late quaternary hydrological dynamics in the middle kalahari forcing and feedbacks the kalahari region has become a major source of quaternary palaeoenvironmental data derived primarily from the analysis of geomorphological proxies of environmental change one suite of data from palaeolacustrine landforms has recently provided a new record of major hydrological changes in the last 150 ka burrough s l thomas d s g bailey r m 2009 mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system quaternary science reviews in press here we present an improved analysis of the drivers and feedbacks of lake level change utilising information from three main sources data from the lake system itself from analyses of other late quaternary records within the region and from climate modelling simulations using the hadley centre coupled climate model hadcm3 suggest that once triggered the lake body was large enough to potentially affect both local and regional climates surface waters and their interactions with the climate are therefore an important component of environmental dynamics during the late quaternary through its capacity to couple middle kalahari environments to distant forcing mechanisms and to itself force environmental change we demonstrate that the existence or absence of megalake makgadikgadi adds a new level of complexity to the interpretations of environmental proxy records in southern africa s summer rainfall zone

growth by extension and reworking of a south western kalahari linear dune optically stimulated luminescence osl dating studies of linear longitudinal dunes have been used extensively to elucidate late quaternary environments and climates in arid or formerly arid regions yet understanding of the development of such dunes is incomplete in particular conflicting opinions have been presented regarding the propensity of linear dunes to migrate laterally the degree to which they rework their own sediment during accumulation and whether they form primarily by extension as opposed to lateral sand movement from adjacent interdunes this study focuses on this last point although the importance of the other controversies is discussed in context a simple linear dune in the south western kalahari which has a prominent termination on a pan playa surface provides an opportunity to directly test hypotheses of dune extension chronostratigraphy along a 600 m transect along the crest of the dune constrained by 42 osl ages reveals that the dune grew by extension on occasions in the late pleistocene and early holocene but has also been subject to reworking along its length which has continued until recent times dune development by extensional growth is suggested to operate under environmental conditions more conducive to net accumulation whereas reworking is largely independent of conditions throughout the last 18 ka and may represent seasonal fluctuations in the position of the dune crest the relative significance of these two modes of development is suggested to be a key control on the efficacy of linear dunes as archives of environmental and climatic change copyright 2011 john wiley sons ltd

optically stimulated luminescence osl dating and palaeoenvironmental studies of pan playa sediment from witpan south africa abstract robust dateable sources of palaeoenvironmental proxy data are scarce in the southwestern kalahari desert and this study investigates the potential of pan playa floor sediments as an archive of late quaternary environmental change augering has revealed the presence of up to 3 m of clay and silt rich deposits in the base of witpan a small pan basin set amongst linear and lunette dunes the weakly stratified deposits include aeolian quartz sands and evaporites amongst a clay rich groundmass and are believed to have accumulated on a wetter than present pan surface the aeolian quartz fraction has been dated with optically stimulated luminescence osl and reveals accumulation of at least 50 cm of sediment at around 20 ka and previous accumulation at around 32 ka the northern and southern sections of the pan are shown to maintain some hydrological independence attributed to bedrock outcropping and also show distinct differences in their physical sedimentology biogenic proxies are poorly preserved with neither diatoms nor pollen found in adequate quantities although phytoliths found in both the pan floor sediments and the fringing lunette dune may offer a more resilient palaeoenvironmental indicator the possible value of pan floor sediments as dryland archives of physical and chemical and possibly selected biogenic palaeoenvironmental proxies combined with osl constrained chronologies should not be discounted

a 250 000 year record of lunette dune accumulation on the southern high plains usa and implications for past climates abstract a concentration of lake playa basins occurs on the southern high plains shp of northwest texas and eastern new mexico associated with these lake playas are lee side lunettes positioned on their southeast margins ranging in height from 1 5 to 10 m an osl dating program was applied to 30 samples from lunettes associated with large lakes and small playa basins samples were extracted from trenched dune sections or from deep cores earlier shp lunette investigations show depositional ages primarily in the late wisconsin and holocene this research extends the timing of lunette accretion to the middle pleistocene the earliest recorded deposition for these features the expanded chronology permitted investigation into dune morphology on nested lunettes built on contracting lake margins outer lunettes formed prior to inner dunes but simultaneous deposition occurred on downwind ridges as younger lee side dunes were constructed large lake lunettes were inactive during discreet shp pluvial episodes from early wisconsin to lgm conversely these lunettes accreted when climatic conditions promoted basin desiccation and aeolian deflation this suggests their mode of formation contrasts with lunette models recognized for other regions from post lgm to earliest holocene active lunette accretion occurred from 16 to 11 ka followed by a significant period of lunette construction during the mid holocene late holocene lunette deposition was interrupted by intervals of landscape stability lunette deposition between 1300s and 1700s corresponds with drought intervals recognized in tree ring records from adjacent regions recent lunette activity on the plateau is contemporary with the 1930 s dust bowl further insight into shp response to changing climatic conditions was given by comparing lunette depositional events with previous investigations on sedimentation intervals for draws lake playa basins and sand sheets

the leaf wax biomarker record of a namibian salt pan reveals enhanced summer rainfall during the last glacial interglacial transition abstract conventional continental geoarchives are rarely available in arid southern africa therefore palaeoclimate data in this area are still patchy and late quaternary climate development is only poorly understood in the western kalahari salt pans playas ephemeral lakes are common and can feature quasi continuous sedimentation this study presents the first climate related biomarker record using sediments from the omongwa pan a kalahari salt pan located in eastern namibia our approach to reconstruct vegetation and hydrology focuses on biogeochemical bulk parameters and plant wax derived lipid biomarkers n alkanes n alkanols and fatty acids and their compound specific carbon and hydrogen isotopic compositions the presented record reaches back to 27 ka during the glacial rather low 2h values of n alkanes and low sediment input exclude a strong influence of winter rainfall n alkane and n alkanol distributions and 13c values of n hentriacontane n c31 indicate a shift to a vegetation with a higher proportion of c4 plants at the end of the last glacial maximum until the end of heinrich stadial i ca 18 14 8 ka which we interpret to indicate an abrupt excursion to a short wetter period likely to be caused by a temporary southward shift of the intertropical convergence zone shifts in 2h values of n c31 and plant wax parameters give evidence for changes to drier conditions during early holocene comparison of this dataset with representative continental records from the region points to a major influence of summer rainfall at omongwa pan during the regarded time span and demonstrates the potential of southern african salt pans as archives for biomarker based climate proxies

playa lake basins on the southern high plains of texas and new mexico part i hydrologic geomorphic and geologic evidence for their development playa lake basins of the southern high plains texas and new mexico may originate wherever water periodically can collect in a surficial depression they expand however by hydrologic and geomorphic processes including 1 dissolution of lithologic carbonates by infiltrating water 2 transport downward of fine grained clastic and organic material by the infiltrating ground water leading to continuing processes of oxidation and carbonate dissolution in the subsurface and 3 eolian removal of clastic material from the floor of playa lakes which at some sites appears to have deepened playa depressions evidence for largely hydrologic processes of playa basin development on the southern high plains includes 1 a geographic occurrence restricted to relatively flat areas of the high plains surface that have poorly developed fluvial drainage and which are underlain by generally unsaturated clastic and calcrete beds 2 a tendency to occur where water collects and infiltrates as along ephemeral streams and lineations suggestive of fracture systems and 3 hydrologic geochemical petrographic and bore hole data which suggest that recharge to the high plains aquifer is principally from playa lakes that various geochemical changes including carbonate dissolution and enhancement of secondary porosity occur as water moves downward through the unsaturated zone beneath playa lakes and that calcrete beds often are missing or significantly dissolved beneath playa floors

aeolian system responses to global change challenges of scale process and temporal integration aeolian sediment systems are extensive components of the earth s surface not just in today s active desert environments but in coastal locations and as presently stable loess and peri desert ergs all these systems are subject to potentially significant 21st century changes in dynamics due to global warming impacts on atmospheric circulation sediment moisture and vegetation cover but do we know enough in the critical areas of science to allow robust models of likely future dynamics to be developed since the establishment of modern aeolian science research has largely taken two divergent routes 1 small scale investigations of the processes of wind shear sediment entrainment and transportation and 2 landform and landscape analyses with bedform systems described and relationships to circulation explained an intermediate sedimentological route has generated attempts towards a more integrated understanding of system behaviour at a range of scales four recent developments provide the potential for more robust multiscale integrations of aeolian system behaviour these are 1 advances in empirical measurement that allow wind power and sediment flux relations to be better described 2 modelling of dune and dust dynamics and interactions with key controls 3 monitoring systems that allow high resolution observations of sediment flux variations to be recognized and aeolian deposit structures to be understood and 4 chronometric advances that permit the assessment of the frequency and drivers of dune system activity in the past we explore and analyse these methodological advances and their potential contribution to the multiscale integrations that are essential for better informed predictions of future global aeolian system dynamics considering whether the integration of these advances in reductionist and holistic elements of aeolian science represent an example of the effective application of the principles of earth system science copyright 2008 john wiley sons ltd

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

dates of holocene icelandic volcanic eruptions from tephra layers in irish peats tephra from historic and prehistoric eruptions of oraefajokull and hekla iceland have been found in irish peats using a series of stratigraphically related high precision radiocarbon measure ments the date of a known age eruption has been satisfactorily estimated based on the same techniques the calendrical date of the hekla 4 eruption has been estimated as 2310 20 bc

multiphase quaternary highstands at lake ngami kalahari northern botswana large lake basins now almost entirely devoid of water in the kalahari s semi arid environment can be clearly identified from landsat imagery of northern botswana these basins are delineated by a series of beach ridges marking the former shorelines of an inundated area that at its largest extent encompassed 60 000 km 2 in the last 30 yr over 150 radiocarbon ages have been produced from three component basins that make up the palaeo makgadikgadi system consisting of the ngami mababe and makgadikgadi basins thepaucityofwellpreservedorganicmaterialintheregionhasledtothese 14 cagesbeingderivedfrominorganiccarbonates whose open system behaviour and polygenetic origin frequently result in unreliable dates from uncertain contexts and then only within the temporal limits of the radiocarbon method the application of optically stimulated luminescence osl dating to beach ridge sediments from lake ngami shaw p a bateman m d thomas d s g davies f 2003 holocene fluctuations of lake ngami middle kalahari chronology and responses to climatic change quaternary international 111 1 23 35 improved chronological resolution but was limited by the use of hand dug pits the new application of osl to samples derived from deep coringofbeachridgeshasallowedaccesstoamuchlonger threedimensional geomorphicrecordthanpreviouslyavailable seventyfour ages new osl ages from shorelines are presented allowing for the first time the opportunity to unravel the complex history of lake stages in the ngami basin multiple lake highstands are identified in the period 0 3 ka to 140 ka with several causes of these events includingtropicalandlocalclimatesandupstream channelavulsion identified tounravelthefullpaleaoclimatic significance of these events it will be necessary to identify the timing of high stands in the other terminal basins within the okavango system 2007 elsevier b v all rights reserved

salt mineral distribution patterns in soils of the otjomongwa pan namibia abstract the deposits of the otjomongwa pan southwestern kalahari namibia contain halite thenardite and minor amounts of calcium bearing sulfate minerals the deposits show vertical variations in salt content evaporite mineralogy and thenardite morphology with similar patterns throughout the basin the salt minerals were formed by evaporation of groundwater within a groundmass of lacustrine deposits that did not contain synsedimentary evaporites lateral variations in total salt content are related to the direction of groundwater flow during a period with high groundwater levels following the end of lacustrine sedimentation in the pan basin this was followed by a period without any groundwater influence that continues to the present during this stage leaching by rainwater occurred resulting in changes in evaporite mineralogy morphology and distribution

ams radiocarbon dating and varve chronology of lake soppensee 6000 to 12000 14c years bp for the extension of the radiocarbon calibration curve beyond 10000 14c y bp laminated sediment from lake soppensee central switzerland was dated the radiocarbon time scale was obtained using accelerator mass spectrometry ams dating of terrestrial macrofossils selected from the soppensee sediment because of an unlaminated sediment section during the younger dryas 10000 11000 14c y bp the absolute time scale based on counting annual layers varves had to be corrected for missing varves the soppensee radiocarbon verve chronology covers the time period from 6000 to 12000 14c y bp on the radiocarbon time scale and 7000 to 13000 calendar y bp on the absolute time scale the good agreement with the tree ring curve in the interval from 7000 to 11450 cal y bp cal y indicates calendar year proves the annual character of the laminations the ash layer of the vasset killian tephra massif central france is dated at 8230 140 14c y bp and 9407 44 cal y bp the boundaries of the younger dryas biozone are placed at 10986 69 cal y bp younger dryas preboreal and 1212 86 cal y bp allerod younger dryas on the absolute time scale the absolute age of the laacher see tephra layer dated with the radiocarbon method at 10 800 to 11200 14c y bp is estimated at 12350 135 cal y bp the oldest radiocarbon age of 14190 120 14c y bp was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile for the late glacial the offset between the radiocarbon 10000 12000 14c y bp and the absolute time scale 11400 13000 cal y bp in the soppensee chronology is not greater than 1000 years which differs from the trend of the u th radiocarbon curve derived from corals

radiocarbon dating of a recent high latitude peat profile stor amyrân northern sweden the value of both high precision hp and ams 14c determinations in the fine resolution dating of recent peat at stor amyr n near umea northern sweden has been explored a detailed chronology of accumu lation based on 14c an occurrence of the askja ad 1875 tephra and 241am measurements has been derived for the last 700 years this shows significant changes in the mass balance of the peat profile with minimum rates of net carbon sequestration overlapping with the period of minimum spring and summer temperature documented by published tree ring evidence the paper presents a methodology for calculating empirically past changes in the rate of net carbon sequestration in boreal peatlands and for exploring the effects of climatic variations and possible future global warming on these rates

reconstructing paleoenvironments and palaeoclimates in drylands what can landform analysis contribute quaternary period palaeoenvironmental and palaeoclimatic reconstructions are based on a wide and diverse array of proxy data sets some of which are geomorphological in nature in drylands where organic proxies may be limited the use of landforms is particularly important but challenging the capacity to establish the age of depositional forms particularly through the use of luminescence dating has advanced the use of landforms in dryland palaeo research though interpretation of these geoproxy records can be complex especially at the nexus of palaeoclimate and palaeoenvironmental interpretations of past conditions in this paper the use of aeolian and lacustrine forms in quaternary research is considered focusing on the relationships between dynamics form and climate and on the essential linkage between process research and palaeoenvironmental research it is concluded that landform analysis is a critical part of dryland palaeoenvironmental climate reconstruction contributing a different set of data compared to other data sources in terms of the elements of past conditions that are revealed five principles are identified to improve the use of geoproxy records in quaternary research 1 greater use of geomorphic process studies by quaternary scientists to better inform palaeolandform interpretation 2 further development of the use of chronometric data especially in terms of interpreting large data 3 interpret landform records in location specific contexts not in general terms 4 capitalise of the complexity of spatially extensive landform records which may offer better representations of real quaternary environmental complexity than at a point proxies 5 establish ways of integrating spatially extensive geoproxy records with other palaeoenvironmental records these challenges are major but not insurmountable and should represent goals for geomorphologists chronologists and quaternary scientists alike copyright 2011 john wiley sons ltd

mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system abstract a distinct series of beach ridges marking the former shorelines of large inter connected lacustrine basins in the kalahari can be clearly identified from landsat imagery and shuttle radar topography mission srtm data these basins which form the terminal sump of the okavango system in northern botswana are now almost completely dry during the quaternary they were intermittently occupied by large stable lake bodies and are thought to have periodically filled to a point of coalescence inundating an area that at its largest extent encompassed 66 000 km 2 poor chronological control has previously limited the utility of this important palaeo archive as part of a region wide lake palaeo shoreline research programme a systematic optically stimulated luminescence osl dating programme has utilised a lightweight hydraulic auger to take samples at depth from relict shoreline features twenty drill sites have generated 140 samples for dating establishing a firm chronology for multiple lake full phases in all three component basins ngami mababe and makgadikgadi of this mega lake this paper presents the final set of ages in the programme derived from four cores from the western and north eastern shorelines of makgadikgadi and uses these ages to establish a chronology of mega lake high stands during the last 300 ka providing a rare directly dated long terrestrial record of positive hydrological excursions within the southern hemisphere

complex holocene lunette dune development south africa implications for paleoclimate and models of pan development in arid regions closed depressions pan or playa basins are very common landscape features in arid or formerly arid regions many have associated downwind dune assemblages lunettes that have been explained in terms of deflation of sediments from the basin these widespread features have also been used as proxies of late quaternary rainfall and atmospheric circulation change we use a detailed program of optically stimulated luminescence dating at witpan south africa to show that lunette construction may be rapid and spatially complex this study presents 33 ages from 9 sample sites on the dune that show how accumulation of the present dune largely occurred over the past 2 k y but with marked sectoral variability in accumulation rates and timing variability is attributed largely to local sediment supply factors geochemical analysis shows that primary deflation from the pan has not contributed significantly to the construction of much of the current lunette most sand is derived from recycling of older lunette sediments preserved today at only a few locations and from neighboring linear dunes these findings if representative of lunettes in other localities have marked implications for the types of paleoclimatic information that these features may yield

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

absolute dating of the late glacial period in switzerland using annually laminated sediments abstract results of a high resolution late glacial ams 14 c chronology from rotsee central switzerland have given evidence that the atmospheric radiocarbon concentration was not constant between 13 000 and 9500 yr b p this resulted in three marked phases of constant radiocarbon age at 12 700 at 10 000 and at 9500 yr b p new results of a late glacial varve chronology from soppensee central switzerland suggest that the younger two phases of constant 14 c age each had a duration of ca 400 calendar years the length of the late glacial chronozones has been calculated on the basis of these replicate varve counts and a comparison with their estimated duration in radiocarbon years shows that the estimated duration of the chronozones bolling ca 800 calendar yr vs 1000 14 c yr and younger dryas ca 900 calendar yr vs 1000 14 c yr agree with the expected time span whereas the estimated duration of the allerod chronozone ca 400 calendar yr vs 1000 14 c yr is substantially shorter than expected furthermore a tentative comparison of varve ages and 14 c ages suggests that the varve chronology is more than 1000 yr offset toward older ages from the radiocarbon chronology during the late glacial period

a calendar age estimate of the younger dryas holocene boundary at krakenes western norway the younger dryas holocene transition yd h in the sediments of krakenes lake western norway is well marked both lithologically and palaeobiologically at 756 5 cm in the investigated core a ser

late quaternary lunette dune sedimentation in the southwestern kalahari desert south africa luminescence based chronologies of aeolian activity abstract through the application of luminescence dating techniques great advances have recently been made in the understanding of the late quaternary histories of many dryland regions including southern africa here this work has largely applied optical dating to sediments from the extensive linear dune systems which dominate the kalahari region of the central southern african interior relatively little attention has been given to localised aeolian accumulations such as lunette dunes despite their wide distribution over many parts of the region in particular the arid southwest kalahari to redress this we consider the palaeoenvironmental significance of pan margin lunettes and investigate the timing of lunette dune development in the southwest kalahari through the application of optical dating to sediments from lunette dunes associated with four closed basins pans ages show that localised aeolian activity occurred frequently throughout the past 18 ka indicating that the factors controlling lunette sedimentation are markedly different from those determining regional linear dune development it is proposed that the mechanisms controlling sediment supply to lunette dunes are controlled at both the regional and local pan specific scales by factors such as groundwater levels where pans support more than one discrete lunette the time since any individual lunette crest received significant accumulations of sediment increases with distance away from the pan margin outer and inner lunette sequences may be chronologically disparate features inner lunette formation may arise in response to modifications to the local atmospheric boundary conditions by the presence of large downwind outer lunette features or by shifts in sediment supply

groundwater recharge in the kalahari with reference to paleo hydrologic conditions the kalahari is situated in the semi arid center of southern africa and can be characterized as a savannah with a sandy subsurface deep groundwater tables and annual rainfall ranging from 250 mm in the southwest to 550 mm in the northeast a high infiltration rate and high retention storage during the wet season and subsequent high transpiration by the dense vegetation during the dry season make that very little water passes the root zone and contributes to aquifer recharge a lively debate has continued for almost a century on the question whether the kalahari aquifers are being replenished at all under present climatic conditions the present paper reports on results of an extensive recharge research project at the eastern fringe of the kalahari which is the most favorable part for groundwater replenishment additional observations were made in the central kalahari environmental tracer studies and groundwater flow modeling indicate that present day recharge is in the order of 5 mm yr 21 at the eastern fringe of the kalahari where annual rainfall exceeds 400 mm figures in the order of 1 mm were obtained from the central kalahari with lower precipitation a dry valley system refers to more humid paleo climatic conditions with a higher groundwater recharge a tentative reconstruction of the groundwater depletion history suggests a time lapse of several thousands of years since the end of the last wet period q 2000 elsevier science b v all rights reserved

the chronology of the last termination a review of radiocarbon dated high resolution terrestrial stratigraphies abstract the last termination is traditionally subdivided into the oldest dryas bolling older dryas allerod younger dryas and preboreal chronozones this paper briefly summarizes the history of the late weichselian chronostratigraphic system and gives an overview of recent developments in radiocarbon dating terrestrial records between 15 000 and 10 000 14 c years bp problems inherent in the traditional chronostratigraphy are discussed in the light of new and more advanced dating possibilities including accelerator mass spectrometry ams measurements on terrestrial macrofossils new results obtained using ams 14 c dated varve sequences are compared with each other and with the marine u th coral record in addition the importance of time synchronous marker horizons as a tool for long distance correlation between different archives is illustrated

the action of wind and water in a mid cretaceous subtropical erg margin system close to the variscan iberian massif spain aeolian processes and ephemeral water influx from the variscan iberian massif to the mid cretaceous outer back erg margin system in eastern iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements remains of aeolian dunes encased in ephemeral fluvial deposits aeolian pods demonstrate intense erosion of windblown deposits by sudden water fluxes the alternating activity of wind and water led to a variety of facies associations such as deflation lags desert pavements aeolian dunes pebbles scattered throughout dune strata aeolian sandsheets aeolian deposits with bimodal grain size distributions mud playa ephemeral floodplain pebble sand and cobble sand bedload stream pebble cobble sand sheet flood sand bedload stream debris flow and hyperconcentrated flow deposits sediment in this desert system underwent transport by wind and water and reworking in a variety of sub environments the nearby variscan iberian massif supplied quartzite pebbles as part of mass flows pebbles and cobbles were concentrated in deflation lags eroded and polished by wind driven sands facets and ventifacts and incorporated by rolling into the toesets of aeolian dunes the back erg depositional system comprises an outer back erg close to the variscan highlands and an inner back erg close to the central erg area the inner back erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits in the inner back erg area ephemeral wadis desiccated after occasional floods were mud cracked and overrun episodically by aeolian dunes subsequent floods eroded the aeolian dunes and mud cracked surfaces resulting in largely structureless sandstones with boulder size mudstone intraclasts floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes the remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands upon desiccation deflation resulted in lags of coarser grained sediments a renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions synsedimentary tectonics caused the outer back erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands ephemeral water flow to the outer back erg area supplied pebbles eroded aeolian dunes and produced hyperconcentrated flow deposits fluidization and liquefaction generated gravel pockets and recumbent folds dune damming after sporadic rains the case of the namib desert monsoonal water discharge thar desert and meltwater fluxes from glaciated mountains taklamakan desert are three potential non exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the cretaceous desert margin system an increase in relief driven by the aptian anti clockwise rotation of iberia led to an altitude sufficient for the development of orographic rains and snowfall which fed melt water fluxes to the desert margin system quartzite conglomerates and sands dominantly consisting of quartz and well preserved feldspar grains which are also observed in older cretaceous strata indicate an arid climate and the mechanical weathering of precambrian and palaeozoic metamorphic sediments and felsic igneous rocks unroofing of much of the cover of sedimentary rocks in the variscan iberian massif must therefore have taken place in pre cretaceous times

late quaternary dynamics of southern africa s winter rainfall zone abstract variations in the nature and extent of southern africa s winter rainfall zone wrz have the potential to provide important information concerning the nature of long term climate change at both regional and hemispheric scales positioned at the interface between tropical and temperate systems southern africa s climate is influenced by shifts in the intertropical convergence zone the westerlies and the development and position of continental and oceanic anticyclones over the last glacial interglacial cycle substantial changes in the amount and seasonality of precipitation across the subcontinent have been linked to the relative dominance of these systems central to this discussion has been the extent to which the region s glacial climates would have been affected by expansions of antarctic sea ice equatorward migrations of the westerlies more frequent intense winter storms and an expanded wrz this paper reviews the developing body of evidence pertaining to shifts in the wrz and the evolution of ideas that have been presented to explain the patterns observed dividing the region into three separate axes along the western and southern margins of the continent and across the interior into the karoo and the kalahari a range of evidence from both terrestrial sites and marine cores is considered and potential expansions of the wrz expansions are explored despite the limitations of many of the region s proxy records a coherent pattern has begun to develop of a significantly expanded wrz during phases of the last glacial period with the best documented being between 32 17 ka while more detailed inferences will require the recovery and analysis of longer and better dated records this synthesis provides a new baseline for further research in this key region

geomorphological contributions to palaeolimnology on the african continent abstract article history received 19 december 2007received in revised form 5 july 2008accepted 22 july 2008available online 3 august 2008keywords quaternarybeach ridgeshorelinelakemultiproxyosl lakes are highly informative repositories of information of the terrestrial response to regional and global climatedrivers in quaternary studies lake oor records are now frequently used to establish the magnitude timing andgeographicalextentofhumid aridtransitionsovertimescalesof10 2 10 4 years whiletheresolutionof thisrecordisunparalleled much of the geochemical and sedimentary da ta is challenging to interpret and highly basin speci c geomorphologicalproxies particularlyshorelines offeranadditionaloralternativerecordoflakehistory withrecenttechnological advances facilitating both access to and the utility of this proxy record recent advances in opticallystimulated luminescence osl dating allow the determination of the age of beach ridge emplacement in theabsence of organic material while the availabilityof shuttle radar topography mission srtm data in conjunctionwith digital elevation models dem aids in the identi cation of shoreline features and the topographicreconstruction of the former extent of palaeolakes here we highlight and illustrate the use of lacustrine shorelinefeatures for unravelling a quaternary climate signal wit hin africa from otherwise inaccessible and undatablepalaeolake records in the semi arid and arid subtropics an d identify their contribution towards high resolutionmultiproxy reconstructions of tropical low latitude quaternary environments and climates 2008 elsevier b v all rights reserved

40ar 39ar and u pb evidence for late proterozoic grenville age continental crust in north central cuba and regional tectonic implications renne p r mattinson j m hatten c w somin m onstott t c millfin g and linares e 1989 4 ar 39ar and u pb evidence for late proterozoic grenville age continental crust in north central cuba and regional tectonic implications precambrian res 42 325 341 central cuba is composed of fault bounded tectonostratigraphic terranes juxtaposed and deformed during plate collision and subsequent transform motion between the caribbean and north american plates in the late mesozoiccenozoic one of these the las villas terrane contains crystalline basement rocks thought to be pre upper jurassic on stratigraphic grounds the socorro complex occurs in the northwestern las villas terrane and consists of marbles and siliciclastic metasedimentary rocks and the rio carla granite an 4 ar 39ar plateau date of 903 5 7 1 ma for phlogopite from a marble corroborates previous k ar dates from this unit and establishes unambiguously a late proterozoic age for high grade metamorphism discordance of the 4 ar agar age spectrum can be reliably attributed to diffusive ar loss which if modeled as an episodic thermal event implies a reheating age that closely coincides with the late cretaceous paleogene collision between the caribbean and north american plates u pb zircon data indicate an intrusive age of 172 4 ma for the rio carla granite and reveal an inherited zircon component with an age of 900 ma radio isotopic data from the socorro complex display no evidence of pan african age thermal overprinting these observations combined with constraints provided by published results from nearly pangean landmasses suggest that the complex lay substantially to the southwest present day co ordinates during the early paleozoic following its genesis in the mid mesozoic the caribbean plate evidently transported fragments of an extensive grenville age belt that spanned the americas during the late proterozoic

late quaternary highstands at lake chilwa malawi frequency timing and possible forcing mechanisms in the last 44 ka the extensive shoreline deposits of lake chilwa southern malawi a shallow water body today covering 600 km2 of a basin of 7500 km2 are investigated for their record of late quaternary highstands osl dating applied to 36 samples from five sediment cores from the northern and western marginal sand ridges reveal a highstand record spanning 44 ka using two different grouping methods highstand phases are identified at 43 7 33 3 ka 26 2 21 0 ka and 17 9 12 0 ka total error method or 38 4 35 5 ka 24 3 22 3 ka 16 2 15 1 ka and 13 5 12 7 ka finite mixture model age components with two further discrete events recorded at 11 01 0 76 ka and 8 52 0 56 ka highstands are comparable to the timing of wet phases from other basins in east and southern africa demonstrating wet conditions in the region before the lgm which was dry and a wet lateglacial which commenced earlier in the southern compared to northern hemisphere in east africa we find no evidence that wet phases are insolation driven but analysis of the dataset and gcm modelling experiments suggest that heinrich events may be associated with enhanced monsoon activity in east africa in both timing and as a possible causal mechanism

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

late quaternary lake level fluctuations in the mababe depression middle kalahari palaeolakes and the role of zambezi inflows abstract a systematic drilling and optical dating programme on middle kalahari beach ridge relict shoreline sediments has enabled the identification of multiple episodes of lake high stands of an extensive palaeolake system at the terminus of the okavango delta northern botswana this paper presents 23 ages from the mababe depression and establishes four shoreline construction phases in the late quaternary coeval with other sub basin lake high stands lake ngami these synchronous lake phases result from a coalescence of the sub basins into a unified palaeolake lake thamalakane covering an area of 32 000 km2 six additional ages are also presented from the chobe enclave to the north of the basin where shoreline ridges were emplaced at the same time as lake thamalakane phases this suggests that increased flow in the chobe and zambezi system significantly contributed to the middle kalahari lake phases in both the post glacial and holocene periods the integration of these new data and their compatibility with other regional and tropical palaeo archives is discussed in the light of understanding quaternary climate drivers within the kalahari

the continental tree ring record absolute chronology 14c calibration and climatic change at 11 ka abstract tree ring chronologies are unique archives for various parameters indicating climatic change the wood structure of trees deposited in river gravel below the water table is well preserved even after several millennia and it provides information on a time scale of solar years during the past 25 years in the hohenheim tree ring laboratory long tree ring chronologies have been constructed now reaching back to 11 400 yr dendro b p in this contribution we demonstrate the evidence for climatic change in the early holocene which can be obtained both from botanical properties e g parameters of ring growth and from the isotopic information recorded in tree rings

late quaternary environmental change in central southern africa new data synthesis issues and prospects much of the interior of central southern africa is a sand sea within which aeolian and lacustrine landforms and sediments of local and regional extent are preserved closed cave sites are restricted to very few locations while fluvial systems traverse the margins of the interior until the early 1990s chronologies of late quaternary environmental and climatic changes developed for this region were based on only a limited number of proxy data sets derived largely from lacustrine deposits and precipitates in particular directly determined ages from aeolian deposits the most extensive suite of features in the region were absent the application of luminescence dating techniques to dune sediments and the development of further detailed chronologies from cave precipitates is now providing a more comprehensive record for the last 50 ka with some chronologies extending back a further 100 ka we present and review these data assess their contribution to enhanced understanding of late quaternary environmental changes in the region and for the first time assess them against corrected radiocarbon ages from lacustrine sites it is concluded that there is now an enhanced understanding of the spatial and temporal complexity of climate changes affecting the region in the last glacial cycle including a complex record of punctuated aridity but that many issues including data set integration and forcing mechanism controls are imperfectly understood

a gis based reconstruction of late quaternary paleohydrology lake eyre arid central australia lake eyre is the terminal playa in a large closed basin which receives the majority of its moisture from the summer monsoon modern lake eyre receives intermittent floodings at times of increased monsoon intensity generally associated with the la nin a phase of the enso cycle lake eyre was a perennial lake during several phases of increased monsoon activity during the late quaternary specifically about 125 ka 80 ka 65 ka and 40 ka magee 1997 late quaternary environments and palaeohydrology of lake eyre arid central australia unpubl ph d thesis australian national university canberra these lake highstands are reflected by elevated shorelines mapped around lake eyre and to a lesser degree around the frome gregory system to the southeast of lake eyre comprehensive research in the lake eyre catchment over the last several decades has constrained the ages and elevations of these shoreline deposits which now enable us to use digital elevation models to map these paleo lakes by incrementally filling each lake meter by meter the areas and volumes of the paleo lakes are calculated and the paleohydrologic processes including the flow direction across spillovers are reconstructed at the peak 125 ka highstand lake eyre stood at 10 m australian height datum ahd and covered nearly 35 000 km 2 more than three times the area of the current playa together with the frome gregory system it held 430 km 3 of water by contrast the deepest historic filling held 30 km 3 these lake levels represent climatic conditions very different from the modern situation due to discontinuous preservation of the shoreline deposits around the lakes and due to the scale of the lake systems mapping the former levels of lake eyre and the frome gregory system has been impossible prior to the availability of a digital elevation model paramatizing the area volume relationships of water required to fill the lake to varying levels will provide data for quantification of climate and precipitation changes over time h 2003 elsevier b v all rights reserved

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

environmental conditions and geomorphologic changes during the middle upper paleolithic in the southern iberian peninsula article i nfo this study utilizes geomorphology marine sediment data environmental reconstructions and the gorham s cave occupational record during the middle to upper paleolithic transition to illustrate the impacts of climate changes on human population dynamics in the western mediterranean geomorphologic evolution has been dated and appears to be driven primarily by coastal dune systems sea level changes and seismo tectonic evolution continental and marine records are well correlated and used to interpret the gorham s cave sequence specific focus is given to the three hiatus sections found in gorham s cave during heinrich periods 4 3 and 2 these time intervals are compared with a wide range of regional geomorphologic climatic paleoseismic faunal and archeological records our data compilations indicate that climatic and local geo morphologic changes explain the homo sapiens spp occupational hiatuses during heinrich periods 4 and 3 the last hiatus corresponds to the replacement of homo neanderthalensis by h sapiens records of dated cave openings slope breccias and stalactite falls suggest that marked geomorphologic changes seismic activ ity and ecological perturbations occurred during the period when homo replacement took place

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

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

relationship of salinity of groundwater to recharge in the southern kalahari desert abstract occurrences of modern groundwater in the kalahari formation aquifer suggest current recharge taking place in the dry river channels as well as through thin sand cover where the pre kalahari erosional surface is shallow or exposed in the pan belt of the western part of the area studied the kalahari formation seems to form a common aquifer with certain parts of the underlying dwyka formation it is presumed that the large pans there are superimposed on a pre existing drainage system dating back to a pre kalahari epoch the highly concentrated brine in the dwyka formation in the pan belt is a shallow phenomenon caused by insufficient flushing of the low lying pans seasonal fluctuations in the pans force the brine up to where it undergoes evaporation resulting in evaporites which occasionally leach back to the ground the occurrence of brines however does not prove that these are outlets of a basin which is recharged in the east and hence represent apparent salinity growth it only suggests a dry period which followed the pre holocene high lake level and caused the brine formation these brines will remain unflushed as long as the current climatic conditions prevail

a holocene late pleistocene aeolian record from lunette dunes of the western free state panfield south africa the greatest concentration of pans in southern africa occurs in the western free state province south africa a feature of many free state pans is their fringing lunettes located on the southern

from landform to process morphology and formation of lake bed barchan dunes makgadikgadi botswana abstract a suite of crescentic landforms is visible from remotely sensed imagery within the ntwetwe panpan in the makgadikgadi basin botswana we investigate the most distinct of these landforms using morphometric measurements sedimentary data and optically stimulated luminescence osl signal analysis comparative analysis with previously published barchan morphological data sets suggest the ntwetwe features fall within the spectrum of morphometric parameters found in a range of barchan dunefields from around the world there is currently insufficient comparative morphometric data from sub aqueous dunefields to be able to distinguish the particular formative environment of the dune osl signal analyses however support the hypothesis of grove 1969 grove a t 1969 landforms and climatic change in the kalahari and ngamiland geographical journal 135 191 212 that the last deposition of the sediments within the ntwetwe forms was most likely aeolian in origin luminescence signal analysis is employed to investigate potential transport and bleaching environments of the sediments forming the features but results in this case do not shed further light on the formative conditions of these enigmatic landforms

luminescence based dune chronologies in southern africa analysis and interpretation of dune database records across the subcontinent abstract over 600 luminescence ages have to date been published from southern africa s continental dunefields and isolated dunes providing a rich record of aeolian system dynamics during the late quaternary the majority of records come from sites within the five linear dune dominated dunefields of the kalahari with lesser representation of other major dune areas including the namib and west coast dunefields and of other dune types including lunettes and transverse forms dune database records are analysed not only in terms of the evidence they provide for late quaternary environmental changes over the last 190 ka the purpose for which most ages have been produced but in terms of the analytical techniques used data quality and data presentation as these all impact on how dune luminescence ages have been or should be interpreted as a tool for palaeoenvironmental and dune development studies it is concluded that even despite the number of dated dune records from southern africa there is a marked spatial unevenness within and between dunefields in the data available for assessing dune depositional ages and conditions however this is not a situation that can simply be improved upon by adding more and more ages to the full set of records it is both necessary to appreciate the spatial differences in dune sensitivities to activation and relationships to potential changes in hydrological and other activity controls and to establish better tools and approaches for analysing a rich but presently environmentally ambiguous record of dune accumulation

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

a 106ka paleoclimate record from drill core of the salar de atacama northern chile abstract a 100 m long salt core sqm 2005 from the salar de atacama northern chile 23 s 68 w a dry lake bed contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central andes of south america six u series disequilibrium dates range sequentially from 106 1 6 4 to 5 4 2 7 ka based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods saline lakes and expanded mudflats existed in the salar de atacama from 75 7 to 60 7 ka and from 53 4 to 15 3 ka with the wettest perennial lake interval from 26 7 to 16 5 ka short relatively wet periods also occurred in the holocene from 11 4 to 10 2 ka and from 6 2 to 3 5 ka these wet periods at salar de atacama correspond well with other late pleistocene climate records from the central andes that are a function of the net hydrologic budget the minchin tauca lake sequence from salar de uyuni bolivia is synchronous with the 53 4 15 3 ka saline lake wet period at salar de atacama the tauca phase coincided with the wettest perennial lake interval at salar de atacama from 26 7 to 16 5 ka the coipasa lake phase from uyuni was probably contemporaneous with the early holocene wet period at salar de atacama from 11 4 to 10 2 ka the early holocene wet interval at salar de atacama was also synchronous with the maximum holocene lake levels of the chilean altiplano lakes to the east and with grass rich rodent middens between 11 8 and 10 5 ka in age from the atacama basin the lake period at salar de atacama between 26 7 and 15 3 ka compares closely with low 18o values low anion concentrations and high accumulation rates from the sajama glacial ice core southwestern bolivia between 25 and 15 5 ka it is concluded that wet and dry phases were synchronous in the central andean plateau of southwestern bolivia and along the western flank of the andes of northern chile over the past 50 kyr this region which today receives its moisture from the amazon basin to the east probably also did so in the past the wet periods at salar de atacama are in phase with january insolation maxima at 15 s at 70 45 and 20 ka which suggests that past changes in summer insolation influenced precipitation patterns in the central andes however there are no major wet periods linked to the january insolation maximum at 93 ka and the present day extremely dry climate in the atacama desert is associated with a peak in summer insolation therefore there must be other important influences over precipitation in the central andes which modify the first order insolation controls

a stable isotope tree ring timescale of the late glacial holocene boundary late glacial and holocene tree ring chronologies like deep sea sediments or polar ice cores contain information about past environments changes in tree ring growth rates can be related to past climate anomalies and changes in the isotope composition of tree ring cellulose reflect changes in the composition of the atmosphere and the hydrosphere we have established a 9 928 year absolutely dated dendrochronological record of holocene oak quercus robur quercus petraea and a 1 604 year floating late glacial and early holocene chronology of pine pinus sylvestris from subfossil tree remnants deposited in alluvial terraces of south central european rivers the pine sequence provides records of dendro dated 14c 13c and 2h patterns for the late younger dryas and the entire preboreal 10 100 9 000 yr bp through the use of dendrochronology radiocarbon age calibration and stable isotope analysis we suggest that the late glacial holocene transition may be identified and dated by 13c and 2h tree ring chronologies

the history and nature of wind erosion in deserts recently the importance of wind erosion has been reevaluated many low angle surfaces developed on susceptible materials possess closed depressions pans and these often have a distinctive morphology and lunette dunes on their lee sides it has also become apparent that in drylands there are extensive areas of stone pavements some of which have been molded by deflation however it is now recognized that other horizontal sorting processes have played a role especially movement of fines by overland flow vertical sorting associated with wetting and drying salt heave bioturbation frost action and dust accretion have also played a role in hyperarid areas especially with unidirectional winds bedrock outcrops and old lake beds have been molded to give aerodynamic forms called yardangs the study of dust storms by analysis of climatological data and remote sensing has revealed the importance of deflation especially in hyperarid areas with centripetal drainage deflation hot spots such as the bo

present day lunette sediment cycling at witpan in the arid southwestern kalahari desert abstract witpan is a pan depression in the southwestern kalahari desert the pan fringing lunette dune has a number of notable characteristics a highly active crest the lower lunette pediment is cemented and the lower lunette supports a highly developed and active gully system geomorphological and sedimentological considerations are used to evaluate the interaction of wind and water in shaping contemporary lunette processes it is considered that like other pans in the area groundwater activity influences pan floor sediment availability and transport that the present highly sea sonal climatic regime permits the interaction of aeolian transport of sediment to the dune and its return to the pan floor by water during storm events creating a cycling process favoured by sedimentary properties that promote surface runoff

an absolute chronology for the raised beach and associated deposits at sewerby east yorkshire england the raised beach sediments revealed in the cliffs at sewerby east yorkshire are widely regarded as ipswichian in age previously reported evidence for this dating is reviewed and new results from a range of luminescence dating techniques applied to the blown sand deposit overlying the raised beach are reported these provide the first absolute date for the sewerby site of 120 84 11 82 ka which places the blown sand at the boundary between oxygen isotope stages ois 5e and 5d as the underlying raised beach is little older than the blown sand it probably formed during ois stage 5e as suggested by the faunal evidence

late quaternary palaeohydrological changes in the northern namib sand sea new chronologies using osl dating of interdigitated aeolian and water lain interdune deposits abstract ephemeral rivers today terminate in playas adjacent to the eastern part of the namib sand sea although there is evidence that these fluvial systems penetrated further west in the past there are water lain sediments exposed in interdune areas of the northern namib sand sea associated with the former course of the tsondab river which are central to palaeoenvironmental reconstruction in the region these deposits indicate that there was increased moisture availability in this presently hyper arid region and or the catchments of the rivers to the east of the sand sea in the great escarpment until now the chronology for the deposition of these sediments has been based on radiocarbon 14 c dates on carbonate materials the validity of these ages is problematic and 14 c limits the timescale to which these sediments can be dated the water lain units are bracketed by aeolian sand units which are highly suitable for optically stimulated luminescence osl dating here 24 osl ages from three sites associated with the former course of the tsondab river are presented allowing a reassessment of the timing of sediment deposits and the west to east progression of the terminus of the tsondab river during the late quaternary narabeb which is 60 km north west of the current end point of the tsondab river at tsondab vlei contains eight mud units six of which are shown to be of marine oxygen isotope stage mis 5 128 75 ka age water lain units at hartmut pan 55 km north west of tsondab vlei are dated by osl to between 16 9 0 9 ka and 12 7 0 1 ka at ancient tracks closest to the tsondab vlei 6 km west mud units are younger and placed between 12 0 0 7 and 12 8 0 8 ka 11 5 0 5 10 5 0 5 ka and after 10 5 0 5 ka this new chronology is compared with other key regional records to identify potential regional relationships and forcing factors there is greatest correspondence with the records in the north of the summer rainfall zone a revision of both old and young 14 c ages on carbonate materials calls for revision of other 14 c chronologies in the region and highlights the problems with the continued used of histograms of 14 c ages to indicate periods of increased humidity in southern africa

palaeoenvironmental reconstructions from linear dunefields recent progress current challenges and future directions abstract this paper reviews recent progress in the use of linear dunes as geoproxies of late quaternary environmental change summarises the challenges facing their use and explores some potential solutions to these challenges large areas of the swathes of linear dunes which occupy the continental interior of southern africa australia and parts of central asia and southern america currently have limited or negligible aeolian activity they have been recognised as offering potential information about past environments for more than a century but only with the widespread application of luminescence dating during the 1990s did they realistically start to offer the prospect of being an extensive dateable proxy of late quaternary palaeoenvironments and possibly palaeoclimates dating aeolian dune sands with luminescence methods is generally although not always relatively straightforward over the past twenty years a large number 1000 of luminescence ages have been added to the global dataset yet there has also been significant criticism of some of the rationale underpinning much of the interpretation of the records derived at the landscape scale developments of arguably equal importance have come from improved geomorphological understanding based on the wider availability of remotely sensed data and the paradigm of dunefield evolution as a self organising complex system current challenges are identified in three key regions incomplete understanding of how the process geomorphology of linear dunes affect the accumulation and preservation of sediment a lack of clarity regarding the temporal and spatial scale of the response in a dynamic environmental setting and uncertainty surrounding the drivers of changing rates of net accumulation solutions to these challenges lie within diverse research methodologies certainly further field study is required with improvement required in understanding system responses to changing environmental stimuli at scales from sedimentological to landscape in parallel the full implications of complex systems approaches to aeolian geomorphology for linear dunes lag behind the adoption of the concept to some other dune forms e g barchans the relationship between observed dune complexity and age from field data complicates previous suggestions that dune patterning may be purely a function of development time parallel to this lies the need to improve interpretation of the results of dune geochronological studies a suggestion is offered which aims to test the statistical significance of dune accumulation time series by comparison with a modelled system with unchanging external forcing despite the initial promise of linear dune records as a revolutionary source of palaeoenvironmental information in drylands the outcomes to date have been coarse although still valuable in resolution perhaps the most valuable realization has been that geomorphological understanding of these widespread landforms is incomplete

palaeoenvironmental reconstruction of kathu pan south africa based on sedimentological data abstract several studies have highlighted the importance of collecting well dated records of palaeoenvironmental changes on desert margins particularly in the semi arid interior of southern africa here we describe sediments at three sites in kathu pan a pan complex overlying karstic bedrock at the southern edge of the kalahari basin sinkholes have exposed sedimentary sequences dating back to the pleistocene making it possible to document multiple palaeoenvironmental regimes in this landscape using a multi analytical sedimentological approach including micromorphology energy dispersive x ray spectrometry electron microprobe loss on ignition laser diffractometry and luminescence dating we demonstrate that the sediments at kathu pan represent an environment fluctuating among a number of thresholds for accumulation of different kinds of transported and authigenic sediments within the pleistocene sands at the base of our studied sedimentary sequence the presence of palygorskite indicative of less extreme evaporative control represents a semi arid environment from 156 11 ka to 32 2 ka marine isotope stages 6 3 increased moisture availability at 84 4 ka and at 96 5 ka possibly during marine isotope stages 5a and 5c respectively is reflected in the sands by the formation of palygorskite in concert with the deposition and oxidation of organic material as the climate became increasingly arid possibly in response to global cooling during the last glacial maximum 21 2 ka kathu pan crossed a threshold and deposition of caco3 dominated over that of palygorskite in the holocene beds within our studied unit alternating caco3 and organic dominated deposits sometimes in very fine laminae reflect an increase in the amplitude of either seasonal or annual changes in water availability

wind energy variations in the southwestern kalahari desert and implications for linear dunefield activity the southwestern kalahari linear dunefield which displays marked morphological variability possesses a partial but temporally and spatially variable vegetation cover and has frequently been described as a palaeodunefield palaeo status has been ascribed on the basis of several criteria including the presence of vegetation but also because dunes are thought to be out of alignment with modern resultant potential sand moving wind directions and because present day wind energy is regarded as low for the period 1960 1992 wind data from eight dunefield meteorological stations are analysed in detail to examine these assertions potential sand transport directions including spatial and temporal variations and potential drift directions for the windiest three month periods are calculated and explained it is concluded that the present day potential sand transport environment is markedly variable from year to year and from place to place while periods of low sand transport energy do occur it is also noted that the 1980s possessed considerable potential for sand transport in the dunefield directional variability is also relatively high perhaps exceeding that under which linear dunes can be expected to form because linear dune aeolian activity has a number of states however the present day wind environment may allow dune surface aeolian activity to occur which does not alter the overall pattern of the dunes

new radiocarbon dates for the vedde ash and the saksunarvatn ash from western norway abstract the vedde ash bed mid younger dryas and the saksunarvatn ash early holocene are important regional stratigraphic event markers in the north atlantic the norwegian sea and the adjacent land area it is thus essential to date them as precisely as possible the occurrence of the saksunarvatn ash is reported for the first time from western norway and both tephras are dated precisely by ams analyses of terrestrial plant material and lake sediment at krakenes the vedde ash has been previously dated at sites in western norway to about 10 600 yr b p it is obvious in the younger dryas sediments at krakenes and its identity is confirmed geochemically the mean of four ams dates of samples ofsalix herbacealeaves adjacent to the tephra is 10 310 50 yr b p the saksunarvatn ash is not visible in the early holocene lake sediment at krakenes after removal of organic material and diatoms the identity of the tephra particles was confirmed geochemically and their stratigraphic concentration was estimated from curve matching of a series of seven ams dates of terrestrial plant macrofossils and whole sediment the radiocarbon age of the ash is 8930 9060 yr b p corresponding to an age of 9930 10 010 cal yr b p 7980 8060 cal yr b c

deposition and early alteration of evaporites summary the depositional settings for primary and early diagenetic evaporite deposits generally fall into three categories marginal mixed shallow subaqueous and subaerial shallow and deep subaqueous these three environmental groupings hold for both marine and nonmarine settings although the details of continental evaporites may be far more complex than in most marine fed water bodies the primary evaporite morphologies from many continental playa hypersaline marine and marine marginal depositional settings are reasonably well understood because of the numerous detailed studies of recent holocene and cenozoic deposits that serve as models for sedimentary interpretation the sedimentological features that develop in deeper water settings are inferred based on examination of unaltered cenozoic deposits each environmental setting develops characteristic depositional features and patterns and one facies grades into the next because there may be significant physiochemical changes in water composition during deposition as well as sudden change s in both water depth and basinal circulation description and interpretation of evaporative rocks should not be based on mineralogy alone but on the distinct sedimentary characteristics of each part of a deposit in cases where sediments still reflect their primary mineralogy and morphology most of the environments can now be recognized however geochemical studies are commonly required to determine the source s of the original water the determinative geochemical techniques that presently serve as a support to sedimentologic study include studies of fluid inclusions bromine content of chloride salts and the stable isotopes of strontium sulphur carbon and oxygen only after these and perhaps other chemical analyses are considered can the full depositional history of a region be reasonably unravelled

geomorphological evolution of mediterranean enclosed depressions in the late glacial and holocene the example of canohes roussillon se france the origin and evolution of the enclosed depressions pans of southern france during the period from the late glacial to the holocene are discussed on the basis of newstratigraphical geophysical and chronological 14c data from the canohes depression roussillon southern of france and its nearby environment the canohes depression is non karstic excavated from pliocene arkosic sands that were shaped by eolian erosion during cold stages of the middle and upper pleistocene the timing and controlling factors of eolian carving of the depression are discussed on the basis of geomorphological data surrounding alluvial terrace chronology preserved ledge within the depression and alluvial infill of the depression formation of the depressionwas controlled locally by climate variability and its consequences on vegetation and water table position and regionally by the sea base level the enclosed depression probably started to form during mis 6 reaching its maximum depth during mis 2 climate variability in the region is recorded in the depression s infill the basal deposits are of fluvial origin and record the increase of moisture and temperature during the early late glacial the first lacustrine deposits are observed during the bolling gi 1e stage while continental sedimentation and drying occurred during the allerod and younger dryas stages during the early and middle holocene lacustrine conditions prevailed except during short periods of drying the specific evolution of the canohes depression as regards other such formations is discussed in light of regional deglaciation and climate chronology a regional synthesis of eolian erosion is proposed

origin and morphology of barchan and linear clay dunes in the shuhongtu basin alashan plateau china abstract clay dunes are characterized by a relatively high content of silt and clay and are typically developed on the lee side margin of closed basins in arid and semi arid areas although they are widely distributed aeolian landforms on earth little is known about their development and distribution in asia our field investigations have identified for the first time the occurrence of clay dunes in the alashan plateau north china the clay dunes occur in three isolated lowland areas of the suhongtu sht basin and their morphologies barchans hooked barchans asymmetrical barchans and linear or seif dunes differ substantially from those of the well studied clay dunes in australia africa and north america these differences could be mainly attributed to the asymmetrical bimodal wind regime prolonged drought and sediment physical properties which indicate that dunes of any type can be formed in sand silt or clay based on the known evolution of the sht paleo lake basin and regional climate change we infer that the landscape of modern clay dunes in the desert of the alashan plateau does not predate mis 5 and probably formed during the late holocene analyses of grain size distributions and the contents of trace and rare earth elements combined with geomorphological characteristics indicate that the source sediments of the clay dunes are mainly local cretaceous tertiary and quaternary red fluvial lacustrine mudstone and sediments while the ultimate source is the weathered and denuded products of granitoids of the east altay mountains comparison of the morphology and alignment of the clay dunes with the prevailing wind pattern tends to support tsoar s 1984 model of the transition in dune shape from barchans to seif or linear dunes during 2003 2013 the seif or linear dunes of the sht basin migrated laterally and elongated northeastward at rates of about 2 4 m yr and 16 20 m yr respectively