what are the best radar wavelengths incidence angles and polanzations for discrimination among lava flows and sedimentary rocks a statistical approach linear discriminant analysis of multifrequency and multipolarization radar scatterometer data of lava flows and sedimentary rocks indicates that the lava flows sampled at the snake river plain idaho and the sedimentary formations sampled at the san rafael swell utah can be discriminated from one another the necessary radar backscatter data and optimum wavelengths polarizations and incidence angles among those available for these problems are indicated by the discriminant analysis program for separation of the lava flows shorter wavelengths and smaller incidence angles are best for the sedimentary rocks conversely the longer wavelengths and somewhat larger incidence angles are preferred separation among the lava flows was slightly better using horizontally polarized data while vertical polarization gave better separation with the sedimentary rocks the method developed here may provide a rationale for user selection tion of operating parameters for advanced radar systems such as the shuttle imaging radar c sir c and that proposed for the earth observation system eos the analysis is being extended to other study sites for which we have scatterometer data to determine the generality of the results reported here

a quad pol radar scattering model for use in remote sensing of lava flow morphology abstract mapping of spatial variations in surface roughness over large regions is required to understand the nature of volcanic terrains an invertible scattering model for quad polarization radar data is presented to assist in the remote sensing analysis of lava flow surface morphology this model permits separation of the polarized part of the radar echo into quasispecular dihedral and small perturbation scattering components based on an assumed surface dielectric constant tests are presented for a quad pol scene of craters of the moon national monument in idaho where there are a number of basaltic lava flows of differing surface morphology comparison of calculated model components with the observed morphology of the lava flows suggests that this technique may be useful for the remote description of changes in surface roughness the scattering mechanisms chosen to represent the polarizing behavior of the real surface display correlations which indicate that they are sensitive to the expected scales of roughness

a unique lacustrine mixed dolomitic clastic sequence for tight oil reservoir within the middle permian lucaogou formation of the junggar basin nw china reservoir characteristics and origin abstract the middle permian lucaogou formation in the jimusaer sag of the southeastern junggar basin nw china was the site of a recent discovery of a giant tight oil reservoir this reservoir is unusual as it is hosted by lacustrine mixed dolomitic clastic rocks significantly differing from other tight reservoirs that are generally hosted by marine lacustrine siliciclastic calcitic sequences here we improve our understanding of this relatively new type of tight oil reservoir by presenting the results of a preliminarily investigation into the basic characteristics and origin of this reservoir using field petrological geophysical including seismic and logging and geochemical data field and well core observations indicate that the lucaogou formation is a sequence of mixed carbonate mainly dolomites and terrigenous clastic mainly feldspars sediments that were deposited in a highly saline environment the formation is divided into upper and lower cycles based on lithological variations between coarse and fine grained rocks in particular dolomites and siltstones are interbedded with organic rich mudstones in the lower part of each cycle whereas the upper part of each cycle contains few dolomites and siltstones tight oil accumulations are generally present in the lower part of each cycle and dolomites and dolomite bearing rocks are the main reservoir rocks in these cycles including sandy dolomite dolarenite dolomicrite and a few dolomitic siltstones optical microscope back scattered electron and scanning electron microscope imaging indicate that the main oil reservoir spaces are secondary pores that were generated by the dissolution of clastics and dolomite by highly acidic and corrosive hydrocarbon related fluids

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

mapping exposed and buried lava flows using synthetic aperture and ground penetrating radar in craters of the moon lava field the craters of the moon com lava field has a multiple eruptivehistory burialofolderflowshasresultedincomplex subsurface stratigraphy for the older eruptive periods the locations of source vents and the extension of lava flows are eitherspeculativeorunknown becausetheyareburiedunder more recent pyroclastics in this study we used surface and subsurface backscatter characteristics of the p and l band polarimetric airborne synthetic aperture radar airsar data and ground penetrating radar gpr soundings to resolve different exposed and buried lava flows our primary objective is to define the most effective polarization and frequency for mapping resolving and characterizing different lavatypesinthevolcanicfield polarimetricanalysisofairsar images from com allows a clear recognition of the aa and pahoehoe lava types as a result of the variability in their roughness our results suggest that the hv cross polarized airsar l band is capable of producing a detailed map delineating surface lava with different surface backscattering properties an accuracy assessment utilizing the geological map of the inferno cone area was performed to quantify the reliability of differentiating lava types and mapping the lava flows extension below loose pyroclastics using airsar data results shows an ability of p band sar to map buried structures up to 3 meters deep under loose cinder and ash deposits resolvingburiedfissures outcrops andlavaflowsthat were validated with ground truth gpr surveys the techniquesusedinthisstudyprovideatooltoassessvolcanichazardsinremoteandinaccessibleplaces alsoitcouldbeanaid in the study of other planets and planetary bodies in the solar system

digital topography of volcanoes from radar interferometry an example from mt vesuvius italy a new airborne radar technique can generate digital topographic data for volcanoes at a scale of 10 m spatial and 1 5 m vertical with a swath width of 6 4 km called topsar the intrument is an interferometric radar flown on the nasa dc 8 aircraft topsar data permit the quantification of volcano slopes volumes and heights and as such will be valuable for the analysis of lava flows domes and lahar channels this instrument will be flown over several volcanoes in the near future providing volcanologists with valuable data sets for the analysis of high resolution topography we briefly illustrate the potential use of topsar data through examples from mt somma and vesuvius italy

sandstone diagenesis and reservoir quality prediction models myths and reality models and concepts of sandstone diagenesis developed over the past two decades are currently employed with variable success to predict reservoir quality in hydrocarbon exploration not all of these are equally supported by quantitative data observations and rigorous hypothesis testing simple plots of sandstone porosity versus extrinsic parameters such as current subsurface depth or temperature are commonly extrapolated but rarely yield accurate predictions for lithified sandstones calibrated numerical models that simulate compaction and quartz cementation when linked to basin models have proven successful in predicting sandstone porosity and permeability where sufficient analog information regarding sandstone texture composition and quartz surface area is available analysis of global regional and local data sets indicates the following regarding contemporary diagenetic models used to predict reservoir quality 1 the effectiveness of grain coatings on quartz grains e g chlorite microquartz as an inhibitor of quartz cementation is supported by abundant empirical data and recent experimental results 2 vertical effective stress although a fundamental factor in compaction cannot be used alone as an accurate predictor of porosity for lithified sandstones 3 secondary porosity related to dissolution of framework grains and or cements is most commonly volumetrically minor 2 exceptions are rare and not easily predicted with current models 4 the hypothesis and widely held belief that hydrocarbon pore fluids suppress porosity loss due to quartz cementation is not supported by detailed data and does not represent a viable predictive model 5 heat flow perturbations associated with allochthonous salt bodies can result in suppressed thermal exposure thereby slowing the rate of quartz cementation in some subsalt sands

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

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

two crustal low velocity channels beneath se tibet revealed by joint inversion of rayleigh wave dispersion and receiver functions abstract competing geodynamic models such as rigid block extrusion continuous deformation and the mid lower crustal flow have been proposed to describe the growth and expansion of eastern tibet however the dynamic processes responsible for plateau evolution and deformation remain poorly understood partly due to resolution limitations of previous models of lithospheric structure on the basis of joint inversion of rayleigh wave dispersion and receiver functions using data from a newly deployed seismic array we have obtained a high resolution 3d image that reveals the distribution of low velocity zones lvzs with unprecedented clarity the prominent feature of our model is two low velocity channels that bound major strike slip faults in se tibet and wrap around the eastern himalaya syntaxis consistent with the clockwise movement of crustal material in this region most large earthquakes in this region occurred in the boundaries of the lvzs we propose that ductile flow within these channels in addition to shear motion along strike slip faults played a significant role in accommodating intensive lithospheric deformation during the eastward expansion of tibet in the cenozoic

ground penetrating radar sounding in mafic lava flows assessing attenuation and scattering losses in mars analog volcanic terrains we conducted low frequency 16 to 100 mhz ground penetrating radar surveys on the eroded lava flows at craters of the moon idaho usa volcanic field to evaluate the potential of future radar sounding investigations on mars to map shallow subsurface features radar sounding profiles were obtained from three locations above a lava tube across a volcanic rift and over a scoria cone results were combined with laboratory permittivity and magnetic permeability measurements of field collected samples to deconvolve the electromagnetic attenuation and scattering losses from the total losses and therefore separately quantify both effects on the radar penetration depth our results demonstrate a constrained performance for low frequency sounding radars to characterize mafic arid volcanic terrains that contain a significant amount of ferro oxides 14 mainly in the form of olivine and magnetite penetration depths of 35 m were achieved at a frequency of 100 mhz and depths of 80 m were achieved at 16 mhz with an effective dynamic range of 60 db results indicate that for frequencies below 100 mhz the electromagnetic attenuation dominated the signal losses while above this frequency threshold the volume scattering dominated the losses over our frequency range the observed electromagnetic attenuation and penetration depths were strongly dependent on the magnetic losses ground porosities and degree of heterogeneity rather than the sounding frequency in light of these results we suggest average attenuation and scattering losses measured in terms of db m and discuss the expected penetration depth for the mars orbital radar sounding instruments sharad and marsis in mafic volcanic terrains

carbonate equilibria and ph buffering by organic acids response to changes in pco2 abstract organic acid anions such as acetate a natural product of the thermal breakdown of kerogen may buffer the ph of natural formation waters the extent of ph buffering by acetate should determine whether an increase in the partial pressure of carbon dioxide p co 2 will lead to calcite dissolution porosity enhancement or calcite precipitation porosity destruction successful prediction of porosity therefore requires a quantitative understanding of this process this paper presents computer simulations of the response of the acetic acid carbonate system to changes in p co 2 for typical reservoir fluid compositions and temperatures the effects of variations in temperature ionic strength initial ca 2 concentration and the magnitude of the change in p co 2 were investigated natural formation waters from cenozoic reservoirs in the gulf coast basin and california show maximum organic acid concentrations at 100 20 c at 100 c the simulations show that for concentrations of acetic acid up to 0 06 m 3600 mg l 1 increases in the p co 2 of initially calcite saturated solutions will promote calcite undersaturation at higher temperatures equivalent buffering responses occur at lower acetic acid concentrations but acetic acid concentrations in natural formation waters also decrease rapidly with increasing temperature since present day concentrations of acetic acid in formation waters from cenozoic reservoirs rarely exceed 0 06 m increases in p co 2 will generally promote calcite dissolution by these waters in the gulf coast basin variation in organic acid concentrations as a function of reservoir age suggests that reductions in dissolved organic acid concentrations over geologic time have been relatively small it can be concluded therefore that at any point in the histories of these reservoirs an increase in p co 2 would have promoted calcite dissolution despite the effects of ph buffering by acetate since increases in p co 2 will in most cenozoic basins promote calcite dissolution knowledge of the location and timing of co 2 production in the subsurface can more easily be applied to the prediction of calcite cementation and dissolution

distribution and occurrence of aliphatic acid anions in deep subsurface waters abstract this study reports 144 new analyses of short chain aliphatic acid anions acetate propionate butyrate and valerate in formation waters from eight localities eastern venezuelan basin denver basin eastern green river basin red desert and washakie basins wamsutter arch san juan basin piceance basin raton basin gulf coast basin and the western overthrust reservoir temperature does not predict total or relative abundance of aliphatic acid anions but does predict maximum total concentrations of these species maximum concentrations increase to 90 c above 90 c maximum concentrations decrease above 250 c maximum concentrations should not exceed 1 mg 1 the general order of dominance is acetate propionate butyrate valerate but for coal associated waters is propionate acetate butyrate valerate lack of longer chain aliphatic acid anion dominance over acetate at low reservoir temperatures may suggest hydrologie communication with deeper reservoirs

constraints on the development of secondary porosity in the subsurface re evaluation of processes abstract secondary porosity formed by the dissolution of grains and cements is of great economic importance in both clastic and carbonate reservoirs a review of the commonly proposed mechanisms for the production of secondary porosity indicates that meteoric water penetration and mixing corrosion may be able to create significant volumes of secondary porosity in the shallow subsurface leaching by acidic fluids generated by solution of co 2 or monocarboxylic acids both derived during the thermal maturation of organic matter or by acidic fluids created by clay mineral reactions in shales are the most commonly proposed mechanisms by which secondary porosity is said to form in the deep subsurface however these mechanisms suffer from great difficulties in producing significant volumes of secondary porosity once mass balance and fluid migration problems are taken into account it is highly likely that the correct mechanism for the creation of economically significant amounts of secondary porosity in the deep subsurface is yet to be found

petrologic and experimental evidence for the etching of garnets by organic acids in the upper jurassic morrison formation northwestern new mexico abstract the upper jurassic morrison formation in the southern part of the san juan basin contains uniquely etched detrital garnets characterized by smooth crystallographically controlled faceted surfaces the etched garnets occur in relatively homogeneous morrison sandstones in discrete stratigraphic zones that are bounded above and below by sandstones bearing unetched garnets diagenetic alterations associated with etched garnets include etched staurolite skeletal plagioclase regularly interstratified illite smectite iron rich chlorite ankerite albite diagenetically altered organic poor uranium ore and extensive secondary porosity etching of garnets and partial to complete dissolution of other aluminosilicate minerals were caused by high concentrations of organic acids generated during the maturation of epigenetic organic matter predominantly type iii kerogen in the morrison formation the presence of authigenic phases that form near 100 c indicates that temperatures were high enough during diagenesis to cause the thermal degradation of kerogen the subsequent release of reactive organic acids promoted a variety of water rock reactions this hypothesis was corroborated by experiments in which dicarboxylic acid solutions created facets on garnets identical to those developed on naturally etched morrison garnets the excellent complexing ability of organic acid anions accounts for the characteristic lack of alteration products on etched surfaces

carboxylic acid anions in formation waters san joaquin basin and louisiana gulf coast u s a implications for clastic diagenesis reply to discussion by p d lundegard and l s land abstract macgowan and s urdam 1990a suggested some modifications to the model of lundegard and land 1989 to make it more geologically and geochemically reasonable the predictive power of such a geochemical model is wholly dependent on the species modeled and the constants used any model that excludes important species or important thermodynamic data or one that couples certain reactions in an unrealistic way may produce results which are not geologically or geochemically reasonable w k harrison pers commun 1988 y k kharaka pers commun 1991 we have long recognized that under early burial diagenetic conditions aluminosilicate hydrolysis generally controls formation water ph surdam and eugster 1976 mariner and surdam 1970 taylor and surdam 1981 and that during intermediate burial either aqueous co2 or caa species in the absence of aqueous s species or other weak conjugate acid base pairs will dominate formation water alkalinity and control ph surdam et al 1989c we reassert that the model of lundegard and land 1989 does not take into account the relative importance of pco2 and of concentrations of both ca2 and caa and their relative organic metal complexes to carbonate mineral stability in sandstones in the zone of intermediate burial clastic diagenesis cf the models of surdam et al 1984 and surdam and crossey 1985 the usefulness of such models is predicted on the completeness of the model and the use of the best most accurate thermodynamic data also geologically realistic concentrations of critical species are required for reasonable modeling to be done although their model is vigorously defended in the discussion of lundegard and land 1989 lundegard and land 1993 we continue to disagree that their analysis of their model conditions are either geologically or geochemically satisfying we agree with the fundamental approach and philosophy of lundegard and land 1989 lundegard and land 1993 it is of the utmost importance to determine from experimental geochemical petrographic and geological data what the controls on ph and alkalinity in formation waters are as well as the exact thermodynamic speciation of aqueous moieties and the stability of detrital and authigenic minerals lundegard and land 1993 raise an additional point about caa reaction with carbonate minerals in shales although fisher and lewan 1989 lewan 1989 and macgowan and surdam 1990b have demonstrated that caa generated in shale likely migrate in the oil phase along incipient shale microfractures to the sandstone reservoir and thus are likely to not react much with the shale finally we agree with lundegard and land that these areas require much additional experimental and field analysis and petrographic study

preliminary analyses of sir b radar data for recent hawaii lava flows abstract the shuttle imaging radar sir b experiment acquired two l band 23 cm wavelength radar images at about 28 and 48 incidence angles over the kilauea volcano area of southeastern hawaii geologic analysis of these data indicates that although as lava flows and pyroclastic deposits can be discriminated pahoehoe lava flows are not readily distinguished from surrounding low return materials preliminary analysis of data extracted from isolated flows indicates that flow type i e as or pahoehoe and relative age can be determined from their basic statistics and illumination angle

radar polarimetry analysis tools and applications the authors have developed several techniques to analyze polarimetric radar data from the nasa jpl airborne sar for earth science applications the techniques determine the heterogeneity of scatterers with subregions optimize the return power from these areas and identify probable scattering mechanisms for each pixel in a radar image these techniques are applied to the discrimination and characterization of geologic surfaces and vegetation cover and it is found that their utility varies depending on the terrain type it is concluded that there are several classes of problems amenable to single frequency polarimetric data analysis including characterization of surface roughness and vegetation structure and estimation of vegetation density polarimetric radar remote sensing can thus be a useful tool for monitoring a set of earth science parameters

the impact of organic fluids on the carbon isotopic compositions of carbonate rich reservoirs case study of the lucaogou formation in the jimusaer sag junggar basin nw china abstract the processes involved in the interaction between organic fluids and carbonates and the resulting effect on reservoir quality during the evolution and maturation of organic matter remain unclear despite the fact that these processes influence the carbon and oxygen isotopic compositions of carbonates here we provide new insights into these processes using data obtained from a detailed analysis of a mixed dolomitic clastic and organic rich sedimentary sequence within the middle permian lucaogou formation in the junggar basin of nw china the techniques used during this study include drillcore observations thin section petrography scanning electron microscopy sem and electron probe microanalysis and carbon and oxygen isotope analyses oil grades and total organic carbon toc contents represent the amount of oil charging and the abundance of organic fluids within a reservoir respectively and both negatively correlate with the whole rock 13c and 18o of the carbonates in the study area indicating that organic fluids have affected the reservoir rocks secondary carbonates including sparry calcite and dolomite overgrowths and cements are common within the lucaogou formation well developed sparry calcite is present within dark mudstone whereas the other two forms of secondary carbonates are present within the dolomite rich reservoir rocks in this formation comparing thin section petrology with 13c compositions suggests that the carbon isotopic composition of matrix carbonates varies little over small distances within a given horizon but varies significantly with stratigraphic height as a result of the development of secondary carbonates the net change in whole rock 13c as a result of these secondary carbonates ranges from 1 8 to 4 6 with the secondary carbonates having calculated 13c compositions from 18 6 to 8 5 that are indicative of an organic origin the positive correlation between the concentration of fe within matrix and secondary carbonates within one of the samples suggests that the diagenetic system within the lucaogou formation was relatively closed the correlation between 13c and 18o in carbonates is commonly thought to be strengthened by the influence of meteoric water as well as organic fluids however good initial correlation between 13c and 18o of whole rock carbonates within the lucaogou formation resulted from the evaporitic sedimentary environment was reduced by organic fluids to some extent consequently the 13c 18o covariations within these sediments are not always reliable indicators of diagenetic alteration by organic fluids or meteoric water the characteristics and 13c compositions of the sparry calcite within the formation is indicative of a genetic relationship with organic acids as a result of the addition of organic co2 to the reservoir further analysis suggests that both carbonate and feldspar were dissolved by interaction with organic co2 however dissolved carbonate reprecipitated as secondary carbonates meaning that the interaction between organic fluids and dolomites did not directly improve reservoir quality although this process did enhance the dissolution of feldspar and increase porosity this indicates that the 13c and 18o of secondary carbonates and their influence on whole rock carbonate isotopic values can be used to geochemically identify the effect of organic fluids on closed carbonate rich reservoir systems

structural controls on localized intraplate deformation and seismicity in southern australia insights from local earthquake tomography of the flinders ranges data from an array of 24 seismometers are used to image the crust beneath the flinders ranges southeast australia with the goal of improving our understanding of crustal structure rheology and the mechanism responsible for the localized intraplate deformation that characterizes this region a subset of p and s wave traveltimes is inverted to jointly recover earthquake hypocenters p wave velocity structure and v p v s anomalies the p wave velocity model reveals a spatial correlation between major negative velocity perturbations and concentrations of seismicity in particular a cluster of seismicity is observed within a distinct low velocity region between the archean mesoproterozoic gawler craton and the palaeo mesoproterozoic curnamona province from 7 to 20km depth we postulate that this may be associated with a pre existing structural weakness in the crust that arises primarily from rifting between the curnamona province and the gawler craton another area characterized by a high level of seismicity overlies a major sequence of n s trending ross delamerian thrust faults which correspond to a band of low v p and particularly v p v s the lack of evidence for elevated heat flows in both of these seismogenic regions suggests that thermally induced weakness is unlikely to play a dominant role instead the dynamic behavior of this intraplate region appears to be caused by a serendipitously oriented regional stress field provided by far field forces that originate from the boundary between the pacific and australian plates which acts upon preexisting structural weaknesses in the lithosphere

carboxylic acid anions in formation waters san joaquin basin and louisiana gulf coast u s a implications for clastic diagenesis abstract carboxylic acid anions caa in formation waters are of interest to studies of clastic diagenesis because of their ability to buffer formation water eh and ph and thus substantially contribute to controls on carbonate mineral stability and their ability to complex and transport al and si from the site of aluminosilicate mineral dissolution during diagenesis carboxylic acid anions are also extremely important to the aqueous geochemistry of ca fe mn pb and zn some formation waters from sedimentary basins contain high concentrations of caas the analyses of 20 formation waters from the san joaquin basin california and 20 formation waters from the louisiana gulf coast basin presented in this study show concentrations as high as 8100 ppm monofunctional and 370 ppm difunctional cca by comparison previously reported analyses indicate monofunctional caa occir in concentrations up to 10 000 ppm and difunctional caa may occur in concentrations up to 2610 ppm analyses of drilling muds and scale soaps presented in this study show that few if any difunctional caa in the study area can be attributed to contamination from these sources additionally aqueous extracts of crude oils contain both mono and difunctional acid anions as do the aqueous and petroleum phases of hydrous pyrolysates previously unreported dissolution experiments equilibrium computer simulations and hydrous pyrolysis experiments support those already published and suggest that caa are generated during thermal maturation of kerogen and expelled from the shale along oil wet microfractures upon entering the water wet sandstone pore the hydrophilic caa partition into the aqueous phase organic inorganic reactions may occur which from caa metal complexes because the complexes are hydrophobic they partition in the petroleum phase where present carboxylic acid anions are of great importance to clastic diagenesis over the temperature range in which they dominate fluid alkalinity certainly no other viable mechanism has been advanced which adequately explains the observed aluminosilicate mineral dissolution with subsequent mass transfer of a1 as well as the carbonate mineral diagenetic successions observed in sand shale systems world wide the utility of modeling these observations of organic inorganic diagenesis is limited only by the ability to model the concentration and distribution of caa through space and time

contrasting magma types and steady state volume predictable basaltic volcanism along the great rift idaho the great rift is an 85 km long 2 to 8 km wide volcanic rift zone in the snake river plain idaho three latest pleistocene to holocene basaltic lava fields craters of the moon kings bowl and wapi are located along the great rift the craters of the moon lava field is a composite of more than 60 lava flows 25 cinder cones and at least 8 eruptive fissure systems it covers 1 600 km2 and contains 30 km3 of lava flows and associated pyroclastic deposits field radiocarbon and paleomagnetic data show that the craters of the moon lava field formed in eight eruptive periods each of which was typically several hundred years or less in duration and was separated from others before and after by intervals of several hundred to several thousand years the first eruptive period began 15 000 yr b p and the latest eruptive period ended 2100 yr b p the small kings bowl lava field 3 3 km2 0 01 km3 and the larger wapi lava field 330 km2 6 km3 both formed 2250 yr b p three magma types have fed flows along the great rift the types are 1 a contaminated type that has a sio2 range of 49 64 and commonly shows petrographic evidence of contamination 2 a fractionated type that has a sio2 range of 44 54 and shows no evidence of contamination and whose chemical and mineralogical variation can be accounted for mainly by crystal fractionation and 3 a snake river plain type that has a sio2 range of 45 48 shows little evidence of fractionation and is represented by kings bowl wapi flows and olivine basalts of the snake river plain the contaminated and fractionated magma types were erupted at the craters of the moon lava field and the snake river plain magma type was erupted at the kings bowl and wapi lava fields these relations imply that the magma reservoirs are spatially isolated the magma output rate for the craters of the moon segment of the great rift was constant at 1 5 km3 1 000 yr for the period from 15 000 to 7000 yr b p the rate increased to 2 8 km3 1 000 yr from 7000 to 2000 yr b p mainly as a result of the addition of contaminated magma to the nearly constant output rate of fractionated magma the craters of the moon segment of the great rift has experienced quasi steady state volume predictable volcanism for the last 15 000 yr the recurrence interval of eruptive activity for the craters of the moon lava field ranges from several hundred to 3 000 yr because the present interval has lasted 2 100 yr another eruptive period seems likely to occur within the next 1 000 yr the steady state volume predictable relationship suggests that 5 6 km3 of lava will be erupted in the next eruptive period

correlation of carbon dioxide abundance with temperature in clastic hydrocarbon reservoirs relationship to inorganic chemical equilibrium the mol co2 of gas reservoired in sandstones tends to increase with increasing temperature along both the us gulf coast and the norwegian continental shelf each of these provinces displays identical linear correlations between temperature and the log of the partial pressure of co2 i e pco2 in the reservoir fluid that is the product of the mol co2 the reservoir pressure this correlation is the same both in gulf coast reservoirs younger than 17 ma and in norwegian reservoirs of jurassic to triassic age 144 245 ma indicating that it is not dependent on reaction kinetics norwegian shelf data indicate that the same correlation also applies for gas condensate and oil reservoirs we suggest that the log pco2versus temperature correlation is the result of inorganic chemical equilibria between feldspar clay and carbonate minerals a trend of decreasing ph with increasing temperature is fixed by equilibria between aluminosilicate minerals feldspar kaolinite at lower temperatures followed by various reactions between kaolinite illite chlorite and feldspar as temperatures exceed 110 140 c responding to the ph set by the aluminosilicate system co2 activity in the formation water and thereby co2 partial pressure in any gas phase present is controlled by equilibrium with carbonate minerals this model predicts that co2 released by organic maturation will in general result in precipitation of carbonate minerals below 100 120 c and that there should be widespread carbonate dissolution at higher temperatures

a type of continuous petroleum accumulation system in the shulu sag bohai bay basin eastern china abstract this study analyzed crude oils from the lower part of the third member of the eocene shahejie formation es 3 l and three prospective source rocks from the shulu sag bohai bay basin eastern china using a variety of organic geochemical methods biomarker characteristics were used to interpret source rock organic matter input and depositional environment and oil source rock correlation the biomarker data indicate that the crude oils originated from the es 3 l source rock which contains a mixture of plankton and land plant organic matters deposited in brackish fresh water under reducing conditions the oil in the es 3 l is self sourced instead of migrated from the overlying source rocks the petroleum generation potential of the es 3 l source rock was evaluated using organic geochemistry total organic carbon toc values for approximately 100 samples are between 1 02 and 4 92 wt and hydrogen indices range from 285 to 810 mg hydrocarbons g toc the es 3 l source rock contains mainly type ii and iii kerogen and most of the samples are thermally mature the data show that the es 3 l source rock has good potential for liquid hydrocarbon generation the es 3 l rock also acts as the oil reservoir having very low bulk porosity and permeability various types of storage space in the marlstone and carbonate rudstone in the es 3 l of the shulu sag include 1 fractures 2 intergranular pores 3 dissolution pores 4 organic matter pores 5 intragranular pores and 6 seams around gravels pore size ranges from nanometers to millimeters because the oil was generated and stored in es 3 l strata which lack any obvious trap and seal and have low permeability the unit represents a continuous petroleum accumulation

organic geochemistry and reservoir characterization of the organic matter rich calcilutite in the shulu sag bohai bay basin north china abstract although extensive studies have been conducted on unconventional mudstone shales reservoirs in recent years little work has been performed on unconventional tight organic matter rich fine grained carbonate reservoirs the shulu sag is located in the southwestern corner of the jizhong depression in the bohai bay basin and filled with 400 1000 m of eocene lacustrine organic matter rich carbonates the study of the organic matter rich calcilutite in the shulu sag will provide a good opportunity to improve our knowledge of unconventional tight oil in north china the dominant minerals of calcilutite rocks in the shulu sag are carbonates including calcite and dolomite with an average of 61 5 wt the carbonate particles are predominantly in the clay to silt size range three lithofacies were identified laminated calcilutite massive calcilutite and calcisiltite calcilutite the calcilutite rocks including all the three lithofacies in the third unit of the shahejie formation in the eocene es3 have total organic carbon toc values ranging from 0 12 to 7 97 wt with an average of 1 66 wt most of the analyzed samples have good very good or excellent hydrocarbon potential the organic matter in the shulu samples is predominantly of type i to type ii kerogen with minor amounts of type iii kerogen the temperature of maximum yield of pyrolysate tmax values range from 424 to 452 c with an average of 444 c indicating most of samples are thermally mature with respect to oil generation the calcilutite samples have the free hydrocarbons s1 values from 0 03 to 2 32 mg hc g rock with an average of 0 5 mg hc g rock the hydrocarbons cracked from kerogen s2 yield values in the range of 0 08 57 08 mg hc g rock with an average of 9 06 mg hc g rock and hydrogen index hi values in the range of 55 749 mg hc g toc with an average of 464 mg hc g toc the organic rich calcilutite of the shulu sag has very good source rock generative potential and have obtained thermal maturity levels equivalent to the oil window the pores in the shulu calcilutite are of various types and sizes and were divided into three types 1 pores within organic matter 2 interparticle pores between detrital or authigenic particles and 3 intraparticle pores within detrital grains or crystals fractures in the shulu calcilutite are parallel to bedding high angle and vertical having a significant effect on hydrocarbon migration and production the organic matter and dolomite contents are the main factors that control calcilutite reservoir quality in the shulu sag

carboxylic acid anions in formation waters san joaquin basin and louisiana gulf coast u s a implications for clastic diagenesis reply to critical comment by j s hanor l s land and g l macpherson

lava flow surface roughness and depolarized radar scattering surface roughness has a strong controlling influence on radar scattering and other types of remote sensing observations we compare field measurements of surface topography and dielectric constant for a range of lava flow textures to aircraft multipolarization radar observations at 5 7 24 and 68 cm c l and p band wavelengths the roughness is found to vary with scale in a self affine fractal manner for scale lengths between 25 cm the smallest horizontal step size and 3 5 m this result is used to demonstrate that a two component surface description consisting of the fractal dimension and rms height or slope at some reference scale can resolve some of the ambiguities in previous efforts to quantify roughness at all three radar wavelengths the hv backscatter cross section is found to vary in an approximately exponential fashion with the rms height or allan deviation at some reference scale up to a saturation point where the surface appears entirely diffusely scattering to the radar based on these observations we use a parameter defined as the ratio of rms height to the particular scale of measurement backscatter values at 24 cm wavelength and the topographic profile data were used to derive expressions which link the hv radar cross section to or to the analogous wavelength scale rms slope these equations provide a reasonable fit to 24 and 68 cm echoes and for rough surfaces at 5 7 cm but yield poor results for 5 7 cm echoes on smooth terrain we conclude that the roughness at the two larger scales is well described by a single fractal dimension and rms height but that texture at very small scales is characterized by different statistics this inference is supported by analysis of 5 cm horizontal spacing topographic profiles the relationships defined here allow determination of the surface rms height or slope at the scale of the radar wavelength given radar data at additional wavelengths a more complete view of the statistical properties of the surface can be developed such techniques may be useful in analyses of synthetic aperture radar images for terrestrial volcanic areas magellan data for venus and other planetary radar observations

geologic analyses of shuttle imaging radar sir b data of kilauea volcano hawaii analyses of imaging radar data of volcanic terranes on earth and venus have emphasized the need for a clearer understanding of how these data can be most effectively used to accomplish important volcanological goals including the interpretation of eruptive styles and the characterization of the geologic history of volcanic centers the second shuttle imaging radar experiment sir b obtained two digital images over the summit caldera and the southwest rift zone of kilauea volcano in 1984 our geologic analyses of these images indicate that sir b data are particularly useful for delineating the distribution and surface textural variations of a9a lava flows for mapping large scale topographic features with radar facing slopes and for identifying an areally extensive pyroclastic deposit analyses of the sir b data of kilauea however do not permit unambiguous identification of landforms such as pahoehoe lava flows cinder cones and fissures although separation of low return units such as pahoehoe lava flows and adjacent pyroclastic ash is not greatly improved using standard image enhancement techniques the texture analysis technique applied here did facilitate discrimination of such smooth surfaced volcanic deposits although analyses of the sir b data permit a generally accurate interpretation of the eruptive history of kilauea the inability to distinguish low return pahoehoe flows results in misinterpretation of several aspects of kilauea volcanism suggesting that caution should be exercised in the interpretation of sar data of volcanic terranes

radar polarization properties of volcanic and playa surfaces applications to terrestrial remote sensing and venus data interpretation the radar polarization properties of lava flows in hawaii kilauea and arizona sp flow and two play a surfaces lunar lake nevada and lavic lake california are compared to the predicted behaviors of theoretical scattering models at 5 7 cm and 24 cm wavelengths kilauea lava flows can be modeled by a combination of facet and diffuse dipole like scattering scattering by rock faces on the scale of the radar wavelength is proposed to account for much of the facet return the radar echoes at 24 cm wavelength from sp flow are on average consistent with entirely diffuse scattering but there are regions within the flow where circular polarization ratios exceed unity suggesting a coherent scattering effect 68 cm data for the lava flows show evidence of radar penetration and volume scattering the playa surfaces are characterized by polarization properties which in some cases are qualitatively consistent with the first order small perturbation model but the echoes do not closely match the predictions of this model for any reasonable dielectric constant value these results show that it may be difficult to construct invertible models for the polarization behavior of some surfaces the playas whereas for others the kilauea lava flows the scattering properties can be successfully modeled the first order small perturbation model is not appropriate for inverse modeling of most terrestrial lava flows though very smooth surfaces on venus may be amenable to the use of this model high circular polarization ratios observed for sp flow tentatively attributed here to coherent backscatter may be analogous to arecibo observations of high reflectivity areas on venus

quantitative roughness characterization of geological surfaces and implications for radar signature analysis stochastic surface models are useful for analyzing in situ roughness profiles and synthetic aperture radar sar images of geological terrain in this paper two different surface models are discussed surfaces with a stationary random roughness conventional model and surfaces with a power law roughness spectrum fractal model in the former case it must be considered that for short profiles l 200l sub 0 the measured values of rms height s and correlation length l may be significantly smaller than the intrinsic values s sub 0 and l sub 0 in the latter case rms height and correlation length depend on the profile length l and the surface is better characterized by slope and offset of the roughness spectrum which are independent of l the sensitivity of the sar signature to variations in surface roughness parameters is evaluated by means of theoretical scattering models for smoother geological surfaces such as most arid terrain types single scattering is dominant which means that the roughness parameters can be determined from sar data using comparatively simple algorithms multiple scattering processes on rough surfaces such as a a lava and variations of the local incidence angle due to large scale terrain undulations make the retrieval of roughness parameters by means of inverse modeling much more complex field data of surface roughness indicate that rougher geological surfaces may be in the diffractal regime at higher radar frequencies in which the scattering characteristics deviate significantly from the patterns observed for stationary surfaces on the basis of surface and scattering models recently published observations of roughness data and radar signatures from volcanic alluvial and arid surfaces are examined

preliminary observations of volcanoes with the sir c radar the two flights of the shuttle imaging radar sir c x sar in april and october 1994 provided a wealth of new image data over many of the world s volcanoes including 13 of the 15 international decade volcanoes a first look at these data shows that mapping of remote volcanoes e g nyiragongo and nyamuragira in africa will now be easier especially when aided by the collection of multi parameter radar data over better known analogous volcanoes such as kilauea hi the utility of the radar to identify different types of lava flows is shown for fernandina volcano galapagos islands growth of mudflow deposits lahars that were emplaced on mount pinatubo philippines during the six months between the two missions is also illustrated additionally interferometric radar data were collected over several active volcanoes the potential uses of these data for topographic mapping and ground deformation studies are discussed

carboxylic acid anions in formation waters san joaquin basin and louisiana gulf coast u s a implications for clastic diagenesis critical comment the analyses of carboxylic acid anions caas in san joaquin basin and louisiana gulf coast formation waters published by macgowan and scrdam 1990 do little to resolve the important question of whether caas are of great significance to clastic diagenesis over the temperature range in which they dominate fluid alkalinity as advocated by these two authors comparison of their analyses with analyses of formation waters from the same wells previously published by three independent research groups hanor and workman 1986 land et al 1988 and land and macpherson 1989 and fisher and boles 1990 a body of data not discussed in their article reveals that most of the macgowan and surdam values are grossly inflated relative to the previous analyses table 1 fig 1 cedures of llco et al 1982 while field procedures for caas now normally include the addition of a bactericide to the sample an independent check on the upper limit of total caas which could have been present in this water is provided by the results of an alkalinity titration to ph 2 5 also published by hanor and workman 1986 which show that the total concentration of weak acid anions bicarbonate plus caas could not have exceeded approximately 428 mg 1 the alkalinity determinations were done shortly after collection on separate untreated aliquots stored in gas tight glass containers further details are given in workman 1985

predictive models for sandstone diagenesis abstract factors governing the evolutionary path that sandstone and shale sequences follow during burial diagenesis include provenance and depositionally controlled compositional and textural elements near surface redox reactions organic inorganic interactions within the zone of intermediate burial diagenesis deep diagenetic reactions which include abiotic thermal sulfate reduction carbonate mineral alteration and quartz cementation and the potential for meteoric influx and renewal of near surface processes due to uplift exposure and or base level fluctuation as a consequence the use of thermal exposure indicators to describe the extent of diagenesis such as r0 or time temperature history indicators such as tti must be used with caution though useful in predicting general trends in porosity loss due to simple compaction they have little utility in making forward predictions of anomalously high porosity e g preserved and or enhanced porosity or anomalously low porosity a more useful approach whereby the processes controlling porosity evolution are evaluated in terms of the depositional hydrologic burial and thermal histories is presented here

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

marcasite in black shales a mineral proxy for oxygenated bottom waters and intermittent oxidation of carbonaceous muds abstract black shales in the geologic record have long been considered to reflect deposition under anoxic or even euxinic conditions although bottom water anoxia favors deposition of black shales certain biological indicators such as benthic fossils and bioturbation suggest that bottom water conditions may not have been as persistently anoxic as commonly presumed examination of twelve marine carbonaceous shale bearing units ranging in age from middle proterozoic to cretaceous suggests that in addition to paleontological clues early diagenetic marcasite formed in uncompacted surficial sediments is a reliable indicator of oxygen bearing bottom waters marcasite requires low ph values to form and oxidation of already existing sedimentary pyrite provides a plausible chemical scenario to achieve that condition in the studied examples degraded pyrite framboids and corrosion features on pyrite grains indicate partial pyrite destruction in surface sediments and suggest that intermittent reoxidation of earlier formed iron sulfides may indeed have generated the low ph values required for marcasite formation thus observations of textures spatially associated with secondary marcasite growth are consistent with a scenario whereby oxygen in overlying sea water drove downward migration of oxidation fronts pervasive marcasite in black shales from a wide range of occurrences suggests multiple reoxygenation events during the deposition of these shale units and calls for more dynamic ocean circulation than previously assumed the latter consideration may for example prove important for those instances where a black shale is associated with an oceanic anoxic event oae because these are commonly presumed to have been deposited under fully anoxic conditions

terrestrial analogues for lunar impact melt flows abstract lunar impact melt deposits have unique physical properties they have among the highest observed radar returns at s band 12 6 cm wavelength implying that they are rough at the decimeter scale however they are also observed in high resolution optical imagery to be quite smooth at the meter scale these characteristics distinguish them from well studied terrestrial analogues such as hawaiian p hoehoe and a lava flows the morphology of impact melt deposits can be related to their emplacement conditions so understanding the origin of these unique surface properties will help to inform us as to the circumstances under which they were formed in this work we seek to find a terrestrial analogue for well preserved lunar impact melt flows by examining fresh lava flows on earth we compare the radar return and high resolution topographic variations of impact melt flows to terrestrial lava flows with a range of surface textures the lava flows examined in this work range from smooth hawaiian p hoehoe to transitional basaltic flows at craters of the moon cotm national monument and preserve in idaho to rubbly and spiny p hoehoe like flows at the recent eruption at holuhraun in iceland the physical properties of lunar impact melt flows appear to differ from those of all the terrestrial lava flows studied in this work this may be due to a differences in post emplacement modification processes or b fundamental differences in the surface texture of the melt flows due to the melts unique emplacement and or cooling environment information about the surface properties of lunar impact melt deposits will be critical for future landed missions that wish to sample these materials

seismogenic structure in the source zone of the 1918 m7 5 nanao earthquake in the northern south china sea abstract as a typical rifted margin the coastal region of the northern south china sea has experienced many large crustal earthquakes in the past 400 years for example two destructive earthquakes with m7 0 in 1600 and m7 5 in 1918 occurred close to the nanao island however the mechanism of these earthquakes and seismotectonics of the region are still unclear in this work we make the first study of the detailed three dimensional crustal structure in the source zone of the 1918 nanao earthquake m7 5 using newly acquired wide angle seismic reflection data our results show that current seismicity mostly occurred in a midcrustal low velocity zone or its nearby high to low velocity transitional areas we ascertain locations of the ene strike littoral fault zone and the nw strike huanggangshui fault based on the seismic reflection profiles these faults have caused a large scale vertical dislocation of the sedimentary basement the structure of the upper crust is very heterogeneous containing many high or low velocity anomalies however the lower crustal structure is less heterogeneous mainly characterized by low velocity mostly in the northern part of the study area and high velocity mainly in the southern part the crust in the seismicity zone shows strong heterogeneity reflecting highly cracked structural features possibly caused by destructive earthquakes we infer that the midcrustal low velocity zone and the intersection between the littoral fault zone and the huanggangshui fault could reflect weak structures in the crust and form a local stress buildup which strongly affected or controlled the generation of intraplate seismicity the 1918 nanao earthquake very likely occurred within the current seismicity zone with a depth range of 15 25 km estimated from our tomographic images and previous geological and geophysical results

estimates of surface roughness derived from synthetic aperture radar sar data radar remote sensing data provide a unique perspective on the earth s crust and the processes that have influenced its evolution physically based models are required however to relate the geophysical quantities being measured by the radar sensor to useful geologic information synthetic aperture radar sar data over the cima volcanic field in the mojave desert of california are quantitatively connected with microtopography through inversion of a radar backscatter model changes in surface roughness inferred from the derived microtopography are modeled and found to be consistent with aeolian mantling as surfaces age estimated rates of aeolian deposition for the cima area are compared to the lunar crater volcanic field in nevada rates of deposition appear to be higher at cima volcanic field most likely because of its proximity to soda lake the main source of the aeolian material

water rock interaction in tertiary sandstones san joaquin basin california u s a diagenetic controls on water composition three water types are recognized among petroleum associated waters of the southern san joaquin basin 1 meteoric water 2 diagenetically modified connate water and 3 mixed meteoric modified connate water the diagenetically modified connate marine water can be further subdivided into three types 1 fully mg depleted mg 1 mole of the sum of na k ca and mg 2 partially mg depleted and 3 ca enriched enrichment in ca which is the sharpest chemical divide found for the diagenetically modified connate water is the result of feldspar albitization the ca enriched waters are also rich in total dissolved al up to 6 mg l 1 and exhibit lighter 18o values than other diagenetically modified connate waters the total dissolved al abundance in these waters may be due to the presence of organic complexing agents simple and aromatic organic acids and phenolics the lighter 18o values are probably due to both albitization and the lack of substantial clay diagenesis illitization of smectite

oilfield waters and sandstone diagenesis abstract the evolution of the organic geochemistry and carbonate alkalinity of oilfield waters is apparently regular and predictable this evolution can be typified by five generalizations 1 at or near 80 c there appears to be an exponential rise in the concentration of organic acid anions 2 the maximum concentration of organic acid anions occurs over approximately the 80 100 c temperature interval 3 the highest concentrations of difunctional acid anions are associated with the other organic species maxima 4 difunctional acid anions are the first to be decarboxylated typically at temperatures of 100 110 c 5 with increasing temperature 110 130 c monofunctional acid anions begin to become decarboxylated resulting in a fluid alkalinity dominated by bicarbonate dissolution experiments using artificial and natural oilfield waters demonstrate that mono and difunctional carboxylic acid anions and hydroxybenzoic acid anions present in both oilfield waters and the aqueous phase of hydrous pyrolysates are capable of greatly enhancing al si fe and ca concentrations in solutions from dissolution of minerals by organometallic complexation this enhancement of mineral solubility has been called upon to explain aluminosilicate dissolution porosity which is quantitatively important in many subsurface reservoirs certainly no other viable mechanism has been proposed to explain aluminum transport in the subsurface when integrated into basin models the regular evolution of organic and carbonate alkalinity in oilfield waters and the changing mineral stabilities that accompany that evolution help explain commonly observed diagenetic sequences in clastic systems

midcrustal low velocity layer beneath the central himalaya and southern tibet revealed by ambient noise array tomography 1 ambient noise tomography has been becoming an important tool to image the shallow lithospheric structure of the earth using 2 months of ambient noise data from 20 stations of the himalayan nepal tibet seismic experiment we investigate the upper and middle crustal structure in the central himalaya and southern tibet about 120 interstation rayleigh wave empirical green s functions with sufficient signal to noise ratio are obtained and used for group velocity dispersion analysis in the period range 6 25 s using frequency time analysis technique the obtained dispersion data are then used to construct 2 d group velocity maps at the short periods from 9 to 15 s the distribution of rayleigh wave velocities delineates several distinct low and high velocity zones separated mainly by geological boundaries the high group velocity zone is located mainly around regions with plutonic rocks and the low group velocity zone is located around regions with sedimentary or metasedimentary rocks finally we invert for the shear velocity structure in the upper and middle crust along a n s trending cross section at the longitude 86 5 e we observe a clear low velocity layer in the middle crust about 10 25 km depth distributed on both sides of the indus yarlung suture zone the existence of this midcrustal low velocity zone suggests a mechanically weaker middle crust beneath the central himalaya and southern tibet which might decouple the upper crustal deformation from that of the lower crust in the tibetan himalayan orogenic processes

the 2001 bhuj earthquake tomographic evidence for fluids at the hypocenter and its implications for rupture nucleation 1 the january 26 2001 bhuj earthquake mw 7 6 is one of the most catastrophic indian earthquakes we have investigated the 3 d seismic velocity and poisson s ratio structures of the bhuj source area to understand the probable cause of triggering the earthquake we used 1948 p and 1865 s wave high quality arrival times from 331 aftershocks recorded at a temporary seismic network significant variations up to 5 in velocity and 10 in poisson s ratio are revealed in the aftershock area the mainshock is located in a distinctive zone characterized by high vp low vs and high poisson s ratio in the depth range of 20 to 30 km and extending 15 to 30 km laterally this feature is very similar to that of the 1995 kobe earthquake zhao et al 1996 the anomaly may be due to a fluid filled fractured rock matrix which might have contributed to the initiation of the bhuj earthquake

fluid geochemistry of the acqui terme visone geothermal area piemonte italy the main geothermal reservoir of acqui terme visone hosts na cl waters which are in chemical equilibrium at 120 130 c with typical hydrothermal minerals including quartz albite k feldspar illite chlorite or smectite anhydrite calcite and an unspecified ca al silicate in the acqui terme visone area these geothermal waters ascend along zones of high vertical permeability and discharge at the surface almost undiluted or mixed with cold shallow waters to the sw of acqui terme other ascending geothermal waters either undiluted or mixed with low salinity waters enter relatively shallow secondary reservoirs where they reequilibrate at 65 70 c both chemical and isotopic data indicate that bacterial so4 reduction affects all these waters especially those discharged by the secondary reservoirs therefore geothermal waters must get in contact with oil acquiring the relatively oxidized organic substances needed by so4 reducing bacteria this oil water interaction process deserves further investigations for potential economic implications

the snake river plain idaho representative of a new category of volcanism studies of the volcanic geology of the snake river plain idaho and comparison with other basaltic regions suggest a new category of volcanic activity termed basaltic plains volcanism typified by the snake river plain this style of volcanism is intermediate between basaltic flood or plateau eruptions and hawaiian volcanism characteristics that are common to both hawaiian and plains volcanism are multiple lava flow units which erupt primarily from point sources formation of low shields and frequent emplacement through lava tubes or channels characteristics that are common to both flood basalts and plains volcanism are high volume flows vents aligned along rift zones and planar surfaces the recognition of plains volcanism in other areas provides a means to interpret the style of eruption and volcanic history

a three dimensional vp vs and vp vs crustal structure in fujian southeast china from active and passive source experiments abstract fujian southeastern china has experienced multistage tectonic activities since the neoproterozoic era and is currently influenced by collision between the eurasian and philippine sea plates topography fault zones and patterns of seismicity are the imprints of tectonic evolution historically there have been several catastrophic earthquakes in the southeastern part of fujian to understand the crustal structure related to the fault zones we performed vp vs and vp vs travel time tomography using joint inversion of active and passive sources a total of 75 827 and 31 044 arrivals of p and s waves respectively from 33 explosions and 2543 earthquakes are used in our study as a result seismicity has indicated that two ne strike seismogenic zones the zhenghe dapu and changle zhaoan fault zones are currently active low vp vs ratios in inland fujian imply that the crust is mainly composed of felsic rocks as part of the eurasian continental crust which is consistent with geological observations at the surface based on vp tomography the thickness of the crust along the coastline is shallower than that on land which is related to higher heat flow and the bouguer anomaly this shallow crust phenomenon near the coastline could be related to the regional extensional stress the remaining structure of the back arc extension that stretched the continental crust during the mesozoic era or and the cenozoic extension due to south china sea opening in taiwan strait

pahoehoe and aa lavas a discussion and continuation of the model of peterson and tilling abstract the graphical method of peterson and tilling for representing the behaviour of a lava flow is considered in terms of simple rheological theory assuming that a lava may be approximately described as a bingham fluid this approach helps resolve an apparent anomaly in the original treatment of peterson and tilling with respect to the representation of the pahoehoe to aa transition it also suggests further methods for quantitatively defining the limits of the pahoehoe and aa fields and the transition threshold zone

distribution and significance of dicarboxylic acid anions in oil field waters the origin distribution and interactions of low molecular weight organic acid anions have become an intensively studied field in geochemistry since their widespread occurrence in formation waters of sedimentary basins was first documented by carothers and kharaka 1978 high concentrations up to 10 000 mg 1 of monocarboxylic mainly acetate propionate and butyrate and dicarboxylic mainly oxalate malonate and succinate acid anions have been reported from many sedimentary basins with the highest values present in relatively young cenozoic age petroleum reservoir rocks at subsurface temperatures of 80 120 c see lundegard and kharaka 1990 for a recent review with references geochemical interest in these organic anions stems mainly from their important role in mineral diagenesis in sedimentary basins kharaka et al 1986 macgowan and surdam 1990 in particular these species act as sources or sinks of protons as a source of co2 and as ph and eh buffering agents lundegard and kharaka 1990 they also form complexes with cations and metals such as ca a1 fe pb and zn kharaka et al 1985 harrison and thyne 1992 data on the concentrations of monocarboxylic acid anions in subsurface waters from many sedimentary basins worldwide are available and are generally accepted as representing the aqueous concentrations at depth data on the concentrations of dicarboxylic acid anions are much more limited some reported values are controversial and the total values reported range widely from 0 to 2640 mg 1 surdam et al 1984 kharaka et al 1986 barth 1987 macgowan and surdam 1988 1990 because of the wide range in the reported concentrations and because dicarboxylic acid anions generally form stronger complexes with a1 fe and other cations than do monocarboxylic acid anions we resampled four oil wells in the san joaquin basin california in order to better assess the role of these acid anions in water rock interactions in sedimentary basins