iron and graphite associated with fossil bacteria in chert abstract the mineralization associated with fossilized bacteria in 2 0 ga stromatolitic grey chert from the gunflint iron formation has been examined using electron microprobe techniques and transmission electron microscopy tem x ray diffraction showed that the chert consisted mainly of quartz with small amounts of calcite lepidocrocite hematite and graphite in petrographic thin sections fossilized remains of both filamentous and coccoid microorganisms were detected by optical microscopy electron microprobe analyses of these fossilized bacteria revealed high concentration of si and o as expected for the quartz matrix of the chert trace amounts of al s c fe and cl were also present fragments of microfossils were observed by tem examinations of finely ground chert selected areas of this cellular debris generated graphitic electron diffraction patterns with spacings at d 3 38 2 04 and 1 23 a individual cell fragments were also found in successive stages of mineralization from amorphous to microcrystalline iron oxides

depositional environment and mechanism of preservation of microfossils upper proterozoic bitter springs formation australia microfossils preserved in black chert nodules from the upper proterozoic bitter springs formation of australia represent the preserved remnants of cyanobacterial communities that inhabited a series of nonmarine saline lakes and ponds groundwaters of halite salinity pickled the microorganisms and thus inhibited their early bacterial degradation these same groundwaters were saturated in silica so that upon evaporation the silica and halite precipitated and formed a series of chert concretions nodules and bipyramidal quartz crystals where the chert nodules formed in areas of buried cyanobacterial mats further degradation of the buried sheaths and cells was arrested and the microorganisms were preserved

paleolakes and impact basins in southern arabia terra including meridiani planum implications for the formation of hematite deposits on mars 1 the hematite deposit in meridiani planum was selected for a mars exploration rover mer landing site because water could be involved in the formation of hematite and water is a key ingredient in the search for life our discovery of a chain of paleolake basins and channels along the southern margin of the hematite deposits in meridiani planum with the presence of the strongest hematite signature adjacent to a paleolake basin supports the possible role of water in the formation of the hematite and the deposition of other layered materials in the region the hematite may have formed by direct precipitation from lake water as coatings precipitated from groundwater or by oxidation of preexisting iron oxide minerals the paleolake basins were fed by an extensive channel system originating from an area larger than texas and located south of the schiaparelli impact basin on the basis of stratigraphic relationships the formation of channels in the region occurred over much of mars history from before the layered materials in meridiani planum were deposited until recently the location of the paleolake basins and channels is connected with the impact cratering history of the region the earliest structure identified in this study is an ancient circular multiringed basin 800 1600 km diameter that underlies the entire meridiani planum region the mer landing site is located on the buried northern rim of a later 150 km diameter crater this crater is partially filled with layered deposits that contained a paleolake in its southern portion

recent ventifact development on the central oregon coast western usa the unusual location of ventifacts on a boulder built jetty at the mouth of the siuslaw river oregon coast western usa allows ventifact age and wind abrasion rates to be estimated with some precision the jetty was built mainly between 1892 1901 and extended throughout the twentieth century consideration of historical shoreline position and the history of jetty construction and repair suggests the ventifacts have formed since about 1930 morphologically the ventifacts are aligned south to north reflecting winter winds and sediment transport from the adjacent beach wind parallel grooves and ridges with sharp sinuous crests are developed on inclined boulder surfaces on top of the jetty and reflect suspended sand transport in wind vortices deeply pitted surfaces on steep boulder surfaces nearest the beach reflect impact by saltating sand grains based on present wind regimes 1992 2000 from three regional weather stations southerly winds above the sand transport threshold occur for 21 9 29 6 per cent of the time based on estimated depth of loss from boulder surfaces wind abrasion rates are calculated to be on the order of 0 24 1 63 mm a 1 this is the first well constrained field estimate of ventifact age and ventifaction rate from a modern coastal environment copyright c 2003 john wiley sons ltd

in situ identification pairing and classification of meteorites from antarctica through magnetic susceptibility measurements we report on the effectiveness of using magnetic measurements in the search for meteorites on the antarctic ice sheet which is thus far the earth s most productive terrain magnetic susceptibility measurements carried out with a pocket meter sm30 during the 2003 04 pnra meteorite collection expedition to northern victoria land antarctica proved to be a rapid sensitive non destructive means for the in situ identification pairing and classification of meteorites in blue ice fields characterized by the presence of moraines and glacial drifts e g miller butte roberts butte and frontier mountain magnetic susceptibility measurements allowed discrimination of meteorites from abundant terrestrial stones that look like meteorites thanks to the relatively high magnetic susceptibility of the former with respect to terrestrial rocks comparative measurements helped identify 16 paired fragments found at johannessen nunataks thereby reducing unnecessary duplication of laboratory analyses and statistical bias following classifications schemes developed by us in this and previous works magnetic susceptibility measurements also helped classify stony meteorites directly in the field thereby providing a means for selecting samples with higher research priority a magnetic gradiometer capable of detecting perturbations in the earth s magnetic field induced by the presence of meteorites was an efficient tool for locating meteorites buried in snow along the downwind margin of the frontier mountain blue ice field based on these results we believe that magnetic sensors should constitute an additional payload for robotic search for meteorites on the antarctic ice sheet and by extension on the surface of mars where meteorite accumulations are predicted by theoretical works lastly magnetic susceptibility data was successfully used to cross check the later petrographic classification of the 123 recovered meteorites allowing the detection of misclassified or peculiar specimens

metallic ion binding by bacillus subtilis implications for the fossilization of microorganisms the silicification of bacterial cells has been followed in a laboratory simulation by electron microscopy and energy dispersive x ray spectroscopy structural degradation of the bacteria was not influenced by silica availability but the remains of degraded cells did promote the precipitation of silica in contrast cells reacted with ferric iron before aging remained intact and structures conforming to the original morphology of the bacteria were preserved by silicification the binding of metallic ions by microbial cells in particular the retention of iron is therefore considered to be an important contributing factor to the fossilization of microorganisms

quaternary landscape development alluvial fan chronology and erosion of the mecca hills at the southern end of the san andreas fault zone abstract quantitative geomorphic analysis combined with cosmogenic nuclide 10 be based geochronology and denudation rates have been used to further the understanding of the quaternary landscape development of the mecca hills a zone of transpressional uplift along the southern end of the san andreas fault in southern california the similar timing of convergent uplifts along the san andreas fault with the initiation of the sub parallel san jacinto fault suggest a possible link between the two tectonic events the ages of alluvial fans and the rates of catchment wide denudation have been integrated to assess the relative influence of climate and tectonic uplift on the development of catchments within the mecca hills ages for major geomorphic surfaces based on 10 be surface exposure dating of boulders and 10 be depth profiles define the timing of surface stabilization to 2 6 5 6 1 3 ka qyf1 surface 67 2 5 3 ka qvof2 surface and 280 24 ka qvof1 surface comparison of 10 be measurements from active channel deposits qac and fluvial terraces qt illustrate a complex history of erosion sediment storage and sediment transport in this environment beryllium 10 catchment wide denudation rates range from 19 9 3 2 to 149 22 5 m ma and demonstrate strong correlations with mean catchment slope and with total active fault length normalized by catchment area the lack of strong correlation with other geomorphic variables suggests that tectonic uplift and rock weakening have the greatest control the currently measured topography and denudation rates across the mecca hills may be most consistent with a model of radial topographic growth in contrast to a model based on the rapid uplift and advection of crust

nw african hydrology and vegetation during the last glacial cycle reflected in plant wax specific hydrogen and carbon isotopes abstract we present a hydrologic reconstruction of the sahara sahel transition covering the complete last glacial cycle 130 ka based on a combination of plant wax specific hydrogen d and carbon isotopes 13c the d and 13c signatures of long chain n alkanes from odp site 659 off nw africa reveal a significant anti correlation complementary to published pollen data we infer that this plant wax signal reflects sensitive responses of the vegetation cover to precipitation changes in the sahel region as well as varying contributions from biomes north of the sahara c3 domain by north east trade winds netw during arid phases especially the northern parts of the sahel likely experienced crucial water stress which resulted in a pronounced contraction of the vegetation cover thus reducing the amount of c4 plant waxes from the region the increase in netw strength during dry periods further promoted a more pronounced c3 plant wax signal derived from the north african c3 plant domain during humid periods the c4 dominated sahelian environments spread northward into the saharan realm in association with lower netw inputs of c3 plant waxes arid humid cycles deduced from plant wax d are in accordance with concomitant changes in weathering intensity reflected in varying major element distributions environmental shifts are generally linked to periods with large fluctuations in northern hemisphere summer insolation during marine isotope stages 2 and 3 when insolation variability was low coupling of the hydrologic regime to alkenone based estimates of ne atlantic sea surface temperatures becomes apparent

numerous unpaired meteorites exposed on a deflating playa lake at lucerne valley california abstract out of 16 well characterized 1 to 37 g meteorite specimens recovered from lucerne dry lake an approximately 3 7 km playa in the southern mojave desert of california there are 9 separate ordinary chondrite finds the ratio of independent meteorites to total number of specimens 0 6 is among the highest in the world this is due to lack of initial deep burial of the small meteorites significant deflation of the lake exposing falls of individual stones or small numbers of paired meteorites and the absence of a large meteorite shower in the region playas appear to be excellent candidates for high yield meteorite collecting areas

the dar al gani meteorite field libyan sahara geological setting pairing of meteorites and recovery density as of july 2001 1238 libyan meteorites have been reported most were found in two areas called dar al gani and hamadah al hamra dar al gani is located on a plateau of marine carbonate rocks with marly components eight hundred and sixty nine meteorites between 6 g and 95 kg totalling 687 kg have been found here but the calculated mean recovery density is comparatively low with one meteorite on 6 5 km2 dar al gani is a perfect site for the recognition and preservation of meteorites the existence of meteorites is the result of a combination of specific geological and geomorphological conditions there is a bright colored old limestone plateau 2 ma under arid weather conditions over long periods of time with rapid elimination of surface water if present and low erosion rates the preservation of meteorites is guaranteed through the absence of quartz sand on the plateau strongly reducing wind erosion and a basic environment emerging from the carbonate ground retards rusting of metallic meteorite components a supposed soil cover during pluvial times has probably protected older meteorites and led to a concentration of meteorites of different periods an evaluation of dar al gani meteorites suggests the existence of at least 26 strewnfields and 26 meteorite pairs reducing the number of falls to at most 534 shock and weathering grades as a tool for the recognition of pairings turned out to be problematic as several strewnfields showed paired meteorites which had been classified to different shock and weathering grades

terrestrial ages of meteorites from the nullarbor region australia based on 14c and 14c 10be measurements we have investigated the terrestrial ages or residence times of 78 meteorites representing 73 discrete falls recovered in western australia and one from south australia using both 14c measurements and also 14c 10be the samples studied included two ureilites one ck and one el chondrite we have included 10be measurements from 30 meteorites including some meteorites for which the 14c terrestrial age was previously determined we find that the 14c 10be terrestrial ages are more precise than 14c alone as we can correct for shielding effects in general the two different age determinations age by 14c 10be are precise to 0 5 1 ka and 14c alone within 1 2 ka however measurement of the 14c age alone gives good agreement with the 14c 10be for most samples the study of the terrestrial ages of meteorites gives us useful information concerning the storage and weathering of meteorites and the study of fall times and terrestrial age we have compared the terrestrial ages to weathering degree of oxidation estimated from mossbauer studies and d17o in this study we found that weathering is not well correlated with terrestrial age for nullarbor meteorites however there is a good correlation between degree of oxidation and d17o the implications for the study of terrestrial ages and weathering from other desert environments will be discussed

synapsid burrows and associated trace fossils in the lower jurassic navajo sandstone southeastern utah u s a indicates a diverse community living in a wet desert ecosystem abstract enigmatic structures in the lower jurassic navajo sandstone near moab utah occur at three localities below carbonate beds that record interdune lake deposits these structures are interpreted as mammal and therapsid burrows based on their architectural and surficial burrow morphologies type i large diameter and type ii mega diameter burrows type i burrows include sinuous tunnels y and t branched tunnels sinuous ramps and chambers and weather into mounds averaging 33 m 22 m and extend 1m above the surface type i burrows are dorsoventrally flattened in cross section averaging 9 3 cm wide and 4 2 cm high and are sand filled and structureless type i burrows mostly have smooth walls though some have scalloped walls type ii burrows are simple inclined tunnels 35 cm wide and 20 cm high and exhibit well preserved bilobate morphology along the underside of the tunnel the walls preserve a series of 3 or 4 thin 4 8 mm inclined scratch marks from the upper part of the wall and along the floor the great complexity and high density of type i burrow systems is best explained by multiple individuals living together in social groups these burrows are more complex than early triassic therapsid burrows from south africa and are most similar to burrows of extant social e g voles and eusocial mammals e g naked mole rats type ii burrows were likely constructed by therapsids based on burrow size and comparison to permian and triassic therapsid burrows from south africa and antarctica

meridiani planum hematite deposit and the search for evidence of life on mars iron mineralization of microorganisms in rock varnish the extensive hematite deposit in meridiani planum was selected as the landing site for the mars exploration rover opportunity because the site may have been favorable to the preservation of evidence of possible prebiotic or biotic processes one of the proposed mechanisms for formation of this deposit involves surface weathering and coatings exemplified on earth by rock varnish microbial life including microcolonial fungi and bacteria is documented in rock varnish matrices from the southwestern united states and australia limited evidence of this life is preserved as cells and cell molds mineralized by iron oxides and hydroxides as well as by manganese oxides such mineralization of microbial cells has previously been demonstrated experimentally and documented in banded iron formations hot spring deposits and ferricrete soils these types of deposits are examples of the four water rock interaction scenarios proposed for formation of the hematite deposit on mars the instrument suite on opportunity has the capability to distinguish among these proposed formation scenarios and possibly to detect traces that are suggestive of preserved martian microbiota however the confirmation of microfossils or preserved biosignatures will likely require the return of samples to terrestrial laboratories

the flux of meteorites to the earth and weathering in hot desert ordinary chondrite finds abstract the abundance of ferric iron produced by weathering in ordinary chondrites collected from hot desert regions is related to their terrestrial age enabling a variety of processes involved in meteorite weathering to be deduced fe0 fe2 fe3 content was measured quantitatively by 57fe mossbauer spectroscopy it is observed that meteorites from different regions are oxidised at different rates we also propose the tentative hypothesis that one source of scatter in total oxidation versus terrestrial age for a region is climatic change a mechanism to explain the variable response to climatic conditions involves the high initial porosity of samples being reduced as ferric oxides and other alteration products are produced reliable recovery data from a meteorite accumulation site roosevelt county new mexico usa and a quantitative measure of weathering and terrestrial age permit an estimate of the flux of meteorites to the earth s surface having established a decay constant for meteorites and accounting for the area of searches and pairing we estimate an accumulation rate of 159 falls of mass greater than 20 g per 106 km2 per yr this calculation is distinct from but in broad agreement with previous estimates from camera observations suggesting that the accumulation rate of meteorite falls to the earth s surface has remained essentially unchanged over the last 50 000 years at between 59 and 159 falls of mass exceeding 20 g per 106 km2 per yr the error for both methods is approximately a factor of 2

characteristics and occurrence of wind erosion features in the namib desert small scale features resulting from wind erosion are widespread in the namib desert they include selective erosion of lithological variations etching flutes and grooves facetting of clasts and residual boulders and smoothing and polishing of rock surfaces large scale features are tentatively identified and are restricted to the southern namib with its high energy unidirectional wind regime wind erosion features are best developed on fine grained rocks of intermediate hardness they are oriented towards or parallel to modern strong winds the turbulent flow of wind armed only with dust particles is probably more important than wind driven sand in creating smooth polished rock surfaces flutes and grooves wind driven sand appears to be significant only in facetting rock masses

tectonics and surface effects of the supercontinent columbia abstract assembly of the supercontinent columbia at about 1 85 1 90 ga coincided with several events that affected the entire earth the oldest worldwide network of orogenic belts formed at the same time although some granite granodiorite gg suites had formed earlier the gg suites became common in the 1 8 1 9 ga orogenic belts these suites succeeded the older tonalite trondhjemite granodiorite ttg suites which were not produced after 1 8 ga changes on the earth s surface at 1 8 1 9 ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes all of these surface changes occurred as columbia accreted and the assembly of columbia may have contributed to the drastic changes in the earth s surface environment as well as to the evolution of primitive life forms

the importance of wind as a driver of earthen heritage deterioration in dryland environments abstract dryland regions are exposed to extreme environmental conditions that create hotspots of weathering and erosion many earthen heritage sites are located in these dryland regions and experience extensive deterioration driven by interactions with environmental processes however previous research has focused largely on the role of rain as a driver of deterioration this study combines approaches from geomorphology with understandings of earthen materials from heritage science to investigate the relative importance of wind and rain in driving earthen heritage deterioration in drylands we use geomorphological signatures to infer the environmental histories of earthen walls with a range of known ages at suoyang ancient city china using semi quantitative deterioration assessments we find rain driven deterioration features to be associated with the loss of larger volumes of material and to have higher persistence than wind driven deterioration features however we argue that the high frequency nature of wind events means that wind is an important initiator of deterioration across the site in addition walls exposed to the prevailing wind are dominated by wind driven deterioration features outcomes from this study present an opportunity for earthen heritage conservation to investigate potential strategies to minimise wind speed at earthen heritage sites in drylands

origin of graphite and temperature of metamorphism in precambrian eastern ghats mobile belt orissa india a carbon isotope approach abstract the carbon isotope composition of graphite and carbon and oxygen isotope composition of associated calcite from different locations of the eastern ghats mobile belt egmb of orissa have been measured in order to understand the origin of graphite the 13c values of graphite range from 2 4 to 26 6 forty four of sixty one samples have 13c values less than 20 most of these low 13c values graphite corresponds to schists and disseminations in khondalite and calc silicate granulites thus indicating graphitization of organic matter the remaining light carbon graphite occurs as veins which is the result of graphitization of transported organic matter the graphite with intermediate 13c value 13 to 19 indicates carbon contributions from both organic and carbonates sources and or mantle sources the higher 13c values graphite 2 4 to 8 8 represent mantle carbon and or carbonate sources without significant contribution from organic carbon the temperatures of metamorphism have been estimated using carbon isotope ratios of graphite and associated calcite of calc silicate granulites where typical cation exchange thermometer assemblages are lacking and significant mineral reaction textures used to calculate pressure temperature of metamorphic events are absent metamorphic temperatures obtained 945 c are close to the ultrahigh temperature reported from the egmb the minimum temperature estimated using the graphite carbonate carbon isotope ratio is 90 c the lower estimates of temperatures probably indicate changes in the carbon isotope ratio of calcite by decarbonation reaction or armoring of carbonaceous matter in silicates during metamorphism preventing continuous exchange with calcite

biologically mediated dissolution of volcanic glass in seawater we studied the effects of biological mediation on the dissolution of basaltic glass in seawater experiments with typical seawater microbial populations were contrasted with a sterile control and reactions were monitored chemically and isotopically biologically mediated experiments produce twice the mass of authigenic phases than abiotic experiments and the phases are different abiotic alteration of glass dissolves basaltic si and ca and scavenges seawater mg while biotic alteration removes ca from seawater such opposing behavior of ca and mg in biotic and abiotic alteration of basaltic glass may have important implications for the carbon cycle and the exchange processes between ocean crust and seawater 87sr 86sr data of glass and alteration products suggest that biological mediation enhances both the diffusion of seawater sr into glass by a factor of 3 4 and the dissolution of basaltic sr into seawater by a factor of 20 40 the dependence of chemical exchange processes between seawater and glass on biological activity implies that chemical fluxes from water rock interaction at low temperatures may change as life on earth evolves

13c 12c exchange between calcite and graphite a possible thermometer in grenville marbles the fractionation of 13c between calcite and graphite cc gr is consistently small 2 6 4 8 permil in 34 assemblages from upper amphibolite and granulite facies marbles of the grenville province in 25 samples from the adirondack mountains new york it decreases regularly with increasing metamorphic temperature the fractionations are independent of absolute 13c values of calcite 2 9 to 5 0 for t 600 800 c the adirondack data are described by cc gr 0 00748t c 8 68 this good correlation between and t suggests that carbon isotope equilibrium was attained in these high grade marbles and that the theoretical calculations of this fractionation by bottinga are approximately 2 permil too large in this temperature range because of the relatively high temperature sensitivity suggested by these results and by bottinga s calculations and the pressure independence of isotope fractionation cc gr may provide a very good thermometer for high grade marbles comparison of this field calibration for cc gr vs temperature with results from other terranes supports the utility of cc gr for geothermometry and suggests that graphite is much more sluggish to exchange than calcite that exchange between calcite and graphite occurs at temperatures as low as 300 c and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500 600 c because 13c exchange is an unavoidable metamorphic process at temperatures above 300 c high values of 13c gr in moderate to high grade carbonate bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite

metal fixation by bacterial cell walls all biomass contains a significant quantity of metallic constituents and mineralization in living and dead biodebris may contribute to element transport from the hydrosphere into sediments the anionic cell walls of bacteria are remarkable in their ability to fix metals and provide sites for nucleation and growth of minerals results presented show the types of cell wall polymers that are responsible for metal binding in walls of gram positive and gram negative bacteria

the densest meteorite collection area in hot deserts the san juan meteorite field atacama desert chile we describe the geological morphological and climatic setting of the san juan meteorite collection area in the central depression of the atacama desert chile our recovery activities yielded 48 meteorites corresponding to a minimum of 36 different falls within a 3 88 km 2 area the recovery density is in the range 9 12 falls km 2 depending on pairing making it the densest among meteorite collection areas in hot deserts this high meteorite concentration is linked to the long standing hyperaridity of the area the stability of the surface pebbles ma and very low erosion rates of surface pebbles approximately 30 cm ma 1 maximum the san juan meteorite population is characterized by old terrestrial ages that range from zero to beyond 40 ka and limited weathering compared with other dense collection areas in hot desert chemical weathering in san juan is slow and mainly controlled by the initial porosity of meteorites as in the antarctic and other hot deserts there is an overabundance of h chondrites and a shortage of ll chondrites compared with the modern falls population suggesting a recent few ka change in the composition of the meteorite flux to earth

ventifacts on earth and mars analytical field and laboratory studies supporting sand abrasion and windward feature development abstract terrestrial ventifacts rocks that have been abraded by windblown particles are found in desert periglacial and coastal environments on mars their abundance suggests that aeolian abrasion is one of the most significant erosional processes on the planet there are several conflicting viewpoints concerning the efficacy of potential abrasive agents principally sand and dust and the relationships between wind direction and ventifact form our research supported by a review of the literature shows that sand rather than dust or other materials is the principle abrasive agent on earth and mars relative to dust sand delivers about 1000 the energy onto rock surfaces on a per particle basis even multiple dust collisions will do little or no damage because the stress field from the impact is much smaller than the spacing of microflaws in the rock the abrasion profiles of terrestrial ventifacts are consistent with a kinetic energy flux due to saltating sand not airborne dust furthermore scanning electron microscope images reveal surfaces that are fractured and cleaved by sand grain impact with respect to their distribution ventifacts are found in regions that contain sand or did so in the past but are not found where only dust activity occurs contrary to some published reports our evidence from field studies analytical models and wind tunnel and other experiments indicates that windward not leeward abrasion is responsible for facet development and feature formation pits flutes and grooves leeward abrasion is confined to fluvial conditions in which the high viscosity and density of water are able to entrain sand size material in vortices therefore ventifacts and abraded terrain provide an unambiguous proxy for the direction of the highest velocity winds and can be used to reconstruct palaeowind flow

tissint martian meteorite a fresh look at the interior surface and atmosphere of mars tissint morocco is the fifth martian meteorite collected after it was witnessed falling to earth our integrated mineralogical petrological and geochemical study shows that it is a depleted picritic shergottite similar to eeta79001a highly magnesian olivine and abundant glass containing martian atmosphere are present in tissint refractory trace element sulfur and fluorine data for the matrix and glass veins in the meteorite indicate the presence of a martian surface component thus the influence of in situ martian weathering can be unambiguously distinguished from terrestrial contamination in this meteorite martian weathering features in tissint are compatible with the results of spacecraft observations of mars tissint has a cosmic ray exposure age of 0 7 0 3 million years consistent with those of many other shergottites notably eeta79001 suggesting that they were ejected from mars during the same event

bacteria as nucleation sites for authigenic minerals in a metal contaminated lake sediment abstract sediment samples contaminated with metals arising from mine tailings drainage were obtained from lower moose lake in the onaping region near sudbury ontario canada the samples were examined by electron microscopy selected area electron diffraction and energy dispersive x ray spectroscopy individual bacterial cells and their remains were prominent as nucleation sites for both metal sulfides and a complex polymorphic fe al silicate the principal metal sulfide species associated with the bacteria were amorphous mackinawite fes 1 x and microcrystalline millerite nis trace amounts of cu and zu were also detected in some of the sulfide precipitates at least two structural forms of the fe al silicate were present and energy dispersive x ray spectroscopy point analyses revealed corresponding differences in chemical composition poorly ordered limonitic clay type phases had a granular morphology and contained less fe than well developed crystalline material which generated hexagonal diffraction patterns with reflections d 4 60 and 2 55 characteristic of an interstratified chamositic clay

the rock abrasion record at gale crater mars science laboratory results from bradbury landing to rocknest ventifacts rocks abraded by wind borne particles are found in gale crater mars in the eastward drive from bradbury landing to rocknest they account for about half of the float and outcrop seen by curiosity s cameras many are faceted and exhibit abrasion textures found at a range of scales from submillimeter lineations to centimeter scale facets scallops flutes and grooves the drive path geometry in the first 100 sols of the mission emphasized the identification of abrasion facets and textures formed by westerly flow this upwind direction is inconsistent with predictions based on models and the orientation of regional dunes suggesting that these ventifact features formed from very rare high speed winds the absence of active sand and evidence for deflation in the area indicates that most of the ventifacts are fossil features experiencing little abrasion today

features and characterization of graphite in almora crystallines and their implication for the graphite formation in lesser himalaya india layers bands lenses and pockets of graphite are confined to mica schists garnet mica schist micaceous quartzites and black carbonaceous phyllites of the almora group forming graphite prospect in indian lesser himalaya the field and microscopic features of graphite reveal that the graphite in almora group was crystallized from metamorphism of the organic material before himalayan thrusting upto 100 m size nodular and 5 m size circular features points to the involvement of biogenic carbonaceous material in graphitization as also substantiated by 13c values and probably by the presence of v and p associated with this graphite impurities consisting si al mg o fe ti v ca and k are common with graphite these are derived from associated minerals such as muscovite quartz biotite garnet etc raman shifts obtained from this graphite suggest that it is an ordered graphite with its fine dust scattered in the host rocks the calculated degree of graphitization varies from 64 to 89 with no systematic spatial variation in the estimated temperatures cf 485 568 c of graphite formation within this range the temperatures for the intensely folded graphite are higher probably promoted by the himalayan tectonics although high end thermal records reported from the almora group are not evident in graphite however these temperatures obtained from graphite match with host rock thermometry implying that the graphite was formed during regional metamorphism

climate and rock weathering a study of terrestrial age dated ordinary chondritic meteorites from hot desert regions abstract ordinary chondrites oc recovered from the desert areas of roosevelt county new mexico the nullarbor region of western australia and the algerian and libyan sahara for which 14c terrestrial ages have been determined were examined by 57fe mossbauer spectroscopy oc were chosen as a standard sample to investigate weathering processes as their well constrained trace and bulk element chemistry normative mineralogy and isotopic composition define a known pre weathering starting composition given that terrestrial ages are known it is possible to compare initially very similar samples that have been subsequently weathered in a range of climatic regimes from the present day to 44 ka bp in addition recently fallen equilibrated oc contain iron only as fe0 and fe2 thus the abundance of ferric iron is directly related to the level of terrestrial weathering mossbauer spectroscopy identifies two broad types of ferric alteration paramagnetic phases akaganeite lepidocrocite and goethite and magnetically ordered principally magnetite and maghemite oc finds show a range in the percentage of total fe existing as fe3 from zero to over 80 however oxidation is comparable between fragments of the same oc separated since their time of fall i e paired meteorites our results indicate several features of meteorite weathering that may result from climatic or geomorphologic conditions at the accumulation site 1 saharan samples are overall less weathered than non saharan samples which may be related to the relatively recent age ca 20 ka of the saharan accumulation surface 2 broad differences between sites in the rate of weathering arising from regional differences in climate 3 consistent differences in the weathering products between samples that fell during humid periods and those that fell during more arid periods those falling during humid periods contain a higher proportion of magnetically ordered ferric oxides 4 one region the nullarbor that shows a variation in the total amount of ferric species that closely matches the climatic record for this area of australia for the last 30 ka points 3 and 4 may be related to the identification of a rapid initial weathering phase the majority of weathering occurs in the first few hundred years after fall followed by passivation of weathering by porosity reduction porosity reduction and the associated restriction in the ability of water to penetrate the sample appears to be the mechanism whereby a weathering assemblage formed during the brief initial period of oxidation is preserved through subsequent climatic cycles over the terrestrial lifetime of the sample

meteorites from the united arab emirates description weathering and terrestrial ages we report on the first meteorite search campaign in the united arab emirates uae the geology and proximity of our search region suggest that it is the north western extension of the oman meteorite fields we found 26 ordinary chondrites bringing the total number of official meteorites from the uae to 28 the campaign was organized and conducted in close cooperation with the uae government and the main masses of the meteorites remained in the country where they will become part of an exhibition the bulk composition of five meteorite and three soil samples indicates an uptake of u mo sr ba li and pb from the soil into the meteorites during terrestrial weathering terrestrial ages determined from 14c decay of 21 meteorites range from recent falls to 24 4 ka with two meteorites having 37 ka and approximately 39 ka respectively weak correlations between weathering degree meteorite bulk chemical composition and terrestrial age suggest highly localized weathering conditions possibly related to abundant occurrences of sabkhas in the search region

role of biomineralization as an ultraviolet shield implications for archean life cyanobacteria isolated from the krisuvik hot spring iceland were mineralized in an iron silica solution and irradiated with high levels of ultraviolet light analysis of the rates of photosynthesis chlorophyll a content and phycocyanin autofluorescence revealed that these mineralized bacteria have a marked resistance to uv compared to nonmineralized bacteria naturally occurring sinters composed of iron silica biominerals collected from

distribution of terrestrial age and petrologic type of meteorites from western libya abstract a group of 54 meteorites have been recovered from daraj western libya after assessment of pairing of samples using petrologic criteria 14 c terrestrial ages were obtained on 13 samples selected from 9 different fall events eleven of the ages range from 3500 to 7600 years with only two samples having ages in excess of 10 000 years the cut off in ages may be related to the timing of climatic changes in the hammadah al hamra

meteoritic and bedrock constraints on the glacial history of frontier mountain in northern victoria land antarctica abstract in 2001 a small h4 chondrite frontier mountain fro 01149 was found on a glacially eroded surface near the top of frontier mountain antarctica about 600 m above the present ice level the metal and sulphides are almost completely oxidized due to terrestrial weathering we used a chemical leaching procedure to remove weathering products which contained atmospheric 10 be and 36 cl in a ratio similar to that found in antarctic ice the fro 01149 meteorite has a terrestrial age of 3 0 0 3 myr based on the concentrations of the cosmogenic radionuclides 10 be 26 al and 36 cl this age implies that fro 01149 is the oldest stony meteorite fossil meteorites excluded discovered on earth the noble gas cosmic ray exposure age of fro 01149 is 30 myr the meteorite thus belongs to the 33 myr exposure age peak of h chondrites the bedrock surface on which fro 01149 was found has wet based glacial erosional features recording a former high stand of the east antarctic ice sheet this ice sheet evidently overrode the highest peaks 2800 m a s l of the inland sector of the transantarctic mountains in northern victoria land we argue that fro 01149 was a local fall and that its survival on a glacially eroded bedrock surface constrains the age of the last overriding event to be older than 3 myr the concentrations of in situ produced cosmogenic 10 be 26 al and 21 ne in a glacially eroded bedrock sample taken from near the summit of frontier mountain yield a surface exposure age of 4 4 myr and indicate that the bedrock was covered by several meters of snow the exposure age is also consistent with bedrock exposure ages of other summit plateaus in northern victoria land

sahara and sahel vulnerability to climate changes lessons from holocene hydrological data abstract the examination of more than 1500 paleohydrological dated records collected between 10 and 28 n during the last 50 years have been used to improve our knowledge and understanding of the sahara and sahel vulnerability to the atlantic monsoon changes in the long term we have analyzed the distribution of water bodies mainly lakes and wetlands over time and space the central saharan massifs played a major role in favoring water supply to the lowlands throughout the whole african humid period in addition distinct east west dynamics is recorded with humidity starting and stopping several millennia earlier to the east than to the west of the sahara a series of time lags are discussed 1 between the maximum of deep fresh water lake formation during the early holocene and the maximum of water body extensions during the mid holocene which highlight the primary role of aquifer water level in lake response to climate change 2 between the hydrological history of the sahara and the sahel and the forcings mainly insolation changes during the early and mid holocene which involves complex interactions between remnant ice sheet in the northern hemisphere open water bodies in the sahara and sahel and the atlantic monsoon system

carbonaceous material in the ryoke metamorphic rocks kinki district japan abstract carbonaceous material in the ryoke pelitic metamorphic rocks in the wazuka area kinki district japan has been studied by x ray diffraction xrd analysis detrital graphite in the lower grade rocks is recognized in both x ray diffractograms and transmission electron micrographs progressive graphitization is considered to have proceeded continuously on the basis of the xrd data of the bulk concentrates of carbonaceous material and a conspicuous asymmetric shape of xrd peaks in lower grade samples is ascribed to the mixture of carbonaceous materials with different crystallinities fully ordered graphite does not occur until the highest grade part of the chlorite biotite zone the variation of degree of crystallinity of carbonaceous materials inferred from xrd data is consistent with the prograde mineral zones the temperatures for the development of fully ordered graphite are estimated to be between 410 and 440 c in regional metamorphism through comparing the xrd data from low medium and high pressure types of metamorphic terrains