isolation of diagenetic overgrowths on quartz sand grains for oxygen isotopic analysis abstract diagenetic overgrowths on detrital quartz sand grains in sandstones can be isolated for direct measurement of their oxygen isotope ratios interfacial materials between detrital cores and diagenetic overgrowths are dissolved by etching with dilute hf the weakened interface breaks when grains are agitated ultrasonically subsequent particle size separation is an effective means of concentrating the diagenetic component

geological controls on gas saturation in the yanchuannan coalbed methane field southeastern ordos basin china abstract the paper investigates lateral variation of gas saturation and its geological controls of the no 2 coal seam in the permian shanxi formation based on coal samples from 21 exploration wells in the yanchuannan coalbed methane cbm field southeastern ordos basin china the data set reveals that gas saturation of the no 2 coal seam shows a high lateral variation from 32 44 to 89 69 and that there is an overall trend in gas saturation with depth overprinted by four other factors 1 influence of faults 2 secondary biogenic gas generation 3 local top seal conditions and 4 variations in coal properties the reverse faults f1 and f2 are effective barriers horizontally for the hydraulic communication and divide our study area into relatively closed and recharge zones gas saturation of the relatively closed zone is generally higher than that in the recharge zone in the recharge gas saturation increases generally along the flow pathway of groundwater with the exceptions of the areas affected by secondary biogenic gas the stable isotope compositions suggest that late stage biogenic methane was generated via co 2 reduction associated with meteoric water recharge which significantly contributes to higher gas saturation than expected meanwhile the biogenic gas generation was is restricted to shallow depths the apparent variations in local areas of lithology of the overlying stratum next to the coal seam suggest that the top seal conditions are deteriorative which can cause gas dissipation and reduce gas saturation remarkably integrally for the variations in coal properties gas saturation has a general positive relationship with coalification and weak negative correlations with moisture content and ash yield but the relationships lacks statistical significances gas saturation is not associated with coal maceral in the study area

geothermometry and geochemistry of aqueous and oil bearing fluid inclusions from fateh field dubai abstract the production of oil from fateh field dubai is principally from the cretaceous mishrif formation porosity in the reservoir facies is partly occluded by late coarse grained calcite cement this cement contains both aqueous and oil bearing fluid inclusions fluid inclusion geothermometry was used to determine the temperature of that cement precipitation and calculate its timing relative to basin burial history these data were related to source rock maturation and from that the timing of oil migration was inferred to be oligocene to mid miocene which is geologically contemporaneous with early petroleum generation r 0 0 5 0 6 in the khatiyah source rock the fluid inclusions were analyzed by a thermal decrepitation gas chromatography technique benzene and low molecular weight paraffins were present and a series of normal alkenes was tentatively identified in the aqueous inclusions fresh oil inclusions consisted of c 1 n c 25 compounds whose light hydrocarbon composition was consistent with derivation from an early mature source rock altered petroleum residues detected in many mishrif samples are contained either in inclusions or along crystal cleavages these materials are the subject of an ongoing geochemical study of fateh field

an improved method for reconstructing the stratigraphy and bathymetry of continental margins application to the cenozoic tectonic and sedimentary history of the congo margin a number of techniques such as backstripping and forward modeling have been previously used to reconstruct the tectonic sedimentary and thermal history at passive margins still these techniques are generally inaccurate in places such as the west african margin where the stratigraphic record is disrupted by continuous faulting of the sediment pile caused by salt tectonics and by erosional unconformities the ability to reconstruct the stratigraphy salt thickness and water depth along profiles of these types of margins is important for determining the factors controlling the geological history of the margin and the evolution of hydrocarbon systems to reconstruct the stratigraphy paleowater depths and salt flowage on a profile across the congo margin we combined backstripping and palinspastic reconstruction this enabled us to restore the faulting and salt flowage and simultaneously to take into account the isostatic response of the lithosphere to sediment loading and unloading this method allowed us to estimate the paleowater depth as well as the stratigraphy and the geometry of the sedimentary section on the profile through time the determination of the regional isostatic response of the lithosphere is performed with the use of a new model to estimate the flexural rigidity of continental lithosphere to demonstrate this method we perform the cenozoic reconstruction of the congo margin the results yield a coherent geological history of the margin from the eocene to the present in the eocene the margin was a carbonate ramp with a deep seated shelf break 600 m during the eocene oligocene transition intermediate water depth oceanic currents triggered submarine erosion of the eocene slope and shelf from the miocene to the present we observe a large increase in the input of terrigenous clastic sediments as a result the shelf prograded 40 km across the eocene ramp as the clastic sediments prograded across the margin into the deep basin faulting of the sediment pile and salt withdrawal caused the formation of grabens in places where salt swells had previously formed finally the reconstruction suggests that the congo margin was uplifted by at least 330 m between the late oligocene and the middle miocene

modeling of gas generation from the cameo coal zone in the piceance basin colorado the gas generative potential of the cretaceous cameo coal in the piceance basin northwestern colorado was evaluated quantitatively by sealed gold tube pyrolysis the h c and o c elemental ratios show that pyrolyzed cameo coal samples follow the van krevelen humic coal evolution pathway reasonably simulating natural coal maturation kinetic parameters activation energy and frequency factor for gas generation and vitrinite reflectance ro changes were calculated from pyrolysis data experimental ro results from this study are not adequately predicted by published ro kinetics and indicate the necessity of deriving basin specific kinetic parameters when building predictive basin models using derived kinetics for ro evolution and gas generation basin modeling was completed for 57 wells across the piceance basin which enabled the mapping of coal rank and coalbed gas potential quantities of methane generated at approximately 1 2 ro are about 300 standard cubic feet per ton scf ton and more than 2500 scf ton in situ dry ash free coal at ro values reaching 1 9 gases generated in both low and high maturity coals are less wet whereas the wetter gas is expected where ro is approximately 1 4 1 5 as controlled by regional coal rank and net coal thickness the largest in place coalbed gas resources are located in the central part of the basin where predicted volumes exceed 150 bcf mi 2 excluding gases in tight sands

ar ar dating of k feldspar in low grade metamorphic rocks example of an exhumed mesozoic accretionary wedge and forearc south island new zealand 1 new 40ar 39ar ages from detrital k feldspars and metamorphic white micas from the eastern province terranes of new zealand have been used to investigate the thermo tectonic history of different parts of an exhumed mesozoic forearc basin and accretionary wedge k feldspars from barely metamorphosed sedimentary host rocks mainly record detrital source area ages whereas those from zeolite and prehnite pumpellyite facies host rocks have textures and argon age spectra that indicate recrystallization during regional low temperature metamorphism the results contribute to a model that genetically links thermo tectonic events across the accretionary wedge and forearc basin elements of the convergent margin and into the median batholith arc probably by the early cretaceous and possibly by the middle jurassic thus even though multidiffusion domain mdd models cannot be used to make inference on cooling histories in such situations the k feldspar argon thermochronometer can provide useful information on the timing of geological events in sub greenschist facies rocks

the effects of depositional environment on vitrinite fluorescence intensity abstract the effects of depositional environment on vitrinite secondary fluorescence properties were investigated using a quantitative fluorescence microscopical technique fluorescence intensities relative to a uranyl glass standard were obtained on vitrinites formed under varying degrees of marine influence interpretations of the coals depositional environment used in this study were based on paleoenvironmental studies of the overlying strata some possible paleoenvironmental mechanisms responsible for diversity within this petrographic property are discussed

diagenesis of the lower cretaceous arkoses of the angola margin petrologic k ar dating and 18 o 16 o evidence abstract the lower cretaceous arkoses of the angola offshore basin have been extensively diagenetically altered the results of a multidisciplinary study which included petrography k ar dating and 18o 16o and 13c 12c ratio measurements combined with fluid inclusion data provide information about the timing and temperatures of formation of the diagenetic cements as well as the nature and origin of the diagenetic fluids during burial k feldspar overgrowths formed at around 100 ma followed by discrete development of quartz overgrowths locally both are preceded by chlorite rim cement then chronologically dolomite calcite and clay cements precipitated the microcrystalline clays are an imii ordered illite smectite of eocene age 50 ma and or a pure illite of miocene age 16 ma both are commonly mixed with a fe rich chlorite fluid inclusion data walgenwitz and pagel 1984 walgenwitz et al 1985 1989 from the k feldspar quartz and dolomite cements indicate that diagenetic fluids were high temperature 110 165 c brines 24 wt eq nacl estimated temperatures of formation of the diagenetic clays based on k ar ages and burial history curves are 66 125 c for the imii illite smectite and 140 195 c for the illite these data suggest the existence of high geothermal gradients during the cretaceous and a diminution of the geothermal gradient from cretaceous to present the 18o 16o ratios indicate that diagenetic fluids were enriched in 18o with 18o values between 1 7 and 9 5 per rail for the imii illite smectite and between 5 6 and 10 5 per mil for the k feldspar dolomite and illite cements such values preclude any significant direct contribution of meteoric water these 18o rich brines probably derived from the aptian evaporites overlying the sediments studied

thermo chronological approach to reservoir diagenesis in the offshore angola basin a fluid inclusion 40 ar 39 ar and k ar investigation 1 microthermometric analyses of fluid inclusions and geochronological surveys of authigenic silicates in neocomian sandstones and albian dolomitic reservoirs from the offshore angola basin have allowed determination of the age and the physical chemical conditions for fluid migration in a late diagenetic stage the 40 ar 39 ar laser probe dating of adularia overgrowths from the albian reservoirs shows that the trapping of primary aqueous and oil inclusions occurred during the early miocene 25 6 or 3 2 ma the k ar age of authigenic illites from the neocomian sandstones is slightly younger 19 or 1 ma and the crystallization of regular illite smectite mixed layers is related to a previous eocene to paleocene diagenetic stage 51 58 ma there appears to have bee both a regional and vertical variation in the salinity of aqueous fluids during the miocene the fluid inclusion trapping temperatures were estimated by correcting the homogenization temperatures of aqueous fluids assuming that pressures during the miocene were close to the present reservoir pressures and by intersecting the isochores of aqueous and oil inclusions assuming they were trapped at strictly similar pressure and temperature conditions the fluid inclusion temperatures are consistent with those derived from the tetrahedral aluminum content aliv of authigenic chlorites 168 206 degrees c in the albian reservoirs at depths between 2350 and 3580 m and 175 237 degrees c in the neocomian sandstones at depths between 2770 and 4470 m in both reservoir formations miocene tempe atures were higher than the present ones and related either to deeper burial or higher geothermal gradient

separation kar dating and 18o16o ratio measurements of diagenetic k feldspar overgrowths an example from the lower cretaceous arkoses of the angola margin abstract k feldspar overgrowths adularia on detrital k feldspar were removed from the lower cretaceous 130 115 ma arkoses of angola and concentrated for oxygen isotopic analysis and k ar dating the concentration technique consisted of etching with dilute h2sif6 followed by ultrasonic agitation and particle size separation the diagenetic k feldspar content of each of fourteen subfractions as estimated by cathodoluminescence was between 45 and 92 percent the rest being mostly detrital microcline and in some cases small amounts of quartz and or albite extrapolation of 40 ar 40 k and 18 o 16 o ratios indicated a k ar age of the adularia of 98 16 ma and a 18o of 20 2 0 8 per mil smow the age is consistent with petrographic observations which suggest that precipitation of adularia occurred relatively early in the diagenetic history the k ar age together with the 18o value burial history and fluid inclusion data indicate that adularia formed at relatively shallow depth

origin of minerals in joint and cleat systems of the pottsville formation black warrior basin alabama implications for coalbed methane generation and production coalbed methane is produced from naturally fractured strata in the lower pennsylvanian pottsville formation in the eastern part of the black warrior basin alabama major fracture systems include orthogonal fractures which consist of systematic joints in siliciclastic strata and face cleats in coal that strike northeast throughout the basin calcite and minor amounts of pyrite commonly fill joints in sandstone and shale and less commonly cleats in coal joint fill calcite postdates most pyrite and is a weakly ferroan coarse crystalline variety that formed during a period of uplift and erosion late in the burial history pyrite forms fine to coarse euhedral crystals that line joint walls or are complexly intergrown with calcite stable isotope data reveal large variations in the carbon isotope composition of joint and cleat fill calcite 10 3 to 24 3 peedee belemnite pdb but only a relatively narrow range in the oxygen isotope composition of this calcite 16 2 to 4 1 pdb negative carbon values can be attributed to 13c depleted co2 derived from the oxidation of organic matter and moderately to highly positive carbon values can be attributed to bacterial methanogenesis assuming crystallization temperatures of 2050c most joint and cleat fill calcite precipitated from fluids with 18o ratios ranging from about 11 to 2 standard mean ocean water smow uplift and unroofing since the mesozoic led to meteoric recharge of pottsville strata and development of freshwater plumes that were fed by meteoric recharge along the structurally upturned southeastern margin of the basin influxes of fresh water into the basin via faults and coalbeds facilitated late stage bacterial methanogenesis which accounts for the high gas content in coal and the carbonate cementation of joints and cleats diagenetic and epigenetic minerals can affect the transmissivity and storage capacity of joints and cleats and they appear to contribute significantly to interwell heterogeneity in the pottsville formation in highly productive coalbed methane fields joint and cleat fill calcite have strongly positive 13c values whereas calcite fill has lower 13c values in fields that are shut in or abandoned petrographic analysis and stable isotope geochemistry of joint and cleat fill cements provide insight into coalbed methane reservoir quality and the nature and extent of reservoir compartmentalization which are important factors governing methane production

maximum diagenetic temperature in a petroleum source rock from venezuela by fluid inclusion geothermometry abstract the maximum diagenetic temperature in the la luna petroleum source rock from a well in venezuela was determined by fluid inclusion geothermometry the result of 145 160 c is in good agreement with the formation temperature deduced from well logs being 157 c the results further indicate that quartz vein fillings were formed 4 ma ago at t 125 130 c at the onset of liquid hydrocarbon expulsion from the source rocks

predicting boundary shear stress and sediment transport over bed forms to estimate bed load sediment transport rates in flows over bed forms such as ripples and dunes spatially averaged velocity profiles are frequently used to predict mean boundary shear stress however such averaging obscures the complex nonlinear interaction of wake decay boundary layer development and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress particularly skin friction which is critically important in predicting skin friction over 2d bed forms the approach is based on combining the equations describing the mechanics of the internal boundary layer with semi empirical structure functions to predict the velocity at the crest of a bed form where the flow is most similar to a uniform boundary layer significantly the methodology is directed toward making specific predictions only at the bed form crest and as a result it avoids the difficulty and questionable validity of spatial averaging the model provides an accurate estimate of the skin friction at the crest where transport rates are highest simple geometric constraints can be used to derive the mean transport rates as long as bedload is dominant

hump shaped 40ar 39ar age spectra in k feldspar and evidence for cretaceous authigenesis in the fountain formation near eldorado springs colorado the fountain formation near eldorado springs co usa shows evidence of alteration by hydrothermal fluids that precipitated authigenic potassium feldspar adularia as rims on detrital feldspars and as interstitial cement deposits detailed 40ar 39ar step heating experiments of samples from the fountain formation reveal age spectra having a characteristic hump at laboratory temperatures between 900 and 1080 c the humps appear to be related to the presence of adularia laser analyses of small grains of adularia indicate that the hump can be physically dissected unlike age gradients found in igneous feldspars such behavior is consistent with the mixing of gas from two or more generations of k feldspar each having unique diffusion properties the feldspars studied here indicate that two pulses of 150 c hydrothermal fluids migrated through the fountain formation at 135 and 94 ma prior to the main phase of laramide tectonic activity in the region the limited occurrence of authigenic cements suggests that reactivation of the underlying precambrian idaho springs ralston creek shear zone was significant enough to heat and mobilize large quantities of meteoric fluids in addition these data also suggest that cretaceous movements along the transcontinental arch correlated with stratigraphic events began approximately 40 million years earlier than previously thought

potassium distribution and metasomatism in pelites and schists how and when relation to postdepositional events a large global database for over 9000 archean to holocene pelites in numerous basins has been developed to evaluate diagenetically unaltered and altered compositions the mineralogy and geochemistry of quaternary muds and ancient mudstones provide first order controls on diagenetic potassium metasomatism in pelites clay mineralogy of quaternary muds is dominated by smectite and kaolinite with minor detrital mica and illite thus k2o is 4 k al is 0 25 and k rb is 220 in most quaternary muds with diagenetic alteration of clays to illite smectite and illite k2o content increases to 4 8 and k al rises to 0 2 0 5 or more in extreme potassium metasomatism authigenic k feldspar develops sources of potassium are internal to shale sandstone units wherein detrital k feldspar is dissolved during diagenesis providing k for clay illitization in closed system isochemical alteration as in some gulf coast and north sea basin cases potassium in amounts greater than that available from closed system alteration is provided from extraformational circulating brines in open system diagenesis k rb with diagenesis varies according to whether the metasomatizing fluid was relatively poor in rb seawater derived brines or richer in rb as in many hydrothermal waters diagenetic fluids may originate from seawater or meteoric water enriched in cations by water rock interactions along their subsurface migration paths and or by dissolution of evaporites potassium metasomatizing fluids penetrate low permeability pelites through faults fractures and microfractures and by diffusion in the mineral matrix typically k metasomatism possibly with pb zn cu ba and f mineralization occurs long after sediment deposition and burial at temperatures of 50 to 150 c related to tectonic activity and fluid movement different modes of metasomatism are recognized and correlated with geological setting in the passive margin gulf coast tertiary basin open system k metasomatism where present is limited to areas adjacent to steeply dipping growth faults which act as conduits for episodic pulses of altering fluids migrated upward from deeper basin sources in contrast widespread pervasive open system k metasomatism produced by continuous long term gravity advective and diffusive flow of brine from the late paleozoic appalachian ouachita wichita mountains highland to altered earlier paleozoic shales plus sandstones bentonites and carbonates in the illinois and anadarko ardmore foreland basins this mode of k alteration following major mountain building events is characteristic of many precambrian and paleozoic collision orogens and associated foreland basins another mode is in rift basins with no external drainage in which indigenous waters are evaporated to brines these brines cause albitization of k feldspar to yield potassium for illitization of detrital clays

thermogenic and secondary biogenic gases san juan basin colorado and new mexico implications for coalbed gas producibility the san juan basin is the most prolific coalbed gas basin in the world with 1992 production exceeding 440 gcf footnote 12 4 billion m3 resources of approximately 50 tcf 1 4 trillion m3 and proved reserves of over 6 tcf 170 billion m3 coalbed gas wells with the highest production initial potential greater than 10 mcf day or 0 28 million m3 day occur in the overpressured north central part of the basin hydrologic analysis indicates that overpressure in the fruitland formation is artesian in origin and represents repressuring that developed during the middle pliocene highly permeable laterally continuous coal beds override abandoned shoreline pictured cliffs sandstones and extend to the elevated recharge area in he northern basin to form a dynamic regionally interconnected aquifer system coal rank and basin hydrodynamics control the composition of fruitland coalbed gases which varies significantly across the basin chemically dry gases in the north central part of the basin coincide with meteoric recharge and regional overpressure the consistency of methane dgr13c values across the basin the presence of isotopically heavy carbon dioxide in coalbed gases and bicarbonate in formation waters and biodegraded n alkane distributions of some coal extracts indicate that coalbed gases in the north central basin are a mixture of thermogenic 25 50 secondary biogenic 15 30 and migrated thermogenic 12 60 gases migrated conventionally and hydrodynamically trapped gases in situ generated secondary biogenic gases and solution gases result in gas content that plot on or above the coal sorption isotherm bacteria transported basinward in groundwater flowing from the elevated northern basin margins metabolized wet gas components n alkanes and organic compounds in the coal and generated secondary biogenic methane and carbon dioxide subsequent to coalification uplift erosion and cooling these gases may be limited to basin margins where shallow depths and structural deformation result in higher permeability or may extend more than 35 mi 56 km basinward from the recharge zone the presence of appreciable secondary biogenic gas indicates an active dynamic flow system with overall permeability sufficient for high productivity basin hydrogeology reservoir heterogeneity location of permeability barriers no flow boundaries and the timing of biogenic gas generation and trap devel pment are critical for exploration and development of unconventional gas resources in organic rich rocks

evolution of coal bed methane in southeast qinshui basin china insights from stable and noble gas isotopes abstract the late carboniferous early permian coal seams of the qinshui basin in shanxi province are the most prolific producer of coalbed methane cbm in china methane formed in the late triassic during deep burial and reheating in late jurassic early cretaceous driven by magmatic underplating basin inversion brought the coal seams to 400 700 m from the surface in the mid late cenozoic here we present results of a study aimed at understanding the origin of the methane and how it was affected by cenozoic exhumation of the basin methane from a 12 km traverse perpendicular to the basin margin in the southeast part of the basin have stable isotope compositions 13c 30 2 to 35 2 and d 155 to 194 indicating a thermogenic origin with limited biogenic input they are however lighter than expected based on coal maturity and c1 c2 c3 1000 are significantly higher than typical thermogenic methane 90 of the radiogenic 4he produced in the coals has been lost prior to equilibrium between gas and water phase in the reservoir this likely occurred in response to gas loss process during rapid exhumation in cenozoic showing that the he and ar content of natural gases is a sensitive indicator of gas loss event caused by recent basin inversion the event may have led to the loss of up to 44 of the methane from the coal seams this study demonstrates the importance of basin inversion on gas preservation in shallow cbm and shows that in contrast to 13cch4 the light noble gases are essential for tracing such a process

early formation of k feldspar in shallow marine sediments at near surface temperatures southern israel evidence from k ar dating authigenic k feldspar was investigated in two albian to turonian sections in israel using k ar and ar ar dating x ray diffraction scanning electron microscopy and chemical analysis both sections comprise a similar succession of shallow marine limestones dolomites and marls with some sandstone and shale beds of continental origin the hcl insoluble residue fraction of the studied samples consists of clays quartz feldspars goethite and trace amounts of heavy minerals most of the insoluble residues have a relatively high k feldspar content that has an adularia habit and is concentrated in the 4 7 m size fraction the authigenic origin of the k feldspar in the fine silt fraction is indicated by its high content relative to quartz the uniform and idiomorphic shape of the crystals and its limited size range of the fine silt 4 7 or 4 10 m separates 40 have ages that are similar to stratigraphic ages within the analytical and biostratigraphic errors ar ar dating of a fine silt fraction with 94 k feldspar 4 10 m sample gyp 7 yields a plateau age identical to the total gas age and similar to the stratigraphic age these results indicate that the k ar age is not a mixture between detrital and late diagenetic k feldspar ages but is rather an age of formation within a few million years after deposition it is suggested that the early formation of the k feldspar was associated with dolomitization and was induced by residual brines as part of a reflux process

thermal cracking of kerogen in open and closed systems determination of kinetic parameters and stoichiometric coefficients for oil and gas generation abstract the purpose of the study is to compare artificial maturation of kerogens representative of the main types of organic matter kerogen types i ii ii s and iii in open and anhydrous closed pyrolysis systems the generated compounds are fractionated according to their thermal stability into six chemical classes c 1 c 2 c 5 c 6 c 14 c 15 saturates c 15 aromatics and nsos which include resins and asphaltenes in both systems primary cracking of kerogen can be described by two main reactions oil generation together with early gas generation followed by late gas production mass balances obtained in the two pyrolysis systems are reasonably similar although some secondary cracking of the nsos and underestimation of methane potential due to incomplete pyrolysis may occur in the open system kinetic parameters of thermal cracking are derived from experiments in the open system using an optimization procedure which determines a unique frequency factor and a weight distribution of chemical classes for a discrete series of activation energies the resultant frequency factors are checked with those obtained for specific molecular tracers such as n c 12 and n c 24 alkanes generated from kerogens in open and closed systems under isothermal conditions the results show that using a unique frequency factor as determined by optimization is correct for type i ii and ii s kerogens this factor is more questionable however when the distribution of activation energies is very broad such as for type iii coals based on this study a strategy for determination of kinetic parameters on any new source rock sample is proposed

airborne lidar measurements of wave energy dissipation in a coral reef lagoon system 1 quantification of the turbulent kinetic energy dissipation rate in the water column e is very important for assessing nutrient uptake rates of corals and therefore the health of coral reef lagoon systems however the availability of such data is limited recently at lady elliot island lei australia we showed that there was a strong correlation between in situ measurements of surface wave energy dissipation and e previously reineman et al 2009 we showed that a small airborne scanning lidar system could measure the surface wavefield remotely here we present measurements demonstrating the use of the same airborne lidar to remotely measure surface wave energy fluxes and dissipation and thereby estimate e in the lei reef lagoon system the wave energy flux and wave dissipation rate across the fore reef and into the lagoon are determined from the airborne measurements of the wavefield using these techniques observed spatial profiles of energy flux and wave energy dissipation rates over the lei reef lagoon system are presented the results show that the high lidar backscatter intensity and point density coming from the high reflectivity of the foam from depth limited breaking waves coincides with the high wave energy dissipation rates good correlations between the airborne measurements and in situ observations demonstrate that it is feasible to apply airborne lidar systems for large scale long term studies in monitoring important physical processes in coral reef environments when added to other airborne techniques the opportunities for efficient monitoring of large reef systems may be expanded significantly

hydrodynamic forces on larvae affect their settlement on coral reefs in turbulent wave driven flow this study investigates a key aspect of how ambient flow affects the recruitment of water dispersed marine larvae onto benthic substrata the sweeping away of larvae that have landed on surfaces through a combination of field and laboratory measurements we studied how waves interact with a complex substratum to affect hydrodynamic forces encountered by microscopic larvae sitting at different positions on the bottom terrain we used larvae of the nudibranch phestilla sibogae settling onto coral reefs as the system to address this question laser doppler anemometry was utilized within a laboratory flume to measure water velocities encountered 200 m mf rom coral surfaces by microscopic larvae sitting at different locations within a reef of the branching coral porites compressa comparing wave driven flow based on conditions measured over p compressa reefs in hawaii with unidirectional flow of the same mean velocity we found that peak shear stresses along coral surfaces were 15 times greater and hydrodynamic forces on larvae were 10 times higher in wave conditions peak forces on larvae sitting on the reef top were 3 10 times greater than on larvae 5 10 cm below the reef top intermittent bursts of high velocity which occurred more often at the reef top than within it determined the settlement probability for larvae in different reef microhabitats the faster and more strongly a larva sticks to a surface the higher the probability of successful settlement using values for p sibogae adhesive strength we predict they can settle only on sheltered surfaces within reefs

application of 40ar39ar laser probe and step heating techniques to the dating of diagenetic k feldspar overgrowths abstract the feasibility of determining the age of diagenetic k feldspar overgrowths utilizing 40 ar 39 ar step heating and laser probe dating techniques was tested on samples from the lower cretaceous arkoses of the angola offshore basin a previous study of these samples combining cathodoluminescence and k ar dating indicated that the k feldspar diagenetic overgrowths were 98 16 ma and the detrital cores were 516 26 ma conventional 40 ar 39 ar step heating of overgrown grains from the bulk k feldspar fraction failed to unambiguously distinguish detrital from diagenetic ages similarly step heating analysis of overgrowth concentrates 84 diagenetic did not yield any distinct plateau age attributable to the diagenetic k feldspar detrital and diagenetic k feldspars from the arkoses studied appear to release their ar over similar ranges of temperature partial laser fusion of individual overgrown grains using lowenergy short duration laser pulses carefully focussed on the overgrowth yielded mixed ages with ar contributed from both the overgrowth and the core heat conduction calculations indicate that conductive heating through the core overgrowth boundary is not responsible for partial degassing of the core rather beam scattering along intragrain structural defects and incipient melting of the core must occur a more successful approach involved total laser fusion of individual grains from the overgrowth concentrates which were physically separated from their detrital core one limitation of this approach was that because of the young age and the small size of the diagenetic feldspar simultaneous fusion of several grains was required for accurate age determination our results suggest that future investigations will greatly benefit from the use of on line cathodoluminescence capability to reduce the possibility of contamination by detrital material and the use of a laser beam whose wavelength is strongly absorbed by diagenetic k feldspar

a modified approach to estimating coal and coal gas resources example from the sand wash basin colorado the significant increase in united states gas production from coal beds over the past 5 yr has encouraged exploration and development of coal gas resources worldwide accurate assessment of coal and coal gas resources and delineating areas within basins containing the largest resources are important aspects of resource development previous resource studies may have overestimated or underestimated coal gas resources because the ash and density terms of resource equations were inconsistently or inappropriately considered in basins where coal analysis data are sparse coal gas resources are best calculated on an ash free basis the density contrast between ash forming minerals and organic matter is large enough that the weight percent ash is much larger than the corresponding volume percent therefore a correction factor relating weight percent ash free coal and ash yield determined from proximate analysis to ash free coal volume is required to accurately calculate coal gas resources rather than using one density value as has been done in previous studies our calculations require that bulk coal density including mineral matter be distinguished from ash free coal density coal and coal gas resources of the williams fork and fort union formations in the sand wash basin determined from modified resource equations are 291 billion tons short tons 264 billion t metric ton and 79 tcf footnote 2 2 tm3 these resources are significantly higher than previous estimates of basin resources of 34 5 billion tons 31 3 billion t of coal and 14 tcf 0 4 tm3 of coal gas the williams fork formation contains 79 of the coal and 95 of the coal gas resources reflecting greater maximum burial depth and higher gas contents the fort union formation contains 21 of the coal but only 5 of the coal gas resources coal gas resources are greatest in the central part of the basin where williams fork resources approach 70 gcf footnote mi sup 2 0 8 gm3 km2 in comparison the san juan basin the nation s most prolific coal gas producing basin has maximum coal gas resources approaching 35 gcf mi2 0 4 gm3 km2 the high resource density in the sand wash basin is due to greater net coal thickness rather than high gas content

natural hydraulic fracturing of tight gas sandstone reservoirs piceance basin colorado natural fractures form preferred pathways for basinal fluid flow and associated heat and mass transport in gas sandstone reservoirs with low matrix permeability fractures provide flow pathways between organic rich source and reservoir layers during gas charge and between matrix pores hydraulic fractures and the well bore during production while the formation of natural fractures has previously been associated with gas generation and pore fluid pressure increase through a process referred to as natural hydraulic fracturing other driving mechanisms such as stress changes by tectonic or exhumation processes remained viable alternatives to test whether these mechanisms contributed to fracture development we investigated the spatial and temporal distribution of fracture formation and its relationship to gas generation migration and charge in sandstone of the cretaceous mesaverde group across the entire production interval on a basinwide scale using fluid inclusion microthermometry of crack seal fracture cement formed concurrently with fracture opening we observed temperature trends that when compared with temperature evolution models of the formation date fracture formation between 41 and 6 ma in the northern and between 39 and 6 ma in the southern piceance basin the onset of fracture formation 20 30 m y prior to maximum burial eliminates changes in stress state associated with exhumation as a mechanism for triggering the onset of fracture formation instead calculated paleo pore fluid pressures of 40 90 mpa 5800 13 000 psi during fracture opening and the presence of methane rich inclusions in fracture cement suggest that fracture formation was aided by high pore fluid pressures during gas generation in organic rich shales and coals and associated charging of adjacent and interlayered sandstone reservoirs a 10 20 m y age progression in the onset of fracture formation from deeper to shallower horizons of the mesaverde group is consistent with gas generation and onset of fracture formation activated by burial temperature with limited upward migration of gas at this stage of reservoir evolution this age progression with depth is inconsistent with fracture formation triggered by changes in stress conditions associated with tectonic or structural processes expected to affect the entire formation synchronously our observations are thus most consistent with fracture formation by natural hydraulic fracturing in response to gas generation in interbedded source layers and reservoir charge based on widespread observations of fractures with similar structural and diagenetic attributes we consider natural hydraulic fracture formation in response to thermocatalytic gas generation to be a fundamental mode of brittle failure in otherwise structurally quiescent basins

testing the basin centered gas accumulation model using fluid inclusion observations southern piceance basin colorado the upper cretaceous mesaverde group in the piceance basin colorado is considered a continuous basin centered gas accumulation in which gas charge of the low permeability sandstone occurs under high pore fluid pressure in response to gas generation high gas pressure favors formation of pervasive systems of opening mode fractures this view contrasts with thatofothermodelsoflow permeabilitygasreservoirsinwhich gas migrates by buoyant drive and accumulates in conventional traps with fractures an incidental attribute of these reservoirs we tested the aspects of the basin centered gas accumulation model as it applies to the piceance basin by determining the timing of fracturegrowth and associated temperature pressure and fluid composition conditions using microthermometry and raman microspectrometry of fluid inclusions trapped in fracture cement that formed during fracture growth trapping temperatures of methane saturated aqueous fluid inclusions record systematic temperature trends that increase from approximately 140 to 185 c and then decrease to approximately 158 c over time which indicates fracture growth during maximum burial conditions calculated pore fluid pressures for methanerich aqueous inclusions of 55 to 110 mpa 7977 15 954 psi indicate fracture growth under near lithostatic pressure conditions consistent with fracture growth during active gas maturation and charge lack of systematic pore fluid pressure trends

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

boundary layer turbulence and flow structure over a fringing coral reef measurements of velocity and rates of turbulence were made across a fringing coral reef in the gulf of aqaba red sea to determine the effect that the rough topography has on boundary layer mixing and flow dynamics observations were made at two fore reef sites and a nearby sandy slope the friction velocity u and drag coefficient cd were determined directly from turbulent reynolds stresses measured using acoustic doppler velocimeters values of cd for the coral substrates ranged from 0 009 to 0 015 three to five times greater than over the sandy bottom site the turbulence dissipation rate e was determined by fitting spectra of vertical velocity to the theoretical 5 3 law expected for the inertial subrange of turbulence there was a local balance between production and dissipation of turbulent kinetic energy signifying that we could estimate u from either the mean velocity profile turbulence or dissipation rate of turbulent kinetic energy estimates from all three measures agreed well with mean u uo ranging from 0 10 6 0 03 to 0 12 6 0 03 indicating that existing turbulent boundary layer flow theory can be applied to flows over the rough topography of coral reefs the bottom topography by enhancing both reef scale and local drag and mixing levels allows reef biota to more effectively exchange dissolved and particulate matter with oceanic waters

origin of reservoir fractures in little knife field north dakota thin vertical planar fractures observed in the mission canyon formation at the little knife field are naturally occurring and appear to be extension fractures the predominant east west trend of the fractures measured in oriented core from six wells parallels the contemporary maximum horizontal compressive stress in the williston basin the fractures occur only in carbonate units but within the carbonates their occurrence is not lithology dependent fracture density measured in cores of the reservoir carbonates averages 1 ft 3 m of fracture per 2 3 ft 7 m of core the formation and mineralization of reservoir fractures were the most recent diagenetic events in the mission canyon formation at little knife study of aqueous and hydrocarbon fluid inclusions associated with the fractures reveals 1 fractures formed after the strata were buried to at least their present depth of 9 800 ft 2 987 m which indicates their age is post mesozoic 2 the pore fluid pressure gradient was normal hydrostatic immediately after if not during fracture system development 3 formation water salinity has remained fairly constant since fracture initiation 4 migration of hydrocarbons into the reservoir probably preceded fracture genesis and 5 methane concentration may have decreased since fracture initiation

evidence for late paleozoic brine migration in cambrian carbonate rocks of the central and southern appalachians implications for mississippi valley type sulfide mineralization abstract many lower paleozoic limestones and dolostones in the valley and ridge province of the central and southern appalachians contain 10 to 25 weight percent authigenic potassium feldspar this was considered to be a product of early diagenesis however 40 ar 39 ar analyses of overgrowths on detrital k feldspar in cambrian carbonate rocks from pennsylvania maryland virginia and tennessee yield late carboniferous early permian ages 278 322 ma simple mass balance calculations suggest that the feldspar could not have formed isochemically but required the flux of multiple pore volumes of fluid through the rocks reflecting regional fluid migration events during the late paleozoic alleghanian orogeny microthermometric measurements of fluid inclusions in overgrowths on detrital k feldspar and quartz grains from unmineralized rocks throughout the study area indicate homogenization temperatures from 100 to 200 c and freezing point depressions of 14 to 18 5 c 18 21 wt nacl equiv the apparent similarity of these fluids to fluid inclusions in ore and gangue minerals of nearby mississippi valley type mvt deposits suggests that the regional occurrences of authigenic k feldspar and mvt mineralization may be genetically related this hypothesis is supported by the discovery of authigenic k feldspar intergrown with sphalerite in several mines of the mascot jefferson city district e tennessee regional potassic alteration in unmineralized carbonate rocks and localized occurrences of mvt mineralization are both explainable by a gravity driven flow model in which deep brines migrate towards the basin margin under a hydraulic gradient established during the alleghanian orogeny the authigenic k feldspar may reflect the loss of k during disequilibrium cooling of the ascending brines mvt deposits are probably localized manifestations of the same migrating fluids occurring where the necessary physical and chemical traps are present

modeling hydrocarbon generation from the paleogene source rocks in liaodong bay bohai sea a study on gas potential of oil prone source rocks abstract the exploration history of bohai sea reveals that liaodong bay is relatively rich in natural gas which is mainly gas condensate however the source rocks in liaodong bay share a medium maturity level with values of ro being generally three immature paleogene source rocks were selected to complete gold tube pyrolysis experiments the experiment results reveal that the secondary gas from oil cracking can be neglected until the cumulative yields of c6 c14 compounds reach the maximum corresponding to ro 1 3 above ro 1 3 oil starts to crack to wet gases substantially based on comparative analysis of pyrolysis results and source rock geochemical parameters we constructed a hydrocarbon generation model especially for hydrocarbon gas and validated the calculated ro values for pyrolysis conditions the c1 c5 yields for source rocks at 1 3 ro in gold tube pyrolysis approximate the maximum gas yield for source rock in open system pyrolysis indicating the majority of primary gas from kerogen cracking has been generated at 1 3 ro with its yields being 156 ml g toc 100 ml g toc and 117 ml g toc for ed3 es1 and es3 source rocks respectively this suggests that source rocks with ro

occurrence and geochemistry of natural gases piceance basin northwest colorado the piceance basin is a hydrocarbon rich province that has natural gas production from reservoirs ranging in age from late jurassic to eocene and large undeveloped resources of natural gas in coal beds and tight sandstone reservoirs of cretaceous age gases from all producing intervals are of predominantly thermal origin and become isotopically heavier delta isotope 13 c 1 51 3 to 29 1 o oo and chemically drier c 1 c 1 5 0 26 to 1 00 with increasing thermal maturity of reservoirs r o 0 45 to 2 40 over a depth range of 1100 to 11 702 ft 335 3567 m scatter in trend is attributed to source rock differences and considerable vertical and lateral migration based on chemical and isotopic composition three major types of gases can be distinguished those generated from mixed type ii and iii kerogens those from dispersed type iii kerogen and those from coal gases generated from mixed type ii and iii kerogens are produced from the upper jurassic morrison formation the lower cretaceous cedar mountain formation the upper cretaceous dakota sandstone the upper cretaceous mancos b producing interval and marginal marine sandstones of the upper cretaceous iles producing interval these gases are associated with minor amounts of oil and probably were generated from kerogen in the marine mancos shale gases generated from dispersed type iii kerogen are produced from nonmarine sandstones of the upper cretaceous williams fork producing inter al and from thermally immature reservoirs in the overlying paleocene and eocene fort union and wasatch formations these nonassociated gases contain large amounts of co 2 and probably were generated from carbonaceous shales in the williams fork producing interval their presence in immature fort union and wasatch reservoirs implies considerable vertical migration the third type of gas is methane rich is produced by devolatilization of humic coal and is generally in coal beds of the cameo fairfield zone of the williams fork producing interval these gases are not the major source for adjacent sandstone reservoirs a fourth distinct type of isotopically light thermogenic gas occurs in immature reservoirs of the eocene green river formation this gas is inferred to have migrated from u identified deeper more mature source rocks

ar ar dating of authigenic k feldspar quantitative modelling of radiogenic argon loss through subgrain boundary networks we have analysed two distinct generations of authigenic k feldspar in fucoid bed sandstones from an t sron and skiag bridge nw highlands scotland which have experienced post growth heating to levels in excess of the predicted ar closure temperature authigenic k feldspars show microtextural similarities to patch perthites that is subgrains separated by dislocation rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon the two generations of authigenic k feldspar in the fucoid bed sandstones can be distinguished by different microtextural zones bulk mineral compositions fluid inclusion populations and inferred temperatures and chemistries of parent fluids ar ar age data obtained using high resolution ultraviolet laser ablation show that the first cementing generation is ordovician and the second cementing generation is silurian modelling of ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono thermal thrust model assuming transient heating of the fucoid beds is inconsistent with observed data removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed ar ar ages for both generations of cement alternatively ar diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the fucoid bed palaeothermal maxima and determined ar ar age ages for the two generations of k feldspar cement based on this alternate explanation we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic k feldspars explaining the apparent robustness of authigenic k feldspar with respect to ar retention

fluid inclusion petrography and tectonic burial history of the al ali no 2 well evidence for the timing of diagenesis and oil migration northern oman foredeep cores cut in shallow marine lower and middle cretaceous carbonates in the al ali no 2 well umm al qaiwain united arab emirates display a five stage sequence of calcite cementation fracturing and stylolitization these stages are correlated with the tectonic history of the northern oman orogeny occurrence of fluorescent hydrocarbon fluid inclusions is restricted to stage 2 and stage 3 fracture filling calcites that are crosscut by stylolites stylolite formation during rapid burial beneath abyssal campanian foredeep sediments restricts hydrocarbon migration to post mid cenomanian and pre mid campanian time

mass transfer limitation of nutrient uptake by a wave dominated reef flat community maximum rates of phosphate nitrate and ammonium uptake by a reef flat community were estimated from rates of frictional dissipation that were calculated from the attenuation of waves propagating over the kaneohe bay barrier reef flat time averaged flow speeds across the entire study area ranged from 0 08 to 0 22 m s 21 observed decreases in wave energy fluxes and near bottom orbital velocities gave a mean estimate for the bottom friction coefficient cf of 0 22 6 0 03 friction coefficients were used to estimate nutrient mass transfer coefficients of 5 9md 21 for phosphate and 9 16 m d 21 for ammonium and nitrate wave heights offshore of kaneohe bay were also used to estimate an annual phosphate mass transfer coefficient of 8 6 2md that was determined from measured changes in phosphate concentrations across the reef flat we conclude that rates of phosphate uptake by the kaneohe bay barrier reef flat community are occurring near the limits of mass transfer net primary production is a major pathway by which mass and energy flow into coral reef ecosystems the uptake of dissolved nutrients is often the rate limiting step for net pri mary production in marine ecosystems thus a knowledge of the kinetics of nutrient uptake by coral reef communities is necessary for assessing how nutrient loading rates change in response to natural or anthropogenic increases in nutrient concentrations bilger and atkinson 1992 proposed that nutrient uptake by shallow reef communities was limited by mass transfer the physical transfer of nutrients across con centration boundary layers covering the surfaces of reef au totrophs these authors used mass transfer correlations for rough surfaces taken from the engineering literature to cor relate maximum rates of nutrient uptake with the frictional characteristics of experimental reef communities subse quent studies demonstrated the ability of such mass transfer correlations to predict nutrient uptake kinetics for experi mental reef communities within closed recirculating flumes atkinson and bilger 1992 bilger and atkinson 1995 thomas and atkinson 1997 and a large experimental me socosm atkinson et al 2001 the results of these studies made it clear that shallow water reef communities are ca pable of taking up nutrients from the water column at rates that are limited by mass transfer however it had not yet been demonstrated whether in situ rates of nutrient uptake

seascape level variation in turbulence and wave generated hydrodynamic signals experienced by plankton abstract plankton exhibit diverse and dramatic responses to fluid motions and these behaviors are likely critical for survival and fitness fluid motions can be generated by organisms or by physical processes including turbulence and surface gravity waves physical processes vary geographically in their intensity and generate hydrodynamic signals experienced by plankton as fluid forces on their sensory receptors in this synthesis we review how turbulence and waves vary in space the scales and statistics of their motions and the forces exerted on plankton we then quantify the hydrodynamic signals produced by turbulence and waves in four seascape types surf zones inlets and estuaries the continental shelf and the open ocean using published dissipation rates wind and wave data from buoys and observations from two coastal sites in massachusetts usa we relate these geographic patterns in signals to the observed behaviors of example species and to the forces sensed by typical plankters with different receptor types turbulence generated shears are largest in the surf zone inlets and estuaries while wave generated accelerations are larger offshore as a result each seascape exhibits some range of combined shears and accelerations that is distinct these signals generate forces on plankton that vary among habitats and with plankton size and swimming speed spatial patterns in fluid forces create a potential mechanism for dispersing larvae to distinguish habitats by their hydrodynamic signatures however turbulence can be strong in all seascapes and may cause widespread interference in signaling among predators and prey plankton with a single receptor type could identify nearshore habitats while those with multiple receptor types potentially could distinguish inshore vs offshore seascapes or decode signals produced by physical processes and by other organisms

a model of passive settlement by planktonic larvae onto bottoms of differing roughness a simple one dimensional advection diffusion model was developed lhat predicts rates of settlement by larvae transported passively within turbulent boundary layers onto bottoms of differing roughness the model describes depth limited boundary layers and considers variation in boundary shear velocity larval fall velocity and the height and areal density of bottom roughness features larvae were allowed to settle onto the bottom but not onto roughness features the model predicts that rates of settlement should increase monotonically with areal density of roughness features relatively flat bottoms should experience rates of settlement 2 4 times higher than bottoms with low densities of roughness features but l 2 orders of magnitude lower than bottoms with relatively high densities of roughness whereas roughness density defines the direction of differences in settlement expected the degree of difference is also affected by the height of roughness features and the ratio of larval fall velocity to shear velocity the dispersal of marine benthic organisms of many species occurs through the water column via larval transport or by the swimming or drift of adults factors affecting settlement on the bottom by potential colonists thus have been the focus of considerable study laboratory and field studies show that larvae and adults exhibit complex behaviors and are capable of distinguishing among potential settlement sites based on diverse cues meadows and campbell 1972 gray 1974 crisp 1984 woodin 1986 hydrodynamic processes also exert important influences on dispersal and settlement patterns of oceanic circulation affect broad scale zoogeographic distributions ekman 1967 scheltema 1974 produce tidal to interannual fluctuations in larval recruitment shanks 1986 roughgarden et al 1988 and can accumulate lar

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

clay mineral assemblages and analcime formation in a palaeogene fluvial lacustrine sequence maiz gordo formation palaeogen from northwestern argentina abstract the palaeogene maiz gordo formation is one of the main lacustrine events recorded in northwestern argentina it consists of sandstone mudstone and limestone beds 200 m thick deposited in a brackish alkaline lake and braided alluvial systems the maiz gordo lake evolved mainly as a closed system with brief periods as an open one x ray diffraction xrd and scanning electron microscopy sem were used to study samples from seven sites corresponding respectively to proximal intermediate and transitional positions of the fluvial environment and marginal and inner lake environment focusing on the clay mineralogy and analcime formation the basinward zonation of diagenetic minerals identified in the maiz gordo lake was mordenite analcime k feldspar although not a typical zonation of saline alkaline lakes it does indicate an increase in salinity and alkalinity towards the centre in proximal fluvial settings smectite predominates at the base of the sequence with scarce kaolinite towards the top a striking increase in kaolinite content suggests a change from a relatively arid climate with alternating humid and dry seasons towards a warm and humid climate kaolinite content clearly decreases in a basinward direction such a variation is attributable to changes in hydro geochemistry denoting the progressive influence of the brackish and alkaline lake water on interstitial pores sem images of intermediate fluvial samples reveal authigenesis of illite at the expense of kaolinite booklets in littoral and inner lake settings the clay fraction is composed of muscovite sometimes with subordinate smectite analcime occurs in variable amounts in all sedimentary facies in rock pores or filling veins it forms subhedral square to hexagonal or anhedral rounded crystals denoting that they coarsened at low to moderate degrees of supersaturation although the mordenite identified in a fluvial level would have been the precursor of analcime in the maiz gordo basin no textural evidence of analcime formation through replacement of mordenite or other precursor zeolite was found hence it is more probable that analcime formation took place by direct authigenic precipitation or through the reaction between interstitial brines and clay minerals or plagioclase

variable gas saturation in coalbed methane reservoirs of the black warrior basin implications for exploration and production abstract gas saturation is highly variable in carboniferous coalbed methane reservoirs of the black warrior basin usa and diverse geologic data derived from more than three decades of exploration and development provides insight into the origin of this variability and the consequences for production performance coalbed methane is produced from numerous thin 0 3 to 95 importantly this range of variation is commonly developed among closely spaced seams within the same well exploration has to date been successful where coal seams are in the thermogenic gas window geochemical evidence indicates that thermogenic gases have been altered by subsurface water movement and may have been augmented with late stage biogenic gases particularly in areas affected by fresh water recharge adsorption isotherms of coal samples in the black warrior basin typically have langmuir volume between 15 and 30 cm3 g and langmuir pressure between 2 and 6 mpa both langmuir pressure and langmuir volume correlate significantly with coal rank in deep normally pressured coal beds where reservoir pressure is substantially above langmuir pressure even a small degree of undersaturation can necessitate prolonged dewatering before a large reservoir volume can reach the critical desorption pressure permeability moreover decreases exponentially with depth which can make dewatering coal seams deeper than 800 m difficult where reservoir pressure is relatively low however isotherm geometry indicates that significantly undersaturated reservoirs can be near the critical desorption pressure consequently areas of underpressure favor high gas production along with minimal water production

observations of spatial flow patterns at the coral colony scale on a shallow reef flat 1 although small scale spatial flow variability can affect both larger scale circulation patterns and biological processes on coral reefs there are few direct measurements of spatial flow patterns across horizontal scales 1 had similar spatial patterns to wakes while higher frequency variations 0 05 0 1 hz kc 1 had no observable spatial structure on the reef flat both drag and inertial forces exerted by coral colonies could have significant effects on flow but within different frequency ranges drag dominates for low frequency flow variations and inertial forces dominate for higher frequency variations including the wave band our scaling analyses suggest that spatial flow patterns at colony and patch scales could have important implications for both physical and biological processes at larger reef scales through their effects on forces exerted on the flow turbulent mixing and dispersion

state of the art of research in kinetic modelling of oil formation and expulsion abstract the last ten years have seen a rapid development in the understanding of petroleum generation and expulsion by a combined use of natural series and experimental simulation this knowledge is now used to develop mathematical models which reproduce the kinetics of petroleum generation and migration in the purpose of basin evaluation by a combination of observation of homogeneous geochemical series experimental simulation and mathematical modelling it has been now established that parameters governing the quantity and composition of petroleum are temperature type of organic matter time or heating rate catalysis by clay minerals which would produce important amounts of isoalkanes is not necessary to produce petroleum the role of minerals although still controversial is rather to retain the heavy fraction of petroleum pressure seems to have a limited influence within the range for effective source rocks kerogen is a tremendously complex macromolecule which is now insufficiently characterized to develop fundamental predictive models of thermal cracking i e involving intermediates such as radicals and olefins such models presently apply only to the cracking of simple molecules hexane hexadecane at limited degrees of cracking for this reason kinetic models are still empirically calibrated on pyrolysis experiments and or on natural maturation trends the most popular models involve a series or a continuous distribution of parallel reactions to describe primary cracking i e direct formation of mobile compounds from kerogen these are generally calibrated against open system pyrolysis with various temperature programs consideration of natural maturation trends i e decrease in petroleum potential may be used also for calibration but discrepancies of organic matter properties availability of deep samples and uncertainties on thermal history limit the effectiveness of such methods whatever the method main activation energies are found in the range 45 60 kcal mol secondary cracking which refers generally to cracking of mobile compounds cannot be modelled from open system pyrolysis nor from natural series unknown residence times but only from closed system pyrolysis although models of primary and secondary cracking still need experimental improvements and more realistic kinetic schemes their ability to predict quantities and composition of petroleum depends primarily on migration which is poorly known indeed migration controls the residence time of petroleum in hot zones of sedimentary basins and thus determines the extent of oil conversion into gas as reproduced by recent numerical models preliminary studies documenting the interactions between thermal cracking and expulsion are shown from haltenbanken area and paris basin in the last few years a kind of agreement has been reached that primary migration was most likely occuring in a separate phase from water and that a sufficient concentration of petroleum must be generated for expulsion to start indeed high expulsion efficiencies over 50 are systematically found for rich and mature source rocks a further understanding of primary migration requires observations of natural series petrophysical studies of source rocks porosities under 10 permeabilities in the nanodardy range thermodynamic investigation of unconventional multiphase organic systems kerogen liquid s gas and experimental simulation under stress this on going research should enable models to track correctly migration paths and thermal history of petroleum fluids as necessary to model their composition

39ar 40ar laser probe dating of terrestrial rocks we have shown that for metamorphosed granites as well as for metamorphosed sediments it is possible to obtain a reliable k ar age from a sample as small as 0 2 g samples with ages as young as 40 m y are easily studied there is no reason to believe that the method could not be used for samples considerably younger the main application of the laser will probably be for cases where the same mineral species has been formed during two distinct metamorphic events in the same rock in this case it is difficult if not impossible to make a mineral separate suitable for a 39 ar 40 ar study we have shown that in the case of an old granite the biotite in one sample distinctly shows thermal events at 1600 m y whileits primary cooling age is 2100 m y the thermal release study yields a good plateau age roughly an average age of the two thermal events an other interest of this method is demonstrated by argon dating of two different kinds of glaucophane only one of theseshowing argon in excess

petrology geochemistry provenance and alteration of pennsylvanian permian arkose colorado and utah late paleozoic and modern feldspathic clastic sediments of the colorado rockies were derived from dominantly igneous and meta igneous precambrian basement rocks average composition expressed as gazzi dickinson qfl quartz feldspar lithicfragments is 36 64 0 in modern stream sands for the cutler formation is 54 46 0 for the minturn formation is 57 43 0 and for the fountain formation is 51 49 0 no major mafic components are present in the provenance as indicated by low co cr and ni abundances although higher fe and mg abundances in cutler formation rocks indicate derivation from somewhat more mafic provenance than the fountain and minturn formation rocks fountain formation rocks are more altered by predepositional weathering diagenesis and holocene weathering than their equivalents in the minturn and cutler formations thus plagioclase is albitized and clay altered or absent in the fountain formation whereas it is abundant and much less altered in the minturn and cutler rocks fountain formation sandstone in the steamboat mountain section lacks remaining detrital plagioclase but contains authigenic albite as overgrowths on and replacement of detrital k feldspar and as pore filling crystals in the eldorado springs section there is extensive epithermal potassic alteration in the fountain formation from the detrital assemblage quartz plagioclase k feldspar biotite muscovite to the assemblage quartz k feldspar authigenic adularia illite muscovite kaolinite k and rb have been metasomatically added to these rocks with concomitant removal of ca na co cr cu ni ga th u zn ba ce la and y during passage of hydrothermal fluids apparently in the tertiary these fluids were probably heated by deep seated magma adjacent to the colorado lineament and or range front faults that served as geothermal water conduits toward the surface

40ar 39ar thermochronometry of k feldspar from the ktb borehole germany abstract the great depth and relatively steep geothermal gradient 29 c km of the ktb deep crustal borehole located in the bavarian region of germany provides the basis for our study of diffusive argon loss in k feldspar the observed borehole temperature at 9 km is 265 c which reaches well into the argon closure interval for k feldspar 125 350 c four microcline and two adularia samples distributed relatively evenly down the 9 1 km deep borehole were analyzed by the 40ar 39ar method the thermal histories of the shallow samples are consistent with existing thermochronologic data from the borehole after correction for chlorine correlated excess 40ar the deepest two samples result in age spectra that record zero apparent ages over the first few percent of 39ar released which is predicted by diffusion theory where a range of diffusion volumes are present inverse modeling of the argon kinetics of these two deep samples reveals that the present elevated geothermal gradient in the borehole has existed for only the last approximately one million years recent volcanism within 30 km of the borehole is likely the source of this present day thermal pulse

steps toward dating early diagenetic k feldspar by the 40ar 39ar method abstract authigenic sedimentary low temperature k feldspar separated from albian turonian carbonates in israel was dated by the step heating 40ar 39ar method in contrast to high temperature k feldspars ca 90 of the radiogenic ar was released at temperatures lower than 600 c and fusion mostly occurred below 750 c though formed under low temperature ar loss in all but one sample is estimated to be less than 2 nevertheless the effect of 39ar recoil is evident in some separates probably due to their very fine size 4 10 m the plateau age of one sample with the highest content of authigenic k feldspar 93 96 ma is slightly younger than the assumed stratigraphic age and thus defines the timing of an early diagenetic event within a few million years after deposition other samples where a plateau age could be determined yield ages slightly older strong acid etching 7 n hno3 85 c of the k feldspar enriched fraction may have improved the 39ar 40ar spectra but did not eliminate the presence of minute quantities of detrital k bearing minerals though the present set of data is insufficient for a clear cut conclusion the activation energy of the authigenic k feldspar is in the range of 14 26 kcal mol 1 s 1 much lower than that of magmatic and hydrothermal k feldspars and can probably be attributed to the heating schedule and the small crystal size it is not clear whether the formation at low temperatures

dissipation of wave energy and turbulence in a shallow coral reef lagoon received 6 april 2011 revised 14 november 2011 accepted 3 january 2012 published 10 march 2012 1 simultaneous in situ measurements of waves currents and turbulence are presented to describe dissipation rates of wave energy and turbulent kinetic energy in the windward coral reef lagoon system at lady elliot island lei australia the dissipation of wave energy in the lagoon is tidally modulated and strongly correlates with frictional dissipation due to the presence of the extremely rough bottom boundary the observed turbulent kinetic energy tke dissipation rate in this wave dominated lagoon is much larger than recently reported values for unidirectional flows over natural fringing coral reefs the correlation between the wave dissipation and is examined the average rate of dissipation induced by the rough turbulent flow was estimated directly from the observed coupled with both a depth integrated approach and with a bottom boundary layer scaling rates of tke dissipation estimated using the two approaches approximate well within a factor of 1 5 to 2 4 to the surface wave energy dissipation rate the wave dissipation and friction factor in the lagoon can be described by a spectral wave frictional model with a bottom roughness length scale that is approximately constant across the lagoon we also present estimates of dissipation induced by the canopy drag force of the coral heads the dissipation in this case is enhanced and becomes more significant for the total energy dissipation when the water depth in the lagoon is comparable to the height of the coral heads

understanding k feldspar 40ar 39ar data reconciling models methods and microtextures several descriptions of argon diffusion in k feldspar have been developed including the quantitative multiple diffusion domain mdd and multipath models and the qualitative recrystallization model these models remain contentious and the natural range in behaviour remains poorly understood feldspars from the klokken syenite intrusion show a systematic relationship between 40 ar 39 ar age and microtexture suggesting that the loss of argon from different feldspars operates via different mechanisms such that the existing models represent only end member scenarios the mdd model can yield reliable thermal history information only for feldspars with pristine microtexture with this model best viewed as a cipher for the real but unknown domain structure in such samples

quantitative evaluation of gas generation from the upper paleozoic coal mudstone and limestone source rocks in the ordos basin china abstract significant quantities of tight gas resources have been discovered in the upper paleozoic interval in the ordos basin central china the gas is believed to have been derived primarily from the upper paleozoic coal mudstone and limestone source rocks an integrated organic geochemistry and basin modeling approach was applied to quantitatively evaluate gas generation from the three types of source rocks source specific gas generation kinetics were first established on the basis of sealed gold tube pyrolysis experiments gas generation was then modeled in 1d and 3d using the source specific kinetics obtained the results show that 1 near the depositional and thermal center e g well zt 1 gas generation occurred much earlier and was greater than that of the sh 360 well which is away from the depositional and thermal center 2 c2 c5 gases in the zt 1 well underwent thermal cracking while gases in the sh 360 well did not experience any secondary thermal alteration 3 hydrocarbon gases were mainly generated during the early cretaceous 135 96 ma and the late jurassic 161 135 ma 4 the cumulative amounts of gas generation from the coal mudstone and limestone source rocks are 147 23 1012 57 85 1012 and 12 73 1012 m3 respectively with coal seams being a major contributor about 67 6 to the upper paleozoic gas system followed by the mudstone about 26 6 and limestone about 5 8 by comparing with previous work and a default kinetics basin model our source specific kinetics basin model is more suitable for simulating gas generation in the upper paleozoic source rocks within the ordos basin