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

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

correlation and dating of quaternary alluvial fan surfaces using scarp diffusion great interest has recently been focused on dating and interpreting alluvial fan surfaces as a complement to the radiometric methods often used for surface exposure dating this paper illustrates a rapid method for correlating and dating fan surfaces using the cross sectional shape of gullies incised into fan surfaces the method applies a linear hillslope diffusion model to invert for the diffusivity age t m2 using an elevation profile or gradient slope profile gullies near the distal end of fan surfaces are assumed to form quickly following fan entrenchment scarps adjacent to these gullies provide a measure of age the method is illustrated on fan surfaces with ages of approximately 10 ka to 1 2 ma in the arid southwestern united states two areas of focus are death valley california and the ajo mountains piedmont arizona gully profile morphology is measured in two ways by photometrically derived gradient slope profiles and by ground surveyed elevation profiles the t values determined using ground surveyed profiles are more consistent than those determined using photo derived t values however the mean t values of both methods are comparable the photometric method provides an efficient way to quantitatively and objectively correlate and relatively date alluvial fan surfaces the t values for each surface are determined to approximately 30 50 accuracy

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

estimating ages of late quaternary stream terraces from analysis of weathering rinds and soils rates of growth of rock weathering rinds and rates of changes of soil morphologic and chemical properties that are calibrated at sites of known ages produce powerful tools for estimating ages of geomorphic surfaces particularly when materials datable by conventional methods are not widespread sequences of latest quaternary stream terraces from the south island of new zealand are ideally suited for application of these calibrated age techniques because climate and source materials for terrace deposits are internally consistent within two regions west land and marlborough modal and mean thicknesses of weathering rinds formed in surface cobbles of torlesse graywacke provide age estimates for latest pleistocene and holocene stream terraces in marlborough with uncertainties estimated at 5 to 40 modal rind thickness of subsurface cobbles provides age estimates for latest quaternary westland sites with uncertainties of 10 to more than 50 few dated soils are available to constrain rates of soil development in westland and marlborough furthermore soils were sampled from only one pedon on each surface morphologic data however provide least squares age estimates for westland sites with uncertainties typically greater than 100 and the calibration data can further bracket likely soil ages to less than 50 uncertainty the regression data from marlborough are less reliable but profile index ratios help bracket ages to at least 50 distributions of oxalate extractable fe and ai and total major element concentrations allow age estimates for westland and marlborough soils with uncertainties estimated at 15 to 50 despite these uncertainties the three techniques combine to provide age estimates with the high resolution needed to examine details of fault slip rates or stream downcutting the calibration data and weathering rates used herein are applicable only to the new zealand region studied although similar calibrated age techniques should provide high resolution dating in many other regions such techniques are particularly useful when multiple approaches are available to provide independent cross checks

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

hydrological response of a dryland ephemeral river to southern african climatic variability during the last millennium a long term flood record from the buffels river the largest ephemeral river of nw south africa 9250 km2 was reconstructed based on interpretation of palaeoflood documentary and instrumental rainfall data palaeoflood data were obtained at three study reaches with preserved sedimentary evidence indicating at least 25 large floods during the last 700 yr geochronological control for the palaeoflood record was provided by radiocarbon and optically stimulated luminescence osl dating annual resolution was obtained since the 19th century using the overlapping documentary and instrumental records large floods coincided in the past within three main hydroclimatic settings 1 periods of regular large flood occurrence 1 large flood 30 yr under wetter and cooler prevailing climatic conditions ad 1600 1800 2 decreasing occurrence of large floods 1 large flood 100 yr during warmer conditions e g ad 1425 1600 and after 1925 and 3 periods of high frequency of large floods 4 5 large floods in 20 30 yr coinciding with wetter conditions of decadal duration namely at ad 1390 1425 1800 1825 and 1915 1925 these decadal scale periods of the highest flood frequency seem to correspond in time with changes in atmospheric circulation patterns as inferred when comparing their onset and distribution with temperature proxies in southern africa

the 1988 orange river flood upington region northwestern cape province rsa this paper describes aspects of the 1988 orange river flood the orange river is a perennial bedrock controlled river which experienced severe flooding flood peak 8300 m3 s 1 during february april of 1988 this flood resulted in the loss of life and damage in excess of 126 million negligible bank erosion took place in the main channel margins due to the stabilizing effect of tree lined banks in contrast areas removed from the channel margin were characterized by erosion and deposition within the confines of the natural flood channels macroturbulence gave rise to scour holes which sometimes amalgamated into large erosion fields acres in extent in many cases scour holes were present but macroturbulence originating obstacles were not and it is suggested that these were removed by flood erosion processes in some instances amalgamation of scour hole trails orientated down current led to the formation of steep sided flood channels deposition took the form of large sandsheets constructed from fluvial dune fields and braid bar accumulations post flood winds reworked some of the deposited sand into aeolian dunes

paleoflood hydrology origin progress prospects from an origin in diverse studies of flood geomorphology and quaternary geology paleoflood hydrology emerged as a geophysical and an applied hydrological science during the 1970s and 1980s since acquiring its formal name in 1982 the most productive approach in paleoflood hydrology has become energy based inverse hydraulic modeling of discrete paleoflood events recorded in appropriate settings as slackwater deposits and other paleostage indicators swd psi or as various threshold indicators of non exceedence technological advances particularly in hydraulic modeling and geochronology were instrumental in moving the discipline to its present status the most recent advances include 1 new techniques for the accurate geochronology of flood sediments notably tams radiocarbon analyses and osl dating and 2 the phenomenal increase in computer power that allows complex hydraulic calculations to become feasible for routine studies from its initial demonstration in the southwestern united states swd psi paleoflood hydrology proved its widespread applicability to various landscape environments particularly important studies have been accomplished in australia china india israel south africa spain and thailand paleoflood hydrology has also generated its share of controversy in part because of the differing viewpoints and attitudes of the two scientific traditions from which it emerged quaternary geology geomorphology versus applied hydrologic hydraulic engineering nevertheless the future growth of the discipline is assured given the rapid pace of discoveries that it engenders indeed so many international studies exist that it is appropriate to pursue global syntheses to address interesting and timely questions of extreme flood phenomena in relation to global climatic change

short duration holocene lakes in the mojave river drainage basin southern california stratigraphic sedimentologic and pedologic studies of beach ridge and lacustrine deposits indicate that up to five times during the holocene shallow lakes covered silver lake playa in southeastern california for periods of years to decades the two youngest lacustrine events at about 390 90 yr b p and 3620 70 yr b p coincide with the early and late neoglacial episodes of north america increasing evidence in recent years from other nonglaciated areas leads us to conclude that the effects of these climatic episodes were much more widespread than previously thought the climate during these episodes was characterized by an increased frequency of winter storms in the southwestern united states causing wetter conditions that affected diverse hyperarid environments in the mojave desert and adjacent regions we propose that this wide areal coverage was caused by large scale winter atmospheric circulation patterns which are probably related to changes in sea surface temperatures and oceanic circulation in the eastern north pacific ocean

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

exploring the frequency size relationships of pipe collapses in different morphoclimatic regions abstract piping is an important land degradation process that occurs in almost all climatic zones this study analyses for the first time the frequency size distribution of different types of pipe collapses pcs sinkholes and compound depressions related to the coalescence of sinkholes compound sinkholes and elongated blind gullies exploring the frequency size relationships of pcs provides critical morphometric information about this hazardous erosion and ground stability process as well as its impact on hillslope denudation hillslope channel coupling and landscape development the analysis has been performed with field based inventories of pcs from five catchments located in two different morphoclimatic environments one in the semi arid ebro depression ne spain valpalmas catchment and four in the humid bieszczady mts se poland in total 724 pcs were mapped among which 335 pcs in valpalmas and 389 pcs in the bieszczady mts the morphometric analyses were based on the major axis the maximum length or width and area of the pcs despite differences between study areas from ne spain and se poland related to climate conditions rainfall regime soil water storage capacity spatial pattern of pipe networks vegetation cover and land use empirical cumulative frequency curves of pcs show similar patterns in all study sites indicating similar overall effects of piping erosion the size distribution of the inventoried pcs can be modelled satisfactorily with logarithmic functions with high goodness of fit values r2 0 93 for each type of pc and the combined set of pcs sinkholes and compound sinkholes blind gullies mapped in each area and in the five catchments together the pcs mapped in valpalmas are displaced towards larger dimensions attributable to local factors the applicability and limitations of frequency size relationships of pcs for geomorphological studies and hazard assessment are discussed

paleohydrologic bounds and extreme flood frequency of the upper arkansas river colorado usa article i nfo article history the upper arkansas river basin has experienced notable large floods including the event of 2 6 june 1921 that devastated the city of pueblo colorado we investigated flood and paleoflood hydrology at strategic sites to determine the frequency and geographic extent of extreme floods within the basin for a dam safety application streamgage historical and paleoflood data were utilized to develop frequency curves at sites near salida cotopaxi parkdale and pueblo soil stratigraphic descriptions radiocarbon dating and hydraulic modeling were used to estimate paleoflood nonexceedance bounds at the four sites which ranged from 400 to 2200 ybp for late holocene surfaces to late pleistocene surfaces near cotopaxi peak flow data are from lower magnitude snowmelt runoff in may and june in the upper basin and from high magnitude rainfall runoff from june to august in the lower basin flood frequency curves reflect this transition near parkdale from snowmelt to extreme rainfall runoff for similar return periods paleoflood peak discharges increase from about 480 m 3 s upstream at loma linda to about 4250 m 3 s downstream near pueblo this increase is attributed to the larger rainfall component derived from lower elevations between loma linda and pueblo return periods for design floods at pueblo dam exceeded 10 000 years based on paleoflood frequency curve extrapolations

paleohydrology of extraordinary floods along the swakop river at the margin of the namib desert and their paleoclimate implications abstract the swakop river is a major ephemeral river drainage basin area about 30 000 km 2 crossing the western namib desert its hydrology and limited water resources depend on storms and floods therefore the hydrology and flow regime in the swakop river basin determines the availability of water for human use in this study we present a millennia long record of extreme floods using paleoflood hydrological methods and optically stimulated luminescence osl ages the record includes 44 large floods ranging in date from the late pleistocene to the present the oldest six to eight floods are dated from the late pleistocene to the mid holocene between 14 900 1700 and 5100 620 years ago with calculated peak discharges of 550 1280 m 3 s 1 eighteen floods eleven of which were between 1000 and 1600 m 3 s 1 occurred between 740 90 and 190 10 years ago additional 17 later floods occurred between about ad 1850 and 1963 with peak discharges between 100 and 1000 m 3 s 1 the historical record which partly parallels the latter period recorded 17 large floods during the period 1893 1963 flood frequency analysis ffa of the combined systematically gaged record 1963 2003 and the paleoflood record since ad 1270 740 90 years the most complete record was applied using the maximum likelihood method a two component extreme value distribution tcev estimates the 1 annual exceedance probability magnitude using only the systematic gaged record at 520 m 3 s 1 the combined paleoflood historical and gage records resulted in a much larger magnitudes for the 1 annual exceedance probability flood magnitude of 1320 1350 m 3 s 1 the 0 1 annual exceedance probability magnitude is estimated at 770 m 3 s 1 and 2100 2150 m 3 s 1 respectively the hydroclimatic interpretation of this paleoflood record is complex due to the discontinuity of the record during the late holocene our flood data show three intervals differing in their flood regime 1 1280 80 to 740 90 years bp with one extraordinary flood 200 m 3 s 1 about every 180 years 2 740 90 to 200 45 14 c years bp with one large flood per 80 years and 3 200 45 14 c years bp to ad1963 with one large flood per 7 years interval 2 represents large floods probably related to the transition from a drier climate to the colder and probably wetter climate of the little ice age lia the third period relates to the end of the lia and to a wetter period of the 19th and early 20th centuries in which more rainfall in the kalahari and namib deserts and many historical floods were documented the presence of three distinct calcretes rich in calcified rhizoliths at one of the sites two of which were dated by osl to 13 2 1 9 ka and 8 8 1 0 ka indicates at least locally higher moisture availability than in the current semiarid climate the presence of denser vegetation can be associated with increased groundwater seepage and wetter climatic conditions

stratigraphic evidence for the ross orogeny in the ellsworth mountains west antarctica implication for the evolution of the paleo pacific margin of gondwana early paleozoic crustal deformation has been recognized along the paleo pacific margin of gondwana including southern africa saldanian tectonism and the transantarctic mountains of east antarctica ross orogeny previously no stratigraphic evidence for the ross orogeny had been recognized within the ellsworth mountains of west antarctica believed to have been contiguous with the transantarctic mountains prior to the mesozoic breakup of gondwana a disconformity between middle to upper cambrian heritage group and upper cambrian to devonian crashsite group strata indicates that the ross orogeny did affect the ellsworth mountains providing additional evidence that these rocks were once part of east antarctica fluvial conglomerates overlying platform carbonates of the upper heritage group were derived in part from plutonic volcanic and metamorphic terranes in east antarctica elsewhere in the ellsworth mountains the disconformity is expressed by an abrupt change from shallow carbonate platform deposits to siliciclastic shelf deposits similarities in lower paleozoic stratigraphy between the ellsworth mountains parts of the pensacola mountains east antarctica and eastern south africa imply that these regions were inboard of the zone of deformation that affected the proto pacific margin of gondwana during the ross orogeny and saldanian tectonism

soil catenas on pinedale and bull lake moraines willow lake wind river mountains wyoming abstract soils in coarse grained tills on pinedale about 20 000 years old and bull lake about 140 000 years old moraines show significant variaton with slope position and age soils on the pinedale moraine are mostly non calcareous typic cryoborolls with a bw c profiles that thicken considerably downslope these soils are weakly developed due to their youth and to the unstable steep up to 24 highly convexo concave slopes soils on the bull lake moraine are mostly argic cryoborolls with a bt c profiles these soils are more strongly developed than soils at similar positions on the pinedale moraine because the bull lake moraine is older and has less steep up to 16 more gently curved slopes the soils on the bull lake moraine contain more clay a higher proportion of pedogenic clay more weathered stones and more free sesquioxides erosion and dry conditions at the convex summit and shoulder sites on the bull lake moraine have resulted in thin soils with minimal argillic horizons these soils are only slightly more strongly developed than soils at analogous sites on the much younger pinedale moraine in contrast at the concave sites in downslope positions the soils on the bull lake moraine are much more strongly developed than analogous soils on the pinedale moraine slow deposition of weathered material probably transported by creep has acted concurrently with pedogenesis to form soils with thick homogeneous argillic horizons the relationship between hillslope curvature and soil properties on both moraines is shown by significant correlations between soil properties and the second derivative of the hillslope profile this relationship is probably due primarily to the interaction of soil formation and soil creep

the gondwana plate margin in the weddell sea sector zircon geochronology of upper paleozoic mainly permian strata from the ellsworth mountains and eastern ellsworth land antarctica abstract zircon geochronology has been applied to upper paleozoic mainly permian strata from the ellsworth mountains and from enigmatic outcrops in eastern ellsworth land to aid in constraining their locations in the weddell sea sector of the gondwana plate margin detrital zircons from two polarstar formation ellsworth mountains sandstones yielded maximum depositional ages of 270 ma and 260 ma detrital zircons from permian beds at erehwon nunatak and beds of uncertain age at fitzgerald bluffs both in eastern ellsworth land gave maximum depositional ages of 264 ma and 525 ma respectively two polarstar formation tuffs gave ages of 258 0 2 1 ma and 262 6 2 2 ma the polarstar formation probably spans the entire permian the quartzite at fitzgerald bluffs is comparable in composition and detrital zircon signature to devonian sandstones in both the ellsworth and transantarctic mountains evaluation of the polarstar formation with respect to permian strata in the southern karoo and falkland islands suggests deposition in a separate and distinct basin which was related to that in the transantarctic mountains a separate depositional basin forms an additional constraint on the location of the ellsworth whitmore block adjacent to the coats land pensacola mountains region the eastern ellsworth land outcrops are inferred to document a small continental block located proximal to the ellsworth whitmore mountains block during gondwana time

analyses of the magnitude and frequency of a 400 year flood record in the fish river basin namibia abstract ephemeral rivers in dryland regions exhibit a high interannual variability of streamflow regime mainly dominated by floods in these environments floods are a water resource and a potential hazard with important socioeconomic implications the fish river 86 600 km2 is the largest ephemeral stream in namibia and recently also the focus of new development plans including construction of the largest dam in namibia the hydrological analysis to support decisions implies large uncertainties owing to spatial limited and short hydrological records since 1962 here we investigate the current and past patterns of extreme floods combining instrumental historical and palaeoflood records palaeoflood studies were performed at two reaches with preserved sedimentary evidence at the upper sector vogelkranz upstream of hardap dam 13 catchment area and in the lower part of the river in the fish river canyon national park 70 catchment area in the hardap reach the palaeoflood record identified at least eight large floods during the last 350 years with the largest flood reaching a minimum discharge of 4800 m3 s 1 150 year return period in the fish river canyon reach the sedimentary record shows at least 12 large floods over the last 400 years the largest with an estimated minimum discharge of 8700 m3 s 1 the elevation of alluvial surfaces without flood evidence provided an upper bound for flood stages associated with discharges of 6400 m3 s 1 and 16 140 m3 s 1 for the upper and mid lower fish river respectively in the upper reach the flood frequency analysis ffa combining systematic and palaeoflood data provided lower discharges 25 of the flood quantiles than the ones using only systematic data sets in the fish river canyon reach incorporation of the palaeoflood data into the ffa results in slightly higher values in the magnitude of the higher flood quantiles 4 7 the ffa analysis using an upper limited lognormal distribution function ln4 fitted with palaeoflood data shows a good performance with a slow behaviour approaching the upper limit our flood frequency results suggest that the hardap dam should increase the spillway capacity and safety check flood of the original design in order to satisfy the dam safety criteria however the projected reevaluation figures calculated from conventional hydrological methods results in an overestimation of the safety floods according to our estimations

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

reply to r leb hooke s discussion of use of multiparameter relative age methods for age estimation and correlation of alluvial fan surfaces on a desert piedmont eastern mojave desert california

cambrian palaeomagnetic data confirm a natal embayment location for the ellsworth whitmore mountains antarctica in gondwana reconstructions summary the ellsworth whitmore mountains ewm are one of five terranes that form west antarctica constraining the positions of these terranes in pre break up gondwana is crucial to understanding the history of the palaeo pacific gondwana margin we report the results of a detailed palaeomagnetic investigation of the ewm which comprises some 150 sites in six formations ranging in age from cambrian to permian five of the studied units yield only viscous remnant magnetizations of recent age or unstable natural remanent magnetizations the remaining unit the mid late cambrian frazier ridge formation yielded stable magnetizations at 16 of 35 sites this component passes a fold test at the 95 per cent confidence level indicating that it pre dates permian deformation and we argue that it is of primary origin the resulting palaeopole 9 n 293 e a95 5 1 is in good agreement with two previously published palaeopoles from similarly aged rocks in the ewm collectively these data indicate that the ewm were located in the natal embayment prior to gondwana break up and underwent 90 of anticlockwise rotation during break up all three studies however yield inclinations

detrital zircon provenance of upper cambrian permian strata and tectonic evolution of the ellsworth mountains west antarctica abstract detrital zircons from the upper cambrian devonian sandstones crashsite group n 485 and carboniferous tillite whiteout conglomerate n 81 of the ellsworth mountains antarctica record a steady supply of neoproterozoic pan african orogeny 550 600 ma grenville 1000 ma and neoarchean 3000 3500 ma zircons into the northern marginal basin of gondwana the overlying permian glossopteris bearing polarstar formation shales n 85 have the same zircon provenance as underlying units but also include a dominance of depositional age 263 ma euhedral zircons which are interpreted to be of local volcanic arc origin modeling of detrital zircon provenance suggests that source areas were present in pan african and laurentian crust throughout the paleozoic we also report calcite twinning strain results 12 strain analyses n 398 twins for the cambrian minaret fm in the heritage range which is predominantly a layer parallel shortening strain in the direction wsw ene of permian gondwanide orogen thrust transport there is a secondary sub vertical twinning strain overprint the initiation of localized lower middle cambrian rifting heritage group deposition in grenville aged crust as gondwana amalgamated and the subsequent jurassic counterclockwise rotation of the ellsworth whitmore terrane out of the permian gondwanide belt into central antarctica each remain tectonic curiosities

late quaternary history of the chemehuevi mountain piedmont mojave desert deciphered using 10be and 26al we used the cosmogenic nuclides 10 be and 26 al as cosmic ray dosim eters to track sediment movement across the incised chemehuevi mountain piedmont surface the piedmont extends 12 km from highland source basins to an ephemeral wash at the toe of the piedmont nuclide activity in sediment from steep source basins and from the bedrock pediment allows us to estimate rates of sediment generation and thus the rate at which sediment is supplied to the piedmont from weathering rock analysis of amalgamated sediment samples collected along 4 km long transects spaced at 1 km intervals from the mountain front provide context for understanding nuclide activity in sediment samples collected from two soil pits and demonstrate that sediment steadily moves down the channel network samples from the two soil pits allow for estimates of sediment deposition rates and thus further illuminate piedmont history model results suggest that the chemehuevi mountains are eroding about 40 mm ky 1 whereas the mountain proximal bedrock pediment and the interpiedmont saw tooth range are eroding more slowly 10 to 21 mm ky 1 and 9 5 mm ky 1 respectively cosmogenic nuclide profiles in two soil pits suggest a complex history of deposition at rates between 19 to 39 mm ky 1 and stability over the past 60 ky a change in process from sediment deposition to sediment transport occurred distally on the piedmont approximately 8 ky ago while the mid piedmont piedmont surface has been stable since the mid holocene the incised chemehuevi mountain piedmont is changing at rates similar to planar and uniformly active piedmonts such as those adjacent to the iron and granite mountains all three piedmonts have average sediment grain velocities of decimeters per year long term source basin erosion rates between 35 to 40 mm ky depositional hiatuses around the pleistocene holocene climatic transition from moister to drier conditions and pleistocene deposition rates of 18 to 39 mm ky such similarity in piedmont behavior despite clear differences in morphology and appearance might suggest large scale geologic and climatic controls on the generation transport and deposition of sediment in the mojave desert

paleoflood evidence for a natural upper bound to flood magnitudes in the colorado river basin the existence of an upper limit to the magnitude of floods in a region is a long standing and controversial hypothesis in flood hydrology regional envelope curves encompassing maximum flood magnitudes stabilize with progressive increases in the areal coverage and period of observation wolman and costa 1984 however the short lengths of conventional gaging records limit substantial advances in testing whether this stabilization is evidence of an upper limit in the colorado river basin there are 32 120 station years of gage data but the average period at a gaging station is only 20 years with most stations having less than 70 years of observation paleoflood magnitudes derived from sediments of large prehistoric floods from 25 sites on rivers in arizona and utah provide additional data to extend the records of the largest floods the paleoflood data identify the maximum flood discharges that have occurred on individual rivers over the last several hundred to several thousand years even with this increase in the observational period the largest paleoflood discharges do not exceed the upper bound of maximum peak discharges delineated by the envelope curve derived from the available gaged and historical records this result accords with the hypothesis of an upper physical limit for flood magnitudes and suggests that for the colorado river basin the upper limit can be approximated by existing systematic and historical data for large floods similar relationships also hold when paleofloods and gaged records are presented for the subregion of southern arizona

development of kinematic partitioning within a pure shear dominated dextral transpression zone the southern ellsworth mountains antarctica the heritage range of the southern ellsworth mountains west antarctica is composed of cambrian to permian sedimentary and volcanic rocks which were deformed during the permo triassic gondwanian orogeny the structural grain of the heritage range exhibits a previously unrecognized 18 swing from 333 153 in the north to 315 135 in the south a change in structural and kinematic style accompanies this strike swing with a structure consistent with near orthogonal shortening present in the south and a structural style consistent with dextral transpression within the central and northern heritage range kinematic partitioning is present within the central heritage range where strikeparallel contemporaneous domains of dextral and reverse shear have developed simultaneously with the regional cleavage comparison of the structure and kinematics within both structural domains suggests that the central and northern heritage range experienced pure shear dominated dextral transpression with an approximate angle of relative shortening of 65 70 results derived by integrating field data into a published kinematic partitioning model suggest relatively efficient kinematic partitioning has occurred however such efficient partitioning cannot be explained by strain partitioning models based purely on plate boundary conditions therefore it is proposed that pre existing weak structures were present within the unexposed basement facilitating the apparent high percentage of kinematic partitioning

paleoflood hydrology and extraordinary flood events paleoflood hydrology is the study of past or ancient flood events the most accurate technique involves the analysis of slackwater deposits and paleostage indicators swd psi slackwater deposits are sand and silt emplaced from suspension in exceptionally deep high velocity floods that characterize narrow deep canyons in resistant geologic materials these and other paleostage indicators are used to establish hydraulic grade lines for the generating flow events favorable sites for slackwater deposition include channel margin areas where stresses and velocities are reduced below critical values necessary to maintain fine grained bedload material sand and silt in suspension computerized procedures for hydraulic flow modeling are used to tie the elevations of the highest slackwater deposits to surveyed river cross sections the flood discharges calculated by this method can be calibrated through the study of modern floods on gaged rivers correlation of multiple swd psi sites along a river reach is used to identify the maximum paleostage achieved by a given flood advances in the dating of flood deposits permit estimates of flood frequency to be made extending over a data base of thousands of years the major geochronologic tool is radiocarbon dating of various kinds of organic matter intercalated with the slackwater deposits an important development is the use of the tandem accelerator mass spectrometer for direct measurement of 14c tiny blebs of charcoal seeds and other organics can be analyzed in order to date ancient flood deposits of hydrologic significance since swd psi studies yield very accurate determinations of paleoflood ages and magnitudes there is a pressing need for new statistical procedures that make optimum use of the information content in paleoflood records for flood frequency analysis nevertheless swd psi paleoflood hydrology has moved beyond the research phase its use should be encouraged in evaluating past experience of extraordinary floods at appropriate hazardous sites

a quantitative comparison of soil development in four climatic regimes abstract a new quantitative soil development index based on field data has been applied to chronosequences formed under different climatic regimes the four soil chronosequences developed primarily on sandy deposits have some numeric age control and are located in xeric inland merced calif xeric coastal ventura calif aridic las cruces n mex and udic susquehanna valley pa soil moisture regimes to quantify field properties points are assigned for developmental increases in soil properties in comparison to the parent material currently ten soil field properties are quantified and normalized for each horizon in a given chronosequence including two new properties for carbonate rich soils in addition to the eight properties previously defined when individual properties or the combined indexes are plotted as a function of numeric age rates of soil development can be compared in different climates the results demonstrate that 1 the soil development index can be applied to very different soil types 2 many field properties develop systematically in different climatic regimes 3 certain properties appear to have similar rates of development in different climates and 4 the profile index that combines different field properties increases significantly with age and appears to develop at similar rates in different climates the soil development index can serve as a preliminary guide to soil age where other age control is lacking and can be used to correlate deposits of different geographical and climatic regions

a record of rapid holocene climate change preserved in hyrax middens from southwestern africa the discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central namib desert africa is providing unprecedented insight into the region s environmental history high resolution stable carbon and nitrogen isotope records spanning 0 11 700 cal calibrated yr b p indicate phases of relatively humid conditions from 8700 7500 6900 6700 5600 4900 and 4200 3500 cal yr b p with a period of marked aridity occurring from 3500 until ca 300 cal yr b p transitions between these phases appear to have occurred very rapidly often within 200 years of particular importance are 1 the observed relationship between regional aridifi cation and the decline in northern hemisphere insolation across the holocene and 2 the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing together these elements call for a fundamental reexamination of the role of orbital forcing on tropical african systems and a reconsideration of what factors drive climate change in the region the quality and resolution of these data far surpass any other evidence available from the region and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern africa

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

the last millennium largest floods in the hyperarid kuiseb river basin namib desert the largest kuiseb river floods initiate at the basin s semi arid headwater downstream along the hyperarid namib desert these floodwaters are feeding shallow alluvial aquifers the only available water for human activity and for the natural ecology here we characterize the largest floods and their changing frequency and magnitudes using palaeohydrological methods along 120 km of the rivers canyon 35 palaeoflood deposit sites were identified at five of these sites we conducted stratigraphic and geochronological analyses and flood discharge estimations the upper bound of the largest flood over the late holocene is 1475 m 3 s 1 over the last 1300 years more than ten floods have exceeded 1250 m 3 s 1 an additional 33 floods exceeded 400 m 3 s 1 the last millennium was characterized by one large flood every 30 40 years during the periods 1250 1335 1355 1565 and 1715 ad to the present a slight increase in flood frequency not magnitude occurred during 1565 1715 ad one large flood in 20 years and during two short episodes 1185 1205 and 1335 1355 ad seven and four floods in 20 years respectively these episodes of increased flood frequency are associated with other proxy records of higher water availability in the namib copyright 2013 john wiley sons ltd

glacial sequence near mccall idaho weathering rinds soil development morphology and other relative age criteria abstract the sequence of glacial deposits near mccall idaho previously assigned to the pinedale and bull lake glaciations contains deposits of four different ages these ages are defined by multiple relative age criteria including weathering rinds soil development surface rock weathering morainal morphology and loess stratigraphy the thickness of weathering rinds on basaltic clasts is statistically representative and reproducible and can be used to estimate numerical ages following in order of decreasing relation to age are soil development surface rock weathering and moraine morphology the glacial deposits near mccall appear to correspond to times of high worldwide ice volume indicated by the marine oxygen isotope record pilgrim cove and mccall deposits both assigned to the pinedale glaciation are late wisconsin in age perhaps 14 000 and 20 000 years respectively they represent a rare case in which deposits of pinedale age can be separated by relative age data timber ridge deposits assigned to the bull lake glaciation have subdued but well preserved morainal morphology relative age data indicate that they are pre wisconsin in age probably about 140 000 150 000 years old although we cannot exclude an older age williams creek deposits are clearly distinct from and intermediate in age between mccall and timber ridge deposits weathering rinds and the inferred ages of the other deposits suggest an early wisconsin age for williams creek deposits

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

morphological and chemical characteristics of soil catenas on pinedale and bull lake moraine slopes in the salmon river mountains idaho abstract morphological and chemical properties of soils developed on moraines of granitic composition and forested with lodgepole pine in bear valley idaho change significantly with age and slope position soil development on pinedale and bull lake moraine slopes of similar curvature and steepness was assessed at the summits shoulders backslopes and footslopes of both catenas and at the toeslope of the bull lake catena many soil properties show trends in development with both age and slope position these properties include clay content clay film development color plagioclase weathering and dithionite citrate extractable iron fed the degree of development of all these properties is greater on the bull lake catena relative to that on the pinedale catena this trend reflects increased soil development with age on both catenas development of soil properties is commonly highest at the footslope or toeslope sites and minimum at the backslope site downslope changes are attributed to both colluviation and pedogenic processes including sorting of sediments during downslope transport greater accumulation of eolian materials transported to downslope sites by surface processes and greater in situ weathering of mineral grains at the footslope and toeslope sites

discussion of use of multiparameter relative age methods for age estimation and correlation of alluvial fan surfaces on a desert piedmont eastern mojave desert california

sedimentology of high stage flood deposits of the tagus river central spain abstract this paper details the sedimentology of high stage flood deposits with the definition of sedimentary environments and their characteristic sequences along two bedrock reaches of the tagus river central spain high stage flood deposits accumulated in bedrock canyons include slackwater flood deposits swd and other types of deposits located at flow separation zones and associated with slow moving flow 1 these flood deposits are common indirect indicators of flood stages used in palaeoflood studies for estimating the discharges associated with quaternary floods depositional environments of flood deposits include 1 channel widening 2 canyon expansion 3 bedrock obstacles and 4 backflooded areas along tributary streams these flood deposits can be found associated with other non fluvial environments namely aeolian reworked and slope washflow facies channel widening due to flood stage variations comprises internal and external zones of the channel margins and their characteristic sequences contain similar facies to those of alluvial floodplains canyon expansion environments favour vertical accretion of slackwater units and the development of flood deposit benches which contain four sequences related to bench elevation and distance from the channel s main thread of flow at the lee side of bedrock obstacles characteristic sedimentary sequences are dominated by reverse flow structures e g climbing ripples migrating upstream due to eddies with a high sand concentration flood deposits located within tributary mouths contain typical sequences of reworked floodplain deposits backflooding of tributaries during flood stages produces deposition from suspension of sand silt and clay within three sequences characterised by non structure or parallel lamination and intense bioturbation a better understanding of the flood deposit sequences may contribute to the characterisation of flood magnitudes and flood hydraulics and can also be applied to some ancient depositional environments

tectonic history of the ellsworth mountains west antarctica reconciling a gondwana enigma early paleozoic orogenesis has been recognized along the southern african saldanian orogeny and east antarctic ross orogeny sectors of the gondwana paleo pacific margin however the absence of a contemporaneous orogenic event in the ellsworth mountains of west antarctica once a contiguous part of this margin has resulted in their geology being considered enigmatic in this contribution widespread detailed structural studies from all stratigraphic levels of the ellsworth mountains allow their tectonic evolution to be reassessed geochemical stratigraphic and structural data indicate that the middle to upper cambrian heritage group developed in a continental rift basin multiple observations of the crucial end cambrian contact between this rift sequence and the overlying crashsite group reveal the contact to be regionally conformable there are localized outcrop scale unconformities furthermore structural continuity can be demonstrated across this key boundary thus precluding the possibility of an end cambrian orogenic event the entire stratigraphic succession was affected by two post permian phases of deformation d1 structures are locally developed and superimposed by the main dextral transpressive d2 permian triassic gondwanian deformation event d2 is succeeded by an episode of extension orthogonal to orogenic strike recent geochronological data on the early paleozoic evolution of the cape fold belt reveal a strong tectonostratigraphic correlation with the ellsworth mountains indicating that this sector of the gondwana paleo pacific margin was affected by middle to late cambrian rifting a new tectonic model is proposed for the southwestern paleo pacific margin of gondwana that accounts for the presence of rifting along a margin otherwise dominated by active subduction

suggested terminology for quaternary dating methods abstract classification of quaternary dating methods should be based on the level of quantitative information and the degree of confidence contained in the age estimates produced by the dating methods we recommend the use of the terms numerical age calibrated age relative age and correlated age to describe these levels we also classify dating methods by type into sideral isotopic radiogenic chemical and biological geomorphic and correlation methods the use of absolute is inappropriate for most dating methods and should be replaced by numerical the use of date should be minimized in favor of age or age estimate we recommend use of the abbreviations ka and ma for most ages calender dates can be used where appropriate and yr b p can be used for radiocarbon ages

a new late middle cambrian paleomagnetic pole for the ellsworth mountains antarctica abstract a paleomagnetic study of the late middle to possibly early late cambrian liberty hills formation in the ellsworth mountains antarctica reveals a stable magnetization with positive fold and reversal tests the paleopole is based on 16 sites from volcanic and sedimentary rocks and lies at lat 7 3 n and long 326 3 e documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm a 95 6 0 circ end document the new paleomagnetic data support the view that the ellsworth mountains are part of a microplate the ellswo

the influence of bedrock weathering on the response of drainage basins and associated alluvial fans to holocene climates san bernardino mountains california usa the primary factors that control alluvial fan evolution still remain in question particularly for the holocene holocene centennial and millennial scale climate fluctuations are relatively subtle and more frequent than those of glacial interglacial transitions therefore intrinsic factors such as rock type or basin size are hypothesized to moderate significantly the influence of holocene climate and climate change on alluvial fan processes here we examine variability in styles and rates of alluvial fan aggradation along a single mountain front that is characterized by basins of varying size and rock type carbonate versus granite basin rock type is more closely correlated to variability in the episodic nature and magnitude of alluvial fan aggradation than is basin area bedrock physical and chemical weathering properties control sediment delivery to the piedmont and thus influence alluvial fan aggradation we suggest that the particle size of grus produced by weathering of granitic rocks fosters sedi

bayesian flood frequency analysis with paleohydrologic bound data 1 it is valuable to construct likelihood functions that rigorously incorporate measurement errors and annual peak discharge historical and paleohydrologic bound information in bayesian flood frequency analyses estimates of primary posterior modes for common three parameter frequency distributions are constructed using simulated annealing and the simplex method parameter and flood frequency probability intervals are calculated directly by systematic parameter space integration bayesian flood frequency analyses with annual peak discharge historical and paleohydrologic bound data for the santa ynez river california and the big lost river idaho demonstrate that paleohydrologic bounds reduce quantile biases by placing large observed peak discharges in their proper long term contexts and substantially narrow peak discharge confidence intervals when estimating floods with low exceedance probabilities

paleofloods and a dam failure flood on the virgin river utah and arizona abstract flood deposits on the virgin river in southern utah and northern arizona preserve a record of the magnitude and frequency of the largest natural floods that have occurred on the river since ad 900 in the virgin river gorge several of the natural paleoflood discharges were comparable with or even greater than the flood from a catastrophic dam failure in 1989 that produced an estimated peak discharge of 1730 m3 s 1 in this reach of the virgin river to estimate the paleoflood discharges the heights of slackwater flood deposits in the lower bedrock gorge of the virgin river were compared with water surface elevations calculated with the hec 2 step backwater hydraulic model the timing of the paleofloods was determined by the ages of layers rich in human artifacts that are interbedded with the flood deposits the estimates of both the 1989 flood and the paleofloods were carried out in the virgin river gorge about 60 km downstream of the dam break site no natural floods of this magnitude have occurred within the relatively short period of the gaged record this study illustrates how incorporating rare extreme events from the long term paleoflood record improves the database for flood frequency analysis the 1989 flood serves as an analog to the effects of rare natural floods with similar magnitudes along the lower virgin river

quantifying sediment transport on desert piedmonts using 10be and 26al in situ produced 10 be and 26 al measured in 40 sediment samples collected from the iron and granite mountain piedmonts eastern mojave desert provide a unique view of piedmont modification processes and process rates over the 10 3 to 10 5 year time scale cosmogenic nuclide based models suggest that the iron and granite mountains generate 0 11 0 13 and 0 082 0 097 m 3 of sediment per year per meter of rangefront respectively the sediment moves down the piedmont in an active transport layer atl which is 20 to 30 cm thick based on visual observations measurements of depth to a buried b horizon cosmogenic nuclide data and maximum ephemeral channel depths sediment in this layer is well mixed vertically and horizontally on the 10 2 year time scale indicating that the small ephemeral channels which dominate the piedmont surface migrate quickly interpretive models of increasing nuclide activities at depth in two pits suggest steady sediment deposition on the piedmont at rates between 17 21 and 38 45 m ma 1 until the late pleistocene epoch when a discontinuity to markedly lower nuclide activities in the isotopically well mixed active transport layer suggests that deposition stopped a significant change in piedmont behavior nuclide activities in 10 amalgamated surface samples each collected along a different 4 km long transect increase steadily away from the mountain front thus we infer that sediment is uniformly dosed by cosmic rays as it is transported down the iron and granite mountain piedmonts interpretive models suggest that long term average sediment speeds down the iron and granite mountain piedmonts are a few decimeters to a meter per year d 2002 published by elsevier science b v

gondwanian age dextral transpression and spatial kinematic partitioning within the heritage range ellsworth mountains west antarctica the ellsworth mountains west antarctica consist of two mountain ranges the sentinel and heritage ranges the more southerly heritage range is composed of a lower paleozoic sedimentary and volcanic rock sequence deformed during a single major deformation event in the early mesozoic this gondwanian orogeny possibly resulted from andean style convergence along the southern margin of gondwana prior to break up of the super continent and the subsequent translation of the ellsworth mountains from a position close to the natal embayment of southern africa to that of the present day rocks of the heritage range are intensely folded with close to tight upright to inclined folds plunging gently about a horizontal axis trending nnw sse locally folds plunge moderately to subvertical toward the nnw possessing asymmetries consistent with a dextral sense of shear cleavage is generally axial planar displaying downdip and strike parallel stretching lineations that are frequently associated with domains of reverse and dextral shear striking parallel to the regional structural grain the spatial and temporal relationship of fractures developed within these domains as a result of noncoaxial shear in addition to the progressive incremental strain histories derived from mineral fibres in strain shadows indicate the contemporaneous nature of these shear domains strain analysis of deformed tuffaceous diamictites and oncolithic limestones reveal k values 1 mean 0 59 throughout the heritage range the coexistence of strike parallel dextral oblique and reverse shear domains abrupt reorientation of progressive strain axes steep cleavage dips and k values 1 are all consistent with a dextral transpressive deformation regime previously unrecognized in the ellsworth mountains a model of highly oblique pure shear dominated transpression associated with efficient spatial partitioning of the strike slip component of shear is proposed to describe the structural relationships observed

are the benches at mormon point death valley california usa scarps or strandlines the benches and risers at mormon point death valley usa have long been interpreted as strandlines cut by still stands of pluvial lakes correlative with oxygen isotope stage ois 5e 6 120 000 186 000 yr b p and ois 2 10 000 35 000 yr b p this study presents geologic mapping and geomorphic analyses gilbert s criteria longitudinal profiles which indicate that only the highest bench at mormon point 90 m above mean sea level msl is a lake strandline the other prominent benches on the north descending slope immediately below this strandline are interpreted as fault scarps offsetting a lacustrine abrasion platform the faults offsetting the abrasion platform most likely join downward into and slip sympathetically with the mormon point turtleback fault implying late quaternary slip on this low angle normal fault our geomorphic reinterpretation implies that the ois 5e 6 lake receded rapidly enough not to cut strandlines and was 90 m deep consistent with independent core studies of the salt pan no evidence of ois 2 lake strandlines was found at mormon point which indicates that the maximum elevation of the ois 2 lake surface was 30 m msl thus as measured by pluvial lake depth the ois 2 effective precipitation was significantly less than during ois 5e 6 a finding that is more consistent with other studies in the region the changed geomorphic context indicates that previous surface exposure dates on fault scarps and benches at mormon point are uninterpretable with respect to lake history

use of multiparameter relative age methods for age estimation and correlation of alluvial fan surfaces on a desert piedmont eastern mojave desert california numerical and calibrated age determinations of the late quaternary alluvial fan deposits of the soda mountains piedmont in the mojave desert provide an opportunity to study the utility of the multiparameter relative age ra method for distinguishing and mapping geomorphic surfaces on a desert piedmont most ra parameters could not discriminate between deposits of holocene age although pavements have formed over locally significant parts of surfaces as young as middle holocene several parameters including lithologic composition particle size soil development and varnish cover permit distinguishing between holocene surfaces and late pleistocene surfaces statistically significant differences in initial particle size and lithology of the deposits inferred to be the result of complex interaction among hillslope alluvial fan and eolian processes and climatic change create conditions unfavorable for use of most ra techniques in contrast soil profile development and varnish cover data are successful in discrimination among deposits of holocene and pleistocene age this is attributed to the development of pedogenic features and varnish that are strongly dependent on dust influx and to the relatively minor dependence of these features on differences in the depositional character of the fan

differential effects of base level tectonic setting and climatic change on quaternary alluvial fans in the northern great basin nevada usa

manganese accumulation in rock varnish on a desert piedmont mojave desert california and application to evaluating varnish development abstract rock varnish coatings tend to become thicker darker and more continuous over time leading to the use of changes in overall varnish color and the percentage of clast surfaces covered by varnish as relative age indicators manganese is the most characteristic element of subaerial rock varnishes and the progressive development of varnish coats can be quantified by measuring the amount of mn accumulated on a given area of rock surface manganese oxides were dissolved off varnished clasts collected from alluvial surfaces on the soda mountains piedmont in the mojave desert california and the amount of mn was measured using inductively coupled plasma emission spectroscopy on the distal piedmont maximum varnish development increases from a mid to late holocene surface typically containing up to 0 15 mg cm2 of accumulated mn to an early to mid holocene surface with up to 0 21 mg cm2 however varnish is less developed on a nearby late pleistocene surface suggesting extensive abrasion of clasts on the pleistocene desert pavements or disturbance of the clasts varnish is better developed on the proximal piedmont typically containing up to 0 30 mg cm2 of mn although varnish from a pleistocene surface is again no better developed than from a nearby early to mid holocene surface these data demonstrate that rock varnish can show significant spatial variation in degree of development on geomorphic surfaces of similar age and imply that collecting varnish as old as a geomorphic surface may be difficult on surfaces as young as late pleistocene

the allochthony of the argentine precordillera ten years later 1993 2003 a new paleobiogeographic test of the microcontinental model abstract recent and new faunal data from the cambrian to silurian rocks of the precordillera famatina and northwest argentina basins are used to discriminate between different paleogeographic models and especially to establish to what extent they are compatible with a previous conclusion that the precordillera is a laurentian derived microcontinent there is no paleontological evidence to support a para autochthonous gondwanan origin of the precordillera the strong differences in the cambrian trilobite faunas and lithologic successions preclude a common origin of the precordillera terrane eastern antarctica and south africa recent discoveries of brachiopods and organisms of the phylum agmata strengthened laurentian affinities during the cambrian the latest cambrian early ordovician faunas that inhabited the autochthonous northwest argentina basin including the western puna volcaniclastic successions are mostly peri gondwanan the early ordovician brachiopods ostracods and trilobites display mixed laurentian baltic and avalonian biogeographical links supporting a drifting of the precordillera across the iapetus ocean increasing gondwanan elements during the llanvirn along with varied geological evidence indicate that the first stages of collision may have begun at that time involving a major change in the plate kinematics the distribution of facies and faunas basin development and timing of deformation are interpreted as resulting from a north to south diachronous closing of the remnant basin during the last phases of convergence and oblique collision of the precordillera terrane with the gondwana margin the high level of endemism of caradoc faunas may be a consequence of the rearrangement and partial isolation of sedimentary areas during the strike slip movement of the colliding precordillera plate with respect to the gondwana margin suggested relationships between facies distribution geographic barriers and faunal migrations before and during the collision are depicted in a series of schematic reconstructions at five time slices from late cambrian to silurian

paleohydrological indicators in playas and salt lakes with examples from canada australia and africa abstract the sedimentary records of playas and salt lakes provide some of the best evidence for hydrological change in a region these records are comprised of siliciclastic sediments and chemically precipitated minerals that typically vary temporally and spatially in some cases the interpretation is straightforward with mineralogical sequences related to changing brine concentrations and hydrology as well as to climate in other cases it is difficult to identify the controlling factors which include climate groundwater geological setting and basin morphology in addition diagenesis commonly affects the sedimentary record models of lake level fluctuations are given for basins in the canadian prairies and southeastern australia the lake manitoba model is based mainly on secondary changes associated with pedogenesis that alters the deeper water sediment during low water stages smaller canadian lakes in more arid regions display a larger variety of diagnostic paleohydrological indicators such as specific carbonate and salt mineralogy nature of bedding grain size and secondary alterations decreasing water levels in shallow lakes tend to show a progression from clastics to carbonates to salts and then back to clastics as groundwater levels fall below the lake floor similar parameters are used in australian lakes the hydrological model for the lake tyrrell playa in victoria whose present ionic composition is similar to seawater shows clastics being deposited when average lake levels are high followed by deposition of primary carbonates gypsum and halite once seasonal drying on the lake floor begins secondary gypsum grows within already deposited sediment and clay pelletization in the capillary fringe of surface sediment leads to basin deflation and the accumulation of adjacent eolian lunettes continued water level decline leads to pedogenesis subsequent lake level rises in all of these models may initiate sedimentation in any part of the hydrological cycle and a complete cycle in the sedimentary record appears to be uncommon

from dust to varnish geochemical constraints on rock varnish formation in the negev desert israel abstract chemical compositions of rock varnish from the negev desert of israel and local settled dust were used to constrain the mechanisms of varnish formation and patterns of mn enrichment and accumulation in the varnish rock varnish was sampled from coeval undisturbed prehistoric flint artifacts along a south north climatic transect 30 120 mm yr of rain our analyses indicate that mn ba and pb in the varnish are significantly enriched 100 in respect to the local settling dust and that mn content systematically fluctuates with depth in the varnish the varnish and settled dust data combined with basic thermodynamic and kinetic reasoning are used to constrain the following geochemical model of rock varnish formation dust accumulates in micro basins on exposed rock surfaces under ph 8 common negev value and during wetting by dew and rain mn in the dust is mobilized and leached to a depth of 5 m under the varnish surface where hollandite mn oxides precipitate and are adsorbed onto and between the porous clay minerals that comprise most of the varnish during its mobile phase mn oxide is negatively charged and adsorbs rare earth elements once the solution dries abrasion removes the upper weakly cemented dust sediment which contains mainly si al and fe which are not mobile at ph 8 ca is also removed in large quantities mn ba pb and the ree are deposited at a depth and thus protected from erosion reoccurrences of these processes result in a noticeable accumulation of these elements but not of si al or fe the alternating mn rich and mn poor laminas form as a result of a competition between the leaching rate of mn and the adhesion rate of the clay minerals when moisture is high low lamina with high low mn clay mineral ratio forms

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