comparison of the vertical distributions of cloud properties from idealized extratropical deep convection simulations using various horizontal resolutions abstractthe authors coarse grained and analyzed the output from a large eddy simulation les of an idealized extratropical supercell storm using the weather research and forecasting wrf model with various horizontal resolutions 200 m 400 m 1 km and 3 km the coarse grained physical properties of the simulated convection were compared with explicit wrf simulations of the same storm at the same resolution of coarse graining the differences between the explicit simulations and the coarse grained les output increased as the horizontal grid spacing in the explicit simulation coarsened the vertical transport of the moist static energy and total hydrometeor mixing ratio in the explicit simulations converged to the les solution at the 200 m grid spacing based on the analysis of the coarse grained subgrid vertical flux of the moist static energy the authors confirmed that the nondimensional subgrid vertical flux of the moist static energy varied with the subgrid fractional cloudiness according to a fun

growth faults and fault related structures of prograding terrigenous clastic continental margins abstract growth faults are the structural manifestation of the inherent tensional stress regime that is focused at the upwardly convex margin of a prograding continental platform extension and faulting may be triggered by either gravitational gliding or spreading extensional faulting results in both lateral translation and subsidence of the down faulted sediment mass consequently outer platform and upper slope facies are expanded and disproportionately preserved relative to paralic or deep water facies specific growth fault geometries and patterns are related in part to the depositional history and style of the prograding margin unusually continuous and low angle master faults are proposed to result from a history of rapid progradation of a deltaic depocenter onto an older retrograditional slope growth fault zones function as major conduits for large scale circulation of both ground waters and hydrocarbon fluids within the sedimentary prism

devillier field chambers county texas effects of growth faults and deltaic sedimentation on hydrocarbon accumulation in a stratigraphic trap devillier field is an overpressured gas reservoir producing from upper vicksburg lower oligocene loxostoma b delicata sands which pinch out near the crest of a structure located on the downthrown side of the vicksburg flexure the field is located 50 mi 80 km east of houston in northeastern chambers county texas a structure map of the lower frio upper oligocene shows south southeast regional dip over the field an isopach map of the upper vicksburg shows north northwest dip and thickening of sands and shales into the vicksburg flexure northwest of the field correlation of stratigraphic units indicates maximum growth across the flexure during upper vicksburg deposition based on analysis of composition sorting and grain size of detrital minerals and quartz from cores and cuttings the field pay the loxostoma sand is interpreted to have been deposited as a delta distributary mouth bar sand pinchout of this sand facies against a prodelta shale facies has resulted in creation of a true stratigraphic trap the first year s production per well averaged 1 0 bcf gas and 13 000 bbl condensate for the seven wells completed since the field discovery in 1975 calculated open flows have ranged as high as 600 000 mcf day gas from an average net sand interval of 25 ft 7 6 m at depths between 10 550 and 10 750 ft 3 216 and 3 277 m most of the remaining undiscovered reserves in mature petroleum provinces will be found in similarly small but significant and economic subtle traps

geochemical facies analysis of fine grained siliciclastics using th u zr rb and zr rb sr ratios abstract abundance of the trace elements zr rb sr th and u may provide insight into the sedimentological origin of fine grained siliciclastic sediments provided that the units are derived from similar source areas as demonstrated here with suites of the fine grained jurassic and cretaceous rocks from the barents sea and svalbard zr rb ratios can be interpreted to indicate grain size variations while zr rb sr values reflect variations in the siliciclastic versus carbonate contents the th u ratio can be applied as an indicator of the redox conditions in 3d plots such as presented here the interplay between these geochemical factors can be interpreted in terms of the sedimentological evolution of the depositional basin the geochemical facies analyses show that similar depositional conditions existed on the jurassic shelf in the two studied localities the succeeding prodeltaic cretaceous beds were generally coarser grained and deposited in ventilated depositional conditions

scale dependence of reflection and transmission coefficients well logs show that heterogeneities occur at many different depth scales this study examines the effects of these heterogeneities on the propagation of seismic waves and specifically the dependence of reflection and transmission on the spatial scale content of the medium wavelet transformations are used to filter certain spatial scales from an acoustic sonic log the scale filtered logs are used to construct layerstack models for which reflection and transmission seismograms are computed the modified logs are also used to calculate frequency dependent reflection and transmission coefficients as functions of scale content it is observed that features shorter than one fourth of the dominant wavelength have little effect on the reflection and transmission of seismic waves features larger than the dominant wavelength affect arrival times of individual packets within the wavetrain but often these features hardly alter the overall appearance of individual wave packets reflection and transmission coda ar

heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin of china this study characterizes the vertical heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin based on core description thin sections observation geological chemistry data interrogation and qemscan image analysis lithofacies associations mineralogy graptolite species occurrence rock fabrics as well as toc total organic carbon and gas content change noticeably and regularly in the lower silurian longmaxi marine shale within sequence stratigraphic framework lithofacies associations mainly include in situ graptolite rich and siliceous shale in the transgressive systems tract tst micro offsite graptolite rich shale and shale interbedded with siltstone laminaes in the early highstand systems tract ehst and micro offsite graptolite rich and carbonate rich shale in the late highstand systems tract lhst the tst has a greater abundance of diplogratus than ehst and lhst and has a lesser level of monograptus which is conversely higher in the ehst and lhst the tst shale is silica rich while the lhst shale is generally clay rich the ehst shale is more balanced in its silica and clay content than the tst and lhst are the sedimentary structure and fabric of shale shows that shale is homogenous in the tst with laminaes well developed in the ehst but decreasing in the lhst toc and gas content are highest in the tst and decrease upward the tst with high toc high gas content high brittle minerals silica rich and anoxic suboxic to dysoxic sedimentary environment is the most potential shale gas target interval in the study area our research also shows that the toc mainly controls shale gas accumulation and that the redox conditions mainly control the preservation of organic matter the silica also plays a significant role in shale gas content due to its contribution to hydraulic fracturing finally the study proposes a depositional and heterogeneity model for the lower silurian longmaxi marine shale in the study area

the use of vertical wind shear versus helicity in interpreting supercell dynamics a series of idealized simulations of supercell storms are presented for environments representing straight through circular hodographs to clarify the character of the storm dynamics over the large spectrum of hodograph shapes commonly observed the primary emphasis is on comparing and contrasting recent theories of supercell dynamics based on updraft shear interactions storm relative environmental helicity sreh and beltrami flow solutions to help clarify the degree to which each theory can represent the essential storm dynamics one of the particular questions being addressed is whether storm dynamics are significantly different for straight versus curved hodographs which has become a point of some controversy over recent years in agreement with previous studies the authors find that the physical processes that promote storm maintenance rotation and propagation are similar for all hodograph shapes employed and are due primarily to nonlinear interactions between the updraft and the ambient shear associated with the localized development of rotation on the storm s flank significant correlations between the updraft and vertical vorticity are also observed across the shear spectrum and in agreement with predictions of linear theories associated with sreh this correlation increases for increasing hodograph curvature however storm steadiness and propagation must already be known or inferred for such concepts to be applied thus limiting the applicability of this theory as a true predictor of storm properties tests of the applicability of beltrami solutions also confirm reasonable agreement for purely circular hodographs for which the analytical solutions are specifically designed however analysis of the model results indicates that the terms ignored for such solutions representing the nonlinear effects associated with storm rotation are more significant than those retained over most of the hodograph spectrum which severely limits the general applicability of such analyses

the nature and significance of condensed sections in gulf coast late neogene sequence stratigraphy abstract because it lends itself to predictable interpretations sequence stratigraphy is gaining acceptance as a unifying concept in stratigraphy in general and in exploration in particular any regional seismic stratigraphic study must be predicated on a sound chronostratigraphic framework among the components of stratigraphic sequences and depositional systems the condensed section is probably the most fundamental stratigraphic unit condensed sections are relatively thin highly fossiliferous hemi pelagic beds that form at the time of maximum transgression most reliable biostratigraphic datums occur within them and being regionally widespread they are excellent chronostratigraphic markers since they are the only consistent tangible stratigraphic unit which ties deep water and shelf environments they are of paramount importance in delineating sequence boundaries and systems tracts this paper discusses various criteria for recognizing condensed sections and documents 20 seismically resolvable condensed sections in the pre wisconsin plio pleistocene to uppermost miocene of the gulf coast they are recognized by abundance and species diversity peaks and are calibrated in terms of the foraminiferal and calcareous nannofossil datums within them all of these condensed sections are associated with an increase in paleo water depth as indicated by the chronostratigraphic control provided by planktonic datums they are not random events and can be shown to be regionally correlative the scheme presented here has been developed in conjunction with seismic sequence studies and has been integrated with regional seismic grids sixteen of these condensed sections are maximum flooding events four of them have been found to develop between lowstand slope fans and lowstand prograding wedges the characteristics of condensed sections in various paleo environmental settings are discussed and the miocene pliocene transition of the gulf coast is related to global eustatic events

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

geochemistry of the extremely high thermal maturity longmaxi shale gas southern sichuan basin abstract the marine shale of the silurian longmaxi formation in southern sichuan basin china is characterized by its huge thickness 100 600 m high toc values 0 35 18 4 favorable types of organic matter i and ii1 high ro values 1 8 4 2 abundant brittle minerals average 56 3 and strong gas generation intensity particularly its bottom section which has toc 2 and thickness of 20 70 m has recently been a main target for shale gas exploration and development geochemical parameters of 13 gas samples from longmaxi shale from 10 wells were analyzed in this study wetness of the gas molar fraction of ethane through pentanes in total gaseous hydrocarbon is only 0 24 0 70 making the longmaxi shale gas among the driest in the world carbon isotopic compositions of the alkane gases from longmaxi shale are characterized by 13c1 13c2 13c3 with the most positive 13c1 values in the world a positive relationship was observed between its 13c1 and 13c2 values reflecting the extremely high thermal maturity of the source rock 2hch4 values range from 140 to 151 and the 2hc2h6 values range from 130 to 173 the hydrogen isotopic compositions were mainly characterized by 2hch4

molecular isotopic characterisation of hydrocarbon biomarkers in palaeocene eocene evaporitic lacustrine source rocks from the jianghan basin china immature organic matter in lacustrine source rocks from the jianghan basin eastern china was studied for distributions and stable carbon isotopic compositions 13 c of hydrocarbon biomarkers all of the bitumens contain isorenieratane 13 c ca 17 indicating the presence of chlorobiaceae and thus periods of euxinic conditions extended into the photic zone aliphatic hydrocarbon fractions are dominated by pristane and phytane and contain relatively low amounts of 4a and 4 methylsteranes c 30 13 c ca 16 believed to originate from 4 methylsterols in dinoflagellates 13 c values of gammacerane ca 24 and c 30 17 21 h hopane ca 23 are consistent with an origin from bacterivorous ciliates that fed on chlorobiaceae the bitumens contain low relative amounts of organo sulphur compounds one rock contains c 37 and c 38 n alkanes 13 c ca 36 derived from alkadienes and alkenones of prymnesiophytes the distributions of hydrocarbon biomarkers suggest that they were initially sulphurised during early diagenesis and later released during early thermal maturation

estimation of marine shale methane adsorption capacity based on experimental investigations of lower silurian longmaxi formation in the upper yangtze platform south china abstract methane adsorption experiments were performed on eight lower silurian longmaxi moisture equilibrated shale samples from the upper yangtze platform south china at pressures up to 12 mpa at 20 c 40 c 60 c 80 c and 100 c to investigate the effects upon methane adsorption capacity and to estimate the variation of methane adsorption capacity as a function of depth and burial history the methane adsorption capacity of the longmaxi shale shows a significant positive correlation with total organic carbon toc content which is accompanied by an increase in bet brunauer emmett teller surface area and total pore volume a quadratic relationship was observed between clay content and methane adsorption capacity there is a threshold clay content 42 3 44 4 in this trend methane adsorption capacity declines with increasing clay content below the threshold and later increases with increasing clay content the langmuir pressure decreases exponentially with the reciprocal of temperature and the langmuir volume decreases linearly with temperature the isosteric heat of adsorption and standard entropy for the longmaxi shale ranges from 10 34 to 11 67 kj mol and from 57 04 to 61 32 j mol k respectively which are clustered around kerogen type i using these relationships a computational scheme was developed to calculate methane adsorption capacity as a function of toc content temperature and pressure based on the langmuir equation this algorithm was applied to estimate methane adsorption capacity of the longmaxi shale as a function of depth due to the dominating effect of pressure methane adsorption capacity increases initially with depth through a maximum and then decreases as a result of increasing temperature at a greater depth the maximum gas adsorption capacity is typically located at a depth range between 800 and 1350 m with toc content increasing the curves shift continuously towards higher adsorption capacity furthermore the maximum methane adsorption capacity moves higher and shifts to a deeper depth as toc content increases ultimately four principal dynamic evolutionary stages of methane adsorption capacity of the longmaxi shale over geologic time as a function of burial history were reconstructed

three dimensional sequence stratigraphy and subtle stratigraphic traps associated with systems tracts west cameron region offshore lousiana gulf of mexico abstract three dimensional sequence stratigraphy is a potent exploration and development tool for the discovery of subtle stratigraphic traps reservoir morphology heterogeneity and subtle stratigraphic trapping mechanisms can be better understood through systematic horizontal identification of sedimentary facies of systems tracts provided by three dimensional attribute maps used as an important complement to the sequential analysis on the two dimensional seismic lines and the well log data on new prospects as well as on already producing fields the additional input of sequential analysis on three dimensional data enables the identification location and precise delimitation of new potentially productive zones the first part of this paper presents four typical horizontal seismic facies assigned to the successive systems tracts of a third or fourth order sequence deposited in inner to outer neritic conditions on a clastic shelf the constructiion of this synthetic representative sequence is based on the observed reproducibility of the horizontal seismic facies response to cyclic eustatic events on more than 35 sequences registered in the gulf coast plio pleistocene and late miocene offshore louisiana in the west cameron region of the gulf of mexico the second part shows how three dimensional sequence stratigraphy can contribute in localizing and understanding sedimentary facies associated with productive zones a case study in the early middle miocene cibicides opima sands shows multiple stacked gas accumulations in the top slope fan prograding wedge and basal transgressive systems tract of the third order sequence between sb 15 5 and sb 13 8 ma

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

sedimentology geochemistry and paleoenvironmental reconstruction of the cretaceous yolde formation from yola sub basin northern benue trough ne nigeria abstract sedimentology organic and inorganic geochemical studies were applied on sediments of the cretaceous yolde formation from yola sub basin northern benue trough northeastern nigeria with an attempt to determine the sedimentary facies paleo redox condition and to re construct the palaeo depositional environments eight 8 facies were identified on the basis of lithology grain size ichnofossils degree of bioturbation and sedimentary structures these facies constitute four facies associations the fa 1 offshore marine fa 2 offshore transition to lower shoreface fa 3 middle shoreface and fa 4 upper shoreface the succession of these facies associations indicates storm and wave influenced offshore shoreface depositional environments for the formation molecular organic geochemical investigation suggests deposition under sub oxic marine environment with major contribution of phytoplankton bacteria and minor amount of terrigenous organic matter xrd mineralogical assessment and major and trace elements geochemistry revealed that the yolde formation sediments were sourced from continental areas of passive continental margin setting and deposited in semiarid climate under suboxic shallow marine conditions related to the first marine transgression that occurred in the benue trough during the late cretaceous period

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

deposition and interpretation of long narrow sandbodies underlain by a basinwide erosion surface cardium formation cretaceous western interior seaway alberta canada abstract sand bodies of the cardium alloformation burnstick allomember occur in three parallel linear trends in the garrington caroline crossfield and lochend oilfields they are extremely long up to 100 km straight and narrow up to 4 km and are encased in marine mudstones suggesting their former interpretation as offshore bars our study of 189 cores and over 800 resistivity well logs shows that below the burnstick the hornbeck allomember consists entirely of dark mudstones deposited in quiet water the hornbeck burnstick contact where seen in cores is extremely sharp in cross sections resistivity well log markers are truncated by the lower surface of the burnstick and the sand bodies rest in asymmetrical one sided elongate scours with erosional relief of up to 7 m above he scoured surface there is a basal lag of mudstone intraclasts and chert pebbles overlain by a sandier upward succession of mudstones sandstones and conglomerates the sandstones are extensively burrowed but show some cross stratification the burnstick sandier upward succession is overlain by black mudstones of the raven river allomember the morphology of the scoured surface as defined in isopach maps does not indicate its formation in an open marine setting the long straight asymmetrical scours are parallel to regional strike and do not suggest subaerial erosion instead we suggest that a major relative lowering of sea level first exposed the hornbeck mudstones to subaerial erosion subsequently marine transgression of this surface removed evidence of its subaerial exposure pauses in transgression stillstands resulted in incised shoreface profiles the asymmetrical scours and at this time rivers supplied coarse sediment to the shoreface this sediment was reworked alongshore to form what are now the very long straight narrow sand bodies continued transgression resulted in the burial of the shoreface sand bodies by black mudstone basal part of the raven river allomember incised shoreface environments provide an alternative to the offshore bar settings suggested for other long linear sand bodies

timing of late cenozoic tidewater glaciation in the far north pacific the onset of late cenozoic glacial events in the far north pacific ocean is recorded by ice rafted debris in the yakataga formation in the gulf of alaska the dating of these events is controversial ages based on molluscs suggest that initial late cenozoic tidewater glaciation occurred in the early middle miocene 15 16 ma previous work on planktic foraminifera indicates that this event is no older than late miocene probably latest miocene 5 6 ma resolution of this problem is important because the yakataga formation is the thickest most complete and best exposed repository of late cenozoic glaciomarine rocks in the northern hemisphere investigation of this record has broader implications for global temperature gradients paleoceanographic development of the far north pacific and northern hemisphere glacial history new planktic foraminiferal data from onshore and offshore yakataga formation sections in the gulf of alaska are compared to a regional depositional and chronostratigraphic framework in order to test whether the yakataga record is anomalous or consistent with the paleoclimatic record of the north pacific this comparison reconfirms that initial glaciomarine rocks of the yakataga formation are no older than late miocene new paleomagnetic data suggest that the base of the yakataga formation is within the lower gilbert polarity chron consistent with the planktic foraminiferal dating and k ar dates on glauconite correlation of the yakataga record to key offshore sections in the far north pacific deep sea drilling project dsdp sites 178 183 192 provides additional insights into the paleoclimatic significance of these rocks uplift of the alaska coastal ranges a necessary prelude to alpine glaciation occurred during late miocene time diatom biofacies dsdp sites 183 192 indicate warm middle miocene conditions climatic deterioration during the late middle and early late miocene time and initial tidewater glaciation between 5 0 and 6 7 ma a relatively warm mid pliocene interval succeeded this initial glaciation which was in turn followed by hemisphere scale glaciation beginning at 2 5 ma this second phase of yakataga glaciation may have begun as early as 3 0 3 5 ma glaciomarine rocks in the basal yakataga formation mark an important climatic event in the north pacific ocean they are latest miocene in age consistent with regional climatic information and not a middle miocene climatic anomaly

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

significance of coniferous rain forests and related organic matter in generating commercial quantities of oil gippsland basin australia contrary to the conventional belief that humic coal generates primarily gas 3 billion bbl of recoverable oil has been discovered in the humic coaly succession of the fluviodeltaic latrobe group upper cretaceous tertiary that serves as both the reservoir and the source for hydrocarbons in the offshore gippsland basin of southeastern australia evidence for generation of liquid hydrocarbons from the coaly succession includes 1 similarity of n alkane distribution in the oil and in the coal extracts 2 high wax content of oil up to 27 by weight 3 high ratio of pristane phytane in oil 5 6 and 4 dominance of c29 steranes in the oil in the gippsland basin coniferous rain forests dominated by kauri vegetation flourished in a raised bog setting present temperate climate and kauri vegetation of new zealand are considered to be the modern analog to the gippsland basin the coniferous vegetation provided large quantities of hydrogen rich exinite macerals such as cutinite and resinite with potential to generate oil high rainfall raised ground water level low oxygen high acidity and low nutrient conditions of a raised bog setting were suitable for preserving organic matter a comparison of gas chromatograms of oils in the gippsland basin with gas chromatograms of oils generated by hydrous pyrolysis in the laboratory from the immature source rocks suggests that the paraffinic fraction of the oil was derived from coal and the naphthenic fraction was derived chiefly from resin

high precision radiogenic strontium isotope measurements of the modern and glacial ocean limits on glacial interglacial variations in continental weathering existing strontium radiogenic isotope 87sr 86sr measurements for foraminifera over quaternary glacial interglacial climate cycles provide no evidence for variations in the isotope composition of seawater at the 9 13 ppm level of precision however modelling suggests that even within this level of uncertainty significant up to 30 variations in chemical weathering of the continents are permitted accounting for the longer term rise in 87sr 86sr over the quaternary and the apparent imbalance of sr in the oceans at the present day this study presents very high precision 87sr 86sr isotope data for modern seawater from each of the major oceans and a glacial interglacial seawater record preserved by planktic foraminifera from ocean drilling program odp site 758 in the north east indian ocean strontium isotope 87sr 86sr measurements for modern seawater from the atlantic pacific and indian oceans are indistinguishable from one another 87sr 86sr 0 7091792 0 0000021 n 17 at the level of precision obtained in this study 4 9 ppm 2 this observation is consistent with the very long residence time of sr in seawater and underpins the utility of this element for high precision isotope stratigraphy the 87sr 86sr seawater record preserved by planktic foraminifera shows no resolvable glacial interglacial variation 87sr 86sr 0 7091784 0 0000035 n 10 and limits the response of seawater to variations in the chemical weathering flux and or composition to 4 9 ppm or less calculations suggest that a variation of 12 around the steady state weathering flux can be accommodated by the uncertainties obtained here the new data cannot accommodate a short term weathering pulse during de glaciation although a more a diffuse weathering pulse accompanying protracted ice retreat is permissible however these results still indicate that modern weathering fluxes are potentially higher than average over the quaternary and such variations through glacial cycles can also account for the longer term rise in 87sr 86sr over this time interval the very high precision measurements made for the marine 87sr 86sr record in this study place clear limits on the magnitude and timing of changes in the chemical weathering flux during glacial interglacial cycles further constraints must be sought from even higher precision measurement or elements with shorter residence times in the ocean such as osmium os that have the capacity to respond to short term variations in input

organic geochemical and mineralogical characterization of the lower silurian longmaxi shale in the southeastern chongqing area of china implications for organic matter accumulation abstract abundant in organic matter the lower silurian longmaxi shale in the upper yangtze platform south china has been demonstrated to play important roles in the petroleum system as both a good source rock and a shale gas reservoir in order to better understand the heterogeneous organic matter accumulation of such shales in the southeastern chongqing area the vertical variations of total organic carbon toc contents mineral concentrations and biomarker distributions were systematically analyzed in this study the longmaxi formation consists of fine grained siliciclastic rocks deposited in a restricted marine shelf environment and it can be further subdivided into two members the lower member is enriched in toc whereas a diminished toc content is documented in the upper member laterally the toc content gradually drops southeast ward in the study area the mineralogical compositions dominated by quartz and clay and to a lesser extent feldspar and carbonate show good correlations with toc contents vertically especially in the lower member saturated and aromatic hydrocarbon biomarkers indicate a dominant organic matter origin from lower hydrobionts algae and bacteria in a reducing marine environment negative correlation relationships between toc contents and terrigenous clastic minerals indicate the predominant role of dilution of terrigenous clastic materials in controlling the organic matter accumulation the sea level drop combined with the continuously active xuefeng uplift contributed to more terrigenous clastic inputs into the study area which resulted in a significant reduction of toc content in the upper longmaxi member

the characteristics and significance of conventional and unconventional sinian silurian gas systems in the sichuan basin central china abstract oil and gas discoveries within proterozoic cambrian strata and the majority of shale gas production occurs in relatively stable tectonic regions and characterised by moderate thermal maturity r o o 2 5 the system comprises two components namely a conventional sinian cambrian dolomite hosted gas resource and an unconventional cambrian silurian shale gas deposit both represent trillion cubic meter accumulations the migration accumulation type sinian cambrian gas system is a result of numerous processes including 1 paleo high trapping within a relatively stable tectonic setting 2 appropriate source materials located in a paleo rift trough 3 large scale dolomite grainstone reservoirs located near the paleo high 4 adequate gas produced from in situ crude oil cracking and 5 gypsum salt and shale cap rock preservation the self contained source reservoir cambrian silurian shale gas system is localized by deepwater organic rich shelf facies characterized by high silicon and calcium contents the recent discovery of these two massive gas fields in old and over matured sedimentary strata has effectively extended the upper maturity limit of r o over 3 0 which may indicate the efficacy of broadening current natural gas exploration areas thus potentially increasing global natural gas resources significantly furthermore the discovery may spark interest in natural gas exploration in widely distributed old strata thus encouraging co development of conventional and unconventional petroleum accumulations

the end ordovician glaciation and the hirnantian stage a global review and questions about late ordovician event stratigraphy abstract this paper proposes a global review of hirnantian event stratigraphy the hirnantian gssp in south china is tentatively correlated with latest ordovician strata from the peri gondwanan glacial regions problems of biostratigraphical correlation are highlighted at a worldwide scale the major biostratigraphically useful fossil groups graptolites chitinozoans brachiopods conodonts acritarchs are analysed and their limits for global correlation of the uppermost ordovician are discussed palaeobiogeographical disparities are invoked as the primary cause of the difficulty in establishing an effective late ordovician global biostratigraphical scheme as an alternative correlative tool the hice hirnantian isotopic curve excursion event is often put forward in the literature however carbon isotope chemostratigraphy shows like biostratigraphy some limits to the present state of knowledge no good independent biostratigraphical control of the hice exists in both shallow carbonate deposits and deeper shaly ones recent studies have also demonstrated inconsistencies between carbon isotopic signals obtained from organic 13corg and inorganic 13ccarb carbon species further complicating the use of the hice as an isochronous benchmark all of these difficulties for hirnantian event stratigraphy are discussed in detail in order to enable them to be overcome in the future precise late ordovician and early silurian event stratigraphies are essential for the understanding of the mechanisms linked to the first of the big five extinctions

latent heating and mixing due to entrainment in tropical deep convection abstractrecent studies have noted the role of latent heating above the freezing level in reconciling riehl and malkus hot tower hypothesis hth with evidence of diluted tropical deep convective cores this study evaluates recent modifications to the hth through lagrangian trajectory analysis of deep convective cores in an idealized high resolution cloud resolving model crm simulation that uses a sophisticated two moment microphysical scheme a line of tropical convective cells develops within a finer nested grid whose boundary conditions are obtained from a large domain crm simulation approaching radiative convective equilibrium rce microphysical impacts on latent heating and equivalent potential temperature e are analyzed along trajectories ascending within convective regions of the high resolution nested grid changes in e along backward trajectories are partitioned into contributions from latent heating due to ice processes and a residual term that is shown to be an approximate representati

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

dinosteranes 4 23 24 trimethylsteranes and other biological markers in dinoglagellate rich marine sediments of rhaetian age abstract alkane biological marker distributions and concentrations have been determined in 18 samples from a section of rhaetian age from the bristol trough and a quantitative micropalaeontological analysis carried out taking into account previous geological investigations of the sequence three end member depositional settings have been recognised from changes in total organic carbon content the biological markers and the micropalaeontological composition these depositional environments are attributed as follows the first which occurs in the lower part of the section corresponds to deposition in a supratidal sabkha type setting with the major organic input being of allochthonous origin the second also in the lower part of the section indicates the occurrence of periods of marine incursion with enhanced salinity resulting from evaporation in the upper part of the section marginal marine conditions are apparent with higher organic carbon biological marker and amorphous organic matter contents at the top suggesting the establishment of more stable conditions of oxygen depletion some sediments in the sequence are notable for containing an abundance of cysts of rhaetogonyaulax rhaetica one of the oldest marine dinoflagellates comparison of microfossil abundances with hydrocarbon abundances extends the circumstantial evidence for the dinophyceae being the major biological source of dinosteranes 4 23 24 trimethylcholestanes and some other 4 methyl steranes in marine sediments the presence of dinosteranes and their 24 ethyl counterparts extends the stratigraphic range of occurrence of such components back to the rhaetian c 31 methyl steranes in the sediments from the second depositional setting are tentatively assigned a 4 22 23 24 tetramethyl sterane skeleton and a dinoflagellate origin

representing equilibrium and nonequilibrium convection in large scale models a new diagnostic convective closure which is dependent on convective available potential energy cape is derived under the quasi equilibrium assumption for the free troposphere subject to boundary layer forcing the closure involves a convective adjustment time scale for the free troposphere and a coupling coefficient between the free troposphere and the boundary layer based on different time scales over land and ocean earlier studies with the ecmwf integrated forecasting system ifs have already demonstrated the model s ability to realistically represent tropical convectively coupled waves and synoptic variability with use of the standard cape closure given realistic entrainment rates a comparison of low resolution seasonal integrations and high resolution short range forecasts against complementary satellite and radar data shows that with the extended cape closure it is also possible independent of model resolution and time step to realistically represent nonequilibrium convection such as the diurnal cycle of convection and the convection tied to advective boundary layers although representing the late night convection over land remains a challenge a more in depth regional analysis of the diurnal cycle and the closure is provided for the continental united states and particularly africa including comparison with data from satellites and a cloud resolving model crm consequences for global numerical weather prediction nwp are not only a better phase representation of convection but also better forecasts of its spatial distribution and local intensity

changes in marine productivity and redox conditions during the late ordovician hirnantian glaciation abstract changes in marine productivity and redox conditions during the end ordovician hirnantian glaciation and ordovician silurian transition were investigated through mo isotope and major and trace element analyses of the wangjiawan hubei province and nanbazi guizhou province sections from the yangtze platform of south china katian shales of the wufeng formation which yield the graptolites dicellograptus complanatus dicellograptus complexus and paraorthograptus pacificus were deposited under euxinic conditions at both localities as shown by high mo ef u ef and 98 mo values a major sea level regression during the hirnantian glaciation resulted in shallowing and a shift toward better oxygenated conditions within the yangtze sea as well as deposition of thin bedded siliceous sediments calcirudite debris flows and limestone turbidites of the kuanyinchiao formation the base of which correlates with the first phase of the end ordovician mass extinction the termination of the hirnantian glaciation at the top of the kuanyinchiao formation was associated with a major sea level transgression a rapid expansion of euxinia in the yangtze sea as documented by a return of high mo ef u ef and 98 mo values and the second phase of the mass extinction during which the cool adapted hirnantian fauna went extinct the long term cooling trend of the middle and late ordovician which culminated in the hirnantian glaciation was driven by enhanced burial of organic carbon as documented by 13 c carb 13 c org and 34 s py records increased organic carbon burial was linked to high rates of marine productivity as shown by high toc and biogenic ba concentrations especially at the deeper less restricted wangjiawan locale producing the hice hirnantian isotopic curve excursion 13 c carb excursion the locus of organic carbon burial during the hirnantian crisis shifted to deeper water environments that were located outside the study region the relatively rapid onset and termination of the hirnantian glaciation were probably due to crossing of tipping points in the late ordovician climatic oceanic system

convectively induced secondary circulations in fine grid mesoscale numerical weather prediction models abstractmesoscale numerical weather prediction models using fine grid o 1 km meshes for weather forecasting environmental assessment and other applications capture aspects of larger than grid mesh size convectively induced secondary circulations ciscs such as cells and rolls that occur in the convective planetary boundary layer pbl however 1 km grid spacing is too large for the simulation of the interaction of ciscs with smaller scale turbulence the existence of ciscs also violates the neglect of horizontal gradients of turbulent quantities in current pbl schemes both aspects poorly resolved ciscs and a violation of the assumptions behind pbl schemes are examples of what occurs in wyngaard s terra incognita where horizontal grid spacing is comparable to the scale of the simulated motions thus model ciscs m ciscs cannot be simulated reliably this paper describes how the superadiabatic layer in the lower convective pbl together with increased horizontal resolution allow the critical ra

black shale grey shale fossils and glaciers anatomy of the upper ordovician silurian succession in the tazzeka massif of eastern morocco abstract a 400 m thick clastic succession of late ordovician through silurian age crops out in the tazzeka massif eastern morocco biostratigraphic data chitinozoa acritarchs constrain these rocks to the late katian through hirnantian coeval with glaciation in gondwana with a 8 myr hiatus at the ordovician silurian boundary sedimentological analysis reveals six facies associations including interbedded black and grey shale couplets poorly oxygenated shelf sediments a bioturbated shale with wave rippled sandstone inner shelf deposits several occurrences of diamictite of probable glaciogenic origin interbedded sandstone and mudstone storm and fair weather wave agitated shoreface rippled sandstone storm return flow deposits and amalgamated sandstone deposits delta front debris flows direct evidence for glaciation in the hirnantian deposits is poor third order sequence stratigraphic analysis reveals two transgressive systems tracts late katian and intra hirnantian two highstand systems tracts both intra hirnantian lowstand wedges probably corresponding to two principal glacial lowstands two maximum flooding surfaces late katian and intra hirnantian and a major ravinement surface hirnantian silurian contact remote from the centre of glaciation the tazzeka succession is suggested to be an excellent reference section with which to understand glacially moderated sea level changes in the late ordovician silurian late llandovery or younger shale geochemistry indicates organic enrichment toc 4 5 this organic enrichment greatly increases the known extent of the upper of two silurian organic shales across north africa potential hydrocarbon source rocks across the region

black shale deposition in an upper ordovician silurian permanently stratified peri glacial basin southern jordan abstract the lower palaeozoic upper ordovician silurian succession of north africa contains one of the world s most prolific black shale source rocks yet the origin of these rocks remains contentious the black shale of the batra formation in jordan was deposited at high palaeolatitude during rapid hirnantian to early silurian deglaciation here we report geological and organic geochemical results that provide evidence for an increase in photic zone primary productivity during ice melting the decay of this organic matter through oxidative respiration resulted in euxinia which enhanced the potential for organic matter preservation the occurrence of isorenieratane in all samples indicates euxinia extended from the photic zone to the sediment water interface the stratified basins and fjords of east antarctica provide a likely modern analogue

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

geological controls and estimation algorithms of lacustrine shale gas adsorption capacity a case study of the triassic strata in the southeastern ordos basin china abstract high pressure methane adsorption experiments on a series of triassic lacustrine shale moisture equilibrated samples from the southeastern ordos basin china were conducted at pressure up to 20 mpa two of which were measured at 30 c 40 c 50 c 60 c and 70 c and seven were performed under reservoir temperature from 48 c to 62 c to investigate the effect of organic matter content maturity mineralogical compositions and reservoir conditions temperature and pressure on the methane sorption capacity the total organic carbon contents tocs range from 0 91 wt to 6 11 wt the thermal maturities as inferred from rock eval analysis range from low mature to high mature the minerals of the shale samples are dominated by clays 36 57 wt and quartz 19 44 wt for the entire shale samples the dominant clay minerals are mixed layer illite smectite with some illite and no smectite exists corresponding to a stage of late diagenesis the studied samples have n2 bet surface areas ranging between 1 47 and 9 21 m2 g and pore volumes of 0 013 0 034 cm3 g the methane sorption capacities of moisture equilibrated shale samples show a positive correlation with toc contents and bet surface areas no relationship was observed between the clay contents and methane sorption capacities indicating that clay minerals do not significantly contribute to methane sorption capacity in these organic shales the langmuir pressure pl increases exponentially with temperature and the langmuir volume vl decreases linearly with temperature a computational scheme has been developed to calculate the methane sorption capacity of shales as a function of toc content temperature and pressure based on langmuir sorption isotherm function using this algorithm methane sorption capacity of organic shales as function of depth can be obtained due to the predominating effect of pressure the methane sorption capacity increases with depth initially through a maximum and then decreases due to the influence of increasing temperature at a greater depth the maximum gas sorption capacity typically occurs at a depth range between 400 and 900 m with toc content increasing the maximum methane sorption capacities of organic shales and the corresponding depths increase

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

geochemical evidence for oxygenated bottom waters during deposition of fossiliferous strata of the burgess shale formation abstract deciphering the oxygenation potential of bottom waters during deposition of the fossiliferous strata of the burgess shale is key to understanding the paleoecology of the organisms preserved as fossils and the processes involved in their preservation methods of paleo redox determination that are based upon trace fossils organic carbon content or size analysis of pyrite framboids are problematic when applied to the burgess shale fortunately patterns in redox sensitive trace elements hold great potential for determining paleo redox conditions for these greenschist facies rocks because they are independent of both age and metamorphic grade four burgess shale type bst fossil bearing sections were studied three lie within the burgess shale formation whereas one lies within the slightly younger duchesnay unit of the middle chancellor formation the geochemical proxies of seawater redox conditions that were used are mo u th v cr v v ni ni co and v sc each of these redox sensitive indices suggests that oxygenated conditions prevailed in the overlying seawater during deposition of beds within which bst preservation developed non fossiliferous beds at the base of the mt stephen trilobite beds yield three geochemical indices v v ni v sc ni co that indicate deposition under dysoxic to anoxic conditions thus the only beds to have been deposited under anoxic conditions are barren of fossils of soft bodied taxa further contradicting the notion that bottom water anoxia is a factor in bst preservation the laminated nature of the burgess shale and evidence for subsurface anoxia coupled with evidence for oxygenated bottom waters presence of bacterial mats and surficial trace fossils suggest that the burgess shale was deposited in the exaerobic zone oxic anoxic boundary at the water sediment interface implications of this reinterpretation of the depositional environment of the burgess shale include 1 taphonomic models for bst preservation must account for the presence of oxygen in bottom waters 2 paleoecological interpretations of the burgess shale need to account for a probable autochthonous benthic component in what is a complex assemblage of fossils that includes elements derived from the platform and 3 the possibility of burgess shale communities based upon chemosynthesis and or bacteria grazing must be considered

late quaternary mediterranean sapropels iii assessment of source of input and palaeotemperature as derived from biological markers abstract sources of input contributing to the organic matter of four different mediterranean sapropels s1 s5 s6 s7 are inferred from the relative distributions of terrigenous and marine biological markers in these quaternary deposits the relative terrigenous contribution does not vary significantly within the marine contribution there is a significant compositional variation a contribution from dinoflagellates is relatively important in the s1 sapropel whereas sapropels s6 and s7 are characterized by a relatively large contribution from prymnesiophyte algae and planktonic cyanobacteria the abundance of diatoms in sapropel s5 as deduced from microscopic observations is probably reflected by a high concentration of loliolide variations in sea surface water temperatures can be deduced from the relative abundance of di and triunsaturated c37 ketones uk37 index and from the relative abundance of esterified 27 nor 24 methylcholesta 5 22e dien 3 ol and cholesta 5 22e dien 3 ol sti index these two molecular temperature indices are consistent with the 18o record and with the pollen record of the sapropels investigated

sedimentation rate dilution preservation and total organic carbon some results of a modelling study abstract a modelling exercise was undertaken to evaluate the positive preservational and negative diluent effects of sedimentation rate sr on the total organic carbon toc content of marine sediments and to use multiple regression analysis of modern data to predict toc data presented show the predicted marine toc using the carbon burial efficiency be versus sr relationship of betts and holland betts j n holland h d 1991 the oxygen content of ocean bottom waters the burial efficiency of organic carbon and the regulation of atmospheric oxygen palaeogeography palaeoclimatology palaeoecology global and planetary change section 97 5 18 calculated for a range of sr water depths primary productivities and four fixed be values the results suggest that the preservation effect of sr only enhances toc at 5 cm ka in oxic regimes after which dilution occurs if carbon supply is held constant above 35 cm ka there is no appreciable difference in toc regardless of whether the sea floor is anoxic or not below 10 cm ka there is a strong divergence in oxic and anoxic toc values observed positive correlations of sr and toc at 5 cm ka are largely an artefact of including sites from shallower depths and or higher productivities multiple regression analysis mra of modern marine sediment data suggests that once re scaled to allow for their non linear effect dissolved oxygen values may be a significant additional variable in determining the toc predicting an approximately 2 5 4 0 times higher toc in anoxic facies compared with fully oxic ones 4 ml l dissolved oxygen all other things being equal the mra also indicates a generally negative partial correlation between carbon delivery flux and be in modern sediments producing a significant moderating effect on the predicted toc

a combined eddy diffusivity mass flux approach for the convective boundary layer a better conceptual understanding and more realistic parameterizations of convective boundary layers in climate and weather prediction models have been major challenges in meteorological research in particular parameterizations of the dry convective boundary layer in spite of the absence of water phase changes and its consequent simplicity as compared to moist convection typically suffer from problems in attempting to represent realistically the boundary layer growth and what is often referred to as countergradient fluxes the eddy diffusivity ed approach has been relatively successful in representing some characteristics of neutral boundary layers and surface layers in general the mass flux mf approach on the other hand has been used for the parameterization of shallow and deep moist convection in this paper a new approach that relies on a combination of the ed and mf parameterizations edmf is proposed for the dry convective boundary layer it is shown that the edmf approach follows naturally from a decomposition of the turbulent fluxes into 1 a part that includes strong organized updrafts and 2 a remaining turbulent field at the basis of the edmf approach is the concept that nonlocal subgrid transport due to the strong updrafts is taken into account by the mf approach while the remaining transport is taken into account by an ed closure large eddy simulation les results of the dry convective boundary layer are used to support the theoretical framework of this new approach and to determine the parameters of the edmf model the performance of the new formulation is evaluated against les results and it is shown that the edmf closure is able to reproduce the main properties of dry convective boundary layers in a realistic manner furthermore it will be shown that this approach has strong advantages over the more traditional countergradient approach especially in the entrainment layer as a result this edmf approach opens the way to parameterize the clear and cumulus topped boundary layer in a simple and unified way

the convective boundary layer in the terra incognita numerical simulations of a convective boundary layer cbl are performed to investigate model behavior in the terra incognita also known as the gray zone the terra incognita of the cbl refers to a range of model grid spacing that is comparable to the size of the most energetic convective eddies which are on the order of the boundary layer depth using the rayleigh benard thermal instability as reference a set of idealized simulationsisused toshow that grayzone modelingisnot onlya numericalchallenge but also poses dynamical difficulties when the grid spacing falls within the cbl gray zone grid dependent convection can occur the size of the initial instability structures is set by the grid spacing rather than the natural state of the flow this changes higher order flow statistics and poses fundamental difficulties for gray zone modeling applications

3 d seismic is the promise fulfilled since the first 3 d survey 17 years ago companies of the shell group have operated over 250 such surveys outside north america and as non operating partners have been involved in many others the method s power to produce high resolution images of the subsurface has been thoroughly proven and it has become increasingly apparent that subsurface models resulting from mapping with 2 d seismic lack the detail provided by the 3 d method also amplitude effects caused by variations in porefill and or lithology and more easily seen on 3 d seismic than on 2 d profiles thus in addition to its initial use for structural mapping 3 d seismic is used increasingly to evaluate trends in reservoir quality

ordovician and silurian sea water chemistry sea level and climate a synopsis following the cambrian explosion and the appearance in the fossil record of most animal phyla associated with a range of new body plans the ordovician and silurian periods witnessed three subsequent major biotic events the great ordovician biodiversification event the end ordovician extinction the first animal extinction and second largest of the five mass extinctions of the phanerozoic and the early silurian postextinction recovery there are currently no simple explanations for these three major events combined extrinsic geological and intrinsic biological factors probably drove the biodiversifications and radiations and the appearance and disappearance of marine habitats have to be analysed in the frame of changing palaeogeography palaeoclimate and sea water chemistry the present paper reviews the relationships of the three biotic events to chemical and physical processes occurring in the ocean and atmosphere during the ordovician and silurian including sea level changes geochemical proxies 13c 18o 87sr 86sr of the ocean waters and the evolution of the atmosphere oxygen and carbon dioxide content less

late ordovician to earliest silurian graptolite and brachiopod biozonation from the yangtze region south china with a global correlation late ordovician to earliest silurian is an important geological period marked by large geological and biological events however the strata and fossils of this interval are not complete in many parts of the world based on studies of 43 sites in south china in particular the continuous sections on the yangtze platform we recognize a complete succession including seven graptolite zones and two shelly faunas in ascending order the graptolite zones are the dicellograptus complanatus dicellograptus complexus paraorthograptus pacificus including lower subzone tangyagraptus typicus subzone and diceratograptus mirus subzone normalograptus extraordinarius normalograptus ojsuensis normalograptus persculptus akidograptus ascensus and parakidograptus acuminatus zones the shelly faunas are the foliomena nankinolithus and hirnantia faunas which may be correlated with d complanatus zone and n extraordinarius n ojsuensis to part of n persculptus zones respectively the biozonation through this interval from the yangtze region can be correlated with that of other parts of the world such as dob s linn in scotland spain and portugal thuringia saxonia bavaria bohemia poland kazakhstan kolyma malaya peninsula yukon canadian arctic islands nevada argentina niger and victoria australia the hirnantian substage which has been proposed by us recently includes the n extraordinarius n ojsuensis zone hirnantia fauna and n persculptus zone the base of the hirnantian substage is marked by the first appearance data fads of n extraordinarius and n ojsuensis which have been determined to be synchronous on a global scale

long lived glaciation in the late ordovician isotopic and sequence stratigraphic evidence from western laurentia the timing and causes of the transition to an icehouse climate in the late ordovician are controversial results of an integrated 13c and sequence stratigraphic analysis in nevada show that in the late ordovician chatfieldian stage mid caradoc a positive 13c excursion in the upper part of the copenhagen formation was closely followed by a regressive event evidenced within the prominent eureka quartzite the chatfieldian 13c excursion is known globally and interpreted to record enhanced organic carbon burial which lowered atmospheric p co2 to levels near the threshold for ice buildup in the ordovician greenhouse climate the subsequent regressive event in central nevada previously interpreted as part of a regional tectonic adjustment is here attributed in part to sea level drawdown from the initiation of continental glaciation on gondwana this drop in sea level which may have contributed to further cooling through a reduction in poleward heat transport and a lowering of p co2 by suppressing shelf carbonate production signals the transition to a late ordovician icehouse climate 10 m y before the widespread hirnantian glacial maximum at the end of the ordovician

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

pliocene holocene evolution of depositional conditions in the eastern mediterranean role of anoxia vs productivity at time of sapropel deposition a multiproxy geochemical study of nine sapropel layers from odp hole 964a odp leg 160 in the eastern mediterranean spanning the pliocene holocene time interval provides new insights into the evolution of sapropel deposition paleoenvironmental proxies were used for reconstruction of productivity ba derived from marine barite oxygen conditions trace metal ratios and sedimentary regime clay minerals detrital elements these proxies reveal a significant increase in river runoff relative to decreasing aeolian input during sapropel deposition over the whole time interval ba excess supports the argument that a significant increase in export productivity is the main triggering mechanism for sapropel deposition although preservation also played an important role furthermore major differences exist in depositional conditions including both oxygenation and productivity since the pliocene productivity fluctuated substantially and was higher during the pliocene and pleistocene than during the holocene at the same time decreasing oxygen availability parallels the enhanced productivity dysoxic to anoxic conditions appear to coincide with marine productivity maxima thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation this correspondence supports the hypothesis that productivity fluctuations resulting from climate oscillations were the main cause of enhanced organic matter contents and also a main controlling factor for reduced oxygen availability

on the mass flux representation of vertical transport in moist convection abstractthis study investigates to what extent the convective fluxes formulated within the mass flux framework can represent the total vertical transport of heat and moisture in the cloud layer and whether the same approach can be extended to represent the vertical momentum transport using large eddy simulations less of six well documented cloud cases including both deep and shallow convection two methods are used to decompose the les resolved vertical fluxes decompositions based on the coherent convective features using the mass flux top hat profile and by two dimensional fast fourier transform 2d fft in terms of wavenumbers the analyses show that the convective fluxes computed using the mass flux formula can account for most of the total fluxes of conservative thermodynamic variables in the cloud layer of both deep and shallow convection for an appropriately defined convective updraft fraction a result consistent with the mass flux dynamic view of moist convection and previous studies however