early diagenetic silica deposition in algal cysts and spores a source of sand in black shales abstract devonian black shales deposited on the north american craton contain abundant tasmanites cysts although these are typically flattened because of compaction a small proportion are filled with diagenetic silica the latter are spherical to ellipsoidal 0 1 0 5 mm and filled with chalcedony microquartz and megaquartz and single quartz crystals chalcedonic cyst fillings are preserved best in cheat and phosphate nodules whereas megaquartz and single quartz crystals are most common in shale matrix together with colloform textures this suggests that the various silica types originated from recrystallization of early diagenetic silica deposits thin sandstone beds in the chattanooga shale e g bransford sandstone contain abundant quartz sand that is much coarser than the detrital quartz component of the underlying black shales because of this their quartz component is thought to have been transported over considerable distances from the basin margin however because certain shale horizons contain as much as 10 silicified cysts that upon reworking could have yielded quartz grains of fine to coarse sand size the quartz component of these sandstone beds may actually have formed in situ indeed petrographic examination of the sandstone beds shows them to contain quartz grains with morphological and textural features of cyst quartz e g rounding sphericity chalcedony pyrite inclusions lobate grain margins thus silica deposition in algal cysts may provide a significant component of intrabasinal quartz sand in shale sequences distinction of this type of quartz from extrabasinal detrital quartz is important to the reconstruction of the depositional history of shale sequences

reverse engineering mother nature shale sedimentology from an experimental perspective abstract experimental study of the sedimentology of shales can take a variety of forms at its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior or one can manipulate mud in a tank or bucket to gain insights into its rheology this approach was championed over a century ago by sorby and the insights gained can be quite profound more recently tank and settling tube experiments of animal sediment interactions compaction behavior and sediment unmixing via re suspension have proven to be highly informative in spite of their simplicity flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms in flume experiments however it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments although much flume work on muds has been conducted by hydraulic engineers the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different though not mutually exclusive products from such experiments engineers and hydrologists are commonly concerned with quantifying fluid flow properties whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds the latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water there are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology

quartz cementation in late cretaceous mudstones northern north sea changes in rock properties due to dissolution of smectite and precipitation of micro quartz crystals abstract late cretaceous mudstones from two wells located in the northern north sea and the norwegian sea have been examined with respect to quartz cement two different types of quartz cement type 1 and type 2 have been identified using sem eds cl analysis of drill bit cuttings at depths 2370 2670 m 80 85 c type 1 appears as relatively large aggregates 30 100 m of depth temperature related crypto or microcrystalline to macrocrystalline irregular quartz cement formed by local re crystallization of biogenic silica the cl responses of type 1 quartz cement give a clear indication of an authigenic origin type 2 quartz cement represents relatively high amounts of extremely fine grained micro sized 1 3 m crystals embedded as discrete short chains or small clusters nests within the illitized clay matrix the cl responses of micro quartz crystals indicate an authigenic origin the micro quartz is most probably sourced from silica released during the smectite to illite dissolution precipitation reaction the petrographic evidence indicates that most of the silica released by the smectite to illite reaction has not been exported out of the mudstones the silica released produce a subtle inter connected micro quartz network interlocked with aggregates of micro quartz and authigenic clay crystals this micro quartz cementation process causes a significant and sharp change in the mudstone stiffness at the onset of the chemical compaction regime this is indicated by an abrupt increase in well log velocity vp and change in seismic facies close to 2500 m 80 85 c

organic matter accumulation in the upper devonian duvernay formation western canada sedimentary basin from sequence stratigraphic analysis and geochemical proxies abstract we present a model for organic carbon accumulation in the upper devonian duvernay formation of the western canada sedimentary basin relating total organic carbon toc concentrations to a high resolution geochemical and organic petrologic database and comparing these to a core based sequence stratigraphic interpretation many previous source rock studies have suggested that organic matter is enriched in transgressive systems tracts or at maximum flooding surfaces an observation that is commonly attributed to an assumed relationship between water depth and oxygen levels our data set enables us to associate total organic matter content and organic assemblages with particular systems tracts and to examine how the organic assemblages change across the basin tested against proxies for redox conditions and bioproductivity to relate relative sea level to specific mechanisms for organic accumulation the duvernay formation comprises three third order depositional sequences superimposed on a second order late transgressive systems tract and early highstand systems tract sequences are composed almost entirely of transgressive systems tracts and highstand systems tracts with a lowstand systems tract only at the base of the upper cycle that marks the second order sea level turnaround depositional facies generally vary from bioturbated carbonate rich siltstones to siliceous mudstones from the platform margins to basin center organic petrologic analysis records predominantly amorphous organic matter and solid bitumen with much less abundant vitrinite and inertinite organic matter type indicated by rock eval analysis shows that in most cases high total organic carbon toc content is associated with better quality organic matter high hydrogen index and vice versa indicating more reducing conditions or higher bioproductivity were responsibility for organic enrichment however near carbonate reefs hydrogen index is uncorrelated with toc indicating that here dilution by carbonate minerals was the primary control on organic enrichment across most of the basin highest tocs are recorded just above the second order maximum flooding surface secondary peaks in toc are recorded above the maximum flooding surface in the upper third order cycle and in the transgressive systems tract of lower third order cycle low toc values are recorded in the lowstand systems tract and in the middle and upper third order transgressive systems tracts almost up to the maximum flooding surfaces throughout much of the basin proxies for relative sea level restriction of water masses mo toc redox conditions mo al and s fe and bioproductivity biogenic silica coincide these relationships demonstrate that organic carbon accumulation resulted from influxes of nutrient rich upwelled water during high sea level thus toc values are highest in the upper part of transgressive systems tracts and lower highstand systems tracts anoxia typically developed as a result of bioproductivity and enhanced organic matter accumulation but was not itself a trigger for organic sedimentation near carbonate reefs however varying sea level regulated carbonate sedimentation rate and organic matter dilution and bioproductivity had less impact on organic matter concentrations thus toc was high when carbonate deposition was low during transgressions which forced carbonate reefs to backstep limiting carbonate sedimentation in deeper water area

organic matter rich shales of china abstract organic matter rich shales are the main target rocks for unconventional oil and gas exploration and development across the world in china shale gas geological resources are estimated as approximately 110 1012 m3 with recoverable gas reserves of ca 20 1012 m3 recoverable shale oil reserves are estimated as ca 5 109 t a total 35 important organic matter rich shale units have been recognized from mesoproterozoic to cenozoic strata across the entire china these shales are categorized according to their origin under marine marine nonmarine transitional and lacustrine conditions shales of marine origin with ca 9 1012 m3 recoverable resources dominate china s potential in terms of total volume of organic carbon currently the most favorable marine shales for oil and gas exploration are found in the sichuan basin within the lower cambrian qiongzhusi formation and in the wufeng longmaxi formations of uppermost ordovician through lower silurian a fortuitous combination of of sea level variations of paleo productivity of tectonic activity causing development and migration of partially closed deep basin depocenters and of sediment accumulation rates controlled the extensive deposition and distribution of organic matter rich shales in these wufeng and longmaxi formations organic matter rich shales in marine nonmarine transitional facies associated with coal measures occur in north china within the carboniferous and permian and in south china within the permian these carboniferous permian organic matter rich shales are important source rocks for the gas fields in the ordos and sichuan basins abundant organic rich shales are also widely distributed within coal bearing clastics and coal measure shales of fluvial lacustrine and swamp facies in upper triassic to middle jurassic successions of many basins lacustrine organic rich shales were deposited during the permian through neogene in various freshwater to saline lake settings lacustrine organic matter rich shales are the main oil source rocks in the songliao bohai bay ordos and junggar basins lacustrine algae contributed to the rain of organic matter and the preservation of organic matter and distribution of organic rich shale was controlled by lake currents water depth and oxygen poor conditions with enhanced preservation when buried by turbidity currents algal blooms were partly induced by trace nutrients from volcanic ash falls in all of these lacustrine basins seawater intrusion into the freshwater lake of the songliao basin promoted some episodes of black shales saline lacustrine basins such as middle permian junggar basin contain organic rich dolomite mudstone that mainly formed during hot climate conditions when the lakes had high salinity and stratified water columns that deprived the bottom waters of oxygen thereby preserving massive amounts of organic matter laminated calcite rich mudstone in the saline lacustrine settings formed in more brackish waters under stable warm conditions and weak biological activity the modeling of the factors controlling the distribution of organic matter rich shales within china s basins is important for the exploration and development of unconventional oil and gas resources

ordovician k bentonites issues in interpreting and correlating ancient tephras abstract prominent upper ordovician k bentonites include the deicke and millbrig beds in the late ordovician of eastern north america and the kinnekulle k bentonite in the uppermost sandbian of baltoscandia these beds are thought to represent some of the largest ash fall deposits known in the phanerozoic record this report presents a comprehensive study of biotite compositions from the three beds covering a far more extensive geographic range than has previously been described these data show that the kinnekulle and millbrig are multiple event ash beds some parts of which are indistinguishable from one another tectonomagmatic discrimination diagrams combined with mg number data indicate that the deicke millbrig kinnekulle sequence represents the progressive transformation from calc alkaline to peraluminous magmatic sources consistent with a model of progressively evolving magmatism during the closure of the iapetus ocean it is concluded that the millbrig and kinnekulle beds are coeval and represent primarily simultaneous episodes of explosive volcanism although it cannot be excluded that some portions of both beds were produced by the same event

hydrothermal origin of syndepositional chert bands and nodules in the mesoproterozoic wumishan formation implications for the evolution of mesoproterozoic cratonic basin north china abstract abundant chert bands and nodules are discovered throughout the mesoproterozoic wumishan formation 1 5 ga in the north china block the middle part of the wumishan formation consists of cyclic deposition of calcareous shale massive microbial dolostone thrombolites and stromatolites and laminated dolostone chert bands occur most abundantly in the laminated dolostone although they are also found with lower abundance in other lithologies chert bands are normally parallel to the bedding plane and show soft deformation structures suggesting early silicification at or near the water sediment interface the wumishan chert is composed of two types of silica fabric the microcrystalline and cryptocrystalline quartz that derives from the replacement of host dolomitic rock and the mosaic chalcedonic quartz representing typical void filling precipitation we measured the germanium silica ratios ge si and the ree compositions of the chert bands nodules collected from a 60 m interval in the middle part of the wumishan formation in the mopanyu section ge si ratios of the buck samples measured by icp ms range from 13 6 to 35 6 mol mol additional la icp ms analyses allow the measurements of individual silica fabric providing more detailed information about the geochemistry of chert nodules and bands ge si ratios of the replacive chert vary between 10 and 20 mol mol while the mosaic chalcedonic quartz has wider range of variation 1 1 93 2 mol mol these values are 1 order of magnitude higher than the modern seawater value 0 72 mol mol but is within the range of hydrothermal fluids 3 4 51 3 mol mol average 13 mol mol n 101 suggesting hydrothermal fluid as an important si source this conclusion is consistent with the positive eu anomaly in the ree pattern a mass balance calculation indicates that hydrothermal fluid would account for 10 15 20 25 40 55 and 75 of si for the fluid temperature of 100 c 150 c 200 c and 250 c respectively although large igneous provinces are not discovered in the north china block during the deposition of the wumishan formation the studied wumishan cherts have significant contribution from hydrothermal fluid which might be related to the early rifting activities in the north china block before the breakup of supercontinent nuna

pore characterization and shale facies analysis of the ordovician silurian transition of northern guizhou south china the controls of shale facies on pore distribution abstract the ordovician silurian wufeng longmaxi formations in the upper yangtze platform have been considered as the most promising shale play in china however few studies of detailed shale facies and their influence on pore distribution have been conducted therefore it is important to describe the heterogeneity of shale facies in detail and elucidate their relationship to pore networks and development seven distinct facies were identified on the basis of their characteristic physical biological and chemical attributes ion milled samples from all facies were examined with sem for identification of pore types point counting was used to quantify porosity four major pore types appear dominant framework pores phyllosilicate framework pf pores intrapores within inorganic grains and organic matter om pores due to variability in composition and depositional setting of the different facies pore networks are not uniform framework pores between detrital grains and pf pores are widespread in bioturbated claystones pores in black siliceous shales are dominated by framework pores supported by authigenic silica most of these are filled with kerogen bitumen that is host to foam and bubble type om pores intrapores within calcite or dolomite grains are common in fossiliferous mudstones and black dolomitic siltstones but are isolated and do not contribute to productive porosity in muddy siltstones pf pores are well developed within silty bands initial framework pores within silty beds or laminae however were subsequently cemented by calcite or destroyed by compaction as most of primary pf pores and primary frameworks pores are lost during compaction porosity is highly dependent on the population of framework pores between authigenic quartz grains secondary cracking of amorphous organic matter added porosity after initial infilling of porosity by oil and bitumen migration therefore porosity is mainly controlled by abundance of authigenic silica and toc in spite of differences of burial diagenesis among various facies understanding these main controls on porosity should be helpful to predict and find and more porous facies and have a significant impact on future gas exploration in the wufeng longmaxi formations

extensive authigenic quartz overgrowths in the gas bearing haynesville bossier shale usa abstract in sandstone reservoirs despite grain rearrangement during compaction significant pore volumes may be retained prior to the onset of late diagenetic quartz cementation in mudstone reservoirs grain rearrangement during compaction results in significant pore volume reduction prior to late diagenesis where quartz overgrowths have been previously reported in post compaction mudstones they have been in volumetrically low concentrations and interpreted as anomalous occurrences quartz cementation alters rock brittleness resulting in changes to mechanical fracture properties quartz overgrowths reduce reservoir porosity and permeability we present petrographic evidence of two phases of quartz cement in the haynesville bossier shale i grain replacive and ii quartz overgrowths carbonate grain replacement is volumetrically low petrographic evidence indicates three processes in the development of quartz overgrowths mica and pyrite are i engulfed and ii displaced by quartz overgrowth cement the absence of a supportive primary granular framework surrounding engulfed detrital and early authigenic minerals would indicate that quartz overgrowths are also iii replacive pressure dissolution of detrital quartz silt grains and smectite to illite transformation are likely sources of silica for quartz cement this study is the first to document large scale replacive authigenic quartz overgrowth development within a producing mudstone

geochemical characteristics and depositional environments of cherts and associated rocks in the franciscan and shimanto terranes abstract analyses of 122 jurassic cretaceous rock samples from the franciscan terrane california and 24 cretaceous samples from the shimanto terrane southwest japan show that the cherts and associated rocks accompanied by pillow basalts are enriched in fe and mn which may have been derived from hydrothermal activities the results of the fraction analyses for terrigenous basaltic hydrothermal and biogenic end members in the franciscan rocks show that hydrothermal emanations caused iron and manganese enrichment in the rock samples and played an important role in the formation of siliceous rocks vertical variations of the hydrothermal fraction and tio2 normalized values for hydrothermal elements such as fe mn ni zn y and pb show a possibility that the bedded cherts of the franciscan terrane were deposited in a hydrothermal field on or near some active oceanic ridge for more than 30 ma and were a remnant slice of oceanic crust added to the north american continent on the other hand from the field occurrences and vertical variations of tio2 normalized values of hydrothermal elements the shimanto rocks are inferred to have been deposited in a hemipelagic environment such as marginal and inter arc basins

silica diagenesis of neogene diatomaceous and volcaniclastic sediments in northern japan marine diatomaceous siliceous sediments in neogene sections of northern japan contrast with the monterey shale of california in containing many intercalations of acidic volcaniclastic sediments diagenesis of these sediments from deep boreholes and surface sections was investigated three diagenetic zones biogenic opal opal ct and quartz zones are recognized in siliceous sediments corresponding roughly to amorphous silica low cristobalite and quartz zones in acidic vitric volcaniclastic sediments opal ct consists almost exclusively of silica and water while low cristobalite contains appreciable amounts of a1 ca na and k in subsurface sections values of d 101 spacing of opal ct decrease progressively with increasing burial depth the progressive ordering is not associated with additional silica cementation in surface sections the behaviour of d 101 spacing is complicated owing to the modification of the progressive ordering developed during burial diagenesis by later silica cementation during uplift the cementing opal ct is probably precipitated from percolating groundwater which dissolves siliceous skeletons in porous diatomaceous mudstones overlying the opal ct porcellanite opaline cherts that form during burial diagenesis are designated as early opaline chert while those which form during uplift are later opaline chert the later opaline chert contains two groups of opal ct one is progressively ordered opal ct and the other is additionally cemented opal ct with higher d 101 spacing than that in the host porcellanite in diatomaceous siliceous sediments early opaline chert is scarce most if not all opaline cherts in surface sections are of later origin

shrimp zircon u pb geochronological and whole rock geochemical evidence for an early neoproterozoic sibaoan magmatic arc along the southeastern margin of the yangtze block abstract it has been generally accepted that the south china block was formed through amalgamation of the yangtze and cathaysia blocks during the proterozoic sibaoan orogenesis but the timing and kinematics of the sibao orogeny are still not well constrained we report here shrimp u pb zircon geochronological and geochemical data for the taohong and xiqiu tonalite granodiorite stocks from northeastern zhejiang southeastern margin of the yangtze block our data demonstrate that these rocks dated at 913 15 ma and 905 14 ma are typical amphibole rich calc alkaline granitoids formed in an active continental margin combined with previously reported isotopic dates for the 1 0 ga ophiolites and 0 97 ga adakitic rocks from northeastern jiangxi the timing of the sibao orogenesis is thus believed to be between 1 0 and 0 9 ga in its eastern segment it is noted that the sibao orogeny in south china is in general contemporaneous with some other early neoproterozoic 1 0 0 9 ga orogenic belts such as the eastern ghats belt of india and the rayner province in east antarctica indicating that the assembly of rodinia was not finally completed until 0 9 ga

combined sem and reflected light petrography of organic matter in the new albany shale devonian mississippian in the illinois basin a perspective on organic pore development with thermal maturation abstract organic matter hosted pores are an important aspect of pore systems in unconventional gas shale reservoirs along with thermal maturity organic maceral type critically controls the development of secondary organic matter hosted pores three new albany shale samples devonian mississippian kerogen type ii sequence having thermal maturities ranging from a vitrinite reflectance ro of 0 55 to 1 42 were analyzed using a reflected light microscope and a field emission scanning electron microscope organic pores were examined in specific organic macerals and solid bitumen at different thermal maturities vitrinite and inertinite derived from terrestrial woody materials occur as discrete particles in this black shale within the resolution limits of the scanning electron microscope these two macerals do not appear to display enhanced secondary pores associated with increases in thermal maturity cellular pores 0 2 10 m in inertinite were observed throughout the entire maturity range and were typically filled with authigenic quartz or solid bitumen because of thermal degradation amorphous organic matter was not observed at maturities greater than ro 0 80 alginite derived from tasmanites cysts matures later than amorphous organic matter and is still present at ro 0 80 however it is in the process of transforming to pre oil bitumen and shows weak orange yellow fluorescence compared to strong greenish yellow fluorescence in lower maturity samples at a maturity of ro 1 42 alginite could no longer be observed as a distinct phase because of its complete transformation to hydrocarbons and bitumen alginite began to develop secondary pores when it was in the process of transforming to pre oil bitumen which indicates that some liquid and gaseous hydrocarbons left the alginite during this part of the maturation process solid bitumen developed along the original amorphous organic matter networks and now occupies interparticle space between quartz dolomite k feldspar clay and mica grains as well as the cellular pores in inertinite particles solid bitumen becomes smaller and more porous with thermal maturation and thus becomes increasingly unidentifiable with the optical microscope solid bitumen hosted pores 20 1000 nm are the main organic pore type documented in the studied samples and they are more common in shales within the gas window than those in the oil window secondary nanopores in the solid bitumen network play a significant role in hydrocarbon storage and migration

multi stage cu remobilization of the huping metamorphic hydrothermal deposit in the southern north china craton abstract the zhongtiao region is a well endowed cu metallogenic province in the southern north china craton and contains a large number of early precambrian cu deposits of different styles most of which have been subjected to the ca 1 85 ga regional metamorphism however whether there was any role for the proterozoic metamorphism on the extensive cu mineralization is yet to be well understood this paper presents an integrated investigation on the field geology mineral chemistry fluid inclusion and c h o s isotopes of the huping metamorphic hydrothermal deposit in the neoarchean paleoproterozoic zhongtiao metamorphic terranes and reveals multi stage cu remobilization that formed and upgraded the cu deposits in the region we identified three stages of syn to post metamorphic cu remobilization transportation in the huping cu deposit including i early mechanical transport ii intermediate metamorphic hydrothermal remobilization and iii late meteoric fluid incursion in stage i sulfides were remobilized and transported internally under lower greenschist facies metamorphism forming the veinlet disseminated ores and chalcopyrite avg 34s 2 1 similar to the chlorite amphibole schist wall rocks in stage ii the immiscibility of metamorphic fluids avg 18o 4 6 and d 56 6 from the metamorphic terranes triggered the precipitation of higher 34s chalcopyrite avg 8 0 led by the incorporation of extra sulfur during the fluid migration in stage iii incursion of meteoric fluids into the waning metamorphic hydrothermal system formed the barren quartz calcite veins avg 18o 0 09 and 13c 0 88 during these cu remobilization processes the earlier formed sulfides were chemically stable during the mechanical transfer by regional metamorphism and deformation subsequently the immiscibility of metamorphic fluids induced significant cu remobilization and precipitation in the metamorphic hydrothermal system we thus propose a model of multi stage mechanical and chemical cu remobilization for the huping cu deposit which highlights the crucial impacts of metamorphic remobilization processes on the regional cu mineralization in the zhongtiao region

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

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

intensity of quartz cathodoluminescence and trace element content in quartz from the porphyry copper deposit at butte montana textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope sem cl refl ect the physical and chemical environment of quartz formation variations in intensity of sem cl can be used to distinguish among quartz from superimposed mineralization events in a single vein in this study we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events this technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in butte montana analyzed veins include early quartz molybdenite veins with potassic alteration pyrite quartz veins with sericitic alteration and main stage veins with intense sericitic alteration cl intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions isotopes trace elements etc from specific mineralizing episodes furthermore cl intensity increases proportional to temperature of quartz formation such that plutonic quartz from the butte quartz monzonite bqm that crystallized at temperatures near 750 c luminesces with the highest intensity whereas quartz that precipitated at 250 c in main stage veins luminesces with the least intensity trace element analyses via electron microprobe and laser ablation icp ms indicate that plutonic quartz and each generation of hydrothermal quartz from butte is dominated by characteristic trace amounts of al p ti and fe thus in addition to cl intensity each generation of quartz can be distinguished based on its unique trace element content aluminum is generally the most abundant element in all generations of quartz typically between 50 and 200 ppm but low temperature main stage quartz containing 400 to 3600 ppm al is enriched by an order of magnitude relative to all other quartz generations phosphorous is present in abundances between 25 and 75 ppm and p concentrations in quartz show little variation among quartz generations iron is the least abundant of these elements in most quartz types and is slightly enriched in cl dark quartz in pyrite quartz veins with sericitic alteration titanium is directly correlated with both temperature of quartz precipitation and intensity of quartz luminescence such that bqm quartz contains hundreds of ppm ti whereas main stage quartz contains less than 10 ppm ti our results suggest that ti concentration in quartz is controlled by temperature of quartz precipitation and that increased ti concentrations in quartz may be responsible for increased cl intensities

silica diagenesis in the lower paleozoic wufeng and longmaxi formations in the sichuan basin south china implications for reservoir properties and paleoproductivity abstract silica diagenesis is one of the most important aspects of black shale diagenesis and critically controls the reservoirs properties of black shales three stratigraphic sections of the wufeng and longmaxi formations in the sichuan basin along a proximal to distal transect were investigated to study quartz types and their silica sources as well as their influences on reservoirs properties including rock mechanical properties and porosity preservation six types of quartz including detrital quartz recrystallized radiolaria siliceous fossil fragments microcrystalline quartz quartz overgrowth and hydrothermal quartz veins were identified based on their occurrences and morphologies under the petrographic microscope and scanning electron microscope and cathodoluminescence color and intensity original biogenic silica now exists as recrystallized radiolaria and microcrystalline silica in the mudstone matrix and follows systematic distribution patterns both laterally and stratigraphically the biological origin of this silica component is supported by the presence of recrystallized radiolaria with preserved spines preservation of ghosts of the central capsule serrated edges reflecting the spherical lattices of the outer shell and in addition preserved sponge spicules a further source of silica for microcrystalline quartz formation was silica released in the course of clay mineral smectite to illite transformation the different types of quartz make different contributions to the reservoir properties of shales with microcrystalline quartz having the most important impact microcrystalline quartz enhances the rock mechanical properties of shales and protects initial porosity from mechanical compaction through a rigid framework of interconnected diagenetic silica grains pores between microcrystalline quartz grains are shielded from complete mechanical compaction and provide space for accumulation of bitumen and oil later in burial history subsequently these pore filling organic matter develop secondary organic nanopores at higher thermal maturity although biogenic silica content has been used as a paleoproductivity proxy the method used to calculate it is based on questionable assumptions and model parameters need to be fine tuned for a given shale succession on the basis of petrographic observations in addition the commonly observed positive correlation between total organic carbon toc and biogenic silica is invalid for very low sedimentation rates and extremely high concentrations of biogenic silica from low to extremely high biogenic silica content in organic rich sediments a parabolic relationship between toc and biogenic silica should be common

biogenic silica and organic carbon fluxes provide evidence of enhanced marine productivity in the upper ordovician lower silurian of south china abstract biogenic silica is a powerful palaeoproductivity proxy in palaeomarine environments and is significant within shale gas reservoirs demonstrating the association of marine hydrocarbon source rocks with the abundance of micro siliceous fossils yet detailed studies that investigate this strong alliance in the ordovician silurian transition are still lacking the bulk of toc in marine sediments is commonly assumed to have been derived predominantly from marine phytoplankton with modern ocean surveys indicating good correspondence between silica content and primary productivity this study discovers a strong positive correlation between biogenic silica bio si and toc in the upper ordovician lower silurian wufeng and longmaxi formations of south china in the jiaoye 41 5 r 0 68 p

origin of chert in lower silurian longmaxi formation implications for tectonic evolution of yangtze block south china abstract upper ordovician katian to lower silurian rhuddanian strata in the middle upper yangtze block south china contain extensive chert beds although the origin of microcrystalline silica in these cherts is largely unknown in this study the mineralogy and structure of chert as well as major trace and rare earth elements are used to determine the origin of microcrystalline silica in 29 chert samples from longmaxi formation rhuddanian in baizitian outcrop west of kangdian uplift ku results show that 21 of the 29 chert samples have a biogenic origin 2 indicate a hydrothermal origin and 6 show a mixed origin cherts from baizitian outcrop are compared to contemporaneous cherts deposited east of ku cherts both east and west of ku are mainly biogenic in origin which is attributed to high productivity in the paleo seaway hydrothermal microcrystalline silica is relatively uncommon in the longmaxi formation across the middle upper yangtze block and only occurs in baizitian outcrop terrigenous influx contributed to chert accumulation both east and west of ku however cherts east of ku received much more clastic material than those in baizitian outcrop a comparison of chert composition and geochemistry to geological reconstructions of the middle upper yangtze block reveal that accumulation of hydrothermal chert is closely linked to tectonic evolution during the early silurian the middle upper yangtze block was in a compressional tectonic regime with limited heat supply and hence low hydrothermal circulation this is manifested in the paucity of hydrothermal microcrystalline silica in cherts east of ku in contrast hydrothermal microcrystalline silica in cherts west of ku is interpreted to have formed in an extensional tectonic regime with sufficient heat supply this research demonstrates that chert source is in part tectonic controlled and chert geochemistry can be used in reconstructing paleoenvironments

ocean euxinia and climate change double whammy drove the late ordovician mass extinction the late ordovician mass extinction lome ca 445 ma was the first of the big five phanerozoic extinction events and comprised two extinction pulses proposed kill mechanisms include glacially induced global cooling and the expansion of water column anoxia and or euxinia sulfidic conditions but no general consensus has been reached with regard to the precise role of these mechanisms a more definitive understanding is hampered by poorly constrained temporal links between the extinction pulses and climate change and by uncertainty over the spatial distribution and intensity of euxinia here we utilize fe speciation and mo concentrations in addition to the chemical index of alteration weathering proxy to reconstruct ocean redox conditions and climate change across a late ordovician to early silurian shelf to slope transect on the yangtze shelf sea a siliciclastic dominated shelf basin in south china these data show two cycles of expanded euxinia corresponding to the two pulses of the lome suggesting a strong causal relationship significantly we show that intermittent or weak euxinia developed during the first extinction pulse which likely accounts for the loss of benthic fauna and some planktonic organisms and nektonic groups by contrast the development of more intense euxinia throughout the water column during the second pulse likely drove survival fauna to extinction superimposed upon this significant global cooling occurred across the first extinction phase reflecting a secondary role in driving the extinction of certain low latitude taxa

geochemical characteristics and geological significance of the bedded chert during the ordovician and silurian transition in the shizhu area chongqing south china a large amount of bedded chert widely deposited during the ordovician and silurian transition in south china in this study analyses of the petrographic characteristics the major elements and rare earth elements rees were conducted on 31 bedded chert samples obtained from the wufeng and longmaxi formations at the qiliao section in the shizhu area of the sichuan basin to determine the sedimentary environment and the origin of the bedded chert during the ordovician and silurian transition the following conclusions were obtained 1 the bedded chert in the wufeng and longmaxi formations at the qiliao section originated mainly from terrigenous input and siliceous organisms and suffered slightly influence in hydrothermal fluid 2 siliceous organisms was a key factor controlling the differences in the sio2 content of the bedded chert in the wufeng and longmaxi formations at the qiliao section and 3 the bedded chert in the wufeng and longmaxi formations deposited in a continental margin environment d

organic matter content and type variation in the sequence stratigraphic context of the upper devonian new albany shale illinois basin abstract organic matter quantity and type are important parameters in conventional source rock evaluation and unconventional shale oil gas reservoir characterization understanding the stratigraphic distribution of organic matter content and type in black shale successions is critical for identifying potentially productive intervals because organic matter can adsorb large amounts of oil and gas detailed examination of total organic carbon content organic petrographic composition and high resolution 8 cm spacing geochemical proxies in a sequence stratigraphic framework were conducted on an early mature 0 55 ro new albany shale core of the illinois basin to study the influence of relative sea level fluctuations on paleoproductivity clastic supply bottom water redox conditions and their combined control on total organic carbon distribution pattern and organic maceral variation marine organic matter including amorphous organic matter and alginite mainly derived from tasmanites cysts is the dominant organic matter in the new albany shale terrestrial organic matter accounts for stratigraphically amorphous organic matter content increases in transgressive systems tracts reaches a maximum near the maximum flooding surface and decreases in highstand systems tracts enrichment of broken tasmanites cysts and their detrital infills are an indicator of high energy environments and could possibly indicate lowstand systems tracts the stratigraphic distribution of organic matter content and type may result in cyclic stratigraphic variations of hydrocarbon generation potential and oil saturation and influence the development of secondary organic pores when the new albany shale is within the oil and gas windows

grain assemblages and strong diagenetic overprinting in siliceous mudrocks barnett shale mississippian fort worth basin texas porosity permeability and total organic carbon toc in a heterogeneous suite of 21 high maturity samples vitrinite reflectance 1 52 2 15 from the barnett shale in the eastern fort worth basin display few correlations with parameters of rock texture fabric and composition these factors being mostly obscured by the effects of a protracted history of diagenesis diagenesis in these rocks includes mechanical and chemical modifications that occurred across a wide range of burial conditions compaction and cementation have mostly destroyed primary intergranular porosity the porosity average 5 vol by gas research institute helium porosimetry and pore size 8 nm median pore throat diameter are reduced to a degree such that pores are difficult to detect even by imaging ar ion milled surfaces with a field emission scanning electron microscope the existing porosity that can be imaged is mostly secondary and is localized dominantly within organic particulate debris and solid bitumen the grain assemblage is highly modified by replacement a weak pattern of correlation survives between bulk rock properties and the ratio of extrabasinal to intrabasinal sources of siliciclastic debris higher porosity permeability and toc are observed in samples representing the extreme end members of mixing between extrabasinal siliciclastic sediment and intrabasinal derived biosiliceous debris reservoir quality in these rocks is neither more strongly nor more simply related to variations in primary texture and composition because the interrelationships between texture and composition are complex and importantly the diagenetic overprint is too strong

hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication od ocean ridge activity adachi m yamamoto k and sugisaki r 1986 hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication of ocean ridge activity sediment geol 47 i25 148 analyses of 42 cretaceous rock samples from deep sea drilling project dsdp leg 32 in tile northern pacific show that chert and porcellanite are enriched in fe mn p cu ba mo ni and pb relative to both triassic biogenic cherts of central japan and cretaceous dsdp cherts of leg 62 the iron enrichment up to 6 68ve fe20 as total iron is most prominent in chert immediately overlying basal basah which is the only chert free of radiolarians and veined by megaquartz containing many fluid inclusions chemical features characterized by a low ratio for a1 ai fe mn and ai z tio 2 and a high ratio for total fe2oj tio 2 mno tio 2 and mo tio 2 as well as petrological evidence indicatc that the cherts formed in an intense submarine hydrothermal environment on or near the cretaceous japanese spreading center which separated the kula plate from the pacific plate the spreading rate of the cretaceous japanese spreading center estimated from the chemical composition of the cherts was about 3 7 cm r i the rate is comparable to that inferred from the geomagnetic data

hydrothermal origin of late proterozoic bedded chert at gusui guangdong china petrological and geochemical evidence the late proterozoic bedded chert from gusui in guangdong province southern china is characterized by bedded laminated massive and pseudobrecciated structures the chert is depleted in tio2 al2o3 and most trace elements however it is enriched in ba as sb hg and se in al fe mn ternary diagrams it falls into the hydrothermal field factor analysis shows that many elements show up in the principal trace element factor suggesting their enrichment results from leaching of the country rock by hydrothermal solutions the chert has low ree concentrations and displays an ree pattern consistent with a hydrothermal origin it may have formed in a late proterozoic rift or extension zone developed within the yunkai continental margin back arc basin with a fault system linking it to an unknown heat source at depth

importance of volcanic glass alteration to sediment stabilization offshore japan a minor amount ca 1 wt of amorphous silica cement sourced from volcanic glass inhibits consolidation of hemipelagic sediment approaching the nankai trough subduction zone throughout the shikoku basin the distribution and nature of the cement were examined via secondary and backscattered electron imaging the amorphous silica occurs as altered material in contact with volcanic glass coating grains including grain contacts and filling pores based on chemical and petrographic evidence the cement is probably sourced from volcanic glass this is in contrast to a previous suggestion that this silica cement is sourced dominantly from biogenic silica amorphous silica sourced from disseminated volcanic glass shards has the ability to form a thin coating on clay dominated sediment throughout the shikoku basin measured amorphous silica content in hemipelagic sediments suggests that the cementing process is active throughout the shikoku basin at sites separated by 500 km the cementation process may occur in other locations where sediment containing hydrated disseminated volcanic glass is buried sufficiently for heat to facilitate alteration i e central america cascadia and the gulf of alaska

the nature of porosity in organic rich mudstones of the upper jurassic kimmeridge clay formation north sea offshore united kingdom abstract analyses of organic rich mudstones from wells that penetrated the upper jurassic kimmeridge clay formation offshore united kingdom were performed to evaluate the nature of both organic and inorganic rock constituents and their relation to porosity in this world class source rock the formation is at varying levels of thermal maturity ranging from immature in the shallowest core samples to mature in the deepest core samples the intent of this study was to evaluate porosity as a function of both organic macerals and thermal maturity at least four distinct types of organic macerals were observed in petrographic and sem analyses and they all were present across the study area the macerals include in decreasing abundance 1 bituminite admixed with clays 2 elongate lamellar masses alginite or bituminite with small quartz feldspar and clay entrained within it 3 terrestrial vitrinite fusinite semifusinite grains and 4 tasmanites microfossils although pores in all maceral types were observed on ion milled surfaces of all samples the pores largely nanopores with some micropores vary as a function of maceral type importantly pores in the macerals do not vary systematically as a function of thermal maturity insofar as organic pores are of similar size and shape in both the immature and mature kimmeridge rocks if any organic pores developed during the generation of hydrocarbons they were apparently not preserved possibly because of the highly ductile nature of much of the rock constituents of kimmeridge mudstones clays and organic material inorganic pores largely micropores with some nanopores have been observed in all kimmeridge mudstones these pores particularly interparticle i e between clay platelets and intraparticle i e in framboidal pyrite in partially dissolved detrital k feldspar and in both detrital and authigenic dolomite are noteworthy because they compose much of the observable porosity in the shales in both immature and mature samples the absence of a systematic increase in organic porosity as a function of either maceral type or thermal maturity indicates that such porosity was probably unrelated to hydrocarbon generation instead much of the porosity within mudstones of the kimmeridge appears to be largely intraparticle and interparticle adjacent to inorganic constituents so the petroleum storage potential in these organic rich mudstones largely resides in inorganic pores

hydrothermal venting and basin evolution devonian south china constraints from rare earth element geochemistry of chert this paper presents rare earth element ree geochemistry of siliceous deposits from which hydrothermal activity and basin evolution are elucidated in the late devonian in the yangshuo basin south china where siliceous deposits widely occurred as nodular chert in the deep water limestones and bedded chert interbeded with tuffaceous chert in the early late devonian both nodular and bedded cherts are characterized by very low la abundances avg 2 07 and 2 49 ppm respectively intermediate negative ce anomalies ce ce avg 0 69 and 0 61 slight to intermediate positive eu anomalies eu eu avg 1 33 and 1 57 and low to intermediate shale normalized lan ybn values avg 0 86 and 0 52 and intermediate lan cen values avg 1 61 and 1 72 these suggest both nodular and bedded cherts formed in the open marine basin of south china rather than in the intracontinental rift basin as previously assumed with involvement both with seawaters as indicated by intermediate negative ce anomalies and generally lree depleted patterns and hydrothermal vent fluids as indicated by convex less lree depleted patterns with apparent positive eu anomalies in comparison with nodular and bedded chert the tuffaceous chert has the highest la abundances avg 17 11 ppm similar ranges of ce anomalies avg 0 63 and lan cen values avg 1 77 but lower lan ybn values avg 0 48 and no apparent positive eu anomalies avg 0 97 this suggests that the tuffaceous fallouts were also significantly modified by the hydrothermal fluid and seawater rapid spatial variations of eu eu values and degree of lree depletions in the studied basin are recognized characterizing a spatially differential hydothermal activity that is not well discriminated by major element features such a difference in hydrothermal activity is interpreted as having been related to the intensity and depth of syndepositional tectonic activity reconciling the structural pattern unraveled by stratigraphic packages d 2005 elsevier b v all rights reserved

the impact of rock composition on geomechanical properties of a shale formation middle and upper devonian horn river group shale northeast british columbia canada the geomechanical properties of a shale reservoir are essential both to the development of natural fractures and to the formation s response to hydraulic fracture stimulation we evaluate the rock mechanical properties in the middle and upper devonian horn river group shale including the evie and otter park members and the muskwa formation applying core hardness measurements and log derived young s modulus poisson s ratio and brittleness and relate these to shale composition and texture clay content is the most significant factor controlling the brittleness of shale rocks the effect of quartz content on rock mechanical properties depends on the type of quartz present in the rock authigenic quartz is positively correlated with brittleness but detrital quartz has little or no effect factor analysis indicates that carbonate increases brittleness while no obvious correlation between toc content and brittleness was observed depositional facies are related to geomechanical properties because each facies has a distinctive composition massive mudstone and pyritic mudstone are relatively brittle because of abundant authigenic quartz cement laminated mudstone and bioturbated mudstone are relatively ductile because most detrital carbonate and quartz grains are set in a matrix of clay minerals brittleness in the horn river group shale shows both geographic and stratigraphic variability increasing brittleness in the northwest part of the basin largely results from greater distance from the clastic sediment source the otter park member represents a period of major relative sea level fall and is relatively ductile because of its high clay content whereas the underlying evie member and the overlying muskwa formation are relatively brittle because of high carbonate and biogenic silica content respectively

quartz types in the upper pennsylvanian organic rich cline shale wolfcamp d midland basin texas implications for silica diagenesis porosity evolution and rock mechanical properties

regional depositional changes and their controls on carbon and sulfur cycling across the ordovician silurian boundary northwestern guizhou south china abstract the controls of regional depositional environment on stable isotope records spanning the ordovician silurian boundary on the yangtze platform have seldom been investigated the objectives of this study include reconstruction of regional depositional settings and assessment of how sedimentary processes may have influenced carbon and sulfur isotopic fractionation seven shale facies have been recognized in the wufeng longmaxi interval from two locations completely bioturbated claystone of the basal wufeng formation accumulated on a shallow oxygenated muddy shelf overlying faintly banded black siliceous shale suggests deposition under deep anoxic conditions interrupted by episodes of dysoxia muddy fossiliferous facies of the guanyinqiao formation reflects a glacial sea level lowstand setting and the observed proximal to distal heterogeneity of facies matrix supports shallowing in the proximal area overlying faintly banded black shale of the longmaxi formation tells of a post glacial transgression the carbonaceous deposits are overlain by banded gray and dark gray muddy siltstones and suggest a shoaling upward trend the shallow water facies display relatively heavier 13 c org values whereas deep water facies are characterized by lower 13 c org values discrepancies between hirnantian positive 13 c org excursions in proximal and distal areas probably reflect spatial gradient in seawater 13 c dic induced by glacioeustasy deposits accumulated under oxic and physically dynamic conditions display strong positive 34 s sulfide excursions perhaps a consequence of diagenetic sulfate reduction occurred at some depth below the sediment water interface and removed from the sulfate pool of overlying water column negative relationship between 34 s sulfide and toc indicates that redox conditions and physical reworking of sediment at the sediment water interface controlled the rate of microbial sulfate reduction and sulfur isotope fractionation overall co variation of lithofacies and isotopic records suggests that local heterogeneity of seawater chemistry and sedimentary dynamics may exert partial controls on biogeochemical processes and amplify the magnitude of the hirnantian isotopic excursions in the proximal area

expanding the size of multi parameter metasomatic footprints in gold exploration utilization of mafic dykes in the canadian malartic district quebec canada ore forming hydrothermal fluids react differently with different country rocks but few studies have applied this knowledge with the specific goal of expanding the size of hydrothermal footprints in mineral exploration to develop this concept 122 metamorphosed mafic dykes from the world class canadian malartic gold district 18 6 moz au were sampled and analyzed for mineralogy physical properties and lithogeochemistry partial and total digestion the mafic dykes intrude mainly metasedimentary rocks post date d1 deformation and cross cut early d2 quartz monzodiorite intrusions but they were deformed and altered during d2 deformation mineralization and metamorphism they can be subdivided into three groups group 1 dykes are least altered characterized by amphibole rich regional metamorphic assemblages and distributed throughout the pontiac subprovince group 2 and 3 dykes underwent ore related hydrothermal biotite calcite pyrite alteration and are associated with density and volume adjusted concentration gains of over 100 in au w te c s ag cs mo cu k rb se u pb ba f bi sn they define a metasomatic footprint up to 6 km away from the deposit toward the se and up to 2 km away from the deposit toward the sw fifty eight variables that define halos around the canadian malartic deposit have been identified and integrated using principal component analysis pc1 explains 30 of the variance separates least mobile elements from ore related elements and is interpreted to reflect the ore forming alteration process pc2 and pc3 represent igneous processes pc4 highlights the calcite pyrite and biotite alteration spatial variations of the modal abundances of amphibole biotite calcite and pyrite are the simplest expression of the metasomatic footprint and they can easily be documented during exploration at the camp scale

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

mechanical properties of organic matter in shales mapped at the nanometer scale abstract the mechanical properties of organic matter strongly affect the way shales deform and fracture however the way organic matter responds to mechanical stresses is poorly understood representing a critical obstacle to assessing oil and gas production in shale formations little is known about the mechanical properties of organic matter in fine grained rocks primarily because it often occupies tiny nanometer scale voids between the mineral grains which cannot be accessed using standard mechanical testing techniques here we use a new atomic force microscopy technique peakforce qnm to map the mechanical properties of organic and inorganic components at the nanometer scale we find that the method is able to distinguish between different phases such as pyrite quartz clays and organic matter moreover within the organic component young s modulus values ranged from 0 to 25 gpa in 3 different samples all of which come from thermally mature type ii iii source rocks in the dry gas window a modal value of 15 16 gpa was measured with additional peaks measured at 10 gpa in addition the maps suggest that some porous organic macerals possess a soft core surrounded by a harder outer shell 50 100 nm thick thus our results demonstrate that the method represents a powerful new petrographic tool with which to characterize the mechanical properties of organic rich sedimentary rocks

diagenetic origin of quartz silt in mudstones and implications for silica cycling mudstone the most abundant sedimentary rock type1 composed primarily of clay or silt sized particles contains most of the quartz found in sedimentary rocks2 these quartz grains which are chemically and mechanically resistant and therefore preserve their characteristics well have long been considered to be derived from the continental crust1 here we analyse quartz silt from black shales in the eastern usa dating back to the late devonian period about 370 million years ago using backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe our results indicate that up to 100 of the quartz silt in our samples does not originate from the continental crust instead it appears to have precipitated early in diagenesis in algal cysts and other pore spaces3 with silica derived from the dissolution of opaline skeletons of planktonic organisms such as radiolaria and diatoms transformation of early diatoms into in situ quartz silt might explain the time gap between the earliest fossil occurrences of diatoms about 120 myr ago4 and molecular evidence for a much earlier appearance between 266 or even 500 myr ago5 6 moreover if many other mudstone successions show similarly high proportions of in situ precipitated rather than detrital quartz silt the sedimentary record in mudstones may have been misinterpreted in the past with consequences for our estimates of palaeoproductivity as well as our perceptions of the dynamics and magnitude of global biogeochemical cycling of silica

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

sedimentological and geochemical characterization of the upper permian transitional facies of the longtan formation northern guizhou province southwest china insights into paleo environmental conditions and organic matter accumulation mechanisms abstract characterized by high toc content and large cumulative thickness the upper permian marine continental transitional facies of shales are widely distributed in southwest china and are currently becoming a prospective area for shale gas exploration and production compared to marine shales the organic matter om accumulation model and paleo environmental conditions remain unclear in transitional settings in this study core descriptions thin section and scanning electron microscopy sem observations x ray diffraction xrd mineralogical analysis and a major trace and rare earth element analysis were integrated to document the varying lithofacies paleo environmental conditions and om accumulation mechanisms for the upper permian transitional facies of the longtan formation in northern guizhou province southwest china six major lithofacies including carbonaceous mudstones siliceous clay mixed mudstones argillaceous mudstones silty shales muddy siltstones and calcareous clay mixed shales were identified the xrd analysis and sem images suggest that clay average 51 2 wt and siderite average 17 3 wt are the dominant minerals in the longtan formation which is different from the mineralogical composition of typical marine shales which are generally dominated by quartz e g horn river shale in the western canada sedimentary basin and the barnett shale in the fort worth basin furthermore the sedimentological and geochemical analyses suggest that the paleo environmental conditions and om accumulation mechanisms of the transitional facies of the longtan formation are different from those of marine shales and can be summarized as follows 1 terrestrial plant fragments mainly contribute to the toc contents of the longtan formation 2 paleoproductivity is generally the major influencing factor of om accumulation in marine shales but is relatively low during the deposition of the longtan formation 3 terrestrial om input redox conditions and sedimentation rate are the major factors controlling om accumulation and 4 most of the silica content has detrital origin instead of biogenic origin in the longtan formation

facies patterns and geography of the yangtze region south china through the ordovician and silurian transition abstract lithofacies and biofacies changes through the ordovician and silurian transition on the yangtze platform are coincident with stepwise mass extinctions recovery events global sea level changes and regional palaeogeographic configurations facies patterns through three intervals the late mid ashgill hirnantian and early rhuddanian indicate that black shale occupied most of the yangtze platform region during the late mid ashgill and early rhuddanian while the hirnantian possesses more diverse facies types the black shale was replaced by carbonate facies during the hirnantian coincident with a global sea level low stand biofacies changes from the late mid ashgill graptolitic to the hirnantian shelly facies were apparently signalled by gradual and diachronous existence of a mixed facies the manosia facies in the yangtze region however the biofacies change was abrupt from the hirnantian to the early rhuddanian when graptolitic facies occupied most areas on the yangtze platform leaving only a very narrow limited belt of shelly facies along the southern margin of the platform in northern guizhou the early rhuddanian unified biofacies pattern is a result of a global sea level rise which may be synchronized with a recovery bioevent of graptolites after hirnantian mass extinction

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

spatial variation of carbon isotopic compositions of carbonate and organic matter from the late ordovician sedimentary succession in the yangtze platform south china implications for sea level eustacy and shoaling of marine chemocline abstract spatial correlation of isotopic chemostratigraphy across ancient epeiric basins is of particular interest in the field of geology this study examines the carbon isotopic compositions of carbonate and organic matter from the late ordovician sedimentary succession in the yangtze platform including the linxiang lx formation deposited in the bottom and the tiezufeike tzfk daduhe ddh wufeng wf formations in the top paired 13ccarb and 13corg analyses of the upper ordovician strata on the yangtze platform were recorded and the results show that the rocks in the lx formation have high 13ccarb and 13corg values relative to those in the ddf tzfk wf formations additionally a variation of 2 was found between shallow and deep water settings during the late ordovician heavier 13ccarb and 13corg values are observed at the wukemuchang wkmc and wanhe wh sections representing the shallow regions of the yangtze platform relative to the tianjiawan tjw and tianba tb sections representing the deeper margin of the yangtze platform we suggest that the variations of 13c in carbonate and organic matter are related to the sea level eustacy and shoaling of marine chemocline 1 sea level rise driven decrease in local scale carbonate weathering 2 decreased decomposition of organic matter under anoxic conditions and 3 incorporation of non photosynthetic chemoautorophic bacteria living in deeper waters the 13c 13c 13ccarb 13corg values in both the wh and wkmc sections display an increasing trend upward from the lx formation to the overlying strata varying from 27 8 to 31 2 and from 28 1 to 31 1 respectively these increased 13c values are related to the enhanced nutrients and correspondingly high primary productivity and thus that the anoxic water conditions and high primary productivity may be the significant factors in the deposition of late ordovician black shales

cathodoluminescent textures and the origin of quartz silt in oligocene mudrocks south texas abstract in subsurface mudrocks of the oligocene frio formation in south texas a substantial proportion of silt size quartz 10 62 m manifests cathodoluminescence cl that varies greatly in intensity within each particle giving rise to textures that differ greatly from grain to grain in contrast most quartz grains of sand size 62 m have cl that is relatively homogeneous within individual grains a substantial percentage of the quartz within silt grains is very weakly luminescent no depth trend in the occurrence of luminescent textures in detrital quartz is observed suggesting that the component of dark possibly low temperature silt size quartz is not related to chemical processes in the present burial setting paleogene rhyolites of west texas are a partial model for the source rocks that supplied sediment to the frio formation phenocrystic quartz in these volcanics has uniform cl similar to that observed in the frio sand fraction whereas complex cl structure seen in the associated groundmass bears many similarities to the cl textures observed in frio silts this observation further supports the idea that cl structure of detrital quartz in the frio is most likely an inherited feature if the quartz with dark cl is of low temperature origin it would help to elucidate the relatively 18o enriched isotopic values reported for mudrock quartz in the frio

metamorphism and gold mineralization in the blue ridge southernmost appalachians lode gold mineralization in the blue ridge of the southernmost appalachians is hosted by metavolcanic rocks e g anna howe mine al royal vindicator mine ga metaplutonic rocks e g hog mountain mine al and metasedimentary rocks e g lowe tallapoosa and jones vein mines al most gold occurs in synkinematic quartz or plagioclase or pyrite or pyrrhotite or chlorite veins localized along polydeformational faults that juxtapose rocks with significantly different peak metamorphic mineral assemblages mineralogy chemistry and o and h isotope studies suggest that the three types of host rocks have undergone differing amounts and types of alteration during mineralization limited wall rock alteration in metavolcanic and metasediment hosted deposits and relatively extensive wall rock alteration in granitoid hosted deposits suggests that most deposits formed from fluids that were close to equilibrium with metavolcanic and metasedimentary rocks stable isotope compositions of the fluids calculated from vein minerals and vein selvages are consistent with a predominantly metasedimentary fluid source but vary from deposit to deposit 22 to 47ppm delta d 4 5ppm delta 18 o and 5 7ppm delta 34 s at anna howe and royal vindicator 48 to 50ppm delta d 9 13ppm delta 18 o and ca 19ppm delta 34 s at lowe and jones vein and 22 to 23ppm delta d 8 11ppm delta 18 o 9 10ppm delta 34 s and 6 delta 13 c at hog mountain silicate mineral thermobarometry of vein vein selvage and wall rock mineral assemblages indicate that mineralization and regional metamorphism occured at greenschist to amphibolite facies 480 degrees or 75 degrees c at anna howe 535 degrees or 50 degrees c at 6 4 or 1 kbars at lowe 530 degrees or 50 degrees c at 6 9 or 1 kbars at tallapoosa and 460 degrees or 50 degrees c at 5 5 or 1 kbars at hog mountain oxygen isotope fractionation between vein minerals and selvage minerals consistently records equilibration temperatures that are similar to or slightly lower than those estimated from silicate thermometry auriferous veins contain numerous fluid inclusions that were emplaced in several stages and can be subdivided into five compositional types based on salt and co 2 concentrations fluid inclusion isochores for early formed inclusions from these veins intercept the pressure and temperature conditions estimated from silicate mineral thermobarometry and stable isotope thermometry and are compatible with entrapment at those conditions these fluids exhibit significant variation in salinity x sub nacl equiv 0 0 0 2 and co 2 x sub co 2 0 0 0 2 suggesting variation in fluid wall rock interaction that accompanied gold deposition during declining temperatures less abundant and later fluids within the veins are dominantly co 2 the association of gold mineralization with structurally controlled concordant and discordant quartz sulfide veins and the temperatures and pressures of wall rock alteration and regional metamorphism indicate that the present distribution of gold is a result of metamorphism during progressive d 2 d 3 deformation isotopic data for alteration envelopes date this event as alleghanian 279 or 14 ma k ar whole rock and 343 or 18 ma k ar biotite at lowe and 315 or 18 ma rb sr whole rock isochron 87 sr 86 sr i 0 7061 or 0 0008 and 294 or 16 ma k ar whole rock at hog mountain available data are compatible with development of the lodes during early alleghanian overthrusting of allochthons over sedimentary rocks of the autochthonous north american margin the implication is that the fluids were derived from metasedimentary and or metavolcanic formations in the lower parts of the crystalline thrust stack or possibly from underlying autochthonous sedimentary formations ascended along permeable fault zones and were emplaced as veins into dilatent areas in and adjacent to the fault zones

provenance interpretation of quartz by scanning electron microscope cathodoluminescence fabric analysis we used a cathodoluminescence cl detector attached to a scanning electron microscope sem to study patterns of variable intensity cl in quartz grains from a variety of igneous metamorphic sedimentary and shock deformed meteorite impact rocks distinctive fabrics in quartz grains revealed by sem imaged differential cl include zoning healed fractures complex shears planar features shocked quartz dark cl streaks and patches indistinct mottled texture and nondifferential low contrast cl zoning is common in volcanic quartz and some plutonic quartz zoned plutonic quartz is distinguished from volcanic quartz by the presence of closed fractures and dark cl streaks and patches metamorphic quartz displays either an indistinct mottled texture or nearly uniform nondifferential cl quartz from rocks severely deformed by tectonism displays a complex pattern of multiple small scale shears quartz from meteorite impact sites and some system boundaries is characterized by intricate patterns of planar features presumably created by shock metamorphism thus the sem cl fabric analysis technique provides a rapid method for distinguishing quartz from a variety of source rocks

quartz types and origins in the paleozoic wufeng longmaxi formations eastern sichuan basin china implications for porosity preservation in shale reservoirs abstract quartz in shales has been demonstrated to exert a significant effect on shale gas production by influencing rock mechanical behavior and reservoir porosity however quartz types and origins in shales are complicated and challenging to study due to their fine grained nature in this study we propose combining thin section images scanning electron microscopy sem images energy dispersive spectroscopy eds maps cathodoluminescence cl images and geochemical data to investigate quartz types and origins in shale formations shale samples from the ordovician wufeng silurian longmaxi formations eastern sichuan basin china were used to study quartz types origins and the effect of quartz cementation on porosity development samples from the wufeng longmaxi formations have toc contents in the range of 0 5 4 7 wt averaging 2 7 wt and are currently in the thermally overmature stage five types of quartz including silt size detrital quartz siliceous skeletal fragments quartz overgrowth clay matrix dispersed microquartz and aggregates of euhedral quartz were identified the ternary diagram of fe al mn the cross plot of sio2 versus zr and the cross plot of si versus al suggest that the dissolution and reprecipitation of siliceous skeletons may provide the major source of silica for quartz cementation in the lower part of the wufeng longmaxi formations and released silica as a result of smectite to illite transformation is also important for authigenic quartz formation in the upper part of the wufeng longmaxi formations our sem images suggest that the rigid framework formed by quartz cementation not only prevents primary interparticle pores from compaction but also favors the generation of organic matter associated pores

provenance analysis by single quartz grain sem cl optical microscopy abstract the integration of panchromatic scanning electron microscopy cathodoluminescence sem cl with optical microscopy analysis on single quartz grains is a new technique to interpret provenance of quartz rich sediments the combination of information gained from sem cl on textural features and cl response with information from optical microscopy allows distinction of different quartz types much more easily then with conventional microscopy or color cl analysis features visible by sem cl include zoning microcracks deformation fractures and lamellae diagenetic crushing recrystallization and strength and texture of cl response features visible by optical microscopy include embayments open fractures extinction behavior and mono poly and microcrystallinity the key is to integrate cl and optical properties of the same quartz grains in order to reduce ambiguities inherent in both techniques used on their own our technique is well suited for distinguishing between plutonic volcanic and metamorphic quartz in coarse to medium grained sand or sandstone this simple and inexpensive approach can easily be combined with other provenance techniques in this paper we outline the combined sem cl optical microscopy technique and demonstrate its application with examples from the south island of new zealand

controlling factors on the formation and distribution of sweet spot areas of marine gas shales in south china and a preliminary discussion on unconventional petroleum sedimentology abstract shale gas resources in china are abundant with the marine shales accounting for the largest proportion i e 13 1012 m3 the wufeng longmaxi shale system deposited across the late ordovician and early silurian transition in south china is currently the target for shale gas exploration and development in china its annual output in 2018 reached 10 8 109 m3 making china the largest shale gas production region outside north america within this shale system the sweet spot intervals of shale gas formed vertically and sweet spot areas of shale gas formed regionally the sweet spot intervals occur mainly at the bottom of the wufeng longmaxi shale and are 10 40 m in thickness the sweet spot interval is characterized by high total organic carbon toc and gas contents relatively high porosity high brittle mineral content and abundant lamination fissures and fractures the formation of shale gas sweet spot intervals is mainly controlled by four factors in south china they are anoxic shelf environment abundant nano pores in organic matter sealed roof and floor strata and abundant lamination and high silica content in shale respectively as the regional extension of the sweet spot intervals the formation of the sweet spot area requires all the controlling factors for the sweet spot interval it was born in regional anoxic shelf with stable tectonics and preserved in relatively stable tectonic zones three sweet spot areas are identified for the wufeng longmaxi shale in south china i e fuling weiyuan fushun yongchuan and changning zhaotong areas the total area is about 2 104 km2 with technically recoverable resources of 3 3 1012 m3 in addition with the rapid progresses of exploration and development of unconventional petroleum resources such as shale gas the petroleum industry around the world extends to unconventional petroleum resources gradually accomplishing an important change of petroleum geology research focus from conventional to unconventional unconventional petroleum geology research focuses on continuously or semi continuously distributed sweet spot areas for which the formation would be the result of coupling sedimentology from several geological events such as global or regional tectonic activity volcanic eruption climate change anoxic water biotic mass extinction and radiation and gravity current it is necessary to innovatively construct new insights of unconventional petroleum sedimentology in order to enrich and improve the petroleum sedimentology research and its application therefore the concept of unconventional petroleum sedimentology is proposed and its research task method aim and importance are preliminarily discussed

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

variability of rock mechanical properties in the sequence stratigraphic context of the upper devonian new albany shale illinois basin abstract rock mechanical properties of tight shale reservoirs are important parameters in the exploration and development of unconventional shale oil and gas understanding the stratigraphic variability of rock mechanical properties in black shale successions is important for identifying promising intervals for hydraulic stimulation high resolution hardness tests 6 cm spacing with an equotip bambino 2 hardness tester were conducted on a new albany shale core to study the stratigraphic variability of rock mechanical properties combined with high resolution geochemical analyses 8 cm spacing acquired with a portable x ray fluorescence spectrometer it is possible to relate hardness variability to shale composition the results of our study suggest an average quartz content of about 28 for the entire succession approximately half of that amount 13 is interpreted to be of biogenic origin biogenic quartz mainly derived from dissolution of radiolaria occurs as authigenic quartz precipitated in tasmanites cysts and as microcrystalline quartz precipitated in the shale matrix petrographic observations indicate that the hardness of the new albany shale is critically controlled by biogenic quartz content not by total quartz content as suggested in multiple prior studies biogenic quartz forms an interconnected stiff framework which increases the hardness of shales in contrast dispersed hard grains e g detrital quartz feldspar and dolomite do not contribute to brittle behavior when examined under a scanning electron microscope hard shales are rich in biogenic quartz and contrast visibly with soft shales that are characterized by high contents of clay minerals negative correlation between hardness and al2o3 content as well as differential compaction of clay minerals around hard grains indicate that clay minerals are an important ductile component in the new albany shale although the general softness of kerogen suggests that there should be an influence of organic matter on hardness this effect is counteracted by biogenic quartz cementation which has a comparable stratigraphic distribution pattern we propose a new mineral composition based brittleness index on the basis of biogenic quartz content to characterize the brittleness of tight shale reservoirs within a sequence stratigraphic context the hardness of the new albany shale increases in transgressive systems tracts reaches a maximum at maximum flooding surfaces and decreases in highstand systems tracts with the exception of the blocher member maximum flooding surface intervals have the highest potential to develop brittle fractures and should be potential targets for hydraulic stimulation

quartz types authigenic and detrital in the upper cretaceous eagle ford formation south texas usa abstract lithologic heterogeneity of the eagle ford formation in south texas arises from mixing of extrabasinal grains of siliciclastic composition with intrabasinal grain assemblages composed dominantly of marine carbonate with a lesser component of biosiliceous debris detrital quartz in particular is derived from both extrabasinal and intrabasinal sources posing a challenge for the use of bulk compositional data for mudrock classification extrabasinal detrital quartz supplied along a major axis of siliciclastic influx the woodbine depositional system of east texas is reduced to a minor part of the grain assemblage in south texas petrographic evidence and point count results indicate that around 85 percent of total quartz in these rocks equal to about 12 6 volume percent is authigenic thus significant quantities of authigenic silica are not restricted to siliceous mudrocks but can be found in carbonate rich mudrocks as well formerly opaline skeletons of radiolaria the dominant source of silica for authigenic quartz precipitation are only poorly preserved by replacements including calcite dolomite pyrite and quartz dissolved silica released by dissolution of radiolarians and perhaps also by volcanic glass dissolution is re precipitated in a variety of forms including matrix dispersed microquartz cement fillings within primary intragranular pores and grain replacement of both calcareous and siliceous allochems the mass balance of dissolved silica mobilized from radiolarians and other reactive silicates and the precipitation of authigenic quartz is uncertain because the initial volumes of now dissolved detrital material versus the final volume of authigenic material quartz and other authigenic silicates cannot be determined with accuracy

late kinematic timing of orogenic gold deposits and significance for computer based exploration techniques with emphasis on the yilgarn block western australia abstract orogenic gold deposits are a widespread coherent group of epigenetic ore deposits that are sited in accretionary or collisional orogens they formed over a large crustal depth range from deep seated low salinity h2o co2 ch4 n2 ore fluids and with au transported as thio complexes regional structures provide the main control on deposit distribution in many terranes first order faults or shear zones appear to have controlled regional fluid flow with greatest ore fluid fluxes in and adjacent to lower order faults shear zones and or large folds highly competent and or chemically reactive rocks are the most common hosts to the larger deposits focusing of supralithostatic ore fluids into dilatant zones appears to occur late during the evolutionary history of the host terranes normally within d3 or d4 in a d1 d4 deformation sequence reactivation of suitably oriented pre existing structures during a change in far field stress orientation is a factor common to many deposits and repeated reactivation may account for multiple mineralization episodes in some larger deposits absolute robust ages of mineralization support their late kinematic timing and in general suggest that deposits formed diachronously towards the end of the 100 to 200 m y long evolutionary history of hosting orogens for example in the yilgarn block a region specifically emphasised in this study orogenic gold deposits formed in the time interval between 40 and 90 m y with most about 60 to 70 m y after the youngest widespread basic ultrabasic volcanism and towards the end of felsic magmatism the late timing of orogenic gold deposits is pivotal to geologically based exploration methodologies this is because the present structural geometries of i the deposits ii the hosting goldfields and iii the enclosing terranes are all essentially similar to those during gold mineralization at least in their relative position to each other thus interpretation of geological maps and cross sections and three dimensional models can be used to accurately simulate the physical conditions that existed at the time of ore deposition it is particularly significant that the deposits are commonly related to repetitive and predictable geometries such as structural heterogeneities within or adjacent to first order structures around rigid granitoid bodies or in specific locked up fold thrust structures importantly the two giant greenstone hosted goldfields kalgoorlie and timmins show a remarkably similar geometry at the regional scale computer based stress mapping and gis based prospectivity mapping are two computer based quantitative methodologies that can utilize and take advantage of the late timing aspect of this deposit type to provide important geological aids in exploration both in broad regions and more localized goldfields both require an accurate and consistent solid geology map stress mapping requires knowledge of the far field stresses during mineralization and the empirical prospectivity mapping requires data from a significant number of known deposits in the terrane the kalgoorlie terrane in the yilgarn block meets these criteria and illustrates the potential of these methodologies in the exploration for orogenic gold deposits low minimum stress anomalies interpreted to represent dilational zones during gold related deformation coincide well with the positions of known goldfields rather than individual gold deposits in the terrane and there are additional as yet unexplained anomalies the prospectivity analysis confirms that predictable and repetitive factors controlling the siting of deposits are i proximity to and orientation and curvature of granitoid greenstone contacts ii proximity to segments of crustal faults which strike in a preferred direction iii proximity to specific lithological contacts which have similar preferred strike iv proximity to anticlinal structures and v the presence of preferred reactive host rocks e g dolerite the prospectivity map defines a series of anomalous areas which broadly conform to those of the stress map 78 correspondence the most prospective category on this map covers less than 0 3 of the greenstone belts and yet hosts 16 of the known deposits which have produced 80 of known gold thus it discriminates in favour of the larger economically more attractive deposits in the terrane the successful application of stress mapping and prospectivity mapping to geology based exploration for orogenic gold deposits indicates that more quantitative analysis of geological map data is a profitable line of research the computer based nature of these methodologies is ideal for the production of an ultimate integrated deposit target map which can be compared to other more conventional targeting parameters such as geophysical and geochemical anomalies such an integrated strategy appears the way forward in the increasingly difficult task of cost effective global exploration for orogenic gold deposits in poorly exposed terranes

origin properties and implications of solid bitumen in source rock reservoirs a review abstract this paper reviews the significance of solid bitumen with emphasis on source rock reservoirs we discuss difficulties and discrepancies with terminology especially those terms related to the origin of solid bitumen and its physical and chemical properties various definitions of solid bitumen have their own justifications and can be used provided there is clarity about which defining criteria are being considered difficulties in conforming to chemical solubility or origin related definitions lead us to suggest adapting the reflectance of solid hydrocarbon as a practical choice for placing the boundary between solid bitumen and pyrobitumen and 1 50 is proposed as the boundary value it has to be noted that this boundary may be shifted down to 1 3 for sulfur rich kerogen recently much progress has been made by combining imaging and physical adsorption techniques in porosity studies and so the porosity of solid bitumen is given special emphasis comparing pore characteristics obtained from sem versus those generated by gas adsorption mercury intrusion or neutron scattering techniques indicates that the sem pore inventory fails to account for the smallest pores we review the implications of the abundance of solid bitumen on reservoir quality porosity permeability and producibility based on examples of selected sequences one of the difficulties in predicting the influence of solid bitumen bearing horizons on reservoir quality arises from the problems with detecting organic phases using various logging techniques the use of specialized techniques such as nmr logging that allows two dimensional t1 and t2 measurements should be expanded and other potential techniques need to be further researched and tested certain aspects of the properties of solid bitumen that are not as well understood such as its hydrocarbon generation potential or its role in hydrocarbon migration are also discussed with the aim of identifying further research that could lead to a better understanding of the role that solid bitumen plays in unconventional reservoirs

silica activity and the smectite illite reaction early silicate diagenesis is characterized by the precipitation of minerals with high silica activity such as opaline silica smectite and clinoptilolite and by pore water silica activities exceeding quartz saturation with burial this early high silica activity diagenesic facies is succeeded by a low silica activity facies distinguished by quartz precipitation and progressive development of illite as the nonexpandable component of mixed layer clays we suggest that the smectite illite reaction occurs as a consequence of the reduction of silica activity at the onset of quartz precipitation data from oceanic and sedimentary basins confirm that the smectite illite reaction does not control aqueous silica activities where the smectite illite reaction occurs at higher temperatures aqueous silica activities likewise reach quartz saturation at higher temperatures

frequency dependence of susceptibility in magnets with uniaxial and triaxial anisotropy characterization of minerals in rocks and soils provides a window into environmental processes and improves the interpretation of paleomagnetic measurements mineral composition size and shape can be constrained using magnetic measurements for small minerals a promising measurement is the frequency dependence of magnetic susceptibility the size and shape dependence of the in phase component and out of phase component are derived for arbitrarily oriented superparamagnetic and single domain magnets with uniaxial and triaxial anisotropy in a fluctuating field a single magnet has a thermal response parallel to the easy axis and instantaneous rotation of the moment perpendicular to it the size and temperature variations have the same form as in earlier theories in which all the magnets are aligned with the field and can be easily adapted to the methods of shcherbakov and fabian 2005 and egli 2009 for finding size distributions using multiple temperatures and frequencies these inversions are inherently non unique and complicated by non sd contributions but some robust constraints can be put on the volume distribution if the commonly used ratio fd is 10 or greater the anisotropy of the out of phase component opams has the same sense as thermoremanent magnetization trm and can be used to correct the paleofield direction along with the anisotropy of the in phase component ipams it can be used to gain quantitative information on the deformation of the host rock for the line plane or march deformation model opams and ipams are calculated and it is shown how they can be used to accurately represent the strain anisotropy