ammonium in granites and its petrogenetic significance abstract ammonium is present as a trace constituent in all granites with an average concentration of 45 ppm nh4 equivalent to 35 ppm of elemental n it shows wide variations related to petrography and region but the only significant correlation between ammonium and other geochemical parameters is that it is most abundant in peraluminous granites and least abundant in peralkaline granites these variations can be related to a the amount of sedimentary material in the magmatic source region and b redox conditions in the source region the ammonium content of granitic magmas can also be modified by fractionation or contamination hydrothermal alteration has a major effect on the ammonium content of granitic rocks and variation due to this cause may exceed the magmatic variation most hydrothermally altered granites are enriched in ammonium as a result of the transfer of ammonium from sedimentary country rocks by the hydrothermal fluids

morphology of transverse aeolian ridges tars on mars from a large sample further evidence of a megaripple origin abstract using hirise digital terrain models dtms we developed a large morphological dataset to examine the three dimensional shape size and scaling of martian transverse aeolian ridges tars considerable debate exists on the characteristic morphology of tars and the origins of these enigmatic bedforms some researchers suggest polygenesis or multiple classes of similar bedforms reliably characterizing the morphology of tars is an essential prerequisite to developing and evaluating process based models of tar genesis and unraveling aeolian processes on the surface of mars we present measurements of tar morphology from a large dtm derived dataset n 2295 we focused on tars with simple morphologies in order enable more defensible discretization histograms and cumulative log frequency plots of morphometric parameters length width height elongation ratio and wavelength indicate the sample represents a continuum of bedforms from a single population a typical tar from our dataset is 88 5 m long longest planview axis 17 3 m wide shortest planview axis 1 3 m tall and has a wavelength of 25 8 m combined with these data the bulk of evidence presented to date suggests that interpreting tars as megaripples is the most viable working hypothesis

gypsum gravel devils in chile movement of largest natural grains by wind whirlwinds dry convective helical vortices move large gypsum crystals in the andes mountains of northern chile the crystals are entrained from a saline pan surface where they grew in shallow surface brines they are transported as much as 5 km and deposited in large dune like mounds the dune gravel is cemented relatively quickly by gypsum cement precipitating from near surface saline groundwater resulting in gypsum breccia this marks the first occurrence of gravel sized grains moved efficiently in air by suspension provides a new possible interpretation for some ancient breccias and conglomerates and improves understanding of limits of extremity of earth surface environments

constancy of silicate mineral weathering rate ratios between natural and experimental weathering implications for hydrologic control of differences in absolute rates abstract inverse models which apportion watershed effluxes geochemical mass balance over estimated mineral surface area give weathering rates for individual silicate minerals e g feldspar 1 3 orders of magnitude slower than laboratory rates comparisons of rates calculated from several recent watershed geochemical mass balance studies with experimentally determined rates reveal that the ratio of mineral weathering rates for a given silicate mineral pair determined in an internally consistent field study equals the ratio of rates for the same minerals in any internally consistent set of laboratory experimental data thus the coefficient which corrects the weathering rate for any mineral from a laboratory data set to a field setting is identical to the corresponding coefficient for any other mineral in the same data sets the correction factor linking experimental and natural rates must be independent of composition physical e g hydrologic controls rather than compositional or chemical controls cause the difference between weathering rates in nature and the laboratory because flow in natural weathering profiles is spatially heterogeneous not all of the potentially available surface in natural systems actually participates in reactions with pore fluids

effect of fault bend on the rupture propagation process of stick slip abstract an experimental study of stick slip is performed to examine the effect of a fault bend on the dynamic rupture propagation process a granite sample used in the experiment has a pre cut fault that is artificially bent by an angle of 5 6 at the center of the fault along strike and accordingly the fault consists of two fault segments the rupture propagation process during stick slip instability is investigated by analyzing the records of shear strain and relative displacement measured with strain gauge sensors together with the hypocenters of ae acoustic emission events detected with piezoelectric transducers the observed rupture propagation process of typical stick slip events is as follows 1 the dynamic rupture started on a fault segment is stopped near the fault bend 2 the rupture propagation is restarted near the bend on the other fault segment 10 8 ms to 3 5 s after the stop of the first rupture the delay time of the second rupture decreases with an increase in the slip amount of the first rupture or a decrease in the normal stress acting on the fault segment where the second rupture started 3 the restarted rupture is not arrested by the presence of a fault bend and slip occurs over the entire fault we theoretically analyze the stress concentration near the fault bend to find that the normal stress produced by the preceding slip near the fault bend plays an important part in controlling the rupture propagation a numerical simulation based on a rate and state dependent friction law is performed to interpret physically the retarded rupture in the experiment the observed time interval of 10 8 ms to 3 5 s between the first rupture and the second is explained by the numerical simulation suggesting that the rate and state dependence of rock friction is a possible mechanism for the retarded rupture on the fault

megaripple flattening due to strong winds abstract megaripples in nahal kasuy in the southern negev desert of israel are characterized by a mean wavelength of about 70 cm and by a bimodal distribution of coarse and fine particle sizes the latter property being a pre requisite for their formation in our three year project megaripple development was monitored using a digital elevation model dem constructed from above ground stereo digital photographs temporal dynamics of wind power drift potential dp were measured and grain size analyses were performed on samples taken from different parts of the megaripple the coarse grains that protect the crest enable the ripple to grow but when ripple height becomes too high the bed shear stress increases thus allowing the wind to move the armoring layer when this happens during strong wind storms the megaripple will flatten and even disappear as was observed in our field study we present measurements that for the first time directly show the megaripple to normal ripple transition and we suggest two possible physical processes as potential causes of this phenomenon megaripple flattening can occur either when the wind exceeds the fluid threshold for a sufficient length of time or after a sequence of storms with winds blowing from the same direction

wind formed gravel bed forms wright valley antarctica 1 bed forms composed of gravel size particles 50 of particles 4 mm are observed in the wright valley of the mcmurdo dry valley system in antarctica these bed forms are characterized by a very asymmetrical shape with a mean aspect ratio of 0 025 standard deviation 0 005 mean wavelength of 2 7 m 0 49 m and a mean height of 0 06 m 0 01 m particle size analysis of the bed form sediments shows bimodality with a peak near 9 mm and another between 0 5 mm and 0 25 mm time integrated sediment trap samples of horizontal saltation and creep flux indicate the flux of particles 4 mm during the two year monitoring period was extremely low measurements of the horizontal displacement of tracer particles 14 mm 12 mm 10 mm 8 mm and 6 mm diameter placed onto the bed forms corroborate the low particle flux measurements and limited movement of particles the bed forms share form and grain size characteristics with both ripples and mega ripples showing poor sorting of particles across a single wavelength except for a slight coarsening at the crest similar to ripples but their sinuosity suggest that transverse instabilities affect their formation similar to mega ripples based on the data for the prevailing environmental conditions it can be argued that the wright valley form is an expression of gravel particles moved solely by highly intermittent creep processes this also argues for the need for a very long period of time for their evolution on the order of centuries

the carolina sandhills quaternary eolian sand sheets and dunes along the updip margin of the atlantic coastal plain province southeastern united states the carolina sandhills is a physiographic region of the atlantic coastal plain province in the southeastern united states in chesterfield county south carolina the surficial sand of this region is the pinehurst formation which is interpreted as eolian sand derived from the underlying cretaceous middendorf formation this sand has yielded three clusters of optically stimulated luminescence ages 1 75 to 37 thousand years ago ka coincident with growth of the laurentide ice sheet 2 28 to 18 ka coincident with the last glacial maximum lgm and 3 12 to 6 ka mostly coincident with the younger dryas through final collapse of the laurentide ice sheet relict dune morphologies are consistent with winds from the west or northwest coincident with modern and inferred lgm january wind directions sand sheets are more common than dunes because of effects of coarse grain size mean range 0 35 0 59 mm and vegetation the coarse grain size would have required lgm wind velocities of at least 4 6 m sec accounting for effects of colder air temperatures on eolian sand transport the eolian interpretation of the carolina sandhills is consistent with other evidence for eolian activity in the southeastern united states during the last glaciation

aeolian granule ripple deposits namibia granule ripples are a common feature of most dunefields yet they have seldom been recognized in ancient deposits although granule ripples are common in erosional settings such as windward slopes of dunes or scour surfaces in interdunes they nevertheless migrate laterally and leave distinctive deposits that can be recognized in ancient rocks these deposits have characteristics of type b sand sheet deposits including poured in texture curving ripple trough tangential coarse grained foresets irregular silty layers well sorted coarse and fine layers either horizontal or within foresets and fine layers in ripple troughs wind tunnel experiments suggest that under low velocity wind conditions granule ripples grow to a significant degree as parasites dependent on saltation of fine sand grains whose impact moves the larger grains of the granule ripple although the depositional surface of granule ripples is commonly coated with a layer of coarse grains this is in most places only a few grains thick underlying deposits commonly have a poorly sorted or poured in texture this texture results from an admixture of fine grains that fall among the spaces between the larger grains during deposition

frequency magnitude and characteristics of aeolian sediment transport mcmurdo dry valleys antarctica 1 due in part to the challenging environment of earth s high latitude regions available information on cold climate effects on aeolian processes in these areas remains limited data from these areas however provide insight into the physics of sediment transport by wind and the controls on erosive winds in proximity to ice caps and topographic influences this study presents a 2 year record of meteorological saltation activity horizontal saltation flux and particle size distribution data from four sites in the mcmurdo dry valleys of antarctica 2008 to 2010 saltation measurements revealed daily and seasonal patterns with spring and summer sediment transport events occurring between 09 00 and 24 00 hours due to thermally generated winds fall and winter events occur at any time of day with the strongest associated with foehn winds threshold wind speed at 4 2 m in all seasons for all locations was 10 m s 1 saltation occurred in the temperature range 40 c to 5 c westerly winds in the fall winter and easterly winds in spring summer are associated with the majority of transport events the sand in transport is mainly 250 to 500 m in diameter and poorly sorted the integrated saltation flux varies over three orders of magnitude among the sites with the lowest mean flux recorded in the taylor valley 2 9 kg m 1 day 1 and the highest in the eastern victoria valley 2271 kg m 1 day 1 for 24 hours of continuous saltation the percentage of time saltation active at these locations annually is 2 4 and 13 respectively for the victoria taylor and wright valleys

kinetic nitrogen isotope fractionation associated with thermal decomposition of nh3 experimental results and potential applications to trace the origin of n2 in natural gas and hydrothermal systems abstract ammonia nh3 is the major intermediate phase in the pathway of nitrogen n transfer from the fixed n phases e g in crustal material to free n2 e g in natural gas reservoirs and volcanic gases yet the n isotopic behavior during these n cycling processes remains poorly known in an attempt to contribute to the understanding of n cycling using n isotopes we carried out laboratory experiments to investigate the n isotopic effect associated with thermal decomposition of ammonia 2nh3 n2 3h2 pure nh3 with initial 15 n nh 3 of 2 relative to air standard was sealed into quartz tubes and thermally decomposed at 600 700 or 800 c from 2 hours to 500 days with the progress of the reaction the 15n of the remaining nh3 and the accumulated n2 increased from 2 to 35 and from 20 to 2 respectively the differences of the n isotope fractionations at the three temperatures are not significant modeling using the rayleigh distillation model yielded similar kinetic n isotope fractionation factors n 2 nh 3 of 0 983 0 002 for 600 700 and 800 c applied to geological settings this significant isotope discrimination 17 associated with partial decomposition of nh3 nh4 from crustal sources 15naverage 6 3 can produce mantle like i e 5 or even lower 15n values of n2 this may explain the large variation of 15n 20 to 30 of n2 in natural gas reservoirs it can also possibly explain the extreme 15n depletion of n2 in some volcanic gases this possibility has to be carefully considered when using n isotopes to trace geological n cycling across subduction zones by analysis of volcanic n2

lower tertiary and upper cretaceous source rocks in louisiana and mississippi implications to gulf of mexico crude oil the lower tertiary sparta formation wilcox group and the midway group in southern louisiana include organic rich source facies that generate crude oil at relatively high thermal maturities the wilcox group is an important source of wilcox crude oil and regional kerogen variations explain two crude oil subfamilies wilcox crude oils in downdip areas of southern louisiana migrated short distances but long range lateral migration about 150 km best explains wilcox crude oils far updip from mature source rocks crude oils in oligocene and younger reservoirs in southern louisiana migrated vertically from deep lower tertiary source rocks some crude oils in upper cretaceous tuscaloosa reservoirs were emplaced by long range lateral migration from tuscaloosa source rocks g ven little evidence of upper tertiary source rocks and the overmaturity problems of mesozoic source rocks most crude oils in upper tertiary and pleistocene reservoirs of the gulf continental shelf are best explained by vertical migration from deep lower tertiary source rocks even so it is simplistic to assume an exclusive lower tertiary origin many tertiary and pleistocene crude oils of this study probably include an overprint of high maturity hydrocarbons from mesozoic sources

nitrogen in rock occurrences and biogeochemical implications 1 there is a growing interest in the role of bedrock in global nitrogen cycling and potential for increased ecosystem sensitivity to human impacts in terrains with elevated background nitrogen concentrations nitrogen bearing rocks are globally distributed and comprise a potentially large pool of nitrogen in nutrient cycling that is frequently neglected because of a lack of routine analytical methods for quantification nitrogen in rock originates as organically bound nitrogen associated with sediment or in thermal waters representing a mixture of sedimentary mantle and meteoric sources of nitrogen rock nitrogen concentrations range from trace levels 200 mg n kg 1 in granites to ecologically significant concentrations exceeding 1000 mg n kg 1 in some sedimentary and metasedimentary rocks nitrate deposits accumulated in arid and semi arid regions are also a large potential pool nitrogen in rock has a potentially significant impact on localized nitrogen cycles elevated nitrogen concentrations in water and soil have been attributed to weathering of bedrock nitrogen in some environments nitrogen released from bedrock may contribute to nitrogen saturation of terrestrial ecosystems more nitrogen available than required by biota nitrogen saturation results in leaching of nitrate to surface and groundwaters and where soils are formed from ammonium rich bedrock the oxidation of ammonium to nitrate may result in soil acidification inhibiting revegetation in certain ecosystems collectively studies presented in this article reveal that geologic nitrogen may be a large and reactive pool with potential for amplification of human impacts on nitrogen cycling in terrestrial and aquatic ecosystems

nitrogen isotope geochemistry of organic matter and minerals during diagenesis and hydrocarbon migration the magnitude of isotopic variations between organic and inorganic nitrogen was examined in samples from three stacked hydrocarbon reservoirs in the fordoche field louisiana gulf coast basin usa measurements were made of 15n in kerogen bitumen oil formation water and fixed nh4 extracted from mudstones nonproductive sandstones and productive sandstones nitrogen isotope fractionation occurs because 14n is released preferentially to 15n from organic molecules during thermal maturation released 14n goes into solution or may be adsorbed by minerals leaving crude oil enriched in 15n diagenetic clay minerals e g illite commonly form in the temperature range of hydrocarbon generation and nh4 may be fixed in clay interlayers with an isotopic ratio similar to that of the migrating fluids results indicate that the influence of organic matter on mineral 15n depends on the timing of authigenic mineral formation relative to fluid migration the average 15n of kerogen 3 2 0 3 and fixed nh4 from mudstones 3 0 1 4 is similar while bitumen increases from 3 5 to 5 1 with depth in deep reservoir sandstones 100 c the 15n of crude oil averages 5 2 0 4 similar to the 15n of bitumen in the proposed source rocks formation waters are 14n enriched with an average 15n of 2 2 2 6 fixed nh4 15n values lie between that of the oil and water the average 15n of fixed nh4 is 3 0 1 2 in productive sandstones and 0 2 2 4 innonproductive sandstones in the shallower reservoir sandstones 90 c fixed nh4 is apparently not influenced by the presently associated fluids productive and nonproductive sandstones have distinctly low average 15n values 1 2 0 8 yet crude oil 11 1 0 3 and water 3 8 0 1 have been 15n enriched by 6 relative to the deeper reservoirs this suggests that the present fluids migrated into the reservoir after authigenic illite had formed fluids become enriched in 15n during migration and the amount of enrichment may be a function of the amount of interaction with argillaceous sediments

morphodynamics of small scale superimposed sand waves over migrating dune bed forms 1 the kinematics and morphodynamics of low amplitude small scale sand waves developed over migrating dunes are examined using data drawn from laboratory experiments we refer to the superimposed features as sand sheets a general descriptive term for low amplitude bed waves that are not easily classified as ripples dunes or bars within the experiments the sheets formed downstream of the reattachment point at a distance that was invariant with dune size some sheets lacked slip faces composed of sand grains avalanching down a slope near the angle of repose over equilibrium dunes three to four sand sheets were observed per 100 s sheet thickness was 10 of the height of the dune upon which they were superimposed they migrated at 8 to 10 times the dune rate they had nearly constant lengths over the full range of dune lengths and flow conditions and they had aspect ratios of 0 025 dunes and sand sheets represent distinct scales of sediment transport with different migration rates however sediment transport rates calculated from the sand sheet and dune morphologies are nearly identical for transport equivalence to occur sand sheets migrating at 10 times the dune rate must be 0 1 times the size which is consistent with the morphological observations superimposed bed waves on dunes are often considered simply as additional roughness elements but these results indicate that such bed waves are the agency by which the dune bed form itself moves downstream

a 3 d viscoelastoplastic model for simulating long term slip on non planar faults summary the geometrical complexity of non planar faults is known to affect not only fault slip rates but also crustal deformation and seismicity in the surrounding region but implementing non planar faults in numerical models has been challenging we have developed a 3 d viscoelastoplastic finite element model to simulate long term steady state fault slip along conceptual restraining bends and crustal deformation around them by incorporating plastic yielding in both fault zones and the surrounding crust this model can predict the quasi steady state stress field and strain partitioning while avoiding pathological stress build up encountered in traditional viscoelastic models here we detail the formulation of this model and explore major model parameters the model results show that restraining bends tend to impede fault slip increase shear stress in the surrounding crust and localize strain in a pair of belts off the fault zone these effects are enhanced by high viscosity in the lower crust and upper mantle high aspect ratio of bend width over fault length fast relative motion of fault blocks and high fault friction these model results may help explain the diffuse deformation surrounding the big bend of the san andreas fault and the more confined deformation around the lebanon bend of the dead sea fault

boulder weathering in mcmurdo dry valleys antarctica abstract earth s dynamic surface undergoes a continuous cycle of mountain building and denudation one of the important links in this cycle is the break up and comminution of the rocks that allows for effective transportation of debris by surface processes the starting and end points in this transformation are well known bedrock and boulders on one end and silt and clay on the other however the existing knowledge of the rates and processes responsible of the intermediate steps is currently limited to fill this gap in knowledge we studied boulders and their weathering products in the mcmurdo dry valleys antarctica that have been weathering for hundreds of thousands of years sub aerially exposed at the ground surface our study boulders of locally distinct lithology have trails of rock fragments leading downhill revealing the rate of weathering and subsequent transport rate of the fragments the rock fragments emanate from the source boulder and decrease in size as the distance downslope increases we measured the fragment sizes and distances for various lithologies on varying slope angles we found that large fragments up to 0 4 m in diameter can be transported up to 60 m downslope by unknown processes the total length of the fragment trail increases with the slope angle the maximum transport distances of sandstone boulders are approximately 10 times longer than other lithologies which may be explained by the larger observed fragment sizes of the sandstones on the other hand measurements of the smaller generally less than 0 04 m diameter fragments that are transported by wind revealed much shorter transport distances

the rate of granule ripple movement on earth and mars abstract the rate of movement for 3 and 10 cm high granule ripples was documented in september of 2006 at great sand dunes national park and preserve during a particularly strong wind event impact creep induced by saltating sand caused 24 granules min 1 to cross each cm of crest length during wind that averaged 9 m s 1 at a height well above 1 m which is substantially larger than the threshold for saltation of sand extension of this documented granule movement rate to mars suggests that a 25 cm high granule ripple should require from hundreds to thousands of earth years to move 1 cm under present atmospheric conditions

sedimentology and climatic environment of alluvial fans in the martian saheki crater and a comparison with terrestrial fans in the atacama desert abstract the deflated surfaces of the alluvial fans in saheki crater reveal the most detailed record of fan stratigraphy and evolution found to date on mars during deposition of at least the uppermost 100 m of fan deposits discharges from the source basin consisted of channelized flows transporting sediment which we infer to be primarily sand and gravel sized as bedload coupled with extensive overbank mud rich flows depositing planar beds of sand sized or finer sediment flow events are inferred to have been of modest magnitude probably less than 60 m3 s of short duration and probably occupied only a few distributaries during any individual flow event occasional channel avulsions resulted in the distribution of sediment across the entire fan a comparison with fine grained alluvial fans in chile s atacama desert provides insights into the processes responsible for constructing the saheki crater fans sediment is deposited by channelized flows transporting sand through boulder sized material and overbank mudflows sand size and finer and wind erosion leaves channels expressed in inverted topographic relief the most likely source of water was snowmelt released after annual or epochal accumulation of snow in the headwater source basin on the interior crater rim during the hesperian to amazonian periods we infer the saheki fans to have been constructed by many hundreds of separate flow events and accumulation of the necessary snow and release of meltwater may have required favorable orbital configurations or transient global warming

sedimentology of cold climate aeolian sandsheet deposits in the askja region of northeast iceland active aeolian sandsheets cover an area of 270 km2 in the askja region of ne iceland the sandsheet is divided into i a deflationary upwind part that is characterised by deflation lags ventifacted boulder fields and restricted aeolian sand patches in the lee of obstacles ii an accumulating central part that is characterised by continuous aeolian sand cover up to 10 m thick where three scales of aeolian ripples are evident along with larger scale forms including longitudinal zibars and iii a downwind part that is currently subject to aeolian bypass with only localised accumulation occurring in topographic hollows between basaltic lava fields trains of aeolian granule megaripples are a characteristic landform of the downwind part of the sandsheet these sinuous crested oblique bedforms attain heights of 0 35 m and downwind spacings of 6 m they are composed principally of low density pebble grade pumice clasts and other reworked volcaniclastic detritus derived from the nearby askja volcanic centre the distribution of landforms across the sandsheet reflects a regional aeolian sediment budget that is controlled by dynamic interactions between glacial ice margin fluvial aeolian and volcaniclastic processes under the influence of a distinctive climatic regime sediment supply at the upwind sandsheet margin adjacent to the dyngjujokull glacier increases during summer periods when rates of glacial ablation are at a maximum longer term controls on sediment supply rate are determined by episodes of glacier surging and retreat and by periodic eruptions of volcaniclastic debris from the askja volcanic centre the availability of sediment for aeolian transport is controlled by the level of the groundwater table the depth and continuity of the permafrost layer in the proglacial area the degree of development of armoured pebble lags and freezing of the sandsheet surface during winter months the transport capacity of the wind varies on a seasonal basis with mean wind velocities and wind gustiness reaching a maximum during winter periods both winter and summer mean wind velocities have been steadily increasing since formal records began in 1969 the suite of aeolian landforms developed within the askja region as defined by sediment texture and composition and bedform scale morphology and spatial distribution reflects a special set of controlling circumstances which mean that the askja sandsheet deposits differ significantly from those described from elsewhere

relation of vertical flux of particles smaller than 10 μm to total aeolian horizontal mass flux at owens lake the vertical flux of particles smaller than 10 m for a saline playa surface the particle size composition of which was classified as loam textured was estimated for a highly wind erodible site on the playa of owens dry lake in california the ratio of this vertical flux to the horizontal flux of total airborne material through a surface perpendicular to the soil and to the wind fa qtot is 2 75 10 4 m 1 this is consistent with that ratio for sand textured soils and suggests that the binding energy and size of saltating particles for the tested surface material at owens lake is of the same order as that for sandier soils the horizontal mass flux of saltating grains q in the reported wind erosion event is 51 3 of the total horizontal mass flux qtot therefore the ratio of fa q is 5 4 10 4 m 1

nitrogen in future biosphere studies this article suggests a theme for future nitrogen studies involving the functioning and evolution of the biosphere together with certain aspects of human biology it is hoped that this theme could be developed into a multi authored book at some point in the future although numerous new case studies may be required the biosphere can be considered to be a single interactive system comprised of numerous component parts including the atmosphere rain rivers lakes oceans continental ecosystems marine ecosystems soils and sediments in order to study the internal complexity of each of the components and the relationships that exist between them one can choose a common theme the author believes that nitrogen is a good prospect because of its ubiquitous nature and complex chemistry the burial of sedimentary volatiles in the continental crust has contributed to the long term chemical evolution of the exterior environments of the earth the most marked effects notably the accumulation of atmospheric oxygen have been due to the burial of reduced carbon an understanding of the passage of sedimentary volatiles through the crust will provide important constraints on the evolution of the biosphere and may lead to a more meaningful comparative planetology carbon is difficult to trace through crustal processes because its high temperature form graphite is incompatible with the crystal structures of silicate minerals however the high temperature form of sedimentary nitrogen ammonium readily enters into potassic minerals and it can be easily traced through crustal processes herein the fate of sedimentary nitrogen is traced from wet sediments through metamorphic rocks into granites and other crustal melts without the trapping of nitrogen in the crust and the liberation of oxygen that is a consequence of biological nitrogen fixation the n2 o2 of the atmosphere may have been about 82 9 to 16 3 and the total atmospheric pressure about 1 2 atm most of the changes in the oxygen content is due to dilution by nitrogen with only about 5 of the present atmospheric oxygen being a consequence of nitrogen fixation the ancient continental surfaces would have been volcanic deserts containing little 1 ppm or no nitrogen today nitrogen rich soils support continental ecosystems one can use nitrogen as a window to speculate on the colonisation of the continents by land plants herein nitrogen fixation by legumes is considered in detail and by drawing analogies with the present day the author speculates on the colonisation of the continents by land plants having speculated on the co evolution of the atmosphere soils and continental ecosystems one can place a human being in the centre of a tropical forest and begin to examine how they relate to the modern biosphere the chosen example is the metabolism of plant protein and the roles of glutamate dehydrogenase gdh vitamin b2 and flavin mononucleotide fmn the realisation of this theme would imply numerous new case studies notably those concerning the continental crust where nitrogen studies were linked to mineralogy petrology and other geochemical tracers including sr o al and k and where the short range order of 15n were taken into consideration

the significance of fixed ammonium in palaeozoic sediments for the generation of nitrogen rich natural gases in the north german basin in contrast to predominantly hydrocarbon rich natural gases in the western part of the central european basin ceb accumulations of natural gases from the eastern part of the north german basin ngb are nitrogen rich with up to 90 n2 this study is focused on the behaviour of fixed ammonium in clay minerals of organic rich palaeozoic sediments in the eastern part of the ngb as a major source of nitrogen rich natural gases carboniferous shales have been investigated for a better understanding of nitrogen fixing during diagenesis storage during burial and release during devolatilization processes or fluid rock interactions the total nitrogen contents in the studied carboniferous shales of the ngb reach up to 2700 ppm with an inorganic fixed portion in the form of nh4 n of more than 60 the results of this study indicate an increasing proportion of the mineralogically fixed ammonium with increasing thermal maturity and storage up to catagenetic conditions the isotopic composition of fixed nh4 is relatively homogeneous in the majority of the shales and ranges from 1 to 3 5 in contrast samples from the basin centre show a significant decrease in ammonium contents down to 460 ppm coupled with a shift in 15n up to 5 6 suggesting a release of nitrogen on a large scale calculation of nitrogen loss and isotopic fractionation indicate that more than 30 of nitrogen was released as ammonium probably as a consequence of fluid rock interaction with highly saline brines

geologic nitrogen in terrestrial biogeochemical cycling recent research implicates geologic nitrogen as a large and reactive pool of nitrogen that can have significant ecological effects this study was conducted to determine the landscape distribution of geologic nitrogen and the fate of this nitrogen during rock to soil transformation in the lower mokelumne river watershed located in the western sierra nevada of california mineralogy and chemistry were determined for six major lithologies in the study area to examine the spatial distribution of nitrogen in bedrock in addition soil samples were collected from two watersheds having high stream water nitrate concentrations to determine the fate of nitrogen during weathering and soil formation with the exception of diorite all bedrock contained detectable concentrations of nitrogen 153 1801 and 98 739 mg n kg 1 for metasedimentary and metavolcanic lithologies respectively a significant amount of nitrogen was released during soil formation 2350 and 2570 kg n ha 1 for soils formed on greenstone and slate respectively this amount of nitrogen represents from 30 to 50 of the current soil nitrogen pool in these ecosystems nitrogen released from bedrock contributes to an excess of available nitrogen relative to biotic demands leading to nitrate leaching and elevated concentrations of nitrate in stream water given the widespread occurrence of geologic nitrogen and the large global inventory of nitrogen contained within bedrock the role of geologic nitrogen as a source of nitrogen for terrestrial biogeochemical cycling must be considered

clay mineral authigenesis in coal and shale from the anthracite region pennsylvania textural chemical and mineralogical analyses of authigenic clays in anthracite rank coal and associated shale from eastern pennsylvania have allowed a better understanding of the parameters controlling diagenesis and perhaps coalification in this region minerals in anthracite occur in distinct assemblages associated with the following microenvironments coal matrix two orthogonal joint sets termed systematic and nonsystematic cleat and a third joint set mineralogical differences among microenvironments allow inferences about clay mineral origins and the parameters that controlled mineral authigenesis kaolinite occurs in the shale and all microenvironments within the coal seam authigenic minerals that replaced preexisting kaolinite during the latest stage ofcoalification anthracitization at t 200 c include nhu rich illite pyrophyllite and the following minerals which are primarily restricted to the systematic cleat set tosudite rl ordered dioctahedral mixed layer chlorite smectite sudoite di trioctahedral chlorite and rectorite rlordered mixedjayer paragonite smectite alteration of smectite to illite may be responsible for formation of authigenic illite and na bearing illite which are present only in the shale and coal matrix and fe al rich chlorite and quartz in the third joint set the chemical components for authigenesis appear to have multiple sources ai and si from preexisting kaolinite and quartz n from local organic matter mg and na for tosudite sudoite and rectorite largely from metasomatic hydrothermal fluids fe and mg for fe al rich chlorite from smectite illitization minerals in the shale the coal matrix and the nonsystematic cleat set are interpreted to represent authigenesis in a low permeability environment closed system alteration however the assemblage sudoite tosudite rectorite in the systematic cleat set is interpreted to be the result ofone or two stages ofhydrothermal alteration open system alteration we suggest hat differences in minerals between the two nearly perpendicular cleat sets are the result of permeability differences which were maintained by an anisotropic lateral stress field created by plate convergence during the alleghanian orogeny hydrothermal alteration may be related to large scale basinal flow induced by alleghanianage uplift such migrating fluids could also have transported heat from depth and thereby significantly increased the rate and rank ofcoalification in this region

a comparison of methods used to estimate the height of sand dunes on mars the collection of morphometric data on small scale landforms from other planetary bodies is difficult we assess four methods that can be used to estimate the height of aeolian dunes on mars these are 1 stereography 2 slip face length 3 profiling photoclinometry and 4 mars orbiter laser altimeter mola results show that there is good agreement among the methods when conditions are ideal however limitations inherent to each method inhibited their accurate application to all sites collectively these techniques provide data on a range of morphometric parameters some of which were not previously available for dunes on mars they include dune height width length surface area volume and longitudinal and transverse profiles the utilization of these methods will facilitate a more accurate analysis of aeolian dunes on mars and enable comparison with dunes on other planetary surfaces

finite element analysis of fault bend influence on stick slip instability along an intra plate fault earthquakes have been recognized as resulting from stick slip frictional instabilities along the faults between deformable rocks a three dimensional finite element code for modeling the nonlinear frictional contact behaviors between deformable bodies with the node to point contact element strategy has been developed and applied here to investigate the fault geometry influence on the nucleation and development process of the stick slip instability along an intra plate fault through a typical fault bend model which has a pre cut fault that is artificially bent by an angle of 5 6 at the fault center the numerical results demonstrate that the geometry of the fault significantly affects nucleation termination and restart of the stick slip instability along the intra plate fault and all these instability phenomena can be well simulated using the current finite element algorithm

nitrogen release from rock and soil under simulated field conditions abstract a laboratory study was performed to simulate field weathering and nitrogen release from bedrock in a setting where geologic nitrogen has been suspected to be a large local source of nitrate two rock types containing nitrogen slate 1370 mg n kg 1 and greenstone 480 mg n kg 1 were used along with saprolite and bc horizon sand from soils derived from these rock types the fresh rock and weathered material were used in batch reactors that were leached every 30 days over 6 months to simulate a single wet season nitrogen was released from rock and soil materials at rates between 10 20 and 10 19 mol n cm 2 s 1 results from the laboratory dissolution experiments were compared to in situ soil solutions and available mineral nitrogen pools from the bc horizon of both soils concentrations of mineral nitrogen no 3 nh 4 in soil solutions reached the highest levels at the beginning of the rainy season and progressively decreased with increased leaching this seasonal pattern was repeated for the available mineral nitrogen pool that was extracted using a kcl solution estimates based on these laboratory release rates bracket stream water no 3 n fluxes and changes in the available mineral nitrogen pool over the active leaching period these results confirm that geologic nitrogen when present may be a large and reactive pool that may contribute as a non point source of nitrate contamination to surface and ground waters

a finite element analysis of tidal deformation of the entire earth with a discontinuous outer layer tidal deformation of the earth is normally calculated using the analytical solution with some simplified assumptions such as the earth is a perfect sphere of continuous media this paper proposes an alternative way in which the earth crust is discontinuous along its boundaries to calculate the tidal deformation using a finite element method an in house finite element code is firstly introduced in brief and then extended here to calculate the tidal deformation the tidal deformation of the earth due to the moon was calculated for an geophysical earth model with the discontinuous outer layer and compared with the continuous case the preliminary results indicate that the discontinuity could have different effects on the tidal deformation in the local zone around the fault but almost no effects on both the locations far from the fault and the global deformation amplitude of the earth the localized deformation amplitude seems to depend much on the relative orientation between the fault strike direction and the loading direction i e the location of the moon and the physical property of the fault

experimental determination of the ammonium partitioning among muscovite k feldspar and aqueous chloride solutions abstract the cation exchange equilibria muscovite nh 4 cl tobelite kcl kal 2 alsi 3 o 10 oh 2 nh 4 cl aq nh 4 al 2 alsi 3 o 10 oh 2 kcl aq k feldspar nh 4 cl buddingtonite kcl kalsi 3 o 8 nh 4 cl aq nh 4 alsi 3 o 8 kcl aq are determined by hydrothermal experiments at 400 500 600 c at 400 mpa and piston cylinder experiments at 500 600 c at 1500 mpa along the entire k nh4 compositional range the composition of solid phases are determined by xrd emp and ftir methods nh4 k ratios in coexisting 2 3 molal chloride solutions by ion chromatography muscovite tobelite and k feldspar buddingtonite form complete solid solutions series at all conditions consistent phase relations and mass balances indicate equilibrium between solid solutions and fluids in both the k nh4 muscovite and k nh4 feldspar fluid systems nh4 strongly fractionates into the fluid in the range from 400 to 600 c 400 to 1500 mpa fractionations are slightly temperature and pressure dependent the distribution coefficient k d solid fluid x nh 4 solid x k solid x k fluid x nh 4 fluid varies within the experimental range from 0 10 at xkbulk 0 81 to 0 46 at xkbulk 0 20 for muscovite fluid and from 0 05 at xkbulk 0 91 to 0 70 at xkbulk 0 15 for feldspar fluid nh4 is preferentially incorporated into feldspar relative to mica with kdfsp ms ranging between 1 36 and 2 0 at 400 mpa and between 1 13 and 1 5 at 1500 mpa as xkbulk varies from 0 15 to 0 89 results are evaluated thermodynamically assuming equal mixing of nh4cl and kcl in the fluid mixing energies of solids were estimated using multidimensional regression and a regular solution model for the muscovite tobelite equilibrium values of s 11 7 j k 1 mol 1 v 2 1 j mpa 1 mol 1 and w 4 6 kj mol 1 and for the k feldspar buddingtonite equilibrium s 8 8 j k 1 mol 1 v 1 1 j mpa 1 mol 1 and w 5 4 kj mol 1 were derived results are used to calculate partition coefficients d among phases at very low nh4 bulk concentrations between 400 and 600 c dnh4fluid ms ranges from 7 to 8 at 400 mpa and is 5 at 1500 mpa dnh4fluid ms is 6 to 7 at 400 mpa and about 5 at 1500 mpa dnh4fsp ms is between 1 and 1 2 at all conditions partition coefficients are valid for nh4 contents of up to several hundred ppm in mica and feldspar well within the concentration range observed in many rocks combining the data with that of k nh4 partitioning between phlogopite and fluid results in dnh4phl ms 3 5 and dnh4phl ms 3 at 550 c 200 to 400 mpa nh4 concentrations in coexisting muscovite biotite and k feldspar from a variety of rocks show near equilibrium distributions nh4 k partitioning between major k bearing minerals and saline fluids allows for assessment of the dehydration history of metamorphic rocks during prograde metamorphism water is progressively produced by dehydration reactions and expelled along rock s p t path nitrogen is subsequently removed due to preferred fractionation of nh4 into fluids the remaining nh4 is continuously redistributed among muscovite and biotite and at higher grades k feldspar with biotite as the main solid phase carrier of ammonium the large fractionation effect of nh4 among most phases highlights its potential as tracer of devolatilization processes and fluid rock interactions

development of stratigraphically controlled eolian modified unconsolidated gravel surfaces and yardang fields in the wind eroded hami basin northwestern china

changes in the saltation flux following a step change in macro roughness author s gillies john a etyemezian vicken nikolich george nickling william g kok jasper f

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

ammonium halos in lithogeochemical exploration for gold at the horse canyon carbonate hosted deposit nevada u s a use and limitations abstract rock samples taken from the oxidized open pit to depths of 55 m of the carbonate hosted horse canyon gold deposit contain no nh4 samples from the unoxidized zone at the bottom of the pit in the protore however contain as much as 1 44 nh4 1 12 n the presence of nh4 was confirmed by mass spectrometry from these results it is concluded that samples from any oxidized environment e g outcrops soils likely will have lost all or most of any nh4 originaly present in minerals such as buddingtonite of nh4 containing clays this limits the use of nh4 halos in lithogeochemical exploration programs the most reliable application of lithogeochemical studies based on nh4 halos will likely be based on samples from drill cores and other situations where the samples have always been in a reducing environment analysis for nh4 by ir spectroscopy the method preferred by most previous workers is subject to several inherent problems the main one being the presence of the co32 ion whose absorbance at about 1430 cm 1 coincides with that used to determine nh4 the removal of co32 and other phases e g organic matter which may cause analytical difficulties by chemical treatment is not recommended because it is not possible to predict the effect of such treatment on any one of several possible minerals which may contain nh4 it is suggested that the most efficient method of analysis of rock samples for nh4 or n which can be assumed to represent nh4 will be to analyze the samples after heating to 550 c at which temperature all organic nh4 and n is removed by oxidation any remaining nh4 n determined on this residue can be assumed to originate in nh4 containing mineral structures

geologic nitrogen and climate change in the geochemical budget of karkevagge swedish lapland abstract while nitrogen is an essential nutrient for plant growth in the terrestrial environment and generally fixed by biological processes in soils in arctic and alpine environments n is a severely limited nutrient because of both climatic and soil constraints it is widely believed that geologic nitrogen is such a small component of the nitrogen cycle that this source is generally not viewed as being a significant component however it has been estimated that in fact as much as 20 of the total nitrogen budget may be stored in geological materials and where n is severely limited such as in arctic and alpine environments geologic n may in fact be a dominant source of n for biological processes nitrogen saturation may therefore have substantial impacts on geochemical cycles involving both soil and water chemistry in order to determine the potential for the rocks and soils of karkevagge to be significant sources of n samples of the principal rock units of the valley along with soil developed on a variety of rock types were sampled ammonia ammonium contents were determined using ion chromatography ammonia ammonium contents of the sampled rock materials display a wide range of abundances with marble containing a mean nh4 abundance of 4300 mg n kg quartz schist 1600 mg n kg biotite schist 4300 mg n kg and garnet mica schist 4500 mg n kg soil ammonia ammonium abundances were found to be 1600 mg n kg n pool abundances range from 2 5 kg m3 for marble to 8 7 for garnet mica schist soil n pools were found to be 3 0 kg m3 the inorganic n present as ammonia ammonium measured in bedrock represents substantial n input into the geochemical budget the n in bedrock originates from organically bound nitrogen associated with sediment or geothermal waters representing a mixture of sedimentary mantle and meteoric sources nitrogen in the soil originates from the weathering of n rich rocks the presence of unweathered nitrate minerals or fluid inclusions released to the soil and ultimately to plants by assimilation by biota or nitrification geologic nitrogen in karkevagge rocks and soils may represent a large and reactive pool with the potential for considerable impact on the geochemical system to investigate the potential responses of nitrogen release as well as other nutrients to increasing co2 concentration scenarios flow through leaching experiments were conducted on crushed rock samples and soils from the study area leaching experiments revealed two to three fold increases in both n and k release with a tripling of carbon dioxide concentrations ammonium shows more rapid release than potassium which suggests substantial changes in nitrogen cycling with increasing co2 enrichment of the atmosphere

fe iii reducing bacteria in deeply buried sediments of the atlantic coastal plain the possibility that microorganisms are catalyzing the ongoing reduction of fe iii in the sediments of deep 20 250 m aquifers was investigated acetate oxidizing fe iii reducing bacteria were recovered from deep subsurface sediments but only from sediments in which it appeared that fe iii reduction was the terminal electron accepting process for oxidation of organic matter the fe iii reducing microorganisms were capable of reducing ferric oxides present in deep subsurface sediments although fe iii reduction in subsurface sediments is frequently regarded as an abiological reaction the enzymatic reduction of fe iii by microorganisms reported here is the first mechanism of any kind actually shown to have the potential to couple the oxidation of organic matter to carbon dioxide with the reduction of fe iii under the environmental conditions typically found in deep aquifers we propose that microbially catalyzed fe iii reduction is responsible for such late postdepositional phenomena as the formation of variegated red beds and the release of high concentrations of dissolved iron into anaerobic ground waters

discrete element modeling of stick slip instability and induced microseismicity using particle flow code a discrete element model is presented in this paper that allows direct modeling of stick slip behavior in pre existing weak planes such as joints beddings and faults the model is used to simulate a biaxial sliding experiment from literature on a saw cut specimen of sierra granite with a single fault the fault is represented by the smooth joint contact model also an algorithm is developed to record the stick slip induced microseismic events along the fault once the results compared well with laboratory data a parametric study was conducted to investigate the evolution of the model s behavior due to varying factors such as resolution of the model particle elasticity fault coefficient of friction fault stiffness and normal stress the results show a decrease in shear strength of the fault in the models with smaller particles smaller coefficient of friction of the fault harder fault surroundings softer faults and smaller normal stress on the fault also a higher rate of displacement was observed for conditions resulting in smaller shear strength an increase in b values was observed by increasing the resolution or decreasing the normal stress on the fault while b values were not sensitive to changes in elasticity of the fault or its surrounding region a larger number of recorded events were observed for the models with finer particles smaller coefficient of friction of the fault harder fault surroundings harder fault and smaller normal stress on the fault the results suggest that it is possible for the two ends of a fault to be still while there are patches along the fault undergoing stick slips such local stick slips seem to provide a softer surrounding for their neighbor patches facilitating their subsequent stick slips

a wind tunnel investigation of particle segregation ripple formation and armouring within sand beds of systematically varied texture this paper reports on a wind tunnel investigation of particle segregation ripple formation and surface armoring within sand beds of systematically varied particle size distribution from coarsely skewed to bimodal by design the system was closed with no external inputs of mass from an external particle feed particles too coarse to travel in saltation for the given range in wind speed were dyed red in order to distinguish them in optical images from finer sand particles which could be entrained into the unidirectional airflow a 3d laser scanner measured the changing bed topography at regular time intervals during 18 experiments involving varied combinations of wind speed and bed texture image classification techniques were used to investigate the coincident self organization of the two populations of particles as distinguished by their colour as soon as saltation commenced some of the red particles segregated into thin discontinuous patches particle trapping and sheltering on these rough patches was strongly favoured causing them to grow preferentially during the earliest stages of formation bedform growth coincided with i rapid coarsening of the surface texture and ii the merging of proto ripple crests to generate larger rhythmic bedforms of lower frequency consistent with previous work ripple size was observed to increase under stronger winds when not exceeding the threshold for entrainment of the coarse mode or red particles from the crest with declining rates of mass transport and particle segregation as the bed surface armoured and the consequent deceleration of ripple propagation through to the end of each experiment all surfaces eventually attained a steady state morphometry at saturation the largest ripples developed upon beds having the lowest initial concentration of red particles this article is protected by copyright all rights reserved

nitrogen distribution in lower palaeozoic slates phyllites of the meguma supergroup nova scotia canada implications for au and zn pb mineralisation and exploration abstract major and trace elements and nitrogen were analysed in 59 cambrian and ordovician slates phyllites of various lithostratigraphic levels within the meguma supergroup 14 ordovician slates phyllites of the ovens gold mineralisation and 16 ordovician slates phyllites of the eastville pb zn cu mineralisation the fixed nitrogen content and the normative n fix k 2 o ratio of muscovite separates members of the goldenville sandstone greywacke quartzite dominated and halifax formation slate phyllite dominated low fixed nitrogen concentration is related to high manganese concentration black slates phyllites of the saddle reef type au mineralisation in the ovens area are characterised by high fixed nitrogen and a high normative n fix k 2 o ratio of muscovite the nitrogen is of secondary hydrothermal origin therefore it might be possible to use the fixed nitrogen as an exploration tool for black slates phyllite hosted gold mineralisation in nova scotia mineralised slates phyllites of the eastville stratabound pb zn mineralisation cannot be distinguished from nonmineralised time equivalent lithologies on the basis of the fixed nitrogen distribution or the n fix k 2 o ratio of muscovite

seasonal and event scale variations in solute chemistry for four sierra nevada catchments abstract hydrobiogeochemical processes controlling stream water chemistry were examined in four small 2 catchments having contrasting bedrock lithologies in the western sierra nevada foothills of california the mediterranean climate with its cool wet and hot dry cycle produces strong seasonal patterns in hydrological biological and geochemical processes stream water solutes fall into three general groups according to seasonal fluctuation in concentration strong rainy season minimum dry season maximum cl so 4 2 base cations weak rainy season minimum dry season maximum si and rainy season maximum dry season minimum no 3 and k solute dynamics in soil solutions and stream water suggest that mixing of drainage waters from bedrock and soil sources regulate stream water solute concentrations patterns are further altered by the leaching of solutes accumulated in the soil over the summer period of desiccation and the temporal discoupling of nutrient cycles that occurs due to differences in the timing between vegetation growth late spring and leaching early winter solute concentrations are remarkably similar between watersheds with varying bedrock types with the exception of nitrate sulfate and bicarbonate three watersheds have nitrogen bearing metasedimentary bedrock that contributes to elevated nitrate concentrations in stream waters watersheds whose bedrock includes mineralized veins of sulfide and carbonate minerals similarly have greater sulfate and bicarbonate concentrations in stream water hydrobiogeochemical processes are highly dynamic at the seasonal and storm event temporal scales and spatially complex at the watershed scale making management of stream water chemical composition such as nitrate concentrations very challenging

nitrogen production from geochemical weathering of rocks in southwest montana usa 1 a 30 day time course laboratory weathering experiment was conducted using rock samples collected from the west fork of the gallatin river watershed wfw in southwestern montana usa the goal of these experiments was to quantify the amount of labile nitrogen in rock samples collected from the watershed and determine if chemical weathering is a source of dissolved nitrogen in stream water several rock samples investigated produced nitrate in significantly higher concentrations than the silica bead control p 0 05 and the data were consistent with elevated no3 concentrations measured in associated wfw streams isotopic analyses of 15n no3 in 22 stream water samples from the wfw and four rock water extracts from the laboratory experiments indicated that the isotopic composition of no3 was comparable with rocks and stream water samples in the same watershed and differed strongly from waters downstream of development we suggest that the no3 measured in wfw streams includes nitrogen derived from mineral dissolution products from soils and rock the results presented herein further indicate that rock weathering is a source of stream water n in the west fork watershed and inform water quality assessment total maximum daily load development and the relative influences of natural and anthropocentrically derived n sources across this developing mountain watershed

nitrogen and carbon flow from rock to water regulation through soil biogeochemical processes mokelumne river watershed california and grand valley colorado 1 soil denitrification is an ecologically important nitrogen removal mechanism that releases to the atmosphere the greenhouse gas n2o an intermediate product from the reduction of no3 to n2 in this study we evaluate the relationship between soil carbon and denitrification potential in watersheds with bedrock acting as a nonpoint source of nitrogen testing the hypothesis that nitrate leaching to stream water is in part regulated by denitrification two sites one in a mediterranean climate and the other in an arid climate were investigated to understand the interplay between carbon and denitrification potential both sites included carbonaceous bedrock with relatively high nitrogen concentrations 1 000 mg n kg 1 and had low background nitrogen concentrations in surface and groundwater there was a net accumulation of carbon and nitrogen in soil relative to the corresponding bedrock with the exception of carbonaceous shale from the arid site there the concentration of carbon in the soil 15 620 mg c kg 1 was less than the shale parent 22 460 mg c kg 1 consistent with the bedrock being a source of soil carbon rates of denitrification potential 0 5 83 g n kg 1 hr 1 derived from laboratory incubations appeared to be related to the ratio of dissolved organic carbon and nitrate extracted from soils these data indicate that microbial processes such as denitrification can help maintain background nitrogen concentrations to tens of m n in relatively undisturbed ecosystems when nitrogen inputs from weathering bedrock are accompanied by sufficient organic carbon concentrations to promote microbial nitrogen transformations

isotopic variations of the fixed nitrogen in metamorphic rocks the content and isotopic composition of fixed nitrogen nh 4 n in metasedimentary rocks phyllites mica schists and gneisses from prograde metamorphic zones in the erzgebirge saxon ore mountains g d r were measured and show that the nitrogen content decreases and 15n increases with increasing metamorphic grade the geochemical and isotopic behaviour of nitrogen during contact metamorphism was investigated in a mica schist profile through the contact aureole of a granitic pluton the nitrogen concentrations of the wall rocks decrease towards the contact whereas the 15n values become higher various model experiments were carried out in the laboratory to explain the changes observed in the rock samples the nitrogen isotope fractionation factor was determined for the isotopic exchange in the system ammonium sulphate ammonia at 250 c 1 0143 0 0012 and 350 c 1 0128 0 0006 in accordance with the model experiments the conclusion seems warranted that the change in nitrogen content and its isotopic composition in rocks during metamorphic processes depend mainly on the metamorphic temperature

field weathering rates of mt st helens tephra the initial stages of chemical weathering in tephra were examined under field conditions in a cool and humid forest ecosystem in the cascade mountains of washington unleached tephra from the 1980 eruption of mt st helens was applied in 5 cm and 15 cm depths to simulate natural tephra deposition leachate solutions from the tephra were then collected and analyzed over a 4 year period concentrations of dissolved elements were combined with the water fluxes to determine elemental fluxes from tephra and to estimate chemical weathering rates solutions leached from the tephra layer indicate incongruent dissolution resulting in formation of a cation depleted silica rich leached layer on glass and mineral surfaces measured weathering rates were 1 3 orders of magnitude less than comparable rates reported in the literature for laboratory dissolution studies but considerably greater than those measured for entire watersheds in field studies dissociation of carbonic acid originating primarily from upward transport of carbon dioxide from the buried soil was the dominant source of protons for weathering reactions weathering rates in the 5 cm treatment were approximately twice those of the 15 cm treatment a greater flux of co2 per unit volume of tephra in the 5 cm treatment is believed to be responsible for the differential weathering rates

fault geometry and the dynamics of the 1999 chi chi taiwan earthquake the 1999 m 7 6 chi chi taiwan earthquake produced a data set of unparalleled size and quality particularly in the near source region where data have been previously quite scarce the large amount of near source data allows the verification of many predictions of thrust fault behavior for faults that intersect the surface of the earth through rigorous three dimensional dynamic models of the chi chi earthquake it can be shown that many aspects of the observed near source ground motion in this event are direct effects of the asymmetrical dipping fault geometry these effects include the hanging wall moving more than the footwall with strongly peaked velocities right at the fault trace and a transition from predominantly thrust motion in the south of the fault to largely left lateral motion in the north building on the work of oglesby and day 2001 the current work helps to delineate the effects of fault geometry nonuniform prestress and dynamic waves on the physics of the chi chi earthquake and dip slip faults in general in particular we find that a completely homogeneous prestress pattern still fits the gross features of the near source ground motion quite well additionally the strike slip component of motion near the fault trace is seen to be a combination of dynamic and static effects finally dynamic overshoot is seen to be much larger for dip slip faults than for otherwise identical vertical faults the results emphasize the necessity of rigorous models that correctly account for both the effects of fault geometry and dynamic waves in the rupture and slip processes manuscript received 31 july 2000

evaluation of saltation flux impact responders safires for measuring instantaneous aeolian sand transport intensity the measurement of aeolian sand transport rates on small scales is of interest to the development and testing of detailed models of sand movement by wind this paper reports on laboratory evaluations and preliminary field tests of a new design of a piezo electric impact responder called a safire capable of measuring saltation impacts at a frequency of 20 hz the advantages of the safire are 1 that it provides high frequency measurements 2 that it presents a minimal obstruction to the wind flow no scour observed in the field and 3 that it is of a relatively low cost laboratory calibrations were performed with a vertical gravity flume generating known sand grain fluxes using both mixed sand and specific size fractions initial tests investigated three fundamental characteristics correspondence between digital and analogue signals generated by the instrument directional response of the probe and linearity of instrument response to mass flux instrument calibration included determination of the momentum threshold required for the sensor to register a grain impact based on this lower limit and the known distribution of grain size and speed at different fall heights a prediction is made as to the sand grain flux the safire ought to measure which is then compared with the signal response the result of this comparison is an assessment of the instrument s efficiency in counting saltating grains these safires were also deployed in the field as part of a larger investigationof spatio temporal transport variability thisexperiment providedthe opportunity to compare the instrument s performancewithtraditional sandtraps andthispaperdevelopsmethodsandassumptionsrequiredtoconvertmeasurements from impact responders to traditional mass transport rates the evaluations indicate that improvements to the instrument production process are required to ensure a standard momentum threshold among individual instruments furthermore the sensor design needs to be reconsidered in order to eliminate the variation in response depending on azimuth direction so that the sensor is uniformly omni directional d 2003 elsevier b v all rights reserved

diagenesis of ammonium during hydrocarbon maturation and migration wilcox group louisiana u s a abstract as organic matter matures n is released in the reduced form as nh4 and substitutes for k in clay minerals as oil forms an abundance of n is generated coincident with the formation of authigenic illite this study suggests that nh4 released from organic matter during maturation migrates through sandstones together with the pore fluids and volatile phases generated from the migrating crude oil this causes anomalously high nh4 substitution in authigenic illites fixed nh4 concentrations in illite are a product of both hydrocarbon maturation and migration concentrations of fixed nh4 from organic rich mudstones in two wilcox group oil fields show a general increase with depth coincident with increasing organic maturation reservoir sandstones containing crude oils have fixed nh4 concentrations as much as two times those of the mudstones when values are normalized to the quantity of clay minerals fixed nh4 concentrations in the gaseous portion of the reservoir are three times as high two out of five sandstones from a dry hole adjacent to a producing oil field contain anomalously high 2 above mean concentrations of fixed nh4 with respect to total organic centent this together with a high production index and hydrogen index in those units suggests that migrating hydrocarbons may have influenced the fixed nh4 concentrations

granule ripples in the kumtagh desert china morphology grain size and influencing factors granule ripples are found mainly in four regions of the kumtagh desert in china they are characterized by an asymmetrical shape with gentle lower slopes on both sides and abrupt crests the ripples tend to be oriented perpendicular to the prevailing winds except when they form near obstacles such as yardangs the wavelengths range between 0 31 m and 26 m and heights h range from 0 015 m to 1 m the relationship between wavelength and height can be described by a simple linear function and the mean ripple index h is about 20 4 for the study sites the sediments are poorly sorted with negative to very negative skewness at lee and stoss slopes and between ripple troughs which confirms the poured in and shadow appearance described by previous researchers the bimodal or trimodal distributions of grains with modes of 1 16 0 5 and 3 16 and the enrichment of coarse particles at the ripple surface with coarse granule contents ranging between 5 2 and 62 1 indicate that the underlying layer is the original sediment source and that the granule ripples resist erosional processes although the impact of saltating particles and consequently the creep and reptation of coarse grains are responsible for granule ripple initiation at a micro scale however the characteristics of local sediments wind regimes and topographical obstacles as well as the feedbacks among bedform and airflow more strongly affect the development and alignment of granule ripples at a macro scale

transverse instability of megaripples as a result of their inherent differences in stability sand ripples and megaripples exhibit variations in terms of their wavelengths and grain size distributions unimodal for sand ripples and bimodal for megaripples while sand ripples form almost straight lines megaripples have greater sinuosity due to their transverse instability a property that causes small megaripple undulations to grow with time the origin of the instability is due to variations in megaripple height variations that do not diminish over time and due to the inverse dependence of ripple drift velocity on the height thus the taller regions of ripples will move more slowly than the adjacent shorter portions an outcome that promotes further perturbation growth we show an example based on fi eld work of the transverse instability of megaripples the instability growth rate depends on the difference between the heights of the different segments of the megaripple in contrast to the underlying instability of megaripples normal sand ripples are essentially stable and are not affected by transverse perturbations instead reacting quickly to the wind which tends to smooth ripple height irregularities the transverse instability of megaripples derives from the composition of their crests which comprise coarse particles that allow initial perturbations in ripple height to grow further the results suggest a physical mechanism for the transverse instability of megaripples and new insight into the spatial patterns of sand ripples

precambrian ammonium biogeochemistry a study of the moine metasediments scotland abstract the content and isotopic composition of ammoniacal nitrogen have been determined in a suite of amphibolite facies metasediments of precambrian age whole rock samples and mica separates from the moine succession proterozoic of scotland were analysed by a combination of capacitance manometry and static vacuum mass spectrometry prior to the analyses the presence of the ammonium ion was confirmed by obtaining infrared ir absorption spectra from the micas principally biotites whole rock ammonium contents are high for amphibolite facies metasediments 140 422 ppm the ammonium ion was not detected in the ir absorption spectra of biotites from one schist however this sample contains neither garnet nor white mica for most of the samples the 15n values are very positive between 12 4 and 16 6 with one sample having a lower value of 8 4 the major variations between samples can be interpreted in terms of original sedimentary features for the ammonium bearing samples muscovites have concentrations between 365 and 633 ppm biotites between 845 and 1739 ppm for individual samples nh4 mu nh4 bi varies between 0 31 and 0 43 a much narrower range than has been reported previously there are no significant or consistent differences in 15n between co existing biotite and white mica nor between the 15n values of the mineral separates and their respective whole rock values the latter suggests minimal selective partitioning of isotopes between micas and plagioclase feldspar the only other potential host for ammonium in the rocks assuming that the ammonium has been derived from organic matter originally present at the time of deposition and by comparison with previous studies it can be inferred that the original 15n value of the moine sediments was somewhere between 5 and 10 similar to recent sediments this suggests that the nitrogen cycle in the proterozoic shelf sea from which the moine sediments were deposited was broadly similar to the present day overall the study underlines how under developed the n system is compared to other stable isotope systems notably c and s and we use the opportunity to highlight some areas that could be developed in the future however one aspect is clear future ammonium studies of metamorphic rocks will need to be performed at high resolution visible scale of heterogeneity with strong mineralogical petrological and field controls

authigenic k nh4 feldspar in sandstones a fingerprint of the diagenesis of organic matter abstract in arkosic sandstones of the san joaquin and los angeles basins presently at temperatures between 35 c and 174 c trace amounts of authigenic k nh4 feldspar are present as microfracture fillings and overgrowths on detrital k feldspar microchemical analyses of this authigenic phase reveal up to 80 mole buddingtonite the largest ammonium concentrations are observed in a sandy interval of the antelope shale 80 mole and in the stevens sands 50 mole of the san joaquin basin this latter unit was deposited as a turbidite in the organic rich fruitvale shale an equivalent of the antelope shale the lowest ammonium contents 0 16 mole are present in the shallow marine vedder sands and the marginal marin san joaquin formation in the same basin petrographic 18o 13c and 87sr 86sr analyses of a dolomite cement that postdates authigenic k nh4 feldspar indicate that the feldspar precipitated below 28 c in the zone of methanogenesis from pore waters with the same sr signature as sea water at the time of sedimentation authigenic k nh4 feldspar is thus an early diagenetic phase that crystallized prior to oil migration under anoxic conditions when organic matter releases ammonium the source of ammonium is bacterial decay of organic matter in the sandstones themselves and or in contemporaneous shales

eolian features produced by the december 1977 windstorm southern san joaquin valley california high wind velocities during a windstorm in december of 1977 in the southern san joaquin valley california created eolian features and effects of a magnitude not previously reported in the literature three principal mechanisms of sediment movement by wind were studied by examining the size distribution of deposits in telephone poles saltation and suspension feeder pens and abandoned buildings saltation and suspension and gravel ripples surface creep the maximum grain sizes of rocks lodged in telephone poles at heights of 240 160 and 80 cm are 7 mm x 11 mm x 6 mm 10 mm x 15 mm x 6 mm and 20 mm x 23 mm x 5 mm respectively in some areas with rocky soils lag materials formed gravel ripples

spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces application to meridiani planum mars the landscape seen by the mars exploration rover mer opportunity at meridiani planum is dominated by eolian wind blown ripples with concentrated surface lags of hematitic spherules and fragments these ripples exhibit profound spatial grain size sorting with well sorted coarse grained crests and poorly sorted generally finer grained troughs these ripples were the most common bed form encountered by opportunity in its traverse from eagle crater to endurance crater field measurements from white sands national monument new mexico show that such coarse grained ripples form by the different transport modes of coarse and fine grain fractions on the basis of our field study and simple theoretical and experimental considerations we show how surface deposits of coarse grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces activation of meridiani planum coarse grained ripples requires a wind velocity of 70 m s at a reference elevation of 1 m above the bed from images by the mars orbiter camera moc of reversing dust streaks we estimate that modern surface winds reach a velocity of at least 40 m s and hence may occasionally activate these ripples the presence of hematite at meridiani planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments however the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site

boron isotope geochemistry during diagenesis part ii applications to organic rich sediments the measured clay water isotope fractionation for boron was applied to natural organic rich sediments undergoing illitization two field areas were chosen that show illitization occurring over a range of temperatures 80 500 c samples representing diagenetic temperatures of illitization 80 200 c are from the gulf of mexico sedimentary basin at 4 to 6 km depth in the eocene wilcox fm and jurassic norphlet fm the higher temperatures of illitization 200 500 c occur in a contact metamorphic aureole of the cretaceous pierre shale near walsenburg colorado here the kinetics of the illitization reaction are more rapid than in a slowly subsiding sedimentary basin but the chemical and mineralogical variations are minimized as complete illitization occurs over a small lateral distance in a single bentonite layer these studies indicate that b isotopes provide a more sensitive indicator of fluid variations in sedimentary basins than o isotopes and that b isotope analyses of authigenic illite can be a valuable geochemical tracer of fluid rock interactions boron isotope ratios in authigenic illite pore filling and muscovite stylolites from reservoir sandstones in the gulf of mexico are distinct from adjacent illitic mudstones whereas the oxygen isotopic ratios show little variation fluids in equilibrium with the mudstones cannot precipitate the authigenic clays with higher d 11 b values measured in the hydrocarbon reservoirs this suggests that the reservoir fluids were not in communication with the adjacent mudstone pore fluids but were introduced from another source area perhaps carrying a b isotopic label derived from the hydrocarbon source region authigenic illite formed in the pierre shale meta bentonite shows large isotopic fractionations of boron 20 during illitization at high temperatures incorporation of 500 ppm b in illite formed at 500 c shows that illite is a host for b even at metamorphic temperatures by using the experimentally derived b isotope fractionation data for silicates the measured d 11 b values of i s could be predicted by using a rayleigh fractionation model oxygen isotopic variations were negligible over this temperature range and thus provide little information on the mechanism of illitization copyright 2001 elsevier science ltd

gravel mantled megaripples of the argentinean puna a model for their origin and growth with implications for mars gravel megaripples in the puna of argentina are the most extreme aeolian megaripples on earth and are useful analogs for aeolian processes on mars field observations supplemented by experimental and numerical constraints on wind characteristics and aeolian transport reveal their conditions of formation and growth to be an aeolian geomorphology perfect storm the bedforms are formed on a substrate of weakly indurated ignimbrite aeolian deflation of which yields a bimodal lag of lithics and pumice clasts onto an undulating surface under normal wind conditions in this region the lithics are organized into bedforms on local upslopes and highs through creep induced by the impact of saltating sand and pumice the gravel bedforms grow through shadowing and trap sand and silt that is gradually kinetically sieved down to lift the gravel mantle upwards to form the megaripples these observations connote that the largest features are not ripples in the sense of migrating bedforms but rather nucleation sites of wind transported sediment strong control by bedrock topography means that the largest bedform wavelengths are not a result of particle trajectories and this complicates their comparison with other ripples and may require a new classification of relevance to mars the puna megaripples are morphologically and contextually similar to small ripple like transverse aeolian ridges tars moreover the puna gravels have similar equivalent weight mg to those composing granule ripples at meridiani planum and their local origin may have implications for the origin of sediment in martian aeolian bedforms finally the stable yet dynamic character of the puna megaripples could help reconcile current models of tars with periodic bedrock ridges that may be produced by aeolian erosion

the influence of organic matter on the boron isotope geochemistry of the gulf coast sedimentary basin usa large variations in the boron isotopic composition of sedimentary environments make boron an attractive monitor of fluid rock interactions during diagenesis studies of b in marine sediments have shown that preferential adsorption of 10b on clay minerals leaves pore waters enriched in 11b during diagenesis clay minerals recrystallize and incorporate 10b into the mineral structure spivack a j palmer m r edmond j m 1987 the sedimentary cycle of the boron isotopes geochim cosmochim acta 51 1939 1949 this process should cause a depletion of b in the pore water with an increase in the 11b in the gulf coast sedimentary basin usa however there is a general increase in b content of formation waters land l s macpherson g l 1992 origin of saline formation waters cenozoic section gulf of mexico sedimentary basin geochim cosmochim acta 76 1344 1362 moldovanyi e p walter l m 1992 regional trends in water chemistry smackover formation southwest arkansas geochemical and physical controls aapg bull 76 864 894 and a decrease in 11b with depth this suggests that another source of 10b exists in deep basinal environments we know that oil reservoir brines are commonly enriched in boron collins a g 1975 geochemistry of oilfield waters elsevier new york p 496 therefore this study examines organic matter as a possible source of boron during thermal maturation samples of water oil and cored sediments were collected from three stacked hydrocarbon reservoirs in the gulf of mexico sedimentary basin at a depth of 3500 4350 m extraction of boron from organic matter oil and kerogen was done by parr bomb volatilization with mannitol used as a b complexing agent the isotope ratios were measured using negative thermal ionization and compared to in situ analyses using secondary ion mass spectrometry the 11b values of pore filling clays in sandstone reservoirs is 2 2 the b content of the clay averages 144 ppm oil field waters show a range in b content from 8 85 ppm and 11b values from 28 to 37 increasing from the lowest to the uppermost reservoir there is an apparent 11b enrichment of fluids with progressive migration through clay rich sediments very little b ppb was found in the oil but kerogen extracted from the oil source rock sassen r 1990 lower tertiary and upper cretaceous source rocks in lousiana and mississippi implications to gulf of mexico crude oil aapg bull 74 857 878 contains significant b 140 ppm with a 11b of 2 2 similar to the pore filling clay minerals in the sandstones while kerogen comprises only 2 of the sedimentary basin its influence can be significant if b with distinctly low 11b is released over a specific temperature interval during thermal maturation the release of b from organic compounds could cause the observed regional 10b enrichment in waters deep in the gulf coast basin

ammonium concentration and nitrogen isotope composition in metasedimentary rocks from different tectonometamorphic units of the european variscan belt the content and isotopic composition of ammonium nh4 were measured by using kjeldahl distillation for 63 samples of predominantly metasedimentary rocks from two different geological settings of the european variscides i e the erzgebirge and the zone of erbendorf vohenstrauss in germany the studied erzgebirge schists represent an early paleozoic passive margin sequence that reappears in different deep subducted metamorphic units this allows an efficient examination of nitrogen loss and isotope fractionation during prograde metamorphism ammonium is found to be progressively depleted accompanied by a shift in 15n from the low grade units 2 kbar 300 c with 638 124 ppm and 15n 2 2 0 6 to the garnet phyllite unit 9 kbar 470 c with 621 190 ppm and 15n 3 5 0 9 the mica schist eclogite unit 12 kbar 550 c with 394 113 ppm and 15n 3 9 0 8 and to the gneiss eclogite unit 12 kbar 730 c with 99 32 ppm and 15n 7 7 2 0 using equilibrium models for rayleigh distillation and batch volatilization suggest that the nitrogen depletion took place by ammonia release only for the mica schists this isotope fractionation can be explained by the loss of molecular nitrogen in comparison with the early paleozoic schists the proterozoic ortho and paragneisses of the erzgebirge gneiss unit 6 8 kbar 650 c contain significantly lower amounts of ammonium 70 ppm and reach relatively low 15n values 2 5 to 3 6 the paragneisses from the zone of erbendorf vohenstrauss zev sampled from the ktb pilot hole represents a separate tectonometamorphic unit that has undergone polyphase metamorphic conditions with the major imprint being amphibolite facies 7 kbar 650 700 c the metagraywackes have nh4 contents of 80 ppm and 15n of approximately 6 gneisses in the vicinity of a late cataclastic shear zone at 2000 m depth are characterized by a shift in nh4 250 ppm and 15n up to 12 which suggest late fluid rock interactions with a nitrogen and 15n enriched fluid

evolution of the yardangs at rogers lake california yardangs are streamlined wind eroded hills common to most deserts yardangs at rogers lake mojave desert california have streamlined forms characteristic of objects eroded by moving fluids a teardrop shape that approaches an ideal 1 4 width to length ratio in wind tunnel simulations miniature forms of various shapes changed sequentially by 1 erosion of the windward corners 2 erosion of the windward slope 3 erosion of the leeward corners and flanks and 4 erosion of the leeward slope prominent mechanisms in yardang evolution apparently are abrasion at the windward end and deflation and reverse air flow near the middle and at the downstream end width to length ratios of yardangs are grossly similar to those of some fluvial and glacial streamlined landforms the low kinetic energy of wind relative to ice and water the erosional resistance to wind of most rocks the rarity of long term unidirectional winds and the presence of running water topographic roughness and vegetation all limit the abundance of yardangs

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

illite smectite structural changes during metamorphism in black cambrian alum shales from the baltic area illite smectite i s from cambrian black shale of both early diagenetic and anchimetamorphic grade was investigated to determine the mechanism of the clay transformation the layer sequences the distribution of thicknesses of coherent scattering domains csds and the three dimensional ordering were determined by x ray diffraction xrd the proportions of cis vacant cv and transvacant tv 2 1 layers were determined by thermal analysis and the proportion and distribution of interlayer ammonium by xrd and by infared spectroscopy ir the structural formulae were determined from total chemical analysis and mossbauer and 27al nmr spectroscopies and the particle shape and size investigated by atomic force microscopy afm in the early diagenetic samples the i s is composed of two phases one of which contains 0 05 and the other 0 25 smectite s interlayers the first phase does not change during metamorphism in the second phase 0 20 s are converted to tobelite t layers through fixation of formula 1 but the i layers are not changed simultaneously the proportion of cv layers changes from 0 18 to 0 02 and the tetrahedral substitution of al for si is parallel to the increase in t layers all i interlayers contain 0 75k per o10 oh 2 further more the metamorphism results in increasing mean thickness of csds from 5 1 6 8 nm for the low diagenetic samples to 6 7 8 4 nm for the anchimetamorphic samples we conclude that the tobelitization was accompanied by transformation of cv to tv 2 1 layers adjacent to the smectite interlayers and formation of tv layers adjacent to the newformed tobelite interlayers in otherwise intact crystallites this mechanism only partly resembles the tobelitization previously observed in the upper jurassic north sea oil source rocks i s in these rocks contained tv 2 1 layers and t interlayers formed through solid state al for si substitution in the tetrahedral sheet and by ammonium fixation in the corresponding interlayers these different mechanisms are probably because the north sea i s originated from weathered illite like the cambrian high illitic phase whereas the cambrian low illitic phase undergoing the transformation originated from cv smectite of volcanic origin the results indicate that the illitization in oil source rocks is linked to oil generation and that it deviates from the illitization in other rocks because of the supply of ammonium formed during oil generation and the fixation of this ammonium in the former smectite interlayers 1 embed tex math 1 gif

earthquake rupture process recreated from a natural fault surface what exactly happens on the rupture surface as an earthquake nucleates spreads and stops we cannot observe this directly and models depend on assumptions about physical conditions and geometry at depth we thus measure a natural fault surface and use its 3 d coordinates to construct a replica at 0 1m resolution to obviate geometry uncertainty we can recreate stick slip behavior on the resulting finite element model that depends solely on observed fault geometry we clamp the fault together and apply steady state tectonic stress until seismic slip initiates and terminates our recreated m 1 earthquake initiates at contact points where there are steep surface gradients because infinitesimal lateral displacements reduce clamping stress most efficiently there unclamping enables accelerating slip to spread across the surface but the fault soon jams up because its uneven anisotropic shape begins to juxtapose new high relief sticking points these contacts would ultimately need to be sheared off or strongly deformed before another similar earthquake could occur our model shows that an important role is played by fault wall geometry although we do not include effects of varying fluid pressure or exotic rheologies on the fault surfaces we extrapolate our results to large fault systems using observed self similarity properties and suggest that larger ruptures might begin and end in a similar way although the scale of geometrical variation in fault shape that can arrest a rupture necessarily scales with magnitude in other words fault segmentation may be a magnitude dependent phenomenon and could vary with each subsequent rupture

fixed ammonium in clays associated with crude oils abstract the association of ammonium nh 4 silicates with organic rich sedimentary environments has stimulated interest in the chemical cycle of n and its possible application as an indicator of in situ organic maturation reactions or crude oil migration fixed nh 4 in clay minerals was determined from three hydrocarbon occurrences of similar depositional environment but different ages depth and thermal maturity to determine whether anomalously high nh 4 substitution occurs near mature hydrocarbons results show higher fixed nh 4 concentrations in marginally mature mudstones than in immature sediments the highest fixed nh 4 concentrations were found in clays from sandstone reservoirs containing migrated crude oil fixed nh 4 in clays from holocene oil seep sediments in the gulf of mexico continental slope offshore louisiana averages 0 08 wt and increases with depth in shallow cores 420 cm reflecting an early diagenetic trend that is apparently not influenced by migrating crude oil programmed pyrolysis shows that the sediments are thermally immature av t max 419 c high hydrogen index values av 359mg g are the result of biodegraded crude oil and a high oxygen index av 182mg g reflects the presence of authigenic carbonate fixed nh 4 averages 0 16 wt in wilcox group eocene mudstones enclosing two sandstone reservoirs at fordoche field onshore louisiana in comparison to these mudstones anomalously high nh 4 fixation appears to occur in reservoir clay minerals pyrolysis shows that the sediments are marginally mature for crude oil generation av t max 432 c average hydrogen index 187 mg g and oxygen index values 75 mg g are consistent with oil prone type ii and type iii kerogen increased pyrolysis production index values and solvent extraction shows the presence of migrated crude oil this suggests that a reaction which releases nh 3 during crude oil generation or migration is recorded bynh 4 substitution in clays fixed nh 4 and total organic carbon toc at fordoche field show no statistically significant correlation suggesting that nh 4 substitution in clay minerals is not simply related to the amount of organic matter in the section but is also influenced by the presence of crude oil once nh 4 has been fixed in clays it is a more stable hydrocarbon proximity indicator than pore fluid tracers because it is less influenced by later chemical or geological changes

nitrogen isotope compositions of metasedimentary rocks in the catalina schist california implications for metamorphic devolatilization history abstract in the catalina schist subduction zone metamorphic complex california metasedimentary rocks show a decrease in n concentration and an increase in 15nair with increasing metamorphic grade lowest grade lawsonite albite rocks contain 632 185 ppm n with 15 n 1 9 0 6 whereas highgrade amphibolite equivalents contain 138 76 ppm n with 15 n 4 3 0 8 loss of n accompanied devolatilization reactions that evolved h2o rich c o h s n fluids through consumption of chlorite and phengitic white mica and production of mineral assemblages containing muscovite biotite garnet and kyanite whole rock n concentrations of up to 200 ppm in veins and pegmatites produced during high p t metamorphism reflect the redistribution of n during devolatilization and partial melting of the metasedimentary rocks bulk fluid rock n isotope fractionations 15n 15nfluid 15nrock of 1 5 1 were calculated with the rayleigh distillation equation taking into account variability in rock composition by comparison of samples with similar k2o concentrations these fractionations are similar to but slightly lower than published calculated fractionations for n2 nh4 exchange at the temperature range of 350 600 c over which most of the devolatilization occurred in the catalina schist approximately 3 4 to 2 25 the n systematics appear to be explained by n2 nh4 exchange and a devolatilization process intermediate in behavior to batch volatilization and rayleigh distillation the observed shifts in n concentration and 15n cannot be explained by nh3 nh4 exchange at these temperatures using the equilibrium models the distillation devolatilization process implicated in this study may govern the behavior of other trace elements partitioned into hydrous fluids during devolatilization e g b cs u similarity of the calculated fluid 15n 1 5 to 5 5 with compositions of natural gases inferred to be derived from metasedimentary sources indicates the possibility of using n as a tracer of large scale volatile transport

anthropic pedogenesis of purple rock fragments in sichuan basin china abstract considerable amounts of rock fragments are found in many purple soils developed from purple rocks in the sichuan basin of southwestern china we describe the effects of anthropic pedogenetic processes on purple rock fragments associated with soil amelioration by determining changes in rock fragment size distribution transformation of p and k of purple rocks into soils and the complexing of purple rock particles soil mineral particles with organic matter during anthropic pedogenesis of purple soils in sichuan basin of southwestern china the pedogenetic capacity of rock fragments can be expressed by the content of r 0 891 0 961 n 16 digging simulated by sieving and crop planting facilitate pedogenesis of purple rock fragments and their mineral nutrient transformations the soil mineral particles preserve 18 36 of the organic carbon added as corn straw the organic carbon is complexed after corn straw is mixed with

ammonium as a biomarker in precambrian metasediments abstract the following article assesses the potential of ammonium as a biomarker in precambrian metasediments a modern marine environment is considered to highlight the processes that contribute to the isotopic composition of organic nitrogen notably the roles played by nitrogen fixing organisms cyanobacteria and denitrifying bacteria the carbon and nitrogen biogeochemical cycles are compared and contrasted unlike carbon the major nitrogen isotope variations may be controlled by local environmental conditions such as season of the year and water depth however such local environmental factors may have been superimposed on more gradual changes related to the long term chemical evolution of the exterior environments of the earth the great potential of nitrogen as a biomarker is that the breakdown product of organic nitrogen ammonium behaves like a trace element and is stable in high temperature crustal processes thus ammonium may survive as a biomarker when all other evidence for former life has been destroyed and ammonium studies may be able to identify sedimentary pelitic components in high grade precambrian terrains previous results from precambrian rocks are reviewed to highlight that very little work has been completed to date and that only very general conclusions can be drawn much work needs to done in order to understand the basic biogeochemistry and geochemistry of crustal nitrogen and it is suggested that the best way to proceed is by numerous detailed case studies the interpretation of isotope ratios in ancient sediments usually assumes uniformitarianism and the justification of this approach is considered briefly overall this article highlights the under developed potential of precambrian ammonium biogeochemistry and suggests area for future research not only does the development of the subject have implications for the search for former life on mars but it may also open up new areas of precambrian research

the origin of the transverse instability of aeolian megaripples abstract flat sand beds subjected to wind stress are unstable and the wind action results in two types of aeolian sand ripples normal ripples and megaripples the distinction between the two types is based on two characteristics i the normal ripple pattern usually has a wavelength of up to 30 cm while the megaripple wavelength is on the order of meters and ii unimodal distributions of sand grain size lead to normal ripples while bimodal distributions result in megaripples on mars the distinction between the two types is more difficult to ascertain because the length scales of normal ripples and megaripples can overlap and often there is no detailed information regarding their grain size distribution unlike normal ripples megaripples show transverse instability whose mechanism remains elusive resulting in a much larger sinuosity of the crestline than normal ripples in this study we investigate the megaripples transverse instability by using field measurements wind tunnel experiments and numerical simulations of a three dimensional ripple model we show that a coarse grains accumulate at megaripple crests with a corresponding reduction of the lateral sand transport along the crest and b the transverse instability of megaripples is generated by a positive feedback between the height of the crest and the accumulation of coarse grains with more grains accumulating on the higher portions of the crest the outcomes of this positive feedback are that the thickness of the coarse grain armoring layer along the crest is not uniform and that it correlates with the crest height in turn these height differences drive the transverse instability such that higher portions of the ripple migrate more slowly than the lower sections creating a wavy crestline an analysis of martian ripple images shows variations in the sinuosity index suggesting that this characteristic can be useful in distinguishing between normal ripples and megaripples on mars

largest wind ripples on earth unique wind ripples attaining heights to 2 3 m wavelengths to 43 m and a crest maximum grain size of 19 mm occur on the argentine puna plateau at 4000 m altitude these are the largest ripples reported on earth comparable only to mars counterparts they form in the presence of high proportions of low density pumice clasts 0 91 g cm 3 although crests are exclusively composed of varnished normal density clasts 2 43 g cm 3 mature ripple profiles are partly excavated on bedrock so they form by a combination of deflation winnowing of finer grains minor wind drift of fine gravel and lagging of clasts 4 cm the large ripple size appears to be related to strong winds dense saltation layers and a long time for evolution ripple sizes are smaller on obstacles as compared to flat terrain there is a lack of correlation between clast size wavelength and the extreme ripple size in spite of the thin atmosphere all of which suggest that while small scale gravel ripples may form according to a reptation model their evolution into large scale types may relate to aerodynamic instabilities originating at the saltation curtain air interface

geochemical and tectonic uplift controls on rock nitrogen inputs across terrestrial ecosystems rock contains 99 of earth s reactive nitrogen n but questions remain over the direct importance of rock n weathering inputs to terrestrial biogeochemical cycling here we investigate the factors that regulate rock n abundance and develop a new model for quantifying rock n mobilization fluxes across desert to temperate rainforest ecosystems in california usa we analyzed the n content of 968 rock samples from 531 locations and compiled 178 cosmogenically derived denudation estimates from across the region to identify landscapes and ecosystems where rocks account for a significant fraction of terrestrial n inputs strong coherence between rock n content and geophysical factors such as protolith i e parent rock grain size and thermal history are observed a spatial model that combines rock geochemistry with lithology and topography demonstrates that average rock n reservoirs range from 0 18 to 1 2 kg n m 3 80 to 534 mg n kg 1 across the nine geomorphic provinces of california and estimates a rock n denudation flux of 20 92 gg yr 1 across the entire study area natural atmospheric inputs 140 gg yr 1 the model highlights regional differences in rock n mobilization and points to the coast ranges transverse ranges and the klamath mountains as regions where rock n could contribute meaningfully to ecosystem n cycling contrasting these data to global compilations suggests that our findings are broadly applicable beyond california and that the n abundance and variability in rock are well constrained across most of the earth system

supply limited horizontal sand drift at an ephemerally crusted unvegetated saline playa a site at owens dry lake was observed for more than 4 years the site was a vegetation free saline playa where the surface formed ephemeral crusts crusts that form after rainfall sometimes these crusts were destroyed and often a layer of particles on the crust would engage in vigorous aeolian activity three phases of active sand drifting are defined as almost no movement extreme supply limitation loose particles on crust with some degree of sand drift moderate supply limitation and unlimited source movement corresponding to a destroyed surface crust unlimited supply these phases occurred 45 49 and 6 of the time respectively the accumulation of loose particles on the crust was mostly the result of in situ formation crusted sediments with loose particles on top can exhibit mass flux rates about the same as for noncrusted sediments crusted sediments limit or eliminate sand drift in two conditions for rough crusts that effect a sufficiently high threshold friction velocity above the wind friction velocity and for limited amounts of loose particles on the crust where particle supply is less than would be transported in normal saltation for a thick sandy surface these supply limited cases are similar to wind erosion of limited spilled material on a hard concrete surface we quantified supply limitation by defining a potential or supply unlimited sand drift function q ag where a represents supply limitation that decreases as the particle source is depleted here q is the mass of sand transported through a surface perpendicular to the ground and to the wind and having unit width during time period t and g u u2 u2 t dt for u u t g is integrated for the same time period t as for q u is the friction velocity of the wind and u t is the threshold friction velocity of the wind hard crusts usually formed in the summer tended to show almost no change of threshold friction velocity with time and often gave total protection from wind erosion rough crusts provided sufficient protection expressed as high threshold friction velocities for these high threshold friction velocities aeolian activity was greatly reduced or practically prevented the softest crusts usually formed in the winter provided much less protection and sometimes were destroyed by the wind following this destruction the potential or supply unlimited sand drift would be observed

construction of an intraplate fault system model of south australia and simulation tool for the iservo institute seed project to foster ongoing international cooperation beyond aces apec cooperation for earthquake simulation on the simulation of solid earth phenomena agreement was reached to work towards establishment of a frontier international research institute for simulating the solid earth iservo international solid earth research virtual observatory institute http www iservo edu au this paper outlines a key australian contribution towards the iservo institute seed project this is the construction of 1 a typical intraplate fault system model using practical fault system data of south australia i e sa interacting fault model which includes data management and editing geometrical modeling and mesh generation and 2 a finite element based software tool which is built on our long term and ongoing effort to develop the r minimum strategy based finite element computational algorithm and software tool for modelling three dimensional nonlinear frictional contact behavior between multiple deformable bodies with the arbitrarily shaped contact element strategy a numerical simulation of the sa fault system is carried out using this software tool to demonstrate its capability and our efforts towards seeding the iservo institute

grain size segregation and stratigraphy in aeolian ripples modelled with a cellular automaton aeolian ripples are distinguished by coarse grained crests finegrained troughs and thin veneers of coarse grains on the upwind stoss slopes migration of these sorted bedforms during periods of net deposition results in a characteristic inversely graded stratigraphy that distinguishes aeolian sandstones from those of fluvial origin1 here we investigate the formation and evolution of aeolian ripples using a cellular automaton model of a sandbed which incorporates two grain sizes and is subject to the impacts of episodically hopping saltating grains using this model we identify the physical processes responsible for both the spatial sorting and the stratigraphic signature of the ripples high energy saltating grains are found to eject small grains preferentially from the impact site leading to a coarsening of the heavily bombarded stoss slopes coarse grains do not in general leap far enough to escape the shadow zones on the downwind lee slopes and therefore tend to accumulate and cycle around the ripple crests small grains on the other hand are ejected at higher velocities enabling them to hop further incorporating net deposition into the model results in a stratigraphy closely resembling thin planar laminae pinstriping found in aeolian sandstones the inverse grading of grain sizes is a direct consequence of their different hop lengths

relations of ammonium minerals at several hydrothermal systems in the western u s abstract ammonium bound to silicate and sulfate minerals has recently been located at several major hydrothermal systems in the western u s utilizing newly discovered near infrared spectral properties knowledge of the origin and mineralogic relations of ammonium minerals at known hydrothermal systems is critical for the proper interpretation of remote sensing data and for testing of possible links to mineralization submicroscopic analysis of ammonium minerals from two mercury and gold bearing hot springs deposits at ivanhoe nevada and mclaughlin california shows that the ammonium feldspar buddingtonite occurs as fine grained euhedral crystals coating larger sulfide and quartz crystals ammonium feldspar seems to precipitate relatively late in the crystallization sequence and shows evidence for replacement of nh4 by k or other monovalent cations some buddingtonite is observed in close association with mercury but not with gold ammonioalunite is found in a variety of isolated crystal forms at both deposits nitrogen isotopic values for ammonium bearing minerals show a 14 range in composition precluding assignment of a specific provenance to the nitrogen the correlations of nitrogen isotopic values with depth and ammonium content suggest some loss of nitrogen in the oxidizing supergene environment possibly as a metastable mineral the high ammonium content in these hydrothermal systems the close association to mercury and the small crystal size of the ammonium bearing minerals all suggest that ammonium may be transported in a late stage vapor phase or as an organic volatile such a process could lead to the formation of a non carbonaceous organic aureole above a buried geothermal source the discovery of a 10 km outcrop of ammonium minerals confirms that significant substitution of ammonium in minerals is possible over an extensive area and that remote sensing is a feasible means to detect such aureoles

nitrogen isotope tracers of high temperature fluid rock interactions case study of the catalina schist california abstract nitrogen isotope data for metasomatized rocks veins and pegmatites in the catalina schist subduction zone metamorphic complex allow futher characterization of complex high p t metasomatic proceses and evaluation of the scales of isotopic equilibration and fluid transport during subduction zone metamorphism throughout the catalina schist n resides predominantly as nh4 in white mica which occurs in nearly all bulk compositions i e metasedimentary metamafic and to a lesser extent metaultramafic melange at all grades within each metamorphic unit of the catalina schist ranging in grade from lawsonite albite to amphibolite facies 15n values of mica in metasomatized metamafic and metaultramafic rocks are consistent with the metasomatic addition of n from nearby devolatilizing metasedimentary rocks into the initially n poor mafic and ultramafic rocks within each unit uniformity of mica 15n in metasomatized rocks relative to the 15n of metasedimentary rocks in the same unit implies mixing of n from nearby heterogeneous metasedimentary sources perhaps producing fluids with unifrom 15n at up to the kilometer scale however the trend in 15n of metasedimentary sources with increasing metamorphic grade is inconsistent with larger scale up temperature transfer of fluid in this case n2 bearing in the catalina schist paleosubduction zone such flow at scales of up to tens of kilometers has been inferred through previous oxygen isotope study nitrogen isotope compositions are instead believed to have been controlled at a more local scale than the o isotope systematics due to the more rock dominated fluid rock mass balance for n the 15n of muscovite in leucosomes and pegmatites in amphibolite grade metasedimentary exposures matches that of muscovite in metasedimentary hosts implying minimal n isotope fractionation during migmatization processes and possible transfer of metasedimentary n isotope signatures in silicate melts these results illustrate the potential of the n isotope system to yield valuable information regarding fluid rock interactions in the crust and mantle the data for the catalina schist demonstrate the ability of n isotopes to trace the transfer of sediment derived c o h s n fluids and silicate melts and show the expected benefit of the n isotope system in having a differing fluid rock mass balance relative to the more commonly used stable isotope systems that can yield unique constraints in quantitative models of crustal fluid processes