indicators of aqueous alteration in cm carbonaceous chondrites microtextures of a layered mineral containing fe s o and ni a petrographic and transmission electron microscopy study of the mighei murchison and murray cm carbonaceous chondrites shows that much of the cm matrix material was probably produced by aqueous alteration of olivine pyroxene sulfide and metal the amount of cm matrix appears to be proportional to the degree of alteration as suggested by mcsween 1979 and microtextures of pcp poorly characterized phase provide evidence of the progressive alteration pcp is divided into two major types one occurs in chondrules and aggregates and consists largely of an fe ni s o phase type i and the other occurs in matrix and consists of the fe ni s o phase and cronstedtite in various proportions type ii microtextures of pcp suggest that it resulted from a three stage alteration process 1 1 type i was produced by alteration of kamacite in chondrules and aggregates presumably early in the parent body regolith 2 2 as the alteration advanced olivine and pyroxene were converted to serpentine type i pcp separated from chondrules and aggregates into the matrix during regolith gardening simultaneously the fe ni s o phase reacted with si released by alteration of olivine and pyroxene producing well formed platy cronstedtite and coherent intergrowths of the fe ni s o phase and cronstedtite the fe ni s o phase also recrystallized into platy and pod like crystals fe s ni cr and p were leached out of type i pcp and were deposited as small grains of fe ni sulfides magnetite chromite and a mineral unidentified containing fe ni cr and p as a result pcp came to consist primarily of the fe ni s o phase and cronstedtite i e type ii pcp 3 3 during continued alteration the well formed crystals of the fe ni s o phase cronstedtite and their intergrowths in type ii pcp were replaced by poorly formed fibers in comparison to other cm chondrites mighei murchison and murray are relatively unaltered their matrices retain abundant amounts of the fe ni s o phase and cronstedtite commonly as distinctive pcp grains which account for a large proportion of the fe in these meteorite matrices in more altered cm chondrites much of the fe ni s o phase was probably consumed to produce cronstedtite magnetite and sulfides with further alteration cronstedtite itself reacted with the serpentine to form ferroan serpentine thus the cm matrix was increasingly enriched in mg with alteration and pcp was increasingly degraded and intimately mixed with the magnesian phyllosilicates

elephant moraine 96029 a very mildly aqueously altered and heated cm carbonaceous chondrite implications for the drivers of parent body processing elephant moraine eet 96029 is a cm carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration a later phase of heating and terrestrial weathering the presence of phyllosilicates and carbonates within chondrules and the fine grained matrix indicates that this meteorite was aqueously altered in its parent body features showing that water mediated processing was arrested at a very early stage include a matrix with a low magnesium iron ratio chondrules whose mesostasis contains glass and or quench crystallites and a gehlenite bearing calcium and aluminium rich inclusion eet 96029 is also rich in fe ni metal relative to other cm chondrites and more was present prior to its partial replacement by goethite during antarctic weathering in combination these properties indicate that eet 96029 is one of the least aqueously altered cms yet described cm2 7 and so provides new insights into the original composition of its parent body following aqueous alteration and whilst still in the parent body regolith the meteorite was heated to 400 600 c by impacts or solar radiation heating led to the amorphisation and dehydroxylation of serpentine replacement of tochilinite by magnetite loss of sulphur from the matrix and modification to the structure of organic matter that includes organic nanoglobules significant differences between samples in oxygen isotope compositions and water hydroxyl contents suggests that the meteorite contains lithologies that have undergone different intensities of heating eet 96029 may be more representative of the true nature of parent body regoliths than many other cm meteorites and as such can help interpret results from the forthcoming missions to study and return samples from c complex asteroids

sedimentology of the cold climate coal bearing lower permian lower freshwater sequence of tasmania abstract the lower permian lower freshwater sequence of tasmania consists of fluvial and coastal sediments deposited in a cold climate setting adjacent to ice ridden shallow seas the sequence represents a regressive pulse during the filling of a marine basin possibly a fjord up to 150 km wide and more than 270 km long occupied by glaciers in the late carboniferous the climatic conditions during the early permian in tasmania are revealed by 1 well developed continental scree breccias 2 the flora glossopteris gangamopteris assemblage 3 rarity of fossils in tidal deposits 4 the structure of the trace fossil population intense bioturbation in offshore muds 5 the foramol nature of the fauna of the marine beds below and above the lower freshwater sequence a fauna dominated by brachiopods and bryozoa and containing eurydesma and 6 features of the sediments themselves such as lonestones in muddy offshore marine deposits and oxygen isotopes of associated marine carbonates although the sedimentation in the lower freshwater sequence is qualitatively analogous to that of the quaternary of canada the fluvial and coastal sediments do not show evidence of ice rafting nor of frozen ground lack of such evidence suggests a cold temperate rather than a subpolar setting

hydrogen isotope fractionation in leaf waxes in the alaskan arctic tundra abstract leaf wax hydrogen isotopes dwax are increasingly utilized in terrestrial paleoclimate research applications of this proxy must be grounded by studies of the modern controls on dwax including the ecophysiological controls on isotope fractionation at both the plant and landscape scales several calibration studies suggest a considerably smaller apparent fractionation between source water and waxes eapp at high latitudes relative to temperate or tropical locations with major implications for paleoclimatic interpretations of sedimentary dwax here we investigate apparent fractionation in the arctic by tracing the isotopic composition of leaf waxes from production in modern plants to deposition in lake sediments using isotopic observations of precipitation soil and plant waters living leaf waxes and waxes in sediment traps in the brooks range foothills of northern alaska we also analyze a lake surface sediment transect to compare present day vegetation assemblages to eapp at the watershed scale source water and eapp were determined for live specimens of eriophorum vaginatum cottongrass and betula nana dwarf birch two dominant tundra plants in the brooks range foothills the d of these plants xylem water closely tracks that of surface soil water and reflects a summer biased precipitation source leaf water is enriched by 23 15 relative to xylem water for e vaginatum and by 41 19 for b nana evapotranspiration modeling indicates that this leaf water enrichment is consistent with the evaporative enrichment expected under the climate conditions of northern alaska and that 24 h photosynthesis does not cause excessive leaf water isotope enrichment the eapp determined for our study species average 89 14 and 106 16 for b nana n alkanes and n acids respectively and 182 10 and 154 26 for e vaginatum n alkanes and n acids which are similar to the eapp of related species in temperate and tropical regions indicating that apparent fractionation is similar in arctic relative to other regions and there is no reduced fractionation in the arctic sediment trap data suggest that waxes are primarily transported into lakes from local watershed scale sources by overland flow during the spring freshet and so dwax within lakes depends on watershed scale differences in water isotope compositions and in plant ecophysiology as such the large difference between our study species suggests that the relative abundance of graminoids and shrubs is potentially an important control on dwax in lake sediments these inferences are supported by dwax data from surface sediments of 24 lakes where eapp relative to dxylem averages 128 13 and 130 8 for n acids and n alkanes respectively and co varies with vegetation type across watersheds these new determinations of plant source water seasonality and eapp for the arctic will improve the dwax paleoclimate proxy at high latitudes

multiple water isotope proxy reconstruction of extremely low last glacial temperatures in eastern beringia western arctic abstract precipitation isotopes are commonly used for paleothermometry in high latitude regions here we present multiple water isotope proxies from the same sedimentary context perennially frozen loess deposits in the klondike goldfields in central yukon canada representing parts of marine isotope stages mis 4 3 and 2 allowing us to uniquely corroborate fractionations and temperature conversions during these late pleistocene cold stages we include new and existing proxy data from relict wedge ice a direct archive for snowmelt relict pore ice an archive for bulk soil water integrating year round precipitation and hydrated volcanic glass shards and fossil plant waxes which are also thought to integrate year round precipitation but are subject to large fractionations in some cases our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean new transfer functions calibrated specifically for northern north america d precip 3 1 c 1 t 155 and 18 o precip 0 41 c 1 t 20 2 and novel insights on the apparent net fractionation correction for eastern beringian steppe tundra plant waxes e wax precip 59 10 the snowmelt origin of wedge ice ensures a relatively constrained winter spring seasonality of contributing precipitation as supported by the consistency between water isotope measurements from late holocene wedge ice and modern winter spring precipitation wedge ice dating to the transitional mis 3 2 is isotopically depleted relative to modern spring winter precipitation by an amount that indicates a temperature depression of 14 5 c below modern the soil water origin of pore ice and other proxies integrating year round precipitation from soil water allows for a more variable precipitation seasonality the isotopic composition of modern pore ice is consistent with mean annual precipitation however the isotopic composition of pore ice during mis 3 2 converges on wedge ice values signalling an increase in the ratio of cold to warm season precipitation integrated by pore ice during glacial times possibly due to drier summers as supported by the fossil record and climate model simulations in the study region water isotope proxies integrating year round precipitation may overestimate annual temperature differences between today and recent cold stages due to transient precipitation seasonality as detected here and thus are best interpreted as upper bound estimates based on these proxies we estimate that annual temperatures during mis 4 3 2 and 2 were depressed below the modern climate to a maximum of 18 c 16 c and 21 c 4 5 c respectively our study highlights the value of multiple water isotope proxies towards understanding changes in precipitation seasonality and developing robust reconstructions of past climate and may be particularly important for studies of the major climate transformations over glacial interglacial timescales

high precision oxygen three isotope analyses of anhydrous chondritic interplanetary dust particles abstract oxygen three isotope ratios of three anhydrous chondritic interplanetary dust particles idps were analyzed using an ion microprobe with a 2 m small beam the three anhydrous idps show 17o values ranging from 5 to 1 which overlap with those of ferromagnesian silicate particles from comet wild 2 and anhydrous porous idps for the first time internal oxygen isotope heterogeneity was resolved in two idps at the level of a few per mil in 17o values anhydrous idps are loose aggregates of fine grained silicates 3 m in this study with only a few coarse grained silicates 2 20 m in this study on the other hand wild 2 particles analyzed so far show relatively coarse grained few m igneous textures if anhydrous idps represent fine grained particles from comets the similar 17o values between anhydrous idps and wild 2 particles may imply that oxygen isotope ratios in cometary crystalline silicates are similar independent of crystal sizes and their textures the range of 17o values of the three anhydrous idps overlaps also with that of chondrules in carbonaceous chondrites suggesting a genetic link between cometary dust particles wild 2 particles and most anhydrous idps and carbonaceous chondrite chondrules

the full glacial environment of the northern seward peninsula alaska reconstructed from the 21 500 year old kitluk paleosol abstract paleoenvironmental conditions are reconstructed from soils buried under volcanic ash ca 21 500 years ago on the seward peninsula soil development was minimal reflecting the continuous regional deposition of loess which originated from river floodplains and the exposed chukchi shelf cryoturbated soil horizons ice wedges and ice lens formation indicate a permafrost environment and mean annual temperatures below 6 to 8 c shallow active layers average 45 cm minimal evidence for chemical leaching of soils and the presence of earthen hummocks indicate a cold and seasonally dry climate neither steppe nor polar desert soils are appropriate analogues for these zonal soils of loess covered central beringia no exact analogues are known however soils underlying dry tundra near the arctic coast of northern yakutia russia and under moist nonacidic tundra of the alaskan north slope have properties in common with the buried soils

incompletely transformed serpentine type phyllosilicates in the matrix of antarctic cm chondrites abstract recent hrem high resolution electron microscopy investigation has shed light on the characterization of matrix phyllosilicates in cm chondrites in examining the antarctic cm chondrite yamato 793321 by hrem mineral grains which show an ed electron diffraction pattern consisting of both olivine and serpentine spots show disordered and defect structures in patchy hrem images these data are interpreted as representing an intermediate phase in the transformation from serpentine to olivine this is the first description of such an intermediate phase in belgica 7904 phyllosilicates seem to have been almost completely transformed to olivine it is suggested that it formed by heating of matrix phyllosilicates preliminary heating experiments on murchison also a cm chondrite showed that the matrix phyllosilicates transformed to a phase which gave an ed pattern and hrem image similar to those for yamato 793321 the results of these heating experiments support the formation of the intermediate phase by transformation from phyllosilicate to olivine during a heating event at a late stage

oxygen and carbon isotopes of early permian cold water carbonates tasmania australia abstract the permian carbonates of tasmania formed at a paleolatitude near 80 s during the gondwanan ice age contain abundant dropstones and are associated with glaciomarine sediments a shallow marine carbonate depositional model with floating icebergs calved from an adjacent ice shelf grading into an ice sheet has been proposed as the sea level rose during relatively warmer periods large volumes of melt waters mixed with marine waters retarding limestone deposition and causing deposition of shales siltstones these phases are preserved in the stratigraphic record as interbedded units australian permian brachiopods and molluscs are characterized by unusually light o18 pdb values and heavier c13 pdb values than those that occur in many modern cool temperate to subpolar cold water carbonates tasmanian permian whole rock o18 pdb values fall at the edge of the normal marine limestone field of keith and weber 1964 and range towards lighter values down to 16 9 pdb the o18 values of cements 7 6 to 25 6 pdb in the tasmanian early permian limestones partly overlap with those o18 values obtained for fresh water cements in the early permian continental tillites from antarctica and south africa gondwanaland indicating that the early permian sea was diluted by isotopically light melt waters during warming phases the o18 values of permian fauna if one assumes no diagenetic equilibration give unrealistic paleotemperatures because of this variable melt water dilution of the permian sea however calculated o18 values corresponding to marine c13 values of brachiopods and eurydesma and extrapolated from a model based on the linear trend of c13 o18 in modern and last glacial cold water carbonates give reasonable estimates of australian permian temperatures of up t 15 c with the coldest waters of less than 4 c around tasmania the sequential deviation lines of o18 c13 of both cements and the fauna associated with these cements indicate that the original o18 value of fauna was as high as 6 pdb this calculated original o18 value indicates an average seawater temperature for tasmania in the early permian of 1 8 c similar to the present average 1 9 c water temperature near ice shelves around antarctica the o18 values of ements suggest that the tasmanian limestones reacted with subfreezing melt waters during early diagenesis the o18 composition of the early permian sea is inferred to have been about 1 2 pdb similar to that observed during the pleistocene glaciations and was diluted by melt water as light as o18 smow 31 at 5 c 26 pdb in variable amounts it is unlikely that the o18 composition of the wellmixed open permian sea ever reached a value as light as o18 pdb 6 it is suggested that the permian sea c13 value was about 2 pdb heavier than that of modern and pleistocene seawater

stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

shock fabrics in fine grained micrometeorites the orientations of dehydration cracks and fracture networks in fine grained unmelted micrometeorites were analyzed using rose diagrams and entropy calculations as cracks exploit pre existing anisotropies analysis of their orientation provides a mechanism with which to study the subtle petrofabrics preserved within fine grained and amorphous materials both uniaxial and biaxial fabrics are discovered often with a relatively wide spread in orientations 40 60 brittle deformation cataclasis and rotated olivine grains are reported from a single micrometeorite this paper provides the first evidence for impact induced shock deformation in fine grained micrometeorites the presence of pervasive low grade shock features in cm chondrites and cm like dust anomalously low density measurements for c type asteroids and impact experiments which suggest cm chondrites are highly prone to disruption all imply that cm parent bodies are unlikely to have remained intact and instead exist as a collection of loosely aggregated rubble pile asteroids composed of primitive shocked clasts

hydrologic cycling over antarctica during the middle miocene warming global warmth 20 15 million years ago allowed vegetation to grow on formerly ice covered areas of antarctica leaf wax and pollen data show that this growth was supported by increased hydrologic activity over the antarctic coast derived from a local moisture source

climatic and hydrologic variability during the past millennium in the eastern rocky mountains and northern great plains of western canada modelling of tree ring 13 c and 18 o data from the columbia icefield area in the eastern rocky mountains of western canada provides fuller understanding of climatic and hydrologic variability over the past 1000 yr in this region based on reconstruction of changes in growth season atmospheric relative humidity rhgrs winter temperature twin and the precipitation 18 o twin relation the little ice age ad 1530s 1890s is marked by low rhgrs and twin and a 18 o twin relation offset from that of the present reflecting enhanced meridional circulation and persistent influence of arctic air masses independent proxy hydrologic evidence suggests that snowmelt sustained relatively abundant streamflow at this time in rivers draining the eastern rockies in contrast the early millennium was marked by higher rhgrs and twin and a 18 o twin relation like that of the 20th century consistent with pervasive influence of pacific air masses because of strong zonal circulation especially mild conditions prevailed during the medieval climate anomaly ad 1100 1250 corresponding with evidence for reduced discharge in rivers draining the eastern rockies and extensive hydrological drought in neighbouring western usa 2008 published by university of washington

coupled thermal and hydrological evolution of tropical africa over the last deglaciation we analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the congo river outflow and the results enabled us to reconstruct large scale continental temperature changes in tropical africa that span the past 25 000 years tropical african temperatures gradually increased from 21 to 25 c over the last deglaciation which is a larger warming than estimated for the tropical atlantic ocean a direct comparison with sea surface temperature estimates from the same core revealed that the land sea temperature difference was through the thermal pressure gradient an important control on central african precipitation patterns

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

oxygen and asteroids hundreds of thousands of asteroids have been discovered in the asteroid belt and in near earth space oxygen is an abundant element in meteorites and presumably in most asteroids spectral reflectance measurements of asteroids in the visible and near infrared can identify oxygen bearing minerals such as those found in the olivine pyroxene and serpentine groups due to their distinctive absorption features interpretation of the mineralogy of asteroids is complicated by the effects of space weathering which tends to redden and darken the surfaces of asteroids asteroids are primarily classified into a number of taxonomic classes and subclasses according to their spectral properties in the visible wavelength region however asteroids with similar spectral properties in the visible may have different spectral properties in the near infrared and therefore different interpreted mineralogies definite trends in the abundances of different taxonomic classes versus heliocentric distance are apparent these trends appear to be a function of both composition differences and degree of heating however dynamical processes have significantly affected these trends close observation of asteroids by spacecraft such as near shoemaker to 433 eros and hayabusa to 25143 itokawa are currently the best way to discern the mineralogies of individual asteroids

permafrost response to last interglacial warming field evidence from non glaciated yukon and alaska abstract we present stratigraphic observations from three sites in eastern beringia ch ijee s bluff in northern yukon and nearby exposures on the old crow river the palisades on the yukon river in alaska and placer mining exposures at thistle creek in west central yukon which provide insight into the response of permafrost to regional warming during the last interglaciation chronology is based on the presence of old crow tephra an important regional stratigraphic marker that dates to late marine isotope stage 6 supplemented by paleoecology and non finite 14c ages on wood rich organic silts old crow tephra overlies several relict ice wedges at the palisades and thistle creek indicating that permafrost at these sites did not thaw completely during the last interglaciation prominent deposits of last interglacial wood rich organic silt are present at multiple sites in eastern beringia and probably represent accumulations of reworked forest vegetation due to thaw slumping or deposition into thermokarst ponds or depressions consistent stratigraphic relations between these deposits old crow tephra and ice wedge pseudomorphs at our three study sites and at least six other sites in eastern beringia suggest that thaw of shallow permafrost was widespread during the last interglaciation limited stratigraphic evidence suggests that thaw was probably on the order of meters rather than 10s of meters the ubiquity of shallow permafrost degradation during the last interglaciation suggests that current ground warming may foreshadow widespread near surface thaw under even modest future warming scenarios however the persistence of relict pre last interglacial ice wedges highlights the potential for the regional antiquity of discontinuous permafrost and provides compelling field evidence for the long term resilience of deep permafrost during sustained periods of warmer than present climate

morphology and recent sediments of the lower anastomosing reaches of the attawapiskat river the attawapiskat river is one of the major low gradient rivers which cross the flat wetlands of the hudson bay lowland it has a nival regime leading to strong short duration spring floods during which considerable amount of sediment is carried for the remainder of the year only organic matter is transported in solution and suspension the land is isostatically rebounding after the pleistocene glaciations the river downcuts through the softer holocene estuarine basal clays and the pleistocene tills to the paleozoic carbonate bedrock the river develops an anastomosing pattern in the lower reaches and it acquires an irregular meandering character inland it does not construct a significantly thick delta as the river borne sediments are dispersed along the coasts by tides longshore currents and ice rafting the river is subjected to frequent ice jams in its lower reaches as warmer southern waters flow toward the still frozen mouth and sea during the jams secondary channels become active floodings develop and sedimentation occurs on the levees ice scours and ice rafted materials affect the river banks greatly the principal sedimentary environments within the river consist of 1 erosional shoals covered by boulder and pebble lags over till 2 sorted coarse to medium sized sands in junction bars downstream from islands these sands frequently develop gas bubbles and they contain characteristic fining upward sequences from boulder pavements at the base grading up into rippled sand with abundant organic matter grading up into laminated silt and sand and organic matter 3 secondary channels which develop thin silty and clay drapes on eroded hard substratum and are filled eventually by thick peats and 4 river banks which show well developed regressive sequences from pleistocene tills at the base overlain by estuarine sparsely fossiliferous clays capped by thin conglomeratic units with abundant reworked macoma balthica shells grading upward into upper tidal flat sand irregularly laminated sand and silt of marshes and regular interbedding of sand silt and organic layers of the levees at the top

full glacial paleosols in perennially frozen loess sequences klondike goldfields yukon territory canada perennially frozen loess deposits in the klondike goldfields include paleosols formed in full glacial environments correlated by alaskan distal tephra with marine isotope stages mis 2 and 4 patterns of organic and inorganic carbon and clay distribution microstructures and profile morphologies indicate that soil formation occurred in a base rich environment in which organic matter accreted predominantly as root detritus at sites approximately 20 km apart the expression of cryoturbation and ice wedge development decreases in strength upward in loess paleosol sequences correlated with mis 4 suggesting increasing aridity configurations of cryoturbation features and ice wedge thaw unconformities the presence of numerous ground squirrel burrows and an absence of peat accumulation suggest that these substrates were predominantly welldrained with active layers of equal or greater thickness than in modern soils on similar sites in the west central yukon some characteristics of these paleosols are similar to those of modern steppe and tundra soils consistent with plant macrofossil evidence for local ecological diversity during full glacial conditions in eastern beringia

significantly warmer arctic surface temperatures during the pliocene indicated by multiple independent proxies temperatures in the arctic have increased by an astounding 1 c in response to anthropogenic forcing over the past 20 years and are expected to rise further in the coming decades the pliocene 2 6 5 3 ma is of particular interest as an analog for future warming because global temperatures were signifi cantly warmer than today for a sustained period of time with continental confi gurations similar to present here we estimate mean annual temperature mat based upon three independent proxies from an early pliocene peat deposit in the canadian high arctic our proxies including oxygen isotopes and annual ring widths mat 0 5 1 9 c coexistence of paleovegetation mat 0 4 4 1 c and bacterial tetraether composition in paleosols mat 0 6 5 0 c yield estimates that are statistically indistinguishable the consensus among these proxies suggests that arctic temperatures were 19 c warmer during the pliocene than at present while atmospheric co 2 concentrations were 390 ppmv these elevated arctic pliocene temperatures result in a greatly reduced and asymmetrical latitudinal temperature gradient that is probably the result of increased poleward heat transport and decreased albedo these results indicate that arctic temperatures may be exceedingly sensitive to anthropogenic co 2 emissions

sedimentary conditions and deposits of akimiski strait james bay canada abstract akimiski strait is a wide 17 20 km shallow emergent 0 70 cm per century waterway in james bay it is localized in a saddle of a paleozoic reef track which has been enhanced and molded by pleistocene glaciers drumlinoid ridges form the till cores of shoals and islets of the strait the boundary conditions of the strait change throughout the year as it is covered by ice for six months during spring break up the strait remains clogged with ice at its northern approach for several weeks and acts as a large tidal inlet it is during this period that most of the fluvial sediments are carried to sea other sediments are obtained by erosion of the pleistocene tills and holocene subtidal clays and silts exposed in nearshore areas resuspension of nearshore material is achieved through the action of wind driven short choppy waves and ice scour tides are the most important process for the redistribution of sediments along the coast both flooding onshore and flooding and ebbing into and out from the strait generating locally powerful 2 m s 1 reversing currents ice rafting and ice pushing are important processes in this frigid environment particularly in upwind sides of shaols and at or near river mouths different intertidal sedimentary sequences develop as functions of sediment supply and exposure of the environments to ice currents and waves the eastern shores and the southern shoals of the strait develop pebble lags over till covered by thin 5 20 cm drapes of silty sand trapped and protected from erosion by algae in these shores and in emerging small islands significant sedimentation 1 1 5 m thick occurs in the marshes where the suspended load of tidal waters is trapped by vegetation the western shores of the strait receive considerable amounts of sediment from large rivers and are affected by strong tidal longshore currents thick 3 4 m and narrow tidal flats and marshes develop on the maincoast the shoals of the northern part of the strait have characteristic sediments those near the western shore have thin up to 80 cm tidal silty sand deposits locally heavily burrowed by macoma balthica those strung across the northern approach to the strait have well developed thin coarse sand dune fields indicating a prevalent ebb flow out of the strait

mineralogy and noble gas signatures of the carbonate rich lithology of the tagish lake carbonaceous chondrite evidence for an accretionary breccia abstract the carbonate rich lithology of the tagish lake carbonaceous chondrite was characterized by noble gas mass spectrometry synchrotron x ray diffraction analysis and transmission and scanning electron microscopy noble gas analysis was performed on two samples and the results showed that primordial noble gases are abundant and solar noble gases are absent in the samples of carbonate rich lithology the concentrations of ne a2 and e in both samples are at the maximum level observed for ci and cm chondrites suggesting high abundances of presolar diamonds and sic graphite respectively the cosmic ray exposure age cannot be determined precisely because the shielding depth of our tagish lake samples is unknown but the minimum exposure age was determined to be 5 5 0 7 myr on the basis of cosmogenic 21ne concentrations and the highest 21ne production rate x ray and electron microscopic study showed that the carbonate rich lithology is dominated by loosely packed porous matrix that consists mainly of fine grained saponite and ferromagenesian carbonate the matrix contains very few chondrules but many fine grained clasts having angular shape with longest dimensions up to 1 mm the clasts differ from host matrix in both texture and mineralogy they are massive compacted material with porosity much lower than matrix and contain abundant magnetite and a coherent intergrowth of serpentine and saponite that is rare in matrix the presence of texturally and mineralogically distinct clasts indicates that the carbonate rich lithology is a breccia but the absence of solar noble gases and impact induced deformational features in host matrix distinguish it from an asteroid regolith breccia our results instead indicate that it is an accretionary breccia formed by simultaneous accretion of diverse objects in a massive dust cloud the clasts often enclose chondrules and anhydrous silicate fragments such as low iron manganese enriched olivines this observation and their highly compacted angular morphology suggests that the clasts derive from earlier formed chondritic materials which have experienced compression and fragmentation due to mild impacts and from which they were excavated and incorporated into the final rock it is thus suggested that in the course of planetesimal formation agglomeration and disagglomeration of small parent bodies occurred repeatedly in a dense dust cloud where solar wind from the infant sun was shielded the fine grained ferromagnesian carbonates must have precipitated from aqueous solutions after the assembly of the tagish lake asteroid from recycled materials from previous bodies because the carbonates coat the surfaces of pores and fill in veins in the clasts

comparison of soil derived tetraether membrane lipid distributions and plant wax δd compositions for reconstruction of canadian arctic temperatures abstract polar amplification of climate warming has received much attention as these rapidly rising temperatures have the potential to alter ecosystem function and biogeochemical cycles in particular carbon preserved in arctic tundra soil and permafrost may be especially vulnerable resulting in carbon cycle perturbations providing an additional positive feedback to climate change reliable methods for reconstructing past temperature changes in polar regions have been established from ice cores and marine sediments however techniques for the continental terrestrial environments are lacking but are imperative to examine polar amplification of climate warming here we compare two molecular methods for reconstructing continental annual mean air temperature mat for the canadian arctic based on the distribution of soil bacterial derived glycerol dialkyl glycerol tetraether gdgt membrane lipids mbt cbt proxy and the hydrogen isotopic composition d of plant wax derived n alkanes these two proxies were applied to both modern soil and paleosols collected from the yukon territory canada to evaluate both the accuracy of the reconstructed absolute temperatures as well as the relative change in temperature between the last glacial and the holocene branched gdgt based estimates using the recently revised mbt cbt calibration are overall higher by ca 6 c compared to the original calibration mat estimates for modern soils based on the original mbt cbt calibration are comparable with those based on the d of extracted c29 n alkanes and instrumental data however produced a 6 c higher temperature signal for the glacial paleosols therefore branched gdgt based temperature reconstructions for glacial soils in the high arctic may represent the higher temperatures at the time of soil formation when bacterial activity was optimal whereas d of c29 n alkane plant lipids appear to integrate an average annual signal when used in tandem these geochemical proxies may provide a more comprehensive method for reconstructing arctic paleoclimate

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

constraints on the application of the mbt cbt palaeothermometer at high latitude environments svalbard norway abstract branched glycerol dialkyl glycerol tetraethers gdgts are membrane lipids of unknown bacteria that are ubiquitous in soil and peat two indices based on the distribution of these lipids in soils the cyclization of branched tetraethers cbt and the methylation of branched tetraethers mbt indices have been shown to correlate with soil ph and mean annual air temperature mat and soil ph respectively and can be used to reconstruct mat in palaeoenvironments to verify the extent to which branched gdgts in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a mat of

decoupled warming and monsoon precipitation in east asia over the last deglaciation our understanding of the continental climate development in east asia is mainly based on loess paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes delta o 18 of stalagmites from several chinese caves based on these records it is thought that east asian summer monsoon easm precipitation generally follows northern hemisphere nh summer insolation however not much is known about the magnitude and timing of deglacial warming on the east asian continent in this study we reconstruct continental air temperatures for central china covering the last 34 000 yr based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess paleosol sequence from the mangshan loess plateau the results indicate that air temperature varied in phase with nh summer insolation and that the onset of deglacial warming at similar to 19 kyr bp is parallel in timing with other continental records from e g antarctica southern africa and south america the air temperature increased from is c at the onset of the warming to a maximum of 27 degrees c in the early holocene similar to 12 kyr bp in agreement with the temperature increase inferred from e g pollen and phytolith data and permafrost limits in central china comparison of the tetraether membrane lipid derived temperature record with loess paleosol proxy records and stalagmite 5180 records shows that the strengthening of easm precipitation lagged that of deglacial warming by ca 3 kyr moreover intense soil formation in the loess deposits caused by substantial increases in summer monsoon precipitation only started around 12 kyr bp ca 7 kyr lag our results thus show that the intensification of easm precipitation unambiguously lagged deglacial warming and nh summer insolation and may contribute to a better understanding of the mechanisms controlling ice age terminations

carbonaceous micrometeorites from antarctica over 100 000 large interplanetary dust particles in the 50 500 micrometers size range have been recovered in clean conditions from approximately 600 tons of antarctic melt ice water as both unmelted and partially melted dehydrated micrometeorites and cosmic spherules flux measurements in both the greenland and antarctica ice sheets indicate that the micrometeorites deliver to the earth s surface approximately 2000x more extraterrestrial material than brought by meteorites mineralogical and chemical studies of antarctic micrometeorites indicate that they are only related to the relatively rare cm and cr carbonaceous chondrite groups being mostly chondritic carbonaceous objects composed of highly unequilibrated assemblages of anhydrous and hydrous minerals however there are also marked differences between these two families of solar system objects including higher c o ratios and a very marked depletion of chondrules in micrometeorite matter hence they are chondrites without chondrules thus the parent meteoroids of micrometeorites represent a dominant and new population of solar system objects probably formed in the outer solar system and delivered to the inner solar system by the most appropriate vehicles comets one of the major purposes of this paper is to discuss applications of micrometeorite studies that have been previously presented to exobiologists but deal with the synthesis of prebiotic molecules on the early earth and more recently with the early history of the solar system

soil organic carbon pools in the northern circumpolar permafrost region of all soils in the northern permafrost region is approximately 18 782 10 3 km 2 o r approximately 16 of the global soil area in the northern permafrost region organic soils peatlands and cryoturbated permafrost affected mineral soils have the highest mean soil organic carbon contents 32 2 69 6 kg m 2 here we report a new estimate of the carbon pools in soils of the northern permafrost region including deeper layers and pools not accounted for in previous analyses carbon pools were estimated to be 191 29 pg for the 0 30 cm depth 495 80 pg for the 0 100 cm depth and 1024 00 pg for the 0 300 cm depth our estimate for the first meter of soil alone is about double that reported for this region in previous analyses carbon pools in layers deeper than 300 cm were estimated to be 407 pg in yedoma deposits and 241 pg in deltaic deposits in total the northern permafrost region contains approximately 1672 pg of organic carbon of which approximately 1466 pg or 88 occurs in perennially frozen soils and deposits this 1672 pg of organic carbon would account for approximately 50 of the estimated global belowground organic carbon pool

the isotopic composition of volatiles in the unique bench crater carbonaceous chondrite impactor found in the apollo 12 regolith abstract projectiles striking the moon have modified its crust and delivered volatile elements to its interior and surface direct evidence of impactor origins is recorded by the rare occurrence of sub cm sized meteorite fragments identified in apollo samples and lunar meteorites the bench crater meteorite is a millimetre sized carbonaceous chondrite collected in regolith on the rim of bench impact crater at the apollo 12 landing site transmission electron microscopy has previously shown that bench crater contains abundant hydrated silicates establishing the survivability of hydrated material impacting the lunar surface to provide further information on the volatile inventory of the bench crater meteorite we report here the isotope compositions of hydrogen nitrogen carbon and oxygen this is the first direct isotopic analysis of meteoritic material delivered to the lunar surface and provides context for volatile and organic element signatures in lunar regolith samples and the survivability of volatile material delivered to planetary surfaces during impact bombardment the bench crater meteorite is characterised by d values ranging between 36 40 and 200 40 and bulk average 13 c of 13 30 and 15 n of 40 36 all uncertainties at the 2 confidence level the oxygen isotope compositions measured in situ in matrix silicates and magnetite in bench crater are consistent with those measured in matrix and magnetite in ci and cm chondrite falls altogether these new h c n and o isotope data coupled to mineralogical and geochemical observations suggest that bench crater may have been derived from an asteroidal parent body not represented in the terrestrial meteorite collection this is a crucial outcome in the current context of sample return missions to carbonaceous asteroids and more broadly for investigating the flux of material delivered to the earth moon system through time

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

the environmental water of the middle eocene arctic evidence from δd δ18o and δ13c within specific compounds abstract the extensive vertical exposure 150 m of terrestrial sediments on axel heiberg island which contain thick fossiliferous lignites presents an exceptional opportunity to follow the establishment and re establishment of arctic metasequoia forests during the middle eocene we compared d values in n alkanes of chain length 23 25 27 and 29 with 18 o values in phenylglucosazone p g derived from cellulose we also analyzed abundance of ferns gymnosperms and angiosperms using pollen and spores isolated from each lignite our results showed that forest composition was altered upon uplift as gymnosperms became more abundant within the relatively well drained upland sediments this was also reflected in the small 1 but significant increase in the 13 c value of tom from lowland to upland environments however neither the d values of n alkanes nor the 18 o in p g were statistically different in the upland sediments as compared to the lowland sediments from this we inferred that the oxygen isotope signature of environmental water available to the forests for plant growth was relatively uniform throughout the time of the fossil forests the d value of environmental water implied by both n alkanes and p g ranged from 168 to 131 and was considerably enriched compared to all environmental water samples available from the modern arctic region

the nanoscale mineralogy of fe ni sulfides in pristine and metamorphosed cm and cm ci like chondrites tapping a petrogenetic record we have sampled sulfide grains from one pristine cm2 chondrite yamato y 791198 one thermally metamorphosed cm2 chondrite y 793321 and two anomalous metamorphosed cm ci like chondrites y 86720 and belgica b 7904 by the focused ion beam fib technique and studied them by analytical transmission electron microscopy tem our study aims at exploring the potential of sulfide assemblages and microstructures to decipher processes and conditions of chondrite petrogenesis complex exsolution textures of pyrrhotite crystallographic nc type with n 6 troilite and pentlandite occur in grains of y 791198 and y 793321 additionally polycrystalline 4c pyrrhotite pentlandite magnetite aggregates occur in y 791198 pointing to diverse conditions of gas solid interactions in the solar nebula coarser exsolution textures of y 793321 grains indicate higher long term average temperatures in the 100 c range compared to y 791198 and other cm chondrites sulfide mineralogy of y 86720 and b 7904 is dominated by aggregates of pure troilite and metal indicating metamorphic equilibration at sulfur fugacities fs2 of the iron troilite buffer absence of magnetite in equilibrium with sulfide and metal in y 86720 indicates higher peak temperatures compared with b 7904 in which coexistence of troilite metal and magnetite constrains metamorphic temperature to less than 570 c nc pyrrhotite occurs in both meteorites as nm wide rims on troilite grains and together with frequent anhydrite indicates a retrograde metamorphic stage at higher fs2 slightly above the fayalite magnetite quartz pyrrhotite buffer fine grained troilite olivine intergrowths in both meteorites suggest the pre metamorphic presence of tochilinite serpentine interlayer phases pointing to mineralogical cm affinity pseudomorphs after euhedral pyrrhotite crystals in y 86720 in turn suggest ci affinity as do previously published o isotopic data of both meteorites

branched tetraether membrane lipids associated with rhizoliths in loess rhizomicrobial overprinting of initial biomarker record abstract loess palaeosol sequences are considered important terrestrial archives for studying quaternary climate recent studies have shown that calcified roots rhizoliths can be significantly younger than surrounding terrestrial sediment loess and that loess organic matter may be contaminated with root derived carbon from post sedimentary deep rooting plants branched glycerol dialkyl glycerol tetraethers gdgts are membrane lipids produced by unknown bacteria in soil and are increasingly being used as palaeoclimate proxies the aim of this work was to examine the impact of the temporal decoupling between rhizoliths and loess on the abundance and composition of branched gdgts and consequently on the application of branched gdgts as proxies in loess deposits branched gdgts in rhizoliths and the surrounding sediment from a loess palaeosol sequence in nussloch sw germany were examined their composition varied between the rhizolith and loess which may reflect the fact that branched gdgts were biosynthesized at different times late pleistocene for loess and holocene for rhizoliths and therefore under different environmental conditions a large difference ca 7 c in branched gdgt reconstructed palaeotemperature was observed between rhizoliths and loess in addition the reconstructed temperatures were the opposite from those expected from the assumed depositional ages of branched gdgts this might be explained by the post sedimentary input of root associated microorganism derived branched gdgts to loess which might have led to an overprint of the initial branched gdgt signal in the sediment our results suggest that post sedimentary penetration of deep rooting plants in loess might entail uncertainty regarding the application of branched gdgt palaeoproxies and that caution should be exercised in interpreting temperature estimates derived from branched gdgts in loess palaeosol sequences this is of special importance for loess where rhizoliths are abundant and where non calcified root remains of different age from that of the sediment are possible in addition the gdgt concentration in rhizoliths and surrounding loess supports the hypothesis of a heterotrophic lifestyle for branched gdgt producing bacteria

root associated branched tetraether source microorganisms may reduce estimated paleotemperatures in subsoil abstract branched glycerol dialkyl glycerol tetraethers gdgts are complex lipids of high molecular weight recently discovered in soils and suggested to be produced by still unknown bacteria the relative distribution of these compounds was shown to depend on environmental parameters mainly temperature and ph over the last years an increasing number of studies have focused on the application of branched gdgts as paleoclimate proxies but only a few were performed in terrestrial archives in this study branched gdgts were analyzed in calcified and non calcified living and dead roots in surrounding soil and sediment and in reference material distant from the roots samples were mainly collected from subsoil of two forest sites near sopron hungary where soils developed on fluvial sand and loess deposits respectively branched gdgts were more abundant in root samples and or surrounding rhizosphere compared to reference material suggesting that branched gdgt source microorganisms are closely associated with the root surface in subsoil the gdgt based temperature estimates from former roots and surrounding sediments were mainly lower than those from reference material in both loess and sand profiles this is likely due to the post sedimentary incorporation of branched gdgts deriving from microorganisms that fed on root organic matter in terrestrial sediments in contrast branched gdgt derived temperatures do not seem to be influenced by the presence of roots in topsoil which may be related to the much higher density of recent roots in topsoil than in subsoil this argues for a more homogeneous distribution of root associated microorganisms especially in densely rooted topsoils in addition we show that sample pre treatment may have an effect on the abundance and distribution of branched gdgts indeed washing root samples with ultrapure water might lead to a decrease in gdgt abundance and an increase in temperature estimates likely due to the removal of particles adhering to the root surface decarbonatization of root and surrounding sediment had only a limited effect on gdgt derived parameters taken together these results suggest that paleoenvironmental data obtained from branched gdgts in terrestrial archives might depend on the way the samples were collected and prepared and should be interpreted with caution especially in loess paleosol sequences where the frequency of calcified roots can be locally very high

vegetation buried under dawson tephra 25 300 14c years bp and locally diverse late pleistocene paleoenvironments of goldbottom creek yukon canada paleoecological research at goldbottom creek in the klondike region of yukon territory nw canada documents an in situ riparian grassy meadow that was buried during the winter or early spring by dawson tephra near the onset of marine isotope stage mis 2 ca 25 300 14 c years bp analyses of vascular plant macrofossils bryophytes pollen insects and paleosols from the riparian meadow contrast with evidence for well drained upland steppe tundra habitats obtained from fossil arctic ground squirrel middens within the same valley the mesic valley bottom vegetation consisted of grasses deschampsia caespitosa alopecurus sedges carex horsetail equisetum cf palustre diverse bryophytes and few forbs upland habitats with dry loessal soils along the valley slopes contained graminoids elymus festuca kobresia myosuroides sage artemisia frigida and diverse steppe and tundra forbs phlox hoodii plantago cf canescens anemone patens var multifida bistorta vivipara draba these paleoecological data highlight the effect of topographic position and moisture on substrates and their control on local scale habitat variability this study represents the first recorded in situ riparian surface from the unglaciated pleistocene refugium of beringia and provides well documented evidence for local habitat heterogeneity and ecosystem structure within the mammoth steppe biome other radiocarbon dated paleoecological data from our study sites indicate that full glacial steppe tundra habitats in west central yukon territory were established during the later stages of the mis 3 interstadial by 29 000 14 c years bp the diverse data obtained through integration of multiple paleoecological methods

deposition of polar carbonates during interglacial highstands on an early permian shelf tasmania abstract the early permian lower parmeener supergroup contains two bioclastic limestones that accumulated during the period of prolonged deglaciation of southern gondwana as the region moved equatorward from 80 s to 70 s the darlington and berriedale limestones formed in neritic environments in areas where abundant ice rafted debris testifies to numerous icebergs and glendonites indicating near freezing seawater these limestones consist of argillaceous and clean bioclastic floatstone rudstone and grainstone that contain a high abundance low diversity heterozoan assemblage of calcareous invertebrates the components are dominated by large robust brachiopods bryozoans and eurydesma bivalves sponge spicules and crinoids are also common whereas coralline algae and conodonts are conspicuously absent carbonates were deposited on the middle shelf during sea level highstands below the iceberg grounding line where the faunal communities remained undisturbed in this setting the organisms were outboard of significant terrigenous sediment influx and brackish water which were trapped on the inner shelf by bathymetry and icebergs strong bottom currents also prevented the deposition of fine grained siliciclastics by continuous winnowing of the pure limestone facies upwelling of nutrient rich water inferred from the distribution of phosphate promoted high primary productivity which fueled this carbonate factory and inhibited dissolution of the biogenic carbonate

problems of a late palaeozoic glaciation in australia and subsequent climate in the permian the most recent information suggests two periods of glaciation separated by a considerable time interval the first is found in the namurian early carboniferous and may extend into the beginning of the late carboniferous evidence for the carboniferous glaciation is largely or entirely redeposited striated clasts known only from the new england area of northeastern new south wales these are considered to represent montane type glaciation associated with a developing alpine chain after a long interval glacial deposits are then found in many parts of australia in the asselian the lowest stage of the permian and the glaciation may extend into the beginning of the sakmarian the following stage in western australia a number of major fluctuations are recorded in the asselian the end of the glaciation seems to be associated with a worldwide eustatic rise in sea level in the tastubian the lower stage of the sakmarian after the tastubian no direct verifiable evidence indicates glaciation in the permian in australia or any other part of the world in australia there is no clear evidence on the climate in the interval between the two glacial periods but in south america and other parts of the world a warm interval is reported at this time most of the glacial debris is now found in sedimentary basins which were developing contemporaneously with the glaciation and is of a wet based type glaciers were active on steep hinterland carrying debris in adjacent water covered basins but how far the ice may have spread over lower lying land areas in not clear there is no real evidence of a thick dry based ice sheet like that of present antarctica after the tastubian there are a number of major fluctuations in climate during the rest of the permian at times seasonal ice and or perhaps icebergs may have been active but fluctuations which were cool or warm temperate or in some places in australia even subtropical or tropical are found in the sterlitamakian upper sakmarian beginning and end of the baighenzhinian upper artinskian kungurian kazanian and dzhulfian all separated probably by colder and in some cases considerably colder periods comparison of the marine faunas of the carboniferous and permian suggests that the levipustula fauna may not represent as cold sea water as the eurydesma fauna

modeling the influence of a reduced equator to pole sea surface temperature gradient on the distribution of water isotopes in the early middle eocene proxy based climate reconstructions suggest the existence of a strongly reduced equator to pole temperature gradient during the azolla interval in the early middle eocene compared to modern changes in the hydrological cycle as a consequence of a reduced temperature gradient are expected to be reflected in the isotopic composition of precipitation d 18o the interpretation of water isotopic records to quantitatively reconstruct past precipitation patterns is however hampered by a lack of detailed information on changes in their spatial and temporal distribution using the isotope enabled version of the national center for atmospheric research ncar atmospheric general circulation model community atmosphere model v 3 isocam3 relationships between water isotopes and past climates can be simulated here we examine the influence of an imposed reduced meridional sea surface temperature gradient on the spatial distribution of precipitation and its isotopic composition in an early middle eocene setting as a result of the applied forcings the eocene simulation predicts the occurrence of less depleted high latitude precipitation with d values ranging only between 0 and 140 compared to present day 0 to 300 comparison with early middle eocene age isotopic proxy data shows that the simulation accurately captures the main features of the spatial distribution of the isotopic composition of early middle eocene precipitation over land in conjunction with the aspects of the modeled early middle eocene climate hence the included stable isotope module quantitatively supports the existence of a reduced meridional temperature gradient during this interval

the cm carbonaceous chondrite regolith diepenveen a carbonaceous chondrite was recovered immediately after the fall near the village of diepenveen in the netherlands on october 27 1873 but came to light only in 2012 analysis of sodium and poly aromatic hydrocarbon content suggests little contamination from handling diepenveen is a regolith breccia with an overall petrology consistent with a cm classification unlike most other cm chondrites the bulk oxygen isotopes are extremely 16o rich apparently dominated by the signature of anhydrous minerals distributed on a steep slope pointing to the domain of intrinsic cm water a small subset plots closer to the normal cm regime on a parallel line 2 lower in 17o different lithologies in diepenveen experienced varying levels of aqueous alteration processing being less aqueously altered at places rather than more heated the presence of an agglutinate grain and the properties of methanol soluble organic compounds point to active impact processing of some of the clasts diepenveen belongs to a cm clan with 5 ma cre age longer than most other cm chondrites and has a relatively young k ar resetting age of 1 5 ga as a cm chondrite diepenveen may be representative of samples soon to be returned from the surface of asteroid 162173 ryugu by the hayabusa2 spacecraft

regional atmospheric circulation change in the north pacific during the holocene inferred from lacustrine carbonate oxygen isotopes yukon territory canada analyses of sediment cores from jellybean lake a small evaporation insensitive groundwater fed lake provide a record of changes in north pacific atmospheric circulation for the last 7500 yr at 5 to 30 yr resolution isotope hydrology data from the southern yukon indicate that the oxygen isotope composition of water from jellybean lake reflects the composition of mean annual precipitation 18op recent changes in the 18o of jellybean sedimentary calcite 18oca correspond to changes in the north pacific index npi a measure of the intensity and position of the aleutian low al pressure system this suggests that 18op variability was related to the degree of fractionation during moisture transport from the gulf of alaska across the st elias mountains and that holocene shifts were controlled by the intensity and position of the al following this model between 7500 and 4500 cal yr b p long term trends suggest a predominantly weaker and or westward al between 4500 and 3000 cal yr b p the al shifted eastward or intensified before shifting westward or weakening between 3000 and 2000 cal yr b p rapid shifts eastward and or intensification occurred 1200 and 300 cal yr b p holocene changes in north pacific atmospheric circulation inferred from jellybean lake oxygen isotopes correspond with late holocene glacial advances in the st elias mountains changes in north pacific salmon abundance and shifts in atmospheric circulation over the beaufort sea

sedimentology of the ekwan shoal akimiski strait james bay canada abstract one of the steepest depositional coasts of western james bay is found along the west shores of akimiski strait north of the mouth of the ekwan river this shore receives considerable amounts of sediment during the spring break up of the rivers the sediments are stored on the steep narrow tidal flats and marshes and in thinner up to 80 cm drapes on till cored shoals that parallel and protect the coast the low areas between the shoals and the mainland are swept and reworked by relatively powerful 2 m s 1 reversing currents due to flooding and ebbing of tides into the strait a series of distinct environments and sedimentary facies develop on this western coast and its antecedent longshore shoal the outer part of the shoal is characterized by tidal bedding macoma balthica burrows and considerable ice scour the inner part of the shoal has winnowed sand the greatest abundance of macoma and well developed flaser bedding the longshore tidal channel separating the shoal from the mainland has coarse sand lags in the shallower parts and silty sand in deeper protected areas the steep tidal flats develop laminated silty sands locally saturated and slumping toward the channel the high saturation of the sediments inhibits colonization of the flats by macoma the narrow marshes have characteristic vegetation zonation with puccinellia phryganodes colonizing the lower marsh the sedimentary sequence of the marsh displays irregular bioturbated laminated sequences of silt silty sand and organic matter

thermally metamorphosed carbonaceous chondrites from data for thermally mobile trace elements we report radiochemical neutron activation analysis rnaa data for u co au sb ga rb cs se ag te zn in bi tl and cd ordered by increasing ease of vaporization and loss from the murchison cm2 chondrite during open system heating in nine antarctic c2 and c3 chondrites these meteorites exhibit properties obtained by reflectance spectroscopy o isotopic mass spectrometry and or mineralogy petrology suggesting thermal metamorphism in their parent bodies five of these meteorites asuka a 881655 yamato y 793495 y 790992 pecora escarpment pca 91008 and y 86789 paired with y 86720 exhibit significant depletion of the most thermally mobile 1 5 trace elements which is consistent with open system loss during extended parent body heating under conditions duplicated by week long heating of the murchison c2 chondrite heated at 500 700 c in a low pressure initially 10 5atm h2 atmosphere from earlier data three other c3 chondrites allan hills alh 81003 alh 85003 and lewis cliffs lew 85332 show significant cd depletion nine additional c2 and c3 chondrites show no evidence of mobile trace element depletion including y 793321 which by all other criteria was mildly metamorphosed thermally either metamorphism of these nine meteorites occurred under closed conditions and or alteration took place under such mild conditions that even cd could not be lost the rnaa data suggest that 10 of the 46 antarctic carbonaceous chondrites including 4 of 37 from victoria land and 6 of 9 from queen maud land exhibit open system loss of at least some thermally mobile trace elements by heating in their parent bodies whereas none of the 25 non antarctic falls experienced this these results are consistent with the idea that the antarctic sampling of near earth material differs from that being sampled today

deposition of the lower feather conglomerate a permian braided river deposit in southern victoria land antarctica with notes on the regional paleogeography abstract the feather conglomerate is a body of subarkosic coarse sandstone and conglomerate 200 m thick part of the victoria group beacon supergroup in southern victoria land this paper discusses the lower part of the formation deposited on an alluvial plain some time in the middle to late permian and considers some paleogeographic implications study of a well exposed section at mount bastion has provided detailed data for facies and paleocurrent analysis and on paleosols that are well developed there vertical burrows skolithos are also common the lower feather conglomerate at mount bastion is divided into five facies associations based on the braided stream facies defined by miall the most common 71 of the 125 m thick section is trough cross bedded and horizontally bedded coarse sandstone interpreted as flood deposited channel sand the other facies are mainly sand and mud deposited from waning flood waters the south platte river appears to provide a moderately close modern analogue for lower feather rivers paleocurrent directions from trough cross bedding indicate deposition in low sinuosity channels and bed thickness and scour depths suggest an average bankfull depth of 1 or 2 m schumm s equations yield the following values for average channel and flood plain variables assuming a bankfull depth of 1 m mean annual flood discharge 149 m 3 s 1 slope 1 644 and flood stage mean velocity 1 9 m s 1 drainage area and channel length upstream are estimated at 13 500 km 2 and about 300 km respectively the mount bastion section contains 13 paleosols on average 1 m thick the paleosols are characterised by up to four horizons vein networks and iron and clay pans these features suggest development in a temperate subhumid or humid climate over thousands of years permian strata 650 km to the north were deposited from broad shallow low sinuosity rivers like the lower feather on a west sloping flood plain probably part of the same drainage basin in contrast permian strata only 400 km south of the feather outcrop were deposited from meandering rivers flowing southward from the lack of room for a headwaters region we believe the two drainage basins have been juxtaposed since the permian by left lateral movement of at least several hundred kilometres probably along the transform fault postulated to run down the ross sea and crossing the transantarctic mountains as the byrd fault the lower feather flood plain sloped inland from the late permian coastline which ran approximately down the present eastern coast of australia towards west antarctica however lower feather rivers probably reached the coast near tasmania after an arcuate course of 2000 km this implies deposition on an inland high plain elevation about 100 m with a subhumid and high seasonal climate which is consistent with inferences from sand mineralogy and the paleosols

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

hydrological and temperature change in arctic siberia during the intensification of northern hemisphere glaciation abstract the pliocene epoch represents an analog for future climate with atmospheric carbon dioxide concentrations and continental configurations similar to present although the presence of multiple positive feedbacks in polar regions leads to amplified climatic changes conditions in the pliocene terrestrial arctic are poorly characterized high latitude sedimentary records indicate that dramatic glacial advance and decay occurred in the pliocene arctic with attendant effects on global sea level understanding these deposits and their implications for earth s future requires developing a sense of climatic evolution across the pliocene pleistocene transition and during the intensification of northern hemisphere glaciation inhg 2 7 million yr ago ma here we reconstruct arctic terrestrial environmental change from 2 82 2 41 ma marine isotope stages mis g10 95 using the distribution of branched glycerol dialkyl glycerol tetraethers brgdgts and the isotopic composition of plant leaf waxes dwax in a sedimentary archive from lake el gygytgyn northeast russia our records reveal changes in proxy behavior across this interval that we attribute to changing boundary conditions including sea level sea ice vegetation and pco2 during different miss we find that brgdgt temperatures and dwax are decoupled for most of the record although both show an increasing range of glacial interglacial variability following inhg dwax is stable from mis g10 g4 despite changes in vegetation and temperature suggesting different sources or pathways for moisture to lake el gygytgyn during the late pliocene

criteria for recognition of cold water carbonate sedimentation berriedale limestone lower permian tasmania australia abstract the permian berriedale limestone is an alternating sequence of limestone and calcareous shale associated with marine glacial terrigenous sediments it was deposited at a paleolatitude near 80 s during the gondwanan permo carboniferous ice age dropstones commonly disrupt laminae range widely in size and composition and reveal glacially derived shapes and textures under the sem there is a lower diversity of fauna mostly bryozoans brachiopods and pelecypods and non skeletal grains mostly intraclasts than in warm water limestones the vertical variation in depositional microfacies through shale limestone shale beds indicates that the shallow marine limestones formed during the lowering of sea level in colder periods as the sea level rose during warmer periods a shower of dropstones preceded shale deposition for this mason dropstones are more numerous around the contacts between limestone beds and overlying shale beds but rare in the middle or base of limestone beds icebergs calved from adjacent glaciers were floating and the surface water temperature was near freezing during limestone deposition upwelling cold currents provided nutrients and maintained calcium carbonate at saturation well developed rhombs in micrite microspar and spar and length slow elongate rhombs and poikilotopic rhombic plates both formed by accretion of rhombohedra indicate low mg calcite precipitated from seawater at a temperature of 3 c these cements are overlain by micrite marine mud dropstones and geopetal fillings of well sorted internal sediments and are cut by borings all proving both synsedimentary ages and submarine origin of these cements the calcium carbonate content in these cold marine waters fluctuated ranging from undersaturated destructive diagenesis pits etchings rhombic pores and dissolution features to saturated constructive diagenesis as the sea level rose during warmer periods large volumes of melt waters mixed with marine waters the mixing zone cements succeeding marine cements are cloudy inclusion rich coarse plates up to a few mm these crystals grew embedding or nucleating over early formed crystals and previously cemented both fillings and encrustations bioclasts the mixing zone cementation is preceded by erosion of early formed crystals the eroded crystals now occur as inclusions in mixing zone cements the field microfacies and diagenetic criteria evolved in this study might be used for recognition of a wide spectrum of cold water carbonates temperate subpolar and glacio marine

depositional framework of permian coal bearing strata southern victoria land antarctica abstract the permian weller coal measures of antarctica are exposed in a narrow belt that extends along the edge of the polar plateau from the mawson glacier to the mulock glacier in southern victoria land these rocks record a rapid change from glacial to postglacial conditions with the establishment of polar peat forming conditions during the late paleozoic in antarctica the 222 m thick weller consists of interstratified fine to coarse grained quartzo feldspathic sandstone laminated siltstone mudstone and coal regional lithofacies patterns and paleocurrent orientations define a narrow elongate basin in the lower weller coarse grained sandstone sheets occur along both eastern and western basin margins these deposits are similar to those of modern sandy braided streams toward the axis of the basin this lithofacies grades into coarse grained tabular sandstone lateral accretion beds suggest that deposition of this lithofacies occurred within meandering streams coarse grained basin margin deposits interfinger with fine grained basin axis lithofacies of interstratified laminated siltstone and graded sandstone beds deposited from suspension and underflow currents within a lacustrine environment in the upper weller braided stream deposits dominate much of the basin grading downstream into meandering streams establishment of vegetation in southern victoria land occurred immediately following late paleozoic deglaciation upward in the weller the distribution of plant fossils and coal seams is lithofacies dependent thick coals and abundant plant fossils occur in meandering stream lithofacies while they are scarce within the lacustrine and braided stream deposits abrasion during transport probably contributed to the destruction of vegetable material in the braided stream environments and to material introduced into the axial lake depositional patterns within the weller coal measures are similar to those in the takrouna formation in northern victoria land similarities suggest deposition in either the same or a similar basin comparison of the weller coal measures with permian strata in the central transantarctic mountains suggest deposition in two separate basins which are now juxtaposed across the byrd glacier the sight of a possible cenozoic strike slip fault causes for the formation of the depositional basin containing the weller coal measures are unknown however the geometry of the basin and the regional distribution of lithofacies are similar to those of rift basins and to basins excavated by glacial erosion the ultimate cause of basin subsidence however may be related to long distance stress produced during late paleozoic orogenic activity along the paleo pacific margin of antarctica

cold climate peat formation in canada and its relevance to lower permian coal measures of australia abstract canada is a vast cold country large expanses of wetlands occur whose characters change predictably over continental distances along north south temperature gradients and coastal inland precipitation trends the changing climatic conditions during the holocene have influenced the initiation and rates of peat formation for instance most of the peats of south central canada are not older than 5000 years b p those in the arctic regions are fossil deposits of the hypsithermal times of 7 8000 years b p maintained at the surface because of the low rates of peat oxidation an analysis of the environments of formation and of the stratigraphy of recent peats which formed under cold to cold temperate climate in canada forms the basis for a comparative study and a better understanding of the permo carboniferous coals of gondwanaland brazil south africa and australia much of the stratigraphic complexities that occur in the peat sequences are blurred out during organic decomposition and metamorphism leading to coal formation however some of the major features of the sequences that develop in string fens from basal sedge peats up to sedge woody peats and in boreal and cold temperate bogs and swamps from basal lacustrine deposits with some reworked and algal rich sediments grading upward into sedge peats to sphagnum sedge peat to sphagnum woody or just woody peats may be recognizable in banded coal seams it is suggested that future detailed comparative microfacies analyses of the cold peat sequences of canada and the lower permian coal seams of australia will allow better reconstructions and understanding of ancient wetlands without exclusively using the less appropriate albeit better known recent models of subtropical swamps

macrofossil and pollen evidence for full glacial steppe within an ecological mosaic along the bluefish river eastern beringia abstract plant and insect macrofossil assemblages dating to the full glacial late wisconsinan are rare from eastern beringia here we present an assemblage of fossil pollen insect and plant macrofossils recovered from alluvium at the bluefish exposure northern yukon territory nine ams radiocarbon ages place these data between ca 18 880 16 440 14c yr bp 22 313 19 597 cal yr bp these data indicate that xeric steppe rich in bunchgrasses poa and elymus artemisia frigida and diverse forbs was interspersed within a mosaic of local vegetation types including mid rich fens mesic graminoid meadows steppe tundra and herb tundra macrofossils and minor pollen of tundra forbs suggest steppe tundra plant associations within midslope elevations and discontinuous herb tundra on high elevation uplands on exposed bedrock ridges the composition and distribution of local vegetation was dependent on available moisture drainage aspect and elevation compositional and physiognomic similarities can be made with extrazonal steppe dominated dry slopes and high elevation steppe tundra ecotones in central alaska and yukon territory our paleoecological data reflect environments inhabited by the diverse late pleistocene bluefish caves fauna including woolly mammoth horse steppe bison and saiga antelope

distribution of branched gdgts in surface sediments from the colville river alaska implications for the mbt cbt paleothermometer in arctic marine sediments significant climate fluctuations in the arctic over the recent past and additional predicted future temperature changes highlight the need for high resolution arctic paleoclimate records arctic coastal environments supplied with terrigenous sediment from arctic rivers have the potential to provide annual to subdecadal resolution records of climate variability over the last few millennia a potential tool for paleotemperature reconstructions in these marine sediments is the revised methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy based on branched glycerol dialkyl glycerol tetraethers brgdgts in this study we examine the source of brgdgts in the colville river alaska and the adjacent simpson lagoon and reconstruct temperatures from simpson lagoon sediments to evaluate the applicability of this proxy in arctic estuarine environments the colville catchment soils fluvial sediments and estuarine sediments contain statistically similar brgdgt distributions indicating that the brgdgts throughout the system are soil derived with little alteration from in situ brgdgt production in the river or coastal waters temperatures reconstructed from the mbt cbt indices for surface samples show good agreement with regional summer june through september temperatures suggesting a seasonal bias in arctic temperature reconstructions from the colville system in addition we reconstruct paleotemperatures from an estuarine sediment core that spans the last 75 years revealing an overall warming trend in the twentieth century that is consistent with trends observed in regional instrumental records these results support the application of this brgdgt based paleotemperature proxy for subdecadal scale summer temperature reconstructions in arctic estuaries containing organic material derived from sediment laden episodic rivers

seasonality of the late pleistocene dawson tephra and exceptional preservation of a buried riparian surface in central yukon territory canada abstract the late pleistocene dawson tephra was deposited by one of the largest quaternary eruptions in northwestern north america its distribution is known sparsely from sites near the source area in southwestern alaska and central yukon territory where more than 20 occurrences are documented in the klondike region dawson tephra erupted about 25 300 14 c yr bp near the onset of the last glaciation and provides a stratigraphic marker across eastern beringia we report radiocarbon ages paleobotanical data and cryostratigraphic observations from a new dawson tephra locale at goldbottom creek in the klondike region of yukon territory which collectively indicate that the eruption occurred in the late winter or early spring multiple fining upward tephra rich ice beds are interpreted as remnants of surface icings which presently are common in the region during spring a buried in situ riparian meadow preserved below the icing and tephra consists of abundant tufted hair grass deschampsia caespitosa with interspersed horsetails equisetum cf palustre and mosses detrital plant remains and preserved in situ grass inflorescences entombed in the icing had expelled their fruits consistent with a late season surface when the icing was active the extraordinary thickness of dawson tephra in central yukon likely reflects reworking of a winter deposited tephra by snow melt in the spring following the eruption indicating that the primary thickness may be overestimated at valley bottom sites winter deposition of the tephra may have in part minimized the terrestrial ecological impacts of the eruption on zonal steppe tundra vegetation through the retransportation of tephra from hillslopes to the riparian areas where the tephra became incorporated into local fluvial systems

cold climate fluvial to paralic coal forming environments in the permian collinsville coal measures bowen basin australia abstract the middle permian collinsville coal measures of the northern bowen basin illustrate a range of cold to cold temperate coal forming environments cold climate is indicated by glossopteris flora in the coal measures and by restricted marine fauna dominated by brachiopods and bryozoa in correlative marine sequences of the back creek group which contains also abundant lonestones dropstones sedimentation was characterised by an overall transgression interrupted by local fluvial and coastal progradation in a shallow epicontinental sea during a relatively quiescent tectonic period six sedimentary environments are represented fluvial fluvio paralic barrier strandplain back barrier tidal flat and open marine the basal coal formed from peat of swamps of abandoned areas of gravelly braided streams and is massive dull and with high ash 20 low sulphur 1 contents overlying coals developed from peats formed in fluvio paralic and paralic environments and thicker seams are generally brighter with low to moderate ash 8 17 and moderate to high total sulphur 1 6 contents seams associated with fluvial influence show splits and high ash yield while seams associated with coastal deposits show high sulphur levels up to 21 in contrast to reported models of coal forming environments no clearly defined deltaic or inter distributary bay fill sequences were identified in the area studied rather vast freshwater wetlands backed low gradient progradational coasts locally having bars and barriers the barriers were not prerequisites for substantial peat accumulation although may have locally assisted peatland development by raising the profile of coastal equilibrium

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

the paradox between low shock stage and evidence for compaction in cm carbonaceous chondrites explained by multiple low intensity impacts abstract petrographic analysis of eight cm carbonaceous chondrites eet 96029 lap 031166 lon 94101 met 01072 murchison murray sco 06043 que 93005 by electron imaging and diffraction and x ray computed tomography reveals that six of them have a petrofabric defined by shock flattened chondrules with the exception of murchison those cms that have a strong petrofabric also contain open or mineralized fractures indicating that tensional stresses accompanying the impacts were sufficient to locally exceed the yield strength of the meteorite matrix the cms studied span a wide range of petrologic subtypes and in common with rubin 2012 we find that the strength of their petrofabrics increases with their degree of aqueous alteration this correspondence suggests that impacts were responsible for enhancing alteration probably because the fracture networks they formed tapped fluid reservoirs elsewhere in the parent body two meteorites that do not fit this pattern are met 01072 and murchison both have a strong petrofabric but are relatively unaltered in the case of met 01072 impact deformation is likely to have postdated parent body aqueous activity the same may also be true for murchison but as this meteorite also lacks fractures and veins its chondrules were most likely flattened by multiple low intensity impacts multiphase deformation of murchison is also revealed by the microstructures of calcite grains and chondrule defined petrofabrics as revealed by x ray computed tomography the contradiction between the commonplace evidence for impact deformation of cms and their low shock stages most belong to s1 can be explained by most if not all having been exposed to multiple low intensity i e

bulk mineralogy of individual micrometeorites determined by x ray diffraction analysis and transmission electron microscopy abstract bulk mineralogy of individual fine grained micrometeorites from 50 to 200 m in diameter was determined on the basis of the powder x ray diffraction patterns and the observation of internal textures by a transmission electron microscope tem x ray diffraction analysis of 56 micrometeorites indicated that 42 11 and 3 samples are olivine rich pyroxene rich and phyllosilicate rich micrometeorites respectively among the phyllosilicate rich micrometeorites one contains saponite and other two contain serpentine no samples contain both saponite and serpentine we found that saponite rich micrometeorite was weakly heated which results in shrinkage of 001 basal spacing of saponite down to 9 7 a and that cronstedtite which is commonly contained in cm chondrites occurs in serpentine rich micrometeorites micrometeorites that consist entirely of anhydrous minerals and amorphous phases are predominant in the samples studied the major phases of such micrometeorites are olivine low ca pyroxene magnetite and fe sulfide and the average abundances are 65 17 11 and 7 wt respectively when the total abundance of the four minerals are normalized to 100 wt the relative mineral abundance varies greatly between samples low ca pyroxene olivine ratios range from 0 to 3 5 with a mean of 0 3 tem observations of inner portions of some micrometeorites revealed that they are aggregates of very small equigranular grains 100 nm of olivine magnetite or low ca pyroxene olivine magnesiowustite the textures are very similar to those of hydrous carbonaceous chondrite that was experimentally heated to temperature below melting point thus suggesting that the micrometeorites had been hydrous particles but were decomposed by the brief heating upon atmospheric entry it is newly found that magnesiowustite was formed in micrometeorites instead of magnetite as a product of phyllosilicate decomposition under low oxygen fugacity the decomposed hydrous micrometeorites gave two types of characteristic x ray diffraction patterns 1 broad olivine and magnetite reflections or 2 variable intensities of magnesiowustite reflections together with magnetite low ca pyroxene and olivine reflections twenty nine olivine or pyroxene rich micrometeorites showed such diffraction patterns thus suggesting that more than half of micrometeorites investigated must be decomposed hydrous particles the results confirmed that hydrous dust particles are much more abundant in the interplanetary space than in the micrometeorites recovered on the earth

branched glycerol dialkyl glycerol tetraethers in pleistocene loess paleosol sequences three case studies abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are membrane lipids presumably derived from anaerobic heterotrophic soil bacteria empirical studies have shown that the composition of branched gdgts in topsoils varies in degree of cyclization and methylation expressed as cbt and mbt i e cyclization and methylation index of branched tetraethers depending on soil ph and mean annual air temperature mat here we present results from three case studies namely three well studied loess paleosol sequences lpss in which we measured the branched gdgts in order to test the applicability of these biomarkers for paleoclimate reconstruction the results show that major disagreements exist between expectations based on available stratigraphic pedological and geochemical data on the one hand and gdgt derived reconstructions on the other hand caution is therefore advised when interpreting the respective indices in lps studies we discuss several potential directions for future research i some of the target peaks in the hplc chromatograms consist of multiple unidentified compounds this needs to be addressed by way of improved component separation identification and new calibration studies ii factors other than mat and soil ph that could affect membrane composition should be further investigated e g nutrient availability and redox conditions as well as seasonality and changes in bacterial communities iii gdgts may be produced in non negligible amounts at depth and thus overprint the original in situ signal a concern that could be termed growth depth effect iv gdgts should also be analyzed in dust source regions and contemporaneous eolian sediments in order to address a potential redeposition effect

yamato 793321 cm chondrite dehydrated regolith material of a hydrous asteroid abstract based on the reflectance spectra surface materials of many c g b and f type asteroids are altered by heating and consist of low crystalline dehydrated phyllosilicates similar to heated hydrous carbonaceous chondrites however meteorites of this kind studied so far were not samples from the asteroid regolith but from the asteroid interior they lack both of two properties characteristic for regolith materials lithologies with impact induced brecciation and noble gases from implanted solar winds thus no meteorite samples have ever been identified as a real sample of c g b and f type asteroid regolith here i report the discovery of a meteorite having mineralogical and isotopic signatures expected for regolith samples of these asteroids through the investigation of seven cm carbonaceous chondrites the meteorite is the yamato y 793321 cm carbonaceous chondrite it exhibits a variety of petrologic features that are characteristic of active regolith material chondrules are crushed matrix is comminuted and coarse silicate crystals show deformation and characteristic planner fractures due to repeated impacts synchrotron x ray diffraction analysis showed that fine grained matrix is dominated by amorphous silicates with minor amounts of olivine and magnetite which was produced by dehydration of preexisting hydrous phases probably serpentine during impact induced heating at 500 c in addition isotopic analysis revealed that the meteorite is enriched in implanted solar noble gases suggesting that it was once located at surface layers of a parent asteroid all results taken together demonstrate that y 793321 is a regolith breccia of a hydrous asteroid which underwent impacts heating dehydration and solar wind implantation at the surface layers of the asteroid the reflectance spectrum of this meteorite matches well with those of asteroids c g b and f confirming that it was derived from these asteroid surfaces

pleistocene graminoid dominated ecosystems in the arctic abstract we review evidence obtained from analyses of multiple proxies floristics mammal remains paleoinsects pollen macrofossils plant cuticles phytoliths stable isotopes and modeling that elucidate the composition and character of the graminoid dominated ecosystems of the pleistocene arctic the past thirty years have seen a renewed interest in this now extinct biome sometimes referred to as tundra steppe steppe tundra in north american sources while many questions remain converging evidence from many new terrestrial records and proxies coupled with better understanding of paleoclimate dynamics point to the predominance of xeric and cold adapted grassland as the key former vegetation type in the arctic confirming earlier conjectures completed in the 1960s 1980s a variety of still existing species of grasses and forbs played key roles in the species assemblages of the time but their mixtures were not analogous to the tundras of today local mosaics based on topography proximity to the ice sheets and coasts soil heterogeneity animal disturbance and fire regimes were undoubtedly present however inadequate coverage of terrestrial proxies exist to resolve this spatial heterogeneity these past ecosystems were maintained by a combination of dry and cold climate and grazing pressure disturbance by large e g mammoth and horse and small e g ground squirrels mammals some recent studies from eastern beringia alaska suggest that more progress will be possible when analyses of many proxies are combined at local scales

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

shock induced volatile loss from a carbonaceous chondrite implications for planetary accretion solid recovery impact induced volatile loss experiments on the murchison c2m meteorite indicate that for an impact of a given velocity h 2o and total volatiles are driven from the sample in the same proportion as present initially we infer that the volatiles other than h 2o driven from the meteorite also have the same bulk composition as those of the starting material thus the early bulk composition of an impact induced atmosphere of a planet growing by accretion from material like murchison would be the same as the volatile composition of the incident planetesimals incipient devolatilization of murchison occurs at an initial shock pressure of about 11 gpa and complete devolatilization occurs at a pressure of about 30 gpa if an earth sized planet were formed from the infall of planetesimals of murchison composition incipient and complete devolatilization of accreting planetesimals would occur when the planet reached approximately 12 and 27 respectively of its final radius thus impact induced devolatilization of accreting planetesimals and of the hydrated surface would profoundly affect the distribution of volatiles within the accreting planet for example for a cold homogeneous accretion of a planet prior to metallic core formation and internal differentiation the growing planet would have a very small core with the same volatile content as the incident material a volatile depleted mantle and an extremely volatile rich surface

molecular records of continental air temperature and monsoon precipitation variability in east asia spanning the past 130 000 years our current understanding of past changes in east asian summer monsoon easm precipitation intensity derives from several loess paleosol sequences and oxygen isotope 18o records of well dated stalagmites although temperature is generally presumed to have had minimal impact on easm records past air temperature dynamics over east asia are so far relatively poorly understood mainly due to the lack of tools to reconstruct continental paleotemperatures here we report a high resolution record of east asian air temperature over the past 130 000 years based on soil bacterial lipid signatures preserved in a loess paleosol sequence from the mangshan loess plateau in china we find that maximum local insolation is the main driver of air temperature although greenhouse gas concentrations and southern hemisphere climate may influence temperature at times when insolation is weak causing a decoupling with easm precipitation intensity direct comparison of our temperature record with precipitation induced changes in past soil ph derived from the same suite of lipids confirms this decoupling subsequent cross spectral analysis of the two molecular proxy records reveals that variations in monsoon precipitation consistently lag those in air temperature throughout the whole record at the dominant precession band the length of this lag is variable however and increases as glaciation develops this observation is consistent with an increasing influence of northern hemisphere ice sheets on the modulation of easm response to insolation forcing during ice ages

bright carbonate veins on asteroid 101955 bennu implications for aqueous alteration history introduction carbonaceous asteroids formed early in solar system history and experienced varying degrees of aqueous water rock and thermal alteration most models of the evolution of these asteroids suggest that aqueous alteration was driven by hydrothermal convection however it is debated whether this alteration occurred in a chemically closed or open system the bulk chemical compositions of the carbonaceous chondrite meteorites imply that the system was closed models predict that large scale fluid flow in an open system took place on at least some asteroids in this scenario fluids would have flowed through fractures from the interior and minerals would have precipitated into these fractures forming veins rationale global spectral observations by the osiris rex origins spectral interpretation resource identification and security regolith explorer spacecraft have shown that carbon bearing materials including organics and or carbonates are widespread on the surface of near earth asteroid 101955 bennu to understand the composition of these carbon bearing materials and their implications for bennu s aqueous alteration history we examined visible near infrared spectra obtained at resolutions of 4 m in the region around the mission s primary sampling site nightingale we compared these spectra with laboratory spectra of organics and carbonates broadband panchromatic images of the nightingale region at pixel scales of 1 4 cm allowed us to search for surface features that could contextualize the spectral data results on the basis of the wavelength position and shape of spectral absorption features the closest matches to a subset 15 of spectra collected in the nightingale region are the carbonate minerals calcite dolomite and magnesite with calcite being the most prevalent these minerals are found in the highly aqueously altered cm and ci group carbonaceous chondrites proposed meteorite analogs of bennu bright centimeters thick roughly meter long veins are apparent in images of some boulders near the nightingale site the veins have albedos of 10 to at least 19 much brighter than bennu s average of 4 4 these albedos are consistent with the veins being filled by carbonates with minor abundances of opaque materials such as magnetite and organics the albedos are too high for the veins to be dominantly composed of organics or any other material that has been identified on bennu except carbonates there are only a few bright vein filling materials found in meteorites and carbonate is the only one of these that is plausibly present on bennu linear mixture modeling suggests that only a small fraction of a spectrometer field of view conclusion the observed bright veins on bennu are most likely dominantly composed of carbonates the detection of these meter sized putative carbonate veins indicates that extensive water flow occurred in a chemically open hydrothermal system on the larger parent asteroid of bennu before the catastrophic disruption of the parent asteroid led to bennu s reaccumulation as a rubble pile kinetic modeling assuming a calcite vein composition shows that a hydrothermal system kilometers in size with alteration likely taking place over thousands to millions of years would have been needed to create veins of the dimensions preserved in the constituent boulders of bennu some cm and ci group meteorites have very small micrometers to millimeters carbonate veins or presumed vein fragments veins on the scale that we observe on bennu are not present in meteorites it is possible that such veins are present on other carbonaceous asteroids that have not been observed by spacecraft we predict that the sample of bennu s surface material that is planned to be returned to earth by the osiris rex spacecraft will contain carbonates and that they will be distributed with a structure and scale distinct from those that occur in meteorites

glacier advance in southern middle latitudes during the antarctic cold reversal the geographic extent of cooling associated with the antarctic cold reversal is unclear dating of glacial moraines in new zealand suggests that the cooling extended into the southern mid latitudes possibly as a result of the northward migration of the southern subtropical front

thermoluminescence properties and age estimates for quaternary raised marine sediments hudson bay lowland canada thermoluminescence tl analyses of quaternary nearshore marine sediments from the hudson bay lowland revealed relatively high light emissions and linear growth curves to at least 400 gy above the natural dose initial results indicate that anomalous fading may be circumvented by a preheating at 150 c for 16 h without substantial thermal draining of stable tl components both the total bleach method with unfiltered sunlamp light and the partial bleach method with light blocked below 400 nm resulted in overbleaching and thus overestimates of age a tl age estimate of 5 3 0 8 ka on the holocene control sample similar to the radiocarbon age was obtained using the partial bleach method with light blocked below 540 nm this same method yielded an average tl age estimate of 73 10 ka for a pleistocene unit which corresponds to the amino acid based age estimate of ca 76 ka the agreement of the two age estimates is encouraging since both methods rely on separate assumptions that have not been independen