pb isotope fingerprinting of mesothermal gold deposits from central victoria australia implications for ore genesis new pb isotope data from three major mesothermal lode gold deposits ballarat west tarnagulla maldon in central victoria support a model whereby the metals derived from a large reservoir with a long residence time in the crust below the palaeozoic lachlan fold belt the pb isotopic ratios of least radiogenic samples from these deposits are in close agreement with published pb signatures for turbidite hosted gold deposits and for devonian granites elsewhere in the lachlan fold belt despite their spatial distribution and variations in the geological setting the pb signatures point to the extraction and transport of metals from a crustal source area by long lasting large scale hydrothermal systems resulting in the prominent homogenisation of pb isotopic ratios the enduring interaction between large hydrothermal systems and an extensive crustal source reservoir were a vital pre requisite in the formation of the victorian gold province in this regard the prospectivity of victoria is analogous to world class ore provinces elsewhere such as the archaean yilgarn block in western australia

portable controlled field experiments to resolve human impacts in geomorphology abstract geomorphologists have long been challenged by the need to separate the impact of human activities from change that would have occurred without human interference one research strategy is to utilize portable controlled field experiments in which the magnitude of driving forces e g rain or wind can be set and where it is possible to sample the landscape according to the variety in natural variables and human effects this paper reviews the use of portable field rainfall simulators and portable field wind tunnels with two case studies explored in detail the first case study involves a portable field rainfall simulator that was used to examine magnitude and persistence of erosional impacts from wildfires in the greater yellowstone ecosystem the second case study involves a portable field wind tunnel that was used to examine impacts on rates of sand transport from military maneuvers on the fort bliss military reservation in southern new mexico both pieces of equipment satisfied the guidelines posed by previous studies proved ideal for hypothesis testing and yielded results that could not have been easily achieved by other research strategies the rainfall simulation experiments revealed that post fire soil loss was controlled by the percent litter cover the logging history before the fires and the percent silt content of soils the wind tunnel experiments revealed the effect of tanks increasing sand transport through destroying the soil crust churning the soils and crushing the vegetation

regional structural controls of gold mineralisation bendigo and castlemaine goldfields central victoria australia the bendigo and castlemaine goldfields are classic examples of structurally controlled orogenic gold deposits in the bendigo zone of central victoria se australia detailed mapping and biostratigraphic interpretation has led to a better understanding of the regional structural controls of this type of gold quartz mineralisation mineralised quartz veins are hosted by the castlemaine group an early to middle ordovician turbidite succession at least 3 000 m thick gold deposits are controlled by low displacement faults that are clustered into several belts the goldfields indicating a regional structural control the timing of mineralisation overlapped with that of the major period of deformation including folding cleavage development and regional faulting the bendigo and castlemaine goldfields are located in an area termed the whitelaw thrust sheet bounded by two unmineralised high displacement regional scale faults mapping has revealed an interrelationship between the regional scale faults regional structural style and goldfield location the goldfields lie immediately west of the boundary between the upper and lower portions of the thrust sheet and are characterised by symmetric folds with sub horizontal to synclinal enveloping surfaces relatively low co axial strains and moderate cleavage development the non gold bearing areas immediately east of each goldfield correspond with the lower part of the whitelaw thrust sheet and are characterised by higher non coaxial strains stronger cleavage and folds with wide west dipping limbs giving rise to easterly vergent sections and steeply west dipping enveloping surfaces that mineralisation was an integral part of the thin skinned style of deformation in the central bendigo zone is indicated by timing relationships and the interrelationship between local scale mineralised structures and regional scale features such as large displacement unmineralised faults regional variations in fold style and overall thrust sheet geometry the work supports previous models that suggest mineralised fluids were focussed along a linked system of deep seated faults the primary conduits may have been major regional scale intrazone faults which are inferred to sole into detachments near the base of the castlemaine group it is proposed that these structures linked with minor intrazone faults and then with networks of low displacement mineralised faults that were strongly controlled by folds the location of minor intrazone faults was probably controlled by internal thrust sheet geometry the distribution of gold deposits and of gold production suggests that maximum fluid flow was concentrated along the eastern margins of networks of low displacement faults

chronology of deformation within the turbidite dominated lachlan orogen implications for the tectonic evolution of eastern australia and gondwana ar ar data from fabric forming white mica in slates syntectonic quartz veins and granitic mylonites constrain the timing of metamorphism deformation and exhumation in the lachlan orogen australia these data also help define the tectonic evolution of the tasmanides during paleozoic time the lachlan orogen formed by the progressive accretion of a thick turbidite fan sequence and volcanic terrains to gondwana during the closing of a small marginal ocean or back arc basin this tectonic setting was similar to the present western and southwestern pacific region accretion of the lachlan orogen to gondwana occurred by closing of the basin system by subduction accretion processes and some translation the process is typified in the western lachlan orogen by a major eastward migrating deformation involving chevron folding and faulting over an eastward propagating decollement melange zone and is recorded by ar ar mica ages ranging from 455 ma in the western part to 390 ma in the eastern part in the central lachlan orogen deformation migrated southwestward from 440 430 to 405 ma away from the high temperature wagga omeo metamorphic complex where deformation metamorphism occurred between 440 and 400 ma in the north 400 ma mica ages record deformation and inversion of structures in the cobar basin in the eastern lachlan orogen ar ar mica dates range from 450 to 340 ma ages of 455 445 ma are yielded by the narooma accretionary complex 405 390 ma ages are found along the major thrust faults bounding high grade metamorphic complexes and 360 340 ma cooling ages are found in the inverted extensional basins e g hill end and related structural zones the ar ar results also document periods of reactivation on early formed structures during later deformation elsewhere in the orogen

wind erodibility of soils at fort irwin california mojave desert usa before and after trampling disturbance implications for land management recently disturbed and control i e less recently disturbed soils in the mojave desert were compared for their vulnerability to wind erosion using a wind tunnel before and after being experimentally trampled before trampling control sites had greater cyanobacterial biomass soil surface stability threshold friction velocities tfv i e the wind speed required to move soil particles and sediment yield than sites that had been more recently disturbed by military manoeuvres after trampling all sites showed a large drop in tfvs and a concomitant increase in sediment yield simple correlation analyses showed that the decline in tfvs and the rise in sediment yield were significantly related to cyanobacterial biomass as indicated by soil chlorophyll a however chlorophyll a amounts were very low compared to chlorophyll a amounts found at cooler desert sites where chlorophyll a is often the most important factor in determining tfv and sediment yield multiple regression analyses showed that other factors at fort irwin were more important than cyanobacterial biomass in determining the overall site susceptibility to wind erosion these factors included soil texture especially the fine medium and coarse sand fractions rock cover and the inherent stability of the soil as indicated by subsurface soil stability tests thus our results indicate that there is a threshold of biomass below which cyanobacterial crusts are not the dominant factor in soil vulnerability to wind erosion most undisturbed soil surfaces in the mojave desert region produce very little sediment but even moderate disturbance increases soil loss from these sites because current weathering rates and dust inputs are very low soil formation rates are low as well therefore soil loss in this region is likely to have long term effects published in 2006 by john wiley sons ltd

source requirements for the golden mile kalgoorlie significance to the metamorphic replacement model for archean gold deposits the golden mile at kalgoorlie represents a giant archean hydrothermal gold system localized by ductile shear zones and hosted mainly by a differentiated tholeiitic sill chlorite carbonate and pyrite alteration zones cover the whole mineralized area 1 km 3 km and calculations suggest that for the golden mile production around 1200 t au the amounts of components added to these alteration zones are 340 mt co2 20 mt k and 5 mt s if one adopts a metamorphic replacement model for gold mineralization in which all ore components derive from devolatilization of greenstones at amphibolite facies or above these data suggest that a source area involving a 5 km thick greenstone slab of area 8 km 8 km could produce the necessary co2 k s h2o and au this is considered a reasonable volume of greenstone belt and under such a model the minimum spacing of large gold deposits would be approximately 20 km along strike neither special au enriched source rocks nor unreasonably large volumes of greenstone b

syn metamorphic gold mineralisation invincible vein nw otago schist new zealand the invincible vein fills a fault zone which strikes northeast and dips steeply southeast in the lower rees valley nw otago the vein cuts north striking foliation in lower greenschist facies otago schist structures associated with the fault zone are both brittle and ductile and the fault zone has had a complex history of post mineralisation reactivation mineralised vein material filling parts of the fault zone consist of quartz albite muscovite chlorite calcite pyrite arsenopyrite and minor gold these minerals have been strained and locally recrystallised during ductile deformation fluid inclusion homogenisation temperatures 140 175 c and ice melting temperatures 0 to 1 c indicate that the mineralising fluid was low salinity low co2 water with a density between 0 88 and 0 93 g cm3 arsenopyrite geothermometry implies a temperature of mineralisation of 370 70 c mineralisation pressure lay between 2 and 5 kbar mineralisation pressure temperature conditions and mineralogy are essentially the same as for metamorphism of the host schist vein calcite oxygen isotope ratios 12 to 15 per mil are similar to host schist values carbon isotope ratios of vein calcite 3 to 5 per mil are distinctly different from ratios in host schist 7 to 10 per mil elevated vein cr contents and isotopically depleted carbon data are consistent with some degree of equilibration with metavolcanic rocks it is inferred that metavolcanic rocks of the underlying aspiring terrane were a significant source for mineralising fluid and metals invincible mineralisation occurred in the latter stages of metamorphism and is the earliest recognised gold bearing vein system in the otago schist

geologic framework and tectonic evolution in western victoria australia abstract the stawell zone is interpreted to be part of the eastern extension of the adelaide fold belt into victoria the cambro ordovician turbidite sequence of the stawell and glenelg zones rests on a pile of late proterozoic metavolcanic rocks rather than cambrian metavolcanic units that are characteristic of the lachlan fold belt early deformation events d 1 d 3 in the stawell zone pre date granite emplacement and were synchronous with regional fold forming events that accompany thrust movements along discrete detachment surfaces the thrust system follows a ne se trending strike with an e directed translation of the tectonic units the steep 60 predominantly w dipping thrusts represent high strain zones localised in relatively weak cambro ordovician quartz rich turbidites that are sandwiched along the boundaries of the late proterozoic metavolcanics overprinting the early thrust system are d 4 d 6 deformation events that include reverse strike slip and normal faults the grampians extensional basin overlying the late proterozoic to ordovician sequence records a significant change in the tectonic regime operating during the late silurian early devonian it has been subjected to a middle devonian compressional deformation event d 4 with the development of thrust and fold structures this deformation is also superimposed on the thrusted and folded d 1 to d 3 sequence to the east of the grampians half graben producing further thrusts a gradual change from a ne sw to a n s stress field produces oblique strike slip faults normal faults of probably early cretaceous age transect the entire sequence the proterozoic cambrian sequence has been affected by a low p high t mid greenschist facies regional metamorphic event peak metamorphic conditions have been inferred from metavolcanic rocks and mafic units derived from a strongly differentiated tholeiitic suite at stawell these have been calculated to be 1 7 0 7 2 kbar and 450 20 2 c the advective heat input necessary to create this low p high t metamorphic event is attributed to penetrative deformation and strain partitioning between the crust and the mantle lithosphere which in turn causes crustal thickening associated compression and the observed d 1 to d 3 structures on the surface

effects of soil moisture and dried raindroplet crust on saltation and dust emission 1 field experiments using a sand particle counter and an optical particle counter clarified the links between saltation and dust emission under wet and weakly crusted conditions in a fallow field previously cultivated with wheat in australia a crust was formed by the impact of raindroplets after small precipitation events a little soil moisture enhanced the strengths of crust and aggregation even though the soil was dried dust concentration was proportional to friction wind velocity but the proportionality was dependent on ground surface conditions such as the minimally dispersed particle size distribution of parent soil and the presence or absence of crust

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

surface properties of stabilizing coastal dunes combining spectral and field analyses the coastal dunes of israel have been undergoing a process of stabilization since 1948 one of the major features of this process is a change in the surface properties of the dunes the development of a biological soil crust bsc and a change in the properties of the sand grains themselves in ashdod at the southern coastal plain of israel sand properties that include the bsc their fines silt and clay content and free iron oxide indicating their degree of rubification have been analysed in detail using field and lab spectroscopy methods in addition sand erosion and deposition were measured using erosion pins to determine their effect on the presence of the above mentioned factors it was found that the bsc over these dunes is comprised of green algae that differs in its reflectance spectra from cyanobacterial crust especially in the blue band the crust was found to be particularly developed in the stable areas mainly the interdunes and on the north facing slopes rather than on the south facing slopes a positive correlation was found between the crust fines and chlorophyll content with stable areas showing more developed bsc the stable areas showed also a lower albedo and slightly more developed reddish colour indicating a slightly higher rate of rubification this study demonstrates that the intensity of sand erosion deposition rates affects soil properties with the bsc being the fastest to react to the stabilization process months to several years followed by the content of fine particles several years to a decade whereas the rubification process is a much weaker marker and may need much longer time periods to develop decades to centuries

tectonic constraints on the timing relationships of metamorphism fluid production and gold bearing quartz vein emplacement abstract there is an ongoing discussion about the genetic significance of the postmetamorphic emplacement of many gold mineralizations as a contribution to this discussion this paper reviews the timing relationships between metamorphic devolatilization and metamorphism at different crustal levels for different tectonic processes for example denudation accompanying or following thickening causes metamorphism to occur later at depth than at shallow levels thus many internally heated terrains e g barrovian terrains are of deep later type that is peak metamorphism and devolatilization at deeper levels occurs at later times metamorphic processes of the deep later type may produce and release metamorphic fluids during prograde metamorphism at depth and precipitate them in the form of postmetamorphic quartz veins at shallow levels magmatic heating from below on the other hand is a deep earlier process causing inverse timing relationships in many metamorphic terrains deep later and deep earlier processes may compete for example if denudation at the surface accompanies heating from below if denudation and heating from below are of similar duration deep later characteristics prevail and a strongly bi modal age distribution of peak metamorphism in different crustal levels may arise the upper crust will experience metamorphism early but largely contemporaneously and the lower crust will experience metamorphism much later this process is particularly favourable for substantial simultaneous devolatilization of large sections of the lower crust to postdate metamorphism at shallow levels thus such processes may result in late infiltration events in cooling rocks of low metamorphic grade the common observation of postmetamorphic fluid infiltration and mineralization may therefore indicate but does not require that the mineralising fluids are related to the same metamorphic event

evidence for externally derived vein forming and mineralising fluids an example from the magdala gold mine stawell victoria australia abstract mineralogical and microfabric studies of the magdala gold deposit together with isotopic and fluid inclusion studies have shown that the mineralising fluid is externally derived the host rocks to the quartz veins do not possess any significant amounts of gold whereas the quartz veins can contain 7 g t gold the walls to the quartz veins possess alteration haloes in the form of stilpnomelane porphyroblasts attesting to the fact that the fluid in the veins was out of equilibrium with the host rocks the distribution of alteration haloes that occur parallel to the quartz vein margins necessitates that a subvertical fluid gradient be more or less constant during the deposition process in order to produce the observed architecture of the alteration haloes quartz lodes possess 18 o values that range from 15 8 to 17 3 per mil while associated host rocks range between 9 7 to 12 per mil in the metabasalts and 10 2 to 14 1 per mil in the volcanogenic and metasedimentary rocks the dissimilarity of 18 o values between host rocks and quartz veins suggests that there has been a high fluid influx in the veins implying external buffering four types of fluid inclusions were distinguished on the basis of spatial arrangement and composition using the laser raman spectroscopy method the salinity of the fluid inclusions range from 0 7 to 8 4 wt nacl equivalent suggesting that gold was deposited due to the influx of different external fluids the association of pyrite arsenopyrite pyrrhotite with gold and with pges suggests that these fluids have a lower crustal origin and may have originated from the upper mantle and mixed with fluids derived from deep seated metasediments

distribution of orogenic gold deposits in relation to fault zones and gravity gradients targeting tools applied to the eastern goldfields yilgarn craton western australia a quantitative spatial analysis of mineral deposit distributions in relation to their proximity to a variety of structural elements is used to define parameters that can influence metal endowment deposit location and the resource potential of a region using orogenic gold deposits as an example geostatistical techniques are applied in a geographic information systems based regional scale analysis in the high data density yilgarn craton of western australia metal endowment gold production and gold rank per square kilometer is measured in incremental buffer regions created in relation to vector lines such as faults the greatest metal tonnages are related to intersections of major faults with regional anticlines and to fault jogs particularly those of dilatant geometry using fault length in parameter search there is a strong association between crustal scale shear zones faults and deposits nonetheless it is the small scale faults that are marginal or peripheral to the larger scale features that are more prospective gravity gradients depicted as multiscale edges or gravity worms show a clear association to faults that host gold deposits long wavelength long strikelength edges interpreted as dominantly fault related have greater metal endowment and provide a first order area selection filter for exploration particularly in areas of poor exposure statistical analysis of fault fold and gravity gradient patterns mainly affirms empirical exploration criteria for orogenic gold deposits such as associations with crustal scale faults anticlinal hinge zones dilational jogs elevated fault roughness strong rheological contrasts and medium metamorphic grade rocks the presence and concurrence of these parameters determine the metallogenic endowment of a given fault system and segments within the system by quantifying such parameters the search area for exploration can be significantly reduced by an order of magnitude while increasing the chance of discovery

metatholeiites and interflow sediments from the cambrian heathcote greenstone belt australia sources for gold mineralization in victoria metatholeiites and interflow sediments of cambrian age are exposed in the lake cooper quarry located in the northern segment of the heathcote greenstone belt central victoria australia the exposed sequence is 281 m thick and comprises nine massive to pillowed lava flows and seven interflow sequences the metabasalts from the lake cooper quarry have strong petrological and geochemical similarities to normal midocean ridge basalts n morb and to metabasalts from greenstone suites elsewhere in victoria suggesting that they have not been exposed to extensive hydrothermal alteration the interflow sediments in the quarry are subdivided into units comprising finely bedded sulfides layers of sulfidic carbonaceous argillites chert and sedimentary carbonate rocks unusual mineral assemblages in these sediments as well as their trace element concentrations and rare earth element signatures suggest an exhalative volcanogenic origin whereas gold values in the tholeiites from the lake cooper quarry generally remain below 2 to 5 ppb gold contents in the interflow sediments which are also characterized by elevated as cu and zn values range from 5 to 243 ppb and average 67 ppb on the basis of sedimentological features and sulfide petrology accumulation of the ore metals in these sediments is inferred to have occurred during deposition of the exhalative precipitates possibly as a result of extraction and transfer of ore metals from the thick boninite sequence known to occur below the tholeiites in victoria mass balance calculations show that remobilization of gold from the interflow sediments by metamorphic fluids and subsequent redeposition within dilatation zones and structural traps at higher crustal levels during the early to middle paleozoic could account for a significant component of the central victorian gold province thus these exhalative metasediments might have played a vital role in accumulating preconcentrating and providing the gold required to form the world class turbidite hosted lode deposits in the lachlan fold belt of victoria

alpine turf exfoliation pans in lesotho southern africa climate process morphological linkages abstract although alpine pans have been reported from a variety of mountain regions these have received limited research attention and are thus amongst the least known of closed basins this study investigates macro and fine scale morphological attributes and the process dynamics of alpine turf exfoliation pans in the high drakensberg of lesotho southern africa climate data temperature precipitation and wind are used to better ascertain climate surface process linkages and how these may be associated with the observed morphological phenomena thirty pans were assessed for both macro and fine scale aspect controlled morphological attributes during 2005 tinytag temperature loggers recorded ground temperatures on various pan riser aspects to establish the potential for cryogenic activity similarly wind speed and direction data from 2001 were used to identify the potential role of wind as an erosion and transportation mechanism the number and total weight of detached turf clumps accumulated at the base of various pan riser aspects were determined in july 1999 september 2001 and september 2004 it is suggested that the pans originated through initial turf disruption by animal trampling and turf burning followed by the cryogenic up heave of sediments the pans typically elongate towards the southeast as they enlarge demonstrate most active erosion on eastern and southeastern riser aspects and host seasonal micro echo and micro climbing dunes along such riser aspects it is concluded that an annual cyclic seasonal pattern of contemporary climate driven geomorphic processes dominated by strong northwesterly winds control the fine scale morphological evolution of alpine turf exfoliation pans in the lesotho highlands

soil crusting on sandy soils and its influence on wind erosion abstract under rainfall a crust forms at the surface of most soils for soils rich enough in clay clay content 5 it is well known that a physical crust is responsible for a supply limitation of particles available for wind erosion sandy soils are very prone to crusting as well as to wind erosion indeed structural sieving crusts develop on sandy soils even after light rainfalls this kind of crust shows a loose sand layer at the surface overlying a thin layer where fine particles are concentrated the main objectives of this study were to determine whether such a crust formation limits the availability of 1 sand grains for entrainment into saltation and 2 fine particles for uptake into a vertical wind erosion flux suspension in atmosphere of particles

the stabilizing role of bonding agents on the entrainment of sediment by wind well sorted fine sand pretreated with varying concentrations of two soluble salts mgcl2 and cacl2 was tested for threshold shear velocity in a recirculating wind tunnel these tests demonstrate that even relatively low surface salt concentrations can significantly increase threshold shear velocity however the relationships between surface salt concentration and threshold shear velocity for the two salts were not significantly different which is similar to the results for monovalent chlorides presented by nickling ecclestone a general relationship between threshold shear velocity and total surface soluble salt content is presented

effects of microbiotic crusts under cropland in temperate environments on soil erodibility during concentrated flow several studies illustrate the wind and water erosion reducing potential of semi permanent microbiotic soil crusts in arid and semi arid desert environments in contrast little is hitherto known on these biological crusts on cropland soils in temperate environments where they are annually destroyed by tillage and quickly regenerate thereafter this study attempts to fill the research gap through a a field survey assessing the occurrence of biological soil crusts on loess derived soils in central belgium in space and time and b laboratory flume 2 m long experiments simulating concentrated runoff on undisturbed topsoil samples 0 4 0 1 m2 quantifying the microbiotic crust effect on soil erosion rates three stages of microbiotic crust development on cropland soils are distinguished 1 development of a non biological surface seal by raindrop impact 2 colonization of the soil by algae and gradual development of a continuous algal mat and 3 establishment of a well developed microbiotic crust with moss plants as the dominant life form as the silt loam soils in the study area seal quickly after tillage microbiotic soil crusts are more or less present during a large part of the year under maize sugar beet and wheat representing the main cropland area on average the early successional algae dominated crusts of stage 2 reduce soil detachment rates by 37 whereas the well developed moss mat of stage 3 causes an average reduction of 79 relative soil detachment rates of soil surfaces with microbiotic crusts compared with bare sealed soil surfaces are shown to decrease exponentially with increasing microbiotic cover b 0 024 for moss dominated and b 0 006 for algae dominated crusts in addition to ground surface cover by vegetation and crop residues microbiotic crust occurrence can therefore not be neglected when modelling small scale spatial and temporal variations in soil loss by concentrated flow erosion on cropland soils in temperate environments copyright 2007 john wiley sons ltd

dry lake beds as sources of dust in australia during the late quaternary a volumetric approach based on lake bed and deflated dune volumes abstract dust affects earth s climate ecology and economies across a broad range of scales both temporally and spatially and is an integral part of the earth s climate system previous studies have highlighted the importance of inland lake beds to dust emissions both locally and globally this study aims to explore the relative volumetric importance of ephemeral lakes that emit dust to the australian southeastern dust path over the last glacial cycle srtm dems and gis analyses of long term up to 80 ka lake bed deflation volumes and deposition of sand sized sediment onto downwind source bordering dunes were used to derive estimates of transported dust mass a strong power relationship was found between lake area and the mass of deflated lake bed sediments total dust masses for the largest 53 lakes in southeastern australia were derived using the relationship between lake area and dust mass and used to determine an upper value for total dust mass deflated from lake beds in southeastern australia ephemeral lake derived dust was found to represent at most 13 of the dust derived from southeastern australia deposited in the southern pacific over the last 80 ka or 22 over the last 40 ka lake eyre the largest lake has contributed at most 3 of the australian southeast dust plume these results imply that there are significant additional sources of dust in australia over these timescales such as floodplains or dunefields and that modelling must allow for diverse climatic and geomorphic controls on dust production

threshold friction velocities and rupture moduli for crusted desert soils for the input of soil particles into the air desert soils having clay crusts mostly from the mojave desert were tested for threshold friction velocity the friction velocity at which soil erosion begins with an open bottomed wind tunnel the soils were also tested for content of clay water soluble material calcium carbonate organic material mineralogy of clay and of salts soil moisture modulus of rupture and crust thickness if no loose material existed on the soil surface crusts having modulus of rupture greater than 0 7 bar and crust thickness of 0 7 cm to 0 3 cm were effective in protecting against wind erosion disturbed clay crusts having modulus of rupture before disturbance greater than 2 bar with thickness less than 1 9 cm did not experience significant wind erosion modulus of rupture was related to composition of soil but was shown to depend mostly on clay content soil composition is related to modulus of rupture in an empirical equation

biological soil crust development and its topsoil properties in the process of dune stabilization inner mongolia china this study was undertaken at horqin sand land inner mongolia northern china field samples of biological soil crusts bscs and underlying topsoil 0 5 cm under bsc were taken in areas of different dune stabilization stages and their physicochemical properties were analyzed including particle size distribution bulk density organic matter nitrogen phosphorus electrical conductivity ec ph and caco3 content the results revealed that semi mobile dunes semi fixed dunes and fixed dunes had developed a physical crust algae crust and moss crust respectively the thickness hardness water content fine fraction and nutrient contents of bscs were gradually increasing along the dune stabilization gradient meanwhile bsc establishment and development enhanced the bulk density silt and clay content and nutrients of the topsoil under it in an increasing tend from semi mobile dune to fixed dune organic matter concentrations and other nutrients in the 0 5 cm topsoil layer under bscs were significantly higher compared to unconsolidated soil control moreover there were strong significant positive correlations between topsoil and bscs organic matter total nitrogen available nitrogen available phosphorus caco3 and 0 05 mm particle content suggesting that bscs have an influence on some of the properties of the underlying topsoil

bedding parallel veins and their relationship to folding abstract laminated bedding parallel veins hosted in turbiditic sandstone shale sequences from central victoria australia consist of stacked millimetre thick sub parallel sheets of quartz separated by micaceous layers wall rock slivers and pressure solution seams they have very high length to thickness ratios are laterally continuous over tens to hundreds of metres and have relatively uniform thickness compared to other vein types they are intimately associated with and folded by chevron folds and the quartz grain shape elongation lineation is commonly orthogonal to mesoscopic and macroscopic fold hinge lines the bedding parallel veins have two morphological forms type i are thin commonly 5 10 cm laminated veins which have complex microstructures dominated by phyllosilicate inclusion surfaces related to oblique opening along bedding with varying rates of deposition opening relative to shear displacement slip along the bedding surfaces more common are type ii thicker generally

the microstructure of microbiotic crust and its influence on wind erosion for a sandy soil surface in the gurbantunggut desert of northwestern china abstract microscopic examination of microbiotic soil crust shows that the profiles of soil with a dense cyanobacterial cover had two different layers a surface thin layer composed of aeolian born materials and an organic layer formed by filamentous cyanobacteria associated with sand particles the results indicate that microbiotic cover is an important determinant of sand fixation in the gurbantunggut desert northern part of xinjiang northwestern china microscopic examination of microbiotic crusts in this study revealed an intricate network of filamentous cyanobacteria and exopolysaccharides which binds and entraps sand grains and conglutinate fine particles with each other resistance to wind erosion paralleled the different disturbance levels on microbiotic soil crust sandy soil surface disturbances resulted in greatly decreased soil resistance to wind erosion maximum wind tunnel velocity in this test 25 m s 1 did not lead to any wind erosion on the surface of undisturbed microbiotic soil crust i e 100 covered by microbiotic soil crust as for different disturbance levels the highest threshold friction velocity was seen in the sand surface with 10 disturbance of microbiotic crust the surface microbiotic soil crusts have great effects on wind erosion rates wind erosion rates for sandy soil with 0 crust cover was about 46 21 17 times the soil with 90 crust cover at wind velocities of 18 22 25 m s 1 respectively this study confirms that the planners and managers of nature reserves in this area should understand the important ecological roles of microbiotic crust in desert ecosystems the reduction of trampling on the soil will eventually result in the re establishment of biological crusts and their associated organisms and ultimately lead to lower levels of wind erosion additionally strategies should be developed to manage livestock and oil exploration in order to avoid concentrated zones of impact

temporal aspects of the abrasion of microphytic crusts under grain impact wind tunnel simulations of the response of two moss crusts to grain impact indicate that given sufficient time these surfaces will deteriorate under very low wind velocities only slightly above u t for the loose saltating grains in parallel with these experiments the frequency distributions of ultimate strength and penetration energy were determined for each of the two crust types via penetrometry pohlia was found to be stronger than tortula but even so both of these crusts had ultimate strengths 20 350 times higher than the force delivered by a single grain impacting each surface at a velocity of 1 ms 1 in comparison the modulus of deformation and penetration energy data were very similar for the two surface types especially for the weakest areas of crust development this observation is in accord with the wind tunnel simulations that also found no consistent difference in the response of these two crust types to impact in comparison with crusts formed by clay and salt fibrous microphytic crusts are morphologically complex and typically weak the notable elasticity of these surfaces does reduce the force of grain impact and thereby provides some protection against rupture one of the central conclusions of this study suggests that not only is the particle kinetic energy at impact important in crust breakdown but also tiny fractures at points of localized stress concentration contribute to a progressive reduction in the integrity of the filament net in some of the experiments conducted as part of this study up to 50 or more minutes of constant bombardment was required to produce small abrasion marks on selected areas of the microphytic crust this study prepares a foundation for future experiments needed to examine the breakdown of complex crusts formed in nature copyright 2002 john wiley sons ltd

sediment yield on a devastated hill in southern china effects of microbiotic crust on surface erosion process in southern china most of the forests consist of pinus massoniana but they are usually poor thin and deteriorated due to human intervention such as cutting removal of litter for fuel and over grazing therefore exposed bare soil is found in many devastated hills as a consequence both the direct runoff percentage and the sediment yield are very high in order to understand the surface erosion processes in this environment we measured sediment yield and surface erosion depth in terms of catchment scale and carried out in situ sprinkling experiments focusing on the spatial variability of surface conditions and sediment sources the results of sediment yield measurements at the end of headwater catchment suggest the following characteristic 1 the surface water is capable of transporting more material than is supplied by detachment that is the sediment discharge process is detachment limited in situ sprinkling experiments indicate that 2 in the lower part of the hillslope where the surface is covered by microbiotic crust the ratio of surface runoff to rainfall is high but sediment yield is small 3 in the upper part of the hillslope where there is no microbiotic crust the ratio of surface runoff to rainfall is low but sediment yield is large measurements of surface erosion depths indicate that 4 microbiotic crusts provide a high degree of protection against soil erosion even though the surface runoff ratio is large at the lower hillslope consequently the surface erosion depth is almost zero at the lower part of hillslope 5 the main source of sediment was the upper part of hillslope based on these indications it can be concluded that when the sediment discharge process is detachment limited the effect of the surface crust and or the vegetation cover on the sediment discharge process is great that is the spatial variation of the surface crust and or the vegetation cover controls the source of sediment

a geochronological framework for orogenic gold mineralisation in central victoria australia new 40ar 39ar geochronological data support and significantly expand upon preliminary age data that were interpreted to suggest an episodic and diachronous emplacement of gold across the western lachlan fold belt australia these geochronological data indicate that mineralisation in the central victorian gold province occurred in response to episodic eastward progressing deformation metamorphism and exhumation associated with the formation of the western lachlan fold belt initial gold formation throughout the stawell and the bendigo structural zones can be constrained to a broad interval of time between 455 and 435 ma with remobilisation of metals into new structures and or new pulses of mineralisation occurring between 420 and 400 ma and again between 380 and 370 ma linked to episodic variations in the regional stress field and during intrusion of felsic dykes and plutons this separation of ages is incompatible with the view that gold emplacement in the western lachlan fold belt was the result of a single orogen wide event during the devonian a distinct phase of gold mineralisation characterised by elevated cu mo sb or w is associated with both late silurian to early devonian 420 to 400 ma and middle to late devonian 380 to 370 ma magmatism when crustal thickening and shortening during the ongoing consolidation of the western lachlan fold belt led to extensive melt development in the lower crust and resulted in widespread magmatism throughout central victoria these 420 to 400 ma and 380 to 370 ma occurrences best exemplified by the wonga deposit in the stawell structural zone and many of the woods point deposits in the melbourne structural zone but also evidenced by occurrences at fosterville and maldon in the bendigo structural zone clearly formed synchronous with or post date the emplacement of plutons and dykes and thus are spatially if not genetically related to melt generation at depth this later magmatic associated and polymetallic type of gold mineralisation is economically subordinate to the earlier metamorphic associated type of gold deposition in the stawell and bendigo structural zones but tends to be the dominant style in the melbourne zone these new geochronological constraints together with zircon u pb data from felsic intrusive rocks of known relationship to gold mineralisation demonstrate that initial hydrothermal alteration associated with gold emplacement in the western lachlan fold belt was metamorphic related predating the emplacement of granite plutons by as much as 80 million years this timing differs from other important orogenic gold districts where gold deposition is closely associated spatially with felsic magmatism the early introduction of metamorphically derived fluids well before magmatism may reflect variations in the timing of peak metamorphic conditions at different crustal levels in an accretionary prism undergoing simultaneous deformation and erosion consequently no genetic link exists between the main phase s of gold mineralisation and magmatism in the central victorian gold province with the exception of formation of a minor magmatism related and geochemically distinct mineralisation style at about 420 to 400 ma and again at about 380 to 370 ma the apparent spatial relationship between gold mineralisation and felsic intrusions is merely the result of melts and fluids being channelised along the same structures

thrust related strain gradients and thrusting mechanisms in a chevron folded sequence southeastern australia an e directed imbricate fan thrust system within a chevron folded monotonous quartz rich turbidite succession shows marked gradients in strain from the upper to lower parts of individual thrust sheets upper parts of thrust sheets show low to moderate strains xz strains 30 1 tight inclined chevron folds ila 30 with predominantly w dipping axial surfaces intense phyllitic cleavage with a strong down dip mineral stretching lineation and long curved tapering quartz pressure shadows on pyrite such differences in fold geometry the intensity of the cleavage and the geometry of quartz fibres in pressure shadows require thrust sheet emplacement to be synchronous with the internal deformation of sheets thrust sheets show a change from an approximately constant volume plane strain coaxial deformation in their upper parts to non coaxial high strain deformation with incremental i between those expected for pure shear and simple shear i e 0 i 5 45 in their basal parts observed geometries and intensities reflect partitioning of strain and deformation mechanisms within individual thrust sheet volumes both during the initiation and propagation of subsurface detachment faults and with their emplacement to shallower crustal levels strain softening related to chevron folding and more intense cleavage development within a 500 m basal zone has controlled the emplacement of these turbidite dominated thrust sheets transport and internal deformation of the thrust sheets did not involve gravitationally induced spreading but required either a push from the rear or some form of underthrusting

application of mineral equilibria modeling to constrain t and x co2 conditions during the evolution of the magdala gold deposit stawell victoria australia mineral equilibria modeling involving solid solution calculations has been combined with mineral assemblage information from the alteration zones associated with gold mineralization to determine the t and xco2 conditions for the formation of the magdala gold deposit at stawell victoria australia economic gold mineralization is primarily hosted within the stilpnomelane alteration zone of the stawell facies that is adjacent to the magdala basalt evolution of the magdala gold deposit involved at least three fluid infiltration events 1 a co2 bearing fluid during the d2 deformation event produced carbonate spots throughout the chlorite zone 2 a co2 s k bearing fluid accompanied the d3 4ab deformation and produced a muscovite zone and siderite rims on ankerite and 3 a co2 k s au bearing fluid during the d4c deformation event produced the stilpnomelane zone of the stawell facies the proximal and distal alteration zones within the magdala basalt and the main economic gold mineralization mineral equilibria modeling constrains the temperature of formation of the magdala deposit to t 345 390 c at 3kbar substantially lower than indicated by other previous classical thermobarometry methods furthermore this method has allowed the characterization of the mineralizing fluid and constrained its composition to xco2 0 08 at 3kbar the timing and composition of the mineralizing fluids are similar to that of metamorphic fluid generated from devolatilization of a greenstone pile with peak of metamorphism occurring earlier and at deeper levels in the crust

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

effect of soil crusting on the emission and transport of wind eroded sediment field measurements on loamy sandy soil field data are reported for the horizontal and vertical flux of wind eroded sediment on an agricultural field in northern germany measurements were made during a windstorm that hit the region on 18 may 1999 the magnitude of both fluxes was significantly affected by the presence of a surface crust covering the test field measuring the physical crust strength at 45 locations with a torvane the relationships between crust strength and the horizontal fh and vertical fv sediment fluxes were investigated both fluxes decreased as the surface crust became stronger the decay behaved as an exponential function for both types of flux the horizontal sediment flux over a crusted surface can be accurately predicted by completing marticorena and bergametti s journal of geophysical research 100 1995 16415 erosion model with a crust function the vertical particle flux over crusted soil can be calculated by adding a similar function to alfaro and gomes s journal of geophysical research 106d 2001 18075 dust production model the study also suggests that the gradual bombardment of a surface crust by impacting particles does not immediately result in a decay of the crust s protective effect provided that the crust has a minimum thickness however once the crust becomes perforated its protective effect disappears very quickly leading to much higher horizontal and vertical sediment fluxes than predicted for undamaged crusted soil

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time

chronometric calibration of mid ordovician to tournaisian conodont zones a compilation from recent graphic correlation and isotope studies three available graphic correlation analyses are used to calibrate mid palaeozoic conodont zonations sweet s scheme for the mid to upper ordovician kleffner s for the mid to upper silurian and murphy berry s for the lower and middle lower devonian the scheme of sweet is scaled by applying the high precision u pb zircon date of tucker and others for the rocklandian and linked with that of kleffner by scaling the graptolite sequence of the ordovician silurian global stratotype section to fit two similarly derived dates from this sequence the top of kleffner s scheme all of murphy berry s as well as standard zones to the frasnian are calibrated by using tie points of the latest cambridge bp time scale gts 89 however the recent microbeam zircon date by claoue long and others for the hasselbachtal devonian carboniferous auxiliary stratotype is used to calibrate the standard famennian zones also the similarly derived but preliminary determination reported by roberts and others from the isismurra formation of new south wales is tentatively taken as the top of the tournaisian and so used to calibrate tournaisian zones despite the considerable extrapolation required to compile these schemes and their inherent errors the resultant time scale closely agrees with other dates of tucker and others from the llanvirn as well as the gts 89 homerian gorstian tie point this suggests that stratigraphic methods can be usefully applied to geochronometry the llandovery appears to have lasted longer 16 m y than usually envisaged and the ordovician silurian boundary may need to be lowered to approximately 443 5 ma certainly chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high resolution dating for their calibration will be crucial to more accurate biochronometries

wind erosion of crusted soil sediments saltating particles increase the rate of dust release from sediments in arid and semi arid areas they also break interparticle bonds in aggregated and crusted soils thereby increasing the number of particles available for entrainment this pilot study examines rates of erosion in relation to the flux of saltating grains for three crusted sediments of different strengths dislodgement of surface particles decreases with increasing crust strength as measured by a cylindrical flat ended penetrometer in addition initial dust release from craters formed by single impactors in unaggregated soil is examined in relation to the associated saltator the volume of material removed depends linearly on the kinetic energy of the abraders

flexural slip generated bedding parallel veins from central victoria australia abstract thin continuous laminated bedding parallel quartz veins bpvs with slip striated and fibred vein walls occur within slates or at their contact with sandstones on the limbs of chevron folds in the bendigo castlemaine goldfields southeastern australia two microstructural types of bpv i and ii have been previously recognized and are confirmed in this study both types are concluded to have formed during and or after crenulation cleavage the first tectonic axial planar structure in the wallrock slates and during flexural slip folding type i bpvs consist of syntaxial phyllosilicate inclusion trails parallel to bedding enclosing inclined inclusion bands the latter formed by detachment of wallrock phyllosilicate particles from the walls of pressure solution segmented discordant tension veins type i bpvs are formed by bedding parallel shear and grow in width by propagation of the discordant veins into the bpv walls type ii veins are composed of quartz bands separated by wallrock slate seams which have split away from the vein wall during dilatant shear opening they incorporate numerous torn apart fragments of crenulated wallrock slate type i bpv inclusion band average spacing of 0 5 mm probably represents the magnitude of slip increments during stick slip flexural slip folding activity

intracrustal detachments and implications for crustal evolution within the lachlan fold belt southeastern australia seismic reflection profiling in the southern lachlan fold belt australia indicates geometrically complex mid to lower crustal detachments possibly associated with crustal thickening by tectonic underplating of collided microplates and or oceanic plateaus low angle detachments either intersect or sole into the crust mantle boundary forming a crustal stacking wedge typical of lithospheric or a type subduction upper crustal reflections show that major moderately to steeply dipping reverse faults exposed at the surface flatten with depth and have listric form the chevron folded quartz rich turbidite sequence of the lachlan fold belt is therefore allochthonous with respect to the lower crust like the northern appalachian maritimes the lachlan fold belt has a composite crust with diverse lower crustal blocks overlain by allochthonous imbricated terranes of the surface rocks

role of biological soil crusts in affecting soil evolution and salt geochemistry in hyper arid atacama desert chile abstract eight soil profiles either barren or covered with biological soil crusts bscs were sampled at multiple depths in a remote valley in the atacama desert chile to explore the impact of bscs on soil evolution and salt geochemistry bsc sites had thicker soil profiles compared to non bsc sites which could be a result of past geological processes and also partially accounted for by the establishment of bscs that can help limit erosion and promote significant soil accumulation the greater abundances of fine particles below bscs could essentially be attributed to the ability of bscs to trap more fine grains the generally higher salt ion inventories but smaller salt ion concentrations in soil profiles beneath bscs were probably due to that bscs can promote the retention of salt ions and insoluble dust simultaneously but the latter to a greater extent nitrate oxygen isotopes indicated the predominant existence of atmospheric nitrate in the soils suggesting biological processes of bscs may not significantly impact the ion accumulation or distribution in the underlying soils a mechanism of consistent soil accumulation via the retention of atmospheric deposition and occasional interruption of subsurface collapsing due to erosion processes was proposed to explain the development of soil profiles and different landscape features as well as the role of bscs in soil evolution in this study area the soil ages were estimated to be around 440 ky based on the proposed soil accumulation mechanism

crustal scale fluid pathways and source rocks in the victorian gold province australia insights from deep seismic reflection profiles deep seismic reflection data collected across the western lachlan orogen of southeast australia have provided important insights into crustal scale fluid pathways and possible source rocks in one of the richest orogenic gold provinces in the world the profiles span three of the most productive structural zones in victoria the stawell bendigo and melbourne zones zone scale variations in the age and style of gold deposits correspond with differences in crustal structure and composition the bilateral distribution of gold production in the stawell and bendigo zones is related to the v shaped crustal scale geometry of the two zones in cross section major first order faults like the east dipping moyston fault and a set of west dipping listric faults within the bendigo zone were probably major fluid conduits in the lower to middle crust during gold mineralization first order faults in the stawell and bendigo structural zones appear to have accommodated large scale thickening down to the lower crust the faults converge in a region beneath the western bendigo zone where a thick section of mafic volcanic rocks and lesser sedimentary rocks are identified as a likely common source of gold bearing fluid that was largely generated by late ordovician to early silurian metamorphism the areas with the greatest gold endowment lie above lower crustal regions that have preserved the thickest succession of fertile mafic igneous rocks up to about 25 km thick they also correspond to a region of thin or absent precambrian lithosphere mafic rocks in the stawell zone and far western bendigo zone were probably partly consumed by cambrian west dipping subduction similar rocks in the rest of the bendigo zone lay outside the influence of cambrian subduction accretion and were deformed later probably beginning in the late ordovician early silurian benambran orogeny during crustal scale imbrication this imbrication preserved much of the mafic rocks to form the lower to middle crust first order listric faults in the bendigo zone are interpreted as major controls on the locations of goldfields even though they are largely unmineralized near the present surface the shallow dipping segments of first order listric faults were favorably oriented for reactivation at the time of gold mineralization and acted as major fluid conduits in the lower to middle crust in contrast the upper steeply dipping segments of first order listric faults were unfavorably oriented for reactivation and were poor fluid conduits the seismic data show that the transition from predominantly shallow to steeply dipping fault segments occurs in the middle to upper crust near the boundary between thick imbricated metavolcanic rocks that lie immediately below 6 to 15 km of folded metasedimentary rocks this transition may have coincided with fluid escape zones that aided the transfer of permeability away from first order faults and into the overlying fold dominated turbidites this transfer of permeability was enhanced by the growth of subvertical fold related fault and fracture meshes in the upper crustal turbidites the fault and fracture meshes consisted of bedding parallel faults limb thrusts and tension vein arrays that developed along fold hinges in the bendigo zone individual fold hinges and regional fold culminations were important controls on the distribution of fluid flow fluid flow was partly syndeformational but overlapped into the immediate postdeformational period of the benambran orogeny later reactivation of first order faults in the late silurian to early devonian and again in the late devonian led to further although less important mineralizing events as fluids exploited the preexisting fault architecture deeply penetrating north dipping listric faults in the less gold rich melbourne zone cut into inferred proterozoic basement and may have been fluid conduits during a late devonian mineralizing event

wind transport of sand surfaces crusted with photoautotrophic microorganisms abstract wind tunnel experiments show that while surfaces inoculated with photoautotrophic organisms are stable in winds up to 19 m s 1 only filamentous cyanobacteria especially nostoc commune afford considerable protection against abrasion from windborne particles crusts formed by the polysaccharide secreting alga chlamydomonas acidophila break down easily under impact the entrainment of large low density aggregates possibly contributing to higher transport rates than would otherwise be expected for untreated sediment surface disintegration encompasses a suite of complex scale dependent processes which vary with the structure thickness and strength of the crust independent measurements of crust strength based on flexure testing are in good agreement with wind tunnel evaluation of crust stability the accommodation of a relatively large amount of deformation without rupture is an important property of fibrous photoautotrophic mats perhaps outweighing consideration of their peak strength

crust strength a wind tunnel study of the effect of impact by saltating particles on cohesive soil surfaces a wind tunnel study examined the effect of distributions of saltating particles on sediment surfaces which were characterized by distributions of their tensile strength the sediments consisted of varying proportions of large sand sized particles with a fine particle cement the energies of the impacting particles and the surface strengths were compared with the mass of material lost from the surface it is important to consider distributions of parameters rather than mean values only since abrasion and erosion may occur from surfaces not predicted from average strength and saltation velocities at the impact velocities used in this study mean velocity 4 4 m s 1 with standard deviation of 0 51 surfaces containing less than 12 per cent fine material were easily eroded but insignificant erosion occurred when the fine particle content exceeded 60 per cent small amounts of cementing material were easily ruptured allowing the large sand grains to be moved largely in creep by the bombarding particles a significant amount of energy was lost to the bed as the percentage of fine material increased the surface became more difficult to break up and less energy was lost to the bed the probability that erosion will occur for known energy distributions of impacting particles and surface strength can be calculated and the mass loss increases exponentially with a decrease in the percentage of fine cementing particles copyright 2001 john wiley sons ltd

importance of biological loess crusts for loess formation in semi arid environments the essential abiotic components for loess formation are material dust atmospheric circulation wind suitable surface conditions for the trapping of aeolian material and for the subsequent development of typical loess sedimentary structures in spite of the world wide distribution of loess deposits knowledge of the processes of dust accumulation and its transformation to mature loess sediment is still inadequate loess accumulation appears greatest during the most arid periods and in semi arid regions biological crusted surfaces bcs are of potentially great importance in loess formation especially in semi arid regions bcs are highly specialized extremophile communities and apparently play an important role in atmospheric dust trapping and erosion prevention results indicate that cyanobacterial strains isolated from current carpathian basin loess exhibit specific morphological and eco physiological characteristics that play a key role in loess formation warranting adoption of the new term biological loess crusts blc a model of the influence of cyanobacterial blc life strategies on loess formation explains trapping accumulation and preservation as well as loess texture and structure this potential significance of blc in the accumulation and preservation of loess sediments may be considered as a model suitable model database for recognition of bioorganic modification of geological strata mycosporine and scytonemin pigments can serve as blc biomarkers elucidating their role in soil evolution and in aiding paleoclimatic paleoenvironmental and paleovegetation reconstructions

a fluid inclusion study of the fosterville mine a turbidite hosted gold field in the western lachlan fold belt victoria australia abstract gold mineralisation at fosterville occurs in association with disseminated arsenopyrite and pyrite adjacent to a complex series of quartz carbonate veins along two nnw trending fault zones quartz carbonate veins which have formed in dilational fractures within the sulphide ore zone have 18 o values between 16 0 and 17 6 and contain the following types of fluid inclusions type ia two phase liquid rich inclusions with less than 10 vol vapour and no detectable gases type ib two phase inclusions with approximately 10 vol co 2 rich vapour type ii co 2 bearing inclusions with 30 vol vapour and type iii liquid h 2 o and liquid plus vapour co 2 inclusions with variable h 2 o co 2 ratios raman microprobe analysis showed that types ib ii and iii contain co 2 with variable amounts of n 2 and ch 4 in some inclusions type 1a aqueous inclusions from stage 4 of the paragenesis have salinities ranging from 5 to 7 wt nacl equivalent whereas the co 2 bearing inclusions in the same stage have average salinities around 3 5 4 0 wt nacl equivalent the co 2 bearing inclusions exhibited two different types of homogenisation behaviour vapour rich type ii and iii inclusions either homogenised to vapour or showed near critical behaviour by gradual fading of the meniscus with homogenisation temperatures from 234 to 384 c and a mode at 270 c liquid rich co 2 bearing inclusions homogenised to the liquid phase with a bimodal distribution the majority of inclusions homogenised between 243 c and 314 c with a mode around 270 c but a secondary mode occurs around 180 c this mode corresponds fairly closely to the mode observed for the aqueous type 1a inclusions at 170 c the variable salinities coexisting liquid and vapour rich inclusions and the overlap of the homogenisation temperatures suggest that phase separation has occurred during vein formation and the resulting depth of mineralisation is estimated to be between 2 6 and 5 7 km gold precipitation resulted from the partitioning of h 2 s into the vapour phase during fluid unmixing which was enhanced both by the decreasing pressure as fluid flowed from the faults and veins into the host rocks and by the addition of n 2 and ch 4 comparisons with available fluid inclusion data for the western lachlan fold belt indicates that the fosterville gold field formed at lower temperatures and at a higher crustal level than the quartz reef style of gold deposits in the bendigo ballarat zone the fluids at fosterville also contain greater amounts of n 2 and ch 4 suggesting that the mineralising fluids penetrated further into the host rocks and reacted either directly with carbonaceous matter or with reduced fluids contained within the host rocks

late structural control of mesothermal vein hosted gold deposits in central victoria australia mineralization mechanisms and exploration potential abstract comparison of the structural relationships between five gold deposits in ordovician rocks of the central victorian slate belt reveals a similar history and structural control of gold mineralization large quartz veins spatially associated with gold mineralization such as the famous saddle reefs of bendigo formed during the second deformation earlier than the gold mineralization itself where they were overprinted by the effects of the fourth deformation they provided structural sites for gold deposition on their boundaries with country rock where brecciation jostling and fracture were favoured access of fluids resulting from metamorphism and deformation to the brecciated fractured and jostled blocks of country rock created conditions suitable for the precipitation of gold through a sequence of alteration replacement and infill the dominant structural relationships that resulted in the generation of these sites were a the high angle of the axial plane of the fourth deformation to earlier structures and b the presence during mineralization of large pre existing quartz veins that acted as structural discontinuities on which brecciation could occur these factors allow a predictive capacity for exploration in the region

recalibrating aeolian sand transport models a quality controlled data set comprising measurements of aeolian sand transport rates obtained at three disparate field sites is used to evaluate six commonly employed transport rate models those of bagnold kawamura zingg owen hsu and lettau and lettau and to recalibrate the empirical constants in those models shear velocity estimates were obtained using the von karman constant and an apparent von karman parameter models were recalibrated using non linear regression and non linear regression with least squares lines forced through axes origins recalibration using the apparent von karman parameter and forced regression reduced the empirical constants for all models the disparity between the predictions from the different models is reduced from about an order of magnitude to about a quarter of an order of magnitude the recalibrated lettau and lettau model provided the greatest statistical agreement between observed and predicted transport rates with a coefficient of determination of 0 77 evaluation of the results suggests that our estimations of threshold shear velocity may be too slow causing errors in predicted transport rates copyright 2012 john wiley sons ltd

the role of aeolian dust in ecosystems abstract the recent upsurge in research attention to aeolian dust has shown that dust transport systems operate on very large spatial and temporal scales and involve much larger quantities of sediment than was previously realized an inevitable consequence of this is that researchers from a range of neighbouring disciplines including ecology are beginning to realize that this new knowledge has important implications for their study areas in the present paper we examine the ecological implications real and potential of this expanding knowledge of dust transport systems with a particular emphasis upon the australian dust transport system we track these ecological effects from source to sink at source wind erosion soil vegetation relationships are often dominated by temporal changes in rainfall nine years of measurements in the channel country of the lake eyre basin australia show that vegetation and soils in dune fields can recover from drought whereas on inter fluve grasslands uni directional and negative successional vegetation changes can result from wind erosion during drought on floodplains both wind erosion and vegetation responses are complicated by flood frequency up to 1999 flooding of saline claypans did not increase vegetation but did increase wind erosion through the supply of alluvial fines however after three floods within as many months vegetation became established and wind erosion rates were dramatically reduced wind erosion research attention is now gradually turning from the physical to the organic content of eroded dusts in australia organic matter content can reach 65 by mass but this cannot be explained by removal of soil organic matter alone biological soil crusts not only stabilize soils against wind erosion but contribute to some of the organic dusts the role of dust as a vector for pathogens is an area which deserves greater research attention in the future downwind from source we show that dust contributions to soils are more widespread and more variable in time and space than earlier work on dust derived loess soils has suggested recent studies also show positive dust impacts upon nutrient budgets within distant forest ecosystems and significant contributions to river nutrient loads especially in the arid sectors of internally draining river basins the number of studies of dust impacts upon marine ecosystems is increasing dramatically studies of dust within antarctic ice cores combined with dust modelling provide compelling evidence that increased soluble iron rich dust inputs to the southern ocean have stimulated phytoplankton populations modern process studies are however yet to clearly demonstrate these relationships finally we examine the potential for major dust impacts upon global climates using its positive and negative effects upon solar radiation and precipitation as examples of the complexity and importance of this new research area

micromorphology and significance of the surface crusts of soils in rangelands near cobar australia abstract micromorphological observations were made on thin sections of surface crusts from the uppermost 50 mm of red earths near cobar new south wales samples were collected to represent six classes of surface conditions important to plant growth the crusts consisted of an upper zone comprising cryptogamic mats litter and transported soil aggregates and a lower zone of layers of generally laminated sands silts and clays crusts from class 1 surfaces which showed little evidence of erosion were loosely structured bioturbated and lacked sealing properties crusts from classes 2 to 4 in which erosion was increasingly evident contained decreasing proportions of cryptogams exhibited decreasing evidence of bioturbation and increasing proportions of platy and sealing structures crusts from class 5 found in areas of marked colluvial deposition had a wide range of properties whereas crusts from class 6 consisted primarily of litter deposited under trees the major processes responsible for crust formation are considered to be a combination of erosion by raindrop impact redeposition by rainwash and colonisation by cryptogams micromorphological properties of the crusts are believed to affect lodgement and germination of seeds and the infiltration and runoff of water thereby influencing plant growth dry matter production ranged from 2 3 t ha 1 on soils with class 1 surfaces to 0 1 t ha 1 on soils with class 4 surfaces cryptogam mats also afford protection of the underlying materials from erosion and also promote aggregation cryptogams are therefore considered highly desirable components of the crusts

effects of river regulation on aeolian landscapes colorado river southwestern usa 1 connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions this study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid colorado river corridor southwestern usa by quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources this work demonstrates for the first time that the flow and sediment limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line dune fields decoupled from fluvial sand supply have more ground cover biologic crust and vegetation and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply the proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach marble grand canyon arizona than in a much less regulated reach with otherwise similar environmental conditions cataract canyon utah the interconnections shown here among river flow and sediment aeolian sand transport and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments because fluvial aeolian coupling is common globally it is likely that similar sediment transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously

influence of cryptogamic crust disturbance to wind erosion on sand and loam rangeland soils a portable field wind tunnel was used to assess the sediment flux rates of loam and sand textured soils in the mallee region of southeastern australia three levels of crust disturbance nil moderate and severe simulating stock trampling were investigated the results demonstrated the importance of cryptogamic crusts in binding the soil surface and providing roughness after the soil was moderately disturbed on the loamy soil the crust helped maintain sediment flux rates below the erosion control target to 5 g m 1 s 1 for a 65 km h 1 wind measured at 10 m height once the crust was severely disturbed sediment fluxes increased to 1 6 times the erosion target on the sandy soil even with no crust disturbance the sediment flux was 1 6 times the erosion control target disturbing the crust increased sediment fluxes to a maximum of 6 7 times the erosion control target removal of the crust also decreased the threshold wind velocity that resulted in an increase to the ris k of erosion from 5 per cent to 20 per cent 1998 john wiley sons ltd