xerolysis a hypothetical process of clay particles weathering under sahelian climate abstract in arid lands the soil surface commonly is characterized by textural and structural differentiation compared with deeper horizons this is traditionally attributed to mechanical transfer of material by wind and runoff that contributes to sealing and crusting another process however was previously interpreted in the niger republic at the surface of irrigated alluvial soils the process called xerolysis is controlled by ultradesiccation under the sahelian climate and induces clay weathering and dissolution the study areas are at the sona station and the tillakaina station where two irrigated perimeters extend on alluvial deposits of the niger river fifteen soil profiles eight at sona and seven at tillakaina were sampled in and out the irrigated perimeters the particle size distribution was determinated by sedimentation and centrifugation methods the clay fractions were studied by x ray diffractometry of which the first order peaks were decomposed with a decomposition model transmission electron microscopy microdiffraction patterns from selected area electron diffraction and energy dispersive x ray analysis the particles were clearly identified as beidellite kaolinite and mica the decomposition analysis of the x ray patterns from the

influences of quaternary climatic changes on processes of soil development on desert loess deposits of the cima volcanic field california summary soils formed in loess are evidence of both relict and buried landscapes developed on pliocene to latest pleistocene basalt flows of the cima volcanic field in the eastern mojave desert california the characteristics of these soils change systematically and as functions of the age and surface morphology of the lava flow four distinct phases of soil development are recognized phase 1 weakly developed soils on flows less than 0 18 m y old phase 2 strongly developed soils with thick argillic horizons on 0 18 0 7 m y old flows phase 3 strongly developed soils with truncated argillic horizons massively impregnated by carbonate on 0 7 to 1 1 m y old flows and phase 4 degraded soils with petrocalcic rubble on pliocene flows a critical aspect of the development of stage 1 soils is the evolution of a vesicular a horizon which profoundly affects the infiltration characteristics of the loess parent materials laboratory studies show that secondary gypsum and possibly other salt accumulation probably occurred during the period of phase 1 soil development slight reddening of the interiors of peds from vesicular a horizons of phase 1 soils and presence of weakly developed b horizons indicates a slight degree of in situ chemical alteration however clay and fe oxide contents of these soils show that these constituents as well as carbonates and soluble salts are incorporated as eolian dust in contrast to phase 1 soils chemical and mineralogical analysis of argillic horizons of phase 2 soils indicate proportionally greater degrees of in situ chemical alteration these data the abundant clay films and the strong reddening in the thick argillic horizons suggest that phase 2 and phase 3 soils formed during long periods of time and periodically were subjected to leaching regimes more intense than those that now exist flow age data and soil stratigraphic evidence also indicate that several major loess deposition events occurred during the past 1 0 m y loess events are attributed to past changes in climate such as the pleistocene to holocene climatic change that periodically caused regional desiccation of pluvial lakes reduction of vegetational density and exposure of loose unconsolidated fine materials during times of warmer interglacial climates precipitation infiltrates to shallower depths than during glacial periods extensive saline playas which developed in the mojave desert during the holocene are a likely source of much of the carbonates and soluble salts that are accumulating at shallow depths both in phase 1 soils and in the formerly noncalcareous nongypsiferous argillic horizons of phase 2 and 3 soils

groundwater microtemperature and strain summary groundwater temperatures were measured in deep boreholes of the tokai district an earthquake prone region in central japan with precise thermometers observed temperatures have a resolution of better than 1 m c and were made simultaneously with observations of crustal strain sharp peaks of periods about 12 and 24 h were found in the fine spectra of groundwater temperature the 12 h period components were found to be of tectonic origin although 24 h components are of artificial origin e g water pumping at some stations the groundwater temperature change is explained by the adiabatic temperature change of either water or rock the water temperature observation sites are grouped by the phase differences of the 12 h period variations this classification coincides well with the independent grouping obtained according to the resemblance of the strain change

airborne dust and its significance to soils abstract movement of mineral dust by the atmosphere has been underway for ages but efforts to assess its magnitude and significance have come largely in the last century attempts to identify and understand effects of the dust on soils are even more recent mostly in the last 30 years airborne movements have several forms dust is transported by large storms that can be spectacular dust is also moved by smaller pulses and in a rather continuous flux most movement is within continents or from continents to nearby oceans but fine dust fine silt and clay is carried from one continent to another prime sources of the dust are the deserts and semi arid regions of the world for example large quantities of dust are carried out of the sahara every year quantities of dust carried by individual pulses from the small ones to the massive storms extend from a few thousand to 150 million metric tons during the course of a year the total quantities can be large one example is an estimate that on the average 770 million metric tons originating in the western united states are carried 2300 km each year that amount would add roughly 3000 kg ha 1 yr 1 to soils between the rocky mountains and the mississippi river small pulses and the near continuous flux add between 100 and 200 kg ha 1 yr 1 to soils of the eastern united states on the average comparable quantities are being added to soils in other parts of the world as well airborne accessions of dust have a variety of effects in soil development and on soils after they have been formed dust dominates processes of genesis in a few soils affects horizon differentiation appreciably in many more is a primary source of constituents essential to some horizons and layers in a number of soils provides the bulk of the material for silty surface horizons in many soils and can contribute supplies of nutrient elements for plants examples of all such effects are covered in this review first among these effects to be recognized even though not understood were the silty surface layers that failed to match underlying horizons later recognized was airborne dust as a source of calcium carbonate for calcic horizons that the dust could add significant quantities of nutrient elements as for example south of the sahara came into the picture even later the beneficial effects of airborne dust to many soils raises an interesting question is the dust more or less useful in its new location than it was in its source area an adequate answer to that question would provide an improved basis for assessing the effects of wind erosion

paleoclimatic implications of holocene plant remains from the sierra bacha sonora mexico abstract a total of 93 plant taxa were identified from 11 packrat neotoma sp midden samples from the sierra bacha on the coast of the gulf of california near puerto libertad sonora mexico nine indurated samples have radiocarbon dates ranging from 9970 to 320 yr b p sonoran desertscrub was present on rocky slopes throughout the holocene early holocene assemblages dominated by fouquieria columnaris boojum tree reflect vegetation and climate more like modern baja california with greater winter rainfall and cooler summers middle holocene vegetation was essentially modern with modest indications of greater monsoonal rainfall even though cold water upwelling locally inhibits summer precipitation the results are similar to all previous midden reconstructions of early and middle holocene climates in the sonoran desert but contradict general atmospheric circulation model simulations

pedogenesis and mineralogy of a halaquept in niger west africa bui e n and wilding l p 1988 pedogenesis and mineralogy of a halaquept in niger west africa geoderma 43 49 64 in a fossil river valley of niger known ae the dallol bosso an aquic soil environment has feoxide segregation coupled with biological so reduction and na co formation by evaporative pull depth to the water table ph and water soluble salts fluctuate seasonally but most of the year the water table is within 1 m of the surface the presence of na2c03 is inferred from salt efflorescences and a ph of 9 at the soil surface in the dry season the zone of fe oxide accumulation occurs between 30 and 54 cm and a soil layer with greyish green color and reduced fe is present at the top of the water table on the basis of field and laboratory characteristics the soil is classified as an aeric halaquept mineralogical analyses xrd ir and sem show that goethite is the dominant iron oxide mineral and suggest that silica translocation in an iron rich soil environment is promoting neoformation of iron rich beidellite

paleopedologic and geomorphic evidence for holocene climate variation shortgrass steppe colorado usa abstract radiocarbon dates of paleosols in northeastern colorado indicate distinct periods of stability and soil formation with intervening periods of instability resulting in soil truncation or burial a combination of pedologic and geomorphic indicators were used to resolve the duration of and prevailing climate during these periods five sites each having a paleosol were examined using both traditional soil analyses and grain size statistics the latter to decipher the mode of parent material deposition twenty local stream dune and bedrock deposits were analyzed using grain size statistics to establish benchmarks for comparison with soils field investigation supported by grain size frequency statistics indicate early holocene middle holocene and contemporary soils all formed in alluvium organic c and phytolith data suggest the early and middle holocene climatic conditions were more favorable for plant productivity than the present climate soil development in early and middle holocene paleosols suggests wetter soil moisture regimes than present low parent material carbonate contents suggest an eolian source for the carbonate in the bk and btk horizons the presence of paleosol btk horizons suggests a decrease in precipitation at the end of soil forming intervals followed by drought and subsequent soil burial

regional aeolian dynamics and sand mixing in the gran desierto evidence from landsat thematic mapper images spatial variations in sand composition were mapped on a regional scale in a terrestrial sand sea the gran desierto of sonora mexico mesoscale mapping on a satellite image base allowed quantitative interpretation of the dynamic development of sand sheets and dunes the results were used to interpret the quaternary geologic history of the tectonically active region at the mouth of the colorado river landsat thematic mapper multispectral images were used to predict the abundance of different mineralogies of sand grains in a mixed aeolian terrain a spectral mixing model separated the effects of vegetation and topographically induced shading and shadow from the effects produced by different mineral and rock types compositions determined remotely agreed well with samples from selected areas within the spectral limitations of the thematic mapper a simple discrimination capability for active versus inactive sand surfaces is demonstrated based upon differences in the percentage of low albedo accessory grains occurring on dormant aeolian surfaces a technique for discriminating between low albedo materials and macroscopic shade is implemented by combining thermal images with the results of the spectral mixing model the image analysis revealed important compositional variations over large areas that were not readily apparent in the field

sources and distribution of late quaternary silt in the surficial sediment of the northeastern continental shelf of the united states abstract the sources and distribution of silt in the surficial sediment of the northeastern continental shelf of the united states and the gulf of maine were determined by the analysis of quartz grain roundness and surface textures three distinct populations of silt are present in the surficial sediment of the continental shelf and the gulf of maine each population is represented by a suite of quartz silt grains with distinctive roundness and surface texture characteristics is derived from a different source and is distributed throughout different parts of the study area the first population is represented by rounded and subrounded quartz silt grains with weathered surfaces quo end member 1 quo it was apparently derived from the cretacious tertiary and quaternary sdiments of the atlantic coastal plain and is most abundant on the continental shelf between cape cod and cape hatteras which is underlain and bordered by coastal plain strata and on the western and eastern rims of the gulf of maine which are also underlain by coastal plain strata the second population is represented by very angular quartz silt grains with microfractures and fracture faces quo end member 2 quo it was apparently derived from the late wisconsin glacial and periglacial deposits of the northeast united states and is most abundant within and downdrift from the glaciated part of the study area and in the modern depocenters of rivers which drain glaciated terranes in new york and new england the third population is represented by subangular and subrounded quartz silt grains with crystalline nodes grain embayments and secondary quartz overgrowths quo end member 3 quo it was apparently derived from precambrian paleozoic and early mesozoic crystalline and sedimentary rocks of the appalachian mountains and is most abundant in the modern and ancient depocenters of the appalachian rivers of the eastern united states

luminescence chronology of the inland sand dunes from se india abstract records of past climate changes have been preserved variously on the earth s surface sand dunes are one such prominent imprint and it is suggested that their presence is an indicator of periods of transition from arid to less arid phases we report inland sand dunes from andhra pradesh se india spread over an area of 500 km 2 75 km inland from the east coast the dune sands are examined to understand their provenance transportation timing of sand aggradation and their relationship to past climates the dune distribution grain morphology and the grain size studies on sands suggest an aeolian origin physiography of the study area heavy mineral assemblage and abundance of quartz in the parent rocks indicate that the dune sands are largely derived from first order streams emanating from hills in the region and from weathering of the nellore schist belt it appears that the geomorphology and wind direction pattern both facilitated and restricted the dune aggradation and preservation to a limited area osl dating of 47 dune samples ranged from the present to 50 ka thereby suggesting a long duration of sand dune aggradation and or reworking history

geomorphological features of the archaeological marine area of sinuessa in campania southern italy abstract submarine surveys carried out since the 90s along the coastland of sinuessa allowed us to draw up a geomorphological map with archaeological findings along the sea bottom 650 m off and 7 m depth a campanian ignimbrite bedrock was detected dated 39 kyr bp its position is incompatible with the current sea level towards the northern edge of the shoal a depressed area with 24 cubic elements in concrete was surveyed these artefacts pilae are typical of roman maritime structures widespread along the southernmost phlegrean coast beachrocks and accessory landforms at the same depth of bedrock suggest that this was emerging and attended by man in roman times even for activities related to port facilities submerged palaeo channels in alignment of current watercourses on the mainland dissect the shoal these channels were moulded in subaerial environment during wurm glaciation following the tuff deposition and then were drowned by sea level rise the northernmost channel next to the pilae likely allowed transit and manoeuvring of roman ships the discovery along the seabed of a large stump of lead anchor hundreds of roman amphorae and fragments as well as of a depression of millstone confirm this finding probably the sinuous physiography favored the choice of this site for the docking of sinuessa as sheltered from storms

coseismic changes in groundwater temperature of the usu volcanic region observations of groundwater temperature to an accuracy of 0 001 c or better have been made at about 30 wells in various areas of impending earthquakes in japan the main aim of the observations was to monitor the crustal strain and or the movement of groundwater which relate to earthquake occurrence one thermometer was installed at a depth of 200 m in an active volcanic area usu where an upward movement of the magma is occurring we report here that there was a generally increasing temperature trend at this location 0 3 c in the half year of observation decreases in the rate of increase preceded intense local earthquake activity temperature jumps were accompanied by large local earthquakes with magnitudes up to 4 2 and the polarity of the steps corresponded to the location of hypocentres this is probably the first microtemperature measurement made in the proximity of seismic activity

soil carbonate genesis in the pinacate volcanic field northwestern sonora mexico uranium series methods were used to date and evaluate pedogenic caco3 genesis in the pinacate volcanic field northwestern sonora mexico soils are developed in eolian deposits on lava flows 230th234u dates of pedogenic carbonate are mininum soil ages because of 1 the time needed to yield clasts from flows and to accrete enough carbonate to sample 2 subsequent additions of uranium and 3 continued solution and reprecipitation of carbonate rinds k ar dates of basalt flows are maximum soil ages maximum and minimum rates of caco3 accumulation are calculated from the th u dates and k ar dates respectively the mean maximum rate is 0 13 g caco3 cm2 1000 yr and the mean minimum rate is 0 05 g caco3 cm2 1000 yr least squares regressions of pedogenic carbonate and clay content and of th u ages against k ar ages suggest additions to soils from atmospheric sources throughout the late quaternary morphology of pedogenic carbonate and laboratory data for soluble salts indicate that the climate of the pinacate has not changed significantly during the past 150 000 yr soil variability is influenced by proximity of the eolian source near the periphery of the pinacate carbonate and clay are evenly distributed throughout soil profiles within the volcanic field carbonate and clay are concentrated in soil horizons suggesting that additions from atmospheric sources are slow enough to allow translocation

soil forming intervals caused by eolian sediment pulses in the lahontan basin northwestern nevada we have studied a series of toyeh post isotope stage 2 eolian dust fall was the source of fines and salts in these soils apparently this influx was concentrated during two brief intervals or pulses one during the holocene and one during the previous isotope stage 5 interpluvial leaching during the sehoo pluvial removed salts from churchill soils carbonate and soluble salts now observed in the churchill soils represent a toyeh overprint on the churchill profile these pulses of fine sediment and accompanying salts are tantamount to the soil forming intervals that morrison described in the lahontan area episodic eolian dustfall provides fine particles of silicates calcite and soluble salts that infiltrate into the clast supported alluvial piedmont sediments several hundred playas exist in the basin and range each providing directional dust contributions that influence local and regional soil development we counsel caution in assuming constant gradual development of soil properties without due consideration of paleoenvironmental influences on soil forming factors

chronology of lava and associated soils near san miguel new mexico abstract a lava flow in southern new mexico extends into the rio grande valley from the lower la mesa geomorphic surface a relict basin floor of middle pleistocene age three buried soils occur beneath the lava at its east end in places the lava itself is buried by a sediment in which a soil has formed pedogenic carbonate was used to calculate the age of this soil using a soil of lower la mesa as a chronological guide both the latter soil and the rio grande valley must be less than about 620 000 yr old according to dated volcanic ash and are estimated to be about 500 000 yr old based upon this age and a total of 1200 kg m2 pedogenic carbonate in the lower la mesa soil the carbonate accumulated at an average rate of about 2 4 kg m2 1000 yr using the same rate of carbonate accumulation the postlava soil took about 180 000 yr to form however not quite all of the pedogenic carbonate in this soil has been accounted for and a general figure of 200 000 yr is suggested for its approximate age the geological setting indicates that the age of the lava should be very close to the age of the postlava soil and a general figure of 200 000 yr is also suggested for approximate age of the lava this contrasts with a new k ar age of 490 000 30 000 yr which is considered to be too old however two previously obtained k ar ages of 232 000 80 000 and 154 000 119 000 yr are much closer to the estimate based on pedogenic carbonate the landscape of the soil that buries the lava differs from the landscape of the lower la mesa soil that was used as a chronological guide the rate of carbonate movement into the soils could also differ and for this reason the age obtained by pedogenic carbonate is considered tentative

comparison of postseismic groundwater temperature changes with earthquake induced volumetric strain release yudani hot spring japan we observed temporal variations of the groundwater temperature during two observation periods may 1983 july 1984 september 1991 august 1995 at yudani hot spring in tottori prefecture japan the groundwater temperature is affected by tides atmospheric pressure changes and earthquakes assuming that volumetric strain change is the cause of these temperature changes we calculated the respective strain sensitivities of the groundwater temperature as a result the sensitivities estimated from theoretical volumetric strain changes by earthquake fault models are more than 1 000 times larger than those from tides and atmospheric pressure we infer that the actual volumetric strain changes near yudani hot spring due to the earthquakes are larger than theoretical strain changes calculated by earthquake fault models

lateral moraines of glacier de tsidjiore nouve form development and implications the relationship between supraglacial lateral moraines and lateral dump moraines at arolla switzerland is discussed a detailed study of the lateral moraines of glacier de tsidjiore nouve reveals their complex form as superimposed and nested ridges and the current mode of development possibly related to the passage of a kinematic wave sedimentological analysis indicates that much of the constituent debris is of supraglacial origin it is transported either directly from the base of slopes flanking the pigne d arolla ice fall or via englacial septa comprising marginal sediment incorporated in the accumulation zone a calculation of the volume of debris in the lateral moraines suggests that glacier de tsidjiore nouve has recently been more active in transporting and depositing supraglacial debris than in glacial erosion sensu stricto

particle size characteristics of suspended sediment transported in meltwater from the gangotri glacier central himalaya an indicator of subglacial sediment evacuation abstract proglacial meltwater streams draining out of the himalayan glaciers carry considerable amounts of suspended sediment with a variety of particle sizes because of the supraglacial englacial and subglacial debris as well as formation of sediments from erosion by the movement of the ice this paper examines particle size transported in the proglacial meltwater stream of gangotri glacier for seven consecutive melt seasons may october 2000 2006 in order to provide information on i temporal variations in the particle size distribution ii texture and mineralogy of the sediments and iii origin and evacuation pattern of the sediments our results indicate dominance of silt size 0 002 0 06 mm particles 71 followed by sand size 0 06 0 6 mm particles 24 and clay size

an assessment of the hydrogeochemistry of two wetlands located in bihar state in the subtropical climatic zone of india a total of 30 water samples and 8 sediment samples were collected and chemically analysed for major ions na k mg2 ca2 hco3 so42 cl no3 silica po43 f trace elements fe mn ni cd zn pb cu minerals and nutrients to determine the factors that control the chemistry of water in the kawar tal and kusheshwar asthan wetlands in the bihar state of india these analyses indicate that ca2 and hco3 ions are the most dominant ions in both of the wetlands it also indicates rock weathering is a major source of ions in these wetlands particularly the dissolution of carbonate minerals the hydrogeochemistry of water in kusheshwar asthan is favouring kaolinite formation and in kawar tal favouring kaolinite gibbsite formation quartz 36 clay minerals 21 and chlorite 10 are the dominant minerals in both the wetlands orthoclase 12 49 calcite 7 51 and illite 4 89 minerals are only available in kawar tal surface sediment while albite 6 29 and biotite 13 6 minerals are only available in kusheshwar asthan total carbon 3 inorganic carbon 0 9 organic carbon 2 1 total sulphur 0 0008 nitrogen 0 55 and phosphate 0 96 are available in kawar tal surface sediments while total carbon 2 38 inorganic carbon 0 55 organic carbon 1 84 total sulphur 0 001 nitrogen 0 62 and phosphate 0 64 are available in kusheshwar asthan surface sediments the study indicates wetlands are rich in nutrient for biological activities and are sufficient to support the biodiversity but few locations are influenced by anthropogenic activities which cause the increase of sulphur chloride iron and lead

influence of sieving time on the efficiency and accuracy of grain size analysis of beach and dune sands grain size is a fundamental property of sediments and is commonly used to describe sedimentary facies and classify sedimentary environments among the various conventional techniques utilized to determine grain size frequency distributions sieving is the most widely applied procedure the accuracy of such analyses is among other factors strongly dependent on the sieving time however despite a substantial amount of research in this field optimal sieving times for different types of sediments have to date not been established in this article the influence of sieving time on grain size analyses of medium grained microtidal and mesotidal beach and dune sands has been determined to assess the precision of important textural parameters such as median grain size sorting skewness and kurtosis an error analysis was carried out for different sieving times 2 5 10 15 and 20 minutes after calibrating the analytical and sampling methodologies significant deviations were registered when sieving time was less than 10 minutes however such deviations were very small and grain size distributions remained almost identical for sieving times of 10 minutes and longer relative errors being as low as 0 in some cases

cosmogenic dating of fluvial terraces fremont river utah absolute dating of river terraces can yield long term incision rates clarify the role of climate in setting times of aggradation and incision and establish the rates of pedogenic processes while surface exposure dating using cosmogenic 10be and 26al would seem to be an ideal dating method the surfaces are composed of individual clasts each with its own complex history of exposure and burial the stochastic nature of burial depth and hence in nuclide production in these clasts during exhumation and fluvial transport and during post depositional stirring results in great variability in clast nuclide concentrations we present a method for dealing with the problem of pre depositional inheritance of cosmogenic nuclides we generate samples by amalgamating many individual clasts in order to average over their widely different exposure histories depth profiles of such amalgamated samples allow us to constrain the mean inheritance to test for the possible importance of stirring and to estimate the age of the surface working with samples from terraces of the fremont river we demonstrate that samples amalgamated from 30 clasts represent well the mean concentration depth profiles show the expected shifted exponential concentration profile that we attribute to the sum of uniform mean inheritance and depth dependent post depositional nuclide production that the depth dependent parts of the profiles are exponential argues against significant post depositional displacement of clasts within the deposit our technique yields 10be age estimates of 60 9 102 16 and 151 24 ka for the three highest terraces corresponding to isotope stages 4 5d and 6 respectively the mean inheritance is similar from terrace to terrace and would correspond to an error of 30 40 ka if not taken into account the inheritance likely reflects primarily the mean exhumation rates in the headwaters of order 30 m ma

pedogenic carbonate cutans on clasts in soils as a record of history of grassland ecosystems pedogenic carbonate cutans coatings pendants rinds on coarse clasts are common in stony soils of arid and semiarid regions dominated by open vegetation this paper gives an overview of the potential of the carbonate cutans for paleograssland research using data from literature and personal observations carbonate coatings are stratified into distinct microlamina which can provide a record of local environmental changes lamina made of a rather pure calcium carbonate with better formed and parallel oriented crystals seem to be indicative of relatively dry phases that were less favorable for biological activity a high content of admixtures poorer formed and randomly oriented calcite crystals presumably mark wetter periods characterized by climatic amelioration at a most general level n 13 c of the cutan carbonate can provide information on the type of photosynthesis of local vegetation whereas n 18 o in carbonate material of the coatings correlates with oxygen isotopic composition of precipitation water at the site and is sensitive to fluctuations in temperature to obtain chronological evidence on cutan formation the 14 c and th u methods can be applied with certain limitations additionally cutan growth rates can be used to evaluate the age of these features fl 2002 elsevier science b v all rights reserved

groundwater microtemperature in earthquake regions microtemperature measurements of groundwater with a relative precision better than 1 1000 c have been made in several seismically active areas in japan the measured temperatures show clear coseismic signals as well as a correlation with atmospheric pressure simultaneous observations at various depths have shown that these temperature changes were not induced by simple groundwater level changes also distinctive signals occurred before several earthquakes and seem to be caused by a different mechanism than the coseismic signals the microtemperature at some observation sites shows excellent correlation with records of nearby sensitive borehole strainmeters simultaneous recording of microtemperature and strain has been initiated in some boreholes

characteristics of stone covers on the surface of basalt flows in arid northeast jordan variations in the stone covers on desert surfaces have implications for the operation of hydrological processes some recent attention has been given to the difficulties of identifying and quantifying relevant characteristics of stone covers investigation of how such characteristics vary in relation to geological and topographical controls are limited results are presented of a field study of the characteristics of stone covers on four lithologies in the late tertiary to quaternary basalt plateau of northeast jordan marked variations occur in clast dimensions and the characteristics of sorting between lithologies which are likely to affect hydrological response a more subtle control relating to slope conditions is superimposed on the lithological differences r and q mode factor analysis identifies groupings within the data which demonstrate the distinctiveness of different lithologies characteristics of the stone covers on sites affected by human occupation are markedly different from undisturbed sites on the same lithology

isotopic evidence for eolian recycling of pedogenic carbonate and variations in carbonate dust sources throughout the southwest united states using isotopic ratios of sr c and o we trace calcium carbonate through surface systems across a wide region of semi arid terrain in arizona southwestern usa in order to evaluate the contribution of cations from silicate weathering to soil carbonate we present 87sr 86sr ratios of soil carbonate parent rock dry river course silts floodplain playa dust and rain samples as well as 18o and 13c values of selected samples results show that both parent rock and dust are important sources of cations for soil carbonate in this inland setting where bedrock is dominated by silicate lithologies dust in southeast arizona has higher 87sr 86sr ratios 0 7100 0 7123 than phanerozoic sea water 0 7070 0 7096 these high ratios derive ultimately from silicate rocks our 18o and 13c data show clearly that the dominant source of carbonate dust is eroded older soil carbonate not bedrock limestone because dust contributes significantly to newly forming soil carbonate some products of silicate weathering may reside in soil carbonate two or more times before being removed from the region and this recycling retards the rate at which the products of silicate weathering enter the sedimentary system comparison of the 87sr 86sr ratios of carbonate dust from southeast arizona with those from surrounding regions shows that dust 87sr 86sr ratios and by inference carbonate dust sources vary on a scale of 200 300 km in the southwest united states

hydrological discharges and motion of fels and black rapids glaciers alaska u s a implications for the structure of their drainage systems characteristics of the hydrology and motion of black rapids and fels glaciers alaska were observed from 1986 to 1989 hydrological measurements included stage electrical conductivity and suspended sediment concentration in the discharge stream of each glacier and were made at 0 5 1 h intervals continuously through most of the melt seasons variations in the glacier speed were monitored through the full year at a number of locations along the length of each glacier using time lapse photography 1 d time resolution strain meters 0 5 1 h resolution and seismometers set up to count acoustic emissions both glaciers show similar seasonal diurnal and short term event changes in hydrological discharges and ice speed the hydrological behavior is analyzed in terms of a fast sub system composed of surface streams moulins and large tunnels with discharge that responds rapidly and a slow sub system composed of heterogeneous small passageways through the ice and distributed over the bed that maintain approximately uniform discharge over a day the timing and amplitude of water discharge in the diurnal cycle indicate that roughly 10 40 of the water is routed directly into the fast system the remaining 90 60 of the water enters the slow system dilution of the solute discharged from the slow system by the variable discharge in the fast system results in changes in water discharge and solute concentration that are approximately equal in relative amplitude and inversely related a small time lag from discharge maximum minimum to solute minimum maximum suggests that the fast system is confined to roughly the lowermost 30 40 of the full glacier length the residence time of water in the fast system is short compared to 1 d the slow system contains both short and long residence time passages characteristics of the diurnal cycles are somewhat variable through the melt season but no systematic evolutionary patterns were discerned even though large changes in the mean discharges of water and solutes occur which suggests parallel evolution of the variables that control the response of the fast system events were characterized by contemporaneous increases in suspended sediment concentration in the discharge water and distinct changes in straining on the glaciers events caused by increases in melt or precipitation related to weather and events related to release from reservoirs internal to the glaciers could be distinguished based on the changes in electrical conductivity of the discharge water the correlated changes in sediment discharge and motion of the glaciers indicate that the events were associated with temporary modifications of the slow passages distributed over the bed that allowed enhanced sliding and access of basal water flow to erosion products hydrological differences between black rapids and fels glaciers can be explained by differences in the size of the glaciers if there is a difference in bed structure that explains the difference in dynamics surge black rapids glacier versus non surge fels glacier it does not affect the hydrological parameters that were observed

evaluating the potential of sem eds analysis for fingerprinting suspended sediment derived from two contrasting topsoils sediment source fingerprinting can provide information on the contribution of various sediment sources to the suspended load of a stream this study was conducted to evaluate the potential of sem eds analysis scanning electron microscopy energy dispersive spectrometry to fingerprint two types of topsoil in a research basin a black chernozemic farmland soil and a grey podzolic forest soil simulated suspended sediment samples were prepared from each of the two soils and sem eds analysis of these samples provided information about the size distribution mineralogy and morphology of the particles the two simulated suspended sediment samples were similar in particle size distribution mineralogy and total chemistry so that these characteristics did not provide a distinctive fingerprint for the two topsoils an important difference between the two simulated suspended sediment samples was the morphology of the clay class particles consisting of water stable clay aggregates clay class particles derived from the grey forest soil were irregular whereas those derived from the black farmland soil were rounded this difference in particle morphology can be explained by the difference in land use and may provide a distinct fingerprint for each topsoil

quaternary soils and dust deposition in southern nevada and california eoliandustconstitutesmuchofthepedogenic material in late pleistocene and holocene soils of many arid regions of the world comparisonofthecompositionsand influx rates of modern dust with the eolian component of dated soils at 24 sites in southern nevada and california yields informationon 1 thecompositionandinflux rate of dust in late pleistocene and holocene soils 2 paleoclimate and its effects on the genesis of aridic soils especially with regard to dustfall events 3 the timing and relative contribution of dust from playa sources versus alluvial sources and 4 the effects of accumulation of dust in soil horizons the 2mmfractionsofaandbhorizons of soils formed on gravelly alluvial fan deposits in the study area are similar to moderndustingrainsize contentofcaco3and salt majoroxides andclaymineralogy thus they are interpreted to consist largely of dust the major oxide compositions of the shallow soil horizons are nearly identical to that of the modern dust but the compositions of progressively deeper horizons approachthatoftheparentmaterial theclay mineralogyofmoderndustatagivensiteis similar to that of the av horizons of nearby holocene soils but is commonly different from the mineralogies of deeper soil horizonsandoftheavhorizonsofnearbypleistocenesoils theseresultsareinterpretedto indicate that dust both accumulates and is transformed in av horizons with time changes in soil accumulation rates provide insights into the interplay of paleoclimate dustsupply andsoil formingprocesses modern dust deposition rates are more than large enough to account for middle and late holocene soil accumulation rates at nearly all sites however the early holocene soil accumulation rates in areas near late pleistocene pluvial lakes are much higher than modern rates and clearly indicate a dust deflation and deposition event that caused rapid formation offine grained shallow soil horizons on uppermost pleistocene and lower holocene deposits we interpret late pleistocene soil accumulation rates to indicate that dust deposition rates were low during this period but that increased effective moisture during the late wisconsinan favored translocation of clay andcaco3fromnearthesurfacetodeeper inthesoilprofile pre latepleistocenerates are very low in most areas mainly due to a pedogenic threshold that was crossed when accumulations of silt clay and caco3 began to inhibit the downward transport of eolian material but in part due to erosion

anthropogenic units fingerprinted by ree in archaeological stratigraphy mas d is spain case abstract on occasions archaeologists have to deal with serious difficulties to differentiate between processes that ultimately are responsible for the formation of stratigraphic units sometimes we face problems related with depositional units in multilayered deposits and other times we ask for the character of some dark surface soils very similar to natural paleosols and usually associated with archaeological findings in both cases the problems we must address concern the relative impact of human activities the imbalance between anthropic and natural processes in the formation of archaeological deposits is crucial for a correct interpretation of the processes involved in the formation of archaeological sites but also of their occupation abandonment dynamics and the understanding of their spatial behaviors and relationship with the environment in this paper we propose a new methodological approach for the identification of anthropogenic fingerprints in stratigraphic units through rare earth elements ree soil analysis the role of ree for the effective identification of sediment provenance due to their coherent behavior during weathering erosion and fluvial transportation and their high resistance to chemical mobilization is well known in other areas of knowledge we try to explore its potentiality in a challenging archaeological context our purpose was to identify human traces in stratigraphic units where archaeological materials are scarce or absent intertwined with others richer in archaeological remains by the determination of multiple elements and statistical studies we believe that rare earth elements ree soil analysis provides unique insights for a better characterization of natural and archaeological sediments but more importantly to recognize different stages of the gradient we expect to discern between natural versus anthropic units and between primary versus secondary deposits redeposition using the case of the neolithic site of mas d is alicante spain as an example the application of the principal component analysis pca remarks differences in ree values those analysis show differences between units of undoubtedly anthropogenic origin and control samples taken from natural sediments including marls bedrock in their vicinity but also we could notice finer nuances like the degree of human contributions to paleosols formation

paleoearthquakes and eolian dominated fault sedimentation along the hubbell spring fault zone near albuquerque new mexico the hubbell spring fault zone forms the modern eastern margin of the rio grande rift in the albuquerque basin of north central new mexico knowledge of its seismic potential is important because the fault zone transects kirtland air force base sandia national laboratories and underlies the southern albuquerque metropolitan area no earthquakes larger than m l 5 5 have been reported in the last 150 years in this region so we excavated the first trench across this fault zone to determine its late quaternary paleoseismic history our trench excavations revealed a complex 16 m wide fault zone overlain by four tapered blankets of mixed eolian sand and minor colluvium that we infer were deposited after four large magnitude surface rupturing earthquakes although the first oldest rupture event is undated we used luminescence thermoluminescence and infrared stimulated luminescence ages to determine that the subsequent three rupture events occurred about 56 6 29 3 and 12 1 ka these ages yield recurrence intervals of 27 and 17 k y between events and an elapsed time of 12 k y since the latest surface rupturing paleoearthquake slip rates are not well constrained but our preferred average slip rate since rupture event 2 post 56 ka is 0 05 mm yr and interval slip rates between the last three events are 0 06 and 0 09 mm yr respectively vertical displacements of 1 2 m per event and probable rupture lengths of 34 43 km indicate probable paleoearthquake magnitudes m s or m w of 6 8 7 1 future earthquakes of this size likely would cause strong ground motions in the albuquerque metropolitan area

the influence of bulk shape factors on settling velocities of natural sand sized sedimentary suites settling rates of natural sand size particles are influenced to some extent by their shapes and this may be an important factor in using settling rates to estimate grain size in order to gauge the sensitivity of this influence two natural sand populations from the mesozoic nubian sandstones of southern israel with a high probability of being similar in their bulk shape characteristics were examined in sieved fractions for their shape characteristics and settling rates fine surface features roundness and surface roughness were evaluated using fourier shape analytical methods significant differences in bulk shape were detected and their influence on settling rates was measured empirically in a settling tube the most marked differences were in the coarse grain sizes and to a lesser extent in the intermediate sizes sampling of raw settling data at closely spaced time intervals yielded high resolution grain size frequency plots which were usually polymodal in nature subtle shape contrasts which are an important influence on settling rates are thus an important consideration when working at this level of sensitivity natural sand populations which have followed a more varied provenance or process pathway could be expected to have even greater contrasts in settling rates than the samples analysed here thus it is recommended that the bulk shape factor should be taken into account in order to minimize errors in the conversion of settling times to grain size an easy method outlined in this paper is through the establishment of an empirically derived calibration curve for each individual suite of sand undergoing analysis sieved samples derived from a split of the total composite sample undergoing analysis forms the basis of the calibration and hence a correction factor converting sieve diameters to true diameters must be applied in this research nominal section diameters were obtained optically through an image analyser

the original shapes of quartz silt grains a test of the validity of the use of quartz grain shape analysis to determine the sources of terrigenous silt in marine sedimentary deposits abstract the results of a study of the original shapes of quartz silt grains that are released from plutonic metamorphic and sedimentary rocks of varied age origin and lithology are reported the purpose of the study is to demonstrate the validity of quartz grain shape analysis as a technique for determining the sources of terrigenous silt within marine sedimentary deposits by showing that different sources of terrigenous silt release quartz silt grains with different shapes there are four major types of sources that release quartz silt grains with different and distinctive shapes crystalline rocks release a mixture of crystalline grains with subrounded and subangular outlines crystalline nodes and grain embayments and fractured grains with angular outlines microfractures deformation sheets and fracture faces quartz cemented sedimentary rocks release overgrown grains with subangular to angular outlines and quartz overgrowths and lesser numbers of rounded grains with rounded and subrounded outlines and abraded grain surfaces glacial deposits release fractured grains with angular outlines microfractures deformation sheets fracture faces micro blocks and comminution debris lastly quartzose multicyclic sediments release abundant rounded grains with rounded or subrounded outlines and abraded and weathered surfaces therefore the results indicate that quartz grain shape analysis is generally a valid technique for determining the sources of silt however there are exceptions to this generalization for there are some sediment sources e g first cycle coastal plain sediments that inherit and release grain shape types which are released from other sediment sources e g crystalline rocks thus the application of quartz grain shape analysis to the study of the sources of terrigenous silt for a given study area requires some knowledge about the major sediment sources which are available to that study area for this knowledge will define the limitations of this sourcing technique

parent material influence on soil distribution and genesis in a paleudult and kandiudult complex southeastern usa parent materials greatly influence soil development and the distribution of soils on the southeastern us coastal plain we examined the physical chemical and mineralogical properties of 11 pedons in a 1 ha plot on the upper coastal plain of georgia usa uniformity of parent materials was assessed by sand grain size characteristics the soils have sandy epipedons of variable thickness and argillic horizons of variable texture six of the pedons also have kandic horizons they are classified us soil taxonomy in psammentic grossarenic arenic and typic subgroups of paleudults and kandiudults loamy pedons possess argillic horizons with two distinct increases in clay and greater differences between eluvial and illuvial horizons than sandy pedons the upper boundary of the argillic horizon is approximately parallel to the present geomorphic surface suggesting that it is associated with the contemporary surface discontinuities identified by changes in sand grain size ratios and plots of the third skewness and fourth kurtosis moments of sand grain distribution roughly correspond to the bottom of the solum our data suggest that there are both eolian and fluvial components in the solum whereas subjacent horizons are completely derived from fluvial deposits sandier pedons have greater gibbsite kaolinite ratios possibly because greater permeability has enhanced leaching and si loss our data suggest parent materials largely control soil distribution over this plot

black carbon fire fingerprints in pleistocene loess palaeosol archives in germany past environmental changes were frequently accompanied by changes in fire regimes however the extent to which the residue of ancient fires black carbon bc is abundant in pleistocene palaeosols remains largely unknown and whether and to which degree its occurrence and composition relates to pedogenetic processes and palaeoenvironmental change we studied three pleistocene loess palaeosol sequences from western germany for systematic variation in bc quantity and quality during marine isotope stages 5e to 4 ca 130 65 ka bp using the benzene polycarboxylic acid bpca oxidation method palaeopedogenetic processes were elucidated from grain size distribution colour organic and inorganic carbon and ba sr ratio the results showed that bc peaked during phases of soil formation indicated by increases in ba sr carbonate loss and colour change its concentration reached 0 6 2 1 g bc c kg of former topsoil the content was close to the detection limit in the parent loess and subsoil suggesting that there was little if any vertical translocation parameters for bc quality i e proportion of mellitic acid were typical for bc derived from the burning of grass and leaves as common for tundra like and forest steppe vegetation dominating in stadials and interstadials of the weichselian glaciation we conclude that bc was preserved in and bears comparable information in the three palaeosols hence we recommend bpca analysis of terrestrial archives for regional fire regime assessment in the pleistocene

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

size shape and orientation of grains in sands and sandstones image analysis applied to rock thin sections abstract a computer based image analysis system is used to determine the grain size distribution grain shape and grain orientation from rock thin sections a monte carlo simulation allows correction of the grain size distribution for the corpuscle effect grains cut marginally in the thin section plane have smaller apparent diameters thin section derived grain size distributions of modern and ancient samples have been compared with distributions obtained from sieving of the same samples different grain shape parameters have been compared with the wadell formula the grain orientation can be easily and reliably measured in thin sections from different cuts of a sample grain orientation data can help to determine paleocurrent directions

the changing nature of rainfall during the early history of mars abstract several explanations have been proposed for the temporal differences in geologic processes associated with the modification of martian impact craters which occurred throughout the noachian and the formation of valley networks which occurred during the noachian hesperian transition here we show that it could be a result of the changing nature of rainfall as the primordial atmospheric pressure on mars waned through time we calculate the terminal velocity and resulting kinetic energy from raindrops 0 5 mm in diameter that would impact the surface of mars in a co 2 rich atmosphere ranging in pressure from 0 5 to 10 bars our analyses indicate that the primordial atmosphere of mars could not have exceeded 4 0 bars as raindrop sizes would have been limited to

mineralogy of salt efflorescences in paddy field soils of kollo southern niger abstract this study examines the mineralogy of salt crusts developed on the irrigated paddy soils in the soudano sahelian region of niger it involved field observations supplemented by laboratory determinations powder xrd sem edax ir spectral analyses the salt crusts were found in the concave zones near to the dike along the niger river they consisted of white mamillated konyaite crystals supported by a continuous hexahydrite crust upslope konyaite disappeared progressively and the discontinuous crust was constituted by hexahydrite only at a few centimeters below the soil surface epsomite crystallized in the cracks and voids in the subsoil gypsum and calcite were deposited the salt minerals were distributed vertically and laterally in the soil horizons according to the chemical composition of shallow groundwater in particular the namg ion ratio the water table depth and the extent of surface runoff human activity particularly superfluous irrigation constitutes the most pertinent explanation of the salinization processes at kollo

the lower colorado river valley a pleistocene desert abstract a chronological sequence of plant macrofossil assemblages from twenty five pack rat middens provides a record of desert scrub vegetation for most of the last 13 380 yr b p from a hyperarid portion of the lower colorado river valley at the end of the late wisconsin and probably during much of the quaternary the picacho peak area imperial county california supported a typical mohave desert association of larrea divaricata creosote bush coleogyne ramosissima blackbrush yucca brevifolia joshua tree and y whipplei whipple yucca recent arrivals of sonoran desert plants such as olneya tesota ironwood and fouquieria splendens ocotillo suggest that the area supported relatively modern sonoran desert scrub species for relatively short periods during interglaciations

using quartz grain size and shape analysis to distinguish between aeolian and fluvial deposits in the dallol bosso of niger west africa size and fourier shape characteristics of quartz sand grains were determined by computerized image analysis in order to distinguish between aeolian and fluvial soil parent materials in the dallol bosso in niger factor analysis of grain size distributions gave four sand end members that can be related to fluvial transport dynamics operating when the sediments were initially deposited the medium to fine and more angular shaped sand fractions are being reworked by wind aeolian deposits were well sorted whereas fluvial deposits were poorly sorted in both size and shape although gross shape characteristics lower harmonics of fourier series expansion indicated a common source rock for all sands the aeolian sands were well rounded whereas the fluvial sands tended to be more angular upper harmonics of fourier series

late glacial and holocene record of climatic change in the southern rocky mountains from sediments in san luis lake colorado usa abstract large rapid climate changes occurred over the last glacial cycle in the southwestern united states and elsewhere in many regions of the world some of these changes were attributed to alternations between stadial and interstadial conditions in the north atlantic but intense debate exists on how climate anomalies in the north atlantic transmit to the southwest here we report a sediment record from san luis lake in southern colorado through analyses of grain size magnetic susceptibility mg ca total inorganic carbon 18 o and 13 c to indicate climatic and environmental changes in the southern rocky mountains over the last 16 5 ka we found that san luis lake remained hydrologically closed most of the time but overflowed during the second half of the mystery interval the big wet 15 7 14 9 ka and the latter part of the mid holocene the neopluvial 4 3 ka over the course of the last deglaciation san luis lake underwent a series of large millennial scale hydroclimatic changes such as the big dry 16 5 15 7 ka the big wet the bolling allerod dry 14 9 12 7 ka and the younger dryas wet 12 8 11 6 ka corresponding to warm cold phases in the high latitude northern hemisphere the north american monsoon waxed during the pre boreal interval 11 6 10 5 ka and waned through the holocene in phase with northward and southward displacement of the intertropical convergence zone itcz the san luis lake basin was relatively dry in the early holocene 10 5 6 7 ka wet and fluctuating in the mid holocene 6 7 2 6 ka and dry and less variable in the late holocene 2 6 0 ka we found evidence that extreme pluvial episodes of the southern rocky mountains and elsewhere in the american southwest were coeval with cold phases of the north pacific our results highlight the role of the north pacific in modulating atmospheric circulations over the region on millennial timescales

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

style and timing of glacial and paraglacial sedimentation in a monsoon influenced high himalayan environment the upper bhagirathi valley garhwal himalaya abstract the gangotri glacier at the source of the ganges river has fluctuated greatly throughout the late quaternary in response to climatic oscillations this has resulted in impressive moraines paraglacial debris flow fans and terraces along the upper stretches of the bhagirathi valley cosmogenic radionuclide crn dating of glacial and paraglacial landforms shows that fans terraces and associated moraines formed approximately synchronously as the landscape readjusted to changing environmental conditions this synchronicity suggests that fan and terrace formation is intimately related to glaciation and that fluctuations in glacial and associated environments during times of climatic instability cause rapid sediment transfer and resedimentation of glacial landforms the crn dates show that all existing glacial and paraglacial landforms in the upper bhagirathi valley formed during the late pleistocene and holocene this demonstrates that in this high mountain environment paraglacial and glacial landforms are eroded and resedimented within about 20 000 years furthermore this testifies to the dynamic nature of glacial environments in monsoon influenced high mountain regions

degradation of quaternary cinder cones in the cima volcanic field mojave desert california basaltic cinder cones in the cima volcanic field record a detailed history of progressive erosion in the arid environment of the eastern mojave desert these cones range in age from 0 015 m y to 1 09 0 08 m y as dated by radiocarbon or k ar analyses of the youngest lava flows from each cone cone heights range from 50 to 155 m and basal widths range from 400 to 915 m on younger cones height width ratios average 0 17 and crater width cone width ratios average 0 42 the degradational morphology of these cones displays several trends that are closely related to cone age 1 crater width cone width ratios decrease from 0 48 on the youngest cone to 0 21 on the oldest cone with a preserved crater 2 mean maximum side slopes tan sc decrease from 0 575 on the youngest cone to an average of 0 41 on the oldest cones studied 3 debris apron height cone height ratios increase from 0 10 on the youngest cone to an average of 0 34 on the oldest cones 4 cone drainage evolves from irregularly spaced rills and gullies on the youngest cone to regularly spaced gullies on 0 20 to 0 35 m y old cones to valleys as much as 110 m wide and 10 m deep on cones 0 59 m y old and older these trends form the basis of an empirical model of cinder cone degradation in arid environments this model documents 1 an erosional loss of 15 of cone volume during the first million years 2 progressive decline of cone slope at an average rate of 0 006 103 yr and cone height at an average rate of 2 25 cm 103 yr 3 initial rapid stripping of the loose cinder mantle from upper cone slopes accompanied by rapid debris apron formation and 4 a gradual transition between 0 25 and 0 6 m y from relatively uniform stripping of upper slopes to localized fluvial dissection of both cone slopes and debris apron this transition is apparently controlled by a concomitant change from diffuse subsurface drainage within the pervious cinder mantle to concentrated surface flow across the heterogeneous assemblage of agglutinate layers dikes and ponded flows of the cone interior

development of spatially diverse and complex dune field patterns gran desierto dune field sonora mexico the pattern of dunes within the gran desierto of sonora mexico is both spatially diverse and complex identification of the pattern components from remote sensing images combined with statistical analysis of their measured parameters demonstrate that the composite pattern consists of separate populations of simple dune patterns age bracketing by optically stimulated luminescence osl indicates that the simple patterns represent relatively short lived aeolian constructional events since 25 ka the simple dune patterns consist of i late pleistocene relict linear dunes ii degraded crescentic dunes formed at 12 ka iii early holocene western crescentic dunes iv eastern crescentic dunes emplaced at 7 ka and v star dunes formed during the last 3 ka recognition of the simple patterns and their ages allows for the geomorphic backstripping of the composite pattern palaeowind reconstructions based upon the rule of gross bedform normal transport are largely in agreement with regional proxy data the sediment state over time for the gran desierto is one in which the sediment supply for aeolian constructional events is derived from previously stored sediment ancestral colorado river sediment and contemporaneous influx from the lower colorado river valley and coastal influx from the bahia del adair inlet aeolian constructional events are triggered by climatic shifts to greater aridity changes in the wind regime and the development of a sediment supply the rate of geomorphic change within the gran desierto is significantly greater than the rate of subsidence and burial of the accumulation surface upon which it rests

can high resolution 3d topographic surveys provide reliable grain size estimates in gravel bed rivers high resolution topographic surveys such as those provided by structure from motion sfm contain a wealth of information that is not always exploited in the generation of digital elevation models dems in particular several authors have related sub metre scale topographic variability or surface roughness to sediment grain size by deriving empirical relationships between the two in fluvial applications such relationships permit rapid analysis of the spatial distribution of grain size over entire river reaches providing improved data to drive three dimensional hydraulic models allowing rapid geomorphic monitoring of sub reach river restoration projects and enabling more robust characterisation of riverbed habitats however comparison of previously published roughness grain size relationships shows substantial variability between field sites using a combination of over 300 laboratory and field based sfm surveys we demonstrate the influence of inherent survey error irregularity of natural gravels particle shape grain packing structure sorting and form roughness on roughness grain size relationships roughness analysis from sfm datasets can accurately predict the diameter of smooth hemispheres though natural irregular gravels result in a higher roughness value for a given diameter and different grain shapes yield different relationships a suite of empirical relationships is presented as a decision tree which improves predictions of grain size by accounting for differences in patch facies large improvements in d50 prediction are possible sfm is capable of providing accurate grain size estimates although further refinement is needed for poorly sorted gravel patches for which c axis percentiles are better predicted than b axis percentiles

geomorphic features and associated iron oxides of the dallol bosso of niger west africa summary ironstone occurs in four landscape positions in the dallol bosso valley of niger 1 on a high plateau 2 on terraces 3 in dunes and 4 in partially or completely filled channels the fe oxide mineralogy of the older plateau and terrace ironstones contrast with that of the newly formed pedogenic ironstone of the valley plateau ironstone is characterized by a hematiterich phase whereas terrace gravels are goethitic in the valley ironstone occurs at the base of dunal soils along the contact between medium to fine eolian sands and coarser fluvial sands there it consists of quartz sand cemented by goethite a maghemite hematite association occurs at the top of the ground water table neoformation of the valley mineral phases occurs in an aquic soil environment and is driven by the large amount of surface evaporation in the semi arid climate the presence of fe in the ground water of the dallol bosso suggests an active process of fe movement there is an abundant reservoir of fe in the plateau ironstones that may be slowly released by physical and chemical weathering although the source of the fe is speculative secondary fe phases are likely to continue to form as the dallol bosso landscape evolves

sources and dispersal of late quaternary silt on the northern gulf of mexico continental shelf abstract the surficial sediments of the northern gulf of mexico continental shelf consist of large volumes of silt and clay and lesser amounts of sand of late quaternary age a study of the roundness and surface textures of quartz silt grains in these surficial sediments was conducted to determine the sources and dispersal patterns of this size fraction and to gain a better understanding of late quaternary sedimentation on this shelf the results indicate that there are six distinct silt provinces within the study area that can be distinguished on the basis of grain roundness and surface textures three of the provinces are characterized by relatively angular quartz silt grains on the average and an abundance of first cycle crystalline quartz grains the remaining three provinces are characterized by relatively rounded quartz silt grains and an abundance of multicyclic sedimentary rounded grains the dispersal patterns of these six provinces are partly controlled by the late wisconsinian paleogeography thus a comparison of the dispersal patterns with the locations of the modern and ancient fluviodeltaic depocenters allows the identification of these six provinces as deposits of the rio grande the coastal plain streams of south texas the brazos and colorado river the mississippi the mobile river and the rivers of the southeastern united states however the dispersal patterns have also been modified by the prevailing shelf and longshore currents and there is up to 400 km of downcurrent displacement of silt from its late wisconsinian sites of deposition on some parts of the shelf

k ar dating of the cima volcanic field eastern mojave desert california late cenozoic volcanic history and landscape evolution thirty four k ar ages and supporting paleomagnetic measurements from flows of the cima volcanic field provide a detailed volcanic history and a temporal basis for analysis of evolving landforms the cima field has undergone three periods of volcanic activity spanning late miocene through latest pleistocene time 1 7 6 to 6 5 2 4 5 to 3 6 and 3 1 0 to at least 0 015 m y ago these precisely dated sequences afford a unique opportunity to quantify the long term effects of pedogenesis and erosion on volcanic landforms in an arid environment morphologic and pedologtc data indicate that the most stable geomorphic surfaces in the field occur on flows between 0 25 and 0 75 m y old younger flows are dominated by eolian aggradation and outcrop rubbling and older flows are dominated by surface runoff and fluvial dissection a process response model involving progressive pedogenesis and a subsequent shift from infiltration to surface runoff is proposed to explain this temporal variation in land surface stability