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

desert pavements and associated rock varnish in the mojave desert how old can they be desert pavements are common features of arid landscapes and have been widely used as a relative age indicator of the geomorphic surfaces upon which they are developed in this study i examined the patterns of pavement development as a function of elevation in the mojave desert as well as the causes for the gradual disappearance of pavement at high elevations pavement density as measured by percentage of pebble coverage decreases systematically with elevation gain by 3 per 100 m from 95 coverage below 500 m to less than 60 at 1700 m plants appear to be the main agent of pavement disruption plant density decreases as pavement density increases burrowing by rodents and crusting by cryptobiota also disrupt pavement development at higher elevation during the last glacial maximum plant communities were displaced 1000 1400 m downward in the mojave desert pavements today generally do not survive above the blackbush coleogyne ramossisma sagebrush artemisia tridentata zone evidence from packrat middens shows that these and other plants typical of high elevations today grew as low as 300 400 m during the last glacial maximum i suggest that during the last glacial maximum desert pavements were confined to the lowest alluvial fans of death valley and adjoining low valleys no alluvial desert pavements above 400 m in the region are older than the latest pleistocene by the same reasoning desert varnish on desert pavements above 400 m may all be holocene in age except where developed on stable boulders

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

alignment of stone pavement clasts by unconcentrated overland flow implications of numerical and physical modelling the crucial role of stone pavements in arid environments for aeolian or alluvial processes and as numerical dating tools is increasingly acknowledged this role is based on the assumption that stone pavements are stable landforms formed gradually over time and predominantly by vertical processes however this is challenged by evidence of stone pavement clast reworking or burial bimodal mostly slope aspect symmetrical clast orientation is a frequent phenomenon in various study areas it implies that stone pavements may be influenced by unidirectional lateral processes besides vertical ones here the finding of lateral processes contributing to stone pavement evolution is supported by numerical modelling and physical experiments these unequivocally show that unconcentrated overland flow can transport clasts to form a closely packed stone mosaic with characteristics similar to those of natural stone pavements the commonly observed length axes orientation angle of 40 14 for natural stone pavement clasts is consistently reproduced by angle dependent force equilibrium monte carlo runs confirm the natural scatter and allow characterization of the control parameters of clast orientation the model explains up to 70 of the natural variance it is further validated by flume experiments which confirm model predictions of single object orientation angles experiments with multiple objects yield artificial stone pavements with properties similar to those found in the field the unidirectional lateral process acting on natural stone pavements requires the presence of a vesicular horizon this underlines the tight genetic coupling of this common epipedon feature and the clast cover the presented findings highlight the role of stone pavements as process and environment proxies however stone pavements represent information since the last surface disturbance only this has to be considered when using them as age indicators copyright 2013 john wiley sons ltd

analysis of dolines using multiple methods applied to airborne laser scanning data abstract delineating dolines is not a straightforward process especially in densely vegetated areas this paper deals quantitatively with the surface karst morphology of a miocene limestone occurrence in the styrian basin austria the study area is an isolated karst mountain with a smooth morphology former planation surface of pliocene age densely vegetated mixed forest and with a surface area of 1 3 km 2 the study area is located near the city of wildon and is named wildoner buchkogel the aim of this study was to test three different approaches in order to automatically delineate dolines the data basis for this was a high resolution digital terrain model dtm derived from airborne laser scanning als and with a raster resolution of 1 1 m the three different methods for doline boundary delineation are a the traditional method based on the outermost closed contour line b boundary extraction based on a drainage correction algorithm filling up pits and c boundary extraction based on hydrologic modelling watershed extracted features are integrated in a gis environment and analysed statistically regarding spatial distribution shape geometry elongation direction and volume the three methods lead to different doline boundaries and therefore investigated parameters show significant variations the applied methods have been compared with respect to their application purpose depending on delineation process between 118 and 189 dolines could be defined the high density of surface karst features demonstrates that solutional processes are major factors in the landscape development of the wildoner buchkogel furthermore the correlation to the landscape evolution of the grazer bergland is discussed

on the size distribution of solution dolines in carbonate karst lognormal or power model abstract dolines or closed karst depressions are the most characteristic feature of karst landscapes the two main types of doline are those formed by the removal of material by solution and those formed by the geological processes of collapse or suffosion solution dolines are most frequently found in carbonate karst in high relief karst massifs various algorithms can be used to identify and delineate dolines in high resolution digital elevation models dem where the lower size limit is determined by the resolution of the dem i e the size of the cell or the dem pixel in terrain units the work presented here addresses the size distribution of dolines which is a significant component of the geomorphometric analysis of dolines on the basis of experimental results various authors have advocated the lognormal or the power distribution as the best fit to experimental data a power distribution is consistent with a fractal structure implying the fractal nature of the sizes of dolines which in turn may reflect a relationship between size and the structural controls of fracture networks and the fractal fragmentation of the terrain this paper presents case studies of four karst landscapes that are representative of karst massifs in spain two of these are located in the pyrenees in the north of spain and two are located in the betic mountains in the south of spain in all four cases a lognormal distribution provides a bad fit while a power law distribution provides a good fit in three cases and in the fourth case provides a good fit for dolines that have a diameter greater than 50 m

evolution and degradation of flat top mesas in the hyper arid negev israel revealed from 10be cosmogenic nuclides mesas are ubiquitous landforms in arid and semiarid regions and are often characterized by horizontal stratified erodible rocks capped by more resistant strata the accepted conceptual model for mesa evolution and degradation considers reduction in the width of the mesa flat top plateau due to cliff retreat but ignores possible denudation of the mesa flat top and the rates and mechanism of erosion in this study we examine mesas in the northeastern hyperarid negev desert where they appear in various sizes and morphologies and represent different stages of mesa evolution the variety of mesas within a single climatic zone allows examination of the process of mesa evolution through time two of the four sites examined are characterized by a relatively wide 200 230 m flat top and a thick caprock whereas the other two are characterized by a much narrower remnant flat top several meters and thinner caprock we use the concentration of the cosmogenic nuclide 10be for a determining the chronology of the various geomorphic features associated with the mesa and b understanding geomorphic processes forming the mesa the 10be data combined with field observations suggest a correlation between the width of flat top mesa and the denudation and cliff retreat rates our results demonstrate that a cliff retreat rates decrease with decreasing width of the flat top mesa b vertical denudation rates increase with decreasing width of the flat top mesa below a critical value 60 m for the negev desert c the reduction in the width of the flat top mesa is driven mainly by cliff retreat accompanied by extremely slow vertical denudation rate which can persist for a very long time 106 ma and d when the width of the mesa decreases below a certain threshold its rate of denudation increases dramatically and mesa degradation is completed in a short time copyright 2014 john wiley sons ltd

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

late quaternary geomorphology and soils in crater flat yucca mountain area southern nevada crater flat is an alluvium filled structural basin on the west side of yucca mountain nevada which is under consideration for a high level nuclear waste repository north trending late quaternary faults offset alluvium in crater flat both along the canyons of the western flanks of yucca mountain and out on the piedmont slope we believe the initial lack of young offsets at yucca mountain was in part due to unrecognized late quaternary stratigraphy we hypothesize that alluviation in the yucca mountain region was more active during the late quaternary than previously thought several techniques were tried to test this hypothesis results are compared with previous soils and surface exposure dating studies and correlated to stratigraphy of other late quaternary units in the southern nevada death valley and mojave desert areas and provide new stratigraphic data relevant to understanding climatic alluvial processes in the basin and range province during the late quaternary 76 refs 7 figs 6 tabs

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

slip rate of the calico fault implications for geologic versus geodetic rate discrepancy in the eastern california shear zone 1 long term 10 5 years fault slip rates test the scale of discrepancy between infrequent paleoseismicity and relatively rapid geodetic rates of dextral shear in the eastern california shear zone ecsz the calico fault is one of a family of dextral faults that traverse the mojave desert portion of the ecsz its slip rate is determined from matching and dating incised pleistocene alluvial fan deposits and surfaces displaced by fault slip a high resolution topographic base acquired via airborne laser swath mapping aids in identification and mapping of deformed geomorphic features the oldest geomorphically preserved alluvial fan unit b is displaced 900 200 m from its source at sheep springs wash in the northern rodman mountains this fan deposit contains the first preserved occurrence of basalt clasts derived from the pipkin lava field and overlies quaternary conglomerate deposits lacking these clasts the 40 ar 39 ar dating of two flows from this field yields consistent ages of 770 40 ka and 735 9 ka an age of 650 100 ka is assigned to this fan deposit based on these ages and on the oldest cosmogenic 3 he exposure date of 653 20 ka on a basalt boulder from the surface of unit b this assigned age and offset together yield a mid pleistocene to present average slip rate of 1 4 0 4 mm yr ayounger fan surface unit k records 100 10 m of dextral displacement and preserves original depositional morphology of its surface granitic boulders and pavement samples from this surface yield an average age of 56 4 7 7 ka after taking into account minimal cosmogenic inheritance of granitic clasts the displaced and dated k fans yield a slip rate of 1 8 0 3 mm yr distributed deformation of the region surrounding the fault trace if active could increase the overall displacement rate to 2 1 0 5 mm yr acceleration of slip rate from an average of 1 4 mm yr prior to 50 ka to 1 8 mm yr since 50 ka is possible though a single time averaged slip rate of 1 6 0 2 mm yr satisfies the data these rates are faster than any other paleoseismic or long term slip rate yet determined for other dextral faults in the mojave desert and imply that fault slip rates and earthquake productivity are heterogeneous across this portion of the ecsz total displacement across the calico fault diminishes northward as shear is distributed into folding and sinistral faults in the calico mountains this pattern is consistent with an approximately threefold drop in geologic slip rate as the calico fault steps over onto the blackwater fault and demonstrates the significance of fault interaction for understanding the pattern of present day strain accumulation in the ecsz

hydraulics of interrill overland flow on stone covered desert surfaces the hydraulics of interrill overland flow on stone covered desert surfaces depend on the resistance to flow which may be partitioned into grain resistance form resistance wave resistance and rain resistance efforts to model large scale roughness in open channels suggest that resistance to overland flow on such surfaces is a function of grain reynolds number froude number flow depth and the size shape spacing and pattern of the roughness elements the effect of flow depth on flow resistance f is often hidden in the flow reynolds number re in laboratory and field studies alike f re relations have been found to be convex upward and negatively sloping and these shapes have been explained in terms of the progressive inundation of the roughness elements where laboratory or field based models have been developed for predicting f they invariably contain percent stone cover the prominence of this variable reflects the strong influence of stone size and spacing on flow resistance a laboratory study shows that where the froude number f 0 50 wave resistance increases with stone cover and dominates resistance to flow on all surfaces with stone covers greater than 10 a field study indicates that where f 0 50 and wave resistance is inconsequential grain and form resistance typically account for about 5 and 95 of f respectively these findings have important implications for sediment transport modeling because percent grain resistance is equal to percent grain shear stress and it has recently been suggested that in overland flow as in river flow sediment transport capacity is determined by grain shear stress rather than total shear stress a laboratory study however demonstrates that this is not the case sediment transport capacity is in fact greater than predicted by grain shear stress because energy dissipated in the wakes of roughness elements in overland flow is transformed into turbulence sufficiently close to the bed to affect sediment transport

cosmogenic 3he exposure ages of pleistocene debris flows and desert pavements in capitol reef national park utah abstract the quaternary history of the capitol reef area utah is closely linked to the basaltic andesite boulder deposits that cover much of the landscape understanding the age and mode of emplacement of these deposits is crucial to deciphering the quaternary evolution of this part of the colorado plateau using cosmogenic 3 he exposure age dating we obtained apparent exposure ages for several key deposits in the capitol reef area coarse boulder diamicts capping the johnson mesa and carcass creek terraces are not associated with the bull lake glaciation as previously thought but were deposited 180 15 to 205 17 ka minimum age and are the result of debris flow deposition desert pavements on the johnson mesa surface give exposure ranging from 97 8 to 159 14 ka and are 34 96 kyears younger than the boulder exposure ages the offset between the boulder and pavement exposure ages appears to be related to a delay in pavement formation until the penultimate glacial interglacial transition or periodic burial and exposure of pavement clasts since debris flow deposition incision rates for the capitol reef reach of the fremont river calculated from the boulder exposure ages range from 0 40 to 0 43 m kyear 1 maximum rates and are some of the highest on the colorado plateau

luminescence ages for alluvial fan deposits in southern death valley implications for climate driven sedimentation along a tectonically active mountain front abstract controversy exists over whether alluvial fan sedimentation along tectonically active mountain fronts is driven by climatic changes or tectonics knowing the age of sedimentation is the key to understanding the relationship between sedimentation and its cause alluvial fan deposits in death valley and throughout the arid southwestern united states have long been the subjects of study but their ages have generally eluded researchers until recently most mapping efforts have recognized at least four major relative age groupings q1 oldest q2 q3 and q4 youngest using observed changes in surface soils and morphology relation to the drainage net and development of desert pavement obtaining numerical age determinations for these morphologic stages has proven challenging we report the first optically stimulated luminescence osl ages for three of these four stages deposited within alluvial fans along the tectonically active black mountains of death valley deposits showing distinct remnant bar and swale topography q3b have osl ages from 7 to 4 ka whereas those with moderate to poorly developed desert pavement and located farther above the active channel q3a have osl ages from 17 to 11 ka geomorphically older deposits with well developed desert pavement q2d have osl ages 25 ka using this osl based chronology we note that alluvial fan deposition along this tectonically active mountain front corresponds to both wet to dry and dry to wet climate changes recorded globally and regionally these findings underscore the influence of climate change on alluvial fan deposition in arid and semi arid regions

a soil chronosequence in the semi arid environment of patagonia argentina abstract soil development with time was investigated on beach ridges with ages ranging from about 1380 to 6240 14c years bp at the eastern coast of central patagonia the main pedogenic processes are accumulation of organic matter and carbonate leaching and accumulation within the upper part of the soils soil formation is strongly influenced by incorporation of eolian sediments into the interstitial spaces between the gravel of which the beach ridges are composed different amounts of eolian material in the soils lead to differentiation into leptosols containing 10 fine earth in the upper 75 cm and regosols containing 10 fine earth soil depth functions and chronofunctions of organic carbon calcium carbonate ph ca zr mg zr k zr na zr fe zr mn zr and si al obtained from x ray fluorescence analysis were evaluated to establish soil chronofunctions mean values of the horizon data of 0 10 cm below the desert pavement were used which were weighted according to the horizon thicknesses the depth function of ph shows a decrease towards the surface indicating leaching of bases from the upper centimeters chronofunctions of ph show that within 6000 radiocarbon years of soil development ph drops from 7 0 to 6 6 in the leptosols and from 8 1 to 7 5 in the regosols the higher ph of the regosols is due to input of additional bases from the eolian sediments chronofunctions of ca zr and k zr indicate progressive leaching of ca and k in the regosols showing close relationships to time r2 0 972 and 0 995 na leaching as indicated by decreasing na zr ratios shows a strong correlation to time only in the leptosols r2 0 999 both leptosols and regosols show close relationships to time for fe zr r2 0 817 and 0 824 mn zr r2 0 940 and 0 803 and si al 0 971 and 0 977 indicating enrichment of fe and mn and leaching of si leaching of mobile elements takes place on a higher level in the regosols than in the leptosols from the beginning of soil formation hence a significant part of the eolian sediments must have been incorporated into the beach ridges very soon after their formation

filling the gap osl data expanding 14c chronologies of late quaternary environmental change in the libyan desert several decades of geomorphological and archaeological research in the libyan desert conducted by the cologne projects b o s and acacia have yielded a wealth of radiocarbon data from archaeological sites and over the last decade also 48 osl ages mainly from aeolian deposits this paper focuses on the combination of both data sets in order to obtain a synthesis of late quaternary occupational and environmental history in this region case studies demonstrate that despite a poorer time resolution of osl chronologies compared to 14 c data osl ages can be more consistent with the archaeological context particularly if the dating of charcoals poses problems due to poor quality or re deposition comparison of data sets from the egyptian sand seas and from the wadi howar sudan shows that in both cases osl and 14 c data cover complementary time slices on the regional scale however contradictory intervals of aeolian accumulation are documented which can be explained by the different environmental histories the results accentuate that interpretation of osl data has to be done in the context of the entire environmental systems including the effective geomorphological processes r 2007 elsevier ltd and inqua all rights reserved

an integrated framework to identify and analyze karst sinkholes abstract sinkholes are the most typical surface feature of karst landscapes their correct mapping is of great importance for a proper assessment of the possible occurrence of new events and the likely effects they could have on the anthropogenic environment in this work we compare and discuss different ways to map sinkholes including heuristic approach automatic mapping through different resolution dtms and digital aerial photo interpretation aimed at highlighting advantages and drawbacks of the multiple approaches for our purpose we use a study area in the murge of apulia se italy where many sinkholes of several typologies are present to characterize the landscape to evaluate the reliability of the sinkhole mapping we set up a conceptual methodology that integrates a semi automatic method with the heuristic approach with a special focus on the importance of incorporating digital stereoscopic interpretation in detail we used as input two dtms at different resolution aimed to test the robustness of the automatic method in different circumstances comparison of the data produced by the different approaches illustrated how the number density and boundaries of the sinkholes may vary as a function of the input data the automated mapping provides reliable results in terms of number dimensions and morphometric attributes of sinkholes and appears to be particularly useful when large areas must be analyzed within the whole process we stress the role of the expert geomorphologist who must determine the accuracy of the product obtained with the automated mapping by correcting eliminating features not attributable to karst processes the presented approach highlights the potential of digital stereoscopy in substantially decreasing the errors encountered with traditional analog mapping simultaneously reducing the working time significantly

26al 10be dating of an aeolian dust mantle soil in western new south wales australia abstract aeolian dust mantle soils are an important element of many landscapes in south eastern australia though the age of these aeolian deposits has not been radiometrically determined at fowlers gap in western new south wales surface cobbles of silcrete and quartz overlie a stone free aeolian dust mantle soil which has a thickness of about 1 6 m the clay rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer modelling in situ cosmogenic 26 al and 10 be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks reveals that each has experienced a complex exposure burial history due to the absence of quartz stones or sand at intermediate depths our cosmogenic 26 al and 10 be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial various scenarios of stone formation transport burial and exhumation were tested that constrain the age of the deposit to range from 0 9 0 2 ma to 1 8 0 2 ma based largely on different assumptions taken for the time dependency of the net sedimentation rate this corresponds with the initiation of the simpson desert dune fields and the deflation of lakes in central australia which probably responded to the shift to longer wavelength larger amplitude quaternary glacial cycles at around 1 ma sensitivity analyses were carried out to identify those parameters which better constrained model outputs within model errors which largely are the result of analytical errors in measured 26 al and 10 be concentrations all three competing theories of colluvial wash upward displacement of stones and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement

geomorphology and quaternary geology of the dakhla oasis region egypt abstract dakhla oasis 25 5 n 29 e occupies a structurally localized depression at 90 140 m above sea level 1200 km 2 in area below a 300 m escarpment bordering the libyan plateau western desert of egypt semi arid intervals of the quaternary period generated eight sedimentary formations separated by erosion during hyper arid intervals sediments comprise three generations of colluvial fluvial fanglomerates two generations of tabular spring laid clastic and chemical sediments two generations of mound springs and basinal sediments of fluvio lacustrine evaporitic pluvio aeolian and aeolian origins discussion of these sediments is organized according to geomorphic region from north to south plateau scarp and piedmont lowland and cuesta plain chronological evidence is restricted to many radiocarbon dates of holocene cultural material associated with playa sediments 9 4 5 ka a th u isochron age of 62 0 7 6 ka for basinal evaporites and two th u ages of 176 and 170 ka for a boulder of derived travertine the regional quaternary sequence is reconstructed from stratigraphic and geomorphic relationships of the sediments and erosion surfaces it is broadly similar to sequences earlier reconstructed in the topographically similar kharga oasis region 150 km to the east and kurkur oasis 400 km to the south southeast speculations on chronology and driving mechanism are offered in conclusion

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

relation between infiltration and stone cover on a semiarid hillslope southern arizona abstract a knowledge of the spatial distribution of infiltration rates is essential to the application of realistic distributed rainfall runoff models in semiarid areas one method of determining this distribution is to develop a predictive equation based on a readily observable surface property such as stone cover previous studies of the relation between infiltration and stone cover on shrub covered semiarid hillslopes have yielded both positive and negative correlations it is suggested that positive correlations result where infiltration measurements are confined to areas between large shrubs negative correlations on the other hand reflect pronounced shrub intershrub differences in infiltration and stone cover and are found where both shrub and intershrub areas are sampled in this study of a semiarid hillslope in southern arizona both shrub and intershrub areas are sampled and a negative correlation is obtained between infiltration and stone cover this correlation arises from the fact that under shrubs fine sediments have accumulated primarily as a result of differential splash whereas between shrubs such sediments have been selectively removed by a combination of rainsplash and overland flow leaving behind a gravel lag consequently infiltration rates are higher under shrubs than between them owing to the higher percentage of sand in the surface soil the larger quantity of organic matter both within the soil and on its surface and the greater digging and burrowing by animals in addition simulated rainfall experiments imply that shrubs with moderately dense canopies are more effective than adjacent surface gravels in dissipating the kinetic energy of raindrops and thereby reducing surface sealing and promoting infiltration inasmuch as the field site is typical of gentle shrub covered piedmont hillslopes over much of the sonoran desert inverse relations between infiltration rate and stone cover are probably characteristic of such hillslopes and may be used to predict the spatial distribution of infiltration rates for inclusion in rainfall runoff models

co development of alluvial fan surfaces and arid botanical communities stonewall flat nevada usa arid alluvial fan and fluvial dry wash surfaces in stonewall flat nevada usa are characterized using surface geomorphic surveys soil pits botanical line surveys and varnish microlamination dating techniques active and abandoned washes and active fan surfaces are dominated by primary geomorphic processes of high energy sedimentation from flash floods these surfaces are characterized by bar and swale topography a lack of stone pavements soil horizons and rock varnish younger terraces and slightly older intermediate fan surfaces are in transition from primary sedimentation processes to lower energy secondary surface modifying processes of sheet wash and eolian transport and deposition these surfaces are characterized by faint to no bar and swale topography incipient to moderately well developed pavements and soil horizons and abundant coppices old and stable fan surfaces are dominated by lower energy secondary processes and manifest well developed pavements soils and sparse coppices around widely distributed shrubs varnish microlamination dating yields ages of 13 15 ka for intermediate fan surfaces and 25 55 to 86 75 ka for stable fan surfaces plant communities co developing with these surfaces affect and are affected by both primary and secondary geomorphic fan processes relatively active surfaces contain few woody species co dominance of shrubs and annuals with abundant annuals between the shrubs is characteristic of surfaces transitional from primary processes to secondary processes stable surfaces dominated by secondary processes are characterized by woody perennials with long lived woody species inhabiting the oldest surfaces feedback mechanisms between early botanical communities and eolian deposition affect coppice and pavement development in turn these surface features control both the composition and distribution of botanical communities on older more stable surfaces published 2012 this article is a u s government work and is in the public domain in the usa

human occupations and environmental changes in the nile valley during the holocene the case of kerma in upper nubia northern sudan abstract our article presents a detailed holocene archaeological sequence from the nile valley at kerma in upper nubia northern sudan this sequence retraces the evolution of human populations thanks to the study of several sites supported by 90 14c dates reconstruction of the environmental changes was supported by a study of dated stratigraphic sections located near the archaeological sites studied and illustrates the effects on human occupation of changes in river flow and floods which are in turn forced by climatic changes the results shed new light on the evolutionary dynamics of the holocene populations in nile valley little known due to the numerous hiatuses in occupation when compared with the situation in the sahara and the rest of the nile valley they confirm that the initial occupation took place ca 10 5 kyr bp after the start of the african humid period followed by a migration towards the banks of the nile commencing 7 3 kyr bp they also confirm the appearance of the neolithic by ca 8 0 kyr bp the kerma stratigraphic sequences show two prosperous periods 10 8 and 7 6 kyr bp and two hiatuses in the occupation of the sites 7 5 7 1 and 6 0 5 4 kyr bp resulting from increased aridity

alluvial sediment or playas what is the dominant source of sand and silt in desert soil vesicular a horizons southwest usa 1 vesicular a av soil horizons form beneath desert pavements from the accretion of aeolian sediment dust commonly thought to be derived primarily from desiccating pluvial lakes and playas with contributions from ephemeral washes and alluvial fans particle size distributions of av horizons are typically bimodal with primary modes of very fine silt and fine sand suggesting that the horizon matrix is derived from multiple sources here we conduct detailed chemical and physical analysis of both av horizon soil samples and potential sources of aeolian sediment to better constrain the relative contributions of dust associated with the development of av horizons geochemical data from both sand 125 250 m and silt 2 32 m fractions in av horizons and potential dust sources in the eastern mojave desert and western sonora desert usa point to large contributions from nearby sources including distal alluvial fans and washes and comparably lower contributions from regional sources such as playas the silt mode is derived from suspension transport of dust and the fine sand mode is derived from saltating sand the desiccation of pluvial lakes in the mojave desert is commonly believed to have driven episodes of aeolian activity contributing to sand dunes and av horizon formation we propose that alluvial fans and washes are underappreciated as desert dust sources and that pulses of dust from late pleistocene and holocene alluvial fans dwarfed pulses of dust from desiccating pluvial lakes in the eastern mojave desert

correlations of cave levels stream terraces and planation surfaces along the river mur timing of landscape evolution along the eastern margin of the alps the transition zone of the eastern alps to the pannonian basin provides one of the best sources of information on landscape evolution of the eastern alpine mountain range the region was non glaciated during the entire pleistocene thus direct influence of glacial carving as a landscape forming process can be excluded and relics of landforms are preserved that date back to at least the late neogene in this study we provide a correlation between various planation surfaces across the orogen basin transition in particular we use stream terraces planation surfaces and cave levels that cover a vertical spread of some 700 m our correlation is used to show that both sides of the transition zone uplifted together starting at least about 5 ma ago for our correlation we use recently published terrestrial cosmogenic nuclide tcn burial ages from cave sediments new optically stimulated luminescence osl ages of a stream terrace and u th ages from speleothems minimum age constraints of cave levels from burial ages of cave sediments covering the last 4 ma are used to place age constraints on surface features by parallelizing cave levels with planation surfaces the osl results for the top section of the type locality of the helfbrunn terrace suggest an early wurm development 80 5 3 7 to 68 7 4 0 ka the terrace origin as a penultimate gravel deposit in classical alpine terminology riss is therefore questioned u series speleothem ages from caves nearby indicate formation during marine isotope stages mis 5c and 5a which are both interstadial warm periods as osl ages from the terrace also show a time of deposition during mis 5a ending at the mis 5 4 transition this supports the idea of temperate climatic conditions at the time of deposition in general tectonic activity is interpreted to be the main driving force for the formation and evolution of these landforms whilst climate change is suggested to be of minor importance obvious hiatuses in miocene to pleistocene sediments are related to ongoing erosion and re excavation of an uplifting and rejuvenating landscape

climate induced changes in sediment supply revealed by surface exposure dating of sijiquan river terraces northeastern tibet abstract in this paper we report cosmogenic isotope evidence for dramatic changes in sediment supply during glacial interglacial climatic cycles in the late quaternary previous work on fluvio glacial processes in cold environments has qualitatively revealed that significant increases in debris production occurred in glacial periods due typically to accelerated glacial and periglacial processes on high relief slopes resulting in river aggradation accumulation in the drainage in interglacial periods rivers behave in the opposite way forming incised valleys however little has been studied on climatically controlled production and reworking processes with radiometric evidence the evidence presented here is from the northeastern margin of the tibetan plateau where lateral growth of the plateau is now ongoing reconstructions of fluvial response to quaternary glacial fluctuations are crucial also to better understand the active tectonic process in the region using geomorphological information the sijiquan river drainage basin on the north of the east kunlun mountains was investigated detailed geomorphological mapping of fluvio glacial landforms indicates two phases of aggradation each of which was followed by valley incision 10 be and 26 al concentrations in fluvial terrace deposits suggest that these two aggradational phases correspond most likely to the penultimate and last glacial periods assuming a low rate of surface erosion on the terraces and zero inherited concentration on the other hand present day river gravel has higher concentrations in amalgamated samples of 10 be and 26 al than the terrace deposits surface exposure and burial analyses based on grain by grain measurements of both 10 be and 26 al indicate that the present day river gravel consists mostly of reworked grains from terrace deposits and underlying fluvio lacustrine rocks in the drainage basin it is concluded that significant changes in clastic sediment supply occur in cold environments in response to glacial interglacial cycles clastic sediments are transported from mountain slopes much more directly in glacial periods than in interglacial periods this violates the common assumption for surface exposure dating that the inherited cosmogenic isotope concentration is constant through time

morphometric properties of dolines in matarsko podolje sw slovenia matarsko podolje in sw slovenia is a karstic surface with many dolines which appear between the flysch composed brkini hills in the ne and mt slavnik in the sw we have analyzed dolines to find the morphometric parameters of the depth area volume and circularity index and also calculated the doline density and pitting index all parameters were also calculated separately for individual lithological units to explain the variations of the calculated values among these groups morphometry was performed in gis environment on a 1 1 m digital elevation model with bare earth obtained by lidar the results show a high density of dolines 94 dolines km2 and also a high pitting index rp 8 27 compared to other studies there are some significant differences between the measured values in individual lithologies as the depths areas and volumes are largest in dolomitic beds other beds include various types of limestones and carbonate breccia the median values of depth area and volume are 2 98 m 541 m2 and 690 m3 the circularity index is also lowest in dolomite beds and kozina limestones however the differences are not so pronounced as for areas and volumes dolines longer axes are parallel to the directions of major structural elements however more detailed mapping should be done to confirm the influence of faults and fracture zones on the doline geometry

the vesicular layer and carbonate collars of desert soils and pavements formation age and relation to climate change abstract the vesicular fine grained a horizon av is the widespread ubiquitous surficial horizon of desert soils in diverse landforms and parent materials of varying ages now known to form mostly through accumulation of eolian dust recent studies show that dust accumulation and concomitant soil development are genetically linked to stone pavement formation changes in the magnitude of eolian activity and effective leaching related to quaternary climatic changes are also hypothesized to have influenced the evolution of the av horizon numerical modeling geochronologic and field laboratory studies elucidate the nature of pedogenic processes controlling compositional evolution of av how the changing av horizon increasingly influences soil infiltration and carbonate translocation and accumulation and the control that clasts of the evolving pavement exert on pedogenic processes results of a model that determines soil bulk chemical composition based on mixing of estimated proportions of externally derived eolian material and parent materials imply that the evolution of the soil bulk composition is strongly influenced by av horizon formation the early development of a weakly to moderately developed av horizon directly over gravelly parent material in late and middle holocene soils moderately influences soil infiltration but significant leaching of very soluble materials and some carbonate in dust are permitted in older pleistocene soils however the texturally more mature av and underlying cumulic nongravelly horizons more strongly limit the rate and depth of leaching and soil bulk composition therefore more closely approximates a simple mixture of dust and parent material other aspects of av horizon development and its relations to the pavement are evaluated through studies of pavement clasts with coatings of soil carbonate referred to as carbonate collars development of a numerical model that integrates soil hydrology a co2 production diffusion model calcite kinetics and thermodynamic considerations composition and thermal characteristics of pavement clasts and the textural and structural properties of the surface horizon provides the basis for testing a hypothesis of collar formation model results combined with results of 13c and 18o analyses of collar carbonate demonstrate how precipitation of calcite on pavement clasts and within the av is favored at a depth much shallower than that indicated by the classic carbonate depth climate relationship of jenny and leonard jenny h j leonard c d 1935 functional relationships between soil properties and rainfall soil science 38 363 381 and arkley arkley r j 1963 calculations of carbonate and water movement in soil from climatic data soil science 96 239 248 or simulated by numerical models of carbonate accumulation simultaneous development of thick carbonate collars and the av horizon requires the sustained pavement clast av horizon coupling for at least centuries to possibly millennia new thermoluminescence ages also indicate that much of the av horizon formed in the holocene and that it is certainly much younger than the older pleistocene pavements this supports the previously proposed hypothesis that increased dust flux during the pleistocene to holocene transition triggered and or greatly accelerated av horizon development an understanding of the genesis of collars provides not just an understanding of how carbonate can accumulate in surface environments but it also provides important clues into processes of pavement evolution and preservation of av horizons during long glacial periods the av horizon is not merely an insignificant surficial zone of recent dust accretion instead its development profoundly influences the genesis of desert soils and pavements

identification of karst sinkholes in a forested karst landscape using airborne laser scanning data and water flow analysis abstract karst sinkholes dolines play an important role in a karst landscape by controlling infiltration of surficial water air flow or spatial distribution of solar energy these landforms also present a limiting factor for human activities in agriculture or construction therefore mapping such geomorphological forms is vital for appropriate landscape management and planning there are several mapping techniques available however their applicability can be reduced in densely forested areas with poor accessibility and visibility of the landforms in such conditions airborne laser scanning als provides means for efficient and accurate mapping of both land and landscape canopy surfaces taking the benefits of als into account we present an innovative method for identification and evaluation of karst sinkholes based on numerical water flow modelling the suggested method was compared to traditional techniques for sinkhole mapping which use topographic maps and digital terrain modelling the approach based on simulation of a rainfall event very closely matched the reference datasets derived by manual inspection of the als digital elevation model and field surveys however our process based approach provides advantage of assessing the magnitude how sinkholes influence concentration of overland water flow during extreme rainfall events this was performed by calculating the volume of water accumulated in sinkholes during the simulated rainfall in this way the influence of particular sinkholes on underground geomorphological systems can be assessed the method was demonstrated in a case study of slovak karst in the west carpathians where extreme rainfalls or snow thaw events occur annually we identified three spatially contiguous groups of sinkholes with a different effect on overland flow concentration these results are discussed in relation to the known underground hydrological systems

late pleistocene glaciations of the arid subtropical andes and new results from the chajnantor plateau northern chile abstract the spatiotemporal pattern of glaciation along the andes mountains is an important proxy record reflecting the varying influence of global and regional circulation features on south american climate however the timing and extent of glaciation in key parts of the orogen particularly the deglaciated arid andes are poorly constrained we present new cosmogenic 10 be and 36 cl exposure ages for glacial features on and near the chajnantor plateau 23 s the new dates although scattered due to cosmogenic inheritance imply that the most recent extensive glacial occupation ended before or during the global last glacial maximum lgm we discuss this new record in the context of published glacial chronologies from glacial features in peru bolivia and northern chile rescaled using the latest cosmogenic 10 be production rate calibration for the tropical andes the results imply regionally synchronous moraine stabilization ca 25 40 ka 15 17 ka and 12 14 ka with the youngest of these moraines absent in records south of 20 s including in our new chajnantor area chronology this spatial pattern implicates easterly moisture in generating sufficient snowfall to glaciate the driest parts of the andes while allowing a role for westerly moisture possibly modulated by the migration of the southern westerly wind belt in the regions near and south of the atacama desert

post miocene subtropical karst evolution lower suwannee river basin florida morphometric characteristics of 25 000 karstic depressions suggest that the last phase of the post miocene karstic evolution within the lower suwannee river basin of florida has been controlled by the lower sea level stands of the pleistocene and the formation of the suwannee river during the pleistocene as interglacial seas retreated marine terraces formed by sequential sea level lowstands and the time period of subaerial exposure diminished toward the sea consequently geomorphologically younger karst landforms formed as the elevation of marine terraces decreased the evolutionary geomorphological development of this heavily karstified region produced more frequent and or larger and more complex depressions at higher elevations a geographic information system analysis of morphometric and spatial distribution parameters of the karstic depressions within the lower suwannee river basin reveals that the florida karst is represented by broad shallow depressions with an average density of 6 07 km 2 and an average pitting index of 14 5 morphometric and spatial distribution parameters of karstic depressions show a great variation within the lower suwannee river area and thus preclude a simple morphoclimatic classification of karst landforms the tertiary carbonate rocks of the subtropical florida karst have relatively less joint frequency and significant primary porosity and do not produce the extreme karst landforms observed in the massive limestones of the tropics

karst database implementation in minnesota analysis of sinkhole distribution this paper presents the overall sinkhole distributions and conducts hypothesis tests of sinkhole distributions and sinkhole formation using data stored in the karst feature database kfd of minnesota nearest neighbor analysis nna was extended to include different orders of nna different scales of concentrated zones of sinkholes and directions to the nearest sinkholes the statistical results along with the sinkhole density distribution indicate that sinkholes tend to form in highly concentrated zones instead of scattered individuals the pattern changes from clustered to random to regular as the scale of the analysis decreases from 10 100 km2 to 5 30 km2 to 2 10 km2 hypotheses that may explain this phenomenon are 1 areas in the highly concentrated zones of sinkholes have similar geologic and topographical settings that favor sinkhole formation 2 existing sinkholes change the hydraulic gradient in the surrounding area and increase the solution and erosional processes that eventually form more new sinkholes

biogeomorphology of a mojave desert landscape configurations and feedbacks of abiotic and biotic land surfaces during landform evolution abstract terrestrial ecosystems can be more holistically understood by investigating the morphology of landscape mosaics the assemblage of their ecological communities and the linkages and feedbacks between the mosaics and communities the overarching objectives of this study were to 1 study the abiotic and biotic configurations of landform units as mosaics within a mojave desert chronosequence and 2 elucidate their potential feedbacks interactions and dynamics during landform evolution seven landform units distributed over three geomorphic ages were identified including young bars and swales intermediate aged flattened bars flattened swales and bioturbation units and old desert pavements and shrub zones these landform units were characterized according to abiotic and biotic land surface properties landform units were statistically distinct and predictable based on a specific suite of abiotic and biotic properties vascular plant functional group and biological soil crust community diversity varied with geomorphology with greatest diversity associated with bars and shrub zones and lowest diversity associated with desert pavements biological soil crust communities were controlled by geomorphic age surface rock size and protruding rocks with young bar units having the highest abundance and diversity perennial forbs were observed in old shrub zones with small rocks and few protruding rocks a high clast density and a finer sized clast distribution were found particularly in desert pavements and flattened swales and generally inhibited biological soil crust and plant cover evolutionary trajectories for landforms of a lower piedmont landscape can be dominated by either abiotic and biotic landform processes these two trajectories are distinctly different and are associated with their own unique linkages feedbacks and dynamics of abiotic and biotic land surface properties producing a highly diverse desert landscape

evolution of desert pavements and the vesicular layer in soils of the transantarctic mountains abstract compared to mid latitude deserts the properties formation and evolution of desert pavements and the underlying vesicular layer in antarctica are poorly understood this study examines the desert pavements and the vesicular layer from seven soil chronosequences in the transantarctic mountains that have developed on two contrasting parent materials sandstone dolerite and granite gneiss the pavement density commonly ranges from 63 to 92 with a median value of 80 and does not vary significantly with time of exposure or parent material composition the dominant size range of clasts decreases with time of exposure ranging from 16 64 mm on holocene and late quaternary surfaces to 8 16 mm on surfaces of middle quaternary and older age the proportion of clasts with ventifaction increases progressively through time from 20 on drifts of holocene and late quaternary age to 35 on miocene aged drifts desert varnish forms rapidly especially on dolerite clasts with nearly 100 cover on surfaces of early quaternary and older age macropitting occurs only on clasts that have been exposed since the miocene a pavement development index based on predominant clast size class pavement density and the proportion of clasts with ventifaction varnish and pits readily differentiated pavements according to relative age from these findings we judge that desert pavements initially form from a surficial concentration of boulders during till deposition followed by a short period of deflation and a longer period of progressive chemical and physical weathering of surface clasts the vesicular layer that underlies the desert pavement averages 4 cm in thickness and is enriched in silt which is contributed primarily by weathering rather than eolian deposition a comparison is made between desert pavement properties in mid latitude deserts and antarctic deserts

large near surface nitrate pools in soils capped by desert pavement in the mojave desert california we found exceptionally high nitrate levels up to 12 750 kg ha 1 at shallow depths 1 m in soils mantled by desert pavement a common land surface feature in arid regions nearby soils without desert pavement had nitrate contents that were one to two orders of magnitude lower the soil conditions coincident with desert pavement i e stability antiquity and virtually no leaching favor the retention and accumulation of nitrate delivered by atmospheric deposition or in situ fixation the nitrate stored in soils under desert pavement is a previously unrecognized pool of nitrogen that has the potential to increase the global nitrogen inventory for near surface desert soils to five times previous estimates its near surface occurrence makes this labile nitrogen pool particularly susceptible to mobilization by climate change or human disturbance risking contamination of surface and groundwaters

optically stimulated luminescence osl dating and spatial analysis of geometric lines in the northern arabian desert abstract in this paper we generate chronological constraints through optically stimulated luminescence osl dating on extensive prehistoric stone structures that stretch out in the arabian desert and appear as geometric lines known as the works of the old men two major types of the works that are common throughout the arabian desert are the wheels and the more intensively investigated desert kites here osl dating was applied to wheels in the wadi wisad area in the eastern badia of jordan osl dating generated ages that fall into the late neolithic to chalcolithic and early bronze age periods this chronological spectrum is consistent with the well documented prehistoric activities at the archaeological site of wisad pools also located in the wadi wisad area spatial analyses of the works in wadi wisad and in the azraq oasis revealed that 1 the wheels are organized in clusters 2 the spatial distribution of the wheels is predetermined by the kites 3 the kites were most probably created earlier than the wheels in the study areas and 4 a cluster of wheels nearby the azraq oasis tentatively demonstrates ranking and perhaps tendency for alignment although this is not the case for the other wheel clusters studied despite the progress toward understanding the chronological and spatial aspects of the wheels a great deal of research remains to resolve the actual nature of these enigmatic stone structures

sinkhole distribution in a rapidly developing urban environment hillsborough county tampa bay area florida sinkhole formation in florida is a common event the florida karst plain is significantly altered by human development and sinkholes cause considerable property damage throughout much of the state we present in this paper a morphometric analysis of karst depressions in the tampa bay area and the relation with the known distribution of sinkholes we selected the tampa bay area because it is particularly susceptible to the evolution of karst depressions in relation with development of the built up environment karst depressions were mapped from the 1 24 000 usgs topographic maps and a morphometric analysis was performed by using parameters such as shape circularity index perimeter area length width and orientation maps showing the distribution of depression density and the sectors with greatest areas of karst depression were produced using a gis these results were compared with data compiled from the database of sinkhole occurrences in florida maintained by the florida geological survey our analysis demonstrates that the distribution of new sinkhole occurrences differs from the distribution of existing sinkholes indicating that there are processes acting today that are influencing karst landscape formation that are different from those acting in the past

gis based analysis of doline density on taurus mountains turkey the taurus mountain is one of the most important karstic region of the world and dolines are characteristics landforms of this area however the number and distribution of doline are unknown in the study area the aims of this study are to explain the total number of dolines distribution of doline density effects of slope conditions and the change of doline orientation in the taurus mountains according to the 1 25000 scale topographic maps utilized in this study a total of 140 070 dolines were determined in a 13 189 km2 area on eleven high karstic plateaus bordered by steep slopes and deep gorges these plateaus are substantially affected by highly faulted and jointed systems and about 80 of each plateau is covered with neritic limestone the dolines are located at an elevation between 10 and 2870 m average elevation of all dolines is 1842 m 90 of dolines are located between 1300 and 2270 m and only 5 of dolines found under 1330 m according to this results the densest doline zone corresponds to the alpine and periglacial zone above the treeline doline density reaches 100 doline km2 on mt anamas and the seyran geyik and akdag ranges as well as the taseli plateau maximum density 187 doline km2 is found on the akdag mountains however 66 of the study area is characterized by low density 29 9 with moderate density 3 4 with high density and 0 7 with very high density the highest doline densities are seen on gentle slopes 15 25 km2 and steep slopes 35 km2 are limited doline distribution according to the rose diagram formed by the azimuths of the long axis of the dolines at the central taurus two direction are dominant in doline orientations nw se and ne sw however dominant directions are ne sw at eastern ne sw and nw se at central and nw se at western part of the central taurus according to this elongations doline orientations are formed an arc which is formed by tectonic evolution of the central taurus

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

cosmogenic 36cl dating of a young basaltic eruption complex lathrop wells nevada it has been proposed that the lathrop wells volcanic center a late quaternary basaltic complex in southern nevada has erupted more than once in common with most quaternary basalts this volcanic center has proved difficult to date by k ar and other commonly employed methods we have measured the accumulation of 36 cl in 11 samples from lava flows and volcanic bombs and obtained a combined average age of 81 7 9 ka with no systematic differences between sample subsets collected from different volcanic features the 36 cl dates do not support a history of multiple eruptions but neither do they completely preclude the possibility

pliocene paleoclimate and east antarctic ice sheet history from surficial ash deposits the preservation age and stratigraphic relation of an in situ ashfall layer with an underlying desert pavement in arena valley southern victoria land indicate that a cold desert climate has persisted in arena valley during the past 4 3 million years these data indicate that the present east antarctic ice sheet has endured for this time and that average temperatures during the pliocene in arena valley were no greater than 3 c above present values one implication is that the collapse of the east antarctic ice sheet due to greenhouse warming is unlikely even if global atmospheric temperatures rise to levels last experienced during mid pliocene times

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

incision rate of the yellow river in northeastern tibet constrained by 10be and 26al cosmogenic isotope dating of fluvial terraces implications for catchment evolution and plateau building unlike other large rivers flowing out of tibet the yellow river escapes from the plateau towards the ne crossing no less than five nw se striking actively growing ranges and intervening basins thick plio quaternary deposits and fluvial terraces testify to a phase of aggra dation and sediment infill up to the average surface elevation 3200 3250 m a s l of the gonghe guide and qinghai lake basins a set of seven main terraces across the gonghe basin suggests progressive down cutting of the yellow river carving the 500 m deep longyang gorge at the basin exit 10be and 26al concentrations in quartz of surface and sub surface samples of four terraces constrain the timing of incision by determining the burial age of the deposit and the exposure age of its surface modelling the depth dependence of the 10be concentration and the 26al 10be ratio allows us to constrain the onset of the ongoing phase of incision to 120 250 ka these ages suggest long term incision rates between 2 6 mm a together with the present morphology of the yellow river terraces across the gonghe basin and the longyang gorge our results imply rapid river catchment evolution and interaction between river dynamics tectonic and climate in northeastern tibet

response of desert pavement to seismic shaking hector mine earthquake california 1999 1 the october 1999 mw 7 1 hector mine earthquake in the mojave desert california generated characteristic surface disturbances on nearby desert pavements these disturbances included 1 zones of wholesale gravel displacement interspersed with zones of intact pavement 2 displaced and rotated cobbles 3 moats around loosened embedded boulders 4 filling of abandoned cobble sockets boulder moats and other depressions with gravel and 5 formation of narrow subparallel linear strips of exposed fine grained subpavement matrix matrix lineations clasts displaced from matrix lineations and from cobble sockets tended to move downslope sharp boundaries of matrix lineations and slope controlled displacement directions on slopes of only a few degrees indicated that clasts remained close to the pavement surface during shaking the regular few decimeter spacing of matrix lineations suggests the presence of standing waves during seismic shaking boulder moats probably have good preservation potential and at some desert pavement locations might provide information on paleoseismic shaking although readily produced by coseismic shaking displaced cobbles are unreliable indicators of past earthquake activity because of potential multiple origins for an assumed earthquake recurrence interval of 10 ka seismically driven sediment fluxes similar to those generated by the hector mine earthquake at the lavic siding pavement study site may be marginally competitive with aseismic smoothing mechanisms driven by bioturbation rainbeat and wash for a 1 ka recurrence interval seismic smoothing is likely to play a significant role in pavement evolution

late pleistocene human occupation of the hyperarid core in the atacama desert northern chile abstract few archeological sites in south america contain uncontroversial evidence for when the first peopling of the continent occurred largely ignored in this debate extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability here we report on a rare 12 13 ka human occupation from quebrada mani site qm12 a plantless near rainless landscape 1240 m asl and 85 km from the pacific ocean located in the hyperarid core of the atacama desert this location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central andes during the latest pleistocene excavations at qm12 yielded a diverse cultural assemblage of lithics burned and cut bones marine gastropods pigments plant fibers and wooden artifacts alongside a prepared fireplace sixteen radiocarbon dates from site qm12 on charcoal marine shells animal dung plant remains and wood reveal that the occupation took place between 12 8 and 11 7 ka these results demonstrate that the atacama desert was not a barrier to early american settlement and dispersal and provide new clues for understanding the cultural complexity and diversity of the peopling of south america during the last glacial interglacial transition

the degassing character of a young volcanic center cerro negro nicaragua cerro negro volcano is a young basaltic cinder cone which is part of the nicaraguan volcanic arc eruptive activity at cerro negro is characterized by explosive strombolian to subplinian eruptions driven by volatile rich basaltic magma ascending rapidly from various crustal depths 15 to 6 km resulting in the onset of precursory activity only 30 min before an eruption in this paper we present a comprehensive degassing characterization of the volcano over a 4 year period aimed at improving our understanding of the magmatic plumbing network and its relationship with regional tectonics a total of 124 individual soil gas samples were collected between 2010 and 2013 and analyzed for stable carbon isotopes 13c from co2 high temperature fumaroles were sampled for 18o d and 3he 4he isotope analysis and major degassing zones were mapped using soil co2 flux measurements gases at cerro negro are characterized by a strong 3he 4he mantle signature 6 3 to 7 3 ra magmatic 13c ratios 2 3 to 3 0 meteoric 18o and d ratios and stable co2 fluxes 31 t d 1 the lack of 13c fractionation and an increase in the relative mantle component from 2002 to 2012 suggest that the volatile flux at cerro negro originates from the mantle and ascends to the surface via a series of crustal fractures that act as permeable conduits despite the lack of new eruptions the hydrothermal system of cerro negro continues to evolve due to seasonal inputs of meteoric water slope failures that expose and bury sites of active degassing and bursts of regional seismicity that have the potential to open up new conduits for gas release as well as magma continuing geophysical and geochemical monitoring of the main edifice and the recently formed south zone is essential as the volcano remains overdue to erupt

structural controls on distribution of dolines on mount anamas taurus mountains turkey abstract solution dolines are characteristic landforms on the high plateaus of the taurus mountains in this study the effects of tectonic structures drainage and slope conditions on the distribution and morphometric properties of dolines in the western part of the central taurus are explained to delimit the dolines 1 25000 scale topographic maps were used the uppermost closed contour lines were digitized as polygons and the elevation long and short axes elongation ratios orientation angles of the polygons were calculated the doline density is compared with drainage density and mean slope values a total of 111 rose diagrams were created in order to illustrate the superficial distribution of orientation as a result a total of 10 652 dolines were detected in a 711 km2 doline area and maximum density reaches 123 dolines km2 however according to the doline density two distinct regions were detected high density r1 and low density r2 correlations between drainage density slope angle and doline density are negative in the two regions according to negative correlations the drainage density is not a determinant factor in r1 while it is a determinant factor in r2 a 30 slope angle in km2 limits doline distribution on the plateau surface the orientation of all doline long axes is nw se which is parallel to the general orographic extent of mount anamas however different orientations were detected and these orientations were showed in farther sub regions according to the 111 gridded rose diagrams the overall result of this study is that the fault and joint systems that developed on the thick bedded limestone between thrust faults affected the doline density while lateral strike slip normal faults and joint systems in front of the thrust belt were more effective on the geometric shapes of dolines

rock varnish evidence for latest pleistocene millennial scale wet events in the drylands of western united states rock varnish from late to latest pleistocene geomorphic features in the drylands of the western u s provides evidence of nine millennial scale wet events from 11 500 18 000 calendar yr b p represented by regionally replicable and approximately evenly spaced manganese and barium rich dark bands in varnish microstratigraphy preliminary radiometric age calibration indicates that these events appear to be broadly coeval with millennial scale cooling events identified in the greenland ice sheet project 2 gisp2 ice core record six of these wet events are associated with the cold intervals of the younger dryas and heinrich event h1 and the other three with the short lived cooling phases of the intra allerod cold period the older dryas and the oldest dryas these results combined with our previous documentation of millennial scale wet events in the holocene varnish record for the same region indicate that such wet oscillations in the western u s may be parts of regionally widespread manifestation of well documented pervasive millennial scale cycles of the north atlantic climate

desert pavements as indicators of soil erosion on aridic soils in north east patagonia argentina abstract desert pavements are prominent features of many geomorphic surfaces in arid and semiarid lands in the semiarid soils of north eastern patagonia gravel cover in the shrub interspace areas of shrub dominated communities is generally high and contrast with that of grass dominated patches where gravel cover is either absent or negligible in the present study we analyze the relationship between soil erosion and desert pavement formation in three sites the upper middle and lower slope positions of a flank pediment where well conserved soils served as reference areas we used the gravel cover and mass as well as the thickness of the remnant a horizon as determined by the depth of the bt horizon of a xeric calciargid as measures of soil erosion surface gravel at four cardinal points in respect to mounds associated with shrub clumps was collected and the depth to the bt horizon was determined the mean thickness of the a horizon in the well conserved soils were 11 3 10 0 and 13 5 cm for the upper middle and lower slope positions respectively for the same positions the mean coarse fragment contents 2 0 mm in the 0 10 cm depth of the a horizon in the well conserved soils were 144 92 and 119 g kg 1 and the mean surface gravel mass in the eroded patches were 5 3 3 1 and 4 7 kg m 2 surface gravel mass and depth of the remnant a horizon gave different estimates of the magnitude of soil erosion in the flank pediment thus the mean maximum soil loss as determined by the mean gravel mass on the soil surface for the upper middle and lower slope positions were 28 3 68 2 27 0 63 8 and 31 5 56 4 mm respectively these figures increased to a mean of 50 0 52 5 and 82 0 mm for the same positions when soil loss was determined as the difference between the thickness of the a horizon of the well conserved soil and that of the remaining a horizon in eroded patches the loss of the a horizon by wind and water erosion seems to initiate the change from grass steppe to a stable shrub steppe characterized in the shrub interspaces by well developed desert pavements the strong correlation between surface gravel mass and the thickness of the remaining a horizon indicates that accelerated soil erosion has played an important role in the formation of desert pavements and that desert pavements are good indicators of the extent and intensity of the erosion process in the punta ninfas area

young displacements on the atacama fault system northern chile from field observations and cosmogenic 21ne concentrations 1 we present the first numerical age constraint for young deformation of the atacama fault system afs in northern chile the young activity of the afs is expressed by several fault scarps which affects alluvial fan sediments of the eastern side of the coastal cordillera 23 30 23 42 s detailed mapping of alluvial fans reveals a complex relationship between fault motion erosion and alluvial fan development an older group of alluvial fans became inactive prior to the scarp formation younger alluvial fans arising directly from feeder channels and entrenched in the fault scarps posts date the scarp formation the youngest slip on the afs is recorded by headward eroding channels entrenched across the scarp which are in turn displaced vertically 0 3 0 5 m by the fault quartz fragments in four sites on the older inactive fan group were analyzed for cosmogenic 21ne concentrations yielding an average age of 424 151 ka the upper limit for the recent activity of the fault combined with the height of fault scarp we calculate a 0 01 mm yr minimum vertical fault slip rate thus young displacement on the afs is quaternary in age and confined to the late pleistocene

active basement uplift of sierra pie de palo northwestern argentina rates and inception from10be cosmogenic nuclide concentrations quaternary tectonic and denudation rates are investigated for an actively growing basement anticline the sierra pie de palo range which belongs to the andean foreland of northwestern argentina 28 s 33 s in this study a detailed morphometric analysis of the topography is combined with in situ produced cosmogenic10be concentrations measured in 1 surface boulders abandoned on alluvial terraces affected by fault activity along the north bounding fault and growth of the basement fold along the southeastern border 2 bedrock outcrops corresponding to an exhumed and folded regional erosion surface and 3 fluvial sediments sampled at the outlets of several watersheds along the eastern and northern borders of the range incision and uplift rates have been estimated at approximately 0 5 and 1 mm yr when integrated on holocene and pleistocene time scales in close agreement with both long term structural and basin evolution data and short term gps derived velocity field analyses cosmogenic derived denudation and uplift rates combined with geomorphic characteristics of watersheds and river channels allows estimating the onset of the uplift at 4 6 ma followed by a more recent period of topographic rejuvenation at roughly 1 2 ma probably synchronous with steepening of the eastern and northern flanks of the anticline

timing and controls on late quaternary landscape development along the eastern sierra el mayor range front in northern baja california mexico abstract the sierra el mayor sierra cucapa mountain range in northern baja separates the colorado river delta from the laguna salada basin and is important in terms of understanding the structural transition from the northern gulf extensional province to the san andreas system one of the principal quaternary landscape features of the eastern sierra el mayor sierra cucapa is a prominent surface that slopes 1 2 eastward towards the colorado river delta along the eastern side of the sierra el mayor and facing the colorado river delta but not along other piedmont mountain fronts that face the delta this surface is terminated by a series of stepped terrace surfaces the terrace surfaces are cut into fluvial deltaic deposits from the colorado river delta system and are capped by 1 m thick gravels optically stimulated luminescence ages from interbedded coarse sands in the capping gravels of the upper surface and two of the inset terraces range from 17 to 31 ka average 24 3 ka but lack a systematic age trend from upper to lower surface the underlying fluvial deltaic deposits have older optically stimulated luminescence ages of 31 to 39 ka and suggest colorado river delta deposition during the relatively stable interstadial of the middle wisconsinan substage marine isotope stage 3 when sea level was ca 60 to 80 m samples from depth profiles in the capping gravels and from the top of the upper surface have a mean 10 be terrestrial cosmogenic nuclide age of 59 5 ka when corrected for inheritance an average age of 21 ka is computed for exposure of the capping gravels on the upper surface and inset terraces which is in the range of the optically stimulated luminescence burial ages both the upper surface and inset terraces formed 17 30 ka at a transition time from dry to relatively wet climate when increased aggradation caused alluvial fan development on the upper surface regionally these surfaces correlate with the q2c q3a age deposits of the southwestern north america alluvial fan and terrace deposits sea level was also falling rapidly at this time which may have caused the colorado river to become entrenched near the range front thus allowing rapid response and down cutting to form the inset terraces on the east side of the sierra el mayor facing the delta assuming the 34 ka delta deposits graded to a base level that was 60 to 80 m during marine isotope stage 3 the computed surface uplift rate for the eastern side of the sierra el mayor is 2 1 2 7 mm yr this uplift may be accommodated on a fault or fault system that is a southward extension of the mexicali spreading and seismic zone that is buried beneath the colorado river delta east of the sierra el mayor the uplift rates from this study are consistent with geologic and geodetic data for the sierra el mayor and sierra cucapa and account for much of the missing extensional strain across the area

formation mechanisms and control factors of vesicular soil structure abstract vesicular structure is a widespread feature of soils in arid environments typically associated with stone pavements it has a major control function for dust and water fluxes and hence for site ecology previous models of vesicular structure formation and stability are inconsistent and mostly focused on the investigation of isolated control parameters to test existing models to infer plausible mechanisms of vesicular structure formation and to unveil controlling environmental and sedimentological parameters we present quantitative data of vesicle properties of artificial and natural vesicles vesicles are not unstable but their changes in size are non linear with time they form due to surface sealing by puddling and by a wetting front which advances downward thereby elevating gas pressure within the sediment matrix translocation of clay or precipitation of calcium carbonate support vesicle stabilisation vesicular structure forms within a wide range of environmental and sedimentological settings at least 6 3 15 7 mm of water per wetting cycle 0 70 sand content 0 8 5 6 ms cm electric conductivity and 1 28 calcium carbonate content high sand contents favour larger and rounder vesicles whereas increasing calcium carbonate content has the opposite effect the concentration of dissolved ions does not considerably influence vesicle formation under an artificial cover stone vesicles could not be created at all whereas they were concentrated around stone margins the main limiting factor for vesicle formation in natural environments is root activity the type and density of surface cover determine fine material fluxes into the aggregates of vesicular horizons the shape of vesicles may be related to dust influx intensity accordingly horizons with spherical vesicles may indicate constant low dust influx on poorly vegetated surfaces and be therefore used as proxies of environmental conditions

age of unstable bedrock landforms southwest of yucca mountain nevada and implications for past ground motions we determine minimum exposure ages for unstable outcrops at three sites in amargosa desert southwestern nevada including a site at the southern end of yucca mountain varnish microlamination dating techniques provide minimum exposure ages of 12 5 36 k y for the unstable outcrops of welded tuff including a 24 k y age for the south yucca mountain site the youngest exposure age 12 5 k y is found at the site located only 10 km from the death valley furnace creek fault suggesting outcrops may be more frequently modified when close to major active earthquake sources a simplistic stability assessment of the south yucca mountain outcrops suggests peak ground accelerations pgas may not have exceeded about 1 g uncertainty bounds 0 5 2 g in at least 24 k y a pga of 1 g is consistent with the predicted 24 k y return period pgas from the near decade old yucca mountain probabilistic seismic hazard psh model except for the ninety fifth percentile and above we gain confidence in our interpretations by additionally observing 1 minimal damage to the south yucca mountain outcrops from a recent moderate earthquake that is estimated to have produced a pga of less than 0 1 g there i e motions less than 0 5 g do not significantly damage the outcrops and 2 severe damage to similar volcanic outcrops associated with pgas of the order 0 5 1 g near a nuclear blast site from the 1960s these observations support our suggestion that pgas greater than 0 5 1 g have not occurred at the south yucca mountain site for a time period of at least 24 k y significant seismic events that substantially modify the outcrops and produce associated rubble fields may therefore occur on longer time scales

desert pavement an environmental canary abstract ongoing disruption of ancient varnished desert pavement surfaces near death valley national park is inferred to be the result of unusually intense animal foraging activity increased levels of bioturbation are associated with enhanced vegetation growth stimulated by recent el nino precipitation the occurrence of abundant recently overturned varnished clasts suggests that the pavement disturbances reported here are rare on the millennial time scale of desert varnish formation these observations suggest the possibility that changes in desert pavement surfaces may provide early hints of future changes in desert ecology and environment