modelling controls on aeolian dune field pattern evolution a second generation source to sink cellular automaton based model presented here captures and quantifies many of the factors controlling the evolution of aeolian dune field patterns by varying only a small number of parameters the role of sediment supply sediment availability and transport capacity together defined as sediment state in the development and evolution of an aeolian dune field pattern over long time scales is quantified from model simulations seven dune field patterns can be classified from simulation results varying the sediment supply and transport capacity that control the type and frequency of dune interactions the sediment availability of the system and ultimately the development of dune field patterns this model allows predictions to be made about the range of sediment supply and wind strengths required to produce the dune field patterns seen in the real world a new clustered dune field pattern is identified from model results and used to propose an alternative mechanism for the formation of superimposed dunes bedforms are hypothesized to cluster together simultaneously forming two spatial scales of bedforms without first developing a large basal dune with small superimposed dunes manipulation of boundary conditions produces evolving dune fields with different spatial configurations of sediment supply trends of spacing and crest length increase with decreasing variability as the dune field matures this simple model is a valuable tool which can be used to elucidate the dominant control of aeolian sediment state on the construction and evolution of aeolian dune field patterns

investigation of the sand sea with the tallest dunes on earth china s badain jaran sand sea abstract china s badain jaran sand sea features the tallest dunes on earth and a unique mega dune lake landscape it had been explored little until the 1990s though early scientific explorations surrounding the sand sea had begun by the early 20th century heated debates now focus on the desert environment and particularly how the mega dunes and desert lakes develop and evolve this paper reviews the status of these debates and summarizes the supporting evidences the environmental research mainly concerns formation and evolution of the sand sea and its relationship with climate change the proposed formation time ranges from the early pleistocene to the holocene opinions vary about climate change on different time scales the reconstructed climate change history is shorter than the sand sea s history with the longest record extending to the late pleistocene the mega dune research focuses on sediments dune morphology and formation processes it remains unclear whether the mega dunes result primarily from wind action control by the underlying topography or groundwater maintenance the sources of lake water are also debated but there are four main hypotheses atmospheric precipitation groundwater from nearby areas precipitation and snowmelt in remote areas such as the qilian mountains and the qinghai tibetan plateau or paleowater that formed during past periods of wet climate we believe that the sand sea deserves further study in terms of its dune geomorphology evolution and hydrology and their responses to climate change meteorological and hydrological observations and monitoring in the sand sea are particularly necessary

controls on sand ramp formation in southern namibia sand ramps have the potential to provide rich palaeoenvironmental information in dryland regions wherein proxy records are typically scarce however current knowledge of the geomorphic controls and processes of sand ramp formation is limited this study provides a data rich examination of the key factors controlling sand ramp formation the location and morphology of 75 sand ramps in southern namibia are examined the sediments and chronologies of 10 sand ramps are studied in detail using 51 osl dates and 83 grain size and loi samples heavy mineral assemblages are used to determine the provenance of 10 samples and osl sensitivity is used to explore geomorphic processes of 8 samples sand ramp morphology can be grouped into one of four classes of increasing size and complexity and is closely linked to the available accommodation space heavy mineral assemblages indicate local sediment sources and all 75 studied sand ramps are within 4 km of a large ephemeral river channel or within 5 5 km of a dune field therefore accommodation space and sediment supply are identified as the primary controls of sand ramp formation sedimentology and osl sensitivity suggest a complex interplay of aeolian fluvial and colluvial processes contribute to sand ramp formation with large variability observed between ramps three of the ten dated sand ramps have been present in the namibian landscape for 100 ka eight sand ramps show episodic deposition between 75 12 ka and five show evidence of surface reworking over the past 2 ka environmental sensitivity is likely to be linked to the size and availability of the accommodation space therefore individual sand ramps are expected to reflect local environmental conditions recording when an abundant sediment supply coincided with available accommodation space whilst a regional analysis of multiple sand ramps with chronometric data offers the potential to identify larger scale palaeoenvironmental controls of sediment supply

morphology of transverse aeolian ridges tars on mars from a large sample further evidence of a megaripple origin abstract using hirise digital terrain models dtms we developed a large morphological dataset to examine the three dimensional shape size and scaling of martian transverse aeolian ridges tars considerable debate exists on the characteristic morphology of tars and the origins of these enigmatic bedforms some researchers suggest polygenesis or multiple classes of similar bedforms reliably characterizing the morphology of tars is an essential prerequisite to developing and evaluating process based models of tar genesis and unraveling aeolian processes on the surface of mars we present measurements of tar morphology from a large dtm derived dataset n 2295 we focused on tars with simple morphologies in order enable more defensible discretization histograms and cumulative log frequency plots of morphometric parameters length width height elongation ratio and wavelength indicate the sample represents a continuum of bedforms from a single population a typical tar from our dataset is 88 5 m long longest planview axis 17 3 m wide shortest planview axis 1 3 m tall and has a wavelength of 25 8 m combined with these data the bulk of evidence presented to date suggests that interpreting tars as megaripples is the most viable working hypothesis

copper chelated bacteriochlorophyll e homologues in sediment from an anoxic lake lake abashiri japan copper chelated bacteriochlorophyll e homologues have been identified in laminated sediment from the meromictic lake abashiri using atmospheric pressure chemical ionization liquid chromatography mass spectrometry since they are the second most abundant chloropigment derivatives in the sediments these novel compounds may be important intermediate products of bchl e diagenesis in this anaerobic environment

thermal history of type 3 chondrites from the antarctic meteorite collection determined by raman spectroscopy of their polyaromatic carbonaceous matter abstract this paper is focused on the characterization of the thermal history of 151 cv co and unequilibrated ordinary chondrites uocs from the nasa antarctic meteorite collection using an approach based on the structure of the included polyaromatic carbonaceous matter determined by raman spectroscopy 114 out of these 151 chondrites provided raman spectra of carbonaceous matter and allowing to assign a petrologic type which mostly reflects the peak temperature experienced by the rock on the parent body a thorough review of literature shows however that it is not possible to deduce a peak temperature because accurate calibration is not available twenty three new weakly metamorphosed chondrites have been identified mil 07671 cv3 1 dom 08006 co3 0 dom 03238 mil 05024 mil 05104 mil 07193 co3 1 til 82408 lar 06279 ll3 05 3 1 eet 90628 l3 0 gro 06054 que 97008 l3 05 alha 77176 eet 90066 lar 04380 met 96515 mil 05050 l3 1 alha 78133 eet 87735 eet 90909 lew 87208 pre 95401 l3 05 3 1 mcy 05218 h3 05 3 1 and met 00506 h3 1 this study confirms that the width of the d band fwhmd and the ratio of the peak intensity of the d and g bands id ig are the most adapted tracers of the extent of thermal metamorphism in type 3 chondrites it also unambiguously shows thanks to the large number of samples that the width of the g band fwhmg does not correlate with the maturity of polyaromatic carbonaceous matter this parameter is nevertheless very valuable because it shows that raman spectra of cv chondrites preserve memory of either the metamorphic conditions possibly oxidation controlled by aqueous alteration or the nature of the organic precursor oxidation memory is our preferred interpretation however an extensive petrologic characterization of this cv series is required to get firm conclusions pre graphitic carbonaceous matter is reported in seven chondrites and is even the only carbonaceous material detected in the chondrites alha 78119 and dav 92302 this pre graphitic carbonaceous matter cannot be formed through radiogenic thermal metamorphism without metal catalysis shock metamorphism is another possible process for accounting its formation but it appears less plausible

preliminary characterisation of porphyrins from the gafsa basin tunisia evidence for metal free benzo porphyrins from an immature sediment abstract five metal free porphyrin fractions were isolated chromatographically from an immature chert of the gafsa basin paleocene tunisia each fraction was analysed by electron ionisation tandem mass spectrometry in addition to the expected aetioporphyrin iii and deoxophylloerythroetioporphyrin dpep an isomeric c 32 cap porphyrin which probably bears an extended isocyclic ring was also detected a c 31 cap component bearing one unsubstituted position was isolated c 33 and c 34 benzo dpep porphyrin as well as a c 33 tetrahydrobenzo dpep porphyrin were also present which indicates that such compounds are generated in immature sediments

presolar silicates in the matrix and fine grained rims around chondrules in primitive co3 0 chondrites evidence for pre accretionary aqueous alteration of the rims in the solar nebula abstract to investigate the origin of fine grained rims around chondrules fgrs we compared presolar grain abundances elemental compositions and mineralogies in fine grained interstitial matrix material and individual fgrs in the primitive co3 0 chondrites allan hills a77307 lapaz icefield 031117 and dominion range 08006 the observation of similar overall o anomalous 155 ppm and c anomalous grain abundances 40 ppm in all three co3 0 chondrites suggests that they all accreted from a nebular reservoir with similar presolar grain abundances the presence of presolar silicate grains in fgrs combined with the observation of similar estimated porosity between interstitial matrix regions and fgrs in lap 031117 and alha77307 as well as the identification of a composite fgr a small rimmed chondrule within a larger chondrule rim in alha77307 all provide evidence for a formation of fgrs by accretion of dust grains onto freely floating chondrules in the solar nebula before their aggregation into their parent body asteroids our study also shows systematically lower abundances of presolar silicate grains in the fgrs than in the matrix regions of co3 chondrites while the abundances of sic grains are the same in all areas within errors this trend differs from cr2 chondrites in which the presolar silicate abundances are higher in the fgrs than in the matrix but similar to each other within 2 errors this observation combined with the identification of localized micrometer scaled aqueous alteration in a fgr of lap 031117 suggests that the lower abundance of presolar silicates in fgrs reflects pre accretionary aqueous alteration of the fine grained material in the fgrs this pre accretionary alteration could be due to either hydration and heating of freely floating rimmed chondrules in icy regions of the solar nebula or melted water ice associated with 26 al related heating inside precursor planetesimals followed by aggregation of fgrs into the co chondrite parent body

pigment preservation and remineralization in oxic coastal marine sediments abstract complex mixtures of sedimentary chlorophyll degradation products were measured using high performance liquid chromatography hplc in 210 pb dated box and piston core sediments sediments were collected from dabob bay washington a coastal marine fjord conducive to studies yielding an understanding of the remineralization and diagenesis of organic carbon greater than 99 of the pheopigment flux out of the water column does not accumulate in the top 2 cm of sediment surface sediment pigment profiles indicate that pheophorbides are the dominant pheopigments observed with concentrations decreasing rapidly with depth concentrations of chlorophyll c derivatives also decrease rapidly but ratios of a c pheopigments remain within ranges reported for natural and cultured phytoplankton sharp pheopigment concentration decreases within the bioturbated surface sediments as defined by 210 pb activities were modeled using a one dimensional mixing model the in situ pheopigment decomposition rate corrected for bioturbation and sediment accumulation corresponds to an approximate half life of 40 days sedimentary humic acid fulvic acid and residual humin associated pheopigments in sediments which had been previously acetone extracted to remove the lipophilic pheopigment fraction were typed by chromic acid oxidation and release of pyrrole derived maleimides this humic associated pyrrole derived nitrogen while a small fraction of total sedimentary or humic nitrogen accounted for 16 75 of the total sedimentary pheopigment accumulation and may be significant in understanding the diagenetic fate and transformation of pheopigments to petroporphyrins

the henryville bed of the new albany shale ii comparison of the nickel and vanadyl porphyrins in the bitumen with those generated from the kerogen during simulated catagenesis abstract the ni ii and vo ii porphyrin distributions in the bitumen from the henryville bed of new albany shale clark county indiana are compared with those of porphyrins isolated from a single new albany shale kerogen aliquot by five sequential pyrolyses 110 450 c both the bitumen and the pyrolysates contained ni ii and vo ii complexes of at least three skeletal types deoxophylloerythroetioporphyrin dpep etioporphyrin etio and tetrahydrobenzo dpep thbd ni ii benzo dpep and vo ii benzo dpep and vo ii benzo type porphyrins were detected in the pyrolysates but not in the bitumen it was concluded from a comparison of porphyrin distributions in the pyrolysates that porphyrins were liberated from the kerogen by enhanced solubilization and or desorption into the solvent rather than by kerogen porphyrin carbon carbon bond cleavages substantial amounts of organically combined nickel and vanadium remain in the kerogen after pyrolysis and may comprise porphyrin and non porphyrin complexes the similarity of the porphyrins in the bitumen and the pyrolysates indicates that porphyrins in the bitumen were released as a result of kerogen maturation the similarity of the ni ii etio adn dpep species to the corresponding vo ii porphyrins indicates that both metal complexes had a common premetallation tetrapyrrole precursor and that this precursor may have been associated with the evolving kerogen

geomorphology of the megadunes in the badain jaran desert the badain jaran desert features the highest megadunes on earth and a unique megadune lake alternation landscape based on field survey and interpretation of aerial photographs this paper examines the general characteristics of the badain jaran megadunes their morphometry and formation as well as the formation of megadune lake alternation landscape it is suggested that the megadunes in the badain jaran desert were developed in a low wind energy environment the compound transverse megadunes the dominant megadune type have a similar wind regime to barchanoid dunes and the compound star megadunes which occur near the mountains have a similar wind regime to star dunes similar to the barchanoid dunes the height base area and spacing of the compound transverse megadunes show reasonably good inter correlation the base area of the megadunes and the area of the leeward interdune lake basins are also inter correlated the alignment and spacing of the badain jaran megadunes implies that wind is the most important factor in their development the morphology underneath the megadunes does not determine the general pattern of the megadunes as previously suggested repetitions of dune fixation and reactivation in the development process played an important role in increasing the megadunes height hence their size the interdune lakes in the megadune area were mainly formed by talus springs and are only partly fed by atmospheric precipitation

a reappraisal of the metamorphic history of eh3 and el3 enstatite chondrites abstract the thermal history of a series of eh3 and el3 chondrites has been investigated by studying the degree of structural order of the organic matter om located and characterized in matrix areas by raman micro spectroscopy by comparison with unequilibrated ordinary chondrites uocs and co and cv carbonaceous chondrites the following petrologic types have been assigned to various e chondrites sahara 97096 and allan hills 84206 3 1 3 4 allan hills 85170 and parsa 3 5 allan hills 85119 3 7 qingzhen macalpine hills 88136 and macalpine hills 88184 3 6 3 7 the petrologic type of qingzhen is consistent with the abundance of the p3 noble gas component a sensitive tracer of the grade of thermal metamorphism the petrologic types are qualitatively consistent with the abundance of fine grained matrix for the whole series no significant effects of shock processes on the structure of om were observed however such processes certainly compete with thermal metamorphism and the possibility of an effect cannot be fully discarded in particular in the less metamorphosed objects the om precursors accreted by the eh3 and el3 parent bodies appear to be fairly similar to those of uocs and co and cv carbonaceous chondrites raman data however show some slight structural differences that could be partly accounted for by shock processes the metamorphic history of eh3 and el3 chondrites has often been described as complex in particular regarding the combined action of shock and thermal metamorphism because om maturity is mostly controlled by the temperature of peak metamorphism it is possible to distinguish between the contributions of long duration thermal processes and that of shock processes comparison of the petrologic types with the closure temperatures previously derived from opaque mineral assemblages has revealed that the thermal history of eh3 and el3 chondrites is consistent with a simple asteroidal onion shell model thermal metamorphism in enstatite chondrites appears to be fairly similar to that which takes place in other chondrite classes the complex features recorded by mineralogy and petrology and widely reported in the literature appear to be mostly controlled by shock processes

spatial analysis of sand dunes with a new global topographic dataset new approaches and opportunities on june 29 2009 version 1 of the aster gdem advanced spaceborne thermal emission and reflection radiometer global digital elevation model was made available at no cost or restrictions to users worldwide via electronic download the aster gdem provides expanded spatial coverage and better resolution than other global digital elevation models dems in this paper we demonstrate how the aster gdem provides new opportunities for investigating large aeolian sand dunes in three dimensions two dune specific spatial analysis methods are presented to illustrate potential applications of these data for discriminating dune generations and quantifying spatial variations of sediment supply moreover we review how existing and emerging fields of dune pattern analysis and simulation modeling will be able to make significant advances through application of these data potentially leading to future progress in studies of dune morphodynamics environmental controls and paleoenvironmental reconstructions copyright 2010 john wiley sons ltd

evolution of the raman spectrum of carbonaceous material in low grade metasediments of the glarus alps switzerland terra nova 22 354 360 2010 abstract the raman spectrum of carbonaceous material cm from advanced diagenesis 200 c to low grade metamorphism 320 c is documented in the helvetic flysch of the glarus alps switzerland the spectrum is complex with several defect bands at 1200 d4 1350 d1 1500 d3 and 1620 d2 cm 1 we document the evolution of these bands relative to the graphite g band with increasing metamorphic grade and we show that this qualitative evolution may be used as a proxy for temperature in the glarus alps we develop a robust peak fitting method and propose quantitative parameters that may be used as proxies for thermal metamorphism in this region further work in other geological contexts is needed to assess whether the spectral evolution observed in the glarus alps may be generalized and to critically assess the potential for calibrating a general empirical and quantitative thermometer based on the raman spectrum of cm in low grade rocks

the classification and complex thermal history of the enstatite chondrites we have carried out instrumental neutron activation analyses of 11 enstatite chondrites and electron microprobe analyses of 17 enstatite chondrites most of which were previously little described we report here the third known eh5 chondrite lew 88180 and an unusual el6 chondrite lew 87119 new data on four el3 chondrites alh 85119 eet 90299 pca 91020 and mac 88136 which is paired with mac 88180 and mac 88184 the second el5 chondrite til 91714 and an unusual metal rich and sulfide poor el3 chondrite lew 87223 the often discussed differences in mineral composition displayed by the eh and el chondrites are not as marked after the inclusion of the new samples in the database and the two classes apparently experienced a similar range of equilibration temperatures however texturally the el chondrites appear to have experienced much higher levels of metamorphic alteration than eh chondrites of similar equilibration temperatures most of the petrologic type criteria are not applicable to enstatite chondrites and unlike the ordinary chondrites texture and mineralogy reflect different aspects of the meteorite history we therefore propose that the existing petrologic type scheme not be used for enstatite chondrites we suggest that while textural type reflects peak metamorphic temperatures the mineralogical type reflects equilibration during postmetamorphic probably regolith processes unlike the ordinary chondrites and eh chondrites el chondrites experienced an extensive low temperature metamorphic episode there are now a large number of enstatite meteorite breccias and impact melts and apparently surface processes were important in determining the present nature of the enstatite chondrites

spatial self organization in geomorphology from periodic bedforms and patterned ground to scale invariant topography a rich diversity of spatial order can be discerned in landforms and small scale features of landscapes with spatial order ranging in scale from 107 m to 10 2 m and in geometry from pronounced two dimensional periodicity to three dimensional scale invariance ripples of wind blown sand with their strikingly uniform spacing and mountainous topography with its fractal characteristics illustrate the range of geomorphic self organization patterns on the land surface are often very distinct easily observed and readily studied because of their accessibility and yet the systematic quantitative study of geomorphic self organization is only in its infancy it offers difficult challenges but also exceptional opportunities particularly for those versed in modern techniques used in studies of self organization in this overview diverse examples of spontaneous organization in geomorphic systems and recent pertinent studies are described starting with spatial structures that are generally most distinct and best understood they include 1 periodic structures that form on various substrates as water or air transports erodes and deposits sediments ripples and dunes meanders and bar pool topography of rivers and rhythmic shoreline features 2 polygonal patterns that result either from the growth cracks in such contrasting media as freezing lava and frozen ground or from freeze thaw alternations in soils 3 large scale periodic structures dictated by the deformation of magma or of the earth s crust linear arrays of evenly spaced volcanoes and sequences of alternating valleys and mountain ranges and 4 scale invariant structures revealed in drainage networks and topography

extending the applicability of the raman carbonaceous material geothermometer using data from contact metamorphic rocks the degree of graphitization of carbonaceous material cm has been widely used as an indicator of metamorphic grade previous work has demonstrated that peak metamorphic temperature t o f regional metamorphic rocks can be estimated by an area ratio r2 of peaks recognized in raman spectra of cm the applicability of this method to low pressure 50 that adequately reflects the range of sample heterogeneity using this procedure with 532 nm laser and adapting our new calibration the errors of the raman cm geothermometer for contact metamorphic rocks decrease to 30 c

porphyrin geochemistry of atlantic jurassic cretaceous black shales abstract late jurassic early cretaceous black shales and an overlying sequence of albian campanian zeolitic claystones from the falkland plateau dsdp ipod leg 71 site 511 were analyzed for tetrapyrrole pigment type and abundance the black shale sequence was found to be rich in dpep series dominated free base nickel ni and to a lesser extent vanadyl v 0 porphyrins a low level of organic maturity i e precatagenesis is indicated for these strata as nickel chelation by free base porphyrins is only 50 75 complete proceeding down hole to 627 meters sub bottom electronic and mass spectral data reveal that the proposed benzo dpep bd and tetrahydrobenzo dpep thbd series are present in the free base and ni species as well as the more usual occurrence in v 0 porphyrin arrays highly reducing conditions are suggested by an abundance of the pah perylene substantial amounts of the thbd bd series and a redox equilibrium between free base dpep and 7 8 dihydro dpep series which exist in a 7 1 molar ratio the albian campanian claystone strata were found to be tetrapyrrolepoor and those pigments present were typed as cu ni highly dealkylated c26 max etioporphyrins thought to be derived via redeposition and oxidation of terrestrial organic matter om results from the present study are correlated to our past analyses of jurassic cretaceous sediments from atlantic margins in an effort to relate tetrapyrrole quality and quantity to basin evolution and om sources in the proto atlantic

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

eolian ripples as examples of self organization in geomorphological systems abstract ripples arise spontaneoulsy from sandy beds subjected to winds sufficient to cause the saltation of surficial grains while the initially fastest growing wavelengths are 4 6 times the mean hop length of grains impelled downwind by long trajectory high energy saltating grains the ripple wavelengths developed over long periods can be several times this numerical simulations based upon techniques pioneered by p k haff and coworkers reveal that a complex process of ripple coalescence is responsible for this evolution of the ripple field small fast moving ripples catch up with and are absorbed by larger slower forms each such merger resulting in a growth of the mean wavelength and a decline in the relative dispersion of the wavelengths an heuristic argument is presented which accounts for the fast initial growth and subsequent slowing of growth of the mean wavelength as the ripple field evolves ripple cross sectional shape appears to be controlled in large part by a distrianment function which represents the declining likelihood of a grain stopping on a surface as it slopes more steeply downwind that the resulting asymptotic wavelength in the simulations depends strongly upon impact angle supports sharp s 1963 suggestion that the length of the shadow zone plays an important role in controlling the final ripple wavelength

organic matter and metamorphic history of co chondrites abstract the metamorphic grades of a series of eight co3 chondrites alha77307 colony kainsaz felix lance ornans warrenton and isna have been quantified the method used was based on the structural grade of the organic matter trapped in the matrix which is irreversibly transformed by thermal metamorphism the maturation of the organic matter is independent with respect to the mineralogical context and aqueous alteration this metamorphic tracer is thus valid whatever the chemical class of chondrites moreover it is sensitive to the peak metamorphic temperature the structural grade of the organic matter was used along with other metamorphic tracers such as petrography of opaque minerals fa and fs silicate composition in type i chondrules presolar grains and noble gas p3 component abundance the deduced metamorphic hierarchy and the attributed petrographic types are the following alha77307 3 03 for most metamorphosed objects the peak metamorphic temperature can be estimated using a geothermometer calibrated with terrestrial metasediments beyssac o goffe b chopin c and rouzaud j n 2002 raman spectrum of carbonaceous material in metasediments a new geothermometer j metamorph geol 20 859 871 a value of 330 c was obtained for allende cv chondrite warrenton and isna consistent with temperatures estimated from fe diffusion weinbruch s armstrong j and palme h 1994 constraints on the thermal history of the allende parent body as derive from olivine spinel thermometry and fe mg interdiffusion in olivine geochim cosmochim acta 58 2 1019 1030 from the ni content in sulfide metal assemblages zanda b bourot denise m and hewins r 1995 condensate sulfide and its metamorphic transformations in primitive chondrites meteorit planet sci 30 a605 and from the d002 interlayer spacing in poorly graphitized carbon rietmeijer f and mackinnon i 1985 poorly graphitized carbon as a new cosmothermometer for primitive extraterrestrial materials nature 315 733 736 the trapped noble gas and c content appear to be sensitive but not precise metamorphic tracers indicating that the ornans paradox does not exist major problems with the current petrologic types derived from induced thermoluminescence are pointed out

parabolic megadunes in a subtropical quaternary inland dune field southwestern pampas argentina abstract the utracan paleo dune field la pampa province argentina southern south america was examined by remote sensing morphometric analyses and field surveys as a case study of complex megadunes of inland deserts the paleo dune field is within the utracan argentino valley one of the transverse valleys of la pampa province excavated into a regional structural plain similar paleo dune fields occur within these valleys utracan dunes are mostly stabilized by grasses deeply disturbed by cattle grazing and agriculture the paleo dune field is formed by complex parabolic megadunes with superimposed dunes parabolic megadunes present lengths of trailing arms of 3 3 12 9 km widths between them of 2 2 9 km and heights of 7 38 m the position of the dune noses at the northeastern tip of the bedform and measured sw ne orientation of arms indicate a mean transport direction to azimuth 68 2 above the parabolic arms and isolated in the paleo dune field there are compound blowout dunes clusters of several blowouts forming a larger bedform they show the depositional lobes to the ne with a measured mean transport direction to azimuth 58 1 the sw ne longitudinal length varies between 324 and 1302 m and the nw se transverse length between 114 and 622 m other parabolic arms show low

dunes on the skeleton coast namibia south west africa geomorphology and grain size relationships simple and locally compound transverse and barchanoid dunes dominate the 2000 km2 skeleton coast dunefield in northwestern namibia south west africa dune height and spacing are closely correlated r 0 89 and decrease across the dunefield from southwest to northeast with an accompanying change from transverse to barchanoid ridges and ultimately barchans the dunes are aligned transverse to the dominant strong south and south southwest onshore winds alignment patterns indicate that surface roughness changes between coastal plain and dunes cause dune forming winds to swing to the right over the dunes but resume their original direction beyond grain size and sorting vary at three scales the dune the dune landscape and through the dunefield overall the sands derived from three localities by deflation from beaches supplied by vigorous longshore drift become progressively finer and better sorted across the dunefield paralleling changes in dune height and spacing a statistically significant relationship r 0 65 was established between dune spacing and the phi grain size of the coarser fraction of the dune sands demonstrating the importance of the protective effects of coarse grains and suggesting that the morphometry of simple transverse dunes may be controlled by the scale of turbulence associated with the threshold wind speed required to move the coarsest fraction of the dune sand

the piancaldoli meteorite a forgotten primitive ll3 10 ordinary chondrite the piancaldoli ordinary chondrite fell in northern italy on august 10 1968 preliminary studies led to its classification as an ll3 4 unequilibrated ordinary chondrite however recent developments in classification procedures have prompted us to re examine its mineralogical petrographic spectroscopic chemical and isotopic features in a multi technique study raman spectra and magnetic properties indicate that piancaldoli experienced minimal thermal metamorphism consistent with its high bulk hydrogen content and the cr contents of ferroan olivines in its type ii chondrules in combination with findings of previous studies our data thus confirm the variability of cr contents in ferroan olivines in type ii chondrules as a proxy of thermal metamorphism furthermore our results reveal that piancaldoli is less altered than previously reported and should be reclassified as an ll3 10 unequilibrated ordinary chondrite our results also imply that the bulk deuterium enrichment as observed in piancaldoli ll3 10 bishunpur ll3 15 and semarkona ll3 00 is a specific signature of the most primitive unequilibrated ordinary chondrites based on our results we propose that to date piancaldoli is the second least altered unequilibrated ordinary chondrite fall after semarkona this work reiterates the importance of meteorite collections worldwide as fundamental resources for studying the formation conditions and evolution of our solar system

pattern analysis of simple transverse dunes in china s qaidam basin north of the kunlun mountains aeolian dune field patterns represent the spatial distribution of various combinations of landforms formed by the wind and are self organizing geomorphic features of the landscape to explore how the desert landscape evolves we selected a region with shifting sands in china s qaidam basin north of the kunlun mountains which developed in the late holocene using the method of geomorphic pattern analysis we calculated dune field pattern parameters in the study area and analyzed their spatial distribution we found that the sandy land had a range of dune types that formed diverse spatial combinations and the geomorphic patterns reflected the characteristics of a relatively early stage in the evolution of the dune field the patterns at a given location were related to the distance from the sediment source area by analyzing boundary conditions in this region we developed a conceptual model of the pattern of geomorphic evolution of simple transverse dunes this model provides insights into the geomorphic evolution process in the study region

high molecular weight and acid extractable chlorophyll degradation products in the black sea new sinks for chlorophyll abstract chlorophyll degradation products incorporated into solvent extractable high molecular weight material and into material which is only accessible with strong acid are identified in surface sediment the acid extractable chlorophyll degradation products and the solvent extractable high molecular weight chlorophyll degradation products each comprise approx 30 of total sedimentary chlorophyll degradation products in the high molecular weight phorbin fraction only phorbins derived from chlorophyll a were identified whereas in the acid extractable material porphyrins as well as phorbins derived from chlorophyll a were identified the acid extractable fraction contains approximately one half the amount of porphyrins and phorbins as does the solvent extractable material

mineralogy and petrology of amoeboid olivine inclusions in co3 chondrites relationship to parent body aqueous alteration petrographic and mineralogic studies of amoeboid olivine inclusions aois in co3 carbonaceous chondrites reveal that they are sensitive indicators of parent body aqueous and thermal alteration as the petrologic subtype increases from 3 0 to 3 8 forsteritic olivine fa0 1 is systematically converted into ferroan olivine fa60 75 we infer that the fe si and o entered the assemblage along grain boundaries forming ferroan olivine that filled fractures and voids as temperatures increased fe 2 from the new olivine exchanged with mg 2 from the original aoi to form diffusive haloes around low feo cores cations of mn 2 ca 2 and cr 3 were also mobilized the systematic changes in aoi textures and olivine compositional distributions can be used to refine the classification of co3 chondrites into subtypes in subtype 3 0 olivine occurs as small forsterite grains fa0 1 free of ferroan olivine in petrologic subtype 3 2 narrow veins of feo rich olivine have formed at forsterite grain boundaries with increasing alteration these veins thicken to form zones of ferroan olivine at the outside aoi margin and within the aoi interior by subtype 3 7 there is a fairly broad olivine compositional distribution in the range fa63 70 and by subtype 3 8 no forsterite remains and the high fa peak has narrowed fa64 67 even at this stage there is incomplete equilibration in the chondrite as a whole e g data for coarse olivine grains in isna co3 8 chondrules and lithic clasts show a peak at fa39 we infer that the mineral changes in aoi identified in the low petrologic types required aqueous or hydrothermal fluids whereas those in subtypes 3 3 largely reflect diffusive exchange within and between mineral grains without the aid of fluids

diagenetic and catagenetic pathways for porphyrins in sediments abstract porphyrins from a range of sediments have been studied in order to deduce the diagenetic processes involved in the formation and alteration of porphyrins in sediments and oils porphyrins from e1 lajjun shale jordan have been studied in detail a c 33 di dpep vanadyl porphyrin has been isolated and characterised by mass spectrometry and nuclear magnetic resonance spectrometry the proposed structure explains the origin of di dpep and rhodoporphyrins etioporphyrins are thought to arise from oxidative cleavage of chlorophyll derivatives and not from thermal cleavage of dpep molecules a change in dpep to etioporphyrin ratio occurs because of generation of etioporphyrins from kerogen and also because of the higher thermal stability of etioporphyrins compared with dpep molecules

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

nanosims isotopic investigation of xenolithic carbonaceous clasts from the kapoeta howardite abstract we report on the investigation of presolar grains and organic matter om in 14 xenolithic carbonaceous clasts c clasts identified in the kapoeta howardite based on high resolution nanosims hydrogen carbon nitrogen and oxygen isotopic imaging data the 14 c clasts are 50 200 m in size and consist of one cm like and 13 ci like clasts which are classified based on their mineralogies the clasts from this study are likely sourced from an ice bearing parent body either an icy asteroid or a comet originating from the outer solar system according to the following mineralogical observations 1 in two ci like clasts embayments of magnetite grains between the c clast and the host howardite point to aqueous alteration occurring on vesta as a result of melting the ice embedded in the c clasts 2 all of the c clasts especially the 13 ci like clasts likely originated from the same parent body because i the 14 c clasts are clustered in the thin section and ii the clasts show a much higher ratio of ci like to cm like clasts with respect to those reported in the literature four presolar silicon carbide sic and two presolar silicate grains were identified in the c clasts in addition all the c clasts contain moderate bulk d and 15n enrichments with the presence of sub micron to micron sized d and 15n hotspots indicating the presence of primitive organic material comparison of the abundances and isotopic compositions of presolar grains and om in these c clasts with literature data for different samples of primitive extraterrestrial material provides support for 1 the genetic linkage of xenolithic c clasts to highly aqueously altered but minimally heated carbonaceous chondritic materials and 2 a homogeneous distribution of circumstellar and interstellar materials in the protoplanetary disk the low amounts of heat experienced by the c clasts suggest that they arrived at vesta and or vestoids at low speeds after the late heavy bombardment in the inner solar system 3 5 4 0 gyr ago

identification of runoff type and an assessment of water balance for the megadune area of the badain jaran desert the badain jaran desert contains numerous megadunes that are characterised by the largest height difference in the world various rare landforms are also found on the slopes of the badain jaran megadunes including spring streams surface infiltration excess runoff erosion rills caused by surface runoff slow seepage runoff as well as physical and chemical sediment resulting from subsurface lateral flow outflows a variety of analyses were performed using electron microscope observation x ray diffraction particle size analysis and field survey investigating properties such as the mineral composition of the chemical sediment the particle size composition of the physical sediment and aeolian sand runoff type the recharge conditions of precipitation to groundwater and lake water and the water balance of the megadune area the formation of the different types of runoff demonstrates that although precipitation in this area is low effective heavy precipitation processes characterised by single events of more than 15 mm are present that likely act as a source for groundwater seven indicators including the formation of spring water at the bottom of megadunes multiple runoff types as well as both physical and chemical sediments clearly show that precipitation in the area reaches the bottom of megadunes via infiltration which constitutes an effective supply of lake water and groundwater the water resisting property of the fine sand layer is likely the reason why the region is characterised by an outflow of subsurface runoff with the latter and its sediment further confirming that the area also possesses a positive water balance this positive water balance is the result of four unique characteristics the presence of effective heavy precipitation low transpiration due to scarce vegetation the high infiltration rate of the sand layer and the small depth of the sand layer affected by evaporation this in turn means that atmospheric precipitation is sufficient to supply groundwater leading to the development of the numerous lakes found in the desert area water balance calculations revealed that after accounting for evaporation transpiration and other sources of consumption of atmospheric precipitation around 134 648 4 135 976 9 m3 of water per square kilometre per year is still supplied to the groundwater and lake water

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

analysis of large aeolian wind blown bedforms using the shuttle radar topography mission srtm digital elevation data abstract dry land areas cover large parts of the land masses of earth of these a large portion is mantled by aeolian wind blown deposits and subjected to aeolian process i e the transport of sand or dust by wind one of the most prominent morphologies created by wind driven deposits are dunes and in their larger form draas or mega dunes these mega dunes tend to be widely spaced very large often forming a base on which smaller dunes form producing a compound dune pattern in february 2000 the shuttle radar topography mission onboard the space shuttle endeavour flew an interferometric radar system whose objective was to create a dem of nearly all earth land masses in this paper dem data from the c band 90 m data set and the x band 30 m data set were used to map and characterize the height and spacing of the large sand seas ergs on earth only the larger forms of dunes could be mapped reliably the dune spacing and heights extracted from the srtm dems tended to be in overall agreement with those reported in the literature in a comparison between the x band and the c band data it was found that the x band data are more sensitive to the smaller scale undulations on the compound dunes and better revealed the full height of the dunes

disentangling nebular and asteroidal features of co3 carbonaceous chondrite meteorites abstract analyses of olivines and low ca pyroxenes in a suite of porphyritic chondrules of types ia and ii in each of ten co3 chondrites and comparisons with similar chondrules in ll chondrites suggest that the co3 chondrites may be divided into a metamorphic sequence of subtypes 3 0 to 3 7 chondrules in allan hills a77307 and colony which we classify as type 3 0 show only igneous zoning whereas in the other more metamorphosed type 3 1 3 7 co chondrites chondrule silicates are enriched in feo most markedly in olivine crystals near the rims of type ia chondrules and along cracks the feo enrichments in metamorphosed chondrules result largely from equilibration by solid state diffusion between chondrules and feo rich matrices type 3 1 3 7 co chondrites were formed from chondrites like colony and alh a77307 in heated asteroids or planetesimals we find no evidence for nebular condensation of fayalite rims around these chondrules as reported for cv3 chondrites or nebular modification of chondrule silicates as favored by some workers metallic fe ni in alh a77307 contains up to 0 1 1 wt cr si and p as in the least metamorphosed ordinary chondrites and cm2 chondrites and grains of cohenite fe3c and haxonite fe23c6 these carbides which are the first reported in carbonaceous chondrites are associated with pentlandite and magnetite as in certain ll3 chondrites we assign the following petrologic subtypes to other co chondrites kainsaz 3 1 felix 3 2 alh 82101 and ornans 3 3 lance and alh a77029 3 4 alh a77003 3 5 warrenton 3 6 and isna 3 7

vanadyl porphyrins in exploration maturity indicators for source rocks and oils abstract the porphyrin maturity parameter pmp which is derived from the vanadyl porphyrin distribution is an excellent parameter for 1 identifying the zone of hydrocarbon generation from marine source rock extracts and 2 determining from oils the thermal maturity of their source rocks at expulsion the pmp is measured using a methodology which is inexpensive reliable and faster than earlier methods allowing it to be used as a routine exploration tool the pmp may be a more reliable maturity indicator for marine organic matter than some conventional methods such as vitrinite reflectance unlike most conventional maturity parameters guided by processes other than kerogen conversion the reactions causing pmp evolution directly monitor the generation of bitumen and the concurrent thermal degradation of kerogen measurements on hydrous pyrolyzates from the monterey formation offshore california source rock bitumens from the devonian mississippian bakken shale williston basin and miocene monterey equivalent source strata san joaquin basin california illustrate the method in all cases reviewed so far pmp begins increasing at the onset of hydrocarbon generation and increases systematically and predictably as kerogen decomposition proceeds in oils generated from high s marine kerogens pmp reflects the maturity of the source rock at the time of oil expulsion provided that the oil does not undergo subsequent reservoior maturation or mixing with in situ bitumen

short duration thermal metamorphism in cr chondrites cr chondrites are considered as one of the most primitive classes of meteorites most of them experienced a mild aqueous alteration and show no evidence of significant effect of thermal metamorphism we present here a search for low degree metamorphic effects in cr chondrites we studied 15 cr chondrites using different metamorphic indicators 1 structure and ni content of metal grains 2 hydration state of matrix 3 structure and composition of organic matter the different metamorphic indicators show that two of the analyzed cr chondrites gra 06100 and gro 03116 experienced thermal metamorphism indeed all of the metal grains in gra 06100 and half of the metal grains in gro 03116 show ni rich phases the matrix of gra 06100 is almost completely dehydrated and the matrix of gro 03116 is partially dehydrated raman spectra of organic matter in these two meteorites are clearly different from those obtained for organic matter in the other cr chondrites which resemble raman spectra of organic matter in unmetamorphosed cm2 meteorites ir spectra of insoluble organic matter extracted from gra 06100 and gro 03116 show lower carbonyl abundance and higher ch2 ch3 ratio with respect to organic matter of unmetamorphosed chondrites the other cr chondrites analyzed here lack these characteristics and only show a few metal grains with ni rich inclusions our results also show that the metamorphic effects observed in gra 06100 and gro 03116 are different from those observed in type 3 chondrites which experienced long duration metamorphism of radiogenic origin we infer that thermal processing in these two crs extended over a short duration and was triggered by impacts

pattern analysis and dating for the badain jaran dune field northwestern china pattern analysis can estimate dune formation ages judge wind conditions and extract environmental signals from the common pattern parameters of active dune field for the extraterrestrial dune fields this method is a great advantage while many in situ and laboratory techniques cannot do anything an ideal location for the large scale pattern analysis test is the badain jaran desert where the tallest terrestrial aeolian dune occurs in this study the function forms of pattern parameters varying with the dune construction time are established according to the natural evolution of a dune field in the duration of over 10 years it is revealed that the relations between pattern parameters and time display power functions in which the unknown coefficients in different conditions of wind regimes and sand availabilities can be estimated from the absolute ages of local deposits from the northwest to southeast of the badain jaran desert the dune crest length and mean spacing increase and the defect density decreases the pattern ages change correspondingly dune orientation mostly ranges between 10 circ and 60 circ the crest length ages indicate that the modern active dune field began to form at about 20 75 ka bp the dunes in the southeast and northeast are older than those in the western this work confirms that pattern analysis offers an effective dating method for hard to reach or large scale dune fields

a preliminary study of the dynamics of a modern draa algodones southeastern california usa a transverse crescentic draa in the algodones dune field california was monitored for a year using surface process mapping aerial photography and supplemental wind measurement the draa is oriented by the long term resultant wind whereas its superimposed features are in equilibrium with the bedform modified secondary airflow surface airflow and the movement of superimposed bedforms is typically oblique or parallel to the draa brinkline particularly on the lee slope comparison of measurements of draa movement and sand deposition on the lee slope with expected rates calculated from wind data and draa size confirm that there is a significant component of sand flow parallel to the draa brinkline the internal structure being generated at the base of the draa lee slope is inferred from the surface processes active there within the space of a kilometer two types of compound cross strata separated by an area of simple cross strata are being produced this has significant implications for interpretations of ancient aeolian strata variations in internal structure types found in lateral sequence may be generated by one complex bedform and these cross strata may be simple or compound second order bounding surface orientations indicate resultant primary palaeowind directions compound cross strata dip directions indicate secondary flow conditions the existence of cross strata dip directions oblique or perpendicular to the second order surface indicates longitudinal secondary flow on the lee face but not necessarily a longitudinal or oblique draa without further detailed knowledge about various draa configurations and behaviour stratification attributed to draas can be used only to interpret activity on the lower draa lee face

phorbin steryl esters in black sea sediment traps and sediments a preliminary evaluation of their paleooceanographic potential abstract the distributions of pyropheophorbide a steryl esters in one year deployments of sediment traps at two locations in the black sea are described in nearly all our trap samples phorbin steryl esters pses contribute a significant portion of the total phorbin flux the relative abundances of sterols esterified to pyropheophorbide a varied throughout the year and we suggest these changes result from the observed seasonal variation of phytoplankton species in the overlying water column the distribution of free sterols in a one year composite sediment trap sample closely approximates the distribution of sterols derived from the hydrolysis of sedimentary pses collected at an adjacent site from these results we suggest that the distribution of sedimentary pse sterols provides a record of sterol deposition to the sediment water interface esterification of sterols to pyropheophorbide a apparently prevents the preferential removal of 4 desmethyl sterols relative to 4 methyl sterols and the reduction of stenols to stanols during degradation analysis of pses in a gravity core covering the last 8 10 kyr shows that the abundance and distribution of pses change with downcore variations in sedimentology detailed analysis of pses in sediments may therefore provide a means to evaluate paleooceanographic changes in phytoplankton community structure and sterol early diagenesis the synthesis nmr ci ms and visible spectroscopic properties of four abundant pses found in the black sea are also described

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

precursor and metamorphic condition effects on raman spectra of poorly ordered carbonaceous matter in chondrites and coals abstract geothermometers based on raman spectrometry of carbonaceous matter and covering a wide range of temperatures 100 650 c have been developed over recent years while raman data have been largely interpreted in terms of temperature they are also the fingerprint of certain metamorphic conditions especially in the low temperature range relevant to poorly ordered carbonaceous matter this study investigates the raman spectra of two series of chondritic carbonaceous matter and coal samples formed from different precursors and under different metamorphic conditions the raman spectra of polyaromatic carbonaceous matter pcm from 42 chondrites and 27 coal samples measured with visible 514 nm and ultra violet 244 nm excitation wavelengths are analyzed the raman spectra of low rank coals and chondrites of petrologic types 1 and 2 which contain the more disordered pcm reflect the distinct carbon structures of their precursors the 514 nm raman spectra of high rank coals and chondrites of petrologic type 3 exhibit continuous and systematic spectral differences reflecting different carbon structures present during the metamorphism event they result from differences in the chemical structures of the precursors concerning for instance the reticulation of polyaromatic units or an abundance of ether functional groups or possibly from a lack of carbonization processes to efficiently expel oxygen heteroatoms due to weak lithostatic pressure and confinement these results suggest that the use of low temperature carbon thermometers should be restricted to a given geological context at the same time the sensitivity of raman spectra to precursors and certain metamorphic conditions could be used to obtain information other than temperature the analysis also provides evidence of the accretion of relatively homogeneous pcm precursors among ordinary co and cv carbonaceous chondrite parent bodies given that the 514 nm raman spectra of pcm efficiently trace the metamorphism grades looking closer however the 514 nm raman data are more scattered in chondrites than in coals and the maturity tracers are less sensitive and miscorrelate with the atomic h c ratio suggesting slight compositional and structural differences among the pcm precursors accreted

a test of granulometric control of desert dune geometry i g wilson s hypothesis of coarse tail grain size control of dune spacing was derived from three dunefields in the sahara and although it was supplemented by measurements of spacing from other parts of the world the grain size data come only from north africa in this paper the hypothesis is tested in the australian dunefields australian dunes do not form separate categories on a p20 s twentieth percentile spacing plot and when placed on wilson s diagram the australian data form a continuum between dunes and draas ripples maintain their identity suggesting that the average saltation length of sand controls ripple wavelength while dunes and wilson s draas are formed by secondary flow of some kind in australia the spread of data on the p20 s diagram indicates that grain size is not the prime control on s data from australia and the sahara indicate that direct linear relationships between s and h dune spacing and height means respectively for blocks of dunes occur but they have different slopes in different areas these differences possibly reflect variations in vegetation and substrate as well as differences in wind regime the separation of dunes from draas in the sahara reflects the greater role of grain size in an area where coarse grains frequently occur in dune crests the relative paucity of coarse grains in australian dune crests may reflect the fine grained alluvium from which the dunes are derived these differences may be ascribed to differing topography in australia and the sahara

controls of eolian dune size and spacing data for the namib and gran desierto sand seas suggest that the controls of dune size and spacing are complex the relation between dune height and spacing varies with dune type and location and reflects both dune dynamics vertical accretion vs migration or extension and availability of sand there is no general relation between dune spacing and grain size in the namib sand sea the height of compound and complex dunes draas is inversely proportional to potential sand transport rates whereas the height of dunes superimposed on their flanks varies directly with potential sand transport rates these observations can be combined with data on dune spacing to demonstrate the existence of a hierarchy of eolian dunes each element of which responds to variations in sand transport rates at different temporal and spatial scales whereas the morphology of individual simple dunes and superimposed dunes on draas is related to contemporary rates and directions of sand transport the morphology and development of draas reflects long term and regional patterns of sand transport and deposition

a terrestrial analog for transverse aeolian ridges tars environment morphometry and recent dynamics abstract transverse aeolian ridges tars are a distinct aeolian bedform found on mars the formative processes evolution and geological significance of tars is poorly understood fundamentally it is unknown whether tars are dunes mega ripples or another bedform type we examined aeolian bedforms in the lut desert of iran as a terrestrial analog for martian tars from an objective sampling strategy with high resolution satellite imagery we developed a large morphometric dataset for comparison with existing martian tars we also examined the dynamics of the lut bedforms between 2004 and 2012 to determine if they were static or migrating results indicate that the range in the dimensions length width height and wavelength of the lut bedforms and martian tars overlap suggesting lut bedforms are a viable terrestrial tar analog our sample yielded median values of 55 18 m 9 80 1 02 m and 20 m for length longest planview axis width shortest planview axis height and wavelength respectively cumulative log frequency plots of morphometric parameters suggest the sample is from a single population and process mechanism although the vast majority of lut bedforms examined were static between 2004 and 2012 some migrated up to 0 09 myr 1 on average this is much slower than nearby dunes 4 12 myr 1 but is explained by the existence of a surface lag of coarse particles on the tar like bedforms the combination of morphometry surface sedimentology and slow migration rate indicate the lut bedforms are mega ripples which provides evidence supporting interpretation of martian tars as mega ripples testing the mega ripple hypothesis for martian tars requires measurements of their sedimentology which may be possible with the mars science laboratory rover curiosity as well as expanded measurements of tar morphometry to constrain their size shape and scaling

chemical and physical studies of type 3 chondrites iv annealing studies of a type 3 4 ordinary chondrite and the metamorphic history of meteorites abstract samples of a type 3 4 chondrite have been annealed at 400 1000 c for 1 200 hours their thermoluminescence properties determined and analyzed for k na mn sc and ca by instrumental neutron activation analysis after annealing at 900 c the samples showed a 50 decrease in tl sensitivity while after annealing at 1000 c it fell to 0 1 0 01 times its unannealed value and loss of na and k occurred the tl and compositional changes resemble those observed for the equilibrated kernouve chondrite after similar annealing treatments except that the sharp tl decrease and element loss occurred at 1100 c this difference is presumably due to petrographic differences in the feldspar of the two meteorites the temperature and the width of the tl peak showed a discontinuous increase after annealing at 800 c peak temperature jumped from 130 to 200 c and peak width increased from 90 to 150 c the activation energies for these tl changes are 7 10 kcal mole similar increases in the tl peak temperature have been reported in tl studies of amelia va albite where they were associated with the low to high temperature transformation however the activation energy for the transformation is 80 kcal mole these changes in tl emission characteristics resemble trends observed in type 3 ordinary chondrites and it is suggested that type 3 3 3 5 chondrites have a low feldspar as tl phosphor and 3 5 have high feldspar as the phosphor thermoluminescence therefore provides a means of palaeothermometry for type 3 ordinary chondrites

geomorphological hierarchies for complex mega dunes and their implications for mega dune evolution in the badain jaran desert abstract the evolution of mega dunes is sometimes attributed to factors other than the wind but evidence for this is lacking it is assumed that the dominance of wind in maintaining the evolution of mega dunes should be characterized by regular height spacing relationships that have been found for simple dunes or wind ripples which are dominantly formed by the wind in this context we studied the height spacing relationship for the complex reversing mega dunes in the badain jaran desert which features the tallest mega dunes in the world the complex mega dunes were divided into three hierarchical orders according to the cumulative probability plots of dune height and spacing measurements and the coefficients of variability of dune heights and spacings were in accordance with values reported for other deserts the relationship between dune spacing and height for all the three orders of dunes could be expressed reasonably well by a uniform linear function that was also applied to the height wavelength relationship for wind ripples in other deserts this relationship was found to be similar to those for several other deserts and subaqueous bedforms this implies that there should be few unique factors in maintaining the evolution of complex mega dunes in the badain jaran desert compared with the superimposed simple dunes and dunes in other deserts dune fields and subaqueous bedforms and that the tallest mega dunes on the earth can be maintained by the wind

petrography stable isotope compositions microraman spectroscopy and presolar components of roberts massif 04133 a reduced cv3 carbonaceous chondrite here we report the mineralogy petrography c n o stable isotope compositions degree of disorder of organic matter and abundances of presolar components of the chondrite roberts massif rbt 04133 using a coordinated multitechnique approach the results of this study are inconsistent with its initial classification as a renazzo like carbonaceous chondrite and strongly support rbt 04133 being a brecciated reduced petrologic type 3 3 vigarano like carbonaceous cv chondrite rbt 04133 shows no evidence for aqueous alteration however it is mildly thermally altered up to approximately 440 c which is apparent in its whole rock c and n isotopic compositions the degree of disorder of c in insoluble organic matter low presolar grain abundances minor element compositions of fe ni metal chromite compositions and morphologies and the presence of unequilibrated silicates sulfides within type i chondrules from rbt 04133 appear to be pre accretionary i e did not form via aqueous alteration providing further evidence that some sulfide minerals formed prior to accretion of the cv chondrite parent body the thin section studied contains two reduced cv3 lithologies one of which appears to be more thermally metamorphosed indicating that rbt 04133 like several other cv chondrites is a breccia and thus experienced impact processing linear foliation of chondrules was not observed implying that rbt 04133 did not experience high velocity impacts that could lead to extensive thermal metamorphism presolar silicates are still present in rbt 04133 although presolar sic grain abundances are very low indicating that the progressive destruction or modification of presolar sic grains begins before presolar silicate grains are completely unidentifiable

granule ripples in the kumtagh desert china morphology grain size and influencing factors granule ripples are found mainly in four regions of the kumtagh desert in china they are characterized by an asymmetrical shape with gentle lower slopes on both sides and abrupt crests the ripples tend to be oriented perpendicular to the prevailing winds except when they form near obstacles such as yardangs the wavelengths range between 0 31 m and 26 m and heights h range from 0 015 m to 1 m the relationship between wavelength and height can be described by a simple linear function and the mean ripple index h is about 20 4 for the study sites the sediments are poorly sorted with negative to very negative skewness at lee and stoss slopes and between ripple troughs which confirms the poured in and shadow appearance described by previous researchers the bimodal or trimodal distributions of grains with modes of 1 16 0 5 and 3 16 and the enrichment of coarse particles at the ripple surface with coarse granule contents ranging between 5 2 and 62 1 indicate that the underlying layer is the original sediment source and that the granule ripples resist erosional processes although the impact of saltating particles and consequently the creep and reptation of coarse grains are responsible for granule ripple initiation at a micro scale however the characteristics of local sediments wind regimes and topographical obstacles as well as the feedbacks among bedform and airflow more strongly affect the development and alignment of granule ripples at a macro scale

petrographic chemical and spectroscopic evidence for thermal metamorphism in carbonaceous chondrites i ci and cm chondrites abstract we present a comprehensive description of petrologic chemical and spectroscopic features of thermally metamorphosed ci like and cm and cm like chondrites only two such ci chondrites have so far been discovered i e y 86029 and y 82162 thermal metamorphism in these chondrites is apparent in their low contents of h2o c and the most thermally labile trace elements partial dehydration of matrix phyllosilicates and abundance of thermally decomposed ca mg fe mn carbonates which apparently resulted from heating of mg fe carbonate precursors the cm chondrites exhibit a wide range of aqueous and thermal alteration characteristics this alteration was almost complete in y 86720 and y 86789 which also escaped alternating episodes of oxidation and sulfidization experienced by the others thermal metamorphism in the cm chondrites is apparent in loss of thermally labile trace elements and also in partial to almost complete dehydration of matrix phyllosilicates heating was less uniform in them than in ci chondrites this dehydration is also evident in strength and shapes of integrated intensities of the 3 m bands except in pca 91008 which experienced extensive terrestrial weathering tochilinite is absent in all but y 793321 probably due to heating textural evidence for thermal metamorphism is conspicuous in blurring or integration fusion of chondrules with matrix in the more extensively heated 600 c cm chondrites like pca 91008 and b 7904 tem and xrd analyses reveal that phyllosilicate transformation to anhydrous phases proceeds via poorly crystalline highly desiccated and disordered intermediate phases in the least and moderately heated 400 600 c carbonaceous chondrites like wis 91600 pca 91008 and y 86029 these findings are significant in that they confirm that these phases occur in meteorites as well as terrestrial samples thermal alteration in these meteorites can be used to identify other carbonaceous chondrites that were thermally metamorphosed in their parent bodies combining rnaa trace element data for experimentally heated murchison cm2 samples with petrographic and spectroscopic data these thermally metamorphosed carbonaceous chondrites can be ordered by severity of open system heating as 400 c y 793321

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

effects of weathering on nickel and vanadyl porphyrins of a lower toarcian shale of the paris basin the effects of weathering on the organic matter within a narrow sediment interval from surficial to 10 m depth belonging to the lower toarcian shales of the paris basin were studied at a molecular level among the compositional changes observed the most striking feature is a severe breakdown of the metalloporphyrins ni and vo at the surface as evidenced by quantitative data in addition this degradation of the geoporphyrins is accompanied by substantial modification of their composition with preferential degradation of porphyrins with exocyclic rings over polyalkylporphyrins these quantitative and qualitative changes are thought to result from exposure of the sediment to weathering conditions more specifically abiotic oxidation is likely to be the main weathering process responsible for this superficial alteration of the sedimentary porphyrins this is particularly suggested by oxidation experiments carried out on a mixture of sedimentary nickel and vanadyl porphyrins where oxidation of the former complexes occurs at a faster rate thus geoporphyrins may be used as molecular indicators to evaluate the degree of oxidation of weathered geological samples containing this kind of molecule

isotopic diversity in interplanetary dust particles and preservation of extreme 16o depletion two interplanetary dust particles idps investigated by nanosims reveal diverse oxygen isotope compositions at the micrometre scale the oxygen isotope values recorded at different locations across the single idp fragments cover a wider range than the bulk values available from all idps and bulk meteorites measured to date measurement of h c and n isotopes by nanosims and the use of scanning and transmission electron microscopy sem and tem to determine elemental compositions and textural information allows for a better understanding of the lithologies and organic signatures associated with the oxygen isotope features idp balmoral a 15 m sized fragment with a chondritic porous cp idp like texture contains a region a few micrometres in size characterised by 16o depleted isotope signatures in the range 17o 18o 80 to 200 the remainder of the fragment has a more 16o rich composition 18o 0 20 similar to many other idps and bulk meteorites other than in discrete pre solar grains such extreme 16o depletions have only been observed previously in rare components within the matrix of the acfer 094 meteorite however tem imaging and feo mgo si ion ratios indicate that the 16o depleted regions in balmoral did not form by the same mechanism as that proposed for the 16o depleted phases in acfer 094 as the level of 16o depletion is consistent with that expected from isotope selective self shielding it is likely that the 16o depleted reservoir was located close to that where oxygen self shielding effects were most pronounced i e the outer solar nebula or even interstellar medium individual regions within idp lumley cover a range in 18o from 30 to 19 with the oxygen isotope values broadly co varying with d 13c 15n light element ratios and texture the relationships observed in lumley indicate that the parent body incorporated material at the micrometre scale from discrete diverse isotopic reservoirs some of which are represented by inner solar system material but others which must have formed in the outer solar system the idp fragments support a model whereby primary dust from the early solar nebula initially formed a variety of reservoirs in the outer solar nebula with those at lower au incorporating a higher proportion of inner solar system chondritic dust than those at larger au these reservoirs were subsequently disrupted into micrometre sized clasts that were re incorporated into idp parent bodies presumably at large au these results reveal that any models accounting for mixing processes in the early solar nebula must also account for the presence of an extremely 16o depleted reservoir in the comet forming region

formation and evolution of the badain jaran desert north china as revealed by a drill core from the desert centre and by geological survey abstract the deserts in north china are regarded as direct records of the process of inland asian aridification amongst these deserts those proximal to the chinese loess plateau clp are especially important because of their role as sediment source areas in order to investigate the formation history of the badain jaran desert the largest desert proximal to the clp a 310 m long drill core was obtained from the desert centre which reached the underlying basement rock the lithology of the core consists of an upper layer of aeolian sand with three intercalated layers of lacustrine sediments overlying alluvial fluvial deposits which are developed unconformably over red coloured basement rock a geological survey indicates that the lower red coloured basement rock is of late cretaceous age and is cut by a mesozoic erosion surface widely developed over the badain jaran area on the basis of optically stimulated luminescence and electron spin resonance dating and stratigraphic correlation a preliminary chronological framework was established which was improved by tuning the aeolian sand proportion of the drill core to earth orbital obliquity and precession this final chronology suggests that 1 the basal age of the desert strata is at least 1100 ka corresponding to the formation of the badain jaran desert and 2 that the formation of the erosion surface terminated and the surface had begun to subside by at least 1200 ka the formation of the desert can be summarized as follows the alluvial fluvial fan formed by the heihe river draining the qilian mountains provided sufficient sedimentary material to form the desert under an arid climate while the asian winter monsoon and the westerlies entrained the clastic sediments from the fan area which finally accumulated downwind more distant sediment transport was prevented by the intervening mountainous terrain these coupled processes were driven by tibetan plateau uplift and ongoing global climatic cooling after initial formation of the desert three humid phases occurred in mis 13 15 mis 5 and the holocene during which extensive lakes developed the sequential drying out of the lakes may reflect inter relationships between global climate and the intensity of the asian summer monsoon and the westerlies

age and dynamics of linear dunes in the namib desert bristow c s duller g a t lancaster n 2007 age and dynamics of linear dunes in the namib desert geology 35 6 555 558 sponsorship american chemical society

optical dating reveals that the height of earth s tallest megadunes in the badain jaran desert of nw china is increasing abstract the badain jaran desert bjd in nw china is well known for its unique landscape of megadunes coexisting with permanent lakes the megadunes are already the tallest sand dunes on earth and some of them are up to 400 m high however it is unclear whether or not the height of the megadunes is continuing to increase under present climatic and environmental conditions in order to determine the growth status of the megadunes we collected 26 samples from the windward slopes of two megadunes for optically stimulated and infrared stimulated luminescence dating the results show that the thickness of the modern eolian sand layers increases from the lower part of the windward slopes with a thickness of less than 1 m to more than 2 m in the middle and to 9 m in the upper part this indicates that the height of the megadunes is continuing to increase under modern conditions the surface sediments from the base of the windward slope and the adjacent lake basin have relatively old ages of 6 7 ka indicating that these areas are eroding the recent eolian sands of the upper part of the megadunes likely originated from the base of the dunes or from the lake basin the megadunes in the bjd are currently becoming increasingly high and steep due to the upward migration and accumulation of sand particles increased humidity and a weakened wind regime in northern china related to ongoing climatic warming are likely the main factors in maintaining the growth of the megadunes

phytoplankton assemblage in the plio pleistocene record of lake baikal as indicated by sedimentary steryl chlorin esters abstract past changes in phytoplankton assemblages in lake baikal over the last 4 5 ma both in population and composition are inferred from the downcore profiles of the relatively stable chlorophyll derivatives steryl esters of pyropheophorbides a and b steryl chlorine esters sces in the 0 200 m section of the bdp 98 drill core supplemented by the data on biogenic silica bsi and total organic carbon toc contents sces a and b dominate among sedimentary chlorophyll derivatives in the bdp 98 sediments except for the upper few meters indicating their high stability during diagenetic alteration of sediments the depth age profiles of sces a are consistent with bsi and toc profiles and are interpreted as reflecting primary productivity of the lake in the past baikal proxies reveal close correlation with marine oxygen isotope records mis stratigraphy these observations confirm that climate change in the northern hemisphere has been a primary factor controlling the total phytoplankton productivity in lake baikal during the last several million years among sces a c30 dinostanol sce a a marker of dinoflagellates was identified by gc ms analysis sce b a marker of green algae was identified by its uv vis spectrum the ratio of c30 sce a to total sces a tsces a was higher during 4 5 4 2 and 1 7 1 3 ma suggesting that dinoflagellates proliferated preferentially in those periods the early pleistocene maximum of this ratio corresponds to the broad minimum of diatom abundance previously suggested to have recorded a prolonged regional cooling an abrupt increase in the sce b tsces a ratio was observed at 2 5 2 6 ma indicating that green algae containing chlorophyll b have proliferated in lake baikal during this period this interval has also been suggested to contain evidence for a significant regional cooling based on minima of diatom abundance and bsi in sediments the depth profile of c27 5 cholesterol sce a relative to tsces a showed a trend similar to that of bsi suggesting that c27 5 sce a tsces a ratio is a potential marker of diatoms in lake baikal certain mismatches between the lake baikal profiles of biological indicators and the marine oxygen isotope records as well as the slight temporal offsets between different lake baikal biological marker signals suggest that the regional component of climatic and or lacustrine environmental changes also have played a role in determining the composition of the lake baikal plio pleistocene phytoplankton assemblage

a theoretical model for aeolian impact ripples new insights into the grain bed impact process arising from both numerical and physical experiments involving single grain impacts lead to a more complete conceptual model of the aeolian saltation process that in turn allows a simple model of aeolian impact ripples to be developed the saltating population may be idealized as consisting of 1 long trajectory high impact energy constant impact angle successive saltations and 2 short trajectory low impact energy reptations it is argued that the spatial variations in mass flux due to the reptating population lead to the growth and translation of impact ripples using the sediment continuity equation an expression for the spatial variation in the ejection rate of reptating grains from a sinusoidally perturbed bed and a probability distribution for the reptation lengths a simple stability analysis demonstrates that the flat bed is unstable to small amplitude perturbations a fastest growing wavelength emerges that is roughly six times the mean reptation length and is only weakly dependent upon the detailed shape of the probability distribution of reptation lengths the results match well with the observed initial wavelengths in wind tunnel experiments

organic thermometry for chondritic parent bodies abstract a unique spectroscopic feature has been identified in a study of twenty five different samples of meteoritic insoluble organic matter iom spanning multiple chemical classes groups and petrologic types using carbon x ray absorption near edge structure xanes spectroscopy the intensity of this feature a 1s exciton appears to provide a precise measure of parent body metamorphism the intensity of this exciton is also shown to correlate well with a large negative paramagnetic shift observed through solid state 13c nmr experiments reveal that upon heating primitive iom is transformed into material that is indistinguishable from that in thermally processed chondrites including the development of the 1s exciton a thermo kinetic expression is derived from the experimental data that allows the intensity of the 1s exciton to be used to estimated the effective temperature integrated over time a good correlation is observed between the intensity of the 1s exciton and previously published microraman spectral data these data provide a self consistent organic derived temperature scale for the purpose of calibrating raman based thermometric expressions

palaeoenvironmental reconstructions from linear dunefields recent progress current challenges and future directions abstract this paper reviews recent progress in the use of linear dunes as geoproxies of late quaternary environmental change summarises the challenges facing their use and explores some potential solutions to these challenges large areas of the swathes of linear dunes which occupy the continental interior of southern africa australia and parts of central asia and southern america currently have limited or negligible aeolian activity they have been recognised as offering potential information about past environments for more than a century but only with the widespread application of luminescence dating during the 1990s did they realistically start to offer the prospect of being an extensive dateable proxy of late quaternary palaeoenvironments and possibly palaeoclimates dating aeolian dune sands with luminescence methods is generally although not always relatively straightforward over the past twenty years a large number 1000 of luminescence ages have been added to the global dataset yet there has also been significant criticism of some of the rationale underpinning much of the interpretation of the records derived at the landscape scale developments of arguably equal importance have come from improved geomorphological understanding based on the wider availability of remotely sensed data and the paradigm of dunefield evolution as a self organising complex system current challenges are identified in three key regions incomplete understanding of how the process geomorphology of linear dunes affect the accumulation and preservation of sediment a lack of clarity regarding the temporal and spatial scale of the response in a dynamic environmental setting and uncertainty surrounding the drivers of changing rates of net accumulation solutions to these challenges lie within diverse research methodologies certainly further field study is required with improvement required in understanding system responses to changing environmental stimuli at scales from sedimentological to landscape in parallel the full implications of complex systems approaches to aeolian geomorphology for linear dunes lag behind the adoption of the concept to some other dune forms e g barchans the relationship between observed dune complexity and age from field data complicates previous suggestions that dune patterning may be purely a function of development time parallel to this lies the need to improve interpretation of the results of dune geochronological studies a suggestion is offered which aims to test the statistical significance of dune accumulation time series by comparison with a modelled system with unchanging external forcing despite the initial promise of linear dune records as a revolutionary source of palaeoenvironmental information in drylands the outcomes to date have been coarse although still valuable in resolution perhaps the most valuable realization has been that geomorphological understanding of these widespread landforms is incomplete

porphyrins in upper jurassic source rocks and correlations with other source rock descriptors the porphyrin content and composition in the extractable organic matter has been analysed in 13 kimmeridge clay source rocks spread from the north to the south of the norwegian continental shelf the samples are predominantly immature early mature the distribution of nickel and vanadyl porphyrins within the samples is markedly different effects of the thermal maturity on the composition of porphyrins is evaluated and compared with biomarker parameters based on sterane and hopane ratios maturity is modelled using partial least squares pls multivariate analysis with t max as a maturity indicator porphyrin parameters based on the total carbon number distribution of dpep and etio series from the mass spectral data of the nickel and vanadyl porphyrin fractions effectively describe the t max of the samples with a better correlation than aliphatic biomarker ratios selected porphyrin and biomarker ratios were used for principal component analysis pca modelling and found to describe two types of variation that may be indicative of the prevailing depositional redox conditions

iron porphyrins in the permian kupferschiefer of the lower rhine basin n w germany immature samples of the permian kupferschiefer from the lower rhine basin in n w germany were analysed for tetrapyrrole pigment type and abundance the sediment thought to have been deposited in a marine regime with enhanced salinity was found to contain high concentrations of metalloporphyrins the porphyrins are complexed to nickel ni and oxovanadium v 0 but high abundances of iron fe porphyrins were also detected using uv visible spectroscopy and mass spectrometry the presence in the latter of series of aetioporphyrins cycloalkanoporphyrins di cycloalkanoporphyrins and benz cycloalkanoporphyrins was confirmed by accurate mass measurements hplc co injection of deoxophylloerythroetioporphyrin c32 dpep with the demetallated iron porphyrins indicated its presence in the sediment as an iron complex the study provides the first evidence for the occurrence of fe porphyrins in geological samples other than coals and lignites and reports the highest concentrations in sedimentary organic matter to date

origins of etioporphyrins in sediments evidence from stable carbon isotopes abstract in samples of the julia creek and condor oil shales australia albian and early tertiary respectively etioporphyrin iii is significantly depleted in 13 c 4 relative to porphyrins derived from chlorophylls this isotopic difference suggests a large contribution from some independent source the haem group found in cytochromes derived from microbial sources is the most likely candidate

the henryville bed of the new albany shale i preliminary characterization of the nickel and vanadyl porphyrins in the bitumen the nickel vanadium ni ii porphyrin and vo ii porphyrin concentrations in the bitumen of an organic rich sample of the henryville bed of the new albany shale mississippian devonian indiana u s a were determined the bitumen contains 1776 g nickel g and 1550 g vanadium g bitumen the porphyrin concentrations of 9900 g g and 9100 g g respectively are higher than those reported in most source rock bitumens or crude oils the similar abundances of ni ii and vo ii porphyrins indicates a depositional environment for this sample that is transitional between strongly anoxic vo ii porphyrins dominant and less anoxic in which ni ii porphyrins dominate the ni ii and vo ii porphyrins in the bitumen occur as etioporphyrin etio deoxophylloerythroetioporphyrin dpep and tetrahydrobenzo dpep thbd species in the order of abundance etio dpep thbd for ni ii and dpep etio thbd for vo ii porphyrins the dpep etio ratios of 1 4 for the vo ii series and 0 91 for the ni ii series and a vitrinite reflectance of 0 5 0 6 are consistent with the organic matter in the new albany shale being of intermediate maturity the carbon number distributions of the etio dpep and thbd porphyrins of the two metals are very similar this similarity and the fact that carbon numbers of both ni ii and vo ii porphyrins extend at least to c36 suggests that the ni ii and vo ii porphyrins have originated via similar geochemical pathways in the new albany shale the major pathway appears to be release of the porphyrins during kerogen catagenesis

a method for semi automated objective quantification of linear bedforms from multi scale digital elevation models the increasing availability of large detailed digital representations of the earth s surface demands the application of objective and quantitative analyses given recent advances in the understanding of the mechanisms of formation of linear bedform features from a range of environments objective measurement of their wavelength orientation crest and trough positions height and asymmetry is highly desirable these parameters are also of use when determining observation based parameters for use in many applications such as numerical modelling surface classification and sediment transport pathway analysis here we 1 adapt and extend extant techniques to provide a suite of semi automatic tools which calculate crest orientation wavelength height asymmetry direction and asymmetry ratios of bedforms and then 2 undertake sensitivity tests on synthetic data increasingly complex seabeds and a very large scale 39 000 km2 aeolian dune system the automated results arecompared with traditional manually derived measurements at each stage this new approach successfully analyses different types of topographic data from aeolian and marine environments from a range of sources with tens of millions of data points being processed in a semi automated and objective manner within minutes rather than hours or days the results from these analyses show there is significant variability in all measurable parameters in what might otherwise be considered uniform bedform fields for example the dunes of the rub al khali on the arabian peninsula are shown to exhibit deviations in dimensions from global trends morphological and dune asymmetry analysis of the rub al khali suggests parts of the sand sea may be adjusting to a changed wind regime from that during their formation 100 to 10 ka bp

structural characterization by raman hyperspectral mapping of organic carbon in the 3 46 billion year old apex chert western australia abstract the 3 46 billion years old apex chert pilbara craton western australia is well known for hosting the oldest highly disputed microfossils on earth this rock has a complex history of thermal alteration that includes circulation of hydrothermal fluids lower greenschist facies regional metamorphism and post metamorphic weathering by meteoric fluids carbonaceous material occurs in the sedimentary stratiform part of the chert as well as the underlying intruding hydrothermal black chert veins in order to identify a least altered remnant of early life it is necessary to develop a method that enables rapid evaluation of cm structural order on a small spatial scale here we present the detailed characterization of cm in the apex chert by raman hyperspectral mapping it is shown that this approach gives better estimates of average raman band ratios than individual point analyses and it is demonstrated that significant differences in structure exist between cm in the stratiform part of the apex chert and cm in an underlying black chert vein the large raman map based datasets also reveal that significant mixing took place between these two end members cm s indicating that the apex chert has been thoroughly altered by hydrothermal fluid circulation at the brecciated intersection between the stratiform chert and the intrusive hydrothermal chert vein very poorly ordered cm was found that is not in line with lower greenschist facies regional metamorphism it is speculated here that this cm represents an organic fraction that was introduced or thoroughly altered by late stage meteoric fluids alternatively the ubiquitous presence of hematite in this sample caused a perturbation in the raman spectra of the cm leading to an artifact in the calculated raman based band ratios overall it can be concluded that the best preserved cm occurs in the stratiform parts of the apex chert while earlier discussions on organic microfossils in this rock often focused on parts of the chert that either represented the hydrothermal veins or the brecciated intersection between the veins and the stratiform part

dunes of the gran desierto sand sea sonora mexico the gran desierto sand sea contains dunes of crescentic and star form in simple compound and complex varieties the dunes have developed in bimodal to complex wind regimes of intermediate energy transitions from simple through compound to complex crescentic dunes are associated with regional changes in wind regimes growth of large star dunes takes place by merging of smaller crescentic and reversing dunes from southerly directions and reworking of sand by northerly and westerly winds although wind regimes appear to be the major control of dune morphology in this sand sea there is a close correlation between the spacing of simple crescentic dunes and the grain size of the coarse 20th percentile

distribution of aliphatic amines in co cv and ck carbonaceous chondrites and relation to mineralogy and processing history the analysis of water soluble organic compounds in meteorites provides valuable insights into the prebiotic synthesis of organic matter and the processes that occurred during the formation of the solar system we investigated the concentration of aliphatic monoamines present in the hot acid water extracts of the unaltered antarctic carbonaceous chondrites dom 08006 co3 and mil 05013 co3 and the thermally altered meteorites allende cv3 lap 02206 cv3 gra 06101 cv3 alh 85002 ck4 and eet 92002 ck5 we have also reviewed and assessed the petrologic characteristics of the meteorites studied here to evaluate the effects of asteroidal processing on the abundance and molecular distributions of monoamines the co3 cv3 ck4 and ck5 meteorites studied here contain total concentrations of amines ranging from 1 2 to 4 0 nmol g of meteorite these amounts are one to three orders of magnitude below those observed in carbonaceous chondrites from the ci cm and cr groups the low amine abundances for cv and ck chondrites may be related to their extensive degree of thermal metamorphism and or to their low original amine content although the co3 meteorites dom 08006 and mil 05013 do not show signs of thermal and aqueous alteration their monoamine contents are comparable to those observed in moderately extensively thermally altered cv3 ck4 and ck5 carbonaceous chondrites the low content of monoamines in pristine co carbonaceous chondrites suggests that the initial amounts and not asteroidal processes play a dominant role in the content of monoamines in carbonaceous chondrites the primary monoamines methylamine ethylamine and n propylamine constitute the most abundant amines in the co3 cv3 ck4 and ck5 meteorites studied here contrary to the predominance of n amino acid isomers in co3 and thermally altered meteorites there appears to be no preference for the larger n amines

the occurrence of high molecular weight humic material in recent organic rich sediment from the namibian shelf abstract the molecular size distribution of humic substances has been investigated in two recent sediment samples of different ages taken from a single core sample collected off walvis bay south west africa extractable humic acids were found to be by far the major form of organic carbon in both sediments the near surface younger sample containing predominantly high molecular weight 100 000 molecular weight humic acids and little fulvic acids whilst the deeper older sample contained relatively less humic acid and relatively more fulvic acid of a range of molecular weights a significant age difference was found between the 300 000 molecular weight and the the data suggest that in this rapidly accumulating organic rich sediment the first step en route from the planktonic matter to the humic complexes is direct and rapid incorporation of the biogenic material into high molecular weight humic acids

development and steady states of transverse dunes a numerical analysis of dune pattern coarsening and giant dunes we investigate the development and steady states of transverse dunes for ranges of flow depths and velocities using a cellular automaton dune model subsequent to the initial bed instability dune pattern coarsening is driven by bed form interactions collisions lead to two types of coalescence associated with upstream or downstream dominant dunes in addition a single collision ejection mechanism enhances the exchange of mass between two adjacent bed forms throughpassing dunes the power law increases in wavelength and amplitude exhibit the same exponents which are independent of flow properties contrary to the wavelength dune height is limited not only by flow depth but also by the strength of the flow superimposed bed forms may propagate and continuously destabilize the largest dunes we identify three classes of steady state transverse dune fields according to the periodicity in crest to crest spacing and the mechanism of size limitation in all cases the steady state is reached and maintained through the dynamic equilibrium between flow strength and dune aspect ratio in the limit of low flow strength where it becomes the primary factor of size limitation the bed shear stress in the dune trough regions is close to its critical value for motion inception comparisons with natural dune fields suggest that many of them may have reached a steady state finally we infer that the sedimentary patterns in the model may be used to bring new constraints on the development of modern and ancient dune fields