estimating the age of desert alluvial surfaces with spaceborne radar data abstract we present a new dating approach for desert alluvial surfaces that utilizes radar image data to obtain regional scale correlations between dated surfaces and surfaces of unknown ages the study was carried out along the arava segment of the dead sea transform north of the gulf of elat aqaba using advanced land observation satellite alos phased array type l band synthetic aperture radar palsar data with 6 12 m pixel resolutions nineteen independently dated quaternary morphostratigraphic alluvial units 5 to 1910 ka from eight different sites with variable lithologies carbonate magmatic chert were examined in order to develop test and validate the proposed approach expanding on previous studies that established the characteristic smoothing of desert alluvial surface through time and the capability of measuring such roughness variations with radar we employed a pixel aggregation approach that yielded a robust r 2 0 95 power law relation between the average radar backscatter value from the surface ar and the abandonment age t of the unit as measured with independent methods such as luminescence and or cosmogenic radionuclide dating we found that 1 this ar t correlation can be inverted to obtain calibrated radar based t estimates as old as 1 5 ma with 35 uncertainty 2 alos palsar 6 m pixel images acquired at incidence angles of 34 38 yielded optimal results 3 a sample of at least 70 contiguous radar pixels was required to capture the natural roughness variability of the surfaces examined and 4 surface lithology did not exert a primary effect on t inversions validation experiments yielded radar based ages of 3 1 91 32 484 169 and 1604 561 ka that compare to holocene 56 14 540 60 and 1590 250 ka ages previously determined for the same surfaces respectively we propose that with region specific calibrations spaceborne radar data can be used to quantitatively estimate the age of abandoned alluvial units across regional scales

weathering of superficial limestone debris in a hot desert environment abstract weathering of superficial limestone debris is described from stone pavements on the hamada de meski in southeast morocco the dominant features are due to surface and subsurface solution mechanical weathering and aeolian action have only a limited effect microfeatures produced by solution include solution facetting microrills solution pits case hardening micropitting or vesicular weathering and possibly surface crazing such microforms are the most likely representatives of a truly arid karst

granular disintegration of gneiss and migmatites summary weathering of precambrian gneiss and granitoid migmatites in the kora area of central kenya is essentially a two stage process in the first stage the rocks experience granular disintegration due to the widening of grain boundary microcracks and loosening of the rock structure sem and microprobe data indicate that during this stage chemical alteration of biotite and feldspars is limited and occurs mainly on grain margins and along microcracks no evidence has been found to suggest that stresses created by extensive alteration and expansion of biotite are primarily responsible for granular disintegration the second stage of weathering involves development of intragranular microcracks and progressive chemical decomposition with leaching of ca mg na and k from biotite and feldspars

the micromorphology of gypsum and halite in reg soils the negev desert israel gypsum and halite are the most common salts in reg soils developed on alluvial parent material under extremely arid conditions in the negev desert israel the aim of this paper is to document the changes in the micromorphology of these salts at different stages of reg soil development on two alluvial fan chronosequences the micromorphological analyses included thin section observations and scanning electron microscope and electron microprobe analyses in this arid soil environment gypsum and halite possess a variety of crystal forms which may change with depth in a single profile and or between profiles of different ages the variety of crystal forms results from changes in the microenvironmental conditions that occur in desert reg soils over time poikilitic lenticular gypsum is found in all reg soils and is distributed throughout the profiles the conditions needed for such crystals to form are high ionic impurities and deposition in a void system where space is not limiting microcrystalline alabastrine gypsum is only found in mature reg soils and is crystallized when the profile has high amounts of fine material and a well developed desert pavement in a well developed reg soil profile indicators such as a well developed desert pavement and high amounts of fine earth limit the leaching depth and cause gypsum deposition from supersaturated soil solutions under high evaporation rates close to the surface prismatic and fibrous gypsum are less common low amounts of prismatic gypsum are found in young and mature soils while fibrous gypsum is found only in mature soils in re cemented shattered gravel the halite crystal form is mainly cubic with low amounts of host material incorporated into the crystal it occurs predominantly in mature reg soil profiles through the crystallization from supersaturated soil solutions at the depth of maximum water penetration although the alabastrine prismatic and fibrous gypsum and cubic halite are deposited in a displacive manner no correlation was found between their occurrence and the distribution of shattered gravel in the soil profile

physical weathering in arid landscapes due to diurnal variation in the direction of solar heating despite the prominent role of physical weathering in arid and semi arid landscapes there has been little study of the specifi c processes responsible for the rapid breakdown of subaerially exposed rocks for example many boulders and cobbles in deserts exhibit fi ne near vertical cracks although workers have hypothesized that these and other cracks are initiated by diurnal heating and cooling no convincing specifi c mechanism for their formation has been proposed we have characterized these cracks at eight sites on surfaces of different ages in the mojave sonoran and chihuahuan deserts and the high desert of central new mexico our data reveal four basic types of cracks longitudinal surfaceparallel fabric related and meridional the orientations of the fi rst three types are associated with clast shape and rock fabric the azimuths of meridional cracks however are preferentially aligned north south typically with a nonrandom multimodal distribution we propose that these cracks are caused by tensile stresses that arise in the interior of clasts due to strong radial gradients in temperature that evolve and rotate in alignment with the sun s rays we suggest that the multimodal nature of crack orientations may be in part attributable to the seasonally varying latitude dependent solar elevation angle over millennial time scales we suggest that this thermal cracking is an effi cient weathering process that together with cumulic soil epipedon development creates the key attributes of most desert pavements in addition to individual clasts exposed on desert surfaces this mechanism of cracking is potentially signifi cant in other climates and on other planets as well as for rock outcrops and for man made structures

pedogenic evidence of urmia lake s maximum expansion in the late quaternary abstract the urmia lake recession and the resulting increase in vast barren area around it has been rapid in recent decades and thus has attracted attention of environmentalists and geoscientists alike however evidence for its different strandlines and the largest extension of the lake during the late quaternary has not been reported yet the principal goals of the current research were to figure out pedological evidence of its maximum expansion during the late quaternary and mapping out the different strandlines along the western shores of urmia lake over time thirty two soil pedons at different landscape positions geomorphic surfaces and distances from urmia lake were studied during autumn in 2013 and 2014 micromorphological and mineralogical studies were performed for some diagnostic horizons results showed along the transect under study three different entities diagnostic of the lake s history 1 lithological discontinuities 2 saline lacustrine sediments 3 buried soils however almost 2 km from the closest pedon to the lake no evidence of saline playa sediments were detected based on previous chronology results from urmia lake which indicated high lake levels with very low salinity since about 180 ky bp the sediments of this part of the study area were considered to have been deposited at the same period of time indicating a maximum expansion of urmia lake during the late quaternary the current results demonstrate that soil pedons which were situated at various distances from urmia lake denote different stages of the lacustrine evolution along with the distance from the lake the development of soils increases due to a longer and more intensive impact of pedogenic processes on the topstratum the overall soil system becomes more mature the study of buried soils and their comparison to upper non buried soils revealed that in some cases the buried soils were more evolved than their upper soils or vice versa through these observations the periods of exposure to soil forming processes after each sedimentation period was detected and schematic diagrams illustrating periods of highstands and lowstands recessions of urmia lake were reconstructed this study demonstrates that even though multiple episodes of lake recession were apparent the level of urmia lake increased during hydroclimatic events conducive to lake expansion which affected the soil evolution due to several fluctuations during the late quaternary

transition from arid to hyper arid environment in the southern levant deserts as recorded by early pleistocene cummulic aridisols abstract the time at which deserts established their current arid or hyper arid conditions remains a fundamental question regarding the history of earth cosmogenic isotope exposure ages of desert pavement and welded calcic gypsic salic reg soils that developed on relatively flat alluvial surfaces 2 ma ago in the negev desert indicate long geomorphic stability under extremely dry conditions over a short interval during their initial stage of development between 1 2 ma these cumulative soils are characterized by calcic soils reaching maximum stage iii of carbonate morphology this interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern negev desert since 1 ma pedogenesis changed toward more arid soil environment and the formation of gypsic salic soil horizons that were later followed by dust accumulation the dichotomy of only moderately developed calcic soil stages ii iii during a relatively long time interval 105 106 years indicates an arid environment that does not support continuous development but only occasional calcic soil formation the very low 18o and relatively high 13c values of these early pedogenic carbonates support soil formation under arid climatic conditions such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture this in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate at 1 ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern negev desert leading to deposition of soluble salts and dust deposited in the soils the combination of long term hyperaridity scarcity of vegetation and lack of bioturbation salts cementation dust accumulation and tight desert pavement cover has protected the surfaces from erosion forming one of the most remarkably stable landscapes on earth a landscape that essentially has not eroded but accumulated salt and dust for more than 106 yr

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

complex exposure histories of chert clasts in the late pleistocene shorelines of lake lisan southern israel activities of 26 al and 10 be in five chert clasts sampled from two beach ridges of late pleistocene lake lisan precursor of the dead sea in southern israel indicate low rates of chert bedrock erosion and complex exposure burial and by inference transport histories the chert clasts were derived from the senonian mishash formation a chert bearing chalk which is widely exposed in the nahal zin drainage basin the drainage system that supplied most of the material to the beach ridges simple exposure ages assuming only exposure at the beach ridge sampling sites range from 35 to 354 ky using the ratio 26 al 10 be total clast histories range from 0 46 to 4 3 my unrelated to the clasts current position and exposure period on the late pleistocene beach ridges 160 177 m below sea level optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20 0 s 1 4 ka and 36 1 s 3 3 ka these ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of lake lisan which suggest that the lake reached its highest stand around 27 000 cal years bp if the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50 1300 ky and 390 3130 ky respectively alternatively the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock back calculating such rates of rock erosion suggests values between 0 4 and 12 m my 1 t he relatively long burial periods indicate extended sediment storage as colluvium on slopes and or as alluvial deposits in river terraces some clasts may have been stored for long periods in abandoned pliocene and early pleistocene routes of nahal zin to the mediterranean before being transported again back into the nahal zin drainage system and washed on to the shores of lake lisan during the late pleistocene copyright 2003 john wiley sons ltd

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

transformation induced jointing as a gauge for interfacial slip and rock strength various theoretical and numerical models have been proposed in order to explain joint formation and spacing in layered rock series however most of these models assume that the interfaces between the rock layers are perfectly welded i e no slip occurs and that all the layers are subjected to the same remote strain due to various processes e g tectonic processes other factors may also induce extensional strain in rocks e g phase transformations however such processes may induce different amounts of strain on the layers in a rock series leading to a strain mismatch between these layers in this paper we present a 1 d finite difference linear elastic model which allows joint formation within the middle layer in a three layer rock series and is induced by a strain mismatch between the fractured central layer and the surrounding matrix furthermore the central layer in our model is not necessarily welded to the matrix layers and is allowed to slip along the interfaces between these layers if the shear strength of the material at the interface is reached we find that the final fracture spacing to layer thickness ratio s tf in such layered systems is directly proportional to the ratio of the tensile and shear strength of the material changes in the material properties such as the shear modulus or young s modulus do not affect these results a natural analog of joint formation driven by phase transformations is found in the orthopyroxenite dykes of the leka ophiolite complex loc norway joint formation in orthopyroxenite dykes results from serpentinization driven expansion of the surrounding dunite matrix detailed field studies and measurements 583 sample points yield s tf ratios between 0 1 and 1 0 with a mean value of 0 45 0 20 we demonstrate that the strain mismatch driven joint formation associated with interfacial slip explains the low s tf ratios obtained from field measurements and may also help us constrain rock strength

salt fretting in the valley cliff of the asama volcano region japan on the pumice flow deposits of the asama volcano japan many salts such as halite nacl gypsum caso4 2h2o hexahydrite mgso4 6h2o and mirabilite na2so4 10h2o crystallize at the base of south facing valley cliffs the zone of salt efflorescence and of resulting polygonal rind correspond to the zones of notch formation and high water content the main conditions for salt crystallization and polygonal rind formation are 1 the existence of groundwater containing a high concentration of cl so ca2 mg2 and na 2 a valley cliff material with a high capillary action and small tensile strength and 3 low humidity and a high ground surface temperature derived from the direct incidence of sunshine given the right conditions salt weathering can occur not only in the arid regions but also in humid temperate inland regions

stages and rate of the gravel shattering process by salts in desert reg soils abstract gravel shattering by salts is a common process in gravelly young to mature desert reg soils the shattered gravel is found on the surface and in the b and c horizons down to a maximum depth of 50 cm field studies on the process of salt weathering in deserts are scarce therefore the objectives of this study are to present the stages of development of the gravel shattering process by salts in desert reg soils and to discuss factors influencing the rate of development under natural conditions prevailing in the negev desert the studied reg soils were developed on two alluvial fan chronosequences in the negev desert the fan of nahal ze elim and the fan of nahal shehoret the development of the shattering process can be divided into five stages a e based on chemical physical and micromorphological features of the reg soils stages a d very young yo young reg soils represent the early holocene to the present some 14 000 years salinity values are between 0 27 16 mmho cm and the percentage of the shattered gravel is between 20 and 70 the shattered gravel however still maintains its original shape stage e mature reg soil represents the middle pleistocene to early holocene or 500 000 years salinity values at this stage reach 62 mmho cm although part of the gravel does not keep its original shape and starts to disperse in the profile the percentage of shattered gravel is only 75 80 it was found that the process of salt shattering in reg soils does not depend on concentrations or mineralogy of the salts but on the micro environmental conditions of the soil profile the process requires extreme and rapid variations of temperatures and moisture conditions such as found close to the soil surface to cause salt crystallization in a confined system with time the sealing of the soil surface through the development of desert pavement and a gravel free b horizon results in a change in the soil micro environment this change impedes the process irrespective of the amounts concentrations and types of salt minerals which exist in the profile the fact that in extreme arid regions the gravel shattering process develops primarily close to the reg soil surface suggests that it can be used to identify buried reg soils and to reconstruct climatic and micro environmental conditions of paleosols

measuring the time and scale dependency of subaerial rock weathering rates over geologic time scales with ground based lidar the evolution of roughness as a function of surface age was used to quantify weathering rates on rocky desert surfaces surface topography on eight late quaternary alluvial terraces which record the weathering of holocene 5 1 ka boulder strewn deposits into mature 87 2 ka desert pavements in the negev desert of israel was measured with ground based lidar roughness on each terrace was characterized with power spectral density psd analysis and changes in psd as a function of length scale 0 04 1 50 m and surface age were used to estimate diminution weathering rates of the surface rocks we found psd values that systematically increase as a power law function of roughness exponent of 2 0 and decrease as an inverse power law function of surface age this psd evolution indicates a fragmentation rock weathering process driven by salt shattering throughout the 87 k y period examined psd analysis of the lidar data also revealed weathering rates that increase with rock size and decrease as an inverse power law function of time from initial values 20 mm k y to 1 mm k y within 60 k y

the role of the nile in initiating a massive dust influx to the negev late in the middle pleistocene the late middle pleistocene initiation of loess accretion in the negev desert israel resulted from a chain of events starting with the exposure of shallow offshore nile delta sands beginning 180 ka during a period of glacially lowered eustatic sea level this exposure allowed the formation of the dunes of the sinai negev erg and the eastward movement of the dunes under the gusty glacial time winds in northern sinai this eastward dune advance occurred by eolian saltation that generated the coarse silts that accumulated downwind as loess we postulate that the absence of earlier negev loess is not a result of interglacial erosion as previously proposed but is due to the relatively recent convergence of the above conditions necessary for loess formation we based our interpretation on analyses of two long term natural dust traps and the association of coarse quartz silt production with the advancing quartz rich dunes over this carbonate terrain although the nile delta is considered an early to middle pleistocene feature and therefore could have been the source of sand throughout the quaternary it attained the shallow depth range of glacial interglacial sea level changes only during late marine oxygen isotope stage 7 to early stage 6 allowing its wide exposure in quaternary times prior to erg formation negev dust was finer composed of silt and clays derived from distal sources in the sahara and arabian deserts

a theoretical model of the fracture of rock during freezing we present a mathematical model for the breakdown of porous rock by the growth of ice within cracks the model is founded upon well established principles of fracture mechanics and recent advances in soil physics ijong with the assumption that progressive crack growth results from water migrating to ice bodies in cracks much as water migrates to ice lenses in freezing soil our model predicts crack growth rates compatible with empirical data calculations for a granite and a marble indicate that sustained freezing is most effective in producing crack growth when temperatures range from 4 c to 15 c at higher temperatures thermodynamic limitations prevent ice pressure from building up sufficiently to produce significant crack growth at lower temperatures the migration of water necessary for sustaining crack growth is strongly inhibited in hydraulically open systems in which pore water pressure remains near atmospheric pressure during the freezing process crackgrowth rates during continuous cooling will generally be greatest at low rates of cooling less than 0 1 0 5 c h at higher rates of cooling the influx of water to growing cracks is significantly inhibited the model delineates clearly the role of material parameters elastic moduli fracture mechanical properties grain size and shape and crack size environmental conditions temperature temperature gradient water pressure and time in frost damage to rocks our calculations along with recent experimental work on water migration in freezing rocks fukuda 1983 lead us to question the widely accepted importance of two phenomena freezing of water in sealed cracks and freeze thaw cycling in the fracture of rock exposed to natural freezing conditions

indicators of faulting events and periods of quiescence in desert alluvial fans the main objective of the present paper is to present an integrated approach to the study of faulting stages in coarse alluvial deposits the study site is the alluvial fan of nahal shehoret presently under an extremely arid regime the exposure of fault scarps on the fan surfaces enables the identification of several geomorphic indicators employed in analysing and separating faulting events and periods of quiescence a the nature of fault scarp topography b soil catenary development on fault scarps c buried paleosols in alluvial deposits d colluvial bodies e rotated clasts along fault planes these indicators enable us to determine at all sites studied the total amount of displacement to separate faulting events and the amount of their displacement per event and to evaluate scarp stability and the duration of periods of tectonic quiescence

the evolution of holocene reg gravelly soils in deserts abstract reg soil is an aridisol developed upon a stable alluvial surface composed of sand to coarse gravel the objectives of the present study were 1 to examine the initial evolution of reg soil properties with time 2 to assess and explain the rates of development of different properties 3 to establish the suitability of different soil properties for relative age dating the time dependent soil properties examined were 1 mechanical weathering of surficial rocks and desert pavement evolution 2 chemical and biological weathering of surficial rocks 3 the thickness of soil profiles and soil horizons 4 soil texture in the different horizons 5 salts and gypsum distribution and concentration in different soil horizons 6 degree of mechanical weathering of gravel in c horizons fifteen successive surfaces of the nahal wadi ze elim sequence of alluvial fans were selected for study dead sea region israel under an extremely arid climate the sequence is of holocene age 14 000 years b p to recent the main conclusions are 1 reg soils develop rather fast in several 10 3 years since their initiation however the various soil properties developed at different rates 2 the rates of change of three soil properties decrease with time these are the texture in different horizons change in added airborne and rain washed dust salinity within the soil profile change in added salts and gypsum and the amount of mechanically shattered rocks 3 soil thickness is established rather rapidly young and older holocene soil have practically the same depth surficial weathering rates appear to remain fairly constant with time 4 in coarse gravel the evolution of reg soils is dependent on added fines and salts of airborne origin and the resultant changing hydrologic regime in the soil profile the run off infiltration ratio changes as more fines and salts are added to the soil profile and as desert pavement develops 5 surficial features and fine clay in the soil profile may be used for approximate dating of otherwise undatable holocene alluvial surfaces salts and gypsum content should be cautiously used in a rather general way

relief inversion in the avrona playa as evidence of large magnitude historical earthquakes southern arava valley dead sea rift the arava valley section of the dead sea transform dst in southern israel is characterized by the absence of seismic activity in recent times however paleoseismic analysis of sediments in the avrona playa a pull apart basin along the dst reveals that at least six m 6 tectonic events have affected the avrona playa in the last 14 000 yr the recurrence interval of the events is approximately 2000 yr trenched normal faults and push up ridges in the playa show that the upper 2 m of the deformed sedimentary sequence consists of playa deposits with uniform soil development the deformed sediments and the soil are typical of basins with an endoreic fluvial system based on the limiting age of the sequence and the extent of soil development faulting in the playa followed by compression and uplift occurred in the last 1000 yr this most recent tectonic event displaced the surface by at least 1 m consistent with a m 6 5 earthquake this earthquake changed the morphology of the avrona playa from a closed system with internal drainage to an open basin resulting in relief inversion the seismic quiescence in the arava may indicate a seismic gap in this segment of the dst

evolution of reg soils in southern israel and sinai abstract reg soils mostly camborthids and gypsiorthids cover some 15 of the negev and sinai deserts analytical data of seven profiles on depositional surfaces of increasing age in the negev show clear relationships between ages of surfaces and soil profile features exemplified in the development of the cambic salic and gypsic horizons the youngest soil a coarse desert alluvium soil typic torriorthent of dry wadi beds up to a few thousand years old has little profile differentiation and is generally non saline or slightly saline on the higher terraces connected with the lisan formation about 70 000 12 000 years b p clear profile differentiation and the beginning of development of cambic horizons can be discerned evident in their colour textural p differences the soils are already saline and somewhat gypsiferous both soils are not yet defined as regs because of their negligible or restricted profile differentiation reg soils on the older and higher geomorphic surfaces in the arava rift valley several hundred thousand years old have well differentiated profiles with cambic salic and gypsic horizons below their stony desert pavements typical reg soils have light coloured vesicular horizons over mellow very pale brown loam frequently with laminar structure almost completely stone free layers the reddish brown loamy to clay loam b horizons are very saline and show intensive salt weathering of gravels gypsic and petrogypsic horizons occur at depth such reg soils represent the stable surfaces and soils of deserts and were developed over a long period of desert weathering

influence of parent material and grain size on carbonate coatings in gravelly soils palo duro wash new mexico abstract close examination of carbonate coatings found on the bottoms of pebbles from gravelly soils indicates that soil hydraulic conductivity and respiration rate have a strong influence on the carbonate morphology of aridic soils clast size and lithology strongly correlate with coating thickness because of the nature of unsaturated flow within macropores of gravelly soils thicker coatings are found at the bottom of larger clasts coatings are thickest on limestone pebbles that commonly display dissolution features at their tops model values for soil co 2 based on gas diffusion predict soil atmospheric condition where soil water can remain undersaturated with respect to calcite and dissolve calcareous pebbles throughout the depth of the soil profile this coupled with soil hydrology creates a microenvironmental condition where the largest limestone clasts have the thickest coating a second phenomenon that is apparent from close observation of coatings is that soils containing abundant fines and translocated dust in the matrix have continuous coatings continuous coatings are absent however in soils that do not neighbor a dust source or do not have sufficient fines in the matrix in these soils coatings are almost completely absent from sand and granule size particles suggesting that zones of preferential flow in the soil inhibit carbonate precipitation in parts of the soil profile these inconstancies in the continuity and thickness of coatings suggest that stage iii morphology may not develop at the same rate even locally

experimental investigation of silt formation by static breakage processes the effect of temperature moisture and salt on quartz dune sand and granitic regolith weathering simulations carried out using a climatic cabinet have demonstrated that diurnal temperature and humidity variations typical of those occurring in warm desert environments are ineffective in causing static breakage of quartz dune sand and polymineralic regolith sand grains wetting and drying combined with temperature variations was also found to be a relatively ineffective weathering process these results suggest that crack tip processes are insignificant where mineral grains are not subject to static loading sodium sulphate weathering was found to cause slight damage to quartz dune sand grains and major damage to first cycle regolith grains feldspars and mica in the regolith sands were more susceptible to salt action than quartz salt weathering of the regolith sands produced substantial quantities of silt in the size range typically found in natural loess deposits

carbonate deposition during a time of mid latitude ocean cooling early permian subtropical sedimentation in the sverdrup basin arctic canada abstract carbonate rocks of the lower permian sakmarian to kungurian raanes and great bear cape formations accumulated in the sverdrup basin during a critical transition period when ocean waters cooled dramatically these rocks have many attributes similar to sediments deposited in modern subtropical zones the biota is dominated by a heterozoan assemblage of pelmatozoans bryozoans and brachiopods with the addition of photozoan elements such as fusulinids and colonial corals associated with the change in the sverdrup basin from a tropical to subtropical environment is the first occurrence of glauconite iron oxides and storm deposits the shift in depositional conditions is interpreted to reflect decreased seawater temperature that was brought about by a northward migration to a mid latitude position frequented by storms oceanographic change however was not unidirectional but was complicated by concomitant variations in sea level and oceanography recorded as three distinct phases determined by water depth and temperature 1 rocks of the raanes and lower great bear cape are deep water and heterozoan 2 the middle great bear cape records shallow water subtropical conditions with fusulinids and large colonial corals 3 the upper great bear cape is entirely heterozoan in all locations and by implication all depths all post raanes and great bear cape rocks of the sverdrup basin are entirely heterozoan taking caution for possible evolutionary changes subtropical carbonates can be recognized in rocks much older than previously believed the most important components for identifying subtropical carbonates of the past are large benthic foraminifers in an otherwise heterozoan assemblage and as such the ability to delineate this carbonate realm in the past is currently restricted to times when large benthic foraminifers grew in shallow marine environments