geochemistry of the ungrouped carbonaceous chondrite tagish lake the anomalous cm chondrite bells and comparison with ci and cm chondrites i have determined the composition via instrumental neutron activation analysis of a bulk pristine sample of the tagish lake carbonaceous chondrite fall along with bulk samples of the ci chondrite orgueil and of several cm chondrites tagish lake has a mean of refractory lithophile element cr ratios like those of cm chondrites and distinctly higher than the ci chondrite mean tagish lake exhibits abundances of the moderately volatile lithophile elements na and k that are slightly higher than those of mean cm chondrites refractory through moderately volatile siderophile element abundances in tagish lake are like those of cm chondrites tagish lake is distinct from cm chondrites in abundances of the most volatile elements mean ci normalized se co zn co and cs co for tagish lake are 0 68 0 01 0 71 0 07 and 0 76 0 02 while for all available cm chondrite determinations these ratios lie between 0 31 and 0 61 between 0 32 and 0 58 and between 0 39 and 0 74 respectively considering petrography and oxygen isotopic and elemental compositions tagish lake is an ungrouped member of the carbonaceous chondrite clan the overall abundance pattern is similar to those of cm chondrites indicating that tagish lake and cms experienced very similar nebular fractionations bells is a cm chondrite with unusual petrologic characteristics bells has a mean ci normalized refractory lithophile element cr ratio of 0 96 lower than for any other cm chondrite but shows ci normalized moderately volatile lithophile element cr ratios within the ranges of other cm chondrites except for na which is low iridium co ni and fe abundances are like those of cm chondrites but the moderately volatile siderophile elements au as and sb have abundances below the ranges for cm chondrites abundances of the moderately volatile elements se and zn of bells are within the cm ranges bells is best classified as an anomalous cm chondrite

fluid evolution in cm carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates the oxygen isotopic compositions of calcite grains in four cm carbonaceous chondrites have been determined by nanosims and results reveal that aqueous solutions evolved in a similar manner between parent body regions with different intensities of aqueous alteration two types of calcite were identified in murchison mighei cold bokkeveld and lapaz icefield 031166 by differences in their petrographic properties and oxygen isotope values type 1 calcite occurs as small equant grains that formed by filling of pore spaces in meteorite matrices during the earliest stages of alteration on average the type 1 grains have a 18o of 32 36 vsmow and 17o of between 2 and 1 most grains of type 2 calcite precipitated after type 1 they contain micropores and inclusions and have replaced ferromagnesian silicate minerals type 2 calcite has an average 18o of 21 24 vsmow and a 17o of between 1 and 3 such consistent isotopic differences between the two calcite types show that they formed in discrete episodes and from solutions whose 18o and 17o values had changed by reaction with parent body silicates as predicted by the closed system model for aqueous alteration temperatures are likely to have increased over the timespan of calcite precipitation possibly owing to exothermic serpentinisation the most highly altered cm chondrites commonly contain dolomite in addition to calcite dolomite grains in two previously studied cm chondrites have a narrow range in 18o 25 29 vsmow with 17o 1 to 3 these grains are likely to have precipitated between types 1 and 2 calcite and in response to a transient heating event and or a brief increase in fluid magnesium calcium ratios in spite of this evidence for localised excursions in temperature and or solution chemistry the carbonate oxygen isotope record shows that fluid evolution was comparable between many parent body regions the cm carbonaceous chondrites studied here therefore sample either several parent bodies with a very similar initial composition and evolution or more probably a single c type asteroid

a profound meteoric water influence on genesis in the permian waterberg coalfield south africa evidence from stable isotopes abstract the coal bearing sediments of the grootegeluk formation of the waterberg coalfield contain siderite ankerite and calcite of various forms that precipitated during deposition and diagenesis and have highly variable d18o and d13c values spherulitic siderite which is present predominantly as early diagenetic nodules 1 5 mm in diameter in coal and carbonaceous mudrock in the lower part of the grootegeluk formation has relatively high d13c values up to 8 pdb and d18o value between 9 and 15 v smow granular siderite d13c values l9 to 14 and d18o values between 12 and 22 ankerite is present only in minor amounts d18o values between 16 and 20 and d13c values 12 the oxygen and carbon isotopic values of cleat filling calcite which is present only in coal seams has d18o values between 12 and 22 and d13c values between 15 and 7 fine grained calcite disseminated in carbonaceous mudrock and as inclusions in kaolinite is present only at the base of the grootegeluk formation and has d13c values between 7 and 3 and d18o values 15 the calcite lenses are interpreted to be synsedimentary and to have precipitated from depositional waters with d18o value of 13 spherulitic siderite and disseminated calcite precipitated during early diagenesis dominated by anaerobic microbial decomposition of organic matter granular siderite formed at higher temperatures d13c values 12 of the cleat filling calcite indicate a predominantly organic source for the carbon but the erratic and wide range of the d18o values do not allow distinction between precipitation daring burial or later during uplift of the sediments stable isotope data of the carbonates are consistent with precipitation from meteoric water but estimation of temperatures of formation are not reliable because burial processes result in highly d18o depleted pore water

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

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

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

mineralogy of the msl curiosity landing site in gale crater as observed by mro crism orbital data acquired by the compact reconnaissance imaging spectrometer for mars crism and high resolution imaging science experiment instruments on the mars reconnaissance orbiter mro provide a synoptic view of compositional stratigraphy on the floor of gale crater surrounding the area where the mars science laboratory msl curiosity landed fractured light toned material exhibits a 2 2 m absorption consistent with enrichment in hydroxylated silica this material may be distal sediment from the peace vallis fan with cement and fracture fill containing the silica this unit is overlain by more basaltic material which has 1 m and 2 m absorptions due to pyroxene that are typical of martian basaltic materials both materials are partially obscured by aeolian dust and basaltic sand dunes to the southeast exhibit differences in mafic mineral signatures with barchan dunes enhanced in olivine relative to pyroxene containing longitudinal dunes this compositional difference may be related to aeolian grain sorting

characteristics distribution origin and significance of opaline silica observed by the spirit rover in gusev crater mars 1 the presence of outcrops and soil regolith rich in opaline silica 65 92 wt sio2 in association with volcanic materials adjacent to the home plate feature in gusev crater is evidence for hydrothermal conditions the spirit rover has supplied a diverse set of observations that are used here to better understand the formation of silica and the activity abundance and fate of water in the first hydrothermal system to be explored in situ on mars we apply spectral chemical morphological textural and stratigraphic observations to assess whether the silica was produced by acid sulfate leaching of precursor rocks by precipitation from silica rich solutions or by some combination the apparent lack of s enrichment and the relatively low oxidation state of the home plate silica rich materials appear inconsistent with the originally proposed hawaiian analog for fumarolic acid sulfate leaching the stratiform distribution of the silica rich outcrops and their porous and brecciated microtextures are consistent with sinter produced by silica precipitation there is no evidence for crystalline quartz phases among the silica occurrences an indication of the lack of diagenetic maturation following the production of the amorphous opaline phase

the oxygen isotopic composition of olivine and pyroxene from ci chondrites the ci chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere however their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the ci parent body precursors to this alteration namely olivine and pyroxene are extremely rare in ci chondrites precluding previous measurements of their oxygen isotopic composition we report ion microprobe analyses of oxygen isotopes in single olivine and pyroxene grains separated from ci chondrites orgueil and ivuna the ci chondrite olivine and pyroxene grains most likely represent liberated chondrule phenocrysts based on petrographic chemical and isotopic evidence consistent with crystallization from a melt the oxygen isotope data form an array that falls nearly along the carbonaceous chondrite 16o mixing line with 18o values ranging from 9 3 to 12 3 o and 17o from 11 3 o to 7 8 o consistent with nebular processes being the source of the oxygen isotopic compositions the degree of 16o enrichment in orgueil olivines is negatively correlated with feo content but the exact nature and timing of the process that introduced this variation remains unknown the pyroxene oxygen isotopic compositions are similar to those of olivines with 5 mol fayalite the oxygen isotopic analyses of the olivine and pyroxene in ci chondrites have been used to revise previous models for the isotopic evolution of ci materials our data require more complete gas solid equilibration in the nebula and constrain the initial aqueous fluids on the ci parent body to have lower 17o values than previously postulated the refined model indicates that the temperature of aqueous activity on the ci parent body was no higher than 50 c and the fluid rock ratio was significantly less than previously estimated even prior to alteration and formation of secondary minerals the ci chondrites were the most 16o depleted carbonaceous chondrites and thus the solids originally contained in the ci chondrites are the most equilibrated nebular materials represented in the carbonaceous chondrites the data suggest the oxygen isotopic composition of average solar system to be approximately equivalent to average terrestrial oxygen as recorded in the compositions of terrestrial and lunar basalts

the paris meteorite the least altered cm chondrite so far the paris chondrite provides an excellent opportunity to study cm chondrules and refractory inclusions in a more pristine state than currently possible from other cms and to investigate the earliest stages of aqueous alteration captured within a single cm bulk composition it was found in the effects of a former colonial mining engineer and may have been an observed fall the texture mineralogy petrography magnetic properties and chemical and isotopic compositions are consistent with classification as a cm2 chondrite there are 45 vol high temperature components mainly type i chondrules with olivine mostly fa0 2 mean fa0 9 with granular textures because of low mesostasis abundances type ii chondrules contain olivine fa7 to fa76 these are dominantly of type iia but there are iiab and iib chondrules ii a b chondrules with minor highly ferroan olivine and iia c with augite as the only pyroxene the refractory inclusions in paris are amoeboid olivine aggregates aoas and fine grained spinel rich ca al rich inclusions cais the cai phases formed in the sequence hibonite perovskite grossite spinel gehlenite anorthite diopside fassaite and forsterite the most refractory phases are embedded in spinel which also occurs as massive nodules refractory metal nuggets are found in many cai and refractory platinum group element abundances pge decrease following the observed condensation sequences of their host phases mn cr isotope measurements of mineral separates from paris define a regression line with a slope of 53mn 55mn 5 76 0 76 106 if we interpret cr isotopic systematics as dating paris components particularly the chondrules the age is 4566 44 0 66 myr which is close to the age of cai and puts new constraints on the early evolution of the solar system eleven individual paris samples define an o isotope mixing line that passes through cm2 and co3 falls and indicates that paris is a very fresh sample with variation explained by local differences in the extent of alteration the anhydrous precursor to the cm2s was co3 like but the two groups differed in that the cms accreted a higher proportion of water paris has little matrix 47 plus 8 fine grained rims and is less altered than other cm chondrites chondrule silicates except mesostasis cai phases submicron forsterite and amorphous silicate in the matrix are all well preserved in the freshest domains and there is abundant metal preserved metal alteration stage 1 of palmer and lauretta 2011 metal and sulfide compositions and textures correspond to the least heated or equilibrated cm chondrites category a of kimura et al 2011 the composition of tochilinite cronstedtite intergrowths gives a pcp index of 2 9 cronstedtite is more abundant in the more altered zones whereas in normal highly altered cm chondrites with petrologic subtype 2 6 2 0 based on the s sio2 and feo sio2 ratios in pcp or tochilinite cronstedtite intergrowths rubin et al 2007 cronstedtite is destroyed by alteration the matrix in fresh zones has ci chondritic volatile element abundances but interactions between matrix and chondrules occurred during alteration modifying the volatile element abundances in the altered zones paris has higher trapped ne contents more primitive organic compounds and more primitive organic material than other cms there are gradational contacts between domains of different degree of alteration on the scale of 1 cm but also highly altered clasts suggesting mainly a water limited style of alteration with no significant metamorphic reheating

synthesis and model of formation water flow alberta basin canada based on a large amount of publicly available data several studies have previously examined the flow of formation waters in different parts of the alberta basin offering various interpretations as to the causes of the observed pressure regime and flow pattern however there has been no synthesis of these diverse studies on a basin wide basis accordingly these studies are critically reviewed in this paper and synthesized in a new basin scale model of the flow of formation waters in the alberta basin the proposed regional scale model has significant implications for understanding hydrocarbon migration pathways ore genesis the geothermal regime and deep waste disposal in the alberta basin several flow systems each one driven by a different mechanism are identified together with the main processes leading to the nonhydrostatic pressures observed in the basin two megahydrostratigraphic successions and associated flow systems are recognized the first succession corresponds to the pre cretaceous passive margin stage of basin development and consists of thick carbonate dominated aquifer systems separated by shaly aquitards and evaporitic aquicludes a northeastward basin scale flow system is driven by basin topography with recharge in montana and discharge in northeastern alberta southwest to northeast regional scale flow adjacent to the fold and thrust belt is probably the result of past tectonic processes the salinity of formation water in pre cretaceous aquifers is high and generally increases both northward and with depth this variability is the result of increased water rock reactions mineral solubility with increased temperatu e and of incomplete flushing by meteoric water as a result of salinity variations flow retarding buoyancy effects can be important the second megahydrostratigraphic succession corresponds to the post jurassic foreland stage of basin evolution and consists of thick shaly aquitard systems and relatively thin sandstone aquifers in the southwestern part of the basin flow in isolated aquifers is driven southwestward by erosional rebound in the thick intervening shales downdip toward the fold and thrust belt the salinity of formation waters in the post jurassic aquifers is low mixing of waters and interference between the major flow systems takes place along the pre cretaceous unconformity where successively older pre cretaceous aquifers subcrop from west to east flow in shallow lo al systems at the top of the sedimentary succession is driven by local topography

exploring fractionation models for martian magmas 1 martian primary compositions i e magmas that did not experience fractionation and or contamination after extraction from the mantle occur as a subset of martian meteorites and a few lavas analyzed on the planet s surface by rovers eruptions of primary magmas are rare on earth and presumably on mars previous studies of fractional crystallization of martian primary magmas have been conducted under isobaric conditions simulating idealized crystallization in magma chambers polybaric fractionation which occurs during magma ascent has not been investigated in detail for martian magmas using the melts algorithm and the pmelts revision we present comprehensive isobaric and polybaric thermodynamic calculations of the fractional crystallization of four primary or parental martian magmas humphrey fastball y 980459 shergottite and nakhlite parental melts using various pressure temperature paths oxygen fugacities and water contents to constrain how these magmas might evolve we then examine whether known martian alkaline rock compositions could have formed through fractional crystallization of these magmas under the simulated conditions we find that isobaric and polybaric crystallization paths produce similar residual melt compositions but given sufficient details we may be able to distinguish between them we calculate that backstay gusev crater likely formed by fractionation of a primary magma under polybaric conditions while jake m gale crater may have formed through melting of a metasomatized mantle crustal assimilation or fractional crystallization of an unknown primary magma the best fits for the backstay composition indicate that consideration of polybaric crystallization paths can help improve the quality of fit when simulating liquid lines of descent

diagenesis and reservoir quality of overpressured deep water sandstone following inorganic carbon dioxide accumulation upper miocene huangliu formation yinggehai basin south china sea abstract turbidite deposits overpressure hydrothermal fluid activity and co 2 accumulations are the basic geologic characteristics of the upper miocene huangliu formation sandstone reservoir in the dongfang gas field yinggehai basin this study aims to unravel the timing and origin of dissolution in sandstone and evaluate the effects of inorganic co 2 accumulation on reservoir quality a comparative study between area dfx 1 co 2 rich and area dfx 2 co 2 poor has illustrated the differences in diagenetic alteration and the effects of co 2 accumulation on the sandstone reservoir diagenetic alteration of sandstones in area dfx 1 was characterised by intense dissolution and medium cementation dissolution of silicates following inorganic co 2 charging in the dfx 1 area created a higher percentage of dissolution porosity 41 0 53 9 of total visible porosity compared with minor dissolution porosity in the dfx 2 area 16 7 29 6 of total visible porosity small amounts of kaolinite authigenic quartz ankerite and siderite were precipitated by co 2 water rock reactions in area dfx 1 these minerals are almost absent in area dfx 2 the carbonate cement of the huangliu formation sandstone in area dfx 1 is characterised by light 13 c 3 3 to 1 6 pdb which is consistent with formation from inorganic carbon the timing of dissolution by inorganic co 2 is suggested to be at about 0 4 ma based on the previous simulation experiments in the two areas studied overpressure was caused by pressure transmission along deep open faults and was not related to mudstone undercompaction overpressure did a little to contribute to porosity preservation co 2 accumulating at low partial pressures related to hydrothermal fluid flow cannot make a net increase in porosity in the huangliu formation sandstone of the dongfang gas field

genetic mechanism of high quality reservoirs in permian tight fan delta conglomerates at the northwestern margin of the junggar basin northwestern china fan delta conglomerate reservoirs in the permian jiamuhe formation in the zhongguai area at the northwestern margin of the junggar basin northwestern china are reservoirs for large accumulations of natural tight gas the tight conglomerates and sandstones are mainly litharenites with a large amount of texturally and compositionally immature volcanic clastic materials core porosities demonstrate the development of anomalously high porosities at depths of 3200 4200 m 10 500 13 800 ft and 4500 4900 m 14 800 16 100 ft the permian reservoirs experienced initial rapid subsidence uplift and further subsidence and diagenetic reactions occurred in these reservoirs involving compaction precipitation of chlorite clays calcites zeolites iron oxides kaolinite and quartz cements and dissolution of unstable minerals including analcite laumontite feldspars and rock fragments low porosity reservoirs with extensive compaction and or cementation of calcite and heulandite ca consist of only few visible secondary pores formed by dissolution of feldspars and rock fragments reservoirs with anomalously high porosity however experienced relatively weak compaction and contain significant amounts of secondary pores formed by dissolution of mainly laumontites some feldspars and rock fragments comprehensive studies of sedimentary features and diagenesis of the reservoirs indicate that these anomalously high porosities originate from chronological coupling of four important geological processes 1 sedimentary facies and detrital compositions controlled distribution of various zeolites in reservoirs with abundant laumonites developed in reservoirs in the fan delta front subfacies 2 early precipitation of the laumontites inhibited compaction during deep burial however they provided unstable minerals for secondary porosity development 3 the permian reservoirs experienced subaerial exposure erosion during the uplift stage and meteoric freshwater leached laumontite cements and aluminosilicate grains to form secondary pores in reservoirs beneath the unconformity 4 hydrocarbon emplacement at relative shallow depth during a second subsidence period preserved the secondary pores in reservoirs by retarding late carbonate cementation

use of statistical analysis to formulate conceptual models of geochemical behavior water chemical data from the botucatu aquifer in sao paulo state brazil water chemical data from the botucatu sandstone aquifer in the sao paulo state part of the parana basin brazil was evaluated using geochemical methods and two statistical analyses cluster analysis and factor analysis the results were used to develop a conceptual geochemical model in which three geochemical regions were identified and their chemical behavior was modeled the characteristic chemicals changing from the recharge area to the center of the basin are sio2 hco3 and ca2 na co32 and so42 the distribution of the chemicals is interpreted as controlled by different water rock interaction processes in the different regions in the recharge area dissolution of alkali feldspar minerals in the sandstone is the main reaction observed in the mid section of the basin calcite dissolution results in high calcium and bicarbonate concentration in the center of the basin leakage from underlying layers becomes the governing factor

neutron background environment measured by the mars science laboratory s dynamic albedo of neutrons instrument during the first 100 sols 1 the dynamic albedo of neutrons dan instrument on board mars science laboratory has been operating successfully since the landing and has been making measurements regularly along curiosity s traverse at the surface dan measures thermal e 0 4 ev and epithermal neutrons 0 4 ev e 1 kev while operating in two different modes active and passive the active mode uses a pulsed neutron generator png to study the geological characteristics of the subsurface in the passive mode dan measures the background neutron environment this paper presents results of measurements in the passive mode from landing through to sol 100 and provides an interpretation of the data based on extensive monte carlo simulations the main observations are summarized as follows 1 the thermal neutron counts vary strongly along the rover traverse while the epithermal counts do not show much variation 2 the neutrons from the multi mission radioisotope thermoelectric generator mmrtg are a larger contributor to the dan passive data than the galactic cosmic ray gcr induced neutrons 3 for the mmrtg neutrons both the thermal and the epithermal counts increase as a function of the subsurface water content 4 on the other hand for the gcr induced neutrons the thermal counts increase but the epithermal counts decrease as a function of the subsurface water content and 5 relative contributions by the mmrtg and gcr to the dan thermal neutron counts at the rocknest site where the rover was stationed from sol 59 to sol 100 are estimated to be 60 and 40 respectively

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

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

groundwater geochemical evolution in the northern portion of the guarani aquifer system brazil and its relationship to diagenetic features abstract the groundwater flow pattern in the northern portion of gas guarani aquifer system is characterized by the existence of four regional recharge areas located in sao paulo mato grosso do sul and goias states from these areas of recharge the regional flow is radial and directed toward the center of the parana sedimentary basin local discharge occurs in portions of outcrop regions the groundwater has low mineralization and can be classified as ca or ca mg hco 3 type na hco 3 type and na hco 3 cl so 4 type this sequence represents the hydrochemical evolution the mechanisms responsible for this evolution are dissolution of feldspars and removal of the carbonate cement from the sandstone mineral framework followed by ion exchange responsible for the increase in the na concentration and decrease of ca and finally enrichment in cl and so 4 derived from underlying aquifer units the hydrochemical evolution is consistent with diagenetic features that are observed in the sandstones with the presence of siliceous cement in the outcrop areas and carbonate cement toward the center of parana basin

snc meteorites are they martian rocks snc shergottite nakhlite chassignite achondrites are similar in many respects to terrestrial basaltic and ultramafic rocks several independent geochemical and petrological characteristics suggest that they formed on mars these include young 1 3 b y crystallization ages evidence for a magmatic history too complex for an asteroid possibility of garnet in the source region calculations of the magnitude of the gravity field necessary for crystal accumulation by settling presence of trapped gases similar to the the martian atmosphere and other features consistent with what is known about mars however the dynamical difficulties of ejecting meteorites from planetary surfaces are formidable

aqueous alteration and brecciation in bells an unusual saponite bearing cm chondrite the petrological and mineralogical characteristics of the unusual cm2 chondrite bells have been investigated in detail by scanning electron microscopy sem electron microprobe analysis epma and transmission electron microscopy tem bells is a highly brecciated chondrite which contains few intact chondrules a very low abundance of refractory inclusions and is notable in having an unusually high abundance of magnetite which is disseminated throughout the fine grained matrix fragmental olivines and pyroxenes are common and based on compositional data appear to have been derived from chondrules as a result of extensive brecciation the fine grained mineralogy of matrix in bells differs considerably from other cm chondrites and has closer affinities to matrix in ci chondrites the dominant phases are fine grained saponite interlayered with serpentine and phases such as tochilinite and cronstedtite which are typical of cm chondrite matrices are entirely absent pentlandite pyrrhotite magnetite anhydrite calcite and rare ti oxides also occur as accessory phases based on its oxygen and noble gas isotopic compositions zadnik 1985 rowe et al 1994 bells can be considered to be a cm2 chondrite although its bulk composition shows some departures from the typical range exhibited by this group however these variations in bulk chemistry are entirely consistent with the observed mineralogy of bells the unusual fine grained mineralogy of bells matrix can be reasonably attributed to the combined effects of aqueous alteration and advanced brecciation in a parent body environment extensive brecciation has assisted aqueous alteration by reducing chondrules and mineral grains into progressively smaller grains with high surface areas which are more susceptible to dissolution reactions involving aqueous fluids this has resulted in the preferential dissolution of fe rich chondrule olivines which are now completely absent in bells although present in other cm chondrites the formation of saponite in bells probably resulted from the dissolution of relatively silica rich phases such as pyroxene and olivine that were derived from chondrules the result of such dissolution reactions would be to increase the activity of silica in the fluid phase at least on a localized scale stabilizing saponite in preference to serpentine an increase in asio2 would also have destabilized preexisting cronstedtite which may have reacted to form magnetite and mg fe serpentine under conditions of constant o2

the secondary history of sutter s mill cm carbonaceous chondrite based on water abundance and the structure of its organic matter from two clasts sutter s mill is a regolith breccia composed of both heavily altered clasts and more reduced xenoliths here we present a detailed investigation of fragments of sm18 and sm51 we have characterized the water content and the mineralogy by infrared ir and thermogravimetric analysis tga and the structure of the organic compounds by raman spectroscopy to characterize the secondary history of the clasts including aqueous alteration and thermal metamorphism the three methods used in this study suggest that sm18 was significantly heated the amount of water contained in phyllosilicates derived by tga is estimated to be approximately 3 2 wt this value is quite low compared with other cm chondrites that typically range from 6 to 12 wt the infrared transmission spectra of sm18 show that the mineralogy of the sample is dominated by a mixture of phyllosilicate and olivine sm18 shows an intense peak at 11 2 lm indicative of olivine fig 1 if we compare sm18 with other cm and metamorphosed cm chondrites it shows one of the most intense olivine signatures and therefore a lower proportion of phyllosilicate minerals the raman results tend to support a short duration heating hypothesis in the id ig versus fwhm d diagram sm18 appears to be unusual compared to most cm samples and close to the metamorphosed cm chondrites pecora escarpment pca 91008 and pca 02012 in the case of sm51 infrared spectroscopy reveals that olivine is less abundant than in sm18 and the 10 lm silicate feature is more similar to that of moderately altered cm chondrites like murchison or queen alexandra range que 97990 raman spectroscopy does not clearly point to a heating event for sm51 in the id ig versus fwhm d diagram however tga analysis suggests that sm51 was slightly dehydrated as the amount of water contained in phyllosilicates is approximately 3 7 wt which is higher than sm18 but still lower than phyllosilicate water contents in weakly altered cm chondrites altogether these results confirm that fragments with different secondary histories are present within the sutter s mill fall the dehydration that is clearly observed for sm18 is attributed to a short duration heating based on the similarity of its raman spectra to that of pca 91008 because of the brecciated nature of sutter s mill and the presence of adjacent clasts with different thermal histories impacts that can efficiently fragment and heat porous materials are the preferred heat source

linking the influence of diagenetic properties and clay texture on reservoir quality in sandstones from nw borneo abstract reservoir studies in the sandakan sub basin nw borneo are challenging and inexplicable due to complex diagenetic effects such as compaction cementation dissolution and depositional means including grain size sorting and packing with reference to clay texture these diagenetic effects together impart significant amounts of uncertainty on reservoir quality assessment in this regard we documented the mineralogical diagenetic and reservoir properties of sandstones from the sandakan formation nw borneo through thin sections sem xrd xrf he porosimeter and poroperm in order to analyze the influential parameters we used matrix grain rearrangement and clay coating around detrital grains for the reservoir quality our results show that the sub litharenites to quartz arenite that dominate in the sandstones are drawn from recycled orogenic sand furthermore reservoir properties of the sandstones were ascertained to be controlled by diagenesis micro quartz with clay coatings and pressure dissolution of feldspar with the alteration of lithic fragments the result shows that the physical compaction rearrangements and ductility of grains were the reasons that reduced porosity and permeability the main reason for porosity reduction in the present study is pressure dissolution that resulted in the form of chemical compaction induced by micas with grain contacts nonetheless through sem and petrography clay coatings around the grains and dissolution of feldspar were found to optimally contribute to the preservation of reservoir properties dissolution of feldspar and kaolinization resulted in the formation of secondary porosity that allows meteoric water to percolate through the open and detachment spaces of quartz or other grains this percolation is also responsible in enhancing the pore throat radii in the reservoir media of the analyzed sandstones these traits are obliging to diagenetic effects on porosity and permeability which are linked with the physical compaction and clays coating to reduce and preserve the reservoir properties respectively of same type of reservoirs globally

secondary porosity formed by deep meteoric leaching botucatu eolianite southern south america the botucatu sandstone of the parana basin of brazil a jurassic eolianite exhibits unusually deep basinwide penetration of meteoric water this flow of dilute groundwater has removed calcite cement for an average distance of about 140 km from the outcrop and down to a burial depth of about 250 m feldspar has been leached from the framework for about 30 km downdip transforming what was deposited as a feldspathic sandstone into a diagenetic quartz arenite on outcrop these two dissolution processes have generated appreciable secondary porosity by weathering reactions at sites far removed from contact with the atmosphere between 100 and 500 pore volumes of water have passed through the aquifer system to produce this leaching making this an end member case of extensive meteoric diagenesis of sandstone consideration of other basins with meteoric incursion suggests that basin scale leaching is favored when uplift of one margin provides a steep gradient and there is a downdip escape route via faults or outcrop of the aquifer cratonic basins close to rifted continental margins seem to provide the best chance of meeting these conditions

mineralogy of the light toned outcrop at meridiani planum as seen by the miniature thermal emission spectrometer and implications for its formation 1 analysis of miniature thermal emission spectrometer mini tes data has led to the recovery of a pure end member spectral shape related to the light toned outcrop observed at meridiani planum data from the mer mossbauer spectrometer apxs and previous mini tes measurements were used to constrain a spectral library used to determine the mineralogy of the outcrop from this spectral shape linear deconvolution of the outcrop spectral shape suggests that it is composed primarily of al rich opaline silica mg ca and fe bearing sulfates plagioclase feldspar nontronite and hematite conversion of modeled mineralogy to chemistry shows good agreement with the chemical composition of the outcrops determined by apxs details of the analysis procedure and implications for the formation of the outcrop are discussed along with terrestrial analogs of the ancient environment at meridiani

geochemical and isotopic characteristics of spring and groundwater in the state of sao paulo brazil abstract a study of spring water shows that a correlation exists between the physical and chemical characteristics of the water and the lithology from where it issues water from crystalline rock can be classified as ca 1bmg bicarbonate with low conductivity and temperature water from sediments and or weathered crystalline rock as ca 1bmg chloride sulfate and from volcanic rock diabase and basalt as na bicarbonate water monthly samples of eight springs and of rain water in the region of aguas da prata were analyzed for the deuterium and 18 o isotopic contents expressed as d and 18 o in order to determine the origin of these waters the coincidence of the isotopic values of spring water with the regional meteoric line indicates a local source of recharge chemical anomalies of groundwater in the shallow bauru and basalto aquifers in the parana basin are probably caused by ascending water from the confined deep botucatu piramboia aquifer through fracture and fault zones

fluid flow and chemical alteration in carbonaceous chondrite parent bodies abstract carbonaceous chondrites are a class of primitive meteorites that likely represent early solar system materials thus providing critical insights about planetary evolution however evidence shows that they have undergone considerable processing elucidating the complex formation history of aqueously altered chondrite groups has been a principal objective of cosmochemistry fulfilling this objective requires understanding the nature of the water rock interactions involved many current alteration models are generally founded upon an assumption of uniform alteration in a closed system in these models different chondrite groups must originate on separate parent bodies contrary to this common view we show that chondrite data are consistent with non uniform alteration in a convecting system so that multiple chondrite groups can form within a single body

diagenesis and reservoir quality of sandstones with ancient deep incursion of meteoric freshwater an example in the nanpu sag bohai bay basin east china abstract an example of diagenesis and reservoir quality of buried sandstones with ancient incursion of meteoric freshwater is presented in this study the interpretation is based on information including porosity and permeability petrography stable isotopic composition of authigenic minerals homogenization temperatures th of aqueous fluid inclusions afis and pore water chemistry these sandstones closely beneath or far from the regional unconformity formed during the late paleogene period are located in the thick shahejie formation in the gaoliu area of nanpu sag bohai bay basin east china early diagenetic calcite cements were leached to form intergranular secondary pores without precipitation of late diagenetic calcite cements in most sandstones feldspars were leached to form abundant intragranular secondary pores but with small amounts of concomitant secondary minerals including authigenic quartz and kaolinite the mass imbalance between the amount of leached minerals and associated secondary minerals suggests that mineral leaching reactions occurred most likely in an open geochemical system and diagenetic petrography textures suggest that advective flow dominated the transfer of solutes from leached feldspars and calcites low salinity and ion concentrations of present pore waters and extensive water rock interactions suggest significant incursion of meteoric freshwater flux in the sandstones distances of the sandstones to the regional unconformity can reach up to 1800 m while with significant uplift in the gaoliu area the burial depth of such sandstones below sea level can be less than 800 1000 m during the uplift and initial reburial stage significant uplift during the oligocene period provided substantial hydraulic drive and widely developed faults served as favorable conduits for downward penetration of meteoric freshwater from the earth s surface unconformity to these sandstone beds extensive feldspar leaching has been occurring since the uplift period coupled high th 95 115 c of afi and low 18 o smow values 17 20 within the quartz overgrowths show that quartz cementation occurred in the presence of diagenetic modified meteoric freshwater with 18 o smow values of 7 2 indicating that authigenic quartz only have been formed during the late reburial stage when meteoric fresh water penetration slowed down secondary pores in thin sections and tested porosity suggest that meteoric freshwater leaching of feldspars and calcite minerals generated approximately 7 10 enhanced secondary porosity in these sandstones meteoric freshwater leaching reactions cannot be ignored in similar sandstones that located deep beneath the unconformity with great uplift moving these sandstones above or close to sea level and with faults connecting the earth s surface with the sandstone beds

oxygen isotope constraints on the alteration temperatures of cm chondrites abstract we report a systematic oxygen isotopic survey of ca carbonates in nine different cm chondrites characterized by different degrees of alteration from the least altered known to date paris 2 7 2 8 to the most altered alh 88045 cm1 our data define a continuous trend that crosses the terrestrial fractionation line tfl with a general relationship that is indistinguishable within errors from the trend defined by both matrix phyllosilicates and bulk o isotopic compositions of cm chondrites this bulk matrix carbonate bmc trend does not correspond to a mass dependent fractionation i e slope 0 52 as it would be expected during fluid circulation along a temperature gradient it is instead a direct proxy of the degree of o isotopic equilibration between 17 18 o rich fluids and 16 o rich anhydrous minerals our o isotopic survey revealed that for a given cm no carbonate is in o isotopic equilibrium with its respective surrounding matrix this precludes direct calculation of the temperature of carbonate precipitation however the o isotopic compositions of alteration water in different cms inferred from isotopic mass balance calculation and direct measurements define another trend cmw for cm water parallel to bmc but with a different intercept the distance between the bmc and cmw trends is directly related to the temperature of cm alteration and corresponds to average carbonates and serpentine formation temperatures of 110 c and 75 c respectively however carbonate o isotopic variations around the bmc trend indicate that they formed at various temperatures ranging between 50 and 300 c with 50 of the carbonates studied here showing precipitation temperature higher than 100 c the average 17 o and the average carbonate precipitation temperature per chondrite are correlated revealing that all cms underwent similar maximum temperature peaks but that altered cms experienced protracted carbonate precipitation event s at lower temperatures than the least altered cms our data suggest that the 17 o value of ca carbonates could be a reliable proxy of the degree of alteration experienced by cm chondrites

the origin and evolution of the peace vallis fan system that drains to the curiosity landing area gale crater mars the landing site for the curiosity rover is located at the distal end of the peace vallis fan in gale crater peace vallis fan covers 80 km2 and is fed by a 730 km2 catchment which drains an upland plains area through a 15 km wide gap in the crater rim valley incision into accumulated debris delivered sediment through a relatively low density valley network to a main stem channel to the fan an estimated total fan volume of 0 9 km3 matches the calculated volume of removal due to valley incision 0 8 km3 and indicates a mean thickness of 9 m the fan profile is weakly concave up with a mean slope of 1 5 for the lower portion numerous inverted channels outcrop on the western surface of the fan but on the eastern portion such channels are rare suggesting a change in process from distributary channel domination on the west to sheet flow on the eastern portion of the fan runoff discharge watershed area to produce the fan is estimated to be more than 600 m perhaps as much as 6000 m indicating a hydrologic cycle that likely lasted at least thousands of years atmospheric precipitation possibly snow not seepage produced the runoff based on topographic data peace vallis fan likely onlapped bradbury rise and spilled into a topographic low to the east of the rise this argues that the light toned fractured terrain within this topographic low corresponds to the distal deposits of peace vallis fan and in such a setting lacustrine deposits are expected

the origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter extraterrestrial organic matter in meteorites potentially retains a unique record of synthesis and chemical thermal modification by parent body nebular and even presolar processes in a survey of the elemental and isotopic compositions of insoluble organic matter iom from 75 carbonaceous ordinary and enstatite chondrites we find dramatic variations within and between chondrite classes there is no evidence that these variations correlate with the time and or location of chondrite formation or with any primary petrologic or bulk compositional features that are associated with nebular processes e g chondrule and volatile trace element abundances nor is there evidence for the formation of the iom by fischer tropsch type synthesis in the nebula or in the parent bodies the elemental variations are consistent with thermal maturation and or oxidation of a common precursor for reasons that are unclear there are large variations in isotopic composition within and between chondrite classes that do not correlate in a simple way with elemental composition or petrologic type nevertheless because of the pattern of elemental variations with petrologic type and the lack of any correlation with the primary features of the chondrite classes at present the most likely explanation is that all iom compositional variations are the result of parent body processing of a common precursor if correct the range of isotopic compositions within and between chondrite classes implies that the iom is composed of several isotopically distinct components whose relative stability varied with parent body conditions the most primitive iom is found in the cr chondrites and bells cm2 isotopically the iom from these meteorites resembles the iom in interplanetary dust particles chemically their iom resembles the chon particles of comet halley despite the large isotopic anomalies in the iom from these meteorites it is uncertain whether the iom formed in the interstellar medium or the outer solar system although the former is preferred here

oxygen isotopes in separated components of ci and cm meteorites oxygen isotopic compositions have been determined for whole rock and separated components from the ci chondrites alais ivuna and orgueil and from the atypical cm chondrites bells and essebi the composition of ci matrix is in agreement with previous measurements and is systematically different from that of cm matrix probably due to warmer and wetter conditions of aqueous alteration for ci matrix although bells matrix is like that of other cm chondrites the matrix of essebi falls in the ci field essebi also contains abundant magnetite like cis and unlike other cms the isotopic compositions of magnetite in alais ivuna orgueil and essebi define a trend with 17o of 1 3 to 1 8 distinctly out of isotopic equilibrium with the phyllosilicates in each meteorite the magnetite serves as an isotopic tracer for the fluid which brought about aqueous alteration and oxidation and thus provides additional evidence for a gaseous reservoir in the solar nebula which was more 16o depleted than the earth

matrix mineralogy of the orgueil ci carbonaceous chondrite a petrographic and transmission electron microscopic study of the orgueil ci carbonaceous chondrite shows that the matrix consists mainly of fe bearing mg rich serpentine and smectite saponite as well as a poorly crystallized fe rich material that contains minor variable s and ni the fe rich material is probably ferrihydrite a ferric hydroxide the ferrihydrite occurs in small particles 80 a in diameter and the s and ni are probably adsorbed on its surfaces the serpentine and saponite occur in poorly crystallized fine crystallites fine phyllosilicates that are intimately associated with the ferrihydrite coarsely crystallized phyllosilicates coarse phyllosilicates occur in clusters relatively free of ferrihydrite the ferrihydrite is a major matrix constitutent and probably accounts for most of the fe3 as well as the superparamagnetic fraction in the orgueil matrix the textures suggest that the fine phyllosilicates resulted from alteration of the coarse phyllosilicates the alteration probably involved a substantial amount of water and coincided with the period of sulfate vein formation during the aqueous alteration magnetite grains disaggregated from framboids and fe ni sulfides were replaced by ferrihydrite simultaneously aqueous solutions reacted with the coarse phyllosilicates and precipitated ferrihydrite producing intimate pervasive mixtures with the fine phyllosilicates the matrix mineralogy of the orgueil chondrite suggests that orgueil experienced considerably different alteration conditions from the cm chondrites the mineralogical and petrological differences between ci and cm chondrites can not simply be explained as the result of different degrees of aqueous alteration

correlated alteration effects in cm carbonaceous chondrites three parameters are proposed to determine the relative extent of alteration in cm chondrites the mineralogic alteration index monitors the relative progress of coupled substitutions in the progressive alteration of cronstedtite to mg serpentine and increases with increasing alteration to calculate values of this index an algorithm has been developed to estimate the average matrix phyllosilicate composition in individual cm chondrites the second parameter is the volume percent of isolated matrix silicates which decreases with progressive alteration due to mineral hydration finally the volume percent of chondrule alteration monitors the extent of chondrule phyllosilicate production and increases as alteration proceeds these parameters define the first cm alteration scale that relies on multiple indicators of progressive alteration the following relative order of increasing alteration is established by this model murchison bells pollen murray mighei nogoya cold bokkeveld the relative degree of aqueous processing cochabamba and boriskino experienced is less precisely constrained although both fall near the middle of this sequence a comparison between the mineralogic alteration index and literature values for the whole rock chemistry of cm chondrites reveals several correlations a positive nearly linear correlation between bulk h content and progressive cm alteration suggests an approximately constant production rate of new phyllosilicates relative to the mineralogical transition from cronstedtite to mg serpentine the abundance of trapped planetary 36ar decreases systematically in progressively altered cm chondrites suggesting the wholesale destruction of primary noble gas carrier phase s by aqueous reactions because low temperature fluid rock reactions are generally associated with large isotopic mass fractionation factors we also compared our model predictions with 18o values for bulk cm samples although some of these data are poorly resolved the order of increasing 18o values approximates the order of increasing alteration predicted by our model parameters multiple correlations between diverse alteration parameters strongly suggest that a different cm chondrites experienced similar kinds of processes and conditions and b cm materials experienced in situ alteration on the cm parent body or bodies

identification and description of a silicic volcaniclastic layer in gale crater mars using active neutron interrogation the dynamic albedo of neutrons instrument aboard the mars science laboratory rover curiosity has been used to map a stratigraphically conformable layer of high sio material in gale crater previous work has shown that this material contains tridymite a high temperature low pressure felsic mineral interpreted to have a volcanic source rock we describe several characteristics including orientation extent hydration and geochemistry consistent with a volcaniclastic material conformably deposited within a lacustrine mudstone succession relationships with widely dispersed alteration features and orbital detections of hydrated sio suggest that this high sio layer extends at least 17 km laterally mineralogical abundances previously reported for this high sio material indicated that hydrous species were restricted to the amorphous non crystalline fraction which is dominated by sio the low mean bulk hydration of this high sio layer 1 85 0 13 wt water equivalent hydrogen is consistent with silicic glass in addition to opal a and opal ct persistent volcanic glass and tridymite in addition to opal in an ancient sedimentary unit indicates that the conversion to more ordered forms of crystalline sio has not proceeded to completion and that this material has had only limited exposure to water since it originally erupted despite having been transported in a fluviolacustrine system our results including the conformable nature large areal extent and presence of volcanic glass indicate that this high sio material is derived from the product of evolved magma on mars this is the first identification of a silicic volcaniclastic layer on another planet and has important implications for magma evolution mechanisms on single plate planets

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

carbonate abundances and isotopic compositions in chondrites we report the bulk c abundances and c and o isotopic compositions of carbonates in 64 cm chondrites 14 cr chondrites 2 ci chondrites lew 85332 c2 kaba cv3 and semarkona ll3 0 for the unheated cms the total ranges of carbonate isotopic compositions are 13c 25 75 and 18o 15 35 and bulk carbonate c contents range from 0 03 to 0 60 wt there is no simple correlation between carbonate abundance and isotopic composition or between either of these parameters and the extent of alteration unless accretion was very heterogeneous the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the cm parent body probably prior to or at the start of aqueous alteration most of the ranges in cm carbonate isotopic compositions can be explained by their formation at different temperatures 0 130 c from a single fluid in which the carbonate o isotopes were controlled by equilibrium with water 18o 5 and the c isotopes were controlled by equilibrium with co and or ch4 13c 33 or 20 for co or ch4 dominated systems respectively however carbonate formation would have to have been inefficient otherwise carbonate compositions would have resembled those of the starting fluid a quite similar fluid composition 18o 5 5 and 13c 31 or 17 for co or ch4 dominated systems respectively can explain the carbonate compositions of the cis although the formation temperatures would have been lower 10 40 c and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the cms the cr carbonates exhibit a similar range of o isotopes but an almost bimodal distribution of c isotopes between more 13c 65 80 and less altered samples 13c 30 40 this bimodality can still be explained by precipitation from fluids with the same isotopic composition 18o 9 25 and 13c 21 or 8 for co or ch4 dominated systems respectively if the less altered crs had higher mole fractions of co2 in their fluids semarkona and kaba carbonates have some of the lightest c isotopic compositions of the meteorites studied here probably because they formed at higher temperatures and or from more co2 rich fluids the fluids responsible for the alteration of chondrites and from which the carbonates formed were almost certainly accreted as ices by analogy with cometary ices co2 and or co would have dominated the trapped volatile species in the ices the chondrites studied are too oxidized for co dominated fluids to have formed in their parent bodies if ch4 was the dominant c species in the fluids during carbonate formation it would have to have been generated in the parent bodies from co and or co2 when oxidation of metal by water created high partial pressures of h2 the fact that the chondrite carbonate c h2o mole ratios are of the order predicted for co co2 h2o ices that experienced temperatures of 50 100 k suggests that the chondrites formed at radial distances of 4 15 au

quantitative impact of diagenesis on reservoir quality of the triassic chang 6 tight oil sandstones zhenjing area ordos basin china abstract the upper triassic chang 6 sandstone an important exploration target in the ordos basin is a typical tight oil reservoir reservoir quality is a critical factor for tight oil exploration based on thin sections scanning electron microscopy sem x ray diffraction xrd stable isotopes and fluid inclusions the diagenetic processes and their impact on the reservoir quality of the chang 6 sandstones in the zhenjing area were quantitatively analysed the initial porosity of the chang 6 sandstones is 39 2 as calculated from point counting and grain size analysis mechanical and chemical compaction are the dominant processes for the destruction of pore spaces leading to a porosity reduction of 14 2 20 2 during progressive burial the porosity continually decreased from 4 3 to 12 4 due to carbonate cementation quartz overgrowth and clay mineral precipitation diagenetic processes were influenced by grain size sorting and mineral compositions evaluation of petrographic observations indicates that different extents of compaction and calcite cementation are responsible for the formation of high porosity and low porosity reservoirs secondary porosity formed due to the burial dissolution of feldspar rock fragments and laumontite in the chang 6 sandstones however in a relatively closed geochemical system products of dissolution cannot be transported away over a long distance as a result they precipitated in nearby pores and pore throats in addition quantitative calculations showed that the dissolution and associated precipitation of products of dissolution were nearly balanced consequently the total porosity of the chang 6 sandstones increased slightly due to burial dissolution but the permeability decreased significantly because of the occlusion of pore throats by the dissolution associated precipitation of authigenic minerals therefore the limited increase in net porosity from dissolution combined with intense compaction and cementation account for the low permeability and strong heterogeneity in the chang 6 sandstones in the zhenjing area

mineralogy aqueous alteration and primitive textural characteristics of fine grained rims in the y 791198 cm2 carbonaceous chondrite tem observations and comparison to alha81002 abstract transmission electron microscopy tem was used to study the microtextural and mineralogical characteristics of fine grained rims in the unbrecciated cm2 chondrites y 791198 and alha81002 in an effort to provide constraints on the origins of the rims themselves our tem observations show that the rims in y 791198 are composed of two distinct types of region sulfide poor and sulfide rich that are intermixed in a complex manner at the micron to submicron level the sulfide poor regions are largely composed of amorphous silicate material or nanocrystalline serpentine but rare fibrous and coarse grained serpentine grains have also been identified no fine grained cronstedtite or tochilinite were observed although coarse grained lumps of tochilinite are present in the rims in contrast the sulfide rich regions are characterized by the presence of a myriad nanometer sized fe ni sulfide grains pentlandite with some ni rich pyrrhotite embedded within an amorphous silicate similar in composition to that of the sulfide poor regions the sulfide rich regions also contain rare phases such as olivine and fe ni metal grains with grain sizes that are always 100 nm in size z contrast scanning transmission electron microscopy stem reveals that the fine grained rims consist of a mosaic of irregularly shaped sulfide poor and sulfide rich regions with sizes of about 0 2 0 5 m that have been compacted together during parent body lithification despite aqueous alteration the distinct mineralogical characteristics of these different regions are preserved on a fine scale and probably represent primitive heterogeneity in the dust from which these rims formed serpentine is much better developed and more widespread in the fine grained rims of alha81002 than y 791198 complex mats of serpentine fibers are commonly found and cronstedtite and tochilinite are plentiful anhydrous minerals such as olivine are rare and have usually been replaced by serpentine like y 791198 all the fine grained rims studied in alha81002 show the same mineral assemblages and textural characteristics throughout and between rims the homogeneity of the mineralogy textural relationships and degree of hydration in the rims of these two chondrites is more consistent with parent body alteration than with pre accretionary alteration

basin scale evolution of formation waters a diagenetic and formation water study of the triassic chaunoy formation paris basin abstract formation waters and their movements within basins are commonly attributed with responsibility for patterns of cementation and porosity loss within reservoirs and aquifers it is thus important to understand when and how waters move in the subsurface we have studied the evolution and movement of formation water in the triassic chaunoy formation of the paris basin nw europe to define the way in which the water has evolved and to interpret water movement patterns using mineral isotope and fluid inclusion data in conjunction with detailed formation water analyses the chaunoy formation is cemented with different types of dolomite calcite and quartz cement we have studied the evolution of waters in terms of oxygen carbon and strontium isotopes and salinity connate waters were meteoric in origin but strongly influenced by the proximity of a playa lake input of palaeo meteoric water which entered the chaunoy via eastern halite bodies resulted in highly saline formation water for the majority of the chaunoy formation from about 100 ma until and for some time after maximum burial saline waters spread into the aquifer initially taking a west north west trajectory and then switching to a west south west pattern in the eocene following the alpine orogeny and localised uplift of the basin margin the southern portion of chaunoy received fresh low salinity meteoric water it is likely that formation water was lost from the chaunoy in a more central part of the basin via sub vertical cross formational flow to the mid jurassic dogger formation to accommodate the influx of fresh water

assumptions about the presence of natural glasses on mars natural glasses occur not only on earth but also in lunar rocks and in some meteorites on geological grounds natural glasses could be expected on the surface of mars and their presence would have important implications for the weathering and alteration of the near surface layer ultramafic and mafic magmatism rich in iron and some volatiles appears to have been important on mars as has been impact cratering volcanism and possibly hydrothermal alteration available data indicate that we can presume the past or present existence of volcanic basaltic glasses impact glasses formed by thermal fusion of meteorite impact targets and diaplectic mainly maskelynite glasses conditions appear unsuitable for the formation of tektites on the martian surface and the production of measurable amounts of fulgurite or combustion glass seems improbable prospects for the remote and in situ identification of martian glasses and their subsequent weathering products are discussed and include orbital reflectance and thermal emission spectroscopic measurements and mossbauer spectroscopy from a surface lander

oxygen isotopic ratios of primordial water in carbonaceous chondrites abstract in this work i estimate the 18 o and 17 o values of primordial water in cm chondrites to be 55 13 and 35 9 respectively based on whole rock o and h data also i found that the o and or h data of antarctic meteorites are biased which is attributed to terrestrial weathering this characteristic o isotopic ratio of water together with corresponding water abundances in cm chondrites are consistent with the origin of water as ice processed by photochemical reactions at the outer regions of the solar nebula where mass independent o isotopic fractionation and water destruction may have occurred another possible mechanism to produce the inferred o isotopic ratio of water would be o isotopic fractionation between water vapor and ice which likely occurred near the condensation front of h2o snow line in the solar nebula the inferred o isotopic ratio of water suggests that carbonate in cm chondrites formed at low temperatures of

mapping mars geochemically using multivariate cluster analysis we identify six distinct geochemical provinces on mars from the concentrations of k th fe si ca cl and h 2 o determined by the mars odyssey gamma ray spectrometer the results show that the martian surface is dominated by basaltic rocks that vary in their abundance of incompatible k th and major elements fe si and ca these chemically distinct geochemical provinces are in large contiguous regions comprising a mixture of geologic units the k th ratios are uniform among the geochemical provinces to prevent measurable fractionation of k from th aqueous events must have been brief and or the total throughput of water small the muted weathering effects led to deposition of younger sedimentary deposits with the same compositions as older igneous units explaining why a geochemical province may contain mapped units with the same composition but a range of ages