an experimental investigation of mechanisms involved in bed load sheet production and migration 1 field measurements indicate that in gravel bed rivers bed load may not be a one to one response to shear stress but may instead fluctuate a great deal over time for a given flow condition both in flume and field experiments these fluctuations were often associated with migration of low relief bed forms called bed load sheets whereas several studies have described bed load sheets as a consequence of grain sorting little is known about the mechanisms responsible for their production and migration these were investigated in flume experiments a set of 20 experiments was conducted under constant feeding rate conditions with mixtures of different uniform sediments and for slopes varying from 0 8 to 9 except for runs performed in high flow conditions we observed periodic bed load sheet production and migration associated with fluctuations of bed slope bed state bed fining and paving and bed load observations allowed us to conclude that bed load sheets resulted from very efficient vertical and longitudinal grain sorting that produced periodic local bed aggradation and erosion clearly observed in the upstream section of the flume fractional transport rates were measured in one run combined with the results of experiments previously conducted by authors with uniform sediments this experiment showed that the highest peak solid discharges were essentially caused by the much greater mobility of the coarser gravels when transported within bed load sheets a scenario is proposed for the mechanisms involved in bed load sheet production and migration

tidal fluctuations in a leaky confined aquifer dynamic effects of an overlying phreatic aquifer tidal fluctuations in a leaky confined coastal aquifer are damped significantly due to leakage into an overlying phreatic aquifer jiao and tang 1999 presented an analytical solution to a simple model describing this phenomenon their solution assumes that the tidal fluctuations in the overlying phreatic aquifer are negligible i e a static phreatic aquifer here we examine dynamic effects of the overlying aquifer based on a new approximate analytical solution the numerical results indicate that the dynamic effects can be significant for a relatively large leakage and a high transmissivity of the phreatic aquifer

experimental study of incipient motion in mixed size sediment transport rates of five sediments were measured in a laboratory flume three of these sediments had the same mean size the same size distribution shape and different values of grain size distribution standard deviation the critical shear stress for incipient motion of the individual size fractions within these sediments was estimated as that shear stress that produced a small dimensionless transport rate the sorting of the sediment mixture had little effect on the critical shear stress of individual fractions once the median size d50 of the mixture and a fraction s relative size di d50 are accounted for our data combined with previously published data show a remarkably consistent relation between the critical shear stress of individual fractions and the fraction s relative grain size despite a broad variation in the available data of mixture sorting grain size distribution shape mean grain size and grain shape all fractions in a size mixture begin moving at close to the same value of bed shear stress during steady state transport conditions this result is apparently true for transport systems where the transport rates of individual fractions are determined solely by the flow and bed sediment recirculating systems as well as for systems where the fractional transport rates are imposed on the system feed systems this equivalence in initial motion results is important because natural transporting systems often show attributes of both types of behavior in an unknown combination

matrix and whole rock fractionations in the acfer 094 type 3 0 ungrouped carbonaceous chondrite abstract we used the electron microprobe to study matrix in the ungrouped type 3 0 carbonaceous chondrite acfer 094 using 7 7 point focused beam arrays data points attributable to mineral clasts were discarded the grid areas show resolvable differences in composition but differences are less pronounced than we observed in studies of cr2 lapaz icefield lap 02342 wasson and rubin 2009 and co3 0 allan hills a77307 brearley 1993 a key question is why acfer shows an anomalously uniform composition of matrix compared with these other carbonaceous chondrites both whole rock and matrix samples of acfer 094 show enhancements of ca and k it appears that these reflect contamination during hot desert weathering by contrast the whole rock abundance of na is low although weathering effects are responsible for some fractionations it appears that nebular effects are also resolvable in matrix compositions in acfer 094 as with lap 02342 we infer that the observed differences among different areas were inherited from the solar nebula and may have been carried by porous chondrules that experienced low about 20 degrees of melting acfer 094 has been comminuted by one or more impact events that may also have caused volatile loss thus despite preserving evidence e g an exceptionally high content of presolar sic implying a high degree of pristinity acfer 094 is far from pristine in other respects this evidence of comminution and an o isotopic composition similar to values measured in metamorphosed cm chondrites suggest that acfer was hydrated before being outgassed by the inferred impact event convection within the plume associated with the impact event probably also contributed to the homogenization of the acfer 094 matrix

oxygen isotopes in r chondrite magnetite and olivine links between r chondrites and ordinary chondrites ion microprobe studies yield 17o 17o 0 52 18o values in magnetite from the rumurti chondrite rc pca91241 which is paired with pca91002 of 3 1 to 3 9 slightly higher than that in o from whole rock r samples despite 17o values in whole rock rcs that are much by ca 1 6 higher than in whole rock ll chondrites the 17o in r magnetite is much lower by ca 2 than the values 4 to 7 from ll3 semarkona and ngawi choi et al 1998 the 18o values in pca magnetite 15 to 10 are the lowest known in meteorites well below the range in semarkona 4 to 9 on a 17o 18o diagram both magnetite data sets form linear arrays with slopes of ca 0 7 indicating mixing of o from different isotopic reservoirs the slopes and intercepts of the two arrays are similar enough to permit them to be segments of a single array this suggests that in rcs and ll chondrites magnetite formed from the same raw materials by the same processes probably by aqueous alteration of metal in an asteroidal setting we observed 17o values in olivines and pyroxene from rcs ranging from 1 2 to 2 9 and 18o from 1 4 to 9 1 these compositions scatter in the same general range observed in chondrules from ordinary chondrites the similarity in the o isotopic composition of minerals that preserve a record of formation in the solar nebula supports a model in which rcs formed from nebular components similar to those in h chondrites but with a matrix chondrule ratio several times higher in the rcs and with more extensive aqueous alteration in the rcs than in known h chondrites we postulate that the matrix in r chondrites has 17o higher than whole rock values we suggest that the original 17o value of h2o in the rc body was similar to that incorporated into the ordinary chondrites previously estimated by choi et al 1998 to be ca 7 in the ll parent body

density porosity and magnetic susceptibility of carbonaceous chondrites abstract we report physical properties bulk and grain density magnetic susceptibility and porosity measured using nondestructive and noncontaminating methods for 195 stones from 63 carbonaceous chondrites grain densities over the whole population average 3 44 g cm 3 ranging from 2 42 g cm 3 ci1 orgueil to 5 66 g cm 3 cb bencubbin magnetic susceptibilities in log units of 10 9 m3 kg 1 averaged log 4 22 ranging from 3 23 cv3 axtell to 5 79 cb bencubbin porosities averaged 17 ranging from 0 for a number of meteorites to 41 for one stone of the co ornans notably we found significant differences in porosity between the oxidized and reduced cv subgroups with the porosities of cvo averaging approximately 20 and cvr porosities approximately 4 overall porosities of carbonaceous chondrite falls trend with petrographic type from type 1 ci near 35 type 2 cm cr averaging 23 type 3 cv co 21 to type 4 ck and some co averaging 15 there is also a significant decrease in porosity between meteorites of shock stage s1 and those of s2 indicative of shock compression

fayalitic olivine in cv3 chondrite matrix and dark inclusions a nebular origin fayalitic olivine fa32 is the major component of the matrices and dark inclusions of cv3 and other unequilibrated chondrites it occurs most commonly as rims veins and halos in and around chondrule silicates in the allende type cv3oxa chondrites and to a much lesser extent in the reduced cv3r and bali type cv3oxb chondrites the olivines have distinctive platy tabular and lath or irregular shaped crystals with the ratio of the two types varying widely in cv3oxb chondrites matrix fayalitic olivines range up to fag99 9 whereas in the other cv3 chondrites the range is much smaller the platy and tabular anisotropic forms of the fayalitic olivines strongly suggest growth from a vapor and the nature of the occurrences suggests that cv3 matrices are unequilibrated mixtures of nebular materials we argue that the parent body hydration dehydration model has numerous inconsistencies that make this hypothesis highly unlikely these include 1 there is no direct evidence linking fayalitic olivine to precursor phyllosilicates 2 dehydration of phyllosilicates cannot explain the wide range of morphologies of the fayalitic olivines 3 fayalitic olivine clearly predates the formation of the hydrous phases in cv3 chondrites and is one of the phases that breaks down to form phyllosilicates keller et al 1994 4 the unequilibrated nature of the matrix including fine scale zoning in 10 m sized fayalitic olivine crystals would not survive the parent body metamorphism required in the dehydration model 5 a dark inclusion in the ningqiang chondrite contains fayalitic olivine rimmed by glassy and microcrystalline material zolensky et al 1997 which probably formed by radiation damage this indicates that the fayalitic olivine was exposed to solar radiation in a nebular setting 6 some allende chondrules contain unaltered primary anhydrous glassy mesostasis in contact with the host matrix e g ikeda and kimura 1995 chondrule mesostases would not have survived parent body hydration without becoming hydrated and would probably not survive the metamorphic heating required in the dehydration scenario 7 single platy and barrel shaped crystals of fayalitic olivine are present in accretionary rims in calcium aluminum rich inclusions cais macpherson and davis 1997 which developed in the nebula 8 matrix lumps completely encased in chondrules in ordinary chondrites contain mainly fayalitic olivine scott et al 1984 which indicates a nebular origin 9 oxygen isotopic compositions of allende matrix and dark inclusions strongly indicate little or no hydration for allende and its components clayton 1997 we favor a nebular vaporization recondensation model in which vaporization of chondritic dust produced a fayalite rich vapor followed by formation of the fayalitic olivine by direct recondensation from the vapor epitactic growth on surfaces of existing forsterite and enstatite in chondrules and replacement of existing forsterite and enstatite by gas solid exchange

tide induced head fluctuations in a confined aquifer with sediment covering its outlet at the sea floor 1 a confined coastal aquifer usually extends under the sea for some distance with its submarine outlet covered by a thin layer of sediment with properties dissimilar from the aquifer previous theoretical studies neglected this outlet capping in this paper an analytical solution is derived for a confined aquifer subject to tidal fluctuations with a leaky boundary condition at the outlet capping for the cases that offshore length of the aquifer and or the leakance of the outlet capping are either zero or infinity existing solutions in literature are obtained it is shown that our analytical solution can also be used to describe the tidal wave propagation in a confined aquifer extending infinitely under a tidal river the full solution agreed well with the observations in a piezometer in the jahe river basin in china 200 m inland from the coastline where the tide induced head fluctuations without delay were observed but cannot be explained using previous analytical and numerical solutions ignoring the effect of the outlet capping the sensitivity analysis showed that the combined actions of the tidal loading and outlet capping lead to complex dependency of the head fluctuation on the outlet capping s leakance when the offshore confined aquifer is short the inland head fluctuation increases with the outlet capping s leakance in this case significant negative phase shift occurs if the leakance is small for offshore aquifer length greater than a threshold value the inland head fluctuations are independent of this length and the outlet capping s leakance

collisional facilitation of aqueous alteration of cm and cv carbonaceous chondrites abstract cm chondrites exhibit a strong correlation between the degree of alteration and the extent of particle alignment i e the strength of the petrofabric it seems likely that the s1 shock stage of essentially every cm and the high matrix abundance 70 vol of these samples ensured that the shock waves that produced cm petrofabrics by collapsing matrix pores and squeezing chondrules into pore spaces were significantly attenuated and were too weak to damage olivine crystal lattices random collisions on the cm body produced petrofabrics and created fractures in the target rocks subsequent impact mobilization of water caused hydrated phases to form preferentially in the more fractured regions those with the strongest petrofabrics the less deformed less fractured cm regions experienced lower degrees of aqueous alteration many cv3 chondrites also have petrofabrics roughly half are from the oxidized bali like subgroup cv3 oxb roughly half are from the reduced subgroup cv3 r and none is from the oxidized allende like subgroup cv3 oxa which is less altered than cv3 oxb nearly all cvs with petrofabrics are s3 s4 and nearly all cvs that lack petrofabrics are s1 oxidized cvs have much higher porosities typically 20 28 than reduced cvs 0 6 8 facilitating more extensive aqueous alteration the cv3 r chondrites formed from low porosity material that inhibited oxidation during alteration the oxidized cv subgroups formed from higher porosity materials the cv3 oxb samples were shocked became extensively fractured and developed petrofabrics the cv3 oxa samples were not shocked and never developed petrofabrics when water was mobilized both sets of porous cv chondrites became oxidized the more fractured cv3 oxb subgroup was more severely altered

erosion of sand from a gravel bed abstractcleaning of fine sediment out of gravel streambeds has become an important method to restore affected stream habitats introducing the increased flows needed to entrain fine sediments without eroding the coarser fractions of the bed and potentially destroying its usefulness as a habitat requires careful selection of flow strength toward this end a series of flume experiments was conducted on the entrainment of sand from immobile gravel beds to determine the depth to which the sand could be eroded without the gravel being mobilized a series of steady flows was imposed on three gravel beds filled with sand with median sizes of 0 2 0 3 and 0 9 mm the shear stress of the series of flows ranged from just above the critical shear stress for initiation of motion of the sand up to 0 9 times the critical stress of the 36 1 mm gravel the experiments continued until the rate of fine sediment exiting the channel was very small it was found that the cleanout depth of the sand was reasonably predicted b

an analytical solution for tidal fluctuations in unconfined aquifers with a vertical beach 1 the perturbation technique has been commonly used to develop analytical solutions for simulating the dynamic response of tidal fluctuations in unconfined aquifers however the solutions obtained from the perturbation method might result in poor accuracy for the case of the perturbation parameter being not small enough in this paper we develop a new analytical model for describing the water table fluctuations in unconfined aquifers based on laplace and fourier transforms in the new approach the mean sea level is used as the initial condition and a free surface equation neglecting the second order slope terms as the upper boundary condition numerical results show that the present solution agrees well with the finite different model with the second order surface terms unlike teo et al s 2003 approximation which restricts on the case of shallow aquifers the present model can be applied to most of the tidal aquifers except for the very shallow one in addition a large time solution in terms of sine function is provided and examined graphically with four different tidal periods

bleached chondrules evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites we present the first detailed study of a population of texturally distinct chondrules previously described by kurat 1969 christophe michel levy 1976 and skinner et al 1989 that are sharply depleted in alkalis and al in their outer portions these bleached chondrules which are exclusively radial pyroxene and cryptocrystalline in texture have porous outer zones where mesostasis has been lost bleached chondrules are present in all type 3 ordinary chondrites and are present in lower abundances in types 4 6 they are most abundant in the l and ll groups apparently less common in h chondrites and absent in enstatite chondrites we used x ray mapping and traditional electron microprobe techniques to characterize bleached chondrules in a cross section of ordinary chondrites we studied bleached chondrules from semarkona by ion microprobe for trace elements and h isotopes and by transmission electron microscopy chondrule bleaching was the result of low temperature alteration by aqueous fluids flowing through finegrained chondrite matrix prior to thermal metamorphism during aqueous alteration interstitial glass dissolved and was partially replaced by phyllosilicates troilite was altered to pentlandite but pyroxene was completely unaffected calcium rich zones formed at the inner margins of the bleached zones either as the result of the early stages of metamorphism or because of fluid chondrule reaction the mineralogy of bleached chondrules is extremely sensitive to thermal metamorphism in type 3 ordinary chondrites and bleached zones provide a favorable location for the growth of metamorphic minerals in higher petrologic types the ubiquitous presence of bleached chondrules in ordinary chondrites implies that they all experienced aqueous alteration early in their asteroidal histories but there is no relationship between the degree of alteration and metamorphic grade a correlation between the oxidation state of chondrite groups and their degree of aqueous alteration is consistent with the source of water being either accreted ices or water released during oxidation of organic matter ordinary chondrites were probably open systems after accretion and aqueous fluids may have carried volatile elements with them during dehydration individual radial pyroxene and cryptocrystalline chondrules were certainly open systems in all chondrites that experienced aqueous alteration leading to bleaching

influence of sand on hydraulics and gravel transport in a braided gravel bed river measurements in a braided reach of the proglacial white river washington are used to compare the bed load capacity and competence of flow over the predominant gravel bed and over a narrow ribbon of mobile sand which extended alongside the talweg analysis of 144 velocity profiles and 222 bed load samples shows that shear stress and roughness height were significantly lower over sand than gravel but maximum bed load diameter and total gravel transport rate significantly higher as were transport rates of given size fractions at similar shear stresses these differences in competence and capacity are explained by relative size effects on the threshold shear stress for entrainment the influence on gravel transport of local variation in bed material size may explain the self sorting of bed load sheets described by other workers however in channels like that described here the continuous longitudinal ribbon of sand allows the flow to develop a lower shear stress over the smoother bed which partly offsets the relative size effects on competence and capacity

matrix material in type 3 chondrites occurrence heterogeneity and relationship with chondrules abstract matrix material in type 3 chondrites forms rims on chondrules metal sulfide aggregates ca al rich inclusions and chondritic clasts it also forms lumps up to a millimeter in size which may contain coarser silicates chondrules of all types were found with internal matrix lumps that appear to have entered the chondrules before the latter had crystallized mean concentrations of mg na al and ca in matrix occurrences show up to fivefold variations in a single chondrite variations between mean matrix compositions of individual type 3 ordinary chondrites are almost as large and partly reflect systematic differences between h l and ll matrices such variations are probably a result of nebular separation of feldspathic material and ferromagnesian silicates compositions of chondrules and their matrix rims are normally unrelated although rim compositions are correlated with those of matrix lumps inside chondrules a single chondrule was found with a composition nearly identical to that of its internal matrix lump suggesting that some chondrules may have formed from matrix material matrix lumps are as heterogeneous as chondrules but mean chondrule and matrix compositions differ even allowing for possible loss of metallic fe ni during chondrule formation since bulk compositions of matrix lumps and rims have probably not changed significantly since their formation except for fe mg exchange our matrix samples cannot represent typical chondrule precursor materials

quantified whole section trace element mapping of carbonaceous chondrites by synchrotron x ray fluorescence microscopy 1 cv meteorites abstract we present the application of a new synchrotron based technique for rapid mapping of trace element distributions across large areas of the cv3 meteorites allende and vigarano this technique utilizes the australian synchrotron x ray fluorescence microscopy xfm beam line with its custom designed and built x ray detector array called maia xfm with maia allows data to be collected using a 2 m spot size at very low dwell times 0 1 0 5 ms resulting in maps of entire thin sections in 5 h maia is an energy dispersive detector system with a large collection solid angle which allows full spectral acquisition and high sensitivity hence there is no need to constrain the elements of interest a priori we collected whole section maps 2 cm 1 cm from 3 thick sections of allende and a single map 2 cm 1 5 cm from a thick section of vigarano our experimental conditions provide data for elements with 20 z 40 k shell ca through zr and the l emissions of os ir pt au and pb we illustrate the unique capabilities of this technique by presenting observations across myriad length scales from the centimeter scale down to the detection of sub micrometer particles within these objects our initial results show the potential of this technique to help decipher spatial and textural variations in trace element chemistry between cais chondrules matrix and other chondritic components we also illustrate how these datasets can be applied to understanding both nebular and parent body processes within meteorites

determining the length of confined aquifer roof extending under the sea by the tidal method abstract the main task in studying saline intrusion into an aquifer is to determine the position of the saline water freshwater interface for a confined aquifer this position is determined mainly by the roof length of the aquifer extending under the sea this information can be obtained from fluctuations of the groundwater level caused by tidal fluctuations of the sea in this paper a mathematical model of confined groundwater level fluctuations is constructed on the condition that the roof length is finite taking account of the continuity of flow between the inland and offshore aquifers allows a general formula to be calculated for the groundwater level fluctuations in terms of the tidal fluctuations and the length of the confined aquifer under the sea the actual roof length can be computed by comparison of the observed groundwater level fluctuations with those computed by the formula under various assumptions concerning the roof length the method is applied to an aquifer on the beihai peninsula in the guangxi province of china

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

a clast of bali like oxidized cv material in the reduced cv chondrite breccia vigarano the cv vigarano type chondrites are a petrologically diverse group of meteorites that are divided into the reduced and the ball like and allende like oxidized subgroups largely based on secondary mineralogy weisberg et al 1997 krot et al 1998b some chondrules and calcium aluminum rich inclusions cais in the reduced cv chondrite vigarano show alteration features similar to those in allende metal is oxidized to magnetite low ca pyroxene forsterite and magnetite are rimmed and veined by ferrous olivine fs 40 50 and plagioclase mesostases and melilite are replaced by nepheline and sodalite sylvester et al 1993 kimura and ikeda 1996 1997 1998

aqueous alteration of the bali cv3 chondrite evidence from mineralogy mineral chemistry and oxygen isotopic compositions abstract a petrographic geochemical and oxygen isotopic study of the bali cv3 carbonaceous chondrite revealed that the meteorite has undergone extensive deformation and aqueous alteration on its parent body deformation textures are common and include flattened chondrules a well developed foliation and the presence of distinctive 100 planar defects in olivine the occurrence of alteration products associated with the planar defects indicates that the deformation features formed prior to the episode of aqueous alteration the secondary minerals produced during the alteration event include well crystallized mg rich saponite framboidal magnetite and ca phosphates the alteration products are not homogeneously distributed throughout the meteorite but occur in regions adjacent to relatively unaltered material such as veins of altered material following the foliation the alteration assemblage formed under oxidizing conditions at relatively low temperatures oxygen isotopic compositions for unaltered regions in bali fall within the field for other cv3 wholerocks however the oxygen isotopic compositions of the heavily altered material lie in the region for the cm and cr chondrites the heavy isotope enrichment of the altered regions in bali suggest alteration conditions similar to those for the petrographie type 2 carbonaceous chondrites

measuring and defining bimodal sediments problems and implications gravel bed rivers close to the transition to a sand bed often have bimodal grain size distributions these can be quantified in several ways giving wide differences in derived statistics and calculations problems associated with measuring summarizing and defining bimodality are examined using evidence from flume experiments and a simple numerical simulation of sand deposition no single index of bimodality serves all purposes alternatives are suggested measured near bed hydraulic properties relate more closely to grain size statistics calculated by area than by volume this has implications for the abrupt downstream transition often found from gravel to sand bed

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

bedload transport in gravel bed streams with unimodal sediment bedload transport in many gravel bed streams becomes highly complicated because of the nonuniformity of the grain size and the vertical stratification of channel bed material a new relation for computing bedload transport rates in gravel bed streams is proposed here in an effort to account for the variation of the makeup of the surface material within a wide range of shields stresses the relation employs a two parameter approach one related to the material in the pavement and the other to that in the subpavement layers the mode is used to represent the grain sizes of each layer available bedload transport data from gravel bed streams with unimodal sediment are used to test the accuracy of the relation a comparison with other bedload transport relations is also considered

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

phyllosilicate rich chondrule rims in the vigarano cv3 chondrite evidence for parent body processes abstract a petrographic and scanning electron microscopic study of the vigarano cv3 carbonaceous chondrite reveals that a small proportion 5 of the fine grained rims surrounding chondrules consist mainly of phyllosilicates saponite and serpentine and minor but variable amounts of ferrihydrite most of the rims consist mainly of fe rich olivine the phyllosilicate rich rims and the chondrules that they enclose show abundant evidence of aqueous alteration low ca pyroxene and olivine at chondrule margins have been partially replaced by phyllosilicate rich materials producing embayments on chondrule surfaces fe ni metal fe sulfide and magnetite in the chondrules have also been partially replaced by fe hydroxide due to preferential replacement of low ca pyroxene and olivine sulfide magnetite and fe hydroxide remain exposed at chondrule margins we discovered a clast 0 7 0 9 mm in size containing several chondrules embedded in a phyllosilicate rich matrix that is almost identical in mineralogy texture and composition to the rims we also found numerous small clasts 20 400 m in size consisting of a similar phyllosilicate rich material in the host vigarano meteorite many of the clasts include fragments of chondrules amoeboid olivine aggregates and ca al rich inclusions these clasts also show abundant evidence of aqueous alteration which is similar to that observed in the rims and their host chondrules from these observations we conclude that the chondrule rim assemblages and the clasts are a part of the same precursor chondrite which was fragmented during brecciation on the meteorite parent body we interpret that a portion or portions of the vigarano parent body was aqueously altered and the interchondrule matrix was largely converted to phyllosilicates and ferrihydrite this hydrated portion was later fragmented and brecciated by impacts as fragmentation occurred preferentially along the phyllosilicate rich porous matrix most of the ejected clasts consisted of a chondrule rimmed by remnant matrix the clasts were rounded by abrasion during brecciation and transportation and finally mixed into an anhydrous portion in the regolith from which the vigarano meteorite was derived some of the phyllosilicate rich rims show evidence for partial dehydration during heating before final incorporation into the regolith these results taken together suggest that the vigarano parent body was spatially heterogeneous in degree of aqueous alteration and thermal metamorphism and the host vigarano meteorite is a breccia consisting of numerous clasts from many different locations

an analytical solution and case study of groundwater head response to dual tide in an island leaky confined aquifer 1 this paper presents an analytical solution of groundwater head response to dual tide fluctuation in the transect of an island leaky aquifer system comprising a confined aquifer and its overlying semipermeable confining layer both layers terminate at the coastlines on two sides of the island solution analysis indicates that the tidal waves from the two sides of the island transect interfere at the middle of the island and the interference decreases to zero as the horizontal length of the aquifer increases to infinity the leakage of the overlying confining layer enhances the landward attenuation of the tidal head fluctuation and shortens the time lag between the head and tide fluctuations the solution agreed well with the observations in eight piezometers in garden island on the continental shelf of western australia reported by trefry and bekele 2004

sand transport over an immobile gravel substrate abstractexperiments were conducted in a laboratory flume channel to evaluate the effects of increasing amounts of sand on its transport over and through an immobile coarse gravel bed detailed measurements of sand transport rate bed texture and bed topography were collected for four different discharges at approximately the same flow depth of 0 2 m for 11 different elevations of sand in the gravel bed sand transport was measured using both physical samples and a density cell for a given flow rate increases in the elevation of sand relative to gravel resulted in decreases of bed shear stress from 32 44 and increases in sand transport by three orders of magnitude for the highest two discharges the sand merged into a small number of long and low bed forms that translated through and over the gravel bed a collapse of the transport data was accomplished by relating the sand transport rate to the bed shear stress scaled by the cumulative probability distribution function of the gravel surface evaluated

incipient motion of sand gravel sediment mixtures experiments on the incipient motion of gravel and sand mixtures of 0 100 10 90 25 75 45 55 and 100 0 percent ratios of gravel and sand respectively were made in a laboratory flume a series of transport experiments was made for each of the five sediment beds and the critical shear stress for motion was calculated for 12 size ranges by interpolating or extrapolating the bed shear stress for a very small transport rate the sand in each of the five bed mixtures began to move at nearly the same bed shear stress all gravel sizes began to move at nearly the same bed shear stress in the 100 gravel experiments but in the sand gravel experiments the gravel showed an increase in critical shear stress with increasing size reasons for this change in the initiation of motion of the gravel from the 100 gravel to the sand gravel mixtures may result from the abundant sand sized sediment inhibiting the formation of a coarse bed surface layer in the sand gravel experiments

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

variable density flow in porous media steady state distributions of water potential and salt concentration in coastal aquifers are typically modelled by the henry problem which consists of a fully coupled system of flow and transport equations coupling arises from the dependence of water density on salt concentration the physical behaviour of the system is fully described by two dimensionless groups i the coupling parameter alpha which encapsulates the relative importance of buoyancy and viscous forces and ii the peclet number mbox textit pe which quantifies the relative importance of purely convective and dispersive transport mechanisms we provide a systematic analytical analysis of the henry problem for a full range of the peclet number for moderate mbox textit pe analytical solutions are obtained through perturbation expansions in alpha this allows us to elucidate the onset of density driven vertical flux components and the dependence of the local hydraulic head gradients on the coupling parameter the perturbation solution identifies the regions where salt concentration is most pronounced and relates their spatial extent to the development of a convection cell next we compare our solution to a solution of the pseudo coupled model wherein flow and transport are coupled only via the boundary conditions this enables us to isolate the effects caused by density dependent processes from those induced by external forcings boundary conditions for small mbox textit pe we develop a perturbation expansion around the exact solution corresponding to mbox textit pe 0 which sheds new light on the interpretation of processes observed in diffusion experiments with variable density flows in porous media the limiting case of infinite peclet numbers is solved exactly for the pseudo coupled model and compared to numerical simulations of the fully coupled problem for large mbox textit pe the proposed perturbation approach is applicable to a wide range of variable density flows in porous media including seawater intrusion into coastal aquifers and temperature or pressure driven density flows in deep aquifers

critical shear stress of natural sediments the critical shear stress of individual fractions ci in unimodal and weakly bimodal sediments shows little variation with grain size and depends only on the mean grain size bf the mixture for strongly bimodal sediments ci increases with grain size an apparent result of a lateral segregation of the finer and coarser fractions on the bed surface that causes ci to deviate from size independence in the direction of unisize shields values a quantitative definition of mixture bimodality may be used to estimate the degree of mixture bimodality beyond which a substantial size dependence of ci is observed and to predict the variation of ci with grain size in bimodal sediments because properties of sediment grain size distributions other than bimodality appear to have little influence on ci the trends presented here for 14 unimodal and bimodal sediments may be quite general

alteration processes in the cv chondrite parent body based on analysis of nwa 2086 meteorite analysis of the nwa 2086 cv3 chondrite showed a matrix chondrule ratio of 52 similar to bali mokoia and grosanaja nearly twice as many chondrule fragments as intact ones demonstrate that an early fragmentation phase occurred prior to final accretion after this event no substantial mechanical change or redeposition is evident rims with double layered structures were identified around some chondrules which in at least one case is attributed to an accretionary origin the rim s outer parts with a diffuse appearance were formed by in situ chemical alteration during this later process mg content decreased fe content increased and olivine composition was homogenized producing a rim composition close to that of the matrix this alteration occasionally happened along fractures and at confined locations and was probably produced by fluid interactions iron oxides are the best candidate for a small grain sized alteration product however technical limitations in the available equipment did not allow exact phase identification these results suggest that nwa 2086 came from a location possible more deeply buried in the cv parent body than mokoia or bali and suffered less impact effects although there is no evidence of sustained thermal alteration this meteorite may represent a sample of the cv parent asteroid interior and provide a useful basis for comparison with other cv meteorites in the future

alkali differentiation in ll chondrites abstract the ll group chondrites krahenberg krbg and bhola are heterogeneous agglomerates containing a variety of lithic fragments and chondrules as well as crystal fragments the fe fe mg content of most olivine grains is uniform fa28 although a few with distinctly lower fe contents were found fa19 both meteorites contain large cm sized fragments with high enrichments of k 12 rb 45 and cs 70 relative to ll chondrites while the ree concentrations are normal except for a negative eu anomaly na and sr are depleted 0 5 and the na k weight ratio is 0 33 compared to 11 in the host however there is no difference in the sum of na k atoms also the major elements si al mg ca and fe are nearly the same in fragments as in the host material the k rich igneous lithic fragments have a microporphyritic texture of euhedral to skeletal olivines in a partly devitrified glass with 4 k2o the main pans of both krbg and bhola contain mesostasis glasses in porphyritic chondrules and lithic fragments with varying k content 0 1 8 6 k2o and na k ratios 0 2 100 crystalline plagioclase is depleted in k with an average na k ratio of 22 i e higher than that for ordinary chondritic plagioclase 8 4 olivines in the large k rich fragments and in the host meteorites have the same iron content fa28 indicating that both formed under the same oxygen fugacity and probably on the same parent body conceivable mechanisms for the formation of the k rich rocks from normal ll chondrite parent material are 1 magmatic differentiation 2 na k exchange via a vapor phase 3 silicate liquid immiscibility 4 volatilization and condensation in impact events process 2 appears most feasible for forming a rock enriched only in k and heavier alkalies and depleted in na without noticeably changing other elements including the ree

approach to separate sand from gravel for bed load transport calculations in streams with bimodal sediment the bed material found in gravel bed streams is nonuniform in terms of grain size and can typically be classified as unimodal or bimodal the latter type of sediment distribution is usually represented by two modes one of sand size and another of gravel for this case the movement of one mode becomes nonlinearly influenced by the other as a result the presence of the two modes in a bimodal material complicates the calculation of bed load transport rates the present study proposes an approach to separate the calculation of bed load transport rates for bimodal materials into two independent fractions of sand and gravel thereby rendering the bed sediment into two unimodal components this approach is accomplished by decoupling the two fractions through scaling the reference shields stresses of the sand and gravel modes to match the value of the mode of unimodal materials consequently the contribution of each fraction to bed load can be estimated using a suitable relation derived for unimodal materials laboratory and field bed load data available in the literature are used to examine the validity of the overall approach

a new analytical solution of tidal water table fluctuations in a coastal unconfined aquifer this paper presents a new perturbation solution of the non linear boussinesq equation for one dimensional tidal groundwater flow in a coastal unconfined aquifer built upon the work of parlange et at parlange j y stagnitti f starr j l braddock r d 1984 free surface flow in porous media and periodic solution of the shallow flow approximation j hydrol 70 251 263 the solution adopts a new perturbation parameter that is by definition less than unit and thus is applicable to a wider range of physical conditions within the constraint of the boussinesq approximation this approach avoids a secular term in the third order perturbation equation of parlange et at 1984 enabling the derivation of the third and higher order solutions in comparison with a numerical exact solution the new perturbation solution is shown to be slightly more accurate than that of parlange et at 1984 with the second order approximation the obtained third order solution exhibits considerable improvement in accuracy in relatively simple analytical forms the present perturbation solution will help to understand better the non linear characteristics of tidal water table fluctuations as modeled by the non linear boussinesq equation in coastal unconfined aquifers c 2007 elsevier b v all rights reserved

determination of the petrologic type of cv3 chondrites by raman spectroscopy of included organic matter abstract this paper reports the first reliable quantitative determination of the thermal metamorphism grade of a series of nine cv3 chondrites allende axtell bali mokoia grosnaja efremovka vigarano leoville and kaba the maturity of the organic matter in matrix determined by raman spectroscopy has been used as a powerful metamorphic tracer independent of the mineralogical context and extent of aqueous alteration this tracer has been used along with other metamorphic tracers such as fe zoning in type i chondrules of olivine phenocrysts presolar grain abundance and noble gas abundance bulk and p3 component the study shows that the petrologic types determined earlier by induced thermoluminescence were underestimated and suggests the following values pt allende axtell 3 6 pt bali mokoia grosnaja 3 6 pt efremovka leoville vigarano 3 1 3 4 pt kaba 3 1 the most commonly studied cv3 allende is also the most metamorphosed bali is a breccia containing clasts of different petrologic types the attribution suggested by this study is that of clasts of the highest petrologic types as pointed out by iom maturity and noble gas bulk abundance cv3 chondrites have complex asteroidal backgrounds with various degrees of aqueous alteration and or thermal metamorphism leading to complex mineralogical and petrologic patterns fe mg chemical zoning in olivine phenocrysts on the borders of type i chondrules of porphyritic olivine and pyroxene rich textural types has been found to correlate with the metamorphism grade this suggests that chemical zoning in some chondrules often interpreted as exchanges between chondrules and nebular gas may well have an asteroidal origin furthermore the compositional range of olivine matrix is controlled both by thermal metamorphism and aqueous alteration this does not support evidence of a nebular origin and does not necessarily mirror the metamorphism grade through fe mg equilibration on the other hand it may provide clues on the degree of aqueous alteration vs thermal metamorphism and on the timing of both processes in particular mokoia experienced significant aqueous alteration after the metamorphism peak whereas grosnaja which has similar metamorphism grade did not

the onset of metamorphism in ordinary and carbonaceous chondrites ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by xray mapping techniques a variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe scanning electron microscopy sem transmission electron microscopy tem and cathodoluminescence cl methods the distribution of cr in feo rich olivine systematically changes as metamorphism increases between type 3 0 and type 3 2 igneous zoning patterns are replaced by complex ones and cr rich coatings develop on all grains cr distributions in olivine are controlled by the exsolution of a cr rich phase probably chromite cr in olivine may have been partly present as tetrahedrally coordinated cr3 separation of chromite is nearly complete by petrologic type 3 2 the abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type tem shows this to be the result of crystallization of albite residual glass compositions systematically change during metamorphism becoming increasingly rich in k glass in type i chondrules also gains alkalis during metamorphism both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules the matrix in the least metamorphosed chondrites is rich in s and na the s is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules alkalis initially leave the matrix and enter chondrules during early metamorphism feldspar subsequently nucleates in the matrix and na re enters from chondrules these metamorphic trends can be used to refine classification schemes for chondrites cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3 0 and 3 1 into types 3 00 through 3 15 on this basis the most primitive ordinary chondrite known is semarkona although even this meteorite has experienced a small amount of metamorphism allan hills alh a77307 is the least metamorphosed co chondrite and shares many properties with the ungrouped carbonaceous chondrite acfer 094 analytical problems are significant for glasses in type ii chondrules as na is easily lost during microprobe analysis as a result existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised

matrices of type 3 ordinary chondrites primitive nebular records petrologic studies were made on the fine grained matrices of type 3 ordinary chondrites of the lowest petrologic subtype the matrix minerals in order of abundance are olivine fo99 to fo9 enstatite or bronzite augite or subcalcic augite albite fe ni metal troilite magnetite spinel mgal2o4 chromite and calcite fe and mg rich fluffy particles and albite like particles are also major constituents the chemical compositions of olivine and pyroxenes vary within and among the chondrites and are in gross disequilibrium showing that the matrix materials were hardly heated after their formation textural relationships indicate that magnesian olivine was formed after ca pyroxene followed by intermediate to iron rich olivine intermediate olivine was formed from enstatite and metallic iron under relatively oxidizing conditions the observations indicate that matrices of chondrites are neither the fragments of chondrules nor the precursors of chondrules they were mostly the products of condensation and reaction among solids and or between solids and the ambient gas mostly at low temperatures and thus they contain records of primitive processes in the nebula in order to explain the presence of olivines more iron rich than fo50 the presence of free sio2 or a high activity of sio2 in the gas is necessary which was not shown in previous thermochemical calculations mineral assemblages of matrix minerals of chondrites of different chemical groups differ systematically according to oxidation state of the parental meteorites indicating that they were formed at different oxygen fugacities the rims of chondrules and surrounding matrix materials must have accreted onto chondrules during turbulent movements of the nebula

shock metamorphism of carbonaceous chondrites abstract we have studied shock effects in carbonaceous chondrites using optical microscopy of thin sections and find that our petrographic classification of progressive shock metamorphism in ordinary chondrites can also be applied to carbonaceous chondrites we find that sixty nine carbonaceous chondrites can be assigned to four shock stages si to s4 largely on the basis of shock effects in olivine the least shocked chondrite groups are cm2 and co3 thirty six out of thirty eight members are classified as shock stage s1 differences between the mean shock levels of certain groups of chondrites e g co3 and cv3 are probably due to stochastic differences in the sampling of their parent bodies however there is an overall tendency for the mean shock level of carbonaceous chondrites and ordinary chondrites to increase with increasing petrologic type that may reflect real differences in the shock level of near surface materials on their parent bodies caused by intrinsic variations in the chemical and physical properties of these materials petrologic type 2 and 3 chondrites are more porous and richer in volatiles than types 4 to 6 the greater porosity of types 2 3 causes higher post shock temperatures and melting at lower pressures and the higher volatile contents ensure that strongly shocked material is more readily dispersed on release from high pressure we suggest that type 2 3 material shocked above 20 30 gpa normally escapes from the parent asteroids and forms particles that are too small to survive as meteorites in the cv3 group there is a correlation between the degree of chondrule flattening and the intensity of shock metamorphism analogous to that discovered in ordinary chondrites by sneyd et al 1988 suggesting that shock rather than static overburden pressure is responsible for chondrule flattening we infer that the correlations are due to collapse of pores under shock pressures of at least 5 10 gpa and that shock is an important process affecting many physical properties of type 2 4 chondrites

clastic matrix in eh3 chondrites patches of clastic matrix 15 to 730 m in size constitute 4 9 vol of eh3 yamato y 691 and 11 7 vol of eh3 allan hills alh 81189 individual patches in y 691 consist of 1 25 vol relatively coarse opaque grain fragments and polycrystalline assemblages of kamacite schreibersite perryite troilite some grains with daubreelite exsolution lamellae niningerite oldhamite and caswellsilverite 2 30 vol relatively coarse silicate grains including enstatite albitic plagioclase silica and diopside and 3 an inferred fine nebular component 45 vol comprised of submicrometer size grains clastic matrix patches in alh 81189 contain relatively coarse grains of opaques 20 vol kamacite schreibersite perryite and troilite and silicates 30 vol enstatite silica and forsterite as well as an inferred fine nebular component 50 vol the o isotopic composition of clastic matrix in y 691 is indistinguishable from that of olivine and pyroxene grains in adjacent chondrules both sets of objects lie on the terrestrial mass fractionation line on the standard three isotope graph some patches of fine grained matrix in y 691 have distinguishable bulk concentrations of na and k inferred to be inherited from the solar nebula some patches in alh 81189 differ in their bulk concentrations of ca cr mn and ni the average compositions of matrix material in y 691 and alh 81189 are similar but not identical matrix in alh 81189 is much richer in mn 0 23 0 05 versus 0 07 0 02 wt and appreciably richer in ni 0 36 0 10 versus 0 18 0 05 wt than matrix in y 691 each of the two whole rocks exhibits a petrofabric probably produced by shock processes on their parent asteroid

compositional and petrographic similarities of cv and ck chondrites a single group with variations in textures and volatile concentrations attributable to impact heating crushing and oxidation abstract greenwood et al 2010 gathered data on o isotopic and elemental compositions and reevaluated literature data for cv and ck chondrites they concluded that these two chondrite groups originated on the same parent asteroid with ck chondrites being metamorphosed cv chondrites which are otherwise missing types 4 through 6 to test this interpretation we have gathered new instrumental neutron activation analysis inaa data for cv and ck chondrites and reexamined their petrographic features the new inaa data like the older data show scatter attributable to weathering effects but we conclude that the refractory lithophile abundances are the same in cv and ck in agreement with the greenwood et al interpretation several volatile elements are significantly lower in ck than in cv chondrites among the elements we determine the greatest difference between cv and ck is found for br for which the cv ck ratio is 4 as and sb are about 20 lower in ck than cv and smaller differences are observed for zn ga and se it seems likely that volatiles were lost during impact heating events that also provided the heat responsible for metamorphic recrystallization within statistical uncertainty chondrules in cv and ck chondrites are the same size and have similar textural distributions a significant petrographic difference between ck and cv chondrites cited by kallemeyn et al 1991 was the much higher percentage of igneous rims around cv chondrules however we now recognize that many chondrules in ck3 8 nwa 1559 have igneous rims and in ck4 chondrites igneous rims are recognizable by their associated sulfide rich rings there are no quantifiable cv ck differences in igneous rim abundances we used ca and al maps to show that ck chondrites have cai abundances similar to those of cv chondrites it thus appears that there are no resolvable pre metamorphic petrographic differences between cv and ck chondrites we recommend that the ck designation be abandoned and that the cv group be acknowledged as spanning the range of petrologic types 3 6 we suggest that ck3 chondrites be designated cv3oxk most ck4 chondrites are highly fragmental collisional crushing appears to be much more common than in cv chondrites it seems likely that ck chondrites formed from reduced cv3 materials after the latter was impacted buried aqueously altered and annealed

an analytical solution of groundwater response to tidal fluctuation in a leaky confined aquifer an analytical solution is derived to investigate the influence of leakage on tidal response in a coastal leaky confined aquifer system the analytical solution developed here is more general than the traditional solution obtained by ferris 1951 which can be regarded as a special case of the solution presented in this paper this solution is based on a conceptual model under the assumption that the groundwater level in the confined aquifer fluctuates in response to sea tide while that of the overlying unconfined aquifer remains constant this conceptual model is supported by numerous field studies by previous researchers which have demonstrated that the tidal response in an unconfined aquifer may be negligible compared to that in a confined aquifer the leakage has a significant impact on the tidal behavior of the confined aquifer hypothetical studies indicate that both tidal amplitude of groundwater head in the aquifer and the distance over which the aquifer can be disturbed by the sea tide will be considerably reduced because of the existence of leakage this analytical solution is used to investigate the tidal and piezometer data at the chek lap kok airport hong kong special administrative region people s republic of china

bedload transport in gravel bed streams field data obtained from oak creek are used to study the bedload transport in gravelbed streams a similarity approach is used to delineate a functional relationship obtained for the bedload transp

fluvial transport of sand and gravel mixtures with bimodal size distributions abstract initiation of motion and fractional transport rates of sediments with bimodal size distributions were measured in a laboratory channel and in a natural channel transport experiments were conducted with unimodal 100 sand and 100 gravel bed sediments and three bimodal mixtures of the two sediments 10 gravel 90 sand 25 gravel 75 sand and 45 gravel 55 sand in the bimodal sediment beds the critical shear stress for the initiation of motion showed very little change with grain size for the sand sizes but increased with grain size for the gravel sizes for low flow strengths only the sand sizes were in transport while for the highest flow strengths the bed load sediment size distribution approached that of the bed material

fractionated matrix composition in cv3 vigarano and alteration processes on the cv parent asteroid abstract although cv3 vigarano is one of the most primitive cv chondrites it has lost most of the s from the matrix matrix na is also depleted relative to the concentration in bulk cv chondrites we used a matrix grid technique to study thirteen 50 50 m regions in vigarano in each area we used an electron microprobe to gather data with an electron beam 3 m in width we found two end member types of matrix textures one is coarse and porous has lower fe contents and lower analytical totals it appears to be contaminated with comminuted chondrule debris the other is finer grained and appears smooth its mean composition has higher fe but lower s and al contents than the coarse matrix areas our tentative interpretation is that the larger grain size of the coarse areas resulted from the admixing of comminuted chondrule materials and thus that the initial fraction of nebular fines was higher in the fine matrix regions aside from volatiles the overall composition of vigarano matrix is similar to that observed in matrix grid studies of other carbonaceous chondrites al si fe and mn have high whole chondrite normalized abundance ratios ca concentrations are low and highly variable because asteroidal alteration effects are present in our sample it is difficult to resolve nebular signatures in the compositions of the grid areas

tide induced groundwater fluctuation in a coastal leaky confined aquifer system extending under the sea this paper presents the analytical solution of groundwater response to tidal fluctuation in a coastal multilayer aquifer system consisting of a leaky confined aquifer a semipermeable layer and an unconfined aquifer the semipermeable layer or the roof of the leaky confined aquifer extends under the sea comparisons are made with solutions derived previously which considered only a single aquifer zero extension of the roof or infinite roof length and demonstrate that the previous solutions are special cases of the solution presented here a hypothetical example is used to discuss the impact of the dimensionless roof length dimensionless leakage and tidal efficiency on the groundwater level fluctuations in the inland part of the confined aquifer the fluctuation decreases significantly with the roof length when the roof length is small but is insensitive to the change of roof length when the roof length is greater than a threshold the impacts of leakage from the offshore and inland portions of the confining unit are different leakage from the offshore portion tends to increase the fluctuation of the groundwater level while leakage from the inland portion tends to decrease the fluctuation the fluctuation increases as the tidal efficiency increases this fact is significant only when the roof length is great and leakage is small