integrated geochemistry organic petrology and sequence stratigraphy of the triassic shublik formation tenneco phoenix 1 well north slope alaska u s a abstract the tenneco phoenix 1 well recovered continuous core through the shublik formation allowing an uncommon opportunity to comprehensively study organic and lithostratigraphic facies variations in a known hydrocarbon source rock interval the lower portion of the cored shublik formation represents part of a transgressive systems tract tst and is characterized by alternating well laminated and bioturbated shales a pronounced condensed section occurs at the top of this interval the shublik formation above the maximum flooding surface mfs represents initial deposits of a highstand systems tract hst it contains coarser grained material and is more bioturbated than the base of the unit the distribution of oil prone facies within the shublik formation is dependent on stratigraphic position and is predictable within a sequence stratigraphic framework the transgressive portion is dominated by oil prone facies while the upper regressive portion is predominatly gas prone to non source well laminated organic rich oil prone intervals in the phoenix core correspond to uranium anomalies on the spectral gamma ray log an organic petrologic study of 54 core samples from the shublik formation is consistent with log analysis and source rock geochemistry both subtle and dramatic organic facies changes characterize the tst fluorescent amorphinite marine alginite and other exinites are the dominant kerogen macerals subtle variation in the maceral concentration of this oil prone organic debris is typical of this interval however there are four major changes in kerogen composition in this transgressive interval these changes include fluctuations in kerogen composition that reflect likely variations in those factors that controlled deposition and preservation of the organic matter in the shublik formation there is another significant reduction in the amount of oil prone kerogen in the condensed section at the top of the tst non fluorescent amorphinite is the dominant organic matter type in general fluctuations in kerogen composition are much less pronounced in the hst when compared with the tst fluorescent amorphinite is the dominant kerogen type but there is also 10 15 vitrinite with comparable amounts of inertinite the amount of these maceral types gradually increases stratigraphically upward in the hst because of this source rocks in this interval tend to be gas prone however there is no significant change in the apparent origin of the organic matter immediately across the mfs there is still considerable kerogen of marine origin in the hst

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

influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales abstract previous work has suggested that the laminated organic rich and bioturbated organic poor shales of the camp run member of the late devonian early mississippian new albany shale formed under anoxic and oxygenated bottomwater conditions respectively and that the interbedding of the two facies was due to the vertical oscillation of a water column anoxic oxic boundary where it impinged on the basin margin we have extended this analysis by examining the chemical and mineralogical differences between the two shale facies in a single borehole core by seeking evidence for deposition of the laminated shales under bottom water oxia or anoxia and by determining whether the laminated shales formed when the carbon supply to the sea floor was higher the results of this study show that the laminated and bioturbated shales are mineralogically and chemically distinct relative to al an index of the aluminosilicate content si ti fe p na ba co cr cu mo ni v zn and zr are all higher whereas mn ca mg and sr are lower in the laminated compared with the bioturbated shales the differences are due to a higher quartz feldspar titanite ilmenite and zircon content in the laminated shales probably indicating a coarser grain size and the greater abundance of manganoan calcite in the bioturbated shales dissolved oxygen was present in bottom waters during the deposition of some of the laminated shale intervals because of the presence of manganoan calcite a phase that can only form in sediments with an oxic surface in addition the organic matter preserved in the two shale types is isotopically different 13corganic values are 1 9z permil lighter on average in the laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals suggesting that nutrient drawdown was less during the deposition of the organic rich laminated shales the chemical mineralogical and isotopic contrasts between the two shale facies of the camp run member indicate that the conditions of sedimentation were different during their deposition the difference was possibly related to variations in sea level which would have caused the camp run shoreline to move closer to and farther from the core site causing in turn the deposition of coarser and finer grained sediments that contained different mixtures of marine and terrestrial organic matter bottomwater conditions were anoxic during deposition of most laminated intervals bottom water anoxia or dysoxia led to decreased burial and preservation of the essential nutrient phosphorus in the laminated organic rich shales relative to the rocks deposited beneath better oxygenated bottomwaters increased availability of phosphorus in the water column on long timescales leads to increased productivity and a higher settling flux of organic matter causing bottom water oxygen levels to fall this is consistent with the nitrogen isotope evidence suggesting that production was probably higher during the deposition of the organic rich shales thus production variations coupled with enhanced sedimentary regeneration of phosphorus from sediments related to low oxygen bottom water concentrations provide a general mechanism for the formation of the alternating facies of this member of the new albany shale

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

geochemical and isotopic evidence for paleoredox conditions during deposition of the devonian mississippian new albany shale southern indiana the upper part of the new albany shale is divided into three members in ascending order these are 1 the morgan trail member a laminated brownish black shale 2 the camp run member an interbedded brownish black and greenish gray shale and 3 the clegg creek member also a laminated brownish black shale the morgan trail and camp run members contain 5 to 6 total organic carbon toc and 2 sulfide sulfur isotopic composition of sulfide in these members ranges from 5 0 to 20 0 c s plots indicate linear relationships between abundances of these elements with a zero intercept characteristic of sediments deposited in a non euxinic marine environment formation of diagenetic pyrite was carbon limited in these members the clegg creek member contains 10 to 15 toc and 2 to 6 sulfide sulfur isotopic compositions of sulfide range from 5 0 to 40 the most negative values occur in the uppermost clegg creek member and are characteristic of syngenetic pyrite formed within an anoxic water column abundances of carbon and sulfur are greater and uncorrelated in this member consistent with deposition in as euxinic environment in addition dop degree of pyritization values suggest that formation of pyrite was generally iron limited throughout clegg creek deposition but sulfur isotopes indicate that syngenetic water column pyrite becomes an important component in the sediment only in the upper part of the member at the top of the clegg creek member a zone of phosphate nodules and trace metal enrichment coincides with maximal toc values during euxinic deposition phosphate and trace metals accumulated below the chemocline because of limited vertical circulation in the water column increased productivity would have resulted in an increased flux of particulate organic matter to the sediment providing an effective sink for trace metals in the water column phosphate and trace metals released from organic matter during early diagenesis resulted in precipitation of metal rich phosphate nodules

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

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

the genesis of coal from the viewpoint of coal petrology abstract the genesis of the microscopic constituents of coal macerals and of maceral associations microlithotypes representing various coal facies is discussed in the light of recent advances that have been made in the study of coals and modern peats peat microscopy especially promoted the understanding of humification and biological gelification both of which are decisive for the genesis of huminites vitrinites in brown coals and hard coals respectively microbial activity during peatification has been documented by chemists microbiologists and petrologists and recently by electron microscopical observations in coals this activity leads to the incorporation of lipid substances into the humic matter and later influences the chemical physical and technological properties of vitrinites geochemical gelification transforms the huminites of brown coals into the vitrinites of bituminous coals and is probably caused by the onset of bitumen generation in coal in this process the hydrogel brown coal is transformed to the bitumogel bituminous coal coal as a source rock for oil has become an important research subject for coal petrologists and oil exploration the formation of more or less liquid bitumen and its later cracking to gaseous hydrocarbons leads to the coalification jumps of the macerals especially liptinites and vitrinites and to the generation of secondary macerals like exsudatinite bitumen and micrinite dead carbon bituminization in coal has been revealed by the use of fluorescence microscopy which also found the presence of new liptinite macerals bituminite fluorinite and exsudatinite and suggests a higher proportion of algal material in coals than was thought earlier the genesis of various types of inertinite macerals will probably become an increasingly important subject of research especially with regard to rank inertinites that seem to attain their high inertinitic reflectance initially during coalification besides the origin of macerals the origin of various coal facies in terms of maceral associations is considered in relation to the palaeogeographic depositional milieu the peat forming vegetation palaeoclimate water and nutrient supply acidity marine and calcareous influence and fire with examples from euramerican carboniferous coals gondwana coals and tertiary brown coals vegetation water and oxygen supply eh conditions are most important for the generation of coal facies vegetation has been reconstructed with the help of palaeobotany including palynology cuticular analysis and wood anatomy in brown coals and with the study of petrified permineralized peats preserved in coal balls the microscopical investigations of botanically recognizable plant remains isolated from coals or accompanying rocks has been especially informative however the results of palynological and cuticular analyses should be evaluated with caution considering the varying resistance of palynomorphs and cuticles and in the case of palynomorphs their possible extrapaludal origin microscopical studies of modern peats that were derived from different types of vegetation growing in different hydrological environments have been very helpful in interpreting coal facies especially in brown coals the much disputed origin of brown coal lithotypes is considered in detail for hard coals there seems to be agreement that coal layers rich in vitrites and liptinite poor clarite were deposited in wet forest swamps that microlayered liptinite rich clarites are sub aquatic humic muds and that inertinite rich durites represent oxidized peats the origin of liptinite rich durites is controversial either subaquatic muds or oxidized peats the latter perhaps from raised bogs a recent trend in the literature is the assumption that many if not all mineable coal seams have been deposited in raised bogs under ombrogenous oligotrophic conditions although raised bogs with a dense arborescent vegetation are known from borneo it seems not probable that most seams which were deposited in foredeeps or steadily sinking graben zones are of ombrogenous origin although a succession from relatively wet and eutrophic to relatively dry and oligotrophic conditions may be true for occasional seams but as in modern peats striking changes of coal facies are commonly caused by hydrological events e g inundations as a consequences of crevasses or of fires that burned the peat the origin of the inertinite rich gondwana coals is discussed in relation to their specific climatic conditions and a comparison with sub arctic peats is recommended coals influenced by marine and calcareous conditions are characterized by high contents of sulfur and pyrite as well as by hydrogen rich vitrinites with a relatively low reflectance and high fluorescence all due to a strong bacterial activity in peats of low acidity proposals for further research are made in the conclusions

geochemical constraints on the origin and volume of gas in the new albany shale devonian mississippian eastern illinois basin this study involved analyses of kerogen petrography gas desorption geochemistry microporosity and mesoporosity of the new albany shale devonian mississippian in the eastern part of the illinois basin specifically detailed core analysis from two locations one in owen county indiana and one in pike county indiana has been conducted the gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales gas origin was assessed using stable isotope geochemistry measured and modeled vitrinite reflectance values were compared depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail the shallower owen county location 415 433 m 1362 1421 ft deep contained significant additions of microbial methane whereas the pike county location 832 860 m 2730 2822 ft deep was characterized exclusively by thermogenic gas despite differences in the gas origin the total gas in both locations was similar reaching up to 2 1 cm3 g 66 scf ton lower thermogenic gas content in the shallower location lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures was compensated for by the additional generation of microbial methane which was stimulated by an influx of glacial melt water inducing brine dilution and microbial inoculation the characteristics of the shale of the maquoketa group ordovician in the pike county location are briefly discussed to provide a comparison to the new albany shale

caco3 precipitation kinetics in waters from the great bahama bank implications for the relationship between bank hydrochemistry and whitings the source of whitings on the great bahama bank and their relationship to major changes in the chemistry of bank waters have been among the longest and most hotly debated topics in carbonate geochemistry in this paper we demonstrate that the reaction kinetics of calcite with bank waters for a given saturation state are similar to but somewhat slower 2 to 3 times than with gulf stream water the interpretation of the reaction kinetics of suspended bank sediment with bank water requires that the precipitating phase be about twice as soluble as aragonite good agreement at equivalent saturation states was found between experimental precipitation rates and those calculated for the rate of change of bank water chemistry in the region of whitings these results indicate that the dominant mode of carbonate removal is via precipitation on resuspended sediments rather than the rapid pseudo homogeneous precipitation of calcium carbonate in the water column resulting in the formation of a whiting estimates indicate that single aragonite needles may be resuspended many times over a period of decades during which they experience repeated overgrowth a major portion 98 of suspended calcium carbonate is outside the visually dramatic whitings thus as visually spectacular as they are whitings do not represent a short term locally massive precipitation of carbonate on the great bahama bank nor are they even likely to be the dominant sites of carbonate removal in this region although future refinements are needed that include seafloor processes we have at this point arrived at a mechanistic kinetic model that provides a reasonably quantitative explanation for the hydrochemistry of the carbonate system on the northern great bahama bank

phosphorus burial as a function of paleoproductivity and redox conditions in arabian sea sediments in this study the response of sedimentary phosphorus p burial to changes in primary productivity and bottom water oxygen concentrations during the late quaternary is investigated using two sediment cores from the arabian sea one recovered from the continental slope and the other from the deep basin the average solid phase p speciation in both cores is similar authigenic and biogenic fish debris apatite make up the bulk of the p inventory ca 70 whereas p adsorbed to iron oxides organic p and detrital apatite constitute minor fractions postdepositional redistribution has not significantly altered the downcore distribution of total solid phase p phosphorus burial efficiencies are generally lower during periods of increased paleoproductivity this is caused by a partial decoupling of the p export flux consisting primarily of particulate organic p and the p burial flux consisting primarily of biogenic and authigenic apatite and b the lack of increased rates of authigenic cfa formation during periods of higher p deposition in addition fluctuations in bottom water oxygen concentrations may have affected p burial in continental slope sediments the results of this study indicate that higher primary productivity induces more efficient p cycling on time scales exceeding the oceanic p residence time this process may induce higher surface water productivity thus creating a positive feedback loop in the arabian sea this feedback mechanism may have contributed to changes in sea surface productivity on sub milankovitch time scales because p regenerated on the continental slopes of the oman and somalian coastal upwelling zones is reintroduced into the photic zone relatively fast

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

a role for organic petrology in integrated studies of mudrocks examples from devonian black shales of the eastern us abstract over the years the study of mudrocks has lagged far behind that of other lithologies a circumstance that is in part due to their fine grained nature and in part due to economic realities yet within petroleum systems mudstones are usually the main source of hydrocarbons and typically are also important as hydrocarbon seals recent work on late devonian mudstones from the eastern us shows that much progress can be made through an integration of outcrop study macro and micropaleontology ichnofossils gamma ray spectroscopy microscopic examination of thin sections in transmitted and reflected light electron microscopy sem bse electron microprobe carbon and sulfur isotopes and organic geochemistry erosion surfaces within this black shale succession have been traced over large distances and provide the foundation for a sequence stratigraphic re interpretation of these rocks evidence of storm wave reworking of the seabed as well as the realization that benthic colonization was much more widespread than previously believed suggest that anoxic conditions in the water column were not a controlling factor in the accumulation of the large quantities of organic matter found in these shales these distal devonian shales accumulated slowly and allowed accumulation of large proportions of organic matter in modern settings of abundant organic matter accumulation the original material is broken down by bacteria within a matter of months into a mass of largely unidentifiable organic particles and extracellular bacterial slime although one can still find identifiable material within this mass slime and amorphous material strongly dominate after burial and maturation this material turns into the various organic macerals that organic petrologists are accustomed to describe one might wonder in this context how much information about the origin of a given mudstone unit can we hope to extract through organic petrology in order to illustrate how organic petrology of mudrocks can contribute to their better understanding late devonian black shales of the eastern us will be examined from a sedimentological perspective combining sedimentologic and geochemical data with basic observations on organic petrology illustrates how the latter can contribute to more realistic scenarios of black shale genesis

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

comparative optical properties of macerals and statistical evaluation of mis identification of vitrinite and solid bitumen from early mature middle devonian lower mississippian new albany shale implications for thermal maturity assessment abstract vitrinite reflectance vro in is used routinely to quantify thermal maturity in sedimentary basins reflectance and fluorescence of other macerals such as solid bitumen and amorphous organic matter aom can provide an independent means to assess thermal maturity and hydrocarbon generation potential however similarity in petrographic characteristics of these macerals solid bitumen and vitrinite in particular often causes difficulties with their identification and consequently reflectance can be measured on misidentified particles making reported vro values unreliable the purpose of this study is to compare reflectance values of various macerals in early mature shales and to evaluate the implications of misidentifying solid bitumen and vitrinite for assessing thermal maturity to address this issue 15 organic matter rich samples from the middle devonian lower mississippian new albany shale from a corehole in daviess county indiana were selected these samples were chosen because they had distinct and easily identified aom solid bitumen vitrinite and inertinite particles allowing for statistically relevant comparisons vro values 0 57 to 0 65 of the studied sample suite cover the early mature stage and expressed no trend with depth in comparison reflectance values of solid bitumen bro and aom aomro from the same samples are lower and range from 0 44 to 0 52 and 0 27 to 0 31 respectively these differences are accompanied by corresponding differences in chemistry of macerals as demonstrated by the micro ftir technique specifically compared to vitrinite and inertinite solid bitumen shows lower aromaticity and compared to aom and alginite it exhibits shorter aliphatic chains reflectance was observed to vary systematically samples having higher vro also feature elevated solid bitumen and aom reflectance values the relationship between vitrinite and solid bitumen can be expressed by the following equation vitrinite reflectance equivalent vroe in 0 83 bro 0 22 whereas for vitrinite and aom vroe 0 84 aomro 0 38 statistical evaluation of the differences in reflectance values caused by maceral misidentification indicates that in extreme cases when a petrographer cannot distinguish between vitrinite and solid bitumen the reflectance can be shifted by 0 06 0 09 for this set of samples such a difference could shift maturity assessment from early mature to immature in more common cases when the analyst can distinguish between the macerals but has difficulties with their overlapping reflectance interval the reflectance difference that results from misidentification is only within a 0 0 0 02 range therefore if the level of uncertainty in maceral identification can be determined the calculation of vroe values from measured bro can reduce inaccuracy in vro values for interpreting the thermal histories of sedimentary basins which in turn is essential for the assessment of oil and gas resources and for building a successful exploration model

pyrolysis gas chromatography mass spectrometry to characterize organic matter and its relationship to uranium content of appalachian devonian black shales gas chromatographic analysis of volatile products formed by stepwise pyrolysis of black shales can be used to characterize the kerogen by relating it to separated identified precursors such as land derived vitrinite and marine source tasmanites analysis of a tasmanites sample shows exclusively n alkane and alkene pyrolysis products whereas a vitrinite sample shows a predominance of one and two ring substituted aromatics for core samples from northern tennessee and for a suite of outcrop samples from eastern kentucky the organic matter type and the u content 10 120ppm show variations that are related to precursor organic materials the samples that show a high vitrinite component in their pyrolysis products are also those samples with high contents of u

mud re distribution in epicontinental basins exploring likely processes abstract fine grained clastic sediments are very common in the interior deposits of ancient epicontinental seas not only do they make up the gross lithology in these basins but they can also be traced for more than 1000 km offshore from basin margins given that epicontinental seas were overall shallow and in many parts most likely less than 100 m deep basin floor slopes can safely be expected to be in the 0 01 to 0 001 range for much of depositional history known processes that bring muds to the basin margin and beyond are hypopycnal river plumes hyperpycnal fluvial discharge events storm setup relaxation flows and gravity driven fluidized muds with the exception of river plumes all of these processes require the presence of sufficient slope for sustained movement due to that constraint these processes combined might in the majority of situations have been able to move muddy sediments on the order of 100 km offshore whereas this is sufficient to distribute mud across marginal shelf seas it becomes problematic in the case of much larger epicontinental seas for example those of upper devonian or upper cretaceous times extended in places for thousands of kilometers and thus a process is needed that can move muddy sediments the rest of the way flume studies of the bedload transport of mud combined with observations from the rock record suggest that wind or tide induced bottom current circulation was most likely essential for moving muddy sediments from the periphery of epicontiental seas to their interiors remobilization of seafloor muds during frequently recurring lowering of sea level is likely to have aided in this process

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

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

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

hydrocarbon biomarkers thermal maturity and depositional setting of tasmanite oil shales from tasmania australia this study represents the first geological and organic geochemical investigation of samples of tasmanite oil shale representing different thermal maturities from three separate locations in tasmania australia the most abundant aliphatic hydrocarbon in the immature oil shale from latrobe is a c19 tricyclic alkane whereas in the more mature samples from oonah and douglas river low molecular weight n alkanes dominate the extractable hydrocarbon distribution the aromatic hydrocarbons are predominantly derivatives of tricyclic compounds with 1 2 8 trimethylphenanthrene increasing in relative abundance with increasing maturity geological and geochemical evidence suggests that the sediments were deposited in a marine environment of high latitude with associated cold waters and seasonal seaice it is proposed that the organism contributing the bulk of the kerogen tasmanites occupied an environmental niche similar to that of modern sea ice diatoms and that bloom conditions coupled with physical isolation from atmospheric co2 led to the distinctive isotopically heavy 13c values 13 5 to 11 7 for the kerogen 13c data from modern sea ice diatoms 7 supports this hypothesis isotopic analysis of n alkanes in the bitumen 13 5 to 31 suggest a multiple source from bacteria and algae on the other hand the n alkanes generated from closed system pyrolysis of the kerogen 15 are mainly derived from the preserved tasmanites biopolymer algaenan the tricyclic compounds mean 8 both in the bitumen and pyrolysate have a common precursor they are consistently enriched in 13c compared with the kerogen and probably have a different source from the n alkanes the identification of a location where the maturity of the tasmanite oil shale approaches the oil window raises the possibility that it may be a viable petroleum source rock

analysis of marine environmental conditions based onmolybdenum uranium covariation applications to mesozoic paleoceanography article i nfo article history accepted 13 september 2011 available online 17 september 2011 patterns of uranium molybdenum covariation in marine sediments have the potential to provide insights re garding depositional conditions and processes in paleoceanographic systems specifically such patterns can be used to assess bottom water redox conditions the operation of metal oxyhydroxide particulate shuttles in the water column and the degree of water mass restriction the utility of this paleoenvironmental proxy is due to the differential geochemical behavior of u and mo 1 uptake of authigenic u by marine sediments begins at the fe ii fe iii redox boundary i e suboxic conditions whereas authigenic mo enrichment re quires the presence of h2s i e euxinic conditions and 2 transfer of aqueous mo to the sediment may be enhanced through particulate shuttles whereas aqueous u is unaffected by this process in the present study we examine u mo covariation in organic rich sediments deposited mostly in the western tethyan region during oceanic anoxic events oaes of early jurassic to late cretaceous age our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regard ing water mass restriction and the operation of particulate shuttles in depositional systems these insights will help to address contentious issues pertaining to the character and origin of mesozoic oaes such as the degree to which regional paleoceanographic factors controlled the development of the oaes

concentration oxidation state and particulate flux of uranium in the black sea abstract in contrast to its unreactive behavior in the open ocean uranium is removed from seawater to sediments of anoxic marine basins four biogeochemical processes have been proposed to account for this removal active uptake by organisms whose remains are preserved by the anoxic conditions of the sediments complexation of u vi by particulate organic matter chemical reduction of soluble u vi to insoluble u iv which is scavenged to the sediments by settling particles and precipitation of uranium within the sediments themselves the black sea is the largest anoxic marine basin in the world today waters below 150 200 m are anoxic and h2s levels build up to about 400 mol 1 1 in the bottom water maximum depth 2200 m concentrations of total u and the oxidation state of dissolved u were measured throughout the water column while particulate u fluxes were determined from time series sediment trap samples collected in the deep anoxic zone bottom waters were depleted in u by 40 relative to the initial u content of the water two independent methods gave residence times of dissolved u in the deep water column of about 103 years uranium occurred throughout the water column as soluble chemically labile reducible u vi rather than the thermodynamically favored u iv uranium is neither reduced to u iv by the high levels of h2s nor is it rapidly scavenged from the water column as would be expected for strongly hydrolyzed tetravalent actinides like u iv fluxes of particulate authigenic u measured with sediment traps are at least two orders of magnitude less than the rate of authigenic u burial in black sea sediments therefore the first three processes listed above contribute negligibly to the deposition of u in the sediments of anoxic marine basins such as the black sea the dominant removal process must involve precipitation of u in the sediments rather than scavenging from the water column

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

model for transgressive black shales many black shales in thick epicontinental basinal successions formed beneath an oxygen restricted puddle of deep water other black shales formed during rapid transgression when basinal deposition expanded to cover basin margin areas normally characterized by shallow water deposition an expanding puddle model is developed from the early jurassic of england wherein rapid sea level rise leads to marine sediment starvation due to sediment entrapment in flooded river valleys subsidence sea level rise and decreased sediment supply during early transgression are suggested to lead to rapid deepening and therefore the expansion of the are of the puddle such that in previously shallow water areas black shales rest on condensed basal transgressive lags or unconformities that in turn rest on shallow water facies reestablishment of sediment influx and aggradation in excess of any continued sea level rise cause shallowing throughout the basin and the cessation of black shale formation

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

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

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

organic matter variations in transgressive and regressive shales abstract organic matter in the upper cretaceous mancos shale adjacent to the tocito sandstone in the san juan basin of new mexico was characterized using organic petrology and organic geochemistry differences in the organic matter found in these regressive and transgressive offshore marine sediments have been documented and assessed within a sequence stratigraphic framework the regressive lower mancos shale below the tocito sandstone contains abundant well preserved phytoclasts and correspondingly low hydrogen indices total organic carbon values for the regressive shale are low sediments from the transgressive systems tract tocito sandstone and overlying upper mancos shale contain less terrestrially derived organic matter more amorphous non structured protistoclasts higher hydrogen indices and more total organic carbon advanced stages of degradation are characteristic of the phytoclasts found in the transgressive shale amorphous material in the transgressive shale fluoresces strongly while that found in the regressive shale is typically non fluorescent data from pyrolysis gas chromatography confirm these observations these differences are apparently related to the contrasting depositional styles that were active on the shelf during regression and subsequent transgression it is suggested that data from organic petrology and organic geochemistry provide greater resolution in sedimentologic and stratigraphic interpretations particularly when working with basinward fine grained sediments petroleum source potential for the regressive lower mancos shale below the tocito sandstone is poor based on abundant fluorescent amorphous material high hydrogen indices and high total organic carbon the transgressive upper mancos shale above the tocito sandstone possesses excellent source potential this suggests that appreciable source potential can be found in offshore fine grained sediments of the transgressive systems tract below the condensed section and associated downlap surface organic petrology can be used to accurately predict petroleum source potential the addition of simple fluorescence microscopy greatly enhances this predictive ability because non generative amorphous material is generally non fluorescent organic petrology must also be used to properly evaluate the utility of t max from programmed pyrolysis as a thermal maturity indicator organic matter dominated by autochthonous amorphous protistoclasts exhibits lower t max values than that which is composed of mostly phytoclasts

organic carbon losses during burial and thermal maturation of normal marine shales the percentage of organic carbon lost during the burial diagenesis of normal marine shales those originally deposited in oxygenated bottom waters can be estimated by using the ratio of organic carbon c to pyrite sulfur s and assuming that the mean initial burial value of c s for such sediments has been approximately constant since the devonian plots of mean c s vs vitrinite reflectance r sub 0 for some sedimentary basins of jurassic and carboniferous age show a monotonic decrease of c s with increasing r sub 0 macrofossils

redox conditions associated with organic carbon accumulation in the late devonian new albany shale west central kentucky illinois basin abstract factors affecting organic carbon accumulation in marine basins may include surface water productivity enhanced preservation due to bottom water anoxia protection by and adsorption onto clays and variations in sediment supply in this study geochemical proxies for the new albany shale of the illinois basin were examined for ten cores from the outcrop belt in west central kentucky in an attempt to evaluate redox conditions associated with organic carbon enrichment in these cores the late devonian new albany shale is represented by the clegg creek camp run morgan trail and the blocher members specifically c s relationships degree of pyritization dop t and c s fe relationships along with redox sensitive trace elements e g v and mo and ratios ni co v cr and v v ni were used to assess redox conditions in addition organic carbon to total phosphorus ratios c org p tot were used to assess levels of paleoproductivity that were possibly enhanced by the productivity anoxia feedback mechanism results suggest variable bottom water conditions existed during accumulation of the new albany shale of west central kentucky including predominantly anoxic conditions for the clegg creek member dysoxic conditions for the camp run and morgan trail members and dysoxic to oxic conditions for the blocher member however throughout deposition all members exhibited some variability in redox conditions thus overall lowest oxygen levels were likely experienced during deposition of the clegg creek followed by the camp run and morgan trail members the blocher member was probably deposited under conditions closer to normal marine yet still dysoxic at most times high c p ratios observed in these members suggest regeneration of p enhanced productivity and sequestration of organic carbon as described by the productivity anoxia feedback paf mechanism during anoxic periods variations in redox indications obtained from different proxies suggest that multiple parameters should be utilized rather than relying on a single proxy reasonably good agreement is seen between c s dop t c s fe and mo levels ni co and v cr tend to agree well with each other but suggest higher oxygen levels than the other proxies values for v v ni tend to be an outlier suggesting more anoxic to euxinic conditions compared to other proxies

on the origin and significance of pyrite spheres in devonian black shales of north america abstract devonian black shales deposited on the north american craton contain abundant tasmanites cysts that are typically preserved as flattened circular discs on bedding planes work by the present authors shows that cysts can be preserved as pyrite infill casts that are expressed as sand size whole and geopetal half spheres of pyrite at the bases of thin black shale layers these occur in situ at many stratigraphic levels in the distal prodelta facies of the catskill delta complex of new york as well as in laterally equivalent black shales in tennessee and kentucky reworked pyrite casts usually dominated by whole spheres form lenticular lag accumulations and hydraulic placers together with plant debris and phosphatic particles bone debris conodonts an earlier model for the formation of pyrite spheres in gas bubbles is rejected in favor of formation within uncompressed tasmanites cysts direct observation of cyst cuticle in association with pyrite spheres suggests that localized bacterial sulfate reduction in tasmanites interior voids led to formation of localized pyrite deposition in a manner similar to that described from certain ammonoid chamber settings cyst fill commenced with formation of framboidal pyrite followed by later diagenetic pyrite cementation between framboids these fills show geopetal features and appear to have formed within the redox zone below the sediment water interface although described here from the upper devonian comparable pyrite textures are also known from proterozoic cambrian ordovician and silurian sediments they probably occur throughout the sedimentary record and in mudstone successions they may prove to be an important source of sand size grains in areas far removed from the basin margins as such they may be important for detection of erosive events and strong bottom currents and provide valuable information about the depositional history of mudstone successions

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

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

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

geochemical paleoredox indicators in devonian mississippian black shales central appalachian basin usa the degree of anoxia that existed during accumulation of devonian mississippian black shales in central kentucky has been debated widely in this study geochemical data were used to elucidate paleodepositional environments for these units using analyses from ten cores collected from the outcrop belt in central kentucky sulfur carbon and selected trace element relationships were compared the sunbury shale tournasian lower mississippian and the cleveland and huron members of the ohio new albany shale fammenian upper devonian show different relationships between carbon sulfur and trace elements c s fe relationships for the sunbury suggest anoxic possibly even euxinic conditions prevailed during sediment accumulation analysis of c s fe data suggests that the cleveland may have accumulated under anoxic conditions with intermittent dysoxia whereas the huron member may have accumulated under a relatively wide range of conditions from anoxic to dysoxic to possibly oxic these three units exhibit different degrees of trace element enrichment with the approximate order of enrichment relative to an average shale being mo pb zn v ni cu cr co the sunbury shows the highest levels of enrichment followed by the cleveland with the huron showing only slight enrichment for most of these trace elements differing degrees of enrichment may reflect differences in depositional environment during accumulation high mo concentrations in the sunbury generally 200 550 ppm may infer euxinic conditions prevailed during sediment accumulation the cleveland and the huron both show considerably lower mo contents averaging around 100 ppm geochemical ratios including ni co v cr and v v ni also indicate variable paleoredox conditions for these shales based on previously established thresholds v cr and ni co ratios infer at least anoxic conditions during accumulation of the sunbury anoxic to dysoxic conditions during cleveland accumulation and dysoxic to oxic conditions for the huron v v ni ratios tend to indicate consistently lower oxygen regimes than do other paleoredox indicators and this discrepancy is greatest for the huron member it is suggested that thresholds established for paleoredox indicators in previous studies should not be applied strictly but that relative differences in these indicators collectively can infer variations in the degree of anoxia in addition relationships between corg and redox elements may help elucidate the role of anoxia in om accumulation it may be concluded from this study that the devonian mississippian black shales of central kentucky accumulated under variable bottom water conditions at least anoxic conditions prevailed during accumulation of much of the sunbury shale and the upper part of the cleveland member and possibly euxinic conditions for the sunbury bottom water conditions may have been intermittently anoxic and dysoxic during deposition of the lower cleveland during accumulation of the huron member it is likely that conditions ranged from anoxic to dysoxic to marginally oxic possibly being close to normal marine conditions at times during accumulation of the lowermost huron sediments

sequence stratigraphy in the middle ordovician shale successions mid east korea stratigraphic variations and preservation potential of organic matter within a sequence stratigraphic framework abstract the jigunsan formation is the middle ordovician shale dominated transgressive succession in the taebaeksan basin located in the eastern margin of the north china platform the total organic carbon toc content and some geochemical properties of the succession exhibit a stratigraphically distinct distribution pattern the pattern was closely associated with the redox conditions related to decomposition bulk sedimentation rate dilution and productivity to explain the distinct distribution pattern this study attempted to construct a high resolution sequence stratigraphic framework for the jigunsan formation the shale dominated jigunsan formation comprises a lower layer of dark gray shale deposited during transgression and an upper layer of greenish gray siltstone deposited during highstand and falling stage systems tracts the concept of a back stepped carbonate platform is adopted to distinguish early and late transgressive systems tracts early and late tst in this study whereas the highstand systems tracts and falling stage systems tracts can be divided by changes in stacking patterns from aggradation to progradation the late tst would be initiated on a rapidly back stepping surface of sediments and just above the surface exhibits a high peak in toc content followed by a gradually upward decrease this trend of toc distribution in the late tst continues to the maximum flooding surface mfs the perplexing toc distribution pattern within the late tst most likely resulted from both a gradual reduction in productivity during the late tst and a gradual increase in dilution effect near the mfs interval the reduced production of organic matter primarily incurred decreasing toc content toward the mfs when the productivity was mainly governed by benthic biota because planktonic organisms were not widespread in the ordovician results of this study will help improve the understanding of the source rock distribution in mixed carbonate siliciclastic successions within a stratigraphic framework particularly for unconventional shale reservoirs

the quantification and application of handheld energy dispersive x ray fluorescence ed xrf in mudrock chemostratigraphy and geochemistry abstract traditionally analytical techniques such as wavelength dispersive x ray fluorescence wd xrf inductively coupled plasma icp and mass spectrometry icp ms instrumental neutron activation analysis inaa or stationary bench top energy dispersive x ray fluorescence ed xrf have been used to generate quantitative geochemical results however a more efficient means of data collection using portable ed xrf instrumentation now allows the investigator to acquire rapid non destructive quantitative measurements on drill core and clean flat rock surfaces in addition to pressed powder pellets typically used in wd xrf analysis similar to traditional xrf methods quantification using the handheld ed xrf requires a matrix specific calibration unfortunately very few internationally accepted mudrock or shale reference materials exist and their elemental ranges provide inadequate coverage for the geochemical diversity of mudrocks in order to return reliable calibrated results a unique set of reference materials has been developed that incorporates a wide range of mudrock elemental compositions the current method provides elemental calibrations for major elements heavier than sodium and the following trace elements ba v cr ni cu zn rb sr y zr nb mo th and u a comparison of handheld energy dispersive and wavelength dispersive x ray fluorescence ed xrf and wd xrf results from pressed powder pellets of mississippian age barnett shale of north central texas usa is presented in order to evaluate the reliability of the reference calibration and the quantification of unknown samples using two different instrument platforms it will be demonstrated that calibrated results from the handheld ed xrf effectively define chemostratigraphic changes in real time as a consequence quantified results can be used immediately to assess changes in bulk mineralogy paleo redox conditions and to link down core geochemical changes to stratigraphic sedimentological and paleoenvironmental observations

refining 2 km of ordovician chronostratigraphy beneath anticosti island utilizing integrated chemostratigraphy new high resolution chemostratigraphy in combination with updated biostratigraphy refines the chronostratigraphic resolution of the nearly 2 km thick ordovician section below anticosti island a total of 1414 horizons spaced at 1 0 1 5 m intervals were sampled from the new associated consolidated paper nacp drill core and analyzed for major and trace elemental composition by portable x ray fluorescence analyzer pxrf select micrite and calcareous shale powders were then analyzed for 13ccarb number of samples n 364 and 87sr 86sr n 25 our results indicate a floian to early darriwilian f3 dw1 age for the romaine formation a middle darriwilian to sandbian dw2 sa1 age for the mingan formation a lower to mid katian ka1 ka2 age for the macasty formation an upper katian ka3 age for the lower vaureal formation an uppermost katian ka4 age for the upper vaureal and a hirnantian h1 age for the ellis bay formation this integrated chemostratigraphic and biostratigraphic synthesis es

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

discovery of agglutinated benthic foraminifera in devonian black shales and their relevance for the redox state of ancient seas abstract agglutinated foraminifera are benthic organisms that occur in marginal marine to bathyal environments though some taxa can live in oxygen deficient environments they require at least some oxygen in order to persist at the seafloor the discovery that they occur widely in late devonian black shales has a bearing on the boundary conditions required for episodes of extensive carbon sequestration in marine sediments and their connection to atmospheric composition and global climate devonian black shales of the eastern us have been studied extensively to determine the fundamental controls on carbon burial and a range of mechanisms has been proposed finding agglutinated benthic foraminifera in these black shales refocuses the debate about their origin and points to limitations of earlier models

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

redox dynamics in the chesapeake bay the effect on sediment water uranium exchange the effect of seasonal variations in productivity and redox dynamics on the sediment water exchange of uranium was investigated on a twelve cruise time series in the chesapeake bay the deep waters of the bay undergo seasonal anoxia in response to high primary productivity and water column stratification from late spring to early fall dissolved oxygen was used to monitor water column redox conditions and dissolved iron manganese and sulfide were measured to monitor sediment redox conditions dissolved 238u was measured in the water column and sediment porewaters to monitor water column sediment exchange uranium incorporation in bay sediments results from two distinct processes productivity dependent scavenging from the water column and redox dependent cycling of uranium between sediments and bottomwater uranium is removed from surface waters of the bay by scavenging with biodetritus during periods of high primary productivity bottomwater and sediment redox conditions determine whether this particle bound uranium is buried or released to overlying water particulate uranium is released to bottomwaters and porewaters during the degradation of biodetritus and oxidation of authigenic uranium low oxygen in bottomwaters in the summer results in minimal exchange of uranium between the sediments and bottomwater due to the stability of reduced u iv high bottomwater oxygen concentrations associated with bay turnover in the fall results in release of authigenic uranium by oxidation to the soluble vi form enrichment of uranium in fall bottomwater suggests that authigenic uranium is very labile when exposed to oxic environmental conditions this process is enhanced by physical mixing when anoxic sediments are resuspended into the oxic bottomwaters

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

geodetic measurement of the local elastic response to the changing mass of water in lago laja chile abstract a geodetic station antc built in bedrock in southern chile is undergoing non steady vertical motion within a range of nearly 50 mm these fluctuations are dominated by the earth s local elastic response to the changing weight of water in a reservoir located about 20 km away there is also an annual periodic component of motion that is attributed to global and regional patterns of loading as well as a steady tectonic signal the local loading response constrains the average elastic structure of the area and implies a stiffness that falls near the lower end of the range observed in rock samples