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

the loess and loess like deposits along the sides of the western mediterranean sea genetic and palaeoclimatic significance abstract the loess and loess like deposits on the northern and southern sides of the western mediterranean generally dating to the upper pleistocene are derived from aeolian mobilization of dust from local sources and from their sedimentation where trapped in a dense steppe environment these aeolian deposits however differ from each other as regards the nature of the source material the sedimentary processes and the post depositional weathering loess deposits are more frequent on the north side of the mediterranean where deposited in attenuated periglacial conditions than in north africa where they accumulated in peridesert areas during pluvial periods

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

late quaternary slip on the santa cruz island fault california the style timing and pattern of slip on the santa cruz island fault were investigated by trenching the fault and by analysis of offset late quaternary landforms a trench excavated across the fault at christi beach on the western coast of the island exposed deformation of latest pleistocene to holocene sediments and pre quaternary rocks recording repeated large magnitude rupture events the most recent earthquake at this site occurred ca 5 ka coastal terraces preserved on western santa cruz island have been dated using the uranium series technique and by extrapolation using terrace elevations and the eustatic record offset of terraces and other landforms indicates that the santa cruz island fault is predominantly left lateral having a horizontal slip rate of not more than 1 1 mm yr and probably about 0 8 mm yr the fault also has a smaller reverse component slipping at a rate of between 0 1 and 0 2 mm yr combined with measurements of slip per event this information suggests a long term average recurrence interval of at least 2 7 k y and probably 4 5 k y and average earthquake magnitudes of mw 7 2 7 5 sense of slip recurrence interval and earthquake magnitudes calculated here for the santa cruz island fault are very similar to recent results for other faults along the southern margin of the western transverse range including the malibu coast fault the santa monica fault the hollywood fault and the raymond fault supporting the contention that these faults constitute a continuous and linked fault system which is characterized by large but relatively infrequent earthquakes

optically stimulated luminescence dating of late quaternary loess deposits in the coastal region of north china provenance and paleoclimatic implications abstract the aeolian deposits in the coastal region of north china are important for reconstructing paleoclimate in this paper chronology climatic proxies and chemical compositions of four loess sections were studied optically stimulated luminescence osl dating results indicate that the coastal loess was accumulated during late quaternary with ages ranging from the penultimate glacial period to the latest holocene both granulometric characteristics and geochemical properties indicate that the dust provenance of the coastal loess is partially different from that of the chinese loess plateau characterized by more proximal contributions except distal dust transported by northwesterly winter winds from the inland gobi and sand deserts the coastal loess also contains proximal local coarse particles which were derived from the exposed shelf as well as neighboring hills multiple climatic proxies including color magnetic susceptibility and particle size parameters correlate well with the marine specmap 18o record indicating that climatic changes in the coastal region of north china during the late quaternary was mainly controlled by variations of the east asian monsoon driven by changes in global ice volumes

origin of bermuda s clay rich quaternary paleosols and their paleoclimatic significance red clayey paleosols that are chiefly the product of aerosolic dust deposition are interbedded in the quaternary carbonate formations of the bermuda oceanic island system these paleosols provide a basis for reconstructing quaternary atmospheric circulation patterns in the northwestern atlantic geochemical analyses were performed on representative paleosol samples to identify their parent dust source fine grained fractions were analyzed by energy dispersive x ray fluorescence to determine trace element zr y la ti and nb concentrations and to derive geochemical signatures based on immobile element ratios these ratios were compared with geochemical signatures determined for three possible sources of airborne dust 1 great plains loess 2 mississippi river valley loess and 3 saharan dust the zr y and zr la ratios provided the clearest distinction between the hypothesized dust sources the low ratios in the paleosol b horizons most closely resemble saharan dust in the 2 m size class fraction contributions from the two north american loessial source areas could not be clearly detected thus bermuda paleosols have a predominantly saharan aerosolic dust signature saharan dust deposition on bermuda during successive quaternary glacial periods is consistent with patterns of general circulation models which indicate that during glacial maxima the northeast summer trade winds were stronger than at present and reached latitudes higher than 30on despite lower than present sea surface temperatures in the north atlantic

geochemical evidence for airborne dust additions to soils in channel islands national park california there is an increasing awareness that dust plays important roles in climate change biogeochemical cycles nutrient supply to ecosystems and soil formation in channel islands national park california soils are clay rich vertisols or alfi sols and mollisols with vertic properties the soils are overlain by silt rich mantles that contrast sharply with the underlying clay rich horizons silt mantles contain minerals that are rare or absent in the volcanic rocks that dominate these islands immobile trace elements sc th la and ta nd cr and rare earth elements show that the basalt and andesite on the islands have a composition intermediate between upper continental crust and oceanic crust in contrast the silt fractions and to a lesser extent clay fractions of the silt mantle have compositions closer to average upper continental crust and very similar to mojave desert dust island shelves exposed during the last glacial period could have provided a source of eolian sediment for the silt mantles but this is not supported by mineralogical data we hypothesize that a more likely source for the silt rich mantles is airborne dust from mainland california and baja california either from the mojave desert or from the continental shelf during glacial low stands of sea although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin the eolian silt mantles constitute an important medium of plant growth and provide evidence that abundant eolian silt and clay may be delivered to the eastern pacifi c ocean from inland desert sources

source regions and formation of the loess sediments on the high mountain regions of northwestern china loess on the high mountains of northwestern china is largely controlled by the topographic features distributed mainly on the northern slopes of the tianshan and kunlun mountains as well as in the ili valley between the northern and central tianshan ranges loess distributed in different regions has different ages with the oldest early pleistocene loess occurring in the ili valley geochemical mineralogical and granulometric analyses demonstrate that the loess in the three different regions has different provenance the loess on the northern tianshan and kunlun mountains is mainly derived from the junggar and taklimakan deserts respectively whereas the loess in the ili valley is derived mainly from the sary ishikotrau desert located in the republic of kazakhstan however these deserts serve mostly as holding areas for the silts rather than original source regions the production of the silt sized particles is mainly associated with glacial abrasion and tectonic induced rock denudation thus the loess in the studied regions can be described as mountainous loess rather than simply glacial loess or desert loess it is unlikely that the mechanisms of loess formation are the same in different regions given their dependence on specific geomorphological conditions and associated processes

geochemical variations in peoria loess of western iowa indicate paleowinds of midcontinental north america during last glaciation peoria loess deposited in western iowa during the last glacial maximum lgm shows distinct geochemical and particle size variations as a function of both depth and distance east of the missouri river geochemical and particle size data indicate that peoria loess in western iowa probably had two sources the missouri river valley and a source that lay to the west of the missouri river both sources indicate that lgm paleowinds in western iowa had a strong westerly component similar to interpretations of previous workers a compilation of loess studies in iowa and elsewhere indicates that westerly winds were dominant during loess transport over much of the midcontinent south of the laurentide ice sheet which is not in agreement with paleowinds simulated by atmospheric general circulation models agcms agcms consistently generate a glacial anticyclone with easterly or northeasterly winds over the laurentide ice sheet and the area to the south of it loess deposition in the midcontinent during the lgm may be a function of infrequent northwesterly winds that were unrelated to the presence of the glacial anticyclone

the geochemistry of loess asian and north american deposits compared abstract loess is widely distributed over asia and north america and constitutes one of the most important surficial deposits that serve as terrestrial records of the quaternary the oldest pleistocene loess in china is likely 2 6 ma thus spanning much or all of the pleistocene in north america most loess is no older than the penultimate glacial period with the exception of alaska where the record may go back to 3 0 ma on both continents loess deposits date primarily to glacial periods and interglacial or interstadial periods are represented by paleosols both glacial and non glacial sources of silts that comprise the bulk of loess deposits are found on both continents although loess has been considered to be representative of the average upper continental crust there are regionally distinctive compositions of loess in both asia and north america loess deposits in asia from yakutia tajikistan and china have compositionally distinct major element compositions due to varying abundances of silicate minerals carbonate minerals and clay minerals in north america loess in the mississippi river valley the great plains and alaska are also distinguishable with regard to major element composition that reflects highly diverse source sediments trace element geochemistry sc th zr and the rare earth elements also shows regional diversity of loess bodies in both asia and north america on both continents most loess bodies show significant contributions from later cycle altered sedimentary rocks as opposed to direct derivation from igneous rocks further some loess bodies have detectable contributions from mafic igneous rocks as well as major contributions from average upper crustal felsic rocks intercalated paleosols in loess sections show geochemical compositions that differ significantly from the underlying loess parent materials ratios of soluble to insoluble elements show depletions in paleosols due to chemical weathering losses of calcite dolomite plagioclase mica apatite and smectite in asia and north america the last interglacial paleosol is more weathered than equivalent modern soils which could be due either to a climate that was warmer and more humid a longer period of pedogenesis or both in asia early pleistocene loess and paleosols are both more weathered than those from the middle and late pleistocene forming prior to a mid pleistocene aridification of asia from uplift of the tibetan plateau understanding the geochemistry of loess and paleosols can tell us much about past atmospheric circulation past temperature and moisture regimes and even tectonic processes

atmospheric dust in modern soil on aeolian sandstone colorado plateau usa variation with landscape position and contribution to potential plant nutrients rock derived nutrients in soils originate from both local bedrock and atmospheric dust including dust from fardistant sources distinction between fine particles derived from local bedrock and from dust provides better understanding of the landscape scale distribution and abundance of soil nutrients sandy surficial deposits over dominantly sandstone substrates covering vast upland areas of the central colorado plateau typically contain 5 40 silt plus clay depending on geomorphic setting and slope excluding drainages and depressions aeolian dust in these deposits is indicated by the presence of titanium bearing magnetite grains that are absent in the sedimentary rocks of the region thus contents of far traveled aeolian dust can be estimated from magnetic properties that primarily reflect magnetite content such as isothermal remanent magnetization irm isothermal remanent magnetization was measured on bulk sediment samples taken along two transects in surficial sediment down gentle slopes away from sandstone headwalls one transect was in undisturbed surficial sediment the other in a setting that was grazed by domestic livestock until 1974 calculation of far traveled dust contents of the surficial deposits is based on measurements of the magnetic properties of rock surficial deposits and modern dust using a binary mixing model at the undisturbed site irm based calculations show a systematic down slope increase in aeolian dust ranging from 2 to 18 of the surface soil mass similar to the down slope increase in total fines 18 39 of surface soil mass a combination of winnowing by wind during the past and down slope movement of sediment likely accounts for the modern distribution of aeolian dust and associated nutrients at the previously grazed site dust also increases down slope 5 11 in sediment with corresponding abundances of 13 25 fines estimates of the contributions of aeolian dust to the total soil nutrients range widely depending on assumptions about grain size partitioning of potential nutrients in weathered bedrock nevertheless aeolian dust is important for this setting contributing roughly 40 80 of the rock derived nutrient stocks p k na mn zn and

dust accumulation in the new zealand region since the last glacial maximum abstract loess is widespread in new zealand deposits 1 m thick cover 10 of the land area it has mainly been derived from dust deflated from river floodplains during the last glacial maximum lgm dust accumulation continues today downwind of major river floodplains most loess is quartzofeldspathic having its origins in mesozoic and neogene rocks of the axial ranges and hill country in the central north island there are deposits of volcanic loess derived from aeolian reworking of tephras loess morphology and properties vary greatly due to diverse parent materials post depositional climates and drainage conditions the widespread 26 170 cal yr kawakawa tephra provides a datum for calculating mass accumulation rates mars rates are mostly within the range 70 150 g m 2 yr 1 but enhanced deposition at one site gave a rate of 360 g m 2 yr 1 contemporary mars of 40 100 g m 2 yr 1 were determined for distances of 1 75 0 4 km downwind of the rakaia river lgm mars of quartz for two marine cores p69 q858 drilled 100 300 km east of new zealand are 40 70 g m 2 yr 1 the mar of the aeolian component of p69 is estimated to be ca 15 g m 2 yr 1

geochemical and mineralogical evidence for sahara and sahel dust additions to quaternary soils on lanzarote eastern canary islands spain africa is the most important source of dust in the world today and dust storms are frequent on the nearby canary islands previous workers have inferred that the sahara is the most important source of dust to canary islands soils with little contribution from the sahel region soils overlying a late quaternary basalt flow on lanzarote canary islands contain in addition to volcanic minerals quartz and mica exotic to the island s bedrock kaolinite in the soils also likely has an exotic origin trace element geochemistry shows that the soils are derived from varying proportions of locally derived basalt and african dust major element geochemistry clay mineralogy and interpretation of satellite imagery suggest that dust additions to the canary islands come not only from the sahara desert but also from the sahel region

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

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

cambrian acritarchs from the bourinot belt cape breton island nova scotia age and stratigraphic implications1this article is one of a series of papers published in cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology we present the first description of organic walled microfossils from cambrian strata of the bourinot belt central cape breton island age diagnostic acritarchs have been recovered from the dugald

late quaternary monsoon patterns on the loess plateau of china china s loess plateau was formed under special conditions the tectonic movement topographical characteristics and monsoon patterns combined to create a favourable environment for the accumulation of thick loessic deposits the loess plateau itself is part of the monsoon triangle of china a region very susceptible to climatic changes throughout the upper pleistocene the palaeoenvironment on the loess plateau alternated from steppe to deciduous forest and coniferous forest in response to shifts in the atmospheric circulation three monsoon patterns appear to be indicated 1 a full glacial monsoon pattern 18000 15000 yr bp which induced a cold and dry climate favouring loess accumulation in steppe conditions 2 an interglacial monsoon pattern last interglacial and holocene in which a warm humid climate prevailed with deciduous forests leaving palaeosols interbedded within the loess sequence and 3 a transitional or interstadial monsoon pattern 50 000 23 000 yr bp in which the climate was cold and humid in the loess plateau encouraging the development of coniferous forest

geochemistry of eolian dust in pacific pelagic sediments implications for paleoclimatic interpretations geochemical data rees th sc were determined for the operationally defined eolian dust oded fraction 63 m of late quaternary sediment samples n 57 from the north and equatorial pacific ocean paleoclimate studies commonly have assumed that this sediment fraction represents eolian materials from continental source regions this study shows on the basis of geochemical data published mineralogical data and mixing models that the oded fraction actually is a mixture of materials from two endmember sources the continental crust eolian transported weathering products and the oceanic crust primarily volcanogenic material mixing model results show that the average ash content is significant in the oded fraction equatorial pacific 43 north pacific 24 we have used this information to reconsider and refine the results of previous paleoclimate studies in the northwest pacific the flux of the eolian fraction is greater during glacial stages and shows a latitudinal maximum between 35 n and 42 n eolian fluxes are greatest during interglacial periods in the equatorial pacific these results are consistent with previous interpretations in contrast to previous assumptions eolian mass accumulation rates may not be a valid indicator of paleo aridity because they are correlated with grain size furthermore the relative abundance of the two endmembers is correlated with the average grain size of the dust fraction the continental crust component is associated with larger grains this compositional effect should be considered in future studies which commonly utilize grain size as a proxy indicator of paleo wind intensity

rates and processes of soil development on quaternary terraces in cajon pass california field and laboratory analyses of soils on 11 well dated fluvial terraces spanning the past 0 5 m y demonstrate that a threshold governs changes in several morphological and chemical characteristics of increasingly older soils correlations with respect to time among iron species soil morphology and soil silt and clay demonstrate that the chronosequence at cajon pass reflects primarily an evolutionary largely time dependent trend and does not reflect differences in external factors such as climate most of the soil development on holocene terraces of the cajon pass area is due to physical incorporation of eolian dust and organic material into initially very permeable gravels this process decreases soil permeability and is conducive for an increase in the magnitude of chemical weathering latest pleistocene and older pleistocene soils have developed clay and authigenic iron oxide rich b horizons at the expense of organic matter rich a horizons and color b horizons as the extent of chemical weathering has increased this conversion of the soil from a noncolloidal system to a much more colloidal system takes place over a relatively short period of time 4 000 yr and is herein defined as a type of pedologic threshold in the cajon pass area the attainment of the threshold and subsequent development of the argillic b horizon of soils on latest pleistocene terraces occurred during the holocene thus the absence of argillic horizons in soils on holocene terraces is attributable to simply their younger age rather than to the pleistocene to holocene climatic change the threshold is a function of several variables including influx rate of eolian dust and initial soil permeability therefore the time required to attain the threshold will vary in chronose quences characterized by geomorphic or geographic settings that are different from conditions found in cajon pass

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

geochemical evidence for the origin of late quaternary loess in central alaska loess is extensive in central alaska but there are uncertainties about its source and the direction of paleo winds that deposited it both northerly and southerly winds have been inferred the most likely sources of loess are the tanana river south the nenana river southeast and the yukon river north late quaternary loess in central alaska has immobile trace element compositions cr sc th ta th sc th u eu eu gdn ybn that indicate derivation mostly from the tanana river however other ratios as sb zr hf lan ybn and quantitative modeling indicate that the yukon river was also a source during the last glacial period there may have been a longer residence time of the siberian and canadian high pressure cells along with a strengthened aleutian low pressure cell this would have generated regional scale northeasterly winds and explains derivation of loess from the yukon river however superim posed upon this synoptic scale circulation there may have been strong southerly katabatic winds from expanded glaciers on the northern flank of the alaska range these winds could have provided eolian silt from the tanana river yukon river and tanana river sediments are highly calcareous whereas fairbanks area loess is not this suggests that carbonate leaching in loess kept ahead of sedimentation and that late quaternary loess in central alaska was deposited relatively

a cool eastern pacific ocean at the close of the last interglacial complex abstract new high precision thermal ionization mass spectrometric tims u series ages of solitary corals balanophyllia elegans from several marine terrace localities along the california and southern oregon coasts date to the 80 000 yr bp high stand of sea correlative with marine isotope substage 5a late in the last interglacial complex ages of multiple corals from localities north of point ano nuevo central california and san nicolas island southern california suggest that this high sea stand could have lasted at least 8000 yr from 84 000 to 76 000 yr bp these ages overlap with those from marine deposits on tectonically stable bermuda and tectonically emergent barbados higher elevation terraces at two california localities in the palos verdes hills and on san nicolas island have corals with ages that range mostly from 121 000 to 116 000 yr bp correlative with marine isotope substage 5e these ages are similar to those reported for other terraces in southern california but are younger than some ages reported from hawaii barbados and the bahamas marine terrace faunas are excellent proxies for nearshore marine paleotemperatures during past high sea stands terraces on the palos verdes hills and san nicolas island dated to the 120 000 yr bp high sea stand have dominantly zoogeographically neutral species in exposed coastal localities indicating nearshore waters similar to those of today in contrast 80 000 yr bp exposed coastal localities typically have molluscan faunas characterized by numerous extralimital northern species and a lack of extralimital southern species these fossil assemblages are indicative of nearshore water temperatures that were cooler than modern temperatures at 80 000 yr bp waters at least as warm as today s at 120 000 yr bp and cooler than present at 80 000 yr bp are in excellent agreement with marine alkenone records and coastal vegetation records derived from pollen data from both southern and northern california decreased insolation or increased upwelling seem inadequate to explain the cool waters off the pacific coast from southern oregon to southern california at 80 000 yr bp we propose that a stronger california current or at least one with a greater component of subarctic waters may explain cooler than modern coastal waters during the 80 000 yr bp high sea stand

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

a soil chronosequence on quaternary marine terraces san clemente island california a soil chronosequence on marine terraces was examined on san clemente island california in an arid mediterranean climate in order to see which soil properties differ most systematically with time ages of the geomorphic surfaces were determined by radiocarbon uranium series and amino acid racemization techniques and range from 1 000 000 yrs soils on surfaces 200 000 yrs old are vertisols or alfisols with vertic properties such as slickensides and cracks and they exhibit both prismatic and angular blocky sphenoidal or only angular blocky structure solum thickness increases linearly with age of geomorphic surface clay soluble salts ald smectite mica ratios in the clay fraction and quartz plagioclase ratios in the silt fraction when expressed as profile summations show increases with age of geomorphic surface the best fit regression equations are linear with the exception of ald which is best expressed as a power function important soilforming processes appear to be alteration of mica to smectite accumulation at depth of soluble salts derived from marine aerosols possibly additions of eolian materials clay illuviation in the younger soils and pedoturbation in the older soils the observations reported here allow the following conclusions to be drawn about soils in this environment 1 certain soil properties which show distinct trends with time can be used for relative age dating in geomorphic and stratigraphic studies 2 soils have not reached a steady state condition with respect to many of their properties and 3 alfisols and mollisols with natric b horizons may be precursors to vertisols

atmospheric mineral dust in dryland ecosystems applications of environmental magnetism irm mean of 67 samples 6 72 10 3 am 2 kg 1 is more than two orders of magnitude greater than that for underlying paleozoic and mesozoic sedimentary rocks this contrast is mainly caused by the presence of silt size titanium bearing magnetite particles in the surficial deposits and their absence in bedrock because of their size composition and isolated location the magnetite particles represent a component of atmospheric dust likely deposited over the past few centuries the positive correlation of sediment irm values with amounts of potential plant nutrients reveals the importance of atmospheric dust to soil fertility over much of the american southwest subsequent disturbance of landscapes by domestic livestock grazing as an example commonly results in wind erosion which then depletes exposed surfaces of original aeolian magnetite and associated fine grained sediment declines in soil fertility and water holding capacity in these settings can be estimated in some field settings via decreases in magnetic susceptibility relative to nearby undisturbed areas along gentle hillslope gradients of the colorado plateau field measures for aeolian magnetite demonstrate that the redistribution of deposited atmospheric dust influences landscape level patterns in the distribution of invasive exotic plant species our results indicate that environmental magnetism has high potential for assessing the development and degradation of dry landscapes elsewhere

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

airborne dust transport to the eastern pacific ocean off southern california evidence from san clemente island 1 islands are natural dust traps and san clemente island california is a good example soils on marine terraces cut into miocene andesite on this island are clay rich vertisols or alfisols with vertic properties these soils are overlain by silt rich mantles 5 20 cm thick that contrast sharply with the underlying clay rich subsoils the silt mantles have a mineralogy that is distinct from the island bedrock silt mantles are rich in quartz which is rare in the island andesite the clay fraction of the silt mantles is dominated by mica also absent from local andesite and contrasts with the subsoils dominated by smectite ternary plots of immobile trace elements sc th la and ta nd cr show that the island andesite has a composition intermediate between average upper continental crust and average oceanic crust in contrast the silt and to a lesser extent clay fractions of the silt mantles have compositions closer to average upper continental crust the silt mantles have particle size distributions similar to loess and mojave desert dust but are coarser than long range transported asian dust we infer from these observations that the silt mantles are derived from airborne dust from the north american mainland probably river valleys in the coastal mountains of southern california and or the mojave desert although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin examination of satellite imagery shows that easterly santa ana winds carry abundant dust to the eastern pacific ocean and the california channel islands airborne dust from mainland north america may be an important component of the offshore sediment budget in the easternmost pacific ocean a finding of potential biogeochemical and climatic significance

the last interglacial period on the pacific coast of north america timing and paleoclimate new high precision u series ages of solitary corals balanophyllia elegans coupled with molluscan faunal data from marine terraces on the pacific coast of north america yield information about the timing and warmth of the last interglacial sea level highstand balanophyllia elegans takes up u in isotopic equilibrium with seawater during growth and shortly after death corals from the second terrace on san clemente island offshore southern california the third terrace on punta banda on the pacific coast of northern baja california and the discovery point formation on isla de guadalupe in the pacific ocean offshore baja california date to the peak of the last interglacial period and have u series ages ranging from ca 123 to 114 ka the first terrace on punta banda has corals with ages ranging from ca 83 to 80 ka which corresponds to a sea level highstand formed in the late last interglacial period u series analyses of corals from the cayucos terrace central california and the nestor terrace at point loma southern california show that these fossils have evidence of open system history similar to what has been reported by other workers for the same localities nevertheless a model of continuous secondary u and th uptake shows that two ages of corals are likely present at these localities representing the ca 105 and ca 120 ka sea level highstands reported elsewhere u series ages of last interglacial corals from the pacific coast overlap with but are on average younger than the ages of corals from barbados the bahamas and hawaii this age difference is explained by the nature of the geomorphic response to sea level change fringing or barrier reefs on low latitude coastlines have an accretionary growth style that keeps pace with rising sea level whether on a tectonically rising or stable coastline in contrast midlatitude high energy coastlines are sites of platform cutting during the early part of a sea level high stand and terrace scouring and concomitant sediment and fossil deposition as sea level starts to recede the youngest ages of corals from the pacific coast suggest that sea level was still relatively high at ca 116 ka which is not in agreement with other estimates of relatively large global ice volume at that time reliably dated ca 120 ka marine terrace deposits on the pacific coast have fossil mollusks that indicate water temperatures as warm or warmer than at present in contrast ca 80 ka marine deposits reported here and elsewhere have fossil mollusks indicating cooler than modern water temperatures the presence of both ca 105 ka and ca 120 ka corals on the nestor and cayucos terraces explains a previously enigmatic mixture of warm water and cool water mollusks at ca 105 ka a relatively high sea level with cool waters may have captured the terrace formed during the 120 ka sea level highstand in areas of low uplift rate the inference of cooler than modern waters off the pacific coast of north america at ca 80 ka and ca 105 ka based on marine terrace faunas does not agree with estimates of sea surface temperatures derived from alkenone studies in the santa barbara basin however cooler water temperatures at these times are in agreement with paleotemperature estimates from planktonic foraminiferal data for the santa barbara basin all records from central california to baja california whether from marine terraces or offshore cores indicate at least seasonably warmer than modern waters during the peak of the last interglacial period at ca 120 ka

aeolian origin and palaeoclimatic implications of the red clay north china as evidenced by grain size distribution the red clay is an important deposit underlying the quaternary loess palaeosol sequence in the chinese loess plateau being regarded as an excellent record of palaeoclimate changes in the late tertiary several properties of the red clay have been measured previously in order to derive climatic information however the sedimentary processes involved and the origin of the materials remain controversial here we present results of grain size analyses of the red clay from four representative sites in the chinese loess plateau in particular their grain size distribution is compared with that of typical quaternary aeolian loess palaeosol as well as lacustrine and fluvial sediments it appears from the sedimentological evidence that the major part of the red clay is of aeolian origin it is rather similar in some of its properties to the quaternary loessic palaeosols the dust forming the red clay was transported by a wind system that was weaker than that involved in the accretion of the quaternary loess furthermore the red clay sediment has been modified by post depositional weathering copyright 2001 john wiley sons ltd

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

last glacial loess in the conterminous usa the conterminous united states contains an extensive and generally well studied record of last glacial loess the loess occurs in diverse physiographic provinces and under a wide range of climatic and ecological conditions both glacial and non glacial loess sources are present and many properties of the loess vary systematically with distance from loess sources united states midcontinent last glacial loess is probably the thickest in the world and our calculated mass accumulation rates mars are as high as 17 500 g m 2 yr at the bignell hill locality in nebraska and many near source localities have mars greater than 1500 g m 2 yr these mars are high relative to rates calculated in other loess provinces around the world recent models of last glacial dust sources fail to predict the extent and magnitude of dust flux from the mid continent of the united states a better understanding of linkages between climate ice sheet behaviour routing of glacial meltwater land surface processes beyond the ice margin and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region r 2003 elsevier ltd all rights reserved

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

timing and origin for sand dunes in the green river lowland of illinois upper mississippi river valley usa abstract the recent increase in dune studies in north america has been heavily focused in the great plains while less attention has historically been given to the dune fields east of the mississippi river here we report ages and suggest a potential sediment source for sand dunes in the green river lowland illinois which may provide a better understanding of the dynamic interactions between eolian glacial lacustrine and fluvial processes that shaped the landscapes of the upper midwest seven coherent optically stimulated luminescence ages osl or optical ages obtained from four sites suggest that major dune construction in the green river lowland occurred within a narrow time window around 17 500 ago this implies either an enhanced aridity or an episodic increase of sediment supply at 17 500 years ago or combination of the both contrary to previous assertions that dune sand was sourced from the deflation of the underlying outwash sand deposited when the lake michigan lobe retreated from the area we propose that green river lowland dunes sand originated from the green bay lobe through the rock river specifically sediment supply increased in the rock river valley during drainage of glacial lake scuppernong which formed between 18 000 and 17 000 years ago when the green bay lobe retreated from its terminal moraine the lake drained catastrophically through the rock river valley providing glacial sediment and water to erode the preexisting sandy sediments throughout the remainder of the late pleistocene the laurentide ice sheet drained into larger more northerly glacial lakes that in turn drained through other river valleys therefore the dunes in the green river lowland formed only during the catastrophic drainage of glacial lake scuppernong but were stabilized through the remainder of the pleistocene this scenario explains the abrupt dune construction around 17 500 years ago and explains the lack of later dune activity up to the pleistocene holocene transition osl and radiocarbon ages also indicate that dunes were reactivated during the early middle and late holocene some eolian activation occurred within well defined dry intervals in the upper midwest suggesting that increased aridity may have been the primary driver in mobilizing sand however many ages do not correspond to drier periods in contrast to the relative coherency of the pleistocene osl ages from multiple study sites the holocene osl ages do not overlap from one site to another suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation in the holocene therefore we conclude that the combined effect of localized disturbances and greater aridity acted in concert to increase eolian sand activity in the holocene the multiple periods of eolian activity during the holocene suggest a high potential for future sand activation in the region and these results are informative for environmental prediction and potential future mitigation

grain size variation on dunes in the southwest kalahari southern africa abstract grain size parameters mean standard deviation skewness and kurtosis were determined for 83 sediment samples from six dune cross profiles and one 28 km long profile on dunes in the southwest kalahari desert in southern africa although some studies elsewhere and previous studies in the kalahari have reported significant grain size variation over dune cross profiles data presented here show no systematic variation of grain size parameters except that sediments from the crest of a dune are almost invariably better sorted indicated by the standard deviation of the sample than samples from the base or plinth of the dune the proportion of fines 63 m in plinth sediments is also greater than in crest samples there is no significant trend in grain size parameters along the length of a linear dune this lack of significant pattern corresponds with similar findings for central australian dunes

evidence for the timing and duration of the last interglacial period from high precision uranium series ages of corals on tectonically stable coastlines the last interglacial period has a timing and duration that can be estimated from u series dating of emergent coral bearing deposits on tectonically stable coastlines high precision dating from bermuda the bahamas hawaii and australia suggests that the last interglacial period had a sea level at least as high as present from 128 000 to 116 000 yr b p sea level reached a near present level more quickly after the close of the penultimate glacial period than at the close of the last glacial period and the duration of high sea level is longer than that implied by the deep sea record c 2002 university of washington

holocene loess deposition and soil formation as competing processes matanuska valley southern alaska although loess paleosol sequences are among the most important records of quaternary climate change and past dust deposition cycles few modern examples of such sedimentation systems have been studied stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the matanuska valley in southern alaska show that loess deposition there began sometime after f6500 14 c yr b p and has continued to the present the silts are produced through grinding by the matanuska and knik glaciers deposited as outwash entrained by strong winds and redeposited as loess over a downwind distance of f40 km loess thickness sand content and sand pluscoarse silt content decrease whereas fine silt content increases loess deposition was episodic as shown by the presence of paleosols at distances 10 km from the outwash plain loess source stratigraphic complexity is at a maximum i e the greatest number of loesses and paleosols at intermediate 10 25 km distances from the loess source surface soils increase in degree of development with distance downwind from the source where sedimentation rates are lower proximal soils are entisols or inceptisols whereas distal soils are spodosols ratios of mobile cao k2o and fe2o3 to immobile tio2 show decreases in surface horizons with distance from the source thus as in china where loess deposition also takes place today eolian sedimentation and soil formation are competing processes study of loess and paleosols in southern alaska shows that particle size can vary over short distances loess deposition can be episodic over limited time intervals and soils developed in stabilized loess can show considerable variability under the same vegetation d 2004 university of washington all rights reserved

relations between morphology air flow sand flux and particle size on transverse dunes taklimakan sand sea china field experiments on two isolated transverse dunes with different scales in the taklimakan sand sea show that particle size and slope control the threshold shear velocity and sand flows on the stoss of the dunes the decreased threshold shear velocity and the unsaturated sand flows are the main reasons why sands are not deposited at the toe of the dunes the particle size controls sand flux through its influence on the aerodynamic roughness elements and threshold shear velocities the sand flux is different for dune surfaces with different particle size distributions under the control of the medium to low stress of the drifting sand winds the results of the field experiments and particle size analysis showed that sand transport had little influence on the particle size distributions the mean particle size being transported on the stoss is lower than that on the dune surface it is difficult to determine whether or not the wind is fully saturated with sands when sand flux calculation is mainly dependent on the shear velocity and the mean particle size the sands within some range of the particle size are transported and developed into simple transverse dunes and then the interdune surface is coarsened and alternated with the draas in the taklimakan sand sea copyright 2002 john wiley sons ltd

fault related fold growth and isostatic subsidence california channel islands in the northern channel islands of california preservation of paleo shoreline features both as uplifted landforms onshore and subsided depositional features offshore has allowed precise measurement of late quaternary fold growth relative to sea level and has helped to disentangle the relative contributions of tectonic forcing and isostatic response we precisely measured several hundred points on uplifted pleistocene coastal terraces of santa cruz and anacapa islands the elevations of which document anticlinal growth of the islands since at least 400 ka we also interpreted a dense grid of seismic reflection profiles that image a complex of eustatic lowstand deltas that record regional subsidence surrounding the uplifting structure we combined onshore uplift with offshore subsidence measurements to produce a quantitative mass balance of structural growth since 400 ka the data outlined above were then used to test the hypothesis that subsidence around the northern channel islands represents the flexural isostatic response to tectonic loading of the islands calculations of cumulative uplifted mass and cumulative subsided mass across the structure closely match the values predicted for density driven isostatic compensation and local flexural support although the wavelength of flexure predicted for the study area suggests that an additional component of flexural support may extend distally 10s of kilometers into the surrounding offshore basins in the northern channel islands isostatic subsidence is explicitly manifested because erosional mass removal is small because the crust here is relatively thin and weak and most importantly because sea level provides an absolute datum against which to measure vertical deformation an explicit treatment of the interplay between crustal thickening erosional denudation surface uplift and isostatic response helps to illustrate the conditions under which isostatic subsidence may or may not be a significant process where surface denudation rates approach the rate of rock uplift for example isostatic subsidence will approach zero in contrast failure to recognize isostatic subsidence in earthquake hazard studies can lead to order of magnitude errors in slip rate and hazard estimates

sr nd isotopic characteristics of the northeast sandy land china and their implications for tracing sources of regional dust abstract the sr nd isotopic study of the northeast sandy land nesl china is of great significance for a thorough understanding of the dust system in this area the 162 bulk

geochemical evidence for african dust inputs to soils of western atlantic islands barbados the bahamas and florida 1 we studied soils on high purity limestones of quaternary age on the western atlantic ocean islands of barbados the florida keys and the bahamas potential soil parent materials in this region external to the carbonate substrate include volcanic ash from the island of st vincent near barbados volcanic ash from the islands of dominica and st lucia somewhat farther from barbados the fine grained component of distal loess from the lower mississippi river valley and wind transported dust from africa these four parent materials can be differentiated using trace elements sc cr th and zr and rare earth elements that have minimal mobility in the soil forming environment barbados soils have compositions that indicate a complex derivation volcanic ash from the island of st vincent appears to have been the most important influence but african dust is a significant contributor and even mississippi river valley loess may be a very minor contributor to barbados soils soils on the florida keys and islands in the bahamas appear to have developed mostly from african dust but mississippi river valley loess may be a significant contributor our results indicate that inputs of african dust are more important to the genesis of soils on islands in the western atlantic ocean than previously supposed we hypothesize that african dust may also be a major contributor to soils on other islands of the caribbean and to soils in northern south america central america mexico and the southeastern united states dust inputs to subtropical and tropical soils in this region increase both nutrient holding capacity and nutrient status and thus may be critical in sustaining vegetation

geoarchaeological and chronometrical evidence of early human occupation on lanzarote canary islands abstract two desert loess paleosol sequences in sediment traps were investigated using pedo stratigraphy sedimentology soil mineralogy and irsl dating so far we cannot recognise significant irsl age underestimates from the polymineral fine grain fraction of our samples we establish a first palaeoclimatic sequence spanning the past ca 200 ka which can be compared to data from other canary islands and surrounding areas including terrestrial and deep sea records more humid phases on lanzarote are apparently triggered by milankovich forcing but the climate remained semi arid to arid all over the past 200 ka the onset of human occupation of the island during a slightly moister period is bracketed between 5 and 10 ka based on the occurrence of archaeosediments containing bones of ovicaprid this is the first proof of much earlier occupation than witnessed so far from archaeological records the early subsidiary economy had a strong impact on soil stability and landscape shaping of the island

geochemistry of sediments from the huaibei plain east china implications for provenance weathering and invasion of the yellow river into the huaihe river abstract the sediments of the huaibei plain in semi humid mid eastern china represent valuable geological records with respect to eolian fluvial interactions depositional environments and climate change in this region provenance and weathering conditions are often reconstructed using sedimentary geochemistry methods in this study an 8 m core from huainan and a set of loess samples from northern and southern china were analyzed for major trace and rare earth elements rees results were compared to determine the samples provenance the major trace rare earth elements contents and grain size distribution were found to fluctuate widely in the 2 8 m section of the huainan core and more narrowly closer to the surface 0 2 m this suggests a provenance shift at a depth of 2 m the tio 2 al 2 o 3 sio 2 al 2 o 3 th nb la nb values and ree patterns in the upper core 0 2 m are similar to those found in samples from the chinese loess plateau clp these results suggest that the clp in northern china is likely to be the primary origin of the upper part 0 2 m of the huainan core compared with clp samples the upper part of the huainan core exhibits lower k 2 o al 2 o 3 values and higher chemical alteration indices this is indicative of the material s substantial weathering during transportation and re deposition and implies that these sediments could reasonably be classified as typical recycled loess the sediments may have been transported from the clp to huainan as yellow river flood events probably during the last deglaciation 13 2 ka as a result of increased precipitation along with glacier and snow melt in the upper reaches of the yellow river catchment during this period this suggests that the yellow river may have migrated into the huaihe river catchment much earlier than the earliest historical records 361 bce suggest the implications of this would be profound with respect to chinese history

aeolian dust in colorado plateau soils nutrient inputs and recent change in source aeolian dust windblown silt and clay is an important component in arid land ecosystems because it may contribute to soil formation and furnish essential nutrients few geologic surfaces however have been characterized with respect to dust accumulation history and resultant nutrient enrichment we have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes unconsolidated sandy sediment on isolated surfaces in the canyonlands region of the colorado plateau differs greatly in mineralogical and chemical composition from associated bedrock mainly aeolian sandstone detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility but magnetite is absent in nearby bedrock a component of the surficial deposits must be aeolian to account for the abundance of magnetite which formed originally in far distant igneous rocks particle size analysis suggests that the aeolian dust component is typically as much as 20 30 dust inputs have enriched the sediments in many elements including p mg na k and mo as well as ca at sites where bedrock lacks calcite cement soil surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades some of the recently fallen dust may result from human disturbance of land surfaces that are far from the canyonlands such as the mojave desert some land use practices in the study area have the potential to deplete soil fertility by means of wind erosion removal of aeolian silt

australian dust deposits modern processes and the quaternary record abstract dust raising and transport are common and important processes in australia today the aridity of the australian continent and high climatic variability result in widespread dust raising in the arid and semi arid areas and transport to the humid margins and surrounding oceans the supply of erodible particles appears to be the greatest limitation on total flux of transported dust dust raising is greatest in the lake eyre basin including the simpson desert and murray darling basin where internal drainage renews supplies of fine particles to the arid zone in the west and northwest dust entrainment is low despite considerable aridity the marine record of dust flux shows at least a threefold increase in dust flux compared with the holocene in the last glacial maximum in both tropical and temperate australia driven by weakened australian monsoon rains and drier westerly circulation respectively despite the widespread confirmation of aeolian dust deposits in southeastern and southwestern australia dated or quantified records are extremely rare the dominant model of australian dust deposits the clay rich parna is shown to be poorly substantiated while modern and ancient dust deposits examined in detail are shown to bear a strong similarity to conventional definitions of loess

secular geochemical variations of the lower cretaceous siliciclastic rocks from central tibet china indicate a tectonic transition from continental collision to back arc rifting abstract fifty five lower cretaceous siliciclastic rocks from central tibet were analyzed for major and trace elements in an attempt to evaluate their provenance and the type of tectonic setting in which they were deposited the spatial temporal variation of both sediment maturity indices sio 2 al 2 o 3 la v and zr tio 2 the ratios of immobile trace elements cr th th sc th co la sc and la co and sio 2 k 2 o na 2 o eu eu gd yb n and ferromagnesian contents displays that the berriasian valanginian bv sediment could have been derived from northern orogenic source areas whereas the hauterivian lower barremian hb sediment could have been closely related to the syndepositional volcanism in the northern lhasa block itself the na 2 o al 2 o 3 k 2 o al 2 o 3 relations also place approximately half of hb samples in the field of volcanic rocks of back arc rifting origin whereas little volcanic clasts exist in the bv rocks there are distinct signatures that the mafic ultramafic materials in the bv rocks were derived from oceanic island basalts ophiolites in the bangong nujiang suture therefore the collisional orogen due to the qiangtang lhasa collision should have played a key role in supply of the sediments during bv time bimodal sedimentary basaltic and rhyolitic tuffs with respective distinguished geochemical features exist in the hb sequence therefore a distinct tectonic transition from continental collision to back arc rifting in central tibet is believed to have occurred during early cretaceous time extreme depletion of na of most lower cretaceous samples compared to the upper crust and their high average chemical index alteration cia values and th u ratios point out the source rocks formed in tropical climatic regions with little tectonic uplift although the weathering degree of the source rocks for hb samples could likely have been affected by the syndepositional volcanism during middle cretaceous time the entire southern eurasian margin could have been characterized by a series of back arc rift basins including those in kohistan and ladakh