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

tectonic significance of paleobotanically estimated climate and altitude of the late eocene erosion surface colorado erosion beveled the laramide front range uplift in colorado to a surface of low relief by the end of the eocene this study uses j a wolfe s new multivariate climate analysis techniques to determine the paleoelevation of this regional surface by examining the overlying 35 ma florissant flora a multiple regression model explaining 93 3 of the variance in mean annual temperature was developed using wolfe s dataset of 31 leaf physiognomic character states for 86 modern vegetation sites these character states were scored on 29 species collected from one facies of the florissant lake beds the paleotemperature estimate of mean annual temperature 10 7 plus minus 1 5c derived from these data when combined with sea level temperature and terrestrial lapse rate implies a late eocene paleoelevation of 2 4 2 7 km pliocene uplift is thus not required to explain the present elevation of 2 5 km it is unclear when and why the southern rocky mountains achieved this elevation magmatic crustal thickening can explain the late eocene high elevation of the southern rockies but neither this mechanism nor compressive thickening explains why the great plains which are tied to the florissant elevation by the wall mountain tuff were also high this paleoelevation estimate indicates that regional surfacesmore of planation could be formed at high elevation in the eocene probably because of peculiarities of the eocene climate less

sediment transport and topographic evolution of a coupled river and river plume system an experimental and numerical study sediment transfer from rivers to the ocean is the fundamental driver of continental sedimentation with implications for carbon burial land use dynamics and unraveling global climate change and earth history from sedimentary strata coastal rivers are dynamically coupled to their offshore plumes at the river mouth creating regions of nonuniform flow that can dictate patterns of erosion and deposition both onshore and offshore however there are limited experimental and modeling studies on sediment transport and morphodynamics of coupled river and river plume systems and their response to multiple flood events to address this knowledge gap we developed a quasi 2 d morphodynamic numerical model and conducted exploratory flume experiments in a 7 5 m long flume where a 10 cm wide river channel was connected to a 76 cm wide ocean basin both the numerical model and the flume results demonstrate that 1 during low discharge flows backwater hydrodynamics cause spatial flow deceleration and deposition in the river channel and the offshore plume area and 2 during high flows the water surface is drawn down to sea level resulting in spatial flow acceleration and bed scour during high discharge flows we also found that the offshore river plume self channelized owing to both levee formation and bed scour our study suggests that coastal rivers may be in a perpetual state of morphodynamic adjustment and highlights the need to link rivers and river plumes under a suite of flow discharges to accurately predict fluvio deltaic morphodynamics and connectivity between fluvial sediment sources and marine sinks

stable isotope based paleoaltimetry abstractthe quantitative estimation of paleoaltitude has become an increasing focus of earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts as well as the influence of mountain belt growth on regional and global climate the general observation of decreasing 18o and 2h values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation these studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming in this review we provide a theory behind the application of stable isotope based approaches to paleoaltimetry we apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations examples of the application of paleoaltimetry techniques to himalaya tibet and the andes are discussed

timing of tibetan uplift constrained by analysis of volcanic rocks the tibetan plateau has had a central role in the development of recent models for the mechanics of mountain belts1 2 and cenozoic global climate change3 the present elevation and extensional deformation of the plateau probably result from uplift owing to convective thinning of the underlying lithospheric mantle1 2 an age for the uplift would provide a valuable constraint on these models but because recently proposed indicators of uplift are all climate dependent they are equivocal possibly reflecting global cooling rather than regional uplift4 here we present new geochemical data on post mid miocene lavas from the plateau which show that the lavas were derived from the lithospheric mantle simple thermal arguments indicate that the generation of such magmas also necessitates thinning of the lithospheric mantle thus volcanism is coincident with uplift providing a climate independent means of dating the onset of uplift dating by the laser 40ar 39ar technique places the beginning of this volcanism and therefore the time of uplift of the tibetan plateau at 13 myr ago

bubble migration and coalescence during the solidification of basaltic lava flows the initial size distribution of gas bubbles in lava flows is modified by bubble rise and coalescence during post eruptive cooling and crystallization a simple model which computes the effects of rise and coalescence accounts for observed features and may provide a means whereby the initial bubble size distribution can be inferred a model lava flow of assumed thickness viscosity and volume percentage of gas bubbles is given an initial bubble size distribution bubbles coalesce due to differences in their relative rise velocities using a gravitational collection kernel the process may be modeled by numerical integration of the stochastic collection equation which yields the change in the number density spectrum of the population from the number densities of all pairs of bubbles and their probabilities of collision bubbles rise and coalesce within a fluid interior sandwiched between fronts of crystallization that advance inward from top and bottom bubbles that are overtaken by the crystallization f

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

observations and analysis of the horizontal structure of a tidal jet at deep scour holes scour in the vicinity of a hydraulic structure may compromise its geotechnical stability or that of nearby structures much fundamental research has been dedicated to the understanding and prediction of these processes in order to enable the efficient design of mitigation measures while most of these efforts consider laterally uniform flows nonuniformity is the rule rather than the exception this study presents field observations near the storm surge barrier in the eastern scheldt estuary the netherlands where significant scour holes have developed the tidal flow through this semi open barrier exhibits characteristics of a shallow jet a pronounced contraction of this jet toward the nearby scour hole during particular stages of the tidal cycle is revealed attributed to potential vorticity conservation the depth averaged vertical vorticity increases proportionally to the depth increase measurements show a vertically uniform velocity profile in the scour hole that is attributed to a reduction of the adverse pressure gradient due to the contraction that suppresses boundary layer separation from the upstream slope of the scour hole a positive feedback mechanism is thus revealed lateral velocity gradients lead to relatively high near bed velocities in the scour hole which enhances erosion causing an even stronger horizontal contraction maintaining the scouring potential if the upstream flow field is laterally uniform observed around slack tide horizontal contraction does not occur and the boundary layer separates from the upstream slope the scour depth will then tend to an equilibrium the results infer the importance of the nonuniformity of the horizontal flow field

terrestrial cosmogenic nuclides as paleoaltimetric proxies the production rates of terrestrial in situ cosmogenic nuclides depend on the altitude and can therefore be used to constrain paleoaltitudes if the history of cosmogenic nuclide production in a region can be constrained this chapter discusses the theory behind cosmogenic nuclide paleoaltimetry sampling strategies and practical limitations of the technique three exposure scenarios may allow for the calculation of past altitudes 1 exposure for a finite time period at a single elevation and without erosion or burial followed by immediate shielding from further production of cosmogenic nuclides 2 steady uplift of a surface throughout nuclide production without erosion or burial and 3 exposure of a sample without erosion or burial for a sufficient duration that the concentration of a cosmogenic radionuclide has reached equilibrium to constrain paleoelevation all exposure scenarios require independent evidence of the depth history of a sample during exposure to cosmic rays because production rates attenuate rapidly in rock depth profiles and measuring multiple nuclides allow for better constraints of parameters in paleoaltitude calculations

pore characterization and shale facies analysis of the ordovician silurian transition of northern guizhou south china the controls of shale facies on pore distribution abstract the ordovician silurian wufeng longmaxi formations in the upper yangtze platform have been considered as the most promising shale play in china however few studies of detailed shale facies and their influence on pore distribution have been conducted therefore it is important to describe the heterogeneity of shale facies in detail and elucidate their relationship to pore networks and development seven distinct facies were identified on the basis of their characteristic physical biological and chemical attributes ion milled samples from all facies were examined with sem for identification of pore types point counting was used to quantify porosity four major pore types appear dominant framework pores phyllosilicate framework pf pores intrapores within inorganic grains and organic matter om pores due to variability in composition and depositional setting of the different facies pore networks are not uniform framework pores between detrital grains and pf pores are widespread in bioturbated claystones pores in black siliceous shales are dominated by framework pores supported by authigenic silica most of these are filled with kerogen bitumen that is host to foam and bubble type om pores intrapores within calcite or dolomite grains are common in fossiliferous mudstones and black dolomitic siltstones but are isolated and do not contribute to productive porosity in muddy siltstones pf pores are well developed within silty bands initial framework pores within silty beds or laminae however were subsequently cemented by calcite or destroyed by compaction as most of primary pf pores and primary frameworks pores are lost during compaction porosity is highly dependent on the population of framework pores between authigenic quartz grains secondary cracking of amorphous organic matter added porosity after initial infilling of porosity by oil and bitumen migration therefore porosity is mainly controlled by abundance of authigenic silica and toc in spite of differences of burial diagenesis among various facies understanding these main controls on porosity should be helpful to predict and find and more porous facies and have a significant impact on future gas exploration in the wufeng longmaxi formations

epeirogenic motions of africa as inferred from cretaceous shoreline deposits epeirogenic motions can be quantified if paleodatum planes can be recognized these motions have been determined for the time interval mid cretaceous cenomanian to recent in continental africa using the vertical displacement of ancient shoreline sediments and other nearshore or low elevation deposits that are inferred to represent a cenomanian sea level datum plane the cretaceous trans saharan seaway brought shoreline sediments deep into the african continental interior and additional data suggest that most of the remaining terrestrial regions were also low lying during the cenomanian the present elevations of the sea level sediments indicate that large portions of africa have undergone epeirogenic uplift since the cenomanian the character of the motions in north africa can be described as small scale high amplitude 3 km doming separated by relatively flat lying areas of deposition the largest single epeirogenic feature is the uplift associated with red sea and east african rift development the timing of post cenomanian epeirogenic motions can be further constrained using paleontologic k ar faulting paleodrainage and sedimentary data the most likely causal mechanism for african epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the african lithosphere

deep water depositional mechanisms and significance for unconventional hydrocarbon exploration a case study from the lower silurian longmaxi shale in the southeastern sichuan basin the purpose of this work was to study the depositional mechanisms and significance of the longmaxi shale in the sichuan basin in southern china seven lithofacies were identified based on the detailed observation of outcrops and cores using petrographic and scanning electron microscope examination of thin sections and other data analyses 1 laminated calcareous mudstone 2 laminated carbonaceous mudstone 3 laminated silty mudstone 4 laminated claystone 5 laminated siliceous shale 6 siltstone and 7 massive mudstone the laminated mudstone and laminated claystone originated from suspension deposition and siliceous shale is associated with ocean upwelling whereas massive mudstone and siltstone were primarily deposited by turbidity currents the depositional mechanisms have a great effect on the source rock and reservoir properties suspension deposition near oceanic upwelling zones can provide favorable conditions for the production and preservation of organic matter and are thus conducive to the formation of high quality source rocks total organic carbon content up to 5 4 the reservoir storage spaces are primarily interlaminated fractures and organic pores with good physical reservoir properties high porosity permeability and brittle mineral content turbidity currents may carry a large quantity of oxygen to the seafloor resulting in the oxidation of organic matter which is unfavorable for its preservation the lithofacies formed by turbidity currents have relatively low total organic carbon contents average 1 structural fractures and intergranular pores are the primary storage spaces that are present in the reservoir in summary organic rich shale and siliceous shale that was deposited from suspension near upwelling zones are key exploration targets for shale oil and gas the widely distributed multilayer tight sandstone is important in the exploration for tight oil a better understanding of the deposition mechanism and its effect on oil reservoirs may assist in identification of favorable areas for exploration

affinity and similarity of local scour holes at bed sills 1 excessive erosion of gravel bed rivers represents a hazard which is often controlled by the construction of bed sills shape and volume of equilibrium local scour holes at bed sills in high gradient streams were investigated by analyzing steady flow experimental data scour profiles were normalized by scaling the depths and the longitudinal distance from the upstream sill with the maximum dimensions of the scour hole results exhibited a universal geometrical affinity of the scour geometrical similarity was also found to occur but only in a limited range of physical conditions evidence on the scaling nature of the scour hole shapes has important implications on the prediction of the eroded volume in turn a correct evaluation of the eroded volume is necessary for the optimization of the design of the intersill distance prediction formulae are proposed which link the eroded volume to the geometrical hydraulic and sediment properties

lithospheric structure of tibet and western north america mechanisms of uplift and a comparative study we seek to determine the mantle lid thickness of the lithosphere and to constrain the mechanisms that are responsible for the cenozoic uplift of the tibetan plateau located behind the himalaya collision zone and the western united states located behind the san andreas transform convergent plate boundary selected first p arrivals of international seismological centre isc data at distances less than 22 are analyzed by the two station method to constrain the upper mantle structure of the basin and range br colorado plateau cp great plains gp and tibetan plateau tp the data are presented as plots of apparent velocity versus distance to the second station we show that these observations of apparent velocities versus distance as well as those that concern the attenuation of sn provide estimates of the mantle lid thicknesses we obtain the following mantle lid thicknesses br 20 40 km cp 35 50 km gp 150 195 km and tp 135 180 km sn is not observed for paths beneath the br and cp while sn efficiently propagates beneath the gp sn is also observed beneath most of tibet except in the north central part of the tp a possible interpretation of our observations is that indian continental lithosphere underthrusts only about the southern 2 3 of tibet

dissolution of marine shales and its influence on reservoir properties in the jiaoshiba area sichuan basin china abstract the dissolution of marine shales and its influence on reservoir physical properties was revealed based on shale samples from the ordovician silurian wufeng and longmaxi formations in the southeast of the sichuan basin china three kinds of gas storage spaces were formed by dissolution including intergranular dissolution interd pores intragranular dissolution intrad pores and dissolution microfractures dmf the diameters of the interd and intrad are 10 2 72 4 m and 0 13 1 52 m respectively the apertures of the dmf are between 0 5 and 11 2 m the dissolution effect resulted in a diagenetic environment for quartz cementation and a material basis for calcite veins the main controlling factors of the dissolution effect are the mineral constituent content in the matrix the amount of organic matter and the strata burial rate dissolution pores and fractures play important roles in shale gas enrichment and migration the porosity of shale reservoirs with dmf is twice the porosity of reservoirs without dmf and the spaces formed by dissolution pores and fractures are well connected a new model for shale gas flow in shale reservoirs was proposed which provides a new understanding for the connection between organic material pores and the results can be used for shale reservoirs worldwide

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

bubble coalescence in basalt flows comparison of a numerical model with natural examples gas accumulation in magma may be aided by coalescence of bubbles because large coalesced bubbles rise faster than small bubbles the observed size distribution of gas bubbles vesicles in lava flows supports the concept of post eruptive coalescence a numerical model predicts the effects of rise and coalescence consistent with observed features the model uses given values for flow thickness viscosity volume percentage of gas bubbles and an initial size distribution of bubbles together with a gravitational collection kernel to numerically integrate the stochastic collection equation and thereby compute a new size spectrum of bubbles after each time increment of conductive cooling of the flow bubbles rise and coalesce within a fluid interior sandwiched between fronts of solidification that advance inward with time from top and bottom bubbles that are overtaken by the solidification fronts cease to migrate the model predicts the formation of upper and lower vesicle rich zones separated by a vesicle poor interior the upper zone is broader more vesicular and has larger bubbles than the lower zone basaltic lava flows in northern california exhibit the predicted zonation of vesicularity and size distribution of vesicles as determined by an impregnation technique in particular the size distribution at the tops and bottoms of flows is essentially the same as the initial distribution reflecting the rapid initial solidification at the bases and tops of the flows many large vesicles are present in the upper vesicular zones consistent with expected formation as a result of bubble coalescence during solidification of the lava flows both the rocks and model show a bimodal or trimodal size distribution for the upper vesicular zone this polymodality is explained by preferential coalescence of larger bubbles with subequal sizes vesicularity and vesicle size distribution are sensitive to atmospheric pressure because bubbles expand as they decompress during rise through the flow the ratio of vesicularity in the upper to that in the lower part of a flow therefore depends not only on bubble rise and coalescence but also on flow thickness and atmospheric pressure application of simple theory to the natural basalts suggests solidification of the basalts at 1 0 0 2 atm consistent with the present atmospheric pressure paleobathymetry and paleoaltimetry are possible in view of the sensitivity of vesicle size distributions to atmospheric pressure thus vesicular lava flows can be used to crudely estimate ancient elevations and or sea level air pressure

stable isotopic evidence for a pre middle miocene rain shadow in the western basin and range implications for the paleotopography of the sierra nevada 1 a recently proposed method for approximating the paleorelief of mountain belts makes use of the predictable relationship between the isotopic depletion of precipitation and the net elevation of an orographic barrier over which an air mass rises this rain shadow effect often creates desert regions on the lee side of mountain belts in which precipitation is isotopically light changes in the isotopic composition of precipitation can be estimated from the isotopic composition of authigenic or pedogenic minerals which can then be used to infer both the development of relief during orogenesis as well as the stability of a rain shadow formed by developing mountains the 18o of smectites formed from the weathering of middle miocene to late pliocene volcanic ashes currently exposed in the rain shadow of the modern sierra nevada of california show no indication of large scale late cenozoic surface uplift of the sierra and corresponding regional rain shadow development rather smectite isotope data tentatively suggest that elevations may have decreased over this time by as much as 2000 m toward the southern end of the range and 700 m in regions farther north this suggests that the modern rain shadow cast over the western basin and range has been in existence since pre middle miocene and that the sierra nevada have been a prominent orographic barrier since before this time these interpretations are in accord with several recent studies also suggesting a possible cenozoic elevation loss of an already developed sierra nevada mountain range

diagenetic variation at the lamina scale in lacustrine organic rich shales implications for hydrocarbon migration and accumulation abstract lacustrine carbonate rich shales are well developed within the mesozoic cenozoic strata of the bohai bay basin bbb of eastern china and across southeast asia developing an understanding of the diagenesis of these shales is essential to research on mass balance diagenetic fluid transport and exchange and organic inorganic interactions in black shales this study investigates the origin and distribution of authigenic minerals and their diagenetic characteristics processes and pathways at the scale of lacustrine laminae within the es4s es3x shale sequence of the bbb the research presented in this study is based on thin sections field emission scanning electron microscope fesem and sem catholuminescence cl observations of well core samples combined with the use of x ray diffraction xrd energy dispersive spectroscopy electron microprobe analysis and carbon and oxygen isotope analyses performed using a laser microprobe mass spectrometer the dominant lithofacies within the es4s es3x sequence are a laminated calcareous shale lcs 1 and a laminated clay shale lcs 2 the results of this study show that calcite recrystallization1 is the overarching diagenetic process affecting the lcs 1 related to acid generation from organic matter om thermal evolution this evolutionary transition is the key factor driving the diagenesis of this lithofacies while the transformation of clay minerals is the main diagenetic attribute of the lcs 2 diagenetic differences occur within different laminae and at variable locations within the same lamina level controlled by variations in mineral composition and the properties of laminae interfaces the diagenetic fluid migration scale is vertical and responses dissolution and replacement are limited to individual laminae between zero and 100 m in width in contrast the dominant migration pathway for diagenetic fluid is lateral along the abrupt interfaces between laminae boundaries which leads to the vertical transmission of diagenetic responses the recrystallization boundaries between calcite laminae act as the main migration pathways for the expulsion of hydrocarbons from these carbonate rich lacustrine shales however because the interaction between diagenetic fluids and the shales themselves is limited to the scale of individual lamina this system is normally closed the occurrence of abnormal pressure fractures can open the diagenetic system however and cause interactions to occur throughout laminae in particular the closed open c o diagenetic process at this scale is critical to this shale interval multi scale c o systems are ubiquitous and episodic ranging from the scale of laminae to the whole basin observations show that such small scale systems are often superimposed onto larger ones to constitute the complex diagenetic system seen within the bbb combining fluid transport material and energy exchange and solid liquid and organic inorganic interactions

vesiculation of basaltic magma during eruption vesicle size distributions in vent lavas from the pu9u9o9o kupaianaha eruption of kilauea volcano are used to estimate nucleation and growth rates of h 2 o rich gas bubbles in basaltic magma nearing the earth9s surface 120 m depth by using well constrained estimates for the depth of volatile exsolution and magma ascent rate nucleation rates of 35 9 events cm 3 s 1 and growth rates of 3 2 x 10 4 cm s are determined directly from size distribution data the results are consistent with diffusion controlled growth as predicted by a parabolic growth law this empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings in addition perturbations in the measured size distributions are used to examine bubble escape accumulation and coalescence prior to the eruption of magma

scouring at bed sills as a response to flash floods the temporal development of clear water local scour depth at bed sills in uniform gravel beds is considered experiments are presented on the development of scour holes under unsteady hydraulic conditions with the triangular shaped hydrographs tested being of different durations and different rates of flow variation based on the experimental results and a theoretical framework a method is given for the definition and prediction of the scouring process under unsteady flows in terms of a dimensionless temporal parameter a flash flood is here defined as an event for which the scour doesn t attain its potential magnitude i e the equilibrium value for the peak hydrograph flow rate this flood nature is dependent on both the characteristics of the flood event itself and the characteristics of the stream a quantitative measure of what constitutes a flash flood is given in terms of the identified temporal parameter results show that the ratio between the final scour depth and the potential scour depth

grain size distribution of volcaniclastic rocks 1 a new technique based on functional stereology the power of explosive volcanic eruptions is reflected in the grain size distribution and dispersal of their pyroclastic deposits grain size also forms part of lithofacies characteristics that are necessary to determine transport and depositional mechanisms responsible for producing pyroclastic deposits however the common process of welding and rock lithification prevents quantification of grain size by traditional sieving methods for deposits in the rock record here we show that functional stereology can be used to obtain actual 3d volume fractions of clast populations from 2d cross sectional images tests made on artificially consolidated rocks demonstrate successful correlations with traditional sieving method we show that the true grain size distribution is finer grained than its representation on a random 2d section our method allows the original size of vesicular pumice clasts to be estimated from their compacted shapes we anticipate that the original grain size distribution of welded ignimbrites can also be characterized by this method our method using functional stereology can be universally applied to any type of consolidated weakly to non deformed clastic material regardless of grain size or age and therefore has a wide application in geology

modelling time varying scouring at bed sills in this paper a modelling approach is presented to predict local scour under time varying flow conditions the approach is validated using experimental data of unsteady scour at bed sills the mode

analysis of vesicular basalts and lava emplacement processes for application as a paleobarometer paleoaltimeter abstract we have developed a method for determining paleoelevations of highland areas on the basis of the vesicularity of lava flows vesicular lavas preserve a record of paleopressure at the time and place of emplacement because the difference in internal pressure in bubbles at the base and top of a lava flow depends on atmospheric pressure and lava flow thickness at the top of the flow the pressure is simply atmospheric pressure while at the base there is an additional contribution of hydrostatic lava overburden thus the modal size of the vesicle bubble population is larger at the top than at the bottom this leads directly to paleoatmospheric pressure because the thickness of the flow can easily be measured in the field and the vesicle sizes can now be accurately measured in the lab because our recently developed technique measures paleoatmospheric pressure it is not subject to uncertainties stemming from the use of climate sensitive proxies although like all measurements it has its own sou

underwater sand bed erosion and internal jump formation by travelling plane jets theory and experiments are used to investigate the water and sediment motion induced along a sea bed by travelling plane jets steadily moving jets are considered and represent an idealization of the tools mounted on ships and remotely operated vehicles rovs for injection dredging and trenching the jet induced turbulent currents simultaneously suspend sand from the bed and entrain water from the ambient to describe these processes a shallow flow theory is proposed in which the turbulent current is assumed stratified into sediment laden and sediment free sublayers the equations are written in curvilinear coordinates attached to the co evolving bed profile a sharp interface description is then adopted to account rigorously for mass and momentum exchanges between the bed current and ambient including their effects on the balance of mechanical energy travelling wave solutions are obtained in which the jet induced current scours a trench of permanent form in a frame of reference moving with the jetting tool depending on the operating parameters it is found that the sediment laden current may remain supercritical throughout the trench or be forced to undergo an internal hydraulic jump these predictions are confirmed by laboratory experiments for flows with or without jump in which the current remains attached to the bed bottom profiles computed by the theory compare favourably with imaging measurements

early evolution of the earth accretion atmosphere formation and thermal history atmospheric and thermal evolution of the earth growing by planetesimal impacts was modeled by taking into account the blanketing effect of an impact induced h2o atmosphere and the temperature dependence of h2o degassing when the water content of planetesimals is larger than 0 1 by weight and the accretion time of the earth is less than 5 107 years the surface of the accreting earth melts and thus a magma ocean forms and covers the surface the formation of a magma ocean will result in the initiation of core mantle separation and mantle differentiation during accretion once a magma ocean is formed the surface temperature the degree of melting in the magma ocean and the mass of the h2o atmosphere are nearly constant as the protoplanet grows further the final mass of the h2o atmosphere is about 1021 kg a value which is insensitive to variations in the model parameter values such as the accretion time and the water content of planetesimals that the final mass of the h2o atmosphere is close to the mass of the present oceans suggests an impact origin for the earth s hydrosphere on the other hand most of the h2o retained in planetesimals will be deposited in the solid earth free water within the proto earth may affect differentiation of the proto mantle in particular the mantle feo abundance and the incorporation of a light element in the outer core

influence of paleorelief on the mid miocene climate variation in southeastern washington northeastern oregon and western idaho usa abstract terrestrial climate proxy records repeatedly show spatial heterogeneity because regional climate condition is largely influenced by the relationship between large scale atmospheric circulation patterns and regional topographic features the paleosols developed on the top of columbia river basalt flows emplaced between 15 3 and 15 8 ma in the northwestern united states show significant spatial variations in the mid miocene soil forming processes the paleosol in the northwestern part of the study area has the least degree of chemical weathering fine scale and very shallow penetrating depth of root traces with the estimated paleoprecipitation and paleotemperature of about 550 mm and 16 c respectively the paleosols in the southeastern part of the study area indicate more intense chemical weathering with the estimated paleoprecipitation and paleotemperature of approximately 1400 to 1500 mm and 17 c respectively the spatial variations in paleo pedogenesis were predominantly affected by spatial heterogeneity in the mid miocene regional climate and regional paleotopographic features taking the other ancient soil forming factors including time parent rock materials and biological activities into account we suggest that intrusions of hot columbia river basalt magma into the crust were responsible for the regional surface uplift and the paleoclimate heterogeneity because the major vent systems of the columbia river basalt eruptions were located in the area where development of the mid miocene high topography existed within the blue mountains paleotopography of the earth s surface can be reconstructed by the paleoprecipitation and paleotemperature estimations from several spatially distributed chrono stratigraphic paleosols although it is difficult to estimate the magnitude of the paleorelief precisely

erosion by planar turbulent wall jets new scaling laws are presented for the spatial variation of the mean velocity and lateral extent of a two dimensional turbulent wall jet flowing over a fixed rough boundary these scalings are analogous to those derived by wygnanski et al 1992 for the flow of a wall jet over a smooth boundary they reveal that the characteristics of the jet depend weakly upon the roughness length associated with the boundary as confirmed by experimental studies rajaratnam 1967 these laws are used in the development of an analytical framework to model the progressive erosion of an initially flat bed of grains by a turbulent jet the grains are eroded if the shear stress exerted on the grains at the surface of the bed exceeds a critical value which is a function of the physical characteristics of the grains after the wall jet has been flowing for a sufficiently long period the boundary attains a steady state in which the mobilizing forces associated with the jet are insufficient to further erode the boundary the steady state profile is calculated separately by applying critical conditions along the bed surface for the incipient motion of particles these conditions invoke a relationship between the mobilizing force exerted by the jet the weight of the particles and the local gradient of the bed use of the new scaling laws for the downstream variation of the boundary shear stress then permits the calculation of the shape of the steady state scour pit the predicted profiles are in good agreement with the experimental studies on the erosive action of submerged water and air jets on beds of sand and polystyrene particles rajaratnam 1981 the shape of the eroded boundary at intermediate times before the steady state is attained is elucidated by the application of a sediment volume conservation equation this relationship balances the rate of change of the bed elevation with the divergence of the flux of particles in motion the flux of particles in motion is given by a semi empirical function of the amount by which the boundary shear stress exceeds that required for incipient motion hence the conservation equation may be integrated to reveal the transient profiles of the eroded bed there is good agreement between these calculated profiles and experimental observations rajaratnam 1981

epeirogeny and eustatic sea level changes as inferred from cretaceous shoreline deposits applications to the central and western united states uplift and subsidence histories of continental margins are by now reasonably well understood in the context of plate tectonics but the epeirogenic movements of continental interiors have been neither well documented nor properly understood epeirogenic movements are important to recognize when reconstructing paleogeography and may yield information regarding mantle dynamics and the amplitudes wavelengths and rates of lithospheric flexure sediments deposited at or near sea level can be used as a worldwide datum against which to measure postdepositional epeirogenic movements the present elevations of shoreline sediments of epicontinental seas deposited during sea level highstands at particular times in the past define a warped surface documenting subsequent epeirogeny of continental interiors when the amplitude of sea level rise during transgression is small relative to the observed epeirogenic motions the diachronous shoreline deposits represented in the entire transgressive surface can be used as a datum in the analysis thus greatly augmenting the available data and areal coverage if a stable frame of reference can be defined a eustatic sea level correction can be applied to every continent the elevation of the upper cenomanian mid cretaceous shoreline gives little evidence of warping tilting or uplift in central cratonic north america but indicates that a large area of the western united states including the colorado plateau has undergone more than 2 km of post cenomanian epeirogenic uplift

reattached turbulent submerged offset jets on rough beds with shallow tailwater this study investigates the characteristics of reattached plane turbulent offset jets in channels with rough beds and shallow tailwater depths the flow consists of a deflecting free jet caused by the coanda effect and the evolving wall jet past reattachment in limited tailwater conditions the jet flow is affected by the relative tailwater depth or the submergence parameter which is defined with respect to the maximum b jump at a negative step the results show that for an offset height larger than the jet thickness the forward flow momentum local maximum velocity and wall shear stress decrease faster in the longitudinal direction in the offset jet than in plane turbulent wall jets the influence of roughness on reattached offset jets appears to be less than that in submerged wall jets on a similar rough bed the presented results and the comparative analysis with respect to wall jets in hydraulic jumps are significant for controlling and implementing similar flows on rough beds with variable downst

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

geochemical evaluation of fenghuoshan group lacustrine carbonates north central tibet implications for the paleoaltimetry of the eocene tibetan plateau abstract a sedimentologic petrologic and geochemical evaluation of lacustrine carbonates from the eocene oligocene fenghuoshan group of north central tibet provides insight into the paleoenvironmental and paleolimnological setting of the hoh xil basin during the mid tertiary fenghuoshan lacustrine rocks consist primarily of carbonate mudstones and wackestones these carbonates are generally less than 3 m in thickness and are intercalated with siliciclastic lacustrine and fluvial alluvial plain deposits individual limestone beds coarsen and contain increasing amounts of siliciclastic material upward fenghuoshan carbonates also contain abundant ostracode bivalve and charaphyte fossils sedimentologic evidence suggests that carbonate deposition occurred in shallow relatively short lived lacustrine systems that were subsequently filled by alluvial deposits of coeval fluvial systems stable c and o isotopic analysis of fenghuoshan carbonates show 18o values ranging from 11 7 to 10 3 vienna pee de

erosion by submerged circular jets an experimental study on the erosion of sand beds by impinging submerged circular water jets shows similarities between air sand system and water sand system it is shown that there are significant differences between the two systems regarding the depth and radial extent of the scour hole

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

hydraulics of submerged jet subject to change in cohesive bed geometry the results of an experimental investigation of the time variation of scour hole and the flow characteristics of the quasi equilibrium state of scour of a cohesive bed downstream of an apron due to a submerged horizontal jet issuing from a sluice opening are presented experiments were carried out with natural cohesive sediment for various sluice openings jet velocities and lengths of apron attempts are made to explain the similarity existing either in the process of scour or in the scour profiles that the scour holes follow downstream of an apron the scour profiles at different times follow a particular geometrical similarity and can be expressed by a polynomial using relevant parameters the characteristic parameters affecting the time variation of scour depth are identified based on the physical reasoning and dimensional analysis an equation for time variation of maximum scour depth is obtained empirically the diffusion characteristics of the submerged jet growth of boundary layer thickness velocity distribution within the boundary layer and shear stress at the quasi equilibrium state of scour are also investigated the expression of shear stress is obtained from the solution of the von karman momentum integral equation

basalt vesicularity as a measure of atmospheric pressure and palaeoelevation the pressure in and thus the size of a bubble in a lava flow is determined by the atmospheric pressure and the hydrostatic pressure of the overlying lava if atmospheric sea level pressure is known or assumed vesicle size distributions in basalt flows can thus be used as an indicator of the palaeoelevation of emplacement1 here we show by analysis of the vesicle size distribution of basalt samples collected from the summit and base of mauna loa volcano in hawaii that the technique provides estimates of ambient pressure that are accurate to within 0 1 bar and thus estimates of elevation with a resolution of about 1 400m this palaeoaltimetric technique should find useful application in palaeogeographical reconstruction2 for times when sea level pressure was similar to the present value conversely if the elevation of emplacement is known our technique should be able to provide a measure of sea level palaeopressure unlike palaeo botanical methods for estimating elevations3 6 this method does not have to assume a relationship between temperature and altitude on the other hand its use is restricted to lava flows that have had a simple emplacement history

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

paleoaltimetry incorporating atmospheric physics and botanical estimates of paleoclimate we present a method for deducing paleoaltitudes that incorporates basic physical principles of atmospheric science and inferences of paleoclimates from plant leaf physiognomy we exploit the average west to east flow of the atmosphere at mid latitudes and a thermodynamically conserved variable in the atmosphere moist static energy the combined internal latent heat and gravitational potential energy of moist air to develop a method that relies on a parameter that varies with height in the atmosphere in a predictable fashion because the surface distribution of moist static energy is constrained by atmospheric dynamics and thermodynamics the combined internal and latent heat energies also known as the moist enthalpy should only vary with altitude provided we know the distribution of moist static energy thus we avoid having to make assumptions about the mean annual temperature lapse rate which varies spatially and temporally owing to unpredictable variations in atmospheric water vapor to estimate a paleoaltitude therefore we require 1 a priori knowledge of the spatial distribution of moist static energy for the paleoclimate and 2 the ability to estimate paleoenthalpy for two isochronous locations one at sea level the other at some unknown elevation to achieve this we investigated the spatial distribution of moist static energy for the present day climate of north america to estimate the deviations in moist static energy from zonal invariance in parallel we quantified the relation between moist enthalpy and plant leaf physiognomy of modern forests assuming that such deviations from zonal invariance and such relationships between physiognomy and enthalpy apply to ancient climates and fossil leaves these investigations yield an uncertainty estimate of 910 m in the paleoaltitude difference between two isochronous fossil assemblage locations

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening