origins and paleoceanographic significance of laminated muds from the ulleung basin east sea sea of japan abstract a detailed facies analysis of long piston core sediments from the ulleung basin reveals four mud facies laminated mud crudely laminated mud bioturbated mud and homogenous mud the laminated and homogeneous muds were most likely deposited from turbidity currents whereas the bioturbated and crudely laminated muds were formed by hemipelagic pelagic sedimentation under well oxygenated and poorly oxygenated bottom water conditions respectively a detailed analysis of vertical distribution of the mud facies together with a chronostratigraphic framework derived from correlative tephra layers with known eruption ages reveals paleoenvironmental changes during the late quaternary during the period between 49 and 23 ka eustatic lowering of sea level facilitated frequent slope failure resulting in repeated deposition of fine grained turbidites on the basin floor normal hemipelagic sediments were intensively bioturbated under well oxygenated bottom water conditions during the period between 23 and 13 to 11 ka deposition from turbidity currents continued but hemipelagic sediments were non bioturbated under poorly oxygenated bottom water conditions the bottom water deoxygenation is attributed to further lowering of sea level during the last glacial period and consequent intensified stratification in the water column by freshwater supply to the nearly isolated sea primary laminae preserved in the crudely laminated mud generally exhibit low compositional bimodality in backscattered electron images which suggests low surface primary productivity and presence of superficial micro bioturbation after rapid rise of sea level at 13 to 11 ka the slopes were stabilized and pelagic sedimentation has prevailed under well oxygenated bottom water conditions

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

characteristics of silty laminae in zhangjiatan shale of southeastern ordos basin china implications for shale gas formation shale oil and gas have been discovered in the lacustrine organic rich zhangjiatan shale of the upper triassic yanchang formation ordos basin china core observations indicate abundant silty laminae in the producing shales this study documents the stratigraphic distribution of silty laminae and their relationship with interlaminated clay laminae the type structure and characteristics of pores and mineral composition of silty laminae were observed and analyzed through thin section and scanning electron microscopy x ray diffraction low pressure formula 1 and formula 2 adsorption mercury porosimetry and helium pycnometry results from silty laminae are compared with those of clayey laminae the frequency and thickness of silty laminae vary over a wide range the thickness ranges from 0 2 to 4 mm and is 1 5 mm on average the frequency ranges from 4 to 32 laminae m and is 23 laminae m on average the thickness percentage of silty laminae in the measured segments ranges from 6 to 17 silty laminae consist of quartz feldspar mixed layer montmorillonite and chlorite in comparison to clayey laminae non clay detrital grains are larger quartz and feldspar are more common and clay minerals are less abundant pores in silty laminae are primary interparticle dissolutional intercrystalline and microfracture types mesopores 2 50 nm in diameter and macropores 50 nm 1 m are common whereas micropores formula 3 are rare the distribution of pore diameters is multimodal however microscopic pores with a diameter commonly smaller than 100 nm are common in clayey laminae thus pore volume and surface area of micropores in silty laminae are less than those in the adjacent clayey laminae and vice versa for meso and macropores the porosity of shales increases with the proportion of silty laminae in the shales the silty laminae provide the storage space and flow conduit for oil and gas and they play a significant role in the migration accumulation occurrence and amount of gas in the shales 1 embed mml math 1 gif 2 embed mml math 2 gif 3 embed mml math 3 gif

nannofacies analysis as a tool to reconstruct paleoenvironmental changes during the early toarcian anoxic event the black shales of lower toarcian schistes carton in france jet rock in england posidonia shale in germany are sediments formed by fine alternations of millimetric to sub millimetric clear and dark laminae a study of polished core surfaces dotternhausen core sw germany was carried out in sem in order to characterize the micro fabrics of different laminae and their content in nannofossils two main intervals were recognized where fabrics and nannofossil content are significantly different in the clay rich interval characterized by high wt toc and a large negative carbon isotope excursion both in carbonates and organic matter the dominant micro fabrics are well foliated or lumpy giving evidence of the absence or reduction of benthic life nannofossils are scarce and only concentrated in discrete laminae separated by large abiotic intervals assemblages are indicative of a deep nutricline but sporadic nutrient inputs occurred as demonstrated by fluctuation in abundance of specimens of the biscutaceae nutrients were probably delivered to the german basin via riverine influx different sized framboids of pyrite were recognized in this interval the smallest ones 2 m being probably precipitated in an anoxic and sulphidic water column the clay rich interval was likely deposited during low sea level in a restricted basin these conditions were followed by a sea level rise and better water mass circulation within the german basin sedimentation records an increase in carbonate deposition organic matter content decreased and carbon isotopes came back to pre excursion values micro fabrics became less markedly laminated pyrite framboids nearly disappeared and rich and diversified nannofossil assemblages are recorded sea water conditions were probably highly fluctuating as indicated by alternation of intervals dominated in turn by schizosphaerella spp flourishing under generally oligotrophic conditions where nutrients were temporarily available in surface waters due to storms and by crepidolithus spp a deep dweller the results of this work fit well with a silled basin model

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

black shale deposition and faunal overturn in the devonian appalachian basin clastic starvation seasonal water column mixing and efficient biolimiting nutrient recycling integrated geochemical data suggest that black shale deposition in the devonian geneseo formation of western new york was initiated by the coincidence of siliciclastic starvation and the intensification of seasonal water column stratification and mixing once established however black shale deposition was maintained through efficient recycling of biolimiting nutrients which enhanced primary productivity recycling efficiency was achieved through a positive feedback loop of oscillating benthic redox conditions that enhanced n and p regeneration from sediments sustained high primary productivity by returning nutrients to the photic zone during mixing and ensured a downward flux of organic matter that drove or enhanced the episodic development of benthic anoxia during stratification this feedback was ultimately disrupted by rising siliciclastic influx which diluted organic matter and restored benthic redox stability the abrupt overturn of diverse long standing appalachian basin marine communities may have been the result of trophic resource destabilization during geneseo deposition

holocene precipitation changes in the maya forest yucatan peninsula mexico abstract holocene fossil pollen samples n 38 from lake silvituc in mexico were analyzed with the analog technique using modern pollen samples n 98 of the yucatan peninsula mexico calculated dissimilarity indices allow us to reconstruct the vegetation and to develop a precipitation record for the last 7900 years the middle holocene shows a gradual increase of precipitation and a marked drop in reconstructed precipitation around 4200 bce during the late holocene two phases were identified phase i 2500 bce 1 ce shows the greatest increase in precipitation with four peaks around 1200 bce 650 bce 200 bce and 1 ce also a period of increased precipitation resulted for the period between 200 and 500 bce periods of reduced precipitation were detected at 900 1100 bce 500 600 bce and 100 190 bce phase ii 1 2000 ce encompasses several strong dry events during the following periods 150 300 ce 750 900 ce 1050 1180 ce and 1530 1580 ce a strong reduction of 32 in precipitation in the late preclassic period 100 300 ce was detected non analogs of phase ii are associated with periods of reduced precipitation and fall into time periods of extended droughts related to the maya late classic and the little ice age a limiting factor on the use of analogs for tropical forests is that a combination of different analogs for the same fossil pollen signal exists interpretation under these circumstances requires good knowledge of the ecology of the taxa and a priori characterization of the modern samples

geochemical characteristics in the longmaxi formation early silurian of south china implications for organic matter accumulation abstract the organic rich early silurian sediments longmaxi formation on the yangtze platform are considered to be one of the main source rocks in south china in order to investigate the mechanism of organic accumulation multiple geochemical proxies including redox parameters s c and trace element ratios productivity indices p and ba contents and clastic influx indicator ti al ratios are presented here from the hehua section yichang hubei province the longmaxi sediments have high toc contents 3 00 10 85 avg 5 63 low pyrite sulfur contents 0 42 1 14 avg 0 59 high p 0 02 0 44 avg 0 12 and ba contents 576 65 2542 43 ppm avg 1592 17 ppm calculated s c th u ni co v cr and v v ni ratios are 0 05 0 24 avg 0 12 0 23 9 86 avg 2 30 2 65 46 24 avg 15 46 0 27 14 42 avg 3 75 and 0 36 0 96 avg 0 75 respectively s c and trace element ratios together with pyrite morphology suggest dysoxic anoxic conditions prevailed during deposition of the longmaxi intervals which was mainly caused by a worldwide marine transgression after the melting of gondwana glaciation productivity proxies indicate that the organic rich longmaxi sediments were deposited in moderate to high primary productivity water columns the consistent ti al ratios suggest a rather homogeneous nature for the detrital supply geochemical data provide a good constraint on the accumulation of organic matter and relevant oceanic environment anoxic conditions together with relatively high productivity were likely responsible for the accumulation of organic rich sediments during the longmaxi interval

palaeoenvironmental and palaeoceanographic controls on black laminated mudrock deposition example from devonian carboniferous strata alberta canada abstract sedimentological palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling in tandem with an expanded and intensified oxygen minimum zone promoted deposition of upper famennian to lower tournaisian laminated organic rich mud rocks of the exshaw formation on the alberta cratonic platform exshaw mud rocks represent the culmination of an upper devonian transgression that commenced with deposition of open marine carbonates of the big valley formation the transgression was abruptly halted at the devonian carboniferous boundary by a rapid eustatic sea level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the exshaw formation the siltstones grade into laminated organic lean mud rocks to the north in more distal offshore shelf settings these mudrocks reflect a period of low primary production but continued anoxia of bottom waters continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward located physical barrier following this event was a relative sea level rise that led to deposition of black laminated mudrocks of the banff formation

mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet 1 in the shiquanhe area of far western tibet mid cretaceous strata lie unconformable on ophiolitic melange and jurassic flysch associated with the bangong nujiang suture zone on the basis of our mapping and geochronologic studies we suggest that these cretaceous strata were shortened by 57 over a north south distance of 50 km during late cretaceous early tertiary time the late cretaceous narangjiapo thrust placed permian strata 20 km over ophiolitic melange and cretaceous strata north of the narangjiapo thrust 40 km of shortening was accommodated by the late cretaceous early tertiary south directed jaggang thrust system that involves jurassic flysch and cretaceous strata and roots into a decollement within ophiolitic melange the most recent shortening was accommodated to the south of the narangjiapo thrust along the north dipping shiquanhe thrust the shiquanhe thrust cuts flat lying 22 6 0 3 ma volcanic rocks and underlying folded tertiary nonmarine strata in its footwall and was likely active during slip along the oligocene gangdese thrust system of southern tibet ophiolitic melange and structurally overlying jurassic flysch near shiquanhe are interpreted to represent remnants of a subduction accretion complex and forearc basin respectively that were obducted southward onto the margin of the lhasa terrane during late jurassic early cretaceous closure of the bangong nujiang ocean subsequent imbrication of the obducted sheet could have produced the two east west trending belts of ophiolitic melanges separated by 100 km in western tibet late cretaceous early tertiary thin skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of lhasa terrane rocks beneath the obducted ophiolitic melange and the qiangtang terrane to the north

detrital quartz and quartz cement in upper triassic reservoir sandstones of the sichuan basin characteristics and mechanisms of formation based on cathodoluminescence and electron backscatter diffraction analysis abstract the relationship between detrital quartz grains and silica cement is significant because cement is often a major cause of porosity reduction in oil and gas reservoirs thus degrading hydrocarbon reservoir quality on the other hand the attributes of grain surfaces may inhibit cementation thus preserving porosity in the reservoirs in this study we focus on the microstructures in quartz grains and secondary overgrowths quartz cement in the heavily cemented sandstones from uplifted upper triassic siliciclastic rocks in the southern sichuan basin china electron backscatter diffraction ebsd optical and cathodoluminescence cl imaging methods have been used to address the microstructural and crystallographic attributes of the detrital grains and their overgrowths this study confirms that 1 the overgrowth zones of quartz are clearly visible in optical and cl images 2 all silica overgrowths are perfectly crystalline quartz 3 quartz cements have a syntaxial relationship with the host detrital grain indicating crystallographic continuity between the detrital quartz and its overgrowth and 4 crystallographic maps confirm that dauphine twins commonly occur both in the detrital grains and in the quartz cement most dauphine twins are developed at grain grain contacts including the margins of detrital grains where they are in contact with quartz cement some twins are limited to a single grain whereas others cross grain cement boundaries based on these twin distributions we can distinguish inherited twins from twins that formed during after burial compaction this study documents the grain deformation structures induced by sedimentary compaction and these structures can be accurately illustrated by ebsd data

palaeoceanographic controls on geochemical characteristics of organic rich exshaw mudrocks role of enhanced primary production organic rich source rocks have generally been attributed to enhanced preservation of organic matter under anoxic bottom waters here geochemical analysis of kerogen and whole rock samples of organic rich lithofacies b1 and organic lean lithofacies b2 laminated mudrocks of the devonian carboniferous exshaw formation alberta highlight the importance of primary production in governing the quantity and quality of organic matter lower si al k al ti al and quartz clay ratios in lithofacies b2 similar maceral types and the laminated fabric of the two lithofacies indicate that the quality and quantity of organic matter are not related to grain size redox or organic matter source changes high total organic carbon toc and hydrogen index hi low oxidation index ox i ratio of oxygen functional groups to aliphatic groups derived by ftir lighter 15ntot and heavier 13corg isotopes indicate that kerogen of lithofacies b1 accumulated during periods of high organic carbon production and delivery of relatively fresh labile well preserved organic matter to the sea floor in contrast low toc hi high ox i heavier 15ntot and lighter 13corg isotopes indicate low primary productivity and delivery high recycling and poor preservation of organic matter during accumulation of lithofacies b2

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

palaeo flux records from electron microscope studies of holocene laminated sediments saanich inlet british columbia holocene varved sediments recovered from saanich inlet odp leg 169s have been analysed using high resolution scanning electron microscope techniques the individual centimetre scale varves form couplets comprising diatom ooze diatomaceous mud deposited during spring to autumn and silty clay deposited during winter each individual varve may contain up to 19 laminae recording sub seasonal to seasonal scale processes these intra annual laminae contain a range of components including pelagic faecal pellets and aggregates of diatomaceous material the combination of these individual components in varying proportions with a heterogeneous sediment leads to a range of laminae fabrics these include intact monospecific skeletonema costatum and thalassiosira pacifica diatom oozes and highly fragmented aggregate and faecal pellet dominated diatom oozes which are typically chaetoceros spp dominated additional laminae fabrics include diatomaceous mud stringer type diatomaceous mud which contains discrete diatom aggregates homogeneous and pelleted silty clay the varved diatom succession typically commences in early spring with thalassiosira spp chaetoceros spp followed by chaetoceros spp in late spring during late spring early summer blooms of s costatum may be recorded and summer to autumn production is characterised by one to several chaetoceros spp dominated blooms inter annual variability in diatom flux typically comprises the presence absence of thalassiosira spp and s costatum in addition resting spores of chaetoceros spp thalassiosira nordenskioeldii and leptocylindricus danicus are intermittently recorded there is a major change in varve thickness from thinner varves prior to approximately 2100 yr bp to thicker varves after this date which is attributed to increased terrigenous input throughout the varve the identification of laminae fabrics diatom successions and a unique massive interval has enabled an inter site correlation between sites 1033b and 1034b

laminae characteristics and influence on shale gas reservoir quality of lower silurian longmaxi formation in the jiaoshiba area of the sichuan basin china abstract widely developed in shale strata laminae are the most typical shale sedimentary structure to investigate their influence on shale gas reservoir quality we conducted complementary studies by integrating microscopic observations geochemical analyses field emission scanning electron microscopy fe sem imaging and mercury intrusion capillary pressure micp techniques the microscopic observation of thin sections enabled us to detect the laminae characteristics including the density and maximum thickness of individual lamina and three types and stages of lamina development were identified the total organic carbon toc content mineral composition natural fracture pore type pore size distribution porosity permeability and tortuosity were investigated in these different laminae types using fe sem micp and geochemical analysis combining the laminae characteristics and pore structure we concluded that the organic pores and total pore area are mainly affected by the toc content whereas the development of the laminae controls the inorganic macropore scale and affects the pore size distribution in addition we found that the excessive development of shale laminae is not conducive to organic matter accumulation because of the change in redox condition and because it has an adverse impact on the formation of complex artificial fractures during hydraulic fracturing

the effect of interbedding on shale reservoir properties north sea oil is overwhelmingly generated in shales of the upper jurassic basal cretaceous kimmeridge clay formation once generated the oil is expelled and ultimately migrates to accumulate in sandstone or carbonate reservoirs the source rock shales however still contain the portion of the oil that was not expelled as a consequence such shales and juxtaposed non source lithofacies can form the targets for the exploration of unconventional oil in this paper we examine part of the kimmeridge clay formation as a hybrid shale resource system within which hot shale and organic lean sandstone and siltstone intervals are intimately interbedded this hybrid system can contain a greater volume of oil because of the increased storage capacity due to larger matrix porosities of the sand silt interbeds together with a lower adsorptive affinity in the interbedded sandstone the relationship between the estimated volume percentages of sand and mudstone and free oil determined from rock eval s1 yields is used to place limits on the drainage of oil from source mudstone to reservoir sand at the decimeter scale these data are used to determine oil saturations in interbedded sand mudstone sequences at peak oil maturity higher values of free hydrocarbon as evidenced by the s1 value in mudstone suggest that more oil is being retained in the mudstone while higher s1 values in the interbedded sands suggest the oil is being drained to saturate the larger pore spaces high silica content in the interbeds confirms the brittleness in this mudstone sandstone lithofacies an important factor to be considered for fracture stimulation to successfully work in a hybrid system the key points of this hybrid unconventional system are the thickness storage capacity and the possibility to capture a portion of the expelled as well as retained oil

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

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

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

the characteristics and source of laminated mud at lake barrine northeast australia abstract in a small 1 km 2 crater lake in the australian upland tropics 17 15 s 145 38 e 721 m a s l laminated mud has accumulated throughout the past 5 ka it is limited to a central region below 50 67 m of water where it is protected by a monimolimnion the contents of the laminae e g total lake products organic detritus diatoms pollen grains vivianite crystals distinguish two contrasting types namely detritus rich and detritus poor judged against radiocarbon dates over long sequences these couplets are not annual gravimetric mineralogical and chemical observations on the mud and on suspended organic and inorganic matter caught through several periods indicate some diagenetic changes across the mud water interface diatom analyses do not assist in relating mud type to source or period of origin the most likely mechanism of lamination is that continuous deposition of clay with small and varied detrital accompaniment is periodically enhanced by greater detrital input this occurs in some but not all periods of winter isothermy when ground temperatures fall to zero and below on several consecutive nights this leads to the stirring of sediments in water shallower than 50 m and their relocation in the deeper meromictic zone fine variations in e g diatom content partly independent of lamination type probably contain a wealth of detail about the lake s environmental history

sequence stratigraphy of the kingak shale jurassic lower cretaceous national petroleum reserve in alaska beaufortian strata jurassic lower cretaceous in the national petroleum reserve in alaska npra are a focus of exploration since the 1994 discovery of the nearby alpine oil field 400 mmbo these strata include the kingak shale a succession of depositional sequences influenced by rift opening of the arctic ocean basin interpretation of sequence stratigraphy and depositional facies from a regional two dimensional seismic grid and well data allows the definition of four sequence sets that each displays unique stratal geometries and thickness trends across npra a lower to middle jurassic sequence set includes numerous transgressive regressive sequences that collectively built a clastic shelf in north central npra along the south facing lobate shelf margin condensed shales in transgressive systems tracts downlap and coalesce into a basinal condensed section that is likely an important hydrocarbon source rock an oxfordian kimmeridgian sequence set deposited during pulses of uplift on the barrow arch includes multiple transgressive regressive sequences that locally contain well winnowed shoreface sandstones at the base of transgressive systems tracts these shoreface sandstones and overlying shales deposited during maximum flooding form stratigraphic traps that are the main objective of exploration in the alpine play in npra a valanginian sequence set includes at least two transgressive regressive sequences that display relatively distal characteristics suggesting high relative sea level an important exception is the presence of a basal transgressive systems tract that locally contains shoreface sandstones of reservoir quality a hauterivian sequence set includes two transgressive regressive sequences that constitute a shelf margin wedge developed as the result of tectonic uplift along the barrow arch during rift opening of the arctic ocean basin this sequence set displays stratal geometries suggesting incision and synsedimentary collapse of the shelf margin

significance of lamination in toarcian lower jurassic shales from yorkshire great britain abstract lamination in shales is an important feature useful in providing clues to ancient sedimentary environments and processes variations in types of lamination in toarcian lower jurassic shales of yorkshire great britain are related to changes in sedimentary processes x radiography petrography and scanning electron microscopy techniques reveal three lamination types in the dark grey grey shales and black jet rock and bituminous shales jurassic shales fine lamination is produced in deeper more offshore anaerobic conditions in which suspension settling dominates thick lamination indicates the influence of bottom flowing currents in shallow water wavy lamination is produced by benthic microbial mats the toarcian transgressive shale sequence shows a progressive change from thick to wavy to fine lamination relating to progressive changes in the sedimentary processes operating in the environment the examples of various unique macro and microfabrics associated with lamination type offer a useful frame of reference for interpretation of conditions of shale formation

predominance of stratified anoxic yangtze sea interrupted by short term oxygenation during the ordo silurian transition abstract the ordo silurian transition was a critical interval in geological history during which profound biotic climatic and oceanic changes occurred in order to explore the oceanic palaeoredox changes multiple geochemical proxies including ratios of s c fehr fet fep fehr and dop values are presented here from three sections wangjiawan western hubei sanjiaguan northern hunan and nanbazi northern guizhou across the ordo silurian boundary on the yangtze platform these palaeoredox data indicate a predominance of stratified anoxic ferruginous ocean on the yangtze block during this transition which was interrupted by a brief episode of oceanic oxygenation in the early hirnantian this oxygenation temporally coinciding with the end ordovician glaciation and global glacio eustatic sea level fall likely resulted from enhanced circulation of polar cold dense oxygen rich water onto the low latitude shelf the prior and subsequent longer term episodes of anoxic ocean particularly the later one which started in the late hirnantian occurred in parallel with the rapid climatic warming and sea level rise which could have slowed down oceanic circulation thereby enhancing oceanic stratification anoxia and organic preservation oceanic redox changes together with rapid climatic and sea level fluctuations were likely responsible for the stepwise massive demise of the ordo silurian biotic crisis

lamina scale analysis of sedimentary components in cretaceous black shales by chemical compositional mapping implications for paleoenvironmental changes during the oceanic anoxic events abstract relative abundances and distribution patterns of mineral components in finely laminated livello bonarelli lb black shale from the cenomanian turonian boundary cretaceous were investigated by 10 m resolution compositional mapping using an electron probe microanalyzer sedimentary components such as biogenic silica si bio calcium phosphate calcium carbonate and pyrite were reconstructed by image processing of the compositional maps total organic carbon c org content was also determined at a sampling interval of 1 5 mm the depth profiles of these sedimentary components covering 60 of the total 104 cm lb sequence indicate the highly variable nature of their deposition especially the c org contents vary widely ranging from org are clearly discernible in the lb and correspond to dark colored intervals repeated occurrences of c org rich and si bio rich intervals are one of the most prominent features in the lb these features could be explained partly by dilution of c org by si bio but largely by the presence of two distinct paleoenvironmental settings one involves predominant deposition of organic matter and the other is dominated by si bio deposition the thickness of individual intervals varies widely mostly ranging from 1 5 to 35 mm representing oceanic changes on the order of 10 3 10 4 years furthermore we found 100 m scale laminations of fine grained pyrite aluminosilicate and calcium carbonate which when superimposed on the alternation of c org rich and si bio rich intervals suggests 10 2 year scale fluctuations in oceanic environments

parallel lamination formed by high density turbidity currents experiments were conducted in order to investigate processes of sediment transport and deposition from sustained turbidity currents with initial volume fraction sediment concentration of 0 20 0 25 and 0 35 parallel lamination was formed at bed aggradation rates up to 4 mm s 1 and bedload layer sediment concentration up to 0 36 this observation contradicts the generally held assumption that parallel lamination forms only from low density flows and at low bed aggradation rates this misconception illustrates a poor understanding of threshold values of grain support mechanisms in the bedload layer the present results bring new insight into understanding sediment transport in the deep sea and interpreting the sedimentary record

porosity characteristics of the devonian horn river shale canada insights from lithofacies classification and shale composition abstract this study evaluates pore systems of the horn river shale in western canada sedimentary basin from lithofacies classification of core samples to micro scale pore structure investigation samples from the middle and upper devonian horn river shale sequence were examined by core description porosity measurement sem and tem imaging of ion milled samples and nitrogen adsorption analysis in order to develop a better understanding of the controls of organic and inorganic rock constituents on porosity development and pore microstructure five primary shale lithofacies were identified by hand core and thin section analyses massive mudstones massive mudstones with pyrite streaks laminated mudstones bioturbated mudstones and carbonates porosity ranges from 0 62 to 12 04 and shows wide variation between different lithofacies massive mudstones and pyritic mudstones with high total organic carbon toc content have the highest porosity whereas bioturbated mudstones and carbonates with low toc content have the lowest porosity sem and tem images suggest that several kinds of sites for porosity development are present including organic matter pyrite framboids clay platelets quartz rims carbonate grains and microfractures a general positive relationship between toc and porosity indicates that a large proportion of pores are developed in organic matter results from the nitrogen adsorption analysis suggest that samples with more organic matter tend to develop smaller pores thus while porosity development is a combined function of organic matter mineral components fabric and fractures it is most affected by organic matter concentration the muskwa formation and the evie member have more gas storage capacity as they primarily consist of massive mudstones and pyrite rich mudstones showing the best porosity the otter park member has lower porosity which may relate to the fact that its lithofacies mainly consists of laminated mudstones and bioturbated mudstones

geochemical characteristics redox conditions and organic matter accumulation of marine oil shale from the changliang mountain area northern tibet china abstract the organic rich changliang mountain oil shale located in the north qiangtang depression northern tibet is considered to be excellent mineral resource in china the changliang mountain oil shale reported here was deposited in a tidal flat lagoon environment and is characterized by black thin layered oil shales intercalated with dark gray marls here we present geochemical data from the changliang mountain oil shale profile in order to investigate the mechanism of organic matter om accumulation and to establish the formation model for the marine oil shale deposition total organic carbon toc values range from 2 96 to 23 47 in the oil shale samples while the marl samples contains low toc contents ranging from 0 06 to 0 21 in the organic rich oil shale sediments many redox indicators including mo al ratios v cr ratios th u ratios ni co ratios and the relationship of mo to toc suggest a deposition under dysoxic to anoxic environments subsequently the bottom water evolved into an oxic water body when the organic poor marls were deposited however the negative and or weak relationship between toc and productivity indices p ti and ba al indicates that om accumulation was not controlled mainly by primary productivity but dysoxic anoxic bottom water environment a stratified water column may be initiated by the supply of fresh water from the continent nearby combining with warm and humid climate which is beneficial to the reproduction of marine organisms the death and bury of these organisms could lead to the formation of dysoxic anoxic bottom waters and enhance the preservation of om in this study a preservation model of the changliang mountain oil shale was established the model implies that excellent preservation is the major controlling factor for om enrichment in the oil shale layer in addition factors such as mixed deposition with clay minerals and detrital matter input cannot be ignored for their influence on om enrichment