evidence for cavity dwelling microbial life in 3 22 ga tidal deposits cavities are considered plausible and favorable habitats for life on early earth in such microenvironments organisms may have found an adequate protection against the intense ultraviolet radiation that characterized the archean ozone free atmosphere however while there is clear evidence that benthic life existed in the paleoarchean the oldest traces of cavity dwelling microbes coelobionts have been found in neoarchean rocks here we present the results of a detailed investigation of early silicified cavities occurring in the oldest well preserved siliciclastic tidal deposits the 3 22 ga moodies group of the barberton greenstone belt south africa downward growing microstromatolitic columns composed of kerogenous laminae are commonly present in planar bedding parallel now silica filled cavities that formed in sediments of the peritidal zone in situ 13cpdb pdb peedee belemnite measurements of the kerogen range from 32 3 to 21 3 and are consistent with a biogenic origin scanning electron microscopy analysis of the silicified cavities shows well preserved chains of cell sized molds that are interpreted as fossil filamentous microorganisms the geological context the morphology of the microstromatolites the 13c composition of the kerogen and the presence of microfossils all suggest that a microbial community inhabited the cavities these results extend the geological record of coelobionts by 500 m y supporting the view that cavities were among the first ecological niches to have been occupied by early microorganisms

salt weathering simulation using a single immersion technique samples of concrete were subjected in an environmental cabinet to six different diurnal cycles of temperature and humidity change representative of desert surface conditions in the presence of a range of saturated salt solutions the samples were not subjected to repeated immersion or continuous partial immersion as has been the case in most previous experiments breakdown did occur nonetheless the two most effective cycles were one from egypt with a very high daytime maximum and one from the negev with high nocturnal humidity conditions cycles with relatively modest temperature and humidity cycles were ineffective in causing debris liberation

on the nonuniqueness of sediment yield at the catchment scale the effects of soil antecedent conditions and surface shield the understanding of reasons leading to nonuniqueness of soil erosion susceptibility is still inadequate yet indispensable for establishing general relations between runoff volume and sediment yield to obtain relevant insights we performed a series of numerical simulations with a detailed hydrodynamic model using synthetic storms of varying intensity duration and lag time between events as representations of different hydrologic response conditions in a zero order catchment the design targeted to generate surface flow and perturb soil substrate by a first rainfall event creating a set of initial conditions in terms of flow and deposited sediment prior to the onset of a subsequent rainfall event due to the differential effect of re detachment and re entrainment processes on soil particles of varying sizes the deposited sediment mass formed shielding layer one of the essential results is that unless the initial condition of flow and sediment is identical the same volume of runoff can generate different total sediment yields and their variation can reach up to 200 the effect is attributed to two major conflicting effects exerted by the deposited initialization soil antecedent condition sediment mass erosion enhancement because of supply of highly erodible sediment and erosion impediment because of constrain on the availability of lighter particles by heavier sediment consistently with this inference long term simulations with continuous rainfall show that a peculiar feature of sediment yield series is the existence of maximum before the steady state is reached the two characteristic time scales the time to peak and the time to steady state separate three characteristic periods that correspond to flow limited source limited and steady state regimes these time scales are log linearly and negatively related to the spatially averaged shields parameter the smaller the rainfall input and the heavier a given particle is the larger the two scales are the results provide insights on how the existence of shield operates on erosion processes possibly implying that accurate short term predictions of geomorphic events from headwater areas may never become a tractable problem the latter would require a detailed spatial characterization of particle size distribution prior to precipitation events

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

diversity of iron and silica precipitation by microbial mats in hydrothermal waters iceland implications for precambrian iron formations direct examination of microbial mats from icelandic hot springs with transmission electron microscopy and energy dispersive x ray spectroscopy revealed a consortium of bacterial cells in varying stages of mineralization differences in observed mineralogy largelyreflectdifferencesinthechemistryofthehydrothermalwaters silica richspheroids formedepicellularlyoncellwallsandsurroundingsheathsandcapsulesofmicroorganisms and insomecases intracellularlywhenpresumablythecell s hadlysed commonly these precipitateswereobservedcoalescingtoformamatrixofamorphoussilicathatcompletely encapsulated the cells and or replaced their cytoplasmic material however in other cells the precipitates were composed of amorphous granules made exclusively of iron and silica inapproximatelyequalproportions atonelocality thebacteriaformedseveralepicellular iron minerals ranging from iron mineralized capsules tofine grained spheroids of amorphous ferric hydroxide and acicular aggregates of goethite the complete encrustation of bacterial cells by silica iron or a combination of both may greatly enhance their preservation potential such that these mineralized microorganisms may conceivably represent future microfossils thus we may be witnessing contemporaneous biomineralization processes that are similar to those of the geologic past particularly with regard to the origin of some precambrian banded iron formations

the martian subsurface as a potential window into the origin of life few traces of earth s geologic record are preserved from the time of life s emergence over 3 800 million years ago consequently what little we understand about abiogenesis the origin of life on earth is based primarily on laboratory experiments and theory the best geological lens for understanding early earth might actually come from mars a planet with a crust that s overall far more ancient than our own on earth surface sedimentary environments are thought to best preserve evidence of ancient life but this is mostly because our planet has been dominated by high photosynthetic biomass production at the surface for the last 2 500 million years or more by the time oxygenic photosynthesis evolved on earth mars had been a hyperarid frozen desert with a surface bombarded by high energy solar and cosmic radiation for more than a billion years and as a result photosynthetic surface life may never have occurred on mars therefore one must question whether searching for evidence of life in martian surface sediments is the best strategy this perspective explores the possibility that the abundant hydrothermal environments on mars might provide more valuable insights into life s origins ancient hydrothermal deposits formed in the martian subsurface may be the best targets for finding evidence for ancient life on mars and clues about the origin of life on earth

weathering rates of sandstone in a semi arid environment hunter valley australia the rate of sandstone weathering in the semi arid climate of the hunter valley new south wales australia has been estimated from observations of gravestone weathering in the area the gravestone data points to two distinct stages in the weathering process the first stage covering the first century of exposure is characterised by a relatively low recession rate of 0 5 mm 100 years this is followed by a second stage in which the rate of weathering increases sharply to ca 2 5 mm 100 years the non linear nature of the weathering trends over time suggests that during the first century of exposure structural changes took place within the sandstone material which lay the foundation for accelerated weathering after further exposure laboratory trials were also conducted to identify the effectiveness of different weathering processes in the decay of sandstone in this region of the four processes examined only the freeze thaw cycle produced a significant degree of mass loss and is therefore most likely a strong contributor to the weathering of sandstone in this region

laboratory simulation of the wick effect in salt weathering of rock the wick effect is the upward migration of saline solutions into rocks and their subsequent crystallization lower carboniferous sandstone blocks of rectangular shape have been subjected to this process in the laboratory using a range of salt types a range of salt concentrations and various mixtures of salts some treatments produced severe disintegration notably sodium carbonate and a mixture of sodium carbonate with magnesium sulphate whereas other salts including sodium chloride and gypsum were much less effective the debris produced by this experimental salt weathering included appreciable quantities of silt sized material which were analysed with a laser granulometer such material could provide a source for desert loess

magnetic gradients in sedimentary basins examples from the western canada sedimentary basin mapping very weak and subtle magnetic anomalies associated with sedimentary formations such as those within the western canada sedimentary basin wcsb called for the development of an ultrahigh resolution three component magnetic gradient system scintrex survey and exploration technologies 3d gm was an attempt at developing a high precision helicopter towed three component magnetic gradient bird combining the benefits of measured gradients with low sensor ground clearance fugro airborne surveys heli triax system is a redesign of the 3d gm platform addressing some hardware and other limitations of the older system both platforms were used to fly a combined total of eight test surveys and 15 proprietary surveys within the wcsb

making loess sized quartz silt data from laboratory simulations and implications for sediment transport pathways and the formation of desert loess deposits associated with the sahara abstract results from a series of laboratory simulations designed to investigate quartz silt generation by a number of geomorphic mechanisms are reviewed these findings are then used to discuss potential sediment pathways involved in the formation of desert loess deposits and a pathway is presented to show a proposed sequence of events involved in the formation of the loess deposits associated with the sahara the results indicate that both fluvial and aeolian systems can be very effective at producing quartz silt it is suggested that fluvial systems within hot desert environments may play a central role in both the production and distribution of loessic silt first the highly energetic but periodic fluvial regimes associated with arid and semi arid environments may be responsible for considerable quantities of particle comminution second the intermittent nature of these systems will help maintain geomorphologically active surfaces from which silt sized material can be easily deflated as well as fluvial comminution a range of weathering mechanisms and aeolian abrasion may also be responsible for the generation of silts in desert loess consequently silt sources and mechanisms of silt generation are likely to be much more diverse for desert loess than those associated with glacial loess

genetic modelling for banded iron formation of the hamersley group pilbara craton western australia abstract the banded iron formation bif of the hamersley group pilbara craton western australia particularly from the well studied dales gorge member is unique in its lateral stratigraphic and petrological continuity throughout an area exceeding 60 000 km 2 enabling reasonable estimates for the annual input of components to the depository in the model of this paper varying supply of materials for the medley of mesoband types particularly of iron and silica in the oxide bif can be accommodated by the interaction of two major oceanic supply systems 1 surface currents and 2 convective upwelling from mid oceanic ridge mor or hot spot activity both modified by varied input of pyrochastic material 1 the surface currents were saturated in silica and carried minimal iron due to photic precipitation but were periodically recharged by storm mixing precipitation from them gave rise to the banded chert rich horizons including the varves whose regular and finely laminated iron silica distribution resulted from seasonal meteorological influences 2 precipitation from convection driven upwelling of high iron solution from mor or hot spot activity periodically overwhelmed the delicate seasonal patterns of 1 to produce the iron dominated mesobands a wide range of intermediate mesoband types resulted where the deep water supply was modified by varied mor activity or by partial blocking of upwelling waters by surface currents such as by the present el nino during these periods of oxide dominated bif silica was deposited from saturated solution mainly by evaporative concentration and iron by oxidation due to photolysis and photosynthetically produced oxygen superimposed on these supply differences was the varying effect of fine aluminous ash from dominantly northern distal volcanic sources changing the meteorological and depositional conditions occasional input of extremely fi ash during bif precipitation produced mesoband cm scale variations involving increased carbonate silicate precipitation sustained volcanic periods resulted in s macroband deposition chert carbonate silicate bif with shale gradually returning to the dominant hematite magnetite chert bif as the volcanic input waned during volcanic periods the normally high capacity of sunlight to precipitate ferric iron directly by photolytic oxidation of ferrous iron and by photosynthetic production of oxygen was modified by turbidity in the atmosphere aerosols and dust and in the water colloids from reactive ash s surface precipitated ferric hydroxyoxide redissolved in the presence of decaying organic matter in the subphotic zone augmenting the iron content of the zone precursor ferrous carbonates and silicates were precipitated when the iron concentration of this sub photic zone exceeded their respective solubilities during volcanism the increased availability of nutrients particularly phosphorus to surface waters increased the organic contribution despite lower light values leading to an almost total absence of ferric iron oxides in the s macrobands i e no magnetite or hematite cooling of warm silica saturated sea water during these periods of olcanic winter increased the ratio of precipitation of silica to iron which however was still controlled by seasonal conditions intermediate concentrations of organic matter insufficient to totally convert the ferric compounds either during precipitation or diagenesis resulted in overgrowths of magnetite on hematite and eventually in the substantial conversion of hematite to magnetite where higher temperatures were achieved during low grade regional metamorphism changes in sea level to explain facies changes in bif are not required in this model but are not excluded the preferred conditions are for a very low oxygen to anoxic atmosphere a much higher level of mor activity than at present the presence of photosynthetic plankton the absence of si silica secreting organisms and a deep sea water temperature higher than 20 c however none of these conditions is essential to the model a narrow carbonate bank is postulated for part of the fortescue river valley area during marra mamba iron formation times basal hamersley group with bif precipitation on either side the reef is postulated to have grown northward becoming a major shallow water carbonate platform on the pilbara continent during upper marra mamba iron formation and wittenoom dolomite times but ceased to play an important role in subsequent periods

scaling and elevation in river networks the analysis of large river networks obtained from digital elevation models has given insight into the variation of channel slope with scale investigators have recently suggested that channel slopes are self similar with magnitude or area as a scaling parameter our data indicates otherwise in particular the variance of channel slope is larger than that predicted by simple self similarity this suggests multiscaling the scaling exponent for the standard deviation is approximately half the corresponding exponent in the relationship of the slope mean to magnitude or area a model for channel slopes based on a point process of elevation drops along the channel is presented the model reproduces observed multiscaling properties when the density of elevation increments is related to area or magnitude as a

the interaction between armouring and particle weathering for eroding landscapes the interaction between particle weathering and surface armouring and its effect on erosion has been investigated the effect of soil armouring is to decrease sediment transport with time by preferentially stripping away fine particles on the other hand the effect of weathering which breaks down the particles in the armour is generally believed to increase erosion by extending an existing armouring model armour and using a variety of published weathering mechanisms this interaction has been explored the model predicts that while this is generally true in some cases erosion can be decreased by weathering when the particles generated by weathering were approximately of equal diameter erosion increased while armouring decreased when weathering produced very fine particles by spalling erosion increased and armouring also increased when weathering produced a range of particles from fine to coarse the armour layer broke down and erosion decreased relative to the no weathering case this latter decrease in erosion was due to the high entrainment of coarser transportable materials from the bed decreasing the sediment transport capacity of the flow in these studies clear regimes could be identified where erosion was limited by either the energy of the flow alone i e transport limited or the rate of weathering weathering limited however for some mechanisms there was an interaction between the two which we called weathering transport limited copyright 2006 john wiley sons ltd

modelling landscape evolution geomorphology is currently in a period of resurgence as we seek to explain the diversity origins and dynamics of terrain on the earth and other planets in an era of increased environmental awareness yet there is a great deal we still do not know about the physics and chemistry of the processes that weaken rock and transport mass across a planet s surface discovering and refining the relevant geomorphic transport functions requires a combination of careful field measurements lab experiments and use of longer term natural experiments to test current theory and develop new understandings landscape evolution models have an important role to play in sharpening our thinking guiding us toward the right observables and mapping out the logical consequences of transport laws both alone and in combination with other salient processes improved quantitative characterization of terrain and process and an ever improving theory that describes the continual modification of topography by the many and varied processes that shape it together with improved observation and qualitative and quantitative modelling of geology vegetation and erosion processes will provide insights into the mechanisms that control catchment form and function this paper reviews landscape theory in the form of numerical models of drainage basin evolution and the current knowledge gaps and future computing challenges that exist copyright 2010 john wiley sons ltd

aeromagnetic surveying using a simulated unmanned aircraft system carleton university and sander geophysics are developing an unmanned aircraft system uas for aeromagnetic surveying as an early indication of the expected performance of the unmanned aircraft system a simulated unmanned aircraft system suas was built the simulated unmanned aircraft system is a t shaped structure configured as a horizontal gradiometer with two cesium magnetometers spaced 4 67 m apart which is the same sensor geometry as planned for the unmanned aircraft system the simulated unmanned aircraft system is flown suspended beneath a helicopter an 8 5 km 2 area in the central metasedimentary belt of the grenville province near plevna ontario canada was surveyed with the simulated unmanned aircraft system suspended 50 m above ground the survey site was chosen on the basis of its complex geological structure the total magnetic intensity tmi data recorded were compared to that obtained during a conventional fixed wing survey and a ground survey transverse magneto gradiometric data were also recorded by the simulated unmanned aircraft system the simulated unmanned aircraft system total magnetic intensity data have a higher resolution than the conventional fixed wing data and were found to have a similar resolution to that of the ground survey data the advantages of surveying with the simulated unmanned aircraft system were 1 the acquisition of a detailed data set free of gaps in coverage at a low altitude above the terrain and 2 substantial saving of time and effort in the survey site the 4 67 m simulated unmanned aircraft system gradiometer measured the transverse magnetic gradient reliably up to an altitude of 150 m above ground

geochemical characteristics of archean cherts and other sedimentary rocks in the pilbara block western australia evidence for archean seawater enriched in hydrothermally derived iron and silica abstract geochemical and mineralogical characteristics of archean sedimentary rocks such as cherts banded iron formations bifs shales and sandstones collected from the pilbara block western australia were studied lithologic features of various types of chert occurring within the pilbara supergroup are closely related to their chemical compositions red and brown bands of banded cherts generally show a higher fe 2 o 3 total iron as fe 2 o 3 concentration than do other cherts whereas grey greenish grey and pale yellowish grey cherts are characteristic of relatively higher concentrations of al and ti white cherts are generally composed almost exclusively of sio 2 geochemical characteristics of the cherts suggest that they were precipitated from hydrothermal solutions evidence for the hydrothermal origin includes 1 low mno fe 2 o 3 values 2 low concentrations of heavy metals 3 positive euanomalies 4 low co zn and ni zn values and 5 high concentrations of mn and fe in carbonates positive correlations between fe and heavy metals such as ni and zn imply the intermittent precipitation of fe oxides hydroxides along with these heavy metals in the ancient ocean cherts except for grey greenish grey and pale yellowish grey cherts are highly depleted in detrital materials this may have been caused by rapid precipitation of hydrothermally derived fe and si the archean pilbara ocean is believed to have been enriched in fe and si derived from hydrothermal activity

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

the weathering rates of some sandstone cliffs central weald england short term 1 30 months weathering rates were obtained for steep cliffs of cretaceous ardingly sandstone in southern england using a new photographic method mean rates for an exposed and a sheltered outcrop were 0 11 and 0 033 mm a 1 respectively significant p 0 1 positive correlations were obtained with illumination and algal biomass and a significant negative correlation p 0 05 with slope angle there was no correlation with grain size porosity or mean surface temperature highest weathering rates were observed on south and west facing exposed cliffs the results are discussed with reference to algal growth climate and wind direction

bacterial s layer preservation and rare arsenic antimony sulphide bioimmobilization in siliceous sediments from champagne pool hot spring waiotapu new zealand siliceous sinter loose sediments and suspended flocs in champagne pool an anoxic hot 75 c spring at waiotapu new zealand are composed of opaline silica and metal rich sulphides that contain many well preserved mineralized microbes detailed analysis by transmission electron microscopy and energy dispersive spectrometry has shown that bacterial cell wall and capsular material is preserved by the immobilization of high levels of as sb and s in the organic matrix calculation of the probable metal species in the spring water suggests that arsenic and antimony are present in solution as negative and neutrally charged sulphide or hydroxide complexes such as has 2 s 4 h 3 aso 3 and hsb 2 s 4 the early adsorption of these complexes onto reactive groups on the bacterial surface may be paramount in the excellent preservation of cell morphology as biomineralization progresses biomineral composition commonly becomes dominated by the precipitation of a supersaturated al rich amorphous silica phase biomineralization commonly preserves s layers an ordered mosaic of proteins on the outer surface of the cell wall these are the finest ultrastructure details thus far found in microbes preserved by hydrothermal mineralization and can be used as an aid to identify microfossils the s layers preserved here probably belong to clostridium thermohydrosulfuricum or desulfotomaculum nigrifacans

effects of rock fragments on soil erosion by water at different spatial scales a review this paper reviews the various effects of rock fragments on soil erosion by water since these effects are scale dependent they are investigated at three different nested spatial scales the microplot 4 10 6 100m2 the mesoplot 10 2 102 m2 and the macroplot 101 104 m2 for each scale the corresponding process mechanisms are discussed particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes at the mesoplot scale i e on interrill areas rock fragments at the soil surface can have negative as well as positive effects on sediment yield these ambivalent effects are conditioned by the type of fine earth porosity soil surface slope vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion at the microplot scale i e the soil surface area which is covered by a single rock fragment and at the macroplot scale i e upland areas where both interrill and rill erosion takes place rock fragments at the soil surface have a negative effect on sediment yield in these two scales rock fragments can thus be considered as natural soil surface stabilizers at the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function the scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses these findings have implications for erosion modelling and soil conservation

laboratory simulation of rock weathering by salt crystallization and hydration processes in hot arid environments the results of a series of experiments are reported in this paper which were designed to differentiate between the forces of crystal growth and hydration in salt weathering using a single salt hydrate system sodium sulphate five contrasting rock types and several diurnal temperature relative humidity cycles which permitted or inhibited these processes and simulated ground surface climates in hot arid environments it was shown that hydration of sodium sulphate is an effective mechanism of rock disintegration but that it is significantly less destructive than crystal growth pressure crystallization of thenardite na2so4 is in turn more effective in rock weathering than the crystal growth of mirabilite na2so4 10h2o in general rates of disintegration were most rapid where the diurnal temperature range was extreme and relative humidity lowest

defining biominerals and organominerals direct and indirect indicators of life abstract by introducing the new term organomineral to apply to minerals that are affected by organics mostly life related but not directly produced by living cells we hope to increase the accuracy of the terminology in present usage we believe that the term biomineral does not describe all mineral deposits precisely enough and offer case studies to support instances where the use of the new term organomineral is more appropriate we provide examples of some materials that are biominerals such as those in diatoms and human bones and which perform a functional purpose we then attempt to show that terminology can sometimes mislead investigators drive the direction and prejudice interpretations of scientific investigation this is achieved by presenting case studies of minerals that have been investigated as biominerals although they may not actually be directly controlled by biology for this reason we pay special attention to desert varnish hot spring siliceous deposits stromatolites and bacterial encrustations we go on to explain why we regard biominerals as direct indictors of life whereas organominerals should be treated as indirect indicators of life that require careful characterization to establish the origin of contained organics and whether these are biotic in origin how organic compounds are preserved and transformed in sedimentary environments and in the mineral matrix is as highly relevant to the study of modern earth environments as it is in the search for the oldest evidence of life in the terrestrial rock record it is also important to many disciplines such as microbiology and archaeology and especially to scientists planning missions to look for evidence of life on other planetary surfaces

morphological adaptations of 3 22 ga old tufted microbial mats to archean coastal habitats moodies group barberton greenstone belt south africa microbial life was well established and widespread by the paleoarchean however the degree of evolutionary advancement such as microbial motility intra and inter species interactions phototropism or oxygenic photosynthesis by that time remains highly debated the 3 22 ga moodies group in the barberton greenstone belt bgb south africa are earth s oldest well preserved siliciclastic tidal deposits they exhibit a unique assemblage of microbial mats providing an excellent opportunity to decipher the morphological adaptations of microbial communities to different paleoenvironmental settings the fossil mats are preserved as kerogenous laminations 0 5 1 mm thick that can be traced laterally for 15 km in a 1000 m thick succession of fine to coarse grained tidal sandstones and conglomerates we here present a detailed stratigraphic and depositional facies analysis documenting the association of the three principal mat morphotypes with specific environmental settings 1 planar type in coastal floodplain 2 wavy type in intertidal and 3 tufted type in upper inter to supratidal facies all mat types indicate a flourishing phototrophic biota moreover the tufted morphology suggests an intricate level of coordinated growth commonly known from cyanobacterial mats in modern environments

frost action and hydration as rock weathering mechanisms on schist a laboratory study recently it has been proposed that stress generated by the adsorption of water to clay surfaces in argillaceous rocks may be an important agent of mechanical weathering in polar and alpine environments implying that long held views on the status of frost action in these areas may be in need of revision this study documents the response under controlled experimental conditions of aggregates of fresh and partlyweathered schist and fresh pre cut schist blocks to 500 accelerated 12 hour freeze thaw and hydration dehydration cycles aggregate samples subjected to freezing cycles produced the largest amounts of material in the less than 2 mm size range an average of 8 per cent and 16 per cent for the fresh and partly weathered aggregates respectively whereas humidity cycles above and below freezing yielded lesser amounts 3 per cent and 4 per cent respectively the fresh schist blocks were found to be highly resistant to both mechanisms only those experiencing freeze thaw oscillations produced measurable amounts of detritus although hydration effects were not as effective as frost action in causing particle size reduction in aggregates the two mechanisms may well reinforce one another in periglacial environments enhancing the ability of these areas to serve as source regions for loess

modeling weathering pathways and processes of the fragmentation of salt weathered quartz chlorite schist 1 the relationship between the rate of rock breakdown and environmental and geological factors must be understood in order to establish the conditions under which weathering limits erosion in this study qualitative and quantitative models of the rock fragmentation process are fitted to previously published data obtained from laboratory salt weathering trials of quartz chlorite schist weathering was modeled as a combination of 1 a fragmentation event that fragments the parent particle into a number of daughter particles while preserving mass and 2 a fracture probability that determines the probability that a fragmentation event will occur in a given time period we show that observations of the complex breakdown of salt weathered schist are consistent with model assumptions of a simple fracture geometry model and an increase in fracture probability with time for the fragmentation geometry the best fit to the experimental data was achieved by assuming that each fragmentation event involves splitting of the parent particle into two daughter fragments of equal volume for the fragmentation rate the data could best be described with a fracture probability and hence the weathering rate that increased linearly with time this paper shows that it is possible to use a physically based fragmentation model to infer the process of fragmentation for individual particles using a time evolving particle size distribution for the weathering rock fragments

field calibration of sediment flux dependent river incision 1 bed erosion and sediment transport are ubiquitous and linked processes in rivers erosion can either be modeled as a detachment limited function of the shear stress exerted by the flow on the bed or as a transport limited function of the sediment flux capacity of the flow these two models predict similar channel profiles when erosion rates are constant in space in time but starkly contrasting behavior in transient settings traditionally detachment limited models have been used for bedrock rivers whereas transport limited models have been used in alluvial settings in this study we demonstrate that rivers incising into a substrate of loose but very poorly sorted relict glacial sediment behave in a detachment limited manner we then develop a methodology by which to both test the appropriate incision model and constrain its form specifically we are able to tightly constrain how incision rates vary as a function of the ratio between sediment flux and sediment transport capacity in three rivers responding to deglaciation in the ladakh himalaya northwest india this represents the first field test of the so called tools and cover effect along individual rivers

ignimbrite as a substrate for endolithic life in the hyper arid atacama desert implications for the search for life on mars the hyper arid core of the atacama desert in chile is considered the driest and most life limited place on earth with few habitats capable of sustaining an active microbial ecosystem as such it is one of the best terrestrial analogues of the extreme arid conditions on mars and an ideal environment to explore survival and biological adaptation strategies as the environment becomes increasingly dry here we show that weakly welded rhyolitic ignimbrites in this desert are abundantly colonized by endolithic cyanobacteria and associated heterotrophic bacteria we propose that the porous ignimbrite interior provides protection from damaging uv radiation and excessive levels of visible light rock porosity also favors cell hydration through water retention after scarce rainfall events even when the surrounding environment remains stubbornly dry this is the first known example of an endolithic microbial community colonizing ignimbrite rocks in an extremely dry environment the existence of a habitat capable of supporting abundant phototrophic and heterotrophic communities in an environment that precludes most life forms suggests that if similar deposits are found on mars these should be considered important targets in the search for life indeed ignimbrite rocks have been tentatively identified in gale crater the landing site of the mars science laboratory msl mission and could be directly analyzed by its rover curiosity

laboratory simulation of the salt weathering of schist ii fragmentation of fine schist particles recent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data and in particular data describing the size distribution of the weathered rock fragments to enable future development of rock breakdown models for use in landscape evolution and soil production models laboratory work was undertaken to extend existing schist salt weathering fragmentation studies to include an examination of the breakdown of sub millimetre quartz chlorite schist particles in a seasonally wet tropical climate laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution the results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown the fragmentation of the schist is characterized by splitting of the larger fragments into mid sized product with finer material produced possibly from the breakdown of mid sized fragments when weathering is more advanced salinity the salt addition method and temperature were all found to affect weathering rates subtle differences in mineralogy also produce variations in weathering patterns and rates it is also shown that an increase in drying temperature leads to accelerated weathering rates however the geometry of the fracture process is not significantly affected copyright 2006 john wiley sons ltd

the silica cycle in the precambrian abstract whereas the modem silica cycle is heavily dependent on the biology of silica secreting organisms such as the diatoms the precambrian silica cycle was dominated by inorganic reactions among dissolved silica clay and zeolite minerals and organic matter there is no evidence for deposition of a layered amorphous silica but abundant evidence for diagenetic silicification in the neoproterozoic the time period chosen for this analysis the influx of silica to the neoproterozoic ocean would have been governed as today by the balance among tectonism weathering and hydrothermal input the evidence of neoproterozoic rocks favors tectonic and weathering regimes not very dissimilar to those of the early phanerozoic and hydrothermal inputs significantly altered at certain periods one flux would have been very different the present diffusional influx of silica from interstitial waters into the oceans would have been altered to an efflux from the oceans to interstitial waters reactions of dissolved silica with inorganic phases would have controlled silica concentrations at a level of about 60 ppm this figure is based on experimental determinations of solubility and silica sorption on clay minerals and zeolites as silica in interstitial waters was lowered by opal ct precipitation a diffusional efflux from the ocean into the sediment was set up silicification would have started in early diagenesis as opal ct precipitated from interstitial waters diffusion of silica from overlying seawater declined as the sediment was buried a few hundred meters and the diffusion path lengthened during this still relatively shallow burial silicification continued but this time powered by hydrologie transport of dissolved silica from coastal plain sediments during transgressions and regressions thus the major removal of silica from the neoproterozoic ocean took place by diagenetic reactions

earliest microbially mediated pyrite oxidation in 3 4 billion year old sediments abstract pyrite fes2 oxidation in modern sedimentary environments is neither a purely chemical nor purely microbial process but it is significantly enhanced by the activity of microorganisms that use reduced forms of iron and sulphur in their metabolisms on the early earth where oxygen levels were thought to be

restricted shallow water sedimentation of early archean stromatolitic and evaporitic strata of the strelley pool chert pilbara block western australia abstract the 3 4 ga old strelley pool chert is a 25 m thick sedimentary unit near the top of the predominantly volcanic warrawoona group in greenstone belts of the eastern pilbara block western australia it is here subdivided into 5 members containing 13 lithofacies the basal member i is composed of quartzose sandstone deposited in a high energy wave or tide dominated shallow water system overlying this are members ii and iii which make up the bulk of the formation and were deposited in a low energy partially restricted hypersaline basin they record a predominantly regressive succesion of deposits including subaqueous laminite stromatolite and evaporite stromatolite carbonaceous laminite black and white banded chert evaporite and intraformational detrital units deposited under intermittently to predominantly exposed conditions and subaerially deposited windblown sand evaporite and evaporite solution layers members iv and v record the progradation of a volcaniclastic alluvial fringe the strelley pool chert represents an association of sedimentary environments directly comparable to that observed in modern low energy shallow marine carbonate evaporite systems such as along the trucial coast of the persian gulf and abundantly developed in phanerozoic carbonate platform deposits there is no evidence however that uniquely identifies the environment as having been marine deposition may have taken place in either a large hypersaline lake or a restricted marine basin evidence of predominantly low energy depositional conditions and a paucity of terrigenous detritus indicate that sedimentation was dominated by orthochemical and biological processes silicified evaporites including coarsely crystalline layers resembling messinian selenite are widespread and similar to younger evaporite deposits they clearly indicate that evaporites were common within shallow water archean sequences the presence of an assemblage of biogenic deposits including organic laminite stromatolites encrusting carbonaceous mats carbonaceous granules and oncolites deposited under conditions ranging from fully subaqueous to nearly subaerial and locally evaporitic points to the existence of an ecologically and probably biologically diverse microbial community 3 4 ga ago

theoretical constraints on oxygen and carbon dioxide concentrations in the precambrian atmosphere simple one dimensional climate models suggest that carbon dioxide concentrations during the archean must have been at least 100 1000 times the present level to keep the earth s surface temperature above freezing in the face of decreased solar luminosity such models provide only lower bounds on co2 so it is possible that co2 levels were substantially higher than this and that the archean climate was much warmer than today periods of extensive glaciation during the early and late proterozoic on the other hand indicate that the climate at these times was relatively cool to be consistent with climate models co2 partial pressures must have declined from approximately 0 03 to 0 3 bar around 2 5 ga ago to between 10 3 and 10 2 bar at 0 8 ga ago this steep decrease in carbon dioxide concentrations may be inconsistent with paleosol data which implies that pco2 did not change appreciably during that time oxygen was essentially absent from the earth s atmosphere and oceans prior to the emergence of a photosynthetic source probably during the late archean during the early proterozoic the atmosphere and surface ocean were apparently oxidizing while the deep ocean remained reducing an upper limit of 6 x 10 3 bar for po2 at this time can be derived by balancing the burial rate of organic carbon with the rate of oxidation of ferrous iron in the deep ocean the establishment of oxidizing conditions in the deep ocean marked by the disappearance of banded iron formations approximately 1 7 ga ago permitted atmospheric oxygen to climb to its present level o2 concentrations may have remained substantially lower than today however until well into the phanerozoic

the onset and early evolution of life the tension between co 2 dissolved at relatively high atmospheric pressure in the hadean ocean and h 2 generated as ocean water oxidized ferrous iron during convection in the oceanic crust was resolved by the onset of life we suggest that this chemosynthetic life emerged within hydrothermal mounds produced by alkaline solutions of moderate temperature in the relative safety of the deep ocean fl oor exothermic reaction between hydrothermal h 2 hcoo and ch 3 s with co 2 was catalyzed in inorganic membranes near the mound s surface by mackinawite fes nanocrysts and ready made clusters corresponding to the greigite fe 5 nis 8 structure such clusters were precursors to the active centers e g the c cluster fe 4 nis 5 of a metalloenzyme that today catalyzes acetate synthesis viz the bifunctional dehydrogenase enzyme acs codh the water and some of the acetate h 3 c coo produced in this way were exhaled into the ocean together as fl uid waste glycine h 3 n ch 2 coo and other amino acids as well as tiny quantities of rna generated in the same milieu were trapped within tiny iron sulfi de cavities energy from the acetate reaction augmented by a proton gradient operating through the membrane was spent polymerizing glycine and other amino acids into short peptides upon the phosphorylated mineral surface in turn these peptides sequestered and thereby protected the catalytically and electrochemically active pyrophosphate and iron nickel sulfi de clusters from dissolution or crystallization intervention of rna as a polymerizing agent for amino acids also led to an adventitious though crude process of regulating metabolism a process that was also to provide genetic information to offspring the fl uxes of energy and nutrient available in the hydrothermal mound commensurate with the requirements of life encouraged differentiation of the fi rst microbes into two separate domains at the bifurcation the bacteria were to specialize in acetogenesis and the archaea into methanogenesis representatives of both these domains left the mound by way of the ocean fl oor and crust to colonize the deep biosphere once life had emerged and evolved to the extent of being able to reduce nitrogen for use in peptides and nucleic acids light could have been used directly as an energy source for biosynthesis certain bacteria may have been able to do this where protected from hard uv by a thin coating of chemical sediment produced at a subaerial hot spring operating in an obducted and uplifted portion of the deep biosphere

soil landscape response to mid and late quaternary climate fluctuations based on numerical simulations abstract we use a numerical dynamic soil landscape model to study one aspect of the spatio temporal soil landscape evolution process the effect of climatic fluctuations on soil grading distribution in space and time in response to the interplay between physical weathering and surface erosion soil mineralogical fluxes we simulate a synthetic soil landscape system over the middle and late quaternary last 400 ka the results show that 1 soil landscape response to climate change is non linear and highly spatially variable even at hillslope scale and 2 soil landscape adjustment to climate change can lag tens of thousands of years and is both spatially and temporally variable we propose that the legacy of past climatic condition i e last glacial maximum in modern soil landscape systems vary considerably in space this implies that the spatiotemporal uniformity in which soil is typically described in earth system modeling and analysis e g carbon cycle grossly underestimates their actual complexity

an investigation into the relationship between salt weathering debris production and temperature an investigation using laboratory simulation has been made using air temperature data for tunisia antarctica and southwest england an experiment with a 50 cycle run produced results which showed significantly greater debris production in the antarctica and tunisian simulations than in the southwest england simulation using x ray analysts to determine salt penetration an inverse relationship between salt penetration and debris production was seen to exist this could be the result of evaporation in the tunisian simulation and rapid freezing in the antarctic simulation concentrating salts in the upper layers of the rock samples in the southwest england simulation no freezing and relatively high humidities allowed greater penetration thus distributing an equal input of salt over a greater area the author tentatively suggests the possible existence of a parabolic relationship between salt weathering and temperature

the long term stability of engineered landforms of the ranger uranium mine northern territory australia application of a catchment evolution model there is a need to assess the long term stability of engineered landforms associated with the rehabilitation of ranger uranium mine northern territory australia as it is a requirement that mill tailings must be contained for periods in excess of 1000 years the geomorphic model siberia is calibrated on hydrologic and erosion data collected by a combination of monitoring and rainfall simulation experiments on the waste rock dumps of ranger preliminary analysis of ranger s preferred above grade option suggests that erosion of the order of 7 to 8 m will occur on the structure in a period of 1000 years this depth of erosion may be sufficient to compromise the integrity of containment it is shown that siberia has significant advantages over steady state erosion models suggestions are made for the design that will enhance the stability of the structure and extend the structural life of the containment 1998 john wiley sons ltd

on the persistence of weathering abstract the term weathering has been in use for a very long time but it has come to mean different things to different people and hence as scientific short hand it no longer functions here we question the tenets underpinning the most common usage of the term and note that the climate process linkage implicit to the term is often missing and amounts to misdirection rather than climate as the primary driver behind specific weathering processes it is argued that rock properties constitute the dominant control further a case is made for reconsideration of our present bipartite mechanical chemical division of weathering processes and of the weathering processes currently deemed to be those that occur as process studies become evermore reductionist in nature so the functionality of the term comes more and more into question the linkage between process and landform the scaling up attribute is seen as a current weakness and one that will become more confusing as reductionist approaches continue as a way forward it is suggested that weathering stripped of specific preconceived notions of specific processes be envisaged as a function of energy transfer and be investigated in that light identification of new processes as well as restructuring of known processes particularly when considering weathering on other planets is a potential outcome of such an approach with a process foundation rooted in energy transfer rock decay provides a better umbrella term and liberates researchers from the inescapable conceptual baggage implicit to the term weathering

the effects of sediment transport weathering and aeolian mechanisms on soil evolution aeolian derived soils are found throughout the world soil evolution processes in aeolian dominated landscapes differ from processes in bedrock weathering landscapes by a number of key aspects including the lack of 1 soil production depth dependency 2 surface armoring and 3 grain size self organization in the soil profile we use here a soil evolution model marm5d to study the differences between aeolian and bedrock weathering dominated landscapes by analyzing soil evolution on a hillslope under various aeolian and bedrock soil supply settings subject to fluvial and diffusive sediment transport the model simulates spatial and temporal variation in soil particle size distribution psd and profile depth for each grid cell on the landscape as a function of physical weathering aeolian deposition and diffusive and fluvial sediment transport our results indicate that surface armoring plays a major role in soil evolution under bedrock weathering dominated conditions armoring reduces soil erosion and in conjunction with depth dependent soil production leads to steady state soil grading and depth and a relatively uniform soil distribution in contrast aeolian dominated landscapes tend to have considerable spatial variability in soil depth and psd our results also indicate that in contrast with diffusive transport which is assumed to be psd independent fluvial sediment transport is strongly influenced by the soil production mechanism aeolian or bedrock weathering based on the results presented here we propose that aeolian dominated landscapes are more responsive to environmental changes e g climatic and anthropogenic compared with bedrock weathering landscapes we further propose that this sensitivity may help explain the patchy soil distribution that is often observed in aeolian dominated regions

quantifying biomineralization of zinc in the rio naracauli sardinia italy using a tracer injection and synoptic sampling abstract streams draining mined areas throughout the world commonly have high concentrations of zn because zn is not easily removed from stream water and because it can be toxic to aquatic organisms its presence is a persistent problem the discovery of biomineralization of zn bearing solids in the mine drainage of rio naracauli in sardinia italy provides insights into strategies for removing zn and improving water quality in streams affected by mine drainage until now the transport and attenuation of zn has not been quantified in this stream setting a continuous tracer injection experiment was conducted to quantify the biomineralization process and to identify the loading of constituents that causes a change from precipitation of hydrozincite zn5 co3 2 oh 6 in the upstream reach to precipitation of a zn silicate phase downstream based on the mass load calculations derived from the tracer experiment about 1 2 kg day of zn is sequestered in hydrozincite this biomineralization represents nearly 90 removal of zn other elements such as pb and cd also are sequestered either in the hydrozincite or in a separate phase that forms simultaneously in the lower 600 m of the stream where the zn silicate forms as much as 0 7 kg day zn are sequestered in this solid but additions of zn to the stream from groundwater discharge lead to an overall increase in load in that portion of the rio naracauli

the marm spatially distributed soil evolution model a computationally efficient modeling framework and analysis of hillslope soil surface organization 1 hillslope surface armouring and weathering processes have received little attention in geomorphologic and hydrologic models due to their complexity and the uncertainty associated with them their importance however in a wide range of spatial processes is well recognized a physically based armouring and weathering computer model armour has previously been used to successfully simulate the effect of these processes on erosion and soil grading at a hillslope scale this model is however computationally complex and cannot realistically be applied over large areas or over long periods of time a simplified process conceptualization approach is presented named marm which uses a novel approach of modeling physical processes using transition matrices which is orders of magnitude faster we describe in detail the modeling framework we calibrate and evaluate the model against armour simulations and show it matches armour for a range of conditions the computational efficiency of marm allowed us to easily examine time and space varying relationships between erosion and physical weathering rates at the hillslope scale for erosion dominated slopes the surface coarsens over time while for weathering domination the surface fines over time when erosion and weathering are comparable in scale a slope can be weathering dominated upslope where runoff and therefore erosion is low and armouring dominated downslope in all cases for a constant gradient slope the surface armour coarsens downslope as a result of a balance between erosion and weathering thus even for weathering dominated slopes the surface grading catena is dependent on armouring through the balance between weathering and armouring we also observed that for many slopes the surface initially armours but after some period of time space and rate dependent weathering begins to dominate and the surface subsequently fines depending on the relative magnitude of armouring and weathering the final equilibrium grading of the slope may be finer or coarser than the initial conditions the results demonstrate the complexity of the evolution of surface grading and the balance between the armouring and weathering processes they also point toward inherent organization of surface grading on the hillslope driven by erosion even for extremely high weathering rates the implications for natural landforms are discussed we also plot and quantify for the first time a log log relationship between surface grading contributing area and slope for a range of weathering rates the results show that this log log relationship is robust the log log scaling is constant in space and true even for extreme weathering rates this has potentially important implications for soil geomorphology it suggests that an analytical solution can be found for soil grading catena this might allow us to more easily map soil distribution as a function of topographic characteristics

quantifying and modeling post failure sediment yields from laboratory scale soil erosion and shallow landslide experiments with silty loess rainfall events on steep hillslopes can cause both soil erosion and shallow landslides these processes interact with each other and need to be studied in an integrated way to understand hillslope sediment yields the main aim of this research is to study post failure sediment yield following landslides that alter local slope gradients a laboratory flume under a rainfall simulator was used to quantify erosion and shallow landslides in fine grained silty loess soils the flume was divided into an upper and a lower section the slopes of which could be altered a total of 12 experiments were conducted on slopes ranging from 35 to 47 in the upper and 5 to 10 in the lower flume sections shallow landslides were triggered in four of the 12 experiments sediment and runoff were collected from the flume outlet every minute during landslides and every 10 min before and after landslides changes in the soil slope after landslides occurred were recorded results showed that peak sediment yields were related to landslide occurrence and proximity to the outlet post failure reduction in sediment yields was related to the evolution of the hillslope after slope failures a simple rule based soil redistribution model of runout distance was validated using the experimental results the water erosion prediction project wepp model was used to simulate runoff and soil erosion during pre and post failure rainfall events predicted runoff rates and sediment yields using wepp were in good agreement with those measured in both pre and post failure events indicating that the model can be used successfully as part of an integrated approach to modeling sediment yields in landslide prone landscapes

in situ silicification of an icelandic hot spring microbial mat implications for microfossil formation transmission electron microscopy and energy dispersive x ray analysis revealed that filamentous phototrophic bacteria resembling chlorojlexus aurantiacus underwent rapid silicification in an icelandic hot spring microbial mat the mineralization associated with the cells occurred both extracellularly within and on the external sheaths of the bacteria and intracellularly within the cytoplasm the exceptional preservation of the bacterial sheaths is due to the presence of distinct mineral nucleation sites this results in the production of silica casts of the bacteria which bear a striking resemblance to microbial remains in ancient microfossil assemblages rcsumc les analyses par microscopie clectronique i transmission et par 1 6nergie dispersive des rayons x ont rcvcl6 que les bactkries filamenteuses phototrophes ressemblant b chlorojlexus aurantiacus ont subi une silicification rapide au sein d un tapis microbien de source therrnale en islande la mineralisation associee aux cellules se presente sous forme extracellulaire b l interieur de et sur la membrane externe des bacteries et sous forrne intracellulaire i l interieur du cytoplasme la preservation exceptionnelle de la membrane des bacteries est due b la presence de sites de nucleation minerale disperses le resultat est la production des moulages siliceux des bactkries affichant une resemblance remarquable avec les vestiges microbiens d anciens assemblages microfossiles traduit par la raaction fossil evidence of the earth s earliest biosphere shows that complex communities of microorganisms were abundant and well distributed throughout the precambrian era among the richest beds of microbial fossils are those found in the gunflint iron formation north of lake superior in canada barghoorn and tyler 1965 the early archaean apex chert of australia schopf and packer 1987 schopf 1993 and the riphean section of the anabar uplift in russia sergeev 1993 all ranging in age from 0 8 to 3 5 ga the distribution and types of microorganisms preserved as cellularly intact microfossils are remarkably similar to those in modern microbial mats in which organic rich layers formed by cyanobacteria and or other types of filamentous bacteria alternate with layers that are comprised of detrital inorganic sediment and authigenic mineral precipitates morse and mackenzie 1990 these benthic microbial communities are considered to be analogous and possibly homologous with those that were preserved billions of years ago as stromato

mechanisms of loess sized quartz silt production and their relative effectiveness laboratory simulations the production of loess sized quartz silt is frequently ascribed to glacial grinding mechanisms in this study a series of laboratory simulations was set up the purpose of which was to demonstrate that a range of geomorphic mechanisms are capable of producing silt under laboratory conditions the geomorphic mechanisms investigated were aeolian abrasion fluvial comminution glacial grinding salt weathering and frost weathering the results confirmed that under laboratory conditions all of these mechanisms were capable of producing silt the relative effectiveness of these mechanisms at producing silt under laboratory conditions was then calculated in order to provide a starting point for a consideration of their potential effectiveness within the natural environment these results indicate that fluvial and aeolian activity are highly effective at producing quartz silt over short time periods in a dust storm of four days duration 287 g of silt could potentially be produced from every kilogram of sand entrained while fluvial comminution in a turbulent fluvial environment could potentially produce 900 g of silt from every kilogram of sand entrained within 32 h over longer periods of time the glacial grinding and weathering mechanisms represent more continuous and hence more effective silt producing mechanisms although it is realised that the relative importance of each silt producing mechanism will differ spatially and temporally due to differences in climate relief geology and geomorphic history the findings from this work do have implications for the genesis of loess deposits they demonstrate that glacial and cold weathering processes are not solely responsible for fine particle formation and that efficient silt producing mechanisms can operate within a variety of environments under suitable conditions weathering together with episodic contributions from aeolian and fluvial mechanisms could be responsible for a considerable proportion of global quartz silt production

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

mining soil databases for landscape scale patterns in the abundance and size distribution of hillslope rock fragments landscape scale variation in rock fragments on soil mantled hillslopes is poorly understood despite the potential importance of rock fragments in soil weathering and coarse sediment supply to river networks we explored the utility of soil survey databases for data mining with the goals of identifying landscape scale patterns in the abundance and size distribution of rock fragments diameter d 2 mm and potential controls on grain size production we focus on data from three regions the hawaiian islands and the sierra nevada and cascade mountains where elevation transects span a range of environmental conditions we selected pedons from pits dug on hillslopes with active soil production and transport for the 27 pedons selected we constructed depth averaged grain size distributions and calculated the mass fraction of rock fragments frf and the median rock fragment grain size d50rf we also categorized as bimodal size distributions with a clear breakpoint between fine and coarse modes several strong patterns emerge from the data we find rock fragments in 85 of the pedons primarily in distinct coarse modes within bimodal size distributions values of frf and d50rf are strongly correlated although the best fit power law scaling between frf and d50rf differs between the warmer hawaiian and colder sierra nevada and cascade mountain sites we also find a regional contrast in the variation in frf with elevation frf declines with elevation in hawaii but increases in the mainland sites although this contrast could be an artifact of variable lithology precipitation may influence many patterns in the data lower mean annual precipitation correlates with higher frf dominantly bimodal distributions and surface enrichment in the vertical distribution of rock fragments these observations may be useful in refining models of coarse sediment supply to rivers and suggest opportunities for future work to test mechanistic hypotheses for rock fragment production on soil mantled hillslopes copyright 2011 john wiley sons ltd

elucidating the geogenic and pedogenic pathways of formation of soils of peninsular india signatures of past landscape modifications abstract the soils of modified landforms of peninsular india present an opportunity to unearth soil and landscape evolution we explore the potential of vertical texture contrast vtc soils as signatures of past landscape modifications and associated soil formation in peninsular india we studied six vtc soils occurring on different geological formations for their morphology geochemistry and mineralogy in order to interpret the geogenic and pedogenic pathways of their formation the presence of a lithological discontinuity with sharp contrast in particle size in pedons p1 and p3 suggested that fluvial sedimentary layering led to their formation pedons p2 and p5 are examples of buried soils where basaltic alluvium of varying thickness is overlying the soils of granitic and gneissic complex origin these soils are potential proxies of landform changes attributable to paleo alluvial mass deposition possibly during the late pleistocene pedon p4 is a relict paleosol in which the presence of a ck horizon between the argillic bt and bc horizons indicates sedimentation of stratified rocks geogenic followed by clay illuviation pedogenic during the past wet climate the occurrence of smectite dominant shrink swell s w soil pedon p6 over the shale parent material suggests that the s w soil is from a transported alluvium of weathering deccan basalt our results demonstrate the usefulness of vtc soils in interpreting the climate shift driven soil landscape evolution in peninsular india and elsewhere

microbes in caves agents of calcite corrosion and precipitation abstract diverse biogenic and abiogenic processes produce calcite speleothems from a biogenic perspective cave microbes mediate a wide range of destructive and constructive processes that collectively influence the growth of calcite speleothems and their internal fabrics destructive processes include substrate breakdown by dissolution boring and residue micrite production whereas constructive processes include microbe calcification trapping and binding of detrital particles to substrates and microbial induced calcite precipitation biogenesis can be established from 1 the presence of mineralized microbes 2 fabrics such as stromatolite like structures that can be attributed to microbial activity and or 3 geochemical proxies carbon and oxygen isotopes lipid biomarkers considered indicative of microbe activity such criteria have for example been used to demonstrate microbial involvement in the formation of pool fingers stalactites stalagmites cave pisoliths and moonmilk nevertheless absolute proof of microbial biogenesis in calcitic speleothems is commonly difficult because taphonomic processes and or diagenetic processes commonly mask evidence of microbial activity the assumption that calcitic speleothems are abiogenic which has been tacitly assumed in many studies is dangerous as there is clear evidence that microbes thrive in most caves and can directly and indirectly influence calcite precipitation in many different ways

a physical explanation for an observed area slope elevation relationship for catchments with declining relief a general relationship between the contributing area slope and mean elevation of catchments with relief declining after a tectonic uplift event is presented this relationship is based on the continuity equation for runoff and erosion processes in the catchment the key hypothesis underlying this relationship is that as a catchment declines the nondimensionalized catchment approaches a constant form this hypothesis is verified for computer simulated catchments the area slope elevation relationship covers several cases catchments declining toward a peneplain catchments declining from a high slope dynamic equilibrium resulting from a high rate of tectonic uplift to a low slope one resulting from a lower rate of tectonic uplift and catchments declining from an elevated initial condition as for example in the decline of a mine spoil heap a previously published relationship between slope and area for catchments in dynamic equilibrium and based on runoff and erosion physics is shown to be a special case of this general relationship the new area slope elevation relationship is compared with data from simulated catchments and a field catchment it is thus shown that for declining catchments the area slope elevation relationship is a good predictor of catchment form for catchments with declining relief it is argued that the slope area elevation relationship is sufficient with the planiform drainage pattern to completely define the elevation properties of the catchment such as for instance the hypsometric curve

weathering of granitic rocks by chlorides effect of the nature of the solution on weathering morphology five granites from nw spain were subjected to two salt spray weathering tests under controlled atmospheric conditions granite samples were exposed to a sodium chloride solution in the first test and to a complex solution sea water in the second subsequent examination of the rocks by light and petrographic microscopy clearly demonstrated the development of different weathering morphologies in each test the distribution of dissolved ions in samples taken at different depths from the weathered surfaces at the end of the experiments and the changes in weight of the samples during the tests also differed in our opinion these results were determined by the nature of the solution used although sodium chloride is the predominant salt in sea water the presence of other ions modifies its solubility thereby varying the dynamics of mobility and precipitation and thus the weathering morphology that develops copyright 2003 john wiley sons ltd

a physical explanation of an observed link area slope relationship an observed log log linear relationship between channel slope and contributing area is explained by the erosional physics that lead to catchment form it is postulated that tectonic uplift is in balance with the fluvial erosion down wasting that dominates catchment erosion and it is shown that this relationship results in the observed log log linear relationship at dynamic equilibrium in addition it has been observed that there are deviations from this log log linear relationship near the catchment divide with observed slopes being lower than those predicted from the relationship this is explained by noting that for small areas fluvial erosion effects are dominated by soil creep and rain splash modeled by diffusive physics the area at which this deviation from log log linearity occurs is that point on the hillslope at which diffusive physics like soil creep and rain splash begin to dominate fluvial erosion these predictions are confirmed by numerical simulations using a catchment evolution model

laboratory simulation of the salt weathering of schist 1 weathering of schist blocks in a seasonally wet tropical environment data describing sediment generation focusing on the temporal evolution of size gradation are required for the prediction of long term landform evolution this paper presents such data for the salt weathering of a quartz chlorite schist obtained from the ranger uranium mine in northern australia rock fragment samples are subjected to three different climate regimes 1 a dry season climate 2 a wet season climate both based on observations at the ranger site and 3 an oven drying sequence designed to test the sensitivity of the weathering process by exposing the rocks to more extreme temperatures two mgso4 salt solutions are applied one being typical of wet season runoff and the other a more concentrated solution salt solution is applied daily in the wet season experiments and once only at the beginning of the dry season experiments results of the experiments reveal four stages of weathering the kinetics of each stage are described and related to the formation of sediment of different sizes wet season climate conditions are shown to produce greater moisture variability and lead to faster weathering rates however salt concentrations in the wet season are typically lower and so when climate is combined with observed salt concentrations the dry and wet season experiments weather at approximately equal rates finally small variations in rock properties were shown to have a large impact on weathering rates leading to the conclusion that rock weathering experiments need to be carefully designed if results are to be used to help predict weathering behaviour at the landscape scale copyright 2006 john wiley sons ltd

spherical prism magnetic effects by gauss legendre quadrature integration summary regional spherical coordinate observations of the earth s crustal magnetic field components are becoming increasingly available from shipborne airborne and satellite surveys in assessing the geological significance of these data theoretical anomalous magnetic fields from geologic models in spherical coordinates need to be evaluated this study explicitly develops the elegant gauss legendre quadrature formulation for numerically modelling the complete magnetic effects i e potential vector and tensor gradient fields of the spherical prism we also use these results to demonstrate the magnetic effects for the crustal prism and to investigate the crustal magnetic effects at satellite altitudes for a large region of the middle east centred on iran

the marm3d spatially distributed soil evolution model three dimensional model framework and analysis of hillslope and landform responses 1 we present a three dimensional landscape pedogenesis model marm3d matrices armour 3d which simulates soil evolution as a function of erosion and pedogenic processes the model simulates the discretized soil profile for points on a spatial grid the approach using transition matrices is computationally efficient and allows the simulation of large scale spatial coupling and long term soil evolution we study the effect of the depth dependent soil weathering rate i e the rate of soil particle breakdown and bedrock lowering rate i e the rate of conversion of bedrock to soil the difference in depth dependent weathering functions has a significant effect on the in profile soil properties through depth specifically particle size grading however the depth dependency has a relatively minor effect on the surface properties of the soil profile with all weathering functions generating very similar surface properties the surface properties were a function of the cumulative amount of weathering i e the integral of the weathering function over exhumation with finer surface grading for higher weathering rates soil thickness could be estimated without explicitly modeling soil thickness thickness was negatively correlated with surface median grain size as thickness decreases the surface grading coarsens this was driven by surface erosion where as surface grading coarsens erosion decreases and the soil deepens weathering and erosion interact to spatially organize the surface soil grading with a log log relationship between surface grading contributing area and local slope this relationship was independent of the weathering function this relationship might be useful for the spatial description of soil properties in digital soil mapping

a one dimensional model for simulating armouring and erosion on hillslopes 2 long term erosion and armouring predictions for two contrasting mine spoils this paper investigates the dynamics of soil armouring as a result of fluvial erosion for a non cohesive sandy gravel spoil from the ranger mine australia and a cohesive silt loam spoil from the northparkes mine australia using a model for hillslope soil armouring these long term predictions concentrate on the temporal and spatial changes of the spoil grading and erosion over 100 200 years for the flat cap regions 1 2 and steep batter edges 10 30 typically encountered on waste rock dumps the existence of a significant rock fragment fraction in the ranger spoil means that it armours readily while northparkes does not for ranger the waste rock showed reductions in 1 cumulative erosion of up to 81 from that obtained by extrapolating the initial erosion rate out 100 years and 2 the erosion year by more than 10 fold for northparkes reductions were less marked with the maximum reduction in erosion year being 37 after 200 years for ranger the reductions were greatest and fastest for intermediate gradient hillslopes for the steepest hillslopes the armouring decreased because the flow shear stresses were large enough to mobilize all material in the armour layer model uncertainty was assessed with probabilistic confidence limits demonstrating that these erodibility reductions were statistically significant a commonly used hillslope erosion model sediment flux 1 discharge m1 slope n1 was fitted to these predictions the erodibility 1 and m1 decreased with time which was consistent with our physical intuition about armouring at ranger the parameter m1 asymptoted to 1 5 1 6 while at northparkes it asymptoted to 1 2 1 3 at ranger transient spatial trends in armouring led to a short term 50 200 years in the future reduction in n1 to below zero under certain circumstances recovering to an asymptote of about 0 5 1 at northparkes n1 asymptoted to about 0 6 with no negative transients predicted the m1 and n1 parameters predicted for ranger were shown to be consistent with field data from a 10 year old armoured hillslope and consistent with published relationships between erodibility and rock content for natural hillslopes copyright 2007 john wiley sons ltd

an evaluation of an enhanced soil erosion and landscape evolution model a case study assessment of the former nabarlek uranium mine northern territory australia the assessment of post mining landscapes as case studies is an important part of the evaluation of current rehabilitation practices a necessary part of this assessment is to predict the surface stability of the landform using erosion and landform evolution modelling techniques in the short term erosion on a rehabilitated mine site can lead to increased sediment loads and transport of other mine related contaminants in downstream waterways it is well recognized that in many mine areas the erodibility of surface materials can and does vary this is a particularly significant issue on mine sites where the surface conditions may range from areas of undisturbed natural surface materials waste rock dumps constructed with materials exhumed from the sub surface and other areas that have a mix of waste rock and soil to enhance the growth of vegetation a further significant issue is that when the subsurface materials are exposed to surface conditions they can weather rapidly changing their erodibility this paper uses a new version of the siberia landscape evolution and soil erosion model to evaluate the former nabarlek uranium mine site in the northern territory australia this new version of siberia uses spatially variable erosion and hydrology parameters across the study domain to represent different erodibilities of surface materials thus allowing better representation of catchment heterogeneity the results demonstrate that the model predicts erosion rates similar to that of other modelled results and independent field data providing confidence in the model and its parameterization the tailings deposited in the mined out pit and capped with waste rock appear to be safely encapsulated for the modelled period copyright 2008 john wiley sons ltd and commonwealth of australia department of the environment and water resources supervising scientist

mathematical modeling of whole landscape evolution abstract the mathematical modeling of landform evolution consists of two components the processes represented i e considered dominant in the model and the typically computer model representation of these processes this review discusses the current debates surrounding processes represented in landform evolution the potential impact on both evolving landforms and computer model structure is discussed issues specifically discussed include a the fundamental nature of mass conservation and the role of detachment and transport limited processes in mass conservation equations b the interaction between detachment and transport limitation in channels c the role of hillslope erosion and soil properties and their interaction with channel processes d the interactions with tectonics when applying these models at large scale e depositional structures and implications for paleo climatic interpretation f engineering applications of these models and g numerical issues in the computer imp

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

a one dimensional model for simulating armouring and erosion on hillslopes 1 model development and event scale dynamics this paper presents an erosion model armour which simulates time varying runoff erosion deposition and surface armour evolution down a hillslope either as a result of a single erosion event or as the cumulative impact of many events over periods up to decades armour simulates sediment transport for both cohesive and non cohesive soil and dynamically differentiates between transport limited and source limited processes a variety of feasible processes for entrainment of different size classes can be modelled and evaluated against data the generalized likelihood of uncertainty estimation glue technique was used to calibrate and validate armour using data collected during rainfall simulator experiments at two contrasting sites 1 non cohesive stony sediments at ranger uranium mine northern territory australia and 2 cohesive silty sediments at northparkes gold mine nsw australia the spatial and temporal variations of model predictions within the individual runoff events showed that some entrainment processes could not model the spikes in concentration and subsequent depletion while the hiding model of andrews and parker best simulated the concentration trends for both calibrated and independent runoff events armour also successfully captured the coarsening of the surface material though small over the duration of the rainfall simulator trials this was driven by the depletion of the finest size class of the soil for a constant discharge armour simulated higher sediment flux at the start of the storm with the sediment flux and concentration diminishing with time for natural rainfall a power law relationship between sediment flux and discharge was observed the calibration exercise showed that sediment concentration and discharge alone are insufficient to calibrate all aspects of the physics in particular the armour depth this appears to be because the armouring during the short duration events is driven by depletion of the finest classes of the sediments diameters less then 62 5 mm which are not normally measured copyright 2006 john wiley sons ltd

the role of moisture cycling in the weathering of a quartz chlorite schist in a tropical environment findings of a laboratory simulation long term weathering of a quartz chlorite schist via wetting and drying was studied under a simulated tropical climate cubic rock samples 15 mm 15 mm 15 mm were cut from larger rocks and subjected to time compressed climatic conditions simulating the tropical wet season climate at the ranger uranium mine in the northern territory australia fragmentation moisture content and moisture uptake rate were monitored over 5000 cycles of wetting and drying to determine the impact of climatic variables five climatic regimes were simulated varying water application temperature and drying one of the climatic regimes reproduced observed temperature and moisture variability at the ranger uranium mine but over a compressed time scale it is shown that wetting and drying is capable of weathering quartz chlorite schist with changes expected over a real time period of decades while wetting and drying alone does produce changes to rock morphology the incorporation of temperature variation further enhances weathering rates although little fragmentation occurred in experiments significant changes to internal pore structure were observed which could potentially enhance other weathering mechanisms moisture variability is shown to lead to higher weathering rates than are observed when samples are subjected only to leaching finally experiments were conducted on two rock samples from the same source having only subtle differences in mineralogy the samples exhibited quite different weathering rates leading to the conclusion that our knowledge of the role of rock type and composition in weathering is insufficient for the accurate determination of weathering rates copyright 2005 john wiley sons ltd

post fire hillslope debris flows evidence of a distinct erosion process abstract after wildfire a hitherto unexplained erosion process that some authors have called miniature debris flows on hillslopes and that leave behind levee lined rills has been observed in some regions of the world despite the unusual proposition of debris flow on planar hillslopes the process has not received much attention the objectives of this study were to 1 accumulate observational evidence of hillslope debris flows hdf as we have defined the process to 2 understand their initiation process by conducting runoff experiments on hillslopes to 3 propose a conceptual model of hdf and to 4 contrast and classify hdf relative to other erosion and transport processes in the post wildfire hillslope domain hdf have been observed at relatively steep slope gradients 0 4 0 8 on a variety of geologies and after fire of at least moderate severity and consist of a lobe of gravel to cobble sized material 0 2 1 m wide that is pushed by runoff damming up behind it during initiation runoff moved individual particles that accumulated a small distance downslope until the accumulation of grains failed and formed the granular lobe of the hdf hdf are a threshold process and runoff rates of 0 5 l s 1 2 l s 1 were required for their initiation during the experiments the conceptual model highlights hdf as a geomorphic process distinct from channel debris flows because they occur on planar unconfined hillslopes rather than confined channels hdf can erode very coarse non cohesive surface soil which distinguishes them from rill erosion that have suspended and bedload transport on a matrix of slope and grain size hdf are enveloped between purely gravity driven dry ravel and mostly runoff driven bedload transport in rills

microbiological processes in banded iron formation deposition banded iron formations have been studied for decades particularly regarding their potential as archives of the precambrian environment in spite of this effort the mechanism of their deposition and specifically the role that microbes played in the precipitation of banded iron formation minerals remains unresolved evidence of an anoxic earth with only localized oxic areas until the great oxidation event ca 2 45 to 2 32 ga makes the investigation of o2 independent mechanisms for banded iron formation deposition relevant recent studies have explored the long standing proposition that archean banded iron formations may have been formed and diagenetically modified by anaerobic microbial metabolisms these efforts encompass a wide array of approaches including isotope ecophysiological and phylogeny studies molecular and mineral marker analysis and sedimentological reconstructions herein the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post depositional alteration are described the main findings of recent years are summarized and compared here and suggestions are made regarding cross disciplinary information still required to constrain the role of the biosphere in banded iron formation deposition

impact of slope aspect on hydrological rainfall and on the magnitude of rill erosion in belgium and northern france abstract the impact of slope aspect on hydrological rainfall and on the magnitude of rill erosion has rarely been studied the dominant wind direction in belgium and northern france is the southwest which brings large amounts of rain with it we investigated whether this leads to greater rates of rill erosion on the southwestern slopes due to the greater amount of hydrological precipitation on these slopes the study was executed on six barren conical spoil heaps which are excellent study objects to bring the slope aspect in relation with rill erosion three indicators for rill erosion volume of rills drainage density and mean distance of the head cut of the five uppermost rills till the top of the spoil heap were associated with four explanatory factors slope gradient vegetation density rock fragment cover and slope aspect the amount of hydrological rainfall is the greatest on the western and southwestern slopes as a result the largest volume of rills was measured on the slopes facing the southwest 96 which indicates that there is a connection between the slope aspect and the magnitude of rill erosion on the northeastern 32 and eastern 36 slopes the volume of rills is lower due to the effect of rain shadow the other explanatory factors showed little influence on the magnitude of rill erosion as the spoil heaps were selected to be similar in as many parameters as possible

rock moisture content in the field and the laboratory and its relationship to mechanical weathering studies rock moisture content is a major control of mechanical weathering particularly freeze thaw and yet almost no data exist from field situations this study presents moisture content values for rocks taken from a variety of positions and conditions in the maritime antarctic additional information regarding the amount of water the rock could take up as observed from laboratory experiments is also presented the results show that the approaches used in simulation experiments particularly that of soaking a rock for 24 hours may produce exaggerated results it was found that the saturation coefficient s value was a good indicator of frost susceptibility based on water content but that the derivation of that value may underestimate the potential of some rocks the distribution of moisture within rocks is seen as an important but unkown factor the results of these field moisture contents suggest that for simulations of freeze thaw or hydration to be meaningful then they should have rock water contents based on field observations

experimental study of iron and silica immobilization by bacteria in mixed fe si systems implications for microbial silicification in hot springs the immobilization of silica and iron by the bacteria bacillus subtilis was monitored in controlled microcosms to elucidate the role iron may play in aiding bacterial silicification in hot springs silica and iron immobilization was monitored as a function of bacterial concentration iron concentration and silica concentration both undersaturated and oversaturated with respect to amorphous silica results demonstrate that bacterial cells do immobilize more fe than bacteria free systems in solutions with iron concentrations 50 ppm fe however as iron concentrations increase the difference between fe immobilization in bacterial and bacteria free systems decreases as non bacterially mediated precipitation processes dominate additionally bacterial systems that had immobilized more fe compared with bacteria free systems did not immobilize more silica than bacteria free systems by comparing molar ratios of silica in solution bacterially bound fe it is evident that insufficient iron is bound to the bacterial surface to act as an effective salt bridge for silica sorption this appears to be because much of the iron is immobilized by non bacterially mediated precipitation of phases such as fe oh 3 and poorly ordered hydrous iron silicates it follows that in silica enriched hot springs silica and iron immobilization processes are significantly dominated by non bacterially mediated precipitation any bacterially mediated processes are exceedingly small and outside the resolution of these experiments