high latitude aurora during steady northward interplanetary magnetic field and changing imf by 1 high latitude transpolar arcs tpas are often observed during northward interplanetary magnetic field imf of these theta aurora are seen when transpolar arcs move in the dawn or dusk direction across the entire polar region in response to imf by changes periods of study were chosen when by changes sign during steady northward imf in order to determine the influence of imf bx by the strength of the imf the solar wind and earth dipole tilt on the occurrence and motion of high latitude tpas forming theta aurora for a 4 5 year period there are 55 events for which imf bz is northward for at least 2 hours before and at least 3 hours after a by sign change of these 19 occurred when the polar satellite was over the northern hemisphere for the duration of the event we find that for northward imf and a by sign change theta aurora are almost always formed in the northern hemisphere regardless of bx and dipole tilt this implies that theta aurorae form simultaneously in both hemispheres imf by does not appear to influence the intensity and duration of the arc strongest uv emissions occur in the summer hemisphere evolution time has a fairly complex dependence on solar wind parameters

a comparison of osl ages derived from silt sized quartz and polymineral grains from chinese loess abstract recent work watanuki et al submitted has shown by comparison with independent age control that silt sized quartz grains extracted from japanese loess can be used for optically stimulated luminescence osl dating for equivalent doses of up to 425 gy 500 ka at these sites further comparison with infrared ir stimulated and post ir blue stimulated osl showed that the latter signal gave accurate ages and was probably dominated by quartz whereas the former systematically underestimated ages in the range 30 600 ka and showed fading in laboratory tests the main source of the loess deposits in japan is the chinese mainland in eastern asia loess is widely distributed by the prevailing westerly winds and one of the main sources is in the western desert areas of china unfortunately independent age control is very unusual in loess deposits in china and there is little evidence for the accuracy of existing luminescence ages from this material as an alternative approach this study builds on the japanese results by using loess from two chinese sites and examining the relationship between single aliquot regeneration dose ir and post ir blue stimulated luminescence ages from polymineral samples and blue stimulated quartz luminescence ages the normalized blue stimulated osl intensity from quartz from the eastern site was about 10 times that from the west suggesting either a different source of material or less likely an increase in quartz sensitivity with transport distance by comparison with quartz results we conclude that in our samples of chinese loess the post ir blue stimulated osl is the more reliable polymineral signal when compared with the ir signal it may nevertheless include a feldspar component and this should be tested for using laboratory fading experiments

the potential of osl and tl for dating lateglacial and holocene dune sands tested with independent age control of the laacher see tephra 12 880 a at the section mainz gonsenheim abstract optically stimulated luminescence osl and thermoluminescence tl are applied in this study to date a lateglacial and holocene aeolian sediment sequence quartz and potassium rich feldspars extracted from dune sands from western germany were dated using both multiple aliquot ma and single aliquot sa protocols for luminescence dating this particular dune section was chosen for this test study because an independent age control is provided by a horizon of the laacher seetephra 12 880 a in contrast to the results for potassium feldspars which show underestimation of up to 25 the quartz fraction provides promising results with respect to the presumed geological ages

late pleistocene fluvial dynamics in the hochrhein valley and in the upper rhine graben chronological frame during the pleistocene the rhine glacier system acted as a major south north erosion and transport medium from the swiss alps into the upper rhine graben which has been the main sediment sink forming low angle debris fans only some aggradation resulted in the formation of terraces optically stimulated luminescence osl and radiocarbon dating have been applied to set up a more reliable chronological frame of late pleistocene and holocene fluvial activity in the western hochrhein valley and in the southern part of the upper rhine graben the stratigraphically oldest deposits exposed a braided river facies yielded osl age estimates ranging from 59 6 6 2 to 33 1 3 0 ka the data set does not enable to distinguish between a linear age increase triggered by a continuous autocyclical aggradation or two or more age clusters for example around 35 ka and around 55 ka triggered by climate change including stadial and interstadial periods sensu dansgaard oeschger cycles the braided river facies is discontinuously hiatus covered by coarse grained gravel rich sediments deposited most likely during a single event or short time period of major melt water discharge postdating the last glacial maximum osl age estimates of fluvial and aeolian sediments from the above coarse grained sediment layer are between 16 4 0 8 and 10 6 0 5 ka and make a correlation with the late glacial period very likely the youngest fluvial aggradation period correlates to the beginning of the little ice age as confirmed by osl and radiocarbon ages

late pleistocene braided rivers of the atlantic coastal plain usa abstract infrared landsat imagery band 4 clearly reveals braided river patterns on late pleistocene terraces of unglaciated rivers in the atlantic coastal plain of the southeastern united states a region that presently exhibits meandering patterns that have existed throughout the holocene these pleistocene braided patterns provide a unique global example of river responses to late quaternary climate changes in an unglaciated humid subtropical region at 30 35 north latitude detailed morphological and chronological results are given for the oconee altamaha river valley in georgia and for the pee dee river valley in south carolina including 15 optically stimulated luminescence osl dates and four radiocarbon dates correlative examples are drawn from additional small to large rivers in south and north carolina osl and radiocarbon 14 c dates indicate distinct braiding at 17 30 ka within oxygen isotope stage 2 ois 2 and braiding probably existed at least during parts of ois 3 and possibly ois 4 back to ca 70 ka the chronology suggests that braiding is the more common pattern for the late quaternary in the southeastern united states braided terraces appear to have been graded to lower sea levels and are onlapped by holocene floodplain deposits up to 10 60 km from the coast the braiding probably reflects the response of discharge and sediment yield to generally cooler and drier paleoclimates which may have had a pronounced runoff season sedimentation of eolian dunes on the braid plains is coeval with braiding and supports the conclusion of dry soils and thin vegetation cover during the late pleistocene our chronological data contribute to a body of literature indicating that reliable osl age estimates can be obtained from quartz rich bed load sand from braided rivers based on good correlations with both radiocarbon dates from braided fluvial sediment and osl dates from stratigraphically correlative eolian sand

revealing the coastal event history of the andaman islands bay of bengal during the holocene using radiocarbon and osl dating earthquakes that trigger tsunamis are of great geological ecological and socio economic importance the knowledge of the recurrence interval of these events will give information about the hazard for a region coastal sediments on the andaman islands located in the eastern bay of bengal were investigated to find evidence for palaeotsunamis and palaeoearthquakes fieldwork was conducted on red skin island and north cinque island south of south andaman sediment material from event layers was dated by optically stimulated luminescence and radiocarbon dating method the results show evidence possibly for one earthquake at about 1 000 or 3 000 years before the present together with deposits from possible tsunamis and storms the complex pattern of co and post seismic uplift and subsidence of the andaman islands is reflected in the investigated sections and made it possible to reconstruct an event history for the last 3 000 years

late pleistocene and early holocene climate and limnological changes in the sierra nevada california usa inferred from midges insecta diptera chironomidae chironomid and stratigraphic analyses of a lake sediment core recovered from a high elevation lake in the central sierra nevada california usa was undertaken to assess chironomid community development during the pleistocene holocene transition and to quantitatively reconstruct the thermal regime that existed during this interval between 14 800 cal yr bp and 13 700 cal yr bp the chironomid community consisted almost exclusively of heterotrissocladius suggesting this period was characterized by extremely cold climatic conditions evidence of post glacial climatic amelioration as manifested by increases in thermophilous chironomid taxa head capsule concentrations and taxon richness and diversity commenced at approximately 13 300 cal yr bp in order to quantify the magnitude of the water temperature changes associated with post glacial climatic amelioration a recently developed chironomid based inference model for surface water temperature was applied to the subfossil chironomid assemblages the one component weighted averaging partial least squares wa pls model has an r2jack 0 72 rmsepjack 1 1 c and a maximum bias of 1 24 c the reconstructed surface water temperatures suggest a minimum warming of approximately 4 7 c occurred during the pleistocene holocene transition however warming during this interval may not have been monotonic evidence of the younger dryas has been previously discovered in the study area and adjacent regions our research indicates that changes in chironomid community composition and an inferred short term cooling event occurred between 12 000 cal yr bp and 11 500 cal yr bp which may represent a local manifestation of the younger dryas chironomid community development during the pleistocene holocene transition appears to primarily reflect the influence of changing climate conditions

natural responses to quaternary climatic change in the greater nevada test site region u s a abstract many natural processes particularly those that occur at or near the earth s surface e g erosion infiltration soil formation and plant growth are influenced or altered by climatic change migration of hazardous and radioactive contaminants into and through the environment depends on these natural processes climatic fluctuations can affect the nature magnitude and rate of these processes in any long term environmental evaluation of natural processes responses to climatic change must be considered four generalized categories of natural responses to quaternary climatic change are recognized for the greater nevada test site nts region of southern nevada and adjacent california 1 biologic 2 geomorphic 3 hydrologic including surface and subsurface and 4 pedologic diagenetic specific examples that correspond to the four categories illustrate the broad range of complex natural processes that are affected by climatic change these responses dictate the potential effect of climatic change on waste isolation and contaminant transport this effect is being examined by existing and planned environmental restoration and waste management programs within the region regulatory requirements for many of these programs include long term 10 000 year waste isolation because of radiologic components an overview is presented of the slowly growing data base of the complex relationships between climate and natural processes that must be considered in performance and risk assessments for environmental programs in this region limitations in and inconsistencies between various data sets are noted as appropriate in particular better quantified estimates or ranges of estimates of magnitudes and rates are commonly needed for these processes and responses these estimates allow climatic change and related responses to be incorporated explicitly into conceptual and numerical models and into performance and risk assessments of the various environmental restoration and waste management programs within the greater nts region

testing optically stimulated luminescence dating of sand sized quartz and feldspar from fluvial deposits abstract we apply single aliquot optically stimulated luminescence osl dating to quartz and feldspar rich extracts from fluvial channel deposits of the rhine meuse system in the netherlands the time of deposition of these deposits is tightly constrained by radiocarbon dating or historical sources this allows us to compare osl ages obtained on quartz and infrared osl ir osl ages obtained on potassium rich feldspar with independent ages over the range of 0 3 13 ka we show that the quartz osl ages are in good agreement with the expected age using ir osl dating of feldspar we find a slight age overestimate for the youngest sample whereas for older samples the age is significantly underestimated we also apply osl dating to older fluvial and estuarine channel deposits with limited independent chronological constraints comparison of feldspar ir osl ages with the quartz osl ages up to 200 ka shows a clear trend where the former severely underestimates the latter this trend is similar to that found for the samples with independent age control indicating that the feldspar ir osl ages are erroneously young for the entire age range in the youngest samples incomplete resetting of the ir osl signal prior to deposition probably masks the age underestimation we show that the ir osl age underestimation is partly caused by changes in trapping probability due to preheating correction for this phenomenon improves the ir osl ages slightly but does not provide a complete solution to the discrepancy we suggest that in the light of the problems encountered in the ir osl dating of feldspar quartz is the mineral of choice for osl dating of these deposits however feldspar dating should continue to be investigated because it has potential application to longer time scales

evolution and environmental impacts of the eruption of laacher see volcano germany 12 900 a bp abstract laacher see volcano lsv 40 km south of bonn explosively erupted ca 6 3 km 3 of chemically strongly zoned phonolite magma probably during spring 12 900 years ago the resulting eruption column having reached at least 20 km in height the bulk of the laacher see tephra lst was deposited east of the volcano within the neuwied basin lst ashes form the most important stratigraphic marker in lateglacial deposits over much of central europe a minimum of 2 mt total s was calculated to have been released during the eruption by comparing pre and posteruptive volatile concentrations in glass inclusions and pumice matrix glasses because a separate s bearing vapor phase was probably present in the magma prior to eruption as indicated by the high melt h 2 o contents close to saturation level the actual amount of s released during the eruption could have significantly exceeded 2 mt the sulfuric acid aerosol layer resulting from the massive stratospheric s input probably resided in the stratosphere for years and most likely had a significant impact on climate and thus the environment increased precipitation in central europe and or impairment of the vegetation cover for several years is suggested by several proxies especially increased sediment supply into lakes proximal to the eruptive center major environmental impacts include an initial blast that felled trees up to 4 km away from vent fast deposition of huge tephra volumes led to the complete disruption of rhine river within the lower neuwied basin and the damming up of a lake ca 140 km 2 in areal extent sudden collapse of the temporary tephra dam caused a catastrophic flood wave downstream whose deposits are recognized as far north as bonn reworking of unconsolidated tephra deposits over several 100 km 2 was widespread and extensive generating abundant lahars and flood plain deposits a braided river system established in neuwied basin probably persisted up to several years recent reports for a second eruption of lsv are not confirmed

optical dating of young coastal dunes on a decadal time scale we explore the use of quartz optically stimulated luminescence osl dating for reconstructing coastal evolution on a time scale of decades to a few hundred years samples are taken from the accretionary south west coast of texel a barrier island just offshore of the northern netherlands the ages of dune ridges are known from historical sources an excellent chronology with a decadal accuracy exists for the past 260 years osl ages of less than 10 years on the youngest samples indicate that the osl signal of the quartz grains is very well zeroed prior to deposition and burial osl ages of five samples from a 250 year old dune ridge are indistinguishable and the osl ages on 17 out of 20 samples are in excellent agreement with the well known independent age controls our results highlight the potential of osl dating for high resolution reconstruction of coastal evolution over the past few centuries

thermal tl and optical stimulated luminescence osl techniques for dating quaternary colluvial volcaniclastic sediments an example from the crati basin northern calabria abstract within the colluvial clastic deposits of the crati basin near the village of tarsia a decimetre to metre thick volcaniclastic stratum outcrops interbedded within poorly structured sandy pelitic deposits the volcaniclastic stratum is structureless powdery pinkish grey or yellowish brown slightly pedogenized towards the top and characterized at the base by centimetre sized clasts of crystalline rocks the depositional and textural features suggest a primary fall out of volcanic ash during a period when the climate favoured modification of the landscape and re mobilization of the ash as mud flows with the first rainy episode this area was subjected to strong uplift 0 7 mm yr and climatic effects of the last glacial maximum and the preservation of this volcaniclastic stratum represents an unusual and exceptional event the volcanic ash representing the principal component of the deposit is composed of shards and pumices of phonolithic composition with millimetre sized phenocrysts of sanidine the non volcanic component consists of quartz clasts and to a much lesser extent feldspars and fragments of metamorphic rocks thermal tl and optical stimulated luminescence osl techniques were used to date the potassium feldspar crystals of volcanic origin and the quartz crystals from the non volcanic component the stratum contains sediments of different origins the feldspar fraction was subjected to high temperatures at the moment of volcanic emission zeroing the internal luminescence clock the quartz fraction was exposed to light probably only at the moment of sedimentation with the possibility of only partial bleaching of luminescence signal osl ages are chronologically undistinguishable between the quartz and feldspar fractions the quartz and feldspar fraction ages obtained by osl are respectively 28 3 ka and 27 2 ka tl measurements reveal an age of 41 3 ka for the quartz fraction and 33 3 ka for the feldspar fraction the age and chemical and mineralogical composition of the volcanic fraction indicate the source for the large explosive eruptions occurred in the campanian area ischia flegrei southern italy between 42 and 25 ka

palynological evidence for early holocene aridity in the southern sierra nevada california sediments of balsam meadow have produced a 11 000 yr pollen record from the southern sierra nevada of california the balsam meadow diagram is divided into three zones 1 the artemisia zone 11 000 7000 yr b p is characterized by percentages of sagebrush artemisia and other nonarboreal pollen higher than can be found in the modern local vegetation vegetation during this interval was probably similar to the modern vegetation on the east slope of the sierra nevada and the climate was drier than that of today 2 pinus pollen exceeded 80 from 7000 to 3000 yr b p in the pinus zone the climate was moister than during the artemisia zone 3 fir abies cupressaceae and oak quercus percentages increased after 3000 yr b p in the abies zone as the modern vegetation at the site developed and the present cool moist climatic regime was established decreased fire frequency after 1200 yr b p is reflected in decreased abundance of macroscopic charcoal and increased concentration of abies magnifica and pinus murrayana needles

revealing the pace of river landscape evolution during the quaternary recent developments in numerical dating methods during the last twenty years several technical developments have considerably intensified the use of numerical dating methods for the quaternary the study of fluvial archives has greatly benefited from these enhancements opening new dating horizons for a range of archives at distinct time scales and thereby providing new insights into previously unanswered questions in this contribution we separately present the state of the art of five numerical dating methods that are frequently used in the fluvial context radiocarbon luminescence electron spin resonance esr 230th u and terrestrial cosmogenic nuclides tcn dating we focus on the major recent developments for each technique that are most relevant for new dating applications in diverse fluvial environments and on explaining these for non specialists therefore essential information and precautions about sampling strategies in the field and or laboratory procedures are provided for each method new and important implications for chronological reconstructions of quaternary fluvial landscapes are discussed and where necessary exemplified by key case studies a clear statement of the current technical limitations of these methods is included and forthcoming developments which might possibly open new horizons for dating fluvial archives in the near future are summarised

late quaternary hillslope evolution recorded in eastern south african colluvial badlands abstract infrared stimulated luminescence irsl ages have been obtained from a sequence of sandy colluvial deposits in northern kwazulu natal comparison of the irsl ages on sand sized potassium rich feldspars with radiocarbon dates on a horizon organic matter from buried palaeosols within the colluvial succession shows good agreement between the dating techniques when compared with palaeoenvironmental records the data suggest that the colluvium accumulated during arid stages of the late quaternary whilst pedogenesis repeatedly occurred at intervals of hillslope stability which may reflect periods of greater humidity temperature does not seem to have been a forcing factor in the landscape development extensive colluviation took place during the arid last glacial maximum but the occurrence of several palaeosols indicates that it was a time of fluctuating climatic conditions

n alkane evidence for the onset of wetter conditions in the sierra nevada california usa at the mid late holocene transition 3 0 ka abstract n alkane biomarker distributions in sediments from swamp lake sl in the central sierra nevada of california usa provide evidence for an increase in mean lake level 3000 yr ago in conjunction with widespread climatic change inferred from marine and continental records in the eastern north pacific region length distributions of n alkane chains in modern plants growing at sl were determined and compared to sedimentary distributions in a core spanning the last 13 ka as a group submerged and floating aquatic plants contained high proportions of short chain lengths nc27 were dominant changes in the sedimentary n alkane distribution over time were driven by variable inputs from plant sources in response to changing lake level sedimentation and plant community composition a shift toward shorter chain lengths nc21 nc23 occurred between 3 1 and 2 9 ka and is best explained by an increase in the abundance of aquatic plants and the availability of shallow water habitat in response to rising lake level the late holocene expansion of sl following a dry mid holocene is consistent with previous evidence for increased effective moisture and the onset of wetter conditions in the sierra nevada between 4 0 and 3 0 ka

thirty thousand years of vegetation changes in the alabama hills owens valley california abstract twenty packrat neotoma middens recovered from three sites 1265 1535 m in the alabama hills inyo county california provide a ca 31 450 yr record of vegetation change located ca 7 km east of the sierra nevada the middens document that utah juniper juniperus osteosperma joshua tree yucca brevifolia and bitterbush purshia tridentata occupied the site between 31 450 and 19 070 yr b p joshua tree and bitterbush departed by ca 17 760 yr b p with cliffrose purshia mexicana and joint fir ephedra viridis appearing by 13 350 yr b p blackbush coleogyne ramosissima and cholla opuntia echinocarpa entered the record between 9540 and 7990 yr b p utah juniper and other species now extralocal to the sites departed and modern components such as wolfberry lycium andersonii and rubber rabbitbrush chrysothamnus teretifolius appeared the middle holocene records little variation in plant macrofossil composition however pollen analysis reflects an increase in aquatic pollen types which might suggest more open conditions the transition to the modern vegetation associations at the sites occurred after ca 2800 yr b p the record from the alabama hills correlates well with that of other regional vegetation data but documents conditions of increasing aridity earlier than many other packrat midden sites a shift in understory vegetation between 19 070 and 17 760 yr b p may reflect a transition from glacial maximum to post maximum conditions in the eastern sierra nevada

the distribution of apparent dose as determined by optically stimulated luminescence in small aliquots of fluvial quartz implications for dating young sediments abstract we noted recently murray et al 1995 that quartz samples taken from in channel fluvial deposits have apparent doses ranging over several orders of magnitude we suggested that these dose distributions are best explained by a mixture of a small number of poorly bleached grains and a larger number of well bleached grains in this paper we examine the distribution of apparent dose in small aliquots each composed of 2000 grains of different particle size fractions 63 90 m 90 125 m 125 180 m 180 212 m 212 250 m diameter from two samples collected from the murrumbidgee river new south wales australia the samples are of known burial age the first being 70 years old and the second being its modern equivalent 0 2 gy the difference in the lowest apparent dose in the two samples is considered to be the result of their different burial times we suggest a method for dating recently deposited

a holocene pollen record of persistent droughts from pyramid lake nevada usa pollen and algae microfossils preserved in sediments from pyramid lake nevada provide evidence for periods of persistent drought during the holocene age we analyzed one hundred nineteen 1 cm thick samples for pollen and algae from a set of cores that span the past 7630 years the early middle holocene 7600 to 6300 cal yr b p was found to be the driest period although it included one short but intense wet phase we suggest that lake tahoe was below its rim for most of this period greatly reducing the volume and depth of pyramid lake middle holocene aridity eased between 5000 and 3500 cal yr b p and climate became variable with distinct wet and dry phases lake tahoe probably spilled intermittently during this time no core was recovered that represented the period between 3500 and 2600 cal yr b p the past 2500 years appear to have had recurrent persistent droughts the timing and magnitude of droughts identified in the pollen record compares favorably with previously published y 18 o data from pyramid lake the timing of these droughts also agrees with the ages of submerged rooted stumps in the eastern sierra nevada and woodrat midden data from central nevada prolonged drought episodes appear to correspond with the timing of ice drift minima solar maxima identified from north atlantic marine sediments suggesting that changes in solar irradiance may be a possible mechanism influencing century scale drought in the western great basin d 2004 university of washington all rights reserved

an organic geochemical record of sierra nevada climate since the lgm from swamp lake yosemite abstract sediment records from swamp lake sl in the central sierra nevada california provide evidence of climatic change on millennial and centennial timescales over the last 20 000 years total organic carbon toc abundance varied in concert with elemental and isotopic tracers of organic matter c n 13 c org 15 n biogenic silica content total magnetic susceptibility and sediment lithology we interpret the down core proxy records as representing the response of the lake environment in terms of temperature seasonal ice cover mixing regimes runoff and in situ om and nutrient cycling to shifting climate states these environmental factors in turn drove changes in algal productivity om sources microbial om regeneration and secondary production and detrital input the late pleistocene 19 7 10 8 cal kyr bp was dominated by fluctuations between relatively warm dry intervals with high toc 17 4 16 5 15 8 15 0 13 9 13 2 11 4 11 0 cal kyr bp and cold wet intervals 16 5 15 8 14 8 13 9 13 1 11 6 11 0 10 7 cal kyr bp characterized by low toc and high detrital input the holocene 10 7 cal kyr bp present was characterized by three abrupt increases in toc after 10 8 8 0 and 3 0 cal kyr bp and numerous century scale fluctuations toc increases reflected enhanced lake productivity and om recycling and reduced detrital input in response to changing winter temperature and hydrologic regimes inferred environmental changes at sl correlate with other sierra nevada paleorecords and with reconstructed sea surface temperatures along the california margin parallel changes in the sl and sst records over the past 20 000 years provide new evidence that continental climate in the sierra nevada and the california current system have responded on multiple timescales to common drivers in north pacific ocean atmospheric circulation

paleo environment and radiocarbon calibration as derived from lateglacial early holocene tree ring chronologies abstract we present an overview of the extended hohenheim oak chronology hoc and the dendrochronologically dated preboreal pine tree ring chronology ppc both provide an absolute annual time frame of the holocene extending into the younger dryas yd back to 11 919 bp two floating pine and larch chronologies are 14 c dated covering large parts of the lateglacial dendro ecological parameters such as ring width and stable isotope variation are used to infer past environmental conditions 14 c analyses on decadal sections provide a high precision high resolution data set for calibration of the radiocarbon time scale based on a marked change in ring width and growth pattern the yd termination is clearly identified in the german pine chronology its absolute age of 11 570 bp appears synchronous within the errors of the respective chronologies to related signals in the greenland ice cores grip gisp2 and in lacustrine varve sequences the 14 c age of the laacher see tephra lst is determined from a series of decadal tree ring samples to 11 063 12 14 c bp the calibrated range is 13 010 13 200 cal bp the climatic impact of the lst is reflected in the growth pattern of our tree ring chronologies

measurement of equivalent doses in quartz from contemporary water lain sediments using optically stimulated luminescence the single aliquot technique and its derivatives are very attractive for the measurement of the very small doses found in young materials because they inherently avoid concerns about low dose non linearity and can offer high precisions a modification is outlined to the single aliquot regeneration and added dose sara protocol mejdahl and botter jensen 1994 quaternary geochronology quaternary science reviews 13 551 5541 to permit its application to sedimentary quartz using the optically stimulated luminescence signal this revised protocol is then used to determine the doses found in several contemporary fluvial sediments and one coastal beach sand thought to be deposi ted by recent wave action two over bank river deposits were both homogeneously well bleached with doses of 0 4 gy although most of the grains in three channel deposits from a range of catchment sizes were also well bleached contamination by a small proportion of very poorly bleached quartz grains prevented the measurement of the dose in the majority the beach deposit was homogeneously bleached and contained a dose of about 0 02 gy it is concluded that over bank sites may provide accurate dates for samples older than a few hundred years but that the heterogeneity of the channel sites limits the accuracy of dates less than a few thousand years

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

new osl dating of uk loess indications of two phases of late glacial dust accretion in se england and climate implications windblown dust deposits or loess locally known in the uk as brickearth blanket many parts of southern england outside the limits of the british and irish ice sheet the best studied loess exposures occur in kent southeast england where the deposits are believed to be late glacial in age new sedimentological evidence is presented for phases of accretion with two distinct units a calcareous brickearth exhibiting periglacial cryoturbation and a non calcareous massive brickearth optically stimulated luminescence osl dating has been applied to chemically isolated modal quartz silts to derive a chronology for sediment accretion and to better understand the palaeoclimatic significance of these deposits

optical resetting in large drainage basins tests of zeroing assumptions using single aliquot procedures abstract optical resetting of previously accumulated charge populations at the time of transportation and burial of sediments remains a critical assumption in luminescence dating this is particularly the case for fluvial sediments we have tested the extent of bleaching in fluvial environments by applying the single aliquot regeneration sar equivalent dose d e determination technique coupled with tests for partial bleaching in the majority of cases samples collected from a point bar complex on the colorado river texas exhibit evidence of incomplete bleaching use of the minimum sar d e in these cases resulted in estimated residual ages of c 100 300 years in a similar examination of sar d e s for bed load samples collected along the loire river we observe a monotonic decrease in effective equivalent dose d e from values of 14 10 2 and 3 2 mean median and minimum gy at source down to 3 3 3 6 and 1 6 gy in the first kilometre of transportation down to levels of 0 3 0 2 and 0 0 gy for transportation distances exceeding 300 km we observed virtually no effect on the d e in the bed load of the introduction of trunk tributary streams and conclude that the likelihood of resetting of osl in large fluvial systems is somewhat more effective that previously considered when the recycling of sediments down the system are borne in mind

forcing of large scale cycles of coastal change at the entrance to willapa bay washington abstract anomalous morphological features within large estuaries may be 1 recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes and 2 possible predictors of cycles of future coastal change at the entrance to willapa bay washington chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of cape shoalwater northward channel migration since the late 1800s conforms to the long term net sediment transport direction what requires explanation is periodic southward relocation of the trunk channel by as much as 5 km and attendant construction of moderately large sand spits on the north side of the bay such as kindred island tokeland peninsula and cape shoalwater both autocyclic and allocyclic processes may have been responsible for trunk channel realignment and associated spit deposition channel recycling may occur when the main channel becomes overextended to the north and the tidal flow is inefficient because of its decreased gradient and increased susceptibility to shoaling by the growth and migration of tidal sand ridges under those conditions trunk channel relocation would be facilitated by increased wave heights and water levels of el nino winter storms however co seismic subsidence is the most likely mechanism for abruptly increasing sand supply and longshore transport that would favor discrete periods of channel relocation and spit deposition unless external forcing changes sand supply and predominant sediment transport directions in the future the relative rise in sea level frequent winter storms and local deficit in the sand budget assure that beach erosion will continue at the mouth of this large estuary

luminescence dating of holocene aeolian sand movement thy denmark abstract we report on the application of optically stimulated luminescence dating to an investigation of the frequency of periods of aeolian sand movement and dune formation on the coast of thy holocene aeolian sediments interleaved with peaty palaeosols form some of the most complete successions known in western denmark samples were taken from a coastal exposure and an inland archaeological site dosimetry was based on laboratory gamma spectrometry and quartz luminescence measurements used the single aliquot regenerative dose protocol and 470 30 nm stimulation the sand samples cover an age ranging from about 100 years to 4500 years the youngest dates give us confidence that the material was well bleached at deposition good agreement was obtained with the radiocarbon palaeosol ages we identify three main periods of aeolian sand movement starting at about 4200 2700 and 900 years ago at least during the latter two periods significant aeolian sand movement occurred all three phases of aeolian activity were separated by long periods of stability and soil formation a more recent episode of dune formation restricted to the coast and beginning less than 200 years ago may have been triggered by modern coastal erosion

packrat midden evidence of late quaternary vegetation change in the white mountains california nevada packrat neotoma spp middens from the white mountains indicate climatic and plant community conditions for the last 19 000 yr during full glacial times ca 19 000 yr b p and at the pleistocene holocene boundary juniper woodlands were 600 m lower in elevation than at present midden assemblages and stable isotope data suggest lower temperatures and increased precipitation relative to the present into the early holocene two early holocene middens ca 8000 yr b p from lower elevations of the white mountains contain fragments of pinyon pine and indicate that both pinyon and juniper grew at a site that today supports only a pinyon woodland two middle holocene middens ca 5000 yr b p indicate that there was an upward migration of pinyon juniper woodlands along a high elevation ecotone but little change in the middle of the pinyon juniper woodland middens from the late holocene indicate that present day plant communities were in place by ca 2000 yr b p or before

solar wind dependence of the occurrence and motion of polar auroral arcs a statistical study 1 polar uv images from a 3 month period in winter 1998 1999 are used for a statistical study of polar arcs the study covers all auroral arcs that are located poleward of the northern auroral ova

3 d geometry and luminescence chronology of quaternary soft sediment deformation structures in gravels northeastern brazil abstract this paper reports and describes soft sediment deformation in gravels and gravelly sediments in quaternary alluvial deposits of the potiguar basin northeastern brazil deformation structures were measured in terms of geometry size and relationship with sedimentary bedding using geological mapping and ground penetrating radar tl and osl irsl methods following mar and sar protocols were used to date sediments and soft sediment deformation events our results indicate that soft sediment deformation structures are widely distributed in several stratigraphic intervals of alluvial channel deposits in a low lying topographic valley depending on their geometry and composition two types of soft sediment deformation structures occur pockets and dome like load structures these structures resulted from the shaking of sediments with a reverse density gradient system which caused collapse and realignment of pebbles these features are similar in morphology and size to modern examples of seismically induced soft sediment deformation in coarse sediments tl and osl ages indicate that sediment deposition and associated soft sediment deformation occurred at least six times from 352 ka to 9 ka

assessing ams 14c ages of detrital organics from holocene and late pleistocene moraines east central sierra nevada california usa obtaining age estimates of moraines which have insufficient carbon for conventional 14 c dating may be possible by ams 14 c dating of detrital organic material in the till matrix sufficient detrital carbon was available in the till matrix of holocene and late pleistocene moraines of upper laurel creek canyon east central sierra nevada california for ams 14 c measurements radiocarbon analysis of till matrix organics from the moraine closest to the headwall ml reveals an age of 2875 60 bp eth 13550 the next oldest moraine m2 yields 4450 60 bp eth 12810 m3 the oldest moraine in the bloody mountain cirque yielded organics with a radiocarbon age of 13 600 120 bp eth 12812 while results are preliminary these ages are among the first on till matrix in the sierra nevada and are consistent with geomorphic context other palaeoecologic records in the sierra nevada and palaeolake records in the western united states

luminescence dating of archaeological materials using a new technique based on single aliquot measurements abstract a dating method based on single aliquot luminescence dose determination was applied to quartz and feldspars from heated archaeological materials the problem of changes of sensitivity to radiation resulting from signal erasure in regeneration measurements was studied in some detail and a new method based on single aliquot regeneration measurements within an added dose framework which appears to eliminate the problem of sensitivity change is proposed preliminary dating results mainly using quartz obtained with the new method are presented

holocene loess sedimentation along the qilian shan china significance for understanding the processes and timing of loess deposition abstract we present optical ages for well preserved loess deposits along the qilian shan a 500 km long mountain belt forming the tectonically active northeastern margin of the tibetan plateau loess on tectonically controlled fill terraces along the shiyou and baiyong rivers was dated by applying the single aliquot regeneration sar technique to coarse grained 90 160 m quartz samples additional measurements on polymineralic fine grained 5 10 m samples were carried out to allow a comparison between various optical dating techniques currently in use the results demonstrate that i loess accumulation started between 13 and 11 ka b p continuing to the present ii mean loess accumulation rates range between 9 and 16 cm ka 1 and iii holocene loess is not restricted to certain sites only but is a prevalent phenomenon along the qilian shan mountain front the absence of loess deposits of late pleistocene age is a result of a combination of cold and dry climate conditions strong winds and the absence of a vegetation cover during the last glacial period only with the change to a warmer and moister climate at the onset of the holocene did a plant cover develop which acted as a dust trap thus initiating the formation of loess

paleoproduction and environmental change at mono lake eastern sierra nevada during the pleistocene holocene transition abstract the late quaternary limnological history of mono lake 16 6 4 3 cal kyr bp a hydrologically closed basin in the eastern sierra nevada california is inferred based on a multi indicator analysis of a long 10 8 m composite sediment core constructed from overlapping deepwater piston cores the composite core dated by 14c and tephra correlation shows variations in sedimentology magnetic susceptibility elemental geochemistry and stable isotopes through time consistent with changes in aquatic productivity hydroclimate and volcanism in the late pleistocene deepwater stratigraphy was influenced by high amplitude water level changes and runoff from a glaciated watershed in contrast mono lake s elevation was lower in the early to middle holocene low amplitude water level changes wave reworking of the shoreline and water column stratification were important controls on facies during that time the data suggest that the chief controls on organic facies development in mono lake productivity preservation and dilution dynamics are sensitive to climate changes that influence lake level elevation water chemistry and the position of deltas the study shows that deepwater sediments from certain locales in mono lake are well preserved continuous and can be reliably dated with 14c applied to terrestrial materials when paired with precisely dated paleoshoreline data these sediments provide a high resolution archive of deglacial and holocene environmental information for the eastern sierra nevada

sedimentary charcoal as an indicator of late holocene drought in the sierra nevada california and its relevance to the future a holocene record of climate fire and vegetation regimes was reconstructed for siesta lake yosemite national park california using fossil pollen and charcoal from lake sediments these reconstructions were generated to provide a long term perspective on drought in the sierra nevada the sedimentary record is in agreement with other long term records of climate and vegetation from the sierra nevada and the records of climate and fire for the last c 1000 years are in agreement with tree ring and hydrological studies this correspondence suggests that sedimentary charcoal and pollen are reliable indicators of change in climate vegetation and fire frequency through time the fire frequencies associated with the droughts of the mediaeval warm period are only half as great as those recorded during the early holocene insolation maximum model results suggest that the temperature increases associated with the insolation maximum are a good analogue for those expected with global warming if this is the ca

late pleistocene vegetation of kings canyon sierra nevada california seven packrat midden samples make possible a comparison between the modern and late pleistocene vegetation in kings canyon on the western side of the southern sierra nevada one modern sample contains macrofossils and pollen derived from the present day oak chaparral vegetation macrofossils from the six late pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers juniperus occidentalis pinus cf ponderosa and p monophylla the pollen spectra of these pleistocene middens are dominated by pinus sp taxodiaceae cupressaceae taxaceae tct and artemisia sp mesophytic conifers are represented by low macrofossil concentrations sequoiadendron giganteum is represented by a few pollen grains in the full glacial edaphic control and snow dispersal are the most likely causes of these mixed assemblages the dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the sierra nevada these assemblages suggest that late wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values this conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late wisconsin the records in these middens also suggest that s giganteum grew at lower elevations along the western side of the range and that p monophylla was more widely distributed in cismontane california during the pleistocene

late neanderthals at jarama vi central iberia previous geochronological and archaeological studies on the rock shelter jarama vi suggested a late survival of neanderthals in central iberia and the presence of lithic assemblages of early upper paleolithic affinity new data on granulometry mineralogical composition geochemical fingerprints and micromorphology of the sequence corroborate the previous notion that the archaeological units jvi 2 1 to jvi 2 3 are slackwater deposits of superfloods which did not experience significant post depositional changes whereas the artifact rich units jvi 3 and jvi 1 mainly received sediment inputs by sheetwash and cave spall new ams radiocarbon measurements on three samples of cut marked bone using the ultrafiltration technique yielded ages close to or beyond the limit of radiocarbon dating at ca 50 14c ka bp and hence suggest much higher antiquity than assumed previously furthermore elevated temperature post ir irsl luminescence measurements on k feldspars yielded burial ages for subunits jvi 2 2 and jvi 2 3 between 50 and 60 ka finally our reappraisal of the stone industry strongly suggests that the whole sequence is of mousterian affinity in conclusion jarama vi most probably does not document a late survival of neanderthals nor an early upper paleolithic occupation in central iberia but rather indicates an occupation breakdown after the middle paleolithic

depositional environment and luminescence chronology of the hoarusib river clay castles sediments northern namib desert namibia abstract the clay castles in the hoarusib river valley are fine grained deposits in a tributary immediately upstream of a narrow gorge sedimentological analysis reveals three lithofacies associations 1 channel facies association near the mouth of the tributary 2 back flow facies association in the middle section and 3 silt and massive sand facies association in the head of the tributary overall sedimentary architecture shows that aggradation of the main hoarusib channel led to back flooding into the tributary and the deposition of massive fine grained deposits decreased discharge competency increased sediment load and the presence of narrow gorges within the main valley are suggested as reasons for the aggradation inter fingering of desert derived sediments channeled down the tributary and backflow sediments from the main river indicate an increase in both upland and desert rainfall during the course of sedimentation optically stimulated luminescence osl dating of these deposits indicates formation between 44 and 20 ka with the possibility that deposition occurred during two phases of rapid sedimentation at ca 42 and 25 ka

late holocene dune accretion and episodes of persistent drought in the great plains of northeastern colorado abstract the great plains of the mid west usa contain dunefields which display stratigraphic evidence of episodic sand drift throughout the holocene and in some cases the late pleistocene widespread aeolian activity has been linked to persistent megadroughts caused by a weakening of the tropical moisture laden circulation from the gulf of mexico and equatorial pacific infrared stimulated luminescence irsl dating has been applied to two exposures in the fort morgan dunefield of northeastern colorado where radiocarbon dated buried soils provide ages for land surface stability irsl ages show that sand drift occurred episodically during the late holocene at 4 85 2 37 1 06 0 80 0 6 0 53 and 0 37 ka

simultaneous optical observations of transpolar arcs in the two polar caps optical observations with de 1 and viking demonstrate conclusively that transpolar arcs can be present simultaneously at polar latitudes in both hemispheres the arcs observed here are aligned parallel to one another on opposite sides of the magnetic pole and relative to the noon midnight meridian are rotated slightly in the counterclockwise direction when viewed from above the north pole

subsidence of ionospheric flows triggered by magnetotail magnetic reconnection during transpolar arc brightening a transpolar arc tpa which extended from postmidnight to prenoon was seen on 16 september 2001 in the northern hemisphere under northward interplanetary magnetic field imf bz and weakly dawnward imf by conditions super dual auroral radar network detected significant westward plasma flows just equatorward of the poleward edge of the midnight sector auroral oval these plasma flows were confined to closed field lines and are identified as the ionospheric plasma flow signature of tail reconnection during imf northward nonsubstorm intervals trinnis these trinni flows persisted for 53 min from prior to the tpa appearance to the cessation of tpa growth they are usually observed before and during intervals when tpas are present but in this case subsided after the tpa was completely connected to the dayside additional slower flows across the open closed polar cap boundary were seen at the tpa onset time in the same magnetic local time sector as the nightside end of the tpa these ionospheric flows suggest that magnetotail reconnection significantly contributed to the tpa formation as proposed by milan et al 2005 https doi org 10 1029 2004ja010835 we propose a possible scenario for an absence of the trinni flows during the tpa brightening by considering the relation between the extent of the magnetotail reconnection line mapped onto nightside auroral oval and the tpa width trinni flows would subside when the extent of x line is comparable to the tpa width therefore our results suggest that the fate absence or presence of trinni flows on closed field lines during the tpa formation would be closely related with magnetotail reconnection extent

the paleoecology and stratigraphy of nichols meadow sierra national forest california usa sediment stratigraphy and pollen plant macrofossil and charcoal analyses along with nine radiocarbon dates from nichols meadow provides the most intensive investigation of sierra nevada montane meadow development and paleoecology during pollen zone nm i ca 18 500 12 500 yr b p the nichols meadow area contained a stream during the tioga glacial stage the presence of high artemisia and gramineae pollen percentages along with a very low pollen influx rate reflects a cold dry steppe woodland environment pollen zone nm ii ca 12 500 8800 yr b p documents the development of a lower montane forest and giant sequoia sequoiadendron giganteum community which existed around a small meadow the higher sediment accumulation rates suggest that fallen trees contributed to the aggregation of meadow sediments arly holocene aridity is recorded in pollen zone nm iii ca 8800 6000 yr b p by poorly preserved pollen we infer that the forest trees closed in on the meadow and occupied the meadow floor the reduction in available moisture caused giant sequoia to become locally extinct in the nichols meadow area probably moving into their current distribution within the nelder grove pollen zone nm iv 6000 yr b p present reflects the development of the modern nichols meadow less sand in the meadow sediments due to stable vegetation surrounding nichols meadow allowed the increased retention of ground water this along with the neoglacial cooling trend at ca 3000 yr b p caused ground water to rise and saturate the meadow these events excluded the conifers from the meadow surface and allowed herbaceous vegetation associated with wet meadows to dominate overgrazing and channeling of the meadow s outflowing stream caused the water table to drop resulting in the incision of the meadow

developments in optically stimulated luminescence and photo transferred thermoluminescence dating of young sediments application to a 2000 year sequence of flood deposits this paper demonstrates how optically stimulated luminescence osl and photo transferred thermoluminescence pttl can be used to date young 0 2000 year old flood deposits on the bank of a major river in the southern tablelands of southeastern australia quartz grains extracted from these deposits do not show a detectable dose dependent sensitivity change following optical stimulation this allows a recently proposed regeneration based protocol sara to be used to estimate the equivalent dose de acquired since burial for the oldest sample a dependence of de on pre heat temperature is removed by heating to at least 180 c for 10 s before stimulation values of de are reported for six samples using both osl and pttl values ranged between 0 4 and 6 5 gy with overall uncertainties usually 7 the values of de obtained using osl and pttl are in agreement dose rates are calculated from detailed analyses of environmental radionuclide concentrations and the resulting luminescence dates range from 100 13 to 1920 130 years before present the uncertainties include systematic effects for two layers where there is age control by 14c dates the luminescence dates are in good agreement unfortunately the limitations of the 14c data preclude firm conclusions about the size of any effective age residual at deposition for the luminescence samples although this is likely to be 50 100 years it is concluded that luminescence dating offers a considerable improvement over other techniques including 14c for recently transported fluvial sediments

paleofire reconstruction for high elevation forests in the sierra nevada california with implications for wildfire synchrony and climate variability in the late holocene abstract here we present two high resolution records of macroscopic charcoal from high elevation lake sites in the sierra nevada california and evaluate the synchroneity of fire response for east and west side subalpine forests during the past 9200 yr charcoal influx was low between 11 200 and 8000 cal yr bp when vegetation consisted of sparse pinus dominated forest and montane chaparral shrubs high charcoal influx after 8000 cal yr bp marks the arrival of tsuga mertensiana and abies magnifica and a higher than present treeline that persisted into the mid holocene coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the sierra nevada after 3800 cal yr bp independent fire response occurs between 9200 and 5000 cal yr bp and significant synchrony at 100 to 1000 yr timescales emerges between 5000 cal yr bp and the present especially during the last 2500 yr indistinguishable fire return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late holocene fires after 1200 cal yr bp are often synchronous and corroborate with inferred droughts holocene fire activity in the high sierra nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the el nino southern oscillation

timing of the last sequence boundary in a fluvial setting near the highstand shoreline insights from optical dating we investigated by means of optical dating the chronostratigraphic nature of the sequence boundary associated with the last glacial in a sandy to gravelly compound paleovalley fill just landward of the highstand shoreline in the rhine meuse delta netherlands laterally extensive fluvial strata deposited during oxygen isotope stage 4 coeval with a major sea level fall unconformably overlie estuarine deposits from stage 5 or fluvial deposits from the penultimate glacial stage 6 these chronostratigraphic relationships differ substantially from widely used models and indicate 1 that sequence boundary formation in this setting was associated with the onset of pronounced sea level fall shortly after 80 ka 2 that the time gap represented by the sequence boundary may be extremely small 10 k y 3 that the age of the sequence boundary may decrease both updip and downdip of the highstand shoreline and 4 that our study does not provide viable diagnostic criteria for a sea level controlled sequence boundary above the falling stage systems tract despite the high frequency high amplitude glacio eustatic regime that might be considered ideal for the formation of an unambiguous unconformity the last sequence boundary in this setting is commonly cryptic

late glacial and early holocene vegetation and climate change near owens lake eastern california abstract pollen and algae from owens lake in eastern california provide evidence for a series of climatic oscillations late in the last glaciation juniper woodland which dominated the owens valley from 16 200 to 15 500 cal yr b p suggests much wetter conditions than today although still wetter and cooler than today the area then became fairly warm and dry with woodland being replaced by shrubs mainly sagebrush from 15 500 to 13 100 cal yr b p next chenopodiaceae shadscale increased woody species declined and lake levels fell all evidence for a brief ca 100 200 yr drought about 13 000 cal yr b p the climate continued to oscillate between wet and dry from 13 000 to 11 000 cal yr b p after 11 000 cal yr b p low lake levels and the increased dominance of desert shrubs indicate the beginning of warm dry holocene conditions the region s climate was unstable during the younger dryas but uncertainities in dating prevent identification of the younger dryas interval in the owens lake record comparison of the owens lake record with studies in the sierra nevada and great basin suggest that the climate was generally wetter between 13 000 and 11 000 cal yr b p with warmer summers although no consistent pattern of climate change emerges

late wisconsin paleoecologic record from swamp lake yosemite national park california a 7 86 m sediment core from swamp lake in yosemite national park california provides a continuous record of environmental change over the last ca 16 000 yr as inferred from pollen macrofossil and microscopic charcoal analyses the core stratigraphy documents late wisconsin tioga stage deglaciation between 16 000 and 13 700 yr b p approximately 6000 3500 yr earlier than higher elevation sierra nevada records the core includes five volcanic ash layers chemically identified as four mono craters ashes and the tsoyawata ash mt mazama oregon the fossil record shows that herbs and sagebrush dominated the glacial environment at swamp lake by 12 000 yr b p a mixed conifer forest composed of high and mid elevation conifers grew around the lake suggesting a cool wet late glacial environment the modern sierra montane forest did not become established until ca 10 400 yr b p when maximum charcoal concentrations and minimum fir pollen percentages indicate an early holocene xeric period the record suggests that a cooling trend began ca 6500 yr b p and persisted until ca 3700 yr b p when the modern climatic regime was established

optically stimulated luminescence dating of a stratigraphic late glacial holocene sequence in the po plain bubano quarry bologna italy abstract quartz and k feldspars from an exposed 14 m thick undisturbed succession of silty clay late glacial holocene sediments in the po plain bubano quarry bologna province italy were optically dated for part of the sequence three radiocarbon ages and palynological dating provide an independent age control the separation procedures whose effectiveness was checked at each step by means of quantitative x ray powder analysis qxrpd and single aliquot regenerative dose protocols adopted are discussed in general the quartz optically stimulated luminescence osl ages are systematically younger than those obtained with feldspars probably due to the presence of medium component in the osl decay the evidence of contribution from the low sensitivity light traps has been checked using lm osl measurements and the equivalent doses have been calculated considering only the contribution of fast components moreover a residual presence of feldspars in the quartz separated fraction even if not detected by qxrpd could account for the observed underestimation the osl ages were consistent with the radiocarbon chronology

quantification of the transient response to base level fall in a small mountain catchment sierra nevada southern spain 1 we integrated optically stimulated luminescence dating and 10be cosmogenic nuclide measurements to quantify short to medium term 102 104 years catchment dynamics and response to active tectonics in the 27 km2 rio torrente catchment sierra nevada southern spain rapid base level fall has triggered knickpoint migration up both trunk and tributary channels resulting in two distinct geomorphic zones 1 a steep lower catchment with concordant rates of hillslope erosion and channel incision over both short 100 years 5 8 mm yr 1 and medium 12 ka 5 1 mm yr 1 timescales and 2 a low relief soil mantled upland topography with uniformly low bedrock and hillslope erosion rates 0 05 0 02 mm yr 1 the uniformity of erosion in this upland surface indicates that catchment topography was previously in steady state rapid river incision below the channel knickpoints has resulted in the development of steep landslide dominated hillslopes that are essentially tracking the incising channel the magnitude of base level fall required to generate these steep hillslopes is 100 m at least 50 m of this base level fall occurred during the past 21 ka these steep hillslopes are eroding back into the low angled upland surface at a much slower rate than the channel knickpoint consequently the trunk channel knickpoint has already reached the catchment headwaters while hillslopes continue to adjust to the new base level indicating that the channel profile will regain equilibrium form long before hillslopes thus hillslopes are the limiting factor for the duration of landscape transience in this small mountain catchment

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

effects of storminess sand supply and the north atlantic oscillation on sand invasion and coastal dune accretion in western portugal holocene forested coastal dunes fringe the atlantic coast of western portugal mapping of dunes in the field and using air photographs shows a range of forms reflecting dominant northwest and westerly onshore wind regimes planting of maritime pine forests in the thirteenth and twentieth centuries was initiated because of sand invasion causing problems for human settlement and agriculture early holocene dunes have a well developed podsol and date to 9 7 and 8 2 ka suggesting at least some of these sands may have been emplaced during a global cooling event significant transgressive dune accretion at 2 2 and 1 5 ka implies abundant sand supply and strong onshore winds the most recent dune building period dates to ad 1770 1905 and coincides with a predominantly negative winter north atlantic oscillation index naoi accretion of dunes along the portuguese coast appears out of phase with dune development in southwest france which may reflect different atlantic storm tracks driven by changes in the domin

the transition of very coarse grained meandering to straight fluvial drainage systems in a tectonized foreland basement landscape during the holocene se germany a joint geomorphological geological study abstract very coarse grained meandering to straight fluvial drainage systems evolved during the holocene

luminescence chronology of the bama beach ridge chad basin north eastern nigeria the mega lake chad palaeo beach ridge is covered by aeolian deposits the elevation 320 335 and 338 m a s l is the rim to the southwestern shores of mega lake chad and the initial deposits of this palaeo beach are believed to have been guided by a neotectonic fault line trending nnw sse luminescence dating was conducted on quartz grains extracted from sedimentary layers of the ridge section samples from the highest point on the ridge have revealed that aeolian deposits covering the ridge date from 3 3 0 31 ka at 2 m to 6 6 0 64 ka at about 5 m a water laid deposit of fine to medium sands from 5 m to 8 m depth has ages of 6 1 0 54 to 9 6 0 7 ka and fine medium to coarse sand from 10 to 17 m depth have ages from 18 4 1 5 to 26 4 9 3 ka

late weichselian and holocene palaeogeography of the rhine meuse delta the netherlands abstract a large number of lithological borehole descriptions 14c dates archaeological artefacts and gradients of palaeochannels were used to reconstruct the holocene development of the rhine meuse delta data were stored in a geographical information system database that enables generation of palaeogeographical maps for any time during the holocene the time resolution of the palaeogeographic reconstruction is about 200 years during the holocene avulsion was an important process resulting in frequent shifts of areas of clastic sedimentation palaeogeographic evolution of the rhine meuse delta is mainly governed by complex interactions among several factors these are 1 location and shape of the late weichselian palaeovalley 2 sea level rise which resulted in back filling of the palaeovalley 3 peat formation which was most extensive in the western part of the back barrier area especially between 4000 and 3000 14c yr bp this more or less fixed the river pattern at that time and resulted in few avulsions 4 neotectonics differential tectonic movements of the peel horst and roer valley graben seem to have influenced river behaviour formation of an asymmetrical meander belt location of avulsion nodes especially from 4500 to 2800 14c yr bp when the rate of sea level rise had decreased after 2800 14c yr bp the sea level rise further decreased and the tectonic influence still may have influenced avulsions but from then on other factors became dominant 5 increased discharge sediment load and or within channel sedimentation after 2800 14c yr bp river meanders of rhine distributaries as well as the single channel of the meuse show remarkable increases in wavelength interpreted as a result of increased bankfull discharge and sediment load increased discharge may initially have been caused by a higher precipitation after 2000 14c yr bp both discharge and sediment load seem to have increased as a result of human influence alternatively decreasing gradients as a result of sea level rise may have caused an increased within channel sedimentation and channel widening which would also lead to increased meander wavelengths 6 composition of the river banks meandering river channels tend to adhere to the sandy margins of the late weichselian palaeovalley and a high channel sinuosity is found in areas where river banks consist of sand 7 marine ingressions e g the ad 1421 st elizabeth s flood caused large scale erosion in the southwestern part of the fluvial deltaic plain 8 human influence since about ad 1100 human influence dominated the palaeogeographic evolution rivers were embanked and dredged meanders were cut off and for the meuse a new distributary canal the bergsche maas was dug in ad 1904 discharge distribution over the various channels is strictly controlled nowadays an unusual feature of the delta is the prolonged existence of the oude rijn channel belt

optical dating of holocene dune sands in the ferris dune field wyoming abstract optical dating of late quaternary quartz dune sands from the clear creek portion of ferris dune field wyoming demonstrates the considerable potential of the technique as a chronostratigraphic tool a sequence of radiocarbon dated holocene interdune strata permit optical dating of the intercalated dune sand to be tested the concordance is good the optical dates for the aeolian deposits not datable by radiocarbon suggest that aeolian sedimentation at clear creek peaked during two relatively short phases at ca 8500 and 4000 yr b p the dates indicate that aeolian accumulation maxima at least in the clear creek area may not be synchronous with previously defined phases of marked aridity

a late quaternary chironomid inferred temperature record from the sierra nevada california with connections to northeast pacific sea surface temperatures chironomid remains from a mid elevation lake in the sierra nevada california were used to estimate quantitative summer surface water temperatures during the past 15 000 yr reconstructed temperatures increased by 3 c between lake initiation and the onset of the holocene at 10 600 cal yr bp calibrated years before present temperatures peaked at 6500 cal yr bp displayed high variability from 6500 to 3500 cal yr bp and stabilized after 3500 cal yr bp this record generally tracks reconstructed santa barbara basin sea surface temperatures ssts through much of the holocene highlighting the correspondence between sst variability and california land temperatures during this interval

chronology and the upper dating limit for loess samples from luochuan section in the chinese loess plateau using quartz osl sar protocol abstract luminescence dating of loess older than 100 ka has long been a challenge it has been recently reported that using optically stimulated luminescence osl of fine grained quartz 4 11 m extracted from loess the range of luminescence dating could be pushed to 0 6 ma with osl ages being in agreement with independent ages watanuki t murray a s tsukamoto s 2005 quartz and polymineral luminescence dating of japanese loess over the last 0 6 ma comparison with an independent chronology earth and planetary science letters 240 774 789 the aim of this study is to provide a luminescence chronology 20 samples for the standard luochuan loess section and to further examine the upper limit of quartz osl dating for chinese loess the growth curve does not saturate at 700 gy and should allow reliable equivalent dose d e determination up to at least 400 gy however when compared with independent chronological control the d e that could be treated as reliable is less than 230 gy corresponding to 70 ka in age for chinese loess and the d e larger than 230 gy should be underestimated ages for samples from the lower part of palaeosol s1 are severely underestimated with the maximum age of 95 ka for a sample from the bottom of this palaeosol much younger than the expected age of 128 ka the maximum d e obtained for sample l9 m collected from loess layer l9 which is below the matuyama brunhes b m boundary whose age is 780 ka is only 403 gy which corresponds to an age of 107 ka the cause of underestimation is not yet clear the previous results by watunuki et al 2005 on the extension of osl dating of loess to 0 6 ma is not confirmed when evaluating the validity of osl ages in s1 another possibility is to question the already established chronological frame for luochuan section which is based on the hypothesis of continuous dust deposition the assumption of an erosion hiatus between l2 and s1 could make the osl ages look reasonable however if this is the case then it is difficult to explain why the age of sample l9 m is only 107 ka which could be treated as a saturation age while the osl can provide a correct age for loess as old as 94 9 ka for sample lc22 collected from the bottom of s1 much work is required to clarify these confusions

isochron dating of sediments using luminescence of k feldspar grains sponsorship research grant council of the hong kong special administrative region china project 7106 02p 7032 05 and 7035 06

extremely high latitude auroras over 1600 defense meteorological satellite program north polar images from the winters 1972 1973 1974 1975 were studied for the occurrence of auroral arcs at corrected geomagnetic latitudes greater than 80 auroras at these latitudes are designated extremely high latitude auroras and are categorized by the local time sectors in which they occur and their relationship to discrete oval arcs a data base of 300 cases of cap auroras was formed for correlation studies with geomagnetic activity indices and solar wind parameters by far the greatest number of extremely high latitude auroras occur in the morning sector and appear to be expansions of the system of morning oval arcs poleward the remaining categories include evening arcs expanding into the cap single sun aligned arcs and midnight sector oval auroras expanding into the cap except for the last category the auroras occur for similar magnetospheric conditions moderate values of kp and dst but comparatively low values of ae they also occur preferentially for high solar wind speed and for positive bz while far less clear their location in the cap shows a dependence on by morning evening arcs occur with greater frequency for negative positive by

optically stimulated luminescence dating of late holocene raised strandplain sequences adjacent to lakes michigan and superior upper peninsula michigan usa this study evaluates the accuracy of optically stimulated luminescence to date well preserved strandline sequences at manistique thompson bay lake michigan and tahquamenon and grand traverse bays lake superior that span the past 4500 yr the single aliquot regeneration sar method is applied to produce absolute ages for littoral and eolian sediments sar ages are compared against ams and conventional 14 c ages on swale organics modern littoral and eolian sediments yield sar ages b100 yr indicating near if not complete solar resetting of luminescence prior to deposition beach ridges that yield sar ages b2000 yr show general agreement with corresponding 14 c ages on swale organics significant variability in 14 c ages n2000 cal yr b p complicates comparison to sar ages at all sites however a sar age of 4280 f 390 yr uic913 on ridge77 at tahquamenon bay is consistent with regional regression from the high lake level of the nipissing ii phase ca 4500 cal yr b p sar ages indicate a decrease in ridge formation rate after 1500 yr ago likely reflecting separation of lake superior from lakes huron and michigan this study shows that sar is a credible alternative to 14 c methods for dating littoral and eolian landforms in great lakes and other coastal strandplains where 14 c methods prove problematic

optically stimulated luminescence dates for late pleistocene sediments from stensnaes northern jutland denmark abstract quartz and feldspars from late pleistocene deposits have been studied using the single aliquot regenerative protocol eleven samples were collected from a single deposit on the north west coast of jutland denmark from geological evidence we interpret this sedimentary sequence to be glaciofluvial three samples glaciolacustrine six samples and glaciomarine two samples feldspar fading was measured after storage at elevated temperature and was undetectable for five samples in the remainder fading was between 5 and 9 nevertheless the overall agreement between the quartz and feldspar dates was very good the conventional interpretation of the nine freshwater samples is that they were deposited by the late weichselian ice our luminescence ages are significantly older than the time at which this event is believed to have started in this region and they are independently supported by one 14 c age

mathematical modeling of whole landscape evolution abstract the mathematical modeling of landform evolution consists of two components the processes represented i e considered dominant in the model and the typically computer model representation of these processes this review discusses the current debates surrounding processes represented in landform evolution the potential impact on both evolving landforms and computer model structure is discussed issues specifically discussed include a the fundamental nature of mass conservation and the role of detachment and transport limited processes in mass conservation equations b the interaction between detachment and transport limitation in channels c the role of hillslope erosion and soil properties and their interaction with channel processes d the interactions with tectonics when applying these models at large scale e depositional structures and implications for paleo climatic interpretation f engineering applications of these models and g numerical issues in the computer imp

130 000 yr continuous pollen record from clear lake lake county california pollen analysis of a 115 m sediment core from clear lake lake county california provides a climatic record that is continuous for the past 130 000 yr the pollen record reflects migrations of the tree species of the california coast ranges in response to the climatic changes of the last glacial cycle during interglacials the clear lake pollen rain was dominated by quercus oak pollen during cooler periods oak pollen was replaced by pollen of coniferous species the curve for quercus pollen strongly resembles and is used to correlate with both deep sea oxygen isotope curves and the climatic record from certain european pollen studies

luminescence dating using feldspars a test case from southern north island new zealand abstract luminescence dating using coarse grain potassium rich feldspars is applied to a suite of 12 dune sands collected from southern north island new zealand the expected ages of the samples range from modern to 350 ka luminescence ages were calculated using thermoluminescence and infra red stimulated luminescence measurements to determine total bleach and regeneration equivalent doses for each sample no systematic difference was observed between any of these different methods withstanding the uncertainties in the independent ages of some samples comparison of the luminescence ages with those suggested by the independent age control suggests that reliable luminescence ages can be obtained for samples younger than 130 ka luminescence ages for older samples appear to underestimate the true age and it is suggested that this may be due to long term fading of the luminescence signal as suggested by mejdahl 1989