depositional facies of a mud shoreface in suriname south america a mud analogue to sandy shallow marine deposits abstract immense volumes of argillaceous muds are being deposited along the world s longest continuous mud coastline which faces the open equatorial atlantic not only are these muds deposited in an environment normally associated with sand deposits but just as in sandstones sedimentary structures within these muds record the dynamic processes that deposited them this study investigates a 100 km long portion of the suriname coast utilizing cores bathymetric surveys and field observations from nearshore and innershelf environments using terminology borrowed from sand coastlines the innershelf nearshore of suriname is divided into transition zone shoreface foreshore and backshore the transition zone consists of a mix of offshore sands and shoreface muds shoreface and foreshore are subdivided into bank and interbank zones these zones are transitory because mud banks which make up the bank zones migrate westwardly mud banks are up to 5 m high 50 to 60 km long 10 to 20 km wide and oriented at oblique angles to the coastline these banks generally consist of fluid muds which are so fluid that they interact with surface waves causing them to be altered and damped banks are attached to the shoreline and commonly produce progradation of the coastline substrate within the interbank zone is more consolidat d than within the mud banks because of lack of wave dampening wave energies are relatively high within the interbank zone producing erosion of the shoreface and shoreline sand beaches are generally formed within the erosional interbank shoreline the vertical sedimentary sequence within the shoreface muds is a record of bank migration and other sedimentary processes present wave and current energies are recorded by scour and fill features discontinuity features micro cross laminations lenticular laminations and parallel to subparallel laminations laminations appear to be created by boundary layer shearing within fluid muds which are above wave base and made mobile by wave generated shore parallel currents large scale evidence for migration of the mud banks is westward dipping acoustical reflectors within the banks these reflectors which are over a kilometer apart mark the boundaries of annual migration events biogenic structures are generally absent within the fluid bank muds but are present within the more consolid ted interbank zone and associated with discontinuity features which are buried interbank surfaces migration and vertical stacking of mud banks are recorded by vertical sequences of massive and laminated muds which were deposited by mud banks and discontinuity features which were formed by interbank zones the coastal deposits of suriname are a mud analogue to nearshore and innershelf sand deposits transition zones of both mud and sand systems reflect a transition from offshore to shoreface processes and sediments both mud and sand shoreface foreshore systems reflect sediment input and wave current and tidal processes that act on them mud banks of suriname resemble linear sand ridges on the continental shelf of the eastern u s a in shape oblique orientation to the coastline and orientation with respect to dominant direction of transport processes the sequence of massive and laminated muds with discontinuity features resembles laminated to burrowed sequences found in ancient and recent nearshore and shallow marine sands

specific surface area and pore size distribution in clays and shales one of the biggest challenges in estimating the elastic transport and storage properties of shales has been a lack of understanding of their complete pore structure the shale matrix is predominantly composed of micropores pores less than 2 nm diameter and mesopores pores with 2 50 nm diameter these small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore size distribution is critical to understand the shale pore network historically mercury intrusion techniques are used for pore size analysis of conventional reservoirs however for unconventional shale reservoirs very high pressures 414 mpa 60 000 psi would be required for mercury to access the full pore structure which has potential pitfalls current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales nitrogen gas adsorption techniques can be used to characterize materials dominated by micro and mesopores 2 50 nm a limitation of this technique is that it fails to measure large pores diameter 200 nm we use a nitrogen gas adsorption technique to study the micro and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques our results on pure clay minerals and natural shales show that i they have a multiscale pore structure at different dimensions ii fine mesopores with a characteristic 3 nm pore size obtained with n2 gas adsorption are associated with an illite smectite group of clays but not with kaolinite iii compaction results in a decrease of pore volume and a reduction of pore size in the inter aggregate macropores of the illitesmectite clays while the fine intra tachoid mesopores are shielded from compaction iv for natural shales mineralogy controls the pore size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite smectite type of clays in the rock our assessment of incompressible 3 nm sized pores associated with illite smectite clays provides an important building block for their mineral modulus

high resolution facies analyses of mudstones implications for paleoenvironmental and sequence stratigraphic interpretations of offshore ancient mud dominated successions abstract the extent of lithofacies variability in fine grained sedimentary rocks is very poorly known in comparison to that present in coarser grained clastic and carbonate successions the absence of this information means that sediments present on continental shelves are rarely considered as integrated systems because fine grained facies such as shales are mostly excluded from sophisticated regional facies models to shed light upon lithofacies and grain size in shale dominated successions so that they can be incorporated into shelf wide depositional models the blackhawk formation of the mancos shale campanian age exposed in the book cliffs utah was investigated using combined field whole rock geochemical optical and electron optical methods these sediments show systematic grain size variations are intensely bioturbated and composed predominantly of detrital clays mainly dioctahedral micas quartz and feldspar with minor pyrite and organic matter they are organized into very thin 10 mm upward fining genetic beds they exhibit both systematic lateral 103 m scale and vertical 10 2 to 100 m scales lithofacies variability preferentially cemented units occur close to sequence boundaries unconformities these cemented units typically contain a very different detrital assemblage including significant quantities of chlorite from the rest of the succession and are located close to levels where there are marked stacking pattern discontinuities overall lithofacies variability is interpreted in terms of deposition occurring on an oxic continental shelf with the coarser grained facies being deposited in proximal settings offshore transition zone in contrast to the finer grained units that were deposited in more distal environments offshore zone storms are interpreted to have been the dominant mechanism dispersing the sediment once deposited the surface layers of the sediment were intensely reworked by burrowing organisms preferential preservation of ichnogenera from mid and lower tiers suggest that the depositional environment was energetic and erosion commonly removed the surface sediment layers prior to deposition of thin 10 2 m storm beds the larger scale 100 m upward coarsening units that are composed of stacked beds are interpreted to be parasequences preferential cementation at levels where large scale stacking patterns change is interpreted to occur at horizons where there were breaks in sediment accumulation and bacterial metabolic processes were able to supply sufficient solutes to fill uncompacted pore space with cement the presence of a very different detrital assemblage in these units suggests that winnowing occurred despite their relatively innocuous appearance in the field these surfaces are likely to be significant bypass surfaces over which sediment was delivered to the deeper parts of the basin during times of relative lowstand of sea level

formation of nanoporous pyrobitumen residues during maturation of the barnett shale fort worth basin abstract hydrocarbon generation reactions occur within organic rich shales as a response to thermal maturation here we report observations on samples from the organic rich mississippian barnett shale gas system fort worth basin texas usa at varying stages of thermal maturation a multiscale characterization was achieved using a combination of compositional organic geochemistry and spectromicroscopy techniques including synchrotron based scanning transmission x ray microscopy stxm and transmission electron microscopy tem we document the chemical evolution of the macromolecular structure of barnett shale kerogen with increasing maturity from an immature kerogen containing a significant aliphatic component and an important concentration of oxygen and sulfur containing functional groups to an overmature kerogen dominated by poorly condensed aromatic structures in addition to the presence of bitumen in samples of oil window maturity very likely genetically derived from thermally degraded kerogen the formation of nanoporous pyrobitumen has been inferred for samples of gas window maturity likely resulting from the formation of gaseous hydrocarbons by secondary cracking of bitumen compounds

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

pore types and pore size distributions across thermal maturity eagle ford formation southern texas pore types pore size and pore abundance vary systematically across thermal maturity in the eagle ford formation maverick basin southern texas scanning electron imaging of 20 samples from four wells is used to assess the complex response of pores to chemical and mechanical processes entailing both destruction of primary porosity and generation of secondary pores primary mineral associated pores are destroyed by compaction cementation and infill of secondary organic matter whereas secondary pores are generated within organic matter om destruction of primary pores during early burial to 0 5 occurs by compaction of ductile detrital om and clays and to a lesser degree as a result of cementation and infill of secondary om larger pores are associated with coccolith debris the dominant om is spatially isolated detrital om stringers porosity is volumetrically dominated average 6 2 by relatively large mostly interparticle mineral associated pores median size 51 6 nm 0 000002 in detection limit near 3 4 nm 0 00000012 0 00000015 in at low maturity porosity and pore size correlate directly with calcite abundance and inversely with om volumes at higher maturity further destruction of primary pores occurs through cementation secondary om infill and greater compaction mineral associated pores are present at high maturity 1 2 1 3 but are smaller median size 30 2 nm 0 0000011 in and less abundant average of 2 5 than at low maturity a large portion of om within high maturity samples is diagenetic in origin and has pervaded into primary pore space coating cement crystals and filling intraparticle pores substantial mineral associated porosity is locally present in samples where incursion of primary pore space by secondary om has not occurred abundant secondary porosity is generated as om matures into the wet gas window porosity in most high maturity samples is volumetrically dominated average of 1 3 by smaller om hosted pores median size 13 2 nm 0 00000051 in

cherty stringers in the barnett shale are agglutinated foraminifera abstract masses of microcrystalline quartz are abundant within several lithologies in the barnett shale lower mississippian of central texas a typical quartz mass is elongated parallel to bedding and contains a central planar microporous structure that suggests collapse of a formerly hollow spheroidal or tubular body an integrated imaging approach utilizing transmitted polarized light microscopy secondary and back scattered electron imaging cathodoluminescence imaging and x ray mapping reveals these quartz masses to be composed primarily of quartz cemented silt size detrital quartz with a minor admixture of detrital ca plagioclase and dolomite microcrystalline quartz rich masses in the barnett shale are interpreted as agglutinated foraminifera that have been dramatically collapsed during compaction locally a significant portion of the total detrital quartz resides within these biogenic accumulations this study highlights the potential for using these imaging techniques to investigate agglutinated foraminifera in lithified materials that are not amenable to disaggregation and extraction of three dimensional specimens the combined imaging techniques provide an unambiguous view into aspects of skeletal ultrastructure such as particle size and sorting that cannot be readily obtained from either conventional light microscopy or sem these techniques reveal that agglutinated foraminifers are abundant in several lithologies of the barnett shale pointing to the possibility that application in other organic rich shales may reveal these organisms to be more widespread than previously recognized comparative observations in devonian shales of the central eastern united states support this prediction

experimental deposition of carbonate mud from moving suspensions importance of flocculation and implications for modern and ancient carbonate mud deposition abstract flume experiments with fine grained carbonate particles 62 5 m show that they form floccules that travel in bedload form current ripples and deposit laminated sediments in order to compare our flume experiments to work on sand transport we ran flume experiments with medium sand and observed that the velocities at which sand grains started to move and form ripples were in the same range as those where floccules move and form ripples these ripples are in essence identical to those formed by clay mineral floccules or sand grains under similar conditions in light of previous experiments with clay minerals these results indicate that of the key controls on mud deposition flocculation and suspended sediment concentration are more important than particle mineralogy or water chemistry and are about as important as bottom shear stress for deposition suspensions of carbonate mud show the same pattern of flocculation ripple formation and bed accretion as observed previously in experiments with clay mineral suspensions the resulting carbonate mud deposits show internal low angle 2 5 degrees laminae and in plan view a pattern of ripple foresets that is identical to rib and furrow structure in sandstones just as previously assumed for terrigenous muds there has been a long standing notion that accumulation of abundant carbonate mud reflects quiescent conditions of offshore and deeper water environments these experiments demonstrate unequivocally that carbonate muds can also accumulate in energetic settings in the sedimentary record of carbonate rocks interbedded grainstones and lime mudstones may thus not necessarily reflect shifts in depositional energy or water depth but alternatively may imply a shift in supplied sediment type the observations we report suggest that published interpretations of ancient lime muds and derived paleoceanographic conditions may need to be reevaluated

small scale 5 0 m vertical heterogeneity in mudstones implications for high resolution stratigraphy in siliciclastic mudstone successions 48 mudstone samples from the peterborough member oxford clay formation have been analysed to determine the small scale vertical and lateral lithofacies variability in this succession the samples were collected every 0 15 m from saxon and king9s dyke brickpits whittlesey peterborough uk over a short vertical interval 15 m the sampled interval spans the obductum to the grossouvrei subzones of the callovian upper jurassic lithofacies present were described using combined field logging optical and backscattered electron optical techniques the succession predominantly comprises silt rich mudstones with subordinate clay rich mudstones shell beds and shell pavements the individual units are variously composed of detrital clay quartz pyrite calcite with minor apatite kaolinite and glauconite in some units millimetre scale upward fining couplets are present elsewhere the original bedding structures have been destroyed by bioturbation comparison of successive thin sections reveals that upward coarsening is present on a metre scale and that shell enriched units are located close to the tops of these upward shoaling units comparison of samples collected laterally on a 0 01 1 0 m scale from the same level 3 0 m below the top of bed 14 indicates that there is lateral lithofacies variability the small scale 0 001 m couplets are interpreted to be beds deposited by waning flow currents significant breaks between these depositional events allowed a dysaerobic infauna to colonize the sediment the metre scale upward coarsening intervals which are capped by shell enriched units are interpreted to be parasequences the observed small scale lateral lithofacies variability is interpreted to be a product of small but significant vertical miscorrelation errors rather that systematic lateral facies changes these data suggest that producing reliable bed scale lateral correlations over distances of more than 1 km in this and successions like it will be very difficult

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

radiocarbon dating of sediments by accelerator mass spectrometry abstract accelerator mass spectrometry allows the measurement of the abundance of carbon isotopes in much smaller samples 1 mg of carbon in the form of graphite than conventional methods of radiocarbon dating the small sample requirement widens the potential for sediment dating in this study fractions of the sedimentary organic matter for example humic acid lipid macrofossils were isolated and each fraction dated to yield a suite of dates for one sediment sample owing to the complexity of most sedimentary environments a conventional radiocarbon date reflects the input of sediment from different sources with different carbon reservoirs which may combine to alter the date of the event that is required i e the date of sedimentation an estimate of the date of sedimentation may be made by taking specific fractions of the sedimentary organic matter which can be characterized and dated for example the lipid fraction which can be sub divided for analysis to yield information on the relative input of terrestrial and aquatic organic matter results have been obtained for five peat samples the dates of the more water soluble components of the sedimentary organic matter tending to be younger than the lipid samples

mudstone lithofacies in the kimmeridge clay formation wessex basin southern england implications for the origin and controls of the distribution of mudstones abstract lithofacies analysis has been undertaken on a suite of apparently monotonous organic rich mudstones from the upper jurassic kimmeridge clay formation kcf in the wessex basin southern england using a combination of hand specimen description whole rock geochemistry optical petrography and electron optical petrography five lithofacies have been identified these are clay rich mudstones silt rich mudstones nannoplankton rich mudstones laminated mudstones and concretionary carbonates these facies can be distinguished from one another on the basis of physical sedimentary structures and the relative proportions of allochthonous autochthonous and diagenetic components in each all five of the kcf lithofacies studied were deposited in a marine shelf environment below fair weather wave base but in relatively shallow water close to storm wave base deposition occurred in regions where sand and other coarse clastic allochthonous debris were not being supplied and the bottom waters varied from oxic to anoxic the main factors influencing the development of the five facies were distance from source area primary productivity bottom water anoxia absolute bathymetry clastic dilution and local sediment accumulation rates specifically the clay rich mudstones were deposited in regions farthest down the sediment transport paths commonly in areas by passed by the main sediment supply and beneath surface waters of relatively low primary productivity in contrast the silt rich mudstones were deposited in more proximal areas closer to the source of the sediment in regions where surface productivity and sediment accumulation rates were much higher the nannoplankton rich mudstones accumulated beneath regions where productivity in the surface water layers was fairly high dominated by coccolithophoroid production and the supply of clastic sediment was insufficient to significantly dilute the autochthonous fraction of the sediment unlike the other facies laminated mudstones were deposited in areas where the bottom waters were anoxic surface productivity was enhanced and local sediment accumulation rates were high the concretionary carbonates were precipitated by diagenetic processes in areas where sediment accumulation rates were very low these facies descriptions have enabled a detailed sedimentological study of the kimmeridge clay formation to relate depositional and diagenetic processes directly to the facies present thereby allowing classical facies analyses to be undertaken on apparently homogeneous mudstone successions

the cenomanian turonian eagle ford group of south texas insights on timing and paleoceanographic conditions from geochemistry and micropaleontologic analyses abstract the interbedded organic rich marls and limestones of the eagle ford group of south texas were deposited on the shelf of the central texas platform during the upper cenomanian through the turonian micropaleontological analyses of thin sections and residue samples from subsurface cores taken in atascosa and karnes counties yielded 13 biostratigraphic datums which were integrated with calcareous nannofossil datums stable carbon isotopic and bulk inorganic geochemical analysis to gain an understanding of the paleoceanographic conditions of the study area and their relationship to regional and global events the paired thin section residue sampling was necessitated by poor recovery of planktonic foraminifera in washed samples which were however abundant in most thin sections lower eagle ford marls were deposited under euxinic conditions produced by a stratified water column periodic enhanced water column mixing increased oxygen levels and surface water primary productivity which promoted calcite diagenesis and generation of limestones containing calcispheres and radiolaria an oxygenated bottom water mass entered the basin in the uppermost cenomanian prior to the onset of oceanic anoxic event oae 2 causing a spike in benthic foraminiferal diversity and decreasing preservation of organic matter although the lower portion of the upper eagle ford is age equivalent to oae2 as indicated by positive shift in 13corg it contains less organic matter and evidence of more oxygen than the lower eagle ford so deposition of the eagle ford black shales is not contemporaneous to oae2

origin of limestone marlstone cycles astronomic forcing of organic rich sedimentary rocks from the cenomanian to early coniacian of the cretaceous western interior seaway usa abstract we present an integrated multidisciplinary study of limestone marlstone couplets from a continuously cored section including parts of the upper buda limestone the entire eagle ford group boquillas formation and lower austin chalk from the shell iona 1 research borehole texas usa which provides a 8 million year myr distal clastic sediment starved intrashelf basin record of the early cenomanian to the earliest coniacian stages results show that despite variable yet minimal diagenetic overprints several unambiguous primary environmental signals are preserved and support greater water mass ventilation and current activity promoting increased silica carbonate productivity during the deposition of limestone beds compared to deposition of marlstone beds which reflect greater organic matter productivity and preservation furthermore our astronomical analyses demonstrate that the limestone marlstone couplets in the iona 1 core reflect climatic forcing driven by solar insolation resulting from integrated milankovitch periodicities in particular we propose that obliquity and precession forcing on the latitudinal distribution of solar insolation may have been responsible for the observed lithological and environmental variations through the cenomanian turonian and coniacian in this mid latitude epicontinental sea setting our data also suggests that rhythmic lithological alternations deposited in greenhouse periods in general may simply reflect climate driven cycles related to earth sun dynamics without the need to invoke significant sea level variations

origin and characterization of eagle ford pore networks in the south texas upper cretaceous shelf abstract recent studies have shown that the loss of primary pores and the development of secondary pores in mudrocks are primarily controlled by burial diagenesis of the mineral matrix and thermal maturation of organic matter om however the lack of quantitative data on nanometer to micrometer scale rock properties has limited the ability to define and predict petrophysical properties and fluid flow in these fine grained rocks to upscale these rock properties quantitative data are needed at multiple scales representative eagle ford group samples were collected from continuous cores taken from two adjacent oil producing wells in karnes county texas to investigate small scale variations in mineralogy diagenesis and pore type point count and pore tracing methods were used to systematically quantify pore types and determine the size and shape of the identified pores the two cores from the eagle ford are dominated by modified mineral pores although secondary om pores in migrated petroleum bitumen are also important the mineral pore network includes 1 primary mineral pores originally saturated with formation water and 2 modified mineral pores containing migrated petroleum bitumen and or residual oil the om pore network includes 1 primary om pores and 2 secondary om pores including relatively large less abundant om bubble pores and relatively small more abundant om spongy pores the abundance of om spongy pores correlates positively with total organic carbon toc content and that of mineral pores weakly correlates with the volume of quartz plus feldspar studied samples have similar thermal maturities although samples from one deeper core are slightly more mature than the other except for thermal maturation the strong micrometer scale heterogeneity of rock components and properties texture fabric mineralogy and toc impacts the abundance distribution and type of pores this micrometer scale heterogeneity in porosity and pore networks would in turn significantly impact matrix permeability

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

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

high resolution stratigraphy and facies architecture of the upper cretaceous cenomanian turonian eagle ford group central texas rock based studies of the eagle ford group of central texas demonstrate that mudrock deposition is more complicated than previously supposed x ray diffraction x ray fluorescence total organic carbon toc and log data collected from eight cores and two outcrops demonstrate that bottom current reworking and planktonic productivity are primary depositional controls acting independently from eustatic forcing central texas eagle ford facies include 1 massive argillaceous mudrock 2 massive foraminiferal calcareous mudrock 3 laminated calcareous foraminiferal lime mudstone 4 laminated foraminiferal wackestone 5 cross laminated foraminiferal packstone grainstone 6 massive bentonitic claystone and 7 nodular foraminiferal packstone grainstone high degrees of lateral facies variability characterized by pinching and swelling of units lateral facies changes truncations and locally restricted units are observed even at small lateral scales 50 ft 15 m at 10 mi 16 km and greater lateral spacings core and geochemical data significantly underestimate intraformational facies variability approximately 73 of units can be successfully correlated across a distance of 500 ft 152 m 35 are traceable across 1 mi 1 6 km and only 16 of beds are correlative across 10 mi 16 km geochemical proxies enrichment in molybdenum and other trace elements indicate that maximum anoxia occurred within the bouldin member despite being composed of the most calcareous and high energy facies comparison of total gamma ray gr logs to computed gr logs is requisite because gr alone may provide misleading determination of facies toc content depositional environment and sequence stratigraphic implications

influence of maceral composition on geochemical characteristics of immature shale kerogen insight from density fraction analysis abstract variations in the relative proportions of individual macerals in shales can significantly influence the geochemical characteristics of bulk organic matter density fractions of kerogen from the thermally immature new albany shale devonian and mississippian with contrasting maceral compositions exhibit strong geochemical differences the parental shale is characterized by a vitrinite reflectance ro of 0 45 a total organic carbon content of 13 wt and a sulfur content of 6 2 wt organic matter is dominated by amorphinite and alginite with vitrinite and inertinite accounting only for 1 by volume alginite dominated density fractions density ca 1 0 1 15 g cm3 contain significantly more aliphatic hydrogen a stronger carboxyl carbonyl contribution and reduced fourier transform infrared spectroscopy absorbance in the 1000 to 1100 cm 1 region assigned to ether bonds c o c as compared to the amorphinite dominated density fraction density ca 1 2 1 6 g cm3 aromaticity generally increases from alginite dominated to amorphinite dominated fractions density fractions dominated by amorphinite are more deuterium depleted dn values of nonexchangeable hydrogen up to 105 than alginite rich density fraction dn values reach 90 in contrast changes in relative proportions of alginite and amorphinite in the new albany shale do not significantly affect the amount of isotopically exchangeable hydrogen in total hydrogen i e hydrogen exchangeability alginite is relatively 13c enriched whereas density fractions having a high content of amorphinite are relatively 13c depleted our results suggest that even small bulk geochemical and isotopic differences can gain relevance after deconvolution from maceral related variability the masking influence of maceral abundance patterns must be considered when interpreting bulk geochemical data as paleoenvironmental proxies the findings of this study on shale and type ii kerogen are relevant for all types of kerogens in sediments and rocks

bib sem study of the pore space morphology in early mature posidonia shale from the hils area germany abstract this contribution reports on the study of the pore space morphology in two early mature vr r 0 59 and 0 61 samples of posidonia shale from the hils syncline in germany using broad ion beam bib polishing and high resolution scanning electron microscopy sem this allows imaging pores with resolution down to 10 nm in equivalent diameter d eq and quantitative estimation of porosity using a combination of bse and se detectors and semi automatic segmentation of the gigapixel images the representative elementary area of the samples on the scale of a few mm is inferred to be about 140 140 m 2 pore morphologies and pore sizes are clearly related to the mineral fabric with large differences very large typically several microns pores with internal faceted crystal morphology in recrystallized calcite clasts and smaller pores d eq cf schizosphaerella nanofossils typically 200 nm pores are less common in organic material and in pyrite aggregates pore characteristics are very similar for both samples and porosity resolvable by bib sem is 2 75 and 2 74 pore size distribution can be described by a power law with an exponent about 2 0 and 2 2 respectively for the pore population excluding the fossils pores in the carbonate fossils show dual power law distribution with power law exponents of about 1 and 3 by extrapolating the power law distribution for each sample total porosity is estimated to be 4 8 0 9 1 7 and 6 5 2 7 7 2 respectively this estimate can be compared with 3 4 3 7 and 3 3 3 6 as measured by mercury injection porosimetry we interpret this difference to reflect the unconnected for mercury part of the porosity comparison of imaged pores and mercury injection porosimetry suggest a very high pore body to pore throat ratio this results in a pore model where large pores represented mainly by pores in fossils and calcite grains are connected via a low porous and low permeable clay rich matrix with pore throats below 10 nm in both samples