modeling of the transport and deposition of tungsten in the scheelite bearing calc silicate gneisses of the montagne noire france scheelite bearing calc silicate gneisses csg oceur in the montagne noire within a series of dominant micaschists detailed petrographical and mineralogical studies reveal three successive stages of metamorphism and hydrothermal alteration 1 stage 1 a regional metamorphism at 550 c and 4 5 kb where no mineralization is formed 2 stage 2a a hydrothermal alteration at 500 to 450 c and 4 to 3 kb which is characterized by an intense sericitization of feldpars and deposition of sn in sn bearing cale silicates and 3 stage 2b a hydrothermal alteration characterized by the crystallization of idocrasegrossular in csg with concomittant precipitation of scheelite tungsten was transported through the micaschist environment and deposited as scheelite only in the csg of stage 2b at relatively low pressures to characterize the mechanism of tungsten transport tungsten speciation at high p t and scheelite solubility in aqueous solations buffered by the csg and by the micaschists assemblages were calculated it was found that h2wo 0 4 hwo 4 and wo 2 4 are the dominant tungsten aqueous species in h2o nacl one molal solutions at 500 c and 2 4 kb calculations also indicate that scheelite deposition is controlled by decreasing pressure and increasing activity of aqueous calcium in this system this is consistent with the petrographical and mineralogical observations the consequences of the presence of volatiles n2 ch4 co2 in the regional fluids were examined by determining the effect of n2 on tungsten speciation and scheelite solubility the addition of n2 up to 10 mol to the mineralizing fluids results in a marked increase in h2wo 0 4 and hwo 4 concentrations relative to wo 2 4 and in a large decrease of scheelite solubility this mechanism favours scheelite precipitation and accounts for the commonly observed association of w and sn deposits with graphitic series generating mixed volatiles fluids

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

salt weathering simulations under hot desert conditions agents of enlightenment or perpetuators of preconceptions because of access difficulties and inhospitable environmental conditions our understanding of rock weathering in hot deserts has been strongly influenced by laboratory simulations however a risk exists that results may come to owe more to experimental design than to actual environmental conditions experienced at the atmosphere rock surface interface this was especially true in early salt weathering simulations that seemingly sought to reinforce the orthodoxy of a physically dominated weathering environment driven by extremely high absolute temperatures and large diurnal temperature ranges however improvements in environmental sensors over the last 20 years have established the complexity of desert climates and the importance of microclimatic controls and allowed considerable refinement of experimental design this overview evaluates the implications of recent simulation studies and presents new information on possible fatigue effects of differential thermal expansion of salts and the salt weathering of test blocks under compressive loading in doing so it demonstrates how physical rock properties change during experimentation the importance of short term surface temperature fluctuations distinctions between the weathering of unconfined debris and larger rock surfaces the importance of moisture and salt applications that replicate their availability in deserts the importance of rock thermal properties in controlling their weathering response in environments dominated by radiative heating and cooling and the overall complexity of weathering regimes

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

cracks in desert pavement rocks further insights into mechanical weathering by directional insolation the formation of cracks is a fundamental first step in the physical weathering of rocks in desert environments in this study we combine new field data from the mojave u s gobi mongolia and strzelecki australia deserts that collectively support the hypothesis that meridional cracks cracks with orientations not readily attributable to rock anisotropies or shape in boulders or cobbles form due to tensile stresses caused by directional heating and cooling during the sun s daily transit the new studies indicate that rock size surface age and latitude play important roles with respect to their influence on rock fracture rock size and pavement surface age exert an influence on the development of rock cracks as the average clast size of mature desert pavements may be at or below the threshold clast size for thermal cracking of rocks latitude controlled seasonal temperature variations play a key role as demonstrated by 1 tightly clustered mean resultant orientations that differ by latitude as predicted in mcfadden et al 2005 and 2 very cold wintertime temperatures and strong diurnal gradients that may favor crack development in wintertime given the likelihood for strong clast heating during early morning hours the consistent evidence for meridional cracks in surfaces of diverse age and desert environments climate vegetation and distance of clast transport indicate that directional insolation may play the key role in initially generating and propagating rock fractures rather than a secondary role as implied in recent field and modeling studies of physical weathering in deserts

effect of moisture and temperature conditions on the decay rate of a purple mudstone in southwestern china soil formation and geomorphology are primarily influenced by the rock decay which in turn is strongly determined by moisture and temperature conditions however it remains unclear whether rock decay is dominated by thermal stresses or by hydration disintegration and there is little information on mudstone decay rate in southwestern china this study hypothesized that rock decay is dominated by hydration mechanism and focused on the physical decay characteristics of typical purple mudstones using a combination of field and laboratory based experiments the bedrock of a penglaizhen group j 3 p in yanting county sichuan province southwestern china was exposed and covered with nylon fabric in situ soil depths of 10 20 40 and 60 cm were laid on this nylon fabric in 2003 and the decay rate the quantity of clastic particles 2 mm that were decayed from the bedrock in t km 2 yr 1 under the nylon fabric was measured both in 2005 and 2009 in addition fresh mudstones sampled from the matoushan group k 2 m the tuodian group j 3 t and the lufeng group j 1 l in yuanmou county shuangbai county and lufeng county of yunnan province southwestern china respectively were subjected to alternating applications of moisture temperature and their interaction seven treatments in the laboratory and their decay ratios the mass of decayed rock of 2 mm clastic particles to sampled rock mass in percent were measured in 2010 in the field the decay rate of the bedrock showed a significant p 0 05 positive relationship with both the daily moisture and temperature variation at the interface between the soil and bedrock in the laboratory results showed that the effect of moisture variation but not temperature alternation on rock decay was apparent suggesting that purple rock decay is dominated by hydration mechanism freezing thawing in particular affects the sampled rocks because it causes more spalling and fracturing the j 3 t rock had the highest decay ratio because it had the highest clay mineral content and porosity of the three rock types hierarchical clustering analysis suggested that the variation of moisture content and h2o phase solid or liquid within rock plays a key role in rock decay processes both field and laboratory studies consistently showed that the alteration of wetting drying and freezing thawing as well as moisture content substantially influenced rock decay c 2012 elsevier b v all rights reserved

the nature and pattern of debris liberation by salt weathering a laboratory study a laboratory simulation of salt weathering was used to ascertain the effects of sodium sulphate and sodium carbonate under negev conditions using a single immersion technique three main points were addressed what are the grain size and textural characteristics of the debris liberated from limestones and a sandstone what do scanning electron microscope observations of the weathered samples tell us about the decay processes involved and how does the rate of debris liberation change during the course of 100 cycles the grain size characteristics of the liberated debris tended to be multimodal and were related to the original petrological characteristics of the rock large amounts of fines were produced which are believed to be analogous to the rock flour of arid areas blistering was also observed scanning electron microscope analysis revealed differences in the style of attack for different rock types and salt treatments and revealed the pattern of salt crystallization in pores and the nature of cracking the rate of debris liberation tended to decline or remain constant through time the reasons for this remain obscure but it is evident that diurnal cycles of temperature and humidity change can cause continuing rock weathering long after the initial input of salt to the rock has taken place

the ebro and the rhone deep sea fans first comparative study abstract bathymetric and continuous seismic profiles enable us to define the main morphological and structural outlines of the ebro and rhone deep sea fans despite great differences of morphology and volume these two fans are characterized by a similar structure with a 500 milliseconds thick series of superposed lenticular acoustic units lying above more homogeneous sediments these units are tentatively attributed to channel infilling associated with overbank deposits shifting through time nevertheless some of them may represent large sedimentary slides especially off the ebro river

seismic evidence of widespread mass transport deposits in the rhone deep sea fan their role in the fan construction abstract in the rhone deep sea fan mass transport deposits are represented either by transparent or by chaotic echo facies they cover a very large area of this fan both superficially and interbedded in the sedimentary column these deposits played an important role in the fan construction by blocking the paths of detrital feeding and leading to the creation of new ones

contour scaling of a sandstone by salt weathering under simulated hot desert conditions a laboratory study has been used to investigate relationships between salts and contour scaling a weathering feature commonly observed on rock surfaces in salt rich environments surface disaggregation and essentially surface parallel cracks were produced in sandstone blocks using 10 per cent solutions of sodium sulphate and magnesium sulphate applied daily to single exposed surfaces for sixty days a control block soaked once in saturated magnesium sulphate and subsequently wetted daily with distilled water showed extensive surface disaggregation but no cracking both surface disaggregation and subsurface cracking were associated with relative concentrations of microcrystalline salt a tentative model of contour scaling is proposed which involves linking together potential cracks by salt induced fracturing of intervening crack stopping grains further control blocks treated respectively with 10 per cent and saturated sodium chloride showed no evidence of subsurface cracking and only limited surface disaggregation of the saturated block

the origin of honeycomb weathering honeycomb weathering occurs throughout the world but the origin remains a matter of controversy wind erosion exfoliation frost shattering and salt weathering have been proposed as explanations although few attempts have been made to substantiate these hypotheses with chemical or mineralogical studies chemical analyses and field observations indicate that honeycomb weathering in coastal exposures of arkosic sandstone near bellingham washington results from evaporation of salt water deposited by wave splash microscopic examination of weathered surfaces show that erosion results from disaggregation of mineral grains rather than from chemical decomposition thin walls separating adjacent cavities seem to be due to protective effects of organic coatings produced by microscopic algae inhabiting the rock surface cavity walls are not reinforced by precipitation of elements released by weathering as has often been suggested at other locations honeycomb weathering develops rapidly and can be observed on surfaces that were planar less than a century ago

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

detailed morphology sedimentary structure and evolution of the continental margin of the western provencal basin south of france since the late miocene abstract seabeam bathymetry and high resolution seismic profiles allow the study of different sedimentary units existing off western provence and to establish their continuity throughout the continental margin from the shelf to the rise the morphology of the slope is greatly controlled by gravity processes leading to phenomena such as canyon piracy or channel avulsion this morphology quite accurately expresses the configuration of the old underlying sedimentary and tectonic structures the sedimentary structure of this domain is the result of the complex arrangement of lobes and ridges that originated from different continental sources and were deposited during different epochs of the plio quaternary knowledge of the old hydrographic networks draining provence during the different quaternary climatic stages allows palaeogeographic reconstructions to be proposed linking these sedimentary units to their continental sources

exploitation of inherited weakness in fire damaged building sandstone the fatiguing of shocked stone abstract the problem of the long term impact of historical fire on masonry is not clearly understood much research focuses on the damage that is caused by fire in isolation and omits to investigate the subsequent exploitation of weaknesses inherited from fire events fire can for example cause significant physical chemical and mineralogical change to sandstone which may then be exploited by background environmental factors such as salt and freeze thaw weathering to explore this experimentally blocks of peakmoor sandstone were subjected to a real fire as well as lime rendering removal and frost cycle pre treatments and their subsequent response to salt weathering cycles was monitored by weight loss and visual assessment of the pattern of surface damage results illustrate that the post fire deterioration of sandstone is strongly conditioned by fracture networks and soot cover inherited from the fire the exploitation of fractures can lead to spalling during salt weathering cycles this takes place as granular dissagregation steadily widens cracks and salts concentrate and crystallise in areas of inherited weakness soot cover can have a profound effect on subsequent performance it reduces surface permeability and can be hydrophobic in character limiting salt ingress and suppressing decay in the short term however as salt crystals concentrate under the soot crust detachment of this layer can occur exposing fire damaged stone beneath understanding the subsequent exploitation of stone exposed to fire damage by background environmental factors for example salt weathering temperature cycling is key to the post fire management of stone decay

the possible role of clay minerals in salt weathering abstract results of a salt weathering experiment on a laminated sandstone are reported it is observed that laminae which contain smectite clays break down more readily than those with little clay this preferential breakdown may be related to the swelling of the clays which assists salt weathering processes per se and or secondary microporosity created by the clays which could enhance salt weathering effects it is not possible at this point in time to state definitively the effects that the presence of clay has upon salt weathering but suggestions for future research are made

sedimentary mechanisms and underlying tectonic structures of the northwestern mediterranean margin as revealed by comprehensive bathymetric and seismic surveys abstract the tectonic structures lithological contrasts and sedimentary processes of the northwestern mediterranean margin are revealed by a comprehensive survey including recently acquired seabeam and seismic profiling data mass wasting by gravity flow processes occurs over this entire area gravity slides are concentrated on the thick plio quaternary formations located in the interchannel areas they can lead to surprisingly steep walls and contribute to the widening of the canyons the contrasts between these superficial formations and the underlying neogene formations are morphologically well expressed the slide products sometimes directly observed as voluminous erratic blocks can seal the deep sea channels and cause their migrations areal extent of these slides can be very large especially with respect to the small size of the basin however the turbidity currents are the main gravity flow processes leading to the construction during the quaternary glacial epochs of the rhone deep sea fan and other sedimentary ridges they are responsible for the formation of particular bedforms such as circular depressions into the valley floors or sediment waves on the interchannel areas the wide extent of the gravity flow processes can be explained by the particular geological setting of this margin which is a mountainous borderland with steep slopes and rapid deposition of undercompacted sediments the general instability is favored by recent tectonic movements linked with the alpine setting and especially in the deepest areas by the lubricating effects of the underlying messinian salt layer under the loading effect of the sedimentary cover this salt layer crops out around the rhone deep sea fan as a peripheral belt of diapirs having shapes controlled by deep tectonic structures

near bottom sedimentation processes revealed by echo character mapping studies northwestern mediterranean basin subbottom echoes recorded on 3 5 khz echo sounders in the northwestern mediterranean basin from 1978 to 1991 can be classified into five main categories of echo character 1 continental shelf cs echo character characterizes the continental platform and areas of shallow relief and commonly is related to consolidated sediments 2 hyperbolic h echo character is recorded from areas with rough bottom morphology echo type h1 corresponds to steep slopes echo type h2 reflects very coarse grained sediments deposited by energetic turbidity currents 3 bedded b echo character is widely observed throughout the study area and corresponds to terrigenous deposits distributed by turbidity currents echo type b1 is related to thin turbidites deposited on overbank portions of channel levees by lateral overflow of turbiditic currents moving down the channels echo type b2 corresponds to coarser turbiditic materials 4 rugged r echo character is observed in the axes of submarine canyons and channels and characterizes hard sea floor with coarse heterogeneous turbiditic deposits subjected to energetic gravity flow processes 5 transparent t echo character is ubiquitous in the study area and is attributed to mass movement deposits the widespread occurrence of those deposits testifies to the general instability of the study area types and distribution of echo character throughout the study area show the importance of gravity dominated depositional processes turbidity currents and mass wasting in this region this remobilization of siliciclastic sediments induced by high sediment rates steep slopes and halotectonics theoretically could create potential hydrocarbon reservoirs within the deep water portions of the continental margin

a quantitative determination of the effect of moisture on purple mudstone decay in southwestern china aims the moisture condition is well known to be a key factor that apparently influences rock decay but little is known about the quantitative correlations between a rock s decay rate and its moisture content which makes it difficult to quantitatively predict the rate of rock decay under varied moisture conditions thus in this paper our aim is to observe the decay rates of various purple mudstones with different moisture contents and to develop an equation to calculate the decay rate

complex weathering in drylands implications of stress history for rock debris breakdown and sediment release abstract weathering studies have often sought to explain features in terms of a prevailing set of environmental conditions however it is clear that in most present day hot desert regions the surface rock debris has been exposed to a range of weathering environments and processes these different weathering conditions can arise in two ways either from the effects of long term climate change acting on debris that remains relatively static within the landscape or through the spatial relocation of debris from high to low altitude consequently each fragment of rock may contain a unique weathering related legacy of damage and alteration a legacy that may greatly influence its response to present day weathering activity experiments are described in which blocks of limestone sandstone granite and basalt are given stress histories by subjecting them to varying numbers of heating and freezing cycles as a form of pre treatment these imposed stress histories act as proxies for a weathering history some blocks were used in a laboratory salt weathering simulation study while others underwent a 2 year field exposure trial at high mid and low altitude sites in death valley california weight loss and ultrasonic pulse velocity measurements suggest that blocks with stress histories deteriorate more rapidly than unstressed samples of the same rock type exposed to the same environmental conditions laboratory data also indicate that the result of imposing a known weathering history on samples by pre stressing them is an increase in the amount of fine sediment released during salt weathering over a given period of time in comparison to unstressed samples

morphostructure growth patterns and tectonic control of the rhone and nile deep sea fans a comparison the rhone and the nile rivers shape the sediment distribution of the ligurian and the levantine basins in the mediterranean sea respectively both rivers cut huge canyons in their bed rock during the messinian desiccation of the mediterranean and the subsequent early pliocene marine transgression reached far inland both in france and in egypt the sediment supply of both rivers was affected by climatic variations during the pleistocene but whereas glacial periods were associated with reduced water flow in the rhone they can be correlated with enhanced flow of the nile the sediment distribution and accumulation patterns of both rivers built large deltas on their continental shelves during high sea level stands during lowstands both rivers flowed as far as the shelf e ge and transported their sedimentary load through the continental slopes directly to their deep sea fans the patterns of sediment distribution and accumulation in the marine basins of the ligurian and the levantine seas were affected also by pliocene quaternary tectonic activity and halokinetic offsets that led to sediment instability the present hydrographic and sedimentological regimes of both rivers do not represent their natural potential due to artificial interference the principal economic significance of the deep sea fan accumulation process is the transportation of medium and coarse grained sediments into the deep marine basin considering the effect of these sediments on stratal permeabilities and hydrocarbon potential the presented comparative overview emphasizes recent and subrecent sedimentological aspects that are critical to petroleum exploration in active and extinct deep sea depositional environments

volcanogenic exhalative tungsten mineralization of proterozoic age near santa fe new mexico and implications for exploration a stratabound tungsten scheelite occurrence is exposed in proterozoic 1650 1720 ma metamorphic terrane near santa fe new mexico and may be the first volcanogenic exhalative tungsten deposit recognized in the united states the tungsten bearing horizon is composed of disseminated scheelite within epidote actinolite rock exhibits pronounced mineralogic zoning and anomalous metal contents and is localized along the contact between sulfide bearing felsic tuffs and cherts and barren basalts and mafic sediments it is interpreted as a syngenetic tungsten deposit exhaled as a chemical sediment at the close of a volcanic cycle and subsequently metamorphosed to lower amphibolite facies and deformed we suggest that other tungsten deposits in precambrian terrane in the western united states may also be volcanogenic exhalative application of this model to exploration could lead to additional discoveries

revisiting dirt cracking as a physical weathering process in warm deserts abstract a half century ago c d ollier proposed that insolation driven temperature changes expand and contract fill in fissures enough to widen cracks a process that would permit progressively deeper penetration of fissure fills that would in turn generate a positive feedback of greater and greater strain until desert boulders and bedrock shatters although desert physical weathering by dirt cracking has occasionally been cited this hypothesized process remains without support from subsequent research here field observations electron microscopy x ray powder diffraction particle size analysis and laboratory experiments shed new light on dirt cracking little clear evidence supports the original notion of expansive pressures from thermal fluctuations however mineralogical high resolution transmission electron microscopy back scattered electron microscopy and experimental evidence support two alternative processes of widening fractures wetting and drying of fills inside fissures and the precipitation and remobilization of calcium carbonate a re envisioned dirt cracking wedging process starts with calcium carbonate precipitating in fissures less than 5 m wide first precipitation and then ongoing dissolution of this laminar calcrete opens enough space for dust to penetrate into these narrow fractures wetting of expansive clays in the fissure fill exerts enough pressure to widen and deepen the fissure allowing the carbonate precipitation process to penetrate even deeper and allowing even more dust to move into a fracture as the dust infiltrates its texture changes from a chaotic mix of particles to an alignment of clays parallel to fissure sides this parallel alignment could increase the efficiency of fill wedging ollier s concept of a positive feedback remains supported each increment of fracture deepening and widening permits more even deeper infiltration of laminar calcrete and dust field and electron microscope observations of rock spalling in the winter of 2010 are consistent with ollier s hypothesis that dirt cracking is a common physical weathering process in deserts that splits rocks of all different sizes

simulating weathering of basalt on mars and earth by thermal cycling physical weathering induced by heating and cooling may cause rock breakdown on mars and earth we report results from parallel weathering simulations on basalt blocks exposed to diurnal cycles representing mars like two simulation runs from 55 to 20 oc and 75 to 10 oc 1 100 relative humidity 4 8 mbar pressure co 2 atmosphere and hot arid earth 23 72o c 30 100 relative humidity conditions under earth conditions thermally pre stressed blocks showed measurable strength declines whilst salt pre treated blocks showed strength gains under mars like conditions pre stressed blocks recorded greater or similar strength declines and salt pre treated blocks showed more muted strength declines than under earth conditions the results imply that on earth and mars diurnal cycling of temperature alone can cause deterioration of basalt with a pre existing stress history the type of stress history is important with salt pre treatment affecting the response of thermally pre stressed blocks under both earth and mars conditions

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

controls on the geotechnical response of sedimentary rocks to weathering weathering reduces the strength of rocks and so is a key control on the stability of rock slopes recent research suggests that the geotechnical response of rocks to weathering varies with ambient stress conditions resulting from overburden loading and or stress concentrations driven by near surface topography in addition the stress history experienced by the rock can influence the degree to which current weathering processes cause rock breakdown to address the combined effect of these potential controls we conducted a set of weathering experiments on two sedimentary lithologies in laboratory and field conditions we firstly defined the baseline geotechnical behaviour of each lithology characterising surface hardness and stress strain behaviour in unconfined compression weathering significantly reduced intact rock strength but this was not evident in measurements of surface hardness the ambient compressive stress applied to samples throughout the experiments did not cause any observable differences in the geotechnical behaviour of the samples we created a stress history effect in sub sets of samples by generating a population of microcracks that could be exploited by weathering processes we also geometrically modified groups of samples to cause near surface stress concentrations that may allow greater weathering efficacy however even these pronounced sample modifications resulted in insignificant changes in geotechnical behaviour when compared to unmodified samples the observed reduction in rock strength changed the nature of failure of the samples which developed post peak strength and underwent multiple stages of brittle failure although weakened these samples could sustain greater stress and strain following exceedance of peak strength on this basis the multi stage failure style exhibited by weaker weathered rock may permit smaller magnitude higher frequency events to trigger fracture through intact rock bridges as well as influencing the characteristics of pre failure deformation these findings are consistent with patterns of behaviour observed in field monitoring results

a preliminary scanning electron microscope study of honeycomb weathering of sandstone in a coastal environment honeycomb weathering has been observed in a carboniferous sandstone at a coastal location near ballycastle on the north coast of northern ireland specimens of this sandstone have been analysed by x ray diffraction scanning electron microscopy and energy dispersive spectrometry results reveal that calcium sulphate gypsum is the only salt present and is found only at and immediately below the rock surface sem observations suggest that crystallization of salts in pores could easily dislodge quartz grains to promote granular disintegration whilst etching of quartz grain surfaces attests to chemical weathering activity within the rock however the reason for the development of the honeycomb pattern is not known

variable weathering response in sandstone factors controlling decay sequences differences in weathering response characteristics of fine and coarse grained stanton moor sandstone samples were assessed in a laboratory weathering simulation experiment using a variable combination of salt weathering and freeze thaw cycles preliminary analysis of permeability characteristics identified similar mean values for each type of stanton sandstone but significant differences in the range of values between the two sample sets with coarse grained samples of stanton moor sandstone displaying a restricted range of values in comparison to fine grained samples which showed much greater within block variation data indicated that the greater the range in initial permeability values the greater the potential for salt and moisture ingress and retention and hence eventual disruption of the fabric of the stone experimental data also identified different stages in decay sequences with significant structural change occurring during the initial preparatory stage before material breakdown and loss became apparent evidence suggests that relatively minor structural and mineralogical differences between samples of the same stone type can have a significant influence on weathering behaviour resulting in distinct rates and patterns of breakdown copyright 2005 john wiley sons ltd

the relations between modulus of elasticity and temperature in the context of the experimental simulation of rock weathering by fire fires occur frequently in many biomes and generate high temperatures on the ground surface there are many field examples of fire causing rock disintegration the simulation of fire in the laboratory using a furnace and the monitoring of changes in rock modulus of elasticity with a grindosonic apparatus reveal that different rocks respond differently to heating significant decreases in elasticity occur at temperatures as low as 200 c and granites display particularly marked reductions extended periods of heating are not required for significant reductions to occur it is postulated that the degree of change in elasticity as a result of simulated fire is such that rock outcrops subjected to real fires are likely to be sufficiently modified as to increase their susceptibility to erosion and weathering processes

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

recent depositional patterns of the nile deep sea fan from echo character mapping the nile deep sea fan was surveyed in 1998 using swath multibeam bathymetry backscatter imagery and 3 5 khz and seismic profiling on the basis of this new data set the fan has been divided into three main provinces western central and eastern recent sedimentary patterns as deduced from echo character mapping show that gravity induced sedimentary deposits are predominant and are expressed through either slides debris flows or turbidites turbidity processes are particularly active in the westernmost province through a well developed network of deep sea channels this network controls turbiditic flows that subsequently overflow levees mass wasting processes are extremely efficient all over the nile deep sea fan in the upper central province a broad allochthonous tongue of mass flow deposits generated by slope destabilizations may have led to channel avulsions and migrations in the eastern province a northwest southeast deformed belt resulting from combined deep seated and salt related tectonics contains large proportions of destabilized sediments i e originating from destabilization processes such as mass movements probably settled by recent tectonic activity this article highlights 1 the influence of both thin skinned and thick skinned tectonics on sedimentary distribution and 2 the predominance of gravity induced sediments turbidites slides and mass flows in such submarine fans the distribution of debris flows and sedimentary deposits settled by turbidity currents appears fundamental in predicting reservoir geometry and economic potential

stratabound tungsten mineralization in regional metamorphic calc silicate rocks from the austroalpine crystalline complex austria stratabound tungsten mineralization in regional metamorphic calc silicate rocks of probably lower paleozoic age is described from the polymetamorphic austroalpine crystalline complex acc of the eastern alps scheelite bearing calc silicate rocks which are often associated with marbles and tourmalinites are intercalated conformably with metaclastic rocks alkalipoor calc silicate rocks with high amounts of clinozoisite zoisite grossular quartz plagioclase etc are the most important host rocks for tungsten mineralization these unusual calc silicate rocks are products of regional metaorphism and are interpreted as reaction skarns they have formed in the presence of a water dominated fluid phase with very low xco2 in the koralpe estimated p t conditions are 650 700 c at 5 7 kb the mineralogical composition and the mineral zoning of the calc silicate rocks is controlled by the degree of the hercynian and eoalpine metamorphism there are no signs of graniteelated skarn formation tungsten preconcentration is thought to be syngenetic syndiagenetic it is genetically linked to exhalative hydrothermal processes in other lower paleozoic terrains of the eastern alps

thermal properties as controls on rock surface temperature maxima and possible implications for rock weathering four rock types basalt sandstone granite and chalk are examined with respect to the maximum surface temperatures which they experience when subjected to similar conditions of exposure rock temperature measurements are reported for an urban environment and for two experimental situations in which an infrared lamp is used to simulate heating under cold and hot conditions differences in rock temperatures are discussed with reference to thermal rock properties albedo specific heat capacity and thermal conductivity some natural situations are suggested in which thermal rock properties could conceivably play a role in determining the extent to which rocks would be affected by particular weathering processes

corroded cobbles in southern death valley their relationship to honeycomb weathering and lake shorelines in southern death valley pits similar in morphology to honeycomb weathering herein referred to as corrosion pits occur on the surfaces of cobbles that are associated with wave produced benches the pitted cobbles include a variety of igneous metamorphic and siliciclastic rocks corrosion pits are rare to absent in limestones or dolomites pit morphology is controlled by cobble lithology in massive rocks the pits are arcuate elongate and gently tapering corrosion of laminated or foliated rocks has produced irregular more jagged pits the presence of desert varnish has strongly inhibited the corrosion process the corroded cobbles are inferred to reflect both chemical and physical weathering of rocks along pleistocene lacustrine strandlines corrosion took place through salt weathering and or heat moisture expansion processes and through chemical dissolution of selected minerals as a result of splash zone wetting and drying the ancient lake waters may have had high ph and high total dissolved solids contents the recognition of corroded cobbles may be important in the reconstruction of the position of ancient shorelines for certain types of alkaline lakes and in the reconstruction of their ancient chemistries

microclimate and weathering in the central namib desert namibia data on rock surface microclimates at four sites kleinberg vogelfederberg gobabeb and ganab along a transect across the central namib desert over a 3 year period have been collected alongside some shorter term data sets rock surface temperature rst air temperature wind relative humidity and surface wetness data are presented here weathering of exposure blocks of local marble and granite has also been monitored over the 3 year period with change observed visually and with scanning electron microscopy complex temporal patterns of rock temperature fluctuations are observed over the 3 years although the four sites show very similar overall trends suggesting spatial homogeneity in the rock surface temperature regime relative humidity and surface wetness data show clear differences between the four sites related to the frequency of fogs granite blocks show no visible changes after 2 years of weathering whereas marble blocks especially those at ganab show sem evidence of structural weakening after 1 year

current denudation rates in dolostone karst from central spain implications for the formation of unroofed caves abstract rock tablets of known weight were buried in the soil of a karst region in central spain to evaluate the carbonate weathering during a period of a year the experiment was conducted at two different soil depths 5 10 and 50 55 cm from the surface the parental rock used in the experiment is composed of dolomite and magnesite with variable proportion of accessory minerals and minor elements soil mineral and chemical composition as well as its texture was also characterized meteorological conditions at the site together with temperature and co2 in both soil levels were monitored sets of tablets were retrieved after 6 and 12 months of the start of the experiment to account for seasonal weathering different lithologies do not exhibit significant differences in weathering although a large inter sample variability is attributed to variable size and distribution of the porosity results show an enhanced weathering during the wet and cold season that accounts for 78 1 of the total annual weathering rock tablets examined under scanning electron microscopy prior and after exposure to natural environment show that most of the material lost occurred along cracks edges or large pores although dissolution is a common process most of the weathering is due to crystal detachment rock tablets at the depth of 5 10 cm were weathered 68 1 more than those set at 50 55 cm from the surface higher soil moisture and concentration of co2 were found deeper in the soil which likely enhanced the dissolution of carbonate however physical weathering dominated weight loss of rock tablets at both soil depths especially at the 5 10 cm level where soil thermal and moisture cycles were more frequent and greater denudation rate calculated from the 12 months set provides values of 2 48 1 07 m yr and 1 75 0 66 m yr at the depths of 5 10 and 50 55 cm respectively since the conditions at the average contact between soil and bedrock are similar to those at the 50 55 cm depth we consider that this is a more reliable denudation rate for the studied location during the studied period the calculated weathering rate suggests that denudation has a limited contribution to the thinning of bedrock over caves at this site therefore we consider that the formation of unroofed caves in this region most likely results from the thinning of bedrock cover over caves due to collapse of blocks from their ceilings

a non destructive method of determining rock strength rock material strength is an important component of many geomorphological studies current methods for determining this parameter result in sample destruction preventing further analysis a new non destructive technique is described for indirectly determining material strength by measuring dynamic young s modulus tests have been conducted on jurassic portland limestone and upper cretaceous chalk to assess the apparatus young s modulus is becoming an increasingly important rock material property

implications of salt sediment interactions on the architecture of the gulf of lions deep water sedimentary systems western mediterranean sea we integrated structural analysis of multichannel seismic data and isopach maps of the quaternary sedimentary cover to evaluate how salt tectonics has influenced the stratigraphic evolution offshore the gulf of lions the interplay between salt tectonics and sedimentation occurs at two scales at local scale listric normal faults create bathymetric relief able to deviate sediment transport axes with implications on depocenters configuration at depocenter scale overburden vertical movements due to salt evacuation or salt diapiric rise create sub basins providing accommodation space for clastic deposition these mechanisms have significant implications on the architecture and the internal organization of turbidite systems offshore the gulf of lions

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

the origin and significance of a thick deposit of pteropod shells in the rhone deep sea fan abstract an exceptionally thick deposit of gastropod shells mainly pteropods and heteropods has been found in a core sampled in a distributive channel of the rhone deep sea fan radiocarbon dating as well as the zoogeographic and climatic distribution of the fauna show that this layer has been deposited during the holocene period whereas the underlying muddy sediment is of wurmian age this change of sedimentation can be related to a strengthening of the bottom currents in the rhone deep sea fan especially in its distributive channels since the end of the glacial times from a more general point of view this could to a certain extent be related to the important changes that occurred in the mediterranean sea since this epoch