effects of biological crust coverage on soil hydraulic properties for the loess plateau of china biological soil crusts bscs are ubiquitous living covers that have been allowed to grow on abandoned farmlands over the loess plateau because the grain for green project was implemented in 1999 to control serious soil erosion however few studies have been conducted to quantify the effects of bsc coverage on soil hydraulic properties this study was performed to assess the effects of bsc coverage on soil hydraulic properties which are reflected by the soil sorptivity under an applied pressure of 0 s and 3 s cm saturated hydraulic conductivity k wetting front depth wfd and mean pore radius for the loess plateau of china five classes of bsc coverage i e 1 20 20 40 40 60 60 80 and 80 100 and a bare control were selected at both cyanobacteria and moss covered sites to measure soil hydraulic properties using a disc infiltrometer under 2 consecutive pressure heads of 0 and 3 cm allowing the direct calculation of s s k and the wfd was measured onsite using a ruler immediately after the experiments of infiltration the results indicated that both cyanobacteria and moss crusts were effective in changing the soil properties and impeding soil infiltration the effects of moss were greater than those of cyanobacteria compared to those of the control the s s k wfd and values of cyanobacteria covered soils were reduced by 13 7 11 0 13 3 10 6 and 12 6 on average and those of moss covered soils were reduced by 27 6 22 1 29 5 22 2 and 25 9 respectively the relative soil sorptivity under pressures of 0 rs and 3 rs cm the relative saturated hydraulic conductivity rk the relative wetting front depth rwfd and the relative mean pore radius r decreased exponentially with coverage for both cyanobacteria and moss covered soils the rates of decrease in rs rs rk rwfd and r of cyanobacteria were significantly slower than those of moss especially for the coverage of 0 40 with smaller ranges the variations of soil hydraulic properties with bsc coverage were closely related to the change in soil clay content driven by the bsc coverage on the loess plateau the results are useful for simulating the hydraulic parameters of bsc covered soils in arid and semiarid areas

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the cm chondrites aqueous alteration of primitive meteorites was among the earliest geological processes during the evolution of our solar system clumped isotope thermometry of carbonates in the cm chondrites cold bokkeveld murray and murchison demonstrates that they underwent aqueous alteration at 20 71 c from a fluid with 18 o vsmow of 2 0 to 8 1 and 17 o vsmow of 0 1 to 3 0 the 13 c vpdb values of these carbonates exhibit a negative correlation with the 18 o vsmow of their formation waters consistent with formation and escape of 13 c depleted ch 4 during aqueous alteration methane generation under these conditions implies that the alteration fluid was characterized by an eh 0 67 and ph 12 5 or lower at the highest alteration temperatures our findings suggest that methane generation may have been a widespread consequence of planetesimal and planetary aqueous alteration perhaps explaining the occurrence of methane on titan triton pluto and other kuiper belt objects

relict and other anomalous grains in chondrules implications for chondrule formation we have identified relict olivine and pyroxene grains in chondrules from ordinary and carbonaceous chondrites that probably did not crystallize in situ some of these olivines are clear but others contain fine grained fe ni dusty olivines and resemble previously described occurrences in ordinary chondrites there are also chondrules in which all olivine is dusty we conclude 1 not all relict olivines are dusty 2 not all dusty olivines crystallized outside the chondrule in which they occur and 3 some dusty olivines were produced during chondrule formation by a reduction process that affected the whole chondrule the occurrence of dusty olivines and relict pyroxenes and olivines in chondrules from carbonaceous as well as ordinary chondrites supports the argument that chondrules from all chondrites had similar origins and histories we propose that chondrules and mineral fragments were transported across f o2 gradients in the solar nebula while they were hot or were reheated in an environment different from the one in which they formed partially molten chondrules sometimes incorporated mineral grains or chondrules with different redox states producing compound chondrules and chondrules containing anomalous grains dusty olivines may also have formed when hot chondrules were transported to regions of lower oxygen fugacity

olivine in terminal particles of stardust aerogel tracks and analogous grains in chondrite matrix abstract the dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the wild 2 samples we present 68 analyses of olivine fa 0 97 in the coarse grained terminal particles of stardust aerogel tracks and a comprehensive dataset 10 3 analyses of analogous olivine grains 5 30 m isolated in ci cm cr ch co cv3 oxidized cv3 reduced c3 ungrouped acfer 094 and ningqiang l ll 3 0 4 eh3 and kakangari chondrite matrix these compositions reveal that wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite forming regions the wild 2 olivine includes amoeboid olivine aggregates aoas refractory forsterite type i and type ii chondrule fragments and or microchondrules and rare relict grain compositions in addition we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low temperature aqueous processing in the kuiper belt the generally low cr content of feo rich olivine in the stardust samples indicates that they underwent mild thermal metamorphism akin to a petrologic grade of 3 05 3 15

microbiotic crust control of runoff generation on sand dunes in the negev desert 1 the general belief that dune sands in arid regions are not likely to generate runoff and that runoff necessitates wet conditions is examined runoff generation was measured within an arid dune field in the western negev desert israel during 1990 1994 on 16 plots 1 2 6 6 m2 constructed along a continuum of crust covered crust the relationships between chlorophyll a and carbohydrates of the microbiotic crust and runoff yield were studied whereas chlorophyll a 15 45 mg m 2 and carbohydrates 4 9 17 6 g m 2 of the cyanobacterial crusts showed positive linear relationships with runoff coefficients a significant reduction in runoff yield was obtained once the moss dominated crust with 53 54 5 mg m 2 chlorophyll a and 28 5 28 9 g m 2 of carbohydrates which inhabited the wettest habitat within the dune field was also included in the analysis contrary to previous assumptions that an increase in runoff generation occurs on arid and semiarid sand dunes in wet climates wet climates may lead to the establishment of moss dominated crusts that in turn decrease runoff yield

large igneous province on the us atlantic margin and implications for magmatism during continental breakup rifted continental margins commonly include sections of igneous rock more than twice as thick as normal oceanic crust explanations for this voluminous magmatic accretion during rifting include plume models1 3 which require a deep seated thermal or chemical anomaly in upwelling mantle and non plume models4 7 which call on broad shallow thermal anomalies and or rapid upwelling of mantle through the melting zone new seismic models from two transects across the continent ocean transition on the us atlantic margin8 10 confirm the presence of a 20 25 km thick igneous section here we argue that the similarity of the crustal structure on these and two previous transects spanning 1 000 km of the margin and the association of thick igneous crust with the east coast magnetic anomaly11 imply that the thick igneous section extends along the entire margin and may have a volume of as much as 3 2 106 km3 the distribution of volcanic and plutonic rocks details of the seismic structure and lack of independent evidence for a hotspot are difficult to reconcile with plume models and suggest that non plume processes created the thick igneous crust

abundances of presolar silicon carbide grains in primitive meteorites determined by nanosims abstract it has been suggested that the matrices of all chondrites are dominated by a common material with ivuna like ci abundances of volatiles presolar grains and insoluble organic matter iom e g alexander 2005 however matrix normalized abundances of presolar silicon carbide sic grains estimated from their noble gas components show significant variations in even the most primitive chondrites huss and lewis 1995 huss et al 2003 in contradiction to there being a common chondrite matrix material here we report presolar sic abundances determined by nanosims raster ion imaging of iom extracted from primitive members of different meteorite groups we show that presolar sic abundance determinations are comparable between nanosims instruments located at three different institutes between residues prepared by different demineralization techniques and between microtomed and non microtomed samples our derived sic abundances in cr chondrites are comparable to those found in the ci chondrites 30 ppm and are much higher than previously determined by noble gas analyses the revised higher cr sic abundances are consistent with the crs being amongst the most primitive chondrites in terms of the isotopic compositions and disordered nature of their organic matter similar abundances between cr1 cr2 and cr3 chondrites indicate aqueous alteration on the cr chondrite parent body has not progressively destroyed sic grains in them a low sic abundance for the reduced cv3 rbt 04133 can be explained by parent body thermal metamorphism at an estimated temperature of 440 c minor differences between primitive members of other meteorite classes which did not experience such high temperatures may be explained by prolonged oxidation at lower temperatures under which sic grains formed outer layers of sio2 that were not thermodynamically stable leading to progressive degassing destruction of sic

crustal structure of the goban spur rifted continental margin ne atlantic summary we present results that constrain the crustal structure across a typical non volcanic rifted continental margin the goban spur in the ne atlantic traveltime and amplitude modelling of wide angle ocean bottom seismograph profiles shows that the continental crust thins in a seaward direction to about 7 km before it breaks to allow a new oceanic spereading centre to develop the crustal velocity structure the stretching factors and the density distribution inferred from gravity anomalies are consistent with bulk pure shear stretching for the development of the rifted continental margin the seismic velocity structure of the thinned continental crust suggests that thinning was accompanied by only limited igneous intrusion and extrusion in the upper crust the adjacent oceanic crust is abnormally thin 5 4km this is explained most readily by accretion at a very slow spreading centre approx 11 mm yr full rate although additional cooling by conductive heat loss from the parent mantle as it rose slowly beneath the stretched and thinned continental lithosphere together with minor igneous intrusion into and surface flows onto the adjacent continental crust may also have reduced the oceanic igneous thickness immediately adjacent to the continent ocean transition

self consistent rolling hinge model for the evolution of large offset low angle normal faults the nature of the physical processes responsible for the formation of continental and oceanic metamorphic core complexes is widely debated the controversy focuses primarily on whether the low angle normal faults observed in these environments formed and slipped at low angles or were rotated from an original high angle orientation after large offsets we describe a self consistent numerical model for the extension of a brittle layer that can spontaneously produce normal fault structures in our formulation a fault or faults form because strength is locally reduced with increasing strain if the reduction in fault strength is 10 of the total strength of the layer then faults lock after an offset smaller than the layer thickness and new faults form larger strength reduction leads to single faults that continue to slip no matter how large the fault offset if the strength reduction occurs by the loss of cohesion then we see the unlimited offset faults for layers 11 22 km thick for reasonable values of cohesion the key result of this study is that structures very similar to those observed in both oceanic and continental core complexes are produced by rotation of the inactive part of the model fault after very large offset

the break up of continents and the formation of new ocean basins rifted continental margins are the product of stretching thinning and ultimate break up of a continental plate into smaller fragments and the rocks lying beneath them store a record of this rifting process earth scientists can read this record by careful sampling and with remote geophysical techniques these experimental studies have been complemented by theoretical analyses of continental extension and associated magmatism some rifted margins show evidence for extensive volcanic activity and uplift during rifting at these margins the record of the final stages of rifting is removed by erosion and obscured by the thick volcanic cover other margins were underwater throughout their formation and showed rather little volcanic activity here the ongoing deposition of sediment provides a clearer record during the last decade vast areas of exhumed mantle rocks have been discovered at such margins between continental and oceanic crust this observation conflicts with the well established idea that the mantle melts to produce new crust when it is brought close to the earth s surface in contrast to the steeply dipping faults commonly seen in zones of extension within continental interiors faults with very shallow dips play a key role in the deformation immediately preceding continental break up future progress in the study of continental break up will depend on studies of pairs of margins which were once joined and on the development of computer models which can handle rigorously the complex transition from distributed continental deformation to sea floor spreading focused at a mid ocean ridge

deciphering continental breakup in eastern australia using low temperature thermochronometers 1 first order topographical features at high elevation passive margins have the potential to store information about the early stages of continental rifting which are usually lost in the sediment record in this study we present a new combination of apatite fission track and u th he analyses from two coast perpendicular traverses to decipher the time of formation and evolution of the escarpment at the southeastern australian margin a combination of inverse and forward modeling of the apatite fission track aft and he data indicates that the coast experienced a rapid denudational event starting at 110 10 ma at least 15 myr before seafloor spreading 85 ma in agreement with the hypothesis that rifting at magma poor margins evolves slowly thus the enhanced denudation is not related to the synbreakup base level drop but it may have been related to a thermally driven transient surface uplift considerations on isostatic flexure and rigidity of the lithosphere indicate that unless significant synrift brittle movements are assumed to have occurred along margin parallel faults that are no more visible the coast must have experienced a higher geothermal gradient than normal the evolution of the rest of the coastal plain may have taken up to 90 myr in agreement with numerical models of passive margins evolution the u th he ages across the coastal plain are consistent with an in place excavation scenario of a high rift shoulder and they rule out the possibility of a constant retreat of the escarpment aft he data from the plateau indicate that the highlands remained stable throughout continental breakup experiencing rates of erosion of 5 10 m myr since at least 200 ma

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

primordial oxygen isotope reservoirs of the solar nebula recorded in chondrules in acfer 094 carbonaceous chondrite abstract highly precise and accurate ion microprobe analyses of oxygen three isotope ratios in chondrules from the acfer 094 one of the most primitive carbonaceous chondrites show that chondrules preserve evidence for oxygen isotope heterogeneity in chondrule forming regions of the solar nebula identical 17 o values in most minerals and glass within each chondrule indicate that the oxygen isotope ratio in chondrule melt did not change during or after crystallization nearly half of the chondrules studied contain small amounts of olivine grains that have an oxygen isotope anomaly relative to other minerals and glass in the same chondrule most chondrules in acfer 094 can be classified into two oxygen isotope groups 17 o 2 and 17 o 5 indicating that the final melting of chondrules occurred within two distinct oxygen isotope reservoirs probably representing the local protoplanetary disk immediately before planetesimal formation one of these reservoirs 17 o 2 is observed from chondrules in other carbonaceous chondrites and from crystalline silicates in comet wild 2 suggesting that crystalline silicates formed in an oxygen isotope reservoir of 17 o 2 were widely distributed in the outer asteroid belt and throughout the outer solar nebula oxygen three isotope ratios of minerals in chondrules from acfer 094 are distributed along a newly defined primitive chondrule minerals pcm line which has slope 1 17 o 0 987 0 013 18 o 2 70 0 11 and intersects the terrestrial fractionation line at 18 o 5 8 0 4 these data are distinct from and plot between the ccam and young and russell lines the pcm line is interpreted to represent the mixing trend of extreme oxygen isotope reservoirs in the early solar system that were the primary oxygen isotope reservoir of solids that accreted to form planets including the earth

radar enabled recovery of the sutter s mill meteorite a carbonaceous chondrite regolith breccia doppler weather radar imaging enabled the rapid recovery of the sutter s mill meteorite after a rare 4 kiloton of tnt equivalent asteroid impact over the foothills of the sierra nevada in northern california the recovered meteorites survived a record high speed entry of 28 6 kilometers per second from an orbit close to that of jupiter family comets tisserand s parameter 2 8 0 3 sutter s mill is a regolith breccia composed of cm mighei type carbonaceous chondrite and highly reduced xenolithic materials it exhibits considerable diversity of mineralogy petrography and isotope and organic chemistry resulting from a complex formation history of the parent body surface that diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to c class asteroids are interpreted

water repellency and pore clogging at early successional stages of microbiotic crusts on inland dunes brandenburg ne germany abstract biological soil crusts play a key role for hydrological processes in many open landscapes they seal the topsoil and generate surface run off utilization of the mineral substrate at early stages of microbiotic crusts was investigated using scanning electron microscopy sem water repellency indices were measured using the ethanol water microinfiltrometer method and steady state water flow was determined on the dry crusts and after 300 600 1200 and 1800 s of wetting thus allowing to follow pore clogging through swelling of extracellular polymeric substances eps it was found that water repellency increases with initial crust development where filamentous cyanobacteria and filamentous green algae were dominating but decreases as coccal algae bryophytes and fungi associated with bryophytes emerged swelling of eps took place immediately after wetting and its influence on steady state water flow was most pronounced when filamentous cyanobacteria and algae partially filled in the matrix pores and enmeshed sand grains still leaving micropore channels available for free water infiltration but prior to appearance of coccal algae bryophytes and associated fungi which formed a dense cover on the surface it was concluded that a new phase of crust succession was accompanied by easier wettability but slower infiltration transition from hydrophobicity to pore clogging as ruling mechanisms causing water run off may occur during wetting of individual biological crusts but also during crust succession over time

oxygen isotope systematics of chondrule phenocrysts from the co3 0 chondrite yamato 81020 evidence for two distinct oxygen isotope reservoirs high precision oxygen three isotope measurements of olivine and pyroxene were performed on 33 chondrules in the yamato 81020 co3 0 chondrite by secondary ion mass spectrometry in chondrules where oxygen isotopes were measured in both olivine and pyroxene the majority of grains have similar values indicating co magmatic crystallization however many chondrules contain relict grains with unique oxygen isotope ratios a striking feature of yamato 81020 chondrules is a bimodal distribution of oxygen isotope ratios as those with mg 97 phenocrysts range in 17o from 4 8 to 6 5 5 5 group and those with mg 96 36 phenocrysts have 17o values of 2 1 to 3 0 2 5 group a single mg 99 6 barred olivine chondrule has a 17o of 3 3 we discuss that 17o 5 5 chondrules are derivative of a reservoir with limited dust enrichment 100 solar system which yielded a relatively reduced chondrule forming environment in contrast the 17o 2 5 chondrules may have been influenced by 16o poor h2o ice that sublimed and then homogenized with precursor material the addition of h2o when combined with high dust enrichment 1000 solar system and greater bulk fe content could have induced an oxidized environment at high temperatures forming mg 96 36 chondrules among the 33 chondrules studied the al mg relative ages of 20 had been obtained previously comparing the oxygen isotope ratios and the 26al ages of these chondrules it is likely that the 5 5 and 2 5 oxygen isotope reservoirs existed contemporaneously this implies that the snow line was spatially fixed during chondrule formation and separated the co chondrite accretion region into two distinct volumes of precursors

algae influence the hydrophysical parameters of a sandy soil abstract article history received 2 august 2011received in revised form 31 january 2012accepted 3 february 2012available online xxxxkeywords algaebiological soil crustsoil water repellencysand dunesorptivityhydraulic conductivity biological soil crusts have a major effect on water ow in soils two study sites located at a pine forest gladecovered with a biologicalsoil crust formed the basis of our study the sand soil atthe surface glade soil wascompared to a control soil pure sand with limited impact of vegetation or organic matter occurring at50 cm depth beneath a glade area to assess the in uence ofalgae in the biological soil crust on the propertiesof pure sand a coccal green alga choricystis minor lamentous green alga klebsormidium subtile and stra menopile alga tribonema minus were isolated from the top layer of glade soil and grown in the lab in petridishes on sterile pure sand as monoalgal and bialgal c minor and k subtile crusts for 3 5 7 9 11 13 15 17 19 and 21 days atthe end ofeach growth stage the hydrophysicalparametersof crusted sand were estimat ed after drying at 50 c for 15 h equivalent to a 3 day hot spell and compared to the parameters of puresand the hydrophysical parameters were substantially different between the two surfaces the glade soilhad an index of water repellency about 18 times that of pure sand and the persistence of water repellencyalmost 54 times that of pure sand both sorptivity and hydraulic conductivity in the glade soil were about7 those of the pure sand respectively the growth of arti cial algal crusts characterized by an increase inorganic carbon content from 0 16 to 0 33 resulted in an increase in water drop penetration time of thedried crusts up to 14 times that of the pure sand and a decrease in the water sorptivity of the dried crustsup to 10 that of the pure sand whereas k subtile crusts both monoalgal and bialgal with c minor hadup to a 9 decrease in hydraulic conductivity compared to pure sand there was no impact of monoalgalc minor and t minus crusts on hydraulic conductivity k subtile was possibly limited to surface growth whereas c minor and t minus penetrated to depth consequently k subtile may have clogged the toppores more effectively than the other two strains the water repellency cessation time increased with anincrease in water drop penetration time for all the dried monoalgal and bialgal crusts used in this study agreater impact of k subtile on the shifts in hydraulic behaviour could in uence water capture and storage potentially decreasing evaporation during dry periods but enhancing overland ow diminishing leachingduring wet periods 2012 elsevier b v all rights reserved

properties and spatial distribution of microbiotic crusts in the negev desert israel abstract playing a cardinal role in surface stabilization and in carbon and nitrogen fixation microbiotic crusts play a crucial role in arid regions where they may serve as useful biomarkers for wind power and wetness duration this is especially the case on relatively unstable and infertile sand dunes in the negev desert where high correlations between the crust chlorophyll content and the daytime wetness duration were found yet only scarce data are available as to the possible link between the chlorophyll content and other physical color thickness strength crack density surface roughness and infiltrability and biological protein carbohydrate organic matter and species composition factors which determine in turn the crust type and its effect upon geomorphological and ecological processes no data are available on crust type distribution these were the aims of the current research when a cluster analysis was performed five types of microbiotic crusts were defined four of which were cyanobacterial a d and one moss dominated crust e the crusts differed in their physical and biological properties they showed an increase in chlorophyll content protein carbohydrates and organic matter from a to e with concomitant increase in species diversity thickness roughness and strength but with some variables crack density and infiltrability showing a reversed trend at the moss dominated crust the increase in the biomass components of the crust and the gradual change of the physical properties are explained by the improved physical conditions primarily wetness duration which facilitates longer hours of photosynthetic activity and consequently the introduction of additional more mesic species such as green algae lichens and mosses extended wetness duration was found to shift the crust type from cyanobacterial to moss dominated crust the spatial distribution of the crusts as verified by crust mapping coincided with the daylight surface duration which in turn was controlled by topography aspect angle and slope position it implies that whereas initial physical conditions dictates species composition and thus crust type the crust type in turn is responsible for characterizing the physical properties of the surface which may largely affect ecological and geomorphological processes

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

why aqueous alteration in asteroids was isochemical high porosity high permeability carbonaceous chondrite meteorites are the most compositionally primitive rocks in the solar system but the most chemically pristine ci1 and cm2 chondrites have experienced pervasive aqueous alteration apparently within asteroid parent bodies unfractionated soluble elements suggest very limited flow of liquid water indicting a closed system at scales large than 100 s m consistent with data from oxygen isotopes and meteorite petrography however numerical studies persistently predict large scale 10 s km water transport in model asteroids either in convecting cells or via exhalation flow an open system at scales up to 10 s km these models have tended to use permeabilites in the range 10 13 to 10 11 m2 we show that the permeability of plausible chondritic starting materials lies in the range 10 19 to 10 17 m2 0 1 10 d around six orders of magnitude lower than previously assumed this low permeability is largely a result of the extreme fine grain size of primitive chondritic materials applying these permeability estimates in numerical models we predict very limited liquid water flow distances of 100 s m at most even in a high porosity water saturated asteroid with a high thermal gradient over millions of years isochemical alteration with flow over minimal lengthscales is not a special circumstance it is inevitable once we consider the fundamental material properties of these rocks to achieve large scale flow it would require average matrix grain sizes in primitive materials of 10 s 100 s m orders of magnitude larger than observed finally in addition to reconciling numerical modelling with meteorite data our work explains several other features of these enigmatic rocks most particularly why the most chemically primitive meteorites are also the most altered

petrographic and oxygen isotopic study of refractory forsterites from r chondrite dar al gani 013 r3 5 6 unequilibrated ordinary and carbonaceous chondrites we have conducted petrographic chemical and in situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated r chondrite refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low feo and high refractory lithophile element rle contents refractory forsterites are typically enriched in 16o relative to normal olivine independent of the bulk o isotope ratios of the parent meteorites analyses of refractory forsterites spread along a 17o mixing line with 17o ranging from 2 to 10 due to similarities in oxygen isotopes and chemical compositions we conclude that refractory forsterites of various types of chondrites come from a single common reservoir implications of this hypothesis for the chemical and o isotope evolution of silicates in the early solar nebular are discussed

assessment of physical and hydrological properties of biological soil crusts using x ray microtomography and modeling biological soil crusts bscs are formed by aggregates of soil particles and communities of microbial organisms and are common in all drylands the role of bscs on infiltration remains uncertain due to the lack of data on their role in affecting soil physical properties such as porosity and structure quantitative assessment of these properties is primarily hindered by the fragile nature of the crusts here we show how the use of a combination of non destructive imaging x ray microtomography xmt and lattice boltzmann method lbm enables quantification of key soil physical parameters and the modeling of water flow through bscs samples from kalahari sands botswana we quantify porosity and flow changes as a result of mechanical disturbance of such a fragile cyanobacteria dominated crust results show significant variations in porosity between different types of crusts and how they affect the flow and that disturbance of a cyanobacteria dominated crust results in the breakdown of larger pore spaces and reduces flow rates through the surface layer we conclude that the xmt lbm approach is well suited for study of fragile surface crust samples where physical and hydraulic properties cannot be easily quantified using conventional methods

an american on paris extent of aqueous alteration of a cm chondrite and the petrography of its refractory and amoeboid olivine inclusions paris is the least aqueously altered cm chondrite identified to date classified as subtype 2 7 however literature data indicate that some regions of this apparently brecciated meteorite may be subtype 2 9 the suite of cais in paris includes 19 spinel pyroxene inclusions 19 spinel inclusions 8 spinel pyroxene olivine inclusions 43 pyroxene inclusions 8 pyroxene olivine inclusions and 3 hibonite bearing inclusions both simple and complex inclusions are present some have nodular banded or distended structures no melilite was identified in any of the inclusions in the present suite but other recent studies have found a few rare occurrences of melilite in paris cais because melilite is highly susceptible to aqueous alteration it is likely that it was mostly destroyed during early stage parent body alteration two of the cais in this study are part of compound cai chondrule objects their presence suggests that there were transient heating events probably associated with chondrule formation in the nebula after chondrules and cais were admixed also present in paris are a few amoeboid olivine inclusions aoi consisting of relatively coarse forsterite rims surrounding fine grained porous zones containing diopside and anorthite the interior regions of the aois may represent fine grained rimless cais that were incorporated into highly porous forsterite rich dustballs these assemblages were heated by an energy pulse that collapsed and coarsened their rims but failed to melt their interiors

the importance of experiments constraints on chondrule formation models abstract we review a number of constraints that have been placed on the formation of chondrules and show how these can be used to test chondrule formation models four models in particular are examined the x wind model sudden exposure to sunlight 0 1 au from the proto sun with subsequent launching in a magnetocentrifugal outflow solar nebula lightning nebular shocks driven by eccentric planetesimals and nebular shocks driven by diskwide gravitational instabilities we show that constraints on the thermal histories of chondrules during their melting and crystallization are the most powerful constraints and provide the least ambiguous tests of the chondrule formation models such constraints strongly favor melting of chondrules in nebular shocks shocks driven by gravitational instabilities are somewhat favored over planetesimal bow shocks

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles the iam 9 transect at 40 20 n we present a crust and mantle velocity structure for the west iberia passive continental margin derived from a 320 km long wide angle seismic profile acquired in the southern iberia abyssal plain we observe a 170 km wide ocean continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault bounded blocks of continental crust the profile lies 40 km south of the transect sampled by ocean drilling program odp legs 149 and 173 the transition zone structure can be divided into an upper layer 2 4 km thick with velocities of between 4 5 and 7 0 km s 1 and generally a high velocity gradient 1 s 1 and a lower layer up to 4 km thick with a velocity of 7 6 km s 1 and a low velocity gradient a weak moho reflection in this zone was seen only on wide angle profiles at an offset of 30 km the upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope conversely the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust on the coincident seismic reflection profile fault bounded crustal blocks identified in unequivocal extended continental crust are not observed in the transition zone the upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges but no oceanic layer 3 velocity structure is present while magnetic anomalies have been identified within the transition zone they have not been modeled successfully as seafloor spreading magnetic anomalies nor do they generally form long linear margin parallel features finally odp boreholes 40 km north of our profile and within the interpreted transition zone have recovered up to 140 m thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material we conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust although current melting models predict a considerably thicker crust of decompression melt products we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite

cm and co chondrites a common parent body or asteroidal neighbors insights from chondrule silicates abstract by investigating the petrology and chemical composition of type ii feo rich chondrules in the mighei like carbonaceous cm chondrites we constrain their thermal histories and relationship to the ornans like carbonaceous co chondrites we identified feo rich relict grains in type ii chondrules by their fe mn ratios their presence indicates chondrule recycling among type ii chondrules the majority of relict grains in type ii chondrules are feo poor olivine grains consistent with previous studies chemical similarities between cm and co chondrite chondrules indicate that they had similar formation conditions and that their parent bodies probably formed in a common region within the protoplanetary disk however important differences such as mean chondrule size and the lower abundance of feo poor relicts in cm chondrite type ii chondrules than in co chondrites suggest cm and co chondrules did not form together and they likely originate from distinct parent asteroids despite being aqueously altered many cm chondrites contain pre accretionary anhydrous minerals i e olivine that are among the least thermally metamorphosed materials in chondrites according to the cr 2 o 3 content of their ferroan olivine the presence of these minimally altered pre accretionary chondrule silicates suggests that samples to be returned from aqueously altered asteroids by the hayabusa2 and osiris rex asteroid sample return missions even highly hydrated may contain silicates that can provide information about the pre accretionary histories and conditions of asteroids ryugu and bennu respectively

three dimensional mapping of seismic reflections from the crust and upper mantle northwest of scotland abstract a survey area 190 km by 110 km to the northwest of scotland on the uk continental shelf has been the site of intense exploration using the deep seismic reflection technique a closely spaced grid of deep reflection data totalling 1600 line km has been acquired by the birps group between 1981 and 1987 the majority of the data were recorded to 15 s two way travel time 50 km depth profiles with recording times up to 60 s 230 km depth were also acquired the survey includes a two ship synthetic aperture profile the slave line which synthesises a 0 16 km offset cdp profile the main features revealed and consistently imaged across the survey area by this combined dataset are an upper crust containing half graben style basins bounded to the west by planar faults a reflective lower crust and dipping and sub horizontal high amplitude reflections within the mantle three dimensional mapping of the dipping reflectors shows a complex package of reflections which updomes into the lower crust in the central area of the survey disrupting the moho and continuing into the uppermost mantle where it thins to a couplet of reflections in the north and south of the survey area this structure is observed only in the mantle to a depth of 80 km this dataset is unique in deep seismic reflection profiling in terms of the quality of the image returned the great depth to which reflections are imaged and the intensity of surveying of the lower crust and upper mantle the continuity and strength of the reflectors seen on these records show that even at the great depths at which these structures exist the seismic reflection technique is able to image them as high amplitude coherent and highly continuous reflections the reflections are interpreted as shear zones or faults within the lower crust and upper mantle this indicates that in this part of the world at least both the lower crust and upper mantle are able to sustain discrete zones of deformation

an engineering approach to fingered vadose pollutant transport abstract results of many independent experimental findings related to fingered preferential flow are combined into a concise conservative engineering methodology for predicting pollutant transport through fingered flow paths preferential flow can occur in all textures of soil with fingering occurring in less structured coarse soils giving over to macropore flow in finer textured soil regimes a simple example comparing groundwater loading of naphthalene using plug flow and fingered flow assumptions illustrates that fingered flow can increase contaminant loading to groundwater aquifers by over two orders of magnitude at sites with coarse vadose zone materials

understanding the thermal evolution of deep water continental margins areas of exploration for new hydrocarbons are changing as the hydrocarbon industry seeks new resources for economic and political reasons attention has turned from easily accessible onshore regions such as the middle east to offshore continental shelves over the past ten years there has been a marked shift towards deep water continental margins 500 2 500 m below sea level in these more hostile regions the risk and cost of exploration is higher but the prize is potentially enormous the key to these endeavours is a quantitative understanding of the structure and evolution of the thinned crust and lithosphere that underlie these margins

the hatton bank continental margin ii deep structure from two ship expanding spread seismic profiles summary the continent ocean transition adjacent to hatton bank was studied using a dense grid of single ship and two ship multichannel seismic profiles the interpretation of the explosive expanding spread profiles esps which were shot as part of this survey are discussed here in detail extensive seaward dipping reflectors are developed in the upper crust across the entire margin these seaward dipping reflectors continue northwards on the faeroes and voring margins where they have been shown to be caused by basaltic lavas as well as on the conjugate margin of east greenland the dipping reflectors are an important feature of the rifting history of the margin and show that extensive volcanism was associated with the extension the esps show clear seismic arrivals out to ranges of 100 km wide angle moho reflections can be seen on all the lines as well as good mid and lower crustal arrivals the determination of seismic velocity structure was constrained by ray tracing and by amplitude modelling using reflectivity synthetic seismograms the results from the esps show that there is a thick region of lower crustal material beneath the margin with an unusually high crustal velocity of 7 3 7 4 km s this lower crustal material reaches a maximum thickness of 14 km beneath the central part of the margin and is terminated at depth by the moho the lower crustal lens of high velocity material is interpreted as underplated or intruded igneous rocks associated with the large volumes of extrusive basaltic lavas now seen as dipping reflectors on the margin

infiltration through three contrasting biological soil crusts in patterned landscapes in the negev israel abstract we examined the role of soil crusts in infiltration processes in three contrasting environments in the northern central and central western negev israel the removal of a thin cyanobacterial dominant crust from a sandy dune at nizzana in the central western negev and of a well developed lichen dominant and a cyanobacterial dominant crust from a loess covered hillslope at sayeret shaked in the northern negev resulted in three to fivefold increases in sorptivity and steady state infiltration under both ponding and tension the removal of a depositional crust colonised by cyanobacteria from a loess floodplain at sede zin in the central negev resulted in an increased infiltration under tension but had no significant effect under ponding we attribute the lack of effect under ponding to exposure of surface silts to water which resulted in the clogging of matrix pores and surface sealing the removal of the crusts in all three landscapes influences resource flows particularly the redistribution of runoff water which is essential for the maintenance of desert soil surface patterning it would also have marked effects on germination establishment and survival of vascular plants and soil biota leading ultimately to desertification

oxygen isotope ratios of feo poor chondrules in cr3 chondrites influence of dust enrichment and h2o during chondrule formation abstract we present detailed electron microprobe analyses and oxygen three isotope measurements by high precision secondary ion mass spectrometry on 45 type i feo poor chondrules fragments and 3 type ii feo rich chondrule fragments from meteorite hills 00426 and queen alexandra range 99177 two of the most primitive cr3 chondrites type i chondrules fragments have mg s defined as the mg of constituent olivine and or low ca pyroxene ranging from 94 2 to 99 2 type ii chondrule fragments have mg s of 53 63 oxygen three isotope measurements plot on the slope 1 primitive chondrule mineral pcm line within chondrules 17 o 17 o 0 52 18 o values of coexisting olivine pyroxene and plagioclase are homogeneous with propagated uncertainties of 0 3 this indicates each phase crystallized from the final chondrule melt and that efficient oxygen isotope exchange occurred between ambient gas and chondrule melt among type i chondrules there is a well defined increase in 17 o from 5 9 to 1 as mg s decrease from 99 2 to 96 type ii chondrule fragments are comparatively 16 o poor 17 o 0 2 0 6 the relationship between mg and 17 o among type i chondrules confirms that addition of a 16 o poor oxidizing agent to the highest mg chondrule precursors resulted in forming lower mg cr chondrules using aspects of existing equilibrium condensation models and a mass balance we estimate that type i cr chondrules formed at dust enrichments of 100 200 from dusts with 0 0 8 times the atomic abundance of ice relative to ci dust the type ii chondrule fragments are predicted to have formed at ci dust enrichments near 2500

heat flow and thermal evolution of a passive continental margin from shelf to slope a case study on the pearl river mouth basin northern south china sea abstract the pearl river mouth basin prmb the largest basin in the northern continental margin of the south china sea scs has been one of the key areas to characterize geothermal field and thermal evolution of a passive continental margin the thermal history of the pearl river mouth basin is related to the seafloor spreading of the scs in the late early oligocene heat flow measurements show that the prmb is characterized by a high background heat flow with average heat flow of 71 8 13 6 mw m2 the present day heat flow of the northern scs increases from the northern shelf with the thick crust to the southern slope with the thinned crust this study employs forward and inverse modeling to simulate the rift and post rift processes exampled by four wells at different structural settings two thermal evolution models of the prmb are established for continental shelf and continental slope in the continental shelf heat flow increased rapidly twice during the syn rift stage and then followed by continuous thermal subsidence with heat flow value decreased during the post rift stage while the heat flow in the slope continuously increased due to lithospheric thinning mantle upwelling and resulting multi episode seafloor spreading in scs during the neogene post rift stage which is different from the previously proposed decreasing heat model for the slope during the post rift heat flow gradually reduced after the cessation of the sea floor spreading 10 ma the local multi staged magmatic activities mainly contribute to the high level of maturity in the liwan sag located in the lower slope

tectonic implications of exposure of lower continental crust beneath the iberia abyssal plain northeast atlantic ocean geophysical evidence we present new seismic data from a basement high beneath the southern iberia abyssal plain that appears from the latest ocean drilling program odp results and indirectly from various seismic observations to consist of lower continental crustal material this is a unique opportunity to use seismic profiles and other geophysical evidence to investigate the tectonic process which led to the exhumation of these rocks we infer that the lower crust was exhumed at the seafloor and then uplifted toward the end of rifting our results lead to the following new observations low angle detachment faults previously reported along the east west lusigal 12 profile across the southern iberia abyssal plain penetrate both the 3 10 km thick continental crust and unusually the uppermost mantle processing of new multichannel seismic reflection profiles across the basement high on which odp sites 900 1067 and 1068 are located reveals that the high is bounded by a previously unsuspected steep landward dipping normal fault on its east flank basement cores from the above odp sites also reveal that the high is not capped by the previously predicted early syn rift sediment but by rocks from the lower continental crust these unexpected observations are incorporated into a new tectonic model of the development of this part of the west iberia margin which is also consistent with other geophysical observations a novel feature of this model is the proposal that the seaward edge of the continental crust is thinned to 3 6 km by a currently poorly understood process the model implies three stages of deformation 1 lithospheric extension principally by symmetric pure shear which leads to a 10 km thick crust in which the lower crust is largely absent over the axial zone and the crust mantle boundary forms a shear zone 2 further thinning and then dissection of the most distal continental crust by seaward dipping low angle normal faults 3 inception of a high angle landward dipping normal fault that offsets the tectonized crust mantle boundary and uplifts the lower crust to the crest of the basement high on which odp sites 900 1067 and 1068 were drilled

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs

fire severity and surface rock fragments cause patchy distribution of soil water repellency and infiltration rates after burning although fire induced soil water repellency swr and its effects on soil hydrology and geomorphology have been studied in detail very few studies have considered the effect of rock fragments resting on the soil surface or partly embedded in soil in this research we have studied the effect of rock fragments on the strength and spatial distribution of fire induced swr at different fire severities a fire affected area was selected for this experiment and classified into different zones according to fire severity unburned low moderate and high and rock fragment cover low 60 during 7 days after fire swr and infiltration rates were assessed in the soil surface covered by individual rock fragments and in the midpoint between two adjacent rock fragments with maximum spacing of 20 cm swr increased with fire severity rock fragments resting on the soil surface increased the heterogeneity of the spatial distribution of fire induced swr swr increased significantly with rock fragment cover in bare areas under moderate and high fire severity but quantitatively important changes were only observed under high fire severity in areas with a low rock fragment cover water repellency from soil surfaces covered by rock fragments increased relative to bare soil surfaces with increasing swr in areas with a high rock fragment cover swr increased significantly from non covered to covered soil surfaces only after low severity burning rock fragment cover did not affect infiltration rates although it decreased significantly in soil surfaces after high severity burning in areas under low and high rock fragment cover copyright 2013 john wiley sons ltd

the potential roles of biological soil crusts in dryland hydrologic cycles biological soil crusts bscs are the dominant living cover in many drylands of the world they possess many features that can influence different aspects of local hydrologic cycles including soil porosity absorptivity roughness aggregate stability texture pore formation and water retention the influence of biological soil crusts on these factors depends on their internal and external structure which varies with climate soil and disturbance history this paper presents the different types of biological soil crusts discusses how crust type likely influences various aspects of the hydrologic cycle and reviews what is known and not known about the influence of biological crusts on sediment production and water infiltration versus runoff in various drylands around the world most studies examining the effect of biological soil crusts on local hydrology are done by comparing undisturbed sites with those recently disturbed by the researchers unfortunately this greatly complicates interpretation of the results applied disturbances alter many soil features such as soil texture roughness aggregate stability physical crusting porosity and bulk density in ways that would not necessarily be the same if crusts were not naturally present combined these studies show little agreement on how biological crusts affect water infiltration or runoff however when studies are separated by biological crust type and utilize naturally occurring differences among these types results indicate that biological crusts in hyperarid regions reduce infiltration and increase runoff have mixed effects in arid regions and increase infiltration and reduce runoff in semiarid cool and cold drylands however more studies are needed before broad generalizations can be made on how biological crusts affect infiltration and runoff we especially need studies that control for sub surface soil features such as bulk density micro and macropores and biological crust structure unlike the mixed effects of biological crusts on infiltration and runoff among regions almost all studies show that biological crusts reduce sediment production regardless of crust or dryland type copyright 2006 john wiley sons ltd

fe mn systematics of type iia chondrules in unequilibrated co cr and ordinary chondrites we have examined fe mn systematics of 34 type iia chondrules in eight highly unequilibrated co cr and ordinary chondrites using new data from this study and prior studies from our laboratory olivine grains from type iia chondrules in co chondrites and unequilibrated ordinary chondrites uoc have significantly different fe mn ratios with mean molar fe mn 99 and 44 respectively olivine analyses from both these chondrite groups show well defined trends in mn versus fe afu and molar fe mn versus fe mg diagrams in general type iia chondrules in cr chondrites have properties intermediate between those in uoc and co chondrites in most uoc and cr type iia chondrules the fe mn ratio of olivine decreases during crystallization whereas in co chondrites the fe mn ratio does not appear to change it is difficult to interpret the observed fe mn trends in terms of differing moderately volatile element depletions inherited from precursor materials instead we suggest that significant differences in the abundances of silicates and sulfides metals in the precursor material as well as open system behavior during chondrule formation were responsible for establishing the different fe mn trends using fe mn mg systematics we are able to identify relict grains in type iia chondrules which could be derived from previous generations of chondrules including chondrules from other chondrite groups and possibly chondritic reservoirs that have not been sampled previously

field evidence of a negative correlation between saturated hydraulic conductivity and soil carbon in a sandy soil this study was performed as a part of the grasslanddestabilization experiment at the university of nebraska sbarta brothers ranch site bbrs in the eastern nsh figure 1 which investigates the ecological and geomor phic stability of the nsh from an interdisciplinary perspec tive and focuses on atmosphere land surface groundwaterinteractions wang et al 2008 the nebraska sand hills isthe largest native grassland stabilized sand dune area inthe western hemisphere and an important groundwaterrecharge source for the high plains aquifer loope andswinehart 2000 mean annual temperature at the site is8 1 c and mean annual precipitation is 576 mm about90 of the landscape at the site is composed by uplanddunes and dry interdunal areas covered by native warm season grasslands while the remaining 10 consists of wetmeadows and wetlands holocene dune sands overlie qua ternary and or pliocene alluvial sand and silt with low somcontent throughout the nsh