living on the edge evaluating the impact of stress factors on animal sediment interactions in subenvironments of a shelf margin delta the mayaro formation trinidad abstract integrating sedimentological and ichnological characteristics of the gelasian mayaro formation along the se coast of trinidad allows recognition of a river dominated and wave influenced shelf edge deltaic succession of the paleo orinoco river developed under strong slope instability four main sedimentary settings and twelve subenvironments developed on and beyond the outer shelf i e at the shelf margin have been identified extreme paleoenvironmental conditions make the succession rarely and sporadically colonized ichnologic evidence suggests that shelf edge deltas are among the most stressful marine environments due to a combination of physicochemical factors in response to the intrinsic sedimentary processes and the relative hierarchy of their influences specific to every subenvironment within any particular subenvironment the relative dominance of the fluvial feeder system the action of waves and rare influence of tides and slope instability determine the combinations and ranking of stress factors river dominated shelf edge delta subenvironments demonstrate the extreme influence of stress factors related to channel activity e g salinity changes high sedimentation and erosion rates flocculation of mud seasonal variations of fluvial flux whereas subenvironments dominated by waves storms and oceanic swells away from the axial feeder s are mostly influenced by barform morphodynamics and its effects on local physiography the paleo orinoco delta is represented not only by the delta lobe s developed at the shelf edge but by delta lobe s formed on the outer shelf as well outer shelf deltaic subenvironments manifest typical ichno sedimentological signatures of a normal wave influenced in this case inner shelf delta being susceptible to extensive gravitational instabilities the delta system suffered from canyonization and smaller gullying and subsequent filling n b hereafter we use the term canyon for both canyons and smaller gullies the shelf edge delta system was also associated with shelf attached mass transport systems such depositional subenvironments dominated by slope instability and sediment gravity flows appear to be the most unconducive for benthic colonization resulting in almost complete absence of bioturbation characterization of the stress factors as the functions of parameters arising from specific sedimentary and or oceanographic processes chemical conditions and preservational constraints specific to each subenvironment leads to the construction of a comprehensive ichnological and depositional analog model for shelf edge deltas in general and for the accommodation driven low latitude shelf edge deltas at an active oblique foreland setting in particular

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

signatures of climate vs sea level change within incised valley fill successions quaternary examples from the texas gulf coast abstract the passive margin texas gulf of mexico coastal plain consists of coalescing late pleistocene to holocene alluvial deltaic plains constructed by a series of medium to large fluvial systems alluvial deltaic plains consist of the pleistocene beaumont formation and post beaumont coastal plain incised valleys a variety of mapping outcrop core and geochronological data from the extrabasinal colorado river and the basin fringe trinity river show that beaumont and post beaumont strata consist of a series of coastal plain incised valley fills that represent 100 kyr climatic and glacio eustatic cycles valley fills contain a complex alluvial architecture falling stage to lowstand systems tracts consist of multiple laterally amalgamated sandy channelbelts that reflect deposition within a valley that was incised below highstand alluvial plains and extended across a subaerially exposed shelf the lower boundary to falling stage and lowstand units comprises a composite valley fill unconformity that is time transgressive in both cross and down valley directions coastal plain incised valleys began to fill with transgression and highstand and landward translation of the shoreline paleosols that define the top of falling stage and lowstand channelbelts were progressively onlapped and buried by heterolithic sandy channelbelt sandy and silty crevasse channel and splay and muddy floodbasin strata transgressive to highstand facies scale architecture reflects changes through time in dominant styles of avulsion and follows a predictable succession through different stages of valley filling complete valley filling promoted avulsion and the large scale relocation of valley axes before the next sea level fall such that successive 100 kyr valley fills show a distributary pattern basic elements within coastal plain valleys can be correlated with the record offshore where cross shelf valleys have been described from seismic data falling stage to lowstand channelbelts within coastal plain valleys were feeder systems for shelf phase and shelf margin deltas respectively and demonstrate that falling stage fluvial deposits are important valley fill components signatures of both upstream climate change vs downstream sea level controls are therefore interpreted to be present within incised valley fills signatures of climate change consist of the downstream continuity of major stratigraphic units and component facies which extends from the mixed bedrock alluvial valley of the eroding continental interior to the distal reaches wherever that may be at the time this continuity suggests the development of stratigraphic units and facies is strongly coupled to upstream controls on sediment supply and climate conditions within hinterland source regions signatures of sea level change are critical as well sea level fall below the elevation of highstand depositional shoreline breaks results in channel incision and extension across the newly emergent shelf which in turn results in partitioning of the 100 kyr coastal plain valleys moreover deposits and key surfaces can be traced from continental interiors to the coastal plain but there are downstream changes in geometric relations that correspond to the transition between the mixed bedrock alluvial valley and the coastal plain incised valley channel incision and extension during sea level fall and lowstand with channel shortening and delta backstepping during transgression controls the architecture of coastal plain and cross shelf incised valley fills

extraordinary biomass burning episode and impact winter triggered by the younger dryas cosmic impact 12 800 years ago 2 lake marine and terrestrial sediments abstractpart 1 of this study investigated evidence of biomass burning in global ice records and here we continue to test the hypothesis that an impact event at the younger dryas boundary ydb caused an anomalously intense episode of biomass burning at 12 8 ka on a multicontinental scale north and south america europe and asia quantitative analyses of charcoal and soot records from 152 lakes marine cores and terrestrial sequences reveal a major peak in biomass burning at the younger dryas yd onset that appears to be the highest during the latest quaternary for the cretaceous tertiary boundary k pg impact event concentrations of soot were previously utilized to estimate the global amount of biomass burned and similar measurements suggest that wildfires at the yd onset rapidly consumed 10 million km2 of earth s surface or 9 of earth s biomass considerably more than for the k pg impact bayesian analyses and age regressions demonstrate that ages for ydb peaks in charcoal and soot across

small scale stratigraphy in a large ramp delta recent and holocene sedimentation in the volga delta caspian sea the volga delta differs from all other major deltas in the world by its extremely gentle onshore and offshore gradient f5 cm km and by being affected by the rapid sea level changes of the caspian sea at rates up to a hundred times the global sealevel rise this paper reports 1 the morphological and facies development of part of the lower delta during the last full sealevel cycle between 1929 and 1995 as monitored using remote sensing and field mapping and 2 the holocene development of the delta from outcrop data and augered transects during a sea level fall of 3 m between 1929 and 1977 rapid progradation of levees composed of fine sand took place along over 800 distributary channels along the delta front smaller distributaries became filled with clay and organics during the 3 m sea level rise from 1977 to 1995 aggradation occurred leading to deposition of silt and clay on the levees and minor filling of the flood basins sedimentation rates as established with 137 cs dating are up to 2 5 cm year total thickness of holocene deposits in the lower delta plain is 4 10 m

geological controls on matrix permeability of devonian gas shales in the horn river and liard basins northeastern british columbia canada abstract controls of matrix permeability are investigated for devonian gas shales from the horn river and liard basins in northeastern british columbia canada mineralogy is varied with high carbonate high quartz and moderate quartz carbonate and clay rich strata quartz content varies between 2 and 73 carbonate varies between 1 and 93 and clay varies between 3 and 33 the toc content ranges between 0 3 and 6 wt and porosity varies between about 1 and 7 for horn river basin samples quartz is mainly biogenic in origin derived from radiolarians toc content increases with the quartz content suggesting the toc and quartz both are derived from siliceous phytoplankton a positive relationship between porosity and quartz content is due to the positive relationship between quartz and toc matrix permeability parallel to bedding varies between 7 5e 02 and 7 1e 07 md at an effective stress of 15 mpa variation in permeability is due to a complex combination of factors that includes origin and distribution of minerals pore size distribution and fabric mercury intrusion capillary curves indicate that the higher matrix permeability values 2e 03 md occurs in samples that contain interconnected pore apertures greater than 16 m even when these samples may contain less macropores than low permeability samples the fabric of high permeability samples can be either isotropic or anisotropic however permeability of anisotropic samples is more sensitive to changes in effective stress than isotropic samples more highly anisotropic samples contain moderate amounts of quartz carbonate and in some clay high permeability samples that contain a more balanced ratio between micro meso and macroporosity would not only have faster flow rates but also greater access to sorbed gas within the microporosity compared to samples that lack mesopores several muskwa samples compared to evie and besa river samples contain higher quartz moderate clay and high toc content coupled with high permeability less sensitivity to effective stress and balanced ratios between micro meso and macroporosity would be a lower exploration risk due a greater propensity to fracture the ability to produce and store hydrocarbons due to higher toc contents and greater communication between macropores and micropores in the organic and clay fractions

radiocarbon simulation fails to support the temporal synchroneity requirement of the younger dryas impact hypothesis fine scale temporal processes such as the synchronous deposition of organic materials can be challenging to identify using 14 c datasets while some events such as volcanic eruptions leave clear evidence for synchronous deposition synchroneity is more difficult to establish for other types of events this has been a source of controversy regarding 14 c dates associated with a hypothesized extraterrestrial impact at the younger dryas boundary ydb to address this controversy we first aggregate 14 c measurements from northern hemisphere ydb sites we also aggregate 14 c measurements associated with a known synchronous event the laacher see volcanic eruption we then use a monte carlo simulation to evaluate the magnitude of variability expected in a 14 c dataset associated with a synchronous event the simulation accounts for measurement error calibration uncertainty old wood effects and laboratory measurement biases the laacher see 14 c dataset is consistent with expectations of synchroneity generated by the simulation however the ydb 14 c dataset is inconsistent with the simulated expectations for synchroneity these results suggest that a central requirement of the younger dryas impact hypothesis synchronous global deposition of a ydb layer is extremely unlikely calling into question the younger dryas impact hypothesis more generally

flexural cantilever models of extensional subsidence in the munster basin sw ireland and old red sandstone fluvial dispersal systems

remigration and leakage from continuous shale reservoirs insights from the sichuan basin and its periphery china shale gas in the sichuan basin and its periphery potentially plays an important role in the world shale gas industry an understanding of remigration and leakage from continuous shale reservoirs is very important for shale gas exploration especially in the sichuan basin and its periphery the shale gas accumulation models that relate to remigration and leakage were developed within the wufeng and longmaxi black shales in the jiaoshiba and the youyang blocks first a tectono sedimentary history of the wufeng and longmaxi black shales in the sichuan basin and its periphery was developed based on the published literature the history exhibits a continuous distribution of high quality wufeng and longmaxi black shale which is the foundation of the shale gas formation second the shale gas remigration accumulation model in the anticlines was clarified by using data collected from the shale gas fields in jiaoshiba block the shale gas model for the jiaoshiba block was developed on the basis of a continuous shale reservoir distribution differentiated structural deformation and a gas self sealed system third the shale gas fault failure leakage model in the fault blocks and the erosion model in the residual areas were revealed based on the shale reservoir and shale gas content heterogeneity in the youyang block these two models were validated by available data including 13 two dimensional seismic lines and 2 shale gas exploration vertical wells in the youyang block shale gas areas with high gas resource and gas production rates in the anticlines were defined by the remigration accumulation model the fault failure leakage model was used to find shale gas with limited commercial potential whereas commercial shale gas was largely lacking according to the erosion residual model the study on remigration and leakage from continuous shale reservoirs in the sichuan basin and its periphery can be used to better understand and improve the exploration efforts based on resource preservation

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

hydrocarbon generation and shale gas accumulation in the longmaxi formation southern sichuan basin china abstract the gas bearing longmaxi formation fm records a complex tectonic history in which variations in structural and burial history directly effect the hydrocarbon maturation process through analysis of the tectonic burial history hydrocarbon maturity and easy r o numerical simulations we examine three areas representing the full spectrum of geological variability in the southern sichuan basin the changning area the luzhou area and the zigong area zishen well 1 following deposition of the longmaxi fm all three areas underwent five major tectonic events of subsidence and uplift showing an overall long term oscillation of the basin the longmaxi fm has undergone three major heating stages caledonian hercynian orogenesis time the high geothermal gradient field of hercynian and indosinian time approximately 200 300 ma and the yanshanian himalayan stage the high geothermal gradient stage is associated with extensive emeishan flood basalts or concealed basalts which could have played an important role in hydrocarbon maturation the maturation process can be divided into five stages caledonian hercyninan indosinian yanshanian and himalayan in the yanshan period the highest heating temperature of organic matter exceeded 200 c and the maturation level was more than 2 4 producing large amounts of natural gas which is the main accumulation period of shale gas in the longmaxi fm due to the large amount of hydrocarbon generated a large number of micropores were formed from organic matter evolution especially nanoscale pores during the middle diagenesis stage the longmaxi fm shale gas accumulation process is divided into four periods the source reservoir cap deposition period the initial accumulation period the main accumulation period and the adjustment period in the main accumulation period pyrolysis gas was dominant which was stored within the pores diagenetic fractures and structural fractures in adsorbed and free state ways forming the basic pattern of the longmaxi fm shale gas the current burial depth and structural stability of the longmaxi fm are critical to gas reservoir protection

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

reconstruction of paleoceanic redox conditions of the lower cambrian niutitang shales in northern guizhou upper yangtze region abstract the paleoceanic redox conditions and the vertical and spatial distribution of organic matter rich lower cambrian niutitang shales are varied in the upper yangtze region china an integrated approach including organic geochemistry major and trace elemental geochemistry and x ray diffraction xrd mineralogy was used to characterize changes in redox conditions and to determine key controls on organic matter accumulation during deposition of the lower cambrian niutitang shales a 202 m long cored well located in kaiyang county in northern guizhou china was thoroughly characterized by the integrated approach in this study vertically total organic carbon toc rich siliceous and argillaceous black shales were developed in the lower and middle niutitang formation and toc lean silty shales were found in the upper niutitang formation the toc content in the lower and middle niutitang shales ranges from 0 27 to 6 7 with an average value of 2 1 and it decreases from 0 30 to 0 11 in the upper niutitang formation shales the toc rich siliceous shales in the lower niutitang formation were characterized by high total sulfur content enrichment in redox sensitive trace elements high corg p ratios and high authigenic mo u covariation indicating they were deposited under persistent anoxic conditions most organic rich shales from the middle niutitang formation were deposited under anoxic conditions whereas a few intervals having low toc contents were deposited in a predominantly oxic depositional environment in contrast the upper niutitang formation were deposited under fully oxic conditions a combination of high primary productivity and enhanced organic preservation under euxinic water column conditions is the key control on organic matter accumulation in the lower niutitang formation shales however a coupling of redox depositional environment and terrestrial mineral dilution plays an important role in organic matter accumulation and preservation in the middle niutitang formation similar organic matter abundance distribution and carbon isotope excursion of organic matter in the sediments deposited at different depositional facies on the yangtze platform suggest regional isotopically homogenous organic carbon input due to the widespread transgressive event with deep basinal waters being transported into the shallow shelf environments at the base of the lower cambrian as a result 13corg distribution patterns can be used as a stratigraphic correlation marker in the upper yangtze region

geological and geochemical characteristics of marine continental transitional shale from the lower permian taiyuan formation taikang uplift southern north china basin abstract in recent years extensive studies have been conducted on conventional shale gas resources but little work has been performed on the resource potential of marine continental shales this paper takes the lower permian taiyuan shale in the taikang uplift of the southern north china basin as an example to characterize a transitional shale reservoir the results indicate that the taiyuan shale has high toc values averaging 2 67 and contains type iii gas prone organic matter the shale has high ro values averaging 3 44 and tmax ranges from 424 c to 601 c with respect to fracability or brittleness the content of brittle minerals in the taiyuan shale ranges from 21 to 71 averaging 45 55 and the average content of clay minerals is 44 1 based on sem and sem with ar ion milling observation interparticle pores intraparticle pores and microfractures are developed in the taiyuan shale which can provide reservoir space for the accumulation of shale gas organic matter pores rarely appear due to the organic type and high maturity the results of this study can guide the shale gas exploration of taiyuan formation in the taikang uplift of the southern north china basin

gas bearing property of the lower cambrian niutitang formation shale and its influencing factors a case study from the cengong block northern guizhou province south china abstract to gain a better understanding of the gas bearing property of lower cambrian niutitang formation shale and its influencing factors the shale gas bearing conditions gas content and composition in the cengong block were investigated in this work based on wells cy1 tx1 and tm1 the niutitang shale reservoir is characterized by large thickness abundant organic matter with an average total organic carbon content of 4 74 and high quartz content averaging 53 9 therefore it has good shale gas bearing potential the results of water immersion and ignition tests intuitively revealed the existence of shale gas based on the occurrence of continuous dense clusters of bubbles and long flames of 1 2 m the langmuir volumes of shale samples from well tm1 which ranged from 1 70 to 5 53 m3 t were positively associated with toc content and brunauer emmett teller surface area indicating a strong adsorption capacity and significant adsorbed gas potential however large differences were observed among the three wells with regard to gas bearing properties wells cy1 and tx1 had average total gas contents of 1 25 and 0 33 m3 t respectively the gas composition of well tm1 was dominated by nitrogen n2 with contents generally exceeding 95 furthermore the gas from well tx1 was mainly composed of methane with an average content exceeding 80 burial depth and toc and quartz contents had significant control on the vertical distribution of gas content and local tectonic preservation conditions resulted in differences of gas bearing properties among various wells the measured lost and total gas contents all presented positive correlations with toc quartz contents and porosity and were negatively related to clay content the shale formed in deep water shelf environments had better gas bearing properties than that formed in shallow water shelf environments the broad axis of the box syncline in the cengong block is a favorable location for shale gas accumulation and fault development affects the shale gas plane distribution because of the influence of faults the shale of well tm1 had low hydrocarbon content furthermore based on the combined patterns of folds and faults as well as other special specific factors a classification scheme of shale gas accumulation patterns in south china was developed

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

channel fill and sheet flood facies sequences in the ephemeral terminal river gash kassala sudan abstract detailed facies analysis of the river gash fluvial sediments on two dimensional profiles across and along the main channel has revealed a number of facies and two distinct types of sequences channel fill and sheet flood sequences it seems that each sequence type is produced by specific depositional event and both sequences represent two end members for suite of mixed sequences the facies and sequences show rapid lateral variability and they merge and interfinger with each other they also show partial to complete modification due to subsequent floods and stage variation it seems that the thick sediments of the river gash in the kassala area were produced in two phases first by braided channel aggradation and lateral migration second by both channelized and unchannelized sheet flood deposition deposits of these two phases contribute to the sediments of the present day gash fluvial basin in the kassala area the gash sediments show some similarities and differences to those of ephemeral and low sinuosity braided streams the predominance of sheet flood deposits is consistent with the ephemeral flashy high flow regime in the river gash the non conformity of the river gash depositional style with the braided model of fluvial deposition may be due to this semi arid terminal flashy character which has control on the depositional processes and patterns

sedimentation in a discharge dominated fluvial lacustrine system the neogene productive series of the south caspian basin azerbaijan abstract the largely lower pliocene productive series and its regional equivalents contain the major hydrocarbon reservoirs of the south caspian basin examination of outcrops in the apsheron region azerbaijan has resulted in re interpretation of the depositional environments of the productive series the lower part of the productive series consists of sandstones and mudstones interpreted as channelised and sheetflood fluvial deposits intercalated with mudstones that represent short lived lacustrine transgressions of a regional caspian lake the upper productive series pereriva and younger suites comprises sandstone prone intervals interpreted as deposition during periods of increased fluvial discharge and sediment supply and mudstone prone intervals interpreted as deposition during periods of decreased discharge and therefore coarse grained sediment starvation sand prone reservoir intervals in the pereriva and overlying balakhany suites mainly comprise amalgamated low sinuosity braided fluvial sheet sandstones mudstone rich intervals form inter and intra suite seals comprising alluvial plain and lacustrine facies the succession displays an overall fining up trend which is controlled by long term climatic cooling decreased fluvial discharge and reduced coarse clastic input the modern volga caspian system is a partial analogue for the lower productive series in the apsheron region where fluvial and lacustrine conditions alternate on a low gradient ramp without evidence for a shelf break lake eyre australia may be a modern analogue for the upper productive series where there are fewer lacustrine influences discernible in the sedimentology and the overall setting resembles a dryland river terminal fan

electrical properties and its correlation to the petrology of the upper yangtze organic shales abstractshale gas is a particularly important research target on chinese energy resources especially in the upper yangtze region complex topography and geologic conditions challenge seismic exploration of shale gas in this area and ground based electromagnetic em methods are used to aid recognition of the best reservoirs however the electrical properties of organic shale epos and its correlation to shale gas petrology remain poorly understood we studied epos and their correlation to shale petrology by measuring and analyzing the petrochemical features and complex impedance of rock samples from the silurian longmaxi and cambrian niutitang formations in the upper yangtze southwest china our study indicates that the organic shale in the upper yangtze features low resistivity and high polarizability in terms of a high negative phase but no obvious low resistivity is observed among shaly sandstone and shales with lower and higher total organic carbon pyrite and quartz contents in the organic shal

fracture development in paleozoic shale of chongqing area south china part one fracture characteristics and comparative analysis of main controlling factors abstract natural macro and micro fractures in the longmaxi shale lower silurian from yuye 1 well and the niutitang shale lower cambrian from yuke 1 well are characterized regional geological structural evolution and shale geochemistry including toc and mineral composition etc are analyzed the controlling factors of natural fractures in palaeozoic shale in the southeast of chongqing have been confirmed which have been analyzed qualitatively or semi quantitatively the results show that fractures are abundant in both the longmaxi shale and niutitang shale due to the multiphase strong tectonic movement in the southeast of chongqing therefore tectonic factors are the principal factors that control fracture development in the paleozoic shale of this region followed by the mineral composition of the shale vertically the mineral composition of shale in yuke 1 well has a high dispersion degree and a strong heterogeneity the dispersion coefficients of quartz and dolomite were 0 48 and 1 respectively therefore the development and distribution of fractures are controlled by quartz and dolomite content in the niutitang shale moreover the quartz content shows positive correlation with the fractures quantity and fractures are most abundant where dolomite content up to 64 7 while the mineral composition of shale in yuye 1 well has a low dispersion degree and a strong homogeneity in a vertical position the dispersion coefficients of quartz and plagioclase were 0 15 and 0 26 respectively which shows unconspicuous control effect for fractures therefore the development and distribution of fractures are mainly controlled by the toc content moreover the toc content shows positive correlation with the fractures quantity fractures are sealed by calcite quartz and pyrite although sealed fractures do not contribute to the permeability of the reservoir they are important planes of weakness that tend to be reactivated by hydraulically induced fractures sem images show that intergranular pore is connected by microfractures thereby the validity of porosity has been improved the mixed network of microfractures and micropore provide enhanced permeability or storage capacity for the reservoir

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

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

facies and evolution of the modern brazos delta texas wave versus flood influence abstract in order to better define the facies architecture and processes controlling the evolution of wave dominated deltas a detailed sedimentary and geomorphologic study was undertaken on the brazos delta texas the delta has formed since 1929 when the brazos river was diverted by the u s army corps of engineers the brazos delta is composed primarily of fine grained sediments prodelta clay constitutes more than half of the sediment volume thick sands are restricted to the narrow delta front environment whereas back bar lagoonal clays are a significant component of the delta plain sequence the facies architecture is not representative of the classic strandplain model for wave dominated deltas this is due to the strong influence of floods on deltaic evolution in early 1992 statewide flooding gave rise to a major constructional phase of the delta significant quantities of fine grained sediments were deposited in the prodelta one year after the onset of flooding a channel mouth bar emerged offshore of the river mouth and enabled progradation of the delta similar flood events that occurred during 1941 1957 and 1965 were recorded as ridge trough pairs in the delta headland the brazos delta is therefore fluvially influenced during floods and wave influenced during intervening periods

the geometry and internal architecture of stream mouth bars in the panther tongue and the ferron sandstone members utah u s a abstract clinothems are seaward dipping beds which are deposited during the progradation of delta front mouth bars measurements taken from clinothems in the field and from geospatially constrained photo realistic virtual outcrops were used to record clinothem dip maximum bed thickness and bed thickness every 10 m along a series of depositional dip oriented profiles from two ancient river dominated delta successions which crop out in central utah usa these data show systematic changes in bed dip and bed thinning which highlight discrete packaging of the beds into bedsets interpreted to represent the progradation of stream mouth bars in the delta front individual bedsets are characterized by a progressive steepening of beds coupled with a more rapid thinning systematic collection of 2800 locations along 73 separate clinothems from the panther tongue sandstone member and parasequence 1f from the ferron sandstone were used to study the relationship between bed thickness dip and decay gradient parameter which describes the down dip bed thinning clinothems in the panther tongue are much longer and more gently dipping than the clinothems in the ferron sandstone in both systems beds can be clustered into groups bedsets which show a systematic decrease in values and an increase in dip angle boundaries between the groups are defined by a sudden increase in values and a concurrent decrease in dip angle these bedsets are interpreted to represent individual stream mouth bars which amalgamate to form mouth bar complexes within the delta front sand bodies the use of virtual outcrops was essential for the collection of the large volumes of thickness data and the recognition of very subtle 1 changes in dip angle which have made these interpretations possible

paleo sedimentary environment in relation to enrichment of organic matter of early cambrian black rocks of niutitang formation from xiangxi area china abstract early cambrian organic rich black rocks are extensively distributed in the southern china in this study we have discussed the relation of paleo sedimentary environments with enrichment of organic matter based on toc data we divided the niutitang formation into three parts upper middle and lower the amount of total organic carbon in the lower 1 55 wt and the upper part 1 35 wt of niutitang formation is significantly smaller than the middle part 8 0 wt which suggest initial transgression and regression stages of the sea level respectively the middle part from both sections longbizui and sancha contains higher toc content which is a clue of intense transgression stage of sea level with high bio productivity kerogen type index kti using different macerals specify the organic matter in these black rock series is mainly type i with a minor amount of type ii1 moreover these black rocks were deposited in weak to moderately restricted hydrographic conditions the heterogenic mineral composition was also observed in these black rocks including quartz clay gypsum pyrite barite dolomite and plagioclase quartz content in the middle part is relatively higher than the upper and the lower part displays a strong positive relation with toc which suggests the main source of quartz during deposition of the middle part was biogenic quartz during early cambrian period due to extension between the yangtze and the cathaysian plate the hydrothermal fluids rich in uranium vanadium molybdenum zinc barium etc from the deeper part of the earth crust and entered the ocean basin through extensional remnant fissures and cracks and due to upwelling phenomena entered to the shelf area these nutrient rich deep crustal fluids at the surface of the sea enhanced the evolution and breeding of planktons and other marine life meanwhile it upsurges the bio productivity additionally it creates bottom water hypoxia which is favourable for the preservation of organic matter in the sedimentary rocks the main factors responsible for the enrichment of organic matter in these early cambrian black rock series of niutitang formation were a hydrographic restriction hydrothermal activities and paleo redox conditions respectively

depositional patterns following the 1870s avulsion of the saskatchewan river cumberland marshes saskatchewan canada abstract the avulsion of the saskatchewan river cumberland marshes east central saskatchewan canada has resulted in new floodplain deposition over an area of more than 500 km2 since beginning in the 1870s the avulsion deposits are predominantly fine grained and could be otherwise classifiable as overbank sediments in alluvial floodplains presumed to be supplied by intermittent flooding of dominant master channels the north angling and cadotte channels are older pre existing channels that were intercepted and appropriated by the expanding avulsion following annexation of the north angling channel stable cohesive banks inhibited channel enlargement and crevassing forcing the increasing discharges to be accommodated by overbank flow and in the process enhancing new levee aggradation these levee deposits coarsen upward and thin downstream as a result of greater competence and higher proximal deposition rates brought on by the larger flows in contrast the cadotte channel responded to increasing discharges by levee breaching giving rise to splay progradation and floodbasin filling the cadotte splay complex formed from the avulsively annexed cadotte channel represents a small but typical area of the avulsion belt facies characteristics and interrelationships examined from auger borings and vibracores are presented to illustrate patterns of deposition and floodplain development avulsive flooding initially raised local water surface elevations deepening small existing lakes and creating new shallow 1 2 m deep lakes on the floodplain surface deposition began when levees of the cadotte channel were breached allowing water and coarser sediment to spread as sheet like flows while finer sediment was carried and deposited farther into the basin later as the proximal splay sheets coalesced and grew basinward flows became channelized and progradation of mouth bars into marshes and shallow lakes together with deposition of interchannel fines became dominant forming coarsening upward sequences further floodplain aggradation developed by overbank flooding when splay channels became stabilized and bordered by levees gradual abandonment was accompanied by deposition of organic rich fine grained sediment on top of the progradational sequences throughout the avulsion the north angling channel has stood as an older alluvial ridge separating two broad areas of avulsive deposition its recent levee deposits now grade basinward into these new floodplain sediments composed of thicker heterogeneous predominantly upward coarsening and rapidly deposited facies of the avulsion

controls on methane sorption capacity of indian coals details of methane sorption properties of some indian coals ranging in rank from high volatile bituminous c 0 62 ro max to medium volatile bituminous coal 1 46 ro max were investigated to determine the major factors influencing gas adsorption capacity and desorption rate variables studied included moisture content mineral matter content rank and coal type maceral composition adsorption isotherm analysis of dry coals showed that adsorption capacity followed a second order polynomial trend with rank equilibrium moist samples showed a linear increase in adsorption capacity with rank and had a significantly reduced adsorption capacity compared to the dry coals with the reduction being related to the moisture content mineral matter acted as a simple diluent to the gas adsorption capacity of the coals and was found to be nonadsorbent adsorption capacity moist was reduced by 0 32 cm3 g 10 ft3 gas t for every 1 increase in the ash yield bright and dull coal lithotypes showed strong separation in their adsorption capacities on an as analyzed basis with the bright coals adsorbing greater quantities of gas on a dmmf basis however no relationship was observed between coal type and gas storage capacity comparison of maceral composition with adsorption capacity dry confirmed this observation effective diffusivity de of methane through the coal was seen to be affected by coal type and rank effective diffusivity de decreased as rank increased which is related to the increasing microporous nature of the coal bulk coals tested had 2 3 times larger effective diffusivities than bright coals and dull coals had intermediate rates the larger de values for the bulk coals may be related to the presence of collodetrinite coupled with mineral matter which acts as higher permeability pathways for the gas compared with the high ash dull coals dominated by inertinite macerals differences were noted with similar age permian australian coals where methane adsorption capacities were larger and coal type had a stronger influence on adsorption capacity begin page 202

alluvial sedimentation patterns in the munster basin ireland post caledonian southern ireland witnessed the development of a ne sw orientated half graben known as the munster basin more than 7 km of non marine sediments accumulated in the basin during the late middle and late devonian marine conditions became established in the southern part of the basin at the end of the devonian in this paper a model for the evolving style of sedimentation in the basin and its periphery is constructed with the aim of identifying the major factors which controlled sedimentation patterns and the architecture of the basin fill the depositional history of the basin is considered in terms of four successive episodes during episode i gravelly alluvial fans flanked upland areas around the northeastern and northern basin perimeter these graded southwestwards to a floodplain dominated by sheet floods in the western part of the basin the first of three major fluvial influxes into the basin commenced during episode ii the first influx developed into a large sandy braided complex the sediment was derived from a distant source area located to the north and west of the basin and was transported diagonally across the basin towards the southeast episode iii witnessed a second influx which drained into the basin from the northeast and north river channels were of low sinuosity and graded distally to an ephemeral playa lake episode iv was marked by a third fluvial influx from the west and northwest this was confined to the southern half of the basin and drainage was directed towards the east the fluvial distributaries were flanked by permanently flooded overbank areas this influx coincided with the first marine transgression which advanced westwards the end of episode iv coincided with the beginning of the carboniferous and was marked by a major marine transgression sediment input to the basin was influenced by stable areas occupied by granitic plutons on either side of the basin and a southward downthrowing fault along its northern margin the drainage direction was principally controlled by e w trending within basin faults and an e w trending stable area located to the south the basin was fundamentally of the axial transport type the main drainage having been directed towards the east though there was also a strong lateral influx from the north northwest and northeast stable areas around the basin periphery resulted in either no sediment preservation or sequences of multistorey channel deposits while thick sequences dominated by fine grained floodplain or overbank deposits characterized areas of higher subsidence rate within the basin movement on the northern basin margin fault was probably the major cause of the first fluvial influx while regional subsidence of the basin and its northern periphery resulted in the second influx the third influx was a response to local subsidence in the southern part of the munster basin this also contributed to the simultaneous westward marine transgression in this area towards the end of the devonian source area denudation and retreat in association with a sea level rise were ultimately responsible for terminating the alluvial regime in the munster basin

organic rich marcellus shale lithofacies modeling and distribution pattern analysis in the appalachian basin the marcellus shale is considered to be the largest unconventional shale gas resource in the united states two critical factors for unconventional shale reservoirs are the response of a unit to hydraulic fracture stimulation and gas content the fracture attributes reflect the geomechanical properties of the rocks which are partly related to rock mineralogy the natural gas content of a shale reservoir rock is strongly linked to organic matter content measured by total organic carbon toc a mudstone lithofacies is a vertically and laterally continuous zone with similar mineral composition rock geomechanical properties and toc content core log and seismic data were used to build a three dimensional 3 d mudrock lithofacies model from core to wells and finally to regional scale an artificial neural network was used for lithofacies prediction eight petrophysical parameters derived from conventional logs were determined as critical inputs advanced logs such as pulsed neutron spectroscopy with log determined mineral composition and toc data were used to improve and confirm the quantitative relationship between conventional logs and lithofacies sequential indicator simulation performed well for 3 d modeling of marcellus shale lithofacies the interplay of dilution by terrigenous detritus organic matter productivity and organic matter preservation and decomposition affected the distribution of marcellus shale lithofacies distribution which may be attributed to water depth and the distance to shoreline the trend of normalized average gas production rate from horizontal wells supported our approach to modeling marcellus shale lithofacies the proposed 3 d modeling approach may be helpful for optimizing the design of horizontal well trajectories and hydraulic fracture stimulation strategies

sediment accumulation in a modern epicontinental shelf setting the yellow sea sediment accumulation in the yellow sea epicontinental shelf environment is investigated on 100 yr and 1000 yr time scales using 210pb and 14c geochronologies the distribution of modern 210pb accumulation rates in the yellow sea reveals that the loci of modern huanghe sediment accumulation are the topset 1 2 mm yr foreset 4 9 mm yr and proximal bottomset deposits 2 4 mm yr of the shandong subaqueous delta which extends south from the shandong peninsula 210pb rates in the distal bottomset deposits of the subaqueous delta in the central and southern yellow sea are generally low 0 3 0 9 mm yr a sediment budget demonstrates that between 9 15 of the annual huanghe discharge is accumulating in the yellow sea about two thirds of this sediment is accumulating in the topset foreset and proximal bottomset deposits of the shandong subaqueous delta with the remaining third accumulating as widespread distal bottomset deposits 14c age dates of subaqueous delta sediments indicate that the thick 40m clinoform structure formed predominantly between 6200 and 4060 yrs b p at rates approaching 20 mm yr observations in the yellow sea as well as on the amazon and ganges brahmaputra shelves demonstrate that subaqueous deltaic stratigraphy is the general rule where major rivers enter energetic shelves whether epicontinental or pericontinental the development of extensive bottomset deposits may be restricted to epicontinental shelf environments and may be diagnostic of sedimentation in this type of setting

mechanisms of shale gas storage implications for shale gas exploration in china this article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in china at a given temperature and pressure the gas sorption capacities of organic rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter mineral composition especially clay content moisture content pore volume and structure resulting in different ratios of gas sorption capacity gsc to total organic carbon content for different shales in laboratory experiments the gsc of organic rich shales increases with increasing pressure and decreases with increasing temperature under geologic conditions assuming hydrostatic pressure gradient and constant thermal gradient the gsc increases initially with depth due to the predominating effect of pressure passes through a maximum and then decreases because of the influence of increasing temperature at greater depth this pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in gsc of organic rich shales over geologic time as a function of burial history at an elevated temperature and pressure and with the presence of moisture the gas sorption capacities of organic rich shales are quite low as a result adsorption alone cannot protect sufficient gas for high maturity organic rich shales to be commercial gas reservoirs two models are proposed to predict the variation of gsc and total gas content over geologic time as a function of burial history high contents of free gas in organic rich shales can be preserved in relatively closed systems loss of free gas during postgeneration uplift and erosion may result in undersaturation the total gas contents lower than the sorption capacity and is the major risk for gas exploration in marine organic rich shales in china

kinematic evolution of the patagonian retroarc fold and thrust belt and magallanes foreland basin chile and argentina 51 30 s the kinematic evolution of the patagonian fold and thrust belt and cogenetic magallanes retroarc foreland basin is reconstructed using new geologic mapping two dimensional 2 d seismic reflection data and zircon u pb geochronology results span an 160 km wide transect of the thrust belt and magallanes basin near 51 30 s and highlight the influence of inherited extensional structures on basin paleogeography syntectonic sedimentation and late cretaceous neogene foreland shortening south of 50 s the patagonian fold and thrust belt developed on oceanic and attenuated crust of the predecessor late jurassic rocas verdes rift basin resulting in a collisional nature to early fold and thrust belt development and foreland sedimentation atop rifted south american crust we identify six principal stages of development between late cretaceous and neogene time a palinspastic restoration indicates 32 40 km 19 23 of retroarc shortening following closure of the rocas verdes basin and incipient growth of the thrust belt more than half of the estimated crustal shortening occurred synchronously with the deep water phase of late cretaceous foreland basin sedimentation subsequent deformation migrated into the foreland accounting for 12 km of shortening across the cretaceous early miocene basin fill thick skinned thrust faulting along multiple detachment levels in paleozoic metamorphic basement resulted in 5 km of foreland uplift and exposure of preforeland basin deposits the final phase of early miocene deformation ca 21 18 ma may reflect enhanced coupling between the continental and oceanic lithospheres causing foreland basement uplifts as the chile ridge spreading ridge approached the trench we speculate that neogene foreland shortening was accommodated by reactivation of mesozoic normal faults zones and accounts for broad uplift of the patagonian fold and thrust belt

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

sedimentary response to a tectonically induced sea level fall in a shallow back arc basin the mulichinco formation lower cretaceous neuquen basin argentina this study examines the sedimentary response to a tectonically driven relative sea level fall that occurred in the neuquen basin west central argentina during the late early valanginian early cretaceous at this time the basin lay behind the emergent andean magmatic arc to the west following the relative sea level fall sedimentation was limited to the central part of the neuquen basin with the deposition of a predominantly clastic continental to shallow marine wedge on top of basinal black shales this lowstand wedge is called the mulichinco formation and consists of a third order sequence that lasted about 2 myr and contains high frequency lowstand transgressive and highstand deposits significant variations in facies depositional architecture and internal organization of the sequence occur along depositional strike these variations are attributed mainly to tectonic and topographic controls upon sediment flux basin gradient fault tilting and shifting of the depocentre through time these controls were ultimately related to asymmetrically distributed tectonic activity that was greater towards the magmatic arc in the west the superposition of fluvial deposits directly upon offshore facies provides unequivocal evidence for a sequence boundary at the base of the mulichinco formation however the mulichinco sequence boundary is marked by shallow low erosional relief and widespread fluvial deposition the surface lacks prominent valleys traditionally associated with sequence boundaries this non erosive sequence boundary geometry is attributed to the ramp type geometry of the basin and or rapid uplift that limited stratigraphic adjustment to base level fall significant along strike facies changes and a low relief sequence boundary are attributes that may be common in tectonically active semi enclosed basins e g shallow back arc basins foreland basins

a multiphasic younger dryas cold period recorded in sediments of lake steisslingen sw germany a biomarker perspective abstract the younger dryas 12 680 11 590 yr bp was the last millennial scale cold event of the quaternary when a mean annual temperature decline of 3 5 c impacted severely on the environment whereas pollen distributions document changes in land vegetation details of limnic ecosystem responses to the cooling event and to its recovery are still not well known here we studied the laminated sediments of lake steisslingen sw germany deposited between 13 500 and 11 100 yr bp in order to investigate the evolution of an aquatic ecosystem bulk sediment and organic matter composition mark onset and termination of the younger dryas but remain monotonous through this interval requiring application of organic and isotope geochemical techniques to follow past ecosystem dynamics the younger dryas is characterized by both an abrupt appearance and demise of long chain alkenones indicative for haptophyte algae based on algal and bacterial biomarker distribution the younger dryas can be divided into three stages each characterized by the dominance of a microorganism group the first phase was dominated by nc17 alkanes and hopanoids indicative of cyanophytes and heterotrophic bacteria the second phase shows a proliferation of cold adapted haptophyte algae while in the latest phase highly branched isoprenoids hbi reveal an aquatic community shift towards diatoms heterocyte glycolipids document a moderate change in n2 fixing cyanobacterial community structure over the allerod younger dryas transition but show a marked collapse of the cyanobacteria association at the younger dryas preboreal climate recovery terrigenic wax lipids indicate significant changes in vegetation between the allerod younger dryas and preboreal chronozones but remain homogeneous within the younger dryas

stratigraphic evolution of an outcropping continental slope system tres pasos formation at cerro divisadero chile depositional slope systems along continental margins contain a record of sediment transfer from shallow water to deep water environments and represent an important area for natural resource exploration however well preserved outcrops of large scale depositional slopes with seismic scale exposures and tectonically intact stratigraphy are uncommon outcrop characterization of smaller scale depositional slope systems i e 600 m thick succession units 3 and 4 which is interpreted as reflecting increased gradient conditions as the system accreted basinward

support for two subglacial impact craters in northwest greenland from earth gravity model eigen 6c4 and other data abstract we support the very recent discovery of two impact craters under the ice of northwest greenland hiawatha glacier and paterson these discoveries are based mainly on geology and bedrock topography we added an analysis of gravity field aspects descriptors in addition to the traditional gravity and magnetic anomalies the gravity aspects the marussi tensor of the second derivatives the gravity invariants and their special ratio strike angles and virtual deformations provide more complex and comprehensive information about the underground density variations due to a causative body than ordinary gravity anomalies they show signals typical for the individual geological features like a mountain volcano fault river valley paleo lake ground water hydrocarbon mineral deposits etc as well as for the targets known as impact craters our method has been tested on various geological features on the earth and the moon the gravity aspects are in our case derived from the recent global static combined earth gravity field model eigen 6c4 with a ground resolution 9 km and a precision 10 mgal a further data come from the digital magnetic field database emag 2 with resolution 5 km our method is novel and independent of anything which led to discoveries of these craters in greenland

enhanced bioturbation on the down drift flank of a turonian asymmetrical delta implications for seaway circulation river nutrients and facies models extant models predict delta front environments down drift of river mouths as unfavourable for organisms because of the physico chemical stresses caused by sediment and fresh water influx this study however finds evidence for near optimal living conditions down drift of contemporaneous mouth bars and distributary channels as well as at the tops of abandoned lobes in part of the asymmetrical notom delta complex of the ferron sandstone turonian south eastern utah usa presented herein is a sedimentological and ichnological model using thirty two detailed measured sections along a 16 km transect through two continuously exposed ca 10 m thick allomembers containing delta front mouth bar and distributary channel facies azimuths from sedimentary structures show south eastward deflection of near shore palaeocurrents relative to the inferred north south shoreline as well as minor reversal of flow two end member trace fossil suites are recognized in delta front sandstones i a stressed suite of low abundance low diversity diminutive traces reflecting mobile deposit feeding resting and locomotion behaviours and ii a comparatively unstressed high abundance moderate diversity suite with a regular heterogeneous distribution of deep vertical or u shaped suspension feeding burrows which in places thoroughly homogenize the sandstones the down drift side of the delta was colonized by suspension feeders during seasonal reversal of the seaway gyre when mud plumes were swept northward or when river derived nutrients were sufficiently concentrated relative to fresh water and sediment input during normal seaway circulation very high sedimentation rates and mud laden wave dampened waters down drift of the river mouths heightened the preservation potential of the pervasively bioturbated facies up drift of the river mouths these bioturbated facies were either not preserved or not developed until the lobe was abandoned this alternative model for delta planform asymmetry contributes to the refinement of facies models for deltaic systems and provides a framework for predicting the distribution of bioturbation enhanced porosity and permeability in lobe deflected deltas

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

characteristic trace fossils in nearshore to offshore sequences upper cretaceous of east central utah more than 20 trace fossil species occur in marine facies of the cretaceous star point and blackhawk formations in the book cliffs and wasatch plateau provinces of utah major genera include ancorichnus arenicolites aulichnites chondrites conichnus cylindrichnus medousichnus ophiomorpha palaeophycus planolites rosselia schaubcylindrichnus scolicia skolithos teichichnus teredolites and thalassinoides newly named taxa include ancorichnus capronus medousichnus loculatus and rosselia chonoides most trace fossils occur in characteristic albeit intergradational ichnofacies correlative with major lithofacies of regressive nearshore to offshore sequences the latter include foreshore foreshore shoreface transition shoreface and offshore facies landward facies are typified by clean well sorted well stratified sparsely burrowed sandstones seaward facies except where interrupted by hummocky bedded sandstones exhibit successively less pure less well sorted and stratified more intensely

ichnology of prodeltaic hyperpycnite turbidite channel complexes and lobes from the upper cretaceous prairie canyon member of the mancos shale book cliffs utah usa

ichnological signatures from wave and fluvial dominated deltas the la anita formation upper cretaceous austral magallanes basin patagonia abstract depositional processes operating in deltaic shorelines create a variety of physico chemical stressful conditions that impact directly on benthic fauna the ichnological signatures of deltaic successions reflect these physico chemical stresses such as rapid sediment influx elevated water turbidity periodically reduced oxygenation salinity fluctuations and wave and tidal energy in the campanian la anita formation of the austral magallanes basin two examples of deltaic successions each showing different relative dominance of wave and fluvial processes are described in detail allowing the recognition of contrasting stresses that acted differentially in a wave dominated fluvial influenced delta and a fluvial dominated delta variations in the burrowing intensity and ichnodiversity allowed us to discriminate the different physico chemical stresses in the wave dominated fluvial influenced deltaic deposits the alternation between fair weather waves and storm events acted as the main controlling factor on benthic fauna in the facies of the prodelta and distal delta front displaying facies crossing and horizontal elements attributable to the skolithos and cruziana ichnofacies such as arenicolites isp chondrites isp cylindrichnus isp diplocraterion isp gyrochorte isp ophiomorpha isp palaeophycus isp planolites isp rhizocorallium isp rossellia isp schaubcylindrichnus isp and skolithos isp water turbidity and periodically reduced bottom water oxygenation conditions also played an important but subordinate role the proximal delta front and distributary and terminal distributary channel deposits show low burrowing intensities and ichnodiversities with structures attributable to the depauperate skolithos ichnofacies with few diplocraterion isp gordia isp lockeia isp macaronichnus isp ophiomorpha isp schaubcylindrichnus coronus and siphonichnus isp showing stress conditions associated with rapid sediment influx high energy and reduced salinity conditions related to fluvial discharges as the most important controlling factors periodically fluctuations in salinity conditions due to river discharges and channel avulsion may have also played important roles the fluvial dominated deltaic deposits show that the controlling factors were associated with fluvial discharge and river sediment influx with no clear influence of wave or tidal action the facies of the distal delta front were controlled by episodic sedimentation elevated water turbidity periodically reduced oxygenation and salinity fluctuations the associated trace fossil suite consists of a monospecific assemblage of ophiomorpha isp and sparse palaeophycus isp the proximal delta front and the distributary channel deposits are mostly unburrowed locally displaying a few arenicolites isp lockeia isp ophiomorpha isp psilonichnus isp and teredolites isp the development of these suites was controlled mainly by heightened sedimentation rates influx triggered by high fluvial discharges elevated water turbidity due to heightened suspended load and buoyant plumes periodic fluctuations in salinity conditions caused by river discharges and channel avulsion interdistributary areas are characterized by facies preserving evidence that reduced oxygenation was the most important controlling factor in this subenvironment fluvial processes generate the most extreme stressful conditions for benthic colonization by tracemakers wave processes tend to buffer the stresses produced by river discharge the effect of waves on fluvial stress is reflected in the higher bioturbation intensities and ichnodiversities that the wave dominated deltaic deposits of the la anita formation delta show in relation to the fluvial dominated ones

reservoir evaluation of the lower silurian longmaxi formation shale gas in the southern sichuan basin of china abstract the lower silurian longmaxi formation the palaeozoic is organic rich black shale in the southern sichuan basin the yangtze plate of china this study analyses the lateral extent and thickness burial depth total organic carbon content and thermal maturity of the longmaxi formation black shale as the key features of the shale gas reservoir the thickness of the black shale ranges from 10 to 170 m the thickest reservoir is located in changning naxi yongchuan region the toc of the shale at the bottom of the formation 50 m thickness is above 2 0 the lateral distribution of toc varies with the lateral distribution of thickness with the maximum toc in the gongxian luzhou yongchuan region the burial depth ranges from 2000 to 4500 m the shale is thermally over mature the evaluation of reservoir characteristics indicates that the longmaxi formation has conditions appropriate for shale gas accumulation and thus resource potential in the southern sichuan basin of china the objective of this preliminary evaluation of the reservoir characteristics is to locate potential areas favourable for exploration the most favourable areas are defined here as those where the thickness of black shale is more than 100 m and the burial depth is less than 3000 m these cover approximately 12 600 km 2 the most favourable areas which cover an area of approximately 5100 km 2 are located in the northeast luzhou region