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

paleosols and their relevance to precambrian atmospheric composition various paleosols have been reported from within the witwatersrand and ventersdorp supergroups south africa they were studied in an attempt to constrain the amount of oxygen available in the atmosphere during deposition of the gold and uranium bearing witwatersrand conglomerates the majority of these horizons do not have any physical characteristics of paleosols and none of them have a chemistry consistent with weathering suggesting they have been subjected to modification by later alteration processes a similar chemistry indicating overprinting of any original soil chemistry has been reported from paleosols elsewhere elliot lake region canada hekpoort basalt south africa but it does not appear that significant cognizance has been taken of this fact when using these paleosols to determine the composition of the precambrian atmosphere it is concluded here that characteristics previously attributed to precambrian weathering in an oxygen deficient atmosphere are better explained by post buria

mudstone petrology of the mesoproterozoic unkar group grand canyon u s a provenance weathering and sediment transport on intracratonic rodinia abstract the synthesis of mudstone petrology and interbedded sandstone detrital zircon geochronology provides insights into the provenance weathering regime hydrodynamic effects and diagenesis of the mesoproterozoic unkar group unkar mudstones were derived largely from the grenville orogen go of southwest texas and the adjacent yavapai mazatzal ym and southern granite rhyolite sgr terranes detrital zircon data indicate distinct pulses of go derived sediment during hakatai and dox formation deposition whereas shinumo sediment contains a larger component of ym and sgr material an increase in plagioclase and biotite abundances in the dox further suggest an orogenic pulse bulk chemistry including elevated cr and ni abundances and ree systematics implicate a heterogeneous provenance for unkar sediment best approximated by a mix of granite or granodiorite with some basalt weathering of unkar sediment as determined from mudstone and crystalline source bulk chemical trends is characterized as moderate cia values between 55 and 70 indicative of a temperate climate in an orogenic setting small less than 10 wt amounts of detrital kaolinite and chlorite are consistent with a moderate temperate weathering regime illite the dominant clay mineral in the unkar group is largely the 2m1 polytype and detrital in origin however it is estimated that 7 of the k in the escalante creek member results from k metasomatism and may form up to 15 wt authigenic 1m or 1md illite the clay size fraction and zircon are the chief contributors to the ree budget in unkar mudstones lithostratigraphic variations in the hree distributions can be attributed partially to variable zircon abundance in the silt size fraction a likely function of hydrodynamic sorting age constraints on the duration of unkar group sedimentation range from 30 to 100 my for the 1100 m conformable shinumo dox succession and result in compacted sedimentation rates of between 1 0 and 3 6 cm 103 yr these rates are comparable to mesozoic foreland basin settings

the flin flon paleosol and the composition of the atmosphere 1 8 bybp within the 1800 to 1900 my old flin flon snow lake greenstone belt amisk group volcanics are overlain by missi group fluvial sediments several localities along the missi amisk contact the volcanics show evidence of subaerial weathering field relationships mineralogical evidence and chemical analyses confirm that this alteration zone is a paleosol pedogenic fabrics and mineralogy were somewhat obscured by greenschist grade metamorphism associated with the hudsonian orogeny 1750 my this is especially true in the upper meter of the paleosol where metamorphic paragonite and sericitic micas developed in a crenulated fabric this metamorphism did not however obliterate the imprint of weathering on the amisk volcanics features characteristic of well drained modern soils are evident in the paleosol corestones of spheroidally weathered pillow lavas occur at depth within the paleosol cr horizon the corestones decrease in size upward and eventually disappear into a hematite rich horizon at the top of the paleosol these macroscopic changes are accompanied by a decrease in cao and mgo and by an increase in al2o3 tio2 and total iron toward the paleosol missi contact ferrous iron decreases upward toward the contact feo was apparently oxidized to ferric iron and retained within the paleosol during weathering the oxidation and retention of iron within the flin flon paleosol indicates that po2 was probably or 10 2 p a l at the time of weathering the behavior of iron in the flin flon paleosol contrasts sharply with its behavior in the 2200 my hekpoort paleosol which is strongly depleted in iron this difference suggests that a significant increase in the ratio of po2 pco2 in the atmosphere took place between 2200 and 1800 mybp

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

drought drove forest decline and dune building in eastern upper michigan usa as the upper great lakes became closed basins current models of landscape response to holocene climate change in midcontinent north america largely reconcile earth orbital and atmospheric climate forcing with pollen based forest histories on the east and eolian chronologies in great plains grasslands on the west however thousands of sand dunes spread across 12 000 km 2 in eastern upper michigan eum more than 500 km east of the present forest prairie ecotone present a challenge to such models we use 65 optically stimulated luminescence osl ages on quartz sand deposited in silt caps n 8 and dunes n 57 to document eolian activity in eum dune building was widespread ca 10 8 ka indicating a sharp sustained decline in forest cover during that period this decline was roughly coincident with hydrologic closure of the upper great lakes but temporally inconsistent with most pollen based models that imply canopy closure throughout the holocene early holocene forest openings are rarely recognized in pollen sums from eum because faint signatures of non arboreal pollen are largely obscured by abundant and highly mobile pine pollen early holocene spikes in nonarboreal pollen are recorded in cores from small ponds but suggest only a modest extent of forest openings osl dating of dune emplacement provides a direct spatially explicit archive of greatly diminished forest cover during a very dry climate in eastern midcontinent north america ca 10 8 ka

dynamics and sources of last glacial aeolian deposition in southwest france derived from dune patterns grain size gradients and geochemistry and reconstruction of efficient wind directions abstract dune pattern grain size gradients and geochemistry were used to investigate the sources and dynamics of aeolian deposition during the last glacial in southwest france the coversands form widespread fields of low amplitude ridges zibars whereas younger dryas parabolic dunes mainly concentrate in corridors and along rivers spatial modelling of grain size gradients combined with geochemical analysis points to a genetic relationship between coversands and loess the latter resulting primarily from dust produced by aeolian abrasion of the coversands the alluvium of the garonne river provided also significant amounts of dust at a more local scale the geochemical composition of loess shows much lower scattering than that of coversands due to stronger homogenisation during transport in the atmosphere overall sandy loess and loess deposits decrease in thickness away from the coversands dune orientation and grain size gradients suggest that the efficient winds blew respectively from the w to the nw during the glacial and the w sw during the younger dryas a comparison between the wind directions derived from the proxy data and those provided by palaeoclimatic simulations suggests a change of the main transport season ground surface conditions and their evolution throughout the year i e the length of the season with snow and frozen or moist topsoil and the seasonal distribution of wind speeds able to cause deflation are thought to have been the main factors that controlled the transport season in the study area

effect of the advent and diversification of vascular land plants on mineral weathering through geologic time the origin of vascular land plants in the silurian and their subsequent diversification have had a major effect on mineral weathering through geologic tune the presence of vascular plants reduces the stability of soil minerals through a net export of ions from soil waters and through the release of complexing organic acids by root mycorrhizae additional factors that dictate the nature of plant induced mineral weathering are 1 the differences in nutrient dynamics between evergreen and deciduous species 2 the role of specific nutrient sinks biomass storage and secondary soil mineralization and outputs runoff etc in plant ecosystems and 3 the effect of long and short term ecosystem disturbances first order increases in overall mineral weathering probably took place in the middle paleozoic and early tertiary following the initial colonization and diversification of land plants and the radiation of deciduous angiospenns second order fluctuations would typify time intervals where paleoecosystem disturbances were maximized such as periods of climatic instability

volcanic components in pelitic sediments the origin of the clay minerals present in pelitic sediments has been widely debated weaver1 suggests that illite and interstratified illite smectite i s dominate the association of illite with marine sediments2 and the proposal3 4 that illite forms from smectite an expandable clay mineral sometimes referred to as montmorillonite in the marine environment has also been discussed weaver5 argues for a continental origin of illite produced by weathering of k feldspar others6 9 have shown that smectite and i s 20 50 illite are converted to i s of higher illite content 60 80 in pelitic sediments by low grade metamorphism per cent illite will always refer to the per cent illite in i s the designation should not be confused with the content of discrete illite or mica commonly present in these sediments here we present clay mineral and k ar data for cretaceous marine shales from the western interior of north america demonstrating a volcanic origin for much of these sediments this observation is correlated with eustatic sea level rise increased volcanic activity sedimentary preservation of organic matter and incorporated into a petrogenetic tectonic model for pelitic sediments

aeolian sediment in raised bog deposits halland sw sweden a new proxy record of holocene winter storminess variation in southern scandinavia cores of peat taken from two raised bogs in the near coastal part of halland sw sweden were examined for their content of wind transported clastic material the boarps mosse core has a length of 262 cm and covers the last 2850 years age model based on three radiocarbon dates while the hyltemossen core has a length of 347 cm and records the last 7000 years age model based on eight radiocarbon dates the peat contains aeolian quartz silt and sand from trace amount to more than 10 weight of the dry peat sample and the grain size composition of the minerogenic sediment indicates that the material is composed of both far travelled dust and local wind eroded silt and sand grains larger than 0 2mm are present in many intervals and probably record niveo aeolian transport in connection with severe snowstorms a systematic count of quartz grains between 0 2 0 35mm and larger than 0 35mm was carried out to determine variations in aeolian sand influx asi and winter wind climate with time the boarps m

probabilistic petrophysical properties estimation integrating statistical rock physics with seismic inversion a joint estimation of petrophysical properties is proposed that combines statistical rock physics and bayesian seismic inversion because elastic attributes are correlated with petrophysical variables effective porosity clay content and water saturation and this physical link is associated with uncertainties the petrophysical properties estimation from seismic data can be seen as a bayesian inversion problem the purpose of this work was to develop a strategy for estimating the probability distributions of petrophysical parameters and litho fluid classes from seismics estimation of reservoir properties and the associated uncertainty was performed in three steps linearized seismic inversion to estimate the probabilities of elastic parameters probabilistic upscaling to include the scale changes effect and petrophysical inversion to estimate the probabilities of petrophysical variables andlitho fluid classes rock physics equations provide the linkbetween reservoir properties and velocities and lin

chemical overprinting of magmatism by weathering a practical method for evaluating the degree of chemical weathering of granitoids abstract quantitative determination of the degree of chemical weathering of rocks is a fundamental task in environmental and engineering geology and many weathering indices based on whole rock chemistry have been proposed however most classical indices are of limited application to granitoids in a wide area because these lithotypes generally exhibit wide chemical variation arising from their petrogenesis the chemical evolution produced during rock weathering therefore overprints pre existing magmatic chemical variation this problem can cause many classical weathering indices to yield misleading results this study proposes a method that compensates for the influence of petrogenesis on calculation of the weathering index the method is based on a bivariate plot of the magmatic chemical variation mcv in granitoids and the degree of chemical weathering dcw the mcv axis must be based on an element that reflects magmatic processes and is also relatively immobile during rock weathering in this study tio 2 contents are utilized for the mcv the dcw axis is fundamentally defined by the ratios of more mobile to less mobile elements during weathering and hence many classical indices can be applied the improved value of the degree of chemical weathering dcw i for a weathered rock is derived by dcw i s mcv cv mcv 1 dcw 1 where mcv 1 is the measured composition e g tio 2 content of the weathered rock dcw 1 denotes the ratios of more mobile to less mobile elements of the weathered rock the s parameter is the slope of the least square linear regression for fresh granitoids in the mcv dcw relationship mcv cv is a correction factor which is given by the average point on the mcv axis e g average tio 2 of the fresh rocks this method is useful for evaluating the degree of weathering of various granitoids and enhances the practical application of many weathering indices

geochemistry of archean shales from the pilbara supergroup western australia archean clastic sedimentary rocks are well exposed in the pilbara block of western australia shales from turbidites in the gorge creek group ca 3 4 ae and shales from the whim creek group ca 2 7 ae have been examined the gorge creek group samples characterized by muscovite quartzchlorite mineralogy are enriched in incompatible elements k th u lree by factors of about two when compared to younger archean shales from the yilgarn block alkali and alkaline earth elements are depleted in a systematic fashion according to size when compared with an estimate of archean upper crust abundances this depletion is less notable in the whim creek group such a pattern indicates the source of these rocks underwent a rather severe episode of weathering the gorge creek group also has fairly high b content 85 29 ppm which may indicate normal marine conditions during deposition rare earth element ree patterns for the pilbara samples are characterized by light ree enrichment lanybn 7 5 and no or very slight eu depletion eueu 0 82 0 99 a source comprised of about 80 felsic igneous rocks without large negative eu anomalies felsic volcanics tonalites trondhjemites and 20 mafic ultramafic volcanics is indicated by the trace element data very high abundances of cr and ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for

the inqua dunes atlas chronologic database the inqua dunes atlas project has developed a global digital database of chronological information for periods of inland or continental sand dune accumulation and stabilization the database comprises information on the site location including coordinates dune type and stratigraphic context pertinent analytical information e g luminescence procedures and literature citations to the original data source this paper discusses the background to the project the concept and structure of the chronologic database that forms its core and gives some examples of the scope of the database and ways in which it can contribute to greater understanding of the spatial and temporal variability in dune development

sand drift events and surface winds in south central sweden from the deglaciation to the present abstract during the transition from the last glacial into the holocene interglacial the atmospheric circulation in the north atlantic area changed from a glacial mode influenced by the presence of large ice sheets into a system more similar to that of the present day this change had implications for wind temperature and precipitation patterns that can be traced in geological archives here we focus on reconstructing past wind directions over southern scandinavia as inferred from the net sediment transport direction of inland dunes in south central sweden we analysed single dunes and dune fields along a 540 km long s n transect with lidar light detection and ranging derived dems digital elevation models to determine their geomorphological type and the directional mode of the wind that led to their formation luminescence ages of sand drift and dune formation were compiled from previous studies allowing us to build a chronology of sand drift after the deglaciation of south central sweden the majority of the dunes appear to have been formed by westerly or northwesterly winds and stabilised 10 5 9 0 ka although this is rather close in time to the local deglaciation for the northern sites it is long after the disappearance of ice from the more southern sites the coeval dune stabilisation over such a large geographical area suggests that regional environmental conditions played an important role it is likely that an unstable climate in conjunction with low groundwater tables during the early holocene locally delayed vegetation from stabilising the dunes

aspects of climatic influence on the clay mineralogy and geochemistry of soils palaeosols and clastic sedimentary rocks climate strongly influences soil clay mineralogy and bulk chemical composition in humid climates chemical weathering is at its most intense and virtually all primary bedrock minerals suffer complete breakdown they are replaced by authigenic hydrated oxides of fe and al together with halloysite and kaolinite in deep profiles these minerals develop where the residence time of water in the soil is slight longer residence times lead to higher solute concentrations and the stabilization of smectite authigenic palygorskite and sepiolite may form in highly saline alkaline soils the stability of these precipitated minerals is problematic they may be metastable or even unstable all other clays found in soils are unstable being incomplete solid state hydrolysis products of substrate minerals the balance between stable metastable and unstable minerals and the rate of profile development are both much influenced by temperature rainfall and activities of soil biota themselves reflecting climate bedrock influence is greatest under conditions of low to moderate precipitation where unstable minerals persist local topography however also strongly influences both the rate and products of chemical weathering quite independently of climate on the grand scale tectonic factors may constrain the time available for profiles to develop hence the extent to which bedrock minerals survive or are altered mountain soils reflect local climate and bedrock composition much more than latitude the sediments delivered to major basins today do not reflect global soil distribution patterns the bulk composition of suspended sediment entering the indian ocean for example is rather similar to that entering the arctic ocean sediment dispersal patterns can also confuse climatic signals a problem not encountered with palaeosols authigenic clays formed within sedimentary basins and post depositional burial alteration of both sediments and buried soil profiles must lead to interpretational ambiguities climatic signals are likely to survive best in bulk compositional data although diagenetic reactions at depths in excess of about 2 km do not appear to be isochemical and in the distribution of more stable yet climatically sensitive minerals kaolinite as opposed to illite chlorite

formation of parabolic dunes from barchan and transverse dunes along israel s mediterranean coast the mediterranean coastal dunes of israel underwent a land use change during the second half of the 20th century due to intense agricultural and pastoral activity the coastal dunes were stripped of natural vegetation until the end of the first half of the 20th century the barchan and transverse dunes were shaped by strong southwesterly winter winds a decrease in human activity during the second half of the 20th century brought about a renewal of natural vegetation on the dune crest the only area with neither erosion nor deposition the establishment of vegetation on the crest changes the dynamics of these barchan and transverse dunes so that not all of the sand eroded from the windward side is carried to the lee slip face some is trapped by plants consequently there is a change in the shape of the windward slope from convex to concave and the dune gradually becomes parabolic in this study we trace the morphodynamics of the dunes by analysing 12 sets of aerial photographs which were taken from 1944 to 1995 the average rate of advance of 15 dunes has decreased from 3 4 m a 1 to 1 9 m a 1 while the vegetation cover has increased from 4 3 to 17 per cent during this period copyright 2002 john wiley sons ltd

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

geochemical character of silurian volcanism in sw ireland the dunquin group mid silurian of dingle southwest ireland is a sequence of basaltic to rhyolitic lavas and pyroclastic rocks interbedded with shallow to non marine sediments that records one of only four known outbreaks of silurian volcanicity south of the iapetus suture in the british isles new geochemical petrographic and field evidence indicate that the volcanic sequences exposed in the dunquin inlier and the islands of beginish and inishvickillane could have formed by fractionational crystallization in a layered repeatedly replenished basaltic magma chamber the site of which is probably coincident with an intense aeromagnetic anomaly to the southwest of inishvickillane the volcanic suite is subalkaline transitional between calc alkaline and tholeiitic and is non bimodal high lile hfse ratios and high lree concentrations suggest that the parent basaltic magmas were generated at a destructive continental margin although subduction may have ceased before eruption

alumina rich rocks from the early precambrian of the kaapvaal craton as indicators of paleosols and as products of other decompositional reactions within early archaean to early proterozoic pelites and volcanics of the kaapvaal craton rocks with above 20 al2o3 are widely distributed the alumina rich nature of these rocks is ascribed to decompositional reactions during which up to about 60 of the original material was leached out of the source rock and removed in solution many of these rocks also show diagenetic enrichment in k2o of up to 10 the decomposition reactions in many cases affected the source rocks without disturbing fine structures such as perlitic devitrification cracks in volcanic glass granules the origin of the majority of these rocks can be ascribed to decomposition during subaerial weathering they represent paleosols for other occurrences the stratigraphic context rules out an explanation as paleosols the origin of this type is ascribed to subaqueous decomposition of lavas or tuffs assisted by hydrothermal exhalations it is shown that alumina rich rocks in greenschist belts almost exclusively formed subaqueously whereas the younger occurrences mostly are of weathering origin geotectonic differences are invoked to explain this contrast rocks of similar chemical composition are described from the canadian shield zimbabwe western australia india and the baltic shield they illustrate that the preservation potential of these rocks is high only the study of the stratigraphic context will allow a conclusion on whether a particular occurrence is the product of weathering or subaqueous decomposition

mapping lithofacies and pore fluid probabilities in a north sea reservoir seismic inversions and statistical rock physics reliably predicting lithologic and saturation heterogeneities is one of the key problems in reservoir characterization in this study we show how statistical rock physics techniques combined with seismic information can be used to classify reservoir lithologies and pore fluids one of the innovations was to use a seismic impedance attribute related to the vp vs ratio that incorporates far offset data but at the same time can be practically obtained using normal incidence inversion algorithms the methods were applied to a north sea turbidite system we incorporated well log measurements with calibration from core data to estimate the near offset and far offset reflectivity and impedance attributes multivariate probability distributions were estimated from the data to identify the attribute clusters and their separability for different facies and fluid saturations a training data was set up using monte carlo simulations based on the well log derived probability distributions fluid substitution by ga

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

modal and geochemical compositions of the lower silurian clastic rocks in north qilian nw china implications for provenance chemical weathering and tectonic setting abstract the north qilian orogenic belt records the transition from ordovician marine back arc basin to early devonian terrestrial molasse basin as the central qilian block was sutured to the north china craton the detrital framework and geochemical composition of lower silurian sedimentary rocks within the north qilian belt record the provenance tectonic setting and a variety of sedimentary processes that operated during transport from source to sink the petrological and geochemical characteristics of sandstones siltstones and shales in the western segment of the north qilian belt indicate a generally low degree of chemical weathering of source area s and limited sorting prior to deposition these characteristics suggest an active tectonic setting in contrast samples studied from the eastern part of the north qilian belt indicate low to moderate chemical weathering and low to moderate hydraulic sorting such characteristics imply a more stable tectonic setting geochemical data including eu eu ti nb th sc and co th ratios suggest contrasting source regions for the western and eastern segments of the north qilian belt sources in the west included basement rocks of the central qilian block and the north china craton in addition western sources may have included mafic rocks located within the north qilian arc in contrast data derived from eastern samples suggest a felsic provenance that probably formed part of the basement complex in the central qilian block and the north china craton overall detrital and geochemical data combined with the regional geology suggest a foreland basin setting that formed during collision of the central qilian block with the north china craton

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

the sturgeon falls paleosol and the composition of the atmosphere 1 1 ga bp a paleosol is exposed along the north bank of the sturgeon river some 25 km sw of baraga michigan the paleosol was developed on hydrothermally altered keweenawan basalt and is overlain by the jacobsville sandstone textures mineralogy and chemical composition change gradually upwards from unweathered metabasalt through the paleosol to the contact of the paleosol with the jacobsville sandstone many of these changes are similar to those in modern soils developed on basaltic rocks however k has clearly been added to the paleosol probably by solutions which had equilibrated with k feldspar in the jacobsville sandstone the keweenawan basalt was oxidized quite extensively during its conversion to greenstone during weathering the remaining fe2 was oxidized to fe3 and was retained in the paleosol the composition of the parent greenstone and its change during weathering can be used to define an approximate lower limit to the ratio of the o2 pressure to the co2 pressure in the atmosphere during the formation of the paleosol formula see text free o2 must have been present in the atmosphere 1 1 ga ago but its partial pressure could have been 10 3 times lower than in the atmosphere today

rapid oceanic and atmospheric changes during the younger dryas cold period the younger dryas event which began approximately 12 900 years ago was a period of rapid cooling in the northern hemisphere driven by large scale reorganizations of patterns of atmospheric and oceanic circulation 1 3 environmental changes during this period have been documented by both proxy based reconstructions 3 and model simulations 4 but there is currently no consensus on the exact mechanisms of onset stabilization or termination of the younger dryas 5 8 here we present high resolution records from two sediment cores obtained from lake krakenes in western norway and the nordic seas multiple proxies from lake krakenes are indicative of rapid alternations between glacial growth and melting during the later younger dryas meanwhile reconstructed sea surface temperature and salinity from the nordic seas show an alternation between sea ice cover and the influx of warm salty north atlantic waters we suggest that the influx of warm water enabled the westerly wind systems to drift northward closer to their present day positions the winds thus brought relatively warm maritime air to northern europe resulting in rising temperatures and the melting of glaciers subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice which forced the westerly winds back to the south cooling northern europe we conclude that rapid alternations between these two states immediately preceded the termination of the younger dryas and the permanent transition to an interglacial state the impact of freshwater pulses released from northern hemisphere ice sheets on the north atlantic meridional overturning circulation has been suggested as a likely mechanism for the younger dryas cooling 7 11 in addition a responsive sea ice cover has been proposed as a mechanism that could rapidly alter the heat exchange between the ocean and atmosphere during the last glacial period 12 13 the roles of the ocean and the atmosphere in triggering the climate shifts around the younger dryas are much discussed 9 these hypotheses are difficult to resolve partly because the temporal resolution of most palaeoclimate archives is too coarse to enable the anatomy of the younger dryas stadial to be adequately described 14 to address these questions we here present a lake sediment record at sub annual resolution together with new data on the sea surface conditions of the norwegian atlantic current nwac throughouttheyoungerdryasstadial fig 1

groundwater ferricretes from the silurian of ireland and permian of the spanish pyrenees abstract haematite nodule horizons occur in alluvial lacustrine deposits from the mill cove formation silurian of dingle ireland and the unidad roja superior permian of the spanish pyrenees these horizons generally less than 1 m thick are not associated with palaeosol profiles but are hosted by laminated or structureless bioturbated mudstones to sandstones the sequences contain weakly developed calcrete profiles the haematite nodules are interpreted as having formed around fluctuating water tables and are analogous to present day groundwater ferricretes laterites or plinthites fe2 mobilised during periods of reducing groundwaters was segregated into ferric oxide nodules during falls in the water table or during influxes of oxygenated meteoric waters the prevailing climate during deposition of both sequences was probably semi arid and the presence of ferricrete like horizons is not evidence of humid climates the horizons represent early diagenetic effects not related to prevailing soil moisture regime

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

geochemical records of qionghai lake sediments in southwestern china linked to late quaternary climate changes abstract knowledge of the chemical weathering history under the subtropical monsoonal climate will help to resolve the discrepancies regarding how climate conditions constrain chemical weathering major element and rare earth element ree compositions of the qionghai lake sediments in sichuan province southwestern china were analyzed aiming to provide information on sediment source discrimination and history of chemical weathering intensities and its responses to variations of indian summer monsoon ism and paleoclimate conditions as revealed by the a cn k diagram and other provenance proxies including tio2 zr ratio th sc vs zr sc and la th vs hf diagrams as well as the ree characteristics the source of qionghai lake sediments was felsic rocks additionally these sediments were subjected to small changes in provenance sedimentary sorting and recycling and weak diagenesis after deposition and or metasomatism indicating original signals were maintained on the intensity of chemical weathering of source area the chemical weathering intensities inferred from cia chemical index of alteration values have significantly fluctuated over the past 28 kyr reflecting three stages of paleoclimate evolution which is consistent with grain size characteristics carbonate contents low frequency magnetic susceptibilities toc and biomarker proxy paq the cia values changed significantly during the typical warm and cold climate events including the last glacial maximum heinrich 1 cold event younger dryas and holocene climatic optimum and generally exhibited an increasing trend in amplitude correspondingly in concert with the climate shifting from cold and dry to warm and humid conditions generally warm and humid climate conditions suggest enhanced chemical weathering intensity whereas weak chemical weathering denotes cold and dry climate in the ism region in addition sequential variations of the cia values during the past 28 kyr may reflect changing chemical weathering processes in responses to the varying intensities of indian summer monsoon and the climate conditions forced by the northern hemisphere solar insolation

modeling elastic properties in carbonate rocks carbonate limestone and dolomite reservoirs account for approximately 50 of oil and gas production worldwide however seismic responses in carbonate rocks are poorly understood in addition dhi ranking and avo classification systems developed for clastic rocks are unlikely to be applicable to carbonate rocks an accurate and physically sound carbonate rock physics model is needed to address these technical issues

a new velocity model for clay sand mixtu res1 none of the standard porosity velocity models e g the time average equation raymer s equations is satisfactory for interpreting well logging data over a broad depth range clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and p wave transit time because clays are composed of fine sheet like particles they normally form pores with much smaller aspect ratios than those associated with sand grains this difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations a velocity model for clay sand mixtures has been developed in terms of the kuster and toksoz effective medium and gassmann theories in this model the total pore space is assumed to consist of two parts 1 pores associated with sand grains and 2 pores associated with clays including bound water the essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays because of this porosity in shales affects elastic compliance differently from porosity in sand stones the predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandstones and shales

abrupt reorganization of north pacific and western north american climate during the last deglaciation dramatic hydroclimate shifts occurred in western north america during the last deglaciation but the timing and mechanisms driving these changes are uncertain and debated and previous modeling has largely relied on linear interpolations between equilibrium snapshot simulations using a published transient climate simulation and a range of proxy records we analyze the region s climate evolution in order to identify the mechanisms governing hydroclimate shifts a rapid loss of ice around 14 000 years ago causes an abrupt reorganization of the circulation which precipitates drying and moistening of southwestern and northwestern north america respectively the atmospheric circulation transitions between two states on a timescale of decades to centuries during which time the westerly jet shifts north by about seven degrees in contrast to previous studies we find that changes in the water budget of western north america prior to this event are not attributable to variations in the position of the jet but rather to the intensity of moisture transport into the continent

storminess variation during the last 6500 years as reconstructed from an ombrotrophic peat bog in halland southwest sweden cores taken from an ombrotrophic peat bog in the coastal zone of halland southwest sweden were examined for wind transported mineral grains pollen and humidity indicators the core covers the period from 6500 cal yr bp to present ombrotrophic conditions existed from ca 4200 cal yr bp onwards bog surface wetness fluctuated strongly until ca 3700 cal yr bp with an apparent dominance of dry summer conditions from 4800 4500 cal yr bp local wet shifts occurred around 4300 2800 2400 and 1500 cal yr bp whereas the most recent 600 years of the record show increasingly dry conditions mineral grain content interpreted as aeolian sand influx asi was used as a proxy for winter storm frequency and intensity until ca 1500 cal yr bp after which increasing human impact as reconstructed by pollen analysis became a second important potential cause for increased sand drift strongly increased storminess occurred at 4800 4200 2800 2200 1500 1100 and 400 50 cal yr bp indicating a dominance of cold and stormy winters during these periods many of these storm periods apparently coincide with storm events in other sites in southwestern scandinavia suggesting that our asi record reflects a regional scale climatic signal furthermore these stormy periods correlate to well known cold phases in the north atlantic region suggesting a link to large scale fluctuations in atmospheric circulation patterns less

zircon u pb ages and hf isotopes of paleozoic metasedimentary rocks from the habahe group in the qinghe area chinese altai and their tectonic implications abstract as one of the largest accretionary orogens in earth s history the central asian orogenic belt has attracted much attention in the past two decades but there are still many unresolved issues regarding its tectonic nature and evolution this is the case with the chinese altai whose tectonic provenance remains controversial especially for the paleozoic era as the most widely exposed meta sedimentary rocks in the chinese altai the habahe group was previously considered as representing a component of precambrian micro continent forming at a passive continental margin our new u pb data for detrital zircons from the habahe group in the qinghe region of the eastern chinese altai indicate that the strata were deposited from the late silurian to early devonian 427 405 ma and experienced regional metamorphism in the middle devonian 383 9 ma as constrained by the age of youngest detrital zircons 427 13 ma the age 405 3 ma of the tonalite that intrudes the habahe group and the metamorphic age of 383 9 ma additionally the majority of zircons from the habahe group have positive ehf t values 0 22 15 02 these data combined with geochemical features and maturity of the sedimentary rocks indicate an immature provenance for the habahe group with the source materials mainly derived from a juvenile crust with some old continental components the juvenile crust was most likely formed in a subduction zone developing in the chinese altai during early middle paleozoic time new geochemical data presented in this study suggest that the chinese altai was a transitional arc during early paleozoic time similar to the japan type arc with involvements of old continental components therefore it is proposed that the chinese altai was likely rifted from the south margin of the siberia craton probably related to the break up of the rodinia supercontinent and then experienced accretion and reworking with the subduction of the paleo asian ocean during early paleozoic time

reconstructing a high paleolatitude mesozoic paleoenvironment from a truncated and deeply buried regolith norwegian north sea abstract the paleoregolith in this study was unconformably overlain by lower cretaceous valanginian marine deposits of the asgard formation and buried below two kilometers of sediments on the utsira high norwegian north sea the upwards intensification of chemical alteration manifested in the replacement of feldspars by clays leaching of base cations and reduced mechanical rock strength in addition to the presence of terrestrial biotitic features suggested weathering during subaerial exposure of the utsira high during the mesozoic the paleoregolith can be divided into three weathering facies altered coherent rock saprock and saprolite whereas the absence of true soil horizons suggested erosional truncation of the regolith before burial possible remnants of the eroded soil were identified as pedogenic mud aggregates in the overlying asgard formation bearing similar compositional characteristics as the saprolite clay mineralogy bulk geochemical composition micromorphology and depth of biotic features were used to reconstruct the paleoenvironmental conditions that prevailed during the formation of the regolith in the mesozoic north sea our results point to a regolith formation under periodically water restricted conditions promoting the co existence of interstratified illite smectite beidellite and kaolinite deep presence of endomycorrhizae the fungal extension of the root structure and precipitation of iron oxide nodules application of recently developed geochemical climofunctions indicated that the regolith formed in a mesic 10 12 c and subhumid 1157 1406 mm yr environment and under strongly acidic soil conditions ph 5 2 5 6

petrophysical seismic inversion conditioned to well log data methods and application to a gas reservoir hydrocarbon reservoirs are characterized by seismic welllog and petrophysical information which is dissimilar in spatial distribution scale and relationship to reservoir properties we combine this diverse information in a unified inverse problem formulation using a multiproperty multiscale model linking properties statistically by petrophysical relationships and conditioningthemtowell logdata twoapproacheshelpus 1markov chainmontecarlosampling whichgeneratesmanyreservoir realizationsforestimatingmediumpropertiesandposteriormarginalprobabilities and2optimizationwithaleast squaresiterativetechniquetoobtainthemostprobablemodelconfiguration our petrophysical model applied to near vertical anglestacked seismicdataandwell logdatafromagasreservoir includesadeterministic component based on a combination of wyllie and wood relationships calibrated with the well log data and a random component based on the statistical characterization of the deviations of well log data from the petrophysical transform at the petrophysical level the effects of porosity and saturation on acoustic impedance are coupled conditioning the inversion to well log data helps resolve this ambiguity the combination of well logs petrophysics and seismic inversion builds on the correspondingstrengthsofeachtypeofinformation jointlyimproving 1 cross resolution of reservoir properties 2 vertical resolution of property fields 3 compliance to the smooth trend of property fields and 4 agreement with well log data at well positions

holocene environmental change in subarctic aeolian dune fields the chronology of sand dune re activation events in relation to forest fires palaeosol development and climatic variations in finnish lapland sand dune stratigraphy radiocarbon dated charcoal layers palaeosol development and luminescence dating are used to reconstruct the holocene environmental history of the dune fields in finnish lap

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

elastic anisotropy of shales accompanying the resource potential of gas shales is a new interest in understanding the physical and petrophysical properties of shales shale by geochemical or stratigraphic measures is arguably the most common lithology encountered in sedimentary basins despite this shales remain little studied while engineers and explorationists focused on conventional reservoirs geophysicists did this knowing full well that often a reflection coefficient from a reservoir was controlled by the shale properties of the cap rock we compensated for this ignorance by arguing that shales are deposited in deepwater environments in which lateral and vertical changes are slow and therefore inconsequential we further compounded this ignorance by assuming that the shales were isotropic an example of the consequences of this ignorance was clearly documented by margesson and sondergeld 1999 engineers share culpability for this ignorance too since most of the drilling problems occur in shales and most of the lithologies d

barchan dunes stabilized under recent climate warming on the northern great plains we use light detection and ranging lidar imagery and optical stimulation luminescence dating to show that stable parabolic dunes on the canadian prairies originated from active barchan dunes 200 years ago residual dune ridges marking former lower stoss slope positions of migrating dunes record the transformation of barchan dunes to parabolic dunes between a d 1810 and 1880 parabolic dunes stabilized by ca a d 1910 with a few larger dunes and blowouts still active today a dry cool climate permitted sand transport to out compete vegetation stabilization and with lowered water tables maintain desert like barchan dunes with bare interdune sand sheets these findings explain why dune fields of the southern canadian prairies are currently more active than those of the united states great plains and the observation that dunes have stabilized under twentieth century warming our results emphasize the importance of viewing dune field responses to short term disturbances in the context of longer term system response particularly when relatively modest climatic changes can cause major shifts in dune activity

palaeoclimatic evidence from sand seas abstract sand seas can be an important source of information on the quaternary history of many deserts because sand seas appear to react sensitivity to climatic changes the quality of palaeoenvironmental information obtained from them is frequently much better than that from adjacent rocky desert areas patterns of dune alignments may be used to reconstruct the wind directions that formed currently inactive or fixed dunes and thus can provide information on palaeocirculation patterns the climatic conditions under which these dunes formed can be examined using palaeoclimatic models to explore the combinations of wind velocity rainfall and evaporation rates required to reactivate them choice of appropriate values for these parameters may be hampered by the problems of dating episodes of dune activity in many sand seas the best palaeoclimatic information comes from studies of interdune lacustrine or playa deposits which may reflect increased local rainfall or higher groundwater discharge or greater penetration of the sand sea by rivers with headwaters outside the desert caution should be taken in the interpretation of such deposits for juxtaposition of aquatic and aeolian environments can occur even in modern hyperarid and seas the record of climatic changes preserved in the deposits of modern sand seas suggests that periods of dune formation may have been interrupted by long periods of stability which may also have included deposition of interdune lacustrine deposits for example within the past 40 000 years active dune formation in many sand seas appears to have been restricted to the interval between about 20 000 and 12 000 yr b p and to the late holocene approximately 1 4 to 1 3 rd of the time

chemistry and mineralogy of precambrian paleosols at the base of the dominion and pongola groups transvaal south africa abstract we have studied alteration zones found between sedimentary rocks of the lowest proterozoic dominion and archean pongola groups and underlying granitic rocks transvaal south africa the alteration zones have a transitional lower boundary primary igneous minerals are gradually destroyed upward toward the contact with overlying sedimentary rocks ca mg na p and mn are progressively lost upwards in the zone the chemical and mineralogical variations and available stratigraphic evidence are all consistent with the interpretation that these zones are paleosols formed by precambrian weathering 2 8 3 0 ga ago after formation the paleosols underwent metasomatism and metamorphism sericite now present in the paleosols was probably formed by low temperature potassium metasomatism of original clays andalusite in the pre pongola paleosol was probably formed by metamorphism of original clays in impermeable zones which prevented groundwater flow and potassium metasomatism the dominion paleosol was investigated at three localities the effects of weathering were similar at the three sites except for the behavior of iron one site lost about 20 of iron whereas the other sites lost 75 and 80 of initial iron content the differences in iron loss may be due to variation in soil ventilation and diffusion of atmospheric gases as a function of grain size and topography variations in iron loss may be used to place some constraints on the composition of the precambrian atmosphere given constraints imposed by dominion paleosols overlying uraniferous conglomerates requirements for chemical weathering and the greenhouse effect and possible presence of non diffusing photochemical oxidants the partial pressures of oxygen and carbon dioxide gases probably are in the ranges po1 0 02 to 0 5 pal present atmospheric level and pco2 5 to 30 pal

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

late pleistocene eolian features in southeastern maryland and chesapeake bay region indicate strong wnw nw winds accompanied growth of the laurentide ice sheet abstract inactive parabolic dunes are present in southeastern maryland usa along the east bank of the potomac river more elongate and finer grained eolian deposits and paha like ridges characterize the potomac river patuxent river upland and the west side of chesapeake bay these ridges are streamlined erosional features veneered with eolian sediment and interspersed with dunes in the low relief headwaters of potomac and patuxent river tributaries axis data for the dunes and ridges indicate formation by wnw nw winds optically stimulated luminescence and radiocarbon age data suggest dune formation from 33 15 ka agreeing with the 30 13 ka ages denny c s owens j p sirkin l rubin m 1979 the parsonburg sand in the central delmarva peninsula maryland and delaware u s geol surv prof pap 1067 b 16 pp suggested for eolian deposits east of chesapeake bay age range and paleowind direction s for eolian features in the bay region approximate those for late wisconsin loess in the north american midcontinent formation of midcontinent loess and bay region eolian features was coeval with rapid growth of the laurentide ice sheet and strong cooling episodes 18o minima evident in greenland ice cores age and paleowind direction coincidence for eolian features in the midcontinent and bay region indicates strong mid latitude wnw nw winds for several hundred kilometers south of the laurentide glacial terminus that were oblique to previously simulated anticyclonic winds for the last glacial maximum

origin of the wunugetushan porphyry cu mo deposit inner mongolia ne china constraints from geology geochronology geochemistry and isotopic compositions abstract the wunugetushan porphyry cu mo deposit is located in the southeastern margin of the mongol okhotsk orogenic belt and in the northwestern segment of the great xing an range ne china the orebodies of this deposit are mainly hosted in the monzogranitic porphyry stock and in contact with the granitic porphyry dyke and biotite granite batholith the shrimp zircon u pb dating of the granitic porphyry dyke yielded ages of 201 4 3 1 ma 2 mswd 1 5 these results indicate that the magmatism in the wunugetushan area might have occurred at ca 201 ma in the early jurassic and that the mineralization age ca 181 ma of this deposit is later than the age of intrusive granitic porphyry in the area geochemically the wunugetushan granitoids belong to high k calc alkaline and shoshonitic series enriched in k rb nd and pb and depleted in sr nb ti and p with negative eu anomalies in situ hf isotopic analyses of zircons using la mc icp ms indicate that the ehf t values for zircons from a granitic porphyry sample vary from 2 4 to 11 8 and that the corresponding crustal model ages tdmc vary from 483 to 1088 ma the least altered monzogranitic porphyry granitic porphyry and biotite granite yielded relatively uniform end t values from 1 0 to 0 6 and low 87sr 86sr i ratios ranging from 0 704387 to 0 708385 the geochemical and sr nd hf isotopic data for the granitoids indicate that the source magma for these rocks could be derived from a juvenile lower crust the 34s values of sulfides show a narrow range 0 76 to 3 20 similar to those of magmatic sulfur further implying a lower crust origin based on the results of this study and the regional geodynamic evolution it is proposed that the formation of the wunugetushan deposit and associated granitoids should be linked to the southeastward subduction of the mongol okhotsk oceanic plate beneath the erguna massif during the early jurassic and that the monzogranitic porphyry intrusions in wunugetushan area probably provided important ore metals responsible for the large scale cu mo mineralization

a practical model for organic richness from porosity and resistivity logs a practical method the delta log r technique for identifying and calculating total organic carbon in organic rich rocks has been developed using well logs the method employs the overlaying of a properly scaled porosity log generally the sonic transit time curve on a resistivity curve preferably from a deep reading tool in water saturated organic lean rocks the two curves parallel each other and can be overlain since both curves respond to variations in formation porosity however in either hydrocarbon reservoir rocks or organic rich non reservoir rocks a separation between the curves occurs using the gamma ray curve reservoir intervals can be identified and eliminated from the analysis the separation in organic rich intervals results from two effects the orosity curve responds to the presence of low density low velocity kerogen and the resistivity curve responds to the formation fluid in an immature organic rich rock where no hydrocarbons have been generated the observed curve separation is due solely to the porosity curve response in mature source rocks in addition to the porosity curve response the resistivity increases because of the presence of generated hydrocarbons the magnitude of the curve separation in non reservoirs is calibrated to total organic carbon and maturity and allows for depth profiling of organic richness in the absence of sample data this method allows organic richness to be accurately assessed in a wide variety of lithologies and maturities using common well logs

delayed hydrological response to greenland cooling at the onset of the younger dryas in western europe during the younger dryas cold event about 12 800 years ago environmental change in western europe seems to occur 170 years after cooling over greenland lake sediment analyses confirm this delay and suggest european hydrological and vegetation change occurred only after the build up of sea ice in the north atlantic pushed the westerly wind system south

a monte carlo approach to the joint estimation of reservoir and elastic parameters from seismic amplitudes inversion of seismic data and quantification of reservoir properties such as porosity lithology or fluid saturation are commonly executed in two consecutive steps a geophysical inversion to estimate the elastic parameters and a petrophysical inversion to estimate the reservoir properties we combine within an integrated formulation the geophysical and petrophysical components of the problem to estimate the elastic and reservoir properties jointly we solve the inverse problem following a monte carlo sampling approach which allows us to quantify the uncertainties of the reservoir estimates accounting for the combination of geophysical data uncertainties the deviations of the elastic properties from the calibrated petrophysical transform and the nonlinearity of the geophysical and petrophysical relations we implement this method for the inference of the total porosity and the acoustic impedance in a reservoir area combining petrophysical and seismic information in our formulation the porosity and impedance are related with a statistical model based on the wyllie transform calibrated to well log data we simulate the seismic data using a convolutional model and evaluate the geophysical likelihood of the joint porosity impedance models applying the monte carlo sampling method we generate a large number of realizations that jointly explain the seismic observations and honor the petrophysical information this approach allows the calculation of marginal probabilities of the model parameters including medium porosity impedance and seismic source wavelet we show a synthetic validation of the technique and apply the method to data from an eastern venezuelan hydrocarbon reservoir satisfactorily predicting the medium stratification and adequate correlation between the seismic inversion and well log estimates for total porosity and acoustic impedance

the metamorphic characteristics of metapelites of the mashan group in mashan area eastern heilongjiang province china constraint on the crustal evolution of the jiamusi massif abstract mashan complex in the southeastern margin of the jiamusi massif has traditionally been interpreted to be the oldest stratigraphic sequence in eastern ne china here we investigated the mashan complex in the ximashan area and present lots of new la icp ms zircon u pb petrological and mineralogical chemical data in addition with phase equilibria modeling to constrain the timing of metamorphism p t conditions and the p t path of the mashan complex and furthermore to deduce the crustal evolution of the jiamusi massif the protoliths of the metapelites from the mashan complex in the ximashan area are clay rocks and sandstones whose provenance is dominantly felsic rocks which formed from a continental island arc three metamorphic generation assemblages m2 m4 are recognized in the studied samples a peak granulite facies stage a post peak near isothermal decompression stage and a late near isobaric cooling stage which together define a clockwise p t path it reveals important information related to the collision orogeny subsequent uplift and post collision process zircon u pb dating of two metapelitic samples yielded metamorphic ages of the older group varying from 535 6 to 480 5 ma which can be perfectly correlated with the age range 501 6 to 498 6 ma of magmatic activities recorded by the gneissic granite sample the data presented here together with those published allow us to preliminarily infer that the peak of the granulite facies metamorphism in the ximashan area of the jiamusi massif might have occurred at 530 500 ma the younger of the metamorphic ages 476 453 ma should be regarded as the age of late stage therefore a collision orogeny regime is favored to interpret the metamorphic evolution of metapelites of the mashan group in the mashan area

deep weathering of granitic rocks a case of tunnelling in nw spain abstract this paper highlights a case of extensive development of saprolith from granitic bedrock in nw spain the weathering front at the study area extends to more than 250 m in depth the drilling of a railway tunnel madrid galicia high speed line through the bedrock and saprolith resulted in significant technical issues and economic losses cross sections revealing the 3d complexity of saprolith development are mainly based on fieldwork boreholes laboratory tests and the excavation works saprock is always observed overlying unweathered igneous bedrock two saprolite facies one clay rich and the other clay poor overlie the saprock the recognition is based on several criteria these deposits gradually thicken from the boundaries between the granitoid and metasedimentary roof pendants factors controlling saprolith development are discussed and the chemical and mineralogical changes and trends that occur are described variations in some geotechnical properties and the loss of quality of the rock masses from an engineering perspective are also quantified

late eocene clay boron derived paleosalinity in the qaidam basin and its implications for regional tectonics and climate abstract the qaidam basin located on the northeastern tibetan plateau and containing cenozoic sediments with a maximum thickness of 12 000 m is an ideal place to study the phased uplift of the ne tibetan plateau and regional climate change the estimation of the paleosalinity of sedimentary environments not only helps to evaluate the evolution of lakes in this region but offers insights into contemporaneous climate change we present detailed geochemical and mineralogical investigations from the lacustrine interval of the hongliugou section in the northern qaidam basin to reconstruct salinity fluctuations in the paleolake during the late eocene era 42 0 35 5 ma the clay mineral assemblages mainly contain smectite illite chlorite kaolinite and irregular illite smectite mixed layers clay boron derived paleosalinity estimates equivalent boron content couch s paleosalimeter and b ga ratios along with other proxies sensitive to salinity changes e g rb k ratios and ostracod assemblages collectively indicate an overall brackish sedimentary environment with a higher salinity period at approximately 40 0 39 2 ma this higher salinity period indicates a more arid environment and is probably related to global cooling however the global cooling in late eocene cannot explain the overall stable long term salinity pattern implying that other factors exist we propose that the migration of the yiliping depression depocenter in the northern qaidam and increased orographic rainfall induced by late eocene tectonic activity at the northern margin of the basin might have partly offset the increase in salinity driven by global cooling

paleodust deposition and peat accumulation rates bog size matters abstract we present a high resolution peat paleodust and accumulation rate record spanning the last 8300 years from draftinge mosse 400 ha southern sweden 57 06 27 6 n 13 42 54 1 e the record was analysed for peat accumulation rates par elemental concentrations mineralogy and plant macrofossil content five periods of increased mineral deposition were recorded the first event occurred between 6280 and 5570 cal bp during the fen to bog transition this is followed by four atmospheric mineral dust events de which were recorded in the ombrotrophic section of the sequence at cal bp 2200 1385 1150 830 590 and from 420 to the present statistical analysis and elemental ratios indicated that both the mineralogy and grain size shifted when the system transitioned from fen into bog showing that the governing transport process shifted with the peatland succession stages this highlights the importance of identifying peatland succession stages within peat paleodust studies following all four de increases in par were observed implying a coupling to dust deposition comparison of de and par with a paleodust record from store mosse a 20 times larger bog located ca 18 km away kylander et al 2016 showed that both par and dust deposition are largely represented by single core reconstructions indicating that they are driven by a common climate forcing mechanism however higher par and dust deposition rates were observed in the more moderately sized draftinge mosse suggesting that the size of the bog is important to consider in peat paleodust studies furthermore the smaller bog responded more rapidly to hydrological changes indicating that the size of the bog affects its buffering capacity authigenic carbonates observed here during episodes of rapid peat growth coincide with changes in ree ratios indicating that authigenic peat processes potentially cause ree fractionation

early holocene terrestrial climatic variability along a north atlantic island transect palaeoceanographic implications a synthesis of the early holocene climatic development in the north atlantic region is presented based on three previously published lake records from southern greenland lake n14 iceland lake torfadalsvatn and the faroe islands lake lykkjuvotn the interval 11500 8500 cal bp has been divided into five phases with respect to the inferred strength of the north atlantic current nac and irminger currents ic phase 1 11 500 10 750 cal bp was characterised by the first establishment of the nac and ic in the vicinity of the studied sites interrupted by the preboreal oscillation around 11 200cal bp phase 2 10 750 10 100 cal bp was marked by a further warming step in southern greenland rather concordant with a change into colder and more variable winters on the faroe islands it is proposed that this could partly be related to a series of melt water outbursts disturbing the thermohaline circulation in the eastern atlantic ocean resulting in a warming trend in the western region during phase 3 10 100 9400cal bp the strength of the ic reaching northwestern iceland intensified a more stable regime in surface circulation was established at the onset of phase 4 9400 8900 cal bp in southern greenland and was followed by a change towards further warm conditions on iceland at the onset of phase 5 8900 8500 cal bp c 2007 elsevier ltd all rights reserved

tropical chemical weathering of hillslope deposits and bedrock source in the aburra valley northern colombian andes abstract tropical chemical weathering produces extensive lateritization and formation of deep weathering profiles both processes are fundamental to landscape evolution and slope instability the aburra valley of the northern colombian andes is characterized by tropical conditions the valley slopes are mostly covered by hillslope deposits originating from four basement rock suites which comprise contrasting granitoid volcanic sedimentary ophiolitic and metamorphic sources respectively tropical chemical weathering of the aburra hillslope deposits and their respective bedrock were examined using x ray fluorescence and x ray diffraction analysis to document and quantify their chemical weathering profiles compositions and mineralogical properties the chemical index of alteration cia loss on ignition loi and the mobiles index imob were used to quantify the degree of weathering of hillslope deposits and bedrock source weathering trends were analyzed using a cn k and a cnk fm diagrams the material mantling the slopes in the aburra valley records an intense weathering history chemical weathering is characterized by increased development of clay minerals kaolinite halloysite and iron and aluminum sesquioxides lateritization characterizes the final stage of the weathering profiles concentrations of cao na2o k2o decrease markedly in the weathering products compared to the fresh bedrock source whereas concentrations of al2o3 fe2o3 and mgo increase significantly cia ratios of matrix slope deposits derived from all four sources near 100 whereas those of boulder slope deposits and saprolites are lower but exceed source rock values different a cn k weathering paths are evident for each lithotype validating the correlation established between the hillslope deposits and their various parents chemical weathering indices in some samples are strongly influenced by the presence of sesquioxides as reflected by high loi anomalously low cia and varying enrichment trends on the a cnk fm diagrams consequently different chemical indices based on different criteria need to be combined to obtain best results as illustrated here by the combination of loi cia and imob the overall results suggest that tropical conditions have dominated for a long time in the northern colombian andes leading to uniformly high weathering indices in matrix slope deposits irrespective of parent lithotype prolonged warm and humid conditions could thus be responsible for the weathering and remobilization of extensive old hillslope deposits during the quaternary however in addition to the influence of climatic factors tectonism has also undoubtedly influenced slope evolution in the aburra valley

abrupt regime shifts in the north atlantic atmospheric circulation over the last deglaciation we analyze modeling results of the north atlantic atmospheric winter circulation from a transient climate simulation over the last 21 000 years in agreement with previous studies we find that the midlatitude jet stream assumes a strong stable and zonal disposition so long as the north american ice sheets remain in their continent wide last glacial maximum lgm configuration however when the laurentide lis and cordilleran ice sheets separate ca 14 000 years ago the jet stream abruptly changes to a tilted circulation regime similar to modern the proposed explanation is that the dominant stationary wave source in the north atlantic sector changes from the lis to the cordilleran mountain range during the saddle collapse as long as the lis dominates the circulation retains the zonal lgm state characterized by prevalent stationary wave reflection in the subtropical north atlantic when the cordillera takes over the circulation acquires its modern disposition

the lower crust of the dharwar craton southern india patchwork of archean granulitic domains u pb geochronological major and trace element and isotope geochemical data identify crustal domains of contrasted petrological origins and histories in the lower crust of the dharwar craton all affected by granulite facies metamorphism and deformation in the neoarchean four lower crustal domains have been identified and investigated across the neoarchean amphibolite to granulite facies transition zone 1 in the southern part of the western dharwar craton wdc high grade metamorphism affects rocks formed before 3 0 ga high grade metamorphism is recorded at ca 2 51 ga followed by possible complex cooling and resetting until 2 2 ga 2 the br hills mm hills domain represents the lower crust of the central dharwar province cdp which is here defined as a transitional crust between the old 3 ga wdc and the eastern dharwar province edp not older than 2 7 ga this granulitic domain contains the oldest rocks of the dharwar craton with ttg suites formed at ca 3 4 ga and ca 2 6 ga suites of probable crustal recycling origin both suites are involved in 2513 5ma granulite facies metamorphism 3 the nilgiri granulitic domain is tectonically juxtaposed with the deepest level of the wdc as a consequence of neoarchean dextral slip along the moyar shear zone the massif consists of rocks of orogenic affinities formed between 2 70 and 2 56 ga and overprinted by granulite facies metamorphism at 2518 10 ma 4 the krishnagiri domain exposes the deepest levels of the eastern dharwar craton it is composed of ttg and calc alkaline igneous protoliths formed between 2 55 and 2 53 ga migmatization in the upper part of the domain took place at 2507 6ma and granulite facies overprint in the deepest parts of the domain is constrained at 2516 5 ma the krishnagiri domain was magmatically accreted to the lower crust of both the cdp and edp by interaction with mafic magmatism inducing reworking of the 2 7 2 6 ga or older overlying crust the nilgiri granulites share several temporal and petrological properties with the madras granulites that make the easternmost outcrop of the dharwar craton we tentatively suggest that the nilgiri and madras granulites evolved as parts of a common madras domain in the lower crust of the edp before activation of the moyar shear zone in this sense the nilgiri massif may be considered as an allochtonous unit in a context of neoarchean ultra hot orogeny in south india

variability and seasonality of north atlantic climate during the early holocene evidence from faroe island lake sediments based on their position in relation to major ocean currents palaeoclimatic archives in the faroe islands are expected to be sensitive recorders of variations in north atlantic circulation the multiproxy analysis magnetic susceptibility total carbon nitrogen and sulphur biogenic silica grains 255 mu m of a lacustrine record with both winter and summer climate indicators illustrates the variability of faroese climate during the early holocene c 11 300 10 240 cal yr bp and allows comparison with other records in the region our high resolution record suggests a period of predominantly winter cooling and increased storminess centred at c 11 150 cal yr bp followed by a period of stability between c 11 000 and 10 680 cal yr bp which correlates with a time when the north atlantic was particularly free of meltwater incursions after c 10 680 cal yr bp both winter and summer indicators show an increase in variability broadly synchronous with increased variability at other north atlantic sites within this time period a predominantly winter cooling centred at c 10 600 cal yr bp a winter summer cooling centred at c 10 450 cal yr bp and a winter summer cooling centred at c 10 300 cal yr bp are recorded these distinctive coolings correspond to periods of ice core delta o 18 inferred lowered atmospheric temperatures over greenland and the reoccurrence of meltwater outbursts at c 10 600 10 500 and 10 350 cal yr bp less

the loess cover of northeastern wisconsin abstract we present the first study of the distribution genesis and paleoenvironmental significance of late pleistocene loess in northeastern wisconsin and adjacent parts of michigan s upper peninsula loess here is commonly 25 70 cm thick upland areas that were deglaciated early and remained geomorphically stable preferentially accumulated loess by providing sites that were efficient at trapping and retaining eolian sediment data from 419 such sites indicate that the loess was mainly derived from proglacial outwash plains and to a lesser extent hummocky end moraines within and near the region particularly those toward the east of the loess deposits most of the loess was transported on katabatic winds coming off the ice sheet which entrained and transported both silt and fine sands the loess fines markedly and is better sorted distal to these source regions only minimal amounts of loess were deposited in this area via westerly winds this research 1 reinforces the observation that outwash plains and end moraines can be significant loess sources 2 provides evidence for katabatic winds as significant eolian transport vectors and 3 demonstrates that the loess record may be variously preserved across landscapes depending on where and when geomorphically stable sites became available for loess accumulation

early holocene dune field development in dalarna central sweden a geomorphological and geophysical case study bonasheden sweden s largest continuous dune field situated in the county of dalarna central sweden has been investigated using lidar light detection and ranging remote sensing ground penetrating radar as well as by field observations and luminescence dating the use of lidar in conjunction with geographic information system gis software proved to be efficient in mapping the inactive dune field and classifying the dune morphology especially when slope raster images were used the dunes have formed mostly by winds from the northwest nw and are of a transverse type still other dune types such as parabolic dunes and transverse dunes with a deviating orientation are present also there seems to be different generations of dunes suggesting a complex palaeowind environment with a change from predominantly north westerly winds to more westerly winds luminescence dating finally allows us to have an absolute chronology of the development of the bonasheden dune field revealing formation of the dune field closely following the de glaciation of this part of sweden c 10 5ka the well preserved transverse shape of the majority of the dunes suggests rapid stabilization by vegetation although sand drift still seems to have been active on a noticeable scale for at least 1500years and also occasionally and patchy as coversand deposition during the late holocene a simple model is proposed for the dune field development of bonasheden based on our findings this model is a useful addition since the majority of present day dune field models focus on the formation of parabolic dunes or large unvegetated dune fields our results suggest that most models cannot adequately simulate the formation of such small dune fields as that of bonasheden with apparently rapidly fixated transverse dunes in a previously glaciated now vegetated area less

comparative geochemistry of pleistocene and paleoproterozoic huronian glaciogenic laminated deposits relevance to crustal and atmospheric composition in the last 2 3 ga abstract comparison of the major and trace element geochemistry of glaciogenic laminated deposits of pleistocene and paleoproterozoic age from an area north of lake huron ontario has revealed differences and similarities that may provide insight into the erosional history of part of the archean superior province of the canadian shield during the last 2 ga and some aspects of the evolution of the earth s atmosphere both the major element and trace element compositions of the ancient and recent glacial deposits are very similar the paleoproterozoic mudstones are however enriched in fe and u characteristics that may reflect the oxygen content of the archean early paleoproterozoic atmosphere hydrosphere system strong ca depletion is exhibited by the paleoproterozoic glaciogenic argillites but is absent from the pleistocene samples the proterozoic argillites have slightly higher values for a chemical index of alteration than those of pleistocene muds these characteristics may reflect the acid natur

storm controlled oblique dunes of the oregon coast the large mean height 25 m spacing 300 m relatively straight crested dunes of the central oregon coast migrate an average of 3 8 m yr toward an azimuth of 26 the dunes are transverse to the strong south southwesterly winter storm winds that are responsible for their basic form orientation and migration the dry moderate north northwesterly summer winds modify the dune form but not the dune trend comparison of the sand transport calculated from wind data and the transport measured from dune migration indicates that the actual transport by the wet southerly winds is only one third of the amount calculated assuming dry conditions the resultant vector mean transport rate as recalculated by comparison of the measured and initially calculated rates is 34 m 3 m yr toward an azimuth of 45 the dunes are thus oblique by our definition of an oblique dune angle between dune trend and resultant transport direction between 15 and 75 the internal structures of the dunes confirm northward migration during wet conditions evidence for deposition during wet conditions includes slipface deposits deformed mostly by sliding and various structures formed by the adhesion of sand grains to wet surfaces most summer deposits are not preserved but those on the basal apron the gentle north slope at the base of the winter slipface have a high preservation potential a depositional model based on dune climbing predicts that the preserved record of oblique dunes formed by an obtuse bimodal wind regime would consist of tabular sets of crossbeds in which the dip angles increase upward from the base of each set

deglacial eolian regimes in new england ventifact bearing cover sands wind driven lacustrine spits and fluted bedrock outcrops in new england indicate that a strong anticyclonic circulation under moist periglacial conditions accompanied early recession of the laurentide ice sheet dunes from this interval are conspicuously absent an abrupt shift to warmer and drier conditions during the bolling allerod period 12 7 11 ka was apparently associated with rapid accretion of transverse dunes built by northeast winds along the shore of new england9s largest ice recessional lake by the time of lake drainage however the anticyclonic circulation had been replaced by a northwesterly wind regime resulting in erosion of the older deposits the development of parabolic dunes and gradual stabilization associated with revegetation reactivation of the dunes was associated with a return to colder and windier conditions during the younger dryas 11 10 ka and with anthropogenic changes during the historic period but not during holocene time

a polygenetic palaeosol from the silurian wenlock of southwest ireland a problematic palaeosol unit caps a thick basalt at the top of the clogher head formation dunquin group late wenlock silurian in the dingle peninsula southwest ireland the main part of the unit consists of an altered calc alkaline basalt with a fine clay assemblage of chlorite corrensite and smectite probably resulting from weathering during wenlock times the uppermost part of the unit consists of detrital silicates which were admixed by bioturbation and well defined burrow fills are present the underlying weathered basalt was possibly truncated before the detrital horizon was deposited and finally the whole unit underwent a phase of surface water gleying a catenary relationship existed locally with the pseudo gley developed lower in the landscape while contemporaneous basalts in topographically higher better drained areas largely escaped the effects of gleying these now exhibit reddened tops the complex history and the possiblity of the incompleteness of the profile makes accurate assessment of the soil climate function difficult however the occurrence of calcrete bearing palaeosols in the overlying mill cove formation supports the view that the basalt was weathered under a sub humid or semi arid climate considering the alteration of the dunquin group to actinolite prehnite grade the preservation of the smectite is highly unusual there is no evidence for its origin due to more recent weathering or interstratal neoformation it is thus interpreted as a relict product of the original weathering phase

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

weathering of chlorite and mica in a new brunswick podzol developed on till derived from chlorite mica schist abstract a study was made of the weathering of trioctahedral iron rich chlorite and dioctahedral mica in a spodosol haplorthod developed on till derived from chlorite mica schist chlorite in the clay of the b and c horizons has weathered to small amounts of regularly interstratified chlorite vermiculite vermiculite and goethite chlorite vermiculitization is associated with a loss of iron and aluminum and appears to result in a change toward dioctahedral structure chlorite and its trioctahedral vermiculitic products are absent from the clay silt and sand of the ae horizon which is probably due to decomposition by organic acids mica in this soil weathers and expands to dioctahedral regularly interstratified mica ermiculite and discrete vermiculite products that increase in abundance towards the profile surface and are dominant in the clay of the ae horizon amounts of mica derived vermiculite products decrease with increase in particle size and are practically absent in the sand of the ae horizon comparing mineral weathering in this spodosol with that in other soils developed on similar greenschist material but in warmer climates or during longer times shows that amounts of chlorite derived vermiculite in the subsoils of the latter soils are much larger decrease towards the profile surface and increase with larger particle size the evidence indicates that weathering of chlorite to vermiculite and accumulation of the vermiculite products are optimal in non eluvial moderate weathering conditions

a novel geochemical approach to paleorecords of dust deposition and effective humidity 8500 years of peat accumulation at store mosse the great bog sweden both bog surface wetness and atmospheric dust deposition are intricately linked to changes in the hydrological cycle and pairing these types of records at the same site provides complementary infor

glacial anticyclone recorded in palouse loess of northwestern united states climate simulations for the last glacial maximum using general circulation models typically show a glacial anticyclone that produced an easterly wind anomaly south of the north american ice sheets evidence of this phenomenon has not been found in eolian sedimentary deposits that record surface wind patterns luminescence ages of loess and accompanying paleoecologic records from opal phytoliths and paleosol units across the columbia plateau washington state united states document a decrease up to fivefold in regional dust production and accumulation from 35 ka to 15 ka this interval corresponds to simulations indicating that a glacial anticyclone weakened prevailing south southwesterly winds that have shaped the eolian landscape of the columbia plateau since at least 75 ka at the same time that the glacial anticyclone suppressed dust production and accumulation enhanced cold and dry conditions resulted in soil formation dominated by intense bioturbation in periglacial steppe accompanied by shallow calcium carbonate precipitation this is the first evidence from eolian deposits in north america verifying that the glacial anticyclone altered surface wind patterns and affected eolian systems during the last glacial maximum

seismic anisotropy of shales shales are a major component of sedimentary basins and they play a decisive role in fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure shale anisotropy needs to be quantified to obtain reliable information on reservoir fluid lithology and pore pressure from seismic data and to understand time to depth conversion errors and non hyperbolic moveout a single anisotropy parameter thomsen s parameter is sufficient to explain the difference between the small offset normal moveout velocity and vertical velocity and to interpret the small offset avo response the sign of this parameter is poorly understood with both positive and negative values having been reported in the literature is sensitive to the compliance of the contact regions between clay particles and to the degree of disorder in the orientation of clay particles if the ratio of the normal to shear compliance of the contact regions exceeds a critical value the presence of these regions acts to increase and a change in the sign of from the negative values characteristic of clay minerals to the positive values commonly reported for shales may occur misalignment of the clay particles can also lead to a positive value of for transverse isotropy the elastic anisotropy parameters can be written in terms of the coefficients w 200 and w 400 in an expansion of the clay particle orientation distribution function in generalized legendre functions for a given value of w 200 decreasing w 400 leads to an increase in while for fixed w 400 increases with increasing w 200 perfect alignment of clay particles with normals along the symmetry axis corresponds to the maximum values of w 200 and w 400 given by w max 200 10 8 2 and w max 400 3 2 8 2 a comparison of the predictions of the theory with laboratory measurements shows that most shales lie in a region of the w 200 w 400 plane defined by w 400 w 200 w max 400 w max 200

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

mid to late holocene aeolian activity recorded in a coastal dunefield and lacustrine sediments on andoya northern norway in an effort to reconstruct past aeolian activity a foredune stratigraphy and a continuous lake sediment record from the largest dunefield on andoya northern norway have been investigated the dunefield extends landwards in a north eastward direction and consists of several parabolic dunes foredunes and blowouts the sediment record 169 cm from the nearby lake latjonna and the foredune stratigraphy 10 m covers the last 6200 and 3700 cal yr bp respectively both sites possess sediments deposited after the tapes transgression maximum 6800 cal yr bp which reached a level of 7 8 m a s l at the study site the lake sediment record consists of several units dominated by sand grains interspersed by more organic rich beds the core has been examined by x ray fluorescence xrf magnetic susceptibility ms and loss on ignition loi mineral grains were detected by wet sieving of the ignition residue ir and the influx of sand grains to latjonna was calculated based on the weight of sand grains

a rock physics driven bayesian inversion for toc in the fuling shale gas reservoir abstract total organic content toc is an important indicator in the evaluation of the organic abundance and production potential of shale reservoirs the conventional approach to toc estimation is to correlate toc with inverted elastic parameters in a linearized empirical equation however this approach ignores complex rock physics properties such as complex mineralogy and pore space in the shale while generating smooth low resolution results this paper proposes a rock physics based method to forward model the seismic and elastic response of the shale reservoir and then invert using a bayesian approach to derive key parameters such as the toc total porosity and the fractional volume of brittle minerals and to delineate the sweet spots in an unconventional shale reservoir