reservoir heterogeneity and quality of khuff carbonates in outcrops of central saudi arabia abstract the khuff carbonates host several main gas reservoirs in the middle east these reservoirs are known for their heterogeneity both of sub seismic scale and beyond the interwell spacing to get a better insight in these reservoirs the heterogeneity of the upper khartam member placed in a high frequency sequence stratigraphic framework was studied with a lateral resolution between logged sections of 5 m the sedimentology and sequence stratigraphy of four outcrop localities were studied and approximately 600 samples were collected for petrographic porosity and permeability analyses seventeen lithofacies types were recognised and six major diagenetic processes could be differentiated in the studied outcrops dissolution is likely the result of intensive circulation of meteoric water undersaturated with respect to calcite significantly cementation has blocked most of the original intergranular porosity pore lining detrital clay severely impacted reservoir permeability and complicated the pore geometry dolomitization is associated with the upper khuff sudair boundary and is likely the result of influx of water highly saturated with mg 2 that developed during the deposition of the sudair evaporites finally stylolites are to a major extend controlled by lithofacies and geobody configuration ten porosity types could be namely intergranular intragranular shelter dissolution enlarged moldic vuggy micro porosity and porosity in relation to dolomite dedolomite dolomite leaching and fracture development overall intertidal creeks are characterized by a complex and heterogeneous pore geometry if compared to the intertidal channels and this can be attributed to the geobody architecture with intertidal creeks being composed of dense and small tidal bodies 1 m in length and 20 cm in thickness while intertidal channels are composed of thick amalgamations of intertidal channels 5 m by 50 cm most critically the horizontal reservoir quality was influenced differentially by diagenesis which resulted in a lateral segmentation of single bodies into different hydraulic units the differential mold filling calcite cements have significantly reduced porosity and permeability generally mineral content has little impact on the reservoir quality although clay minerals played a central role in lining the pore space and affecting permeability finally horizontal reservoir heterogeneity seems to have been controlled by fractures and stylolites which respectively acted as conduits to and barriers for vertical fluid flow and hence controlled the differential cementation and dissolution processes

mixing processes in modern estuarine sediments from the gulf of khambhat western india abstract sandy and muddy detritus from two distinctive end member provenance terrains basaltic and granitic are transported to the estuaries of the gulf of khambhat by fluvial discharge and opposing tidal currents making this embayment ideal for investigating the effects of mineralogical and geochemical mixing on sediment composition in estuarine depositional systems rivers flowing predominantly from the north over precambrian metasediments and granites supply a felsic plutoniclastic sand to the gulf whilst a mafic volcaniclastic sand sourced by deccan basalts is transported by rivers draining the western ghats and from the local coastal erosion in the southern part of the gulf sediments from the tapti estuary are rich in basaltic rock fragments 50 and are characterised by a distinctly basaltic source composition la sc 0 25 0 86 th sc 0 12 0 40 cr th 13 121 eu eu 0 93 1 68 and lree hree 2 96 6 57 by contrast the sediments of the sabarmati inner estuary are rich in quartz grains 80 as evident from the major and trace element compositions la sc 1 38 6 63 th sc 0 58 2 98 cr th 0 58 19 39 eu eu 0 46 0 86 and lree hree 2 90 11 40 the detrital compositions of the remaining major estuaries the narmada dhadhar and mahi scatter across a broad range in a qfr diagram and contain varying amounts of quartz feldspar and rock fragments in the narmada estuary the mixed signature characterised by ree values including eu eu 0 42 2 28 and lree hree 4 37 14 80 is caused by the presence of diverse rock types that crop out in the source area in the mahi estuary which largely flows across felsic source terrains the compositional signature is controlled by mixing of felsic detritus from riverine input with mafic sediments from seaward side in the estuary the two end member detrital compositions plutoniclastic and volcaniclastic are mixed in the macro tidal estuaries mixing of sediment takes place where fluvial currents and tidal flows interact and the proportion of mixing varies systematically from outer to central to inner estuary a high degree of mixing of felsic sediments with deccan basalt derived sediments takes place in the outer estuary resulting in felsic mafic ratios of 40 60 sediments in the central estuaries 65 35 and in the fluvial dominated inner estuaries 90 10 are characterised by moderate to minor degrees of mixing the mixing in estuaries is systematic and is reflected in both the mineralogy and geochemistry of the sediments provenances of ancient estuarine successions should therefore be interpreted with great care incorporating awareness of the mixing processes which influence sediment compositions to different degrees in estuaries especially those characterised by strong tidal currents

field scale reservoir zonation of the albian turonian sarvak formation within the regional scale geologic framework a case from the dezful embayment sw iran abstract the albian turonian sarvak formation is the second most important reservoir of iran in this study an integrated field scale reservoir zonation is applied to the sarvak reservoir in one oil field of the dezful embayment sw iran to understand the distribution of speed barrier and baffle zones the geologic controls of depositional and post depositional factors on the suggested reservoir zonation are also discussed here based on the results the studied reservoir is composed of seven zones with different reservoir qualities the best reservoir zones show considerable amount of dissolution pores and are developed beneath regional scale paleo exposure surfaces that are also recognizable in coeval strata on the arabian plate these surfaces represent recurring subaerial exposure episodes during the development of the sarvak formation through which meteoric diagenesis highly affected the rock record leading to the development of paleo karst profiles with noticeable dissolution pores in the strata beneath the paleo exposure surfaces however the long lasting emergence time of the mid turonian exposure mt es the interface between the sarvak formation and overlying ilam formation caused the over maturation of the related paleo karst profile and the deterioration of the created reservoir quality the results of this study reveal the effects of regional scale geologic controls on the reservoir characteristics of the sarvak formation and may be also applicable to the reservoir characterization of other time equivalent strata in the arabian plate

flow unit concept integrated approach to reservoir description for engineering projects abstract the successful application of secondary and tertiary oil recovery technology requires an accurate understanding of the internal architecture of the reservoir engineers have difficulty incorporating geological heterogeneity in their numerical models for simulating reservoir behavior the concept of flow units has been developed to integrate geological and engineering data into a system for reservoir description a flow unit is a volume of the total reservoir rock within which geological and petrophysical properties that affect fluid flow are internally consistent and predictably different from properties of other rock volumes i e flow units flow units are defined by geological properties such as texture mineralogy sedimentary structures bedding contacts and the nature of permeability barriers combined with quantitative petrophysical properties such as porosity permeability capillarity and fluid saturations studies in the subsurface and in surface outcrops have shown that flow units do not always coincide with geologic lithofacies the flow unit approach provides a means of uniquely subdividing reservoirs into volumes that approximate the architecture of a reservoir at a scale consistent with reservoir simulations thus reservoir engineers can incorporate critical geological information into a reservoir simulation without greatly increasing the complexity of their models this approach has advantages over more traditional methodsmore of reservoir zonation whereby model layers are determined on the basis of vertical distributions of permeability and porosity from core analyses and wireline logs less

distribution of rare earth elements and other high field strength elements in glacial meltwaters and sediments from the western greenland ice sheet evidence for different sources of particles and nanoparticles although global warming increases meltwater input into the oceans rather little is known about the distribution of high field strength elements such as the rare earths and y rey zr hf th and u in arctic glacial meltwaters and glacial fed rivers we studied glacial meltwater and glacial fed rivers from the kangerlussuaq area and a glacial fed lake and its meltwater inflow in the isua area both in the western part of the greenland ice sheet gris trace element concentrations were determined in 0 2 m filtered water samples dissolved fraction in the respective filter residues particulate fraction and in ambient sediments including cryoconite from a meltwater pond on the surface of the gris we also measured truly dissolved rey concentrations in a 10 kda ultrafiltered sample from glacial fed watson river shale normalized sn rey patterns of the particulate fraction and ambient sediments including cryoconite are rather similar to those of local archean gneisses and show positive eusn anomalies this rules out asian dust which does not show positive eusn anomalies as a possible source of these aluminosilicate particles but suggests that local archean basement is eroded and currently transported by ice water and wind to the depositional sites in front of and onto the gris all 0 2 m filtered glacial fed rivers show very unusual reysn patterns in comparison to tropical temperate and boreal rivers and are significantly enriched in light relative to heavy rey for glacial fed watson river the 99 of la and 78 of yb in the latter are associated with nanoparticles and colloids although the reysn patterns of the 0 2 m filtrates are rather similar to those of the particulate fraction and ambient sediments they lack any eusn anomalies whereas the 0 2 m filtrates from a meltwater pond on the surface of the gris show positive eusn anomalies similar to but somewhat smaller than the cryoconite while the water from the meltwater pond carries nanoparticles derived from local archean sources the lack of eusn anomalies in the glacial fed rivers suggests that their nanoparticle and colloid load represents atmospheric dust that is remobilized from greater depth in the gris most of this dust probably originated from eastern asia and shows a rey distribution similar to post archean upper continental crust i e lacks any eusn anomaly hence rey geochemistry suggests that the particulates and the nanoparticles colloids in these arctic meltwaters are derived from different sources

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

facies discrimination in a mixed fluvio eolian setting using elemental whole rock geochemistry applications for reservoir characterization abstract fluvio eolian successions are generally characterized by a high degree of complexity and internal heterogeneity quantifying the rapid facies changes in time and space is a major challenge to characterization of hydrocarbon reservoirs we present a method for facies discrimination in fluvio eolian successions the method presented here is developed on the modern fluvio eolian sediments from the skeleton coast dune field namibia the examined sediments comprise eight different facies types eolian dune sands interdune fluvial channel sands intraerg mass flow deposits intraerg hyperconcentrated flow deposits fluvial channel sands fluvial mud lacustrine heterolithic sand and lacustrine heterolithic mud the contrasting provenance of the fluvial and eolian sediments results in a distinct source fingerprint which can be discriminated using elemental whole rock geochemistry a multivariate statistical technique performed on the geochemical data has enabled discrimination of seven of the eight facies types furthermore the facies discrimination method allowed a quantitative estimate of the degree of fluvial reworking of eolian sand the skeleton coast dune field was chosen as a test area for geochemical facies discrimination because of its remarkable difference between the immature fluvial source and the mature quartz rich eolian source we hope that the method presented here can be applied to subsurface data from geological settings with the same difference in fluvial and eolian sources it is furthermore hoped that the method can be used in more complex sedimentological settings

improved provenance tracing of asian dust sources using rare earth elements and selected trace elements for palaeomonsoon studies on the eastern tibetan plateau abstract the asian monsoon forms an important part of the earth s climate system yet our understanding of the past interactions between its different sub systems the east asian and indian monsoons and between monsoonal winds and other prevailing wind currents such as the westerly jet is limited particularly in central asia this in turn affects our ability to develop climate models capable of accurately predicting future changes in atmospheric circulation patterns and monsoon intensities in asia provenance studies of mineral dust deposited in terrestrial settings such as peat bogs can address this problem directly by offering the possibility to examine past deposition rates and wind direction and hence reconstruct past atmospheric circulation patterns however such studies are challenged by several issues most importantly the identification of proxies that unambiguously distinguish between the different potential dust sources and that are independent of particle size in addition a single analytical method that is suitable for sample preparation of both dust source i e desert sand soil and receptor i e dust archive such as peat or soil profiles material is desirable in order to minimize error propagation derived from the experimental and analytical work here an improved geochemical framework of provenance tracers to study atmospheric circulation patterns and palaeomonsoon variability in central asia is provided by combining for the first time mineralogical as well as major and trace elemental sc y th and the rare earth elements information on chinese central chinese loess plateau northern qaidam basin and taklamakan badain juran and tengger deserts indian thar desert and tibetan eastern qinghai tibetan plateau dust sources quartz feldspars and clay minerals are the major constituents of all studied sources with highly variable calcite contents reflected in the cao concentrations chinese and tibetan dust sources are enriched in middle ree relative to the upper continental crust and average shale but the thar desert has a ree signature distinctly different from all other dust sources there are significant differences in major trace and ree compositions between the coarse and fine fractions of the surface sands with the finest 2 o 3 fe 2 o 3 mno mgo and k 2 o and the all ree normalized to post archean australian shale paas are particle size independent tracers of which combinations of y ree la yb y tb y la and eu eu can be used to distinguish the thar desert the chinese deserts the chinese loess plateau and the tibetan soils their independence upon grain size means that these tracers can be applied to the long range provenance tracing of asian dust even when only bulk samples are available in the source region combinations of la th y tb y ree sc la and y er distinguish the tibetan soils from the chinese loess plateau and the chinese deserts la th and notably th ree isolate the signature of the badain juran desert and the combination of sc la and y er that of the taklamakan desert the similarity in all trace and ree based provenance tracers between the northern qaidam basin and tengger desert suggests that these two deposits may have a common aeolian source

the use of mineral interfaces in sand sized rock fragments to infer ancient climate the kinds of mineral interfaces preserved in rock fragments of modern plutoniclastic sand are closely correlated with climate and topography in the source area stepwise linear regression analysis of the relationship among environmental and petrographic parameters for sand collected from 16 drainages of varying morphology developed on five granodiorite plutons demonstrates that sand composition varies systematically with temperature and precipitation and drainage steepness and area for small drainages in temperate climates the durability of each kind of mineral interface in sand sized rock fragments derived from the plutons depends on mechanical chemical and textural factors interfaces are mechanically stressed by differential expansion of minerals during unroofing interfaces between minerals of similar expansibility compressibility are more likely to remain uncracked and thus survive weathering the rate and extent of chemical dissolution of interfaces depends on the crystallography and chemistry of adjoining minerals interfaces between minerals of similar structure that have short atomicbond lengths are more likely to survive mineral inclusions are texturally isolated from rock disaggregating processes and thus more likely to survive interfaces of opaque with tectosilicate minerals are enriched relative to other interfaces by progressive disaggregation the rate and extent of which increase with increasing temperature interfaces of biotite with tectosilicates are depleted relative to other interfaces with increasing precipitation regression analysis yields statistically plausible testable models of the dependence of modem sand composition on modern climate such models can be used to quantitatively estimate ancient mean annual air temperature and precipitation based on ancient sand composition

minero petrographical features of weathering profiles in calabria southern italy abstract the paper reports interdisciplinary research of weathering profile stages on gneiss with regard to tectonic and landscape evolutions of the western sila grande massif southern italy the outcropping rocks consist of medium to coarse grained biotite garnet and sillimanite gneiss bgs g and medium to coarse grained biotite muscovite migmatitic gneiss m g the bgs g rocks are fractured and weathered with either massive or foliated texture whereas the m g rocks are intensely weathered and fractured with a massive texture and frequent pegmatite veins petrographical and mineralogical variations show that both gneissic rocks bgs g and m g samples underwent weathering processes characterized by a progressive chemical attack on the labile minerals with generation of neoformed minerals and substitution of the original rock fabric the weathering processes produced phyllosilicates and fe oxides neoformed clay minerals and ferruginous products replaced feldspars and biotite during the most advanced weathering stage microfractures and morphological variations occur on the original rock and thereby affect the surrounding landscape processes the weathering profile mineralogy and rock textures viewed in the context of landscape evolution provide useful insights into the widespread slope movement phenomena in the sila grande massif gneiss

influence of granitoid textural parameters on sediment composition implications for sediment generation the aim of this study is to determine and characterise the control exerted by parent rock texture on sand composition as a function of grain size the sands investigated were generated from granitoid parent rocks by the rhone damma and sidelen glaciers which drain the aar massif in the central alps switzerland and were deposited in glacial and fluvio glacial settings mechanical erosion comminution crystal breakdown and abrasion and hydraulic sorting are the most important processes controlling the generation of sediments in this environment whereas chemical and or biochemical weathering plays a negligible role by using a gis based microscopic information system mis five samples from the glacier drained portions of the aar basement have been analysed to determine textural parameters such as modal composition crystal size distribution and mineral interfaces types and lengths petrographic data of analysed sands include traditional point counts gazzi dickinson method minimum of 300 points as well as textural counts to determine interface types frequency and polycrystallinity in phaneritic rock fragments according to pettijohn s classification grain size dependent compositions vary from feldspathic litharenite 0 fraction via lithic arkose 1 and 2 to arkose 3 and 4 compositional differences among our data set were compared to modern plutoniclastic sands from the iberian massif spain and the st gabriel mts california usa which allowed us to assess the role exerted by glaciers in generating sediments by combining data from the mis with those from petrographic analysis we outlined the evolution of mineral interfaces from the parent rocks to the sediments

mineral dust impact on snow radiative properties in the european alps combining ground uav and satellite observations in this paper we evaluate the impact of mineral dust md on snow radiative properties in the european alps at ground aerial and satellite scale a field survey was conducted to acquire snow spectral reflectance measurements with an analytical spectral device asd field spec pro spectroradiometer surface snow samples were analyzed to determine the concentration and size distribution of md in each sample an overflight of a four rotor unmanned aerial vehicle uav equipped with an rgb digital camera sensor was carried out during the field operations finally landsat 8 operational land imager oli data covering the central european alps were analyzed observed reflectance evidenced that md strongly reduced the spectral reflectance of snow in particular from 350 to 600 nm reflectance was compared with that simulated by parameterizing the snow ice and aerosol radiation radiative transfer model we defined a novel spectral index the snow darkening index sdi that combines different wavelengths showing nonlinear correlation with measured md concentrations r2 0 87 root mean square error 0 037 we also estimated a positive instantaneous radiative forcing that reaches values up to 153 w m2 for the most concentrated sampling area sdi maps at local scale were produced using the uav data while regional sdi maps were generated with oli data these maps show the spatial distribution of md in snow after a natural deposition from the saharan desert such postdepositional experimental data are fundamental for validating radiative transfer models and global climate models that simulate the impact of md on snow radiative properties

a new model of pore structure typing based on fractal geometry abstract in this study we report a physics based model for pore structure typing in which a generalized model is also derived to calculate the specific surface area of the grains in this model a new pore structure type indicator is defined to characterize the discrepancies of pore structures based on the fractal geometry theory and a modified kozeny carman equation we compared the proposed model with the conventional model by comprehensive experimental tests in 130 low permeability sandstone cores from the dongfang gas reservoir in the south china sea the fractal dimension of the grain dg was first accurately calculated through thin section analysis the results show that grains of low permeability sandstone indeed have the bifractal distribution with constant radius boundaries of approximately 30 m potentially accounting for the multiscale of pore spaces compared with the conventional model considering the complex pore and grain size distributions as well as irreducible water saturation the developed model as a generalized expression performs better in pore structure typing with higher correlation coefficients in porosity permeability and structural coefficients pore radius relationships due to the newly identified indicator with a wider range finally a multiscale workflow was proposed to analyze the petrological and structural features of pore structures by two dimensional core images thin sections scanning electron microscope mercury intrusion tests and three dimensional micro computed tomography this work enables us to explain the genetic types and differences of the pore structure and may help to characterize the internal connection of the grain structure pore structure flow mechanism in hydrocarbon exploration and development

grain size control on sr nd isotope provenance studies and impact on paleoclimate reconstructions an example from deep sea sediments offshore nw africa five sediment cores from offshore nw africa were analyzed for strontium and neodymium isotope ratios to reconstruct temporal variations in continental weathering regimes sediments were taken from three time slices with well known and distinctive environmental conditions present day dry and warm similar to 6 ka wet and warm and similar to 12 ka dry and cold terrigenous sediment samples were split into two size fractions to distinguish between the two dominant transport mechanisms offshore nw africa fluvial 0 10 mu m and aeolian 10 40 mu m sr isotope data record evidence of marked grain size control with higher isotopic ratios in the fine fraction in contrast epsilon nd values are largely unaffected by grain size minor variability in nd isotope data at each sampling site indicates near constant sources of terrigenous matter over the last similar to 12 ka variations in sr isotope ratios are interpreted to reflect major changes in the evaporation precipitation balance we suggest that the sr nd isotope data record a latitudinal shift of the northern limit of the african rainbelt and associated wind systems causing changes in the humidity and rate of chemical weathering over nw africa while hyperarid conditions prevailed similar to 12 ka more humid conditions and intensified monsoonal rainfall at similar to 6 ka resulted in greater breakdown of easily weathered k bearing phases and increased sr 87 sr 86 in the detritus in late holocene times the monsoonal circulation diminished resulting in a return to arid conditions our results clearly show that it is of vital importance in paleoenvironmental studies to carry out isotopic analyses on individual sediment fractions that were carried to the studied deposition site by distinct sediment transport mechanisms if isotopic analyses are carried out on bulk sediments the observed variability in isotopic values most likely represents changes in the particle size and mixing proportions of the sediment subpopulations

influence of tectonism and climate on lithofacies distribution and sandstone and conglomerate composition in the archean beaulieu rapids formation northwest territories canada abstract the 0 2 1 km thick archean beaulieu rapids formation is a late orogenic tectonically controlled sedimentary sequence overlying the beaulieu river volcanic belt unconformably on the west and bordering the major n trending beniah lake fault on the east local porphyry stocks characteristic of late orogenic successions were emplaced along strike of the fault four lithofacies comprise the beaulieu rapids formation 1 the 20 320 m thick conglomerate i 2 the 10 305 m thick siltstone sandstone 3 the 20 120 m thick conglomerate ii and 4 the 40 320 m thick quartz rich sandstone lithofacies stacking displays two distinct large scale fining upward sequences represented by the 300 375 m thick conglomerate i and sandstone siltstone sequence a and the 300 400 m thick conglomerate ii and quartz rich sandstone sequence b fining upward sequences a bounding unconformity and the beniah lake fault are compelling indicators of tectonic influence on sedimentation conglomerate i was deposited by debris flows traction currents and sheetfloods on the proximal medial and distal portions of alluvial fans or fan deltas respectively the overlying siltstone sandstone contains two distinct lithological units a sandstone dominated unit formed from fluvial dune migration and overbank deposition in a sandy braidplain setting with scattered ponds whereas sedimentary structures in the siltstone dominated unit are consistent with lacustrine deposition a second phase of tectonic uplift produced sequence b conglomerate ii was deposited in a proximal braided stream setting characterized by abundant longitudinal gravel bars the quartz rich sandstone developed from dune migration on a sandy braidplain mineralogy and textures reflect high sediment influx limited transport distance local sources and climatic influence clast populations in conglomerate indicate a prevalent mafic volcanic source whereas sandstones contain prominent quartz av 76 with subordinate feldspar 13 and lithic fragments 11 the disparity between clast and sandstone composition is a function of chemical weathering typical of a humid climate source areas are restricted to the mafic dominated beaulieu river volcanic belt the 2 8 ga gneisso plutonic sleepy dragon complex and fault related porphyry stocks the humid weathering aggressive archean climate was responsible for destroying labile minerals and lithic fragments in proximal source rocks rich in plagioclase accounting for the high quartz component in the sandstones the beaulieu rapids formation is similar to modern strike slip basins that form along major fault zones in terms of basin geometry faulted and unconformable contacts lithological units and sedimentary facies stacking and organization fault controlled basins of this nature commonly develop during the last stage of terrane accretion on archean cratons

rare earth elements of aeolian deposits in northern china and their implications for determining the provenance of dust storms in beijing this paper contributes to a better understanding of the source of dust storms in northern china and the relationship between these sources and other aeolian sediments in this region sediment samples in potential source areas were collected from the hunshandake sandy land heaven desert the loess deposits of the bashang area the mountainous basins and valleys north of beijing and from the badain jaran desert and hulunbaier sandy land fig 1 dust samples were collected in beijing during two dust storms in march 2002 and april 2006 the laboratory methods used in this study included measurements of abundance of trace elements in particular the rare earth elements rees mineral assemblages and grain size the ree contents eu and ce anomalies show clear differences between various deposits provenance is considered to be the key factor influencing ree patterns in the study areas the ree abundances and patterns indicate that the aeolian sand north of beijing such as in the heaven desert is mainly of local origin rather than from desert encroachment from the north the mineral grains carried in dust storms however are highly mixed and may come partly from local sources but mainly from distant desert regions in western china

provenance of cryoconite deposited on the glaciers of the tibetan plateau new insights from nd sr isotopic composition and size distribution

origin of loess deposits in the north tian shan piedmont central asia abstract loess deposits are widely distributed along the mountain piedmonts of central asia the transport processes and origins of central asian loess sediments remain poorly understood here we investigate the origin and formation of loess along the northern piedmont of the tian shan based on trace element including rare earth element ratios and multidimensional scaling analysis our results indicate that the loess has undergone weak chemical weathering using a selection of geochemical fingerprinting techniques based on pearson correlation and kruskal wallis h tests we establish a genetic link between alluvial proluvial fans plains deserts and loess along the tian shan piedmont in northern kyrgyzstan and southern kazakhstan the unsorted sediments on the piedmont slopes and alluvial proluvial plains are common sources for both deserts and loess to the north of the tian shan dune sediments are not the main source of the fine grained loess origin and formation of central asian loess is strongly dependent on local topographic context and wind dynamics only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made

geochemical evidence for sources of surface dust deposited on the laohugou glacier qilian mountains abstract atmospheric dust deposited on glacier surfaces can decrease snow albedo by enhancing lighting absorption and by forming cryoconites via microbial activity which accelerates glacier melt using snow and cryoconite sampled from the laohugou glacier no 12 in the qilian mountains during spring 2012 and summer 2014 this work investigates the sr nd isotopic and rare earth element ree geochemistry of dust and its environmental significance results demonstrate that dust rees possess lower eu eu and l hree and higher gd yb n values compared with that of the mu us and hobq deserts but yield higher la yb n l hree la sm n and la yb n ratios than that of the taklimakan desert the ree composition of glacier surface dust is similar to the material from nearby arid regions such as the qaidam basin and the tengger and badain jaran deserts surrounding the eastern tibetan plateau the e nd 0 values of glacial dust resemble the isotopic ratios of the qaidam badain jaran tengger deserts and local dust e nd 0 value of 13 6 but differ from that of the taklimakan desert which has higher 87 sr 86 sr ratios analysis of air mass trajectory also indicates a potential dust input from the surrounding areas to the alpine glaciers in the qilian mountains these results strongly indicate that the dust source from the arid northern tibetan plateau region was the dominant contributor to atmospheric dust deposition on the glacier surface rather than dust originating from the long range transport of taklimakan desert material

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

sr nd isotope evidence for modern aeolian dust sources in mountain glaciers of western china in order to apportion the dust sources of mountain glaciers in western china the sr nd isotopic compositions of insoluble particles were determined in snow samples collected from 13 sites the combined plot of 87 sr 86 sr and

flow unit modeling and fine scale predicted permeability validation in atokan sandstones norcan east field kansas characterizing the reservoir interval into flow units is an effective way to subdivide the net pay zone into layers for reservoir simulation commonly used flow unit identification techniques require a reliable estimate of permeability in the net pay on a foot by foot basis most of the wells do not have cores and the literature is replete with different kinds of correlations transforms and prediction methods for profiling permeability in pay however for robust flow unit determination predicted permeability at noncored wells requires validation and if necessary refinement this study outlines the use of a spreadsheet based permeability validation technique to characterize flow units in wells from the norcan east field clark county kansas that produce from atokan aged fine to very fine grained quartzarenite sandstones interpreted to have been deposited in brackish water tidally dominated restricted tidal flat tidal channel tidal bar and estuary bay environments within a small incised valley fill system the methodology outlined enables the identification of fieldwide free water level and validates and refines predicted permeability at 0 5 ft 0 15 m intervals by iteratively reconciling differences in water saturation calculated from wire line log and a capillary pressure formulation that models fine to very fine grained sandstone with diagenetic clay and silt or shale laminae the effectiveness of this methodology was confirmed by successfully matching primary and secondary production histories using a flow unit based reservoir model of the norcan east field without permeability modifications the methodologies discussed should prove useful for robust flow unit characterization of different kinds of reservoirs

sandstone body and shale body dimensions in a braided fluvial system salt wash sandstone member morrison formation garfield county utah excellent three dimensional exposures of the upper jurassic salt wash sandstone member of the morrison formation in the henry mountains area of southern utah allow measurement of the thickness and width of fluvial sandstone and shale bodies from extensive photomosaics the salt wash sandstone member is composed of fluvial channel fill abandoned channel fill and overbank flood plain strata that were deposited on a broad alluvial plain of low sinuosity sandy braided streams flowing northeast a hierarchy of sandstone and shale bodies in the salt wash sandstone member includes in ascending order trough cross bedding fining upward units mudstone intraclast conglomerates single story sandstone bodies basal conglomerate abandoned channel fill multistory sandstone bodies and overbank flood plain heterolithic strata trough cross beds have an average width thickness ratio w t of 8 5 1 in the lower interval of the salt wash sandstone member and 10 4 1 in the upper interval fining upward units are 0 5 3 0 m thick and 3 11 m wide single story sandstone bodies in the upper interval are wider and thicker than their counterparts in the lower interval based on average w t linear regression analysis and cumulative relative frequency graphs multistory sandstone bodies are composed of two to eight stories range up to 30 m thick and over 1500 m wide w t 50 1 and are also larger in the upper interval heterolithic units between sandstone bodies include abandoned channel fill w t 33 1 and overbank flood plain deposits w t 70 1 understanding w t ratios from the component parts of an ancient sandy braided stream deposit can be applied in several ways to similar strata in other basins for example to 1 determine the width of a unit when only the thickness is known 2 create correlation guidelines and maximum correlation lengths 3 aid in interpreting the controls on fluvial architecture and 4 place additional constraints on input variables to stratigraphic and fluid flow modeling the usefulness of these types of data demonstrates the need to develop more data sets from other depositional environments

sourceland controls on the composition of beach and fluvial sand of the northern tyrrhenian coast of calabria italy implications for actualistic petrofacies abstract the northern tyrrhenian margin of calabria in southern italy provides a natural laboratory for sampling sand at different scales small drainages first order rivers draining mountain ranges second order and marine environments beach to deep marine third order calabrian mountain ranges represent an uplifted and variable dissected thrust belt constituted by palaeozoic through pleistocene plutonic metamorphic ophiolitic carbonate and siliciclastic rocks the modern setting includes a mountainous coast having high rates of fluvial discharge and the deep marine paola basin the composition of modern fluvial and beach sands is useful for the interpretation of sediment transported into deeper water environments modern beach and fluvial sands of the northern tyrrhenian margin of calabria define three distinct petrologic provinces from north to the south 1 the lao littoral province has calclithite sand derived from erosion of dominantly carbonates of the southern apennines 2 the coastal range littoral province has quartzolithic sand derived from dominantly metamorphic schist and phyllite coastal range and 3 the santa eufemia littoral province has quarzofeldspathic sand derived from dominantly metamorphic coastal range and sila massif and plutono metamorphic mount poro provenances deep marine turbidites of the paola basin have basinwide quartzolithic turbidite sands having close compositional relations with coastal range littoral petrofacies only at the northern boundary of the paola basin calclithite turbidite sand record deep water dispersal of the lao littoral sands comparison of detrital modes from mainland to deep marine environments contribute to the models of dispersal pathways and geographical extension of actualistic sand petrofacies

cryoconite on a glacier on the north eastern tibetan plateau light absorbing impurities albedo and enhanced melting cryoconite is a dark coloured granular sediment that contains biological and mineralogical components and it plays a pivotal role in geochemistry carbon cycling and glacier mass balance in this work we collected cryoconite samples from laohugou glacier no 12 lhg on the north eastern tibetan plateau during the summer of 2015 and measured the spectral albedo to explore the impacts of this sediment on surface ablation the ice melting differences between the cryoconite free removed ice and the intact layers were compared the results showed that the mean concentrations of black carbon bc organic carbon oc and total iron fe in the lhg cryoconite were 1 28 11 18 and 39 94 mg g 1 respectively bc was found to play a stronger role in solar light adsorption than oc and free fe in addition ice covered by cryoconite exhibited the lowest mean reflectance i e 1 and free fe bc and oc were estimated to contribute 1 01 0 99 and 0 76 cm d 1 respectively this study provides important insights for understanding the role of cryoconite in the glacier mass balance of the northern tibetan plateau

geostatistical modelling of compositional variability across granitoid complexes its relevance to petrogenetic interpretations and specification of parent rock properties in sediment generation models abstract sediment generation models need an accurate specification of the fundamental properties of parent rocks and their variability at the scale of first order mono lithologic drainage basins georeferenced point count data of five extensively surveyed plutons were extracted from the literature to examine the spatial variability of modal composition in granitoids point count data must be considered inherently noisy from the point of view of geospatial analysis because sampled areas thin sections are small compared to the average crystal size of granitoids geostatistical modelling of such data is further complicated by the fact that crucial information on short range variability is unavailable because sampling was carried out according to more or less regular patterns to achieve an equal density of data coverage across plutons geostatistical modelling of compositional data was carried out by transforming the data to centred log ratios and calculating their principal components pcs the pc scores were used as input for a geostatistical workflow based on ordinary kriging coupled with cross validation and stochastic simulation to assess the predictive capabilities of the models sets of omnidirectional exponential variogram models with fixed range and sill and variable nugget were used for each pluton the local neighbourhood search radius for geostatistical interpolation was set equal to the range variogram modelling was formulated as an optimisation problem aimed at estimating the nugget for which the mean squared cross validation prediction error reaches its minimum the best model of each pluton was selected from all possible combinations of models obtained from the pcs results of a permutation test indicate that the residuals of observed and predicted compositions do not exhibit significant cross covariance within the search radius adopted and may be interpreted as stationary random errors which suggests that little may be gained by application of co kriging random sampling from the geostatistical models indicates that up to several hundreds of specimens must be analysed to successfully predict the area weighted mean modal composition of plutons and its spatial covariance structure as depicted in single component and qapf streckeisen maps an illustration of the internal consistency of the log ratio approach and petrogenetic models is provided by the analysis of the compositional pattern in one of the granite complexes which can be explained by the combined effects of mixing and fractionation the volumes sampled by bulk geochemical analysis are equivalent to the areas of thin sections and geochemical data of coarse crystalline rocks are thus subject to the same limitations as modal analyses the combined data reduction and geostatistical modelling strategy outlined in this study is expected to be particularly efficient for the modelling of such high dimensional data the advent of quick non destructive measurement techniques such as xrf and nir is expected to play a crucial role in future attempts at rigorous quantitative mapping of lithosomes if sediment generation can be simulated the uncertainties associated with the initial conditions area weighted means of parent rock properties can be propagated all the way through to uncertainties of predicted sediment properties

provenance of aeolian sediment in the taklamakan desert of western china inferred from ree and major elemental data abstract to identify the provenance of aeolian deposits in the extensive dune field in the taklamakan desert is of great importance for understanding the formation of this the largest sand sea in china the opinions from earlier studies are quite dipolar and are as follows a local origin of the dune sands in different parts of the desert on the basis of various heavy mineral assemblages and b strong homogenization of the sands in the entire taklamakan on the basis of geochemical data from whole rock samples by separately examining the ree characteristics and major elemental composition in coarse and fine fractions of the samples from aeolian deposits this paper provides new data for interpreting sources of aeolian deposits in the taklamakan the sampling sites are distributed in four different fluvial systems i e the areas of the keriya river niya river and cele river in the southern part and the northern margin near the tarim river fig 1 our results show that there are some significant differences in concentrations of trace elements and in ree features between the coarse and the fine fractions of the aeolian sediment the major elemental and ree data suggest that the coarser sand is different from area to area in the desert rather than a homogenization of the entire basin the fine fractions mainly silts are more homogenized the regional difference of coarse fractions in the study areas is consistent with the fluvial and wind systems in the basin this confirms that the sands are often mixed between the northern and southern parts but there is much less mixing along the east west direction it should be emphasized that not only glacial and aeolian processes but also fluvial and lacustrine processes have jointly contributed to the formation of the huge sand sea in addition little variation is found between old and young sands in two sediment sequences in the central part of the desert indicating consistency of sand sources in a given site during the last 40 ka

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

weathering of gneiss in calabria southern italy abstract the effects of weathering in a mediterranean climate on the mineralogy and microfabric of paleozoic gneiss of the sila massif calabria southern italy have been studied field observations show highly weathered rock forms a residual soil micromorphological and mineralogical properties of bedrock and saprolite show that the weathering process is characterized by at least two major stages having two distinct rock microfabrics in the first stage the morphological features of the original rock are preserved and weathering is manifested mainly by microfracturing and large portions of the rock remain unaltered the second stage of weathering involves further development of microcracks and progressive chemical attack on the minerals this latter stage occurs along both compositional and microstructural discontinuities with etch pitting of feldspar and neoformation of clay minerals and ferruginous products replacing feldspar biotite and iron bearing garnet the determination of quantitative petrographic indices provides a measure of the various stages of weathering

accelerated glacier melt on snow dome mount olympus washington usa due to deposition of black carbon and mineral dust from wildfire assessing the potential for black carbon bc and dust deposition to reduce albedo and accelerate glacier melt is of interest in washington because snow and glacier melt are an important source of water resources and glaciers are retreating in august 2012 on snow dome mount olympus washington we measured snow surface spectral albedo and collected surface snow samples and a 7 m ice core the snow and ice samples were analyzed for iron fe used as a dust proxy via inductively coupled plasma sector field mass spectrometry total impurity content gravimetrically bc using a single particle soot photometer sp2 and charcoal through microscopy in the 2012 summer surface snow bc 54 50 g l fe 367 236 g l and gravimetric impurity 35 18 mg l concentrations were spatially variable and measured broadband albedo varied between 0 67 0 74 bc and dust concentrations in the ice core 2011 summer horizon were a magnitude higher bc 3120 g l fe 22000 g l and gravimetric impurity 1870 mg l corresponding to a modeled broadband albedo of 0 45 based on the measured bc and gravimetric impurity concentrations the big hump forest fire is the likely source for the higher concentrations modeling constrained by measurements indicates that the all sky 12 h daily mean radiative forcings in summer 2012 and 2011 range between 37 53 w m 2 and 112 149 w m 2 respectively with the greater forcings in 2011 corresponding to a 29 38 mm d enhancement in snowmelt the timing of the forest fire impurity deposition is coincident with an increase in observed discharge in the hoh river highlighting the potential for bc and dust deposition on glaciers from forest fires to accelerate melt

provenance of volcaniclastic beach sand in a magmatic arc setting an example from lipari island aeolian archipelago tyrrhenian sea lipari an active volcanic island in the aeolian magmatic arc is an excellent area to determine the effects of multiple source lithology climate weathering transport and depositional environment on epiclastic sand composition volcaniclastic sand samples from 12 modern beaches were petrographically characterized using the gazzi dickinson method and the proportions of source rocks in combination with topography in associated coastal drainage basins were quantified using gis several types of bedrock in the 12 drainage basins that are the likely prominent sources for sand at each sampled beach were recognized and divided into two categories of provenance lithotypes lavas and pyroclastic rocks ranging in composition from basaltic andesitic to andesitic to rhyolitic volcanic lithic fragments from lipari beach sand consist of colourless and black glassy volcanic fragments with lathwork felsitic vitric and microlitic textures moreover high amounts of detrital less durable minerals such as pyroxene olivine and fe oxides illustrate how the analysed sands preserve the source rock s provenance signals applying the concept of sand generation index we see that these lithotypes have different propensities to create detritus in terms of both grain size and composition clastic contribution from pyroclastic rock outcrops such as pumice is not found in the size ranges studied suggesting that these pumiceous source rocks probably only produce gravel or very fine sand and silt this finding has implications for the stratigraphic record because pumice clasts ranging from medium to fine grain size could be underrepresented in older volcaniclastic deposits and overrepresented in other size fractions

uses and misuses of compositional data in sedimentology this paper serves two goals the first part shows how mass evolution processes of different nature become undistinguishable once we take a size limited noisy sample of its compositional fingerprint processes of exponential decay mass mixture and complementary accumulation are simulated and then samples contaminated with noise are extracted the aim of this exercise is to illustrate the limitations of typical graphical representations and statistical methods when dealing with compositional data i e data in percentages concentrations or proportions the second part presents a series of concepts tools and methods to represent and statistically treat a compositional data set attending to these limitations the aim of this second part is to offer a state of the art compositional data analysis this includes descriptive statistics and graphics the biplot ternary diagrams with confidence regions for the mean regression and analysis of variance models to explain compositional variability and the use of compositional information to predict environmental covariables or discriminate between groups all these tools share a four step algorithm 1 transform compositions with an invertible log ratio transformation 2 apply a statistical method to the transformed scores 3 back transform the results to compositions and 4 interpret results in relative terms using these techniques a data set of sand petrographic composition has been analyzed highlighting that finer sands are richer in single crystal grains in relation to polycrystalline grains and that grain size accounts for almost all compositional variability a stronger water flow river discharge favors mica grains against quartz or rock fragment grains possibly due to hydrodynamic sorting effects a higher relief ratio implies shorter residence times which may favor survival of micas and rock fragments relatively more labile grains

stratigraphic well correlations for 3 d static modeling of carbonate reservoirs the principles and purposes of stratigraphic well correlation in carbonate sedimentary systems are defined and discussed within the context of static reservoir modeling the challenge of well correlations is to relate the heterogeneities measured at core and well scales to the spatial heterogeneities at reservoir and flow unit scales the introduction of a priori knowledge in the process of stratigraphic well correlation is critical to support the stratigraphic rules and to establish a coherent geological and petrophysical concept the links between well correlation and geostatistics are discussed with regard to the stationarity hypothesis and property trend analysis we stress that wells are incomplete and biased samples of the geological reality which is not dependent unlike the dynamic reservoir behavior on the well numbers location and spacing stratigraphic rules are applied as a function of the well spacing relative to the geological reality a simple trigonometric method combining angle of base profile paleobathymetry and well spacing is introduced to check the validity of the well correlation in carbonate ramp like systems two models based respectively on outcrop and subsurface with seismic data are discussed in detail to show the combined influence of the data set sedimentary systems and diagenetic transformations on stratigraphic well correlations

initial generation of sand across climate zones of the mojave sierra nevada and klamath batholiths in california u s a the generation of modern plutoniclastic sediment across california varies with climate resulting in significant mineralogical and geochemical differences between parent rock weathering profile material and low order stream sand with average precipitation of 15 cm yr in the arid zones and 120 cm yr in the temperate zones feldspar is relatively decreased in stream sand compared to parent rock by 2 and 20 respectively potassium feldspar is more resistant to weathering than plagioclase but is less stable than quartz in temperate climates hornblende and biotite are more easily weathered in temperate than arid climates although their occurrence in medium grained stream sands is affected by hydraulic sorting and comminution during transport temperate climate sands have lower concentrations of cao and na2o compared to k2o and al2o3 reflective of the expected faster loss of plagioclase than potassium feldspar during weathering with the exception of biotite the mineralogy of medium grained stream sand reflects that of medium grained weathering profile material in both climates confirming the findings from constant climate case studies that the composition of proximal sand is largely achieved within weathering profiles and during initial erosion we encourage continued attention to climate as a control on sand composition in provenance and paleoclimate studies where a moderate precipitation shift is capable of producing a significant loss of feldspar the differential response of common minerals to chemical weathering should be considered for studies and modeling related to bedrock erodibility sediment supply and landscape evolution

gneiss saprolite weathering and soil genesis along an east west regolith sequence ne brazil abstract the pressure to increase biomass production worldwide has pushed the boundaries of agricultural lands towards fragile soils this process is particularly intense in pernambuco state ne brazil pernambuco features a moisture gradient with soils developed from similar gneisses resistant structures within the rock influenced the internal movement and distribution of water consequently influencing regolith genesis this paper presents the mineralogical characteristics of three regolith profiles with shallow soils here assumed to be soils in which the top of the cr horizon is at a depth of 1 5 m or less along a transect at 8 s and discusses their weathering and pedogenetic processes samples were investigated via optical microscopy and scanning electron microscopy sem x ray diffraction xrd and total chemical analysis by inductively coupled plasma atomic emission spectrometry icp aes the presence of weathering resistant quartz veins and planes in the rock structure played a central role in controlling the water dynamics and the advancement of the weathering front therefore desilication was dominantly controlled by the pore network hence the weathering indexes did not differ appreciably among the climatic zones and both 1 1 and 2 1 type clays were found in all profiles although the amount of clay minerals that formed and the degree of dissolution of the primary minerals varied among the climate types from an agricultural perspective the thinness of these soil profiles and the presence of leucocratic layers are the main drawbacks of the regoliths whereas the capacity to supply plant nutrients via primary mineral dissolution near the root zone can be an advantage

the impact of micro to macro scale geological attributes on archie s exponents an example from permian triassic carbonate reservoirs of the central persian gulf abstract enormous and inherent heterogeneity of carbonate reservoirs causes problems in the estimation of their geological and petrophysical attributes the major part of this heterogeneity is due to the various pore types and structures of these reservoirs water saturation is economically one of the most important characteristics of any producing reservoir archie introduced practical exponents which are fundamental parameters for saturation calculation in this research the effect of geological factors controlling archie s exponents including depositional and diagenetic characteristics in a sequence stratigraphic framework in permian triassic carbonates of persian gulf basin was carried out rock typing approach has been used for assigning reservoir characteristics to geological parameters five digenetic facies that were determined according to petrographic studies wire line logs sem and conventional core analysis as well as mercury injection tests were grouped into four rock types using lucia diagram archie s exponents were calculated for different rock types results showed that porosity value and pore type have an important effect on the exponents this effect could be traced vertically in macro scale using sequence stratigraphic concept grainstone facies with high m values are located in early hst and late tst tight grainstone or mud dominated facies with low m values are located in early tst and late hst

quantitative models of sediment generation and provenance state of the art and future developments abstract an overview of quantitative approaches to analysis and modelling of sediment generation and provenance is presented with an emphasis on major framework components as determined by means of petrographic techniques conceptual models of sediment provenance are shown to be consistent with two classes of numerical statistical models i e linear mixing models and compositional linear models these cannot be placed within a common mathematical framework because the former requires that sediment composition is expressed in terms of proportions whereas the latter requires that sediment composition is expressed in terms of log ratios of proportions additivity of proportions a fundamental assumption in linear mixing models cannot be readily expressed in log ratio terms linear mixing models may be used to describe compositional variability in terms of physical and conceptual un mixing models of physical un mixing are appropriate for describing compositional variation within transport invariant subpopulations of grains as a result of varying rates of supply of detritus from multiple sources conceptual un mixing governs the relations among chemical mineralogical and petrographic characteristics of sediments which represent different descriptive levels within a compositional hierarchy compositional linear process models may be used to describe compositional and or textural evolution resulting from selective modifications induced by sediment transport as well as chemical and mechanical weathering current approaches to modelling of surface processes treat the coupled evolution of source areas and sedimentary basins in terms of bulk mass transfer only and do not take into account compositional and textural sediment properties moving from the inverse modelling approach embodied in provenance research to process based forward models of sediment generation which provide detailed predictions of sediment properties meets with considerable albeit not insurmountable problems strategies for developing more advanced parameterizations of sediment properties and for simulating their evolution are proposed and expansion of current data acquisition protocols is discussed in the light of data requirements for such advanced sediment generation models inclusion of sediment generation modules in models of landscape evolution and basin filling will mark a significant step towards full fledged source to sink simulations of earth surface processes

geochemical and isotopic studies of aeolian sediments in china the sr and nd isotopic rare earth element ree and major element compositions together with mineral and grain size proportions are reported for aeolian loess deposits and desert sands from several chinese localities the study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments and to constrain the provenance of chinese loess samples include loesses from the tarim and junggar basins and desert sands from the taklimakan desert in north west china loess from the ordos area and desert sands from the tengger and mu us deserts in north central china as well as loess and desert sands from the naiman area north east china ree distributions show minimal variation among the chinese loess deposits whereas those for the desert sands show regional variations new isotopic data document a latitudinal variation in sr and nd isotopic features for the loesses and desert sands the naiman and junggar loesses have distinctly lower 87sr 86sr ratios and higher end 0 values than the loesses from the tarim basin the ordos area and the loess plateau among the desert sands the naiman samples have higher end 0 values than the taklimakan tengger and mu us samples isotopic data suggest that loesses of the loess plateau were supplied from the tarim basin loesses and taklimakan desert sand and that the naiman loesses were supplied from the junggar basin loesses the latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the tianshan and west kunlun mountains which are possible sources for the loesses and desert sands these inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over east asia

nd and sr isotopic characteristics of chinese deserts implications for the provenances of asian dust silicate nd sr isotopes of the fine grained fractions of the 10 major deserts and sandy lands in north china and the loess in chinese loess plateau were systematically investigated wide ranges in nd sr isotopic compositions have been observed the results of the 7 0 b the deserts on the northern margin of tibetan plateau with end 0 ranging from 11 9 to 7 4 and c the deserts on the ordos plateau with the lowest end 0 11 5 the distribution of the threes isotopic regions is controlled by the tectonic setting in north china which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the nd sr isotopic signatures of these deserts could be quit stable over the past million years on the sub tectonic time scales if there is any desert at those times the nd sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region b suggesting that the main source regions of the last glacial loess in the chinese loess plateau are badain jaran desert tengger desert and qaidam desert also the comparison between the nd sr isotopes of the 5 lm silicate fractions of the deserts and the ancient dust falls in the north pacific and greenland show that the asian end members of these dust falls are derived most from the deserts in the isotopic region b and less from those in the isotopic region c

sr and nd isotopic composition of dust in dunde ice core northern china implications for source tracing and use as an analogue of long range transported asian dust abstract this study presents the sr and nd isotopic composition of dust from a shallow dunde ice core 38 06 n 96 24 e 5325 m a s l northern china in order to trace its source regions and the provenance of long range transported lrt asian dust dunde dust samples show similar sr 87 sr 86 sr averages 0 719982 and varies between 0 715220 and 0 721874 and nd e nd 0 averages 10 6 and ranges from 11 1 to 9 9 isotopic composition to desert sand from taklimakan and qaidam revealing that the tarim and qaidam basins are the most possible source areas for dunde dust while the contribution from badain jaran and tengger seems very small or unlikely our results indicate that materials from taklimakan can be entrained from the tarim basin and transported to qilian shan by westerlies under the present climate the sr nd isotopic composition of dunde dust which is a good analogue for the long range transported asian dust resembles that of north pacific and greenland dust indicating that the important provenance of end members of the asian dust seems to be taklimakan on a regional scale

integration of geology petrophysics and reservoir engineering for characterization of carbonate reservoirs through pickett plots the concept of rock fabric has been shown to be very useful for characterization of carbonate reservoirs this study shows that a pickett crossplot of interparticle porosity vs true resistivity in some cases apparent resistivity or true resistivity affected by a shale group should result in a straight line for intervals with a constant rock fabric the slope of the straight line is related to the porosity exponent m the water saturation exponent n and the size of the particles forming the interparticle porosity different slopes are obtained for different rock fabrics the method helps to reconcile geology to fluid flow by illustrating the important link between geology petrophysics and reservoir engineering lines of constant rock fabric are displayed on a pickett plot together with water saturation permeability process speed k capillary pressure curves pore throat apertures r35 and rp35 kozeny s constant fs2 and height above the free water table pattern recognition while placing all these data in a consistent form on a pickett plot allows determination of flow units and a more rigorous characterization of carbonate reservoirs the method is aimed at heterogeneous carbonate reservoirs which have a limited amount of hard data the use of this technique is illustrated with data from the mission canyon formation in the little knife field of north dakota where a significant volume of oil in place is below the structural closure and updip wells penetrate microports that provide an effective seal in this stratigraphic trap

quantitative analysis of crystal interface frequencies in granitoids implications for modelling of parent rock texture and its influence on the properties of plutoniclastic sands abstract generation of sediments from crystalline rocks is the result of a complex and incompletely understood suite of processes the time evolution of the rock fragment assemblage in sands derived from granitoids is determined by the relative strengths of crystal interfaces and their abundances in the parent rock in this study we highlight the role of crystal interface frequencies in granitoids strong evidence for non random texture with significant implications for predicted interface frequencies have been reported in previous studies we analysed available interface frequency data from granitoids using methods of compositional data analysis and connected our results to existing texture classifications on average granitoids display a high degree of ordering with significant depletion of isomineralic interfaces relative to expectations based on random texture analysis of 210 normalized interface frequency distributions from nine different granitoids reveals a consistent pattern of variation among interface frequencies which suggests a single underlying petrogenetic process related to the combined effects of nucleation and textural equilibration coarsening in view of the large scatter of relative interface frequencies within and among granitoids we propose to model their distribution empirically for the purpose of calibrating sediment generation studies multivariate normal distributions of centred log ratio transformed relative frequencies are capable of capturing 95 of the observed variability with a limited number of dimensions as a rule of thumb the number of dimensions needed to approximate interface frequency counts can be taken equal to the number of mineral classes which is much smaller than the number of interface classes mathematical analysis shows that the joint variability of rock texture and composition may be factorized into three statistically independent measures modal composition crystal size probability density functions and normalized interface frequencies the potential independence of these measures permits objective identification of petrogenetically significant correlations among them which will be indicated by statistically significant cross covariances at this stage inferences from microscopic texture analysis cannot be extrapolated to the scale of entire drainage basins in which sediments are generated because insufficient data are available on the large scale spatial heterogeneity of texture and composition of granitoid parent rocks

quantitative analysis of the joint variability of rock texture and composition in thin section the generalized griffiths descriptor and its application to sediment generation from granitoids abstract the general protocol for quantitative petrographic description of clastic sediments envisioned by j c griffiths approximately 60 years ago is built on specification of the following five statistically independent fundamental properties of aggregates modal composition spatial arrangement size distributions shape distributions and orientation distributions of the elements each element is represented by a grain falling into one of an exhaustive set of petrographic classes we introduce the so called generalized griffiths descriptor ggd which extends this protocol to igneous and metamorphic rocks statistical independence of the fundamental properties permits rigorous testing of petrogenetic hypotheses as well as simulation of rocks based on any conceivable combination of them the benefits of a unifying scheme for description of crystalline parent rocks and their weathering products are illustrated by exploratory analysis of a petrographic data set derived from five granodiorites from across north america comprising the parent rocks and three size fractions coarse medium and fine of their detritus compositional data analysis is used to estimate sediment generation and evolution sge trajectories for each of the plutons sampled the bulk mineral composition and the mineral composition of the rock fragment assemblage display a common trend of relative depletion of quartz and k feldspar with decreasing grain size compensated for by relative enrichment of biotite and accessory minerals the evolution of crystal interface composition suggests that the balance between chemical and mechanical weathering may be reflected in relative stabilities of crystal interfaces we propose a computationally efficient stereological inversion procedure for estimating the parameters of crystal size probability distributions in rocks based on the assumption of lognormality the lognormal distribution is an acceptable default model for crystal size in granitoids at the level of individual thin sections about 87 passes the tests for lognormality but less so at the level of entire plutons only 62 success ratio the current implementation of the ggd is not yet complete because it deals explicitly with the first three fundamental properties only as a consequence of adopting the simplifying assumption that all elements which make up a rock are spherical shape and orientation distributions may be included in future implementations of the ggd dedicated data sets comprising sediments generated from a single parent rock under different conditions will be needed to advance sge studies by shedding more light on the balance between chemical and mechanical weathering

application of reservoir geology to enhanced oil recovery from upper devonian nisku reefs alberta canada the upper devonian west pembina reef trend of west central alberta contains recoverable reserves of over 79 106 m3 500 million bbl of oil and 1 4 1010 m3 500 billion ft3 of gas within approximately 50 pinnacle reefs in the nisku formation although the oil is saturated with gas at original reservoir pressure primary depletion would soon lower the reservoir pressure below the bubble point decreasing recovery thus pressure maintenance is applied early in the producing life of the pools through waterflood or miscible flood schemes selection of the appropriate enhanced recovery scheme depends upon the internal flow unit geometry of the reefs the bigoray nisku c pool and the pembina nisku l pool for end members of the reservoir spectrum they can be used as flow unit models in the geological input for reservoir simulation studies the bigoray nisku c pool is dominantly limestone the primary textures well preserved in this reef provide the key to interpreting the relict textures in fully dolomitized reefs a well displayed ecological zonation of rugose corals passes vertically upward into laminar stromatoporoids which in turn pass into solenoporacean algae the coral and stromatoporoid zones each contain two generic flow unit types depending upon the presence or absence of dolomitization the incipient reef facies and the algal cap with associated tidal flat sediments represent two additional flow units due to the presence of horizontal permeability barriers associated with the limestone lithology the pool is developed with a waterflood displacement scheme ultimate recovery is estimated to be on the or er of 0 55 106 m3 3 5 million bbl or 46 of original oil in place ooip the pembina nisku l pool is a completely dolomitized reef representative of the majority of the reefs in the nisku fairway in contrast to the bigoray nisku c pool the complete dolomitization reduces the number of generic reservoir flow units observed in the l pool reef from six to three due to the excellent reservoir quality and absence of horizontal permeability barriers it is being exploited by a vertical miscible flood the nisku l pool is one of the largest pinnacle reefs discovered in the nisku reef fairway and contains an estimated 5 106 m3 31 million bbl ooip ultimate recovery is estimated to be approximately 4 1 106 m3 25 8 million bbl or 82 of ooip

weathering erosion and sediment composition in a high gradient river calabria italy source rock lithology and immediate modifying processes such as chemical weathering and mechanical erosion are primary controls on fluvial sediment supply sand composition and chemical index of alteration cia of parent rocks soil and fluvial sand of the savuto river watershed calabria italy were used to evaluate the modifications of source rocks through different sections of the basin characterized by different geomorphic processes in a sub humid mediterranean climate the headwaters with gentle topography produce a coarse grained sediment load derived from deeply weathered gneiss having sand of quartzofeldspathic composition compositionally very different from in situ degraded bedrock maximum estimated cia values suggest that source rock has been affected significantly by weathering and it testifies to a climatic threshold on the destruction of the bedrock the mid course has steeper slopes and a deeply incised valley bedrock consists of mica schist and phyllite with a very thin regolith which provides large cobble to very coarse sand sediments to the main channel slope instability with an areal incidence of over 40 per cent largely supplies detritus to the main channel sand sized detritus of soil and fluvial sand is lithic estimated cia value testifies to a significant weathering of the bedrock too even if in this part of the drainage basin steeper slopes allow erosion to exceed chemical weathering the lower course has a braided pattern and sediment load is coarse to medium fine grained the river cuts across palaeozoic crystalline rocks and miocene siliciclastic deposits sand sized detritus contributed from these rocks and homogenized by transport processes has been found in the quartzolithic distal samples field and laboratory evidence indicates that landscape development was the result of extensive weathering during the last postglacial temperature maximum in the headwaters and of mass failure and fluvial erosional processes in the mid and low course copyright 2000 john wiley sons ltd

the paleoproterozoic waterberg group south africa provenance and its relation to the timing of the limpopo orogeny abstract four paleoproterozoic formations of the waterberg group in south africa are composed of coarse clastic detritus derived from erosion of the limpopo belt timing of the limpopo orogeny an event involving the collision of the kaapvaal and zimbabwe cratons has long been a contentious issue the results of point counting major and trace element geochemistry and u pb detrital zircon geochronology indicate that the waterberg sedimentary formations in the study area were primarily sourced by siliceous rifted margin sedimentary and minor mafic volcanic rocks of the archean beit bridge complex limpopo central zone the volumetrically predominant beige brown sandstones in the four studied formations are quartz rich with average qfr ratios of 80 7 13 blouberg 70 19 11 setlaole 88 5 7 makgabeng and 89 3 8 mogalakwena chert and arenite account for 90 of lithic fragments in all formations with minor siliceous gneiss fragments although all formations are silica enriched the makgabeng dune samples produce extremely high sio2 abundances 92 99 wt which are attributed to the presence of silica cement and quartz within rock fragments geochemically the stratigraphically highest mogalakwena formation is unique with elevated ti and zr values and intra formational differences in ree patterns the latter feature is consistent with a mixed provenance volumetrically minor green and purple sandstones in the waterberg formations contain the greatest cr ni ti and v abundances which supports localized derivation from a mafic or ultramafic source chemical index of alteration cia values range from 57 to 89 which could indicate significant chemical weathering of the source rocks but a plot of th sc versus zr sc illustrates that the sandstones have undergone recycling which was probably responsible for enrichments in al2o3 relative to na2o3 cao and k2o combinations of well rounded and subangular quartz grains support a recycled origin detrital zircons in the lowermost blouberg formation produced a wide array of ages ranging from ca 3379 to 2043 ma the youngest peak at 2046 ma is also the largest and represents the maximum age of deposition for the formation additional peaks at 3281 ma 3330 ma and 3379 ma are consistent with ages previously determined from the beit bridge complex whereas peaks at 2578 ma and 2649 ma coincide with ages determined from gneisses of the limpopo central zone derivation of detritus from the beit bridge complex is directly indicated by sedimentary and siliceous gneiss fragments in the sandstones subrounded quartz grains suggestive of relatively short transport distances green and purple sandstone drapes derived from mafic volcanic units and paleocurrent patterns consistent with south to southwest flow directions therefore the timing of deposition of the blouberg formation 2046 ma equates to the end stages of the limpopo orogeny this negates previous suggestions that the limpopo orogeny occurred only during the neoarchean