multiple dating approaches applied to the recent sediments in the yangtze river changjiang subaqueous delta the accumulation rate of recent deposits in a delta environment is critical to the study of delta dynamics and their sustainable management the most commonly used dating approach for recent 100

spatial and temporal patterns of aeolian activities in the desert belt of northern china revealed by dune chronologies abstract as a part of the inqua project a global digital database and atlas of quaternary dune field and sand seas 337 age records from the desert dunes of china and 20 from mongolian dune fields have been compiled in the database this has opened the possibility of exploring and synthesizing the quaternary environmental changes in the asian mid latitudes dune fields directly from the on site aeolian sand archives this paper assessed the sand dune chronologies in terms of geographical distribution data quality and their implications for late quaternary palaeoenvironmental reconstructions the available ages are concentrated mainly in the last 20 ka and many are from the fields of stabilized dunes in the eastern portion of the desert belt in northern china the number of records and the ratio between the records of stable state and the total records could act as a proxy for the palaeoenvironmental interpretation the aeolian sand activities deciphered from the chronological data in the eastern portion of the desert belt in northern china show a reasonable correlation with the general global climatic curves at the glacial interglacial timescales the limited aeolian sand records from the glacial period however hamper the understanding of the detailed features e g forms and processes of the dune fields during glacial times in the last two millennia however there has not been any meaningful correlation between aeolian dune activity and climatic variation at the centennial time scales probably due to the complexity of the aeolian sand systems and human interventions extending the coverage of dune chronology both temporally and spatially is urgently needed for a full understanding of the environmental changes in the dune fields

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

osl chronology of sand deposits and climate change of last 18 ka in gurbantunggut desert northwest china the development of the gurbantunggut desert is mainly controlled by the westerly wind and at present has little influence from indian and southeast asian monsoons a combined study using optically stimulated luminescence osl dating ground penetrating radar gpr surveys and climatic proxies analysis was carried out in the southern part of the desert the chronology extends back to 18 ka and is constructed based on 16 osl ages from boreholes in the linear dune body and the inter dune area the chronology suggests that sand deposition in the last 18 ka experienced two rapid accumulation phases at 11 and 2 5 ka ago which were also evident from the gpr surveys these periods relate to increased aridity in the region five climate phases are identified from the last 18 ka based on the osl chronology and climatic proxy analysis with grain size and magnetic susceptibility measurements the deglacial period 18 3 10 4 ka is characterized by climate instability and possible glacial melting events the holocene optimum peaked 8 5 ka and terminated 3 6 ka ago when the regional climate became arid osl samples from the dune body cluster around 2 5 ka which indicates rapid advance extension of dune bodies at this time copyright 2011 john wiley sons ltd

identification of well bleached grains in the optical dating of quartz abstract a simple means of identifying poorly bleached samples is proposed for the dating of quartz using the single aliquot additive dose optically stimulated luminescence osl protocol for a well bleached sample it is shown that the equivalent dose d e does not change with the ratio of the natural osl from a brief 0 1 s stimulation to the 110 c thermoluminescence from a subsequent small test dose in contrast in a poorly bleached sample the d e increases strongly at higher values of the ratio these observations suggest that this ratio can be used as an indicator of whether or not a sample is well bleached the osl tl ratio is also likely to be sensitive to such factors as thermal history and feldspar contamination

age dependence of luminescence signals from granitic and mylonitic quartz abstract granite and mylonitic samples with an age range of 11 3300 ma were collected from different regions of china several luminescence signals were measured from the extracted quartz age dependence has been observed in their luminescence signals including the sensitivity of the 110 c tl peak the temperature of the high temperature tl peak and the regenerated tl with dose other luminescence signals show little age dependence the tl reaches maximum at about 160 c in the quartz samples which is significantly different from signals from sediments it is concluded that the luminescence signals may lead to the establishment of a new geochronological method for the whole earth history

origin of eolian sand mobilization during the past 2300 years in the mu us desert china abstract eolian sand dunes and sand sheets are extensive in the semiarid regions of northern central china previous studies indicated that these eolian sands mainly formed during historical times however the sand sources and their reworking processes have not been well studied and even the reasons for their occurrence are still controversial field investigation and sedimentary evidence indicate that both the inner mu us desert and its southern marginal region both sources of modern eolian sand are largely associated with reworking of sands of the last glaciation based on geological documentary and archaeological data three phases of land cultivation during the past 2300 years together with historical droughts high wind energy and the easily reworked sand sources largely account for the occurrence of active sand dunes and sand sheets in the mu us desert

holocene lake level history of the tangra yumco lake system southern central tibetan plateau massive carbonate banks representing ancient lacustrine deposits are exposed in the catchment of the lake tangra yumco southern central tibetan plateau and nearby lake xuru co nine sediment samples were taken below and above these lacustrine deposits to determine periods of changing lake level using optically stimulated luminescence osl applying a multiple aliquot regeneration mar protocol according to facies and stratigraphy samples below the carbonate banks indicate a rising and samples from above a falling lake level the results indicate that the rising lake level of tangra yumco passed the sampling location at 10 5 and 2 1 ka while a falling lake level passed the sampling location at 0 9 ka the rising lake level of xuru co passed the sampling location at 7 9 and 1 7 ka and a falling lake level at 0 5 ka showing a similar trend as at tangra yumco combining these results with recalculated cosmogenic nuclide ages and previously published feldspar luminescence data allows the establishment of

post glacial entrenchment and knickpoint migration of the yarlung tsangpo gorge southeastern tibetan plateau abstract the formation of the yarlung tsangpo river system is commonly thought to be controlled by tectonic processes initiated several million years ago however climate change may also play an important role in guiding drainage evolution here we reconstruct the drainage history of the yarlung tsangpo gorge using field observations age constraints from optically stimulated luminescence and radiocarbon dating paleosalinity reconstruction and grain size analysis of lacustrine deposits and river valley characteristics field observations clay boron derived paleosalinity reconstruction and grain size analysis of lacustrine deposits demonstrate that a closed inland saline lake existed upstream of the yarlung tsangpo gorge implying that cutting of the gorge postdated this paleolake optically stimulated luminescence and radiocarbon dating suggest that the paleolake formed at least 51 ka and terminated after 13 ka with a shift in global climate following the last glacial maximum the paleolake drained by river capture and the gorge entrenchment commenced at the village of jiala northwest of the namche barwa peak approximately 13 10 ka ago the evolution of the yarlung tsangpo occurred on a remarkably short timescale of just tens of thousands of years in response to drainage system reorganization the yarlung tsangpo incised at an average rate of at least 26 mm yr the rapid fluvial incision initiated at jiala 13 ka ago propagated rapidly upstream at 2 12 m yr the yarlung tsangpo knickpoint has not stabilized but will likely continue to migrate upstream

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

luminescence dating of sand loess sequences and response of mu us and otindag sand fields north china to climatic changes the sand loess transition zone in north china is sensitive to climate change and is an ideal place to investigate past environmental changes however past climate change at millennial centennial timescales in this region has not been well reconstructed because of limited numerical dating alternations of sandy loam soils with aeolian sand layers in the mu us and otindag sand fields which lie along the sand loess transition zone indicate multiple intervals of dune activity and stability this change is probably a response to variations of the east asian monsoon climate during the late quaternary the single aliquot regeneration sar optically stimulated luminescence osl dating protocol which has been successfully applied to aeolian deposits worldwide is applied to these two sand fields in this study the osl ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale sections in both sand fields contain aeolian sand beds recording millennial scale episodes of dry climate and widespread dune activation including episodes at about the same time as heinrich event 5 and the younger dryas in the north atlantic region these results demonstrate the potential of aeolian sediments in semi arid north china to record millennial scale climatic events and also suggest that dry wet climate variation at the desert margin in china may be linked to climatic change elsewhere in the northern hemisphere through atmospheric circulation this article was published online on 27 november 2008 an error was subsequently identified this notice is included in the online and print versions to indicate that both have been corrected 16 december 2008 copyright 2008 john wiley sons ltd

optical dating of dune sands in the northeastern deserts of china abstract optical dating has been used to obtain the ages of fossil stabilized sand dunes from four sections in the northeastern deserts of china our results indicate that the optically stimulated luminescence ages of the four sections correlate well even though the samples were collected from different deserts about 600 km apart our results also indicate that active dune formation in this region lasted from the last glacial maximum to about 10 ka and that the warm climate of the holocene was interrupted by a cold dry dune formation episode about 3 5 1 7 ka the holocene optimum in this region is between 10 and 3 6 ka and a later warm humid dune stabilization phase lasted from at least 1 6 to 1 0 ka the youngest age on the uppermost sand unit yielded an age of only 40 yr supporting the previous argument that the existence of modern active eolian sands in the regions with a mean annual precipitation of up to 450 mm is not mainly due to drought but to extensive land cultivation over historic time from the luminescence properties of the quartz grains it is hypothesized that the sands in most of the sections are probably derived from more than one source with a minor source of quartz having a different thermal history before deposition

dune activity as a record of late quaternary aridity in the northern kalahari new evidence from northern namibia interpreted in the context of regional arid and humid chronologies abstract sediments from presently vegetated linear dune ridges in the caprivi strip of northern namibia are optically dated to assess the timing of dune building phases and aridity in the late quaternary the dunes have been constructed from sediments likely to have been initially transported into the area by fluvial processes dune sediments do not preserve obvious evidence of hiatuses in deposition in the dated period 48 121 ka but continuous deposition and therefore continuous aridity is considered unlikely given differences in dated phases compared with chronologies from western zimbabwe to the southeast and western zambia to the north that include ages derived from the same equivalent sampling depths laboratory experiments provide evidence that dune sediments have not been bioturbated since deposition such that sample palaeodoses determined from different sampling depths are a true reflection of the duration of sediment burial independent chronologies from cave sediments provide evidence that humid episodes have occurred in the region within the dated range of dune construction it is concluded that dune construction in the late quaternary has been punctuated that the preserved record reflects the attributes of the aeolian processes that affect linear dune development and that the late quaternary record of dune building in the middle and northern kalahari was spatially complex

optical dating of holocene sediments from the yangtze river changjiang delta china abstract establishing a reliable chronology is essential for understanding delta evolution which is normally performed using radiocarbon 14c dating and the recently emerging technique of optically stimulated luminescence osl the application of the latter one to the holocene yangtze river changjiang delta deposit is still quite limited in this study two 60 9 m long cores were collected from taizhou tz and nantong nt within the paleo incised valley of the yangtze river and a total of seven and nine osl samples were collected from the tz and nt cores respectively in addition ten accelerator mass spectrometry ams 14c ages of the tz core were presented with eight ams 14c ages that were previously obtained from the nt core the single aliquot regenerative dose sar protocol was applied to coarse silt sized 45 63 m and fine sand sized 90 125 m quartz the results showed that the grains in the 45 63 m size fractions appeared to be better bleached than those in the 90 125 m size fractions and the detection of insufficiently bleached sediments is required in order to obtain accurate age estimates the ages adopted for the samples range from 3 ka to 9 ka for the tz core and from 1 ka to 14 ka for the nt core which were in general internally coherent within the limits of experimental errors and with respect to their stratigraphic order the ams 14c age of the tz core were significantly older than their osl ages while those from the nt core generally showed good agreement with their osl ages one should be cautious when using ams 14c to date deltatic deposits based on the osl ages two periods of rapid accumulation rates can be found in both cores which are linked to the rapid sea level rise in early holocene and migration of delta front facies in late holocene these investigations indicate that osl technique is an effective method with which to date holocene deltaic deposits especially in coarse sedimentary layers where organic carbon material is sparse

shrinking lakes in tibet linked to the weakening asian monsoon in the past 8 2 ka expansion or shrinkage of closed lakes is a natural response to fluctuations in precipitation and evaporation linked closely to changes in strength or position of atmospheric circulation in tibet there are many such lakes with paleo shorelines that can be used for reconstructions of climate history despite the fact that many paleo shorelines are well preserved in tibet dating them has been seriously hindered by various difficulties here we present the first optical dating chronology for a series of paleo shorelines in zhari namco the third largest inland lake in central tibet our results indicate that the lake level has dropped 128m over the past 8 2ka younger shorelines are found at lower altitudes indicating that the shorelines follow a geomorphic chronological order and a broadly continuous trend of stepwise shrinkage the surface area of zhari namco has shrunk in size from 4605km2 at 8 2ka ago to 996km2 at present 300km3 of water has been lost from this lake such a loss in water implies a significant reduction in precipitation over the past 8 2ka a likely result of a weakening asian monsoon following the decreasing precipitation since the early holocene this area has become increasingly arid

geochemical evidence for an eolian sand dam across the north and south platte rivers in nebraska abstract geochemical and geomorphic data from dune fields in southwestern nebraska provide new evidence that the nebraska sand hills once migrated across the north and south platte rivers and dammed the largest tributary system to the missouri river the lincoln county and imperial dune fields which lie downwind of the south platte river have compositions intermediate between the nebraska sand hills quartz rich and northeastern colorado dunes k feldspar rich the most likely explanation for the intermediate composition is that the lincoln county and imperial dunes are derived in part from the nebraska sand hills and in part from the south platte river the only mechanism by which the nebraska sand hills could have migrated this far south is by complete infilling of what were probably perennially dry north platte and south platte river valleys such a series of events would have required an extended drought both for activation of eolian sand and decreased discharges in the platte river system a nearby major tributary of the north platte river is postulated to have been blocked by eolian sand about 12 000 14c yr b p we propose that an eolian sand dam across the plattes was constructed at about this same time

580 000 year environmental reconstruction from aeolian deposits at the mu us desert margin china abstract a 76 7 m thick section of aeolian sediment is exposed in the transition zone between the mu us desert and the loess plateau of northern china the aeolian sediments contain sand beds loess layers and palaeosols the particle size distribution data and the sem examination of quartz grains suggest the sand beds are wind blown origin palaeomagnetic measuring combined with thermoluminescence tl dating and pedostratigraphic correlation suggests the studied aeolian sequences were deposited within about 580 kyr the sand layers appear to reflect the episodic extensions of mu us desert during phases of active dune formation and intensified winter monsoon both the stratigraphy and the proxy climatic curves such as bulk magnetic susceptibility and grain size indicate that large amplitude second order climatic oscillations occur during both glacial and interglacial periods it is worth noting that nearly all the interglacial soils can be sub divided by the intercalated sand or loess beds this second order climatic oscillations are on the order of 10 000 of years which may reflect the precession scale variations of southeast summer monsoon driven by the orbital pacing of insolation in low latitudes

response of surface processes to climatic change in the dunefields and loess plateau of north china during the late quaternary this paper draws on recent optically stimulated luminescence osl dating to evaluate the long held assumption that dust accumulation rates in the loess plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time because both are controlled by the strength of the asian monsoons and also possibly because the dunefields are proximal loess sources the results show there is little evidence that high rates of loess accumulation coincided with well dated episodes of extensive dune activity in the mu us otindag and horqin dunefields at 11 8 ka and 1 0 ka explanations for the apparent lack of coupling include local variation in the trapping of dust and post depositional preservation of the loess and dune sediments in response to varying local environmental conditions in addition a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields the results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale the dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale but the timing of late quaternary dune activity along with a variety of other evidence indicates that moisture changes in many of the drylands of northern china may not be in phase with precipitation in core regions of the asian monsoons copyright 2011 john wiley sons ltd

optical dating of an offset river terrace sequence across the karakax fault and its implication for the late quaternary left lateral slip rate abstract the karakax fault is one of the largest left lateral strike slip faults at the rim of the northwestern tibetan plateau in this study the optical dating techniques were applied to the taersayijilega river terraces which were transversely cut and offset by the karakax fault six fluvial sand samples from the river terraces were collected and dated the results show that the terraces t2 t5 have ages of 14 5 1 0 ka 21 2 1 2 ka 28 5 1 7 ka and 39 7 2 5 ka respectively by interpreting high resolution satellite images the horizontal displacements of the four river terraces are estimated at 160 m 235 m 260 m and 365 m respectively based on the ages and offsets of the terraces the average left lateral slip rate of the karakax fault was estimated at 7 8 1 6 mm a during the late quaternary such rate of the karakax fault is significantly higher than that of the longmu gozha co fault suggesting that the karakax fault plays an important role in accommodating eastward movement of the tibetan plateau at the northwest during the late quaternary

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

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

timing and spatial distribution of loess and loess like sediments in the mountain areas of the northeastern tibetan plateau abstract most studies on landscape evolution on the tibetan plateau during the late quaternary have mainly focused on using lacustrine records however mantles of sandy silt and paleosols also provide valuable archives for reconstructing holocene paleoenvironmental change yet little is known about the distribution and timing of these late quaternary aeolian sediments to enhance understanding and knowledge of aeolian sediments in tibet and to help reconstruct the nature of late glacial through mid holocene landscape development a loess paleosol sequence the suohuduo section located at the eastern margin of the tibetan plateau at about 4000 m above sea level is examined using sedimentological geochemical and geochronological methods a chronostratigraphy is established using nine optically stimulated luminescence and one radiocarbon ages sedimentation increased during the late glacial and the early holocene with an upwards fining of sediments in the lower part of the section two mid holocene paleosols that date to about 8 5 ka to 7 ka and 5 5 ka to 4 ka reflect more humid climate conditions during the mid holocene than earlier times the upper part of the section is mainly silt which reflects a more open landscape with higher aridity since 4 to 3 ka this time these data support evidence for similar climate paleoenvironmental change in adjacent regions on the tibetan plateau

biotite breakdown and the formation of gahnite in metapelitic rocks from kemio southwest finland the formation of ferroan gahnite by breakdown of zinc bearing biotite has been studied in metapelitic gneisses from the kemio region in southwestern finland spinel compositions range from herc50 gahn40spin10 to herc15gahn82spin3 biotite contains up to 0 24 wt zno individual spinel grains show a gradual compositional zoning owing to increasing zinc contents towards the grain margins

large scale controls on the development of sand seas in northern china abstract although sand seas are located in arid regions given that the proportions of dune areas vary greatly from region to region they are clearly influenced by other factors as well as aridity this paper discusses the distribution pattern and major features of sand seas and large fields of stabilized dunes in northern china and demonstrates the main influences on their development it appears that the availability of onsite loose sediments not wind strength is critical to the occurrence of the sand seas on a regional scale tectonic endorheic basins or areas of alluvial fans or forelands of mountain ranges are advantageous to the accumulation of fluvial sediments and thus are ideal locations of large sand seas in an arid climate the large dune fields currently stabilized by vegetation were active sand seas during the drier periods of the late pleistocene and early holocene the distribution patterns of chinese sand seas suggest that the height or size of the dunes in the sand seas are determined more by the availability of sands than any other potential factors as the sand seas in china account for a large portion of deserts in the middle latitudes of the northern hemisphere taklamakan is the second largest sand sea on earth knowledge of these sand seas past changes is important for understanding climatic changes in the terrestrial regions of mid latitudes

magma genesis in a late proterozoic proto oceanic rift ree and other trace element data from the keweenawan mamainse point formation ontario canada abstract the keweenawan mamainse point formation of ontario consists of a sequence of tholeiitic lavas and transitional basalt dykes with trace element characteristics similar to other proto oceanic rift sequences stratigraphic variation of geochemistry allows the subdivision of the sequence into five series each of which has suffered shallow level fractional crystallization differences in incompatible element ratios and ree patterns however can only be explained by variations in the melting process ree modelling suggests that parental magmas may have been derived from a heterogeneous mantle with flat chondritic and lree depleted sources however the systematic evolution of ree patterns and other trace elements are better explained by dynamic partial melting within two subsequent rising mantle diapirs

thermoluminescence chronology of sand profiles in the mu us desert china abstract thermoluminescence tl is used to calculate the ages of two sand loess profiles in the marginal zone of the mu us desert china alternating units of dune sand and loess with palaeosols in the two profiles imply episodes of dune formation separated by periods of loess accumulation and pedogenesis our results indicate that there are three layers of dune sand intercalated in sediments of the last full glacial cycle suggesting the occurrence of three arid episodes during this time the first arid episode within this period occurred between

holocene environmental changes in the central inner mongolia based on single aliquot quartz optical dating and multi proxy study of dune sands abstract alternating units of dune sands and paleosols in the central inner mongolia imply multiple episodes of dune building and stabilization in response to the waxing and waning of the east asian monsoon such eolian deposits were dated by using the single aliquot quartz optical dating method combined with the multi proxy study on the deposits the past environmental changes during the holocene have been reconstructed our results indicate that widespread eolian sand mobilization occurred in the studied region during the beginning of the early holocene from 11 5 ka to 9 ka the climate became warm and humid during the period between 9 ka and 5 6 ka holocene optimum after 5 6 ka the region again became arid as inferred from dune building however the environmental changes during the late holocene have been affected by both climate and human impacts and the presence of desert environment in such semiarid region is not only the result of climatic drought of the late holocene but also related to poor land use practices

palaeoclimatic and palaeoenvironmental implications of late pleistocene aeolian sand in the jin shaan gorges of the yellow river valley revealed by luminescence chronology river valleys are critical water gas rock interactions zone where close interaction between fluvial and aeolian deposition are a pronounced feature in arid semi arid and semi humid environments

late quaternary aeolian activity in gonghe basin northeastern qinghai tibetan plateau china abstract aeolian deposits at four sites in the gonghe basin were used to reconstruct the history of aeolian activity over the late quaternary these deposits include well sorted aeolian sand paleosols and or loess aeolian sand represents dune field expansion and or dune buildup whereas paleosols indicate stabilization of dunes accompanying ameliorated vegetation cover on the basis of 25 dates by optically stimulated luminescence osl it appears that aeolian activities occurred episodically at 33 5 20 3 13 9 11 8 11 0 9 4 7 8 and 5 7 5 5 ka which is largely consistent with the recent findings from the adjacent semi arid areas aeolian sand mobility occurring during the early to mid holocene conflicts with a climatic optimum inferred from lacustrine records in the northeastern qinghai tibetan plateau this inconsistency may be resolved by interpreting aeolian activity as a response to decreased effective moisture due to enhanced evaporation induced by higher summer insolation at that time together with local terrain and its effects on moisture our results suggest that aeolian sand and paleosol cannot be simply ascribed to regional dry and wet climates respectively and they most likely reflect changes in effective moisture

optical dating reveals that the height of earth s tallest megadunes in the badain jaran desert of nw china is increasing abstract the badain jaran desert bjd in nw china is well known for its unique landscape of megadunes coexisting with permanent lakes the megadunes are already the tallest sand dunes on earth and some of them are up to 400 m high however it is unclear whether or not the height of the megadunes is continuing to increase under present climatic and environmental conditions in order to determine the growth status of the megadunes we collected 26 samples from the windward slopes of two megadunes for optically stimulated and infrared stimulated luminescence dating the results show that the thickness of the modern eolian sand layers increases from the lower part of the windward slopes with a thickness of less than 1 m to more than 2 m in the middle and to 9 m in the upper part this indicates that the height of the megadunes is continuing to increase under modern conditions the surface sediments from the base of the windward slope and the adjacent lake basin have relatively old ages of 6 7 ka indicating that these areas are eroding the recent eolian sands of the upper part of the megadunes likely originated from the base of the dunes or from the lake basin the megadunes in the bjd are currently becoming increasingly high and steep due to the upward migration and accumulation of sand particles increased humidity and a weakened wind regime in northern china related to ongoing climatic warming are likely the main factors in maintaining the growth of the megadunes

a fluvial terrace record of late quaternary folding rate of the anjihai anticline in the northern piedmont of tian shan china abstract crustal shortening of the tian shan range in northwest china has largely been accommodated by fold and thrust belts that mark the northern and southern mountain boundaries which were formed during the basinward propagation of the deformation front of tian shan investigating the deformation rates of active folds anticlines in the mountain piedmonts within different timescales is important for understanding the mountain building and front propagation processes of the tian shan in this study we investigate the late quaternary folding rate of the anjihai anticline one of the major anticlines in the northern piedmont of tian shan our study is based on optically stimulated luminescence osl dating and topographic measurements of folded river terraces three well preserved fluvial terraces across the anjihai anticline were identified and dated to be 3 6 0 1 ka 9 0 0 6 ka and 53 3 2 2 ka respectively these terrace ages are combined with shortening and uplift of the terraces estimated using an area conservation method and the terrace height profiles to evaluate the average shortening and uplift rates our results show that the minimum shortening rate of the anjihai anticline is 0 4 mm a between 53 ka and 9 ka and 1 1 mm a over the past 9 ka and the corresponding minimum uplift rates are 0 5 mm a and 1 4 mm a respectively if a local sedimentation rate of 0 3 mm a is taken into consideration the shortening rate is 0 7 mm a between 53 ka and 9 ka and 1 3 mm a since 9 ka and the corresponding uplift rates are 0 8 mm a and 1 5 mm a respectively these data suggest that the anjihai anticline has accommodated 20 25 of the total shortening across the whole eastern tian shan 5 mm a in the holocene our results suggest that the holocene is a relatively tectonically active time interval since the late pleistocene the late quaternary shortening rate of the anjihai anticline is much higher than its long term average shortening rate 0 2 mm a since its formation at 7 4 ma a similar situation has also been observed for other active folds in the northern and southern piedmonts of tian shan the higher late quaternary folding rate is possibly attributed to the gradual propagation of the tian shan towards its northern and southern foreland basins in the quaternary

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

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

loess deposits in beijing and their paleoclimatic implications during the last interglacial glacial cycle abstract loess paleosol sequences are important terrestrial paleoclimatic archives in the semi arid region of north central china compared with the numerous studies on the loess of the chinese loess plateau the eolian deposits near beijing have not been well studied a new loess section in the northeast suburb of beijing provides an opportunity for reconstructing paleoenvironmental changes in this region an optically stimulated luminescence osl chronology yields ages of 145 1 to 20 5 ka demonstrating that the loess deposits accumulated during the last interglacial glacial cycle high resolution climatic proxies including color index particle size and magnetic parameters reveal orbital scale climatic cycles corresponding to marine oxygen isotope stages mis 6 to mis 2 in contrast to the loess deposits of the central loess plateau loess near beijing is a mixture of distal dust materials from gobi and sand deserts in the arid part of northwestern china and proximal local alluvial sediments climatic change in beijing during the last interglacial glacial cycle was controlled primarily by the changing strength of the east asian monsoon paleosols developed during the last interglacial complex between 144 0 and 73 0 ka and the interstadial of the last glaciation between 44 6 and 36 2 ka being associated with an enhanced summer monsoon in response to increased low latitude insolation and a weakened siberia high loess accumulation occurred during cold dry stages of the last glaciation in response to the intensified winter monsoon driven by the strengthened siberia high and its longer residence time

the timing and environmental significance of late quaternary linear dune development in western zambia optical luminescence dates for 19 samples from the degraded linear dune field of western zambia indicate multiple periods of regional dune building for the late quaternary 32 000 27 000 16 000 13 000 10 000 8000 and 5000 4000 yr ago these dates show that the last glacial maximum was not the only time when dune construction commonly linked to marked aridity occurred in central southern africa during the late quaternary whereas rainfall significantly less than today s ca 1400 mm yr 1 is a prerequisite for dune construction in the area adequate sediment supply also determines dune construction and preservation so that dune building cannot be simply and singularly linked to marked aridity the zambezi river system is proposed as an important source of dune sediments with the nature of linear dune activity explaining why stacked sediments preserve several phases of dune formation chronologies of dune construction in western zimbabwe and the southwest kalahari are in broad agreement with our zambian chronology and support a model of rainfall shifts along a sw ne gradient with some notable disparities these are probably a function of interregional sediment supply differences the number of samples used to delimit constructional periods and the multicausal nature of forcing mechanisms