geochemical evaluation of flowback brine from marcellus gas wells in pennsylvania usa large quantities of highly saline brine flow from gas wells in the marcellus formation after hydraulic stimulation fracking this study assesses the composition of these flowback waters from the marcellus shale in pennsylvania usa concentrations of most inorganic components of flowback water cl br na k ca mg sr ba ra fe mn total dissolved solids and others increase with time from a well after hydraulic stimulation based on results in several datasets reported here the greatest concentration of cl in flowback water is 151 000 mg l for total ra combined 226ra and 228ra in flowback the highest level reported is 6540 pci l flowback waters from hydraulic fracturing of marcellus wells resemble brines produced from conventional gas wells that tap into other paleozoic formations in the region the br cl ratio and other parameters indicate that both types of brine formed by the evaporation of seawater followed by dolomitization sulfate reduction and subsurface mixing with seawater and or freshwater trends and relationships in brine composition indicate that 1 increased salt concentration in flowback is not mainly caused by dissolution of salt or other minerals in rock units 2 the flowback waters represent a mixture of injection waters with highly concentrated in situ brines similar to those in the other formations and 3 these waters contain concentrations of ra and ba that are commonly hundreds of times the us drinking water standards

clay mineral diagenesis and quartz cementation in mudstones the effects of smectite to illite reaction on rock properties abstract the late cretaceous to early tertiary sequence of the voring and more basins from the norwegian sea has been examined with respect to mineralogy based on 319 cutting samples from five wells a clear relationship between mineralogy and well log data is demonstrated a significant change with respect to velocity porosity and density occurs within the depth interval corresponding to 80 90 c at shallow depths temperatures

how the technical differences between shale gas and conventional gas projects lead to a new business model being required to be successful abstract this paper will make the case that the unconventional natural gas business is not the same as the conventional natural gas business the skills involved in finding developing and producing discreet pools of oil and gas are not identical to those for shale gas projects however they are similar enough that many companies large and small have not recognized this difference and have not changed their business models those companies are struggling to succeed others have become huge successes seemingly overnight this paper is based primarily on our experience as a junior oil and gas start up company with three different shale gas plays as well as my observations as president of one of the first junior companies in canada to become involved in shale gas our first shale gas play was the liard basin besa river shale play in northeast british columbia in western canada we tried conventional approaches with the usual business model and failed worse we had to go back to the beginning of the learning curve and start over more recently we have applied the new technical methods in our utica shale gas play in quebec in eastern canada with great technical success however other orders of magnitude factors required for success have stalled our progress as we struggle with acquiring new skills in public policy and politics based on these experiences it is our belief that geology and sound science still matters now more than ever it is our position that new skills and approaches are needed in areas that have not been the traditional strengths of our industry

geochemical and geological characteristics of the lower cambrian shales in the middle upper yangtze area of south china and their implication for the shale gas exploration abstract during the early cambrian the middle upper yangtze area of south china evolved to an open shelf with anoxic bottom waters prevailing in most places accumulated black shales in this area named niutitang formation qiongzhusi formation in some places thus become the prospective resources for shale gas exploration and development based on compiled petrological and organic geochemistry data and other information obtained by relevant laboratory tests and field investigation we documented regional distributional patterns of lower cambrian organic rich shales in the middle upper yangtze area according to their lateral extent thickness total organic carbon thermal maturity and burial depth this study also features the general reservoir properties of dark shales in this area together these results highlight several most favorable areas including youyang xiushan huayuan suiyang daozhen dejiang shiqian sinan yinjiang jiangkou tongren songtao and huangping shibing for shale gas exploration

orogenesis vs diagenesis can we use organic rich shales to interpret the tectonic evolution of a depositional basin abstract black shales from the southern appalachian basin and the southwest welsh basin have anomalous u pb and nd model ages suggesting syn and post depositional resetting of the sm nd and u pb isotopic systems this alteration to the primary detrital signature of these two shale sequences is indicative of black shale diagenetic depositional processes that obscure paleo environmental and provenance information recorded prior to and during deposition the trace element and isotopic signatures of these two shale sequences reveal a syn post depositional history that is de coupled from the coeval orogenic history of the region making it difficult to reconstruct the tectonic and oceanographic conditions present at the time of deposition both the ordovivian welsh basin and the devonian appalachian basin sequences host ree and u bearing diagenetic phosphate minerals that play a critical role in the whole rock ree and u budgets in the welsh basin shales early diagenetic apatite and a later monazite phase dominate the ree budget and cause the redistribution of ree early in the basin s history ca 460 ma this redistribution is recorded by the sm nd system 450 90 ma and the nd model ages that are anomalously old by as much as 20 t dm 2 0 ga this early history is complicated by a permo triassic fluid event affecting the whole rock u budget and resetting the u pb isotopic system at 193 45 ma the appalachian basin sequence appears to have a much less complicated history yet still records a significant disturbance in both the sm nd isotopic system 392 76 ma and the pb isotopic system 340 50 ma at about the time of deposition ca 365 ma these two sequences suggest a pattern of diagenetic disturbance common to black shales these processes are unique to black shales and must be considered when interpreting provenance and paleo environmental information from the black shale sequences although these rocks are susceptible to alteration the alteration may provide extensive information on the post depositional history of the basin while still retaining some primary depositional information if black shale processes are considered during the interpretation of isotopic and trace element signatures from organic rich shales it may be possible to recover an extensive basin history

generation transport and disposal of wastewater associated with marcellus shale gas development 1 hydraulic fracturing has made vast quantities of natural gas from shale available reshaping the energy landscape of the united states extracting shale gas however generates large unavoidable volumes of wastewater which to date lacks accurate quantification for the marcellus shale by far the largest shale gas resource in the united states we quantify gas and wastewater production using data from 2189 wells located throughout pennsylvania contrary to current perceptions marcellus wells produce significantly less wastewater per unit gas recovered approximately 35 compared to conventional natural gas wells further well operators classified only 32 3 of wastewater from marcellus wells as flowback from hydraulic fracturing most wastewater was classified as brine generated over multiple years despite producing less wastewater per unit gas developing the marcellus shale has increased the total wastewater generated in the region by approximately 570 since 2004 overwhelming current wastewater disposal infrastructure capacity

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

geologic analysis of the upper jurassic haynesville shale in east texas and west louisiana the upper jurassic haynesville shale is currently regarded as one of the most prolific emerging shale gas plays in the continental united states it has estimated play resources of several hundred trillion cubic feet and per well reserves estimated as much as 7 5 bcf the reservoir spans more than 16 counties along the boundary of eastern texas and western louisiana although this basin has a long history of exploration and analysis of its mesozoic section a comprehensive subsurface study characterizing the haynesville shale has not been conducted this article is the first to address the structural setting stratigraphy depositional environment and facies fracturing and production challenges of the haynesville shale gas play basement structures and salt movement influenced carbonate and siliciclastic sedimentation associated with the opening of the gulf of mexico the haynesville shale is an organic and carbonate rich mudrock that was deposited in a deep partly euxinic and anoxic basin during the kimmeridgian to the early tithonian related to a second order transgression that deposited organic rich black shales worldwide the haynesville basin was surrounded by carbonate shelves of the smackover and haynesville lime louark sequence in the north and west several rivers supplied sand and mud from the northwest north and northeast into the basin haynesville mudrocks contain a spectrum of facies ranging from bioturbated calcareous mudstone laminated calcareous mudstone and silty peloidal siliceous mudstone to unlaminated siliceous organic rich mudstone framboidal to colloidal pyrite is variably present in the form of concretions laminae and individual framboids and replaces calcite cement and mollusk shells haynesville reservoirs are characterized by overpressuring porosity averaging 8 to 12 sw of 20 to 30 nanodarcy permeabilities reservoir thickness of 200 to 300 ft 70 to100 m and initial production of as much as 30 mmcf day reservoir depth ranges from 9000 to 14 000 ft 3000 to 4700 m and lateral drilling distances are 3000 to 5000 ft 1000 to 1700 m typical haynesville wells exhibit a steeper decline curve 80 in the first year than other shale gas plays which is attributed to a very high overpressure

experimental studies of mineralogical assemblages of metasedimentary rocks at earth s mantle transition zone conditions metasedimentary rocks a major component of the continental crust are abundant within ultra high pressure uhp metamorphic terranes related to continental collisions the presence of diamond coesite and relics of decompressed minerals in these rocks suggests that they were subducted to a depth of more than 150 250 km reconnaissance experiments at 9 12 gpa and 1000 1300 c on composi tions corresponding to felsic rocks from diamond bearing uhp terranes of germany and kazakhstan show that at higher pressures they consist of majoritic garnet al na rich clinopyroxene stishovite solid solution of kalsi3o8 naalsi3o8 hollandite topaz oh and tio2 with a pbo2 structure comparison of our data with experiments conducted by others at similar p t conditions shows differences which are due to variations in bulk chemistry and the type of starting material gel oxides minerals these differences may affect correct establishment of the point of no return of subducted continental lithologies this paper discusses the implication of the experimental data with regard to naturally existing uhp metamorphic rocks and their significance for our understanding of the deep subduction of continental material

an integrated assessment of a type euxinic deposit evidence for multiple controls on black shale deposition in the middle devonian oatka creek formation an integrated lithologic paleontologic and multi proxy geochemical study of the middle devonian oatka creek formation a black shale in the northern appalachian basin indicates that a number of different factors contributed to organic carbon rich black shale deposition conditions leading to this organic rich sedimentary deposit were ultimately controlled by a relative sealevel rise dominantly eustatic but with possible contributions from local tectonics which cut off the supply of carbonate to the basin geochemical proxy evidence such as mo ti fe ti corg spy and 34spy suggests that as sealevel continued to rise after the carbonate supply was cut off a threshold was crossed at which point conditions in the basin shifted from dominantly anoxic to dominantly euxinic anoxic sulfidic bottom waters concurrent with the shift to dominantly euxinic conditions the supply of siliciclastic sediments was cut off resulting in a condensed horizon as evidenced by the elemental ratios of si al and k fe mg and the relative concentration of eolian silt as determined petrographically and from scanning electron microscopy sediment starvation in the basin appears to have facilitated the biogeochemical re cycling of c n and p specifically the elemental ratios of c n and p and the stable carbon isotope composition of organic matter suggest that the preferential regeneration of p under anoxic conditions and of n during the oxic phase of oxic anoxic oscillation led to enhanced primary production in surface waters thereby maintaining euxinic conditions in the bottom waters through respiration of settling organic matter finally it is observed that though conditions in the basin seem to have remained consistently anoxic sulfidic for some time after the initial shift to euxinic conditions a progressive increase in siliciclastic sedimentation led to a corresponding decrease in the enrichment of various redox related elements illustrating the overriding control that sedimentation can have on geochemical proxy records

trace metal distribution and mobility in drill cuttings and produced waters from marcellus shale gas extraction uranium arsenic barium development of unconventional shale gas wells can generate significant quantities of drilling waste including trace metal rich black shale from the lateral portion of the drillhole we carried out sequential extractions on 15 samples of dry drilled cuttings and core material from the gas producing middle devonian marcellus shale and surrounding units to identify the host phases and evaluate the mobility of selected trace elements during cuttings disposal maximum whole rock concentrations of uranium u arsenic as and barium ba were 47 90 and 3333 mg kg 1 respectively sequential chemical extractions suggest that although silicate minerals are the primary host for u as much as 20 can be present in carbonate minerals up to 74 of the ba in shale was extracted from exchangeable sites in the shale while as is primarily associated with organic matter and sulfide minerals that could be mobilized by oxidation for comparison u and as concentrations were also measured in 43 produced water samples returned from marcellus shale gas wells low u concentrations in produced water 0 084 3 26 g l 1 are consistent with low oxygen conditions in the wellbore in which u would be in its reduced immobile form arsenic was below detection in all produced water samples which is also consistent with reducing conditions in the wellbore minimizing oxidation of as bearing sulfide minerals geochemical modeling to determine mobility under surface storage and disposal conditions indicates that oxidation and or dissolution of u bearing minerals in drill cuttings would likely be followed by immobilization of u in secondary minerals such as schoepite uranophane and soddyite or uraninite as conditions become more reducing oxidative dissolution of arsenic containing sulfides could release soluble as in arsenate form under oxic acidic conditions the degree to which the as is subsequently immobilized depends on the redox conditions along the landfill flow path the results suggest that proper management of drill cuttings can minimize mobilization of these metals by monitoring and controlling eh ph and dissolved constituents in landfill leachates

quantification of loss of calcite pyrite and organic matter due to weathering of toarcian black shales and effects on kerogen and bitumen characteristics abstract comparison of geochemical data on posidonia shale early toarcian from a shallow unweathered core and from adjacent weathered exposures of the same fades was performed results revealed that quantitatively the most affected petrographic constituent is pyrite and that organic matter and carbonate were also altered by weathering due to this process of weathering the bulk composition of organic matter especially the molecular composition of soluble organic matter and the fluorescence colour of organic particles are changed estimates of weathering rates reveal that the annual release of sulphur and organic carbon from black shales may significantly add to anthropogenic pollution

element release and reaction induced porosity alteration during shale hydraulic fracturing fluid interactions the use of hydraulic fracturing techniques to extract oil and gas from low permeability shale reservoirs has increased significantly in recent years during hydraulic fracturing large volumes of water often acidic and oxic are injected into shale formations this drives fluid rock interaction that can release metal contaminants e g u pb and alter the permeability of the rock impacting the transport and recovery of water hydrocarbons and contaminants to identify the key geochemical processes that occur upon exposure of shales to hydraulic fracturing fluid we investigated the chemical interaction of hydraulic fracturing fluids with a variety of shales of different mineralogical texture and composition batch reactor experiments revealed that the dissolution of both pyrite and carbonate minerals occurred rapidly releasing metal contaminants and generating porosity oxidation of pyrite and aqueous fe drove precipitation of fe iii oxy hydroxides that attenuated the release of these contaminants via co precipitation and or adsorption the precipitation of these oxy hydroxides appeared to limit the extent of pyrite reaction enhanced removal of metals and contaminants in reactors with higher fluid ph was inferred to reflect increased fe oxy hydroxide precipitation associated with more rapid aqueous fe ii oxidation the precipitation of both al and fe bearing phases revealed the potential for the occlusion of pores and fracture apertures whereas the selective dissolution of calcite generated porosity these pore scale alterations of shale texture and the cycling of contaminants indicate that chemical interactions between shales and hydraulic fracturing fluids may exert an important control on the efficiency of hydraulic fracturing operations and the quality of water recovered at the surface

uk shale gas the story so far abstract the uk s first well to encounter shale gas was drilled into the upper jurassic kimmeridge clay in 1875 but its significance was not realised at the time 25 years ago research at imperial college applied the us shale gas paradigm to evaluate the uk s shale gas potential shale sequences with potential for gas production were identified in carboniferous strata in the midlands and in jurassic strata particularly in the weald without encouragement from her majesty s government no exploration resulted from this initial research publication of the results of the project was rejected by many uk journals it was finally published in the usa in 1987 subsequent evaluations of uk petroleum resources by the department of energy and its descendants published in 2001 and 2003 omitted any mention of shale gas resources recent timely re evaluations of the uk s shale gas potential have been carried out by the british geological survey and the department for energy climate change in 2008 the 13th round of onshore licensing resulted in the award of several blocks for shale gas exploration though bids were often based on a quest for both shale gas and conventional prospects cuadrilla resource s preese hall no 1 well drilled in 2010 was the first well drilled to specifically test for uk shale gas the same drilling and fracturing techniques that led to the shale gas renaissance in the usa are now being applied to extracting oil from organic rich shales that are currently in the oil window it is interesting to speculate that oil may be produced by such techniques from the thermally mature jurassic shales in the wessex and weald basins in the southern uk

mineralogy and trace element geochemistry of gas shales in the united states environmental implications abstract this paper presents a compilation of published mineralogic and trace element data from nine gas shales in the united states formations analyzed include the antrim bakken barnett eagle ford haynesville marcellus new albany utica and woodford these mineralogic and trace element data can be used to assess the potential for environmental impacts during hydraulic fracturing impacts addressed in this study include 1 the potential for acid rock drainage generation during gas shale weathering 2 the distribution of trace elements in gas shales and comparison with regulatory guidelines and 3 the implications for environmental management of well cuttings the use of the mineralogic data to assess the fracability of the gas shales is also considered compilations of the mineralogy and geochemistry of gas shales can be a valuable resource for managing real and perceived environmental problems associated with their exploitation comprehensive environmental assessment to fully address these issues in addition to other potential environmental impacts will require collection and collation of additional data on the mineralogy and trace element geochemistry of gas and other hydrocarbon producing shales

organic maturity elastic properties and textural characteristics of self resourcing reservoirs abstractorganic rich rocks have long been recognized as source rocks for clastic reservoirs but more recently they have gained importance as reservoirs however the processes of kerogen maturation and hydrocarbon transport and storage are still poorly understood some empirical relations have been developed to relate the increase in elastic modulus with increasing maturity a systematic study of the cause for this increase in elastic modulus is still lacking and information about seismic and mechanical properties of kerogen and its alteration products is scarce consequently any rock models must rely on anecdotal or extrapolated data about various types of kerogen our experiments address this paucity of data by grain scale modulus measurements coupled with careful field emission scanning electron microscopy fesem microstructural assessments on organic rich bakken formation shale samples with a range of maturities carefully acquired and detailed fesem images help to understand the microstructural c

multiple controls on the preservation of organic matter in devonian mississippian marine black shales geochemical and petrographic evidence geochemical and petrographic analysis of an interval of black shales between the huron shale member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian suggests that multiple controls influenced the accumulation of organic matter stratigraphic trends were determined following detailed analysis of a core from the central appalachian basin d6 montgomery county ky specifically c s fe relationships mo v v ni ni co and v cr were used to assess paleo redox conditions during sediment accumulation the role of clastic input was evaluated using ti al k al and si al and c p was used as a proxy for paleoproductivity the terrestrial to marine maceral ratio t m vitrinite plus inertinite alginite plus bituminite was used to evaluate changes in om source c s fe relationships and trace element ratios suggest anoxic conditions prevailed during deposition of much of the upper part of this interval however bottom water conditions were intermittently dysoxic during accumulation of the huron shale member and possibly dysoxic to marginally oxic during accumulation of the lowermost huron shale member productivity appears to have been an important factor in the accumulation of corg and high c p ratios are consistent with a productivity anoxia feedback mechanism in addition nutrients from increased terrestrial weathering may have contributed to enhanced productivity variations in sediment influx may also have influenced corg concentrations through sediment starvation one of the more significant observations in this work is an increase in terrestrial om inertinite and vitrinite up section which may reflect vegetative changes occurring on land during this time interval most of this increase is due to inertinite much of which appears to be fusinitic in origin and hence may be fossil charcoal this latter observation has implications for the expansion of land plants into drier niches and for late devonian atmospheric oxygen levels introduction of more resistant terrestrial om to anoxic basins may have been an important factor in the preservation of high carbon 10 intervals especially in the cleveland member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian

p wave velocity and anisotropy of lawsonite and epidote blueschists constraints on water transportation along subducting oceanic crust p wave velocity vp and the anisotropy of lawsonite and epidote blueschists were measured up to 1 0 gpa and 400 c using the ultrasonic pulse transmission technique the slowest vp in the direction normal to foliation is similar between lawsonite and epidote blueschists 7 0 7 2 km s at 1 0 gpa and room temperature while the fastest vp in the direction parallel to lineation markedly differs between lawsonite blueschists 7 4 7 6 km s at 1 0 gpa and room temperature and epidote blueschist 7 9 km s at 1 0 gpa and room temperature crystallographic orientation measurements for main constituent min erals revealed that both epidote 0 1 0 axes fastest vp direction in epidote single crystal and amphibole 0 0 1 axes fastest vp direction in amphibole single crystal are preferentially oriented parallel to lin eation to enhance vp anisotropy of the epidote blueschist in contrast lawsonite 0 0 1 axes fastest vp direction in lawsonite single crystal are oriented subnormal to foliation whereas amphibole 0 0 1 axes are oriented subparallel to lineation so that relatively weak vp anisotropy was observed in the lawsonite blueschist our experimental results in conjunction with recent seismological observations suggest that the vp of the subducting oceanic crust at 50 km has been observed in several subducting slabs however the high vp values at 50 km depth are difficult to be explained by blueschists this indicates that the blueschist would be at least partially transformed to hydrous mineral bearing eclogite at 50 km depth in subducting oceanic crusts

the elasticity of lawsonite at high pressure and the origin of low velocity layers in subduction zones abstract subduction zones exhibit faster seismic wave velocities compared to the surrounding mantle due to the recycling of relatively cold oceanic lithosphere in certain subduction zones however a 5 10 km thick low velocity layer lvl has been inferred to exist along the top surface of the subducting slab at depths of up to 250 km shear wave velocities in particular within these layers have been estimated as up to 10 slower than the surrounding mantle we have conducted high pressure ultrasonic interferometric measurements to gain insight into the elastic properties of lawsonite caal 2 si 2 o 7 oh 2 h 2 o a hydrous mineral phase stabilized under cold subduction zone conditions in addition we have computed the full elastic constant tensor at elevated pressures and temperature using static electronic structure calculations and molecular dynamics simulations the bulk and shear modulus obtained from theory and experiments are in good agreement we find that lawsonite has an unusually low shear modulus at high pressure and its formation in subducted oceanic crust can explain some seismic evidence for lvl at depths exceeding 100 km to approach estimated lvl velocities requires lawsonite to form in the subducting crust as a result of a fluid influx due to the breakdown of other hydrous minerals such as serpentine the formation of lawsonite additionally lowers seismic velocities because it forms at the expense of garnet a mineral with relatively fast seismic velocities lvl observations may therefore be used to place constraints on the amount of h 2 o subducted into the deep mantle

the hydrothermal transformation rate of kaolinite to muscovite illite batch reactor experiments were performed to measure the rate of the reaction 1 5 kaolinite k muscovite h 1 5 water at temperatures ranging from 250 to 307 c in these experiments the rate of kaolinite conversion to muscovite illite was monitored as the rate of production of h runs were performed in small volume 50 ml titanium hydrothermal reactors charged with well crystallized georgia kaolinite indian ruby muscovite and 25 ml of kcl solution 0 5 2 0 m both solids and solutions were monitored at specific intervals throughout each experiment the determined rate law is dmh dt dmk dt amm k mk k mh where mk and mh are the concentrations of potassium ion and hydrogen ion k and k are the forward and reverse rate constants in kg m 2 sec 1 am is the total surface area of the muscovite in m2 and m is the mass of the solution in kg the initial rate method was used to find k and k was found by fitting data to an integrated rate equation temperature functions for the rate constants are in k 12 90 1 87 104 t r2 0 98 and in k 6 03 1 21 104 t r2 0 95 the activation energies ea for the forward and reverse reaction are 155 15 kj mol 1 and 101 10 kj mol 1 respectively

geochemical evolution of organic rich shales with increasing maturity a stxm and tem study of the posidonia shale lower toarcian northern germany hydrocarbon generation and retention processes occurring within gas shales as a response to increases in thermal maturation are still poorly constrained while efforts have been directed at unravelling the resource potential composition and textures of these economically important unconventional systems their spatial variability in chemistry and structure is still poorly documented at the sub micrometer scale here we have characterized samples of the lower toarcian posidonia shale samples from northern germany at varying stages of thermal maturation using a combination of compositional organic geochemistry and spectromicroscopy techniques including synchrotron based scanning transmission x ray microscopy stxm we document geochemical and mineralogical heterogeneities down to the nanometer scale within the investigated samples as a function of their level of thermal maturity in particular authigenic albite crystals containing nanometric halite inclusions have been documented within the investigated mature and overmature samples the presence of such tracers of palaeobrine carbonate interactions supports a maturation scenario for the lower toarcian posidonia shale intimately related to ascending brine fluids rather than a maturation scenario solely resulting from high heat flows in addition various types of asphaltene and nso rich bitumen have been detected within the same samples very likely genetically derived from thermally degraded organic precursors furthermore the formation of nanoporous pyrobitumen has been inferred for samples of gas window maturity likely resulting from the formation of gaseous hydrocarbons by providing in situ insights into the fate of bitumen and pyrobitumen as a response to the thermal evolution of the macromolecular structure of kerogen the results reported here constitute an important step towards better constraining hydrocarbon generation processes during natural shale gas maturation

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

effect of diagenesis on trace element partitioning in shales abstract in order to investigate the partitioning of trace elements in mineral phases of black shales and diagenetic remobilization of trace elements within these phases we isolated major black shale components sulfide carbonate silicate and organic and analyzed the isolated fractions as well as corresponding whole rock for their trace element composition by drc icp ms this study focused on black shales of different grades of thermal maturity from the ordovician utica shale magnafacies of quebec usm immature tmax 20 50 c ro 140 c ro 1 analysis of the isolated rock fractions revealed that the carbonate fraction preserves a sea water like rare earth elements ree abundance pattern with enrichment of the heavy rare earth elements hree dy lu relative to light rare earth lree la sm the sulfide and organic fractions show a slight enrichment in the lree mass balance calculations showed that the organic fraction contains up to about 20 of total trace element content of the whole rock with the sulfide and carbonate fractions each containing less than 10 the partitioning and fractionation of trace elements between different phases may have important implications for paleoenvironmental reconstructions and provenance studies our data suggest that the whole rock signature may be less representative of source area or depositional environment but rather reflects the diagenetic history this is especially the case in organic rich sediments such as black shales where the organic fraction hosts up to 20 of the trace element content of the whole rock

laboratory earthquakes triggered during eclogitization of lawsonite bearing blueschist abstract the origin of intermediate depth seismicity has been debated for decades a substantial fraction of these events occurs within the upper plane of wadati benioff double seismic zones believed to represent subducting oceanic crust we deformed natural lawsonite rich blueschist samples under eclogite facies conditions 1 5 p 3 5 gpa 583 k t 1121 k using a d dia apparatus installed at a synchrotron beamline continuously monitoring stress strain phase changes and acoustic emissions aes two distinct paths were investigated i heating during deformation at pressures 2 5 gpa to maximum temperatures ranging from 762 to 1073 k during which lawsonite and glaucophane became gradually unstable while entering the stability field of lawsonite eclogite and the breakdown reaction of lawsonite was only crossed in case of the highest final temperature ii heating while deforming at a pressure

correlating norm with the mineralogical composition of shale at the microstructural and bulk scale abstract hydrocarbons produced via hydraulic fracturing of shale formations frequently contain elevated quantities of technologically enhanced naturally occurring radioactive materials tenorm that are difficult to dispose of and can be harmful to the environment this research investigates the elemental composition of seven major shale formations at the bulk and microstructural scale to better understand the relationship between major naturally occurring radioactive elements norm and organic phases within shales bulk mineralogy analysis was performed via powder x ray diffraction to identify which shales were ideal for hydraulic stimulation based on the content of ductile and brittle minerals to complement the xrd quantitative evaluation of minerals by scanning electron microscopy qemscan was performed to identify non crystalline phases and provide spatial mapping of the minerals through the shale samples in addition xrd and qemscan were used to determine the total sulfur and carbonate content as this greatly contributes to the acidity of the shale and subsequently u and th migration select samples were characterized by scanning electron microscopy energy dispersive x ray spectroscopy sem edx to reveal the presence of heavy metals i e u pb near hydrocarbon rich regions of the shale the norm content and organic content were also correlated using gamma well logging

open system chemical behavior in deep wilcox group mudstones texas gulf coast usa abstract wilcox group mudstones have been mechanically and geochemically transformed over a temperature range of 20 200 c our research controlled for provenance and age by sampling from five wells parallel to the paleodepositional axis all within the houston delta system across the sampled depths mudstone porosity has been reduced from 25 to

release of selected chemical elements from shale drill cuttings to aqueous solutions of different ph abstract the effect of ph changes on leachability of light and heavy metals from shale drill cuttings generated from unconventional shale gas production was investigated cuttings being the primary byproduct generated from drilling operations belong to the potentially hazardous type of wastes due to presence of heavy and radioactive elements and remains of drilling fluid in this regard assessment of potentially dangerous components pdcs from rock waste materials was performed by application of batch leaching tests which has provided information on the sensitivity of leaching under externally imposed changes in ph natural or caused by treatment in specific scenarios the description of shale rocks mineralogical and chemical properties was performed by means of x ray fluorescence spectroscopy diffractometry as well as scintillation spectrometry the concentrations of released constituents due to the leaching tests were measured by atomic absorption spectrophotometry results were compared and discussed accordingly with the waste acceptable criteria of elution limits analysis of the substrate revealed that the elemental composition was dominated by light elements whereas heavy metals were present in trace amounts however noticeable release of barium 2 0 4 6 was also recorded which has originated from not only rock material but also drill mud minor mobility was observed for transition elements such as cr co fe mn ni zn cu and pb results revealed that drill cuttings follow the requirements for other than hazardous and municipal type of deposition with exception for barium moreover content of radioactive isotopes fulfill the requirements range of acceptable concentrations

signature of pending earthquake from electromagnetic anomalies two electromagnetic em anomalies have been detected in the vlf frequency band before the athens earthquake eq mw 5 9 sept 7 1999 with the following characteristics i the first and second anomaly lasted for 12 and 17 hours respectively with a cessation of 12 hours ii the second anomaly ceased at about 9 hours before the eq iii the larger anomaly the second one contains approximately 80 of the total em energy received iv no em disturbance has been recorded in the vhf frequency band unlike with other cases e g the kozani grevena and egion eratini earthquakes the fault modeling of the athens eq based on information obtained by radar interferometry predicts two faults the main fault segment is responsible for 80 of the total energy released while the secondary fault segment for the remaining 20 moreover a recent seismic data analysis supports the hypothesis that a two event solution for the athens eq is more likely than a single event solution in addition the absence of surface rupture explains the absence of em detection in the vhf frequency band the present analysis reveals that the properties of the preseismic electromagnetic anomalies might be considered as signatures of a pending earthquake

an evaluation of trace element release associated with acid mine drainage the determination of trace element release from geologic materials such as oil shale and coal overburden is important for proper solid waste management planning the objective of this study was to determine a correlation between trace element residency and concentration to trace element release using the following methods 1 sequential selective dissolution for determining trace element residencies 2 toxicity characteristic leaching procedure tclp and 3 humidity cell weathering study simulating maximum trace element release two eastern oil shales were used a new albany shale that contains 4 6 percent pyrite and a chattanooga shale that contains 1 5 percent pyrite each shale was analyzed for elemental concentrations by soluble adsorbed organic carbonate and sulfide phases all leachates were analyzed to determine total trace element concentrations

sulfate mineral crusts from pyrite weathering and acid rock drainage in the dakota formation and graneros shale jefferson county nebraska pyrite weathering in the uppermost dakota formation and lower graneros shale cretaceous near fairbury nebraska produces acid materials and soils typically ph 6 acid rock drainage ph 2 5 and surface crusts of gypsum and the hydrated fe3 and al sulfate minerals copiapite alunogen metahohmannite coquimbite paracoquimbite and meta alunogen the fe and al minerals produced by acid sulfate weathering are relatively rare heretofore undocumented from nebraska and form in quantity only during episodes of dry weather lasting up to several weeks the maturation of mineral crusts on the dakota formation involves the dehydration of hydrous fe3 and al minerals precursor fe2 sulfates as found in many other cases of pyrite weathering were not observed in surface crusts during the study period surficial mineral crusts on the graneros shale consist only of gypsum with included clay minerals and quartz derived from the underlying shale the processes described herein are noteworthy in a regional geochemical and hydrogeological context and also by virtue of their apparent dependency on weather conditions the acid sulfate weathering sites described herein seem to be relatively unique in the surrounding region nonetheless the study of these sites suggests that there are potentially widespread effects of natural acid sulfate weathering associated with the dakota formation and other pyritiferous cretaceous strata in the region and that the localized effects of anthropogenically induced acid sulfate weathering in roadcuts quarries and other excavations can present engineering problems acid sulfate weathering is likely to have influenced the development of regional groundwater chemistry during the quaternary and may create adverse engineering and environmental conditions such as the retardation of vegetation cover encouragement of subsoil gypsum growth acceleration of shale slaking and possibly even the corrosion of roadbed materials

estimations of clarkes for carbonaceous biolithes world averages for trace element contents in black shales and coals abstract black shale and coal clarke values are the average trace element contents in the world black shales and coals these calculations are made in russian geochemistry but up to now are poorly known in the west modern tables of black shale and coal clarkes are presented based on comprehensive calculations using very large amount of information thousands analyses of black shales coals and coal ashes for trace elements in black shale geochemistry three figures were calculated for each main lithologies terrigenous tuff chert and carbonate two clarke estimations are presented named lithological k1 and lithostratigraphical k2 in coal geochemistry seven figures were calculated for each trace element average content in hard coals and their ashes average content in brown coals and their ashes average content in all coals and their ashes and coal affinity index or coalphile index average content in all ashes clarke values of sedimentary rocks the black shale and coal clarkes presented here provide an important scientific base for many geochemical comparisons and issues

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

the stability and composition of phengitic muscovite and associated phases from 5 5 to 11 gpa implications for deeply subducted sediments abstract the stability and composition of phengitic muscovite was investigated from 5 5 11 gpa 700 1150 c in synthesis experiments performed in a multianvil apparatus starting materials consisted of natural minerals with a bulk composition similar to that of a k deficient intermediate dioctahedral trioctahedral mica phengitic muscovite was found to be stable from 5 5 11 gpa at 900 c phengite melting occurs between 1075 1150 c at 7 8 gpa and 1000 1050 c at 10 gpa at 10 11 gpa 800 c octahedral cation deficient ocd muscovite and k hollandite are observed rather than phengite the average phengite content of muscovite is positively correlated with pressure ranging from 3 65 si pfu at 5 5 gpa to 3 81 si pfu at 11 gpa the maximum phengite content of stable muscovite appears to be 3 80 3 85 si pfu most phengite examined exhibits at least minor solid solution towards phlogopite averaging 2 04 0 06 2 octahedral cations pfu the hydrous phases phengite lawsonite topaz oh and mg pumpellyite occur between 6 8 gpa 700 900 c with increasing pressure lawsonite and mg pumpellyite dehydrate to form garnet between 8 9 gpa with increasing temperature mg pumpellyite lawsonite and topaz oh devolatilize to form garnet and kyanite between 900 1000 c at 7 8 gpa phengitic muscovite and topaz oh would be stable in hydrous sediments in cool mature subduction zones to depths exceeding 360 km while lawsonite and mg pumpellyite would be stable to 240 300 km allowing the transport of h2o contained in these phases deep into the upper mantle in warmer subduction zones the dehydration of mg pumpellyite lawsonite and topaz oh as well as the melting of phengite would result in fluid release at depths of 180 240 km the presence of phengite at far greater depths than the zone of melt generation beneath arcs 100 150 km requires a mechanism such as the partitioning of k be b ba and rb into migrating fluids rather than the simple dehydration of phengite beneath arcs in order to provide for the transfer of these slab signature elements from phengite into arc magmas

sodium calcium ion exchange in the weathering of shales implications for global weathering budgets unpolluted rivers and streams that drain marine shales show an excess of sodium compared to chloride and a deficiency of calcium and magnesium compared to sulfate and alkalinity this is due in part to cation exchange of sodium for divalent cations on clay minerals consideration of the global weathering budget suggests that up to 34 of the sodium in the total dissolved stream load may be due to cation exchange rather than sodium production via silicate dissolution weathering reactions these results suggest that the weathering budgets for sodium and calcium are in need of revision because of the inclusion of cation exchange processes in the weathering cycle this implies that silicate dissolution is less important in determining the composition of global river water than was previously thought

dehydration of lawsonite could directly trigger earthquakes in subducting oceanic crust intermediate depth earthquakes in cold subduction zones are observed within the subducting oceanic crust as well as the mantle in contrast intermediate depth earthquakes in hot subduction zones predominantly occur just below the mohorovicic discontinuity these observations have stimulated interest in relationships between blueschist facies metamorphism and seismicity particularly through dehydration reactions involving the mineral lawsonite here we conducted deformation experiments on lawsonite while monitoring acoustic emissions in a griggs type deformation apparatus the temperature was increased above the thermal stability of lawsonite while the sample was deforming to test whether the lawsonite dehydration reaction induces unstable fault slip in contrast to similar tests on antigorite unstable fault slip that is stick slip occurred during dehydration reactions in the lawsonite and acoustic emission signals were continuously observed microstructural observations indicate that strain is highly localized along the fault r1 and b shears and that the fault surface develops slickensides very smooth fault surfaces polished by frictional sliding the unloading slope during the unstable slip follows the stiffness of the apparatus at all experimental conditions regardless of the strain rate and temperature ramping rate a thermomechanical scaling factor for the experiments is within the range estimated for natural subduction zones indicating the potential for unstable frictional sliding within natural lawsonite layers

chemical and mineralogical analysis of devonian black shale samples from martin county kentucky carroll and washington counties ohio wise county virginia and overton county tennessee u s a abstract core samples of devonian shales from five localities in the appalachian basin have been analyzed chemically and mineralogically the amounts of major elements are similar however the minor constituents organic c s phosphate and carbonate show ten fold variations in amounts trace elements mo ni cu v co u zn hg as and mn show variations in amounts that can be related to the minor constituents all samples contain major amounts of quartz illite two types of mixed layer clays and chlorite in differing quantities pyrite calcite feldspar and kaolinite are also present in many samples in minor amounts dolomite apatite gypsum barite biotite and marcasite are present in a few samples in trace amounts trace elements listed above are strongly controlled by organic c with the exception of mn which is associated with carbonate minerals amounts of organic c generally range from 3 to 6 and s is in the range of 2 5 amounts of trace elements show the following general ranges in ppm parts per million co 20 40 cu 40 70 u 10 40 as 20 40 v 150 300 ni 80 150 high values are as much as twice these values the organic c was probably the concentrating agent and the organic c and sulfide s together created an environment that immobilized and preserved these trace elements closely spaced samples showing an abrupt transition in color also show changes in organic c s and trace element contents several associations exist between mineral and chemical content pyrite and marcasite are the only minerals found to contain sulfide s in general the illite chlorite mixed layer clay mineral shows covariation with organic c if calcite is not present the enriched trace elements are not related to the clay types although the clay and organic matter are intimately associated as the bulk fabric of the rock

material balance assessment of the new albany chesterian petroleum system of the illinois basin the new albany chesterian petroleum system of the illinois basin is a well constrained system from which petroleum charges and losses were quantified through a material balance assessment this petroleum system has nearly 90 000 wells penetrating the chesterian section a single new albany shale source rock accounting for more than 99 of the produced oil well established stratigraphic and structural frameworks and accessible source rock samples at various maturity levels a hydrogen index hi map based on rock eval analyses of source rock samples of new albany shale defines the pod of active source rock and extent of oil generation based on a buoyancy drive model the system was divided into seven secondary migration catchments each catchment contains a part of the active pod of source rock from which it derives a petroleum charge and this charge is confined to carrier beds and reservoirs within these catchments as accountable petroleum petroleum losses or undiscovered petroleum a well constrained catchment with no apparent erosional or leakage losses is used to determine an actual petroleum charge from accountable petroleum and residual migration losses this actual petroleum charge is used to calibrate the other catchments in which erosional petroleum losses have occurred petroleum charges determined by laboratory pyrolysis are exaggerated relative to the actual petroleum charge rock eval charges are exaggerated by a factor of 4 14 and hydrous pyrolysis charges are exaggerated by a factor of 1 7 the actual petroleum charge provides a more meaningful material balance and more realistic estimates of petroleum losses and remaining undiscovered petroleum the total petroleum charge determined for the new albany chesterian system is 78 billion bbl of which 11 4 billion bbl occur as accountable in place petroleum 9 billion bbl occur as residual migration losses and 57 6 billion bbl occur as erosional losses of the erosional losses 40 billion bbl were lost from two catchments that have highly faulted and extensively eroded sections anomalies in the relationship between erosional losses and degree of erosion suggest there is potential for undiscovered petroleum in one of the catchments these results demonstrate that a material balance assessment of migration catchments provides a useful means to evaluate and rank areas within a petroleum system the article provides methodologies for obtaining more realistic petroleum charges and losses that can be applied to less data rich petroleum systems

source rocks and petroleum systems in the hungarian part of the pannonian basin the potential for shale gas and shale oil plays abstract the objectives of our study were to assess the thickness lateral extent organic richness and maturity of the potential source rocks in hungary and to estimate the volumes of hydrocarbons generated in order that potential shale gas and shale oil plays could be identified and characterised the upper triassic kossen marl in south west hungary could represent the best potential shale gas shale oil play due to its high organic richness high maturity and the presence of fracture barriers the area of gas and oil generative maturity is around 720 km 2 with the unexpelled petroleum estimated to be up to 9 billion barrel oil equivalent the lower jurassic sediments of the mecsek mountains and under the great plain contain fair quality gas prone source rocks with low shale gas potential except for a thin toarcian shale unit which is richer in organic matter the latter could form a potential shale gas play under the great hungarian plain if it is thicker locally the lower oligocene tard clay in north east hungary could represent the second best potential shale oil play due to its organic richness favourable maturity and large areal extent 4500 km 2 with around 7 billion barrel oil equivalent estimated in place volume of petroleum middle miocene marine formations could represent locally developed shale gas plays they have fair amounts of organic matter and a mixture of type ii iii kerogen but their vertical and lateral variability is high the upper miocene lacustrine endr d marl contains less organic matter and the kerogen is mainly type iii which is not favourable for shale gas generation the high carbonate and clay content plus the lack of upper and lower fracture barriers would represent additional production challenges

control of 36cl production in carbonaceous shales by phosphate minerals abstract when using 36cl to date very old groundwater in regional aquifer systems knowledge of the subsurface 36cl input into the aquifer system is essential although 36cl can be produced through nuclear reactions in the subsurface in many situations the input of 36cl into sedimentary aquifer systems by this avenue of production can be neglected this is a valid assumption when investigating long flowpath groundwater systems composed of sandstones limestones and shales of typical composition these rock types are not sufficiently enriched in radioactive elements to produce significant 36cl in the deep subsurface carbonaceous shales on the other hand can concentrate the radioactive elements necessary to produce significant 36cl in the deep subsurface chlorine 36 ratios 36cl cl for a suite of late devonian and pennsylvanian carbonaceous shales were calculated from bulk rock chemistry as well as measured using accelerator mass spectrometry the poor agreement between calculated and measured ratios is the result of the assumption of chemical homogeneity used by the calculation algorithm an assumption that was not satisfied by the carbonaceous shales in these shales organic matter clay minerals and accessory minerals are heterogeneously distributed and are physically distinct on a micron order scale although organic matter and clay minerals constitute the overwhelming bulk of the shales it is the phosphate minerals that are most important in enhancing and suppressing 36cl production minerals such as apatite and carbonate apatite francolite by including uranium rare earth elements rees and halogens have an important impact on both neutron production and thermal neutron absorption by incorporating both uranium and fluorine phosphate minerals act as neutron production centers in the shale increasing the probability of 36cl production by incorporating rees and chlorine phosphate minerals also act to shield 35cl from the thermal neutron flux effectively suppressing the production of 36cl to reconcile the measured 36cl ratios with the ratios calculated assuming chemical homogeneity the shales were artificially split into three fractions organic clay mineral and phosphate mineral neutron production was calculated separately for each fraction and the calculation results demonstrated that the phosphate fraction exerted much more control on the 36cl ratio than the organic or clay mineral fractions by varying the uranium and chlorine contents in the phosphate fraction a new heterogeneous 36cl ratio was calculated that agreed with the measured ratio for the overwhelming majority of the carbonaceous shales when using rock chemistry to calculate the 36cl ratio rock types that show mineralogical heterogeneity on a micron scale can be divided into bulk fractions and accessory fractions for separate calculations of neutron production and neutron absorption in this manner a more accurate heterogeneous 36cl ratio can be calculated for the rock as a whole

black shales in ukraine a review abstract as a result of a long lasting and complex geological history organic matter rich fine grained rocks black shales with widely varying ages can be found on ukrainian territory several of them are proven hydrocarbon source rocks and may hold a significant shale gas potential thick silurian black shales accumulated along the western margin of the east european craton in a foreland type basin by analogy with coeval organic matter rich rocks in poland high toc contents and gas window maturity can be expected however to date information on organic richness is largely missing and maturity patterns remain to be refined visean black shales with toc contents as high as 8 and a type iii ii kerogen accumulated along the axis of the dniepr donets rift basin ddb they are the likely source for conventional oil and gas oil prone serpukhovian black shales accumulated in the shallow northwestern part of the ddb similar black shales probably may be present in the lviv volyn basin western ukraine middle jurassic black shales up to 500 m thick occur beneath the carpathian foredeep they are the likely source for some heavy oil deposits toc contents up to 12 type ii have been recorded but additional investigations are needed to study the vertical and lateral variability of organic matter richness and maturity lower cretaceous black shales with a type iii ii kerogen toc 2 are widespread at the base of the carpathian flysch nappes but oligocene black shales menilite fm rich in organic matter 4 8 toc and containing a type ii kerogen are the main source rock for oil in the carpathians their thermal maturity increases from the external to the internal nappes oligocene black shales are also present in crimea maykop fm these rocks typically contain high toc contents but data from ukraine are missing

halogen f cl br i behaviour in subducting slabs a study of lawsonite blueschists in western turkey abstract we examined the f cl br and i abundance of minimally retrogressed lawsonite blueschists from the tavsanli zone in northwest turkey to evaluate the behaviour of halogens in subduction zones and to determine the role coexisting high pressure minerals may play in transporting the halogens to the earth s mantle the blueschists contain sodic amphibole and lawsonite with variable amounts of phengite and chlorite and minor apatite a positive correlation between cl br and i contents in bulk rocks suggests their overall coherent behaviour in subduction zones although high ratios of i cl and br cl compared to altered oceanic crust indicate that cl is preferentially lost relative to br and i before or during blueschist metamorphism iodine and f are enriched relative to altered oceanic crust suggesting incorporation from marine sediments in situ analyses of minerals in thin sections reveal f preferentially concentrates in apatite avg 3 13 wt over phengite 482 ppm lawsonite avg 413 ppm and na amphibole 257 ppm chlorine also preferentially resides in apatite 138 ppm followed by equal partitioning between phengite 59 ppm and na amphibole 56 ppm and lower concentrations in lawsonite 27 ppm upon apatite decomposition at a depth of 200 km f may redistribute into lawsonite and phengite in slabs whilst cl is likely expelled to the overlying mantle wedge given the stability of lawsonite and phengite to a depth of 280 300 km in cold subduction zones they may transport f beyond subarc depths contributing to the high f in magmas derived from the deep mantle