soil mineralogy trends in california landscapes california s diverse environmental gradients serve as natural experiments for examining controls on soil mineral distribution in landscapes in this paper we use example soilscapes from throughout california to examine how lithology climate topography and duration of pedogenesis interact to produce distinctive weathering environments and characteristic suites of soil minerals seven soil geomorphic sequences were assembled from the literature to illustrate major soil mineralogical trends 1 granitic terrain of the peninsular ranges 2 granitic terrain of the central sierra nevada 3 andesitic terrain of the northern sierra nevada 4 fluvial terraces on the east side of the great valley 5 marine terraces of the central coast 6 ultramafic terrain of the klamath mountains and 7 an alluvial fan in the mojave desert results of this analysis show that kaolin is present in virtually all pedons irrespective of climate parent material age or topographic position kaolin does not form in ultramafic soils due to insufficient aluminum many secondary clay minerals reflect the state s strong climatic influence with palygorskite smectite and vermiculite in the dry hot environments hydroxy interlayered minerals gibbsite and short range ordered minerals in the cool moist environments in arid and semi arid regions the distribution of calcite gypsum and soluble salts is strongly related to patterns of eolian dust deposition and water infiltration and leaching

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

origin and significance of calcium carbonate in soils of southwestern patagonia abstract a soil chronosequence spanning the last 0 76 1 0 ma shows a progressive increase in calcium carbonates based on 1 thickness of the bk bck horizons 2 maximum carbonate stage 3 profile accumulation of pedogenic carbonates and 4 mass flux of ca from a geochemical mass balance we favor a dust origin of the carbonates because 1 the till parent materials contain low amounts of caco3 2 there is minimal evidence for weathering of ca bearing minerals in the soil 3 the amount of caco3 in the profile is far in excess of what could be released by weathering 4 dust collected from the study area is enriched in caco3 and 5 a source area for the carbonates was identified although there likely were changes in dust deposition rates during the quaternary our calculations suggest that the current deposition rate of 0 18 g caco3 m 2 yr 1 is comparable to the long term profile accumulation rate of 0 16 g caco3 m 2 yr 1 230th u disequilibrium ages of carbonate pendants are consistent with cosmogenic surface exposure ages indicating that this method has potential for dating other geomorphic surfaces in patagonia cryogenic processes have affected many of the pedons particularly during the last glacial maximum

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

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

simulating the 128 ka antarctic climate response to northern hemisphere ice sheet melting using the isotope enabled hadcm3 warmer than present antarctic and southern ocean temperatures during the last interglacial approximately 128 000 years ago have been attributed to changes in north south ocean heat transport causing opposing hemispheric temperature anomalies we investigate the magnitude of antarctic warming and antarctic ice core isotopic enrichment in response to northern hemisphere meltwater input during the early last interglacial a 1 600 year hadcm3 simulation driven by 0 25 sv of meltwater input reproduces 50 60 of the peak southern ocean summer sea surface temperature anomaly sea ice retreat and ice core isotope enrichment we also find a robust increase in the proportion of cold season precipitation during the last interglacial leading to lower isotopic values at the antarctic ice core sites these results suggest that a hadcm3 simulation including 0 25 sv for 3 000 4 000 years would reconcile the last interglacial observations providing a potential solution for the last interglacial missing heat problem

a soil chronosequence study of the reno valley italy insights into the relative role of climate versus anthropogenic forcing on hillslope processes during the mid holocene abstract relatively few soil chronosequences with good age control exist for late pleistocene and holocene deposits in the mediterranean region of europe yet surface soils and their young buried counterparts can provide meaningful information about the timing and processes of landscape response to external forcing such as climate or anthropogenic change here we present the results of a study that examines a well dated chronosequence of nineteen soil exposures in surficial deposits ranging in age from hundreds of years to hundreds of thousands of years located in the reno river valley near bologna italy the soil forming climate of the reno valley sits on a threshold between that which facilitates the accumulation of caco 3 and that which facilitates the translocation and formation of clay minerals and iron oxides once formed secondary iron oxides are relatively immobile in oxidizing conditions in the soil profile and therefore consistently record age trends with feo fed ratios decreasing predictably with soil age for all soils in the chronosequence the morphology of secondary carbonate accumulation and its depth of leaching also vary predictably with soil age but only for soils younger than about 12 000 years in these young soils horizons that contain secondary carbonate progress from relatively shallow stage i bk horizons in late holocene aged soils to deeper stage iii bk horizons in latest pleistocene aged soils in soils older than approximately 12 000 cal ybp however carbonate dissolution during wetter climates and the addition of colluvium and or dust to terrace surfaces become important factors in the preservation of carbonate in the profile and carbonate content is not predictable by age alone without significant depositional additions these older soils become decalcified pedogenic carbonate precipitated during drier climates is susceptible to dissolution during wetter periods as evidenced by discontinuous carbonate coatings on grains in some soils therefore overall measurable pedogenic carbonate content is spatially and temporally variable as a function of input of fresh carbonate and locally controlled soil moisture conditions particle size does not decrease predictably with soil age for reno valley soils and appears to be strongly influenced by parent material variability in younger soils and by dust additions in older soils our detailed examination of soil stratigraphy in the reno valley revealed evidence of significant aggradation of colluvium and tributary fans in the middle holocene between 6000 and 4000 ybp this aggradation pre dates bronze age agricultural expansion and appears to be instead attributable to the climate conditions of the middle holocene that have been documented elsewhere in italy for this time period this study demonstrates that late pleistocene and holocene surface soils in the mediterranean region of europe can effectively help elucidate rates and processes of landscape evolution

a new formation process for calcic pendants from pahranagat valley nevada usa and implication for dating quaternary landforms abstract it has been assumed that soil pendants form in a similar manner as stalactites in which innermost laminae are the oldest and outer laminae are the youngest this study presents a new interpretation for soil pendant development pahranagat valley nevada pendants contain features indicating continued precipitation through time at the clast pendant contact implying that the oldest deposits are not always found at the pendant clast contact as other studies have assumed these features include a void at the clast pendant contact where minerals such as calcium carbonate silica and or fibrous silicate clays precipitate in addition fragments of the parent clast and detrital grains are incorporated into the pendant and are displaced and or dissolved and result in the formation of sepiolite this study indicates that pendants are complex open systems that during and after their formation undergo chemical changes that complicate their usefulness for dating and paleoenvironmental analyses

rates of soil development from four soil chronosequences in the southern great basin abstract four soil chronosequences in the southern great basin were examined in order to study and quantify soil development during the quaternary soils of all four areas are developed in gravelly alluvial fans in semiarid climates with 8 to 40 cm mean annual precipitation lithologies of alluvium are granite gneiss at silver lake granite and basalt at cima volcanic field limestone at kyle canyon and siliceous volcanic rocks at fortymile wash ages of the soils are approximated from several radiometric and experimental techniques and rates are assessed using a conservative mathematical approach average rates for holocene soils at silver lake are about 10 times higher than for pleistocene soils at kyle canyon and fortymile wash based on limited age control holocene soils in all four areas appear to develop at similar rates and pleistocene soils at kyle canyon and fortymile wash may differ by only a factor of 2 to 4 over time spans of several millennia a preferred model for the age curves is not linear but may be exponential or parabolic in which rates decrease with increasing age these preliminary results imply that the geographical variation in rates within the southern great basin mojave region may be much less significant than temporal variation in rates of soil development the reasons for temporal variation in rates and processes of soil development are complexly linked to climatic change and related changes in water and dust erosional history and internally driven chemical and physical processes

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

quantification of unsaturated zone alteration and cation exchange in zeolitized tuffs at yucca mountain nevada usa abstract zeolitized horizons in the unsaturated zone uz at yucca mountain nevada usa are an important component in concepts for a high level nuclear waste repository at this site the use of combined quantitative x ray diffraction and geochemical analysis allows measurement of the chemical changes that accompanied open system zeolitization at yucca mountain this approach also provides measures of the extent of chemical migration that has occurred in these horizons as a result of subsequent cation exchange mass balance analysis of zeolitized horizons with extensive cation exchange drill hole uz 16 and with only minimal cation exchange drill hole sd 9 shows that al is essentially immobile although zeolitization occurred in an open system the mass transfer of constituents other than water is relatively small in initial zeolitization in contrast to the larger scales of cation exchange that can occur after zeolites have formed cation exchange in the clinoptilolite mordenite zeolitized horizons is seen in downward diminishing concentration gradients of ca mg and sr exchanged for na and to lesser extent k comparison with data from drill hole sd 7 which has multiple zeolitized horizons above the water table shows that the upper horizons accumulate ca mg and sr to such an extent that transport of these elements to the deepest uz zeolitized horizon can be blocked quantitative analysis of zeolite formation yields insight into processes that are implied from laboratory studies and modeling efforts but are otherwise unverified at the site such analysis also yields information not provided by or contradicted by some models of flow and transport the results include the following 1 evidence of effective downward flow through zeolitic horizons despite the low permeability of these horizons 2 evidence that alkaline earth elements accumulated by zeolites are mostly derived from eolian materials in surface soils 3 validation of the very effective operation of unsaturated zeolitic horizons as cation exchange barriers 4 independent support of models that indicate average water infiltration rates of 5 mm yr over the past 10 ma and 5 evidence that the presence or absence of cation exchange profiles can be used to identify those portions of the site where transport through the uz is concentrated this last point is relevant to repository design because a knowledge of where transport takes place can be used to advantage in defining the boundaries of a repository such that high flux portions of the site can be avoided

on the rocks quantifying storage of inorganic soil carbon on gravels and determining pedon scale variability abstract the storage and flux of carbon from soils the planet s third largest carbon pool strongly influence the global carbon cycle and are essential but poorly constrained parameters for global climate models an estimated 40 of all soil carbon is stored as inorganic carbonate minerals despite a recognition of the importance of soil inorganic carbon sic in soil carbon storage few studies have quantified pedon scale variability in sic storage we examine different stages of carbonate development and accumulation rates between gravelly and non gravelly soils studies often ignore carbonate coatings on gravels in measurements of soil inorganic carbon sic by quantifying and differentiating the fine 2 mm fractions of sic in the reynolds creek experimental watershed in southwestern idaho we show that gravel coatings contain up to 44 of total sic at a given site among the 26 soil sites examined throughout the watershed an average of 13 of the total sic is stored as carbonate coatings within in the gravel fraction we measured a high level of pedon scale field variability up to 220 among the three sampled faces of 1 m 3 soil pits analytical error associated with the modified pressure calcimeter 0 001 0 014 is considerably less than naturally occurring heterogeneities in sic within the soil profile this work highlights and quantifies two sources of uncertainty in studies of sic needed to inform future research first in gravelly sites the 2 mm portion of soils may store a large percentage of sic second sic varies considerably at the pedon scale so studies attempting to quantify carbon storage over landscape scales need to consider this variability

late quaternary environmental changes in the upper las vegas valley nevada abstract five stratigraphic units and five soils of late pleistocene to holocene age crop out in dissected badlands on corn creek flat 30 km northwest of las vegas nevada and at tule springs nearer to las vegas the record is dominantly fluvial but contains evidence of several moister marsh forming periods the oldest unit b dates perhaps to the middle wisconsin and the more widespread unit d falls between 30 000 and 15 000 yr b p unit d therefore correlates with pluvial maximum lacustrine deposits elsewhere in the great basin standing water was not of sufficient depth or extent during either period to form lake strandlines between 14 000 and 7200 yr b p unit e standing surface water gradually decreased a trend also apparent in great basin pluvial lake chronologies during the same period groundwater carbonate cementation and burrowing by cicadas cicadae accompany the moist phase units after 7200 yr b p increased wind action decreased biotic activity and at least 25 m of water table lowering accompanied widespread erosion of older fine grained deposits based on pack rat midden and pollen evidence this coincides with major vegetation changes in the valley from sagebrush dominated steppe to lower mohave desertscrub

compositions of modern dust and surface sediments in the desert southwest united states 1 modern dusts across southwestern united states deserts are compositionally similar to dust rich av soil horizons depths of 0 0 5 cm and 1 4 cm at 35 sites for common crustal elements but distinctly different for some trace elements chemical compositions and magnetic properties of the soil samples are similar among sites relative to dust sources geographic areas and lithologic substrates exceptions are li u and w enriched in owens valley california and mg and sr enriched in soils formed on calcareous fan gravel in southeast nevada the av horizons are dominated by dust and reflect limited mixing with substrate sediments modern dust samples are also similar across the region except that owens valley dusts are higher in mg ba and li and dusts both there and at sites to the north on volcanic substrates are higher in sb and w thus dust and av horizons consist of contributions from many different sources that are well mixed before deposition modern dusts contain significantly greater amounts of as cd cr cu ni pb and sb than do av horizons which record dust additions over hundreds to thousands of years these results suggest that modern dust compositions are influenced by anthropogenic sources and emissions from owens dry lake after its artificial desiccation in 1926 both modern dusts and av horizons are enriched in as ba cu li sb th u and w relative to average crustal composition which we interpret to indicate that the geologic sources of dust in the southwestern united states are geochemically distinctive

fibrous clay minerals in the soils of namaqualand south africa characteristics and formation abstract palygorskite or sepiolite containing soils occur at elevations up to 1000 m in gently sloping landscapes formed by aeolian sands or by strongly eroded pedisediments overlying the namaqualand metamorphic complex the unconsolidated sands are in various stages of calcretization most of the soils are sandy shallow non saline with a ph ranging between 7 2 and 8 2 carbonate contents are low but increase towards the calcretized horizons most of the carbonates appear in the form of nodules in the clay fractions palygorskite or sepiolite dominate and are accompanied by illite and non expanding 14 a minerals or mixed layer minerals dta tga and chemical analysis indicate that the sepiolite is fe rich and contains organic material trapped within its channels the highest concentrations of the fibrous clay minerals commonly occur in the bottom horizons it is postulated that they formed pedogenically from silica released by silicates and mg derived from mg rich carbonates introduced by aeolian accretion this hypothesis is supported by a decrease in mg ca of the carbonates with soil depth another possible mg source considered is sea spray soil water extract compositions are not compatible with fibrous clay mineral stability electron micrographs of sepiolite clays suggest alteration into sheet clay minerals

correlation between long term pedogenic caco3 formation rate and modern precipitation in deserts of the american southwest abstract the rates of caco 3 formation in desert soils of the american southwest are highly variable and potentially useful in estimating the age of soil profiles the objective of this study was to examine the correlation between the long term rate of caco 3 formation ltr and modern mean annual precipitation map and temperature mat ltr is not significantly related to temperature but is linearly related to map ltr 0 0150 map 37 r 2 0 924 the slope of the regression is significantly different from 0 0 and is equivalent to a calcium concentration of 6 0 mg liter 1 in rainfall however the intercept term which suggests a lower limit of precipitation for caco 3 formation of 37 mm is not significantly different from 0 0 the ltr map relationship may be useful in estimating the age of soil profiles by the caco 3 method in the desert southwest

pedogenesis of siliceous calcretes at yucca mountain nevada abstract siliceous calcretes in faults near yucca mountain nevada have been interpreted by some observers as evidence of seismically triggered eruptions of deep water such an origin could have important consequences if yucca mountain is developed as an unsaturated site for disposal of high level nuclear waste at odds with this hypothesis are the absence of features that should be present at fault fed springs e g fissure ridge mounds with microterraces and the preservation within root casts of delicate pedogenic microfossils such as calcified filaments and needle fiber calcites chemical evidence of pedogenic origin is found in fe and sc enrichments that require prior weathering of detritus in the calcretes as opposed to direct incorporation of adjacent unweathered bedrock carbonate and silica abundances and accumulation rates are well within the scope of pedogenic processes sources of carbonate are eolian whereas silica is derived in part by dissolution of local volcanic glasses but also by extensive dissolution of unstable silica minerals tridymite and cristobalite that are abundant in the local tuffs the siliceous calcretes at yucca mountain are pedogenic and provide no evidence in support of conjectured spring activity

diagenetic replacement controlled by force of crystallization many diagenetic replacements in sedimentary rocks occur along thin solution films between the authigenic and host phases rather than conventionally invoking bulk pore water undersaturation for host phase dissolution we propose that many diagenetic replacements occur by a force of crystallization controlled replacement mechanism whereby nonhydrostatic stresses resulting from authigenic crystal growth are principally responsible for host phase dissolution this model explains diagenetic features such as the restriction of host phase dissolution to authigenic host crystal contacts and euhedral authigenic crystal faces in planar contact with unreplaced host phases as well as the relative replacement tendencies of some common authigenic minerals

precipitation in southern nevada the distribution of precipitation in both time and space in the southern nevada area is examined it is concluded that this area can be divided into two zones of precipitation separated by a transition zone on the basis of annual average precipitation one region relative to the other area is defined to be a deficit annual average precipitation region this observation could have a significant impact on groundwater recharge estimates and on the siting of facilities which must be protected from flash floods in addition precipitation records at two stations in the southern nevada area were examined and point intensity duration relationships were derived for these stations

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

duripans of idaho u s a in situ alteration of eolian dust loess to an opal a x ray amorphous phase abstract micromorphological techniques were used to study the silicification process in a wide range of duripans from idaho u s a investigations indicated that once loess was incorporated into a carbonaterich pan it was altered in situ to an opal a x ray amorphous phase loess became incorporated by at least two pathways each of which had a distinctive micromorphic signature the first pathway began immediately above the duripan as calcite encapsulated eolian materials to create sand sized loess agglomerates incorporation was completed either as the upward developing duripan enveloped the agglomerates or as they filled fractures in the duripans and were subsequently cemented by calcite after encasement of the loess agglomerates within the duripan aluminosilicate minerals were embayed by reaction with the calcareous soil solution the most altered loess agglomerates consisted of opal a x ray amorphous material and calcite the second pathway was initiated when fractures in the duripan were filled by eolian dust to create pedotubules the tops of pedotubules had a fabric similar to unaltered loess silasepic plasmic however the bottoms of pedotubules were invariably altered to a microgranular array of opal a and calcite impetus for alteration appears to have been high ph created by closed system conditions combined with increased surface free energy of minerals caused by elevated grain to grain pressures which led to enhanced solubility of aluminosilicate minerals the incorporation of loess and its subsequent alteration may be an important process in the silicification of calcareous pans

geomorphic controls on biological soil crust distribution a conceptual model from the mojave desert usa abstract biological soil crusts bscs are bio sedimentary features that play critical geomorphic and ecological roles in arid environments extensive mapping surface characterization gis overlays and statistical analyses explored relationships among bscs geomorphology and soil characteristics in a portion of the mojave desert usa these results were used to develop a conceptual model that explains the spatial distribution of bscs in this model geologic and geomorphic processes control the ratio of fine sand to rocks which constrains the development of three surface cover types and biogeomorphic feedbacks across intermontane basins 1 cyanobacteria crusts grow where abundant fine sand and negligible rocks form saltating sand sheets cyanobacteria facilitate moderate sand sheet activity that reduces growth potential of mosses and lichens 2 extensive tall moss lichen pinnacled crusts are favored on early to late holocene surfaces composed of mixed rock and fine sand moss lichen crusts induce a dust capture feedback mechanism that promotes further crust propagation and forms biologically mediated vesicular av horizons the presence of thick biogenic vesicular horizons supports the interpretation that bscs are long lived surface features 3 low to moderate density moss lichen crusts grow on early holocene and older geomorphic surfaces that display high rock cover and negligible surficial fine sand desert pavement processes and abiotic vesicular horizon formation dominate these surfaces and minimize bioturbation potential the biogeomorphic interactions that sustain these three surface cover trajectories support unique biological communities and soil conditions thereby sustaining ecological stability the proposed conceptual model helps predict bsc distribution within intermontane basins to identify biologically sensitive areas set reference conditions for ecological restoration and potentially enhance arid landscape models as scientists address impacts of climate change and anthropogenic disturbances

relationship between climate and vegetation and the stable carbon isotope chemistry of soils in the eastern mojave desert nevada abstract the relationship between the stable c isotope composition of the soil environment and modern climate and vegetation was determined empirically along a present day climatic transect in the eastern mojave desert the 13c of the soil co2 and carbonates decreased with increasing elevation and plant density even though plant assemblages at all elevations were isotopically similar several factors including differences in the ratios of pedogenic of limestone calcite and differences in past vegetation were considered as explanations of this trend however it appears that in the sparsely vegetated mojave desert the 13c of pedogenic carbonate is controlled by differences in plant density and biological activity this relationship may provide a tool for assessing past vegetational densities as long as the vegetation is isotopically homogeneous

soil formation on calcium carbonate rich parent material in the outer carpathian mountains a case study abstract in this study ten stratified calcium carbonate rich soil profiles from the polish outer carpathians were investigated in order to identity the influence of parent material variability and slope processes on soil diversity and their evolution moreover we evaluated the morphological and physico chemical soil properties to recognize the diagnostic horizons and classification of such soils while it is usually thought that carbonate rich soils are considered as formed in situ these study soils clearly presented layering and contribution of materials as they were developed from mixed substrates of different origin e g as the result of mass movements and possible aeolian silt contribution irrespective of the type of parent material every investigated soil showed traces of slope processes resulting in heterogeneous soil profiles further a few different patterns of primary calcium carbonate arrangement were found in general the studied soils were characterized by enrichment with calcium carbonate not only due to inheritance from calcium carbonate rich parent material but also translocation of calcium carbonate within soil profiles the latter depending on soil stratification based on the obtained results four pathways of soil evolution were formulated leptosols which represent initial calcium carbonate rich soils may evolve in different directions first formation of the thick layer suitable for cambic horizon development under deciduous forests which enables the classification of such soils as cambisols depends on slope processes and allochthonous material deposition in turn the decrease of mineralization rates for organic matter delivery of soil material from the upper parts of the slope as well as mixing of organic matter by mesofauna result in the formation of mollic horizons and transformation of leptosols into phaeozems further erosion and redeposition of fine soil material provide two types of slope sediments i those with silt loam texture dominance and ii clay loams interstratified with silty substrates the first type of sediments are more suitable for water percolation and after carbonate leaching clay dispersion and translocation occur in such materials luvisols may develop sediments with a prevalence of clay loam aided stagnosol formation in which pools of carbonates were stabilized due to the reduction of water percolation leading to stagnation

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

influence of soil development on the geomorphic evolution of landscapes an example from the transverse ranges of california soil development can significantly influence the topographic evolution of a tectonically deforming mountain piedmont faults and folds associated with the north frontal thrust system deform piedmont sediments of variable compositions along the north flank of the san bernardino mountains the topographic expressions of folds with similar structural characteristics diverge appreciably primarily as a function of differences in sediment composition and associated soil development soils with petrocalcic horizons in limestone rich deposits are resistant to erosion and anticlinal folds form prominent ridges folds forming in granite derived deposits with argillic soil horizons are eroded and or buried and are therefore topographically less pronounced we propose that these landform contrasts can be explained by differences in soil controlled hydrologic and erosion characteristics of deposits without calling upon changes in tectonic style along the mountain front

morphology and genesis of carbonate soils on the kyle canyon fan nevada u s a the physical and chemical properties of soils formed in an arid climate on calcareous alluvium of the kyle canyon alluvial fan southern nevada were studied in order to infer the rates and relative importance of various soil forming processes these studies included field and microscopic observations and analyses of thin sections major oxides extractable iron and clay minerals the results are interpreted to reflect five major pedogenic processes 1 the calcic horizons and calcretes of kyle canyon soils form by precipitation of caco3 derived from eolian dust and alluvium as clast coats matrix cement and massive layers 2 the a and uppermost b horizons are essentially dust derived for they contain large amounts of detrital material not present in the alluvial parent material and their major oxide content is similar to that of modern dust 3 clay particles are translocated from a into b horizons 4 iron bearing minerals in the near surface b horizons are slowly oxidized 5 carbonate and aluminosilicate grains are both displaced and replaced by pedogenic caco3 the silica released by replacement of aluminosilicates may be locally precipitated as amorphous or opaline silica and or incorporated into newly formed palygorskite and sepiolite rates of soil development at kyle canyon are approximate due to uncertainties in age estimates some soil field properties change at rates that are similar to rates for soils formed in rhyolitic parent material near mercury nevada the rate of accumulation of caco3 3 5 g m 2 yr 1 at kyle canyon is an order of magnitude faster than that near mercury but is comparable to rates calculated for soils in southern new mexico and utah

the distribution and discrimination of shallow authigenic carbonate in the pliocene pleistocene palomas basin southern rio grande rift nine types of authigenic carbonate are present in the pliocene pleistocene alluvial fan and axial fluvial sediment of the palomas half graben in the southern rio grande rift pedogenic and other vadose carbonate includes 1 pedogenic carbonate of stage ii and stage iii morphology underlying bw and bt horizons 2 mudstones in which the carbonate nodules may be pedogenic or the result of shallow groundwater invasion of the vadose zone 3 pedogenic calcic nodules and tubules in eolian sand and 4 gully bed cement of proximal fan conglomerates formed by infiltration and evaporation of surface runoff shallow groundwater carbonate exists as 5 thin 30 50 cm massive beds with an upper fringe of nodules and tubules precipitated at the water table and in the capillary fringe 6 thick 1 5 3 m massive beds deposited by lateral flow of groundwater or at springs and 7 thin 30 cm calcified root mats associated with near surface water saturated sediment or springs phreatic spar cements 8 occupy the interstices of conglomerates and sandstones and locally exist as 9 oriented concretions groundwater carbonates are best developed near the toes of the large hanging wall derived alluvial fans whereas phreatic cement preferentially exists in footwall derived alluvial fan conglomerates pedogenic carbonate is distinguished from groundwater carbonate by the association with other diagnostic paleosol horizons a predominantly vertical arrangement of root traces peds desiccation cracks and calcic tubules and by gradational contacts the 13 c and 18 o values are similar among pedogenic and shallow groundwater carbonate although locally nodules in eolian sand and gully bed cement have higher 18 o values perhaps due to the effects of evaporation some phreatic cements may be distinguished from pedogenic and shallow groundwater carbonate by lower values of 13 c and 18 o authigenic carbonate in footwall derived alluvial fan sediment has consistently higher values of 13 c than that in hanging wall derived sediment which may reflect differences in vegetative type and or density on either side of the basin

dating constituent formation in soils to determine rates of soil processes a review abstract rates of soil processes are poorly known one approach to determine them could be through the radiogenic isotopic dating of soil constituents such methods have been recently used to date minerals in soils and weathering profiles thanks to the development of high resolution techniques such as 40ar 39ar u series of micro drilled samples u series by laser ablation and u th he and to the development of suitable methodology expanding application of the techniques to a variety of supergene minerals e g fe and mn oxihydroxides carbonates etc in this paper we identify i the main soil constituents that can be dated through these isotopic methods that are mainly fe oxides mn oxides pedogenic carbonates and organic matter ii the main pedogenic processes that leads to their formation in soils and iii the different soil settings that allow transforming soil constituent ages into rates of soil processes namely growth bands transformation fronts and chronosequences

soil evolution along an altitudinal transect in the eastern mojave desert of nevada u s a amundson r g chadwick o a sowers j m and doner h e 1989 soil evolution along an altitudinal transect in the eastern mojave desert of nevada u s a geoderma 43 349 371 six soil profiles were examined along an altitudinal transect from 840 to 2170 m in the eastern mojave desert of southern nevada the soils formed on gravelly limestone alluvium which varied in age from holocene to mid pleistocene climate and vegetation varied from an arid desert scrub community at the low elevation to a sub humid coniferous forest at the highest elevation silicate clay mineralogy was similar to that of the parent material in all the holocene soils but differed with elevation in the mid pleistocene soils these being dominated by palygorskite at 1400 m and smectite at 2150 m pedogenic carbonate content of the bk horizons and morphologic stage of carbonate accumulation increased with soil age with the exception of the 2150 m site where excess moisture leaches carbonate out of the profile dcb extractable iron increased with both age and elevation whereas soil organic c and c02 increased primarily with elevation reflecting the gradient in moisture regime and biologic productivity aeolian dust may have a strong role in the formation of the vesicular platey surface horizons at many of the sites

rare earth and other trace and major elemental distribution in a pedogenic calcrete profile slimene ne tunisia a calcrete profile developed on the top of a calcareous consolidated dune located in a coastal area of ne tunisia semi arid climate was studied with the aim to investigate the behavior of the chemical elements rare earth elements ree and other trace and major elements during the processes associated with calcrete formation particularly dissolution and precipitation of carbonates in the vadose zone the profile shows a vertical sequence with clear zonations from the surface downwards a reddish soil at the land surface a nodular horizon a laminar structured level and the consolidated old dune chemical and mineralogical analyses of samples from all levels were performed by neutron activation analysis and x ray diffraction bulk samples and 2 m fraction detailed studies of iron speciation and iron minerals were done by mossbauer spectroscopy microfauna mineralogical and chemical variations in the slimene weathering profile point to a long term aerial exposure of the old dune in a semi arid carbonated environment leading to the development of a pedogenic calcrete profile the mineralogical variations with depth indicate carbonate dissolution at the surface and downward leaching of calcium secondary carbonates overgrow primary ones and precipitate as coating or concretions below minerals found in the upper levels correspond to original materials of the old dune and also weathering phases and atmospheric inputs phyllosilicates decrease while calcite and k feldspars increase with depth kaolinite was the only clay mineral found in the old dune illite and chlorite were also found in all samples with calcrete authigenic smectite formation occurs above the laminar structured calcrete due to restricted drainage conditions the most significant chemical variations associated with the calcrete formation are i enrichment of co u br and ree in calcrete ii depletion of middle ree in the upper levels particularly eu and enrichment of middle ree and heavy ree in calcrete and iii hf zr cr th cs ta ga rb and k appear to be retained in the upper levels where calcite has been dissolved here iron is more reduced fe3 occurs in iron oxides goethite and hematite and clay minerals the ratio goethite hematite appears to increase down the profile and fe2 is mainly present in clay minerals

investigation of limestone and dolomite clast alteration in petrocalcic horizons southern nevada usa abstract petrocalcic horizons formed on quaternary surfaces in southern nevada contain altered limestone and dolomite clasts in the enveloping carbonate matrix three profiles from two geomorphic surfaces contain pebble to cobble clasts with distinct voids and alteration textures at their tops clast and alteration zone characteristics were analyzed with scanning electron microscopy energy dispersive x ray spectroscopy x ray diffraction electron microprobe analysis and with an inductively coupled plasma spectrophotometer limestone and dolomite clasts display considerable top down alteration marked by vertical tubular voids and an increase in neoformed fibrous clay in the altered regions downward percolating soil waters moved through the cemented horizon and contacted the upper clast boundaries as evidenced by selective alteration and void development at the tops of clasts the preservation of voids indicates that alteration and void development began no earlier than initial petrocalcic formation when soil matrix pore spaces were largely filled with pedogenic carbonate undersaturation of soil fluids with respect to primary clast components ca and or mg and or increased pco2 under conditions enhanced during wetter pluvial climates is interpreted to drive dissolution and alteration of clasts in these horizons resulting morphological and mineralogical changes in these petrocalcic horizons may mark past climate and geomorphic influence on their development over time misinterpretation of parent material provenance as a result of selected removal of individual clast lithologies may occur

differentiation of pedogenic and lithogenic carbonate forms in texas abstract sixteen pedons representing soils developed from limestone and fluvial deltaic sediments were sampled in central and western texas 300 800 mm annual precipitation to differentiate pedogenic secondary and lithogenic inherited carbonate forms by field and laboratory techniques lithogenic carbonate forms identified in the field included indurated limestone bedrock and coarse limestone fragments lithorelicts field identified pedogenic forms included petrocalcic horizons thin laminar cappings on indurated limestone carbonate joint seams pendants on pebbles and carbonate films and threads on ped faces small

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

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

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

pedogenesis on talus slopes the buckskin range nevada usa abstract soil development on steep mountainous topography generally leads to thin and undifferentiated pedons on talus slopes of the buckskin mountains a fault blocked range of west central nevada usa thick differentiated pedons occur talus occurs on the western front where block rotation has formed very steep slopes and consists of angular dacite cobbles and boulders the study area is arid averaging less than 20 cm of precipitation per year typical pedons consist of surface talus filled with vesicular non structured sandy loam to loam material this material overlies clay textured prismatic and blocky structured horizons mostly rock free that in places are over 1 m thick pedons are classified as fine mixed mesic xeralfic paleargids soil macro and micromorphological features soil mineralogy and soil chemical and physical attributes suggest the following developmental sequence which began sometime before the middle pleistocene the talus serves as a baffle to collect eolian dust once eolian dust accumulates to a threshold thickness primary minerals are transformed in situ mostly to a smectitic clay as clay content increases a second threshold level is reached at which time the horizon of clay enrichment has sufficient strength and shrink swell potential to support and raft the talus upward the exposed talus can then continue to trap eolian dust the soil profile thickens and the pedon is protected from erosion a variation of this soil cumulation process may be partially responsible for textural b horizon formation in avid and semiarid climates

pedogenic replacement of aluminosilicate grains by caco3 in ustollic haplargids south central montana u s a abstract a chronosequence of calcic soils formed on granitic glaciofluvial terrace deposits of rock creek and the clarks fork in south central montana shows progressive replacement of aluminosilicate parent material grains by calcium magnesium carbonate the terraces range from late pliocene to holocene in age as dated by tephrochronology correlation and stream incision rates replacement is first seen in soils that are as old as 120 000 yr the amount and degree of replacement increase in soils older than 120 000 yr along with the development of calcic horizons under the petrographic microscope carbonate replacement of quartz feldspars and the groundmass of andesite grains in rock creek soils is shown by embayed grains networks of carbonate along cracks and between parts of polycrystalline grains and optically aligned grain fragments within carbonate masses microprobe data suggest that silica is released by replacement because it is absent from carbonate filled spaces and is depleted in corrosion pits little microscopic evidence exists to support displacement of framework grains by carbonate because fragments of a single grain are rarely rotated out of optical alignment in the calcic soils of rock creek k fabric grains floating in a carbonate matrix may form by both replacement and displacement

debris flow dominance of alluvial fans masked by runoff reworking and weathering arid alluvial fan aggradation is highly episodic and fans often comprise active and inactive sectors hence the morphology and texture of fan surfaces are partly determined by secondary processes of weathering and erosion in addition to primary processes of aggradation this introduces considerable uncertainty in the identification of formative processes of terrestrial and martian fans from aerial and satellite imagery the objectives of this study are i to develop a model to describe the sedimentological and morphological evolution of inactive fan surfaces in arid settings and ii to assess the relative importance of primary processes of aggradation and secondary processes of weathering and reworking for surface morphology and sedimentology and for the stratigraphic record we studied an alluvial fan characterized by a recently active sector and a long abandoned inactive sector along the coast of the hyperarid atacama desert here rates of primary geomorphic activity are exceptionally low because of extreme aridity while weathering rates are relatively high because of the effects of coastal fogs long term processes of fan aggradation and reworking were determined through sedimentological facies analysis of stratigraphic sections ground surveys for textural and morphological patterns at the fan surface were integrated with remote sensing by an unmanned airborne vehicle uav discharges and sediment transport capacities were calculated to estimate the efficiency of secondary runoff in reshaping the inactive fan sector stratigraphic sections reveal that the fan was dominantly aggraded by debris flows whereas surface morphology is dominated by debris flow signatures in the active sector and by weathering and runoff on the inactive sector on the latter rapid particle breakdown prevents the formation of a coarse desert pavement furthermore relatively frequent local runoff events erode proximal debris flow channels on the inactive sector to form local lag deposits and accumulate fine sediment in low gradient distal channels forming a well developed drainage pattern that would suggest a runoff origin from aerial images nevertheless reworking is very superficial and barely preserved in the stratigraphic record this implies that fans on earth and mars that formed dominantly by sporadic mass flows may be masked by a surface morphology related to other processes

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

influence of climate and eolian dust on the major element chemistry and clay mineralogy of soils in the northern bighorn basin u s a abstract soil chronosequences in the northern bighorn basin permit the study of chronologic changes in the major element chemistry and clay mineralogy of soils formed in different climates two chronosequences along rock creek in south central montana formed on granitic alluvium in humid and semiarid climates over the past two million years a chronosequence at the kane fans in north central wyoming formed on calcareous alluvium in an arid climate over the past 600 000 years detailed analyses of elemental chemistry indicate that the soils in all three areas gradually incorporated eolian dust that contained less zirconium considered to be chemically immobile during weathering than did the alluvium b and c horizons of soils in the wettest of the chronosequences developed mainly at logarithmic rates suggesting that leaching initially rapid but decelerating dominated the dust additions in contrast soils in the most arid of the chronosequences developed at linear rates that reflect progressive dust additions that were little affected by leaching both weathering and erosion may cause changes with time to appear logarithmic in a horizons of soils under the moist and semiarid climatic regimes clay minerals form with time in the basal b and c horizons and reflect climatic differences in the three areas vermiculite mixed layer illite smectite and smectite form in the soils of the moist climate chronosequence smectite forms in the semiarid climate chronosequence and smectite and palygorskite form in the arid climate chronosequence

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

reconstructing paleosalinity from δ18o coupled model simulations of the last glacial maximum last interglacial and late holocene reconstructions of salinity are used to diagnose changes in the hydrological cycle and ocean circulation a widely used method of determining past salinity uses oxygen isotope ow residuals after the extraction of the global ice volume and temperature components this method relies on a constant relationship between ow and salinity throughout time here we use the isotope enabled fully coupled general circulation model gcm hadcm3 to test the application of spatially and time independent relationships in the reconstruction of past ocean salinity simulations of the late holocene lh last glacial maximum lgm and last interglacial lig climates are performed and benchmarked against existing compilations of stable oxygen isotopes in carbonates oc which primarily reflect ow and temperature we find that hadcm3 produces an accurate representation of the surface ocean oc distribution for the lh and lgm our simulations show considerable variability in spatial and temporal ow salinity relationships spatial gradients are generally shallower but within 50 of the actual simulated lh to lgm and lh to lig temporal gradients and temporal gradients calculated from multi decadal variability are generally shallower than both spatial and actual simulated gradients the largest sources of uncertainty in salinity reconstructions are found to be caused by changes in regional freshwater budgets ocean circulation and sea ice regimes these can cause errors in salinity estimates exceeding 4 psu our results suggest that paleosalinity reconstructions in the south atlantic indian and tropical pacific oceans should be most robust since these regions exhibit relatively constant ow salinity relationships across spatial and temporal scales largest uncertainties will affect north atlantic and high latitude paleosalinity reconstructions finally the results show that it is difficult to generate reliable salinity estimates for regions of dynamic oceanography such as the north atlantic without additional constraints

clay accumulation and argillic horizon development as influenced by aeolian deposition vs local parent material on quartzite and limestone derived alluvial fans where precipitation is ample udic moisture regimes and evidence of illuviation clear argillic horizon genesis is often easily understood in drier climates aridic to ustic argillic horizons are often interpreted as relict features of the pleistocene however in high montane western landscapes where climate falls in between these two extremes the role of aeolian clay inputs vs in situ weathering contributing to clay formation is of debate two mollisols one developed in quartzite alluvium charkiln series 3 pedons and one in limestone alluvium troughspring series one pedon were examined to determine whether atmospheric dust or local geologies contribute to their development and whether bt horizons in both pedons were argillic horizons we hypothesize that both soils have argillic horizons and that clays are derived from site parent materials thin section specimens of bt horizons and sand and silt fraction grains were prepared and examined using a petrographic microscope regional dust xrd mineralogic data were compared to xrd rock fragment and soil mineralogic data clay films while seen in all field pedons were very few and faint in the troughspring series illuviation of clays was evident in thin sections of the charkiln pedons but not the troughspring pedon in the charkiln series illuviation is observed as clay depleted a horizons clay accumulating b horizons clay bridging clay films on grains and in channels in the troughspring pedon clay depleted a horizons and clay accumulating b horizons very few clay films on grains and some pressure features in packing voids are seen but grain bridging and coatings on channels are not observed while local geologies influence soil mineralogy in both series aeolian dust deposition is as significant and its affect is further enhanced by organic acid weathering from an overlying pinyon juniper woodland and the current ustic climate regime while evidence of an argillic horizon is seen in the charkiln series excess ca in soils is believed to be inhibiting illuviation in the troughspring series and thus preventing argillic horizon development

a review on the potentiality of rare earth elements to trace pedogenetic processes abstract this review aims at considering the use of rees to trace pedogenetic processes in order to quantify the respective contribution of the successive processes on pedogenesis we first consider the origins and contents of rees in soils to assess their natural occurrence and tackle the common data treatment used to interpret their concentrations we review subsequently the impact of the different pedogenetic processes on the fate of rees in soils from their release into a soil solution by primary mineral heavy minerals phosphates silicates and carbonates dissolution during weathering to their fixation on or into main ree bearing secondary minerals clay minerals fe mn oxides and carbonates then their mobilization by plant recycling and organic matter and finally the impact of argilluviation and redox processes on their fractionation we conclude that rees much more than other trace elements can interestingly trace the considered processes that are encountered in a large diversity of non polluted soils arising from diverse parent materials weathering generally fractionates rees and accounts for a significant part of the variation in the initial ree stock of the soils plant recycling induces a weak mobilization of rees and their accumulation in topsoil argilluviation can be traced using the mree enrichment and the eu anomaly of the clay minerals redox processes can be traced by the ce anomaly caused by the precipitation of cerium on mn oxides to use rees as tracers of pedogenetic processes we recommend to i precisely characterize the ree bearing minerals ii adapt the choice of reference s for normalization and iii perform mass balance calculations

millennial scale climate oscillations recorded in the lower danube loess over the last glacial period abstract in this study we provide a correlative age model for last glacial loess at the rasova valea cu pietre site in the lower danube region based on the correlation of palaeoenvironmental proxies to independently dated palaeoclimate archives luminescence dating and independent age control provided by the geochemically confirmed presence of the campanian ignimbrite ci tephra the ci tephra originating in the phlegrean fields of southern italy has been dated elsewhere by 40ar 39ar to 39 40 ka bp and is frequently found in the lower danube loess as such the ci tephra represents a valuable temporal and stratigraphic maker across loess deposits in the region our age model facilitates high resolution correlation of palaeoenvironmental features observed at rasova to palaeoclimate archives in greenland and the black sea mediterranean area we observe semi cyclic behaviour of the frequency dependent magnetic susceptibility throughout the profile which we ascribe to millennial scale climate variability also observed elsewhere in the black sea region this is the first study to clearly identify millennial scale climate variability over the holocene and last glacial in the lower danube loess proxy variability in the holocene indicates continuous aeolian sedimentation through this epoch

desert pavement characteristics on wadi terrace and alluvial fan surfaces wadi al bih u a e and oman abstract in arid mountain areas the dating and correlation of alluvial depositional surfaces is often uncertain especially in regions where the geomorphology is not well known surface modification by the development of soil and desert pavement may allow the correlation of geomorphic surfaces and estimation of at least their relative ages pleistocene wadi terraces and associated alluvial fans occur in wadi al bih u a e and oman for which correlations and age relationships are not known three age related groups of fans and terraces have been identified and mapped on the basis of their morphostratigraphic relationships deposition of the oldest terrace sediments and associated fans followed a long period of sustained incision after miocene uplift of the region the younger two groups of terraces and fans are inset within the older group to identify the gross effects of pavement development comparisons have been made between terrace surface and subsurface particle size distributions the older terraces have finer surface sediments and a greater contrast between finer surface and subsurface sediments than the younger terraces this reflects the degree of pavement development particle size on the fan surfaces is comparable with that on the equivalent terrace surfaces criteria for the classification of pavements were developed based on clast fracturing and angularity size sorting packing and surface texture from which a simple index of pavement development has been derived other properties rock varnish and weathering characteristics were also recorded but these proved to be less discriminatory than pavement characteristics the pavement data have been augmented by observations on soils detailed studies of pavements on terraces 8 sites 12 samples covering the three age groups and fans 5 sites 10 samples covering the three age groups allow differentiation between age groups the three terraces show three different age related pavement types expressed by differences in the pavement development index weakly developed pavements little fracturing sub rounded clasts some modification of the depositional fabric incipient soil development stage i caco3 accumulation occur on the youngest terrace and fan surfaces moderately developed pavements clast fracturing sub angular clasts moderate sorting and packing deeper soil development stage ii caco3 accumulation occur on the middle terrace and fan surfaces well developed pavements complete clast fracturing into small angular fragments mature sorting and packing of the pavement surface deep soil development with strong horizonation stage iii caco3 accumulation occur on the highest terrace and oldest fan surfaces there are minor differences between the youngest pavements on terraces and fans which reflect initial sedimentological differences these differences become less as the pavements develop on the basis of comparative studies the oldest terrace is estimated to date from sometime prior to ca 100 ka bp the second terrace and the most extensive fan surface from the late pleistocene and the youngest terrace and fan phase from the latest pleistocene or early holocene

carbonate and elemental accumulation rates in arid soils of mid to late pleistocene outwash terraces southeastern wind river range wyoming usa an important result of the past few decades of soil geomorphic research is the awareness of the major role of dust and related carbonate precipitates in arid soils the temporal evolution of soils developed on outwash terraces is still a matter of debate particularly regarding the type of evolution progressive evolution and constant rates vs complex and or interval accumulation rates progressive or regressive evolution possible soils on a chronosequence of outwash terraces just outside and downstream of canyon mouths of the wind river range usa were analysed for carbonate accumulation organic carbon and poorly crystalline pedogenetic oxyhydroxides stocks and pathways of chemical weathering the soils and their carbonate stocks in the fine earth fraction 2 mm can be used as a relative dating tool and appear to correlate with regional glacial chronostratigraphy pinedale c 20 ky bull lake with two different units around 160 and 260 ky and sacagawea ridge c 660 ky carbonate stocks of soils on these terraces increase with increasing soil age but at generally decreasing rates a quasi steady state situation however was not reached before 1 my the time split approach showed that caco3 accumulation rates were the highest during marine isotope mis cold stages 2 13 g caco3 m2 y presumably due to a sparse vegetation cover during mis2 pinedale and 8 lower bull lake compared to organic carbon c 8 10 kg corg m2 the inorganic carbon stocks of the fine earth fraction were much higher c 60 kg cinorg m2 although the dominant pedogenic process here appears to be carbonate accumulation chemical weathering and elemental leaching also are significant weathering data were obtained using immobile elements and rare earth elements ree as tracers chemical weathering and related leaching were particularly notable for na originating from plagioclase in addition pedogenetic al and mn oxyhydroxides accumulate 220 and 32 g m2 respectively after 660 ky these form at relatively low rates however when compared to moister and cooler conditions at higher altitudes in the wind river range due to the dry climate under which the terrace soils formed annual precipitation 32 cm yr 1 weakly crystalline and amorphous fe oxyhydroxide is rapidly transformed into crystalline forms hematite over time consequently the stocks of weakly crystalline and amorphous fe oxyhydroxide was significantly lower in the 660 ky soils 50 g m2 than in the holocene soils 1000 g m2 the development of soils on quaternary outwash terraces in this region is controlled through the rates of aeolian influx over time as modified by glacial interglacial climate variations rather than by moisture availability consequently carbonate accumulation rates in these soils are influx limited rather than moisture limited

compound soil horizons with mixed calcic and argillic properties examples from the northern great basin usa abstract palaeosols between deposits of the last two deep lake cycles in the northern great basin have multiple carbonate engulfed horizons and compound calcic and argillic properties at depth they are difficult to explain pedogenetically because they bifurcate in places especially in basin centres where they are separated by sediments of a minor lake expansion of probable early wisconsinan age one sequence of processes can account for all phenomena two cycles of colluviation and synchronous admixture of loess particles were each succeeded by the formation of an argillic over a calcic horizon carbonate enrichment resulting from the later period of soil formation affected the buried older soil this led to welding of the two soils and the formation of a compound horizon carrying the argillic properties of the first and the calcic properties of the second pedogenic phase steady aeolian influx to the same soil surface the commonly invoked mechanism cannot explain the bifurcated palaeosols and is not needed to explain the welded ones