dating the quaternary progress in luminescence dating of sediments abstract luminescence dating comprises a collection of numerical age techniques that are among the most significant chronological tools currently used in quaternary research this paper briefly reviews the key historical developments in luminescence dating from its roots in thermoluminescence dating of heated minerals to the development of optical dating methods for sunlight exposed sediments we describe the principles and practicalities of the various techniques commonly used in luminescence dating including multiple aliquot single aliquot and single grain procedures and we discuss some of the latest approaches to recognising and minimising potential errors in age estimation e g by means of component analysis and dose distribution methods in optical dating the overview also introduces the other papers in this special issue of quaternary science reviews which address a selection of important issues in basic research technique development and application of luminescence dating to critical questions in the geological and archaeological sciences illustrated with examples from around the world and the last million years of earth history

sand ramps in the golden gate highlands national park south africa evidence of periglacial aeolian activity during the last glacial abstract sand ramps have been identified in a side valley on the southern side of the little caledon river in the golden gate highlands national park free state south africa the site lies in the foothills of the northern drakensberg maluti mountains and this study aims to explore the potential of such deposits to add to the sparse palaeoenvironmental record of the region up to 11 m of aeolian sand banked against north facing slopes is exposed by fluvial incision through the deposits revealing interbedded fluvial lenses and palaeosols the region is currently devoid of significant aeolian sediment transport or deposition and supports well developed grassland vegetation these deposits testify to former conditions different from those of today which would have been characterised by depleted vegetation and a different wind and or climatic regime biogenic proxies are absent from the deposits but optically stimulated luminescence osl dating of the sediments reveals that they accumulated at intervals throughout much of the last glacial event from around 45 to 16 ka these dates are consistent with those of vegetation changes from palaeoecological sites elsewhere in the region and also with dated evidence for niche glaciation further south in the high drakensberg evidence from this study supports significant landscape changes in the drakensberg during the last glacial with the foothills in the region of golden gate highlands national park subject to aeolian processes under a periglacial environment

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

mineral magnetic characteristics of podzolic soils developed on sand dunes in the lake gosciaz catchment central poland a number of samples from the a0 a2 b and c horizons have been collected from podzolic soils in the lake gosciaz catchment in central poland the catchment is very uniform consisting of 2 6 m high sand dunes with sparse stands of pine and a grass undervegetation radiocarbon dates of fossil soils covered by dune sand within the same type of environment as the lake gosciaz catchment indicate that the main dune forming phase is of older dryas age magnetic measurements have been carried out on bulk samples and on particle size fractions from the different soil horizons with respect to our mineral magnetic study it can be concluded that the soils are very uniform over the entire catchment relatively high concentrations of magnetic grains are found in the humus layer particularly in the 4 m size fraction as indicated by the highest x xfd sirm and hirm values the most likely mechanism for the magnetic enhancement in these podzolic top soils is continued burning processes low magnetic concentrations in the a2 horizon are due to eluviation and chelation local conditions can lead to a range of magnetic minerals precipitating in the b horizon

palaeoclimate records from ois 8 0 5 4 recorded in loess palaeosol sequences on the matmata plateau southern tunisia based on mineral magnetism and new luminescence dating mineral magnetic studies of loess palaeosol sequences on the matmata plateau southern tunisia coupled with a new chronology based on luminescence dating confirm the presence of at least four phases of pedogenesis during the period 100 250 ka inter site correlations between the reddened fersiallitic palaeosols confirms that despite modern gullying processes the records are regional and repeatable the palaeosol magnetic signal is controlled by the formation of secondary ferrimagnetic minerals which may be easily detected by magnetic susceptibility and frequency dependent susceptibility measurements comparison of the magnetic record with global proxy climate records shows a correlation with loess palaeosol sequences in china and the marine oxygen isotope oi record during stages 8 0 5 4 preliminary attempts to infer palaeoprecipitation levels from modern analogues of soil magnetism climate associations suggests that during the periods 100 120 ka and 200 ka precipitation was 400 mm a 1 compared with modern precipitation 150 mm a 1

the possible role of magnetic measurements in the discrimination of sahara sahel dust sources the mineral magnetic properties of deposited dusts collected along a broadly north to south transect across niger have been investigated on both a bulk and particle size specific basis dusts display a general north to south gradient in fine grained ferrimagnetic mineral magnetite maghemite concentrations with samples south of the sahara sahel transition south of 15 5o n generally containing greater concentrations than dusts from further north where the climate is much drier this distinction is seen especially clearly in the clay 2 m fraction which harbours the products of weathering and pedogenesis this gradient in ferrimagnetic mineral concentrations broadly parallels that previously reported for surface soils sands across a similar latitudinal range we suggest that the regional distinction in both dust and surface soil sand magnetic properties can be related to differences in weathering regime between the arid saharan parts of the transect and the sahel sites where higher rainfall has permitted stronger weathering and pedogenesis given that the weathering related magnetic signatures in the clays dominate the magnetic properties of the 16 m fractions in these samples and that this particle size component is most likely to be involved in long range transport magnetic measurements hold out the potential of discriminating sahara and sahel dusts deposited in remote areas copyright 2011 john wiley sons ltd

luminescence dating of sand ramps in the eastern mojave desert abstract until recently the timing of the movement of sand and accumulation of sand by aeolian processes in the eastern mojave desert has remained the subject of speculation the results of a luminescence dating program involving 78 samples of material from nine sand ramp complexes have enabled recognition of regional and local patterns of sand accumulation in the eastern mojave the study area extends from lake manix in the west to the colorado river in the east the periods of accumulation have been identified on the basis of quartz tl dating and potassium feldspar tl and irsl dating at a regional scale two major depositional phases can be identified 1 late pleistocene 20 30 ka with sequences at hank s mountain balch dale lake and the big marias and 2 late pleistocene early holocene 15 7 ka with sequences at cat dune dale lake iron mountain big marias above palaeosol and at the western end of the study area at soldier mountain 20 7 ka late holocene sequences appear to be much more localized and are confined to the west cronese old dad mountain and balch sand ramps the earliest phases of sand accumulation on the ramps studied immediately predate the formation of pluvial lake mojave ca 24 5 ka the later main phases of accumulation coincide with the existence of lake mojave and the end of accumulation on the majority of the sand ramps immediately post dates the final end of intermittent lake mojave iii 9 7 ka the continuity of sand supply to potential deflation areas is seen as a critical condition for accumulation of material on the sand ramps during the late quaternary in the eastern mojave

luminescence dating of mojave desert sands abstract infra red stimulated luminescence has been used to date periods of sand deposition in the mojave desert california dates from the cronese basins kelso dunes and silver lake are compared with published irsl ages to provide evidence for discrete pulses of sand accretion during the late pleistocene and holocene linked to both arid and pluvial climates a critical factor in aeolian deposition throughout this area is shown to be the availability of sand from existing source areas

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

development and environmental significance of an eolian sand ramp of last glacial age central iran abstract a 25 m thick section of mostly eolian sediment is exposed in the stream cut flank of a sand ramp accumulated in a mountain saddle near ardakan playa central iran the well sorted eolian sediments of the ramp contain talus beds and incipient paleosols morphology and bedding structures imply that southeasterly winds were primarily responsible for deposition of the eolian sand optical dating shows that the sand was deposited near the last glacial maximum within about 5000 yr surface stabilization lack of surface scree and the development of a stream cut between the mountain and the ramp show that sediment accumulation ceased after this time the siberian high pressure system may have been established over central iran during the last glacial maximum causing cooler temperatures and a prevalence of southeasterly winds these colder windier conditions would have led to frost shattering and eolian transport both of which are not significant processes today but which are evident as past processes from the ramp sediments

holocene landscape response to seasonality of storms in the mojave desert abstract new optically stimulated and radiocarbon ages for alluvial fan and lake deposits in the mojave desert are presented which greatly improves the temporal resolution of surface processes the new mojave desert climate landscape record is particularly detailed for the late holocene evidence from ephemeral lake deposits and landforms indicates times of sustained stream flow during a wet interval of the latter part of the medieval warm period at ca ad 1290 and during the little ice age at ca ad 1650 the former lakes postdate megadroughts of the medieval warm period whereas the latter match the maunder minimum of the little ice age periods of alluvial fan aggradation across the mojave desert are 14 9 cal ka and 6 3 cal ka this timing largely correlates to times of increased sea surface temperatures in the gulf of california and enhanced warm season monsoons this correlation suggests that sustained alluvial fan aggradation may be driven by intense summer season storms these data suggest that the close proximity of the mojave desert to the pacific ocean and the gulf of california promotes a partitioning of landscape process responses to climate forcings that vary with seasonality of the dominant storms cool season pacific frontal storms cause river flow ephemeral lakes and fan incision whereas periods of intense warm season storms cause hillslope erosion and alluvial fan aggradation the proposed landscape process partitioning has important implications for hazard mitigation given that climate change may increase sea surface temperatures in the gulf of california which indirectly could increase future alluvial fan aggradation

environmental magnetism a practical guide j walden f oldfield j and smith eds technical guide no 6 quaternary research association london 1999 243 pp price 17 00 9 00 to qra members isbn 0 907780 42 3

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

determining location and magnitude of historical pre 1963 events in the rio grande rift region using intensity information abstract we used intensity information from five calibration earthquakes to estimate an intensity attenuation model for the rio grande rift region encompassing west texas new mexico and southern colorado the attenuation model lies between similar models developed for the basin and range province and central and eastern north america analysis of two test earthquakes occurring in 1931 and 2014 validated that the intensity attenuation relation adequately predicted the events magnitudes and epicenters we then analyzed intensity information for nine historical 1906 1960 earthquakes to determine their magnitudes and epicenters our results indicate that the largest earthquakes of the 1906 socorro new mexico sequence had intensity magnitudes m i 5 7 5 9 and may represent north to south migration of seismicity associated with the socorro magma body moderate earthquakes in 1935 and 1960 also are associated with the magma body the 1938 arizona new mexico border earthquake sequence occurred about 50 km northeast of the ongoing 2014 arizona new mexico border sequence the 17 september earthquake of the 1938 sequence had an m i 4 1 that was about 1 0 units less than that of the 29 june 2014 arizona new mexico event m i 4 9

stone movement on hillslopes in the mojave desert california a 16 year record previous research has shown that either hydraulic action or creep may be the dominant process transporting coarse debris down hillslopes in the american southwest this study analyses the movement over 16 years of painted stones on two hillslopes in the central mojave desert to ascertain which of these two processes dominate in this region the distance moved m is found to be directly related to length of overland flow x and hillslope gradient s and inversely related to particle size d the fact that m is more highly correlated with x than with s suggests that hydraulic action rather than creep is the dominant process it is concluded that this is probably the case over most of the mojave and sonoran deserts on slopes up to at least 24 and that it is only at higher elevations where winters are more severe that creep may become dominant

pedogenic factors affecting magnetic susceptibility of the last interglacial palaeosol s1 in the chinese loess plateau the magnetic susceptibility has been used as a quantitative or semi quantitative proxy for reconstructing the summer monsoon intensity in the chinese loess plateau based on extensive studies on climatic or and environmental mechanisms producing the magnetic susceptibility signatures however the precise nature of the link between past climates and the susceptibility signatures has remained uncertain primarily due to lack of our understanding in the nalizing and preserving processes of the signatures this paper attempts to examine the reliability or acceptability of this summer monsoon proxy from non magnetic perspectives of soil forming processes we chose nine sections along two transects one across the western part of the chinese loess plateau and another across the eastern part several conclusions can be drawn from our analytical data first clay translocation within the s1 palaeosol pro les as indicated by eld observed clay coatings on ped faces in bt and bk horizons and demonstrated by laboratory analysed clay contents must have moved some of the magnetic minerals downward so that the susceptibility re ects only the post translocation distribution of the magnetic susceptibility producing minerals second the best developed palaeosol s1s3 at most of the sections studied is not expressed by the magnetic susceptibility because this palaeosol developed in underlying coarse loess l2 and coarse textures tend to lower the susceptibility third carbonate concentration is normally negatively correlated with the magnetic susceptibility or simply suppresses the magnetic susceptibility peak when the susceptibility enhancement exceeds the carbonate dilution effect to conclude extreme caution must be observed when using magnetic susceptibility signatures to retrieve high resolution records of the last interglacial palaeoclimate in the chinese loess plateau copyright 2004 john wiley sons ltd

a conceptual model for the enhancement of magnetic susceptibility in soils abstract mineral magnetic properties of soils can be strongly influenced by soil forming factors understanding how climate influences magnetic transformations in soils may offer insight into paleoclimate and the pedologic history of landscapes based on our experience with soils in california and hawaii we have developed a conceptual model of the pathways that can lead to enhancement of the magnetic susceptibility in soils we base our model on three sources of iron in soils magnetite maghemite and other iron bearing minerals we find that preferential accumulation transformation diagenesis lessivage neoformation authigenesis and solubilization are the main processes that convert the primary lithogenic minerals inherited from soil parent material to the secondary pedogenic minerals found in the solum biosynthesis is included in the model but does not appear to be an important process in aerobic soil environments our model shows that a major process in the enhancement of eluvial and illuvial horizons is neoformation of secondary magnetite and maghemite resulting from precipitation of iron from the soil solution the processes and products in the model are independent of whether the parent material is transported alluvium or loess or residuum for the soils that we have studied the rates of susceptibility enhancement are shown to be dependent on climate and parent material

on the formation of sand ramps a case study from the mojave desert sand ramps are dune scale sedimentary accumulations found at mountain fronts and consist of a combination of aeolian sands and the deposits of other geomorphological processes associated with hillslope and fluvial activity their complexity and their construction by wind water and mass movement means that sand ramps potentially hold a very rich store of palaeoenvironmental information however before this potential can be realised a full understanding of their formation is necessary this paper aims to provide a better understanding of the principal factors influencing the development of sand ramps it reviews the stratigraphic chronometric and sedimentological evidence relating to the past development of sand ramps focussing particularly on soldier mountain sand ramp in the mojave desert as well as using observations of the modern movement of slope material to elucidate the formation of stone horizons within sand ramps findings show that sand ramps cannot easily be interpreted in terms of a simple model of fluctuating palaeoenvironmental phases from aeolian dominated to soil fluvial dominated episodes they accumulate quickly perhaps in 5 ka probably in a single phase before becoming relict based on the evidence from soldier mountain they appear strongly controlled by a window of opportunity when sediment supply is plentiful and cease to develop when this sediment supply diminishes and or the accommodation space is filled up contemporary observations of stone movement both on rock and sandy sloping surfaces in the mojave region indicate movement rates in the order of 0 6 and 11 mm yr 1 which is insufficiently fast to explain how stone horizons could have been moved across and been incorporated into sand ramps on multiple occasions stone horizons found within the aeolian sediments lack evidence for soil development and are interpreted as very short term events in which small streams moved and splayed discontinuous stone horizons across the sand ramp surface before aeolian deposition resumed surface stone horizons may form by creep from mountain slope sources across sand ramps but require enhanced speed compared to measured rates of runoff creep we propose the mechanism of fluvio aeolian creep our study suggests that current models of alternating aeolian and colluvial deposition within sand ramps their palaeoenvironmental significance and indeed how sand ramps are distinguished from other dune forms require amendment

palaeoclimatic implications of the magnetic record from loess palaeosol sequence viatovo ne bulgaria summary loess palaeosol deposits in the lower danube area represent the southeastern edge of the loess cover in europe detailed rock magnetic investigations of the loess palaeosol sequence in viatovo in ne bulgaria reveal that magnetite and maghemite of very fine superparamagnetic grain size are responsible for the magnetic enhancement of palaeosol units a detailed palaeoclimatic record is obtained through high resolution measurements of magnetic susceptibility frequency dependent magnetic susceptibility and caco3 content magnetic proxies indicate a more warm and humid climate during the development of the older palaeosol units s4 s6

sources of fine grained magnetic minerals in sediments a problem revisited progress in the discrimination of fine grained magnetic minerals in sediments and sediment sources using measurements of magnetic susceptibility at two frequencies and of magnetic remanence generated by a combination of direct and alternating currents is summarized the former measurements yield values for low field and frequency dependent susceptibility lf and fd respectively the latter generate an anhysteretic remanent magnetisation arm that when normalized to the dc bias field can be represented as the susceptibility of arm arm using quotients derived from lf fd and arm to generate bi logarithmic plots it is possible to discriminate between assemblages dominated by magnetic minerals formed through pedogenesis and those arising from the presence of magnetotactic bacteria that use chains of magnetic particles to seek optimum environments in surface sediments sediments to which both types of magnetic mineral contribute occupy positions between the envelopes of values typical of soil d

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

morphology and architecture of a late pleistocene cliff front dune mallorca western mediterranean cliff front dunes are a common coastal feature but this is the first time that the structures indicative of their formation are documented a late pleistocene cliff front dune in southern mallorca has been studied owing to early lithification of the calcarenite its morphology is well preserved the dune occurs in front of a curved near vertical coastal cliff but the bedform cannot be classified as a fixed echo dune the dune grew with time and its brinkline gradually moved closer to the cliff front in the final stage of evolution the top of the dune reached a height of at least 23 m the dune is composed of wind ripple strata these strata are arranged in critical to supercritical climbing dune cross stratification recording its growth stages the angle of climb of the dune increases toward the cliff and reaches 50 the morphological features of cliff front dunes result from both cliff slope and whether the cliff front is curved or straight

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

mineral magnetic characterization of sediment sources from an analysis of lake and floodplain sediments in the catchments of the old mill reservoir and slapton ley south devon uk research on suspended sediment transport in the catchments of the old mill reservoir and slapton lower ley south devon has attempted to discriminate changing catchment sources on the basis of downcore variations in the mineral magnetic properties of lake reservoir and floodplain sediments here we examine these downcore variations and also explore the variability in catchment sources and the influence of topographic controls on mineral magnetic signatures of topsoils and subsoils particle size controls on the mineral magnetic signatures are explored by an analysis of a fractionated sediment sample whilst the possible impact of diagenesis is assessed by an examination of the mn profiles in the lake and reservoir sediments from this analysis it is evident that the mineral magnetic signatures of well sorted floodplain deposits are more likely to reflect the particle size composition of the transported material by contrast the mineral magnetic record in the sediment of slapton ley appears to be most strongly influenced by dissolution of magnetic minerals the sediment of the old mill reservoir provides the only suitable record for the application of a simple mixing model which is developed in order to quantify changes in the relative contribution of topsoil and subsoil through time the research has important implications for attempting to reconstruct sediment sources in highly eutrophic lakes and emphasizes the uncertainty in the application of simple mixing models 1998 john wiley sons ltd

biofilm related calcification sediment trapping and constructive micrite envelopes a criterion for the recognition of ancient grass bed environments micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms these are referred to as destructive micrite envelopes and have long been recognized as reflecting an important early diagenetic process recent analysis of sediments collected from back reef environments at discovery bay north jamaica however has demonstrated envelope formation on the surfaces of carbonate grains clearly distinct from the micrite filling of microborings such constructive envelopes occur almost exclusively in sediments from grass bed environments and are always intimately associated with biofilms comprising abundant mucilage cyanobacteria bacteria and diatoms it is suggested that these envelopes represent a product of both biologically mediated micrite precipitation occurring within the biofilm mucilage and around the biofilm components i e cyanobacteria and diatoms and associated trapping of carbonate mud and fine grained sediment their recognition only within grass bed sediments may enable their use as a diagnostic feature of grass bed environments or vegetation stabilized substrates in the rock record

a solution to anomalous fading and age shortfalls in optical dating of feldspar minerals abstract recent reports of age underestimations for events of interest in both palaeoclimatology and archaeology have led to questioning the validity of using luminescence for dating sediments the commonly designated culprit is anomalous fading of feldspar luminescence we investigated the differential fading rates of single feldspar grains in sediment samples from different geological domains of north america and deduced how one could extrapolate to zero fading this is shown to resolve an extreme case of optical age underestimation documented for the late pleistocene norfolk formation a key palaeoclimate stratigraphic unit exposed along the north american atlantic coast

luminescence dating of late quaternary aeolian deposits at dale lake and cronese mountains mojave desert california abstract relict aeolian deposits and landforms that can provide important information on the timing geographical extent and intensity of periods of aeolian sand accumulation are widespread in the mojave desert california the pleistocene part of the record is mostly undated the stratigraphy and sedimentology of sites near dale lake dale lake sand ramp and the cronese mountains cat dune were studied and luminescence dating techniques used to try to establish a chronological framework for the deposits the dating of these sites proved difficult with major disparities between the results of quartz and feldspar thermoluminescence tl dating particularly where the sediments comprised a mixture of aeolian and colluvial meterial however initial results based on quartz tl and feldspar infra red stimulated luminescence dating indicate the existence of two main periods of late pleistocene aeolian deposition between 35 to 25 ka and 15 to 10 ka

geomorphology and sediments of sand ramps in the mojave desert abstract sand ramps are amalgamated accumulations of aeolian fluvial and talus deposits they have developed as a result of the interactions of wind blown sand and desert piedmont processes adjacent to mountain ranges in the mojave desert and occur next to regional and local sand transport corridors sand ramps are dominated by aeolian sand that was deposited as sand sheets against the mountain front but also include significant fluvial units periods of geomorphic stability are represented by paleosols and talus accumulations the sand ramps provide a record of the response of aeolian processes to climatic change in the mojave desert most are now relict features and accumulated in periods of higher sediment supply from fluctuating and or desiccating paleolakes during the late pleistocene and early holocene